Abstract

Unsorted sands containing little gravel and much disseminated kaolin constitute the Upper Cretaceous section from central Georgia at least to central South Carolina. Lenses of relatively pure kaolin occur largely in two areas. The series rests unconformably on crystalline rocks. A gentle unconformity separates the Cretaceous beds from overlying Tertiary beds, and both have been dissected by erosion that began in the Pliocene. Yellow iron-oxide stains and a little bauxite have been formed in the kaolin lenses during this long period of weathering.The Cretaceous sediments were derived from the crystalline rocks by vigorous erosion on a youthful surface, and accumulated in coalescing deltas of coarse feldspathic sands. Most of the iron in the source rocks was taken into solution at the source in mildly acid ground and surface waters, and was removed to the sea.Kaolinite was formed by decomposition of the detrital feldspar in exposed parts of the deltas, and, through low-gradient erosion of the sands, collected in ponds formed as cut-off segments of the distributaries. Soft kaolin was precipitated slowly in fresh acidic water. Wave erosion breached some ponds, admitting sea water in which kaolin was coagulated rapidly and is harder. The pyrite in such kaolin was probably formed through the reduction of sulfates, with soluble iron available. As these processes operated, the sea advanced truncating the series by wave-base erosion.

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