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

phylogeography of benthic invertebrates in deep waters a case study of sternaspis cf williamsae annelida sternaspidae from the northwestern pacific ocean abstract although the deep sea is a vast ecosystem gene connectivity is not well understood in the northwestern pacific ocean especially around the okhotsk sea the okhotsk sea and the neighboring pacific ocean together are attractive regions to study the population connectivity of deep sea organisms because these regions are connected through shallow straits except for the bussol ca 2300 m and kruzenshtern ca 1900 m straits members of the family sternaspidae annelida inhabit various water depths ranging from intertidal to abyssal zones sternaspids are therefore interesting subjects for studying the evolutionary shifts in bathymetric distribution and phylogeography in deep waters sternaspid worms were collected from the deepest part of the okhotsk sea the kuril basin and the northwestern pacific ocean lower bathyal and abyssal depths of the kuril kamchatka trench off northeastern and central japan this molecular phylogenetic study which is the first focusing on the sternaspidae suggests the presence of many cryptic species that were collected far from the type locality mainly based on shield morphology and molecular phylogenetic analysis using the mitochondrial coi gene we found a wide distribution of sternaspis cf williamsae over the northwestern pacific ocean and a different species of the sternaspid caulleryaspis cf nuda in the okhotsk sea the isolation by distance ibd test based on the mitochondrial coi gene and nuclear its2 region suggests moderate ibd for s cf williamsae over 1500 km from kuril to central japan

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

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

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

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

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

assessing uncertainties in balanced cross sections abstract balanced structural cross sections are models that are fit to incomplete data the models are under constrained with respect to any particular two dimensional line length model but enough data generally exists to yield a well constrained area balance solution furthermore the area balance encompasses all possible line length solutions therefore where the primary objective of section balancing is the determination of horizontal shortening magnitude area balancing provides an analytical solution we use this analytical solution to develop a comprehensive robust analysis of the uncertainty in shortening estimates resulting from cross section balancing the analytical solution allows us to propagate errors formally on the input parameters stratigraphic thicknesses depth to decollement eroded hanging wall cutoffs through the equations and produce the resulting uncertainty on the magnitude of shortening balanced cross sections from the subandean belt of the central andes are used to demonstrate the relative importance of stratigraphy and eroded hanging wall cutoffs in the contribution to the overall error

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

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

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

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

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

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