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

Key words: 
• Minghe basin /
• Upper Jurassic /
• river /
• Markov chain maths simulation

Abstract: 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 ofthe previous biostratigraphical research, this paper researches the evolutionary characteristics of sedimentary facies of XiangtangFormatin of Jurassic system in Yaojie region, Minhe basin by means of the method of markov chain mathematical mock. There-fore, the evolutionary characteristics of the sedimentary facies have been understood. Xiangtang Formation is divivided into three sections J₃x₁,J₃x₂,J₃x₃ according to charateristics of rocks, constructures, sedi-mentary structure etc. 13 kinds of rock element has been recognized in the Formation, which consist of several facies sequence bytranforming and combinating each other. Every facies sequence represents a kind of law of sequence which reflects the sedimentaryprocess and environment, thus, it can be served as an important factor to analyze sedimentary facies and small facies. The researchresults are as belows: J₃x₁ section's alluvial-fan facies; the channel, which developed a macro-unconvex eroded basis, was filled by greyish greenmassive conglomerate and sandy conglomerate lens, which is interpreted as the ephemeral channel on alluvial fan top. Middle partis the interbeds of greyish green plate shaped middle-fine sandstone which contains gravels with thinner mudstone, representing issediments formed between both cnannel of alluvian fan. Upper part greyish green purple thinner mudstone beds containning thin-ner sandstone beds were deposited in alluvial plain. Lower J₃x₂ section's braided river facies: Channel sandy bars developed very well, but the sediments of floody plain smalt fa-ties is poor. The sandy rudite,sandstone containing gravels and standstone with trough cross bedding is the main sediments, andthe structures of scours and filling occurs frequently in lower part. Charateristics of probability cumulative curve show water is shal-low with a high-speed flow. Upper J₃x₂ section's alluvial fan facies: Rythmite bed of pale sandstone and mudstone take over the main proportion, and thedeposits of the alluvial fan plain occupy the majority of all facies, which shows the characteristics of alluvial fan's deposits in frontof fault in basin. J₃x₃ section's meandering river facies: the deposits of levee and flood plain developed extremely well, of which sediments aremostly fine. The structures of sediments filling in channel are mainly plate cross beddings, and the probability cumulative curve ofsandstone of point bar shows out low sections of heap-supspend. Levee sediments are rythmite interbed of which probability cu-mulitive curve is a single line type, and suspend composition takes over 9096.Above that are the flood plain sediments which con-sist of the great set of mudstone.fine sandy mudstone and poor coal beds.