Study On Geochemical Controls Of Sedimentary Environment And Provenance Of Mesoproterozoic Bingmagou Formation In Yichuan,Western Henan Province

For the proterozoic tectonics and sedimentary evolution history of the southern North China craton,scholors did lots of work on the Paleaoproterozoic Xiong'er Group and its Meso-Neoproterozoic sedimentary covers,and gave their explains.But an obviously ignored strata is the Mesoproterozoic Bingmagou Foamation,which is formed between the two big geological events.Its sedimentary environment,provenance,tectonic background and links to the beneath Xiong'er Group and above marine sediments are still unknown because of little work on it.Thus,this paper studies sedimentary evolution,provenance and geological backgrounds of Bingmagou Formation based on the theories and ways of sedimentology,structural geology,geochemistry,and tectonics.And the results are as follows:(1)Mesoproterozoic Bingmagou Formation in Yichuan area of the southern north china craton consists of conglomerate,glutenite,sandstone and silty mudstone from down to up,makes a set of fan delta sedimentary system,the main body of the delta is the fan delta plain and the fan delta front,that goes along with the size characteristics unfolded by particle size analysis.(2)For the geochemical characteristics,REEs of sandstone and argillaceous rocks share a similar distribution pattern.Differentiation between light and heavy rare earth elements is obvious.Sandstone ? REE range of 50.95 ~ 50.95(10-6,similarly hereinafter),an average of 114.66,Eu anomaly value between 0.6 ~ 0.9,shows a weak negative anomaly;Ce/Ce * exception is not obvious;Large ion lithophile Rb,Ba,Sr content change is big;high field strength elements have enrichments of La,Ce,Nd,Hf.Pelite ? REE range of 238.43 ~ 238.43,283.69 on average,Eu negative anomaly is apparent,range of 0.66 ~ 0.73;Enrichment of Ba,Nb,Sr loss,Rb,Th,La,Ce,Nd,Zr and Hf,presents the obvious "three two valley a flat peak" of the form.(3)The early stage of the paleosalinity affected by periodic flood,and there was a slight fluctuations,reducing enhancement,namely the increase of the depth of the water and salinity of the late gradually rising trend,in line with the characteristic of the transgression.(4)Background decision diagrams of argillaceous rocks and sandstones show that the geological background is continental island arch.And provenance of the mesoproterozoic Bingmagou Formation is mainly volcanic rock debris from Xiong'er Group,mixed by some older supercrustal materials,namely a mix of new and old.Provenance area is the distributed area of Xiong'er Group and the north China continental crystalline basement zones nearby.It means the tectonic of north china craton is a subduction zone.The direction of provenance is from south to north,the bingmagou formation is formed in an extensional back-arch basin.So,according to the analysis results above,it can be concluded that the Mesoproterozoic Bingmagou Formation represents a fan delta environment transition from land to marine under a background of continental island arc,which is well relate the Xiong'er Group to the developpment of meso-neoproterozic sedimentary covers.Thus the sedimentary period of Bingmagou Formation is very important to the development of the back-arc basin.