Diagenetic processes in Quaternary fossil bones from tropical limestone caves

Abstract

Quaternary fossils from limestone caves bear various diagenetic features due to the complex nature of sedimentary processes. However, few studies have addressed the problem of diagenetic changes in fossils from tropical-wet environments. We study Quaternary fossil bones from different sites of a tropical limestone cave in northeastern Brazil. These fossils show diverse diagenetic features. The approach encompassed the use of scanning electron microscopy, Raman spectroscopy, and X-ray diffraction to understand the modification of the fossil bone structure, chemical composition, and mineral assemblage during the diagenesis processes. We describe a model for fossil diagenesis in tropical limestone caves that involves early and advanced diagenetic stages, which produce two routes with different endmembers. The diagenesis in the cave alters the crystallinity and ordering of hydroxyapatite. The recrystallization of hydroxyapatite appears to be strongly influenced by dripping water that is rich in calcium carbonate, which leads to crystal formation with higher crystallinity. In the absence of calcium carbonate, hydroxyapatite diagenesis involves crystal growth but not necessarily dissolution of the original material, which enables remarkable preservation of the biological structure.

Microbial degradation of Pleistocene permafrost-sealed fossil mammal remains

“…This contributes to the bioapatite composition in extant remains, where the actual carbonate content varies among different species and increases with age within a given species (Legros et al, 1987). Mineral re-crystallization into hydroxyapatite results from postmortem unstable conditions (e.g., Sillen and Parkington, 1996; de Sousa et al, 2020). The deficit in the sum of oxides measured by the EMP analysis could be a result of the porous structure of the bone material and the presence of organic components or carbonates or both.…”

Bone Molecular Modifications Induced by Diagenesis Followed-Up for 12 Months

“…They suggest that mineral dissolution has a minor contribution. Crystallization occurs by nucleation and precipitates in the free space left by the previous mineral or in the vascular structure [ 4 ].…”

“…Bone diagenesis hampers the work of forensic investigators in the evaluation of skeletal remains, such as age, sex and postmortem intervals. Numerous studies have focused on the evaluation of diagenetic processes over long timescales (~millions of years) [ 4 , 5 , 6 ] but fewer over short timescales (between days and thousands of years) [ 7 , 8 ]. Bone diagenesis was evaluated by histology [ 9 ], chemistry [ 10 ] or physicochemical [ 11 ] approaches, allowing a better understanding of the complexity of the mechanism.…”

Determining the diagenetic paths of archaeofaunal assemblages and their palaeoecology through artificial intelligence: an application to Oldowan sites from Olduvai Gorge (Tanzania)

“…This explains why cut marks from PTK are macroscopically better preserved than cut marks from DS; the latter also displays a higher degree of alteration, with several low‐topographic areas exhibiting some leaching of the external cortical surfaces of fossils in addition to a higher degree of manganese‐staining. Manganese coating on bones is typical of humid environments and caves (Cukrowska et al ., 2005; Shahack‐Gross et al ., 1997; de Sousa et al ., 2020; Stathopoulou et al ., 2013). Manganese becomes more abundant in acidic soils and decreases as pH increases (Goldberg and Macphail, 2009).…”