Thin Section Studies Research Articles

First occurrence in life position of two Triassic brachiopod species (Thecideida) from NE Italy: Paleoecological considerations

The San Cassiano Formation from the Dolomites, NE Italy, is a Ladinian–Carnian (Middle – Upper Triassic) lithostratigraphic unit belonging to the Western Tethys domain. In this formation numerous groups of marine invertebrates from reef communities have been reported. In particular, brachiopods are represented by different orders. Thecideids are the most abundant and diverse, with different species of the genus Thecospira. Despite the apparent abundance, only one report exists of a thecideid of the genus preserved in life position: Thecospira tyrolensis. In this study, we describe and discuss the first finding of Thecospira semseyi and Thecospira tenuistriata in life position based on the study of thin sections of Cipit boulders. Seemingly, the Th. semseyi shells were not firmly attached to the substrate by a small cementation surface; therefore, they could have lived embedded into the biogenic matrix. By contrast, Th. tenuistriata displays an umbonal region modified in a cementation area, allowing the attachment to the bio-builder. Most samples don’t show any signal of transport since all specimens are articulated and are still attached to the substrate. Besides, the commissures are partially opened, free of any encrustation of sponge or bryozoan growing. The preservation of brachiopods suggests that the samples of both species were fossilized in life position. Moreover, Th. semseyi and Th. tenuistriata continued to live although the host’s fabric was imbibing the brachiopods’ ventral valve. This shows that thecideids were important components of Tethys reef communities.

Structural Analysis and Micro-Deformations Syn- to Post-Folding of the Visean limestones

The Allochthonous Visean limestones of the Eastern part of the Moroccan central massif, occurring along the front of the Jebel Bou Khmis thrust fault, between Mrirt and Amghass, have undergone a structural and microtectonic study, aiming to study fracturing and its relationship between folding. The microtectonic studied sites were selected in different folds and in different parts of the same fold (long and short limbs and in the hinge) in order to study the relationship with fold geometry and fracturing, and to show the control of the facies and its importance in the genesis of fracture networks. The sub-vertical fractures family appear to be anterior to sub-horizontal once. They correspond to the first deformation accompanying the first shortening phases during the layer parallel shortening (LPS). The horizontal fractures were developed by accommodating of the fold when extending vertically during the amplification of the hinge. These three fracture families are syn- to post major folding phase that generated penetrative NE-SW oriented cleavage. The same results were obtained from microscopic study of thin sections, selected among oriented limestone samples, within oolites, calcite crystals and fluid inclusions.

The Facies Analysis, Evolution, and Coal-Bearing Source Rock Features of the Middle–Late Triassic Shallow-Water Delta in the North Carnarvon Basin, Northwest Shelf of Australia

The sedimentary facies, architecture, and depositional mechanism of deltaic systems have been one of the global research hotspots in recent decades; however, the detailed distribution, sedimentary evolution, source rock potential, and major control factors of the coal-bearing shallow-water delta are still unclear. A typical shallow-water braided delta with coal-bearing source rocks developed in the Middle–Late Triassic Mungaroo Formation of the North Carnarvon Basin, which can be a good study area for an analysis of coal-bearing source rocks. In this study, the sedimentary facies, distribution and evolution, and coal-bearing source rock features of the Triassic strata were analyzed based on the integrated study of wireline logs, drilled cores, thin sections, seismic facies and attributes, and geochemical data. A range of shallow-water delta sedimentary facies was identified, including the proximal delta plain channel/interdistributary bay, distal delta plain channel/interdistributary bay, and the delta front. The coal-bearing shallow-water delta system of the Middle–Late Triassic Mungaroo Formation was characterized by the largest scale delta system with relatively broad proximal and distal delta plains and relatively narrow delta front subfacies. The scale of the delta system showed a trend of increasing from the Early Triassic Locker Shale to the Middle–Late Triassic Mungaroo Formation and then decreasing to the Late Triassic Brigadier Formation. The distal delta plain subfacies of the Mungaroo Formation should have the highest potential coal-bearing source rock, and the proximal delta plain also can be a favorable target for source rock evaluation. The major control factors of the coal-bearing source rocks of the Mungaroo shallow-water delta mainly included the Triassic megamonsoon climate, the topographic features, eustatic changes, and provenance supply. The proximal and distal delta plains of the shallow-water delta system with thin coal seams, carbonaceous mudstone, and dark mudstone lithologies’ association could be a favorable source rock exploration facies for the next stage of natural gas field exploration.

Keratose sponges in ancient carbonates – A problem of interpretation

AbstractReports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine to peritidal carbonates include cases interpreted to be keratose sponges. However, living keratose sponges have elaborate, highly elastic skeletons of spongin (a mesoscopic end‐member of a hierarchical assemblage of collagenous structures) lacking spicules, thus have poor preservation potential in contrast to the more easily fossilized spicule‐bearing sponges. Such interpreted fossil keratose sponges comprise diverse layered, network, amalgamated, granular and variegated microfabrics of narrow curved, branching, vesicular–cellular to irregular areas of calcite cement, thought to represent former spongin, embedded in microcrystalline to peloidal carbonate. Interpreted keratose sponges are presented in publications almost entirely in two‐dimensional (thin section) studies, usually displayed normal to bedding, lacking mesoscopic three‐dimensional views in support of a sponge body fossil. For these structures to be keratose sponges critically requires conversion of the spongin skeleton into the calcite cement component, under shallow‐burial conditions and this must have occurred prior to compaction. However, there is no robust petrographic–geochemical evidence that the fine‐grained carbonate component originated from sponge mummification (automicritic body fossils via calcification of structural tissue components) because in the majority of cases the fine‐grained component is homogenous and thus likely to be deposited sediment. Thus, despite numerous studies, verification of fossil keratose sponges is lacking. Although some may be sponges, all can be otherwise explained. Alternatives include: (i) meiofaunal activity; (ii) layered microbial (spongiostromate) accretion; (iii) sedimentary peloidal to clotted micrites; (iv) fluid escape and capture resulting in bird's eye to vuggy porosities; and (v) moulds of siliceous sponge spicules. Uncertainty of keratose sponge identification is fundamental and far‐reaching for understanding: (i) microfacies and diagenesis where they occur; (ii) fossil assemblages; and (iii) wider aspects of origins of animal clades, sponge ecology, evolution and the systemic recovery from mass extinctions. Thus, alternative explanations must be considered.

Extreme diagenesis in the Late Pleistocene stratigraphic sequence of Grotta Guattari (central Italy) and its impact on the archaeological record

Grotta Guattari is a key cave site for Mediterranean prehistory. It is where a perfectly preserved paleo-surface, littered with bones and containing a Neandertal cranium, was exposed in 1939. Recent research, moreover, has yielded even more Neandertal remains in a side chamber that had remained unexplored. This paper gives an account of the stratigraphic sequence of the atrial portion of Grotta Guattari described in 1989 along the walls of the 1939 to 1950 excavation trenches. This key sequence, capable of elucidating the sequence of events recorded in Grotta Guattari, remained until now unstudied. The stratigraphy represents the interval between ca 125 ky BP (Marine Isotope Stage – hereafter, MIS – 5.5 or Tyrrhenian transgressive cycle) and ca 50 ky BP (MIS 3). Grain size, chemical, and heavy mineral analyses were coupled with the micromorphological study of thin sections, corroborated by SEM/EDS chemical determinations and XRD analyses. The presence of secondary Ca–Al and Ca–Fe phosphates, formed in response to the weathering of guano, indicates that part of the archaeological record (bones and ash) has weathered away. Weathering was so intense that also the more unstable mineral species, especially augite, disappeared from the heavy mineral assemblage. The differential preservation of the archaeological record shall therefore be taken in consideration when interpreting in behavioural terms old and new excavation data.

Petro-Archaeometric Study of Pre-Roman Pottery from the Archaeological Site of Bec Berciassa (Roccavione, Cuneo, North-West Italy): Technological Remarks from Petrographic Study of Tempers

The petro-archaeometric study of ceramics from the Rittatore excavations, Bec Berciassa archaeological site, was carried out on pottery sherds attributed to an older phase dating back to the Late Bronze Age. This collection represents a small sampling of pottery and the chronology of most of this material is homogeneously ascribable to a period between the 6th and the beginning of the 4th century BC (Iron Age). In addition to the archaeometric study, a geological survey highlighted the resources of the area potentially useful for the development of prehistoric communities, including resources that could be used for ceramic production. A thin section study under optical microscope distinguished five ceramic mixtures. They are mostly coarse-grained, hiatal, and serial-textured, calibrated with the addition of fillers. The fine matrix is homogeneous in composition, although with compositional variations in Fe2O3. Therefore, it is possible to hypothesise a single source of supply. The different types of filler can be traced back to minerals and rocks found outcropping within the basins of the Gesso and Vermenagna rivers and thus potentially present as pebbles in their beds. Calc-schists, sparitic calcite, magmatic rocks (granites and aplites), and sericite-schists have been used since the Bronze Age; quartz sandstones and quartzites are only present in Iron Age pottery. At a macroscopic level, all these filler agents are light in colour, tending to white, almost as if the colour and homogeneity of the geological material were a criterion of choice dictated more by tradition and know-how rather than by any particular technological choice.

Evolution process and factors influencing the tight carbonate caprock: Ordovician Yingshan Formation from the northern slope of the Tazhong uplift, Tarim Basin, China

The tight limestone of the Yingshan Formation (Ordovician) is a local tight carbonate caprock in the Ordovician Tarim Basin. It vertically overlaps with the hydrocarbon reservoirs. The diagenesis and evolution processes affect the closure of this type of caprock, but it has been scarcely studied. This research utilized detailed laboratory experiments such as thin section study, cathodoluminescence (CL) examination, isotopic analysis (carbon, oxygen, and strontium isotopes), fluid inclusion, and the well-logging data to evaluate the evolution process and factors influencing the tight carbonate caprock of the Ordovician Yingshan Formation from the northern slope of the Tazhong uplift, Tarim Basin, China. The tight carbonate rocks of the Yingshan Formation in the study area are mainly composed of micrite and grainstone. The caprock thickness of the upper Ying 1 and the upper Ying 2 members of the Yingshan Formation are 15–44 m and 8–80 m, respectively, showing good continuity. However, the seal rocks in the other members of the Yingshan Formation are discontinuous. Low energy facies zone, vertical vadose zone, slow flow zone, and zone with weak tectonic destruction are the main areas of caprock distribution. Karstification in the epigenetic stage and cementation in the burial stage are the crucial factors affecting the evolution and distribution of carbonate seal rocks. Paleogeomorphology, phreatic surfaces, original sedimentary environment, and fault distribution influence the karstification, thus enhancing the macro heterogeneity of caprock. Cementation is controlled by buried fluids (formation water, hydrocarbons, hydrothermal fluid) and improves the micro sealing of the caprock. Multistage tectonic movements and changes in the fluid environment constantly change the sealing property of the caprock, and the reservoir and seal rock can transform each other in the process of evolution. These results suggest carbonate reservoirs evaluation can thus be enhanced by combining caprock evolution to analysis effectiveness. This research explains the mechanism of the spatial distribution of carbonate caprocks and provides the theoretical basis for carbonate reservoirs exploration.

The method of determination of the kerogen and bitumoids content in the Artinskian sediments of an oil and gas field of the Orenburg region by well logging data

The lithological and geochemical studies of the Artinskian carbonate sediments of one of the gas and oil fields in the southwest of the Orenburg region revealed a significant amount of indigenous organic matter in the productive intervals of the section. The study of thin sections established that the organic matter content in the examined rocks reaches 3.75 wt%, with the average value of this parameter being 1.05 wt%. The article is devoted to the development of methods for estimating the content of kerogen and bitumens in rocks according to well logging data.

Comparative evaluation of airborne AVIRIS-NG and spaceborne PRISMA hyperspectral data in identification and mapping of altered/weathered minerals in Jahazpur, Rajasthan

The present study addresses a comparative evaluation of airborne AVIRIS-NG and spaceborne PRISMA hyperspectral datasets for mapping hydrothermally altered minerals in Jahazpur town (25°25′23.37″N; 75°06′23.17″E) of Bhilwara district in southeastern Rajasthan. This area is located in Aravalli Craton which host notable base metal mineralization namely Rampura-Agucha, Pur-Banera and Rajpura-Dariba. The hyperspectral datasets were classified using spectral angle mapper which identified talc, soapstone, and kaolinite clay minerals in the study area. The samples were collected from the identified areas. Their spectral signature was compared with AVIRIS-NG, PRISMA, and USGS mineral spectral library and showed greater similarity in spectral absorption features. Conventional geological techniques such as thin section studies and XRD diffraction pattern analysis were carried out to validate the presence of minerals in the study area. Comparative analysis shows AVIRIS-NG and PRISMA sensor capability to identify altered/weathered minerals. The PRISMA dataset did not identify small surface exposure of talc deposit at the Padampura location due to its low spatial resolution (30 m) and SNR values. In contrast, AVIRIS-NG imagery successfully maps this exposure in the classified mineral map. The types of alteration in the area show formation of talc mineral from dolomite and argillic alteration resulting in kaolinite and montmorillonite formation. Therefore, airborne AVIRIS-NG proves its efficiency in mapping of relatively small surface exposure of altered minerals compared with the spaceborne PRISMA hyperspectral dataset.

Dynamic failure behavior and damage evolution process of holed sandstone under impact loads

In this research, the damage process and dynamic failure behavior of some sandstone rocks, containing an elliptical hole, were evaluated. For this reason, a series of laboratory tests under both static and dynamic loads in 4 different orientations of the elliptical hole was performed. Modified Split Hopkinson Pressure Bar testing machine was employed to apply impact load. Dynamic fracture evolution was recorded by utilizing a high-speed camera to evaluate the macro damage evolution process. Scanning electron microscope analysis and thin section studies were also used to assess mineral's behavior regarding micro-crack evolution. Furthermore, the experimental tests were numerically simulated, and strain energy density and dynamic stress concentration factor were measured to evaluate the effect of elliptical hole inclination on dynamic response. The results indicated that when the largest diameter is perpendicular to core axis, the rock shows the lowest strength in both static and dynamic loading conditions. Also, with increasing hole inclination, both strain energy density and dynamic stress concentration factor decreased. Evaluation of fracture surface indicated that grain-boundary cracks are the dominant type of cracks and iron oxide cement distribution has a vital role in the development of the cracks.

Microbial Biofilms at Meat-Processing Plant as Possible Places of Bacteria Survival.

Biofilm contamination in food production threatens food quality and safety, and causes bacterial infections. Study of food biofilms (BF) is of great importance. The taxonomic composition and structural organization of five foods BF taken in different workshops of a meat-processing plant (Moscow, RF) were studied. Samples were taken from the surface of technological equipment and premises. Metagenomic analysis showed both similarities in the presented microorganisms dominating in different samples, and unique families prevailing on certain objects were noted. The bacteria found belonged to 11 phyla (no archaea). The dominant ones were Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. The greatest diversity was in BFs taken from the cutting table of raw material. Biofilms’ bacteria may be the cause of meat, fish and dairy products spoilage possible representatives include Pseudomonas, Flavobacterium, Arcobacter, Vagococcus, Chryseobacterium, Carnobacterium, etc.). Opportunistic human and animal pathogens (possible representatives include Arcobacter, Corynebacterium, Kocuria, etc.) were also found. Electron-microscopic studies of BF thin sections revealed the following: (1) the diversity of cell morphotypes specific to multispecies BFs; (2) morphological similarity of cells in BFs from different samples, micro-colonial growth; (3) age heterogeneity of cells within the same microcolony (vegetative and autolyzed cells, resting forms); (4) heterogeneity of the polymer matrix chemical nature according to ruthenium red staining.

Reservoir rock typing and electrofacies characterization by integrating petrophysical properties and core data in the Bangestan reservoir of the Gachsaran oilfield, the Zagros basin, Iran

The super-giant Gachsaran oilfield is situated in the Dezful Embayment of the Zagros basin. The main goal of this study is to characterize the reservoir rock types by integrating the available geological and petrophysical studies in the Bangestan reservoir along with adopting a way to figure out the optimal number of electrofacies codes. At the first step, the types of porosity and geological microfacies were studied by using 163 thin sections from the core samples. The microscopic studies revealed that fractures and intraparticle interstices are the most common porosities types. Also, they resulted in the identification of 4 microfacies in the Bangestan reservoir. In a complementary study, the Velocity-Deviation Log (VDL) was employed to determine the dominant pore types. By comparison of the VDL values and thin section studies’ results, it was deduced that high micro-porosities along with hairline fractures are the predominant pore types of the Bangestan reservoir. At the second step, the optimal number of reservoir rock types (RRT) was determined by using the concept of hydraulic flow units. Thus, six flow units were distinguished by utilizing the Flow Zone Indicator (FZI) method in which the reservoir properties were improved from RRT-1 toward RRT-6. In the third step, the data clustering analysis, known as the electrofacies analysis, was employed to identify the accurate petrophysical rock types based on the meaningful segregation of capillary pressure curves within each electrofacies code and then propagated in non-cored intervals and boreholes. In this research, an optimal number of 7 electrofacies were identified by employing the petrophysical curves including effective porosity (PHIE), bulk density (RHOB), sonic (DT), and water saturation (SWE), along with considering the number of reservoir rock types and the defined geological microfacies, as well as the relations of the available capillary pressure data within different electrofacies codes. The validity of the proposed electrofacies was scrutinized through petrophysical results including shale volume, water saturation, and effective porosity. In the end, the electrofacies codes were compared to the defined geological microfacies. Finally, this study shows that the correlation of capillary pressure data and electrofacies codes can be resulted in figuring out the optimal number of electrofacies codes. In addition, by trying to honor the link between geological microfacies, capillary pressure, and petrophysical curves, the constructed electrofacies model, as a suitable practical integrated rock typing method, can be the foundation of property modeling, guide the spatial distribution of reservoir properties in the 3D model, aids to model the dynamics of fluid flow more realistically in reservoir simulation phase, and ultimately be beneficial for further development and production decisions in the Bangestan reservoir of the Gachsaran oilfield.

Digital rock physics: Defining the reservoir properties on drill cuttings

Well drilling with core extraction is one of the most expensive procedures in the oil industry. The potential alternative, which may open opportunities for cost-efficient acquisition of petrophysical data, can be an approach based on digital analysis of drill cuttings. The main purpose of this research was to evaluate the possibility of using digital cuttings analysis and rock physics for reservoir properties evaluation. The carbonate samples of core and cuttings were simultaneously collected from the same intervals during the drilling of deviated wells in the Carboniferous reservoir of the oil deposit in the Republic of Tatarstan, Russia. Based on the core analysis using the optical study of thin sections and XRD, we investigated sedimentological and mineralogical features and classified all lithotypes of well intervals. The standard samples were produced from all defined facies and their reservoir properties were studied in routine tests. The largest cuttings from each well interval were separated and their structures were compared using μCT with core subsamples of the same intervals. We assessed the changes of cuttings structure occurring in the drilling process, which include the colmatation of the pore space with drilling fluid and disintegrated rock particles and the formation of secondary fractures. Detailed analysis of cuttings from one well interval consisting of the border between the facies of high porous grainstones with packstones and dense micrite limestones demonstrated that high porous varieties were eroded in the drilling process. The analysis of chemical composition using XRF-mapping, XRD and SEM with EDS showed that most of the cuttings were constituted by disintegrated rock particles or form elements (e.g. separate fusulinids) cemented by drilling mud. However, more durable cuttings from dense micrite limestones facies were generally retained their dominant calcite composition and original rock structure, with only secondary fractures. Finally, we analyzed pore space properties and performed digital simulations of wave propagation velocities to compare the characteristics of these cuttings and core subsamples from this lithotype, scanned in the same μCT settings. The results demonstrate close characteristics of porosity 0.08–0.6%, dominant pore sizes 1–60 μm and velocities Vp = 6130–6240 m/s, Vs = 3180–3230 m/s. However, the comparison of obtained values with measured on standard samples shows a significant difference, which is caused by deviation from REV. The potential use of cuttings for assessing reservoir and petrophysical properties can be possible in case of provision with the factors of cuttings structure alteration, representativity of samples, as well as optimization for these purposes of the drilling process with cuttings selection.

Micromorphological structure of maritime antarctic cryosols (King-George and Livingston Islands, West Antarctica)

Cryosols of the Antarctic maritime area are much different from the continental ones. The relatively moderate climate conditions in Maritime Antarctica and a strong interaction between the biotic and abiotic environment are drivers for more intensive soil formation processes than in the continental regions. Soil formation studies from the Maritime Antarctica are, however, rather rare. Therefore, micromorphological investigations on polar soils can contribute to more comprehensive information on soil genesis in Antarctica. In this study, we applied the micromorphological study of thin sections from soil micromonoliths to assess the intensity and trends of the pedogenic processes in selected soils from two adjacent islands of the South-Shetland archipelago: King George Island and Livingston Island. The results obtained show that regional lithology and the origin of the incoming organic matter mainly determine the micromorphological structure of the local soils. Soil matrix micromorphological properties and features (mineralogical content, weathering stage and even partly grain-size distribution) are mainly defined by pyroclastic particles due to recent and ancient volcanic eruptions. The presence of rounded grains and aggregated mineral particles is the evidence of marine origin of the sediments. Ornithogenic soils show the clear evidence of the organic plasma formation and mineral particles aggregation via the zoogenic organic substances provided by penguins which is a unique specifics of the maritime Antarctic soils.

Hydrocarbon prospectivity of the miocene-pliocene clastic reservoirs, Northern Taranaki basin, New Zealand: integration of petrographic and geophysical studies

In this study, it is aimed to characterize the Early pliocene sandstone (EP-SD) and the Late Miocene-Early Pliocene Mangaa sandstone reservoirs and the efficiency of their sealing cap rocks using the petrographical and petrophysical data of these sandstone zones in northern Taranaki basin, New Zealand. The prospective potential reservoirs were studied using impregnated thin sections, XRD data analysis, and well log data (self-potential, gamma-ray, sonic, density, neutron, shallow\\deep resistivity and PEF) to characterize the reservoir zones, in addition to Mercury intrusion capillary pressure data (MICP) to check the efficiency of some potential seals. The EP-SD and the Mangaa sandstone units are typically poorly consolidated very fine sandstone to siltstone, with porosities averaging 25%. The sands are composed of quartz (38.3–57.4%), with common feldspars (9.9–15.2% plagioclase, and 2.7–6.3% K-feldspars) and up to 31.8% mica. In Albacore-1 well to the north of the Taranaki Basin, the Mangaa formation includes three separate for each of the EP-SD zones (EP-SD1, EP-SD2, and EP-SD3), and the Mangaa sequence (Mangaa-0, Mangaa-1, and Mangaa-2). The thin section studies indicate that, the studied samples are grouped into greywackes, arenites and siltstone microfacies with much lithic fragments and feldspars, sometimes with glauconite pellets. From the XRD data, it is achieved that the mineral composition is dominated by quartz, mica/illite, feldspars, and chlorite. The petrophysical investigation revealed absence of pay zones in the EP-SD zones, and presence of thin pay zone with net thickness 5.79 m and hydrocarbon saturation of about 25.6%. The effective porosities vary between 23.6 and 27.7%, while the shale volume lies between 12.3 and 16.9%. Although the shale content is relatively low, the relatively high API (50–112 API of average 75 API) is contributed by the relatively high K-feldspar content and intercalations with thin siltstone and muddy siltstone beds. Sealing units include the intra-formational seals within the Mangaa sequence, mudstones and fine grained units overlying the Mangaa and further intra-formational mudstones, within the shallower EP-SD units. The efficiency of these seals indicates the capability to trap 16.4–40.6 m gas or 17.4–43.0 m oil which is relatively low in correlation with their efficiency in the central parts of the Taranaki Basin Overlying the primary seals, mudstones of the Giant Foresets Formation provide additional regional seal.

Lithotypes, Facies, and Sources of Sedimentary Rocks in the Barguzin Valley of the Baikal Rift System

Lithological, petrographic, and lithogeochemical data are given for sedimentary rocks of alluvial, lacustrine-marsh, and lacustrine facies in the Barguzin valley, uncovered by new boreholes. During petrographic studies of thin sections, the main lithotypes of stratons of rift basins were identified. According to the mineral composition of the rocks, petrochemical and microelement characteristics, a conclusion was made about the origin of sedimentary deposits as a result of erosion of the granite basement rocks.

Depleted mantle beneath an oceanic island arc: New insights into peridotites of the RasKoh ophiolite, western Pakistan

The RasKoh ophiolite of the Sorap Massif, western Pakistan, is a relatively little known body in the vast Alpine–Himalayan orogenic belt (AHOB). This paper focuses on the RasKoh peridotites to better understand the origin and evolution of the ophiolite. Field observations, confirmed by thin-section study, identified three types of peridotite; lherzolite, harzburgite, and dunite, which commonly have gradational boundaries. The mineral compositions of the peridotites (olivine, Cr-spinel, and pyroxene) suggest that these ultramafic rocks mostly represent refractory residues of mantle peridotites after ~12 to 25% partial melting and various degrees of melt-rock reaction. This interpretation is supported by variable contents of major elements and the chondrite-normalized rare earth element (REE) patterns. Enrichment of water-soluble elements, such as Rb, Ba, Sr, and light rare earth elements (LREE) also indicate infiltration of fluids into the depleted peridotites. Synthesizing available geological information with our new geochemical data, we suggest that the RasKoh ophiolite is a fragment of a former Triassic to Jurassic oceanic plate that became a mantle wedge above an intra-ocean subduction zone during the Cretaceous. Fluids from the subducted plate re-enriched the depleted peridotites of the RasKoh island arc. The ophiolite was emplaced during collision between the RasKoh island arc to the south and the Chagai continental arc to the north leading to exhumation of the re-enriched peridotites. This new model is much simpler than most previous ones and better explains the tectonic evolution of western Pakistan.

Integrated Porosity Classification and Quantification Scheme for Enhanced Carbonate Reservoir Quality: Implications from the Miocene Malaysian Carbonates

The pore system in carbonates is complicated because of the associated biological and chemical activity. Secondary porosity, on the other hand, is the result of chemical reactions that occur during diagenetic processes. A thorough understanding of the carbonate pore system is essential to hydrocarbon prospecting. Porosity classification schemes are currently limited to accurately forecast the petrophysical parameters of different reservoirs with various origins and depositional environments. Although rock classification offers a way to describe lithofacies, it has no impact on the application of the poro-perm correlation. An outstanding example of pore complexity (both in terms of type and origin) may be found in the Central Luconia carbonate system (Malaysia), which has been altered by diagenetic processes. Using transmitted light microscopy, 32 high-resolution pictures were collected of each thin segment for quantitative examination. An FESEM picture and a petrographic study of thin sections were used to quantify the grains, matrix, cement, and macroporosity (pore types). Microporosity was determined by subtracting macroporosity from total porosity using a point-counting technique. Moldic porosity (macroporosity) was shown to be the predominant type of porosity in thin sections, whereas microporosity seems to account for 40 to 50% of the overall porosity. Carbonates from the Miocene have been shown to possess a substantial quantity of microporosity, making hydrocarbon estimate and production much more difficult. It might lead to a higher level of uncertainty in the estimation of hydrocarbon reserves if ignored. Existing porosity classifications cannot be used to better understand the poro-perm correlation because of the wide range of geological characteristics. However, by considering pore types and pore structures, which may be separated into macro- and microporosity, the classification can be enhanced. Microporosity identification and classification investigations have become a key problem in limestone reservoirs across the globe.

Natural factors related to the differential heating of aggregates exposed to microwaves

The heating produced by microwaves has been demonstrated to be effective in materials such as aggregates, although notable differences in heating have been observed between different types of aggregates. The geological factors of each material are responsible for these differences in heating due to compositional elements such as the mineralogy and chemistry of the material and physical characteristics such as crystal size and apparent density.The study of each of these characteristics could unravel the factors determining differential heating in aggregates, which would be relevant for different applications in the mining industry (heating, drying, and comminution) and in civil engineering in self-healing (microcrack repair) or winter road maintenance (surface de-icing).This paper investigates the influence of microwave heating on the chemical, mineralogical, and physical properties of aggregates susceptible to be used in asphalt mixtures. For this, aggregates with different characteristics have been selected. Various tests were conducted to determine the factors affecting heating: thin-section studies (mineralogy and crystal size), XRD (mineralogy) and XRF (chemistry) composition studies, and bulk density of the rocks. These results were correlated with dielectric permittivity data (loss tangent) and direct heating data (parameter T70). Both techniques have proven helpful as an indicator of susceptibility to microwaves. Finally, multiple regression models were proposed to apply this knowledge to any rocks suitable as aggregate.

Characteristics and Genesis of the Es1 Productive Sandstone Reservoir (Paleogene), Nanpu Sag, East China

AbstractThe Shahejie Formation is a fundamental rock unit for hydrocarbon exploration and production in the Nanpu Sag, Bohai Bay Basin. Methodology including thin sectioning, core observations, fluorescence, scanning electron microscopy, cathodoluminescence, fluid inclusion, laser scanning confocal microscopy and geochemical analysis (C, O isotopes) were all utilized to investigate the reservoir characteristics and origin of the Es1 Sandstone. Thin section study showed that the reservoir rock consisted of feldspathic litharenite and lithic arkose. The reservoir pores are categorized as intergranular pores, fracture pores, dissolution pores and intergranular cement dissolution pores. The studied sandstone had good porosity (0.05%–35%) and permeability (0.006–7000 mD). The Es1 reservoir is classified as a fractured reservoir, a primary intergranular pore‐associated reservoir and a dissolution reservoir. Deposition, diagenesis and tectogenesis are the main factors that played important roles in the development of the reservoir. Sedimentation is the foundation and assumption for reservoir development, but the effective reservoir is primarily controlled by primary pores, fractures, lithofacies, tectonic elements and dissolution pores. Moreover, compaction, fracture filling and cementation were the primary sources of reservoir densification. The reservoir was progressively formed through the influence of different geological and diagenetic events. The present study provides significant information and references for hydrocarbon exploration and development in the Nanpu Sag.