Abstract
The Middle-Upper Triassic section of the Paraná Basin is included in the Santa Maria Supersequence. This stratigraphic unit is classified as a second-order Supersequence, being subdivided into three third-order sequences in which four Assemblage Zones (AZ) based on tetrapods are recognized. In this work, chemical analyses of fossils and hosting rocks of each AZ were performed in order to verify whether the geochemical patterns of the rocks could serve to distinguish them even in the absence of fossils. For this purpose, nine samples of fossils and their sedimentary matrices were analyzed, by ICP-MS. The results show that there were changes in the chemical parameters in force at the depositional time of each sequence (and corresponding AZ). In general, the lower portion of the package was deposited under more basic and dry environmental conditions, indicated by the Ca and Ba concentrations found in the rocks and bones that contains them. By its turn, the top of the section is characterized by more acid and humid conditions, evidenced by Al, Si, and Sr increase. Such a geochemical shift from dry to humid conditions occurred just at the beginning of the Late Triassic and is probably related to the Carnian Pluvial Episode.
Highlights
The Paraná Basin (PB) is filled with an 8,000 m thick sedimentary package
This facies change followed by geochemical variations record the passage from more basic conditions to a more acid environment
The sedimentary matrices of the Santacruzodon Assemblage Zones (AZ) can be diagnosed by the low contents of As
Summary
The Paraná Basin (PB) is filled with an 8,000 m thick sedimentary package. This package does not display a depositional continuity, but polycyclic events resulting from successive sedimentation episodes related to the tectonic events that hit the SW portion of the Gondwana (Milani 1997, Milani et al 1998). The Middle-Upper Triassic strata (Santa Maria Supersequence — SMS sensu Zerfass et al 2003, Horn et al 2014, Horn et al 2018a, 2018b) that occurs only in Rio Grande do Sul State (Fig. 1) are worldwide recognized by their vertebrate fossil content. It includes Synapsida — dicynodonts and cynodonts (taxa containing the sister-group of mammals) — and Diapsida — rhynchosaurs and archosaurs, including the first dinosaur representatives (Schultz et al 2000, Langer et al 2007). Many outcrops of the Santa Maria Supersequence that occur near the fossiliferous localities do not contain fossils, being tentatively associated to a biozone due to its geographical proximity or lithological similarities
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
