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 km 2 . 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 rocklimestone-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.

Earliest Silurian graptolites from Kalpin, western Tarim, Xinjiang, China

“…From southeast to northwest, four tectonic units form the Northwestern Tarim palaeoplate: the Tarim platform, the northern Tarim depression, the northern Tarim uplift, and the southern Tian Shan mobile belt (Chen et al 1995, Feng et al 2007Fig. 1A).…”

“…The major portion of the material was Figure 1. A -geological setting of the Kalpin region, modified after Feng et al (2007) and Chen et al (2000).…”

Late Paleozoic magmatism in South China: Oceanic subduction or intracontinental orogeny?

“…Furthermore, Permian sedimentary basins in the SCB are intracontinental fault basins or rifting basins [51][52][53]. Paleogeographic reconstruction shows that the coastal region of Zhejiang-Fujian Province was an "old land" during Late Devonian to Late Carboniferous, and the entire SCB was covered by seawater in Early Permian [54][55][56]. Because Early Permian is regarded as global icehouse period [57][58][59], extensive marine sedimentation in the SCB during this period should result from the regional subsidence of a continental margin by tectonics rather than by the increase of the global sea level.…”

“…Another possible reason is that the orogenic belt has been severely eroded. Paleogeographic reconstruction shows the eastern South China has experienced a tectonic uplifting since the late Early Permian, which may cause the extensive erosion of the orogen and westward Paleo-waterflow [25,55,56] and provide massive clastic materials to the inland basins (e.g. Shaoguan, Leiyang, Ji'an and Yongding areas).…”

Microfacies and platform characteristic of the Ordovician in the northwestern Tarim Basin, NW China

“…Many oil reservoirs have been discovered in the Tarim basin. Previous studies shows the palaeogeographic of the Tarim basin; shallow platform and various banks deposited in the western area of the basin; the slopes and ramps developed in the east and south part [1] ;types of the reservoirs: dolomitize reservoir, grainy banks reservoir and reef-bank complexes reservoir as a result of environmental change [2] . This paper is to present the different microfacies; to interpret the depositional environment of the Ordovician based on field and petrographic observation, which are beneficial for further exploration of the carbonate bank reservoirs.…”