12.07.2015 Views

Download Guidebook as .pdf (3.4 Mb) - Carolina Geological Society

Download Guidebook as .pdf (3.4 Mb) - Carolina Geological Society

Download Guidebook as .pdf (3.4 Mb) - Carolina Geological Society

SHOW MORE
SHOW LESS
  • No tags were found...

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

COQUINAS OF THE NEUSE FORMATIONthe modern and ancient barrier systems in the region differingonly in their rather limited lateral extent and lack of <strong>as</strong>sociatedback barrier salt marsh sediments. The interpretationof environment of deposition favored here is one of shorefacesediments deposited from the level of the subaeriallyexposed beach to below the level of low tide, where depositionoccurred within a largely sediment starved b<strong>as</strong>in. As sealevel rose the shoreface environment shifted laterally landwardby storm wave action eroding sediment from the foot ofthe shoreface and redepositing it at the top, on the subaerialbeach. The deposited material w<strong>as</strong> a mixture of old reworkedsediment from previous beach face deposits and what fluvialsediment that had accumulated after the l<strong>as</strong>t high stand Theresultant fossil <strong>as</strong>semblage consisted of varying amounts ofin situ forms such <strong>as</strong> Donax variabilis, proximal indigenousforms such <strong>as</strong> Cr<strong>as</strong>sostrea virginica and N<strong>as</strong>sarius obsoletus,distal indigenous forms like Aequipectin gibbus and Sider<strong>as</strong>trearadians, exotic forms like the terrestrial mammalianbones, and remanie forms reworked from older strata <strong>as</strong> evidencedby the amino acid racemization results of Wehmillerand others (1995). The modern equivalent of this is the beachdeposits found just south of Fort Fisher. There the sedimenton the beach contains an abundance of modern and fossilshells, blocks of coquina, and debris that h<strong>as</strong> recently arrivedfrom the Cape Fear River.CONCLUSIONSThe term "Cape Fear Coquina" should be suppressedand in its place the name Neuse Formation should be usedboth for the coquina and the <strong>as</strong>sociated arenaceous shell h<strong>as</strong>hand carbonate free sands. The coquin<strong>as</strong> represent a post depositionaldiagenetic product of a shell bearing sand depositedin a shoreface environment. Initial diagenesis took place ator near an ancient water table where dissolution of aragoniticbiocl<strong>as</strong>ts gave rise to calcite spar cements and the formationof the coquina. The ferrugenous sands which were in the p<strong>as</strong>twere referred to <strong>as</strong> the "Kure Sand" also represent a productof the diagenesis of both the coquin<strong>as</strong> and the <strong>as</strong>sociatedunlithified sands which were the precursors to the coquina.Here. diagenesis took place during subaerial exposure whereoxygenated meteoric waters both dissolved calcium carbonateand oxidized what iron bearing heavy minerals werepresent, resulting in a ferrugenous stained insoluble residue.The exposed coquin<strong>as</strong> and ferrugenous residue sands representonly the present surficial expression of a much thickersediment package of limited lateral extent. These weredeposited during a minor sea level high stand whichoccurred after isotope stage 5 but before stage 2, a period oftime dating from approximately 75 ka to 55 ka beforepresent or isotope stage 3.ACKNOWLEDGMENTSI am grateful to William J. Cleary and William B. Harrisfor their reviews of the manuscript, to Victor Zullo for hisintroduction to the coquina and its fauna, and to JodyDuMond, who <strong>as</strong> a high school student <strong>as</strong>sisted in the collectionand identification of the fossils from Snows Cut.REFERENCESBlackwelder, B.W., 1981 Late Cenozoic stages and Molluscansones of the U.S. Middle Atlantic Co<strong>as</strong>tal Plain. Journal ofPaleontology, v. 55, pt. II of II, supplement to no.5; Paleontological<strong>Society</strong>, Memoir 12, 34 p.Carter, J. G., Gallagher, P. E., Valone, R. E., and Rossbach, T. J.,1988, Fossil Collecting in North <strong>Carolina</strong>: North <strong>Carolina</strong>Department of Environment, Health, and Natural Resources,Division of Land Resources, <strong>Geological</strong> Survey Section Bulletin89.Chappel, J. and Shackleton, N.J., 1986 Oxygen isotopes and sealevel. Nature v. 324, p. 137-140.Dockal, J. A., 1992 Radiocarbon dating of late Pleistocene marinedeposits, New Hanover County, North <strong>Carolina</strong>. <strong>Geological</strong><strong>Society</strong> of America Abstracts With Programs, v. 24, No.2, p.12.Dockal, J. A., 1995a Evaluation of an apparent Late Pleistocene(25-40 ka BP) sea level high stand: An artifact of a greatlyenhanced cosmic ray flux of -60 ka BP. Journal of Co<strong>as</strong>talResearch, v. 11, No.3, p. 623-636.Dockal, J. A. 1995b Documentation and evaluation of radiocarbondates from the "Cape Fear Coquina" (Late Pleistocene) ofSnows Cut, New Hanover County, North <strong>Carolina</strong>. Southe<strong>as</strong>ternGeology, v. 35, No.4, p. 169-186.Du Bar, J.R., Johnson, H.S., Jr., Thorn, B, and Hatchell, W.O., 1974Neogene stratigraphy and morphology, south flank of the CapeFear Arch, North and South <strong>Carolina</strong>. In: Oaks, R.Q. and DuBar, J.R. (editors) Post-Miocene stratigraphy centra and southernAtlantic Co<strong>as</strong>tal Plain. Utah State University Press, Logan,Utah, p. 139-173.Du Bar, J.R. and Solliday, J.R. 1963 Stratigraphy of the Neogenedeposits, lower Neuse estuary, North <strong>Carolina</strong>. Southe<strong>as</strong>ternGeology, v. 4, p. 213-233.Fallaw, W. 1973 Depositional environments of marine Pleistocenedeposits in southe<strong>as</strong>tern North <strong>Carolina</strong>. <strong>Geological</strong> <strong>Society</strong> ofAmerica Bulletin, v. 84, no.1, p. 257-268Fallaw, W. and Wheeler, W.H., 1969, Marine fossiliferous Pleistocenedeposits in southe<strong>as</strong>tern North <strong>Carolina</strong>. Southe<strong>as</strong>ternGeology, v. 10, no. 1, p. 35-54.Folk, R. L., 1980, Petrology of Sedimentary Rocks: Hemphill PublishingCo., Austin, Tex<strong>as</strong>, 182 p.Heckel, P.H. 1972. Recognition of Ancient Shallow Marine Environments.In: Rigby & Hamblin (editors) Recognition ofAncient Sedimentary Environments. SEPM Special PublicationNo.16, p. 226-286.Mixon, R.B., 1986 Depositional environments and paleogeographyof the intergalcial Flanner Beach Formation, Cape Lookoutarea, North <strong>Carolina</strong>. <strong>Geological</strong> <strong>Society</strong> of America CentennialField Guide-Southe<strong>as</strong>tern Section, p. 315-320.Mixon, R.B. and Pilkey, O.H., 1976 Reconnaissance geology of the17

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!