The Stratigraphic Attributes Of Baitushan Formation In Baicheng,Jilin Province Indicate The Sedimentary Environment

The stratum of the Baitushan Formation is the lower limit of the Quaternary in the Songnen Plain.Its lithology is the accumulation of gray-white sand and gravel,with gray-white clay lens and very fine sand-fine sand lens.Early understanding of its strata is limited to lithology,and mineralogical and geochemical properties have not yet been involved.Fine stratigraphic attributes are the key to stratigraphic division and comparison,as well as the reconstruction of structure-landform-climate-water system evolution and other surface processes.This research is of great significance to the stratigraphic division of the eastern foot of the Greater Hinggan Mountains and the reconstruction of the sedimentary environment of the Songnen Plain.For this reason,this paper takes the standard profile of Baitushan Formation in Ping’an Town,Baicheng,Jilin Province as the research object,and reveals its chemical weathering,sedimentary cycle,sedimentary process,provenance and sedimentary environment based on sedimentology,mineralogy and geochemical stratigraphic attributes.The results show that:（1）The Baitushan Formation is composed of gray-white and yellow-brown sand and gravel,mixed with grayish-white clay,yellow-white muddy silt and extremely fine sand lens,and tabular cross-bedding can be seen locally.The gravel diameter is mainly20-80 mm with no obvious orientation and poor sorting.The roundness is mainly from sub-round to sub-angular.The weathering degree is from weak to medium weathering,and the matrix is sand-silt and mud.The gravel composition is mainly tuff（48.11%）,followed by rhyolite（23.58%）and quartz（20.75%）,granitic rocks（4.72%）and sedimentary rocks（2.83%）.（2）The heavy minerals in the Baitushan Formation are mainly white titanite（27.71%）,epidotite（25.17%）and ilmenite（17.28%）,followed by zircon（4.35%）,magnetite（3.48%）,anatase（3.22%）and hematite（2.46%）.The contents of rutile,turmaline and garnet are less（<1%）.Soft and hard manganese ore was found in some samples.The unstable minerals（apatite,hornblende,etc.）which are barely visible indicate that the sediments of the Baitushan Formation were subjected to a higher degree of chemical weathering.（3）Higher CIA and Rb/Sr ratios and A-CN-K diagrams indicate that the sediments of Baitushan Formation experienced A higher degree of chemical weathering.The low Si O₂/Al₂O₃ratio and the WIP-CIA and Th/Sc-Zr-Sc binary diagrams indicate that the sediments of Baitushan Formation are the products of the first cycle.（4）The ratio of gravel lithology to inactive elements（TiO₂-Ni,La/Th-Hf,La/Sc-Co/Th and Ti O₂-Zr）shows that the sediments of Baitushan Formation are middle-acid magmatic parent rocks from the Greater Hinggan Mountains.（5）Sedimentology and element geochemistry reveal that the Baitushan Formation belongs to the accumulation of alluvial-diluvium in the warm and dry oxidation condition.