Limestone Microfacies Research Articles

Lithostratigraphy and limestone microfacies of the Oligocene lagoonal, coral patch reef-bearing Maʼahm Beds (South Mawaleh, Oman)

Lithostratigraphy and limestone microfacies of the Oligocene lagoonal, coral patch reef-bearing Maʼahm Beds (South Mawaleh, Oman)

Calcareous algae and foraminifera of the microfaunistic horizon XIII (Visean stage) of the middle part of the central paraxial zone Dnipro-Donets Depression (Ukraine)


 
 
 Visean deposits of exploration-production well 363 Yablunivs’ka contain predominantly carbonate and argillaceous rocks from the Prylutsʹkyy boundary (lower Visean). This study presents limestone microfacies and foraminiferal and calcareous algal associations of the paraxial zone in the Dnipro-Donets Depression. The foraminiferal association is represented by 26 genera, whereas the algal association is composed of 24 identified species and specimens in open nomenclature representative of 31 genera, including a new species, Atractyliopsis berezovia sp. nov., and a species of calcareous algae, which is first described for Dnieper-Donets Depression, Asphaltina cordillerensis. Fossil associations of calcareous algae characterize Palaeoberesella lahuseni – Exvotarisella index – Nanopora woodi zone, which correlated with the foraminiferal Uralodiscus rotundus and Paraarchaediscus koktjubensis. Green algae are predominant within the calcareous algae from carbonate deposits of the core No 3. This predominance indicates a warm and shallow-water sedimentation platform. Many archedicids indicates that the bottom substrate is represented by soft silt. Well-developed radiant layer of archaediscida indicates to the favorable habitat conditions. From the middle part of the layer, the role of red algae, whose thally has a crusty and leaf-like shape, as well as green Koninckopora sp. and Coeloporella sp., begins to grow quantitatively. This indicates an insignificant shallowing of the sedimentation basin. Visean limestones belong to the facies of the open marine platform, zone 7 (shallow undathem). According to the results of micropaleontological analysis the boundary of XIIIl and XIIIu microfaunistic subhorizon of Dnipro-Donets Basin identified at the depth of 4435.96 m. The foraminifera and algae representation is given at the 8 paleontological plates.
 
 

Habitats in the Pre-Taghanic (Givetian, Middle Devonian) muddy carbonate ramp at Miłoszów (Holy Cross Mountains, Poland): geochemical and microfacies evidence

The well-known fossiliferous and lithologically variable Middle Devonian Shaly-Calcareous Skały Formation in the Łysogóry Region (northern part of the Holy Cross Mountains, central Poland) was studied for the first time in terms of elemental geochemistry, carbon isotope stratigraphy and limestone microfacies. Three Lower to Middle Givetian marly-limestone successions, exposed at Miłoszów, represent middle to outer facies belts of the vast carbonate ramp, characterized by very rich epifaunal and infaunal benthic life in muddy, oxic, eutrophic, and photic zone habitats. Brachiopods and occasionally corals (in mesophotic association), erect branching bryozoans, and tiny crinoids played a leading role among flourishing sessile suspension-feeders. High-energy storm events, possibly even a tsunami, during the brief Early Givetian time strengthened a prolific carbonate ooze delivery system from shallow ramp areas, including restricted back-ramp lagoons and a variety of organic buildups, populated by corals and stromatoporoids. The ecologically mixed skeletal grain association is characterized by the rich occurrence of a typical lagoonal biota, calcispheres and amphiporoids. The effective carbonate factory declined stepwise regionally during the Middle Givetian because of an intermittent progradation of the deltaic system of the Świętomarz Beds, linked with climate cooling and the activation of block movements. The regional carbonate crisis resulted in the demise of diverse benthic life, including the prolific calcified microbiota. The higher Skały Formation succession, deposited between the important Kačák and Taghanic bioevents, is noticeable for a background carbon-isotope pattern in carbonate and organic matter signatures, with the baseline δ 13 C carb values between 1‰ and 2‰. The microfacies and chemostratigraphic data confirm that at least the lower pumilio bioevent was not recorded in the Łysogóry Region.

Microfacies and composition of ferruginous beds at the platform-foreland basin transition (Late Albian to Turonian Natih Formation, Oman Mountains): Forebulge dynamics and regional to global tectono-geochemical framework

Two forebulge successions exist in the Oman Mountains at the platform-foreland basin transition between the Late Albian to Turonian Natih Formation and the foreland basin shales of the Late Cretaceous Muti Formation. Forebulge creation is suggested by limestone microfacies analyses and analyses of ferruginous crusts and oolites, showing rapid changes in bathymetry and relative sedimentation rate. Each succession displays basal shallow subtidal limestone, passing upward directly to ferruginous crusts and then to Fe-rich oolites deposited in shallower and agitated water. Each succession is topped by clayey layers. Microfacies and lithological evolution of the two successions are alike, suggesting repetitively similar depositional and tectonic conditions. As both sequences occur at the same site, lateral forebulge migration possibly did not occur, suggesting an overall stationary vertical and stepwise forebulge development. The compositional evolution of the ferruginous crusts was complex and includes postdepositional diagenetic effects of the rocks. Both ferruginous crusts once consisted of iron sulfides, implying at least slightly reducing conditions during their formation, associated with water-deepening events. Both oolite levels contain chlorite, hematite, quartz, calcite and apatite. They also contain fragments of chlorite and hematite as nuclei, suggesting that these fragments derived from preexisting ferruginous crusts. Iron oxyhydroxides and clinochlore within the oolites reflects bathymetric changes to more oxidizing aqueous conditions, associated with water-shallowing events. Fe-rich anoxic to sub-oxic sea water of the marine foreland basin was the source for the crusts and oolites which coincided with a high rate of global Cretaceous ocean crust production and related hydrothermalism as well as the regional proximity of an active spreading axis. Fe was probably stabilized in ocean water as organic Fe complexes and Fe colloids.

Limestone Microfacies Punung Formation at Bangbang River, Sumbermanjing Wetan, Malang, East Java

Malang and Wonosari areas are located in Southern Mountains of Java, and their rock variations are comparable. Study focuses on limestone found at Sumbermanjing Wetan, Malang, that has been identified as part of Wonosari Formation. This place is closer to Punung area as viewed from the type location. Limestone microfacies approach is used to determine whether the limestone belongs to Wonosari or Punung formations. Methods used to identify standard microfacies types and facies zone are measured stratigraphy, petrographic analysis, and microfossil analysis. Measured stratigraphy was conducted along Bangbang River, and seven limestone samples were collected for analysis. Findings showed three standard microfacies types: SMF-5 characterized by packstone or rudstone with a mudstone matrix, SMF-8 characterized by wackstone or floatstone with complete fossils, and SMF-18 characterized by grainstone or packstone with abundant foraminifera or algae. Limestone belongs to facies zone (FZ) 7 - 8, which is characterized by presence of packestone, wackestone, clay sized limestone, and benthic algae foraminifers. Limestone ages range from Middle to Upper Miocene (N12 - N16), were formed in an inner Neritic. Limestone is equivalent to Wonosari and Punung Formations, based on standard microfacies type, facies zone, and age range. When lignite intercalation are present, the limestone is equivalent to the Punung Formation.

The Sedimentology of the Late Campanian–Maastrichtian Sequence, Southwestern Iraq

Petrography, diagenesis, and facies analyses as well as the depositional environments of the late Campanian-Maastrichtian sequence in southwestern Iraq are studied in five keyholes. The sequence incorporates parts of the Hartha, Shiranish and Tayarat Formations. The Hartha Formation comprises creamy and organodetrital dolomite, grey dolomitic marl, and evaporites. The Shiranish Formation is composed of grey marl and claystone, whereas the Tayarat Formation is composed of grey ash, along with tough and fossiliferous dolomitic limestone inter-bedded with grey mudstone layers and/or wisps. Several diagenetic processes affected the sequence, such as neomorphic replacement, dissolution, dolomitization, and sulphate development. Some of these processes obliterated the primary textures.
 The late Campanian-Maastrichtian sequence consists of three microfacies (Dolomitic Intraclastic Limestone, Dolomitized Biomicrite, and Biomicrosparite Microfacies) and two lithofacies (Mudrock and Sulphates-Rock Lithofacies), in addition to Fine- to Medium-Crystalline Dolomite Lithotype.
 The Hartha Formation is evaporitic, possibly with supratidal sabkha deposits. The overlying Tayarat and Shiranish Formations reflect deposition in a warm tropical to subtropical reefal and open marine conditions, as deduced from faunal assemblages. Some effects of deep marine condition are evident by the presence of Shiranish facies. The sequence represents deposition in the central reef- fore reef area. The absence of isolated back-reef lagoon facies suggests that the reef was patchy without isolation of water in the middle shelf region. However, at the top of the sequence, i.e. at the end of the Cretaceous Period, restricted lagoons seem to have dominated the studied succession.

REE Characteristics of Lower Cretaceous Limestone Succession in Gümüşhane, NE Turkey: Implications for Ocean Paleoredox Conditions and Diagenetic Alteration

Trace and rare earth elements (REEs) are considered to be reliable indicators of chemical processes for the evolution of carbonate systems. One of the best examples of ancient carbonate successions (Berdiga Formation) is widely exposed in NE Turkey. The Lower Cretaceous limestone succession of Berdiga Formation may provide a case study that reveals the effect of ocean paleoredox conditions on diagenetic alteration. Measurement of major, trace and REEs was carried out on the Lower Cretaceous limestones of the Berdiga Formation, to reveal proxies for paleoredox conditions and early diagenetic controls on their geochemistry. Studied micritic limestone microfacies (MF-1 to MF-3) indicate deposition in the inner platform to a deep shelf or continental slope paleoenvironment during the Hauterivian-Albian. The studied limestone samples mainly exhibit low Mg-calcite characteristics with the general chemical formula of Ca98.35–99.34Mg0.66–1.65(CO3). They are mostly represented by a diagnostic REE seawater signature including (1) slight LREE depletion relative to the HREEs (ave. 0.72 of Nd/YbN and ave. 0.73 of Pr/YbN), (2) negative Ce anomalies (Ce/Ce* = 0.38–0.81; ave. 0.57), (3) positive La anomaly (La/La* = 0.21–3.02; ave. 1.75) and (4) superchondritic Y/Ho (ave. 46.26). Studied micritic limestones have predominantly low Hf (bdl to 0.5 µg/g), Sc (bdl to 2 µg/g) Th (bdl to 0.9 µg/g) contents suggesting negligible to minor shale contamination. These findings imply that micritic limestones faithfully record chemical signals of their parental and diagenetic fluids. The succession also exhibits high ratios of Eu/Eu* (1.01–1.65; ave. 1.29 corresponding to the positive Eu anomalies), Sm/Yb (1.26–2.74; ave. 1.68) and La/Yb ratios (0.68–1.35; ave. 0.9) compared to modern seawater and wide range of Y/Ho ratios (29.33–70.00; ave. 46.26) which are between seawater and hydrogenetic Fe-Mn crusts. Several lines of geochemical evidence suggest water-rock interaction between parental seawater and basaltic rocks at elevated temperatures triggered by hydrothermal activity associated with Early Cretaceous basaltic magma generation. The range of Ce/Ce* values is suggestive of mostly oxic to dysoxic paleoceanographic conditions, with a sudden change to dysoxic conditions (Ce/Ce* = 0.71–0.81), in the uppermost part of the MF-1. This is followed by an abrupt deepening paleoenvironment with a relative increase in the oxic state of the seawater and deposition of deeper water sediments (MF-2 and MF-3) above a sharp transition. The differences in microfacies characteristics and foraminifera assemblage between MF-1 and overlying facies (MF-2 and MF-3) may also confirm the change in paleoceanographic conditions. Therefore, REEs data obtained from studied limestones have the potential to contribute important information as to regional paleoceanographic conditions of Tethys during an important period in Earth history.

Siliceous rocks from the southern part of the Kraków-Częstochowa Upland (Southern Poland) as potential raw materials in the manufacture of stone tools – A characterization and possibilities of identification

The Upper Jurassic sediments from the Kraków-Częstochowa Upland developed as carbonates, mostly limestones, which represent the microbial-sponge megafacies that were typical of the northern margin of the Tethys Ocean. Outcrops of these rocks are scattered along an extended belt ranging from Portugal to the Caucasus Mts. One of the common features of the bedded limestones belonging to this megafacies is the local occurrence of chert concretions.The siliceous rocks embedded within the Upper Jurassic sequences from the southern part of the Kraków-Częstochowa Upland originated from a broad spectrum of limestone silicification processes and are represented by chert concretions, bedded cherts and epigenetic siliceous rocks. These rocks served as raw materials in the production of stone tools from the Middle Palaeolithic onwards. These tools have been studied extensively by archaeologists.This paper presents the identification of the above mentioned types of siliceous rocks used in the manufacture of tools based upon (i) microscopic observations of thin sections which reveal the primary microfacies of limestones subjected to silicification, and (ii) X-ray diffraction analyses, including the determination of the crystallinity index of SiO2. Unfortunately, the available research methods do not permit the identification of the varieties of chert concretions to an extent that would permit them to be even roughly connected with particular outcrops or, at least, with particular regions of the occurrence of siliceous raw materials on a Pan-European scale. Macroscopic criteria have recently been adopted in archaeological classifications aimed at determining the origin of stone tools and drawing conclusions as to the source outcrops or regions. However, regrettably, these have proven groundless from the geological point of view.

Late Cretaceous to early Eocene geological history of the eastern Ionian Basin, southwestern Greece: A sedimentological approach

Sedimentological studies of the Upper Cretaceous–lower Eocene limestones in the western part of the Ionian basin (Araxos area) indicate that these deposits are composed of calciturbidites interbedded with breccia-microbreccia. Breccia - microbreccia deposits are structureless, display channelized geometry with calciturbiditic blocks internally to the channels. Most of the clasts were sourced from the underlying Lower Cretaceous “Vigla limestones”. Calciturbidites include Ta to Te Bouma sub-divisions, and are organized in cycles that form channelized deposits with a high degree of amalgamation. Statistical analysis confirms the presence of order in the sub-division sequence. The thickness of event beds in the studied section shows a lognormal statistical distribution, typical of turbidite successions. Limestone microfacies suggest deep-water deposits and reworked shelf deposits.The intense extensional tectonic activity in the Ionian basin during the Early Cretaceous, with synthetic and antithetic faults, produced active platform margins and asymmetrical grabens. In this regime, large amounts of coarse-grained material became available and accumulated in the basin. High slope gradients led to slumping. During the Late Cretaceous, the uplifted margins of the grabens caused erosion of the pre-existing deposits of the Lower Cretaceous “Vigla Formation”. This event led to the accumulation of channelized microbreccia and breccia units and transport of platform deposits by turbidity currents. The Early Cretaceous to early Eocene depositional history in the Ionian Basin indicates that the regional tectonic activity, rather than the eustatic sea-level changes, was the major factor that influenced the basin evolution, suggesting a syn-rift stage being active from the Jurassic to the early Eocene.

Contribution to the stratigraphy and sedimentology of the Upper Jurassic – lower Eocene succession of the Mitla–El Giddi stretches, west Central Sinai, Egypt

The present study deals with the stratigraphy, petrography and facies analysis of the stratigraphic succession of Mitla-El Giddi stretches (west Central Sinai, Egypt). Lithostratigraphically, the study area is covered by a thick succession extending from Late Jurassic to early Eocene time. This succession is subdivided into the Masajid Formation (Upper Jurassic (Oxfordian) at the base followed upwardly by the Risan Aneiza Formation (Lower Cretaceous (? Aptian- Albian), the Galala Fm. (Cenomanian), the Abu Qada Formation (lower Turonian), the Buttum Formation (middle Turonian), the Wata Formation (middle–upper Turonian), the Themed Formation (Coniacian–Santonian), the Sudr Chalk (Campanian–Maastrichtian), the Mitla Formation (= Esna Shale) (Paleocene–lower Eocene), the Thebes Formation (lower Ypresian) and the Minia Formation (upper Ypresian) at top. The Aptian – Albian Risan Aneiza Formation is first recorded at G. El Hamra in the study area. As well, a new formational name (the Mitla Formation) is used to describe the Paleocene – lower Eocene unit equivalent to the Esna Shale due to variation in lithology mainly represented by chalky limestone and argillaceous limestone. Many unconformities, represented by variable sedimentologic features, i.e., red paleosols, conglomerates, crustified laminated limestone and glauconitic facies were investigated and mostly attributed to the Syrian Arc System.The petrographic investigations especially for the lithified rocks revealed eighteen limestone microfacies, three dolostone microfacies and four sandstone microfacies, besides the non-lithified shale, sandy shale, clay and marl lithofacies. The recognized facies and their related paleoenvironments document lateral and common vertical transition between inner, middle and outer ramp setting. These facies could be subdivided into eight associations that are related to six depositional environments: peritidal flat/beach clastics, peritidal flat carbonates, lagoonal clastics, lagoonal carbonates, high energy shoal of ooids and patch reefs (oolitic shoal), intertidal-subtidal open marine, storm influenced subtidal open marine (mid-ramp) and hemipelagic outer ramp facies.The study indicates that, the area was controlled by a long-term transgressive phase and several higher order sea level fluctuations during the deposition of the studied succession. The main factors controlling the ramp deposition and the described events are; structure control mainly Syrian Arc deformation, eustatic sea level fluctuations combined with environmental influences such as autochthonous carbonate productivity-siliciclastic supply and paleorelief conditions.

Carbonate Platform Development in an Intraoceanic Arc Setting: Costa Rica’s Largest Limestone Sequence - The Fila de Cal Formation (Middle Eocene to Lower Oligocene)

The limestones of the Fila de Cal Formation build the largest carbonate platform sequence of Costa Rica extending over 180 km from southern Costa Rica into the Panamanian boarder area of David. The detailed limestone microfacies analysis and micropaleontologic dating based on the contained larger foraminiferal assemblages of 22 samples selected from the most representative exposures reveal three main carbonate facies: (1) Eoannularia eocenica-bearing spiculite facies from the Middle Eocene, (2) large lepidocyclinid-nummilitid facies from the Upper Eocene lead by the Lepidocyclina chaperi-Lepidocyclina tobleri panamensis assemblage and (3) dominant Lower Oligocene Lepidocyclina yurnagunensis-Lepidocyclina undosa assemblage. These three biostratigraphically successive facies record circa 14 to 19 m.y. of continuous shallow-marine carbonate sedimentation in the Pacific frontal arc region of southern Costa Rica. During this time large communities of benthic organisms: larger foraminifera, calcareous algae, corals, bryozoans, mollusks and equinoderms rapidly grew in warm tropical waters to build the largest and long-lasting carbonate platform on the Costa Rican arc. The carbonate sedimentation ended abruptly with accumulation of thick volcaniclastic marine platform-to-slope deposits of the Térraba Formation. Tectonically, the Fila de Cal carbonate platform development coincides with rapid convergence rates of the Farallón plate beneath southern Central America leading to strong arc uplift and new widespread neritic environments. The correlation with contemporaneous carbonate arc sequences clearly indicates that primarily their proximity to the inner volcanic arc areas and strong subsidence in response to emerging volcanic edifices are probably the main factors that controlled growing and persistence of carbonate environments within the arc setting.

Some carbonate rocks utilized as a building material rocks, Egypt

Studies of the geochemical, mineralogical, petrographical characteristics and the physicochemical properties were carried out on some carbonate rocks, so as to throw light on the possibility of utilizing them as a building stones. The dolomitic and dolostone rocks of Gebel Ataqa and Giran El-Ful quarries have been acquiring potential application in building and industry. Petrographically, the dolomite rocks of the Gebel Ataqa quarries are characterized by dolo-biomicrosparite and dolomitic limestone microfacies for Hassan Alaam quarry and dolosparite microfacies for Arab Contractors quarry, while those of Giran El-Ful (Abu Roash area) are mainly dolo-biomicite microfacies and dolostones. They are deposited in mixing zone environment. Mineralogically, XRD patterns indicate the dolomites of the Ataqa and Giran El-Ful quarries are non-stoichiometric. XRD with DTA revealed that the rocks of the three quarries are consisting mainly of dolomite (Ataqa quarries), calcite and ankarite (Abo Roash quarry), as the main constituents, besides quartz and halite as minor constituents. Geochemically, the normative dolomite contents in the studied rocks with an average ~ 90, ~ 35, and ~ 31% for Arab Contractors, Hassan Alaam and Giran El-Ful quarries; respectively. Thus, the dolomitization was more effective in the Cretaceous carbonates at Arab Contractors quarry than those in the Middle Eocene in Hassan Alaam and Giran El-Ful quarries. Arab Contractors have very high Mg content followed by Hassan Alaam, though impoverished in Na2O, K2O, Al2O3, Fe2O3, SO3, SiO2, TiO2, and Cl. Giran El-Ful quarry has very high Fe2O3 and MgO contents; on the other hand, poor in Na2O, K2O, Al2O3, SO3, SiO2, TiO2, and Cl. Sr contents indicate that the dolomite crystals were deposited in mixing zone environments. The total radioactivity measurements are ranging from 2 to 8 ppm for U and from 3 to 9 ppm for Th. The radioactivity measurements are approximately against to the background level of carbonates, and they are in the permissible limits for carbonates used in cement industries and as building stones. The dolomitic and dolostone rocks of the three quarries are proved chemically suitable for the industries relevant to crushed aggregates and lime production. Physically–mechanically examination revealed that the youngest carbonate deposits in the Middle Eocene (Hassan Alaam quarry) rocks have relatively low porosity, water absorption, and crushability, and highest compressive strength compared with those carbonate rocks of the two other quarries of Upper Cretaceous (Arab Contractors and Giran El-Ful). The petrographical, geochemical, and physical–mechanical observations recommended that the carbonates rocks of Hassan Alaam and Arab Contractors quarries in Gebel Ataqa area clearly can be used in the production of crushed aggregates to utilize in the concrete works. On the other hand, Giran El-Ful quarry can be used only in the mechanical sawing and in the production of limestone blocks.

PETROPHYSICAL AND SEDIMENTOLOGICAL CHARACTERIZATION OF THE APTIAN SHU'AIBA (LOWER QAMCHUQA) FORMATION RESERVOIR AT THE KHABBAZ OILFIELD, NORTHERN IRAQ

The Aptian Shu'aiba Formation is a shallow‐marine carbonate which occurs in the subsurface of central and southern Iraq and in other parts of the Arabian Plate including Oman, the UAE and Saudi Arabia. An equivalent unit is exposed at outcrop in northern Iraq where it is known as the lower part of the Qamchuqa Formation. For this study, core, cuttings and well log data from six wells in the Khabbaz oilfield (20 km SW of Kirkuk) were used to investigate the reservoir properties of the Shu'aiba Formation. The formation is 180–195 m thick at Khabbaz field and the reservoir section can be divided into three lithological units: an upper unit (A, 8–15 m thick) consisting of partly dolomitized marly limestones; a middle unit (B, 52–56 m thick) which is composed of vuggy dolomitic limestone and dolostone; and a lower unit (C, >110 m thick) which consists of shale‐rich and dolomitic limestones. Limestone microfacies include shelfal bioclastic wackestones, Orbitolina bioclastic packstones, Orbitolina grainstones, and pelagic bioclastic wackestones. Dolomite fabrics show little variation and are dominated by coarse crystalline planar‐e types. Most matrix porosity is associated with intercrystalline pores in medium‐crystalline (100–50 µm) planar‐e dolostone. Fracturing of variable intensity has resulted in a flow type which is dominated by fracture flow superimposed on matrix flow.

Auto recognition of carbonate microfacies based on an improved back propagation neural network

Though traditional methods could recognize some facies, e.g. lagoon facies, backshoal facies and foreshoal facies, they couldn’t recognize reef facies and shoal facies well. To solve this problem, back propagation neural network (BP-ANN) and an improved BP-ANN with better stability and suitability, optimized by a particle swarm optimizer (PSO) algorithm (PSO-BP-ANN) were proposed to solve the microfacies’ auto discrimination of M formation from the R oil field in Iraq. Fourteen wells with complete core, borehole and log data were chosen as the standard wells and 120 microfacies samples were inferred from these 14 wells. Besides, the average value of gamma, neutron and density logs as well as the sum of squares of deviations of gamma were extracted as key parameters to build log facies (facies from log measurements)—microfacies transforming model. The total 120 log facies samples were divided into 12 kinds of log facies and 6 kinds of microfacies, e.g. lagoon bioclasts micrite limestone microfacies, shoal bioclasts grainstone microfacies, backshoal bioclasts packstone microfacies, foreshoal bioclasts micrite limestone microfacies, shallow continental micrite limestone microfacies and reef limestone microfacies. Furthermore, 68 samples of these 120 log facies samples were chosen as training samples and another 52 samples were gotten as testing samples to test the predicting ability of the discrimination template. Compared with conventional methods, like Bayes stepwise discrimination, both the BP-ANN and PSO-BP-ANN can integrate more log details with a correct rate higher than 85%. Furthermore, PSO-BP-ANN has more simple structure, smaller amount of weight and threshold and less iteration time.

Dolomitization in the Carbonate Rocks of the Upper Turonian Wata Formation, West Sinai, NE Egypt: Petrographic and Geochemical Constraints

This study discusses the mechanism of dolomitization of carbonate rocks of the Upper Turonian Wata Formation in west Sinai, Egypt. It has been done in terms of study of textural, mineralogical, and geochemical characteristics of the dolostones and dolomitic limestones of the Wata Formation. The Wata Formation is composed mainly of dolostone and dolomitic limestone intercalated with few shale and sandstone beds. Beside the studied dolostone facies, five associated limestone microfacies have been identified. The limestone microfacies also provide an evidence of sparse dolomitization.Dolomites occur as replacive dolomites with minor dolomite cements. Four textural types of dolomite are distinguished: (1) fine-crystalline, planar-s (subhedral, hypidiotopic) replacive dolomite; (2) medium-to coarse-crystalline, planar-e (euhedral, idiotopic) replacive dolomite; (3) medium-crystalline, planar-s (subhedral, hypidiotopic) replacive dolomite, and (4) fine-crystalline, planar-e (euhedral, idiotopic) void-filling dolomite cements. The recorded dolomite is nearly non-stoichiometric (CaCO3 ranges from 51 to 56 mol % with an average of 53.5 mol %) and has similar geochemical features. It has δ18OVPDB values range from −7.16‰ to +0.26‰ and δ13C VPDB values vary between −0.52‰ and +5.2‰. Its strontium content lies between 11 and 53 ppm.Petrographic investigations and geochemical data indicated that the dolomitization of the studied carbonates probably took place in a meteoric water-sea water mixing zone at shallow burial depth during the early stage of diagenesis. In this situation, the dolomitization was developed through an increase of Mg/Ca ratio of the pore water, with no salinity increase. The increase of Mg/Ca ratio took place by two possible ways: (1) through leaching of Mg from high Mg-calcite grains (micrite) and aragonitic shells in the studied limestone (2) through leaching of Mg adsorbed on clays of the adjacent mudrock horizons. Such leaching brought about by freshwater-dominated fluid during meteoric water diagenesis.

Damage quantification of built stone on Dark Gate (Belgrade, Serbia): sample of damage index application for decay rate evaluation

The Dark Gate is the monument of culture, part of the cultural and historical complex of the Belgrade Fortress. It is constructed of limestone blocks that after 270 years of exposure to environmental conditions and different anthropogenic influences show wide ranges of decay forms. During 2007, detail registration of all built limestone microfacies and weathering forms was done using tools of monument mapping. A correlation scheme “intensity– damage category” was made according to the type, intensity, and distribution of damage forms. For quantification of decay rate of the Dark Gate, damage indices were calculated on the bases of mapping results. Calculated values of damage indices (>3) reflected differences between separate zones of the gate (south–north facades, east–west oriented parts of the gate). This approach allowed assessment and comparison of weathering rates according to the gate’s position and the exposure of the stone to environmental influences. The linear damage index showed that the moderate damage is the dominant category on the entire monument, while the progressive damage index implies to the need of urgent intervention. After 7 years, re-evaluation of these parameters was done. New data of weathering mapping and recalculated values of damage indices reflected significant acceleration in decay rate. By comparing weathering maps and values of damage indices from 2007 and 2014, the eastern part of the gate was separated as the zone of the monument that had suffered the heaviest damage. Differences among the values of damage indices showed that the position of the gate is one of the main causes of the present state of stone blocks built in the Dark Gate. They also showed that a carefully made damage category scheme is a key diagnostic tool in each restoration project.

Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra

Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra

Limestone Microfacies of Baturaja Formation along Air Rambangnia Traverse, South OKU, South Sumatra

DOI: 10.17014/ijog.v1i1.173Limestones of the Baturaja Formation occur at Air Rambangnia traverse, South Ogan Komering Ulu, South Sumatra, and they are used as objects for microfacies studies. The microfacies studies are based on a detailed petro­graphic analysis of thirty four limestone samples, taken from the traverse. Four types of the limestones are identified such as wackestone, packstone, grainstone, and floatstone. At least five microfacies form the limestone succesion of the Baturaja Formation. They are interpreted as sedimentary facies of very restricted bay and pond, back reef local slope, slope and shelf edge, winnowed platform edge sand, and reef flank facies.

Palynology and Microfacies of Lower Devonian Mixed Carbonate-Siliciclastic Deposits in Podolia, Ukraine

Investigation of mixed carbonate-siliciclastic Lower Devonian deposits have been carried out in the Ivanye Zolote and Ustechko sections in Podolia, Ukraine. Based on palynomorph evidence, the age of the samples studied is late Lochkovian, not older than the NM Oppel Miospore Zone, specifically the Si Lineage Zone. The presence of acritarchs and chitinozoans points to dominantly marine depositional conditions. However, a regressive environmental change to-ward more brackish conditions is indicated by a decrease in the taxonomic diversity of acritarchs in the topmost samples, the simultaneous disappearance of chitinozoans, and an increase in leiosphaerid frequency. Furthermore, evolution of limestone microfacies demonstrates a progressive transition from a shrinking marine basin toward a brackish, storm-af-fected muddy lagoon, manifested by recurrent profusion of impoverished, mostly opportunistic and euryhaline shelly benthos (nuculanid bivalves, leperditicopids and other ostracods, terebratulid brachiopod...

Black-crust growth and interaction with underlying limestone microfacies

Abstract Black crust growth mechanisms on three French building stones are described using diagenetic models that reveal the close links between the crust–stone interfaces and the microfacies of the host limestone. Each limestone is representative of a specific sedimentary facies and displays mixed pore structure: crinoidal limestone (Euville limestone), oolitic limestone (Savonnières limestone) and bioclastic matrix-supported limestone (Courville limestone). The crinoidal limestone is mainly made of well-developed calcitic cement (spar syntaxial calcite) with low macrocroporosity (15–20 vol. %). The oolitic limestone is macroporous (30–40 vol. %), oolite nucleus being partially or completely dissolved. The third building stone studied is less porous (14 vol. %) but presents a significant microporosity. Weathering of the Euville limestone proceeds primarily through preferential exploitation of cleavages and microcracks and secondly by progressive recrystallization in the areas separated by previous gypsum fill-in (micro-box work). In the Savonnières limestone (oolitic limestone), gypsum recrystallization could occur without microcracks: elements are sometimes nearly totally weathered, while the palisadic calcitic cement surrounding the oolites was still preserved. In the matrix-supported limestone (Courville limestone), weathering could deeply affect the matrix while elements are not weathered. When a layer of microcrystalline calcite is observed on the surface of the limestone, however, the black crust growth seems to be limited to the external part of the stone. Porous characteristics of limestones directly depend on sedimentary and diagenetic phases developed. The pore network controls moisture movement and also determines the reactivity of the stone to gypsum recrystallization.