Mineralogy of sandstones of the Pirambóia and Botucatu formations in Central-East State of São Paulo

Abstract

The sandstones of the Pirambóia Formation are submature to mature subarkoses and those of the Botucatu Formation are mature to supermature subarkoses and quartzarenites. The mineralogical provinces of these formations are two: the A province occurs predominantly in the Pirambóia Formation and the B province in the Botucatu Formation. These two provinces interdigitate. During the transportation and deposition of these sandstones, the minerals strongly suffered lengthy eolian abrasion and selective sorting, and were later modified by diagenesis and weathering. The sediments of these formations in the central and southwest parts of the studied area were chiefly derived from crystalline rocks, and partially from pre-existing sediments; those in the northeast part were chiefly derived from pre-existing sediments and partially from crystalline rocks. In the depositional period of the Botucatu Formation, a basic volcanism took place in the source area and supplied mostly angular, euhedral magnetite and ilmenite. The textural and compositional characteristics of the minerais from both units indicate that these sediments were prirnarily transported and deposited in eolian environrnents.