Global geoheritage significance of Ordovician stratigraphy and sedimentology in the Cliefden Caves area,central western New South Wales

Globally significant geoheritage features of the Cliefden Caves area, in the Belubula River Valley between Orange and Cowra in central western New South Wales, comprise a richly fossiliferous shallow-water limestone succession of Late Ordovician age (the Cliefden Caves Limestone Subgroup) overlain by deep-water laminites and allochthonous limestones of the Upper Ordovician Malongulli Formation. Key features of the Ordovician geology of the Cliefden Caves area that have been identified using the Geoheritage Toolkit as being of international significance are the abundance of unique and exceptionally diverse fossils in the Fossil Hill Limestone (forming the lower part of the Cliefden Caves Limestone Subgroup), which supplement detailed interpretation of carbonate-dominated deposition within an Ordovician volcanic island setting. The fossiliferous limestones preserve biostromes and local small bioherms of stromatoporoids and corals, and recurrent in situ and disarticulated/imbricated Eodinobolus shell beds formed in shallow, quiet-water, dominantly muddy carbonate sediments that passed up-sequence to clay-free carbonate environments. These mud-dominated carbonate sediments are interspersed with higher-energy conditions, represented by skeletal, lithoclastic and calcrete-ooid grainstones overlying disconformities, leading to the identification of subaerial disconformities and associated diagenesis in the Fossil Hill Limestone. The Fossil Hill Limestone is succeeded by massive limestones in the middle part of the Cliefden Caves Limestone Subgroup and then, in turn by the Vandon Limestone and the deeper-water graptolitic laminites of the Malongulli Formation—this completes a succession that is rarely preserved in the geological record, further enhancing the geoheritage significance of the Cliefden Caves area.     

四川旺苍志留系鲕粒灰岩特征及地质意义

近期在川西北旺苍地区早志留世南江组中首次发现了鲕粒灰岩.它们多以10 cm左右的薄层夹持在页岩或粉砂质泥岩中, 沉积相分析显示该段地层总体应属于均斜缓坡沉积体系.说明这些鲕粒是由异地搬运而来, 在旺苍附近可能会存在相当规模的鲕粒滩.在显微镜下可观察到, 其中的鲕粒类别单一, 鲕粒紧密排列, 并呈现一定程度的压缩变形, 局部壳层呈锯齿状, 也指示这些鲕粒曾经历过高能分选和搬运, 以及压实成岩作用等.氧碳同位素测试显示, 这些鲕粒灰岩沉积时的古温度大体为25~31 ℃, 表明早志留世的上扬子地台应处于中低纬度干热或温暖的古气候带.除去古气候及古地理学方面的意义, 当前鲕粒灰岩的发现还为该区油气勘探提供了重要的储层信息.      

石灰岩热膨胀特性试验研究

以石灰岩为研究对象,对其在高温作用下的热膨胀特性进行了试验研究。为弄清产生热膨胀的原因,对高温后石灰岩试件的孔隙率、超声波速和元素组成进行了试验研究。试验结果表明,高温作用下石灰岩将发生热膨胀,热膨胀量与试验时间的关系曲线可分为4个阶段,热膨胀量的大小与试验温度有关且为非线性关联;高温后石灰岩的孔隙率变化总体呈随温度升高而增加趋势,且以500℃为分界温度,分为缓慢增加和急剧增加2个阶段。而超声波速检测表明,高温后试件内超声波传播速度变化规律复杂,呈波浪形;高温后试件组成元素检测表明,试件内主要元素含量发生了较大变化;试件内孔隙、裂隙变化和组成、矿物成分分解是导致试件发生热膨胀的主要原因。     

东庞矿奥灰含水层多分支水平孔卡埋钻事故处理

近年来,随着定向钻进技术的不断发展,随钻测量技术和受控定向螺杆钻具的制造工艺日趋成熟。地面定向水平钻孔在石油、天然气、页岩气、盐矿等领域得到广泛应用。地面定向水平分支孔注浆在煤矿防治水领域的应用开始大面积推广,在钻进过程中经常发生各种各样事故,造成大量的人力、物力、财力的损失,甚至导致全孔报废及人员伤亡。因此,如何减少或是避免事故的发生,保证钻进工作的顺利进行,是当前面临的重要课题。本文结合冀中能源股份有限公司东庞矿9400采区奥灰含水层区域注浆改造一期工程钻探工程DB2-E3地面定向水平孔施工时发生卡埋钻事故成功处理的实例,总结了水平注浆孔卡埋钻事故预防措施,对水平孔安全施工具有一定参考意义。     

皖北新元古界望山组灰岩微量元素地球化学特征*

为研究皖北新元古界望山组灰岩地球化学特征及地质背景,对该地区灰岩进行了系统的岩石学和微量元素地球化学测试。研究结果表明：望山组灰岩中,元素U、Pb、Sr、Sm富集,Nb、Pr、Zr、Hf明显亏损;稀土总量偏低（6.68～42.78 μg/g）,轻稀土略亏损,Nd_SN/Yb_SN值在0.65～0.91之间变化,轻重稀土分异微弱,灰岩样品均具有程度不同的La和Y正异常。U、Th、Ce等元素特征反映了研究区望山组形成于缺氧的水体环境,Sr/Ba、Sr/Cu值反映了望山组灰岩形成于盐度较大的海水环境和干旱的气候条件;La-Th-Sc和Th-Sc-Zr/10图解指示望山组灰岩可能形成于大陆岛弧环境。     

灰岩-泥灰岩韵律层的差异成岩作用

灰岩-泥灰岩韵律层包括结核状灰岩到灰岩和泥灰岩互层,广泛分布在陆棚及深海环境中,出现于各地质时期,是研究高分辨率地层学和环境恢复的理想工具.但是成岩作用在灰岩-泥灰岩韵律层形成过程中的作用一直存在分歧,有的学者认为差异化学压实成岩作用加强了原始沉积的差异,有的学者认为成岩作用不仅能够强烈歪曲原始环境特征,还可以通过自身...     

滇东地区峨眉山地幔柱活动的沉积响应

对滇东地区峨眉山玄武岩下伏茅口组灰岩进行地层对比表明,地幔柱上涌导致的隆升开始于茅口期,表现为茅口组同沉积过程中断层差异升降形成的水下隆升;而现今看到的茅口组的地层减薄正是水下隆升形成的沉积地层厚度差异和沉积后地表隆升剥蚀的共同结果,但沉积后隆升的规模远远小于前人估算的千米级别。会东大桥-普格-布拖一带发育的砾岩表明峨眉山玄武岩喷发的多期次性和砾岩的水下泥石流成因,根据其分布范围划定了第一期岩浆喷发之后滇东地区的抬升剥蚀以西昌-巧家断裂和普雄-普渡河断裂为东界。根据上述地质证据,总结了滇东地区二叠纪的构造-沉积演化模型。     

Very low temperature,natural deformation of fine grained limestone: a case study from the Lucania region,southern Apennines,Italy

Abstract

The deformation behavior of fine grained limestones from the Monte Sirino area (Lucania region) of the southern Apennines has been analysed by constraining microstructural observations and crystallographic fabrics with data on the metamorphic conditions of deformation. X-ray and infrared analysis of clay minerals, together with illite ‘crystallinity’ data, suggest that the studied rocks underwent very low grade metamorphism in the deep diagenetic zone. The limestones consist of very fine grained (<10 μm) aggregates of micrite. Elliptically-shaped radiolarians, preserved as moulds with coarser (>20 μm) crystalline fillings, provide common strain markers. Optical microstructures and strain analysis indicate heterogeneous intracrystalline strain in the coarser (>50 μm) calcite. On the other hand, SEM and TEM observations, and crystallographic fabrics determined by X-ray texture goniometry, indicate a deformation involving not only intracrystalline slip, but also an important component of grain boundary sliding in the fine grained matrix. The inferred microscopic deformation mechanisms are compared with constitutive flow laws derived from experimental studies. For the maximum inferred temperature of deformation of 250 °C and geologic strain rates of 10^?13?10^?15 s^?1, deformation mechanism maps for calcite suggest twinning and other glide mechanisms to be active in grains larger than about 5?10 μm. Smaller grains would be mostly deformed by grain size sensitive creep mechanisms, which include both diffusion mass transfer processes and grain boundary sliding. Deformation features observed in the study limestones are compatible with the prediction of such temperature-dependent mechanism maps. © 2001 Éditions scientifiques et médicales Elsevier SAS     

蠕虫状灰岩特征和成因新探

下扬子地区下三叠统中广泛分布着一种外貌独特的灰岩——蠕虫状灰岩,这种灰岩出现在该区深水和浅水的多种环境中,具有灰泥结构和粒泥(或泥粒)结构;斜层理、生物扰动构造和压扁透镜状构造。蠕虫状灰岩是多成因的,各成因之间有着一定的联系,其中,先期形成的可被后期形成的叠加和改造。沉积作用、沉积分异作用是形成蠕虫状灰岩的一个重要前提,而生物扰动作用、水流作用和压实、压溶作用则是形成各种蠕虫状灰岩的关键。     

重庆地区茅口灰岩的岩溶类型与发育特征

重庆地区茅口灰岩按埋藏条件和岩溶发育特征,可分为裸露型现代岩溶、隐伏型岩溶晶洞与东吴运动古岩溶三类。通过对各类岩溶发育特征及矿井的充水充气影响进行研讨,目的在于指导煤矿深部的开采和天然气钻探。