Characteristics And Significance Of Algal Reefs In The Paleoproterozoic Dongye Formation In The Middle Taihang Mountains

The research area is located in the South Xijiao area of Pingshan County in the middle of Taihang Mountain,which belongs to the central part of North China Craton and is adjacent to the eastern landmass.In the Paleoproterozoic period,affected by the tectonic process,it formed a NNE trending rift basin and developed a set of carbonate formations.In a field geological exploration,it is found that there are abundant nuclear algal reefs in the dolomite of Dongye formation in the study area.The algal reefs contains three forms:mound,irregular and lenticular,which are mainly composed of nuclear dolomite and nuclear dolomite.According to the morphology of the nucleated stone,it can be divided into three types: spherical,irregular and strip nucleated stone under the microscope.The reaction hydrodynamic conditions are weakened in turn.The measured section of Dongye formation shows that the whole section is relatively continuous.The algal reefs are mainly located in the middle of the section of Dongye formation.The U-Pb age of the slate under the algal reefs shows that the clastic materials of Dongye formation are mainly from the surrounding Neoproterozoic granitic complex.Combined with the age analysis of the predecessors,the algae reef of the Dongye Formation was formed in 2.0Ga,forming an older age.The emergence of nuclear reefs has not been found throughout the contemporary strata.Therefore,the preliminary determination of the nuclear rock reef is a new discovery.Based on the analysis of the geochemical elements of the Dongye formation in the Paleoproterozoic,it is found that the algal reefs of the Dongye formation formed in the warm oxidation environment.The Dongye formation mainly develops three facies zones:tidal flat,shoal and shallow sea shelf,including four subfacies: intertidal zone,supratidal zone,beach margin slope and reef shoal subfacies.A comprehensive analysis of the algae reefs of the Dongye Formation was carried out in a shoal environment,and a sedimentary facies model map was established.Algal reefs are mainly controlled by geotectonics,paleoclimatic environment,hydrodynamic conditions,biological processes and input of terrigenous clasts,among which hydrodynamic conditions and geotectonics are the main controlling factors.Algae multiply in the muddy clear water,which secretes a large amount of mucus to capture the surrounding debris,forming different types of nucleation stones under different hydrodynamic conditions,and then a large amount of mucus secreted by the algae reef will stick to the nucleus.The knot finally formed the algae reef.The algal reefs in the study area were formed in the base environment with high hydrodynamic conditions,warm climate,abundant algal organisms and a small amount of debris.In combination with the occurrence of a large number of stromatolites in Taihang Mountain in this period,they all reflect the characteristics of quasi platform in the period of Paleoproterozoic Dongye sedimentation: stable sedimentary base,warm sea water,and superior environment for the growth of algae and other organisms.It is speculated that the North China platform has been basically formed in the Paleoproterozoic.