Geosciences Research

7

Authors: Ashutosh Kainthola, Dhananjai Verma, T N Singh

Hill stations which are favoured tourist destinations are mostly accessible by road excavated on the hill slopes. These roads cut slopes pose a grave threat to life and local economics in case of a slope failure. Proper study is called for to mitigate this danger of these slope failures which are especially rampant during the rainy season. In the present study a road cut slope along SH-72 near Mahableshwar, Maharashtra, India, has been numerically simulated using finite element and finite difference techniques to appraise their stability under dry and saturated conditions.

12

Authors: Baljeet Singh

In the present work, a problem on the reflection of elastic waves at a plane surface of an elastic half-space is considered. The elastic half-space is assumed homogeneous and isotropic. The plane surface of half-space is subjected to impedance boundary conditions, where normal and tangential tractions are proportional to normal and tangential displacement times frequency, respectively. The reflection coefficients of reflected P and SV are obtained in closed form for incidence of P or SV waves. These reflection coefficients depend on the angle of incidence, impedance parameters and other material parameters. The material parameters of Diabase (dark-colored igneous rock), Limestone (sedimentary rock) and Gneiss (high grade metamorphic rock) are chosen to compute the reflection coefficients for certain ranges of angle of incidence and impedance parameters. The effect of impedance boundary on the reflection phenomena is shown graphically for three different rock materials (Diabase, Limestone and Gneiss).

9

Authors: Omowumi Ademila

Engineering impact of lateritic soils underlying some failed roads and highways in Akure, southwestern Nigeria was investigated with the aim of evaluating its competence for highway pavement structures. Twenty-eight bulk soil samples of lateritic soil were collected from five failed sections and two stable sections for index and strength tests related to road construction. The soils from the stable sections have higher specific gravity (2.73-2.86) with less amount of clay (23.68%) and indicate A-6 and A-2-6 on the AASHTO classification system compared to soils from the failed sections of A-7-6 implying poor quality subgrade. High water absorption capability, high proportion of fines (> 57%) and high values of linear shrinkage (> 8%) of soils from failed sections caused pore water pressures to develop, resulting in loss of strength with percentage reduction in strength up to 79%. The predominance of fines in the lateritic soils, low California bearing ratio (14-32% unsoaked; 3-11% soaked) and low strength characteristics (angle of friction: 13-17°, shear strength: 79-108kN/m2) are responsible for the degree of instability witnessed. The poor geotechnical properties ofthe lateritic soils of failed sections imply that they are unsuitable for use as subgrade materials inroad construction and even in other engineering structures. Importance of detailed sampling oflateritic soils is stressed for correct assessment of highway subgrade soils. The results of this studywill be useful in rehabilitation and reconstruction works of the failed sections of the road and properdocumentation of this investigation is recommended for future pavement design and construction ofroads.

11

Authors: Ahmed F. Elaksher

This paper discusses integrating multiple remotely sensed measurements, spatiotemporal databases, coastal hydrological modeling, and geospatial information analysis to study the impact of water level changes on the shoreline geometry in order to support coastal geospatial information systems and decision making. Different shorelines are generated using a CTM and a WSM. The CTM is generated using multiple remotely sensed datasets and spatiotemporal databases, while the WSM is provided using a coastal hydrological model. Two shoreline generalization schemes are implemented to simplify the shoreline geometry. Experiments for estimating the shoreline geometry at different water levels were performed using each generalization scheme. The relationship between the shoreline geometry and the water levels was studied. High correlation between water level changes and the changes in the shoreline geometry was observed. The proposed algorithm can be used in creating or updating coastal geospatial databases, managing the dynamic natural of shorelines, and making scientific decisions in coastal environments.

16

Authors: Van Phan T.H, Timothée Bonnet, Stéphane Garambois, Delphine Tisserand, Fabrizio Bardelli, Rizlan Bernier-Latmani, Laurent Charlet

Heavy arsenic (As) contamination of groundwater is investigated in the An Giang province of Vietnam to better understand the interplay between surface sedimentology and anoxic aquifer. In particular, the present study aims to compare As concentrations measured in groundwater pumped from 40 shallow wells (< 40 m in depth) along the lower Mekong stream with surface variations of electrical conductivity measured using an electromagnetic geophysical device (EM 31). Based on the analytical results for groundwater, core sediments and geophysical data, we show the permeability and clay content of surface soil derived through EM conductivity measurement to have a positive and significant correlation (R2 = 0.83, n = 27) with the distribution of As concentration in shallow aquifers. This indicates that the presence of soil and subsoil claypan can enhance the reducing conditions in the aquifer. The results also suggest the important role of HCO3-, Fe/Mn (oxyhydr)oxides and clay minerals in mobilizing As groundwater leading to a major health threat to local people of this province.

7

Authors: P K Yadav

In the recently drilled deeper boreholes by HZL new intersection of lead and zinc ores have established depth ward continuity of ores of previous boreholes and have thus augmented reserves considerably. It has suggested revision of ore forming concepts and also that in the Rajpur Dariba area further search for Zn-Pb should be carried out using new innovative techniques. Success often requires supplementing standard procedures with the effective use of new exploration methods: the kind that can see deeper, are more definitive, and more efficient to ore discovery. The conventional methods have their place, but these are proving to be less effective as new terrains are increasingly more difficult to explore. Present studies have helped in searching new controls of mineralisation and in formulation of new ore guides for future search of new ore bodies. On the basis of present studies like facies of volcano-sedimentary sequence, textures, structures, ore microscopy, environment of ore deposition, characters of mineralisation, ore facies, sequence stratigraphy, airborne and ground geophysics new evidences for ore genesis have been collected. In Sindesar Khurd these studies have suggested vent complex type of hydrothermal sedex deposit. Rajpura Dariba deposit displays biphase mineralisation including stratiform sulphides and post metamorphic epigenitacally melt introduced independently. Salient features of vein ores such as occurrences as pods, segregation veins or open space fillings traversing the banded ores, absence of deformation and recrystalisation textures indicate that these veins are post-metamorphic and could have formed from a different ore fluid. The cavity filling nature of vein ore and their occurrence in irregular shear planes suggest their environment of ore formation was different than imprints of metamorphism in banded ores. The source of this fluid could be intrusive granite located during present studies. Now with an objective of searching new ore zones more evidences like faults and shear zones which are loci for ore in volcanoclastic rocks and calc silicate marble is the best host. Other evidences of ore forming processes and characters of volcanic rocks are also helpful in ore search. These strategies are discussed in this paper to search new local targets for selecting new drill sites.

13

Authors: V.A. Guryanov, A. Yu. Peskov

This paper attempts to summarize and systematize findings of geological, geophysical, geochronological and geochemical studies over the past three decades on Late Paleoproterozoic granitoids, basites and sedimentary-volcanic rocks of the Ulkan trough in the southeastern flanking of the Siberian Platform, which make it possible to identify their sources and to reconstruct conditions and geodynamic settings of their formation. Rocks of the Ulkan volcano-plutonic complex are found to form in an anorogenic environment under intra-continental extension in relation to the mantle plume activity at 1.77 – 1.70 Ga. Based on geodynamic criteria, five stages recognised in the evolution of the Ulkan paleorift system can be grouped into three major stages of the Late Paleoproterozoic intra-plate magmatism. The study of data made it apparent that the Ulkan paleorift system has characteristics of a three-armed structure indicative of the intense rifting in response to the hot spot activity; the Ulkan alkaline-granitic batholith with its distinct metallogenic specialization for rare-earth elements (REE) and rare earth metals (REM) could be such a hotspot-type diapir. Tectonically, the triple junction appears as a zone that underwent intense intra-plate alkaline-granitic magmatism in the Late Paleoproterozoic and hosts ore targets unique in scale and diversity (Be, Ta, Nb, TR, Zr, U, Au, Li, Sn, Mo, P, and Ti) with ages in the 1.72 – 1.67 Ga range. Rare-metal and REE deposits are essentially the product of rare-metal alkaline granitic magmatism and most likely related to the evolution of the mantle source in the course of plume activity. The presence of both subalkaline granitoids and volcanic rocks (K-series) and alkaline granites, comendites and pantellerites (Na-series) intensely fractionated and enriched to a maximum degree in most noncoherent elements, as well as Zr, Mn, F, Fe, Ti, is characteristic of the Ulkan anorogenic magmatism. Granitoids of the Ulkan paleorift structure and its southern flanking foldbelts have mixed mantle-crustal sources. Subalkaline granites are derived from a source containing material from lower continental crust and alkaline granites from a mantle source containing the OIB-type component. The origin of the Ulkan-Bilyakchan volcano-plutonic belt initiated as an intracontinental system along the southeastern edge of the Siberian Platform is considered to be related to hot spots of this type.

21

Authors: Risto J. Pirjola, David H. Boteler

To assess the geomagnetic hazard to power systems, it is necessary to model the Geomagnetically Induced Currents (GIC) produced during space weather storms. This requires knowledge of the geoelectric fields that drive GIC. In the time domain, the geoelectric fields can be calculated using a convolution integral including the geomagnetic field or its time derivative and an impulse response function for the Earth. In principle, the integral extends to infinity but for practical calculations the impulse responses must be truncated at a finite length. In this paper, we investigate the effects of the truncation on the calculation of the geoelectric fields. We consider how long the impulse responses need to be to obtain sufficiently accurate geoelectric field values. It is found that the high-pass impulse response used with geomagnetic data can be truncated very early, e.g. at 1 h, while the low-pass impulse response used with geomagnetic time derivative data must be extended much longer, e.g. until 24 h.

5

Authors: Viacheslav. A. Bezverkhnii

Spectral and wavelet analysis reveal the chain of close phase and coherence relationships at the obliquity frequency in variations of the tilt of the Earth’s rotational axis (obliquity), frequency of large volcanic eruptions (Ef) along the Pacific Ring of Fire, and climate characteristics, represented by the relative content of oxygen-18 (δ18O) in the calcite of fossil benthic foraminifers (prominent LR04 stack), Antarctic and Greenland ice core data. The links revealed show that powerful 41,000-year rhythms in the Plio-Pleistocene climate variations can be caused by geophysical and geochemical effects of global volcanic activity which is induced by the forced obliquity oscillations.

8

Authors: A.K. Naithani, J.K. Jain, Prasnna Jain, L.G. Singh, Rabi Bhusan

Engineering geological foundation investigations are essential for important civil structures to provide permanent data set for geological interpretations. At Rawatbhata, India, two units of 700 MW each Pressurized Heavy Water Reactor (PHWR) type Nuclear Reactors are being constructed adjacent to existing Rajasthan Atomic Power Project (RAPP) units 1 to 6. Engineering geological mapping on 1:100 scale was carried out for Nuclear Building-8 structures to evaluate the design basis foundation parameters. 1 m x 1 m grids were prepared for mapping of the floors and walls. Based on the field observations and evidences, it was found that the floor area consists of fine to medium grained, compact quartzitic sandstones. The floor region was seen to contain certain iron stained and fractured zone. No evidence of faulting was observed on the surface of the floor areas. However, there were some isolated patches of soft, weathered/altered rock and small fractures in the rocks. The intact rock properties at the foundation levels were evaluated considering the necessity in the overall context of the design requirements of the foundations. Geotechnical assessment of the foundations of RB-8, RAB-8 and ECCS north and south pits was done on the basis of detailed engineering geological mapping, geological drill holes logging data, rock mass permeability values, geophysical profiling and laboratory test results. Based on investigations recommendations for the treatment of foundations were given. Consolidation grouting up to 9 m depth in the foundation using primary at 6 m spacing and secondary holes at 3 m spacing was recommended. After detailed investigations it was found that, the foundation is suitable to locate a nuclear power plant.

19

Authors: Cyril C. Okpoli, Michael A. Oladunjoye

Aeromagnetic dataset over Ado-Ekiti Southwest (sheet 244) was processed to interpret the geology structure and estimate the depth to bedrock of magnetic sources as well as to deduce the basement architecture and their trends. Aeromagnetic dataset were collected, filtered, inverted, and enhanced using appropriate software packages and subsequently employed to generate a model of the subsurface basement topography. The data processing steps involved were Butterworth filtering, reduction to the equator, analytic signal, upward continuation, Tilt angle derivative, Average power spectrum and Euler/Werner deconvolution. The result shows that magnetic intensity from Butterwort ranges from -173.3 to 150.8 nT; Reduction to the pole varies from -213.1 to 314.1 nT; upward continuation at 100m ranges from 156.1 to 142.4 nT and analytical signal varies from 0.0 to 0.4 nT. The magnetic intensity distribution was found to depend on the size, depth of burial, and the thickness of low susceptibility superficial material overlying the magnetite rich crystalline rocks. Tilt angle derivative disclose the presence of fold, shearing, contacts, lineaments with its orientations while the 3D Euler deconvolution > 2000 and dike model fits the Werner function. The average radial power analysis delineated shallow sources ranging from 0.34 km - 0.49 km and deeper sources ranging from 0.45 – 1.25 km. Pseudogravity result is 0.103g/cc which trends in NE-SW direction. The lineaments directions are in NE-SW, NW-SE and E-W directions which are Pan-African, Kibaran and Liberian Orogenies that occurred in the region. Modeled maps of upward continuation, analytical signal, tilt derivative, pseudo gravity average power spectrum and 3D Euler /Werner deconvolution revealed the basement architecture including structural lineaments with its orientations and the depth to the magnetic sources of the study area.