Allocyclic and autocyclic controls on Pleistocene – Holocene lacustrine deposits: Pueyrredón Lake, Santa Cruz, Argentina

HORTA LUIS RUBÉN (1-2), GEORGIEFF SERGIO M. (1), BUSNELLI JOSÉ (1), ASCHERO CARLOS (1-2).

Mendoza

Congreso; International Sedimentological Congress; 2010

IAS

Allocyclic and autocyclic controls on Pleistocene – Holocene lacustrine deposits: Pueyrredón Lake, Santa Cruz, Argentina Pueyrredón Lake is located 150 m asl at the northwest end of Santa Cruz Province in Argentina, extending into Chile as Cochrane Lake. Pueyrredón Lake is bordered by the Colorada Range to the northwest, San Lorenzo Massif and Belgrano Hill (2305m) to the southwest, and San Lorenzo (3706m) and Chivas (1804m) Hills to the south and west. Four lacustrine deposits surrounding Pueyrredon, Posadas, and Salitroso Lakes were identified at different altitudes during field surveys. These deposits were found at 180-190, 200, 310, and 400 m asl. They are mainly composed by siltstones and mudstones varying from 1 to 10m in thickness, and contain fine parallel lamination, convolute strata, gastropods, and fossil teeth. Underlying these fine-grained deposits are massive siltstones and sandstones with randomly placed, angular to subangular pebbles at altitudes of 180-190 and 310 m asl. These massive coarse-grained deposits reach 1.5 m in thickness and are interpreted as diamictites. Sedimentologic logs were measured along the exposures of the fine-grained deposits to characterize lateral and vertical facies changes. Lithologic samples were analyzed in the laboratory to determine grain size variation and mineralogy using a magnifying glass (x80) and a petrologic microscope. Data indicate that three fan deltas entered Pueyrredon Lake from the southern ranges. These fan deltas show variations in their radii through time with partial control from wave erosion. The largest fan delta is located far away from the Andes, indicating deep erosion elsewhere. These fan deltas along with neighboring alluvial fans exhibit large terraces at certain levels indicating perhaps either tectonic or glacial control in their formation. The fine-grained deposits at 400 m asl show convolute lamination, flame structures, and intensive synsedimentary faulting and folding which may indicate tectonic influence. The different altitudes of these sedimentary deposits were mapped with Ilwis software using Landsat 7 ETM and SRTM (Shuttle Radar Topography Mission) in order to create a Digital Elevation Model. This model shows that Pueyrredón, Posadas, and Salitroso Lakes were connected, perhaps during the last glacial period.