Facies, Sequence Stratigraphy and Diagenesis of Selected Tertiary Cores, North Carolina

By

LAGESSE, JENNY, H., and J.F. READ

Virginia Tech, Blacksburg, VA, 24061

     The sequence stratigraphic framework of Paleogene continental shelf sediments of North Carolina has been based on quarry exposures and well cuttings from exploratory wells.  This study documents the facies, sequence stratigraphy and bounding surfaces of several Tertiary cores. These include the Kure Beach core, N.C. drilled by the USGS-NC Earth Sciences Coalition, and other previously selected shallow cores. The Kure Beach core is strategically important because it is located in an area that underwent much Tertiary incision by the Gulf Stream and is located near one of the basin-bordering arches.

     Facies in the core include near-shore marine quartz sands and mollusk sands, grading offshore into foram quartz silts, and black shale (in Paleocene and Oligocene), open shelf bryozoan-echinoderm grainstone/packstone, and deep shelf, fine skeletal wackestone/mudstone, foram silts and planktic foram marls.  These facies formed on the swell-wave and current swept continental shelf, which had a distinctive inner shelf, shelf break, deep shelf, and continental slope morphology.  Paleosols are not developed on sequence boundaries, which are marine condensed surfaces (hardgrounds).  The hardgrounds are actually multiple cemented surfaces, with multiple phases of cavity formation and sediment infiltration, and they commonly are overlain by phosphatic clasts reworked from underlying units, some of which are cemented lowstand sands veneering sequence boundaries.   These hardgrounds formed during boundary current sweeping.  The bryozoan facies contrast with similar facies elsewhere in that they formed in warm water (but non-tropical), rather than a cooler water setting.  Local dolomitization of sequences may have occurred in deeper marine, reducing conditions, and porosity is being gradually plugged by calcite cementation, initially under marine conditions, but now as part of the regional aquifer system.