A late Middle Pleistocene lowstand valley of the Solo River on the Madura Strait seabed, geology and age of the first hominin locality of submerged Sundaland

The island of Java (Indonesia) is renowned for its Pleistocene hominin-bearing vertebrate fossil sites. Recently, a marine sand extraction work in the Madura Strait, off the coast of Surabaya, hit upon vertebrate-rich sandstones. More than 6000 vertebrate fossils have been retrieved from the dredged sand, amongst which are two skull fragments ascribed to Homo erectus. The fossils form the first vertebrate record from submerged Sundaland, the lowland plains that connected the great islands of western Indonesia to the Asian mainland during Middle and Late Pleistocene lowstands. Here we present the results of a comprehensive study of the age, depositional background and landscape setting of the subsea fossil locality. The fossiliferous sandstones form the fill of a lowstand valley of the Solo River. The material was OSL-dated to 162 +/- 31 and 119 +/- 27 ka, which links the valley to the lowstand of MIS6. Fluvial backfilling was probably related to the stage of rising sea-level in the run-up to MIS5. The top of the valley fill consists of marine sandstones, pointing to valley drowning and a change to estuarine conditions, probably during peak highstand conditions of MIS5e. The Madura Strait submerged valley is of similar age as the Solo terrace of Ngandong, one of the richest Homo erectus sites of Java and regarded as yielding the youngest record of this species.