variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

sedimentary response to milankovitch type climatic oscillations and formation of sediment undulations evidence from a shallow shelf setting at gela basin on the sicilian continental margin abstract a multi proxy chronological framework along with sequence stratigraphic interpretations unveils composite milankovitch cyclicity in the sedimentary records of the last glacial interglacial cycle at ne gela basin on the sicilian continental margin chronostratigraphic data including foraminifera based eco biostratigraphy and 18 o records tephrochronological markers and 14 c ams radiometric datings was derived from the shallow shelf drill sites geob14403 54 6 m recovery and geob14414 27 5 m collected with both gravity and drilled mebo cores in 193 m and 146 m water depth respectively the recovered intervals record marine isotope stages and substages mis from mis 5 to mis 1 thus comprising major stratigraphic parts of the progradational deposits that form the last 100 ka depositional sequence calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher frequency 20 ka sea level cycles punctuating this 100 ka cycle this becomes most evident in the alternation of thick interstadial highstand hst wedges and thinner glacial forced regression fsst units mirroring seaward shifts in coastal progradation albeit their relatively short lived depositional phase these subordinate hst units form the bulk of the 100 ka depositional sequence two mechanisms are proposed that likely account for enhanced sediment accumulation ratios sar of up to 200 cm ka during these intervals 1 intensified activity of deep and intermediate levantine intermediate water liw associated to the drowning of mediterranean shelves and 2 amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions equally the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of mis 5 interstadials which bear a striking resemblance to modern equivalents forming on late holocene prodeltas of other mediterranean shallow shelf settings

influence of the atlantic inflow and mediterranean outflow currents on late quaternary sedimentary facies of the gulf of cadiz continental margin abstract the late quaternary pattern of sedimentary facies on the spanish gulf of cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the atlantic inflow currents flowing southeastward across the cadiz shelf toward the strait of gibraltar an inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10 20 m that extends deeper and obliquely down paleo valleys as a result of southward down valley flow a mid shelf holocene mud facies progrades offshore from river mouth sources but atlantic inflow currents cause extensive progradation along shelf toward the southeast increased inflow current speeds near the strait of gibraltar and the strong mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf at the outer shelf edge and underlying the mid shelf mud and inner shelf sand facies is a late pleistocene to holocene transgressive sand sheet formed by the eustatic shoreline advance the late quaternary pattern of contourite deposits on the spanish gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges coincident with the northwestward decrease in outflow current speeds from the strait there is the following northwestward gradation of contourite sediment facies 1 upper slope sand to silt bed facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins by comparison the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean outflow current the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies radiocarbon ages verify that the inner shelf shoreface sand facies sedimentation rate 7 1 cm kyr mid shelf mud facies maximum rate 234 cm kyr and surface sandy contourite layer of 0 2 1 2 m thickness on the cadiz slope 1 12 cm kyr have deposited during holocene time when high sea level results in maximum water depth over the gibraltar sill and full development of the atlantic inflow and mediterranean outflow currents the transgressive sand sheet of the shelf and the mud layer underlying the surface contourite sand sheet of the slope correlate respectively with the late pleistocene sea level lowstand and apparent weak mediterranean outflow current

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

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

review of the late quaternary stratigraphy of the northern gulf of cadiz continental margin new insights into controlling factors and global implications abstract over the past decades the northern gulf of cadiz has been the focus of a wide range of late quaternary seismic and sequence stratigraphic studies either addressing the slope contourite depositional system cds or the development of the continental shelf yet high resolution seismic data bridging between these domains and age information have remained sparse this study based on new high resolution reflection seismic profiles calibrated to iodp expedition 339 sites u1386 u1387 now presents an updated stratigraphic framework that integrates for the first time the late quaternary records of the northern gulf of cadiz middle slope to shelf off the guadiana river seismic stratigraphic analysis of the stacking depocenter distribution stratal architecture and facies of the seismic sub units reveals the influence of 100 kyr sea level variations paced by milankovitch eccentricity cycles tectonics manifesting as two pulses of uplift and margin progradation sediment supply and bottom current activity this work furthermore contributes to the application and understanding of high resolution late quaternary sequence stratigraphy firstly the proposed sequence stratigraphic interpretation shows that adaptations to the basic models are required to integrate the shelf and slope record and to account for the presence of a significant alongslope bottom current controlled component secondly the results confirm that the sequences are dominantly composed of regressive deposits whereas the preservation of transgressive to highstand deposits is more irregular significantly the common assumption that successive major glacial lowstands are consistently recorded as well marked shelf wide erosional unconformities is demonstrated to be occasionally invalid as tectonics can obliterate this one to one relationship

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

landscape evolution and geodynamic controls in the gulf of cadiz huelva coast sw spain during the late quaternary abstract the coastal evolution of the el abalario area huelva southern spain during the late pleistocene and holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence osl dating new data come from the analysis of soft sediment deformation palaeosols geomorphological mapping and published seismic surveys on the onshore and offshore gulf of cadiz the present structure of el abalario dome resulted from the complex interaction of littoral catchment processes and sea level changes upon an emergent coastal plain conditioned by the upwarping of the underlying pliocene pleistocene prograding deltaic sequence upwarping is probably related to escape of over pressurized fluids accompanied by dewatering prior to and during ois oxygen isotopic stage 5 continued upwarping produced the large nw se gravitational fault of torre del loro tlf in the southwestern flank of the dome roughly parallel to the present coastline during ois 5 ois 4 the resulting escarpment favoured the accumulation of aeolian sand dunes units u1 u2 and u3 from ois 5 to early ois 1 unit u1 ois 5 ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions unit u2 accumulated mainly during ois 4 and ois 3 with prevailing w e winds the supersurface between u2 and u3 records a part of ois 2 with relative low sea level sedimentation of unit u3 took place during the last deglaciation radiocarbon and osl ages with prevailing w sw winds under a temperate moist climate that became more arid towards the top holocene a major supersurface with an iron crust like layer ssfe developed during the holocene climatic optimum ois 1 under wetter and more temperate conditions than before fossilizing the tlf the supersurface is covered by younger aeolian dunes u4 u5 u6 and u7 transported by w sw winds since the late neolithic chalcolithic cultural period 5 0 ky cal bp

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

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

middle upper pleistocene record of 100 ka depositional cycles on the southern tuscany continental margin tyrrhenian sea italy abstract five unconformity bounded depositional sequences have been seismically defined on the tyrrhenian margin offshore southern tuscany italy the set of sequences encompasses a 500 ka interval each sequence recording a 100 ka orbitally driven climate eustatic cycle similarly to most of quaternary continental margins sequences on the southern tuscany margin show an overall regressive motif reflecting shelf sediment progradation basically during the prolonged phases of sea level fall that characterise the middle upper pleistocene 100 ka cyclicity on seismic profiles however progradational units within each sequence display a variable clinoform geometry interpreted as a record of the alternation of highstand falling and lowstand intervals within 100 ka cycles the observed geometric variability is thus used as a key for separating systems tracts otherwise merging into a general progradational regressive sedimentary body composing the bulk of each sequence on a longer term the interplay between sea level changes modulated by 100 ka cycles and regional subsidence controls the stratigraphic architecture and the growth pattern of the continental margin this effect is documented by the overall aggradational retrogradational stacking pattern of sequences superimposed on shelf margin progradation and reflecting the renewal of accommodation space landward of the shelf margin and its exploitation at each cycle

the cadiz margin study off spain an introduction abstract the cadiz continental margin of the northeastern gulf of cadiz off spain was selected for a multidisciplinary project because of the interplay of complex tectonic history between the iberian and african plates sediment supply from multiple sources and unique mediterranean gateway inflow and outflow currents the nature of this complex margin particularly during the last 5 million years was investigated with emphasis on tectonic history stratigraphic sequences marine circulation contourite depositional facies geotechnical properties geologic hazards and human influences such as dispersal of river contaminants this study provides an integrated view of the tectonic sediment supply and oceanographic factors that control depositional processes and growth patterns of the cadiz and similar modern and ancient continental margins

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

contourite characterization and its discrimination from other deep water deposits in the gulf of cadiz contourite depositional system this project was funded through the joint industry project supported by bp eni exxonmobil total wintershall dea and tgs within the framework of the drifters research group at royal holloway university of london rhul in conjunction with the projects ctm 2012 39599 c03 cgl2015 66835 p ctm2016 75129c3 1 r cgl2016 80445 r aei feder ue and b rnm 072 ugr18 this research used data and samples collected by iodp expedition 339 aboard the joides resolution data was acquired at the xrf core scanner lab at marum center for marine environmental sciences university of bremen germany our thanks to dr javier dorador rhul uk for the high resolution core imaging treatment to dr david roque icman csic spain for his help in the hydrographic panels from fig 2 and to dr angel puga bernabeu university of granada spain for revision that helped to improve the original version of the manuscript before submission this study significantly benefited from discussions with all who attended the iodp exp 339 mow meeting in heidelberg germany in january 2019 we would like to thank associate editor dr adam mcarthur and the three reviewers dr rachel brackenridge dr giancarlo davoli and dr adriano viana for their positive and constructive comments that helped us improve the manuscript

surface facies and sediment dispersal patterns southeastern gulf of cadiz spanish continental margin abstract grain size of 294 samples and mineralogical analysis of 364 surface samples from the spanish continental shelf and upper slope of the gulf of cadiz delineate four sediment facies that derive mainly from siliciclastic sources the northern area is formed by the mud rich prodelta of the guadalquivir river parallel to the coast and progradational towards the southeast it exhibits a typical bulk mineral association of illite smectite kaolinite chlorite in the north central area there is a smaller coarser grained prodelta in the bay of cadiz linked to the guadalete river which offshore becomes connected to the guadalquivir prodelta its mineral association is quartz illite kaolinite chlorite in the southern area where fluvial input is negligible the characteristic coarse grained facies generally corresponds to relict late pleistocene reworked deposits the typical mineral association is quartz calcite aragonite smectite mixed layer clay minerals the fourth area corresponds to the shelf break and upper slope offshore cadiz bay where a westward grain size coarsening differentiates the deposits of the last low sea level stand and no typical mineral association exists the mineralogy of the terrigenous deposits indicates a source area from paleozoic sequences of the sierra morena to the north and the subbetic units and gibraltar flysch to the east the neogene deposits of the guadalquivir depression are an additional source of shelf sediments the surface sediment distribution on the inner continental shelf is largely determined by the southeastern atlantic water flow the terrigenous input from rivers and the shelf physiography sediment dispersal on the outer continental shelf and upper slope in contrast largely reflects the location of low sea level stand the development of palimpset deposits and the location of the mediterranean undercurrent over the margin

holocene highstand deposits in the gulf of cadiz sw iberian peninsula a high resolution record of hierarchical environmental changes a comparison of the internal structure of holocene highstand shallow marine deposits with emerged spit bar systems in the gulf of cadiz margin sw iberian peninsula is presented in order to increase the knowledge about the patterns of environmental fluctuations of sub milankovitch periodicity during the recent highstand period a high resolution seismic database of boomer profiles was interpreted focusing on shallow marine deposits of the gulf of cadiz shelf such as the guadalquivir river prodelta the guadiana river depositional system and the faro tavira infralittoral prograding wedge the results indicate that the internal architecture of recent highstand shelf deposits is complex as the recognition of three main types of seismic unit motifs suggests the existence of a hierarchical pattern of environmental fluctuations a major scale motifs the most significant feature observed in the seismic records is the pervasive occurrence of two major scale motifs lower and upper within the holocene highstand systems tract b intermediate scale motifs each major scale motif is composed of two intermediate scale motifs defining four intermediate scale motifs h1 to h4 c minor scale motifs the internal structure of major and intermediate scale motifs reveals a high degree of environmental variability during the recent highstand probably led by climatic cyclicities of submillenial scale the lower major scale motif is characterised by alternating progradational aggradational minor scale motifs whereas the upper major scale motif presents a more uniform internal structure dominated by progradational units the influence of two distinct trends or asymmetric cycles of sea level change seems to have been significant in the generation of the major scale architecture the transition between both major phases was probably related with a major sea level rise other factors such as changes in the magnitude and or direction of storm events and climatically induced changes of sediment supply are proposed to have controlled the generation of intermediate and minor scale architectures

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

unroofing incision and uplift history of the southwestern colorado plateau from apatite u th he thermochronometry the source of buoyancy for the uplift of cratonic plateaus is a fundamental question in continental dynamics the 1 9 km uplift of the colorado plateau since the late cretaceous is a prime example of this problem we used apatite u th he thermochronometry 230 analyses 36 samples to provide the fi rst single system regional scale proxy for the unroofi ng history of the southwestern quadrant of the plateau the results confi rm overall southwest to northeast unroofi ng from plateau margin to plateau interior a single phase of unroofi ng along the plateau margin in late cretaceous to early tertiary sevierlaramide time contrasts with multiphase unroofi ng of the southwestern plateau interior in early and mid to late tertiary time the early cretaceous was characterized by northeastward tilting and regional erosion followed by aggradation of 1500 m of upper cretaceous sediments along the eroded plateau margin sevier laramide denudation affected the entire southwestern plateau was concentrated along the plateau margin and migrated from northwest to southeast following a period of relative stability of the landscape from ca 50 30 ma signifi cant unroofi ng of the southwestern plateau interior occurred between ca 28 and 16 ma additional denudation north of the grand canyon took place in latest tertiary time mid tertiary dates from the grand canyon basement at the bottom of the upper granite gorge limit signifi cant incision of the modern grand canyon below the kaibab surface to 1500 m difference in vertical structural position if these models are correct they indicate that a proto grand canyon of kilometer scale depth had incised post paleozoic strata by the early eocene evidence for kilometerscale mid tertiary relief in northeast fl owing drainages along the plateau margin as well as the mid tertiary episode of plateau interior unroofi ng imply that the southwestern plateau interior had attained substantial elevation by at least 25 20 ma if not much earlier these observations are inconsistent with any model calling for exclusively late tertiary uplift of the southwestern plateau sevier laramide plateau surface uplift and incision thus result from one or more processes that enhanced the buoyancy of the plateau lithosphere expanding the cordillera s orogenic highlands into its lowstanding cratonic foreland the onset of the laramide slab s demise at ca 40 ma and the major pulse of extension in the basin and range from ca 16 10 ma appear to have had little infl uence on the denudation history of the southwestern plateau in contrast the post laramide unroofi ng episodes may be explained by drainage adjustments induced by rift related lowering of regions adjacent to the plateau without the need to otherwise modify the plateau lithosphere our data do not preclude a large component of post early eocene elevation gain or the geodynamic mechanisms it may imply but they do point toward laramide age buoyancy sources as the initial cause of signifi cant surface uplift ending more than 500 m y of residence near sea level

sedimentological and paleoenvironmental characterisation of transgressive sediments on the guadiana shelf northern gulf of cadiz sw iberia during the transgression following the last glacial maximum four backstepping parasequences were deposited on the northern gulf of c shelf sw iberia in contrast to other areas on the shelf these transgressive deposits are at or very close to the surface to the southeast of the guadiana estuary mouth this is particularly true for transgressive parasequence tc possibly associated with the younger dryas event and the youngest parasequence td probably linked to a slow down in sea level rise at around 8 2 ka bp both of which form a sandy transgressive bulge on the upper middle shelf the older and more distal parasequence tc is characterised on seismic records by convex low angle sigmoidal clinoforms and contains high amounts of quartz and bioclasts in contrast the younger and more proximal parasequence td shows relatively steep concave prograding clinoforms and contains high amounts of quartz and other terrigenous components but comparatively low amounts of bioclasts furthermore the difference in age between both parasequences is clearly marked by a difference in the content of glauconite the results indicate that sediments found in parasequence tc are associated with deposition related to storm events with frequent reworking of components and the more proximal and younger sediments in td are the result of rapid sediment accumulation related to floods in the guadiana river basin possibly during the transition from a dry cold period to a warmer more humid period when vegetation cover was lowest and flood frequency increased additionally accumulations of terrigenous components directly associated with the guadiana river basin found on the outer shelf indicate that at least during the beginning of the transgression overflow channels active during large scale flood events may have spilled material to an area located immediately to the south of the guadiana estuary mouth r 2004 elsevier ltd and inqua all rights reserved

occurrence of acoustic masking in sediments in two areas of the continental shelf of spain ria de muros nw and gulf of cadiz sw abstract zones of acoustic masking in sediments in the continental shelf of cadiz and in the ria de muros have been mapped utilizing 3 5 khz and uniboom seismic reflection records in cadiz the masking may be generated by shell beds source of the shells is a pliocene conglomerate that corresponds to the acoustic basement in the area acoustic masking in the sediments of ria de muros was generated by the presence of gas within the sediments the gas is due to the decay of organic matter within the sediments that area of acoustic masking in the ria de muros roughly coincides with the zone of mud with high 15 5 organic content and that gas bubbles were noted in the water column in the same region support this hypothesis

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

evolution of the late miocene mediterranean atlantic gateways and their impact on regional and global environmental change marine gateways play a critical role in the exchange of water heat salt and nutrients between oceans and seas as a result changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate as well as having a profound impact on local environmental conditions mediterranean atlantic marine corridors that pre date the modern gibraltar strait closed during the late miocene and are now exposed on land in northern morocco and southern spain the restriction and closure of these miocene connections resulted in extreme salinity fluctuations in the mediterranean leading to the precipitation of thick evaporites this event is known as the messinian salinity crisis msc the evolution and closure of the mediterranean atlantic gateways are a critical control on the msc but at present the location geometry and age of these gateways are still highly controversial as is the impact of changing mediterranean outflow on northern hemisphere circulation here we present a comprehensive overview of the evolution of the late miocene gateways and the nature of mediterranean atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins we also consider the possible impact of evolving exchange on both the mediterranean and global climate and highlight the main enduring challenges for reconstructing past mediterranean atlantic exchange

forced regressive wedge in the mesoproterozoic koldaha shale vindhyan basin son valley central india abstract the present paper highlights the sequence development within the mesoproterozoic koldaha shale member of the kheinjua formation vindhyan supergroup which records the occurrence of a forced regressive wedge and associated discontinuity surfaces at the base of the wedge nine lithofacies have been identified within the study area that are grouped into three lithofacies associations varying in depositional setting from outer shelf through shoreface foreshore beach to continental braidplain the outer shelf sediments are aggradational to slightly progradational representing highstand systems tract the rapidly progradational wedge shaped shoreface to foreshore beach succession occurs sharply or erosively above the outer shelf sediments and is bounded by a regressive surface of marine erosion rsme at the base and by a subaerial unconformity at the top this along with its downstepping trajectory supports deposition of this sedimentary wedge during falling sea level a laterally extensive soft sediment deformation zone occurs at the base of the wedge the forced regressive wedge is incised by fluvial braidplain deposits that rest on an erosive surface representing a sequence boundary the thin braidplain deposits are the product of aggradation during a subsequent early rise in relative sea level and thus they are inferred to represent a lowstand systems tract the constituent architectural elements that characterize the braidplain deposits are downstream accretion elements and small channel elements further landward the base and top of the shoreface wedge merge to form an unconformity across deposits that rest directly on the outer shelf sediments the identification of forced regressive wedges has significant economic importance in view of the potential occurrence of hydrocarbons within the proterozoic formations

patterns of bottom current flow deduced from dune asymmetries over the gulf of cadiz shelf southwest spain abstract the analysis of dune like morphologies on the gulf of cadiz continental shelf using high resolution seismic reflection profiles and sediment samples reveals a well defined distribution pattern controlled by the area s hydrodynamics these bedforms are considered to be modern features from the holocene and therefore they provide information about the bottom circulatory patterns established over the continental shelf most of the submarine dunes have been identified over a shallow physiographic feature named the barbate high the current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents in which the process of current direction reversal related to the tidal cycle in the straits of gibraltar seems to be involved eastward oriented submarine dunes located on the onshore zones of the inner shelf are generated by the atlantic inflow which over these shallow zones is mainly orientated towards the east during high tide conditions in the straits of gibraltar bedforms oriented westwards and west northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the gulf of cadiz continental shelf this flow is attributed to the influence of ebb tidal currents which move preferentially towards the west over these zones as a result of this complex bottom flow pattern a clockwise sand transport pattern over the barbate high is established

post glacial sequence and sedimentation in the western bohai sea china and its linkage to global sea level changes abstract post glacial sedimentary sequences provide a unique window for observing depositional and environmental responses to rapid changes in global climate and sea level here we integrate seismic records and the lithological variations of sediment cores from western bohai bay china in order to reveal the history of sedimentation and its linkages to global sea level changes since marine isotope stage 2 mis 2 the post glacial succession consists of six seismic units su1 su6 in descending order which are bounded by six key reflection surfaces t 0 r 1 r 2 r 3 t 1 and t 2 respectively corresponding to six depositional units du1 du6 identified in sediment cores together they comprise the latest sequence of infilling of western bohai bay where su6 is associated with the lowstand systems tract lst su5 is associated with the transgressive systems tract tst and the last four units of su4 su1 comprise the complex highstand systems tract hst during the interval of the mis 2 22 11 6 kyr bp sea level lowstand the lst was formed in a long term environment of sub aerial exposure or fluvial floodplain the tst is composed of transgressive deposits formed during the interval of global sea level rise and is characterized by a retrogradational feature from a swamp to a tidal flat environment and then to an estuarine subtidal environment a series of sedimentary facies transitions represent abrupt sea level rises in the early holocene which may correspond to the events mwp 1c 8 2 ka event and mwp 2 erosional trenches were well developed within su5 in the central eastern region and were probably part of a transgressive waterway system rooted from bohai strait they demonstrate that bohai bay experienced strong tidal erosion in the early holocene as a result of its morphology which consisted of a long narrow embayment the complex hst was initially formed at ca 7 cal kyr bp when sea level essentially stabilized in a highstand and developed rapidly after ca 6 cal kyr bp when the yellow river supplied large amounts of sediment to the western or southwestern margin of bohai bay its complex internal structure is related to the configuration of three flooding surfaces caused by changes in sediment supply and which in historical times separated four stages of river discharge mainly from the yellow river during ca 7 0 3 4 cal kyr bp the yellow river at one time emptied into the southwestern margin of bohai bay forcing its subaqueous delta to extend over the southern area of western bohai bay while open shelf sedimentation in the central and northern area of bohai bay consisted of the accumulation of a shelly layer subject to intensive storm reworking during ca 3 4 1 cal kyr bp the yellow river once discharged into the central and northern parts of western bohai bay forming two detached subaqueous deltas during ca 1 0 8 cal kyr bp the yellow river discharged into the central region stacking a subaqueous delta confined by the two older underlying subaqueous deltas during the last 800 years the discharge of the yellow river out of bohai bay has dominated coastal marine sedimentation which has a complex provenance

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

seismic stratigraphy of the gulf of cadiz continental shelf a model for late quaternary very high resolution sequence stratigraphy and response to sea level fall

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

numerical simulation of holocene depositional wedge in the southern po plain northern adriatic sea italy abstract in the last 10 kyr bp a coastal depositional wedge formed along the southern po plain margin shoreline regression accelerated abruptly in the iron age and especially in the last 2 kyr due to the increased woodland removal on the apennines the deposition of the holocene sedimentary wedge is simulated here along four coast tranversal transects using a finite element two dimension mathematical model the model was constrained using the present topographic surface the maximum flooding line of the holocene transgression architecture and texture of depositional wedge the location of coastlines aeolian dunes and ancient offshore delta sand the sediment volume required to calibrate the simulations along the sections ranges from about 165 000 870 000 m3 m 1 the maximum tectonic subsidence varies from 0 1 to 0 7 mm yr 1 the minimum sand amount required by the model to stop the accelerated erosion of the cervia beach is about five times the one employed in recent april 2002 recovery works

rock fragments from mud volcanic deposits of the gulf of cadiz an insight into the eocene pliocene sedimentary succession of the basin abstract two hundred clasts from the mud breccia extruded by the yuma mud volcano in the gulf of cadiz are used to establish an offshore stratigraphy the clasts are a very complex mixture of material from the sedimentary successions through which the mud volcano erupted and provide important information about the composition and genesis of deep seated strata we deal with fragments of rocks that were deposited millions of years ago subsequently buried and later erupted on to the seafloor rock fragments from the mud breccia studied in thin section under a polarizing microscope provide genetic indications suggestive of deep sea conditions during the accumulation of strata a reconstruction of the sedimentary succession through which the yuma mud volcano erupted and the depositional evolution of the gulf of cadiz was made on the basis of lithology and age determinations of the rock age and depositional environment documented by the clasts indicate that a marine basin existed in the gulf of cadiz area at least from the eocene and that in the early and middle eocene a deep sea fan depositional environment prevailed in the region resulting in the accumulation of thick turbidites the late eocene and oligocene are not represented among rock fragments from the mud breccia suggesting regional uplift and non deposition in the area sedimentation was re established in the miocene with the accumulation of a clayey aquitanian burdigalian succession pelagic carbonate sedimentation became predominant in the langhian time the serravallian early tortonian is characterized by a high supply of terrigenous material resulting in the deposition of turbiditic clays and sands shallow water sedimentation with accumulation of carbonate rocks prevailed in the basin during the middle tortonian

the sandy channel lobe depositional systems in the gulf of cadiz gravity processes forced by contour current processes abstract the sedimentation in the gulf of cadiz ne atlantic ocean is significantly controlled by the mediterranean outflow water mow along its pathway onto the continental slope the mow is canalized by contourite channels some of them feeding gravity sandy channel lobe depositional systems firstly recognized in previous study habgood et al 2003 deep water sediment wave fields bottom current sand channels and gravity flow channel lobe systems gulf of cadiz ne atlantic sedimentology 50 3 483 510 using very high resolution acoustic data and cores a detailed characterization and a new evolution pattern of these channel lobe depositional systems is established complex internal geometry of the lobes shows several depositional units revealing a polyphase evolution of these systems with a general progradation punctuated by retrogradation and avulsion phases a gravity origin controlled by contouritic processes and climatic changes is demonstrated for the feeding and the evolution of these sandy channel lobe depositional systems climate oscillations via the mow variations act as a major forcing of the activity of the channel lobe depositional systems during the late quaternary

large scale sediment bodies and superimposed bedforms on the continental shelf close to the strait of gibraltar interplay of complex oceanographic conditions and physiographic constraints a previously unknown field of large scale sedimentary bodies has been mapped and studied on the continental shelf off the cape trafalgar near the strait of gibraltar with particular emphasis on the relationship between large scale sediment bodies and the superimposed bedforms this study is based on a grid of 975 km of high resolution seismic profiles collected at water depths ranging between 15 and 60 m high variability of large scale sedimentary bodies is attributed to the complex interaction of hydrodynamic agents the most prominent sedimentary features are sand banks and ridges that indicate long term southwest and southward directed sediment transport patterns possibly due to the interplay of two dominant current systems flowing southward and westward these sediment bodies evolve laterally to distinct external geometries such as sand shoals in shallow water and sand sheets in the vicinity of larger sand banks that indicate moderate current velocities in addition pre existing physiography is considered to play a role in the generation of certain sediment bodies developed over inclined surfaces or confined laterally by elevations relationships between superimposed bedforms mostly very large dunes and underlying sediment bodies vary across the study area most superimposed bedforms occur over the complex mosaic of sediment banks and sheets suggesting the interaction of several high energy currents with different directions such as tidal and or wind driven currents copyright 2010 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

sedimentary response to climate and sea level changes during the past 400 ka from borehole prad1 2 adriatic margin 1 borehole prad1 2 was drilled in 186 m water depth on the upper slope of the central adriatic in the frame of profiles across mediterranean sedimentary systems promess1 european union funded project the borehole penetrated 71 2 m through a stratigraphic interval characterized by subparallel seismic reflections and uniform seismic units according to an age depth model based on several independent proxies including foraminifera and nannoplankton stratigraphy 18o curves and magnetostratigraphy the cored interval records marine isotope stages and substages mis from mis1 to the top of mis11 thus encompassing the past 370 ka prad1 2 therefore represents an unprecedented continuous record through the last four glacial interglacial cycles from a proximal continental margin setting where depositional sequences are typically composed of progradational units these progradational units record dominantly interglacial intervals mis5 mis7 and mis9 and appear composed of thicker highstand deposits hst formed during interstadials and thinner forced regression units fsst deposited during stadials above distinctive downward shift surfaces the development of thicker highstand deposits with a distinctively thicker bottomset reflects enhanced shore parallel advection any time sea level rise leads to the drowning of the adriatic shelf triggering the formation of dense water and vigorous cyclonic circulation this advection mechanism persisted in each cycle throughout the early phases of the sea level fall but progressively decreased as sea level fall proceeded approaching the maximum lowstand position when most of the shelf became exposed relative sea level falls punctuating interglacials within each 100 ka cycle were thus accompanied by a dearth in sediment flux on the outer shelf the alternation of hst and fsst progradational wedges with markedly different thickness and downlap geometry of their bottomsets is the most evident stratigraphic signature within each 100 ka depositional cycle of the impact on the shelf of higher frequency 20 ka sea level cycles and concomitant supply fluctuations

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

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

interaction of tectonic and depositional processes that control the evolution of the iberian gulf of cadiz margin abstract this study provides an integrated view of the growth patterns and factors that controlled the evolution of the gulf of cadiz continental margin based on studies of the tectonic sedimentologic and oceanographic history of the area seven sedimentary regimes are identified but there are more extensive descriptions of the late cenozoic regimes because of the larger data base the regimes of the mesozoic passive margin include carbonate platforms which become mixed calcareous terrigenous deposits during the late cretaceous early tertiary the oligocene and early miocene terrigenous regimes developed in contrast over the active and transcurrent margins near the african iberian plate boundary the top of the gulf of cadiz olistostrome emplaced in the late miocene is used as a key horizon to define the post orogenic depositional regimes the late miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the miocene atlantic mediterranean gateways the terrigenous drift depositional regime of the early pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the mediterranean outflow currents that developed after the opening of the strait of gibraltar the late pliocene and quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels deposition of shelf margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence during the highstand regimes of the holocene inner shelf prograding deltas and deep water sediment drifts were developed under the influence of the atlantic inflow and mediterranean outflow currents respectively a modern human cultural regime began 2000 years ago with the roman occupation of iberia human cultural effects on sedimentary regimes may have equalled natural factors such as climate change interplay of tectonic and oceanographic controls dominated the evolution of the cadiz margin during the cenozoic depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional atlantic inflow currents on the shelf and mediterranean outflow currents on the slope the entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the betic and rif gateways which become closed during the late miocene and after the messinian by the opening of the strait of gibraltar strong current development during eustatic sea level highstands of the pliocene and quaternary has controlled deposition because of maximum sill depths at gibraltar for water circulation lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf more recently the human industrial revolution has caused heavy metal contamination of sediment and water over the cadiz margin human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed future research efforts will need to focus on 1 the effect of increased mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages 2 assessments of geologic hazards for planning man made shoreline structures developing offshore petroleum resources and maintaining undersea communications cables and 3 confirmation of the general geologic history of the cadiz margin

late pleistocene holocene sediments on the spanish continental shelves model for very high resolution sequence stratigraphy abstract sequence stratigraphy analysis of high resolution seismic profiles geopulse uniboom and 3 5 khz of late pleistocene holocene sediments has been carried out on five sectors of the spanish continental margin four types of depositional settings are distinguished in these sectors 1 low subsident ramps alboran margin cadiz gulf 2 high subsident 2m kyr ramps alicante valencia 3 ria type morphology on the atlantic passive margin ria de muros and 4 fault scarp morphology systems with subsidence balearic margin a type 1 sequence is interpreted in all these sectors being composed of lowstand systems tract transgressive systems tract and highstand systems tract this conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle characteristic shelf features such as terraces terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub sequences in all the systems tracts which must be related to very short period sea level stillstands and fall we propose a very high resolution sequence stratigraphy model in which the last sea level hemicycle is punctuated by p cycles 4500 years which give rise to the neo glacial events h cycles 2200 950 years and c cycles 500 50 years these cycles interact with each other thus establishing the placing of the high and low sea levels this attention to detail 1 explains sedimentary evolution on both the shelf and upper slope during late pleistocene holocene time 2 illustrates some departures from the classical sequence stratigraphy model and 3 also demonstrates that the late pleistocene holocene eustatic curve is not one simple transgression but is modulated by three differing period cycle groups below the milankovitch band our model is delimited by fluctuating sea level during pleistocene holocene times such features should be identifiable on any continental margin however localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle

tectonic evolution of the upper allochthon of the ordenes complex northwestern iberian massif structural constraints to a polyorogenic peri gondwanan terrane the upper allochthon of northwest iberia represents the most exotic terrane of this part of the european variscan belt recent advances in the metamorphic petrology structural geology and geochronology of the upper allochthon in the ordenes complex are integrated into a synthesis of its tectonic evolution constraining the main tectonothermal events important aspects of this synthesis are 1 the interpretation of cambro ordovician magmatism and earliest metamorphic event as the result of drifting of a peri gondwanan terrane 2 the subsequent shortening and crustal thickening of the terrane related to its subduction and accretion to laurussia 3 a younger cycle of shortening and extension resulting from convergence between lau russia and gondwana and 4 the emplacement of this exotic terrane as the upper allochthon together with underlying ophiolitic and basal allochthons during the laurussia gondwana collision implications derived from the well established tectonothermal sequence are discussed in the context of paleozoic paleogeography and geodynamics the evolution of this part of the belt is related first to the closure of the tornquist ocean and later to that of the eastern branch of the rheic ocean furthermore the relative paleopo sitions of the upper allochthon and the iberian autochthon in northern gondwana are discussed 2007 geological society of america all rights reserved

eustatic and tectonic control on deposition and lateral variability of quaternary regressive sequences in the adriatic basin italy abstract during the late pleistocene sea level variations related to glacio eustatic cycles induced the deposition of four regressive sequences on the western continental shelf of the adriatic basin the four sequences are bounded by erosion surfaces that formed during sea level fall sub aerial exposure of the shelf and subsequent sea level rise and erosional reworking the sequences and the erosion surfaces at their top numbered 1 4 top down are correlated on distances in the order of 300 km in the central and south adriatic core control on deposits of the most recent depositional sequence sequence 1 suggests that each sequence records a fourth order ca 100 120 kyr cyclicity of sea level change within each depositional sequence progradational units representing highstand to forced regression are dominant whereas transgressive deposits are absent or reduced in both thickness and lateral extent sequences are thus referred to as regressive sequences deposition during sea level fall occurred on an overall subsiding shelf through the dispersal of fine grained sediment supplied from the adjacent alpine and apennine chains this resulted in stacked forced regression deposits thick enough to survive complete removal during subsequent phases of sub aerial and marine erosion erosion and or non deposition were enhanced only where tectonic uplift and morphological highs further reduced the remaining accommodation space resulting in local thickness reduction or in the non preservation of the regressive sequences at larger scale thickness variability and depocenter distribution north and south of the gargano promontory an uplifted block bisecting the adriatic foreland reflect differential deposition and preservation of regressive deposits as a function of contrasting tectonic setting and resulting physiography of the shelf and upper slope

quaternary stratigraphic stacking patterns on the continental shelves of the southern iberian peninsula their relationship with global climate and palaeoceanographic changes abstract a quaternary stratigraphic stacking pattern on the continental shelves of the southern iberian peninsula has been determined by analysing and comparing a dense network of low medium high and very high resolution mono channel and multi channel reflection seismic lines and well log data four major low resolution depositional sequences related to a 3rd order cycle at 1 4 1 6 ma have been recognised in the pliocene quaternary sedimentary record m p1 p2 p3 q i and q ii they are separated by four discontinuities corresponding to the most drastic changes in climate and palaeoceanography affecting the atlantic and mediterranean linkage and especially to the most prominent sea level falls in the messinian m at 5 5 ma in the lower pliocene at 4 2 ma in the upper pliocene at 2 4 ma and in the mid pleistocene at 900 920 ka mpr these major sequences were built up by asymmetrical sea level cycles the regressive and lowstand system tracts are the best developed deposits controlling the main progradation of the shelf basinwards as well the quaternary shelf stratigraphy can be divided into asymmetric 3rd order sequences of 800 ka q i and q ii and into 4th order asymmetric sequences of approximately 400 ka q1 q4 200 ka a h and 100 ka on low medium and high resolution seismics the overall architectural stacking of the shelf shows a change after the mpr discontinuity characterised by well differentiated sequences of shelf break wedges with progradational sigmoid configurations assumed to be related to approximately 100 ka sea level cycles this change in the configuration of the shelf wedges during the quaternary is attributed to the onset of the 100 ka eccentricity orbital cycles which abruptly increased the amplitude of sea level variations 100 120 m during the last 900 920 ka

headland associated banner banks generated during the last deglaciation near the strait of gibraltar gulf of cadiz sw spain the inception and evolution of large scale bedforms on the barbate platform gulf of cadiz sw iberian peninsula are investigated based on a detailed study of multibeam bathymetric data high resolution seismic profiles and tidal current simulations elongated rocky outcrops and several large scale bedforms classified as sand banks were identified on the platform barbate zahara el palmar el varadero and canos de meca banks the barbate and zahara banks exhibit the most complex internal stratigraphic architecture which comprises five seismic units the basal unit u1 is interpreted as incised valley infill and is overlain by nearshore bars u2 two high energy growth phases u3 and u4 that combine progradation and accretion form the present day external bank shape superimposed bedforms covered these banks under the modern hydrodynamic regime u5 the multiphase accretion and progradation of u3 and u4 in the zahara and barbate banks were closely linked to the presence of a palaeo headland termed here as palaeo cape trafalgar and strong tidal current eddies that resulted from the progressive flooding of the barbate platform during the last deglaciation this configuration was relatively stable while the rocky outcrops were exposed to sub aerial conditions forming a palaeo coast with coastal bluffs we suggest that during this period of coastal stabilization u3 and u4 grew as banner banks on either side of the palaeo cape trafalgar the present study proposes that the configuration of palaeo headland associated with palaeo banner banks zahara and barbate banks along each side of the palaeo cape trafalgar represents a transgressive analogue model of headland associated tidal bank systems developed in funnel shaped coastal systems terminating in narrow straits