Coastal-Open Marine Depositional System in the Kalpingtag Group of the Upper Silurian-Lower Ordovician in Kalping, Northwest Tarim Basin, China

The Upper Silurian-Lower Ordovician Kalpingtag Group, exposed in Kalping area, records part of the infill of the Tarim basin. The Kalpingtag Group has been subdivided into three informal lithologic units: lower, middle and upper, from field observations. Six facies associations (offshore, lower shoreface-offshore, lower shoreface, middle shoreface, upper shoreface, upper shoreface, foreshore) are recognized within the Kalpingtag Group. The sequence records that the Kalpingtag area has grown a complete transgression and regression process of deposition. The lower member of the Kalpingtag Group forms a reprogradational sequence in vertical, and the upper member of the Kalpingtag Group forms a progradation sequence in vertical.