Abstract: Carboniferous Systems in Brazilian Basins: Lithostratigraphy and Biostratigraphy

Medeiros, R. A. and Lemos, W. B. - DEGEO/UFRGS

Carboniferous sequences occur in the Solimões, Amazon, Parnaiba, Alagoas, Sergipe, Tucano Norte, and Paraná basins. The sediments of these basins may be grouped in two major depositional sequences separated by an unconformity. Non- deposition and erosion took place due to tectonic movements associated with mississipian orogenic pulses. These facts are best studied in the Solimões, Amazon and Paraná basins.

To understand the evolution of the carboniferous deposits in the lower sequence it is necessary to report to Devonian transgressions, mainly the frasnian maximum inundation shales in the Solimões and Amazon basins. They are the most important source rocks in these basins, for oil accumulated in Devonian and carboniferous reservoirs. Carboniferous high stand sandstones prograded basinward and are preserved in many areas where the erosion did not reach them. In the lower sequence, shale beds contain lingula, fish, and plant remains. Also contained are limestones and dolomite with braquiopods, briozoans, foraminifera and conodonts.

In the Paraná basin, the lower sequence was not recognized because the erosion was strong and glaciogenic valleys were excavated in the Devonian shales. The valleys filled with clastic are prospective plays for petroleum exploration.

In the Solimões and Amazon basins the upper sequence was deposited over the erosion surface and is characterized by a hot desertic environment, where the facies are dominantly sandstones from Aeolian origin, evaporites and calcarenites. Fossils include braquiopodes, gastropods, briozoans, ostracods, corals, cephalopods and fish remains. The basis for biostratigraphic studies are conodonts, fusulinides and palinomorphs.

The Paraná basin seems to be associated with a cold desertic environment, with no conodonts or fusulinides.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil