【作者】 王平康；

【导师】 王成善； 黄永建；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2009， 硕士

【摘要】 松辽盆地位于中国东北部,是我国大型白垩纪沉积盆地,是亚洲古陆上最大的白垩纪湖盆之一,是我国陆相白垩系发育最完整的地区。白垩纪青山口组沉积时期是松辽盆地首次最大湖侵期。青山口组一段(K2qn1)沉积期间的海侵事件以及当时古湖泊水体性质研究,一直以来都是松辽盆地的研究热点。“松科1井”的实施获得了连续的高分辨率沉积记录,为高分辨率的古环境、古气候重建提供了理想的研究材料。黄铁矿是富有机质沉积的一种特征矿物,是恢复沉积环境的一种重要指标。大量研究表明,沉积黄铁矿形态学研究能提供有关沉积环境和早期成岩过程的有用信息。本论文利用反光显微镜和扫描电镜对“松科1井”南孔青山口组一段泥岩样品中黄铁矿形态观察发现,青一段泥岩中存在二种基本的黄铁矿形态,即莓球和自形晶,以及由这两种形态衍生而来的集合体形态。在对不同黄铁矿形态的成因探讨的基础上,依据黄铁矿莓球大小分布对底层水体氧化还原条件的指示原理,认为青一段沉积期底层水体氧化还原条件曾发生过从含氧-贫氧静滞-缺氧含氧-贫氧的变化过程。通过对青一段泥岩有机碳含量与黄铁矿硫含量比值(C/S)分析,表明青一段沉积期湖泊水体盐度变化具有一定的阶段性,并指出海侵可能是造成湖泊水体咸化最直接的原因。综合底层水体氧化还原条件变化和古盐度变化等分析结果,将青一段沉积期湖泊水体环境的演化划分为五个阶段。I阶段(泉四段末期)属淡水环境;II阶段发生海侵,水体开始咸化,但盐度分层较弱,底层水体为含氧-贫氧状态;III阶段持续海侵,水体咸化程度最大,盐度分层强烈,底层水体呈静滞-缺氧状态;IV阶段海侵结束,大量淡水注入,呈咸水-半咸水环境,底层水体含氧;V阶段呈咸水环境,底层水体呈含氧-贫氧状态。此外,基于能谱分析结果认为不同形态黄铁矿S:Fe原子比值可能代表不同的黄铁矿形成阶段以及基于X射线粉晶衍射分析结果认为黄铁矿最小微晶大小与莓球直径间可能存在着一种正相关关系。但此方面工作还有待进一步研究。更多还原

【Abstract】 Songliao Basin, located in northeastern China, is a large-scale Cretaceous sedimentary Basin in China, and one of the most big Cretaceous lake in Asia. The Qingshankou period in Cretaceous is the time when the first large-scale lacustrine transgressive events happened in the Songliao Basin. For a long time, transgressive events and the properties of the ancient lake during deposition of the Qingshankou Formation Unit 1(K2qn1) have been the research focuses in the Songliao Basin.“SLCORE I”has taken continuous high-resolution sedimentary records. So it has provided ideal materials for the high-resolution paleoenvironment and paleoclimate reconstruction. In the organic matter-rich sedimentary pyrite are a characteristic mineral and an important indicator for recovering depositional environment. Numerous studies show that study of sedimentary pyrite morphology may provide useful information on depositional environments and early diagenic processes.In this study reflecting microscope and Scanning Electron Microscopic (SEM observations indicate that euhedral crystals and framboids are the dominant textural forms of pyrite in the K2qn1 mudstone samples from the south well of“SLCORE I”. Pyrite framboidal size distribution indicates that redox condition in the bottom water had been changed from oxic-dysoxic to euxinic-anoxic to oxic-dysoxic during K2qn1 deposition. Moreover, organic-to-pyrite sulfur ratio indicates that paleosalinity change in the lake had a certain stage during K2qn1 deposition. Transgression may be the most direct reason caused for the water salinization.Mainly based on results of the analysis of the bottom water redox conditions and paleosalinity change, the evolution of lake water environment has been divided into five stages during K2qn1 deposition, i.e., in the first stage (I) the lake is a freshwater environment; In the second stage (II) transgression occurred and the water beginning salinization, but salinity stratification was weak, and the bottom water environment was in an oxic-dysoxic state. In the third stage (III) transgression continued, strong salinity stratification, and the bottom water environment was in a euxinic-anoxic state. In the fourth stage (IV) transgression ended, and the bottom water environment was in an oxygen state. In the fifth stage (V) the bottom water environment was in an oxygen-dysoxic state. In addition, Energy Dispersive X-ray Spectrometer (EDS) analysis results indicate S:Fe atomic ratio may be a indicator for the stage of pyrite formation. Using X-ray diffraction (XRD) analysis results, we found that there may be a positive correlation between framboid diameter and minicrystal size of pyrite. However, in this regard remains to be further studied.更多还原