Quartz Grains Research Articles

Microtextures on Quartz Grain Surfaces in the Beach Sediments of Southern Hodeidah, Red Sea Coast, Yemen

Surface features of quartz grains on the Al-Haymah and Moushij beaches of the coastal area in the southern Red Sea of Yemen were analyzed by a scanning electron microscope (SEM) to deduce the provenance and depositional environment of sediments. The microtextures on quartz grains were classified into mechanical, chemical, and mechanical/chemical origins. The quartz grains from the two beach areas were rounded to subrounded in shape. Rounded quartz grains with a combination of bulbous and broken edges indicated a recycled provenance. Mechanical features such as V-shaped marks and straight and curved scratches revealed the combination of fluvial and high-energy subaqueous beach environments, whereas aeolian grains are mainly marked by crescentic percussion marks, elongated depressions, and upturned plates. Chemical features such as solution pits, silica globules, trapped diatoms, and adhering particles in quartz grains indicated a diagenetic environment and silica re-precipitation in a coastal environment. In general, the microtextures identified on quartz grains reveal that sediments are influenced by wind, fluvial, and subaqueous marine environments and are derived from nearby and distal sources.

Petrography of Sandston Units in Gercus Formation, Shaqlawa and Dokan areas Northern Iraq

The present study deals with the petrographic investigations revealed that the sandstone of Gercus Formation the studied samples of sandstone units composed primarily of rock fragments (sedimentary, igneous and metamorphic), quartz grains (monocrystalline and polycrystalline), and feldspars (orthoclase, microcline and plagioclase). These components are cemented by carbonate and iron oxides. The studied sandstones are classified as litharenites, Sandstone rocks of Gercus Formation are chemically and mechanically unstable due to the high percentage of rock fragments ,such a grain assemblage infers that the source of the rock fragments is nearby. The petrographic analyses indicate that the studied sandstones are immature mineralogically because of high content of unstable components, such as lithic fragments and feldspars. the tectonic provenance for Gercus formation can be described as lithic recycled.

OSL and radiocarbon dating and evidence of palaeo-wildfires in Quaternary deposits of the Tacutu basin, northwestern Brazil

This work presents data on charcoal fragments found in Cenozoic deposits of the Boa Vista Formation and the first absolute dating for this unit. The methodology consisted of the definition of sedimentary facies, as well as the establishment of depositional age using optically stimulated luminescence (OSL) in quartz grains. Analysis was carried on charcoal samples with the help of Scanning Electron Microscopy (SEM), AMS 14C dating, and organic petrography. The facies analysis identified four distinct facies: lateritic massive gravel facies (Gcm1), ferruginous massive gravel facies (Gcm2), massive sand facies (Sm) and fossiliferous massive sand (Smf). The ages of the deposits ranged between 105,2 and 3,2 thousand years before present, indicating that this unit is positioned in the Upper Pleistocene-Upper Holocene transition. The anatomical structures observed in SEM are well preserved and the studied charcoal samples have angiospermic affinity. Two episodes of fires were identified with range ages between 5663 and 3377 cal years BP, with burning temperature varying from 340 °C to 400 °C.

Porosity distribution in the Devonian Antrim Shale: Controlling factors and implications for gas sorption

Unconventional reservoirs, such as oil and gas shales, are characterized by diverse and heterogeneous pore systems, and their detailed knowledge is critical for understanding fluid storage and transport mechanisms. The Devonian Antrim Shale in the Michigan Basin is an unconventional, primarily biogenic gas accumulation with a technical recoverable resource of 19.9 Tcf. While its general formation properties are known, the details of porosity distribution and pore morphology are lacking. This study provides a comprehensive description of the total porosity, pore size distribution, pore morphology and mineral associations for various members of the Antrim Shale sampled at three locations across the basin, and then investigates the factors controlling porosity distribution and the implications for gas sorption. Results indicate that the black-shale members, the Lachine and Norwood, are characterized by a lower porosity (0.1–2%) compared to the organic-lean members, the Paxton and Upper Antrim (2–7% porosity). Total porosity tends to decrease with the increase in organic content in the Antrim Shale as organic matter, in particular solid bitumen, occludes available pore space between mineral grains in the organic-rich black shale members. Organic matter displays little to no porosity of its own at the SEM resolution, but gas adsorption measurements indicate the presence of micropores (<2 nm), whose amount correlates positively to the total organic content. The Norwood member (TOC values up to 25%) is characterized by the largest share of micropores (up to 37% of the total porosity volume), while the organic-lean Paxton Member (TOC < 6%) has the least amount of microporosity (1–6%). Only the Lachine Member and select Upper Member samples showed larger organic matter pores, visible in the SEM images (∼50–100 nm). Mesopores (2–50 nm) are the dominant pore size group in the Antrim Shale, forming 45% to 76% of the pore space, and most of the pores are interparticle and intraparticle pores in and around clays, quartz, feldspar and pyrite grains. No single mineral component influences the total porosity distribution, but clay content exhibits a weak positive correlation to the meso-macro porosity. As microporosity is known to contribute the most to gas adsorption capacity of unconventional reservoirs, TOC appears to be most important factor controlling both CH4 and CO2 storage potential of the Antrim Shale. The Norwood Member, characterized by the highest TOC and microporosity volume as well as surface area of the micropores, is predicted to have the highest gas adsorption capacity but direct sorption measurements will be needed to confirm that. This study highlights some important differences with previous observations about porosity relationship to organic and mineral components of shale reservoirs, and expands the understanding of shale pore systems in the low-maturity range of organic-rich shales.

Correction: Bernardi et al. OH-Defects in Detrital Quartz Grains from the Julian Basin (NE Italy and Slovenia): A Fourier Transform Infrared Study. Geosciences 2022, 12, 90

The authors would like to correct the published article [...]

Mineralogical characteristics and genesis mechanism of glauconite in the meso-neoproterozoic and cambrian strata in north China

Glauconite is a special mineral indicator of sedimentary facies and is widely developed in the Meso-Neoproterozoic and Cambrian strata in North China. A systematic study on the occurrence characteristics and genetic mechanism of glauconite is of great geological significance for the reconstruction of paleogeographic environments in North China. The results show that glauconites are well-developed in the Meso-Neoproterozoic Tieling, Xiamaling, Changlongshan, and Jingeryu formations and the Cambrian Xuzhuang Formation, with granular, cemented, fecal pellet, and halo - rimmed forms. The oxide components of glauconite mainly include K2O, Si2O, Al2O3, TFeO, MgO, etc. Moreover, the study area mainly developed low mature to mature glauconite based on the analysis of K2O content, color, SEM energy spectrum and XRD, and the maturity of glauconite in the Longshan and Jiguanshan areas is lower than that in the Jizhou area. The K, Fe, Mg, and Al ions source of glauconite is sufficient, and the parent rocks also provide sufficient substrate favorable for the formation of glauconite in the study area. Glauconites with different substrate components indicate different formation mechanisms. The glauconite with quartz and feldspar grains as the substrate is of a pseudomorphic replacement genesis, while the glauconite with biotite as the substrate is of a layer lattice theory genesis, and cemented glauconite is of an authigenic precipitation genesis. Furthermore, the study revealed that glauconites with fecal pellets and stromatolites as substrate are a combination of biogenesis and verdissement or authigenic precipitation, and halo - rimmed glauconite is of a combination of pseudomorphic replacement and authigenic precipitation. According to the findings, the evolution of K2O-TFeO in Precambrian glauconite is not only controlled by a specific substrate, but also by specific chemical conditions. Because of the differences in composition of solubility of the substrate, the pH conditions of the pore water required for glauconization are different. The sedimentary environment and substrate type affect the form and genetic mechanism of glauconite, but the varied pH conditions suitable for the substrate and the sub-oxide environment near the Fe oxidation-reduction interface are the necessary conditions for glauconization. As a result, glauconite can be used as a signature mineral for the palaeo-redox facies. The study provides insights into the formation mechanism of different glauconite in the process of sedimentation or diagenesis, and the scientific basis for the restoration of diagenesis conditions and the paleogeographic environment in North China.

Water release and homogenization by dynamic recrystallization of quartz

Abstract. To evaluate changes in water distribution generated by dynamic recrystallization of quartz, we performed infrared (IR) spectroscopy mapping of quartz in deformed granite from the Wariyama uplift zone in NE Japan. We analyzed three granite samples with different degrees of deformation: almost undeformed, weakly deformed, and strongly deformed. Dynamically recrystallized quartz grains with a grain size of ∼10 µm are found in these three samples, but the percentages of recrystallized grains and the recrystallization processes are different. Quartz in the almost-undeformed sample shows wavy grain boundaries, with a few bulged quartz grains. In the weakly deformed sample, bulging of quartz, which consumed adjacent host quartz grains, forms regions of a few hundred micrometers. In the strongly deformed sample, almost all quartz grains are recrystallized by subgrain rotation. IR spectra of quartz in the three samples commonly show a broad water band owing to H2O fluid at 2800–3750 cm−1, with no structural OH bands. Water contents in host quartz grains in the almost-undeformed sample are in the range of 40–1750 wt ppm, with a mean of 500±280 wt ppm H2O. On the other hand, water contents in regions of recrystallized grains, regardless of the recrystallization processes involved, are in the range of 100–510 wt ppm, with a mean of 220±70 wt ppm; these values are low and homogeneous compared with the contents in host quartz grains. These low water contents in recrystallized regions also contrast with those of up to 1540 wt ppm in adjacent host grains in the weakly deformed sample. Water contents in regions of subgrains are intermediate between those in host and recrystallized grains. These results for water distribution in quartz imply that water was released by dynamic recrystallization.

Luminescence dating of anthropogenic deposits from Tall Zarʿa in the Jordan Valley

AbstractThis study uses quartz‐based optically stimulated luminescence dating to determine when a massive fortification wall (W11186) was constructed in the archaeological site of Tall Zarʿa in the Jordan Valley. A total of 11 samples of sediments were taken from a trench on the north side of the wall (extramuros). The extracted quartz grains had good luminescence characteristics and were identified as well bleached by comparison with feldspar infrared‐stimulated luminescence (IRSL) ages. The optical ages showed that the deposition against the wall occurred in two different periods. The first was around 3.20 ± 0.07 ka ago (Iron Age), and the second was around 2.28 ± 0.08 ka (Hellenistic period). Human activity was evident because of the intermixing of cultural material with the presumed naturally deposited units.

Micro- and Macro-scale Mechanical Properties of Meta-cherts as Concrete Aggregates

This paper presents the measurement of the tensile strength, Young’s modulus, and linear coefficient of thermal expansion in a meta-chert. Two areas are targeted in this aggregate - a white area where quartz grains are densely compacted and a gray area where the quartz grains are coarser. The macro- and micro-scale data are compared. Young’s modulus is not significantly different between macro-scale compression and micro-scale tension loading in the white region. Macro-scale splitting and micro-scale direct tensile strengths exhibit similar bimodal behavior due to the failure mechanisms of these two distinct areas. The macro- and micro-scale coefficients of thermal expansion are similar for the gray region, reflecting the quartz nature. Conversely, the micro-scale coefficient of thermal expansion of the white area shows a different behavior.

Impact of magmatic intrusion on diagenesis of shallow marine sandstones: An example from Qasim Formation, Northwest Saudi Arabia

Igneous intrusions are common in sedimentary basins, and their occurrence can significantly affect the diagenesis and reservoir quality evolution of sandstones, thereby strongly impacting their hydrocarbons-, geothermal-, and CO2-storage potentials. The Qasim sandstones in the Tabuk region (NW Saudi Arabia) experienced shallow burial diagenesis (&amp;lt;2 km) when the Tertiary magma intruded to form basaltic sills (0.4–4 m thick). The sedimentology, tectono-stratigraphic framework, provenance, and chemostratigraphy of the Qasim Formation have been extensively covered in the literature. However, the impact of the magmatic intrusion on diagenesis and reservoir quality evolution of the sandstones remains enigmatic. This study employed thin-section petrography, QEMSCAN, XRD, SEM, and energy-dispersive spectrometer analyses to investigate the role of magmatic intrusion on diagenesis and reservoir quality of the Qasim sandstones. The results of the study indicate that reservoir porosity is principally influenced by primary depositional characteristics (grain size and sorting), diagenetic alterations, and magmatic intrusions. Sandstones with coarser grain size and better sorting have the best intergranular porosity and vice versa. The “normal” diagenetic processes that have significantly affected the reservoir porosity of the sandstones occurred during both shallow burial (eodiagenesis) and uplift (telodiagenesis). The eogenetic alterations include mechanical compaction, early diagenetic cementation by calcite, pyrite, and kaolinite, whereas the telogenetic alterations include the formation of kaolinite, goethite, hematite. Overall, mechanical compaction is the main driver for porosity loss in the sandstones. The intrusion-related diagenetic processes include the dissolution of quartz grains, rounded quartz overgrowths, and calcite cement, and the transformation of kaolinite into dickite and chlorite. Detrital quartz and rounded quartz overgrowths have undergone dissolution due to acidic pore fluids from magma and high temperature. The transformation of kaolinite into dickite occurred in a dissolution-recrystallization fashion, and the amounts of kaolinite and dickite increase in fine-grained sediments away from sill contact due to hydrodynamic processes that deposited muscovite (which form kaolinite) in low energy environments. The chloritization of kaolinite was localized, and the magma-induced dissolution of goethite likely supplied the requisite high Fe content. Additionally, the intrusion has resulted in the dissolution of the early calcite and increase in porosity towards the sill contact. However, values for compactional porosity loss have relatively remained similar both at and away from the sill contact, as the sill is too thin to exert significant vertical loading. This study has relevance to understanding hydrocarbon exploration and exploitation in sediment-lava sequences, and to understanding the development of sediment-lava systems.

Characterisation of carbonate lake sediments as a potential filler for polymer composites

Abstract The purpose of the study was to determine whether lake sediments could be a potential raw material for the plastics industry. The examined samples were obtained in a complex process of sediment collection from Lake Swarzędzkie located in the region of Wielkopolska, Poland, followed by granulometric analysis by sieving and quartz grain shape analysis, with preparation of geotechnical sheets. The works involved the examination of physico-chemical characteristics of carbonate lake sediments and the analysis of impact of the sediments’ depth extraction on their chemical composition and physico-chemical properties. The lake sediment consists mainly of calcium carbonate (CaCO3) and can be a potential filler for plastics. Tests were carried out to determine chemical composition of the sediments and their thermal stability. The thermogravimetric analysis showed the three stages of the thermal decomposition. Sediments in deeper layers of the lake are characterised by the presence of not only CaCO3 and silica, but also other chemical compounds, including aluminosilicates. In addition, as the depth increases, the average size of sediment particles changes, with the main fraction particle size being the smallest for the material from the 6–12 m depth. Additionally, carbon content systematically decreases with increasing depth.

Microcracking behavior and damage mechanism of granite subjected to high temperature based on CT-GBM numerical simulation

Studying the high-temperature impact on microcracking behavior of granite is of great significance to geothermal energy extraction and deep engineering disaster prevention. Therefore, a thermo-mechanical coupled numerical model of granite is established based on computed tomography and grain-based model (CT-GBM) to investigate the impact of high temperature upon microcracking behavior of granite, and to further discuss the thermal damage mechanism. The results show that the thermal damage of granite mainly develops in the form of tensile failure. The development of intra grain cracks can be roughly divided into three periods featuring quiet (room temperature ∼ 300℃), stable development (300℃∼450℃) and unstable development (450℃∼600℃). The development of grain boundary cracks first appeared at the feldspar-quartz grain boundary, but the feldspar-feldspar grain boundary cracks prevail at high temperature (above 332℃) due to the large proportion of feldspar in granite. The phenomenon of stress concentration in granite under high temperature becomes growingly obvious with the increase of temperature, and such phenomenon is more obvious in grain boundaries than in mineral grains, which is the reason of microcracking and prevail of grain boundary cracks. In addition, the thermal damage degree of mineral grains and grain boundaries is described quantitatively through the self-defined crack coefficient. It is discovered that under the joint influence of thermal expansion characteristics and mechanical properties of minerals, the damage of grain boundaries between different minerals is more serious than that in identical minerals, and the damage of quartz grain is more serious than that of feldspar and mica.

Spatial variability of petrofacies using supervised machine learning and geostatistical modeling: Sycamore Formation, Sho-Vel-Tum Field, Oklahoma, USA

The Sycamore Formation at the Sho-Vel-Tum Field primarily consists of clay-rich mudstones (Mdst) and quartz-rich siltstones. The clay-rich Mdst are mainly composed of clays, quartz grains, some allochems, and detrital organic matter. The siltstones are structureless and are divided into two petrofacies: high porosity and permeability massive calcareous siltstones and low porosity and permeability massive calcite-cemented siltstones. Core and well-log data provide mineralogical, lithologic, and porosity information that is useful to define petrophysical facies (petrofacies) and to create facies logs within the Sycamore Formation. We used the data to establish the Sycamore Formation stratigraphic architecture and to map its spatial variability and reservoir properties. To classify the Sycamore Formation petrofacies in noncored wells, we developed a machine learning-based workflow that compares more than 1800 classification models and selects the best combination of well logs, algorithms, and hyperparameters to predict defined petrofacies. The process includes combinations of well logs that were optimized in four classification algorithms: artificial neural network, K-nearest neighbor, support vector machine, and random forest. To adjust each classifier, we used a grid search and a fivefold cross validation to find the best combination of three hyperparameters to improve results of each algorithm. This workflow allows for the efficient extraction of information from cores at a low cost. After we generated the petrofacies logs in noncored wells, we combined them with multiple constraints to create a 3D petrofacies model for the Sycamore Formation at the Sho-Vel-Tum Field and analyze the stratigraphic and diagenetic controls on petrofacies and its impact in reservoir quality.

Earth observation approach for targeting stratiform deposit of manganese in central India

The stratiform manganese deposits, hosted within the Sausar Group of rocks, in Madhya Pradesh state of India, has undergone polyphase deformation and metamorphism. The region is an enterprising geosite to understand the lithological and tectonic control on manganese mineralization. We have carried out a conjugate remote sensing based analysis using Visible, Near Infrared and Short Wave Infrared bands (VIS-NIR-SWIR) of optical imagery from multiple sensors supplemented with analysis of L-band microwave data over the Balaghat district of Madhya Pradesh to delineate prospective areas for manganese exploration, supported by the lab and field-based evidence.The enhanced image products (i.e.band ratios, principal components) and spectral anomaly map derived from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) and Sentinel-2B multispectral bands are used to delineate the lithological contrast of the host rock and indicate key locales of mineralization. The geological structures interpreted using the merged product of Advanced Land Observation Satellite Phased Array L-band SAR (ALOS PALSAR −1), Landsat 8 PC bands (2 & 3) and the processed Horizontal Gradient Magnitude (HGM) from advanced satellite gravity model (EIGEN-6C4), illustrates the structural control on the mineralization. The petrological details derived from the host rock samples shows microstructures like micro-folding, foliations, quartz grain elongation etc., thus representing the microscale deformations within the rock units occurring in the area.The lab-based spectral signatures of manganese-bearing host rock was resampled to image spectra and spectral anomaly map using ConstrainedEnergyMinimization(CEM), which shows good correlation with the existing mine locations.The information from remote sensing and lab analysis has been integrated thematically using the knowledge-based Weighted Sum Method (WSM) with existing mine locations as the training dataset. The derived mineral prospect map indicates several new areas of manganese prospectivity which can serve as a guide for detailed future explorations in the region .

Interdependence between bacterial EPS and early grain coat development

AbstractBacteria are the most abundant forms of life we know on our planet, able to survive in a variety of habitats, that play an important role in mineral formation and transformation processes. Here, we present laboratory experiments in which unconsolidated quartz grains were seeded with Geobacter sulfurreducens cells and exposed to a mineral medium solution for 96 hours at temperatures of between 60°C and 120°C. Experimental data show the interdependence between extracellular polymeric substances (EPS) and the early formation of grain‐coating material. The occurrence of EPS promotes the development of web and bridging structures binding the quartz grains and creating EPS‐coated surfaces. With increasing temperature, an amorphous mineral phase grows preferentially on these surfaces suggesting that EPS can act as a template for mineral nucleation. At temperatures &gt;100°C, the order of crystallinity of the amorphous authigenic phase increases, transitioning to poorly‐ordered rosette‐like textures.

Petrographic studies and mineralogical characterization of the Dellen impactites

AbstractThe impact origin of the Early Cretaceous (140.82 ± 0.51 Ma) 20‐km diameter Dellen structure was proven in the late 60s based on the discovery of planar deformation features (PDFs) in quartz grains. Although decades have passed, impactites found from the crater have not received much attention. Thus, this study provides a detailed petrological and mineralogical description of impactites from Dellen. Impactites were classified based on mineralogical observations using the latest recommendations of nomenclature. The studied samples include impact melt rocks (clast rich, clast poor, and clast free), suevitic impact breccias, shocked and unshocked granite, and a shatter cone. Altogether, 16 samples with different lithologies were studied using a polarization microscope. Selected samples were studied with an energy dispersive spectroscopy detector attached to the scanning electron microscopy. PDFs were indexed using a four‐axis universal stage from seven samples. Selected samples for PDF studies consisted of clast‐rich impact melt rocks (DEL10, DEL13, D99), suevitic impact breccias (DEL14, DEL16, DEL24), and shocked granite target rock (DEL17). A total of 197 PDF sets in 113 quartz grains were studied, and 186 sets resulted in rational crystallographic orientations. Common orientations include π{101̅2}, ω{101̅3}, z{101̅1}, ξ{112̅2}, and {101̅4}. In suevitic impact breccias and impact melt rocks, ballen silica and plagioclase with checkerboard texture were abundant. The petrographic results in Dellen impactites indicate a range of shock pressures from at least 2 to over 60 GPa, based on diagnostic shock metamorphic features in minerals and the occurrence of impact melt rock.

A refined recycled carbonatite model for the δ13C negative anomaly in the upper Doushantuo Formation

The upper Doushantuo Formation (terminated at 551 Ma) in the Yangtze platform keeps a large carbonate δ13C (carbon isotope composition) negative anomaly, which has been proposed to be related to the Shuram Excursion (SE). However it is still controversial whether such anomaly records the carbon isotope variation of seawater caused by oxidizing dissolved organic carbon (DOC) or the input of a local exotic carbon reservoir. Here, we conducted further chemical and mineralogical studies of samples from the 13C-depleted strata of the Doushantuo Formation at Jiulongwan. The 13C-depleted strata are featured by flat REY patterns and constant δ13Ccarb (δ13C of carbonate) but variable δ13Corg (δ13C of organic carbon), which disagree with the prediction of DOC oxidation model. Euhedral quartz grains separated from these strata show bluish-violet catholuminescence indicating a high temperature origin. Carbonate inclusions are found in some of these quartz grains. Above chemical and mineralogical features of the 13C-depleted strata can be explained by the previously suggested recycled carbonatite model. However, zircons separated from the 13C-depleted carbonates record not only a young age of 567.17 ± 3.57 M, but also two old age clusters of 640 ∼ 960 Ma and 1760 ∼ 2160 Ma. The young age of 567.17 ± 3.57 Ma may record the carbonatite magmatic activity. The age spectrums of old zircons imply that the recycled carbonatite is more likely to be transported and deposited in the intra-shelf area with other clastics through weathering.

Exhumation of the Higher Himalaya: Insights from Detrital Zircon U–Pb Ages of the Oligocene–Miocene Chitarwatta Formation, Sulaiman Fold–Thrust Belt, Pakistan

This study reports the detrital zircon U–Pb ages of the post collisional Chitarwatta Formation, exposed along the western margin of the Indian plate at the Sulaiman fold–thrust belt (SFB), Pakistan. The Chitarwatta Formation overlies the shallow marine carbonate sequence of the Kirthar Formation and represents an Oligocene–Miocene transitional marine sequence. The sequence consists of sandstone, siltstone, and mudstone. The sandstone consists predominantly (79–82%) of quartz grains. The framework grains are sub-angular to sub-rounded and show recycled orogenic provenance. The detrital zircon U–Pb age data show the dominant population between 390 Ma and ~1100 Ma, which is ~70% of the total population. In addition to this, a significant percentage of the younger detrital ages exist between ~40 Ma and ~120 Ma. This younger age cluster indicates the northern sources, including the Kohistan–Ladakh arc (KLA) and Karakoram block (KB), whereas the provenance for the 390–1100 Ma detrital zircon is likely the Higher Himalaya (HH), with contribution from Tethyan Himalaya (TH). This post-collisional scenario suggests that the Chitarwatta Formation received detritus from the northern sources through a drainage system, named as the Indus drainage system. A comparison with the coeval units in the north (Murree Formation, Dagshai Formation, and Dumre Formation) suggests that the sediments may have been delivered through the same drainage system that shares similar detritus. Relying on the contribution of the HH detritus, we propose that the HH uplifted during the Oligocene–Miocene along the Main Central Thrust (MCT) and provided detritus to the foreland basin.

Combustion Metamorphism in Mud Volcanic Events: A Case Study of the 6 May 2000 Fire Eruption of Karabetova Gora Mud Volcano

The violent eruption of Karabetova Gora mud volcano on 6 May 2000 (Taman Peninsula, 45°12′16″ N; 36°47′05″ E) triggered gas ignition as a giant straight-flow vertical gas flare. The 400 m high, short-lived (~15 min) gas flare left no thermal halo on the ground surface, but the thermal shock caused melting or annealing of mud masses which became dispersed in ≤2 m3 blocks to distances within 30 m around the volcano conduit. The flare reached the maximum temperatures (~1400–1540 °C) at heights from 75 to 250 m, as estimated by a numerical simulation in SigmaFlow. Bulk melting of dehydrated mud masses was mostly limited to &lt;1.5 cm near the surface of the blocks. Porous paralavas at the site consisted of low- and high-silica K-Al glasses (70%–80%) with residual unmolten grains of detrital quartz and fine (&lt;30 µm) new phases: main intermediate members of the magnetite–ulvöspinel solid solutions and plagioclase (An45-61Ab37-44Or2-11 to An73-90Ab10-27Or0.5-1), minor cordierite (XFe = 26%–46%), pigeonite (XFe = 42%–60%), tridymite, cristobalite, and rare mullite. The metapelitic rocks affected by combustion metamorphism were heterogeneous in terms of phase composition and texture. They failed to attain homogeneity due to the high viscosity of anhydrous silicate melts and brevity of the thermal impact. The revealed features of rocks altered by a giant gas fire may serve as a proxy for phase transformation patterns in highly disequilibrium conditions of a thermal shock, far from the formation conditions of ordinary metamorphic rocks.

Aeolian processes on the outwash plain in the Oświęcim Basin, southern Poland

Abstract This article presents the results of studies on aeolian processes in the Oświęcim Basin in southern Poland. There are only a few large dunes in the western part (Woszczyce area) of the vast area of the Basin (about 1800 km2), and several dozen small forms (1–3 m high) in the central part (Świerczyniec area) All these forms are located on the outwash plain from the Odra Glaciation – dunes in the proximal part of sandur and small forms in the distal part. Grain size indices were determined for all samples taken at 17 sites, and quartz grain abrasion was examined using mechanical graniformametric and morphoscopic methods. The study found that the fluvioglacial deposits are not very diverse in grain size but significantly differentiated in terms of the degree of aeolization. In the proximal part of the outwash plain, deposits are characterized by very poor abrasion of quartz grains, two-three times worse than those from the distal part. Aeolian sands, in terms of grain size, do not differ essentially from fluvioglacial deposits, and in the distal part of sandur, there are no differences in the abrasion of the quartz grains. Conversely, in the proximal part, there was a significant increase in the degree of aeolization of the dune deposits compared to the source fluvioglacial deposits.