DEPOSITIONAL AND ENVIRONMENTAL CONTEXT FOR HOMO ERECTUS INTO THE SOLO BASIN, CENTRAL JAVA, INDONESIA

On-going work in the Sangiran dome, the primary stratigraphic window for the Plio-Pleistocene deposits of the Solo Basin of Central Java, is focusing on identifying depositional environments and paleopedological settings associated with early Homo erectus dispersal into East Asia. The stratigraphically lowest H. erectus fossils in the basin occur in the upper reaches of the Sangiran Formation. H. erectus fossils increase in abundance in the overlying Bapang Formation, indicating a hominin species well established on the Sunda subcontinent. The Sangiran Fm. consists primarily of fossiliferous shallow marine siltstones and mudstones that grade upward to lacustrine siltstones, mudstones and lignite. Fossil wetland soils in the upper part of the Sangiran indicate that fully emergent, lake or marsh edge environments were present when Homo erectus arrived in the area. The Bapang Formation represents a significant sedimentary environment change to an aggrading fluvial system. The Bapang consists of a series of upward-fining cycles with soil formation in the upper, fine-grained sediments of each cycle. Soil carbonate content and the abundance of grass rizoliths increase upsection in Bapang paleosols. A series of ⁴⁰Ar/³⁹Ar plateau ages on hornblende separates from epiclastic pumice in the deposits indicate that H. erectus arrived before 1.5 Ma, and continued to occupy the area for at least 500,000 years. Sediments and associated paleosols indicate overall aggradation and drying through the early Pleistocene and the presence of tropical grassland/savanna during much of the time H. erectus was present.