facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

macaronichnus and contourite depositional settings bottom currents and nutrients as coupling factors abstract the trace fossil macaronichnus segregatis degiberti 7 15 mm in diameter is recorded for the first time in deep marine contourites which were deposited in a late miocene outer shelf to upper slope of the rifian corridor morocco macaronichnus is typical of shallow marine mainly foreshore environments it is produced by deposit feeding opheliid polychaetes in high to intermediate latitudes this record supports the significance of bottom current processes on environmental conditions as a major limiting factor affecting the macrobenthic trace maker community mediterranean overflow water during the late miocene enabled a high nutrient supply to the seafloor favouring colonization by macaronichnus producers thus m s degiberti should be used as an indicator for nutrient availability instead of mainly a palaeodepth indicator this finding provides significant information for oceanographic and environmental reconstructions related to contouritic processes as well as to contourite characterization

high resolution image treatment in ichnological core analysis initial steps advances and prospects abstract ichnological studies have become popular during the last decades particularly those associated with the development of two major concepts the ichnofacies model and ichnofabric approach they have driven ichnology into diverse fields of earth sciences including paleoecology sedimentology paleoceanography and basin analysis as well as applied fields for the oil and gas industry and aquifer characterization whereas early ichnological analyses focused on outcrops later the number of ichnological studies on well cores increased noticeably still ichnological research on cores is hampered by certain limitations i e mainly narrow exposed surface and the characterization of ichnological properties is complicated when cores are involved to facilitate ichnological analysis in cores from modern deposits several techniques among them x rays magnetic resonance and computed tomography have been used with the development of computer software a new high resolution image treatment has emerged as a powerful tool in different branches of ichnological studies especially for cores from modern marine deposits because applications are numerous and perhaps not familiar to all the scientific community this paper provides an overview of the usefulness of image treatment in ichnological analysis its first steps and subsequent development the novel techniques most recently used in the study of cores from modern marine deposits and some challenges for future research

surface sediment response to deepwater circulation on the blake outer ridge western north atlantic paleoceanographic implications abstract two transects of box core hydrographic and photographic stations were made along the blake outer ridge on the southeastern u s continental rise to study how circulation patterns affect surface sediment properties circulation is strongest at 4200 m on the flanks of the ridge and is reflected in the suspended particulate distribution a second turbidity maximum at 3600 m suggests that there may be a second axis of circulation at this depth the intense circulation on the flanks of the ridge has resulted in winnowing of the sediment revealed by coarsening and flattening of the grain size distribution in the detrital silt fraction and concentration of carbonate by the formation of a foraminiferal lag deposit the mean grain size of the detrital silt fraction on the crest of the ridge decreases southeastwards with increasing distance from upstream sediment sources shifts in the position and strength of the western boundary undercurrent affect the distance that relatively coarse silt is transported downcore changes in grain size can therefore be used as paleoceanographic proxy for changes in deepwater circulation

ichnofacies distribution in the eocene early miocene petra tou romiou outcrop cyprus sea level dynamics and palaeoenvironmental implications in a contourite environment ichnological analysis of the carbonate contourite drift at the petra tou romiou outcrop southern cyprus reveals a relationship between sea level dynamics shoreline position sedimentation rate flow hydrodynamics and trace fossil assemblages the base of the outcrop is composed of chalky deposits showing the zoophycos ichnofacies attributes the transition to the first contouritic interval beds is marked by the gradual disappearance of zoophycos and dominance of horizontal traces this change is caused by a gradual sea level fall determining an increase in proximity and energy conditions in the environment that favoured the development of distal cruziana ichnofacies upper contouritic interval beds contain abundant burrow systems with vertical components increased ichnodiversity particularly among vertical morphologies coincides with the appearance of teichichnus gyrolithes and rare ophiomorpha revealing a transition to the proximal cruziana ichnofacies related with the maintenance of the previous trend toward more proximal and higher energy settings the differentiated ichnofacies in the petra tou roumiou carbonate drifts are controlled by complex interactions between variable environmental factors with sea level dynamics playing a major role

post lgm upward shift of the mediterranean outflow water recorded in a contourite drift off nw spain abstract the nw iberian continental margin is characterised by a complex morphology and by a sedimentary system which was highly dynamic over glacial to interglacial times the sedimentary history of the continental slope was strongly influenced by the interaction of bottom currents with topographic highs of structural origin leading to the accumulation of several sediment drifts a combined analysis of gravity cores from different water depth with hydroacoustic data reveals the vertical behaviour of the upper mediterranean outflow water mow core after the last glacial maximum lgm a coarser grained interval during deglacial and early holocene times 17 2 to 9 9 cal ka bp points to an increase in bottom current strength this increase in velocity was probably related to oceanic density fronts which migrated through the 300 m thick transition zone between the underlying labrador sea water and the overlying mow radiocarbon dates timed the current strengthening to 17 2 cal ka bp and a following weakening of the bottom current to 13 3 cal ka bp at 1965 m water depth and to 9 9 cal ka bp at 1885 m water depth the depth dependent current weakening suggests an upward shifting of the transition zone by 80 m that was related either to an overall shallowing of mow or a vertical contraction of this water mass the upward movement happened over a time interval of approximately 3 4 thousand years in addition sediment core analysis reveals significant lateral heterogeneities within cm to dm thick sediment layers in the contourite drift these heterogeneities suggest a need of a detailed core coverage across current influenced deposits for palaeoceanographic studies to minimize misinterpretations

late quaternary sediment flux on sedimentary drifts in the northeast atlantic abstract comparison between the last glacial and holocene periods of the terrigenous and carbonate sediment flux distributions in the whole northeastern atlantic basin points out the role of deep circulation relative to other processes during the holocene the global terrigenous flux is similar to that during the glacial period 4 compared with 4 7 g cm 2 ky 1 despite a general decrease of terrigenous supplies the flux distribution however is different high values are located in areas of bottom current sedimentation contourite drifts instead of along continental margins where downslope processes are dominant and areas with major ice rafting the global carbonate flux is higher during the holocene 3 compared with 1 5 g cm 2 ky 1 but the carbonate flux distribution matches that of the terrigenous flux both flux patterns are strongly controlled by reworking and redeposition of sediments by bottom currents flux variation in three cores collected on the feni gardar and faro drifts compared to areas of little or no bottom current activity highlights the deep water circulation fluctuations since the last glacial maximum in areas dominated by downslope processes bay of biscay or by ice rafted sediment deposition mid atlantic ridge around 45 n the sediment fluxes are maximum during the deglacial warming and minimum during the holocene period areas dominated by bottom current sedimentation are all characterized by highest sedimentation during the holocene but the flux variations reveal that the norwegian sea water overflow nswo and the mediterranean outflow mo fluctuated differently according to the regional climatic context and the latitudinal transgression of climatic warming on the feni and gardar drifts higher holocene fluxes coincide with the re initiation of nswo at about 10 000 yrs bp the highest flux on the gardar drift results from a stronger outflow across the iceland faeroe ridge than across the faeroe scotland ridge this flow is responsible for high sediment fluxes all along the eastern side of the mid atlantic ridge as far south as 45 n on the faro drift the reactivation of the mediterranean outflow mo took place earlier as three episodes of greater bottom current activity occurred since about 15 000 yrs bp fluxes are maximum during the deglacial warming and remain high during the holocene

contour current accumulation off the vema channel mouth southern brazil basin pattern of a contourite fan abstract in the southern part of the brazil basin 3 5 khz echosounding reveals the existence of a cone shaped sedimentary accumulation 4480 m depth this sediment body is interpreted as deposited by the antarctic bottom water currents aabw at the downstream exit of deep valleys cutting through the rio grande rise it is located between two major channels that prolonged northeastward the valleys into the brazil basin the vema channel in the southeast and the sao paulo abyssal gap in the northwest as a consequence most of the aabw flow is channelized in two branches deposition of the current transported particles occurs below the shear zone which takes place between the two branches the quaternary sediments consist of silty clayey muddy contourites associated with manganiferous deposits the accumulation is built by lateral migration of secondary channels and by lateral construction of lobes between the two major channels which are both well stabilized on account of a morphotectonic control on their location the entire sediment body progrades upward and downstream toward the northeast on the basis of morphological seismic and lithological arguments we would like to propose the name of contourite fan for such a contour current controlled accumulation

the vema channel physiography structure and sediment current interactions abstract the east flank of the vema channel in the southwestern atlantic is an opportune location for interpreting the pleistocene holocene record of deep thermohaline circulation the channel and the adjacent sediment covered rio grande rise intersect each of the principal sub thermocline water masses of the western atlantic we analyzed a suite of 25 giant gravity cores in transects extending between 1400 and 4150 m depth this interval includes the upper and lower branches of circumpolar water north atlantic deep water and antarctic bottom water the late pleistocene holocene sediments along these transects are pelagic carbonates with excellent stratigraphic continuity shallower and deeper regions are relatively unsuitable due to poor core recovery or widespread erosional unconformities extensive hydrographic and direct current observations near the location of our prime coring transect at 30 s indicate a notable cross channel asymmetry in the abyssal hydrography and velocity structure which is reflected in the underlying lithofacies distribution the near bottom flow field shows marked temporal and spatial variability on a local scale even in the channel axis where one would anticipate relatively steady uniform flow much of this variability appears to reflect the effects of transient mesoscale eddies rather than regional variations in the integrated north ward transport of aabw in spite of temporal variations in the flow field the nadw aabw transition zone appears to have remained remarkably stable over time scales of 10 5 10 6 yrs on geological evidence discussed elsewhere in this volume jones 1984 jones and johnson 1984 this observation is somewhat surprising because in the modern oceans the density contrast between nadw and aabw is relatively small if the transition zone between the two water masses has indeed remained relatively stationary then the density determining water properties t and s may also have remained relatively constant with only the rates of production changing if this interpretation proves correct upon further studies it implies that pale oceanographic interpretations of deep thermohaline flow should in some instances utilize geological indices of non conservative water properties e g co 2 13 c for monitoring paleocirculation changes

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

contourites from eirik ridge south of greenland abstract the eirik ridge is an 800 km long submarine sediment drift south of greenland in waterdepths of 2000 3500 m it has been constructed largely by bottom currents formed from cold norwegian sea water that overflows across the denmark strait ice rafting and normal hemipelagic settling may also contribute some sediment to the drift three cores recovered from the drift contain fine grained clayey and silty contourites these show a high degree of bioturbation in 99 of the core material primary lamination has been partially or totally disturbed where preserved contourite laminae consist of simple silt and clay alteration without systematic thickness variation and are largely composed of biogenic debris with some terrigenous material by contrast fine grained parallel laminated spill over turbidites on the levees of the nearby northwest atlantic mid ocean channel namoc in the center of the labrador sea are little affected by bioturbation and show systematic upward thickness variations between successive silt and clay laminae

weddell sea abyssal sediments a record of antarctic bottom water flow abstract deep circulation in the weddell sea is a clockwise gyre with bottom water formed by mixing along the southern and western margins most antarctic bottom water originates here leaving the weddell sea to the east depths 4500 m or to the north depths 16 m ma sediments from the deep weddell basin are hemipelagic muds with ash laminae and mainly in the centre of the gyre distal turbidites derived from the southwest thin debris flows occur near seamounts the hemipelagic muds become coarser from the centre to the edge of the gyre winnowing by strong bottom currents is localised along the northern margin of the basin the absence of diatoms from the weddell basin sediments may result from dissolution as well as low productivity sediments from jane basin consist of alternating diatomaceous and barren hemipelagic muds considered to represent interglacial and glacial conditions respectively the diatomaceous sediments contain more silt suggesting that bottom water flow increases during interglacial periods

model for turbidite to contourite continuum and multiple process transport in deep marine settings examples in the rock record abstract petrological analysis of geological sections in st croix in the caribbean the niesenflysch in switzerland and the annot sandstone in the french maritime alps sheds light on multiple process transport in deep marine settings a model depicting a turbidite to contourite continuum of stratal types is applied to these three rock units recognition of a diverse suite of bedforms coupled with analysis of paleocurrents helps to better interpret depositional origin and basin paleogeography the st croix strata record emplacement by gravity flows and subsequently by bottom currents flowing parallel to the base of slope these sediments accumulated on a lower slope apron a niesenflysch section in the swiss alps west of adelboden includes turbidites which were deposited at fairly regular intervals beyond the base of slope in a setting more distal than that of the st croix sequences most of these turbidites appear to have been partially reworked by bottom currents related to basin circulation or to density flows from the basin margins in the annot sandstone reworked turbidites termed transitional variants and packets of entirely rippled strata are observed in submarine fan and slope sequences in the peira cava area in contrast to those in st croix and the niesenflysch the current emplaced deposits of the annot sandstone are directly associated with fan valley deposits such rippled strata in channels are deposits of gravity flow origin which were subsequently reworked downslope by currents generated by successive gravity flows they also occur on levees by overbank flow consideration of multiple process transport is of special help to interpret sections which are poorly exposed or which can be examined in cores or which are located in sequences that have been highly deformed structurally

the influence of bottom currents on the zambezi valley morphology mozambique channel sw indian ocean in situ current observations and hydrodynamic modelling abstract mixed turbidite contourite systems can be found in oceans where bottom currents and turbidity currents interact the zambezi turbidite system located in the mozambique channel sw indian ocean is one of the largest sedimentary systems in the world in length and area of the related catchments the oceanic circulation in the mozambique channel is intense and complex dominated by eddies flowing southwards and deep currents flowing northwards along the mozambican margin current measurements obtained from moorings at 3400 4050 m water depth in the zambezi and tsiribihina valleys show periods of intense currents at the seafloor with peaks of 40 50 cm s 1 that last up to one month and are not related to turbidity currents these strong bottom current events are correlated with a change in current direction and an increase in temperature the periods of current intensification may be related to eddies since they present similar frequencies around 7 per year moreover modelling results show that during periods of intense deep circulation an anticyclonic eddy is present between the mozambican slope and the centre of the mozambique channel which may block the northward transport of the deep water mass and thus enhance the southward transport along the western slope of madagascar according to our hydrodynamic modelling of the circulation near the seafloor intense currents are often present along the zambezi valley especially along the valley flanks multi channel seismic reflection data show that the zambezi turbidite system does not show the typical characteristics of turbidite systems being dominated by erosional processes which mainly affect the valley flanks levees associated with the valley are absent in the main axis of the system the effect of bottom currents on sedimentation in the basin is evidenced by the low sedimentation rates that witness winnowing in the basin the presence of contouritic sand in the zambezi valley flanks and the abundance of current related bedforms observed in multibeam bathymetry and seismic data the intense oceanic processes observed in the mozambique channel may transport a large part of the fine sediment out of the basin and erode the seafloor even at great depths therefore the zambezi turbidite system could at present be considered as a mixed turbidite contourite system with important implications for source to sink studies

shallow plio pleistocene contourites on the hebrides slope northwest u k continental margin abstract british geological survey borehole 88 7 was drilled on the continental margin of the northeast rockall trough in a water depth of 560 m with the intention of coring an unbroken plio pleistocene succession the borehole penetrated 102 m of pleistocene and tertiary sediments with 60 recovery the majority of the plio pleistocene succession is composed of bioturbated muds and sandy muds with rare dropstones in most of the core bioturbation has obscured any primary sedimentary structures although in places the muds are laminated and graded on a centimetric scale subtly different trace fossil assemblages in the homogeneous and laminated core indicate that the preservation of laminae is not simply the result of a decrease in burrowing activity x radiographs of the apparently homogeneous sections of core indicate that both coarsening and fining upward sequences between 5 and 50 cm in thickness are present particle size analysis has identified larger variations in grain size over several metres sands in the plio pleistocene are not common and comprise under 8 of the total succession most of which directly overlie older tertiary sediments the mineralogy of the plio pleistocene sands implies reworking of the lower beds and their base is marked by a conglomeratic lag deposit the change between homogeneous and laminated muds appears to be the result of variations in the style of sediment deposition at times deposition rate was relatively rapid and formed a laminated sediment with a trace fossil assemblage containing bedding parallel forms this more rapid sedimentation rate may be the result of greater down slope transport of material to the north or south of 88 7 giving rise to the lateral redistribution of fine sediment which was laid down in laminated beds similar in form to distal turbidites when this lateral source was not present the background sedimentation of ice rafted and ice margin derived material gave rise to a poorly sorted deposit which was reworked into both coarsening and fining upward units which have similarities with muddy contourites all the plio pleistocene muds have been influenced by along slope currents during deposition

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

post miocene disconformities and paleoceanography in the atlantic sector of the southern ocean abstract the magnetostratigraphy and biostratigraphy of 166 islas orcadas piston cores in the atlantic sector of the southern ocean reveal disconformities in the sedimentary record which are attributed to bottom current erosion the hiatus frequency as a function of water depth reveals both shallow erosion by circumpolar deep water cdw and deep erosion by antarctic bottom water aabw the post miocene history of erosion by both bottom currents is delineated by analysis of areal and temporal fluctuations of hiatus frequency erosion by cdw caused disconformities on the maud rise astrid ridge indian antarctic ridge scotia sea and islas orcadas rise the shallow disconformities increased in frequency and size from 4 0 to 1 0 ma with two periods of distinctly widespread disconformities from 5 5 to 4 5 ma and 2 5 to 1 5 ma after 1 0 ma the frequency and extent of the hiatuses decreased erosion by aabw caused disconformities in the weddell abyssal plain argentine basin and through a narrow conduit in the south sandwich basin downstream from the bullard fracture zone the deep disconformities increased in frequency and size from 4 5 to 5 0 ma 3 5 to 4 0 ma and from 1 0 to 2 5 ma after 1 5 ma the frequency and extent of hiatuses decreased fluctuations in hiatus frequency are consistent with results of a similar study in the southeast indian ocean and may be correlated with paleoceanographic events southern ocean cooling and possible re establishment of the west antarctic ice sheet and fringing ice shelves at 4 3 3 5 ma was accompanied by increased aabw and cdw activity the formation expansion of the northern hemisphere ice sheets at 2 5 3 0 ma resulted in a decrease in aabw velocity and was accompanied by increased cdw activity both deep and shallow bottom currents increased in velocity during the late matuyama chron 2 0 1 5 ma as a result of antarctic cooling after 1 0 ma however the frequency and extent of shallow and deep hiatuses was reduced and the modern extent of hiatuses is the lowest within the post miocene

contourite drift molded by deep mediterranean outflow since its inception in early pliocene time the deep mediterranean outflow has eroded and sculptured the southern iberian margin the 50 km long 300 m thick faro drift constructed by this powerful bottom current has been the subject of detailed study sandy silty and muddy contourite facies can be clearly characterized and a distinctive vertical arrangement or sequence of these facies can be related to hydrodynamic fluctuation these results are important for the identification of ancient contourites the reconstruction of paleocirculation patterns and documentation of the effects of quaternary climates on the mediterranean outflow

understanding of hydraulic properties from configurations of stochastically distributed fracture networks a systematic investigation of the effect of configurations of stochastically distributed fracture networks on hydraulic behaviour for fractured rock masses could provide either quantitative or qualitative correlation between the structural configuration of the fracture network and its corresponding hydraulic behaviour and enhance our understanding of appropriate application of groundwater flow and contaminant transport modelling in fractured rock masses in this study the effect of block sizes intersection angles of fracture sets standard deviations of fracture orientation and fracture densities on directional block hydraulic conductivity and representative elementary volume is systematically investigated in two dimensions by implementing a numerical discrete fracture fluid flow model and incorporating stochastically distributed fracture configurations it is shown from this investigation that the configuration of a stochastically distributed fracture network has a significant quantitative or qualitative effect on the hydraulic behaviour of fractured rock masses compared with the deterministic fracture configurations that have been extensively dealt with in a previous study this investigation is expected to be more practical and adequate since fracture geometry parameters are inherently stochastically distributed in the field moreover the methodology and approach presented in this study may be generally applied to any fracture system in investigating the hydraulic behaviours from configurations of the fracture system while establishing a bridge from the discrete fracture network flow modelling to equivalent continuum modelling in fractured rock masses copyright 2007 john wiley sons ltd

identification of ancient sandy contourites proposed criteria for the identification of ancient sandy contourites include occurrence thin beds reworked sandy turbidites coarse lag structure bioturbated no regular vertical sequence orientation of cross lamination perpendicular to regional downslope paleocurrents grain size silt or sand little mud low or negative skewness fabric grain orientation and composition downslope and along slope provenance concentrations of heavy minerals a suggested three stage approach to recognition of sandy contourites in the field involves work on a progressively increasing scale with particular emphasis on paleocurrent data the various deep water settings in which disparate current directions may occur are summarized and those in which sandy contourites may be formed and recognizably preserved are indicated a broad definition of the term contourite is now possible because of the widespread documentation of contourites even in freshwater environments along slope flow that is persistent in time and space is a requirement

photographic evidence of variable bottom current activity in the suruga and sagami bays central japan abstract complex patterns of bottom current behaviour were clarified by studies of sedimentary features and orientations of benthic animals in the deep suruga and sagami bays on the pacific side of central honshu japan both the suruga and sagami bay measure about 60 km in length as well as in width at their mouths and are about 1500 m deep in their central portions the size of each bay is comparable to that of ancient forearc basins the bottom sediments are characterized by turbidites and slump deposits at 32 stations on the bottom of the bays deep sea photographs were taken most of which clearly indicate bottom current activity current induced bottom features are current lineations moat like scours around resistant objects crag and tail structures behind obstacles ripple marks sand ridges and deformed biogenic structures such as burrows mounds tracks and faeces these features are produced by bottom currents with rather high velocities other important current indicators are some benthic organisms which in general show a sensitive response to currents and adopt particular orientations typical examples of megabenthos identified in the bottom photographs as effective current indicators are the small deimatid holothurian peniagone japonica the benthic shrimp glyphocrangon hastacauda sea anemones and sea pens among them the orientation of peniagone japonica shows abrupt changes of current direction with time for example from n 0 to sw 240 during 15 min and from n to s and back to n a complete rotation during 40 min the results of these observations indicate that the bottom currents in deep bays tend to fluctuate rapidly in velocity and direction probably owing to strong internal tidal waves in the very steep embayments upslope currents appear to be present at the mouths of submarine canyons thus it should be borne in mind that palaeocurrent analysis of ancient bottom current deposits or contourites is limited in application

side scan targets in lake superior evidence for bedforms and sediment transport a high resolution side scan sonar survey of the lake bed off the keweenaw peninsula lake superior demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m numerous lineations which run parallel to the shore appear to be sand ribbons a field of sedimentary furrows which occurs in one area demonstrates the long term directional stability of the near bottom flow large 100 300 m in diameter 2 5 m deep unusual ring like or arcuate depressions are common throughout the western half of lake superior these rings themselves do not appear to have been formed by bottom currents but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed off the keweenaw peninsula the forms of the rings have been modified by bottom currents the bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified

contourite facies model improving contourite characterization based on the ichnological analysis abstract the calcareous contourites from the late oligocene and early miocene in the petra tou romiou type section southern cyprus have been studied in detail being regarded as outstanding examples of fossil bioclastic contourites and representative of the standard facies model of contourite bigradational sequence these bigradational sequences of sand dominated contourites consists of whitish calcarenite beds with wavy layering in the middle portion of the sequence gradual alternations of whitish and greenish calcilutites appear above and below these calcarenites the internal wavy layering is composed by compacted interlayers and non compacted interstratified layers in the present study an in depth ichnological analysis of the bigradational sequence has been conducted focusing on ichnological features such as length shape diameter and orientation of individual burrow segments the configuration of burrow systems as well as external features fill material and finally taphonomy trace fossil assemblages differ containing planolites isp chondrites isp and thalassinoides isp at the compacted interlayers and non compacted layers bearing only planolites structures the compacted interlayer structures are flattened and elliptical containing similar fill material as the calcilutite host sediment though lighter in color in the non compacted layers planolites are near un deformed being cylindrical and tubular with circular to sub circular cross sections these are located mainly at the base or occupy the entire layer locally showing longitudinal striae planolites reinecki ksi ziewicz and filled with calcarenite material the different trace fossil assemblages in the compacted layers and non compacted interlayers varying in fill material evidence an original primary differentiation presumably indicative of fluctuating paleoenvironmental conditions in consecutive non compacted layers the distribution of planolites is separated by compacted interlayers this indicates that the middle portion of the contourite type facies with internal wavy layering underwent a multiphase deposition in the non compacted layers the almost undeformed planolites marked by striae is consistent with a higher substrate consistency which is interpreted as being associated with sedimentary condensation or omission immediately before the next compacted interlayers were deposited this evidence clearly supports the contention that sedimentary processes governing contourite deposition were intermittent rather than continuous as traditionally proposed these findings raise basic questions regarding the bottom current processes and consequent bedform development in these deep marine environments

forearc tectonic evolution of the south shetland margin antarctic peninsula the main provinces of the south shetland margin antarctic peninsula characterized on the basis of multichannel seismic long range side scan sonar and swath bathymetry data include from northwest to southeast 1 the oceanic crust of the former phoenix plate flexed down toward the margin and affected by normal faulting in the upper crust 2 a narrow trench with a horizontally layered sediment fill which onlaps the thin sedimentary cover on the oceanic crust and shows incipient deformation near its landward edge 3 an accretionary prism with a complex internal structure the toe of which is overthrust above the youngest trench deposits 4 a midslope forearc basin with an asymmetric synformal structure and 5 the continental shelf which includes two distinct tectonic provinces calculations of the late cenozoic convergence history at the trench indicate a rapid decrease in convergence rate after 6 7 ma from about 60 mm yr resulting from the slowing and eventual cessation of spreading on the antarctic phoenix ridge once spreading had completely ceased 3 5 2 4 ma the convergence rate at the trench equalled the rate of extension in bransfield strait which was probably less than 10 mm yr at first but may have increased since 1 3 ma and this in turn would imply a corresponding increase in convergence rate above the basal detachment the toe of the accretionary prism is composed of a stack of thrust fault bounded wedges laterally and vertically segmented by normal faults most of the trench fill sediments are overthrust by the toe of the accretionary prism and subducted beneath it for as far as they can be traced on the seismic profiles this suggests that there may be tectonic erosion of the forearc since a large part of the trench sediment appears to be derived from erosion on the forearc slope the forearc basin records a long history of subsidence during which the depocenter migrated landward paralleling retrogradational erosion of the distal margin of the basin subduction of the hero fracture zone at approximately the same location since 10 ma may have enhanced tectonic erosion of the accretionary prism in the forearc basin a synform is coincident with a bathymetric reentrant but its axis is oblique to the trends of both the basin and the fracture zone the origin of this synform and the final phase of uplift of the blueschist facies terrane on which smith island stands are probably related to their position above the subducting fracture zone ridge the present elevation of smith island is thought to result from uplift which followed a ridge crest trench collision directly southwest of the hero fracture zone at 5 5 ma the northwestern edge of the mesozoic to early cenozoic arc batholith trending northeast southwest on the shelf is proposed to have acted as a backstop to the accretionary prism during cenozoic subduction

cenozoic prograding sequences of the antarctic continental margin what balance between structural and eustatic control multichannel seismic reflection profiles across the antarctic continental margin commonly reveal prograding sedimentary sequences that are bounded by unconformities these sequences are as much as 5 km thick and where sampled are composed entirely of late eocene early oligocene and younger glacial rocks on nonpolar margins prograding sequences generally are attributed to relative changes in sea level sediment supply and tectonism around antarctica ice sheets have also been important in controlling the geometry and location of prograding sequences the antarctic sequences may provide a proximal record of major cenozoic ice volume changes and related sea level changes not obtainable from low latitude continental shelves presently the antarctic record is poorly known because of limited core data two categories of prograding p and aggrading a sigmoidal sequences are observed around antarctica 1 p sequences that build principally outward common and 2 ap sequences that build largely upward and outward less common p sequences may result principally from grounded ice sheets and ap sequences from open marine basinal processes major rift embayments of antarctica e g eastern ross sea eastern weddell sea lambert graben wilkes basin are also pathways for major ice movement in general most areas with p sequences lie within or adjacent tomore mesozoic or older rift embayment whereas the primary area with ap sequences eastern ross sea lies within a likely cenozoic rift embayment the pacific side of the antarctic peninsula where cenozoic ice sheets and cenozoic tectonism have been active is also marked by a p sequence scientific drilling on the antarctic continental shelf has recovered openwater glacial deposits ross sea as well as glacial diamicts that were deposited beneath and in front of grounded glacier ice ross sea and prydz bay less

key evidence for distal turbiditic and bottom current interactions from tubular turbidite infills abstract infilling of trace fossils can serve as a proxy for sediment otherwise missing from basin deposits the petra tou romiou section southern cyprus includes calcilutite calcarenite material that represents deep marine deposits of eocene age lateral and vertical variation indicates pelagic gravitational and bottom current processes simultaneously influencing sedimentation detailed ichnological analysis resolved interactions between these deep marine sedimentary processes in this distal marine setting calcarenite turbiditic beds occur as well preserved and continuous tabular beds that disappear laterally in some cases trace fossils infilled with calcarenitic material are termed tubular turbidites these structures correspond to actively filled planolites formed in softground conditions and infilled by calcarenitic sediment interpreted as the record of missing turbiditic deposits when calcarenite turbiditic beds disappeared due to erosion the variable preservation of calcarenite turbidite beds along with the presences of tubular turbidites indicate rapid erosion following turbidite deposition and post depositional reworking of turbidites by bottom currents a refined interpretation of tubular turbidites can help constrain sedimentary processes that form deep marine deposits and as such has considerable paleoceanographic and economic implications

traction structures in deep marine bottom current reworked sands in the pliocene and pleistocene gulf of mexico the pliocene pleistocene sequence cored in the ewing bank and garden banks areas in the gulf of mexico provides an example of deep marine sand reworked by bottom currents a distinctive attribute of these sands is their traction structures which include cross stratification current ripples and horizontal lamination these sands also exhibit sharp upper contacts inverse size grading mud offshoots and flaser bedding an important aspect of these structures is their occurrence in discrete units but not as part of a vertical sequence of structures such as the bouma sequence presumably the loop current a strong wind driven surface current in the gulf of mexico impinged on the sea bottom as it does today and resulted in bottom current reworked sands a depositional model is proposed in which the bottom current reworked sands tend to develop a facies in interchannel slope areas that is distinctly different from channel levee turbidite facies

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

quantitative characterisation of contourite deposits using medical ct abstract five sediment cores retrieved from four different depositional contouritic morphological settings a sheeted drift a confined mounded drift a mounded elongated drift and a plastered drift from the northern gulf of cadiz and the alboran sea have been analysed using medical x ray computed tomography medical ct a quantitative approach has been used resulting in a workflow that delineates several radio density ranges based on the hounsfield unit hu histogram of each core and tracks these ranges throughout the cores in order to derive the geological significance the radio density ranges of all cores have been compared to non destructive continuous chemical and physical proxies as well as grain size measurements the highest correlations occurred between high hu and proxies indicating elevated bottom currents such as zr al and sortable silt additionally a continuous increase in average hu and inferred bottom current velocities needed for the creation of the specific contourite setting could be observed throughout the five cores despite imperfections and the requirement of additional research promising results have been obtained which could improve the detection of diagnostic criteria for contourites moreover the ct data can give more conclusive evidence on the nature of the contourite sedimentary sequence boundaries

the contour current flow along the southern iceland faeroe ridge as documented by its bedforms and asymmetrical channel fillings abstract the iceland faeroe ridge is a natural barrier to the exchange of water masses between the norwegian greenland sea and the north atlantic basin the main overflow of cold and dense water from the norwegian greenland sea through the faeroe channels results in the generation of an intense contour current flow below 600 m water depth along its southern flank side scan sonar surveys revealed an extensive pattern of various bedforms with current indicators matching well with contour flow directions previously inferred from oceanographic measurements in the shallow ridge crest area only minor current induced bedforms were observed reflecting the relatively weaker intensities of overflow across the ridge in addition to the observed bedforms surveys of a nearby ridge parallel channel system also located on the southern flank of the iceland faeroe ridge document an asymmetrical sedimentation pattern with northern channel flanks displaying condensed sedimentation this asymmetrical sedimentation pattern is attributed to the influence of the coriolis force which is the ultimate driving mechanism for the generation of contour current systems

high resolution digital image treatment to color analysis on cores from iodp expedition 339 approaching lithologic features and bioturbational influence abstract color analysis was conducted on selected cores from sites u1385 and u1389 from iodp expedition 339 based on a recently developed high resolution digital image treatment to explore its relationship with lithologic features e g percentage of sand this first step can be of potential usefulness in characterizing discriminating between different types of registered sediments in the iodp expedition 339 turbidites contourites and associated sediments and then for more general studies involving different lithologies sedimentary parameters and ichnological variations differentiation between types of deposits holds particular interest in the context of the mediterranean outflow water mow evolution and related depositional processes whose study was one of the main aims of iodp expedition 339 color characterization was executed on high resolution digital images by applying a method based on adjustment modification including levels brightness and vibrance followed by pixel measurement the applied methodology allows for a precise characterization of colors improving upon previous color descriptions by means of munsell color conducted on board during expedition 339 itself the studied interval is subdivided into four parts based on grain size analysis and color according to pixel values these parts are identified as a 120 b 90 c 140 and d 160 being well correlated with the corresponding lithology parts a and c with similar pixel values correspond to calcareous silty mud mudstone part b would correlate with calcareous silty sand sandstones and part d corresponds to calcareous mud sand content distribution throughout the studied interval bears a close relationship with the differentiated parts a to d intervals having a higher percentage of sand present a lower mean pixel value and darker color whereas the finer grained intervals contain sediments lighter in color represented by higher pixel values however as proved the proposed relationship between color sedimentological features type of sediment must be considered with some caution ichnological analysis reveals the influence of trace fossils on color variations in the sediment regardless of the size of traces and amount of bioturbation the infilling material of trace fossils being the most determinant factor thus lower bioturbated surfaces 6 by small trace fossils chondrites show higher influence on color variations 102 vs 107 than higher bioturbated surfaces 25 by large trace fossils thalassinoides 110 vs 112 due to the color of the infilling material 56 in the case of chondrites and 90 in the case of thalassinoides thus a detailed ichnological analysis should accompany the sedimentological study of deep sea modern cores in order to avoid misinterpretations of the sedimentological parameters involved

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

sedimentological effects of strong southward flow in the straits of florida abstract periodic southerly currents along the western side of the straits of florida are sufficiently strong to erode the seafloor and create large sand waves and coral mounds up to several meters high mapping with side looking sonar and visual observations from the nuclear research submarine nr 1 show that the sand waves are confined to an area about 2 km wide but over 70 km long southerly currents in excess of 50 cm s 1 were measured during our dives and the size of the bedforms and grain size of sediments suggests currents could attain velocities of 100 cm s 1 the eastern boundary of the sand waves terminates abruptly with an erosional cliff or a series of erosional steps grades to a zone of nondeposition and then to an area of sediment accumulation in the central straits are regions of ripples megaripples and small coral mounds that indicate persistent flow to the north chemical as well as current erosion appears to be altering the seafloor on the southern side of the northwest providence channel which feeds into the straits of florida relict lithoherms are abundant in this channel but they are much smaller than those observed further north in the straits of florida bedforms and current measurements show a strong northwest flow in the channel along the south wall

estimating the intensity of rock discontinuities this paper presents an approach for estimating the intensity of discontinuities and formulating intensity and orientation as a fracture tensor specifically the size distribution and the number of discontinuities are estimated first from which the fracture tensor is then derived discontinuity size distribution is inferred from the trace data sampled in circular windows by using a general stereological relationship between the true trace length distribution and the discontinuity diameter distribution assuming circular shaped discontinuities because the measured trace lengths are biased a method is proposed to estimate the true trace length distribution for circular window sampling circular window sampling has the advantage of automatically eliminating the orientation bias when estimating the true trace lengths a method is then presented with which the total number of discontinuities in an objective volume can be estimated from the number of discontinuities observed in normal size boreholes and using the inferred discontinuity diameter from the circular window sampling on the rock surface with the derived size distribution and number of discontinuities the intensity of discontinuities which is the total surface area of discontinuities per unit volume can then be calculated and included in a new definition of a fracture tensor an application of the approach to analyze simulated discontinuities produces satisfactory results

late quaternary sediment pathways through the deep ocean east of new zealand late quaternary sediment pathways through the deep ocean east of new zealand were determined using sand sized mica tracers in conjunction with physical oceanographic seismic and stratigraphic data results indicate that in glacial times micaceous sediment derived mainly from low grade metamorphic rocks of the eastern south island was delivered by rivers directly to bounty trough here turbidity currents transferred the sediment 1000 km eastward to the bounty fan on the 4500 m deep southwest pacific basin a western boundary current wbc flowing over the fan redirected the sediment 1000 km to the north and northwest where it eventually accumulated as a drift deposit near hikurangi trough the drift also received mica that had been transported 700 km along hikurangi trough from mainly plutonic sources on the northwestern south island interglacial episodes witnessed a major change in transport paths river borne sediment was diverted away from bounty trough which became a site of predominantly calcareous pelagic sedimentation denied the lateral injection of terrigenous sediment the wbc nevertheless continued to supply small quantities of mica to the drift through erosion of existing glacial deposits on the bounty fan the paucity of interglacial mica on the drift indicates it is also receiving little terrigenous sediment by way of hikurangi trough

continental shelf progradation by sediment drift accretion multi channel seismic profiles from the canterbury basin on the eastern margin of the south island of new zealand reveal the importance of current activity in shaping a neogene shelf sediment prism the shelf prism prograded across a broad near horizontal platform in water depths of 1 000 to 1 750 m the platform was formed above a condensed section of late eocene to late oligocene limestones which overlie cretaceous to paleogene rift fill and transgressive sediments the neogene sediment prism contains sediment drifts which are as much as 25 km long and 15 km wide and extend up to 1 600 m uncompacted vertically individual drifts migrated westward and can be traced between dip profiles revealing that the long axes of most are subparallel to the present coastline and shelf edge channel like features at the landward edges of the drifts correspond to residual space left between the landward prograding off shelf sediment drift and the adjacent shelf foreslope erosion or slow deposition characterized the foreslope progradation of the shelf was by the accretion of successive sediment drifts before ca 11 5 ma pink horizon the shelf edge parallel drifts were distributed across the central part of the basin whereas subsequently they were concentrated to the northeast the seismic architecture of the neogene sediment prism results from the interplay of an abundant western sediment source and an offshore boundary current system present day ocean circulation involves northward flow along the east coast of the south island the basin may have been subjected to a middle miocene to late pliocene phase of intensified flow caused by local topographic enhancement and or global paleoceanographic events current activity has played a crucial role in the sedimentary evolution of the canterbury basin neogene shelf prism

a two step homogenization based permeability model for deformable fractured rocks with consideration of coupled damage and friction effects abstract the permeability variation induced by anisotropic damage of rock blocks and nonlinear deformation of fractures is modeled with a two step homogenization technique for deformable fractured rocks containing arbitrarily distributed penny shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of much large scales the proposed model accounts for the influences of the microstructural alteration of rock blocks and fractures at the laboratory scale and the development pattern of the fracture system as well as the rock fracture interaction at the field scale on the permeability of a fractured rock under mechanical loading or excavation condition the proposed model was first validated by laboratory data of compression tests with permeability measurements on the beishan granite coupled shear flow tests with hydraulic conductivity measurements on a granite fracture and anisotropic strength tests on the martinsburg slate with good agreement between the model predictions and the laboratory measurements numerical simulations were finally performed to examine the excavation induced permeability change in the surrounding granitic rock of the stripa tunnel demonstrating the importance in considering both the damage of rock blocks and the deformation of fractures for better understanding the excavation induced permeability change in the surrounding rock near the excavation surface

a late pleistocene time series of bottom current speed in the vema channel abstract a coarsening of the mean particle size of the carbonate free silt fraction from sea floor samples below 4000 m in the vema channel has been used to separate high velocity antarctic bottom water aabw from the overlying slower north atlantic deep water nadw a time series of fluctuations in bottom current speed within the modern aabw nadw transition zone was examined by determining the particle size distribution of sediments from eight gravity cores with a high resolution stratigraphy for the past 250 kyrs the bottom current paleospeed was inferred from a correlation of particle size in seafloor samples with mean current speed from nearby current meters the mean bottom current speed at depths comparable to modern aabw was highest 7 10 cm s during interglacial to glacial transitions corresponding to the oxygen isotopic stage 6 7 and 4 5 boundaries and at present the mean bottom current speed at depths comparable to modern nadw was nearly uniform for most of the past 250 kyrs except during glacial oxygen isotopic stage 2 when the speed dropped to 2 cm s or one half of the present speed the application of the calibrated particle size method to examine bottom current paleospeed allows testing of paleoceanographic models which rely on assumptions or inferences of changes in bottom water production rate during the late pleistocene paleoclimatic fluctuations

ichnological analysis of contourites past present and future abstract contourite deposits are significant facies in deep water sedimentary environments because they record critical paleoclimatological and paleoceanographic data contourite research also informs slope stability geological hazard assessment and petroleum exploration scientific consensus has not converged on several key aspects of contourite interpretation however some researchers interpret bioturbation as a diagnostic feature that differentiates contourites from associated facies e g turbidites while other researchers consider bioturbation to be of second order importance this work reviews existing literature and relevant field data to better define the role of ichnological analysis in contourite research review of significant contributions by earlier studies including formalization of terminology bioturbation burrow etc can help constrain wider usage of ichnological concepts e g ichnofacies and ichnotaxonomic analysis this paper also revisits ichnological data in paleoenvironmental interpretations reservoir characterization and the rare example of ichnofacies and ichnofabric analyses designation of diagnostic criteria can promote the use of ichnological information in contourite research regardless of consensus concerning bioturbation as a diagnostic criterion in contourite characterization ichnological data can still inform interpretations and integrate with other techniques to advance understanding of contourite sedimentary facies for a broad range of applications

facies and ichnology of an upper cretaceous chalk contourite drift complex eastern denmark and the validity of contourite facies models the upper cretaceous chalk of the danish basin has been interpreted as a major contourite complex on the basis of high resolution seismic data the sea floor had a pronounced topography with kilometre wide ridges and valleys up to almost 200 m deep interpreted to have been formed by contour parallel bottom currents only few ancient contourite systems have been recognized mainly based on sedimentary facies and only rarely on architecture and morphology two cored boreholes 345 and 443 3 m deep through the danish chalk contourite complex offer a unique possibility to compare seismic and sedimentary facies the contourite chalk is completely bioturbated except for thin intraclast conglomerates and a few thin levels showing possible primary lamination in terms of lithology and trace fossils the contourite chalk is similar to horizontally bedded pelagic chalk uninfluenced by bottom currents published contourite models cannot normally be used for the chalk because of the very fine grain size generally complete bioturbation and lack of any vertical trends in grain size on a millimetre to centimetre scale it is thus only rarely possible to document the influence of bottom currents on the basis of facies analysis alone and this can be inferred only by architectural analysis of seismic scale outcrops

the early neogene continental rise off the eastern united states abstract single and multichannel seismic data were used to investigate depositional components comprising the late oligocene middle miocene constructional phase of the united states atlantic continental rise in the georges bank blake plateau region the seismic sequence studied was bounded by the eocene oligocene age horizon a u unconformity at the base and a newly defined late middle miocene age horizon g at the top late oligocene middle miocene accretion onlapping the paleocontinental slope and downlapping onto horizon a u basinward was derived primarily from erosion of the uplifted central appalachian mountains this accretion up to 3 2 km thick was characterized by seven depocenters the lower paleocontinental slope upper rise depocenters situated off southern new england and the delmarva peninsula were interpreted as deep sea fan complexes or a broadly overlapping series of sedimentary blankets a whereas the closely associated oceanographer and wilmington depocenters were inferred to be levee complexes immediately north of the developing blake bahama outer ridge two n ne oriented sediment ridges that were probably built by gulf stream flow during an early miocene sea level lowstand were observed on the lower continental rise the proto hatteras and mytilus outer ridges from 0 4 to 0 8 km thick were probably formed from the wilmington and oceanographer levee complexes in early middle miocene time through the interaction of the growing levee complex with the sw moving abyssal current late middle miocene 12 11 5 ma bottom current erosion created the horizon g unconformity and brought to an end this initial stage of continental rise construction nevertheless the basic morphological framework that controlled late neogene and quaternary continental rise evolution was now in place

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

a fossil carbonate contourite drift on the lower ordovician palaeocontinental margin of the middle yangtze terrane jiuxi northern hunan southern china abstract the early ordovician tremadocian in part of jiuxi northern hunan province comprises a succession of deep water carbonate sediments deposited on a palaeocontinental margin at the southern edge of the yangtze platform a distinctive elongate mound like form some 350 450 m thick can be recognized lying between shallow water platform carbonates and deeper water mudstones this elongate body here called the jiuxi drift is made up dominantly of sediments interpreted as contourites on the basis of their mid to base of slope location alongslope current indicators features of traction flow processes coupled with intense bioturbation and distinctive contourite sequences typically 30 80 cm thick five contourite facies are recognized calcilutites calcisiltites calcarenites calcirudites possibly contourite lag deposits and bioclastic contourites hemipelagites and turbidites make up only a small proportion of the drift which accumulated at an average sedimentation rate of 38 m m y large scale cross stratified units found in parts of the calcilutitic contourite section are believed to result from seafloor development of mudwaves and or erosional furrows under the influence of a semipermanent bottom current regime

characterization and identification of bioturbation associated high permeability zones in carbonate reservoirs of upper cretaceous khasib formation ad oilfield central mesopotamian basin iraq abstract high permeability zones hpz are common occurrences in carbonate reservoirs of the middle east and act to improve productivity in primary depletion but lead to water breakthrough in secondary depletion bioturbation aggravated the reservoir heterogeneity of the khasib formation carbonates in ad oilfield iraq resulting in the development of hpz the observations of cores and thin sections measurements of porosity permeability capillary pressure and probe permeability were conducted to investigate the characteristics and genesis of the hpz well log responses of the hpz in cored wells were analysed to identify the hpz in uncored wells and predict its distribution results demonstrate that the hpz is demarcated by glossifungites ichnofacies and thalassinoides ichnofabric the burrow systems filled passively with overlying sediments that were apparently different from the unbioturbated matrix in terms of the lithologic associations pores types and pore connectivity the burrow systems which contribute to the high permeability of the hpz were merely composed of grainstone with well connected interparticle pores and vugs the matrix comprises packstone and hardground associated strongly cemented grainstone which developed some fractures and exhibited poorly connected pores including intraparticle moldic and residual interparticle pores the arithmetic mean permeability of the hpz is 241 0 md which is much higher than that of the non hpz 17 3 md the entry pressure and pore throat radius of the burrows in hpz is 0 02 0 05 mpa and 5 20 m respectively which reveal the high quality pore structure of the burrow systems there is strong heterogeneity within the hpz the permeability of burrow systems could reach up to 10133 5 md with an arithmetic mean permeability of 712 2 md while the permeability of the matrix is only 0 05 to 69 29 md with an arithmetic mean permeability of 8 7 md interconnected burrow networks in the hpz were formed by bioturbation the efficiency of connectivity of the hpz was further enhanced by the early dissolution occurred within burrow architecture and matrix in the meteoric freshwater environment these resulted in the formation of the high permeable network composing of interparticle pores vugs and the dissolution enlarged fractures the high permeable burrow systems and low permeable matrix jointly contributed to the distinct well log responses which are markedly different from the conventional shoal hpz the bioturbated hpz can be identified by medium natural gamma gr high bulk density value rhob low acoustic transit time value dt low compensated neutron nphi high deep induction value rild and high microspherically focused resistivity value msfl a well log model based three cutoffs namely rhobnor dtnor rild msfl and gr was built and shows good prediction of the hpz

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

current controlled sedimentation in the equatorial atlantic examples from the southern margin of the guinea plateau and the romanche fracture zone abstract 3 5 khz and seismic reflection data were used in a study area of bottom current control of sedimentation in two areas of the equatorial atlantic a 100 km long segment of the romanche fracture zone rfz and a 30 km wide sector of the southern margin of the guinea plateau the rfz is the most important conduit for antarctic bottom water aabw into the eastern atlantic at mid depths ca 1500 4500 m north atlantic deep water nadw spreads southwards and eastwards whereas at the surface directly overlying the rfz is the equatorial divergence a zone of high biological production on the guinea margin a mixture of aabw nadw moving north washes the foot of the continental rise below 4250 m and the overlying nadw hugs the slope contours another divergence zone lies just to the north of this area on the southern margin of the guinea plateau sediment accumulation is controlled by contour currents within the nadw deposits are concentrated into a series of slope parallel sediment drift the surfaces of which are moulded into standing sediment waves in the slack region between areas of eroded or condensed sequences marking the loci of higher velocity current cores the outer edge and upper slope of the plateau under the influence of high velocities in the equatorial surface water are swept bare of unconsolidated sediment the lower rise sediments washed by the weak mixed aabw nadw water mass are generally flat surfaced in the rfz restricted sediment deposition and accumulation as well as the reworking of sediment surfaces document the influence of bottom currents flat surfaced sediments deposited on the floor of the axial valley below the ca 4500 m ccd are ponded into basins at the foot of the valley walls by a weak aabw on the northern flank of the north ridge pillsbury seamount and on the south ridge the overlying nadw has moulded the thin sediment cover into sediment waves a thicker accumulation of generally flat surfaced ponded sediments in the suspended valley were apparently deposited under a weaker current regime in the lee of the pillsbury seamount stronger bottom currents as well as steepness of slope appear to prevent sediment deposition on both the upper slope and crest of the north ridge

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

lateral variability of ichnofabrics in marine cores improving sedimentary basin analysis using computed tomography images and high resolution digital treatment abstract major ichnofabric attributes may be related to a number of limiting marine parameters for tracemakers with paleoenvironmental significance including ocean atmosphere dynamics this is why ichnofabric analysis has proven to be a very useful tool in sedimentary basin analysis as well as in other earth science disciplines although it is a comparatively recent approach in ichnological research ichnofabric characterization is usually based on 2d visual observations of a single view in both outcrops and cores yet ichnofabric features can vary vertically and laterally within a very short distance which may lead to misinterpretations here a new methodological approach is presented allowing for a more objective evaluation of ichnofabric features based on the high resolution digital treatment of computed tomography images on marine sediments cores the method evaluates variations in ichnoassemblages cross cutting relationships and the degree of bioturbation structures in nearby selected images pertaining to several sections of the same interval of a core average values of the obtained data imply a significant improvement of the resolution than 2d observations and therefore a more precise and objective characterization of ichnofabrics the usefulness of the method and its differences with respect to traditional ichnofabric analysis are exemplified by a study of the gravity core fsg09 10 galicia bank domain nw iberian peninsula showing as a very significant tool to interpret paleoenvironmental changes i e sedimentation rate nutrient availability and bottom water oxygenation from the last glacial maximum lgm to heinrich event 1 he1 this example reveals the importance of proposed methods in order to characterize the ichnofabrics including their lateral variability with clear implications for future research on basin analysis

seismic stratigraphy of late cenozoic sediments in the northern labrador sea a history of bottom circulation and glaciation the seismicstratigraphy of the upper 1 km of sediment in the northern labrador sea has been determined from the examination of about 26 000 line kilometres of seismic profiles four key reflectors a to d have been correlated with deep sea drilling project dsdp and ocean drilling program odp holes and range in age from mid pliocene to approximately mid pleistocene ten seismic facies have been distinguished and are interpreted as resulting from slope progradation turbidite deposition in channels and on the basin floor and widespread contourite deposition tertiary sediments are predominantly hemipelagic or contourite but in the mid pliocene turbidite deposition began in the northeast labrador basin which might reflect either greenland glaciation or lowering of sea level at the same time widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom water circulation probably reflecting high latitude cooling this was followed by a return to less dynamic c

comment on internal waves an under explored source of turbulence events in the sedimentary record by l pomar m morsilli p hallock and b badenas earth science reviews 111 2012 56 81 this discussion is an attempt to alert the sedimentologic community that there is an immediate need to carry out fundamental research on process sedimentology of internal waves and internal tides in modern oceans despite the exhaustive theoretical experimental observational and numerical analyses of modern internal waves and internal tides by oceanographers with their focus on ocean mixing and modeling there are absolutely no core based studies by sedimentologists on the origin of primary sedimentary structures formed by baroclinic currents associated with internal waves and internal tides in modern marine environments as a consequence there are no objective sedimentological criteria for distinguishing internal wave deposits amid this knowledge vacuum the temptation to interpret ancient rock record as internal wave deposits must be tempered

mid depth calcareous contourites in the latest cretaceous of caravaca subbetic zone se spain origin and palaeohydrological significance abstract deep marine carbonates of late campanian to early maastrichtian age that crop out in the subbetic zone near caravaca se spain contain a thick succession of dm scale levels of calcareous contourites alternating with fine grained pelagites hemipelagites these contourites characterised by an abundance and variety of traction structures internal erosive surfaces and inverse and normal grading at various scales were interpreted as having been deposited under the influence of relatively deep ocean currents based on these contourites a new facies model is proposed the subsurface currents that generated the contourites of caravaca were probably related to the broad circumglobal equatorial current system the strongest oceanic feature of cretaceous times these deposits were formed in the mid depth 200 600 m hemipelagic environments at the ancient southern margin of iberia this palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage through which the broad equatorial current system flowed in the westernmost area of the tethys seaway regional uplift related to the onset of convergence between iberia and africa probably favoured the generation of the contourites during the late campanian to the early maastrichtian

quantitative estimation of bioturbation based on digital image analysis quantitative determination of modification of primary sediment features by the activity of organisms i e bioturbation is essential in geosciences some methods proposed since the 1960s are mainly based on visual or subjective determinations the first semiquantitative evaluations of the bioturbation index ichnofabric index or the amount of bioturbation were attempted in the best cases using a series of flashcards designed in different situations recently more effective methods involve the use of analytical and computational methods such as x rays magnetic resonance imaging or computed tomography these methods are complex and often expensive this paper presents a compilation of different methods using adobe photoshop software cs6 for digital estimation that are a part of the idiap ichnological digital analysis images package which is an inexpensive alternative to recently proposed methods easy to use and especially recommended for core samples the different methods similar pixel selection method spsm magic wand method mwm and the color range selection method crsm entail advantages and disadvantages depending on the sediment e g composition color texture porosity etc and ichnological features size of traces infilling material burrow wall etc the idiap provides an estimation of the amount of trace fossils produced by a particular ichnotaxon by a whole ichnocoenosis or even for a complete ichnofabric we recommend the application of the complete idiap to a given case study followed by selection of the most appropriate method the idiap was applied to core material recovered from the iodp expedition 339 enabling us for the first time to arrive at a quantitative estimation of the discrete trace fossil assemblage in core samples

radiolarian contourites record eocene aabw circulation in the equatorial east atlantic abstract 50 m of middle eocene pure radiolarian ooze were drilled at odp site 660 in the equatorial east atlantic 80 km northeast of the kane gap the oozes comprise a 10 m high and 2 km broad mound of seismic reverberations covered by manganese rich sediment and contain trace amounts of sponge spicules and diatoms negligible organic carbon 0 15 clay and variable amounts of pyrite the yellow to pale brown silty sediments are relatively coarse grained 30 45 coarser than 6 m little bioturbated and commonly massive or laminated on a cm scale the unlithified radiolarian ooze may indicate an interval of high oceanic productivity probably linked to a palaeoposition of site 660 close to the equatorial upwelling belt during middle eocene time the absence of organic matter however and both the laminated bedding and the mound like structure of the deposit on the lower slope of a continental rise indicate deposition by relatively intense contour currents of oxygen rich deep water which passed through the kane gap winnowed the fine clay fraction and prevented the preservation of organic carbon the ooze may be either a contourite lag deposit or a contourite accumulation of displaced radiolarians originating south of the kane gap and being deposited in its northern lee thus documenting the passage of a strong cross equatorial bottom water current formed near antarctica these eocene contourites may be an analogue for ancient radiolarites in the tethyan ocean

numerical experiments on permeability tensor and its application to jointed granite at stripa mine sweden rock masses containing a large number of geological discontinuities called joints are treated as homogeneous anisotropic porous media a permeability tensor hydraulically equivalent to a flow network formed by joints is formulated in terms of two tensors and a nondimensional scalar both depending only on the geometrical aspects of joints such as the spacing size orientation and aperture two dimensional numerical analyses on seepage flow through the networks support the validity of the present theory the information about the geometry of joints which is obtained from the ventilation drift at stripa mine sweden is interpreted to give the corresponding permeability tensor the permeability tensor is compared with the result of the large scale hydraulic conductivity test with the conclusion that it provides a reasonable prediction for the hydraulic properties of stripa jointed granite

ordovician contourites in the lachlan fold belt eastern australia abstract the ordovician sequence in the northeastern lachlan fold belt consists of three lithologic units representing an overall fining upward succession from turbidites to black shale the lowest unit dominated by turbidite beds represents a small segment of an extensive ordovician submarine fan sequence that covered much of southeastern australia the overlying unit consists predominantly of ripple bedded sandstone with beds 3 5 cm thick these beds are texturally mature containing heavy minerals mica and silt concentrated on the cross laminae the ripple bedded unit has a mean palaeocurrent trend to 321 which is at 60 to sole marks and almost normal to the trend of ripple cross bedding in the underlying and associated turbidite beds this unit is here interpreted as a sandy contourite sequence that can be attributed to contour currents moving northwards along the eastern margin of gondwana from areas of subpolar downwelling off southern africa and america the two major fining upward successions in the ordovician sequence in southeastern australia may reflect eustatic sea level rises during the middle and late ordovician and thus provide evidence of interglacial periods in the darrawilian and late gisbornian to bolindian the contourites would have accumulated in the latter stages of the glacial periods after sea level had risen sufficiently to cut off major sediment supply to the submarine fan but before the temperature had risen to the extent of preventing deep thermohaline circulation

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

sediment flux patterns in the northeastern atlantic variability since the last interglacial abstract the distribution of terrigenous and carbonate absolute accumulation rates in the northeastern atlantic during the last climatic cycle shows that climate and sediment accumulation are closely coupled either directly or through oceanic circulation and eustatic variation the strong contrast between the glacial and holocene flux distribution is related to oceanic circulation changes either surface circulation which governs both the ice rafting supply and the planktonic biogenic production or more particularly deep circulations via the reinitiation of the iceland scotland overflow glacial erosion and the low sea level stand enhance the terrigenous supply but the holocene deep circulation reinforcement leads to important material reworking as a consequence an almost constant average sediment flux is obtained 4g 2 ky 1 during the holocene compared to 4 7 g cm 2 ky 1 during the glacial period during the holocene period the notable increase in mean carbonate flux from 1 5 to 3 g cm 2 ky 1 is associated with carbonate biogenic production but the carbonate flux distribution shows the influence of redistributive agents on margins fluxes do not simply decrease from continental sources to the oceanic basin eustatic drops leads to a shift in the areas of preferential accumulation from the upper to the lower slope during the deglacial warming period the fluxes are respectively an average of two and three times higher than during the holocene and the glacial periods their importance highlights the major impact of rapid climatic changes finally local conditions the location of terrigenous sources and the presence of contour currents are among the many factors which will modify the trends observed on a global scale

lateral variability in shallow marine ichnofabrics implications for the ichnofabric analysis method ichnological analysis commonly undertaken both in the field and in core studies is generally carried out in vertical logged successions this work documents the results of a detailed ichnofabric study of two highly bioturbated sandstone beds separated by a mudstone within the thick lower jurassic succession of the yorkshire coast uk the two sandstone beds contain relicts of hummocky cross stratification and rare bioclasts of bivalves and belemnites bioturbation of the beds is intense and the diversity of trace fossils is considerable trace fossils present include teichichnus rectus teichichnus isp a thalassinoides isp palaeophycus heberti diplocraterion parallelum rhizocorallium rosselia socialis schaubcylindrichnus isp chondrites isp planolites isp and phycosiphon incertum ichnofabrics were studied at 5 m intervals parallel to the modern cliff line which is parallel to the inferred jurassic palaeo coastline the results demonstrate that there is considerable patchiness to ichnofabric even in a comparatively simple depositional setting such as a storm influenced shelf this observation is in line with studies of the modern sea floor the implications of patchiness in ichnofabric are broad ranging but most importantly suggest that caution is needed in the use of ichnofabric analysis for intra regional correlations

ichnological analysis the common ground between ichnofacies workers and ichnofabric analysts abstract this work compares the approaches taken by the two schools of applied ichnology ichnofacies and ichnofabric analysts and proposes an integrated approach for future improvement there are many similarities between the two approaches which mainly differ in the resolution at which ichnological analysis is undertaken ichnofabric work is by necessity performed on a bed by bed basis and interpreted at a scale consistent with that of the sedimentologist s facies ichnofacies studies in contrast seldom report bed by bed changes in ichnological content instead highlighting bedset to facies association scale changes in ichnology through comparison with summary models of ichnological trends this work highlights the fact that workers from both schools utilize the same tools with slightly different emphases to reach their ichnological conclusions contention between the two schools has in recent years centred upon which is the better method for studying trace fossils an artificial construct that detracts from the fact that both are extremely useful to sedimentological and palaeoenvironmental studies ichnofabric analysis is in addition a highly effective means of documenting bioturbated sedimentary fabrics as the basis for petrophysical studies ichnofacies and ichnofabric analysts use the same toolbox of ichnological methods to determine ancient palaeoenvironments the scale of observation is generally different but the results closely comparable the recognition of key stratal surfaces on ichnological grounds is also possible with both methodologies ichnofacies analysts look to recognise glossifungites ichnofacies firmgrounds in offshore mudstones ichnofabric studies would look to recognise overprinting of fabrics created by groups of organisms from different palaeoenvironments but associated with the same key surface it is proposed that the terms ichnofacies method and ichnofabric analysis are abandoned in favour of a neutral ichnological analysis method encompassing the approaches and terminology of both to produce a unified scientifically rigorous user friendly methodology

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

a novel sedimentological method based on ct scanning use for tomographic characterization of the galicia interior basin abstract non destructive techniques of core analysis especially of marine cores are being broadly employed for sedimentary paleoceanographic and paleoclimate research in particular computed tomography scanning ct scanning allows acquisition of 3d and 2d images according to desired planes and thus the identification of sedimentary structures large grains and their distributions as well as direct measurements of material densities the most significant contribution of this technique is the possibility of getting results before opening the core in this work ct scan data obtained for five cores from the galicia interior basin gib nw peninsula iberia are presented and discussed focussing on 1 methodology of the ct scan use 2 tomographic description of sedimentary facies identified in the gib 3 treatment of the numeric data obtained with ct scanning using specific software anidoc and 4 comparison of tomographic data with data obtained by conventional methodologies of core analysis the most singular feature of gib cores is the presence of ice rafted debris ird deposited during late pleistocene heinrich events he which can be easily recognized using the ct scan by the presence of high radio density grains immersed in a low radio density matrix comparison of ct scan data with analytical sedimentary data and he proxies performed on the cores validates the ct scanning method as a powerful tool to improve correlations identify well constrained events and make more accurate basin reconstructions without opening all the cores in an oceanographic study

late quaternary deep ocean circulation a review of paleoceanographic studies dealing with late quaternary deep water circulation in the oceans is presented these studies which are based on the analysis of deep sea benthic foraminiferal faunal and geochemical data and sedimentological data are discussed in light of physical oceanographic conditions in the modern ocean we include in this review a re evaluation of benthic foraminiferal data from north atlantic and southern ocean piston cores and suggest that the dominance of uvigerina during glacial intervals reflects increased amounts of organic carbon at the sea floor compared to modern values a number of geochemical studies have suggested that the production or characteristics of north atlantic deep water nadw changed during glacial times although these changes have been thought to result from a cessation of overflow water from the norwegian greenland seas it is suggested here that seasonal sea ice cover was possible over southern portions of the norwegian sea during glacial intervals the presence of seasonally open water would have allowed norwegian sea overflow water to have been produced although perhaps at lower volumes and with different hydrographic properties than at present the record of antarctic bottom water aabw circulation does not show a simple relationship with paleoclimatic oscillations indicating that changes in oceanographic conditions in the southern ocean had little effect on aabw formation the aabw record contrasts with the glacial interglacial cycles of nadw suggesting no direct link between aabw and nadw circulation a variety of data suggests that changes in pacific deep water circulation occurred as a result of glacial production of north pacific deep water or from an increased flux of southern ocean water

drifts and ponds of reworked pelagic sediment in part of the southwest pacific abstract since the late oligocene a bottom current that decelerates as it leaves the constricted samoan passage has deposited patches of reworked sediment on a blanket of paleogene clay and on a scoured terrain of mesozoic outcrops the sediments preserve a record of fluctuations in the geological effect and by inference the velocity of the pacific s western boundary current an area of 750 km 2 sediment drift was studied in detail with 18 cores and observations from a near bottom instrument it has rapid vertical and lateral facies changes from nodule covered zeolitic clay to radiolarian clay and ooze related to temporal and spatial changes in rate of deposition of current transported particles the source of most of the radiolaria is erosion of older outcrops upstream or current trimming of the drift margins so the siliceous ooze may be considered a variety of muddy contourite small ferromanganese concretions on the surface of a slowly accumulating part of the drift are arranged in long narrow stripes resembling abyssal furrows similar patterns believed to be caused by erosional bedforms were mapped by side scan sonars on the corrugated surfaces of ponds of calcareous turbidites other pelagic carbonate beds within the drifts were rapidly deposited from thermohaline currents it may be difficult to distinguish some calcareous contourites from turbidites after textures have been altered by early diagenesis but identifications based on field relations and topographic situation can be supported by detailed lithologic study the times of most rapid drift deposition from the bottom current were late oligocene early miocene probably caused by initiation of this western boundary flow from antarctica and late miocene early pliocene probably caused by intensified bottom circulation following glacial expansion

comment on ichnological analysis of contourites past present and future by francisco j rodriguez tovar and f javier hernandez molina earth science reviews 182 2018 28 41 abstract by their impressive paper title ichnological analysis of contourites past present and future rodriguez tovar and hernandez molina 2018 have implied that the paper is about a comprehensive review of the topic in space i e global and time i e past present and future but in reality the paper has covered only three case studies in europe in the real world bioturbation and burrows are not unique to contourites they are equally abundant in turbidites hyperpycnites tempestites and even in deformed seismites therefore the immediate challenge is in distinguishing contourite facies from other facies e g hyperpycnites with intense bioturbation disappointingly the review has neglected to address this fundamental issue without resolving the basic issue of distinguishing contourites any ichnological analysis of contourites is purely academic and has no relevance in advancing contourite research

the depositional pattern and distribution of glacial interglacial sequences on the antarctic peninsula pacific margin the outer shelf on the antarctic peninsula pacific margin south of 63 30 s is underlain by pliocene pleistocene prograding sequences which have been produced mainly by the action of ice sheets grounded out to the shelf edge at times of glacial maximum most sediment in these sequences has probably been transported to the margin in a deforming basal till which implies deposition on a broad front a line source a representative prograding sequence mapped across an extensive network of multichannel seismic reflection lines has an elongate depocentre on the upper palaeoslope which is consistent with the grounded ice sheet model however it is likely that each sequence recognized on existing multichannel seismic data represents several ice advances depth to surface maps reveal a broad variation along the margin in the amount of progradation reflecting differences in sediment supply the pattern of progradation and the bathymetry of the outer shelf suggest that the main depocentre in the area studied was fed by an ice stream at times of glacial maximum seismic lines across the margin farther to the southwest indicate the existence of other depocentres several broad depositional lobes have probably coalesced to form the extensive outer shelf the present continental slope is smooth and steep and is not cut by major canyons a downslope change in seismic facies and scouring on the uppermost rise probably reflect downslope transitions from slumps to debris flows to turbidity currents these processes are likely to be most active at times of glacial maximum deep drilling data indicate that the rise sediments consist mainly of terrigenous turbidite and ice rafted detritus a marked upward change in seismic facies on the continental rise indicates a change to a higher energy sedimentary regime and appears to correlate with the start of glacial progradation on the shelf

sedimentation on the feni drift and late glacial bottom water production in the northern rockall trough abstract between the last glacial maximum 18 ka and the present day a variety of contrasting oceanographic conditions including changes in surface and bottom water circulation patterns have existed in the north atlantic evidence for the presence of bottom currents in winnowed silt horizons in the feni drift suggests that deep water may have been produced in this region during glacial deglacial intervals current activity and thus perhaps deep water production was apparently intermittent and may have been controlled by a process analogous to the formation of labrador sea water this involves cooling and deep ocean convection during winter months physical factors controlling this production would be temperature and salinity of upper waters which would govern the density and wind stress necessary for vertical overturn coupled with absence of ice cover evidence of bottom current activity suggests that deep water production occurred in the rockall trough throughout termination 1a which closely corresponds to fairbanks 1989 meltwater pulse 1a mwp 1a production of deep water in this region apparently ceased shortly after the decline in influence of the meltwater influx

danian lower selandian microcodium rich calcarenites of the subbetic zone se spain record of nereites ichnofacies in a deep sea base of slope system abstract the olivares formation a lower paleogene unit of the subbetic zone in southern spain is mostly composed of calcarenites comprising 60 90 of resedimented microcodium remains which are intercalated in hemipelagic marls rich in planktonic foraminifera microcodium is formed on the roots of terrestrial plants adapted to live on carbonate rich substrates its occurrence in the olivares formation entailing a massive resedimentation from a subaerially exposed carbonate source area new field observations demonstrate that the unit was deposited at the base of a faulted slope within a graben flanked by massifs of mostly jurassic carbonates while an ichnological analysis shows an abundant and moderately diverse trace fossil assemblage consisting of 30 ichnospecies belonging to 21 ichnogenera the nongraphoglyptid assemblage 24 ichnospecies 16 ichnogenera is dominated by chondrites ophiomorpha planolites and scolicia zoophycos isp is common while cladichnus gordia helminthopsis multina nereites parahaentzscheliana polykampton spirophycus strobilorhaphe and thalassinoides isp are scarce or rare in the graphoglyptid assemblage 6 ichnospecies 5 ichnogenera helminthorhaphe is common scarce and belorhaphe desmograpton paleodictyon and urohelmintoida are scarce rare this trace fossil assemblage with abundant scolicia and nereites and frequent graphoglyptids can be assigned to the deep sea nereites ichnofacies within the nereites ichnofacies the ophiomorpha rudis and paleodictyon subichnofacies are readily differentiated and the nereites subichnofacies probably also occurs pointing to vertical changes in the turbiditic system most likely related to a coeval sea level rise that eventually resulted in the flooding of the emergent microcodium producing carbonate massifs

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition