STABLE ISOTOPES, RARE EARTH ELEMENTS AND PETROGRAPHIC ANALYSIS OF VERTEBRATE FOSSILS FROM SOLIMÕES FORMATION (UPPER MIOCENE, ACRE BASIN, BRAZIL): EXPECTED INSIGHTS ON PALEOECOLOGY, PALEOENVIRONMENT AND TAPHONOMY

Upper Miocene deposits of Solimões Formation have been extensively studied, especially in the past few decades. The fossil record is mostly comprised of vertebrate remains but invertebrate, ichnofossils and wood are also recorded. The genesis and depositional environments of Solimões Fm. deposits are, however, still a matter of controversy. Some authors argued that marine incursions could have reached some areas of Acre basin during the upper Miocene, although others refute this hypothesis claiming that the environment of deposition was dominated by river, swamps and lakes.

In an effort to contribute to the paleoenviromental and paleoecological debate of Solimões Fm., stable oxygen isotope analysis of cortical bone and tooth enamel of a variety of taxa will be performed , including crocodile, turtle, fish, mammals (armadillo and rodent) and frog from four paleontological sites (Talismã, Niterói, PRJ20 e PRJ26). Additionally, petrographic and rare earth element analysis will be performed as well, aiming to evaluate diagenesis, time and spatial averaging.

It is well known, based on living organisms, that δ¹⁸O values will vary with habitat, location, diet, thermoregulatory and osmoregulatory physiology. If marine incursions happened, it will be expected to find relatively homogenous and higher values of δ¹⁸O in aquatic organisms (turtle, crocodile and fish) compared to freshwater datasets. Furthermore, rare earth elements and petrographic analysis can shed lights on the diagenetic nature of the bonebeds improving the quality and robustness of our oxygen isotope analysis.