Emergence of the Earliest Exposed Land in the Bumiayu Sub-Basin, Central Java, and Its Implications for Early Hominin Presence in Northwestern Java

Harman Rachmadhan1*, Aswan2, Thomas Sutikna1, and Sofwan Noerwidi1

The Bumiayu Sub-Basin in Central Java preserves a key Plio–Pleistocene record of environmental change from shallow-marine and marginal-marine settings to estuarine, fluvial, and fully terrestrial landscapes. This study examines stratigraphic, sedimentological, paleontological, and geomorphological evidence to identify the earliest emergence of exposed land in the Bumiayu area and to assess its archaeological significance in relation to early hominin presence. Measured sections, facies associations, paleosol development, lignite-bearing intervals, freshwater molluscan assemblages, vertebrate fossil occurrences, and channelized coarse clastic deposits collectively indicate a progressive regression and terrestrialization of the basin. These changes mark the establishment of stable subaerial surfaces, freshwater availability, vegetated floodplains, and lowland habitat mosaics that would have supported vertebrate occupation and created favourable conditions for hominin movement and landscape use. The occurrence of terrestrial vertebrate remains together with the presence of intact lithic raw materials within fluvial deposits further suggests that Bumiayu may have formed part of an important ecological and geographic corridor in northwestern Java during the Plio–Pleistocene. Although direct evidence of hominin occupation remains limited, the geological and paleoenvironmental framework strongly indicates that the first emergence of land in Bumiayu constituted a critical precondition for biotic expansion and possible early human activity. These results highlight the importance of integrating geological and archaeological perspectives in reconstructing early human-environment interactions in Java.