EVIDENCE OF ANCIENT GLACIATIONS IN THE NORTHEASTERN SERTÃO

Abstract

The current hot northeastern sertão in Brazil was once a scenario in the Earth's geological past close to the south pole and included in the part of a giant continent, the Gondwana. The ancient ice that covers this region in the past was not preserved in the geological record. Sediment remains composed of gravel, sand, and clay transported by the ice were the unique record documented throughout the time. During the burial, these sediments become a rock succession, evidence from the passage of glaciers in the sertão once upon millions of years ago. At least two glaciations are documented in these Sertão rocks in 440-430 and 360-425 million years ago, during the Silurian and Devonian periods. The glaciation evidence is recorded in the Parnaíba Basin as a matrix-supported conglomerate with clasts of different rocks named diamictite. After the glacier advance that deposited the diamictite, the succession is underlaid by organic matter-rich-marine shales, sometimes containing debris from the melting of icebergs. These glacial deposits are usually sandwiched by fluvial-deltaic succession and are considered stratigraphic marks for the global correlation of this part of the Brazilian northeast.