Rock Types Research Articles

Short-term sedimentary evidence for increasing diatoms in Arctic fjords in a warming world

Arctic fjords are hotspots of marine carbon burial, with diatoms playing an essential role in the biological carbon pump. Under the background of global warming, the proportion of diatoms in total phytoplankton communities has been declining in many high-latitude fjords due to increased turbidity and oligotrophication resulting from glacier melting. However, due to the habitat heterogeneity among Svalbard fjords, diatom responses to glacier melting are also expected to be complex, which will further lead to changes in the biological carbon pumping and carbon sequestration. To address the complexity, three short sediment cores were collected from three contrasting fjords in Svalbard (Krossfjorden, Kongsfjorden, Gronfjorden), recording the history of fjord changes in recent decades during significant glacier melting. The amino acid molecular indicators in cores K4 and KF1 suggested similar organic matter degradation states between these two sites. In contrast to the turbid Kongsfjorden and Gronfjorden, preserved fucoxanthin in Krossfjorden indicated a continuous increase in diatoms since the mid-1980s, corresponding to a 59 % increase in biological carbon pumping, as quantified by the δ13C of sedimentary organic carbon. The increasing biological carbon pumping in Krossfjorden is further attributed to its hard rock types in the glacier basin, compared to Kongsfjorden and Gronfjorden, which are instead covered by soft rocks, as confirmed by a one-dimensional model. Given the distribution of rock types among basins in Svalbard, we extrapolate our findings and propose that approximately one-fifth of Svalbard's fjords, especially those with hard rock basins and persistent marine-terminated glaciers, still have the potential for an increase in diatom fractions and efficient biological carbon pumping. Our findings reveal the complexity of fjord phytoplankton responses and biological carbon pumping to increasing glacier melting, and underscore the necessity of modifying Arctic marine carbon feedback to climate change based on results from fjords underlain by hard rocks.

A new method of rock type identification based on transformer by utilizing acoustic emission.

The characterization and analysis of rock types based on acoustic emission (AE) signals have long been focal points in earth science research. However, traditional analysis methods struggle to handle the influx of big data. While signal processing methods combined with deep learning have found widespread use in various process analyses and state identification, effective feature extraction using progressive fusion technology still faces challenges in the field of intelligent rock type identification. To address this issue, our study proposes a novel framework for rock type identification based on AE and introduces a new signal identification model called 3CTNet. This model integrates convolutional neural networks (CNNs) and Transformer encoder, intelligently identifying AE of different rock fractures by establishing dependencies between adjacent positions within the data and gradually extracting advanced features. Furthermore, we experimentally compare five oversampling methods, ultimately selecting the adaptive synthetic sampling method (ADASYN) to balance the dataset and enhance the model's robustness and generalization ability. Comparison of the internal structure of our model with a series of time series processing models demonstrates the effectiveness of the proposed model structure. Experimental results showcase the high identification accuracy of the intelligent rock type identification model based on 3CTNet, with an overall identification accuracy reaching 98.780%. Our proposed method lays a solid foundation for the efficient and accurate identification of formation rock types in geological exploration and oil and gas development endeavors.

Grey-box solution for predicting thermo-mechanical response of rocks

Evaluating the thermo-mechanical response of rocks under high temperature treatments is crucial for various engineering geology projects. Current predictions of rock thermo-mechanical response rely on simplistic mathematical fittings treating temperature as a reduction factor, while existing machine learning algorithms often present practical challenges due to their black-box solutions. In this study, highly practical grey-box solutions, utilizing gene expression programming (GEP) are proposed for forecasting rock strength following high-temperature treatments. The dataset, comprising temperature, rock type, rock density, sample size, crack damage stress, confining pressure, and elastic modulus, serves as input parameters, with rock strength from triaxial compression tests as the output. Three grey-box solutions (mathematical formulations) based on distinct input parameter sets are proposed, all demonstrating excellent accuracy with high R2-values (R2 > 0.95) and low error values across both the training and testing phases. Feature importance analysis highlights crack damage stress, confining pressure, and elastic modulus as statistically significant parameters influencing the strength of rocks subjected to high temperatures. External validation of the proposed models indicates strong generalization capabilities, underscoring their ability to perform well beyond the training data. Furthermore, a monotonicity study demonstrates that the proposed models align with the expected physical processes. The proposed formulations offer valuable field implications, effectively addressing the limitations of labor-intensive and costly laboratory processes for evaluating rock thermo-mechanical responses.

Mineralogical Characterization and Geochemical Signatures of Supergene Kaolinitic Clay Deposits: Insight of Ropp Complex Kaolins, Northcentral Nigeria

This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM).

A numerical strain-softening solution of a circular opening in nonlinear yield rock masses

Strain-softening behavior occurs when the surrounding rock reaches its peak load, complicating the prediction of stress and displacement. The linear Mohr-Coulomb yield criterion and semi-linear Hoek-Brown yield criterion are widely used in elastoplastic analysis. However, the established criteria struggle to universally describe the nonlinear behavior of various rock types. This study aims to overcome the difficulty and propose the solution of surrounding rock in a circular tunnel following any nonlinear yield criterion and plastic potential function. The derivation of the equivalent cohesive strength and frictional angle for an arbitrary nonlinear yield criterion in the form of σ1=fσ3 using the secant method, along with the determination of the equivalent dilatancy angle for any nonlinear plastic potential functions, was conducted. Concerning the elastoplastic solution of a thick-cylinder, a numerical strain-softening solution for a circular tunnel in nonlinear yield rock masses was derived. Verification of the proposed solution was performed against the established analytical and/or numerical elasto-(brittle-)plastic and strain-softening solutions in rock masses following the Mohr-Coulomb, (generalized) Hoek-Brown, and unified strength criteria. The impact of critical plastic shear strain on displacement, plastic radius, and residual radius was further analyzed. The predictions of displacement and residual region for the Jinping II project also meet the field test results.

Prediction of Rock Unloading Strength Based on PSO-XGBoost Hybrid Models.

Rock excavation is essentially an unloading behavior, and its mechanical properties are significantly different from those under loading conditions. In response to the current deficiencies in the peak strength prediction of rocks under unloading conditions, this study proposes a hybrid learning model for the intelligent prediction of the unloading strength of rocks using simple parameters in rock unloading tests. The XGBoost technique was used to construct a model, and the PSO-XGBoost hybrid model was developed by employing particle swarm optimization (PSO) to refine the XGBoost parameters for better prediction. In order to verify the validity and accuracy of the proposed hybrid model, 134 rock sample sets containing various common rock types in rock excavation were collected from international and Chinese publications for the purpose of modeling, and the rock unloading strength prediction results were compared with those obtained by the Random Forest (RF) model, the Support Vector Machine (SVM) model, the XGBoost (XGBoost) model, and the Grid Search Method-based XGBoost (GS-XGBoost) model. Meanwhile, five statistical indicators, including the coefficient of determination (R2), mean absolute error (MAE), mean absolute percentage error (MAPE), mean square error (MSE), and root mean square error (RMSE), were calculated to check the acceptability of these models from a quantitative perspective. A review of the comparison results revealed that the proposed PSO-XGBoost hybrid model provides a better performance than the others in predicting rock unloading strength. Finally, the importance of the effect of each input feature on the generalization performance of the hybrid model was assessed. The insights garnered from this research offer a substantial reference for tunnel excavation design and other representative projects.

APPLICATION OF PRIMARY AND SECONDARY RESISTIVITY PARAMETERS IN EVALUATING AQUIFER POTENTIAL AND VULNERABILITY WITHIN KABBA, NORTH CENTRAL NIGERIA

The study area depends on groundwater as a major source of potable and healthy water supply. However, its occurrence and quality vary with low yield or abortive borehole drilled in some part. Therefore, there is need to properly investigate the geology and groundwater condition of the area using Vertical Electrical Sounding (VES) and Dar Zarrouk parameters. The different rock types identified are migmatite-gneiss, granite-gneiss, schist, and charnockite. Forty (40) VES was carried out which revealed five to four geo-electric layers. These are top soil, lateritic clay, confining weathered basement, weathered/fractured basement aquifers and fresh basement. The types of curves identified are HA and KQ. The average depth to groundwater is 55.00m, this indicate that borehole should be drilled within or above the average depth to avoid later drying of wells. The value of aquifer resistivity and thickness was used to calculate longitudinal conductance, transverse resistance, hydraulic conductivity and transmissivity. The longitudinal conductance varies from poor to good in protective capacity class and revealed that the groundwater is easily exposed to contamination. The aquifer resistivity, thickness with transverse resistance, hydraulic conductivity, and transmissivity were used to classified the groundwater into different zones. The groundwater potential within the study area varies from low to very good with most of the area having moderate potential zones distributed mainly within the migmatite gneiss and the schist. The study area has fractures that can produce water for domestic, agricultural and industrial purpose and the result can be used for proper management of groundwater resources.

Potential Carbon Content and Inorganic Carbon Sequestration in the Karst Area of Silokek Geopark, Sijunjung Regency

Climate change caused by increasing greenhouse gas emissions, especially CO2, and deforestation, is an urgent global issue. The REDD+ program initiated by the UN aims to reduce carbon emissions and increase carbon storage in forests. One of the forests that can reserve carbon is the karst area with the ability to reserve carbon dioxide (CO2). This study aims to determine the potential carbon content and carbon dioxide (CO2) sequestration. This study was conducted using the chip sampling method and the XRF (X-ray Fluorescence) method analysis. Based on the research results, it is known that the Silokek Geopark karst area has three different limestone rock characteristics, and sample 3 is the type of rock with the highest CaO percentage. The potential inorganic carbon content is 4,908.07 tons/ha and carbon absorption is 18,012.60 tons/ha, categorized as high. The inorganic carbon content in the Silokek Geopark area is lower than the Biduk-biduk Karst area which is influenced by the area volume area and type of rock composition.

Numerical and experimental studies on the motion and deposition of collapsing rock clusters: Effect of rock particle sphericity

In this paper, a series of experimental and numerical tests are carried out to study the effect of rock particle sphericity on the motion and deposition of collapsing rock clusters. To this end, three kinds of typical rock particles with different sphericity (i.e., pebble, rubble and block) are used for experiments and a special laboratory setup that involves a chute with two inclined sections is designed to reproduce their natural motion. Then, a three-dimensional modelling of collapsing rock cluster incorporating rock particles with different sphericity is developed using spherical harmonics function reconstruction. The sphericity of particle effect on the motion and deposition of rock cluster is studied experimentally and numerically in terms of the average velocity and deposition zone. There has a good agreement between them. In addition, some potential factors such as rock particle size, cluster mass and component are investigated and discussed. The obtained results may facilitate the current knowledge on the dynamic behavior of collapsing rock clusters effect of particle sphericity.

Experimental study on dynamic response of hard rock blasting under in-situ stress

Deep mine rock mass is in high static stress and dynamic disturbance coupling conditions, its mechanical properties and failure mode is different from the shallow rock mass, which leads to low rock blasting efficiency and engineering geology hazards. In-depth research on the dynamic response of rock blasting under in-situ stress will help to optimize the blasting design, improve the blasting efficiency and safety of blasting operations, and provide theoretical support for rock blasting in deep mines. In this study, the blasting experiment was conducted on granite specimens under different biaxial static stress conditions. Meanwhile, the dynamic response of rock blasting was monitored, collected, and analyzed using a high-speed digital image correlation (DIC) measurement system, a strain wave acquisition system, and an acoustic emission (AE) system. The results show that small and medium pre-static loads inhibit blast crack propagation, at which time the cumulative AE hits from dynamic loads (CAECd) are more than those from pre-static loads (CAECs), but large pre-static loads promote crack propagation, at which time CAECs are more than CAECd. Secondly, as pre-static load increases, the specimen's maximum strain (εmax) decreases first and then increases, but as lateral pressure coefficient (K) increases, the εmax in the direction of lower static stress decreases gradually and the εmax in the direction of higher static stress remains constant. In addition, the confining pressure magnitude and K affect the area and shape of the failure zone of the specimen, as well as the size and propagation direction of the radial crack. Especially when the confining pressure is high, the specimen will undergo shear failure, and the smaller K is the more serious the shear failure. Finally, the failure criterion of rock under dynamic-static coupling conditions is proposed based on the energy index, and different failure types of rock are discussed.

Linking petrophysical heterogeneity and reservoir rock-typing of the post-rift shallow marine siliciclastics to their depositional setting: The Upper Cretaceous Bahariya reservoirs, north Western Desert, Egypt

The upper Cretaceous clastic facies of the Bahariya Formation host the main reservoir intervals in the north Western Desert (NWD) of Egypt. These clastics were deposited in a parallic depositional environment characterized by different scales of reservoir heterogeneities. However, the link between these heterogeneities and the depositional setting of the reservoir facies is still blurred. In this study, we investigate a highly-heterogeneous reservoir facies of Bahariya Formation in Yasser Field wells, NWD in order to construct a predictive framework for the distribution of the best reservoir rock types (RRTs) and flow zones. Seismic stratigraphy was integrated with core sedimentology to understand the depositional architecture of the reservoir facies. Moreover, conventional core analysis and wireline logs were interpreted to evaluate the scales of lithological and petrophysical heterogeneities in the different RRTs.In the studied Yasser Field, the Bahariya Formation consists of tidal facies deposited in a wide range of tidally-influenced conditions. The seismic facies varies greatly with variation in the tidal regime. Best reservoir rock types RRTs are associated with tidal channels and amalgamated tidal bars (RRTI). RRTI rocks represent the main fluid flow conduits in the studied Bahariya reservoir. Lithological and petrophysical heterogeneities are more prominent in the tidal mud flat and mixed tidal flat facies which form RRTIII rocks. Linking seismic with sedimentary facies enabled us to predict the distribution of the best reservoir flow zones in the study region. The present results establish a framework for predicting the optimum reservoir quality facies based on integrating seismic, sedimentary and petrofacies. This framework could be applied in analogous tidally-influenced reservoir facies with high depositionally-controlled pore system heterogeneity.

Application of magnetic data and satellite spectral imaging in identifying gold mineralization zones and its associated subsurface structures at Fawakheir-Attala area, Central Eastern Desert, Egypt

The Fawakheir-Attala gold mining zone in Egypt’s Central Eastern Desert features a diverse range of rock formations, including Precambrian crystalline rocks and Phanerozoic sedimentary formations. These formations encompass gneisses, metavolcanics, metasediments, a metagabbro-diorite complex, Dokhan volcanic rocks, and granitic rocks, alongside lower and upper Nubia sandstones. Faults and shear zones are pivotal in controlling gold mineralization within the area, indicative of substantial mineral wealth. This study aimed to map subsurface structural characteristics and investigate gold mineralization zones using aerial magnetic data and ASTER remote sensing, the latter of which played a crucial role in highlighting the surface exposure of alteration zones. Geological surveys combined with remote sensing techniques were employed to identify rock types and mineralization zones, while magnetic methods, including aeromagnetic surveys and ground-based studies, were used to reveal underlying structural properties and fault systems. Analysis of aeromagnetic data revealed a large mineralization zone running from the Fawakhir Gold mine through the Attala Gold mine in a NW–SE direction. Various structural trends and faults, including NW–SE, NE–SW, E–W, and N–S directions, were identified, strongly associated with hydrothermal alteration zones and gold mineralization. Shallow basement relief was observed in the eastern and central regions, contrasting with deeper formations and greater relief in the western section. Land magnetic surveys were utilized to identify new areas for gold mineralization, with geochemical analysis confirming gold content in quartz veins and host rocks. The integration of magnetic and remote sensing techniques effectively highlighted alteration zones indicative of potential mineralization, which could have a subsurface continuation, aiding in the identification of gold occurrences connected to faults, lineaments, and mineralization zones.

Uniaxial compressive strength prediction based on measurement while drilling data: A laboratory study

The uniaxial compressive strength is one of the most important basic parameters of rock, which is essential for surrounding rock stability analysis and support scheme design of underground engineering. At present, it is time consuming and costly to take a large amount of core samples for laboratory testing, and the mechanical properties of the cores may be affected by mining disturbance, which can easily lead to inaccurate result. The measurement while drilling (MWD) technology provides a new approach to solve the above challenge. The key to implementing this technology is to establish a correlation model between drilling parameters and rock mechanics parameters. Based on the characteristics of polycrystalline diamond compact (PDC) bits in drilling and rock breakage, this paper analyzes the mechanical state of the bit in breaking rock. A theoretical correlation model between the torque, feed force of the bit and the uniaxial compressive strength of the rock has been developed. To verify the accuracy of the theoretical model, the uniaxial compressive strength of five different types of rocks (red sandstone, green sandstone, limestone, marble and shale) was obtained through laboratory mechanical tests. The torque Mb, feed force Fb and other parameters in the drilling process of these five rocks were tested through the newly developed MWD test system. The correlation between the drilling parameters and the uniaxial compressive strength of rock was established. The results showed that the feed force Fb and torque Mb measured at five different types of rocks indicate a linear increasing trend with an increase in depth of cut h. Meanwhile, a strong linear relationship between the feed force Fb and torque Mb is evident. This paper proposes an MWD-based method to rapidly conduct the in-situ measurement of the uniaxial compressive strength of various rocks.

Geochemical anomaly separation based on geology, geostatistics, compositional data and local singularity analyses: A case study from the kuh panj copper deposit, Iran

This study combines geochemical anomaly separation with geostatistical approaches and compositional data analysis. To have a reasonable model for abnormal areas, suggesting the optimal drilling coordinates, one needs to consider some effective geological controllers on the mineralization such as lithology, alteration, and tectonic processes. The lithogeochemical samples at 608 locations were processed from the copper porphyry mineralization area of Kuh Panj, Iran, to illustrate the proposed approach. The heterogeneity of rock type domains was detected using contact analysis. Based on this, plurigaussian simulation made it possible to model the uneconomic dykes of the area. Copper-molybdenum grades and filler as geochemical components were transformed into multivariate normal data using isometric logarithmic ratio-flow anamorphosis. Hierarchical rock type-grade simulation reproduced the grade behavior at hard rock type boundaries. Selection of a dense and regular simulation grid minimized the smoothing effect caused by interpolation of the singularity index values. Finally, unsupervised machine learning identified the anomaly zone by clustering the results of the singularity analysis. Validation using drilling data and the geological map shows that the anomaly separation, considering the geological conditions and the compositional nature of the geochemical data, can provide a reliable model of the geochemical anomalies in the Kuh Panj deposit.

Germanium and its isotopes as indicators of hydrogeochemical conditions in a terrestrial geothermal system (Karkonosze granitoid, Sudetes, Poland)

The germanium content and its isotope ratio in thermal waters, aquifer rocks and main silicate minerals in a terrestrial groundwater system located in a granitic pluton (Karkonosze granitoid, Sudetes, Poland) have been investigated. This is the first extensive Ge isotope study carried out in both groundwater and aquifer rocks to better understand previously the identified enrichment of groundwater relative to rocks. This research also provides the first data on δ74/70Ge for hybrid acid rocks formed by mixing magmas from two different sources (mantle- and crustal-derived) and main silicate minerals. The Ge isotopic composition in different facies of granite (porphyritic, equigranular) is comparable (δ74/70Ge of 0.43–1.23‰) to its hybrid rocks (quartz diorite–granodiorite, microgranular magmatic enclaves, composite dykes) – 0.79–1.27‰. However, the range of variability of this feature is quite wide. The minerals have δ74/70Ge values of 1.01–1.04‰ in quartz, 0.84–0.90‰ in alkali feldspars, 0.76–0.88‰ in plagioclase, and 0.36–0.39‰ in biotite. The thermal waters are enriched in heavy Ge isotopes (δ74/70Ge of 1.21–2.78‰) relative to the aquifer rocks (δ74/70Ge of 0.43–1.27‰). Currently, the most likely explanation for this is the influence of secondary mineral phases formed in the geothermal granitic system. This comprises the preferential incorporation and adsorption of light Ge isotopes in/onto iron oxide/hydroxides and clay minerals. The other theoretical explanation, i.e., sulfide formation, is unlikely due to the unfavourable hydrogeochemical conditions in the studied system. The δ74/70Ge values of thermal waters are similar to those of previously studied continental geothermal waters (1.65–3.29‰; Siebert et al., 2011) and fresh groundwater (2.24–4.02‰; Baronas et al., 2020), confirming that groundwater enrichment in heavy Ge isotopes relative to aquifer rocks may be widespread in the upper continental crust. Variation in the isotopic composition of the studied thermal waters is a result of the aquifer rock mineralogy and, in some cases, mixing of the old deep-circulating thermal water with the shallow modern cold groundwater. The general similarities in the chemical composition of the studied waters are due to the influence of porphyritic granite, which is the dominant rock type in this aquifer system. Some differences in chemical composition, including differences in the Ge isotopic composition, are related to the local distribution of hybrid rocks and sulfides. The δ74/70Ge and Ge/Si ratios have been shown to be sensitive indicators of local hydrogeochemical conditions in an alimentation zone and a near-borehole zone of particular water intakes.

Piecewise Linear Strength Models for Analyzing Multiple Failure Mechanisms in Rocks Materials.

Rock materials failures are accompanied by the co-existence of various failure mechanisms, including rock fracturing, shearing, and compaction yield. These mechanisms manifest macroscopically as multiple failure modes and nonlinear strength characteristics related to stress levels. Considering the limitations of current rock mechanics strength theories, which are primarily derived from single failure mechanisms, this study evaluates the applicability of alternative strength theories. Based on the extensional-strain criterion and the PMC (Paul-Mohr-Coulomb) model, a piecewise linear strength model was proposed that is suitable for analyzing multiple failure mechanisms in rocks, revealing the intrinsic mechanisms of multi-mechanism rock material failure. A multiple failure mechanism strength model in the form of inequalities was proposed, using the generalized shear stress, mean stress, and stress Lode angle as parameters. Strength tests conducted on sandstone and granite rock material samples under different stress conditions revealed distinct piecewise linear strength characteristics for both rock types, validating the rationality and applicability of the multiple failure mechanism model. The findings construct a multi-mechanism failure model for rocks, providing enhanced predictive capabilities and aiding in the prevention of rock structural failures.

Development of fluid pathways and associated diagenetic variations in a natural CO2 leaking fault zone.

Abstract Permeability within fault zones can vary through time due to repeated deformation events and rock–fluid interactions. Understanding the history of fault zone alteration is critical when building hydrogeologic models and evaluating the risk of mechanical rock failure during subsurface storage. Newly acquired drill core recovered within the fault damage zone and fault core of the Little Grand Wash fault (LGWF) is combined with observations from outcrop, optical petrography, computerized tomography image analysis, and ultrasonic velocity measurements to characterize the rock types and preserved structural deformation features within this fault zone. These data are used to understand the history of mechanical rock failure and mineralization associated with this fluid-charged fault system. We identify multiple structural features and use their cross-cutting relationships to understand the history of deformation and their association with changes in fault zone permeability and rock mechanical properties. At the LGWF zone, structural deformation features vary temporally and are used to recognize a decoupling between fault slip and fluid flow. The formation of most open-mode veins occurred after shear failure within the LGWF zone. Early-developed shear bands are cut by carbonate veins, that are in turn cut by shear fractures, followed by a second phase of vein formation and ultimately by folding in the fault core. This sequence of formation reflects changes in mechanical rock properties due to subsurface rock–fluid interactions and indicates that the alteration of rock matrix by secondary carbonate cement results in increased unconfined compressive strength, decreased permeability, and increased ultrasonic velocity. In this fault zone, and possibly other fault zones, the changes in rock properties associated with deformation can be detected through their geophysical response.

Experimental study on evaluating fracture processes of different rocks using multiple physical parameters

To improve the accuracy of rock fracture evaluation, three types of rocks with different lithologies, namely, granite, coal, and sandstone, were processed into cuboid samples with unilateral notches for three-point bending tests. Real-time data were obtained via load, resistance, and acoustic emission (AE) monitoring. Various fracture patterns of the fractured rocks were collected, and the correlations between multiple physical parameters were determined. The results indicated that granite had the highest fracture toughness and initial fracture energy required for macroscopic fracturing, followed by sandstone, which had the lowest fracture toughness and initial fracture energy. The primary crack participated in the fracture process of coal and produced the most complex crack morphology, exhibiting the characteristics of “Progressive fracture” different from the “Instantaneous fracture” of granite and sandstone. The crack length reached 90.5 mm, which was much longer than that of sandstone. The temporal characteristics obtained from multiple physical quantities were synchronized with the fracture behavior. The resistivity increased gradually with the fracture, and the resistivity fluctuation caused by crack propagation increased. The resistivity change rate of granite was the highest when macrofractures occurred, whereas that of coal after complete fracture was the highest. Rock fracture produced a large number of AE events with small amplitude and low peak frequency, concentrated in the 100 ± 50 kHz band. The AE count corresponded to the crack propagation process, and the AE location indicated the crack complexity. The peak change rate of the resistivity was used to evaluate the fracture performance and exhibited a significant linear relationship with the peak load, fracture toughness, and initial fracture energy. The relationship between the accumulated AE energy and the fracture length was a quadratic function, which was used to evaluate the fracture complexity. The multiple physical quantity monitoring method is promising for predicting the fracture behavior of rocks.

Petrophysical and petrographic data correlation and the discrimination of magmatic environments and processes in Santos Basin, offshore SE Brazil

The igneous rocks in the context of oil & gas exploratory sedimentary basins have been a paradigm and challenge for industry and academia due to the difficulty of reconnaissance and interpretation using indirect methods, e.g. geophysical data. We presented the combination of the petrographic and well log data of distinct magmatic sections from wells of Santos Basin, SE Brazil. Effusive and explosive felsic rocks, mafic volcanic subaerial and subaqueous and plutonic mafic rocks were recognized by petrography and petrophysics proprieties data, as radioactive (GR), electric resistivity (R), acoustic property (Δt), porosity (Φ) and density (ρ), showed different patterns along sections. This enables the division on magmatic subsections and allowed the recognition of rock types and igneous setting. The compositional influences are clearly distinguished by GR, as felsic and mafic rocks, presence of amygdales in mafic effusive rocks and inter-pillow intervals in subaqueous environments, can interfere with GR patterns. In plutonic environment, GR can show evidence of magmatic differentiation. Δt and Φ are directly proportional with similar pattern and both are inversely proportional to R and ρ. Felsic rocks, effusive or explosive, and inter-pillow intervals makes Φ and ρ curves closer. Less dense and more porous rocks, as explosive, tend to imprint the Φ and ρ pattern to the left of the log. Welding processes are distinguished by gradual decrease of Φ and increase of ρ. Otherwise, denser mafic rocks, volcanic or plutonic, tend to show separate Φ and ρ curves on the right of the log, while amygdaloidal portions are lighter and more porous than the massive one, showing the separate pattern on the left. The subaqueous mafic volcanic rocks imprint GR, ρ and Φ intermediate patterns between mafic massive and amygdaloidal. The recognition of the type of magmatic rock, the environment and the physical properties can aid to improve not only the decisions of exploration and production but also the elaboration of a geodynamic context for offshore sedimentary basins.

Grain textural bias in detrital single-mineral provenance studies

Detrital single-mineral geochemistry and geochronology are strong tools in provenance studies and indicate great potentials in addressing issues in earth sciences. Various biases (both natural and artificial) exist objectively and may mislead provenance interpretations. Both the sedimentary sorting process and hand-picking in-laboratory processing may lead to analyzed grain textural (e.g., size and shape) variability and thus may introduce biases in single-mineral provenance analysis. Here, we take the Mesozoic–Cenozoic Qaidam basin, northeastern Tibet, as an example to investigate the relationship between single-mineral grain texture and detrital zircon geochronological and detrital tourmaline, rutile and garnet geochemical data and to explain how grain texture affects detrital single-mineral provenance interpretations. Results indicate that Precambrian zircons take less proportions in coarse (>125 μm), subrounded and high aspect ratio (>2) fractions than Phanerozoic zircons. Parent rock lithology discrimination results of detrital tourmaline and garnet in different grain size fractions show significant differences. Zr-temperature values of detrital rutile have an increasing trend with increasing grain size. The geochemistry of detrital tourmaline, rutile and garnet shows no dependence with grain aspect ratio and roundness. We suggest that inheritance of grain texture features from parent rocks is the major reason. Detrital zircons from recycled (meta)sedimentary rocks tend to be smaller and more rounded than those from igneous rocks. Detrital tourmaline, rutile and garnet grains from different parent rock types vary in size. Grain textural bias may cause the underestimated contributions of the Qilian Shan to the Cenozoic Qaidam basin if small detrital zircons were not involved in the analysis. Quantitative description of the source-to-sink system of the Cenozoic Qaidam is also influenced by grain textural bias. This study highlights the underestimated grain textural bias in single-mineral provenance studies. We suggest that a comprehensive understanding of potential sedimentary sources, depositional processes, sample petrographic features and laboratory analysis procedures is important to reliable provenance interpretations and to related implications in earth sciences.