【作者】 杨扬；

【导师】 高福红；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2014， 博士

【摘要】 本文以歧口凹陷古近系沙河街组白云岩为研究对象，利用有序度分析、稳定同位素分析、主量微量元素和稀土元素分析，确定了沙河街组白云岩的岩石学特征、成因机理以及成岩流体特征。基于上述研究，并结合全球古气候和海平面变化研究成果，最终确定了歧口凹陷始新世—渐新世的古气候为逐渐变冷过程，并在晚始新世和早渐新世发生过两次海侵作用。这对于歧口凹陷白云岩储层的进一步油气勘探工作有重要的意义。稀土元素、锶同位素和流体包裹体均一温度综合分析表明，沙三段白云岩几乎不受火山热液的影响。沙二段白云岩整体表现出火山热液作用的特征，但沙二上段白云岩受影响较大。沙一下段和沙一上段白云岩样品受火山热液作用较小。火山热液作用在深度2300m附近对白云岩的影响程度最大。碳氧同位素研究表明，歧口凹陷沙河街组沉积时期的古气温自沙三段至沙一段总体为逐渐降低的过程，在沙二下段时期和沙一下段时期分别有两次突然升温事件。自沙三段至沙一段，白云岩的碳同位素在大洋缺氧事件和甲烷化作用的影响下发生了明显正偏移。这与全球始新世—渐新世古气候变化和碳酸盐岩的碳同位素正偏相一致。主量微量元素和稀土元素分析结果表明，白云岩歧口凹陷沙河街组沉积时期发生了两次海侵作用。沙二下段时期海侵规模较小，沙一下段时期海侵规模大，并持续到沙一上段时期。全球范围内始新世至渐新世时期的海平面表现出长期下降的趋势，在始新世晚期和渐新世早期出现两次明显的升高。歧口凹陷的两期海侵作用的发生时间分别与这两次海平面升高相一致，与该时期两次升温事件有关。更多还原

【Abstract】 This paper analyses the order degree, stable isotope, major element, trace element andrare earth element (REE) of dolostones from the Paleogene Shahejie Formation in the Qikoudepression, eastern China, with the goal of determining the petrological features, genesis andcharacteristics of diagenetic fluid of dolostones in the region. These geochemical data,together with changes of paleoclimate and sea level worldwide, which are of significantimplication for revealing the palaeoclimatic and ancient environmental evolution that spansthe Eocene and Oligocene in the Qikou depression. Main achievements are as follows:Dolostones of Es3occur in the north of Qikou depression, dolomicrite play a dominantrole. Dolostones of Es2x develop in the north and west of Qikou depression, which are mainlycomposed of dolomicrite and crystallitic dolostone. Dolostones of Es2s occur in the north ofQikou depression, the main rock type is dolomicrite. Dolostones of Es1s and Es1x prevail inthe entire depression, which are mainly composed of dolomicrite, crystallitic dolostone,laminar algal dolostone and crystalline bioclastic dolostone.Dolomicrites of Es3and Es2in the Qikou depression are related to the burialdolomitization, and the genesises of crystallitic dolostones are related to the meteoric water.The genesises of crystallitic dolostones from Es1x are related to the methanation, both laminaralgal dolostones and crystalline bioclastic dolostone are related to the burial dolomitization, butthe later are buried superficially. The genesis of crystallitic dolostones from Es1s are related tothe methanation, some dolomicrites, laminar algal dolostones and crystalline bioclastic dolostones are related to the burial dolomitization, but most of them are influenced bymethanation.Cenozoic volcanic rocks are widespread in the south of Qikou depression, but decline inthe north, in the west are rather poorly developed. Dolostones from Es3almost not affected byvolcanic hydrotherm. Parts of dolostones from Es2x are affected by volcanic hydrotherm.Intense volcanic hydrotherm occurred in the Es2s, the dolostones show obviouscharacteristics of hydrothermal carbonate. Dolostones from Es1x and Es1s are with the littleeffect of volcanic hydrotherm. The depth of the most significant influence by volcanichydrotherm is2300m.A hot climate prevailed during the Es3, but this shifted to a cold climate in the Es1, andthere are two temperature rise events during the Es2x and Es1x, respectively. This change inclimate is concordant with the paleoclimate changes that spans the Eocene and Oligoceneworldwide. From Es3to Es1, the positive excursion in carbon isotope ratios caused by oceanicanoxic event and methanation, which is consistent with the positive excursions of carbonisotope at the at the Eocene–Oligocene boundary across the world.Two transgressions occurred during the Es3to Es1in the Qikou depression. Thesmall-scale transgression in Es2x had influenced dolostones from north and west of thisdepression. During Es1x, almost all the dolostones underwent an interaction of sea-water,even some samples show typical characteristics of marine carbonate. The influence oftransgression lasted until Es1s, both the scale and intensity are reduced.On a global scale, the sea level fell gradually from Eocene to Oligocene. However, therewere obvious sea levels rised during the late Eocene and early Oligocene, respectively.Time of the two transgressions happened in the Qikou depression are concordant with the sealevel rise events, this as a result of temperature rise events during this period.更多还原