bluuebunny/crossref_metadata_2025_split 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

Abstract
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 &lt; garnet &lt; 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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.