大兴安岭中段索伦地区林西组岩石地球化学特征与沉积构造环境

大兴安岭中段林西组是重要的含烃源岩层位,烃源岩的形成与生烃母质生物活动和埋藏时的古气候、古构造、古环境息息相关。通过岩石地球化学分析可以恢复林西组沉积时期的气候与构造环境,利用Sr、Li、Ga 含量、Sr/Ba 值、U/Th 值、δU及Sr/Cu 值,从古盐度、氧化还原环境、古气候等方面分析了索伦地区林西组的沉积环境,认为林西组沉积时可能经历了中等—较强风化后的再沉积作用,总体为淡水—微咸水的氧化环境,气候温湿; Al₂O₃/(Al₂O₃+Fe₂O₃)值、K₂O/Na₂O- SiO₂关系以及稀土元素特征表明: 林西组形成于靠近大陆岛弧的活动大陆边缘,由早期弧后盆地的海陆过渡相半咸水环境向陆相的淡水环境演变,有利于有机质的富集和保存,是寻找烃源岩的有利层位。研究成果可为该区烃源岩勘查提供指导。

Geochemical characteristics and sedimentary tectonic environment of Linxi Formation in Suolun area of central Greater Khingan Mountains

The Linxi Formation in central Greater Khingan Mountains is an important hydrocarbon source rocks strata. The formation of hydrocarbon source rocks is closely related to the paleoclimate, palaeostructure and palaeo-environment during the propagation and burial of hydrocarbon generation parent organisms. The climatic tectonic environment of Linxi Formation in sedimentary period can be restored through the geochemical analysis of rock data. Based on the Sr, Li and Ga content, the Sr/Ba ratio, the U/Th ratio and δU method, the Sr/Cu ratio, the authors in this paper have analyzed the sedimentary environment of Linxi Formation from the ancient salinity, re-dox environment, and the ancient climate. The results show that the Linxi Formation might be formed by resedimentation after middle-strong weathering. The oxidative deposition environment is freshwater-brackish water, and the paleoclimate is warm humid climate. The Al₂O₃/(Al₂O₃+Fe₂O₃) and K₂O/Na₂O- SiO₂ ratios, the content and parameters of rare earth elements were used to indicate the sedimentary environment of Linxi Formation. The results show that the Linxi Formation was formed in the active continental margin tectonic environment near the continental island arc, and the paleoenvironment evolved from the sea-land excessive brackish water to the continental freshwater environment in the early retroarc basin. The Linxi Formation is favorable for enrichment and preservation of organic matter, which is the beneficial horizon for hydrocarbon source rocks.This study can provide guidance for the esploration of hydrocarbon source roaks in this area.