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Title:: Geochemical Characteristics and Their Paleoclimatic Significance of the Varve from Dakangpu Layer of Lower Cretaceous Yixian Formation in Yixian Basin of the Western Liaoning, China

Author(s):: WANG Tie-hui; GONG En-pu; CHEN Xiao-hong; XU Jiang; HUANG Wen-tao; 1. School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, Liaoning, China; 2. School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004, Hebei, China

Keywords:: geochemistry; varve; Yixian Formation; source; chemical index of alteration; index of component variability; tectonic setting; sedimentation rate

Abstract:: The varves are well developed in Dakangpu layer profile (auxiliary standard stratigraphic profile) of Yixian Formation in Yixian Basin of the western Liaoning, and cover 60%-70% of the deposition layer, which provide a good material for the study of palaeoenvironment during the depositional period. Based on the study on the petrology and geochemistry of varves, the paleoclimate, source and change of salinity of Dakangpu depositional period were discussed. The results show that the chemical index of alteration (CIA) is between 65 and 67 within a small range, and is insensitive to climate changes; w(Rb)/w(Sr) is low and increases gradually from bottom to top, suggesting the climate in Dakangpu depositional period is warm and moist with the trend from dry cold to warm humid; the couplet thickness of varve decreases gradually from bottom to top, and the precipitation gradually decreases; the index of component variability (ICV) changes from 1.3 to 11.6, more than 1, representing the existence of initial depositional product and active tectonic setting during the depositional period; the source of Dakangpu layer is dominated by partial acid volcanic rocks, such as the primary volcanic rocks of Yixian Formation; w(La)_n/w(Yb)_n is greater than 1, and the retention time of REE is longer in the lake with a low sedimentation rate; w(La)_n/w(Yb)_n decreases gradually from bottom to top, and the sedimentation rate and the lake salinity are gradually increased.