关于Eofletcheria minima Lin et Chow的讨论

本文对 Eofletcheria minima Lin et Chow 分类位置重新修订,把该生物以动物界珊瑚动物门类中转移到植物界红藻门类里,并定名为 pseudoeofletcheria minima(Lin et Chow)Comb.nov.;同时认为生物化石分类的鉴定质量,对古生态的研究程度所做出的质量有重要的影响,同样古生态学的研究亦有助于重新去思索和确定一些生物化石的分类归属位置。     

Limestone weathering in Eastern Australia. Part 2: Surface micromorphology study

Results from long term microerosion meter (MEM) studies indicate that microenvironments are characterized by different erosion rates. A complementary study, carried out on the same sites, examines the microscale morphology in each environment. Optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes. Under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora. Sites permanently covered by soil or stream water have only dissolution etch features, though stream sites may exhibit microfractures. Sites with periodic exposure exhibit both dissolution and biological etch features. The natural environment is more accurately reflected by allowing some microflora colonization of MEM sites rather than preventing colonization by artificial means.     

河北唐山地区中寒武统张夏组鲕粒灰岩的岩石学研究

本区张夏组鲕粒灰岩内,广泛见到细径放射鲕和较粗的同心-放射鲕.放射鲕中存在连生体,我们称之“连生鲕”.与赵震等(1984)人工合成的静水鲕对比,区内放射鲕亦系静水条件下生成;因未见长串连生体,仅呈现数鲕(2—4个)连生,表明鲕粒生成后遭到搅动水拆开.由此可以认为,本组鲕粒灰岩属间歇高能成因模式的产物。又按该类岩石显示的成岩特征,可知本区鲕粒灰岩经历过多种成岩环境,至今仍保留较为明显的大气成岩环境的标志.     

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.     

Environmental impact on construction limestone at humid regions with an emphasis on salt weathering,Al-hambra islamic archaeological site,Granada City,Spain: case study

Al-hambra is an immense and valuable archaeological site in Spain built on Sabika hill with red brick and natural sandy limestone. It exhibits weathering features indicating salt weathering process. The main aim of this study is to examine weathering processes and intensity acting on Al-hambra. Rock petrography and mineralogical composition have been examined using thin sections, scanning electron microscope, X-ray diffraction and X-ray fluorescence; limits of rock’s physical parameters using ultrasonic waves and mercury porosimeter; rock salt content through hydrochemical analysis. Salts attacking this structure are mainly from wet deposition of air pollutants on the long term chemical alteration of rock’s carbonate content to its equivalent salts. The salts’ concentration limit within the examined rock samples is considerably low but it is effective on the long run through hydration of sulphate salts and/or crystallization of chloride salts. Rock texture type and its silica as well as clay content reduces its resistance to internal stresses by salts as well as wetting and drying cycles at such humid area. The recession in limits of physical parameters examined for deep seated and weathered limestone samples quantitatively reflects weathering intensity on Al-hambra.     

Leakage below dam sites in limestone terrains by enhanced karstification: a modeling approach

Unnaturally high hydraulic gradients below dam sites enhance dissolutional widening of fractures in limestone. A model is presented which suggests that under unfavorable conditions, leakage rates could become unbearably high during the lifetime of the dam. At the beginning when water is impounded, leakage rates are low and increase slowly. A positive feedback loop, however, causes a sudden dramatic increase of leakage within a few years. Deep grouting becomes necessary to prevent such failures. Inefficiencies in grouting may leave some open fractures in the grouting curtain. These fractures widen faster than pathways below the grouting curtain, and reduce the effect of the grouted region located below. Therefore, open fractures act in a similar way as reduction of the grouting depth.     

Triassic mid-oceanic sedimentation in Panthalassa Ocean: Sambosan accretionary complex, Japan

Abstract   The Sambosan accretionary complex of southwest Japan was formed during the uppermost Jurassic to lowermost Cretaceous and consists of basaltic rocks, carbonates and siliceous rocks. The Sambosan oceanic rocks were grouped into four stratigraphic successions: (i) Middle Upper Triassic basaltic rock; (ii) Upper Triassic shallow-water limestone; (iii) limestone breccia; and (iv) Middle Middle Triassic to lower Upper Jurassic siliceous rock successions. The basaltic rocks have a geochemical affinity with oceanic island basalt of a normal hotspot origin. The shallow-water limestone, limestone breccia, and siliceous rock successions are interpreted to be sediments on the seamount-top, upper seamount-flank and surrounding ocean floor, respectively. Deposition of the radiolarian chert of the siliceous rock succession took place on the ocean floor in Late Anisian and continued until Middle Jurassic. Oceanic island basalt was erupted to form a seamount by an intraplate volcanism in Late Carnian. Late Triassic shallow-water carbonate sedimentation occurred at the top of this seamount. Accumulation of the radiolarian chert was temporally replaced by Late Carnian to Early Norian deep-water pelagic carbonate sedimentation. Biotic association and lithologic properties of the pelagic carbonates suggest that an enormous production and accumulation of calcareous planktonic biotas occurred in an open-ocean realm of the Panthalassa Ocean in Late Carnian through Early Norian. Upper Norian ribbon chert of the siliceous rock succession contains thin beds of limestone breccia displaced from the shallow-water buildup resting upon the seamount. The shallow-water limestone and siliceous rock successions are nearly coeval with one another and are laterally linked by displaced carbonates in the siliceous rock succession.     

Carbonate deposits on submerged seamounts in the northwestern Pacific Ocean

Abstract   The lithology of shallow-water carbonates collected from 19 sites on 16 seamounts in six areas of the northwestern Pacific Ocean using the Deep-sea Boring Machine System are described. The areas include the Amami Plateau, Daito Ridge, Oki-Daito Ridge, Urdaneta Plateau, Kyushu-Palau Ridge and Ogasawara Plateau. Chronological constraint is provided by calcareous nannofossil biostratigraphy, planktonic foraminiferal biostratigraphy, larger foraminiferal biostratigraphy and strontium (Sr) isotope stratigraphy. Large amounts of shallow-water carbonates accumulated on the seamounts during the Oligocene, a relatively cool period, whereas limited carbonate deposits formed during the Early Miocene, a relatively warm period. This might indicate that deposition of shallow-water carbonates on seamounts in the northwestern Pacific Ocean was not necessarily controlled by climatic conditions, but was related to volcanism and tectonics that served as foundations for reef/carbonate-platform formation. Remarkable differences in biotic composition exist between Cretaceous and Cenozoic shallow-water carbonates. Late Cretaceous shallow-water carbonates are distinguished by the occurrence of rudists, solenoporacean algae and microencrusters. Middle Eocene to Early Oligocene shallow-water carbonates are dominated by Halimeda or nummulitid and discocyclinid larger foraminifers. Scleractinian corals became common from the Oligocene onward. Nongeniculate coralline algae and larger foraminifers were common to abundant throughout the Eocene to the Pleistocene. The replacement of major carbonate producers in the shallow-water carbonate factory during post-Cretaceous time is in accordance with previous studies and is considered to reflect a shift in seawater chemistry.     

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.     

南沙群岛岛礁地形地貌TM影像特征分析

根据南沙海区的地形地貌特征，利用TM图像，对不同的珊瑚礁、珊瑚沙发育状况和岛礁的地质特征与生态特征进行了分析，研究了水下礁、滩的物质组份、发育程度及TM影像特征，提出了30m以浅岛礁分类方法，查清了南沙海域岛、礁、滩、沙的形态和分布，细化并完善了南沙群岛岛礁分类。