Sedimentation Processes in Anchialine Caves of the Yucatan Peninsula - The Role of Karst Topography and Vegetation

Abstract

Understanding the mechanisms that control sedimentation in the anchialine caves of the Yucatan Peninsula, Mexico is vital for interpreting the sedimentary deposits therein. External forcing mechanisms of varying scales, such as eustatic sea-level rise and large storm events, can have a significant influence on the rate and composition of sediment transported and deposited in the cave. Using sediment cores, high resolution radiocarbon dating, cave mapping and continuous aquifer attribute data, it was shown that sedimentation patterns in the cave were not controlled by sea-level rise/fall alone. Overlying vegetation and cave physiography were controlling factors which resulted in sedimentation in the cave being transient in time and space. The coastal aquifer responded to seasonal variations in precipitation but also showed a broad regional response to intense rainfall associated with Hurricane Ingrid in 2013. Due to the extensive hydraulic conductivity of the aquifer, the hydrologic response to Hurricane Ingrid was shorted lived (weeks) while its effect on sedimentation in the cave lasted for months. Sedimentation rates in the cave did not respond to elevated precipitation alone but showed a link with overlying vegetation. In regions of the cave with overlying mangrove forest, sedimentation was significantly higher than areas with tropical forest coverage. Mangrove forests baffled sediment creating an aquitard which resulted in the ponding of meteoric waters and subsequent enrichment in nutrients. Nutrient rich meteoric waters were funneled into cenotes increasing primary productivity for organic matter sediment production. Sedimentary deposits in anchialine caves are subject to punctuated sedimentation as a result of external forcing mechanisms or triggers. In the case of Yax Chen the trigger for sedimentation was not contemporaneous with Holocene sea-level rise. This has important implications for the use of cave sediments as proxies for sea-level research and paleo hurricane studies.