bluuebunny/crossref_metadata_2025 huggingface dataset:
Decomposition of Primary Minerals and the Process of Bauxitisation in Shevaroy and Kolli Hills, Salem District, Tamil Nadu
Authors: Krishna Rao G. , Borreswara Rao C.
Published: November 2024

The bauxite deposits of Shevaroy and Kolli hills have been investigated to understand the processes involved in decomposition of the primary minerals leading to bauxitisation. The charnockitic suite of rocks underlying the bauxite deposits consists of quartz, plagioclase and potash feldspars, ortho- and cline-pyroxenes, garnet and secondary hornblende. During weathering, feldspars directly give rise to gibbsite and sometimes through kaolinite as an intermediate product. Under similar drainage conditions plagioclase feldspars in particular and mafic rocks in general are found to be more favourable for direct bauxitisation than potash feldspars and felsic rocks. The secondary product from pyroxenes (and hornblendes) is usually goethite but rarely clay minerals of nontronite group. Gibbsite in minor amounts is believed to be another secondary mineral in addition to goethite in the case of garnet alteration. Quartz is subject to dissolution and is replaced by gibbsite and goethite towards the final stages of bauxitisation. Order of mineral stability for weathering is, feldspars=pyroxenes < garnet < quartz.

Secondary enrichment bauxite and/or laterite as a result of migration and reprecipitation of aluminium and iron hydroxides has been observed. Hematite and boehmite are believed to have been formed in the advanced stages of weathering under an acidic environment during these secondary processes.
The Paleogeographic Distribution of Devonian Acritarchs and Biofacies Belts
Authors: Nautiyal Avinash Ch.
Published: November 2024

When the composition of presently commonly known, approximately Lower to Upper Devonian acritarch assemblages in North-South American and West European and North African continental blocks bordering the Atlantic, as shown in a palinspastic map of Bullard et al, (1965) is plotted, four microplankton (acritarch) biofacies belts are conspicuous: I, the Cymatiosphaera/Multiplicisphaeridium biofacies belt; II, the Polyedryxium biofacies belt; III, the Veliferites/Pterospermopsis biofacies belt; and IV, the Maranhites/Navifusa biofacies belt. The four biofacies belts are not directly influenced or controlled by sedimentary facies (lithofacies) differences and not owing to nonsimultaneity of the microplankton assemblages compared and discussed. They are essentially paleolatitudinally influenced and it is proposed that they reflect differences in paleoclimate. The Cymatiosphaera/Multiplicisphaeridium biofacies belt is related to warmer climate, the Polyedryxium biofacies belt belongs to warmer to intermediate climate, whereas the Veliferites/Pterospermopsis biofacies belt and Maranhites/Navifusa biofacies belt being characteristic of the cooler climate.
Mineralogy of Coexisting Zoisite-Clinozoisite and Epidote from Sakarsanahalli, Kolar, Karnataka
Authors: Narayanan Kutty T. R. , Anantha Iyer G. V.
Published: November 2024

X-ray, infrared spectra and chemical data reveal that the pink mineral from the calc-silicate rocks of Sakarsanahalli, Kolar, is a mixed phase of zoisite and clinozoisite. It is generally cloudy due to fine inclusions of plagioclase. Polymorphic transformation relations could be observed in it. The mixed crystals are found to be stable when the replacement of Al by Fe3+ is less than 10 atom per cent. The yellow-green to green mineral, on the other hand, is monophasic epidote, with 30 to 35 atom per cent Al being substituted by Fe3+. Hydrothermal experiments show that zoisite-clinozoisite transforms to zoisite-epidote (iron-rich clinozoisite) pair at higher temperature and pressure. However, larger Fe3+ activity upsets this transformation relation, where the monoclinic epidote phase alone is stabilised.
Post-Kurnool Thrust and other Structural Features in the Northeast Part of the Palnad Basin, Krishna District, Andhra Pradesh
Authors: Natarajan V. , Rajagopalan Nair S.
Published: November 2024

In the northeast part of the Palnad Basin, Krishna district, Andhra Pradesh, interesting structural features are noticed in Precambrian sedimentary rocks. A prominent thrust which has brought the Cumbums over the younger Kurnools, and other primary and secondary structures in the rocks are significant and help in deciphering structural events. The thickness of the Narji limestones based on the structural studies is estimated to be 300 m and not 6400 m as suggested by Heron.
Iron-Manganese Ratios in Wolframites as Geologic Thermometers
Authors: Singh V. K. , Varma O. P.
Published: November 2024

Based on the available data, relationship between chemical composition and depositional temperature of wolframites is illustrated by means of a curve, which provides information about the temperatures of deposition of wolframites from their estimated iron-manganese ratios, whose validity as reliable geothermometers, hitherto controversial, is re-established by this study.
Relation between Coplanar Folds of Variable Orientation, Stretching Lineation and Thrust in the Daling and Associated Rocks from the Inner Tectonic Belt of Sikkim Himala
Authors: Roy Subimal Sinha
Published: November 2024

The second generation deformation structures in the Daling metamorphic rocks and in the associated basement granitic mylonite in a part of the Sikkim Himalayas are represented by variably orientated coplanar minor folds of three morphologic types, and a stretching fabric, transverse to the thrust-front. Strain analysis on the dimensionally orientated deformed clastic grains in metagraywacke and semipelite indicates that the deformation during second folding phase was close to plane strain. Interrelation between folds, stretching fabric and thrusts suggests that thrusting did not take place parallel to the planes of maximum shear strain. Generation of these related structures is explained in a model of rotational three-dimensional progressive deformation. Ductile thrusting is suggested to have been caused by flattening process by high longitudinal strain, parallel to the principal deformation plane. The direction of thrusting is indicated by the stretching lineation, but the component of horizontal displacement of rocks may not be as large as usually postulated.
Mineralogy and Genesis of Fluorite Deposits of Chandidongri, Madhya Pradesh
Authors: Balasubramaniam K. S. , Bhosale J. S.
Published: November 2024

Fluorite occurs as replacement and cavity filling type in a shear zone traversing the Dongargarh granites where basic rocks' are encountered. This region is different in two ways: 1. presence of basic rocks in the shear zone and 2. absence of any calcareous type of rocks as compared to other fluorite occurrences like Ambadongar in Gujarat and Kahela-Mandokipal in Rajasthan. Fluorite, tysonite, borofluorite and yittrofluorite are the minerals identified. Geochemical studies combined with thermodynamic data throw a better light on the genesis of the fluorite deposits of this area which can be classified as low temperature hydrothermal.
Superposed Folding in the Northern Part of the Gangpur Series, Orissa
Authors: Chaudhuri A. K. , Pal A. B.
Published: November 2024

Precambrian metasediments in the northern part of the Gangpur Series, represented by mica schist, phyllite-slate, and schistose quartzite have been investigated over an area of 50 sq km around Lase (22°21' ; 84°45') of Sundargarh district, Orissa. Structural analysis reveals that the earliest folds in bedding (S1) were reclined in nature, but they have been blurred by the profuse development of axial plane schistosity (S2). S2, however, shows upright to slightly overturned folds plunging moderately to E to ESE. The most dominant attitude of S2 nearly normal to the regional fold axis points to the reclined geometry of the folds in S1. Non-penetrative fracture cleavage surfaces (S3) have developed parallel to the axial planes of S2-folds, generally displacing the folded segments. The S3-surfaces, however, show appreciable fanning.
Exploration and Mine Development of Bandalamottu Lead Deposit in Guntur District, Andhra Pradesh
Authors: Vijayaraghavan P. N. , Tiwari R. K.
Published: November 2024

Mineralisation is essentially confined to dolomitic host rock. The strict lithological control of mineralisation with its width extremes and layering defined by the bedding planes in the dolomite and the folding of mineralised zones conforming in style to that of the host rock are strong field evidences to suggest syngenetic origin of the deposit.

Due to structural complexity of the deposit, basic information from 100 m spaced drill intersections does not give correct picture regarding the disposition of ore bodies. No fixed norms for mining could, therefore, be established in advance and every mineralised section will have to be negotiated depending upon the structural domain and allied features governing the mineralisation in that particular section.
An Estimation of Temperatures of Intrusion of Indian Carbonatites Using Calcite-Dolomite Geothermometry
Authors: Sethna S. F. , Viladkar S. G.
Published: November 2024

The temperatures of crystallization of 23 calcitic carbonatites have been estimated on the basis of the amount of MgCO3 going into solid solution with calcite. Majority of the carbonatites have a temperature of crystallization between 350° to 475° C., while the one at Sevattur shows a rather high temperature of crystallization (about 600° C). There is a distinct relation between grain size and temperature of crystallization for the Amba Dongar carbonatites.
P-T Conditions of Granulite-Upper Amphibolite Facies Metamorphism in the Precambrian Granitic Rocks of the Chipurupalle-Razam Area of the Eastern Ghats
Authors: Dhana Raju R.
Published: November 2024

In the Chipurupalle-Razam area, garnetiferous and orthopyroxene-bearing granitic rocks and their associated Khondalite Group constitute the Precambrians of the Eastern Ghats. The mineral assemblages and textural features of the different rock types indicate that the rock types in the area were subjected to at least two periods of metamorphism.

The first period of metamorphism under conditions of granulite facies was around a minimum temperature of the order of 600° to 700°C, but below 800°C, with Pload of about 6 to 7 kb. The second period of metamorphism under the upper almandine-amphibolite facies conditions took place above 550° and below 700°C at about 1.5 kb PH2O. The bulk composition of the rock is the primary controlling factor for the presence or absence of garnet, orthopyroxene, and sillimanite, as well as the composition of individual minerals like biotite, garnet, and orthopyroxene.
Chemical Classification of the Intermediate and Acid Rocks (Deccan Trap) of Salsette Island, Bombay
Authors: Sethna S. F. , Batnwala H. K.
Published: November 2024

The intermediate and acid rocks of Salsette Island, Bombay, that were collectively identified as rhyolites, rhyodacites and trachytes by previous workers, have been remapped to locate the outcrops of acid and intermediate rocks separately. Eighty-one samples, collected systematically, have been analysed for Na2O and K2O contents and thirty-five of these for major elements. On the basis of geochemistry and mineralogy these rocks have been classified into five groups, viz., (I) potassic rhyolites, (2) sodipotassic rhyolites, (3) potassi-sodic rhyolites, (4) quartz-rich trachytes, and (5) quartzbearing trachytes.
Exploration for Bauxite in Sri Lanka, Preliminary Investigations
Authors: Dissanayake C. B. , Vitanage P. W.
Published: November 2024

Preliminary geochemical investigations for bauxite in Sri Lanka show the existence of laterite deposits containing bauxitic material approaching the lower limit of commercial grade. The geochemical processes responsible have followed two paths resulting in the formation of lateritic bauxite and lateritic iron ore. While the few samples analysed do not give any information regarding the possible reserves of commercial grade bauxite, the existence of economically important bauxitic material, particularly in the Highlands of Sri Lanka has been confirmed.
Fossil Floral Assemblages in the East Coast Gondwanas - A Critical Review
Authors: Venkatachala B. S.
Published: November 2024

Palynological investigations carried out during recent years from the Coastal Gondwana sediments have necessitated rethinking on earlier age assignments made on the basis of mega plant fossils.

The Sriperumbudur Beds, Raghavapuram and Vemavaram Shales, Sivaganga Beds and Athgarh Sandstones were dated as Late Jurassic on the basis of Ptilophyllum flora occurring in them and the absence of Weichselia and Onychiopsis. Foraminiferal evidences ascribed an Early Cretaceous age. This discrepancy between plant and animal fossil evidences was attributed to differential evolutionary rates. An Early Cretaceous age assignment is now favoured on the basis of the occurrence of important taxa of stratigraphic value such as: Impardecispora purverulentus, and/or I. apiverrucata, Crybelosporites stylosus, Polycingulatisporites reduncus, Ischyosporites crateris, Aequitriradites spinulosus, Microcachryidites antarcticus, and Staplinisporites caminus.

The plant megafossil assemblage, though distinct; might not be representative or complete. The age cannot be assigned on negative evidences such as the absence of certain fossils. The frequently mentioned discrepancy in age inferred from faunal and floral evidences appears a fallacy. The incompleteness of the evidence, either faunal or floral, is a reality and should be ascribed to our inability to find forms rather than their actual absence.
Palaeocene-Eocene Boundary in Cauvery Basin
Authors: Mohan Madan , Kumar P. , Narayanan V.
Published: November 2024

The authors favour the placement of Palaeocene-Eocene boundary at the Pseudohastigerina wilcoxensis datum. In the Cauvery basin subsurface, seemingly continuous late Palaeocene-Early Eocene successions are known only in the basinal depressions, which have been exemplified by the Chidambaram well data. Unless the sequences are well represented by cores, problems arise in delineation of Palaeocene-Eocene boundary in the flanks of ridges/highs in Cauvery basin as the index Palaeocene planktonic foraminifera are sometimes found reworked in the Eocene zones.

The occurrence of Nummulites, whose earliest occurrence is lately being attributed to the basal Eocene in the European basins, in the Cauvery basin Palaeocene corresponding to the Globorotalia velascoensis and Globorotalia pseudomenardii Zones - has been stressed. Further research is necessary in order to establish the evolutionary appearance level of these camerinids in the Indian subcontinent.
Mesozoic-Cainozoic Boundary in Assam
Authors: Sah S. C. D. , Singh R. Y.
Published: November 2024

The vertical distribution of significant phytoplankton, spore-pollen and foraminiferal guide fossils are detailed with special reference to palyno-stratigraphic investigations in the South Shillong Plateau. The diagnostic features of the Maestrichtian-Danian-Palaeocene intervals are summarised. Biostratigraphic evidences favour the placing of the Mesozoic-Cainozoic boundary between the Mahadeo Formation (Maestrichtian) and the overlying Langpar Formation (Danian).
Upper Cretaceous & Lower Tertiary Foraminiferal Genus Bolivinoides from the Cauvery Basin, South India and its Palaeobiogeographical Significance
Authors: Govindan A.
Published: November 2024

Five species of Bolivinoides are reported for the first time from the Upper Cretaceous and Lower Tertiary subsurface sediments of the Cauvery Basin, South India. The Stratigraphic ranges of these species are compared with established planktonic foraminiferal zones. The morphological variation of the genus has been analysed. The palaeobiogeographical significance of this form is discussed. In the light of the present find of Bolivinoides, palaeoclimatic conditions of the Cretaceous shelf seas of the basin has been suggested.
Provenance and Al/Si Order-Disorder of Detrital Alkali Feldspars
Authors: Basu Abhijit
Published: November 2024

The principle that detailed characterization of minerals enhances petrogenetic interpretation is extended to sedimentary petrology by estimating the Al/Si order-disorder of detrital alkali feldspars from Holocene fluvial sands derived from granite plutons. A weathering-independent characterization of the influence of source rocks on daughter sands is based on structural state determination of 42 detrital alkali feldspars. Structural states were estimated from refined unit cell parameters derived from slow oscillatory difractograms. .

None of the studied feldspars show anomalous cell dimensions as inferred from b-c plots. In addition, estimates of Or content from refined cell volumes correspond very well with microprobe measurements of the Or contents of the same grains. In crystalline rocks, however, many alkali feldspars have anomalous cell dimensions; their estimated and measured Or contents are also often widely different. This suggests that detrital alkali feldspars may be amenable to rapid x-ray methods of structural state determination.

Detrital alkali feldspars in sands derived from pre-Mesozoic plutons are triclinic with a relatively low structural state (average ? bc=0.975; t1(o)=0.479).

The age of the parent pluton may be a factor in controlling the relative structural states of detrital feldspars derived from the pluton. Alternatively, the difference in ordering between the two groups of feldspars might reflect the differences in the thermal history of the different zones of the parent batholith supplying feldspars. It is possible that the rapidly cooled outer shells of plutons are quenched at higher temperatures than their relatively slowly cooled cores. Thus the outer shells would tend to produce alkali feldspars with relatively higher structural states than those coming from the core. If so, a vertical sequence of sediments derived from systematic unroofing of a batholith should reflect this change in feldspar structural state.
Metamorphic History of the Precambrian Rocks of the Narmada Section, Southwest of Jabalpur, M.P.
Authors: Agrawal V. N.
Published: November 2024

The Precambrian rocks of the Narmada section, southwest of Jabalpur, which bear imprint of several periods of deformation, are found to have undergone Barrovian type of regional metamorphism with garnet-staurolite-sillimanite assemblages in the higher grades. An increase in the metamorphic grade is indicated by successive development of a higher grade mineral assemblage, as also a coarser metamorphic fabric, as the rocks are followed to the east. Textural evidence is given to show that metamorphism in the area has been a polyphase event, the main episodes of crystallisation having occurred before, during and after the second (F2) fold phase. The metamorphic climax, marked by the development of sillimanite, is shown to have occurred after the second fold movement. That higher temperatures prevailed in the Tilwaraghat section through successive metamorphic episodes is shown by the development of higher grade minerals and a coarser rock fabric in the above area than anywhere to the west of it. Retrogression was negligible in this area, while extensive retrogression occurred in the western part, particularly between the water falls and Lamhetaghat.
The Occurrence of Marine Palaeocene Outcrop in the Surat-Broach Area, Gujarat
Authors: Samanta Bimal K.
Published: November 2024

The occurrence of marine Palaeocene sediments with age-diagnostic larger foraminifera in Surat-Broach area was first reported by Narayana Rao (1939) from Tarkeshwar, near Surat. A perusal of the publications bearing on the Lower Tertiary stratigraphy and foraminifera of the area revealed that the foraminiferal limestone band from Tarkeshwar originally dated as Palaeocene was later assigned to the Upper Eocene by Narayana Rao himself. This is also supported by an examination of the material collected from the Surat-Broach area during the present investigation. Up to the present there is no authentic record of the occurrence of marine Palaeocene outcrop in the Surat Broach area.
Sedimentary Structures in the Tertiary Rocks of South Gujarat and Their Environmental Significance
Authors: Gadekar D. R.
Published: November 2024

Planar cross stratification, trough cross stratification, imbricate structure and channel structure observed in Jhagadia, Babaguru and Tarakeshwar Formations indicate fluvial depositional environment. Oscillation ripple marks preserved in the Kand Formation suggest transitional conditions. Graded bedding seen in Jhagadia, Tarakeshwar and Vagalkhod Formations indicate deposition by turbidity currents. Convolute laminations and ball and pillow structure by sediments belonging to Babaguru Formation indicate intrastratal deformation and slumping, perhaps on a delta. Colour banding observed in the sandstones of the Babaguru Formation suggests oxidising environment in a tranquil water body.
Petrography and Genesis of Nahan Phosphorite Himachal Pradesh-Northwest Himalayas
Authors: Chaudhri R. S. , Gupta G. D.
Published: November 2024

Nahan Phosphorite is classified into three types: fragmental phosphorite, pelletal phosphorite and nodular phosphorite. X-Ray Diffraction studies show that francolite (carbonate fluorapatite) constitutes the main phosphate mineral. It is concluded that the Nahan Phosphorite accumulated in shallow marine waters where euxinic conditions prevailed locally.
Some Uncommon Phenomena in Ptygmatic Structures
Authors: Mitra S. , Datta J.
Published: November 2024

In ptygmatic structures formation of' clods' at the nodes of folds and fragmentation of the ptygma are common features. A rheological model has been set-up to generate such structural elements by considering the deforming vein to be elastic-plastic and embedded in a Newtonian viscous matrix. Because of elastic-plastic character, some regions of the vein will flow elastically and some plastically. Flow of paths of these generate complicated flow lines and with progressive deformation the vein tears off along these lines. Ptygmatic field structures have been classified and their modes of generation discussed.
Carbonatite Complex near Borra, Visakhapatnam District Andhra Pradesh
Authors: Ramam P. K. , Viswanathan T. V.
Published: November 2024

The carbonate rocks near Borra, hitherto considered as crystalline limestones forming part of the khondalite group of metasediments of the Eastern Ghats mobile belt, have been identified as carbonatites. Genetically associated rocks include pyroxenite and syenite, characteristic of alkalic carbonatite complexes. Phlogopitization, local domingup and other features characterstic of forceful intrusion of carbonatites have been noticed. Characteristic rare-earths include Ce and La. The rare earth mineral identified is bastnaesite. The typical zirconium mineral is badleyite. Relative rarity of magnetite and pyrochlore makes the complex' atypical'. The Borra carbonatite is the oldest known occurrence in the country; the K-Ar dating of the phlogopite has given an age of 1490± 50 million years. It is surmised that the apatite-magnetite veins associated with a possible carbonatite at Kasipatnam and the Borra carbonatite are localised along a deep seated NW-SE fault system in the Eastern Ghats mobile belt.
The Dariba Main Lode of Rajpura-Dariba Zinc-Lead-Copper Belt, Udaipur District, Rajasthan
Authors: Chauhan D. S.
Published: November 2024

The Dariba Main Lode is characterized by a complex assemblage of metallic sulphides and sulphosalts. Primary sedimentary fabric is evident by the occurrence of sphalerite, pyrite and occasionally galena, and rarely chalcopyrite, in the form of conformable layers, interbedded with the host rocks throughout the exposed length in the underground mine. Early diagenetic pyrite is found as tiny isolated grains as well as framboids, in which the first form is always dominating. This reflects two different pathways of pyrite formation.

Distinct mesoscopic folds are found in the bedded ores which show their general trend congruous to the "major folds of the region. ' Healed' breccias and fractures often occur associated with the folded and conformable ores in which the sulphides appear mobilized and recrystallized.

Folded pyrite-graphite schist laminites show excellently developed axial and bedding plane cleavages along which the pyrite has been recrystallized into aggregates of elongated crystals due to outlasting effect of shears. Pressure shadow structures showing elongated crystals of pyrite bordered by sphalerite and/or galena are also frequently observed along the bedding plane cleavages. Typical metablastic textures are exhibited by large euhedral crystals of pyrite and arsenopyrite and triple-point junctions shown by sphalerite and pyrite.

The ore features suggest that the Rajpura-Dariba-Bethumni deposits are essentially syn-sedimentary.
Structural Analysis of a Part of the Sausar Group Rocks in Chikla-Sitekesa Area, Bhandara District, Maharashtra
Authors: Sarkar S. N. , Gautam K. V. V. S. , Roy Sajalendu
Published: November 2024

Systematic analysis of structural geometry of a part of the Sausar Group rocks in Chikla-Sitekesa area throws new light on the tectonic pattern and evolution of the area. The country rocks mainly include Tirodi gneiss, Sitasaongi, Lohangi, Mansar, Chorbaoli and Junewani Formations and three ore-horizons of the Sausar Group in which four types of s-planes (S1-S4) and six types of linear structures (L1-L6) have been recognised.

For tectonic analysis the area has been subdivided into three sectors and 15 subareas and selective and synoptic p and lineation diagrams of megafabric elements (1500 s-planes and 516 lineations) have been critically studied along with the structural maps. The results indicate that the rocks of the area exhibit triclinic symmetry in megascopic, mesoscopic and macroscopic scale with reference to all structural elements, though there are domains of monoclinic symmetry with reference to one or more fabric elements.

Kinematic analysis indicates the generation of isoclinal (B1) folds and rootless hinges with axial planes mostly dipping SSE due to rotational stress (P1) along N168°N348° with anticlockwise rotation sense when looking ENE. Considerable variation in the orientation of the first fold axes may be due to inhomogeneity of rock pile, irregular distribution of stresses and different degrees and phases of deformation. Subhorizontal stress (P2) acting along N10°-N190° with deformation plane dipping steeply westward is responsible for the generation of east to southeast plunging L5 puckers and minor (B2) folds along with steeply dipping S3 planes on S2, Stress (P3) acting along N146°-N326° seems to have generated widely spaced kink bands and gentle superimposed L6 folds on S2 in Sector-I and Sector-III and macroscopic scale anti formal B3 fold (Alesur: antiform) in Sector-II. The rocks represent B1 ? B2? B3 tectonites formed during successive deformation phases (F1-F3) of the Sausar orogenic cycle.
Structure of the Kashmir Himalaya from Deep Seismic Soundings
Authors: Kaila K. L. , Krishna V. G. , Roy Chowdhury K. , Narain Hari
Published: November 2024

Deep Seismic Sounding (DSS) studies carried out for the first time in the syntaxial bend of the Himalaya in Kashmir region during 1974 and 1975 have revealed the deep crustal and upper mantle structure in the region of the great Himalaya Karakorum-Pamir ranges. The Moho which is at a depth of about 45 km near Sopur changes rapidly to 54 km depth in the region of Wular lake from where it continues to go still deeper towards NNE, attaining a depth of about 64 km near Kanzalwan. Then there is a deep fault displacing Moho to a depth of 76 km, which then rises to about 62 km under the Nangaparbat shot point. Similarly the Moho, along profile 2, is found to be at a depth of about 53 km in the region about 10 km NNW of Tral going still deeper towards NNW and attaining a depth of about 64 km in the region about 17km NE of Srinagar. Further NNW, in the region of Kanzalwan, there seems to be some flattening of the Moho boundary which is at a depth of about 70km. Beyond Kanzalwan both the profiles 1 and 2, reveal a change in the dip direction on the Moho boundary which then starts rising up towards Nangaparbat. This updip of the Moho boundary in the region between Kanzalwan and Nangaparbat is an indication of the upwarp of the Moho in this region, which could be responsible for the uplift of the Nangaparbat massif. The crustal block in the Kashmir Himalayan region between Sopur and Kanzalwan and between Tral and Kanzalwan appears to be bounded by two large-angle deep-faults which extend down almost to the Moho boundary.

A number of deep reflections have been recorded along profile 3 indicating deep reflecting boundary at a depth of about 140km extending right from beneath Nangaparbat to the great Pamir ranges which is inferred as representing the top of the asthenospheric layer.
Modification of Flexural Folds by Flattening Process-Examples from the Aravalli Rocks of Zawar Mine Area, Rajasthan
Authors: Roy Ashit Baran
Published: November 2024

Study of two broadly similar folds from the Aravalli rocks of Zawar Lead-Zinc Mines area south of Udaipur in Rajasthan, shows that the folds are tight to isoclinal with wavelength/amplitude ratio between 0.35 to 0.37. The thickened hinges and the stretched limbs (v?2/?1=0.3) of the folds, and the weakly convergent pattern of the isogon lines suggest that the folds belong to the flattened parallel type. The axial plane cleavage in the rocks is a crenulation cleavage formed by microfolding and migration of quartz from the limbs, which make an angle less than 40° with the axial surfaces of the microfolds. Although some slip has occurred along the cleavage after it formed, this slippage has not altered the shapes of the folds to any great extent. The folds are thought to have been modified by post-buckling homogeneous strain aided by migration of quartz from the limbs to the hinges of the folds.
Geomorphology of Visakhapatnam, Andhra Pradesh
Authors: Prudhvi Raju K. N. , Vaidyanadhan R.
Published: November 2024

The major geomorphic units of the town of Visakhapatnam are the hill slope elements of free face and debris slope, along with piedmont fans, colluvium and pediment. Waltair Uplands are mainly made up of small detached hills, large accumulations of red sands, often dissected into miniature badlands, and patches of dune sands. Laterites are present both as altered product of hard rock as weIl as colluvium. The coastal zone contains stacks, wave-cut platform, beach and sand dunes. A study of logs of more than 1000 bores put in the tidal basin and features reported and observed here and elsewhere along the coast indicates that during the commencement of Holocene (since 10,000 years B.P.), the sea level might have been about 7 metres higher than the present sea level before it went down to as low as 25 metres and rising again to the present level.
The Deccan Trap Basalt Flows of the Bor Ghat Section of Central Railway
Authors: Karmarkar B. M.
Published: November 2024

On the basis of their form the flows are divided into four Groups: (1) thick extensive flows of compact basalt, (2) tabular flows of amygdaloidal basalt, (3) thin irregular flows of amygdaloidal basalt; and (4) thick irregular flows of amygdaloidal basalt. Flows of Groups 1 and 2 appear to be the products of fissure type of volcanicity. The irregular form and small size of flows of Groups 3 and 4 suggest that they were formed by eruption of viscous lava in small quantities. The small basaltic intrusions found associated with these flows probably represent the cracks through which magma rose.

Two entirely different types of volcanicity dominated at different times in this area. Eruptions producing flows of Groups 3 and 4 were prevalent in the early period, while fissure type of activity producing flows of Groups 1 and 2 took place in the later period. The flows appear to have come in quick succession without any intertrappean interval.
Geology and Geochemistry of Anorthosites of Karnataka Craton and their Tectonic Significance
Authors: Ramakrishnan M. , Viswanatha M. N. , Chayapathi N. , Narayanan Kutty T. R.
Published: November 2024

Anorthosites of Karnataka occur in two distinct tectonic milieu, within a major arcuate zone, namely, (i) as minor differentiates of gabbro in the ultramafic-mafic complexes emplaced in Archaean high-grade supracrustal belts and the 'Dharwar type' greenstone belt of Shimoga; and (ii) as layered concordant sheets, and as cumulates in a layered basic pluton occurring within the gneissic complex of Archaean high grade terrain. Their absence in 'Keewatin type' greenstone belts and the other  'Dharwar type' belts of Bababudan and Chittadurga is probably due to their location away from the arcuate zone in Karnataka Craton. This arcuate zone reflects a progressive vertical zonation of the crust to deeper levels from northwest to southeast.

The anorthositic rocks of mafic-ultramafic complexes are nonlayered and extensively deformed, whereas those of the high grade terrain show layering and cumulus textures. In the transitional zone, the anorthositic rocks of mafic-ultramafic complexes show cumulus textures, thereby indicating a genetic connection between the anorthosites of two tectonic milieu.

Whole-rock chemistry of the anorthosites of Karnataka indicates differentiation trend of iron-poor environment comparable to other Archaean anorthosites. They are enriched in CaO and A12O3 Niggli mg against Cr or Ni shows positive correlation, corresponding to an igneous parentage for the original rock. Similarly, the plot of Niggli c against mg, c against (al-alk) and 100 mg-c-(al-alk) diagrams exhibit a well defined igneous trend. A common differentiation trend is shown by anorthosites of Karnataka, even though they occur in two distinct tectonic milieu. The singularised trends support the view that the ultramafic-mafic complexes are possibly derived by the dismembering of the basal parts of the layered complexes. The Archaean anorthosites of Karnataka, although comparable broadly to lunar anorthosites, are not related to the early history of the Earth-Moon system.
Chemical Studies on Insoluble Carbonaceous Matter from Precambrian Sediments from Onverwacht Group of South Africa by Electron Spin Resonance and X-Ray Diffraction Techniques
Authors: Karkhanis Suresh N.
Published: November 2024

Electron spin resonance and X-ray diffraction techniques are used to study insoluble carbonaceous matter from Precambrian sediments. Techniques for sample preparation are described. The ESR data when correlated with XRD data show striking parallelism between carbonisation of coal and organic matter during incipient metamorphism. The method is potentially applicable to studies of diagenesis and low rank metamorphism of organic matter in sediments and could be extended to study the levels of organic metamorphism to determine the thermal history of sedimentary basins.
Programme for Computation of Grain-Size Data on Programmable Desk Calculators
Authors: Bhattacharya G. C. , Hashimi N. H.
Published: November 2024

The programme for computation of grain size data on the DCM desk calculators (MOSCAL-1080 PS and MICROSYSTEM 1101) is described. In these programmes the weight percentages or sample weights are used to compute standard statistical parameters by the method of moments. Details are given on data preparation and operation of the programme. A flow chart and the programme are given along with a test problem.
Geological Setting and Mineralogy of the Chromite and Some Associated Minerals of Kathapal, Dhenkanal District, Orissa
Authors: Chakraborty K. L. , Baidya Tapan
Published: November 2024

The chromitite lodes are emplaced in serpentinites as banded layers, lenses or clots. The ores are high alumina chromite with RO:R2O3 ranging from 0.92 to 1.08 and formed by magmatic segregation.

Hydrothermal alteration has produced different chrome-bearing silicates like kammererite, uvarovite, chrome-amphibole, and chrome-bearing chalcedony, which occur either as transgressing veinlets in chromitites or in the interspaces between chromite grains. The primary dunite-peridotite has been altered to massive and compact serpentinite.
Volcanism in the Younger Dharwar Rocks Near Medur Dharwar District, Karnataka
Authors: Ziauddin M. , Roy Abhinaba , Biswas S. K. , Gururaja Rao T. P.
Published: November 2024

Andesite lavas are associated with pyroclastics and a few sheet-like porphyritic flows. The volcanism is considered to have been of mixed eruptions indicating sufficient fluidity and low gas content. The andesitic lavas are characterised by well developed pillow structure. They are interlayered with pyritiferous and carbonaceous argillites indicating volcanic eruption under submarine condition.

The lavas occupy the central part of a major refolded antiformal anticline plunging to the west. They have undergone metamorphism only up to the green-schist facies of regional metamorphism. Carbonatisation of lavas is a common feature, particularly in andesite.
An Approach to Use Repeat MSS Imageries for Vedavati Catchment in Karnataka and Andhra Pradesh
Authors: Ramesam V. , Achutha Rao A.
Published: November 2024

Of all the modern Remote Sensing Techniques, multi-spectral (MSS) imagery taken through satellites is proving to be a highly useful reconnaissance tool for earth resources evaluation studies. The synoptic view of the changes in the areal spread of surface water reservoirs, soil moisture zones etc., as provided by the repeat imageries is of particular significance to hydrologists. Though the repeat imageries were used to monitor flood effects, there does not seem to be much effort in using them for estimating the component of surface water change in the hydrological balance.

This paper illustrates an approach to estimate the changes in surface water storage in 7300 sq km of the Bhairavanithippa catchment (a part of the Vedavati River Basin) in parts of Karnataka and Andhra Pradesh. The study indicates that the depression storage in a normal rainfall year may be around 95 MCM and in a drought year as low as 26 MCM. The Sources of error in these estimates can be lessened to a great extent by a Man-Machine interaction.
Archaean Geology Investigations in Southern India
Authors: Pichamuthu C. S.
Published: November 2024

A brief review is made of the investigations conducted on the Archaean rocks of southern India from the time of Newbold (1838) to the present. Problems connected with Dharwar stratigraphy and the relationship of Peninsular Gneiss to Dharwar schists and charnockites have given rise to considerable differences of opinion and the main features of these controversies are summarised. Much of the confusion is due to the fact that terms like 'Dharwar' and 'Peninsular Gneiss' have been used in very different senses by individual workers. Geochemical and geochronological investigations are of recent origin and have yielded some interesting results. An account is given at the end of some of the problems in Precambrian geology that are still awaiting solution in southern India.
Exploration Planning for Sandur Manganese Ores
Authors: Mishra R. N.
Published: November 2024

Three prevailing ore types viz., stratiform, podiform and tabular deposits occur at the incidence ratio of 75:6:19. The stratiform orebodies can be designated as plenemensurate and regular; the podiform types as partimensurate and complicated; and the tabular ones as extramensurate and irregular.

Based on the study presented here, a stratiform body may be explored on 100m × 100m square grid by core-drilling for the results to remain within the confidence level of ±20%; while pediform bodies may be explored with jack hammer-cum-diamond drilling at 50m × 50m square grid and the tabular deposits at 20 m × 20m square grid with deep pits-cum-drilling for the results to remain at the same level of assurance.
Petrology and Geochemistry of a Recently Discovered Nickeliferous Serpentinite in Sri Lanka
Authors: Dissanayake C. B. , Van Riel B. J.
Published: November 2024

Geological and geochemical investigations of a serpentinized ultramafic body in the south of Sri Lanka have revealed the presence of nickel in the range 0.8-1.9%. Nickel is present in silicate form in the serpentine minerals. The typical tropical climate prevailing has been responsible for the formation of a deep weathering profile conducive to the residual enrichment of nickel. Cobalt, chromium and zinc are also present, though in lesser quantities when compared to nickel. The opaque minerals consisted of magnetite, chromite/picotite and other spinels. The leaching of silica and magnesium had resulted in the formation of chert, agate, chalcedony and carbonate veins respectively.
Photo-Geomorphic Features in Chintapalle Area Over Eastern Ghats in Andhra Pradesh
Authors: Prudhvi Raju K. N. , Vaidyanadhan R.
Published: November 2024

Study of aerial photographs of an area of about 2000 sq km around Chintapalle in Visakhapatnam district of Andhra Pradesh, shows that broad structural trends are clear only where there are no laterite caps. The lateritic cappings show off on higher altitudes with light tone and generally across structural trends. The cappings, aligned ENE-WSW with a general altitudinal accordance, are suggestive of their occurrence over remnants of a single planar surface. The criteria identified may be applicable elsewhere in the Eastern Ghat terrain for locating lateritic cappings. Such an exercise appears vital in the present context, as many of the laterite caps of the Eastern Ghats are proved to be good bauxite deposits.
Positive Evidence of a Precambrian Tectonic Phase in Central Nepal, Himalaya
Authors: Kumar Ravindra , Shah A. N. , Bingham D. K.
Published: November 2024

An angular unconformity between fossiliferous Early-Middle Palaeozoic and Precambrian rocks, yet not known in the Himalaya, has been discovered in Central Nepal. The underlying Precambrian rocks show at least one additional distinct foliation and lineation than the overlying Early-Middle Palaeozoic rocks. This deformation is attributed to a Precambrian tectonic phase.
Geochemistry and Origin of Acidic Rocks from Jaspa and Rohtang, Himachal Pradesh
Authors: Divakara Rao V. , Radhakrishna T. , Srikantia S. V.
Published: November 2024

Geochemical investigations on the Jaspa granites and Rohtang gneisses from Himachal Pradesh indicate that the Rohtang gneisses are the migmatlsed/granltised products of the pre-existing metasediments and the Jaspa granite is an intrusive granite. Field relationship suggests that the Jaspa granite is a post-tectonic intrusive while the migmatisation/granltisation of the gneisses appear to be pre-and syntectonic and might have continued into the post-tectonic period.
An Outline of the Structural Set-Up of the Kumaun Himalaya
Authors: Valdiya K. S.
Published: November 2024

The Kumaun Himalaya embraces all the four Himalayan physiographic-geologic subprovinces. (1) The northern Tethys Zone constituted of Late Precambrian to Cretaceous sediments, is demarcated against the Great Himalaya to the south by the steeply-dipping Malari Thrust. This synclinorial zone, exhibiting Jura-type folding, is split up by imbricate thrusts in northeastern Kumaun giving rise to schuppen structures. Along the indo-Tibetan border, large-scale thrusting has brought Ophiolitic melange and a sheet of ultrabasics of the Kailas-Mansarovar area in Tibet over the Cretaceous flysch of Malla Johar. (2) The Great Himalaya is a colossal tectonic slab of the granite-injected katazonal early Precambrian metamorphics of the Vaikrita Group penetrated by Tertiary granite. It is demarcated by the Malari and Vaikrita thrusts. Exhibiting homoclinal structure, the Great Himalaya is characterized by plastic deformation and fluidal folding throughout its extent. The Valkrita Thrust marks abrupt change in the grade of metamorphism from the katazonal metamorphics to epizonal metasediments of the Lesser Himalayan Munsiari Formation at the base. (3) The mylonitized and retrograded metamorphics and Precambrian augen gneisses and synkinematic granodiorites of the Munsiari Formation, sandwiched between the Vaikrita and Munsiari Thrusts at the base of the Great Himalaya, represent the root of the Almora Nappe and its four klippen that cover vast areas of the Lesser Himalaya in the eastern half of Kumaun. The Munsiari extends northwest to Join up with the Jutogh of Himachal Pradesh. Imbricately underlying the Almora nappe iS the second thrust sheet of weakly metamorphosed early Riphean flysch penetrated by voluminous granitic porphyroids of the Ramgarh Group. The northwestern prolongation of this nappe is involved, together With the underlying quartzites, in tectonic imbricate-splitting. One of the sheets of this schuppen zone extends northwest to join up With the Chail Nappe of Himachal. In the inner Lesser Himalaya the crystalline klippen are underlain by a vast thrust sheet of Berinag quartzites (=Nagthat Formation) and penecontemporaneous basic volcanics. This Berinag Nappe is the base-cut and beheaded northern extension of stupendous Krol Nappe that imbricately underlies the Ramgarh and/or Almora nappes of the outer Lesser Himalaya. The synclinorial Krol Nappe comprises, in addition to the lithological Unit of the Berinag Nappe several other formations. Under the nappes in the inner Lesser Himalaya complexly folded and faulted autochthonous Early Riphean flysch (Damtha Group) and Middle Riphean to Vendian Tejam Group (Deoban + Mandhali Formations) are exposed. (4) The molasse subprovince of the Siwalik is an autochthon, separated from the Ganga plams presumably by a deep Himalayan Frontal Fault. The single-range homoclinal Slwalik Unit of eastern sector splits up westward into two major ranges showmg Jura-type folding and thrusting with the intervening synclines filled With subrecent gravels, giving rise to intermontane flat plains or 'duns'.
Controls of Asbestos Mineralisation in the Roro Ultramafics, Singhbhum District, Bihar
Authors: Ballurkar Ashok , Pal P. C.
Published: November 2024

The ultramafics of Roro are layered bodies comprising two major lithological units-serpentinised pyroxenites (SPX) and serpentinised saxonites (SSX). Ribbon zones of chrysotile mineralisation are found localised in thin granular serpentinite (SR) horizons at the contacts of 'the SPX and SSX layers in cross folded portions of these ultramafic bodies.

The SSX rock is typically a clot-bearing one, comprising poikilitic clots of saxonitic composition embedded in relatively olivine-rich and more serpentinised groundmass. Two controls for chrysotile localisation can be readily identified in the Roro ultramafics. The lithological control is provided by extensively serpentinised interfaces of the already partially serpentinisied pyroxenitic and saxonitic layers. These horizons of secondary serpentinisation (viz., the SR horizons) appear to have resulted from either a fusion of the SPX and SSX rocks at their contacts or, alternately, from the segregation of the SSX clots at the interfaces of these layers and their subsequent serpentinisation. The composition of the SSX rock therefore appears to have been a vital factor in fibre development in the SR horizons. The structural control is considered to have been provided by the superposition of structural deformations due to Singhbhum orogeny over those caused by the older Iron ore orogeny.

Fibre development is indicated to be a dynamothermal process in the structure-restricted zones of secondary serpentinisation in an already serpentinised ultramafic body.