DOI: 10.1594/pangaea.869205
title: Outcrops with stratigraphy investigated in Rio Grande do Sul, Brasilia

description: Stratigraphy, sedimentology and paleoecology of Mesozoic continental sequences in the Depressao periferica, Rio Grande do Sui, Brazil, are subject of a DFG (German Research Foundation) research project. Results of the first two years period of activities in which the Geologicai-Paleontological Institutes of the Universities of Kiel and Frankfurt/M. in collaboration with the Departamento de Geociencias, University of Santa Maria in Camobi, RS, were involved are reported here. A second phase of field activities is planned for the time period from fall 1993 to the spring of 1995.The stratigraphic boundaries of the investigation are the underlying sediments of the Permian Passa Dais-Series and the overlying basalts of the Serra Geral Formation, covering the time span of 235 Ma to 133 Ma. A subordinate, chronostratigraphic system encompassing the sediments of this time period has yet to be established and extensive hiatuses are to be expected. Correlations with the lschigualasto Formation in NW-Argentina support the assumption that the upper Santa Maria Formation (Aiemoa member) falls in the mid Carnian. This is the only reasonable certain chronostratigraphic date from the Mesozoic of the Depressao periferica established at the present time.The classical tetrapod sites of the Triassic Santa Maria Formation all fall within the Alemoa-Member, the sediments of which were deposited under in part evaporitic conditions on playa mud flats. Evidence points to isochronic sedimentation and discounts the possibility of a diachronic genesis.The Santa Maria Formation and the underlying Sanga do Cabral Formation are placed together in the Rio do Rasta Subgroup as a genetic unit in accordance with the original definition, which conflicts with present day usage of the names. The Rio do Rasto Subgroup pinches out west of Sao Francisco do Assis and east of the Taquarl river. The entire Rio do Rasto Formation is enclosed in eolic sediments, indicating an extensive sedimentation complex arising from a persistently subsiding playa areal within the Botucatu desert. Beyond the range of the Rio do Rasto Subgroup, it is difficult or impossible to distinguish between the eolic sediments of the older, underlying Rosario do Sui Formation and the overlying, younger Botucatu Sandstone Member. As such, the entire paleogeographically and genetically uniform sedimentation complex is compiled together under the term Botucatu Group.The Sanga do Cabral Formation is characterized by an abundance of detritic micas (muscovite and biotite). K/ Ar dating have indicated a preliminary age for muscovite of 418 ± 8 Ma and 423.5 ± 9.7 Ma. Presumably, they originated from volcanites, subvolcanites and pyroclastics of the Camaqua Group (Brasiliano molasse). As such, the Precambrian/ lower Paleozoic Escudo Sui in Rio Grande do Sui was exposed and eroded to the level found today at the time of deposition of the Sanga do Cabral Formation.
description: Supplement to: Böger, Horst; Kowalczyk, Gotthard (1993): Stratigraphische, sedimentologische und paläoökologische Untersuchungen im Mesozoikum der Depressão Periférica in Rio Grande do Sul, Brasilien. Berichte-Reports, Geologisch-Paläontologisches Institut der Universität Kiel, 63, 72 pp