Vindhyan Basin Research Articles

Magmatic underplating associated with Proterozoic basin formation: insights from gravity study over the southern margin of the Bundelkhand Craton, India

Abstract. Extension tectonics responsible for intracratonic rift basin formation are often the consequences of active or passive tectonic regimes. The present work puts forth a plume-related rifting mechanism for the creation and evolution of two Proterozoic sedimentary basins outlining the Bundelkhand Craton, namely the Bijawar and Vindhyan basins. Using global gravity data, a regional-scale study is performed over the region encompassing the southern boundary of the Bundelkhand Craton consisting of the Bijawar Basin, Vindhyan Basin, and Deccan basalt outcrops. The gravity highs in the central part of the complete Bouguer anomaly and the upward-continued regional anomaly, derived from global gravity grid data, suggest that the Vindhyan sedimentary basin overlies a deeper high-density crustal source. The deepest interface as obtained from the radially averaged power spectrum analysis is observed to occur at a depth of ∼30.3 km, indicating that the sources responsible for the observed gravity signatures occur at larger depths. The 3D inversion of complete Bouguer anomaly data based on Parker–Oldenburg's algorithm revealed the Moho depth of ∼32 km below the Vindhyan Basin, i.e., south of the craton. The 2D crustal models along two selected profiles showcase a thick underplated layer with a maximum thickness of ∼12 km beneath the southern part of the Bundelkhand Craton. The inferred large E–W-trending underplating and deciphered shallower Moho beneath the regions south of the exposed Bundelkhand Craton point to crustal thinning compensated for magmatic emplacement due to a Paleoproterozoic plume activity below the craton margin.

VISACOP 2023: A National Seminar on the Vindhyan Basin of India

VISACOP 2023: A National Seminar on the Vindhyan Basin of India

Crustal structure across the Central part of Narmada-Son Lineament, India based on the interpretation of aeromagnetic and gravity data: Geological implications

Narmada-Son Lineament (NSL) is a prominent geo-tectonic feature located in central India, characterised by complex geological structures and evolution history. In this study, we present a detailed joint interpretation of the aeromagnetic and gravity anomaly maps to delineate the crustal structure in order to address the thermo-tectonic activity below the NSL region. The NW-SE linear trend observed in the aeromagnetic anomaly map correlates well with the major tectonic elements of the NSL and the Vindhyan basin. The low-pass filtered regional gravity anomaly map and corresponding residual anomaly map revealed several crustal-scale structural features in the study area. The Curie depth map of the region prepared from the magnetic anomaly map shows the variation between 24-48 km. The corresponding heat flow map correlates well with the trends in surface heat flow data. The gravity-derived Moho depth map reveals that the values vary between 30-40 km in the NSL region with deeper Moho below the Vindhyan basin. Further, the crustal models obtained from the constrained potential field modelling for two long transects across the NSL in the present study area revealed i) the absence of crustal underplating in the eastern part of NSL below Hirapur-Mandla region, ii) the presence of mid-crustal horst like structure below NSL in both the transects, iii) undulating Moho with higher density crustal rocks within the NSL compared to the surrounding areas. The modelled crustal structure and the analysis of Curie depth as well as heat flow maps of the study area, reveal that the NSL region was affected by repeated tectonic activities since the Proterozoic times, and the present-day tectonics of this belt is greatly influenced by the reactivation of pre-existing faults along the NSL.

Structure and geodynamic evolution of the lithosphere below Northwest Indian Shield: Constraints from geological, geochronological and multi-scale potential field modelling

The Northwest Indian shield (NWIS) comprises of Archean cratons such as the Bundelkhand (Bh.C), Marwar (MC) and Dharwar (DC), the intervening Proterozoic mobile belts, the Aravalli Delhi Fold Belt (ADFB), Narmada-Son Lineament (NSL) and the Vindhyan basin (VB), the Mesozoic Cambay (CR) and Kutch rift basin (KB) basins and the Saurashtra Continental Block (SCB). The region is covered by thick traps of Deccan Volcanic Province (DVP) thereby masking the geological structures. In this study, we carry out a seismically constrained multi-scale geopotential field interpretation along two long corridors that cut across major Precambrian terrains of the NWIS. The models reveal the Moho varying between 30 and 45 km and LAB between 120 and 180 km. The derived crustal architecture shows that i) the ADFB and NSL are bounded by deep crustal faults having denser crustal rocks, ii) shallow Moho below DVP and CR, iii) presence of thick underplated layer at the base of lower crust in the entire region indicating a strong magmatic imprint. Correlation of modelled lithosphere structure with the structural geological and geochronological data across different terrains of the region suggests that the localized thickening of lithosphere below the ADFB and NSL could be the imprint of paleo-subduction during Proterozoic period, whereas, the thin lithosphere observed below NWIS as a whole represents lithosphere delamination caused by two major LIP events such as 800 Ma Malani and 65 Ma Deccan events. Hence, the proposed evolutionary models across the Precambrian terranes adequately explain the geopotential observations with linkages to present-day lithosphere below NWIS.

Diagenesis, facies and palaeocurrent analysis of Upper Rewa Sandstone around Sagar, Central India

The stratigraphic surface represented by a major contact between the Archean Bundelkhand Granite and the extensive Proterozoic Vindhyan sediments is a regional basement cover unconformity. This crystalline–sedimentary interface reflects an intense weathering of continental crust during marine transgression. Three time-transgressive sand deposition events viz. Kaimur, Rewa and Bhander are mainly witnessed during the entire Vindhyan sedimentation. Stratigraphically, the Upper Rewa Sandstone comprises one of these events in the Vindhyan Basin. Considerable progress has been made in interpreting these sandstones as a function of entirely marine process to a combination of tidal–fluvio–eolian activities. All the results have so far been attained on the basis of sedimentary facies, provenance, palaeocurrent analysis, and some of petrography. A distinct differentiation between marine and fluvial components of the Upper Rewa Sandstone still remains uncertain. Here, we use diagenesis as a parameter for the first time along with facies and palaeocurrent analysis to acquire a clear comprehension of marine- and fluvial-dominated processes. The present study spans 27 square kilometer area covering 15 stratigraphic sections with a collection of 571 directional data from the facies specific sedimentary structures, and 28 samples obtained for the thin section analysis.The lower unit of the Upper Rewa Sandstone shows facies association typical of tidal environment, along with polymodal palaeocurrent. These rocks are well sorted and dominantly lithified by authigenic cement. Profuse development of a complex of syntaxial, passive pore fills, and grain replacive cements reflect normally pressured nature of the lower unit sandstones. The upper unit of the Upper Rewa Sandstone however, reveals a facies pattern resembling fluvial processes and unimodal palaeocurrent plot. They exhibit poor sorting, siliceous, and ferruginous matrix, and development of intense stylolites. Since, pressure solution is a dominant mode of lithification; the upper unit rocks therefore, are overpressured. Sand deposition event pertaining to the Upper Rewa Sandstone is found to comprise both marine and fluvial processes. Such a diagenesis based approach can be applied for marking a possible facies based unconformity between genetically different depositional units.

Soft-sediment deformation structures in the Mesoproterozoic Kaimur Sandstone, Vindhyan Supergroup (Central India), and their seismotectonic implications

The unequivocal identification of soft-sediment deformation structures (SSDS) is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary basins. This paper reports and discusses, for the first time, the occurrence of several cm- to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group (Vindhyan Supergroup), exposed at the Hanumandhara Hill of Chitrakoot-Satna border region, Madhya Pradesh State, India. The SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture, which are sandwiched between nearly horizontally undeformed sandstone beds. The SSDS consist of load structures (load casts, flame structures, pseudonodules and ball-and-pillow structures), contorted lamination, convolute lamination, boudins and pinch-and-swell structures, deformed cross-stratification, slump structures, clastic injections, fluid escape structures, and syn-sedimentary fractures/faults. The present study suggests that the formation of these SSDS is essentially related to a combination of processes (gravitational instability, liquefaction, fluidization, and fluid escape) predominantly induced by seismic shocks. In addition, the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh waves. Considering the observed types of SSDS, their lateral homogeneity and geographic distribution along with the geodynamic framework of the Vindhyan Basin, the whole area can be tentatively attributed to having experienced moderate- to high-magnitude (M ≥ 5) seismicity. The present study combined with earlier reports of seismically-induced SSDS, from other regionally disposed formations belonging to the Lower (e.g., Kajrahat Limestone, Chopan Porcellanite, Koldaha Shale, Rohtas Limestone, and Glauconitic Sandstone of the Semri Group) and Upper (e.g., Bhander Limestone of the Bhander Group) Vindhyan Supergroup, respectively, provides evidence for the constant regional-scale seismo–tectonic activity within the Paleo-Mesoproterozoic Vindhyan Basin. Importantly, this observation further suggests that the intracratonic basins can be active tectonically contrary to the earlier propositions.

Application of paleo-structural and seismic sequence stratigraphy analysis to determine the potential plays within the Proterozoic sequence of the Ganga Basin, India

Gas discovery in Nohta-2 well from Proterozoic Rohtas plays in Vindhyan Basin, south of Ganga Basin has been a significant lead to suggest that Proterozoic sediments underneath Ganga Basin could be prospective. With this in view, the Govt. of India (GOI) acquired 1350 LKM (Line kilometer) of 2D regional seismic lines to image the Proterozoic sediments for the first time within the basin under National Seismic Program (NSP). The present study is carried out to understand the paleo structures, the nature of the sedimentary sequences, and the trapping mechanism to further visualize the prospectivity of the Proterozoic sequence within the basin. The paleo-tectonic and seismic sequence stratigraphy analysis reveals that the Proterozoic sediments were deposited in the passive margin setting in shallow marine and tidal conditions with several progradations and retrogradation cycles. Precisely, it is noticed that the Proterozoic sediments experienced two stages of progradations and retrogradations. That was followed by a long non-depositional hiatus (>500 Ma) spanning from the Paleozoic to Mesozoic ages which led to a regional unconformity throughout the basin as well as other local unconformities and hydrocarbon traps within the Proterozoic sediments. Four giant structural traps (>300 km2) and one combination trap (>500 km2) are identified within Neo-Proterozoic to Meso-Proterozoic sequence and are expected to be prospective. However, with more exploration efforts and additional data, these traps may lead to a paradigm shift in exploration strategy and discoveries in near future within the basin.

Organic Matter (OM) Associated Uranium Mineralisation in Kaimur Group of Vindhyan Supergroup near Maha-Rampura, Gwalior District, Madhya Pradesh, India

Abstract The Proterozoic Vindhyan Supergroup overlying Bundelkhand Granite Complex (BGC) presents an ideal environment for exploration of uranium mineralisation. Recent exploratory drilling in Kaimur Group of sandstone overlying unconformably the basement Bundelkhand granite at Maha Rampura area has revealed a significant correlatable uranium mineralisation. The mineralisation hosted by subfeldspathic arenite with reddish/ greenish shale intercalations enriched with organic matter is delineated. The subfeldspathic arenite has a definite marker bed with 1-2 m thickness located ~ 30 m to 40 m above the unconformity. Organic matter (OM) is disseminated in subfeldspathic arenite and occurs within intergranular spaces as rounded globules. Uranium occurs within the subfeldspathic arenite as primary minerals i.e. uraninite and coffinite as well as in adsorbed form on organic matter and clay within the marker horizon. Significant correlatable uranium mineralisation with primary uranium minerals in Maha Rampura area thus opens up a broad exploration target in the entire Vindhyan Basin.

Mineralogy, Organic Richness and Macerated Microbial Studies of the Rohtasgarh Shales in the Vindhyan Basin, India: Implications for Gas Generation Potential

Abstract The Proterozoic black shales of Rohtas Subgroup in Vindhyan basin are analyzed to assess their hydrocarbon generation potential. A total of 50 core samples of shales and limestones were collected from borehole core of Rohtasgarh limestone in Amehta mine, Vindhyan basin located in Katni district, Madhya Pradesh. The petrographic analysis, X-Ray diffraction, rock eval pyrolysis and maceral studies were carried out on separated black shales from the carbonates. The study presents that the Rohtas Subgroup of Semri Group consists of greyish to black limestone, greyish to greyish black shales, calcareous shales, silicified shales, pyritic shales and dark black shales alterations with limestones. XRD study reveals the presence of quartz (23.4%), plagioclase feldspar (21.9%), siderite (10.9%), aragonite (2.93%), calcite(1.9%), hematite (4.23%), illite (1.27%), kaolinite (3.2%), pyrite (3.86%), dolomite (8.2%), chlorite (2.43%), gypsum (4.02%), albite (3.4%), potassium feldspar (1.9%) in the samples, where smectite is dominating clay and feldspar in the form of potassium and plagioclase feldspar is the chief constituent among the detrital framework grains. The total organic content (TOC) of the shale units ranges from 0.22 wt. % to 1.08 wt.%, whereas hydrogen index (HI) ranges from 11 to 90 mg HC/g TOC, oxygen index (OI) ranges from 1.08 to 31.82 mg CO2/gTOC, Tmax ranges from 431 to 525°C, production index (PI) ranges from 0.11-1.0. Unstructured organic matters are extracted through maceration techniques, which infer thermal maturity stages of the shales. The dark brown to black in colour of the studied palynomorphs extracted from the Rohtasgarh shales inferred strong thermal alternation of the source rock over geological time. High thermal alteration index (TAI) of Rohtasgarh shales (3.5) suggests the presence of post maturated organic matters with gas prone type III & IV kerogen. The organic richness, kerogen type, thermal maturity of Rohtasgarh limestone in the study area signify poor to fair hydrocarbon generation potential.

Shallow marine glauconitization during the Proterozoic in response to intrabasinal tectonics: A study from the Proterozoic Lower Bhander Sandstone, Central India

Glauconite forms authigenically by the replacement of quartz and feldspar substrates within the Precambrian Lower Bhander Sandstone (LBS) of the Vindhyan Basin. The glauconite exhibits consistently high K2O (7.08–8.62 wt%) and low to moderate TFe2O3 (6.20–18.5 wt%). The X-Ray Diffraction study reveals an evolved to highly evolved glauconitic mica structure. The deposition of mudstone-dominated LBS took place in a shallow marginal marine environment within a low gradient epeiric sea. The overall fining upward succession of the LBS comprises multi-storied, meter scale progradational cycles defined by red mudstone and sandstone–siltstone alternation in ascending order. The repetitive cycles indicate recurrent low-magnitude basin subsidence of the epeiric seafloor. Slump folds and slide planes, associated with the wedge-shaped mud pebble conglomerate, mark each episodes of basin subsidence. The glauconite occurs within sandstone and the sandy matrix of a wedge-shaped conglomerate at the base of a shallowing upward cycle which starts with a grey colored mudstone. The enrichment factors of redox-sensitive elements elucidate sub-oxic depositional condition during the glauconitization. The redox-sensitive element ratios (V/Cr, V/Sc) corroborates the sub-oxic depositional condition for the glauconitic interval and oxic environment for the encasing sediments. The formation of glauconite in the LBS corresponds to the deepening of the basin in response to the tectonic subsidence. The meter scale progradational cycles, recording the transition from suboxic to oxic conditions, corresponds to tectonically-induced deepening and subsequent filling. This study recognizes the significance of intrabasinal tectonics in facilitating suitable redox conditions for the glauconitization process within Proterozoic shallow epeiric sea deposit.

GIS based integration of multi-spectral remote sensing and morphostructural analysis for delineating potential areas of hydrocarbon exploration in Western Vindhyan Basin, India

The Chambal Valley forms the western part of the Proterozoic Vindhyan Basin that has been less studied and poorly explored from the hydrocarbon perspective than its eastern counterpart—the Son Valley Vindhyans. In the present manuscript, attempts have been made to use remote sensing and GIS (geographic information system) based analysis to focus on the northern part of Chambal Valley to decipher its tectonics and structural configuration, its tectonic relation with the Son Valley Vindhyans, Bundelkhand Massif and Ganga Basin. This study also assumes significance as it attempts to delineate potential lead areas for hydrocarbon exploration in Chambal Valley. As part of the study, a detailed spectral analysis based on image data sets is carried out to identify areas of microseeps as proxies of potential hydrocarbon accumulations. Also, a neotectonics-based geomorphic analysis is carried out to delineate a fault network and geomorphic highs that act as aliases to subsurface faults and structural highs. The results are subsequently validated by available geophysical data and extensive fieldwork, and suggest four structural trends in the Chambal Valley as striking NE-SW, E-W, NW-SE and N–S, of which the NW-SE trend is the oldest, followed by the NE-SW, E-W and N–S trends. A GIS-based analysis of the E-W trends indicates that these are probably manifestations of the westward continuity of E-W-trending shear zones developed in Bundelkhand massif within the basement of the Chambal Valley. Further remote sensing studies of the shear zone network exposed in the Bundelkhand massif indicate the pattern to be replicated on a larger scale in the morphostructural fault layout in the adjacent Ganga Basin, implying these shear zones may be continuing in the basement of Ganga Basin and controlling structures developed later, and consequently the different petroleum system elements in the basin. A dip data based structural analysis of the Chambal Valley describes a regional synform attributed with an almost vertical NW-SE-trending axial trace. This axial trace may be in continuity with the NE-SW-trending synformal axis of the Son Valley with its trajectory sympathetic to the southern boundary of the Bundelkhand massif and the Central Indian Tectonic Zone (CITZ) – Aravalli Delhi Fold Belt (ADFB) geometry. Finally, based on the integration of the results of spectral and morphostructural analysis, a number of potential areas of hydrocarbon exploration are demarcated in the study area.

Foreland Basin Geometry and Disposition of Major Thrust Faults as Proxies for Identification of Segmentation along the Himalayan Arc

Abstract Along-arc variation in the geometry of the décollement surface at a convergent margin is one of the significant parameters to assess the likely magnitude of a major/great earthquake. It is linked to the crustal/lithospheric structure and pre-existing tectonic fabric of the underthrusting plate. For the Himalayan collision belt, segmentation of the Indian lithosphere along the arc has been suggested based on seismological and GPS studies, and by analysis of topography and Bouguer gravity anomaly data. These studies, confined to the Himalaya-Tibet region, linked major segmentation boundaries to three transverse ridges in the Ganga basin. Since the formation of the Indo-Gangetic foreland basin is also controlled by the thermomechanical properties of the underthrusting Indian plate, in the present work, we study the Himalaya-foreland basin system for possible segmentation of the Indian lithosphere. We analyse the foreland basin width vis-à-vis the disposition of major thrust faults along several profiles cutting across the Himalayan arc to test a possible correlation between these two parameters. The results suggest a major segmentation boundary along the Indo-Nepal border in addition to other previously discussed segmentations coinciding with major transverse ridges in the Ganga basin. This segmentation boundary coincides with the Great Boundary fault separating the Aravalli Delhi fold belt (ADFB) from the Vindhyan basin further south. We infer a possible role of this boundary in limiting westward propagation of the rupture front of the 1505 paleo-seismic event and seismicity of the ADFB through coupling between the Himalayan collision belt and the intraplate Indian shield region.

Magneto-thermometric modeling of Central India: Implications for the thermal lithosphere

We estimated the Curie depth using magnetic anomalies in the tectonically complex central Indian shield. The modified centroid method for the scaling distribution of sources is applied to aeromagnetic data and satellite magnetic data (EMAG2) to estimate the Curie depths. We selected 80% overlapping with a window length of 300 × 300 km2 for Curie depth estimation. The estimated Curie depths are 22–46 km being shallower in the Bastar craton, northern end of the Aravalli-Delhi fold belt, and eastern part of Central Indian tectonic zone in the Deccan Volcanic Province. Deeper Curie depths are found in the eastern parts of the Aravalli-Delhi fold belt, Deccan Volcanic Province to the south of Tapti basin, parts of the Ganga and Vindhyan basins. The heat flow values estimated from the Curie depths vary from 30 to 90 mW/m2 being higher are in the northern part covering the Aravalli-Delhi fold belt and the Ganga basin and low heat flow values in the remaining study region. The computed thermal lithospheric thickness ranges 62–120 km, being 62 km thin in the Vindhyan basin, 68 km in the Aravalli-Delhi fold belt, and 73 km in the Bastar craton. We noticed a relatively thick thermal lithospheric thickness of 99 km beneath the foreland Ganga basin and 100 km in the Bundelkhand craton. The thermal lithosphere beneath the Deccan Volcanic Province is found to have a thickness ~ 120 km , which is interpreted as due to the rapid cooling of the lithosphere after Reúnion plume activity. Probably, the plume activities in the past could have modified the thermal lithospheric structure beneath central India. The upper mantle in the Deccan Volcanic Province to the south of the Tapti basin and the Aravalli-Delhi fold belt show magnetic character.

Geochemistry and hydrocarbon source rock potential of shales from the Palaeo-Mesoproterozoic Vindhyan Supergroup, central India

With increase in shale gas exploration, inorganic and organic geochemical investigations of shale have become extremely important. Here, we explore the six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from Son valley sector, Vindhyan Basin with an aim to understand provenance conditions, palaeoclimate, tectonic setting and hydrocarbon generation potential. Whole rock geochemistry indicates Vindhyan sediments derived from felsic source(s) except for Sirbu shale that indicates additional influx of mafic rocks with differentiated felsic source. A comparative study of Vindhyan shale rare earth elements (REEs) points to Mahakoshals and Chhotanagpur gneissic complex (CGC) as probable sediment provenance for Vindhyan sediments. CIA analysis, after necessary corrections for K-metasomatism, suggests evolution in weathering and palaeoclimate indicating a transformation from moderate weathering conditions with warm and humid climate during lower Vindhyan deposition to intense weathering conditions with hot and humid climate during upper Vindhyan deposition. Trace (La/Y vs. Sc/Cr) and REE analysis indicates passive margin setting for Vindhyan sediments whereas a wide range spanning passive to active continental margin setting is also inferred using (Th-Sc-Zr/10) and (Th–La-Sc) ternary diagrams. However, these tectonic discriminant diagrams lack in explaining rift- or sag-related origin of any intracratonic basin such as the Vindhyan Basin. The total organic carbon (TOC) content in Vindhyan shales ranges from 0.29% to 8.44%. The thermally liberated hydrocarbon (S1) values range from 0.01 to 0.18 mg HC/g rock (milligram hydrocarbon per gram of rock sample), whereas hydrocarbon from cracking of the kerogen (S2) shows values ranging from 0.04 to 0.47 mg HC/g rock. Based on modified Van Krevelen correlation (HI vs. Tmax) diagram, organic matter from Arangi and Bijaygarh shales is characterized as thermally mature, Type III kerogen of gas prone character indicating good to very good gas generation potential.

A combined geochemical, Nd, and stable Ca isotopic investigation of provenance, paleo-depositional setting and sub-basin connectivity of the Proterozoic Vindhyan Basin, India

Geochemical and isotopic investigation of Proterozoic clastic and chemical sedimentary rocks provide insights into surface conditions of the early Earth. The mid-Proterozoic Vindhyan Basin of central India, comprising ~5 km thick, mostly undeformed and unmetamorphosed clastic and chemical sediments, is one such archive which is exposed in two sub-basins, the Son Valley Vindhyan sub-basin in the east (SVV) and Chambal Valley Vindhyan sub-basin in the west (CVV). Geochemical and Nd isotopic compositions of siliciclastic sedimentary rocks from the CVV sub-basin are reported in order to understand the provenance of the Vindhyan sediments in this sub-basin and the results are compared with the provenance of the sediments exposed in the SVV sub-basin to evaluate whether the two sub-basins had shared a common provenance. Elemental ratios, such as Th/Co, La/Sc suggest that the clastic sedimentary rocks from the CVV have dominantly upper crustal silicic/felsic provenances and are broadly similar to those of equivalent stratigraphic horizons from the SVV. Initial Nd isotopic composition (εNd(t)) of the siliciclastic rocks from the Lower Vindhyans of the CVV, calculated at their respective times of deposition, suggest sediment derivation from the Banded Gneissic Complex, Berach Granitoids, 1.82 Ga continental arc granitoids of the Aravalli Range and the Hindoli Volcanics. In contrast, the εNd(t) values of the Upper Vindhyan siliciclastics suggest that the Delhi Belt granitoids were the primary source of detritus during the deposition of these sediments. Paleo-depositional environment and connectivity between the SVV and CVV sub-basins are evaluated using geochemical, radiogenic Nd, and stable Ca isotopic compositions of carbonates from both sub-basins. Non-redox sensitive REY anomalies and Y/Ho ratios of carbonates from the two sub-basins suggest deposition in an epeiric sea with limited connection to the open ocean. Neodymium isotopic compositions of the carbonate units suggest that the two sub-basins were connected during the deposition of both Lower and Upper Vindhyan sediments. Carbonates from both sub-basins record a significant shift towards more radiogenic Nd isotopic compositions around 1.6 Ga, possibly as a result of an Andean-type arc magmatism in near vicinity of the Son Valley sub-basin. The δ44/40Ca compositions of the SVV carbonates are typically lower than the CVV carbonates. This difference is likely due to greater freshwater input in the SVV sub-basin which is consistent with the existence of paleo-gradients in the Vindhyan Basin.

Petrology and geochemistry of mafic plugs associated with the Semri Group of the Vindhyan Supergroup in the eastern part of the Son valley, Central India: Implications for bimodal volcanism

The intrabasinal felsic pyroclastics and rhyolite in the lower part of Semri Group of Vindhyan Supergroup are intruded by 3–11 m thick mafic plugs. These mafic bodies intrude Kajrahat Limestone of Semri Group. Earlier studies pertaining to these dykes are restricted to petrography; however, geochemical data on these rocks are lacking. Ca‐plagioclase, augite, and enstatite‐bearing dolerites show sub‐alkaline nature with basaltic andesitic (52–56% SiO2) composition. They exhibit moderate incompatible trace elemental enrichment, characterized by enriched LREE and depleted HREE [(La/Yb)N = 3.5–5.7] contents akin to those reported from the intraplate continental rift‐related basalts. Moreover, high Ba, Th, U together with the low Nb, Ta, and Ti values suggests crustal contamination. Chondrite‐normalized REE patterns and trace element ratios when compared to continental rift basalts show similarity with them. Th/Ta and La/Yb discriminant diagram represents mixed sources and characterizes the occurrence in the sub‐continental lithosphere. High La/Nb, La/Ta ratios, and positive Eu anomaly indicate that the basalt was derived from a depleted mantle source but mixed with crustal components. It is further supported by the ratios of Yb/Ta, Nb/Ta, and Zr/Hf indicating crustal contamination. In this article, we report the petrological and geochemical characteristics for the bimodal volcanics in order to understand their magma source and implications on tectonic setting in the lower part of Vindhyan Basin.

Environmental issues in karst terrain: an example from Central India

In this paper, an attempt has been made to highlight the nature of karst in central India and evaluate possible effects of environmental degradation of groundwater due to indiscriminate disposal of various types of wastes into karst terrains without subjecting them to any treatment before disposal. Karst features associated with carbonate rocks of the Proterozoic Vindhyan basin in central India and environmental issues related to the same area’s groundwater resources are briefly given. Based on the process of formation, karst may be categorized as True karst (holo-karst) and (ii) Fluvial karst. On the other hand, based on the types of cover, karsts are classified into three types: (i) Covered karst, (ii) Soddy karst, and (iii) Buried karst. Three types of karst landforms identified in carbonates rocks of the Vindhyans are (i) Superficial landforms (Karren), produced mainly by solution action on the rock surfaces, (ii) Landforms due to fluvial erosion, and (iii) Underground landforms, i.e., Caves. In a particular hydrogeologic setting, the groundwater system consists of minor secondary porosity modified by solution activities. Accordingly, two types of groundwater flow systems (diffuse and conduit) occur in carbonate rocks. Due to karstification, limestones constitute the most productive aquifer in the area. It is noted that untreated municipal and industrial wastes are disposed of directly in surface water bodies and streams and associated sinkhole depressions in limestone terrain. Secondary openings being interconnected with each other gradually carry these pollutants to groundwater reservoirs in karst aquifers. The continued influx of pollutants to groundwater reservoirs through interconnected secondary voids would cause severe groundwater pollution in the long run and degrade the groundwater quality in karst aquifers for various usages.

Shales of Palaeo-Mesoproterozoic Vindhyan Basin, central India: insight into sedimentation dynamics of Proterozoic shelf

AbstractThe Vindhyan Supergroup represents the largest Proterozoic sedimentary basin fill in the Indian shield. In addition to some significant palaeobiological discoveries, the sedimentary sequence of the Vindhyan, particularly its argillaceous intervals, holds crucial information for our understanding of sedimentation dynamics in Proterozoic clastic shelves. Here we attempt an extensive, although not exhaustive, review of the physical characteristics of six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from the Son valley sector, Vindhyan Basin, augmented with new observations to unravel the status of current understanding in terms of palaeo-flow dynamics, shelf sedimentation processes and dispersal pattern, depositional cyclicity and basinal tectonics. The sedimentary attributes of Vindhyan shales reveal their deposition largely in relative bathymetry fluctuating from distal shoreface or inner shelf (near to fair-weather wave base) to distal shelf below storm wave base. More often than not, the Vindhyan shelf was storm-infested and the operation of both storm-generated return flow and Coriolis-force-guided geostrophic currents are documented from different stratigraphic intervals of argillaceous successions. The thick arenaceous intervals interrupting the deposits of the Koldaha, Rewa and Sirbu shales at multiple stratigraphic levels indicate the presence of a fan delta and braided fluvial system during intermittent regressive stands of sea level or event deposition during a sea-level highstand, respectively. Based on facies pattern and flow vectors, a rift-related half-graben model is inferred for Arangi and Koldaha shale and a low-gradient stable-shelf model with well-defined energy gradient is proposed for successions from Rampur shale onwards.

Innovative Energy Solutions-Shale Gas In India

Shale gas is a major domestic option for natural gas of a country where conventional gas reserves had been used up. It is entrapped in between shale formations, having low permeability that makes its commercial production extremely difficult. Major constituent is methane which is utilized for synthesizing Ammonia and Methanol. Natural Gas Liquids (NGLs) constituents such as Ethane, Propane and Butane are utilized for Ethylene synthesis. Ethylene synthesized by Shale gas is preferred over that of manufactured by Naphtha.CO2, N2 and H2S are small fraction non-hydrocarbon constituents. Production of shale gas had lowered the dependency of nations to Middle-east for their energy needs but shale production comes at a high cost of environment degradation. About 3% of extracted gas is being released in the atmosphere, fracturing of underlying rocks can induce small earthquakes and quick exhaustion of shale wells in comparison to conventional gas wells are major disadvantages. Fracking fluid being used for Hydraulic Fracking consists of large quantities of water, sand and chemicals. After the process, vital fractions of it left underground can possibly pollute underground water sources. A long term study of the process is still desired in order to reveal exact intricacies of Environment Contamination. A Shaft is drilled into the ground up to the depth of gas bearing layer Fracking fluid is then pumped using high performance pumps. Fluid mixture penetrates into the rock layer and produces innumerable tiny cracks. Water acts as solvent, sand holds up the opening, Chemicals condense water, kill off bacteria and dissolve minerals. Production of shale gas then begins. After the reserve is exhausted, some amount of fracking fluid is pumped in again and then the drill hole is sealed. A general observed fact is that in every hydrocarbon producing nation there is an equal likelihood regarding the presence of shales holding hydrocarbons. As published in the report of EIA, June 2013 amount of shale gas resources in India is 584 tcf and the technically recoverable amount is about 96 tcf (Cambay, Krishna-Godavari, Cauvery, Damodar Valley, Upper Assam, Pranhita-Godawari, Rajasthan and Vindhyan basins). Vital task before shale gas production includes the ultimate analysis of geological properties of shales in order to produce gas/oil from them. In this regard, government with the support of many private agencies had drilled several thousand wells (mainly in Cambay, KG and Cauvery basins).These wells had provided extensive data on extent, depth and nature of shale formations in sedimentary basins. However, a lot of work is still left to actually start commercial production of shale gas on Indian soil.

Pyrite Textures, Trace Elements and Sulfur Isotope Chemistry of Bijaigarh Shales, Vindhyan Basin, India and Their Implications

The Vindhyan Basin in central India preserves a thick (~5 km) sequence of sedimentary and lesser volcanic rocks that provide a valuable archive of a part of the Proterozoic (~1800–900 Ma) in India. Here, we present an analysis of key sedimentary pyrite textures and their trace element and sulfur isotope compositions in the Bijaigarh Shale (1210 ± 52 Ma) in the Vindhyan Supergroup, using reflected light microscopy, LA-ICP-MS and SHRIMP-SI, respectively. A variety of sedimentary pyrite textures (fine-grained disseminated to aggregates, framboids, lags, and possibly microbial pyrite textures) are observed reflecting quiet and strongly anoxic water column conditions punctuated by occasional high-energy events (storm incursions). Key redox sensitive or sensitive to oxidative weathering trace elements (Co, Ni, Zn, Mo, Se) and ratios of (Se/Co, Mo/Co, Zn/Co) measured in sedimentary pyrites from the Bijaigarh Shale are used to infer atmospheric redox conditions during its deposition. Most trace elements are depleted relative to Proterozoic mean values. Sulfur isotope compositions of pyrite, measured using SHRIMP-SI, show an increase in δ34S as we move up stratigraphy with positive δ34S values ranging from 5.9‰ (lower) to 26.08‰ (upper). We propose limited sulphate supply caused the pyrites to incorporate the heavier isotope. Overall, we interpret these low trace element signatures and heavy sulfur isotope compositions to indicate relatively suppressed oxidative weathering on land during the deposition of the Bijaigarh Shale.