桦甸盆地始新世古湖泊生产力与有机质富集机制

Productivity of Eocene ancient lake and enrichment mechanism of organic matter in Huadian Basin

通过对桦甸盆地桦甸组泥岩和油页岩样品的地球化学分析并利用有机碳法定性和定量恢复始新世古湖泊生产力,探讨湖泊演化过程中生产力变化、水体环境及其有机质富集机制。结果表明:桦甸组古湖泊生产力的演化由大到小为中部含油页岩段、上部含煤段、下部含黄铁矿段;中部油页岩段沉积时期湖泊生产力最高,最大值达1 033.09 g/(m2.a),为富营养湖,该时期有机质来源以藻类和细菌为主,湖泊水体环境为稳定缺氧的淡水—半咸水还原环境,反映了高的湖泊生产力与藻类勃发有关,直接影响有机质来源和丰度,湖水盐度的交替变化使底层水处于稳定的缺氧条件,是有机质保存的良好环境;上部含煤段和下部黄铁矿段沉积时期为明显的贫营养湖,水体均为缺氧的淡水环境,生产力平均值分别为153.26和143.82 g/(m2.a);高湖泊生产力是油页岩中有机质富集的首要条件,高的湖泊生产力和稳定的底层水缺氧是有机质富集的最理想环境。

Based on the geochemical research of mudstone and oil shale of Huadian formation, the productivity of Eocene Pa- leo-Huadian lake was qualitatively and quantitatively recovered by using the organic carbon method, and the water environ- ments, paleoproductivity change during the lake evolution and enrichment mechanism of organic matter were discussed. The results show that the evolution order of paleoproductivity in Huadian Basin is middle oil shale member, upper coal member and lower pyrite member. The highest paleoproductivity achieves at 1 033.09 g/（ m2 ~ a） during the sedimentary period of middle member of Huadian formation. The ancient lake is in eutrophic state. The bacteria and algae are dominate in organic matters and the lake water is in steady hypoxic and fresh-brackish reduction environment during this stage, which reflects that the high paleoproductivity is mainly contributed by algae and directly influences the origin and abundance of organic matters. The ahernative salinity change of lake water makes the bottom water be in a steady hypoxic environment, which is a favorable environment for organic matter conservation. The lakes during the lower member and upper member of Huadian formation are in obvious mesotrophic state and fresh hypoxic environment, and the average paleoproductivity is 143.82 g/（ m^2 . a） and 153.26 g/（ m^2 .a） respectively. High paleoproductivity is the first condition for organic matter enrichment of oil shale, andsteady hypoxic environment in bottom water is the most favorable environment for organic matter enrichment.