Siliceous Limestone Research Articles

99/01621 The influence of limestone addition at different positions on gaseous emissions from a coal-fired circulating fluidized bed combustor : Hao, L. and Gibbs, B. M. Fuel, 1998, 77, 14, 1569–1577

The presented study aims to investigate the gaseous fluoride and sulfur dioxide (SO2) pollution level in the kitchen, traditional flue-curing barn and outdoor environment and to find economically feasible method to reduce fluorine and sulfur release. The gaseous fluoride and SO2 concentrations in air of outdoor environment, kitchen and traditional flue-curing barn were determined in 56 households in coal-burning endemic fluorosis areas of Zhaotong. Among these, 21 households in Yujiawan Village, Zhenxiong County, Zhaotong City were chosen for this experiment to reduce gaseous fluoride and SO2 concentration in traditional flue-curing barn air by using calcined dolomitic siliceous limestone (CDSL) instead of clay mixed with coal. The result showed that: (1) gaseous fluoride and SO2 concentration in the outdoor air in Mangbu Township area was 0.51 μg dm−2⋅day and <0.05 mg m−3, respectively and in Xiaolongdong Township was 2.7 μg dm−2 day and <0.05 mg m−3, respectively while in Zhaotong City these concentration were lower than the ambient air standard (3 μg dm−2⋅day and 0.5 mg m−3, respectively). (2) The indoor gaseous fluoride concentration (3.7 μg m−3) in air of kitchen with the improved coal stove was within the reference value (10 μg m−3); SO2 concentration (0.94 mg m−3) in kitchen air had decline, but its concentration was still higher than indoor air quality standard (0.5 mg m−3). (3) Average concentration of gaseous fluoride and SO2 in air of traditional flue-curing barn of Xiaolongdong Township was 7.2 μg m−3 and 6.8 mg m−3 respectively, and in Yujiawan village were 10.1 μg m−3 and 14.4 mg m−3, respectively. (4) After using the calcined dolomitic siliceous limestone instead of clay mixed with coal, gaseous fluoride and SO2 concentration in the traditional flue-curing barn air decreased of 45% and 91%, respectively. The gaseous fluoride and SO2 pollution in the traditional flue-curing barn is very serious. The corn and chili baked by open stoves in traditional flue-curing barn (baking room) was also seriously polluted by fluoride and sulfur. After using the calcined dolomitic siliceous limestone instead of clay mixed with coal, gaseous fluoride and SO2 concentration in the traditional flue-curing barn air have declined markedly. The way of adding calcined dolomitic siliceous limestone instead of clay as a binder for briquette-making is an economically feasible way to control the indoor pollution of fluorine and sulfur in coal-burning endemic in Zhaotong, Yunnan.

Persistence of pre-metamorphic C and O isotopic signatures in marbles subject to Pan-African granulite-facies metamorphism and U–Th mineralization (Tranomaro, Southeast Madagascar)

The status of fluid regimes during the Pan-African granulite-facies metamorphism in Southern Madagascar was examined by means of a mineralogical and stable isotope study of marble lithologies. In the granulitic Tranomaro area, which is made up of metasedimentary rocks (metapelitic, leptynitic (felsic) and calc–silicate metasediments) and intruded by syn-granulitic granitic bodies, syn-granulitic mineralization (Th–U) and metasomatic transformations (marbles→pyroxenites) demonstrate that fluid circulation has occurred. The Tranomaro marbles can be subdivided into two compositional groups, either Mg-poor or Mg-rich. This division reflects pre-metamorphic compositional differences rather than different P–T–X CO 2 histories. On a regional scale, the marbles display a large variation in δ 18 O (from +19 to +6.5‰ relative to SMOW) but have a more restricted δ 13 C range (from +1.4 to −2.5‰ relative to PDB). The lowest δ 18 O values are observed in magnesian marbles, whereas calcic ones do not have δ 18 O values lower than +13.5‰. Both initially low and high δ 18 O marbles may have locally been infiltrated by the syn-metamorphic fluid flow which gave rise to pyroxenites and Th–U ores (thorianite). δ 18 O values of carbonate in Mg-rich marbles evolve from +7 up to 8.5‰ towards the contact with a metasomatic pyroxenite in a meter-scale profile across an infiltration zone. The mineralogy, as well as the large and small-scale isotopic results argue for: (i) a pre-metamorphic origin for the isotopic variations, probably related to pre-granulitic dolomitization, (ii) a lack of pervasive fluid infiltration capable of erasing pre-metamorphic isotopic compositional differences, (iii) an absence of mantle-derived C-bearing fluids in the infiltrated zones. For the area as a whole, the present data are consistent with the decarbonation of impure siliceous limestones and dolostones coupled with fluid release from syn-metamorphic granitic intrusions.

Effect of aggregate particle size and composition on expansion of mortar bars due to delayed ettringite formation

The effect of aggregate composition and particle size on the expansion of mortar bars, due to delayed ettringite formation (DEF), was evaluated by heat-curing mortar bars made with basalt, dolostone, granite, limestone, siliceous limestone, and pure crystalline quartz. Subsequent to heat curing, the mortar bars were subjected to 3 thermal cycles to accelerate the formation of DEF. They were then stored in lime water for 59 days and length change was monitored. Only mortar bars made with quartz aggregate showed significant expansion. Expansion was found to be inversely proportional to the particle size of the quartz aggregate. The amount of ettringite formed in the mortar bars was shown to be proportional to their rate of expansion.

Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA

The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and amount of fluid flow during contact metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite (Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically. At the peak of metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward. Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (<1615 mol/cm2). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm2. The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from the fluid source along contacts between limestone and more siliceous rocks point to strong control of flow geometry at the 0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict correctly fundamental aspects of contact metamorphic fluid flow.

Effect of Slag on Expansion Due to Alkali Aggregate Reaction in Concrete

The efficacy of ground granulated blast furnace slag in controlling expansion caused by alkali-aggregate reaction was evaluated using both concrete prism and accelerated mortar bar testing. Six aggregates were included in the program; four of these were classified as alkali-silica reactive (siliceous limestone, sandstone, greywacke, and granite), one as alkali-carbonate reactive (dolomitic limestone), and one as nonreactive (dolostone). The partial replacement portland cement with slag in the range of 25-65% was effective in retarding the rate of expansion and limiting the ultimate expansion at 2 years in concrete prisms cast with all four alkali-silica reactive aggregates. However, the minimum level of slag required to control expansion to an acceptable level, (for example, 0.04% at 2 years) was found to vary depending on the nature of the aggregate and the amount of alkali present in the concrete. There appears to be a reliable correlation between the expansion of mortar bars after 14 days storage in 1M NaOH at 80 deg C and the expansion of concrete prisms after 2 years storage over water at 38 deg C. The accelerated mortar bar test appears to be an appropriate tool for determining the minimum safe level of slag required for a particular reactive aggregate source. The use of slag also reduced the initial rate of expansion of concrete prisms containing the alkali-carbonate reactive (ACR) aggregate. However, the expansion at 2 years exceeded 0.20% for all slag levels tested (25-65%), and this final expansion was actually greater for concretes with 25-50% slag than for the control concrete. The expansion of mortar bars was less than 0.10% at 14 days for all the mixes tested, which confirms the unsuitability of this test for detecting ACR aggregates.

Microspar development during early marine burial diagenesis: a comparison of Pliocene carbonates from the Bahamas with Silurian limestones from Gotland (Sweden)

ABSTRACTComparison of ultrastructures in Pliocene periplatform carbonates from the Bahamas with Silurian limestones from Gotland (Sweden) reveals that despite the differences in primary sediment composition and age, they reflect a similar mechanism of lithification. In both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis. Neither significant compression nor meteoric influence are necessary for the formation of calcite microspar. A model is proposed for the process of microsparitic cementation of fine‐grained aragonite needle muds comprising four stages: (1) unconsolidated, aragonite‐dominated carbonate mud; (2) precipitation of microspar that engulfs aragonite needles; (3) dissolution of aragonite, resulting in pitted surfaces of the microspar crystals; and (4) slight recrystallization. Our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite.

Guerrero-Morelos Platform drowning at the Cenomanian–Turonian boundary, Huitziltepec area, Guerrero State, southern Mexico

Facies successions in three stratigraphic sections (Barranca del Tigre, Axaxacoalco, and Zotoltitlán, Guerrero State, southern Mexico) that comprise middle Cenomanian to lower Turonian rocks of the central part of the Guerrero-Morelos Platform, indicate the drowning of some parts of the platform near the Cenomanian-Turonian boundary. In the western part of the study area (Barranca del Tigre section), Cenomanian shallow-marine limestones (mainly subtidal facies) with abundant benthic fauna (mainly foraminifera) pass upwards to a 7-m-interval of Turonian open-marine nodular limestones with few benthic organisms and then to dark-grey and black laminated pelagic limestones and marls. In the west-central part (Axaxacoalco section), Cenomanian restricted shallow-marine limestones (intertidal to subtidal facies) change abruptly upwards to Turonian black and dark-grey laminated pelagic limestones and marls with only pelagic fauna (calcisphaerulids, planktonic foraminifera, and radiolaria). In the eastern part of the study area (Zotoltitlán section), Cenomanian restricted shallow-marine limestones (mainly intertidal facies) are overlain by 45 m of open-marine limestones showing up-section a rapid decrease in benthic diversity until only calcisphaerulids and echinoderm fragments occur. Overlying these rocks, there are 65 m of nodular shaly limestones in thick strata with renewed benthic fauna, 80 m of shaly and silty limestones intercalated with claystones and some siltstones, and finally, dark grey/black laminated pelagic limestones and marls. The facies successions in the stratigraphic sections suggest the progressive drowning of the Guerrero-Morelos Platform around the Cenomanian-Turonian boundary. We attribute the drowning of some parts of the platform to the occurrence of the Cenomanian-Turonian anoxic event. The impingement of anoxic waters over the platform could produce the drastic reduction of the carbonate producing benthos observed in the stratigraphic sections and therefore a reduction in carbonate accumulation rates. Subsidence and the late Cenomanian-earliest Turonian sea-level rise were then able to drown the platform. This occurred first in the western part, where subtidal conditions dominated and an irreversible drowning occurred, allowing the deposition of organic-rich pelagic sediments over pre-existing shallow-marine carbonates. At the same time, the eastern part, where intertidal conditions dominated, changed to open-marine conditions, shallow first and deep later. Here, a temporal restoration of shallow open-marine carbonate sedimentation resulted, but eventually this region was also drowned, probably by the interplay of terrigenous-clastic supply to the platform and a new impingement of anoxic waters.

Scanning electron microscopy of polished, slightly etched rock surfaces: A method to observe palynomorphsin situ

Abstract Scanning electron microscopy of polished, slightly etched rock surfaces provides excellent observation conditions for palynomorphs. In the present study, samples from micritic limestone‐marl alternations in the Silurian of Gotland, Sweden, and from Pliocene limestones of the Bahamas are used. The Silurian limestones contain three‐dimensionally preserved acritarchs, chitinozoans, and prasinophytes, allowing the study of the outer and inner wall surfaces. In contrast, siltstones and marls provide slightly to strongly deformed, partly damaged specimens, which become completely flattened and crushed when the sediment is highly compacted. The observation of palynomorphs in polished surfaces can be considered as a complementary method to the standard preparation technique of hydrofluoric and hydrochloric digestion of rock samples, where it is possible that parts of the palynological spectrum may be lost during heavy‐liquid separation, filtering, centrifugation, or bleaching procedures. The detailed obs...

Estimating the alkali contribution from fly ash to expansion due to alkali—aggregate reaction in concrete

This paper reports the findings from an investigation to determine the ‘effective’ alkali contribution from jly ash to the expansion of concrete containing natural reactive UK aggregates. Concrete prism expansion tests were carried out using flint/chert sand (from three different sources), a crushed siltstone and a crushed siliceous limestone; results are also reported for a gre-vwacke aggregate. Fly ash from three commercial sources was used. The results demonstrate that the ‘efective’ alkali contribution from the fly ash, estimated from expansion results, varies depending on the level of replacement and nature of the reactive aggregate. With moderately reactive aggregates, such as flint, 25% fly ash was found to be effective in preventing cracking, regardless of the OPC alkali content. However, with more reactive aggregates (i.e. aggregates that react at lower alkali levels), Fly ash concrete expanded at lower OPC alkali contents than control specimens, indicating an ‘efective’ alkali contribution from the fly ash. Higher levels of fly ash are required to prevent cracking with these aggregates. Effective alkali ‘contributions’ (from fly ash) determined for a particular aggregate are not applicable to concrete containing other reactive aggregates, and specifications need to be cognizant of the need for higher ash replacement levels with more reactive aggregates.

Alkali-Aggregate Reactivity Problems with Cambrian Dolomite and Eocene Limestones of Azad Kashmir

Aggregates which are alkali-expansive include argillaceous dolomite, dolomitic limestone, siliceous limestone and silicate rocks. Alkali-aggregate reactions are agitated by the availability of alkalies, availability of water and cement water reaction, and some admixtures of organic and inorganic material used in concrete, temperature changes, and rain water absorption. The alkali content of cement manufactured in Pakistan varies with the geographical location because of the change in the chemical composition of raw materials. The objective of this paper is to indicate the distribution of major areas in Azad Kashmir where alkali-aggregate reactions are a serious problem within the context of the geological framework of the country. Methods for the recognition and control of alkali-aggregate reactions and suggested mechanisms of expansion are also outlined. (A)

Middle‐Upper Ordovician trilobites and stratigraphy along the Kyrkbäcken rivulet in the Röstånga area, southern Sweden

Abstract Middle‐Upper Ordovician strata are well exposed along the Kyrkbacken rivulet in the Rostanga area of Scania. The investigated sequence, comprising c. 25 m and dipping c. 40° towards the south, consists largely of siliceous limestones, mudstones, shales, and K‐benton‐ites. The section is generally richly fossiliferous and has yielded bivalves, brachiopods, cephalopods, gastropods, graptolites, ostracodes, conodonts, and trilobites. Nineteen trilobite species have been identified. The stratigraphical subdivision is based on the succession of trilobites and on lithology. The lower part of the section represents the Sularp Shale and contains a great number of K‐bentonites. It is overlain by the Skagen Limestone. Black, bituminous limestones or dark grey, calcareous mudstones containing, e.g, Tretaspis ceriodes, are referred to the Mossen Formation. The middle and upper part of the section contains shales of the Jerrestad Formation, which has yielded a diverse trilobite fauna containing, among others,...

Gypsum karst of the Baltic Republics

The Baltic Republics of Estonia, Latvia and Lithuania have karst areas developed in both carbonate and gypsiferous rocks. In the north, within the Republic of Estonia, Ordovician and Silurian limestones and dolomites crop out, or are covered by glacial Quaternary sediments. To the south, in Latvia and Lithuania, gypsum karst is actively developing in evaporites of Late Devonian (Frasnian) age. Although gypsum and mixed sulphate-carbonate karst only occupy small areas in the Baltic countries, they have important engineering and geo-ecological consequences. Due to the rapid dissolution of gypsum, the evolution of gypsum karst causes not only geological hazards such as subsidence, but it also has a highly adverse effect on groundwater quality. The karst territory of the Baltic states lies along the western side of the area, called the Great Devonian Field that form part of the Russian Plain. Within southern Latvia and northern Lithuania there is an area, exceeding 1000 sq. km, where mature gypsum karst occurs at the land surface and in the subsurface. This karst area is referred to here as the Gypsum Karst Region of the Baltic States. Here the surface karst forms include sinkholes, karst shafts, land subsidence, lakes and dolines. In Lithuania the maximum density of sinkholes is 200 per sq. km; in Latvia they reach 138 units per sq. km. Caves, enlarged dissolution voids and cavities are uncommon in both areas.

Siliceous rocks of the Culm Basin, Germany

Abstract The classic Dinantian cherts of the Rhenish Massif and Harz Mountains, Germany, were analysed for their petrography and sedimentology. They occur in five lithostratigraphic units: the Lower Alum Shale Formation, the Black Chert Formation, the Pale Chert Formation, the Siliceous Limestone Formation, and the Siliceous Transitional Formation (upper Hastarian to Asbian, CuII to CuIIIα of the German cephalopod zonation). Mafic volcanic rocks are locally associated with these strata. Four regional facies zones have been defined. Radiolarian chert, spiculitic chert, homogeneous chert, and silicified quartz-trachytic tephra and tuffite are the main chert types. These mostly form current-laminated grey, black, greenish or reddish beds rhythmically alternating with layers of siliceous mudstone and, in places, variably intercalated with grey and black mudstones and siltstones, phosphorites, metabentonites, limestone turbidites, greywackes and quartz arenites. The siliceous rocks were deposited in a moderately deep (upper bathyal) strait of an equatorial sea that was part of palaeo-Tethys. Westward-driven nutrient-rich currents from the palaeo-Pacific Ocean favoured high radiolarian fertility. Relatively pure biosiliceous ooze was deposited under temporarily anoxic conditions when, due to dry climate and high sea-level, detrital input decreased. Deposition of the siliceous facies ended with increased detrital input and breakdown of the ocean-current system due to the collision of Laurasia and Gondwana during the Variscan Orogeny.

Aggregate Polishing Resistance Pre-Evaluation

Current methods of pre-evaluation of aggregates for bituminous surface courses such as the British Pendulum and British Polishing Wheel and chemical or mineralogical methods are only able to identify clearly aggregates with a high probability of performing well. There is little agreement among researchers as to what engineering properties will provide adequate frictional resistance at various average daily traffic (ADT) levels. The lack of agreement has led to conservative polish-resistance specifications and subsequently higher pavement costs. The Tennessee Textural Retention Method (TTRM) uses single size aggregate (6.35 to 9.52 mm), the Los Angeles Abrasion device, and a modified version of the AASHTO TP 33 device to evaluate particle shape and texture throughout simulated aging. In this evaluation, using 25 Tennessee aggregates, the TTRM was used to characterize aggregate polish-resistance performance at various ADT levels by comparing the results obtained on other aggregates with the results from field proven performers. The TTRM ranked all Tennessee proven performing siliceous limestones and gravels in the appropriate ADT category for which they are currently approved. In addition, new promising aggregate sources were revealed. The test method had a coefficient of variation for aggregate ratings of less than 3 percent for a nine-sample repeatability test. In addition, the maximum coefficient of variation of voids tests at any given aging revolution for an individual aggregate never exceeded 2 percent. The method may be helpful in pairing aggregate polish-resistance performance with pavement need based on ADT.

Role of fluid flow in the contact metamorphism of siliceous dolomitic limestones; discussion and reply

Role of fluid flow in the contact metamorphism of siliceous dolomitic limestones; discussion and reply

Séismites dans le Jurassique supérieur du Bassin anglo-parisien (Normandie, Oxfordien supérieur, Calcaire gréseux de Hennequeville)

Synsedimentary deformation structures are observed on the armorican border of the Anglo-Paris Basin in the late Oxfordian “Calcaire greseux de Hennequeville” Formation. These detrital sediments are well exposed on the Normandy coast between Trouville and Honfleur, outcropping both in the cliffs and on the beach. They comprise silty limestone with abundant sponge spicules ( Rhaxella) deposited in a restricted subtidal depression mostly above the storm-wave base, and located in the northern flanks on the Sables de Glos delta. The formation is subdivided into three members. Deformational structures observed at a centimetre to metre scale and associated with massive early diagenetic cherts, are developed only in the middle member which is 1.5 m thick. This depositional environment was the shallowest of the whole formation. The soft-deformation structures are various, comprising: (1) low-amplitude structures observed at the lower and upper surfaces of the limestone beds; (2) features with a “wash-basin form”; (3) boudinage structures; and (4) large-scale “ball and pillow” structures or “blagues à tabac” (“tobacco-pouches” showing vertical dimension of over 1 m and observed only in a few sections of the cliffs). All deformational structures are overlain by undisturbed silty limestones and silty clays, suggesting a synsedimentary deformation. The soft deformations are interpreted to have been induced by the liquefaction of unconsolidated spiculitic silty muds during earthquakes. Liquefaction may have been induced by a number of processes which affect grain-supported sediments. A seismic origin is supported not only from particular palaeogeographic context (by reference to the whole NW of Europe in the late Oxfordian), but also by the great lateral extent of the deformational structures which occurs along more than 4 km of coastal outcrops. There is only one deformed unit. The morphology and size of the seismites are directly controlled by the stratonomy and thicknesses of the limestone. Most of the structures have a dominant vertical trend, with an upward or a downward polarity. Earthquakes are always difficult to recognize in the sedimentary record. They were recorded in the case of the “Calcaire gréseux de Hennequeville” because of a set of exceptional conditions which led to their preservation. These were: seismic activity associated with recurrent faulting; alternating beds of porous, wet and well sorted fine sands with muds favourable to thixotropic processes, and deposition in a relatively protected depositional environment.

Well-preserved fungal spores from Jurassic rocks of Hells Canyon on the Idaho–Oregon border

Palynoflorules containing sparse but regularly occurring chitinous-walled fungal, probably ascomycete, spores have been obtained from silty limestone nodules in the Jurassic Coon Hollow Formation in the Wallowa terrane in Hells Canyon, Idaho. The fungal spores are associated with moderately abundant embryophytic spores and pollen that suggest late Early Jurassic to early Middle Jurassic age, which agrees with dating provided by marine animals stratigraphically just above. The fungal spores constitute the most diverse such assemblage of robust-walled spores described from pre-Cretaceous rocks. Two new species of the fossil fungal spore form-genusDiporicellaesporites, D. idahoensisandD. serratulus, and one new species of form-genusFractisporonites, F. pittsburgensis, are described.

Significance of Silurian stromatolite-sphinctozoan reefs

Upper Silurian (Ludlovian) limestones from the Heceta Formation of southeastern Alaska (Alexander terrane) contain skeletal stromatolite reefs and stromatolite mud mounds that were colonized by sphinctozoan sponges. Internal growth cavities, synsedimentary marine cements, and stromatolite debris flows in slope deposits indicate that these reefs grew with relief at the seaward margin of the carbonate platform. The biotas under study have evolutionary significance because they contain the earliest widespread reef-building sphinctozoans and represent a previously unrecognized stage in the evolution of Phanerozoic microbial-metazoan (predominantly poriferan) reefs. On the basis of the presence of Silurian stromatolite-sphinctozoan deposits in southeastern Alaska, southwestern and west-central Alaska, and the Urals, this study also establishes a Late Silurian paleobiogeographic connection between the Alexander terrane, cratonic northwestern North America, and the Uralian region.

TRIASSIC STRATIGRAPHY AND SEDIMENTARY EVOLUTION OF THE ANNAPURNA TETHYS HIMALAYA (MANANG AREA, CENTRAL NEPAL)

After initial opening of Neotethys in the Permian, thermal subsidence and deepening continued in the Triassic. In the Scythian, three pelagic nodular carbonate intervals of Early Griesbachian to Early Dienerian, Early to mid-Smithian and latest Smithian to earliest Aegean age are interbedded with shelfal shales (Tamba Kurkur Formation). Ammonoid-and conodont-rich condensed carbonates were deposited on the outer shelf, with maximum depths around 150+200 m reached during transgressive stages. The Anisian to lowermost Norian shelfal succession mostly consists of marly limestones and marls (Mukut Formation). Thick calcareous siltstones rapidly accumulated in the Carnian, testifying to a new stage of tectonic extension affecting the Tethys Himalayan passive margin. The thick Tarap Formation of largely mid-Norian age points to strong continuing subsidence. Interbedded siltstones and subarkosic sandstones (lower member) are locally overlain by coral-bearing patch reefs (middle member). Chamosite-bearing hybrid arenites deposited at transgressive stages characterize the upper member. The Triassic succession is capped by subarkoses and quartzarenites, interbedded with dolomitic to bioclastic hybrid sandstones and silty limestones (Quartzite Series), in turn overlain by the Kioto Limestone.

High-purity limestones in England and Wales

Abstract Most limestone is used in the construction industry principally as an aggregate and in the manufacture of cement. A high degree of chemical purity in these limestones is not usually necessary although some restrictions on contaminants may be made. Around 10 million tonnes of limestones are used annually for industrial purposes which require ‘high-purity’ limestone or limestones of specific physical properties which are, at least to some extent, related to the purity of the limestone. Such limestones are used in the iron and steel industry, in the chemicals industry, in glass making, in fillers and pigments and in a wide range of other industries. An increasingly important use of ‘high-purity’ limestone is in flue gas desulphurization schemes in power generation plants. This paper describes the broad geological resources of high-purity limestone in England and Wales. Most high-purity deposits occur within the Carboniferous Limestone of the Peak District, the Mendips, South and North Wales, parts of the northern Pennines and around the fringes of the Lake District. Large areas of the Chalk outcrop also contain high-purity resources, particularly part of the Upper Chalk outcrop of southern England and in the Burnham and Welton chalk outcrops of northern England. The dolomites and dolomitic limestones of the Permian Magnesian Limestone also locally contain consistently pure deposits. Jurassic, Devonian and Silurian limestones are mainly of low chemical grade.