r selected benthic foraminifera with associated bacterial colonies in upper pleistocene sediments of the ross sea antarctica implications for calcium carbonate preservation investigations on foraminifera from upper pleistocene holocene sediments cored in the continental slope of the western ross sea 2383 m water depth revealed that the record of calcareous assemblages was restricted to a limited time interval approximately 6 kyr and characterized by a dominance of phytodetritus exploiting taxa such as alabaminella weddellensis and epistominella exigua rod shaped calcified fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces either as clusters or as isolated cells suggesting that significant changes from underto oversaturated conditions with respect to calcium carbonate in the chemistry of the seawater developed before the final burial of the foraminiferal tests we postulate that bacterial activity on a microenvironmental scale interface and pore water in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities 1999 elsevier science b v all rights reserved

exhumation of messinian evaporites in the deep sea and creation of deep anoxic brine filled collapsed basins abstract the first part of the paper summarizes some basic concepts concerning a the distribution of messinian evaporites in the deepest parts of the mediterranean sea and b the mediterranean ridge accretionary wedge and its peculiar characteristics deriving from the presence of a substantial evaporitic body in the deforming sedimentary prism then five brine filled anoxic collapsed basins tyro bannock urania atalante and discovery discovered from 1983 to 1994 are presented and discussed in their physiographic geologic hydrologic and geochemical characters high density brines deriving from submarine dissolution of outcropping or subcropping evaporites accumulate at the bottom of collapsed basins if they are not swept away by submarine currents the interface separating normal sea water from high density brines is sharp with a density contrast of about 20 and lies at 3200 3500 m below sea level strong bacterial activity is developing at the interface and living bacteria have been recovered from the anoxic salty brines thickness of the brines may be up to 500 m thermal stratification has been observed in three brine lakes exhumation and dissolution of messinian evaporites in the mediterranean ridge occur in different tectonic settings pull apart basin tyro subducting seamount close to the outer deformation front bannock basin top of a backstop urania atalante and discovery basins chemistry of the brines is strongly variable and suggests dissolution of different layers or levels of the messinian suite discovery brines are the saltiest ever recorded in natural environment their saturation in mg chloride bischofite the end product of sea water evaporation suggests that the deepest parts of the eastern mediterranean were close to dryness at the end of the salinity crisis strongly supporting the deep basin desiccation model

towards a formal description of foraminiferal assemblage formation in shallow water environments qualitative and quantitative concepts the use of foraminifera in palaeoenvironmental reconstructions e g sea level may be complicated by processes such as infaunal test production taphonomic degradation and bioturbation which act to modify contemporary analogue surface assemblages during and subsequent to burial understanding the palaeoenvironmental significance of these processes is limited by the absence of a clear theoretical description of the mechanics of foraminiferal assemblage formation a conceptual framework is proposed which describes assemblage formation in terms of the balance of test inputs and losses within a volume of sediment undergoing burial through the upper sedimentary zones of test production taphonomic processes and bioturbation a corresponding mathematical model is described and shown to explain empirical dead test distributions in terms of empirically defined standing crops sedimentation and mixing rates together with model estimates of standing crop turnover and or taphonomic decay rates this approach provides a quantitative basis for understanding assemblage formation and for comparing assemblage forming processes between species environments and study sites rates of standing crop turnover and taphonomic loss are identified as the primary unknowns in the study of foraminiferal assemblage formation these multiple unknowns make interpretations of cored data ambiguous emphasising the need for a detailed and coherent framework of theory and assumptions for understanding the mechanics assemblage formation if interpretations are to be clear and conclusive

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

the spatial and vertical distribution of living stained benthic foraminifera from a tropical intertidal environment north queensland australia we investigated the distribution of living stained benthic foraminifera across a tropical intertidal shoreline adjacent to cocoa creek queensland australia for the purpose of better understanding the nature of test production and ultimately fossil assemblage development within such environments short cores up to 1 m were collected during the wet and dry season along an elevational gradient comprising non vegetated intertidal mudflat and higher intertidal mangrove forest environments the distribution of stained specimens can be broadly delineated into assemblages characterising upper mangrove 2 64 2 91 m above lowest astronomical tide lat and low mangrove mudflat 1 62 2 18 m above lat environments agglutinated species were generally limited to upper mangrove stations calcareous species occurred within all of the intertidal environments examined but differ in their composition between upper and lower intertidal settings upper mangrove faunas were characterised by the agglutinated species arenoparrella mexicana haplophragmoides wilberti miliammina fusca miliammina obliqua and trochammina inflata and the calcareous species helenina anderseni live stained assemblages at lower intertidal elevations were dominated by the calcareous species ammonia aoteana as well as rosalina spp elphidium oceanicum triloculina oblonga ammonia pustulosa and shackoinella globosa absolute densities of stained specimens were lowest within the low mangrove sediments 6 8 specimens per cm2 but higher within the upper mangrove 25 249 specimens per cm2 and mudflat 8 77 specimens per cm2 abundances within mudflat sediments varied seasonally being significantly larger in the wet season whereas those within mangrove zone sediments changed little through the year stained foraminifera were found to a maximum depth of 50 cm at cocoa creek extending to the greatest depth at the upper mangrove stations and were generally shallowest beneath the lower mangroves all stations had over 50 of their foraminiferal standing crop below the upper 1 cm although at most stations 10 of living specimens occurred within this layer comparison of this data with dead assemblages suggests that 1 abundances of stained specimens averaged over two sampling events reasonably approximate aggregate in situ test production and 2 a clear enrichment of infaunal species occurs within the mangrove the latter effect was less conspicuous on the mudflat due to high rates of mixing and assemblage time averaging which obscure the signal of test production within the dead assemblages in both cases the validity and stratigraphic resolution of surface assemblages for sea level and other palaeoenvironmental reconstructions is questionable

multi elemental composition of authigenic carbonates in benthic foraminifera from the eastern bering sea continental margin international ocean discovery program site u1343 abstract bering sea sediments represent exceptional archives offering the potential to study past climates and biogeochemistry at a high resolution however abundant hydrocarbons of microbial origin especially along the eastern bering sea continental margin can hinder the applicability of palaeoceanographic proxies based on calcareous foraminifera due to the formation of authigenic carbonates nonetheless authigenic carbonates may also bear unique opportunities to reconstruct changes in the sedimentary redox environment here we use a suite of visual and geochemical evidence from single specimens of the shallow infaunal benthic foraminiferal species elphidium batialis saidova 1961 recovered from international ocean discovery program iodp site u1343 in the eastern bering sea to investigate the influence of authigenic carbonates on the foraminiferal trace metal composition our results demonstrate that foraminiferal calcite tests act as a nucleation template for secondary carbonate precipitation altering their geochemistry where organoclastic sulphate reduction and anaerobic oxidation of methane cause the formation of low and high mg calcite respectively the authigenic carbonates can occur as encrusting on the outside and or inside of foraminiferal tests in the form of recrystallization of the test wall or as banding along natural laminations within the foraminiferal test walls in addition to mg authigenic carbonates are enriched in u ca mn ca fe ca and sr ca depending on the redox environment that they were formed in our results demonstrate that site specific u ca thresholds are a promising tool to distinguish between diagenetically altered and pristine foraminiferal samples important for palaeoceanographic reconstructions utilising the primary foraminiferal geochemistry consistent with previous studies u mn ratios of foraminifera at iodp site u1343 increase according to their degree of diagenetic alteration suggesting a potential response of authigenic u mn to the microbial activity in turn linked to the sedimentary redox environment

bacterial mats from crater lake oregon and their relationship to possible deep lake hydrothermal venting crater lake is located in a caldera on mt mazama a volcanic centre in the oregon cascades which has been active for more than 400 000 years1 the 594 m deep lake is a consequence of a climactic eruption which occurred 6 845 50 years ago however caldera volcanism took place as recently as 4 000 years ago1 it has been suggested that some of the physical and chemical features of the lake result from hydrothermal inputs2 7 here we present submersible observations of the bottom of crater lake which reveal communities of bacteria that are usually associated with anomalously warm saline waters the bacteria seem to derive energy from the oxidation of ferrous iron to fuel their metabolism we propose that the mats are indicators of diffuse hydrothermal venting into the deep lake

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

gelatinous pellicles in deep anoxic hypersaline basins from the eastern mediterranean abstract gelatinous pellicles have been observed in three out of ten cores recovered from the bannock basin or bacino bannock and in two dredges from its flanks during a cruise of the r v bannock in the eastern mediterranean similar pellicles have also been detected in two cores recovered from the tyro basin the bannock and tyro basins are brine filled depressions which are presently characterized by anoxic sedimentation in the bannock basin also gypsum precipitation occurs the gelatinous pellicles some millimeters thick and dark grey to greenish in color are always found in very dark colored sediments of quaternary age these pellicles have been investigated by optical microscopy by scanning electron and transmission electron microscopy and by flash pyrolysis gas chromatography and flash pyrolysis gas chromatography mass spectrometry to decipher their nature abundant skeletal tests of siliceous and calcareous planktonic organisms radiolaria diatoms silicoflagellates formainifera and nannofossils are observed together with amorphous organic matter the pellicles enclosing these remains consist of organic matter they foliate into submillimetric undulating and anastomosing microlaminae cellular structures are never observed neither in the pellicles nor in the microlaminae organic geochemical analyses point to a high contribution of terrestrial material the organic matter of the pellicles investigated consists of a coal like material it is suggested that the pellicles are originally formed at the brine seawater interface but subsequently sink to the bottom due to increasing load of entrapped biogenic and non biogenic detritus

geologic characterization of the type cored section for the upper cretaceous austin chalk group in southern texas a combination fractured and unconventional reservoir a rock based geologic characterization was completed on a continuous core through the austin chalk group section an active exploration target in southern texas because this core located in the pearsall field is continuous and includes both lower and upper contacts it can be used as the type cored section for the southern texas austin chalk several general lithofacies are defined two lithofacies lithofacies 1 and 2 are highly bioturbated and have low to moderate organic matter content and are poor to moderate source rocks two other lithofacies lithofacies 3 and 4 are laminated lithofacies 3 containing some burrows and lithofacies 4 containing no burrows both lithofacies are good source rocks organic matter in the laminated lithofacies 3 and 4 and some of the organic matter in the bioturbated lithofacies 2 are dominated by type ii kerogen suggesting the section can be self sourcing a general trend is observed whereby lithofacies that were deposited under more oxygenated conditions increase in abundance up section and is related to a decrease in total organic carbon and hence source rock quality the primary oil and gas production is from fractures with possible later production from the nano to microporous matrix after pressure drawdown pore types are predominantly interparticle nano to micropores and lesser intraparticle nanopores as defined by loucks et al 2012 porosity is less than 8 and permeability is less than 0 05 md and ranges down into the nanodarcy range the type cored section adds to the understanding of the southern texas austin chalk by providing a geological description of lithofacies stacking patterns source rock quality characterization and reservoir quality the type core can be used as a comparison section to other cored sections of the austin chalk

recent calcium carbonate dissolution in the barents sea paleoceanographic applications abstract studies of benthic foraminifera in surface sediments of the arctic epicontinental barents sea show several indications of calcium carbonate dissolution low values of calcium carbonate correspond to low ratios of calcareous agglutinating foraminifera planktic benthic foraminifera high ratios of living dead foraminifera corroded calcareous foraminifera and high numbers of exposed organic linings of foraminifera dissolution increases eastwards and northwards in the study area we suggest that the dissolution is caused by the presence of dense cold saline and co 2 rich bottom water which is linked to sea ice production and the position of the oceanic polar front we also think calcium carbonate dissolution in this area indicates a sink for atmospheric co 2

setting and tectonic evolution of some eastern mediterranean deep sea basins abstract nine discrete deep sea basins seven from the calabrian and mediterranean ridges and two from the strabo trench were explored geologically during several cruises carried out from 1978 to 1984 in the eastern mediterranean the seven basins displaying similar geological features calabrian and mediterranean ridges may be divided into three groups on the basis of their size 1 very small basins botticelli and raffaello basins whose area ranges from 1 1 to 4 3 km 2 2 small basins ares aphrodite and katia basins from 7 to 13 km 2 and 3 large basins bannock and cleft basins from 22 to 74 km 2 the two basins from the strabo trench tyro and kretheus basins whose areas range from 16 to 20 km 2 are considered separately tectonics is the most important element affecting basin formation processes progressive folding and faulting of messinian pliocene and quaternary sediments in the calabrian and mediterranean ridges allows the infiltration of water into the subbottom and dissolution of messinian evaporites so that collapse of the overlying unconsolidated plio quaternary cover creates local distensive tectonics superimposed on the regional compressive tectonic setting the size of the basins reflects different steps in this process very small basins are related to the fracturing occurring at the top of anticlines small basins originate when anticlines are faulted and large amounts of water are able to reach the evaporites and increase the intensity of leaching finally large basins are related to regional tectonic lineaments both compressive large reverse faults overthrusts and strike slip salt diapirism may be associated with some of these situations the process responsible for the tyro and kretheus basins formation is the pull apart mechanism connected with the strike slip motion occurring in that area the geometric position of subaqueously dissolved evaporites seems to influence the environment on the basin floor brines originating from the dissolution of buried evaporites are thought to disperse in the subbottom whereas brines originating from dissolution of evaporites cropping out on the basin walls can flow to the floor and cause stagnation only if the shape of the basin prevents the action of bottom currents

stratigraphy and sedimentation in the anoxic bannock basin eastern mediterranean abstract ten gravity and or piston cores raised from the floor and the eastern flank of the bannock basin and from nearby plateaus were investigated lithologically and biostratigraphically the bannock basin is a large rimmed depression with a vertical relief of over 600 m containing deep seated brines the brines are derived from submarine dissolution of messinian evaporites in a physiographic setting deep rimmed basin that does not permit dilution and removal by bottom currents plateau cores range in age from holocene emiliania huxleyi acme zone to middle pleistocene pseudoemiliania lacunosa zone they consist of low sedimentation rate pelagic sediments with sapropels and tephras as minor isochronous lithologies two cores on the flanks recovered pliocene pelagic sediments one of these cores displays an unconformable contact between holocene anoxic sediments and early pliocene reticulofenestra pseudoumbilica zone marls the other core is entirely pliocene consisting of a debris flow with a matrix that is referred to the discoaster tamalis subzone cores from the deeper part of the basin consist of laminated non bioturbated poorly oxygenated dark sediments rich in h 2 s and containing large gypsum crystals organic carbon content is higher than in normal eastern mediterranean pelagic sediments but lower than in true sapropels the kerogen is dominated by amorphous organic matter although the oxygen content of the bottom waters was not measured sedimentary evidence suggests that poorly oxygenated but not entirely anoxic conditions exist in the basin at the sediment water interface in particular benthic foraminifers would be much less abundant than they actually are and org c content would be higher if bottom waters were anoxic poor oxygenation started to develop in the bannock basin some 180 ka b p after the deposition of sapropel s 6 as documented in core 84 02 this long lasting period of anoxia strongly differs from the short anoxic episodes in the eastern mediterranean that were controlled by glacial interglacial changes the bannock basin anoxia is a result of brine formation causing strong density stratification with a density contrast 20 that is much higher than the density contrast derived from changes in thermohaline circulation during glacial interglacial times during these eastern mediterranean basin wide euxinic episodes the boundary between oxygenated and anoxic waters was much shallower than the 3200 m interface recorded in the bannock basin reworked and displaced foraminiferal faunas were found in the pliocene sediments recovered in the flank cores in particular the occurrence of abraded tests of the shallow water form elphidium spp of bulimina costata and of other displaced taxa does suggest that the area was subject to deposition by turbidity currents originating on the african margin and that in pliocene times no rimmed basin was in existence

gypsum precipitation from cold brines in an anoxic basin in the eastern mediterranean in 1968 hot brines from which gypsum had precipitated were discovered in the red sea in a divergent plate boundary setting with hydrothermal activity1 we now report the discovery of cold brines in an entirely different geodynamic situation a convergent plate boundary in the eastern mediterranean where the heatflow is very low2 and no hydrothermal activity occurs decimetric pure gypsum crystals precipitate from the cold brines which occupy the bottom of a rimmed anoxic basin near the southern edge of the mediterranean ridge close to the sirte abyssal plain nucleation of the crystals does not occur at the surface but from the deep brines because the salinity of the water is normal down to the depth of 3 000 m we propose the name bacino bannock for this basin after the consiglio nazionale delle ricerche r v bannock from which the bottom water brines were surveyed and sampled

pleistocene benthic foraminifers in the arctic ocean implications for sea ice and circulation history abstract three sediment cores from the northwind mendeleev and lomonosov ridges distributed across the western arctic ocean were investigated for foraminiferal composition with a focus on benthic assemblages this investigation provides insights into middle to late pleistocene history of paleoceanographic and sea ice conditions on multi millennial time scales calcareous foraminiferal abundances and assemblage composition show stratigraphically consistent development including glacial interglacial variability and long term evolution of foraminiferal assemblages major long term changes occurred at the end of the mid pleistocene transition estimated ca 0 7 0 8 ma and later near the bottom of marine isotope stage 7 ca 0 25 ma and near the top of mis 5 ca 0 1 ma these changes include notably a diminishing role of phytodetritus related species such as epistominella exigua at the expense of oligotrophic species adapted to live under persistent sea ice presumably indicating an overall expansion of year round ice cover in the arctic during the pleistocene the pronounced mpt shift from mostly seasonal to perennial sea ice was coeval and possibly related to a growth of north american ice sheets and the beginning of glacially controlled sedimentation in the western arctic ocean the ca 0 25 ma transition interpreted as another step in sea ice expansion also co occurs with signs of ice sheet expansion in both north america and especially eurasia the apparent synchronicity of major steps in sea ice and glaciation histories necessitates a more in depth investigation of feedbacks involved and broader linkages beyond the arctic region the ca 0 1 ma change in foraminiferal assemblages marks a consistent stratigraphic event expressed notably in a proliferation of the cosmopolitan species oridorsalis tener although its paleoenvironmental significance is not yet fully understood

preservation of benthic foraminifera and reliability of deep sea temperature records importance of sedimentation rates lithology and the need to examine test wall structure preservation of planktic foraminiferal calcite has received widespread attention in recent years but the taphonomy of benthic foraminiferal calcite and its influence on the deep sea palaeotemperature record have gone comparatively unreported numerical modeling indicates that the carbonate recrystallization histories of deep sea sections are dominated by events in their early burial history meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment pore fluid interaction here we report an investigation of the impact of extreme change in sedimentation rate a prolonged and widespread upper cretaceous hiatus in the north atlantic ocean on the preservation and 18o of benthic foraminifera of middle cretaceous age nannofossil zone nc10 uppermost albian lowermost cenomanian 99 ma ago from multiple drill sites at sites where this hiatus immediately overlies nc10 benthic foraminifera appear to display at least moderate preservation of the whole test however on closer inspection these tests are shown to be extremely poorly preserved internally and yield 18o values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus these high 18o values are interpreted to indicate alteration close to the seafloor in cooler waters during the late cretaceous hiatus intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates

preservation of siliceous microplankton in surface sediments of the northern red sea abstract we studied the siliceous microplankton assemblages mainly diatoms from plankton tows mesh size 20 m and surface sediment samples collected along a n s transect in the northern red sea 28 21 n in addition we analyzed differences similarities between plankton and sediment assemblages within a brine filled basin the southern basin of the shaban deep and compared these assemblages with those from outside the brine plankton samples revealed the overwhelming dominance of diatoms over other siliceous groups diatoms accounted for ca 97 of all biosiliceous particles at 120 20 m vs 2 9 silicoflagellates and 0 4 radiolarians and ca 94 at 200 120 m vs 4 5 silicoflagellates and 1 6 radiolarians in general a marine warm water tropical subtropical diatom assemblage characterizes the plankton samples representatives of the nitzschia bicapitata group are by far the most abundant contributors at both depth intervals average 43 ranging from ca 30 in the north to ca 60 in the south biogenic opal content in non brine surface sediments is very low below 0 2 wt sio2 and concentration of siliceous microorganisms is also low and of the order of 5 103 104 microorganisms g 1 dry sediment diatoms are the main contributors to the opal signal in the 20 40 m fraction while they share dominance with radiolarians in the 40 m fraction total diatom concentrations average 1 2 104 valves g 1 in the 20 40 m fraction and 4 103 valves g 1 in the 40 m fraction robust taxa of warm water affinity alveus marinus azpeitia neocrenulata azpeitia nodulifera and roperia tesselata characterize the surface sediments in contrast biogenic opal content in brine surface sediment samples is much higher than in the non brine samples ranging from 2 8 to 3 8 wt sio2 and concentration of siliceous microorganisms is 3 4 orders of magnitude higher in addition here diatoms dominate the opal signal the taxa found in these samples are a mixture of non brine and plankton samples and fragile forms e g n bicapitata group neodelphineis indica are well preserved in these sediments thus brine sediments in this region seem to offer a great potential for palaeoenvironmental studies

hardground formation in the bannock basin eastern mediterranean abstract twenty kilogrammes of crusts and slabs of indurated carbonate sediment usually referred to as hardgrounds were dredged along the eastern steep wall of the bannock basin during the 1984 cruise of r v bannock the crusts range in thickness from one to a few centimetres and the fragments of these crusts are irregular in shape their surface is always uneven and their colour ranges from white to brownish dark grey some slabs are impregnated along one side by ferromanganese sesquioxides and borings occur in several samples serpulid tubes have been observed in one instance the borings and serpulids suggest formation of the hardgrounds at or close to the sediment water interface and exposure at the seafloor the degree of lithification is generally different on the inferred upper and lower sides of the slabs an upward increase of lithification across the slabs is reflected by mineralogy ultrastructure and stable isotope composition of the carbonate x ray diffraction analyses indicate high magnesian calcite as the predominant carbonate with minor amounts of low magnesian calcite and dolomite occasionally large gypsum crystals are attached to the hardgrounds and sometimes smaller ones are dispersed through the carbonate matrix an increase in diagenesis is reflected by the passage from friable nodular nannofossil chalk to nannofossil limestone and hard xenotopic calcite micrite overgrowth of coccoliths and internal cementation of the tests of planktonic foraminifera by high mg calcite increase from chalk to limestone in the hard fully cemented micrites coccoliths can no longer be recognised in the xenotopic fabric pteropods occur as dissolution moulds with aragonite preserved as only tiny relics carbon and oxygen isotope analyses were performed on different samples the progressive lithification to chalk and limestone is marked by a shift in the 18 o values from 1 2 to 5 4 pdb this change indicates that precipitation of high mg calcite and possibly also recrystallisation of the original biogenic carbonate took place within cold and hypersaline brines which were enriched in 18 o the oxygen isotope data suggest that lithification and gypsum precipitation occurred under identical conditions the carbon isotope data show progressive diagenetic change from values near 1 to values of 3 this change may reflect a contribution of methanogenetic co 2 to the hypersaline brine

a review of the ecological and taphonomic controls on foraminiferal assemblage development in intertidal environments intertidal foraminifera from surface sediments are commonly used as a high resolution indicator of sea level change the integrity of this approach is based upon the assumption that surface assemblages are similar in composition to their buried fossil counterparts this assumption may in some cases be inappropriate due to subsurface or infaunal production and taphonomic alteration here we review the current understanding of foraminiferal production and taphonomic loss in intertidal environments and examine the extent to which these processes can affect the development of foraminiferal assemblages in intertidal environments as a sediment layer undergoes burial dead tests are added at a rate proportionate to the standing crop at that depth as a consequence test accumulation within the layer is proportionate to the depth integrated standing crop depending on the nature of its vertical living distribution the upper 1 cm of sediment may therefore not adequately characterise a given species total input instead a comparison of each species contribution to the entire depth integrated living community may offer a better a priori estimate of relative input to the sediment column this provides an improved base line for identifying true taphonomic trends downcore the potential for infauna to create discrepancies between surface and subsurface assemblages may be minimised however where 1 reproduction is concentrated near to the sediment surface transforming an apparent infaunal standing crop into an effective epifaunal production 2 the living fauna is composed similarly at all depths of production and or 3 intense bioturbation homogenises the upper sediment layers the likely decline in the intensity of taphonomic processes with depth may mean that the foraminiferal production from different depths may not experience taphonomic processes uniformly consequently in addition to their possible gradual enrichment due to subsurface production infaunal species may be preferentially preserved by virtue of their production closer to the base of the taphonomically active zone additionally homogenisation of the sediment column by reworking may mix temporally and perhaps environmentally distinct faunas affecting the stratigraphic integrity of the sediment deposit the most important taphonomic processes in intertidal environments are those associated with early diagenesis while the organic cements of agglutinated taxa may be directly oxidised the associated changes in the saturation state of porewaters with respect to calcium carbonate may affect calcareous species the type of diagenetic reaction operating within the sediment provides a quantitative control on agglutinated test degradation but a largely qualitative control on calcareous preservation in addition calcareous test preservation is dependent upon the rate with which organic matter is supplied while agglutinated test preservation is independent of organic matter concentrations although the specific morphological pathways of test degradation for calcareous species are well understood the stages under which agglutinated tests are lost are less clear the combined but varying influences of production infaunal and species composition taphonomic processes and bioturbation may create complex pathways in the transition from live to dead to fossil assemblages understanding the extent to which infauna taphonomic loss and sediment reworking affect assemblage development in different intertidal environments is essential in order to interpret the fossil record

formation of hematite in the euxinic orca basin northern gulf of mexico abstract the orca basin is a depression in the northern continental slope of the gulf of mexico which is partially filled with hypersaline anoxic brine pool sediment cores taken from this basin show millimeters to centimeters thick red layers within typical dark anoxic muds chemical and x ray mineralogical analyses reveal that the red laminae are invariably enriched in iron in the form of hematite they are formed primarily by interaction of ferrous iron in the brine with dissolved oxygen from overlying seawater during isolated incidences of enhanced mixing a cross the normally stable oxic anoxic boundary the presence of hematite red layers within generally anoxic sediment cores would complicate interpretation in the sedimentary record and limit the usefulness of hematite as an indicator for environment of deposition it also demonstrates that the close association of iron formation with interbedded sulphic shales observed in many proterozoic iron formations is practically feasible the processes associated with the formation of hematite in red layers might affect the extent and nature of organic matter eventually deposited in the basin as well a fact of considerable significance for petroleum source bed formation

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

impact des ecosystemes microbiens sur la sedimentation impact of microbial ecosystems on sedimentation abstract the microbial communities which often give rise to the fine lamination in sediments are very diverse both in species composition e g phototrophic and chemotrophic bacteria fungi algae and metabolism e g oxygenic and anoxygenic photosynthesis organic and inorganic chemosynthesis anaerobic and aerobic respiration organic and inorganic fermentation these microbial ecosystems have separated for more than 3 5 ga 3500 m y they intervene in the biostructuration of sediments by active mineral deposition particle trapping and sediment stabilisation they build bioconstructions stromatolites oncolites oolites and microbial bioherms further they are active in a number of biogeochemical biomineralisation processes including phosphatogenesis carbonate genesis and the formation of iron ore and sulfur deposits and petroleum and kerogen they are also active agents in the biocorrosion and bioerosion of sedimentary rocks under marine and terrestrial conditions since they have an enormous capacity for proliferation microbial laminated communities invade new habitats practically instantaneously where suitable energy sources and gradients for electron flow are available in addition such microbial systems are excellent and sensitive paleoecological indicators in order to study their impact on sedimentation and fossilisation a close collaboration between geologists and microbiologists is needed only in this way can the nature of fossil microbial ecosystems and the metabolisms that were at work be recognized and reconstructed

syndepositional dissolution of calcareous foraminifera in modern shallow water sediments abstract dissolution of calcareous tests in waters undersaturated with respect to calcium carbonate causes postmortem changes to assemblages of modern benthic foraminifera comparison of the percentage of agglutinated tests in the living and dead assemblages from the same sample enables the amount of dissolution to be quantified re examination of data from the continental shelf off new york and the estuarine chezzetcook inlet canada reveals major dissolution losses which lead to dead assemblages rich in agglutinated tests it is probable that partial dissolution of the calcareous component of modern assemblages is more widespread than has been recognised

stratigraphy and sedimentation in the western strabo trench eastern mediterranean abstract three piston cores ranging in length from 501 to 921 cm raised from the adjacent mediterranean tyro and kretheus basins and their intervening sill confirmed previous findings of persistent anoxia and extended our knowledge of the stratigraphic record the two cores from the basinal settings contain a bronze age homogenite this tsunami induced turbidite is only 28 cm thick in the shallower kretheus basin whereas it has a thickness of 235 cm in the deeper tyro basin the recovery of the homogenite in these subbasins of the western strabo trench demonstrates that the tsunami wave turned west of crete and arrived here with a velocity sufficient to remobilize unconsolidated sediments draping the basin slopes the holocene and uppermost pleistocene sedimentary record is characterized by numerous millimetric to centimetric sand layers containing reworked pliocene and miocene foraminifers the repetitive siliciclastic turbidites interfered with the normal eastern mediterranean succession of sapropels and tephras and document a strong neotectonic activity related to the presence of an active trench on the floor of ponded rimmed basins like the tyro and kretheus basins the sand layers are associated with anoxic sediments whereas they are associated with normal well oxygenated marls on the sill which lies above the anoxic oxic interface basin anoxia is interpreted as the result of submarine dissolution of messinian evaporites giving rise to deep seated brines extraformational reworking documents the occurrence of pre messinian fossiliferous sediments exposed on the trench wall and subject to submarine erosion the stratigraphic time framework is given by nannofossil biostratigraphy corroborated by lithostratigraphic correlation of isochronous lithologies sapropel and tephra chronology a drastic change in sedimentary regime is recorded at approximately 70 ka b p emiliania huxleyi acme e huxleyi zonal boundary older sediments which were only recovered in core 37 from the sill separating the tyro and kretheus basins are pelagic with an almost typical eastern mediterranean succession of sapropels and tephras no siliciclastic turbidites and no extraformational reworking are noticed in sediments older than 70 000 years we conclude that the trench system became active just at that time a thick layer of plurimillimetric pumice bubbles was discovered within sapropel s 6 indicating a strong explosion of a nearby volcano at 180 ka b p but we have no analytical data yet to substantiate the provenance of the volcanogenic deposits

relationship of foraminifera and thecamoebian distributions to sediments contaminated by pulp mill effluent saguenay fiord quebec canada gravity cores and grab samples collected in the saguenay fiord between 1976 and 1988 contain the record of a 20th century benthic marine environment contaminated primarily by organic matter discharges from several local pulp and paper mills spiroplectammina biformis is the dominant arenaceous species its living percent abundance decreases between 1982 and 1988 as a consequence of the apparent recolonization of the upper reaches of the fiord by several arenaceous taxa the most important beingtextularia earlandi cassidulina reniforme the dominant living calcareous species shows about a three fold increase in relative abundance over the six year interval grab sample observations also suggest a recolonization of some formerly barren benthic environments near the head of the fiord by foraminiferal species between 1982 and 1988 this recolonization may reflect the combined effect of government regulations imposed on local industrial polluters in the early 1970 s and the capping of a large area of contaminated sediment by a layer of clay that was transported to the basin at the head of the fiord as the result of a catastrophic landslide in 1971 x radiographs of core sections from a basin at the head of the fiord show sharp laminations that reflect both the absence of bioturbators and the seasonal variation of fluvial depositional processes organic waste deposition from pulp and paper mill outfalls first increased around 1910 and shows a first order inverse relationship to benthonic foraminiferal assemblage diversity the presence of only allochthonous thecamoebian and reworked planktonic foraminifera tests in many benthonic foraminifera barren core intervals supports the idea that common indigenous estuarine species such asspiroplectammina biformis were excluded from these areas at certain times as a consequence of pollution stress rather than having been removed from the sediment record as a result of post depositional diagenetic effects however future studies of estuarine pollution history based on proxy foraminiferal data from cores must give greater emphasis to distinguishing ecological stress responses from diagenetic process i e test dissolution effects since both mechanisms can be reflected in the proxy pollution signal in a similar way

deep mid water bacterial mats from anoxic basins of the eastern mediterranean peculiar pellicles have been recorded in the extant anoxic hypersaline basins of the bannock area and the western strabo trench eastern mediterranean discrete layers of pellicles were found in 29 cores they are oriented parallel to bedding planes or are folded within the sandy base of turbidites and within slumped sediments in addition similar pellicles occur at the surface of or interlocked within gypsum crystals recovered from the bannock area the pellicles are 0 5 3 mm thick and dark greenish grey in colour they foliate into very small 1 mm undulating and anastomosing microlaminae entrapping abundant biogenic and inorganic particles the amorphous organic matter of the pellicles is most probably produced by bacterial masses linked to mineralization processes of the organic debris anaerobic sulphate reducing bacteria desulphovibrio are abundant and the presence of methane bacteria is likely detailed analyses with the light microscope and scanning electron microscope yielded differences and similarities concerning ultrastructure content abundance and morphotypes of the bacterial pellicles from the bannock area and the western strabo trench a consistently well developed ultrastructure comprising thin microlaminae characterizes the bannock pellicles whereas the ultrastructure of the tyro and poseidon pellicles is usually not organized siliceous microfossils are abundant in samples from both sites but centrate diatoms prevail in the bannock pellicles whereas pennate diatoms are overwhelmingly dominant in the tyro and poseidon pellicles calcareous micro and nannofossils together with pyrite framboids are more abundant in samples from the bannock area bacteria are extremely abundant in samples from the bannock area and three different morphological types have been distinguished only one type of bacteria was commonly observed in pellicles from the western strabo trench basins pellicles form at the normal seawater brine interface as substantiated by transmittance profiles and bacteriological investigations therefore the term deep mid water bacterial mats is proposed herein for these peculiar layers after bacterial mats grow at the interface they are included within the sediments by following one of two different paths a when pelagic sedimentation prevails pellicles sink to the basin floor due to the increasing load of biogenic and inorganic detritus and b under a tectonically active regime turbidity currents and slumps can disrupt the interface and destroy the floating mats in the latter case fragments of pellicles are transported to the bottom within the gravity flows

modern seawater acidification the response of foraminifera to high co2 conditions in the mediterranean sea abstract the seas around the island of ischia italy have a lowered ph as a result of volcanic gas vents that emit carbon dioxide from the sea floor at ambient seawater temperatures these areas of acidified seawater provide natural laboratories in which to study the long term biological response to rising co 2 levels benthic foraminifera single celled protists are particularly interesting as they have short life histories are environmentally sensitive and have an excellent fossil record here we examine changes in foraminiferal assemblages along ph gradients at co 2 vents on the coast of ischia and show that the foraminiferal distribution diversity and nature of the fauna change markedly in the living assemblages as ph decreases

origin and variability of a terminal proterozoic primary silica precipitate athel silicilyte south oman salt basin sultanate of oman the precambrian cambrian athel silicilyte is a 400 m thick salt encased siliceous succession in the south oman salt basin it is a self sourcing hydrocarbon reservoir and comprises up to 95 microcrystalline quartz and exhibits wavy discontinuous lamination comprising thin alternating organic rich and silica rich layers textures and geochemical fingerprinting indicate that it is a primary precipitate formed by microbially mediated precipitation of silica from sea water within the water column at the sulphidic oxic interface the unique occurrence of the athel silicilyte in the terminal proterozoic implies that optimal conditions for this style of silica precipitation occurred only briefly basin anoxia coupled with the growth of microbial mats low ph and high silica pore water saturations created optimal chemical conditions for silica precipitation volumes of microcrystalline quartz are highest within the transgressive and early highstand systems tract and towards the centre of the athel basin at the basin margins and within the late highstand systems tract volumes of microcrystalline quartz decreased as the volume of detrital sediment increased mass balance calculations indicate that silica enriched sea water would have been supplied to the basin by infrequent marine incursions that replenished ambient sea water in the upper part of the water column in conclusion precipitation of the athel silicilyte was driven by the coincidence of basin restriction limited clastic input availability of organic matter and water column anoxia the observation that there are few documented examples of chert deposits younger than ca 700 ma prior to the cambrian explosion suggests that although silica budgets within marine basins probably remained high prior to the evolution of silica secreting organisms direct precipitation from sea water was restricted this is tentatively related to the gradual increase in alkalinity of sea water through the palaeo proterozoic and meso proterozoic such that silica precipitation could only occur through the coincidence of basin anoxia and low siliciclastic input

the geometry and rates of microplate motions in the eastern mediterranean sea quantitative constraints by using anoxic basins as piercing points abstract anoxic conditions encountered in small basins on the flanks of the mediterranean ridge are due to the formation of brine pools caused by exposure of messinian evaporites seismic reflection profiles and structural data indicate young active strike slip faulting and thrusting due to collision between microplates to be responsible for the continued isolation of the basins an estimate of 100 000 years for the age of initiation of the tyro and kretheus basins using a finite microplate rotation model for the central and eastern mediterranean sea is in close agreement with coring results in the kretheus basin rates of relative motion with respect to africa of more than 8 cm a 1 along the western strabo trench are supported by these results this study indicates that regional deformation resulting from active plate convergence appears to bear a simple relation to a few finite rotation poles for relative movement between plates and microplates

taphonomy and time averaging of foraminiferal assemblages in holocene tidal flat sediments bahia la choya sonora mexico northern gulf of california abstract foraminiferal reproduction and preservation have been studied in holocene tidal flat sediments of bahia la choya sonora mexico northern gulf of california foraminiferal reproduction at choya bay tends to occur in discrete a few weeks seasonal pulses which are then followed by periods of homogenization and dissolution of several months duration foraminiferal number number of tests gram sediment increases northward across the flat primarily because of decreasing intensity of bioturbation and increasing total carbonate weight percent shell content of sediments despite intensive dissolution of foraminiferal reproductive pulses tests which appear to be relatively fresh are actually quite old up to 2000 years based on 14c dates we hypothesize that after reproduction some tests survive dissolution because of rapid advection burial downward by conveyor belt deposit feeders e g callianassid shrimp polychaete worms into a subsurface shell layer where tests are preserved until exhumation much later by biological activity or storms thus taphonomic grade surface condition of foraminiferal tests in these sediments is not an infallible indicator of shell age time since death the condition of the test surface is indicative of the residence time of the test at the sediment water interface taphonomically active zone and not test age

brine formation and gypsum precipitation in the bannock basin eastern mediterranean abstract sixty kilograms of gypsum crystals were collected at two dredging stations within a small anoxic hypersaline basin named the bannock basin close to the sirte abyssal plain the basin was investigated in some detail by means of ten precision positioned piston and gravity cores one nansen bottle hydrocast and three ctd stations the sediments of the basin floor are dark h 2 s rich and commonly laminated and contain centimetric crystals of gypsum the water column above the basin has normal salinity down to a depth of 3150 m below this depth the basin is filled with hypersaline brines formed from the dissolution of messinian evaporites outcropping on the steep eastern wall when the brines reach the necessary concentration in ca and in so 4 gypsum may precipitate along the steep eastern wall and within the sediments on the basin floor the very recent age of the gypsum is proved by the inclusions of quaternary planktonic fauna formainifera and pteropods and by radiometric techniques

late quaternary sedimentation in the tyro and kretheus basins southeast of crete abstract this paper summarizes micropaleontologic foraminifera calcareous nannoplankton radiolaria pteropods and pollen grains and sedimentologic piston core data from the eastern mediterranean tyro and kretheus basins 14 c datings indicate a holocene age for the tyro basin cores the latter show anoxic bottom conditions throughout while the kretheus basin core indicates anoxic conditions prior to 3000 years ago and oxic conditions after that time resedimentation through slumps turbidity currents and from suspension resulted in high sediment accumulation rates in both basins reworking in the tyro basin predominantly originated from the basin flanks while the presence of common to abundant metamorphic clastics in the kretheus basin points to a more distant source the minoan eruption of santorini ca 3350 yrs b p which is supposed to have caused a gigantic tsunami is linked to the presence of turbidites and a thick homogenite in the tyro basin the same event may be responsible for the initiation of oxic conditions in the kretheus basin