Tonsteins Da Formação Rio Bonito No Depósito De Carvão Candiota, Rs

Radiometric age determination of tonsteins and stratigraphic constraints for the Lower Permian coal succession in southern Paraná Basin, Brazil

“…The age of crystallization of the zircons from the Tonstein A was interpreted as 296 ± 4.2 Ma. The relatively large discrepancy between the age of 267 ± 3.4 Ma obtained by Matos et al (2000Matos et al ( , 2001 for the Tonstein A of Candiota Lower Coal Seam and the data (296-297 Ma) obtained by GuerraSommer et al, (in press-a) could be explained by the probable analyses of zircon grains or groups of zircon grains with some degree of Pb loss, rendering a younger age. Lead loss causes discordant results and strongly affects (reduces) the 206 Pb/ 238 U ages, which are the preferable ages used for Phanerozoic zircons.…”

“…At the Candiota Coalfield, analysis was carried out in tonstein layers from the Lower Candiota Coal Seam: LowCand1 (which corresponds to the Tonstein A previously dated by Matos et al (2000Matos et al ( , 2001 and LowCand2; from the Upper Candiota Coal Seam, analyses were carried out in UppCand 1 (which corresponds to the Tonstein C dated by Guerra-Sommer et al, in press-a) and UppCand2 (Fig. 2a).…”

“…The first attempts to establish radiometric data in clay beds characterized as tonsteins in the southern Brazilian coal succession were made by Matos et al (2000Matos et al ( , 2001. They used IDTIMS U-Pb method to date zircons of the Tonstein A, interbeded with the Lower Candiota Coal Seam (Fig.…”

Permian plate margin volcanism and tuffs in adjacent basins of west Gondwana: Age constraints and common characteristics

“…Although traditionally interpreted as fluviodeltaic (Holz and Dias-Flor, 1984;Lavina et al, 1987), the Rio Bonito sediments have been more recently interpreted as deposited in a fluvial to tide-dominated estuarine environment (Netto et al, 1991, Buatois et al, 2001aHolz, 2003). The contact of the Rio Bonito sediments with the underlying glacigenic deposits of the Itararé Group has been considered an erosional surface associated with a sea-level fall (Matos et al, 2000). The tuffs are composed of rhyolitic glass shards, often replaced by analcite.…”

“…Recent IDTIMS U/Pb dating of zircons in tonsteins from the Rio Bonito Formation exposed along the southern margin of the Paraná Basin provided an absolute age of 267 ± 3.4 Ma (Matos et al, 2001). These tonsteins have been interpreted as tephra (ash layers) horizons deposited in coal-bearing sequences altered to kaolinitic claystones (Matos et al, 2000). The lateral continuity and insignificant thickness variations of the tonstein beds are considered evidence of distal ash fall deposits.…”