川东南—黔北地区龙马溪组地球化学特征与古环境恢复

Geochemical Characteristics and Paleoenvironment Reconstruction of the Longmaxi Formation in Southeast Sichuan and Northern Guizhou

在综合国内外研究成果的基础上,结合川东南-黔北地区志留系龙马溪组的地球化学分析测试资料,着重讨论了微量元素、稀土元素、有机碳同位素与有机碳含量等地球化学特征,并根据这些地球化学指标恢复当时的古环境,认为龙马溪组优质烃源岩主要发育在龙马溪初期的缺氧还原环境,龙马溪后期缺氧环境遭受破坏,有机质保存条件变差,印证了龙马溪早期为深水陆棚和晚期为浅水陆棚的沉积环境。

Shales in the Longmaxi Formation of Lower Silurian having being developed in southeast Sichuan and northern Guizhou are rich in organic matters and are high quality source rocks in marine strata of south China.High quantity and high quality of organic matters are the main condition for high quality source rocks.The paleoenvironment which had an important effect on the quantity and quality of sedimentary organic matters was greatly influenced by the tectonic movement occurred in southeast Sichuan and northern Guizhou since the period of Late Sinian.It has an important geological signification for this region to reveal the paleoenvironment of the source rocks.On the basis of the research data at home and abroad,integrated with the results of geochemical test data of the Longmaxi Formation,we discussed the trace elements,REE geochemical characteristics,stable isotope and organic matters,and recovered the paleoenvironment of the Longmaxi Formation.The results showed that the effective source rocks are mainly concentrated in anoxic reduction environment of deep muddy shelf in the lower part of the Longmaxi Formation.The anoxic environment was destroyed in late Longmaxi stage,as a result of which,the preservation condition of organic matter becomes bad.