Application of 2-D and 3-D Geo-electrical Resistivity Tomography and Geotechnical Soil Evaluation for Engineering Site Investigation:A Case Study of Okerenkoko Primary School,Warri-Southwest,Delta State,Nigeria

In the design of building structures,joint efforts must be decided to resolve the depth of competent layers across the intended site to safeguard the durability of civil engineering structures and to avert the disastrous consequences of structural failure and collapse.In this study,an integrated methodology that employed DC resistivity tomography involving 2-D and 3-D techniques and geotechnical-soil analysis was used to evaluate subsoil conditions for engineering site investigation at Okerenkoko primary school,in the Warri-southwest area of Delta State,to adduce the phenomena responsible for the visible cracks/structural failure observed in the buildings.The results obtained brought to light the geological structure beneath the subsurface,which consists of four geoelectric layers identified as topsoil,dry/lithified upper sandy layer,wet sand(water-saturated)and peat/clay/sandy clayey soil(highly water-saturated).The deeply-seated peat/clay materials(ρ≤20Ωm)were delineated in the study area to the depths of 17.1 m and 19.8 m from 2-D and 3-D tomography respectively.3-D images presented as horizontal depth slices revealed the dominance of very low resistivity materials i.e.peat/clay/sandy clay within the fourth,fifth and sixth layers at depths ranging from 8.68-12.5 m,12.5-16.9 m and 16.9-21.9 m respectively.The dominance of mechanically unstable peat/clay/sandy clay layers beneath the subsurface,which are highly mobile in response to volumetric changes,is responsible for the noticeable cracks/failure detected on structures within the study site.These observations were validated by a geotechnical test of soil samples in the study area.Atterberg’s limits of the samples revealed plasticity indices of zero.Thus,the soil samples within the depth analyzed were representatives of sandy soil that does not possess any plasticity.The methods justifiably provided relevant information on the subsurface geology beneath the study site and should be appropriated as major tools for engineering site assessment/geotechnical projects.

Glacial-interglacial productivity contrasts along the eastern Arabian Sea:Dominance of convective mixing over upwelling

The western continental margin of India is one of the highly productive regions in the global ocean.Primary productivity is induced by upwelling and convective mixing during the southwest and northeast monsoons respectively.Realizing the importance of high primary productivity,a sediment core was collected below the current oxygen minimum zone(OMZ) from the southwestern continental margin of India.This was dated by AMS radiocarbon and as many as 60 paleoclimate/paceoceanographic proxies,such as particle size,biogenic components,major,trace and rare earth elements(REEs) which were measured for the first time to determine sources of sediment,biogeochemical processes operating in the water column and their variations since the last glacial cycle.R-mode factor analysis of comprehensive data indicates that the dominant regulator of paleoproductivity is the southwest monsoon wind induced upwelling.Other paleoproductivity related factors identified are the marine biogenic component and biogenic detritus(as an exported component from the water column added to the bottom sediment).All paleoproductivity components increased significantly during the marine isotope stage-1(MIS-1)compared to those accumulated from MIS-4 to MIS-2.The second group of factors identified are the terrigenous sediments with heavy minerals like zircon and ilmenite.The terrigenous sediment,in particular,increased during MIS-2 when the sea-level was lower;however,the heavy mineral component fluctuated over time implying pulsed inputs of sediment.The diagenetic fraction and reducing component are the third group of factors identified which varied with time with increased accumulation during the MIS transitions.The primary productivity along the southwestern continental margin of India seems to have been controlled principally by the upwelling during the southwest monsoon season that was weaker from MIS-4 to MIS-2,as relative to that during the MIS-1.In contrast,increased glacial productivity noticed in sediments deposited below the current oxygen minimum zone(OMZ) along the north of the study area that can be linked to entrainment of nutrients through the intensified convective mixing of surface water during the northeast monsoon.The sequestration of greenhouse gases by the western continental margin of India was higher during glacial than interglacial cycles.

Geophysical lineaments of Western Ghats and adjoining coastal areas of central Kerala,southern India and their temporal development

A family of geophysical lineaments have been identified in ~15,000 km^2 in central Kerala between9 30'N to 10 45'N and 76 00'E to 77°30′E,integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ~90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of youngergeophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust.They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from(1) the back-thrust from the Himalayan Collision;(2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and(3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.

Studies on Physical, Chemical and Bacteriological Characteristics on Quality of Spring Water in Hajigak Iron Ore Mine, Bamyan Province, Central Afghanistan

The study aimed to assess the physical, chemical and bacteriological quality of drinking water and its potential health effect on study area population. Physical, chemical and bacteriological parameters in six stations of four water springs of Hajigak iron ore mine were studied. These four springs are the predominant source of water in this area. The inhabitant’s villages around the area of interest use these waters 12 months per year without any treatment. Whereas this mine consists of 66% of iron, 6 PPM gold, 26 PPM silver, thorium and some poly metals that directly affect the quality of water. The quality of these water sources has not been investigated and analyzed before for drinking purpose. Therefore studies on spring water quality required analysis for chemical, physical and bacteriological parameters. Chemical and physical analyses revealed that these spring waters are toxic free and the area has very fresh and good quality water based on the guidelines of World Health Organization, national standard of most Asian countries and standard values for Afghanistan. However, the bacteriological analysis detected the E. coli, fecal coli form and total coli form bacteria in water samples that may cause some diseases and health problems.

Studies on Geochemical and Heavy Mineral Characteristics of Sediments of Gosthani River Estuary

The present work deals with the geochemical and heavy mineral characteristics studies of sediments of Gosthani river estuary. The aim of study is to determine the provenance, establish the depositional environment and spatial variability of sediment. From the study it is found that the sediment of Gosthani river contains heavy minerals that consist of Rutile, Garnet, Sillimanite, Staurolite, Monazite, Zercon, Pyroxenes, Epidote, Amphiboles and Opaques minerals. The lesser abundant heavy minerals are amphiboles, zircon, monazite, rutile, staurolite, epidote. These heavy minerals indicate that the sediments were essentially derived from metamorphic provenance varying from medium to high grade and partly from crystalline igneous rocks. Well rounded monazites come from Eastern Ghats. This is based on the occurrence of monazite in pegmatite and charnockites of Eastern Ghats. The various characters of rutile and zircon suggest that each of these minerals has a multisource. According to geochemical studies settling of organic matter is highest in areas where deposition of fine grained sediment takes place. The organic carbon is often a good index for deciphering depositional environment.

Assessment of Geologic Controls of Flooding in Parts of OBIO/AKPOR L.G.A., Rivers State, Nigeria

Flooding of Municipal areas is a frequent environmental occurrence in Rivers State that occurs when rainfall runoff meets land surfaces with low water absorbing capacity or when it overwhelms drainage channels.In order to assess the flood situation in the study area,an integrated method which involves field-measurement,geographic information system(GIS),laboratory analysis of soil samples and topographic studies were employed.Digital elevation model of the study area reveals that the flooded areas are situated in areas with elevations lower than its surrounding,thereby acting as a natural basin to retain flood waters after rainfall.Four holes were drilled to depth of 3 m to obtain soil samples at 1 m sampling interval,from which laboratory analysis was carried out to determine some geotechnical parameters such as soil’s particle size,specific gravity,bulk density,porosity,moisture content,permeability and hydraulic conductivity.Results of the analysis show that permeability,hydraulic conductivity and porosity diminishes with respect to depth.The soil in the flooded areas have high fines content(silt and clay),high bulk density which increase with depth and a specific gravity that is typical of organic rich soils that contain sand mixed with a considerable amount of fines.At Nkpolu,mean permeability rates of 0.003 cm/sec,0.009 cm/sec and 0.033 cm/sec were obtained at 1,2 and 3 m respectively.At Eneka,mean permeability rates of 0.011 cm/sec,0.018 cm/sec and 0.014 cm/sec were obtained at 1,2 and 3m respectively,while at Rukpokwu,mean Permeability rates of 0.021 cm/sec was obtained at 1 m,while 0.006 cm/sec was obtained at 2 and 3 m respectively.The mean hydraulic conductivity for the locations under study is of the order of 10-4 ft/day.This study has shown that the flooded areas are located in low lying urban areas which act as basins,therefore,the top soil is crusted with highly compacted soil horizons beneath.With high and frequent rainfall in the region which generates a lot of runoff,in addition to poor drainage system,flooding in the study area occurs frequently.Therefore,construction and maintenance of efficient drainage channels for an effective solution to urban pluvial flooding in the study area are thereby recommended.

Hydrocarbon Play Assessment of “Oswil” Field, Onshore Niger Delta Region

Hydrocarbon play assessment of any field involves the evaluation of the production capacity of hydrocarbon reservoir unit in the field.This involves detail study of the reservoir petrophysical properties and geological interpretation of structures suitable for hydrocarbon accumulation in the field as observed from seismic reflection images.This study details the assessment of hydrocarbon play in OSWIL field onshore in Niger Delta,with the intent of appraising its productivity using a combination of seismic,well logs,petrophysical parameters and volumetric estimation using proven techniques which involves an integrated methodology.Two reservoir windows“R1”and“R2”were defined from five wells OSWIL-02,04,06,07 and 12.The top and base of each reservoir window was delineated from the wells.Structural interpretation for inline 6975 revealed two horizons(X and Y)and eight faults labelled(F1,F2,F6,F8,F10,F16,F17 and F18).Five faults(F1,F6,F10,F17 and F18)were identified as synthetic faults and dip basin wards while three faults(F2,F8 and F16)were identified as antithetic faults and dips landwards.Time-depth structural map at top of reservoirs R1 and R2 revealed structural highs and closures.These observations are characteristics of growth structures(faults)which depicts the tectonic style of the Niger Delta.Results of petrophysical evaluation for reservoirs“R1”and“R2”across the five wells were analysed.For reservoir“R1”effective porosity values of 27%,26%,23%,20%and 22%were obtained for wells OSWIL-04,12,07,06 and 02 respectively with an average of 23.6%,while for reservoir“R2”effective porosity values of 26%,22%,21%,24%and 23%for wells OSWIL-04,12,07,06 and 02 were obtained respectively with an average of 23.2%.This porosity values correspond with the already established porosity range of 28-32%within the Agbada formation of the Niger Delta.Permeability index of the order(K>100mD)were obtained for both reservoirs across the five wells and is rated very good.Hydrocarbon saturation(Shc)across the five wells averages at 61.6%for reservoir“R1”and 67.4%for reservoir“R2”.Result of petrophysical model for porosity,permeability and water saturation reveal that the reservoir system in R1 and R2 is fault assisted and fluid flow within both reservoirs is aided by presence of effective porosity and faulting.Volumetric estimation for both reservoirs showed that reservoir R1 contains an estimate of 455×106 STB of hydrocarbon in place,while reservoir R2 contains an estimate of 683×106 STB of hydrocarbon in place.These findings impact positively on hydrocarbon production in the field and affirm that the two reservoirs R1 and R2 are highly prospective.

The Response of Geopotential Height Anomalies to El Niño and La Niña Conditions and Their Implications to Seasonal Rainfall Variability over the Horn of Africa

In this study, we unveil atmospheric circulation anomalies associated with the large-scale tropical teleconnections using National Center for Environmental Prediction (NCEP) reanalysis dataset. Composite analyses have been performed to know the impact of large-scale tropical circulations on the Horn of Africa. The composite analysis performed at the geopotential height of 850 Mb and 200 Mb, and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical variability induced climate anomalies in space and time. A substantial decrease in upper-level height (200 Mb) has been observed in the study area during El Niño composite years as compared to the La Niña years. During El Niño conditions, the upper-level divergence initiates low-level vertical motion, thereby enhancing convection, however, during La Niña composite years, nearly contrasting situations are noticed in Belg (February to May) season in Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal during the strong El Niño years, suggesting suppressed convection due to vertical shrinking and enhancement of divergence at the lower level. Compared to the Belg (February to May), geopotential anomalies were generally positive during the Kiremt (June to September) season, thereby suppressing the rainfall, particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an increase in rainfall was observed during the Belg season (February to May).

PALYNOLOGICAL ASSEMBLAGES FROM THE HOLOCENE SEDIMENTS OF THE CHANGJIANG (YANGTZE) RIVER DELTA AND ITS IMPLICATIONS

The palynolpgical study on the Quaternary sediments of 42 cores in the region of the Yangtze River Delta and the sections of 4 relics had been done since 1960. Palynological assemblages from the region of the Yangtze River Delta, showing obviously .common characteristics but with slight differences because of the vast areas covered, can be divided into five spores and pollen zones and three subzones in ascendant order:I.Quercus alienc-Pinus-Cupressaceae-Chenopodiaceae spores and pollen zone reflecting the cool, then cold and dry climate--Preboreal.II.Quercus dentata-Quefcus acutissima-Pinus-Castanea-Artemisia spores and pollen zone reflecting the temperate and cool, but a little dry climate--Boreal.III.Quercus glauca-Caslanopsis-Myrica-Caslanea spores and pollen zone reflecting the hot and moist climate--Atlantic.IV.Quercus acutissima-Pinus-Castanea-Quercus glauca- Chenopodiaceae spores and pollen zone reflecting the warm, and a little dry climate--Subboreal.V.Quercus acutissima-Costarica-Quercus

DISCOVERY OF PEDIASTRUM ASSEMBLAGE FROM SUBMARINE PEAT BED IN EAST CHINA SEA AND ITS IMPLICATION IN SEA LEVEL CHANGE OF THE LATEST PLEISTOCENE

A submarine peat bed has been found in several places of the continental shelf of the East China Sea in the overall marine geological research of the past few years. In addition to fossil sporo-pollens, Pediastrum has been found in the peat bed. Fossil Pediastrum was first recorded by Davis (1916) in Green River Shale,

Climatic periodicities recorded in lake sediment magnetic susceptibility data:Further evidence for solar forcing on Indian summer monsoon

The Indian summer monsoon exhibits considerable spatio-temporal variability.It is therefore important to understand its dynamics and the inherent periodicities.In this study,we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere(TK)-a small lake in southern India.The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data.Significant periodicities in the TK χ_(lf)data are centered at 906,232,147,128,96,61,54 and 44 years,which might have a solar origin.The wavelet power spectrum of the raw and detrended χ_(lf)data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past3700 cal.years B.P.Positive correlation is documented between sunspot activity and TK xif data;crossspectral analysis of the reconstructed sunspot data and TK xif data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both.There is a good match between the TK xif and the reconstructed total solar irradiance data for the past 1200 years.However,an out-of-phase relationship is documented at certain time-intervals,which may be attributed to uncertainties in the age-depth model.The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and,like other archives from different regions in India,the TK lake sediments have also recorded these solar signatures.

Sedimentary sources and processes in the eastern Arabian Sea:Insights from environmental magnetism,geochemistry and clay mineralogy

The spatial distribution patterns of surficial sediment samples from different sedimentary domains(shallow to deep-sea regions) of the eastern Arabian Sea were studied using sediment proxies viz.environmental magnetism,geochemistry,particle size and clay mineralogy.Higher concentrations of magnetic minerals(high x_(lf)) were recorded in the deep-water sediments when compared with the shallow water sediments.The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the x_(ARM)/x_(lf)^(vs).x_(arm_/x_(fd)biplot.However,the other samples are catchment-derived.The high correlation documented for x_(lf).anhysteretic remanent magnetisation(x_(arm)) and isothermal remanent magnetisation(IRM) with Al indicates that the deep-sea surficial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers,the Sindhu(the Indus) and the Narmada-Tapti rivers.A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone(OMZ) but a higher Mn/Al ratio is documented in the lower slope and deep-sea sediments.Clay minerals such as illite(24-48.5%),chlorite(14.1-34.9%),smectite(10.6-28.7%) and kaolinite(11.9-27.5%) dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents.Organic carbon(OC) data indicate a low concentration in the shallow/shelf region(well oxygenated water conditions) and deeper basins(increased bottom-water oxygen concentration and low sedimentation rate).High OC concentrations were documented in the OMZ(very low bottom-water oxygen concentration with high sedimentation rate).The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions(< 1800 m) up to the Chagos-Laccadive Ridge show higher concentrations(average = 58%) when compared to deep basin sediments(average = 44%).Our study demonstrates that particle size as well as magnetic grain size,magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.

Differences in arsenic, molybdenum, barium, and other physicochemical relationships in groundwater between sites with and without mining activities

The characteristic relationships of trace metals and other water quality parameters in a specific region can be affected by anthropogenic activeties. Since the mid-18th century in the southwestern part of the Baja California Peninsula, intermittent gold mining activities have been developed. We analyzed 36 water quality parameters in accordance with the procedures suggested by international agencies to evaluate the impact of this activity and the time of year on the mobilization of trace element levels and their relationships in groundwater. Quantifiable levels of molybdenum help to establish the area influenced by ore deposits because it is one of the three elements in the paragenesis associated to gold. Arsenic in sites closer to ore burning areas was associated with cobalt, indicating the potential presence of a by-product generated from arsenolite;whereas in the non-mineralized area, it was associated with barium, forming a compound that tends to precipitate, thereby maintaining a natural geochemical control in this region. From the sites sampled, 45% exceeded the limit for arsenic (10 μg/l) established by international agencies. During area monitoring with annual precipitation of 207 mm, only seven of 36 parameters analyzed showed significant differences in relation to time of year.

FOSSIL ZYGNEMATACEAE IN THE SEDIMENTS OF THE EAST CHINA SEA AND YELLOW SEA AND ITS PALEOENVIRONMENTAL SIGNIFICANCE

In China, study on fossil Zygnemataceae has newly attracted the attention of palynologists. In our study of the bottom sediments in the East China Sea and Yellow Sea, Zygnemataeeae have for tthe first time been found abundant in many column sections of Late Pleistocene peat bed, often in company with fresh water algae and pollen of hydrophyte, providing a useful evidence for the paleoenvironmental research of the East China Sea and Yellow Sea of that time.

Simultaneous inversion of layered compressional velocity and shear velocity by using plane wave seismogram

A layer-stripping method is presented for simultaneous inversion of compressional velocity and shear velocity in layered medium from single precritical-incident-angle data of P-P and P-SV plane wave seismogram. A finite bandwidth algorithm is provided and results obviously better than previous research work are obtained by the numerical experiments for band-limited seismogram and synthetic data including noise.

LATE PLEISTOCENE STORM DEPOSIT IN WEIZHOU ISLAND OF THE BEIBU GULF

The Weizhou Island is located in the northeastern part of the Beib Gulf (Fig. 1). In Nanwanwei Cliff of this island the basaltic and terrigenous debris are composed

MIGRATION OF PALEOVEGETATIONAL ZONE AND PALEOCLIMATIC CHANGES OF QUATERNARY IN THE COASTAL REGION OF SOUTH CHINA

Migration of vegetational zone during the Quaternary is very obvious, as it is in the north of China. However, there are only a few data about the tropical and the south subtropical zones in the coastal region of South China and few systematic researches have been done. This note deals with sporopollen assemblages of the Quaternary from

NEW KNOWLEDGE OF WUTONG FORMATION DEPOSITION AT THE LOWER YANGTZE AREA

In the light of the plate tectonics the outline of paleogeography, sedimentary properties and facies patterns in the depositional processes of the Wutong Formation at the Lower Yangtze area are discussed. The argument that the Wutong Formation contains not only terrestrial sediments but also marine-terrestrial transitional or marine sediments is expounded to cover the development, evolution and paleoclimate of the Wutong depositional regions.

SOLID STATE HIGH RESOLUTION ^(13)C NMR STUDY OF CHINESE MUDSTONE KEROGENS

Using 13C CP MAS TOSS DD NMR, some rules governing the variations of structureparameter and fractional contents for various aliphatic carbon in the mudstone kerogensburied in different depths in China are first reported in this paper, and the preliminarystudies on their natural evolution as well for the formation of oil and gas have been made.The influence of TCP, TCH, frsc on quantity measurement of CP in kerogens is discussed.

ALGAL, SPORES AND POLLEN ASSEMBLAGES FROM LATE PLEISTOCENE IN THE EAST PART OF THE CHINA SEA AND THEIR PALEOENVIRONMENTS

The paper deals with fossil spores, pollen and algae from the sediments of 70,00-12,000a B. P. in the eastern sea area of China, distinguishing three spores, pollen and algal zones. Zone Ⅰ indicates that the climate was cold, the sea level was lower, the continental shelf of theDonghai Sea (the East China Sea)was exposed as the plain with various grasses thickened and manylakes andswamps dotted in which lived abundant freshwater algae of Pediastrum, Zygnema, etc.The hills in the continental margin were covered by the dark coniferous forests of Abies, Piceaand Pinus. The climate of Zone Ⅱ was warm, resulting in the sea level rising and the con-tinental shelf submerged as neritic environment with a variety of diatoms, dinoflagllate andDictyocha. The vegetation of the hills in the continental margin became mixed forests ofconiferous and broad-leaf trees mainly composed of Pinus and Quercus. Zone Ⅲ indicatesthat the climate became cold again and the continental shelf was exposed as plain with thesame