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本文以宁南盆地北部的贺家口子清水营组剖面为研究目标,对古近纪晚期清水营组的岩性特征、石膏主元素地球化学特征和泥岩有机地球化学特征进行研究,结果表明:清水营组岩性以灰绿-紫红色泥岩、石膏及二者互层为主,可划分为8个二级沉积旋回和3个一级沉积旋回。石膏中CaO含量反映了咸化湖盆中石膏的化学沉积作用,Al_2O_3等为陆源碎屑来源,清水营组下段为盐湖深水环境沉积的纯净石膏;中段石膏沉积的水体较浅。清水营组下段地层泥岩TOC和生烃潜量(S_1+S_2)较高,说明在咸化湖盆演化早期气候较湿润、水体较深;而泥岩降解潜力相对小,反映有机质以高等植物来源为主,陆源输入较多。在此研究基础上,认为宁南盆地清水营组沉积包括:蒸发岩的沉积和碎屑岩的沉积;咸化湖盆演化尚未达到钾盐等盐岩沉淀的高浓缩阶段。咸化湖盆演化主要经历了早期封闭深水盐湖发育阶段、中期封闭浅水盐湖鼎盛阶段和晚期开阔浅水盐湖消亡阶段。宁南盆地古近纪晚期咸化湖盆演化与盆地的持续构造沉降和各次级沉积坳陷最终连为统一的湖泊这一重大区域沉积事件有明显的响应关系。
Based on the profile of Qingshuiying Formation of Hejiakouzi in the northern part of Ningnan Basin, this paper studies the lithologic features, the geochemical characteristics of main elements of gypsum and the organic geochemical characteristics of mudstone in Qingshuiying Formation in the late Paleogene. The results show that: The main lithofacies of the Yingshan Formation are greyish-magenta mudstone, gypsum and interbedded layers, which can be divided into eight second-stage sedimentary cycles and three first-stage sedimentary cycles. The content of CaO in gypsum reflects the chemical deposition of gypsum in salinized lake basins, Al 2 O 3 is the source of terrigenous clasts, and the lower part of Qingshuiying Formation is pure gypsum deposited in salt lake deepwater environment. The TOC and hydrocarbon generation potential (S 1 + S 2) of the mudstones in the lower part of Qingshuiying Formation are higher, indicating that the climate is wetter and deeper in the early evolution of the salty lake basin, while the mudstone degradation potential is relatively small, indicating that the organic matter is derived from higher plant sources Lord, Luyuan input more. On the basis of this study, the sediments of Qingshuiying Formation in Ningnan Basin are believed to include the deposition of evaporites and the deposition of clastic rocks. The evolution of salty lakes has not yet reached the stage of high concentration of salt rocks such as potash. The evolution of the salty lake basin experienced mainly the early closed deepwater salt lake development stage, the mid-term closed shallow water salt lake peak stage and late open shallow water salt lake extinction stage. The evolution of the salinized lake basins in the late Paleogene and the continuous structural subsidence of the basin and the sedimentary events of the secondary sedimentary basins that eventually became the unified lake have a significant response.