LITHOSTRATIGRAPHIC ANALYSIS OF CYCLICAL PHOSPHORITE SEDIMENTATION WITHIN THE MIOCENE PUNCO RIVER FORMATION, NORTH CAROLINA CONTINENTAL SHELF A thesis Presented to the Faculty of the Department of Geology East Carolina University In Partial Fulfillment of the Requirements for the Degree Master of Science in Geology by Patrick M. Mallette October, 1986 ECU LIBRARY Patrick M. Mallette. LITHOSTRATIGRAPHIC ANALYSIS OF CYCLICAL PHOSPHORITE SEDIMENTATION WITHIN THE MIOCENE PUNGO RIVER FORMATION, NORTH CAROLINA CONTINENTAL SHELF. (Under the direction of Dr. Stanley R. Riggs) Department of Geology, October, 1986. ABSTRACT The Miocene Pungo River Formation occurs in outcrop and shallow 2 subcrop across 5000 km of the North Carolina continental shelf in Onslow Bay. The formation contains three N-S trending, unconformity bound, depositional sequences which dip gently seaward. These sequences, referred to as the Frying Pan Sequence (late Burdigalian), Onslow Bay Sequence (Langhian) and Bogue Banks Sequence (Serravallian) are products of third-order sea-level cycles and were originally recognized on the basis of seismic and biostratigraphic techniques. Lithologic descriptions from 95 nine-meter vibracores demonstrate that the depositional sequences can also be distinquished on the basis of their characteristic lithofacies, which reflect deposition in shelf, shelf- margin and shelf environments, respectively. The Frying Pan Sequence comprises four major lithofacies: 1) phosphorite (10-65% phosphate), 2) siliciclastic (sand and mud), 3) mixed carbonate and siliciclastic, and 4) foraminiferal quartz sand. The Onslow Bay Sequence comprises three major lithofacies: 1) biogenic carbonate, 2) interbedded quartz sand and dolosilty mud and 3) organic- rich mud. The Bogue Banks Sequence is subdivided into five major lithofacies: 1) quartz sand, 2) phosphatic quartz sand (3-9% phosphate), 3) phosphorite quartz sand (10-25% phosphate), 4) dolosilty mud, and 5) carbonate. Lithofacies distribution within the Frying Pan and Onslow Bay Sequences is controlled by antecedent topography and location of sediment source areas. In northern Onslow Bay, biogenic carbonate sediments are associated with the Cape Lookout High, a shallow region with low siliciclastic influx. Siliciclastic sediments of central Onslow Bay fine southward away from a source area on the adjacent landmass. Minimum dilution by siliciclastic sediments in southern Onslow Bay, coupled with upwelling and reducing bottom conditions, resulted in accumulation of organic matter and authigenesis of phosphorite and dolomite. Lithofacies distribution within the Boque Banks Sequence could not be directly related to prominent paleotopographic features or sediment source areas. Cyclical patterns of sedimentation within third-order depositional sequences represent the lithologic response to high-frequency glacio- eustatic sea-level fluctuations. The ideal lithic cycle consists of basal muddy siliciclastic sands, overlain by muddy foraminiferal phosphorite sands, overlain by foraminiferal or diatomaceous muds. This vertical succession of lithologies represents deposition during the transgressive phase of a fourth-order sea-level cycle. Ideal lithic cycles are not laterally persistent but grade into either uniform or interbedded sediment sequences. Diagenesis during subaerial and submarine exposure results in dissolution of primary sedimentological components including phosphate, dolomite, calcareous macrofossils, and calcareous and siliceous microfossils, as well as reprecipitation and neogenesis of secondary sedimentological components including phosphate, dolomite, zeolite and calcite cements. r LITHOSTRATIGRAPHIC ANALYSIS (D OF CYCLICAL PHOSPHORITE SEDIMENTATION WITHIN THE MIOCENE PUNGO RIVER FORMATION, NORTH CAROLINA CONTINENTAL SHELF á byPatrick M. MalletteAPPROVED BY:COMMITTEE (MUL.ILDr. Albert C. HineDIRECTOR OF¿GRADUATE STUDIES, DEPARTMENT OF GEOLOGY/ / C- / , Dr. Scott W. Snyder CHAIRMAN OF THE DEPARÍTMENT OF GEOLOGY ^ Dr. Charles Q. Brown DEAN OF THE GRADUATE SCHOOL ACKNOWLEDGEMENTS Funding, for this study was provided through NSF research grants OCE- 8110907, 0CE-83A2777 and OCE-8609161 to co-investigators Drs. Stanley R. Riggs, Albert C. Hine and Scott W. Snyder. The North Carolina Department of Natural Resources and Community Development, Geological Survey Section, and East Carolina University Department of Geology also provided financial assistance. My sincerest appreciation goes to the members of my commitee, Drs. Stan Riggs, Scott Snyder, Lee Otte and A1 Hine, for their untiring support and encouragement during the research and writing stages of this thesis. Stan and Scott deserve special mention as they both allowed and encouraged me to formulate my own ideas and interpretations, but were also quick to point out and argue alternative ideas. I would also like to thank Stephen W. Snyder for providing seismic interpretations and many stimulating ideas regarding what was happening during the ’Mio-Scene'. Many thanks also go to the crews and scientific personnel of the R/V's Eastward, Endeavor, Iselin and Cape Hatteras whose dedication and hard work resulted in the data base utilized in this study. Many former and present students at ECU have made my graduate tenure most enjoyable. They include Doug 'Hambone' Ellington, Randy 'Dolphineus spp.* Powers, David 'Spike' Mallinson, Leonard 'Skynard' Moretz, Tim 'Tree' Auch, Chee 'Ski' Saunders, Jeff 'Spud' Forgang, Walter 'Wally' Hale and my mentor David 'Fat Boy' Reid. To Angela Rich, who stood by me during the production of this thesis, and to my parents. Ginger and Tony Mallette, who convinced me I could do anything I set my mind to, I dedicate this thesis. TABLE OF CONTENTS Page INTRODUCTION 1 REGIONAL PERSPECTIVE 7 Geographic Setting 7 Stuctural and Paleotopographic Controls 7 Regional Stratigraphy 9 PREVIOUS LITRO-, SEISMO- AND BIOSTRATIGRAPHIC WORK 12 OBJECTIVES 19 METHODS OF INVESTIGATION 20 Core Collection and Storage 20 Laboratory Analysis 20 Lithologic Descriptions 21 Stratigraphic Relationships Among Vibracores 21 Textural and Point Count Analysis 23 Acid Insolubles Analysis 24 Scanning Electron Microscopy 24 Geochemical Analysis 25 SEDIMENTOLOGICAL COMPONENTS 26 Siliciclastic Components 27 Biogenic Components 27 Calcareous biogenic components 27 Siliceous biogenic components 28 Organic matter 30 Primary Authigenic Components 32 Phosphate 32 Dolomite 41 Glauconite 42 Secondary Diagenetic Components 42 Zeolite 43 Silica Polymorphs 44 Calcite Cements 45 Phosphate 45 Dolomite 53 Pyrite 53 LITHOLOGIC DESCRIPTIONS 57 Frying Pan Sequence 57 FPS-1 ; 58 FPS-2 62 FPS-3 66 FPS-4 67 FPS-5 67 FPS-6 68 Onslow Bay Sequence 72 OBS-1 72 OBS-2 74 OBS-3 75 OBS-4 77 OBS Outliers 77 Bogue Banks Sequence 80 BBS-1 80 BBS-2 84 BBS-3 86 BBS-4 86 BBS-5 87 BBS-6 87 BBS-7 87 BBS-8 87 DISCUSSION 88 Regional Lithofacies and Lithostratigraphy 88 Frying Pan Sequence 88 Onslow Bay Sequence 95 Bogue Banks Sequence 103 Miocene Sedimentation Within the Onslow Embayment — A Depositional Model 108 Type 1 109 Type II 116 Type III 120 Comparison of Onslow Bay Lithic Cycles to Aurora Lithic Cycles 122 CONCLUSIONS 125 REFERENCES CITED 133 APPENDIX A: Textural and Acid Insolubles Data 140 APPENDIX B: Point Count Data 145 APPENDIX C: Geochemical Data 150 LIST OF FIGURES Figure Page 1. Structural contour map on the base of the Miocene Pungo River Formation and second order paleotopographic controls within the Onslow and Aurora Embayraents 2 2. Graphic log and relationship among major mineralogical constituents within core holes from the Aurora Phosphate District 3 3. Regional distribution of Tertiary and Cretaceous sediment sequences along the continental margin controlled by the Mid-Carolina Platform High 5 4. Interpreted west-east seismic profile from northern Onslow Bay: 22 meter profile 10 5. Correlation of the Pungo River Formation in Onslow Bay to the Vail coastal onlap chart 14 6. Outcrop distribution of Miocene Pungo River Formation sediment sequences within Onslow Bay 15 7. Seismic stratigraphic nomenclature for third- and fourth- order seismic sequences of the Pungo River Formation in Onslow Bay 17 8. Location of vibracores and selected seismic transects 22 9. Classification scheme for sedimentary phosphorites 33 10. Summary of lithologies within the Frying Pan Sequence 59 11. Composite stratigraphic section: Frying Pan Sequence, central Onslow Bay 61 12. Composite stratigraphic section: Frying Pan Sequence, southern Onslow Bay 63 13. 3.5 kHz profile of buried Miocene hardbottom 64 14. Interpreted west-east seismic profile from southern Onslow Bay: EN-8-C 70 15. Summary of lithologies within the Onslow Bay Sequence 73 16. Interpreted east-west seismic profile from northern Onslow Bay: 15 meter profile 78 17. Summary of lithologies within the Bogue Banks Sequence 81 18. Composite stratigraphic section: Bogue Banks Sequence, northern Onslow Bay 83 19. Composite stratigraphic section: Bogue Banks Sequence, central Onslow Bay 85 20. Regional lithofacies distribution within the Frying Pan Sequence 89 21. Regional lithofacies distribution within the Onslow Bay Sequence 96 22. Structure contours on unconformity separating the Frying Pan Sequence from the Onslow Bay Sequence 98 23. Regional lithofacies distribution within the Bogue Banks Sequence 104 24. Structure contours on unconformity separating the Onslow Bay Sequence from the Bogue Banks Sequence 106 25. Classification and genetic interpretation of vertical patterns of sedimentation within the Pungo River Formation of Onslow Bay 110 26. Schematic section illustrating lateral variation in vertical patterns of sedimentation Ill 27. Interpretation of intrabasinal controls on lithofacies distribution: Frying Pan Sequence 127 28. Interpretation of intrabasinal controls on lithofacies distribution: Onslow Bay Sequence 128 29. Interpretation of intrabasinal controls on lithofacies distribution: Bogue Banks Sequence 130 LIST OF PLATES Plate Page 1. SEM micrograph: dolomite encrusting foraminifer 29 2. SEM micrograph: siliceous microfossil hash 29 3. SEM micrograph: pelletai phosphate 37 4. SEM micrograph: freshly fractured surface of phosphate grain 37 5. SEM micrograph: Close-up of Plate 4: void- lining apatite crystallites 38 6. SEM micrograph: Close-up of Plate 4: Bacteria-like structures within phosphate grain 38 7. SEM micrograph: Close-up of Plate 4: Bacteria-like structures in raicroboring within phosphate grain 39 8. SEM micrograph: Clinoptilolite aggregate occuring as moldic infilling of foraminifer 39 9. SEM micrograph: Opal-CT lepispheres from outer portion of chert nodule 40 10. SEM micrograph: Opal-CT lepispheres encrusting detrital grains 40 11. SEM micrograph: Secondary phosphate associated with calcareous microfossils 46 12. SEM micrograph: Secondary phosphate infilling benthic foraminifer 46 13. SEM micrograph: Secondary phosphate infilling benthic foraminifer 47 14. SEM micrograph: Naturally leached primary phosphate 47 15. SEM micrograph: Hollowed primary phosphate grain resulting from severe leaching 48 16. SEM micrograph: laboratory etched pelletai phosphate.... 48 17. SEM micrograph: Incipient dolomite forming on echinoderm spine 54 18. SEM micrograph: Closeup of Plate 17 54 19. SEM micrograph: Closeup of Plate 17 55 20. SEM micrograph: Framboidal pyrite associated with clinoptilolite 55 LIST OF TABLES Table Page 1. Classification of sediraentological components 26 2. Results of total organic carbon (TOC) analyses 31 3. Grain size distribution of sand-sized phosphate vs. other raineralogical components 34 4. Distribution of Type I, Type II and Type III vertical patterns of sedimentation within fourth-order seismic sequences 117 INTRODUCTION Lithologie, geochemical, paléontologie and geophysical data increasingly suggest that variations in eustatic sea level, produced by glaciation-deglaciation episodes, were not restricted to the Pleistocene, but rather occurred throughout much of the Late Tertiary. Coastal onlap curves (Vail and others, 1977; Vail and Hardenbol, 1979) and their implications for Tertiary sea-level fluctuations have been accepted by most workers. Cycles of sea-level change, periods of time during which a relative rise and fall of sea level takes place, are of various orders of magnitude, with smaller-scale cycles superimposed on larger-scale cycles. If upper continental margin sedimentary basins have experienced such fluctuations in sea level during the Neogene, a lithologic response should be evident in the stratigraphic record. Recent studies along the southeastern U.S. continental margin indicate that multiple lithologic transitions (from siliciclastic to authigenic phosphorite to carbonate sediments) occur vertically within the Miocene section and are 5 interpreted to be the the products of fourth-order (10 yrs.) glacio- eustatic sea-level cycles (Riggs and others, 1982; Stephen W. Snyder, 1982; Riggs, 1984; Riggs and others, 1985). The depositional model proposed by these workers is exemplified by the Pungo River Formation within the Aurora Phosphate District (Fig. 1). Four distinct and laterally traceable lithologic units were identified, each representing a lithic cycle that records a sea-level event. Figure 2 documents the sediraentological transitions through each lithic cycle and emphasizes the inverse relationship between siliciclastic and phosphorite sedimentation, both of which are inversely related to carbonate sedimentation. 2 Figure 1. Structural contours (in meters below sea level) on the base of the Miocene Pungo River Formation, North Carolina continental margin. Structural contours deliniate the east-west trending Cape Lookout High, a pre-Miocene paleotopographic feature which separates the Aurora Embayment to the north and the Onslow Embayment to the south. Also note the location of the Aurora Phosphate District, a site of current phosphate raining. Figure 2. Lithologie characteristics and gamma-ray log of Pungo River Formation units A through D within the Aurora Phosphate District (North Carolina Phosphate Corp. core holes HIO and GH8.5; from Riggs and others, 1982). 4 Within correlative strata of the Miocene Calvert Formation in Virginia, Maryland and Delaware, Kidwell (1985) documented six lithic cycles in basin margin sediment sequences at scales similar to those described by Riggs and co-workers. Calvert lithic cycles are bound by disconformable burrowed firmground surfaces and are generally characterized by a basal condensed fossiliferous horizon which grades upward into siltier and less fossiliferous material. This thesis addresses the lithologic complexities within the Miocene Pungo River Formation of the North Carolina continental shelf in Onslow Bay (Fig. 3). The main objective is to establish a lithostratigraphic framework for these sediments and to compare the vertical facies transitions with those in the Miocene section of the adjacent coastal plain. If the Pungo River Formation was deposited in response to high- frequency sea-level fluctuations, as proposed for the coastal plain section, similar sediment sequences should be developed within correlative strata now exposed on the continental shelf. The data base for the study consists of 95 nine-meter vibracores which penetrate the Pungo River Formation in Onslow Bay and extensive high-resolution seismic coverage. Correlation among vibracores was aided by this seismic framework (Stephen W. Snyder, 1982) coupled with biostratigraphic data from investigators working with various microfossil groups (Waters, 1983; Moore and Scott W. Snyder, 1985; Moore, 1986; Powers, 1986, in prep.; Waters and Scott W. Snyder, 1986; Steinmetz, unpub. data; Palmer, unpub. data). The high-resolution seismic and biostratigraphic data base provided a unique opportunity to relate lithologic relationships to chronostratigraphy. A chronostratigraphic approach is vital to 79*>00' 78“00' 77®00' 76«00' 35®00' 34‘'00' 33«00' Figure 3. Schematic outcrop pattern showing the influence of the Mid- Carolina Platform High on the regional distribution of Cretaceous and Tertiary sediments along tlie southeastern U.S, continental margin (from Stephen W. Snyder, 1982). 6 documenting and understanding the lithologic response to high-frequency sea-level events which have influenced Miocene depositional records along the eastern United States continental margin. REGIONAL PERSPECTIVE Geographic Setting Onslow Bay is a modern coastal erabayment along southeastern North Carolina defined by elongate sand shoals extending seaward off Cape Lookout to the north and Cape Fear to the south (Fig. 1). Raleigh Bay and Long Bay, similar geomorphic features, are situated to the north and south, respectively. The continental shelf in Onslow Bay, up to 100 km. wide, extends southeastward to the shelfbreak at the 50-m isobath. Tertiary strata, including the Miocene Pungo River Formation, crop out on the seafloor, dip gently seaward, and are covered by a patchy, thin (<1 m) veneer of mostly relict siliciclastic and biogenic sand of Holocene age (Luternauer and Pilkey, 1967). Erosional remnants of indurated Plio-Pleistocene carbonates and calcareous sandstones occur locally on the shelf as mesa-like platforms (Mearns, 1986); relief of the bounding scarps may be up to 8 m. Rock-dredge hauls and bottom TV data indicate that these carbonate hardgrounds support a fairly diverse modern population of attached epiflora, epifauna, and boring infauna. Structural and Paleotopographic Controls The continental margin of North Carolina is made up of a seaward thickening wedge of late Mesozoic and Cenozoic sediments deposited along the eastern flank of the Carolina Platform, a broad region of shallow pre-Jurassic crust (Klitgord and Behrendt, 1979). The Mid-Carolina Platform High, formerly referred to as the Cape Fear Arch (Stephenson, 1928), represents the shallowest (<1 km.) portion of the Carolina Platform, occurring between Cape Romain, South Carolina and Cape Fear, 8 North Carolina (Klitgord and Behrendt, 1979). The Carolina Platform is a "first-order structure" which has controlled the overall depositional framework of large portions of the continental margin (Riggs, 1984; Riggs and others, 1985). The influence of the Mid-Carolina Platform High on Cretaceous and Tertiary sedimentation is exemplified by a seaward displacement of sediment sequences around the nose of this feature (Fig. 3). Local, or second-order, paleotopographic features determine the location of individual depocenters (Riggs and others, 1985). Neogene sediments infill two second-order embayraents along the North Carolina continental margin. These erabayments, the Aurora Embayment to the north, and the Onslow Embayment to the south, are separated and thus defined by an E-NE trending, pre-Miocene paleotopographic feature (Fig. 1) referred to as the Cape Lookout High (Stephen W. Snyder and others, 1980; Stephen W. Snyder, 1982; Riggs, 1984; Popenoe, 1985; Riggs and others, 1985). Development of the Cape Lookout High is believed to be the combined result of pre-Miocene sediment drift and deposition and Miocene erosiona! processes (Stephen W. Snyder, 1982; Popenoe, 1985). Seismic data of Stephen W. Snyder (1982) indicate that the Cape Lookout High was a topographically positive feature during Miocene deposition. This interpretation is reinforced by lithologic and paléontologie studies (Scarborough, 1981; Scarborough and others, 1982; Katrosh and Scott W. Snyder, 1982; Gibson, 1983) which indicate a shoaling environment in the vicinity of the Cape Lookout High during the Miocene. In the Onslow Embayment, a pronounced thickening of Pungo River sediments occurs to the east of, and in conjunction with, the White Oak 9 Lineament, which is interpreted to be a major submarine erosional scarp (Stephen W. Snyder, 1982; Stephen W. Snyder and others, 1982; Riggs and others, 1985). Up to 25 meters of subsurface relief occur along this feature. Excavation of the White Oak Lineament post-dates initial deposition of Pungo River strata in Onslow Bay, as evidenced by seismic profiles of Stephen W. Snyder (1982) which show truncation of lower (late Burdigalian) units (Fig. 4). The western updip limit of the Pungo River Formation in Onslow Bay occurs to the west of the White Oak Lineament and trends NE-SW from the western end of Bogue Banks to a position east of Cape Fear. Regional Stratigraphy Along the North Carolina continental margin the Miocene Pungo River Formation crops out on the continental shelf in Onslow Bay and occurs in the subsurface on the emerged coastal plain to the north. Pungo River sediments are correlative with the Calvert and Choptank Formations of the Chesapeake Group of Virginia, Maryland and Delaware, and with the Hawthorn Group of Florida, Georgia and South Carolina (Gibson, 1983; Carter, 1984; Riggs, 1984; Riggs and others, 1985). Characteristic of these sediments are anomalous concentrations of authigenic minerals including phosphate, glauconite, zeolite, Mg-rich clays, dolomite and opal-CT (Brown and others, 1972; Riggs, 1984). This mineral assemblage contrasts with the more 'normal* carbonate and siliciclastic sediments of the under- and overlying strata. In the Aurora Embayment, Pungo River sediments unconforraably overlie Eocene, Oligocène and lower Miocene (?) units, depending on geographic 22 METER PROFILE APPROXIMATELY 6 METERS BELOW Î. WEST EAST OB-109 TTW(MRIOLILA-ISMWEVCAOEYNDLS) Figure 4. Interpreted west-east uniboom seismic profile through northern Onslow Bay (22-meter profile) with vibracore locations superimposed (modified from Stephen W. Snyder, 1982). Note differing depositional styles of third-order sequences. The Frying Pan and Bogue Banks Sequences are characterized by vertical aggradation of the paleo-shelf while the Onslow Bay Sequence is characterized by lateral progradation of the shelf margin. Note also severe erosional truncation of late Burdigalian (Frying Pan Sequence) strata; erosional scarp represents the White Oak Lineament of Stephen W. Snyder (1982). See Figure 8 for profile location. o 11 location (Scarborough, 1981; Scarborough and others, 1982; Riggs and others, 1982; Gibson, 1983). In the Aurora Phosphate District (Figs. 1 and 2), the Pungo River overlies the Eocene Castle Hayne Limestone and contains four distinct lithologic units, labeled A through D (oldest to youngest). These units, with facies variations within each, have been traced from the Aurora area southward to the vicinity of the Cape Lookout High (Scarborough, 1981; Scarborough and others, 1982) . Units C and D yield age-diagnostic planktonic forarainifera assignable to foraminiferal zones N8/N9 (Blow, 1979), indicative of a Langhian age (Katrosh and Scott W. Snyder, 1982; Gibson, 1983). The lower units (A and B) are barren of age-diagnostic forarainifera, but preliminary analyses of diatom floras suggest these units are correlative with Burdigalian strata in the Onslow Erabayment (Powers, 1986, in prep.). In the Onslow Embayment, Oligocène strata equivalent to the Silverdale and Belgrade Formations of the adjacent coastal plain unconformably underlie the Pungo River Formation, which is in turn unconformably overlain by Pliocene and Quaternary sediments (Lewis, 1981; Lewis and others, 1982). Biostratigraphic analyses of planktonic foraminifers from the Onslow Embayment yielded age-diagnostic species from Blow's (1979) foraminiferal zones N6 through N9 and Nil through N14, corresponding to a late Burdigalian through early Serravallian age (Waters, 1983; Moore and Scott W. Snyder, 1985; Moore, 1986; Waters and Scott W. Snyder, 1986). These age assignments have been corroborated by analyses of calcareous nannofossils (Steimetz, unpub. data) and siliceous microfossils (Palmer, unpub. data; Powers, 1986). PREVIOUS LITHO-, SEISMO- AND BIOSTRATIGRAPHIC WORK Prior to 1980, most of the studies concerning the Miocene Pungo River Formation dealt with its occurrence on the North Carolina Coastal Plain in and around the Aurora Phosphate District (Brown, 1958; Kimrey, 1964 and 1965; Gibson, 1967; Miller, 1971; Scarborough, 1981; Scarborough and others, 1982). Phosphatic sediments were also described from Quaternary surface sands on the continental shelf of southeastern North Carolina, where they were attributed to reworking from underlying Pungo River sediments (Luternauer and Pilkey, 1967). Miocene sediments were subsequently identified from core samples on the inner continental shelf of Onslow Bay (Meisburger, 1979) and beneath the Quaternary sands on Bogue Banks (Steele, 1980). Extensive geological and geophysical investigations have since been conducted on the occurrence of the Pungo River Formation on the continental shelf within Onslow Bay. These investigations, including this thesis, are part of an ongoing research program, sponsored by the National Science Foundation (NSF) and National Oceanic and Atmospheric Administration (NOAA) and directed by Dr. Stanley R. Riggs and Dr. Scott W. Snyder of East Carolina University and Dr. Albert C. Mine of the University of South Florida. Lewis (1981) and Lewis and others (1982) first described lithologies of the Pungo River Formation where it crops out in Onslow Bay on the North Carolina continental shelf. Based on mineralógica! and textural data from 60 nine-meter vibracores (also used in this study) they subdivided the formation in northern and central Onslow Bay into three lithologic units: 1) quartz sand, 2) biorudite and 3) phosphatic sand. They also described three phosphorite to phosphatic sequences in the 13 Frying Pan Shoals area (southern Onslow Bay), but could not correlate them with sediments in northern Onslow Bay due to stratigraphic complexity and the lack of a seismic and biostratigraphic framework. Utilizing over 10,000 km of high-resolution uniboora, sparker and 3.5 kHz seismic profiling data, Stephen W. Snyder (1982) defined a detailed seismic-stratigraphic framework for the Pungo River Formation in Onslow Bay. He subdivided the Pungo River into three seismic sequences, each bound by major unconformities, and correlated these sequences with the third-order TM 1.4, TM 2.1 and TM 2.2 cycles of global sea-level change proposed by Vail and Hardenbol (1979). Biostratigraphic analyses (Waters, 1983; Moore and Scott W. Snyder, 1985; Moore, 1986; Waters and Scott W. Snyder, 1986; Powers, 1986; Palmer, unpub. data; Steinraetz unpub. data) have demonstrated a late Burdigalian age for the lower third-order sequence, a Langhian age for the middle third-order sequence, and a Serravallian age for the upper third-order sequence. The third- order sequences contain at least 18 smaller-scale seismic sequences which are interpreted to reflect higher frequency, fourth-order cycles of sea- level change superimposed on the third-order cycles defined by Vail and Hardenbol (1979) (Fig. 5). Seismic data indicate that each fourth-order sequence is bound by regional unconformities although Waters (1983) found the hiatuses to be beyond the resolution of planktonic foraminiferal biostratigraphy. Outcrop distribution of these seismic sequences is shown in Figure 6. Stephen W. Snyder (1982) recognized the third-order seismic sequences as products of "discrete depositional episodes distinguishable via well established bounding unconformities as well as their litho-, CYCLES OF RELATIVE CHANGES OF SEA LEVEL BASED ON PHOSPHATE SECTION w w COASTAL ONLAP 9;: (After Vail & Mitchum,1979) NORTH CAROLINA CONTINENTAL MARGIN R S NO FALLING EPOCHS 2 O 0^ Wggwgggqi5WW8mWWWMWteW0WQ9WWWW^^WWWW9flW09WflaBaBBMBBBBBB>99b9999Wj ALTERNATING GLACIAL EPISODES PLEISTOCENE AND PLEISTOCENE DEPOSITION MAJOR GLACIAL EPISODE AND TP3 DEVELOPMENT OF UNCONFORMITY PLIOCENE TP2 UPPER YORKTOWN FM. TP1 Tl\43.3 TM3.2 TM3.1 MAJOR GLACIAL EPISODE AND FOURTH-ORDER -10 I 1— DEVELOPMENT OF UNCONFORMITY SEA-LEVEL CYCLES \ TM2.3 (Snyder, 1982) TM2.2 TM2.1 TM1.4 -20 PRESENT J TM1.3 SEA LEVEL MAJOR GLACIAL EPISODE AND TMJ.2 DEVELOPMENT OF UNCONFORMITY TM1.1 Figure 5. Correlation of third- and fourth-order sequences of the Pungo River Formation in Onslow Bay to the Vail coastal onlap curve. See Figure 7 for current stratigraphic nomenclature. 15 Figure 6. Outcrop distribution of three third-order (Frying Pan, Onslow Bay and Bogue Banks Sequences) and 18 fourth order sequences of the Pungo River Formation in Onslow Bay (modified from Stephen W. Snyder, 1982). 16 bio- and chemostratigraphic characteristics" and stated that "the composite Miocene section is lithologically distinct from the underlying and overlying formations, but transgresses the previously ascribed age boundaries of the Pungo River Formation". On this basis, he developed an informal nomenclature for third-order seismic sequences in Onslow Bay. The lower third-order sequence, designated the Frying Pan "formation" (FPF), comprised six fourth-order seismic sequences (FPF-1 through FPF- 6); the middle third-order sequence, designated the Aurora "formation" (AF), contained four fourth-order seismic sequences (AF-1 through AF-4); and the upper third-order sequence, designated the Bogue Banks "formation" (BBF), included six fourth-order seismic sequences (BBF-1 through BBF-6). Though the proposed nomenclature was based on geophysical recognition criteria and not lithologic criteria, the abbreviated seismic-stratigraphic nomenclature was adopted by others and is well established in the literature (Stephen W. Snyder, 1982; Riggs, 1984; Riggs and others, 1985; Stewart, 1985; Moore and Scott W. Snyder, 1985; Moore, 1986; Waters and Scott W. Snyder, 1986). Stephen W. Snyder (in prep.) has recently revised the seismic-statigraphic nomenclature to reflect its geophysical basis. According to the revised nomenclature, third-order seismic sequences, formerly referred to as formations by Snyder (1982), are now referred to simply as sequences (Fig. 7). Thus, the Frying Pan "formation" becomes the Frying Pan Sequence, with its fourth-order sequences labeled FPS-1 through FPS-6; the Aurora "formation" is renamed the Onslow Bay Sequence, with its fourth-order sequences labeled OBS-1 through OBS-4; and the Bogue Banks "formation" 17 SEISMIC STRATIGRAPHIC NOMENCLATURE OF THE PUNGO RIVER FORMATION; NORTH CAROLINA CONTINENTAL SHELF T. lU O O SNYDER (1982) SNYDER (in press); THIS STUDY o Û. y- THIRD-ORDER FOURTH-ORDER THIRD-ORDER FOURTH-ORDER LU co SEISMIC SEQUENCE SEISMIC SEQUENCE SEISMIC SEQUENCE SEISMIC SEQUENCE ?WWVWWN www'ywN- AAAAAAAAAAwwvwwv BBF-6 BBS-8 ^/vwwwwwwv VWWVWWVWWN BBF-5 BBS-7 wwwwwvww WWWWWWWV BBF-4 BBS-6 LU BOGUE C WWWWWWWV BOGUE kA/WWW\AAAAAA/\ CQ BBF-3 BBS-5 CO > BANKS ^AAAAAAAAAAAAAA/' BANKS WWWWWWWV CO w L. BBF-2 BBS-4 Z 0co "FORMATION" WWWWWWWV WWWWWWWVSEQUENCE BBS-3 vA/WVVVVWVWW\ BBF-1 BBS-2 LU vA/VWW\AAAAAAAA BBS-1 ?WVWWWN ^VWWVWNA AAAAAAAAAA WWVWWV AF-4 OBS-4 o WWWWWWWV ONSLOW WWWVVW\AAAA/\ C CO AURORA AF-3 OBS-3 Ui WWWWWWWV BAY vAAAA/VVVVVVVVVV\ c co "FORMATION" AF-2 OBS-2 o WWWWWWWV SEQUENCE WVWWVWWWV AF-1 OBS-1 sAAAA/VWWN ^VWWWVNA AAAAAAAAAAAAAAAAAAAA FPF-6 FPS-6 WWWWWWWV WWWWWWWV c co FPF-5 FPS-5 *5 FRYING WWWWWWWV FRYING WWWWWWWV O) FPF-4 FPS-4 o PAN PANWWWWWWWV WVWWVWWWV' co FPF-3 0.5% TOC. However, samples from the phosphorite facies and mud facies of southern Onslow Bay contain the highest percentages (ranging from 0.94 to 5.74% TOC). The relative amount of organic matter which accumulates in the sediment column can be related to 1) relative productivity in the overlying waters, 2) grain size of the substrate, 3) redox potential of the depositional environment and 4) mineralogy of associated sediments (Barker, 1980). Increased productivity is directly related to the potential amount of organic matter which may be incorporated within the sediments. Sands tend to have lower organic content than do muds (or shales) as sands tend to accumulate in relatively high energy environments where smaller particles, including organic matter are winnowed and deposited in quieter environments. Also, these higher energy environments are well oxygenated, and organic matter is unstable under oxidizing conditions. Reducing conditions, which may characterize quieter depositional environments where fine-grained sediments accumulate, favor the preservation of organic matter. Clay particles, due to their large surface areas, also tend to adsorb and transfer some types of organic matter from solution into the sediments. 31 Table 2. Results of total organic carbon (TOC) analyses from Pungo River sediments from the Onslow Embayraent (Chris Martens, unpub. data). Samples from the phosphorite facies and mud facies of southern Onslow Bay are denoted with an asterisk (*). NOB = northern Onslow Bay; COB = central Onslow Bay; SOB = southern Onslow Bay. Seismic Sequence Area Core Depth ( m) %T0C BBS-2 COB OB-94 1.0 to 1.1 0.84 BBS-2 NOB OB-72 1.5 to 1.6 0.60 BBS-1 NOB OB-72 4.2 1.22 BBS-1 NOB OB-79 4.5 to 4.6 1.59 BBS-1 NOB OB-79 5.9 to 6.0 1.10 OBS-3 SOB OB-68 1.5 to 1.6 3.15* OBS-2 SOB OB-68 4.8 to 4.9 0.99 OBS-1 NOB 0B-80 4.9 to 5.3 0.70 FPS-6 SOB OB-96 1.4 to 1.5 0.67 FPS-6 SOB OB-96 2.9 to 3.0 0.64 FPS-6 SOB OB-96 4.4 to 4.5 0.88 FPS-6 SOB OB-67 4.5 to 4.6 0.42 FPS-6 SOB OB-67 7.7 to 7.8 0.66 FPS-3 SOB OB-66 3.5 to 3.6 1.11* FPS-2 SOB OB-98 1.4 to 1.5 3.96* FPS-2 SOB OB-98 4.0 to 4.1 5.74* FPS-2 SOB OB-97 1.4 to 1.5 0.54 FPS-2 SOB OB-97 2.9 to 3.0 1.66* FPS-2 SOB OB-97 4.4 to 4.5 2.00* FPS-2 SOB OB-97 5.9 to 6.0 1.92* FPS-2 SOB OB-63 0.15 to 0.25 2.12* FPS-2 SOB OB-63 1.6 to 1.7 4.35* FPS-2 SOB OB-65 3.0 to 3.1 1.41* FPS-2 SOB OB-65 4.7 to 4.8 0.94* FPS-1 SOB OB-64 4.5 to 4.7 3.08* 32 Primary Authigenic Components Primary authigenic components are defined herein as those minéralogie constituents which were precipitated at, or immediately below, the sediment-water interface at or near the time of deposition. Thus, they reflect chemical conditions within the overlying water column and within interstitial waters at the time of formation. Primary authigenic components include phosphate, dolomite and glauconite. Phosphate Phosphate grain types were described and classified on the basis of morphological characteristics according to a scheme developed by Riggs (1979) (Fig. 9). Recognition and identification of phosphatic material was aided by a modified version of the Shapiro method (Shapiro, 1952)) in which the unknown material is dissolved in a solution of concentrated nitric acid and ammonium molybdate. Formation of a yellow precipitate confirms the presence of phosphate. Phosphate occurs chiefly as sand-sized pelletai, intraclastic and skeletal grains, and occasionally as microsphorite and phosphate coated quartz grains, the latter having been eroded from microsphorite pavements. The relative percentage of phosphate versus other mineral constituents within the sand fraction decreases sharply with decreasing grain size (Table 3) and only minor amounts of phosphate occur in the silt fraction. Pelletai grains are spherical to ovoid and range from medium- to very- fine-sand size. Intraclastic grains are irregularly shaped, subangular to rounded, generally larger than pelletai grains, and occur 33 % ORTHOCHEMS Figure 9. Classification scheme for sedimentary phosphate grains (from Riggs, 1979; modified by Scarborough, 1982). 34 Table 3. Grain size distribution of phosphate vs. other mineralogical components in various sand size classes. Numerical values correspond to percent phosphate within each size class Core- coarse sand medium sand fine sand very fine sand Sample 0.5 0 1.0 0 1.5 0 2.0 0 2.5 0 3.0 0 3.5 0 4 .0 0 14-1 84% 82 85 87 85 84 32 5 14-2 48% 44 12 44 39 29 9 2 24-1 90% 81 81 79 86 63 27 9 20-4 — 56 17 38 52 55 32 4 30-2 74% 75 72 83 86 83 33 7 throughout the sand- and granule-size range. Under reflected light, pelletai and intraclastic phosphate typically appears dark brown to very dark brown, and is often highly lustrous owing to a transluscent outer cortex. Skeletal phosphate consists of bone and teeth fragments and the exoskeletal hardparts of inarticulate brachiopods. Skeletal grains are irregularly shaped to platy or rod-shaped, vary from medium sand- to granule-sized and are transluscent amber under reflected light. The principal phosphate mineral in pelletai and intraclastic grains is carbonate fluorapatite, or francolite (Ellington, 1984). Vertebrate skeletal phosphate was originally hydroxyapatite but has since been converted to carbonate fluorapatite following death of the organism (Ellington, 1984). This is an early diagenetic transformation, but because the material was originally apatite it is included with primary components. Based on studies of the Miocene Hawthorn Formation in Florida, Riggs 35 (1979) and Riggs (1980) proposed that pelletai phosphorites were formed from a colloidal suspension of orthochemical phosphorite mud which contained inclusions of planktonic shell debris, organic matter, bacteria, silt-sized dolomite rhombs and minor siliciclastic silt and clay. Phosphate-rich muds were thought to accumulate at the sediment- water interface in high-nutrient, dysaerobic, outer shelf environments. A low diversity, high dominance, soft-bodied infauna of mainly detritus feeders characterized the benthic environment. The organisms ingested the bacteria-rich phosphate muds and excreted compacted fecal pellets which were later indurated. Intraclastic phosphorite was interpreted as rip-up clasts from indurated orthochemical phosporite muds (microsphorite) which had accumulated ini situ in inner shelf environments or in semi-protected coastal environments. Skeletal phosphate is precipitated biochemically as endoskeletal material by nektonic vertebrates and as exoskeletal material by invertebrates. Skeletal phosphate may be deposited in all the above environments. SEM analyses were performed on naturally occuring pelletai and intraclastic grains and on grains which were etched in the laboratory with formic and acetic acid to reveal the grain ultrastructure. Etching demonstrates that all grains contain silt-sized quartz, pyrite, diatom fragments and clay minerals. Etching also revealed a less soluble, apatitic outer cortex surrounding the grains (Plate 3). During etching, grain interiors are progressively hollowed, revealing the less soluble outer cortex. Dissolution in the natural environment produces similar pitted and hollowed grains (Plates 4 and 5); these effects will be discussed under Secondary Diagenetic Components. Unetched grains exhibit 36 a smooth exterior with little pitting (Plate 6), but grain interiors displayed on freshly fractured surfaces are relatively porous (Plate 7). Radial aggregates of apatite(?) crystallites may line the walls of interior voids (Plate 8). Bacteria-like, 1 to 2 urn fusiform structures are very common, occurring individually and as aggregates within the voids (Plates 9 and 10). Similar rod-shaped structures have been reported worldwide in Miocene to Recent phosphorites (Riggs, 1979; Burnett and others, 1980; O'Brien and others, 1981; Baturin, 1982; Mullins and Rasch, 1985). Various interpretations have been presented with several authors noting their morphological similarity to some types of modern bacteria (Riggs, 1979 O'Brien and others, 1981; Mullins and Rasch, 1985). These authors speculate to varying degrees on the extent to which microbial processes may be involved in apatite precipitation. O'Brien and others (1981) suggest microbial processes may play a dominant role in the genesis of the East Australian phosphorites. Other authors interpret these fusiform structures as apatite crystals (Burnett and others, 1980; Baturin, 1982). Baturin (1982) states that "elongated fusiform particles with rounded or splintery tips, up to 1 to 2 urn in size" are an "intermediate stage between amorphous and crystalline phosphate". It is possible that bacteria present within the grains during formation were subsequently phosphatized and thus preserved. If the fusiform structures do represent fossil bacteria the question of whether they played an active role in the process of phosphogenesis is still unanswered. However, there is increasing evidence for bacteria in phosphorites of all ages, and the idea that bacteria are involved in Plate 3. Laboratory etched (50% formic acid, 1.5 hour) pelletai phosphate. Etching leads to hollowing of grain interior leaving a less soluble outer cortex. (Holocene sand, southern Onslow Bay). Plate 4. Intraclastic phosphate exhibiting a pitted surface texture indicative of solutioning. Compare with unaltered phosphate grains in Plate 3. FPS-2, southern Onslow Bay, OB-70, 0.66 m. Plate 3 Plate 4 Plate 5. Pelletai phosphate which has undergone extensive natural dissolution. Less soluble outer cortex is evidenced by hollowing of the grain interior. FPS-2, southern Onslow Bay, OB-70, 0.66 m. Plate 6. Pelletai phosphate. Note smooth exterior surface which lacks solution pitting. FPS-1, southern Onslow Bay, OB-14, 4.25 m. 38 Plate 5 Plate 6 Plate 7. Freshly fractured surface of pelletai phosphate. Note relatively porous interior as compared to exterior surfaces shown in Plate 3. FPS-1, southern Onslow Bay, OB-14, 4.25 ra. Plate 8. Close-up of Plate 5. Radial crystallites of apatite(?) within interior void in pelletai phosphate. Note 'raspberry* texture formed by individual crystal terminations. Plate 9. Close-up of Plate 5. Rod-shaped bacteria-like structures within interior void in pelletai phosphate. Note beginnings of 'raspberry' texture at rod terminations. Plate 10. Close-up of Plate 5. Rod-shaped bacteria-like structures within microboring(?) in pelletai phosphate. Plate 9 Plate 10 41 apatite precipitation is gaining support (Cayeux, 1936; Riggs, 1979; O’Brien and others, 1981; Riggs, 1982; Soudry and Champetier, 1983; Mullins and Rasch, 1985; Prevot and Lucas, 1986). Dolomite Dolomite within Pungo River sediments occurs primarily as individual very-fine sand- to silt-sized rhombs, and less commonly as rhomb aggregates. The rhombs are typically water-clear with sharp crystal edges, implying in situ formation rather than a detrital origin. Rhombs commonly contain white, opaque cores. Some dolomite occurs within all lithofacies, but variations in abundance are often difficult to recognize due to its characteristically fine grain-size. Pungo River dolomite is non-stoichiometric and Mg-depleted; magnesium content ranges from 42 to 48 mole percent (Allen and Baker, 1984; Allen, 1985; Stewart, 1985). Based on oxygen and carbon isotopic analyses and on trace element geochemistry, Allen and Baker (1984) and Allen (1985) concluded that dolomites in the Pungo River Formation were formed as a primary authigenic mineral phase on the continental shelf in o o cool marine pore waters (4 to 13 C) within the zone of sulfate reduction. Sulfate reduction generally occurs within the first few meters of sediment below the sediment-water interface (Berner, 1980). Some dolomite occurs as crystal overgrowths on calcareous biogenic material. This form of dolomite is considered to be diagenetic and will be discussed in the following section. Interpretation of a primary origin for Pungo River dolomites is based on their occurrence as euhedral rhombs showing little abrasion, their occurrence as inclusions embedded 42 within primary phosphate grains, and the isotopic data discussed above. Glauconite Trace amounts of light to dark green, silt-sized to very fine sand- sized particles were routinely encountered during sample description and were referred to as glauconite. Anomalous glauconite percentages of 5 to 7% were recorded in core OB-34, where the material occurs as medium sand- sized, very dark green, subangular to slightly ovoid grains with characteristic syneresis cracks. Light to dark green glauconite is occasionally observed filling skeletal porosity, such as longitudinal tubes in barnacle plates, and microborings in carbonate shell fragments. It is generally rare in Pungo River sediments, but 4 to 5% of the shell fragments in OB-38 exhibit this type of glauconite. According to Odin and Letolle (1980), glauconite forms under slightly reducing conditions on the sea bottom within the upper few centimeters of sediment during periods of reduced rates of sedimentation. These authors separated the authigenesis of glauconite from post-burial diagenesis, citing the necessity of contact with open seawater to supply ions for glauconite crystal growth. According to their model, burial by biogenic or detrital sediments would arrest the process of glauconitization. Secondary Diagenetic Components Secondary diagenetic components result from post-depositional alteration such as dissolution and reprecipitation of primary components, or they may be neogenetic, without a primary mineralogical precursor. 43 Other secondary processes which alter the preservation of primary sediments may include partial or complete dissolution of siliceous and calcareous microfossils and primary phosphate grains. Complete dissolution of foraminifera has been documented (this study) where secondary mineral phases were precipitated as test fillings prior to dissolution. Silica polymorphs, such as opal-CT lepispheres and chert, and possibly high-silica zeolite (clinoptilolite), are interpreted to reflect dissolution and reprecipitation of silica from precursor siliceous microfossils. Dissolution of primary phosphate has produced hollowed and pitted grains similar to those produced by laboratory etching (discussed under primary phosphate above). Secondary sedimentological components include zeolite (clinoptilolite), silica polymorphs (opal-CT lepispheres and chert), calcite cements, phosphate, dolomite and pyrite. Zeolite Clinoptilolite, a high-silica zeolite, was recognized by Lyle (1984) and confirmed through X-ray diffraction, microprobe analyses and by comparative crystal morphology (Scott W. Snyder and others, 1984). Recognition criteria used in this study were crystal morphology and mode of occurrence: primarily as lath-shaped to bladed crystal aggregates which occur as raoldic infillings of benthic and planktonic foraminifers (Plate 11). During descriptions of foram-rich sediment samples, calcareous tests were routinely dissolved in dilute HCl to test for the presence of chamber-filling clinoptilolite. Natural dissolution of calcareous tests also exposes clinoptilolite aggregates within the sediment column. 44 Clinoptilolite, as coarse-silt and sand-sized aggregates, reaches a maximum abundance of 15 to 30% of the total sediment in the sandy to silty, organic-rich (ave. 2.68% TOC; Martens, unpub. data) muds of the southern portion of FPS-2 (cores 27, 28 and 117). Observed abundance of clinoptilolite aggregates in these muds is directly proportional to the degree of foraminiferal dissolution, which increases progressively upward through these cores. The degree of infilling of foraminiferal tests decreases downsection, although this relationship could not be quantified. Associated sediments contain no silica polymorphs and only rare, corroded diatom valve fragments; however, they are laterally equivalent to diatomaceous and cherty sediments to the north (see discussion of FPS-2 in following section). A regional trend from diatomaceous to cherty to zeolitic sediments suggests that dissolution of pre-existing biogenic silica may have provided, at least in part, silica neccessary for neogenesis of clinoptilolite. Dissolution of biogenic silica may have been enhanced through increased pore water alkalinity as a result of sulfate reduction within the organic-rich muds of FPS-2 in southern Onslow Bay (see Table 2). Other silica sources, such as the contribution from clay mineral transformations (ie., smectite to illite) cannot be ruled out. Silica Polymorphs Nodular chert occurs along unconformities within the Frying Pan Sequence, in sediments laterally equivalent to diatomaceous facies within the Frying Pan Sequence and Bogue Banks Sequence and in carbonate-rich sediments within the Onslow Bay Sequence. Nodules are typically olive 45 green to olive gray, conchoidally fractured (resulting from breakage during vibracoring) and may be encased by a white dolomitic rind. On the basis of x-ray diffraction, Stewart (1985) identified the dominant silica phase as opal-CT with minor quartz. Opal-CT lepispheres occur in the outer portions of nodules (Plate 12) and were also observed forming on detrital quartz, feldspar and dolomite grains from core OB-123. These latter grains served as a substrate on which the lepispheres nucleated (Plate 13). Calcite Cements Precipitation of interstitial calcite leads to partial or total lithification of surrounding sediments and occurs primarily in biogenic, carbonate-rich lithologies. Crystal overgrowths on calcareous fossils in otherwise unconsolidated sediments, are the most widespread occurrence of secondary calcite cements. Phosphate Secondary phosphate occurs as a precipitate within foraminiferal tests and as exterior coatings on forarainifera and echinoderm spines (Plates 14, 15 and 16). It is typically transluscent, amber-colored and appears relatively pure with few visible inclusions. This form of phosphate is rare in Pungo River sediments as a whole. It does occur in late Burdigalian to Langhian age sediments (Frying Pan Sequence and Onslow Bay Sequence) in southern Onslow Bay (cores OB-15, OB-17, OB-68 from OBS- outliers; OB-70 from FPS-2) where it is consistently present, although it generally constitutes <10% of the total sediment. Associated sediments are characteristically organic-rich (3.15% TOC in OB-68; Chris Martens, Plate 11. Internal mold of planktonic foraminifer composed of zeolite (clinoptilolite). FPS-2, southern Onslow Bay, OB-70, 1.85 m. Plate 12. Opal-CT lepispheres from outer , less dense dolomitic rind of chert nodule. FPS-2, central Onslow Bay, OB-123, 1.75 to 2.0 m. 46 Plate 11 Plate 12 Plate 13. Opal-CT lepispheres forming on detrital feldspar(?). FPS-2; central Onslow Bay, OB-123, 0.5 to 0.75 meters. Plate 14. Secondary apatite precipitated around and within calcareous microfossils. Clockwise from lower left: filling and clotting echinoderm spine; filling benthic foraminifer; coating planktonic foraminifer and clotting test perforations; planktonic foraminifer without coating or infill gives contrast. FPS-2; southern Onslow Bay, OB-70. 47 Plate 13 Plate 15. Benthic foraminifer (Lenticulina sp.) with secondary apatite test filling has been naturally dissolved. Note prismatic nature of primary test material in sutures, 'glazed' appearance of test outer surface due to apatite(?) coating and lack of solution pitting on chamber filling apatite indicating its lower solubility with respect to primary test material. OBS-3, southern Onslow Bay, OB-68, 1.75 m. Plate 16. Secondary apatite internal mold of benthic foraminfer (Lenticulina sp.). Primary test material is almost completely dissolved although apatite shows no evidence of dissolution. OBS-3, southern Onslow Bay, OB-68, 1.75 m. Plate 15 49 unpub. data), finely mottled, slightly sandy to silty clays. Co- occurring primary pelletai and intraclastic phosphate is generally light orange-brown to light brown with a pitted surface texture. Plates 4 and 5 show the highly leached surface texture of these grains. Locally, increased leaching in the natural environment has dissolved the grain interior producing hollow grains (Plate 5) with a less soluble and/or purer apatitic outer cortex. This dissolution sequence is readily reproducible by differentially etching primary phosphate grains in the laboratory (see Plate 3). The co-occurrence of leached primary phosphate and precipitated secondary phosphate suggests that remobilization of phosphorous during dissolution of primary grains may provide a source of phosphorous for reprecipitation as test fillings and coatings. However, it seems probable that calcareous test material would dissolve simultaneously, as the stability fields of calciura-fluorapatite and calcite are similar. The presence of phosphate infillings in calcareous tests demonstrates that phosphate precipitation predated dissolution of the host forarainifer. Three scenarios are presented below to explain the paragenetic sequence of secondary phosphate precipitation associated with calcareous raicrofossils as observed in cores OB-15, OB-17, OB-68 and OB- 70. Scenario 1. Minor amounts of primary pelletai and intraclastic phosphate form authigenically at or near the sediment-water interface in organic-rich silty clays. The benthic faunal community is populated by foraminifera and echinoderms. 50 Planktonic forarainifera rain down from the overlying water column. 2. Following burial and subsequent subaerial exposure during sea-level lowstands, the pH of porewaters is lowered as a result of oxidation of organic-rich sediments and circulation of meteoric waters. Primary phosphate dissolves and as saturation limits are reached mobilized phosphorous reprecipitates as apatite around and within calcareous microfossils. 3. Following precipitation of secondary apatite, further dissolution leads to the partial or complete destruction of test material and exposure of moldic infills. Although secondary apatite was present during the dissolution event which affected the calcareous test material, the secondary apatite shows no evidence of dissolution due to its lower solubility. This scenario supplies a source of phosphorus for reprecipitation and implies a solubility ranking of associated components where secondary apatite is least soluble, calcareous test material is intermediate and primary phosphate is most soluble. Calcareous test material should be more soluble at a given pH than primary apatite. This somewhat contradictory solubility ranking may be resolved in Scenario II below. Scenario II. 1. Same conditions as item #1 in Scenario I above. 2. Dissolved phosphorous is mobilized within the sediments 51 from a source other than primary phosphate grains, possibly from the breakdown of organic matter, following burial and is precipitated as secondary apatite within and around calcareous raicrofossils. 3. Lowered pH values in sediment porewaters, occurring as in item #3 in Scenario I above, lead to partial or complete dissolution of primary phosphate and calcareous test material but have no visible effect on secondary apatite which infills and coats microfossils. This scenario implies one dissolution event and suggests that no dissolution of primary phosphate or calcareous microfossils took place prior to secondary precipitation of apatite within and around microfossils. Secondary apatite is still the least soluble component when compared to primary phosphate or raicrofossil material; the latter two components cannot be ranked in terms of relative solubility. The actual sequence of events involving the precipitation of secondary apatite and the dissolution of primary phosphate and biogenic calcite probably results from both scenarios operating simultaneously in specific microenvironments. Baturin (1982) reports that carbonic acid ions, ammonia, and phosphorus may accumulate in sediment pore waters as a result of the decay of organic matter and sulfate reduction. Once saturation is reached, phosphate will begin to precipitate on materials of different composition including fossil material, clastic grains and other phosphate grains. He states that indiscriminant precipitation may be related to raicrocenters of high pH on these particles which result 52 from bacterial sulfate reduction, liberation of ammonia from organic matter and solution of carbonates. Scenario III 1. Apatite which infills and coats microfossils was precipitated during the primary phosphogenic episode which produced the pelletai and intraclastic grains. This third scenario is rejected due to a lack of phosphate coated and infilled calcareous microfossils within the major phosphorite lithofacies of FPS-1 (up to 65% phosphate within the total sediment). These phosphorites and their associated microfossil assemblages are interpreted to be situ based on textural relationships which imply little reworking and winnowing ie., a relative lack of coarse-grained siliciclastic material, preserved burrow mottling, lack of current structures, and a well-preserved, unabraded foraminiferal assemblage. Also, Scott W. Snyder and others (1982) and Scott W. Snyder (in press) present evidence that specific low diversity, high dominance benthic foraminiferal faunas predominate in phosphorite horizons in the Pungo River Formation in response to low dissolved oxygen and high nutrient levels associated with environments of primary phosphogenesis. These foraminifers do not exhibit phosphate infillings or exterior coatings. Based on the above evidence, it appears that primary phosphate authigenesis and the formation of pelletai and intraclastic grains can and does occur while calcareous microfossils within the phosphogenic environment remain unaltered. It is for this reason that the occurrence of phosphate-coated and infilled microfossils seems anomalous and appears 53 to be related to secondary diagenesis. Dolomite Subdivision of dolomite into primary and secondary categories is difficult based on visual criteria. Carbon isotope and trace element analyses of Allen (1985) suggest that a portion of the total dolomite in Pungo River sediments is primary. However, some dolomite appears to be secondary. SEM analyses have shown incipient rhombic crystals, presumably dolomite, forming at the expense of calcareous fossil fragments (Plates 17, 18 and 19). Dolomite is also seen encrusting calcareous microfossils, but may simply be using the calcareous grains as a growth substrate. Allen (1985) stated that at least some of the carbon for dolomite production was supplied by precursor calcium carbonate. On this basis, dolomite is included in both primary and secondary categories although, as noted above, subdivision based on visual criteria is difficult. Pyrite Pyrite forms in reducing environments as a common end product of bacterial sulfate reduction in organic-rich sediments (Friedman and Sanders, 1978). Trace amounts of pyrite are often noted in southern Onslow Bay within the mud facies of the Frying Pan Sequence and the Onslow Bay Sequence. These sediments are organic-rich, containing an average of 2.68% TOC (Table 2). Pyrite is recognized by its brassy yellow color and typical fraraboidal habit. It is often precipitated within foraminifera and co-occurs with clinoptilolite, forming fraraboidal aggregates on clinoptilolite crystal laths (Plate 20). This association Plate 17. Secondary(?) dolomite encrusting echinoderm spine. Arrows show locations of close-ups shown in Plates 18 and 19. BBS- 2, northern Onslow Bay, OB-72, 4.0 m. Plate 18. Close-up of Plate 17. Incipient dolomite(?) rhomb on echinoderm spine. Plate 19. Close-up of Plate 17. Incipient dolomite(?) rhomb forming within solution pocket on echinoderra spine. Plate 20. Framboidal pyrite forming on crystal laths of neogenetic clinoptilolite from internal mold of planktonic foraminifer. FPS-2, southern Onslow Bay, OB-70, 0.85 m. Plate 19 Plate 20 56 indicates that pyrite formation, at least in some cases, post-dates precipitation of clinoptilolite and is the basis for classifying pyrite within the secondary-diagenetic category. Some pyrite may be primary authigenic, as trace amounts of disseminated pyrite were noted within primary phosphate grains. LITHOLOGIC DESCRIPTIONS One of the primary objectives of this thesis is to define the mineralogical and textural characteristics within each fourth-order seismic sequence of the Pungo River Formation in Onslow Say. The following sections present the vertical and lateral lithologic characteristics of individual fourth-order seismic sequences. This format provides order to the descriptive sections and a temporal framework for comparison of regional lithologic variation. It is assumed that seismic reflectors represent statal surfaces and unconformities, and therefore, are chronostratigraphically significant (Vail and others, 1977). Lithologic descriptions begin with the northernmost vibracore(s) within a fouth-order seismic sequence and proceed southward. East-west seismic survey transects pass through most vibracore sites and these transects will be mentioned for geographic reference (see Figure 8 for location of transects). Following lithologic descriptions of fourth- order seismic sequences, the regional lithostratigraphic framework and depositional history of the larger third-order sequences is discussed. Frying Pan Sequence The third-order Frying Pan Sequence, of late Burdigalian age, comprises six smaller-scale, fourth-order sequences referred to as FPS-1 through FPS-6, from oldest to youngest (Fig. 6). The Frying Pan Sequence 2 forms a NE-SW outcrop and shallow subcrop pattern covering over 2300 km in Onslow Bay. Fourth-order seismic sequences dip gently to the east and southeast. 58 FPS-1 FPS-1 is continuous in outcrop and shallow subcrop from northern to southern Onslow Bay (Fig. 6). Sinuousity of the outcrop pattern east of Cape Fear is related to underlying flexure basins developed penecontemporaneously with early Miocene deposition (Stephen W. Snyder, 1982) and to subsequent patterns of erosion. Outcrop thickness within FPS-1 averages approximately 5 meters and ranges from 2 meters along the CH-l-B transect to 9 meters along the 1-4 transect. Twenty-four vibracores penetrated FPS-1, recovering 64 meters of section. Seventeen of these vibracores were examined to resolve vertical and lateral lithologic relationships. General lithologic patterns within FPS-1 are summarized in Figure 10. The following lateral variations occur within FPS-1: 1) a southward fining of the sediments, 2) a southward increase in phosphate from <3% to >60% of the total sediment, and 3) a southward increase in foraminiferal abundance which contributes to an overall increase in carbonate content. Vertical lithologic variations within FPS-1 include: 1) siliciclastic sand:mud ratio decreases upward in central and southern Onslow Bay but remains fairly constant in northern Onslow Bay; 2) relative phosphate content increases upward in central Onslow Bay, while in southern Onslow Bay it exhibits an upward increase followed by a decrease; and 3) foraminifera, and rarely diatoms, increase in relative abundance upward through the section. All vertical and lateral trends are related. For example, decreased siliciclastic sedimentation allows phosphate and biogenic (foraminifera and diatoms) sediments to accumulate in increased concentrations. Thus, there is a direct relationship LITHOLOGIES OF THE SEISMIC LATE BURDIGALIAN FRYING PAN SEQUENCES SEQ- PUNGO RIVER FORMATION, N. C. CONTINENTAL SHELF UENCcS NORTHERN AREA CENTRAL AREA SOUTHERN AREA ? DOLOSILTY-MICRITIC, PHOSPIIATIC, FOSSIL- I FERGUS, QUARTZ SANDY BARNACLE HASH UPPER PORTION UNSAMPLED "CHANNEL FACIF,S" EPS #6 BARNACLE GRAVELLY. MUDDY, PHOSPHATIC, FORAMINIFERAL QUARTZ SAND FOSSILIFEROUS QUARTZ SAND MUDDY, PHOSPHATIC QUARTZ SAND SHELL GRAVEI.LY, FOSSILIFEROUS QUAR17, SAND SLIGHTLY MUDDY QUARTZ SAND EPS #5 CLEAN QUARTZ SAND DIATOMACEOUS, QUARTZ SANDY, DOLOSILTY MUD MUDDY QUARTZ SAND mm/Mm INTERBEDDED: EPS #4 CLEAN QUARTZ SAND UNSAMPLED and MOLLUSCAN-BARNACLE SAND AND GRAVEL SLIGHTLY MUDDY, PHOSPHATIC QUARTZ SAND EPS #3 NO OUTCROP MUDCLEAN QUARTZ SAND CHERT DOI.nSllTY ZEOLITIC IRID DOLOSILTY QUARTZ SAND EPS #2 QUARTZ SANDY ZEOLITIC MUD*^LIÎÎI!TLY ^^lnDV QUARTZ SAND QUARTZ SANDY, DIATOMACEOUS TO CHERTY, DOLOSILTY MUD MUDDY, PHOSPHATIC, FORAMINIFERAL QUARTZ SAND HOLDIC LIMESTONE CHERT QUA.,i.. SANDSÍ0NE/HICUOSPHORTIE OUARTZ SANDY, DIATOMACEOUS, DOIXISILTY HIH) MUDDY, FORAMINIFERAL, PHOSPHORITE SAND EPS #1 MUDDY QUARTZ SAND DOLOSILTY, PHOSPHATIC QUARTZ SAND MUDDY PHOSPHORITE SAND MUDDY QUARTZ SAND Figure 10. Summary of lithologies within the (Late Burdigalian) Frying Pan Sequence. See Figures 6 and 8 for outcrop distribution of fourth- order seismic sequences and delineation of "northern, central and southern areas". 60 between the relative percentages of phosphate and biogenic sediments, both of which are inversely related to siliciclastics. In northern Onslow Bay, FPS-1 consists of light olive gray, muddy (<10-36%), very fine to fine quartz sand. Calcareous fossils locally constitute 8-10% of the total sediment and are predominated by recrystallized planktonic foraminifers, echinoderm spines and barnacle plates, all with calcitic overgrowths. Along the 1-6 transect, muddy quartz sands are overlain by indurated, quartz sandy (35-40%), moldic limestone with a thin phosphatic surface interpreted to be a former hardground surface. This carbonate caprock was recovered only in the northernmost core (OB-134), so its lateral continuity is unknown. In central Onslow Bay, muddy (33%) quartz sand grades upward into dolosilty (45%), phosphatic (4%) quartz sand (OB-113) and is capped by quartz sandy (44%), diatomaceous (1%) mud (OB-47) (Fig. 11). Chert nodules occur at the FPS-1 upper surface (OB-47) and are interpreted to reflect dissolution and reprecipitation of biogenic silica during an episode of nondeposition. Southward, core OB-127 encountered light olive gray, muddy (25%), phosphatic (4%) quartz sand which grades upward into olive gray, muddy (25%), phosphorite (35%) and quartz sand. Calcareous fossils which occur in minor abundances (4%) in the lower section, consist chiefly of benthic and planktonic foraminifers and echinoderm spines. Phosphate content continues to increase into southern Onslow Bay where it becomes the dominant mineralogical constituent. In OB-14, cored along the EN-8-C transect, olive gray, muddy (25%), quartz (15%), phosphorite sand grades upward into olive brown, muddy (40%), phosphatic COMPOSITE STRATIGRAPHIC SECTION OB-113B. OB-47. OB-49 AND OB-48 FPS-1.FPS-2 & FPS-3 I-4W PROFILE % SAND-SIZED ? terrigenous % ? phosphate Q SAND SCARBONATE ACID WT. % CORE- ? MUD HSILICEOU6 INSOLUBLE PjOj WT % MflO so lOO SAMPLE : •• SLIGHTLY MUOOY. QUARTZ SAND CLEAN SLIGHTLY CALCAREOUS. QUARTZ SAND QUARTZ AND OOLOSILTY. DIATOMACEOUS. QUARTZ SAND ?V -G L*', ' ^ ;=i^: -”-Z- QUARTZ SANDY cfc=r±z DIATOMACEOUS.OOLOSILTY MUD |L4k%^ n OOLOSILTY PHOSPHATIC QUARTZ SAND OLIGOCENE [Uniampica: ON I-* Figure 11. Composite stratigraphic section: Frying Pan Sequence (FPS-1, FPS-2 and FPS-3), central Onslow Bay. 62 (8%), quartz (11%), foraminiferal sand (Fig. 12). Phosphate occurs predominantly as dark brown, sand-sized pellets with lesser concentrations of intraclasts and skeletal fragments. A discontinuous, calcareous, quartz sandstone (recovered in OB-63) locally caps FPS-1 in the southern area (Fig. 13). Hard-rock borings, dark phosphatic coatings and sulfide(?) stain indicate a former nondepositional, hardbottom surface. FPS-2 FPS-2 is continuous in outcrop and shallow subcrop from northern to southern Onslow Bay (Fig. 6). Outcrop thickness ranges from approximately 3 to 20 meters and averages 9 meters. Ninety-three meters of section were recovered from 20 vibracores, 17 of which were used in this study. General lateral lithologic trends within FPS-2 (Fig. 10) include: 1) a pronounced southward fining of the sediments; 2) a southward increase in phosphate, from <3% to >15% of the total sediment, in the lower portions of the section; and 3) a southward increase in calcareous and siliceous microfossil components. Phosphate content is greatly reduced, however, when compared with the underlying FPS-1 sequence. The <63 urn fraction consists of quartz silt, clay- and silt- sized dolomite rhombs which occur ubiquitously throughout the sequence, along with sand- and silt-sized aggregates of clinoptilolite which reach maximum abundance (up to 30% of the total sediment) in southern Onslow Bay. In northern Onslow Bay, FPS-2 is represented by light olive gray, slightly muddy (15%) quartz sand (OB-110, 1-6 transect). This lithology persists into central Onslow Bay with an increase in mud content to 33%. COMPOSITE STRATIGRAPHIC SECTION OB-14, OB-29B AND OB-117 FPS-1& FPS-2 (EN 8C PROFILE) % SAND-SIZED ? TERRIGENOUS ? PHOSPHATE ’ ICP Analyses East Carolina University Shared Research Resources Laboratory OLIGOCENE Figure 12. Composite a^stratigraphic section Frying Pan Sequence (FPS-1 U) and FPS-2), southern Onslow Bay. Figure 13. East-west 3.5 kHz profile from southern Onslow Bay showing buried Miocene hardground which locally marks the unconformity separating FPS-1 from FPS-2. Relief of buried scarp approximately 3 meters. ^ 65 Visual estimates indicate that 15 to 20% of the total sediment consists of individual silt-sized dolomite rhombs, but, bulk sediment analyses average only 2.52% MgO (OB-49). Dolosilty quartz sand (OB-49) is capped by a horizon of nodular chert (OB-48) and is underlain by light olive- gray, quartz sandy to silty clay (OB-47 and OB-123) (Fig. 11). Centric diatoms are abundant (< 10%) in the sand fraction of OB-47 and in the lowermost portion of OB-49 but were not noted in OB-123. SEM analyses indicate greater abundances of diatoms in the <63 um fraction (Plate 2). Dark olive green chert nodules are common throughout OB-123. SEM analyses of bulk sediment from OB-123 indicate an absence of recognizable diatom valves and an abundance of opal-CT lepispheres (Plates 12 and 13). This lateral relationship between diatomaceous sediments and chert-bearing sediments strongly suggests a biogenic source for reprecipitated silica polymorphs. The dolosilty quartz sand of central Onslow Bay grades laterally into a mud facies (OB-117, OB-29B and OB-14) in southern Onslow Bay (Fig. 12). Zeolite (clinoptilolite) occurs in the sand and silt fraction as finely crystalline aggregates. The larger sand-sized aggregates are recognizable as raoldic infillings of planktonic and benthic foraminifera. Complete dissolution of foraminifera has occurred in the uppermost portions of FPS-2 in southern Onslow Bay leaving only zeolitic, foraminiferal moldic infillings. Carbonate dissolution decreases downward with well preserved foraminifera occurring in the lower portions of the section. Even well preserved foraminiferal tests reveal clinoptilolite infillings when etched with acid. Dolomite in the southern mud facies is generally very fine silt- 66 sized and is often microscopically unresolvable at magnifications below 60X. Presence of dolomite is suggested by moderate to weak reaction of sediment samples in dilute HCl and bulk sediment MgO analyses which range from 1.40 to 3.44% MgO and average 2.45% MgO. FPS-3 FPS-3 crops out in central Onslow Bay, trends into the subsurface in northern Onslow Bay, and crops out in a discontinuous pattern in southern Onslow Bay due to post-depositional erosion (Fig. 6). Outcrop thickness ranges from approximately 5.5 to 25.5 meters and averages 15 meters. The sequence was penetrated by three vibracores, all of which were examined in this study. In central Onslow Bay, two vibracores (OB-48 and OB-129) penetrated FPS-3. Along the 1-4 transect a complete FPS-3 section was recovered (OB-48). Olive gray, clean quartz sand in the lower portion grades upsection to light olive gray, muddy (18%) quartz sand (Fig. 11). Approximately 5% (visual estimate) of the <63 urn fraction consists of dolosilt. Foraminifera, echinoderm spines, ostracodes and barnacle fragments, all abraded and with calcitic overgrowths, represent 12% of the total sediment and occur in the middle part of the FPS-3 section. Along the 1-5 transect, only the upper part of FPS-3 was sampled (OB-129). It is represented by olive gray, slightly muddy (15-20%), phosphatic (7-10%), quartz sand. Foraminifera and rare ostracodes increase upward from 0% to 20% (visual estimate) at the top of FPS-3. Dissolution in dilute HCl occasionally reveals very sparse, incomplete infilling of foraminifera by clinoptilolite (OB-48 and OB-129). 67 Phosphate occurs as very dark brown, fine pellets and fine to medium intraclasts, but there are no distinct vertical trends in abundance. In the southern area the upper portion of FPS-3 consists of olive gray, slightly quartz sandy (5%) mud (OB-66). FPS-4 FPS-4 crops out south of Bogue Banks, continues through central Onslow Bay and trends into the subsurface between the 1-4 and 1-5 transects (Fig. 6). Outcrop thickness ranges from approximately 5 to 11 meters and averages 8 meters. One vibracore (OB-37) penetrated the entire sequence along the 15-meter transect in northern Onslow Bay, recovering an interbedded sequence of clean quartz sand and quartz sandy (40-50%), calcareous biogenic sand and gravel. Quartz sand and calcareous interbeds range from 1.5 to 4.0 meters and 0.6 to 1.0 meters thick, respectively. Biogenic material consists of Mercenaria sp. and other bivalves, barnacle plates, turritelids, scaphopods, ostracodes, echinoderm spines and benthic foraminifers. White, fragmented, abraded and commonly bored macrofossil material occurs with relatively well- preserved material with little abrasion or fragmentation indicating a lack of significant post-mortem transport for the latter. Biogenic material is conspicuously absent in the quartz sand interbeds. FPS-5 The outcrop/shallow subcrop area of FPS-5 is largely confined to northern and central Onslow Bay (Fig. 6). Outcrop thickness ranges from 7.5 to 17 meters and averages 12 meters. Four vibracores penetrated the sequence in the northern and central portions of Onslow Bay (OB-46, OB- 68 50, OB-57 and OB-128). Light olive gray, clean to slightly muddy quartz sand was recovered in the northernmost core (OB-46) along the CH-l-B transect. Visual estimates indicate a relatively uniform section with terrigenous and calcareous mud ranging from 5 to 12%. In the central area, three distinct lithologies were recognized (OB- 50). Light olive gray, diatomaceous (7%), quartz sandy (15%), dolosilty clay constitutes the lower 4.5 meters of core section. Occasional thin laminae (1 to 50 ram) of dolosilty (5-10%), phosphatic (5-10%) fine quartz sand may represent winnowed horizons. The dolosilty clay is overlain by 1 meter of light olive gray, slightly muddy (20%) quartz sand which is in turn overlain by unconsolidated to moderately indurated, light olive gray to yellowish gray, shell gravelly (10-15%), phosphatic (4%), fossiliferous (35%) quartz sand. Shell gravel consists of barnacle plates, gastropods (Ecphora quadricostata) and pecten (Chesapecten sp.) fragments. Sand-sized fossils include benthic forarainifera and echinoderm spines. The quartz sand and fossiliferous quartz sand lithologies were not encountered in the southernmost vibracores (OB-57 and OB-128) where greenish gray, muddy (25-35%) quartz sand grades upward with increasing mud content from the base of the sequence to olive gray, slightly quartz sandy (8%), silty (quartz and dolosilt) clay. Dolosilt content was estimated to increase upward from 10% to 30-40% with a bulk rock value of 5.43% MgO at the top of the section. FPS-6 FPS-6 is characterized by two depositional styles which are reflected in differing patterns of outcrop (Fig. 6). The first style of 69 deposition occurs in the northern and central areas of Onslow Bay where outcrop thickness ranges from approximately 5.5 to 21.5 meters. Seismic reflection and outcrop patterns are similar to the underlying fourth- order sequences, which are relatively thin (generally less than 15 meters), dip gently to the southeast and trend NE-SW in outcrop and shallow subcrop. Seismic profiles interpreted by Stephen W. Snyder (1982 and unpub. data) show that these sequences are bounded by paraconformities or unconformities which generally show little evidence of erosion. The second style of deposition occurs in the southern area. Here, FPS-6 sediments infill a major erosional channel-complex (Fig. 14) which truncates previously deposited strata of the Frying Pan Sequence, as well as the upper portions of pre-Pungo River (Oligocène) sediments. The channel complex is approximately 35 km in length and over 12 km in width and trends roughly N-S. Depth of the channel reaches 25 meters. In the northern and central areas where the "type 1" style of deposition occurs, FPS-6 was penetrated by three vibracores (OB-45, OB-50 and OB-57), two of which recovered only the lowermost portion of the sequence. The northernmost core (OB-45) recovered the upper 5 meters of a 6-meter-thick section along the CH-l-B transect. Here, olive gray, barnacle gravelly (4%), muddy (15-20%), phosphatic (5%), fossiliferous (10%) quartz sand grades upsection with increasing carbonate content (fossil material, calcitic and doloraitic mud) to yellowish brown, muddy (30%), phosphatic (6%), quartz and calcareous sandy (45%) barnacle hash. An indurated horizon occurs in the middle of the section which is otherwise unconsolidated. Throughout the section, calcareous fossils are often overgrown with calcite and dolomite rhombs. EN-8C METERS 50 T(MWIRLILOIASME-VWCOEANDLYS: FRYING PAN SEQUENCE 09 it Oligocène (undiff.)(late Burdigalian) Figure 14. Interpreted west-east uniboom seismic profile through southern Onslow Bay (EN-8C profile) with vibracore locations superimposed (modified from Riggs and others, 1985). Note Late Burdigalian erosional channel which truncates lower Frying Pan Sequence strata. See Figure 8 for profile location. 71 Southward, along the 1-4 transect, the basal 1.5 meters of FPS-6 (OB-50) are represented by light olive gray, clean quartz sand. This lithology grades southward with an increase in mud content to light olive gray, muddy (30%), phosphatic (5%) quartz sand recovered along the 1-5 transect (OB-57). Mud content increases upcore to approximately 45%. Outcrop thickness of FPS-6 in the central area ranges from 15-20 meters. Only the lower 5-6 meters were sampled. In the southern area six vibracores penetrated the channel-fill facies of the "type 2" style of deposition; two of these cores (OB-66 and OB-67) were examined in detail. Spot samples of the remaining four cores confirmed similar lithologies. The channel-fill facies consists of variably muddy (5-20%), foraminiferal (15-50%) quartz sand. Foraminifers are generally well preserved and include abundant planktonic forms. This lithology is very distinctive and has been classified as a major lithofacies within the third-order Frying Pan Sequence. Interpretations concerning depositional history of this lithofacies will be presented in the discussion section. Onslow Bay Sequence The third-order Onslow Bay Sequence of Langhian age contains four, smaller-scale, fourth-order seismic sequences (OBS-1 through OBS-4, from oldest to youngest). The Onslow Bay Sequence trends generally N-S and is 2 present in outcrop and shallow subcrop over an 1100 km area (Fig. 6). Linearity of the updip limit in northern and central Onslow Bay is controlled by the underlying White Oak Lineament and the Onslow Bay Sequence thickens rapidly to the east over this erosional feature (Fig. 4). Therefore, outcrop thicknesses of fourth-order sequences varies according to the the geographic position of their upper bounding unconformities relative to the lineament. A summary of lithologies contained within each fourth-order sequence is presented in Figure 15. OBS-1 OBS-1 occurs in outcrop and shallow subcrop in northern Onslow Bay and trends into the subsurface in central Onslow Bay (Fig. 6). Outcrop thickness ranges from approximately 9 to 32 meters and averages 16 meters. Seven vibracores penetrated OBS-1 (OB-35, OB-38, OB-40, OB-41, OB-44, OB-51 and OB-80); all were examined in this study. Along the 15-meter transect, yellowish light olive gray, quartz and calc-sandy (30-40%), dolosilty mud is overlain by barnacle-plate gravelly (10%), calc-muddy and dolosilty (30%) calcareous and quartz sand (OB-35 and OB-80). Light olive-gray, nodular chert occurs sporadically in the lower section. Overlying lithologies consist of yellowish gray, dolosilty (25-30%), calcareous and quartz sand which abruptly changes upward to yellowish light olive gray, diatomaceous (3%), micritic and L ITHOLOGIES OF THE SEISMIC LANGHIA^1 ONSLOW BAY SEQUENCES SEQ- PUNGO RIVER FOR MATION, N. C. CONTINENTAL SHELF UENCES NORTHERN AREA CENTRAL AREA SOUTHERN AREA DOLOMITIC BARNACLE BIORUDITE CALC-SANDY. DOLOSILTY-MICRITIC MUD UNSAMPLED OBS #4 MICRITIC-DOLOSILTY, CALCAREOUS AND QUARTZ SAND CALCAREOUS GRAVEL, SAND AND MUD UNSAMPLED OBS #3 QUARTZ SANDY MUD MICRITIC-DOLOSILTY, CALCAREOUS AND QUARTZ SAND INTERBEDDED: GLAUCONITIC, PIIOSPHATIC, QUARTZ AND CALC- UNSAMPLED CLEAN TO MUDDY QUARTZ SAND OBS #2 CAREOUS SAND and DOLOSILTY MUD HICRITIC AND DOLOSILTÏ. DIATOMACEOUS MUD INTERBEDDED; "OUTLIERS’ OBS #1 DOLOSILÏÏ, FOSSILIFEROUS QUARTZ SAND CLEAN TO MUDDY QUARTZ SAND and DIATOMACEOUS, DOLOSILTY MUD DOLOSILTY MUD BARNACLE GRAVELLY, MICRITIC-DOLOSILTY, CALCAREOUS AND QUARTZ SAND Figure 15. Summary of lithologies within the (Langhian) Onslow Bay Sequence. See Figures 6 and 8 for outcrop distribution of fourth-order seismic sequences and deliniation of "northern, central and southern areas". 74 dolosilty mud (OB-34). Dried samples of this diatomaceous carbonate mud are extremely "lightweight" which may imply greater concentrations of diatoms than were noted during binocular microscopic examination. Southward, along the 22-raeter transect (OB-38 and OB-40) and along the CH-l-B transect (OB-41 and OB-44), lithologies consist of light olive gray, clean to dolosilty (5-25%) quartz sand interbedded with light olive gray, dolosilty (10-80%) clay. Quartz sand intervals range from 0.5 to 1.0 meters thick while interbeds of dolosilty clay range from 0.10 to 0.25 meters thick. Small amounts of phosphate (2-5%) occur as pellets and intraclasts, and as phosphate-coated quartz grains in the quartz sand intervals. In central Onslow Bay along the 1-4 transect, nine meters of section from the lower half of the sequence (OB-51) consist of clean, slightly phosphatic (3-4%) quartz sand which grades upward with gradually increasing mud content to muddy (30%), phosphatic (4-6%) quartz sand. Phosphate occurs predominantly as fine, very dark brown pellets and rare intraclasts. OBS-2 OBS-2 occurs in outcrop and shallow subcrop throughout central Onslow Bay and trends into the subsurface in northern and southern Onslow Bay (Fig. 6). Outcrop thickness ranges from approximately 4 to 12.5 meters and averages 8 meters. Four vibracores penetrated the sequence (OB-38, OB-39, OB-58 and OB-68); all were used in this study. In the northern area, along the 22-meter transect, OBS-2 consists of coarse, glauconitic (5-7%), phosphatic (4-10%), quartz and calcareous sand (OB-38 and OB-39). Glauconite occurs as discrete, dark green, sand- 75 sized grains with syneresis cracks and as light to medium green pore fillings in porous carbonate skeletal grains. Phosphate occurs as medium sand- to granule-sized dark brown intraclasts. Barnacle plates, pecten fragments and forarainifera comprise the calcareous sand. Most calcareous particles are abraded and overgrown with calcite. To the south, along the 1-5 transect, OBS-2 consists of clean quartz sand interbedded with dolosilty (10-30%) clay (OB-58). Quartz sand intervals range in thickness from 0.3 to 1.6 meters while clayey intervals range from 0.1 to 0.6 meters. Contacts between lithologies are sharp. Nodules of silica-cemented sediment occur in the middle and base of the core. This same interbedded lithofacies was encountered to the south along the CH-4 transect (OB-68). OBS-3 OBS-3 forms a discontinuous outcrop and shallow subcrop pattern in northernmost and southern Onslow Bay (Fig. 6). The sequence does not crop out in the central area. In the northern area, an outcrop thickness of 24 meters was measured from one seismic transect. In the southern area, outcrop thickness ranges from approximately 6 to 33 meters and averages 23 meters. Three vibracores penetrated OBS-3 in the northern area, recovering approximately nine meters of section. Only two of these cores (OB-34 and OB-33) were used in this study as the third (OB-111) represents duplicated section. Two cores were recovered from the southern outcrop area (OB-68 and OB-131). OB-131 contains a lithologic and biologic assemblage common to Pleistocene sediment samples interbedded throughout the core and, therefore, does not represent an 76 OBS-3 lithology as suggested by Stewart (1985). In the northern area along the 15-raeter transect, the lower portion of OBS-3 consists of light olive gray, calc-muddy (15%), calcareous and quartz sand (OB-34). Barnacle and pecten fragments occur in the sand fraction, but most of the calcareous sand is composed of unidentifiable, abraded, biogenic fragments. The upper portion of OBS-3 is represented by two, 1.2- meter-thick fining-upward lithologies (OB-33) in which yellowish gray, calc-muddy (15-35%), calc-sandy (20-40%), barnacle-plate gravel grades upward into light olive gray, calc-sandy (40%) calcareous and terrigenous mud. As in OB-34, biogenic calcareous sand particles are abraded and mostly unidentifiable. In the southern outcrop area, the lowermost portion of OBS-3 consists of moderate olive brown to olive gray, quartz-sandy (35-45%), organic-rich (3.15% TOC; Table 2) mud (OB- 68). Calcareous material constitutes <5% of the sediment and occurs as corroded echinoderra spines, and benthic and planktonic foraminifera. Dissolution of foraminiferal tests, in the sediments and in the laboratory, reveals secondary infillings of amber, transluscent phosphate (Plates 15 and 16; see also discussion under sediraentological components). Planktonic foraminifers are commonly coated with transluscent phosphate. Secondary phosphate represents 2 to 3% of the total sediment. Primary pelletai, intraclastic and skeletal phosphate was estimated at 12% of the total sediment at the base of the section, but it abruptly decreases upward to 1 to 3%. Primary phosphate is atypically light in color and exhibits pitted surface textures indicative of leaching. 77 OBS-4 The outcrop and shallow subcrop pattern of OBS-4 parallels that of OBS-3, as the sequence crops out only in northern and southern Onslow Bay (Fig. 6). Outcrop thicknesses of approximately 9 and 14 meters were recorded in the northern and southern areas, respectively, although only one seismic transect was available for each. Four vibracores were recovered in the northern area. The three used in this study (OB-33, OB- 36 and OB-3) form an eight-meter-thick, composite stratigraphic section, which penetrates the upper and lower sequence boundaries with only minor stratigraphic omission. The lower portion of the sequence consists of moderately to weakly indurated, very light gray to yellowish gray, variably muddy (10-40%; calcareous mud and dolosilt) calcareous sand and gravel (OB-33). Calcareous sand-sized grains are abraded and commonly encrusted with silt-sized dolomite rhombs. Grayish yellow, calc-sandy (20%), dolosilty and calcareous mud (OB-36) overlies the calcareous sand and gravel. Dolosilt appears relatively abundant; a bulk rock value of 8.46% MgO was reported from this lithology. Serravallian-age sediments of the Bogue Banks Sequence unconformably overlie the upper carbonate mud lithology of OBS-4 in core OB-36. However, 2 km to the east OBS-4 is capped by a dolomitic, barnacle biorudite (OB-3). Discontinuity of this caprock indicates the highly erosional nature of the unconformity which separates the Onslow Bay Sequence from overlying sediments of the Bogue Banks Sequence (Fig. 16). OBS Outliers Outliers of Langhian-age sediments (OBS-1?) have been recognized to the west of the main Langhian outcrop area in southern Onslow Bay 15 METER PROFILE METERS WEST EAST O 50 75 (MTTILRLWIISMAOEC-VOWNEADLSY) ? FRYING PAN SEQUENCE lONSLOW BAY SEQUENCE^0 Oligocene '•t;] bogue banks sequence(late Burdigalian) I (Langhian) (Serravallian) Figure 16. Interpreted west-east uniboom seismic profile through northern Onslow Bay (15-meter profile) with vibracore locations superimposed (modified from Stephen W. Snyder, 1982). Note prograding clinoform deposits which infilled the Northeast Onslow Embayment during the Langhian. See Figure 8 for profile location. CO 79 (Fig. 6). These assignments have been primarily based on diatom biostratigraphy (Powers, 1986; in progress) and seismic statigraphy (Stephen W. Snyder, pers. comm.). Vibracores penetrating these outliers (OB-15, OB-16, OB-17 and OB-62) have recovered lithologies which appear very similar to the surrounding Frying Pan Sequence sediments of FPS-2 and FPS-3. Lithologies consist of zeolitic, dolosilty, foraminiferal muds. However, unlike FPS-2 and FPS-3, siliceous microfossils and secondary phosphate were a persistent, but minor (<10%) component. These sediments were originally assigned to the Frying Pan Sequence on the basis of lithology. Bogue Banks Sequence The uppermost third-order sequence of the Pungo River Formation in Onslow Bay, referred to as the Bogue Banks Sequence, has been assigned to the Serravallian stage on the basis of biostratigraphic analyses (Moore and Scott W. Snyder, 1985; Moore, 1986; Powers, 1986; Steinmetz, unpub. data). The Bogue Banks Sequence contains eight outcropping, fourth-order seismic sequences (Fig. 6), BBS-1 through BBS-8, from oldest to youngest. At least one additional fourth-order sequence has been identified in the subsurface and is positioned stratigraphically above BBS-8 (Stephen W. Snyder, 1982) The BBS sequences are present in outcrop to shallow 2 subcrop over an area of 1500 km and trend generally north-south. Lithologic discriptions of fourth-order seismic sequences are summarized in Figure 17. BBS-1 BBS-1 occurs in outcrop to shallow subcrop from northern to southern Onslow Bay (Fig. 6). Outcrop thickness ranges from approximately 13 to 24 meters and averages 20 meters. Thirteen vibracores penetrated the BBS- 1 sequence; 11 of these were examined in detail. In northern Onslow Bay along the 15-meter transect, five vibracores penetrated BBS-1. Four of these cores (OB-36, OB-3, OB-79 and OB-2) represent a complete vertical section approximately 22 meters thick. In the northern area, light olive gray to olive gray, muddy (20-40%), phosphatic (2-4%) quartz sand overlies the Serravallian basal unconformity, sharply contrasting with the underlying dolomitic and calcareous sediments of OBS-4. Muddy quartz sand grades upward with L ITHOLOGIES OF THE SEISMIC SERRAVALL IAN BOGUE BANKS SEQUENCES SEQ- PUNGO RIVER FOR^/lATION, N. C. CON TINENTAL SHELF UENCES NORTHERN AREA CENTRAL AREA SOUTHERN AREA BBS #8 MUDDY, PHOSPHORITE AND QUARTZ SAND 'WÆ^//Æ y//////////////////. BBS #7 '^//////. outcrop/////// Z/////A//Z//////UNSAMPLED ^yM^N/O ////Æ^/. BBS #6 UNSAMPLED // //y/y NO outcrop///^//// y////////////////// BBS#5 CALC-MUDDY, QUARTZ AND CALCAREOUS SAND UNSAMPLED UNSAMPLED //^^^^^^^^OUTCROP UPPER PORTION UNSAMPLEDBBS #4 QUARTZ SANDSTONE CLEAN QUARTZ SAND y//////////////////. UPPER PORTION UNSAMPLED BBS #3 /////// NO OUTCROP ////y/y/y/y y//////////////////. MUDDY, PHOSPHATIC QUARTZ SAND MOLDIC LIMESTONE aÆ^a///a///// BBS #2 MUDDY, PHOSPlIAriC QUARTZ SAND MUDDY, PHOSPHORITE AND QUARTZ SAND /////// NO OUTCROP ///////y QUARTZ SANDY, CALCAREOUS HUD y//////////////y// 1 DIATOMACEOUS, QUARTZ SANDY, DOLOSILTY TtUD FOSSILIFEROUS, QUARTZ SANDY, DOLOSILTY MUD BBS # 1 MUDDY, PHOSPHATIC, QUARTZ SAND MUDDY, GLAUCONITIC, PHOSPHATIC, FOSSIL- UNSAMPLED 1 TFEROUS QUARTZ SANDPHOSPHATIC QUARTZ SAND Figure 17. Surainary of lithologies within the (Serravallian) Bogue Banks Sequence. See Figures 6 and 8 for outcrop distribution of fourth-order seismic sequences and deliniation of "northern, central and southern areas". 82 increasing mud content and a slight increase in phosphate content to olive gray, phosphatic (3-6%), quartz sandy (40-44%) mud. Estimates from OB-3 indicate that phosphate content is variable on a fine scale and may reach 15% in thin (few cm) horizons. To the south along the 22-meter transect, four cores (OB-39, OB- 6/6B, OB-71, and OB-109) recovered a nearly complete composite BBS-1 section, approximately 22 meters thick and with only minor unsampled gaps between cores (Figs. 4 and 18). Yellowish light olive gray, clean (<5% mud), phosphatic (5-8%) quartz sand unconforraably overlies Langhian strata and grades upward into dark olive brown, muddy (33-45%) quartz sand. The muddy quartz sand is overlain by yellowish light olive gray, diatomaceous (Tr-2%), quartz sandy (35-38%), dolosilty mud. The entire sequence is capped by partially indurated, yellowish gray, barnacle gravelly (9%), quartz sandy (30%), dolosilty mud. Overall the section exhibits a fining upward trend with an increase in authigenic (dolosilt) and biogenic (chiefly barnacle) carbonate content. Southward, OB-42 and OB-43 were cored along the CH-l-B transect and recovered six meters of upper BBS-1 section consisting of moderate olive brown, phosphatic (Tr-6%, increasing upward), quartz sandy (35-45%), silty mud. Sand-sized siliceous microfossils (diatoms and radiolarians) were noted in minor (1%) amounts. Southward along the 1-4 transect, OB-52 recovered 1.5 meters from the middle portion of an approximately 13-meter-thick BBS-1 section, encountering light olive gray, quartz sandy (12-33%), clayey dolosilt. A 4 X 3 X 1 cm chert fragment was noted in this lithology and may represent reprecipitated biogenic silica as siliceous raicrofossils are present in COMPOSITE STRATIGRAPHIC SECTION OB-6B, OB-71 AND OB-109 BBS-1 & BBS-2 22 METER PROFILE % % SAND-SIZED E3 GRAVEL ? terrigenous %LITHOLOGY El SAND ? phosphate ACID ? MUD SCARBONATE INSOLUBLE WT. % PjOg WT. % MgO 0 50 iOO 0 10 too 0 60 5 10 BBS-3 ? . . 1 1 . ? . . 00 GLAUCONITIC, ICP An«lyB««: Sail Carolina Uniwaraity Sharad Rataarch Raaourcaa Labaralory OBS-2 LO QUARTZ AND CALCAREOUS SAND Figure 18. Composite stratigraphic section: Bogue Banks Sequence (BBS-1 and BBS-2), northern Onslow Bay. 84 equivalent strata to the north. Fragmentation of the chert nodule was probably produced by the vibracoring process. Bulk sediment analyses reveal relatively high MgO values of over 8.0 weight percent supporting the abundance of dolomite noted during lithologic logging. The southernmost core in BBS-1 (OB-59) recovered two meters of section from the lower to middle portion of an approximately 24-meter- thick section, encountering a lithology similar to that of OB-52 along the 1-5 transect. Here, light gray to yellowish gray, slightly muddy (10- 15%), glauconitic (3-5%), phosphatic (6-7%), fossiliferous (7-8%) quartz sand is overlain by light olive gray, fossiliferous (15-20%), quartz sandy (15-20%), dolosilty mud. Fossil material in the upper lithology includes benthic foraminifers and echinoderra spines with calcite and dolomite overgrowths. The lower lithology contains a similar fossil assemblage with the addition of abraded and fragmented barnacle plates. BBS-2 BBS-2 is present in outcrop and shallow subcrop in northern and central Onslow Bay (Fig. 6) and was penetrated by five vibracores along the 22 meter and 1-4 transects. Outcrop thickness ranges from 7 to 12 meters and averages 9 meters. Along the 22-meter transect, core OB-109 penetrated all but the uppermost portion of the sequence; the lower two-thirds of this core was duplicated by OB-72. The lithology of BBS-2 in this area is depicted in Figure 18 and consists of olive gray, muddy (23-46%), phosphatic (3-8%, increasing upward) quartz sand. The section also contains occasional horizons of highly weathered pecten fragments. Figure 19 depicts the lithology of BBS-2 along the 1-4 transect. COMPOSITE STRATIGRAPHIC SECTION OB-52, OB-94, OB-53, OB-95 AND OB-60 BBS-1, BBS-2 & BBS-3 I-4E PROFILE % % SAND-SIZED ? GRAVEL ? TERRIGENOUS % 13 SAND ? PHOSPHATE ACID LITHOLOGY ? MUD gCARBONATE INSOLUBLE WT. % MgOCORE- METERS 0 5 10SAMPLE 0 60 0 50 too I 50 too 0 6 0 - 1 t 1 MUDDY. 2 QUARTZ SAND (Barnacle Gravelly) 3 4 60- 3 < PHOSPHATIC BBS-3 ?Z-I-3 QUARTZ SANDY MUD 5 60 - 4 -C MUDDY . —p. ?— PHOSPHATIC STRATI- QUARTZ SAND GRAPHIC GAP MUDDY. 65- 1 -C QUARTZ SAND 9 5 - 2 < MOLDIC limestone' 53- 1 -C -0:. - _ - 5 3 - 2 ?{ - p -. - 5 3 - 3 -C ~ -.'p:- ?“ PHOSPHORITE 5 3 - 4 -C AND QUARTZ SAND 53-5 -C P.-- . ? - • ? ? 53-6 -C Z -1 "'/—I (Calc muddy) 5 3 - 7 i 94 - 1 < :-ê:-sZ- 9 4 - 2 1 9 4 - 3 -C - -s- •— -s- CALCAREOUS MUD 5 2-1 -C ?. -C "• DOLOSILTY5 2 - 2 MUD-*r_ — STRATI- graphic LANQHIAN (Unsampled) 'iCP Analyiet East Carolina Univaratty Shared Research Reaowrcea Laboratory OBS-2 00Ln SEQUENCES Figure 19. Composite stratigraphic section: Bogue Banks Sequence (BBS-1 BBS-2 and BBS-3), central Onslow Bay. 86 OB-94 penetrated the basal portion of the section and recovered olive gray, shell gravelly (11%), muddy (23%), phosphorite (25%) and quartz sand which grades upward with a decrease in shell gravel and slight decrease in phosphate (OB-53) into light olive gray, gravelly (0-4%), muddy (21-38%), phosphorite (9-17%) and quartz sand. Visual estimates indicate that phosphate may reach 25% in the middle of the section and that diatoms constitute up to 15% of the sand fraction in the upper section. OB-95 recovered 20 cm of olive gray, quartz sandy (approx. 30%), moldic limestone which caps the sequence. BBS-3 BBS-3 is restricted in outcrop to central Onslow Bay (Fig 6). Along the 1-4 transect two vibracores recovered the lower 9 meters of an approximately 35-meter-thick section. Olive gray, muddy (33-36%) quartz sand (OB-95) (Figure 19) overlies the limestone caprock of BBS-2. Above this lithology a texturally and mineralogically variable section was recovered in OB-60. Light olive gray, muddy (37%), phosphatic (6%) quartz sand changes abruptly upward to phosphatic (3%), quartz sandy (32%) mud which in turn grades upward into barnacle gravelly (0-6%), muddy (18-28%) quartz sand. BBS-4 The outcrop/shallow subcrop area of BBS-4 is restricted to central Onslow Bay (Fig 6). One vibracore (OB-92), adjacent to the 1-4 transect, recovered three meters from the lower portion of an approximately 20- meter-thick BBS-4 section. Spot samples reveal clean (< 10% mud) quartz sand overlain by slightly calc-muddy (10-20%), quartz sand. The core 87 section is capped by dark gray, calcite-cemented, moldic quartz (>50%) sandstone. BBS-5 BBS-5 occurs in outcrop and shallow subcrop from northern to southern Onslow Bay (Fig. 6). Outcrop thickness was measured at 14 meters along the 1-4 transect. Only one core (OB-108, along the 22-meter transect) penetrated the sequence. Spot samples reveal predominantly calcareous sand and mud with lesser admixed quartz sand (25-50%). A few thin (5 to 20 cm) horizons of moldic calcarenite were also noted within the section. BBS-6 No vibracores penetrated BBS-6. BBS-7 No vibracores penetrated BBS-7. BBS-8 BBS-8 is restricted in outcrop/shallow subcrop to northern Onslow Bay (Fig. 6). An approximately 5-raeter-thick BBS-8 section was penetrated by two cores (OB-1 and OB-lOO) along the 15-meter transect. Only one of these cores (OB-1) was used in this study. OB-1 recovered a relatively uniform sediment sequence consisting of olive gray, muddy (16-21%; dolosilt and terrigenous), phosphorite (8-20%) and quartz sand. Dolomite rhombs were also noted in the sand fraction where they constitute 1 to 10 %. DISCUSSION Regional Lithofacies and Lithostratigraphy Frying Pan Sequence The Frying Pan Sequence of late Burdigalian age is characterized by four major regional lithofacies (Fig. 20) which include: 1) a phosphorite lithofacies in the southern area which overlies the Miocene/Oligocene unconformity; 2) a dominantly siliciclastic lithofacies consisting of muddy quartz sand to quartz sandy muds which occupies the northern and central areas and which overlies the phosphorite lithofacies in the southern area; 3) a mixed carbonate and siliciclastic lithofacies in northernmost Onslow Bay which is represented by interbedded, molluscan-barnacle shell gravels and clean quartz sands; and 4) a foraminiferal quartz sand lithofacies in southern Onslow Bay which truncates lithologic units of the phosphorite and siliciclastic lithofacies. All lithofacies except the forarainiferal quartz sand exhibit more or less gradational boundaries. The siliciclastic lithofacies is areally most extensive, occurring in northern, central and southern Onslow Bay. In Figure 20 the siliciclastic lithofacies has been subdivided into quartz sand and mud in order to show regional textural trends. Siliciclastic sediments fine southward as primary authigenic (phosphorite and dolomite) secondary diagenetic (zeolite, opal-CT and chert), and biogenic (calcareous and 89 Figure 20. Regional lithofacies distribution within the (Late Burdigalian) Frying Pan Sequence. 90 siliceous microfossils) components increase. Ultimately, siliciclastics grade into and overlie the phosphorite lithofacies. To the north, clean quartz sands are distinctly interbedded with molluscan-barnacle shell gravels or contain disseminated molluscan-barnacle shell fragments. This mixed carbonate and siliciclastic lithofacies probably represents an interfingering of the siliciclastic lithofacies and a predominantly carbonate lithofacies associated with the Cape Lookout High (Steele, 1980; Scarborough, 1981; Scarborough and others, 1982; Gibson, 1983; see summary of Onslow Bay Sequence). Textural and lithofacies patterns suggest a former siliciclastic source area in the northwest portion of the Onslow Embayment. High-resolution seismic profiling has identified a buried deltaic system in the underlying Oligocène (late Chattian) sequences in this area (Stephen W. Snyder and others, 1982; Stephen W. Snyder, pers. comm.). Reactivation of a similar point source siliciclastic system during the late Burdigalian may have provided a source for siliciclastic sediments. In the southern sector of Onslow Bay, repeated episodes of scouring and subsequent backfilling resulted in deposition of the foraminiferal quartz sand lithofacies. Figure 14 shows the erosional nature of the channel complex which contains this lithofacies. Planktonic to benthic foraminiferal ratios average over 1:1 and the presence of deeper water benthic forms suggests deposition in an open marine environment within the influence of the Gulf Stream (Waters, 1983). This lithofacies cuts into and interupts the general pattern of the underlying lithologic units which are characterized by southward-fining siliciclastics accompanied by increasing authigenic mineral content. Depending on geographic location. 91 the foraminiferal quartz sand lithofacies either overlies or truncates the phosphorite and siliciclastic lithofacies. Various interpretations have been presented concerning the genesis of the erosional channel complex which contains the foraminiferal quartz sand lithofacies. Riggs (1984) and Riggs and others (1985) interpreted the channel to be a product of submarine erosion by Gulf Stream currents during sea-level highstands, and Waters (1983) interpreted the foraminiferal fauna to reflect open marine conditions within the influence of the Gulf Stream. Extensive erosion by Gulf Stream currents during the Miocene along the southeast US continental margin have been documented by Stephen W. Snyder (1982) and Popenoe (1985). Conversely, excavation of the channel system and presumably its subsequent backfilling have been related to fluvial processes during a lowstand of sea level by Hine and Stephen W. Snyder (1985). Numerous smaller channels have been identified on the inner shelf in northern Onslow Bay via seismic profiling and vibracores which penetrate these channels recovered estuarine and fluvial sediments. Sediments which infill the upper portion of the major channel shown in Figure 14 have high concentrations of well preserved foraminifera, relatively high P:B foraminiferal ratios and lithologic uniformity over wide areas. This seems inconsistent with a fluvial origin. It should be noted that the deeper cut-and-fill seismic facies have not been sampled with the vibracorer, and it is possible that estuarine and fluvial sediments could occur in the deeper portions of the channel. Vertical patterns of sedimentation within the Frying Pan Sequence vary geographically in a N-S direction. They are particularly influenced 92 by the siliciclastic source area inferred to lie within the northwestern portion of the study area, the carbonate producing environment associated with the Cape Lookout High in northern Onslow Bay and the area of reduced siliciclastic sedimentation and phosphogenesis in southern Onslow Bay. Vertical lithologic transitions and N-S variations are evidenced in Figures 10, 11, 12 and 13. In northern Onslow Bay, the stratigraphic column is characterized by the alternating influence of siliciclastic and carbonate sedimentation. Interbedded sediment sequences consist of clean to muddy quartz sand and quartz sand interbedded with molluscan and barnacle skeletal material. The central area is predominated by siliciclastic sedimentation and is characterized vertically by alternations of muddy quartz sand and quartz sandy mud. Diatoms are a common, though minor (<10%) constituent within the fine-grained, clayey sediments, but are absent in coarser-grained, sandy lithologies. Calcareous macrofossils and microfossils are generally absent in the central area except in the upper portion of the Frying Pan Sequence (upper FPS-5) where shell gravelly quartz sand and muddy quartz sand sharply overlie diatomaceous, quartz sandy, dolosilty mud. Phosphate content generally does not exceed 10% in the central area, although the highest concentrations occur in sandy intervals which underlie diatomaceous muds. This relationship is noted throughout the Pungo River Formation and will be expanded on in a later section. The Frying Pan Sequence in southern Onslow Bay is characterized by decreased siliciclastic influx which, in part, allowed primary authigenic phosphate and calcareous microfossils to accumulate in increased relative abundances. Muddy phosphorite sand overlies the Miocene/Oligocene 93 unconformity in this area and grades upward into dolosilty mud with increasing forarainiferal content and decreasing phosphate and terrigenous sand content. This lithologic succession is shown in Figure 12. Foraminifera are absent in the upper zeolitic mud, although their former presence is reflected by zeolitic internal molds precipitated prior to post-depositional dissolution. The foraminiferal quartz sand lithofacies of the erosiona! channel complex (FPS-6) directly overlies the zeolitic mud. Discontinuous patterns of sediment accumulation and periods of nondeposition exist within the Frying Pan Sequence as evidenced by sharp contacts between vertically superposed lithologies. These contacts are often marked by a) hardgrounds with bored, mineralogically altered surfaces; b) diagenetic profiles including dissolution of foraminifera, diatoms and phosphate; and c) neogenesis of clinoptilolite, phosphate and calcite cements. Depositional discontinuities usually, though not always, coincide with fourth-order seismic sequence boundaries defined by Stephen W. Snyder (1982). Paleoecological interpretations of benthic foraminiferal- communities from the Frying Pan Sequences in central and southern Onslow Bay indicate a middle to outer shelf environment of deposition. The benthic communities also reflect substrate and water-mass characteristics such as nutrient and dissolved oxygen levels (Waters, 1983; Moore, 1986; Scott W. Snyder, in press). Benthic faunas in the lower to middle portions of the Frying Pan Sequence are predominated by species which today flourish in high-nutrient, low dissolved oxygen environments of sewage outfall areas (Waters, 1983; Moore, 1986; Scott W. Snyder, in press). The occurrence 94 of these particular benthic foraminiferal species are thought to reflect bottom conditions associated with upwelling and phosphogenesis. The upper lithologic units in the Frying Pan Sequence including the foraminiferal quartz sand lithofacies, are characterized by the predominance of foraminifers which require more oxygenated conditions and are less tolerant of high-nutient flux. This suggests cessation of upwelling conditions in the depositional environment. Seismic reflectors within the Frying Pan Sequence dip gently seaward and are parallel to divergent in a seaward direction (Stephen W. Snyder, 1982 and unpub. data). An exception to this general pattern occurs where a large erosional channel has been carved in southern Onslow Bay and reflectors indicate a backfill geometry. Abrupt increases in declivity of the depositional surface occur downdip in the subsurface and probably represent the paleo-shelf-break. Associated downdip lithologies could not be sampled due to depth limitations of the vibracorer. Based on lithologic and lithostratigraphic data, coupled with seismic reflection data and foraminiferal paleoecology, deposition of the Frying Pan Sequence, outcropping on the modern seafloor and described above, appears to represent aggradation of the paleo-shelf due to multiple transgressive events. 95 Onslow Bay Sequence The third-order Onslow Bay Sequence comprises three major regional lithofacies which reflect the influence of differing sediment source areas and their unique environments of subsequent accumulation. The major lithofacies are shown in Figure 21 and include: 1) a predominantly biogenic carbonate lithofacies in northern Onslow Bay associated with the Cape Lookout High; 2) an interbedded quartz sand and dolosilty clay lithofacies in central and southern Onslow Bay associated with the I^ihite Oak Lineament; and 3) a mud lithofacies reflecting reduced influx of siliciclastic sand in southern Onslow Bay within the main outcrop belt of the Onslow Bay Sequence, and in outliers within the outcrop belt of the Frying Pan Sequence. In northern Onslow Bay, the carbonate lithofacies occurs on the southern flanks of the Cape Lookout High and infills a relatively small embayment referred to by Stephen W. Snyder (1982) as the Northeast Onslow Embayraent (Fig. 22). Associated sediments consist of biogenic calcareous muds, sands and gravels, which often contain a dolosilt matrix with subordinate amounts of chert and admixed siliciclastic sands. Barnacle plates are common in the sand and gravel fractions. Phosphate is a minor component (0-3%; rarely up to 10%). Sand-sized glauconite, although a relatively minor component (5-7%), reaches its maximum recorded abundance in the Pungo River Formation of Onslow Bay in this lithofacies. Similar carbonate lithologies have been described from the Pungo River Formation of the adjacent coastal plain and barrier islands in the 96 Figure 21. Regional lithofacies distribution within the (Langhian) Onslow Bay Sequence. 97 vicinity of the Cape Lookout High. Scarborough (1981) and Scarborough and others (1982) described "white to light gray to light olive green, calcareous silty muds to very shelly, calcareous muddy, sometimes gravelly, slightly phosphatic (10%) quartz sands" from drill holes on the northern and southern flanks of the Cape Lookout High (holes CNN-1 and CTN-1, respectively). Overlying this lithology in hole CTN-1 on the southern flanks of the Cape Lookout High were "white slightly phosphatic and quartz sandy, calcareous bioclastic shell hash (barnacles, bryozoans) with less than 20 percent calcite mud". Steele (1980) described similar sediments beneath the Quaternary section from Bogue Banks, a barrier island in northern Onslow Bay. He described cherty, calcareous silt and clay containing approximately 10% each of dolosilt, quartz sand, phosphate and shell fragments underlying calcareous sands and gravels containing abundant shell fragments, including barnacles, with minor quartz sand content . The Cape Lookout High area acted as a shallow, shoaling environment during much of Miocene deposition (Steele, 1980; Lewis, 1981; Scarborough, 1981; Scarborough and others, 1982; Gibson, 1983). Structural contours on the unconformity separating the Onslow Bay Sequence from the underlying Frying Pan Sequence (Stephen W. Snyder, 1982) show the nature of this topographic high (Figure 22). The relative importance of biogenic carbonate production was increased due to low siliciclastic input. In addition. Gulf Stream currents impinged on the Cape Lookout High during Langhian sea-level highstands (Stephen W, Snyder, 1982; Popenoe, 1985), bathing this shallow marine environment with warm surface waters that may have further enhanced carbonate 98 Figure 22. Structural contour map on unconformity separating the Frying Pan Sequence from the Onslow Bay Sequence. Note prominent Cape Lookout High and Northeast Onslow Embayment (modified from Stephen W. Snyder, 1982). 99 production. Carbonate sediments were simultaneously shed off the Cape Lookout High as a series of prograding clinoform deposits that infilled the Northeast Onslow Embayraent (Fig. 16). Southward, the carbonate lithofacies rapidly grades into an interbedded quartz sand and dolosilty clay lithofacies which is interpreted to reflect alternating conditions of deposition. Deposition generally involved the slow accumulation of fine-grained, organic-rich sediments on the upper paleoslope. Fine-grained sedimentation was periodically interrupted by brief episodes of rapid deposition of shelf- derived quartz sands. Diagenesis within the zone of sulfate reduction and in the presence of organic matter could provide a mechanism for forming the silt-sized dolomite noted in the clayey beds (Allen and Baker, 1984; Allen, 1985; Baker and Burns, 1985). \ihile the clayey interbeds represent 'background' sedimentation, the periodic influx of siliciclastic sands appears to be the dominant depositional process in terras of net sediment accumulation. Quartz sand beds exhibit some grading, but any original structures would likely have been destroyed during vibracoring due to the relatively clean, cohesionless nature of the sands. Quartz sand intervals often have a 'salt and pepper' appearance due to minor (<10%) amounts of phosphate-coated quartz grains and aggregates of quartz grains bound by phosphate. The occurrence of these grains in upper slope sands suggests that they were eroded from microsphorite pavements within a contemporaneous phosphogenic environment in adjacent shelf environments to the west. These shelf environments were subsequently destroyed by erosional episodes. 100 The transition from the interbedded lithofacies to the mud lithofacies is probably gradational, but documentation of the exact relationship is hampered by lack of sufficient core control. Muds occurring in the OBS outliers, though lithologically similar to surrounding muds of the Frying Pan Sequence, can be differentiated on the basis of siliceous microfossil content. The muds of the OBS outliers contain up to 10% siliceous raicrofossils, whereas adjacent sediments of the Frying Pan Sequence are devoid of siliceous raicrofossils. As with the regional distribution of lithofacies within the Onslow Bay Sequence, vertical patterns of sedimentation reflect differing sediment source areas and depositional processes associated with shelf- margin paleotopographic features. Vertical sediment sequences within the northern carbonate lithofacies, adjacent to the Cape Lookout High, are generally characterized by extreme textural heterogeneity and consist of variable mixtures of siliciclastic sand, calcareous to dolosilty muds and molluscan-barnacle sands and gravels. Textural and mineralogical variation occurs at scales of less than one meter and no regular patterns were detected. Conversely, other lithologies are characterized by textural and mineralogical uniformity over several meters. In central Onslow Bay, depositional processes associated with the White Oak Lineament (Langhian shelf-edge) are exemplified by the interbedded quartz sand and dolosilty clay lithofacies discussed above. Basically uniform vertical sediment sequences characterize the southern mud lithofacies. Minor fluctuations do occur in raicrofossil content and there is a slight upward decrease in siliciclastic sand. Seismic facies indicate that depositional patterns within the Onslow 101 Bay Sequence are dominated by a series of prograding clinoforms deposited over, and immediately east of the \idiite Oak Lineament (Figure 4). Stephen W. Snyder (1982) interpreted the White Oak Lineament to represent the Langhian shelf-break and linked its development to Gulf Stream erosiona! processes during sea-level highstands. Figure 4 illustrates severe erosional truncation of late Burdigalian (Frying Pan Sequence) strata and clinoform deposits of the Onslow Bay Sequence. Deposition of the Onslow Bay Sequence is interpreted to be similar to that described by Matteucci (1984) for the Plio-Pleistocene depositional sequences in the Cape Fear region of the North Carolina continental margin. During lower stands of sealevel the Gulf Stream axis was displaced seaward allowing for offshelf sediment transport and shelf margin progradation as clinoform deposits. The ensuing rise of sea level caused the Gulf Stream to migrate landward, impinge upon and scour previously deposited strata. Repeated deposition of Onslow Bay Sequence clinoform deposits with apparent toplap geometry suggests a repetitious pattern of deposition followed by erosion as a result of Gulf Stream scouring. An alternative scenario is that the \^ite Oak Lineament represents an early Langhian or latest Burdigalian erosional shoreface produced during a lov/stand of sea level, rather than representing a Gulf Stream erosional track. The work of Belknap and Kraft (1981) and Mine and Stephen W. Snyder (1985) on the U.S. Atlantic shelf indicates that marine transgressions during the Quaternary and the Late Tertiary almost completely remove the coastal sedimentary record in a bulldozer-like fashion down to a depth of the active shoreface. Coastal lithosomes are rarely preserved, occurring only as channel-fill deposits in deeply 102 incised coastal plain stream channels. In northern Onslow Bay, the modern shoreface reaches a depth of 12 meters. The White Oak Lineament reaches a maximum relief of approximately 25 meters. Clean quartz sands which form the bulk of the clinoform deposits could have been deposited in response to a subsequent, relatively slow sea-level transgression. However, the repetitive, distinctly interbedded nature of the sand and clay deposition, and the early diagenetic production of dolosilt produced in wholly marine pore waters (Allen, 1985), is not so readily explained. Therefore, this second interpretation seems unlikely. In conclusion, the lithologic data presented in the preceeding section coupled with seismic reflection profiles of Stephen W. Snyder (1982; and unpub. data) indicate that the Onslow Bay Sequence present in outcrop and in the shallow subsurface represents infilling of the Northeast Onslow Embayment and a progradation of the shelf margin. A complex pattern of deposition followed by erosion is probably due to multiple transgressive-regressive events. Deposition occurred during lowered and intermediate stands of sea level as shelf-derived quartz sands were periodically deposited over the shelf margin and interrupted the ’normal’ accumulation of fine-grained clayey sediments. Highstands of sea level were marked by submarine erosion of previously deposited sediments as the axis of the Gulf Stream shifted landward and impinged upon and scoured the shelf and upper slope. A low energy depositional environment in southernmost Onslow Bay is characterized by accumulation of organic-rich muds in the southern portion of the main Onslow Bay Sequence outcrop belt, and by microfossiliferous, zeolitic, dolosilty mud in the OBS outliers. 103 Bogue Banks Sequence Five regional lithofacies characterize the third-order Bogue Banks Sequence and include the following: 1) a quartz sand lithofacies; 2) a phosphatic quartz sand lithofacies; 3) a phosphorite quartz sand lithofacies; 4) a dolosilty mud lithofacies; and 5) a carbonate lithofacies. Distribution of these lithofacies is shown in Figure 23. Boundaries between the quartz sand, phosphatic quartz sand and phosphorite quartz sand lithofacies are gradational and are defined on the basis of the relative abundance of phosphate (averaging < 3 %, 3-9 % and > 10 %, respectively). Phosphate enrichment and the development of the phosphorite quartz sand lithofacies occurs in northernmost (BBS-1 and BBS-8) and central to southern (BBS-2) Onslow Bay. Contacts between the dolosilty mud lithofacies and over- or underlying 'sand' lithofacies appear fairly sharp in vibracores. Distinct fining southward trends, as noted in the underlying Frying Pan and Onslow Bay Sequences are not apparent in the Bogue Banks Sequence. Intrabasinal controls on lithofacies types, such as siliciclastic sediment source areas and paleotopographic features, are not evident, and, within the limits of core control, lithofacies distribution appears to be generally marked by lateral (N-S) continuity. A predominantly carbonate lithofacies within the Bogue Banks Sequence in north central Onslow Bay was only encountered by one vibracore (OB-108) within seismic sequence BBS-5. Due to lack of core 104 Figure 23. Regional lithofacies distribution within the (Serravallian) Bogue Banks Sequence. 105 control, the lateral extent of this lithofacies is unknown. It is, however, interesting to note that a northern carbonate lithofacies, such as those in the Frying Pan Sequence and Onslow Bay Sequence, is not developed in the Bogue Banks Sequence (Figs. 20, 21 and 23). Structural contours on the top of the Onslow Bay Sequence indicate that the Cape Lookout High, which represented a shoaling environment and provided biogenic carbonate sediments during late Burdigalian and Langhian time, had been reduced to a less prominent feature due to infilling of the Northeast Onslow Embayment (Fig. 24). Carbonate sediments therefore do not appear to exhibit regional distribution which can be related to antecedent topography, but occur within the area shown in Figure 23 and as thin interbeds in predominantly noncarbonate lithologies. The lower portion of the Bogue Banks Sequence is characterized vertically by repetitious alternations of clean to muddy quartz sand and quartz sandy, generally dolosilty mud. Phosphate occurs within the sandy intervals in concentrations up to 20 to 25%. Phosphate content increases upsection (within BBS-1) and to the south (within BBS-2). Diatoms occur within the dolosilty mud overlying phosphatic quartz sand in northern (Fig. 18) and central Onslow Bay and within muddy quartz sand overlying the phosphorite quartz sand lithofacies in central Onslow Bay (Fig. 19). Within the upper portions of the Bogue Banks Sequence a lack of core control prevents adequate assessment of vertical lithologic succession. Cores that were recovered reveal uniform sections within a given area, although lithologies vary from area to area. They consist of clean quartz sand (BBS-4); muddy, quartz and calcareous sand (BBS-5); and muddy, phosphorite and quartz sand (BBS-8). 106 Figure 24. Structural contour map on unconformity separating the OnsloAvr Bay Sequence from the Bogue Banks Sequence. Infilling of the northeast Onslow Einbayment during the Langhian subdued the paleotopographic expression of the Cape Lookout High (cf. Figure 22; modified from Stephen W. Snyder, 1982). 107 Seismic sections presented by Stephen W. Snyder (1982; unpub. data) indicate that deposition of strata assigned to the Bogue Banks Sequence occurred in a shelf environment, as reflectors dip very gently seaward. In fact, four cores (9-meter maximum) obtained along the 15-meter transect and separated E-W by a total of 7 km, recovered equivalent strata (Fig. 16). Lithologic data support the conclusion of deposition in a shelf environment; very coarse sand- to granule-sized quartz and phosphate were routinely noted in sandy lithologies, though in minor amounts (<5%), and may represent lag or winnowed material. Also, vertical patterns of sedimentation, consisting of muddy, phosphatic to phosphorite quartz sand grading upward into microfossiliferous mud, are similar to those noted within the Frying Pan Sequence, which was deposited in a middle to outer shelf setting. 108 Miocene Sedimentation Within the Onslow Embayment: A Depositional Model One of the primary objectives of this thesis is to define vertical patterns of sedimentation within the Pungo River Formation in the Onslow Embayment. It was hypothesized that if the Miocene section along the North Carolina continental margin was a product of multiple transgressive-regressive episodes, cyclical depositional patterns similar to those developed in the Aurora Embayment should be recognized. Deposition of phosphate-bearing lithic cycles in the Aurora Embayment has been related to the combined effects of 1) glacio-eustatic sea-level fluctuations, 2) changing climatic conditions and 3) dynamic interaction of major current systems with the continental margin to produce upwelling, deposition of organic matter and formation of phosphorites and associated sediment types (Riggs and others, 1982; Riggs, 1984). The four cyclical depositional units defined by Riggs and others (1982) in the Aurora Phosphate District (units A through D) (Fig. 2) are lithologically consistent both laterally and vertically over an area of approximately 2 100 km . In the study area in Onslow Bay, Pungo River sediment sequences 2 occur in outcrop to shallow subcrop over a 5000 km area. Over such a broad area, Pungo River sediment sequences are raineralogically and texturally variable and generally tend to reflect relative proximity to local sediment sources and paleotopographic features, both of which exert important controls on the regional distribution of lithofacies. Therefore, it was necessary to define major lithofacies and the basinal characteristics which control their development (discussed in previous sections) before interpreting vertical lithologic variations. Vertical patterns of sedimentation within the Pungo River Formation 109 of the Onslow Embayment can be grouped into three general types (Fig. 25). These three types of depositional patterns are developed on a scale of several meters and variations occur within each type. Type I patterns display a fining upward sequence of lithologies and are similar to cyclical depositional sequences induced by high-frequency sea-level fluctuations, as in the Aurora Phosphate District. Type II patterns develop contemporaneously as lateral equivalents to Type I patterns (Table 4 and Fig. 26). However, Type II patterns do not appear to be sensitive indicators of sea-level events as they are uniform sediment sequences which reflect the dominance and temporal persistence of particular oceanographic and depositional conditions within localized areas. Type III patterns are distinctly interbedded sediment sequences that represent periodic transfer of sediments between significantly different depositional environments during high-energy events. Type III patterns develop contemporaneously with Type II patterns (Table 4 and Fig. 26). Therefore, it is possible that they also represent lateral equivalents of Type I patterns, though this relationship has not been directly demonstrated within the limits of existing core control. Descriptions of these patterns and their genetic interpretations are discussed below. Type I_ Type I patterns appear to reflect the lithologic response to episodes of rising sea level as facies change and migrate through time. Varying sediment types accumulate episodically on the continental shelf as depositional environments respond to changing sea level, climate and lio FINING TYPE I UPWARD SILICICLASTIC (fus) IDEAL Fining upward siliciclastic Authlgenic (phosphorite, sediment in dolomite, organic matter)sequence and response to decreasing P_ inverseiy proper-. _ tional but collectively increase upward through the lithic cycle TYPE 11 Uniform siliciclastic TEMPORAL Texturally and composi- sediment sequence; tionally variabie biogenic may consist of sand- PERSISTENCE OFto (macrofossil) sediment clay-sized material PARTICULAR sequence; vertical depending on energy variation due to type, regime LITHOFACIES size and degree of frag- mentation of biogenic Intrabasinal Controls components and to on Sedimentation Overwhelm amount and grain-size the Effects of Sea-level Rise of admixed siliciclastics on Facies Migration TYPE III UPPER SLOPE (us) SHELF (s) Rapid deposition of O* V- ' Rapid deposition of shelf-derived silici- PERIODIC TRANSFER siliciclastic sands elastics interupts buries benthic 'normal' accumulation OF SEDIMENTS communities of fine-grained sediments BETWEEN — DIFFERENT TYPE II Slow accumulation [ ~ ENVIRONMENTS Sheif substrate of fine-grained doio- DURING ? colonized by caic- mitic/organic-rich(?) HIGH-ENERGY •r * areous macro- andsediments on upper microfauna continental slope DEPOSITIONAL during periods of reduced EVENTS siliciclastic influx Figure 25. Classification, description and genetic interpretation of vertical patterns of sedimentation within the Pungo River Formation in the Onslow Embayment. Vertical patterns of sedimentation are developed and defined at scales of 2 to 10-F meters. Figure 26. Schematic section illustrating lateral variations in vertical patterns of sedimentation as a response to local sediment source areas, paleotopographic features and oceanographic processes. All patterns may develop during a transgressive event and represent lateral time-equivalents. The Type I-ideal pattern bears the closest Ill resemblance to Pungo River Formation lithic cycles resulting from high-frequency sea- level fluctuations described from the Aurora Embayment (Scarborough, 1981; Scarborough and others, 1982; Riggs and others, 1982; Riggs, 1984). 112 oceanographic conditions such as upwelling. Significantly, Type I patterns are best developed in shelf sediments deposited directly above the lower bounding unconformities of the Frying Pan and Bogue Banks Sequences. Where siliciclastic sedimentation dominates the depositional cycle, the Type I pattern is a fining upward siliciclastic sequence (Type I-fus) (Figs. 25 and 26). This pattern develops in areas adjacent to areas of phosphogenesis and biogenic sediment accumulation. Type I-fus patterns may have occurred in response to two processes. First, with rising sea level, the depositional environment became increasingly distant from terrigenous siliciclastic point-sources. With continued rise of sea level, drowning of wide coastal plain valleys would lead to the development of barrier islands and associated estuaries through mainland beach detachment (Swift, 1976). These estuaries could then have acted as sediment sinks, trapping fluvial-borne siliciclastics before they reached the shelf environment. Second, déglaciation and rising sea level took place in response to major climatic changes involving the northward migration of climatic zones. Resulting changes in the amount of precipitation and resulting vegetative cover on the adjacent landmass would have changed the patterns of siliciclastic sediment supply to the continental margin during the sea-level event (Riggs, 1984). Fining upward siliciclastic patterns (Type I-fus) may grade laterally into a more complex vertical succession of lithologies in which primary authigenic (chiefly phosphorite and dolosilt) and biogenic (siliceous and calcareous microfossils) components are superimposed on the fining upward siliciclastic pattern (Figs. 25 and 26). In these 113 lithic sequences, relative abundances of primary authigenic and biogenic sediments (inversely proportional to siliciclastics) collectively increase upward through the depositional cycle. Siliciclastic sediments, transported and deposited through physical processes, dominate the lower portions of the lithic sequence and represent the depositional response to the early stages of transgression. As transgression proceeds, decreasing siliciclastic input coupled with the initiation of upwelling allows authigenic or biogenic sedimentation to increase in relative importance. If physical, chemical an biological conditions are favorable, then phosphate authigenesis reaches a maximum and is recorded in the middle portion of the lithic cycle. Although many questions remain unanswered concerning the origin and depositional environments of sedimentary marine phosphorites, most modern theories (Bentor, 1980; Sheldon, 1981; Baturin, 1982) share common points. Important among these are 1) deposition during transgressive episodes, 2) deposition during periods of reduced siliciclastic sedimentation and 3) upwelling of deeper oceanic waters to provide a steady supply of nutrients, including phosphorus, to the shelf environment where these nutrients are depleted by biological activity and concentrated in the sediments as organic matter (Bentor, 1980). Upwelling currents may be of several types. Riggs (1984) and Stephen W. Snyder and others (1986) advocated topographically induced, dynamic upwelling to explain the episodic occurrence of phosphorites on the southeastern U.S. continental margin. Topographic upwelling occurs as major oceanic current systems, such as the Gulf Stream, impinge upon and are deflected by positive bathymetric features, resulting in 114 upwelling on the downstream side of the high. Episodicity and isolated occurrences of phosphorite deposits can thus be explained if the mechanics of dynamic upwelling are coupled with rising sea level. Phosphogenic episodes might ’turn on and off' in different areas as various topographic features along the continental margin first deflect, and then are overridden by a major current. Repeated deposition of phosphorites within the same area would occur given multiple cycles of sea-level change (Stephen W. Snyder and others, 1986). Therefore, it appears that the phosphorite facies may not be time-transgressive but instead represent episodic sedimentation in response to localized upwelling. During the late stages of a transgressive event, large portions of the depositional environment along the continental margin were increasingly influenced by open oceanic circulation. Siliceous and calcareous microfossils became important sediment contributors, reaching maximum abundance in the finer-grained sediments which cap the lithic sequence. Diatoms and foraminifera generally do not co-occur but instead represent lateral facies equivalents. Planktonic and benthic foraminifera may accumulate in the phosphorite interval but diatoms are rarely noted here. Sheldon (1981; in press) notes that siliceous sediments and phosphorites form a close association in phosphorite- bearing sequences throughout the Phanerozoic, and probably owe their origin to the same oceanic current systems that supply silica, phosphorus and nitrogen. However, their segregation into discrete interbeds and the lack of mutual occurrence remains unclear (Bentor, 1980; Sheldon, 1981; in press). 115 The apparent lack of co-occurrence between diatoms and foraminifera is perhaps due to differing preservational characteristics of siliceous and calcareous skeletal material. Recent phosphorites are presently forming in organic-rich sediments within the oxygen minimum zone (Burnett and otherrs, 1980; Baturin, 1982). Microbial decay of organic matter and sulfate reduction would lead to increased alkalinity, which would not favor the preservation of biogenic opal. The organic-rich muds (0.94- 5.74 % TOC, Table 2) of FPS-2, which overlie FPS-1 phosphorites in southern Onslow Bay, are generally devoid of siliceous raicrofossils, or contain rare, highly corroded valve fragments; but they contain abundant foraminifera and clinoptilolite. Preservation of foraminifera would be enhanced under alkaline conditions associated with sulfate reduction (Deister-Haas, 1978), and dissolved silica from pre-existing diatoms may have been incorporated in the neogenetic clinoptilolite. Although the presence of diatoms does not in itself imply upwelling, diatomaceous sediments characterize areas of modern upwelling and have been used to infer ancient upwelling environments (Heath, 1974; Deister- Haass, 1978; Koopman and others, 1978). Siliceous microfossils usually undergo rapid post-mortem dissolution in the water column and within the sediments due to undersaturation of sea water and interstitial water with respect to silica. Heath (1974) calculated that only 4% of all biogenic opal is incorporated in the sedimentary record, while only 2% is ultimately preserved. When the supply of biogenic opal reaching the seafloor is increased sufficiently to allow saturation of interstitial waters with respect to silica, such as during upwelling events, preservation of diatoms is enhanced (Heath, 1974; Deister-Haass, 1978). 116 Reduced rates of siliciclastic sedimentation are generally regarded as necessary for the accumulation of significant amounts of biogenic silica (McCartan and Andrews, 1985). Thus, increased percentages of both phosphate and diatoms in the upper portions of Type I sequences imply increased primary productivity in the overlying water column as a consequence of upwelling, coupled with reduced rates of siliciclastic sedimentation. Vertical patterns of sedimentation in which muddy siliciclastic sands grade upward into phosphorite and biogenic sediments in a fine- grained siliciclastic matrix represent the ideal Type I pattern (Onslow Ideal Lithic Cycle). The ideal Type I pattern is recognized within FPS- l/FPS-2 in central and southern Onslow Bay (FPS-1 and FPS-2 are considered here as a single lithologic unit) and BBS-1 in northern Onslow Bay (Table 4; Figs. 10, 11, 12, 17, 18 and 19). Cycles which lack equal development of the siliciclastic, authigenic and/or biogenic components are interpreted to develop in the transition zone between siliciclastic Type I and ideal Type I patterns, although a lack of detailed core control in some lithologic units prevents documentation of this relationship. Transitional Type I patterns occur in FPS-5, BBS-1 and BBS-3(?) in central Onslow Bay and within BBS-2 in northern and central Onslow Bay (Table 4). Type II Type II patterns reflect the persistence of particular depositional environments within given geographic areas throughout the depositional cycle. These patterns are exemplified by uniform sediment sequences which a) exhibit little vertical change in mineralogy and texture and are 117 Table 4. Distribution of Type I (fining upward siliciclastic [fus], transitional and ideal), Type II (A and B) and Type III (shelf [s] and upper slope [us]) vertical patterns of sedimentation within fourth- order seismic sequences. Refer to the text and to Figure 25 for definition and interpretation of patterns. A '?’ denotes areas of poor core control. 'n/o' = no outcrop; 'u/s' = unsampled. Seismic NORTHERN AREA CENTRAL AREA SOUTHERN AREA Sequence BBS-8 TYPE II-A n/o n/o BBS-7 u/s n/0 n/o BBS-6 u/s n/o n/o BBS-5 TYPE II-B u/s u/s BBS-4 n/o TYPE II-A(?) n/o BBS-3 n/o TYPE I-transit.(?) n/o BBS-2 TYPE I-transitional TYPE I-transitional n/o BBS-1 TYPE I-ideal TYPE I-transitional n/o OBS-4 TYPE II-B n/o u/s OBS-3 TYPE II-B n/o TYPE II-A OBS-2 TYPE II-B u/s TYPE III-us 0BS-1+ TYPE II-B TYPE III-us TYPE II-A FPS-6 TYPE II-B TYPE II-A(?) TYPE II-B FPS-5 TYPE II-A TYPE I-transitional n/o FPS-4 TYPE III-s u/s n/0 FPS-3 n/o TYPE I-fus TYPE II-A(?) FPS-2* TYPE II-A TYPE I-ideal TYPE I-ideal FPS-1* + includes OBS-outliers FPS-1 and FPS-2 are grouped as a single lithologic unit in this study. 118 generally dominated by siliciclastic sediments (Type II-A), or b) are characterized by mineralogical and textural heterogeneity (Type II-3), where variability occurs at relatively small scales (tens of centimeters) and are generally dominated by biogenic carbonate sediments (Fig. 25). Type II patterns occur where the effects of sediment source areas, paleotopographic features or physical energy regimes overwhelm the effects of depth changes during sea-level fluctuations and control local depositional processes and sediment types to such a degree that facies migration does not occur during a transgressive episode. Thus, the development of the Type I pattern is prevented in these areas. Type II patterns are common throughout the Pungo River Formation in Onslow Bay and occur within every third-order- and locally within nearly all fourth-order seismic sequences (Table 4). Type II patterns may contain primarily siliciclastic, authigenic or biogenic sediments, or various mixtures of these sediment types. Within siliciclastic sediment sequences the Type II-A pattern is most common. Sandy sequences reflect depositional environments which are proximal to siliciclastic sources areas and which represent relatively high energy shelf environments where fine-grained sediments (which cap Type I-fus patterns) were winnowed by waves and currents. These patterns are developed in northern Onslow Bay within FPS-l/FPS-2 and FPS-5 and in central Onslow Bay within FPS-6 and BBS-4, although in central Onslow Bay core control and precise documentation of these patterns are poor. Muddy sequences would, conversely, represent relatively low energy depositional environments which were distal to siliciclastic source areas and where fine-grained sediments could accumulate throughout the 119 depositional cycle. Muddy sequences displaying the Type II-A pattern are restricted to southern Onslow Bay and occur within FPS-3, OBS-3 and OBS- outliers. Documentation of the Type II-A pattern in FPS-3 is tentative due to lack of core control. Sediment sequences bearing significant concentrations of phosphate generally give way above and below to different, though predictable, lithologies which collectively form ideal or transitional Type I patterns. However, sediments within BBS-8 contain 8% to 20% phosphate and display the Type II-A pattern. This sequence is interpreted to consist of sediments, including phosphate, reworked and transported by shelf currents. The Type II-B pattern characterizes biogenic sediment sequences in northern Onslow Bay and occurs within FPS-6, OBS-1, OBS-2, OBS-3, OBS-4, and BBS-5. With the possible exception of BBS-5, where core control is lacking, the persistence of this pattern is interpreted to reflect the influence of the Cape Lookout High on the depositional regime. As discussed earlier, the Cape Lookout High was a shoaling, carbonate- producing environment through the late Burdigalian (Frying Pan Sequence) and particularly during the Langhian (Onslow Bay Sequence). Textural variations are generally related to variation in calcareous macro- and raicrofossil assemblages and are dependent upon 1) the proportion of macro- to microfossils within a given horizon, 2) size variations among individuals within the macro- and microfossil groups and 3) the degree of fragmentation of the fossil material which is related to local energy conditions. The Type II-B pattern also characterizes the foraminiferal quartz sand lithofacies of the Frying Pan Sequence (FPS-6). 120 Compositional variation is related to fluctuations in percent foraminifera (15-50%) vs. siliciclastics. Textural variation is minor with mud content ranging from 5 to 20%. Type III Type III patterns are characterized by interbedded sequences containing two distictly different lithologies. Repetition of interbeds occurs at scales of 0.5 to 3 meters, with little or no gradation between interbeds. Type III patterns develop in areas between two contiguous Type II depositional environments and result from sediment transfer between these environments during periodic, high-energy depositional events. This process is referred to as "punctuated mixing" by Mount (1984). Type III patterns were documented in shelf (Type III-s) and upper slope (Type III-us) settings (Table 4; Fig. 25) within the Frying Pan Sequence and Onslow Bay Sequence, respectively. The Type III-s pattern is exemplified within FPS-4 in northern Onslow Bay (Table 4). In this area, biogenic carbonate sand and gravel are interbedded with clean quartz sand. Carbonate and quartz sand interbeds range in thickness from 0.6 to 1.0 m and from 1.5 to 4.0 meters respectively. Fossil material may be whole and unabraded or abraded and fragmented. Large (up to 4 to 5 cm), well preserved specimens of Mercenaria sp. suggest that the biogenic horizons represent the autochthonous component of this sediment sequence, while the relative lack of fossil material in the quartz sand interbeds suggests that these horizons represent the allochthonous component. This pattern is thought to develop as calcareous raacrofossils and microfossils colonize a benthic 121 shelf environment during periods of reduced siliciclastic influx; periodically, the benthic community is inundated and buried by rapidly deposited siliciclastic sands. Repetition of these alternating conditions would lead to the interbedded sequence described above. Type III-us patterns characterize OBS-1 in southern Onslow Bay and OBS-2 in central and southern Onslow Bay (Table 4). OBS-1 was not sampled in central Onslow Bay, but seismic reflection patterns suggest similar depositional styles. In central and southern Onslow Bay, the interbedded, dolosilty mud and quartz sand lithofacies is interpreted to represent the slow accumulation of fine-grained, possibly organic-rich muds on the upper continental slope. This normal pattern of sedimentation was punctuated by periodic, high-energy events which led to deposition of shelf- derived quartz sand interbeds. Cores OB-41 and OB- 58 clearly display the Type III-us pattern and represent the type cores for the interbedded lithofacies of the Onslow Bay Sequence. Through high-resolution seismic reflection studies, Matteucci (1984) documented extensive asymmetrical sand-waves in modern shelf sands from the Frying Pan Shoals region of southern Onslow Bay. The sand waves are restricted to the sand shoals area but show evidence of active migration. Seaward migration would cause shelf-break spill-over which could produce the Type III pattern, if these sands were deposited over a different lithology characteristic of the slope environment. 122 Comparison of Onslow Bay Lithic Cycles to Aurora Lithic Cycles Of the three general patterns of sedimentation discussed above, the Type I pattern, specifically the Onslow ideal lithic cycle, most closely resembles cyclical patterns of sedimentation resulting from high- frequency sea-level fluctuations within the Pungo River Formation in the Aurora Phosphate District (Scarborough, 1981; Scarborough and others, 1982; Riggs and others, 1982; and Riggs, 1984). Lithic cycles in the Aurora Phosphate District display vertical patterns in which silicilastic and phosphate sediments decrease upsection while carbonate content increases. Thus, the phosphate and siliciclastic components are inversely proportional to each other and are collectively inversely proportional to carbonate (Riggs and others, 1982) (Fig. 2). Ideal type I patterns are not laterally persistent throughout Onslow Bay but are developed in specific, localized areas. Siliciclastic sediments appear to represent the primary diluent material in Onslow Bay lithic cycles. Therefore, relative abundances of phosphate and biogenic sediments are inversely proportional to each other and are collectively inversely proportional to siliciclastic material. Carbonates capping Aurora lithic cycles are usually indurated, bored, moldic limestones and dolostones which mark the culmination of the transgressive, depositional episode (Riggs and others, 1982; Riggs, 1984). Upper portions of Onslow Bay lithic cycles are generally nonindurated, fine-grained sediments containing elevated relative percentages of siliceous and calcareous raicrofossils. Stewart (1985) described barnacle-bryozoan-bivalve biomicrosparites overlying the 123 phosphorite-bearing lithic cycle of FPS-1 in southern Onslow Bay. She interpreted these to represent Miocene cap rocks similar to those described by Riggs from Aurora. This interpretation is incorrect as the ’cap rocks' can be demonstrated to be considerably younger (probably Pleistocene) through geophysical (Stephen W. Snyder, unpub. data; Mearns, 1986) and paleontological methods (V. Zullo, pers. comm, to S. Riggs). Occasionally, relatively thin horizons (!« 109-2 2.5-2.75 BBS-2 tr/67/33 80.9 ÏÎÎ 109-3 4.0-4.25 BBS-2 0/74/36 xU83.1 'r 109-4 5.5-5.75 BBS-2 2/55/43 66.6 >¡í xUT» 109-5 6.0-6.18 BBS-1 9/30/61 41.0 xV Textural % Point Geo- Core- Core Seismic % Acid Count chem Sample # Depth(m) Sequence Gravel/Sand/Mud Insol. Data Data OB 110-1 0.75-1.0 FPS-2 0/85/15 * 110-2 2.25-2.5 FPS-2 0/91/9 * 110-3 3.75-4.0 FPS-2 0/76/24 * 110-4 5.25-5.5 FPS-2 tr/87/13 * OB 113B-1 1.25-1.5 FPS-1 0/54/46 60.7 * * 113B-2 2.75-3.0 FPS-1 0/68/32 81.3 * * 113B-3 4.25-4.5 FPS-1 0/67/33 83.8 * * OB 114-1 6.25-6.5 FPS-1 0/53/47 * 114-2 7.25-7.50 FPS-1 0/50/50 * 114-3 8.0-8.25 FPS-1/01 ig. contam. OB 115-1 5.75-6.0 FPS-1 tr/77/33 * 115-2 6.75-7.0 FPS-1 0/80/20 OB 117-1 2.5-2.75 FPS-2 0/0/100 60.9 •X» 117-2 4.0-4.25 FPS-2 0/0/100 a*70.7 'T* 117-3 5.5-5.75 FPS-2 0/0/100 69.6 * 117-4 7.0-7.25 FPS-2 0/2/98 69.4 117-5 8.5-8.75 FPS-2 0/27/73 72.7 OB 127-1 1.5-1.75 FPS-1 0/67/33 45.6 •X0'r* 127-2 3.5-3.75 FPS-1 0/80/20 62.6 127-3 5.5-5.75 FPS-1 0/68/32 127-4 7.5-7.75 FPS-1 tr/83/17 87.6 * OB 132-1 1.5-1.75 FPS-1 2/73/25 83.1 * 132-2 2.5-2.75 FPS-1 5/67/28 71.9 >îî 132-3 3.5-3.75 FPS-1 1/83/16 81.6 * OB 135-1 2.0 FPS-1 0/74/26 .A.T* 135-2 3.5 FPS-1 0/64/36 * 135-3 5.0-5.25 FPS-1 1/75/24 135-4 6.5-6.75 FPS-1 0/74/26 APPENDIX B. Point count data. Point count analyses were performed on washed sand-sized samples. Percent values have been normalized to reflect percentage of total sediment. Samples are listed sequentially by core number. Heading symbols refer to: TOT TERRIG = total terrigenous QTZ = quartz FED = feldspar MCA = mica HVY = heavy mineral FRM = foraminifer ECH = echinoderm OST = ostracode BIV = bivalve BRN = barnacle UID = unidentifiable carbonate grain DLR = dolomite rhomb LTH = carbonate lithoclast DIA = diatom RAD = radiolarian SPC = siliceous spicule CRT = chert CLN = clinoptilolite PEL = pelletai phosphate INT = intraclastic phosphate SKL = skeletal phosphate MLD = phosphatic biogenic internal molds RPL = biogenic carbonate replaced by phosphate DSC = discoid phosphate GLAU = glauconite PYR = pyrite Sample Depth QTZ FLD MCA HVY FRM ECH OST BIV BRN UID DLR LTH DIA RAD SPC CRT CLN PEL INT SKL MLD RPL DSC GLA PYR 1-1 .75-5.0 57 10 3 2 2 1-2 .75-6.0 59 4 5 2 4 1-3 .75-7.0 61 1 12 l-A .75-8.0 58 3 8 5 -51 .75-9.0 53 2 3 10 4 21- .25-3.5 73 2 1 1 2-2 .75-5.0 67 1 3-2 .25-6.5 72 1 2 3-1 .0-1.25 43 2 3-2 .5-2.75 40 1 4 1 3-3 .0-3.25 43 2 1 3-4 .5-4.75 65 — 4 1 3-5 .0-6.75 68 3 1 3-6 .5-7.75 56 2 6B-1 .0-0.25 51 1 1 — 6B-2 .5-1.75 49 1 1 1 1 6B-3 .0-3.25 54 1 1 1 1 6B-4 .75-5.0 63 1 2 1 6B-5 .4-6.75 84 1 — 2 4 2 1 6B-6 .0-7.25 83 1 1 — 1 -- 2 4 2 14-1 .0-1.25 11 40 3 2 2 14-2 .5-2.75 12 18 18 13 4 14-3 .0-4.25 17 4 26 25 6 20-1 .0-1.25 2 33 1 1 3 20-2 .5-2.75 12 22 3 3 3 1 20-3 .0-4.25 19 18 9 4 2 1 20-4 .5-5.75 17 29 8 8 2 1 29B-1 .25-0.75 25 29B-2 .0-3.25 43 29B-3 .0-6.25 19 146 Sample Depth QTZ FLO MCA HVY FRM ECH OST BIV BRN UID DLR LTH DIA RAD SPC CRT CLN PEL INT SKL MLD RPL DSC GLA PYR 47-1 0.0-0.25 40 — 1 1 1 47-2 2.0-2.25 37 47-3 4.25-4.5 13 47-4 5.5-5.75 28 1 47-5 7.5-7.75 25 -647 8.5-8.75 43 2 4-81 0.8-1.05 75 4 — 48-2 2.25-2.5 77 1 — 1 48-3 4.75-5.0 74 3 1 1 484- 6.75-7.15 82 3 — 2 1 1-94 1.0-1.25 61 4 — 1 1 1 — 49-2 2.5-2.75 70 49-3 8.75-8.9 59 52-1 2.85-3.0 31 1 1 1 252- 3.75-4.0 11 531- 1.25-1.5 63 5 53-2 2.75-3.0 58 2 9 53-3 3.3-3.5 55 1 1 10 53-4 4.25-4.5 43 1 9 53-5 4.75-5.0 47 2 3 53-6 5.25-5.5 51 1 5 53-7 6.25-6.5 48 11 60-1 1.25-1.5 78 60-2 3.5-3.75 63 60-3 6.0-6.25 32 1 — 60-4 7.5-7.75 55 1 1 — 63-1 0.0-0.25 2 9 63-2 1.25-1.5 2 28 63-3 2.25-2.5 18 17 147 Sample Depth QTZ FLDU MCA HVY FRM ECH OST BIV BRN UID DLR LTH DIA RAD SFC CRT CLN PEL INT SKL MLD RPL DSC GLA PYR 71-1 0.25-0.5 30 — — 71-2 0.75-1.0 31 — — 1 1 94-1 0.7-0.95 36 1 — 10 13 1 94-2 1.0-1.10 34 — — 1 5 94-3 1.5-1.75 29 1 95-1 0.1-0.35 62 95-2 0.8-1.05 64 — — 103-1 1.0-1.25 52 — 1 1 103-2 2.5-2.75 59 1 — 103-3 4.0-4.25 74 1 103-4 5.5-5.75 67 1 1 104-1 5.0-5.25 51 1 104-2 6.5-6.75 32 1 18 105-1 0.5-0.75 63 1 1 1 105-2 2.0-2.25 61 3 1 1 105-3 3.5-3.75 53 4 2 4 1 105-4 5.0-5.25 58 7 9 4 1 105-5 6.5-6.75 17 1 19 28 8 109-1 1.5-1.75 61 1 6 1 109-2 2.5-2.75 55 3 3 1 1 109-3 4.0-4.25 64 1 2 1 3 2 1 109-4 5.5-5.75 45 1 1 2 1 -0951 6.0-6.18 21 2 1 2 1 1 1 1 011-1 0.75-1.0 82 1 1 1 __ 110-2 2.25-2.5 86 1 1 1 2 1 1 1 110-3 3.75-4.0 71 I 110-4 5.25-5.5 83 1 2 — 148 Sample Depth UTZ FLÜ MCA HVY FRM ECH ÜST 61V 6RN UID DLR LTH DIA RAD SFC CRT CLN PEL INT SKL MLD RPL DSC GLA PYR 113B-1 .25-1.5 49 1136-2 .75-3.0 64 1136-3 .25-4.5 63 115-1 .75-6.0 15 12 1 25 20 115-2 .75-7.0 42 — 1 3 12 16 117-1 .5-2.75 117-2 .0-4.25 117-3 .5-5.75 117-4 .0-7.75 1 1 117-5 .5-8.75 22 4 127-1 .5-1.75 23 29 11 127-2 .5-3.75 54 12 7 127-3 .5-5.75 56 2 2 127-4 .5-7.75 76 2 135-1 .0-2.25 68 — 1 135-2 .5-3.75 58 -- 1 135-3 .0-5.25 64 2 5 135-4 .5-6.75 71 149 APPENDIX C. Geochemical analyses. Samples were analysed by ICAPES (Inductively Coupled Argon Plasma Emission Spectroscopy) by personnel at the East Carolina Shared Research Resources Laboratory. Values are expressed in wt % with the exception of Cu and Zn which are expressed in ppm. 151 CORE DEPTH (m) UNIT P205 CaO MgO Fe203 A1203 Na2 K20 Ti02 Mn Cu Zn OB-1 3.75-4.00 BBS-8 3.35 17.28 1.18 1.47 2.80 0.74 0.87 0.29 0.04 20 44 OB-1 4.75-5.00 BBS-8 4.10 14.80 2.56 0.78 1.42 0.55 0.63 0.28 0.02 36 41 OB-1 5.75-6.00 BBS-8 4.07 9.85 1.64 1.18 2.40 0.82 0.57 0.29 0.01 31 51 OB-1 6.75-7.00 BBS-8 6.21 14.12 1.22 0.95 1.66 0.67 0.51 0.31 1.28 18 59 OB-1 7.75-8.00 BBS-8 5.82 12.10 1.15 1.33 2.42 0.54 0.80 0.42 0.02 54 68 OB-1 8.75-9.00 BBS-8 5.25 11.40 1.28 1.32 2.37 0.67 0.42 0.49 0.02 52 52 OB-2 3.25-3.50 BBS-1 1.26 5.31 0.69 2.30 3.93 0.68 0.86 1.00 0.04 114 56 OB-2 6.25-6.50 BBS-1 1.92 4,08 0.65 1.99 4.26 0.69 0.89 0.91 0.04 105 67 OB-6B 3.00-3.25 BBS-1 1.62 3.42 0.99 2.07 5.77 1.42 1.48 0.57 0.04 38 75 OB-6B 6.50 BBS-1 2.85 5.57 0.35 0.50 1.51 0.64 0.52 0.25 1.24 14 35 OB-6B 7.00 BBS-1 2.54 5.53 0.36 0.53 1.43 0.59 0.62 0.23 0.02 15 34 OB-9 1.75-2.00 FPS-1 3.36 15.10 0.94 1.73 5.35 1.54 1.61 0.79 0.03 97 88 OB-9 2.75-3.00 FPS-1 3.20 13.00 2.12 1.79 5.52 2.54 1.38 0.65 0.02 84 119 OB-14 1.00-1.25 FPS-1 5.41 29.40 1.31 1.00 2.89 1.42 0.86 0.56 0.02 78 91 OB-14 2.50-2.75 FPS-1 11.70 36.54 1.16 0.95 2.54 1.65 0.60 0.49 0.86 36 116 OB-14 4.00-4.25 FPS-1 14.58 32.69 1.03 1.05 2.48 1.53 0.68 0.58 0.03 45 153 OB-16 0.50-0.75 OBS-u 0.88 5.80 4.86 4.78 10.91 2.40 2.13 0.86 2.11 51 160 OB-16 4.25-4.50 OBS-u 0.84 2.45 3.32 5.00 11.20 2.07 2.16 0.80 0.03 97 120 OB-16 5.75-5.82 OBS-u 1.21 2.50 3.40 5.27 12.00 2.17 2.15 0.85 2.30 50 164 OB-17 3.00-3.25 OBS-u 1.76 13.45 4.11 2.56 6.94 2.14 1.78 0.54 0.05 34 123 OB-17 5.75-6.00 OBS-u 1.22 13.60 2.33 2.20 6.70 2.12 1.55 0,62 0.01 90 104 OB-22 3.25-3.50 FPS-1 6.33 22.94 2.15 1.89 4.56 1.61 0.12 0.51 0.04 40 124 OB-22 5.25-5.50 FPS-1 2.31 18.90 1.42 1.97 3.62 1.30 0.83 0.40 1.44 24 49 OB-24 0.30-0.50 FPS-1 9.26 42.46 1.23 0.99 1.60 1.05 0.37 0.17 0.03 18 74 OB-24 1.00-1.25 FPS-1 23.20 56.00 1.00 0.58 1.00 1.78 0.27 0.11 — 32 128 OB-26 0.25-0.50 FPS-1 8.89 26.27 1.59 1.30 3.58 1.92 0.86 0.67 1.08 43 122 OB-26 1.25-1.50 FPS-1 10.18 36.54 1.44 1.04 2.89 1.60 0.80 0.47 0.03 36 116 OB-26 2.75-3.00 FPS-1 12.90 29.80 1.31 0.85 2.20 1.47 0.47 0.39 0.01 63 124 OB-27 1.25-1.50 FPS-2 0.61 2.58 2.67 4.34 10.10 2.17 2.65 0.89 0.03 109 120 OB-27 7.25-7.50 FPS-2 5.93 18.90 2.32 1.60 4.28 1.62 0.93 0.56 0.02 86 100 OB-28 1.00-1.25 FPS-2 0.96 4.36 3.44 3.36 9.61 2.69 2.43 0.74 0.02 97 122 OB-28 2.00-2.27 FPS-2 0.63 4.42 2.70 4.39 10.40 2.15 2.68 0.91 0.03 111 124 OB-28 3.00-3.25 FPS-2 0.77 4.16 2.95 5.56 12.70 2.40 2.70 1.02 2.44 60 158 OB-29B 0.25-0.50 FPS-2 0.77 27.77 0.77 0.34 0.85 0.34 0.29 0.03 0.96 4 9 OB-29B 3.00-3.25 FPS-2 3.42 15.00 1.49 1.51 4.41 1.37 1.26 0.95 0.03 116 106 OB-29B 6.00-6.25 FPS-1 6.94 35.63 1.07 0.98 2.72 1.26 0.84 0.53 0.03 38 104 OB-33 0.50-0.75 OBS-4 0.21 — 1.66 0.30 0.32 0.61 0.03 0.02 0.29 7 18 OB-33 4.50-4.75 OBS-4 0.27 — 3.41 0.45 0.54 0.66 0.21 0.03 — 13 19 OB-33 6.50-6.75 OBS-3 0.91 1.87 1.18 1.77 0.97 0.42 0.13 0.02 13 50 OB-33 8.25-8.50 OBS-3 1.00 38.40 1.49 1.46 2.51 1.15 0.25 0.19 0.01 19 95 OB-34 3.75-4.00 OBS-1 1.09 15.50 2.77 1.43 2.47 0.81 0.40 0.17 0.01 28 58 OB-34 5.75-6.00 OBS-1 1.08 13.50 2.93 1.62 3.37 0.89 0.73 0.23 0.01 39 74 OB-34 6.75-7.00 OBS-1 1.00 11.98 2.39 1.47 3.23 0.89 0.52 0.22 0.02 18 72 OB-35 0.90-1.15 OBS-1 0.76 58.28 1.87 0.98 1.17 0.63 0,30 0.14 0.02 14 43 OB-35 1.75-2.00 OBS-1 1.23 32.90 6.25 1.56 3.07 0.88 0.67 0.27 0.02 45 65 OB-35 3.75-4.00 OBS-1 1.08 29.90 5.05 1.27 2.48 0.57 0.60 0.25 0.01 44 65 OB-35 5.75-6.00 OBS-1 1.08 29.60 4,23 0.98 2.09 0.58 0.15 0.22 0.01 20 57 OB-35 7.20-7.50 OBS-1 1.10 36.02 3.26 0.84 2.00 0.44 0.48 0.22 0.02 15 64 OB-37 1.50-1.75 FPS-4 0.51 3.59 0.51 0.97 2.73 0.74 0.91 0.36 0.03 95 34 152 CORE DEPTH (m) UNIT P205 CaO MgO Fe203 A1203 NaO K20 Ti02 Mn Cu Zn OB-37 4.75-5.00 FPS-4 0.72 2.54 0.33 0.80 2.37 0.64 0.71 0.70 0.02 80 29 OB-37 8.00-8.25 FPS-4 0.57 24.09 0.15 0.32 0.98 0.49 0.40 0.17 0.03 11 20 OB-38 0.25-0.50 OBS-2 1.93 — 0.98 1.83 0.55 0.66 0.50 0.04 0.02 8 35 OB-38 1.50-1.80 OBS-2 3.33 27.90 1.08 2.74 1.80 1.03 0.40 0.29 0.02 28 45 OB-38 2.25-2.50 OBS-1 1.42 15.53 3.93 0.42 1.05 0.55 0.32 0.18 0.02 11 28 OB-38 3.75-4.00 OBS-1 1.61 9.70 4.08 0.58 1.73 0.75 0.55 0.19 0.02 12 40 OB-38 8.46 OBS-1 1.70 9.22 4.89 0.91 2.53 1.23 0.56 0.22 0.02 16 62 OB-39 8.75-9.00 OBS-2 2.93 35.50 0.97 1.58 0.79 0.46 0.20 0.06 0.01 2 31 OB-42 5.25-5.50 BBS-1 1.83 4.09 1.26 2.40 5.70 1.29 1.42 0.94 0.04 112 109 OB-42 6.25-6.50 BBS-1 1.61 2.90 1.56 2.91 7.54 1.87 1.52 0.81 1.84 49 113 OB-43 1.00-1.25 BBS-1 1.98 5.37 1.66 2.79 6.20 1.57 1.50 0.96 0.04 115 122 OB-43 2.00-2.25 BBS-1 2.06 4.27 0.15 0.32 0.95 0.49 0.36 0.18 0.03 11 18 OB-43 3.50-3.75 BBS-1 1.19 2.32 2.01 3.88 9.96 2.41 1.86 0.98 2.15 64 142 OB-43 4.25-4.50 BBS-1 0.99 2.06 1.79 3.34 8.99 1.83 1.73 0.76 0.03 111 118 OB-45 0.75-1.00 FPS-6 1.24 53.18 2.80 0.80 1.14 0.78 0.31 0.13 0.02 12 34 OB-45 3.00-3.25 FPS-6 2.19 20.35 1.16 0.66 1.46 0.67 0.49 0.21 0.02 15 38 OB-45 4.75-5.00 FPS-6 2.75 14.70 0.50 0.54 1.14 0.51 0.47 0.14 0.01 26 29 OB-47 0.00-0.25 FPS-2 0.79 4.06 2.54 1.99 4.37 1.45 1.24 0.71 0.04 36 87 OB-47 2.00-2.25 FPS-2 0.74 7.48 4.37 1.61 3.84 1.13 1.16 0.70 0.03 86 69 OB-47 4.25-4.50 FPS-2 0.90 4.48 2.66 1.74 4.12 1.38 1.31 0.56 0.04 27 89 OB-47 5.50-5.75 FPS-2 1.12 3.47 1.65 1.78 4.37 1.49 1.31 0.72 0.04 40 99 OB-47 7.50-7.75 FPS-1 1.43 6.59 3.41 2.50 5.88 1.61 1.97 0.71 0.04 42 143 OB-47 8.50-8.75 FPS-1 2.95 10.80 4.26 1.82 4.36 1.02 1.46 0.85 0.03 105 106 OB-48 0.75-1.00 FPS-3 1.24 3.96 1.17 1.15 2.19 0.75 0.76 1.16 0.04 55 53 OB-48 2.25-2.50 FPS-3 0.90 7.42 0.61 0.87 1.95 0.81 0.73 0.89 0.03 42 37 OB-48 4.75-5.00 FPS-3 0.74 8.49 0.62 1.02 1.85 0.69 0.61 0.89 0.04 44 36 OB-48 6.75-7.00 FPS-3 0.75 1.71 0.46 1.24 2.43 0.96 0.94 1.46 0.05 66 47 OB-49 1.00-1.25 FPS-2 0.84 8.12 3.59 1.21 2.61 0.96 0.37 0.75 0.03 85 39 OB-49 4.25-4.50 FPS-2 0.74 4.92 2.46 1.00 3.30 1.05 0.97 0.74 0.02 37 55 OB-49 8.75-9.00 FPS-2 0.99 3.91 1.52 1.27 3.61 1.09 1.67 1.05 1.44 47 57 0B-50 1.00-1.25 FPS-6 1.56 9.38 1.34 0.83 1.75 0.70 0,62 0.34 0.03 19 34 0B-50 2.00-2.25 FPS-5 1.80 21.58 0.78 0.66 1.25 0.60 0.46 0.17 0.02 13 27 OB-50 3.75-4.00 FPS-5 2.03 7.08 0.98 1.30 3.36 1.23 1.10 0.50 0.03 26 64 OB-50 6.00-6.25 FPS-5 2.22 7.92 2.92 1.36 3.50 1.26 0.81 0.65 1.41 31 82 OB-51 2.00-2.25 OBS-1 1.78 3.59 1.25 1.18 2.65 0.92 0.88 0.53 0.03 27 63 OB-51 5.00-5.25 OBS-1 1.57 4.01 1.22 1.38 3.25 0.98 0.92 0.62 0.04 32 64 OB-51 8.00-8.25 OBS-1 1.19 3.82 1.16 1.17 3.12 0.81 1.09 0.43 0.02 55 48 OB-52 2.85-3.00 BBS-1 1.34 14.30 8.28 1.52 3.14 1.28 0.62 0.49 0.02 60 56 OB-52 3.75-4.00 BBS-1 1.40 14.80 8.51 2.29 4.07 1.32 0.90 0.59 0.02 75 76 OB-53 1.25-1.50 BBS-2 3.56 7.48 0.82 1.17 2.33 0.95 0.41 0.21 0.01 23 75 OB-53 2.75-3.00 BBS-2 5.24 14.85 1.31 1.24 2.69 1.13 0.74 0.36 0.03 53 88 OB-53 3.30-3.50 BBS-2 3.90 9.53 1.31 1.28 2.77 1.07 0.65 0.28 0.03 20 90 OB-53 4.25-5.50 BBS-2 8.34 20.50 1.90 1.52 3.63 1.88 0.97 0.54 0.04 39 214 OB-53 4.75-5.00 BBS-2 4.53 27.15 1.72 1.48 3.45 1.61 0.95 0.59 0.04 35 137 OB-53 5.25-5.50 BBS-2 5.01 18.50 1.42 1.43 3.19 1.41 0.63 0.53 0.02 62 134 OB-53 6.50-6.75 BBS-2 0.97 2.07 1.81 3.53 9.03 1.94 1.86 0.77 0.07 52 124 OB-57 1.75-2.00 FPS-6 0.78 2.63 1.27 2.23 6.36 1.75 1.42 0.71 0.03 83 92 OB-57 4.00-4.25 FPS-6 1.86 3.94 1.02 2.00 6.00 1,66 1.50 0.67 0.03 81 88 OB-57 6.50-6.75 FPS-5 1.53 12.97 6.39 3.13 7.51 1.77 1.76 0.59 0.06 35 114 OB-58 3.40-3.45 OBS-2 1.40 6.94 1.96 1.70 3.51 1.33 1.07 0.63 0.03 83 52 153 CORE DEPTH (m) UNIT P205 CaO MgO Fe203 A1203 Na2 K20 Ti02 Cu Zn OB-58 4.40-4.45 OBS-2 1.47 8.05 5.32 4.19 9.03 3.53 1.80 0.61 0.06 38 127 OB-59 6.25-6.50 BBS-1 1.03 20.66 4.77 1.81 5.36 1.82 1.26 0.56 0.04 34 71 OB-59 6.75-7.00 BBS-1 1.27 20.47 6.35 2.46 6.90 2.79 1.27 0.53 1.34 32 91 OB-59 7.80-8.20 BBS-1 2.16 9.92 1.06 1.00 — 1.07 0.26 1.30 16 37 OB-60 1.25-1.50 BBS-3 0.72 2.55 1.12 1.09 4.32 1.29 1.49 0.25 0.01 43 36 OB-60 3.50-3.75 BBS-3 0.76 10.22 1.31 1.31 4.31 1.31 1.22 0.34 0.03 20 46 OB-60 6.00-6.25 BBS-3 1.17 3.57 1.96 2.10 5.40 1.51 1.22 0.40 0.04 26 68 OB-62 3.25-3.50 OBS-u 1.60 10.60 2.49 2.77 5.92 1.80 1.11 0.49 0.02 69 90 OB-62 4.25-4.50 OBS-u 1.69 9.77 3.93 3.16 7.10 1.86 1.47 0.55 0.02 75 116 OB-62 5.75-5.82 OBS-3 1.93 8.21 3.11 3.11 7.50 2.08 1.52 0.61 0.05 40 143 OB-63 0.15-0.25 FPS-2 0.98 10.48 2.17 3.50 8.99 2.19 2.30 0.68 0.05 — OB-63 1.25-1.50 FPS-2 1.10 23.04 1.56 2.33 5.71 1.71 2.08 0.48 0.04 33 96 OB-63 1.60-1.70 FPS-2 1.21 28.43 1.59 2.04 5.32 2.24 1.61 0.40 0.04 — OB-63 2.25-2.50 FPS-2 9.24 32.70 1.40 1.83 2.98 2.03 0.66 0.31 0.01 38 87 OB-64 4.00-4.25 FPS-1 12.47 36.05 1.59 1.22 2.57 1.53 0.76 0.45 0.03 36 120 OB-64 4.50-4.70 FPS-1 14.28 38.57 1.44 1.04 2.34 1.63 0.53 0.34 0.03 31 123 OB-64 4.50-4.75 FPS-1 15.13 42.07 1.38 1.01 2.18 1.55 0.59 0.37 0.03 33 129 OB-64 6.00-6.20 FPS-1 14.60 30.10 1.02 0.73 1.64 1.39 0.19 0.31 0.01 41 118 OB-65 3.00-3.10 FPS-2 0.80 7.61 1.73 1.74 7.42 2.97 1.88 0.61 0.05 35 94 OB-65 4.70-4.80 FPS-2 0.90 4.28 2.25 2.71 8.04 2.14 1.73 0.74 0.05 39 112 OB-66 3.50-3.60 FPS-3 1.77 3.29 1.79 1.65 4.42 1.91 1.32 0.43 0.03 25 105 OB-67 3.25-3.50 FPS-6 1.01 18.40 0.74 0.97 3.64 1.56 1.03 0.70 0.03 79 38 OB-67 4.50-4.60 FPS-6 0.99 20.76 0.79 0.95 3.64 2.49 1.24 0.61 0.04 31 42 OB-67 4.75-5.00 FPS-6 1.15 3.37 1.10 1.01 2.00 0.78 0.47 0.94 0.03 105 41 OB-67 7.70-7.80 FPS-6 1.03 13.11 1.68 1.14 4.59 2.64 1.45 0.67 0.04 32 52 OB-68 1.50-1.60 OBS-3 1.66 11.76 4.12 1.13 4.94 2.20 1.33 0.56 0.04 — — OB-68 4.80-4.90 OBS-2 1.77 5.36 1.92 0.98 2.81 1.23 0.81 0.52 0.03 25 49 OB-71 0.50 BBS-1 3.20 7.71 1.02 1.46 2.98 0.90 0.91 0.53 0.03 29 57 OB-71 1.00 BBS-1 1.42 14.81 5.20 1.65 3.67 1.17 0.91 0.37 0.04 25 77 OB-72 1.00 BBS-2 2.30 18.59 1.42 1.97 3.61 1.27 0.82 0.38 1.40 23 48 OB-72 1.50-1.60 BBS-2 2.99 7.70 0.75 1.14 2.33 0.68 0.78 0.35 0.03 — — OB-72 3.00-3.25 BBS-2 2.60 6.47 1.88 1.91 4.14 1.06 1.25 0.54 0.04 31 82 OB-72 4.00 BBS-1 3.38 13.21 2.67 1.66 3.67 1.12 0.91 0.51 1.45 30 90 OB-7 2 4.50 BBS-1 2.75 5.84 1.66 1.79 3.73 1.14 1.04 0.56 1.54 29 81 OB-79 5.90-6.00 BBS-1 2.20 4.38 1.39 2.91 6.32 0.97 1.27 1.25 0.07 — — OB-80 4.90-5.30 OBS-1 0.99 18.36 1.80 0.88 1.63 0.46 0.49 0.15 0.02 11 29 OB-91 3.50 BBS-1 4.52 13.44 1.79 1.85 2.58 0.62 0.79 1.00 0.06 50 63 OB-91 6.00 BBS-1 1.10 5.47 0.88 2.18 4.08 0.83 1.17 1.16 0.07 56 62 OB-92 3.50-3.75 BBS-4 0.76 26.87 0.76 0.33 0.84 0.33 0.29 0.03 4.00 9 — OB-92 5.00-5.25 BBS-4 0.75 1.67 0.18 0.23 1.11 0.42 0.39 0.03 0.03 — — OB-92 5.50 BBS-4 0.84 1.91 0.24 0.30 1.37 0.45 0.57 0.04 0.00 6 9 OB-92 6.00 BBS-4 0.81 1.66 0.13 0.23 1.16 0.36 0.63 0.03 0.00 13 8 OB-94 0.70-0.95 BBS-2 8.34 24.76 1.52 1.37 2.49 1.52 0.75 0.40 0.03 26 211 OB-94 1.00-1.10 BBS-2 3.33 38.64 1.28 1.13 2.26 0.84 0.53 0.40 0.04 23 102 OB-94 1.50-1.75 BBS-2 1.40 30.00 1.13 1.07 2.28 0.87 0.28 0.44 0.02 46 62 OB-96 1.40-1.50 FPS-6 1.53 39.38 0.76 0.72 1.80 0.99 0.62 0.52 0.04 26 40 OB-96 2.25-2.50 FPS-6 1.73 20.10 0.66 0.98 2.52 1.07 0.70 0.74 0.03 86 48 OB-96 2.90-3.00 FPS-6 1.77 19.51 0.74 1.24 3.53 1.21 1.16 0.85 0.05 40 63 OB-96 4.40-4.50 FPS-6 1.38 12.13 1.22 1.76 5.15 1.42 1.60 0.73 0.05 37 97 OB-96 5.25-5.50 FPS-6 1.54 10.99 1.35 1.96 5.55 1.72 1.77 0.88 0.06 46 101 154 CORE DEPTH (m) UNIT P205 CaO MgO Fe203 A1203 Na2 K20 Ti02 Mn Cu Zn OB-97 1.40-1.50 FPS-2 2.32 7.57 0.83 1.28 4.17 1.77 1.21 0.77 0.04 38 80 OB-97 2.90-3.00 FPS-2 3.13 6.15 1.48 1.68 5.19 2.15 1.28 0.88 0.05 47 113 OB-97 4.40-4.50 FPS-2 1.43 13.57 6.37 1.58 4.77 1.21 1.03 0.63 0.05 5 81 OB-97 5.90-6.00 FPS-2 1.24 2.94 3.14 3.71 9.68 1.66 1.68 0.86 0.06 49 148 OB-98 1.25-1.50 FPS-2 1.53 14.70 2.45 2.86 8.00 2.29 1.13 0.55 0.02 74 124 OB-98 1.40-1.50 FPS-2 1.25 14.05 2.11 2.82 8.68 2.38 1.47 0.60 0.05 46 139 OB-98 3.25-3.50 FPS-2 1.02 19.10 2.18 2.87 7.58 1.91 2.00 0.58 0.02 85 126 OB-98 4.00-4.10 FPS-2 1.00 18.65 2.12 3.48 7.29 2.83 1.90 0.48 0.05 — — OB-103 5.00 FPS-2 1.16 5.02 1.57 1.07 3.27 0.94 0.81 0.89 0.03 104 62 OB-103 5.90 FPS-2 1.13 6.42 1.42 1.14 3.07 0.78 0.95 0.92 0.04 47 63 OB-105 1.25-1.50 FPS-2 1.20 1.10 1.20 3.74 1.20 1.40 0.90 — 110 OB-105 2.25-2.50 FPS-2 2.19 11.34 0.89 1.36 3.72 1.18 1.26 0.97 0.05 52 186 OB-105 3.25-3.50 FPS-2 3.72 13.40 1.66 1.32 3.75 0.98 1.22 0.90 0.03 109 83 OB-105 4.25-4.50 FPS-2 5.58 14.92 0.57 1.06 2.85 1.28 1.02 0.98 0.04 56 81 OB-105 5.25-5.50 FPS-1 9.59 21.00 0.73 1.01 2.73 1.29 0.66 0.69 0.02 82 100 OB-105 6.25-6.50 FPS-1 11.57 25.27 0.75 1.04 2.75 1.35 0.91 0.67 0.03 44 151 OB-105 7.25-7.50 FPS-1 4.38 21.12 0.51 1.24 2.76 0.98 0.92 0.98 0.04 54 79 OB-107 0.50-0.75 FPS-6 1.19 8.18 5.18 4.24 9.83 1.97 2.20 0.68 0.06 42 132 OB-107 1.50-1.75 FPS-6 1.30 2.41 2.65 4.80 10.88 2.08 2.22 0.72 0.06 45 134 OB-107 2.50-2.75 FPS-6 1.46 3.60 2.81 4.54 10.47 2.18 2.03 0.70 0.06 44 156 OB-108 2.25-2.50 BBS-5 0.47 24.03 2.82 1.49 3.30 1.40 0.89 0.21 0.03 16 41 OB-108 3.25-3.50 BBS-5 0.49 16.08 2.11 1.92 4.41 1.95 0.92 0.40 1.40 23 50 OB-108 4.25-4.50 BBS-5 0.39 31.20 1.32 0.38 1.46 0.60 0.56 0.08 0.01 19 13 OB-108 5.75-6.00 BBS-5 0.34 40.67 1.19 0.32 1.19 0.50 0.41 0.07 0.02 7 14 OB-109 1.50 BBS-2 4.11 9.09 1.52 1.20 2.65 0.83 0.84 0.46 0.03 26 63 OB-109 2.50 BBS-2 3.41 6.68 1.51 2.15 4.51 1.14 1.04 0.55 1.58 31 67 OB-109 4.00 BBS-2 3.15 6.64 1.49 2.14 4.56 1.06 1.17 0.51 0.04 31 65 OB-109 5.50 BBS-2 2.89 7.89 ’1.58 1.58 3.83 0.83 1.11 0.42 0.03 23 86 OB-109 6.00 BBS-1 1.17 27.38 5.63 1.27 2.94 0.67 0.84 0.30 0.03 18 46 OB-111 1.75 2.00 OBS-4 0.38 — 3.34 0.51 0.47 0.65 0.11 0.03 0.02 7 21 OB-111 4.50 OBS-3 0.42 1.03 0.46 0.32 0.71 0.03 0.02 0.40 10 18 OB-111 5.00 OBS-3 0.29 — 1.03 0.38 0.35 0.39 0.08 0.03 0.02 7 13 OB-113 1.25-1.50 FPS-1 2.72 14.20 5.37 1.32 2.80 1.16 1.04 0.81 0.05 45 80 OB-113 2.75-3.00 FPS-1 0.93 5.30 2.47 1.34 3.99 1.25 1.33 0.98 0.04 52 61 OB-113 4.25-4.50 FPS-1 0.80 4.39 2.04 1.85 4.40 1.38 1.49 1.06 0.05 52 56 OB-114 6.35-6.60 FPS-1 7.09 45.68 2.83 1.27 1.96 1.22 0.62 0.24 0.03 25 99 OB-114 7.25-7.50 FPS-1 9.46 29.96 2.64 1.10 2.60 1.54 0.50 0.34 0.02 42 105 OB-114 8.00-8.20 FPS-1 11.92 32.95 2.42 1.10 2.05 1.51 0.56 0.33 0.03 35 147 OB-116 0.50-0.75 FPS-1 2.53 28.20 2.20 2.16 5.90 2.50 1.60 0.44 1.20 46 145 OB-116 3.00-3.24 FPS-1 7.58 25.07 1.75 1.49 3.84 1.62 1.15 0.46 0.03 33 112 OB-118 3.00-3.25 FPS-6 1.06 15.50 1.19 0.83 3.53 1.29 1.11 0.52 0.02 65 30 OB-118 4.25-4.50 FPS-6 1.33 12.91 0.65 0.90 3.66 1.33 1.44 0.59 0.04 31 39 OB-118 5.90-6.10 FPS-6 1.15 15.00 0.58 0.89 3.40 1.41 1.00 0.60 0.02 68 35 OB-118 8.90-9.10 FPS-6 1.05 14.50 0.48 0.78 3.01 1.24 0.83 0.55 0.02 59 29 OB-119 3.35-3.60 FPS-1 4.92 18.36 1.89 1.97 5.47 1.70 1.31 0.70 0.04 51 151 OB-120 4.25-4.50 FPS-1 8.36 44.60 1.62 1.84 2.06 1.14 0.66 0.30 0.02 57 131 OB-120 5.90-6.10 FPS-1 15.50 37.20 1.30 0.94 2.32 1.55 0.65 0.41 0.02 69 173 OB-127 1.50-1.75 FPS-1 11.40 25.00 3.34 1.48 3.17 1.25 0.95 0.56 0.02 84 127 OB-127 3.50-3.75 FPS-1 8.37 15.60 1.98 1.14 3.12 1.37 0.78 0.80 0.02 94 128 OB-127 5.50-5.75 FPS-1 2.31 7.92 0.72 1.88 4.50 1.20 1.26 1.10 0.05 56 73 155 CORE DEPTH (m) UNIT P205 CaO MgO Fe203 A1203 Na2 K20 Ti02 îln Cu Zn OB-127 7.50-7.75 FPS-1 1.45 5.24 0.55 1.12 3.48 1.16 1.14 0.84 0.04 41 49 OB-128 1.75-2.00 FPS-5 1.00 5.02 2.96 3.14 8.14 1.66 2.08 0.70 0.03 91 105 OB-128 5.50-5.75 FPS-5 0.95 3.64 1.27 1.97 6.45 1.81 1.90 1.10 0.04 138 65 OB-132 1.50 FPS-1 0.44 7.84 0.61 1.67 4.22 1.18 1.56 0.92 0.05 40 56 OB-132 2.00 FPS-1 0.37 10.62 0.55 1.50 3.94 1.05 1.48 0.88 0.05 38 55 OB-132 2.50 FPS-1 0.81 14.59 0.71 1.90 3.79 1.00 1.26 0.77 0.05 41 51 OB-132 3.00 FPS-1 0.27 18.50 — 1.13 2.52 0.72 0.66 0.86 0.03 97 35 OB-132 3.50 FPS-1 0.36 10.03 0.40 1.27 3.05 0.81 1.25 1.01 0.04 42 50 OB-132 4.10 FPS-1 0.34 9.95 0.37 1.18 2.87 0.90 1.00 1.03 0.04 49 48