Stratigraphy Time And Provenance Analysis Of The Bagongshan Group In The Anyangshan Area Of Huoqiu County In Anhui Province

The Bagongshan Group distributed on the Anyangshan area, the border betweenthe Anhui Huoqiu and Henan Gushi, is composed of a suit of detrital rocks andcarbonate rocks. It is more than1034.9m thick and can be divided into four sectionsfrom bottom to top: the lower section, which contains gray and dark gray thick-beddedlimestone, is248.0m thick; the middle section that contains grayish yellow and grayishyellow-green shale as well as grayish yellow thin-bedded limy dolomite is136.6mthick; the upper section that contains grayish yellow and graypurple shale, silty shale,and grayish yellow thin-middlebedded sandstone interlayers is500.5m thick; and thetop section which contains grayish yellow-grayish white middle-thickbedded quartzsandstones is149.8m thick.Late Carboniferous fossils, such as Boultonia? Tabulata, and spiriferoid specimenswith smooth shells, and bioclastic material, such as crinoid stems and sponge fragmentshave been discovered in the lower part of the strata. These findings demonstrate that thestrata contain fossils are Late Carboniferous in age.In the upper part of strata, based on the U-Pb isotope dating of detrital zircons, thesamples HQ2106and HQ2204have youngest ages of detrital zircon:860±22.2Ma and877±22.6Ma respectively, which indicate the Bagongshan Group detrital rocks in theAnyangshan area should belong to the Qingbaikou (Tonian) of the Neoproterozoic.The detrital composition statistics of sandstones show the average content ofquartzs is95%. Most of quartzs are monocrystalline quartz. There is no feldspar insandstones. The average content of rock debris is3%. Most rock debris aremetamorphic rock debris, followed by sedimentary debris and volcanic debris. Thehigher compositional maturity indicates that the sandstone was transported for a longdistance. Sedimentary facies may be littoral-shelf facies.Mudstone and sandstone geochemical analysis results show that the averagepercentage of SiO2is73.48%, while the SiO2content of sandstones is91.68%andthat of mudstones is55.28%. K2O/Na2O is moderate, the average content values ofAl2O3and SiO2ratio is0.10, and the mean value of Fe2O3*+MgO is5.25%. Meanwhile,the average value of CaO is low, while that of Al2O3/(CaO+Na2O) is relatively high.The contents of the active elements like Na2O and CaO show significant lose. The totalcontent of REE in an average is94.3×10-6. The REE distribution patterns are uniformand similar to NASC, with LREE richment, and negative Eu-anomalies, without Ce-anomalies. The values of La/Yb and (La/Yb)Nare11.73（7.39-17.20）and7.91（4.98-11.60）respectively. The contents of lithophile element, Rb, Cs, Ba and Sr, varygreatly.Geochemical comprehensive analysis of major and trace elements demonstratesthat a set of sedimentary rocks in the Anyangshan area are mainly from continentalisland arc and passive continental margin area. Together with sandstone detritalcomponent QFL analysis, we think that the clastic rocks in this area was most probablydeposited in a passive continental margin.