Geosystems and Geoenvironment最新文献

In the brittle regime, faults tend to be oriented along an angle of about 30$\text{°}$ relative to the principal stress direction. This empirical Andersonian observation is usually explained by the orientation of the stress tensor and the slope of the yield envelope defined by the Mohr-Coulomb criterion, often called critical-stress theory, assuming frictional properties of the crustal rocks ($\mu \approx$ 0.6$-$0.8). However, why the slope has a given value? We suggest that the slope dip is constrained by the occurrence of the largest shear stress gradient along that inclination. High homogeneous shear stress, i.e., without gradients, may generate aseismic creep as for example in flat decollements, both along thrusts and low angle normal faults, whereas along ramps larger shear stress gradients determine higher energy accumulation and stick-slip behaviour with larger sudden seismic energy release. Further variability of the angle is due to variations of the internal friction and of the Poisson ratio, being related to different lithologies, anisotropies and pre-existing fractures and faults. Misaligned faults are justified to occur due to the local weaknesses in the crustal volume; however, having lower stress gradients along dip than the optimally-oriented ones, they have higher probability of being associated with lower seismogenic potential or even aseismic behavior.

Different natural and anthropogenic processes cause pollution of various water bodies worldwide creating numerous health problems for humans. This causes serious concern as water is a basic necessity to all living beings, and needs to be adequately monitored and managed to prevent its contamination. If found contaminated, the water is to be cleaned using suitable water treatment methods keeping in view of WHO regulations before using it for the intended purpose (drinking, irrigation, etc.). Application of different ICP-MS techniques such as classical ICP-MS, ICP-MS/MS, ICP-TOF-MS, HR-ICP-MS, MH-ICP-MS, and MC-ICP-MS for the qualitative and quantitative determination of toxic metals, isotopes and, metal species, and effective monitoring of various other pollutants in drinking water, surface water, groundwater, industrial effluents, and water used for irrigation, aquaculture and for various industries is the focal point of this article. In general, the concentrations of major, minor, and trace element composition of water samples are influenced mainly by the bedrock geology of the point of emergence, as well as by the residence time and the depth of the aquifer. For better management of water resources, it is necessary to have a comprehensive understanding of the quality (with respect to physical, chemical, and biological) requirements, and sustainability of groundwater from a particular source. Identifying the sources of contamination, understanding the health risks associated, and the application of suitable water treatment technique(s) before it is supplied for public consumption. It is also necessary to intensify our studies on the metal species (e.g., As³⁺, Cr⁶⁺ and methyl mercury) in drinking water and their effects on human health, and their regulatory limits in drinking water.

Foraminifers are ubiquitous and abundant organisms in the marine environment, sensitive to different environmental variables such as pH, dissolved oxygen, salinity, temperature, organic matter and substrate. In the present study, environmental variables and benthic foraminiferal assemblages from 32 surface sediment samples belonging to different water depths were studied to understand the shelf and slope environment of the southwestern Bay of Bengal. Statistical methods such as cluster and principal component analysis (PCA) were used to infer the relationship existing among various foraminiferal assemblages, bathymetry, sediment and bottom water characteristics. Statistical analysis yielded four assemblages, of which assemblage-I is dominated by Nonion faba, Rotalidium annectens, Asterorotalia pulchella, Elphidium crispum, and Amphistegina radiata, and is confined to the shallowest inner shelf region (5 to 35 m water depth) with sandy sediments indicating high-energy condition. Assemblage-II is marked by the abundance of Cibicidoides wuellerstorfi, Hanzawaia concentrica, Quinqueloculina agglutinans, Quinqueloculina seminula, Quinqueloculina lamarckiana, Ammonia beccarri, and Ammonia tepida which are associated with the middle shelf region (water depth 35 to 70 m) with sandy to slightly muddy sand sediments. Assemblage-III is dominated by Asterorotalia dentata, Quinqueloculina venusta, Cancris communis, Cassidulina laevigata, and N. costiferum which occur at a depth of 70 to 170 m in the outer shelf, and are highly associated with slightly muddy sand to muddy sand. Whereas, assemblage -IV includes Uvigerina mediterranea, Bolivina dilatata, Bolivina robusta, and Bulimina marginata foraminiferal species that are abundant in the upper slope (170–244 m water depth) and are confined to muddy sand and sandy mud with low dissolved oxygen in the bottom water. The above assemblages depict that the abundance and distribution of foraminifera are largely controlled by substrate, energy conditions and environmental variables such as temperature, salinity, organic matter and dissolved oxygen.

This communication reports the results of geochemical investigations and detrital zircon geochronology of metasediments of the Khammam Schist Belt that occur at the trijunction of the Eastern Dharwar Craton–Bastar Craton–Eastern Ghats Belt. Biotite (X_Mg = 0.46–0.52) and muscovite (Si atom per formula unit (apfu) of 11 O = 3.08–3.17) with alkali-feldspar constitute the mineralogy of studied samples. The Ti content in biotite yields a mean temperature of 652 °C (1σ = 10 °C), and biotite–muscovite pairs yield an average pressure of 0.46 GPa (1σ = 0.06 GPa). Fe-Ti oxides and zircon occur as accessory phases. The Al₂O₃ exhibits a positive correlation with K₂O and TiO_2, which implies that mica and biotite control the major element abundances of studied samples. These samples indicate negative Sr and positive Th anomalies in a Post Archean Australian Shale (PASS) normalised spider diagram. Also, these samples show a nearly horizontal trend with (La/Yb) _PASS varying between 0.56 and 1.92 with a negative to slightly positive Eu anomaly (Eu/Eu* = 1.20, 1σ = 0.38). LA-ICPMS analysis of detrital zircon grains (number of analyses = 100 from two samples) yields ²⁰⁷Pb/²⁰⁶Pb ages range from 1500 to 2600 Ma. The zircons grains with weighted average ages between 2500 Ma, 2400 Ma, 2200 Ma, 2000 Ma, 1900 and 1800 Ma exhibit magmatic and high-temperature deformation features. The 1604 Ma old zircons exhibit homogeneous domains and overgrowths over older zircons, implying metamorphic origin. The Chemical Index of Alteration (CIA = 66 to 77), Chemical Index of Weathering (CIW = 73 to 95), and Plagioclase Index of Alteration (PIA = 81 to 91) values indicate moderate to intense weathering of the source area. Source and tectonic discrimination plots imply a felsic source and active tectonic setting. Accordingly, 1900–1800 Ma old magmatic zircons in the current samples constrain the maximum depositional age for the Khammam Schist Belt. Compared with the detrital zircon geochronology of the North China Craton and East Antarctica, the current samples exhibit peaks at circa 2500 Ma, 2400 Ma, 2200 Ma, 2000 Ma, 1900–1800 Ma, and 1600 Ma, implying Khammam Schist Belt as part of the South India Cratonic Block shares similar geological history with North China Craton and East Antarctica. Our study suggests that North China Craton and East Antarctica were connected with the South Indian Cratonic Block during the Columbia assembly.

The dynamics of aqueous processes within the Eos Chasma region in the trough of Valles Marineris on Mars have been attributed to a variety of Hesperian-aged landforms. We aim to improve the understanding of the geological characteristics of the western part of the Eos Chaos by investigating the morphological, topographical, and thermo-physical characteristics of the western semi-circular segment of Valles Marineris. The western Eos Chaos is characterized by remnants of an elevated crater rim, a central peak, and a circular boundary. Based on these observations, we infer that the study area is an ancient, highly degraded impact crater. Our observations indicate that numerous geological processes, such as fluvial, tectonic, and aeolian processes, have shaped the landforms. For instance, channels on the slope of the wall with a mean v-index of 0.2 indicate a fluvial origin. The chaotic mounds within the study regions are highly degraded. However, the presence of eroded inselberg peaks above the maximum ponding level of eastern Valles Marineris (–3560 m) suggests that both aeolian and fluvial processes have played a role in the denudation of the impact crater. Furthermore, both aeolian and fluvial processes also influenced the morphological evolution of inselbergs of this impact crater of Eos Chaos. The morphological, topographic, and thermal inertia characteristics of the landforms in the Eos Chaos are similar to those found elsewhere in Valles Marineris. In this study, the impact crater of Eos Chaos is considered a sub-region of Valles Marineris, in which evidence for many past geological processes is preserved. Based on possible chronological markers, we have developed a model that explains the evolution of the Eos Chaos impact crater and its incorporation into Valles Marineris.

The tectonics of Southern Granulite Terrane (SGT), one of the most important Archean- Neoproterozoic terrain, is unveiled by the gravity-magnetic signatures associated with the complex shear zone system. The significance of gravity and magnetic anomalies and the comparison between the two elucidate the structural complexity of the region. Though Moyar Bhavani Salem Attur Shear Zone (MBSASZ) and Palghat Cauvery Shear zone (PCSZ) have been identified as the major crustal scale shears, significant difference is being noted in their anomaly pattern. A four-layer crustal model is derived from gravity and magnetic anomalies constrained by seismic information. Along the PCSZ, gravity gradient was subdued and magnetic gradient shows a low in contrast to the magnetic high associated with the MBSASZ suggesting that it might belong to two different crustal terranes. It is evident that the major shear zones of SGT is extending to the offshore region upto continent ocean boundary which suggest that the tectonic events portrayed by SGT is not confined to the terrane alone, and plays an important role in understanding the tectonics in the context of the East Gondwana fragmentation and dispersal.

This research identifies the optimum supervised classification algorithm based on modeling Covid 19 lockdown situations all around the World. The deadly Covid 19 viruses suddenly stopped the fast-moving world and all the commercial and noncommercial activities were stalled for an uncertain period during 2020-2021. In this work, object-based image classification approaches have been used to compare pre-Covid and post-Covid (at the time lockdown) images of the study area. These study areas are Washington DC, USA, Sao Paulo, Brazil, Cairo, Egypt, Afghanistan/Iran border, and Beijing, China. All the study areas possess different geographical conditions but have a similar situation of Covid 19 lockdowns. Six supervised image classification techniques are known as Parallelepiped classification ($PPC$), Minimum distance classification ($MDC$), Mahalanobis distance classification ($MaDC$), Maximum likelihood classification ($MLC$), Spectral angle mapper classification ($SAMC$) and Spectral information divergence classification ($SIDC$) are used to classify the satellite data of the study area. Thus based on classification results and statistical features, it has been observed that $PPC$has obtained the least significant results. In contrast, the most reliable results and highest classification accuracies are obtained through $MDC$, $MaDC$, and $MLC$classification algorithms.

The Bundelkhand Craton and associated basins of Peninsular India have received interest for debates related to research on their records of biological evolution, particularly reported occurrences of materials akin to triploblastic animals. Data related to geochronology and key tectono-stratigraphic markers of the block have been critically analysed and a model of evolution during the Proterozoic Eon is presented. The basement block, the Bundelkhand Granite Complex, evolved in three phases: Phase I (3551–3190 Ma), Phase II (2780–2550 Ma) and Phase III (2450–2250 Ma), followed by tectono-thermal events between the phases, representing temporal unconformities of ∼400 Ma and ∼100 Ma. The last phase of evolution was terminated with the amalgamation of the North Indian Block with the South Indian Block, forming the Satpura Orogen (phase IA) at ∼2250 Ma, which included the Singhbhum Orogenic belt. Orogenic collapse/extension at ∼2150 Ma developed a series of sedimentary basins running parallel to the orogenic belt. These Paleoproterozoic basins include the Mahakoshal, Bijawar, Sonrai and Gwalior basins around the Bundelkhand Granite Complex. The adjacent cratons also developed contemporaneous basins for the deposition of the Aravalli Supergroup (in the Western Indian Block), Cuddapah Supergroup (in the South Indian Block) and a proto-ocean at the site of the Eastern Ghats, extending towards the northern margin of the Singhbhum Block. All these basins had an inversion phase of 1950–1800 Ma, ending with the development of the Aravalli Orogen as well as Satpura Orogen (phase IB) and closing of sedimentation in the Paleoproterozoic basins. A new phase of extension at ∼1750 Ma initiated deposition of the Semri Group and Delhi Supergroup in the Northern and Western Indian blocks. The event was associated with the amalgamation of East Antarctic Block with the South Indian Block forming the Eastern Ghats (phase I)-Dalma Orogen. The later stage of Eastern Ghats (phase I)-Dalma Orogeny ∼1500 Ma was contemporaneous with the Delhi Orogeny (North Delhi Orogeny). The principal compressions acting opposite to each other during the Delhi Orogeny (with southeastward tectonic transport) and Eastern Ghats (phase I)-Dalma Orogeny (with northwestward tectonic transport) caused the second uplift of the Satpura Orogen (Satpura Orogeny II), as well as the uplift of the North Indian Block, developing a first-order spatio-temporal unconformity of ∼300 Ma gap above the Semri Group, till the extensional stress regime of ∼1200 Ma initiated deposition of the Kaimur Group. The closing of the Kaimur Basin took place during the Grenvillian Orogeny of ∼1100 Ma, which developed the Eastern Ghats (phase II) – Rayner Orogen on the eastern margin of Peninsular India. The far-field stress of the Eastern Ghats Orogeny (phase II) developed inversion/uplift in the Satpura Orogen and deposition of the Rewa Group in the North Indian Block. A second uplift of the Eastern Ghats (Eastern Gha