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Petrographic analyses of 500 impregnated sands from the piedmont rivers, coastal plain, beach, shelf, and deep sea off the southeastern United States indicate that they have differences in composition which reflect changes in depositional history.
Piedmont rivers transport mainly nonpolycrystalline quartz (20-80%), polycrystalline quartz (5-50%), microcline (2-15%), orthoclase (0-10%), plagioclase (0-4%), and minor amounts of reworked red sediments. Coastal-plain sands are more quartzose (more
than 90%) and commonly show corrosion indicating postdepositional solution. Rock fragments in these sands consist mainly of reworked Tertiary limestone and sandstone.
Near Cape Hatteras, sands of the shelf and upper slope consist mainly of quartz and are characteristically higher in feldspar (10-15%) than the shelf sands on the south. The feldspar is dominated by orthoclase with minor amounts of plagioclase and microcline. This content is in contrast to the high microcline content of the piedmont, coastal-plain rivers, and "southern" shelf sands but is similar to the mineralogy of the sands from the Hatteras abyssal plain. The relatively plentiful microcline and granitic rock fragments on the shelf between Cape Hatteras and Cape Romain suggest that these surficial sands are the result of reworking of older piedmont-coastal plain sands during late Pleistocene. Farther south of Cape Romain the terrigenous fractions have a piedmont signature but are m ch diluted with relict-residual carbonates and oolitic, algal, and micritic limestone debris.
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