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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 979

Last Page: 979

Title: Miocene Phosphorite Sedimentation on Atlantic Continental Shelf, Onslow Bay, North Carolina: ABSTRACT

Author(s): Stanley R. Riggs, Don W. Lewis, Albert C. Hine

Article Type: Meeting abstract


An extensive sequence of phosphorites outcropping on the Atlantic continental shelf of Onslow Bay, North Carolina, has been delineated by utilizing a series of vibracores and high resolution subbottom profiles (3.5 kHz, uniboom, and sparker). This broad outcrop belt extends 100 km from western Bogue Banks, southwestward across the shelf toward the outer part of Frying Pan Shoals off Cape Fear, North Carolina. Along the outcrop zone the Tertiary phosphorites have been and are presently being eroded, supplying reworked phosphate grains in diluted concentrations to the associated thin Pleistocene to recent sediment and rock blanket. The Tertiary phosphorites are primarily an interbedded sequence of muddy, quartzose phosphorite sands; phosphatic dolosilts; and fossiliferous, olomitic, phosphatic, quartz sands. The sediment sequence closely resembles that found in the Aurora area of the North Carolina Pungo River basin, a major mining district, and is presently considered to be the Pungo River Formation of middle Miocene age. These phosphorites unconformably overlie the slightly glauconitic, calcereous, fine quartz sands, calcarenites, and sandy, moldic limestones of lower Miocene and/or Oligocene age. Small parts of the updip outcrop belt of the Tertiary phosphorites, as well as the downdip section to the southeast, are covered by a thickening sequence of fossiliferous, clayey, quartz sands of the Yorktown Formation (Pliocene). The distribution of the Tertiary phosphorites is primarily related to the Cape Fear arch, a major coastal plain structural element, nd is locally controlled within Onslow Bay by several second order structural features and associated entrapment basins.

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