A HIGH-RESOLUTION HOLOCENE RECORD OF SR/CA AND MG/CA FROM AUTHIGENIC CALCITE IN LAKE JUNIN PERU

Lake Junin (~11°S ) is located at ~4000 between the eastern and western Cordillera of the central Peruvian Andes. Though evidence of alpine glaciation is abundant in the surrounding cordillera, the Junin Basin has not been overridden by glacial ice in at least the past several hundred thousand years. Bedrock of the Junin Basin is dominated by Triassic and Jurassic limestone, and marl has been accumulating in Lake Junin at ~1mm yr-1 for the past ~15 ka. Previous work (Metevier, 2001) on ostracods sampled at 100-500 yr spacing from a 19-meter long core reveal shifts in Sr/Ca and Mg/Ca that track closely changes in *18O of marl (Seltzer et al., 2000), and suggest that the early Holocene was relatively dry and that the moisture balance in the Junin region increased progressively from the late glacial through the Holocene. The purpose of this study is to determine whether marl sampled at a spacing of from ~10-50 yr over the last 8,000 yr of record would reveal a record that is similar to the ostracod-derived metal ratios, and whether the higher resolution record would reveal sub-centennial shifts in regional moisture balance. Results indicate that high resolution marl-derived Sr/Ca and Mg/Ca ratios faithfully replicate the ostracod-derived record and, moreover, record sub-centennial scale shifts in moisture balance in the Junin region. The most notable feature of the record is sub-centennial scale cyclicity in both Mg/Ca and Sr/Ca ratios that are superimposed on 1000-2000 yr-long cycles in these metal ratios. That these cycles are seen in both Sr/Ca and Mg/Ca ratios suggests that they may reflect regional drying and warming cycles.