Sequence Stratigraphy And Lithofacies Palaeogeographic Research Of Carboniferous?Permian In Central And Eastern Inner Mongolia

The Permian?Carboniferous strata in central and eastern Inner Mongolia,with greate thickness and vast dark mudstones,show a fine petroleum geological condition,It's a new goal for petroleum exploration.But no systematic petroleum geological studies have ever been condueted in this area.This article,on the basis of fully absorbing others'data,using the firsthand quantitative information which was obtained from the measured sections carries out field geological survey,establishes isochronous stratigraphic units,identifies the sedimentary facies and sedimentary systems and reconstruct the lithofacies palaeogeography.By means of lithostratigraphic,through regions of our backbone profile and investigation,almostly find out the research area of Permian?Carboniferous formation development characteristics in Inner Mongolia grassland,Chifeng-Kangbao and the Dongwuqi formation zone;Biostratigraphic,isotope stratigraphic studied at the same time,the rock-stratigraphy units and its boundary of the Permian?Carboniferous in the area was correlated and redefineted.According to the results of zircon dating,We have districted Section ? of the original Baotege Formation geological age belongs to the Triassic,stratigraphic age of the original Suolun formation profile which was in Haore township,Sulun town,Wulanhaote region was as same as Zhesi Formation.We establish three biostratigraphic sequence stratigraphic division,roughly identified the stratigraphic age,for the first time comprehensive utilization of biostratigraphic,lithostratigraphic,isotope stratigraphic in the study area,the stratigraphic framework is established.The outcrop sequence stratigraphy was studied,by identifying the five types of sequence interface in the study area.The Permian?Carboniferous is divided into7 second-order sequences and 19 third-order sequences and is divided into seven isochronous stratigraphic units.The study area mainly developed transgressive systems tracts,favorable for the formation of argillaceous rock.The parasequence includes four kinds:coarsening-upward parasequence,fining-upward parasequence,interbeds of clastic rocks and carbonate rocks and interbeds of volcanic rocks and carbonate rocks parasequence.Throgh comprehensive analysis of geology and geochemical sedimentary facies symbol,combining with the spatial configuration of sedimentary facies,7 kinds of depositional systems and 17 kinds of main sedimentary facies have been identified for the Permian?Carboniferous strata.which can be divided into 7 kindsof sedimentary systems:Lakes,normal delta,braided river delta,limited coast(including limited gulf and carbonate platform facies),open coast,shallow sea shelf and bathyal to abyssal depositional systems.The deposition of shallow marine environment is the main part in this area,Summarized the depositional characteristics of Carbonate rock in the study area,which was mainly coast/uplift subsiding carbonate and shell-shoaling carbonate ramp,the second was delta-elevated carbonate platform.Compared with the adjacent area of Beishan area,study area had more stable tectonic environment,more conducive to oil and gas generation and preservation.Based on the previous work,with the new established method how to determine the advantage of sedimentary facies,this thesis reconstruct the lithofacies palaeogeography of the 7 isochronous stratigraphic units.palaeogeographic pattern of Carboniferous in the study area presented,the south was the marine sedimentation,the north of study area was continental or continental sedimentary,the performance of Permian depositional pattern:transgressive in the early stage-rapid regression in middle stage-water was roughly exit in early of late Permian,The paleogeographic characteristics is that shallow sea shelf is the main part,open coast surrounds the land and Carbonate platform concentrated distribution according to different regions,different geological times.After late Permian,sea was dying from west to east,continental sedimentation dominated.Shallow sea shelf sedimentary background was conducive to high-quality hydrocarbon source rocks generation and preservation,for creatied a good paleogeographic conditions,more open coast and delta sedimentary provides oil and gas reservoir with good conditions of sand body.