• 责任者：Ma Lu (Nanjing Institute of Geology and Palaeontology ; Chinese Academy of Sciences ; Nanjing 210008 ; China) ; Zhang Zhili
• 刊名：Acta Palaeontologica Sinica
• 出版年：2013
• 卷期：30(4)
• 关键词：碳酸盐岩 ; carbonate rocks ; 沉积微相 ; sedimentary microfacies ; 塔里木板块 ; Tarim Plate
• 页码：p.344-352
• 图表：4 illus., 53 refs.
• 分类号：0803
• issnNo：ISSN0001-6616
• isbnNo：CN32-1188/Q

     Palaeogeographic patterns, especially of eastern basinward extension, controlled the distribution of the Saergan Formation （Middle-Upper Ordovician transition） and its spatial lithofacies development. This unit has a thicknesses of about ten metres in the Kalpin stratigraphic region and is typically black shale rich in organic matter in tercalated with thin-bedded limestones. A large stratigraphic gap at the southwesternmost Xiker section of Jiashi shows that the Lower-Middle Ordovician Yingshan Formation is unconformably overlain by the uppermost Ordovician Tierekeawati Formation. This could be considered as an exposed and eroded landmass during most of the Middle-Late Ordovician. The Saergan Formation can＇t be recognized at the Yakeruike section in Wushi, located in the northern part of study region. In this area, red coloured silts and sandstones with subordinate thin-bedded dolostones are likely indicators of nearshore conditions dominated by coarse terrigenous sediments. The Saergan Formation is also absent at the Yangjikan section in Kalpin, which is 150 km northeast of the Xiker section. In that region, shallow marine lime- stones from the upper part of the Dawangou Formation are coeval with the Saergan Formation and are conformably o verlain by transgressive red argillaceous nodular limestones of the Kanling Formation （Sanbian, Upper Ordovician）. The black shales that characterize the Saergan Formation are typical stagnant basin deposits. Eastward they are spa tially limited in occurrence to three sections in the Subashi and Dawangou areas of Kalpin County and at Sishichang in Aksu. However, the microfacies of the thin-bedded limestones within the black shales show diverse features. Several layers of packstone or grainstone composed of sand-size debris are commonly found in the lower part of the formation. These grains originally formed in shallower platform and were then redeposited basinward by gravity flows. Bioclastic mudstones, mostly in the upper part of the formation, represent normal stagnant basin sediments. The shortest dis tance between the carbonate platform of the Yangjikan section to the stagnant basin of the Subashigou section is only about 20 km. This suggests that a narrow and steep sloping belt between them promoted the gravity flows.