Endsley, Erin Alison2020-04-212020-04-212007-05https://hdl.handle.net/11299/212431A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Erin Alison Endsley in partial fulfillment of the requirements for the degree of Master of Science, May 2007.Evidence for Holocene droughts in Mesoamerica exists from numerous paleolimnological studies. Speleothems from the Yucatan Peninsula can be used to help constrain the timing, intensity, and regional extent of these droughts. Late Holocene wet/dry cycles are inferred from the oxygen isotope record of speleothem calcite and the timing is constrained using U/Th dating. In the lowland neotropics, there is a strong negative correlation between 𝝳18O of precipitation and rainfall amount, i.e. the "amount effect". The 𝝳18O of speleothem calcite can then be used as a proxy for the relative amount of past precipitation in the Maya Lowlands. A speleothem from Cueva Tzabnah, near Tecoh, Yucatan, Mexico, has a basal date of 1240 ±61 yr BP and a top date of 28 ±21 yr BP, indicating growth during most of the Terminal Classic period of Maya prehistory. Oxygen isotopes were measured at 0.5 mm intervals, with an average value of -5.25%. 𝝳18O values increase near the hiatuses in speleothem growth, interpreted as evidence for the presence of drought conditions. The relative increases in 𝝳18O are dated using U/Th methods to constrain the timing of the drought events. In the top 3mm, the mean 18O value is 2.49% greater than the mean speleothem 𝝳18O value, and possibly represents drier conditions beginning in the mid-15th century AD consistent with a nearby lake sediment core record from Aguada X'caamal (Hodell et al., 2005). Another speleothem from Cueva Colurnnas, near Tzucacab, Mexico, has a basal date of 1347 ±63 yr BP and a top date of 520 ±99 yr BP, and a mean 𝝳18O value of -3.80%. Both speleothems contain evidence for past climate fluctuations during the Terminal Classic period, including a relatively drier period from about 850-900 AD recorded in both speleothems.enPlan As (thesis-based master's degrees)Department of Earth and Environmental SciencesUniversity of Minnesota DuluthMaster of ScienceMaster of Science in Geological SciencesThesis or Dissertation