Browsing by Author "R.N. Tiwari"

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Concentration of heavy minerals in Son River
(1993) R.N. Tiwari; R.N.S. Yadav
Recent sediments of the Son river at Chopan reveal the concentration of 8.46% heavies in coarser (60-120 mesh) and 43.52% in finer fractions (120-230 mesh) by weight. Magnetite is the dominating heavy mineral over the other heavies followed by ilmenite and garnet. The economic minerals indicate the presence of 160.30 kg magnetite, 33.50 kg ilmenite, 22.16 kg zircon and 2.6 kg monazite in one tonne of sediments of size 60-230 mesh. -from Authors
Lithofacies and depositional dynamics of golden Oolite (Bathonian), Kachchh Mainland, Gujarat (India)
(2006) Diwakar Mishra; R.N. Tiwari
The Golden Oolite Member of the Patcham Formation consisting of 84 m thick alternate sequence of limestones and mudstone are well exposed in the Jhura Dome, Kachchh Mainland, Gujarat. Petrographic study of limestones reveals four types of microfacies: oolitic fossiliferous grainstone (A1); fossiliferous intraclastic grainstone (A2); sandy fossiliferous grainstone (A3); and pebbly fossiliferous grainstone (A4). The microfacies normally form microfacies assemblages with calcareous mudstone (B1) and are stacked vertically in ascending order as A1-A3, A1-B1, A4-B1 and A2-B1. The assemblage (A1-A3) is characterised by interbedding of moderately to thickly bedded, hard and compact, golden coloured oolitic fossiliferous grainstone and sandy fossiliferous grainstone exhibiting small scale low angle planar cross beddings. It contains well preserved bioclast. Assemlage (A1-B1) is distinguished by rhythmic alternations of earthy, concretionary calcareous mudstone and moderately to very thickly bedded golden coloured oolitic fossiliferous grainstone showing ripple bedding, abundant bioclast and reworked intraclasts, whereas assemblage (A4-B1) exhibits rhythmic alternations of bioturbated, earthy, concretionary calcareous mudstone and moderately to thickly bedded pebbly fossiliferous grainstone. Assemblage (A2-B1) is characterised by earthy,bioturbated,calcareous mudstone containing thin uneven beds of fossiliferous intraclastic grainstone having micritic intraclast and microfossils. The study of lithofacies suggests two main depositional processes for the formation of golden oolite: (1) The high energy physical sedimentation from current flows during transgression characterized by irregular to sharp nature of basal contact of each cycle, abundance of well preserved bioclasts and reworked intraclasts and large scale ripple bedding; (2) Settling of fines from suspension during fair-weather period as distinguished by homogenous fine grained interbeds of mudstone in the sequence. The transition of facies from A1-A3 to A2-B1 marks deepening upward event during Bathonian period from shallow inner shelf to calcareous mud dominated outer shelf. The energy condition was very high during deposition of the lower and middle part (A1-A3 and A1-B1 assemblage) whereas low to very low as revealed by abundance of bioturbated calcareous mudstone (B1) with episodic interruption of moderate to high energy storm event depositing A4 (pebbly fossiliferous grainstone) microfacies during the upper part (A4-B1 and A2-B1 assemblage) of the sequence. © 2004 Elsevier Ltd. All rights reserved.
Microfacies analysis of transgressive condensed sequence: A study from the oxfordian of Kachchh Basin, Gujarat
(2007) R.N. Tiwari; Diwakar Mishra
1-9 m thick Dhosa Oolite Member of Chari Formation exposed in Kachchh Mainland, western India, represents a condensed transgressive sequence of the Oxfordian age. It is composed of hard and compact, fossiliferous, sandy/conglomeratic oolitic limestone interbedded with friable, thinly bedded calcareous siltstone/fine sandstone. Field & petrographic studies revealed six microfacies namely; (i) sandy/pebbly ironstone (A1); (ii) conglomeratic fossiliferous ironstone (A2); (iii) conglomeratic fossiliferous oolitic packstone (B1); (iv) sandy oolitic packstone (B2); (v) siltstone (C1); (vi) fine grained sandstone (C2). These microfacies are grouped in to three microfacies assemblages namely: (i) sandy oolitic packstone - siltstone assemblage (B2-C1), (ii) siltstone - fine grained sandstone assemblage (C1 - C2) and (iii) conglomeratic fossiliferous oolitic packstone - fine grained sandstone assemblage (C2-B1). The study of microfacies suggests that the deposition of the Dhosa Oolite Member took place in an open marine shallow shelf environment with clear proximal-to-distal trend from southeast to northwest. Two transgressive pulses were responsible for its formation. An earlier slow and frequently interrupted transgression together with subsidence is recorded by abrupt change in clastic grain size, mixing of two lithologies and abundance of siliciclastics in each microfacies. Later, rapid transgression is suggested by the extremely reduced thickness, erosive to irregular contacts, development of intraformational conglomerates, multiphase reworked sediments, an increase in the abundance of carbonates and ammonites and negligible sediment input. Lateral variation in the microfacies and their assemblages together with variable extent of marine mega fauna (ammonites) from southeast to northwest marks the depositional slope of the basin towards northwest during studied interval. The mixed lithologies in this condensed sequence together with the bioturbated nature of sediments suggest that the rate of sedimentation was extremely slow. © Geol. Soc. India.
Provenance study of siliciclastic sediments, Jhura Dome, Kachchh, Gujarat
(2005) Diwakar Mishra; R.N. Tiwari
Provenance of the siliciclastic rocks of Patcham and Chari Formations (Bathonian to Oxfordian) has been ascertained by means of heavy mineral studies. The study shows abundance of transparent heavies like garnet, zircon, tourmaline, staurolite, rutile, hornblende, andalusite, kyanite, anatase and epidote, in decreasing order, and constitute 26.47 percent of total heavies. The opaque group is represented mainly by goethite and limonite, which constitute 73.45 per cent. The statistical data of heavies reveals that garnet, zircon and tourmaline are more or less uniform throughout the stratigraphic column and constitute 43.92 per cent, 22.27 per cent and 19.99 per cent respectively. The average percentage of staurolite and rutile is 5.40 and 4.52. The percentage of anatase, kyanite, hornblende, andalusite and epidote is very less. On the basis of distribution pattern of heavy minerals in stratigraphic column, heavies are grouped into two distinct assemblages i.e. (i) garnet-staurolite-hornblende-kyanite-epidote assemblage, (ii) prismatic and rounded to subrounded grains of zircon-tourmaline-rutile assemblage. The presence of heavy mineral assemblages in the stratigraphic column r eveals that the sediments of Patcham and Chari Formations have been derived mainly from two lithologically different Precambrian terrains; one is dominated by metamorphic rocks and the other is igneous (acid and basic), besides a little contribution of sedimentary source. Source rocks were situated close to basin of deposition in the northeast and east i.e. Aravalli range and north and northwest dominated by granite-syenite suite belonging to Nagar-Parkar Massif. The variable ZTR index indicates manifestation of relief and climatic change in the source area. © Geol. Soc. India.
SEM surface microtextures of quartz grains from Ganga and Yamuna river sediments, Allahabad, U.P
(2004) G.S. Tiwari; R.N. Tiwari; K.N. Singh
Quartz grain surface features of recent sediments samples collected from vertical profiles developed in channel bar, point bar and natural levee deposits around the confluence of the Ganga and Yamuna rivers at Allahabad, UP, were examined under the Scanning Electron Microscope (SEM). The study reveals the existence of several surface features as a result of mechanical and chemical action on the quartz grains. In channel bar and point bar deposits, mechanical features like low relief, v-shaped impact pits of coalescing nature and conchoidal fracture are dominating surface textures, which indicate the high-energy fluviatile depositional environment. Features like surface pits and surface solution are common in quartz grains from natural levee deposits. These surface textures owe their origin to chemical dissolution, which is possible only in low energy conditions associated with the deposition of natural levee and flood plain deposits. © GEOL. SOC.INDIA.
Studies of glass sands occurring around Shankargarh, district - Allahabad with reference to its economic viability
(2003) Ajai Srivastava; R.N. Tiwari; Diwakar Mishra; Kshitij Mohan
The present paper deals with the glass sands occurring around Shankargarh, district Allahabad. The sands in the area are predominantly whitish. However, other colours viz., pink, light yellow, yellow, brown, and red are also commonly found. More than 60 samples representing the vertical and lateral variations of the lithological units were collected from different parts of the area for grain size, mineralogical and geochemical analyses. The grain size analysis reveals that the majority of the grains are rounded, coarse to fine size grade, well sorted, finely skewed and platykurtic. Mineralogical study of the selected glass sand samples shows the presence of light minerals, i.e., quartz, mica, and chert and heavies-rutile, staurolite, tourmaline, and zircon. Opaques include magnetite and ilmenite. Geochemical analysis of these sands reveals a variation in SiO2 in between 97 per cent and 99.01 per cent, whereas Fe2O3 from 0.14 per cent to 1.41 per cent and Al2O3 0.12 to 1.89 per cent. The percentage of iron decreases with the increase of depth, thereby at the base white glass sand of purest variety is met with. Impurities in the form of iron oxide, glistening specks of mica, etc., have been observed in the glass sands. By treatment and beneficiation, iron, and aluminium contents of the glass sands of the area can be reduced for the purpose of making colourless glass. These sands can also be used for making the different types of glass, i.e., lime glass, lead glass, and silicate glass. The glass sands in the area have been found under thin cover of soil with a gentle ground slope. This has provided more time and opportunity for the rain water to percolate through and thereby facilitate the disintegration of the parent rock in the dry summer season.
Study of pollution of the river ganga in the Mirzapur Region (India) and its impact on sediments
(1993) Ajai Srivastava; M.N. Mehrotra; R.N. Tiwari
The paper presents the various sources of pollution in the Mirzapur region, an industralized town in eastern Uttar Pradesh, which lies on the right bank of the river Ganga (Ganges). Municipal and industrial effluents affect the sediment and water of the river. An analysis of the bank sediments revealed the presence of toxic metals, some of them present in greater concentration than those recorded in average shale. The maximum concentrations of Cu, Pb, Ni and Zn in the region, 931, 226, 24 and 717 ppm, respectively, were recorded near the Oliar ghat (landing steps), whereas 138 ppm of Cr was found at the same ghat. Likewise, the maximum value of Co (20 ppm) occurs opposite to the Fathua ghat. These metals present no direct danger to the ecosystem as long as they are tightly bound to the sediments. However, due to a change in the physico-chemical conditions, viz. pH, salinity, redox condition, etc., of the aquatic milieu, these metals from the sediments may pass into the water phase and thus may cause a health hazard. © 1993, Taylor & Francis Group, LLC. All rights reserved.
Vertical successions of channel bar, point bar and natural levee deposits, Ganga and Yamuna river, Allahabad, U.P
(2004) G.S. Tiwari; R.N. Tiwari; K.N. Singh
The modern sediments of Ganga and Yamuna rivers at Allahabad. Uttar Pradesh are studied in 17 vertical sections of channel bar. point bar and natural levee deposits. Based on this study nine lithofacies, i.e. St. SP2, Sp1, Sr1, Sr2, Sl. Sh. Fl and Fm (8-Sand and l- Mud sub-lithofacies) have been identified. An attempt has been made to evolve a generalised lithofacies succession for channel bar, point bar and natural levee deposits. The channel bar exhibits the lithofacies succession of SP2, Spl, Sr2, Sr1 Sh and Fl; St, SP2, Sp 1, Sr1, Sh and Fl succession m point bar and SP2, Sp1, Sr1, Sh. Fl and Fm lithofacies succession in natural levee deposits. No major difference in channel bar and point bar lithofacies succession have been found. The point bars are characterised by trough cross-bedded lithofacies - St, which are formed by the migration of 3-D dunes. The Fm lithofacies is characteristics of natural levee, the muddy deposits often show desiccation cracks. Deposition of mud takes place in low energy conditions mostly during receding floods. © Geol. Soc. India.