Reconstructing the Quaternary landscape evolution and climate history of western Flores: an environmental and chronological context for an archaeological site

The recent discovery of a late-surviving new human species, Homo floresiensis, in western Flores has accentuated our lack of understanding of the history of the genus Homo in Asia and of the environmental challenges that may have influenced these hominins. Western Flores contains a wealth of archaeological and palaeoanthropological material with far-reaching implications for human evolution and for Indonesian, Australian and world archaeology. But the interpretation of this evidence has been hindered by a limited Quaternary context and age control for complex stratigraphies in a region of great geological instability and widespread environmental change. Liang Bua in western Flores is a key site in the Indonesian archaeological record, providing evidence of cave occupation by Homo floresiensis and Homo sapiens, and human evolution and dispersal on the eastern side of Wallace’s Line. In this study, archaeologically-relevant information has been gleaned from an interdisciplinary approach to the analysis of this site, and has established the timing of key events, such as the first exposure of the cave and the nature of, and influences on, human occupation of the cave. This approach incorporated studies of landscape evolution, river terrace and cave development, sedimentology of cave sediments, palaeoclimate signals in speleothems, and a dating strategy utilising novel approaches to luminescence dating. The research reported here provides a chronological and environmental backdrop to the human occupation of Liang Bua. A maximum age of cave occupation is shown to correspond to the time of cave exposure (~190 ka), which also represents a minimum age for the human habitation of the area. In addition, this study has established an age range for the occupation of the cave by Homo floresiensis (95–11 ka), the time of the most intensive phases of occupation (74–61 and 17–11 ka), the depositional age of the holotype skeleton (36–14 ka), and the age of the oldest human skeletal remains found on Flores (95–74 ka). Through the integration of techniques, a framework for terrace development and landscape evolution has been developed to establish the Quaternary Westaway, setting in which the cave was formed and evolved. These techniques have also defined a sequence of geomorphological and sedimentological changes in the cave, enabling the reconstruction of the occupational environment. At least two zones of occupation have been identified: a zone established ~74–61 ka, and a later zone established ~18 ka. The environmental backdrop for the arrival and dispersal of humans throughout Indonesia has been established via a palaeoclimatic and palaeoenvironmental analysis of speleothem records. These records contain evidence of multiple wet phases (110–98, 82–65, 49–39 and 17–5 ka) and a flourishing fauna. The timing of these wet phases correlate with evidence for channel and flowstone formation, episodic erosion events, and the most intensive periods of occupation in the cave. There is also evidence for a prolonged period of reduced rainfall (36–17 ka) in an organic-poor environment, the timing of which correlates with evidence of reduced erosion, pooling and less intense occupation. These correlations suggest that the occupational success of Homo floresiensis in this area was related to the contemporaneous environmental conditions, which, combined with the evidence for at least two volcanic events (one of which may have forced human migration), establish a link between hominids and their environment. The results of this research indicate the value of using an interdisciplinary approach to investigate and interpret archaeological sites in Southeast Asia. By providing an environmental and chronological context for important archaeological finds, we can develop a better understanding of the prehistory of Homo in Asia