| The Qaidam Basin is one of the large-scale multi-energy terrestrial sedimentary basins in China.It has developed thick Cenozoic terrestrial clastic sedimentary rocks.It has recorded the uplift of the Qinghai-Tibet Plateau(Kunlun Mountain)and the left-sliding movement of the Altyn and the sedimentary filling Evolutionary history.The western Qaidam Basin area in the study area is located in the triangle area where the East Kunlun Mountains and Altun Mountains meet.It is one of the important oil and gas accumulation areas in the Qaidam Basin.The oil and gas-bearing formations are mainly Paleogene.The predecessors have done a lot of sedimentology research around the strata dominated by the Paleogene Ganchaigou Formation.However,the sedimentary source research work since the Neogene Shangyoushashan Formation has been relatively weak so far,especially the Qigequan Formation.The study is almost blank,identifying the source of sedimentary debris and exploring the paleoenvironment of sedimentation are of great significance for clarifying the genesis of sand bodies,the history of tectonic events,and prospecting of sedimentary minerals.On this basis,this article relies on data collection,borehole catalog sampling,field outcrop profile surveying work,guided by theoretical knowledge such as sedimentology,sedimentary geochemistry,sequence stratigraphy,structural geology,Quaternary geology and geomorphology,Combined with field gravel statistics,paleoflow direction measurement,indoor rock thin section identification,debris statistics,and rock geochemical analysis,the Quaternary-based clastic petrology and sedimentary paleoenvironment in the western Qaidam Basin,In-depth study on the source of detrital material and the evolution of basin filling.research shows:(1)Through detailed field geology and indoor research work,the Upper Youshashan Formation-Qiqiquan Formation in the Yuejin-Qigequan area in the western Qaidam Basin is mainly a set of detrital sedimentary rocks with mainly gray-brown and green-gray.The calcium content is high and the distribution is uneven;the sedimentary structure is mainly dominated by parallel bedding,common biological relics and syngeneic sedimentary structure,and the deposition is mainly by environmental river-lake sediments;through statistics on the granularity and roundness of the gravel,And the particle size probability curve analysis,the roundness is mainly sub-circle-sub-edge,the particle size is mainly gravel gravel,the particle size curve shows that the gravel sorting is equal-better,reflecting that the gravel in the study area is deposited in river-delta phase Products transported over short distances in the lacustrine sedimentary environment.(2)The analysis results of the gravel composition,detrital composition,and paleo-flow direction of the gravel in the study area show that the gravel composition is mainly dominated by magmatic rocks in the Shangyoushashan Formation and Shizigou Formation.The change,especially the sudden increase in the gravel content of the metamorphic rock components,indicates that there was a significant source area transformation during the Qigequan Formation period;the paleo-flow direction shows that there are two directions of flow in the Qigequan Formation,which point to the direction of the Aral water system and the Altyn Mountains In the direction,Shizigou refers to the trend of switching from Qimantag to Aral water system,and the Shangyoushashan Formation points to the Qimantag direction;the detrital component statistics and the gravel component statistics of the group have basically the same results.The debris of metamorphic rocks in the Qigequan Formation is obviously more than that of the Shangyoushashan Formation and Shizigou Formation,which reflects that the source of the seven spring formations may be a mixture source,but the main source of Altyn is the Shangyuanshashan Formation and Shizigou Formation.Main source is East Kunlun-Qimantag.(3)Through the electronic probe composition analysis of the clastic feldspar and muscovite in the Qigequan Formation in the study area,the results show that the clastic feldspar mainly comes from the source area of the metamorphic rocks;the composition of the muscovite shows that the muscovite in the Qigequan Formation is all Polysilicon muscovite,from the source area of the high-pressure and ultra-high pressure metamorphic rocks,is compared with the number of silicon atoms in the metamorphic mudstone of the South Altyn high-pressure metamorphic belt,and it is found that the composition of some muscovite elements in the Qigequan formation is equivalent to it,indicating that The metamorphic belt may participate in the source supply of the Seven Springs,which further reflects that the Seven Springs have provenances from the Altun Mountains.(4)Through the analysis of main-trace-rare-earth elements,the main element results show that the content of Si O2 is low,and the sandstone types are mainly mixed sandstone,debris sandstone and feldspar sandstone,reflecting the low maturity of sandstone samples,which is Source deposition characteristics.The source rock tectonic background is mainly active continental margin and continental island arc.The source rock types are quartz rich sediment source area and neutral rock igneous source area;CIA and ICV reflect that the sediment in the study area is the first cycle The sediments are very weathered.Trace element geochemistry shows that the source rock properties in the study area are mainly medium-acid rocks and felsic rocks,and the tectonic background is mainly active continental margins and continental island arcs,which are basically consistent with the main element results;the restoration of the sedimentary environment indicates vertical The Shangyoushashan Formation and Shizigou Formation are relatively stable as freshwater sediments formed in arid climate,mainly in the reducing environment,while the Qiquanquan Formation shows a more complex and turbulent sedimentary paleoenvironment,with relatively deep water bodies.Lacustrine facies. |
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