Identification and importance of critical depositional gaps in pitfall cave environments: The fossiliferous deposit of Cuvieri Cave, eastern Brazil

Abstract

The majority of extinct Brazilian late Quaternary mammal (i.e. megafauna) remains comes from cave deposits and was retrieved through excavations lacking detailed stratigraphical context. This poses a major problem since these deposits present multifaceted processes of formation. Based on the meticulous excavation of a pitfall site within Cuvieri Cave, Minas Gerais, eastern Brazil, this article describes a critical, albeit subtle, temporal discontinuity between different fossiliferous sedimentary facies and discusses its significance to the contextualization of the paleontological remains recovered from the site. The discontinuity was described based on sedimentary analyses, bone deposition processes, taxonomy and AMS radiocarbon chronology. Two facies were distinguished and named according to their color and texture: an upper dark brown silt-loam (BSL) and a lower dark reddish brown silt-loam (RBSL). Besides color differences, they present differences in grain size distribution and chemical composition. These analyses show that the RBSL has in its composition only half the sand and one third more the silt than BSL. It also shows that mean percent values for the RBSL in comparison to the BSL are higher for silica (42.35 versus 15.80), aluminum (18.63 versus 7.58) and iron (8.45 versus 3.79) and lower for calcium (10.07 versus 36.14) and volatiles (13.86 versus 30.10). These differences are attributed to changes in sediment source and entrance route. Differences were also observed in the faunal remain analyses. RBSL has abundant megafauna remains originally deposited within this facies, while the scarce megafauna material found in BSL is the result of mixing processes. Despite these differences, animal entrapment is considered the best scenario to explain bone accumulation in both facies. AMS radiocarbon dates indicate that the BSL was deposited during the Holocene, with dates ranging from 8580calyr BP to the present, while the RBSL deposition dates to the Holocene/Pleistocene transition (13,600–10,660calyr BP). Radiocarbon dating also indicates that the subtle erosional surface that limits both facies represents a temporal gap between a minimum age of 8.4calkyr BP and a maximum age of 11.0calkyr BP. The recognition of this discontinuity allows for a more accurate interpretation of bone accumulation, enabling the differentiation of faunal assemblages that might otherwise be considered part of a continuum.