bluuebunny/crossref_metadata_2025 huggingface dataset:
Nagaur-Jhalawar Geotransect Across the Delhi/Aravalli Fold Belt in Northwest India
Authors: Tewari H. C. , Divakar Rao V. , Narayana B. L. , Dixit M. M. , Madhav Rao N. , Murty A. S. N. , Rajendraprasad B. , Reddy P. R. , Venkateswarlu N. , Vuaya Rao V. , Mishra D. C. , Gupta S. B.
Published: November 2024

Lithological, gravity, magnetic, and seismic data within 100 Km corridor of the 400 km long seismic reflection profile are compiled to constitute the NW-SE Nagaur-Jhalawar Geotransect. The transect sequentially cuts across the Neo-Proterozoic Marwar Basin (MB) on the northwest, the Palaeo/Mesoproterozoic Delhi Fold Belt (DFB), the middle/late Archaean Bhilwara Gneissic Complex (BGC) and the MesolNeoproterozoic to early Palaeozoic Vindhyan Basin (VB) at the southeast. The BGC and DFB belts show polyphase deformation and metamorphism.

The BGC within the transect, consists of Sandmata Granulite Complex, followed by amphibolite facies Mangalwar Complex and Greenschist facies Hindoli/Sawar groups. The BGC show evidence of crustal reworking at c.3.0 Ga. The DFB is represented by amphibolite facies metavolcanic-metasedimentary shallow marine sequences and is tectonically highly disturbed. The DFB deposits (c. 2.0 - 1.5 Ga.) were subjected to tectonic deformation during Delhi orogeny (c. 1.5 Ga.), which is marked by syntectonic granitic plutonism. Both, the BGC and OFB also appear to have been affected by Neoproterozoic thermal events and granitic plutonism. The Neoproterozoic MB consists of clayevaporite sequences of shallow oscillatory basin deposits.

Seismic, gravitylmagnetic and magneto-telluric techniques could delineate a number of shallow to deep faults, intrusive bodies and a high conductivity zone. The total magnetic intensity shows a regional increase towards southeast. The Bouguer anomaly values show a steep rise of upto 80 mGal towards the boundary of OFB and BGC. Based on the seismic studies, doubling of the crust under the OFB and vertical intrusion of high density material under the BGC are inferred. The upper crust is, in general, transparent in its reflectivity while the lower crustal reflectivity is high in the transect area, except in the BGC and the VB. A thrust boundary, dipping NW, is present at the eastern margin of the BGC and could be traced up to 30 km depth. The Moho is at a depth of 36-38 km under the MB. Multiple Moho reflections are identified in the DFB crust, the deepest being at 45-50 km depth. In some part of the BGC the Moho can not be identified but in parts it is traced at about 50 km depth, with southeast up dip, before becoming subhorizontal at depth of 41-42 km. It becomes shallower to about 30 km depth at the SE end under the VB.
Driving Forces of Indian Summer Monsoon on Milankovitch and Sub-Milankovitch Time Scales: A Review
Authors: Naidu Pothuri Divakar
Published: November 2024

A scientific consensus exists that tectonic evolution of Himalaya is the main cause of monsoon initiation and evolution in southeast Asia. Several forcing factors such as tectonic, solar insolation, latent heat transport, albedo of the earth surface and deep water circulation changes drive the variability of southwest (SW) monsoon in the Indian subcontinent. Different forcing factors act on different time scales. Arabian Sea sediments consist of distinct fauna that are endemic to areas of upwelling. The SW monsoon wind strength, upwelling in the Arabian Sea and precipitation in the subcontinent are inter linked. Thus Arabian Sea sediments provide a record of past monsoon variability covering a time span of a few million years.

Detailed analysis of numerous monsoon indices and General Circulation Models (GeM) show that SW monsoon was strong during interglacials (warm periods) and weak during glacials (cold periods). Spectral analysis of detailed time series of monsoon indices reveal that the intensity of the SW monsoon fluctuates with periodicities of 100 ka and 23 ka. These periodicities of SW monsoon were attributed to the orbitally induced changes in solar radiation and surface boundary conditions (Milankovitch Theory). Recent high-resolution studies from the Oman Margin provide new evidences on the SW monsoon variability on century time scale and a Sub-Milankovitch Periodicity in the range of 2,200 to 2,400 years. The SW monsoon variability on century scale and high frequency periodicities might be forced by the deep water circulation changes in high latitudes. The present review discusses the atmospheric 14C changes and recent onset of aridity in the tropics, which is also linked to the SW monsoon variability in one way or other.
Cluster Analysis and Nickel Thermometry of Garnet Xenocrysts from Majhgawan Diamondiferous Pipe, Panna District, Madhya Pradesh
Authors: Mukherjee Abhijeet , Rao K. S. , Roy Gautam , Babu E. V. S. S. K.
Published: November 2024

Based on the Q-Cluster analysis of 536 garnet grains, the garnets of Majhgawan are classified as Group 1, Group 2, Group 9, Group 10 and Group 11. Group 10 garnets have very high MgO (21.2%) and moderate to high Cr2O3 (9.5%), combined with low CaO. MgO shows negative correlation with CaO and FeO and this cluster contains a large number of garnet inclusions in diamonds. The major element chemistry of these garnets confirm that they are moderately subcalcic and have high Crcontent with a well-defined Ca-Cr trend. Around twenty percent of garnets show harzburgitic trend indicating low to moderate grade of the pipe. Nickel thermometry has indicated a well-defined geotherm between 1150° - 1400°C and corresponds approximately to a slightly elevated 42 m W/m2 conductive model. Garnets with temperature > 1150°C probably were derived from diamond stability field. Based on Ni-thennometry (using only lower cut-off) omega value is calculated (<30) which suggests an average grade upto 15 ctpht for Majhgawan pipe.
Natural Fresh-Water Ridge as Barrier Against Sea-Water Intrusion in Chennai City
Authors: Ballukraya P. N. , Ravi R.
Published: November 2024

Hydrogeological investigations along the Chennai (Madras) coast showed that groundwater levels are lower than mean sea level, often as much as -3 to -6m. However, the quality of groundwater in the near-surface unconfined aquifer, tapped by shallow wells, is reasonably fresh, though deeper wells show distinct signs of sea-water intrusion. Presence of fresh water below mean sea level in the absence of positive fresh water head is not possible in a coast line having hydraulic continuity with the marine environment. Detailed studies show that a narrow fresh water ridge, created by the beach dune complex, exists along the coast. Along most of the beach ridge groundwater abstraction is relatively less and also there is regular recharge into the aquifers from monsoon rains, and thus the static water level remains slightly above mean sea level along a narrow zone for most of the coastline. This fresh water ridge prevents contamination of the shallow aquifer to the west of the ridge, even though the water levels fall below mean sea level in the aquifer. Where the beach area has been urbanized or where there is large-scale abstraction from beach zone, groundwater has been contaminated with saline water as there is no fresh water barrier in such locations. Thus, the beach area has, to a large extent, safeguarded the shallow aquifers from serious saline water intrusion in Chennai city. This is a fortuitous situation which also selVes as a warning not to urbanise beach zones in coastal cities.
Early-Middle Miocene Planktic Foraminifera from the Quilon Formation, Kerala
Authors: Singh A. D.
Published: November 2024

Praeorbulina glomerosa (Blow), Praeorbulina sicana (de Stefani), Globigerinoides diminutus Bolli are recorded for the first time from the Quilon Formation in a subsurface section at Quilon. These planktic foraminifera are considered as diagnostic forms of the Early-Middle Miocene. Two biostratigraphic subdivisions were established based on the detailed qualitative analysis of planktic foraminiferal assemblages. The co-occurrence of Gs. diminutus and Gs. alttapertura Bolli and the absence of Praeorbulina Olsson in the assemblages of the lower portion of the section suggest this part to be referable to Globigerinatella insueta Zone of Bolli (1966), which is of late Early Miocene age. The assemblages from the upper part of the section are characterised by the presence of Praeorbulina glomerosa, P. Sicana and Gs. diminutus, representing early Middle Miocene Praeorbulina glomerosa Zone of Srinivasan (1989). The Praeorbulina glomerosa Zone (=Zone N8) lies within the European Langhian Stage, whereas the Globigerinatella insueta Zone (=Zone N7) corresponds to the upper part of the Burdigalian Stage. Thus, the stratigraphic age of the Quilon Formation is late Early Miocene to the earliest Middle Miocene (upper Burdigalian to lower Langhian) and not Burdigalian as previously inferred by many workers.
Stable Carbon and Oxygen Isotope Analysis of Natural Calcite and Dolomite Mixtures using Selective Acid Extraction
Authors: Ray Jyotiranjan S. , Ramesh R.
Published: November 2024

Accurate analysis of coexisting calcite and dolomite for d13C and d18O is generally hindered by the difficulty in the physical separation of these minerals. The difference in the reaction rates of calcite and dolomite with phosphoric acid, has been used to chemically separate these carbonates. Previously established procedures are only suitable for samples containing 1:1 calcite-dolomite pairs. However, these are sometimes tedious and time-consuming. Using mixtures of calcite and dolomite, two different selective acid extraction procedures (for reactions at 25°C), one for calcite-rich and the other for dolomite-rich carbonates, have been developed. Reduction of grain size (to 37μm - 45μm) increased the reaction rate and hence decreased the total reaction time to a reasonable interval (=72 hours for dolomite). Applying these procedures, d13C and d18O of calcite and dolomite/ankerite of carbonatites from Amba Dongar and Sung Valley carbonatite complexes of India were measured and their temperatures of crystallization determined. Accurate isotopic compositions of individual carbonates of calcite-dolomite mixtures can be determined for geological interpretations by these procedures.
Inferences on Rhodoids from Neogene Carbonates of Kudankulam, Tamil Nadu
Authors: Ramasamy S. , Armstrong Altrin Sam J.
Published: November 2024

Rhodoids are laminated algal nodules generally found in shallow marine environment. Algal crusts and nodules are poorly exposed between Kudankulam and Sattankulam in the coastal area near Cape Comorin. The thickness of the bed of algal limestone varies from 0.5 to 1.5 m. The occurrence of abraded rhodoids with lack of terrigenous material suggests moderate to high energy depositional condition. The present study of the rhodoids, points out that the Neogene tectonic activity has played a significant role for the development of algal limestone and rhodoids in the study area.
A Mineralogical Analysis of Karst Sediments and its Implications to the Middle-Late Pleistocene Climatic Changes on the Tibetan Plateau
Authors: Zhang David Dian
Published: November 2024

The minerals in various categories of Tibetan karst sediments were divided into three groups: carbonate, iron and silicate. The carbonate minerals, including calcite, aragonite and dolomite, consist mainly of speleothem, tufa and sinter. Most of the speleothems indicates wetter and warmer periods in early and middle Pleistocene, the youngest being 194,000 years old. The second formation of carbonate mineral, tufa, implies an arid period starting 91,000 years BP. The iron minerals, goethite and hematite, are often mixed up with cave alluvial sediments that are interbedded with flowstones, and the depression sediments. They indicate strong oxidizing environments during their deposition, which is absent at present. The clay minerals, specially kaolinite, were contained in cave alluvial, flowstone and the depression sediments as well. Combined with stratigraphic study and U-series dating, the mineral analysis shows that warmer and wetter climates, which were suitable for speleothem development, probably disappeared 200 ka ago, and drier and colder climates dominated this plateau since then.
Isotopic Composition of Middle Old Red Sandstone Carbonates: Implications for the Palaeoenvironment
Authors: Das Nachiketa
Published: November 2024

The carbonates occurring within the sandstones of the Middle Old Red Sandstone of the Orcadian basin (Middle Devonian) in Caithness, N.E. Scotland are of minor abundance, predominantly calcite and may be petrographically ascribed to early diagenetic origin.

Isotopic analyses (C, O, Sr) have been undertaken to elucidate the depositional mileu of these carbonates at two localities, Wick and Reay. Calcite and dolomite coexist in carbonate facies rocks and their similarity in d13CPDB (-4.57 ± 0.64 and -4.56 ± 0.53‰ respectively at Wick and -2.39 ± 0.30 and -2.00 ± 0.48 respectively at Reay) suggest a cogenetic origin at each locality. The d13C values also suggest deposition from lighter, freshwater.

Mean calcite d18OPDB values of -7.76 ± 1.92‰ and -8.76 ± 2.23‰ for Wick and Reay samples respectively also support this contention. Dolomite d18OPDB values are consistently heavier which is not inconsistent with a generally cogenetic origin. The oxygen isotope data reflects a lighter pore fluid composition either because of diagenetic modification by carbonate recrystallization or a greater contribution of freshwater via river supply during sandstone deposition in an ephemerally evaporative lacustrine environment. Mean Sr87/86 value of 0.711167 for the carbonates of Wick confinn a nonmarine origin.
Basement-Cover Relationship in the Khetri Copper Belt and the Emplacement Mechanism of the Granite Massifs, Rajasthan, India
Authors: Gupta Pratip , Guha D. B. , Chattopadhyay B.
Published: November 2024

The Precambrian Khetri Fold Belt in northern Rajasthan, India, is bifurcated by the transverse Kantli Fault into the North Khetri Belt (NKB) and the South Khetri Belt (SKB). A new stratigraphic and structural framework has been proposed for the NKB and the SKB. The NKB and the SKB evolved independently and show different basement-cover relationships. The Proterozoic cover sequence on either side of the Kantli Fault differ significantly from each other in litho-characteristics, specially in the content of felsic-volcanics. The 1832 ± 3 Ma old synsedimentary felsic volcanism in Proterozoic sequence is considered to be coeval with the Jasrapura Granite dated at 1844 ± 7 Ma.

Geochronological data from several granite bodies suggest a plutonic event around 1500 ± 200 Ma which constrains the third phase of deformation in the basement rocks. TWo types of granites are recognised; one akin to the Hercynian-type peraluminuous, compositionally restricted ilmenite-bearing S-type granite and the other Caledonian-type, compositionally restricted I-type granite.

Both forceful ballooning and forceful permitted type processes were responsible for the plutonic activity. Significant amongst the first-type are the Udaipurwati Granite and the Chapoli Granite; the former shows stretching of the sodium-rich early consolidated intrusion as a result of inflation of the potassium-rich central part of the magma balloon.

A general readjustment of the isotopic systems within minerals occurred around 700 - 800 Ma or even later, possibly a Pan-African event, which has been correlated with widespread granitic activity in western Rajasthan.
Behaviour of Stretching Lineations in the Salem-Attur Shear Belt, Southern Granulite Terrane, South India
Authors: Chetty T. R. K. , Bhaskar Rao Y. J.
Published: November 2024

A rare occurrence of both steep and shallow plunging stretching lineations within a single outcrop, has been described from the Salem-Attur shear belt, and the regional variations in the orientation of stretching lineations are discussed in terms of transpressional tectonics in the Cauvery shear system, southern granulite terrane, South India.
Morphotectonic Evolution of the Laterite Profiles over Sukinda Ultramafics, Jaipur District, Orissa
Authors: Som S. K. , Joshi R. , Roy P. K. , Mukherjee M. M.
Published: November 2024

Sukinda ultramafic field of Jajpur district, Orissa is capped by thick lateritic duricrust. Two generations of laterite are inferred in the studied area. The older laterite (in situ) is capped by transported laterite (younger). The entire area is divided into two subareas (A1 and A2) Physiographically, three terraces are identified in A1 area, of which, the oldest one (T3) comprises of insitu lateritic hard crust. The other two terraces (T2 and T1) are made up of valley fill deposits, which are later lateritised. The area A2 shows the lateral continuity of T3 terrace of A1 area along with valley fill deposit of T1 terrace and the absence of T2 terrace. Drainage analysis show the A1 area is structurally more disturbed than A2 area. Correlation of geomorphological evolution and lateritisation indicates three stages of development in the A1 area. Lateritisation was initiated on a comparatively flat ground (T3 terrace) and subsequent destabilisation of the area developed the younger terraces (T2 and T1) with the modification of older laterite profile.
Subsurface Control on Salt-Affected Regions of Indo-Gangetic Basin
Authors: Srivastava Ajay , Singh Ramesh P.
Published: November 2024

Visual interpretation of IRS-lCWIFS image has revealed some important geomorphic features controlled by the fluvial dynamics of the river and the subsurface structural features. Geomorphological features present in this region have been studied and correlated with the subsurface structural features and associated tectonic changes which have occurred in the recent past. Faizabad Ridge is the main tectonic element in the southern part of Indo-Gangetic plain and it has been found to playa key role in the evolution of the contemporary topography. The striking similarities have been observed in the occurrence of subsurface features and geomorphological features allover the peripheral regions of the Faizabad ridge. The severe problem of soil salinity/alkalinity occurring in this patt of the Indo-Gangetic plain is attributed to the changes which occurred in Paleogene period associated with the evolution of the Faizabad ridge in the basement.
Gas-Hydrates - A Synoptic View
Authors: Subrahmanyam C. , Reddi S. I. , Thakur N. K. , Gangadhara Rao T. , Sain Kalachand
Published: November 2024

Large-scale occurrence of gas-hydrates in the marine sediments of outer continental margins is by now well-known. While the methods of tracing gas-hydrate enriched zones, like identifying markers such as bottom simulating reflectors and blanking zones on seismic reflection sections, are well-established, quantification and resource assessment of gas hydrates still remain hazy. Investigations over the classical gas-hydrate enriched Blake outer ridge on the U.S. Atlantic margin have provided new insights into the environs of gas-hydrate occurrences. Deep sea drilling results in this area indicate that the estimates of gas-hydrate from geophysical measurements could be less by an order of three in comparison with those obtained from drilling. Several factors like bathymetry, sediment thickness and sedimentation rates, sea bottom temperature and total organic carbon content, which control gas-hydrate formation, indicate that the shallow sediments in the offshore regions of India could be potentially enriched in gas hydrates. National agencies like the Oil & Natural Gas Corporation, Gas Authority of India Ltd., National Geophysical Research Institute, National Institute of Oceanography and others are now actively involved in assessing the true potential of this anticipated future energy resource. The environmental aspects of gas hydrates like large-scale release of methane gas into the air and slope instabilities and submarine landslides in the continental margins resulting in catastrophic events, however, need to be kept in mind.
Fossil Microbiota from the Vaishnodevi Limestone, Himalayan Foothills, Jammu: Age and Palaeoenvironmental Implications
Authors: Venkatachala B. S. , Kumar Ashok
Published: November 2024

Vaishnodevi Limestone is a distinctive landmark succession in the Jammu Himalaya. Significant biotas have been identified from a well exposed chert outcrop near Bidda and shale near Muttal. The chert biota is dominated by mat forming crustose, coccoid, chroococcacean cyanobacteria that include Eoentophysalis belcherensisand Palaeopleurocapsa wopfnerii. The other coccoid taxa are Myxococcoides grandis, Gloeodiniopsis lamillosa, Eogloeocapsa avzyanica, Sphaerophycus cf., S. medium, Eosynechococccus moorei, E. grantiis, Siphonophycus kestron, S. robustum, Oscillatoriopsis sp., Circumvaginalis elongatus, Archaeoellipsoides major, and A. minor. Stratigraphically this is the oldest biota thus far known from the Vaishnodevi Limestone and is assigned a palaeoproterozoic-Mesoproterozoic age.

The Muttal biota is composed of Siphonophycus kestron, S. robustum, Oscillatoriopsis sp., Calyptothrix spp., Eosynechococcus medius, Archaeotrichion contortum, Archaeollipsoides bactriformis, A. grandis, A. obesus, Arctacellularia ellipsoidea, Nostochomorpha prisca, Paleonostocalia irregularia, Leiosphaeridia laminariala, Leiosphaeridia sp., Lophosphaeridum spp., Micrhystridium spp., Sphaerocongregus sp., Obruchevella sp., Chuaria sp., Kildinosphaera sp., Spiromorpha indet. and vase shaped microfossils (VSMs). The Muttal biota is from the topmost shale unit of Vaishnodevi Limestone and is assigned a Neoproterozoic age.

It is concluded that the age of the Vaishnodevi Limestone spans the entire Proterozoic and deposited in a supratidal to intertidal and subtidal environment within a shallow shelf regime.
Bioclastic Shore Deposits: Indicators of Late Quaternary High Sea in Saurashtra, Western India
Authors: Bhatt Nilesh , Patel M. P.
Published: November 2024

The high energy coastal segment between Okha and Diu in Western Saurashtra is characterised by typical kind of raised bioclastic shore deposits. These occur up to 15 m (max.) above present day mean sea level and about 5 km inland. Variously described as "coast fringing rocks", "Chaya Formation", "ancient beach rocks", "shell limestones", etc., these possess poorly sorted allochems and lithic fragments of coarse sand to gravel size, mostly cemented by aragonitic micrite and occasionally fibrous aragonitic and high magnesian calcite, their pores being infilled by second generation of low magnesian sparry calcite cement. On the western coast of Saurashtra, they underlie coastal dunes and sheets of rniliolitic limestone and form gently seaward dipping sheets and their surfacial exposures are encountered southward only up to Kadwar, near Diu. However, they occur at the base of deep quarries of miliolitic limestone between Kadwar and Mahuva. Looking at the available reliable Th230/U234 and ESR dates of fossil shells from these deposits, they represent a higher sea level during the oxygen-isotope sub-stage 5e. On the South Saurashtra coast, the high coastal cliffs of miliolitic limestone exhibit presence of raised shore platforms and notches which may be related to this high sea after considering the influence of tectonism.
The Tectonic Segments of Northeastern India and Associated Gold Mineralisation
Authors: Sengupta P. R. , Agarwal N. K.
Published: November 2024

Gold in Northeastern India is broadly distributed in three distinct tectonic segments viz., a) The Peninsular Shield extension comprising, mainly Precambrian to Tertiary lithostratigraphic components, b) The Patkai-Arakan-Yoma Mobile Belt comprising Cretaceous-Tertiary gently folded belt, and c) The Brahmaputra-Surma Plains comprising Quaternary clastic derivatives. The first two domains have primary source rocks of gold and PGE while gold has been recovered from the alluvium in the third domain. There is a need for conceptually sustained gold exploration efforts in the region.
The Grain-Size Behaviour and Morphoscopy of Supraglacial Sediments, South of Schirmacher Oasis, E. Antarctica
Authors: Asthana Rajesh , Chaturvedi Arun
Published: November 2024

The present study embodies the description of textural characteristics and quartz grain morphology (under SEM) of sediments occurring in three micro-environments on the polar ice sheet. Coarse to fine grained, largely ill-sorted sediments with a polymodal distribution reflect a varying magnitude in the velocity of the transporting medium. A dominant saltation population with little suspension and lack of rolling population is revealed by cumulative curves which suggests transportation of these supraglacial sediments by wind. The quartz grains bear two generations of mechanical textures and a third phase of chemical textures attributed to glacial and aeolian environments.
Permian Gondwana Sedimentation in Yellandu (Singareni) Coalfield, Andhra Pradesh, India with Notes on Regional Paleogeography and Tectonic History
Authors: Tewari R. C.
Published: November 2024

The Yeliandu coalfield of Andhra Pradesh contains an 850 m Permian Gondwana rocks composed of Barakar, Barren Measures and Raniganj Formations. They are characterised by fining upward cycles. The sandstones are channel shaped, sheet-like and multistoried, and planar and trough cross bedded. The shales are massive to laminated and form thin lenses in the Barakar, but moderately thick sheets in the ovelying Barren Measures and Raniganj Formations. The coal seams are thin and lensoid. Paleocurrent studies suggest consistently northhwesterly dispersal direction areally and temporally. Evidence indicates that initially braided streams at the onset of Early Permian Barakar sedimentation became meandering through time into Barren Measures and Raniganj Formations of Middle and Late Permian, respectively. The close similarity in lithofacies depositional environment and dispersal direction of Permian rocks of Yellandu coalfields and those of neighbouring Pranhita-Godavari basin in the east. and their geological and tectonic setting suggest that the Yellandu coalfield was part of the Godavari basin until the Late Permian or Early Triassic.
Evaluation of Low-Field Hysteresis Loop and Magnetic Susceptibility of Tertiary Basalt from Jos Plateau: Nigeria
Authors: Garde S. C. , Ojelabi E. A.
Published: November 2024

Low-field hysteresis (LFH) loop and relative magnetic susceptibility (RMS) values in a field of 0.5 to 10 Oe has been used to evaluate the stability of magnetic directions of Tertiary basalts from Jos Plateau Nigeria. Graphs of magnetic moments (MM), susceptibility (S) and relative magnetic susceptibility (RMS) against applied field (AF) were plotted. The results showed that in a field of 0.5 to 1.5 Oe, the MM varied linearly with the AF while for Af > 1.5 Oe MM remained approximately constant. Rocks having stable tilted lines without any Rayleigh loop have relative susceptibility values in the range of 0.2 to 0.245 and =0.3 at 10 Oe, an indication of their being paiaeomagnetically stable. Rocks having thin Rayleigh loops had corresponding RMS values in the range 0.15 to 0.19. On the other hand wide loops were found to correspond to RMS value in the range =0.145.
New Record of Sauropod Nest-Sites in Lameta Formation from Jhalod, Panchmahals District, Gujarat
Authors: Roychowdhury Manas , Saha T. K. , Guha Dipayan , Munshi R. L.
Published: November 2024

Sauropod nest-sites having well-preserved tubocanaliculate types of eggs have been found within the Lameta Formation at Ihalod taluka, Panchmahals district, Gujarat. Four morphotypes of eggs have been distinguished based on thickness and microstructure of eggshell. Dinosaur eggs have been found in three horizons in the same stratigraphic section indicating a site fidelity which is for the first time being reported from the Lameta Formation of India.
Petrology and Geochemistry of Mixed Oxide-Silicate Facies Banded Iron Formations from Sandur Schist Belt, India
Authors: Manikyamba C.
Published: November 2024

Mixed oxide-silicate facies banded iron formations are found as thin bands in the Eastern Volcanic Block of the Sandur schist belt They consist of haematite, magnetite, cummingtonite-grunerite and chert/quartz. Chemical constituents are SiO2, Fe2O3 and FeO with no appreciable concentration of any other oxide. This composition is reflected in their trace and REE data, such as high order depletion in geochemical twins like Zr-Hf, V-Sc and Nb-Ta. The REE patterns are highly depleted (SREE 0.96 to 9.98 ppm) with Nd/Yb varying between 2 and 5. Cherty BIFs from this belt, metamorphosed to lowest greenschist facies. show almost identical geochemistry. The available data from this belt and other places indicate that unless impurities from terrigenous and volcaniclastic sources are present, metamorphism from lowest greenschist facies to granulite facies does not make an appreciable change in their trace and REB constituents.
Contrasting Isotopic Mantle Sources for Proterozoic Lamproites and Kimberlites from the Cuddapah Basin and Eastern Dharwar Craton: Implication for Proterozoic Mantle Heterogeneity Beneath Southern India
Authors: Chalapathi Rao N. V. , Gibson S. A. , Pyle D. M. , Dickin A. P.
Published: November 2024

Kimberlites intruding the Precambrian basement towards the western margin of the Cuddapah basin near Anantapur (1090 Ma) and Mahbubnagar (1360 Ma) in Andhra Pradesh have initial 87Sr/86Sr between 0.70205 to 0.70734 and eNd between +0.5 to +4.68. Mesoproterozoic lamproites (1380 Ma) from the Cuddapah basin (Chelima and Zangamarajupalle) and its NE margin (Ramannapeta) have initiail 87Sr/86Sr between 0.70520 and 0.7390 and eNd from -6.43 to -8.29. Combined Sr- and Nd-isotopic ratios suggest that lamproites were derived from "enriched" sources which have time-averaged higher Rb/Sr and lower Sm/Nd ratios than the Bulk Earth whereas kimberlites were derived from "depleted" source with lower Rb/Sr and higher Sm/Nd ratios. Calculated TDM model ages suggest that the lamproite source enrichment (~2 Ga) preceded that of kimberlites (~1.37 Ga). Our work demonstrates the existence of isotopically contrasting upper mantle sources for southern Indian kimberlites and lamproites and provides evidence for a lateral, isotopically heterogeneous mantle beneath the Cuddapah basin and eastern Dharwar craton. The significance of our results in the context of diamond exploration is also highlighted.
Coverage of Indian Earth Sciences in International Bibliographic Databases: GeoRef, GeoSEARCH and MINLIB
Authors: Wilson Graham C. , Mendelsohn Jennifer
Published: November 2024

A comparative survey has been made of three keyword-indexed bibliographic computer databases, focusing on their holdings pertaining to the Indian subcontinent in general and India in particular. The selected databases include two very large, commercially available systems of the broadest scope, namely GeoRef (U.S.A.) and GeoSEARCH (including GeoArchive, U.K.) and a much smaller research database with selective bias toward economic geology and other themes (MINLIB, Canada). Qudstions of coverage, degree of overlap and applicability of these and other databases are addressed, with an eye to the evolving use of this technology in India. In terms of number of articles recovered for the ten States >150,000 km2 in area. Bihar received the densest coverage (1.95 records/100 km2) with Karnataka second (1.64), the least-intensive coverage falling to the largest State, Madhya Pradesh (0.62) and Maharashtra (0.69).
Mineral Chemistry and Genesis of Phlogopites from the Gabbros of Ravipadu, Prakasam Province, Andhra Pradesh, India
Authors: Vijay Kumar K. , Ratnakar J.
Published: November 2024

In the Ravipadu gabbro pluton (RGP), Prakasam province, Andhra Pradesh, phlogopites occur as coronal rims along the interfaces between plagioclase-olivine, pIagioclase-ilmenite and rarely plagioclase-clinopyroxene, and as independent grains grown at the expense of intercumulus pyroxenes.

The changes observed in the chemical composition of phlogopites are in the contents of MgO, FeO1 and TiO2 SiO2 and Al2O3 do not show much variation and K2O is almost constant, Na2O is low and CaO is absent. Calculated end members are rich in phlogopite, Ti-phlogopite and eastonite components.

The phlogopites faithfully record the progressive iron enrichment trend of the original phases and consequently that of tholeiitic parental magma. It is established that in a single phlogopite the Mg number, and Mg, Fe, and Ti contents are controlled by its habit, whereas in a series of rocks the phlogopite composition is steered by the composition of host rock. Concentrations of A1 and K in the Ravipadu phlogopites are independent of chemistry of minerals that are consumed and also evolutionary history of the parental magma but are a signature of "chemical collaboration" of interacting fluid with original mineralogy. Textural features and geochemical traits of the phlogopites suggest probable attainment of perfect equilibrium between the fluid and primary phases during the formation of phlogopites in the RGP.
Geology and Petrochemistry of the Deccan Spilitic Basalts at and around Daman, India
Authors: Sethna S. F. , Javeri Priya
Published: November 2024

Major, trace and rare earth element analyses of spilitic basalts and some dolerite dykes and microprobe mineral analyses of a spilitic basalt are reported. It is postulated that these rocks represent subaqueous flows erupted under fairly shallow water which was insufficient for complete spilitisation of the basalt. The process of metasomatism under subaqueous conditions is considered to have been responsible for the alteration of tholeiite to spilite.
Extension of the Intracratonic Mahanadi Rift Towards the East Coast of India - An Inference from Aeromagnetics and Gravity
Authors: Atchuta Rao D. , Rao Ch. Rama , Bhaskara Rao D. S.
Published: November 2024

Interpretation of the total intensity aeromagnetic anomaly data and the residual gravity data of the pericratonic Mahanadi coastal basin, situated in the east coast of India has brought out NW-SE trending dislocations cutting across these basins and extending into the shelf area. This structure may be inferred as the possible extension of the NW-SE trending intracratonic Mahanadi rift. Depth estimates on the regional aeromagnetic anomalies have brought out a deep-seated sub-basement magnetic marker horizon at depths of 5-6 km in the inferred rift zone and it rises to around 2 km on either side in the onshore region. The trends in the residual gravity map around Cuttack suggests a tectonic environment possibly related to the location of triple junction at this point. This zone lies between shot points SF60 and SP70 of the Konark-Mukundpur DSS profile where it is reported that the energy has been heavily attenuated (at near distances) leading to large jumps in travel time. This zone of anomalous behaviour coincides with the inferred triple junction and calls for further detailed studies.
Trondhjemite and Granodiorite Assemblages from West of Barmer: Probable Basement for Malani Magmatism in Western India
Authors: Pandit M. K. , Shikhawat L. S. , Ferreira V. P. , Sial A. N. , Bohra S. K.
Published: November 2024

The pre-Malani basement, occurring to the southwest of the Malani Igneous Suite in western India is represented by an older, biotite trondhjemite (gneiss) and a younger, hornblende granodiorite. These granitoid assemblages (hitherto mentioned as unclassified granitoids) denote tectonically uplifted basement for the volcano-plutonic Malani magmatism. Biotite trondhjemite with well-developed gneissic fabric is significantly deformed as compared to hornblende granodiorite, which is slightly deformed. The basement granitoids exhibit a well-defined temporal and spatial relationship with each other, and are further intruded by Malani rhyolite/basic dykes. Well-preserved magmatic fabric of rhyolite/basic dykes suggests that the intrusive activity post-dated any deforrnational event. The geochemical signatures of the basement granitoids - moderate silica, high Sr, low FeO/MgO ratio and moderate alkali abundance, are quite distinct from the A-type geochemistry of Malani rhyolite dykes - high silica, high HFSE abundance, high FeO/MgO ratio and high alkali abundance, thus invoking different sources and emplacement history.
Pedogenic Alteration in the Overbank Sediments, North Bihar Plains, India
Authors: Sinha Rajiv , Friend Peter F.
Published: November 2024

The Quaternary successions exposed by excavation in the top 1.5-3.0 m of alluvial tract along a traverse in parts of the Indo-Gangetic plains are analyzed. The traverse extends across some 100 km of the interfan area between the Gandak and Kosi megafans of northern Bihar, eastern India. Most of the successions exhibit a fining upward grain size distribution, bottoming in sand or silt. though the overlying silts or clays are often interrupted by beds of coarse silt and sands. Radiocarbon dating suggests that all of the material was deposited during the last 2500 years and post-depositional pedogenic alteration has taken place. Micromorphological study of this subtle alteration shows (a) weathering of primary grains, (b) decomposition of plant and shell material, (c) carbonate dissolution and precipitation, (d) iron oxide/hydroxide accumulation and (e) illuviation of clays. The minor degree of alteration is contrasted with that reported in other areas of the Indo-Gangetic plains and it is concluded that the north Bihar plains, with an average accumulation rate of the order of 1 mm/a over 103 years has been an area of exceptionally high sedimentation.
Occurrence of a Manganese-Bearing Horizon in the Kaladgi Basin
Authors: Pillai Shilpa Patil , Peshwa V. V. , Nair Sushma , Sharma Mukund , Shukla Manoj , Kale Vivek S.
Published: November 2024

A manganiferous horizon was recorded near Niralkeri, in an intricately folded quartzite-chert breccia-mudstone sequence of the Simikeri Subgroup in the Kaladgi Basin of Karnataka. The nodules collected from this horizon show the presence of todorokite, vemadite and lithophorite in association with quartz and hematite; with MnO-58%.
Elemental Composition of Damodar River Sediments - A Tributary of the Lower Ganga, India
Authors: Singh Abhay Kumar
Published: November 2024

Bed, suspended and core sediments collected from the entire region of the basin were analysed to determine the elemental chemistry of the sediments of the Damodar river basin. The analytical results show that bulk sediment chemistry consists mostly (>75%) of five elements, Si, Al, K, Fe and Na. Mean composition has indicated that the Damodar sediments are depleted in Ca, Mg and heavy metals and enriched in Si and K as compared to the other Indian river basins. The concentrations of heavy metals in the suspended sediments are significantly higher than the bed sediments. In general, heavy metal concentration increases towards the finer size fractions. The depth variation of heavy metals in the core sediments shows no specific trend. Speciation studies show that the lithogenic phase is the major sink for heavy metals. Fe-Mn oxide and organic fractions are the major nonlithogenic phases and Zn is the major constituent of the nonlithogenic phase. Geoaccumulation indices calculated for Fe, Mn, Cu and Zn indicate that Damodar sediments are not polluted with respect to these metals.
Ophiuroid ossicles from the Kallankurichchi Formation (Maastrichtian) of Ariyalur Group, Tamil Nadu, India
Authors: Mallikarjuna U. B. , Sugumaran S. , Nagaraja H. M.
Published: November 2024

This paper reports the finding of ophiuroid ossicIes in the Kallankurichchi Formation (Maastrichtian) of Ariyalur Group, Tamil Nadu. The material is rather ill preserved and represents indeterminate vertebrae, dorsal shields, possible genital bars and some questionable material of uncertain affinity. The palaeoecological implications of these ossicles on the Kallankurichchi Formation are discussed.
Allogenic Control on Late Quaternary Continental Sedimentation in the Mahi River Basin, Western India
Authors: Malik J. N. , Khadkikar Aniruddha S. , Merh S. S.
Published: November 2024

The late Quaternary continental succession exposed along the cliff-like banks (15-35 m) of the Mahi river basin comprises sediments of fluvial and aeolian origin and provides an opportunity to assess palaeoclimatic changes in western India. Seven different facies are recognized in the exposed sediment succession. The trough cross-stratified conglomerates (Gt) formed due to downstream migration of trains of sinuous-crested dunes in shallow channels, whereas the formation of planar cross-stratified gravels (Gp) is attributed to downstream accretion of the avalanching front of a mid-channel bar, The horizontally stratified sands (Sh1 ) represent overbank deposits, while similar facies (Sh2 ) owes its origin to infrequent sheet flooding events. The trough cross-stratified sands (St) appear to be a product of low-stage river processes. The 'loess-like' massive silts (Sim) are of aeolian origin. The calcic palaeosol facies (P) are represented by vertisols at the base and brown soils and calcic red soils towards the top indicating changing palaeoenvironments.

The overall sediment succession was built through three major climate-controlled aggradation phases. Aggradation phase 1, which is represented by gravel-bed rivers and coexistent vertic palaeosols, indicates a significantly wetter climate. Aggradation phase 2 points to a comparatively drier period during which suspended-load rivers existed. Within this phase, red soil formation suggests a climatic amelioration event around 40 ka B.P. to 23 ka B.P. Aggradation phase 3 reflects a period of extreme aridity and is manifested as the capping aeolian facies. This phase is thought to be in tandem with the Last Glacial Stage event. Stabilization of these dunes may have taken place around 6 ka B.P. as suggested by the Thar Desert palynological and lake records.

The modern Mahi channel flows due ssw. However, the palaeocurrent trends of the exposed sediment bodies reveal that the ancient drainage network in the northern sections (upper reaches) flowed due SW-SSW and in the southern sections (lower reaches) SSE, SSW and W. The present day course of Mahi is relatively younger and follows structural lineaments that developed during the Holocene (after 6 ka B.P.). The aIluvial sedimentation record is unrelated to the modern Mahi river, but is a product of ancient late Quaternary rivers which now stand either fully or partially destroyed.
Significant Inferences on Deep Crustal Structure of Deccan Trap Region from Spectral Analyses of Bouguer Anomalies
Authors: Pant P. R. , Agarwal B. N. P. , Choudhury K. , Dasgupta S. P.
Published: November 2024

Qualitative interpretation of the regional Bouguer anomaly map of the Deccan Trap region of peninsular India, based on the anomaly size, its gradient and minor contribution from the shallow crust assessed by the results of other geophysical methods, suggests that the major part of the these anomalies have deep seated origin with 'lows' corresponding to the zones of subsidence and 'highs' to the uplifts involving the crust. Deep faults along the west coast and segmented faults demarcating the Narmada rift valley and Narmada-Son Lineament (NSL) have been delineated. Spectral analysis, matched filter technique for deconvolving gravity effect of sources at a particular depth and a single interface gravimetric inversion scheme have been utilised to delineate density discontinuities and their 3D configurations. The deconvolved gravity effect due to the deepest density interface at a mean depth of 117 km seems to reflect lithospheric variations and is used to distinguish the stable crust from the metastable one. The Moho relief map, apart from structural features, exhibits a good agreement with the results by Deep Seismic Sounding (DSS) in Koyna area and across NSL.

The block-wise analyses reveal higher average depths to Moho and Conrad, which are typical of stable shield crust, in the southern part whereas the northern blocks associated with rift tectonics exhibit considerably thin upper crust (5.8 to 12.6 km) with another crustal interface at a depth in the range of 16.3 to 26.8 km. The latter depth forms the base of the middle crustal layer i.e., top of the lower crustal layer comprising lower mantle derivatives. These inferences are based on the correlation between Bouguer anomaly and upper crustal thickness and layered velocity structure brought out by DSS data across the NSL. Filtered Bouguer anomaly maps have further facilitated the interpretation and better demarcation of structural features inferred from qualitative interpretation.
Mineralogy and Isotopic Composition of Pyrites-Bearing Ejects from a Mud Volcano, Baratang, Andaman Islands
Authors: Achyuthan Hema , Eastoe Chris
Published: November 2024

The Jarawa Creek mud volcano on Baratang Island has produced a variety of ejecta including mud containing illite, kaolinite and microfossils, volcanic glass, brine, methane gas and sulfide nodules. The nodules are of pyrite with a d34S ranging from -3.6 to 25.4‰. Sulfate leached from the mud has d34S values of -9.3 and -11.37‰. Our study reveals that the sulfate could not have been derived either from the nodules themselves or from the sea water or from connate brine. The nodules are of sedimentary origin and the most likely source of sulfate is sedimentary sulfide implying subsurface oxidation and a supply of oxidant possibly in groundwater.
Geology of Mumbai and Surrounding Areas and its Position in the Deccan Volcanic Stratigraphy, India
Authors: Sethna S. F.
Published: November 2024

Field data reveal that the lava flows in Mumbai and surrounding areas erupted after the rifting of the main plateau basalts of the Deccan Volcanic Province. Majority of the lava flows occur as subaqueous lavas forming hyaloclastites, spilitic pillow lavas and partially subaqueous and subaerial flows. The basic lavas are associated with rhyolitic flows and contemporaneous intrusions of basic and trachytic magmas forming hybrid rocks of monzonitic and dioritic variety. It has been shown that petrochemically the basic magma of the area is very different from the magma types associated with the mainland horizontal flood basalts ofthe Deccan Volcanic Province. The basic rocks of the Mumbai-Salsette area show lower concentrations of Cr, Ni, Y, V and Ti; and higber concentrations of K, Rb, Ba, Zr and Nb. Majority of these samples contain similar concentrations of phosphorus except for three Salsette samples which show unusual high values. The volcanics of the Mumbai-Salsette area are classified as forming the Salsette Subgroup with three Formations viz., Mumbai Island, Madh-Utan and Manori.
Evidence for Pre-Grenvillian High-Pressure Granulite Metamorphism from the Northern Margin of the Sausar Mobile Belt in Central India
Authors: Bhowmik Santanu Kumar , Pal Taraknath , Roy Abhinaba , Pant N. C.
Published: November 2024

Distinct lithological associations, structural relationships, and petrographic and geothemobarometric results indicate the presence of reworked granulites of Pre-Grenvillian age from the northern margin of the Sausar mobile belt (SMB) in Central India. In rare residual zones, the mafic granulite-felsic migmatite gneiss association preserves early structures and high-P (~ 10.5 kbar at ~ 775°C) granulite histories which appear to pre-date and bear no relation to ~ 1000 Ma old Sausar orogeny. An isothermal decompression through ~ 5.5 kbar at 750°C from maximum recorded P-T condition, possibly signifies extensional collapse of the crust, previously thickened through collision. During the Sausar orogeny, the granulites were further tectonically interleaved with younger lithological associations. Widespread retrogression in amphibolite and finally in greenschist facies conditions have all but obliterated granulite mineralogy and structure except in rare low-strain domain.