Lacustrine Ostracoda and late Quaternary palaeoenvironments from the Lake Cari-Laufquen region, Rio Negro province, Argentina

Results are presented from a preliminary analysis of late Pleistocene ostracod bearing samples from a lacustrine section collected in the Maquinchao valley in the Cari-Laufquen Lake region (lat. 41°35′S; long. 69°25′W) situated 150 km east of San Carlos de Bariloche on the northern Patagonian steppe. The rich lacustrine ostracod fauna, obtained during the Lagos-Comahue project, has yielded important climatic and environmental information on the late Pleistocene and Holocene of northern Patagonia. The fauna comprised mainly new species of Limnocythere and Eucypris. During the last 13,200 years B.P. (thermoluminescence dating), levels representative of much more humid conditions than those obtained at the present time, are suggested by stratigraphical levels which include those yielding a very abundant fauna of Eucypris fontana (Graf) and Limnocythere rionegroensis Cusminsky and Whatley. These humid climatic levels are overlain by a sequence in which the ostracod faunal abundance decreases very abruptly and this event coincides with the appearance of evaporites suggesting the onset of significantly drier conditions during the Holocene.