effects of different spatial distributions of physical soil crusts on runoff and erosion on the loess plateau in china the response of runoff and erosion to soil crusts has been extensively investigated in recent decades however there have been few attempts to look at the effects of spatial configuration of different soil crusts on erosion processes here we investigated the effects of different spatial distributions of physical soil crusts on runoff and erosion in the semi arid loess plateau region soil boxes 1 5 m long 0 2 m wide were set to a slope of 17 6 10 and simulated rainfall of 120 mm h 1 60 minutes the runoff generation and erosion rates were determined for three crust area ratios depositional crust for 20 33 and 50 of the total slope and five spatial distribution patterns depositional crust on the lower lower middle middle mid upper and upper slope of soil crusts the reduction in sediment loss sediment reduction was calculated to evaluate the effects of different spatial distributions of soil crusts on erosion sediment yield was influenced by the area ratio and spatial position of different soil crusts the runoff rate reached a steady state after an initial trend of unsteadily increasing with increasing rainfall duration sediment yield was controlled by detachment limitation and then transport limitation under rainfall the shifting time of erosion from a transport to detachment limiting regime decreased with increasing area of depositional crust no significant differences were observed in the total runoff among treatments while the total sediment yield varied under different spatial distributions at the same area ratio total sediment yield was the largest when the depositional crust was on the upper slope and it was smallest when the crust was deposited on the lower slope the sediment reduction of structural crust 42 5 66 5 was greater than that of depositional crust 16 7 34 3 these results provide a mechanistic understanding of how different spatial distributions of soil crusts affect runoff and sediment production copyright 2017 john wiley sons ltd

ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

classification of sea floor features associated with methane seeps along the gulf of cadiz continental margin abstract based on recently gathered swath bathymetry high to ultra high resolution seismic and underwater camera data along with dredging and coring samples this paper examines the relationship between sea floor features and the nature of hydrocarbon enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the gulf of cadiz eastern central atlantic a classification into three main groups is proposed on the basis of the morphology and nature of deposits 1 mud volcanoes 2 methane derived authigenic carbonates mdac mounds and 3 crater like pockmarks mud volcanoes are topographically cone shaped sea floor edifices built up from catastrophic mud and fluid degassing intercalated with periods of inactivity so far more than 25 mud volcanoes have been discovered in the gulf of cadiz named in memory of deceased colleagues e g ginsburg and baraza or researchers birth places e g faro cibeles almazan san petersburgh yuma rabat bonjardim coruna gades these structures range from 800 to 2500 m in diameter and tower 150 300 m above the seabed the volcanoes consistently feature a well defined outer ring or circular terrace and an inner dome all mud volcanoes are built up of episodes of mud breccia flows intercalated with deep current deposits with evident indications of gas saturation degassing structures a strong h2s smell and chemosynthetic fauna such as pogonophora sp tube worms and calyptogena sp commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud a fermentation process the result of microbial mediated oxidation of hydrocarbon enriched fluids seems to play an important role in the growth of large deep water carbonate mounds and chimneys during periods of low methane seep fluid pressure more than 400 crater like pockmarks a common sea floor feature in the tasyo field have been observed their seabed diameter ranges from 500 to 3000 m with steep slopes ranging from 12 to 35 according to their internal structure pockmarks can be grouped into 1 pockmarks with low central mounds and 2 crater like pockmarks apparently collapse structures lacking central mounds with a flat to slightly undulating sea bottom surrounded by steep slopes up to 25

mud volcanism in the gulf of cadiz results from the ttr 10 cruise a new deep water mud volcano field between 2000 and 3500 m water depth was discovered in the deep south portuguese margin as well as several new mud volcanoes in the south spanish and western moroccan margins of the gulf of cadiz during the ttr 10 training through research unesco ioc cruise in july august 2000 this work followed the discovery of a large mud volcano field in the gulf of cadiz first investigated during the ttr 9 cruise gardner 2001 geophys res lett 28 339 342 kenyon et al 2000 ioc technical series no 56 the discoveries were made based on a seamap side scan sonar mosaic and multibeam bathymetry seabeam collected in the area by the naval research laboratory nrl washington dc usa in 1992 kindly released for this purpose single channel seismics long range side scan sonar okean tv controlled grab hull mounted 3 5 khz profiler and coring were used to investigate several seafloor features observed on the side scan sonar imagery in the south iberia spanish and moroccan margins of the gulf of cadiz which were confirmed to be mud volcanoes the typical structures related to fluid venting in the gulf of cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m some of these structures appear to be aligned along major conjugate ne sw and nw se trending faults that can be identified on the side scan sonar imagery the new field discovered in the south portuguese margin is the deepest in the gulf of cadiz area and includes three new mud volcanoes bonjardim olenin and carlos ribeiro which seem to be quite active with near surface gas hydrate occurrence and a high saturation in h2s and hydrocarbon gases mainly methane in the mud breccia and overlying pelagic sediments gas hydrates were recovered from the bonjardim mud volcano an intensely gassified mud breccia with one fragment of semi consolidated claystone with a thin bituminous veneer at the surface was recovered from the carlos ribeiro mud volcano the fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of foraminifera three new mud volcanoes were also discovered in the nw moroccan margin rabat student and jesus baraza these show a richer fauna that includes several species of molluscs polychaetes pogonophoran worms crustaceans echinoderms and some fragments of dead coral madrepora and lophelia carbonate crusts were recovered from the student mud volcano the ginsburg mud volcano discovered during the previous ttr 9 cruise was revisited and gas hydrates recovered once again a new mud volcano was also discovered in the spanish margin tasyo where evidence was found of coral build ups on the hard substratum of the mud volcanic edifice

a rational method for estimating erodibility and critical shear stress of an eroding rill abstract soil erodibility and critical shear stress are two of the most important parameters for physically based soil erosion modeling to aid in future soil erosion modeling a rational method for determining the soil erodibility and critical shear stress of rill erosion under concentrated flow is advanced in this paper the method suggests that a well defined rill be used for shear stress estimation while infinite short rill lengths be used for determination of detachment capacity the derivative of the functional relationship between sediment yield and rill length at the inlet of rill flow as opposed to average detachment rate of a long rill was used for the determination of detachment capacity soil erodibility and critical shear stress were then regressively estimated with detachment capacity data under different flow regimes laboratory data of rill erosion under well defined rill channels from a loess soil was used to estimate the soil erodibility and critical shear stress the results showed that no significant change in soil erodibility k r was observed for different slope gradients ranging from 5 to 25 while critical shear stress increased slightly with the slope gradient soil erodibility of the loess soil was 0 3211 0 001 s m 1 the soil erodibility and critical shear stress calculations were then compared with data from other resources to verify the feasibility of the method data comparison showed that the method advanced is a physically logical and feasible method to calculate the soil erodibility and critical shear stress for physically based soil erosion models

gas charged sediments and large pockmark like features on the gulf of cadiz slope sw spain abstract gassy sediments and large seafloor pockmarks are identified from seismic profiles in the gulf of cadiz slope gas charged sediments are represented by zones of acoustic turbidity and other acoustic anomalies on seismic profiles most of the gas is believed to be biogenic in origin resulting from the decay of organic matter contained within rapidly developed regressive shelf margin deltas a group of large asymmetric seafloor pockmarks also occurs downslope of the gassy area both on the seafloor surface and deeply buried in the sediment column sediment sorting by the mediterranean undercurrent seems to act as a controlling factor for the development of each type of gas originated feature the area where the strong mediterranean undercurrent outflow impinges the seafloor is covered by sandy sediments of high porosity which allow the interstitial gas to escape through the sediment pores whereas the areas affected by weaker currents are covered by clays and the gas tends to accumulate in the sediment beneath impermeable horizons

tectonics and mud volcano development in the gulf of cadiz many structures associated with fluid escape including mud volcanoes mud carbonate mounds pockmarks and slides have been identified and characterized in the gulf of cadiz most of the mud volcanoes following ne sw and nw se main trends are found at 350 2000 m depth in the eastern domain of the gulf of cadiz which corresponds to the betic rifean margin scattered mud volcanoes have also been recognized on the lower slope at 2300 3900 m depth the major tectonic structures are thrust faults extensional faults strikeslip faults and diapirs all these tectonic structures have provided escape pathways for overpressured material and fluids or have favoured upward fluid movement along the sedimentary column and eventually the build up of mud volcanoes in this work we present images of the mud volcano plumbing systems and the relationship between regional tectonics and mud volcano development seismic profiles acquired during the tasyo 2000 and mvseis ttr 15 cruises are used to image and interpret the link between the mud volcano edifices and the subsurface tectonic structures

similarity between morphological characteristics of rills and ephemeral gullies in sicily italy this paper reports the results of a field investigation aimed to establish morphological similarity between rills and ephemeral gullies rill measurements were made on 14 plots having a surface area of 22 352 m2 located on a 14 9 slope and on a plot 6 0 m wide and 22 0 m long having a uniform 22 0 slope the plots are located on the experimental station for soil erosion measurements sparacia of the agricultural faculty of palermo university in sicily italy all plots are subjected to natural rainfall the measurements were made immediately following five events between november 2004 and december 2005 the ephemeral gully measurements were made on a cultivated area of about 120 ha located in central sicily which is representative of many soil crop conditions in the mediterranean basin the morphological similarity between rill and ephemeral gully was first tested then a power relationship between rill or gully volume and length theoretically deduced by dimensional analysis and self similarity theory was applied this power relationship needs a different scale factor for rill and gully measurements finally using two dimensionless groups representative of the channel morphology variables the analysis showed that a single relationship can be applied to rill and gully measurements copyright 2009 john wiley sons ltd

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

magnetic impulse events and related pc1 bursts observed by the automatic geophysical observatories network in antarctica magnetic field data obtained by fluxgate and search coil magnetometers installed at four automatic geophysical observatories ago pl p2 p3 and p4 and at south pole and mcmurdo in antarctica and at iqaluit on baffin island are used to study the relationship between magnetic impulse events mies and pc1 bursts at high geomagnetic latitudes the spatial scale sizes of mies are determined in the investigation of the sources of these events in the magnetosphere four mie events with simultaneous pc1 bursts are studied contour plots of mie amplitudes show the scale sizes of the examined mies to be 5 to 7 in the magnetic latitude direction and 40 to 60 in the magnetic longitude direction temporal changes of the ionospheric currents calculated from the fluxgate h and d component data indicate that the convection vortices associated with the mies traveled westward and decayed rapidly an important finding is that mie related pc1 bursts were observed at higher latitude pl p4 near 80 and lower latitude p2 p3 near 70 ago stations and south pole station at 74 with different spectral structures although the pc1 spectral power was always a maximum at south pole station these results imply that pc1 bursts are excited not only in the dayside outer magnetosphere but also in the low latitude boundary layer region

mud volcano gas hydrates in the gulf of cadiz this paper presents new geochemical data on gas hydrate bearing mud volcanoes discovered for the first time in the gulf of cadiz during cruises ttr9 and ttr10 of the r v professor logachev in 1999 2000 the estimated gas hydrate content is 3 16 of sediment volume and 5 31 of pore space volume estimated values of the water isotopic composition for the ginsburg mud volcano are very heavy for 18o up to 53 and light for d up to 210 gas released from the hydrates contains 81 of c1 and 19 of c2 the inferred source of the gas in the hydrates is enriched in c2 c6 5 indicating that the gas has a thermogenic origin gas hydrate of cubic structure ii should be formed from a gas of such composition it is interpreted that the composition of the mud volcano fluid corresponds to deep oil basins below the gulf of cadiz

interactions between soil properties and moisture content in crust formation runoff and interrill erosion from tilled loess soils soil surface seals and crusts resulting from aggregate breakdown reduce the soil infiltration rate and may induce erosion by increasing runoff the cultivated loess areas of northwestern europe are particularly prone to these processes surface samples of ten tilled silty loamy loess soils ranging in clay content from 120 to 350 g kg 1 and in organic carbon from 10 to 20 g kg 1 were packed into 0 5 m2 plots with 5 slopes and subjected to simulated rainfall applied at 30 mm h 1 the 120 minutes rainfall events were applied to initially field moist soil air dried soil and rewetted soil to investigate the effect of soil moisture content prior to rainfall runoff and eroded sediments were collected at 5 minutes intervals aggregate stability of the soils was assessed by measuring particle size distribution after different treatments all soils formed seals runoff rates were between 70 and 90 by the end of the rainfall event for field moist plots there were large differences between soil runoff rates for the air dried and rewetted plots interrill erosion was associated with runoff and sediment concentration in runoff readily reached a steady state value measurements of aggregate stability for various treatments were in good agreement with sealing runoff and erosion responses to rainfall runoff and erosion were lower for air dried plots than for field moist plots and were either intermediate or lowest for rewetted plots depending on soil characteristics soils with a high clay content had the lowest erosion rate when they were rewetted whereas the soil with a high organic carbon content had the lowest erosion rate in air dry conditions the results indicate the complexity of the effect of initial moisture content and the interactions between soil properties and climate

carbonate formation by anaerobic oxidation of methane evidence from lipid biomarker and fossil 16s rdna carbonate chimneys and other carbonate structures occur widespread in the gulf of cadiz and probably reflect the presence of cold seeps and associated release of methane in the geological past possibly in the early pleistocene but it is unclear under what conditions and by which processes these carbonates were formed we studied a fossil methane related carbonate crust collected from the kidd mud volcano in the gulf concentrations of microbial lipids their stable carbon isotope composition sequences of fossil 16s rrna genes of anaerobic methanotrophic archaea in combination with mineralogical and carbon and oxygen isotopic composition of carbonate were obtained for seven different horizons of the crust this combination of organic and inorganic geochemical techniques with molecular ecological methods gave a consistent view on processes resulting in the formation of the crust and indicated that it took place in two phases and in a downward direction archaeal lipid biomarkers and fossil 16s rrna gene sequence data revealed the dominance of archaeal anme 2 group and elevated methane partial pressures during the formation of the top part of the crust the lower part of the carbonate was likely formed in an environment with reduced methane fluxes as revealed by the dominance of fossil remains of anme 1 archaea the combination of these methods can be used as an effective tool to reconstruct in unprecedented detail the palaeo biogeochemical processes resulting in the formation of carbonate fabrics this interdisciplinary strategy may also be applied for other fossil methane derived carbonates generating new concepts and knowledge about past methane related carbonate systems

rill network development and sediment budgets threshold conditions for rill incision are well known but few studies have examined the effect of network geometry on water and sediment fluxes within an evolving rill system this paper reports the first in a series of studies designed to identify the influence of soil properties on rill network and confluence geometry and on water and sediment fluxes in rill systems the object of this study was to prepare detailed rill network water and sediment budgets identifying important sources and sinks simulated rainfall experiments were carried out on a canadian silt loam soil in a 7 1 m 2 4 m flume on a 5 slope rill networks of varying complexity developed which were ultimately constrained by flume boundaries sediment and water fluxes and hydraulic conditions were measured within networks and at a terminal weir networks evolved by initial knickpoint incision in the lower flume as flow shear velocities reached critical levels of 4 5 5 cm s 1 followed by headward migration and tributary development microtopography determined tributary location but the timing and intensity of development were controlled by the incision and migration rate of the main channel which changed local thalwegs and base levels raising shear velocities on side slopes above critical levels sediment discharge at the weir broadly reflected rill incision intensity and transport limited conditions but as active incision moved headward the linkage became attenuated and identification of discrete erosional incidents e g local bank collapse in the signal of the weir record became very difficult detailed water and sediment budgets showed much more complex patterns of localized incision and deposition within networks strongly influenced by local changes in thalweg and in water discharge due to seepage or return flow and by the effect of confluences on hydraulic conditions results indicate the value of detailed sediment budgets in interpreting weir water and sediment flux records and the necessity of linking such measurements for erosion plots and hillslope segments to rill network characterization experimental results are consistent with a simple model of rill system evolution based on channel incision headward migration and the critical shear velocities for rill initiation copyright 2000 john wiley sons ltd

the contourite depositional system of the gulf of cadiz a sedimentary model related to the bottom current activity of the mediterranean outflow water and its interaction with the continental margin the present paper is mostly a synthesis of work conducted on the continental margin of the gulf of cadiz using a broad database collected by several cruises and projects supported by the spanish research council and the nrl and naval oceanographic office usa including bathymetry sidescan sonar imagery seismic profiles sediment cores submarine photographs and physical oceanographic data these data have enabled us to establish a detailed understanding of the morphologic development of the margin its pliocene and quaternary stratigraphy and a full characterization of the contourite depositional system cds generated by the mediterranean outflow water mow the northern margin of the gulf of cadiz shows the following distinct features a an active compressive framework where the cadiz allocthonous unit provides an unstable substratum for late miocene pliocene and quaternary sedimentation b a relative lack of submarine canyons except in the western area of the algarve margin c a very broad continental slope that lacks a marked continental rise d a middle slope dominated by along slope processes driven by the mow which has generated a complex cds during the pliocene and quaternary and e an irregular lower slope and abyssal plain region dominated by down slope processes that is partly detached from an upper slope source region the cds is composed of both depositional and erosive features the main depositional features are characterised by sedimentary wave fields sedimentary lobes mixed drifts plastered drifts elongated mounded and separated drifts and sheeted drifts the main erosive features are contourite channels furrows marginal valleys and moats these various depositional and erosive features have a specific location along the margin and their detailed distribution is essential to understand the present and past interaction of the mow with the middle slope based on this distribution five morphosedimentary sectors have been identified within the cds which from east to west are 1 proximal scour and sand ribbons 2 overflow sedimentary lobe 3 channels and ridges 4 active contourite drifts and 5 submarine canyons the development of the cds has been controlled in general by the pliocene and quaternary environmental and paleoceanographic changes and by the morphology of the margin but in detail the development of each of these sectors is related to systematic deceleration of the mow as it flows westwards to the interaction with the margin bathymetry and to the effects of coriolis force our comprehensive sedimentary model for the cds defines the gulf of cadiz margin as a mixed contourite turbidite system with a detached combined drift fan morphology this is different from many other contourite influenced margins where the contourite processes are dominant on the middle slope and separated from the down slope processes which are characteristic on the lower slope and abyssal plains

laboratory investigations of rill dynamics on soils of the loess plateau of china abstract we conducted a laboratory study on rill network evolution with detailed measurements under controlled experimental conditions the concepts of fractal geometry entropy and topology were used to quantify rill erosion intensity and morphology the objectives of this study are to reveal rill erosion processes and rill network development under different rainfall intensities and to present some indicators to provide a quantitative description of rill morphology a soil pan 5 m long 1 m wide and 0 6 m deep with slope gradient of 20 was subjected to three successive rainfall events under rainfall intensities of 66 94 and 127 mm h 1 the results showed that rainfall intensity played a major role in rill erosion the development of a rill network is most rapid under medium intensity rainfall rainfall intensity that is too weak or too strong is not conducive to rill development as rainfall duration increased under the same rainfall intensity the values of soil loss rill density geomorphologic comentropy and nodes increased rill network development was slow at the early stage but became more rapid at a later stage the results also indicated that the geomorphologic comentropy was the best basic morphological indicator of rill erosion and the number of rill nodes was the best derived morphological indicator of rill morphology which was followed in descending order by the fractal dimension rill density and bifurcation ratio

rill erosion processes on a steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain abstract understanding rill erosion processes is important in the prediction of soil erosion and the prevention of soil loss however limited information is available concerning the impacts of rainfall on rill erosion on steep slopes colluvial deposits with steep slopes make up the packed material underlying the collapsing walls in benggang which collapse due to hydraulic pressure and gravity they contain loose materials and large amounts of coarse particles the objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on the rill erosion process rill development and rill flow dynamic mechanisms on the steep slopes of colluvial deposits the colluvial soils were subjected to simulated rainfall in a 5 m2 5 m by 1 m flume at heavy rainfall intensities 100 120 and 140 mm h 1 and on five steep slopes 20 25 30 35 and 40 rill erosion contributed significantly to colluvial slope erosion on average rills accounted for 61 of the soil loss and the effects of slope gradient were greater than those of the rainfall intensity after rill development rill density rill length width and depth all significantly increased correspondingly the soil loss rate sharply raised and irregularly fluctuated moreover the collapse of rill heads or sidewalls tended to increase the relative contribution to rill erosion and rill development the rill flow was characterized by transitional and subcritical flow regimes the rill flow velocity was the most sensitive hydraulic parameter and the unit stream power provided the optimal hydrodynamic parameter to characterize the dynamic mechanisms of rill erosion on colluvial deposits the collapse of rill heads or sidewalls could result in negative values for critical shear stress critical stream power and critical unit stream power of rill erosion which were 19 pa 5 3 n m 1 s 1 and 0 09 m s 1 respectively these results provide a better understanding of the mechanism of rill erosion on steep slopes

authigenic carbonates from the darwin mud volcano gulf of cadiz a record of palaeo seepage of hydrocarbon bearing fluids hydrocarbon rich fluids expelled at mud volcanoes mvs may contribute significantly to the carbon budget of the oceans but little is known about the long term variation in fluid fluxes at mvs the darwin mv is one of more than 40 mvs located in the gulf of cadiz but it is unique in that its summit is covered by a thick carbonate crust that has the potential to provide a temporal record of seepage activity in order to test this idea we have conducted petrographic chemical and isotopic analyses of the carbonate crust in addition a 1 d transport reaction model was applied to pore fluid data to assess fluid flow and carbonate precipitation at present the carbonate crusts mainly comprise of aragonite with a chaotic fabric exhibiting different generations of cementation and brecciation the crusts consist of bioclasts and lithoclasts peloids intraclasts and extraclasts immersed in a micrite matrix and in a variety of cement types microsparite botryoidal isopachous acicular radial and splayed fibrous the carbonates are moderately depleted in 13c 13c 8 1 to 27 9 as are the pore fluids 13c 19 1 to 28 7 which suggests that their carbon originated from the oxidation of methane and higher hydrocarbons like the gases that seep from the mv today the carbonate 18o values are as high as 5 1 and it is most likely that the crusts formed from 18o rich fluids derived from dehydration of clay minerals at depth pore fluid modelling results indicate that the darwin mv is currently in a nearly dormant phase seepage velocities are 0 09 cm yr 1 thus the thick carbonate crust must have formed during past episodes of high fluid flow alternating with phases of mud extrusion and uplift highlights results of pore fluid modelling indicate low seepage activity at localised sites pore fluids are supersaturated with respect to hydrocarbons of thermogenic origin aom supports vent fauna and results in the formation of authigenic carbonates the carbonate crust has a brecciated appearance and mainly consists of aragonite the crust formation seems to be regulated by changes in fluid and mudflow activity

the imprint of methane seepage on the geochemical record and early diagenetic processes in cold water coral mounds on pen duick escarpment gulf of cadiz abstract the diagenetic history and biogeochemical processes in three cold water coral mounds located in close proximity to each other on pen duick escarpment in the gulf of cadiz were examined the influence of ascending methane rich fluids from underlying sediment strata delineated two mound groups alpha and beta mound showed evidence for the presence of a sulfate methane transition zone smtz at shallow depth whereas gamma mound appeared to lack a shallow smtz in the methane influenced alpha and beta mound upward diffusion of hydrogen sulfide from the shallow smtz caused extensive pyritization of reactive iron phases as indicated by values for the degree of pyritization 0 7 this secondary pyritization overprinted the sulfur isotope composition of sulfides formed during organoclastic sulfate reduction the almost complete consumption of reactive iron phases by upward diffusing sulfide limited dissimilatory iron reduction to the top layer in these mounds while organic matter in the pyritized zones below was primarily degraded by organoclastic sulfate reduction hydrogen sulfide produced during sulfate reduction coupled to the anaerobic oxidation of methane aom diffused upward and induced aragonite dissolution as evidenced in strongly corroded corals in alpha mound this mound has been affected by strong fluctuations in the depth of the smtz as observed by distinct layers with abundant diagenetic high mg calcite with a 13 c depleted carbon isotope composition in the non methane influenced gamma mound low sulfate reduction rates elevated concentrations of dissolved iron and solid phase iron speciation indicated that organic matter mineralization was driven by dissimilatory iron reduction and organoclastic sulfate reduction coupled to oxidative sulfur cycling the latter process led to 34 s depletion in pyrite of up to 70 relative to pore water sulfate

searching for ulf signatures of the cusp observations from search coil magnetometers and auroral imagers in svalbard 1 spacecraft traveling through the cusp at a variety of altitudes have consistently found the cusp to be filled with intense often irregular power in the upper ulf frequency range some ground based studies have observed narrowband waves in this same frequency range in the vicinity of the cusp foot point but it has not been possible with magnetometers alone to either confirm or deny a cusp source for these waves we report here on the first simultaneous collocated observations of a set of induction magnetometers installed at three near cusp sites on svalbard and an all sky auroral imager located at longyearbyen data during northern winters of 2006 2007 and 2007 2008 when the cusp foot point was in darkness showed occasional broadband noise when energetic particle precipitation occurred overhead but on most days no broadband ulf power was observed above the noise level near noon when only soft cusp precipitation or poleward moving auroral forms occurred overhead however on 3 days including 15 january 2007 several bursts of band limited pc 1 2 waves were observed in association with regions of intense soft precipitation that peaked near the poleward edge of the cusp their properties are consistent with an origin in the plasma mantle as observed in a recent satellite ground study by engebretson et al 2005 these observations confirm that even intense cusp precipitation is not effective in generating ion cyclotron waves that penetrate to the ground if it is embedded within the central regions of the cusp whereas regions of enhanced precipitation at the poleward edge of the cusp are associated with observed waves

a spectral approach for analyzing the rill structure over hillslopes part 1 development of stochastic theory abstract the rill structure over the soil surface plays an important role in determining the runoff and sediment loss from hillslopes the microtopography is often complicated and representation of the hillslope surface on a rill by rill basis is uneconomical and impractical a spectral approach combined with a stochastic theory is proposed for the rill profile the theory develops appropriate probability distribution laws for rill amplitudes and rill periods interrill areas under the assumption that the spectrum of the rill profile is narrow banded this study establishes a foundation for future studies dealing with parameter estimation and determining the global roughness and erodibility for runoff and sediment discharge predictions over hillslopes

multidisciplinary study of mud volcanoes and diapirs and their relationship to seepages and bottom currents in the gulf of cadiz continental slope northeastern sector abstract the seabed morphology type of sediments and dominant benthic species on eleven mud volcanoes and diapirs located on the northern sector of the gulf of cadiz continental slope have been studied the morphological characteristics were grouped as i fluid escape related features ii bottom current features iii mass movement features iv tectonic features and v biogenic related features the dominant benthic species associated with fluid escape hard substrates or soft bottoms have also been mapped a bottom current velocity analysis allowed the morphological features to be correlated with the benthic habitats and the different sedimentary and oceanographic characteristics the major factors controlling these features and the benthic habitats are mud flows and fluid escape related processes as well as the interaction of deep water masses with the seafloor topography mud volcano eruptions give rise to mud flows and or aqueous fluid seepage these processes sustain chemosynthesis based communities closely associated with fluid seepage large depressions in the nearby area are influenced by collapse related phenomena where active fluid escape and the erosive effect of bottom currents have been identified when the extrusion activity of the mud volcano is low and the seepage is diffuse authigenic carbonates form within the edifice sediments the bottom current sweeps the seafloor from the se to the nw when the velocity is moderate sedimentary contourite processes take place on both sides of the edifices at high velocities the authigenic carbonates may be exhumed and colonised by species associated with hard substrates small carbonate mounds are found at the summits of some volcanoes and diapirs living corals have been found on the tops of the shallowest mud volcanoes revealing different oceanographic conditions and strong bottom currents that favour the availability of nutrients and organic particles the edifices affected by very high current velocities are located in the channels where erosive processes dominate

seabed morphology and hydrocarbon seepage in the gulf of cadiz mud volcano area acoustic imagery multibeam and ultra high resolution seismic data abstract extensive mud volcanism mud diapirism and carbonate chimneys related to hydrocarbon rich fluid venting are observed throughout the spanish portuguese margin of the gulf of cadiz all the mud volcanoes and diapirs addressed in this paper lie in the region of olistostrome accretionary complex units which were emplaced in the late miocene in response to nw directed convergence between the african and eurasian plates the study area was investigated by multibeam echo sounder high and ultra high resolution seismic profiling dredging and coring the structures observed on multibeam bathymetry at water depths between 500 and 1300 m are dominated by elongate mud ridges mud cones mud volcanoes and crater like collapse structures ranging in relief from 50 to 300 m and size from 0 8 to 2 km in diameter the main morphotectonic features named the guadalquivir diapiric ridge gdr and the cadiz diapiric ridge cdr are longitudinally shaped diapirs which trend ne sw and consist of lower middle miocene plastic marly clays the gdr field and the tasyo field which consist of mud volcanoes and extensive fluid venting related to diapiric ridge development are described in this paper the gdr field is characterised by numerous single sub circular mud volcanoes and mud cones the single mud volcanoes are cone shaped features with relatively gentle slopes of 3 6 consisting of several generations of mud breccia deposition with indications of gas saturation degassing structures and the presence of h2s the mud cones have asymmetric profiles with steep slopes of up to 25 and contain large surficial deposits of hydrocarbon derived carbonate chimneys and slabs the tasyo field is characterised by an extensive concentration of small sub circular depressions oval and multi cone mud volcanoes and large sediment slides mud volcanoes in this area are characterised by moderate slopes 8 12 have bathymetric relief ranging from 100 to 190 m and consist of sulphide rich mud breccia calcite chimneys carbonate crusts and chemosynthetic fauna pogonophora tube worms we propose that all these hydrocarbon seepage structures are related to lateral compressional stress generated at the front of the olistostromic accretionary wedge this stress results in the uplifting and squeezing plastic marly clay deposits additionally the compressional stress at the toe of the olistostrome forms overpressurised compartments which provide avenues for hydrocarbon enriched fluids to migrate

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

late quaternary seismic facies of the gulf of cadiz spanish margin depositional processes influenced by sea level change and tectonic controls abstract seismic facies and quaternary depositional systems of the gulf of cadiz have been characterized by means of high resolution seismic profiles airguns geopulse and ore 3 5 khz a total of 11 pleistocene and two holocene sequences separated by type 1 or type 2 discontinuities were identified the age of the depositional sequences was determined based on foraminifera ages from boreholes and by correlation with seismic profiles of the slope areas with uniform deposition and without significant discontinuities these seismic units have been mapped throughout the margin allowing to establish the correlation with eustatic sea level curves and global climatic trends the distribution and geometry of the units reveals that most of the sedimentary record was developed during episodes of forced regression ten regressive periods corresponding to 5th order cycles arranged into 4th order were distinguished absolute water depths for the development of coastal deposits in each unit were calculated using depth from present day sea level corrected for tectonic subsidence in the area the model for the evolution of the depositional system of the gulf of cadiz continental margin highlights the strong influence of tectonism in the development of depositional bodies controlling the distribution of deposits generally produced during episodes of sea level fall

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

the role of vegetation on gully erosion stabilization at a severely degraded landscape a case study from calhoun experimental critical zone observatory abstract gully erosion was evidence of land degradation in the southern piedmont site of the calhoun critical zone observatory cczo during the cotton farming era understanding of the underlying gully erosion processes is essential to develop gully erosion models that could be useful in assessing the effectiveness of remedial and soil erosion control measures such as gully backfilling revegetation and terracing development and validation of process based gully erosion models is difficult because observations of the formation and progression of gullies are limited in this study analytic formulations of the two dominant gullying processes namely plunge pool erosion and slab failure are utilized to simulate the gullying processes in the 4 km2 holcombe s branch watershed in order to calibrate parameters of the gully erosion model gully features e g depth and area extracted from a high resolution lidar map are used after the calibration the gully model is able to delineate the spatial extent of gullies whose statistics are in close agreement with the gullies extracted from the lidar dem several simulations with the calibrated model are explored to evaluate the effectiveness of various gully remedial measures such as backfilling and revegetation the results show that in the short term the reshaping of the topographical surface by backfilling and compacting gullies is effective in slowing down the growth of gullies e g backfilling decreased the spatial extent of gullies by 21 46 and decreased the average depth of gullies by up to 9 revegetation however is a more effective approach to stabilizing gullies that would otherwise expand if no gully remedial measures are implemented analyses of our simulations show that the gully stabilization effect of revegetation varies over a wide range i e leading to 23 69 reduction of the spatial extent of gullies and up to 45 reduction in the depth of gullies depending on the selection of plant species and management practices

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

assimilation of coastal acoustic tomography data into a barotropic ocean model a data assimilation technique was applied to analyze the first coastal acoustic tomography data obtained in the neko seto channel of the seto inland sea japan on march 2 3 1999 the ensemble kaiman filter technique accompanied by the forecast of error covariances by means of the monte carlo method is found to be best fitted to the present problem because currents in the tomography region are dominated by the strongly nonlinear tidal vortices furthermore the analyzed results are in better agreement with the shipboard adcp results than those obtained by the inverse analysis of the travel time difference data for the pairs of acoustic stations

carbonate mounds in a mud volcano province off north west morocco key to processes and controls abstract this paper presents a new cluster of carbonate mounds discovered in 2002 in the gulf of cadiz off morocco r v belgica 2002 in water depths of 500 to 600 m amidst a field of giant mud volcanoes multibeam bathymetry side scan sonar imagery and 2d seismics are analyzed to present four mound provinces 1 the pen duick mound province on the pen duick escarpment 2 the renard mound province on the renard ridge 3 the vernadsky mound province on the vernadsky ridge and the al idrisi mound province on the gas blanked sediments above the buried al idrisi ridge video imagery and surface samples are described to ground truth the different mound areas the paradox is that nearly no live corals are presently being observed at the surface of the mounds while the mound cores display throughout a high number of reef forming cold water coral fragments scleractinians in association with numerous associated fauna formerly inhabiting the econiches provided by the coral framework environmental and oceanographic conditions during the recent past glacials stadials were probably more favourable for cold water coral growth pore water analyses in on mound cores at the south eastern edge of pen duick escarpment give evidence of focused higher methane fluxes and sulphate reduction rates on mounds than in the surrounding sediments cores from several mounds display horizons of strong corrosion and dissolution of the coral fragments a three phase model for carbonate mound evolution in these settings is proposed 1 in a first stage external controls positive oceanographic and environmental conditions the presence of an active planktonic food chain based on a high primary production and a suitable substrate are responsible for the initiation of cold water coral growth 2 once the cold water corals established an initial framework sedimentation becomes an important factor controlling mound growth the cold water corals baffle the sediments 3 throughout mound growth the mound may episodically be affected by diagenetic processes responsible for aragonite dissolution and probably carbonate precipitation

sedimentary sources of the mud breccia and mud volcanic activity in the western alboran basin during the ttr 17 leg 1 cruise in the west alboran basin gravity cores were acquired from three mud volcanoes mvs dhaka carmen and the recently discovered maya this paper presents micropaleontological and radiocarbon dating results from the three mud volcanoes using cores containing mud breccias overlain by and interbedded with hemipelagic sediments at dhaka mv the mud breccia matrix contains very rare holocene planktonic foraminifera associated with abundant reworked specimens of mixed late cretaceous to mio pliocene age at carmen mv the reworked assemblage is dominated by miocene to pliocene foraminifera occurring together with rare late cretaceous species while at maya mv the mud breccia matrix is characterized by the dominance of santonian maastrichtian forms with subordinate tertiary species shallow water benthic foraminifera such as ammonia spp and elphidium spp are generally rare and randomly distributed but present at all studied sites based on these results we suggest that the main sediment source of the mud breccia extruded at dhaka carmen and maya mvs is possibly the lowermost overpressured olistostromic unit vi aquitanian burdigalian differences in the micropaleontological composition of the mud breccia matrix at different sites are most likely due to differences in the main source layer and in the plumbing systems underneath the mvs radiocarbon dating of hemipelagic sediments associated to the mud breccia allowed to define the age of the latest extrusion activities 0 27 ka to 15 6 ka bp which seem to be episodic short lived and recurrent over thousands of years

the auroral oval position structure and intensity of precipitation from 1984 onward an automated on line data base an on line data base consisting of the auroral oval boundaries structure and particle fluxes from the dmsp f7 and f9 satellites from december 1983 through the present with about an 7 month lag is announced the data are divided into distinct regions e g diffuse aurora discrete aurora cusp proper polar rain etc the magnetospheric sources of the various particle precipitation regions are identified using a sophisticated pattern recognition technique a neural network for each region the boundaries are specified in both geographic and geomagnetic coordinates and the average and peak values of the particle fluxes are given along with the average energies the dmsp satellites are continuously monitored so that data gaps are comparatively rare it is anticipated that the location of the auroral oval and precipitation intensities will be of particular interest to ground based observers although anyone interested in the state of the auroral oval may find it of value span data requests are processed on a completely automated basis with up to 48 hours of auroral oval parameters provided in response to a single request

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

importance of surface sealing in the erosion of some soils from a mediterranean climate abstract poor aggregate stability and high erodibility of soils found in mediterranean climates are often due to low organic matter content the low organic matter content is sometimes compensated for by iron oxides that stabilize soil structure low water stability of aggregates often determines the propensity for soils to form surface crusts and seals wet crusts seals reduce soil infiltration rate and may increase erosion by increasing runoff we conducted rainfall simulation experiments on 30 cm 30 cm plots inclined at 9 slope in which we measured soil splash and wash erosion runoff and splash volume for seventeen california soils the soils ranged in clay content from 8 to 36 esp from

caribbean tectonics and relative plate motions during the last century three different ways of interpreting the tectonic evolution of the gulf of mexico and the caribbean have been proposed taking into account the bailey willis school of a permanent pre jurassic deep sea basin the edward suess school of a subsided continental terrain and the alfred wegener school of continental separation the present investigation is concerned with an outline of an interpretation which follows that of pindell and dewey 1982 an attempt is made to point out ways in which the advanced hypotheses can be tested the fit of africa north america and south america is considered along with aspects of relative motion between north and south america since the early jurasic attention is given to a framework for reconstructing caribbean plate evolution the evolution of the caribbean the plate boundary zones of the northern and southern caribbean and the active deformation of the caribbean plate

measurements of rill and gully erosion in sicily this article reports the results of a field investigation aimed to characterize the morphology of both rills monitored at sparacia experimental area and two ephemeral gullies egs located in the tremamargi basin sicily italy at first the available literature data together with the measurements carried out in this investigation were used to show that the eg length is a key parameter for the estimation of the eroded volume then the comparison among the pairs length and volume corresponding to measured rills egs and gullies showed that the exponent of the power relationship is independent of the channelized erosion type rill eg and gully while a different scale factor has to be used for each erosion process finally a single relationship applicable to all channelized erosion processes was deduced applying the dimensional analysis and the self similarity theory copyright 2011 john wiley sons ltd

an experimental study of rill erosion and morphology abstract rill erosion is recognized as an important process of water erosion on agricultural land the objectives of this study are to examine the effects of rainfall intensity on rill network development and to present some indicators for a quantitative description of rill morphology a soil pan 10 m long 3 m wide and 0 5 m deep and with an adjustable slope gradient from 0 to 30 was subjected to three successive rains under rainfall intensities of 50 and 100 mm h 1 the results showed that rainfall intensity significantly affected rill erosion especially in the active period of rill network development the magnitude of rill erosion was 28 5 and 33 1 kg m 2 and contributed 78 6 and 76 2 to the soil loss under rainfall intensities of 50 and 100 mm h 1 respectively the formation of rill network under the 50 mm h 1 intensity was more complex than that under the 100 mm h 1 intensity for the latter rill networks developed fast and then varied slightly the mean rill inclination angle mean rill density degree of rill dissection and mean rill tortuosity complexity cmean increased with the increase of rains under the same rainfall intensity the value was the optimal derivative morphological indicator to estimate rill erosion and morphology which was followed in descending order by mean cmean and

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

results from a detailed aeromagnetic survey across the northeast newfoundland margin part i spreading anomalies and relationship between magnetic anomalies and the ocean continent boundary abstract a detailed aeromagnetic survey carried out across the northeast newfoundland margin clearly shows the presence of sea floor spreading anomalies 25 to 34 correlation of these anomalies with synthetic profiles shows an increase in the rate of spreading soon after anomaly 27 time three fracture zones can be identified by dislocations in the magnetic anomalies their positions are confirmed on the depth to basement map of this region an eastward extension of the southernmost fracture zone at latitude 49 n matches well with the faraday fracture zone across the mid atlantic ridge and with a basement ridge known as pastouret ridge mapped off goban spur by combining the present survey data with the previously collected shipborne measurements we have also traced the westward continuation of the charlie gibbs fracture zone under the newfoundland shelf a large amplitude magnetic anomaly lies along the margin and separates two zones with different magnetic characteristics long wavelength small amplitude anomalies on the landward side and quasi lineated anomalies on the seaward side seismic data compilations show that this large anomaly coincides with the ocean continent boundary at most places north of flemish cap modelling of the magnetic anomalies indicate that the large amplitude anomaly is caused by the juxtaposition of highly magnetized oceanic crust against weakly magnetized continental crust this situation is similar to that observed across the goban spur margin which is a conjugate of the flemish cap margin the presence of highly magnetized oceanic crust landward of anomaly 34 and within the cretaceous magnetic quiet zone is attested to by the presence of similar large amplitude anomalies south of the flemish cap and goban spur regions but these do not mark the ocean continent transition

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

active mud volcanism in the west alboran basin geochemical evidence of hydrocarbon seepage abstract the west alboran basin was previously classified as a mud volcanic province consisting of two mud volcano mv fields that are inactive at the present day the northern spanish and the southern moroccan fields the discovery of the first active mud volcano carmen cruise ttr 17 in 2008 along with several pockmarks at the central part of the basin motivates more careful geological and geochemical analysis of previous data and comparison to new observations gas bubbling from the crater of carmen mv was observed and recorded using an underwater tv system and a large tv grab sample the gas mainly consisted of methane with less than 1 wetness however all sets of homologues up to pentane were detected in the mud breccia of carmen mv both molecular and stable carbon isotopic compositions and their distribution along the core length suggest a deep thermogenic source of hydrocarbons hcs composition of the pore water from carmen mv also points to a deep source of mud volcanic water the isotopic results indicate that the source of mud volcanic water is the dehydration of clay minerals in the thermal zone of the smectite to illite transformation our observations allow us to infer the presence of structure ii gas hydrates in mud breccia on the top of carmen mv high hc gas saturation in sediments in some pockmarks accompanied with live chemosynthetic fauna directly indicates the strong seepage activity of these structures for the first time authigenic carbonate crusts and chimneys with associated living chemosynthetic bivalves and tubeworms were sampled from a seep site in the west alboran sea authigenic carbonates consist of aragonite and calcite and are characterized by a light carbon isotopic signature up to 37 2 pdb which points to their methane derived origin

neogene to quaternary tectonics and mud diapirism in the gulf of squillace crotone spartivento basin calabrian arc italy abstract the calabrian arc is an arcuate tectonic feature formed during the neogene and pleistocene as a consequence of the progressive retreat of the ionian subduction system it is a key area for understanding the geodynamic evolution of the mediterranean sea the aim of this paper is to investigate the sedimentary dynamics and the possibly active deformation in the gulf of squillace and to highlight their relationships with the fluid escape pathways and mud mobilization the squillace embayment is a marine area belonging to the forearc basin of the calabrian arc at the seaward prosecution of the catanzaro depression by interpreting public seismic profiles at different resolutions calibrated by well logs for hydrocarbon exploration it was possible to define the structural setting and the neogene and quaternary stratigraphic architecture the geologic setting of the gulf of squillace shows the occurrence of normal fault systems cutting through both neogene and quaternary deposits during the messinian trans tensional tectonics led to the formation of a basin whose sediments reached the major thickness in the central portion of the embayment since the early pliocene extensional tectonics was dominant and the basin depocenter progressively changed its orientation creating a narrow basin roughly oriented nw se similar tectonic setting was also present during the pleistocene extension a middle to late pliocene contractional event led to development of a thrust zone in the northern crotone swell mud diapirs that occur in the external area of the gulf of squillace are located close to the pliocene and pleistocene depocenter the overpressure provided by the pliocene and pleistocene sediment accumulation on messinian and pre messinian sediments and the evolution of normal fault systems triggered the mud diapirs formation that progressively developed toward the upper slope extensional deformation and mud diapirism influence the morphologic evolution of the slope and the basin resulting in the retrogressive erosion of canyon heads and gravity driven slope failures

growth and demise of cold water coral ecosystems on mud volcanoes in the west alboran sea the messages from the planktonic and benthic foraminifera the dhaka and maya mud volcanoes mvs located in the mud diapir province in the western alboran basin along the moroccan coasts were cored during the ttr 17 leg 1 cruise cores were taken on the top of the volcanoes at a water depth of 370 m on the dhaka mv core ttr17 ms411g and at 410 m water depth on the maya mv core ttr17 ms419g respectively on both mud volcanoes the extruded mud breccia provides the nucleation point for the colonization and development of cold water corals and associated ecosystems two phases of cold water coral growth are observed 1 between slightly older than 4175 62 years bp and around 2230 59 years bp at dhaka and 2 between slightly older than 15583 185 years bp and around 7613 38 years bp at maya mv on the top of the maya mv only a small patch reef and or isolated corals proliferated whereas a more extended patch reef colonized the top of the dhaka mv at both sites the cold water coral developmentwas triggered by the availability of a suitable substrate for initial coral settling provided either as a firm ground or as single clasts subsequently coral growth was supported by enhanced nutrient flux possibly related to upwelling and or strong currents during the intervals of coral growth planktonic foraminiferal assemblages were dominated by neogloboquadrina incompta the decline of coral ecosystems on the mud volcanoes is accompanied at surface by a shift fromthe n incompta dominated assemblage to a globorotalia inflata dominated assemblage possibly reflecting more oligotrophic conditions this shift is coeval to the passage from wet to arid conditions at the end of the african humid period at mayamv it is interpreted as an effect of an early human impact on a fragile environment which was already stressed by desiccation at the time of the development of complex human society along the mediterranean coasts at dhaka mv

effects of oceanographic changes on controlling the stability of gas hydrates and the formation of authigenic carbonates at mud volcanoes and seepage sites on the iberian margin of the gulf of cadiz abstract the gulf of cadiz is characterized by extensive active and inactive fluid escape structures which manifest as mud volcanoes diapiric ridges pockmarks and cold seeps the high methane content and the presence of gas hydrates in the shallow sediments of the most active fluid escape structures indicate that these are areas of preferential migration and escape of fluids enriched in hydrocarbons and methane extensive fields of methane derived authigenic carbonates are found at fluid escape structures along the upper and mid continental slope where the mediterranean outflow water is in direct contact with the seafloor at water depths generally 1400 m parts of the basin the estimated u th ages of the authigenic carbonates suggest that they were probably formed during discrete episodes of gas hydrate activity that may have occurred as a result of rapid climatic changes such as the termination of the last glacial stage numerical modelling indicates that seafloor temperature variations associated with glacial interglacial cycles and the changes of the mediterranean outflow pathway could have restricted or eliminated the gas hydrate stability zone at the mud volcanoes shallower than 1400 m resulting in intense fluxes of methane rich fluids to the shallow sediments or even the seafloor this fluid flux was recorded by the microbially mediated precipitation of authigenic carbonates

rill erosion and morphological evolution a simulation model a mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment transport and deposition in rills the model mimics the dynamic process of rill evolution including variable rates of sediment redistribution along the bed and changes in local bed morphology the sediment source term in the model uses a point scale probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power the interdependent feedback loops between channel bed morphology local flow hydraulics and local scour and deposition within the framework of the full hydrodynamic equations with inertial terms constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations a series of laboratory flume experiments were performed to evaluate the model initial bed slopes were 3 5 and 7 with step increases of water inflow rates of 7 6 11 4 and 15 2 l min 1 the soil material used in the flume was a kaolinitic sandy clay loam the rill model equations were solved for increasingly complex cases of spatial and temporal variabilities the model followed measured patterns of morphological changes as the rill evolved which suggests that the feedback loops in the model between erosion bed morphological changes and hydraulics were adequate to capture the essence of rill evolution

seafloor expression of sediment extrusion and intrusion at the el arraiche mud volcano field gulf of cadiz 1 the el arraiche mud volcano field consists of eight mud volcanoes up to 255 m high and 5 4 km wide located in the moroccan margin of the gulf of cadiz at water depths between 700 and 200 m available data include detailed swath bathymetry over the entire area dense grids of high resolution seismic data very high resolution deep tow subbottom profiles side scan sonar mosaics over the major structures selected underwater video lines and sediment samples the main morphological aspects of the mud volcanoes are from the margin toward the center a subsidence rim or moat the mud volcano slope in some cases a deep crater and a recent central mud dome at the top the slope is characterized by radial outward sediment flow deposits or by a concentric pattern of terraces and steps the sediment flow deposits can be divided into elongate outflows that accumulate at the base of the slope and short bulky outflow deposits that freeze on the steep slope the crater hosts extruded sediment ranging from fluidized sand to mud breccia with centimeter to meter sized rock clasts issued from several vents within the crater the concentric slope terraces and the central mud dome are interpreted to result from several phases of uplift caused by sediment intrusion or shallow diapirism the mud volcano growth is thus interpreted to result from a combination of extrusive and intrusive processes

ground observations and possible source regions of two types of pc 1 2 micropulsations at very high latitudes we have used 1 year s data from the recently installed magnetometer array for cusp and cleft studies maccs in arctic canada and from two stations of the developing conjugate array of automated geophysical observatories agos in antarctica to study ulf waves in the pc 1 2 100 600 mhz frequency band at cusp and polar cap latitudes 74 80 in this paper we focus on the spectral properties and latitudinal and local time distributions of pc 1 2 events observed during 1994 and use these along with several case studies to infer the source locations of the two major wave types we have observed we found little variation in center band frequency of the pc 1 2 waves we observed but the average event bandwidth was distinctly wider at stations near 80 mlat than at stations near 75 mlat broadband waves with diffuse spectral character dominated at the higher latitudes but their occurrence was confined at most stations to within 4 hours of local magnetic noon waves with narrower bandwidth were much more common in our data set and were the statistically dominant wave type at the lower latitude maccs stations their occurrence was also limited to the dayside but extended both later and more widely in local time than the more broadband waves these multistation observations combined with data from the dmsp imp 8 and geotail satellites suggest the possibility that these two wave types originate in quite different regions near the magnetospheric boundary the more narrowband waves in the subsolar and postnoon equatorial region and the more broadband waves in the high latitude plasma mantle and possibly at the poleward edge of the cusp the cusp itself appears to not be a significant source of pc 1 2 wave activity that can be detected by ground observatories

hydrocarbon derived ferromanganese nodules in carbonate mud mounds from the gulf of cadiz mud breccia sediments and clasts as nucleation sites abstract more than 500 fe mn nodules were sampled during the anastasya 01 cruise tasyo project along the continental margin of the gulf of cadiz eastern central atlantic at the confluence of the mediterranean sea with the atlantic ocean where extensive nodule fields were discovered based on wide previous studies that included swath bathymetry multi channel and very high resolution seismic reflection gravimetry magnetism and underwater photography surveys nodules were collected at water depths ranging from 850 to 1000 m associated with hydrocarbon derived ankerite and dolomite chimneys and crusts thirty six selected samples among the various morphological types were used for the laboratory analysis of physical properties morphology colour surface texture sphericity weight and size mineralogy xrd optical and electronic microscopy and geochemistry xrf aas icp ms epma gc ms s c and o isotopes nodules show a wide range of sizes densities weights and morphologies nodules are formed of multiple millimetre thick layers of fe and mn oxyhydroxides surrounding the nucleus composed of early middle miocene plastic marl the textures developed by the fe and mn oxyhydroxides layers are massive laminated detrital and mottled to dendritic goethite lepidocrocite mn oxides 7 a manganates and 10 a manganates quartz and phyllosilicates are the main components accessory minerals are calcite dolomite siderite rhodochrosite kutnohorite pyrite chalcopyrite potassium feldspar zircon rutile ilmenite and chlorite fe mn carbonates from the siderite rhodochrosite continuous series are forming part of the marl nuclei framboidal filamentous and globular textures are observed in fe mn oxides and pyrite suggesting biogenic origin nodules show a high mean abundance of fe 38 6 moderate mn 6 0 and low contents of trace metals and rees compared to the average content of deep seabed polymetallic nodules from other oceanic areas the mn fe ratio ranges from 0 07 to 0 25 the studied nodules hold in their oxide layers hydrocarbons n alkanes derived from marine bacterial activity aromatic hydrocarbons in the form of phenanthrene are also present which is characteristic of mature petroleum the structure mineralogy and chemical composition in the studied nodules are similar to those of diagenetic hydrogenetic continental margin nodules rather than deep sea nodules we suggest that the formation of this type of nodule occurred through a combined diagenetic hydrogenetic growth process involving fluid venting from deep seated hydrocarbon reservoirs bio mineralization processes and bottom current erosion

experimental study on soil erosion prediction model of loess slope based on rill morphology abstract rill erosion frequently occurs in agriculturally disturbed dry areas despite many research efforts over recent decades the characteristics of rill erosion and its intrinsic mechanisms remain unclear the objectives of this study were to investigate the impacts of rill morphology evolution on rill erosion processes a soil pan 5 m long 1 m wide and 0 6 m deep and with an adjustable slope gradient of 0 30 was subjected to rainfall simulation experiments under three intensities of representative erosive rainfall 66 94 and 127 mm h 1 the rill morphology evolution exhibited significant nonlinear change regulation and the stronger the rainfall intensity the clearer the nonlinear feature the equation between rill morphological characteristics with geomorphological comentropy and bifurcation ratio was generated which indicated that the contribution rate of geomorphological comentropy to sediment yield was 80 and the contribution rate of bifurcation ratio was 20 for the experimental treatments a soil erosion model was constructed with and without rill development and the coefficient to describe the influence of rill development on slope erosion was obtained the rill erosion coefficient was embedded into an existing soil erosion model for steep slopes as a result when rill erosion occurred on the slope the contribution of the rill morphology to the rill erosion was fully realized by the model verification indicated that the accuracy of the model was significantly improved in previous studies the accuracy of slope water erosion prediction model was low because the evolution process of slope topography was not considered our results solve the spatial variability problem in the slope erosion prediction model and improve the simulation accuracy of the soil erosion prediction model on a loess slope

application of lipid biomarkers to detect sources of organic matter in mud volcano deposits and post eruptional methanotrophic processes in the gulf of cadiz ne atlantic abstract the gulf of cadiz is known as an active mud volcano mv and fluid venting region discovered during the training through research ttr expeditions in 1999 ttr 9 here we report a study of lipid biomarkers in the mud breccia matrix from three mvs in this region the lipid biomarker composition revealed strong compositional resemblance as well as similar thermal maturity properties for the studied mvs this indicates that the primary source of the erupted material for these mvs is located in similar litho stratigraphic units in both areas upward migrated fluid went through the sedimentary series of the allochthonous olistrostrome and through the upper cretaceous horizons the relatively immature characteristics of organic matter from both mud breccia rock clasts and matrix together with the more mature properties of hydrocarbon gases from the same sampling locations indicate that source strata for the initial fluid are located deeper in the subsurface than the source strata for the erupted sedimentary material the presence of microbial lipid biomarkers derived from archaea and sulfate reducing bacteria in the mud breccias revealed anaerobic oxidation of methane aom as a dominant microbial process in these habitats our data suggest that the aom derived lipids are at least in part fossil in origin i e they do not reflect active aom communities and thus reflect aom activity in these mvs integrated over time the low concentrations of aom related biomarkers in these mvs suggest relatively low intensities of aom in the studied mv deposits the distribution of biomarkers suggests an abrupt and brief cold seep activity in the past and the absence of a continuous methane influx in the studied locations

distribution morphology and influencing factors of rills under extreme rainfall conditions in main land uses on the loess plateau of china abstract rill erosion is one of the main forms of soil erosion of the hillslopes on the loess plateau of china few studies have evaluated the effects of land use on the distribution and morphology of rills under extreme rainstorms a total of 50 rill survey sites were selected in a typical watershed of the loess plateau of china to investigate the rill distribution and morphology of three land uses fallow land fl slope farmland sf and annual grassland ag under extreme rainstorm conditions called 7 26 rainstorm seven parameters rill width rill depth width depth ratio cross section area rill density degree of rill dissection and rill erosion modulus were used to characterize rill morphology and the basic soil and vegetation properties bulk density particle size distribution and vegetation coverage and topographic factors slope length gradient direction were measured it was found that rills developed on three land uses and those with widths ranging from 5 to 20 cm accounted for 80 rills developed on fl were deeper than those on sf and ag almost all rills on fl had a depth of 5 20 cm 90 3 while the depth of rills on sf and ag were mainly smaller than 15 cm 91 5 and 91 9 respectively in addition to width rill depth and cross section area of sf and ag were also significantly less than those of fl sf and fl had a relatively high width depth ratio and dissection degree however land use had no significant effect on rill density crop plantations sf and grass restoration ag significantly reduced rill erosion modulus 28 70 and 45 07 reduction respectively land use topography soil and vegetation factors significantly affected rill morphology p 0 001 based on redundancy analysis rda and can explain 48 0 of the total variability of rill morphology with slope length vegetation coverage and slope gradient having the greatest influences most of the rill morphological parameters significantly decreased as the vegetation coverage increased but they significantly increased with increasing slope length and slope gradient this study clearly illustrates the severe rill erosion caused by this rainstorm and indirectly indicates that crop harvesting fl aggravates rill erosion and that revegetation ag can effectively contain rill erosion therefore rehabilitation efforts should be focused on revegetation grassland and or woodland on steep slopes to control soil erosion

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

authigenic barite records of methane seepage at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanoes mvs are dynamic features that episodically expel gas charged fluids and mud onto the seafloor transferring various chemical constituents into the overlying water column the temporal variability in mv activity is however poorly understood so their importance as a source of methane ch4 and higher hydrocarbons for the oceanic carbon budget although thought to be significant cannot be properly constrained in this study the history of fluid and gas seepage at the carlos ribeiro mv gulf of cadiz is assessed via geochemical analyses and transport reaction modelling of pore fluids and barium ba rich layers ba fronts in sediment cores recovered along a transect from the eye to the periphery of the mv x ray fluorescence data reveal that ba fronts are absent at the eye while a single front with up to 1740 ppm ba is present at the margin of the summit three ba fronts occur at 45 85 and 130 cm depth within a mudflow to the southeast of the crater spectrometric analyses indicate that barite is the ba rich mineral in these layers upward advecting pore fluids are enriched in barium but depleted in calcium ca2 relative to seawater modelling of the ba2 and ca2 pore fluid profiles indicates that the positions of the ba fronts reflect both the present day hydrodynamic conditions as well as higher fluxes of methane in the past fluid advection appears to have decreased since 340 cal yr before present but degassing of the mudflow is ongoing and is potentially an important source of ch4

emplacement of a passive margin evaporitic allochthon in the betic cordillera of spain the triassic section of the external domain of the betic cordillera is rootless and thus allochthonous the frontal accretionary wedge of the guadalquivir allochthon consists dominantly of triassic evaporites and red beds forming a melange with upper cretaceous paleogene deep water sedimentary rocks throughout the unit jurassic rocks are absent it is here proposed that the widespread triassic evaporites of the guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive margin setting much like the widespread allochthonous salt of the texas louisiana gulf of mexico thus on the betic passive margin allochthonous evaporites were first emplaced during the late cretaceous paleogene later during neogene time these evaporites were overthrusted as an accretionary wedge to form the guadalquivir allochthon a schematic reconstructed position of the guadalquivir allochthon places the original passive margin allochthon in its continental slope setting

potential geologic hazards on the eastern gulf of cadiz slope sw spain abstract geologic hazards resulting from sedimentary oceanographic and tectonic processes affect more than one third of the offshore gulf of cadiz and are identified by interpreting high resolution seismic profiles and sonographs hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km 2 mainly concentrated in the steeper upper slope area besides the presence of steep slopes the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment gassy sediments and associated seafloor pockmarks cover more than 240 km 2 in the upper slope hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong mediterranean undercurrent and the rough seafloor physiography the local intensification of bottom currents is responsible for erosive processes along more than 1900 km 2 in the upper slope and in the canyons eroded in the central area of the slope undermining slopes and causing instability the strong bottom currents also create a mobile seafloor containing bedforms in an area of the gulf that extends more than 2500 km 2 mostly in the continental slope terraces hazards of tectonic origin are important because the gulf of cadiz straddles two major tectonic regions the azores gibraltar fracture zone and the betic range which results in diapir uplift over an area of more than 1000 km 2 and in active seismicity with earthquakes of moderate magnitude also tsunamis produced by strong earthquakes occur in the gulf of cadiz and are related to the tectonic activity along the azores gibraltar fracture zone

methane hydrate bearing sediments pore habit and implications abstract hydrate bearing sediments are relevant to the organic carbon cycle seafloor instability and as a potential energy resource sediment characteristics affect hydrate formation gas migration and recovery strategies we combine the physics of granular materials with robust compaction models to estimate effective stress and capillary pressure in order to anticipate the pore habit of methane hydrates as a function of the sediment characteristics and depth then we compare these results to an extensive database of worldwide hydrate accumulations compiled from published studies results highlight the critical role of fines on sediments mechanical and flow properties hydrate pore habit and potential production strategies the vast majority of hydrate accumulations 92 of the sites are found in fines controlled sediments at a vertical effective stress between z 400 kpa and 4 mpa where grain displacive hydrate pore habit prevails in the form of segregated lenses and nodules while permeation based gas recovery by depressurization is favored in clean coarse sediments gas recovery from fines controlled sediments could benefit from enhanced transmissivity along gas driven fractures created by thermal stimulation

mud volcanoes revealed and sampled on the western moroccan continental margin we surveyed and sampled two active and 3 inactive mud volcanoes on the atlantic continental margin of morocco the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise between 150 250 meters above the seafloor and are the first active methane related mud volcanoes to be identified in this region the inactive volcanoes range in diameter from 1 3 km with relief between 50 and 80 meters gravity cores from the crest of the active mud volcanoes yielded methane hydrates and mud breccia deposits chemosynthetic communities of pogonophora worms and the bivalve solemya were found on the surface of the active mud volcanoes sediment cores from the inactive volcanoes contained hemipelagic sediments rich in foraminifera and ahermatypic coral debris overlying mud breccia

crustal structure beneath the archean proterozoic terrain of north india from receiver function modeling abstract the shear velocity structure of the north indian crust comprising of the archean cratons aravalli bundelkhand and proterozoic vindhyan basin is modeled and compared with the eastern dharwar craton as well the global models for archean and proterozoic terrains the velocity structure is deduced from joint inversion of teleseismic receiver function time series and surface wave group velocity measurements the north indian archean crust is a simple two layered an average v s 3 3 0 1 km s in the upper 10 km increasing to 3 7 0 1 km s in the 26 28 km thick lower crust this upper crustal velocity is significantly less compared to those of either eastern dharwar craton 3 5 3 6 km s or the global average these results suggest presence of a highly silica rich upper crust and an intermediate composition of the lower crust the moho is modeled at a depth of 36 38 km with thin transition 2 km similar to those in eastern dharwar craton in contrast the proterozoic vindhyan basin has significantly deeper moho 44 46 km with a 4 10 km thick underplated layer v s 4 0 km s at the base of the crust the sedimentary layer thickness is 2 4 km the results support the view that proterozoic crust is thicker and underlain by a mafic layer at its base in contrast to a thin archean crust with near absence of the basal layer as observed globally

the gibraltar subduction a decade of new geophysical data the gibraltar arc spans a complex portion of the africa eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity the seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold and thrust belt have led to competing geodynamic models delamination and subduction geophysical data acquired in the past decade provide a test for these models and support a narrow east dipping subduction zone seismic refraction studies indicate oceanic crust below the western gulf of cadiz tomography of the upper mantle reveals a steep east dipping high p wave velocity body beneath gibraltar the anisotropic mantle fabric from sks splitting shows arc parallel fast directions consistent with toroidal flow around a narrow westward retreating subducting slab the accompanying wsw advance of the rif betic mountain belt has constructed a thick pile of deformed sediments an accretionary wedge characterized by west vergent thrust anticlines bathymetric swath mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided subduction has slowed significantly since 5 ma but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge three possible origins for this deformation are discussed gravitational spreading overall nw se convergence between africa and iberia and finally a wsw tectonic push from slow but ongoing roll back subduction in the absence of arc volcanism and shallow dipping thrust type earthquakes evidence in favor of present day subduction can only be indirect and remains the object of debate continued activity of the subduction offers a possible explanation for great m 8 5 earthquakes known to affect the area like the famous 1755 great lisbon earthquake recent gps studies show sw motion of stations in n morocco at velocities of 3 6 mm yr indicating the presence of an independent block a rif betic alboran microplate situated between iberia and africa

field investigation of rill and ephemeral gully erosion in the sparacia experimental area south italy abstract this paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies egs monitored at sparacia experimental area sicily italy the comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases the measurements were used for testing both the empirical relationships between the channel rill egs and gully length and its eroded volume and among the morphological variables length width depth and volume describing the channelized process finally the rill and egs hydraulic geometry was modelled by three well known power equations relating the discharge with the mean flow velocity with the flow depth and with the width of each channel segment respectively the rill measurements also showed that the flow velocity was affected by the rill segment slope while the flow depth and width were controlled by the plot slope therefore three equations taking into account these slope effects were proposed to estimate the hydraulic characteristics of the rills monitored at the sparacia area

morphology and influencing factors of rills in the steep slope in yuanmou dry hot valley sw china abstract it is very important to understand rill morphology in order to understand its dynamics to reveal the morphology and influencing factors of rills in the steep slope rss in the yuanmou dry hot valley the total station photogrammetric technique and microtopographic profiler were used to obtain the parameters of the cross sections and longitudinal profiles of the rss and 12 parameters were used to characterize the rill morphology the results show that the morphology of rills clearly varied between each layer the topography soil properties and ferruginous cemented layer all exerted important influences on the rill morphology the average depth decreased with increasing slope length and the depths dominated by silt and sand were larger than that dominated by clay the average width and average width depth ratio increased with increasing slope length and the width and the width depth ratio that was dominated by clay was larger than that dominated by silt and sand the shape ratio of the rill cross section ranged from 0 50 to 0 58 and the shape of the cross section gradually changed from narrow and deep to wide and shallow with increasing slope length concave convex degree tended to be larger in the segment with ferruginous cement in the longitudinal profile the gradient gradually decreased with decreasing slope gradient and increasing slope length the presence of the ferruginous cemented layer and topsoil crust resulted in abnormal changes in the shape of the rill it is helpful to further understand the mechanisms of rill erosion under different conditions

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

a transtensional basin model for the organya basin central southern pyrenees based on magnetic fabric and brittle structures summary the purpose of this paper is to explain the kinematics of the inverted extensional organy basin centralsouthernpyrenees duringitsextensionalevolution thestudyoftheanisotropy of magnetic susceptibility ams and the study of brittle mesostructures are the instruments used to decipher the extensional kinematics separation of magnetic subfabrics analyses of ams at low temperature and anisotropy of the anhysteretic remanence aarm has been also done to properly interpret the obtained magnetic fabric data the combination of all magnetic fabric and brittle mesostructures analyses has provided new information to clarify thestructuralevolutionofthebasin whichsupportanewtectonicmodelfortheaptian albian basinal stage 20 sites for the magnetic fabric analysis were sampled in aptian lower albian marls the ams ellipsoids obtained at room temperature show their kmin axes perpendicular to bedding and kmax axes oriented nw se in 70 per cent of the samples n s in 15 per cent and ne sw in 15 per cent analyses of ams at low temperature show a better clustering of the axes of the magnetic ellipsoid pointing out that phyllosilicates constitute the carriers of the ams whereas the analyses of the aarm confirm the scattering of the ferromagnetic grains these results suggest that the obtained ams in the organy a basin was acquired during or shortly after deposition of the aptian lower albian marls without any subsequent overprint the direction of the magnetic lineation obtained from the ams at room and low temperatures agrees with the orientation of the stress axes obtained from the analysis of brittle mesostructures mainly faults and calcite filled tension gashes indicating its tectonic origin we interpret the orientation of the magnetic ellipsoids related to the transtensional movements linked to the formation of the organy a basin during the aptian albian interval which are consistent with the eastward displacement and rotation of iberia with respect to europe analysis oftensiongashesalsoindicatesamainnw seextensiondirection whereaspalaeostressanalysis of striated faults shows a more n s trending 3 the transtensional model proposed from magnetic fabric and brittle mesostructures for the organy a basin during the aptian albian is consistent with the creation of a strongly subsiding area south of the axial zone during the cretaceous and implies that rotation and separation of iberia respect to europe took place simultaneously

linked halokinesis and mud volcanism at the mercator mud volcano gulf of cadiz mud volcanoes are seafloor expressions of focused fluid flow that are common in compressional tectonic settings new high resolution 3 d seismic data from the mercator mud volcano mmv and an adjacent buried mud volcano bmv image the internal structure of the top 800 m of sediment at both mud volcanoes revealing that both are linked and have been active episodically the total volumes of extruded mud range between 0 15 and 0 35 km3 and 0 02 0 05 km3 for the mmv and the bmv respectively the pore water composition of surface sediment samples suggests that halokinesis has played an important role in the evolution of the mud volcanoes we propose that erosion of the top of the vernadsky ridge that underlies the mud volcanoes activated salt movement triggering deep migration of fluids dissolution of salt and sediment liquefaction and mobilization since the end of the pliocene since beginning of mud volcanism in this area the mud volcanoes erupted four times while there was only one reactivation of salt tectonics this implies that there are other mechanisms that trigger mud eruptions the stratigraphic relationship of mudflows from the mmv and bmv indicates that the bmv was triggered by the mmv eruptions this may either be caused by loading induced hydrofracturing within the bmv or due to a common feeder system for both mud volcanoes this study shows that the mud volcanoes in the el arraiche mud volcano field are long lived features that erupt with intervals of several tens of thousands of years

geophysical evidence of gas hydrates in shallow submarine mud volcanoes on the moroccan margin 1 gas hydrates inside mud volcanoes have been observed in several locations but are generally found at water depths of 1000 m and deeper we present the first observation of the base of a gas hydrate stability zone within a shallow mud volcano in the el arraiche mud volcano field on the moroccan atlantic margin the mud volcano base is located at about 475 m and is over 125 m high on high resolution seismics we observed an anomalous but coherent reflection under the slopes of the mud volcano the event was interpreted as the base of a gas hydrate stability zone because of its inverse polarity and its morphology far from the crater the event is nearly parallel to the seafloor closer toward the crater the event shallows inside the mud volcano crater no event is observed a stability model using thermogenic gas compositions is applied to local p t conditions indicating that thermogenic gas hydrates can be stable at this depth the high modeled heat flow in the crater of the mud volcano indicates a focused flow of warm fluids below the slopes of the mud volcano the inferred heat flow is also elevated but less high in areas of thermogenic gas production gas hydrates can occur at shallow water depths even in areas with high heat flow this also suggests that dewatering of the accretionary wedge complex is mainly focused along fault surfaces and through seafloor structures such as mud volcanoes

numerical modelling of mud volcanoes and their flows using constraints from the gulf of cadiz it is estimated that the total number of submarine mud volcanoes is between 1000 and 100 000 because many are associated with greenhouse gases such as methane it is argued that the global flux of these gases to the atmosphere from the world s terrestrial and submarine mud volcanoes is highly significant clues to the processes forming submarine mud volcanoes can be found in variations to their height shape surface morphology physical properties and internal structure a model of isostatic compensation between the mud column and the sediment overlying the mud source is used to predict a depth to the mud reservoir beneath mud volcanoes once erupted the general behaviour of an individual mud flow can be described and predicted using a viscous gravity current model the model shows that conical shaped mud volcanoes comprise multiple superimposed radial flows in which the thickness eruption rate and speed of individual mud flows strongly depends on the viscosity density and over pressure of the erupted mud using these parameters the model predicts the lowermost flows will be the oldest thickest and have the greatest length of run out while the uppermost flows will be the youngest thinnest and shortest this model is in contrast to more traditional models of stratiform mud volcano construction in which younger flows progressively bury older ones and travel furthest from the summit applying the model to the two mud volcanoes studied in the gulf of cadiz quantitative estimates are derived for the depths to mud sources exit and flow velocities eruption duration and volume fluxes flow thickness and conduit radii for example with an average kinematic viscosity of 1 5 m2 s 1 for the erupted mud a density of 1 8 103 kg m 3 and a thickness for the youngest flows of about 0 5 m the model predicts a lowermost flow thickness of 3 6 m an average eruption duration of 7 h and a conduit radius of about 9 m to construct a conical shaped mud volcano of 260 m height similar to those studied in the gulf of cadiz is estimated to require a mud source at 4 6 km depth and a total of at least 100 individually erupted flows

gas hydrates in the ginsburg and yuma mud volcano sediments moroccan margin results of chemical and isotopic studies of pore water abstract two active mud volcanoes on the atlantic continental margin of morocco were sampled during a 1999 expedition on the r v professor logachev the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise 150 250 m above the seafloor and are the first active methane related mud volcanoes identified in this region gravity cores from the crest of the active mud volcanoes recovered methane hydrates clathrates thirty five pore water samples were extracted and analyzed from seven gravity cores taken in and around the active mud volcanoes estimated gas hydrate content in mud volcano sediments is 2 11 by volume and 4 19 by pore space chloride ion concentrations of the original mud volcano water are similar to those of surrounding seawater but are isotopically different the water is very high in oxygen to 35 and light in hydrogen to 70 pore water with these features has not been previously described in the published literature

molecular and carbon isotopic variability of hydrocarbon gases from mud volcanoes in the gulf of cadiz ne atlantic investigations of molecular and carbon isotopic variability of hydrocarbon gases from methane through butanes pentanes have been performed on six mud volcanoes from two fluid venting provinces located in the gulf of cadiz ne atlantic the main aims were to define the basic gas types to describe their geochemical characteristics in relationship to their sources and to determine the secondary effects due to migration mixing and microbial alteration hydrocarbon gas data reveal two groups of gases despite the different maturation characteristics both gas groups are allochthonous to the erupted mud breccia and represent a complex of redeposited secondary migrated mixed and microbially altered hydrocarbons it may possibly imply the presence of hydrocarbon accumulations in the deep subsurface of the gulf of cadiz

can rock fragment cover maintain soil and water for saline sodic soil slopes under coastal reclamation abstract seeking a potential erosion control method for saline sodic soil slopes under coastal reclamation is essential we investigated the effect of rock fragment covers rc on the rainfall partitioning infiltration and runoff processes and the erosion processes for saline sodic slopes of 15 and 30 subjected to a 50 min simulated rainstorm with an intensity of 92 mm h 1 six rock fragment covers 0 10 20 40 60 and 80 were investigated soil was packed in 200 cm 100 cm 30 cm flumes divided into two to create two replicates for each treatment two sequential soil erosion events e1 followed by e2 were induced under two rainstorms that were 24 h apart results showed that in general rc had a positive effect on the runoff rate for both slopes a logarithmic relationship existed between the steady state infiltration rate and the rc for the gentler slopes an rc between 40 and 60 could protect the soil from erosion for e2 and e1 e2 events but did not do so for the e1 events alone for the steeper slopes the rc had no effect on soil losses for the e2 and e1 e2 events but increased the soil losses for the e1 events as the situation of rock fragment changed from situation 1 well embedded into the soil surface to situation 4 submerged in water the relationship between rc and soil loss became more complex and might change over time from a positive to a negative one the results suggested that the effect of rc on runoff and soil losses was influenced by the change of rock fragment situations over time during individual rainstorms the benefits of rc might be augmented by using them in combination with another protective measure

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

the el arraiche mud volcano field at the moroccan atlantic slope gulf of cadiz the el arraiche field is a new mud volcano field discovered near the moroccan shelf edge in the gulf of cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m the largest mud volcano in the field al idrissi mud volcano is 255 m high and 5 4 km wide the cluster was discovered during a survey with the rv belgica and studied further during leg 2 of the ttr 12 survey onboard the r v prof logachev the 2002 surveys yielded detailed multibeam bathymetry over a 700 km 2 study area dense grids of high resolution seismic data deep tow sub bottom profiles sidescan sonar mosaics over the major structures selected video imagery lines video guided grab samples dredge samples gravity cores and box cores were collected for groundtruthing purposes eight mud volcanoes in water depths from 200 to 700 m cluster around two sub parallel anticlines and associated active extensional faults rock clasts and regional seismic data locate the el arraiche field over a late miocene pliocene extensional basin the onset of mud volcanic activity is estimated at about 2 4 ma and probably roots in the cretaceous miocene accretionary wedge stacked outflows are visible up to a depth of about 500 m below the sea floor the occurrence of long lived mud volcanoes bear witness to continued overpressure generation at depth either by in situ oil and gas generation or by focussed flow and accumulation in the area geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes the activity of the mud volcanoes is indicated by the thickness of hemi pelagic sediments covering extruded mud breccia the

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

fluid evolution and authigenic mineral paragenesis related to salt diapirism the mercator mud volcano in the gulf of cadiz the formation of mud volcanoes in the gulf of cadiz is closely linked to diapirism in the deep subsurface the mercator mud volcano mmv is a rare example where diapiric emplacement in addition to being key for upward fluid migration is also an important zone for fluid and mineral diagenesis the most intriguing findings in the near surface muds of the mmv are extremely high salinities of up to 5 2 m of nacl from diapiric and evaporitic halite dissolution and the occurrence of authigenic gypsum and anhydrite crystals both of which have not been observed to date in the gulf of cadiz employing a thermodynamic model we elucidate how the interplay of temperature pulses strong salinity gradients and fluid flow dynamically drive mineral dissolution and re formation the strong increase in salinity in the pore fluids has important implications for thermodynamic equilibria by significantly lowering the activity of water thereby raising the gypsum anhydrite transition zone from 1 km to about 400 m sediment depth at the mmv this transition is further shifted to immediately below the seafloor during intervals of active mud and fluid expulsion when the mv surface temperature is heated up to at least 30 c as a consequence precipitation of authigenic gypsum near the sediment surface 1 2 mbsf has been linked to the dissolution of evaporites below the mmv more precisely the mechanisms generating supersaturation in the ascending gypsum saturated mmv fluids are 1 the slow and constant cooling of these fluids along the geothermal gradient during their ascent leading to formation of ubiquitous micro crystals and 2 the more rapid cooling after a heat pulse or transport from greater and warmer depth during an active mud volcano phase leading to the precipitation of cm scale gypsum crystals or even fist size concretions the mmv fluids approaching the salt diapir from farther below have experienced a genesis similar to those of other mud volcanoes in the gulf of cadiz located above deep rooted faults these processes include clay mineral dewatering thermogenic degradation of organic matter and deep high temperature leaching of terrigenous sediments or continental crust

a predictive numerical model for potential mapping of the gas hydrate stability zone in the gulf of cadiz this paper presents a computational model for mapping the regional 3d distribution in which seafloor gas hydrates would be stable that is carried out in a geographical information system gis environment the construction of the model is comprised of three primary steps namely 1 the construction of surfaces for the various variables based on available 3d data seafloor temperature geothermal gradient and depth pressure 2 the calculation of the gas function equilibrium functions for the various hydrocarbon compositions reported from hydrate and sediment samples and 3 the calculation of the thickness of the hydrate stability zone the solution is based on a transcendental function which is solved iteratively in a gis environment the model has been applied in the northernmost continental slope of the gulf of cadiz an area where an abundant supply for hydrate formation such as extensive hydrocarbon seeps diapirs and fault structures is combined with deep undercurrents and a complex seafloor morphology in the gulf of cadiz the model depicts the distribution of the base of the gas hydrate stability zone for both biogenic and thermogenic gas compositions and explains the geometry and distribution of geological structures derived from gas venting in the tasyo field gulf of cadiz and the generation of bsr levels on the upper continental slope

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone