Abstract
AbstractThe taphonomy of Early Permian vertebrates from a sandy facies at the base of the Taquaral Member, Irati Formation, was surveyed in order to acquire data for the interpretation of the sedimentary processes and paleoenvironment of deposition. Six outcrops from the Rio Claro municipality and surrounding areas, from the Brazilian State of São Paulo, were investigated. The vertebrate groups are Chondrichthyes (Xenacanthiformes, Ctenacanthiformes and Petalodontiformes), Osteichthyes (Actinopterygii and Sarcopterygii) and Tetrapodomorpha. They occur as loose teeth, scales, spines and bone remains. The sandy facies is characterized by fining upward deposition. The coarser sandstone immediately above the underlying Tatuí Formation is rich in Chondrichthyes. However, the fine sandstone above, immediately beneath the silty shale facies, is devoid of Chondrichthyes, though Osteichthyes scales, teeth and bones were present. The taphonomy is important for inferring sedimentary processes and then the paleoenvironments. The poor sorting of the sandstone and the presence of fossils that are mostly abraded or worn are indicative of a high energy environment. In contrast, the presence of fossils in a good state of preservation, some without abrasion and breakages are indicative of only limited transport. Differences of fossil spatial density, numbers of specimens and taxa may be explained by the dynamics of deposition, from details of the palaeoenvironment can be obtained.
Highlights
Ordovician to Cretaceous deposits from the southern Brazil intracratonic Paraná basin are grouped into several stratigraphic sequences
Besides the reworked and fragmented fossils, others occur in a good state of preservation, such as teeth with no or very little abrasion or small breakages
The fossil spatial densities are larger at outcrops 1 and 2 and smaller at outcrop 4, the deposits of which are coarser
Summary
Ordovician to Cretaceous deposits from the southern Brazil intracratonic Paraná basin are grouped into several stratigraphic sequences. The thickest are Late Palaeozoic in age, of which the Irati Formation, Permian Cisuralian (Santos et al 2006), is the most outstanding marker of changes in the tectonic behaviour of the basin (Milani and De Wit 2008). Two members of this formation were proposed by Barbosa and. Gomes (1958), the Taquaral Member at the base, succeeded by the Assistência Member. The Taquaral is represented by two facies, the sandy facies, mostly located at the base, and silty-shale. The silty shale facies is thicker (5 to 30m) more homogeneous and more widespread than the sandy facies. Crustaceans and fish remains as the only fossils recovered from this facies (Chahud and Petri 2013a, 2013b)
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