To provide petrographic criteria for interpreting ancient shallow-marine carbonate deposits, 300 grain thin sections from the Carolina continental shelf were studied. The sample area extends from Cape Lookout, North Carolina, to Cape Romain, South Carolina.

Percentage of carbonate grains in this area is chiefly a function of dilution from adjacent terrigenous sources. Skeletal components, the dominant carbonate grain type, form 10-60% of the total sediment and are mainly pelecypods, gastropods, and coralline algae. Foraminifers, bryozoans, echinoderms, barnacles, ostracods, corals, and worm tubes are minor constituents. Nonskeletal constituents consist of peloids, ooids, lumps, and assorted carbonate lithoclasts and usually comprise less than 10% of the total specimens.

Generally, there is a systematic but irregular increase in total carbonate components in a seaward direction. Molluscan assemblages characterize most inner and middle shelf sands, whereas coralline algae are prevalent in outer shelf sands. Other carbonate components show no trends in an offshore direction.

Subsea and subaerial diagenetic processes have affected most of the carbonate grains. Principal diagenetic features are: (1) discrete macroborings and microborings filled with orange-brown cryptocrystalline carbonate, (2) partial or complete micritization skeletal grains with obliteration of skeletal architecture, (3) homogenization of ooids by recrystallization to cryptocrystalline carbonate, and (4) recrystallization of pelecypod fragments to coarse fibrous spar. Carbonate lithoclasts display a variety of diagenetic features that include: aggrading recrystallization of micrite to form pseudospar, development of moldic porosity with or without calcite spar fillings, recrystallization of high-magnesium allochems to low-magnesium calcite, and growth of primary void filling calcite spar

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