Argillaceous Dolomitic Limestone Research Articles

Sustainable development of geological resources: the Characteristics of Red Karst Landscape and Tourism Development in Tongren, Guizhou

<abstract> <p>China is rich in karst resources and famous for its karst landscape. As a part of karst, the popularity of red karst is obviously low and has received little attention; moreover, the related scientific research and tourism development are relatively immature. Therefore, this paper takes the red karst in Tongren, Guizhou as the research object, analyzes the characteristics and causes of the red karst, comprehensively evaluates its landscape value, and puts forward development strategies and protection suggestions. Through the above research, the following three research results are obtained. (1) On the basis of a field investigation and a literature review, the geographical situation, background, and landscape characteristics of the red karst landform and its surrounding areas in Tongren City were investigated in detail. It forms isolated peaks, rock walls, protruding rocks, stone pillars, and other forms. The most prominent features of the red karst landscape in Tongren City are that the color is red and white, and the shape is concave and convex in order. (2) Geochemical test and structural data collection and analyses of the collected samples were performed. The obtain concave layer rock is dolomitic limestone, and that convex lay rock is argillaceous dolomitic limestone. Because the convex layer rock sample is high in silicon element content, the convex layer rock sample is not easy to be weathered, is rich in clay mineral, and is not easy to be corrode; the convex layer rock sample gradually protrudes with the passage of time to form an uneven shape. The red karst landform is developed in either the rock stratum or tectonic zone with moderate tectonic deformation intensity. First, the formation of a single-layer honeycomb morphology requires that the rock stratum is subjected to a sufficient horizontal compressive stress at a certain burial depth. Second, it is necessary to widely exist in areas with relatively gentle rock formation occurrence; too strong of a structural deformation will make the rock formation occurrence steep, which is not conducive to the occurrence of differential dissolution between adjacent strata. (3) Through the construction of an evaluation index system, the red karst in Tongren City is evaluated, and it is concluded that the geological heritage value is high, and the development and utilization conditions are weak. The conclusion of this article is a supplement to the geological and geomorphological system characteristics of southern karst. From the perspective of world natural heritage, the study enriches the academic evidence of red karst and enables its exemplary role to be well played. From the perspective of the tourism development value, more people should be made aware of the diverse types of karst landforms, which provide experience and suggestions for the value of landforms, tourism resources, and tourism development in similar areas.</p> </abstract>

Siliceous and dolomitic-bearing aggregates reaction in Tetramethylammonium hydroxide

Due to argillaceous dolomitic limestones usually contain more or less quartz or micro-crystalline quartz, based on existence of alkali-silica gels in concretes with dolomitic aggregates, lead to alkali-carbonation reaction (ACR) coexists with alkali-silica reaction (ASR) in concrete. This paper focuses on distinguish ASR are affected by the presence of Tetramethylammonium hydroxide (TMAH) solution to offer a better understanding of the effect of ADR on the mitigation process of alkali-carbonation reaction (ACR). In this work, X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM) were carried out analyses of products. The results presented strongly support that the TMAH has no react on reactive silica, and thus stop further attack on the reactive silica by hydroxyl lions. According to the results of the tests, the presence of TMAH is sufficient to promote the ADR in samples with dolomitic aggregates, formation products of brucite and calcite. Therefore, it was concluded that evidence to support the theory of TMAH can distinguish ASR and ADR when dolomitic aggregate bearing quartz.

Diagenetic overprint on negative δ13C excursions across the Permian/Triassic boundary: A case study from Meishan section, China

The Meishan Section D from China is the global stratotype section and point (GSSP) of the Permian-Triassic boundary (PTB). The succession has been divided into 115 beds with the PTB being placed in the middle of Bed 27. In this section and the laterally equivalent Section A, the diagenetic features of Beds 24 to 62 are examined in this study to determine if the negative shift in δ13Ccarb across the Permian-Triassic boundary is diagenetic in origin or not. Bed 24 is formed of skeletal packstones, whereas Beds 25 to 62 are formed of claystones or argillaceous dolomitic limestones. The dolomite crystals are typically <30μm long, subhedral to euhedral, and held in a very fine groundmass formed of calcite and clay minerals. The cathodoluminescent features and backscattered images show that the dolomite crystals are zoned, with a non-luminescent low-calcium calcian dolomite (LCD) core being encased successively by an irregular dull-orange calcite zone, a euhedral bright-orange high-calcium calcian dolomite (HCD) cortex, and an outermost ferroan-HCD zone. Available evidence indicates that the zoned dolomite crystals formed episodically. The dolomite crystals, following their initial syndepositional formation with euhedral LCD cores and HCD cortices, were subsequently modified by calcitization mediated by meteoric water and overgrowth of Fe-rich HCD during burial.The limestones in Bed 24 display δ13C values ranging from +1.72 to +2.92‰, δ18O values from −7.74 to −4.84‰. In Beds 25 to 62, the bulk samples have δ13C values from −0.76 to +1.28‰ and δ18O values from −8.58 to −3.99‰. There is a positive correlation between these isotopic compositions and dolomite content. It is estimated that the first-formed dolomite and the precursor limestones have δ13C value of +2.19‰ and δ18O value of −1.14‰. The dramatic negative δ13C excursions of calcite in Beds 26 and 28 are related to meteoric diagenesis, whereas the negative δ13C excursions of bulk samples in the dolomite-bearing beds are ascribed to the diagenetic modifications that post-dated the initial formation of dolomite. The results show that the δ13C signals recorded in the GSSP that spans the PTB are a mixture of original and diagenetic signals. For the dolomite-bearing bulk samples, diagenesis contributes ~1.7‰ to the negative shift in the δ13C. Hence, diagenetic alteration needs to be considered before using δ13Ccarb to estimate the dissolved inorganic carbon in the ancient oceans and to calculate the global carbon cycle.

Alkali Silica Reaction (ASR) as a root cause of distress in a concrete made from Alkali Carbonate Reaction (ACR) potentially susceptible aggregates

The mechanism of Alkali Carbonate Reaction (ACR) in concrete made from fine-grained, argillaceous dolomitic limestone coarse aggregates remains controversial. ACR distress is described as an increase in volume caused by the crystallization of brucite during the dedolomitization process. However, recent studies by Katayama suggest that ACR is a combination of the “deleteriously expansive Alkali Silica Reaction (ASR) of cryptocrystalline quartz in the matrix of the reactive aggregates and a harmless dedolomitization that produces brucite and a carbonate halo.” We investigated ACR susceptible concrete extracted from a wharf structure in Quebec, Canada, and determined that ASR was the cause of damage. Optical and SEM-EDS analyses identified ASR gel extending from reactive aggregates to the paste, and X-ray elemental mapping confirmed the gel composition. Silica (Si) was found in the matrix of the aggregate and is the source of reactive silica. These results support ASR as the mechanism in ACR susceptible concrete.

Mineralogy and Metasomatic Evolution of Distal Strata-BoundScheelite Skarns in the Riba de Alva Mine, Northeastern Portugal

The metasediment-hosted distal scheelite skarns from the Riba de Alva mine, Barca de Alva-Escalhao region, northeastern Portugal, consist of three main levels of strata-bound, boudin-shaped, 0.5- to 4-m-thick bodies, having a total resource of 380,000 tons (t) with an average grade of 0.51 percent WO3. The boudinage of the Cambrian metasedimentary rocks of the Slate Greywacke Complex occurred early during the Hercynian orogeny, prior to the Granitic Complex intrusion and the skarn-forming process. The Granitic Complex corresponds to reduced, highly evolved, and metallogenically specialized S-type leucogranites, comparable to those commonly associated with Mo-poor W-F skarns. Four different skarn types were recognized: pyroxene skarn with Fe diopside± anorthite; amphibole-epidote skarns with actinolite + clinozoisite ± bytownite ± phlogopite; ore skarn with clinozoisite + scheelite + fluorite + calcite ± labradorite ± apatite ± Fe axinite ± armenite ± scapolite; and late-stage veins with quartz (or fluorite or calcite) ± clinozoisite ± andesine (or albite) ± adularia. Clinopyroxene ranges from Di80Hd20 to Di60Hd40. Amphibole compositions range from actinolite to Mg hornblende and are F rich (0.5–1.9 wt %). Clinozoisite, often zoned with Fe-poor cores, shows little compositional variation in the skarn types, having a low pistacitic component (5–13% Ps). Plagioclase compositions grade from anorthite in pyroxene skarn through andesine and albite in late-stage veins. Phlogopite, as amphibole, is F rich (2.45–4.70 wt %). An extremely pure Mo-free scheelite, the only ore mineral present, is restricted to the ore skarn type. The Riba de Alva skarns were formed, after intrusion of the Hercynian Granitic Complex, by selective infiltrative metasomatic alteration of argillaceous dolomitic limestone. An early stage of prograde alteration led to the formation of the pyroxene skarn, through reaction with an Si-rich and Fe-bearing fluid. Scheelite mineralization occurred during retrograde alteration, which was mainly fracture controlled and is characterized by a pervasive infiltration metasomatism with minor diffusion in the skarn walls. This alteration started with hydration reactions to form amphibole-epidote skarns, probably under lower XCO2 conditions. Ore skarn formation, with scheelite deposition, took place later during this retrograde stage, mainly along veins within the strata-bound boudins, as the result of a decrease in temperature and/or significant changes in the activity of some fluid components such as W, F, Na, Mn, P, and B, and particularly an increase in aCa. Monomineralic late-stage veins represent the waning stage of the skarn-forming process.

Geological and engineering characteristics of expansive soils and rocks in northern Oman

The geology and former climate of northern Oman favoured the formation of smectite clay minerals in certain materials which are implicated in ground heave problems. Investigations have shown that the smectite content of these expansive materials was developed in Oligocene, Miocene and Pliocene times. No evidence of a significant content of smectite was found in pre Eocene strata or in Quaternary strata, except for Desert Fill. It is shown that the main types of expansive materials in northern Oman are bentonitic mudstones, marls and silty mudstones, argillaceous dolomitic limestone, altered conglomerates and the desert fill derived from these. These swelling materials exist as impersistent bands within the bedrock Tertiary conglomerates and limestones. A geotechnical testing program was carried out on undisturbed samples from Sultan Qaboos University staff housing areas where building damage had occurred, to evaluate mineralogical composition, cation content and swelling characteristics. The test results characterized these soils/rocks as highly expansive type with Na-smectite as the dominant clay mineral.

Diagenetic history and source rock potential of the Upper Jurassic Diyab Formation, offshore Abu Dhabi, United Arab Emirates

The Upper Jurassic Diyab Formation is a highly argillaceous dolomitic limestone unit underlying one of the most prolific hydrocarbon reservoirs in the world: the Arab Formation. The Diyab is thought to be the primary source for the Arab in the United Arab Emirates. Thin sections from cores in offshore Abu Dhabi show the Diyab to contain dolomitized grainstones at the base with associated glauconitization and chertification grading upward to olive-green, argillaceous, organically-rich, dolomitic limestones in the upper third of the Diyab, creating a marly texture which persists through to the top of the section. Late diagenetic calcite (and subordinate anhydrite) cement, which include coarse spar as well as blocky and poikilotopic fabrics, occlude much of the secondary porosity and are interpreted to have occurred during burial diagenesis. Dolomite is in the form of euhedral rhombohedra which primarily replace the matrix of the limestones. Allochemical grains, which include peloids, intraclasts and bioclasts, have recrystallized to low Mg-calcite and are partially glauconitized in the lower part of the section. Pressure solution has caused fracturing and stylolitization, fractures being filled by sparry calcite and stylolites by a bituminous residue.

Alkali-reactivity problems with emphasis on Canadian aggregates

The “classical” form of alkali-aggregate reaction involves the disordered forms of silica particularly opal, chert and chalcedony. The alkali-carbonate reaction involves argillaceous dolomitic limestones and the alkali silicate reaction is found in some grey-wackes, phyllites and argillites. Concrete deterioration due to the alkali-silica reaction has been reported from nearly all major geographic regions of Canada. In the very far north expansive cherts were found on Ellesmere Island. On the Prairies chert is common in the gravels derived from various limestone formations in the Cordillera. These cherts seem to show a low level of alkali-expansivity but when this is combined with other forms of attack on concrete it may contribute to durability failure. Chert containing sands and gravels which show a lowlevel of alkali-expansivity are also known from Quebec. Siliceous limestones, some of whichcontain chalcedony, are known from Ontario and Quebec and in some instances, appear to be a major factor in concrete deterioration. The classical areas of alkali-carbonate reaction occur in Kingston and other parts of Ontario. Greywackes, phyllites and argillites associated with alkali-expansive reactions in concrete have been described particularly from the Maritime Provinces, from parts of the Canadian Shield and from the northern part of Ellesmere Island.

Barite nodules of possibly late diagenetic origin from Twitya River area, Mackenzie Mountains, Northwest Territories

Conspicuous spherical and subspherical barite nodules occur in Devonian(?)/Mississippian carbonaceous shales and argillaceous dolomitic limestones in Twitya river area (western foothills of the Backbone Ranges, Mackenzie Mountains, N.W.T.).The majority of barite nodules are spherulitic, composed of grey radiating barite crystals. The microscopic study of barite and of sedimentary fabrics in its host rocks has demonstrated that the crystallization of nodules was a late diagenetic event postdating the formation of carbonate concretions in shales, dolomitization, and the early phase of fracturing, but predating the late phase of fracturing and tectonic deformation. The nodules have clearly developed by replacement of their carbonate host.The middle to late Paleozoic, black shale sequence that occurs on both sides of the Yukon – Northwest Territories boundary at the latitude of Macmillan Pass (Canol road) appears to be in a distinct barite province with numerous occurrences of mostly bedded barite recorded. The presently available evidence indicates that the introduction of barium into the sedimentary basin had probably been syndepositional, followed by diagenetic concentration and barite emplacement well before the 'Laramide Orogeny' and the emplacement of Cretaceous quartz monzonite stocks.

Problematical microstructures from the Waterton Formation (Late Precambrian) of southwestern Alberta

ABSTRACT Tubular microstructures occur in the Waterton and Altyn formations (± 1000 M.Y.B.P.) in Waterton Park and adjoining areas. Loose aggregations of individuals are orientated perpendicularly, horizontally, or at random angles to the bedding planes in argillaceous dolomitic limestones, and consist of sinuous siliceous tubes up to 0.6 cm in length and 0.3 mm in width. Due to their form, size, orientation, and mode of occurrence it is suggested that they represent the activity of small worms, rather than the alternative possibilities that they are algal filaments, or inorganic structures.

MECHANISM AND KINETICS OF EXPANSION IN THE ALKALI-CARBONATE ROCK REACTION

Certain fine-grained argillaceous dolomitic limestones show an increase in solid volume when placed in strong alkali. Mineralogical analysis shows that the dolomite is replaced by magnesium hydroxide (brucite), calcium carbonate, and alkali carbonate. This reaction does not account directly for the expansion, as the volume of the solid products is less than the volume of the dolomite.Expansion is shown to be the result of an increase in solid volume that results from water uptake. The behavior is accounted for by a hypothesis that may be summarized as follows.(1) Alkaline attack on the dolomite crystals releases included clay in an "active" state with an unwetted surface.(2) Some of the Ca++ and Mg++ ions probably present on exchange sites are replaced by Na+ ions.(3) Development of a hydrated double layer made up of oriented water molecules, cations near the newly exposed clay surface, and anions further from the surface.(4) Development of the double layer and accompanying hydration processes cause the water uptake, which leads to expansion.

Stable association wollastonite-anorthite, and other cale-silicate assemblages in amphibolite-facies crystalline schists of Nanga Parbat, Northwest Himalayas

Progressive regional metamorphism and granitization of a dominantly pelitic sequence was essentially isobaric and proceeded on a level of rather high P within the field of amphibolite facies. The transition from kyanite to sillimanite zone does not coincide with the boundary between medium- and high-grade rocks but is displaced toward higher T. Many of the Al-Si-rich high-grade rocks carry stable muscovite. Staurolite, andalusite, and cordierite are characteristically absent. Green hornblende occurs throughout the high-grade zone in rocks of appropriate composition. Calcareous intercalations permit recognition of three distinct zones of high-grade metamorphism. They, and the reactions defining their boundaries, are Reaction (b) is sensitive to PCO2. It is suggested that most of the rocks, especially those with excess silica, were open systems for CO2, so that PCO2≪ Ptotal. Locally, as in some tight marbles, CO2 was retained, and the wollastonite reaction was arrested or altogether prevented, in zone (2) and even in zone (1). Reaction (a), involving no gas phase, is dependent only on P, T. Under the prevailing high pressures, the temperatures required to make reaction (a) proceed to the right, must have been rather high. Quartz-excess and calcite-excess, diopside-bearing assemblages of the three zones are described. Associated K-feldspar is orthoclase with very small — 2V. Metamorphism of argillaceous dolomitic limestones illustrates the principle of preferential decarbonation of Mg. Assemblages include (omitting dominant calcite) : forsterite-spinel-phlogopite, found only in zone (1) ; phlogopite-diopside-(tremolite); diopside-(tremolite)-orthoclase; diopside-(tremolite)-anorthite-(orthoclase); diopside-wollastonite-grossularite (zone 2); diopside-grossularite-quartz (zone 3). Relations of mineral assemblages found in the three talc-silicate zones to bulk compositions are discussed. Boundary layers between diopsidic tale-silicate rocks and associated pelitic schists are described. As a rule, a thin band of para-amphibolite is developed at the contact, characterized by the garnet-free assemblage, green hornblende-anorthite (bytownite)-quartz. In adjacent, partly almandine-bearing biotite-quartz-plagioclase schists, plagioclase ranges from sodic andesine to bytownite. Widespread reverse zoning of this plagioclase is attributed to slow, short-range (a few centimeters) diffusion of anorthite-building substance from the adjacent Ca-richer rock into the schist. Locally, the amphibolite band is lacking, and diopside and biotite mingle in the boundary layer. Although this local association recalls pyroxene hornfels facies, nearby rocks have amphibolite facies mineralogy. Part of the diopsidic tale-silicate rocks of zone (1) show incipient retrogression under conditions of zone (2) or (3), the pair, wollastonite-anorthite (bytownite), being “parasitically” replaced by grossularite. Retrogression below the limits of zone (3) locally displays the assemblage, zoisite-labradorite-grossularite. Calcic scapolite found in some of the high-grade tale-silicate rocks is retrogressive, replacing anorthite (bytownite). Cale-silicate mica schists of higher-medium grade carry mutually stable calcic scapolite, andesine and zoisite, associated with calcite, quartz, local epidote, biotite, muscovite, and garnet. Much of their plagioclase is zoned. Reverse followed by normal zoning is interpreted as a record of the thermal history of metamorphism. Associated non-calcareous mica schists, commonly with almandine and kyanite, carry more sodic plagioclase which is unzoned. Garnet amphibolites of this zone have andesine plus zoisite or epidote, and some contain diopside. Physical conditions of the metamorphism of the high-grade tale-silicate rocks are discussed further, in the light of available experimental data.