Using Paleomagmnetism to elucidate the continental glacial record of southermost Patagonia.

GRIFFING,C.Y., CLAGUE,J.J., BARENDREGT,R.W., ERCOLANO,B., RABASSA,J., CORBELLA, H., ROBERTS,N.J.

Alberta-Edmonton

Conferencia; Canadian Quaternary Association-Canadian Geomorphology Research Group Conference - University of Alberta-Edmonton-August 2013; 2013

Canadian Quaternary Association-Canadian Geomorphology Research Group Conference - University of Alberta-Edmonton

Southernmost Patagonia has a weU preserved record of Pliocene and Pleistocene continental and alpine glaciations. It is the only region in the Southern Hernisphere outside Antarctica where large Pleistocene ice sheets developed, thus it offers a unique opportunity to enhance understanding of global climate vatiability. Previous research on the glacial history of Patagonia is largely based on geomorphology, with relatively few absolute age dates and lirnited study of stratigraphy. Consequently, the number, ages, and geographic extent of individual glaciations are not well understood. Geomorphic evidence of multiple Quaternary glaciations is widespread in the region and includes moraines, erratics, drumlin fields, meltwater channels, and outwash plains. Exposures of glacial sediments are common along the Atlantic coast, the Strait of Magellan, and in road cuts and grave! pits. Most of the glacial deposits are beyond the range of radiocarbon dating. K-Ar and Ar-Ar dating have been used to determine the ages of basalt flows interlayered with till and outwash east of the southem Andes and in areas between the Río Gallegos valley and the Strait of Magellan near the Atlantic coast. These absolute ages suggest that glaciation in Patagonia began in the late Miocene and that the Pleistocene Patagonian ice sheet may have decreased in size with each successive Pleistocene advance. Here, we present the results from a paleomagnetic study of glacial sediments to further constrain the timing of continental glaciation. Remanence directions were deterrnined by principie component analysis on 963 oriented sediment samples. The sed iments are stably magnetized, and provide clear directional data from which polarity can be deterrnined. The majority of sediments in the area are normally magnetized, but sorne sed iments near the outer limit of glaciation, within areas covered by the Patagonian ice sheet during the Great Patagonian Glaciation (GPG), are reversely magnetized. Recent field work indicates that drift of the GPG comprises deposits of severa!glaciations. Our paleomagnetic results, combined with stratigraphic and sedimentologic observations, suggest that the f irst continental glaciation(s) in the region occurred during the Matuyama Reversed Chron (2.6-0.78 Ma) and severa!subsequent glaciations occurred during the Bruhnes Normal Chron (