Provenance of Gondwana Sandstones of the Parana Basin, Brazil

DUTTA, PRODIP K., Indiana State University, Terre Haute, IN, and PAULO R. SANTOS, Instituto de Geosciences, Sao Paulo, Brazil

Gondwana sedimentation in the Parana basin was initiated as a result of epeirogenic uplift of the Brazilian craton during Upper Carboniferous glaciation. Uninterrupted sedimentation continued until the end of the Permian and resulted in deposition of three marine/marginal-marine/continental facies. A second episode of cratonic uplift in Triassic time was responsible for deposition of two additional continental facies.

Based on mineralogical composition of the arenites, five petrofacies have been identified that correspond to five lithofacies. A cyclical compositional trend of the petrofacies, in chronological order from the base, have the following QFL values: 87:9:4 (Petrofacies I) in the glaciomarine facies - 97:3:0 (Petrofacies II) in the marginal marine Coal Measures - 90:9:1 (Petrofacies III) in the continental sandstone-red/green shale facies - 76:23:1 (Petrofacies IV) in the fluvial sand - and 93:7:0 (Petrofacies V) in the eolian sand.

Compositional maturity of Petrofacies II relative to Petrofacies I is attributed to the chemical decay of unstable grains in a humid climate that prevailed during coal formation. The relative immaturity and presence of fresh feldspars in Petrofacies I is presumably due to the presence of some granitic source rock and lack of chemical weathering in the glacial climate. Petrofacies III swings back to immaturity possibly due to the decline of the humid climate as indicated by the absence of coal and the beginning of a global arid trend. Petrofacies IV represents the most immature unit in the entire succession and is related to aridity and another tectonic uplift of the craton that resulted in unroofing of some more granitic rock. Maturity of Petrofacies V relative to the underlying fluvi l sand is possibly due to mechanical destruction of feldspars through eolian processes.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)