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1.
本文介绍在暖温带河口悬移质中发现的石膏颗粒及其表面的新生方解石和霰石晶体。石膏颗粒经受了不同程度的化学和生物化学风化。在一部分风化石膏表面,存在大量的数微米到数十微米大小的方解石和霰石晶体,某些晶体还呈现出亲岩生物遗留的生长纹。由于河口水的溶蚀作用,一部分石膏颗粒已充分碳酸钙化。  相似文献   

2.
Gypsum crusts are broadly defined as accumulations at or within about 10 m of the land surface from 0.10m to 5.0 m thick containing more than 15% by weight gypsum (CaSO4·2H2O) and at least 5.0% by weight more gypsum than the underlying bedrock. The deposits are often, but not invariably, consolidated owing to cementation by gypsum. The crusts are found in many of the world's deserts where mean monthly potential evaporation exceeds mean monthly precipitation throughout the year. Using structural, fabric and textural criteria, three main types of crust may be distinguished:(1) bedded crusts, found either at or beneath the land surface, which are made up of discrete horizontal strata up to 0.10 m thick, each showing a gradation in gypsum crystal size from less than 50 μm at the top to more than 0.50 mm at the base; (2) subsurface crusts, of which there are two forms, one made up of large, lenticular crystals (up to 0.50 m in diameter)—the desert rose crusts—and the other, a mesocrystalline form, with gypsum crystals up to about 1.0 mm in diameter; and (3) surface crusts, which are subdivided into columnar, powdery and cobble forms, all of which are made up of predominantly alabastrine gypsum (crystallites less than 50 μm in diameter). In southern Tunisia and the central Namib Desert, bedded crusts are found around ephemeral lakes and lagoons. They are characterized by size-graded beds, gypsum contents of 50–80% by weight and comparatively high concentrations of sodium, potassium, magnesium and iron. They are interpreted as shallow-water evaporites which accumulate when saline pools evaporate to dryness. Desert rose crusts or croûtes de nappe generally contain 50–70% by weight gypsum, and have higher sodium concentrations than the second subsurface form. Texturally they are characterized by poikilitic inclusion of clastic material within large lenticular crystals. They are interpreted as hydromorphic accretions, which precipitate in host sediments at near-surface water tables through the evaporation of groundwater. The second form of subsurface crust—the mesocrystalline—often occurs in close association with the various surface forms. Unlike the hydromorphic crusts, they are not restricted to low-lying terrain. They are characterized by gypsum contents reaching 90% by weight, and have a close chemical and textural similarity to columnar surface crusts. This mesocrystalline form represents an illuvial accumulation; the surface forms—excluding the bedded crusts—are exhumed examples at various stages of solutional degradation. Subsurface precipitation of gypsum from meteoric waters containing salts leached from the surface, results in displacive gypsum accumulation in the soil zone. In southern Tunisia, the gypsum is derived from sand and dust deflated from evaporitic basins; in the central Namib, salts dissolved in fog water are the most likely source. Where other salts are present, differential leaching may form two-tiered crusts, calcrete—gypsum or gypsum—halite, if rainfall is sufficient to mobilize the less soluble salt yet insufficient to flush the more soluble. Gypsum crust genesis is restricted to arid environments, and if their susceptibility to post-depositional alteration is acknowledged, they can provide valuable palaeoclimatic indicators.  相似文献   

3.
A variety of finely laminated, subfossil, aragonitic stromatolites and oncolites occur on a regressive marginal flat surrounding Marion Lake, South Australia. These algal forms overlie a substrate of coarse, highly porous, moldic aragonitic limestone which passes progressively towards the take centre through a zone of interstatified aragonite and gypsum and ultimately to pure crystalline gypsum. All of these facies overlie Holocene marine carbonate bank sediments which unconformably overlie at least one upper Pleistocene marine unit. Detailed petrographic and stratigraphic studies, combined with comparative studies of related nearby lakes containing a variety of living aragonitic cryptalgalaminates, provide a model for development of the Holocene sedimentary sequence. Marion Lake last became inundated by the sea around 6500 years ago during the Holocene transgression, when a protected marine environment was initiated. Lateral sediment accretion sealed marine passes into the resulting lagoon system soon after sealvel stabilized, and a variety of gypsum and gypsum-carbonate-algal facies evolved. Pure gypsum was deposited in waters 2–3 m deep in the central basin area concurrently with formation of seasonally alternating gypsum and aragonite layers towards basin margins. Blue-green filamentous algae thrived in the shallower marginal areas and at least partly controlled carbonate deposition, which must have occurred during seasonal outflow of carbonate-rich ground water from the calcareous dune aquifer over denser gypsum-saturated waters. These systems eventually migrated towards the centre of the lake to produce the relationships preserved today. The fresher waters also leached the gypsum from the marginal gypsum-carbonate facies. Collapse due to gypsum dissolution, along with aragonite crystallization, combined to form a lake-marginal mega-polygonal facies. Teepee structures formed around polygon margins, with optimum conditions for stromatolite development occurring on the teepee crests. The actual stromatolites which occur around Marion Lake are strongly indurated and involve a variety of morphologies, the most common of which are laterally linked hemispheroids. Stacked hemispheroids and oncolites are also relatively common, along with irregular forms, many of which encrust a variety of substrate irregularities. Vertical relief of the stromatolites varies from centimetres to tens of centimetres and all forms are characterized by extremely fine internal interlaminations of alternate light and dark grey laminae which typically occur several per millimetre. The microstructure comprises micritic aragonite crystals with fibrous habit associated with organic matter, and occasional zones of abundant algal filament molds which are generally oriented normal to the laminae.  相似文献   

4.
The travertine buildings of Budapest show extensive black crust formation, which is related to high concentration of atmospheric pollution and a continental climate. Laminar black crusts, framboidal black crusts and leached white surfaces are compared. Physical properties (Schmidt hammer rebound, Duroscope rebound), mineralogical composition and elemental composition are measured. Framboidal black crusts contain more than 50% of acicular gypsum. The crust surface displays idiomorphic rosette-like gypsum crystals with particulates, calcite and gypsum crystal aggregates. The sulphur isotopic composition of the black crusts pinpoints the involvement of rain and dust in crust formation. Thick framboidal black crust has the lowest strength while thin laminar black crust and white dissolved surfaces show minor decrease in surface strength compared to unaltered travertine. The crusts adhere to the travertine surface and rarely show mechanical decay forms that are typical features of porous limestone ashlars in Budapest.  相似文献   

5.
在藏北羌塘坳陷地区晚侏罗世晚期地层中发现石膏及油页岩,对石膏、油页岩及相应的岩石组合基本特征进行了详细观察描述,并采集了大量油页岩、孢粉及双壳类化石样品.结合区域地质及产出石膏及油页岩地层的沉积学特征简要分析,认为北羌塘坳陷胜利地区晚侏罗世时期具有多次海进、海退,从而形成潮坪、泻湖相环境间歇性沉积,而古气候的变化是导致...  相似文献   

6.
Accumulation of microbial mats and stromatolites dominate in the crystallization ponds of solar salt works west of Alexandria, Egypt. These microbial mats are laminar in the permanent submerged part of the ponds. The microbial mats commonly form sites for growth of gypsum crystals during periods having higher salinity. In the dominant submerged part of the pond, domal stromatolites are common around groundwater seepage holes. In the shallow, intermittent margin of the ponds, the laminated microbial structure forms laterally close-linked hemispheroidal stromatolite type, with unidirectional and multidirectional ripple mark-like morphology on their surface. The microbial laminite and stromatolite types in the modern solar salt works are similar to the organic-rich Miocene gypsum beds of El-Barqan (west Alexandria, Egypt) and Rabigh (north Jeddah, Saudi Arabia). The Miocene organic-rich beds consist of interlayered dark-colored microbial laminae and light-colored gypsum laminae. These beds may have three different variations: regular even lamination, laterally closed-linked hemispheroidal stromatolites, and/or discrete hemispheroidal stromatolites. Petrographic examination of the microbial laminites and stromatolites in the solar salt works and the Miocene gypsum beds indicate that the dark-colored, organic-rich laminae are composed of micritized microbial laminae and/or brown organic filaments. In El-Barqan area, the light-colored gypsum-rich laminae are composed of either gypsum crystal fragments, or lenticular and prismatic gypsum. These gypsum crystals are either entrapped within the microbial filaments or are nucleated at the surface of the microbial laminae to form a radial pattern, whereas in Rabigh area, the light-colored gypsum-rich laminae are composed of secondary porphyrotopic, poikilotopic, or granular gypsum crystals. By comparison of the microbial structure in the Miocene gypsum beds with the recent occurrence of the microbial laminites and stromatolites in the solar salt works, it is demonstrated that the organic-rich Miocene gypsum beds were formed in a very shallow salina with slightly fluctuating brine levels.  相似文献   

7.
何明倩  黄文辉  久博 《地学前缘》2021,28(4):327-336
膏质白云岩是鄂尔多斯盆地中东部下古生界马家沟组M51最有利储层,影响膏质白云岩储层性质的最大因素在于溶蚀作用。本文在已有的研究基础上,应用岩心资料及阴极发光、地球化学等方法,测定M51膏质白云岩及其特殊的示底构造的化学成分,并分析其成因模式。岩心、薄片以及物性资料显示:石膏溶蚀形成的大量膏模孔及伴生的次生孔是储层的主要储集空间,示底构造规模性出现于膏质云岩中。阴极发光、常微量元素分析结果显示:示底构造上部充填埋藏期方解石;下部充填碎屑白云石,与示底构造外围的准同生期泥-粉晶白云石具有相近的地球化学特征,与深部埋藏期形成的细-中晶白云石差异明显。示底构造的演化是膏质白云岩有利储层形成的重要依据,本文依据化学离子平衡原理,对不同成岩阶段发生的溶蚀作用、填充作用进行离子间相互置换的重演,分析得知不稳定的化学组成是石膏易被溶蚀的内在原因,石膏的规模性溶蚀是膏质云岩有利储层形成的关键。  相似文献   

8.
A thick sedimentary sequence comprising fluvial, lacustrine and volcano-sedimentary rocks is present in the Neogene Beypazari Basin, central Anatolia. These units display considerable lateral facies variation and interfinger with alkaline volcanic rocks along the north-eastern margin of the basin. The uppermost Miocene Kirmir Formation contains numerous evaporite horizons. The evaporite sequence is up to 250 m thick and may be divided into four lithofacies. In ascending stratigraphical order these are: (1) gypsiferous claystone facies, (2) thenardite-glauberite facies, (3) laminar gypsum facies and (4) crystalline gypsum facies. These facies interfinger with one another laterally along a section from the margins to central parts of the basin. The lithological and sedimentological features of the Kirmir Formation indicate fluvial, saline playa mudflat, hypersaline ephemeral playa lake and very shallow subaqueous playa lake depositional environments, which probably were influenced by alternating semi-arid and evaporative conditions.  相似文献   

9.
In this study, karstification developed in the Miocene gypsum which covers a large area around Sivas, Turkey, the relation between regional tectonics and karstification, and hydrogeological features have been investigated. The karstic features in the gypsum have developed conforming to the fault zones and the general strikes of gypsum beds. In the study area, numerous dolines (sinkholes) and ponors (swallow holes) of different sizes are observed. Most of these karstic features are in the different-sized longitudinal depressions (troughs) which conform to the tectonic structures. These karstic features occur NE-SW along bedding planes and about NW-SE and NE-SW along fault zones. At the intersections, high-capacity (yield) karst springs (Göydün and Seyfe springs) are observed. The Göydün and Seyfe springs issue from the karstified gypsum aquifer, with an average discharge of 1.10 m3/s and 0.25 m3/s, respectively. In addition, there are some low-yield (a few l/s) springs in the same drainage area. The surface drainage area of the springs is 64 km2, and the precipitation in this area cannot provide the total groundwater discharging from Göydün and Seyfe springs. Water budget calculations indicate that more than 70% of the water discharged by these two springs is provided from the adjacent basins. The Göydün and Seyfe springs are rich in dissolved solids and average electrical conductivities (EC) are about 13?000 μS/cm. The major cations in the waters are Ca and Na; major anions are SO4 and Cl, and the waters are brackish. Because of these properties, especially in summer and autumn, the springs cause extreme salinization in K?z?l?rmak river.  相似文献   

10.
Gypcretes of Miocene age are preserved beneath a 9·53 ± 0·36 Ma ignimbrite along the eastern margin of the Oligo-Pleistocene Calama Basin, northern Chile. They are restricted to a single stratigraphic horizon developed within laterally extensive (>35 km) coalesced alluvial fan deposits, developed along the margin of an endorheic basin. Two types of gypcrete are recognized. Type 1 comprises almost completely gypsum-cemented sandstones containing alabastrine nodules and columns, sub-vertical and horizontal veins of fibrous gypsum and 'v-shaped' cracks infilled by clastic material, and are interpreted as surface weathered gypsic crusts. Type 2 gypcretes are composed of massive, reddened poikilitic and mesocrystalline gypsum (up to 80% of the rock) with isolated bedding-parallel, clast-rich lenses (200 × 30 cm) and sub-vertical veins of fibrous gypsum. The massive texture resembles that of well developed B horizons in Quaternary alluvial desert soils. The crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic (poikilitic) and illuvial (mesocrystalline) processes with the fibrous gypsum veins suggestive of periodic surface exposure.
Gypcrete horizons are up to 25 m thick and composed of both gypcrete types. They represent superimposed phases of surface and subsurface gypcrete development. Quaternary gypcretes are developed in arid climatic regimes, but are not considered to develop under hyper-arid climates. An arid climate is considered to have prevailed in the study area up to 9·5 Ma after which a change to hyper-aridity favoured gypcrete preservation.  相似文献   

11.
山西中奥陶世石膏岩的沉积受到机械沉积作用的影响。区内九种石膏岩分别是不同水深条件下的沉积及交代产物,并可归纳为浪基面下洼地、浅水、滩岛潮坪等三种沉积环境。在空间上,它们彼此依存、转换并连为一体形成一个巨大的浅水蒸发岩沉积。  相似文献   

12.
Well exposed, often laminated gypsum sequences occur in many Quarternary salt lakes in southern South Australia. The gypsum in the salt lakes is classified by increasing grain size into gypsite, gypsarenite and selenite. The salt lakes are classified by age and hydrological setting into coastal salinas which are Holocene sea-water fed groundwater lakes, and continental playas which are late Pleistocene endorheic basins. A study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes. As the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited. Application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non-salina gypsum deposits.  相似文献   

13.
胡光明  张亚金  周雁 《地质科学》2010,45(3):734-744
中下扬子早-中三叠世膏盐层是对早印支运动的沉积响应,本文从膏盐的成因、中下扬子膏盐层位的差异、沉积环境的变迁、膏盐的厚度变化和产状特征、沉积中心和沉降中心的分布等方面,分析早印支运动的表现形式。中下扬子早-中三叠世依次出现陆棚台地(碳酸盐岩)、潟湖—潮坪(白云岩与膏盐)和滨海(碎屑岩),这种大规模海退,正是早印支运动表现为构造抬升的结果。抬升过程中,残留海水在炎热干燥的气候条件下蒸发形成膏盐层,而中扬子的膏盐层位比下扬子低,据此推测中扬子先于下扬子与华北板块碰撞而抬升。平面上,现今构造格局(主要由中印支—早燕山运动形成复向斜、复背斜和推覆构造)的坳陷区主要为白云岩与(硬)石膏互层或石膏夹少量白云岩或云质石膏,膏盐层厚度大,现今构造的隆坳过渡区主要为石膏假晶、含膏云岩、石膏质白云岩、白云岩夹石膏等,膏盐层厚度小,而膏盐的厚度和产状与沉积时的水深和地势直接相关;另外,地层等厚图显示膏盐层主要分布于当时的沉降中心。这些沉积特征显示膏盐沉积时的地势与现今隆坳相间的构造地貌存在一定程度的吻合,说明膏盐沉积时的地层已经发生了轻微的褶皱变形(未见角度不整合和地层缺失)。  相似文献   

14.
鄂尔多斯白垩系地下水盆地蕴藏有丰富的地下水资源,地下水赋存于白垩系砂岩中。为了查明地下水微咸水的成因,对40件地下水样品的水化学组成、SO42-的区域分布特征和28件硫同位素组成进行了分析,并对34件岩石样品进行了溶滤试验研究。结果表明:SO42-是地下水中主要阴离子组分,具有东部低西部高,北部低南部高的区域分带特征;硫酸盐是白垩系地层中主要的易溶盐组分,并以石膏和芒硝形式存在;地下水中SO42-主要来源于地层中石膏和芒硝,其次是地层中的硫化物,少量来源于有机硫。  相似文献   

15.
四川盆地下寒武统膏盐岩发育特征与封盖有效性分析   总被引：2，自引：0，他引：2  
林良彪  郝强  余瑜  淡永  彭勇民 《岩石学报》2014,30(3):718-726
四川盆地下寒武统广泛发育一套膏盐岩,主要沉积于早寒武世龙王庙期。基于四川盆地深井及实测剖面中膏盐岩的识别和统计,发现下寒武统有川南和鄂西两大聚盐区,最厚达690.40m;川南聚盐区西部以含泥含云质石膏岩类和含膏砂泥岩类为主,东部及颚西聚盐区主要为含膏白云岩类。结合前人研究,认为膏盐岩发育于浅水缓坡沉积环境,有潮上萨布哈和缓坡蒸发两类成因。通过对川南聚盐区储盖匹配关系及后期构造与膏盐岩封盖性分析,表明下寒武统膏盐岩与盐下震旦系优质的白云岩储层在空间上具有良好的匹配关系;四川盆地边界大断裂及边界外寒武系的抬升暴露让膏盐岩在盆地外封盖性失效,而在盆地内膏盐岩的封盖性较好。威远气田解剖表明有膏盐岩分布的威远地区成藏,而无膏盐岩分布的资阳地区气藏被破坏,显示了下寒武统膏盐岩在四川盆地油气成藏中具有重要的作用。  相似文献   

16.
The Ringwood evaporite is part of the 900 m.y. old Bitter Springs Formation, a warm-water shallow-marine sequence of stromatolitic dolomite and limestone, microfossiliferous chert, red beds, quartzite, and evaporites. The evaporite at Ringwood comprises two parts: (i) a lower 127 m characterized by brecciated pyritic bituminous dolomite, together with smaller amounts of dolomite-gypsum breccia, friable chloritic dololutite, coarsely crystalline anhydrite, and satin-spar gypsum; and (ii) an upper 133 m which is similar except that bituminous dolomite forms only one bed, and the characteristic rock-type is dolomite-gypsum breccia. The evaporite is overlain by limestone breccia and massive stromatolitic limestone, interpreted as an algal reef. Gypsum is secondary after anhydrite, and the ratio of gypsum to anhydrite increases upwards. The evaporite shows none of the features of a sabkha or desiccated deep ocean basin deposit, and instead is interpreted as the filling of a barred basin which was cut off from the ocean by growth of an algal barrier reef. As circulation became restricted, bituminous dolomite deposited in the lagoon behind the reef, together with pyrite from the destruction by anaerobic bacteria of algal debris derived from the reef. With continued evaporation, brine concentration increased and gypsum precipitated. Occasional dust storms contributed wind-blown clay to the deposit. The barrier reef transgressed diachronously across the evaporite lagoon, and was eventually drowned when normal marine conditions became established. Burial of the evaporite to about 7000 m beneath the succeeding sediments of the Amadeus Basin converted gypsum to anhydrite, and formed chlorite by reaction of clay with dolomite. Late Palaeozoic tectonism folded and brecciated the rocks, and was followed by erosion which eventually exposed the evaporite to ingress of meteoric water. Hydration of anhydrite to gypsum ensued, the reaction becoming less complete with increasing depth from the ground surface.  相似文献   

17.
The Lune River Quarry at Ida Bay, Tasmania exposes numerous palaeokarst features developed in the Ordovician Gordon Limestone. These palaeokarst features contain carbonate and siliciclastic deposits probably representing Late Devonian to early Late Carboniferous and Late Carboniferous karstification and sedimentation. Five facies of palaeokarst deposits are recognised, namely megabreccia, graded‐bedded carbonate, laminated sandstone/siltstone, diamictite/quartz‐lithic sandstone and coarse crystalline calcite. Pyrite, dolomite and sphalerite were emplaced in the palaeokarst deposits after the Carboniferous. These deposits are probably associated with a phase of hydrothermal cave development in Exit Cave, which adjoins the quarry. Pyrite weathering accounts for the abundance of gypsum speleothems and cave breakdown in Exit Cave.  相似文献   

18.
山西省阳泉市山底河煤矿“老窑水”循环系统多年水质监测数据计算结果显示,煤矿酸性“老窑水”的Ca/Mg值普遍偏低,且存在Ca/Mg值随酸化程度的增强（SO42?含量增加或pH减小）而减小的规律。针对这一问题,结合研究区的地球化学物源条件,通过室内试验以及野外监测水样的石膏、方解石、白云石矿物饱和指数与pH变化关系,分析煤矿酸性“老窑水”低Ca/Mg值的成因机制。研究表明:区内石炭系－二叠系的煤系地层中碳酸盐岩夹层、分散状态分布的菱镁矿、黄铁矿是“老窑水”中Ca2+、Mg2+、SO42?的物质来源;在黄铁矿氧化水解形成的以硫酸根为主导的酸性溶液中（pH为2.0~4.5）,代表硫酸对石膏、方解石、白云石可溶解性的饱和指数排序为石膏>方解石>白云石,受石膏在高浓度硫酸活性降低并发生沉淀、方解石溶解受Ca2+同离子效应抑制和饱和状态的平衡调节的综合影响,使Ca2+相对含量减少,由于MgSO4溶度积大于CaSO4,故Mg2+含量未受上述约束（或较低）,脱白云岩化反应可因Ca2+含量随石膏沉淀而继续进行,加之区内有菱镁矿的溶解,使得Mg2+相对含量增加,最终出现了镁矿酸性“老窑水” Ca/Mg值低的结果。Ca/Mg值可作为煤矿酸性“老窑水”的污染特征指标,应用于环境影响评价。   相似文献   

19.
The purpose of this study is to achieve an understanding of the failure mechanisms which caused the Eaux-Bonnes landslide. The geological investigations carried out on the slope of the landslide showed that the sliding mass was cut by numerous faults. The factors controlling the landslide failure were complex, and it is known that neither earthquakes nor heavy precipitation could have triggered the disruption. The groundwater within the solid rock mass has been surveyed, because significant precipitation events during the 2 years preceding the beginning of the paroxysmal phase of the landslide could have led to an increase in pore water pressure along these fractures, thereby triggering the landslide. In order to achieve a full understanding of the failure mechanism, and to identify the origin of the groundwater, a hydrogeochemical survey was carried out over a period of 1 year. The results reveal the existence of high sulphate concentrations in the groundwater originating in springs located at the bottom of the landslide. The sulphate concentrations are correlated with high calcium concentrations, and clearly indicate the presence of gypsum in the vicinity of the lower reaches of the landslide. The presence of gypsum in this area of the Pyrenees suggests that deep groundwater played a role in triggering the landslide.  相似文献   

20.
The Cuddapah basin consists of generally well-preserved Palaeoproterozoic–Neoproterozoic sedimentary and associated volcanic rocks. The detailed lithological studies of sedimentary rocks of Vempalle Formation from the narrow linear belt of 15 km, in the southern margin, show the occurrence of layered gypsum in the cherty dolostone–shale intercalated facies, red shale and phosphatic dolostone facies of the Vempalle Formation. The petromineralogical studies reveal that gypsum is in close association with anhydrites. Microscopically, three different types of gypsum and anhydrite are identified, viz., lath-shaped, equant-shaped and anhedral-shaped grains. The equant variety corresponds to a granular gypsum, whereas the anhedral grains of gypsum exist as the granular and fibrous variety as seen in the hand specimen. The presence of gypsum/anhydrite has been confirmed by the petromineralogical, X-ray diffraction and chemical analytical data. The phosphatic dolostone is the host rock for stratabound type of uranium deposit at Tummalapalle, Cuddapah district, Andhra Pradesh, which is one of the most unique types of uranium mineralisation in the world. Abundant pseudomorphs of gypsum and anhydrite relicts and discontinuous gypsum layers within these dolostones, nodules of chert and gypsum indicate the interrelationship between the diagenesis and genesis of uranium mineralisation which indicates the carbonate precipitation in the sulphate-rich hypersaline environments.  相似文献   

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