Ostracode and C/N based paleoecological record from Santiaguillo basin of subtropical Mexico over last 27 cal kyr BP
Résumé
Changes in ostracode species assemblage suggest presenceof oligohaline and mesohaline waters in the Santiaguillo basin ofsubtropical Mexico over the last ca.27 cal kyr BP. Paleoecologicalreconstruction is based on the distribution of Limnocythere bradburyiForester, Eucandona cf. patzcuaro Tressler, Cypridopsis viduaBrady and Limnocythere ceriotuberosa Delorme. Source of organicproductivity is inferred from C/N ratios. The basin hosted shallowand oligohaline water during the late glacial (ca.27–19 cal kyr BP)and lacustrine phytoplankton contributed to the organic productivity.However, the water body of Last Glacial Maximum (LGM) wasrelatively warmer (>13°C) and more diluted compared to the pre-LGM. Increased salinity and reduced lacustrine productivity atca.19 cal kyr BP marked a shift in the paleoecological conditions.Water body was mesohaline during ca.9.5–4 cal kyr BP andperiodic desiccation of the basin possibly caused the absenceof ostracode valves in sediments of the last ca.3.5 cal kyr BP.Comparison with other proxy-records from the region indicates thatthe hydrological variations in different parts of subtropical north andnorthwestern Mexico were not synchronous during the late Pleistoceneand Holocene.