Sequence stratigraphy and coal accumulation of the Lower Cretaceous Saihantala Formation in Jiergalangtu Sag of Erlian Basin
Wang Shuai1, Shao Longyi1, Yan Zhiming1, Sun Qinping2, Wang Dongdong1, Lu Jing1, Sun Bin2
1 School of Geoscience and Surveying Engineering of China University of Mining and Technology(Beijing),Beijing 100083 2 Langfang Branch of Research Institute of Petroleum Exploration and Development,PetroChina,Langfang 065007,Hebei
Abstract：The Jiergalangtu Sag of Erlian Basin is a continental faulting coal basin and the Early Cretaceous Saihantala Formation is its main coal-bearing strata. In this paper,we studied lithofacies types,sedimentary facies,sequence stratigraphy and coal accumulation characteristics by means of core and drilling data. (1) The Saihantala Formation is mainly composed of sandy conglomerate,sandstone,siltstone,mudstone,carbonaceous mudstone and thick-bedded lignite. Three depositional systems were classified,including fan delta,braided fluvial delta and lake. The fan delta system consists of fan deltaic plain and fan deltaic front facies;the braided fluvial delta system is composed of braided fluvial deltaic plain and braided fluvial deltaic front facies;and the lacustrine system includes littoral lake and shallow lake. (2) Key stratigraphic surfaces, i.e., the unconformity and the erosional base of incised valley filling sandstones,are recognized,and the target coal measures are subdivided into two third-order sequences. Seam thickness and coal accumulation increase from sequence Ⅰ to sequence Ⅱ. (3) The thick coal seams,which were developed from the coastal and shallow lacustrine environments,were mainly formed in the early transgressive systems tract,and the thick coal seams,which were developed from the fan delta or the braided delta environments,were mainly formed at the end of the transgressive systems tract. The thickest coal bed was distributed in the central zone of the sag,which thins out towards northwest and southeast of the basin. Coal accumulation was significantly controlled by basin subsidence,and the increasing rate of accommodation space was well balanced with the rate of peat accumulation,thus forming a regionally very thick coal seam.
Wang Shuai,Shao Longyi,Yan Zhiming et al. Sequence stratigraphy and coal accumulation of the Lower Cretaceous Saihantala Formation in Jiergalangtu Sag of Erlian Basin[J]. JOPC, 2015, 17(3): 393-404.
