The Early Cretaceous Sedimentary Characteristics And Prototype Basin Restoration In Eastern Heilongjiang Province

The basins include Sanjiang basin, Boli basin, Jixi basin, Hulin basin, Ning'anbasin, Hegang basin and Tangyuan fault basin in eastern Heilongjiang Province. It havebeen proved to have practical hydrocarbon prospects according a long-term explorationin the basins refered above. Though each of these basins are isolated nowadays and havebeen reformed consumingly, they were coexist and have the close connection with othersin the same system in early Cretaceous. But these Cretaceous basins rarely have beenstudied as a unite in the east of Heilongjiang province. This paper discusses theformation mechanisms and retoration of prototype basins using stratigraphy,sedimentology, sequence stratigraphy and provenance analysis.Jixi Group and Longzhaogou Group are developed in the early Cretaceous basins inthe east of Heilongjiang Province. Jixi group includes Didao formation, Chengziheformation and Muleng formation, and Longzhuagou group includes Peide formation,Qihulin formation, Yunshan formation and Zhushan formation.Using biolo-stratigraphy,petrology stratigraphy, isotope geochronometry and other methods, this paper point outthat Jixi group and Longzhaogou Group were developed in the same time but in differentplaces. In the two groups, Didao formation is correspond with Peide formation, andChengzihe formation is correspond with Qihulin and Yunshan formation , and Mulengformation is correspond with Zhushan formation respectively.The sedimentary facies in the east of Heilongjiang province is mainly composed ofcontinental facies, and still including marine event sediments in the background ofcontinent, which form the rich and colorful sedimentary systems of the area. Theintegrative analysis of the Sanjing area utilizing cores, field sections, well log, seismicand palaeontologic datas indicates that, the sedimentary assemblages in this area aremostly made up of the continental facies, and others are marine-continental transitionaland marine facies. The continental facies can father be divided into alluvial fan facies,(fan)delta, lacustrine, volcanic-pyroclastic — lacustrine bottom fan facies;themarine-continental transitional facies is devided into delta facies;the marinesedimentary environment can be divided into offshore and shallow marine facies. Thesedimentary features and spread rules of the Early Cretaceous indicate: during thesedimentary periods of Didao (Peide) Formation, the basins are isolated fault basins,which mainly develop alluvial fan-(fan)delta-lacustrine sedimentary systems. during thesedimentary periods of Chengzihe Formation (Qihulin Formation+Yunshan Formation)and Muling Formation (Zhushan formation), the basins are uniform depression basins,which develop fluvial-(fan)delta-shallow lake-semi-lake sedimentary systems,Meanwhile, there exist marine events. The integrative analysis utilizing palaeontologicfossils, geochemistry element ratios and Sr isotope ratio indicates that, there are twoperiods of marine events in Chengzihe Formation and one period of marine event inMuling Formation, the direction of marine transgressions are all from the east of thebasins. The distributions of marine transgressions at the early period of ChengziheFormation are limit, but the ranges of marine transgressions at the late period ofChengzihe Formation and MulingFormation are the whole areas.According to recognize and identify the sedimentary features , sequence boundariesof the Early Cretaceous basins and classify the inner unites of sequence (systems tract) ,the article establishes the sequence stratigraphic framework .One second order sequence(supersequence) and nine third order sequences are distinguished in it. Among them, twothird order sequences are distinguished in Didao Formation, four third order sequencesare distinguished in Chengzihe Formation, and Muling Formation develops threesequences. Among them, the second order sequence is the result of tectonic movements,and the third order sequence is the result of base-level change caused by many kinds offactors, thereby, which can explain the cause of formation of different order sequences.Palaeocurrent analysis in Early Cretaceous in the eastern Hei Longjiang shows thatthe palaeocurrents were dispersed during the Didao Formation, and there was notuniform catchment center, characterized by nearby provenance and multiple supplysources. During the Chengzihe Formation and Muleng Formation, basins which isisolated nowadays had a united catchment center and were characterized by "overflowbasin".The palaeocurrents were primarily come form the western, eastern orsoutheastern basins , which suggests that the provenance maybe was both the XiaoHinggan Mountain-Zhangguangcai Mountain and the region in the east of FujinUpheaval.By the analysis of the composition of sandstone,the heavy mineral assemblageand geochemistry of detrital rocks, it is revealed that during the Didao Formation thesource of sediments was predominantly low grade metamorphic rocks, sharing similarchemical component constitution with the Jiamusi Terrane;during the ChengziheFormation and Muleng Formation there were three large and stable provenancesincluding the western Xiao Hinggan Mountain-Zhangguangcai Mountain, thesoutheastern Nadanhadab Terrane , the east of Fujin Upheaval. The tectonic settings ofprovenances for the Didao Formation, Chengzihe Formation and Muleng Formation isdetermined as the active continental margine.The early Cretaceous prototype basin in the eastern area of Heilongjiang Provinceis considered to be a large submaritime basin according to studying stratigraphy,edimentology, sequence stratigraphy,tectonics, seisemic facies characteristics andprovenance characteristics based on the field geological investigation and officeanalysis.It consists of the isolated fault basins when Didao Formation and it is a largeunited depression basin of Chengzihe and MuLeng Formation. The evidences are: It hassimilar sedimentary filled characteristics in early Cretaceous.The sediments are mainlyclastic rocks with coal bed, volcanic rocks and marine bed;The marine bed can betracked and contrasted;It has similar second order sequences;Nowdays,the isolatedbasins have no border facies and the boundaries are a series of reversed faults, Archaeanstratum thrust on younger stratum after Muleng Formation;Palaeogeographiccharacteristics and provenance analysis also show that it was a sag-basin.Before Cretaceous, The northeasten crust of China became thicking for SiberianPlate and Huabei Plate collision, as well as Jiamusi Terrane and Nadanhada Terraneamalgamation to Eurasia Plate. In the early Cretaceous the thicker crust occured todelamination,later which led to the crust extension ,and the crust heat-subdidence. Itdeveloped a series basins with the Pacific Ocean Plates subduction to the Eurasia Plate,which possessed the abortive continental rift, which interpretes the mechanism of thebasins developed as well. It is a fault stage in Didao Formation , and it is a sag stage inChengzihe Formation and Muleng Formation. Strong movements of Yilan-Yitong Faultand Dunmi Fault reformed the prototype basin, and make a sorts of EW thrust faultsdeveloped. Nowadays there are a relic basins in the eastern area of HeilongjiangProvince.