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

nutrient spatial variation during intrabasinal upwelling at the cenomanian turonian oceanic anoxic event in the westernmost tethys an ichnological and facies approach abstract facies and ichnofabrics of two sections of the cenomanian turonian boundary interval are correlated and compared to evaluate changes in palaeoceanographic conditions controlled by palaeogeography in the distal zone of the westernmost tethys southern iberian continental palaeomargin the oceanic anoxic event oae 2 was interrupted by short aerobic or dysaerobic sub events with slight differences in facies and ichnofabrics these sub events display a tendency to expansion from the more distal section hedionda towards the proximal one el chorro the anoxia spread out from the open sea probably from slope upwellings higher diversity and abundance of trace fossils in comparatively distal position during the pre and post event intervals can be caused by a higher abundance of food available for tracemakers shape of the correlation bands of the oae 2 event suggests that the event started earlier by about a few tens of thousands years in the most distal areas than in proximal slightly higher bottom settings

variscan intracontinental deformation the coimbra cordoba shear zone sw iberian peninsula the coimbra cordoba shear zone is a major lineament roughly parallel to the nw se variscan structures of the southern iberian peninsula inside the shear zone evidence for a non coaxial strain path exists from structural microstructural and lattice preferred orientation data on quartz plane strain is suggested by the study of microstructures in the xy and yz sections in all formations occurring in the shear zone with increasing strain a mylonitic series develops the deformation contemporaneous with epizonal to mesozonal metamorphism is responsible for 1 1 the regional subvertical foliation oblique to the shear zone 2 2 the well defined subhorizontal lineation striking nw se 3 3 the discrete planes of shear roughly parallel to the shear zone the data are interpreted as resulting from a left lateral slip motion with a displacement of at least 72 km in the light of plate tectonics it is inferred that the coimbra cordoba lineament could have been a suture zone which evolved into an intracontinental left lateral shear zone during the variscan orogeny of the ibero armorican arc

turbidites and contourites of the palaeogene lefkara formation southern cyprus abstract deposition of the palaeogene to early neogene calcareous and siliceous deep water sediments of the lefkara formation in cyprus was successively dominated by pelagic turbidity current a return to pelagic and then bottom current processes sedimentation occurred on the distal parts of a carbonate slope apron to basin plain setting located in the western arm of the tethys ocean the early phase of sedimentation directly overlying ocean crust ridge derived volcaniclastics and chemogenic sediments was dominated by pelagic deposition of marl marly chalk and radiolarian rich calcilutite this was followed by a gradual increase in the influx of biogenic turbidites forming both chalk and chert deposits from the north during the early and middle eocene period primarily as a response to tectonic uplift of the kyrenia range slower rates of sedimentation returned during the late eocene to early miocene together with significant hiatuses in the sedimentary record together these reflect the cessation of turbidity current input continued pelagic deposition and the onset of bottom current influence on sedimentation a combination of subtle features and supporting evidence allows the recognition of contourites in all the sections studied together with the interaction of turbidity current and bottom current processes in parts of the lefkara formation

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

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

trace fossils after the k t boundary event from the agost section se spain palaeogene trace fossils penetrate the uppermost cretaceous sediments in the agost section betic cordillera se spain chondrites targionii zoophycos isp planolites isp a planolites isp b thalassinoides isp a thalassinoides isp b thalassinoides isp c alcyonidiopsis longobardiae and diplocraterion parallelum have been identified a well developed endobenthic tiering pattern is interpreted the uppermost tier a represents major benthic activity in the shallowest sediments at or just below the seafloor recorded as bioturbated background only discrete rare planolites the next upper tier b displays the highest trace fossil diversity with planolites in the shallow levels and thalassinoides and alcyonidiopsis at slightly deeper ones the intermediate tier c contains randomly distributed thalassinoides and alcyonidiopsis cross cut by zoophycos and large and medium sized chondrites the deepest tier d contains zoophycos cross cut by medium and mainly small sized chondrites two interpretations are proposed 1 vertical partitioning of a singled multi tiered community under steady stable conditions in well oxygenated water bottom reflecting gradual changes deep into the sediment with decreasing oxygen pore water and benthic food and increasing substrate consistency and 2 sequential colonization and community replacement reflecting the work of two successive communities the first community mainly represented by planolites alcyonidiopsis and thalassinoides was produced in a shallow oxygenated soft substrate probably related to decreasing oxygen content and benthic food availability this community was replaced by deeply burrowing organisms that produced zoophycos and chondrites this sequential colonization can be determined by changes in environmental parameters related to the cretaceous palaeogene k t event or may have resulted from normal ecological and early diagenetic processes

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

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

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

the southern part of the armorican orogeny a result of crustal shortening related to reactivation of a pre hercynian mafic belt during carboniferous time abstract this synthesis of detailed geological and geophysical information relates deep crustal structure to deformation and the emplacement of granites in the south armorican massif and the adjacent continental shelf near the continental margin a zone of geophysical anomalies is regarded as a nearly complete line of suture between a southern continent and america a major mafic body in the trace of the supposed suture in interpreted as a relic of probable oceanic crust which has apparently acted as a deflector of regional strain it is proposed that late in the hercynian collision history during late carboniferous time compressional strain acted across the mafic body and can be directly related to generation of younger regional structures in the metasediments and to localization of granite emplacement

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

modelling of structures representing the south armorican suture abstract the modelling of magnetic structures which constitute a linear marker extending 600 km from the continental shelf off south brittany to the northern part of the aquitaine basin has led to the recognition of a major crustal fault zone this is confirmed by the existence of other geophysical markers gravity and seismicity they all can be interpreted in the light of an inter plate suture model

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

paleomagnetic and ams evidence for a variscan ductile clockwise rotation of the ile de groix blueschists south brittany france consequence on the late hercynian structural pattern of westernmost europe abstract the terrigenous sedimentary rocks and blueschists of the ile de groix france and surrounding sea floor display a complex metamorphic history comprising three major episodes of deformation that took place between 420 and 294 ma paleomagnetic measurements show that three components of magnetization can be isolated the low unblocking temperature component isolated below 300 c is close to the present magnetic dipole field the high component which reaches 580 c and even 680 c in some places corresponds to pre variscan magnetic directions already obtained for armorica since the groix island has always been part of the armorican microplate the corresponding magnetic inclinations can be used for dating tectonic events by comparing with the armorican apparent polar wander path apwp l1 lineations associated with sheath folds are contemporaneous with remagnetization that took place between 336 and 359 ma this is in good agreement with published radiogenic data the anisotropy of the magnetic susceptibility study shows that l1 lineations are the magnetic markers of tectonic rotation part of the dextral d2 ductile rotation of l1 around a vertical axis occurred around 310 ma paleomagnetic data also suggest that the clockwise rotation started earlier near the close of blueschist metamorphic event the clockwise rotation increases towards the southern end of groix where it trends 80 an early magnetization at 420 ma is regarded as the age of the initial emplacement of the klippe of groix restoration of the initial shape of groix island shows that the l1 fabric was broadly east west oriented before its impingement by an unevenness of the south armorican suture zone

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

early ordovician alluvial fan deposits of the marmul oil field south oman fine grained shaly sands of the mahwis formation haima group form one of the reservoir intervals of the marmul field six lithofacies can be distinguished from cores shale clast conglomerates trough cross stratified sands horizontally stratified sands massive sands rippled sands and interbedded shales and sands horizontally stratified sands make up 45 of the cored reservoir two scales of fining upward sequence occur small sequences are 0 3 1 5 m thick and are interpreted as sheetflood deposits on the distal portions of semi arid alluvial fans the larger sequences are 25 50 m thick can be correlated on well logs fieldwide and probably represent periodic tectonic rejuvenation and erosional lowering of the sediment source area it is interpreted from regional correlation sediment provenance and a knowledge of possible source areas that the alluvial fans were predominantly sandy had radii of several tens of kilometres and formed an extensive apron bordering a highland area which lay to the southeast the thinly bedded and shaly character of these sheetflood sands causes problems of petrophysical log evaluation and hence oil in place estimation reservoir quality is related to lithofacies occurrence and variation in grain size the large scale fan sequences correspond to an upward decrease in porosity and permeability and form useful subdivisions for field scale correlation and reservoir prediction