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Sedimentological investigations and geochemical analyses of the Robertson Cave deposit, 7 km south of Naracoorte, South Australia, document a palaeoenvironmental record for the Late Pleistocene and Early Holocene. Three distinct depositional episodes spanning the interval 32 - 8 ka are represented by over 4 m of sediments exposed in the chamber 2 excavation pit. The oldest of the three, the lower unit (>30 ka BP) is dominated by reddish and brown sandy silts. A 20 cm band of red silt horizons that cap this unit contain enriched δ15N values (12 - 15‰), low C/N ratios, significant SO3 (20%) and CaO (18.5%) contents, a high alkyl-C component and phosphorus-rich mineralogy. These unique sediment horizons are interpreted as being derived from the accumulation of bat guano and degraded cave rock fragments. Their presence suggests a period of low sediment input into the cave, possibly reflecting the existence of a stable geomorphic environment prior to 30 ka. The time period 30 - 27 ka saw the rapid deposition of the middle unit, a sequence of coarser homogeneous sands that resulted in the entrance to chamber 2 becoming blocked. These horizon-less sediments, with clear aeolian features, are most likely representative of the drier conditions associated with the Last Glacial Maximum, which peaked at 20 - 17 ka. Deposition into the chamber recommenced at approximately 13 ka and continued until 8 ka, resulting in the accumulation of the upper unit, a sequence of silt, charcoal and organic matter rich horizons. Here, a shift to more 13C-depleted values (-25‰ to -27‰) is evident in the bulk soil organic matter and charcoal between 11 and 10 ka, possibly reflecting a shift from the dry Last Glacial Maximum to the wetter environs of the Holocene. The upper unit may also be a record of burning practices associated with Aboriginal migration to the area. [ABSTRACT FROM AUTHOR]

Abstract: Stable carbon and oxygen isotope ratios of tooth enamel carbonate were collected from both fossils (50–100ka) Tammar Wallaby (Macropus eugeneii) and Western Grey Kangaroo (Macropus fuliginosus) from a Late Pleistocene fossil deposit situated on Kangaroo Island, South Australia. δ 13C and δ 18O data were also obtained for modern equivalents of both species located proximal to the excavation site. Trace element compositions were collected for Sr, Ba, V, Cu, Zr, Y, La, Ca, Nd, and U for modern and fossil teeth, and for local soils. δ 13C data for fossil kangaroo and wallaby range between −5.0 and −18‰, while less 13C enriched values between −18 and −25‰ are observed in modern tooth enamel. Early-formed molars are 13C depleted by ∼2.5‰ compared to late-formed molars, consistent with isotopic offsets observed in modern molars, and with offsets observed from preservation of original biogenic compositions. Overall, carbon isotopes indicate a shift in diet and environmental conditions from C4-inclusive mixed habitats (woods and open grasslands) during the Late Pleistocene, to C3-only wooded and closed canopy habitats today. δ 18O values range between 23 and 30‰ and are indistinguishable for fossil and modern tooth enamel. Oxygen isotope compositions of plants and mammals correlate positively with local water compositions, and negatively with relative humidity. Thus, the lack of oxygen isotope differences for the Late Pleistocene vs. modern day teeth may be attributed to combined lower temperatures (decreasing local water δ 18O) plus decreased relative humidity (increasing plant and mammal δ 18O) in the Late Pleistocene. Trace element data from fossil and modern teeth and from fossil deposit sedimentary material indicate post burial chemical alteration. Excepting Ba and possibly Cu, concentrations of all other elements analysed (Sr, V, Zr, Y, La, Ce, Nd, and U) increased significantly relative to modern teeth (over an order of magnitude shift, with p ≤0.01 for t-tests and Mann–Whitney tests). This diagenetic process may have occurred during the Last Glacial Maximum (LGM), a period of localised wet conditions when significant amounts of soluble soil organic matter accumulated at the fossil site. Trace element analysis of local soils indicates that, relative to soils, teeth strongly prefer Sr and U [K D(fossil tooth/soil)∼10], and exclude Zr, Cu, and possibly V and Ba [K D ≤0.5]. Surprisingly, Rare Earth Elements (REEs) indicate K D values of ∼1. These data imply that Ba is a poor indicator of chemical alteration, while Sr, U, Zr, V, Y, and REEs are particularly sensitive to alteration. Comparisons with other palaeoclimate data suggest that the environmental change on Kangaroo Island from Late Pleistocene to present was greater than on the Nullarbor Plain. [Copyright &y& Elsevier]