Palynology of the Early Pleistocene Kalibiuk and Kaliglagah Formations at Bentasari, Central Java, Indonesia

The Kaliglagah Formation in Central Java, of early Pleistocene age, yields abundant vertebrate fossils that predate the oldest occurrences of Javanese Homo erectus. This formation, together with the underlying Kalibiuk Formation, outcrops in the neighbourhood of Bentasari village, 20 km to the west of the classic outcrops at Bumiayu, Central Java. A 100 m exposure of this section was studied for palynology and sequence biostratigraphy. The analysis suggests that the section studied comprised two transgressive-regressive deltaic packages which probably formed as a result of two 41 kyr obliquity-driven climate cycles. It indicates that the Kalibiuk Formation comprises lower delta plain and delta front sediments that formed part of a large delta which was dominated by mangroves of the family Rhizophoraceae as well as Sonneratia (Sonneratiaceae). The lowermost part of the Kaliglagah Formation also formed on the lower delta plain of this delta, but the vegetation consisted mainly of the mangrove fern Acrostichum (Pteridaceae), together with the mangrove palm Nypa and the climbing fern Stenochlaena palustris (Blechnaceae). The upper part of the studied section of the Kaliglagah Formation formed on the upper delta plain in an open freshwater swamp setting vegetated mainly with Jussiaea (Onagraceae), Pandanus (Pandanaceae), Hanguana (Hanguanaceae) and Polygonum (Polygonaceae). The terra firma vegetation during time of deposition of the succession consisted of grassy savanna in the lowlands, indicating a strongly seasonal climate, and montane forests with Podocarpaceae in the upper catchment. The swamp and terra firma vegetation succession are compared to that in Perning, East Java, and other Javanese hominid sites.

The Kalibiuk and lower part of the Kaliglagah Formation, and also the Pucangan Formation at the Perning Homo erectus site, yielded the age-restricted palynomorph Stenochlaenidites papuanus, the parent plant of which went extinct across Sunda during the early Pleistocene, emphasising the older age of these localities compared to other Javanese hominid sites, such as Sangiran and Trinil where this taxon is missing.