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 ostra cod bearing samples from a lacustrine section collected in the Maquinchao v alley in the Cari-Laufquen Lake region (lat. 41 degrees 35'S; long. 69 degr ees 25'W) situated 150 km east of San Carlos de Bariloche on the northern P atagonian steppe. The rich lacustrine ostracod fauna, obtained during the L agos-Comahue project, has yielded important climatic and environmental info rmation on the late Pleistocene and Holocene of northern Patagonia. The fau na comprised mainly new species of Limnocythere and Eucypris. During the la st 13,200 years B.P. (thermoluminescence dating), levels representative of much more humid conditions than those obtained at the present time, are sug gested by stratigraphical levels which include those yielding a very abunda nt fauna of Eucypris fontana (Graf) and Limnocythere rionegroensis Cusminsk y and Whatley. These humid climatic levels are overlain by a sequence in wh ich the ostracod faunal abundance decreases very abruptly and this event co incides with the appearance of evaporites suggesting the onset of significa ntly drier conditions during the Holocene. (C) 1999 Elsevier Science B.V. A ll rights reserved.