鄂尔多斯盆地早白垩世原始地层厚度恢复及后期改造对矿产成矿（藏）的影响

【作者】 翁望飞；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 构造地质学， 2005， 硕士

【摘要】 鄂尔多斯盆地发育于中晚三叠世-早白垩世,是一个在古生代大华北克拉通盆地上叠合沉积了中生代地层的含油气盆地,有下古生界碳酸盐岩、上古生界海陆过渡煤系地层和中生代内陆坳陷河湖体系（含有风成）等三套沉积盖层。鄂尔多斯盆地含有石油、天然气、煤及铀等众多矿产资源,是中国重要的能源型沉积盆地。论文通过野外剖面观测,测井资料数据分析,研究了鄂尔多斯盆地早白垩世的沉积格局,分析计算了受构造运动作用而抬升遭剥蚀的地层厚度,总结了地层抬升剥蚀对石油、天然气、煤及铀等矿产赋存所带来的影响。 地层剥蚀是多期沉积盆地中普遍存在的现象,特别是代表每一期盆地主要反转期的构造抬升对原始盆地充填层序的剥蚀尤为强烈,这对沉积盆地中油气的生成、运移和聚集等产生重要的影响,且使原来的盆地充填沉积面目全非,同时限制了对盆地构造演化史、盆地充填史、沉积演化史、热史以及油气成藏史的深入研究。因此,地层剥蚀量的恢复和确定在沉积盆地分析中是一项重要的基础工作。目前,已有很多方法应用于沉积盆地地层剥蚀的研究,包括地质方法、地球化学方法及地球物理方法等。本文依据正常压实带泥岩声波时差的变化趋势估算了盆地早白垩世以来遭剥蚀的地层,并结合地层对比法,估算了早白垩世的地层剥蚀厚度,恢复了盆地早白垩世的沉积面貌。 论文在统一编制盆地早白垩世残留地层等厚图、早白垩世地层剥蚀等厚图、早白垩世地层厚度恢复图等图件的基础上,详细分析了盆地早白垩世地层的沉积范围、分布层位。指出盆地早白垩世时为现今盆地形成的主要时期,沉积了由东往西逐渐增厚的地层,沉积东缘达现今黄河并延入山西省境内,而西部则逐渐过渡至六盘山盆地。通过声波时差、联井剖面地层对比等方法估算了盆地早白垩世的剥蚀厚度,总体格局是盆地东部剥蚀程度强烈,盆地西部剥蚀程度较小。 论文从构造演化史,尤其是盆地中新生代以来的构造演化期次上分析了地层遭抬升剥蚀的动力学背景。认为盆地中、新生代以来发生了二次大规模的构造运动,即印支运动、燕山运动和喜马拉雅运动,尤其是燕山运动晚期和喜马拉雅运动对盆地的构造演化起着深远的影响,这两次运动控制着盆地的总体构造、沉积格局。说明了太平洋板块俯冲和青藏高原的隆升过程对鄂尔多斯盆地有远程效应。 最后,本论文在地层抬升剥蚀的基础上分析了岩石减负荷所带来的地层压力变化。并说明了由此对石油、天然气、煤及铀等众多能源矿产赋存成藏所产生的影响。认为地层抬升剥蚀使得地层释压而破裂,产生大量微小裂隙,油气得以再次运移成藏或逸散遭破坏;能使煤炭层位抬升至地表成为露天煤田（神府煤田）或氧化自燃而破坏;油气运移（逸散）过程中产生的H₂s等还原性气体能对地层中铀元素发生化学作用,使得金属铀能富集成藏。更多还原

【Abstract】 Ordos Basin is regarded as one of the most important Mesozoic and Cenozoic petroliferous basin congruence on the Paleozoic Craton in North China Block with the carbonate platform in the Lower Palaeozoic, the transitional deposits of marine and nonmarine intercalated with coal seams in the Upper Palaeozoic and the Inland Sag River-Lake System in Mesozoic, which produces multitude energy resource and mineral product that has been developed since Middle-Late Triassic to Early Cretaceous period. Base on field investigation, analyzing the data of well logging, the author studied the sedimental pattern of Early Cretaceous in Ordos Basin and calculated the denudation thickness caused by the tectonic movement, also the author tried to make available accounts to generalize the effect for petroleum, natural gas, coal and uranium, the mineral product as a result of the tectonic movement.Denudation generally exists in multistage sedimentary basin, especially the denudation of the infilling sequence caused by the tectonic movement in the main reversal stage of the original basin, thus it intensively influents the formation migration accumulation of oil and gas in sedimentary basin, and presents an entirely new appearance of the existing sedimentary basin, meanwhile this restricts the further study of basin tectonic evolutionary history, fill history, sedimentary evolutionary history, heat history as well as the pool-forming history of oil and gas. So the conformity and recovery of the amount of strata denudation are very important tasks in the study of sedimentary basin. At present, many methods have been employed in the research of the strata denudation in sedimentary basin, including geologic method, geochemistry method and physical geography method, and so on. The present paper estimates the denudation since Early Cretaceous based on the change tendency of the acoustic transit time in the normal compacted mudstone belt, and also the paper estimates the thickness of strata denudation in Early Cretaceous in terms of the stratum correlation, and more to recover the sedimentary construction in the basin of Early Cretaceous stage.On the base of the relic isopachous map, denudation isopachous map,thickness recovery map, the present paper completely studies the sedimentary scope and the distribution of the deposits of the basin in Early Cretaceous. The paper also points out that the gradually increasing deposits of Lower Cretaceous in Early Cretaceous was the main stage for the formation of current basin, with the east sedimentary borderline locating around the banks of Yellow River in west of Leuliang Mountains, whereas the western part of the basin gradually transiting into Liupan mountain. Estimating that the denudation thickness in the east part of basin is more intensive than that in the west part of basin by means of acoustic transit time, wells correlation, etc.For the tectonic evolutionary history, especially the background of denudation dynamics in the tectonic evolutionary stages since Mesozoic, three large scale tectonic movements have had happened since Mesozoic: Indo-china movement, Yanshan movement and Himalayan movement. Especially Yanshan movement curtain Ⅱ and Ⅲ, and Himalayan movement affected the tectonicevolution in the basin. Furthermore these two movements controlled holistic tectonic sedimentary pattern of the basin. These have illustrated the control role of the underriding of pacific-oceanic plate and the uplifting of Himalayan fold belt for the Ordos Basin.Finally, the present paper analyzes the change of formation pressure caused by burden-reducing of rock based on the denudation and explains the effects on the pool-forming of multitude energy resource mineral products like petroleunu natural gas、 coal、 uranium and so on. Denudation produces many fractures to release pressure, the slight crevices force the oil and gas to pool forming or dissipation; or force the coal bed to uplift to be an open air coalfield (like Shenfu Coalfield) or suffering from auto ignition. Process of migration of oil and gas produces reductive gas, like H2S, ect, then the chemical action of the gases propels the concentration of uranium.更多还原