| Hailaer-Tamtsag Basin, which is situated in Hulunbuir Pasture Land in the west of GreaterKhingan Range, is a large sedimentary basin located not only in the peripheral area of SongliaoBasin, but also on the early Hercynian accretion fold belt at the southern edge of Siberian Plate.As to Beier Depression, known for its tectonic position at the fault subsidence zone in the centralHailaer-Tamtsag Basin, it·s a Meso-Cenozoic depression superimposed over the Paleozoic InnerMongolia-Great Khingan collisional orogenic belt. Actually controlled by the NE and NEE faults,Beier Depression extends in NE direction with the formations within this area centered by thelower Cretaceous series, which from the bottom up include Tongbomiao Formation, NantunFormation, Damoguaihe Formation and Yimin Formation, among which Nantun Formation arisesin the chasmic stage of the basin to constitute as one of the main target stratums for the study ofthe characteristics of the prototype basin in the research area. In most cases, people have studiedthe sedimentary characteristics of the lower Cretaceous series in Beier Depression in the unit offormationμ. Even as to Nantun Formation, which is also the critical exploration layer in this area,it has just been studied based on the concept of memberμ in the whole Beier or Beixi Region interms of its tectonics and tectonic evolution. As the main oil gas exploration region in HailaerBasin, Beier Depression has been proved through many years· exploration by the predecessors tobe one of the most promising depressions that are rich in oil and gas. Therefore the study of thecharacteristics of the prototype basin for Beier Depression will contribute to the in-depthunderstanding of its depression structure, the properties, the oil-gas migration and accumulationrules and the petroleum accumulation conditions to realize the further progress in the oil-gasexploration. However nowadays, the restoration of the prototype basin and the relevantcharacteristics study has been one of the most difficult problems faced by the geologists. Sinceprototype basin has been created under the effect of a single dynamic mechanism, it has beenfeatured with specific sedimentation type and tectonic entity. As a matter of fact, most of the sedimentary basins have been formed in the tensile stage when there·re numerous opening-closingmovements. Then with the great changes in the tectonic environment, the prototype basin or itsresiduum after the transformation will be superimposed longitudinally, which will lead to thetotally different petroleum accumulation conditions when the properties and ranges vary indifferent stages. Moreover since people can hardly recognize the early basin that has alwayssuffered the transformation made through the tectonic activities in the later stage, it·s absolutely afrontier subject in this field for the study of the reasonable recovery and the feature description ofthe early prototype basin, which has also constituted as one of the main aspects that call forpeople·s great attention in the research of the petroleum system. Therefore in order to have anobjective evaluation of the oil-gas possibility in the sedimentary basin, it·s necessary to restore theprototype basin, so that based on which people might be able to illuminate the transformationcaused by the tectonic activities in the early stage to the basin and the effect of such activities onthe basin formation in the later stage. In view of this, for the purpose to restore the prototype basinof Nantun Formation in Beier Depression of Hailaer Basin, we·ve collected abundant seismic data,logging information and drilling data etc. with the combination of computer technologies andgeological researches to construct a stratigraphic framework in the first beginning for the analysison the identification and classification of the unconformity interfaces and the tectonic styles. Thenthrough the study of the fracture characteristics in this area, we·ve classified the different fracturestages and built separately a construction model for the period of basin formation and atransformation model for the deformation period on the basis of the comprehensive analysis on theregional tectonic background, the tectonic styles and the fracture systems. Finally we·ve made aclassification of the tectonic units according to certain principle. As to the availability of theerosion thickness, by restoring the denudation quantity through the seismic-stratigraphy trendmethod, we·ve calculated the erosion thickness of the prototype basin for Nantun Formation inBeier Depression through the downward continuation of data volume, the interpretation of faultrecovery, the supplementary explanation on the stratum and the interpretation for the recovery ofprototype basin. In the end, we·ve also chosen in the research area separately two geologicalsections to illustrate the evolutionary development of the sections. By comparing the evolvedresult with the original thickness chart obtained for the prototype basin, we·ve corrected andproved further the accuracy in the erosion thickness of the prototype basin for Nantun Formationin Beier Depression.What has been listed below is our main work and the knowledge acquired in this research:1. The development of cap rock in Beier Depression has been involved with four first-ordersequence boundaries (T02, T04, T22and T5seismic reflection layer), which can be grouped intofour tectonic layers, say structural layer of fault depression (Tongbobian Formation and Nantun Formation), structural layer of fault-depression conversion (Damoguaihe Formation and YiminFormation), depression structure layer (Qingyuangang Formation) and shrinking layer (theCenozoic stratum).2. The growth fault in Nantun Formation of Beier Depression has been constituted mainly byNE fracture, NEE fracture and NW fracture with the development of Bayantala presented as a NWboundary fault, the NEE fault in the central area being a master control fault and NE faultdominating in the south as a master control fault. Meanwhile all of the synsedimentary faults arepresented in NE trend.3. In the sedimentary period of Nantun Formation, this area has been controlled by NEE andNE fractures in terms of the tectonics with the NEE fault controlling the formation of Beixi andSudeerte Sub Basin, and the NE fault dominating in the south to show a tectonic framework ofalternate uplifts and depressions in NE trend.4. Nantun Formation of Beier Depression has been featured with a parallel fault depressionstructure with the northwest area centered by the synthetic composite pattern and the south-eastarea presented in a composite graben pattern. As to the superposition mode, it·s characterized withan inherited superposition with the northwest area featured by a synthetic fault superpositionpattern and the southeast presented in a conjugate fault superposition pattern.5. Nantun Formation of Beier Depression can be grouped into seven third-order tectonic units,including: Beixi Sub-Sag, Wunan Sub-Sag, Beizhong Sub-Sag, Beidong Sub-Sag, BayantalaTectonic Belt, Sudeerte Tectonic Belt and Bulehongbusi Uplift. |
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