PALEOGENE MIXED CARBONATE-SILICICLASTIC TEMPERATE/SUBTROPICAL CONTINENTAL SHELF FACIES, COASTAL PLAIN, NORTH CAROLINA

This Paleogene core from the North Carolina Coastal Plain illustrates the typical facies of this temperate to subtropical open shelf succession. Paleogene facies are from shallowest to deepest: quartz sands, sandy whole mollusk grainstone and packstone, and variably sandy mollusk fragment grainstone (shoreface, barrier, lagoon); phosphatic and glauconitic hardgrounds (shallow shelf wave-current swept rocky bottom), locally marine cemented bryozoan echinoderm grainstone packstone (wave-reworked deeper inner shelf), fine skeletal wackstone/mudstone, and silty planktonic marl (subwave base deeper shelf). The Paleogene shelf had a distinctive shallow inner shelf, inner shelf break, deep shelf and shelf-continental slope break profile and contains several supersequences made up of 3rd order sequences. Some supersequence boundaries are extensive hardgrounds. Downdip along the inner shelf margins there may be siliciclastic lowstand wedges, while on the continental slope there may be truncation by Gulf Stream erosion. Transgressive systems tracts of supersequences on the inner shelf are midshelf bryozoan-echinoderm-facies that backstep onto inner shelf quartzose molluscan facies. On the deep shelf, the ancestral Gulf Stream remolded fine grained sediment units. Highstand systems tracts on the inner shelf consist of fine wackestone-mudstone and downdip planktonic and spiculitic marls overlain by a progradational bryozoan-echinoderm grainstone and packstone. In near-shore locations, sea level fall caused these to be overlain by prograding back-barrier silts and shell beds, coastal sands, and sandy molluscan shoreface deposits. On the deep shelf during highstand, there was intense remolding of fine grained sediment bodies into elongate shelf parallel marl lobes by the ancestral Gulf Stream and locally complete removal.