the benthic boundary biofacies model hartland shale member greenhorn formation cenomanian western interior north america abstract well laminated predominantly non burrowed strata of the mid cretaceous western interior basin contain in situ epifaunal body fossils indicative of dysaerobic benthic oxygen levels a gradient of increasing ecological complexity in these dysaerobic faunas is identifiable and reflects improvements in benthic conditions using these faunal assemblages a benthic boundary biofacies model is developed in which the critical redox boundary is in dynamic equilibrium at the sediment water interface variations in bottom water oxygenation as well as substrate characteristics are cited as the controlling factors in the position of this boundary and thus control benthic colonization the model describes a background of low oxygen tolerant flat clam communities which were predominant during deposition of the late cenomanian hartland shale member superimposed on this background a history of brief episodic colonization and sedimentation events reveals a dynamic climate ocean system in the western interior sea which maintained a delicate balance of oxygen deficiency at the sediment water interface

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

carbon isotope signatures of bacterial 28 norhopanoic acids in miocene pliocene diatomaceous and phosphatic sediments abstract a series of c 29 c 31 28 norhopanoic acids occur in neogene marine sediments of the onnagawa funakawa and tentokuji formations northeastern japan and in the monterey formation of california usa the 28 norhopanoic acids exist mainly as free acids but are partly bound to kerogen and the polar fraction of the solvent extract via an ester bond the 13 c depletions of c 29 and c 31 28 norhopanoic acids compared with those of c 30 and c 32 regular hopanoic acids indicate that these 28 demethylated and regular hopanoic acids are derived from different precursor organisms the upper onnagawa formation contains abundant 28 norhopanoic acids and is characterized by the occurrence of calyptogena sp bivalvia which lives in a specific chemoautrophic ecosystem that utilizes chemical substrates from hydrothermal vents or cold seeps the depletion of 28 norhopanoic acids in 13 c compared with kerogen suggests that the 28 norhopanoic acids have been derived from bacteria that utilized 13 c depleted co 2 as their carbon source

paleozoic cambrian through devonian anoxitropic biotopes berry w b n wilde p and quinby hunt m s 1989 paleozoic cambrian through devonian anoxitropic biotopes palaeogeogr palaeoclimatol palaeoecol 74 3 13 the oxygen poor to denitrified waters of modern oceans provide an analog for open ocean conditions which contained the early paleozoic graptolite biotope certain euphausiids other zooplankton and fish as demonstrated in the eastern tropical pacific are found concentrated in and about denitrified waters the boundary zone between oxic and denitrified waters show intense organismal growth due to the increased chemical availability of nutrients as reduced nitrogen compounds such waters are areally limited in the present cold and well ventilated modern ocean the distribution patterns showing attraction to low or oxygen depleted waters anoxitropy in these modern open marine faunas suggest that early paleozoic plankton and nekton preserved in lithofacies formed under low oxygen or anoxic coditions could have been similarly attracted to the more extensive ancient denitrified and anoxic waters the major paleozoic faunal groups in order of their occupation of the niche include agnostid and olenid trilobites graptoloid graptolites styliolinids thin shelled bivalves small orthocone nautiloids and early ammonoids the expansion of low oxygen to anoxic waters across the shelves during warm climates in the early paleozoic may be correlated with major evolutionary radiations in the graptolites and possibly in the early ammonites

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

transfer of germanium to marine sediments insights from its accumulation in radiolarites and authigenic capture under reducing conditions some examples through geological ages in the geosphere germanium ge has a chemical behavior close to that of silicon si and ge commonly substitutes for si in small proportions in silicates studying the evolution of the respective proportions of ge and si through time allows us to better constrain the global si cycle the marine inventory of ge present as dissolved germanic acid is facing two main sinks known through the study of present sediments 1 incorporation into diatom frustules and transfer to sediments by these shuttles 2 capture of ge released to pore water through frustule dissolution by authigenic mineral phases forming within reducing sediments our goals are to determine whether such a bio induced transfer of ge is also achieved by radiolarian and whether ge could be trapped directly from seawater into authigenic phases with no intervention of opal secreting organisms shuttles to this end we studied two paleozoic radiolarite formations and geological formations dated of devonian jurassic and cretaceous deposited under more or less drastic redox conditions our results show that the ge si values observed for these radiolarites are close to slightly above those measured from modern diatoms and sponges in addition our results confirm what is observed with some present day reducing sediments the ancient sediments that underwent reducing depositional conditions are authigenically enriched in ge furthermore it is probable that at least a part of the authigenic ge came directly from seawater the recurrence and extent through time and space of anoxic conditions affecting sea bottoms have been quite important through the geological times consequently the capture of ge by reducing sediments must have impacted ge distribution and in turn the evolution of the seawater ge si ratio

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

foraminiferal records of bottom water oxygenation and surface water productivity in the southern japan sea during 160 15ka associations with insolation changes abstract analyses of the benthic and planktonic foraminiferal record were conducted to understand temporal variations in sea floor oxygenation and surface productivity during periods of dark layer deposition between 160 and 15 ka based on data from sediment core images md01 2407 water depth 932 m from the southern japan sea the dark layers in the core were classified into six types on the basis of benthic foraminiferal assemblages which reflect the nature and amount of organic material on the sea floor as well as the degree of oxygenation of bottom waters three of the dark layer types were deposited in conditions strongly associated with increased surface productivity which correlates with positive or negative peaks of summer insolation in the northern hemisphere during periods of insolation maxima summertime surface productivity was enhanced because of the inflow of nutrient rich surface waters associated with high precipitation in eastern asia caused by intensification of the east asian summer monsoon in contrast relatively sustained organic matter fluxes to the sea floor occurred during insolation minima possibly affected by active vertical mixing when the east asian summer and winter monsoons were both intensified in a given period well oxygenated bottom water environments combined with high surface productivity may have resulted in dark layer deposition because of a combination of strong wintertime water convection and increased summertime surface productivity it is likely that the organic carbon content of sediments underestimates surface productivity during depositional conditions favoring the sedimentary decomposition of organic matter

evidence for a compositional boundary within the lithospheric mantle beneath the kalahari craton from s receiver functions abstract s and p receiver functions from the southern african seismic experiment are analyzed for lithospheric discontinuities beneath the kalahari craton besides the moho the most prominent feature is a discontinuous reduction in seismic velocity of about 4 5 at approximately 150 km depth the discontinuity appears to have a width of about 10 km termed the k discontinuity this feature is restricted to the northern half of the array extending from the zimbabwe craton south to the tml thabazimbi murchison lineament and in the west from botswana to the edge of the kalahari craton in the east it spans several archean sutures and is thus unlikely related to archean tectonics it does however appear to be related to subsequent magmatic episodes the strongest anomaly is coincident with the most intense karoo volcanism and it extends to the northern edge of the bushveld intrusion from mantle xenoliths and xenocrysts the entire lithosphere in this region appears to have experienced a long term infiltration of basaltic melt and metasomatic fluids we propose that the k discontinuity reflects the influence of this melt metasomatic infiltration which has over time intruded and refertilized the lithosphere based on kimberlites pipes that show obvious signs of melt metasomatism and likely karoo influence the observed reduction in seismic velocity is plausibly consistent with the observed major element and volatile enrichment at 150 km depth in such kimberlites if this interpretation is correct then the high temperature kimberlite nodules that most clearly reflect this perturbation likely represent the general state of the lower lithosphere rather than only reflecting local mantle properties in the immediate vicinity of the kimberlite eruption

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

role of bacterial mats in oxygen deficient marine basins and coastal upwelling regimes preliminary report bacterial mats play an important role in the sedimentation history of many marine biogenic regimes observations of the living mats suggest that in shallow waters they are dominated by photosynthetic cyanobacteria while in deeper waters the mats are dominated by nonphotosynthetic sulfur oxidizing bacteria fossilized remains of analogous mat structures from the miocene monterey formation are commonly associated with oil producing and phosphate rich zones preliminary observations suggest that bacterial mats may be a source of the organic matter that in time is thermally altered to hydrocarbons

physical irrigation of relict burrows implications for sediment chemistry abstract relict biogenic structures are common in some areas of the sea floor particularly the deep sea and are potentially irrigated by flow induced by overlying water currents such physically induced irrigation could have major effects on sedimentary solutes and influence interpretation of their measured distributions experiments show that the rate of flow through these uninhabited burrow structures is in some cases comparable to irrigation rates by animals even at the very low mean current velocities expected in the deep sea boundary layer induced irrigation is often sufficient to hold the concentrations of solutes in the burrow water close to that of the overlying water as a result these relict structures may in some ways be functionally equivalent to inhabited burrows with respect to modification of sediment chemistry

trace fossil model for reconstructing oxygenation histories of ancient marine bottom waters application to upper cretaceous niobrara formation colorado abstract trends of decreasing trace fossil diversity burrow size and penetration depth with diminishing oxygen availability in contemporary marine settings have been incorporated with the concept of trace fossil tiering to develop a model for reconstructing the oxygenation history of ancient basin bottom waters more sensitive than traditionally employed criteria the model permits detailed evaluation of relative degree of oxygenation through the recognition of oxygen related ichnocoenosis ori units or units of strata deposited under similar levels of bottom water oxygenation when employed in detailed vertical sequence analyses the model may also be used to construct interpreted oxygenation curves that reflect rates and magnitudes of temporal change in redox conditions the utility of the model is demonstrated by its application to rhythmically bedded calcareous strata of the niobrara formation upper cretaceous exposed in colorado non laminated strata of the niobrara are characterized by four recurring trace fossil suites referred to as the 1 chondrites 2 zoophycos teichichnus 3 planolites and 4 thalassinoides assemblages on the basis of trends in trace fossil diversity burrow diameter and penetration depth these assemblages are recognized as oxygen related ichnocoenoses interpreted oxygenation curves for the basal fort hays member reflect high magnitude redox cycles characterized by rapid deoxygenation events followed by gradual reoxygenation phases curves for the overlying smoky hill member reflect an overall lower degree of oxygenation with more irregular lower magnitude redox fluctuations significant correlation between interpreted levels of paleooxygenation and organic carbon content illustrate the model s potential for evaluating the distribution of organic rich fine grained strata co interpretation of these variables with carbonate content supports the premise that deposition was controlled by paleoceanographic perturbations modulated by milankovitch like climatic cycles comparison with traditionally emphasized macroinvertebrate body fossil criteria clearly demonstrates the greater utility of the trace fossil approach for evaluating paleo oxygenation

rhythmic bedding produced in cretaceous pelagic carbonate environments sensitive recorders of climatic cycles various types of rhythmic bedding are prominent features of cretaceous pelagic carbonates these bedding rhythms are the primary depositional result of variations in carbonate productivity terrigenous dilution redox conditions and or the energy of bottom currents each bedding cycle type is different in its expression in the stratigraphic record but ultimately was caused by rhythmic climatic variations related to variations in receipt of solar insolation as the result of the earth s orbital characteristics the so called milankovitch cycles stratigraphic sequences may contain a single bedding cycle type or a composite of several types although sediment type and sedimentary structures were influenced by variations in local climatic oceanographic tectonic and diagenetic parameters pelagic carbonate environments during the cretaceous were particularly sensitive recorders of orbitally induced changes in worldwide climate

kimmeridge clay sedimentation a new cyclic model abstract the kimmeridgian upper jurassic fine clastic sequences of the boulonnais northern france and dorset southern england represent oxygen controlled environments five facies types with increasingly deteriorating living conditions ranging from normal shelf environments to submarine lifeless desert have been distinguished the widespread occurrence of this facies in the late jurassic north atlantic shelf sea and the palaeogeographic situation require a large scale model to explain the kimmeridge clay sedimentation anoxic conditions are generally explained by one of three models none of which applies directly to the kimmeridge clay a new model derived from the overall palaeogeographic and palaeoclimatic situation is therefore proposed in this model water mass stratification and anoxic bottom conditions refer to a high latitude monsoonal type wind circulation causing a water current and counter current system in the north atlantic shelf sea and the arctic ocean variations in the amount of oxygen in the bottom waters allow recognition of four different cycles with periods ranging from seasonal to 3 107 years they influenced the counter current system and the resulting anoxic conditions

petrology of smoky hill member niobrara chalk upper cretaceous in type area western kansas the smoky hill member of the niobrara chalk is composed primarily of olive gray well laminated to nonlaminated impure chalk which is mostly foraminiferal pelmicrite with packstone or wackestone texture the rock is characterized by well stratified grain fabric ubiquitous constituents include coccolith rich fecal pellets mostly well preserved tests of planktonic forams wisps and silt sized grains of black organic matter fish bones and scales and minute framboids of pyrite or its oxidized equivalent inorganic detritus is common in all samples but only sparse grains of angular quartz silt are detected commonly in thin sections scattered through the member are thick to very thin beds of lighter colored bioturbated probably microbioturbated and granular chalk these are mostly foraminiferal and pelletal micritic wackestones which lack well stratified grain fabric in thin sections fecal pellets are less obvious than in well stratified chalks organic matter is much less common and pyrite framboids are less common in the matrix diagenetic features of smoky hill stratified chalks include compactional deformation of fecal pellets forams burrow structures and macroinvertebrate remains dissolution of aragonitic skeletal material incipient microstylolites sparry calcite cement in foram chambers interstitial calcite cement and secondary calcite overgrowths on coccoliths especially in the matrix bioturbated and granular beds are less well compacted than the stratified chalks and have greater amounts of secondary calcite as interstitial cement and overgrowths on coccoliths in these chalks lithification was initiated earlier than in the stratified chalks bioturbation of these and related kansas chalk deposits produced textures similar to those ascribed by others to deep burial diagenesis and extensive sol tion transfer thin section and scanning electron microscope sem data suggest that most reduction of original porosity to the present average of 38 was accomplished by gravitational compaction the remainder of porosity reduction resulted from the limited addition of secondary calcite which was derived mainly from dissolution of abundant aragonitic skeletal remains and in small part from pressure solution the smoky hill chalk is a pelagic deeper water outer shelf deposit which was laid down mostly as a soft perhaps mostly soupy coccolith rich ooze on a nearly flat sea floor under conditions of normal or nearly normal salinity and generally poor bottom water circulation at irregularly spaced intervals deposition of purer ooze furnished substrates suitable for a burrowing endobenthos which bioturbated sediments and helped to initiate earlier lithification than in nonbioturbated deposits

the exaerobic zone a new oxygen deficient marine biofacies classical biofacies models1 2 for reconstructing palaeoenvironments of strata deposited in oxygen deficient marine settings define three principal facies aerobic 1 0 ml 1 1 o2 dysaerobic 1 0 to 0 1 ml 1 1 o2 and anaerobic 0 1 ml 1 1 o2 zones these models have postulated a decrease in organism size and degree of calcification as well as a drastic reduction in the relative percentage of fauna possessing calcified skeletons as the dysaerobic anaerobic boundary is approached through use of evidence independent of that provided by body fossils we demonstrate here that in portions of the monterey formation miocene california the bivalve anadara montereyana occurs in situ almost exclusively in strata deposited at the dysaerobic anaerobic boundary the occurrence of fossils of large well calcified benthic macroinvertebrates at this redox boundary contradicts classical biofacies models1 2 and there fore provides the basis for definition of a new oxygen related biofacies the exaerobic zone the exaerobic zone concept when adjusted for differences in basin configuration and palaeoceano graphic conditions provides a potentially useful model for explain ing occurrences of shelly benthic fossils within laminated organic rich strata of other phanerozoic marine sequences

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

paleoecology of the marine endobenthos endobenthic animals which reside within the sea bottom include stationary suspension feeders mobile deposit feeders and both stationary and mobile carnivores their activities especially with regard to dwelling feeding walking crawling and resting nesting are recorded as trace fossils abundance diversity and density of some kinds of trace fossils allow interpretation of the population strategies of the trace makers in terms of opportunistic r selected and equilibrium k selected strategies opportunistic ichnotaxa tend to be faciesbreaking traces which are highly localized in low diversity high density trace fossil associations in rocks representing environmental extremes e g variable salinities harsh temperatures low oxygen levels or shifting substrates equilibrium ichnotaxa usually are restricted to particular sedimentary facies and are characteristic of high diversity low dominance trace fossil associations in sediments reflecting stable predictable environmental conditions the most important environmental factors influencing the composition of trace fossil assemblages in marine settings are bathymetry substrate oxygen and hydrodynamic energy the four factors are closely interrelated because as water depth increases there is a general decrease in sediment grain size and hydrodynamic energy of the depositional environment as depth below the water sediment interface increases the firmness of the sediment due to compaction and dewatering increases and the oxygen content of interstitial waters drops drastically marine ichnofacies are largely substrate controlled soupgrounds are water saturated incompetent substrates typified by highly compressed and usually unidentifiable burrows softgrounds commonly contain numerous distinctive burrows and are zoned bathymetrically by the skolithos cruziana zoophycos and nereites ichnofacies firmgrounds are characterized by stiff compacted sediments in which traces of the glossifungites ichnofacies are excavated hardgrounds are cemented substrates in which bioerosion traces of the trypanites ichnofacies are bored woodgrounds are woody materials that have been exposed to the sea and bored by bivalves which produce characteristic traces of the teredolites ichnofacies tiering of endobenthic communities is common and is related to substrate preference of the burrowers and oxygen stratification of interstitial waters

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

deposition of a saline giant in the mississippian windsor group nova scotia and the nascent late paleozoic ice age abstract saline giants are vast marine evaporite deposits that currently have no modern analogues and remain one of the most enigmatic of chemical sedimentary rocks the mississippian windsor group ca 345 ma maritimes basin atlantic canada is a saline giant that consists of two evaporite rich sedimentary sequences that are subdivided into five subzones sequence 1 is composed almost entirely of thick halite belonging to subzone a osagean sequence 2 is in unconformable contact and comprised of stacked carbonate evaporite peritidal cycles of subzones b through e meramecian subzone b the focus of research herein documents the transition from wholly evaporitic to open marine conditions and thus preserves an exceptional window into the processes forming saline giants lithofacies stacking patterns in subzone b reveal that higher order fluctuations in relative sea level produced nine stacked parasequences interpreted to reflect high frequency glacioeustatic oscillations during the onset of the late paleozoic ice age each parasequence reflects progradation of intertidal and sabkha sediments over subtidal carbonate and evaporite deposits dissimilarities in cycle composition between sub basins imply the development of contrasting brine chemistries from differing recharge rates with the open ocean what the windsor group shows is that evaporite type is ostensibly linked to the amplitude and frequency of sea level rise and fall during deposition true saline giants like the basinwide evaporites of sequence 1 apparently require low amplitude long frequency changes in sea level to promote the development of stable brine pools that are only periodically recharged with seawater by contrast the high amplitude short frequency glacioeustatic variability in sea level that controlled the accumulation of peritidal evaporites in subzone b produce smaller subeconomic deposits with more complex facies relationships

composite ichnofabrics and tiering of burrows infaunal communities in marine environments typically are tiered that is different taxa live at different depths within the sediment tiered suites of biogenic structures yield complex biogenic sedimentary fabrics ichnofabrics with the traces of deep burrowing organisms overprinted on those of shallow burrowing organisms careful analysis of crosscutting relationships of burrows in such composite ichnofabrics allows reconstruction of the tiered nature of fossil endobenthic communities it is important to recognize that the best preserved and most prominently displayed trace fossils in most assemblages usually represent the deepest tier thus they were farther removed from the sea floor and therefore less indicative of actual sea floor conditions than the more poorly preserved traces of the shallower tiers on which the deeper traces are juxtaposed

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

trace fossil model for reconstruction of paleo oxygenation in bottom waters recognition of fluctuations in the degree of paleo oxygenation of bottom waters recorded in fine grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions general sedimentary fabric composition of trace fossil assemblages and burrow size and crosscutting relationships have been incorporated into a trace fossil tiering model that permits detailed reconstruction of changes in paleo oxygenation of bottom waters applications of this model to the miocene monterey formation california and the cretaceous niobrara formation colorado indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body fossil information

unburrowed mudstones may record only slightly lowered oxygen conditions in warm shallow basins unbioturbated mudstones and highly bioturbated silty and sandy mudstones from the late albian of alberta canada are characterized by their ichnological foraminiferal and geochemical signatures a comparison of these data sets is undertaken to isolate the dissolved oxygen do conditions that led to the preservation of unbioturbated mudstones versus highly bioturbated silty and sandy mudstones highly diverse and abundant benthic foraminiferal assemblages coupled with conclusive geochemical signatures indicate that unbioturbated mudstones were deposited under oxic bottom waters the paucity of bioturbation in these rocks is attributed to the persistence of low oxic conditions 5 do 2 mg l 1 at the seafloor comparable to the present day gulf of mexico we assert that unbioturbated mudstone should not automatically be attributed to oxygen deficiency 2 mg l 1 instead it may reflect oxygenation sufficient to support benthic microfauna foraminifera but insufficient to sustain a diverse ecosystem of macrofauna burrowing fauna moreover we propose that the distribution of unburrowed mudstones deposited below low oxic waters is predictable a paucity of bioturbation is normal in shallow marine below fair weather wave base to 200 m water depth deposits of subtropical to tropical ocean basins and or semienclosed seaways

centennial to millennial scale changes in oxygenation and productivity in the eastern tropical south pacific during the last 25 000 years oxygen minimum zones omz have expanded in all tropical oceans during the last 50 years resulting in habitat contraction and considerable changes in marine biogeochemistry however for a better understanding of the omz dynamics under the current climate change two questions are relevant 1 how do the magnitude and temporal changes in oceanic dissolved oxygen of the last few decades compare to the natural variability on longer timescales and 2 what were the local and remote factors driving omz changes in the past in the present study we use a stacked record covering the last 25 kyr from the eastern tropical south pacific etsp omz to reconstruct changes in oxygenation and productivity we use a suite of proxies including the presence of laminations redox sensitive metals u mo re ni and cu total organic carbon and 15 n measurements water column denitrification and sediment redox conditions show pronounced centennial to millennial scale variability during the last 25 kyr with oxygenation levels as low as at present global cold periods at different timescales such as the last glacial maximum 23 19 kyr bp and the little ice age 1500 1850 ad were associated with a weak omz and low export production while warm intervals such as the deglaciation part of the medieval climate anomaly and the last 100 years are associated with a stronger omz and high export production water column denitrification and sediment redox conditions were strongly coupled during the last 25 kyr bp apart from one remarkable exception during the antarctic cold reversal sediments were less reducing but the water column denitrification was high resulting in a strong but shallow omz this may have been produced by an enhanced antarctic intermediate water flow contrary to our expectations and modeling predictions for the next few decades we observe a weak etsp omz during the warm mid holocene which may have been the result of a stronger walker circulation that brought oxygen rich waters to intermediate depths off peru via equatorial undercurrents in combination with other paleoceanographic reconstructions our results show that oxygenation variability in the etsp omz was influenced by ocean circulation changes in the tropical pacific high latitude oceanographic and climatic changes and local productivity

a hypersaline ichnoassemblage from the middle triassic carbonate ramp of the tatricum domain in the tatra mountains southern poland abstract the middle triassic of the tethyan domain contains heavily bioturbated carbonates known as vermicular limestones in the tatricum domain in the tatra mountains western carpathians these were deposited on a restricted carbonate ramp below the fair weather wave base sedimentological and geochemical evidence points to a hypersaline depositional environment the vermicular limestones contain an impoverished ichnoassemblage of the cruziana ichnofacies dominated by planolites small size thalassinoides is less common balanoglossites and rhizocorallium are rare and helminthopsis phycosiphon and taenidium are very rare the ichnoassemblage points to environmental stress related foremost to hypersaline conditions and less so to lowered oxygenation trace fossil diversity and abundance diminishes from totally bioturbated limestones to dolomitic limestone and dolostones and disappears in the dolostones probably due to an increase in salinity to values in which burrowing fauna is eliminated the repetitive occurrence of the vermicular limestones and associated facies reflects partly fluctuations of salinity which were probably climatically controlled

significance of lamination in toarcian lower jurassic shales from yorkshire great britain abstract lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes variations in types of lamination in toarcian lower jurassic shales of yorkshire great britain are related to changes in sedimentary processes x radiography petrography and scanning electron microscopy techniques reveal three lamination types in the dark grey grey shales and black jet rock and bituminous shales jurassic shales fine lamination is produced in deeper more offshore anaerobic conditions in which suspension settling dominates thick lamination indicates the influence of bottom flowing currents in shallow water wavy lamination is produced by benthic microbial mats the toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment the examples of various unique macro and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation

chemosymbiont dominated seafloor communities in modern and cretaceous upwelling systems support a new high productivity variant of standard low oxygen models faunal analysis of modern benguela upwelling system namibia and ancient upper cretaceous israel sedimentary records rich in organic matter biogenic silica carbonate and phosphate indicates that contrary to stereotypes of upwelling systems as dead zones macrobenthic communities are present but highly variable biofacies vary with distance from the upwelling core and as a function of both the supply of food to the seafloor and the oxygen demand it creates there under a high organic supply large bodied chemosymbiotic bivalves dominate exaerobic and lower dysaerobic seafloors and deposit feeders are abundant in upper dysaerobic and aerobic zones macrobenthic biofacies under upwelling thus contrast strongly with the overwhelmingly filter feeder dominated biofacies encountered in the dark siliciclastic shales on which standard oxygen restricted biofacies models have been based and argue that mechanistically the low oxygen conditions characterizing those shales reflect ordinary levels of water column productivity and arise largely from water column stratification our biofacies model requires testing in other upwelling records however we expect it to be robust and useful given the long evolutionary histories of the chemosymbiotic and deposit feeding guilds providing a new means for discriminating the relative roles of high organic flux and low ventilation in creating low oxygen conditions at the seafloor

biochronology of triassic bivalves substantial advances by numerous researchers over the past 20 years have made it possible to develop a composite biochronological scheme for the triassic based on the bivalves claraia peribositria enteropleura daonella halobia eomonotis and monotis these bivalves exhibit temporal durations nearly equal to ammonoids and conodonts widely distributed across the tethys panthalassa and boreal regions these bivalves occur in a wide variety of marine facies and water depths but are most notable for their thick shell accumulation in deeper water oxygen deficient environments they were most likely resting or reclining benthos may have housed chemosymbionts and were part of episodic opportunistic palaeocommunities in or near oxygen deficient settings a new biochronological zonation for bivalves is presented that encompasses the entire triassic and is integrated with standard ammonoid schemes the lower triassic is characterized by 2 3 zones of claraia most notably from the eastern tethys representing the entire induan and lower portion of the olenekian later in the olenekian and most notably from the boreal realm species of peribositria included by some workers within bositra provide useful zonal indexes the middle triassic is well represented by enteropleura middle anisian and daonella upper anisian through ladinian in the tethys and north america with significant occurrences through out the circum pacific and boreal realms the upper triassic can be subdivided into 8 13 bivalve zones based on the succession of halobia eomonotis and monotis sensu lato species with best representation in the tethys boreal and eastern panthalassa regions

dorvilleids and arabellids annelida as indicators of dysaerobic events in well laminated non bioturbated deposits of the french mesozoic abstract oceanic anoxic environments are characterized by laminated deposits rich in organic carbon and sparse benthic organisms in anaerobic environments the benthic boundary is free of fauna by contrast in dysaerobic environments the benthos comprises echinoderms bivalves crabs ostracods foraminifera and polychaete annelids which are known from tubes and burrows when extremely low oxygen concentrations are present but not anoxic conditions the only survivors are known by their bioturbation the palynological studies in process on french black shales of the toarcian kimmeridgian and cenomanian turonian boundary provide a good occasion to give an identity to these bioturbations worms involved in the disorganization of sediments are revealed by the remains of their jaw apparatuses which are called scolecodonts and are assigned to the dorvilleidae mochtyellidae complex and arabellidae families the inferred length of the annelids is very small hence the bioturbation is no longer visible after burial diagenesis in this case laminated deposits without benthic fauna and burrows are not necessary anoxic deposits but could be dysaerobic ones

high resolution geochemistry and sequence stratigraphy of the hushpuckney shale swope formation eastern kansas implications for climato environmental dynamics of the late pennsylvanian midcontinent seaway abstract the hushpuckney shale member of the swope formation missourian stage eastern kansas is the core shale of a kansas type cyclothem formed during the late transgressive to early regressive phases of a late pennsylvanian glacio eustatic cycle coeval high frequency climato environmental dynamics of the midcontinent seaway are preserved in the kgs orville edmonds no 1a study core as centimeter scale variation in major components organic carbon authigenic sulfides and phosphate detrital siliciclastics organic macerals trace element redox proxies mo u v zn and ichnofabric features benthic o 2 levels declined sharply from the base of the black shale 0 cm went sulfidic at 4 cm and reached a redox minimum at 21 cm above this level redox potential gradually rose fluctuating between sulfidic and nonsulfidic conditions from 35 cm to the black shale gray shale contact at 52 cm onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft bodied organisms comprised of deep tiered tracemakers tolerant of low o 2 conditions trichichnus and shallow tiered tracemakers favoring soupground helminthopsis or firmground substrates the zoophycos phycosiphon schaubcylindrichnus planolites association most geochemical records exhibit a low order cycle spanning the full 52 cm thickness of the black shale submember reflecting a dominant glacio eustatic control the base and top of the black shale submember record lateral migration of the pycnocline across the midcontinent shelf during the transgressive and regressive phases respectively the maximum flooding surface mfs is at 17 23 cm an interval containing the euxinic peak and characterized by high concentrations of illite representing a cratonic siliciclastic flux and terrestrial organic macerals the product of transient increases in humidity weathering rates and the export of coal swamp vegetation associated with the interglacial highstand of the swope cyclothem although a transgressive surface of maximum starvation sms cannot be confidently identified a phosphate rich regressive condensation surface at 28 34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth a correlative shift in dominance from terrestrial to marine derived organic macerals reflects increased upwelling of nutrient rich deepwaters and enhanced primary productivity penecontemporaneous paleogeographic and climatic factors e g semirestricted circulation monsoonal precipitation predisposed the midcontinent seaway toward sensitivity to high frequency climato environmental fluctuations which are preserved as 2 to 7 cm thick cycles in the study core the 52 cm thick black shale submember contains 12 such high order cycles which have an estimated average duration of 2 to 9 kyr implying a sub milankovitch band i e millennial scale climatic control the results of this study are relevant to the sequence stratigraphic interpretation of kansas type cyclothems the dynamics of gondwanan ice age glacio eustatic cycles and the development of boundary conditions for late pennsylvanian paleoclimate models