Classification and delineation of groundwater–lake interactions in the Nebraska Sand Hills (USA) using electrical resistivity patterns

Lake?Cgroundwater interactions exhibit a complex three-dimensional (3D) structure that is seldom studied. The utility of waterborne electrical resistivity (ER) surveys is explored for characterization of 3D groundwater flow and solute transport patterns for three lakes in the Nebraska Sand Hills, USA. Waterborne ER surveys, using contrasts between lake and groundwater solutes as natural tracers, are useful for inferring 3D patterns of groundwater flow and solute transport as well as classifying groundwater?Clake interactions. Three unique groundwater flow systems are interpreted under each lake from dense networks of two-dimensional (2D) waterborne ER surveys. A lateral transition from high to low ER values beneath the saline Wilson Lake expresses its flow-through regime, where groundwater salinity indicates changes from groundwater inflow to outflow. Alkali Lake ER profiles reveal a prevalent ER increase with depth over the lakebed area that is characteristic of groundwater discharge lakes. ER profiles beneath Gimlet Lake are the most resistive and indicate pockets of high ER related to fresh groundwater discharge into the lake, supporting a flow-through regime with a short flushing time. These ER patterns correctly classify groundwater?Clake interactions and provide high spatial resolution of mixing patterns for systems with varying water salinity.     

Experimental study on the electrical resistivity of soil–cement admixtures

Recently in China, soil–cement is widely used to improve the soft ground in the highway construction engineering. Literature studies are mainly investigating the mechanical properties of the soil–cement, while its properties of the electrical resistivity are not well addressed. In this paper, the properties of the electrical resistivity of the reconstituted soil-cement and the in situ soil–cement columns are investigated. The test results show that the electrical resistivity of the soil–cement increases with the increase in the cement-mixing ratio and curing time, whereas it decreases with the increase in the water content, degree of saturation and water–cement ratio. A simple equation is proposed to predict the electrical resistivity of soil–cement under the condition of the specified curing time and water–cement ratio. It is found that the electrical resistivity has a good relationship with the unconfined compression strength and blow count of SPT. It is expected that the electrical resistivity method can be widely used for checking/controlling the quality of soil–cement in practice.     

Groundwater contamination assessment in Al-Quwy’yia area of central Saudi Arabia using transient electromagnetic and 2D electrical resistivity tomography

Groundwater contamination is one of the most significant problems in arid countries. Al-Quwiy’yia region is an example of an area where the groundwater is contaminated as a result of infiltration of waste water in low-lying areas adjacent to inhabited zones. Such contamination poses significant environmental threats for the surrounding environment and groundwater. Surface observations and spatial distribution of contamination observed in the shallow aquifer indicate that the main contamination sources were from sewage as well as from waste water dumping. However, the main source of water supply for the whole area is groundwater abstracted from the relatively shallow aquifer. Therefore, the transient electromagnetic method (TEM) and 2D electrical resistivity tomography (2D ERT) have been applied close to the waste water dump site to characterize the response of pollution plumes. Both of these geoelectrical techniques are sensitive to electrical conductivity as well as to other physical properties, which are greatly influenced by the polluted groundwater. Therefore, it is possible to profile the contamination plumes, both vertically and horizontally, in the vicinity of the measured stations. The ERT profiles gave detailed information about the lateral distribution of the contaminated groundwater, whereas the TEM demonstrated the vertical extensions.     

The Campanian–Maastrichtian of the Aures Basin,Algeria: Paleobiogeographical distribution of ostracods

A detailed biostratigraphic study of four sections (El Kantara, Menaa, Tighanimine and El Gaâga) in the Campanian–Maastrichtian of the Aures Basin in Algeria allows the identification of 109 ostracod species belonging to 50 genera. From a biochronostratigraphic point of view, none of the identified ostracod assemblages are typically restricted to the Campanian or to the Maastrichtian, but rather characterize a range covering the Campanian–Maastrichtian. As regards the paleobiogeography, the presence of species in common between Algeria and other countries or regions enables us to compile four maps showing the distribution of two provinces that developed during the Santonian-Paleocene, i) the South-West and South Tethyan Margins Province, including North Africa, the Middle East and Arabian Peninsula, and ii) the East Atlantic Margin Province, bordering West and Central-West Africa. We can also recognize relationships between the different regions making up these provinces, which remained under more or less arid, subtropical to tropical climates, with ostracods migrating according to the directions of ocean currents during the Late Cretaceous. The dispersal of the ostracods reflects marine communication between these provinces and India, the southern USA and Jamaica, Brazil and Europe.     

Orbital-scale record of the late Cenomanian–Turonian oceanic anoxic event (OAE-2) in the Tarfaya Basin (Morocco)

High sedimentation rates (up to 12 cm/kyear) of laminated organic carbon-rich biogenic limestones in the Tarfaya Basin provide an unusually high (millennial) resolution record of the late Cenomanian oceanic anoxic event (OAE-2). The global positive carbon-isotope excursion across the Cenomanian–Turonian corresponds to 11 light/dark sedimentary cycles. We interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle. On this timescale, the main increase in ¹³C values occurred over a short time interval of less than 20 kyear in the late Cenomanian and reached a first maximum approximately 15 kyear prior to the bulk (mainly coccoliths) ¹⁸O-derived sea surface maximum temperature that occurs coeval to the extinction of Rotalipora cushmani. Organic carbon-accumulation rates follow obliquity cycles, reaching a maximum approximately 10 kyear after the last occurrence of R. cushmani, then slowly decreasing during the early Turonian. Thus, the maximum temperature and the maximum organic carbon accumulation in the Tarfaya Basin lagged by at least 15 kyear behind the global carbon-isotope shift and a proposed reduction of atmospheric CO₂ content. The climate change across the Cenomanian/Turonian boundary probably occurred independent of CO₂ levels and may have been controlled by different greenhouse gases (water vapour and methane) and changes in ocean circulation (i.e., opening of the Equatorial Atlantic gateway)     

Application of electrical resistivity tomography to evaluate the variation in moisture content of waste during 2 months of degradation

Moisture content is considered to play an important role in the degradation of municipal solid waste (MSW). The present study was carried out to test the use of electrical resistivity tomography (ERT) to estimate the daily variations in the volumetric moisture content (VMC) during waste degradation. The degradation of MSW in a laboratory-scale reactor was monitored daily by ERT and time domain reflectometry (TDR) over a period of 55 days after the waste was landfilled. The bulk electrical resistivity, normalised to a standard temperature of 25 °C, was compared to the VMC obtained by TDR. The relationship between the bulk electrical resistivity and the VMC was not obvious in the upper unit, because there was a bias in the positions of the ERT and TDR measurements due to the settling of the waste. However, the bulk electrical resistivity depended on the VMC in the lower unit of the reactor. According to a power equation fitted in the lower unit, the 2-D distributions of the VMC are presented. Variations in the VMC reflected the processes of waste degradation and leachate transportation. Furthermore, the volume of water stored in the lower unit of the reactor was calculated and found to be consistent with that estimated from the gravimetric moisture content during waste sampling. The data showed that ERT could be used to estimate the variations in moisture content in the initial period following the landfilling of waste.     

Oil charge history of Paleogene–Eocene reservoir in the Termit Basin (Niger)

A total of 73 oils from the sandstone reservoir of Paleocene–Eocene Sokor 1 Formation in the Termit Basin (eastern Niger) were analysed to investigate the distribution characteristics of biomarkers. Most of the oil samples are quite similar in their organic geochemical characteristics and should have been derived from the same source bed/source kitchen. The homogenisation temperatures of aqueous inclusions in Paleocene–Eocene reservoir of the Termit Basin vary with a range of 76–125?°C. By combining the homogenisation temperatures with the burial and geothermal histories reconstructed by 1-dimensional basin modelling, the timing and episode of oil charge can be obtained, i.e. 13 to 0?Ma for Paleocene–Eocene reservoirs in the Termit Basin. Two presentative geochemical parameters, i.e. Ts / (Ts?+?Tm) and 2,4-dibenzothiophene/1,4-dibenzothiophene (2,4-DMDBT/1,4-DMDBT) were applied to trace the oil migration direction and filling pathway. The preferred oil-filling points in the northwest section of the Termit Basin were determined, and the promising exploratory targets were proposed for further oil exploration in this region.     

Evolution of the Landscape of the Western Part of the Turan–Uyuk Basin (Tuva Highland) in the Late Pleistocene

Doklady Earth Sciences - A complex of works including geomorphological deciphering, field survey, drilling, electric prospecting, and dating of deposits using the radiocarbon method and optically...     

Energetic and spatial characterization of seismicity in the Algeria–Morocco region

We estimate the energetic and spatial characteristics of seismicity in the Algeria–Morocco region using a variety of seismic and statistical parameters, as a first step in a detailed investigation of regional seismic hazard. We divide the region into five seismotectonic regions, comprising the most important tectonic domains in the studied area: the Moroccan Meseta, the Rif, the Tell, the High Plateau, and the Atlas. Characteristic seismic hazard parameters, including the Gutenberg–Richter b-value, mean seismic activity rate, and maximum possible earthquake magnitude, were computed using an extension of the Aki–Utsu procedure for incomplete earthquake catalogs for each domain, based on recent earthquake catalogs compiled for northern Morocco and northern Algeria. Gutenberg–Richter b-values for each zone were initially estimated using the approach of Weichert (Bull Seismol Soc Am 70:1337–1346, 1980): the estimated b-values are 1.04 ± 0.04, 0.93 ± 0.10, 0.72 ± 0.03, 0.87 ± 0.02, and 0.77 ± 0.02 for the Atlas, Meseta, High Plateau, Rif, and Tell seismogenic zones, respectively. The fractal dimension D ₂ was also estimated for each zone. From the ratio D ₂/b, it appears that the Tell and Rif zones, with ratios of 2.09 and 2.12, respectively, have the highest potential earthquake hazard in the region. The Gutenberg–Richter relationship analysis allows us to derive that in the Tell and Rif, the number of earthquake with magnitude above Mw 4.0, since 1925 normalized to decade and to square cell with 100-km sides is equal to 2.6 and 1.91, respectively. This study provides the first detailed information about the potential seismicity of these large domains, including maximum regional magnitudes, characteristics of spatial clustering, and distribution of seismic energy release.     

Energetic and spatial characterization of seismicity in the Algeria–Morocco region

We estimate the energetic and spatial characteristics of seismicity in the Algeria–Morocco region using a variety of seismic and statistical parameters, as a first step in a detailed investigation of regional seismic hazard. We divide the region into five seismotectonic regions, comprising the most important tectonic domains in the studied area: the Moroccan Meseta, the Rif, the Tell, the High Plateau, and the Atlas. Characteristic seismic hazard parameters, including the Gutenberg–Richter b-value, mean seismic activity rate, and maximum possible earthquake magnitude, were computed using an extension of the Aki–Utsu procedure for incomplete earthquake catalogs for each domain, based on recent earthquake catalogs compiled for northern Morocco and northern Algeria. Gutenberg–Richter b-values for each zone were initially estimated using the approach of Weichert (Bull Seismol Soc Am 70:1337–1346, 1980): the estimated b-values are 1.04 ± 0.04, 0.93 ± 0.10, 0.72 ± 0.03, 0.87 ± 0.02, and 0.77 ± 0.02 for the Atlas, Meseta, High Plateau, Rif, and Tell seismogenic zones, respectively. The fractal dimension D ₂ was also estimated for each zone. From the ratio D ₂/b, it appears that the Tell and Rif zones, with ratios of 2.09 and 2.12, respectively, have the highest potential earthquake hazard in the region. The Gutenberg–Richter relationship analysis allows us to derive that in the Tell and Rif, the number of earthquake with magnitude above Mw 4.0, since 1925 normalized to decade and to square cell with 100-km sides is equal to 2.6 and 1.91, respectively. This study provides the first detailed information about the potential seismicity of these large domains, including maximum regional magnitudes, characteristics of spatial clustering, and distribution of seismic energy release.

     

4D modelling of fault reactivation using complete paleostress tensors from the Cooper–Eromanga Basin,Australia

Determining fault activity through time has typically utilised high-resolution seismic data to identify stratigraphic thickness changes or displacement vs distance plots; however, this approach is not possible in regions with low-resolution seismic data. We present a new approach for determining fault reactivation (tensile and shear) through time by integrating three-dimensional seismic data, geomechanical modelling and complete paleostress tensors from calcite twin stress inversion. The Cooper–Eromanga Basin is used as a case study to model the stress conditions present during six tectonic events that have affected the basin and, in doing so, constrain the effective paleostress magnitudes through time. Results show that the likelihood of dilation and shear reactivation of individual fault sets varies through time, with N–S- and E–W-striking faults likely to have been open to fluid flow after the critical moment in the hydrocarbon system. These results have substantial implications for hydrocarbon migration pathway models and structural and stratigraphic models for the Cooper–Eromanga Basin. This approach would benefit other provinces with low-resolution seismic data preventing fault growth analysis, or in regions where hydrocarbon migration pathways are poorly defined.     

Magnetostratigraphy of the Campanian–Maastrichtian Bakchar Basin (southeastern West Siberia)

In this paper the results of magnetostratigraphic studies of the Upper Cretaceous penetrated by two wells (S-124 and S-114) drilled in the Tomsk structural-facies zone (Bakchar iron ore deposit) are presented. The obtained biostratigraphic data show that the sediments formed in the Campanian–Maastrichtian time interval. The high-temperature component of the remanent magnetization identified in the rocks allowed us to compile paleomagnetic columns for each well and correlate the columns, using paleontological data, with each other and with the general magnetostratigraphic and magnetochronological scales. In magnetostratigraphic sections of two wells, the Campanian reverse-polarity Slavgorod Formation (R(km)) with a normal-polarity horizon is correlated with Chron C33(r) (top) and C33(n) (bottom) of the Gradstein scale, and the Maastrichtian normal-polarity Gan’kino Formation with a thin reverse-polarity horizon (N(mt)) is correlated with Chron C30 of this scale.     

Multiscale modelling of rainstorm-induced historical intermediate floods (June–November) in the Rhone River Basin

This study reveals the changes and evolution of rainstorm-driven intermediate floods occurring and driving multiple damaging hydrological events in the Rhone River Basin (RRB), since 1500 until 2010. A parsimonious approach was developed to simulate the major hydroclimatological flood-producing forcing, the Multiscale Rainstorm Climate Model (STORMCLIMM). We collected the frequency of intermediate floods—a type of particularly hazardous floods commonly taking place between June and beginning of November—from the RCB to be compared to STORMCLIMM estimates. The latter, smoothed by a moving window of 21 years, results in a high-pass filter in the time domain, which magnifies the signal of forcing variations causing intermediate floods. The RRB showed large temporal variations in both extreme rainstorms and associated multidecadal intermediate-floods (MUDIF) frequency at different climatic periods and land-use systems through historical times. An important peak was observed in the Maunder Minimum (1645–1715 AD). The model allowed detecting MUDIF occurred in the historical times. The situation becomes interesting with respect to recent times, because the Rhone landscape looks more vulnerable in the last decades as a consequence of land-use changes and climate shift towards more erratic and intensive storms. This evidence suggests that the interactions of land-use and climatic changes may turn into considerable vulnerability to fluvial flooding and agro-ecosystem connected to them for upcoming years. The Rhone, for example, provides basis for use of hydrological indicators (such as the one represented by STORMCLIMM) for one site or region and which, through minor modifications, can be made relevant to specific needs.     

The north–south propagating spreading center of the North Fiji Basin. Modeling of the geochemical evolution in periodically replenished and tapped magma chambers

Summary Two main numerical approaches have been previously used to model the behavior of replenished and tapped magma chambers from geochemical data: 1) iterative computations, in which the magma evolution within steady-state reservoirs is modeled cyclically (P-RTF models); each cycle involves adding recharge magma, mixing the remaining liquid together, crystallizing the mixed product, then expelling part of the residual liquid (Model A); the expulsion can also take place after the mixing event but before crystallization (Model B); 2) continuous models (C-RTF models): in the corresponding time-dependent equations, the magma undergoes fractional crystallization with simultaneous replenishment of fresh liquid (Models C and D). A pertinent test of these models requires a cogenetic magmatic series having geochemical data that are not consistent with closed-system fractional crystallization. The northern tip of the north–south propagating spreading center, located in the North Fiji Basin between 18° and 19°S (NS-PSC 18–19°S), responds to this requirement. The lava ages range from 0 to 1Ma. The dredged volcanic rocks studied are cogenetic in a broad sense (constant isotopic and incompatible trace elements ratios). While no petrographic indications of wall-rock assimilation have been found, evidence of magma mixing has been observed in one basaltic sample (ribbon structures). The lavas, which are normal mid-ocean ridge basalts (N-MORBs), are distributed between three homogeneous compositional groups spatially ordered. The most differentiated lavas have a Fe-Ti basalt composition. We find that one version of open-system fractionation in a periodically replenished reservoir (Model B) is consistent with both the petrologic and geochemical data in explaining the formation of the two most mafic lava groups (Group 1, 64mg#61; Group 2, 59mg#52). In our model, the liquids expelled from a first magma chamber at the end of each cycle (Group 1 magmas) feed a second reservoir, which in its turn expels cyclically Group 2 liquids. A part of these expelled liquids are then stocked in a third closed-system magma chamber, where the Fe-Ti basalts (Group 3 lavas: 50mg#46) are generated through additional crystallization. Thus, the NS-PSC 18–19°S lavas seem to have been produced by three magma chambers interconnected by a sill (and/or pipe) network, ending in the last 18km of the northern tip. Consequently, only a small fraction of magma expelled from each open-system magma chamber reaches the surface as lava flows, because a fraction of it migrates from one reservoir to another. The off-axis sampling provides evidence for the persistence of open-system fractionation over time.Received January 23, 2002; revised version accepted May 31, 2003     

Age of granitoids in the Pripechora fault zone of the basement of Pechora Basin: First U–Pb (SIMS) data

Upper Precambrian basement of the Pechora Basin that is located between the Urals and Timan and is a part of the Pechora plate lies beneath 1–7 km of Ordovician-Cenozoic sediment cover. On the base of geophysical data and drilling the basement of the Pechora plate is subdivided into the Timan crustal block and the Bolshezemel crustal block which differ by composition and the character of magmatism. The boundary between the crustal blocks is a system of deep faults called the Pripechora and Ilych-Chikshino faults that strike in a northwestern direction, extending from the Urals to the Pechora Sea. Granitoids of Charkayu complex which were penetrated by several deep boreholes in Pripechora fault zone are interpreted as suprasubduction (island arc and collision) magmas associated with the Timan orogeny. First U–Pb dating (SIMS, using SHRIMP-II and SHRIMP-RG) of zircons from granitoids indicate that granitoid magmatism which accompanied the final stages of the Timanide orogeny occurred in the Late Vendian about 555–544 Ma. The age of zircons from granites of the 1-Charkayu borehole is 544 ± 6 Ma, from granites of 1-East Charkayu borehole is 545 ± 5 Ma, and from granodiorites of 1-South Charkayu borehole is 555 ± 2 Ma.     

Geochemical evolution of groundwater in the Cambrian–Vendian aquifer system of the Baltic Basin

The shallowly buried marginal part of the Cambrian–Vendian confined aquifer system of the Baltic Basin is characterised by fresh and low δ¹⁸O composition water, whereas the deeply settled parts of the aquifer are characterized by typical Na–Ca–Cl basinal brines. Spatial variation in water geochemistry and stable isotope composition suggests mixing origin of the diluted water of three end-members—glacial melt water of the Weichselian Ice Age (115 000–10 000 BP), Na–Ca–Cl composition basin brine and modern meteoric water. The mixing has occurred in two stages. First, the intrusion and mixing of isotopically depleted glacial waters with basinal brines occurred during the Pleistocene glacial periods when the subglacial melt-water with high hydraulic gradient penetrated into the aquifer. The second stage of mixing takes place nowadays by intrusion of meteoric waters. The freshened water at the northern margin of the basin has acquired a partial equilibrium with the weakly cemented rock matrix of the aquifer.     

Characterization of a karstic aquifer using magnetic resonance sounding and electrical resistivity tomography: a case-study of Esta?a Lakes (northern Spain)

The geophysical characterization of a previously unstudied endorheic karstic system is presented. The studied area, known as the Esta?a Lakes, is located in the Pyrenean Marginal Sierras, northern Spain. The Esta?a Lakes are a set of natural water ponds on a bedrock of Triassic evaporites, lutites and carbonates. This wetland is included in the Natura 2000 European network of nature protection areas as a “Site of Community Importance”. Two geophysical techniques were used, magnetic resonance sounding (MRS) and electrical resistivity tomography (ERT), to map the subsurface geology and characterize the aquifer layers and the hydraulic links between the aquifers and lakes. The geophysical data were integrated with the surface geology and data from six boreholes. Ten electrical profiles were performed to identify the thickness of the units and lithological changes, whereas the MRS was used to determine the top of the saturated zone. As result, the aquifer in the Esta?a Lakes system and surrounding area has been identified as Middle Triassic carbonates, which does not correspond with the regional aquifer in the area (Upper Cretaceous and Eocene). This work shows the power of geophysical methods in poorly understood and tectonically complex areas in addition to the standard aquifer tests to evaluate hydraulic properties.     

Use of a new method for determining the vulnerability and risk of pollution of major groundwater reservoirs in the region of Annaba–Bouteldja (NE Algeria)

Scientists are deeply concerned by the state of vulnerability of groundwater reservoirs. It is a complex task because of the difficulties in determining the degree of pollution of the groundwater. Many methods have been adopted like (DRASTIC, GOD, SI, SINTACS…). Another method (Kherici et al. in Geogr Tech 1–14, 2010) is added to identify the vulnerability of groundwater reservoirs and control the evolution of pollutants. The present article targets the determination of the vulnerability and risks of pollution of groundwater reservoirs of a climatic Mediterranean region (Annaba–Bouteldja region). The device used is based on the combination of two criteria: natural factors (thickness of the unsaturated zone, geological facies and degree of self-purification) and the causes of vulnerability and the pollution risks entropic factors (caused by man). The application of Kherici’s method has revealed a distinction between the different degrees of pollution and has allowed a neat classification of the different reservoirs in the study. The results lead to a vulnerability map and the risks of pollution of Annaba–Bouteldja different aquifers. It has also led to the installation of protection areas; sustained by an efficient general evacuation plan of the sewerage net and the construction of treatment station of the sewage effluents in the urbanized areas.     

Origin of petroleum in the Neoproterozoic–Cambrian South Oman Salt Basin

The South Oman Salt Basin (SOSB) is host to the world’s oldest known commercial deposits. Most of the South Oman oils have been proven to be associated with the source rocks of the Neoproterozoic to Cambrian Huqf Supergroup, but the assignment of oils to specific Huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire Huqf sequence, possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition. This study was conducted to establish improved correlations between organic-rich rock units and reservoir fluids in the SOSB through detailed molecular and isotopic analysis of the Huqf Supergroup, with special emphasis directed towards understanding the Ara carbonate stringer play.Unusual biomarkers, tentatively identified as A-norsteranes, show distinctive patterns among carbonate stringer oils and rocks different from those observed in Nafun sediments and Ara rocks from the Athel basin. These putative A-norsteranes form the basis for new oil-source correlations in the SOSB and provide for the first time geochemical evidence of a self-charging mechanism for the carbonate stringer play. The paucity of markers specific to the Nafun Group (Shuram, Buah and Masirah Bay formations) confounds attempts to quantify their respective contributions to Huqf oil accumulations. Nafun inputs can only be determined on the basis of subtle differences between Nafun and Ara biomarker ratios. The most useful geochemical characteristics delineating Nafun Group organic matter from Ara Group intra-salt source rocks included: low relative abundance of mid-chain monomethyl alkanes (X-compounds); low relative abundance of gammacerane, 28,30-dinorhopane, 25,28,30-trinorhopane and 2-methylhopanes; low C₂₂T/C₂₁T and high C₂₃T/C₂₄T cheilanthanes ratio values. Based on these parameters, molecular evidence for major contributions of liquid hydrocarbons from Nafun Group sediments (Shuram, Buah and Masirah Bay formations) is lacking. Our results suggest that the majority of SOSB hydrocarbon accumulations originate from within the Ara group, either from the carbonate stringers or from the package of sediments that comprises the Thuleilat, Athel Silicilyte and U shale formations. Subtle aspects of the composition of some carbonate stringer and post-salt Huqf oils could suggest some degree of sourcing from the Nafun rocks but stronger evidence is needed to confirm this.