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In this paper, detailed petrology, mineral chemistry and geochemistry of lamprophyres from the Rongjeng–Nongchram area, Meghalaya, northeast India, is being reported. These dykes are intruded into the Proterozoic Assam Meghalaya Gneissic Complex and Neoproterozoic porphyritic granites with limited field exposures in two separate clusters controlled by lineaments. These lamprophyres are alkaline, potassic to ultra-potassic, and metaluminous and have been classified into camptonite and sannite from their petrography and geochemical affinity. Resorption texture of biotite in camptonite and compositional zoning in clinopyroxene of sannite indicate their crystallization under in-equilibrium conditions and subsequent interaction with changing composition of the magma(s). Detail geochemistry indicates fractionation as the imperative mechanism during the evolution of the magma(s) and shows heterogeneity at the mantle source and evidence for minimal crustal contamination. Various tectonic discrimination diagrams indicate the emplacement of the lamprophyres in a post-collisional and within plate setting, signifying a possible plume mechanism involved in their emplacement. The affinity of the lamprophyres towards an OIB setting was recorded from the chondrite-normalized REE and primitive mantle-normalized multielement patterns. The geochemistry of the lamprophyres points towards the presence of possible enriched metasomatic pods in the mantle, which might have melted due to the heat from the mantle plume and triggered the emplacement of the lamprophyres in the Rongjeng–Nongchram area. Research highlights: New lamprophyre bodies from Garo Hills, Meghalaya Plateau, NE India, are being reported with detailed petrology, geochemistry, and mineral chemistry. The lamprophyres are of alkaline affinity. The Kerguelen plume played a vital role in the generation of these lamprophyres. There are geochemical signals of the presence of enriched metasomatic pods in the mantle, which were melted due to plume interaction. The study also indicates a distinctive mantle source heterogeneity across the Meghalaya Plateau. [ABSTRACT FROM AUTHOR]

Along the tropical coast, there is cyclic variation in wind, wave currents, water and sediment influx, and the coasts experience a monsoonal storm surge that reaches nearly 2–3 times higher than the rest of the year, and foreshores undergo a complex evolution during an annual cycle. Hence, knowledge of foreshore evolution is critical in shoreline management. In this paper, study results on meso-scale foreshore evolution in a low-energy headland bay beach, situated in the Central West Coast of India near Manki, are discussed based on their seasonal and decadal changes in sandy shoreline configuration, wave refraction, sediment movement and depositional process. Decadal changes in the shoreline configuration indicated headland-side erosion and bay growth whereas the southern end grown seawards between the period 1979 and 2001–2002, while the beaches adjacent to the creek present in the area showed accretion and farther south of the creek showed minor erosion, and the trend continued through 2015. Wave refraction patterns for the waves approaching from northwest (NW), west and southwest (SW) for the wave periods 6, 8, 10 and 12 s indicated (a) wave convergence at the central part of the Manki beach; for the waves approaching from NW for wave periods 6 s; (b) wave divergence for the waves approaching from west with wave periods 6, 8, 10 and 12 s and (c) wave convergence at the bay side for the SW as well as NW approach of waves for wave period 10 s. Seasonal beach modification, in general, indicated post-monsoonal to pre-monsoonal (September to April) accretion and May to September erosion. Foreshore is gentle and dissipative (<6°). Sediments in all the seasons are bimodal (at 2ϕ and 2.752ϕ) in nature, and show dominantly saltation to suspension mode of transport. A parabolic shoreline prediction model indicated negative sediment budget in the central and northern parts of the beach (near the headland) and positive sediment budget at the southern end of the beach. Integration of the foreshore profile, sediment movement pattern, results of parabolic shoreline prediction model and decadal changes in shoreline configuration indicated that sediment budget is a critical issue in headland-bounded beaches, and utmost care is needed in the management of such shore line. Research highlights: This paper uses seasonal variations in the foreshore morphology, beach volume, sediment characteristics and wave refraction pattern to understand the sediment movement within the beach. Based on Hsu et al.'s (2004) model shoreline position is predicted. For a finite sediment input beach, shoreline management strategy is suggested. [ABSTRACT FROM AUTHOR]

The heavy mineral assemblage (HMA) of sandstones belonging to Mesoproterozoic Kaimur Group in the eastern Son valley, Central India, was investigated. The present communication is aimed at assessing mineralogical maturity, quantifying the contribution of heavy fraction to the bulk rock and its REE budget, sediment recycling and provenance. The transparent heavies record a relative decreasing trend upwards from 63 to 36.4% and on the contrary, opaque heavies show gradual increasing trend upwards from 36.4 to 65.4%. Tourmaline in the transparent heavy fraction reveals an overall decreasing trend of 59–22.8%. Whereas, zircon registers an increasing trend of 3.3–9.5% stratigraphically upwards. The contribution of opaque detrital clasts of ferruginous material composed of hematite and magnetite increases in the Upper Kaimur Sandstone. Tourmaline and zircon grains are characterised by etched, pitted and grooved surfaces. Zircon is also present as tiny inclusion within tourmaline and zircon itself. Heavy fraction of Upper Kaimur sandstone from the lower stratigraphic horizon exhibit lower ∑REE as compared to higher levels. The heavy fraction exhibit LREE/HREE < 1 as compared to bulk rock which has 8–10 times higher ratio. Heavy fraction exhibits enrichment in HREE and [Gd/Yb]N = 0.36–0.43, stratigraphically upwards, which is consistent with increasing Zr values suggesting zircon to be the major contributor to the REE budget of Upper Kaimur Sandstones. The percentage contribution of the zircon to the REE budget of bulk rock could have been ~50–60%. ZTR index (99–100) reveals mineralogically mature nature of Kaimur sandstones. Dominance of zircon amongst the heavies and Th/Sc vs. Zr/Sc plot shows the effect of zircon addition and sediment recycling. The plausible explanation for dominance of opaque minerals in HMA in the Upper Kaimur reflects their contribution from Paleoproterozoic metasedimentary rocks of Mahakoshal Group. HMA of Kaimur sandstones suggests derivation from granitic source. Nb/Yb vs. U/Yb diagram indicates that zircon was derived from magmatic arc source, which is in conformity with inference that Bundelkhand Granite Complex and Chhotanagpur Granite complex dominantly contributed to the Lower and Upper Kaimur Groups, respectively. Research highlights: The paper deals with the study of heavy mineral assemblage of the Kaimur Group sandstones, Vindhyan Supergroup, Son Valley, Central India. Provenance, sorting and recycling of the sediments were inferred. The ferruginous clasts found in the Dhandraul Quartzite/Sandstone also have been studied to understand their mineralogy and texture. Tourmaline and zircon dominate the Lower and Upper Kaimur Sandstones, respectively. The provenance of the Lower Kaimur sandstones is Bundelkhand granite, and Upper Kaimur sandstone is Chhotanagpur Gneissic Complex. The dominance of zircon in HMA and Th/Sc vs. Zr/Sc plot shows the significant effect of zircon addition and sediment recycling. The occurrence of ferruginous detrital clasts in Upper Kaimur sandstones can be attributed to increasing detrital input from adjoining Mahakoshal Group that has the presence of BIFs/BHQ/BHJ in the Agori Formation. The heavy fractions from sandstones of Mangesar Formation and Dhandraul Quartzite from different horizons exhibit an increase in Zr and HREE stratigraphically upwards. This suggests remarkable enrichment of HREE, low LREE/HREE, [La/Yb]N <1 and [Gd/Yb]N <1. HREE enrichment is proportional to the Zr concentration signifying the dominant role of zircon amongst the heavies in managing the ΣREE budget of the bulk rock. The percentage contribution of the zircon is calculated to be ~50–60%. [ABSTRACT FROM AUTHOR]

Evidence of frictional melting in the form of pseudotachylite is innumerably found along the Gangavalli fault zone (GFZ), southern India. Such catastrophic deformation influences the strength of rock masses across the fault zone. In this paper, we have investigated the strength variation in fault zone rocks during post-seismic deformation. The experimental study suggests that the average uniaxial compressive strength (UCS) for pseudotachylite hosting charnockite (i.e., Pt-charnockite) is almost double (45.58 MPa) as compared to the pseudotachylite devoid charnockite (i.e., D-charnockite) of 24 MPa. The melt associate seismic deformation shows high stress drop due to melt lubrication at the fault interface and simultaneously produced numerous fractures in the rock. We have determined the stability and denseness of both rock types using acoustic emission (AE) technique that remarks a distinct difference in AE signatures. The analysis indicates a more stable and dense Mogi type-III signature for post-seismic deformed rocks that are assisted by pseudotachylite melt. However, negligible AE energy is observed in the D-charnockite. We proposed that the melt-assisted seismic deformations are more inhibitable to reactivate the slip surfaces than the conventional earthquake-deformed rock having no melting phenomenon and therefore, pseudotachylites enhance the strength of fault zone rocks during post-seismic deformation. [ABSTRACT FROM AUTHOR]

The paper documents occurrence, origin and significance of glauconite-rich intervals at certain specific stratigraphic levels within Early to Middle Eocene Sylhet Formation of Assam and Assam–Arakan Basin. The microfacies with which glauconite is associated are fossiliferous silty shale, glauconitic sandstone, lime mudstone–wackestone and wackestone–packstone. The glauconites occur in three forms, viz., glauconite pellets, infillings within bioclasts and cements (i.e., non-pellet stringers and blebs), representing a complete spectrum of maturity with presence of four types, nascent, slightly evolved, evolved and highly evolved varieties. The elliptical, immatured pellets occur in glauconitic sandstone and exhibit yellowish-green to grass green colour, while relatively matured pellets are dark brownish green to brown, irregular, broken and mostly associated with shale. The Sylhet glauconites indicate deposition in a tide-affected marginal marine to inner-shelf carbonate ramp with low sedimentation rate, and normal marine salinity and represent an overall fining-up 2nd order TST. High-resolution sequence stratigraphic analysis allows to subdivide the 2nd order TST into 3rd order systems tracts: (i) a basal TST, represented by shale/limestone, (ii) an HST incorporating sandstone, limestone and shale, and (iii) a TST at the top. The intervening 3rd order HST is further subdivided into 4th order parasequence sets separated by marine flooding surfaces. Electrolog correlation reveals that the ubiquitous presence of glauconite-rich horizons corresponds to marine flooding events (MFE) of 3rd and 4th order sea-level changes. The glauconites associated with MFE result in a condensed section with minimum sediment supply and provide a key parameter to build the sequence stratigraphic architecture. The occurrences of green clays may possibly owe their origin due to migration of K+/Fe2+ ions from seawater or surrounding sediments to a given reducing microsystem centered on organic debris. The sources of K and Fe are seawater and detrital minerals, respectively, and are achieved by the diffusion-nucleation-crystal growth process. [ABSTRACT FROM AUTHOR]

The occurrence of workable beach placer deposits of garnet and ilmenite along the coastal region of southern Tamil Nadu is known for long. Though the adjoining rivers like Kallar, Vaippar and Vembar are generally thought to be the major contributors of placer minerals, especially garnet, to their respective beaches, none of the river basins has yet been explored. The present paper discusses the distribution, resource potential and geomorphic controls of garnet placer in the Vaippar basin using ArcGIS. Analysis of sediment samples collected from the Vaippar River and its tributaries shows that the concentration of garnet is up to 20 wt.% and predominantly localized in river alluvium, coastal alluvium and pediment. A distribution map of garnet for the entire basin (5508 km2) portrays three zones of enrichment: zone I: 0.06–1.0 million tonnes (Mt); zone II: 1.0–1.1 Mt; zone III: 1.1–1.21 Mt. It is estimated that in zone III (942 km2) for every 100 km2, about 17 km2 area has an average garnet reserve of 1 Mt and this could be profitably mined. [ABSTRACT FROM AUTHOR]

The polymetallic mineral district in the Singhbhum shear zone (SSZ), eastern India, hosts some of the most important Palaeoproterozoic uranium, copper and apatite–magnetite deposits in India. Although the shear zone had been the locale of profuse hydrothermal alteration and there is general consensus about hydrothermal mineralisation, the alteration types vis-à-vis ore mineralisation are not amply clear. In this paper, we describe ore mineralogy and multiple alteration types vis-à-vis uranium-rare earth element (U-REE) mineralisation in the Narwapahar uranium deposit located in the SSZ. Uranium mineralisation is hosted by intensely deformed and metamorphosed tourmalinite, albite schist and chlorite schist, which are mineralogically heterogeneous showing extreme variations in constituent minerals and their modal abundances in the outcrop, hand specimen and microscopic scales often grading to nearly monomineralic rocks. Thorium-poor uraninite is an ubiquitous ore mineral of uranium. High uranium content is also noted in ilmenorutile and some unidentified U silicates. Allanite is the most abundant REE-bearing mineral whereas monazite and xenotime are subordinate. Low-Ti magnetite is nearly ubiquitous in the U ores. Based on locally preserved cross-cutting hydrothermal veins and frozen-in mineral replacement textures, the sequential metasomatic events deciphered from the Narwapahar deposit are B (boron) → Na–Fe (±Ca)→ K–Fe (±Ca)→ K→ H+. Uranium mineralisation is associated with B, Na–Fe and H+ metasomatism and perhaps with K–Fe metasomatism too whereas REE mineralisation is associated with K–Fe metasomatism and resultant hydrothermally altered rocks. The alteration types, especially the well-known pervasive regional-scale alkali metasomatism, the alteration paragenesis as described here and metal association (Fe–Cu–U–REE–Co–Ni–Mo–Au) are akin to Fe oxide (Cu–U–REE) (IOCG)-type mineralisation. The presence of a substantial amount of uranium in ilmenorutile and very fine-grained inclusion of uraninite in magnetite may potentially affect the recovery of uranium during beneficiation leading to low leachability of some uranium ores. The close association of REE-bearing minerals with the U ores requires focused study to examine the potential of U ores as a source of by-product REEs. [ABSTRACT FROM AUTHOR]

Anthropogenic activities such as gold and coal mining, oil and gas production, filling of artificial water reservoirs, harnessing of geothermal energy, etc., have induced/triggered earthquakes. Koyna dam, located in the Deccan volcanic province of India, was impounded in 1962, and soon after tremors were reported from the vicinity of Koyna dam. The largest triggered earthquake of magnitude (M) 6.3 occurred on 10 December 1967. The triggered earthquakes have continued until now and the region has experienced 22 events of an M~5, over 200 events of an M~4 and several thousand smaller events. The reservoir-triggered seismicity has continued until 2021, which is unique. Some of the early investigations, leading to drilling of a 3 km deep pilot borehole at Koyna for near-field studies of earthquakes, and a few recent results are summarised in this paper. Research highlights: Koyna, located near the west coast of India, in the Deccan volcanic province is one of the most prominent sites of artificial water reservoir-triggered seismicity (RTS). Triggered earthquakes started soon after the impoundment of Shivaji Sagar lake created by Koyna dam in 1962 and have continued until now. Unlike other RTS sites where triggered earthquakes did not continue for long, Koyna is still active, and it is estimated that RTS may continue for another one to two decades. Detailed field work and analyses of earthquake data demonstrated that Koyna is a very suitable site for near-field studies of earthquakes: an observation that is much needed to validate earthquake genesis models. International Continental Drilling Programme sponsored workshops and participation of experts from all over the world helped in deciding to dig a 3 km deep pilot borehole. The borehole was completed in June 2017. Recent research studies further demonstrated that the Koyna region is under critical stress. Studies under progress would help in designing the proposed ~7 km deep borehole laboratory. [ABSTRACT FROM AUTHOR]

In slope stability analysis, identification of the mechanism behind slope failure is the key factor during the study. Rock mass characterization and kinematics analysis, like geotechnical investigation methods, are not infallible all the time for the weathered slopes. The presence of different grades of weathered mass on the slope profile acts independently to influence the overall failure pattern. Numerical analysis by finite element method (FEM) is evolved as a primary slope stability analysis tool by overcoming the limitations of the stratified weathered materials on the slope. The paper focuses on the stability analysis of railway-cut laterite slopes of the Eastern Ghats of India. The medium to high-grade metamorphism, followed by physio-chemical weathering, favours the region for more prone to failure. The Force Equilibrium Model and Moment Equilibrium Model have been considered to determine the possibility of independent failure events for the probability analysis. Monte Carlo's probability simulation method has delivered a better result for the weathered slopes by taking many variables for the studied region. A compression study has been made between the outcomes of slope stability analysis methods and the probability analysis models, which provides a comprehensive list of factors to understand the failure mechanism of weathered slopes. [ABSTRACT FROM AUTHOR]

The author presents a number of comments on the article "Volatile Displacement of Meghalaya Coals: A Pointer to Explore Low Sulphur Coals," which was published in the April 2007 issue. He argues that the paper is full of common mistakes, wrong computations, and long-drawn conclusions. In methodology, he notes that the author of the said paper indicates about drawing of regression curves which is wrong.

Deep-sea moorings in the equatorial Indian Ocean were first deployed by India in the year 2000, and currents were measured at three locations ( 77 ∘ E , 83 ∘ E , and 93 ∘ E ) on the equator. In this paper, we present two decades of current observations from these moorings and discuss how the moorings have evolved with time. The observations show that the 180-day (90-day) period dominates the surface and mid-depth (bottom) circulation. Though the Wyrtki Jets are strong, the near-surface currents do not show any clear semi-annual reversals. The reversals become evident only below 100 m. Research Highlights: Twenty years of ocean current data collected at the equatorial Indian Ocean Bottom current data show strong intraseasonal variability Upward phase propagation associated with the semi-annual cycle more prominent for the mid-depth currents The semi-annual reversals not evident every year near the surface [ABSTRACT FROM AUTHOR]

This paper reports quasi-periodic pulsing hiss emissions recorded during daytime in the frequency range of 50Hz-15 kHz at low latitude station Jammu (geomag. lat. = 22°26' N; L = 1.17). It is noted that pulsing VLF emissions are a rare phenomena at low latitudes. The various spectrograms of pulsing VLF hiss emissions presented in this paper clearly show band limited spectrums regularly pulsing with almost equal period of the order of few seconds in the frequency range of ∼3—8 kHz. Generation and propagation mechanism of these emissions are briefly discussed. [ABSTRACT FROM AUTHOR]

Ediacaran to Early Cambrian sequences are well preserved in several synclines within the Lesser Himalaya. We have conducted multi-proxy geochemical and stable isotopic studies on carbonaceous sediments of the basal Tal Group to decipher redox conditions of the Earliest Cambrian Ocean. Organic matter is immature, predominantly aliphatic and likely derived from marine phytoplankton. The S/C(organic) ratios above 0.4; strong enrichment of redox-sensitive trace elements V, Mo, U and Cd; higher DOPT, U/Th, V/Sc, Mo/Sc and V/(V+Ni) ratios; V/Al–U/Al–Mo/Al systematics and U–Mo enrichment factors indicate anoxic to euxinic conditions of deposition. Large variations (5–7‰) in δ13C likely reflect spatial heterogeneity or vertical gradient in DIC compositions of the Early Cambrian Ocean, and possibly capture the part of Basal Cambrian negative Carbon isotope Excursion (BACE). Finely disseminated texture of pyrite framboids with sizes mostly below 10 µm suggest sulfide reduction within the water column in an open system. Isotopically heavy δ34S values (+4.5 to +22.8‰) overlap with the δ34Ssulfate of contemporary Fortunian ocean (+10 to +40‰), suggesting sulfidic conditions and small size of the sulfate reservoir. Whereas the REE+Y proxies of the same set of samples show seawater-like patterns, with strong HREE enrichment, positive Y and La anomalies and negative Ce anomaly (avg. Ce/Ce* = 0.78), indicating REE uptake by phytoplankton from an oxidized-euphotic surface zone. The combined geochemical and isotopic data suggest a strongly stratified ocean with sulfidic bottom water and oxidized surface water. Episodic shoaling of anoxic deep water onto the surface possibly caused the extinction of benthic Ediacaran fauna, and the surface oxidized zone likely provided the niche for further metazoan radiation. [ABSTRACT FROM AUTHOR]

Spring constitutes one of the primary water resources in some parts of the world, such as the Indian Himalayas. However, these remain imperfectly surveyed and delineated far and wide in most areas worldwide. Due to natural and anthropogenic factors, the springs are under great threat. All over the globe, springs have left as data deficit and have not relatively gained considerable attention in comparison to other systems like rivers, streams, lakes, and wetlands. This is also true for India, where most of the research is usually centered on groundwater, rivers, lakes and wetlands. This manuscript presents an overview of studies carried out on various themes of spring water systems, such as characteristics, classification schemes, and different empirical and analytical methods at international and national levels. A comprehensive overview of the literature identified the demand for an integrated approach of different empirical and analytical methods to strengthen the understanding of spring hydrology in the Himalayan region and elsewhere. Research highlights: Springwater system protection needs a forewarning of imminent contamination and thus, an integrated approach of conceptual and management-related groundwater models should be developed in India on a large scale. Empirical and analytical approaches should be used to attain an inclusive understanding of springwater hydrology and water quality. Himalayan springs should be studied considering the current updated classification schemes to obtain a comprehensive understanding of them. Monitoring of data and simulation models should be developed to establish an integrated and comprehensive understanding of Himalayan spring hydrogeology and hydrology. [ABSTRACT FROM AUTHOR]

The seismological data recorded at our four semi-permanent broadband seismographs installed by the CSIR-NGRI, Hyderabad, Telangana in the Aravalli mobile belt (AMB) and Rajasthan craton in the northwest Indian shield during the period 2014–2016 are used in the study. The 16 selected regional Indian earthquakes of Mw 5.5–7.8 that occurred in the North India region recorded at the four seismic stations are used to compute the surface wave (both Rayleigh and Love waves) group velocity dispersion characteristics and average 1-D regional shear wave velocity (Vs) structure beneath the North India which covers the northern part of India between the whole Himalayan region and Rajasthan craton including AMB. First, we compute Rayleigh waves (at 7–87 s) dispersion curves and Love waves (at 7–82 s) group velocity dispersion curves by utilizing the standard frequency time analysis (FTAN) of 3-component broadband data recorded at these four 3-component broadband seismic stations. After that, using the logarithmic stacking technique, we compute the final average stacked fundamental mode dispersion curves of surface waves (both Love and Rayleigh waves) for our study area. Then, we finally invert the final average dispersion curves of surface waves (both Love and Rayleigh waves) to compute the average one-dimensional regional shear velocity structure beneath North India. Our modelling result in North India suggests a two-layered crustal structure with a crustal thickness of 39 km. The thickness of the first crustal layer (upper crust) is 20 km with a shear wave velocity (Vs) of 3.30 km/s. On the other hand, the second crustal layer (lower crust) marks a 19-km thickness with a Vs of 3.70 km/s. Our modelling result suggests that the Vs of the upper mantle is found to be 4.35 km/s below the study region. Research highlights: Modelled average one-dimensional regional Vs structure below northern part of India. A 2-layered crustal velocity model below North India. Upper crust at 20 km thick with Vs of 3.30 km/s. And, lower crust at 19 km thick with Vs of 3.70 km/s. The Moho depth is 39 km and Vs below the Moho depth is found to be 4.35 km. [ABSTRACT FROM AUTHOR]

Cosmic noise absorption (CNA) measurred by imaging riometer, is an excellent tool to passively study the high latitude D-region ionospheric conditions and dynamics. An imaging riometer has been installed at Indian Antarctic station Maitri (geographic 70.75°S, 11.75°E; corrected geomagnetic 63.11°S, 53.59°E) in February 2010. This is the first paper using the imaging riometer data from Maitri. The present paper introduces the details of this facility, including its instrumentation, related CNA theory and its applications. Sidereal shift of around 2 hours in the diurnal pattern validates the data obtained from the newly installed instrument. Moreover, the strength of cosmic noise signal on quiet days also varies with months. This is apparently due to solar ionization of D-region ionosphere causing enhanced electron density where collision frequency is already high. The main objective of installing the imaging riometer at Maitri is to study magneotspheric-ionospheric coupling during substorm processes. In the current study, we present two typical examples of disturbed time CNA associated with storm-time and non-storm time substorm. Results reveal that CNA is more pronounced during storm-time substorm as compared to non-storm time substorm. The level of CNA strongly depends upon the strengthening of convectional electric field and the duration of southward turning of interplanetary magnetic field before the substorm onset. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the impact of changing land use/land cover (LULC) on the hydrological processes in Dal lake catchment of Kashmir Himalayas by integrating remote sensing, simulation modelling and extensive field observations. Over the years, various anthropogenic pressures in the lake catchment have significantly altered the land system, impairing, inter-alia, sustained biotic communities and water quality of the lake. The primary objective of this paper was to help a better understanding of the LULC change, its driving forces and the overall impact on the hydrological response patterns. Multi-sensor and multi-temporal satellite data for 1992 and 2005 was used for determining the spatio-temporal dynamics of the lake catchment. Geographic Information System (GIS) based simulation model namely Generalized Watershed Loading Function (GWLF) was used to model the hydrological processes under the LULC conditions. We discuss spatio-temporal variations in LULC and identify factors contributing to these variations and analyze the corresponding impacts of the change on the hydrological processes like runoff, erosion and sedimentation. The simulated results on the hydrological responses reveal that depletion of the vegetation cover in the study area and increase in impervious and bare surface cover due to anthropogenic interventions are the primary reasons for the increased runoff, erosion and sediment discharges in the Dal lake catchment. This study concludes that LULC change in the catchment is a major concern that has disrupted the ecological stability and functioning of the Dal lake ecosystem. [ABSTRACT FROM AUTHOR]

India Meteorological Department has implemented Polar WRF model for the Maitri (lat. 70°45S, long. 11°44E) region at the horizontal resolution of 15 km using initial and boundary conditions of the Global Forecast System (GFS T-382) operational at the India Meteorological Department (IMD). Main objective of this paper is to examine the performance skill of the model in the short-range time scale over the Maitri region. An inter-comparison of the time series of daily mean sea level pressure and surface winds of Maitri for the 24 hours and 48 hours forecast against the corresponding observed fields has been made using 90 days data for the period from 1 December 2010 to 28 February 2011. The result reveals that the performance of the Polar WRF is reasonable, good and superior to that of IMD GFS forecasts. GFS shows an underestimation of mean sea level pressure of the order of 16-17 hPa with root mean square errors (RMSE) of order 21 hPa, whereas Polar WRF shows an overestimation of the order of 3-4 hPa with RMSE of 4 hPa. For the surface wind, GFS shows an overestimation of 1.9 knots at 24 hours forecast and an underestimation of 3.7 knots at 48 hours forecast with RMSE ranging between 8 and 11 knots. Whereas Polar WRF shows underestimation of 1.4 knots and 1.2 knots at 24 hours and 48 hours forecast with RMSE of 5 knots. The results of a case study illustrated in this paper, reveal that the model is capable of capturing synoptic weather features of Antarctic region. The performance of the model is found to be comparable with that of Antarctic Meso-scale Prediction System (AMPS) products. [ABSTRACT FROM AUTHOR]

Earthquakes are known to have occurred in Indian subcontinent from ancient times. This paper presents the results of seismic hazard analysis of India (6°-38°N and 68°-98°E) based on the deterministic approach using latest seismicity data (up to 2010). The hazard analysis was done using two different source models (linear sources and point sources) and 12 well recognized attenuation relations considering varied tectonic provinces in the region. The earthquake data obtained from different sources were homogenized and declustered and a total of 27,146 earthquakes of moment magnitude 4 and above were listed in the study area. The sesismotectonic map of the study area was prepared by considering the faults, lineaments and the shear zones which are associated with earthquakes of magnitude 4 and above. A new program was developed in MATLAB for smoothing of the point sources. For assessing the seismic hazard, the study area was divided into small grids of size 0.1° × 0.1° (approximately 10 × 10 km), and the hazard parameters were calculated at the center of each of these grid cells by considering all the seismic sources within a radius of 300 to 400 km. Rock level peak horizontal acceleration (PHA) and spectral accelerations for periods 0.1 and 1 s have been calculated for all the grid points with a deterministic approach using a code written in MATLAB. Epistemic uncertainty in hazard definition has been tackled within a logic-tree framework considering two types of sources and three attenuation models for each grid point. The hazard evaluation without logic tree approach also has been done for comparison of the results. The contour maps showing the spatial variation of hazard values are presented in the paper. [ABSTRACT FROM AUTHOR]

This paper deals with the hydrocarbon source rock evaluation of the Subathu Formation exposed at Marhighat on Sarahan-Narag road in Sirmaur district of Himachal Pradesh. Hydrocarbon potential of these sediments is estimated on the basis of palynofacies analysis and thermal alteration index (TAI) values based on the fossil spores/pollen colouration. The analyses are based on the classification and hydrocarbon generation potential of plant derived dispersed organic matter present in the sediments. The palynofacies analysis of Subathu Formation in the area reveal moderate to rich organic matter, with amorphous organic matter constituting the bulk of the total organic matter, followed by charcoal, biodegraded organic matter, fungal remains, spores/pollen and structured terrestrial organic matter. The TAI value for the organic matter in these sediments has been ascertained as 3.00. A dominance of the sapropelic facies (amorphous organic matter) and the measured TAI values for the Subathu sediments in the Marhighat area suggests a good source-rock potential for the hydrocarbon generation. [ABSTRACT FROM AUTHOR]

This paper attempts to estimate the possible rate of land subsidence of Kolkata City including Salt Lake City and the adjoining East Kolkata Wetlands located at the lower part of the deltaic alluvial plain of South Bengal basin. Demand of groundwater for drinking, agricultural and industrial purposes has increased due to rapid urbanization. The subsurface geology consists of Quaternary sediments comprising a succession of clay, silty clay and sand of various grades. Groundwater occurs mostly under confined condition except in those places where the top aquitard has been obliterated due to the scouring action of past channels. Currently, the piezometric head shows a falling trend and it may be accelerated due to further over-withdrawal of groundwater resulting in land subsidence. The estimated mean land subsidence rate is 13.53 mm/year and for 1 m drop in the piezometric head, the mean subsidence is 3.28 cm. The surface expression of the estimated land subsidence is however, cryptic because of a time lag between the settlement of the thick low-permeable aquitard at the top and its surface expression. Therefore, groundwater of the cities and wetland areas should be developed cautiously based on the groundwater potential to minimize the threat of land subsidence. [ABSTRACT FROM AUTHOR]

Thermal infrared spectroscopy is a powerful technique for the compositional analysis of geological materials. The spectral feature in the mid-IR region is diagnostic of the mineralogy and spectral signatures of mixtures of minerals that add linearly, and therefore, can be used as an important tool to determine the mineralogy of rocks in the laboratory and remotely for planetary exploration. The greatest challenge in the emission measurement lies in the measurement of the weak thermal photons emitted from geological materials in a laboratory setup, and accurately records the temperature of the rock sample. The present work pertains to the details of a new Thermal Emission Spectrometer (TES) laboratory that has been developed under the ISRO Planetary Science and Exploration (PLANEX) programme, for emission related mineralogical investigations of planetary surfaces. The focus of the paper is on the acquisition and calibration technique for obtaining emissivity, and the deconvolution procedure to obtain the modal abundances of the thermal emission spectra in the range of 6-25 μm using Fourier Transform Infrared (FTIR) spectroscopy. The basic technique is adopted from the work of Ruff et al (1997). This laboratory at the Department of Earth Sciences, IIT-Bombay is currently developing pure end mineral library of mineral particulates (<65 μm), and adding new end members to the existing ASU spectral library. The paper argues the need for considering Lunar Orbiter Thermal Emission Spectrometer (LOTES) for future Indian Moon mission programme (Chandrayan-II) to determine evidences of varied lithologies on the lunar surface. [ABSTRACT FROM AUTHOR]

In the last thirty years great strides have been made by large-scale operational numerical weather prediction models towards improving skills for the medium range time-scale of 7 days. This paper illustrates the use of these current forecasts towards the construction of a consensus multimodel forecast product called the superensemble. This procedure utilizes 120 of the recent-past forecasts from these models to arrive at the training phase statistics. These statistics are described by roughly 107 weights. Use of these weights provides the possibility for real-time medium range forecasts with the superensemble. We show the recent status of this procedure towards real-time forecasts for the Asian summer monsoon. The member models of our suite include ECMWF, NCEP/EMC, JMA, NOGAPS (US Navy), BMRC, RPN (Canada) and an FSU global spectral forecast model. We show in this paper the skill scores for day 1 through day 6 of forecasts from standard variables such as winds, temperature, 500 hPa geopotential height, sea level pressure and precipitation. In all cases we noted that the superensemble carries a higher skill compared to each of the member models and their ensemble mean. The skill matrices we use include the RMS errors, the anomaly correlations and equitable threat scores. For many of these forecasts the improvements of skill for the superensemble over the best model was found to be quite substantial. This real-time product is being provided to many interested research groups. The FSU multimodel superensemble, in real-time, stands out for providing the least errors among all of the operational large scale models. [ABSTRACT FROM AUTHOR]

Urban agglomerations across the world have witnessed haphazard and unprecedented growth in the recent past, giving rise to urban sprawling. This study analyses the spatio-temporal growth dynamics of 16 major Indian cities (population above one million) using remote sensing approaches. Land Use and Land Cover (LULC) thematic datasets are considered for the years 2005, 2010, 2015, and 2021. The variability of the five LULC classes, viz., urban built-up, vegetation, water body, agriculture, and barren land, implied that urban expansion mostly took place at the cost of barren lands. The urbanised landscape mainly portrayed dispersive outward growth since the beginning of the 21st century, with significant compaction (infill urban growth) near the urban core in recent years. The results derived through Shannon's Entropy, spatial metrics, and urban density gradient analysis (in eight directions) indicated the same. Population density variation with respect to the horizontal urban growth and dynamics in each considered direction, further supported the concept of overcrowded city centres and sprawled outskirts. Besides population density, other factors that could be associated with urbanisation include the local environment, meteorology, and some geophysical characteristics. [ABSTRACT FROM AUTHOR]

The sedimentary sequence of the Ninama Basin is associated with the latest phase of the continental Deccan volcanism of the Indian peninsula. It occurs as inter-, intratrappeans with a 39-m thick sequence comprising Sukhbhadar Formation and Ninama Limestone. The investigation aims to reconstruct its depositional setting based on the lithofacies and inorganic geochemistry to understand the influence of paleosalinity, paleoredox, paleodepth, provenance and paleoclimate on the sedimentation pattern. It is characterized by clastic and chemically formed rocks, including shale, mudstone, siltstone, sandstone and limestone. Facies analysis has revealed seven lithofacies, amongst which four are clastic facies, shale (SH), calcareous shale (CSH), silty mudstone (SM) and lithic greywacke (LGW), and three are carbonate facies, namely, grey-black limestone (GBL), cherty limestone (CL) and marlite (ML). Using geochemical analysis of major oxides and trace elements, ratios of Ca/(Ca+Fe), Sr/Ba, V/(V+Ni), V/Cr, Fe/(Ca+Mg), Ti/Al, Na/K, K/(Fe+Mg), CIA-K and MAP were determined and used to interpret and note the changes in the depositional system. The combined results of the lithofacies and geochemistry indicate that the deposition occurred in three phases. Phase 1 is characterized by high energy conditions in the shallow to moderate depth brackish-saline lake with oxic to dysoxic conditions; Phase 2 is characterized by anoxic deep fresh to the brackish water basin; and Phase 3 is characterized by semiarid conditions, saline, anoxic waters, high evaporation leading to shallowing of the lake, and low to moderate terrestrial input. This lacustrine basin in the paleotopographic low of the Deccan Volcanic Province is characterized by distinct lithology governed by various depositional parameters. A composite depositional model is constructed for the Ninama Basin, reflecting three phases of evolution that are dominantly controlled by the paleoenvironment. Research highlights: The present study focuses on lithofacies and inorganic geochemical analysis of Ninama paleolake sediments, Saurashtra intertrappeans, to interpret their paleosalinity, paleoredox, water depth, provenance, detrital influx, and paleoclimate. Phase 1 deposition was initiated in paleotopographic low of Deccan Traps, in an oxic–dysoxic, high-energy turbulent brackish water environment, in humid conditions. Phase 2 characterizes fine-grained clastic facies deposited in anoxic, fresh-brackish, deep lake waters in humid conditions. Phase 3 marks the shallowing, evident by carbonate facies with low-moderate terrestrial input deposited in saline and anoxic paleolake in semiarid conditions with high evaporation and low-moderate precipitation. The Deccan Traps have influenced the paleolake intertrappean sequence. [ABSTRACT FROM AUTHOR]

Koh-i-Noor and other world-famous diamonds such as Hope, Orloff, Great Mogul, Nizam, and Pitt, well-known in the industry as 'Golkonda Diamonds' are very well recognised for their rare colours, large carat sizes, and because of the paucity of nitrogen atoms majority of them have been classified as Type IIa diamonds. These renowned Golkonda diamonds were recovered from placers mined on the banks of the Krishna River in southern India; however, their primary source rocks (either kimberlites or lamproites) remain questioned and untraced. Precise identification of the primary sources of such large-sized, dominantly Type IIa diamonds (i.e., CLIPPIRS) is crucial for understanding their deep mantle origin, nature and timing of magmatism carrying them and essential from economic and geological perspectives. We employed a multidisciplinary approach incorporating xenocrystic mineral composition and bulk-rock geochemistry, field geological and remote sensing (GIS) studies to locate the probable primary sources of these renowned diamonds, know the origin of Type IIa Golkonda diamonds in southern India, and to understand the mechanism and timing of diamond transport and dispersal as placers in the Krishna River basin. Our study rules out the possibility of various lamproite occurrences of the Eastern Dharwar Craton and Banganapalle conglomerates as being sources of Koh-i-Noor and other Golkonda diamonds. The absence of Type IIa diamonds in the highly diamondiferous Late Cretaceous kimberlites of Wajrakarur likewise excludes them as source of Golkonda diamonds. Among southern India's two significant kimberlite fields, i.e., Wajrakarur and Narayanpet, compositions of indicator minerals from the Wajrakarur Kimberlite Field (WKF) reveal their ultimate diamond preservation potential, presence of strong diamondiferous mantle roots and deeper source regions, hence recognising them to be the potential sources of Golkonda diamonds. GIS and remote sensing tools were used to calculate moisture content, vegetation indices, and to locate paleo-channel of the Penner River, which was primarily responsible for the transportation of diamonds from their Mesoproterozoic (ca. 1.1 Ga) source rocks at Wajrakarur to their final sites of recovery, i.e., Kolluru and other mines situated on the banks of the Krishna River. The occurrence of alluvial placer deposits in Krishna River drainage system is analogous to the Orange River drainage system in South Africa. Both areas have diamonds sourced from primary kimberlite pipes, transported by rivers, and deposited in specific areas. Similarities in the origin, mechanism of diamond transport, dispersal and deposition have played a crucial role in significant diamond production from alluvial deposits in Krishna and Orange Rivers. [ABSTRACT FROM AUTHOR]

This study employs a combination of texture and composition of allanite to investigate the chemical evolution of rare earth elements (REEs) in the hydrothermal veins within the Chhotanagpur Granite Gneiss Complex around Kalapathar area, Purulia district, West Bengal, India. Allanite occurs as pockets and lumps in the hydrothermal veins. Locally, the allanite pockets/lumps have high concentrations of REEs (∑REEs ~9.8 wt.%), Th (up to 1427.2 ppm) and U (up to 642.1 ppm). Three hydrothermal fluids and associated REE mobilization have been distinguished and characterized. The hydrothermal fluid1 causes metasomatic addition of REEs that leads to the formation of early REE-enriched allanite. Hydrothermal fluid2 imposed changes in the texture and composition of the allanite where the early allanite was replaced by relatively REE-depleted allanite following the substitution scheme REE+3 + (Fe+2, Mg+2) → Ca+2 + (Al, Fe+3). The hydrothermal fluid3 is marked by the alteration of allanites to the bastnaesite and monazite. REEs have been transported mainly in aqueous chloro-complexes with high to moderate salinity and low homogenization temperature (257°–361°C). The timing of the hydrothermal event is established through U–Th–total Pb dating of monazite, yielding at around 875 ± 43 Ma. Research highlights: The allanite clots and lumps in hydrothermal veins within CGGC around Kalapathar, Purulia District, West Bengal display high ∑REEs up to 9.8 wt.% along with Th and U up to 1427.22 and 642.14 ppm, respectively. The hydrothermal event has been characterized linked with two distinct varieties of allanite growth. The transportation of REEs occurs in aqueous chloro-complexes during the hydrothermal event. The timing of hydrothermal events and growth of the allanites has been determined. REE-enriched magmatic intrusion. [ABSTRACT FROM AUTHOR]

Bhilangana granitoid is a batholithic size body exposed in Bhilangana Valley and later thrusted over rocks of Lesser Himalaya. It comprises mylonitized porphyritic granite gneiss, psammitic gneiss, and its variants, containing primary biotite and muscovite, and S-type in nature. Bhilangana granitoid is intruded by basic intrusive. The variation in chemical signatures and associated petrogenetic issues of Bhilangana granitoid are dealt with detailed petrographic, geochemical and mineral chemical study. In the vicinity of basic intrusive, the porphyritic granite gneiss shows enrichment of MgO, whereas its evolved part, psammitic gneiss shows more boron enrichment with the presence of tourmaline nodules surrounded by quartzo-feldspathic rim. The major mineral assemblage in Bhilangana granitoid is quartz–K-feldspar–plagioclase–biotite–muscovite with tourmaline, epidote, zircon, ilmenite, apatite and monazite. The granite is peraluminous with ASI values always >1. Biotite shows variation from Fe-rich siderophyllitic to Mg-rich eastonitic composition, indicating involvement of both Al-rich crustal and Mg-rich mafic sources, inferring source heterogeneity or mixing of felsic-mafic magma. Granitoid melt was buffered below QFM to NNO and partly above HM, indicating a strong reducing to the oxidizing condition of melt. The melt was saturated with the presence of 3.3–6.8 wt.% H2O content. The crystallization temperature of Bhilangana granitoid (TZr) ranges between 697° and 807°C with a solidification pressure of about 2.92–4.31 kbar, implying crystallization at a depth of 8.76–13 km. The presence of greisens assemblage of quartz–mica–tourmaline–epidote, along with the presence of fluorite, is a representative greisens assemblage for Sn–W mineralization. Thus, the Bhilangana granitoid represents the fertile nature and potentiality of Sn–W minerals. Research highlights: Bhilangana granitoid is S-type, peraluminous granitoid, formed by anatexis of crustal material The biotite chemistry reveals the variation in the redox condition and modification in the oxidation state, preserved in the different variant of granite representing the magma mixing or source heterogeneity in protolith. The Bhilangana granitoid has attended the crystallization temperature (TZr) of 697–807 °C under pressure of about 2.92–4.31 kb implying the depth of crystallization of 8.76–13 km. The presence of greisenization favours the potential of Sn–W minerals. The geochemical results shows abnormal enrichment of W and Sn in the Bhilangana granitoid. The Bhilangana granitoid appears to have fertile nature for Sn–W mineral potential. [ABSTRACT FROM AUTHOR]

We use the stylolite roughness inversion technique (SRIT) to decipher the principal vertical stress and corresponding burial depth of the Narji Limestone, Cuddapah Basin, India. The method is applied to bedding parallel stylolites (BPS), which are present in carbonate rocks and originated due to pressure dissolution along the contact points between layers and are caused by compaction and deformation of sedimentary rocks. In this study, we analyse the surface roughness of a set of 25 stylolites that run parallel to the sedimentary bedding. The study area is replete with Class 2 (seismogram pinning type) and Class 3 (suture and sharp peak) types of BPS, of which Class 3 is more appropriate for determining the burial depth, which is the dominant type. The results confirm that there are two self-affine scaling regimes in the stylolite morphology, with cross-over lengths (Lc) varying from 0.32 to 0.95. The calculated vertical stress varies from 19.0 to 43.6 MPa, estimating the range of burial depth of the Narji Limestone between 718 m and 1649 m, with a median of 923 ± 92 m. [ABSTRACT FROM AUTHOR]

The mineral assemblages within ductile shear zones, which act as open systems, may be strongly influenced by the occurrence of mass transfer processes induced by the infiltrated composite H2O-rich (+ ±boron ±Al) fluid fluxes and mobilising major elements. Metasomatism is the re-equilibration of a rock involving a change in the chemical composition through the interaction of parent rock with an external fluid phase. In the Sakoli Fold Belt of central India, sillimanite occurrences are associated with two major ductile shear zones, viz., one near the eastern margin, trending N–S; and other, near the northwestern margin trending NE–SW formed contemporaneous with D1 and D3 deformations, respectively. The shear zone rocks include basement slices of granodiorite gneiss, quartzite, quartz vein and intrusive granite. Aluminosilicates of andalusite and sillimanite occur in two mutually exclusive domains. While andalusite is ubiquitous in the host metapelites of Sakoli Group, sillimanite is restricted within the shear zones, preferably in mylonitized granite protoliths. Other minerals associated with sillimanite include abundant fibrolite, tourmaline, dumortierite, rutile, sphene, pyrophyllite, quartz, rare biotite and garnet, together with and secondary muscovite (after feldspar) and kaolinite, etc. It is indicative of interaction between infiltrated high-temperature hydrothermal fluid derived possibly from intrusive granite and the host rocks in the shear zone. No evidence of polymorphic inversion between andalusite and sillimanite nor breakdown reaction from muscovite + quartz → sillimanite+ K-feldspar could be established. Textural evidences suggest the growth of sillimanite and associated tourmaline at two pulses, each coinciding with or outlasting the peak of shear zone deformations and metamorphism in Sakoli rocks. Ductile shear zones in the area may thus represent high alumina hydrothermal alteration zones in granitic rocks through the influx of high-temperature fluids from some deeper source. The infiltrating hydrothermal fluids rich in Al, B, and H2O were channelised along the ductile shear zones. It caused extensive chemical alteration of the host rock giving rise to sillimanite, tourmaline, kaolinite, mica, etc., as metasomatic products. The infiltrating fluid was sufficiently high in temperature (>550°C) to produce sillimanite in the later stages of prograde metamorphism of the Sakoli Group of rocks, restricted to ductile shear zones in two separate tectonic and deformation settings. The anomalous growth of sillimanite in the restricted domains was undoubtedly facilitated by high strain environment of shear zones. Highlights: Two sets of shear zones, N–S and NE–SW related to two generations of deformations, respectively, hosts sillimanite mineralisation. Textural characteristics indicate solid-state growth of sillimanite during the syn- to late-tectonic stages of mylonitization in the shear zones. Infiltrating hydrothermal fluids rich in Al, B, H2O along the ductile shear zones, caused extensive chemical alteration of host rocks. The temperature of the infiltrating fluid was high enough to form sillimanite instead of andalucite as the metastatic product. High strain within shear zones facilitated the growth. Minerals like sillimanite, tourmaline, kaolinite, mica, etc., are metasomatic products. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the dynamics of channel bar morphology of river Raidak-II within the Himalayan foreland basin on multi-decadal timescales (1980–2020). Multi-temporal Landsat satellite images have been used for identifying and monitoring different types of channel bars and their morphological changes. Here, several indices (braiding index, total sinuosity and mode of bar development) are used to measure the braiding intensity. Additionally, fluvio-hydrological and field investigation methods have been adopted to assess the channel form and behaviour affecting the evolution of channel bars. Further, sediment grain size distribution has been analysed to understand the reach-scale variation of instream sediment characteristics. The results show that higher value of all the braiding indices in reach-1 indicates its high braiding intensity compared to other reaches of the river. Numerical investigation shows spatiotemporal dynamics of bar morphology (bar length, bar width, bar area and bar perimeter) of nine stable bars during the period 2000–2020. This study shows the reach-scale variation of different fluvio-hydraulic parameters, which are highly associated with the bar dynamics. Grain size analysis reveals that most of the materials are coarser in the upper and middle reach of the river. Consequently, coarser sediments are being deposited in high energy flow environment of upper and middle reach while finer sediments are deposited by low energy flow regime in the lower reach. However, morphological changes of different types of channel bars indicate their dynamic nature. These changes have occurred due to the collective effects of different factors, including variable discharge, frequent floods, physiographic control, active tectonics, huge sediment supply and channelisation in the study area. Research Highlights: The present study shows higher value of braiding Index, total sinuosity and bar mode in reach-1 indicating its higher braiding intensity compared to another two reaches of the river. The study indicates spatiotemporal dynamics of bar length, bar width, bar area and bar perimeter during the period of 2000–2020. This scientific study exhibits reach scale variation of different fluvio-hydraulic parameters which are highly associated with the spatiotemporal dynamics of bar morphology. The scientific analysis revealed that different types of bars have been developed and modified in the study area due to different natural and anthropogenic factors during recent past time. [ABSTRACT FROM AUTHOR]

A barred tidal flat has grown in the north of Subarnarekha river estuarine system along the western coast of Bay of Bengal, Talsari, Odisha, over the last twenty years, from 2002 to 2022. The channels form an integral part of the tidal flat and act as conduits for supplying and draining sediments with flood and ebb flows. Multiple drainage basins with quantifiably different channel patterns are identified within the Talsari tidal flat. Two major types of tidal channels, namely through-flowing and dead-end channels, are recognized in the Talsari Tidal flat. Channel morphometric analysis reveals that the sand:mud ratio in the tidal flat sediments, along with slope, tidal range, current strength, vegetation cover and climate, strongly controls the channel pattern evolution in drainage basins within the tidal flat. Channel migration and filling patterns develop distinctly different sedimentary bodies with respect to laterally adjacent flat areas. High-energy climatic storms played an important role in transporting silty-muddy sediments to the tidal flat and also brought changes in channel morphometry along with the development of regionally developed scours. [ABSTRACT FROM AUTHOR]

Singhbhum Craton (SC), one of the oldest continental crusts, has a nucleus of Singhbhum Granite Complex with volcano-sedimentary belts in peripheral parts. Deciphering the inter-relationship between volcano-sedimentary packages and surrounding granitoids offers considerable challenges. The present study area lies in the northwestern parts of SC. Lithounits of volcano-sedimentary packages drapes around the Paleoarchean Bonai Granite Complex (BGC). An attempt has been made to understand the basin development over BGC based on the mutual relationship between lithopackages of Iron Ore Group (IOG) and their structural disposition. It is proposed that two distinct basins, Koira and Gurundia, developed over BGC during Mesoarchean. While the Eastern Koira basin witnessed continuous development accompanied by subsidence wherein lithopackages of Bonai–Kendujhar Iron-ore Belt were deposited, Western Gurundia Basin is marked by a hiatus after the deposition of Gurundia quartzite and mafic volcanics in a shoreline to shallow marine environment. Darjing Group of rocks deposited as platformal package over Gurundia, Koira groups and BGC. Litho packages of Koira, Gurundia and Darjing groups exhibit structural unity as they co-deformed during Iron ore orogeny. The first deformation phase has led to a series of NE–SW to ENE–WSW trending low plunging overturned folds with southeasterly vergence. The second deformation, near coaxial with the first, has led to low northerly plunging open folds with steep northwesterly dipping axial planes. BGC occupies the core of a major second-generation fold with volcano-sedimentary sequence draping around it. It is proposed to put them under Iron Ore Super Group (IOSG), where IOGs (Koira and Gurundia groups) represent the lower part and Darjing Group as the upper part. Research Highlights: IOSG consists of IOGs (Koira and Gurundia groups) and Darjing Group as per present observation. Volcano sedimentary litho packages of IOG were deposited in two distinct basins (Koira and Gurundia basins) developed over BGC in a continental shelf-slope facies. Darjing Group deposited all over Gurundia and Koira groups and BGC after a hiatus which is marked by polymictic basal conglomerate. All the litho members of IOSG were co-deformed during Iron-Ore Orogeny (during the formation of Ur) and exhibit two distinct phases of folding as observed from field and this is reported for the first time with an attempt to bring Darjing group within Iron Ore Supergroup (IOSG). [ABSTRACT FROM AUTHOR]

Floods are the most frequent of all natural disasters that occur in India. Although one of the main reasons for these disasters is the variations in monsoon and heavy inflows during the four months of the rainy season, India's asymmetric geomorphic features play an important role in determining the nature and intensity of floods in different regions. The destruction due to floods can be monitored with Internet of Things (IoT) systems. Flood forecasting can be done to warn people and evacuate them to safer places. A real-time end-to-end system generates an early flood alert based on various hydro-meteorological parameters received from sensing devices. In this study, an IoT-based system senses the hydrological data such as water discharge and water level, as well as data related to climate like rainfall, humidity, temperature, wind direction and speed. The task of estimating the water discharge gets difficult since rivers have changing geographic properties. To resolve this issue, a novel technique is proposed to estimate river discharge based on the sectional area and flow of the river. Additionally, the challenges associated with quantifying the overall quantity of rainfall resulting from the unpredictable behaviour of the local meteorological conditions have been addressed. [ABSTRACT FROM AUTHOR]

Aggressive cultivation practised across the Indian subcontinent to meet the growing food demands results in the groundwater at many places being severely affected by salinity, and this is a recognised hazard of agricultural belts. Evaluating spatial variations of salinity hazards is important for managing agricultural activity and implementing suitable and timely remedial measures. A precise representation of spatial variations of groundwater salinity using electrical conductivity (EC) can help identify potential sources and evaluate their severity and spatial impact. Simple spatial interpolation schemes, viz., inverse distance weighted (IDW) and trend surface analysis (TSA) are evaluated with over 250 EC measurements in groundwater during two seasons from saline-impacted regions of northwest India. Considering the three performance metrics, namely, correlation coefficient, root mean square error and mean absolute error, IDW scheme was adjudged better than TSA for both seasons. Interpolation by TSA and contour plot using OriginLab® software resulted in unrealistic (negative) values of EC, whereas IDW was free from such limitations. Errors associated with IDW-based interpolated EC values for this site would be 320–415 μS/cm for pre-monsoon and 630–800 μS/cm during post-monsoon seasons. Refined EC map generated using seasonal IDW interpolation scheme would facilitate timely and cost-effective remediation of salinity hazard, impact assessment of point and non-point sources on salinity hazard. Research highlights: Simple algorithms were examined for spatial interpolation of groundwater EC; IDW was adjudged better over TSA. Seasonal influence on interpolation parameters for EC was highlighted. IDW parameters ascertained from systematic search in this study are different from reported default values in commercially available software. Whereas TSA or default interpolation with OriginLab® resulted in negative(unrealistic) EC values, IDW results were consistent. Refined EC map generated using seasonal IDW interpolation scheme would facilitate: timely and cost-effective remediation of salinity hazard; impact assessment of point and non-point sources on salinity hazard. [ABSTRACT FROM AUTHOR]

The present study attempts to ascertain the sediment provenance of around 6.5-m thick palaeochannel sediment exposed in the vicinity of the Ghaggar–Hakra river system of the alluvial plains of the Haryana state of India. The major element geochemistry indicates that the sediments are arkosic in nature, dominated by quartz, K-feldspar, micas, plagioclase, and clay minerals (chlorite, illite, and a very less amount of montmorillonite). The CIA (chemical index of alteration) values ranged between 63 and 77, indicating moderate degrees of chemical weathering. REE plots show that the Eu anomaly is negative for average Bhor Saidan samples similar to PAAS and UCC, suggesting that they could have been deposited in the foreland basin after being originally produced from differentiated silicic and/or recycled sedimentary sources; nonetheless, a little positive Eu anomaly in the chondrite normalised plot is the result of feldspar and arkosic nature of sediments indicating higher levels of physical over the chemical weathering. Mostly the samples are from Siwaliks. Optically stimulated luminescence (OSL) dating suggests that the sediments are ~11 ka old. Further, the palaeochannel is being incised ~3.3 ka and younger sediments are stratigraphically deposited at lower levels. The discriminant function plots (Roser and Korsch 1988) of sediment samples exhibited that they were deposited in a passive margin setting and came from the interior of cratons or a quartzose sedimentary orogenic terrain. The present work done on the geochemistry of the sediments of a palaeochannel present in the alluvial plains will work as a dot on the map to connect the history of the river drainage system of the area in future studies. [ABSTRACT FROM AUTHOR]

The Asurabandha area on the southern side of the main Sukinda Ultramafic Complex (SUC) in the State of Odisha hosts some irregular and sporadic chromitite bodies which are completely detached from the main SUC. The isolated chromitite bodies are highly altered. Chromitite samples from these isolated bodies have been studied using a polarising petrological microscope, scanning electron microscope (SEM), field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer and the findings are presented here. In this area, we have identified the associated silicate minerals with chromite to be primarily opal-CT and quartz, contrary to the conventional Fe–Mg silicates such as olivine, pyroxene, or serpentine, although in few instances, the Fe–Mg silicates are identified. The original Fe–Mg silicates have almost completely been replaced by the silica polymorphs. Occurrences of opal-CT and quartz have been identified from their prominent X-ray diffraction peaks at d-spacing of 4.10 Å (with a shoulder peak at 4.32 Å) and 3.34 Å, respectively. The phase compositions are also confirmed by SEM-EDAX analyses. The average composition of opal-CT was found to be (in wt.%) SiO2: 95.41, MgO: 1.75 and FeO: 1.74. The presence of MgO and FeO in the composition of opal-CT, along with relict mesh-like micro-structures, indicate its formation by silicification/opalization from serpentines. A low-temperature hydrothermal alteration process driven by Si- and CO2-rich fluids through fractures and fault zones might have caused the removal of Mg and Fe from primary ultramafic silicate minerals and precipitation of opal-CT. This replacement process involved the initial dissolution of serpentine with preferential leaching of the metallic ions (Mg, Fe) and simultaneous precipitation of amorphous silica to form possibly opal-A in the beginning and then to opal-CT which subsequently transforms to microquartz because of the ordering of structure and removal of water through the dissolution–precipitation mechanism. [ABSTRACT FROM AUTHOR]

The Cambay Basin, on the western continental margin of India, is infilled with transgressive Paleocene to early Eocene Cambay Shale Formation. Cores, electrolog data and correlations, and geochemical data allow organofacies characterization of the formation in the Jambusar–Broach area. Eleven transgressive–regressive sequences have been identified within the formation based on electrolog characteristics. Sedimentological analysis indicates that the bottom fining-upward part of these sequences is rich in organic matter. Geochemical data of these sequences of the formation is evaluated in terms of total organic carbon (TOC), source potential (S1 and S2) and thermal maturity index (Tmax). This clearly shows that the formation is a potential source rock for oil/gas generation, mostly with type III and minor contribution of type II organic matter. Vitrinite reflectance (VRo) data suggest that the formation is in the early to late oil generation window. However, an extrapolated trend of VRo vs. depth shows that the formation is falling within a gas window in the deeper part. The geochemical model based on the computed parameters (TOC, HI, source thickness and kinetics) is integrated with the available geological model of the study area. Then, 3D petroleum system modeling is carried out for evaluation of the source potential of the Cambay Shale Formation. Finally, play chance mapping (PCM) is attempted to identify sweet spots. Thus, the overall approach assists in the exploration of unconventional plays in the area. [ABSTRACT FROM AUTHOR]

This paper presents results of a study of long term trends in the characteristics of the within-season temporal profile of southwest monsoon rainfall over western India during the last five decades in relation to global warming induced regional climate change. In contrast to recent climate change analyses and projections, no significant long-term trends have been observed in this study. Slow decadal scale variations observed are analysed in relation to Pacific Decadal Oscillations (PDO). Daily variations in rainfall anomaly show opposite characteristics during negative and positive phases of PDO. The above-normal rainfall (>25%) is found during the starting phase of monsoon in negative PDO. Over the last decade, i.e., during 2000-2007, the seasonal rainfall amount, as well as seasonal span of southwest monsoon over western India is indicative of a gradual increase. [ABSTRACT FROM AUTHOR]

This paper looks at the crucial issue of dry-season groundwater-availability in the state of Maharashtra, India. We look at the two key hydro-climatological measurements which are used to implement groundwater policy in the state, viz., water levels in 5000+ observation wells across the state and aggregate rainfall data. We see that there is substantial variation in groundwater levels within and across the years in most wells. We argue that for a large number of these observation well locations, aggregate rainfall data is inadequate to model or to predict groundwater levels. For this, we use a novel random rainfall coefficient model for the purpose of modelling the effect of rainfall in a composite setting where extraction and changing land-use data is unknown. The observed high variance of this coefficient points to significant variations in groundwater levels, which may only be explained by unmeasured anthropogenic factors. Next, we see that the uncertainty in actual groundwater levels along with scarcity are two distinct features of groundwater availability and will elicit different behaviours from the typical user. Finally, we recommend that quantitative groundwater assessment protocols of the state should move to incorporating data from which extraction and land-use may be modelled. We believe this is one of the first studies where large spatio-temporal scale data gathered by state agencies have been analysed for scientific adequacy. [ABSTRACT FROM AUTHOR]

The ~1.2 Ga Bijaigarh Shale (BS) is a significant geological formation in the Vindhyan Supergroup of Son Valley and is widely targeted for understanding Mesoproterozoic oceanic redox conditions and crustal evolution. In the present study, we have analysed the major, trace and rare earth elements compositions of the BS and attempted to infer the composition, weathering history, and tectonic setting of the Mesoproterozoic continental crust. The BS is comprised of quartz, smectite, kaolinite and illite, with occasional framboidal pyrites. High chemical index of alteration (CIA) and plagioclase index of alteration (PIA) values, and depletion of Na2O, CaO, Sr and Ba imply that the source region underwent a high degree of chemical weathering under warm and humid climatic conditions. Various immobile element ratios in the BS suggest felsic source rocks and insignificant recycling. Fractionated chondrite normalised REE patterns (La/YbN = 6.7–12.3, avg. 9.5) and negative Eu anomalies (Eu/Eu* = 0.50–0.60, avg. 0.53) also indicate felsic provenance. REE mixing modelling implies that the source area was comprised of 40% Mahakoshal Granite, 25% Bundelkhand Granite, 30% Porcellanite and 5% Chhotanagpur Granite Gneiss Complex (CGGC). The sedimentation in Kaimur basin is thought to have begun at ~1.2 Ga, accompanied with the crustal extension in the aftermath of Central Indian Tectonic Zone (CITZ) orogeny (1.6–1.5 Ga) and domal uplift of Bundelkhand craton. The positive areas were created by orogenic movements, which exposed the older crustal blocks containing granites and metamorphic rocks in the CITZ (Chhotanagpur Gneisses and Mahakoshal belt) and Bundelkhand granite complex (BGC). The Mahakoshal Group and CGGC located on the southern side, the BGC on the northern side of the basin, and the uplifted Lower Vindhyans were the likely sources of the BS. Such source areas are also indicated by the palaeoflow directions. [ABSTRACT FROM AUTHOR]

The Saurashtra Horst, south of the Kachchh Rift Basin, is a significant tectonic block in the northwestern Deccan Volcanic Province of India. The Saurashtra Horst belongs to the stable continental region and typically experiences shallow intraplate earthquakes with depths up to 20 km. We analysed spectra of P- and S-waves using 182 broadband seismograms from 40 small earthquakes (M 3.5–5.1). It has been observed that there is a shift in P-wave corner frequency for most earthquakes to the higher side compared to that of S-corner frequency in both regions. The seismic moments measured from primary waves, i.e., M0(P), vary from 7.7 × 1012 to 5.88 × 1016 N-m, and from secondary waves, i.e., M0(S) range from 1.52 × 1013 to 1.88 × 1017 N-m for the southern part of Saurashtra. The corresponding variation of seismic moments for the events in northern Saurashtra is 3.08 × 1012 to 4.50 × 1014 N-m for P-waves and 7.01 × 1012 to 2.34 × 1015 N-m for S-waves. The estimated stress drop values lie in the range of 0.02–20.08 bars and 0.01–9.09 bars for the earthquakes in Saurashtra's southern and northern parts, respectively. The small earthquakes have been found to be self-similar in the southern part, while there is a breakdown of self-similarity for small earthquakes in the northern region. This indicates the diverse stress regimes in the Saurashtra Horst. A scaling relation ( M 0 f c 3 = 2.19 × 10 15 N - m / s 3 ) for the southern part of Saurashtra is obtained during the linear regression investigation among the established seismic moment, i.e., M0, and corner frequency, i.e., fc. The structural heterogeneities corroborate the diversity in source parameters for two different parts of SH in the regions. The variability of stress drops for the best-located events shows that the higher stress drop values correspond to the source zone having lower Vp/Vs and vice versa. [ABSTRACT FROM AUTHOR]

The transition from magmatic to solid-state deformation in granitic rocks is observed either in cases of shear-zone-controlled magma emplacement or in cases of magma-assisted shear-zone nucleation. In the latter case, pre-emplaced granitoid magmas that are later subjected to a dynamic regime with decreasing temperature accommodate stress that causes strain localization. Shear zones in this case are generally restricted to the contact zone between wall rock and granitoid magma, as it represents large viscosity discontinuities. In large granitic provinces (LGPs), however, rheological properties are mainly driven by the changes in physical parameters of granitic magmas, and thus, shear-zone nucleation in magmatic or sub-magmatic conditions cannot be attributed to the viscosity discontinuities caused by the presence of wall rock. Rather, in LGPs, it is only dependent on the rheological discontinuities within the granitic magmas, and thus, a detailed knowledge of the transition from magmatic to solid-state deformation can give important insights into the dynamic history of granitoid magmas in LGPs. The ~2.5 Ga old, voluminous granitoids of Bundelkhand Craton have been affected by multiple shear systems. Among these, the NE–SW and E–W shear systems are major systems that affected the granitoid microstructures. The NE–SW shear system transects the craton as multiple small- and large-scale shear zones, while the E–W shear system is mainly present in the central part of the Bundelkhand Craton. A petrographic study of a ~25 km long, NE–SW trending Baldeogarh shear zone and granite microstructures in associated areas show important magmatic and solid-state deformation features. Overprinting of solid-state deformation over sub-magmatic deformation confirms the progression of deformation with decreasing temperature. Contrary to this, E–W trending microstructures are primarily magmatic to sub-magmatic with rare small-scale solid-state deformation. This indicates that the E–W shear system is older in southern Bundelkhand and was followed by the NE–SW shear system in magmatic conditions. Therefore, the presence of a transition from magmatic to solid-state deformation along the NE–SW trending shear zone indicates that bulk cooling of the granitoid took place while the NE–SW shear system was active. Research Highlights: Transition from magmatic to solid-state deformation in Large Granitic Provinces. Magmatic to solid-state deformation along NE-SW shear zone. Overprinting textures of transition from sub-magmatic to solid-state deformation. [ABSTRACT FROM AUTHOR]

Prediction of the seasonal monsoon rainfall over India relies largely on the well-known relationship with El Niño and Southern Oscillation (ENSO) and is possible because reasonably reliable seasonal predictions of ENSO are now available. Usually, the cold phase of ENSO is associated with above-normal monsoon rainfall and the warm phase of ENSO with below-normal rainfall. There are, however, exceptions: years in the cold phase of ENSO with below-normal monsoon rainfall and even drought conditions. We term these exceptional events 'rogue La Niñas'. Clearly, an explanation of these exceptional cases will improve the predictive skill. Here we show that for the part of the Arabian Sea, east of the upwelling region and north of the equatorial belt (60°–70°E, 10°–23°N), the correlation of outgoing longwave radiation with Indian summer monsoon rainfall is even higher than that with the equatorial central Pacific associated with ENSO. Convection over this region is triggered by ENSO, but is modulated by the underlying sea surface temperature (SST). There is a minimum of SST of about 28.1°C above which the convection over the Arabian Sea is high enough and there are no rogue La Niñas. Furthermore, we show that, in this region, the SST of June–September is related to the SST of April–May. When April–May SST is >29.6°C, June–September mean SST is always >28.1°C and there are no rogue La Niñas; the monsoon rainfall is always normal or above normal as expected with a La Niña. Thus the chance of a rogue La Niña can be predicted from the April–May SST of the Arabian Sea. [ABSTRACT FROM AUTHOR]

Site-specific hydrogeological parameters are a prerequisite to investigate the migration of radionuclides in groundwater due to leaching from low-level solid radioactive waste disposal facility (SRWDF) site. The leaching event is a low probability event due to all the engineered safety features provided in SRWDF, but the impact assessment, even due to this low probability event of leaching is a regulatory requirement. The present study focuses on SRWDF located in Tarapur, India. Hydrogeological parameters such as radionuclide specific distribution coefficient (Kd), hydraulic conductivity (HC) and porosity are estimated for a watershed area in and around the SRWDF. Values of HC and porosity for soil samples collected from the disposal site are found to be in the range 0.006–0.15 cm/s (average 0.059 cm/s) and 25.64–32.62% (average 29.19%), respectively. Average hydraulic gradient is found to be 0.007. Using the estimated values of hydraulic gradient, porosity and HC in Darcy's law, groundwater velocity is calculated as 0.13–3.22 m/day. The distribution coefficient of caesium, the most prevalent radionuclide in low-level solid radioactive waste, is estimated to be ranging between 116.73 and 393.54 ml/g. Physical and chemical characteristics of soil like pH, electrical conductivity, organic matter content, moisture content, CaCO3 content and effective cation exchange capacity (ECEC) are determined experimentally. Correlation among the estimated parameters is also studied. The Kd of caesium is found to be positively correlated with porosity, ECEC, clay and silt fraction of the soil and negatively correlated to sand fraction. The site-specific parameters estimated in this study would be useful for carrying out the radiological impact assessment (RIA) of the SRWDF at Tarapur through the terrestrial pathway. Research Highlights: The values of site-specific distribution coefficient (Kd) of the soil samples range from 116.73 to 393.54 ml/g. Hydrogeological parameters like hydraulic conductivity, porosity, groundwater velocity have been estimated, and the values range from 0.006 to 0.15 cm/s, 25.64 to 32.62% (average 29.19%), 0.13 to 3.22 m/day, respectively. Physico-chemical properties like pH, electrical conductivity, organic matter content, moisture content, CaCO3 content, and effective cation exchange capacity have been estimated. Correlation among estimated parameters is studied. Site-specific Kd is found to be positively correlated with porosity, effective cation exchange capacity, clay and silt fraction of the soil and negatively correlated to sand fraction. [ABSTRACT FROM AUTHOR]

The mafic–ultramafic cumulate rocks and mantle peridotites of an ophiolite are excellent recorders of the geodynamic evolution of a fossil subduction zone. The spectro-radiometric absorption features of olivine, orthopyroxene, clinopyroxene and serpentine, which are the dominant constituents of these ultramafic rocks, have emerged as essential tools for their identification. This study uses six different kinds of ultramafic rock samples – spinel lherzolite, spinel harzburgite, wehrlite, orthopyroxenite, olivine websterite, and dunite compositions from the Nagaland Ophiolite Complex, NE India. These are investigated with integrated petrographic, mineral and bulk rock compositional and reflectance spectroscopic studies to identify the constituent minerals. The study indicates that the most dominant olivine absorption features vary from 1038 to 1049 nm in Ni-poor ultramafic cumulates of wehrlite (Mg# = 89, Ni = 355 ppm) and olivine websterite (Mg# = 90.5, Ni = 361 ppm) to 1066–1097 nm in nickeliferous mantle peridotites of dunite (Mg# = 87, Ni = 3658 ppm) and spinel lherzolite (Mg# = 87, Ni = 2708 ppm) compositions. Reversal of the 625 nm reflectance maximum in olivine occurs for Ni concentrations in the mineral between 2200 and 2955 ppm. The low-Ca pyroxene (cf. orthopyroxene) species show characteristic absorption features at 902–926 nm in lherzolite and harzburgite samples and 918 nm in monomineralic orthopyroxenite. High-Ca pyroxene (cf. clinopyroxene) in most rocks records absorption features at 643–666 and 709–811 nm. The study also recognises major absorption bands at 1382–1400, 1913–1948, and 2304–2326 nm as indicative of secondary hydrous minerals as a product of alteration in the investigated rocks. The significance of major (Mg–Fe) and minor (Mn, Ni and Cr) element compositions of these ultramafic rocks to explain specific spectral signatures in olivine, orthopyroxene and clinopyroxene is discussed. The findings are expected to aid the interpretation of remotely sensed data from terrestrial and extra-terrestrial bodies, mapping ultramafic cumulate and mantle peridotite rocks in remote, covered, and unmapped terranes of ophiolitic origin, and in the process, identification of fossil oceanic subduction systems. [ABSTRACT FROM AUTHOR]

The paper presents the nature of variations of tropospheric and total ozone column retrieved from the Convective Cloud Differential (CCD) technique, Ozone Monitoring Instrument (OMI), and Total Ozone Mapping Spectrometer (TOMS) data, National Aeronautics and Space Administrations (NASA), USA, respectively; surface temperature, relative humidity, total rainfall, ozone precursors (non-methane hydrocarbon, carbon monoxide, nitrogen dioxide, and sulphur dioxide) that are collected from India Meteorological Department (IMD), Alipore, Kolkata; solar insolation obtained from Solar Geophysical Data Book and El-Niño index collected from National Climatic Data Center, US Department of Commerce, National Oceanic and Atmospheric Administration, USA. The effect of these climatic parameters and ozone precursors on ozone variations is critically analyzed and explained on the basis of linear regression and correlation. It has been observed that the maximum, minimum and mean temperature, relative humidity, solar insolation, tropospheric, and total ozone column (TOC) showed slight increasing tendencies from October 2004 to December 2011, while total rainfall and El-Niño index showed little decreasing tendencies for the same period. Amongst selected climatic parameters and ozone precursors, the solar insolation and the average temperature had a significant influence on both, the tropospheric ozone and total ozone column formation. The solar insolation had contributed more in tropospheric ozone than in total ozone column; while El-Niño index had played a more significant role in total ozone column build up than in tropospheric ozone. Negative correlation was observed between almost all ozone precursors with the tropospheric and total ozone. The tropospheric ozone and total ozone column were also significantly correlated. The level of significance and contribution of different climatic parameters are determined from correlation technique and Multiple Linear Regression (MLR) method. The related chemical kinetics for ozone production processes has been critically described. [ABSTRACT FROM AUTHOR]

This paper describes an estimation of endmember compositions followed by the assessment of those results by log-ratio variance analysis. As an appraisal, it deals only with the first objective of an endmember analysis namely, to identify endmembers if they exist by estimating their compositions. Following the creation of the endmember estimates, the computation of an array of log-ratio variances was a key innovation in this type of study. Log-ratio variances revealed intrinsic linear associations between the dominant elements on each of the estimated endmember compositions, largely confirming the endmember analysis. The dataset under study contained the concentrations of 16 elements in 93 samples of deep-sea manganese nodules from the Central Indian Ocean Basin. Many previous analyses of these nodules were undertaken to assess the economic potential of the deposits. This study by contrast, quantified the inter-element associations that account for the nodule compositions. Four endmembers were identified. The elements loaded on each were: (1) Mn, Zn, Ni, Cu, Mn-rich, (2) Fe, Ti, P, Co, Fe-rich, (3) Si, Al, Na, K, clay minerals, (3) Mg, ultramafic material, possibly including Mn, Cr, V, Ca, Na. These latter elements were also detected by their log-ratio variances to be associated with Mg on the 4th endmember. [ABSTRACT FROM AUTHOR]

In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature ( 휃) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number ( R) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH. [ABSTRACT FROM AUTHOR]

It is now well known that there is a strong association of the extremes of the Indian summer monsoon rainfall (ISMR) with the El Niño and southern oscillation (ENSO) and the Equatorial Indian Ocean Oscillation (EQUINOO), later being an east-west oscillation in convection anomaly over the equatorial Indian Ocean. So far, the index used for EQUINOO is EQWIN, which is based on the surface zonal wind over the central equatorial Indian Ocean. Since the most important attribute of EQUINOO is the oscillation in convection/precipitation, we believe that the indices based on convection or precipitation would be more appropriate. Continuous and reliable data on outgoing longwave radiation (OLR), and satellite derived precipitation are now available from 1979 onwards. Hence, in this paper, we introduce new indices for EQUINOO, based on the difference in the anomaly of OLR/precipitation between eastern and western parts of the equatorial Indian Ocean. We show that the strong association of extremes of the Indian summer monsoon with ENSO and EQUINOO is also seen when the new indices are used to represent EQUINOO. [ABSTRACT FROM AUTHOR]