WEATHERING OF SUBSURFACE SANDSTONE CLASTS AND BEDROCK IN A HUMID SUB-TROPICAL FOREST ENVIRONMENT

The weathering processes operating on bedrock and debris exposed in the subaerial environment have been extensively studied, on many rock types and environments. The weathering processes operating in the subsurface environment have not been investigated as widely, particularly in regard to the clasts within soil horizons. In this work, the differences between surface and subsurface weathering effects on sandstone clasts are examined, in a forest soil in the Ouachita Mountains, Arkansas. Visual analysis of the clasts indicated that the effects of weathering varied considerably, but did not confirm the findings of previous studies, which suggested that the degree of alteration was closely associated with depth in the soil profile. The fact that alteration penetrated entire clasts throws doubt on the use of weathering rinds to indicate depth or residence time in the soil profile, and indicates that rock fragment weathering is an active soil-forming process. Preliminary analysis of subsurface weathering of sandstone bedrock suggested an important role for tree roots in promoting solution of the sandstone.