Division and characteristics of Devonian strata in the Karakorum Mountains area in Xinjiang

This paper describes the geological results of 1:50000 geological survey conducted in the West Kunlun Mountains area in Xinjiang. The data were obtained by using profiling and regional geological mapping methods on the Devonian strata of the Karakorum Mountains stratigraphic region. New data concerning lithology and lithofacies, rock association characteristics, contact relationship, biological fossil and the basic sequence were collected. Multiple stratigraphic division and correlation were studied. The Devonian strata were divided in upward succession into Dawangding Formation (Middle- Lower Devonian), Huangyangtan Formation (Middle Devonian), Luoshigou Formation (Middle Devonian) and Tianshendaban (Upper Devonian) Formation, exhibiting comfortable contact relationships. Abundant fossils were found in the Devonian strata except Tianshendaban Formation. Two new formations (Dawangding and Huangyangtan) and six new biostratigraphic units (comprising 3 brachiopoda units, 1 coral unit, 1 ammonite unit, and 1 trilobita unit) were established. Huangyangtan Formation is the major regional ore-bearing bed with gypsum. The lithostratigraphic sequence, biostratigraphic sequence and chronostratigraphic sequence of the Devonian strata in the working area were newly redefined and improved systematically. The study has not only improved the research degree of the Devonian strata in the Karakorum Mountains area but also offered necessary geological history data for the analysis of the geotectonic evolution and the metallogenic regularity in the working area.