琼东南盆地早渐新世—早中新世气候、植被演变及其对海相烃源岩发育的影响

Palaeoclimatic and Palaeofloral Evolution and Their Influences on Organic Matter Enrichment of the Early Oligocene-Early Miocene Marine Shales in the Qiongdongnan Basin

丁文静 李友川 兰蕾 杨树春 刘海钰

DINGWenjing LIYouchuang LANLei YANGShuchun LIUHaiyu

中海油研究总院有限责任公司, 北京 朝阳 100028 中海油海南分公司研究院, 海南 海口 570311

CNOOC Research Institute Co. Ltd., Chaoyang, Beijing 100028, China Research Institute, CNOOC China Limited, Hainan Branch, Haikou, Hainan 570311, China

渐新统—中新统海相泥岩是南海北部天然气的重要来源，其有机质富集机制是琼东南盆地天然气勘探亟需解决的关键问题，为此，选取琼东南盆地15口井400余个海相泥岩样品，分析其热解、总有机碳及代表井的孢粉和分子地球化学数据耦合规律。结果表明，下渐新统崖城组二段是崖城组泥岩的有机质富集段；孢粉对比分析认为，其有机质富集受较湿热的气候中热带—亚热带植物大量勃发影响。陵水组二段上部—三亚组二段泥岩中也发现有机质逐渐富集的规律。生物标志化合物和孢粉记录结合区域气候对比结果表明，琼东南盆地上渐新统—下中新统海相泥岩有机质富集与逐渐温暖湿润的气候背景下，区域植被大量勃发，降水量的显著增加促进了河流—三角洲的发育，扩大了植物碎屑的搬运量、搬运距离和分布范围，促进了海相泥岩中的陆源有机质富集。琼东南盆地海相泥岩有机质富集段的提出对三亚组二段烃源岩埋深较大的乐东凹陷、陵水凹陷的深水天然气勘探具有重要意义。

Natural gases in the northern South China Sea are predominantly derived from the Late Oligocene-Early Miocene marine shales. The organic matter enrichment and its controlling factors are key points for the natural gas exploration in the Qiongdongnan Basin. The organic matter enrichment from the Oligocene to the Early Miocene marine shales from fifteen wells in the Qiongdongnan Basin was found using the data of total organic carbon measurement and Rock-Eval pyrolysis. During the early Oligocene, the Middle Yacheng Formation shales are enriched in terrigenous organic matter, which was thought to be caused by the flourished tropical/subtropical plants in the more humid environment. During the Late Oligocene-Early Miocene, there is also a terrigenous organic matter enrichment. Analyses of plant-derived biomarkers, palynogical records in shales in combination with regional global climate variations suggest the terrigenous organic matter enrichment was in association with warming and humid climate in the Late Oligocene-Early Miocene, during which higher plants flourished and the East Asian summer monsoon coupled with annual precipitation intensified. The significant extra precipitation brought by intensified East Asian summer monsoon was beneficial for the large amount of scattered plant organic matter enrichment and hence the terrigenously-enriched marine shales were more widely deposited in shallow marine environment. The finding of terrigenous organic matter enrichment in the Late Oligocene-Early Miocene marine source rocks was beneficial for the deep-water natural gas exploration in the deeply buried Ledong Sag and the Lingshui Sag in the Qiongdongnan Basin.

10.11885/j.issn.1674-5086.2024.09.12.02