Mineralogical and textural criteria for recognizing remnant Cenozoic deposits on the Piedmont: evidence from Sparta and Greene County, Georgia, U.S.A

Two soilkaprolite profiles from ridge crest sites in central Georgia were investigated for mineralogical and textural trends to help elucidate the relationship between Cenozoic Coastal Plain deposits landward of the Fall Line and the Piedmont. Result from the study of a 10.5 m thick sequence in Sparta, Georgia reveal a deep lateritic profile showing complete loss of plagioclase, gradational loss of K-feldspar, vermiculitization of biotite and precipitation of kaolinite and halloysite within the lower 6 m. The middle section of the sequence is characterized by authigenic kaolinite. halloysite and goethite. The upper 1.35 m is quartz-rich, but also contains K-feldspar, hydroxy-interlayered vermiculite (HIV) and gibbsite. A comparison of grain shape and size indicates a slight textural difference between the upper and middle sections, with the fine sand grains of the upper section being more spherical and less angular. Preliminary results from the study of a 6.35 m sequence in Greene Country, Georgia also reveal a deep lateritic profile. A sharp soil fabric contact, from slightly mottled to highly mottled, occurs 3.1 m below the surface. This profile is characterized by a bimodal clay mineral abundance distribution as a function of depth. This includes an antithetical relationship between kaolinite and HIV, where HIV is abundant at the surface, decreases with depth, increases again at the fabric interface and then decreases with depth. It is suggested that the profiles contain paleosols that are a result of deep lateritic weathering, subsequent allochthonous deposition of a sedimentary cap and then further chemical weathering. The exact relationship between the depositional ages of the veneers and the age, duration and climatic conditions for past weathering events are currently poorly constrained. Recognition of paleo-weathering surfaces has potential importance for our understanding of the record of geologic and paleoclimatic change in the southeastern United States. Identification of such Cenozoic sedimentary veneers and paleosols on the Piedmont also has potential importance for land use practices from the standpoint of better understanding regional soil terrain properties.