MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
YOUNGER DRYAS COOLING IN THE SOUTHERN HIGH LATITUDES? INSIGHTS FROM OXYGEN ISOTOPES OF LAGUNA POTROKAIKE (PATAGONIA, ARGENTINA)
Autor/es:
MAYR, C.; OEHLERICH, M.; LUCKE, A.; WISSEL, H.; HABERZETTL, T.; OHLENDORF, C.; SCHABITZ, F; WILLE, M.; CORBELLA, H.; ZOLITSCHKA, B.
Lugar:
Heidelberg
Reunión:
Simposio; 22nd International Colloquim on Latin America Earth Sciences; 2011
Institución organizadora:
Universitat Heidelberg
Resumen:
The Potrok Aike lake is at present a relevant geoscientific site due to the discovery of a thick package of lacustrine deposits, able to deliver worthy information about climatic and environmental changes at the southern tip of Patagonia and austral tephrochronology (SALSA, PASADO and PIPA projects). The Laguna Potrok Aike (LPA) area is located in the western flank of the Pali Aike volcanic field in the Magellan Basin, 300 kilometres East of the Andean volcanic front and at the edge of huge morainic arches proceeding from the Andes and the Magellan Strait. The predominant fault systems controlling most of the eruptive activity have a NW direction, later followed by faults of E-W and ENE strike. In LPA the stratigraphic column is composed by: Santa Cruz Formation (SCF) deposits; deeply eroded Mio-Pliocene table basalts; till deposits; scoria cones, lava flows and maar phreatomagmatic sediments and glacifluvial, fluvial, aeolian and lacustrine deposits. The Miocene molassic SCF consists of weakly lithified continental tuffaceous sandstones and siltstones, 660m thick at the vertical of LPA. Most of the basaltic outcrops in the area are part of a Mio-Pleistocene back-arc volcanic field. Table mountains, scoria cones, lava flow fields and maars are the main volcanic features. Basaltic table mountains are the oldest volcanic outcrops in Pali Aike. Transitional to alkali basaltic lavas, 10 and more metres thick, lie on the SCF. In the LPA area several scoria cones of Plio-Pleistocene age and alkali basaltic, basanitic and tephritic composition crop out almost devoid of rills, gullies or drainage pattern. The abundance of maars is a characteristic of the Pali Aike volcanic field. Some of these maars are large and shallow, others are smaller and deeper. Mean diameters of the largest maar-craters are: Potrok Aike 4500m, Timote 3100m, and Flamencos (W and E) 1960m and 1470m. Maar-craters developed in a soft-substratum are larger than craters carved in a hard-substratum, and exceptional big craters seem only to occur when country rocks are frozen (permafrost). The Potrok Aike Maar has a broad and flat morphology. The present lake inside the maar’s diatreme (113 masl and 100m deep) has an almost circular shape 3 km Ø. The entire depression is ~4.5 km wide. The maar depression+diatreme ensemble has a champagne glass shape, characteristic of maars erupting in soft-rock environments. The diatreme was carved in brittle lithology of the molassic SCF, crowned by unconsolidated till deposits, and patagonian gravels. Cryogenic features -sand wedges and cryoturbations- affecting tills and overlying materials, attest permafrost conditions; but how many times and when these conditions prevailed is still uncertain. Moreover the soft and unconsolidated country rock allowed the development of inner crater walls of low slope angles which caused a very wide crater. Most of the phreato-magmatic deposits of the surrounding rim have been severely deflated.