Archaeological Sediments as Artefacts

Aitken, Jefley Jane

This thesis focuses on archaeological sediments which are treated as artefacts to reconstruct the prehistoric environment of a 12 m high mound, Khok Phanom Di, in southeastern Thailand. This cultural landform comprises midden, cemetery, industrial and living areas, and overlies a culturally sterile substrate. Eliciting the environment of this substrate is a primary research aim. Early studies indicated that the Holocene marine transgression peaked c.2000 BC (4000 BP) in Southeast Asia (some two thousand years later than the rest of the world) and that the transgression reached five metres above current sea levels (van der Kevie 1971, Geyh et al. 1979). The occupation of Khok Phanom Di dates from c.2000 BC (4000 BP), and early hypotheses regarding the initial environment included offshore islands, barrier spits, sand dunes, closed canopy coastal mangrove forest and a major river estuary. None of these are corroborated by the geoarchaeological data, which point to a stream bank in a floodplain setting.
Chemical and petrographic techniques, bulk composition, grain size distributions, x-ray diffraction and x-ray fluorescence are used to analyse the sediments, and the geomorphology of the region is critically reviewed. These techniques define the sediments geochemically, mineralogically and sedimentologically so that the environment in which they formed can be inferred. As the mound is an entirely cultural deposit (not a geological structure), this aspect includes culturally induced diagenesis. Comparisons of geological deposits and archaeological sediments are used to infer the cultural activities that built up the mound and to identify geoarchaeological signatures. The analyses ascertain the sediment's source, transporting agent and penultimate basin of deposition: weathered leucogranite, water and floodplain. Ceramic industry accoutrements such as potsherds, microsherds, raw material caches and potting tools make up 15-20% of the mound's volume, and another 16-20% comes from shell midden. The range of environmental sources throws light on th,e cultural behaviours and choices that transported the sediments to the mound.
The results of all the geoarchaeological analyses, including a geomorphological review of the region and investigations into coastal morphology of· mangrove habitats, are complementary and consistent. The Holocene marine transgression peaked c.3600 BC (5600 BP) in the Gulf of Thailand and the site was up to 20 km inland when settled. There is no modern evidence indicating a transgressive high over two or three metres above current mean levels and there is no evidence for ma1or oscillations within the broad regional regression. The basal non-cultural layer is consistent with the sediment characteristics of a levee, a river bank built up by the overflow of fine sediments in flood waters. This layer has very little carbonate and organic matter, no foraminifera and some freshwater sponge spicules. It comprises nearly 90% silt of inferred granitic origin and has textural and mineralogical traits that are consistent with general freshwater floodplain deposits analysed elsewhere round the Bangkok plain.
Increased siltation led to the non-viability of local waterways which the people of Khok Phanom Di used for exporting pottery and transporting raw materials. Siltation also caused downstream disruption to favoured estuarine food sources. The breakdown of the transport network resulted in reduced access to estuarine and coastal resources and effectively increased the distance to pottery markets. For these reasons, the site of Khok Phanom Di was abandoned about 1400 BC (3400 BP) by the professional pottery makers.

xxiv, 152, [29] leaves : ill. (some col., some folded) ; 30 cm.

1992Aitken