中国南沙某岛礁深层礁灰岩物理力学特性

随着南沙海域岛礁吹填工程的实践,礁灰岩的物理力学特性也逐渐成为工程地质领域的研究热点。从南沙某岛礁深度为300 m的钻孔中获取礁灰岩岩芯,分别通过纵横波测试,单轴及三轴压缩试验和礁灰岩流变试验。得到：深层礁灰岩岩样的礁灰岩岩石横波速度与纵波速度关系为V_s=0.4447V_p+409.94;礁灰岩破坏后仍然具有较大的承载能力,并且礁灰岩的破裂呈碎条状,沿着生长软弱面破裂,礁灰岩由于溶洞和软弱面的强度随机性致使其强度也表现很强的随机性;礁灰岩加速蠕变的发生的应力阀值约为5~6 MPa,当加载水平达到5~6 MPa时才有加速蠕变的过程。试验结论为南海岛礁工程建设提供依据,也为珊瑚礁工程地质力学特性的深入研究提供参考资料。     

Silica diagenesis in Eocene shallow-water platform carbonates, southern Pyrenees

Spectacularly developed lower Eocene chert in the Corones platform carbonates of the Spanish Pyrenees is concentrated within a restricted, brackish-water, laminated ostracod-rich facies, which also contains abundant sponge spicules. The chert occurs as nodular, bedded and mottled varieties, and four petrographic types of quartz are developed: microquartz; length-fast (LF) chalcedony; megaquartz; and microspheres. δ¹⁸O values of chert range from 29·6‰ to 30·9‰ (SMOW), which correspond to a broad isotope rank common for biogenic and diagenetic replacement cherts. Calcian dolomite crystals with high Fe and Na are disseminated within the microquartz and LF-chalcedony, but are absent from the megaquartz and host carbonate. The chert is closely associated with desiccation cracks and with interstratal dewatering structures. Load casts are silicified, and laminae rich in sponge spicules are convoluted. Early cracks related to dewatering are filled by microquartz and quartz cements. Ostracod shells within chert are locally fractured; those in the host carbonate are commonly flattened. Late fractures are filled by LF-chalcedony and megaquartz. There is much evidence for the dissolution of sponge spicules and their calcitization in the carbonate host rock. Silica for the Corones cherts was derived from sponges during early diagenesis and shallow burial. Early mechanical compaction and sediment dewatering played a major role in sponge spicule dissolution, migration of silica-rich fluids and the consequent precipitation of chert. Quartz cements continued to be precipitated into the burial environment.     

鄂尔多斯盆地东缘奥陶系马家沟组四段豹斑状云质灰岩特征及成因: 以关家崖剖面为例*

鄂尔多斯盆地东缘中奥陶统马家沟组发育豹斑状云质灰岩,因其分布广泛、成因复杂以及具有重要的油气储集意义而长期受到关注。文中以山西省兴县关家崖剖面马家沟组四段顶部为例,依据宏观、微观岩石学特征,结合碳氧稳定同位素、原位激光剥蚀的微量稀土元素等地球化学分析手段,分析了豹斑状云质灰岩的特征及其成因。研究表明,豹斑状云质灰岩的特征为: (1)常发育于(含颗粒)泥晶灰岩中,且向上白云石化程度增强,云质斑块内常伴有针状或板条状石膏假晶;(2)按产状可大致分为水平、斜交和不规则花斑3种类型,分别对应于向上变浅序列的下部、中部和上部,序列顶部多见近原地角砾化;(3)基质灰岩与云质斑块的δ¹³C、δ¹⁸O值较同期海水略显负偏,顶部不规则云质斑块负偏程度最大;(4)“豹斑”与基质灰岩均具有较低的Mn、Sr、Ba等含量和低Mn/Sr值;(5)“豹斑”的ΣREE含量较基质灰岩略低,且皆表现为轻稀土富集、重稀土亏损的稀土配分模式,δCe微弱负异常,δEu无异常。依据上述结果,推测关家崖剖面马四段豹斑状云质灰岩产状受到生物扰动和高频海平面驱动的早成岩期岩溶耦合控制,序列由下至上耦合改造由弱变强,形成下—中部以岩溶影响较小的水平和斜交虫迹为特征、上部叠合岩溶强改造形成不规则花斑的垂向序列组合;早成岩期的暴露岩溶不仅叠合改造生物潜穴,而且蒸发浓缩的有限重卤水沿叠合优势通道优先交代孔渗条件更好的区域,至埋藏时期白云石化作用进一步加强,从而形成了区内类型多样的豹斑状云质灰岩。研究结果还揭示出沉积期微地貌控制的早成岩期岩溶作用是马四段这类特殊的豹斑状云质灰岩或豹斑状云岩储集层形成的关键,且在很大程度上控制了这类储集层的分布,这一认识可为高频暴露驱动的早成岩期岩溶研究提供新的材料。     

南京梁代石刻微侵蚀的研究

从地貌学角度较系统地分析了梁代石灰岩石刻表面自然毁损的微侵蚀机制，本文指出，雨水沿缝合线渗流，经多种地衣及兰藻、绿藻等生物作用而大大加强了溶蚀作用，导致石刻的崩解，并讨论此种特殊微侵蚀形态的形成机制在地貌学理论研究中的意义。     

Plate tectonics,palaeoenvironments and limestone geomorphology in West-Central Britain

The variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt-block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto-Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half-graben structures of the eastern Irish Sea-Cheshire-Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas.     

Simulation of the dissolution of weathered versus unweathered limestone in carbonic acid solutions of varying strength

A simulation was undertaken within a climatic chamber to investigate limestone dissolution under varied carbonic acid (H₂CO₃) strengths as a possible analogue for future increases in atmospheric CO₂ arising from global warming. Twenty‐eight samples cut from a block of Bath (Box Hill) limestone from Somerville College, Oxford, which had been removed during restoration after 150 years in an urban environment, were weighed and placed in closed bottles of thin plastic containing varying concentrations of H₂CO₃. Half of the stone samples were derived from exposed surfaces of the stone block (weathered) while the others were obtained from the centre of the block on unexposed surfaces (unweathered). The purpose of this was to compare dissolution of previously weathered versus unweathered surfaces in strong (pH 4·73) versus weak (pH 6·43) solutions of H₂CO₃. A temperature of c. 19 °C was maintained within the chamber representing a plausible future temperature in Oxford for the year 2200 given current warming scenarios. The simulation lasted 25 days with a few stone samples being removed midway. Stone samples show reduced weight in all cases but one. There was greater dissolution of stone samples in a strong H₂CO₃ solution as conveyed by higher concentrations of total hardness and Ca²⁺ in the water samples as well as enhanced microscopic dissolution features identified using SEM. The simulation confirms that enhanced atmospheric CO₂ under global warming, given adequate moisture, will accelerate dissolution rates particularly of newly replaced limestone building stones. However, previously weathered surfaces, such as those on historical stone exposed for a century or more, appear to be less susceptible to the effects of such increased rainfall acidity. Conservation techniques which remove weathered surfaces, such as stone cleaning, may accelerate future decay of historical limestone structures by increasing their susceptibility to dissolution. Copyright © 2006 John Wiley & Sons, Ltd.     

Engineering Geology of Limestone in Malaysia

This paper provides an overview of the engineering geology of limestone. Limestone is of rather wide occurrence in Malaysia. It is interesting in view of the unique landforms and karstic features that are encountered in limestone terrains, e.g. steep, subvertical limestone cliffs rising abruptly and majestically above the ground surface and highly variable and pinnacled subterranean limestone bedrock. The karstic features and associated engineering geological problems of both the limestone hills and the bedrock are discussed in the paper. Rockfalls, sinkholes, cavities, etc. are some of the common engineering geological problems associated with limestone terrains. Some local case studies are provided as illustrations. Finally the rock mechanical properties of limestone is discussed at the end of the paper.     

四川龙门山地区阳新组灰岩地质特征及用途

二叠系阳新组灰岩厚度240~350 m，走向延伸大于50 km，出露面积15 km²以上，资源储量极为丰富.研究区0.6 km²范围内资源量为5193×10⁴ t.阳新组灰岩CaO含量49.87%~55.74%，MgO含量0.24%~2.80%，SiO₂含量0.38%~5.80%之间，SO₃含量0.01%~0.40%，K₂O+Na₂O含量0.02%~0.12%，均达到Ⅰ级水泥用料要求.饱和抗压强度41.6~82.4 MPa，坚固性1%~3%，压碎指标8.2%~9.6%；所有指标均符合建筑石料用要求.对阳新组灰岩地质特征、物理化学指标的分析评价显示，其可广泛运用于水泥、建筑石料等领域，具有重要的经济价值和意义.     

湖相生物碎屑灰岩热模拟气特征

通过对山东平邑盆地下第三系湖相生物碎屑灰岩加水热模拟气的研究,探讨了热解气的产率、组成及结构参数的变化特征。湖相生物碎屑灰岩热解气总体上以非烃气为主要组分,非烃中又以ＣＯ２含量最高,其高含量与碳酸盐岩分解有关;其次为Ｎ２和Ｈ２,ＣＯ含量甚微。烃气中以烷烃为主,烯烃含量很低。在正异构烃组成中异构烃含量相对高。干燥系数和酸烷比随模拟温度升高而规律变化,可以用来衡量有机质的成熟度。     

海上顶部双驱动联动隔水管钻探取心技术

我国南海海域分布着大量礁灰岩地层,这种地层具有原生孔隙大、压缩性强、容易变形、强度小等特点,因此易渗透、易破碎、易坍塌。在岛礁上钻探也常常出现断钻、垮孔、埋钻等事故。对于海洋礁灰岩地层钻探,不仅要克服陆地上面临的问题,还需要面对更为复杂的海洋环境。为解决海上特殊地层取心困难问题,基于船载无隔水管钻探系统,开发了海上顶部双驱动联动隔水管钻探取心技术。该钻探取心技术方案在西沙海域4个不同的站位进行了海洋钻探试验。试验结果表明,该技术可实现高效率、高岩心采取率的海上礁灰岩取心目的,取心深度可达130.75 m,具有广阔的推广前景。