Sedimentology of the Mid-Carboniferous Basal Fill of the Olta Paleovalley, Eastern Paganzo Basin, Argentina
Date of Award
Master of Science
John L. Isbell
Dyanna M. Czeck, Elmo Rawling
Argentina, Gondwana, Late Paleozoic Ice Age, Paganzo Basin, Paleoclimatology, Sedimentology
As global climate transitioned from the icehouse of the Late Paleozoic Ice Age (LPIA) to greenhouse conditions of the Late Permian, glaciers vanished across Gondwana; however, not all ice centers responded synchronously. The Paganzo basin, northwestern Argentina, was geographically adjacent to significant mid-Carboniferous ice centers that disappeared notably earlier than ice over much of Gondwana. Confining the extent of glacial ice during the LPIA and resolving the timing of its disappearance is of particular interest as this dramatic climatic transition is the closest analogue in Earth history to late Cenozoic climate change, potentially aiding in anticipating the response of modern climate to similar drivers.
The majority of the late Paleozoic glacial record in the region is from paleofjord deposits in the Calingasta-Uspallata, Rio Blanco, and western Paganzo basins, but in the eastern Paganzo basin a paleovalley, only a few hundred meters wide, was cut into the predominantly granitic basement of the Sierra de los Llanos near Olta, in La Rioja Province. The basal fill of the valley was previously interpreted as glacigenic, with the valley carved by either local alpine glaciers or an outlet glacier draining westward from an ice sheet situated over the eastern part of the Paganzo Basin. This study tests the glacigenic setting for the paleovalley.
The strata are dominated by medium to thick-bedded, fine- to coarse-grained sandstones deposited by lacustrine wave activity and underflow currents, and by massive or weakly graded conglomerates deposited by stream and debris flows associated with prograding alluvial fans and fan deltas. Lacustrine sediments interfinger with distal alluvial fan conglomerates along the valley wall, suggesting water was impounded by transverse progradation of the fans across the valley. Bulleted clasts, glacial abrasion marks, diamictites with clast fabrics, and other diagnostic glacial features were not observed. Diamictites were rare and associated with landslide deposits along the valley wall, and soft sediment deformation beneath boulder-rich conglomerates and breccias can be attributed to mass-transport deposits and rock fall off of the steep valley walls. The basal fill of the Olta Paleovalley is interpreted here as a lacustrine depositional environment in a narrow mountain valley and contains no evidence for glacial ice in the eastern Paganzo basin.
Moxness, Levi Darwin, "Sedimentology of the Mid-Carboniferous Basal Fill of the Olta Paleovalley, Eastern Paganzo Basin, Argentina" (2016). Theses and Dissertations. 1295.