The glacial paleovalley of Vichigasta: Paleogeomorphological and sedimentological evidence for a large continental ice-sheet for the mid-Carboniferous over central Argentina

VALDEZ BUSO VICTORIA; JOSE ESPINOZA ABURTO; MILANA JUAN PABLO; DI PASQUO MERCEDES

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020 vol. 106

0895-9811

Valdez V. Buso, Juan Pablo Milana, Mercedes di Pasquo, José Espinoza Aburto, 2020. Paleogeomorphological and sedimentological evidence for a large continental ice-sheet for the mid-Carboniferous over central Argentina. Journal of South American Earth Sciences (submitted june 2020, revision October 2020, accepted november 2020), Vol 106 (2021) - con archivo suplementario (no adjuntado)We present new data on the Vichigasta Carboniferous paleovalley, a glacial trough crucial to understand the type of glaciation that affected western Gondwana during the Late Paleozoic Ice Age (LPIA). The filling of this paleovalley starts soon after the mid-Carboniferous glacial peak. Stage I represents pro-glacial lacustrine deposits with outwash, glacially rafted dropstones, mass transport deposits (MTDs) and turbidites of the trunk and a lateral tributary valley. Base-level drop created the scenario for Stage II outwash deltas and sandur deposits, with westward flow. Stage III represents a flooding at the base of the Bashkirian, characterized by typical transgressive dark shales and distal turbidites. Stage IV represents a highstand prograding turbidite wedge. We worked in a detailed terrain analysis, surveyed the scarce sedimentary record left and recovered a rich palynoflora from mudstones of Stage 3. The almost complete erosion of the fill allowed us to analyze the shape of this paleovalley and compare it to Olta and Malanzan ones. Vichigasta and Malanzan paleovalleys show similar size, a clear Ushape and regular and homogeneous width downslope, a requisite for bypass glacial paleovalleys carved in a subcrop of homogeneous composition (basement), which allow us to interpret them as outlet valleys. Olta paleovalley ranks as tributary as its capacity is only one-third of the others. We also identified a basement highover the Vichigasta valley floor that suggests the presence of a potential drumlin supporting our interpretation as a bypass glacial valley. This post-glacial flooding event is widely observed at other glacial valleys as the Olta Malanzan herein analyzed and others like Las Lajas and Quebrada Grande. The new data from Vichigasta paleovalley reinforce the hypothesis of a large ice-sheet located to the east of the craton.