Rock Samples Research Articles

Assessment of the Suitability of Raw Materials for Construction Manufacturers, from Ellan Anticline, Northwestern Mosul City, Nineveh Governorate, Iraq

The fast population growth and significant urban development put pressure and demand on raw materials that are used for construction like carbonate rocks, clay, and gypsum. Providing new background information for these raw materials that may be suitable for different industries, such as cement, Juss, plaster, building stone, and bricks is aimed in this study. Therefore, the study includes a field reconnaissance of seven sites within the Ellan anticline, northwest of Mosul City, several twenty-five rock samples were collected and analyzed from the best exposures of the formations. The results show that unit C of the lower member and the upper member of the Fatha Formation are suitable raw materials for the manufacturing of the cement industry. Gypsum strata in the Fatha Formation are suitable for multiple industries such as cement, Juss, plaster, building units, light tile or blocks, and for the protection of columns. The chemical results of major oxides for limestone from Euphrates and lower members of Fatha formations (units A and B) show that the mean concentrations of CaO, MgO, and alkali oxides are higher than the limit values in Iraqi standards. The bulk-rock analysis for major element oxides of unit C demonstrates that rocks are within the limit values. In addition, most of the oxides of limestone and marly limestone of the upper member of the Fatha Formation are within the standard quality for the cement industry. Clays from Quaternary sediments were found to be suitable for the cement industry only, while the pre-Quaternary appears to be not suitable for cement or perforated brick industries.

Source Rock Evaluation and Hydrocarbon Generation Potential of the Cretaceous (Dokan and Gulneri) Formations in Bai Hassan-13 Well Section, Kurdistan, North of Iraq

Eleven cutting rock samples from both Dokan and Gulneri formations (Cretaceous) in one subsurface section of Bai Hassan-13 (BH-13) well in northern Iraq were studied by using two techniques for hydrocarbon generation potentiality. The geochemical technique included Rock-Eval Pyrolysis analysis, The optical technique was achieved by studying palynological slides. The rock-Eval pyrolysis results showed that Dokan Formation has total organic carbon (TOC) wt.% ranging between 1.16 % and 2.3 % (good to very good), Gulneri Formation has a high TOC of 1.34 % and 4.64 % (good to excellent) quantity of organic matter. About the quality of organic matter, both Dokan and Gulneri formations are composed of kerogen types I and II. The organic matter of the Dokan Formation is not indigenous (migrated), one sample of the Gulneri Formation is indigenous the other one is located on the slanted line separating the Indigenous from non-indigenous organic matter. The organic matter within the two formations are thermally immature source rock, Therefore, they cannot generate oil and gas. The palynological study revealed that amorphous organic matter is the predominant organic matter component in both formations with more than 89%, whereas phytoclasts and palynomorphs comprised only a few percentages. There is no great variation in the percentages of the mentioned organic matter components, except a slight increase in the percentage of phytoclasts and palynomorphs in the lower part of the Dokan Formation, therefore one primary palynofacies type can be recognized, and divided into two secondary palynofacies. Through plotting Tyson's Amorphous, phytoclasts, and palynomorphs (APP) diagram, it is clear that the two formations are deposited in a distal suboxic to anoxic basin.

A Cryogenian impact structure lurking in the shadows of northern Sweden

AbstractHere we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine‐grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U‐Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary‐ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast‐rich melt rocks to reflect non‐impact‐related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short‐distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.

Anthropogenic Impact on Soils of Cities Irkutsk, Angarsk

The morphological field description of soil profiles of the territory of Irkutsk region was carried out. Samples of soils, soil-forming rocks and vegetation were taken for further physical and chemical analyses to determine soil properties in the studied areas. Sample preparation of soils was carried out, phytotoxicity of soils was analyzed. Processing of the obtained data was carried out, as a result of which the percentage of germination of radish seeds in the upper horizons of soils of the key areas of Irkutsk and Angarsk cities was revealed, the length of shoots and the length of roots in the soils of the studied samples were measured, the index of soil toxicity was calculated.

RECONSTRUCTION OF THE SUBSIDENCE DYNAMICS AND PALAEOTEMPERATURE REGIME OF THE NORTHERN MARGIN OF THE SIBERIAN PLATFORM

The formation mechanisms of sedimentary basins are considered as a response of deep processes in the mantle, therefore they carry important information about the geodynamics and thermal regime of the lithosphere. For different sectors of the northern margin of the Siberian Platform, the dynamics of sedimentation and subsidence was reconstructed. The analysis of subsidence curves shows that during the Late Paleozoic the sedimentary infill formed in the foreland basin environment. In the Late Permian–Early Triassic time, in the central and western sectors, the subsidence was accelerating due to the development of a thick trap complex; after the Permian and Triassic boundary the subsidence slowed down. During the period of trap magmatism, an anomalously high subsidence rate up to 4.8 km/Ma in the central and up to 0.5–1.1 km/Ma in the eastern and western parts was reconstructed. The high rate and short duration of accumulation of volcanogenic sediments can be explained by an episode of short-term extension under the influence of a plume, followed by a long period of thermal subsidence. Numerical modelling of the temperature regime near mafic intrusive bodies was carried out, which showed that when determining the paleoheat flow, the influence of trap intrusions can be traced up to 400–500 m from the contacts. Estimates of the paleoheat flow for the Permian–Triassic stage of tectonic evolution of the eastern sector were obtained. It was calibrated using the PetroMod software package, based on laboratory measurements of modern values of vitrinite reflectance for rock samples from wells, modern temperature and heat flow in the sedimentary cover. It was determined that trap magmatism occurred at temperatures increased to 100 mW/m2, while the mantle component of the heat flow reached 38–72 mW/m2; it is several times higher as compared to modern one. The obtained paleoheat flow estimates for the Late Permian–Early Triassic stage appear to correspond to anomalously high values of modern continental rifts.

Anisotropic induced polarization modeling with neural networks and effective medium theory

Interpreting three-dimensional induced polarization (IP) data requires rock physics models that reflect the omnipresent anisotropy of the Earth’s crust. The Generalized Effective Medium Theory of Induced Polarization (GEMTIP) can model the IP signatures of rocks with polarizable mineral inclusions. However, it is computationally demanding because it requires numerically solving the depolarization tensors of each inclusion. We aim to streamline GEMTIP simulations by (1) integrating anisotropic background conductivity and triaxial ellipsoidal inclusions in the model and (2) estimating the depolarization tensors with a neural network. We validate the neural network predictions against known solutions for spherical and spheroidal inclusions, and we test our method using data from an actual rock sample. The neural network shows a relative sensitivity of 56% to inclusion shape and 44% to host rock anisotropy and is up to 100,000 times faster than numerical integration. We release the pre-trained neural network implementation as an open-source Python package, thereby providing a new method to interpret the IP signatures of anisotropic rocks.

Geochemical Parameters of Oil and Rock Samples from Murzuq Basin, Libya: An Application for Paleoenvironment Description

Seven sedimentary rocks and seven crude oils undertook a geochemical analysis to describe their organic matter type and then tag the Paleoenvironments based on the organic matter. The samples were collected from B1-NC151, A1-NC58, P1- NC1, E1-NC174, D1-NC151, H29-NC115, and D1-NC174 boreholes, located in Murzuq Basin. The study was established to understand life forms in the ecosystem based on biomarkers that biochemical techniques recognized. Microscopy was used for kerogen typing and Spore Color Index reference. Organic matter (EOM) was extracted from cutting samples. Furthermore, hydrocarbons were saturated and aromatic fractionated from the samples to investigate using Gas chromatograph system. Spore color index (SCI), range between 1.5-3.5, Amorphous organic matter (AOM) from 42 to 95 percentage, Phytoclasts % were 4-15.5, and Palynomorphs % range 0.5 to 7.5. The percentage of Carbon 85.66-86.29, Hydrogen 13.16-13.73, Nitrogen 0.06 -0.27, and Sulfur 0.31-0.70, besides wax were measured, ranging among 1.3 to 6.0 %. Pristine/n-C17, Phytane/n-C18, Pristine/Phytane, carbon preference index measurements (CPI) and DBT/P as saturated hydrocarbon ratios from whole oil chromatographs were established. Tricyclic terpanes, hopanes and n-alkanes were distinguishing as the most important oil biomarkers that reserved the characteristics in the Paleoenvironments.

Increasing accuracy in predicting mode I fracture toughness of rock structures: a comparative analysis of the rock engineering system method

The investigation of crack initiation and expansion is vital for the stability of structures. The Mode I fracture toughness (KIc) of rocks is a key property used to predict crack propagation in tension and hydraulic fracturing. Various methods have been introduced to determine KIc, but results differ due to factors like sample dimensions, crack geometry, groove type, and loading conditions. The cracked chevron notched Brazilian disc (CCNBD) sample is commonly used in laboratory tests for its easy preparation. This study employs the rock engineering system (RES) technique to overcome the challenges of time-consuming and costly laboratory tests and the uncertainty in traditional methods (analytical, numerical, experimental, laboratory, regression). Using 88 CCNBD rock samples proposed by ISRM, input parameters include thickness of the disc specimen (B), uniaxial tensile strength (σt), initial crack length (α0), radius of the disc specimen (R), crack length (αB), and the length of the final crack (α1). The RES-based model used 70 data points (80% of the dataset) for development, and 18 data points (20%) for evaluation. Regression analysis compared the performance of the RES method, using statistical indicators such as squared correlation coefficient (R2), mean square error (MSE), and root mean square error (RMSE) to measure accuracy. The RES-based method outperformed other regression techniques, demonstrating significantly enhanced accuracy. This highlights the effectiveness and superior performance of the RES method in estimating fracture toughness, particularly for CCNBD samples, showcasing its potential as a robust analytical tool.

Genesis of an Inorganic CO2 Gas Reservoir in the Dehui–Wangfu Fault Depression, Songliao Basin, China

This study systematically examines the origins and formation mechanisms of inorganic CO2 gas reservoirs located within the Dehui–Wangfu Fault in the southeastern uplift region of the Songliao Basin. The research aims to clarify the primary sources of inorganic CO2, along with its migration and accumulation processes. The identification of the Wanjinta gas reservoir within the Dehui–Wangfu Fault Zone, abundant in inorganic CO2, has sparked significant interest in the pivotal roles of volcanism and tectonic activity in gas generation and concentration. To analyze the release characteristics of CO2, this study conducted degassing experiments on volcanic and volcaniclastic rock samples from various boreholes within the fault trap. It evaluated CO2 release behaviors and controlling factors across varying temperatures (150 °C to 600 °C) and particle sizes (20, 40, and 100 µm). The findings indicated a negative correlation between CO2 release and particle size, with a notable transition at 300 °C—marking this temperature as critical for the release of adsorbed and lattice gases. Moreover, volcaniclastic rocks exhibited higher CO2 release compared to volcanic rocks, attributable to their larger specific surface area and higher porosity. At 600 °C, the decomposition of the rock crystal structure results in substantial gas escape. These observations suggest that the inorganic CO2 in this area derives not only from mantle sources but is also influenced by crustal components. Elevated temperatures prompted by tectonic activity and magmatic intrusion facilitated the degassing of the surrounding rocks, allowing released CO2 to migrate upwards through the fracture system and accumulate in the shallow crust, ultimately forming a gas reservoir. This study enhances the understanding of volcanic rock’s roles in inorganic CO2 gas generation and migration, highlighting the fracture system’s critical controlling influence on gas transport and aggregation. The findings indicate that inorganic CO2 gas reservoirs in the Dehui–Wangfu Fault Zone primarily originate from mantle sources with a mixture of crustal gases. This discovery offers new theoretical insights and practical guidance for the exploration and development of gas reservoirs in the Songliao Basin and similar regions.

Geochemical and mineralogical analysis of low-grade metamorphic rocks and their response to shallow landslide occurrence in Central Nepal

BackgroundThe weathering intensity and geochemical properties of a rock contribute to shallow landslide occurrences. This study aims to establish the role of rock weathering in shallow slope instability in low-grade metamorphic rocks of the Lesser Himalaya region of central Nepal. The rocks of the Kuncha Formation, which consist of phyllites, metasandstones, and gritty phyllites are characterized by the formation of shallow landslides. Field characterization of the rock mass within the landslide body, along with petrographic observations, clay mineral analysis, and major bulk geochemistry were adopted to establish a relationship between rock weathering and landslide occurrence.ResultsThe landslides distributed within the Kuncha Formation in the study area are debris-related slides and falls, rock falls, and complex slides. Microscopic petrographic observation of rock from the landslide area revealed well-developed microcracks and intergranular microfractures within the weathered samples, which suggests extensive disintegration and physical alteration. Kinematic analysis of the landslide slope revealed that discontinuities and bedding planes also affected the failure of the slope. The occurrence of neo-formed clay minerals and the conversion of biotite-muscovite to vermiculite, kaolinite, and mixed-layer clays indicate chemical weathering. The CIA ranges between 71 and 80 for the rock samples and between 72 and 84 for the soil samples, signifying moderate to extreme weathering effects. The higher values of PIA and CIW reveal K-feldspar and plagioclase alteration to clay minerals by weathering and alteration. CIA-LOI plots reveal significant relationships corresponding to weathering effects.ConclusionThe transition of rock from a fresh to a moderately weathered state and the development of clay minerals and major discontinuities played a crucial role in shallow landslide occurrence. The weakened physical properties of the rock mass due to weathering coupled with unfavorable joints and fracture conditions have led to instability of the hillslopes in the study area. It was observed that one of the driving factors that drives slopes to erosion and landslides is weathering. The dominant occurrence of landslides in the weathered rock domain within the study area validates the occurrence of landslides and weathering interconnections.

Machine learning-based optimization of photogrammetric JRC accuracy

To improve the accuracy of photogrammetric joint roughness coefficient (JRC) estimation, this study proposes two optimization models based on ground sample distance (GSD), point density, and the root mean square error (RMSE) of checkpoints. First, an algorithm that automatically generates spatial positions for equipment based on the convergence strategy was developed, using principles of Structure from Motion and Multi-View Stereo (SfM-MVS) and the shooting parameter selection algorithm (SPSA). Second, a portable positioning plate containing ground control points and checkpoints was designed based on optical principles, and a moving camera capture strategy guided by SPSA was proposed. Combining SPSA, portable positioning plate, and moving camera capture strategy, a photogrammetric experiment for small-scale rock samples in the field was conducted, collecting 48 datasets with different shooting parameters. Subsequently, a dataset incorporating GSD, point density, RMSE, and three JRC estimation metrics was established, revealing their correlations and sensitivities. Using seven machine learning algorithms, optimization models for photogrammetric JRC accuracy were developed, with Linear Multidimensional Regression and Gaussian Process Regression models improving JRC accuracy by an average of 85.73%. Finally, the applicability and limitations of the newly proposed method were further discussed.

Presentation of representative shape parameters of porous media based on mathematical computation on images

The shape parameters of porous media are really important to describe the petrophysical and geomechanical parameters of reservoirs. In addition, shape analysis can provide essential information about the origin, transport, deposition history of particles, etc. Because macroscopic properties (such as permeability, diffusion, etc.) are influenced by microscopic properties (such as pore size, grain shape, etc.). So far, various studies have been conducted to calculate some shape parameters, however, there is no comprehensive study that first includes most of the geometric parameters of the shape and then presents the representative shape parameters. Therefore, the aim of this study is to present representative shape parameters of porous media based on mathematical computation on images. The shape parameters studied included roundness, circularity, angularity, convexity, compactness, sphericity, aspect ratio, elongation, eccentricity, shape factor, and regularity. Calculation of shape parameters is done digitally using the developed program. The necessary data for the desired analysis are obtained from real sandstone samples. To develop this research, first, the mentioned shape parameters are calculated using the developed program for all rock samples. Then, by establishing a relationship between the mentioned parameters, the representative parameters that can show the shape of the porous medium are expressed. The results of this study show that the representative shape parameters of the porous medium are compactness, shape factor-round, and aspect ratio, which are good indicators for the shape of the porous medium.

Space and ground based spectroscopic studies and mineral chemistry of rare earth element bearing peralkaline rocks from Siwana Ring Complex, Rajasthan, India

The Neoproterozoic Siwana Ring Complex (SRC) in Barmer district, Rajasthan, India, contains a promising concentration of rare earth elements (REEs). This study uses PRISMA hyperspectral data to map potential high-REE locations using the Spectral Angle Mapper (SAM) classifier. Also, laboratory-based spectroscopy is used to analyse rock samples of peralkaline granite and rhyolite, using spectroradiometer in 400-2500 nm and Fourier Transform Infrared (FTIR) Spectroscopy in 400-4000 cm⁻1 regions. Diagnostic absorption features in the Visible Near Infrared (VNIR) and Short-Wave Infrared (SWIR) regions indicate the presence of REEs, alongside pyroxenes, amphiboles, and phyllosilicates. The data from the FTIR indicates the presence of minerals possessing Si-O, P-O and O-H bonds. Mineral chemistry and geochemistry confirm these findings, indicating the occurrence of REE-bearing minerals such as monazite, REE silicates, and apatite. Ce is found to be the most abundant REE. However, only absorption features related to Nd and Er or Ho are observed which means that these elements are indicators of high concentration of total REE in the samples. The map generated from the PRISMA data aligns well with geochemical data, proving the value of hyperspectral remote sensing in early exploration. This study also highlights laboratory spectroscopy as a valuable complementary tool in mineral exploration. This study provides spectral information for reference for future use on REE bearing peralkaline rocks.

Characterization of Stages of CO2-Enhanced Oil Recovery Process in Low-Permeability Oil Reservoirs Based on Core Flooding Experiments

Understanding the CO2 displacement mechanism in ultra-low-permeability reservoirs is essential for improving oil recovery. In this research, a series of displacement experiments were conducted on sandstone core samples from the Chang 6 reservoir in the Huaziping area using a multifunctional core displacement apparatus and Nuclear Magnetic Resonance (NMR) technology. The experiments were designed under conditions of constant pressure, variable pressure, and constant effective confining stress to simulate various reservoir scenarios. The results indicated that the distribution characteristics of the pore structure in the rock samples significantly influenced the CO2 displacement efficiency. Specifically, under identical conditions, rock cores with a higher macropore ratio exhibited a significantly enhanced recovery rate, reaching 68.21%, which represents a maximum increase of 31.97% compared to cores with a lower macropore ratio. Though fractures can facilitate CO2 flowing through pores, the confining pressure applied during displacement caused a partial closure of fractures, resulting in reduced rock permeability. Based on the oil-to-gas ratio and oil recovery in the outlet section of the fractured rock samples, the CO2 displacement process exhibited five stages of no gas, a small amount of gas, gas breakthrough, large gas channeling, and gas fluctuation. Although the displacement stage of different cores varies, the breakthrough stage consistently occurs within the range of 2 PV. These insights not only enhance our understanding of CO2 displacement mechanisms in low-permeability reservoirs but also provide actionable data to inform the development of more effective CO2-EOR strategies, significantly impacting industrial practices.

Effect of Sandstone Pore Morphology on Mechanics, Acoustic Emission, and Energy Evolution

Roadway section form is an important part of the underground engineering structure, and it directly affects the overall stability of the roadway and the occurrence of underground disasters in coal mines. Based on this, this paper adopts a TYJ-500 electro-hydraulic servo rock shear rheology testing machine to conduct a uniaxial compression test on sandstone containing different prefabricated hole section morphology and analyzes the damage characteristics seen during the damage evolution process, with the help of a high-speed camera and acoustic emission monitoring equipment. The test results show that the pore morphology is the main factor affecting the mechanical parameters of sandstone, and the peak stress and elastic modulus of sandstone with pore sections have the characteristics of increasing and decreasing at the same time, except for the intact rock samples. The pore morphology exhibits central symmetry (circular holes and rectangular holes) damage, more pressure-shear cracks and shear cracks, and the acoustic emission characteristics of high-energy–low-amplitude–low-count of the “two low-trend and one high-trend characteristic curves” attributes; moreover, due to the special existence of its pore morphology, it leads to the rock samples having less energy accumulation and release. The axisymmetric hole types (trapezoidal holes and straight-wall domed holes) are damaged by tensile cracks and shear cracks, and their acoustic emission characteristics show the characteristic properties of “three high-trend characteristic curves” of high-energy–high-amplitude–high-count, and there is a strong elastic energy accumulation and output. The conclusions of this article can provide a certain theoretical basis for the design of coal mine roadway sections in underground structures, failure analysis, and stability evaluation of roadway structures.

Facies Analysis and Depositional Environment of the Euphrates Formation in Selected Sections, Southwestern Iraq

The current study aims to investigate the microfacies, diagenetic processes, and depositional environments of the twenty-three rock samples from the Lower Miocene Euphrates Formation of two outcrops collected at Bahar-Najaf in Najaf governorate and Al-Shinafiya in Diwaniyah governorate, southern Iraq. Thin sections of these samples were prepared; hence, the nature of microfacies and related depositional environments was established. The formation contains abundant benthonic foraminifers and other fossils like miliolids, echinoderm, coral, gastropods, and pelecypods. Seven distinct microfacies were identified: lime mudstone, miliolid packstone, Pelletal Grainstone, Lime Wackestone, Peloidal Grainstone, Oolitic grainstone Microfacies, and fossiliferous packstone packed with bioclasts. Diagenetic processes evidenced in this study are dissolution, neomorphism, cementation, micritization, and dolomitization. The Euphrates Formation was deposited in a shallow marine setting with fluctuating energy levels, ranging from low-energy lagoons to moderate and high-energy shoals and fore-reef environments. Various microfacies indicate a complex depositional environment on a carbonate platform influenced by biota and sedimentary processes. These observations support the inference that the Euphrates Formation accumulated in shallow open marine, inner barrier, and shoal settings, providing a detailed interpretation of its para-depositional and diagenetic development.

Study on the Mechanical and Permeability Evolution of a Composite Rock Mass in an Aquifuge Under Hydraulic Coupling

The lithology and composition type of an aquifuge in overburden play a crucial role in influencing the crack evolution and permeability changes of the aquifuge. This study utilized the high-temperature and high-pressure rock triaxial seepage test system to conduct triaxial compression tests on mudstone, sandstone, and their combined rock samples. The mechanical characteristics and permeability evolution of each lithology law during the failure were investigated. Furthermore, computed tomography (CT) scanning technology was utilized for the three-dimensional (3D) reconstruction and theoretical permeability calculation of single and combined rock samples. The results indicated that the stress–strain curves for single and combined rock samples exhibited similar patterns, which were divided into four stages: pore compaction, linear elasticity, yield deformation, and post-peak residual deformation. The peak strength of rock samples positively correlated with confining pressure. Permeability trends for mudstone and sandstone exhibited an “N”-type pattern characterized by “slow decrease–gradual stabilization–sudden increase–rebound decrease”, while the permeability of mudstone–sandstone combined rock followed a “U”-type pattern of “initial decrease–stabilization–subsequent increase”. Notably, the permeability of the combined rock samples was significantly lower compared to the single rock samples. The failure mode indicated that fractures in a single rock sample transversed the entire sample, whereas failures in the combined rock samples were confined to the mudstone component. This observation accounted for the differences in the permeability changes between the rock sample types. Additionally, the theoretical permeability results from the 3D reconstruction correlated with the experimental results.

Assessment of natural radioactivity in the Higher and Tethys Himalayan Rocks along Manali-Leh Highway, India.

The Higher and Tethys Himalayan region of NW-Himalaya is less explored from the natural radioactivity mapping assessment, though geologically and tectonically, this region is still active. The concentration of primordial radionuclides (226Ra, 232Th, and 40K) in rock samples of the Manali-Leh Highway region of the Himalayas is determined in the present study using the HPGe detector. The radiological hazard parameters are also estimated in terms of radium equivalent activity (Raeq), annual effective dose (Ein and Eout), hazard indices (Hin, Hex, Hα, and Hγ), and gamma absorbed dose rate. SEM-EDS analysis was used to understand the mineralogical composition of the rocks. The activity concentration of 226Ra, 232Th, and 40K radionuclides varies from 1.4 ± 0.9 to 25.3 ± 1.2, 0.7 ± 0.5 to 59.6 ± 1.6, and BDL (below detection limit) to 830.3 ± 45.7Bqkg-1, with an average value of 13.0 ± 1.0, 21.7 ± 1.0, and 243.7 ± 25.2Bqkg-1, respectively. The average of Raeq in the study region lies within the safe limit of 370Bqkg-1. The hazard indices have values < 1, indicating no radiological hazards to the population from the rocks. The annual effective dose also has values less than the global average value. This study revealed that the rocks of the Higher Himalayan region have a higher concentration of natural radioactivity, while the Tethys Himalayan rocks have lower concentrations of 226Ra, 232Th, and 40K radionuclides. The origin of rocks from different lithologies may be the reason for the natural radioactivity variation. The average concentrations of primordial radionuclides in the region are within the world average indicating that the rocks of the region are safe to be used for different purposes.

Field geology under the sea with a remotely operated vehicle: Mona Rift, Puerto Rico

We implemented concepts of field geology at great ocean depths by constructing virtual outcrops from a string of overlapping video frames collected by remotely operated vehicles (ROVs). This lower-cost alternative to drilling boreholes allows stratigraphic extension into the offshore and regional interpretation of marine seismic profiles. The imagery was collected along a dive transect on the western wall of Mona Rift, a deep and narrow rift northwest of Puerto Rico, between water depths of 1560 m and 3927 m. The northern coast of Puerto Rico and its large offshore area are underlain by a mid-Eocene and younger forearc basin topped by a thick carbonate platform. There are no drill holes offshore, and tying seismic lines across the shoreline there is problematic. We describe our virtual outcrop and constrain its age and stratigraphy using seven rock samples collected by ROV and compare the outcrop’s stratigraphy to deep boreholes and outcrops on land. Our formation descriptions and ages agree, for the most part, with those on land, but we identified a 100-m-thick section that is represented on land by an unconformity. Our stratigraphic interpretation indicates lateral variations in formation thicknesses and establishes a cross-section for additional sampling of the Eocene–Pliocene geology. It also suggests that Mona Rift has formed since the mid-Pliocene. The presence or absence of ferromanganese (Fe-Mn) crust on rocks along the transect may be correlated with the smoothness of the rock surface.

Sequence stratigraphic analysis of the late Permian Changhsingian platform marginal reef, Western Hubei, South China

This study presents a comprehensive analysis of the late Permian platform marginal reefs in the Sichuan Basin, focusing on reefal lithofacies and sequence stratigraphic patterns. Field outcrop observations and rock sample analyses from the Jiantianba reef were conducted to establish an evolution model of sponge reef development and spatial distribution. Four stages of marginal carbonate platform were documented: open platform, gently sloping reef, steeply sloping reef, and reef bank system. Distinct lithofacies were identified in these stages, reflecting different depositional environments and growth rates. The gently sloping reef was composed of filled skeleton framestone, filled skeleton bafflestone, and micrite organism limestone, indicating limited reef-building capacity. In contrast, the lithofacies of steeply sloping reefs were composed of open skeleton framestone, open skeleton bafflestone, binding skeleton bafflestone, and benthic organism bindstone, indicating stronger reef-building ability. Based on depositional features and carbon isotopic trends, the reef strata were divided into two sequences. Sequence 1 corresponds to the formation of unit 1, and sequence 2 can be further divided into units 2 and 3. In unit 1, reefs developed in a relatively deeper-water setting. It was characterized by rich micrite limestone, forming a gentle margin. Unit 2 witnessed reef development in shallower waters. Early marine cementation and microbial clots were prevalent, contributing to form a steep margin. In the early stage of unit 3, reefs primarily developed in a tidal-controlled environment. Subsequently, reef strata experienced a transition to a wave-influenced environment, leading to the formation of a reef bank system. In general, sequence 1 mainly formed in a heterozoan-dominated factory, and reefs contributed to a relatively gently sloping platform margin. In contrast, sequence 2 formed in a photozoan-dominated factory, and reefs contributed to a relatively steeply sloping platform margin.