大巴山前缘五峰组-龙马溪组干酪根碳同位素特征与有机质类型

大巴山前缘五峰组-龙马溪组有机质类型组成存在较大争议。在万源曹家、城口周溪、巫溪田坝、巫溪白鹿和巴东两河口等地区采集代表性样品进行有机碳含量、成熟度和干酪根碳同位素分析。五峰组-龙马溪组δ¹³C组成分布为-31.1‰~-28.2‰,田坝地区δ¹³C最轻,两河口地区δ¹³C最重。大巴山前缘干酪根类型是碳同位素组成的主要控制因素,有机质成熟度和有机碳含量影响较小。当有机质处于高成熟演化阶段,有机碳含量越高,δ¹³C组成偏轻;有机质处于过成熟演化阶段,有机碳含量越高,δ¹³C组成偏重,变化幅度小于1.2‰。按照干酪根碳同位素组成划分干酪根类型原则,大巴山前缘五峰组-龙马溪组有机质类型为I型(腐泥型)和Ⅱ₁型(腐殖腐泥型)。

Carbon isotopes and organic matter types in the kerogens from the Wufeng Formation-Longmaxi Formation in the frontal areas of the Daba Mountains

The argument still remains current for the organic matter types in the kerogens from the Wufeng Formation-Longmaxi Formation in the frontal areas of the Daba Mountains. The present paper presents the carbon isotopic analyses of kerogens,total organic carbon contents and organic matter maturity for the samples collected from the stratigraphic sections including the Caojia section in Wanyuan,the Zhouxi section in Chengkou,the Tianba and Bailu sections in Wuxi,and the Lianghekou section in Badong,and gives the δ13C values from -31.1‰ to -28.2‰ for the Wufeng Formation-Longmaxi Formation. There are correlations between δ13C values,total organic carbon contents and maturity of organic matter. There is a negative linear correlation between the organic carbon contents and δ13C values while the maturity values are less than 2%,and a linear positive correlation between the maturity values and δ13C values while the maturity values are more than 2%. Referenced to the previous classification schemes,the organic matter types in the Wufeng Formation-Longmaxi Formation are assigned to the type I (sapropelic) and type II-1 (humosapropelic),which are graded from the type I organic matter in the Tianba section in Wuxi to the type II-1 organic matter eastwards and westwards.