The sedimentary record of wet and dry eolian systems in the Cretaceous of Southeast Brazil: stratigraphic and paleogeographic significance

Patricia Colombo Mescolotti,Lucas Veríssimo Warren,Francisco Sérgio Bernardes Ladeira,Filipe Giovanini Varejão,Mario Luis Assine,Paulo César Fonseca Giannini

doi:10.1590/2317-4889201920190057

Abstract

Abstract Sedimentologic and stratigraphic studies of paleo-deserts from the Brazilian Cretaceous are of great potential to understand the paleoclimate and paleogeography of Gondwana during its final rifting stage. Herein, we describe and discuss two depositional units characterized by two distinct eolian systems that are bounded by a long-lived unconformity. The Lower Unit (Barremian/Aptian) encompasses a wet eolian system composed of dune, interdunes, and ephemeral alluvial deposits. A continuous paleosol horizon in the upper part of the Lower Unit records dune stabilization and end of eolian accumulation, in a period of climate amelioration possibly in the late Aptian. The stratigraphic gap proposed for the unconformity (Cenomanian to Coniacian) coincides with the Cretaceous Thermal Maximum. The Upper Unit (Santonian?/Campanian) comprises dune fields of a dry eolian system capped by the Mata da Corda volcanic rocks. Cross stratification dip directions from both eolian systems shows transport towards SSW. Paleo-winds coming from the northeast quadrant reveal that the continental breakup and drifting had little influence on the surface winds in this Gondwana sector. The Upper Cretaceous paleo-winds are coherent with global paleo-circulation models, based on a high-pressure cell over the South Atlantic proto-ocean, favoring desertification in the inner portion of the southwestern Gondwana.

Highlights

Eolian dune fields dominate the desert landscape and are very sensitive to moisture changes and, they commonly record ancient paleoclimatic fluctuations (Sun and Muhs 2007)
The described stacking pattern of dune and interdune deposits points toward a continuous relative rise in the water table along the geologic time (Kocurek 1996), preserving the sedimentary succession recorded in the Lower Unit of Três Barras Formation
High-magnitude earthquake may have accompanied the explosive Mata da Corda volcanism during the deposition of the Upper Unit of Três Barras Formation and is possibly the trigger of the syn-depositional deformations found in these eolian sandstones, to those described by Netoff (2002)

Summary

Introduction

Eolian dune fields dominate the desert landscape and are very sensitive to moisture changes and, they commonly record ancient paleoclimatic fluctuations (Sun and Muhs 2007). In the Lower Unit, the dune deposits (St2 facies) occasionally exhibit small-scale soft-sediment deformation features (disharmonious folds and fluid escape structures) and carbonate clasts at the base of eolian foresets (Fig. 3I).

Results

Conclusion