Quaternary megafauna bone diagenesis preserved in natural tank deposits from Brazil: Taphonomic and paleoenvironmental aspects

摘要

Tanks are natural, mostly elliptic depressions formed in the igneous or metamorphic basements of northeastern Brazil. The taphonomy of the fossil vertebrate assemblages preserved in tank deposits has been intensely studied. However, so far the focus was mainly on biostratinomic aspects. This paper presents a diagenetic analysis of megafauna bone thin sections from four tank deposits in northeastern Brazil, the interpretation of their diage-netic histories and a comparison between the sites. The geographic proximity of the sites and their similar pa-leoclimatic settings were the likely factors responsible for the similarities observed among the thin sections of different tank deposits. In contrast, some striking differences resulted from the particular characteristics of the areas in which the tank deposits are located, most notably the local geological settings and their distances from nearby drainages. Comparisons with other studies showed that the availability of water and conditions that favored permineralization were common in northeastern Brazil during the Quaternary. Finally, diagenetic contrasts among bones thin sections from the same tank evidence temporal mixing in the vertebrate accumu-lations within these natural-trap deposits.