LACUSTRINE OSTRACODS FROM CHIHUAHUA DESERT OF MEXICO AND INFERRED LATE QUATERNARY PALEOECOLOGICAL CONDITIONS

The paleolake Babicora is located in a tectonic basin in the western part of the Chihuahua Desert in northern Mexico. A 976 cm long sediment core was collected from the central part of the lacustrine basin and 9 different AMS radiocarbon ages constrain the sedimentary sequence between 80 cal kyr BP and present day. The abundance and distribution of the ostracod species in the sediments of upper 755 cm reconstructs the temperature and salinity of the lake water over the last 66 cal kyr BP. We have compared the abundance of the species with concentrations of total organic carbon (TOC) and total inorganic carbon (TIC) measured in the bulk sediment. The ostracod faunal group consists of 5 different species, i.e. Candona patzcuaro, Cypridopsis vidua, Limnocythere bradburyi, L. platyforma and L. ceriotuberosa. C. patzcuaro is the most abundant followed by L. platyforma, C. vidua, L. bradburyi and finally L. ceriotuberosa. For the paleoecological reconstruction, the sediment profile was divided into 5 different zones considering the total abundance of ostracod population and presence of individual species. The topmost 44 cm of the core did not contain ostracods, while abundance varies between 1 and 1441 valves/g in the rest of the sequence. During 66-57 cal kyr BP (zone 5), almost absence of ostracod suggested diluted lake water with abundant fresh water inflow into the basin. Conditions were cooler (13-15 °C) and salinity relatively increased (500-1000 ppm) during 57-49 cal kyr BP (zone 4). The optimal conditions for ostracods were observed during 49-29 cal kyr BP (zone 3), with highest ostracod abundance (45-1441 valves/g). This zone is characterized by fluctuating water temperature (5-32 °C) and salinity (1000-100,000 ppm). During 12-29 cal kyr BP (zone 2), the association of ostracods suggests warm conditions (13-32 ° C) with salinity varying between 1000 and 10,000 ppm. Zone 1 (last 12 cal kyr BP) is characterized by absence of ostracod and precipitation of authigenic calcite representing three arid events identified at ca. 12 cal kyr BP, ca. 3.5 cal kyr BP and ca. 1.3 cal kyr BP. Higher lake productivity reflected in TOC is identified during 66-44 cal kyr BP (zones 3, 4 and 5).