rudist formations in mixed siliciclastic carbonate depositional environments upper cretaceous austria stratigraphy sedimentology and models of development abstract the upper turonian to lower campanian succession lower gosau subgroup of the northern calcareous alps austria provides a model for the development of rudist formations on wave dominated mixed siliciclastic carbonate shelves that were situated on top of an accretionary wedge the rudist formations are present either within parasequences or in non cyclic transgressive successions and include a skeletal mounds up to about 20 m thick that are composed of corals rudists and locally skeletal sponges and b rudist biostromes of less than a metre to several meters in thickness in the coral rudist mounds hippuritids and radiolitids thrived together with scleractinians skeletal sponges and diverse encrusters the mounds are topped by a hippuritid biostrome we distinguish hippuritid biostromes radiolitid biostromes and composite biostromes with a vertical succession from hippuritids to radiolitids the biostromes are less than a metre to a few meters thick and show autochthonous rudist fabrics parautochthonous rudist fabrics and vertical combinations thereof autochthonous rudist fabrics had a simple trophic structure composed of epifaunal suspension feeders whereas parautochthonous rudist fabrics had a more complex trophic structure the rudist biostromes were either terminated by frequent toppling and fragmentation of rudists by burial with sediment or by environmental restriction hippuritids and radiolitids could both colonize and persist in siliciclastic depositional environments overall however the presence abundance of rudists and of intervals of shallow water limestones correlate because the late cretaceous rudists thrived together with hermatypic corals as well as in environments precluded to the latter a larger number of rudist formations and a smaller number of coral rudist formations results in siliciclastic dominated depositional sequences both in the transgressive and in the highstand systems tract coral rudist mounds and rudist biostromes locally accumulated in areas of intermittently reduced siliciclastic input in open lagoons and in the shoreface to inner shelf environment transgression of rocky coasts or of gravelly carbonate beaches is recorded by a basal interval either of cliff talus breccia or of beachface and shoreface conglomerates overlain by a coral rudist mound and or a rudist biostrome with associated bioclastic limestones where siliciclastic input was persistently low the highstand systems tract developed as a regressive carbonate shelf succession that consists in its lower part of coral rudist mounds hippuritid biostromes and bioclastic packstones to grainstones deposited from bioclastic sand bodies whereas the upper part consists of radiolitid biostromes and bioclastic wackestones to packstones the regressive carbonate shelves were narrow and included on a reconstructed internal to external transect micro tidal flats an open lagoon with radiolitid biostromes a dissipative shore zone with bioclastic sand bodies and an inner shelf facies belt with coral rudist mounds and hippuritid biostromes in the contemporaneous mid to outer shelf environment siliciclastics were deposited

patterns in the distribution of aptian rudists and corals within a sequence stratigraphic framework maestrat basin e spain abstract the ecological zonation of and environmental controls on rudist and coral assemblages on carbonate platforms of the old world have received more attention for late cretaceous examples than for their early cretaceous counterparts this study accordingly investigates the vertical and lateral distribution of aptian rudist bivalves and scleractinian corals on a carbonate platform succession from the western maestrat basin e iberian peninsula here colonial corals grew profusely on an isolated platform top environment during an earliest highstand stage of a long term trend of relative sea level as well as on marly slope settings during higher frequency transgressive pulses during the later highstand stage within a longer term relative sea level cycle a facies belt dominated by autochthonous rudist bivalves overlaid the coral meadow that had developed on the isolated platform top the internal part of this carbonate platform with rudists is dominated by slender elevator caprinids such as caprina parvula whereas requieniids and polyconitids predominate in the external zone the abundance of caprinids in the internal platform is remarkable given that caprinid lithosomes of late early aptian age are usually rare in the northern margin of the tethys the proliferation of caprinids in this case was probably favoured by the apparently more isolated nature of the carbonate platform on the slopes the coral communities that flourished during higher frequency transgressive pulses are overlain by carbonates with rudists mainly requieniids shed from the platform top during normal and forced regressive higher frequency changes of relative sea level accordingly the vertical change from coral dominated to rudist dominated facies in both platform top and slope settings records progradation to decipher the long term relative sea level changes that controlled the deposition of this carbonate succession a sequence stratigraphic analysis was performed two depositional sequences including a late early aptian intra dufrenoyia furcata zone forced regressive stage of relative sea level which subaerially exposed and incised the early aptian succession to a depth of 21 m were recognised the incisions were back filled with peritidal deposits during the subsequent marine onlap the rudist and coral bearing carbonates were deposited along platform top to slope profiles lacking a barrier margin and hence lagoon environments

constraints on mantle evolution from 187os 188os isotopic compositions of archean ultramafic rocks from southern west greenland 3 8 ga and western australia 3 46 ga initial 187os 188os isotopic compositions for geochronologically and geologically well constrained 3 8 ga spinel peridotites from the itsaq gneiss complex of southern west greenland and chromite separates from 3 46 ga komatiites from the pilbara region of western australia have been determined to investigate the osmium isotopic evolution of the early terrestrial mantle the measured compositions of 187os 188os 0 0 10262 2 from an olivine separate and 0 10329 3 for a spinel separate from 3 8 ga peridotite g93 42 are the lowest yet reported from any terrestrial sample the corrections for in situ decay over 3 8 ga for these low re os phases are minimal and change the isotopic compositions by only 0 5 and 2 2 for the spinel and the olivine respectively resulting in 187os 188os 3 8 ga 0 1021 0 0002 and 0 1009 0 0002 respectively these data extend direct measurement of os isotopic compositions to much earlier periods of earth history than previously documented and provide the best constraints on the os isotopic composition of the early archean terrestrial mantle analyses of pilbara chromites yield 3 46 ga mantle compositions of 0 1042 0 0002 and 0 1051 0 0002 these new data combined with published initial os isotopic compositions from late archean and early proterozoic samples are compatible with the mantle or at least portions of it evolving from a solar system initially defined by meteorites to a modern composition of 187os 188os 0 0 1296 0 0008 as previously suggested from peridotite xenolith data meisel et al 2001 the associated 187re 188os 0 0 435 0 005 thus chondritic 187os 188os compositions were a feature of the upper mantle for at least 3 8 billion years requiring chondritic re os ratios to have been a characteristic of the very early terrestrial mantle in contrast nonchondritic initial compositions of some archean komatiites demonstrate that os isotopic heterogeneity is an ancient feature of plume materials reflecting the development of variable re os mantle sources early in earth history the lower average 187os 188os 0 1247 for abyssal peridotites snow and reisberg 1995 indicate that not all regions of the modern mantle have evolved with the same re os ratio the relative sizes of the various reservoirs are unknown although mass balance considerations can provide some general constraints for example if the unradiogenic 187os 188os modern abyssal peridotite compositions reflect the prevalent upper mantle composition then the complementary high re os basaltic reservoir must represent 20 to 40 by mass of the upper mantle taken here as 50 of the entire mantle depending on the mean storage age the difficulties associated with efficient long term storage of such large volumes of subducted basalt suggest that the majority of the upper mantle is not significantly re depleted rather abyssal peridotites sample anomalous mantle regions the existence of 3 8 ga mantle peridotites with chondritic 187os 188os compositions and with os concentrations similar to the mean abundances measured in modern peridotites places an upper limit on the timing of a late accretionary veneer these observations require that any highly siderophile element rich component must have been added to the earth and transported into and grossly homogenized within the mantle by 3 8 ga either large scale mixing of impact materials occurred on very short 0 100 myr timescales or the interpretation preferred here the late veneer of highly siderophile elements is unrelated to the lunar terminal cataclysm estimated to have occurred at 3 8 to 3 9 ga

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

patterns and processes of shell fragmentation in modern and ancient marine environments shell fragments are important components of many recent and fossil marine benthic ecosystems and can provide crucial information on past and present environmental conditions interpreting such fragments requires integrated knowledge in various fields and the information potential is therefore rarely optimally utilized this paper uses the definition of a fragment as being a piece of shell having less than 90 of its original form it then outlines the potential characteristics pathways and fates that shells and their fragments can have fragmentation is a key factor shaping the shelly part of death assemblages but it is difficult to interpret because it can be broadly caused by ecological biostratinomic or diagenetic processes and also depends on shell strength strength in turn reflects multifunctionality during ontogeny and depends on a complex set of skeletal and taphonomic factors therefore no particular shell parameter clearly determines strength but thickness microstructure type and degree of organic matrix have the strongest influence on pre and post mortality strength size measurements are usually less important for shell strength than thickness although ecologically complex size refuges from predation do exist similarly shell shape sculptural features and specific aperture types in gastropods provide various defence strategies rather than increasing strength per se key ecological factors of fragmentation include predation due to crushing peeling along with mistaken predation selfinflicted damage during predation and burrowing and more physical aspects such as impacts by stones modern studies must consider damage by benthic commercial fisheries or dredging by scientific vessels key biostratinomic factors include transportinduced abrasion littoral zone of surf washed beaches bioerosion and dissolution mainly sublittoral environments diagenetically fragmentation during compaction mainly occurs when shells are in direct contact with one another or with coarser grains taphonomic features e g drillholes have only minor influence a key step in interpreting fragments is to categorize breakage into repaired versus unrepaired diagnostic versus nondiagnostic and severe versus localized damage quantifying the above categories can then provide useful information on breakage patterns and underlying processes understanding the many characteristics of shells and their fragments is a significant interpretive tool in maximizing the information gain in palaeoecological and taphofacies analyses d 2003 elsevier science b v all rights reserved

biogeography of the lord howe rise region tasman sea abstract the two principal aims of this study were to synthesise physical and biological information to characterise the lord howe rise lhr region and to use recent survey collections of benthic invertebrates mostly large benthic epifauna to describe its biogeography at regional and sub regional scales the lhr region is large 1 95 million km2 spans tropical and cool temperate latitudes 18 4 to 40 3 s and is influenced by several ocean currents notably the east australian current and the tasman front our analyses revealed that biological patterns were related to two groups of geomorphic morphotypes found in this topographically complex region subdued bathymetric features expansive soft sediment basins and plateaus and raised bathymetric features scattered seamounts guyots knolls and pinnacles raised bathymetric features in the lhr region were more likely to support richer and more abundant epifaunal assemblages dominated by suspension feeding invertebrates on hard substrata compared to subdued features which were dominated by infauna and detritivores in soft sediments however this trend does not apply to all raised bathymetric features e g gifford guyot with variations in depth elevation latitude and particularly substrata affected the composition of biological assemblages in addition some demersal fishes ophiuroids and other benthic invertebrates showed distinct north south delineations that coincide with the influence of the tasman front and thermal gradients while the lack of spatially and temporally replicated data in the region limits our interpretation of survey data paleo environmental processes and examples from other regions provide some indication of how dispersal influences migration speciation and endemism in the lhr region although our current knowledge is limited it is hoped that this review will help inform future studies in the area as equitable examination of biological geological and oceanographic characteristics will facilitate future assessments of lhr biogeography and permit the inclusion of this region in biogeographic studies with a national or global context

deep sea surface dwelling enteropneusts from the mid atlantic ridge their ecology distribution and mode of life the ecology distribution and mode of life of three species of surface dwelling enteropneusts is described based on rov observations and samples on the flanks of the northern mid atlantic ridge mar at comparative stations north and south of the sub polar front tergivelum cinnabarinum was most abundant in the north mean 4 56 ind 1000 m 2 3 50 s d and occurred at low densities in the south mean 1 19 1 68 s d yoda purpurata was dominant in the south mean 17 00 ind 1000 m 2 12 32 s d but only one individual was found in the north the within station distribution of all enteropneust species encountered was generally random t cinnabarinum was larger mean total length 142 mm than y purpurata mean total length 70 mm size distributions suggested smaller individuals of both species on the western side of the mar size and density of enteropneusts were generally higher in areas with higher carbon flux to the seafloor a single individual of allapasus isidis was observed drifting and settling to the seafloor at the sw site traces on the seafloor made by t cinnabarinum covered a much higher percentage of the total seabed area surveyed mean 0 323 0 155 s d than those of y purpurata mean 0 034 0 037 s d stable isotope values for t cinnabarinum suggested that it was a typical surficial deposit feeder enteropneusts appear to be abundant and an important bioturbator on the sedimented seafloor of the mar at around 2500 m depth

distribution abundance and trail characteristics of acorn worms at australian continental margins abstract acorn worms enteropneusta which were previously thought to be a missing link in understanding the evolution of chordates are an unusual and potentially important component of many deep sea benthic environments particularly for nutrient cycling very little is known about their distribution abundance or behaviour in deep sea environments around the world and almost nothing is known about their distribution within australian waters in this study we take advantage of two large scale deep sea mapping surveys along the eastern northern lord howe rise and western continental margins of australia to quantify the distribution abundance and trail forming behaviour of this highly unusual taxon this is the first study to quantify the abundance and trail behaviour of acorn worms within australian waters and provides the first evidence of strong depth related distributions acorn worm densities and trail activity were concentrated between transect averaged depths of 1600 and 3000 m in both eastern and western continental margins the shallow limit of their depth distribution was 1600 m the deeper limit was less well defined as individuals were found in small numbers below 3000 down to 4225 m this distributional pattern may reflect a preference for these depths possibly due to higher availability of nutrients rather than a physiological constraint to greater depths sediment characteristics alone were poor predictors of acorn worm densities and trail activity high densities of acorn worms and trails were associated with sandy mud sediments but similar sediment characteristics in either shallower or deeper areas did not support similar densities of acorn worms or trails trail shapes varied between eastern and western margins with proportionally more meandering trails recorded in the east while spiral and meandering trails were both common in the west trail shape varied by depth with spiral shaped trails dominant in areas of high acorn worm densities 2000 3000 m water depth while meandering trails were common over a much broader depth range and were the only trails recorded in deep environments 3000 m while species specific patterns may in part explain these differences evidence suggests that nutrient availability is also likely to be an important driving factor supporting the hypothesis put forward by smith et al 2005 that acorn worms meander when searching for food and form a spiral when feeding in a nutrient rich area

ti in zircon thermometry applied to contrasting archean metamorphic and igneous systems abstract ti in zircon thermometry with shrimp ii multi collector has been applied to two well documented archean igneous and metamorphic samples from southern west greenland zircons from 2 71 ga partial melt segregation g03 38 formed in a small 1000 c yield a low temperature focused normal distribution with a mean of 683 32 c further demonstrated by high resolution ti mapping of two individual grains this distribution is interpreted to represent the temperature of the residual magma at zircon saturation late in the crystallization history of the tonalite hypothetically ti in zircon thermometry on eoarchaean detrital zircons sourced from such a high temperature tonalite would present a low temperature biased image of the host magma which could be misconstrued as being a minimum melt granite multiple analyses from individual zircons can yield complex ti distributions and associated apparent temperature patterns reflecting cooling history and local chemical environments in large magma chambers in addition to inclusions and crystal imperfections which can yield apparent high temperature anomalies zircon surfaces can also record extreme 1000 c apparent ti temperatures in our studies these were traced to 49ti or a molecular isobaric interference contamination derived from the double sided adhesive tape used in sample preparation and should not be assigned geological significance

radiolitid rudist colonisation strategies and biostrome development in moderate energy inner platform environments campanian brac island croatia abstract during the late cretaceous radiolitid rudist bivalves were abundant calcifiers on tethyan shallow water carbonate platforms previous studies have demonstrated various low to high energetic subtidal environments in which vertically growing rudist bivalves lived however the precise mode of colonisation in moderate to higher energetic environments remains unclear the purpose of this study is to elucidate the attachment of rudist juveniles and colonisation strategies on loose grain sediment using three dimensional reconstructions and other quantitative approaches the present data demonstrate that small and thinly walled rudists colonised energetic environments over several generations the main contributors to the biostrome distefanella bournonia and pseudopolyconites followed different strategies within the same ecosystem for instance cylindrical elevator morphotype distefanella built up a generally loose but anchored framework to resist sedimentation and wave energy in contrast bournonia and pseudopolyconites followed a solitary strategy of settlement on any hard substrate preferred growth direction affecting all genera was possibly linked to a predominant direction of water currents

burrow mediated carbonate dissolution in rudist biostromes aurisina italy implications for taphonomy in tropical shallow subtidal carbonate environments abstract in upper cretaceous rudist biostromes at aurisina italy marked taphonomic loss of radiolitids by burrow mediated dissolution and mechanical disintegration illustrates the relation between synecology and early diagenesis in the fossilization of tropical shallow water bioconstructions the studied platform succession accumulated in a prevalently open lagoon with bioturbated carbonate sand rudist thickets bioclastic dunes and areas with shelly lime ooze rudist biostromes consist of radiolitids and hippuritids or of radiolitids only and have an open parautochthonous rudist fabric with a matrix of bioclastic bioturbated wackestone swirly disorientation of bioclasts records early softground bioturbation later firmground burrows comprise an irregular network of tunnels and chambers filled with bioclastic packstone to grainstone the size geometry and sediment fill of the firmground burrows suggest that they were produced by crustaceans radiolitid preservation ranges from complete to relictic radiolitid relicts formed by a spalling and or dissolution of the cellular boxwork ostracum of the attached valve leaving calcite tubes built by a distinct thin ostracal shell layer or b dissolution of the entire shell leaving the sedimentary fills of the intertabular spaces of the attached valve as a diagnostic vestige or c shell dissolution within the firm sediment with subsequent filling of the biomould by bioclastic wackestone to packstone to grainstone loss of radiolitids produced a taphonomic bias towards rudists with non cellular ostracum locally taphonomic loss produced ghost biostromes composed nearly entirely of faint radiolitid relicts shell dissolution resulted from chemical gradients in the sediment within and near the burrows and from enhanced microboring and microbial infestation dissolution of radiolitids was favoured by the combined effects of chemical instability of hypostracal aragonite and by the structure of the calcitic boxwork ostracum of thin walled cells some biostromes are intercalated with or are capped or overlain within a short vertical distance by a hardly recognizable emersion surface as a consequence of the shallow depth of biostrome accumulation taphonomic loss by dissolution is widespread in open parautochthonous rudist fabrics and confirms actuogeological results of other authors that bioturbation mediates carbonate dissolution also under shallow tropical waters supersaturated for calcium carbonate the amount of carbonate dissolved upon burrowing of the biostrome matrix is hardly quantifiable but by analogy to recent carbonate environments may have been large within bioconstructions deep tiered burrowing occurred at least since the carboniferous taphonomic loss by dissolution thus may have been active in the fossilization of tropical shallow water mounds and biostromes over much of phanerozoic times

complex 3670 3500 ma orogenic episodes superimposed on juvenile crust accreted between 3850 and 3690 ma itsaq gneiss complex southern west greenland abstract the itsaq gneiss complex of the nuuk region southern west greenland is dominated by 3850 3690 ma tonalites intruded into and intercalated with lesser amounts of different 3850 3700 ma supracrustal units published whole rock sr and nd isotopic studies demonstrate that the tonalites are juvenile crustal additions from a depleted mantle source from our field studies and shrimp u pb zircon dating we argue that this juvenile crustal accretion was spread over ca 170 m yr 3850 3690 ma following 3850 3690 ma juvenile crustal accretion events the evolution of the itsaq gneiss complex continued with numerous crustal reworking events between 3670 and 3500 ma examples of these reworking events are as follows 1 there is intrusion of several generations of geochemically diverse granites sensu stricto with subordinate gabbros and diorites 2 there are superimposed multiple episodes of amphibolite to granulite facies metamorphism illustrated with akilia island samples by detailed dating of

evidence for a mantle component shown by rare gases c and n isotopes in polycrystalline diamonds from orapa botswana in an attempt to constrain the origin of polycrystalline diamond combined analyses of rare gases and carbon and nitrogen isotopes were performed on six such diamonds from orapa botswana helium shows radiogenic isotopic ratios of r ra 0 14 1 29 while the neon ratios 21 ne 22 ne of up to 0 0534 reflect a component from mantle nucleogenic and atmospheric sources 40 ar 36 ar ratios of between 477 and 6056 are consistent with this interpretation the 129 xe 130 xe isotopic ratios range between 6 54 and 6 91 and the lower values indicate an atmospheric component the he ne ar and xe isotopic compositions and the xe isotopic pattern are clear evidence for a mantle component rather than a crustal one in the source of the polycrystalline diamonds from orapa they 13 c and y 15 n isotopic values of 1 04 to9 79xand 4 5 to 15 5x respectively lie within the range of values obtained from the monocrystalline diamonds at that mine additionally this work reveals that polycrystalline diamonds may not be the most appropriate samples to study if the aim is to consider the compositional evolution of rare gases through time our data shows that after crystallization the polycrystalline diamonds undergo both gas loss that is more significant for the lighter rare gases such as he and ne and secondary processes such as radiogenic nucleogenic and fissiogenic as well as atmospheric contamination finally if polycrystalline diamonds sampled an old mantle 1 3 2 ga the determined xe isotopic signatures which are similar to present morb mantle no fissiogenic xe from fission of 238 u being detectable imply either that xe isotopic ratios have not evolved within the convective mantle since diamond crystallization or that these diamonds are actually much younger d 2005 elsevier b v all rights reserved

the iron rich suite from the amitsoq gneisses of southern west greenland early archaean plutonic rocks of mixed crustal and mantle origin a distinctive group of augen gneisses and ferrodiorites termed the iron rich suite is a component of the early archaean amitsoq gneisses of southern west greenland the iron rich suite outcrops south of the mouth of ameralik fjord in an area that underwent granulite facies metamorphism in the early archaean the iron rich suite forms approximately 30 of the amitsoq gneiss of this area and occurs as sheets and lenses up to 500 m thick the rest of the amitsoq gneisses are predominantly tonalitic granodioritic banded grey gneisses despite intense deformation and polymetamorphism there is local field evidence that the iron rich suite was intruded into the grey gneisses after they had been affected by tectonism and metamorphism the banded grey gneisses are interpreted as 3 700 to 3 800 ma old u pb zircon ages from the iron rich suite give concordia intercepts at circa 3 600 ma

a geochemical characterisation of deep sea floor sediments of the northern lord howe rise abstract this study presents new information on the regional geochemical characteristics of deep sea floor sediments 1300 2423 m water depth on the lord howe rise deep sea plateau and gifford guyot seamount tablemount remote areas off eastern australia the aim was to provide a coherent synthesis for a suite of geochemical data that can be used to make habitat inferences and to develop surrogates of biodiversity sediment characteristics analysed were mineralogy organic carbon and nitrogen concentrations and isotopic compositions and concentrations of major and trace elements we also measured parameters that convey information about the reactivity of organic matter and on the bio availability of bioactive trace elements e g chlorin indices and acid extractable elements surface sediments from the region were calcareous oozes that were carbon lean 0 26 0 1 and had moderate to high chlorin indices 0 62 0 97 with the exception of arsenic inorganic element concentrations were generally low by global standards statistical and geochemical analyses identified two major dimensions of variation in the elemental composition i the degree of mixing between the detrital sediment and carbonate end members and ii the concentrations of bio available bioactive elements the causes of compositional variation are discussed and include i a strong latitudinal gradient in detrital atmospheric dust deposition ii size fractionation and cation exchange of dust components during transit for non carbonates iii water depth controls on carbonate dissolution and iv topographic hydrodynamic focussing of reactive organic matter reactive organic matter indicators were not well correlated with water depth and did not reflect the regional ocean productivity pattern basalt source signatures were not evident in the mineralogy or geochemistry of sediments overlying the seamount or in the vicinity of volcanoes

malaysia airlines flight mh370 search data reveal geomorphology and seafloor processes in the remote southeast indian ocean abstract a high resolution multibeam echosounder mbes dataset covering over 279 000 km2 was acquired in the southeastern indian ocean to assist the search for malaysia airlines flight 370 mh370 that disappeared on 8 march 2014 the data provided an essential geospatial framework for the search and is the first large scale coverage of mbes data in this region here we report on geomorphic analyses of the new mbes data including a comparison with the global seafloor geomorphic features map gsfm that is based on coarser resolution satellite altimetry data and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area our comparison between the new mbes bathymetric model and the latest global topographic bathymetric model srtm15 plus reveals that 62 of the satellite derived data points for the study area are comparable with mbes measurements within the estimated vertical uncertainty of the srtm15 plus model 100 m however 38 of the srtm15 plus depth estimates disagree with the mbes data by 100 m in places by up to 1900 m the new mbes data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the gsfm with a 20 increase in the extent of hills and mountains the new model also reveals four times more seamounts than presented in the gsfm suggesting more of these features than previously estimated for the broader region this is important considering the ecological significance of high relief structures on the seabed such as hosting high levels of biodiversity analyses of the new data also enabled sea knolls fans valleys canyons troughs and holes to be identified doubling the number of discrete features mapped importantly mapping the study area using mbes data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes for example a large series of ridges extending over approximately 20 of the mapped area in places capped by sea knolls highlight the preserved seafloor spreading fabric and provide valuable insights into southeast indian ridge seafloor spreading processes especially volcanism rifting is also recorded along the broken ridge diamantina escarpment with rift blocks and well bedded sedimentary bedrock outcrops discernible down to 2400 m water depth modern ocean floor sedimentary processes are documented by sediment mass transport features especially along the northern margin of broken ridge and in pockmarks the finest scale features mapped which are numerous south of diamantina trench and appear to record gas and or fluid discharge from underlying marine sediments the new mbes data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with mbes the availability of high resolution and accurate maps of the ocean floor can clearly provide new insights into the earth s geological evolution modern ocean floor processes and the location of sites that are likely to have relatively high biodiversity

upper cretaceous ramp limestones from the sorrento peninsula southern apennines italy micro and macrofossil associations and their significance in the depositional sequences abstract the upper cretaceous limestones of the sorrento peninsula are primarily characterized by wackestone packstone with benthic foraminifers thaumatoporellaceans and aeolisaccus sp and by rudist floatstones rudists in growth position are rare most of them appear toppled and locally oriented but not reworked in some cases they form small bouquets no more than 30 cm thick the successions analyzed in the sorrento peninsula encompass a variety of facies representative of inner shelf environments in a ramp like depositional setting on the basis of lithologic and sedimentologic characteristics and on a qualitative analysis of the biofacies three major facies associations have been recognized corresponding to a intertidal silty sand flats and shallow lagoons b subtidal mobile foraminiferal sand sheets c subtidal rudist dwelt sand plain in the lower part of the successions periodic more or less prolonged emersions subaqueous with fresh brackish waters or subaerial exposure are documented the upper part of each succession lacks any emersion evidence submarine exposure surfaces are testified by firmground related features the periodic influence of high energy regimes some storm related events is documented by wave and cross laminations hcs and the lack of fine sediments lithofacies are arranged in depositional cycles that may correspond to individual beds the boundaries of the depositional cycles show evidence of subaerial or submarine exposures the nature and position of these discontinuity surfaces in the successions provide an important clue to interpretation in terms of both depositional environment and vertical evolution the increase in thickness of the depositional cycles and the gradual change from peritidal shallow subtidal cycles to dominantly subtidal cycles document an increase in the amount of accommodation space which resulted from a long term rise in relative sea level a detailed study of benthic associations micro and macrofauna has been carried out in order to identify accurately further signs of periodicity contained within the successions as a whole these upper cretaceous limestones are abundantly fossiliferous with only a moderately diverse fauna there are no significant differences in terms of species the assemblages simply reflecting differences in abundance of the same species taphonomic studies of rudist rich beds permit seven major shell bed types to be distinguished six main foraminiferal assemblages have been detected and the distribution and relative abundance of the species have been examined within the environments inferred through facies analysis the taphonomic data and the foraminiferal assemblage abundance and diversity have been compared with lithologic and sedimentologic data in order to elucidate their distribution within depositional cycles and throughout the successions the successions show little up section changes in lithology and in taxonomic composition of the foraminiferal assemblages it is therefore difficult to establish a paleoenvironmental trend independent of the rudist shell concentrations which do change up section we noticed an overall increase in thickness and abundance of the shell beds and a shift in types of shell concentration and in taxonomic composition these characteristics associated with the upward disappearance of emersion surfaces the higher frequency of storm and or wave intercalations the increase in thickness of the depositional sequences and the gradual change from peritidal shallow subtidal cycles to dominantly subtidal cycles document a general deepening upward trend more open water conditions with a depth between fairweather and storm wave base became established as a result of relative sea level rise and to a consequent increase in the available accommodation space

actinide abundances in ordinary chondrites measurements of 244 pu fission xe u th and light ree lree abundances along with modal petrographic determinations of phosphate abundances were carried out on equilibrated ordinary chondrites in order to define better the solar system pu abundance and to determine the degree of variation of actinide and lree abundances our data permit comparison of the directly measured pu u ratio with that determined indirectly as pu nd nd u assuming that pu behaves chemically as a lree except for guarena and perhaps h chondrites in general pu concentrations are similar to that determined previously for st severin although less precise because of higher trapped xe contents trapped 130xe 136xe ratios appear to vary from meteorite to meteorite but relative to avcc all are similar in the sense of having less of the interstellar heavy xe found in carbonaceous chondrite acid residues the pu u and pu nd ratios are consistent with previous data for st severin but both tend to be slightly higher than those inferred from previous data on angra dos reis although significant variations exist the distribution of our th u ratios along with other precise isotope dilution data for ordinary chondrites is rather symmetric about the ci chondrite value however actinide lree ratios are systematically lower than the ci value variations in actinide or lree absolute and relative abundances are interpreted as reflecting differences in the proportions and or compositions of more primitive components chondrules and cai materials incorporated into different regions of the ordinary chondrite parent bodies the observed variations of th u nd u or ce u suggest that measurements of pu u on any single equilibrated ordinary chondrite specimen such as st severin should statistically be within 20 30 of the average solar system value although it is also clear that anomalous samples exist

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

the early archaean itsaq gneiss complex of southern west greenland the importance of field observations in interpreting age and isotopic constraints for early terrestrial evolution geochemical and isotopic studies of small volumes of variably preserved 3600 ma rocks in gneiss complexes are crucial for documenting early earth history in the itsaq gneiss complex of the nuuk region west greenland there is dispute whether the granitic sensu lato orthogneisses dominating it are mainly products of a single ca 3650 ma crust formation super event or whether they formed in several unrelated events between ca 3850 and 3560 ma which of these interpretations of the dates is correct has major implications regarding what the whole rock radiogenic isotopic record pb pb sm nd rb sr reveals about continental crust formation and early terrestrial differentiation there is also debate whether some west greenland metasedimentary rocks with 12c 13c data interpreted as evidence for life are 3850 ma or only 3650 ma old establishing the correct age for these rocks is important for debates concerning early surficial environments and origin of life controversies have arisen because of different approaches taken by different workers specifically with respect to how much emphasis is placed on field geology in interpreting dates and isotopic data in this paper field observations and sampling from low strain zones where the origin and geological context of the rocks are best preserved and understood are closely integrated with u pb zircon dates and cathodoluminescence cl imagery of the zircons this approach shows that most single phase well preserved meta granitoid samples have simple zircon populations dominated by oscillatory zoned prismatic grains formed when their host magmas crystallized on the other hand migmatites and some strongly deformed banded gneisses have much more complex zircon populations the combined field evidence and zircon geochronology on the itsaq gneiss complex demonstrate that 1 some areas contain exposed orthogneisses formed during multiple magmatic thermal events between ca 3850 and 3560 ma and are not as suggested by kamber and moorbath 1998 dominated by ca 3650 ma granitoids containing abundant 3650 ma zircons inherited from cryptic unexposed older rocks 2 abundant 3750 ma granitoids are present which are locally well preserved 3 some water lain sediments reported as showing c isotope evidence for life were deposited as early as 3850 ma 4 the whole rock sm nd isochron approach fails to distinguish with any confidence 3650 ma from 3800 ma rocks 5 however it reinforces previous indications for markedly depleted 2 5 nd domains in the pre 3750 ma mantle

a unique assemblage of epibenthic sessile suspension feeders with archaic features in the high antarctic we suggest that the epibenthic communities of passive suspension feeders that dominate some high antarctic seafloors present unique archaic features that are the result of long isolation together with the effects of environmental features including reduced terrestrial runoff and favourable feeding conditions these features probably originated during the late cretaceous when the high antarctic environment started to become different from the surrounding oceans modern antarctic communities are thus composed of a mixture of palaeozoic elements taxa that migrated from the deep ocean during interglacial periods and a component of fauna that evolved from common gondwana cretaceous ancestors we explore this hypothesis by revisiting the palaeoecological history of antarctic marine benthic communities and exploring the abiotic and biotic factors involved in their evolution including changes in oceanic circulation and production plankton communities the development of glaciation restricted sedimentation isolation life histories and the lack of large predators the conditions favouring the retention of apparently archaic features in the antarctic marine fauna remain to be fully elucidated but high antarctic communities are clearly unique and deserve special conservation

in situ neutron flux 36cl production and groundwater evolution in crystalline rocks at stripa sweden the meteoric input of36cl due to cosmogenic or nuclear weapon produced36cl cannot contribute significantly to the36cl present in the saline groundwaters up to 700 mg l 1 cl from the stripa granite the extent of in situ production of36cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite the36cl present in the groundwaters is attributed to either admixture of labelled cl from the leptite with cl from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36cl during subsequent groundwater residence within the granite the chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite the implications of36cl in situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed

palaeoecology of chondrodonta bivalvia from the lower aptian cretaceous apulia carbonate platform gargano promontory southern italy abstract chondrodonta is a cretaceous oyster like bivalve with a predominantly calcitic dorso ventrally elongated and slightly inequivalve shell in the tethyan carbonate platforms this taxon occurs commonly in rudist bearing limestone often preserved with still articulated valves the opportunistic chondrodonta had a cemented and gregarious life habit in the apulia carbonate platform gargano promontory southern italy chondrodonta beds occur within lower aptian lagoonal to platform basin margin deposits the studied chondrodonta concentrations which recorded the early evolutionary phase and spreading of this bivalve are made up of specimens ascribed to chondrodonta glabra stanton in the inner platform the meter thick chondrodonta accumulations were originated by autochthonous bouquet like valve aggregates frequently preserved in living position these aggregates constitute superimposed carpets characterized by only a few generations which were affected by mass mortality and rapid burial processes these mass mortalities were related to repeated environmental lethal fluctuations that occurred at the onset of the early aptian oae 1a the quick fluctuations of the chondrodonta populations are typical of unstable and unpredictable environments characterized by significant changes in trophic resources and hyperthermal and acidification peaks the studied chondrodonta specimens show different shell preservation according to their palaeobathymetric location in the shallow water inner platform specimens the internal aragonite shell layer was rapidly dissolved while in deeper water margin ones it was preserved during the early diagenetic phases this different preservation is interpreted as related to different aragonite saturation state of shallow seawater and tentatively connected to the acidification peak that occurred at the onset of the early aptian oae 1a

deep sea bio physical variables as surrogates for biological assemblages an example from the lord howe rise abstract little is known about diversity patterns of biological assemblages in deep sea environments primarily because sampling deep sea biota over vast areas is time consuming difficult and costly in contrast physical mapping capabilities are increasing rapidly and are becoming more cost effective consequently the growing need to manage and conserve marine resources particularly deep sea areas that are sensitive to anthropogenic disturbance and change is leading the promotion of physical data as surrogates to predict biological assemblages however few studies have directly examined the predictive ability of these surrogates the physical environment and biological assemblages were surveyed for two adjacent areas the western flank of lord howe rise lhr and the gifford guyot spanning combined water depths of 250 2200 m depth on the northern part of the lhr in the coral sea multibeam acoustic surveys were used to generate large scale geomorphic classification maps that were superimposed over the study area forty towed video stations were deployed across the area capturing 32 h of seabed video 6229 still photographs that generated 3413 seabed characterisations of physical and biological variables in addition sediment and biological samples were collected from 36 stations across the area the northern lord howe rise was characterised by diverse but sparsely distributed faunas for both the vast soft sediment environments as well as the discrete rock outcrops substratum type and depth were the main variables correlated with benthic assemblage composition soft sediments were characterised by low to moderate levels of bioturbation while rocky outcrops supported diverse but sparse assemblages of suspension feeding invertebrates such as cold water corals and sponges which in turn supported epifauna dominated by ophiuroids and crinoids while deep environments of the lhr flank and lower slopes of the gifford guyot were characterised by bioturbation with high occurrences of trails burrows and mounds evidence for bioturbation was significantly less on the upper sections of gifford guyot with mostly trails on the more sediment starved environments the seamount summit also supported a variety of taxa such as benthic ctenophores and rock associated fishes that were not recorded in the deeper basin habitats physical characteristics of the seabed particularly geomorphology were good predictors of biological assemblage composition and percent cover of key taxa of the nine geomorphic classes assessed in this study six predicted different physical habitats that supported distinct biological assemblages however other classes that were defined by spatial features e g valleys seamount dunes where surficial physical variables were not unique provided little predictive power of biological assemblages but rather had characteristics that were shared with adjacent surrounding geomorphic classes given the growing need to use surrogates in the management and conservation of marine environments these results are promising however our findings suggest that there is a pressing need for careful testing and validation of surrogates such as geomorphic classes before classification schemes can be deemed effective and employed as a management tool to predict seabed habitats and their biological assemblages

the descriptive nomenclature and classification of growth fabrics in fossil scleractinian reefs abstract framework sensu stricto is a concept originally relating to modern reefs and is defined by structural ecological and sedimentological criteria however in the geological literature the term framework has come to be applied to almost any organically influenced in situ accumulation including non calcareous non rigid facies associated with sea grasses this drastic departure from the original meaning is misleading and scientifically unhelpful the concept of wave resistance is integral to that of framework but in the geological record it is not easy to evaluate and the term may be of little comparative use between reef environments it is suggested that the term growth fabric be generally applied as a descriptive term for the presence of aggregated in situ corals or other organisms in growth position within a facies the term growth fabric should be used as an alternative to framework as a purely descriptive term the term framework should be restricted to its original definition and used only where the criteria for framework can be clearly demonstrated two end member types of scleractinian growth fabric genesis are recognised termed superstratal and constratal terms adapted from gili e masse j p skelton p w 1995 rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms palaeogeogr palaeoclimatol palaeoecol 118 245 267 in a superstratal growth fabric the constituent organisms collectively projected decimetres to metres above the substratum creating positive topographic relief in contrast constratal growth is where vertical organic accretion occurred at a similar rate to sediment accumulation hence the majority of the skeletal material remained continuously embedded in the sediments and only a small proportion of the skeleton projected centimetres above the sediment surface the architectural palaeoecological sedimentological and diagenetic implications of different types of growth fabric genesis is discussed a review of the classification of reef fabrics suggests that there is currently no adequate system to describe fossil scleractinian growth fabrics the most commonly used classification of reefal fabrics is that of embry and klovan 1971 embry a f klovan j e 1971 a late devonian reef tract on northeastern banks island northwest territories bull can pet geol 33 730 781 there are a number of shortcomings in this scheme which may be grouped into three categories 1 the interpretative nature of the classification 2 problems in interpreting biological effect from form and 3 insufficient categories to adequately describe mesozoic and cenozoic growth fabrics moreover there appears to be a lack of a standardised nomenclature for growth fabrics which has hindered meaningful comparisons of scleractinian growth fabrics through time and space a descriptive system based on a modification and expansion of the embry and klovan system 1971 is proposed and a revised nomenclature for growth fabrics presented the system is designed to be flexible in its application it can be used simply to describe a growth fabric or through the use of genetic and non genetic modifiers to imply types of reef building processes and growth fabric heterogeneity although the concepts and terminology discussed in this paper relate to scleractinian growth fabric they are equally applicable to fabrics comprising other organisms

quantitative analysis of rudist assemblages a key for palaeocommunity reconstructions the late barremian record from se france abstract the present paper addresses the question of rudist assemblages and their interpretation in terms of ecological entities i e communities quantitative studies performed on rudist assemblages in the barremian platform carbonates of the marseille region se france were based on biological attributes shell size shell thickness packing density packing index coverage and shell contribution and sedimentological attributes from the associated substrate mud content grain size and skeletal contribution to the sediment and bed thickness the studied samples were originally ascribed to four assemblages defined on the basis of semiquantitative data contrasting results were obtained from multivariate analysis applied to biological then to biological plus sedimentological data the latter documents four groups of samples in correspondence with the former assemblages this grouping refers directly or indirectly to critical attributes of communities biomass and substrate evidence for some taxonomic markers and because the assemblages represent recurrent statistical entities corroborate their interpretation as palaeocommunities the method proposed here for the reconstruction of rudist palaeocommunities has a potential for unravelling biological assemblages with a low taxonomic resolution

quantitative stratigraphy of rudist limestones and its bearing on spatial organisation of rudist communities the late barremian urgonian sequences of provence s e france abstract rudist beds in platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france possess a substantial lateral continuity 40 km whereas associated rudist bodies tend to be less continuous transition probabilities markov chain analysis are used at a regional scale to test the lateral continuity of rudist bodies and their four associated rudist assemblages each rudist assemblage has a specific probability to be adjacent to itself or to any one at a local scale analysing the variations of transition probabilities as a function of distance using various proxies shows a periodic spatial trend the style of which depends on the type of rudist assemblage i e community type the foregoing documents two groups with different properties group 1 includes two communities characterised by small forms restricted to very shallow and muddy settings organised spatially into small patches c 1000 1500 m with moderate spacing c 1500 2000 m group 2 includes two communities characterised by mixed size or large forms typical of deeper water and more sandy settings organised spatially into large patches c 3000 m with a larger spacing c 3000 4000 m the internal architecture and the dimensions of these rudist bodies argue against a reefal nature quantitative estimates of lateral continuity and spatial variations of rudist bodies have a significant potential for reservoir modelling of hydrocarbon bearing rudist rich platform carbonates

quantitative study of a hippuritid rudist lithosome in a santonian carbonate platform in the southern central pyrenees abstract the santonian carbonate platform deposits of the sant corneli anticline in the southern central pyrenees contain distinctive lenticular to tabular lithosomes formed by congregations of slender hippuritid rudists here we make a quantitative study of one of the lithosomes in the sant pere de vilanoveta member in the northern side of sant corneli it is exposed over some 4 km along a wnw ese section and shows a remarkably persistent thickness up to a maximum of 5 15 m though for the most part it is less than 3 m thick in the lithosome hippuritid shells are mostly preserved inclined about 30 60 from the perpendicular with respect to bedding the majority of inclined shells lean towards the southwestern to southeastern quadrants the inferred principal downstream direction hippuritids are loosely clustered and supported in a fine bioclastic matrix percentage cover of hippuritids ranges from 19 8 at the base to 31 9 in the middle and top of the lithosome the preliminary data on numerical densities number of individuals per unit area of hippuritids show some clustering around values of about 290 750 individuals per m2 the inclined orientation of hippuritid shells seems original and the result of active growth by the animals the high numerical density of hippuritids at the base of the lithosome may indicate that the hippuritid congregation grew rapidly the congregation appears to have reached an optimal level of density by the middle of the lithosome and to have maintained it through time during the development of the rudist congregation the lithosome lacks relief and has no evidence of any rigid framework

facies architecture and high resolution sequence stratigraphy of an upper cretaceous platform margin succession southern central pyrenees spain abstract excellent exposures of upper cretaceous santonian carbonate platforms on the northern flank of sant corneli anticline southern central pyrenees provide detailed information of facies architecture in both depositional strike and dip directions basic accretional units are differentiated by facies contrast across mappable surfaces these surfaces do not show clear evidence of subaerial erosion and are correlated basinward with bedding planes across which there are subtle changes in skeletal composition two types of basic accretional units have been identified based on bedding patterns internal facies architecture and skeletal composition 1 rudist buildups consist of a rudist and coral belt at the platform margin passing landward into a slender hippuritid lithosome locally overlain by a bioclastic blanket that passes basinward into bioclastic apron like clinobeds and into fine grained packstone wackestone 2 calcarenite wedges consist of yellow brown benthic foraminifer rich grainstones to grain dominated packstones with scattered rudist shells and small coral colonies passing basinward into mud dominated packstones to wackestones with variable siliciclastic content quartz sand to silt and clay rudist buildups and calcarenite wedges alternate although not rhythmically these changes in platform skeletal composition reflect changes in the dominant type of carbonate producing biota independently of the changes in accommodation both types of basic accretional units rudist buildups and calcarenite wedges form simple sequences and parasequences according to internal lithofacies arrangement and inferred sea level cyclicity cycles or paracycles high frequency sea level cyclicity fits in the milankovitch frequency band long term changes in accommodation governing aggradation progradation and backstepping of basic sequences and parasequences reflect tectonic influence rather than long term changes in eustatic sea level

mollusc and brachiopod skeletal hard parts intricate archives of their marine environment the biogenic carbonate hard parts of fossil bivalves cephalopods and brachiopods are among the most widely exploited marine archives of phanerozoic environmental and climate dynamics research the advent of novel analytical tools has led many workers to explore non traditional geochemical and petrographic proxies and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms these considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum this paper evaluates differences and similarities of seawater versus that of body fluids cephalopods bivalves and brachiopods exert a strong biological control on biomineralization that to some degree may buffer their shell geochemistry against secular changes in seawater chemistry disordered amorphous calcium carbonate precursor phases later transformed to crystalline biominerals may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases a reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo environment the impact of what is commonly referred to as biological factors on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon oxygen strontium and traditionally used element to calcium ratios in particular the often used 13ccarb or the mg ca and sr ca elemental proxies are fraught with problems an interesting new research field represents the analysis calibration and application of non traditional proxies to mollusc and brachiopod hard parts examples include the carbonate clumped isotope 47 approach and the analysis of the isotopes of ca mg n li s or element to ca ratios such as li ca or b ca and rare earth elements based on considerations discussed here a series of do s and don ts in mollusc and brachiopod archive research are proposed and suggestions for future work are presented in essence the suggestions proposed here include experimental work also field experiments making use of recent archive organisms or where possible a reasonable recent analogue in the case of extinct groups moreover the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra structures must guide sampling strategies for geochemical analyses where feasible a detailed understanding of the diagenetic pathways and the application of multi proxy and multi archive approaches should form the foundation of fossil carbonate archive research the uncritical compilation of large data sets from various carbonate shelled organisms collected at different locations is not encouraged

sm nd systematics of zircon abstract 147sm 143nd and 146sm 142nd systems were studied in nineteen 3 32 4 02 ga zircon grains from jack hills metaconglomerate 12 of which were previously analyzed for lu hf nd concentrations in the zircons are 0 9 20 ppm the amount of nd recovered was between 13 and 446 pg the analytical precision of 142nd 144nd and 143nd 144nd ratios varied between 0 004 and 0 08 2 m depending on the sample size the 147sm 144nd ratios vary from 0 4 to 1 2 143nd 144nd ratios are variably radiogenic from 0 5125 to 0 5346 combined interpretation of 147sm 143nd and u pb systems shows that lree in zircons are a mixture of a primary component with high sm nd 1 6 2 0 and a secondary younger component with low sm nd determination of initial 143nd of ancient zircons with a precision and accuracy sufficient for petrogenetic interpretations may not be possible because of large errors in the 147sm 144nd ratio which propagate to the uncertainty of 143nd additionally the 143nd values are biased by the presence of secondary nd of unknown age and isotopic composition in more altered zircons the 147sm 143nd system is more promising as a gauge for this secondary alteration related ree component in zircon application of the 146sm 142nd system in zircon to determine the timing of early terrestrial differentiation is promising it will require advancement of the analytical procedures to achieve the lowest possible blanks and maximum sensitivity ion yield as high as 20 30 will be required

stratigraphy and paleoenvironments of rudist biostromes in the upper cretaceous turonian upper santonian limestones of southern istria croatia abstract rudists are well preserved in the upper cretaceous limestones of southern istria where they flourished within different shallow water environments during the turonian to upper santonian in order to determine paleoenvironments a vertical succession of the rich rudist assemblages has been investigated and described within sequence stratigraphy framework the turonian to upper santonian sediments of southern istria in the sense of sequence stratigraphy comprise one complete third order sequence and the beginning of the transgressive systems track tst of the next sequence lower turonian pelagic limestones were deposited on a foundered carbonate platform and represent the beginning of the tst limestones of the late tst lowstand systems track lst were deposited on the inner shelf and the early tst of the next sequence was deposited on the outer shelf all the rudists which appeared after the early turonian disappearance and partial extinction were elevators the genera durania and praeradiolites thrived in bouquets which may coalesce to form thickets in inner shelf environments of the late tst lst their growth depended completely durania or partly praeradiolites on net sediment accumulation the environment in which durania and praeradiolites thrived was subtidal and deep enough to be out of reach of emersion within the same depositional environment these genera were later replaced vertically by radiolites individuals with slim cylindrical shells and wide growth lamellae have full contact within the thickets in which their growth depended little if at all on net sedimentation rate also radiolites occupied the shallower parts of the subtidal zone with a commissure rim rising above the sediment surface renewed deepening in the late santonian resulted in the outer shelf environment of the next tst gorjanovicia together with rare vaccinites flourished after the radiolites gorjanovicia differed from radiolites only in possessing more pronounced vertical ribs in their slightly deeper subtidal environment with pelagic influxes gorjanovicia thrived in bouquets loosely packed gorjanovicia gave vaccinites an opportunity to grow among them the environmental setting of the southern istria rudist biostromes and their correlation with other shallow water deposits in the mediterranean region suggests that a sequence stratigraphy approach can be applied to correlate rudist biostratigraphy on a regional or even inter regional scale

pu xe u xe u pb chronology and isotope systematics of ancient zircons from western australia the presence of xenon isotopes from in situ spontaneous fission of short lived 244 pu has been confirmed in a suite of 16 hadean detrital zircons from western australia in order to investigate the effects of xenon loss on estimates of the inferred pu u ratio we have irradiated the zircons with thermal neutrons to generate xe from 235 u neutron fission 131 xe 134 xe and 132 xe 134 xe ratios have been used to calculate the relative contributions from spontaneous fission of 244 pu and 238 u and neutron fission of 235 u and hence compare nominal pu u ratios and xenon retention ages u xe ages are typically lower than the pb pb ages indicating that xenon loss is common we show how the ternary mixing diagram can be used to place constraints on the timing and extent of this loss and to generate a corresponding pu u xe isochron although the zircons investigated in this study were extracted from the same metasedimentary unit the timing of xenon loss is variable this suggests that the loss may be the result of variable degrees of metamictization from grain to grain inferred pu u o ratios show a general decrease with the discordancy between pb pb and u xe ages for the least discordant samples we infer pu u o 0 008 which is close to the widely adopted chondritic value while we cannot completely exclude the effects of pu u fractionation in magmatic and other processes between formation of the earth and crystallisation of the zircons we conclude that they have been relatively small bfactor 2 and reflect the compatible behaviour of pu and u in the 4 valence state 2007 elsevier b v all rights reserved

facies analysis of an upper cretaceous high energy rudist dominated carbonate ramp matese mountains central southern italy subtidal and peritidal cycles abstract upper cretaceous shallow water limestones rich in rudists have been studied in the matese mountains they show a preponderance of skeletal components molluscs and benthic foraminifers and a lack of non skeletal grains the most prominent sediments of the studied stratigraphic interval are rudist dominated fine to coarse grained lithologies most of the senonian successions are characterized by massive neritic limestones rich in molluscs mostly rudists and subordinate gastropods and a few corals the sediments were generated in situ on shelves where rudist bivalves were the primary sediment producers these sediments were actively moved by storms waves and swells the finer fractions were probably winnowed out and deposited in deeper water well bedded dolomitized mudstones wackestones microbial laminites and benthic foraminifer wackestones characterize some successions where they rhythmically alternate and testify to deposition in tidal flat environments the lithofacies faunal and taphonomic characters and the sedimentary structures are typical of a ramp like open shelf with local peritidal deposition the vertical lithofacies organization consists of numerous decimetre to metre scale shallowing upward subtidal and peritidal cycles a complete transition from peritidal to subtidal cycles has been recognized and documented the peritidal cycles are usually bounded by desiccation surfaces and or dolomitized crusts followed by shallow subtidal to peritidal facies of the next cycle the subtidal cycles are typified by rudist floatstones passing to large scale cross bedded bioclastic packstones grainstones current and storm structures are distinctive features in shallower water environments the effects of submarine erosion prevail hardgrounds commonly developed and the resulting cycles are usually truncated the formation of the peritidal cycles appears to have been controlled by accommodation space in response to fluctuations in relative sea level the formation of the subtidal cycles was determined by sedimentation rates in response to fluctuations in the zones of fair weather and storm wave reworking in turn controlled by relative sea level this indicates that sediment production and supply were important controlling factors in the cycle formation during the early senonian stratigraphic interval the recognition of similar depositional styles in other early senonian successions cropping out in the southern apennines suggests that this type of sedimentation is a recurring attribute of the upper cretaceous open shelves

xenon compositions of magmatic zircons in 3 64 and 3 81 ga meta granitoids from greenland a search for extinct 244pu in ancient terrestrial rocks in order to solve the fundamental problem as to whether the extinct radioactive isotope 244pu was present in the early earth we have analysed xenon in magmatic zircons from three early archaean meta granitoids from greenland two samples a granite sample g97 111 and a ferrogabbro ferrodiorite sample g97 112 are from the same ca 3 64 ga composite intrusion at the mouth of ameralik fjord the third sample sample g97 018 is a ca 3 81 ga tonalite from a locality south of the isua supracrustal belt the 3 81 ga tonalite sample g97 018 and possibly the 3 64 ga granite sample g97 111 magmatic zircons appear to have small excesses of fission xenon different from the 238u derived spontaneous fission xenon this excess fission xenon is consistent with that expected for 244pu derived spontaneous fission and it may indicate that these zircons incorporated 244pu when they crystallised if this is true it suggests the existence of 244pu early in the earth s history furthermore our preliminary investigation supports views that the earth s primitive material had a near chondritic 244pu 238u abundance ratio and that fissiogenic xenon in the atmosphere is of plutonic origin

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

distinguishing core and flank facies based on shell fabrics in lower jurassic lithiotid shell beds abstract lower jurassic larger bivalves mostly represented by the monospecific lithiotid genera lithiotis cochlearites and lithioperna formed large shell accumulations in the shallow water carbonate tethyan and panthalassa margins a quantitative analysis of lithiotid accumulations from the trento platform northern italy was carried out in order to distinguish the distribution of autochthonous parautochthonous and allochthonous lithiotids in the accumulation core and flanks various representative accumulations are characterized with respect to systematic content shell cover shell density disarticulation shell fragmentation and orientation of individual shells lithioperna shows a high shell cover within the accumulation core while that of cochlearites is variable and lithiotis is rare all three lithiotids occur in high densities in the accumulation flanks as expected autochthonous individuals of all three genera are frequent in the accumulation cores where they are preserved in life position in the flanks most bivalves are parautochthonous except for lithioperna which can grow in life position all bivalves in allochthonous shell beds are highly fragmented and disarticulated the studied traits are potentially useful as proxies for distinguishing core or flank facies when the accumulation does not crop out as a whole

archaean fluid assisted crustal cannibalism recorded by low δ 18 o and negative e hf t isotopic signatures of west greenland granite zircon the role of fluids during archaean intra crustal magmatism has been investigated via integrated shrimp u pb 18o and la mc icpms 176hf isotopic zircon analysis six rock samples studied are all from the nuuk region southern west greenland including two 3 69 ga granitic and trondhjemitic gneisses a 3 64 ga granitic augen gneiss a 2 82 ga granodioritic ikkattoq gneiss a migmatite with late neoarchaean neosome and a homogeneous granite of the 2 56 ga qorqut granite complex qgc all zircon grains were thoroughly imaged to facilitate analysis of magmatic growth domains within the zircon analysed there is no evidence for metamictization initial ehf zircon values n 63 are largely sub chondritic indicating the granitic host magmas were generated by the remelting of older un radiogenic crustal components zircon from some granite samples displays more than one 207pb 206pb age and correlated with 176hf 177hf compositions can trace multiple phases of remelting or recrystallization during the archaean model ages calculated using lu hf arrays for each sample indicate that the crustal parental rocks to the granites granodiorites and trondhjemites segregated from a chondrite like reservoir at an earlier time during the archaean corresponding to known formation periods of more primitive tonalite trondhjemite granodiorite ttg gneisses zircon from the 3 69 ga granite the migmatite and qgc granite contains eoarchaean cores with chondritic 176hf 177hf and mantle like 18o compositions the age and geochemical signatures from these inherited components are identical to those of surrounding tonalitic gneisses further suggesting genesis of these granites by remelting of broadly tonalitic protoliths zircon oxygen isotopic compositions n 62 over nine age populations six igneous and three inherited have weighted mean or mean 18o values ranging from 5 8 0 6 to 3 7 0 5 the 3 64 ga granitic augen gneiss sample displays the highest 18o with a mildly supra mantle composition of 5 8 0 6 inherited eoarchaean ttg derived zircon shows mantle like values igneous zircon from all other samples spanning more than a billion years of archaean time record low 18o sub mantle compositions these are the first low 18o signatures reported from archaean zircon and represent low 18o magmas formed by the remelting and metamorphism of older crustal rocks following high temperature hydrothermal alteration by meteoric water meteoric fluid ingress coupled with crustal extension associated high heat flow and intra crustal melting are a viable mechanism for the production of the low 18o granites granodiorites and trondhjemites reported here both high and low 18o magmas may have been generated in extensional environments and are distinct in composition from phanerozoic i type granitic plutonic systems which are typified by increasing 18o during intra crustal reworking this suggests that archaean magmatic processes studied here were subtly different from those operating on the modern earth and involved extensional tectonic regimes and the predominance of remelting of hydrothermally altered crystalline basement

high resolution geomorphic map of a submerged marginal plateau northern lord howe rise east australian margin high resolution multibeam bathymetry is used to map and interpret seabed geomorphology for part of the northern lord howe rise plateau in the tasman sea a mapping system of geomorphic units and elements is used extending the previous hierarchy of geomorphic provinces and features used for the australian margin the mapped area covers 25 500 km2 and incorporates broad ridges valleys and plateaus superimposed on these features are clusters of volcanic peaks smaller ridges holes scarps and aprons an additional characteristic of the seabed in this area is an extensive network of polygonal furrows that covers the plateau and the lower slopes of larger ridges these furrows are formed in stiff unconsolidated carbonate ooze that forms a near continuous sediment cover across the area peaks are the only geomorphic feature not fully draped in pelagic ooze the distribution of geomorphic units suggests strong controls from underlying geological structures in water depths of 1400 to 1600 m some peaks occur in clusters on ridges that sit above acoustic basement highs and volcanic intrusions elsewhere broad plateaus and valleys slope to the southwest following the regional dip of the lord howe rise plateau in contrast localised geomorphic elements such as moats and holes have likely explanation in terms of spatial variations in sedimentation rates in relation to bathymetric highs polygonal furrows are attributed to dewatering processes the geomorphology of the seabed mapped in this study incorporates examples of forms that have not been previously mapped in such detail on the australian margin these are unlikely to be unique to the mapped area of the lord howe rise and can be expected to occur elsewhere on the rise and presumably on other parts of the australian margin with a similar geological history

early archaean amitsoq tonalites and granites of the isukasia area southern west greenland development of the oldest known sial amphibolite facies early archaean amitsoq gneisses envelop and intrude the c 3 800 ma isua supracrustal belt isukasia area southern west greenland most of these gneisses are strongly deformed but in a c 75 km2 augen of lower deformation the amitsoq gneisses are seen to comprise predominantly 3 750 3 700 ma tonalitic grey gneisses that were intruded first by thin bodies of mafic to dioritic composition known collectively as the inaluk dykes and then by c 3 600 ma white gneisses and finally by sporadic c 3 400 ma pegmatitic gneiss sheets the grey gneisses could have formed by partial melting of crust consisting predominantly of basic rocks the inaluk dykes are interpreted as strongly fractionated basic melts of mantle origin contaminated by crustal material the white gneisses consist mostly of medium grained granite and occur as lenses and anastomosing sheets throughout their host of grey gneisses with subordinate inclusions of supracrustal rocks the white gneisses have chemistry compatible with formation by partial melting at depth of a source dominated by grey gneisses the igneous chemistry including ree abundances of the grey gneisses and white gneisses has been modified to varying degrees by metasomatism and assimilation reactions during the crystallisation of the white gneisses and also during subsequent tectonometamorphic events the white gneisses are evidence for considerable reworking by anatexis of sialic crust in the early archaean 150 to 100 ma after its formation the white gneisses and the pegmatitic gneisses show that granitic rocks s s were important in the earliest archaean and are further evidence of the diversity of the oldest known sial

macrofaunal communities within and adjacent to a detritus rich submarine canyon system abstract macrofaunal abundance biomass diversity and species assemblages within scripps and la jolla submarine canyons are compared with those on the nearby continental shelf and slope our primary objective was to examine the effect of detrital aggregates on infaunal communities within canyons two submarines a remotely operated vehicle rov and a soutar box corer were used to collect samples within the canyons organic enrichment by macrophyte detritus was evident from canyon heads down to 550 m and evidence of strong currents coarse sediment was found down to 700 m infaunal density and biomass were higher in the canyons than outside at all depths where comparative data were available 100 500 m infaunal assemblages in canyons were distinct from those at reference stations both the canyon and non canyons samples showed community differentiation with depth species diversity was generally high but decreased with depth outside of canyons and increased with depth within the canyons low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical disturbance submarine canyons are commonly found to contain distinct species assemblages or higher faunal densities and or biomass than nearby non canyon regions at similar depths canyons are regular features along most ocean margins and appear to be important as sites of enhanced secondary production provide diverse habitats and act as conduits of coastal detritus to the deep sea

palaeoecology of corals and rudists in mixed volcaniclastic carbonate small scale rhythms upper cretaceous jamaica abstract the guinea corn formation central jamaica west indies is represented by alternating platform carbonates and volcaniclastic sandstones and siltstones and represents the most landward shift of facies in an upper campanian to maastrichtian transgressive regressive cycle the succession consists of 2 30 m thick rhythms comprising a lower volcaniclastic siltstone sandstone division a middle volcaniclastic siltstone limestone with abundant corals or the rudist antillocaprina stellata and an upper division of rudist rudstones and floatstones the lower division consists of either bioturbated sandy siltstones with lignite and abundant gastropods and infaunal bivalves lower rhythms in the guinea corn formation or interbedded volcaniclastic siltstones and normally graded sandstones the rudist limestones are parallel bedded and consist of high abundance mono to paucispecific assemblages the boundary between the middle and upper parts of rhythms contains a concentration of oncoids with coral nuclei and a mantle of microbial laminates red algae and serpulids four coral assemblages are recognised based on diversity and coral morphology the paracycloseris dasmosmilia assemblage occurs in the lower division of the rhythms and is interpreted as a soft substrate assemblage that was adapted to elevated nutrient levels the ovalastrea actinacis actinacis multicolumnastrea and actinacis calamophyllia gyrodendron assemblages occur in the middle parts of the rhythms and consist of bedded rudstones rudstone mounds and rarer platestones pillarstones and mixstones polyparia arrangements colony morphology and low diversity suggest the ovalastrea actinacis and actinacis multicolumnastrea assemblages were adapted to high sedimentation rates the more diverse actinacis calamophyllia gyrodendron assemblage is interpreted to have grown under more optimum conditions low sedimentation rates and high light intensities rudists are classified on their growth orientation elevator clinger recumbent and on their communal relationships isolated or clustered the cluster elevator biradiolites mooretownensis occurs in the lower division of rhythms and the recumbent a stellata occurs in the middle part of rhythms the upper part of rhythms contains abundant rudists including isolated elevators antillocaprina occidentalis cluster elevators bournonia spp biradiolites jamaicensis thyrastylon spp and chiapasella radiolitiformis and clingers plagioptychus spp with the topmost part contains the large recumbent titanosarcolites

benthic environments of the lord howe rise submarine plateau introduction to the special volume abstract the australian exclusive economic zone eez contains1 6 million km2 of submarine plateaus equal to about 13 8 of the world s known inventory of these features this disproportionate occurrence of plateaus presents australia with an increased global responsibility to understand and protect the benthic habitats and associated ecosystems this special volume presents the results of two major marine surveys carried out on the lord howe rise plateau during 2003 and 2007 during which benthic biological and geological samples underwater photographs video and multibean sonar bathymetry data were collected the benthic habitats present on lord howe rise are dominated by slowly accumulating low energy soft sediment habitats but also include hard rocky substrates covering a small area of volcanic peaks around 31 km2 and parts of other larger seamounts e g the lord howe island seamount which support rich and abundant epifaunal assemblages dominated by suspension feeding invertebrates these rocky habitats appear to qualify as ecologically and biologically significant areas under the united nations convention on biological diversity cbd scientific selection criteria 1 uniqueness or rarity 4 vulnerability fragility sensitivity or slow recovery and 7 naturalness the collection of papers included in this special volume represents a major advance in knowledge about benthic habitats of the lord howe rise but also about the ecology of submarine plateaus in general

rudist coral frameworks associated with submarine volcanism in the maastrichtian of the pachino area sicily maastrichtian strata from the pachino area se sicily provide a model of association between rudist coral frameworks and submarine volcanic activity two successive carbonate units are distinguished a coral rudist bioherms and biostromes developed in a high energy environment b hippuritid build ups and banks overlain by rudist coral clusters which grew under harsher ecological conditions in a weaker current regime at the top of the maastrichtian sequence the growth of rudist coral frameworks ceased as ecological conditions shifted toward restricted environments the inferred succession reflects a gradual decrease in current strengths and water depths related to the maastrichtian regressive phase the frameworks display consistent evolutionary sequences reflecting progressive changes in their biota structure size and shape occurrences of rudist coral frameworks are clearly linked with submarine volcanoes which provided opportunities for their development they sometimes grew in the vicinity of active vent centres a feature reported for the first time in the upper cretaceous

corals to rudists an environmentally induced assemblage succession abstract corals and rudist bivalves commonly coexisted on the shallow carbonate platforms of the cretaceous tethyan realm usually the carbonate platforms show lateral and vertical biotic zonations in general the vertical biotic zonation relates directly to a consistent lateral biofacies pattern coral or coral rudist assemblages occupy more open zones of the platform and rudist dominated assemblages the more restricted zones several corresponding coral to rudist assemblage successions in carbonate platforms have previously been widely interpreted as ecological successions we document some coral to rudist assemblage successions in a well preserved upper cretaceous section in the tremp area of the south central pyrenean unit which are interpreted by contrast as environmentally induced faunal replacements a repeated assemblage succession in the eastern part of the section begins with a coral dominated assemblage and passes up gradually to a mixed coral and rudist assemblage that is succeeded by a paucispecific unit of hippuritid elevator congregations the lower coral rudist units of such successions represent relatively more open marine conditions and the uppermost hippuritid unit relatively more restricted marine conditions this assemblage succession was formed in response to a change in the depositional setting caused by sediment accumulation two consecutive coral dominated assemblages overlain by mixed coral and rudist assemblages constitute a second kind of a sedimentary coral to rudist assemblage succession discussed in this paper its regular recurrence makes up the uppermost part of the section in the east the predominance of platy to low domal coral colonies in the lower units suggests that conditions were initially favourable for horizontal coral growth as the habitat changed these coral assemblages were replaced by massive tabular to large domal coral colonies with the large hippuritid vaccinites and were sometimes succeeded in turn by clustered hippuritid elevators the most important factor causing the replacement was probably the increase in sediment flux associated with turbidity this change in the depositional environment eventually favoured the establishment of rudist elevators well adapted to moderate and intermittent to continuous accumulation of sediment

an ocean facing aptian albian carbonte margin oman a high energy aptian albian platform margin in northern oman fronted onto an open oceanic basin making the area a valuable analogue for coeval guyot margins most similar aged carbonate margins described in the literature faced either intracratonic or minor oceanic basins the studied margin is characterized by a stabilized outer rim which although it did not rise discernibly above the adjacent lagoonal deposits flanked a steep upper slope 32 40 basinwards with a relief of at least 30 m two main facies provided the rigidity of the outer margin lithocodium boundstones that constituted up to 50 of the rock volume and marine fibrous cements that occluded up to 35 of primary pore space in contrast coral rudist patches and other shelly sessile benthos were distributed irregularly and the rudist bioherms of the outer margin were often disrupted with shells being transported and redeposited the inner margin is characterized by wedge shaped storm layers that radiate from the platform top lagoonwards where they interdigitate with carbonate sands and small rudist bioherms polygenetic discontinuity surfaces that bear evidence of both marine hardground and subaerial exposure stages are prominent features of the margin throughout the latest aptian to middle albian the platform succession recorded some 30 relative sea level falls of which seven reached amplitudes of many tens of metres these seven high amplitude falls in sea level are recorded across the entire south eastern portion of the arabian craton and are probably of eustatic origin

the growth fabric of gregarious rudist elevators hippuritids in a santonian carbonate platform in the southern central pyrenees abstract the growth fabrics of living congregations of erect sessile epifauna range between two extremes with superstratal growth the growing skeletons project well metres above the ambient sedimentary surface creating an upstanding framework which may be secondarily filled by sediment as in modern tropical coral reefs with constratal growth by contrast the growing tips of the skeletons project little centimetres from the seafloor such that the bulk of the skeletal fabric is embedded in and supported by the accumulating interstitial sediment as in pinna and oyster beds here we investigate the original growth fabrics and palaeorelief of hippuritid congregations in the santonian rudist formations around the sant corneli anticline near tremp in the southern central pyrenees the study particularly concentrates on a hippuritid lithosome exposed over some 0 25 km2 on the northern flank of the anticline four aspects are analysed 1 the lithosome is shown to have a tabular biostromal geometry and like others in the area is covered by a laterally accreted bioclastic blanket 2 specimens in upright life position show that the pioneers of the paucispecific congregations grew in bouquets but later recruits settled on the flanks of established and fallen shells adults were only loosely clustered and supported by the accumulating interstitial sediment 3 most shells however are now horizontal with respect to the bedding and densely stacked dense horizontal fabric or d h f this fabric is shown to be a result of current induced removal of sediment and toppling of shells 4 in contrast to the open marine aspect of the overlying bioclastic sediments the fine matrix sediment of the hippuritid lithosomes is faunally restricted and appears largely derived from the in situ biodegradation of shells we conclude that the hippuritid congregations grew constratally i e without any supporting biogenic framework and that they formed biostromal accumulations lacking relief so there is no justification for calling them reefs as some authors have done rather these rudists grew as gregarious sediment dwellers in the restricted waters of the platform top where they were sporadically disturbed by storms and eventually blanketed by bioclastic material swept in from the platform margin

species richness and abundance patterns of tethyan cretaceous rudist bivalves mollusca hippuritacea in the central eastern mediterranean and middle east analysed from a palaeontological database abstract data about the stratigraphical and regional distribution of cretaceous rudist bivalves in the central eastern mediterranean and middle east from the barremian to the maastrichtian have been compiled in a taxonomic databank system the investigated region comprises northern central and southern regions of the cretaceous tethys the regionally different quality of taxonomic data is critically discussed both species richness and abundance number of species records peak in the early aptian late cenomanian and early campanian temporal patterns in species richness are examined in relation to evolutionary innovations of the group crises in species richness and abundance during the early and mid cretaceous were coeval with oceanic anoxia associated with platform drowning also regional emergence affected large parts of the apulian plate and other central tethyan carbonate platforms during the mid cretaceous period of globally high sea level so that these crises can be attributed to regional environmental perturbations induced by either oceanic anoxia or tectonic movements the cenomanian turonian transition marks an important faunal turnover as indicated by the demise of taxonomic groups which are characterised by recumbent ecological morphotypes and predominantly aragonitic shells during the turonian they were replaced by associations dominated by largely calcitic radiolitidae and hippuritidae among which elevator morphotypes dominated the stratigraphy of many post turonian deposits in the studied region is too imprecise for a detailed analysis of late cretaceous distributional patterns and the demise of rudists during the maastrichtian in particular the regional pattern of species richness and abundance is similar throughout most of the investigated region a notable exception is the broad north eastern african shelf from libya to lebanon where rudists were almost completely absent after the coniacian this coincided with shallow water phosphorite and black shale formation on the extended shelf of this region indicating the upwelling of nutrient rich waters and stagnant conditions during this time campanian maastrichtian species rich associations thrived along the north eastern afro arabian margin now exposed in south eastern turkey iran the united arab emirates uae and oman this region forms the single distinct faunal province during the cretaceous in the studied region as indicated by an endemism of 40 at the genus level the low species richness and abundance of hippuritidae on turonian maastrichtian central tethyan carbonate platforms when compared with regions having mixed calcareous siliciclastic sedimentation is interpreted to argue against a widespread photosymbiosis in the group several aspects of this study highlight the importance of regional tectonic and oceanographic controls of distributional and perhaps also evolutionary patterns of rudist bivalves their delineation still suffers from the regionally different quality of stratigraphical and taxonomic data

anatomy of an early archean gneiss complex 3900 to 3600 ma crustal evolution in southern west greenland the early archean complex of southern west greenland consists of polyphase tonalitic trondhjemitic granodioritic ttg and granitic amitsoq gneisses with inclusions of volcanic and sedimentary rocks gabbros and ultramafic rocks in this complex rocks of similar appearance and composition were found to be of different ages by u pb zircon dating the amitsoq gneisses comprise 3870 3820 3810 3760 3730 3700 and 3625 ma ttg and 3660 3650 and 3625 ma granites and their inclusions belong to several supracrustal sequences with a similar spread of ages these results show that the complex grew by episodic addition of new ttg and welding together of rocks of different ages a possible plate tectonics scenario is as follows melting of subducted mafic oceanic crust formed 3700 ma microcontinents consisting of ttg suites with predominantly mafic inclusions at 3650 ma collision between microcontinents caused crustal thickening high grade metamorphism and emplacement of leucogranites at 3625 ma subduction at the edge of the 3625 ma continental mass created a new crustal addition comprising both ttg and granite while granites were emplaced into the 3625 ma continental mass