Research On Sedimentary Characteristics Of Yingcheng Formation In Lower Cretaceous In Lishu Fault Depression

Lishu Fault Depression is located in the East fault depressions zone of lower cretaceous，inthe Southeast uplift of Songliao Basin，it is a half-graben depression controlled by SangshutaiFault. Yingcheng Formation(K1y) stratum of Lishu Fault Depression was found oil and gas inseveral wells during Previous work，and it became a important research stratigraphic horizon.Even though many works have been done，previous research on sedimentary characteristics andsedimentary evolution was rough，and it was usually based on the unit of formation or member.Sothe purpose of this paper is to fine describe the sedimentary evolution characteristics of LishuFault Depression.Three3rdsequences were recognized in K1y stratum of Lishu Fault Depression，based oncores，well logging，seismic data and geochemical data. SequenceⅠwas developed at the bottomof the1stMember of Yingcheng Formation(K1y1). Sequence Ⅱ overlay on SequenceⅠand itmainly developed in K1y1.Sequence Ⅲ was basic equivalent to the2thMember of K1y.HST and RST were included in SequenceⅠ，mudstone and silty mudstone was mainlydeveloped in HST，TOC and HI is high，Strong amplitude, parallel reflection structure onseismic，AC and GR are high and Rt is low. Mudstone，silty mudstone and medium sandstonewere developed，TOC and HI become low，The seismic reflection characteristics are weakreflection continuity, weaker amplitude, and the obvious progradation structure characteristics canbeen found，AC and GR reduce but Rt value becomes high.LST，TST，HST and RST were included in SequenceⅡ，and form LST to RST，rockassociation changed from mudstone， silty mudstone and gritstone to mudstone and siltymudstone，then changed to argillaceous siltstone and silty mudstone.TOC and HI first increasethen decrease，The seismic reflection characteristics changed from weak amplitude hummocky to a little good amplitude and parallel, finally become to progradation structure. AC and GR firstincrease then decrease totally，but Rt first decrease then increase.From LST to RST of sequence Ⅲ，rock association changed from mudstone，argillaceoussiltstoneand to mudstone and silty mudstone and sandy conglomerate.TOC and HI value are highit may caused by the entrance of organic matter of terrigenous high plant. The seismic reflectioncharacteristics changed from weak progradation structure into stronger amplitude parallel structure,and finally into a strongest amplitude.AC and GR increase totally，but Rt decrease. According tothis，the fine sequence stratigraphic framework was established.Fan delta and lacustrine are recognized in Lishu fault depression，by core observation，grainsize analysis and microscopic identification. Semi-deep and deep lake subface mainly developedin deep depression area,and it mainly deposited dark mudstone,shore-shallow lake mainlydeposited greyish-green mudstone and light gray mudstone.Fan delta mainly located in edge of thefault depression, Grain size of deposits is coarse and sand conglomerate usually developed andwas poor sorting in the fan delta plain,Totally, sand conglomerate and sandstone are the main rockassociation in fan delta plain.The grain size becomes fine in fan delta front，and the rock becomesbetter sorting and main be sandstone and mudstone. Profan delta mainly developed darkmudstone.On the base of sequence stratigraphic framework establishment and sedimentary facesrecognition，system tract was took as the research unit，and then draw the figures of stratumthickness and ratio of sandstone and stratum thickness.So that to realize the horizontal distributionof sedimentary faces and study the sedimentary evolution.Each of the system tract in K1y ofResearch zone shows the stratum thickness become thin from south of Sangshutai Fault to east andnorth edge of Lishu fault depression. The stratum between Sangshutai Fault and east edge showstwo uplift and two depression-in deep depression zone and secondary sag，the stratum is thick，but the secondary uplift zone between this two zones and the east edge，the stratum is thin，Fromsequence Ⅰto sequence Ⅲ the stratum thickness become thin generally.During K1y，the mainsediment source of the research zone are from north and southeast. In these two zone，the ration ofsandstone and stratum thickness is high，but in the deep depression zone and secondary sag it islow. Sequence Ⅰ，sediment source is a little，but sequence Ⅱ，it become more and sequence Ⅲit become less.And in the RST of sequence Ⅲ，the southeast sediment source disappeared. Sequence Ⅰ developed semi-deep lake and deep lake subface in deep depression zone，north andsoutheast edge developed fan delta front subface，other zone developed shore-shallow lake subface.In sequence Ⅱ，semi-deep lake and deep lake zone became smaller，and fan delta front subfacezone became larger，and in LST and TST it developed fan delta plain subface in north andsoutheast edge，in HST it only developed a small zone of fan delta plain subface in northedge.During sequence Ⅲ semi-deep lake and deep lake zone became further small，and in thenorth and southeast edge of LST and north edge of RST,it developed fan delta plain subface,InRST southeast edge, fan delta front subface became shore-shallow lake subface. In a word，fromSequence Ⅰto sequence Ⅲ，the water changed from deep to shallow.