FACIES, SEQUENCE STRATIGRAPHY AND DIAGENESIS OF PALEOGENE CONTINENTAL SHELF FACIES, NORTH CAROLINA, USA

The mixed carbonate-siliciclastic Paleogene sediments of coastal North Carolina formed on the swell-wave and current swept continental shelf, which had a distinct inner shelf, inner- shelf break, deep shelf, and continental slope morphology. The regional framework of these sediments has been largely based on limited quarry exposures and well cuttings from exploratory oil and gas wells. This study focuses on documenting the facies, sequence stratigraphy, and diagenesis of the Paleogene part of the Kure Beach N.C., core drilled by the USGS-NC Earth Sciences Coalition, and the shallow Onslow and Beaufort County cores housed at the N.C. Coastal Plain Office. 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 and mollusk sands, grading offshore into foram quartz silts and black shales, wave-influenced open shelf bryozoan-echinoderm grainstone/packstone, and deep shelf, fine skeletal wackestone/mudstone, foram silts and planktic foram marls. There are several well-defined sequences within the Kure Beach core. Sequence boundaries are marine condensed surfaces (hardgrounds) which are multiple cemented surfaces, and are commonly overlain by phosphatic clasts reworked from underlying units. These hardgrounds formed during Gulf Stream boundary current sweeping. Initial petrographic studies of the cores indicate that the carbonate cements include local marine bladed, former high Mg calcite cements. Local developed fine dolomites beneath and within organic rich deeper water facies appears to have formed under deeper marine, reducing conditions. These marine phases were succeeded by leaching of molluscan aragonite and deposition of phreatic calcite cements which show distinct zonations (evident using stains and cathodoluminescence) related to fluctuating redox conditions, perhaps influenced by sea level position and deposition of regional, organic rich aquicludes. Porosity is gradually being plugged by processes operating in the regional aquifer system that is still active.