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

Examination of a phytolith assemblage from the archaeological site of Carpe nter's Gap I provides an hitherto unrecognised source of vegetation history for the tropical savannah region of north western Australia. Two predomina nt mechanisms contributed to the formation of the phytolith assemblage: fir stly, the introduction of phytoliths in plant materials brought in by human s. and, secondly, the introduction of phytoliths contained in faecal pellet s deposited by animals. Separating the effects of both mechanisms enables l ocal vegetation patterns, and, by inference, climatic conditions, to be rec onstructed. The period ca. 40,000 years BP was probably wetter than today, allowing the southerly expansion of palms beyond their present day distribu tion. Grassland compositional changes occurred by ca. 33,000 years BP, prob ably resulting from a combination of lowered rainfall, decreased temperatur es and possibly Aboriginal firing activities, A reduction in palm at a simi lar time, followed by its complete disappearance, in association with the l oss of Ulmaceae prior to the Last Glacial Maximum (LGM) indicates a continu ed trend in decreasing water availability. An abundance of Cyperaceae, spon ge spicules and diatoms during the LGM. when considered in conjunction with the other evidence. possibly represents altered human behaviour in respons e to increased aridity. (C) 2001 Elsevier Science Ltd and INQUA. All rights reserved.