Sediment and soil characteristics and an evaluation of their applicability to the irrigation history in Sigiriya, Sri Lanka

Abstract

Palaeoecological studies were conducted in the Sigiriya area in 1992–1995. This paper reports on pilot studies and tentative interpretations regarding sediments deposited in tanks and canals, together with buried soil surfaces under embankments, i.e. bund-fill-ings. Various types of in situ sediments and accumulations served as reference material. The methods applied comprise siliceous
microfossils, pollen, organic carbon, carbonate content, grain size distribution, plant macrofossils and measurements of mineral mag-netic concentrations. Oxidising conditions constitute a problem for the preservation of organic microfossils and macrofossils. The results of the analyses of siliceous microfossils in sediments from the abandoned post-mid-5th century AD reservoir Sigiri MahaVäva and its transbasin canals are in accordance with earlier archaeological interpretations, suggesting that the basin was quickly abandoned and hardly ever put to use again. It also seems possible to identify the abandonment of the irrigation canals in the diatom
assem-blages, but the definition of water-laid sediments in functioning canals by diatom analyses seems less promising. Studies of a village irrigation tank indicate possibilities for future tank sediment studies in combination with archaeological excavations of settlements in order to enhance our understanding of land-use development.