Discussion on Depositional Characteristics and Basin Quality in Kunlun  Orogenic Belt During EarlyMiddle Devonian

Key words: 
• Kunlun Orogenic Belt /
• EarlyMiddle Devonian sedimentation /
• backarc foreland basin /
• peripheral foreland basin /
• tectonic evolution

Abstract: The basic tectonostratum pattern of Kunlun Orogenic Belt, which was the product of oceancontinent transformation and collisional orogeny during Early Paleozoic and Late Paleozoic, was developed on the basis of Paleozoic. The Caledonian collisional orogeny, at the end of Early Paleozoic, made the Early Paleozoic ocean basin close and the whole Kulun area was uplifted to be land. As a sedimentary response to orogeny, the sediments of EarlyMiddle Devonian foreland basin formed at the piedmont area within the suture zone. The EarlyMiddle Devonian of East Kunlun mainly distributes in Middle Kunlun and Southern Kunlun. The northern part has sediments formed in the environment of abyssalbathyal basin, shallow sea shelf and sealand transition facies while the southern part is littoralneritic. The sediments are characterised by wedge shape which becomes thinner from north to south in 3D space. They display characteristics that the environment once changed from abyssalbathyal to shallow sea shelf finally to sealand alternation facies in temporal sequence, which reflect that the basin became shallower upward. The material sources were mainly from the northern part, namely the Early Paleozoic Orogenic Belt of Northern Kunlun, the southern part was secondary source area. Because the sediments developed on the subduction landmass, at the end of Silurian when Qimantage ocean basin had closed, they reflect that they have peripheral foreland basin sedimentary characteristics. In West Kunlun, the Middle Devonian only developed in the northern part, while the southwest was mainly abyssalbathyal basin sediments and the upper developed littoralneritic sediments, the northern part and the southern margin of Tarim basin developed littoralneritic sediments. These sediments are wedgeshaped in 3D space becoming thinner from southwest to northeast. In temporal sequence, their sedimentary environment changed from abyssalbathyal to shallow sea to sealand alternation finally to land facies. They also reflect that the basin became shallower upward. The material sources were mainly from southwest orogenic belt, while the Tarim ancient land in the northeast was secondary source area. Considered that the strata developed in the northern part of Middle Kunlun magmatic backarc, at the end of Ordovician when Kudi ocean basin had closed, it can be concluded that the sedimentary environment is backarc foreland.