RE-EVALUATING PLEISTOCENE SEA LEVEL HISTORY AND SPELEOGENESIS IN THE YUCATAN PENINSULA: U-TH DATING OF POS FROM QUINTANA ROO, MEXICO

Caves in eastern Quintana Roo are assumed to have formed at a fresh-saltwater mixing zone during stable sea levels, but timing of their formation has not been constrained. Caribbean high stand history is mainly derived from a few U-Th coral dates, yet coral growth rates and water depth requirements limit their utility in recording rapid sea level changes. Subaerial speleothems provide additional information during low stands, but most sampling has focused on presently submerged speleothem. Phreatic Overgrowths of Speleothems (POS), which form at the water table under conditions allowing calcite (folia) to precipitate, can form quickly and indicate precise water table elevations. In carbonate platforms with shallow groundwater gradients, the water table is nearly coincident with sea level and therefore POS potentially record high resolution sea level history.

Extensive shallow caves in Quintana Roo provide access to modern water table transects perpendicular to the coastline. POS above and below modern water table have been dated by U-Th methods to further constrain sea levels and cave ages. Preliminary U-Th ages from a stalactite in Jaguar Claw Cave yields an age of ~252 ka BP, and POS (~+7.2 amsl) of ~49 ka BP. Current sea level proxies suggest the latter was a sea level low stand (-40m). Folia from two samples ~1.4m amsl suggest a high stand at ~251 ka BP. Interior stalactite ages yielded ages of ~340 ka BP. Another sample from the same cave at ~1m amsl is 646 ka BP, with overgrowth of 404 ka BP. Additional samples from Solstice cave about 1.5m amsl yield dates of 110 ka BP for the overgrowth and 212.5 ka BP for the interior stalactite.

These results suggest that the caves above modern sea level were considerably larger and subaerial earlier than has been assumed, and suggests that CO₂-driven dissolution at the water table may be important to speleogenesis, rather than exclusively salt-freshwater mixing. Extensive speleogenesis above modern sea level, and older than MIS5 high stand, suggests sea level records may be incomplete and challenges the assumption of regional tectonic stability.