Son Valley Research Articles

Palaeoproterozoic rift-related alkaline magmatism in Bari area, Son valley, Central India

Earlier studies on Palaeoproterozoic (∼1800 Ma) alkaline (shoshonitic) rocks comprised of limited petrochemical data on the Bari syenite and other contiguous felsic rocks emplaced in anorogenic rift setting along the Son-Narmada North Fault (SNNF). Using new major and trace element data-sets, this study offers means of study of origin, source of magma, tectonic settings and geodynamic implications. The major oxide chemistry grouped Bari rocks into high alkali, but low CaO bearing peraluminous alkaline rocks. These rocks represent high abundance of HREE, Zr, Nb, Ga, Y, Eu, Ba and Sr. Primitive mantle normalized REE and trace elemental patterns correspond to A-type suite, suggesting origin of the magma mainly from the mantle. Significantly, anomalous Th/U and Rb/Cs values revealed crustal contamination of the melt, derived from partial melting of the mantle. Moreover, binary data plots between La vs. La/Sm and La vs. La/Yb are pointing towards crustal assimilation which was concomitant with the fractional crystallization of the mantle derived melt. Thus, crustal contamination coupled with the fractional crystallization of the melt mainly contributed to the formation of syenite melt. But, a high degree of partial melting of the lower crust was primarily responsible for the formation of Bari granite. The enrichment of incompatible elements in the syenite rocks suggests involvement of mantle metasomatism in their genesis. The magmatic processes related to the formation of syenite, lamprophyre, ultramafics, mafic and granite bodies were operative in the diverse magmatic realm and initiated earlier at the waning stage of the Mahakoshal orogeny and continental rifting, but magma emplaced later during Post-Mahakoshal orogeny and Pre-Vindhyan sedimentation that also in a rifted basement of the Bundelkhand craton at ∼1800 Ma during the amalgamation of the Columbian Supercontinent.

Spatial and temporal variation in NDVI and NDWI of the Ukhma River Basin, Central India

The present study is a reasonable step on quantitative approaches of water management and advancement of groundwater potential for watershed development of the Ukhma River Basin with the help of remote sensing and GIS techniques. The Ukhma River is one of the significant NW (north-west) flowing tributaries of the Tons River in Central India occupying a 745 sq km area within the Kaimur and Rewa Group of rocks in the Son valley sector. It originates from Ledari Village and joins the Tons River near Deokhar village, Satna District, Madhya Pradesh, Central India. In the present study variations in NDVI and NDWI of the Ukhma River Basin has been measured significantly from 2006-2019. The NDVI and NDWI provide turbidity estimations of the basin's vegetation cover and water resources. The change in NDVI and NDWI detection from 2006-2019 indicates that the area susceptible to erosivity increases the surface runoff reduces the infiltration rate.

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.

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.

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.

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.

Revisiting the boundary between the Lower and Upper Vindhyan, Son valley, India

The placement of the boundary between the Lower and the Upper Vindhyan in the Son valley, an unconformity, has long been at the centre of a raging debate. At the Bundelkhand sector, it is placed between the Rohtas Limestone and the Sasaram Sandstone (Lower Quartzite). On the other hand, in the Son valley sector, it is placed between the Bhagwar Shale and the Kaimur Formation. The recent study reveals the existence of ca. 12 m thick sandstone between the Bhagwar Shale and Rohtas Limestone, traced over 150 km in the Son valley sector. Based on in-depth facies constituents and facies tracts, this sandstone is an exact equivalent of the Sasaram Sandstone in the Bundelkhand sector. Its base is strongly erosional and limestone and chert clasts derived from the underlying Rohtas Limestone are abundantly present at the basal part of the sandstone and the unconformity between the Upper and Lower Vindhyan are likely to be present in between.

Drainage Pattern and its Bearing on Relative Active Tectonics of a Region: A Study in the Son Valley, Central India

ABSTRACT The paper emphasis the participation of different geomorphic parameters related to various characteristics of drainage in evaluation of active tectonics of an area. For the purpose, the morphotectonic evaluations of the Son valley, central India have been carried by involving various drainage related geomorphic indices viz., stream-gradient index (SL), hypsometric integral (HI), drainage basin asymmetry (AF), valley floor height and width ratio (Vf), transverse topographic symmetry factor (T), mountain front sinuosity (Smf), drainage basin shape (BS) and sinuosity index (SI) and relative rock strength (RRS) for classification of relative index of active tectonics (RIAT) in geographic information systems (GIS) environment to understand the role of active tectonics in geomorphologic evolution of the studied region. The established RIAT classes through field validations categorize the valley into four zones such as class 1- low activity ( RIAT < 2.7); class 2-moderate activity ( RIAT =2.7 < 2.99); class 3- high activity (RIAT=2.99 < 3.29); and class 4-very high activity (RIAT>3.29). The sub-dendritic, rectilinear and parallel linear drainage styles in RIAT classified basin reveal the traverse of a network of seventeen faults in association with two major faults namely Son-Narmada-North Fault (SNNF) and Son-Narmada South Fault (SNSF) in variable associations of rocks and multiple types of structural elements present in the Son valley. The signature of vertical upliftments may indicate the instability tectonic activities along the identified network of faults associated with SNNF and SNSF. Hence, the study suggests variable tectonically activeness of area in the Son valley.

Pothole: a unique geomorphological feature from the bedrocks of Ghaghghar River, Son valley, India

ABSTRACTIn this study, we report for the first time, the occurrence of pothole features and the processes of their development on the bedrocks of Ghaghghar River, Son valley, India. Pothole geometries were identified and measured from the middle reaches of Ghaghghar River, where it is flowing exclusively over the Rohtas limestone (a Meso-Proterozoic age) of Vindhyan Supergroup, near to the Gurma village. On the basis of field survey and remote sensing study, it has been ascertained that potholes developed in the river bed were only related to local geological and geomorphological conditions of a stream. They are mainly developed due to abrupt slope change along the river course and usually associated with intersect fractures, joints, and veins in the bedrock. The knick point of the river profile also confirms the abrupt slope change of the river in Gurma region. The river changes its course from E-W to N-S due to Markundi fault (ENE-WSW) occurring in the study area and causes the tectonic disturbances to support the development of potholes. The formations of potholes on bedrock of Ghaghghar River were generally governed by abrasion of rock fragments during high-flow regime. The geometrical dimensions of the potholes are controlled by the joints, fractures, and veins developed in bedrock of the river. The veins are typically calcitic in nature and the orientations of long axis of potholes are analogous to the trend direction of the vein. The collapse bedrocks suggest that a pothole can be formed within a short period, but cannot be fully developed and maintained for a long time in a strong incision of riverbed.

Provenance and Palaeoweathering Attributes of Proterozoic Rock Formations from the Son Valley, Central India

The characteristics of source rocks and weathering of Palaeoproterozoic phyllitic rock of Mahakoshal Group and Mesoproterozoic shales and siliciclastics of Vindhyan Supergroup exposed in Son Valley, Central India have been investigated by analyzing their chemical compositions. The investigations pertaining to the relationship between major-elements were carried out along Parshoi, Chitrangi, and Markundi areas of Son valley, Central, India. The studied rock strata have been classified into three categories namely phyllitic rocks, shales and sandstone. The A-CN-K ternary diagram, CIW, CIA, MIA, and ICV values indicate about the similar provenance or source rocks subjected to severe chemical weathering, under dry and hot-humid climates in a basic and acidic environment with changing lower to higher PCO2 of continental flora. Various geochemical discriminantts diagrams, elemental ratios suggest that rocks are derived from post-Archaean-Proterozoic igneous source. The igneous source was mainly granite with a minor contribution of granodioritic rock, in a passive margin setting. The sediments responsible for formation of shale and sandstones were most likely deposited in the interglacial period in between the Mesoproterozoic and Neoproterozoic glacial times. Compositionally the sandstones is distinctive of cratonic environments with their passive continental margin setting. However, the phyllities of Mahakoshal Group suggests their formation under lower weathering conditions in dry climatic conditions which were operating on more intermediate to basic igneous rocks with abundance of mafic minerals.

Explosive felsic volcanism at Palaeo-Mesoproterozoic boundary from Vindhyan Supergroup, Son Valley, Central India—Evidences of crustal contamination

Vindhyan basin witnessed a widespread explosive type of felsic volcanism at Palaeo-Mesoproterozoic boundary which is manifested as Chopan porcellanite shale. This is exposed as a linear belt along the Son valley in Central India. Porcellanite shale is pyroclastics deposit comprising strongly welded to unwelded ignimbrites. CIA values coupled with A–CN–K systematics provide strong evidence regarding their igneous origin and proximity of the source. The pyroclastics are rhyodacitic to rhyolitic in nature. The enriched LREE, LILE, depleted HFSE and incompatible element ratios such as Nb/Th, La/Sm and Zr/Nb indicate contamination and mixing between mantle-derived rocks and the average continental crust. Five distinct phases of volcanic activity have been identified based on field observations and petrological evidences. Pyroclastics at various stratigraphic levels indicate repeated occurrences of intrabasinal felsic volcanism, pointing to episodic extension, rifting and eruption over a period of time. The present studies have suggested that volcanic activity in Son valley and pyroclastic detritus resulted from a common chamber due to the rejuvenation and activation of deep seated faults like Son-Narmada lineament.

High Resolution Multispectral Satellite Data Interpretation and Limited Ground Checking: A Proxy for Geological Mapping and Uranium Exploration in Mahakoshal Fold Belt of Son Valley Area, Madhya Pradesh

Abstract: This research aims at integrating remote sensing data and field studies to prospect for uranium mineralisation in the Palaeoproterozoic Mahakoshal Group of rocks in the Son valley area, Central India. In present work, a revised geological map of Mahakoshal Fold Belt (MFB) bounded by Son-Narmada north fault (SNNF) and Son-Narmada south fault (SNSF) along Chorhut-Sidhi-Chitrangi sector falling in Sidhi, Rewa and Shahdol districts of Madhya Pradesh has been prepared based on interpretation of digitally enhanced satellite images. The satellite image interpretation is supported by limited field works, radioelemental measurements (eU, eTh and % K) of in-situ rocks by four channel Portable Gamma Ray Spectrometer (PGRS) and existing published geological maps of Geological Survey of India. In search for mineral potential areas, accurate and up-to-date geological maps are essential as it represent the most basic information for carrying out further exploration activities. However, available geological maps of MFB and sedimentary formations of Vindhayan Supergroup along SNNF and Chhotanagpur Granite Gneissic Complex (CGGC) and Gondwana Supergroup along SNSF available in public domain are discontinuous and multi-scaled. Optical bands of Landsat Enhanced Thematic Mapper Plus (ETM+) and Indian Remote Sensing (IRS) PAN of the study area were used in mapping lithological units, structural features and small intrusive bodies. Principal Component Analysis (PCA), Image Fusion, Linear Contrast Stretch, Histogram Equalisation and False Color Composite (FCC) of various band combination and ratio maps were performed in the digital image processing of geo-rectified satellite imageries. In analyzing and interpreting high resolution multi-spectral images, certain standard norms were employed to acquire information about litho-structural features such as topographic, geomorphic and tectonic facets. The main criteria are colour and tones, geomorphology, drainage patterns and vegetation anomalies. The processed Landsat ETM+ images were interpreted and classified to delineate detailed lithological units and structural features in order to update existing geological maps. To validate the prepared litho-structural map, ground survey was carried out along critical geological sections for checking the geological features like rocks, folds, faults, fractures and foliations. While comparing with the ground geological data to that obtained from the satellite imagery, it is observed that remote sensing interpreted litho-structural map is in a class with the ground observations. Various data sets such as unconformable geological contacts, fault breccias zone, lineaments and gamma ray spectrometric data (eU, eTh and % K) based on PGRS study were integrated and modelled using Geographical Information System (GIS) for identifying important prospective horizons for uranium mineralisation in the MFB of Son valley area. It is concluded that the revised large scale geological map is of practical use for not only for mapping of litho-structural architecture, but also in identifying potential areas for ‘vein –type’ uranium mineralisation along the structurally deformed zones of the SNNF, Asmi-Jiawan fault (AJF) and SNSF; and ‘unconformity- type’ of uranium mineralisation in the outliers of Jungel Group. The revised map and radiometric data acquired are useful in formulating exploration strategy for the ongoing uranium exploration in this area

Interpretation of Gravity Anomaly and Crustal Thickness Mapping of Narmada-Son Lineament in Central India

Abstract The Narmada–Son Lineament (NSL) is one of the major lineaments in central India which splits the Indian Peninsula into two parts. The area of study is seismically active and positioned in a multifaceted transition zone with complex geological setting. The gravity anomaly varies from ENE–WSW to NW-SE direction due to the upliftment of Mahakoshal rocks. This includes the presence of meta-volcanic and meta-sedimentary rocks existing along the upper part of the Narmada river as well as western part of the Son valley. This tectonic resettlement process causes changes in the Narmada and Son river courses. In this study, an attempt has been made to estimate the source depth locations and delineation of fault boundaries in parts of the Shahdol - Katni area of the Narmada-Son Lineament (NSL) using 3D Euler deconvolution and horizontal gradient analysis of gravity data. The estimated source depth solutions are projected in between 1 km to 5 km, however, in average, the depths are varying between 2 km to 3 km. The derived result may be useful for further detailed integrated geo-scientific study.

Grain size distribution analysis of sediments containing Younger Toba tephra from Ghoghara, Middle Son valley, India

The Toba super-eruption in northern Sumatra ∼74 ka was the largest eruption of the Quaternary period. Terrestrial deposits of distal Toba tephra have been found across the Indian subcontinent, although few localities have been adequately described with respect to stratigraphy and sedimentary history. This study provides the first detailed description of the Ghoghara 1A ash section, Middle Son Valley, India. The sediment analyses provide insights into the depositional processes in the valley before and after the initial period of ash deposition. Grain size distribution analysis of sediments from Ghoghara 1A indicates that 4–5 cm of primary air-fall ash was laid down at the time of the Toba super-eruption. This study has implications concerning previous isotopic studies in the Middle Son Valley, concluding that reconstructions demonstrative of dramatic ecological changes are questionable.

Geochemical signatures for the grain size variation in the siliciclastics of Kaimur Group, Vindhyan Supergroup from Markundi ghat, Sonbhadra district, (U.P.), India

The chemical composition of siliciclastics from Mesoproterozoic Kaimur Group, Vindhyan Supergroup have been investigated to determine and appraise the influence of the weathering, hydraulic sorting and recycling processes upon source rock signature. The studies pertaining to the relationship between major, trace and REE and the grain size variation were carried out along Markundi ghat section, Sonbhadra district, Son valley. Upper Kaimur Group has been divided into three principal formations-the uppermost-Dhandraul quartzites, Scarp sandstone and Bijaigarh shales. Petrographically, they range from quartz arenite, sublitharenite, subfeldspathic arenite to pyritiferous shale. The elemental enrichment, except for SiO2, is in the following order-Bijaigarh Shale > Scarp Sandstone ≫ Dhandraul Sandstone.

Evaluation of Hydrogeology of the Lower Son Valley Based on Remote Sensing Data

Remote sensing, one of the most important reconnaissance and feature identifying tools generally applied for surface and groundwater investigation, was used for water resources mapping for the lower Son Valley in this study. The mapping was done with the help of Indian Remote Sensing (IRS) satellite imagery IRS-LISS- 1-B1 for January 29, 1991 obtained during the day transit time. The area under study comprises adjoining parts of Uttar Pradesh and Bihar states of India and extends over the seven districts, namely Bhojpur, Rohtas, Patna, Jahanabad, Aurangabad, Ballia and Chapra. Geology of the study area is quite complex, tectonically disturbed and shows four major cycles of depositions after erosions during last one billion years (since Cretaceous). Two lineaments mapped by GSI (Geological Survey of India) in western side of river Son in the Bhojpur district can also be identified by the satellite imagery. In the present study, apart from these lineaments, two new lineaments have been investigated, which run almost parallel to river Ganga in northwest parts of the area in Ballia district. The lineaments may play a very vital role in groundwater monitoring in the area. The detailed study of geomorphology, vegetation and geology of the Lower Son valley on the basis of photo-interpretation techniques for surface features, drainage pattern and density, and drainage texture has been carried out to determine alluvial type, permeability, tributary, etc. These studies and Darcy velocity analysis show that the prospect of water is very good for entire lower Son valley. The Bhojpur district is most prospective for groundwater exploitation.

The Palaeolithic of the Middle Son valley, north-central India: Changes in hominin lithic technology and behaviour during the Upper Pleistocene

The Middle Son valley in north-central India preserves extensive Quaternary alluvial deposits. A long history of archaeological and geological research in the valley has resulted in the discovery of lithic assemblages ranging from Lower Palaeolithic to microlithic, a rich corpus of fossilised faunal remains, and ash deposits from the ∼74,000 year-old Toba supereruption. This paper reviews the chronology and stratigraphy of the valley’s Quaternary sediments, and presents a model that hypothesizes the temporal sequence of important lithic assemblages from excavated and surface contexts. Artefacts in these assemblages are analysed and changes in lithic technology through time are described; this evidence is used to propose shifts in hominin behaviour and demographic structure in this region during the Upper Pleistocene. Recognising gaps in our understanding of the Middle Son record, future avenues of research are recommended that will build upon previous research and address questions of palaeoanthropological significance. The Middle Son valley preserves a long and rich record of hominin occupation from all periods of the Palaeolithic that is rarely paralleled by other sites in India.

Trace element and Nd-isotopic evidence for sediment sources in the mid-Proterozoic Vindhyan Basin, central India

Ancient sediments reflect the compositions of old eroded continental crustal material and preserve geochemical signatures of paleo-tectonic and volcanic events. Geochemical study of such sediments provides insight into tectonic events that shaped the face of the Earth. Nd isotopes are best suited for such studies because rare earth elements (REE), specifically Sm and Nd are not fractionated during post-depositional processes such as erosion, transportation and diagenesis of organic-poor sediments and hence reflect the source composition of these sediments. Sedimentation in the Proterozoic Vindhyan Basin of central India with a ∼4 km thick succession of unmetamorphosed and mostly undeformed sediments lasted over 1000 Ma from ∼1630 Ma up to the Precambrian–Cambrian boundary. These sediments provide an ideal opportunity to study the evolution of ancient continental crust as well as the tectonic evolution of Peninsular India. The occurrence of porcellanites in the lower part of the basin indicates active volcanism during deposition of the Vindhyan sediments. These tuffs show large ion lithophile element (LILE) enrichment as well as depletions in Nb and Ta in primitive mantle-normalized plots, characteristic of an arc volcanic source. In combined trace element ratio plots, these volcanic rocks indicate mixing between mantle-derived melts and the continental crust and overlap with the composition of global arcs. Their initial ɛ Nd at 1630 Ma, ranging from −5.7 to −0.9, is similar to those observed in ‘Andean-type’ continental margin arcs. Trace element concentration patterns as well as Nd isotopic compositions of the clastic and non-clastic sediments of the Vindhyan Basin, from one of the type-localities of the Vindhyan stratigraphy in the Son valley, are vastly different from those of the Bundelkhand granite, which is the basement for these sediments, indicating that these granitic rocks were not a major source of sediments for the Vindhyan Basin. Our Nd isotopic study clearly indicates that sedimentation in the Vindhyan Basin, which lasted over ∼1 Ga, was not continuous. The boundaries between the Semri and Kaimur Groups as well as the Rewa and Bhander Groups are characterized by abrupt changes in the Nd isotopic compositions indicating changes in provenance, with sediments in the Kaimur and Bhander Groups being derived from more juvenile sources compared to the Semri and Rewa Groups, respectively. This inference is also supported by changes in T DM and f Sm/Nd for the sediments across these boundaries. The strikingly different trace element patterns of the Rewa Group sediments compared to the underlying Kaimur sediments indicates that sediment sources also changed across the Kaimur–Rewa boundary. Multiple changes in provenance in the Vindhyan sediments indicate that this basin was tectonically active during the entire span of sedimentation. While there is some uncertainty in determining the exact sources of sediments for the Vindhyan Basin, we argue on the basis of our geochemical, in particular Nd-isotopic ratios data, and available paleocurrent data that majority of the sediments were derived from a now-extinct Andean-type arc source in the south that resulted from a southerly dipping subduction prior to the collision of the Bhandara and Bundelkhand cratons. According to this reconstruction, the Vindhyan Basin was initiated as a foreland Basin after the collision of these two cratons.

Pattern and genesis of lineaments in and across son-Narmada lineament zone in a part of central India around Renukoot, district Sonbhadra, U.P.

Lineament studies are not only important for the interpretation of hidden architectures of the rocks but also can be applied to decipher the analysis of structural deformation patterns and tectonism of a region besides numerous other applications in the field of earth sciences. In central part of India, SonNarmada-Tapti (SONATA) is aprominent ENEWSW trending lineament zone which is bound by two major faults namely Son-Narmada South Fault (SNSF) and Son-Narmada-North Fault (SNNF), reaching upto Moho (Jain et a l . , 1995). The lineament zone extends about 1300 km from southern margin of Kathiawar peninsula in the west to the margins of the Vindhyan basin in the east. Throughout the geological history the zone has witnessed resurgent tectonism (Acharyya and Roy, 2000). According to Jain et al. (1995) and Acharyya and Roy (2000), there seems to have been no major post Vindhyan reactivation of SNNF, on the other hand, SNSF has witnessed protracted reactivation from Precambrian to Phanerozoic. In Precambrian rocks of the Son valley area lineaments have been observed in the Chhotanagpur Granite Gneiss Complex (CGGC), the Mahakoshal Group and the Vindhyan Supergroup (Semri and Kaimur Groups). The presence of lineaments in the Kaimur Group (Upper Vindhayan) attracted the attention of authors because the flat lying horizontally bedded sandstones of the Kaimur Group in the Son valley region are generally considered tectonically undeformed. Therefore, an attempt in the present work has been made to study the lineaments present in the southern part of Sonbhadra district Uttar Pradesh and adjoining regions of neighbouring states, where the Precambrian rocks of the Chhotanagpur Granite Gneiss Complex (CGGC), the Mahakoshal Group and the Semri and Kaimur Groups of Vindhyan Supergroup are exposed. The lineaments occurring across the SONATA zone of this region have been studied in context of their genesis. The study area (Fig. 1) is bound between latitudes 23 ~ 46' N to 24 ~ 42' N and longitudes 82 ~ 35' E to 83031' E forming parts of the Survey oflndia toposheet nos. 63L/14, L/15, L/16; 63 P/2, P/3, P/4, P/6, P/7, P/8; 641/13 and 64M/1 covering 7713 km 2 of area around Renukoot in the Sonbhadra district

Facies and depositional sequence of the Mesoproterozoic Rohtas Limestone: Eastern Son valley, Vindhyan basin

Paleogeography and process-related facies analysis of the shelf-originated Rohtas Limestone of early Mesoproterozoic age has been attempted. Lithology, structure, microfabric and TOC are the mainstay of facies classification. The Rohtas Limestone consists of seven facies; out of which the organic-rich black shale and the crinkle laminated limestone facies dominates the basal part, reveal distinctive fabric of microbial mat origin and represents outer shelf products. With gradual shoaling, the crinkle laminated limestone facies gains importance and locally turns into the nodular limestone facies through early diagenetic modification. The grey shale facies, poor in organic content, replaces them further upward. The other three facies, viz., the thinly laminated heterolithic facies, typified by close alternations between black shale and limestone, the planar laminated limestone facies and the wavy laminated limestone facies alternate with the grey shale facies, progressively dominating the top part of the succession. While the heterolithic facies records deposition across the paleochemocline, the planar laminated and the wavy laminated limestone facies document deposition in shallow agitated shelf. Confined between a condensed zone below and an unconformity above, the overall coarsening upward Rohtas Limestone records development of a HST.