Abstract

River sands in the piedmont province of the southern Appalachians are derived mainly from saprolitic soils on granite, gneiss, and schist and consist mainly of quartz (60 to 80 percent) with minor microcline, orthoclase, and rock fragments. The quartz grains have embayed boundaries representing intense weathering and corrosion within saprolitic soils. When the particles of these soils are sampled, they show embayments on almost every grain. Skeletal-like grains are characteristic of the uppermost soil horizons. With transportation downstream, large (greater than 0 to 5 mm) rock fragments and polycrystalline quartz grains are broken. On entering the coastal plain, the river sands become highly quartzose (90 to 95 percent) within 1 to 5 mi by enrichment from the local coastal plain sediments. The dilution of piedmont-derived sand with Cretaceous and Tertiary coastal plain sand is observed by reduction in feldspar, rock fragments, and polycrystalline quartz, and by the decrease in the amount of embayed quartz grains, and the appearance of locally reworked quartzose sand fragments.

Studies of several soil profiles show that quartz grains in soils of the piedmont are always embayed but that the degree of corrosion is greatest in the uppermost part of the soil horizon. A similar increase in quartz grain solution upward occurs in soils and coastal plain sediments, but many of these grains have been rounded during prior transportation and the degree of corrosion is small. This study suggests that the relative amount of sand-sized embayed quartz is a measure of in situ weathering in a soil profile, but that such quartz is slowly destroyed during subsequent transportation. The presence of embayed quartz in sands does not necessarily indicate a volcanic source terrain as is commonly thought by many petrographers.

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