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Khan Z.A.,Directorate of Geology and Mining | Tewari R.C.,P.A. College
Journal of Earth System Science | Year: 2011

Late Cenozoic fresh water molasses sediments (+6000 m thick) deposited all along the length of the Himalayan fore deep, form the Siwalik Supergroup. This paper reports the results of the paleodrainage and paleohydrology of the Middle Siwalik subgroup of rocks, deposited in non-marine basins adjacent to a rising mountain chain during Pliocene. Well-exposed sections of these rocks have provided adequate paleodrainage data for the reconstruction of paleochannel morphology and paleohydrological attributes of the Pliocene fluvial system. Cross-bedding data has been used as inputs to estimate bankfull channel depth and channel sinuosity of Pliocene rivers. Various empirical relationships of modern rivers were used to estimate other paleohydrological attributes such as channel width, sediment load parameter, annual discharge, and channel slope and flow velocity. Computed channel depth, channel slope and flow velocity are supported independently by recorded data of scour depth, cross-bedding variability and Chezy's equation. The estimates indicate that the Middle Siwalik sequence corresponds to a system of rivers, whose individual channels were about 400 m wide and 5.2-7.3 m deep; the river on an average had a low sinuous channel and flowed over a depositional surface sloping at the rate of 53 cm/km. The 700-km long Middle Siwalik (Pliocene) river drained an area of 42925 km2 to the north-northeast, with a flow velocity of 164-284 cm/s, as it flowed generally south-southwest of the Himalayan Orogen. Bed-load was about 15% of the total load of this river, whose annual discharge was about 346-1170 m3/s normally and rose to approximately 1854 m3/s during periodic floods. The Froude number of 0.22 suggests that the water flows in the Pliocene river channels were tranquil, which in turn account for the profuse development of cross-bedded units in the sandstone. The estimated paleochannel parameters, bedding characteristics and the abundance of coarse clastics in the lithic fill are rather similar to the modern braided rivers of Canada and India such as South Saskatchewan and Gomti, respectively. © Indian Academy of Sciences.


Khan Z.A.,Directorate of Geology and Mining | Tewari R.C.,P.A. College
Journal of Asian Earth Sciences | Year: 2011

The quantitative relationships between lithological variables from the Late Paleozoic coal bearing cycles have been investigated using factor analysis in an attempt to analyze net subsidence during the deposition of these cycles. The results suggest that there are only two non-zero eigenvalues in varimax matrix which indicate that the hyper ellipsoid enclosing the data points have seven axes of zero length and exists an ordinary two dimensional ellipsoid. The data points can be located with reference to two mutually perpendicular axes. Loading on thickness of sandstones, thickness of shale, number of sandstone beds and number of shale beds are extremely high on RF-I and low on the other factor. This would lead to the interpretation that a balance was maintained throughout the Barakar sedimentation between the rate of deposition and the rate of subsidence. On the other hand, loading on number of coal beds is high on ' suggesting that the development of peat swamps (coal beds) is not a normal feature during the Late Paleozoic Barakar sedimentation in this Gondwana sub-basin. © 2010 Elsevier Ltd.


Tewari R.,University of Lucknow | Awatar R.,University of Lucknow | Pandita S.K.,Jammu University | McLoughlin S.,Swedish Museum of Natural History | And 5 more authors.
Earth-Science Reviews | Year: 2015

This first palynological study of the Permian-Triassic succession in the Guryul Ravine, Kashmir, India, reveals impoverished latest Permian spore-pollen assemblages in the uppermost Zewan Formation, a rich palynoassemblage from the basal Khunamuh Formation characteristic of the Permian-Triassic transition zone and depleted Triassic assemblages from higher in the Khunamuh Formation. The collective assemblages can be broadly correlated to the Densipollenites magnicorpus and Klausipollenites decipiens palynozones of peninsular India and to palynofloras spanning the Permian-Triassic boundary elsewhere in Gondwana. Generally, low spore-pollen yields and poor preservational quality of the studied assemblages hinder more precise correlations and are inferred to be a function of an offshore marine depositional setting on the margin of the Neotethys Ocean, and thermal alteration associated with Cenozoic collisional tectonism between India and Asia. © 2014 Elsevier B.V.


Patel D.R.,Directorate of Geology and Mining | Chauhan G.R.,Directorate of Geology and Mining
Journal of the Geological Society of India | Year: 2015

The Mainpat plateau (N22°41′00″ to 22°55′ 00″ and E 83°08′00″ to 83°25′00″) is a table-land, rising >400 m above foothills, consisting of Archaean rocks (granite-gneisses, phyllite etc), Gondwana formations and Deccan basalt. Archaean rocks occur at the foot hills of Mainpat and Gondwana formations are exposed in the western escarpment of Mainpat plateau in turn overlain by the basaltic rock of Deccan Traps at the top. Barakar Formation contains coal seams from few cm to ~9 m are exposed near Chitaghutri, Kodwari, Tirkela, Tekta etc. villages of Lakhanpur tehsil of Surguja district, covered in Survey of India, Toposheet 64 N/1. Coal present in the area contains high volatile matters and high ash in the different seams in different localities. Analysis shows that coal of this area ranges between C and E grade with useful heat value varying from 3461 to 5223 K Cal/kg. This recently discovered area is located between Hasdo–Arand and Mand-Raigarh coalfields. Coal bearing horizon seems to be persistent, beneath the Deccan Traps. © 2015, Geological Society of India.


Ghose N.C.,G 608 | Ghose N.C.,Patna University | Agrawal O.P.,Directorate of Geology and Mining | Chatterjee N.,Massachusetts Institute of Technology
Island Arc | Year: 2010

A variety of low- to high-pressure metamorphic assemblages occur in the metabasic rocks and metachert in the Upper Cretaceous-Eocene ophiolite belt of the central part of the Naga Hills, an area in the northern sector of the Indo-Myanmar Ranges in the Indo-Eurasian collision zone. The ophiolite suite includes peridotite tectonite containing garnet lherzolite xenoliths, layered ultramafic-mafic cumulates, metabasic rocks, basaltic lava, volcaniclastics, plagiogranite, and pelagic sediments emplaced as dismembered and imbricated bodies at thrust contacts between moderately metamorphosed accretionary rocks/basement (Nimi Formation/Naga Metamorphics) and marine sediments (Disang Flysch). It is overlain by coarse clastic Paleogene sediments of ophiolite-derived rocks (Jopi/Phokphur Formation). The metabasic rocks, including high-grade barroisite/glaucophane-bearing epidote eclogite and glaucophane schist, and low-grade greenschist and prehnite-clinochlore schist, are associated with lava flows and ultramafic cumulates at the western thrust contact. Chemically, the metabasites show a low-K tholeiitic affinity that favors derivation from a depleted mantle source as in the case of mid-ocean ridge basalt. Thermobarometry indicates peak P-T conditions of about 20 kb and 525°C. Retrogression related to uplift is marked by replacement of barroisite and omphacite by glaucophane followed by secondary actinolite, albite, and chlorite formation. A metabasic lens with an eclogite core surrounded by successive layers of glaucophane schist and greenschist provides field evidence of retrogression and uplift. Presence of S-C mylonite in garnet lherzolite and 'mica fish' in glaucophane schist indicates ductile deformation in the shear zone along which the ophiolite was emplaced. © 2010 Blackwell Publishing Asia Pty Ltd.


Rao N.V.C.,Banaras Hindu University | Burgess R.,University of Manchester | Lehmann B.,Clausthal University of Technology | Mainkar D.,Directorate of Geology and Mining | And 3 more authors.
Lithos | Year: 2011

We present 40Ar/39Ar whole-rock ages of 63.7±2.7Ma (2σ, 92% Ar release) and 66.6±2.2Ma (2σ, 96% Ar release) for two samples of sub-surface mafic dykes intrusive into the sedimentary rocks of the Mesoproterozoic Chhattisgarh basin, Bastar craton, Central India. The obtained ages are synchronous with those of the Deccan Traps whose nearest exposures are at a distance of ~200km to the west, and the recently dated diamondiferous orangeites (Group-II kimberlites) of the Mainpur area (located ~100km SE within the Bastar craton). The chemical composition of the Chhattisgarh mafic dykes is indistinguishable from the chemostratigraphic horizons of the upper Deccan lavas of the Wai Subgroup (Ambenali and Poladpur Formations) and confirms them to be a part of the Deccan Large Igneous Province (LIP). The geological setting of the Deccan-age mafic dykes in the Chhattisgarh basin is analogous to that observed in other LIPs of the world such as (i) Pasco Basin of NW U.S.A, (ii) Ellisras sub-basin of southern Africa, (iii) Rift basins of New England in the NE U.S.A and (iv) the West Siberian Basin of Russia where LIP-related basalts and sills have been emplaced in distant domains from the main province. The Deccan-age of the Chhattisgarh dykes and the Mainpur orangeites permits a substantial increase of at least 8.5×104km2 in the spatial extent of the Deccan LIP. The temporal link at ~65Ma between the Deccan Traps and (i) sub-surface mafic dykes within the Chhattisgarh basin and orangeites in the Bastar craton, (ii) Ambadongar carbonatite in western India, (iii) Salma mafic dyke in the Eastern Indian craton, (iv) Rajahmundry Traps off the eastern coast of southern India and (v) tholeiitic dykes and basalts from the Seychelles, suggests a common tectonomagmatic control, via a vast mantle plume-head of the order of 2000-2500km. Our study has relevance to the (i) origin (plume vs non-plume) of the Deccan LIP, (ii) plumbing system for Deccan dykes and lavas in domains far away from the presently exposed Trap regions, (iii) palaeo-environmental issues at the K-T boundary and (iv) metallogeny (diamond, Ni-Cu-PGE) in the Bastar craton. © 2011 Elsevier B.V.


Farooqui A.,University of Lucknow | Ray J.G.,St Berchmans College | Farooqui S.A.,Directorate of Geology and Mining | Tiwari R.K.,Geological Survey of India | Khan Z.A.,Directorate of Geology and Mining
Quaternary International | Year: 2010

The southwestern Ghats region of the Indian Peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year. The record of tropical rainforest corresponding to the dynamic series of Pleistocene interglacial/glacial cycles is poorly known from peninsular India. This communication discusses the palynological study of organic matter (OM) deposits (>40 ka BP) in two well sections (Chaganachery, Kerala) from the Indian Peninsula (west coast). A rich archive of tropical rainforest pollen/spores and marine dinoflagellate cysts indicates anoxic fluvio-marine/estuarine depositional environments during warmer climates with an intensified Asian monsoon. The geochemical fingerprinting of glass shards indicates the presence of Youngest Toba ash of ∼74 ka from northern Sumatra, and therefore establishes a time-controlled stratigraphy. Thus, the depositional time period of the OM is related to the sea level highstand of Marine Isotopic Stage 5.1 (∼80 ka) which was the host to the YTT shards. The Late Quaternary pollen/spores diversity suggests that the modern climatic conditions in the southwestern Ghats have facilitated the conservation of moist evergreen rainforest and dry/moist deciduous forest. The pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic Tertiary period from the Indian peninsula. Thus, it appears that the tropical rainforest survived here as 'Plant Refugia' in xeric (glacial) Quaternary periods, perhaps as riparian vegetation, and was rejuvenated during the Holocene as modern extant flora. © 2009 Elsevier Ltd and INQUA.


Lehmann B.,Clausthal University of Technology | Burgess R.,University of Manchester | Frei D.,Geological Survey of Denmark | Belyatsky B.,Russian Academy of Sciences | And 4 more authors.
Earth and Planetary Science Letters | Year: 2010

Recently discovered diamondiferous kimberlite (Group-II) pipes in central India have surprisingly young 40Ar/39Ar whole rock and U-Pb perovskite ages around 65 million years. These ages overlap with the main phase of the Deccan flood basalt magmatism, and suggest a common tectonomagmatic control for both flood basalts and kimberlites. The occurrence of macrodiamonds in the pipes implies the presence of a thick subcratonic lithosphere at the Cretaceous/Tertiary boundary, significantly different from the present-day thickness of the Indian lithosphere. About one third of the Indian lithosphere was lost during or after the Deccan flood basalt event. The superfast northward motion of the Indian plate prior to the collision with Eurasia cannot be related to lithospheric thinning during the Gondwana break-up at 130 Ma, as previously thought. © 2009 Elsevier B.V. All rights reserved.


Chalapathi Rao N.V.,Banaras Hindu University | Lehmann B.,Clausthal University of Technology | Mainkar D.,Directorate of Geology and Mining | Panwar B.K.,Banaras Hindu University
Mineralogy and Petrology | Year: 2012

Widespread and abundant spinel is the only primary mineral of petrogenetic significance preserved in the hydrothermally altered, crater-facies, Neoproterozoic (≥620 Ma) Tokapal kimberlite pipe that intruded the Indrāvati basin, Bastar craton, Central India. Two distinct spinel populations occur: (i) finer-grained (<50 μm) microcrysts which are zoned from titaniferous magnesiochromite-chromite to magnetite; and (ii) larger macrocrysts (>400 μm) with cores having distinctly chromium-rich (Cr 2O 3 up to 63. 67 wt%), and TiO 2-poor (<0.68 wt%) compositions. Based on their morphology and chemical composition the macrocrysts are inferred to be disaggregated mantle xenocrysts and their compositional range extends well into the diamond stability field. However, the reported absence of diamond and other indicator minerals (such as pyrope garnet, chrome diopside and magnesian ilmenite) in the Tokapal pipe is intriguing since diamondiferous cratonic roots are indeed preserved in the Bastar craton, and also the kimberlite itself was derived from a similar source region(s) as that of the well-known diamondiferous Mesoproterozoic (ca. 1,100 Ma) kimberlites from Wajrakarur, Dharwar craton, southern India. Given the large areal extent (>550 ha) of kimberlite, there is a possibility that it contains diamonds but they were not recovered during the sampling. Alternately, highly oxidising conditions imparted by the metasomatic fluids/melts derived from (i) asthenosphere-lithosphere interaction, or (ii) the kimberlite itself might have played an important role in the destruction of diamond, and other indicator minerals. © 2012 Springer-Verlag.


Rao N.V.C.,Banaras Hindu University | Lehmann B.,Clausthal University of Technology | Mainkar D.,Directorate of Geology and Mining | Belyatsky B.,Russian Academy of Sciences
Contributions to Mineralogy and Petrology | Year: 2011

We present mineral chemistry, geochemistry and Sr and Nd isotope data of drillcore samples from the Late Cretaceous (65 Ma), diamondiferous Behradih ultramafic pipe, Bastar craton, Central India, which is emplaced synchronous with the Deccan flood basalt eruption. The rock is affected by pervasive serpentine-talc-carbonate alteration and consists of pelletal lapilli and variously sized olivine and phlogopite macrocrysts, set in a groundmass of abundant clinopyroxene, chrome spinel, apatite, Fe-rich perovskite (<50 μm), zircon, titanite, rutile and calcite. Mineralogical studies identify the Behradih pipe as orangeite (formerly termed as Group II kimberlite) and establish the occurrence of such rocks outside the Kaapvaal craton, southern Africa. As the age of the Behradih orangeite overlaps with that of the main phase of the Deccan flood basalt magmatism, we infer a common tectonomagmatic control vis-a-vis the Deccan-related mantle plume. Trace element ratios and the Nd isotope signatures of the Behradih pipe imply that the Deccan plume has only contributed heat, but not substantial melt, to the Behradih magma with a cause-and-consequence relationship between them. Our study highlights (a) a striking similarity in the genesis of Late Cretaceous orangeites associated with the continental flood basalts in the Kaapvaal and Bastar cratons but related to different mantle plumes and (b) the role of plume-lithosphere interaction in the generation of orangeites. © 2010 Springer-Verlag.

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