PALEOENVIRONMENTAL RECONSTRUCTION OF A PLEISTOCENE LACUSTRINE SEQUENCE FROM FAUNAL ASSEMBLAGES AND OSTRACODE SHELL GEOCHEMISTRY, BAZA BASIN, SE SPAIN

We have reconstructed the Early Pleistocene palaeoenvironmental record for a shallow lacustrine sequence from the Baza Basin (Southern Spain ), using faunal assemblages and the shell chemistry of two ostracode s pecies (Candona sp. and Cyprideis torosa). In the NE basin sector (Orc e area), a Lower Pleistocene lacustrine sequence, up to 10 m thick, co ntains alternating phases of two fossil assemblages which differ in th eir salinity requirements. The faunal assemblages record phases of (1) slightly saline, Ca + bicarbonate-rich water, when freshwater organis ms predominated, and (2) saline, NaCl-dominant water in which marine-l ike organisms lived. The ostracode shells from intervals with a saline fauna have higher deltaO-18 values than those from intervals with a f reshwater fauna. This feature corresponds to a parallel alternation of positive and negative hydrologic balances. deltaO-18 and deltaC-13 va lues from ostracode calcite display a covariant trend which indicates that the ostracodes lived in a closed lacustrine system. The isotopic data show a better agreement with the inferences from faunal assemblag es than with trace element trends. The trace element data, although lo cally fitting well with the isotope and faunal interpretations, sugges t overall that trace element contents in ostracodes are not consistent indicators of salinity and/or temperature variations, but depend on a set of complex factors, which may not be easily deciphered. The alter nation of concentration/dilution phases recorded in the studied sectio n can be correlated with climatic cycles described from synchronous oc ean basin records from the Late Matuyama chron.