A palaeontological and geochemical analysis of vertebrate fossils from a Late Quaternary cave deposit in southeastern Australia with a particular focus on bone surface coatings: Blanche Cave palaeontology and geochemistry.

Abstract

The Naracoorte Caves National Park hosts many well-preserved cave fossil deposits that span the last 500 ka. The sedimentary sequences and fossil bone assemblages across over 50 sites provide insights into past climatic conditions as well as faunal responses to Pleistocene climate change, covering significant events such as the Last Glacial Maximum and the extinction of Australian megafauna. However, faunal assemblages can be easily biased by variations in accumulation mode or bone preservation. In this study, I conducted a palaeontological and taphonomic analysis on fossil bone material from an unfinished excavation in Chamber 1 of Blanche Cave, focussing on bone surface coatings to infer the post-burial conditions of the site. SEM results identified three different coatings: black coatings were manganese, white coatings were gypsum, and crystalline coatings were phosphate. Oxidation of ions by chemolithotrophic microorganisms is hypothesized to be the main mechanism for the formation of the three coatings. Bat guano also plays an important role in altering the soil environment, such as providing sulphur and phosphorus and lowering soil pH. This potentially allows for gypsum and phosphate to be used for tracing past bat activity. The study site also agrees with other synchronous sites at the NCNP (Third Chamber, Blanche Cave and Wet Cave) in terms of its sediment sequence and faunal assemblages with small variability, likely due to variations in entrance size and distance from the accumulation point. Further investigation of authigenic minerals and surface coatings is needed as there is potential for them to be used as environmental proxies. More geochronologic work is needed to more accurately place the site material in context.