Stratigraphic Sequence And The Evolutionary History Of Sunwu-Jiayin Basin

Sunwu-Jiayin Basin, which lies at the north of the famous terrestrial oil-gas-bearing Songliao Basin, is one of the Mesozoic-Cenozoic oil-gas-bearing basins surrounding the Daqing oil field. Being covered by the forests on Xiaoxinganling mountain, and with the complicated geographic conditions, the fundamental geological study in this area is quite poor. Stratigraphic and structural geologic studies refer to the inner basin are based merely on the observation and measuring at the field outcrop, and the physical geographical survey is also roughly, moreover, a synthetically view of those different aspects is lacked. This paper combined the outcrop stratigraphic materials with the newly acquired seismic and borehole data, then discuss the stratigraphic sequences and tectonic characters of this basin, and make a correlation from following subjects of lithostratigraphy, biostratigraphy, chornostratigraphy and basin history with adjacent areas.The main strata sequence of Sunwu-Jiayin Basin is the Mesozoic and Cenozoic. Four regional developed unconformities divided the deposits into 3 sequences: The Early Cretaceous, which is composed of volcano-sedimentary rocks, has been subdivided into the lower part Wuyiling Group and the overlying Yongqing Fm. The early Cretaceous lithostratigraphic units in this basin had been historically and regionally named with 3 different naming systems. We resume the naming (Wuyiling Group and Yongqing Fm)really established in this basin, the other two are abandoned because they were actually established in the adjacent area and their ever uses were the results of correlation which might be defective. The Wuyiling Group is composed of three units, from the bottom up, they are Jieliehe Formation (phyolite, volcanicclast), Hongxiugou Formation (volcanicclast, sand stone), Meifeng Formation (basalt, andesite). The Yongqing Formation lies paraunformitily on them; The Late Cretaceous, which is composed of lacustrine and alluvial sediments, has been subdivided into Jiaying Group and Furao Formation, a angular unconformity separted the two units. From the bottom up, the Jiaying Group is composed of Yongancun Formation, Taipinglinchang Formation, Yuliangzi Formation, and the Furao formation has been dated as the end of Late Cretaceous; The Cenozoic, which deposited continually on the late cretaceous Furao formation, is subdivided into Wuyun formation and Sunwu formation.Eleven seismic lines and two boreholes had been recently finished by Daqing Oil Field Company. Based those data, a series of alternating revisions had been made between the seismic reflection surfaces and the litho interfaces observed from the borehole core and concluded from the electrical curve changes, and then validated them with the outcrop. After those approaches, a new litho units subdivision of JD1 borehole, and JD2 borehole has been finished, and the exist of the late cretaceous Yuliangzi formation in those two borehole were recognized for the first time. Those progresses of lithostratigraphic study inner basin more exactly exposed the sequences and the evolution of Sunwu-Jiaying Basin.Animal and plant fossils are abundantly yield from the Cretaceous deposits. This paper made a comprehensive and systemic summarize of the biostratigraphy, and a discussion of the geologic time combined with the paleontologic study information of northeast China. Seven palynological assemble zones has been established in the Cretaceous strata. Plant mega fossils belong to the Neozamites flora and the early assemble of the Early Cretaceous Ruffordia-Onychiopsis flora, and the Late Cretaceous Metasequoia-Trochodendroides flora. The Late Cretaceous Jiaying Group yield many animal fossils, they belong to Songhuajiang conchostraca fauna, Songliao ostracoda fauna and Albertosaurus-Mandschurosaurus dinosaurian fauna, there are also plenty of gastropods, insects, fishes and turtles fossils.Strata sequences inner Sunwu-Jiaying Basin can be well correlated with adjacent areas, the Wuyiling Group can be correlated with the Xinganling Group distributed in the Daxinganling area, especially the east slope of north great xingan mountain area. Wuyiling Group and Yongqing Formation as a whole are equivalent with the synrift early cretaceous sequences (Huoshiling Fm, Shahezi Fm, Yingcheng Fm) in Songliao Basin, and the Jiaying Group can be correlated with the Late Cretaceous sequences from Yaojia formation, Nenjiang Formation, Sifangtai formation to Mingshui formation.Faults in the basin are mainly NE direction, secondly the NNE and nearly EW directions, they are: Sunwu-Beian fault, Zhanhe fault, Kuerbinhe fault, Jiaying-Mudanjiang fault, Wulaga fault, Xunhe fault. Most of them are basin-controlling faults which accompanied different periods of volcanisms, and they controlled the first structural divisions. Being assisted with the data from the geophysical studies, seven fist structural divisions can be subdivided: Sunwu fault subsidence division, Maolanhe uplifted division, Xunke fault subsidence division, Furao uplifted division, Wuyun fault subsidence division, Jiaying fault subsidence division and Jieliehe uplifted division. The word'four fault subsidence and three uplifted areas'summarizes the panorama of the basin, the structural axes are all NNE direction. Sunwu-Jiaying Basin extends toward north joint to the Bureya-Zeya Basin along the boundary between China and Russia. The main sequences of Bureya-Jieya Basin is the Cretaceous strata which can be correlated with the sequences in Sunwu-Jiaying Basin. The deposits distinguished into two sedimentary cycles. The Early Cretaceous is composed of the Ekaterinoslavka formation, Itikut formation and Poyarkovo formation from the bottom up. Ekaterinoslavka formation could be correlated with the Jieliehe formation in Sunwu-Jiaying Basin, the Lower Itikut subformation could be correlated with the Hongxiugou formation, the Upper Itikut subformation could be correlated with the Meifeng formation, the Poyarkovo formation could be correlated with the Yongqing formation. There is a hiatus after the depositing of the Poyarkovo formation in the both two basins. The Late Cretaceous is composed of the Zavitaya formation and the lower part of Tsagajan formation. The Lower Zavitaya subformation could be correlated with the Yongancun formation and the Taipinglinchang formation. The Upper Zavitaya subformation and the lower part of Tsagajan formation could be correlated with the Yuliangzi formation, the middle and upper part of Tsagajan formation could be correlated with the Furao and Wuyun formation.The Bureya-Zeya Basin stays in the NE direction, including three subsidence areas and two uplifted areas. The Laimengtuofu-Biehuogeer fault subsidence joints with the Sunwu fault subsidence; The Poyarkofo- Ekaterinoslavka fault subsidence extends to Sunwu-Jiaying basin but splits into two units: Xunke fault subsidence and Wuyun fault subsidence; The Arhalin fault subsidence connects to the Jiaying fault subsidences.Based on the stratigraphic and structural characters, Sunwu-Jiaying Basin and Bureya-Zeya Basin could be analyzed as a whole. It's evolutionary history could be correlated with the Songliao Basin, and the it possesses the superimposed basin characters. The basin come through three evolutionary cycles, they are Early Cretaceous, latest Early Cretaceous to Late Cretaceous and Cenozoic.