STRATIGRAPHY OF AND CARBON CONCENTRATIONS IN CLASTIC CAVE SEDIMENTS IN EL TALLONAL CAVE, PUERTO RICO

Cave sediments are quite complex due to the mixtures of sources plus subsequent remobilization and reworking. The extent to which sediments are mobilized and deposited during high flow events is variable and location specific. This variability makes tracing clastic sediments through cave systems based solely on physical sediment characteristics problematic.

Core samples of clastic sediments were taken from a cave in the northern karst region of Puerto Rico and analyzed for total organic carbon, sulfur, and nitrogen. El Tallonal Cave, a privately owned and protected system, is dammed at the resurgence point and used as a private water supply. The cave is a partially-filled vadose passage and contains an unknown volume of sediment. The cave stream is surrounded by sediment banks composed dominantly clay to sand sized particles. The stream channel contains larger clasts from sand to pebble sized. The cave is approximately 60 m long. Sediment cores were taken from the main room of the cave, about 30 m from the entrance. The room is 5 m tall and varies from 6 to 11 m in width.

Sediments were obtained in 30 cm increments from multiple locations in the main room. Cores were collected from the sediment banks on either side on the active cave stream using a spit-spoon auger and manually pushing the core sleeves into the bank. The layered sediments varied from well-sorted clay to clay with some fine sand. Individual layers ranged from 12 cm to less than 1 cm. A few poorly-sorted medium sand to pebble sized layers were present. F_oc (fraction of organic carbon) content is generally less than 1%. Changes with depth were observed; in one core the carbon concentrations ranged from 1% at the top 1 cm to 0.3% only 5 cm below.

The carbon data, coupled with grain size and sediment stratigraphy, can be used to better understand the depositional nature of the clastic cave sediment and the history of sediment input over time. Distinctions between the types of organic carbon may be helpful in distinguishing storms and extreme events in the past.