Time series analysis of daily rainfall and streamflow in a volcanic dike-intruded aquifer system, O��ahu, Hawai��i, USA

A conceptual model of groundwater occurrence was developed for a dike-intruded aquifer system in M??kaha valley, O??ahu, Hawai??i, USA, and used to explain the impacts of water resource development on groundwater levels and streamflow. Time-series analyses were applied to two subsets of daily rainfall, total flow, and baseflow??from the third (1946?C1968) and fourth (1968?C1991) periods of development??to evaluate changes in streamflow response. Autocorrelation, cross-correlation, squared coherency and phase functions were used to estimate the decorrelation lag time, and the correlation length, linearity with frequency, and frequency response delay between rainfall and streamflow. The decorrelation lag time for total flow and baseflow declined by 16?C20?days (d). The correlation length between rainfall and streamflow declined 4?C7?d for total flow and 10?C13?d for baseflow. The squared coherency function indicates an overall decline in linearity between rainfall and total flow across most frequencies. The changes in hydrologic response following increased water-resource development is consistent with a model of groundwater depletion resulting in less groundwater discharge and more induced groundwater recharge. Changes in streamflow response are inconsistent with observed changes in rainfall and imply that streamflow decline is more likely to be the result of groundwater pumping.     

New ophiolite occurrences in Sudan and constraint on the western boundary of the Nubian Shield: Petrographical and geochemical evidence

Important mafic–ultramafic masses have been located for the first time in the intersection area between the Keraf Shear Zone and the Nakasib Suture Zone of the Nubian Shield. The masses, comprising most of the members of the ophiolite suite, are Sotrebab and Qurun complexes east of the Nile, and Fadllab complex west of the Nile. The new mafic–ultramafic masses are located on the same trend of the ophiolitic masses decorating the Nakasib Suture. A typical complete ophiolite sequence has not been observed in these complexes, nevertheless, the mafic–ultramafic rocks comprise basal unit of serpentinite and talc chlorite schists overlain by a thick cumulate facies of peridotites, pyroxenites and layered gabbros overlain by basaltic pillow lavas with dolerite dykes and screens of massive gabbros. Associated with pillow lavas are thin layers of carbonates and chert. The best section of cumulate mafic–ultramafic units has been observed in Jebel Qurun and El Fadlab complexes, comprising peridotites, pyroxenites and layered gabbros. Dolerite dykes and screens of massive gabbros have been observed with basaltic pillow lava sections in Wadi Dar Tawaiy. The basal ultramafic units of the complexes have been fully or partly retrograded to chlorite magnetite schist and talc to talc-carbonate rocks (listowenites), especially in the Jebel Qurun and Sotrebab complexes. Petrographically, the gabbros (layered and massive) and the basaltic pillow lavas show mineral assemblages of epidote amphibolite facies. The mafic members from the three complexes show a clear tholeiitic trend and oceanic floor affinity. The pillow lavas plot in the field of oceanic floor basalt, namely in the back arc field. Primitive mantle normalized spider diagram of the pillow lavas reveals a closer correspondence to Enrich-Mid-Oceanic Ridge Basalt (E-MORB) type, which is confirmed by the flat chondrite normalized Rare Earth Elements (REE) pattern. Field, petrographical and geochemical evidence supports ophiolitic origin of the three complexes. The newly discovered ophiolitic complexes mark the western continuation of the Nakasib Suture Zone.     

Arsenic contamination in groundwater and its proposed remedial measures

Arsenic contamination occurs in groundwater of Bangladesh mainly from the alluvial and deltaic sediments. Arsenic contamination of groundwater in Bangladesh was first detected more than a decade ago and the ’shallow tubewells’ were reported as the main source of arsenic contaminated water. From the nutritional and metabolic points of view, arsenic is likely to adversely affect human health and nutrition. Up to now, several studies have been carried out on this context; however, inadequate knowledge on arsenic sources, mobilization and transport still remains as a constraint due to lack of data, information and technological advances. Thus, a review study has been undertaken on the sources of arsenic, its causes, mobilization, transport, effects on human health, arsenic test procedures and removal methods, in the context of groundwater contamination in Bangladesh, and finally sustainable remedial measures of arsenic have been proposed. This study suggests that laboratory facilities for testing of arsenic and effects of enhanced groundwater pumping, phosphate fertilizer etc., need to be updated, expanded and studied. This review work is significant to further knowledge improvement, as the topic is general and worldwide. It can be concluded that the integration of the proposed remedial measures with the national geographic information system interface database relating to arsenic for analysis, production of hazard maps, and dissemination on television show for the planners, engineers, managers, field supervisors and affected people, can reach at the sustainable solution for mitigating arsenic and associated problems successfully in Bangladesh.     

Taxonomical and Biogeochemical Investigation of Elements in Holocene Mollusk Shells in the South and Southwestern Marmara Basin,Turkey

Concentrations of some heavy metals and trace elements such as Cr, Ga, Ni, Zn, Mo, Cu, Pb, Yb, Y, Nb, Ti, Sr, Ba, Mn, Sc, Co, V, Zr, Fe, Al, W, Se, Bi, Sb, As, Cd in recent mollusk shells and factors affecting their distribution and deposits collected from various depths in the southern and southwestern parts of the Marmara Sea are investigated. The distribution of the elements in the shells is categorized into four groups. Of these, concentrations of 12 elements （As, Bi, Cd, Co, Ga, Mo, Nb, Sb, Se, Sc, W and Yb） are below zero [（0.053-0.79）×10^-6]; concentrations of seven elements （Cr, Ni, Pb, V, Y, Zr and Cu） are （1.0-6.0）×10^-6; concentrations of four elements （Ti, Mn, Ba and Zn） are 10- 20×10^-6; and concentrations of five elements （Si, Al, Fe, Mg and Sr） are （47.44-268.11）×10^-6. The taxonomic characteristics of the 29 elements were studied separately in mollusk shells such as Chamalea gallina （Linn6）, Pitar rudis （Poli）, Nassarius reticulatus （Linn6）, Venerupis senescens （Coocconi）, Mytilus galloprovincialis （Lamarck）, Mytilaster lineatus （Gemelin in Linne） and Chlamys glabra. It was found that, in mollusk taxonomy, the elements have unique values. In other words, element concentrations in various mollusk shells depend mainly on the taxonomic characteristics of mollusks. In various bionomic environments different element distributions of the same species are attributed to the different geochemical characters of the each environment. Data obtained in this study indicate that the organisms are the most active and deterministic factors of the environment.     

The Okavango giant mafic dyke swarm (NE Botswana): its structural significance within the Karoo Large Igneous Province

The structural organization of a giant mafic dyke swarm, the Okavango complex, in the northern Karoo Large Igneous Province (LIP) of NE Botswana is detailed. This N110°E-oriented dyke swarm extends for 1500 km with a maximum width of 100 km through Archaean basement terranes and Permo-Jurassic sedimentary sequences. The cornerstone of the study is the quantitative analysis of N>170 (exposed) and N>420 (detected by ground magnetics) dykes evidenced on a ca. 80-km-long section lying in crystalline host-rocks, at high-angle to the densest zone of the swarm (Shashe area). Individual dykes are generally sub-vertical and parallel to the entire swarm. Statistical analysis of width data indicates anomalous dyke frequency (few data <5.0 m) and mean dyke thickness (high value of 17 m) with respect to values classically obtained from other giant swarms. Variations of mean dyke thicknesses from 17 (N110°E swarm) to 27 m (adjoining and coeval N70°E giant swarm) are assigned to the conditions hosting fracture networks dilated as either shear or pure extensional structures, respectively, in response to an inferred NNW–SSE extension. Both fracture patterns are regarded as inherited brittle basement fabrics associated with a previous (Proterozoic) dyking event. The Okavango N110°E dyke swarm is thus a polyphase intrusive system in which total dilation caused by Karoo dykes (estimated frequency of 87%) is 12.2% (6315 m of cumulative dyke width) throughout the 52-km-long projected Shashe section. Assuming that Karoo mafic dyke swarms in NE Botswana follow inherited Proterozoic fractures, as similarly applied for most of the nearly synchronous giant dyke complexes converging towards the Nuanetsi area, leads us to consider that the resulting triple junction-like dyke/fracture pattern is not a definitive proof for a deep mantle plume in the Karoo LIP.     

塔克拉玛干沙漠腹地冬季大气边界层O3廓线分析

为了揭示塔克拉玛干沙漠腹地冬季大气边界层O3的浓度变化特征,利用系留气艇于2008年1月18—25日在塔中地区进行了大气边界层O3观测试验,结合相关资料,初步分析了塔中地区冬季边界层O3浓度垂直分布特征及其与温度、湿度的关系。其结果是:①塔中地区臭氧浓度集中分布在10~50 ppb之间,其中试验期间观测到O3最大浓度值56.1 ppb,最小浓度为2.6 ppb,臭氧的最大浓度基本都在40 ppb左右,日平均浓度为34.4 ppb。②大气边界层O3的浓度廓线可分为峰值型、均匀型、增长型3种,其中均匀型所占比重最大。③大气边界层O3浓度与温度、湿度密切相关,逆温及空气中水汽的增加会导致臭氧浓度降低。④大气边界层O3有明显的日变化,越贴近地面日变化越明显,其变化特征与太阳辐射有着密切关系。臭氧浓度夜晚较低,日出后开始增加,午后达到一天中的最大值;随着日落,臭氧浓度开始减小,在清晨达到最小值;臭氧浓度日最大值出现在17:00,最小值出现在08:00。     

Geochemical Characteristics,Origin, and Evolution of Ore‐Forming Fluids of the Khut Copper Skarn Deposit,West of Yazd in Central Iran

The Khut copper skarn deposit is located at about 50 km northwest of Taft City in Yazd province in the middle part of the Urumieh‐Dokhtar magmatic arc. Intrusion of granitoid of Oligocene–Miocene age into carbonate rocks of the Triassic Nayband Formation led to the formation of marble and a calcic skarn. The marble contains high grade Cu mineralization that occurs mainly as open space filling and replacement. Cu‐rich sulfide samples from the mineralized marble are also anomalous in Au, Zn, and Pb. In contrast, the calcic skarn is only weakly anomalous in Cu and W. The calcic skarn is divided into garnet skarn and garnet–pyroxene skarn zones. Paragenetic relationships and microthermometric data from fluid inclusions in garnet and calcite indicate that the compositional evolution of skarn minerals occurred in three main stages as follows. (i) The early prograde stage, which is characterized by Mg‐rich hedenbergite (Hd_53.7Di_42.3–Hd_86.1Di_9.5) with Al‐bearing andradite (69.8–99.5 mol% andradite). The temperature in the early prograde skarn varies from 400 to 500°C at 500 bar. (ii) The late prograde stage is manifested by almost pure andradite (96.2–98.4 mol% andradite). Based on the fluid inclusion data from garnet, fluid temperature and salinity in this stage is estimated to vary from 267 to 361°C and from 10.1 to 21.1 wt% NaCl equivalent, respectively. Pyrrhotite precipitation started during this stage. (iii) The retrograde stage occurs in an exoskarn, which consists of an assemblage of ferro‐actinolite, quartz, calcite, epidote, chlorite, sphalerite, pyrite, and chalcopyrite that partially replaces earlier mineral assemblages under hydrostatic conditions during fracturing of the early skarn. Fluids in calcite yielded lower temperatures (T < 260°C) and fluid salinity declined to ～8 wt% NaCl equivalent. The last stage mineralization in the deposit is supergene weathering/alteration represented by the formation of iron hydroxide, Cu‐carbonate, clay minerals, and calcite. Sulfur isotope data of chalcopyrite (δ³⁴S of +1.4 to +5.2‰) show an igneous sulfur source. Mineralogy and mineral compositions of the prograde assemblage of the Khut skarn are consistent with deposition under intermediately oxidized and slightly lower fS₂ conditions at shallow crustal levels compared with those of other typical Fe‐bearing Cu–Au skarn systems.     

Assessment of spatial variations in water quality of Garra River at Shahjahanpur,Ganga Basin,India

Arabian Journal of Geosciences - A comprehensive study on the chemical considerations of thermal waters (springs and geothermal wells) on the performance of solute geothermometers in predicting the...