Journal of the Geological Society of India最新文献

The accurate identification of rock layer interfaces from wireline logs is one of the crucial issue of geological interpretation as we face difficulties in traditional interpretations due to the presence of various kind of high and low frequencies in the log data. Determination of rock boundaries in shallow marine sediments is very important to understand several issues related to the exploration of conventional and non-conventional hydrocarbons. Presently a combined wavelet and Fourier transform-based approach was demonstrated to discriminate the rock layers from wireline log data in Krishna-Godavari basin, which were acquired during the India National Gas Hydrate Program Expedition 02 (NGHP-Exp.-02). Initially, we selected the suitable mother wavelets and optimum level of decomposition to perform the wavelet transform by computing the error between the original log signal(s) and approximation coefficients (cA’s) of the decomposed signal(s) at several decomposition levels. Subsequently, discrete wavelet transform (DWT) of a particular decomposition level was applied to the log signals to obtain the detail coefficients (cD’s), which contain the high-frequency components of the log signals. Further, these high-frequency components of the log signals were utilized in frequency spectrum-based filtering approaches. This approach was adapted to yield information about the abrupt changes occurring in the log signals across the studied depth interval. The combined application of Fourier and wavelet transforms to shallow marine log data demonstrates that this approach is an efficient tool for delineating rock layer boundaries.

The chemistry of the groundwater of north coastal part of Odisha is primarily controlled by weathering of minerals present in basement rocks superimposed by anthropogenic activities and sea water intrusion. The water is hard and alkaline in nature, but most of the constituent ions excluding F^- are within permissible limits for human consumption. Four factors satisfying over 86% of the total variance and three clusters corresponding to geogenic, alkaline and anthropogenic processes have been identified. Ca²⁺, Mg²⁺, Na⁺, K⁺, F⁻, CO₃²⁻ and HCO₃⁻ are geogenic, contributed by the basement rocks and soils. Cl⁻, SO₄⁻ and NO₃⁻ are anthropogenic, derived from haphazard household waste disposal, overflows of septic tanks, return flow from irrigation, animal wastes, manures, soil conditioners and chemical fertilizers. K⁺ and F⁻ belong to both the categories while Na⁻ and Cl⁻ are contributed by saline intrusion to some extent. The pH, total alkalinity and F⁻ represent alkaline component, while HCO₃⁻ is derived from weathering of minerals and influence of atmospheric CO₂. Change of groundwater types from Ca-HCO₃ (fresh water) → Ca-Mg-Cl → Na-Cl (saline water) as well as increase of total dissolved solids in seaward direction indicates the effect of seawater intrusion in the study area. Sympathetic relationship of F” with total alkalinity, pH and Na⁺ as well as negative correlation with Ca²⁺ suggest the prevalence of alkaline environment that favors dissolution of fluoride minerals of the basement rocks. It is suggested to minimize the anthropogenic activities like haphazard waste disposal and excessive use of agrochemicals, adopt artificial recharge measures, take up regular groundwater quality check and aware the public for proper management of groundwater resource in the study area.

Pin-pointing freshwater within saline formations is of utmost importance as filtration and alternate means of public water supply are responsible for high expenditure. Vertical Electrical Sounding (VES) (n=49) was conducted at various locations in the Bichpuri block, Agra district. In this study for VES, the Schlumberger configuration was used. VES data were reconciled with the borehole well log, and drill sample cuttings were utilized to understand sub-surface configuration. Reconciled VES data displayed variation in resistivity layer parameters, i.e., layer thickness & true resistivity of sub-surface. True resistivity spatial models were developed at 25m intervals from the ground surface down to the depth of 150m, based on geo-electric parameters. Resistivity models reveal that freshwater is limited to 55m depth, beyond which groundwater is saline to brackish. The basement was encountered at a depth of 120m and further extended up to 150m. A groundwater potential map was prepared using GIS and divided into 3 categories–good, moderate, and poor. Major habitations of the study area lie in poor groundwater potential zone, which is a cause of concern with the intent on future development. Similar studies can be extended to areas with saline groundwater for mapping freshwater zones.

A comprehensive whole-rock geochemical and mineral chemistry study was carried out of granites from the Narnaul and surrounding isolated hills of North Delhi Mobile Belt, NW India to constrain their genesis, and tectonic environment. The distinctive features of granites are meta to peraluminous nature and decreasing trend of P₂O₅ with high SiO₂ (>71%) ascribed to its metaigneous origin. In detail the chemical diversity of the studied samples is reflected by their affinity to Calc-alkaline to shoshonite series with high K₂O/Na₂O (mostly>1), low MgO (< 0.11%) and variation in Mg# (upto 0.5) and maficity with increasing SiO₂. The positive Eu anomalies, high LILE, highly enriched LREE (La/Sm = 4.13@#@19.33) pattern and comparatively elevated concentrations of Cs, La, Ta, Dy, Zr, Pb and Yb suggest different episodes of magmatic differentiation. Our data indicate that melting of older subduction-related igneous rocks and the underwent fractional crystallization in hydrous conditions is the possible mechanism for the generation of I-type granites in collisional tectonic setting.

This study provides a comparative evaluation of spatio-temporal distribution of soil erosion in Western (Mago Basin) and Eastern (Dibang Basin) basins of Arunachal Pradesh, India as these two basins are vulnerably exposed to soil erosion due to its topographical characteristics of mountainous steep slope and experiences heavy rainfall. The study was carried out for a ten-years period (2003 to 2014) using RUSLE model which encompasses five important factors contributing to soil erosion. Rainfall erosivity (R factor) map was calculated using Climate Prediction Center gridded precipitation. Soil map and soil samples were used to analyze soil erodibility (K factor) map. Slope length and slope steepness (LS factor) maps were computed from SRTM DEM (30 m resolution). MODIS NDVI images were used to obtain cover management (C factor) map. Landuse Landcover map was used to obtained support practice (P factor) map. Higher value in rainfall erosivity and cover management factor was observed in Mago basin which contributed to higher average annual soil loss of 17.423 t ha⁻¹ y⁻¹ in Mago basin and 5.461 t ha⁻¹ y⁻¹ in Dibang basin, whereas the other three factor values were almost the same. The spatial maps showed 56.65% of Mago basin area and 76.27% of Dibang basin area was under the class of slight erosion, with the remaining areas of moderate to severe erosion risk for both the basins. Temporal average soil erosion in Mago basin varied within moderate to very high erosion classes whereas Dibang basin erosion classes varied from slight to moderate. The temporal trend line showed that the overall soil erosion was increasing at an alarming rate for Mago basin whereas a slight increase in Dibang basin was observed.

The Upper Bhander Sandstone Member exposed along the Agra-Fatehpur Sikri tract near Rasulpur (Rajasthan) was investigated for a rare sedimentary structure, Liesegang rings. The studied unit also yielded other sedimentary structures such as cross-bedding, parallel lamination, ripple marks and trough cross-bedding; Liesegang rings were the most common and abundant. Two types of Liesegang rings were identified, one with a central core with outwardly radiating and alternating iron-rich (dark) and iron-poor (light) rings that were usually aligned parallel to the bedding plane (here designated as the Nucleation-type), and the other, that followed a fracture, and are composed of wavy rings (Wavy-type). The studied sandstone unit is quartzarenite type, wherein the monocrystalline plutonic quartz makes up 91% of the total framework grains. The grains are bound by two types of cementing material: silica (occurring as syntaxial overgrowth around detrital quartz grains) and iron oxide; higher amount of iron oxide and secondary porosity was noted. The formation of Liesegang rings involves iron-rich meteoric waters being infiltrated through fractures, pores and more importantly, by the formation of secondary porosity within the sandstone (diagenetic processess). Addition to this microscopic character, other factors that are responsible for the formation of Liesegang rings include surface water, suitable topographic exposure, condensed grid of joint polygons, and composition and thickness of the sandstone beds under study. Detailed microscopic analysis of rings (iron-rich and iron-poor) may provide a better understanding of the pathways of fluid movement enabling the formation of Liesegang rings.

The present research study aims to analyze flood frequency to relate flood magnitudes with corresponding return periods. These estimates are crucial for the development of flood-preventive hydrological infrastructures and flood plain zoning, etc. Basin-wide high intensity of rainfall and high discharge from the upper riparian region during monsoon months creates flooding in the middle and lower reaches of the Ghagra River basin. Therefore, the flood estimates for three gauging sites situated on the mainstream of the Ghagra River viz., Elginbridge, Ayodhya, and Turtipar, have been comprehended using the Gumbel distribution (Extreme Value Type I) method and the Log-Pearson Type III distribution method. Flood estimates are calculated for 1.01, 1.05, 1.11, 1.25, 2, 5, 10, 20, 50, 100, 200, and 500 years return periods considering flood time series of 50 years to reduce estimation uncertainty. The findings of flood frequency analysis (FFA) revealed that the probability of occurrence of the flood is more than 80% at all three sites because Ghagra River can carry around 7800 to 9000 m³/s of water discharge without posing a high risk of levee break. The upper and lower limits of discharge carrying capacity depend on the river’s desiltation process. Hence, the flood occurs almost every year in the basin; its only variation is its severity. The rainfall-runoff relationship is estimated by integrating a simple linear model and for rainfall trend analysis Mann-Kendall is applied. Linear regression analysis-based rainfall-runoff relationship outcomes revealed a significant relationship with a positive correlation coefficient i.e., 0.2722 for Elginbridge, 0.39624 for Ayodhya, and 0.4844 for Turtipar gauging site in the monsoon season but other factors like a high amount of water discharge from dams in upper riparian regions, etc. are also responsible for flooding in the middle and lower reaches. The Mann-Kendall trend analysis shows a decrease in annual average rainfall and rainfall in the monsoon season. Discharge variability indicates the direct relationship between flood fury and changes in climatic patterns in recent decades. This paper identifies that future research is needed to better inform the policy planners who strive to design sustainable infrastructure.