tectono stratigraphy of the orhaniye basin turkey implications for collision chronology and paleogene biogeography of central anatolia abstract located along the izmir ankara erzincan suture iaes the maastrichtian paleogene orhaniye basin has yielded a highly enigmatic yet poorly dated paleogene mammal fauna the endemic character of which has suggested high faunal provincialism associated with paleogeographic isolation of the anatolian landmass during the early cenozoic despite its biogeographic significance the tectono stratigraphic history of the orhaniye basin has been poorly documented here we combine sedimentary magnetostratigraphic and geochronological data to infer the chronology and depositional history of the orhaniye basin we then assess how our new data and interpretations for the orhaniye basin impact 1 the timing and mechanisms of seaway closure along the iaes and 2 the biogeographic evolution of anatolia our results show that the orhaniye basin initially developed as a forearc basin during the maastrichtian before shifting to a retroarc foreland basin setting sometime between the early paleocene and 44 ma this chronology supports a two step scenario for the assemblage of the central anatolian landmass with incipient collision during the paleocene early eocene and final seaway retreat along the iaes during the earliest late eocene after the last marine incursion into the foreland basin our dating for the orhaniye mammal fauna 44 43 ma indicates the persistence of faunal endemism in northern anatolia until at least the late lutetian despite the advanced stage of iaes closure the tectonic evolution of dispersal corridors linking northern anatolia with adjacent parts of eurasia was not directly associated with iaes closure and consecutive uplifts but rather with the build up of continental bridges on the margins of anatolia in the alpine and tibetan himalayan orogens

the crustal domains of the alboran basin western mediterranean the alboran basin in the westernmost mediterranean hosts the orogenic boundary between the iberian and african plates although numerous geophysical studies of crustal structure onshore iberia have been carried out during the last decade the crustal structure of the alboran basin has comparatively been poorly studied we analyze crustal scale images of a grid of new and reprocessed multichannel seismic profiles showing the tectonic structure and variations in the reflective character of the crust of the basin the nature of the distinct domains has been ground truthed using available basement samples from drilling and dredging our results reveal four different crustal types domains of the alboran basin a a thin continental crust underneath the west alboran and malaga basins which transitions to b a magmatic arc crust in the central part of the alboran sea and the east alboran basin c the north african continental crust containing the pytheas and habibas sub basins and d the oceanic crust in the transition towards the algero balearic basin the alboran basin crust is configured in a fore arc basin west alboran and malaga basins a magmatic arc central and east alboran and a back arc system in the easternmost part of the east alboran basin and mainly algero balearic basin the north african continental crust is influenced by arc related magmatism along its edge and was probably affected by strike slip tectonics during westward migration of the miocene subduction system the distribution of active tectonic structures in the current compressional setting generally corresponds to boundaries between domains possibly representing inherited lithospheric scale weak structures

mantle dynamics beneath the gibraltar arc western mediterranean from shear wave splitting measurements on a dense seismic array 1 controversial evolutionary models have been proposed for the gibraltar arc system a complex interaction zone between the eurasia and african plates here we derive new mantle anisotropic constraints from sks splitting measurements on a dense network of about 90 broad band stations deployed over south iberia and north morocco the inferred fast polarization directions fpd clearly show a spectacular rotation along the arc following the curvature of the rif betic chain while stations located at the south and south east edges show distinct patterns these results support geodynamical processes invoking a fast retreating slab rather than convective removal and delamination models the fpd variations along the gibraltar arc can be explained by fossil anisotropy acquired during the western mediterranean eocene subduction while changes to the south and south east of the rif betic chain could be the imprint of a flow episode around an alboran high velocity slab during its miocene fragmentation from the algerian slab

quaternary history of the lake magadi basin southern kenya rift tectonic and climatic controls abstract sediments from the magadi basin south kenya rift preserve a one million year palaeoenvironmental record that reflects interactions between climatic volcanic and tectonic controls climate changes that impacted sedimentation include wet dry cycles on variable timescales and an overall progressive trend towards greater aridity volcanic influences involved inputs of tephra to the basin significant inflow of geothermal fluids and the effects of weathering erosion and transportation of clastics from trachyte and basalt terrains tectonic controls which were often step like reflect the influence of faults that provided pathways for fluids and which controlled accommodation space and drainage directions intensified aridity and evaporative concentration resulted in salinity and ph increasing with time which led to a change from calcite deposition in mildly saline lakes before 380 ka to the later formation of zeolites from reactions of volcaniclastic debris with highly alkaline lake and pore water after 105 ka hyperalkaline conditions led to trona accumulation and increasingly variable rare earth elements rees the presence of mixed saline and freshwater diatom taxa between 545 and 16 ka indicates climate variability and episodic inputs of fresh water to saline lakes calcrete formed in lake marginal settings during semi arid periods tectonic controls operated independently of climate but they interacted together to determine environmental conditions aquatic deposition was maintained during periods of increasing aridity because fault controlled ambient and geothermal springs continued to flow lakewards this recharge in turn limited pedogenesis palaeosols are common in other rift floor sequences trona formed when aridity and evapoconcentration increased but its precipitation also reflects increased magmatic co2 that ascended along faults basin fragmentation and north south fractures caused loss of cross rift east west drainage from rift marginal basalts resulting in reduced transition metals after 545 ka the magadi basin demonstrates how a careful reconstruction of these complex tectono climatic interactions is essential for accurate palaeoenvironmental reconstruction in continental rifts and in other tectonic settings

longitudinal convergence fronts in homogeneous rotating channels in situ observation and remote sensing imagery indicate the presence of velocity convergences located over bathymetric channels in the mouths of tidal estuaries in this paper we present the results of numerical simulations performed to investigate these velocity structures in a rotating channel having a single bathymetric groove the equations of motion for a homogeneous fluid on a rotating earth are solved using a fully spectral code in the across channel i e the vertical or x z plane no along channel flow variations in the y direction are permitted the bottom bathymetry is formed using a unique virtual surface approach goldstein et al 1993 that generates a no slip bottom using feedback forcing a gaussian shaped channel is employed to simulate typical estuarine bathymetry in the along channel direction a constant pressure gradient is imposed and the flow evolves until a steady state results the simulations are performed at high rossby number of order unity based on the width of the groove and a typical surface velocity simulations show the development of a localized along channel jet colocated with an across channel recirculation cell this feature results from the generation of streamwise vorticity through the tilting of planetary vorticity by the vertical shear in the along channel flow the associated across channel surface flow above the jet exhibits convergent and divergent regions which correlate reasonably well with features reported previously in the literature their number position and strength are seen to vary with the along channel reynolds number ekman layer thickness and channel aspect ratio

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

continental subduction intracrustal shortening and coeval upper crustal extension p t evolution of subducted south iberian paleomargin metapelites betics se spain abstract the nevado filabride complex represents the basement and permo triassic cover of the south iberian passive margin metamorphosed during miocene continental subduction under the alboran crustal domain it forms a nappe stack with the thick calar alto unit 6 km thick sandwiched between the ragua unit below and the bedar macael unit above the nappe stacking occurred by ductile flow along basal syn metamorphic shear zones structural analysis of the calar alto unit together with thermobarometric data of samples from both the bottom and top of the unit served us to understand the tectonic significance of this episode of intracrustal shortening in the context of a strongly extended orogen multiequilibrium thermobarometry shows that the calar alto schist underwent a prograde p t path at mantle depths from 1 6 gpa at 450 500 c to 1 0 gpa at 550 570 c during the growth of the schistosity s1 parallel to the compositional layering after detachment from the downgoing slab and underplating the unit underwent nearly isobaric cooling by up to 250 c from peak metamorphic conditions the main crenulation cleavage s2 and the mylonitic foliation sm developed within the crustal nappe stack during decompression and heating sm at the base of the unit grew between 0 8 gpa at 400 c and 0 4 gpa at 500 c while s2 at the top of the unit developed between 0 6 gpa at 300 c and 0 2 gpa at 400 c these shortening structures developed simultaneously to the activity of overlying middle miocene extensional detachments intracrustal shortening and coeval upper crustal extension resulted in a mode of exhumation where the material rise entailed an important horizontal component of displacement at rates of approximately 15 mm year being exhumed along an s shaped p t path after peak metamorphic conditions and its detachment from the subducting slab

slab rupture and delamination under the betics and rif constrained from receiver functions abstract we map the lithospheric structure under the westernmost mediterranean convergent setting interpreting p receiver functions obtained from a dense seismic network no orogenic root occurs under the eastern and great part of the central betics however the subducted south iberian continental lithosphere is found beneath the western betics where the iberian moho reaches depths of approximately 65 km dipping gently towards the se meanwhile at the rif strong crustal and lithospheric thickness contrasts occur across the nekor nw se sinistral fault that overlies the region of present slab tearing east of the nekor fault there is no orogenic root and the crust has been thinned to approximately 22 km whilst to the west the crust reaches 55 km thickness and the maghrebian continental lithosphere is attached to the lithospheric slab imaged by tomography under the alboran basin these data suggest that subduction rollback under the alboran and algerian basins together with continental slab tearing or detachment producing edge delamination under the betics and rif have been the main tectonic mechanisms driving extension magmatism and regional uplift in the westernmost mediterranean since the late miocene until present the surface expression of edge delamination and slab tearing is marked by regional uplift denudation of hp rocks in elongated core complex type domes late miocene volcanism in the eastern betics and rif and by large ne sw strike slip transfer faults like the alpujarras crevillente torcal or nekor faults that accommodate strong gradients in crustal displacements the iberian slab is still attached to the oceanic slab imaged under the alboran basin at the western betics where intermediate depth seismicity recent dextral strike slip faulting and folding could reflect slab tearing meanwhile active faulting and differential gps measured displacements would mark slab tearing beneath the rif coinciding with the trace of the sinistral nekor fault

compressional tectonic inversion of the algero balearic basin latemost miocene to present oblique convergence at the palomares margin western mediterranean interpretation of new multichannel seismic reflection profiles indicates that the palomares margin was formed by crustal scale extension and coeval magmatic accretion during middle to late miocene opening of the algero balearic basin the margin formed at the transition between thinned continental crust intruded by arc volcanism and back arc oceanic crust deformation produced during the later positive inversion of the margin offshore and onshore is partitioned between n50 e striking reverse faults and associated folds like the sierra cabrera and abubacer anticlines and n10 20 e sinistral strike slip faults like palomares and terreros faults parametric subbottom profiles and multibeam bathymetry offshore structural analysis available gps geodetic displacement data and earthquake focal mechanisms jointly indicate that tectonic inversion of the palomares margin is currently active the palomares margin shows a structural pattern comparable to the north maghrebian margins where africa eurasia plate convergence is accommodated by ne sw reverse faults nnw sse sinistral faults and wnw ese dextral ones contractive structures at this margin contribute to the general inversion of the western mediterranean since 7 ma coeval to inversion at the algerian margin shortening at the alboran ridge and al idrisi faults occurred later since 5 ma indicating a westward propagation of the compressional inversion of the western mediterranean

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

degassing of mantle derived co2 and he from springs in the southern colorado plateau region neotectonic connections and implications for groundwater systems groundwaters of the southern colorado plateau arizona transition zone region are a heterogeneous mixture of chemically diverse waters including meteoric epigenic fluids karst aquifer waters and deeply sourced endogenic fluids we investigate the composition of travertine depositing co 2 rich springs to determine the origin transport and mixing of these various components the san francisco mountain recharge area has little surface flow instead waters discharge through major springs hundreds of kilometers away about 70 9340 l s of the total recharge 13 500 l s discharges 100 km to the north in the incised aquifer system at grand canyon most of this water 85 8070 l s emerges through two travertine depositing karst spring systems blue springs 6230 l s and havasu springs 1840 l s about 30 of recharge 4150 l s flows to the south and discharges along nw striking faults in the arizona transition zone forming the base flow for the verde river geochemical data define regional mixing trends between meteoric recharge and different endogenic end members that range from bicarbonate waters to sulfate waters water quality in the region is dictated by the percentage and character of the endogenic inputs that cause a measurable degradation of groundwater quality for water supply sources for the high co 2 include dissolution of limestone and dolostone c carb and external carbon c external c external is computed as the bicarbonate alkalinity dissolved inorganic carbon dic minus the c carb c external dic c carb c external is deconvolved using carbon isotopes into biogenically derived sedimentary carbon c organic and deep co 2 inputs c endogenic measured 13 c values are 17 to 3 versus pee dee belemnite pdb assuming 13 c carb 2 13 c organic 28 and 13 c endogenic 5 water chemistry mixing models indicate that an average of 42 of the total dic comes from dissolution of carbonate rocks 25 from organic carbon including soil respired co 2 and 33 from deep endogenic sources helium isotope values 3 he 4 he in gases dissolved in spring waters in the southern colorado plateau region range from 0 10 to 1 16 r a relative to air indicating that a significant component of the deeply derived fluid is from the mantle mean of 5 asthenospheric or 10 subcontinental lithospheric mantle source measured co 2 3 he ratios of 2 10 9 to 1 4 10 13 are adjusted by removing the proportion of co 2 from c carb and c organic to give values 10 for all but four samples various mixing models using co 2 3 he suggest that the mantle derived components of the co 2 load are highly variable from spring to spring and may make up an average of 10 of the total co 2 load of the regional springs fluid rock interactions involving endogenic fluids are suggested by 87 sr 86 sr 18 o and other tracers the endogenic co 2 component multiplied by discharge for each spring yields an integrated annual flux of deeply derived co 2 to the groundwater system of 1 4 10 9 mol yr this co 2 emission from the colorado plateau region reflects a complex tectonic evolution involving laramide hydration of the lithosphere above the farallon slab addition of fluids from mid tertiary mantle tectonism during slab removal and ongoing fluid movement induced by neotectonic small scale asthenospheric convection

evidence for slab rollback in westernmost mediterranean from improved upper mantle imaging this work is funded by the picasso project nsf grant ear 0808939 the deployment and data processing for spanish stations was funded by consolider ingenio 2010 project topo iberia csd2006 00041 as well as alert es cgl2010 19803 c03 02

a 36cl chronology of lacustrine sedimentation in the pleistocene owens river system we have used 36 cl to date climatically sensitive saline lake sediments from hydrologically closed basins in southeastern california primarily sediments from searles and panamint basins during wet periods of the past 2 0 m y lakes that formed in the closed basins fluctuated in size in direct response to the balance between runoff and evaporation we have compiled a chronology for the km 3 core from searles lake based on ages determined by 36 cl for the evaporites together with those determined by 14 c and u th series for younger sediments and by magnetostratigraphy for older sediments this chronology along with other criteria such as correlations between searles and panamint basins the chloride budget and sedimentology is used to reconstruct the history of lake fluctuations in the paleo owens river system we infer that searles lake desiccated at most twice since 600 ka during the interval around 290 ka and from 10 ka to the present the lake history curve shows that the holocene epoch is anomalously arid major overflows from searles to panamint occurred during the intervals between 1 3 ma and 1 0 ma 750 ka and 600 ka 500 ka and 400 ka and 150 ka and 120 ka comparing the lake fluctuation chronology to the 18 o record of marine foraminifera we infer that the strongest similarity is in the periodicities of the cycles 40 to 50 kyr before the matuyama brunhes magnetic reversal 730 ka and 100 kyr thereafter we find however that at searles lake this fluctuation in the lake chronology is modulated by longer term cycles of aridity and humidity thus although the mid latitude quaternary climate record reflects the mid to high latitude ice volume fluctuations that dominate the marine 18 o record it also contains evidence for climatic forcing of a different type

evaporitic carbonates in the pre salt of santos basin genesis and tectonic implications abstract since the first discoveries of oil accumulations in the carbonate reservoirs of the lower cretaceous barra velha formation of the santos basin their genesis has been the subject of intense discussion different depositional models have been proposed with some authors advocating a microbial origin while others an abiotic origin as travertines or travertine like rocks this search for a modern carbonate analogue for these unusual rocks may have disregarded an intriguing alternative an evaporative model supported by our petrographical and geochemical data evaporitic sediment patterns in endorheic basins in a depositional framework of brine drawdown are dominated by ephemeral salt pan hydrology bedded salt crusts form a stack of subaqueous aligned crystal beds at the sediment water interface salt grows diagenetically within saline and mud layers beneath the dry pan surface finally laminated sediments are deposited we observe a similar cyclic pattern in the pre salt core we described beds of shrub like crystals and diagenetic spherulites growing in magnesium clay matrix are followed by laminites the model we propose attempts to contribute solving the puzzle of pre salt carbonate deposition by integrating sedimentology and geochemistry with basin tectonics our observations and basin tectonics point to the exciting possibility that the sag phase carbonates of the santos campos basin were deposited as the initial transitional stage of a closed sub sea level evaporite basin whose rising salinities culminated in the deposition of halite and bittern salts carnallite sylvite tachyhydrite basinwide evaporites are singular events in the geological record they form when a giant sub sea level basin becomes a sump of continental marine and hydrothermal fluids producing unexpected brine compositions in unusual depositional settings present in ancient evaporitic basins but absent from most modern ones the novelty in this paper is that we apply to pre salt carbonate deposition the sedimentology hydrology and geochemistry of ancient evaporitic basins with this concept in mind we propose a geochemical model for the unusual pre salt carbonate precipitation of the santos basin regarding the walvis rio grande volcanic high as a topographic barrier during the aptian we suggest that the main sources of calcium to the barra velha paleolake were hydrothermal brines mostly from infiltrating seawater that reacted at depth with the basalts of the volcanic barrier hyperextension of the lithosphere with a shallow moho increased geothermal gradients to levels favorable for the generation of hydrothermal cacl2 brines a process facilitated by the already elevated ca ion and low sulfate concentration of the cretaceous ocean these cacl2 rich fluids would pass through the volcanic barrier into a sub sea level paleolake in the rift basin the high salinity paleolake would become saturated in calcium bicarbonate carbonate as internally drained nahco3 bearing alkaline waters formed by physical chemical weathering of penecontemporaneous basaltic rocks mix with the cacl2 bearing hot brines percolating through the barrier producing a hybrid brine 2nahco3 cacl2 ca hco3 2 2nacl such a depositional system integrating the geochemical depositional controls of sag phase carbonates with those of the south atlantic evaporites has important implications for unravelling the genesis of these exotic deposits

upper crustal extension during oblique collision the temsamane extensional detachment eastern rif morocco terra nova 24 505 512 2012 abstract the subducted north maghrebian passive margin was exhumed in the tortonian 11 7 ma by an upper crustal brittle ductile extensional detachment and brittle low angle normal faults in a continental subduction transform setting the temsamane detachment in the eastern rif is defined by a ductile shear zone approximately 100 m thick with a low angle ramp geometry that cuts down into the temsamane fold nappe stack the shear zone shows south westward kinematics and separates lower greenschist 400 c metapelites of the temsamane units below from the anchizone and diagenetic rocks 300 200 c of the ketama aknoul units above to the east the detachment becomes brittle branching into a listric fan that cuts through 10 6 ma sediments and volcanoclastics in the tres forcas cape both the north maghrebian and the south iberian subducted passive margins were exhumed in the betic and rif branches of the gibraltar arc by sw directed brittle ductile detachments during the late miocene in an oblique collisional setting

crustal architecture and tectonic evolution of the gulf of cadiz sw iberian margin at the convergence of the eurasian and african plates 1 the gulf of cadiz located at the southwestern iberian margin is characterized by widespread seismicity compressional and strike slip fault plane solutions and by a large elongated positive free air gravity anomaly the gulf of cadiz gravity high gcgh multichannel seismic profiles across and along gcgh together with bathymetric and gravity data allow us to study in detail the tectonic architecture and crustal structure of the gulf of cadiz the upper shelf and slope of the gulf of cadiz includes the main structural domains of the betic fold and thrust belt in the middle part of the gulf the paleozoic basement crops out on the shallow guadalquivir bank and is associated with the largest signature of the gcgh whereas toward the outer part of the gulf the basement deepens progressively a large nw se normal fault and conjugate ne sw faults define a prominent basement high associated with the gcgh modeling of the gcgh suggests localized crustal thinning of 10 km along the central part of the gulf of cadiz probably generated during the mesozoic rifting episode between the iberian and african plates concentric wedges of fold and thrust belts and large allochthonous masses were emplaced in the gulf of cadiz during the neogene compressional phase the final emplacement of these units becomes progressively young from the se pre early langhian toward the foreland in the nw late tortonian seafloor surface ruptures pockmarks and submarine landslides provide evidence of active faulting in the gulf of cadiz to accommodate the present day convergence between the african and eurasian plates previously extensional faults have probably been reactivated and inverted at depth as suggested by the intermediate depth seismicity

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

acoustic doppler current profiler measurements in coastal and estuarine environments examples from the tay estuary scotland acoustic doppler current profilers adcps provide a means to measure the components of water current velocities in three dimensions such instruments have been used widely by the oil industry in deep offshore waters but their application to nearshore coastal and estuarine environments has been principally confined to the usa using examples of adcp datasets acquired from the macrotidal tay estuary eastern scotland the principles of field deployment data acquisition and forms of output are critically summarised it is shown for the first time in the tay estuary that vertical current velocities are significant and are particularly so in downwelling zones associated with the development and passage of axially convergent tidal fronts the improved understanding of three dimensional water and suspended sediment dynamics in coastal and estuarine waters is crucial to inter alia the sustainable management of effluent discharges and in more general terms it is predicted on the basis of the tay case study that adcp measurements afford significant opportunities to refine understanding of geomorphological processes in a variety of aquatic environments worldwide

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

convergence fronts in tidally forced rotating estuaries in situ observation and remote sensing imagery reveal the presence of longitudinal velocity convergences over bathymetric channels in tidal estuaries we present the results of numerical experiments designed to investigate the cause of these convergences for channels possessing shallow shoal regions and a deeper central region the equations of motion for a homogeneous fluid on a rotating earth are solved using a fully spectral code in the across estuary i e the vertical or x z plane while no along estuary flow variations in the y direction are permitted a gaussian shaped bottom bathymetry is chosen in the along channel y direction we impose a pressure gradient which is the sum of constant and fluctuating parts to simulate the steady and tidally oscillating parts of the estuarine flow the details of the transient response can be complicated but we observe that for most 80 of the tidal cycle there exists a cross estuary recirculation cell colocated with a localized along channel jet both of these are situated over the bottom bathymetric groove the circulation is always clockwise when facing down current this feature results from the generation of stream wise vorticity through the tilting of planetary vorticity by the vertical shear of the along estuary flow a surface convergence divergence pair is associated with the flow the maximum value of each is seen to occur on the edge of the bathymetric feature but may migrate toward or away from the center as long as the current continues in the same direction when the tide reverses the feature reappears on the opposite shoal and the migration of the convergence and divergence extrema begins again we also find that the responses are qualitatively similar for all bathymetric grooves even asymmetrically situated ones provided that the estuary width to depth ratio is of order 100 or larger the rossby numbers are of order unity and the ekman layer thickness to channel depth ratio is greater than 0 65

the seismic reflection character of the continental mohorovicic discontinuity the continental mohorovicic discontinuity is most often interpreted as a step function velocity boundary however on deep crustal seismic reflection profiles reflections at depths where refraction data places the moho have laminated character and are laterally discontinuous these observations on continental reflection data point to a model of the moho that has thin layered rather than block structure previous workers who have synthetically generated seismic responses from various crust mantle boundary models have shown that thin layered models of alternating high and low velocity generate responses that best emulate observed moho arrivals geologic interpretations of the thin layering include relatively undeformed metasediments cumulate layering tectonic banding and lenses of partial melt to obtain more direct geologic evidence a synthetic seismogram is generated from geologic cross sections of the ivrea verbano zone an exposed section through the lower crust and upper mantle the synthetic shows laminations similar to those observed on reflection data without more direct evidence no single geologic interpretation of the moho is reasonable indeed the moho may be a laterally variable boundary its composition and structure dependent upon the geologic history of the overlying crust

active deformation in old oceanic lithosphere and significance for earthquake hazard seismic imaging of the coral patch ridge area and neighboring abyssal plains sw iberian margin recently acquired high resolution multichannel seismic profiles together with bathymetric and sub bottom profiler data from the external part of the gulf of cadiz iberia africa plate boundary reveal active deformation involving old mesozoic oceanic lithosphere this area is located 180 km offshore the sw iberian peninsula and embraces the prominent ne sw trending coral patch ridge and part of the surrounding deep horseshoe and seine abyssal plains e w trending dextral strike slip faults showing surface deformation of flower like structures predominate in the horseshoe abyssal plain whereas ne sw trending compressive structures prevail in the coral patch ridge and seine hills although the coral patch ridge region is characterized by subdued seismic activity the area is not free from seismic hazard most of the newly mapped faults correspond to active blind thrusts and strike slip faults that are able to generate large magnitude earthquakes mw 7 2 8 4 this may represent a significant earthquake and tsunami hazard that has been overlooked so far

a numerical study of lateral grain size sorting by an estuarine front abstract a two dimensional non hydrostatic model of baroclinic flow was applied to an estuarine cross section the model was driven by lateral variations in density and produced the classical bilateral cross sectional recirculation of an axial convergent front simulations of the erosion transport and deposition of sediment by the frontal secondary flows were applied to a range of grain sizes the model predicted considerable lateral variation in grain size deposition across the frontal recirculation zone analogous to the lateral grain size sorting which occurs in river meanders the sorting primarily took place between the frontal surface convergence and the bankward limit of recirculation a series of sensitivity tests revealed that the contribution of the front to lateral grain size sorting was strongly influenced by the lateral channel slopes and lateral density gradient the results from this numerical study support previous suggestions based on observations of near surface discontinuities in sediment concentration across the frontal interface that fronts may act as sieves within the estuarine sediment transport system

high resolution moho topography map beneath iberia and northern morocco from receiver function analysis abstract crustal thickness maps at regional scales are typically compiled using estimations inferred from different geophysical datasets providing a variable coverage of the investigated area consequently spurious effects related to changes in data resolution or artifacts in grid interpolation may affect significant zones of those maps the topoiberia iberarray broad band seismic network covering the iberian peninsula and northern morocco with stations distributed on a regular 60 60 km grid provides a unique opportunity to avoid such technical problems and to obtain a crustal thickness map derived from a same method sampling evenly all the region data from more than 340 stations has been gathered and analyzed using the p to s conversion phases at the moho discontinuity receiver functions the crustal thickness has been inferred applying the classical h stacking technique though in regions of complex crustal structure we have preferred to estimate the thickness directly from the arrival time of the converted phase at some sites the topography of the moho discontinuity is strongly correlated with tectonic processes the investigated area extending from the sahara platform to the bay of biscay has a great geodynamic diversity including north to south crustal imbrication in the pyrenean and cantabrian range a large and relatively undisturbed variscan massif in the center of iberia and areas of complex and still not completely understood geodynamics in the alboran crust domain and the atlas range the crustal thickness map reflects this diversity showing variations reaching 30 km between the thickest and thinnest zones of continental crust the final map has an overall similarity with previous estimations of the crustal thickness using independent data as those coming from more sparse deep seismic sounding profiles but provides further constraints at regional scale

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

the structure of the temsamane fold and thrust stack eastern rif morocco evolution of a transpressional orogenic wedge abstract the structure of the temsamane fold and thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds this ductile stack was formed in an inclined left handed transpressional zone at the north african paleomargin during chattian to langhian times producing two main deformational events the first event d p produced a s p l p planar linear fabric generated in a non coaxial deformation with a top to the wsw sense of movement and was associated to metamorphic p t conditions varying from late diagenesis in the southernmost temsamane outcrops to epizone in the north according to the 40 ar 39 ar ages this deformation occurred at chattian aquitanian times the second deformational event d c event generated ene wsw trending folds with sse vergence and a set of anastomosing shear zones with s m l m planar linear fabric the latter units were generated at around 15 ma langhian and indicate a strong localization of the simple shear component of the transpression moreover this orientation is compatible with the kinematics of the temsamane detachment which can explain most of the uplift of the temsamane rocks from the middle to the uppermost crust the described evolution indicates that collision between the western mediterranean terranes and the north african paleomargin and the formation of the rifean orogenic wedge occurred at chattian to langhian times

density driven secondary circulation in a tropical mangrove estuary abstract observations of suspended sediment concentration ssc salinity and current were made in the normanby river estuary cape york peninsula northern australia the estuarine reaches are approximately 80 km in length and are fringed by mangroves a well developed axial convergence was found to exist almost unbroken for a distance of at least 30 km on flood tides clearly delineated by an accumulation of mangrove leaves and seed pods on the water surface the convergence migrated to the inside of most bends suspended sediment concentration profiles were very well mixed both vertically and laterally salinity profiles showed a cross channel salinity gradient of 0 2 25 m sufficient to form density driven secondary cells the cells produce an effective transverse mixing coefficient of 0 25 m 2 s 1 of the same order of magnitude as the conventional transverse diffusion coefficients for natural meandering channels mangrove seeds were present in the channel centre during flood tides and were moved to the channel banks during ebb tides due to the lateral shear in longitudinal currents mangrove seeds are predicted to move landward up the estuary at a rate of 1 km per day when density driven circulation cells are active influencing mangrove seed dispersal

40ar 39ar age of the cabo de gata volcanic series and displacements on the carboneras fault zone se spain the sw ne trending carboneras fault zone of se spain separates a terrain comprising uplifted massifs of the metamorphic basement of the betic cordilleras and intervening neogene sedimentary basins from the cabo de gata volcanic series along the southeastern boundary of the carboneras fault burdigalian marls and tuffs mark the beginning of the volcanic episode rest unconformably on the basement and were tilted to the vertical during the earliest stages of movement on the fault zone 40 ar 39 ar dating of hornblende grains and igneous clasts from the tuffs constrain the onset of the volcanic episode at 21 ma some 4 ma earlier than previously reported volcanic rocks higher in the sequence that overstep unconformably onto the southern edge of the fault zone yielded an age of 11 ma thus constraining the earliest episode of motion on the fault zone between these age limits the main phase of left lateral strike slip movement on the carboneras fault may be later than this time movements on more northerly strands of the fault zone including the uplift of the sierra cabrera basement block to the nw continued at least through pliocene times the onset of volcanism is broadly coeval with the unroofing of the orogen by extensional collapse and supports earlier inferences of very rapid rates of uplift and cooling of the basement rocks

influence of magmatic hydrothermal activity on brine evolution in closed basins searles lake california evaporites in a 700 m long core km 3 from searles lake california preserve a record of the chemical evolution of inflow waters chemical analyses of fluid inclusions in halite and evaporite minerals show that the major ion composition of inflow waters to searles lake was changed by distant hydrothermal activity associated with magmatism at long valley caldera between 1 27 and 1 0 m y ago below core depths of 291 m the evaporites consist of ca bearing sulfates anhydrite glauberite and halite fluid inclusions in the halite show that parent waters were na cl so42 rich waters above 291 m the evaporites include sodium carbonates pirssonite trona and halite and fluid inclusion brines are na k hco3 co32 cl so42 rich these fluctuations in mineralogy and brine chemistry document an alkalinity spike beginning between 1 27 and 1 0 ma when inflow waters to searles lake crossed the caco3 chemical divide and began to produce alkaline brines that precipitated trona upon evaporation the owens river is a modern chemical analog for inflow water into searles lake beginning between 1 27 ma and 1 0 ma a major contributor of solutes to the owens river is hot creek in long valley caldera which is fed by hydrothermal springs with high alkalinity from magmatically derived co2 the timing of magmatism in owens valley and the appearance of sodium carbonate minerals in core km 3 suggest a causal relationship volcanism and hydrothermal activity provided co2 and elevated alkalinity to searles lake inflow waters 0 5 0 2 m y before the eruptions that formed the bishop tuff and long valley caldera

paleoenvironmental setting mechanism and consequence of massive organic carbon burial in the permian junggar basin nw china abstract the junggar basin in northwestern china is a typical walled sedimentary basin that has a prolonged basin evolution history from the paleozoic to cenozoic and is rich in petroleum resources permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments they have also been exploited for oil and gas for the past several decades in this paper we summarize perspectives on tectonic evolution stratigraphic framework sedimentary environments and the paleoclimate of the permian junggar basin and the adjacent turpan basin further we discuss the mechanism and consequences of massive organic carbon burial based on a compilation of published radiometric dating datasets an updated chronostratigraphic framework was proposed for the junggar basin this framework constrains the ages of two main petroleum source intervals the fengcheng formation and the lucaogou and equivalent formations as early permian and middle permian respectively although a global warming and drying trend was present throughout the permian period the regional climate over the junggar basin was drier in early permian and more humid in the middle late permian with short term climatic fluctuations during the deposition of the two petroleum source intervals dry and temperate climate prevailed and evaporative lacustrine environment dominated organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments leading to one of the richest lacustrine source rock deposits in the world the average organic carbon burial rates were 11 2 gc m2 yr for the lucaogou formation and 3 5 gc m2 yr for the fengcheng formation lower than the average organic carbon burial rate in modern lakes however considering the large areas of global tectonic lakes in the permian period organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution

heterogeneous extension and the role of transfer faults in the development of the southeastern betic basins se spain large strike slip faults in the eastern betics are interpreted to have developed in a transcurrent setting in response to 4 6 mm yr of africa iberia nw se convergence however here we show that some of these faults are transfer faults accommodating heterogeneous late miocene extension the north cabrera dextral fault and other e w to ne sw strike slip faults in the sorbas basin were transfer faults produced under sw ne extension these faults together with related normal faults form the main boundaries of two sedimentary depocenters active between the serravallian and the tortonian the older north cabrera depocenter extended between the serravallian and the early tortonian approximately 13 8 to 9 ma while the younger gacia depocenter formed in response to late tortonian extension approximately 9 to 7 5 ma the latter formed to the west of the north cabrera depocenter by a listric fan of normal faults with sw directed transport that are linked by dextral and sinistral transfer fault segments these faults root on a low angle detachment cutting into the exhumed high pressure nevado filabride complex rocks at 0 8 km depth the present work reveals that 1 this extension was partially coeval with and kinematically linked to sinistral displacement along the carboneras fault farther south in the nijar basin 2 this westward directed extension produced elongated core complexes and tilted blocks to the north of the carboneras fault and magmatic accretion upon thinned continental crust to the south probably in response to slab tearing or detachment and associated edge delamination of the iberian continental lithospheric mantle beneath the betics

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

the role of attenuation in the formation of the railroad valley structural basin east central nevada detachment control of petroleum reservoirs the eastern boundary of railroad valley has long been considered a large displacement steep normal fault by mapping a low angle fault called the white pine detachment wpd from the ranges into the valley we show that steep normal faulting was not a significant process in the formation of railroad valley the wpd or its equivalent extends throughout the white pine and grant ranges as shown by mapping of previous authors well data show that it is also present in railroad valley our structure contour map of the wpd based on surface and subsurface data shows that the wpd dips uniformly from the ranges into railroad valley and is not displaced significantly by high angle faulting even if high angle faulting were assumed the maximum displacement consistent with the data would be 2000 ft 610 m much smaller than the total structural relief of at least 16 000 ft 4880 m between the grant range and the adjacent valley structural elevations in the valley are low because the paleozoic section has been greatly attenuated a related contribution to structural relief is uplifting of the ranges caused by diapiric emplacement of plutons in response to tectonic unloading the wpd is only one of many detachments in railroad valley we propose that most or all of the oil reservoirs are in attenuated brittle blocks between detachments seals are provided by detachments or by the discontinuous nature of associated fracturing attenuation by juxtaposing hot infrastructure rocks with rocks that normally occur thousands of feet above the granitic and metamorphic basement may have contributed to maturation of source rocks begin page 1154

convergence of lateral flow along a coastal plain estuary a set of velocity profiles obtained in the james river estuary with an acoustic doppler current profiler was used in combination with the results of an analytic tidal model to depict the appearance of surface lateral flow convergences v y during both flood and ebb stages of the tidal cycle the bathymetry of the estuary was characterized by a main channel and a secondary channel separated by relatively narrow shoals lateral surface flow convergences appeared over the edges of the channels and were produced by the phase lag of the flow in the channel relative to the shoals flood convergences developed in the late tidal stages and ebb convergences appeared soon after maximum currents most of these convergences caused fronts in the density field and flotsam lines that also appeared over the edges of the channel and that lasted 2 hours the transverse flows associated with the convergences were mostly in the same direction throughout the water column in fact the vertically averaged flow produced the same convergence patterns as those near the surface the analytic tidal model reproduced well the timing and location of the convergences as observed in the james river model results with different bathymetry emulated the results in other estuaries e g axial convergence in an estuary with a channel in the middle this work showed that the strength of lateral convergences along the estuary was proportional to the tidal amplitude and the channel steepness it also suggested that the convergences were produced mainly by the tidal flow interacting with the channel shoal bathymetry i e that they did not require the presence of density gradients however the analytic model underestimated the magnitude of the convergences and did not account for vertical circulations associated with fronts the formation of fronts resulted from the interaction of the tidal flow with the bathymetry and the density field

the flysch trough thrust imbricate betic cordillera a key element of the gibraltar arc orogenic wedge 1 within the betic rif orogenic system the flysch trough units are formed mainly by siliciclastic rocks upper jurassic to lower miocene in age in the gibraltar arc area they are presently deformed as an accretionary prism sandwiched between the fold and thrust belt derived from the south iberian paleomargin sedimentary series and the metamorphic rocks of the alboran domain on top in the northern branch of the gibraltar arc the main tectonic unit of the flysch complex is the aljibe unit which shows a well organized structure of thrust imbricates post lower burdigalian in age in this unit various domains separated by major accommodation zones are characterized by their structural style and vergence this change in structural style can be explained as a consequence of the variations of rock type along the basal decollement finally these thrust systems were affected by extensional low to medium angle faults and large scale very open folds successively the organization of the aljibe unit fits a push from behind mechanism for its emplacement in which the relatively rigid back stop would be represented by the alboran domain with the data presented in this paper it is definitely shown that the aljibe unit is not chaotic as claimed in previous papers and that the tectonic transport direction around the gibraltar arc swings from a northwestward to a westward direction along its northern branch in the vicinity of the straits

tectonic evolution of the betic rif arc new constraints from 40ar 39ar dating on white micas in the temsamane units external rif northern morocco article i nfo the betic rif orogen at the western end of the mediterranean is a key region to improve our knowledge on the africa eurasia convergence the temsamane units in spite of their external position in the rif northern morocco underwent medium pressure low temperature mp lt conditions ca 7 9 kbar 330 430 c we propose a new tectonic and metamorphic evolution scenario for the rif southern branch of the orogen on the basis of first 40 ar 39 ar dating on petrologically and structurally characterized white micas three groups of 40 ar 39 ar ages are observed 1 chattian or older si rich highest pressure mica relics 2 15 12 5 ma corresponding to the micas defining the foliation and 3 messinian or younger late micas and alteration we propose that the mp lt metamorphic event in the external rif is oligocene in age highlighting a subduction event during this period which could be almost contemporaneous with the burial of hp lt units from the internal rif alboran domain the exhumation of these units characterized by an intense e w stretching and by top to the west shear senses is middle to late miocene in age we propose a correlation of tectonic and metamorphic events at the betic rif arc scale we argue that the exhumation of the external units of the rif 1 is younger than that of the alboran domain internal unit of the rif and mirrors a different tectonic setting but 2 strongly resembles to that documented in the lower alboran domain units of the betics we show that a regional e w extension is recorded on both sides of the betic rif arc during the middle miocene this extension probably reflects back arc deformation of an eastward dipping subduction that retreated westward during the middle to late miocene in the western mediterranean

a genetic model for na carbonate mineral precipitation in the miocene beypazari trona deposit ankara province turkey abstract the miocene beypazari trona deposit in central anatolia turkey with estimated reserves of 250 million of tons of soda ash sodium carbonate is the second largest na carbonate deposit in the world petrographic observations of sodium carbonate evaporites from basin center cores show that the evaporites and associated minerals underwent significant early diagenetic mineral transformations in the beypazari basin trona pirssonite and nahcolite are the major evaporite minerals with subordinate bradleyite shortite and thenardite pirssonite occurs in organic rich muds oil shales pirssonite is not a primary mineral but rather appears to have formed diagenetically from displacive gaylussite trona precipitated subaqueously in lake waters and as interstitial phase in playa muds nahcolite is a later diagenetic mineral replacing both trona and pirssonite beds evaporite minerals are closely related to pyrite in oil shales and are also associated with diagenetic silicates mg rich smectites zeolites k feldspar searlesite and idiomorphic quartz formed by reaction of alkaline brines with pyroclastic deposits the proposed sedimentary model involves an alkaline lake in which water depth fluctuated from deep perennial meromictic stratified stages to shallow ephemeral playa lake stages lake margin clastic deposits are absent in the center of the basin wherein na carbonate minerals were formed suggesting the prevalence of a groundwater regime during drawdown events

crustal structure of the betic rif system western mediterranean from local earthquake tomography abstract we have determined the three dimensional p wave velocity structure of the crust and uppermost mantle beneath the iberia africa collision zone using local earthquake tomography we have inverted arrival times of first arriving p phases listed in the bulletins of the instituto geografico nacional and phases picked by us on permanent stations of other regional networks and on temporary broadband stations deployed in the frame of the topo iberia project in total we have used 38 624 p wave arrival times from 2362 local events recorded at 120 seismic stations the most remarkable result is the imaging of a large high velocity body following approximately the western alboran coastline with a horizontal dimension of at least 200 km and extending in depth from the surface down to 24 km this body not imaged previously with this extent using seismic tomography coincides with surface exposures of subcontinental mantle peridotites in iberia and africa and with a belt of positive gravity anomalies we have also found a marked contrast in the seismic velocities of the middle and lower crust of the alboran basin coinciding with the location of the trans alboran shear zone we attribute this contrast to widespread magmatic intrusions in the eastern part of the basin resulting in higher p wave velocities than in the west this contrast would also explain the different orientation of the trans alboran shear zone with respect to the surface features and faults in the alboran basin we also image thick crust beneath the betics and rif accompanied by downgoing lithosphere of the iberian foreland and gulf of cadiz beneath the betic rif alboran system

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

lithosphere scale seismic image of the southern urals from explosion source reflection profiling explosive source deep seismic reflection data from the southern ural mountains of central russia provided a lithosphere scale image of the central eurasian plate that reveals deep reflections 35 to 45 seconds in travel time 130 to 170 kilometers deep from the mantle the data display laterally variable reflectivity at the base of the crust that deepens beneath the central part of the profile documenting a crustal thickness of 55 to 60 kilometers beneath the axis of the orogen these data provide an image of the structure of the crust and underlying mantle lithosphere in a preserved collisional orogen perhaps to the base of the lithosphere

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the luanhe river north china groundwater in the alluvial fan area of the luanhe river north china was monitored every 2 months for a year subsequently the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis hca and a trilinear piper diagram it is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences even if the distance between many of the wells is small also the difference in the ion concentration was found to be up to fivefold for the same monitored well research has indicated that the groundwater s chemical characteristics are mainly controlled by soil type the amount of precipitation the luanhe river the groundwater and human factors the thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow this results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream in the flood season june july and august ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation classification using hca indicates that the samples can be clustered into different groups according to correlation coefficients also the chemical composition of the water from monitoring wells near the luanhe river is approximately consistent with that from the luanhe river this implies that the samples have some compositions resulted from the mixing of groundwater and river water the piper diagram indicates that ca2 mg2 and hco3 ions are the predominant ones present i e the type of groundwater is of the ca mg hco3 type

intratidal dynamics of fronts and lateral circulation at the shoal channel interface in a partially stratified estuary abstractin partially stratified shoal channel estuaries variations in bathymetry at the shoal channel interface generate horizontal shears and density gradients and foam lines characteristic of convergence fronts are frequently observed this study is based on transect data collected every 30 min across the shoal channel interface in south san francisco bay to analyze the dynamics of the transverse circulation and convergence fronts at this interface throughout a tidal cycle during the ebb a lateral density gradient develops as a result of the competition between differential advection of the longitudinal salinity gradient lateral variations in vertical mixing and nonlinear advection terms which are strongest when convergence fronts develop early and late in the ebb the lateral circulation over the slope is characterized by a large intratidal variability reversing three times during the ebb this variability is driven by a balance dominated by inertia and lateral baroclinic pressure gradient duri

the structure of the atlantic mediterranean transition zone from the alboran sea to the horseshoe abyssal plain iberia africa plate boundary abstract the diffusive plate boundary between iberia and africa has been analyzed by means of already published and new 28 multichannel seismic profiles covering most of the atlantic margins of sw spain and nw morocco this region includes the prolongation of the betic rifean tectonic units along the gibraltar arc one of the most characteristic units in the study area is the miocene seismically chaotic unit that has been divided in a tectonic and a gravitational domains in accordance to previous interpretation by torelli et al torelli l sartori r zitellini n 1997 the giant chaotic body in the atlantic ocean off gibraltar new results from a deep seismic reflection survey marine and petroleum geology 14 125 138 in this work we redefine the limits of both domains and rename them as the gulf of cadiz imbricate wedge and the horseshoe gravitational unit we interpret the gulf of cadiz imbricate wedge as a west migrating thick thrust system that build up in a relatively short period of time this unit constitutes the continuation of the miocene chaotic units observed onshore to the front of the external units in the betics and the rif the guadalquivir allochthonous unit and the rides prerifaines the horseshoe gravitational unit covering an approximate area of 18 000 km2 with a volume of around 23 000 km3 is interpreted as giant submarine debris flows sourced from the up building of the gulf of cadiz imbricate wedge surrounding basement highs and the continental iberian slope the fast westward migration of the flysch units the external units and the gulf of cadiz imbricate wedge from the early miocene to the late tortonian corresponds to a different tectonic process than the protracted but slow nnw to nw convergence of africa our interpretation favours the westward slab retreat theory to form the arcuate shape of the atlantic side of the iberia africa plate boundary the subduction mechanism as well as potential roll over was only active from late early miocene to late miocene spanning about 12 myr

hydrogeochemistry of the middle rio grande aquifer system fluid mixing and salinization of the rio grande due to fault inputs abstract deeply derived fluids influence river and groundwater hydrochemistry at the socorro constriction in the central new mexico rio grande rift new hydrochemical transects in the rio grande rift provide three dimensional perspectives on sources contributing to surface and groundwaters in addition to abrupt salinity increases in the rio grande major and trace ion chemistry 18o d 13c 87sr 86sr 3h and 3he 4he variations in springs and wells across the rift are best explained by mixing of deeply derived endogenic fluids containing both mantle and crustal inputs with shallow groundwater endogenic fluids ascend along rift bounding and intra rift faults and can cause increased salinity accompanied by an increase in metals and overall degradation of water quality our data reinforce models that attribute a downstream increase in salinity to geological not agricultural influences hydrochemical mixing of endogenic waters along faults in shallow aquifers has a major influence on groundwater and surface water quality and variability in arid tectonically active regions with important ramifications for water management

structure of an axial convergence zone from acoustic doppler current profiler measurements abstract an acoustic doppler current profiler was used to measure the current distribution in a convergence zone located in the piscataqua river a well mixed estuary in new hampshire u s a the convergence zone was distributed along a line parallel to the channel axis and could be located visually by accumulated debris observations of transverse circulation during the flood tide along a transect crossing the front are presented results show surface currents directed towards the centre of the channel sinking in the middle and divergence towards the sides of the channel at the bottom conductivity and temperature measurements indicate accompanying higher densities in the centre of the channel a simple mathematical model is developed applied and compared with the data major features of the frontal circulation are reproduced indicating that transverse circulation is driven primarily by the cross channel density gradients

high resolution imagery of active faulting offshore al hoceima northern morocco abstract two recent destructive earthquakes in 1994 and 2004 near al hoceima highlight that the northern moroccan margin is one of the most seismically active regions of the western mediterranean area despite onshore geodetic seismological and tectonic field studies the onshore offshore location and extent of the main active faults remain poorly constrained offshore al hoceima high resolution seismic reflection and swath bathymetry have been recently acquired during the marlboro 2 cruise these data at shallow water depth close to the coast allow us to describe the location continuity and geometry of three active faults bounding the offshore nekor basin the well expressed normal left lateral onshore trougout fault can be followed offshore during several kilometers with a n171 e 3 trend westward the bousekkour aghbal normal left lateral onshore fault is expressed offshore with a n020 e 4 trending fault the n030 e 2 bokkoya fault corresponds to the western boundary of the plio quaternary offshore nekor basin in the al hoceima bay and seems to define an en echelon tectonic pattern with the bousekkour aghbal fault we propose that these three faults are part of the complex transtensional system between the nekor fault and the al idrissi fault zone our characterization of the offshore expression of active faulting in the al hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses as well as seismological geodetic and geodynamic data

the green river salt mystery what was the source of the hyperalkaline lake waters abstract bicarbonate rich source waters were needed to form the largest sodium carbonate evaporite deposits in the geologic record the early and middle eocene green river trona nahco 3 na 2 co 3 2h 2 o in the bridger basin wyoming and nahcolite nahco 3 in the piceance creek basin colorado large modern and pleistocene trona deposits are associated with magmatic activity and na hco 3 rich hydrothermal inflow waters either within the depositional basin lake magadi kenya or at great distances searles lake california no evidence exists for magmatic sources of co 2 near the green river formation several regional volcanic centers were active 300 km or more to the north but drainage reconstructions show that waters from these areas did not discharge into the green river formation lakes during evaporite deposition alternatively na hco 3 rich waters could have drained northwestward from the colorado mineral belt to the bridger basin via the proposed aspen river a river originating in the colorado mineral belt sawatch uplift could also have provided source waters to the piceance creek basin field evidence however has not yet documented these flow paths and specific eocene volcanic centers and hydrothermal source areas have yet to be identified other explanations for the elevated alkalinities needed to form thick sodium carbonate evaporites include accelerated silicate mineral weathering rates during a period of high atmospheric p co 2 and eocene warmth amplified chemical weathering may explain the cluster of sodium carbonate evaporites in the usa and china that are eocene in age another possible source of alkalinity to the green river lakes is fault controlled upward migration of a deep sedimentary source of co 2 the large amount of organic matter preserved in the evaporitic wilkins peak and parachute creek members raises the possibility that decay of organic matter in green river lakes could have added sufficient co 2 and alkalinity to produce waters capable of precipitating trona and nahcolite although such degradation of organic matter has not created hyperalkalinity in modern lakes

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use