Kaimur Group Research Articles

Drone-based Magnetics over Mechanized Diamond Mine in Panna District, Madhya Pradesh, India

A drone-based magnetic survey was conducted with a magnetic sensor for the first time in India over a mechanised diamond mine. The paper briefly describes the findings of the drone-based Magnetic surveys over the Majhgawan Diamond Mine in Panna District, Madhya Pradesh, India. The data was interpreted using the Geometrics interpretation software. The experiment showed a promising result in deciphering the lamproite pipe depicted by a magnetic high intruded into the Baghain sandstone of the Kaimur Group. From the total magnetic anomaly map, it can be observed that a high magnetic anomaly of about 27 nT in the central part of the pipe which forms a part of the near-circular anomalous zone, is associated with the diamond-bearing pipe and demarcates its boundary.

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.

Proterozoic basins of the Bundelkhand Craton, India: Correlations and significance in understanding the tectonic evolution

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 Ghats Orogeny phase II) and the Delhi Orogen (South Delhi Orogeny) at ∼1000-950 Ma closed the deposition of the Rewa Group and initiated deposition of the Bhander Group in the North Indian Block and the Sirohi Group in the Western Indian Block. The Pindwara Orogeny of ∼850 Ma in the Western Indian Block caused uplift of the North Indian Block and closed the deposition of the Bhander Group. The orogenic movements at ∼1500 Ma and ∼1100-950 Ma were associated with continental amalgamations along the western and southeastern margin of India, but did not involve any amalgamation in the central part of India, which was affected by reactivation/uplift of an older structural fabric.

Paleoproterozoic thick-skinned tectonics in the Central Indian Tectonic Zone: implications on the tectonic reconstructions of cratonic nuclei

ABSTRACT The Satpura Mountain Belt, or the Central Indian Tectonic Zone (CITZ), is a Paleoproterozoic mountain belt of Central India, with Mesoproterozoic and Neoproterozoic rejuvenation history. Structural studies carried out in the southern margin of this ancient orogenic belt have identified a two-phase evolution. The documentation of mapped fold interference of Type 2 ‘boomerang-shaped’ pattern and the spread of early lineations over the hinge area of second-generation folds provide an estimate of ~40-43° angle between the regional axial directions of the folds of the two orogenic episodes. The map patterns indicate the presence of basement-involved recumbent fold nappes placed above the sedimentary cover sequence. The identified décollement structure on the surface provides information regarding the deformation of the upper crust in ductile manner. The patterns of the deep crustal reflectors mapped through previous deep seismic reflection study interpreted during the present investigation brought out the thick-skinned deformation in the region as well as identification of crustal low-velocity zones of lower strength and a domal geometry of the lower crust. The regional thrusts are found to deform deeper crustal layers, one thrust affecting the crust-mantle boundary. The behaviours of the upper and lower crust in terms of rheological layering have been used to interpret the regional structural style of the lithosphere. The structural features of the region do not support the argument regarding the status of the Central Indian Shear as a suture, but indicate it to be the outermost emergent thrust towards the foreland side. The patterns of dip of the thrusts and thrust transport directions indicate a northward dip of the South Indian Block during the subduction stage and the position of the collisional suture of the Satpura orogen to the north of the Sausar belt. A tectonic model has been proposed here to explain the formation of the Satpura Mountain Belt or CITZ involving subduction-collision at ~2250 Ma, followed by erosion, stretching and basin development between 2100 and 1500 Ma. A collisional event in the eastern and western craton margins of India, at ~1500 Ma, caused the second uplift of the Satpura Mountain Belt and its northern margin, developing a temporal unconformity of ~300 Ma gap between the Semri and Kaimur Groups (Vindhyan Supergroup). A third event in the region at ~950 Ma was similar to the second event. No continental amalgamation took place along the CITZ during the tectonothermal events at ~1500 Ma and ~950 Ma; these involved reactivation of old thrusts and basal accretion which were the effect of far-field stresses emanating from the orogenic events at the eastern margin of the Bastar Craton and western margin of the Aravalli Craton.

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.

Geology, petrology, and geochemistry of the Mesoproterozoic Kaimur Group of rocks of the Vindhyan Supergroup, Eastern India: implications for depositional environment and sequence stratigraphy

Geology, petrology, and geochemistry of the Mesoproterozoic Kaimur Group of rocks of the Vindhyan Supergroup, Eastern India: implications for depositional environment and sequence stratigraphy

Gravity and magnetic surveys for kimberlite structures in Baghain and Rampura-Motwa, Panna Diamond Belt, Madhya Pradesh, India

In order to delineate the kimberlite bodies, gravity and magnetic surveys were undertaken in the Panna Diamond Belt, Madhya Pradesh, in Central Indian Diamond Province. The Panna Diamond Belt lies in the Baghain formations of Kaimur and Rewa group of rocks. The Bouguer anomaly map was based on a total of 259 gravity observations and the total intensity magnetic map was prepared based on 230 magnetic observations in Baghain and Kirwa in the Kaimur group of rocks, and Kitha and Rampura-Motwa regions in the Rewa group of rocks, both groups of rocks form part of the Vindhyan Super Group in the Panna Diamond Belt. The Bouguer gravity maps indicated a high gravity, while the magnetic maps indicated a bipolar nature of anomalies in this area. The Rampura-Motwa area also depicted a significant circular anomaly both in the gravity and magnetic maps in the south western region which belong to the Rewa group of rocks. The spectral density maps and Euler solutions for depth estimation of the probable kimberlitic pipes indicated depths between 60 and 120 m in the surveyed areas. These depths are well correlated with the recent discoveries as provided by drill logs (80 to 150 m depth) of the kimberlites in the Baghain sandstone formations of Kaimur and Rewa group of rocks. The present paper presents some of the probable kimberlitic pipes in this region, which had not been ascertained earlier. The modelled data allow us to confidently interpret the gravity and magnetic response and justify the use of these geophysical methods as successful tools for the exploration of kimberlite pipes in the area.

Molybdenum isotope and trace metal signals in an iron-rich Mesoproterozoic ocean: A snapshot from the Vindhyan Basin, India

Fundamental questions persist regarding the redox structure and trace metal content of the Mesoproterozoic oceans. Multiple lines of evidence suggest more widespread anoxia in the deep oceans compared to today, and iron speciation indicates that anoxia was largely accompanied by dissolved ferrous iron (ferruginous conditions) rather than free sulfide (euxinia). Still, exceptions exist—euxinic conditions have been reported from some ocean margin and epeiric sea settings, and oxic conditions were reported in one deeper water environment and are also known from shallow waters. Constraining the temporal evolution of Mesoproterozoic marine redox structure is critical because it likely governed redox-sensitive trace metal availability, which in turn played a significant role in marine diazotrophy and the evolution of early eukaryotes. Here, we present a new, multi-proxy geochemical dataset from the ~1.2 Ga Bijaygarh Shale (Kaimur Group, Vindhyan Basin, India) emphasizing total organic carbon, iron speciation, and trace metal concentrations, as well as sulfur, nitrogen, and molybdenum isotopes. This unit was deposited in an open shelf setting near or just below storm wave base. Taken together, our data provide a unique snapshot of a biologically important shallow shelf setting during the Mesoproterozoic Era, which includes: 1) locally ferruginous waters below the zone of wave mixing, 2) muted enrichment of trace metals sensitive to general anoxia (e.g., chromium) and variable enrichment of trace metals sensitive to euxinia (e.g., molybdenum and, to a lesser extent, vanadium), 3) general sulfate limitation, and 4) nitrogen fixation by molybdenum-nitrogenase and a dominantly anaerobic nitrogen cycle in offshore settings. Differential patterns of trace metal enrichment are consistent with data from other basins and suggest a largely anoxic ocean with limited euxinia during the Mesoproterozoic Era. Our new molybdenum isotope data—the first such data from unambiguously marine shales deposited between 1.4 and 0.75 Ga—record values up to +1.18 ± 0.12‰ that are analogous to data from other Mesoproterozoic shale units. Ultimately, this study provides a broad, multi-proxy perspective on the redox conditions that accompanied early eukaryotic evolution.

Integrated approach of lithofacies and granulometric analysis of the sediments of the Proterozoic Upper Kaimur Group of Vindhyan Supergroup, Son Valley, India: Palaeo‐environmental implications

Two major facies associations are identified in the Upper Kaimur Group of the Son Valley, namely, tidally influenced fluvial channel facies association and tidal sand flat association. Lithofacies supports the Dhandraul Sandstone as the product of a tidally‐influenced fluvial channel and the underlying Scarp Sandstone as a tidal sand flat, which endorse a tide‐dominated estuarine setting. Grain size analysis shows that most of the sandstone samples are medium‐ to coarse‐grained and only small fractions are of fine‐ and very fine‐grained categories. In general, sediments are moderately well sorted, near‐symmetrical to fine‐skewed and leptokurtic to mesokurtic in nature, suggesting deposition under fluctuating energy conditions in different geomorphic domains from a tidally‐influenced fluvial channel to beach settings. Bivariant plots combining the textural parameters imply that marine processes dominate over fluvial processes in the Upper Kaimur Group sediments. Cumulative curves and C–M plot suggest sediment transport mainly by saltation and bottom suspension processes under varying energy conditions.

Mo-Ni and organic carbon isotope signatures of the mid-late Mesoproterozoic oxygenation

This study performed a redox sensitive trace element (RSTE) and organic carbon isotope investigation on the shallow section of ~1.2 Ga Bijaigarh Shale, Kaimur Group, Vindhyan Supergroup. The results demonstrate that unlike the coeval deeper section, in which Mo and Ni concentrations are several-folds higher compared to the upper continental crust (UCC), the shallow section contains Mo and Ni equivalent to the upper continental crust (UCC). This spatially heterogeneous burial of Mo and Ni is very similar to the modern stratified basins i.e., Black Sea and Cariaco Basin, where Ni and Mo composition of the sediments underlying a shallow oxic water column is comparable to the UCC however, the deeper sediments underlying the anoxic/euxinic contains several folds-higher Mo and Ni compared to the UCC. Bulk precipitation of Mo in a hydrosphere is mainly controlled by sulphide present in the anoxic/euxinic layers of the water column, on the other hand, Ni precipitation is generally controlled by oxygenic primary productivity. Though the shallow section of the Bijaigarh Shale is depleted in Ni, a significant correlation between Ni and TOC is still relevant and indicates an oxygen-rich surface water layer for the respective palaeohydrosphere. Furthermore, δ13C-org values (between −32.0 and −30.4‰) from the shallow section suggests that the organic carbon exported into the sediments during the Bijaigarh Shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers.

Source rock composition of Kaimur Group siliciclastics from Vindhyan Supergroup, Central India: A response to thermal events associated with Bundelkhand Craton and Chhotanagpur Gneissic Complex at ~1.1 Ga

The Kaimur Group of the Vindhyan Supergroup has been divided into six Formations in Son valley sector, in Central part of India, i.e., Sasaram Sandstone, Ghurma Shale, Markundi Sandstone, Bijaigarh Shale, Mangesar Formation, and Dhandraul Sandstone. The comprehensive geochemical datasets for all the individual Formations of the Kaimur Group were generated in order to evaluate the source rock composition, weathering history, and provenance. The field observations, petrography, and geochemistry depict the deposition of the Kaimur sedimentary rocks in two cycles—the fining‐upward sequence from Sasaram to Markundi Sandstone, that was followed by the coarsening‐upward sequence from Bijaigarh shale to Dhandraul Sandstone. The petrography, geochemical classification, and A‐CN‐K plot depicts K‐metasomatism in siliciclastics of Kaimur Group. A‐CN‐K systematics and the CIA values (62–85) reveal that the source rocks of the Kaimur Group siliciclastics have suffered high degrees of chemical weathering under warm and humid climate. Zr/Sc vs. Th/Sc and Rb/Sr values depict zircon addition and sediment recycling. Ternary plots based on modal analysis and tectonic discrimination diagrams based on incompatible elements exhibit the deposition of Kaimur siliciclastics in the craton interior /passive margin (Bundelkhand Craton; BC) to recycled orogen (Chhotanagpur Gneissic Complex;CGC). The incompatible elemental ratios and Qm‐F‐Lt plots shows a fluctuation in provenance of the Kaimur Formations in the lower and upper part. The percentage contribution from the two sources was calculated using a simple arithmetic formulae [ Percentage contibution from a single source= Number of comparable ratios/ Total ratios*100]: Sasaram Sandstone = 82% BC + 18% CGC, Ghurma Shale = 76% BC + 24% CGC, Markundi Sandstone = 65% BC + 35% CGC, Bijaigarh Shale = 62% BC + 38% CGC, Mangesar Formation = 61% BC + 39% CGC, and Dhandraul Sandstone = 42% BC + 58% CGC. Tectonics of the hinterland supplying detritus played an important role in deciphering the provenance of Kaimur siliciclastics. The episodic crustal growth and thermal events taking place in Bundelkhand Craton at 1.1 Ga were witnessed by the emplacement of dykes, which led to the increased detrital input from the source (BC). Later on the upliftment of CGC towards the south during Satpura Orogeny‐II led to increase in input to the Formations of Kaimur Group. Petrological, geochemical signatures, and the evidences of change in paleocurrent direction from SSE–SSW to NW–NNW during Kaimur sedimentation strongly support the gradual shift of provenance from BC to CGC.

Significance of the tuffaceous beds associated with the Bijaigarh Shale of the Kaimur Group, Vindhyan Supergroup, Central India and their correlation with tuffs in other contemporaneous Proterozoic basins

Bijaigarh Formation is lithologically heterogeneous with grain size varying from fine to medium sand to clay. About ~1 m thick tuffaceous beds of rhyolitic to rhyodacitic nature, sandwiched between the Bijaigarh siliciclastics have been reported. We have attempted to distinguish the tuffaceous beds from the adjacent terrigenous sediments of Bijaigarh Shale on the basis of their field disposition, petrographic and geochemical characteristics. The tuffs are characterised by a relatively high content of LILE, HFSE and LREE as compared to Bijaigarh siliciclastics. They reflect their affinity to the felsic magmatic source. The geochemical signatures of the Bijaigarh tuff exhibit quite comparable characters to the contemporaneous (~1000 Ma) tuffs from other Proterozoic basins, viz., Chhattisgarh and Indravati. The extrabasinal sources for the deposition of the Bijaigarh tuff at ~1000 Ma can be inferred which can possibly be correlated with tectonothermal events of the Grenville orogeny. The integration of elemental compositions with mineralogical and textural observations makes possible the establishment of the tuffaceous beds as a stratigraphic marker in the Upper Vindhyan stratigraphy. This will have wider implications for the precise and reliable correlations of the Proterozoic basins of India.

Evolution of the Proterozoic Vindhyan Basin, Rajasthan, India: insights from geochemical provenance of siliciclastic sediments

ABSTRACTThe Vindhyan Basin of western India is a part of the largest Proterozoic sedimentary basin of the Indian subcontinent. Deposited in a largely shallow marine environment, the sedimentary sequence of the basin, known as the Vindhyan Supergroup, is believed to hold clues to our understanding of the evolution of life and climate during the Proterozoic. Inspite of multiple important paleobiological discoveries from these rocks, our knowledge about the development of the basin and responsible regional tectonics had remained rudimentary. Here, we propose a model for the evolutionary history of the Vindhyan Basin based on quantitative provenance analysis through geochemical and isotopic compositions of siliciclastic sediments. According to our model, the basin opened up in a foreland setting during an event that was contemporaneous with the amalgamation of the supercontinent Columbia. In the Lower Vindhyans, most of the sediments were derived from the basement gneisses (BGC-I & II) and a younger differentiated magmatic arc, whereas the >1.7 Ga rocks of the Aravalli and Delhi supergroups formed the source area for the Upper Vindhyans. In comparison to their counterparts in the eastern sector in the Son Valley, the Semri and Kaimur groups of the western sector had a relatively younger provenance; whereas, the Rewa and Bhander groups of both the sectors appear to have shared geochemically similar provenances. Unlike its counterpart in the eastern sector, the provenance of the sediments in the western sector had remained constant across the supposedly 400 million years break in sedimentation between the Lower and the Upper Vindhyans. However, a change in the provenance is observed during the transition from the Kaimur to Rewa group in the western sector which we infer to be a break in the deposition.

Recrystallization and Provenance History of the Upper Kaimur Group Siliciclastics, Son Valley, India: Coupled Petrographic and Fluid inclusion Proxy

Abstract The Mesoproterozoic Kaimur Group belonging to upper part of Vindhyan Supergroup, conformably overlies the carbonate sequence of Semri Group (Lower Vindhyan) in the Son Valley, central India. The Upper Kaimur Group consists of Dhandraul sandstone, Scarp sandstone and Bijaigarh shale. The detrital contents of the Dhandraul and Scarp sandstones are mainly composed of several varieties of quartz followed by feldspar, rock fragments, micas and heavy minerals. Fluid inclusion studies are carried out on the detrital and recrystallized quartz grains of the Dhandraul and Scarp sandstone to know about the fluid phases already present in the source rock and / or introduced in the recrystallisation process. Fluid micro-thermometry reveals the presence of two types of fluids: (i) bi-phase low saline aqueous inclusions, (ii) bi-phase high saline aqueous inclusion. These fluids were trapped during the development of grain and recrystallization processes. The salinity of these inclusions in the quartz grain is in the range of 5.7 to 13.4% suggests that initially there was good proportion of marine water during the initiation of sedimentation. The provenance of these rocks may be granite/metamorphic rocks of Mahakoshal Group and Chhotanagpur granite-gneisses and minor input from Bundelkhand granite complex.

Integrated Petrographic, Mineralogical, and Geochemical Study of the Upper Kaimur Group of Rocks, Son Valley, India: Implications for Provenance, Source Area Weathering and Tectonic Setting

ABSTRACT The upper Kaimur Group (UKG) of the Vindhyan Supergroup in central India, primarily consists of three rock types-Dhandraul sandstone, Scarp sandstone and Bijaigarh shale. The present study aims to reconstruct the parent rock assemblages, their tectonic provenance, mineralogy, weathering intensity, hydraulic sorting and depositional tectonic setting. Samples from the UKG rocks representing the Dhandraul sandstone, Scarp sandstone and Bijaigarh shale were studied using a combination of petrographic, mineralogical, and geochemical techniques. Texturally, medium to coarse grained UKG sandstones are mature and moderate to well sorted. Deficiency of feldspars in these sandstones indicates that the rocks are extensively recycled from distant sources. Their average modal composition for Scarp (avg. Qt99F0.2L0.8) and Dhandraul (avg. Qt99 F0.1L0.8) sandstones, classifies them as quartz arenite to sub-litharenite types, which is consistent with geochemical study. Major element concentrations revealed that sandstones have high SiO2, K2O > Na2O, and low Fe2O3, which are supported by the modal data. On the other hand, sandstone samples are enriched in most trace elements such as Ce, Sr, V, Sc and Zr and depleted in U and Th. The CIA values (43.17-76.48) of the UKG rocks indicate low to moderate weathering, either of the original source or during transport before deposition, which may have related to low-relief and humid climatic conditions in the source area. Further, petrographic and geochemical interpretations indicate that they are derived from craton interior to quartzose recycled sedimentary rocks and deposited in a passive continental margin. Therefore, granitic and low grade metamorphic rocks of Mahakoshal Group and Chotanagpur granite-gneiss, situated on the southern and south-eastern side of the Vindhyan basin are suggested as possible provenance for the UKG rocks.

Depositional environment and tectono-provenance of Upper Kaimur Group sandstones, Son Valley, Central India

The Mesoproterozoic Upper Kaimur Group consists of Bijaigarh Shale, Scarp Sandstone, and Dhandraul Sandstone. Based on the lithofacies data set, two major facies associations were identified, namely—tidal sand flat/sand bar facies association (TSFA) and tidally influenced fluvial channel facies/tidal channel facies association (TIFCFA). The Dhandraul Sandstone has been interpreted as a product of TIFCFA and the underlying Scarp Sandstone in TSFA which endorses a tidal dominated estuarine setting. Detrital modes of the Dhandraul and Scarp Sandstones fall in the quartz arenite to sub-litharenite types. Petrographical data suggest that the deposition of the Upper Kaimur Group sandstones took place in humid climate and was derived from mixed provenances. The sandstone composition suggests detritus from igneous rocks, metamorphic rocks, and recycled sedimentary rocks. The sandstone tectonic discrimination diagrams suggest that the provenances of the Upper Kaimur Group sandstones were continental block, recycled orogen, rifted continental margin to quartzose recycled tectonic regimes. It is envisaged that the Paleo- and Mesoproterozoic granite, granodiorite, gneiss, and metasedimentary rocks of Mahakoshal Group and Chotanagpur granite–gneiss present in the western and northwestern direction are the possible source rocks for the Upper Kaimur Group in the Son Valley.

Stratigraphy and Correlation of Mesoproterozoic Rocks Associated with Mohar Cauldron, Shivpuri District, Madhya Pradesh

Abstract: A circular structure, termed as cauldron of volcanic origin, was located near Mohar village in Shivpuri district (M.P.) in the year 2000. Subsequently, the same structure was called as Dhala structure of impact origin. There may be debate over the origin and evolution of this circular structure, but it is characterized by a unique lithological set-up within the Bundelkhand craton. The circular structure is defined by annular disposition of igneous and sedimentary rocks. This includes a set of felsic volcanic rocks and associated breccias named as Mohar Formation, exposed in the outer rim of the circular structure. The inner part of the circular structure has sedimentary sequence, termed as Dhala Formation. The field relations indicate that the Mohar and Dhala foarmations are younger than Bundelkhand granitoid complex but older than Kaimur Group. This period in Indian stratigraphy corresponds to Semri Group which consists of Porcellanite Formation, the rocks of which have formed due to deposition of volcanic ash. The geochronological data and field relations between different litho-units indicate that the Mohar volcanism which generated large volume of volcanic ash was a possible source for the formation of Porcellanite Formation. The deposition of sedimentary sequence in main Vindhyan basin was continued, whereas the volcanic activity in Mohar area continued till H ≈ 1.0 Ga. Since, acid volcanic activity has been reported in different parts of the world at H ≈ 1.0 Ga., it is possible that the Mohar acid volcanic activity is not an isolated event; instead it may be a part of global volcanic activities around H ≈ 1.0 Ga.

Petrofacies and tectonic setup of Kaimur Group of rocks, Son Valley, India

The paper embodies results of petrofacies and detrital mineralogical aspects of Scarp and Dhandraul sandstones of Upper Kaimur Group, Son Valley. These sandstones are medium to coarse grained and moderately to well sorted. The constituent mineral grains are subangular to subrounded. These sandstones consisting of various types of quartz, rock fragments, mica, feldspar and heavy minerals. The plots of petrofacies in Qt–F–L, Qm–F–Lt, Qp–Lv–Ls and Qm–P–K ternary diagrams reveal that these sandstones belong to the continental block, recycled orogen, rifted continental margin tectonic regime and maturity and stability of the source region. These sandstones were derived from Palaeoproterozoic and Mesoproterozoic granite, granodiorite, gneiss and metasedimentary rocks of Mahakoshal Group and Chotanagpur granite–gneiss. The sediment composition extensively modified during weathering warm humid climate at the surface area and weathering during transport before burial thereby providing mineralogical maturity to the Upper Kaimur Sandstone.

Geochemistry of Rohtas Limestone from Vindhyan Supergroup, Central India: Evidences of detrital input from felsic source

The Rohtas Limestone of Semri Group is conformably overlain by Lower Kaimur Group of Vindhyan Supergroup in the Son Valley, Central India. Lower Kaimur Group comprising Sasaram Sandstone, Ghurma Shale and Markundi Sandstone are dominantly quartz arenite in composition. While, Rohtas limestones are micritic carbonates with considerable input of detrital grains/rock fragments. Major oxide data shows that Lower Kaimur sandstone have SiO2 = 92 wt % while limestone exhibit SiO2 = 9.52 wt %, CaO = 47 wt %. Limestones exhibit Sr = 352 ppm, Zr = 20 ppm, while Lower Kaimur sandstones are enriched in Zr = 400 ppm, due to the presence of heavy minerals like zircon. The average limestone and sandstone shows a fractionated LREE pattern and a nearly flat HREE pattern with a small negative Eu anomaly. REE patterns and abundance of limestone are quite similar and comparable to sandstones from Lower Kaimur than to the pure micritic limestone. This indicates that the REE pattern and abundance of Rohtas limestone have been controlled by detrital components possibly derived from the similar source as that for Lower Kaimur sandstones. Apart from the similarity in the REE patterns of limestone and sandstone, the trace element ratios such as Ti/Zr, La/Sc, Th/Sc, Th/Co, Th/U, Zr/Sc, Ba/Sr, La/Th, La/Th, Zr/Hf, [La/Yb]N, [Ce/Yb]N, [Gd/Yb]N, [Sm/Nd]N, [La/Lu]N and Eu/Eu* strongly support the above inference. The ubiquitously comparable REE patterns and incompatible elemental ratios of Rohtas limestones and Lower Kaimur sandstones indicate their derivation from a similar felsic source. The geochemical signatures suggest that the Bundelkhand Gneissic Complex had significantly contributed sediments to the Vindhyan basin prior and during the deposition of Lower Kaimur Group.

Re–Os depositional age for black shales from the Kaimur Group, Upper Vindhyan, India

Proterozoic sedimentary deposits from the Vindhyan Supergroup, central India are excellent archives of paleo-environmental conditions. Meaningful interpretation of these geological signatures and their global correlation requires depositional age information for the sediments, data on which are limited for the Upper Vindhyan sediments. In this work, Re–Os isotopic study of the Bijaigarh shale, Kaimur Group from the Upper Vindhyan has been carried out to infer their depositional age and paleo-hydrological conditions. The Re–Os isochron for the Bijaigarh shale, a lagoonal deposit with an open ocean connection, provides a depositional age of 1210±52Ma (Model 3; MSWD=69; n=15; 2σ). This age for the Kaimur Group is younger by ~400Ma than the underlying Semri Group (age ~1600Ma), confirming existence of a long sedimentary hiatus between the two groups. The isochron-derived initial 187Os/188Os (Osi) ratio for these shales (~0.6) is higher than those reported for Mesoproterozoic marine shales (~0.3) from other global margins. Osi ratios of shales could be regulated by regional paleo-hydrological conditions; osmium mass balance calculations for the restricted basin of the Bijaigarh shale show that a minor increase in freshwater influx (as low as ~2.4% i.e. salinity change by ~0.8psu) to the euxinic deep water of the basin is sufficient to elevate Osi ratio from 0.3 (marine value) to ~0.6 (Osi ratio of the lagoonal shale). In contrast to lagoonal shales, the Osi ratios of marine shales seem to mimic the seawater 187Os/188Os during their deposition period. Compilation of marine Osi ratios shows coarse synchrony between temporal changes in Osi during the Proterozoic eon and the atmospheric oxygen level, pointing to the dominant role of oxidative continental weathering on paleo seawater 187Os/188Os ratio.