CARBON AND OXYGEN ISOTOPIC COMPOSITION OF SPELEOTHEMS FROM YUCATAN, MEXICO

Carbon and oxygen isotope composition of individual layers of stalagmites Tabi-1 and San-H from central Yucatan, Mexico have been examined to help reconstruct the past climate of the region. The ultimate goal of the project is to determine the role that climate played in the rise and collapse of Mayan culture. The two stalagmites, collected from caves in the northern Yucatan Peninsula, were cut, polished, and dated using a U/Th technique. Samples on the order of 100 µm were drilled from individual layers using a micromill, and the C and O isotopic composition was determined by analysis in an MAT 253 mass spectrometer equipped with a Gasbench sampling device. SAN-H, which formed during the Early Classic to Middle Preclassic time, yielded a range of isotope values for d18O and d13C of -2.3 to -5.5 ‰ and -4.0 to -10.3 ‰, respectively. TABI-I dates from Colonial to Late Classic time periods and has values for d18O and d13C that range from –2.1 to -5.0 ‰ and –4.7 to -9.6 ‰, respectively. Although sample ages are somewhat uncertain at present, the stable isotope trends are systematic, and the d13C record may yield useful information about C3 and C4/CAM vegetation whereas the d18O record may contain useful climate information.