The glacial paleovalley of Vichigasta: Paleogeomorphological and sedimentological evidence for a large continental ice-sheet for the mid-Carboniferous over central Argentina
Journal
Journal of South American Earth Sciences
Date Issued
2021-03
Author(s)
Valdez Buso, Victoria
Milana, Juan Pablo
di Pasquo, Mercedes
Espinoza Aburto, José
Abstract
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 Malanz ' an ones. Vichigasta and Malanz ' an paleovalleys show similar size, a clear U shape 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 high over 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 OltaMalanz ' an 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.


