INTERPRETING DEPOSITIONAL ENVIRONMENTS OF COARSE CLASTIC SEDIMENTS IN BUTLER CAVE, VIRGINIA

This project employs observation, field sedimentology, and image analysis to physically characterize and map the unique clastic sediment facies within Butler Cave, Bath County, VA. Evaluating these deposits presents a valuable insight into the depositional history in the cave and the processes that may be driving cave formation. Previous research has classified these deposits as diamicton facies. We reassess that classification by interpreting the depositional environments of the identified lithofacies and evaluating the potential influence of periglacial processes on their origin. Sedimentological analysis of several sites within the cave revealed several distinct fluvial facies, with all except one being deposited by unidirectional streamflow.

The coarse clastic sedimentology within Butler Cave shows six distinct sedimentary units, each unlithified. Unit CsB is composed of imbricated clast-supported boulders within a sand matrix. Unit CsC is composed of clast-supported granule to boulder-sized clasts with the dominant size being cobbles. Unit CsP is composed of clast-supported pebbles within a sand matrix that contains trough cross-stratification. Unit GS is composed of massive to cross-stratified sand and interfingering granule lags. Unit WsS is composed of well-sorted massive to cross-stratified sand. The above facies are interpreted to be fluvial due to grain rounding, moderate or better sorting, and the absence of a clay matrix. In contrast, unit CmB is composed of clast-supported angular boulders within a clay-sand matrix, which we interpret as a fluid-rich debris flow.

We analyzed the source lithology of gravel-sized clasts in these deposits and identified only local bedrock sources, which indicates that the sediment-rich stream flows entering cave openings were washing in from local slopes. Periglacial slope processes outside the cave may have made these coarse clastic sediments available, but there is no clear evidence of periglacial deposits entering the cave directly. Overall, understanding the deposition of coarse clastic sediment in cave systems is important for understanding the local cave history and has interesting implications for studying the role of physical abrasion in cave formation.