Taphonomy, paleoecology and chronology of a late Quaternary tank (natural reservoir) deposit from the Brazilian Intertropical Region

Abstract

The Brazilian Intertropical Region (BIR) abounds with tank (natural reservoir) deposits, a primary source of late Quaternary megafauna remains. However, most of these important deposits lack comprehensive taphonomic analysis. In this study, we conducted a taphonomic analysis of Quaternary vertebrates from a specific tank deposit located at Fazenda Charco (Poço Redondo, Sergipe State), Brazil. We aimed to: (i) reconstruct the biostratinomic processes that influenced the deposition of vertebrate remains; (ii) interpret some fossildiagenetic features; and (iii) compare our findings with other tank deposits to highlight the main preservation patterns among these deposits. Additionally, we discuss the paleoenvironmental and paleoecological aspects of this vertebrate assemblage. The paleocommunity comprised eighteen individuals, including megamammals and reptiles, with a total of eleven taxa identified in the tank deposit, indicating a highly diversified assemblage. Eremotherium laurillardi and Toxodontinae indeterminate accounted for more than one individual each. Despite the high diversity, taphonomic features suggest the dominance of E. laurillardi in the assemblage and the preservation of bones transported from moderately distant locations to the tank deposit. Furthermore, Fazenda Charco exhibits a complex tank deposit characterized by various taphonomic signatures, including abrasion, trample marks, weathering, fragmentation, staining colors and bioerosions. These findings indicate that the bones underwent reworking events and were exposed to environmental conditions before their final burial. By integrating our taphonomic results with available isotopic, pollen, and speleothem data, we infer that a dry forest, resembling the extant Caatinga biome, prevailed during the past 42,000 years. This suggests a predominantly arid environment with a mosaic of phytophysiognomy dominated by herbs and shrubs. The further integration of taphonomic and paleoecological analyses of fossils from tank deposits will contribute to a more refined reconstruction of the paleoenvironmental scenario and the ecological interactions that occurred during the late Quaternary.