salinization in coastal aquifers of arid zones an example from santo domingo baja california sur mexico groundwater quality in the santo domingo irrigation district area in baja california sur mexico indicates the presence of various salinization processes 1 the geological matter of marine origin comprising the aquifer material suffers diagenetic effects due to its interaction with groundwater of low salinity 2 the effects of intensive agriculture practices produce effluents that infiltrate to the saturated zone and 3 the extraction of groundwater causes modifications in the natural flow system induces lateral flow of seawater from the coast line however groundwater management has been carried out with the belief that the latter is the main source of salinization this has resulted in a policy of installing wells increasingly far from the coast which is not solving the problem irrigation return and seawater that remains in the geological units have been identified as major sources of salinization controls should be imposed when installing wells in contact with clayey units that form the base of the aquifer extracted groundwater consists of a mixture of 1 groundwater of relatively low salinity that circulates in the aquifer and 2 an extreme member with salinity different to seawater contained mainly in formations that have low permeability which limits the aquifer underneath the geochemistry of carbonates and cation exchange reactions both direct and reverse control the concentration of ca mg na and hco3 as well as ph values the concentrations of dissolved trace elements f li ba sr suggest that the extreme saline member is different from the average seawater composition a distinction between the salinization caused by farming practices and that blamed on seawater is defined by the use of no3

ore genesis of pb zn deposits in the nappe zone of northern tunisia constraints from pb s c o isotopic systems abstract the jalta and jebel ghozlane ore deposits are located in the extreme north of tunisia within the nappe zone the mineralization of jalta hosted in triassic dolostones and the overlying mio pliocene conglomerates consists of abundant galena barite and cerussite with accessory sphalerite pyrite and jordanite at jebel ghozlane large pb zn concentrations occur in the triassic dolostones and eocene limestones the mineral association consists of galena sphalerite barite and celestite and their oxidation products cerussite smithsonite and anglesite lead isotope ratios in galena from both districts are relatively homogeneous 206 pb 204 pb 18 702 18 823 207 pb 204 pb 15 665 15 677 208 pb 204 pb 38 725 38 875 the 34 s values for sulfates from both areas 12 2 to 16 2 at jalta and 14 3 to 19 4 at jebel ghozlane are compatible with a derivation of sulfur from marine sulfates possibly sourced from the triassic evaporites the 34 s values of the sulfides have a range between 10 and 12 5 at jalta and between 9 1 and 22 1 at jebel ghozlane the large range of values suggests reduction of the sulfate by bacterial and or thermochemical reduction of sulfate to sulfur the high 34 s values of sulfides require closed system reduction processes the isotopically light carbon in late calcites 6 3 to 2 5 and authigenic dolomite 17 6 suggests an organic source of at least some of the carbon in these samples whereas the similarity of the 18 o values between calcite 24 8 and the authigenic dolomite 24 7 of jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates the secondary calcite isotope compositions of jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200 c but temperatures as low as 50 c may be indicated by the late calcite of jebel ghozlane 18 o of 35 9 given the geological events related to the alpine orogeny in the nappe zone nappe emplacement bimodal volcanism and reactivation of major faults such as ghardimaou cap serrat and the neogene age of the host rocks in several localities a late miocene age is proposed for the pb zn ore deposits considered in this study remobilization of deep seated primary deposits in the paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the nappe zone as a whole

metallogenesis of the siding pb zn deposit in guangxi south china rb sr dating and c o s pb isotopic constraints abstract the siding pb zn deposit is located in the transition zone between the yangtze craton and the cathaysian block on the southwestern margin of the jiangnan orogenic belt and is a representative example of the pb zn deposits found in northern guangxi south china in this study sphalerite rb sr dating and c o s pb isotope analyses were used to investigate the mineralization age and source of the ore forming minerals in the siding pb zn deposit the 13cpdb and 18osmow values of the gangue mineral calcites were determined to be between 5 0 and 1 1 average 2 6 and between 13 2 and 18 4 average 16 4 respectively these values are roughly consistent with those of the carbonate minerals in the ore hosting strata namely 1 63 to 0 83 average 0 34 and 19 0 22 0 average 20 9 respectively indicating a mainly sedimentary origin of the ore forming fluids the 34s values of the ore minerals were determined to be 17 1 to 5 1 average 2 6 while they were 8 6 to 5 1 average 0 8 for sphalerite 7 8 to 2 7 average 1 6 for galena and 17 1 to 2 3 average 7 3 for pyrite the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of the sulfides pyrite galena and sphalerite were determined to be 18 12 18 76 average 18 50 15 66 15 97 average 15 80 and 38 36 39 71 average 38 96 respectively which are consistent with those of limestone in the region 206pb 204pb 17 65 18 77 207pb 204pb 15 60 15 91 and 208pb 204pb 37 82 39 59 pb and s isotope analyses showed that the ore forming materials originated from the crust as also substantiated by the 87sr 86sr i ratios 0 710806 0 713740 of the sphalerite the isochron age determined by rb sr dating was 360 5 0 ma indicating the formation of the siding deposit in the late devonian hercynian period this mineralization age substantially differs from those determined for the dachang tongshanling huangshaping and shuikoushan pb zn deposits on the southern margins of the jiangnan orogenic belt but is comparable with those of the adjacent daliangzi bokouchang and dadongla pb zn deposits in northeastern guizhou we therefore propose that the formation of the siding pb zn deposit is related to a basin scale fluid flow induced by late devonian extensional rifting in south china in response to the tectonic evolution of the southwestern yangtze craton

provenance of early bronze age metal artefacts in western switzerland using elemental and lead isotopic compositions and their possible relation with copper minerals of the nearby valais abstract ten early bronze age bza1 2200 2000 bc copper artefacts from the central valais region from switzerland were studied for their elemental composition and lead isotope ratios in order to answer the archaeological question of a local copper supply a database for copper minerals across the valais switzerland has been established this database contains 69 data on lead isotope ratios as well as additional information on the minerals and geochemical associations for copper minerals from 38 locations in the valais comparisons of the artefacts were also made with data pertaining to minerals from various deposits from europe and anatolia taken from the literature the provenance of the materials is very diverse some of the data are compatible with the data from the copper mineral deposits of the valais region moreover three copper lunulae were identified as possibly tuscan which suggests contacts between italy and the valais region this pattern also establishes a multiplicity of provenances for the metal and cultural influences in the alpine environment of the rhone valley of switzerland at the beginning of the early bronze age

crustal structure of the sheared southwestern barents sea continental margin abstract eighteen expanding spread profiles from the southwestern barents sea continental margin were studied with a variety of seismic interpretation techniques and in conjunction with seismic reflection data the velocity depth profiles from the slope intercept herglotz wiechert and sum methods were compared and contrasted to the velocity depth curve calculated from the iterative forward modelling of the amplitudes the velocity depth profiles derived from the sum and forward modelling of the amplitudes were used to produce synthetics in both the x t and p domains to choose the technique that most accurately represented the data the results showed the oceanic crust at the senja fracture zone to be different from standard oceanic crust with a higher than average velocity for layer 2 of 5 7 6 4 km s 1 and slightly smaller crystalline crustal thickness the continent ocean transition at crustal depths was shown to be narrow in the range of 10 20 km our results were consistent with two different crustal provinces east of the senja fracture zone the tertiary marginal basin and the cretaceous basin region the velocity depth curves enabled us in a gross sense to suggest the depths to deep sedimentary interfaces and the top of the crystalline crust that were normally not observed in the reflection profiles depths down to 20 km were inferred for the base of the sedimentary section in the southwestern barents sea the crust thinned gently towards the continent ocean boundary at the senja fracture zone whereas the crustal thickness changed abruptly below the hornsund fault zone at the margin farther north we associated the change in crustal structure with cenozoic in the thick crust beneath the svalbard platform in the north the depths to mantle determined on the shelf were consistent with that observed on a deep multichannel seismic line that crosses the area

geophysical insights and early spreading history in the vicinity of the jan mayen fracture zone norwegian greenland sea abstract using a new high resolution aeromagnetic survey jas 05 that was acquired along the trend of the jan mayen fracture zone jmfz west of the voring volcanic margin we investigated the geodynamic framework of the early spreading evolution of the norwegian greenland sea the tectonic structure main faults and magnetic chrons have been reinterpreted based on new magnetic gridded data and integrated with bathymetry gravity and seismic data the new interpretation reveals more details about the early spreading history of the norwegian greenland sea in the vicinity of the jmfz although anomalous melt production seaward dipping reflectors underplating associated with the breakup of the mid norwegian margin has been described in many studies we present data that suggest that significant magmatism continued episodically during the opening of the norwegian greenland sea along the trend of the jmfz the voring spur vs an anomalous oceanic high lying north of the eastern segment of the jmfz exhibits a contrasting bouguer gravity low and a complex magnetic signature the gravity signature of the vs can be modelled and explained as an abnormal thick oceanic crust which locally can reach up to 15 km we propose that the thick oceanic crust overcrusting was syn rift and formed during mid to late eocene a plate reconstruction at eocene time suggests that the vs could be part of a triple junction initiated during the breakup between the voring marginal high and the greenland part of the traill voring igneous complex now located offshore east greenland mantle upwelling beneath the early spreading ridge and or local stress reorganisation could have induced transtension and lithospheric thinning along the jmfz and magmatic activity would have increased locally along this leaky transform we suggest that the early tertiary tectono magmatic processes that operated in the norwegian greenland sea are similar to the processes involved in the modern triple junction evolution of the azores plateau region

pb zn deposits and salt bearing diapirs in southern europe and north africa many diapirs with triassic evaporite successions in southern europe and north africa are accompanied by strata bound pb zn mineral deposits these are of two types 1 epigenetic mineralization filling cavities exhibiting analogies with mississippi valley type deposits and 2 syndiagenetic mineralization in sediments rich in organic materials this second type is very similar to the so called volcanic exhalative type in most of these ore deposits diapirism seems to be a determining factor in the development of base metal concentrations diapir growth can be divided into four distinct stages initiation ascent piercement and subsequent deformation study of north african and southern european deposits has led to a genetic model of diapir emplacement and associated pb zn mineralization the source of these metals is unknown the transport of the metals is provided or facilitated by the brine from adjacent triassic evaporites deposition of sulfides occurs where the deep fluids meet the upper beds these deposits can be remobilized with each new phase of diapir growth

the margin between senja and spitsbergen fracture zones implications from plate tectonics abstract analysis of multichannel seismic data from the continental margin off svalbard between the senja and spitsbergen fracture zones suggests that the transition between continental and oceanic crust is located at or close to the hornsund fault zone in the late paleocene early eoeene 57 m y the region between svalbard and northeast greenland was subjected to regional shear movements associated with a transform system between the young lofoten greenland basin and the arctic ocean approximately 50 m y ago the spreading axis migrated to the northeast creating a deep basin north of the greenland senja fracture zone forming the passive margin between bear island and 76 5 n north of 76 5 n the regional transform was maintained at the time of the main reorganization of relative plate motion 36 m y the northern margin evolved a continental fragment was possibly cut off from the svalbard margin forming a small microcontinent the microcontinent appears as the submarine ridge which has been associated with the hovgaard fracture zone it is suggested that the sediments west of the hornsund fault zone are not older than eocene in the south and mid oligocene in the north the position of the spreading axis has greatly influenced the margin sedimentation

saline intrusion and refreshening in a multilayer coastal aquifer in the catania plain sicily southern italy dynamics of degradation processes according to the hydrochemical characteristics of groundwaters the catania plain is a large alluvial depression which represents one of the most important hydrogeological units in eastern sicily a detailed hydrochemical and hydrogeological investigation focussed on its north eastern corner has provided new insights into the past and present relationship between freshwater and seawater in shallow and deep aquifers according to hydrochemical data over the last centuries the area has been affected by local variations of the sea level giving rise to sequential processes of re equilibration of the exchangeable complex involving freshwater and seawater in both surficial and deep aquifers these ongoing processes consist in the refreshening of both deep aquifers 500 m from the shoreline and to a lesser extent due to lower freshwater influx shallow aquifers in the former case there is a shift of the groundwater compositions towards the na hco3 type and a significant drop in the salt contents while in the latter case the salt contents do not drop significantly at a distance 500 m from the shoreline the exchangeable complex of deep aquifers is presently subject to salinization according to the temporal variabilities in the hydrochemical data over the period 1995 96 the apparent dualism can be attributed to a general worsening of the current freshwater seawater relationship in deep aquifers this new tendency appears to be related to a sharp increase in water consumption by the local industrial plant which has reversed the natural refreshening tendency giving rise to a new saline intrusion that is particularly severe close to the shoreline

petroleum geology of tunisia recent discoveries and important oil shows have proven the existence of hydrocarbons in newly identified depocenters and reservoirs in general except for some areas around the producing fields tunisia is largely underdrilled the national company etap has decided to release data and to publish a synthesis on the petroleum geology of tunisia the geology of tunisia provides a fine example of the contrast between alpine folding which typifies northern tunisia and the african craton area of the saharan part eastern tunisia corresponds to an unstable platform forming plains or low hills and extending eastwards to the shallow pelagian sea there are a wide variety of basins central and northern tunisia represents a front basin the saharan ghadames basin or the chott trough are sag basins the gulf of gabes was formed as a distension margin the gulf of hammamet is a composite basin and several transversal grabens cut across the country including offshore and are rift type basins all these features are known to be oil prolific throughout the world two large fields and many modest size pools are known in tunisia oil and gas fields in the surrounding countries namely the saharan fields of algeria and libya the large bouri fieldmore offshore tripolitania and discoveries in the italian part of the straits of sicily suggest a corresponding potential in tunisia exposed paleogeographic and structural maps balanced sections and examples of fields and traps will support an optimistic evaluation of the future oil exploration in tunisia less

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

effect of thermal contrasts on gravity modeling at passive margins results from the western barents sea the western barents sea passive margin is a key locality to demonstrate the effect of the thermal structure of the lithosphere on forward gravity modeling this margin developed by shear motion between the eurasian and greenland plates during the early tertiary and it is a significant border zone between young hot oceanic lithosphere and cooler continental lithosphere we construct two dimensional gravity models of 125 km thick lithosphere based on expansion of mantle rocks determined from thermal modeling the approach has a substantial impact over traditional shallow gravity models here demonstrated on a previously published model on the basis of a 140 mgal free air anomaly the old model proposes an anomalous high density oceanic crust emplaced in a leaky transform adjacent to the continent during early margin development however the lithospheric models predict a homogeneous oceanic crust while preserving regional isostasy at base lithosphere from continent to ocean two further tests agree with this conclusion a map of bouguer corrected ers 1 satellite data reveals no residual anomalies originating from the oceanic crust at the margin admittance analysis shows a strong oceanic lithosphere and the high coherence between bathymetry and free air gravity discounts a significant subsurface load the high gravity anomalies at the margin are thus an edge effect enhanced by sedimentation onto the strong oceanic lithosphere and shaped by the effect of the lithospheric thermal field other results of this work include a new continent ocean boundary map and two crustal transects across the margin

structure of the jan mayen microcontinent and implications for its evolution an extensive seismic survey using ocean bottom seismographs obs was performed in the area across the jan mayen basin north atlantic from the jan mayen ridge to the iceland plateau the jan mayen ridge and surrounding area are considered to be a fragment of a continent which was separated from greenland just prior to magnetic anomaly 6 this study presents the crustal structure of the jan mayen microcontinent and the ocean continent transition to the west of the jan mayen ridge the crustal structures from the centre of the jan mayen ridge to the jan mayen basin are characterized by a deep sedimentary basin a thin basaltic layer within the sedimentary section and extreme thinning of the continental crust towards the iceland plateau the obs data indicate that a continental upper crust v p 5 8 6 1 km s 1 and lower crust v p 6 7 6 8 km s 1 underlie the deep sedimentary basin the thickness of the continental lower crust varies significantly from 12 km beneath the jan mayen ridge to almost zero thickness beneath the northwestern part of the jan mayen basin an ocean continent transition zone is found at the western edge of the jan mayen basin within the 10 km wide transition zone crustal velocities increase towards the iceland plateau and approach the velocities of the oceanic crust obtained at the iceland plateau that is 3 8 5 1 km s 1 oceanic layer 2a 5 9 6 5 km s 1 oceanic layer 2b and 6 8 7 3 km s 1 oceanic layer 3 the crustal model indicates very thin oceanic crust 5 km immediately oceanwards of the ocean continent transition zone beneath the iceland plateau the oceanic crust is thicker 9 km than the typical thickness of normal oceanic crust this might imply that the oceanic crust at the iceland plateau has been generated by asthenospheric material slightly hotter than normal from the crustal structure obtained by the present study it is proposed that the western part of the jan mayen ridge may be referred to as a non volcanic continental margin generated by a long duration of rifting even if the asthenospheric material upwelling along the margin were hotter than normal only small amounts of magmatic intrusions and extrusions would have been generated because of significant conductive cooling under the long duration of rifting

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

extensional collapse related to compressional uplift in the alpine chain off northern tunisia central mediterranean abstract geophysical and geological marine data recently collected allow to outline the structure of the basement involved fold thrust belt developed during the late cenozoic between sardinia and tunisia along the africa europe plate boundary by integrating these with inland data it is possible to document step by step the progression of crustal thickening from north to south and the collapse of the first uplifted northern units while collision was still going on the geodynamic setting suggests that coupled extensional collapse and fold thrust propagation were driven by island arc drifting above a southward retreating subduction zone

marine and human activity influences on the groundwater quality of southern korinthos area greece in this paper the groundwater quality of the southern part of korinthos region north east peloponnese is discussed the geology is characterized by a thick sequence of neogene marls alternating with sandstones overlain by superficial quaternary deposits the latter consist of a mixture of loose materials such as conglomerates marly sandstones sands and clay to silty sands the area is crossed by a fault system parallel to the coastline and the quaternary sediments have formed extended tyrrhenian marine terraces two aquifers have been identified in the area the first is unconfined and occurs within the quaternary sediments whereas the other is a deep confined aquifer occurring within the underlying neogene marl series analysis of hydrochemical evolution over the past 30 years has indicated significant deterioration of quality owing to seawater intrusion and nitrate pollution the various sources of pollution have rendered to a large extent shallow groundwater unsuitable not only for potable water supply but also for irrigation purposes however this is not the case for the deeper confined aquifer statistical analysis was used to explore the evolution of salinization during the years 1968 and 1998 in view of the alarming conditions caused by the documented groundwater quality deterioration the need for integrated water resources management is stressed to maintain the socio economic growth of the region studied copyright 2003 john wiley sons ltd

pbzn mineralization associated with diapirism fluid inclusion and stable isotope h c o evidence for the origin and evolution of the fluids at fedj el adoum tunisia pb zn mineralizations occur in the contact zone to a saliferous diapir and its surrounding cretaceous limestonerich sediments the diapir of triassic formations was initially intruded hot from a depth of 3 7 km during the cretaceous three principal types of mineralization occur bedded vein and massive combined microthermometric and stable isotope h c o studies have characterized three principal thermal events before cool meteoric waters entered the system 1 1 hot 170 250 c saline 22 33 eq wt nacl fluids of probable deep formation water origin with d 43 and 18o 20 precipitated calcite with 13c 8 and celestite in the inner part of the contact zone with the diapir 2 2 hot 100 130 c saline 18 23 eq wt nacl fluids with d 60 and 18o 13 containing co2 n2 and hydrocarbons precipitated sphalerite calcite 13c 9 quartz and minor galena as banded mineralization in the outer part of the contact zone more galena rich vein mineralizations in the contact zone were deposited at similar temperatures from comparable fluids mineralizing solutions are interpreted to be formation waters with the carbonate carbon being derived from organic carbon the colloform textures in the banded mineralization suggest that the nearby sedimentary basin underwent episodic dewatering 3 3 warm 70 90 c saline 16 22 eq wt nacl fluids with d 110 and 18o 10 precipitated calcite with 13c 16 galena rich ore in the massive mineralizations and vein mineralizations in the cenomanian turonian limestones and essentially sulphide free calcite in the banded and contact vein mineralizations a locally derived organic water origin is proposed where both hydrogen and carbon were derived from organic constituents such as petroleum during bacterial sulphate reduction reactions variable d and salinity values suggest mixing processes between the d depleted organic water and a more d rich formation or meteoric water 4 4 low temperature 50 c meteoric waters with d 15 to 25 introduced a second generation of calcite with the carbonate largely coming from the sedimentary carbonates in the massive and turonian vein mineralizations anhydrite was probably converted to gypsum at about this time and before fedj el adoum arrived at its present altitude

a geophysical and geochemical approach for seawater intrusion assessment in the acquedolci coastal aquifer northern sicily vertical electrical sounding ves surveys and chemical analyses of groundwater have been executed in the coastal plain of acquedolci northern sicily with the aim to circumscribe seawater intrusion phenomena this urbanized area is representative of a more general problem interesting most of mediterranean littoral areas where intensive overdraft favors a heavy seawater intrusion through the coastline aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region schlumberger ves together with piezometric and chemical physical information of groundwater allowed us to perform hydrogeological and geophysical elaborations to propose the occurrence of a relatively narrow belt marked by fresh salt water mixing in the considered plain pollution risk studies have been already realized by authors with the proposal to identify by parametric and synthetic zoning of significant hydrogeological elements the most vulnerable sectors in detail an intrinsic vulnerability mapping has been already performed applying the well known sintacs system this paper intends to give in this sector of sicily an example of integration of different methodologies showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better

basin structure on the norwegian margin from analysis of digitally recorded sonobuoys during r v robert d conrad cruise 21 a large number of sonobuoys were recorded in the voring more and adjacent basins at the margin off norway the digital sonobuoy data have been transformed into the domain of intercept time tau and ray parameter p and inverted by the tau sum method to obtain better definition of the near seafloor velocities using also the precritical energy a move out correction has been applied to the tau p data conventional analyses of the x t data were also performed in general the various types of analyses complement each other and should be used interactively together with forward modeling to obtain the optimal velocity depth function the sonobuoy results have outlined in a regional sense the pre cenozoic sedimentary basin at the margin this basin attains a maximum sediment thickness of 8 10 km of which only the upper half is defined by seismic reflection profiling at the outer margin the marginal escarpments form major discontinuities in the lateral velocity distribution the survey has proven that sonobuoy profiles recorded during standard seismic reflection profiling in major marginal basins may provide important new information particularly about the deeper parts of the basins that is not directly available from the reflection profiles

the nansen ridge arctic ocean some geophysical observations of the rift valley at slow spreading rate abstract we have examined continous echo soundings across the nansen rift valley and analysed the first gravity and bathymetric data available across the northern flank of the nansen ridge for comparison with other parts of the mid ocean ridge system the observed width of the inner floor 1 7 5 5 km at a total opening rate of 1 5 cm yr supports the idea of progressive narrowing of the inner floor with decreasing spreading rate for slow spreading ridges however the observed distance between the outer walls 18 22 km or rift valley width 30 33 km suggests that these parameters at least to a first approximation tend towards a minimum value with decreasing spreading rate the relation between gravity and bathymetry along the drift track of ice station fram i tentatively suggests that the sea floor topography of this part of the nansen ridge is supported by a plate with an elastic thickness less than what is observed on the mid atlantic ridge

the value of iodide as a parameter in the chemical characterisation of groundwaters abstract brackish and saline groundwaters can severely constrain the use of fresh groundwaters their chemical characterisation is important in understanding the hydraulic conditions controlling their presence in an aquifer major ions are frequently of limited value but minor ions can be used iodide in groundwater is particularly significant in many environments due to the presence of soluble iodine in aquifer matrix materials iodide is found in groundwaters in parts of the english chalk aquifer in concentrations higher than are present in modern seawater its presence is considered as a indication of groundwater residence and is of use in the characterisation of fresh as well as saline waters under certain circumstances modern seawater intrusion into aquifers along english estuaries produces groundwaters which are easily identified due to iodide enrichment from estuarine muds in other environments iodide concentrations are of value in distinguishing between groundwaters in limestones and shaly gypsiferous rocks as shown by a study in qatar while in an alluvial aquifer study in peru iodide has been used to identify groundwaters entering the aquifer from adjacent granodiorites

the genesis of fluorspar hydrothermal deposits at montroc and le burc the tarn as deduced from fluid inclusion analysis the genetic conditions of two fluorspar hydrothermal deposits are determined by the study of fluid inclusions observations through a cooling and heating stage microscope yield information on the salinity and deposition temperature chemical analysis by crushing and leaching allows determination using chemical geothermometers of the fluid s chemical composition and initial temperature using thermodynamic modeling we describe the evolution of the solution and the process of fluorite deposition from a rock source in a hot reservoir at a temperature close to 300 degrees c to deposition ending close to 180 degrees c

onshore offshore correlation of the llobregat deltaic system spain development of deltaic geometries under different relative sea level and growth fault influences abstract groundwater resources in deltaic aquifers are essential in the mediterranean region to sustain the socio economic development of coastal communities and shallow water ecosystems understanding the geological connection between coastal aquifers and the offshore sedimentary record is important to better predict consequences in terms of water management in spite of this most approaches to postglacial and pleistocene deltaic sedimentation focus either on the offshore or the delta plain few studies correlate and integrate the entire system in the llobregat delta south of barcelona spain onshore offshore correlation is achieved by integrating data from sediment cores acquired on the deltaic plain with seismic profiles from offshore data integration enables the reconstruction of the entire deltaic system providing a more well defined picture and a better understanding of the onshore offshore stratigraphic framework in a late quaternary tectonically active narrow shelf in the western mediterranean basin the late quaternary record in the llobregat delta shows an unusual well preserved transgressive regressive cyclic stacking pattern which displays peculiarities compared with most mediterranean quaternary deltaic shelves given that the transgressive and highstand intervals appear to be significantly preserved both onshore and offshore the preservation of these deposits is attributed to the high subsidence rate on the continental margin controlled by quaternary faults and the structure of the basement and by sediment supply fluctuations depositional sequences also reveal contrasting patterns between the northeastern and southwestern llobregat shelves and show significant variability in the dip direction the results are compared with diverse stratigraphic architectures reported elsewhere and provide information to the ancient delta deposits about the distinct types of deltaic geometries generated under different sea level trends helping to improve sequence stratigraphic models where deltaic geometries generated during specific intervals of the sea level curve are poorly constrained and or documented

small rivers contribution to the quaternary evolution of a mediterranean littoral system the western gulf of lion france abstract along the mediterranean coasts and the atlantic french coast former and actual research programs focused on major river systems estuaries and deltas characterized by a last glacial relative sea level lowstand and incision and a well developed sedimentary incised valley infilling deposited during the following sea level rise and highstand this paper presents the preliminary results of a program focused on a particular area of the gulf of lion coast with a thin sedimentary cover over the substratum and only minor rivers with non apparent and important sedimentary contribution during the late quaternary the results show that in this area the best pliocene to actual sedimentary record is preserved the paper rests on the analysis of an extensive database of recent high resolution and very high resolution seismic reflection lines and previously published core data seismic data show that a major complex of paleovalleys connected with the orb aude and agly rivers is preserved on the inner shelf and adjacent coastal plain on the inner shelf the separated incised valleys merged in a unique broad and shoreparallel incision dipping southward at the southward extremity the incision turns eastward and seaward the basal surface of this incision extends seawards under six to seven late quaternary depositional sequences preserved on the mid and outer shelf the infilling of the complex of paleovalleys is characterized by aggrading deposits attributed to periods of relative sea level rise transgressive systems tracts organized into several subunits bounded by internal discontinuities locally deeply incising the discontinuities are amalgamated surfaces including successive sequence boundaries indicative of phases of relative sea level falls merged with transgressive surfaces indistinct tidal and wave ravinement surfaces the subunits are the part of late quaternary depositional sequences preserved in estuarine environments they are the lateral equivalents of landward fluvial terraces and seaward coastal and prodeltaic deposits on the shelf using borehole dataset the underlying and eroded deposits below the basal unconformity are correlated with pliocene deposits outcropping landward in the hinterland the top of the incised valleys complex is capped by the last glacial lowstand surface of erosion 18 ky b p reworked by the postglacial transgressive surface ts dissociated near the shoreline into a tidal and a wave ravinement surfaces above the ts the very high resolution vhr seismic data in the lagoons the tidal channels and cores reveal in details the stratigraphic architecture of the deposits at the base a small wedge constitutes the postglacial transgressive systems tract tst locally thinning in the areas distant of the sediment point sources the tst is capped by a flat surface of wave reworking maximum flooding surface or mfs prolongating under the leucate lagoon and merging offshore at the seafloor boreholes and vhr seismic lines trough the coastal barrier and in the lagoon show that the shoreline probably migrated far landward at the end of the transgression when the rate of sea level rise decreased strongly the shoreline migrated seaward and prograding and aggrading sandy material with landward muddy lateral equivalent facies deposited early highstand systems tract hst above the mfs offshore fine material deposited as a sigmoidal blanket of mud originating in part from the north east and rhone river under oceanic circulation equivalent to a subaqueous prodelta subsequently the modern beach barrier built up by wave reworking of the early hst this new study of the western part of the gulf of lion inner shelf and littoral illustrates an incised valley complex and thus presents the best preserved example of the sedimentary record of the effects of the relative sea level changes during the pliocene to actual period for the first time the land to sea transition is preserved and the late quaternary depositional sequences are in a great part observed the last post glacial deposits present a simplified but very different organisation compared to a record front of the adjacent rhone river consequently a synthesis is now possible

ree and isotope sr s and pb geochemistry to constrain the genesis and timing of the f ba pb zn ores of the zaghouan district ne tunisia abstract the f ba pb zn ore deposits of the zaghouan district located in ne tunisia occur as open space fillings or stratabound orebodies hosted in jurassic cretaceous and tertiary layers the chondrite normalized rare earth element ree patterns may be split into three groups i normal marine patterns characterizing the wallrock carbonates ii light ree lree enriched slide shaped patterns with respect to heavy ree hree with small negative ce and eu anomalies characteristic of the early ore stages iii bell shaped ree patterns displaying lree depletion as well as weak negative ce and eu anomalies characterizing residual fluids of subsequent stages the 87 sr 86 sr ratios 0 707654 0 708127 8 show that the sr of the epigenetic carbonates dolomite calcite and ore minerals fluorite celestite are more radiogenic than those of the country triassic jurassic cretaceous lower miocene sedimentary rocks the uniformity of this ratio throughout the district provides evidence for the isotopic homogeneity and consequently the identity of the source of the mineralizing fluids this signature strongly suggests that the radiogenic sr is carried by upper paleozoic basinal fluids the 34 s values of barite associated to mineralizations are close to those of the triassic sea water 17 the 34 s values of sulfide minerals range from 13 6 to 11 4 suggesting two sulfur reduced end members bsr tsr with a dominant bsr process taking account of the homogeneity in the pb isotope composition of galenas 18 833 18 954 0 001 15 679 15 700 0 001 and 38 690 38 880 0 004 for the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively a single upper crustal source for base metals is accepted the late paleozoic basement seems to be the more plausible source for f pb zn concentrated in the deposits the genesis of the zaghouan district ore deposits is considered as the result of the zaghouan fault reactivation during the late miocene period

origin of vein hydrothermal carbonates in triassic limestones of the espadan ranges iberian chain e spain dolomitization and hg bearing veins in the lower triassic limestones of the espadan ranges iberian chain e of spain

a case study to assess the potential for saline soil development due to irrigation abstract with the help of a generalized conceptual model for the formation of saline soil we examine whether irrigation proposed for an area near lethbridge alberta will compound an existing salinity problem the geology of the site is characterized by weathered and non weathered tills which overlie cretaceous bedrock locally preglacial sands and gravels occur along the axes of two bedrock valleys beneath the site piezometric data define local groundwater flow from west to east following the regional topographic slope however the depth to the water table is extremely variable and controlled by the preglacial sand and gravel unit the existing problem of soil salinity which is restricted to the western part of the study area is caused by the high water table and large quantities of dissolved mineral mass in the groundwater in the central and eastern part of the area the water table occurs at depths greater than 20m and saline soils have not formed flow modeling along a two dimensional cross section confirms that the water table configuration and hence the distribution of saline soils is controlled by the preglacial deposits indications are that excess recharge due to irrigation will not result in a water table rise unless the quantity involved is considerably larger than the natural rate of recharge thus irrigation will not contributed to a marked increase in the size of the area affected by the saline soil

the western svalbard margin 74 80 n abstract a regional study of the continental margin between the senja and molloy spitsbergen fracture zones reveals that the transition from continental to oceanic crust occurs in a narrow zone beneath the outer shelf and uppermost slope the postulated continent ocean boundary appears to be fault related consisting of sheared and rifted segments the marginal structures are compatible with a plate tectonic model in which the southern greenland sea opened along a northeasterly propagating plate boundary in the eocene whereas the northern greenland sea started opening in the early oligocene the main structure at the margin is the hornsund fault zone which probably reflects an old zone of weakness rejuvenated in the tertiary first by shear and later by extensional movements in the early tertiary local transpressional and transtensional components along the plate boundary are associated with the spitsbergen orogeny emplacement of belts of high density oceanic crust and tectonism in the western barents sea a complex volcanic rifted margin characterized by the bjornoya marginal high links the predominantly sheared margin segments on either side the main ridge like segment of the hovgaard fracture zone was originally part of the spitsbergen margin in a regional sense the hornsund fault zone demarcates the eastern boundary of the tertiary sedimentary wedge which reaches a total thickness of more than 7 km there appears to have been a considerable increase in deposition of sediments the last 5 6 my depocentres located seaward of the east west fjord systems and submarine depressions indicate a relationship between late cenozoic glaciations and high sedimentation rates

prediction of sediment thickness in the norwegian greenland sea from gravity inversion 1 we explore the feasibility of inverting freely available altimetry derived gravity grids for sediment thickness on oceanic crust a four layer earth model is adopted assuming that the gravity signal from the base of the sedimentary layer can be fully isolated from the observed free air gravity the following additional data are required 1 shipboard bathymetry for reliable bouguer correction 2 oceanic crustal ages to correct for gravity anomalies related to the thermal history of lithospheric breakup and seafloor spreading and 3 some wide angle seismic observations of sediment thickness a fixed relationship between the base of the sedimentary layer and the moho is also required because of limited gravity resolution at large depths the final inversion setup searches for three control parameter values density of uppermost sediments density of oceanic crystalline crust and thermal diffusivity of mantle rock that minimize misfit between the earth model and observations applied to the norwegian greenland sea the inversion successfully predicts locations of 20 25 km wide depocenters and crystalline crustal highs yet 1 km thickness errors are common even in well constrained areas the largest errors are associated with underplated crust active mid ocean ridges and the continent ocean boundary indicating locally incorrect assumptions of mantle thermal structure and crystalline crustal thickness the thicknesses of 4 km thick submarine fans are underpredicted probably because of too low sedimentary densities in the earth model if these limitations are acceptable or do not apply because of simple crustal structure gravity inversion may be used for mapping regional sedimentary patterns e g in the arctic ocean

rates of continental breakup magmatism and seafloor spreading in the norway basin iceland plume interaction 1 in year 2000 an ocean bottom seismometer obs profile was acquired across the more margin to the aegir ridge an extinct seafloor spreading axis the margin is an early eocene volcanic passive margin located between the faeroe iceland ridge fir and the east jan mayen fracture zone ejmfz the p wave data were modeled by ray tracing to give a crustal transect showing a 10 11 km thick igneous crust created by breakup magmatism tapering off to magma starved seafloor spreading by c23 time 51 4 ma the location of the ejmfz was reinterpreted from a satellite derived gravity map and spreading direction in the norway basin reevaluated no other fracture zones were confirmed and both thin oceanic crust 4 5 km and lack of fracture zones resemble ultraslow spreading on the arctic gakkel ridge magnetic seafloor spreading anomalies were identified from the magnetic track recorded with the obs profile and half spreading rates were derived early seafloor spreading was slow 15 32 mm yr 1 approaching ultraslow 6 8 mm yr 1 by c20 time 42 7 ma a v shaped pattern seen in the gravity field located only around the northern part of the aegir ridge corresponds to increased crustal thickness in the seismic model recording northeast transport 3 6 mm yr 1 of more melt fertile asthenosphere zones the magma starved character of the norwegian basin seen also during slow seafloor spreading may be the result of depletion of the asthenosphere when the iceland plume constructed the fir to the south as the asthenosphere is subsequently transported into the norway basin

crustal structure of the lofoten vesteralen continental margin off norway abstract by compiling wide angle seismic velocity profiles along the 400 km long lofoten vesteralen continental margin off norway and integrating them with an extensive seismic reflection data set and crustal scale two dimensional gravity modelling we outline the crustal margin structure the structure is illustrated by across margin regional transects and by contour maps of depth to moho thickness of the crystalline crust and thickness of the 7 km s lower crustal body the data reveal a normal thickness oceanic crust seaward of anomaly 23 and an increase in thickness towards the continent ocean boundary associated with breakup magmatism the southern boundary of the lofoten vesteralen margin the bivrost fracture zone and its landward prolongation appears as a major across margin magmatic and structural crustal feature that governed the evolution of the margin in particular a steeply dipping and relatively narrow 10 40 km wide moho gradient zone exists within a continent ocean transition which decreases in width northward along the lofoten vesteralen margin to the south the zone continues along the voring margin however it is offset 70 80 km to the northwest along the bivrost fracture zone lineament here the moho gradient zone corresponds to a distinct 25 km wide zone of rapid landward increase in crustal thickness that defines the transition between the lofoten platform and the voring basin the continental crust on the lofoten vesteralen margin reaches a thickness of 26 km and appears to have experienced only moderate extension contrasting with the greatly extended crust in the voring basin farther south there are also distinct differences between the lofoten and vesteralen margin segments as revealed by changes in structural style and crustal thickness as well as in the extent of elongate potential field anomalies these changes may be related to transfer zones gravity modelling shows that the prominent belt of shelf edge gravity anomalies results from a shallow basement structural relief while the elongate lofoten islands belt requires increased lower crustal densities along the entire area of crustal thinning beneath the islands furthermore gravity modelling offers a robust diagnostic tool for the existence of the lower crustal body from modelling results and previous studies on and off shore mid norway we postulate that the development of a core complex in the middle to lower crust in the lofoten islands region which has been exhumed along detachments during large scale extension brought high grade lower crustal rocks possibly including accreted decompressional melts to shallower levels

evolution of the rhone delta plain in the holocene abstract the delta plain of the rhone shows many sandy beach ridges cropping out at the surface we propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form morphologies of the lobes depend on four principal factors 1 the variation of the relative sea level which constitutes the morphogenic base level 2 the fluvial input volume of water discharge and sedimentary input number and position of the mouths 3 marine dynamics volume and direction of the longshore drift dominant wave direction 4 the accommodation space created by the rise of relative sea level along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea our conclusions are the main holocene paleo delta lobes of ulmet and saint ferreol were contemporaneous being deposited from 4000 to 2000 yr bp however the fluvial style of their downstream channel meandering for ulmet channel and linear for saint ferreol and the lobe morphologies of both channels are contrasted rounded in the case of ulmet and elongated for saint ferreol the role of the accommodation space is confirmed by two recent drillholes traversing the entire holocene succession which reveal a prior stage of sedimentary filling in the case of the saint ferreol lobe thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe the decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of rhone however the high rate of progradation of saint ferreol lobe after 2900 bp is probably a consequence of the increase of human activity after this date the variation of relative sea level remains an important factor controlling the evolution of the rhone delta after 6000 bp the local stabilization of the relative sea level between 4585 bp and 3520 bp played an important role in the triggering of coastal progradation saint ferreol lobe eastern margin rhone delta

origin of the daping gold deposit in the ailaoshan metallogenic belt sw china insights from geology isotope geochemistry and geochronology abstract the daping gold deposit the most representative gold deposit in the ailaoshan metallogenic belt is located between the southeast sanjiang region three rivers jinshajiang lancangjiang and nujiang and the western yangtze block ore bodies in the daping gold deposit are mainly vein types hosted in the late proterozoic diorite and silurian limestone and controlled by nw trending faults la icp ms zircon u pb dating of granodiorite yielded a late eocene age of 36 76 0 38 ma constraining the upper limit of the main mineralization quartz has d values ranging from 80 to 50 4 average 63 1 and 18 o fluid values ranging from 7 29 to 8 29 in the early stage of mineralization in the late stage quartz has d values ranging from 87 to 67 average 77 4 and 18 o fluid values ranging from 0 24 to 3 86 carbonate minerals have 13 c pdb and 18 o smow values ranging from 2 3 to 7 6 average 5 1 and 9 to 14 9 mean 12 6 the sulfides have a narrow range of 34 s values 0 2 to 6 7 average 3 51 in the main stages of mineralization the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of the sulfides range from 18 685 to 18 765 15 653 to 15 728 and 39 014 to 39 280 in general according to the h o c s pb isotopic compositions the ore forming fluids are dominated by metamorphic fluids and the ore forming fluids and materials might have been mainly derived from the mantle and lower crust with a small input of wall rock material they were affected by meteoric water in the late stage of mineralization given the regional geology ore geology ore forming fluids material features and ore forming age the daping gold deposit can be classified as a typical orogenic gold deposit

quaternary siliciclastic sequence stratigraphy of western mediterranean passive and tectonically active margins the role of global versus local controlling factors

combined time domain electromagnetic soundings and gravimetry to determine marine intrusion in a detrital coastal aquifer southern spain summary marine intrusion is undoubtedly the most serious problem facing coastal aquifers that are exploited for use it is also an excellent indicator of the state of the aquifers resources this work proposes the combined application of two complementary geophysical techniques as an effective method for locating the saline wedge on one hand time domain electromagnetic soundings are the most reliable geophysical method for determining low resistivity zones that usually correspond to the presence of seawater although in some cases low resistivities may be due to the properties of the substrate on the other hand gravimetry allows a precise determination of the depth of the aquifer basement thus resolving the above uncertainty information provided by the lithological columns from boreholes has also allowed great precision in the calibration of the results from both techniques this methodology has been applied to the motril salobrena detrital coastal aquifer which has had no problems of marine intrusion to date nonetheless changes in soil use brought about by housing developments golf courses and a proliferation of hothouse agriculture comprise significant shifts in aquifer use in addition the construction of a dam which is drastically reducing the main recharge of the aquifer the guadalfeo river makes it likely there will be profound hydrogeological changes delimiting the extent of the saline wedge is therefore a fundamental step towards quantifying the effects of both the dam and the changes in soil use seawater saturated zones have a resistivity ranging from 0 5 to 5 m detrital sediments 8 400 m carbonates 80 300 m and schists from 2 to 60 m the current position of the saline wedge has been located at 100 200 m from the coastline indicating a healthy state for the aquifer areas with wide and narrow mixing zones have been noted and related to differences in the hydrogeological characteristics of the aquifer

sedimentary sequences in the gulf of lion a record of 100 000 years climatic cycles abstract the wide continental shelf of the gulf of lion up to 70 km has been the object of numerous investigations since the early days of oceanography yet the question of sequences duration the mechanisms of deposition and factors implied remained unanswered a study of a very dense grid of very high resolution vhr seismic reflection sparker data associated with surficial cores both collected by ifremer between 1992 and 2001 on the outer shelf and upper slope offshore of sete in the languedoc region gives a new insight into these issues analysis of the 3d geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms prism pi with low angle clinoforms results obtained from integrating lithology palynology micropaleontology seismic stratigraphy stratigraphic simulation support the hypothesis that the basic depositional pattern records a 100 000 years glacioeustatic interglacial glacial cycle as previously suggested by aloisi aloisi j c 1986 sur un modele de sedimentation deltaique contribution a la connaissance des marges passive these de doctorat d etat universite de perpignan 162 pp prisms pi corresponds to deposition at high sea level and prisms pii to deposition during low sea level at glacial maxima five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles the last five cycles at least are recorded on the shelf of the western part of the gulf of lion

the applicability of earth resistivity methods for saline interface definition direct current resistivity traversing has been used to characterise the nature of the saline interface at te horo on the kapiti coast in new zealand the results show that the interface in the vicinity of the settlement which relies on bores for potable water has intruded inland 10 m further than in undeveloped areas resistivity traversing has been particularly successful in defining subsurface areas of higher salinity by providing a two dimensional image of the bulk resistivity structure the results of the resistivity surveys are supported by bore water chemistry which show evidence of saltwater mixing bores on beachfront properties have concentrations of up to 1 seawater a resistivity formation factor has been derived to allow the pore fluid resistivity to be estimated for future coastal surveys the results also illustrate the problems associated with using standard models to predict the location of the saline interface when small amounts of diffusive mixing occur

the mississippi valley type fluorite ore at jebel stah zaghouan district north eastern tunisia contribution of ree and sr isotope geochemistries to the genetic model abstract the fluorite district of zaghouan north eastern tunisia is characterized by f ba pb zn ore deposits mineralization occurs within stratabound to stratiform bodies either within jurassic back reef limestone uplifted blocks or along unconformity surfaces that separate them from the overlying sequence fluorite mineralization also occurs within fractures crosscutting the uplifted limestone blocks and their overburden despite the similarity of the liassic series throughout the major part of the district stratabound fluorite deposits formed subsequent to a strong epigenetic dolomitization souissi et al 1998 and occurring along the lower middle liassic unconformity are known only at jebel stah and at the adjacent jebel kohol four petrographic types of fluorite are recognized the finely laminated karst deposits fl1a the macrogranular fluorite fl1b resulting from the recrystallization of fl1a and the megacrystalline fluorite fl2 associated to calcite in lodes and fluorite in geodes fl3 this study gives new arguments in terms of the genetic model of the fluorite ore of jebel stah and by using trace metal elements mte rare earth elements ree and sr isotope geochemistry the mte geochemistry shows that the epigenetic dolomites and the fluorite fl1a bear higher concentrations in mn and zn with respect to the fluorites fl1b fl2 and fl3 while the latter are depleted in all mte but enriched in co the similarity of their ree patterns indicates that the latter are coeval and that fl1a fluorite may be considered as the early ore generation the same argument confirms that this geochemical imprint has been inherited from a hydrothermal fluid that had remained in equilibrium with shales at depth fluorite deposition appears related to an oxidized fluid derived from a sedimentary basin fluid circulation may have been triggered in response to hydraulic fracturing within a high geothermal gradient setting especially along the major structural trends fl1b fl2 and fl3 fluorites have been generated from the residual fraction of the ore fluid at later stages of mineralization and in a closed system both mineralization and the epigenetic dolomites are characterized by sr isotope ratios that are higher than the barren lower middle liassic rocks indicating that the sr cannot be derived from the wallrocks however these ratios are higher than the triassic seawater yet consistent with those of the paleozoic period thus the fluorite ore of jebel stah is believed to be remobilized from primary ore deposits which are suspected to be hosted in the late series within this period

a beach ridge progradation complex reflecting periodical sea level and climate variability during the holocene gulf of almeria western mediterranean detailed mapping based on aerial photographs at various scales analysis of morpho sedimentary units and radiocarbon dating of the prograding beach ridge complex of campo de dalias almeria allow the differentiation of six prograding units these are called h1 7400 6000 cal bp h2 5400 4200 cal bp h3 4200 3000 cal bp h4 2700 1900 cal bp h5 1900 1100 cal bp and h6 500 cal bp present h units are deposited during periods of high relative sea level and increased sediment input to the coast they are bounded by large swales or erosional surfaces associated with lower sea levels and reduced input of sediment to the coast these correspond to short periods of increased aridity inside the general arid trend recorded in the western mediterranean since 5 4 ka changes in the flux of atlantic superficial waters into the mediterranean sea and relative strength of the w sw winds account for the recorded oscillations of relative sea level we deduce a decadal periodicity for the deposition of a beach ridge and the adjacent swale and suggest that it is related to fluctuations of the north atlantic oscillation nao index and to variations of solar activity the duration of h units shows a quasi millennial periodicity punctuated by short hundred years episodes of reduced progradation or erosion representing events of increased aridity likely to be related to bond s holocene cold events

the norway basin revisited from continental breakup to spreading ridge extinction abstract we re evaluate the structure and spreading evolution of the southeastern norway basin nb based on a new high resolution aeromagnetic survey nb 07 the survey covers a complete oceanic spreading segment from the continental oceanic transition of the more margin off norway to the aborted aegir ridge the new survey documents a transform margin an orthogonally rifted segment and an oblique sheared volcanic margin formed during the onset of breakup observed from the east jan mayen fracture zone to the faroe platform the detailed fabric of the nb revealed by the new data indicates that two distinct tectonic phases have reshaped the basin before the cessation of seafloor spreading and abortion of the aegir ridge in the late oligocene after continental breakup phase i from c24 to c21r 52 to 49 ma marks the earliest phase of spreading probably initiated in the central and outer part of the more basin during this period competing oceanic segments led to the formation of overlapping systems and pseudo fault development we observe a significant change in the nb s oceanic spreading system in the late early eocene and based on observations from surrounding areas we suggest that this is a record of a major tectonic event in the norwegian greenland sea around c21r 49 47 9 ma during phase ii from c21r to c10 48 to 28 ma of nb s development spreading rates decreased spreading direction changed and the number of faulting with large displacement increased leading to the formation of unexpected n s oriented oceanic fracture zones the fan shaped development of the spreading system initiated around c21r 49 47 9 ma instead of c18 c17 40 38 ma or c24 53 3 52 3 ma as previously proposed these new observations were used to re evaluate the tectonic evolution of the norwegian greenland sea and discuss some implications on the syn and post breakup development of the surrounding continental margins and the evolution of the jan mayen microcontinent

contribution of electrical resistivity tomography to the study of detrital aquifers affected by seawater intrusion extrusion effects the river velez delta velez malaga southern spain abstract the coastal aquifer of the plio quaternary delta sediment deposits of the velez river province of malaga spain presents a highly irregular basement morphology and widely varying fill thickness 10 80 m between neighbouring sectors the basin which is tectonically controlled is filled with lutite facies alternating with channel filling rudites this detrital aquifer is affected by seasonal seawater intrusion extrusion processes due to increasing withdrawal of groundwater for human consumption and irrigation during dry periods a study was performed to improve the hydrogeological knowledge of this coastal aquifer system the study examined the morphology of the impervious substratum the facies distribution and the position of the seawater wedge for this purpose an electrical resistivity tomography ert geophysical technique was used and the tomographic data were calibrated using geological observations and borehole studies an analysis was carried out to compare the direct information obtained from the 35 boreholes with the indirect data corresponding to the four electrical tomography profiles in the study over 9660 resistivity data points were processed the ert profiles perfectly corroborated the information derived from the boreholes the profiles made it possible to detect thickness changes lithological changes and the presence of faults moreover from a hydrogeologic standpoint this research technique is capable of detecting the position of the phreatic level and in coastal aquifers such as the one examined in this study the possible horizontal or vertical penetration of seawater intrusion therefore the electrical geophysical prospecting based on ert can be highly useful in areas lacking sufficient geological information and or mechanical borehole data

architectural stacking patterns of the ebro delta controlled by holocene high frequency eustatic fluctuations delta lobe switching and subsidence processes abstract during the late pleistocene and holocene 125 ka b p to present a type 1 4th order depositional sequence comprising regressive lowstand transgressive and highstand system tracts formed worldwide the holocene 10 ka b p to present part of this contains the latest and present highstand systems tract hst within this and the underlying transgressive systems tract tst of the ebro delta in northeastern spain higher frequency 5th to 6th order sea level fluctuations are recognised these form retrogradational and progradational high frequency depositional sequence sets within the tst and hst respectively each high frequency sequence comprises 1 a basal highly reflective shell lag associated with an erosional transgressive surface 2 aggradational deposits which seawards consist of a wedge of marine clays with transparent seismic facies but inland are represented by thick peats 3 progradational deposits composed of sandy delta front facies displaying slope clinoforms these pass seawards into prodeltaic grey silts and landwards into red silts and pebbly sands of delta plain facies the progradational deposits downlap towards their bases the aggradational deposits formed in response to a period of rising sea level and a rapid increase in accommodation space progradation began when sediment supply to the delta exceeded accommodation space as a result of relative sea level fall the relative sea level curve for the delta has a stepped character caused by the punctuation of the 4th order sea level trend by higher frequency eustatic fluctuations as well as by high subsidence rates of about 1 75 mm per year the tst comprises retrogradational parasequences that onlap the underlying pleistocene gravels the maximum flooding surface separating the tst from the hst was formed about 6900 yrs b p on the basis of14c dating of peats the hst comprises progradational deltaic and aggradational units stacked as progradational high frequency parasequence sets the hst of the ebro delta is compared with other deltaic sequences around the world in particular with that of the mississippi delta a tentative chronology of the high frequency climatic and eustatic oscillations influencing deltaic sedimentation globally over the last 7000 years is presented

origin of siderite mineralization in western guizhou sw china constrains from rees c o sr and s isotopes abstract numerous siderite deposits in western guizhou of sw china are mainly hosted in the middle devonian dolostones the larger caiyuanzi cyz and xiongxiongjia xxj deposits have an ore reserve in excess of 300 mt with an average ore grade of 35 total iron there are banded and massive siderite ores and sulfide siderite ores the major ore mineral is magnesian siderite and gangue minerals are ankerite dolomite kaolinite quartz and carbon there are also metallic minerals including pyrite chalcopyrite and minor galena tetrahedrite and enargite rare earth elements rees and carbon oxygen and strontium isotope data indicate a marine origin of the host dolostones and a hydrothermal metasomatic origin of the siderite mineralization the variations of rees and carbon and oxygen isotopic compositions of siderite from the cyz and xxj deposits reflect the variable mineralization processes and different fluid rock ratios the lree depletion of siderite from the cyz deposit could be due to crystallographic control whereas the lree depletion along with mree enrichment and positive eu anomalies of siderite from the xxj deposit was possibly controlled by both crystallography and fluid composition siderite and calcite have 13 c pdb and 18 o smow values ranging from 8 to 4 01 and from 13 42 to 20 07 respectively the variations in c and o isotopic compositions of siderite and calcite may reflect metasomatic replacement of marine carbonates by hydrothermal fluids at different fluid rock ratios dolostones have 87 sr 86 sr initial values of 0 70844 0 70920 whereas siderite and calcite have values ranging from 0 71396 to 0 71708 negative correlations of initial sr isotope ratios versus carbon and oxygen isotopes of the host dolostones siderite and calcite indicated that carbonate minerals were metasomatic products of marine carbonates by hydrothermal fluids leaching from the proterozoic basement rocks iron was possibly derived from the basement leaching rather than from the continental weathering the 34 s cdt values 19 9 to 13 6 of sulfides associated with siderite indicated that the sulfur was probably derived from the marine sulfates through either bacterial sulfate reduction or organic mediated thermochemical reduction

salinization processes in the unconfined aquifer of bou areg ne morocco a geostatistical geochemical and tomographic study hydrogeological and geochemical data in conjunction with the results of an electrical imaging tomographic survey were examined to determine the main factors and mechanisms controlling the groundwater chemistry and salinity of the unconfined aquifer of bou areg on the mediterranean coast of ne morocco in addition statistical and geochemical interpretation methods were used to identify the distribution of the salinity multivariate statistical analysis cluster and principal component factors revealed the main sources of contamination groups a b and c in the cluster analysis and factors 1 3 factor 1 ce cl k so42 and mg2 factor 2 ca2 hco3 and ph factor 3 no3 represent the signature of seawater intrusion in the coastal zone the influence of marly gypsum outcrops in the upstream zone and anthropogenic sources respectively the ionic delta the ionic ratio the saturation index and stuyfzand s method were applied to evaluate geochemical processes the results obtained indicate on the one hand the phenomenon of salinization in both the coastal and the upstream zones and on the other the dilution of groundwater by recharge cation exchange is shown to modify the concentration of ions in groundwater locally with respect to salinization processes in the coastal zone the results of electrical imaging tomography show that salinity increases both with depth and laterally inland from the coastline due to seawater intrusion

high resolution stratigraphy and evolution of the rhone delta plain during postglacial time from subsurface drilling data bank this study is based upon a large set of core drilling data lithology and well logs of the rhone delta plain extracted from the french geological survey brgm databank the main goals are to set up a sequence stratigraphy model of the postglacial sedimentary bodies of the rhone delta plain and to evaluate the relative importance and influence of the main controlling factors and processes subsidence eustasy sediment yield climate anthropic influence that led to their formation first a detailed study 60 drill holes with tenth meters spacing was performed on a restricted area saint ferreol lobe 1 5 km2 correlation between well logs data and lithological data allows to identify the main sediment lithofacies and key surfaces and to set up a detailed stratigraphic framework postglacial deposits are subdivided into a lower member of coastal plain and backbarrier deposits and an upper member of marine deposits coastal barrier environments following the analysis of 160 wells distributed on the whole delta plain depicts the large scale architecture of postglacial deposits in the upper delta plain fluviatile coastal plain and palustral deposits prevail in the lower delta plain the deposits are made of a lower part of coastal plain deposits organized into four units t1 t4 stacked in a retrograding pattern this lower member is truncated by an erosional surface progressively deepening seaward above an upper member of marine deposits thickening seaward and coarsening upward is organized into five units p1 p5 arranged in a prograding pattern the core drilling data have been correlated with high resolution seismic data on the adjacent shelf and are interpreted in sequence stratigraphy terms the retrogradational units t1 t4 with coastal plain deposits are correlative of shelf units and constitute together trangressive parasequences deposited during phases of slowing down of postglacial sea level rise the upper marine units p1 p5 arranged in a prograding pattern represent parasequences of the highstand systems tract which have prograded since the period of reduced rate of sea level rise at the end of the holocene during this period the evolution of the sedimentary rhone system was controlled by major changes of the hydrologic regime periods of increased sediment discharge aggradation of the floodplain and progradation of the coastline are correlated with the development of the deltaic lobes of the rhone d ulmet unit p3 and of the rhone du bras de fer unit p4 unit p5 correlates with adjacent prograding shelf unit that developed seaward of the present rhone river mouth comparison of sea level history between the eastern part of the rhone delta plain and the rocky coast to the east of marseille suggests that tecto subsident movements account for part of the changes in relative sea level moreover the truncation of transgressive and progradation surfaces the unevenness of the mfs the dilatation of sedimentary record and deformations of key surfaces are also in favor of differential subsidence

biodegradation of hydrocarbons and biogeochemical sulfur cycling in the salt dome environment inferences from sulfur isotope and organic geochemical investigations of the bahloul formation at the bou grine zn pb ore deposit tunisia abstract combined organic geochemical and stable isotope s analyses of samples from the cretaceous bahloul formation tunisia provide insight to oil accumulation processes biogeochemical alteration of hydrocarbons microbial sulfate reduction and mineral deposition at the flanks of the triassic jebel lorbeus diapir forming the bou grine zn pb deposit the sulfur isotopic composition of the metal sulfides correlates with the degree of biodegradation of hydrocarbons with the base metal content and with the proportion of aromatics in the organic extracts the 34 s values are interpreted to reflect bacterial sulfate reduction in a more or less closed system rather than a thermogenic contribution the extent of h 2 s production by the activity of the sulfate reducing bacteria probably was limited by the availability of sulfate which in turn was governed by the permeability of the respective sedimentary sequence and by the distance to the anhydrite cap rock evidence is provided that biodegradation of hydrocarbons and microbial sulfate reduction contribute to the formation of the high grade mineralization inside the bahloul formation at the contact with the salt dome cap rock the metals probably were derived through leaching of deeper sedimentary sequences by hot hypersaline basinal brines evolved by dissolution of salt at the flanks of the diapirs these hot metalliferous brines are proposed to migrate up around the diapir finally mixing with near surface sulfate rich brines in the roof zone when the fluids came in contact with the organic rich sediments of the bahloul formation the dissolved sulfate was reduced by the sulfate reducing bacteria hydrocarbons generated or accumulated in the bahloul formation were utilized by sulfate reducers the occurrence of high amounts of native sulfur in high grade ore samples suggest that the production rate of h 2 s by bacterial sulfate reduction exceeded its consumption by metal sulfide precipitation the supply of dissolved metals probably was the limiting reaction the trend of 34 s of native sulfur s 0 towards lower values to the top of the highly mineralized bahloul profile provides evidence for a biogenic origin of s 0 by sulfide oxidizers the variation in isotopic fractionation between native sulfur and sulfide sulfur in the ore minerals reflects the kinetic isotope fractionation factor connected with metabolic processes and the respective reaction rate during biogenic oxidation of sulfur

volcano tectonic events and sedimentation since late miocene times at the mohns ridge near 72 n in the norwegian greenland sea abstract the combined analysis of structural and magnetic data from the mohns ridge near 72 n in the norwegian greenland sea shows the existence of different phases of seafloor spreading from anomaly 5a 12 ma which represents the limit of the magnetic survey onwards for the period comprised between anomaly 5 9 ma and anomaly 3a 6 5 ma most particularly a dramatic drecrease of spreading rate is observed by as much as 50 between anomaly 3a and 2a 3 2 ma an acceleration of spreading is observed together with a global uplift of the acoustic basement this latter period may correspond to a local enhancement of tectono volcanic activity the existence of ridges located at 25 and 50 km from the ridge axis and parallel to it suggests that both the beginning 5 4 5 ma and the end 3 2 5 ma of this phase were marked by intense volcanism in the sedimentary basins of the survey area two at least intra sedimentary horizons appear at respectively 140 160 ms and 340 360 ms two way travel time beneath the sediments surface using an inferred value of sedimentation rate of 50 70 m myr the age of the first horizon between 3 and 2 ma corresponds to the beginning of mid pliocene glaciations in the northern hemisphere the age of the second one between 6 5 and 4 5 ma to the pliocene miocene boundary our data and other data from other areas indicate that the three major sources of sediments western spitzbergen margin bear island trough and storfjord trough which supply the mohns ridge area near 72 n have been dramatically more active after 5 5 ma in addition local unconformities recorded in the single channel seismic sections indicate that some tectonic event occurred off axis little after the date corresponding to the deposition of the second horizon s2 if one accepts that the knipovich ridge migrated eastward 6 5 ma ago it can be hypothesized that the tectonic release of the lena trough knipovich ridge mohns ridge system forced the sediment production to increase at each one of the three sediment sources after the miocene pliocene transition

evidence of free convection in groundwater field based measurements beneath wind tidal flats free convection caused by salinity differences had not been conclusively detected or measured in the field a field experiment at wind tidal flats on padre island national seashore texas documents salinity driven free convection with both direct head and salinity data and indirect time lapse 3 d resistivity methods evaporative concentration of groundwater near the water table created unstable inverted density gradients reduced groundwater levels and reversed hydraulic gradients these factors allowed plumes or fingers of more saline denser fluid to flow downward into less dense fluid as observed in monitoring wells and 3 d surveys the development of density inversions can overcome the dissipating forces of dispersion and diffusion to create a sufficiently large unstable gradient to induce free convection the development of free convective flow of variable density fluids in groundwater can be detected and monitored through field techniques

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

structures and tectonics of tunisia abstract in the tunisian atlas nothing is known about the nature of the acoustic basement and in the saharan cratonic part only a few deep exploration wells have reached the precambrian below a thick unfolded palaeozoic sequence north of the craton a major set of faults w e or wnw ese represents the southern limit of palaeo tethys thick sequences of marine late carboniferous and permian were developed below the jeffara and chott jerid triassic evaporites are thick below the tunisian atlas which has enabled detachment of the cover from the basement and folding into plis de couverture structures large diapiric intrusions are known especially in the northwestern sillon tunisien tunisian trough from east to west there is a progressive variation from the stable platform on the eastern side to the unstable shelf of western tunisia between these a zone of tectonic instability named the north south axis corresponds to a deep fault system that acted as a positive suture characterized by tilted blocks gaps in sedimentation and reduced or condensed sequences in the north the unstable shelf of western tunisia grades to the deep furrows where the sediments now forming the tellian and numidian nappes were deposited these nappes overthrust the autochthonous foreland during the miocene orogeny the main folding took place in the pliocene and early pleistocene recent tectonic activity occurs along the main fault zones

modes of seawater intrusion during transgressions analytical methods and numerical experiments are used to study salinization of groundwater in response to sea level rise the system that is studied involves a saturated porous medium with an inclined upper surface the upper surface is progressively inundated during sea level rise to simulate transgression the landward migration of the shoreline four modes of seawater intrusion are distinguished 1 horizontal intrusion for slow transgression and a relatively high permeability substrate 2 vertical intrusion by seawater fingering for fast transgression and a sand silt substrate 3 vertical intrusion by diffusion for fast transgression and a low permeability clay substrate 4 vertical intrusion by combined diffusion and low salinity fingering for fast transgression and a clay layer at the seafloor overlying an aquifer these four modes are characterized by the development of very distinctive transition zones between the fresh and salt groundwater domains an analytical expression is derived for the critical transgression rate which separates horizontal mode 1 from dominantly vertical modes 2 4 intrusion for modes 3 and 4 salinization significantly lags behind sea level rise the results are consistent with observations of fossil fresh brackish groundwater beneath many continental shelves and shallow seas

sedimentary and crustal velocities in the norwegian greenland sea refraction and wide angle reflection velocities from the oceanic crust and the overlying sediments in the norwegian greenland sea have been analyzed there is a relatively rapid increase in velocity with depth in the uppermost sediments whereas a low constant gradient is representative of the main sediment sequence two regions the northeastern greenland sea and the oldest parts of the basins have particularly high velocity gradients 0 71 and 0 85 s 1 respectively the high gradient in the northeastern greenland sea is associated with the shear rifted margin off svalbard relatively high sea floor sediment sound velocities are typical of the norwegian greenland sea the crustal velocities fit the houtz ewing model which divides layer 2 into layers 2a 2b and 2c average velocities in the norwegian greenland sea are 3 88 2a 5 18 2b 6 05 2c 6 66 3 and 7 80 4 km s layer 2a is age dependent and has not been observed on crust older than 36 m y the model is not representative of the uppermost crust near the active spreading axis where one has to introduce additional layers or assume continuous velocity changes with depth

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective