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Palaeoenvironmental records and radiocarbon dating at Niah Caves in north-eastern Sarawak M. Bird, C. Hunt and G. Barker

Palaeoenvironmental records and radiocarbon dating at Niah Caves in north-eastern Sarawak

M. Bird, C. Hunt and G. Barker

The Niah caves are located on the edge of the Gunong Subis, a limestone massif on the coastal plain of northeastern Sarawak. Deposits in the caves contain a remarkable record of human occupation dating back into the Pleistocene. The caves were first excavated in the 1950s and the most notable discovery at that time was a human skull (the so-called "Deep Skull"), together with charcoal that yielded a radiocarbon date of c.40,000 years BP. The skull provides the earliest evidence for human settlement on Borneo, but both the stratigraphic context of the skull and the validity of the radiocarbon dates are uncertain, due to a poor understanding of the stratigraphy during the initial excavations and to the fact that radiocarbon dating was in its infancy at the time the samples were dated.

The Niah Caves Project is re-investigating the archaeology of these sites in an effort to establish a coherent stratigraphy and chronology for the deposits. Another aim of the project is to situate the archaeological findings within a regional palaeo-environmental framework. Work at the Australian National University has focused on the use of carbon-isotopes and radiocarbon dating in support of the aims of the larger multidisciplinary and multi-institution project. Samples of charcoal have been dated from positions stratigraphically above the putative location of the Deep Skull. The two samples closest to the skull returned ages of 42,600 ± 670 BP and 41,800 ± 620 BP. These samples were single fragments of charcoal, deposited on the surface of brown silt deposit immediately prior to the covering of both the brown silt deposits and the skull by a debris flow of guano, originating from further inside the cave. The ages of these samples therefore date the debris flow, and provide an upper age limit for the Deep Skull.

Organic carbon from the terminal portions of two speleothems from the cave were dated and returned ages of 4,800 ± 50 and 16,200 ± 120 BP. Two samples from the thick stratified sequence of guano in the cave interior were also dated. A sample from one metre's depth yielded an age of 13,700 ± 90 BP and another from four metres depth returned an age of 29,500 ± 250 BP. The isotopic composition of both speleothem and guano samples suggest a dominance of C3 (forest-derived) carbon in the area of the cave at all these times. The deposit of guano in the interior of the cave is around 10 metres thick and may therefore yield a long record of environmental change in the cave area. Coring of this deposit is planned in 2002.

Sediment cores immediately outside the cave penetrated a mangrove peat relating to a mid-Holocene sea-level highstand, confirming that the caves were situated on an island during the mid-Holocene. The carbon-isotope record of another core from a freshwater lake 50 km east of the caves at 240 m a.s.l., suggests a dominance of forest vegetation in the region back to at least 8,000 BP. Taken together, the sparse isotopic evidence available at the present time suggests a continuity of forest cover in the area since before theLast Glacial Maximum.