Sedimentary Time And Provenance Characteristics Of “Zhenzhenshan Formation” In The Jining Uplift Of Sanjiang Area,Heilongjiang Province

This paper conducts field geological surveys,sporopollen fossils,detrital zircon U-Pb geochronology,and petrogeochemistry in strata that were originally designated as“Carboniferous-Permian Zhenzishan Formation”in the Erlongshan area of Fujin,it determined the sedimentary time limit of the Zhenzishan Formation in the Erlongshan area of Fujin.In addition,it clarified the geochemical characteristics of the sandstone of Zhenzhenshan Formation and discussed the source characteristics of Zhenzhenshan Formation in the Erlongshan area of Fujin.The cathodoluminescence images showed that the zircon particles were mostly sub-circular or short columnar.The zircon Th/U ratio is between 0.35 and 1.42 in most zircon developmental shock zones.Most of the samples are greater than 0.4,which reflects the characteristics of magmatic zircon.According to detrital zircon age data,it has two main age peaks,²67 Ma and⁵12 Ma.A small number of ages ranged¹30 Ma,342 Ma to 394 Ma,643 Ma to 1748 Ma.Among them,the youngest group of detrital zircons has a peak age of 130 Ma.,which stipulates that the formation age of the formation should not be earlier than 130 Ma.In addition,the sporopollen fossils of the research section were dominated by gymnosperm pollen,especially Alisporites and Cedripites.Ferns have less spores and angiosperms pollen.Angiosperm pollen is more common in Cupuliferoidaepollenite sparvulus and Callistopollenites sp.Among them,Borealipollis sp.and Classopollis philosophus?Pflug?emerged as representatives of the early Cretaceous in the early Turban-Sangtan period.In view of the fact that the Upper Cretaceous in the region is mainly a set of rapidly accumulating conglomerate and pebbly coarse sandstone,it is believed that the stable age of the thick sandstone and mudstone formation may be the period from Early Cretaceous to Late Cretaceous.The content of SiO₂ in the sandstone of Zhenzhenshan Formation in Erlongshan area of Fujin is relatively high,ranging from 61.52%to 73.45%with an average of 70.00%.The content of rare earths is high??REE=68.05×10-6¹71.05×10-6?.Rare earth elements have distinct differentiation?LaN/YbN=4.78-14.13?,with LREE enrichment?LREE/HREE=6.31¹0.81?and Eu negative anomaly??Eu=0.58⁰.76?.These geochemical characteristics are similar to those of the upper crust.Geochemical analysis shows that most of the“Zhenzi Mountain Group”sandstones in the Fulong Erlongshan area feature feldspar sandstones.Trace element features are similar to the upper crust.The fractionation of light rare earth elements is relatively high,LREE is enriched,and Eu is negatively related.This indicates that the“Zhenzi Mountain Group”sandstone samples in the Erlongshan area of the Fujin area should originate from similar source areas and that the original rock may be upper crust rocks.The similarity of the distribution pattern of rare earth elements is presumed to be closely related to the source area of the"Zhenzi Mountain Group"sandstone in the area of Fulong Erjin Mountain.It may belong to the source area of the pro-upper crust.The main element characteristic indicates that the parent rock of the sandstone may be an england igneous rock and a quartzite sedimentary rock.According to the characteristic indices of CIA,CIW,PIA,and ICV that characterize the weathering and chemical alteration of the parent rock,the provenance area of the“Zhenzi Mountain Group”sandstone in the Fulong Erlongshan region experienced relatively weak weathering.Also,weaker potassium replacement exists.The geochemical feature discriminative plot shows that the source of the source is part of the source area of ancient sediments on the passive continental margin.Part of the long-term source area from the active continental margin.There are two main age peaks,²67 Ma and⁵12 Ma,representing the main body of the source area,corresponding to the Late Carboniferous-Permian igneous rocks widely distributed in the Jiamusi block,the Early Paleozoic magmatic rocks,and the regional metamorphism of⁵00Ma.The main source area of Zhenzhenshan Formation in Erlongshan area of Fujin is the Late Carboniferous-Permian igneous rock and basement of the Jiamusi block.A small number of¹30 Ma,342 Ma³94 Ma and 643 Ma¹748Ma ages also corresponded to geothermal events in the Jiamusi block and adjacent areas.It shows that a small amount of the source comes from the adjacent geological body of the Jiamusi block.