Prediction of blast-induced flyrock in Indian limestone mines using neural networks

Frequency and scale of the blasting events are increasing to boost limestone production. Mines areapproaching close to inhabited areas due to growing population and limited availability of land resourceswhich has challenged the management to go for safe blasts with special reference to opencast mining.The study aims to predict the distance covered by the flyrock induced by blasting using artificial neuralnetwork （ANN） and multi-variate regression analysis （MVRA） for better assessment. Blast design andgeotechnical parameters, such as linear charge concentration, burden, stemming length, specific charge,unconfined compressive strength （UCS）, and rock quality designation （RQD）, have been selected as inputparameters and flyrock distance used as output parameter. ANN has been trained using 95 datasets ofexperimental blasts conducted in 4 opencast limestone mines in India. Thirty datasets have been used fortesting and validation of trained neural network. Flyrock distances have been predicted by ANN, MVRA,as well as further calculated using motion analysis of flyrock projectiles and compared with the observeddata. Back propagation neural network （BPNN） has been proven to be a superior predictive tool whencompared with MVRA. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Numerical analysis of surface subsidence in asymmetric parallel highway tunnels

Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels(Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and inequidimensional noncircular tunnel.

Investigation of rockfall-prone road cut slope near Lengpui Airport,Mizoram,India

Rockfall is one of severe natural hazards that are frequently reported in northeast region of India. It carries rock block falling from the cliff with high velocities and energies which can result in damages to vehicles, disruption to transportation, injuries and fatalities. The massive rockfall event which occurred in April 2017 on the highway NH-44 A, near Lengpui Airport, blocked the traffic for 1 d, and fortunately,no casualties were reported as the event occurred in the night. This is the only highway connecting the Aizawl city to the airport and the region is highly prone to rockfall events. Hence assessment of rockfall along this highway is necessary. In the current study, rockfall hazard assessment has been carried out on three locations by rockfall hazard rating system(RHRS). During pre-failure analysis, the result shows that most hazardous slopes have RHRS score of 639. The slopes were found to be vulnerable and later on the rockfall activity occurred. Three-dimensional(3 D) stability analysis has been carried out using 3 DEC software package to analyze the failure behavior and to decide the rockfall-prone zone(unstable blocks)for slope. The total displacement of 2.24 cm and velocity of 2,25 mm/s of the failed block have been observed in the numerical analysis. Further, the rockfall vulnerable zone(unstable blocks) is considered to determine the parameters such as run-out distance, bounce height and energies of the falling rock blocks. The maximum total kinetic energy of 5047 kJ has been observed in the numerical analysis with the maximum run-out distance up to 18 m.

Assessment of Rockfall Hazard along the Road Cut Slopes of State Highway-72, Maharashtra, India

Rockfall is a major problem in high hill slopes and rocky mountainous regions and construction of highways at these rockfall prone areas often require stable slopes. The causes of rockfall are presence of discontinuities, high angle cut slopes, heavy rainfall, and unplanned slope geometry etc. Slope geometry is one of the most triggering parameters for rockfall, when there are variations in slope angle along the profile of slope. The Present study involves rockfall hazard assessment of road cut slopes for 15 km distance starting from Mahabaleshwar town along State Highway-72 (SH-72). The vertical to subvertical cut slopes are prone to instability due to unfavorable orientation of discontinuities in slope face of weathered and altered basaltic rockmass. The predominant type of instability has been found as wedge type failure involving medium to large size blocks. In order to investigate the existing stability conditions, analyses were carried out at two locations under different slope conditions. The kinematic analysis was performed using stereographic projection method. RockFall 4.0 numerical simulator software was used to calculate the maximum bounce heights, total kinetic energies and translational velocities of the falling rockmass blocks, and a comparative analysis is presented with increasing the mass of blocks and height of the slope. The result of numerical analysis shows that varying slope angle geometry creates more problems as compared to the mass of blocks in the scenario of rockfall.

Crustal structure and sedimentation history over the Alleppey platform, southwest continental margin of India:Constraints from multichannel seismic and gravity data

The Alleppey Platform is an important morphological feature located in the Kerala-Konkan basin off the southwest coast of India. In the present study, seismic reflection data available in the basin were used to understand the sedimentation history and also to carry out integrated gravity interpretation. Detailed seismic reflection data in the basin reveals that:(1) the Alleppey Platform is associated with a basement high in the west of its present-day geometry(as observed in the time-structure map of the Trap Top(K/T boundary)),(2) the platform subsequently started developing during the Eocene period and attained the present geometry by the Miocene and,(3) both the Alleppey platform and the Vishnu fracture zone have had significant impact on the sedimentation patterns(as shown by the time-structure and the isochron maps of the major sedimentary horizons in the region). The 3-D sediment gravity effect computed from the sedimentary layer geometry was used to construct the crustal Bouguer anomaly map of the region.The 3-D gravity inversion of crustal Bouguer anomaly exhibits a Moho depression below the western border of the platform and a minor rise towards the east which then deepens again below the Indian shield. The 2-D gravity modelling across the Alleppey platform reveals the geometry of crustal extension,in which there are patches of thin and thick crust. The Vishnu Fracture Zone appears as a crustal-scale feature at the western boundary of the Alleppey platform. Based on the gravity model and the seismic reflection data, we suggest that the basement high to the west of the present day Alleppey platform remained as a piece of continental block very close to the mainland with the intervening depression filling up with sediments during the rifting. In order to place the Alleppey platform in the overall perspective of tectonic evolution of the Kerala-Konkan basin, we propose its candidature as a continental fragment.

Stability investigation of road cut slope in basaltic rockmass,Mahabaleshwar,India

Slope failures along hill cut road slopes are the major nuisance for commuters and highway planners as they put the human lives at huge risk,coupled with immense monetary losses.Analysis of these vulnerable cut slopes entails the assessment and estimation of the suitable material strength input parameters to be used in the numerical models to accomplish a holistic stability examination.For the present study a 60 m high,basaltic and lateritic road cut hill slope in Mahabaleshwar,India,has been considered.A number of samples of both basalt and laterite,in their natural state were tested in the laboratory and the evaluated maximum,minimum and mean strength parameters were employed for the three cases in a distinct element numerical model.The Mohr-Coulomb failure criterion has been incorporated in the numerical model for the material as well as the joints.The numerical investigation offered the factor of safety and insights into the probable deformational mechanism for the three cases.Beside,several critical parameters have also been judged from the study viz.,mode of failure,factor of safety,shear strain rate,displacement magnitudes etc.The result of this analysis shows that the studied section is prone to recurrent failures due to the capping of a substantially thick layer of weaker lateritic material above the high strength basaltic rock mass.External triggering mechanisms like heavy precipitation and earthquake may also accelerate the slope failure in this area.The study also suggests employing instant preventive measures to avert the further risk of damage.

Tectonic significance of dykes in the Sarnu-Dandali alkaline complex,Rajasthan, northwestern Deccan Traps

Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual case studies. The Sarnu-Dandali alkaline complex, near the northwestern limit of the Deccan Traps continental flood basalt province, contains mafic to felsic alkaline volcano-plutonic rocks and carbonatites. The complex is situated near the northern end of the 600 km long, NNWe SSE-trending Barmer-Cambay rift. Mafic enclave swarms in the syenites suggest synplutonic mafic dykes injected into a largely liquid felsic magma chamber. Later coherent dykes in the complex, of all compositions and sizes,dominantly strike NNWe SSE, parallel to the Barmer-Cambay rift. The rift formed during two distinct episodes of extension, NWe SE in the early Cretaceous and NEe SW in the late Cretaceous. Control of the southern Indian Dharwar structural fabric on the rift trend, as speculated previously, is untenable,whereas the regional Precambrian basement trends（Aravalli and Malani） run NEe SW and NNEe SSW.We therefore suggest that the small-scale Sarnu-Dandali dykes and the much larger-scale BarmerCambay rift were not controlled by basement structure, but related to contemporaneous, late Cretaceous regional ENEe WSW extension, for which there is varied independent evidence.

Organo-petrographic and geochemical characteristics of Gurha lignite deposits,Rajasthan,India:Insights into the palaeovegetation,palaeoenvironment and hydrocarbon source rock potential

The sedimentary sequence containing lignite deposits in Gurha quarry of the Bikaner-Nagaur Basin(Rajasthan)has been investigated.The samples from lignite and allied shale horizons were evaluated for petrographical,palynological,palynofacies and organic geochemical inferences,to depict the source flora and to reconstruct the palaeodepositional conditions prevailed during the sedimentation.An assessment for the hydrocarbon generation potential of these deposits has also been made.The results revealed the dominance of huminite macerals and phytoclasts organic matter(OM) indicating the existence of forested vegetation in the vicinity of the depositional site.A relatively high terrigenous/aquatic ratio(TAR) and the carbon preference index(CPI) are also suggesting the contribution of higher plants in the peat formation.However,the n-alkane distributions,maximizing at n-C17 and n-C29,showed inputs from the algal communities along with the higher plant derived organic matters.Recovered palynomorphs of the families Onagraceae,Meliaceae,Arecaceae,Rhizophoraceae,Rubiaceae,Ctenolophonaceae, etc.together with oleanene and ursane types of triterpenoids suggest the contribution from angiosperms source vegetation.Interestingly,the presence of Araucareaceae and Podocarpaceae pollen grains shows the existence of gymnosperms vegetation.Further,the presence of tetracyclic diterpanes;demethylated entbeyerane,sandaracopimarane,pimarane,and Kaurane type of compounds confirms the contribution of conifers.The variation in the values of the coefficient of non-equality(H:0.68%-7.56%),the standard deviation(8:0.04%-0.16%) and the coefficient of variability(V:16.10%-46.47%),also shows the heterogeneity in the source organic matter.The various petrographical indices,palynological entities,and geochemical parameters indicate that the peatforming vegetation was accumulated under a mixed environment and fluctuating hydrological settings.The interpretation of palynofacies data on APP(Amorphous organic matter-Phytoclast-Palynomorphs) diagram suggests that the accumulation of organic matter occurred in a dysoxic-suboxic condition in a proximal(to land)setting with the shift to an anoxic condition in distal setting towards the termination of sedimentation.The huminite(ulminite) reflectance(R_r) values(av.0.28%) showed a good relationship with average T_(max) value(414℃),suggesting the immaturity.The TOC content ranges of 13-59 wt.%,and HI values vary between 101 and 546 mg HC/g TOC in the studied samples.Collectively,the studied lignite and shale samples have the admixed kerogens(Type Ⅲ-Ⅱ) and exhibit the ability to generate the gaseous to oil hydrocarbons upon maturation.

Control of rock joint parameters on deformation of tunnel opening

In this paper, stress behavior of shallow tunnels under simultaneous non-uniform surface traction and symmetric gravity loading was studied using a direct boundary element method（BEM）. The existing fullplane elastostatic fundamental solutions to displacement and stress fields were used and implemented in a developed algorithm. The cross-section of the tunnel was considered in circular, square, and horseshoe shapes and the lateral coefficient of the domain was assumed as unit quantity. Double-node procedure of the BEM was applied at the corners to improve the model including sudden traction changes. The results showed that the method used was a powerful tool for modeling underground openings under various external as well as internal loads. Eccentric loads significantly influenced the stress pattern of the surrounding tunnel. The achievements can be practically used in completing and modifying regulations for stability investigation of shallow tunnels.

Geometry and kinematics of brittle deformation in the Central Cameroon Shear Zone (Kékem area): Implication for gold exploration within the Central Africa Fold Belt in Cameroon

The Central Africa Fold Belt(CAFB)is a collision belt endowed with gold deposits in Eastern Cameroon area mined for about 50 years.However,favorable areas for gold exploration are poorly known.This paper presents(1)the kinematics of the brittle deformation in the Kékem area in the SW portion of the Central Cameroon Shear Zone and(2)constraints gold mineralization events with respect to the collisional evolution of the CAFB.The authors interpret that the conjugate ENE to E and NNW to NW trending lineament corresponds to the synthetic(R)and the antithetic(R’)shears,which accompanied the dextral slip along the NE to ENE striking shear.The latter coincides with the last 570-552 Ma D3 dextral simple shear-dominated transpression,which is parallel to the BétaréOya shear zone hosting gold deposits.Gold mineralizations,which mainly occurred during the last dextral shearing,are disseminated within quartz veins associated to Riedel’s previous structures reactivated due to late collisional activities of the CAFB as brittle deformation.Gold mineralizations occurred mainly during the 570-552 Ma D3 event.The reactivation,which might be due to dextral simple shear during mylonitzation,plausibly remobilized the early gold deposits hosted in syn-compressional rocks and/or possibly focused deep-sourced fluid mixed with those released by dehydration.Therefore,the Central Cameroon Shear Zone where Kékem is located,and which shows similar petrographical and structural features to those controling Batouri gold district,is a target area for gold exploration in Cameroon.

Distinct Element Modelling of Mahabaleshwar Road Cut Hill Slope

Reliable estimates of slope stability are essential for safe design and planning of road cut hill slopes which accommo-date a number of tourist destinations around the world. The failure of cut slopes along these hills puts human life in grave danger and it is also disastrous for the economy. In the present study, a section of 100 m high jointed basalt hill slope has been analyzed numerically in a distinct element code, which is apt for simulating the behavior for jointed rock. The analysis was carried out for both the dry and saturated conditions. The distinct element analysis of the hill slope demonstrates it to be marginally stable under dry condition, while for the saturated condition, the hill slope fails along well defined joint planes.

Mica Inclusions inside Host Mica Grains from the Sutlej Section of the Higher Himalayan Crystallines, India—Morphology and Constrains in Genesis

Biotite and muscovite inclusions inside mica host minerals from the Sutlej section of the Higher Himalayan Crystalline were studied under an optical microscope. These inclusions formed possibly by local recrystallization of mica grains during regional prograde metamorphism, with some affected by top-to-SW shear leading to parallelogram shapes. Recrystallization may have been assisted by solution transfer along the cleavage planes of the host grains. The relative competency of deformed phyllosilicate inclusions with the same or different composition to the host depends on the size and orientation of（001） cleavage planes of the inclusions relative to the host. Shearing of mica inclusions led to their parallelogram geometries within the contained mica inclusions. Some of the sheared inclusions deflect cleavage planes in the host minerals and define flanking microstructures. Trapezoidshaped inclusions are a new finding that deserves more attention for their genesis. These structurally anisotropic inclusions did not originate from sub-grains, secondary infillings or retrogression. These inclusions are also not related to pseudomorphism, isomorphism, folding of the bulk rock etc. Some of the inclusions formed by recrystallization of the host mineral during top-to-SW ductile shear.

Investigations on the Possible Re-equilibration of Aqueous Fluid Inclusions in Barite:A Study of Barite and Calcite from the Hutti Gold Deposit,Karnataka,India

Re-equilibration of fluid inclusions in crystals takes place by loss or gain of solvents and solutes from fluid inclusions and by changes in their volumes. Volume change of fluid inclusions are primarily dictated by elastic properties and available slip planes of host crystals. In the present study, the phase-behavior of fluids entrapped in co-precipitated calcite and barite is studied. While calcite contains only biphase fluid inclusions, barite has predominantly monophase fluid inclusions. Fluid inclusion petrography, microthermometry and leachate analysis are used to establish the nature of entrapped fluids and entrapment temperature is substantiated through independent sulfur isotope geothermometry using coexisting barite and pyrite. Phase transitions in the monophase fluid inclusions in barite are explained in terms of over-pressuring of fluids in these fluid inclusions relative to fluids entrapped in calcite owing to the low bulk modulus of barite.

Tonian–Ediacaran Tectonometamorphic History of the Sa'al Complex,Sinai(Egypt):Implications for the Tectonostratigraphic Framework of the Northern Arabian–Nubian Shield

The Sa'al Metamorphic Complex(SMC;southern Sinai)encompasses the oldest arc rocks in the Arabian–Nubian Shield,comprising two non-consanguineous metavolcanic successions(the Agramiya Group and the Post-Ra'ayan Formation)separated by the metasediments of the Ra'ayan Formation.It experienced three distinct deformational events(D_(1)–D_(3))and two low-medium grade regional metamorphic events(M_1–M_(2)).The Agramiya Group and the Ra'ayan Formation experienced all tectonometamorphic events(D_1–D_(3)and M_(1)–M_(2)),whereas the Post-Ra'ayan volcanic rocks were only affected by the D_(3)and M_(2)events.D_(1)is an extensional event and is connected to the late Rodinia break-up(~Tonian;900–870 Ma).The M_(1)metamorphism variably affected the older Agramiya Group,the rhyolitic tuffs experiencing lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks undergoing amphibolite facies metamorphism.The Ra'ayan Formation metasediments experienced upper greenschist to amphibolite facies metamorphism.The upper greenschist facies M_(2)affected the youngest Post-Ra'ayan volcanic rocks and other stratigraphic successions.The compressive D_(2)and D_(3)events were coeval with the accretion of dismembered terranes in the assembly of Gondwana.D_(2)can be linked to the Tonian–Cryogenian arc-arc assembly(~880–760 Ma;in Elat and Sinai),whereas D_(3)and the accompanying M_(2)is constrained to 622–600 Ma(Ediacaran).

Geochemical signatures of potassium metasomatism in anthracite from the Himalayan fold‑thrust belts of Sikkim,India

The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins,as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim,India.The SiO_(2)content(48.05 wt%to 65.09 wt%and 35.92 wt%to 50.11 wt%in the bituminous and anthracite samples,respectively)and the ratio of Al_(2)O_(3)/TiO_(2)(6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples)reveal the intermediate igneous source rock composition of the minerals.The ratio of the K_(2)O/Al_(2)O_(3)in the ash yield of the bituminous coal samples(0.03 to 0.09)may suggest the presence of kaolinite mixed with montmorillonite,while its range in the ash yield of the anthracite samples(0.16 to 0.27)may imply the presence of illite mixed with kaolinite.The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions.The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks,but the anthracite samples plot near the illite feld and are a bit ofset from the weathering trend.This may imply the plausible infuences of the potassium-metasomatism at post coalifcation stages,which is further supported by high K_(2)O/Na_(2)O ratio(29.88–80.13).The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the efect of the epigenetic potassium-metasomatism.The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.

Slope Stability Assessment of Saptashrungi Gad Temple, Vani, Nashik, Maharashtra, India—A Numerical Approach

The worship places in India are usually situated in and around the hilly regions and/or mountainous area and a number of devotees used to visit the holy places in every area for worship. The stability slopes upon which these worship places are located in the hilly and mountainous region are always a major concern. Moreover, heavy precipitation, weathering conditions, seismic disturbances and human activities could cause problem to the stability of such slopes. The effect of slope instability could cause delay in traffic, loss of life of the devotees at pilgrim sites and the loss of the properties. The Saptashrungi gad temple (SGT) situated on basaltic hills belongs to Deccan volcanic and is one among the 51 Shakti Peeths and the most holy place for pilgrims. In this research, the slope stability analysis at SGT hill is assessed using Phase 2, a finite element program along the two parikrama paths: Parikrama Path 1 (or the Badi Parikrama Path “BPP”), and Parikrama Path 2 (or the Chhoti Parikrama Path “CPP”). On the basis of extensive field work, topographic survey, complex geology, orientations of joint sets, hill slope faces and geotechnical conditions, the study area has been divided into eight zones (Zone#01 to Zone#08), and eighteen topographic profiles (AA′ to RR′) are taken from these eight zones for detailed slope stability analysis. The analysis helps to identify the potentially vulnerable slope and zone of instability.

Trace fossil evidences of an Early Miocene paleoseismic event and depositional regime change from the Kutch(Kachchh) Basin

Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures(SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation(KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS,the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity,its ichnologic signature, and the depositional regime change refer to a higher-resolution(i.e., lower-order)sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.

Geomorphic signatures and active tectonics in western Saurashtra,Gujarat,India

Active tectonics in an area includes ongoing or recent geologic events.This paper investigates the tectonic influence on the subsidence,uplift and tilt of western Saurashtra through morphotectonic analysis of ten watersheds along with characteristics of relief and drainage orientation.Watersheds 7-9 to the north(N)are tectonically active,which can be linked with the North Kathiawar Fault System(NKFS)and followed by watersheds 6,10,1,4 and 5.Stream-length gradient index and sinuosity index indicate the effect of tectonic events along the master streams in watersheds 6-9.Higher R^(2)values of the linear curve fit for watershed 7 indicate its master stream is much more tectonically active than the others.The R^(2)curve fitting model and earthquake magnitude/depth analysis confirm the region to be active.The reactivation of the NKFS most likely led to the vertical movement of western Saurashtra.

Assessing the Viability of Gandhar Field in India’s Cambay Basin for CO_(2) Storage

Our research is centered on the Gandhar oil field, which was discovered in 1983, where daily oil production has declined significantly over the years. The primary objective was to evaluate the feasibility of carbon dioxide(CO_(2)) storage through its injection into the siliciclastic reservoirs of Ankleshwar Formation. We aimed to obtain high-resolution acoustic impedance data to estimate porosity employing model-based poststack seismic inversion. We conducted an analysis of the density and effective porosity in the target zone through geostatistical techniques and probabilistic neural networks. Simultaneously, the work also involved geomechanical analysis through the computation of pore pressure and fracture gradient using well-log data, geological information, and drilling events in the Gandhar field. Our investigation unveiled spatial variations in effective porosity within the Hazad Member of the Ankleshwar Formation, with an effective porosity exceeding 25% observed in several areas, which indicates the presence of well-connected pore spaces conducive to efficient CO_(2) migration. Geomechanical analysis showed that the vertical stress(Sv) ranged from 55 MPa to 57 MPa in Telwa and from 63.7 MPa to 67.7 MPa in Hazad Member. The pore pressure profile displayed variations along the stratigraphic sequence, with the shale zone, particularly in the Kanwa Formation, attaining the maximum pressure gradient(approximately 36 MPa). However, consistently low pore pressure values(30-34 MPa) considerably below the fracture gradient curves were observed in Hazad Member due to depletion. The results from our analysis provide valuable insights into shaping future field development strategies and exploration of the feasibility of CO_(2) sequestration in Gandhar Field.

Ooidal ironstones in the Meso-Cenozoic sequences in western Siberia: assessment of formation processes and relationship with regional and global earth processes

This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia.The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology,and in this study,we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed.Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia;the absence of pyrite indicates oxic conditions for the remaining sequence.While goethite formed in oxic depositional condition,chamosite,pyrite and siderite represented hypoxic seawater.Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid.Sediments associated with goethite-chamosite ironstones,encompassing hypoxic intervals exhibit positive cerium,negative europium,and negative yttrium anomalies.Mercury anomalies,associated with the initial stages of hypoxia,correlate with global volcanic events.Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation.Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia,and released iron-rich fluid and methane in coastal and shallow marine environments.This investigation,therefore,reveals a potential geological connection between Large Igneous Provinces(LIPs),marine hypoxia,rifting and the formation of ooidal ironstones in ancient West Siberian Sea.