鄂尔多斯盆地延长组湖相蓝藻及其油源意义  

LACUSTRINE CYANOBACTERIA FROM THE YANCHANG FORMATION IN ORDOS BASIN AND ITS IMPLICATION OF OIL SOURCE

作　　者：吉利明[1,2] 徐金鲤[3] 宋之光[2] 

机构地区：[1]中国科学院地质与地球物理研究所油气资源研究重点实验室,兰州730000 [2]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广州510640 [3]中国石化胜利油田地质科学研究院,东营257015

出　　处：《微体古生物学报》2012年第3期270-281,共12页Acta Micropalaeontologica Sinica

基　　金：国家自然科学基金资助项目(批准号:41172131);中国科学院广州地球化学研究所有机地球化学国家重点实验室基金(编号:OGL-200917)共同资助

摘　　要：通过对鄂尔多斯盆地陇东地区三叠系延长组孢粉型有机壁微体化石的调查,在长73―长72段发现了浮游植物Sigmopollis cf.laevigatoides-Botryococcus braunii组合。该组合以极其丰富的蓝藻占优势,疑源类和绿藻类也较丰富,组合优势度高,而分异度低,常常显示单种优势。大量蓝藻类的勃发指示温暖和富营养的水体环境,与该盆地当时所处的低纬度亚热带气候区相一致,而延长组沉积时期大范围的火山喷发可能为蓝藻的发育提供了丰富的氮、磷等营养物。绿藻类Botryococcus braunii的大量出现表明本地区晚三叠世为淡水—微咸水内陆湖泊。保存完好的蓝藻化石密集成层出现于纹层状富有机质沉积中,显示可能为季节性分层的深水缺氧沉积环境。蓝藻化石分布的高丰度段长73―长72段恰好是本地区的主要烃源岩,并且烃源岩有机碳含量与蓝藻化石丰度密切相关,表明蓝藻类可能是延长组优质烃源岩有机质的重要生物来源。Organic-walled palynomorph microfossils were investigated from the Triassic Yanchang Formation in Eas-tern Gansu, Ordos Basin, and a phytoplankton Sigmopollis cf. laevigatoide – Botryococcus braunii assemblage was recognized in the member Chang 73—Chang 72. The assemblage dominated by extremely rich cyanobacteria and acritarchs and green algae are also abundant. It has a high dominance and a low differentiation, and often shows a single species advantage. The blooming of a large number of cyanobacteria indicates a warm and nutritious water environment, which coincides with the low-latitude subtropical climate of the basin in the Late Triassic. A wide range of volcanic eruptions may provide rich nitrogen, phosphorus and other nutrients for the development of cyanobacteria during the deposition of the Yanchang Formation. The emergence of a large number of green algae Botryococcus braunii indicates the Late Triassic fresh-brackish inland lake conditions in the area. Well-preserved fossils of cyanobacteria accumulated in the laminated organic-rich sediments reflects a seasonal stratification of the deep-water with high abundance of fossil anoxic depositional environment. The Chang 73—Chang 72 is just the main source rocks in this area, and the organic carbon content of the source rocks is closely related to the abundance of cyanobacteria fossils, indicating that cyanobacteria is possibly one of important biological sources of organic matter of the high-quality hydrocarbon source rocks in the Yanchang Formation.

关 键 词：蓝藻 烃源岩 延长组 三叠系 鄂尔多斯盆地 

分 类 号：P618.13[天文地球—矿床学]