• Volume 127, Issue 7

October 2018

• Evolution of Hutti-Maski greenstone belt of the Eastern Dharwar Craton: Evidence for metamorphic and hydrothermal phases from the Hira-Buddini deposit, Raichur district, Karnataka, India

The Hira-Buddini gold deposit is located along the steeply dipping ENE trending sheared contact of felsic and mafic rocks of strike length of about 600 m with mylonitic foliation parallel to the S1 schistosity in amphibolites. Second-generation open folds with axial planes (S2) marked by fractures that are often filled by later calcite veins are observed in surface and underground exposures. Garnetiferous amphibolites occur in patches on the footwall side of the shear in the western part of the deposit. This rock shows garnet porphyroblasts, coarse second-generation hornblende and large grains of biotite that grow over an early S1 fabric which is made up of early hornblende, plagioclase, ilmenite and retrograde first-generation chlorite. Second-generation hornblende and biotite grains make high angles to S1 schistosity and are sub-parallel to S2. Late hydrothermal alteration is marked by an albite-epidote-chlorite-zoisite assemblage. Geothermometric estimates based on garnet-biotite, and garnet-hornblende pairs, as well as Ti in biotite, show that temperatures during D2 deformation that led to the growth of the porphyroblasts were $530{\pm }20^{\circ }\hbox {C}$. The fabric and mineralogy of the rock indicate that porphyroblastic growth of garnet, hornblende and biotite was preceded and succeeded by stages of hydrothermal alteration. Primary gold mineralization is inferred to be associated with the early stage of hydrothermal ingress.

• Assessing the copula selection for bivariate frequency analysis based on the tail dependence test

The flood characteristics, namely, peak, duration and volume provide important information for the design of hydraulic structures, water resources planning, reservoir management and flood hazard mapping. Flood is a complex phenomenon defined by strongly correlated characteristics such as peak, duration and volume. Therefore, it is necessary to study the simultaneous, multivariate, probabilistic behaviour of flood characteristics. Traditional multivariate parametric distributions have widely been applied for hydrological applications. However, this approach has some drawbacks such as the dependence structure between the variables, which depends on the marginal distributions or the flood variables that have the same type of marginal distributions. Copulas are applied to overcome the restriction of traditional bivariate frequency analysis by choosing the marginals from different families of the probability distribution for flood variables. The most important step in the modelling process using copula is the selection of copula function which is the best fit for the data sample. The choice of copula may significantly impact the bivariate quantiles. Indeed, this study indicates that there is a huge difference in the joint return period estimation using the families of extreme value copulas and no upper tail copulas (Frank, Clayton and Gaussian) if there exists asymptotic dependence in the flood characteristics. This study suggests that the copula function should be selected based on the dependence structure of the variables. From the results, it is observed that the result from tail dependence test is very useful in selecting the appropriate copula for modelling the joint dependence structure of flood variables. The extreme value copulas with upper tail dependence have proved that they are appropriate models for the dependence structure of the flood characteristics and Frank, Clayton and Gaussian copulas are the appropriate copula models in case of variables which are diagnosed as asymptotic independence.

• Characterization of organic carbon in black shales of the Kachchh basin, Gujarat, India

Thirty-three black shale samples from four locations on the onland Kachchh basin, western India were analyzed to characterize organic carbon (OC), thermal maturity and to determine the hydrocarbon potential of the basin. Upper Jurassic black shales from the Jhuran Formation (Dhonsa and Kodki areas) are characterized by the presence of chlorite, halloysite, high $T_{\mathrm{max}}$, low OC, low hydrogen index and high oxygen index. These parameters indicate the OC as type IV kerogen, formed in a marine environment. The rocks attained thermal maturity possibly during Deccan volcanism. Early Eocene samples of the Naredi Formation (Naliya-Narayan Sarovar Road (NNSR) and the Matanomadh areas) are rich in TOC, smectite, chlorite and framboidal pyrite, but have low $T_{\mathrm{max}}$. These indicate deposition of sediments in a reducing condition, probably in a lagoonal/marsh/swamp environment. Organic carbon of the Naredi Formation of NNSR may be considered as immature type III to IV kerogen, prone to generate coal. Core samples from the Naredi Formation of the Matanomadh area show two fold distribution in terms of kerogen. Organic carbon of the upper section is immature type III to IV kerogen, but the lower section has type II to III kerogen having potential to generate oil and gas after attaining appropriate thermal maturity.

• Carbon dioxide, water vapour and energy fluxes over a semi-evergreen forest in Assam, Northeast India

The eddy covariance method is a powerful technique for quantification of $\hbox {CO}_{2}$, $\hbox {H}_{2} {\rm O}$ and energy fluxes in natural ecosystems. Leaf area index (LAI) and its changes are significant drivers of $\hbox {CO}_{2}$ and $\hbox {H}_{2}$O exchange in a forest ecosystem due to their role in photosynthesis. The present study reports the seasonal variation of $\hbox {CO}_{2}$ and energy fluxes and their relationship with other meteorological parameters of a semi-evergreen primary forest of Kaziranga National Park, Assam, India during February 2016–January 2017. The diurnal pattern of half hourly average $\hbox {CO}_{2}$ fluxes over the forest was found to be mostly dominated by the incident photosynthetically active radiation. During the period of study, diurnal variations of $\hbox {CO}_{2}$ flux showed a maximum value of $-9.97 \mu mol \hbox {m}^{-2}\hbox {s}^{-1}$ in the month of June during summer which is also the beginning of the monsoon season. The monthly averaged diurnal $\hbox {CO}_{2}$ flux and variation in LAI of the forest canopy closely followed each other. The annual net ecosystem exchange of the forest estimated from the $\hbox {CO}_{2}$ flux data above the canopy is 84.21 g C $\hbox {m}^{-2}\,\hbox {yr}^{-1}$. Further studies are in progress to confirm these findings. The estimated average annual evapotranspiration of the semi-evergreen forest is 2.8 $\pm$ 0.19 mm $\hbox {day}^{-1}$. The study of partitioning of energy fluxes showed the dominance of latent heat fluxes over sensible heat fluxes. The energy balance closure was found to increase with an increase in instability and the highest closure of around 83% was noted under neutral conditions.

• Modelling forest resilience in Hindu Kush Himalaya using geoinformation

Resilience is the capacity of an ecosystem to absorb disturbance and undergo change while maintaining its essential structure, functions, identity and feedbacks. The forests of the Hindu Kush Himalayan (HKH) region are vulnerable to both natural and anthropogenic changes, and the forest land conversion and degradation. Using satellite-derived tree canopy cover percent data and precipitation as the explaining variable, we studied the forest cover resilience in a geospatial framework employing the logistic regression and polynomial equation fitting. Out of the $4.3\,\hbox {million km}^{2}$ geographical areas, $873{,}650\,\hbox {km}^{2}$ (20.20%) was under the forest in 2000 and experienced loss of $11{,}250\,\hbox {km}^{2}$ during 2000–2010. We could model the forest cover and treeless areas fairly than the scrub and grassland owing to the variation in precipitation pattern. The majority of the forest cover (59.3%) has been estimated to have less resilience owing to the receipt of <1650 mm of total annual precipitation, whereas only $375\,\hbox {km}^{2}$ forest area could change to scrub that shows the least resilience. About 94.4% of treeless areas were estimated to be stable, while only 1% $(25{,}200\,\hbox {km}^{2})$ area could accommodate the grassland. The resilient forest areas estimated and observed, owing to the mapping and modelling protocols used in this study, shall be useful in conservation planning in the HKH region.

• Geochemistry and distribution of sediments in the East Indian shelf, SW Bay of Bengal: implications on weathering, transport and depositional environment

Forty-two substrate sediment samples and three cores procured from the shelf region between Chennai and Cuddalore were analyzed to understand the spatial and vertical sediment distribution. Samples subjected to grain size, bulk and clay mineralogical analyses, REE and trace element geochemistry yielded interesting results about the sediment characteristics with respect to the modern day environment. The present study revealed that the study area is characterized by high energy environment marked by predominant composition of medium sand. Results confirmed the evidence of more illite than kaolinite, smectite, and chlorite in the clay mineral assemblage indicating a terrigenous source. Geochemical data also revealed that the enrichment of light rare earth elements (LREE) in the sediments is due to continental source of Precambrian times. High feldspar content in the sediments which is emphasized by bulk mineralogical data displayed positive Eu anomaly. By using the paleoredox index, the area of interest is considered to have undergone no major changes in its depositional settings.

• Application of instantaneous spectral analysis and acoustic impedance wedge modeling for imaging the thin beds and fluids of fluvial sand systems of Indus Basin, Pakistan

Fluvial sand frameworks have magnificent oil and gas reservoirs far and wide. The reservoir sands are exceedingly compartmentalized by the broadened fault framework. So, to distinguish the thin beds of gas-bearing facies is an assessment for band-limited stratigraphic investigation. To conquest this issue, we execute the progressed seismic ascribe methods to the 3D seismic information of the Miano area of the Indus Basin, SW Pakistan. Apparatuses, for example, the seismic amplitude and coherence are discovered less exact for reservoir description. Sweetness analysis indicates the gas-bearing reservoir facies, which are compartmentalized by the NNW–SSE oriented normal fault system. Yet, the continuous wavelet transforms (CWT) of spectral decomposition (SD) separates the thick and thin sand beds of channel sand and point bars, which were not unsurprising utilizing the band-limited seismic properties. 22 Hz demonstrates the best amplitude tuning cube, which recognizes the profitable clastic (sand-filled barrier bars) sequences. The net-to-gross (N/G) examination uncovers the barrier bars as the chief hydrocarbon-bearing facies. 22 to 37 Hz frequencies confirm the occurrence of hydrocarbon sands. The acoustic impedance (AI) wedge model settles the thin beds of barrier bars sands, which are encased inside the shales, and affirm the suggestions for gas-bearing stratigraphic traps.

• Hydrocarbon source rock potential evaluation of the Late Paleocene Patala Formation, Salt Range, Pakistan: Organic geochemical and palynofacies approach

Organic geochemical and palynofacies analyses were carried out on shale intervals of the Late Paleocene Patala Formation at Nammal Gorge Section, western Salt Range, Pakistan. The total organic carbon content and Rock-Eval pyrolysis results indicated that the formation is dominated by type II and type III kerogens. Rock-Eval ${T}_{\mathrm{max}}$ vs. hydrogen index (HI) and thermal alteration index indicated that the analysed shale intervals present in the formation are thermally mature. $S_{1}$ and $S_{2}$ yields showed poor source rock potential for the formation. Three palynofacies assemblages including palynofacies-1, palynofacies-2 and palynofacies-3 were identified, which are prone to dry gas, wet gas and oil generation, respectively. The palynofacies assessment revealed the presence of oil/gas and gas prone type II and type III kerogens in the formation and their deposition on proximal shelf with suboxic to anoxic conditions. The kerogen macerals are dominated by vitrinite and amorphinite with minor inertinite and liptinite. The kerogen macerals are of both marine and terrestrial origin, deposited on a shallow shelf. Overall, the dark black carbonaceous shales present within the formation act as a source rock for hydrocarbons with poor-to-moderate source rock quality, while the grey shales act as a poor source rock for hydrocarbon generation.

• PSHA of Van province for performance assessment using spectrally matched strong ground motion records

Within the framework of the performance based earthquake engineering, site specific earthquake spectra for Van province has been obtained. It is noteworthy that, in probabilistic seismic hazard assessment, as a first stage data from geological studies and records from the instrumental period were compiled to make a seismic source characterization for the study region. The probabilistic seismic hazard curves were developed based on selected appropriate attenuation relationships, at rock sites, with a probability of exceedance 2, 10 and 50% in 50 yrs period. The obtained results are compared with the spectral responses proposed for seismic evaluation and retrofit of building structure in Turkish Earthquake Code (2007), section 7. The acceleration response spectrums obtained from probabilistic seismic hazard analysis are matched to adjust earthquake accelerograms recorded during the 2011 Van earthquakes by using SeismoMatch v2.0 software. The aim of this procedure is to obtain a set of reasonable earthquake input motions for the seismic evaluation of existing buildings.

• Modelling of streamflow in snow dominated Budhigandaki catchment in Nepal

This study has been envisaged to model streamflow runoff-contributed mostly by snowmelt from Budhigandaki catchment in Nepal. Available hydro-meteorological data have been collected from the Department of Hydrology and Metrology, Nepal. The MODIS Aqua (MYD10A2) and Terra (MOD10A2) 8 day maximum snow cover extent product have been used to derive the snow cover area (SCA) in the basin. The modeling of streamflow has been carried out using HEC-HMS and SRM models. The performance of these models have been evaluated by using three well known evaluation criteria NSE,${R}^{2}$ and PEV (percentage error in volume). The values of NSE, ${R}^{2}$ and PEV were found to be 0.944, 0.944 and $-0.3\%$ for SRM and 0.778, 0.785 and $-1.83\%$ for HEC-HMS, respectively. Similarly, in validation period the average values of NSE, ${R}^{2}$ and PEV were found to be 0.811, 0.816 and 2.01% for SRM model and 0.773, 0.777 and 3.5% for HEC-HMS, respectively. Sensitivity analysis of the models revealed that constant loss rate is very sensitive parameters for HEC-HMS model, whereas runoff coefficient is found to be most sensitive parameters for SRM model. In comparison between two models SRM model has given slightly better simulation results compared to HEC-HMS model.

• Spatio-temporal variations in precipitation on the Huang-Huai-Hai Plain from 1963 to 2012

Spatio-temporal variations in precipitation are affecting agricultural production in China in the context of climate change. Based on daily precipitation data from 63 national meteorological stations on the Huang-Huai-Hai Plain from 1963 to 2012, this paper analysed the spatio-temporal variations in precipitation in terms of precipitation days and intensity, using spatial interpolation, linear trend estimation and wavelet analysis. The results indicated that: (i) from 1963 to 2012, the number of annual precipitation days and intensity decreased gradually from the southeast to the northwest. Additionally, the distribution of the extreme precipitation index was similar to that of the annual precipitation index; (ii) the number of annual precipitation days and heavy precipitation days gradually decreased, while precipitation intensity and extreme precipitation days and extreme rainfall intensity remained relatively stable or decreased. The spatial patterns of annual variation trends were considerably different. The annual precipitation days and intensity trends are consistent with the overall trend, while that of the extreme rainfall index in some regions differs from the overall trend; (iii) the precipitation index displayed different periodic oscillations during the period, and the precipitation index values differed at different time scales. However, all the precipitation index values exhibited a 28-yr oscillation.

• Interaction between felsic granitoids and mafic dykes in Bundelkhand Craton: A field, petrographic and crystal size distribution study

In Bundelkhand Craton of central India, mafic dykes intruded when granitoids was partly crystallized. Cuspate–lobate boundary along the contact of granitoids and mafic magma indicates magma mingling in outcrop scale while textural evidence of mingling is represented by acicular apatite morphologies, titanite–plagioclase ocelli and ophitic–subophitic texture, mafic clots, resorbed plagioclase, and hornblende–zircon associations. Mingling also caused thermal exchange and fluid activity along the boundary between two coeval magmas. Crystal size distribution analyses for hornblende in the mafic rocks yield concave up curves which is also consistent with interaction of felsic and mafic magmas.

• Effect of uncertainty in $V_{\mathrm{S}}{-}N$ correlations on seismic site response analysis

This paper studies the reliability of the calculated shear-wave velocity $(V_{\mathrm{S}})$ from different available $V_{\mathrm{S}}$ and SPT-N correlations in terms of seismic site response analysis. In the present study, various $V_{\mathrm{S}}–N$ correlations developed for different regions around the globe have been used to calculate the bound of $V_{\mathrm{S}}$ variations with depth at three different sites in Kolkata city. This bound has later been used to generate the random $V_{\mathrm{S}}$ profiles using the Monte Carlo simulation. Equivalent linear site response analysis has been performed to study the response of those generated profiles under different input motion excitations. Strong-to-weak ground motion records have been used for this purpose. The amplification spectra of the generated $V_{\mathrm{S}}$ profiles using all soil types and specific soil-type $V_{\mathrm{S}}–N$ correlations show significant variations. The study also shows that the $V_{\mathrm{S}}–N$ correlation may result in quite different $V_{\mathrm{S},30}$ values and subsequently it may lead to the different site classes according to the NEHRP 2003 classification. So, the random choice of the $V_{\mathrm{S}}–N$ correlation, where the direct measurement of $V_{\mathrm{S}}$ is not available, may affect the outcome of seismic hazard analysis significantly. The study points out the need for accurate estimation of the $V_{\mathrm{S}}$ profile either from in-situ determination or using site-specific correlation.

• Geochemical assessment of fluoride enrichment and nitrate contamination in groundwater in hard-rock aquifer by using graphical and statistical methods

This systematic study was carried out with objective to delineate the various sources responsible for $\hbox {NO}_{3}^{-}$ contamination and $\hbox {F}^{-}$ enrichment by utilizing statistical and graphical methods. Since Central Ground Water Board, India, indicated susceptibility of $\hbox {NO}_{3}^{-}$ contamination and $\hbox {F}^{-}$ enrichment, in most of the groundwater, $\hbox {NO}_{3}^{-}$ and $\hbox {F}^{-}$ concentration primarily observed >45 and >1.5 mg/L, respectively, i.e., higher than the permissible limit for drinking water. Water Quality Index (WQI) indicates ${\sim }22.81\%$ groundwater are good-water, ${\sim }71.14\%$ groundwater poor-water, ${\sim }5.37\%$ very poor-water and 0.67% unsuitable for drinking purpose. Piper diagram indicates ${\sim }59.73\%$ groundwater hydrogeochemical facies are Ca–Mg–$\hbox {HCO}_{3}$ water-types, ${\sim }28.19\%$ Ca–Mg–$\hbox {SO}_{4}$–Cl water-types, ${\sim }8.72\%$ Na–K–$\hbox {SO}_{4}$–Cl water-types and 3.36% Na–K–$\hbox {HCO}_{3}$ water-types. This classification indicates dissolution and mixing are mainly controlling groundwater chemistry. Salinity diagram indicate ${\sim }44.30\%$ groundwater under in low sodium and medium salinity hazard, ${\sim }49.66\%$ groundwater fall under low sodium and high salinity hazard, ${\sim }3.36\%$ groundwater fall under very-high salinity hazard. Sodium adsorption ratio indicates ${\sim }97\%$ groundwater are in excellent condition for irrigation. The spatial distribution of $\hbox {NO}_{3}^{-}$ indicates significant contribution of fertilizer from agriculture lands. Fluoride enrichment occurs in groundwater through the dissolution of fluoride-rich minerals. By reducing the consumption of fertilizer and stress over groundwater, the water quality can be improved.

• # Journal of Earth System Science

Current Issue
Volume 128 | Issue 8
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019