Sequence stratigraphy of continental Triassic strata of Southernmost Brazil: a contribution to Southwestern Gondwana palaeogeography and palaeoclimate

The continental Triassic succession of southernmost Brazil comprises two second-order depositional sequences-the Sanga do Cabral (Early Triassic) and the Santa Maria (Middle to Late Triassic) supersequences. The first one includes ephemeral, low-sinuosity fluvial deposits developed on a low gradient plain. Based on fossil tetrapods, especially procolophonids, an Upper Induan age is estimated for this sequence. Facies association of the Santa Maria Supersequence indicates low-sinuosity fluvial rivers, deltas and lakes. This supersequence can be further subdivided into three third-order sequences (age provided by palaeovertebrate biostratigraphic data) as follows: Santa Maria I (Ladinian), Santa Maria 2 (Carman to Early Norian) and Santa Maria 3 (probably Raethian or Early Jurassic) sequences. The Gondwanides paroxysms I and 11 in the Sierra de la Ventana-Cape Fold Belt are directly related to the development of both supersequences. The source area of the Sanga do Cabral Supersequence was located to the south. It consisted of an uplifted peripheral bulge situated landward of the retro-foreland system, from where older sedimentary rocks were eroded. The source area of the Santa Maria Supersequence was also positioned southwards and related to the uplifted Sul-Rio-Grandense and Uruguayan shields. The Santa Maria Supersequence stratigraphic architecture is comparable to the Triassic rift basins of Western Argentina. Diagenesis, facies and palacontology of the studied succession suggest a dominantly semiarid climate during the Triassic. (C) 2003 Elsevier Science B.V. All rights reserved.