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[dinosaur] Triassic faunal successions of Paranà Basin, southern Brazil




Ben Creisler
bcreisler@gmail.com

A new paper:


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Cesar L. Schultz, AgustÃn G. Martinelli, Marina B. Soares, Felipe L. Pinheiro, Leonardo Kerber, Bruno L.D. Horn, FlÃvio A. Pretto, Rodrigo T. MÃller & Tomaz P. Melo (2020)
Triassic faunal successions of the Paranà Basin, southern Brazil
Journal of South American Earth Sciences 102846
doi: https://doi.org/10.1016/j.jsames.2020.102846
https://www.sciencedirect.com/science/article/abs/pii/S0895981120303898

Highlights

In Brazil, Triassic tetrapods are known only in the extreme south of the country.
South Brazilian Triassic package includes four biozones based on tetrapods.
The lower tetrapod biozone of the south Brazilian Triassic package is Early Triassic and corresponds to the "Procolophon abundant zone" of the Karoo Basin.
The lower portion of the south Brazilian Middle-Late Triassic package was deposited under more basic and dried environmental conditions and is dominated by synapsids.
The upper portion of the south Brazilian Middle-Late Triassic is characterized by more acid and humid conditions, is dominated by diapsids and presents an increase of diversity compared to the lower portion.


Abstract

The Paranà Basin was filled by a sedimentary package deposited in successive sedimentation episodes related to the tectonic events that hit the SW portion of the Gondwana. The Triassic portion of this package, known worldwide for its continental tetrapod fauna, occurs only in the southern portion of the basin and is represented by 2âs-order sequences: the Sanga do Cabral Supersequence (SCS - Early Triassic) and the Santa Maria Supersequence (SMS - Middle-Late Triassic). The SCS fauna, including temnospondyls, parareptiles (mainly Procolophon), archosauromorphs, putative synapsids, and a number of indeterminate specimens, is traditionally considered Early Triassic and corresponds to the âProcolophon abundant zoneâ of the Karoo Basin (the upper levels of the Lystrosaurus AZ), in the upper Katberg Formation, which is Induan to early Olenekian in age. The sedimentary environment of the SCS is thought to be a wide alluvial plain, in which small and shallow channels spread northwards into a vast semiarid environment. By its turn, the Middle-Upper Triassic Santa Maria Supersequence is divided into four third-order sequences, from base to top: Pinheiros-ChiniquÃ, Santa Cruz, CandelÃria and Mata. Each of these sequences begins with fluvial deposition (low sinuosity rivers) that is overlain by transgressive shallow lacustrine deposits. The first three of these sequences present a very rich record of fossil tetrapods, including four successive faunal associations: Dinodontosaurus Assemblage Zone (Ladinian, within the Pinheiros-Chiniquà Sequence), Santacruzodon AZ (Ladinian/Carnian, in the Santa Cruz Sequence), Hyperodapedon AZ (Carnian) and the Riograndia AZ (early Norian), the latter two respectively at the base and top of the CandelÃria Sequence. In general, the lower portion of the package (Pinheiros-Chiniquà and Santa Cruz Sequences) was deposited under more basic and dried environmental conditions and are dominated by synapsids, while the top of the section (CandelÃria Sequence) is characterized by more acid and humid conditions and by a shift in the faunal content, with diapsids as dominating forms and presenting an increase of diversity compared to the lower biozones.


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