Abstract:

Shidao,an islet of Xisha Islands,is a tableland composed of upper Pleisto-cene bioclastic limestone.Its formation was clearly affected both by sea level fluctuation and crustal movement,suffered a environment of low level and arid climate of postglacial age.Shidao now exhibits a geomorphological envi-ronment of offshore sand bar and lagoon.Therefore,its strata present steeper slope and shows antiform sedimentary structure.According to the joints and calcite developed within spaces of lamellations,it has been subjected to influ-ence of crustal movement.The uncomformity between the upper Pleistocene sediments and recent sedi-ments and the C¹⁴ age dating demonstrates that there had been fluctuation of sea level.This means that a high sea level stage might occur.As for the age reversal of the bioclastic limestones,it is considered to be the result of particular condition of the islet,i.e.the conventional stratigra-phical law does not work in the present islet.Lithofacies of bioclastic limestones,its property,thickness and the pattern of arrangement,has exerted significant influence on the landform of erosion and accumulation of this islet.