Diagnostic Foraminifera and Paleocology of the Pungo River Formation, Central Coastal Plain of North Carolina

Abstract

Benthic foraminiferal assemblages of the Pungo River Formation (middle Miocene) from the central North Carolina Coastal Plain indicate deposition in continental shelf environments. In Beaufort and Pamlico Counties, part of the Aurora Embayment, faunas from the lower part of the formation (units A and B) have an abundance of Buliminella elegantissima, Bulimina elongata, and Elphidium excavatum. Florilus pizzarensis, Cibicides lobatulus, Elphidium limatulum, Nonionella miocenica, Hanzawaia concentrica, and H. nipponica occur sporadically and are of secondary importance when present. High faunal dominance (averaging greater than 50 percent), low diversity values (Shannon-Wiener Information Function averaging 1.4), and rarity of planktonic foraminifera suggest that these units were deposited in inner or middle shelf environments. With the exception of E. limatulum, predominant species from the upper part of the formation (units C. D, and DD) are those that are of secondary importance in the lower units. Faunal dominance averages 33 percent, diversity values are moderate (averaging 2.3), and planktonic specimens are more abundant. These units were deposited in more open water marine environments, probably on the middle or outer shelf. In Craven County, along the northern flank of a pre-Miocene topographic high, the predominant species throughout the formation are Cassidulina laevigata and Uvigerina calvertensis, forms suggesting an outer shelf environment. However, high faunal dominance, moderate diversity values (2.0 to 2.7), and the rarity of planktonic specimens are inconsistent with an outer shelf setting. Perhaps typical offshore species migrated shoreward in response to favorable conditions related to the adjacent high. Assemblages of the unit associated with this high (unit CC) grade laterally into those of units farther north. In Carteret County, south of the high and along the northern edge of Onslow Bay, faunas are similar to those from units C, D, adn DD in the Aurora Embayment. Several species present here are absent in the Aurora Embayment, their migration perhaps prevented by environments associated with the intervening topographic high.