Surface radioactive anomalies at Srisailam sub basin,Cuddapah basin,India

Surface radioactive survey has been carried with portable gamma ray spectrometer(PGRS) about the 45 km2 around the Srisailam sub basin,the surface radioactive anomalies were found at Chennakesavula gutta in the Srisailam sub basin of Cuddapah basin in the age of meso-neo proterozoic,India.The integrated geochemical and radiometric surveys were conducted as part of research work in the Srisailam basin,it has resulted the locating of surface radioactive anomalies near the Chennakesavula gutta.Secondary uranium minerals are observed along with the fracture planes in the Archean basement granite in the proximity of unconformity contact of Srisailam quartzite.The granite underlies the Srisailam formation and forms the source for possible unconformity related uranium mineralisation in the Srisailam sub-basin evidence by the significant radioactive anomalies.The radioactivity recorded by PGRS reflected uraniferous nature of the radioactivity(Average total counts =195 ppm;U = 202 ppm;Th =22ppm;%K = 4.1,n = 15).     

Research Note: First results of a low‐altitude unmanned aircraft system gamma survey by comparison with the terrestrial and aerial gamma survey data

In order to increase the efficiency of geological survey in difficult landscape‐morphological conditions, the authors have developed low‐altitude gamma technology surveys based on a multi‐rotor unmanned aircraft system, also known informally as Drones. These results have been compared against those from standard terrestrial and aerial gamma surveys. The successful results obtained at the reference site show that the developed methodology enables compilation of high‐quality data in difficult landscape conditions. These results yield the same level of information content as standard terrestrial gamma surveys. The exact unmanned aircraft system altitude over the earth must be maintained for carrying out high‐quality surveys. It was found that a CsI(Tl) detector with sizes 80 × 80 mm (vol. 0.4 dm³) enables obtaining of high‐quality radiometric data at altitudes of up to 70 m, at a speed of at least 20 km/h. The authors believe that low altitude ‘quasi‐terrestrial’ gamma surveys with a terrain drape may in the future replace terrestrial gamma surveys since they can offer better effectiveness at a lower cost.     

A post-Transvaal age for the Marydale Formation,Kheis Group,Southern Africa

The metabasic Marydale Formation of the Kheis Group occupies a zone of contact between the Sanama and Kaapvaal structural provinces of South Africa. Stratigraphic relationships between the two provinces are not well understood. Whilst the well-known Kaapvaal basement and supracrustal succession yield radiometric ages older than 1900 m.y., Sanama Province ages reflect a Kibaran(1200 ± 200m.y.) tectogenetic cycle. The age of the Marydale, stratigraphically the oldest Sanama formation, has been variously estimated at2500m.y., about 2000 m.y., or Kibaran, based on controversial field interpretations or on available radiometric data.Rb-Sr data are presented for Marydale samples from a nappe-like body which, having been thrust over the Kaapvaal basement, was shielded from metamorphism. Two types of alteration are described and possible causes of isotopic homogenisation are discussed. It is concluded that an isochron age of 1899± 57m.y. (I = 0.7040 ± 0.0003) represents the age of extrusion of the Marydale volcanics.The stratigraphic controversy is thus resolved, Kheis Group formations being approximately coeval with the Matsap, the youngest formation of the Kaapvaal Precambrian succession. The implications of this and other recent work to theories of crustal evolution are considered. It is suggested that the continental crust of Sanama Province originated partly during the Eburnian(2000 ± 100m.y.) period of African orogeny and partly during the Kibaran tectogenetic cycle during which the province became cratonised and was added to the Southern African cratonic block.     

Geochemical constraints and uranium potential of the younger granitic rocks in El Maghrbia area,Central Eastern Desert,Egypt

The present work deals with the mineralogy,geochemical behavior and uranium potentiality of the monzogranites of El Maghrbia area,which comprise G.El Maghrbia and G.El Eredyia and situated in the central Eastern Desert of Egypt.G.El-Erediya monzogranites represents a promising area for uranium mineralizations.These granites have shear zone filled with red and black silica veins containing many radioactive anomalies with visible yellow secondary uranium minerals.The shear zone is highly affected by different degrees of alterations such as silicification,kaolinitization,sassuritization and ferrugination.Monzogranites of El-Erediya area possess higher values of their radioactivity than in El Maghrbia monzogranites in which eU and eTh,reaches up to 792.3 and 66.81 ppm,whilst average content of eU and eTh in El Maghrabia granites are 3.86 and 8.55 ppm,respectively owing to the presence of radioactive minerals such as uraninite,uranothorite,uranophane,kasolite,betafite,zircon and monazite.Intensive geochemical analyses indicated that,the studied monzogranites are distinctly anomalous in U,where the average U is more than 620-fold the Upper Continental Crust(UCC),marked enrichment( tenfold) of the elements Cd,Mo,Pb,Bi,Nb and W.The Th/U ratio decreases from 2.8,as a chondritic value,to 0.0023 for the studied granites,proposing extreme fractionation towards an extensive secondary migration-in of U.The Zr and Hf are depleted in the studied granites relative to the UCC,whereas Nb and Ta are strongly enriched.The content of Y is about sixfold enriched which reflects relative enhancement of the HREE during the alteration processes.Uranium correlates with Fe_2 O_3,suggesting a possible association between uranium and ferrugination.Thus,the occurrences of uranium are epigenetic by remobilization from the host rock to the sheared zones,probably through metasomatic process where U-Fe-Mg replaced the feldspars in an oxidized condition.The high levels of radioactivity in the rocks being studied it them a priority for discovery and expanding the potentiality of the highly mineralized localities.     

Mapping water table depth using geophysical and environmental variables

Despite its importance, accurate representation of the spatial distribution of water table depth remains one of the greatest deficiencies in many hydrological investigations. Historically, both inverse distance weighting (IDW) and ordinary kriging (OK) have been used to interpolate depths. These methods, however, have major limitations: namely they require large numbers of measurements to represent the spatial variability of water table depth and they do not represent the variation between measurement points. We address this issue by assessing the benefits of using stepwise multiple linear regression (MLR) with three different ancillary data sets to predict the water table depth at 100-m intervals. The ancillary data sets used are Electromagnetic (EM34 and EM38), gamma radiometric: potassium (K), uranium (eU), thorium (eTh), total count (TC), and morphometric data. Results show that MLR offers significant precision and accuracy benefits over OK and IDW. Inclusion of the morphometric data set yielded the greatest (16%) improvement in prediction accuracy compared with IDW, followed by the electromagnetic data set (5%). Use of the gamma radiometric data set showed no improvement. The greatest improvement, however, resulted when all data sets were combined (37% increase in prediction accuracy over IDW). Significantly, however, the use of MLR also allows for prediction in variations in water table depth between measurement points, which is crucial for land management.     

Radiometric ages from Ryukyu arc region and an40Ar/39Ar age from biotite dacite on Okinawa

A biotite dacite that intrudes metamorphic rocks on Okinawa in the Ryukyu island arc has been dated at 12 m.y. by the⁴⁰Ar/³⁹Ar method. The details of this age measurement and a compilation of radiometric ages for the Ryukyu island arc and adjacent regions are presented. These data suggest that from 65 to 12 m.y. ago the magmatic axis of the Ryukyu arc was confined to a very narrow zone along the arc. In Kyushu and Shikoku, the southern Japanese islands, intrusive and volcanic igneous rocks dated as 21?12 m.y. occur over a much wider zone than in the Ryukyu arc. The apparent difference in width of the magmatic zones may be due to different absolute motions of the overthrust plates of those two regions of subduction. The dissimilarity of available radiometric ages for the Ryukyu arc and for Taiwan suggest different histories for the development of these two features. The occurrence of active volcanoes in association with the Okinawa Trough, northwest of the Ryukyu island arc, may indicate that the trough itself developed in the last 12 m.y.     

Understanding airborne radiometric survey signals across part of eastern England

A low‐level airborne radiometric survey provides data on the concentrations of gammaemitting elements including potassium (K), thorium (Th) and uranium (U) in the upper half metre of the soil. Where weathering has not penetrated much beyond this depth, as in the young soils that cover much of England and Wales, the signal is likely to be related to the soil's clay content and its parent material. In these situations radiometric survey could be valuable for mapping soil digitally. We wished to understand how the radiometric signal relates to parent material and soil geochemistry, and to identify the spatial structure, if not the sources, of any unexplained variation. We analysed the joint spatial variation of the airborne gamma signal and high‐resolution soil geochemical survey data across part of eastern England by modelling their coregionalization. We also used reml to assess the joint effects of soil geochemistry and parent material on the radiometric signals of K and Th. The overall correlations of radiometric estimates with soil survey data for K and Th were large, as were the structural correlations for components of variation spatially dependent up to 49 and 16 km for K and Th respectively. This suggests that the radiometric signals for these two elements provide effective estimates of the amounts in the soil and their patterns of distribution. Although class of parent material accounted for a third of of the variance in the radiometric K signal, much of the variation within the classes is explained by geochemistry, suggesting that subtler changes can be detected. A larger proportion of the Th signal was accounted for by parent material. This supports our expectation that radiometric signals for K and Th provide information on parent material in the young landscapes of England and Wales. We are therefore confident that airborne radiometric surveys would be useful for making thematic maps of soil, particularly the soil's texture and closely related properties across England and Wales. Copyright © 2007 Natural Environment Research Council. Published in 2007 by John Wiley & Sons, Ltd.     

Time and duration of lunar highlands crust formation

All radiometric systems indicate that crust-mantle differentiation on the moon is dominated by events which occurred very early in lunar history. However, due to remaining uncertainties in model parameters and assumptions in the calculation of model ages, it is not yet possible to resolve the precise times of occurrence of these events nor the duration of the formation of the highlands crust. The strongest time constraints are offered by direct radiometric ages of samples formed during this earliest period. Two possible candidates for this material, norites 78236 and 73255,27,45, were examined utilizing the Sm-Nd radiometric system. Sm-Nd systematics of 78236 show post-crystallization disturbance but indicate that this norite crystallized in the lunar crust about 4.34 AE ago. Data for 73255,27,45 define an isochron and yield a crystallization age of 4.23 ± 0.05 AE. The initial Nd isotopic composition of both norites is within uncertainty of a “chondritic” reference reservoir at the time of their respective crystallizations. The implications for lunar crustal formation persisting over a time span of close to 350 m.y. are discussed.     

Gamma ray spectrometric analysis of hydrothermally altered dacite samples from the PACMANUS hydrothermal field: Implications for the interpretation of gamma ray wireline measurements

Spectral gamma ray wireline logging derives the concentrations of potassium, thorium, and uranium of the formation by measuring the gamma ray spectrum under the assumption of secular equilibrium. These measurements were carried out in a number of boreholes drilled by Ocean Drilling Program Leg 193 at the PACMANUS hydrothermal field. Spectral gamma ray logs from several of these holes show intervals of increased radioactivity, associated with high uranium values of up to 60 ppm (Snowcap hydrothermal field) and 25 ppm (Roman Ruins hydrothermal field). Nine samples of hydrothermally altered dacite were analyzed using gamma spectrometry to examine the origin of elevated radioactivity and to test for distortion of secular equilibrium. Core spectrometry indicates that secular equilibrium is distorted. Distortion can be explained by either an uptake of nuclides of the lower part of the ²³⁸U decay series, or by removal of ²³⁸U or ²³⁴Th from the rocks. In all cases wireline uranium logs and core spectrometry do not reflect true uranium concentrations of the formation but uranium is overestimated by a factor of 3–4. At Roman Ruins, uranium values from wireline logging show higher uranium concentrations over large intervals than uranium values from core spectrometry and from published core geochemistry, even when a possible leaching of uranium is taken into account. Wireline logs indicate that depth intervals of increased radioactivity are related to the occurrence of stockwork mineralization. In these depth intervals, core recovery was extremely low. In addition to the distortion of secular equilibrium, low core recovery and preferential loss of softer and more altered material cause a sampling bias between core samples and wireline data and may explain the observed difference in uranium concentrations between core and wireline logs.     

Die Erforschung der Natürlichen Radioaktivität von Wolkenelementen und einige damit verbundene Probleme

Summary During a number of years at Vilnius the sounding of clouds has been carried out from airplanes in order to study the contents of radioactive materials accumulated in cumuli. Two methods for taking samples have been used: 1) the collection on cooled surfaces and 2) using the method of filter paper covered with erythrosin and kept in a special collector within the Venturi tube. In the first case radioactivity has been measured with the help of Geiger-Müller counter and in the second by means of nuclear photo emulsion (sensitive to -particles) which was brought into contact with the filter paper moistened in the cloud. This method has made it possible: 1) to measure radioactivity in local zones of a cloud, 2) to measure radioactivity of separate big drops and 3) to study the composition of -radioactivity contained in cloud particles.The magnitude of specific radioactivity of cloud elements appears to be of the same order with the rain drops and at times even greater than that of the rain samples.There exist two types of the distribution of radioactivity in a cumulus according to the height: 1) an increase of radioactivity from the bottom to maximum at the height of 0.6 part of the cloud's thickness and 2) two maxima of radioactivity at the bottom and in the centre. The latter phenomenon is characteristic of thick cumuli where big radioactive drops apparently fall out from the centre. The distribution of radioactivity at different heights correlates well with cloud's liquid-water.In a cumulus there takes a place a process of accumulation of radioactive aerosol with the accumulation coefficient of 1000. This circumstance points to a very important part played by clouds as accumulators of radioactive materials from the air which continuously filters itself through them. And just by this is expressed one of the properties of clouds as purifiers of the atmosphere from radioactive aerosol, for, as theoretical calculations indicate, the ability of drops to absorbe radioactive aerosol diminishes with the process of cloud droplets growing to the size of rain drops.The composition of radioactive materials in cloud elements is very complex. In drogs there appear nearly all the natural radioactive elements (emitting -particles) which exist in the earth's crust.     

Paleomagnetic stratigraphy and radiometric dating of the pliocene volcanic rocks of Aegina,Greece

The island of Aegma includes some of the oldest volcanic rocks in the south Hellenic Arc previous radiometric dates range from 3.87 to 4.4 Ma. The volcanic sequence is divided into nine units on the basis of field relations, petrography and geochemistry, and the characteristic paleomagnetic polarity of each unit has been determined. Two new radiometric dates (2.1 and 3.9 Ma) show that the volcanism spans the Pliocene. A detailed chronology is proposed using the paleomagnetic data which places the most voluminous volcanism in the mid Pliocene.     

Fission track ages of mica belts and some other precambrian muscovites of India

Summary The ages of forty six muscovite samples obtained from mines in the three main mica belts of India, viz. Bihar, Rajasthan and Andhra Pradesh, and areas around Delhi have been measured using improved fission track dating technique. The effect of geological annealing in the samples has been assessed and suitable correction applied to the ages, wherever required; also, uranium concentration has been measured in tight cleavages so as to avoid errors due to epigenetically introduced uranium.The ages agree with the main orogenic-metamorphic cycles in the respective regions and also the ages of pegmatites measured by other radiometric methods. The ages of the three belts have been measured as follows: Bihar mica belt, 700–1100 m.y.; Rajasthan mica belt and Delhi samples 700–1050 m.y.; Andhra Pradesh (Nellore) mica belt, 470–650 m.y. Occurrence of metamorphic event 600 m.y. in Rajasthan is supported by the age of one of the samples.     

Revisiting a classification scheme for U.S.-Mexico alluvial basin-fill aquifers

Intermontane basins in the Trans-Pecos region of westernmost Texas and northern Chihuahua, Mexico, are target areas for disposal of interstate municipal sludge and have been identified as possible disposal sites for low-level radioactive waste. Understanding ground water movement within and between these basins is needed to assess potential contaminant fate and movement. Four associated basin aquifers are evaluated and classified; the Red Light Draw Aquifer, the Northwest Eagle Flat Aquifer, the Southeast Eagle Flat Aquifer, and the El Cuervo Aquifer. Encompassed on all but one side by mountains and local divides, the Red Light Draw Aquifer has the Rio Grande as an outlet for both surface drainage and ground water discharge. The river juxtaposed against its southern edge, the basin is classified as a topographically open, through-flowing basin. The Northwest Eagle Flat Aquifer is classified as a topographically closed and drained basin because surface drainage is to the interior of the basin and ground water discharge occurs by interbasin ground water flow. Mountains and ground water divides encompass this basin aquifer on all sides; yet, depth to ground water in the interior of the basin is commonly >500 feet. Negligible ground water discharge within the basin indicates that ground water discharges from the basin by vertical flow and underflow to a surrounding basin or basins. The most likely mode of discharge is by vertical, cross-formational flow to underlying Permian rocks that are more porous and permeable and subsequent flow along regional flowpaths beneath local ground water divides. The Southeast Eagle Flat Aquifer is classified as a topographically open and drained basin because surface drainage and ground water discharge are to the adjacent Wildhorse Flat area. Opposite the Eagle Flat and Red Light Draw aquifers is the El Cuervo Aquifer of northern Chihuahua, Mexico. The El Cuervo Aquifer has interior drainage to Laguna El Cuervo, which is a phreatic playa that also serves as a focal point of ground water discharge. Our evidence suggests that El Cuervo Aquifer may lose a smaller portion of its discharge by interbasin ground water flow to Indian Hot Springs, near the Rio Grande. Thus, El Cuervo Aquifer is a topographically closed basin that is either partially drained if a component of its ground water discharge reaches Indian Hot Springs or undrained if all its natural ground water discharge is to Laguna El Cuervo.     

A large volume magnetic field free space for thermal demagnetization and other experiments in palaeomagnetism

Summary Three orthogonal coil systems have been constructed within a cube of side 2.5 m to cancel the geomagnetic field to less than 1 gamma over a large volume. The north-south and vertical components are cancelled by systems of four square coils whilst a square Helmholtz pair cancels the east-west component. Cancellation to 1 part in 10⁵ (0.5 gamma in Canberra) is achieved within a sphere of diameter 35 cm, more than 20 times the field-free volume which could be obtained using conventional Helmholtz coils within the available space. Three fluxgate detectors monitor the residual field and their output, taken through a feedback circuit, allows compensation for field variations. The residual field can be maintained to less than 0.5 gamma over the working volume of about 22,000 cm³ during the critical part of a laboratory experiment.     

松科2井东孔营城组高放射性异常层测井响应特征及成因初探

松科2井东孔是松辽盆地科学钻探工程的主体钻孔,按照计划在全井段进行地球物理测井资料采集,为深部资源勘探及白垩纪古气候、古环境研究提供准确和全面的地球物理信息.在诸多测井方法中,自然伽马测井和自然伽马能谱测井能够测量地层的天然放射性强度和铀、钍、钾元素含量等参数,被有效地应用于放射性矿床勘查,尤其是铀资源的勘查与研究;电阻率、声波、密度和中子测井等常规测井和核磁共振成像、电阻率成像、元素俘获谱测井等特殊测井能够获取地层岩性和物性参数等信息,为铀矿勘查提供有力支持.本文利用松科2井东孔自然伽马测井资料来识别高放射性异常层;基于常规测井与特殊测井资料,结合前人的地质研究成果,分析放射性异常层的特征和成因.核测井曲线指示营城组存在两段高放射性异常层,深度分别为3096.8~3102.8 m（I号层）、3168.3~3170.9 m（Ⅱ号层）.I号层自然伽马值最高达360 API,铀含量范围20.5~29.3 ppm,综合测井和岩心资料判断该层为砾岩,具有铀成矿潜力;分析表明,构造条件和后生改造作用是影响I号层铀富集的关键因素,推测断裂-火山活动和盆地抬升剥蚀为含铀地下水及油气运移至I号层提供了通道,油气的后生还原作用最终导致了I号异常层的铀富集.Ⅱ号层自然伽马值最高达250API,钍含量22.4~37.3 ppm,铀含量5.9~11.0 ppm,为集块熔岩及凝灰岩,高放射性异常可能是高钍含量的流纹质成分和粘土矿物对铀的吸附作用导致的.松科2井东孔营城组高放射性异常层具有埋藏深度深、铀含量高等特点,表明松辽盆地深部具有找铀矿前景.     

Long‐term trend analysis for precipitation in Asian Pacific FRIEND river basins

In order to analyse the long‐term trend of precipitation in the Asian Pacific FRIEND region, records from 30 river basins to represent the large range of climatic and hydrological characteristics in the study area are selected. The long‐term trend in precipitation time series and its association with the southern oscillation index (SOI) series are investigated. Application of the nonparametric Mann–Kendall test for 30 precipitation time series has shown that only four of these 30 time series have a long‐term trend at the 5% level of significance. Nevertheless, most of the records tend to decrease over the last several decades. The dataset is further divided geographically into northern, middle, and southern zones, with 20°N and 20°S latitude as the dividing lines. The middle zone has the greatest variation and the southern zone the least variation over the past century. Also, the southern zone has greater variation during the past 30 years. The association between precipitation and SOI is investigated by dividing the precipitation records of each station into El Niño, La Niña, and neutral periods. The Wilcoxon rank‐sum test showed that differences in precipitation for the three classes were most marked in the southern zone of the study area. The frequencies of below‐ and above‐average precipitation for El Niño, La Niña, and neutral periods are estimated for the 30 precipitation time series as well. The results show that the frequencies of precipitation under each set of conditions, with lower precipitation generally associated with El Niño periods in the southern zone. Copyright © 2005 John Wiley & Sons, Ltd.     

Dating results on sedimentary quartz,bones and teeth from the Middle Pleistocene archaeological site of Coudoulous I (Lot,SW France): A comparative study between TT-OSL and ESR/U-series methods

This study presents palaeodosimetric results from the Middle Pleistocene archaeological site of Coudoulous I (Lot, SW France). Nine sedimentary quartz samples (41–60 μm) have been analyzed using a multiple aliquot protocol based on the measurement of the TT-OSL signal. In addition, 7 teeth and 7 bones have been dated by combining the ESR method with U-series analyses. Both methods gave consistent age results allowing correlation of the Early Middle Paleolithic Human occupation of the site to MIS 6 and part of the Lower Paleolithic tools to MIS 7. Beyond the establishment of a radiometric chronology for the Coudoulous I sequence, this study focuses on the information extracted from the intercomparison of the methods. Our data suggest that 1) the TT-OSL signal is stable over at least the last 230 ka (considering the age range of the studied samples), 2) there are not significant problems of incomplete bleaching leading support to the applicability of the TT-OSL technique for sedimentary deposits associated with karstic contexts. This approach highlights the interest of combining luminescence and ESR/U-series methods to discuss the reliability of the dating results.     

Probabilistic earthquake hazard analysis for Cairo,Egypt

Cairo is the capital of Egypt and the largest city in the Arab world and Africa, and the sixteenth largest metropolitan area in the world. It was founded in the tenth century (969 ad) and is 1046 years old. It has long been a center of the region’s political and cultural life. Therefore, the earthquake risk assessment for Cairo has a great importance. The present work aims to analysis the earthquake hazard of Cairo as a key input’s element for the risk assessment. The regional seismotectonics setting shows that Cairo could be affected by both far- and near-field seismic sources. The seismic hazard of Cairo has been estimated using the probabilistic seismic hazard approach. The logic tree frame work was used during the calculations. Epistemic uncertainties were considered into account by using alternative seismotectonics models and alternative ground motion prediction equations. Seismic hazard values have been estimated within a grid of 0.1°?×?0.1 ° spacing for all of Cairo’s districts at different spectral periods and four return periods (224, 615, 1230, and 4745 years). Moreover, the uniform hazard spectra have been calculated at the same return periods. The pattern of the contour maps show that the highest values of the peak ground acceleration is concentrated in the eastern zone’s districts (e.g., El Nozha) and the lowest values at the northern and western zone’s districts (e.g., El Sharabiya and El Khalifa).     

A geomagnetic field reversal time scale back to 13.0 million years before present

The ages of reversals of the Earth's magnetic field have been dated accurately back to 3.4 m.y. ago. Between this time and the age of the Cretaceous-Tertiary boundary, dates for reversals have been calculated assuming a constant rate of sea-floor spreading in the South Atlantic Ocean. The presence of thick piles of lava flows in Iceland allows us to produce independent evidence for the ages of reversals back to 13.0 m.y. B.P. Because of the extreme regularity of extrusion of these lava flows, the measurement of their magnetic polarity allows us to correlate the lava flows which were extruded during the polarity intervals associated with sea-floor spreading anomalies. The measurement of many K-Ar ages on these lava flows also allows us to compare the ages of reversals assumed by the linear interpolation between the ages of 3.4 m.y. and the Cretaceous-Tertiary boundary at 66.5 m.y., with those suggested by the radiometric dates. We find that in general the assumption of constant spreading has been a good one, but suggest a small change in the ages of reversals, amounting to an increase of about 0.27 m.y. in ages of reversals between 8.5 and 13.0 m.y. ago.