treptichnus pedum and the ediacaran cambrian boundary significance and caveats the ediacaran cambrian e c boundary is based on the first appearance of the ichnofossil treptichnus pedum investing an ichnotaxon with such biostratigraphic pre eminence has been the focus of criticism points of contention have revolved around four main issues 1 ichnotaxonomy 2 behavioural significance 3 facies controls and 4 stratigraphic occurrence first confusion results from the fact that treptichnus pedum was originally referred to as phycodes pedum and more recently some authors have placed it in trichophycus or manykodes however the overall geometry of these burrows indicates they belong in treptichnus second regardless of its precise mode of feeding the behaviour involved is iconic of the cambrian explosion third objections are based on the idea that trace fossils show a closer link to facies than body fossils notably in contrast to common assumptions t pedum is not only present in the low energy offshore of wave dominated marine settings but it occurs at considerably shallower water in intertidal and shallow subtidal zones of tide dominated systems as well as in mouth bars of deltaic systems and lower shoreface to offshore transition zones of wave dominated marine settings its broad environmental tolerance supports evolutionary innovations rather than facies controls as the main mechanism underlying the observed vertical pattern of distribution of t pedum in most e c successions comprising shallow marine deposits fourth although treptichnids have been documented below the e c boundary t pedum is not known from ediacaran rocks the delayed appearance of t pedum in e c successions should be analysed on a case by case basis

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

spatangoid produced ichnofabrics bateig limestone miocene spain and the preservation of spatangoid trace fossils a spatangoid produced ichnofabric is described from the miocene bateig limestone se spain this ichnofabric is characterized by the dominant presence of large meniscate burrows bichordites produced by irregular echinoids this constitutes an unusual mode of occurrence for spatangoid bioturbation as their traces are most typically preserved in bases and tops of sandstone event beds in fact despite their important role as burrowers in modern settings that can be extended back to the early cretaceous based on their body fossil record spatangoid trace fossils scolicia and bichordites are comparatively rare several factors play an important role in their preservation mechanism of burrowing sediment characteristics early diagenesis and presence absence of deep tier burrowers spatangoid produced ichnofabrics such as those from the bateig limestone characterize depositional settings with intermittent deposition of event beds where there is an absence of deeper tier bioturbation

palynology dacryoconarids and the lower eifelian middle devonian basal chotec event case studies from the prague and appalachian basins

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

trace fossils biology and taphonomy 1990 special topics in palaeontology 3 280 pp e17 95 pbk e40 00 hbk unwin hyman london isbn 004445 6867 pbk 3035 hbk

plastic deformation and magmatic impregnation in serpentinized ultramafic rocks from the garrett transform fault east pacific rise the microstructural study of a set of serpentinized ultramafic samples dredged in the garrett transform fault shows that these rocks have been deformed plastically at temperatures probably in excess of 1000 c and under moderate deviatoric stresses below 1 kbar such temperature and stress conditions probably prevail in the asthenosphere or in the deepest and hottest part of the lithosphere below the ridge the deformed paragenesis of the studied samples belong to two groups harzburgites with petrological characteristics typical of residual mantle and plagioclase dunites a melt circulated in these two groups of deformed ultramafic rocks at the end of their deep seated plastic deformation this melt crystallized plagioclase clinopyroxene and also possibly orthopyroxene in one sample in dykelets and in interstices between the minerals of the deformed host rock the deformation and magmatic impregnation history of the studied ultramafic samples recall the results of on land studies of the crust mantle transition zone of ophiolitic massifs this suggests that our set of samples may represent fragments of the east pacific rise crust mantle transition zone the deformed ultramafic paragenesis of these samples was chemically modified by interactions with the impregnating melt the deformed spinel was enriched in tio2 and cr2o3 the deformed clinopyroxene and orthopyroxene of the harzburgitic samples were also enriched in tio2 and the orthopyroxene was significantly depleted in al2o3 the high mobility of titanium during the impregnation process suggests that the ti content of a melt often used as an indicator of its degree of evolution or of the degree of partial melting undergone by its source rock may also be modified by melt rock interactions during the circulation of the magma through the crust and upper mantle

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

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

flash flood sediments and ichnofacies of the late pleistocene homeb silts kuiseb river namibia abstract the homeb silt formation consists of eroded remnants of fine grained alluvium that were deposited within the kuiseb river valley in southern namibia during the late pleistocene in holocene times the river deeply incised its valley fill leaving steep walled castles of relict alluvium the homeb silts this study is based on the 25 m thick type exposure of homeb silts at homeb and describes flash flood sediments that were colonised by successive generations of opportunistic arthropods the stacked flood units each comprise a massive tabular siltstone bed overlain by a narrower interval of rapidly alternating sandstone and siltstone with claystone veneers these flood units are interpreted as having accumulated under semi arid climatic conditions by episodic back flooding of the kuiseb river into embayments and tributary mouths soon after deposition as the floodwaters subsided the sediment was colonised by burrowing sediment ingesting organisms mostly arthropods that produced a taenidium ichnofacies after the floodwaters had drained the exposed sediment was colonised by grasses and burrowed by terrestrial arthropods probably ants and termites resulting in an overprint of termitichnus ichnofacies with associated pelletal chambers thirteen horizons of rhizocretions and root tubules occur toward the top of the succession and indicate a gradual reduction in the frequency of flooding these immature calcic palaeosols suggest that the climate in the central namib desert 20 000 years ago was semi arid being wetter and more seasonal than the hyperarid conditions that prevail today

an enigmatic kilometer scale concentration of small mytilids late miocene guadalquivir basin s spain abstract upper miocene heterozoan carbonates crop out extensively in a ne sw trending belt 42 km long and 1 5 8 km wide along the so called el alcor topographic high from carmona to dos hermanas seville s spain these carbonates formed at the southern active margin of the guadalquivir basin the foreland basin of the betic cordillera they change to marls basinward ne and to sands landward se and sw therefore carbonate production was constrained to a limited area in an otherwise siliciclastic shelf the carbonates up to 40 m thick overlie a gradually coarsening upward succession of marls followed by silts and sandstones the carbonate sequence can be divided into three subunits corresponding from bottom to top to lowstand transgressive and highstand system tract deposits the lower subunit exhibiting extensive trough cross bedding is interpreted as a shallow water bar deposit the intermediate subunit onlaps underlying sediments and was deposited in deeper low turbulence conditions the upper subunit deposits accumulated in a well oxygenated outer platform based on benthic foraminiferal assemblages the presence of hummocky and swaley cross stratification in these latter deposits suggests that they were affected by storms pervasive fluid escape structures are also observed throughout the carbonates the three subunits consist of bioclastic packstones to rudstones made up of abundant fragments of small mytilids isotopic data from serpulid polychaete ditrupa tubes show 13c depleted values up to 16 1 whereas 18o yields normal marine values additional isotopic data on shells of scallops oysters and small mussels as well as bulk sediment show diagenetic alterations based on actualistic examples of massive concentrations of mussels the nearly monospecific composition of the el alcor deposits together with negative 13c values of ditrupa tubes indicates that cold seeps presumably promoted carbonate formation however the absence of typical features of cold seep deposits such as authigenic carbonates mediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms makes the large carbonate body of el alcor an unusual cold seep deposit

palaeoecology of an early permian playa lake trace fossil assemblage from castle peak texas usa abstract the early permian choza formation of the clear fork group at castle peak in texas usa contains a diverse and remarkably abundant trace fossil assemblage comprising exquisitely preserved arthropod trackways diplichnites gouldi types a and b diplichnites isp a and b lithographus isp and cf kouphichnium isp striated trails cruziana problematica and isolated resting traces rusophycus carbonarius and r furcosus surface or shallow subsurface grazing trails or burrows gordia indianensis helminthoidichnites tenuis treptichnus isp a nodular trail and unilobate epichnial trails backfilled deposit feeding burrows planolites beverleyensis meniscate backfilled burrows taenidium barretti horizontal branching networks and tetrapod trackways dromopus palmatus erpetopus willistoni varanopus curvidactylus and cf amphisauropus isp trace fossils formed in and around the margins of a shallow ephemeral playa lake within an alluvial plain and provide evidence of temporary communities comprising arthropods most notably notostracan branchiopod crustaceans as well as euthycarcinoids myriapods insects and tetrapods including protorothyridid captorhinid and araeoscelid reptiles and rare amphibians periodic influxes of water into the alluvial plain filled various depressions creating temporary habitats and flourishes of life and activity the trace fossil assemblage is typical of the scoyenia ichnofacies and is similar to other assemblages from a range of different transitional subaqueous to subaerial settings indicating that the distribution of trace fossils is not inextricably linked to the depositional setting itself but rather to the environmental factors that arise such diverse trace fossil assemblages probably reflect relatively long lived ephemeral water bodies whereas more impoverished examples probably represent shorter lived ephemeral water bodies assemblages such as castle peak with abundant delicate arthropod trackways probably reflect low energy conditions conducive to the presence of an abundant vagile epifauna and the preservation of their trackways whereas assemblages with open vertical burrows tend to lack arthropod trackways and probably reflect higher energy conditions trace fossil assemblages dominated by arthropod and tetrapod trackways may represent fleeting preservation windows following sheetfloods on floodplains

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

the impact of ground based glaciogenic seeding on clouds and precipitation over mountains a case study of a shallow orographic cloud with large supercooled droplets this paper examines the impact of ground based glaciogenic seeding on a shallow lightly precipitating orographic cloud with rather large 35 m supercooled droplets the storm was observed on 22 february 2012 as part of the agi silver iodide seeding cloud impact investigation experiment in wyoming the cloud base top temperature was about 5 c 12 c vertical velocity data from an airborne doppler w band 3 mm profiling wyoming cloud radar wcr indicate broad ascent due to the strong wind 20 m s 1 impinging on the terrain and small pockets of intense updrafts the large droplets low droplet and ice particle concentrations and strong updrafts lead to natural snow growth mainly by accretion riming the treated seeded period is compared with the preceding untreated period the main target site located on a mountain pass was impacted by agi seeding according to a trace chemistry analysis of the falling snow data from three radar systems were used in the analysis of the impact of seeding on snow growth the wcr two ka band 1 2 cm profiling micro rain radars and an x band 3 cm scanning polarization doppler on wheels radar this case is complicated somewhat by a natural increase in cloud liquid water and in snow growth by riming starting halfway during the seeding period and continuing after seeding ended composite data from the centimeter wave radar systems indicate an increase in low level reflectivity during seeding even after accounting for the natural trend observed in the upwind control region a precipitation particle probe at the main target site shows an increase in concentration of both small and large hydrometeors

ultramafic and mafic rocks from the garret transform fault near 13 30 s on the east pacific rise igneous petrology serpentinized peridotites metagabbros and fresh basaltic rocks were dredged from the garret transform fault near 13 s on the east pacific rise two dredge hauls taken on the northern wall from about 3100 3600 m consisted of aphyric and picritic basalts while peridotites gabbros and moderately phyric basalts were recovered in a single dredge located near the deepest part 4616 4820 m of the transform valley well preserved igneous textures and mineralogical assemblages enable us to differentiate between tectonites including harzburgites and clinopyroxene bearing harzburgites and cumulates consisting of plagioclase dunite troctolites olivine gabbros and ilmenite gabbros the harzburgites are likely to represent deep seated peridotites left after extraction of basaltic melt during upper mantle partial melting of a lherzolite the ultramafic cumulates underwent some deformation and show textural and mineralogical evidences which suggest formation at a minimum depth corresponding to the very lower crust it is also inferred that the composition of the coexisting liquid along with early cumulus crystals has a ratio mg mg fe2 of 0 7 high cao na2o ratios and a low ni content about 150 ppm when compared to similar rock types from atlantic fracture zones subsequent uplift during rifting of the oceanic lithosphere enhanced plastic deformation subsolidus recrystallization and retrogressive metamorphism of the gabbros and the ultramafics

dredged basalts from the western nazca plate and the evolution of the east pacific rise abstract ocean floor basalts and glasses were recovered from three stations along the western nazca plate from a sublinear topographic feature believed to represent the proto east pacific rise epr and include abyssal tholeiites feti basalts and glasses as well as transitional and little fractionated compositions when compared with their coexisting fresh glasses the feti basalts have higher total alkalies tio2 and mgo and lower feo suggesting that they have also been affected by non oxidative post magmatic alteration processes the feti glasses form a remarkably uniform compositional group through space and time a little fractionated composition having anmg number 73 similar to those reported from the mathematician ridge has higher na2o and tio2 and slightly lower cao than similar compositions from the slowly accreting mid atlantic ridge the basalts and glasses reported here exhibit the compositional diversity expected for propagating rifts and probably represent more than one volcanic episode both geochemical and geophysical interpretations support the inference that the epr grew from miocene times by the progressive growth and propagation of mantle perturbations leaving a remnant sublinear zone of rough topography characteristic of slower accretion as the trace of the proto epr continuing translations and rotations of axial segments are occurring along the epr probably in response to self reorganizations of mantle flow patterns arising from rapid melting and depletion of the source regions the data allow the inference that the youthful rift systems of the eastern pacific are far from thermodynamic equilibrium as might be expected if such systems were to drive fundamental life processes

traces in the dark sedimentary processes and facies gradients in the upper devonian lower mississippian upper shale member of the bakken formation williston basin north dakota u s a reply we welcome the opportunity to respond to schieber s 2014 discussion of egenhoff and fishman 2013 because it enables us to further elaborate on the structures we interpreted as fecal strings attributable to phycosiphon incertum that are visible in mudstone samples collected from the upper shale member of the bakken formation schieber 2014 in his discussion raised four points that can be summarized as 1 the structures interpreted as phycosiphon incertum by egenhoff and fishman 2013 are artifacts introduced during the thin section manufacturing process 2 the structures egenhoff and fishman 2013 interpreted as burrows may instead have formed through depositional processes rather than by bioturbation siltstone laminae could represent the toe portion remaining from a migrating current ripple the siltstone laminae would therefore reflect the original composition of silt rich ripple foresets where they were in contact with the seafloor whereas locations where mud rich forests were in contact with the muddy seafloor would produce the holes seen in the siltstone laminae alternatively currents flowing over previously deposited silt laminae could have scoured and plucked individual silt grains out of the laminae and thereby produced sites that were later filled with mud 3 near surface burrows presumably like those that egenhoff and fishman 2013 observed in the upper shale member would have to be produced in soupgrounds burrows in these freshly deposited muds can be maintained only when stabilized by mucus observations from the recent suggest that these types of burrows are likely produced by nematodes that are only detected using the color differences between the fill and the surrounding rock 4 the amount of compaction can be very high in mudstones therefore the compaction in the upper shale member should have strongly affected original sedimentary features including the burrows the burrows shown by egenhoff and fishman 2013

sedimentologic palaeoecologic taphonomic and ichnologic criteria for high resolution sequence analysis a practical guide for the identification and interpretation of discontinuities in shelf deposits abstract we classify stratigraphic bounding surfaces defined by sedimentologic palaeoecologic or taphonomic and ichnologic criteria our case study refers to a particularly well preserved outcrop of miocene sedimentary rocks on the pacific coast of central costa rica these rocks mainly fine sandstones accumulated in a tropical shallow marine strongly subsiding sand swamped forearc coastal embayment sedimentary bounding surfaces or lithofacies bounding surfaces can be subdivided into erosional and non erosional boundaries between depositional systems in our case study erosional boundaries angular unconformities and erosional disconformities were produced by block tilting tectonic reactivation of cliffs or wave and tidal ravinement during sea level rises and are interpreted as sequence boundaries and bases of parasequence sets respectively non erosional transitions delimit genetically closely related depositional systems sharp contacts are considered as bases of parasequence sets diffuse transitions are interpreted as parasequences palaeoecologically and taphonomically defined fossiliferous bounding surfaces or layers mostly occur within depositional systems they seldom coincide with erosional lithofacies bounding surfaces two types can be distinguished autochthonous and allochthonous fossil concentrations autochthonous fossil concentrations can be grouped into layers with epifaunal and semi infaunal molluscs in growth position layers with infaunal bivalve associations in growth position and coprolith concentrations the majority of these layers is developed as concretion horizons autochthonous fossil concentrations invariably signal a relative rise of sea level and are interpreted as bases of parasequences or parasequence sets allochthonous fossil concentrations can be grouped into fossil concentrations produced by non turbulent shelf currents driftwood concentrations tempestite fossil concentrations fossil concentrations produced by near shore turbulent flow regimes and fossil concentrations produced by tidal currents they are only seldom developed as concretion horizons the appearance of allochthonous fossil concentrations in certain intervals of a given section and disappearance in others is clearly a signal of shallowing or deepening seas fossil concentrations produced by non turbulent shelf currents and driftwood concentrations can be interpreted as bases of parasequences ichnofabrics can be used as an additional tool for the identification and interpretation of bounding surfaces erosional boundaries may be marked by well known features such as gastrochaenolites sequence boundaries may be preceded by thalassinoides boxworks strongly thickened by concretionary growth at non erosional boundaries however trace fossils commonly fail to mark the crucial turning point yet they seem to record environmental changes for instance a coming transgression far earlier than any sedimentary phenomenon or body fossil after prolonged swamping with sand during a relative sea level lowstand they explode in diversity during the following transgression before this transgression produces its own typical sediment equally after the dumping of organic matter during the transgression trace making organisms announce the coming highstand by reworking their habitat to the degree of total destratification before the highstand deposits proper force them to keep up with aggradation which results in the typical highstand selection of deep tier structures thus the degree of reworking by bioturbation seems to be a very good and easily recognizable indicator of the internal architecture of parasequences and parasequence sets

traces in the dark sedimentary processes and facies gradients in the upper shale member of the upper devonian lower mississippian bakken formation williston basin north dakota u s a abstract black organic rich rocks of the upper shale member of the upper devonian lower mississippian bakken formation a world class petroleum source rock in the williston basin of the united states and canada contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts the succession consists of three discrete facies associations fas these comprise 1 siliceous mudstones 2 quartz and carbonate bearing laminated mudstones and 3 macrofossil debris bearing massive mudstones these fas were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system the macrofossil debris bearing massive mudstones fa 3 occur in the proximal facies belt and contain erosion surfaces some with overlying conodont and phosphate lithoclast lag deposits mudstones with abundant millimeter scale siltstone laminae showing irregular lateral thickness changes and shell debris in the medial facies belt quartz and carbonate bearing laminated mudstones dominate exhibiting sub millimeter thick siltstone layers with variable lateral thicknesses and localized mudstone ripples in the distal siliceous mudstone facies belt radiolarites radiolarian bearing mudstones and quartz and carbonate bearing laminated mudstones dominate overall total organic carbon toc contents range between about 3 and 10 wt with a general proximal to distal decrease in toc content abundant evidence of bioturbation exists in all fas and the lithological and toc variations are paralleled by changes in burrowing style and trace fossil abundance while two horizontal traces and two types of fecal strings are recognized in the proximal facies belt only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings bedload transport processes likely caused by storm induced turbidity currents were active across all facies belts suspended sediment settling from near the ocean surface however most likely played a role in the deposition of some of the mudstones and was probably responsible for deposition of the radiolarites the distribution pattern of high toc sediments in proximal and lower toc deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension derived organic carbon in radiolarite laminae the presence of burrows in all fas and nearly all facies in the upper bakken shale member indicates that dysoxic conditions prevailed during its deposition this study shows that in intracratonic high toc mudstone successions such as the upper bakken shale member bed load processes most likely dominated sedimentation and conditions promoted a thriving infaunal benthic community as such deposition of the upper bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world class source rocks

evidence for cnidaria like behavior in ca 560 ma ediacaran aspidella the first appearance of animals in the geological record is a matter of continuing debate how deep were the roots of the cambrian explosion molecular clock estimates indicate that the deepest divergences of the metazoa had occurred by the ediacaran period 635 541 ma yet evidence of animal activity from well below the ediacaran cambrian boundary has been rare and often questionable meanwhile the ediacaran macrobiota has remained enigmatic as emphasized by recent controversial claims that south australia ediacaran forms were not marine animals at all but land based lichens and microbial colonies here we report evidence for animal like behavior in a submerged setting in a key ediacaran form aspidella terranovica billings 1872 a discoidal fossil from the ca 560 ma fermeuse formation of newfoundland canada we describe sedimentary fabrics indicating progressive vertical movement of an organism through sediment in response to an aggrading sediment water interface such equilibrium traces are familiar from the phanerozoic and are observed in partially buried marine animals such as tube anemones today furthermore horizontal trails closely comparable to trails previously described from 565 m y old mistaken point newfoundland are now linked to aspidella our findings constitute evidence of both vertical and horizontal movement in a key ediacaran taxon consistent with an animal of cnidarian grade moreover because aspidella is also reported from the rawnsley quartzite of south australia our evidence conflicts with the proposed radical interpretation of that ediacaran fossil assemblage we demonstrate that at least some ediacaran forms were probably early animals and that they lived underwater

what does ophiomorpha irregulaire really look like ophiomorpha irregulaire is a surprisingly poorly characterised ichnotaxon given its common occurrence in hydrocarbon reservoir facies current debate surrounds the ichnotaxobases suitable for ichnospecific level identification and also the palaeogeographic distribution of the taxon o irregulaire is conventionally characterised in core by the presence of spikey fine grained wall lining pellets since the horizontal meander maze that is also part of the ichnospecific diagnosis cannot normally be demonstrated to resolve ichnotaxonomic issues concerning the validity of pellet morphology as a primary ichnotaxobase material from the type locality is re described cretaceous book cliffs utah with an emphasis on burrow wall morphology comparative neoichnological studies using the callianassid crustacean neotrypaea californiensis were additionally conducted to understand the behaviour of modern taxa that produce burrows closely resembling o irregulaire high resolution three dimensional morphological models were created from specimens of ophiomorpha from the type locality of o irregulaire in utah usa and from eocene deep marine turbidites of the juncal formation california comparison of the morphological features from these two localities as well as specimens observed in core from offshore newfoundland demonstrate conclusively that o irregulaire is not restricted to the cretaceous western interior seaway o irregulaire may have a stratigraphic range from jurassic to recent and occur in palaeoenvironmental settings ranging from shallow marine to continental slope settings the flame like pellet morphology is considered characteristic of the type material and is a valid criterion for identifying o irregulaire in core

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

latitudinal variations in benthic processes in the abyssal equatorial pacific control by biogenic particle flux abstract the equatorial pacific forms a band of high globally significant primary production this productivity drops off steeply with distance from equatorial upwelling yielding large latitudinal gradients in biogenic particle flux to the abyssal seafloor as part of the us jgofs program we studied the translation of these particle flux gradients into the benthic ecosystem from 12 s to 9 n along 135 140 w to evaluate their control of key benthic processes and to evaluate sediment proxies of export production from overlying waters in october december 1992 the remineralization rates of organic carbon calcium carbonate and biogenic opal roughly matched the rain rates of these materials into deep sediment traps exhibiting peak values within 3 of the equator rates of bioturbation near the equator were about ten fold greater than at 9 n and appeared to exhibit substantial dependence on particulate organic carbon flux tracer time scale i e age dependent mixing and pulsed mixing from burrowing urchins organic carbon degradation within sediments near the equator was dominated by a very labile component reaction rate constant k approximately 15 per year that appeared to be derived from greenish phytodetritus accumulated on the seafloor organic carbon degradation at the highest latitudes was controlled by a less reactive component with a mean k of approximately 0 075 per year where measured megafaunal and macrofaunal abundances were strongly correlated with annual particulate organic carbon flux macrofaunal abundance in particular might potentially serve as a proxy for export production in low energy abyssal habitats sedimentary microbial biomass also was correlated with the rain rate of organic carbon but less strongly than larger biota and on shorter time scales i e approximately 100 days we conclude that the vertical flux of biogenic particlues exerts tight control on the nature and rates of benthic biological and chemical processes in the abyssal equatorial pacific and suggest that global changes in productivity on decadal or greater time scales could yield profound changes in deep sea benthic ecoystems

bio retexturing early diagenetic fabric modifications in outer ramp settings a case study from the oligo miocene of the central mediterranean abstract bioturbation is ubiquitous in cenozoic outer ramp settings the oligo miocene ramp carbonate sequences of se sicily and the maltese islands provide specific examples to illustrate the effects of sediment retexturing by burrowers and provide significant conclusions which must be taken into account by sedimentologists when interpreting palacoenvironments thalassinoidean burrow systems may penetrate several metres into the underlying beds with evidence of concentrated activity at selected levels the general intra bed process of this crustacean dominated bioturbation is well documented however the effects when several beds are involved can be dramatic 1 a buried homogeneous wackestone beds can be depleted in lime mud by gallery excavation the dumping of this mud at the sediment surface leads to lime mud enrichment of the contemporary accumulating layer and might be a major factor in the development of the tabular outer ramp bedforms 2 b vertical reworking of unlithified sediment between beds both upwards and down is capable of homogenising two distinctly dissimilar lithologies producing a third which in no way reflects the surface processes of the depositional setting 3 c bioturbation often continues during incipient near seafloor lithification this produces random lateral variations in lithology within single beds the degree of lateral dissimilarity is proportional to the intensity longevity of the bioturbation episode bio retexturing destroys primary depositional fabrics and masks inorganic process related structures it can be as effective a remodelling agent as tidal energy it can texturally remodel areas of high primary permeability into irregular interconnected zones of low permeability as the outer ramp provides a potential fluid migration route from basin to shallow water clearly bio retexturing must exert a major influence on longer term formation wide diagenetic processes

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

multistage hydrothermal alteration of gabbroic rocks from the failed mathematician ridge oxygen isotopic mineralogical and fluid inclusion data are presented for fresh and hydrothermally altered gabbroic rocks from the failed mathematician ridge the mathematician ridge though initially a fast spreading ridge presently has a deep central rift valley more typical of slow spreading rifts the inner rift walls expose rare plutonic rocks uncomplicated by proximity to deep large offset fracture zones undeformed mathematician ridge gabbros preserve most of the original texture and phase compositions and have been only slightly mineralogically or isotopically modified by post crystallization hydrothermal alteration metagabbros have been subjected to a pervasive ductile deformation and recrystallization to foliated rocks composed of aluminous amphibole low calcium plagioclase and ilmenite oxygen isotope and phase chemical data suggest this event began at temperatures of up to 700 c water rock ratios of less than one and produced modified seawater fluids with isotopic compositions of 3 5 6 0 the amphibolites are cross cut by multiple generation quartz epidote veins forming a network replacement of the amphibole grade mineralogies by greenschist grade mineralogies fluid oxygen isotopic compositions of 2 4 and a two phase separation in the fluid captured in conjugate vapor fluid inclusions are all associated with the formation of this network fluid inclusion data for the quartz indicate initial temperatures of over 500 c these samples may represent rocks from the 1 2 km deep plumbing system of black smoker type venting

two bioerosion ichnofacies produced by early and late burial associated with sea level change in bioerosion as in trace fossils as a whole deeply emplaced structures have greater survival value than shallow structures that is to say tiering the relative depth to which rasping etching and boring organisms penetrate their substrate is of paramount importance for the preservation potential of individual trace fossils an entobia ichnofacies is established for trace fossil assemblages dominated by deep tier borings and arising from long term bioerosion such as occurs on sediment free submarine cliffs or hardgrounds a gnathichnus ichnofacies comprises assemblages containing all tiers including superficial sculptures produced by radulation that have very little preservation potential such assemblages occur in short term bioerosion situations as on shell surfaces and hardgrounds buried early by sedimentation

the border ranges ultramafic and mafic complex south central alaska cumulate fractionates of island arc volcanics a discontinuous elongate zone of mafic and ultramafic plutonic rock crops out in south central alaska for a distance of more than 1000 km intermediate and detailed scale geologic mapping petrographic study and compositional data suggest that the plutonic rocks are compositionally petrologically and mineralogically distinct from rocks in mid ocean ridge and back arc basin ophiolites the mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc the mafic ultramafic zone referred to as the border ranges ultramafic and mafic complex brumc is composed of ultramafic cumulates gabbronorite cumulates and massive gabbronorites a very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the brumc a thick sequence of andesitic volcanic rocks the talkeetna formation of early jurassic age lies to the north of and structurally above the mafic ultramafic zone voluminous calcalkaline plutons composed of quartz diorite

new model for the emplacement bioturbation and preservation of fine scaled sedimentary strata we present a new quantitative model for the formation and preservation of sedimentary fabric based on interacting sedimentation and bioturbation the model is one dimensional and is forced by fluctuation of the sedimentation rate which affects deposition of sediment possessing primary depositional fabric primary fabric is modified by bioturbation which is represented as a depth limited reaction term model output includes depth in seabed and preservation quotient a measure of relative preservation of primary versus biogenic fabric at each depth the required parameters sedimentation rate and bioturbation rate can be derived from studies of seabed processes model output can be compared directly to observations of both modern and ancient sedimentary strata

geologic investigations in the cayman trough evidence for thin oceanic crust along the mid cayman rise the mid cayman rise is a 110 km long accreting plate boundary 2cm yr full rate characterized by a deep rift valley eighteen transponder navigated dives were made by the submersible alvin along the rift valley walls in two areas on opposite sides of the rift valley the relief of the walls is produced by a large number of inward facing small throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m from these escarpments 142 samples were collected and gabbroic rocks 116 samples characterized by a wide range of compositions and a complex metamorphic history predominate in number over other rock types basalt serpentinized ultramafic we interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the mid cayman rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt this carapace is und

carbon isotope evidence for the timing of the cretaceous palaeogene macrobenthic colonisation at the agost section southeast spain abstract the cretaceous palaeogene k t boundary section of agost southeast spain one of the most complete sections existing contains a well developed trace fossil assemblage composed of dark and light filled trace fossils registered in the uppermost cretaceous maastrichtian plummerita hantkeninoides biozone sediments the trace fossil assemblage reveals that significant macrobenthic colonisation occurred around the k t boundary interval however difficulties in recognising trace fossils affecting the k t boundary layer as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation with the aim of this characterisation we determined the 13c of the carbonate fraction of dark and light filling materials from the trace fossils since the carbon isotope compositions of uppermost cretaceous and lowermost palaeogene materials are clearly different the data compiled provide evidence for a significant distinction between light filled trace fossils with 13c values higher than 1 6 peedee belemnite pdb and dark filled trace fossils with 13c values between 0 21 and 1 2 pdb most of these being lower than 0 7 pdb the comparison of these values with those from the uppermost maastrichtian to the lowermost danian sediments reveals that the macrobenthic colonisation occurred in different phases across the k t boundary interval

gabbroic xenoliths and host ferrobasalt from the southern juan de fuca ridge rare isotropic gabbroic xenoliths occur in sheet and lobate flow fragments of nearly aphyric ferrobasalt collected along a 12 km section of the southern juan de fuca ridge xenoliths comprise 1 of the dredge contents and range in size from 1 cm3 glomerocryst to 240 cm3 the xenoliths have ophitic to intersertal texture with 5 50 interstitial glass of ferrobasaltic composition more evolved than the host lava on the basis of texture and mineralogy the xenoliths have been subdivided into three types type i plagioclase olivine glass type ii plagioclase augite glass olivine and type iii plagioclase augite olivine glass pigeonite partially inverted fe ti oxides mineral and glass inclusion compositions suggest a sequence of evolution for the three xenolith types in which type i is the least evolved and type iii is the most evolved application of a graphical pyroxene geothermometer to augite in xenolith types ii and iii yields crystallization temperatures of 1100 1200 c and to host lamellae pairs in inverted pigeonite yields subsolidus equilibrium temperatures of 1100 1150 c coexisting titanomagnetite ilmenite pairs in type iii xenoliths yield temperature estimates of 1000 1070 c and log f02 9 7 to 10 8 we infer that the xenoliths represent the partially crystalline mush boundary zone of a magma chamber based on the abundance of interstitial glass zonation of mineral grains in the most crystalline samples and coherence of chemical trends between interstitial glass glass inclusions and mineral phases the evolved composition of the xenoliths provides evidence for the presence of melts more fractionated than the host ferrobasalt in the magma chamber the erupted ferrobasalt is a hybrid lava formed by mixing these highly evolved melts with more primitive melts

trace fossils of talitrid sandhoppers in interglacial littoral calcareous sandstones cornwall u k small 6cm isolated cylindrical shafts observed in carbonate cemented current bedded interglacial littoral sands sandrock in cornwall have previously been interpreted as intrasedimentary stalactites an alternative explanation as trace fossils of the ichnogenus skolithos is proposed probable attribution to talitrid amphipoda sandhoppers in particular talitrus saltator montagu is supported by the similarity of the features to the modern burrows of this organism the facies dependence of the features and by independent evidence on the backshore frontal dune environment of deposition the ecological requirements of t saltator support the interpretation of the raised beaches as interglacial in status based on thermoluminescence tl dating and aminostratigraphy and conflict with a recent suggestion that they may be of cold stage origin

modelling of the oxygen isotope evolution of seawater implications for the climate interpretation of the δ18o of marine sediments it is often argued that the 18o value of oceanic water was maintained close to 0 for hundreds of millions of years as a consequence of oxygen isotope exchange between oceanic crust and seawater however for several decades the interpretation of the biosedimentary oxygen isotope record has conflicted with the igneous record because with increasing age a general trend of decreasing 18o values about 6 is observed in most carbonates cherts and phosphates especially for the paleozoic and early mesozoic we developed a dynamical model of seawater crust interaction that computes the 18o value in these two reservoirs as function of time this model takes into account the continuous production of crust at oceanic ridges its expansion rate the permeability profile with space and time the mineralogical mode of the crust and the kinetics of oxygen isotope exchange between rock forming minerals and seawater the model indicates that the 18o value of seawater may vary by 2 with a time response ranging from 5 to 50 ma for expansion rates of 1 to 10 cm a 1 the variation of 2 is fixed by both integrated water rock ratio and closure time of the seawater crust system by sediments variations in the oxygen isotope ratio of seawater through time have important implications for the interpretation of the systematically low 18o values of pre jurassic marine sediments according to our model marine paleotemperatures could be up to 10 c lower than those expected when applying the classical hypothesis of an ice free ocean with a 18o value of 1

effect of phycosiphoniform burrows on shale hydrocarbon reservoir quality unconventional gas tight gas coalbed methane and shale gas has become an increasingly significant source of energy economic production from such low permeability reservoirs relies upon identifying regions of the reservoir that will yield the highest gas production rates currently available gas recovery technologies are highly dependent on the fracturability of the reservoir zones of enhanced brittleness and permeability within shale gas reservoir horizons are a prerequisite for successful shale gas recovery such brittle zones are directly linked with increased quartz and or carbonate content within the mudstone in mudstones with high clay mineral content quartz may be concentrated and redistributed as a result of burrowing activities of infaunal organisms high quality porosity and permeability zones in shale petroleum reservoirs may be present in the form of silty and sandy tortuous strips of selectively concentrated grains of quartz that constitute burrow halos grain selective burrows therefore can improve reservoir capacity permeability and fracturability and thus control the storativity of the shale petroleum reservoir this study presents three dimensional reconstructions of three different types of phycosiphon like burrows and investigates the possible fluid flow paths caused by the ichnofabric the volumetric approach to the bioturbation generated by phycosiphoniform burrow makers used herein shows that the volume of sediment that becomes more porous and more permeable media within such bioturbated interval can range from 13 to 26 of the total volume the quartzose strips of sediment caused by bioturbation are highly tortuous and interconnected vertically and horizontally thereby increasing both horizontal and vertical permeability additionally the quartz frameworks created by the burrows may locally increase fracturability within otherwise nonbrittle mudstones

mineral relationships in gabbroic rocks from fracture zones of indian ocean ridges evidence for extensive fractionation parental diversity and boundary layer recrystallization

iron bacterial and fungal mats bajocian stratotype mid jurassic northern normandy france abstract the oolithe ferrugineuse de bayeux formation is located at the historical bajocian stratotype of sainte honorine des pertes north of bayeux normandy the condensed formation ranges from the base of the humphriesianum zone to the parkinsoni zone and is divided into four beds of decimetric scale three main microfacies are present 1 oncoid rudstones 2 ooid bioclastic packstones and 3 silty burrowed wackestones packstones sedimentation took place in a very quiet environment below the photic zone and below or near the storm wave base the general setting is a distal carbonate ramp its lower part characterized by hemipelagic sedimentation indicated by the presence of planktonic foraminifers the inferred depth is around 100 m free oxygen concentration was low dysaerobic conditions are indicated by a scarcity of benthic macrofauna ferruginous structures are numerous in the first two microfacies and absent in the last hematite staining is not uniform and follows many sedimentary patterns among the more widespread fe structures are perforation infillings with endolithic micro organisms microstromatolites oncoids ooids blisters coatings and hardgrounds these structures can be associated and none are mutually exclusive hematite coated filaments of different sizes and shapes are observed in the micrite matrix the walls of various organisms the calcite crystals associated with the fe cortical laminations the perforations and burrow the hardgrounds and microstromatolites petrographical and sem examinations suggest that the laminated crusts oncoids and hardgrounds are formed by microbial iron mats dominated by filamentous bacteria and fungi seven types of microbes are recognized filaments five morphotypes spheroidal bodies and stalked bodies filamentous microfossils of type 1 to 4 resemble the present day filamentous bacteria beggiatoales and cytophagaceae because of their large diameter and their branching nature filaments of type 5 are possibly filamentous fungi another argument in favor of fungi is the presence of stalked and spheroidal bodies that resemble zoosporangia and oogonia of some oomycota in deep calm and dysaerobic waters many interfaces e g between aerobic and dysaerobic waters are present in the sediments the stability of the soluble reduced state of iron fe 2 is higher at such interfaces and many ferric iron encrusted microbial fossils are observed iron could thus serve as an electron donor for microbial iron oxidation processes other microbial iron deposition pathways are also possible it appears that regardless of geological age paleozoic mesozoic and geographical location the same microbiological mechanisms are probably responsible for the red color in calcareous stratified or unstratified bodies the presence of fossilized iron encrusted bacteria and fungi at interfaces may therefore serve as an indicator of anoxic to dysaerobic conditions in various paleo micro environments

evidence of liquid dependent ice nucleation in high latitude stratiform clouds from surface remote sensors 1 ground based lidar radar and microwave radiometer observations at eureka canada barrow alaska and over the western arctic ocean measure physical characteristics and morphology of stratiform clouds despite transition of a cold atmosphere 15 c through ice supersaturated conditions ice is not observed until soon after a liquid layer several cases illustrating this phenomenon are presented in addition to long term observations from three measurement sites characterizing cloud phase frequency this analysis demonstrates that clouds composed entirely of ice occur less frequently than liquid topped mixed phase clouds at temperatures warmer than 25 to 30 c these results indicate ice formation generally occurs in conjunction with liquid at these temperatures and suggest the importance of liquid dependent ice nucleation mechanisms

non predatory shell damage in recent deep endobenthic bivalves from spain abstract shells of deep endobenthic bivalves from several localities of the spanish littoral are affected by various modalities of shell damage which cannot be attributed to the direct activity of predators the frequency and morphology of these damage features together with the results of tests with living specimens indicate that they are brought about by the process of burrowing selected aspects of their distribution at the individual and population level also allow us also to differentiate at least two indirect origins for them scape movements from predators and readjustments to storm induced changes in the sediment column as expected the first cause is likely only for some taxa from sheltered coastal environments while the second applies to all samples from exposed shores within this pattern some shell features are recognized at least in part as adaptations to minimize shell damage divaricate ribs in solecurtus strigilatus seem to perform such a function by acting as directions of structural weakness

petrology and mineralogy of dredged gabbro from gettysburg bank eastern atlantic gabbros have been dredged from gettysburg bank 110 km west of portugal on the azores gibraltar fracture zone primary minerals in olivine pyroxene and brown hornblende gabbros are partially replaced by metamorphic minerals igneous textures are inhomogeneously overprinted by a granular polyhedral deformation and a cataclastic deformation amphiboles show characteristics which indicate a transition from crystallisation in a magma chamber to formation of amphibole in solid gabbro under metasomatic conditions of the amphiboles analysed chlorine was present in the green amphiboles but below 0 05 in the brown suggesting the penetration of sea water after the formation of the brown amphibole but during the formation of the green

benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems siliciclastic evaporitic salty and evaporitic carbonatic abstract peritidal sedimentary systems are widely colonized by benthic cyanobacteria that form biofilms and microbial mats the bacterial communities interfere with physical and chemical sedimentary dynamics which is documented by the formation of microbially induced sedimentary structures miss the structures form a new fifth category in the existing classification of primary sedimentary structures siliciclastic depositional systems are dominated by physical dynamics by biostabilization cyanobacteria shelter their substrata against erosion during periods of intensive hydraulic reworking or they permit flexible deformation of sandy sediments during low hydrodynamic disturbance the bacteria enhance deposition of sediments by baffling trapping and binding such biotic physical interference is recorded by miss such as erosional remnants and pockets or planar stromatolites chemical depositional systems include i evaporitic salty environments characterized by evaporation and dissolution and ii evaporitic carbonatic environments that include evaporation dissolution and in situ lithification of organic matter here cyanobacterial mats experience periodical desiccation or evaporation of crystals and mat related structures such as petees and polygonal patterns of cracks are formed cyanobacteria and heterotrophic bacteria provide a chemical microenvironment that supports in situ lithification of organic matter in thin sections carbonate precipitates as ooids or lines of decaying filaments are visible miss occur in modern and ancient depositional systems they record i biological abilities of benthic cyanobacteria to cope with sedimentary dynamics and ii paleoclimate and paleoenvironmental conditions during earth history similar structures are also expected in extraterrestrial paleo environments

mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks mineralogical and isotopic variations observed in altered glassy and crystalline rocksfrom the east pacific rise and the mid atlantic ridge provide information about the temperatures of alteration and seawater rock ratios for various hydrothermal regimes within the oceanic crust a systematic increase in alteration temperature is evident for the glassy rocksin the sequence 1 nontronite and celadonite vesicle fillings 35 c 2 saponite rich pillow breccias 130 170 c 3 calcite rich greenstone breccias and epidote rich greenstone 200 350 c theseresults include the highest temperatures thus far reported for saponite formation the seawater dominated hydrothermal alteration process that formed the saponite rich pillow breccias is characterized by high water rock ratios 0 1 low to moderate temperatures a seawater origin of most of the carbon in vein calcites 13 c 0 and the predominance of fe rich saponite and calcite as secondary phases greenstones chlorite quartz epidote and greenstone breccias chlorite quartz albite calcite are altered in a rock dominated system with lower water rock ratios 50 1 to 13 c 4 the crystalline rocks diabase gabbro and metagabbro are affected to varying degrees by pervasive high temperature seawater interactions that commence soon after solidification producing varying proportions of fine grained secondary minerals including talc smectite chlorite vermiculite actinolite and sodicplagioclase hydrothermal solutions derived from alteration of the crystalline rocks are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal rich deposits associated with the oceanic spreading centers

genesis of andesitic boninitic magmas at mid ocean ridges by melting of hydrated peridotites geochemical evidence from dsdp site 334 gabbronorites abstract the gabbronoritic cumulates drilled at dsdp site 334 mid atlantic ridge off the famous area are neither crystallization products of the associated basalts nor from any morb composition documented along ocean ridges their parent melts are richer in sio2 than morb at a given mgo content as attested by the crystallization sequence starting with an olivine calcic and sub calcic pyroxene assemblages these melts are issued from a source highly depleted in incompatible elements likely residual peridotite left after morb extraction to understand the role of water in the genesis of these lithologies whose occurrence in a mid ocean ridge setting is rather puzzling we performed a geochemical study on clinopyroxene separates following an analytical protocol able to remove the effects of water rock interactions post dating their crystallization accordingly the measured isotopic signatures can be used to trace magma sources we find that site 334 clinopyroxenes depart from the global mantle correlation normal morb values for the 143nd 144nd ratio 0 51307 0 51315 are associated to highly radiogenic 87sr 86sr 0 7034 0 7067 ratios this indicates that the parent melts of site 334 cumulates are issued from a morb source but that seawater contamination occurred at some stage of their genesis the extent of contamination traced by the sr isotopic signature is variable within all cumulates but more developed for gabbronorites sensus stricto suggesting that seawater introduction was a continuous process during all the magmatic evolution of the system from partial melting to fractional crystallization simple masse balance calculations are consistent with a contaminating agent having the characters of a highly hydrated possibly water saturated silica rich melt depleted in almost all incompatible major minor and trace elements relative to morb mixing in various proportions of contaminated melts similar to the parent melts of site 334 cumulates with morb can account for part of the variability in the sr isotopic signature of oceanic basalts among other to the short wavelength isotopic noise superimposed on regional trends we conclude that seawater introduction into residual peridotite at shallow depth beneath mid ocean ridges can lead mantle rocks and their melts to follow complex p t fh2o paths that mimic petrogenetic contexts classically attributed to subduction zone environments like the production of boninitic andesitic magmas

petrology of the east pacific rise crust and upper mantle exposed in hess deep eastern equatorial pacific the hess deep a rifted oval shaped depression located east of the galapagos triple junction at the tip of the cocos nazca ridge about 101 w 2 n was explored in 1988 during 21 submersible dives a total of 11 dives were devoted to the exploration of the e w trending intrarift ridge 15 km in length 3000 5400 m in depth north of the hess deep depression the intrarift ridge represents an outcrop of recent 1 m y crustal and subcrustal material created at the axis of the east pacific rise epr and emplaced during the lithospheric extention responsible for the westward propagation of the cocos nazca rift francheteau et al 1990 the lithospheric block has undergone cataclastic deformation and was dislocated by tectonic activity as attested to by the mixed and erratic distribution of rock types and by the occurrence of polygenic breccias and gabbroic mylonites the samples are metamorphosed to varying degrees but their protolith textures are generally well preserved their relic mineralogy indicates that they consist of harzburgites dunites gabbroic cumulates gabbronorites and olivine gabbros isotropic gabbros dolerites and basalts some samples of refractory harzburgites and most dunitic cumulates with local accumulation of chromite have been impregnated by wehrlitic and gabbroic primitive melts similar to those described from the mantle crust transition zone of the samail ophiolite complex oman the mineral chemistry indicate that the ultramafics partly reequilibrated with the magmatic impregnations in the liquidus solidus temperature range of 980 1100 c the dolerites and basalts have been derived from mid ocean ridge basalt primary melts presenting a broad range of incompatible element composition which suggests intermittent cycles of magmatic processes involving a progressive melting of a composite source with discontinous extraction of liquids as proposed for the epr volcanics near 13 n hekinian et al 1989 most of the rocks underwent partial retrograde metamorphism and recorded several episodes of recrystallization from the upper greenschist facies ultramafics and gabbros to diagenetic alteration volcanics the cumulate gabbronorites the isotropic gabbros and some dolerites were partially albitized and amphibolitized during the penetration of seawater in the ocean crust prior to serpentinization several samples of unfoliated amphibolites are believed to be completely metamorphosed gabbroic rocks the gabbroic cumulates and the plagioclase rich melt impregnations were variably rodingitized presence of various ca silicates such as epidote prehnite hydrogarnet and zeolite in relation to the serpentinization of the peridotites one dive located on the scarps forming the northern wall of the hess deep to the east of the explored area revealed the presence of in situ outcrops of isotropic gabbros doleritic dikes and extrusives and permitted to observe the contact between the sheeted dike complex and the high level isotropic gabbros

what controls the mixed layer depth in deep sea sediments the importance of poc flux the depth of biogenic particle mixing i e the mixed layer depth l is fundamental in models of organic matter recycling and paleoreconstructions for deep sea sediments factors postulated to control l in the oxygenated deep sea include particulate organic carbon poc flux oxygen penetration into the sediment and a balance between the downward mixing and decay of labile poc we explore the dependence of l on biogeochemical characteristics by compiling from 36 sites in three oceans an internally consistent set of deep sea estimates of l poc flux biogenic mixing intensity db and poc reactivity we use excess 210 pb as a tracer for l and db to avoid the confounding effects of tracer dependent mixing we find that l estimated from the penetration depth of excess 210 pb varies systematically with poc flux with an asymptotic function explaining 88 of the variance in l stepwise multiple regression suggests that the penetration depth of excess 210 pb and estimated l is much more likely to be controlled by poc flux than by 1 the sediment inventory of excess 210 pb or 2 biogenic mixing intensity db in addition l is negatively related to oxygen penetration into the sediment r 52 0 629 and not significantly related to predictions of l from a recent mixing poc decay model we conclude that in the food poor deep sea poc flux substantially controls the size and activities of the sediment mixing benthos and in turn the thickness of the biogenic mixed layer thus in contrast to previous suggestions average mixed layer depth is not environmentally invariant but rather responds predictably to ecologically important parameters such as poc flux

ammonoid habitats and habits in the western interior seaway a case study from the upper cretaceous bearpaw formation of southern alberta canada abstract multidisciplinary research on the habitats and life habits of ammonoids of the upper cretaceous bearpaw formation is based on hydrostatics and hydrodynamic aspects of shell shapes occurrence in lithofacies evidence of predation and stable isotopic data the large and well streamlined oxyconic placenticeras with large chitinous anaptychus had the weakest shells known and suffered mosasaur tooth perforations at minimal ambient pressure anomalously light 18 o signatures preserved in their aragonitic shells suggest that they grew in brachyhaline water juveniles and some adults of orthoconic baculites had a vertical life orientation and primarily resided in the lower to middle levels of the water column flourishing during oxygenation events some adults however may have changed to a mainly horizontal swimming habit in mid water attitudinal change is indicated by relative shortening of the body chamber during late ontogeny neutral buoyancy at maturity could have been achieved only with a partially liquid filled phragmocone implying the exceptional use of cameral liquid as an apical counterweight juvenile scaphitids were planktic or sluggishly nektic as implied by sphaeroconic and discoconic immature whorls respectively the adults had different habits as indicated by their strongly modified body chambers which gave high stability suited to vertical swimming adult hoploscaphites and most jeletzkytes with open hooked scaphitoconic body chambers were demersal and lived close to the sea floor during oxygenation events whereas adult rhaeboceras with an elliptical contracted body chamber elliptosphaerocone lived in mid water

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

sedimentological and ichnological characterization of the middle to upper devonian horn river group british columbia canada insights into mudstone depositional conditions and processes below storm wave base abstract the middle and upper devonian horn river group in northeastern british columbia canada consists predominantly of organic rich mudstones that are typically described as black shales this stratigraphic unit has seen substantial exploration and development for natural gas during the last decade although black shales such as the horn river group have historically been interpreted as deposited in anoxic deep water basins detailed sedimentological and ichnological analyses of eleven horn river group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments redox conditions and physical processes resulting in distinctive sedimentary facies this study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total organic carbon content to better understand depositional processes and conditions ten mudstone lithofacies and three lithofacies associations are identified massive mudstones and pyrite rich mudstones display very rare planar lamination and graded beds and scarce bioturbation bi 0 1 and are interpreted to represent anoxic waters below storm wave base swb with conditions of relatively low to moderate energy heterolithic laminated and more bioturbated lithofacies are interpreted to represent oxygenated waters below swb with relatively high energy conditions overall bioturbation intensity varies between moderate to intense bi 3 6 where these lithofacies are not intensely bioturbated oxygenated lithofacies show combinations of well preserved physical sedimentary structures including horizontal parallel lamination soft sediment deformation double mud drapes graded beds and current ripples a third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations mainly based on local changes in the ichnological characteristics these lithofacies show either intense or sparse bioturbation bi 4 6 or bi 0 1 respectively depending on the core location possibly indicating local changes in the depositional conditions and processes e g variations in the oxygen content and or sedimentation rate they can also be found in thick anoxic and oxygenated deposits these lithofacies display intervals of faint lamination amalgamated current ripples and normally graded bedding the cores collectively display significant spatial and stratigraphic heterogeneity in lithology sedimentary structures and bioturbation that are related to relative water depth oxygen content sediment input and deep water currents we interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea level fluctuations although secondary stress conditions e g nutrient content and sedimentation rate may also be important unbioturbated and massive fabrics represent anoxic to dysoxic conditions current generated structures are present mainly in the central and distal parts of the basin and are interpreted to represent the presence of contour currents in the proximal parts of the basin laminated and heterolithic units are more common and more bioturbated than in the central and distal basin this study thus can provide significant insights into other shale basins that show similar lateral and vertical variations integration of multidisciplinary studies particularly sedimentology ichnology and total organic carbon aids in understanding and modeling the complexity of these systems

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

sedimentation pattern in a trans himalayan quaternary lake at lamayuru ladakh india abstract located on the indo tsangpo suture zone lamayuru lake in western ladakh was created by neotectonic instability around 35 40 ka the valley fill sequence about 110 m thick reveals an interplay of lacustrine to fluvio deltaic to colluvial processes operating in response to changing climate and tectonic conditions based on integrated approach of sedimentology and palaeontological analysis we propose a sedimentation model for lamayuru lake with reference to changing climatic conditions and neotectonics the coarsening upward succession was divided into five lithofacies associations associations a e each association comprising one or more lithofacies represents a specific depositional environment and marks an independent episode of sedimentation a dominantly muddy sequence of facies association a a product of a lacustrine environment is followed by coarsening upward cycles association b composed of silt to sand that implies laterally shifting deltas thereafter thick sand and gravel deposits constituting fining upward fu unit cycles associations c and d represent deposition in a fluvial domain the upper part of association d composed of matrix supported gravel horizons was deposited as debris flows and marks the termination of sedimentation in the valley the clastic lithofacies facies associations a to d with plant fragments and charcoal presumably indicate warm humid climatic conditions in contrast association e comprising marl lithofacies occurring at four different levels is biogenic and indicates arid to semi arid climatic phases five main types of trace fossils including rhizoliths seem to be representatives of scoyenia ichnofacies and animal burrows indicating a thin population of soft bodied annelid and arthropod communities living under low energy condition nine fossiliferous horizons have yielded characteristic ostracods charophytes and gastropods indicating shallow low energy and cold water ecological conditions coarsening up lake succession extensive synsedimentary deformation tilting of lake beds and the entrenchment of the lamayuru drainage indicate basin evolution under an effective role of neotectonics in the area

the origin of ice in mountain cap clouds abstract ice crystal development in relatively simple layer clouds was studied using airborne instrumentation the patterns in the development of ice in those clouds suggest that the ice originates in association with the initial condensation process near the upwind edge of the cloud since continued ice production does not occur beyond that region the ice development can be attributed to nucleation there is no evidence for secondary ice generation either condensation freezing or contact nucleation could account for the observed nucleation process but special properties are required for the nuclei in either case ice crystal concentrations show a clear temperature trend as expected for a nucleation process

palynofacies and sea level changes in the middle coniacian late campanian late cretaceous of the east coast basin new zealand abstract a palynofacies analysis of four sections through the paton and herring formations of the east coast basin in southern marlborough indicates that the two formations were deposited on the inner to mid shelf in a marine environment with conspicuous input of plant material from adjacent land area the paton formation was deposited on the inner to mid shelf under oxic conditions and in proximity to a river delta possibly in a deltafront setting its lower part is clearly less marine than its upper part pointing to an overall deepening trend with time the deposition of the herring formation took place farther offshore on the mid shelf in a mud dominated environment under poorly oxygenated conditions at the sediment water interface following a landward shift of shoreline a stratigraphic analysis of changes in palynofacies and lithology through the four sections allows a breakdown of the succession into seven depositional sequences separated by unconformities or their correlative conformities a regional sea level curve for the middle coniacian upper campanian in the east coast basin is proposed on the basis of the inferred sequences and chronostratigraphic control from dinoflagellate biostratigraphy the sea level cycles thus inferred for the east coast basin show a poor correlation with the re scaled haq cycle chart suggesting that regional tectonics rather than eustasi controlled the east coast basin sequences

trace fossil analysis of lacustrine facies and basins abstract two ichnofacies are typical of lacustrine depositional systems the scoyenia ichnofacies characterizes transitional terrestrial nonmarine aquatic substrates periodically inundated or desiccated and therefore is commonly present in lake margin facies the mermia ichnofacies is associated with well oxygenated permanent subaqueous fine grained substrates of hydrologically open perennial lakes bathymetric zonations within the mermia ichnofacies are complicated by the wide variability of lacustrine systems detected proximal distal trends are useful within particular lake basins but commonly difficult to extrapolate to other lakes other potential ichnofacies include the typically marine skolithos ichnofacies for high energy zones of lakes and substrate controlled still unnamed ichnofacies associated to lake margin deposits trace fossils are useful for sedimentologic analysis of event beds lacustrine turbidites are characterized by low diversity suites reflecting colonization by opportunistic organisms after the turbidite event underflow current beds record animal activity contemporaneous with nearly continuous sedimentation ichnologic studies may also help to distinguish between marine and lacustrine turbidites deep marine turbidites host the nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea deep lacustrine environments contain the mermia ichnofacies which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems the lower diversity of lacustrine ichnofaunas in comparison with deep sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation during the mesozoic bioturbation depth was higher in lake margin facies than in fully lacustrine deposits while significant degrees of bioturbation were attained in lake margin facies during the triassic major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the cretaceous

hiatal surfaces from the miocene globigerina limestone formation of malta biostratigraphy sedimentology trace fossils and early diagenesis article i nfo article history received 7 december 2006 accepted 24 january 2008 the miocene globigerina limestone of the maltese islands contains widespread omission surfaces with very different characteristics and origins the terminal lower globigerina limestone hardground tlglhg formed during a period of falling sea level coccolith assemblages suggest shallowness sedimentary structures and trace fossil assemblages indicate increasing frequency of storm events and erosional episodes towards the surface calcite cementation which took place around thalassinoides burrows and formed irregular nodules was followed by dissolution of aragonite it is suggested that lithification was linked to microbial reactions involving organic matter in contrast two later surfaces the terminal middle globigerina limestone omissionground tmglog which marks the lower to middle miocene boundary and the fomm ir rih local hardground firlhg both contain early diagenetic dolomite lithification took place in two phases the dolomite is interpreted to have formed beneath the sea floor it was subsequently exhumed and partially corroded as the precipitation of calcitic and phosphatic cements took place around burrows open to the circulation of sea water

gabbroic rocks from the mathematician ridge failed rift plutonic rocks from the ocean crust provide direct evidence on the petrological processes leading to its formation and evolution the nature of such rocks is important for interpreting the origin of on land ophiolites so far oceanic plutonic rocks have been mainly recovered from slow spreading ridges and their associated fractures1 13 and from trenches14 15 here we report the results of petrological studies of a suite of gabbros and related plutonic and volcanic rocks dredged from the mathematician ridge mr which was a fast spreading ridge 43 mm yr 1 until it was abandoned 3 5 myr ago16 textures and mineral chemistry of the rocks together with structural considerations indicate that before abandonment the mr produced fractionated mid ocean ridge basalt morb and fractionated gabbros the gradual decrease of spreading rate during abandonment resulted in morphological change eruption of more primitive morb and possibly tectonic emplacement of the older ferrogabbros alternatively the latter could have been tectonically emplaced after abandonment

ichnology of the laisong formation late eocene early oligocene of the naga hills indo burma range ibr paleoenvironmental significance abstract the late eocene early oligocene laisong formation basal barail group from the naga hills indo burma range has yielded a low diversity of trace fossils i e chondrites gyrolithes ophiomorpha palaeophycus planolites and thalassinoides three ichnofabrics namely ophiomorpha palaeophycus thalassinoides and chondrites planolites have been identified the ophiomorpha palaeophycus ichnofabric grades upsection into chondrites planolites ichnofabric in a fine to medium grained sandstone unit through a succession of alternating thinly bedded sandstone and mudstone containing thalassinoides ichnofabric the ichnofabric distribution is primarily controlled by the change in depositional energy levels from low to high a low diversity trace fossils and lack of graphoglyptids in the laisong formation of naga hills supports the presence of a proximal part of the hyperpycnal lobes of delta fed marine coarse grained turbidite system

rate of serpentinization in seafloor environments the permeability of partially serpentinized peridotites has been measured near room temperature and found to be in the range of 10 11 to 10 12 darcys or 10 7 to 10 8 cm2 sec 1 comparable to shaley materials serpentinites act as semipermeable membranes to salt ions in ocean crust and deep groundwater environments serpentinization must be a continuous process controlled only by water access to ultramafic rocks through their cover given this it will generate high local strains and stresses with episodic cracking the serpentinization process may also contribute to heat flow and ocean floor topography

observation of playa salts as nuclei in orographic wave clouds during the ice in clouds experiment layer clouds ice l dry lakebed or playa salts from the great basin region of the united states were observed as cloud nuclei in orographic wave clouds over wyoming using a counterflow virtual impactor in series with a single particle mass spectrometer sodium potassium magnesium calcium chloride salts were identified as residues of cloud droplets importantly these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei ccn efficiencies close to sea salt using a suite of chemical characterization instrumentation the playa salts were observed to be internally mixed with oxidized organics presumably produced by cloud processing as well as carbonate these salt particles were enriched as residues of large droplets 19 m compared to smaller droplets 7 m in addition a small fraction of silicate containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes while the high ccn activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments this study provides direct evidence of the importance of playa salts in cloud formation in continental north america has not been shown previously studies are needed to model and quantify the impact of playas on climate globally particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes

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

the south african stereospondyl lydekkerina huxleyi tetrapoda temnospondyli from the lower triassic of australia abstract the rsttetrapodfossilfromtherewanformationofthegalileebasin centralqueensland australia isidenti edas lydekkerinahuxleyi astereospondylfoundelsewhereonlyinthe lystrosaurus assemblage zone of south africa apomorphies shared with l huxleyi are anterior palatal vacuitywith anterodorsal projections from its posterior margin ventral surface of skull roof with series ofthickenedridges conditionunknowninotherlydekkerinids andvomerineshagreenpresent possibleautapomorphic reversal restudy of the only other australian lydekkerinid chomatobatrachus halei shows it to be distinct from l huxleyi the rewan formation undifferentiated in the galileebasin can be correlated with the rewan group of the bowen basin and to the early part of the lystrosaurus assemblage zone of the karoo basin south africa which are of griesbachian age varying palaeoenvironments may contribute to the contrasting nature of the australian and southafrican faunas keywords earlytriassic lydekkerina australia arcadiaformation

bioerosion in shells from the early permian rio bonito formation brazil taphonomic paleobiological and paleoecological implications abstract we report the occurrence of sponge borings in composite molds of heteropectinid shells from early permian marine siliciclastic deposits of the parana basin of southern brazil sponge borings are preserved mainly as chambers entobia and channels entobia and clionolithes three preservational variations of entobia are present morphologically equivalent to the alpha beta and gamma ontogenetic stages of clionid sponges this equivalence suggests that the ontogenetic behavior in clionid sponges remains the same since early permian times and points to a conservative evolutionary trend for this group the pattern of bioerosion and other taphonomic signatures indicate rapid shell burial due to frequent and energetic storm events that might have limited the time available for bioerosion activity the new findings improve the paleozoic record of entobia and clionolithes and indicate that sponge borings have potential to be preserved in ancient siliciclastic rocks

volcanic activity and crust mantle exposure in the ultrafast garrett transform fault near 13 28 s in the pacific the 130 km long garrett transform fault which offsets two ultrafast 14 5 cm yr epr spreading segments is the site of volcanic and tectonic activity evidence for recent volcanic events was observed during several dives on oblique ridges 3100 3500 m high trending 040 alpha beta and gamma and on small constructional mounds located in the central transform basin and eastern valley at a depth of 3500 5000 m the constructional features show a fissured terrain suggesting a component of lithospheric opening the strike slip motion of the transform is inferred at several locations between the two epr transform intersection zones from the presence of abundant sediment free talus with crushed rock debris fresh scarps and well developed striations on outcrops of serpentinized peridotites and metamorphosed volcanic breccia the width of the active tectonic zone varies between 200 and 3000 m in the explored area near the eastern and western epr transform intersection zones along the e w trending median ridge walls in the eastern and western transform troughs of the central basin and at several sites on the south facing wall of the transform domain first escarpment the presence of recent volcanic activity implies that the garrett transform behaves as a leaky transform fault the most common volcanics consisting of plagioclase and olivine phyric lava erupted in the transform are compositionally more depleted k ti 0 08 and less evolved mg 60 70 than the basalts encountered on the southern epr segments mg 40 66 and k ti 0 05 0 25 this suggests that different magmatic conditions are operating in the transform domain the transform strike slip motion is responsible for the emplacement of a sliver of serpentinized peridotite located in an area about 2 km wide and 10 km long along the median ridge at the contact with outcrops of metamorphosed basaltic breccia the ultramafics consist of residual harzburgites often impregnated with irregular lenses and dykes of basaltic liquids plagioclase wehrlite and gabbro and are found associated with troctolites dunite and gabbros the emplacement of the ultramafics and their gabbroic inclusions has resulted in the presence of metamorphosed tectonic breccia forming part of the median ridge in the central transform basin

taphonomy of ghost shrimps decapoda axiidea callianassidae associated with their burrows within a middle miocene mud volcano complex of persian arabian gulf kuwait abstract shallow marine strata of the ghar formation exposed along the kuwait arch in the north of kuwait contains fields of mud volcanoes associated with an assemblage dominated by pectinid bivalves and callianassid ghost shrimps the depositional palaeoenvironment is interpreted to be intertidal to subtidal with the water depth not exceeding 50 m and with normal to hypersaline conditions based on the microfossil assemblage a middle miocene age early langhian is inferred suggesting a longer stratigraphic span of the formation despite the previous studies treating the ghar formation as strictly early miocene callianassid body fossils and numerous trace fossils assignable to ophiomorpha have been identified ghost shrimp remains consisting of isolated cheliped elements are assigned to neocallichirus s l which is the likely producer of ophiomorpha burrows as documented by cheliped elements present within burrows and in the substrate around them stable isotopes discrimination modelling confirmed that fluids in the substrate were derived from at least two sources implying the presence of active mud volcanoes in the environment inhabited by ghost shrimps effusive activity of mud volcanoes further enhanced disarticulation and fragmentation of callianassid remains the micritic matrix of ghost shrimp exoskeletons is indicated to have resulted from a mixture of local seawater with fluid of continental origin this ghost shrimp occurrence is the first formal report of fossil decapod crustaceans from kuwait