Effects of lacustrine hydrothermal activity on the organic matter input of source rocks during the Yanchang period in the Ordos Basin
Effects of lacustrine hydrothermal activity on the organic matter input of source rocks during the Yanchang period in the Ordos Basin
复制标题
鄂尔多斯盆地延长期湖相热液活动对烃源岩有机质输入的影响
DOI：
10.1016/j.marpetgeo.2020.104868
复制
发表时间：
2020
影响因子：
4.2
通讯作者：
Bo Ma
中科院分区：
文献类型：
--
作者：
Liming Ji;Jianfeng Li;Mingzhen Zhang;Hong Lu;Cong He;Peihong Jin;Bo Ma
为揭示鄂尔多斯盆地中晚三叠世延长期湖相热液活动对烃源岩有机质输入和优质烃源岩形成的影响，选取鄂尔多斯盆地南部YK 1井延长组样品，进行了烃源岩评价、元素地球化学分析和孢粉相研究。结果表明，长7-3段发育优质烃源岩。热液活动强度指标（IIHAs）Al/（Al + Fe + Mn）（IIHA 1）和（Fe + Mn）/Ti（IIHA 2）表明，在长7-长6段沉积时期，该湖经历了3期明显的热液活动，其中长7-长3期为热液活动高峰期。延长组烃源岩的主要生烃组分为颗粒状无定形有机质（AOM），其次为藻类和胶凝颗粒。在烃源岩中识别出三种孢粉相组合。A组合分布于长8-长9段和长6-2 + 3段。该组合中的有机质主要由III型和半透明木质纤维素碎片组成，凝胶化颗粒包括占主导地位的有机碎屑。组合B主要分布在长7-3段，以Ⅰ、Ⅱ型有机质为主，藻类和AOM含量高。C组合主要分布在长7-1 + 2段，以Ⅱ型有机质为主，AOM和植屑同时发育。烃源岩中AOM和藻类含量与IIHA的相关性表明，热液活动可能导致了藻类的发育和烃源岩的形成。AOM和藻类的分布在整个长7-3段都表现出持续的高含量，不仅与总有机碳含量、液态烃潜力、氢指数和热液活动高峰相耦合，而且与IIHA也表现出不同程度的相关性。它们之间的关系表明，湖泊热液活动的高峰可能导致藻类和浮游生物大量繁殖，这可能是形成优质烃源岩的重要控制因素之一。IIHA与硫含量的密切关系表明，热液可能进一步剥夺了湖底的氧，形成了有利于有机质保存和优质烃源岩沉积的还原环境。
To reveal the effects of lacustrine hydrothermal activities on the organic matter input of source rocks and the formation of excellent source rocks in the Ordos Basin during the Middle and Late Triassic Yanchang period, samples of the Yanchang Formation in the YK1 well in the southern Ordos Basin were selected; source rock evaluations, element geochemical analysis, and palynofacies studies were systematically conducted. The results show that excellent source rocks are developed in the Chang 7-3 interval. The intensity indicators of hydrothermal activity (IIHAs), namely Al/(Al + Fe + Mn) (IIHA1) and (Fe + Mn)/Ti (IIHA2) show that the lake underwent three episodes of obvious thermal fluid activity during the depositional period of the Chang 7-Chang 6 members of which the Chang 7-3 period was the peak of hydrothermal activity. The main hydrocarbon-generating components in the source rocks of the Yanchang Formation were granular amorphous organic matter (AOM) and algae and gelified particles were the secondary hydrocarbon-generating components. Three palynofacies assemblages have been identified in the source rocks. Assemblage A is distributed in the Chang 8-Chang 9 members and Chang 6-2 + 3 interval. The organic matter present in this assemblage mainly consists of type III and translucent lignocellulosic fragments and gelified particles comprise the dominant organic debris. Assemblage B is distributed in the Chang 7-3 interval which consists mainly of Type I and Type II organic matter and is characterized by high abundances of algae and AOM. Assemblage C is distributed in the Chang 7-1 + 2 interval and consists mainly of Type II organic matter which is characterized by the simultaneous development of AOM and phytoclasts. The correlations between the contents of AOM and algae in the source rocks and the IIHAs indicate that hydrothermal activity may have led to the development of algae and source rock formation. The distribution of AOM and algae show consistently high contents over the entire Chang 7-3 interval which are not only coupled with the peak of total organic carbon content, liquid hydrocarbon potential, hydrogen index, and peak of hydrothermal activity but also shows different degrees of correlation with the IIHAs. Their relationships indicate that the peak of the lake's hydrothermal activity may have induced algae and plankton blooms, which may have been one of the important controlling factors for the formation of excellent source rocks. The close relationship between the IIHA and sulfur content indicates that hydrothermal fluids may have further deprived the oxygen of lake bottom and formed a reducing environment which was helpful for the preservation of organic matter and deposition of excellent source rocks.