Browsing by Author "U.K. Shukla"

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100 kyr sedimentary record of Marginal Gangetic Plain: Implications for forebulge tectonics
(Elsevier B.V., 2019) Rupa Ghosh; Pradeep Srivastava; U.K. Shukla; R.K. Sehgal; I.B. Singh
The Gangetic Foreland is a consequence of continent-continent collision and formation of the Himalayan thrust and fold belt. In the more distal part of the peripheral Gangetic foreland basin, the Late Quaternary sedimentary architecture analysis from 17 stratigraphic successions together with optically stimulated luminescence dating (OSL) divulge interaction of peripheral bulge tectonics and climate over the past ~100 kyr. These sections exhibit three sedimentary packages formed under different environmental conditions. Detailed vertical and lateral sedimentary architecture delineates nine lithofacies that are grouped into three facies associations, (i) flood plain facies association, (ii) channel facies association, and (iii) interfluve facies association. The basal package-I, >114 ka old, was deposited by sandy meandering channels and overlying to this with a hiatus of ~30 ka is package-II, ~80–54 ka, deposited by gravelly rivers. The sediments of both the packages-I, II are derived from rocks exposed in the peripheral bulge region. Overlain package- III, deposited by small meandering channels, consist of the sediments derived from the Himalaya. The results indicate that the duration of 80–54 ka was a period of forebulge uplift when gravelly fans prograded basinward. Below the fan sediments lies a peripheral bulge unconformity marked by regionally significant pedogenic horizon. This pedogenic horizon qualifies as to be termed as peripheral bulge uncomformity. After 54 ka, the fine Himalayan sediments onlap the cratonic sediments implying rather a stable forebulge tectonics coupled with fluctuating climatic conditions, occasionally bringing micaceous gray coloured sand-silt of Himalayan origin. © 2019 Elsevier B.V.
A case of normal regression with sea level transgression: Example from the Ganurgarh shale, Vindhyan basin, Maihar area, M.P., India
(Geological Society of India, 2014) Ali Adnan; U.K. Shukla
The Ganurgarh shale, a formation belonging to the Bhander Group of Vindhyan basin is investigated using field based detailed lithofacies and petrofacies analyses in order to interpret the depositional environment in a sequence stratigraphic context. Five major lithofacies have been recognized consisting of calcareous sandstones, laminated mudstones, rippled siltstones, red-grey shales and sandy limestones characterized by small to large-scale cross-bedding, ripple cross-lamination of wave and current origin, parallel lamination, low-angle horizontal bedding, flaser and lenticular bedding, mud-cracks, salt pseudomorphs, convolute bedding and load structures. The constituent lithofacies are recurring and grouped into three lithofacies associations where, the association A is composed of fining upwards and B with coarsening upwards cycles at the lower and middle levels of the succession respectively, are dominantly arenaceous whereas, the association C occurring at upper levels is fining upwards (FU) and becomes calcareous with meager representation of clastics. Petrographically, the section offers three main petrofacies viz., (a) sandstone- (b) siltstone- (c) sandy limestone-petrofacies. Lithofacies characters complimented with petrography show that deposition occurred within the shoreface (subtidal) to foreshore intertidal domain involving tidal flats with sub-environments ranging from intertidal to supratidal. However, lithofacies associations within the Ganurgarh shale of Maihar area represent a case of normal regression during sea level transgression. In the beginning, probably because of excessive sediment supply the sea level had a falling trend during an overall transgressive phase ultimately culminating into limestone sedimentation. © 2014, Geological Society of India.
Appraisal of groundwater potentiality of multilayer alluvial aquifers of the Varuna river basin, India, using two concurrent methods of MCDM
(Springer Science and Business Media B.V., 2021) Sangita Dey; U.K. Shukla; P. Mehrishi; R.K. Mall
An approach has been made in this study to delineate the groundwater potential zones of the Varuna river basin, Uttar Pradesh, India, using the analytical hierarchy process (AHP) and multi-influence factor (MIF) techniques. The present groundwater estimation exhibits an increase in the draft (10%) due to expansion in population, agricultural extent, and industrialization, which ultimately causes water table depletion. This backdrop justifies the need for this particular analysis in the multilayer aquifers of the central alluvial zone. The shallow aquifers are silty and unconfined, whereas the deeper aquifers are coarse, sandy-gravelly, and semi-confined. Basement faults and highs often control the thickness of aquifers in the subsurface. The study considered an integrated approach of AHP and MIF methods with remote sensing and GIS approaches. Various themes (land use/land cover (LULC), soil type, geology, elevation, slope, rainfall, normalized difference vegetation index (NDVI), drainage density, recharge rate, groundwater depth) determined by considering different conditioning factors and eventually employed for computation of groundwater potential index (GWPI) and classified for identifying the groundwater potential zones (GWPZ). Two methods applied to capture the results in a more tangible form as the AHP model works on building a pair-wise comparison matrix to relate conditioning factors to each other. Still, the MIF model considered interrelations among the conditioning factors. The GWPZ of the study area generates with overlay weighted sum method by integrating all thematic layers. The resulting groundwater potential index map is categorized into three groundwater potential zones, namely good, moderate, and poor. Ultimately, by constructing the receiver operating characteristic (ROC) curves for both the groundwater potential models, determine the efficiency of performances and the GWPZ map validated using yield data collected from wells scattered over the study area. The findings of the present paper have important implications for ensuring exploration and sustainability groundwater plans in that particular area. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Catastrophic environmental transition at the Permian-Triassic Neo-Tethyan margin of Gondwanaland: Geochemical, isotopic and sedimentological evidence in the Spiti Valley, India
(Elsevier Inc., 2016) Nilotpal Ghosh; Asish R. Basu; O.N. Bhargava; U.K. Shukla; Arundhuti Ghatak; Carmala N. Garzione; Arun D. Ahluwalia
Interpreting global consequences of the Permian-Triassic (P-Tr) extinction requires examination across paleogeographic realms of Pangaea. The Spiti Valley in India, remnant of the peri-Gondwanan shelf, preserved trails of this environmental catastrophe in the Neo-Tethys Ocean. We document new sedimentological observations and high-resolution trace element concentrations and carbon, oxygen, lead isotope data across the P-Tr boundary in Spiti. Framboidal pyrites, fossils and laminated lithology of the Late Permian shales indicate deeper anoxic depositional environment while δ13Corg excursions of 2.4‰ and 3.1‰ in Atargu and Guling outcrops, respectively, identify the P-Tr transition across a clayey, partly gypsiferous ferruginous layer. Sedimentological similarities of this layer to other Neo-Tethyan sections from Transcaucasia and Iran indicate subaqueous oxidation of shallow marine sediments on a regional scale. Light Rare Earth Element - enriched Late Permian shales with conspicuous Ce-Eu anomalies reflect their source from the adjacent Panjal Trap basalts (ca. 289 Ma) of Kashmir. Continental crustal Nb-Ta and Zr-Hf anomalies appear at the P-Tr boundary sediments, and prevail through the overlying Early Triassic carbonates. Original Pb isotope ratios, along with an increasing Pb abundance closer to the P-Tr boundary, distinguish the volcanic source of the Late Permian shales from the continental crustal siliciclastic signature of the Early Triassic carbonates. Our δ13Corg, trace element and Pb isotope record from Spiti indicate catastrophic changes in sediment sources and facies, with effects on carbon cycle and are consistent with an abrupt episode of marine regression and erosional forcing, also observed elsewhere along northern Gondwanaland. Simultaneous eruption of Siberian volcanics and bolide impacts in Parana basin of Brazil and elsewhere implicating impact-triggered volcanism, left catastrophic regional-global imprints on sea level, climate, marine anoxia and tectonic stability that connected the P-Tr crisis across terrestrial and marine realms worlwide. © 2015 International Association for Gondwana Research.
Contributions to the Proterozoic–Phanerozoic successions in the Himalaya: Status report 2020-2024
(Springer Nature, 2024) Om. N. Bhargava; Birendra P. Singh; U.K. Shukla; J. Ganai; P. Singh; Alono Thorie; Priyanka Mazumdar
82 publications by Indian geoscientists pertaining to the Proterozoic–Phanerozoic have come out during the last four years (2020–2024). Guide Books for the IGC 2020, GSI publication on the Precambrian sequences and a publication on the evolution of the Lesser Himalaya provide glimpses of regional geology. Other publications deal with geochemistry, sedimentology, isotope geology, palaeontology, and stratigraphy. A succinct summary of the publications is presented with short comments where necessary. © Indian National Science Academy 2024.
COUPLED ROLE OF CLIMATE AND TECTONICS IN THE DEPOSITION OF THE LATE QUATERNARY SEDIMENTARY SEQUENCE IN THE SOUTHERN MARGIN OF THE CENTRAL GANGA PLAIN, INDIA
(SEPM Society for Sedimentary Geology, 2024) Mukesh Yadav; U.K. Shukla; G.P. Gurumurthy; Sajid Ali; Kamlesh Kumar; Anupam Sharma
The Ganga Plain’s sedimentation is primarily controlled by Himalayan tectonics, variations in monsoon intensity, and glacier size. However, the significance of intrabasinal tectonics, which is an interplay of the Himalaya tectonics and basement tectonic configuration of the Ganga Plain, in comprehending the late Quaternary Ganga Plain sedimentation remains unclear. In this study, the sediment provenance and extent of weathering experienced by the sediments are studied using the mineralogical and geochemical (major, trace, and rare earth elements) composition of a sedimentary cliff sequence exposed at the Ramnagar locality near the cratonic peripheral bulge in the southern Ganga Plain. In the Ramnagar cliff sediment section, two sediment packages, designated SP-A and SP-B, are identified based on mineralogy, texture, and geochemistry. These packages of sediments show mild chemical weathering and distinct geochemical compositions. The lower part (SP-A) of the Ramnagar cliff section is characterized by higher contributions from mafic sources (pyroxene, feldspar, and mica as dominant minerals), while the upper part (SP-B) is predominately derived from felsic sources (mica and feldspar as dominant minerals), which are supplied via the peninsular and the Himalayan rivers, respectively. The southern part of the central Ganga Plain shows evidence of a shift in the sediment provenance from mafic to felsic source rock at 40 ka. This study demonstrates how weathering and sedimentation are controlled by both regional tectonics and climate in the southern margin of the central Ganga Plain.; The Director of the BSIP, Lucknow, is thanked by the authors for providing all infrastructural (SAIF) and administrative support to complete the assignment. This work is a part of MY’s doctoral thesis, supported by the funding received from the University Grants Commission (CSIR-UGC JRF fellowship, Roll No. 207693) and recorded as BSIP/RDCC/Publication no. 24/2024-25. The authors also thank Dr. Sheikh Nawaz Ali, Dr. Arvind Kumar Singh, Dr. Naimisha Vanik, Harshita Srivastava, Dr. Masud Kawsar, and Dr. Abhisek Kumar for their constructive suggestions that helped to make the manuscript better. UKS is thankful to the Head of the Department of Geology for providing the working facilities of the Department. We thank editor Dr. Kathleen Marsaglia, Associate Editor Dr. Alberto Resentini, and anonymous reviewers for constructive comments on our manuscript. Ó 2024, SEPM (Society for Sedimentary Geology)
Crocodilian nest in a late cretaceous sauropod hatchery from the type Lameta Ghat locality, Jabalpur, India
(Public Library of Science, 2015) Rahul Srivastava; Rajeev Patnaik; U.K. Shukla; Ashok Sahni
The well-known Late Cretaceous Lameta Ghat locality (Jabalpur, India) provides a window of opportunity to study a large stable, near shore sandy beach, which was widely used by sauropod dinosaurs as a hatchery. In this paper, we revisit the eggs and eggshell fragments previously assigned to lizards from this locality and reassign them to crocodylomorphs. Several features point to a crocodilian affinity, including a subspherical to ellipsoidal shape, smooth, uneven external surface, discrete trapezoid shaped shell units with wide top and narrow base, basal knobs and wedge shaped crystallites showing typical inverted triangular extinction under crossed nicols. The crocodylomorph eggshellmaterial presented in this paper adds to the skeletal data of these most probably Cretaceous-Eocene dryosaurid crocodiles. © 2015 Srivastava et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Decadal scale geomorphic changes and tributary confluences within the Ganga River valley in Varanasi region, Ganga Plain, India
(Elsevier Ltd, 2019) S. Singh; K. Prakash; U.K. Shukla
Allahabad to Buxar, the Ganga River shows distorted menders, huge meander cut-offs, ox-bow lakes, scroll bars and abandoned linear channel belts, all suggesting to a fault system-related tectonic control on the river. The confluence dynamics of northern tributaries Gomati and Varuna Rivers which have shifted progressively from north to south, and confluences of southern tributary Jirgo which shifted from south to north, further corroborate the view and also suggest that the presence of a NE-SW trending dextral strike slip fault having a gravity component. The Ganga River came close to Varanasi around 40 ka ago following a tectonic event that caused extensive liquefaction of the sediments due to a seismic pulse and upheaval in the area. Between 40 to 7ka, the Ganga River was freely oscillating within its valley when another tectonic event took place and the Ramnagar cliff was raised due to upheaval and channel incision along NE-SW trending fault. After 7ka, the Ramnagar cliff was degraded before it was inhabited by man at around 3800 years BP, which have been contemporaneous to antiquity of Varanasi. Based on available remote sensing data, the morphometry has shown that in 1972 active channel covered 12% area in Ganga River Valley and aerial extent remained 8% in 2010. The decrease of sand bar areas (14%–11%) in the studied stretch reflects the decrease in monsoon strength over the last four decades. However, the decline in the aerial extent of relict valley features, viz. meander scars, meander cut-offs and alluvial islands, is quite characteristic and may be related to sediment recycling by migrating channels present within the active channel belt and floodplain areas of the Ganga River. © 2018 Elsevier Ltd and INQUA
Deposition of the Upper Rewa Sandstone Formation of proterozoic Rewa group of the Vindhyan Basin, M.P., India: A Reappraisal
(Geological Society of India, 2015) Anju Verma; U.K. Shukla
The Upper Rewa Sandstone Formation of the Rewa Group in the Vindhyan basin is composed mainly of medium to very fine grained, iron pigmented arenaceous rocks variously interpreted as fluvial, marine or continental deposits. The Upper Rewa Sandstone Formation consists of channelized, laterally shifting sand bodies comprising 1-2 m thick fining upward (FU) sharply/erosionally based cycles. Each shoaling bar cycle is characterized by presence of large scale planar and trough cross-bedding, horizontal bedding showing primary parting lineation, wave and current ripples, herringbone cross-bedding and tidal bundles with double mud-drapes and indicates marine environment of deposition and rule out the possibility of continental sedimentation. However, channelized nature of sand bodies composed of shoaling bar cycles with signatures of wave modification and exposure in the lower part of the succession and well developed horizontally bedded lithofacies showing primary parting lineation and well sorted character of sandstones in the upper part of the succession may imply deposition under subtidal to intertidal setting in estuarine to bordering beach environments. The palaeocurrent study shows polymodal to bimodal and unimodal palaeocurrent patterns. The dominant polymodal palaeocurrent patterns with temporal trends directed towards NW, N and SW also corroborate marine origin and sediment dispersal under combined action of wave and currents. Petrographically, sandstone is quartzarenite and consists of mostly monocrystalline quartz, feldspar, mica, rock-fragments and heavy minerals such as hypersthene, zircon, hornblende, tourmaline, rutile, augite, kyanite and andalusite indicating sediment contribution from mixed sedimentary/metamorphic and igneous source terrain. Qm-F-Lt and Qt-F-Lt plots reveal that the Upper Rewa Sandstone Formation shows continental block province with stable craton (C) and in uplifted basement (B) where C>B. © 2015, Geological Society of India.
Discovery of Elephas cf. namadicus from the late Pleistocene strata of Marginal Ganga Plain
(Geological Society of India, 2016) Rupa Ghosh; R.K. Sehgal; Pradeep Srivastava; U.K. Shukla; A.C. Nanda; D.S. Singh
We describe an elephant skull recovered from a cliff section of Dhasan river of Marginal Ganga Plain. The dental morphology and cranial features of the skull have been compared with the known species of Elephas from the Indian subcontinent. Although it shows very near resemblance to Elephas namadicus, but being an isolated specimen its specific identity cannot be proclaimed with certainty. As such, the specimen is provisionally referred as E. cf. namadicus. The Optically Stimulated Luminescence ages place this find at ~56 ka BP. This is the first chronologically well constrained report of E. cf. namadicus from the Ganga Plain. © 2016, Geological Society of India.
Facies and genetic elements within the Late Miocene Middle Siwalik of the Himalayan foreland basin, India: A response of fan-building processes
(Elsevier B.V., 2023) Tanuja Deopa; U.K. Shukla; Bijendra Pathak
The Himalayan foreland basin originated through the India–Asia continent–continent collision driven by downward flexing of the Indian plate. It forms an ideal assemblage to delineate the role of process-controlled sedimentary fill in basin evolution. This paper provides the first comprehensive account of the lithofacies associations and architecture of the Middle Siwalik succession of the Himalayan foreland basin in the south-central Himachal Pradesh sector, India through detailed sedimentological analysis. Eight lithofacies form three distinct sand, gravel, and silt-mudstone lithofacies associations pertaining to specific depositional environments. Architectural elements have been defined together with bounding surfaces separating them. Sedimentological investigations reveal that the Middle Siwalik sequence represents a flash flood dominated piedmont fan and proximal to middle megafan. The fan expansion cycles indicate tectono-climatically controlled sedimentation in the Middle Siwalik foreland basin. Frequent flooding and a high sedimentation rate were influenced by the tectonic uplift along the reactivated thrusts in the hinterland coupled with phases of monsoonal intensification. © 2023 Elsevier B.V.
Flood Susceptibility Modeling in a Subtropical Humid Low-Relief Alluvial Plain Environment: Application of Novel Ensemble Machine Learning Approach
(Frontiers Media S.A., 2021) Manish Pandey; Aman Arora; Alireza Arabameri; Romulus Costache; Naveen Kumar; Varun Narayan Mishra; Hoang Nguyen; Jagriti Mishra; Masood Ahsan Siddiqui; Yogesh Ray; Sangeeta Soni; U.K. Shukla
This study has developed a new ensemble model and tested another ensemble model for flood susceptibility mapping in the Middle Ganga Plain (MGP). The results of these two models have been quantitatively compared for performance analysis in zoning flood susceptible areas of low altitudinal range, humid subtropical fluvial floodplain environment of the Middle Ganga Plain (MGP). This part of the MGP, which is in the central Ganga River Basin (GRB), is experiencing worse floods in the changing climatic scenario causing an increased level of loss of life and property. The MGP experiencing monsoonal subtropical humid climate, active tectonics induced ground subsidence, increasing population, and shifting landuse/landcover trends and pattern, is the best natural laboratory to test all the susceptibility prediction genre of models to achieve the choice of best performing model with the constant number of input parameters for this type of topoclimatic environmental setting. This will help in achieving the goal of model universality, i.e., finding out the best performing susceptibility prediction model for this type of topoclimatic setting with the similar number and type of input variables. Based on the highly accurate flood inventory and using 12 flood predictors (FPs) (selected using field experience of the study area and literature survey), two machine learning (ML) ensemble models developed by bagging frequency ratio (FR) and evidential belief function (EBF) with classification and regression tree (CART), CART-FR and CART-EBF, were applied for flood susceptibility zonation mapping. Flood and non-flood points randomly generated using flood inventory have been apportioned in 70:30 ratio for training and validation of the ensembles. Based on the evaluation performance using threshold-independent evaluation statistic, area under receiver operating characteristic (AUROC) curve, 14 threshold-dependent evaluation metrices, and seed cell area index (SCAI) meant for assessing different aspects of ensembles, the study suggests that CART-EBF (AUCSR = 0.843; AUCPR = 0.819) was a better performant than CART-FR (AUCSR = 0.828; AUCPR = 0.802). The variability in performances of these novel-advanced ensembles and their comparison with results of other published models espouse the need of testing these as well as other genres of susceptibility models in other topoclimatic environments also. Results of this study are important for natural hazard managers and can be used to compute the damages through risk analysis. Copyright © 2021 Pandey, Arora, Arabameri, Costache, Kumar, Mishra, Nguyen, Mishra, Siddiqui, Ray, Soni and Shukla.
Formation of paleovalleys in the Central Himalaya during valley aggradation
(Elsevier Ltd, 2015) Shipra Chaudhary; U.K. Shukla; Y.P. Sundriyal; Pradeep Srivastava; Poonam Jalal
The formation of paleovalleys in mountainous regions is considered to result from extreme events such as landslides and glacial or landslide lake outburst floods. According to IPCC (2012) the extreme events are rarest of the rare weather/climatic events when the climate/weather variable is significantly above or below the defined threshold value. The present study suggests that paleovalleys can also form during years long periods of valley aggradation. A series of paleovalleys thus formed runs parallel to the present river course. In this study, we suggest that paleovalleys in the Alaknanda valley of the Central Himalaya have formed in two ways: 1) major valley aggradation and 2) local events of landsliding and lake breaching. Most of the paleovalleys in the Alaknanda valley formed during a major valley aggradation phase (between 15 and 8ka). Paleovalleys formed due to local landsliding also formed around 8ka. Local landslides were triggered due to high rainfall in lower valley reaches during unstable climatic conditions. Therefore, the formation of paleovalleys both by regional and local mode within 15-8ka indicates that the valley was receiving excess sediment from upper catchment as well as from lower reaches during this period. This phase of excess sediment supply and valley aggradation coincides well with post glacial climatic amelioration. Therefore the study underlines the role of climate in the time scales of 103 years in shaping the landscape of an active mountain like the Himalaya. The role of other landscape changing agencies such as tectonics and erosion is not accounted in the present study. © 2015 Elsevier Ltd and INQUA.
Heterolithic Lower Rewa Sandstone of the Neoproterozoic Rewa Group, Vindhyan Basin, U. P., India: An example of tidal point bar
(Elsevier B.V., 2020) Anju Verma; U.K. Shukla
The Lower Rewa Sandstone of the Rewa Group exposed in Drummondganj ghat area is about 15 m thick; it shows well developed features of tidal and wave origin. The sandstone succession characterized by Inclined Heterolithic Strata (IHS) is composed of three lithofacies associations namely, i) Sandstone lithofacies association (A), ii) Siltstone lithofacies association (B) and iii) Shale lithofacies association (C). These three lithofacies associations are repetitive and signify vertically stacked parasequences, which are further divisible into smaller hemicycles showing fining upward in terms of grains size and lithology. The studied section is characterized by heterolithic facies, lateral accretion elements (LA surfaces) with tide generated features such as cross-beddings with mudstone drapes, lenticular and wavy bedding, often of wave origin, suggesting a tidal point bar of a sinuous estuarine channel formed along coast line having momentous tidal action, superimposed by significant wave action. The upper part of the section, characterized by erosionally based cross-bedded sand-bodies with occasional mudstone drapes and current modified wave ripples, indicates translation of river-dominated inner part of an estuarine channel over the mixed-energy zone of the estuary in the sense of Dalrymple et al. (1992). The complete Lower Rewa Sandstone represents a 3rd order Highstand Systems Tract (HST). Palaeocurrent pattern is polymodal suggesting subtidal to intertidal sedimentation whereby sediment was moved mainly by tidal action with intermittent wave activity. Petrographic study reveals that the fine to very-fine grained sandstone is quartzarenite, which has been derived from a stable cratonic uplifted basement. © 2020 Elsevier B.V.
High-resolution climatic (monsoonal) variability reconstructed from a continuous ~2700-year sediment record from Northwest Himalaya (Ladakh)
(SAGE Publications Ltd, 2020) Choudhurimayum Pankaj Sharma; Suman Lata Rawat; Pradeep Srivastava; Narendra K Meena; Rajesh Agnihotri; Anil Kumar; Poonam Chahal; S.K.S. Gahlaud; U.K. Shukla
A chronologically well-constrained sedimentary archive from Upshi (Ladakh) was studied using a multi-proxy approach namely palynology, environmental magnetism, total organic carbon (TOC), total nitrogen (TN), stable isotopes of carbon and nitrogen providing a continuous vegetation, and paleoenvironmental history spanning the last ~2700 years with a temporal resolution of ~43 years. Pollen assemblage shows non-arboreal pollen (NAP) and non-pollen palynomorph (NPP) were dominant around the Upshi from ~2646 to 2431 cal. yr BP, indicating warmer conditions. Arboreal pollen (AP) and NAP gradually increased from 2431 to 1860 cal. yr BP in the study area, under warm and wet conditions, corresponding to the Roman Warm Period (RWP). This phase also witnessed enhanced sediment δ15N and χlf values. From ~1860 to ~1154 cal. yr BP increased Chenopodiaceae/Amaranthaceae and substantial spread of NPP suggest decreased temperature and prevalence of cold-dry climate. This period also records declining trends of χlf, δ15N, δ13Corg, TOC, and TN contents. From ~1154 to 293 cal. yr BP, the vegetation type reversed to mixed conifer and broad-leaved forest with significant increase in herbaceous taxa, rising δ15N, δ13Corg, TOC, and TN suggesting warm and wet conditions in the study area. This period broadly corresponds to the ‘Medieval Warm Period’ (MWP). Among all the proxies employed, depth profiles of TOC and TN (wt%) appear to respond best against external climate forcing showing remarkable correlation(s) with residual Δ14C in atmosphere, indicating dominance of intrinsic solar variability on regional climate/environment. The reconstructed recorded is well connected with established historical events and cultural activities of the Eurasian region. © The Author(s) 2019.
Hydrogeochemistry for the assessment of groundwater quality in Varanasi: A fast-urbanizing center in Uttar Pradesh, India
(2011) Nandimandalam Janardhana Raju; U.K. Shukla; Prahlad Ram
The hydrogeochemical parameters for groundwater samples of the Varanasi area, a fast-urbanizing region in India, were studied to evaluate the major ion chemistry, weathering and solute acquisition processes controlling water composition, and suitability of water quality for domestic and irrigation uses. Sixty-eight groundwater samples were collected randomly from dug wells and hand pumps in the urban Varanasi area and analyzed for various chemical parameters. Geologically, the study area comprises Quaternary alluvium made up of an alternating succession of clay, silty clay, and sand deposits. The Total dissolved solids classification reveals that except two locations, the groundwater samples are desirable for drinking, and all are useful for irrigation purposes. The cationic and anionic concentrations indicated that the majority of the groundwater samples belong to the order of Na > Ca > Mg > K and HCO3 > Cl > SO4 types, respectively. Geochemical classification of groundwater based on the Chadha rectangular diagram shows that the majority (81%) of groundwater samples belong to the calcium-bicarbonate type. The HCO3/ (HCO3 + SO 4) ratio (0.87) indicates mostly carbonic acid weathering process due to presence of kankar carbonate mixed with clay/fine sand. The high nitrate concentration (>45 mg/l) of about 18% of the groundwater samples may be due to the local domestic sewage, leakage of septic tanks, and improper management of sanitary landfills. In general, the calculated values of sodium adsorption ratio, percent sodium, residual sodium carbonate, and permeability index indicate good to permissible use of water for irrigation, and only a few locations demand remedial measures for better crop yields. © 2010 Springer Science+Business Media B.V.
Lithofacies of transgressive–regressive sequence on a carbonate ramp in Vindhyan basin (Proterozoic): a case of tidal-flat origin from central India
(Springer Verlag, 2015) Ali Adnan; U.K. Shukla; A. Verma; T. Shukla
Palaeoenvironment of late Proterozoic carbonate deposits of Vindhyan basin of central India has been studied using lithofacies analysis, petrographical character and sediment dispersal patterns. Based on field parameters, 12 lithofacies were identified from five sections. For environmental interpretation, these lithofacies have been grouped into two major lithofacies associations namely a lower association A comprising reefal lithofacies, algal lithofacies, oolitic-intraclastic lithofacies, stromatolitic limestone lithofacies and an upper lithofacies association B, which includes nodular limestone lithofacies, large-scale planar cross-bedded lithofacies, parallel and ripple cross-laminated lithofacies, lenticular and flaser bedded lithofacies, shaly limestone lithofacies, synaeresis cracked lithofacies, deformed limestone lithofacies and finally, channelized and sandy limestone lithofacies. Reefal lithofacies and oolitic-intraclastic lithofacies were deposited under subtidal conditions. Synaeresis cracked lithofacies, lenticular and flaser bedded lithofacies, channelized and sandy limestone lithofacies were deposited under intertidal conditions whereas stromatolitic limestone lithofacies deposition ranged between subtidal to intertidal domains. Lithofacies character of the rock succession as well as the microfacies associations recognized petrographically indicate that the depositional environment belongs to platform interior with restricted circulation to marginal sand shoals in a carbonate ramp setting. Due to calcium-carbonate-saturated water, the diagenesis took place in stagnant marine phreatic environment where little compaction occurred, with abundant micrite as primary groundmass, and rapid cementation by calcite took place. With palaeocurrent current direction towards south and azimuthal dispersion of 270°, a pattern akin to a marine system is corroborated. © 2014, Saudi Society for Geosciences.
Lizard eggs from Upper Cretaceous Lameta Formation of Jabalpur, central India, with interpretation of depositional environments of the nest-bearing horizon
(2008) U.K. Shukla; Rahul Srivastava
A nest with eleven relatively large-sized eggs of lacertilian affinity has been recovered from the Lower Limestone horizon exposed at the type section of the Lameta Formation, Jabalpur (Madhya Pradesh, India). Morpho-structurally, the eggs probably represent a new family as they share common features with the eggs of the living varanid lizard Varanus indicus and a shell microstructure described for geckonids. The close association of a lizard nest and titanosaurid (Sauropoda) eggs raises interesting questions regarding the egg-laying strategies of these differently-sized reptiles. Sedimentological data suggest that the Lower Limestone of Lameta Ghat was deposited in an alkaline lagoon that was connected to a marine embayment by channels. The massive limestone, sandy limestone, and calcareous sandstone lithofacies forming coarsening upward sequence represents sedimentation from deeper to marginal parts of the lagoon that were densely vegetated. Pre-burial meteoric diagenesis of the sediments indicates humid climate. Such conditions might have provided a suitable habitat supporting a large variety of terrestrial life. © 2008 Elsevier Ltd. All rights reserved.
Migration of the Ganga River and development of cliffs in the Varanasi region, India during the late Quaternary: Role of active tectonics
(2012) U.K. Shukla; P. Srivastava; I.B. Singh
The lithofacies constitution of unconsolidated sediments exposed in Ramnagar cliff indicates sedimentation in sinuous channels, associated flood plain areas and ponds that were developed within the Ganga River valley. The Khadar surface represents a raised river valley terrace into which the main river channel along with its narrow floodplain is incised. Ramnagar cliff section has revealed a variety of deformation structures that indicate repeated tectonic activity in the area. Important tectonic features exposed by the cliff section are reverse faults, folds, cracks filled with sparry calcite and soft sediment structures indicating liquefaction of sediments affected by faulting and folding. Optically stimulated luminescence (OSL) dating of sediments and field relationships of tectonic elements indicate that the Ganga River migrated near to Varanasi 40. ka following a tectonic event in the area. Since then, it meandered freely within its valley until 7. ka when another tectonic event took place and Ramnagar cliff was raised to its present heights. The cliff surface was degraded by gulling activity for about 4000. years before it was occupied by man at around 3000. years. BP. © 2012 Elsevier B.V.
Migration of the Ganga river and its implication on hydro-geological potential of Varanasi area, U.P., India
(2008) U.K. Shukla; N. Janardhana Raju
Borehole data reveals that during Late Quaternary, the Ganga river was non-existent in its present location near Varanasi. Instead, it was flowing further south towards peripheral craton. Himalayan derived grey micaceous sands were being carried by southward flowing rivers beyond the present day water divide of Ganga and mixed with pink arkosic sand brought by northward flowing peninsular rivers. Subsequently, the Ganga shifted to its present position and got incised. Near Varanasi, the Ganga river is flowing along a NW - SE tectonic lineament. The migration of Ganga river is believed to have been in response to basin expansion caused due to Himalayan tectonics during Middle Pleistocene times. Multi-storied sand bodies generated as a result of channel migration provide excellent aquifers confined by a thick zone of muddy sediments near the surface. Good quality potable water is available at various levels below about 70 m depth in sandy aquifers. Craton derived gravelly coarse-to-medium grained sand forms the main aquifer zones of tens of meter thickness with enormous yield. In contrast, the shallow aquifers made up of recycled interfluve silt and sandy silt occur under unconfined conditions and show water-level fluctuation of a few meters during pre- and post-monsoon periods. © Printed in India.