Contamination of harbor sediments in the eastern Gulf of Finland (Neva Bay), Baltic Sea

 The areal distribution of oil products and various trace metals have been studied in bottom surface deposits from the harbors of Neva Bay. The data of contents were normalized to natural background concentrations. Also the size and biomass of benthos groups were analyzed. The results show clearly that industrial discharges have elevated levels of contamination in the sediments. Few efficient measures against environmental contamination have been taken. The sediments contain very high concentrations of oil products and such heavy metals as Hg, Pb, Cu, and Zn. The benthic organisms most sensitive to heavy metal contamination are Chironomidae. The dredging and dumping of the contaminated deposits can lead to secondary contamination of the Gulf of Finland and the Baltic proper. Received: 18 November 1996 · Accepted: 17 March 1997     

Hydrochemistry of aquifers in the southern Dead Sea area,southern Jordan

 The demand for water resources in the area south of the Dead Sea due to continued development, especially at the Arab Potash Company (APC) works necessitates that water quality in the area be monitored and evaluated based on the local geology and hydrogeology. The objective of this paper is to provide information on the past and present status of the main aquifers under exploitation or planned for future development. Two main aquifers are discussed: the Safi water field, presently being operated, and the Dhiraa water field, which is being developed. The aquifer developed in the Safi water field is shallow and fed by the Hasa fault system, which drains a significant portion of the Karak mountains. This aquifer seems to be well replenished within the core, where no obvious long-term degradation in water quality can be identified. However, in the low recharge areas within the distal portions of the alluvial fan, there has been a degradation in water quality with time. The degradation is caused by the dissolution of the Lisan Marl, which is present at the outskirts of the fan system, based on hydrochemistry of water in the wells. The Dhiraa field is a deep (800–950 m) aquifer drilled specifically for the extraction of brackish water present in the Kurnub aquifer. Available data indicate that there are at least three distinct water types within this field. These water types are variable in quality, and there may be potential for mixing of these waters, thus affecting the quality of the freshest waters presently available. Tritium and oxygen isotope analysis indicate that the water is old and possibly nonrenewable. Received: 24 July 1995 · Accepted: 26 September 1995     

南海南部北康盆地生物礁的类型及油气勘探前景

南海南部北康盆地发育大量的生物礁,蕴藏丰富的油气资源。文章基于北康盆地高精度地震数据及钻井数据的研究表明,北康盆地的生物礁成像较好、类型齐全,有点礁、台地边缘礁、块状礁、层状礁、塔礁、环礁共6类型。其发育演化可以分为4个阶段,分别为早中新世的初始发育阶段、中中新世早期的繁盛阶段、中中新世晚期的衰退阶段和晚中新世的淹没阶段。古近纪及早中新世的断裂活动产生了大量的构造高点,为生物礁的初始发育创造了条件,而中中新世以来基底快速沉降导致的相对海平面的快速上升决定了生物礁主要发育于中中新世时期,而晚中新世以来相对海平面持续上升,致使生物礁退积到隆起顶部,从而进入淹没阶段。北康盆地的生物礁数量多、规模大,而且很少受后期成岩作用的二次改造,具备优质储层形成的前提。同时,区域烃源岩、疏导体系、盖层及生物礁的分布等油气地质条件,决定了中部隆起西部和东部隆起东部是北康盆地今后生物礁油气勘探的重点区域。     

Radiochemistry of sediments from the southern Dead Sea, Jordan

 A sediment core from the southern Dead Sea was analyzed using gamma spectroscopy as well as ²¹⁰Pb dating in order to ascertain if any radioactive contamination could be detected and to determine the sedimentation rates in the area. Results of this study show no presence of man-made radionuclides in the area. Sedimentation rates were determined to be between 0.25 and 0.4 g/cm²/year. (∼0.5 cm/year), which is in line with what would be expected assuming carbonate layers are annual varves. Received: 31 January 1997 · Accepted: 11 March 1997     

The Early and Middle Miocene transgression at the southern border of the North Sea Basin (northern Belgium)

The Lower–Middle Miocene Berchem Formation of northern Belgium is an essentially sandy sequence with a varying glauconite content and often abundant shelly intervals. The formation was deposited in a shallow marine environment and rests unconformably on stiff Rupelian clays or Chattian sands. The lithological recognition of the four members (Edegem Sands, Kiel Sands, Antwerpen Sands and Zonderschot Sands members) of the Berchem Formation solely based on lithological criteria proved to be difficult, especially in boreholes. The geometry of the Formation in the subsurface of northern Belgium remained largely unknown. Diverse and well preserved dinoflagellate cyst associations have been recovered from the four members in seven boreholes and two outcrops, and allow a refinement of the biostratigraphy of these deposits. A Miocene biozonation defined in mid‐latitude shallow marine deposits in the Atlantic Coastal Plain of the USA (Salisbury Embayment, Maryland) is readily applicable to this material, and has led to a detailed stratigraphic assessment of each member. Three detailed profiles depicting the distribution of the biozones in the subsurface of northern Belgium allow the reconstruction of the geometry and depositional history of the Berchem Formation. The oldest Miocene deposits are of early Burdigalian age and they testify to a transgression, which invaded Belgium from a north–northwestern direction. The maximum flooding took place during early Serravallian times. The upper boundary of the formation is a major erosional surface of late Serravallian or (slightly) younger age. Copyright © 2005 John Wiley & Sons, Ltd.     

Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)

Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS ¹⁴C data and biostratigraphic information were gathered. Based on this multi‐proxy approach, seven lithostratigraphic units (AI, AII, B to F) were distinguished. These consist of fine‐grained clay, silt and mud, and are separated from each other by thin basin‐wide traceable sandy layers (S_ab‐S_ef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain‐size fraction >63μm. In addition, some of the quartz‐grain‐dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin‐wide water‐level low‐stand conditions. These low stands resulted from water‐level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine‐grained units AI, AII to F, in which coarser material is absent, represent water‐level high‐stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen‐1 regression, respectively. We assign the most prominent sandy layer S_ab to the final drainage of the Baltic Ice Lake (Billingen‐2), whereas the sandy layers between units B, C., D and E are related to the Yoldia Sea and Ancylus Lake regressions of the Baltic Sea's history. The uppermost fine‐grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well‐visible sediment colour change from reddish/brown‐to‐grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised.     

Groundwater discharge to the Gulf of Finland (Baltic Sea): ecological aspects

The Gulf of Finland lies in the eastern part of the Baltic Sea. The surface area is 29,700 km² and the average depth of the basin is 38 m. Groundwater discharge to the Gulf of Finland equals 0.6 km³/year and this discharge is composed of many different chemical compounds. Groundwater discharge into the Gulf of Finland is dispersal. The coastal area of the Gulf of Finland can be divided into four zones with different geological, hydrogeological and discharge properties. The amount of direct groundwater discharge to the sea may be estimated using several geological and hydrogeological methods.     

Dinoflagellate cyst biostratigraphy of the Upper Miocene Deurne Sands (Diest Formation) of northern Belgium,southern North Sea Basin

Diverse and well‐preserved palynomorph assemblages recovered from the Deurne Sands, a local member of the Upper Miocene Diest Formation near Antwerp, allow the recognition of dinoflagellate cyst biozones defined in the North Atlantic realm (East Coast, USA) and the North Sea region (Nieder Ochtenhausen well, northern Germany). Based on the dinoflagellate cyst assemblages and the calcareous microfossils, the deposition of the Deurne Sands took place at some time during middle to late Tortonian (Late Miocene). These sands can be correlated biostratigraphically with the Dessel Sands in the Campine area of northern Belgium. This correlation demonstrates the existence of two separate and contemporary depositional areas in northern Belgium during early Late Miocene times. Copyright © 2002 John Wiley & Sons, Ltd.     

Holocene sea-level changes and glacio-isostasy in the Gulf of Finland, Baltic Sea

Shoreline displacement in the eastern part of the Gulf of Finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in Virolahti in southeastern Finland and on the Karelian Isthmus, and in Ingermanland in Russia. Study methods were diatom analyses, sediment lithostratigraphical interpretation and radiocarbon dating. In southeastern Finland, the marine (Litorina) transgression maximum occurred ca. 6500–6200 ¹⁴C yr BP (7400–7100 cal. yr BP). In areas of the slower land uplift rate on the Karelian Isthmus and in Ingermanland, the transgression maximum occurred ca. 6400–6000 ¹⁴C yr BP (7300–6800 cal. yr BP). The highest Litorina shoreline is located at ca. 23 m above present sea-level in southeastern Finland, whereas in the eastern part of the Karelian Isthmus, near St. Petersburg, it is located at ca. 8 m above present sea-level. The amplitude of the Litorina transgression in Virolahti area is ca. 4 m, whereas on the Karelian Isthmus and in Ingermanland the amplitude has varied between 5 and 7 m. The regional differences between areas are solely due to different glacio-isostatic land uplift rates. The seven basins studied in this research were connected to the Baltic Sea basin during the Litorina Sea stage and their diatom and lithostratigraphical records indicate a single, smooth Litorina transgression.     

Arsenic in framboidal pyrite from recent sediments of a shallow water lagoon of the Baltic Sea

Arsenic is a redox‐sensitive element of environmental relevance and often enriched in iron sulphides. Because sediments from the Achterwasser lagoon, a part of the estuarine system of the river Oder, south‐west Baltic Sea, show unexpectedly high pyrite concentrations of up to 7·5 wt% they were used to investigate the influence of authigenic pyrite on the mobility and burial of As in the coastal environment. Micro‐X‐ray‐fluorescence measurements of 106 micrometre‐sized pyrite framboids from the anoxic sediments show highly variable As concentrations ranging from 6 to 1142 μg g^?1. Even within a 1 cm thick layer, the As concentration of different framboids varies greatly and no clear depth trend is visible throughout the 50 cm long sediment core. Pyrite can account for 9 to 55% (average 22%) of the total As budget of the sediments and the degree of trace metalloid pyritization for As ranges from 26 to 61%, indicating that authigenic pyrite formation is an important process in the geochemical cycling of As in coastal sediments. High‐resolution micro‐X‐ray fluorescence mapping of single pyrite grains shows that As is distributed inhomogeneously within larger framboids, suggesting changing pore water composition during pyrite growth. X‐ray absorption near edge structure spectra indicate that As is usually present as As(‐I) substituting S in the pyrite lattice. However, in samples close to the sediment/water interface a considerable part of As is in higher valence states (+III/+V). This can be explained by frequent re‐suspension of the surficial sediments to the oxic water column due to wave action and subsequent re‐deposition, leading to the adsorption of As oxyanions onto pyrite. Although reduced As(‐I) becomes more important in the deeper samples, reflecting decreasing redox potential and a longer time since deposition, the occurrence of oxidized As species (AsIII/AsV) in pyrite in the anoxic part of the sediment suggests formation under dysoxic conditions.     

The Influx of the Tsushima Current into the Central Ulleung Basin of East Sea (Sea of Japan), Korea

A total of 85 samples, collected from the UBGH1-9 core taken from the Ulleung Basin, East Sea, Korea, were analyzed using diatom assemblages. 111 diatom species belonging to 46 genera were identified, and three diatom assemblage zones were established on the basis of occurrence and distribution pattern of diatoms. Diatom assemblage zone I(134.10–174 m) is characterized by a relatively high abundance of marine species, while the increased number of the brackish species is recorded in diatom assemblage zone II(75–125 m). The assemblage zones IIIa became drastic drop of valve abundances and brackish planktons, whereas it became increase during the IIIb. High Td values which indicate an influence of warm current are recorded both in diatom assemblage zone I and III, and low Td values in diatom assemblage zone II. Analysis of diatom assemblages indicating that the depositional condition moved from oceanic to littoral-neritic environments and that paleotemperature underwent a shift from warm to cold condition at the middle interval, and from cold to warm condition in the upper interval of the UBGH1-9 core. This suggests that the lower(130–162 m) and upper intervals(0–20 m) of the UBGH1-9 core were deposited in the warm current condition(Tsushima Warm Current).     

Geochemical assessment of hydrocarbon migration phenomena: Case studies from the south-western margin of the Dead Sea Basin

Calcite veins with fluid and solid bitumen inclusions have been discovered in the south-western shoulder of the Dead Sea rift within the Masada-Zohar block, where hydrocarbons exist in small commercial gas fields and non-commercial fields of heavy and light oils. The gas–liquid inclusions in calcite are dominated either by methane or CO₂, and aqueous inclusions sometimes bear minor dissolved hydrocarbons. The enclosed flake-like solid bitumen matter is a residue of degraded oil, which may be interpreted as “dead carbon”. About 2/3 of this matter is soot-like amorphous carbon and 1/3 consists of n-C₈C₁₈ carboxylic acids and traces of n-alkanes, light dicarboxylic acids, and higher molecular weight (>C₂₀) branched and/or cyclic carboxylic acids. Both bitumen and the host calcites show genetic relationship with mature Maastrichtian chalky source rocks (MCSRs) evident in isotopic compositions (δ¹³C, δ³⁴S, and δ¹⁸O) and in REE + Y patterns. The bitumen precursor may have been heavy sulfur-rich oil which was generated during the burial compaction of the MCSR strata within the subsided blocks of the Dead Sea graben. The δ¹⁸O and δ¹³C values and REE + Y signatures in calcites indicate mixing of deep buried fluids equilibrated with post-mature sediments and meteoric waters. The temperatures of fluid generation according to Mg–Li-geothermometer data range from 55 °С to 90 °С corresponding to the 2.5–4.0 km depths, and largely overlap with the oil window range (60–90 °С) in the Dead Sea rift (Hunt, 1996; Gvirtzman and Stanislavsky, 2000; Buryakovsky et al., 2005). The bitumen-rich vein calcites originated in the course of Late Cenozoic rifting and related deformation, when tectonic stress triggers damaged small hydrocarbon reservoirs in the area, produced pathways, and caused hydrocarbon-bearing fluids to rise to the subsurface; the fluids filled open fractures and crystallized to calcite with entrapped bitumen. The reported results are in good agreement with the existing views of maturation, migration, and accumulation of hydrocarbons, as well as basin fluid transport processes in the Dead Sea area.     

Identification of rumanite (Romanian amber) as thermally altered succinite (Baltic amber)

 Romanian amber (rumanite) has been considered to be a separate species of fossil resin for more than a century. While earlier investigators held it to be very similar to succinite (Baltic amber), modern scholars have assigned it a distinctly different botanical origin. We have found that almost all of the constituents of the ether-soluble fractions of 13 specimens of authentic rumanite identified by gas chromatography–mass spectrometry have previously been reported in the soluble fraction of succinite, including succinic acid and its monoterpene esters. Additionally and significantly, the soluble fraction of rumanite contains a number defunctionalized compounds that do not preexist in succinite, but that are produced by pyrolysis of whole succinite or of its insoluble polymeric fraction. Simultaneous methylation pyrolysis–gas chromatography–mass spectrometry of the polymeric fraction of seven of the rumanite specimens yielded further copious amounts of dimethyl succinate, a number of diterpene resin acid methyl esters, and additional defunctionalized compounds known to be pyrolysis products of succinite. The evidence shows conclusively that the botanical origin of rumanite is not distinct from that of succinite. Rather, rumanite is a succinite that has suffered partial thermal degradation in the course of the folding of the Oligocene Kliwa sandstone formation in which it is most commonly found. Received: 30 December 1999 / Accepted: 16 May 2000     

Hydrogeologic and hydrochemical framework of the shallow groundwater system in the southern Voltaian Sedimentary Basin, Ghana

 The southern Voltaian Sedimentary Basin underlies an area of about 5000 km² in east-central Ghana. Groundwater in the basin occurs in fractures in highly consolidated siliciclastic aquifers overlain by a thin unsaturated zone. Aquifer parameters were evaluated from available aquifer-test data on 28 shallow wells in the basin. Hydraulic-conductivity values range from 0.04–3.6 m/d and are about two orders of magnitude greater than the hydraulic conductivity calculated using Darcy's Law and the average groundwater velocity estimated from carbon-14 dating. Linear-regression analysis of the transmissivity and specific-capacity data allowed the establishment of an empirical relationship between log transmissivity and log specific capacity for the underlying aquifers. Groundwater chemistry in the basin is controlled by the weathering of albitic plagioclase feldspar. The weathering rates of various minerals were estimated using ¹⁴C-derived average velocity in the basin. The weathering rate of albite was calculated to be 2.16 μmol L^–1 yr^–1 with the resulting formation of 3.3 μmol L^–1 yr^–1 of kaolinite and 0.047 μmol L^–1 yr^–1 of calcite. The low porosity and permeability of the aquifers in the basin are attributed to the precipitation of secondary minerals on fracture surfaces and interlayer pore spaces. Received, September 1997 Revised, July 1998, August 1998 Accepted, August 1998     

Dinoflagellate cyst stratigraphy and palaeoenvironment of the marginal marine Middle and Upper Miocene of the eastern Campine area,northern Belgium (southern North Sea Basin)

A stratigraphical and palaeoenvironmental analysis with organic‐walled palynomorphs of the Bolderberg and Diest formations provides new insights in the depositional history during Miocene times at the southern border of the North Sea Basin. The Neogene transgression invaded Belgium from a north–northwestern direction and fully marine sediments were deposited in the northern part of Belgium. The age and the palaeoenvironment of the deposits at the very border of the southern North Sea Basin remained till a few decades ago incomplete. The recovered dinoflagellate cysts, acritarchs and green algae from the Bolderberg Formation in the Wijshagen Borehole indicate a marginal marine depositional environment during late Burdigalian and Langhian times in the eastern Campine area, in contrast to the deeper marine conditions prevailing to the north–northwest. The relative dating of the Bolderberg Formation confirms that maximum flooding occurred during Langhian to early Serravallian times. Deposition apparently took place during the Middle Miocene Climatic Optimum, and ended when the climatic deterioration set in at around 14 Ma. A hiatus spanning ca. 2 Ma separates the Middle Miocene Bolderberg Formation from the Upper Miocene Diest Formation in the eastern Campine area at the border of the North Sea Basin. Copyright © 2007 John Wiley & Sons, Ltd.     

Potential source rocks, organic geochemistry and thermal maturation in the southern depocenter (Kipourio–Grevena) of the Mesohellenic Basin, central Greece

The study area is the southern depocenter (depth > 4200 m) of the Mesohellenic Basin which extends between Kipourio and Grevena, central Greece. The Mesohellenic Basin is a Middle-Tertiary intramontane basin developed within the Hellenide orogen. Previous studies have focused on the depositional environments, configuration and hydrocarbon potential of the basin. In this paper we present additional geochemical and petrographic data from outcrop samples of the basin's southern depocenter, which is considered the most promising area, in terms of hydrocarbon prospectivity. A total number of thirty six samples were analysed: Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance and thermal alteration index, bitumens extraction, liquid chromatography, and GC-MS. The samples were collected from deltaic deposits and submarine fan sediments of Late Eocene to Late Oligocene age. The TOC values of the analysed samples range between rich and very rich and the organic matter consists mainly of type III kerogen and the organic matter consider to be predominately gas prone. The thermal maturity assessed from T_max and vitrinite reflectance shows an immature stage of the organic matter along with the presence of layers having reached the very early mature stage. Vitrinite reflectance measurements and maturity calculations (applying the Lopatin modeling), reveal that the lower part of the depocenter sediments falls within the ‘oil window’. The extractable organic matter (EOM) (mg bitumens/g TOC) indicate the existence of samples (from deltaic deposits) with high ratio of transformation (EOM) (> 100 mg bitumen/g TOC). The GC and GC-MS analyses of the biomarkers indicate mainly the occurrence of terrestrial organic matter reflecting oxidizing conditions and both immature and very early mature stages. The results of the Rock-Eval pyrolysis and the distribution of the isoprenoids support the assumption of the input of an organic matter mixture.     

Endangering of the Upper Jurassic karst-fissured aquifer in the Krakow Upland (southern Poland)

 A karst-fissured aquifer in the Upper Jurassic carbonate rocks of the Krakow Upland shows a very high yield (safe yield 117 000 m³/day) and belongs to the major groundwater basins (MGBs) of Poland. The uncovered character of the aquifer and its hydraulic structure favor the intensive infiltration and migration of anthropogenic pollutants from the surface. This pollution is caused by agriculture and industry in the proximity of Krakow and the Upper Silesian agglomeration. Progressive degradation of groundwater quality on a regional scale results. Evaluation of the endangering of the aquifer studied is based on the analysis of the time interval of vertical water percolation from the surface, the time interval of groundwater horizontal flow through the aquifer and the duration of water residence in the aquifer derived from tritium data. Quaternary and Cretaceous overburden occur in the Krakow Upland in addition to numerous outcrops of limestones. The time interval of vertical water percolation in highly permeable limestones does not exceed 3 years and in the areas covered by overburden it is from several to 50 years. The mean effective time interval of horizontal groundwater flow through the Upper Jurassic rocks along the flow paths ranges from several months in the areas of direct drainage to over 15 years in the elevated areas of local groundwater divides. The age of water in the rock matrix was determined using tritium data interpreted according to an exponential model and it ranges from 70 years to over 130 years. In karst-fissured systems with a high retardation index (R_p=21) the effective time of water circulation in local drainage basins does not exceed 7 years. The Krakow-Wieluń Upland is the most extensive and uniform karst region in Poland. It is a belt of Upper Jurassic limestone extending from Krakcow in the southeast to Wieluń in the northwest on the northeast slope of the Silesian Upland. Residual hills of Paleogene age separated by infilled karst depressions are the most characteristic features of the Krakow-Wieluń Upland. More than 800 small caves are known in this area, but only two of them reach 1 km of aggregate passage length (Gazek and others 1992). Received: 4 December 1996 · Accepted: 29 April 1997     

Land subsidence due to groundwater withdrawal: potential damage of subsidence and sea level rise in southern New Jersey, USA

 Land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region. Groundwater withdrawal results in fluid pressure change in the layers. The pressure change in the layers induces both elastic and inelastic land compaction. The elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent. Groundwater response to barometric pressure change is used to estimate the elastic compaction in this study. The storativity, specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal. The discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern New Jersey. The estimated subsidence is about 2–3 cm near the location of monitoring wells in Atlantic, Camden, Cumberland and Cape May Counties over the past 20 years. If the current trend of water-level drop continues, the average subsidence in southern New Jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years. The rise of global sea level is about 2 mm/year on average. Because of the very gentle slope in southern NJ, the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period. This combination will also accelerate the coastal flooding frequency and the erosion rate of the New Jersey coastal plain, and pose a serious threat to the coastal economy. Received: 15 December 1997 · Accepted: 30 June 1998     

The impact of human activities in the Malia coastal area (Crete) on groundwater quality

The evaluation of the long-term effects of seawater intrusion into the aquifers due to negative water balance and nitrate pollution of drinking-water quality due to human activities requires detailed knowledge of both the transport of the chemical constituents and the geochemical processes within aquifers. Hydrogeological and hydrochemical studies in the unconfined aquifer of Malia have provided the necessary data to define the areas at increased risk from these phenomena. The solution of the second Fick's low under given boundary conditions gave an estimate of the propagation of groundwater pollution by NO₃ ^–. Additionally, in order to simulate the ion concentration changes during a period, for example a period of positive water balance or refreshening, groundwater transport and cation exchange reactions were modelled using the code PHREEQM. Received: 25 July 1997 · Accepted: 4 November 1997     

Detection of subsurface brines, freshwater bodies and the interface configuration in-between by the time domain electromagnetic method in the Dead Sea Rift, Israel

 High radon fluxes in the seismically active Dead Sea Rift seem to be affected by the hydrological system and the different salinities of groundwater bodies involved. The time domain electromagnetic (TDEM) method was employed to delineate those different bodies and the configuration of the interfaces between them. The present hydrological system and the related brines and interfaces are controlled by the Dead Sea base level, presently at 408 m below MSL. TDEM measurements detect low resistivity (<1 ohm/m) units representing brines and the interface between them as well as the overlying fresher water bodies. In addition, high resistivity (freshwater) units are also detected, underlying the brines, related herein to a multiple hydrological system. Low-resistivity brines, detected above the present base level, are interpreted herein as yet unflushed ones which correspond to a former higher base level. Higher sequences, below historical (sixteenth century) base levels, are already devoid of brines, which gives an indication as to the rate of flushing. Received: 3 June 1996 / Accepted: 23 July 1996