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Abstract

J. C. Pashin and R. A. Gastaldo , eds., 2004 , Sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata : AAPG Studies in Geology 51 , p. 147 - 167 .

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Sequence Stratigraphy and Coal Petrology Applied to the Early Permian Coal-bearing Rio Bonito Formation, Paranaacute Basin, Brazil

Michael Holz, Wolfgang Kalkreuth

Instituto de Geociecircncias, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

ACKNOWLEDGMENTS

The study was supported by the Brazilian agency Conselho Nacional de Desenvolvimento Cientifico e Tecnoloacutegico (CNPq) (Research Grant 520332/96-2) and Fundaccedilatildeo de Apoio agrave Pesquisa do Estado do Rio Grande do Sul (FAPERGS) (Research Grant 520271/97). The authors acknowledge Companhia Riograndense de Mineraccedilatildeo and Companhia de Pesquisas de Recursos Minerais for supplying the well logs, cores, and other material essential for this research. CNPq is acknowledged for personal research and study grants to the authors (352887/96-6 and 300971/97-4, respectively). The manuscript benefited from helpful comments by Kevin Bohacs and Cortland Eble.

ABSTRACT

The coal-bearing Early Permian succession of the Paranaacute Basin in southernmost Brazil is linked to a third-order depositional sequence, where the most important coals occur in the initial transgressive systems tract. In the Candiota area, the main coal zone consists of 17 seams, which were analyzed for petrographic properties (macerals, gelification index, tissue-preservation index, vitrinite reflectance). These results are compared to the high-resolution sequence-stratigraphic framework to enhance our understanding of the stratigraphic controls on coal formation, coal distribution, and coal quality, providing guidelines for optimal exploitation.

The results show that local changes in accommodation trends and high sediment influx practically preclude coal formation in the lowstand and highstand systems tracts, whereas major coal development occurred in the transgressive systems tract. Previous HitSeamNext Hit distribution and thickness are controlled directly by flooding events, as depicted by the parasequences mapped in the study area. The main variations in thickness and extent occur at, or close to, the parasequence bounding surfaces. The most important coals, which are as much as 2.50 m in thickness, occur in the initial transgressive systems tract.

Coal petrographic parameters suggest an overall drying-upward trend in the coal seams developed in the upper part of third-order sequence 2, with significant differences of coal properties relative to their stratigraphic position between and within the parasequences. Detailed petrographic analysis of Previous HitseamNext Hit subsections indicates a transgressive nature for the thick coal seams occurring in parasequence 4 (CCI and CCS seams). These are characterized by decreased vitrinite reflectance at the base and top of the coal seams. The high inertinite content of the overlying BL Previous HitseamTop at the top of PS 4 suggest accumulation of the precursor peat in a regressive phase of the parasequence.

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