淤泥堤基上粉细砂排水垫层特性研究

在工程实践中,排水垫层厚度、渗透系数等设计参数高度依赖经验,建筑规范[1]认为粉细砂不宜用于排水垫层。结合上海某围垦工程粉细砂排水垫层的实践与原位观测成果,借助于非线性有限元,对粉细砂排水垫层的特性进行研究,探讨垫层渗透系数、厚度、长度以及堤身相对透水性等主要因素对地基固结排水的影响。在此基础上,提出以导水系数作为垫层设计控制参数,并提出可以考虑以上几个主要因素的垫层设计公式,可为粉细砂取代中粗砂用于垫层设计及施工提供了技术支持。实践证明淤泥地基上利用粉细砂充填土工管袋作为排水垫层是可行的。     

油气藏中沥青垫的研究进展

沥青垫是油气藏中沥青质相当富集的含油储层带，其沥青质的相对含量为２０％￣６０％，而对应的油层中其值不足２０％，沥青垫在凝析油气藏和轻质油藏中出现的频率高，常位于非渗透性隔层之上的高孔隙和较高水平渗透率的砂岩储层中，研究表明沥青垫的主要形成机理为：脱沥青作用，重力分离作用，生物降解作用和油－水相互作用，石油运移作用。     

碳酸盐岩中燧石条带成因争鸣——以北京西山中元古界雾迷山组为例

北京地区中元古界雾迷山组主要由燧石条带白云岩、燧石结核白云岩、叠层石白云岩和少量含陆源粉砂质碎屑的白云岩组成,广泛出露于北京山区,厚度2000~3500 m。以雾迷山组为代表的大量中元古代硅质沉积物的物源和形成原因,一般教科书均认为层状燧石为生物成因,结核状燧石为成岩交代成因。笔者等在北京西山等地多次野外考察发现,剖面上的硅质条带或硅质结核（下一般称燧石席或硅胶席）。 燧石席内部常包裹或胶结有下伏白云岩的砾石并且因混有有机质等,表现为各种暗色或杂色。硅胶席在上覆白云质沉积物堆积之前与其周围的白云质灰泥和粒屑几乎同时形成,燧石透镜体与白云质沉积物之间存在着相互穿插、包裹的关系,但彼此之间边界清晰,无论是白云石粒屑还是硅胶席都没有任何被交代痕迹。因此,笔者等认为：燧石“结核”是硅胶聚集成席,再经压实、固化的结果,其浑圆状边缘是水下硅胶与沉积介质的相变面。硅胶固化作用是雾迷山组中原生燧石的唯一成因。在成岩重力压实过程中,连续分布的原生硅质沉积物会形成布丁或“结核”构造。白云质灰泥和粒屑的胶结速度与硅胶的固化速度之间存在着明显的差异,遇地震等外力作用,软的硅胶席会沿着弱固结的白云岩裂隙向上侵入或向下挤入,形成硅质脉。遇有后期的岩浆侵入或热变质作用的改造,硅质条带和硅质结核的成分和颜色会发生相应的变化,质地变纯,颜色由深变浅,但是仍然保留原生的层理或纹理,容易被误认为是成岩期或成岩后硅质交代碳酸盐矿物而成。     

碳酸盐岩中燧石条带成因争鸣——以北京西山中元古界雾迷山组为例

北京地区中元古界雾迷山组主要由燧石条带白云岩、燧石结核白云岩、叠层石白云岩和少量含陆源粉砂质碎屑的白云岩组成,广泛出露于北京山区,厚度2000~3500 m。以雾迷山组为代表的大量中元古代硅质沉积物的物源和形成原因,一般教科书均认为层状燧石为生物成因,结核状燧石为成岩交代成因。笔者等在北京西山等地多次野外考察发现,二维剖面上的硅质条带或硅质结核在三维实体上实际上是透镜状或席状（下一般称燧石席或硅胶席）。 燧石席内部常包裹或胶结有下伏白云岩的砾石并且因混有有机质等,表现为各种暗色或杂色。硅胶席在上覆白云质沉积物堆积之前与其周围的白云质灰泥和粒屑几乎同时形成,燧石透镜体与白云质沉积物之间存在着相互穿插、包裹的关系,但彼此之间边界清晰,无论是白云石粒屑还是燧石席都没有任何被交代痕迹。因此,笔者等认为：燧石“结核”是硅胶聚集成席,再经压实、固化的结果,其浑圆状边缘是水下硅胶与沉积介质的相变面。硅胶固化作用是北京西山中元古界雾迷山组中原生燧石的唯一成因。在成岩重力压实过程中,连续分布的原生硅质沉积物会形成布丁或“结核”构造。白云质灰泥和粒屑的胶结速度明显快于硅胶的固化速度,遇地震等外力作用,软的硅胶席会沿着弱固结的白云岩裂隙向上侵入或向下挤入,形成硅质脉。遇有后期的岩浆侵入或热变质作用的改造,硅质条带和硅质结核的成分和颜色会发生相应的变化,质地变纯,颜色由深变浅,但是仍然保留原生的层理或纹理,容易被误认为是成岩期或成岩后硅质交代碳酸盐矿物而成。     

Microbially induced sedimentary structures in Archean sandstones: A new window into early life

Until now, the most valuable information on the early life on the Archean Earth derived from bacterial fossils and stromatolites preserved in precipitated lithologies such as chert or carbonates. Also, shales contain complex biomarker molecules, and specific isotopes constitute an important evidence for biogeneicity.In contrast, because of their low potential of fossil preservation, sandstones have been less investigated. But recent studies revealed a variety of ‘microbially induced sedimentary structures — MISS’ that differ greatly from any other fossils or sedimentary structures. ‘Wrinkle structures’, ‘multidirected ripple marks’, ‘biolaminites’, and other macrostructures indicate the former presence of photoautotrophic microbial mats in shallow-marine to tidal paleoenvironments. The MISS form by the mechanical interaction of microbial mats with physical sediment dynamics that is the erosion and deposition by water agitation. The structures occur not only in Archean tidal flats, but in equivalent settings throughout Earth history until today.MISS are not identified alone by their macroscopic morphologies. In thin-sections, the structures display the carpet-like fabrics of intertwined filaments of the ancient mat-constructing microorganisms. Geochemical analyses of the filaments proof their composition of iron minerals associated with organic carbon.In conclusion, microbial mats colonize sandy tidal settings at least for 3.2 Ga years. Therefore, Archean sandstones constitute an important archive for the exploration of early life.     

河北承德寒武系凤山组叠层石生物丘中的沉积组构

河北承德路通沟剖面芙蓉统凤山组中部发育厚层块状叠层石生物丘,构成一个淹没不整合型层序的强迫型海退体系域,指示这些叠层石形成于中高能浅海环境。该生物丘宏观上主要由柱状叠层石组成,叠层石内部纹层较粗糙,在构成叠层石的致密泥晶和微亮晶组构中,还见到球粒、底栖鲕粒及凝聚颗粒等多种生物成因颗粒类型,代表着复杂的微生物活动特征,以此而区别于前寒武纪的叠层石。更为重要的是,叠层石生物丘中的致密泥晶基质中发育一些“石松藻(Lithocodium)”状的钙化蓝细菌菌落残余物,以及一些丝状钙化蓝细菌化石,指示了形成叠层石的微生物席为蓝细菌所主导的微生物席。因此,凤山组叠层石生物丘内复杂而特殊的碳酸盐岩沉积组构为研究叠层石形成过程中复杂的微生物代谢活动所产生的钙化作用机制提供了一个宝贵的地质实例。     

从微观角度认识微生物席在中元古代的繁盛--以豫西云梦山组为例

豫西云梦山组发育了大量的微生物成因沉积构造（MISS）。在地层纵剖面上,毫米级的深色沉积物层和浅色的石英颗粒层交替出现,形成典型的微生物席纹层,代表着微生物席在沉积表面的多次生长和埋藏。深色层包含有泥质物和细砂-粉砂颗粒,被认为是先前微生物席的残留区;浅色层则是较纯净的石英颗粒,由物理沉积作用形成。进一步对纹层区的薄片...     

Access to reeds and mat making in the lower Volta basin of Ghana

This paper explores the origins of pressures on reeds and sedges used for mat making in the lower Volta basin of Ghana, and their impact on the socially embedded system which dictates access to reed fields. Data for the study were collected through field work employing participatory rural appraisal methods in 18 communities, involving 152 mat weavers. The findings showed that the mat‐weaving industry has contributed immensely in providing poor women a means of livelihood but reed marshes in the basin have reduced in recent years due to hydrological changes in the area caused by the damming of the Volta upstream. The decline in the availability of reed is exerting immense pressure on this once freely available resource, thus inducing landlords to impose a price on the rights of entry into marshlands by reed collectors. The imposition of these charges affected the very people that the mat‐weaving industry is targeted to help. The study recommends the local and central government to play a more active role and civil society groups to broaden the livelihood base of women living in this region.