Unveiling the sedimentary infill of the Uruguayan onshore portion of the Pelotas Basin (southeast of Uruguay)

Abstract

The Uruguayan onshore portion of the Pelotas Basin is the Laguna Merin Basin. Despite its interesting geological and geophysical features, such as the highest Bouguer gravity anomaly and the youngest volcanic calderas in the country, it is the least known basin in Uruguay. In this study, a stratigraphic chart is presented for the first time, and an integrated analysis of its sedimentary infill is performed through the acquisition of horizontal-to-vertical spectral ratio data as well as geological and geophysical data available from previous studies. The Cretaceous sedimentary infill was restricted to the rift phase, corresponding to alluvial and fluvial deposits. The Cenozoic sedimentary cover corresponds to continental to marine sedimentary rocks and sediments deposited from the Oligocene to the present day in a drift tectonic framework. It presents a regional areal extension that exceeds the structural rifting borders of the basin. The maximum Cretaceous/Cenozoic sedimentary infill thickness is ~500 m. Cretaceous sedimentary units related to the rift and Oligocene drift phases are only present in the Uruguayan portion of the onshore Pelotas Basin, and the thickness of the Cenozoic drift deposits (from the Miocene to modern deposits) in the Brazilian region is at least twice that in the Uruguayan region.