Lithofacies palaeogeography of the Cambrian in Tarim area

Abstract

The Tarim area in this paper refers to the present Tarim Basin and its surrounding mountains, bounded on the north by the Middle Tianshan Mountains, on the south by the Kunlun Mountains, on the west by the national boundary of China, and on the east by the Altun Mountains. It covers an area of more than 1 000 000 km². Based on the quantitative and qualitative data from the stratigraphy and petrology of outcrop and well sections, and according to the single factor analysis and multifactor comprehensive mapping method, the single factor maps of the Lower, Middle and Upper Cambrian, and the lithofacies palaeogeography maps of the Early, Middle and Late Cambrian of the Tarim area, are compiled. The most important character of these lithofacies palaeogeography maps is quantification, i.e. the determination of each palaeogeography unit based on accurate quantitative data and the quantitative single factor maps. The study marks the first time that this quantitative method has been applied in the Tarim area. In the Early Cambrian, the present Tarim Basin was mainly a carbonate platform, in which there were penebank, dolostone flats, and gypsum-halite lake. The South Tianshan Basin and East Tarim Basin were siliceous rock-limestone-mudstone basins. The Kunlun Platform was situated in the south, where there were two small lands. The Altun Land was situated in the southeast. In the Middle and Late Cambrian, the framework of lithofacies palaeogeography was similar to that in the Early Cambrian; the land area was gradually reduced; the basin area was enlarged; while the Tarim Carbonate Platform changed little. The transgression continued from the Early Cambrian to the Late Cambrian.