Fine-grained Limestone Research Articles

Microfacies and mineralogical analyses of the late cretaceous carbonate rocks from The Central Benue Trough, Nigeria

The Cretaceous limestone facies from Yandev section in the central Benue Trough, Nigeria constitutes parts of the potential reservoirs and sources rocks for petroleum prospects in the basin. The central Benue Trough is the least studied basin among its contemporaries due to lack of subsurface data. Detailed mineralogical, facies analysis and diagenesis of these carbonate rocks in the basin have not received significant study. The aim of this study was to employed multifaceted methodology such as sedimentological, facies analysis petrographic and geochemical approaches which was lacking in previous research in the trough. The sedimentological analysis was done to evaluate fabrics grain sizes, and lithology types. For petrographic analysis, thin sections were prepared and examined under a petrographic microscope and categorized according to Dunham's classification. Geochemical analysis involved X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX) techniques to unveil mineralogical, oxide, and elemental compositions. The sedimentological results revealed light to dark grey medium to fine-grained limestone facies with intercalation of dark grey shales and siltstones. The XRD mineralogy data, revealed calcite (60.00 - 64.10%), quartz (14.30 - 51.00%), albite (12.30 - 19.00%), and chlorite (6.30 - 8.10%). Microfacies results revealed distinct sandy bioclastic wackstone and sparitic intraclastic packstone, as well as micritic intraclastic wackestone and sparitic bioclastic packstone. SEM images highlighted the intricate composition, including elongated structures, whites and dark spots suggesting varying conditions of deposition. Elemental analysis through EDX emphasized significant proportions of carbon, oxygen, sodium, potassium, calcium, silicon, aluminum, iron, and magnesium. Based on sedimentological, biofacies, lithofacies and geochemical evidence we infer that the carbonate sediments were mainly deposited in a shallow marine depositional environment (inner to outer neritic).

Effect of the Textures and Particle Sizes of Limestone on the Quicklime Reaction Activity

Quicklime is not only an important raw material for the steel and nano-calcium carbonate industries but also a key carrier for capturing carbon dioxide in the fight against global warming, and its reaction activity plays a vital role in these processes. Recent studies have found that quicklime produced from limestones with similar chemical compositions under the same production process has significantly different reaction activities, which indicates that something other than the chemical composition of limestone affects quicklime reaction activity. To explore the factors affecting quicklime reaction activity, this study analyzed the textures and calcite particle size of limestone collected from different areas of Guangxi, China, and measures the quicklime reaction activity with different calcination times. It has been found that: (1) limestone with a clastic texture is preferred to that with a crystalline texture (including transition type) in yielding quicklime with higher reaction activity; and (2) for limestone with a clastic texture, fine-grained limestone tends to produce the same or higher quicklime reaction activity with lower energy consumption.

Lower Jurassic trace fossil Zoophycos from the Ksour Mountains of northwestern Algeria and their palaeoecological and palaeoenvironmental significance

The Zoophycos ichnofacies is reported for the first time from the Lower Jurassic (Toarcian) deposits of Algeria. The trace fossil-bearing strata in the Ksour Mountains, northwestern Algeria, are an alternation of fine-grained limestones and marls. The assemblage is characterised by its low diversity, consisting of eight ichnospecies (Chondrites intricatus, C. targionii, Chondrites isp., Palaeophycus isp., Thalassinoides isp., Zoophycos brianteus, Z. cauda-galli, and Zoophycos isp.), representing the Zoophycos ichnofacies ethologically dominated by deposit-feeding behaviours of different producers. The abundance of Zoophycos and Chondrites within a low diversity assemblage suggest stressful conditions most likely indicating oxygen depletion within the sediment. Moreover, the presence of reworked burrows by Chondrites could indicate ecological succession. This is probably due to environmental conditions getting more stressful, and causing the need for exploiting the nutrient stored in the abandoned burrows after the death of the trace maker. This process is primarily associated with an oxygen-depleted environment, compelling the animal to engage in it as a means of obtaining energy, rather than actively searching for food within the sediment. On the other hand, the occurrence of Thalassinoides may indicate an improvement of palaeoecological conditions and short periods with partial increase of oxygenation. The ichnological, palaeontological and palaeoecological data of the studied succession indicate a relatively deep-water environment located well below the storm wave base at a deeper offshore setting.

Clustered stone forest in Pu Dou Chun (Yunnan, China)

One of the unique examples of the development of subsoil karren into a stone forest on the varied geological bedrock of the Lunan surface is revealed to us. Originally of subsoil formation and later denuded, the rounded hills that dissect the karst surface have transformed into a clustered stone forest whose central part usually consists of a larger dissected rock mass with individual stone pillars and teeth at the edge. The geologic profile contains beds of dense, homogeneous and compact fine-grained limestones that alternate with beds of mostly coarse-grained and just as compact dolomitised limestones. These bed properties are also reflected in the exterior of the rock as a diverse relief. The average calcium carbonate content in both types of rocks combined is 97.3%. The rock is thickly bedded to massive; beds are mainly positioned subhorizontally. The contacts between the beds of limestone and dolomitised limestone are sharp and clearly visible, especially in the bottom part of the geologic profile, whereas in the central part, they are often blurred and one type of rock grades continuously into the other. In the areas containing limestone, individual bedding planes are especially visible. As can be inferred, the slightly more porous dolomitised rock, made up of larger particles, disintegrates faster in a more permanently waterlogged acid subsoil environment, where the moisture penetrates it deeper. However, as it takes longer to dissolve, it protrudes from the surface of the dolomitic limestone rock when exposed to moisture from occasional rain. The composition and fracturing of the diverse rock strata decisively influences the shape of the pillars and their rock relief. Larger subsoil rock forms (channels, notches, half-bells) have developed on all rock strata. The diversity of the rock is also reflected by the notches that have formed under the soil along the more rapidly soluble partly dolomite rock strata. Denuded subsoil-shaped pillars are reshaped by rainwater and trickling water. Smaller rock forms carved by rainwater have formed mostly only on evenly composed, fine- grained limestone rock. The tops on such rock are more distinctly conical and blade-like and wider on more slowly soluble rock.

UPPER JURASSIC TO LOWERMOST CRETACEOUS MICROFOSSILS FROM THE HĂGHIMAŞ MOUNTAINS (EASTERN CARPATHIANS, ROMANIA)

The limestones of the Upper Jurassic to lowermost Cretaceous from the Hăghimaş Mountains were studied in two sections from the upper part of the Fagu Oltului valley, a tributary of the Olt River. The lower part of the succession is remarkable for the rich brachiopod fauna contained in a red limestone buildup, documented previously as a stromatactis mud-mound. The mound consists of bioclastic wackestones and packstones with numerous brachiopods, crinoids, and sponges. The mud-mound is covered with intraclastic grainstones and fine-grained limestones with pelagic bivalves. The following lithological units pass into shallow water limestone with nerineid gastropods, calcareous algae and foraminifera, in a regressive sequence. The micropaleontological association identified in the Upper Jurassic to lowermost Cretaceous limestones from Fagul Oltului includes calcareous algae, foraminifera, saccocomid crinoid fragments, annelid worm tubes, sponge fragments, rare calpionellids and microorganisms with an uncertain systematic position. The identified microfossils have a wide stratigraphic distribution. The most important stratigraphic landmarks are Trocholina conica (which does not extend younger than Kimmeridgian) and Calpionella alpina (which does not appear before the upper Tithonian). Based on the whole micropaleontological assemblage, the lower part of the succession (the skeletal mud-mound) can be ascribed to the Kimmeridgian – lower-middle Tithonian, and the upper part to the upper Tithonian – Berriasian.

Lower Ludfordian (Upper Silurian) slope deposits in the Lyagadin section (Ilych River, the Northern Urals)

Research subject. Upper Silurian (Lower Ludfordian) slope deposits of the Lyagadin section (Ilych River, Northern Urals).Materials and methods.The composition and structure of 40 rock samples collected across the section during fieldworks in 2019 were studied. Thin sections were examined under a polarising microscope. Eight samples were investigated by silicate analysis, and clay minerals from 2 samples were determined by X-ray diffraction analysis of oriented samples.Results. The Lyagadin section with a visible thickness of 70 m is represented by an uneven alteration of clayey-siliceouscalcareous schists, micro-grained limestones with burrows, micro-fine-grained layered limestones, fine lime sandstones, coarse- and medium-grained lime sandstones, lime conglogravelites and lime conglobreccias. Clayey-siliceous-calcareous schists and micro-grained limestones with burrows characterise the background periplatform clayey-carbonate deposits. The part of micro-fine-grained layered limestones (their horizontally layered varieties) are bottom current sediments. Gravity flow deposits are represented by clastic rock assemblage. The most characteristic of them is the assemblage composed of lime conglogravelites with an erosional bottom, which pass into gradational-layered lime sandstones, first coarse- and medium-grained, and further the into their fine-grained varieties. They are covered, in turn, with micro- fine-grained limestones with cross or convolute stratifications. That association is interpreted as calciturbidites. Calcidebrites are characterised by lime conglobreccias. The deposits of grainy flows (?) are represented by the layers of lime sandstones not revealing the characteristic features of the Bouma sequence.Conclusion. The reconstructed background sedimentation on the continental slope during Early Ludfordian was characterised by the accumulation of hemi-pelagic clay deposits together with a certain amount of microscopic quartz, orthoclase and organic matter. Periodically appearing thin layers of micro-grained limestones with burrows correspond to the periods of increased supply of carbonate material, which could be attributed to “marine snow”. The irregular nature of the distribution of gravity flow deposits in the Lyagadin section suggests that the studied slope deposits are, most likely, the formation of the outer apron of slope bottom, rather than calciclastic fans.

Sedimentology and Geochemistry of Upper Devonian Deposits in the Southeastern Framework of the West Siberian Geosyneclise

Abstract —We have studied an Upper Devonian volcanoterrigenous carbonate complex in the north of the Kuznetsk trough. The northern part of the complex is subducted beneath the Meso–Cenozoic sedimentary cover of the West Siberian geosyneclise. Analysis of sedimentologic processes, the nature and specific composition of pyroclastic impurity, and the petrographic and chemical compositions of sedimentary rocks makes it possible to reconstruct the facies and geodynamic settings. It is shown that the fine-grained pyroclastic material is predominantly of andesite composition, whereas felsic and mafic volcanic components are subordinate. In the transition from the lower Frasnian to the Famennian, the content of felsic pyroclastic component increases. The geodynamic settings of the shelf and continental slope of the Siberian continent up to its base have been established. Facies analysis shows that the slope is west-facing (in the present-day coordinates). The deposits accumulated mainly in the basin; these are fine-grained terrigenous rocks, fine-grained limestones, slope landslide breccias and olistostromes, turbidites, and “conglomerate-like limestones” (paleoseismites). According to the geochemical data, the Late Devonian paleogeodynamic setting was stable and corresponded to the setting of an active continental margin. Arid to semihumid lithogenesis has been established. Marine sediments formed in an oxidizing environment with good water aeration.

Different Calcium Levels and Two Limestone Granulometries in the Diet of Laying Hens: Performance and Bone Characteristics

The effect of different calcium levels and two limestone granulometries on performance, egg quality, biometry of digestive organs and bone characteristics of light laying hens were evaluated. A total of 270 laying hens were used during 112 days, distributed in a completely randomized design in a 3 x 2 factorial scheme, with 3 levels of calcium (3.8, 4.0 and 4.2%) and 2 limestone granulometries (0.222 and 1.922 mm), totaling 6 treatments with 5 repetitions each. The parameters evaluated were: feed intake, egg production, egg weight and mass, feed conversion per mass and per dozen eggs, albumen, yolk and shell percentage, specific gravity of eggs and shell thickness. In addition, the relative weight of the heart, proventricle, gizzard, liver, pancreas, intestine weight and length, and bone characteristics were also evaluated. A significant interaction was observed for tibia mineral matter. Egg production was influenced by the limestone granulometry, presenting greater value in the treatments which contained fine granulometry limestone. Higher calcium levels of 4.0 and 4.2% provide greater specific density of eggs. Biometric variables and bone characteristics were not influenced by the treatments. In conclusion, it is recommended to use fine-grained limestone (0.222 mm) and a 4% calcium level in diets for light commercial hens, as they improve performance and quality of eggs, without interfering in biometrics of digestive organs and bone characteristics.

Recurrence of Fault Valve Behavior in a Continental Collision Area: Evidence From Tilt/Strain Measurements in Northern Adria

We analyzed the data recorded by the NE-Italy subsurface tilt and strainmeter network evidencing a coherent transient signal in the recordings of four tiltmeter sites in the 1984–1990 period that produced a tilt along the main fractures. Borrowing from classical seismology techniques, we used the uprise times to locate the transient signal source. The propagation velocity is compatible with a fluid diffusion process that starts from a source located close to the hypocenter of the February 10, 1983 Uccea earthquake, MD= 4.2 at the Italy-Slovenia border, at an estimated depth of 10.8 km. Our results add to the previous interpretation of a transient signal recorded by several global navigation satellite system (GNSS) stations in the 2006–2009 period in terms of fluid diffusion below the Bovec basin (Slovenia). That source was located upon continuation to the northwest of the Ravne fault, few kilometers to the northeast from the present one, and about 6 km from the July 12, 2004 Bovec–Krn earthquake, Mw= 5.1, depth ~6.1 km. These observations suggest that the area is subject to fault valve behavior episodes that released fluids trapped at depth to the surrounding region as pore-pressure bulges. The convergence between Alpine and External Dinarides structures in this area puts highly permeable dolomitic limestones in contact with low-permeable fine-grained limestones and flysch formations. Therefore, the conditions for overpressure generation can be created, whereas fault movements, from time to time, in close relation with seismic events, can enable fluid diffusion in the surroundings. We also estimated the possible fluid influx needed to maintain overpressure and possible discharge across both the faults. The study provides insights on pore–fluid pressure variations related to slow slip events from a context different from subduction or transform margins, i.e., in a continental collision area.

Sources and Markets of Limestone Flour in Poland

Limestone flour is used in a variety of industrial sectors such as power and heat generation, glass-making, paper-making, the construction industry and construction materials manufacturing, the production of agriculture, plastics and rubber goods, as well as coal mining, and environmental protection. This paper aims to characterize and interpret the limestone flour supply and demand trends in the main applications in Poland in the last decade. In order to track the changes of domestic consumption for this commodity, its major users have been surveyed along with analyses of data from the Statistics Poland (GUS). The results showed that during 2009–2018 the coal-fired power plants became the biggest customer of limestone flour utilized as a sorbent in the wet flue gas desulfurization method (FGD). This method has been implemented in the vast majority of Polish power plants. It is estimated that in the last decade the total annual production capacity of limestone flour at the milling plants in Poland increased by 1.5 million tons, to around 6.0 million tons. In the forthcoming years, this is expected to continue to increase despite EU restrictions on fossil fuel use (especially hard coal and lignite). Other promising areas of future growth are: for limestone flour of medium quality—the construction materials manufacturing and the construction industry itself, for limestone flour of the highest quality—the glass industry, while for fine-grained limestone flour of high-quality—the plastics and rubber industries. In terms of resource security, it is worth noting that Poland is a country rich in limestone deposits. However, only some of them, that is, limestone rock varieties of the Jurassic and Devonian ages from the Kielce vicinity in central Poland are suitable for the production of high-quality limestone flour for the needs of the mentioned industries. The paper analyses the potential of the limestone flour production from the available limestone rock deposits with respect to the current and future needs of the domestic market in Poland.

Properties of cement composites based on limestone depending on their granulometric composition

Introduction. The use of limestone in cement compositions as an additional cementing agent solves both environmental and economic problems, namely, reduction of construction costs. In this regard, the study of the properties of the granulometric composition and volumetric content of cement composites, containing limestone, becomes increasingly important. The mission of this research is to optimize the properties of composite materials containing Portland cement and limestone by changing the granulometric composition of flour limestone.
 Materials and methods. Limestone, having three different Blaine milling fineness values of 250, 300 and 450 m2/kg, was used; its content reached 10, 15, 25 and 35 %. Cement and sand mortars were applied for testing purposes. The influence of the granulometric composition of limestone on the workability and compressive strength of composite cement was determined.
 Results. The effect of limestone on the limit shear stress becomes more pronounced when the amount of limestone increases to 25 and 35 %. This is most noticeable for limestone with a high content of fine fractions of 5–20 µm. The use of finely milled limestone increases the initial strength of the composite material. By adding 10 and 15 % of such limestone we can increase the strength by 16–20 %, and supplementary 25–35 % of limestone increases strength by 5–8 %. Strength enhancement is due to the reactivity of limestone and formation of calcium hydrocarbon aluminate 3CaO∙Al2O3∙СаСО3∙12H2O, which promotes formation of the crystal framework of the cement matrix. Additional formation of crystalline hydrates in the initial coagulation structure deteriorates the mortar workability, but increases its strength.
 Conclusions. The use of coarse-grained limestone significantly improves mortar workability, while the use of fine-grained limestone increases its content without reducing its strength. The granulometric composition of ground limestone shall be as close as possible to the granulometric composition of cement for the properties of composite materials containing Portland cement and limestone to be optimized.

Ultrasonic modifications of fine-grained limestone concrete

The structure formation of cement stone of fine-grained limestone concrete during hydration hardening of cements and filler based on them occurs due to the development of polydisperse and polymineral conglomerate, a process associated with an increase in the volume of crystallohydrates in relation to the volume of the original cement minerals, mixed with water. Structure formation is accompanied by the process of compaction of the developing system and polycrystallization with the formation of floccules of a porous hydrating mass. In the paper, ultrasonic processing is viewed to accelerate the all- side process of modification of concrete structure and hardening thereby stipulating the growth of strength and durability of concrete.

Lithostratigraphy and biostratigraphy of the uppermost Cretaceous to lowermost Palaeogene shallow-marine succession: top of the Adriatic Carbonate Platform at the Likva Cove section (island of Brač, Croatia)

The Likva Cove section on the island of Brač (Croatia) represents a rare example within the Adriatic Carbonate Platform (AdCP) succession of the basal Palaeocene limestones overlying the uppermost Maastrichtian shallow-platform limestones with evidence of only a brief stratigraphic hiatus at the Cretaceous/Palaeogene (K/Pg) contact. Detailed study of the 50-m-thick section resulted in the description of eight lithofacies arranged into six lithostratigraphic units: (A) rudist limestones, (B) deposits with coral–stromatoporoid patch reefs, (C) bindstones, and (D) fine-grained limestones with benthic and rare planktonic foraminifera in the uppermost Maastrichtian (comprising microfossil assemblage biozones I and II), and (E) limestones with benthic foraminifera (mostly discorbids), ostracods and rare planktonic foraminifera, and (F) ostracod–discorbid limestones in the lowermost Palaeocene (representing microfossil assemblage biozone III).The K/Pg contact is constrained between the last occurrence of Maastrichtian benthic and rare planktonic foraminifera, and the first occurrence of Danian planktonic and benthic foraminifera. The uppermost Cretaceous bed represents a firmground, but low biostratigraphic resolution precludes defining duration of a probable short-lasting hiatus at the K/Pg contact. Planktonic foraminifera are mixed with benthic forms in a 3.5-m-thick interval comprising the K/Pg contact as a consequence of decreased depositional rate and probable storm influence.Top of the section contains well developed coral patch reefs intensely karstified during a long-lasting regional unconformity, which in the studied part of the AdCP commenced in the early Palaeocene, i.e. later than at most parts of the platform. Therefore, the end of AdCP deposition should be locally extended into the Palaeocene in both its NW and SE parts.

The composition and formation conditions of the Upper Lochkovian Valgan Formation (Lower Devonian Ilych River, Northern Urals)

Research subject. A section of the Upper Lochkovian (Lower Devonian) Valgan Formation located in the stratotypic area on the Ilych River, Northern Urals, was investigated. Materials and methods . A study of the composition and structure of rock samples gathered from the section under consideration during fieldwork in 2015 was conducted. Results. The studied section with an exposed thickness of 51 m is characterized by the thin and uneven alterations of calcareous con-glogravelites, coarse-grained and fine-grained organic sandsones, bioclatic-pelitomorphic limestones and argillo-calcareous shales. These rocks demonstrate a gradational and convolute lamination. An individual interval of the studied section contains calcareous conglobreccias layers. The Valgan Formation is characterized by a cyclic structure, with the thickness of individual cyclites ranging from 5.0 to 25 cm. The character of their structure testifies to sedimentation in slope settings. An analysis of clastic material revealed two sources of the basin area formation: near ablation (represented by the fragments of background bioclastic-pelitomorphic limestones) and remote ablation (represented by biohermal rock clasts). It is proposed to consider the Valgan Formation as the Valgan gradation, which extends the Upper Lochkovian sulfate-carbonate Subformation to the east. Conclusions. Therefore, the Valgan gradation should be treated as an intermediate link between shallow-marine Upper Lochkovian biohermal structures and bathyal clayey and siliceous shales.

Mensa ponderaria из Пантикапея?

This paper considers a passportless fragment of a block made of a local dense medium-porous fine-grained limestone which arrived to the Eastern-Crimean Historical and Cultural Museum-Preserve in 2012. The shape of this block and the shape of the remaining hemispheric funnel terminating in a hole allows us to argue that this is a widely spread device in the Ancient world used as a capacity measure for liquid products being on sale — mensa ponderaria. Considered analogies from other Greek poleis show that sekomata were used to exert state control over weights and measures on par with measure vessels.

Fine-grained limestone concrete with improved dissipative properties

Crack propagation in concrete is known to be partially stipulated by the process of energy dissipation. In this study the usage of complex admixture including limestone fines and superplasticizer which enhance crack propagation energy dissipation rate is discussed. Energy dissipation rate and crack propagation are assessed by comparing cracking strains and stress intensity ratios for two sets of specimens, with and without limestone fines. Limestone semi-inert filler acting in a synergetic way with superplasticizer is revealed to enhance crack propagation energy dissipation rate and cracking strains, which makes fine-grained limestone concrete the effective crack-resisting material.

Managing the crack energy dissipation as a way to increase the durability of fine-grained limestone concrete

The durability of fine-grained concrete is associated with the process of cracking. The propagation of cracks depends on the energy dissipation rate. The results of the tests presented show the effectiveness of a limestone microdispersed filler and superplasticizer for increasing the durability of fine-grained carbonate concrete.

Mechanical stratigraphy and structural control of oil accumulations in fractured carbonates of the Irati Formation, Paraná Basin, Brazil

Abstract Fracturing analysis of low-permeability rocks as reservoir analogs have increased in recent years. The main mechanism involved in the development of secondary porosity in low-permeability, fine-grained limestones of the Irati Formation is fracturing. In these rocks, oil accumulates along fracture planes, vuggy porosity, microfractures, breccias, as well as bedding discontinuities. Joints represent the central element for oil migration and the connection between accumulation sites. Joints are unevenly distributed across the succession of rock types, where carbonate rocks have a much denser array of joints than shales and siltstones. From a mechanical stratigraphy point of view, limestones have a brittle behavior and constitute mechanical units. Ductile shale and siltstone are mechanical interfaces capable of blocking joint propagation. Joints running NW-SE are more effective in trespassing the mechanical interface and are, therefore, more persistent. Joints running NE-SW are less persistent because the ductile behavior of the first two shale beds above the limestone blocks their propagation. The spatial arrangement of regional NW-SE and NE-SW joints promoted reservoir connection, allowing oil migration and accumulation. The joints and oil migration (at least three phases) developed as a consequence of the Gondwana Breakup and are also associated with local pressure gradients.

Revised stratigraphy of the Eifelian (Middle Devonian) of southern Belgium: sequence stratigraphy, global events, reef development and basin structuration

The Eifelian lithostratigraphic succession of southern Belgium is here revised based on new field investigations and reconsideration of biostratigraphic data. The Couvin Formation is divided into four members: the Villers-la-Tour Member recorded the onset of stromatoporoid biostromes, the Petigny Member is a dark fine-grained limestone that recorded the Choteč event, the Cul d’Efer Member is dominated by stromatoporoid-coral biostromes. These first three members were previously united in the Foulerie Member and correspond to the transgressive and highstand system tracts of the Middle Devonian 3rd-order sequence MD1. The argillaceous and bioclastic successive units of the Abîme Member recorded the sequence MD2. Laterally, this sequence is only composed of siliciclastic deposits of the Vieux Moulin, Station and Cimetière members of the Jemelle Formation. The highstand system tract is the newly introduced carbonate Vierves Member. Large bioherms, newly described as the Wancennes Formation, recorded the first two sequences MD1 and MD2. A major sequence boundary caps the Couvin Formation and is overlaid by the transgressive and diachronous Chavées Member of the Jemelle Formation with a depositional gap increasing eastwards. The highstand system tract of sequence MD3 is recorded in the bioherms of the Tienne Sainte-Anne Member (upper part of the Jemelle Formation), also capped by a sequence boundary. These bioherms probably acted as highs around which the sandy deposits of the Lomme Formation accumulated as lowstand system tract of sequence MD4. The Hanonet Formation and its crinoidal Wellin Member form the transgressive system tracts of sequence MD4 that terminates in the bioclastic and biohermal Trois-Fontaines Formation (Givetian). The Kačák event is identified in the transgressive system tract of this sequence. The geographic distribution of facies and of reefs in particular led to the recognition of at least six sedimentation areas corresponding most probably to synsedimentary faulted blocks here defined as the Eau Blanche, Viroin, Lesse, Ourthe, Condroz and Sambre blocks. These sedimentation areas structured the Namur-Dinant Basin and recorded distinct depositional history and were probably active during the Devonian and Carboniferous interval.

Sedimentology and geochemistry of the Uk Formation, Upper Riphean, the Southern Urals

Research subject. This article presents new data on carbonate facies of the upperUk subformation, Upper Riphean of theSouth Urals. A particular attention is paid to the distribution of rare-earth elements (REE) and yttrium (Y) in stromatolitic and intraclastic limestones and calcareous shales (bulk samples and their acetic acid leachates).Materials and methods. We have studied lithological features of limestones in the geological section and in thin sections. The contents of trace elements in rocks were determined by the ICP-MS method at the IGG UB RAS (Yekaterinburg), the composition of organic matter was determined at the IPGG SB RAS (Novosibirsk) by gas-liquid chromatography and chromatography-mass spectrometry.Results. The most representative section of the Upper Uk Subformation located along the eastern edge of the town Ust-Katav can be subdivided into several members of different lithology and thickness: (1) biohermdominated member comprising large microbialitic build-ups and inter-bioherm sediments (intraclastic limestones, calcareous biolaminites); (2) transitional member characterised by small bioherms alternating with other carbonates; (3) interbedded coarseand fine-grained limestones. The presence of molar-tooth structures in the carbonate rocks of Uk Formation made it possible to constrain the age of thisUpper Riphean formation to pre-CryogenianConclusions. There are similarities in REE and Y distribution in both clean (devoid of siliciclastic component) bulk limestone samples and in their acetic acid leachates. PAAS-normalised REE + Y patterns demonstrate positive La, Gd, Y anomalies and negative Eu, Ce anomalies. The latter suggest marine depositional environments for theUpper Uk stromatolitic limestones. The results of the pioneering research into the composition of bitumens and biomarkers from the Upper Uk Subformation have shown that carbonates and shales are depleted in the organic matter. The source material for the organic matter was provided by two types of communities comprising both eukaryotes and prokaryotes and inhabiting well aerated environment, perhaps with lowered salinity of marine water.