Environmental history of northwest Australia based on phytolith analysis at Carpenter's Gap 1

Examination of a phytolith assemblage from the archaeological site of Carpenter's Gap I provides an hitherto unrecognised source of vegetation history for the tropical savannah region of north western Australia. Two predominant mechanisms contributed to the formation of the phytolith assemblage: firstly, the introduction of phytoliths in plant materials brought in by humans. and, secondly, the introduction of phytoliths contained in faecal pellets deposited by animals. Separating the effects of both mechanisms enables local vegetation patterns, and, by inference, climatic conditions, to be reconstructed. The period ca. 40,000 years BP was probably wetter than today, allowing the southerly expansion of palms beyond their present day distribution. Grassland compositional changes occurred by ca. 33,000 years BP, probably resulting from a combination of lowered rainfall, decreased temperatures and possibly Aboriginal firing activities, A reduction in palm at a similar time, followed by its complete disappearance, in association with the loss of Ulmaceae prior to the Last Glacial Maximum (LGM) indicates a continued trend in decreasing water availability. An abundance of Cyperaceae, sponge spicules and diatoms during the LGM. when considered in conjunction with the other evidence. possibly represents altered human behaviour in response to increased aridity. (C) 2001 Elsevier Science Ltd and INQUA. All rights reserved.