PALEOENVIRONMENTAL RECONSTRUCTION DURING EARLY TO MIDDLE PLEISTOCENE USING STABLE CARBON ISOTOPE STUDIES, GRAIN SIZE ANALYSES, AND MORPHOLOGIC FEATURES OF PALEOSOLS AT A HOMO ERECTUS LOCALITY IN THE SOLO BASIN, CENTRAL JAVA, INDONESIA

Grain size analyses and stable carbon isotope studies of paleosols were used to reconstruct the paleoenvironment during the Early to Middle Pleistocene at a Homo erectus fossil site in the Sangiran Dome located in the Solo Basin of Central Java, Indonesia. Soil samples were collected from paleosols within the Sangiran and Bapang Formations. Homo erectus fossils occur from the upper part of the Sangiran Formation to the middle to upper Bapang Formation. The upper Sangiran Formation has sediment and paleosol characteristics indicating an organic rich lake margin or marsh environment, while the Bapang Formation represents a sandy braided stream environment with multiple fining upward cycles. Stable carbon isotopes analyses were used to examine the relative abundance of C3 and C4 plants that contributed to the soil organic matter during periods of stability represented by paleosols in the sequence. The d¹³C values of soil organic carbon become lighter up section from -13.6% (Upper Sangiran) to -24.8% (Upper Bapang). This suggests a shift from dominantly C4 flora to a mix of C3 and C4 flora with C3 flora dominant. The paleosol characteristics suggest that the C4 flora were wet tropical grasses, while the C3 flora may have been shrubs and trees adapted to a seasonal dry climate. The up-section drying trend indicated by soil morphology and vegetation changes may indicate a strengthening of the monsoon from the Early to Middle Pleistocene.