Micro Distributive Fluvial System Research Of Sedimentary Structure And Sedimentation Model

Distributive Fluvial System(DFS)refers to deposits of a fluvial system exhibiting a radial planform and distributive channel pattern.Weissmann et al.2010 proposed that Distributive Fluvial System are the main depositional model of sedimentary basins,and used the term DFS to describe fluvial systems in which rivers enter the basin from a vertex and spread radially,these depositional systems are also commonly referred to as alluvial fans,flood fans or Mega fans.The understanding of Distributive Fluvial System has changed the traditional sedimentology,which divides the basin sedimentary system into alluvial fans,braided rivers,curved rivers and deltas,and integrates the sedimentation of each end element into the same sedimentary system.DFS promotes the systematization of the classification of sedimentary systems,and the study of Distributive Fluvial Systems can provide new ideas for determining the spreading pattern of sedimentary systems in terrestrial oil-and gas-bearing basins.After more than a decade of development,the Distributive Fluvial System has been widely used in modern sedimentation,outcrop analysis,subsurface geological comparison,and even planetary sedimentology.However,the research on the sedimentary characteristics and depositional patterns of Distributive Fluvial Systems is mainly confined to satellite images and modern sedimentation,and there is a lack of application of examples combined with the subsurface.The Junggar Basin is a typical terrestrial hydrocarbon-bearing basin,and the Jurassic system at the southern margin of the Junggar Basin is the main force for oil and gas exploration and development.The Honggou section in southern Junggar Basin is a good example for subsurface application of Distributive Fluvial System research because of its complete outcrop and obvious depositional phenomena,which is easy to observe.Therefore,this thesis takes the Honggou section as the research object,through the fine sedimentological analysis of the section,studies the sedimentary palaeoenvironmental and paleoclimatic characteristics of the Honggou Karaza Formation,the characteristics of rock structure and explains its genesis mechanism,summarizes the types of rock phase assemblages,analyzes the characteristics of the architectural structure elements and the criteria of their hierarchical interfaces,clarifies the types of sedimentary phase zones,establishes the architectural structure model of the section,and segments the stratigraphy of the Honggou Karaza Formation.The sedimentary evolution process of the Honggou Karaza Formation is inferred.The fine study of the lithology of the Karaza Formation in the Honggou section shows that the lithology of the Karaza Formation is characterized by large sections of gray and gray-yellow coarse conglomerates,medium and coarse sandstones with thin layers of yellow-brown and yellow fine conglomerates and conglomerate-bearing sandstones.The XRF microconstant element test of the Karaza Formation in the Honggou section shows that the deposition period of the Karaza Formation was supplied by terrestrial sources,and the material source debris is mainly related to water transport products;the microbial rocks found at the bottom of the Cretaceous Qingshuihe Formation in the Honggou section indicate a saline shallow water environment with clear water bodies and moderate waves,and the Fe/Mn ratio of the Karaza Formation reflects that the water depth during the deposition period of the Karaza Formation was less than that of the Qingshuihe Formation.It provides data support for the study in the arid sedimentary context of the Karaza Formation.By interpreting the structural characteristics of the rocks of the Karaza Formation in the Honggou section and its genesis mechanism: seven types of sedimentary structures are developed in the Karaza Formation in the study area: block laminations,recurved laminations,oblique laminations,parallel laminations,trough interlaminations,plate interlaminations and stacked tile laminations.The gravel granular support mode is divided into five types: granular support,multi-level granular support,granular-hybrid base support,hybrid base-granular support,and hybrid base support,and its unit gravel directionality vector L is related to the granular depositional environment,and the value decreases gradually from granular support to hybrid base support,and the L value is positively correlated with the hydrodynamic conditionsThe L value is positively correlated with the hydrodynamic conditions,and the L value is correlated with the hydrodynamic conditions.By combining the lithology,sedimentary structure,rock structure genesis mechanism and other sedimentary characteristics,we can identify two major types of rock phases,conglomerate phase and conglomerate-bearing sandstone phase,which can be further subdivided into massive laminated conglomerate-bearing sandstone phase,multi-level granular-supported conglomerate phase,recursively laminated conglomerate phase and miscellaneous base-supported conglomerate-bearing sandstone phase,parallel laminated conglomerate phase,channeled interlaminated conglomerate phase,plate interlaminated conglomerate sandstone phase,oblique laminated conglomerate sandstone phase phase,oblique laminated conglomerate sandstone phase,and stacked conglomerate phase.The Honggou section of the Karaza Formation has a Micro Distributive Fluvial System,which can be subdivided into three subphases: proximal,middle and distal DFS.The profile was dissected,and 10 different levels of architectural structural elements entities were constructed for the grain layer,layer system,layer system group,river lateral accretion,river lateral accretion,single river channel,river complex,single dolomite,complex dolomite,and Karaza Formation deposits.The development and superposition styles of sand body architectural structural elements in the profile are also summarized: five types of architectural structural elements can be identified in the profile: braided channel(CH),diffuse flow deposition(SF),braided sand island(BS),debris flow deposition(DF),and interchannel(FS).Among them,most of the channels at the distal end of DFS are singly dispersed and small in width,the channels in the middle part of DFS are dispersed or in contact with each other in a superimposed state,and the sand bodies are mostly connected,and the flood flow energy at the proximal end of DFS is the strongest,and the channels are tightly aggregated in a contiguous distribution.Considering the change of gravel sequence in the section and the characteristics of different depositional phase zones in the DFS to divide the deposition periods in the section,and to recover the deposition evolution process of the Karaza Formation,the Karaza Formation can be divided into seven sections from S1 to S7,representing seven deposition periods with a certain degree of cyclicity,and the deposition period of the Karaza Formation as a whole is dominated by progressive accumulation,with local receding accumulation.