Early Pleistocene dates and sedimentary cycles for new Bapang Formation hominins, Central Java, Indonesia

The Sangiran dome, in Java's Solo basin, has yielded nearly 80 Homo erectus fossils, around 50 of which have known findspots. With a 1.66 [+ or -] 0.04 Ma [.sup.40]Ar/[.sup.39]Ar date on pumice reportedly associated with S27 and S31 (Swisher et al. 1994 - Science 283: 1118-1121) the dome may offer evidence that early Homo dispersed to East Asia during the earliest Pleistocene. Unfortunately, this pumice was sampled at Jokotingkir Hill, a central locality with complex litho-stratigraphic deformation and dubious specimen provenance (Larick et al. 2000 - Int. J. Primatol 21: 731-759). We address the sedimentary framework and [.sup.40]Ar/[.sup.39]Ar age for Homo erectus in the dome's SE quadrant, where fossiliferous Bapang (Kabuh) sediments have their largest exposure, least deformation, most complete tephro-stratigraphy, and greatest number of hominin findspots. At five locations, we identify a sequence of sedimentary cycles in which 28 hominin fossils are associated with epiclastic pumice. Eight hornblende separates produce [.sup.40]Ar/[.sup.39]Ar plateau ages ranging from 1.51 [+ or -] 0.08 Ma at the Bapang/Sangiran Formation contact zone, to 1.02 [+ or -] 0.06 Ma for the top of the hominin-bearing sequence. An intermediate level, which produced S17 and three nearly complete new crania, has an [.sup.40]Ar/[.sup.39]Ar age of about 1.25 Ma. The newly dated crania are from the following locations: Tanjung, Tjg-1993.05, comprising the calvarium, most of the maxilla with four teeth, and separate left temporal; Grogolwetan, Gwn-1993.09, conserving the left frontal, the sagittal part of the right frontal, parietals, posterior temporals and the occipital; and Sendangbusik, Sbk-1996.02, consisting of the temporals, portions of the parietals, and the occipital. The Bapang Formation represents an aggraded fluvial system built up on a number of energetic cycles. The new [.sup.40]Ar/[.sup.39]Ar dates are consistent within cycles and the sequence of dates matches the stratigraphy. Finally, new taphonomic evidence derived from the cycles suggests that H. erectus was living at or adjacent to areas where its fossils are found.