bioturbation influence on reservoir quality a case study from the cretaceous ben nevis formation jeanne d arc basin offshore newfoundland canada the delineation ben nevis l 55 well located in the hebron ben nevis field offshore newfoundland targeted the cretaceous ben nevis formation in the petroleum rich jeanne d arc basin this case study focuses on the bioturbated net pay horizons and assesses the importance of animal sediment interactions in controlling the porosity and permeability of sandstone reservoir intervals our data reveal that bioturbation can either reduce permeability and porosity by as much as approximately 33 or enhance it by up to 600 dependent on burrow type and behavior of the trace making organism the net pay interval in the cored interval of ben nevis l 55 is characterized by ophiomorpha dominated ichnofabrics the action of bioturbators can be classified in terms of sediment mixing sediment cleaning sediment packing and pipe work building strategies bioturbation has the potential to 1 increase isotropy or uniformity of grain size by destroying sedimentary laminae through burrow homogenization or 2 decrease isotropy by selectively sorting grains into burrow lining and fill by grain size and through creation of open burrow systems filled with later sediments of differing character to the host sediment the petrophysical characteristics of the reservoir facies are highly dependent on trace fossil morphology presence or absence of burrow linings nature of burrow fills burrow size and bioturbation intensity mudstone rich facies and ichnofabrics containing mudstone filled and or lined burrows e g ophiomorpha and clusters of chondrites have the net effect of permeability reduction in contrast permeability enhancement is documented from muddy sandstone facies with clean sand filled burrows e g thalassinoides and clean sandstones with burrow mottled or diffuse to massive textures

seismic imaging of salt structures in the gulf of mexico in this article we discuss seismic imaging of salt structures in the gulf of mexico with emphasis on the recognition preservation and migration of salt signals we describe three salt imaging technologies

multiple fluid components of salt diapirs and salt dome cap rocks gulf coast u s a abstract salt diapirs contain a few percent of anhydrite that accumulated as residue to form anhydrite cap rocks during salt dissolutions reported 87sr 86sr ratios of these salt hosted and cap rock anhydrites in the gulf coast u s a indicate their derivation from middle jurassic seawater however a much wider range of 87sr 86sr ratios incorporating a highly radiogenic component in addition to the middle jurassic component has been found in several gulf coast salt domes this wide range of 87sr 86sr ratios of anhydrite within the salt stocks records sr contributions from both marine water and formation water that has equilibrated with siliciclastics during cap rock formation this anhydrite either recrystallized in the presence of or was cemented by a low sr fluid with a late cretaceous seawter type sr isotope ratio or simply lost sr during recrystallization later the cap rock was invaded by warm saline brines with high sr isotope ratios from which barite and metal sulfides were precipitated subsequently low salinity water hydrated part of the anhydrite bringing to six the total number of fluids that interacted througout the history of salt dome and cap rock growth the progenitor of these salt diapirs the louann formation is generally thought to have formed from marine water evaporated to halite and rarely higher evaporite facies salt domes in the east texas north louisiana and mississippi salt basins have 87sr 86sr and 34s values that corroborate a mid jurassic age for the mother salt however salt domes in the houston and rio grande embayments of the gulf coast basin have 87sr 86sr ration ranging to values higher than both middle jurassic seawater and all rb free marine phanerozoic rocks these anomalous 87sr 86sr ratios are probably derived from radiogenic sr bearing fluids that equilibrated with siliciclastic rocks and invaded the salt either prior to or during diapirism potential sources of the radiogenic 87sr component include clay and or feldspar located either in older units beneath the louann formation or younger units flanking the salt diapirs and k salts within the louann evaporites because partial sr exchange in anhydrite had to take place in a fluid medium admittance of radiogenic 87sr bearing fluids into the salt may have led to diapirism by lowering the shear strength of the crystalline salt the slight number of anomalous 87sr 86sr values in the interior basins indicates that anomalous values are related to areally discrete structural or stratigraphic controls that affected only the gulf coast basin

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part i detailed study of one oil seeping site abstract we report the geophysical characterisation of natural oil seep sites through a combination of sea surface evidence of oil leakage from spatial imagery with a large collection of seafloor and subsurface geophysical data this paper provides a detailed characterisation of one selected active seep site and identifies possible specific feature of oil seep sites the oil seep is a complex shaped feature on the seafloor consisting of a cluster of heterometric pockmarks inside a main depression area and peripheral metre scale seafloor mounds a strong deformation related to salt tectonics controls the location of the seafloor source by fracturing the overburden the associated thermal anomaly induces a vertical modification position of the base of the gas hydrate stability zone bghsz that is used as a fluid migration route towards the crest of the diapir the combination of local depressions and seafloor amplitude anomalies linked with vertical high amplitude pipes rooted on the bghsz suggests a focused fluid flow towards the seafloor in peripheral areas the seafloor mounds are linked by shallow faults to buried high amplitude patches on sub bottom profiler sections the combination of restricted size seafloor mounds with a progressive deepening of the high amplitude from the seafloor suggests a substantial decrease of the hydrocarbon flow towards peripheral areas the proximity of actively oil supplying seafloor depressions and seafloor mounds shows that the hydrocarbon flow rapidly decreases laterally the thermogenic seep site is affected by two consistent and sub parallel reflections with negative polarity the first is interpreted as the methane related bghsz the second could correspond to the base of a thermogenic bghsz produced by a mixture of heavier gas the seafloor roughness and double bsr appear to be specific features of oil seep sites the geophysical features revealed at a localised study area will be extrapolated towards a larger province for relevance validation

subsalt play gulf of mexico a review exploration for deep water sandstone reservoirs beneath allochthonous salt in the gulf of mexico represents a major new frontier play in north america more than 30 wells thus far have been drilled with subsalt targets resulting in 8 discoveries at least 3 of which are commercial and 3 that have reserves of 100 million bbl oil equivalent or more reservoirs consist of miocene pleistocene sandstones deposited in submarine fan channel system environments on the paleoslope where salt deformation has a complex late cenozoic history salt sheets exist at various stratigraphic levels and have overridden sandstone fairways on the present day outer continental shelf and upper slope where water depths are moderate and where pipeline and other infrastructure facilities already exist potential reserves for the subsalt play have been estimated at 1 2 billion bbl of oil and 15 tcf gas from 25 or more significant fields recent success in the subsalt play has depended upon 1 advances in 3 d three dimensional seismic acquisition and processing in particular 3 d prestack depth imaging and 2 improved geologic modeling of salt deformation and depositional systems in addition better understanding of the drilling risks frequently encountered in penetrating salt sheets has been important progress in all these areas ismore certain to continue and will result in significant new tools and techniques for exploration as a whole less

salt influenced normal fault growth and forced folding the stavanger fault system north sea abstract displacement ratio d r is the ratio between salt thickness t v and sub salt normal fault displacement d d r t v d and it is typically used to predict the degree of geometric and kinematic linkage between sub and supra salt fault populations and the overall structural style in salt influenced extensional settings however we currently lack natural examples of how d r and the underlying geological controls vary and how these may control the three dimensional geometry and evolution of salt influenced normal fault systems furthermore it is currently unknown if kinematic coherence in salt influenced extensional settings can be maintained over relatively long length scales 10 1 10 3 m and for relatively long timeframes and how this may impact the growth and geometry of large throw 500 m salt influenced normal fault systems in this paper we use a 3600 km 2 high quality 3d seismic reflection dataset and borehole data from the stavanger fault system sfs egersund basin eastern north sea basin to investigate i how pre rift salt thickness t v and sub salt fault throw t control the structural style and evolution of a basin bounding salt influenced normal fault system and ii the role salt plays in maintaining kinematic coherence in normal fault systems we demonstrate that i pre rift salt distribution t v specifically its presence in the proto footwall i e when t v 0 is the primary control on partitioning of faulting and forced folding along the fault system and the style of linkage i e hard or soft linkage between sub and supra salt fault populations and ii sub and supra salt fault populations represent brittle elements of a single geometrically and kinematically coherent structure the geometry and evolution of which is related to the ductile translation of strain on a scale up to 8 km and duration c 65 myr that believe is significantly greater and longer than previously documented

metallic sulfide deposits in the winnfield salt dome louisiana evidence for episodic introduction of metalliferous brines during cap rock formation abstract winnfield dome is a shallow piercement salt structure which penetrates late jurassic through early tertiary siliciclastic and carbonate strata of the north louisiana basin quarrying operations in the calcite and anhydrite portions of the cap rock have exposed zones of metallic sulfides and barite within the anhydrite portion of the cap rock sulfides form laminar zones parallel to the tightly intergrown layered anhydrite sulfides occur either as cement between anhydrite grains or as coarse euhedral crystals in open space the sulfide layers are up to several centimeters thick and extend for tens of meters these layers locally thicken into laminated flat bottomed concave downward massive sulfide mounds monoclinic pyrrhotite is the dominant sulfide sphalerite galena or barite may also be present in weathered samples hydrating to gypsum marcasite is common and appears to be an alteration product of pyrrhotite a roughly laminated massive sulfide lens is exposed at the calcite anhydrite transition zone this sulfide body has a maximum thickness of about 5 m 16 ft and extends for about 45 m 150 ft the edges of the lens taper to a layer about 30 cm 1 ft thick which separates the overlying calcite from the anhydrite the massive sulfide lens is comprised of marcasite and pyrite complexly intergrown with calcite gypsum and anhydrite colloform sphalerite galena marcasite pyrite and barite line vugs and fractures pyrrhotite is found locally within the sulfide lens examination of rotary drill samples suggests that massive sulfide concentrations similar to the exposed example are common along the calcite anhydrite transition zone these sulfide concentrations are believed to have originated from the interaction of metalliferous basinal brines with reduced sulfur trapped within the cap rock textural relationships and variations in chemical compositions between the sulfide layers in the anhydrite portion of the cap rock suggest that distinct pulses of metalliferous brines were responsible for the sulfide concentrations anhydrite grains that are completely surrounded by sulfides are euhedral and undeformed similar to the anhydrite disseminated throughout the salt mass anhydrite grains outside the mineralized areas are deformed and tightly intergrown these textures suggest that mineralizing fluids were introduced episodically along the salt anhydrite interface at the zone of salt dissolution before that portion of the anhydrite zone was compressed and accreted to overlying anhydrite cap rock therefore the earliest formed sulfides originating by this mechanism occur at the top of the anhydrite cap rock zone while the last sulfides to form are found at the base extensive sulfide concentrations along the anhydrite calcite contact suggest that this contact also acted as a permeable zone allowing metalliferous brines into the cap rock textural and compositional relationships suggest that sulfides that formed along the anhydrite calcite contact are locally superimposed on sulfides that formed at the salt anhydrite contact

mobilizing salt magma salt interactions salt sequences form an integral part of many sedimentary basins worldwide many of these basins have experienced igneous activity either syn or post deposition of the salt sequences despite this little work has so far been undertaken to understand magma salt interactions within the subsurface and how aspects such as salt halokinesis may be influenced by igneous activity within this paper we detail the first direct description of relationships and textures that are developed during intrusive igneous salt interaction we show that salt composition appears to play a dominant role in controlling where igneous intrusions invade laterally through salt sequences in a sedimentary basin in particular we illustrate that hydrous salts such as carnallite act as preferential horizons for lateral magma intrusion this lithological control appears primarily related to the heating and subsequent dehydration reaction of carnallite which causes the carnallite to behave as viscous fluidal horizons resulting in the non brittle emplacement of magma and spectacular peperitic salt magma mingling textures we suggest that heating and transformation of carnallite and other hydrous salts into viscous fluidal horizons during igneous intrusion within a regional salt sequence may act as a possible trigger for contemporaneous halokinesis by creating fluid like viscous detachment layers over longer time scales however a solidified rigid boxwork of dikes and sills may create zones of increased mechanical strength that will locally inhibit further salt flow

widespread late devonian marine anoxia in eastern north america a case study of the kettle point formation black shale southwestern ontario1 the kettle point formation of southwestern ontario consists of intervals of organic rich interlaminated black shale interbedded with organic poor greyish green mudstones and rare red beds separate

evolution and stratigraphic architecture of marine slope gully complexes monterey formation miocene gaviota beach california abstract three small headlands in the sea cliffs west of gaviota beach california are the remnant fill of three discrete submarine gullies incised into the late miocene submarine slope environment these promontories provide excellent three dimensional exposure of the gully fill in outcrop permitting documentation of their complex internal stratigraphic architecture detailed study of these exposures elucidates the sedimentologic processes that occur in the filling of slope gullies guides interpretation of the acoustic records of otherwise unsampled modern gully systems on continental slopes and provides insight into the heterogeneity that may characterize slope gully petroleum reservoirs we develop a comprehensive facies scheme to describe the variability within these intercalated coarse and fine grained deposits and use two dimensional photopans to interpret the overall depositional system defined by internal bedforms sedimentation units and sediment size each facies records sedimentation under different hydrodynamic conditions and can be genetically related to a discrete depositional mechanism we differentiate channel axis margin and overbank sub environments within the gully fill which together define overall crudely braided low sinuosity channels within the gullies like many modern gully systems the gaviota gullies probably initiated through local slope oversteepening that led to slope failure slumping and initiation of sediment flows erosion and sedimentation from these high density turbidity currents formed the primary depositional process for the gaviota conglomerate units once initiated the gullies acted as sediment conduits from the shelf and possibly onshore regions despite their prevalence on modern upper slopes and their pivotal role in shaping shelf margins and transporting sediment to deeper water the details of submarine slope gully formation and filling remain obscure the gaviota gully complexes provide valuable insights into long term gully fill attributes not easily obtained from modern slope gully systems and rarely preserved in the rock record

doomed pioneers gravity flow deposition and bioturbation in marine oxygen deficient environments isolated horizons of thalassinoides and gyrolithes burrows appear in exclusive association with gravity flow deposits within sequences of nonbioturbated hernipelagic sedimentary rocks of the miocene monterey formation of california and the oligocene miocene san gregorio formation of baja california these burrowed levels are not associated with other ichnogenera such as zoophycos and chondrites we infer a causal relation between gravity flow deposition and the presence of thalassinoides and gyrolithes and suggest that these gravity flows entrained thalassinidean crustacea upon deposition in oxygen deficient environments the surviving borrowers reworked substantial quantities of aminated commonly organic rich sediments in an environment from which they were previously excluded the persistence of or the ecologically rapid return to oxygen depleted conditions limited the survival time and ecological complexity of the transported infaunal dwellers and rendered them doomed pioneers ecological and physiological data support this hypothesis thalassinidean crustacea have the capability to endure turbulent transport and survive up to 5 7 days of anoxia without being severely limited in their biological activities the accurate recognition of doomed pioneer trace fossil assemblages as ephemeral ecological phenomena in otherwise laminated successions may contribute to a better understanding and interpretation of paleo oxygen levels and basin history

stratigraphy and sedimentology of phosphate rich sediments in malta and south eastern sicily latest oligocene to early late miocene the maltese archipelago and south eastern sicily include an uppermost oligocene to upper miocene hemipelagic sedimentary succession representing the malta hyblean plateau which limits the eastern mediterranean to the west this succession hosts a unique and well exposed series of condensed and allochthonous phosphate rich beds which were formed in a sedimentary regime of erosion sediment reworking and frequent gravity flow deposition the combination of nannofossil biostratigraphy and 87sr 86sr isotope stratigraphy allows for the precise attribution of ages to the phosphate deposits and for the distinction of three periods of major phosphogenesis the first phase occurred between 24 5 and 21 ma and 25 and 18 9 ma clustering of ages between 25 and 22 5 ma on malta and sicily respectively the second and third phases of phosphogenesis are documented from the maltese islands and are dated as 17 2 to 13 1 ma and 10 9 to 9 8 ma respectively the phosphate rich beds are associated with hiatuses and phases of important condensation which for the oldest phosphogenic period envelop the time period of 23 2 to 22 ma for the fomm ir rhi bay section malta and from 19 1 to 16 3 ma for the sections of sampieri and modica sicily for the second phase of phosphogenesis on the maltese islands a consistent hiatus was found which embraces the time period of approximately 17 to 15 ma also the third phase of phosphogenesis appears to be associated with a major hiatus which probably envelops the time period between 12 5 and 10 9 ma but a better age control is needed here the correspondence in timing of the maltese sicilian phases of phosphogenesis with major phases of phosphogenesis outside the mediterranean realm to maxima in oceanic phosphorus burial rates and maxima in the 13c benthic foraminiferal record suggests that the palaeoceanographic evolution of the eastern mediterranean was well in phase with that of other ocean basins until at least the early late miocene despite its increasing isolation due to the gradual closure of the eurasian arabian strait and progressive sea level fall

large scale hot water migration systems around salt diapirs in the danish central trough and their impact on diagenesis of chalk reservoirs abstract fracture filling calcite from the piercement fields of east rosa skjold rolf north arne nils and vagn directly underlain by salt diapirs and the dome field dan overlying a deep seated salt structure have been studied by fluorescence and cathodoluminiscence microscopy fluid inclusion microthermometry and carbon and oxygen isotopes the carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured the temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs the flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments the thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water by combining fluid inclusion thermometry with o isotope data for the fracture filling calcites ranges of o isotopic values of the flushing water are deduced in skjold rolf north arne nils and vagn 18o 1 to 7 smow values typical of sedimentary porewater of sea water origin in east rosa 18o 4 and 4 smow which combined with data on fluid inclusion salinities suggest that the flushing waters were responsible for substantial salt dissolution lower 18o values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields in the case of north arne nils vagn and dan 13c values of the fracture filling calcites are similar to those of normal chalk 0 5 to 3 5 however calcites from rolf skjold and east rosa are depleted by 1 8 6 2 and 16 7 respectively only in east rosa is the matrix chalk itself depleted in 13c range 2 0 to 0 7 the low 13c values are interpreted as the result of biodegration sulphate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons this process produced 13c depleted bicarbonate which was incorporated into the fracture filling calcites

effects of the oligocene climatic events on the foraminiferal record from fuente caldera section spain western tethys abstract an expanded succession of upper priabonian upper eocene to chattian upper oligocene hemipelagic marls interbedded with turbiditic sandstone layers is present in the spanish fuente caldera section subbetic zone western tethys we analyzed foraminifera from this section quantitatively with emphasis on biostratigraphy and paleoecology benthic foraminifera indicate an upper to possibly upper middle bathyal depth of deposition for most of the studied section with paleobathymetric analysis made difficult because of the common presence of shallow water taxa some reworked by turbidites and others epiphytic taxa which may have been transported by turbidites or by floating plant material we identified three major biotic and paleoenvironmental events 1 the major planktonic foraminiferal turnover across the eocene oligocene boundary which includes several first and last occurrences as well as a decrease in the percentage of surface water dwellers possibly linked to global cooling 2 a dramatic sea level drop indicated by the presence of a 37 m thick sequence of calcarenites lower half of planktonic foraminiferal zone o2 31 5 ma with abundant trace fossils and allochthonous foraminifera this sea level fall which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin apparently post dated the major glacial expansion on the antarctic continent oi1 33 7 ma and predated the later major expansion oi2 through oi2b 27 30 5 ma thus may have been tectonically controlled 3 a warming event starting in the chattian lowermost part of zone o6 27 1 ma which could be correlated to the globally recognised late oligocene warming event but apparently started somewhat earlier 27 1 ma as compared to 26 5 ma

bioturbation by symbiont bearing annelids in near anoxic sediments implications for biofacies models and paleo oxygen assessments anoxic or nearly anoxic conditions 4 m o2 have long been associated with the absence of bioturbation and animal traces this premise has guided interpretation of paleoceanographic conditions from rocks and sediments we recently observed a high density living assemblage of highly mobile symbiont bearing burrowing phallodrilinid oligochaetes within a nearly anoxic basin 1 m o2 0 02 0 03 ml l 1 on the peru margin 305 m these observations were made during the most intense part of the 1997 98 el nino when there may have been slight oxygenation of an otherwise anoxic basin but oligochaete presence prior to this event is likely the occurrence of symbiont bearing gutless oligochaetes mainly within the upper 5 cm of the sediment column coincided with a bioturbated zone overlying distinctly laminated sediments our observations redefine the lower oxygen limit of macrofaunal bioturbation to 2 m and indicate a need to modify currently accepted ideas about the relationship between bioturbation and paleo oxygen concentration these results also address an ongoing debate about the lifestyles of bioturbating organisms in oxygen poor settings

post cambrian closure of the deep water slope basin taphonomic window exceptional faunas konservat lagerstatten that preserve traces of volatile nonmineralized tissues are statistically overabundant in the cambrian period almost all examples preserved in continental slope and shelf basin environments are of this age the hypothesis that an increase in the amount and complexity of bioturbation was an important agent in the elimination of this deep water slope basin taphonomic window is supported post cambrian ichnofaunal assemblages contain a higher proportion of pascichnia and agrichnia ethologies produced by a mobile infauna they also illustrate the lateral partitioning of organisms into different environmental niches both opportunistic and equilibrium infaunas occur in low oxygen environments in which the preservation of nonbiomineralized tissues was favored direct consumption of carcasses by bioturbating organisms was less important than changes to sediment properties as a result of bioturbation notably enhanced microbial degradation of reactive organic matter increased permeability and the disruption of geochemical gradients necessary for mineral authigenesis

active and passive imaging of hydraulic fractures hydraulic fracturing is a method commonly used to stimulate production in low permeability reservoirs with this method a viscous polymer based fluid is injected into the formation opening a fracture perpendicular to the direction of least principal stress this is followed by injection of a suspension of sand in liquid proppant which prevents the fracture from closing after the fluid pressure is allowed to bleed off after a fracture treatment the reservoir can be produced from the vicinity of a fracture surface which is substantially larger than the surface of the borehole

salt usually seals but sometimes leaks implications for mine and cavern stabilities in the short and long term abstract thick evaporite masses bedded and halokinetic dominated by the mineral halite are currently mined using conventional solution mining techniques after excavation the resulting salt cavities are sometimes used as subsurface storage vessels for hydrocarbons or various types of waste including low level nuclear waste there are plans being discussed to use purposed designed solution cavities in thick salt masses for the long term storage of high level nuclear waste if high level nuclear waste is ever to be safely stored in salt it will involve a need for the encasing salt not to leak over time frames measured in tens of thousands of years understanding how where and why accessible salt masses leak is the rationale for this review it is the first step in assessing it a particular site s salt geology is suitable for storage we know salt can act as an excellent longterm seal over hundreds of thousands of years as evidenced by its ability to hold back significant columns of highly overpressured fluids even in structurally complex settings but we also know that locally salt bodies do occasionally leak large volumes of fluid as evidenced by the loss of a number of salt mines to uncontrolled floods the rapid creation of solution dolines atop subcropping salt masses and to black salt haloes around highly pressurized hydrocarbon reservoirs these types of leakage are usually tied to the edges of a salt body being exposed to longterm crossflows of undersaturated pore waters or to the build up of internal pressure to levels that exceed lithostatic in fact most zones where a salt body is liable to leak or has leaked are indicated by anomalous textural or mineralogical features when compared to the regional character of the salt the time of leakage can be early eogenetic related to burial mesogenetic or related to uplift telogenetic if the salt mass is not entirely dissolved in the fluid crossflow then the remaining salt tends to re seal especially in zones of ongoing salt flow however if non salt sediment remains in the re annealed salt mass it will tend to retain permeability and when intersected in a salt mine or by a well bore it will flow fluid more problematic in terms of significant leakage are zones in contact with an aquifer external to the salt mass these anomalous areas can transfer large volumes of fluid for this reason active telogenetic anomalies in a salt mass are the most problematic in terms of both mine safety and waste storage identifying the type of salt anomaly the time in diagenesis when leakage occurred and proximity and volume of intersected fluids in the zone of leaking salt is fundamental to mine safety and reliable waste storage

pliensbachian environmental perturbations and their potential link with volcanic activity swiss and british geochemical records abstract the mechanisms leading to environmental and climate change prior to and anticipating the well studied toarcian oceanic anoxic event are not completely understood specifically the role of the continuing break up of pangea associated palaeogeographic rearrangements and the influence of volcanic activity are less well known therefore we studied the pliensbachian interval in the open marine hemipelagic section of the breggia gorge in southern switzerland to elucidate the potential impact of these major changes on the environment and climate we identified carbon isotope excursions towards lower values in whole rock carbonates dated from the sinemurian pliensbachian boundary davoei margaritatus and spinatum zones and possibly from the pliensbachian toarcian boundary using the whole rock oxygen isotope record and phosphorus content we associated these events with phases of increased runoff possibly related to climate warming we also established the first mercury hg record for the entire pliensbachian and in order to verify its validity we analysed an additional section located along the dorset coast in southern england the presence of hg spikes common in both sections may indicate the influence of episodes of increased volcanic activity the hg spike during the earliest pliensbachian may coincide with a late phase of the central atlantic magmatic province and or increased rifting linked with the opening of the hispanic corridor further significant maxima in hg contents are observed within the davoei and margaritatus zones and both phases may correspond to early volcanic activity of the karoo ferrar large igneous province further analyses are however needed to corroborate this interpretation and evaluate the importance of organic matter scavenging and detrital input in comparison to volcanic activity

association between wave and current aided hyperpycnites and flooding surfaces in shelfal mudstones an integrated sedimentologic sequence stratigraphic and geochemical approach

definition of sequences through ichnocoenoses and taphofacies an example from the sacaras formation early cretaceous eastern spain abstract an integrated taphonomical ichnological and sedimentological analysis has been carried out on the albian deposits of the sierra helada section province of alicante southeastern spain this allowed recognition and detailed characterization of the shallowing and coarsening upward sequences present in these deposits twenty sequences were detected throughout the section they contain the following from bottom to top 1 the bottom of the sequence characterized by very fine grained marls rich in echinoid tests and echinoid trace fossils with very little evidence of physical reworking it records a distal platform low energy environment 2 marls interbedded with fine grained calcarenites rich in large thalassinoides and slightly reworked echinoid tests with common bioclast armored tubes ereipichnus geladensis recording low energy background conditions but increasing energy of the sedimentary events 3 coarse grained calcarenites rich in different types of small to large thalassinoides and e geladensis horizons showing the intense and frequent action of storms and directed currents on the seafloor and 4 coarse grained cross bedded calcarenites rich in ophiomorpha nodosa deposited under high energy background conditions in the shallowest part of the sequence recording the presence of shifting dunes in the inner platform occasionally also the record of a rapid transgression has been pointed out through the presence of condensed tapho and sedimentary facies and mixed ichnocoenoses at the top of the sequence just after an erosive surface the defined ichnoceonoses and their distribution throughout the sequence reflect the shifting from a distal expression of the cruziana ichnofacies to the shallower archetypal cruziana ichnofacies and finally to the high energy shallow water skolithos ichnofacies the distribution of taphofacies and ichnocoenoses and development of the sequences all through the section show a general transgression followed by a regressive phase which fit with the third order curves described for the area on the basis of pure sedimentological analysis in previous studies castro et al 2008

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

supra salt normal fault growth during the rise and fall of a diapir perspectives from 3d seismic reflection data norwegian north sea abstract normal faulting and the deep subsurface flow of salt are key processes controlling the structural development of many salt bearing sedimentary basins however our detailed understanding of the spatial and temporal relationship between normal faulting and salt movement is poor due to a lack of natural examples constraining their geometric and kinematic relationship in three dimensions to improve our understanding of these processes we here use 3d seismic reflection and borehole data from the egersund basin offshore norway to determine the structure and growth of a normal fault array formed during the birth growth and decay of an array of salt structures we show that the fault array and salt structures developed in response to i late triassic to middle jurassic extension which involved thick skinned sub salt and thin skinned supra salt faulting with the latter driving reactive diapirism ii early cretaceous extensional collapse of the walls and iii jurassic to neogene active and passive diapirism which was at least partly coeval with and occurred along strike from areas of reactive diapirism and wall collapse our study supports physical model predictions showcasing a three dimensional example of how protracted multiphase salt diapirism can influence the structure and growth of normal fault arrays

kilometre scale thermohaline overturn of pore waters in the louisiana gulf coast convincing evidence exists for the large scale convection of sea water through the upper oceanic crust even at considerable distances from mid ocean ridges1 2 there has been considerable interest in verifying the existence of convective overturn of pore fluid in large sedimentary basins a mass transport process which could profoundly influence the transport of heat hydrocarbons metals and diagenetically reactive dissolved constituents3 4 the existence of fluid convection in sediments of the united states gulf coast has been inferred on the basis of the large volumes of fluid necessary to account for the observed diagenetic alteration5 and the existence of thermal anomalies that cannot be explained by simple conductive transport of heat3 6 theoretical rayleigh darcy calculations6 7 support the notion that thermally driven convection is possible here i present geochemical and physical evidence for the existence of density inversions in gulf coast pore fluids sufficient to drive large scale convective fluid flow at rates conceivably as high as metres per year the density inversions are caused in part by the dissolution of salt diapirs and the formation of dense saline brines at shallow depths

cyclically arranged storm controlled prograding lithosomes in messinian terrigenous shelves bajo segura basin western mediterranean abstract this work focuses on a messinian shallow marine terrigenous unit termed the la virgen formation which forms part of the sedimentary infill of the bajo segura basin betic margin of the western mediterranean this formation was deposited during a high sea level phase prior to the onset of the messinian salinity crisis stratigraphically it comprises a prograding stack of sandstone lithosomes alternating with marly intervals 1st order cyclicity these lithosomes are characterized by a homoclinal geometry that tapers distally and interfinger with pelagic sediments rich in planktonic and benthic microfauna torremendo formation an analysis of sedimentary facies of each lithosome reveals a repetitive succession of sandy storm beds tempestites which are separated by thin marly layers 2nd order cyclicity each storm bed contains internal erosional surfaces 3rd order cyclicity that delimit sets of laminae two categories of storm beds have been differentiated the first one includes layers formed below storm wave base swb characterized by traction structures associated to unidirectional flows the second category consists of layers deposited above the swb which display typical high regime oscillatory flow structures the 1st order cyclicity recorded in the la virgen formation corresponds to sapropel homogeneous marl precessional cycles formed in a pelagic basin context torremendo formation

pressure solution in chalk pressure solution residues in the cretaceous to paleocene chalk from the north sea area were studied to understand the pressure solution process and fluid flow residue seams reach lengths and thickness of more than 800 and 0 15 m 2625 and 0 5 ft respectively seams can present significant barriers to fluid flow because they have nannodarcy permeability and hold back large pressure differentials stylolite amplitudes decrease when they merge making it difficult to quantify volume loss measuring amplitudes allows volume loss estimates using a new dissolution ratio method the sum of the thicknesses of all residues is multiplied by the maximum amplitude to residue thickness ratio on average 30 mm 1 2 in of chalk had to be dissolved to produce a 1 mm 0 04 in thick residue the volume loss of chalk from flamborough averages about 50 and is 60 in the machar oil field united kingdom central graben the minimum fluid volume required to produce the volume loss in 1 unit volume of preserved chalk on the machar field is estimated to be 8000 unit volumes this and the stable isotopes of vein carbonates imply that the pressure solution process involved an open fluid system high illite content in mixed layered illite smectite and high illite crystallinity of clays in the pressure solution seams in the machar reservoir indicate high diagenetic maturity with implied temperatures in the range of 200 360c 392 680f which is greater than the present day reservoir temperature of 85c 185f the anomalously hot temperatures are interpreted to be produced by deep mineralizing fluids transported from the central graben the lack of abundant veining in the chalk and the large fluid volumes involved in the chalk dissolution suggest that this was an open pressure solution system

spatial variations in subsurface pore fluid properties in a portion of southeast louisiana implications for regional fluid flow and solute transport abstract fluvial deltaic deposition growth faulting and salt diapirism in the tertiary section of southeast louisiana have combined to produce a structurally complex geologic framework which contains potential pathways for large scale lateral and vertical fluid migration a study has been made of spatial variations in pore water salinity temperature pressure density and viscosity to a depth of 10 000 ft 3 km in a five parish area situated across the northern margin of the south louisiana salt basin to help identify driving forces and pathways for subsurface fluid migration and solute transport three regional hydrologic flow regimes can be defined in the area as a function of depth 1 a shallow hydropressured meteoric flow regime which is driven by differences in topographic elevation 2 an intermediate depth hydropressured thermohaline regime apparently driven in part by variations in pore water density and 3 a deep geopressured regime driven by high pore fluid pressure gradients although the sediments in the area originally contained fresh to marine waters at the time of deposition the interval between 2000 and 10 000 ft is now largely filled with hypersaline waters these brines are derived from the dissolution of salt domes which act as local sources for both saline waters and heat some domes have salinity plumes that extend thousands of feet above the top of salt and many miles laterally two areas in which overpressured saline brines are apparently migrating upward along radial faults into the overlying hydropressured zone appear to be related to deep seated salt structures faults and lack of lateral continuity of interbedded shales have made the sand dominated section to a depth of 10 000 ft hydrologically open on a sub regional scale significant temperature pressure and salinity gradients have made it hydrologically dynamic of economic interest is the possible relation of hydrocarbon migration to the migration of pore water and dissolved salt

evidence for episodic basin dewatering in salt dome cap rocks a detailed record of episodic basin dewatering events is preserved in the anhydrite cap rocks of two gulf coast salt domes metalrich brines were intermittently expelled from geopressured zones deep in the stratigraphic section and were channeled upward along escape structures bounding the salt diapirs overhanging anhydrite cap rock helped to focus some escaping fluid into the zone of dissolution between the top of salt and overlying residual anhydrite cap rock iron lead and zinc sulfide solubilities were exceeded in this zone possibly in response to dissolution and reduction of cap rock sulfates because the metalliferous brines entered the dissolution zone intermittently they were recorded as relatively thin horizontal bands of sulfide sandwiched between thicker accumulations of anhydrite continued dissolution of salt and underplating of residual anhydrite caused the sulfide bands to be displaced upward relative to the base of the cap leading to an inverted stratigraphic record of basin dewatering events paleomagnetic data from the winnfield salt dome suggest that sulfide producing basin dewatering events and anhydrite cap rock accumulation occurred between 157 and 145 ma

origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep sided salt structures egersund basin northern north sea the ingress of meteoric fluids into the crests of salt structures typically results in the formation of anhydrite dominated caprock the migration of connate fluids up the margins of salt structures has also been documented although the products related to this are rarely sampled in the deep subsurface we use 3d seismic reflection and borehole data to document the geometry and lithology of a salt diapir seismic data suggest that a weld is developed along the diapir stem although borehole data indicate that the stem consists of an inner c 1500 m thick halite dominated zone and an outer c 250 m thick anhydrite dominated sheath the anhydrite may have formed early in the basin history as a depositional anhydrite or crestal caprock an alternative interpretation is that the anhydrite represents lateral caprock which formed late in the basin history in response to the migration of nacl poor fluid up the margins of the diapir and dissolution of halite the possibility that lateral caprock may form adjacent to salt structures has implications for understanding the patterns and vigour of groundwater flow in sedimentary basins furthermore our study shows the margins of steep sided salt structures may be misidentified by several hundred metres if time migrated seismic reflection data are used

ephemeral thermal and solute plumes formed by upwelling groundwaters near salt domes geochemical observations made by previous workers indicate that rapid upward advection of hot water has occurred along the flanks of some salt domes in the northern gulf of mexico basin and in the danish central trough the observations are based on pore fluid chemistry and on high temperatures of formation of metal sulfides and other diagenetic minerals near the crests of salt domes some of the diagenetic minerals formed at 40 c to 80 c above the ambient temperature of the host rocks numerical simulations of coupled heat and dissolved salt transport show that thermal perturbations in excess of 60 c can be repeatedly produced near the crest of a salt dome by focused dewatering of a thick strongly overpressured sedimentary interval around the dome in our simulations dewatering was triggered and stopped by cyclically changing the permeability at the salt sediment interface the thermal plumes dissipated within 100 kyr after dewatering ceased stratigraphically shallow brine plumes were also formed by dewatering and these gravitationally unstable plumes dissipated more slowly by sinking within 1 m y simulations showed that free thermohaline convection can also generate thermal perturbations near the crest of a dome in this mode of upwelling thermal perturbations reached 30 c when the vertical permeability of the hydrostatically pressured interval was 10 14 m2 10 mdarcy because such permeabilities seem large for the hydrostatically pressured interval as a whole in the northern gulf of mexico basin the formation of high temperature metal sulfide deposits near the crests of salt domes seems more likely to be due to dewatering of the overpressured interval with very strong focusing of expelled waters along the flanks of salt domes

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

the sediment proximity survey or how to find the salt flank surprises happen while drilling a prospect on the flank of a salt body you may in fact find that the drill penetrates into the salt although every effort may have been made to map the salt face via surface seismic data this is not always achieved with the needed level of accuracy several factors contribute to this uncertainty including the depth and dip of the salt face the complexity of the overlying section and how well it can be characterized poor seismic illumination of the salt flank the seismic acquisition parameters the data processing sequence and the overall quality of the resulting seismic survey

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

evidence for high energy events and shallow water deposition in the chattanooga shale devonian central tennessee usa abstract the upper devonian chattanooga shale of central tennessee a classical black shale was deposited in an epicontinental setting west of the appalachian foredeep its finely laminated and highly carbonaceous nature is commonly interpreted to indicate deposition in comparatively deep and stagnant water interbeds of bioturbated greenish gray shale indicating oxygenated bottom waters are commonly ascribed to pycnocline fluctuations however laminated fine sand and silt and hummocky cross stratification hcs at the base of some of these beds indicates interaction of storm waves with the seabed and suggests that greenish gray shale beds are post storm mud drapes other interesting features are inclined undulose erosion surfaces that are conformably overlain by shale beds sets of inclined shale beds that suggest low angle cross bedding and clearly and uniformly developed alignment of clay particles magnetic fabric studies these observations show that the seabed was at times subject to prolonged erosion by bottom currents erosion surfaces agitation and reworking by storm waves hcs and greenish gray shale beds and sediment transport by long lived bottom currents particle alignment the epicontinental sea setting and the presence of hcs and other storm produced features suggest a relatively shallow water depth possibly only a few tens of meters together with abundant evidence of variably strong bottom currents and bioturbation of black and gray shale beds this suggests that abundant planktonic organic matter production rather than stagnant bottom waters are the primary cause for black shale formation

physiography of the ne margin of the permian salt basin new insights from 3d seismic reflection data three dimensional seismic reflection data from the egersund basin offshore norway image geomorphological features that record mid permian footwall degradation of basin bounding fault systems this ancient landscape was subsequently flooded during the pan european late permian transgression of the north permian salt basin and was fossilized beneath zechstein supergroup evaporites we provide the first conclusive evidence for pre zechstein normal faulting in the egersund basin indicating that extensional strain was shared between permian and late jurassic early cretaceous rift events supplementary materials uninterpreted versions of the seismic sections shown in figure 2 are available are available at www geolsoc org uk sup18678

trace fossils and their palaeoecological significance in lower cretaceous lacustrine conservation deposits el montsec spain abstract la pedrera and la cabrua at el montsec spain are two lower cretaceous lacustrine conservation deposits konservat lagerstatten that have provided a rich diverse and well preserved faunal and floral fossil record although the lithographic limestones where the body fossils are found are finely laminated and essentially undisturbed by bioturbation epigenic trace fossils occur on the surface of certain laminae trace fossils at la pedrera include the fish trail undichna britannica and the arthropod trackway hamipes didactylus while the ichnospecies found at la cabrua are steinsfjordichnus brutoni gordia arcuata cochlichnus anguineus and undichna britannica all but the last corresponding to the activity of small invertebrates the trace fossil occurrences record short term events in a lake bottom that did not support any benthic life for most of its history differences in the trace fossil assemblages for the two localities agree with sedimentological data in attributing a more distal position for la pedrera

the significance of the boundary between the rhoscolyn and new harbour formations on holy island north wales to the deformation history of anglesey the boundary between the rhoscolyn and new harbour formations on holy island anglesey has been described as a high strain zone or as a thrust the boundary is here described at four localities with reference to the contrasting sedimentary and deformational character of the two formations at one of these localities borth wen sandstones and conglomerates at the top of the rhoscolyn formation are followed without any break by tuffs and then mudstones of the new harbour formation it is concluded that there is clear evidence of depositional continuity across the boundary here and that both formations subsequently shared a common two phase deformation the first d1 was manifestly different in intensity and scale in the two formations whereas the second d2 produced very similar structures in both the other three localities provide continuity of sedimentary and tectonic features at this boundary in a traverse along the length of holy island leading us to identify two previously unrecognized major d1 folds in addition to the rhoscolyn anticline at one of these localities holyhead we confirm the presence of skolithos just below the boundary supporting radiometric evidence for a lower cambrian or later age for the rhoscolyn formation a turbidite interpretation for both the rhoscolyn and new harbour formations best fits the available evidence a deep water depositional environment is still compatible with the sporadic presence of skolithos burrows but less so with reported observations of hummocky and swaley cross stratification lower down the south stack group

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

bioturbated oxygenation event beds in siliceous facies monterey formation miocene california abstract predominatly laminated marine diatomaceous sequences deposited in oxygen deficient neogene basins typically contain bioturbated intervals that reflect episodes of improved benthic oxygenation excellent exposures of the siliceous facies of the miocene monterey formation near lompoc central california provided an opportunity to assess the ichnology and sedimentology of 200 such event beds in their general paleogeographic paleoclimatic and sea level context and hence to evaluate the character and causes of associated oxygenation episodes four recurring event bed types type i iv are distinguished on the basis of ichnologic characteristics these types fall into two general groups delineated on the basis of sedimentologic attributes primarily texture group 1 beds type i only have 1 homogeneous bioturbate primary strata that are more clastic rich and much coarser than surrounding laminated diatomites and 2 vertically extensive piped zones characterized by firmground thalassinoides paradoxicus glossifungites ichnofacies these characteristics indicate that group 1 events involve coincident increases in bottom current intensity clastic input and benthic oxygenation some group 1 beds may be the product of turbidity current transport of sediments trauma resistant crustaceans and allochtonous waters however most group 1 beds more likely record climate and sea level mediated migratio of incipient bank top conditions down the flank of a submergent topographic high group 2 beds types ii iii and iv are characterized by primary strata that are only slightly coarser and more clastic rich than surrounding laminites ichnofabrics and trace fossil assemblages which are dominated by burrows of deposit feeders thalassinoides suevicus meniscate backfilled structures and chondrites reflect normal softground substrates and quiet water pelagic deposition zoophycos ichnofacies differences in ichnologic parameters bed thickness adn presence diversity size and vertical extent of discrete burrows in primary strata and or piped zones among the bed types within this group reflect differences in magnitude duration and to a lesser extent frequency of oxygenationepisodes coincident increases in oxygenation and clastic content recorded by group 2 beds are attributed to e1 nino like climatic events gross temporal patterns in the intensity and frequency of these climatic events appear to be linked to the phases of a third order sea level cycle whereas shorter term variations 100 120 ka may have been mediated by milankovitch cyclicity relationships established between bioturbation events and relative water depth are of potential use in reconstructing basin paleogeography and or recognizing the signal of sea level change in the monterey formation and other neogene siliceous sequences

free thermohaline convection beneath allochthonous salt sheets an agent for salt dissolution and fluid flow in gulf coast sediments basinward migration of jurassic salt in the u s gulf of mexico has resulted in the emplacement of large allochthonous salt sheets into shallow miocene to holocene sediments although comparatively little direct information is available on the environment below these salt bodies it is reasonable to suppose that the formation of dense brines by dissolution of the base of these sheets may induce free thermohaline pore fluid convection within the sediments below we derived equations which make it possible to quantitatively estimate rates of dissolution of these subsurface salt structures from these calculations and by geologically realistic numerical simulations it can be shown that free convection beneath allochthonous salt sheets has the potential for being a significant mechanism for both salt dissolution and mass transport even if the underlying sediments have permeabilities as low as 10 17 m2 0 01 md the calculated maximum darcy fluxes and rates of salt dissolution rapidly increase with sediment permeability when the vertical permeability of the underlying sediment is 10 17 m2 0 01 md salt is dissolved from the base of the sheet at an average rate of 3 5 m m y 1 the corresponding fluid velocities are such that over a 10 m y period the integrated fluid flux in the underlying sediments would be 104 m3 m 2 by comparison integrated fluid flux for compactive expulsion is 103 m3 m 2 thus for the offshore sediments of the gulf of mexico thermohaline convection beneath an allochthonous salt sheet is a significant driving mechanism for fluid flow with potentially important implications for heat and mass transport diagenesis and salt tectonics

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

the control of salt supply on entrainment of an anhydrite layer within a salt diapir the influence of four parameters sedimentation rate viscosity of salt stratigraphic location of the anhydrite layer within the salt layer and the perturbation width on salt supply to down built diapirs and its entrainment capacity are studied systematically in numerical models model results show that these four parameters affect salt supply and the evolution history of a salt diapir as such these parameters strongly influence the style and the amount of entrainment of dense inclusions into a diapir in active diapirs i e unburied diapirs salt supply increases with increasing sedimentation rate whereas it decreases with an increase in salt viscosity diapirs initiating from wide perturbation provide more salt supply to feed the diapir presence and initial stratigraphic location of any denser layer e g an anhydrite layer within a salt layer also affects salt supply when lateral forces are negligible salt supply into a diapir depends on these four parameters which directly control the entrainment of any embedded anhydrite layer into the diapir

evolution of the nw margin of the north permian basin uk north sea mapping of depositional zones within the zechstein supergroup using semi regional 2d and 3dseismic data constrains the geological evolution of the northwestern margin of the north permian basinin uk offshore quadrants 14 15 19 20 and 21 four depositional zones are identified on the basis of mappable seismic facies which are assumed to vary with halite content well control characterizes the most reflective seismic facies as an interbedded carbonate and anhydrite shelf succession which grades laterally through clastic rich sequences to the least reflective a thick halite basinal equivalent the trendsof the depositional zones illustrate the geometry of the north permian basin and may have been locally controlled by basement lineaments within the north permian basin a n s trending axis devil s hole high characterized by thick reflective facies separates the central north sea from the forth approaches basin basement fault blocks control facies type and thickness along the northwest margin of the north permian basin in the moray firth area permian tilt of the zechstein shelf related to regional flexure played a role in precipitating gravity driven tectonics within the seismically reflective facies on the east flank of the devil s hole high this permian phase of salt tectonics resulted in numerous intra zechstein structures which can be interpreted as rafted and folded zones of interbedded halite carbonate sulphate and clastics the rafts initially slid downdip towards the main halite basin then their evolution became dominated by differential subsidence of the interbeds which forced salt layers into adjacent passive diapirs this episode predates deposition of the triassic smith bank shales which rest upon the zechstein with local angular unconformity the spatial distribution of zechstein facies influenced the tectonostratigraphy of the triassic jurassic and cretaceous systems boundaries between zechstein facies correspond to the limit of triassic halokinesis on the west central shelf and the limit of detachment of jurassic and lower cretaceous thin skinned tectonics in moray firth half graben

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

estimation of the physical petrophysical and mineralogical properties of messinian salt rocks sicily implications for multidisciplinary applications abstract the messinian salinity crisis msc was a short term 5 96 5 33ma and dramatic paleoenvironmental event which led to the deposition of a thick evaporitic layer throughout mediterranean area however several studies have demonstrated that messinian evaporites have different characteristics and properties from east to west in the mediterranean area and the caltanissetta basin sicily west mediterranean provides an excellent messinian onshore record for investigating evaporitic succession given the scarcity of representative halite samples and at the same time widespread research and scientific drilling in the mediterranean area new physical mechanical petrophysical mineralogical and thermal characterization of messinian halite could provide useful information for several disciplines and applications hence 50 samples of messinian halite were obtained from a sicilian mine italkali analyzed and tested using different instruments ultrasound velocities measured under hydrostatic confining pressure up to 120 mpa ranged from 4210 to 4780 m s and 2510 2650 m s respectively for p and s waves the results further showed that the halite samples had low porosity 2 5 8 5 and negligible permeability demonstrating the weak presence of pores and the total lack of interconnection among them which is typical of rock salt units densities of the halite determined with the hydrostatic weighing method and gas porosimeter were low and ranged from 2 14 to 2 23 g cm3 while high values were obtained for thermal conductivity 17 0 and 32 0 c it is significant that the mineralogical heterogeneity of the halite was due to the presence of clay bearing veins although this work was performed mainly using onshore data and observations the results have wider applications for offshore studies of the msc and its deposits furthermore the study provides important insights for future mediterranean drilling projects geological modelling hydrocarbon exploration and or fluids storage and the understanding of salt rheology under different conditions of pressure and temperature

seismic interpretation and characterization of anhydrite caprocks in the tromso basin sw barents sea abstract the origin of anhydrite caprocks found in many evaporite basins is currently under debate existing models in the literature for anhydrite formation include rotated stratigraphic layering rotated crestal caprock and diagenetic anhydrite in this work we interpret high quality 2d seismic reflection data to understand the processes associated with anhydrite caprock formation our study focuses on anhydrite caprock formation in the tromso basin which represents one of several underexplored salt basins in the arctic we use well log data and seismic stratigraphic as well as seismic attribute analyses to characterize the anhydrite layers associated with salt diapirs our results reveal that the anhydrite layers are high amplitude reflections at the crests which are often found close to the seabed and lateral caprocks on the flanks of salt diapirs a third class of anhydrite layers is folded faulted and boudinaged intrasalt stringers encased by the salt diapirs lateral caprocks in the tromso basin are formed in response to rotated crestal caprock failure the crestal caprocks are secondary in origin occur at shallow depths and are formed as insoluble residues from the dissolution of halite by the ingress of basinal fluids into the tops of diapirs anhydrite stringers or floaters originate from tectonic related multi dimensional salt flow salt diapirs in the tromso basin are associated with varied anhydrite caprocks their formation cannot be fully explained using a single model our work demonstrates from seismic reflection data the occurrence of caprock events that formed progressively on the flanks of salt diapirs due to local folding

geomechanical analysis of a welding salt layer and its effects on adjacent sediments abstract we simulate welding of the source layer of a salt diapir with a forward finite element model and study stresses and deformation in the salt layer and the diapir as well as in their adjacent sediments welded salt layers are abundant in mature salt basins where most or all of the salt has withdrawn into diapirs however there is little understanding of the stress field in these layers and their adjacent sediments we show that salt flow along the source layer leads to significant stress anomalies inside the layer and in adjacent sediments in the source layer salt pressure becomes higher than overburden stress in nearly welded areas and becomes lower than overburden stress in adjacent thicker areas when the source layer welds stresses increase significantly in sediments near the weld tip which helps compaction of these sediments and possibly their fracturing and faulting our model illustrates that all sediments overlying the weld experience this stress increase and the associated material changes as the weld tip propagates along the weld we present natural examples fitting our predictions and discuss the importance of our results for the exploration characterization and production of reservoirs near welded salt layers

igneous mineralogy at bradbury rise the first chemcam campaign at gale crater textural and compositional analyses using chemistry camera chemcam remote microimager and laser induced breakdown spectroscopy libs have been performed on five float rocks and coarse gravels along the first 100 m of the curiosity traverse at bradbury rise chemcam the first libs instrument sent to another planet offers the opportunity to assess mineralogic diversity at grain size scales 100 m and from this lithologic diversity depth profiling indicates that targets are relatively free of surface coatings one type of igneous rock is volcanic and includes both aphanitic coronation and porphyritic mara samples the porphyritic sample shows dark grains that are likely pyroxene megacrysts in a fine grained mesostasis containing andesine needles both types have magnesium poor basaltic compositions and in this respect are similar to the evolved jake matijevic rock analyzed further along the curiosity traverse both with alpha particle x ray spectrometer and chemcam instruments the second rock type encountered is a coarse grained intrusive rock thor lake showing equigranular texture with millimeter size crystals of feldspars and fe ti oxides such a rock is not unique at gale as the surrounding coarse gravels such as beaulieu and the conglomerate link are dominated by feldspathic andesine bytownite clasts finally alkali feldspar compositions associated with a silica polymorph have been analyzed in fractured filling material of preble rock and in stark a putative pumice or an impact melt these observations document magmatic diversity at gale and describe the first fragments of feldspar rich lithologies possibly an anorthosite that may be ancient crust transported from the crater rim and now forming float rocks coarse gravel or conglomerate clasts

salt dissolution and salt related deformation of the forth approaches basin uk north sea abstract this paper addresses the potential role of regional scale salt dissolution as a mechanism responsible for salt related deformation this analysis is based on an investigation of the late permian to triassic succession of the forth approaches basin on the nw margin of the north permian basin and makes use of a regional 2d seismic grid tied to five key exploration wells this basin is ideal for this study because it consists of a deformed central region with a ne sw trending axis and an undeformed periphery which provides a template and key datums for reconstruction of the adjacent zone of deformation structural styles in this zone include simple salt cored anticlines salt walls salt diapirs detachment faults and unusually for the north sea intra zechstein salt cored folds pre triassic detailed mapping was carried out in uk block 26 10 and this shows that the dominant structural trend is ne sw suggesting that basement tilting influenced structural development the stratal geometry of the numerous triassic mini basins is used to constrain the way in which accommodation space in the mini basins was created by depletion of mobile salt the spatial pattern of salt depletion can be accounted for by two contrasting mechanisms or some combination thereof 1 deformation through downbuilding during a phase of regional subsidence or 2 flow induced by regional salt dissolution volumetric arguments necessary to discriminate between these two mechanisms are inconclusive due to later deformation of the top zechstein datum selective preservation of z3 and z4 cycles of the zechstein over large parts of the block 26 10 study area suggests that much of the salt depletion process preferentially removed z2 halite this observation is compatible with a process of subjacent dissolution possibly resulting from low salinity groundwater circulating in the pre zechstein aquifers

the influence of mechanically weak layers in controlling fault kinematics and graben configurations examples from analog experiments and the norwegian continental margin fault systems in extensional basins commonly display geometries that vary with depth reflecting depth and lithology dependent mechanical strength using an experimental approach we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle ductile sand silicone polymer sequences subject to single and polyphase deformation the experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature the latter being representative of decollement horizons experiments series 1 s1 using homogeneous and stratified quartz and feldspar sand produced asymmetric composite single grabens with diverse fault frequencies and fault styles for the graben margin faults for the mechanically stratified experiments with one decollement level series 2 contrasting graben configurations were produced in that the lowermost sequence was characterized by graben geometries of similar type to that of the s1 experiments whereas the sequence above the decollement was characterized by large fault blocks delineated by steepened or oversteepened faults the experiments with two decollements series 3 were displayed similarly but included graben geometries that widened upward with each level being characterized by independent fault systems the results can be used to explain strata bound fault patterns and depth dependent extension as seen in several places along the norwegian continental margin and elsewhere

high temperature diagenesis in shallow chalk reservoir skjold oil field danish north sea evidence from fluid inclusions and oxygen isotopes samples of calcite filled fractures from the chalk reservoir of the skjold oil field were studied by fluorescence microscopy cathodoluminescence microscopy fluid inclusion microthermometry and oxygen and carbon stable isotope and trace element analyses two generations of calcite infilling are tentatively related to two major phases of faulting caused by salt movements owing to recrystallization of the first generation of infillings the chemical isotopic and fluid inclusion data only apply to the later generation results of the fluid inclusion studies suggest a precipitation temperature of the infilling calcite significantly above what it should be applying today s geothermal gradient 52 c km or 2 85 f 100 ft to the past this higher temperature indic tes that hot water ascending from deeper strata may have flushed the reservoir apparently during a late miocene to pliocene faulting phase when ring faults guided the water to the reservoir this feature may be typical of most chalk reservoirs in the danish central graben where diapirs have penetrated the chalk

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine