glacial hydrologic conditions in the black sea reconstructed using geochemical pore water profiles abstract chloride and 18 o compositions of interstitial water extracted from a long sediment core retrieved from the nw coast of the black sea allowed us to constrain the main hydrologic changes of the back sea during the late pleistocene and holocene prior to its reconnection with the mediterranean sea through the marmara sea at approximately 9000 calendar yr before present 9 ka cal bp the black sea has evolved as a fresh to brackish water lake at the time of reconnection hydrologic changes were drastic bottom water salinities changed from a few psu practical salinity unit to 22 psu since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters in order to reconstruct these former concentrations we used an advection diffusion model different scenarios of bottom water chloride and 18 o variations were accounted for in this model in order to simulate present day vertical profiles for concentrations of interstitial water in order to compare them to measured ones the comparison suggests that the glacial black sea was a homogeneous freshwater lake with a 18 o of 10 and a salinity of 1 psu modern hydrologic conditions would only have been reached at 2 ka cal bp concomitant with the onset of coccolith rich thin layers that characterize modern basin sediments such delayed salinization over 7000 yr in the basin may have been due to higher precipitation during the early holocene we also simulated the impact of a catastrophic reconnection and a smoother reconnection both salinity scenarios lead to undistinguishable modelled present day profiles indicating that the precise impact of the last reconnection was lost due to the advection diffusion processes

the influence of tortuosity on molecular diffusion in freshwater sediments of high porosity abstract in sediments diffusive transport of ions and molecules is basically influenced by two sediment characteristics tortuosity and porosity for the first time the formation factor f which combines the effect of tortuosity and porosity on diffusion was quantified in freshwater sediments at submillimeter resolution sediment cores were treated with kcl and f was determined using a resistivity sensor and k selective electrodes f was determined in sediments from different water depths of the eutrophic lake zug switzerland in sandy sediments from a shallow site 12 m depth f increased by approximately 50 within a few millimeters below the sediment surface in clayey and silty sediments from the oxic 160 m depth f increased by only 10 just below the sediment surface values of f were correlated with the porosity at each depth we found close correlations of f 1 02 1 81 for clay silt sediments and f 1 04 1 21 for sandy sediments the exponents are considerably smaller in lake zug than found for marine sediments thus diffusive transport seems to be less affected by tortuosity in this freshwater system

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

numerical methods for the migration of constant offset sections in homogeneous and horizontally layered media this paper describes schemes for the frequency domain migration of constant offset sections in homogeneous and horizontally layered media their main advantage is that individual constant offset sections can be processed in isolation the basis for these schemes is a generalization of the following plane wave analysis of migration for the zero offset case migration can be viewed in the time domain as a process whereby the plane waves echoed from a source to a geophone by a reflecting point are shifted in time to a common intersection the shift applicable to each plane wave can be derived from the knowledge of the diffraction curve for the reflecting point in a neighborhood of the geophone abscissa this time shift in turn determines the phase shift applicable in the frequency domain to the associated fourier component of the seismic section the central part of our methods is the construction of those elements of the diffraction curve pertinent to the shifts from the velocity map of the time section th

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

the discovery of scapolite marbles in the biscay synclinorium basque cantabrian basin western pyrenees geodynamic implications we report the presence of scapolite marbles in the biscay synclinorium of the basque cantabrian basin the link between the mainland pyrenees and the north iberian palaeomargin from their microstructures and mineral assemblages these marbles are correlated with similar marbles formed during the cretaceous metamorphism representative of the north pyrenean zone their setting in an area with northward verging structures leads us to propose a new location of the north pyrenean fault through the basque cantabrian basin available geophysical information gravity and magnetic anomalies is better explained with this new proposal which elucidates a major outstanding matter of pyrenean geology

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

diffusive transport of water in porous feldspars from granitic saprolites in situ experiments using ftir spectroscopy abstract a novel experimental cell was developed for in situ measurements of transport phenomena in porous media using fourier transform infrared ftir spectroscopy the technique was employed at ambient pressure in the temperatures range of 11 44 c to study the h 2 o d 2 o exchange between water saturated weathered feldspars bulk porosity of 5 19 vol for feldspar from granitic saprolites and a surrounding aqueous liquid such measurements are an important step for understanding internal weathering reactions of feldspars in soils and aquifers effective diffusion coefficients d eff for water in water saturated porous feldspars were determined assuming one dimensional diffusion in a quasi homogeneous medium the values of d eff vary from 7 2 10 10 to 1 9 10 11 m 2 s and are 1 2 orders of magnitude lower than the diffusion coefficients d of protons and molecular h 2 o in liquid water the activation energy for the h 2 o d 2 o exchange process in porous feldspars ranges from 7 8 to 18 8 kj mol the results imply that the effective diffusivity of water is mainly controlled by physical properties of the feldspars like porosity pore connectivity pore geometry and distribution perthitic feldspars with homogeneous pore distribution in the albitic lamellas have diffusional tortuosity factors x d d eff between 3 and 10 while alkali feldspars with inhomogeneously distributed and disconnected pores have much higher x values up to 129 diffusion anisotropy has been verified for a vein perthite with diffusion perpendicular to the lamellas being faster by 0 3 0 5 log units than within the lamellas it has to be emphasized that the study is based only on few selected feldspars including perthitic feldspar and additional work on samples with different weathering stages is needed to test the importance of the different parameters controlling diffusive transport in the pore system

predicted tortuosity of muds tortuosity figures prominently in geochemical hydrological and geophysical calculations concerned with sediments but it is a difficult parameter to measure past theoretical models for predicting the tortuosity from porosity data do not work with marine muds and scientists and engineers have had to resort to entirely empirical models without a mechanistic explanation and with unknown predictive power we offer the first geometric model for the dependence of tortuosity on porosity in marine muds the model is based on the tortuosity of separated layers of nonoverlapping disks the fitted geometric constant in this model indicates that natural marine sediments act as if their fabric were made of disks with thickness diameter ratios very close to 1 2 which indicates a blocklike fabric with respect to diffusion the model was also applied to predict the tortuosity of a variety of sediments and soils not in the original database and it provides a satisfactory prediction of the mean trend in these data

triassic paleomagnetism from the western pyrenees revisited implications for the iberian eurasian mesozoic plate boundary since the pioneering studies of van der voo tectonophysics 7 1969 5 and van der voo and boessenkool j geophys res 78 1973 5118 paleomagnetism of permo triassic redbeds and volcanics from the western pyrenees has furnished important contributions for delineating the mesozoic boundary between the iberian and eurasian plates in this paper we present a new paleomagnetic study focussed on triassic red beds 23 sites of the paleozoic basque massifs pbm the aim of this study is to complement previous studies done in those massifs to better constrain the complex kinematics of the western pyrenees two stable magnetic components have been isolated 1 a dual polarity pre folding magnetisation carried by specular hematite and 2 a secondary normal polarity component also carried by hematite our data confirm both the origin and the rotation pattern of the primary remanence described in previous works nevertheless field tests performed on the secondary component do not confirm the earlier interpretations by schott and peres tectonophysics 156 1988 75 as they indicate a synfolding nature of the remagnetisation instead of a post folding origin we consider that the secondary component is better explained if a cretaceous age is considered the presence of such remagnetisation in the western pyrenees strengthens the widespread occurrence of similar remagnetisation events reported in northern iberia in connection with the extensional tectonic events that occurred during cretaceous times a comparison of the rotations recorded by the triassic component and by the remagnetisation indicate that the paleozoic units underwent variable tectonic rotations before the remagnetisation was acquired most likely in connection with the counterclockwise rotation of iberia with respect to eurasia these results favour that the mesozoic plate boundary between the iberian and eurasian plates was a wide domain of distributed deformation and therefore contradict previous interpretations claiming for a discrete plate boundary

geologic map of the basque cantabrian basin and a new tectonic interpretation of the basque arc a new printable 1 200 000 bedrock geological map of the onshore basque cantabrian basin is presented aimed to contribute to future geologic developments in the central segment of the pyrenean cantabrian alpine orogenic system it is accompanied in separate appendixes by a historic report on the precedent geological maps and by a compilation above 350 bibliographic citations of maps and academic reports usually overlooked or ignored that are central to this contribution structural scrutiny of the map permits to propose a new tectonic interpretation of the basque arc implementing previously published partial reconstructions it is presented as a printable 1 400 000 tectonic map the basque arc consists of various thrust slices that can expose at the surface basement rocks palaeozoic to lower triassic and their sedimentary cover uppermost triassic to tertiary from which they are detached by intervening upper triassic evaporites and associated rocks the slice bounding thrusts are in most cases reactivated normal faults active during meso cenozoic sedimentation that can be readily related to basement discontinuities generated during the hercynian orogeny

a review of cretaceous smooth slopes extensional basins along the iberia eurasia plate boundary how pre rift salt controls the modes of continental rifting and mantle exhumation this article points out for the first time a striking correlation between the paleogeography of upper triassic deposits and the mode of crustal stretching around and inside the northern iberia plate during the cretaceous transtensional event first we propose a review of the architecture of the basins which opened during the mid cretaceous times along the iberia eurasia plate boundary similarly to the emblematic parentis basin these basins exhibit a peculiar synclinal shaped profile and are devoid of prominent block faulting the top of the basement is characterized by gentle slopes which dip symmetrically toward the center of the basins as revealed by recent comparisons with geologically constrained rifting models established from the north pyrenean zone this architecture results from the thinning of a heterogeneous continental crust under greenschist facies conditions basement deformations are thus dominantly ductile and are characterized by large scale boudinage hyper thinning and subsequent lateral extraction bulk deformation of the upper and middle crust leads to the formation of anastomosed shear zones and the development of mylonitic fabric tectonic lenses consisting of crustal material remain welded on top of the exhuming mantle the common character shared by all the pre rift sequences of the studied basins is the presence of a thick low strength upper triassic evaporites and clays layer belonging to the keuper group i e pre rift salt and clay unit in the studied basins efficient decollement along the pre rift salt and clay unit triggers mechanical decoupling and gliding of the pre rift cover that remains in the center of the basin thus during the early rifting phase the basement undergoes thinning while the pre rift cover remains preserved in the basin center in response to hyper thinning and horizontal extraction of the continental crust hot mantle is exhumed beneath the pre and syn rift cover subsequent thermal exchange i promotes ductile deformation of the basement and ii induces the development of ht lp metamorphic conditions in the pre rift sediments and at the base of the syn rift flysch levels this thermal event is well recorded in the axial portion of the pyrenean realm future north pyrenean zone as well as in the pre rift sediments of the cameros basin northern spain the architecture of the smooth slopes type basins thus contrasts with the structure of iberia newfoundland atlantic margins which are characterized by i top basement detachment faults accommodating crustal extension through rotation and translation of undeformed basement blocks and ii the individualization of continental extensional allochthons tectonically emplaced over exhumed lower crust or mantle rocks finally using recent paleogeographic reconstructions we show that the distribution of the pre rift salt and clay unit remarkably matches the distribution of the pyrenean and peri pyrenean smooth slopes type basins this allows for the first time to propose a genetic link between the distribution of evaporite bearing pre rift sedimentary formations and the development of smooth slopes basins

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

a paleomagnetic study of the basque arc basque cantabrian basin western pyrenees the basque arc constitutes the northern segment of the basque cantabrian basin in the western part of the pyrenees the main goal of the present study was to find out by means of paleomagnetic analysis if the arched shape of the basque arc has a primary origin due to the development of sedimentary basins related to the opening of the bay of biscay or a secondary origin due to rotations about vertical axes nine volcanic flows of late albian to santonian age 100 83 5 my were sampled together with 10 sedimentary sites marls limestones calcarenites and sandstones of lower jurassic to early eocene age in order to carry out paleomagnetic and rock magnetic experiments 15 paleodirections being obtained in order to analyse these results together with data from previous studies the studied area was subdivided into a western a central and an eastern sector while inclinations of all three sectors show a similar value declinations differ the western sector displays a 37 16 clockwise rotation of its mean paleodeclination the central sector is not rotated 4 9 and both sedimentary sites which make up the eastern sector show counter clockwise rotations 25 11 and 68 9 these results suggest that the shape of the basque arc does not have a primary origin but a secondary origin due to rotations about vertical axes as a result of differential shortening related to post lutetian compressive tectonics which resulted in the formation of the pyrenees

permeability and porosity of hydrate bearing sediments in the northern gulf of mexico abstract hydrate bearing sands are being actively explored because they contain the highest concentrations of hydrate and are the most economically recoverable hydrate resource however relatively little is known about the mechanisms or timescales of hydrate formation which are related to methane supply fluid flux and host sediment properties such as permeability we used logging while drilling data from locations in the northern gulf of mexico to develop an effective medium theory based model for predicting permeability based on clay sized sediment fraction the model considers permeability varying between sand and clay endpoint permeabilities that are defined from laboratory data we verified the model using permeability measurements on core samples from three boreholes and then used the model to predict permeability in two wells drilled in walker ridge block 313 during the gulf of mexico gas hydrate joint industry project leg ii expedition in 2009 we found that the cleanest sands clay sized fraction

matrix diffusion in northern negev fractured chalk and its correlation to porosity abstract in this paper we report on vertical variations in the values of the effective diffusion coefficient determined on 19 chalk samples collected throughout most of the eocene section 285 m in the northern negev desert israel the dependence of the measured values on sample depth porosity permeability and mineralogy was also evaluated finally a correlation between the measured effective diffusion coefficient and porosity is suggested for these samples the calculated values of the diffusion coefficient ranged from 1 22 to 2 55 10 6 cm 2 s these values are significantly higher than those measured on consolidated rock samples and similar to values reported for british cretaceous chalk our results demonstrate that the effective diffusion coefficient values for the eocene chalk in the northern negev desert israel are exclusively dependent on the porosity of the chalk matrix by d e d 0 e 2 m 2 in archie s law and not on its mineralogy or permeability the fitted exponent m falls between the two extreme values of 1 5 and 2 5 that were mentioned by diffusion in natural porous media 1998 for porous media however a linear relationship between the effective diffusion coefficient and porosity fits better the data within the range of the measured of porosities these correlations provide an easier and less costly method of estimating the diffusion coefficient in chalk samples from the eocene group in the northern negev desert israel

paleohydrogeology of the cretaceous sediments of the williston basin using stable isotopes of water 1 hydraulic and isotopic data collected from aquifers are routinely used to characterize hydrogeological conditions within sedimentary basins but similar data from confining units are generally not collected despite their ability to provide insights on important water solute transport controls we characterized paleogroundwater flow and solute transport mechanisms across 384 m of cretaceous shale aquitard in the williston basin canada using high resolution depth profiles of water isotopes 18o 2h water samples were also collected from wells installed in the underlying regional sandy aquifer mannville fm 93 m thick and from seepage inflows into potash mine shafts to 825 m below ground the 1 d numerical transport modeling of 18o profiles provided insight into large scale long term solute transport in both cretaceous sediments and the basin despite the potential for significant advective migration during glaciations molecular diffusion appears to be the dominant solute transport mechanism through the aquitard simulations suggest average vertical groundwater velocities of 0 05 m 10 ka and an average excess hydraulic head of 10 m these values are much less than anticipated by successive glaciations the dominant paleoevent reflected in present day profiles is introduction during the pleistocene of glaciogenic meteoric water to the aquifer underlying the shale likely along an aquifer outcrop area east of the site or through local vertical conduits simulations suggest these recharge events occurred during one or more glacial periods the isotopic profile over the upper 25 m of pleistocene till and shale is consistent with glacial deposition and transport processes within these units over the holocene past 10 ka

an improved technique for computing permeability from nmr measurements in mudstones 1 we develop a technique for extending nuclear magnetic resonance nmr permeability estimation to clay rich sediments our technique builds on the schlumberger doll research sdr equation by using porosity grain size specific surface and magnetic susceptibility data to yield more accurate permeability estimation in mudstones with large pore surface areas and complex mineralogies based on measurements of natural sediments as well as resedimented laboratory mixtures of silica bentonite and kaolinite powders we find that our method predicts permeability values that match measured values over four orders of magnitude and among lithologies that vary widely in grain size mineralogy and surface area our results show that the relationship between nmr data and permeability is a function of mineralogy and grain geometry and that permeability predictions in clay rich sediments can be improved with insights regarding the nature of the pore system made by the kozeny theory this technique extends the utility of nmr measurements beyond typical reservoir quality rocks to a wide range of lithologies