Geosciences Research

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.