民和盆地窑街地区上侏罗统沉积相的马尔可夫链数学模拟

Markov Chain Maths Simulation of Sedimentary Facies of Xiangtang Formation of Jurassic System,in Yaojie Area,Minghe Basin

甘肃窑街地区在晚侏罗世时期发育了大量的冲积扇相、河流相沉积,本文通过对上侏罗统沉积层序的马尔可夫链数学模拟研究表明:该区沉积相演化特征为由早期山前冲积扇相逐渐演变为晚期盆地腹内曲流河相,沉积区为山间内陆盆地河流环境,河流砂体极其发育,有可能成为良好的油气储集层。

Minghe basin is one of the typical continental basins containning coal、oil and gas.The study area- Yaojie region is an inter-mountain river valley depression,where there are the fluvial sediments of 600m in thickness in late Jurassic strata.On the basis of the previous biostratigraphical research,this paper researches the evolutionary characteristics of sedimentary facies of Xiangtang Formatin of Jurassic system in Yaojie region,Minhe basin by means of the method of markov chain mathematical mock.Therefore, the evolutionary characteristics of the sedimentary facies have been understood. Xiangtang Formation is divivided into three sections J_3x_1、J_3x_2、J_3x_3 according to charateristics of rocks,constructures,sedimentary structure etc.13 kinds of rock element has been recognized in the Formation,which consist of several facies sequence by tranforming and combinating each other.Every facies sequence represents a kind of law of sequence which reflects the sedimentary process and environment,thus,it can be served as an important factor to analyze sedimentary facies and small facies.The research results are as belows: J_3x_1 section's alluvial-fan facies:the channel,which developed a macro-unconvex eroded basis,was filled by greyish green massive conglomerate and sandy conglomerate lens,which is interpreted as the ephemeral channel on alluvial fan top.Middle part is the interbeds of greyish green plate shaped middle-fine sandstone which contains gravels with thinner mudstone,representing is sediments formed between both cnannel of alluvian fan.Upper part greyish green purple thinner mudstone beds containning thinner sandstone beds were deposited in alluvial plain. Lower J_3x_2 section's braided river facies:Channel sandy bars developed very well,but the sediments of floody plain small facies is poor.The sandy rudite、sandstone containing gravels and standstone with trough cross bedding is the main sediments,and the structures of scours and filling occurs frequently in lower part.Charateristics of probability cumulative curve show water is shallow with a high - speed flow. Upper J_3x_2 section's alluvial fan facies:Rythmite bed of pale sandstone and mudstone take over the main proportion,and the deposits of the alluvial fan plain occupy the majority of all facies,which shows the characteristics of alluvial fan's deposits in front of fault in basin. J3X3 section's meandering river facies:the deposits of levee and flood plain developed extremely well,of which sediments are mostly fine.The structures of sediments filling in channel are mainly plate cross beddings,and the probability cumulative curve of sandstone of point bar shows out low sections of heap-supspend.Levee sediments are rythmite interbed of which probability cumulitive curve is a single line type,and suspend composition takes over 90%.Above that are the flood plain sediments which consist of the great set of mudstone、fine sandy mudstone and poor coal beds.