New Insights into the Stratigraphic Context and Typology of Stone Artifacts from the Kali Aur, Bumiayu (Central Java)

Eugenius Olafianto Drespriputra Wisnuwardhana1*, Yan Rizal1, Mika Rizki Puspaningrum1, Sofwan Noerwidi2, Thomas Sutikna2, Harman Dwi Rachmadan1,2, Muhammad Wildan Fadlillah1,3, Taufiqurrahman Setiawan2, and Yves Belgiaswara Susilo1,2

In July 2019, a survey conducted by the Regional Agency for Archaeological Research in the Special Region of Yogyakarta reported the first Paleolithic implements from ancient deposits at Bumiayu. Five artifacts were recovered from Kali Gintung, Kali Bodas, and Kali Cisaat, including choppers and chopping tools made of silicified limestone, chalcedony, silicified andesite, and a large flake of fossilized wood. Here we highlight the Kali Aur as an equally promising locality for examining stratigraphic context and the technological characteristics of stone tools. A measured stratigraphic section along the Kali Aur documents ~573 m of Quaternary succession (29 units) based on lithology, sedimentary structures, lithofacies associations, and fluvial architecture. Our interpretation indicates that during the Middle Pleistocene the Aur area had developed into a relatively stable terrestrial setting dominated by fluvial environments, enabling repeated activity surfaces and favouring the concentration and preservation of artifacts within channel and bar deposits, alongside raw-material horizons. The Aur assemblages yield abundant lithics made primarily of chalcedony, silicified coral, silicified tuff, and jasper, with silicified wood also present. Typological categories include pebble tools, chopper tools, chopping tools, flakes, test blocks, and large cutting tools. The assemblage is dominated by massive stone tools, and the majority of artifacts show bifacial shaping, suggesting heavy-duty reduction strategies alongside flake production. Raw materials occur both in situ within stratified layers and as surface finds lacking stratigraphic context, providing a robust basis for provenance-focused studies linking raw-material availability, reduction sequences, and depositional processes within a dynamic Middle Pleistocene fluvial landscape.