bluuebunny/crossref_metadata_2025 huggingface dataset:
Reappraisal of the Delhi Stratigraphy in the Ajmer-Sambhar Sector, North-Central Rajasthan
Authors: Fareeduddin  , Reddy M. S. , Bose U.
Published: November 2024

The supracrustals occurring in the northern sector of the South Delhi Fold Belt (SDFB; main Delhi Synclinorium of Heron, 1953) between Ajmer-Pushkar valley and Sarnbhar Lake in north-central Rajasthan are classified into Anasagar migmatites and the overlying Ajmer Formation comprising Taragarh quartzites and Kalyanipura arkose-pelite-greywacke sequence. The Anasagar migmatites and paragneisses are intruded by Iatero genic granite(1600 Ma) and post orogenic ultramafic and alkaline rocks. Four folding and two shearing movements characterize these rocks. Three metamorphic zones could be identified in these supracrustals with grade increasing towards west: staurolite-kyanite grade (middle arnphibolite facies) in the eastern sector, sillimanite-muscovite grade (upper amphibolite facies) in the central sector, and orthopyroxene-plagioclase and orthopyroxene-sillimanite grade (granulite facies) in the western sector.

The Anasagar and Ajmer supracrustals are deposited in an Early Proterozoic ensialic basin in the Archaean BGC (Banded Gneissic Complex) protocontinent and differ from the other tectono-stratigraphic units of the SDFB in respect of lithological organisation, metamorphism and magmatism besides the latter being decisively of Upper Proterozoic age. The authors, therefore suggest a separate and older stratigraphic status to these supracrustals and delink from the rest of the SDFB stratigraphy.
Late Quaternary Variations in Sedimentation Rate in the Laccadive Trough, Southeast Arabian Sea
Authors: Shankar R. , Manjunatha B. R.
Published: November 2024

Radiocarbon measurements of a core from the Laccadive Trough, SE Arabian Sea have yielded ages which show that sediments from the Pleistocene, Holocene and a transition zone can be recognized by virtue of colour variation. The mean sedimentation rate decreases from 4.11 to 3.15 cm/103yr for Pleistocene and Holocene respectively, witha peak of 6.36 cmcm/103yr determined for the transitional zone. A sediment slump or turbidite emplacement resulting from higher terrigenous influx during the transition period has been inferred. This is in contrast to the bioclastic turbidite of the central continental margin-pelagic region (off Bombay-Ratnagiri sector of western India). The decrease in sedimentation rate from Pleistocene to Holocene can be most likely ascribed to entrapment of riverine sediments in estuaries and continental shelf, as a result of Holocene sea level rise.

The mean sedimentation rate in the Laccadive Trough (3.84 cm/103yr) is lower than that on the northwestern continental margin of India (4.6-9.8 cm/103yr) because of relatively low terrigenous influx from the small west-flowing rivers of Peninsular India. The Holocene sediment thickness in the Laccadive Trough is 35 cm as against 50 cm in the northeastern Arabian Sea. The onset of environmental conditions representative of Holocene is estimated at ca. 9300 yr B.P. which corroborates the date proposed for the northern Indian Ocean.
Geochemistry and Origin of the Granite Gneisses of the Almora Group from Dhunaghat area, District Pithoragarh, U.P.
Authors: Singh B. N. , Goel O. P. , Joshi Mallickarjun , Sheraton J. W.
Published: November 2024

The Precambrian Almora granite gneisses containing numerous schistose enclaves occuras thick and thin bands within the medium-grade Saryu metasediments of Almora Group. Petrography and major and trace element geochemistry of the granite gneisses indicate that they are strongly peraluminous, S-type granites, and were derived by partial meltingofthe meta-arkose/metapelites.
Symplectites in High-Grade Pelitic Gneisses of Usilampatti, Tamil Nadu: P-T Conditions and Geochemistry
Authors: Subba Rao D. V. , Nirmal Charan S. , Narayana B. L. , Naqvi S. M.
Published: November 2024

Occurrence of fine-grained, fingerprint-like symplectic intergrowths of cordierite, K-feldspar and quartz formed due to the retrogressive, garnet breakdown reactions following decompression during uplift, is reported here from metapelites of Usilampatti area. These metapelites consisting of cordierite, garnet, hypersthene, biotite, hercynitic spinel, sillimanite, K-feldspar assemblage were metamorphosed at 6.5-7.5 Kb and 750-800°C. The symplectites were formed at 600-670°C and 5 Kb pressure. The textural and mineralogical evolutions in these metapelites indicate a rapid decompressional P-T evolution. Petrological and geochemica1 data suggest that these metasediments were derived mostly from an evolved basement source of granodiorite-granite composition with a minor basic component.
Potassium - Argon Ages of Dolerite Dykes in Late Archean/Early Proterozoic Closepet Granite
Authors: Dayal A. M. , Padmakumari V. M.
Published: November 2024

Emplacement of the Closepel granite around 2.6 to 2.5 Gaage was the last major event in the crustal formation process in the Dharwar Craton. This granitic body has been intruded by a number of dykes mainly trending E-W or NE-SW between Madhugiri and Tumkur. Potassium-argon ages on these dykes range from 2.5 Ga to 1.2 Ga and can be classified into three different phases. The first phase (2.5-2.4 Ga) dyke activity might be correlated with emplacement of the Closepet Granite. The second phase (1.8-1.6 Ga) of dyke activity could be associated with hypabyssal magmatism connected with the Proterozoic Cuddapah Basin formation and volcanism. The last phase (1.4-1.2 Ga) represents the middle Proterozoic dyke activity during which emplacement of Rapakivi granites and alkaline magmatism were reported.
Structural Styles and Role of Basement Configuration in Hydrocarbon Accumulation Patterns: Cauvery Basin, India
Authors: Prabhakar K. N. , Chandola S. K. , Kumar Rohit , Paul Rama
Published: November 2024

An integrated analysis of basement map and fault patterns has revealed that the Cauvery basin came into existence in a tensional regime which existed during the taphrogenic fragmentation of eastern Gondwanaland (Late Jurassic-Early Cretaceous). The main trend of tectonic elements is NE-SW and it changes to NNE-SSW towards southern part of the basin. This change of trend is attributed to post-rift kinematics associated with counterclockwise movement of the Sri Lankan massif away from the Indian craton. The orthogonal trends which form transfer zones are responsible for conservation of regional extensional strain.

It is observed that there is a good correlation between hydrocarbon occurences, transfer zones and fault sets. Synthesis of tectonic, geochemical and lithostratigraphic data has led to better understanding of the role of Basement Configuration in hydrocarbon accumulation patterns.
Statistical Modelling of Exploration Data for Grade Potential of the Phosphorite Deposit, Khatamba Blocks, Jhabua District, Madhya Pradesh
Authors: Sarkar B. C. , Nayak V. K. , Srinivas Rao P.
Published: November 2024

The Phosphorite deposit (74°25' to 74°26'E : 22°58' to 23°00'N), Jhabua district, Madhya Pradesh, is one of the productive deposits in India, and has evoked great interest with regard to its phosphogenesis, stromatolite association and resource potential. It is a sedimentary-stromatolite type of deposit within the Precambrian metasediments of the Aravalli Supergroup and represents the southern extension of the well known Jhamarkotra phosphorite deposit of Rajasthan. The geological set-up shows that the phosphorite occurs in two separate host rocks of older carbonate and younger chert sediments. Geological Survey of India (Khan et al. 1979), using conventional cross-section method, estimated the weighted average grade of the Khatamba Blocks from the available 21 intersections in 12 trenches as 28.60% P2O5. In the present study, statistical modelling of exploration data of the Khatamba Blocks, using histogram plots, probability diagrams and skewness and kurtosis parameters for 20 intersections reveals a 3-parameter log-normal distribution for accumulation (grade-thickness) and thickness values. The graphical estimate of the average grade from the probability diagrams is 29.59% P2O5 and that estimated by computer is 29.40% P2O5.

A computer programme ONEPOP.FOR in interactive FORTRAN77 has been developed for statistical modelling of the exploration data. Using this approach the grade. estimated for phosphorite deposit of the Khatamba Blocks shows a marginal increase in the value of average grade of P2O5, content as compared to the estimate made by conventional method.
Geochemistry and Petrogenesis of Shonkinite and Associated Alkaline Rocks of Tiruppattur Carbonatite Complex, Tamil Nadu
Authors: Saravanan S. , Ramasamy R.
Published: November 2024

Shonkinite occurring in the carbonatite complex of Tiruppattur, Tamil Nadu is essentially composed of equal proportions of anorthoclase and augite with accessories of olivine, hastingsite, biotite, apatite and magnetite. The carbonatite complex comprises alkaline rocks emplaced in two adjacent structural basins of Sevvattur and Jogipatti. The chemical composition of shonkinite is intermediate between melanocratic rocks, alkali syenites and soda-rich alkali syenites of the Sevvattur structural basin and highly potassic alkaline rocks of the Jogipaui structural basin. Both these basins constitute the carbonatite complex of Tiruppattur. The study of geochemistry of clinopyroxenes in the co-magmatic alkaline series of the carbonatite complex reveals that both the groups of alkaline rocks were derived from shonkinitic parent magma by convection current aided differentiation and fractionation of mafic cumulates with intermittent immiscible separations of carbonate and silicate liquids.
Offshore Structural Trends from Magnetic data over Cauvery Basin, East Coast of India
Authors: Subrahmanyam A. S. , Lakshminarayana S. , Chandrasekhar D. V. , Murthy K. S. R. , Rao T. C. S.
Published: November 2024

Detailed analysis of magnetic and bathymetric data over shelf and slope regions of Cauvery basin, east coast of India. between Mahabalipuram and Vedaranyam demarcated three major offshore lineaments trending N-S, NE-SW and E-W. The N-S lineation has been interpreted as due to dyke intrusions. NE-SW lineament reflects the offshore extension of a major basement depression, viz., the Pondicherry depression. E-W lineation, south of Porto Novo reveals a basement high suggesting the seaward extension of Kumbakonam ridge within the Pondicherry depression. The present analysis gives mosaic of a deep seated graben block flanked by rift related volcanic intrusives over the shelf region of the basin.
Geotectonic and Seisnlic Risk Implications of Ground Level Changes in the Dehradun Region during the 1905-28 Period
Authors: Gahalaut V. K. , Chander R.
Published: November 2024

We interpret here the ground elevation changes along the Saharanpur - Dehradun - Mussoorie line as brought out through the levelling surveys of 1905-07 and 1926-28. These data can be simulated with a model of slips, varying in amount between 3 ± 3 and 16 ± 8 cm, on the same subsurface detachment on which the great Kangra earthquake of 1905 may have occurred as argued elsewhere in the literature. Since ground elevation changes occurred in the Dehradun region during the Kangra earthquake also, we suggest that slips related to plate tectonics on the detachment lead to ground elevation changes partly aseismically during periods between great earthquakes and partly coseismically at the times of such earthquakes. The annual rates of slips obtainable from the above numerical results being much less than the estimated rate of 18 ± 7 mm/year for plate convergence accommodated at the Himalaya, we conclude that earthquake generating strains accumulated in the Dehradun region during the 21 years between the two levelling surveys.
Late Palaeozoic Plant-Geography of the Peri gondwana and Evolution of the Kashmir Basin
Authors: Bajpai Usha , Maheshwari Hari K.
Published: November 2024

A typical Gondwanan Flora comprising species of Trizygia, Glossopteris, Vertebraria, etc. is known from the Kashmir Basin. At certain levels, however, the flora contains some exotic elements, such as Lobatannularia, Sphenophyllum, Kashmiropteris (Protoblechnum/Comsopteris) and Rhipidopsis. All these elements are important constituents of the Cathaysian Flora. In southern Xizang, too, a plant bearing horizon contains elements of both Gondwanan and Cathaysian floras.
REE in Precambrian BIF of Granulite Gneiss Belts of Tamil Nadu
Authors: Subba Reddy N. , Prasad C. V. R. K. , Balaram V.
Published: November 2024

Rare Earth Element (REE) distribution in 10 samples of Precambrian BIF of granulite gneiss belts of Tami! Nadu suggest that the BIP derived their constitutents of iron and silica from hydrothermal source. The BIP thus formed were metamorphosed to granulite fades metamorphism along with the associated volcanogenic products and sediments.
Gondwana Sedimentation in the Chintaiapudi Sub-basin Godavari Valley, Andhra Pradesh
Authors: Lakshminarayana G.
Published: November 2024

A 3000 m thick Gondwana lithic fill consisting of multifacies associations were preserved in a NW-SE oriented intracratonic Chintalapudi sub-basin set across the Eastern Ghat Complex (EGC). Sedimentation commenced with the deposition of diamictite-rhythmite sequence of the Talchir Formation in glacio-lacustrine environment. The succeeding sandstone-coal cyclothems of the Barakar Formation were formed in fluvial-coal swamp complex. The fluvial streams flowed across the EGC, originating somewhere in the southeast beyond the East Coast of India. Phase-wise upliftment of the EGC during Mesozoic imparted changes to the Permian intercontinental drainage system which started supplying increased aJll'lOunt of detritus to the basin. Basin marginal faults were first formed at the beginning of Triassic. Alluvial fans originated in the east and southeast and northwesterly flowing braided streams deposited the conglomerate-sandstone sequence of the Kamthi Formation. The Early Jurassic uplift of the Mailaram high in the north imparted westerly shift to the braided rivers during the Kola sedimentation . Due to prominence of Kamavarapukota ridge in the south by Early Cretaceous, the drainage pattern became centripetal and short-lived high sinuous rivers debouched into the basin. The silting up of the Chintalapudi sub-basin with tbe sandstoneclaystone sequence of the Gangapur Formation marks the culmination of the Gondwana sedimentation, perhaps, coinciding with the breakup of India from the Gondwanaland.
Distribution of Heavy Minerals in Parangipettai (Porto Novo) Beach, Tamil Nadu
Authors: Mohan P. M.
Published: November 2024

Studies on the sediments of Parangipettai (Porto Novo) beach and its surrounding environments (Vellar river, estuary and nearshore environment) reveal that all the environments show texturally different characters but similarity in heavy mineral assemblages with varying percentage of occurrence. The river sediments are coarser (1.48 f) and moderately sorted than estuarine sediments which are finer (4.22f) and poorly sorted. The beach sediment; fall in the size range 2.25f to 2.61f in the southern region and 2.56f to 2.71f in the northern region, and are well to moderately sorted. In nearshore, sediments of the northern region are finer (3.50f) and poorly sorted than those of the southern region, which are coarser (2.98f) and moderately sorted. Sediments of river, bermcrest and backshore of southern beach and bermcrest of northern beach represent near symmetrical skewness and the other remaining beach environments have coarse skewness. Nearshore and estuarine sediments register fine and strongly fine skewed nature. In all the environments, the sediments are leptokurtic except those at low water mark of southern region where they are platykurtic. These variations are due to the physico-chemical conditions, impact of tidal action and longshore movements on the different environments. Conspicuous changes are noticed in the individual heavy mineral concentrations. Based on the mineral assemblage in the riverine environment, it is inferred that the main so~rces for these minerals are the rock types present in the catchment area of the river. The enrichment of some heavy minerals in the beach and nearshore environments suggest that the increment may be due to the addition of these minerals from some other sources like paleo sediments and the present day offshore sediments.
Micromammal-Based Palaeoenvironment of Upper Siwaliks Exposed Near Village Saketi, H. P.
Authors: Patnaik Rajeev
Published: November 2024

Two sections, namely Kanthro and Moginand exposing Upper Siwalik rocks near village Saketi (H.P., India) have yielded a diverse fossil assemblage and evidence for pedogenic modifications. Palaeoecological reconstruction indicates the presence of atleast four palaeocommunities (pond, pondbank, bushland and grassland). Studies concerning taphonomy reveals that there was a gradual accumulation of micro and megafossil remains in shallow seasonal ponds of broad flood plains. It is also noticed that the concentration of some small mammal remains were due to biogenic processes.
New Occurrence of Dinosaur Eggs from Lameta Rocks (Maestrichtian) near Bagh, Madhya Pradesh
Authors: Joshi A. V.
Published: November 2024

New occurrence of well preserved in situ dinosaur eggs have been found in the Lameta rocks, exposed in the vicinity of Bagh village in Dhar district, Madhya Pradesh. In all, three in situ eggs have been recovered, which are spherical in shape having a maximum diameter of 18 cm. The field occurrence and the morphological characters of these eggs, reveal their close affinity towards the sauropod group of dinosaurs.
Petrography and Petrochemistry of the Cordierite Bearing Metapelites of Nartamalai Area, Pudukkottai District, Tamil Nadu
Authors: Nathan N. P. , Sundara Raghavan S. , Natarajan V. , Raman R.
Published: November 2024

Occurrence of cordierite bearing metapelites of Khondalitic suite of rocks is reported from Nartamalai area, Pudukkottai district for the first time. The cordierite bearing gneiss occurs in close association with chamockite and pyroxene granulite in the vicinity of the Nartamalai granites. The mineral assemblages seen in the metapelites are cordierite-almandine-sillimanite-plagioclase-K-feldspar- biotite and quartz. Zircon, magnetite and spinel are the accessory minerals. The texture of the metapelites is generally gneissose except in the eastern part of the area where it simulates a hornfels. The Nartarnalai cordierite contains 59% Mg-cordierite and 41 % Fe-cordierite. The Fe+2/Fe+2+Mg ratio of the Nartamalai cordierite is 0.414 which is strikingly higher than that of the cordierites of regional metamorphism and it is comparable with the Fe2/Fe+2+Mg ratios of the cordieritcs described from hornfels assemblage. The coexisting garnet is an almandine-pyrope with very minor andradite and spessartitc, which is comparable with the garnets of regional metamorphic assemblage. The tie-line joining the composition of the coexisting cordierite and garnet indicates a regional metamorphic environment. An overprint of thermal metamorphism, attributable to the intrusion of Nartamalai granites, on the pre-existing regional metamorphic fabric is suggested.
Relicts of Sedimentary Precursors in Archaean Gneisses : Melukote Paragneiss -An Example from Dharwar Craton, India
Authors: Uday Raj B. , Naqvi S. M.
Published: November 2024

Relicts of sedimentary precursors in the Peninsular Gneisses around Melukote-Katteri area ofDharwarCraton are recognised on the basis of field, petrological and geochemical data. The Melukote gneiss has interbeds of carbonates, quartzites. iron-formations and para-amphibolites with a concordant planar fabric. These gneisses are devoid of mafic-ultramafic xenoliths which are one of the essential characteristics ofthe orthogneiss component of Peninsular Gneiss (PG), The Melukote paragneiss (MG) contains interstitial calcite, relict arkosic texture, subrounded to round quartz, plagioclase and zircon. Two generations of quartz and plagioclase are conspicuous in the MG. The MG are high SiO2 and low Al2O3 Cr and Ni are significantly enriched - up to 334 ppm and 73 ppm respectively. The Rb and Sr contents are lower than the typical tonalite-trondhjemite gneisses (TTG). The high HREE patterns of MG and very low negative Eu anomalies are distinct from those of TTG in the surrounding areas. These data indicate that MG represent first cycle immature sediment derived from a heterogenous provenance.
Sedimentology of Quaternary Alluvial Deposits of the Gandak-Kosi Interfan, North Bihar Plains
Authors: Sinha Rajiv
Published: November 2024

An account of sedimentolpgical characteristics such as grain size distribution, clay mineralogy, sand mineralogy and magnetic susceptibility of the alluvial sediments from the Gandak Kosi interfan area in the Indo-Gangetic plains of north Bihar is presented. Fine-grained sediments consisting of significant percentage of detrital clays and variable carbonate content are present in the plains and are distinctly derived from the Himalaya. Sedimentation in the interfan is episodic through overbank flooding forming thick muddy sequences. Changes in depositional regime occurred because of shifting of channels which, in turn, affected channel proximity of floodplain sites.
Occurrence of Ultramafics of Komatiitic Affinity in the Rikhabdev-Dungarpur Belt, Udaipur and Dungarpur Districts, Rajasthan
Authors: Gathania C. R. , Chattopadhyay A. K. , Sharma B. , Ameta S. S. , Ghosal A. K.
Published: November 2024

Preliminary study of the ultramafic suite of rocks emplaced concordantly in the Proterozoic supracrustals of the southern Rajasthan (Aravalli Supergroup) indicates their komatiitic nature. Though the diagnostic spinifex texture is not observed in the highly serpentinised and metamorphosed ultramafics, the amygdaloidal structure and the previously reported igneous joints provide textural evidences for the extrusion of the ultramafic lava. The altered ultramafics still retain certain chemical signatures (high MgO and Mg-No., low Ti02, Al2O3and alkalis) of standard komatiites.
Mineral Composition and its Bearing on Depositional History of Banded Iron-Formation of Kudremukh Schist Belt, Karnataka
Authors: Khan R. M. K. , Nirmal Charan S. , Arora M. , Naqvi S. M.
Published: November 2024

The iron-formations ofKudremukh mainly contain magnetite, recrystallized chert, gruneritecu mmingtonite (XMg 0.21 to 0.33), hornblende, bioti te along with minor amounts of ankerite (XMg O. 30 to 0.52), calcite (XMg 0.06 to 0.22), chamosite and pyri teo Chamosite, a rare relict mineral, was probably formed by reaction between high Al-clay and Fe. Magnetite was formed during metamorphism. Along with the precipitation of alternating layers rich in silica and iron, clayey material in the form of montmorillonite, illite and/or glauconite along with Fe-Mg carbonates were also deposited, which after metamorphism (430-520°C) gave rise to the present mineralogy.
Rb-Sr Age of the Metaluminous Granitoids of South Khasi Batholith, Meghalaya : Implications on its Genesis and Pan-African Activity in Northeastern India
Authors: Panneer Selvam A. , Prasad R. N. , Dhana Raju R. , Sinha R. M.
Published: November 2024

Metaluminous granitoids of the South Khasi batholith (SKB) in the West Khasi Hills district of Meghalaya define a Rb-Sr whole-rock isochron age of 757 ± 60 Ma, with (87Sr/86Sr) of 0.71069 ±0.00092. SKB and other granitoids of Meghalaya like Mylliem, Nongpoh and Kyrdem have many common features such as the presence of basic enclaves of hornblende gneiss and amphibolite, lateto post-tectonic nature, predominance of biotite amongst mafic silicates, overall metaluminous nature and high (87Sr/86Sr) of more than 0.709. All these indicate much similarity in the genesis of their melts due to partial melting of lower crustal rocks. The Rb-Sr isochron ages of SKB and other granitoids in Meghalaya point to a major tectonomagmatic activity during ca. 760-480 Ma, which is almost coeval with ca. 800-500 Ma Mid-Upper.Pan-African activity. The data, thus imply the possible imprint of the widespread Pan-African activity in northeastern India, besides southern India.
Cretaceous - Paleocene Carbonate Microfacies of Tamil Nadu and Pondicherry
Authors: Guha Asit K. , Mukhopadhyay T. J.
Published: November 2024

Nine types of Standard Microfacies (SMF) are identified in the Cretaceous-Paleocene carbonate sequences of the Ariyalur-Vridhachalam of Tamil Nadu and the Pondicherry areas. Of these four SMFs occur frequently.

The recurrence of SMF types within FZ 7 in successive fonnations of varying thickness indicates multiple transgressive - regressive episodes of unequal areal extent and time interval. A gradual decrease in the number of microfacies types in carbonate lithologies younger than the Turonian suggests progressive stabilization of the shelf. Presence of similar SMF in younger carbonate layers belonging to different areas and ages point to their being time-transgressive lithologic units. The carbonates are of low-Mg calcite variety. Significant depletion of Sr and Na and enrichment of Ba, K and Mn took place due to prolonged diagenetic alteration by meteoric water.
Geotectonic Model of Cambay Basin for Hydrocarbon Exploration from Mature to Immature Stage Using Fractal Geometry
Authors: Singh Ravi Pratap , Pati Prabhash Bihari
Published: November 2024

Geologic processes like structural evolution, sedimentation pattern, fluid distribution are non-linear and therefore, are expected to display chaotic characteristics evidenced by self-similar observations or fractals. A major characteristic of fractal geometry - the invariance of the observations with the scale is used to derive an empirical geotectonic model for the evolution of Cenozoic Cambay Basin and hydrocarbon exploration in it from mature stage to immature stage. The model comprises of two distinct tectonic phases of Paleocene-Early Eocene age and Mid Miocene age separated by a 'Transitional' shallow water sedimentation cycle of Middle Eocene-Early Miocene age. The boundaries of these phases are marked by frequently conspicuous angular unconformities. Most of the seismic energy is absorbedlrenected within these transitional sediments which has restricted hydrocarbon exploration to the Mid-Eocene reservoirs (Kalol-Kadi, Hazad-Ankleswar Fonnations). These are the easy-to-find accumulations and exploration in these sequences is now considered to be in mature stage with dwindling size of new prospects. Need has arisen to look for other prospective reservoirs in the deeper sequences particularly in Paleocene - Early Eocene (Olpad Fonnation) after establishing good source rock potential in it. The presence of hydrocarbons is already established in this sequence but it has remained almost unexplored due to lack of sufficient subsurface data and clear understanding of the tectonics. The model helps in forecasting economic prospects within this sequence in which the configuration of the prospects will be unlike to that of the already known 'conventional' plays of Mid-Eocene age. All the discoveries in this sequence are interestingly fitting well with this model. Moreover the model can be applicable to further deeper sequences as well in other basins like the Bombay offshore, Assam-Arakan and Rajasthan etc. because the analyzable element 'reversal of highlands and lowlands between two tectonic phases' is also observed there on various scales.
Application of Finite-Difference Method in Modelling an Oil Bearing Structure
Authors: Rathor B. S. , Devanandam M. , Mallick K.
Published: November 2024

Finite-difference numerical technique has been in use for over two decades in solving elastic wave equation for the interpretation of seismic response of complex 2-D and to a limited extent, 3-D oil bearing geological structures. The present communication consists of two parts. In the first part, synthetic seismograms have been obtained under plane wave as well as line source excitations for a gas cap structure and over a salt dome/basement undulation. In the second part, seismogram under plane wave conditions has been computed for a geological structure from the Gujarat coast. Some of the faults confining the pay zone between 1800 ms and 1900 ms in the time section are highlighted.
Deformed Cross-Bedding from the Hindoli Group of Rajasthan
Authors: Singh Surendra
Published: November 2024

Deformed cross-bedding is reported from quartzite interbands of the Hindoli Group occurring around Badi Sadri in southeast Rajasthan and is interpreted to be related to the palaeoseismic shocks that might have occurred during its sedimentational history.
Tidal Cyclicity in Lower Bhander Sandstone, Maihar, Madhya Pradesh
Authors: Basumallick S. , Sarkar B. C. , Banerjee S.
Published: November 2024

The Upper Proterozoic Lower Bhander Sandstone, occupying a major part of the Tamasa valley at Maihar, has been thought to be deposited in a tidal flat-lagoon complex,in an intertidal to supratidal environment, dominated by ebb and flood tides. A tidal bundle (a medium grained thicker sandstone unit and a thinner siltstone bed) is thought to bear the imprint of velocity and discharge associated with each tidal current as reflected in the thickness of the layers. Thickness data pertaining to 155 tidal bundles recognized in the exposures have been analysed using techniques of Smoothing, Autocorrelation and Fourier filtering, to reveal whether or not any tidal cyclicity existed. The results amply support not only the presence of alternating high spring-neap-low spring semi-lunar cycles, but a dominant periodicity of 32 bundles corresponding to 16 semi-lunar days.
Study of the Aftershock Activity and Source Parameters of the Latur Earthquake of September 30, 1993
Authors: Ramakrishna Rao C. V. , Solomon Raju P.
Published: November 2024

A total of 45 stations were operated by different agencies to record the aftershocks of the september 30, 1993 Latur earthquake. In the present study 220 aftershocks were located using the combined data set. Most of the epicentres follow the course of river Tirna and confined to area of 10 km radius. To homogenise the estimation of magnitudes an empirical relation for estimating magnitude from signal duration, Ms = -1.6757 ± 1.9484 log D, is derived, where Ms is the surface wave magnitude and D is the total signal duration in sec. The magnitudes can be estimated with an accuracy of + 0.24 units using the above relation, Focal mechanism solutions for six aftershocks are reported in this study. The majority of the solutions are in agreement with the solution of the main shock. The pressure axis as determined from the focal mechanism solutions of the aftershocks is oriented along NE - SW direction.
Structure, Tectonics and Associated Ore Deposits of Subansiri District, Arunachal Pradesh, Eastern Himalaya
Authors: Kumar Surendar , Singh Trilochan
Published: November 2024

The geological setting of the Subansiri District is mostly controlled by the fold belt, a steep sided anticlinorium in the Quartzite - Phyllite Unit of the Bomdila Group that possibly overlies an Older Massif and a concealed deep seated fault. Amongst the economic minerals and are deposits, limestone, dolomite, coal, graphite, and various base metals are of great intetest. Beside these, sulphide mineralisation is quite common. Mainly four controls on the mineralisation have been recognised, which are:

1. Deposits are strata-bound within the Phyllite - Quartzite Unit of the Bomdila Group and the Quartzite Unit of the Miri Group.

2. Ore occurs mostly near the thrust contact zone.

3. The deposits in rocks of both the units are located near the gneissic contact of the Bomdila Group as well as that of the crystallines of the Se La Group.

4. The Pb-Zn, Fe & S in the Bomdila Group show pockets and pinch and swell structures indicating earlier deposits subjected to erosional processes in the earlier phases.

Other deposits are in the Quartzite Unit of the Miri Group which are located close to the crystalline thrust.
Proterozoic Kaimur Group, Son Valley: Fluvio-Marine or Fluvio-Lacustrine?
Authors: Bhattacharyya Ajit
Published: November 2024

The Kaimur Group of the Vindhyan Supergroup in Son Valley is represented by a 8 to 400 m thick siliciclastic sequence covering an area of around 12,000 sq.km. Following the reinterpretation of the Dhandraul Sandstone (the uppennost unit of the Kaimur Group) as deposits of braided ephemeral river, punctuated by aeolian deposits, the long-prevailing shallow-marine interpretation of the sub-Dhandraul sequences has been reexamined. The sub-Dhandraul sandstones and shales reveal that their deposition took place at different depths in a large lacustrine basin affected by fair-weather as well as storm waves.
Sulfur Isotope Variations in Barite and Pyrite of Hydrothermal Barite Deposits of Cuddapah Basin, Andhra Pradesh
Authors: Mukherjee Abhijeet , Ballurkar Ashok
Published: November 2024

The d34S X-CDT values for barite and pyrite range from +23.6 to +25.5 per mil and -0.9 to +1.9 per mil respectively. Data of fluid inclusion studies enable temperature of deposition to be 250°C after pressure correction of homogenization temperatures (Th). The d34S X-CDT values of pyrite and barite suggest igneous source for pyrite and marine for barite implying that they are not formed together. The d34S X-CDT values of barite agree with d34S X-CDT values for contemporaneous Proterozoic sea water.
Mechanism of Microseismic Activity in Kerala - A Suggestion
Authors: Rajendran Kusala , Rajendran C. P.
Published: November 2024

The occasional incidences of microearthquakes in Kerala have been interpreted to be caused by the reactivation of ancient preexisting faults. While not negating the traditional wisdom, we propose an unconventional approach to analyze the mechanism of microseismicity in Kerala. A moot point considered here is the perceptive increase in the frequency of the microearthquakes in the state over the last decade, quite often coinciding with periods of increased rainfall. Although the occurrence of rain may not be a sufficient or necessary condition for the increase in the level of seismic activity, the correspondence between the two appears to be more than casual. On the basis of this observation. we suggest here that the tremors in Kerala may have been caused by transient increase in the hydrostatic pressure at shallow crustal depths. The mechanism of shallow earthquakes may be similar to what is proposed in the "hydroseismicity" model. Changing land use patterns, deforestation, soil erosion and increased siltation in the drainage basins are the robust parameters in this model.
Integrated Foraminiferal and Ammonoid Biostratigraphy of Jurassic Sediments in Jaisalmer Basin, Rajasthan
Authors: Dave Alok , Chatterjee T. K.
Published: November 2024

In the Post-Vindhyan times, major marine transgressions covered the areas of Kutch and Rajasthan, including the Jaisalmer Basin during Jurassic, although minor Permian transgressions are also known. These events could be documented from the well known exposures of Kutch and Rajasthan which entombed classic Cephalopod fauna. The foraminiferal components of Kutch Mesozoic were catalogued by Pandey and Dave (1993), recognizing 13 benthic foraminiferal biozones, establishing 8 chronostratigraphic units (stages).

Within the outcropping marine Middle-Upper Jurassic succession of Jaisalmer, seven benthic foraminiferal zones have been recognized and correlation with Kutch Mesozoic established. However, the succession is interrupted by five hiatuses during - (1) Upper Bathonian, (2) Upper Callovian - Lower Oxfordian, (3) Upper Oxfordian - Lower Kimmeridgian, (4) Middle Kimmeridgian and (5) Upper Kimmeridgian - Lower Tithonian.

Trangressive events during Lower Bathonian, Lower Callovian, Middle - Upper Oxfordian and Lower Kimmeridgian with intervening regressive pulses are also recorded.

Badian, Charian, Dhosaian, Katrolian and Umiaian stages of Kutch ranging in age from Bathonian to Tithonian are recognized.
Origin of Amphibole-Rich Beach Sands from Tila-Mati, Karwar, Central-West Coast of India
Authors: Mislankar P. G. , lyer S. D.
Published: November 2024

The pocket beach at Tila-Mati, Karwar, central west coast of India, is characterised by the occurrence of amphibole-rich (chiefly tremolite-actinolite) coarse sand in the zone of minimal impact of waves and currents.

In the total sediment, grain size and sphericity are directly proportional while a decrease in sphericity results in an increase of amphiboles (60-80%). This is probably due to the elongated nature of the amphibole grains which are abraded in a low energy environment. The Tila-Mati beach sediment has been derived locally by erosion of amphibole schist exposed in a cliff adjacent to the beach.
Orbicular Structures from Lingsugur Area, Raichur District, Karnataka
Authors: Prakash H. S. M.
Published: November 2024

Well developed single shell orbicules and proto-orbicules with hornblende as the nucleus and plagioclase as the shell, are well preserved in a 30 m x 11 m outcrop of diorite at jalibenchi, Lingsugur area, Raichur district. It could also be described as esboitic as the feldspar is oligoclase. The normative anorthite content in the orbicule varies from 26.13% to 33.64%. The solidification indices are low suggesting a slow but steady rate of cooling. The chemical and mineralogical discriminant diagrams show that the orbicular rocks are tonalitic to mafic tonalitic in composition. The two units of the orbicular structure viz., (1) the core made up of hornblende is attributed to have been derived from an enclave of amphibolite which was invaded and shattered by an upwelling hydrous pegmatitic plagioclase vein and gel-like in nature and acted as the cause for the formation of the (2) single shell structure. The monomineralic composition of the shells of orbicules and the unicomponent composition of the plagioclase vein are thus genetically explained.
The Characterization of Metamorphic Facies of Metabasalts of Hutti Greenstone Belt
Authors: Riyaz Ulla M. S. , Pathan A. M. , Maaskant P.
Published: November 2024

The Hutti greenstone belt, containing several promising gold deposits is predominantly composed of metavolcanics represented by basalt with minor felsic volcanics and metasediments. Basalt has undergone regional metamorphism as indicated by the presence of characteristic metamorphic mineral assemblage of plagioclase, amphibole and chlorite. Electron microprobe studies are carried out on these minerals to study the chemistry and the mineral reactions in the rock. The analytical data indicate that plagioclase is andesine, amphibole is magnesio-hornblende and chlorite is ripidolite.

The mineralogical assemblage, the chemistry and in particular the co-existence of hornblende and chlorite in metabasalt indicates a metamorphic grade 'transition between greenschist and amphibolite facies'.
Composition of Smectites in the Lameta Sediments of Central India: Implications for the Commencement of Deccan Volcanism
Authors: Salil M. S. , Pattanayak S. K. , Shrivastava J. P.
Published: November 2024

The studies on the structural formulae of smectites in the Larneta sediments indicate that they are rich in octahedral Fe, Mg and tetrahedral Al. Identical patterns of Mg, Fe and Al abundances in the octahedral and tetrahedral layers respectively, were also observed in the smectites of intertrappean sediments and weathered Deccan Basalts. The thermodynamic components and charge configurations of smectites in the Lameta, intertrappean and Deccan Basalt indicate that they fall within the compositional plane of smectite solid solution. The compositional commonality of smectite in the Lameta sediments with those in the intertrappeans and weathered Deccan Basalt suggests, Smectites in the Lameta sediments are derivatives of Deccan volcanic products. This implies the commencement of Deccan Volcanism during the Maastrichtian Lameta sedimentation or prior to it.
Depositional Environment and Basin Development During Early Palaeogene Lignite Deposition, Western Kutch, Gujarat
Authors: Mukhopadhyay Sanjay Kr. , Shome S.
Published: November 2024

Exploration for lignite by drilling in the early Tertiary Supratrappean paralic sequence on the onshore of western Kutch,Gujarat, provides detailed information on the basement characteristics and palaeoenvironment of lignite deposits. A comprehensive study of outcrop sequence and its dip directional subcrop counterpart reveal that lignite bearing sediments were deposited in three distinct domains; (a) fringe areas of exposed trap rock on mainland, (b) adjacent dip directional subsurface areas on trap basement and (c) areas located beyond the subcrop limit of trap in a basinward direction. Domain (b) is considered most favourable locale for exploration as it contains palaeotopographic lows. A synthesis of outcrop and suberop data helped in identifying three depositional environments for the lignite bearing sediments, namely a prograding delta, back barrier environment and lagoons of foraminiferal bank environments. Vegetation growth and accumulation took place in all the three environments but sizable peat matter are found to occur in transitional lower delta plain, and in the back barrier deposits. These depositional environments and various stratigraphic criteria are used to reconstruct six conceptual models to depict the evolution of early Tertiary basin and accumulation of lignite therein. The significance of stratigraphic markers i.e. Lower Eocene Assilina marl-moll usca coquina bed and the Middle Eocene large Nummulities bed, in locating lignite deposits is also discussed.
Sulphide Mineralization in the Parsoi Formation of Mahakoshal Group, Southern Mirzapur District, U.P.
Authors: Farooq S. , Hasan N.
Published: November 2024

Surface indications of sulphide mineralization were noticed in the form of gossan bands outcropping as cellular, spongy and boxwork structures of limonite in the marble of Parsoi Formation of Mahakoshal Belt near Ningha village in southern Mirzapur district. Investigations reveal that mineralization is localized along fractures, shears and zones of brecciation in the marble, and is controlled by the structural patterns of the host rocks. Sulphide mineral assemblage consists of pyrite, pyrrhotite, cobaltite, chalcopyrite, sphalerite, galena, proustite and pyrargyrite. The sulphides are found to occur in the form of veins, stringers and disseminations. Mineralogical assemblages and textural characteristics of the altered and sulphide zones indicate that mineralization is hypothermal in nature.
Magnetic Polarity Stratigraphy of the Siwalik Sequence of Haripur area (H.P), NW Himalaya
Authors: Sangode S. J. , Kumar Rohtash , Ghosh Sumit K.
Published: November 2024

A 2375 m thick sequence consisting of sandstone-mudstone alterations was sampled for magnetic polarity stratigraphy in Somb Nadi and its tributary, Jamni-Khol in the Haripur area of Himachal Pradesh. 200 palaeomagnetic sampling sites were selected from 45 overbank intervals of fluvial cycles. Only fine-grained sediments were sampled to get the ideal results from stable single domain grains. Progressive thermal demagnetization was carried out at intervals of 25, 50 and/or 100°C. A considerably stable secondary remanant magnetization was removed above 450°C with the isolation of characteristic remnant magnetization component at 600°C. Corrected mean directions for the normal and the reversed sites are D = 349°, I= 28° and D = 168°, I= -28°, respectively. The Tatrot/Pinjor faunal event is recognised on the local magnetic polarity time scale at 2.6 Ma (1685 m level) and the Middle to Upper Siwalik transition (Dhok Pathan/Tatrot boundry) at 5.26 Ma (500 m level), approximately. Predominance of piedmont depositional system at around 3.2 Ma (1450 m level) suggests uplift and denudation of the Outer Leesser Himalaya during this period. First record of the Pre-Tertiary clast-dominated conglomerate is observed at 2.6 Ma and that of Tertiary clast-dominated conglomerate at 1.76 Ma. An average rate of sedimentation of 45 cm/1000 years was observed till 2.6 Ma. Further, it shows increasing and decreasing trend after 2.6 Ma with a maximum value of 54 cm/1000 years and a minimum of 8 cm/1000 years sediment accumulation.
Heavy Mineral Concentration on the Visakhapatnam - Konada Coast as Evidenced by Magnetic Susceptibi1ity and Radioactivity
Authors: Lakshmipatiraju A. , Srinivasa Rao L.
Published: November 2024

Magnetic susceptibility, radioactivity, bulk density (?) and texture of black sands from the Visakhapatnam-Konada belt on the east coast of India were studied. The sands are fine-grained and well sorted with a nearly symmetrical distribution. Mass susceptibility (?) and radioactivity (R.A.) are related to weight percentage of magnetic minerals and grain percentage of radioactive minerals respectively. The magnetic fraction is made up of magnetite and ilmenite. The radioactive minerals present in the sands are monazite and rarely zircon. Susceptibility and R.A. of finer sieve fractions are high, reflecting higher proportions of magnetic and radioactive minerals.

Mass susceptibility, Radioactivity and bulk density of black sands are high south of outcropping rock formations across the coast, reflecting heavy mineral concentration. A structural aspect of the coast, namely the Eastern Ghat formations cutting across the coast, seems to be one of the controls on heavy mineral concentration.
Morphodynamic State of Beaches Between Vaipar and Tiruchendur, Tamil Nadu
Authors: Ramanujam N. , Radhakrishnan V. , Sabeen H. M. , Mukesh M. V.
Published: November 2024

The relationship between the surf zone processes and the morphodynamic state of beaches between Vaipar and Tiruchendur along the southeastern coast of Tamil Nadu was studied through 46 beach profile measurements and other morphological features across and along the shoreline. The energy variations in the beach along with the morphological and sedimentological properties are distinguished by the surf-scale parameter. The dissipative beaches with higher wave heights and low beach gradients yield the higher amount of surf-scale parameter (22.0 to 154.3) whereas at the other extreme, the reflective beaches with steep beach gradients and lower wave height conditions resulted with low surf-scale value (0.5711 to 2.500). Intermediate beach states possessing dissipative and reflective elements with four transitional stages are recognised.
A Note on the Occurrence of Molybdenite at Ashapura, Raichur District, Karnataka
Authors: Prakash H. S. M.
Published: November 2024

A new occurrence of molybdenite is reported from the granites of Ashapura area, 6 km SSW of Raichur town. An E-W trending leucogranite dyke within pink granite shows anomalous concentrations of molybdenum ranging from 15 ppm to 3.26%. Significant concentrations of tungsten (100-900 ppm), silver (upto 11 ppm), copper (upto 665 ppm), platinum (19 to 253 ppb), palladium (60 to 380 ppb) and iridium (7 to 73 ppb) are also observed. The mineralisation occurs along thc western periphery of the granitoid, stretching over 1.5 km from Jalibenchi to Ashapura. Petrologic characters, alteration products and geochemical parameters compare well with granite hosted porphyry type molybdenite mineralisation reported elsewhere.