中元古代微指状叠层石: 超微组构和有机矿化过程

微指状叠层石(microdigitate stromatolites,以下简称MDS)是新太古代—中元古代一种重要的沉积构造。由于其内部以纤维状组构为重要特征,而缺乏直接的微生物化石证据,被认为代表特定海洋化学条件下形成的一种海底碳酸盐沉淀,属无机成因。本文对华北中元古代雾迷山组硅化MDS的显微组构研究发现,其柱体由亚毫米级浅色微亮晶纹层(平均厚约65μm)和暗色微晶纹层(平均厚约680μm)交互叠加而成。前者含较少细菌残余,重结晶显著;后者富含细菌残余、微晶多面体及微球粒,并进一步分为具密集连续次级微纹层的(平均厚约380μm)和具稀疏断续微纹层的(平均厚约300μm)两种暗纹层。这三种纹层在纵向上的规律性交互可能反映了季节性变化。毛发状垂向纤维贯穿于整个柱体,但在亮纹层内稀疏。这种纤维可能由垂向生长的丝状菌束(宽<10μm)矿化而成,有些由微球粒(粒径为10～30μm)定向富集构成。微球粒富含细菌残余、胞外聚合物(EPS)以及与之密切共生的纳米颗粒(粒径<45nm)。纳米颗粒可粘结形成亚μm级多面体,构成碳酸盐晶体生长的基点。包围微球粒的微亮晶环边和纤维组构间的微亮晶条带内少细菌残余,可能属微生物影响的矿化成因,而纤维体和微球粒则是微生物诱发矿化的结果。故中元古代MDS属微生物成因,它所展现的有机矿化过程可能也适用于更古老的叠层石。此外,MDS内有机矿物从纳米颗粒到微球粒的有序聚合可能代表了有机矿化的普遍过程,并可用作判定微生物成因碳酸盐岩的重要标识。     

Reconstruction Paleoclimate Dased on Sporopollen Record of Re’nacuo Lake, Tibet

The sedimentary sequences since 33 ka B.P. to 10 ka B.P. have been established in the Re＇nacuo-Lake, Gaize area of north Tibet, through a study of a lacustrine section. The climate since 33 ka B.P. to 10 ka B.P. may be divided into two cycle include 5 dry phases and 5 moist phases from reconstructing the paleoclimate through a study of sporopollen analysis. It mainly reflects the general regularity of global climatic change through contrasting with the pale environment in northern hemisphere. Our pollen record reveals a regional climate history similar to those from the neighboring sites, including the GISP2, the Guliya ice core and core RM in Zoige, and thus supports the notion that the Qinghai-Tibetan Plateau acts as an important link between climatic events in the North Atlantic realm and the Asian monsoon domain. The response of the Qinghai-Tibet Plateau to the global climatic change is relatively sensitive.     

陆相断陷湖盆生烃潜力的古气候波动响应研究——以东濮凹陷古近系文古4井为例

古气候波动会影响古沉积环境,从而造成沉积物组分的变化,并最终导致沉积岩生烃潜力的变化.陆相断陷湖盆是我国陆相含油气盆地的重要类型,近年来还成为重要的致密油藏勘探区,但关于气候波动对地层生烃潜力影响方面的研究还较为匮乏.东濮凹陷是在中-古生界基底上发育起来的一个新生代断陷咸化湖盆,在构造稳定期其沉积记录主要受短期气候波动...     

Portable seiche gauge

A portable instrument with a power consumption of less than 1 W has been developed to measure water height at temporary locations. The full scale range of the recorder is 500 mm, and resolution is better than 5 mm water height. Results obtained with the instrument are given, showing seiche activity in a lake.     

辽西下白垩统义县组湖相碳酸盐岩中的燧石成因

辽西义县鹰窝山下白垩统义县组砖城子层中部发育一套湖相碳酸盐岩,可识别出4种岩相类型,其中角砾化团块灰岩相中含有大量燧石,所含的燧石可据形态划分为结核状、透镜状和团块状3种类型,据颜色和透明度识别出两种类型。燧石以微晶石英和玉髓为主,含少量的白云石和方解石晶粒。该岩相系相对干旱气候背景下的洪积-漫湖沉积体系中较浅储水洼地沉积,火山活动也具一定的影响力。     

酒泉盆地青西凹陷下沟组湖相热水沉积岩流体包裹体特征

以地质背景和岩石组构分析为基础,系统研究了酒泉盆地青西凹陷下沟组湖相热水沉积岩中的流体包裹体特征。结果表明,热水沉积岩中的原生流体包裹体以气液二相包裹体为主、单一液相和单一气相包裹体较少、偶见含子矿物三相包裹体。成矿流体属NaCl-H2O型热液体系,温度为90～200℃,盐度为8%～22%NaCl,密度为0.99～1.2g/cm3,成矿压力为15～180MPa。结合锶同位素等地球化学资料分析,认为成矿流体属于深循环的下渗湖水与岩浆水共同构成的中低温、中高盐度和中偏高密度混合热卤水。提出以不同产状的重晶石、铁白云石和萤石为代表的热水沉积岩的成矿热流体系统,自主喷流通道、分支喷流通道经喷流口至附近及远端的盆地热卤水沉积区存在温度、盐度、密度和压力等物理化学参数逐渐降低的分带性变化规律。在热流体特征分析基础上,对研究区早白垩世湖底热流体成矿机制和成因模式进行了探讨。     

鄂尔多斯盆地东缘上三叠统延长组砂体结构与层序地层学研究

运用层序地层学原理,对鄂尔多斯盆地东缘上三叠统延长组长7—长4+5曲流河三角洲露头进行深入的研究,划分出低位体系域、湖侵体系域和高位体系域,其内部砂体骨架是由席状化水下分流河道、曲流型分流河道、辫状型分流河道沉积构成。阐述了鄂尔多斯盆地东缘上三叠统延长组层序格架和砂体结构特征,建立了鄂尔多斯盆地层序地层格架内砂体分布模式,构建了层序地层格架内砂体结构与相对湖平面响应模式图。研究表明随湖平面变化层序格架内砂体结构发生规律性变化,低位体系域早期侵蚀,晚期充填呈复合状砂体;湖侵体系域砂体呈孤立状;高位体系域早期砂体发育不全,晚期呈席状砂体。     

Fabrics,facies control and diagenesis of lacustrine ooids and associated grains from the Upper Triassic,southwest England

Petrographic analysis of ooids from the Upper Triassic (Mercia Mudstone Group) of southwest England provides an opportunity to assess in detail the origins, transport pathways and diagenesis of an ancient oolite. The Clevedon Oolite is dolomitized and contains a variety of dissolved ooids (oomoulds) and associated grains. The oomoulds occur in well‐sorted, planar and cross‐stratified grainstones, packstones, sandstones and conglomerates associated with shoreface, intershoal, foreshore, beachrock and littoral strandplain deposits. The ooids grew in suspension in the shoreface zone and developed a radial aragonite microstructure. The ooids grew to 0.80 mm in diameter, after which they fractured or ceased growing. Broken grains deposited on or near mobile shoals were rapidly recoated, while other grains, deposited in less agitated, intershoal and lower foreshore areas, were micritized or microbially bound into grapestone aggregates. Locally peloids, intraclasts, quartz grains and micritized grains from intershoal areas supplied nuclei for ooids on nearby shoals. Grains deposited in foreshore areas were rapidly cemented into beachrock and reworked into conglomerates. Soon after deposition, the ooids were subjected to widespread aragonite dissolution followed by dolomitization. The lack of pre‐dolomitization calcite, together with the abundance of early (pre‐compaction) dolospar cements and fabric‐selective dolomitization of micritic fabrics, suggest aragonite dissolution by dolomitizing fluids. Copyright © 2002 John Wiley & Sons, Ltd.     

川东地区东岳庙段沉积环境演化及其页岩油气富集主控因素分析

川东地区下侏罗统自流井组东岳庙段富有机质泥页岩发育，且在局部地区已获工业页岩油气流，但尚未实现规模开发，其页岩油气富集机理研究滞后于生产实践。本文在野外调查和测试分析的基础上，对其沉积环境演化及页岩油气地质条件进行分析，并探讨其页岩油气富集主控因素，以期为实现东岳庙段页岩油气突破提供有益借鉴。结果显示：川东地区东岳庙段发育一个完整的水进水退沉积旋回，富有机质泥页岩主要发育于中部半深湖相，厚约15~30m，TOC平均为1.79%，以II型有机质为主，热演化程度较高，达凝析油—湿气阶段。以黏土矿物粒间孔和有机质孔为主，脆性矿物含量中等，脆性指数平均为62.1%。平均孔隙度为8.85%，而渗透率极低，均值仅0.239mD，呈现出“高孔低渗”特征，层内油气以侧向运移为主。其页岩油气的富集主要受富有机质泥页岩分布、热演化程度和裂缝发育条件的控制。推论垂向富有机质泥页岩连续发育的现今油气低势区是川东地区东岳庙段潜在的页岩油气高产区。