Post-depositional alteration of humid tropical cave sediments: Micromorphological research in the Great Cave of Niah, Sarawak, Borneo

The post-depositional alteration of cave sediments is of critical importance for the recognition, identification and investigation of geoarchaeological and palaeoenvironmental evidence. There have been relatively few studies of tropical cave sediments using micromorphology and this work represents one of the most detailed with 26 samples taken from deposits in the West Mouth of the Great Cave of Niah that cover the last >∼55,000 BP, and contain the earliest known evidence for the remains of modern humans in Southeast Asia. Cave sediments situated in the humid tropics are subject to relatively high temperatures and moisture conditions that promote high rates of chemical alteration and geomorphic change. This paper outlines those post-depositional features that occurred in situ in the West Mouth and include: translocation and concentration; bioturbation; excrement; bone alteration; plant alteration; clast alteration and guano decomposition. It examines their implications for recognising past human activities (e.g. fire-altered materials), the preservation of archaeological remains, the nature of palaeoenvironments and of localised physical and bio-geochemical processes.