Microstratigraphic Analyses of Depositional Environments Contextualising the Earliest Hominin Remains from Flores Island, Indonesia

Vito C. Hernandez1,2*, Mike W. Morley1,2, Unggul P. Wibowo3, Ruly Setiawan4, Iwan Kurniawan4 and Gerrit D. van den Bergh5

We present the results of a microstratigraphic analyses on the three key stratigraphic units that contextualised the earliest hominin remains excavated from the Mata Menge site, Flores Island, Indonesia. These fossils, recognised as ancestral to Homo floresiensis, represent an important assemblage to understand the evolutionary relationships, behavioural patterns, and adaptive strategies of some of the earliest humans to have crossed from the mainland to islands of Southeast Asia during the late Early Pleistocene. Sediment micromorphology and energy dispersive spectroscopy were used to investigate sediment structure, mineral content and post-depositional alteration across a palaeosol, a fluvially deposited sediment, and a volcanic mudflow. The results reveal that the hominin remains excavated from the fluvial sediments were likely redeposited from a semi-arid alluvial soil. This suggests the increasingly dry environment of the island’s early human inhabitants, and why their fossils preserved well in fluvial deposits and not in the alluvial plains in which they ranged. Together, these results confirm the environmental conditions revealed through isotopic records and paint a picture of the conditions that likely drove the earliest inhabitants of island Southeast Asia towards rivers, streams and coastal environments.