The Analysis Of The Sedimentary System Of The Fourth-Member Of Quantou Group In The South Of Songliao Basin

Songliao basin is a large-scale Mesozoic-cenozoic era sedimentary basin in northeast of our country,which is the fault-cols type of interior basin,filled by the cretaceous non-marine fragmentary rock which reached 7000m thickness in the basin.The south of the songliao basin is consist of southeast uplift zone,the south of the center depression area and the west sloping zone and the north of southwest uplift zone,bounded by the baicheng city and tongliao city in the west,baicheng and harbin city in the north,siping city in the south and the frontier of the basin in the east,which spans the jilin,liaoning and intermongolia provices,the deminsion the basin is about 13.4~*10~4km~2。The cover coat concludes baicheng group,huoshiling group of the Jurassic,shahe group,yingcheng group,denglongku group,quantou group of the under-cretaceous,qingshakou group,yaojia group,nenjiang group,sifangtai group and mingshui group of the upper-cretaceous.This paper aims at the fourth member of the quantou group,researchs the depositional backgroup,the character of the sedimentary facies and the substance source deeply.The purpose is to comprehend the feature of sedimentary microfacies of the fourth member of quantou group in the south of songliao basin,and combined the feature of the depositional environment and the substance source etc.,for the further discussion the sedimentary system distribution characteristics in the south of the songliao basin,and build its mode of deposition.By collecting and researching the drilling information,core logging and its analysical-laboratory reports,well-logging and seismic data of the more than 1400 exploratory wells,to explore the distribution characteristics and the regularity of the fuyu oil-layer.To accomplish the area-wide heavy-mineral distribution diagrams by making use of the area-wide,more than 7200 of 400 wells, heavy-mineral data.To analysis comprehensively the material source by utilizing the sandstone component data,strata-pitch-angle logging information,seismic data and mathematical statistics methods,combining the area-wide heavy-mineral distribution diagrams simultaneously;and portray detailly the distribution extent of the material sources in west,southwest,south and the southeast of the basin,especiallydiscussing systematically whether or not the east provenance existed in order to make further progress in the comprehension of sedimentary system in the fourth-member of quantou group in the south of songliao basin.In the peririod of the deposition in the fourth-member of quantou group,songliao basin had the characteristics of high latitude,drought climate,even topography and monotonous,sterile creature etc.,most of region were exposured and oxygenated environment.On the drought background,the river drained mainly in the form of evaporation,vegetation-consuming,lake at the end of the river and alluvial lake etc..There is no uniform lakeshore line or catchment center.Later the climate turned into warmth and aquosity,so the uniform lakeshore line formed gradually.It is indicated from the evidences of reservoir,bedding,construction,paleobiology,dead-color mudstone etc.,it was lack of large-scale lacustrine deposit,but giving priority to the fluvial facies deposit in most parts of the basin.The river manifested primarily the seasonal flood.In the west of the basin,gulong low-lying area,the river congregated and formed shallow lake.By the study of the sedimentary facies characteristics,it is proved that there are four type of facies in the periods of fourth-member of quantou group:alluvial fan,fan delta,braided stream and meandering stream.theirs distributional characteristics were:in the south of the basin and the basin margin,alluvial-pluvial fans developed;in the south and west of the basin,there was braided river sedimented;in the vast center and the north area,meandering river sedimentary system formed.But there are no alluvial-fan deposit founded in the interior present basin about baokang,huaide,changchun and yushu hydrographical net.It is indicated that the four river systems may come from the exterior of the present basin.The fourth-member of quantou group also possess the point of much sedimentary centers which mainly spread in the area of dalaoyefu,gudian,qiandong,hua'aopao,da'an,xinmiao etc..Some catchment centers are identical with the sedimentary centers,but some are different.To sum up,it has the sedimentary character of much material sources,much alluvial lakes and basinful sand in the period of the fourth-member of quantou group.By use of heavy mineral distribution methods to depict the extent of the sedimentary system and the difference of the depositional environment,we analyze the heavy mineral data of more than 8000data of 500 wells in the research region and make a new recognition about the sedimentary system of the basin.The study shows that the south of songliao basin have 5 type of heavy mineral units.We name them A,B,C,D,E.They symbolize respectively the west sedimentary system,the southwest tongyu sedimentary system,the southwest baokang sedimentary system,the southeast sedimentary system and the east sedimentary system.Based on the heavy mineral data,we consult the seismic data,the information of the sandstone components ,paleostructure material and the results of mathematical statistics to analyze comprehensively the provenances in the sedimentary period of the fourth-member of quantougroup.The research suggests that there are five provenances in the south of songliao basin in that era,namely the west provenance,the southwest tongyu provenance,the southwest baokang provenance,the southeast provenance and the east provenance.there is much difference with the recognition of the predecessor who thought there were three provenances it that period. We have the same research result about the west provenance with the predecessor.While the west provenance consists of tongyu water system and baokang water system,it has proved that they have the great differences in heavy mineral component.The southwest provenance have the characteristic at containing garnet,while baokang water system containing garnet hardly.So they belong to the different sedimentary system.It also proved that tongyu provenance may extend to the north of da'an region.The south baokang provenance mainly develops in the center low-lying zone.We are consistence in the recognition of the southeast provenance with the predecessor basically.But it can be showed from the heavy mineral distribution diagrams that the huaide water system not extend too long.In the gudian area,the wells of gu18,gu52 and gu58 have indicated the feature of baokang water system.So we can know that the huaide water system ended in the area of dalaoyefu.The argument has been existed about the east provenance.So we aim at the east provenance to make abundant research.It has proved the existence of the east provenance by use of the providence of heavy mineral,distinctive mineral,separation factor and REE element data.By analyzing the macroscopical sedimentary background,the characteristics of the precipitation facies band spread and the provenances tracing,we proved that there were five sedimentary systems and seven rivers in the period of the fourth-member of quantou group in the south of the basin.The west sedimentary system mainly upgrowed twain water systems,namely yingtai and baicheng water systems.Yingtai water system was close to the provenance,it has the steeper terrain gradient,mostly upgrows the fan-delta deposit.Baicheng water system extended from the alluvial fan to the interior basin,the ephemeral braided-stream deposits system can be seen.The southwest tongyu sedimentary system briefly developt one water system,that is tongyu water system.That was a major water system with large proportions in that period,only inferior to changchuan and baokang water system.Tongyu water system formed the alluvial fan-braided-stream-and-meandering-stream sedimentary system which has the relatively integrated phase sequence.The southwest baokang sedimentary system mostly upgrows one water system,namely baokang water system,it is far from the provenance,the sediment have to be transported far away,so at the research area,which has the braided-stream-and-meandering-stream sedimentary system,no alluvia-fan was found.The southeast sedimentary system owns two water systems,they are huaide and changchun water system,formed respectically huaide braided-stream-and-meandering-stream sedimentary system and changchun braided-stream-and-meandering-stream sedimentary system.The material source of the east sedimentary system mainly comes from yushuregion,so it is called yushu water system.This water system divaricated in the vicinity of fuyu county seat.One flowed towards the daqing and doublecity,the other went to the direction of changchunling—fuxin-uplift-belt.This water system manifests the characteristics of the typical meandering river in the research area.