Geological Age, Sedimentary Geological Characteristics And Prototype Basin Of The Bingmagou Formation In The South Margin Of The North China Paleocontinent

The Bingmagou Formation exposed in the southwestern Songshan area in western Henan is the earliest continental sedimentary rock system after the cratonization of North China.It is of great significance for understanding the tectonic paleogeographic pattern and evolution of the southern margin of the North China paleocontinent.This article comprehensively used the basic theories and methods such as isotope chronology,sedimentary geology,and historical geotectonic to conduct a comprehensive study on the Bingmagou Formation to analyze and determine its geological age,sedimentary facies and sequence,basin prototype and geotectonic environment,and obtained the following major new understandings:1.The detrital zircon SHRIMP ²⁰⁷Pb/²⁰⁶Pb dating result of the lower and upper sandstones of the third section of the Bingmagou Formation shows that the detrital zircons of the Bingmagou Formation have two peak ages of 2500 Ma and 2700 Ma,respectively,indicating that the sediment source area of the Bingmagou Formation is dominated by Archean crystalline basement rock series.The minimum peak age of the Bingmagou Formation is 2100 Ma,which is consistent with the rift magmatic activity in the middle Paleoproterozoic of the North China paleocontinent.It indicates that the source area has experienced the rift structure in the middle Paleoproterozoic,and the age of the Bingmagou Formation is defined as the end of the Paleoproterozoic after the rift event.2.Based on the new zircon dating results,combined with previous detrital zircon dating data,the comparative study confirms that the age spectrum of clastic zircons of the Bingmagou Formation and the Maanshan Formation is obviously different,and should belong to different tectonic stages,suggesting that the Bingmagou Formation should not be placed within the Wufoshan Group,and should be separated.3.By studying the sequence,sedimentary facies,and sequence of sedimentary facies of the Bingmagou Formation,the Bingmagou Formation has developed three types of sedimentary facies:alluvial fan,braided river delta,and lacustrine facies.In the vertical direction,there is an ingressive sedimentary sequence,which is shown as an alluvial fan from the bottom,gradually upwards through the braided river and braided river delta to the upper lakeside sediment.4.Field surveys of 133 sets of oblique bedding were performed.The horizontally corrected rose diagrams confirmed that the braided paleocurrent of the Bingmagou Formation points north,indicating that the provenance of the Bingmagou Formation is in the south of the study area.5.Based on the above new achievements and combined with the previous data,this paper analyzed and discussed the attributes and geodynamic environment of the prototype basin of the Bingmagou Formation,and comprehensively judged that the Bingmagou Formation may deposit in the passive continental margin basin.