期刊
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
卷 56, 期 -, 页码 265-277出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsames.2014.09.013
关键词
Coal-bearing deposits; Tonstein; Permian; Southern Gondwana; U-Pb geochronology; Volcanism
资金
- Petrobras and its Programa de Fronteiras Exploratorias (PROFEX/Petrobras) [0050.0071390.11.9]
- Padre Milton Valente scholarship
- Brazilian National Council for Scientific and Technological Development (CNPq)
Two ash fall beds (tonstein) sampled from the post-glacial Permian deposits of the Parana Basin have provided new U-Pb radiometric age constraints for this stratigraphic interval. The zircon grains were recovered from tonstein layers interbedded with fine-grained and carbonaceous lithologies in the middle portion of the Rio Bonito Formation. In both samples, the dominant population is interpreted as generated by explosive volcanism, as having formed immediately before the eruption. Based on U-238/Pb-206, the selected zircon grains from the dominant population have weighted mean ages of 290.6 +/- 2.8 Ma and 281.7 +/- 3.2 Ma, corresponding to the Sakmarian and Kungurian ages in the Cisuralian epoch, respectively. These ages constrain the time of the deposition of the tonstein horizons and have important stratigraphic implications for the Late Paleozoic evolution of both the Parana Basin and the southwestern region of Gondwana. The results presented here and the radiometric data already published suggest that deposition of the post-glacial coal-bearing deposits of the Rio Bonito Formation was probably initiated before the Early Permian. Thus, we infer that the climate had already ameliorated by this period in order to allow for the formation and accumulation of peat in this region of Gondwana. (C) 2014 Elsevier Ltd. All rights reserved.
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