Late Glacial to Holocene terrigenous sediment record in the Northern Patagonian margin: Paleoclimate implications

A high-resolution study of clay mineralogy and major element geochemistry has been carried out on a high sedimentation rate deep-sea core recovered off the Taitao Peninsula in southern Chili (46°S) to investigate climate and environmental changes in Northern Patagonia since the Late Glacial period (the last 22 ka BP). The chronology is based upon stable oxygen isotopes of planktonic foraminifera and AMS radiocarbon dating. Smectite/(illite + chlorite) and Ti/K ratios reveal strong changes of the sedimentary sources between the crustal rocks of the Coastal Range and the volcanic rocks of the Andean Cordillera over the last 22 ka BP. Compared to the Holocene, the Late Glacial period was characterized by reduced input of detrital material derived from the high relief of the Andean Cordillera, in agreement with a greater extension of the North Patagonian ice cap that prevented chemical weathering of basalt (smectite production) and induced physical erosion of illite and chlorite from glacial scours. The Glacial period is also characterized by rapid changes of smectite/(illite + chlorite) and Ti/K ratios indicating short-term (centennial-scale) glacier fluctuations. These changes could be the results of southern westerly shifts in the Aysen region alternating periods when glaciers were probably less fed by precipitation (mostly located in the North) and consequently less active to ice accumulation periods. The deglaciation was characterized by a trend towards warmer and more humid conditions, punctuated by a cold and arid period partly coeval with the Antarctic Cold Reversal event. Finally, the Holocene presents warmer and more humid conditions even though short term changes in the smectite/(illite + chlorite) ratio and the δ18O record could be attributed to Neoglacial events in the studied region.