The paleohydrological context of the Iron Age floodplain sites of the Mun River Valley, Northeast Thailand1

Abstract

Many Iron Age sites on the flood plain of the Mun River in northeast Thailand are encircled by channels commonly known as "moats." Also, the sites are closely associated with complex paleochannels of the river. A comparison between the seemingly human-constructed moats and paleochannels provided an opportunity to assess the relationship between prehistoric human settlement and paleohydrological conditions. In this study, the results of physical, sedimentological, and geochemical analyses are used to characterize sediments deposited within the channels around the Iron Age site of Ban Non Wat and within a paleochannel at nearby Ban Non Ngiu. This allowed us to test the results of previous research that has suggested significant changes in the floodplain hydrology and the geoarchaeologically important conclusion that Iron Age human activity was associated with one particular paleohydrological phase. Our analyses broadly confirm the results of previous stratigraphic studies, but add detail regarding sedimentation processes. The evidence indicates that there are significant sedimentological differences within the complex of archaeological channel features, differences that provide critical evidence for the formation and sedimentation processes of the channels. More importantly, comparison between the archaeological features and the natural channel fills highlights the relationships between the archaeological sites and landscape. Drawing also on previously published chronological, geomorphological, and stratigraphical data, it is possible to place the sites into a floodplain hydrological regime that may have been unique to the Iron Age. Specifically, the moats may have been constructed in response to enhanced water availability on the floodplain. The sites, therefore, may reflect a human response to increased availability of water beyond the main river channels. This water supply, however, appears to have been short-lived (centuries at most), and with its loss, the human adaptation to this enhanced natural resource became unviable.

Integrating social and environmental change in prehistory: A discussion of the role of landscape as a heuristic in defining prehistoric possibilities in northeast Thailand

“…Since the encircling earthworks imply a relationship between hydrological conditions and prehistoric settlement, it is reasonable to assume there was a particular association between environment and society in this region. Environmental examination of these sites and their landscapes (Moore 1988a(Moore , b, 1992Boyd et al 1999a, b;Boyd and McGrath 2001a, b;McGrath and Boyd 2001;Boyd 2004Boyd , 2007Boyd , 2008Boyd and Habberfield-Short 2007;Habberfield-Short and Boyd 2007;McGrath et al 2008) has progressed to a point where integration with the archaeology is possible (Figure 1). We now discuss the geoarchaeological and archaeological materials and data specific to our case study before returning to the wider implications of the case study in later sections of this paper.…”

“…Initial recognition of the sites was founded on the identification of encircling earthworks interpreted as defensive and water-management features. Subsequent geoarchaeological study (Boyd et al 1999a, b;McGrath and Boyd 2001;McGrath et al 2008) developed a model of the earliest settlement being along prehistoric rivers. Importantly, these rivers represented a period where the floodplain was better watered than at present, and where the rivers that did flow across the floodplain were more abundant, of a different form, and differently located to those at present.…”

Laterite nodules: A credible source of iron ore in iron age northeast Thailand?

“…Whereas laterite fragments are commonly abundant at these sites, McGrath, Boyd, and Bush (2008) have demonstrated that most of the laterite is not cultural and has been redeposited from surrounding sediments. Thus there is no actual evidence that laterite and slag share a relationship.…”

“…This is a flat region bounded by the Dang Raek Range to the south, the Phetchabun upland to the west, and the Mekong River to the north and east (Figure 1). Many of the archaeological sites are distinctive because of their encircling banks and moats (Higham, 1989(Higham, , 1996Boyd, Higham, & McGrath, 1999;Boyd, 2007;McGrath, Boyd, & Bush, 2008). There is a history of assuming these features to be of a predominantly defensive function, with further related assumptions regarding sociopolitical structure.…”

Social Variation and Dynamics in Metal Age and Protohistoric Central Thailand: A Regional Perspective

“…A phenomenon of long gradual growth in settlement patterns, without abrupt change, was also witnessed in the Phimai region of northeast Thailand where intensive regional exchanges and two levels of economic hierarchy occurred around midiron age (200 b.c.-a.d. 300) . Many constructions of encircling earthworks in this area have been argued to have addressed water availability concerns rather than to serve political purposes (Boyd 2008;McGrath et al 2008). Here such changes occurred around the mid-to late iron age (a.d. 0-600) and preceded any clear evidence for political centralization and the emergence of states.…”