Stratigraphic Attribute Characteristics of Sand and Gravel Accumulation of Sanjiedi profile in Harbin

Key words: 
• Sanjiedi profile /
• Geochemistry /
• Zircon U-Pb dating /
• provenance /
• Sedimentary environment /
• Stratigraphic division

Abstract: [Objective] The previous regional geological data regarded the Sanjie sand and gravel section in Juren Town, Binxian County, Heilongjiang Province as the Luojiaweng Formation, but the study of its stratigraphic properties and sedimentary environment is weak, which greatly limits the in-depth understanding of regional surface processes recorded in this stratum. [Methods] From the perspectives of sedimentology, mineralogy, elemental geochemistry and U-Pb chronology of detrital zircon, the chemical weathering characteristics, source rock properties, sedimentary environment and tectonic setting of the provenance area of this section are discussed. [Results]The results show that the weathered degree of sand and gravel in the three sections is low, the sorting is poor, the roundness is good, and there is no obvious directional arrangement. The gravel lithology is mainly granitic rock (46.31%) and quartzy rock (28.19%), followed by syenite (0.2%), tuff (0.01%) and schist (0.01%). The heavy minerals were mainly sphenite (65.18%) and epidote (11.87%), but the other heavy minerals were less active. Elemental geochemistry reveals that the sediments in the three sections have a weak to moderate degree of chemical weathering, most of the sediments have undergone a primary cycle, and their parent rock type is felsic. According to the geochemical migration and enrichment of elements and the paleoclimate discrimination diagram, the sediment is revealed to be braided river sediment in arid oxidation environment. The zircon U-Pb ages are distributed in a narrow range (134.2~220.3 Ma, with a peak age of ~168 Ma), indicating the detrite contribution from Zhangguangcai Mountain, and indicating the subduction movement of Mudanjiang Ocean and the transformation of extensional environment after the subduction of the eastern oceanic plate to orogeny. Compared with the standard strata of Luojiawang Formation, there are significant differences in sedimentological characteristics, genetic types and geomorphologic characteristics of the three-section section. It is speculated that the formation time of the three-section section is later than that of the standard strata of Luojiawang Formation, and the time is roughly the same as that of Baitushan Formation. [Conclusion]This provides important indications for the division of the Quaternary strata in Harbin and the coupling relationship between regional structure geomorphology climate water system evolution.