HETEROGENEITY OF MARINE REDOX ENVIRONMENT DURING THE SEDIMENTARY PERIOD OF HONGSHUIZHUANG FORMATION IN NORTHERN HEBEI-WESTERN LIAONING

The marine redox conditions during the sedimentary period of Hongshuizhuang Formation and its effects on the preservation of organic matter are still controversial at present. Through analysis of trace elements and REEs in the shale of Hongshuizhuang Formation in western Liaoning, the paper studies the marine redox conditions during this period. The abundance of REEs in the study area is high (167.57×10^-6-316.95×10^-6), and the distribution has typical seawater features, characterized by depleted LREEs and enriched HREEs, obvious negative Ce anomaly, no Eu anomaly and low Y/Ho ratio. The contents of trace elements (V, Cr, Ni, Co, Th and U) are distributed in wide range, indicating that the ocean was under heterogeneous oxidation. Both the indexes of trace elements and REEs reveal the ocean was under partial oxidation and partial reduction condition, and some areas under sulfidic condition. Combined with the redox indexes of Hongshuizhuang Formation in other areas of North China, it is considered that the oxygen content of ocean then had obvious spatial heterogeneity, and the region with high TOC was basically in strongly reduced environment, which has a good correlation with high productivity and rich nutrient elements in the region.