CONSTRAINING THE TIMING OF SEDIMENTATION IN CREVICE CAVE, MISSOURI BY U-TH DATING OF SPELEOTHEMS INTERSTRATIFIED WITH SEDIMENTS

Surface erosion is a destructional process on which age constraints are inherently difficult to place. However, within karst systems, surface erosion can lead to sediment deposition in nearby caves. By using U-Th dating methods, age constraints can be placed on sediment layers interstratified with appropriate speleothem material. In this study, stalagmitic material from Crevice Cave has been identified whose growth has been periodically interrupted by fluvial sedimentation. By dating the interstratified calcites, the timing of sediment deposition in the cave and possibly the relationship to surface erosion can be addressed.

Stalagmite CC-99-3-B was collected while actively growing on a mud bank approximately one meter above the base flow level of the cave stream. Excavation of the mud with the purpose of recovering the complete formation revealed interstratified mud and calcite “fins” draped off the sides of the stalagmite. Approximately 15 cm of interstratified sediment and calcite fins characterize the basal section of CC-99-3-B.

Our reconnaissance U-Th dating reveals that the upper 291 mm (approximately 75 percent) of the stalagmite grew within the last 11,000 years. This Holocene section is separated from the lower 25 percent by a major hiatus, which was deposited between 126,000 and 116,000 years ago. Both periods of calcite deposition contain numerous interstratified layers of sediments. During the Holocene growth period, there are greater than 13 identifiable fins, of which five have been dated. The majority of the calcite fins and interstratified sediments lie between 213.5 and 291.0 mm from the top surface of the stalagmite, and are between 1,495 ± 85 and 10,190 ± 130 years old. During the period from 126,751 ± 1,485 to 117,240 ± 620 years ago, five distinct fins are present.

Our limited data reveal an interglacial character in the sedimentation at this particular site. However, the lack of a glacial-age record could be due to deep burial during glacial time, with subsequent exhumation during the ensuing post-glacial period. With higher resolution dating on CC-99-3-B and with work on other appropriate formations, we can further constrain the timing of cavern sedimentation in Crevice Cave, and possibly link this to surface erosion events.