trace metal geochemistry of remote rivers in the canadian arctic archipelago abstract trace metals are essential micronutrients for phytoplankton as well as useful tracers of biogeochemical processes in aquatic systems the largest arctic rivers are known to play an important role in the cycling of trace metals in the arctic ocean however these systems account for little more than half of arctic freshwater discharge leaving a major gap in our understanding of the trace metal geochemistry from smaller river systems this is especially problematic for rivers draining the arctic coastal margins as these continuous permafrost systems are anticipated to be particularly sensitive to climate change this study presents the first observations of dissolved and particulate trace metal concentrations and lead isotopes in 14 rivers in the canadian arctic archipelago caa dissolved concentrations of aluminum iron manganese nickel copper zinc cadmium and lead display clear spatial variability in their distributions small rivers located in the central islands of the caa have remarkably low concentrations of these trace metals while the rivers draining the southern continental landmass have higher values this geographic variability in dissolved metal concentrations reflects both differences in bedrock geology and the south north environmental gradients in the archipelago we extrapolate these findings to estimate the dissolved trace metal concentrations for other rivers draining the caa based on their geographic location elemental ratios measured in the suspended particulate matter in several rivers indicates a significant enrichment of nickel copper zinc and lead over the crustal composition in particular lead isotope composition shows an extremely large range varying from the highly radiogenic tree river 206pb 207pb 1 5121 in the south to the relatively unradiogenic glacier river 206pb 207pb 1 0153 in the central caa lack of correlation between the pb isotopic composition and pb enrichment suggests pb is derived from within the watershed this work presents the first observations of dissolved and particulate trace metal concentrations in small coastal draining rivers from the caa an important first step in developing a baseline against which to evaluate future change in the high arctic

extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

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

early hettangian benthic planktonic coupling at doniford sw england palaeoenvironmental implications for the aftermath of the end triassic crisis abstract this paper presents a high resolution micropalaeontological study integrated with geochemical and sedimentological analyses of the triassic jurassic tr j transition at the doniford section sw england our analyses indicate the renewal of surface carbonate production in the blue lias formation early hettangian after the end triassic mass extinction based on the high abundance of surface carbonate producers schizosphaerellids which occurred in phase with development at sea floor of calcareous hyaline benthic foraminifers we deduce that a benthic pelagic coupling resulted in both the initial restoration of the biological carbonate pump and also a more efficient export production the presence of monospecific phytoplankton assemblages and benthic foraminiferal assemblages typical of poorly oxygenated environments suggest that the environmental stress continued after the end triassic maximal perturbation complete environmental recovery was prevented by a succession of alternating dysaerobic and anoxic phases that favoured the deposition of black shale sediments the hypothesis of a methane release mechanism as a trigger for the global carbon cycle perturbation and greenhouse conditions during the early jurassic is discounted based on evidence from the decoupled carbon isotope records of carbonate and organic matter apart from local control of a high amplitude sea level change across the tr j boundary the succession and nature of events at doniford are consistent with a scenario of global environmental and biotic changes triggered by the physical and chemical effects of the central atlantic magmatic province camp volcanism a super greenhouse climate in the aftermath of the end triassic mass extinction appears to be the results of the combination of the long term co2 accumulation in the atmosphere system due to the camp volcanic activity as well as the inefficiency of the biological pump due to reduced export production

correlating the end triassic mass extinction and flood basalt volcanism at the 100 ka level new high precision u pb geochronology from volcanic ashes shows that the triassic juras sic boundary and end triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the central atlantic mag matic province to 150 ka this narrows the correlation between volcanism and mass extinc tion by an order of magnitude for any such catastrophe in earth history we also show that a concomitant drop and rise in sea level and negative 13 c spike in the very latest triassic occurred locally in 290 ka such rapid sea level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end triassic extinction and potentially driven by central atlantic magmatic province volcanism

the ellipsactinia limestones of the marsica area central apennines a reference zonation model for upper jurassic intra tethys reef complexes abstract this study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of upper jurassic intra tethys platforms the proposed model is based on the zonation of an upper jurassic reef complex presently exposed in the central apennines excellent exposures allow the reconstruction of the reef profile across the platform margin biota are mainly represented by corals and calcified demosponges distributed with different amounts and aggregating structures along the reef complex microencrusters represent a secondary but important component that actively contributes to the reef construction process reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex revealing a strong reef zonation like the biota the sedimentary features grain size sorting and reworking degree bioerosion cement crusts and cavities show a distinctive distribution along the reef complex three main zones have been recognized along the studied reef complex an internal more protected and deeper zone corresponding to a relatively deep back reef lagoon is dominated by corals and chaetetids a central zone reef flat where well preserved coral bioconstructions give rise to a true but discontinuous framework and a more external zone corresponding to the reef crest characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores the latter forms mound shaped structures playing a role essential for the zoned character of the reef complex these structures actively contribute to the construction of a moderately high topographic relief in the reef crest

hydrodynamic control of the supply of reworked terrigenous sediment to coral reefs in the bay of banten nw java indonesia abstract the bay of banten is an example of a shallow water reef environment adjacent to an eroding delta system where corals survive in turbid conditions this study investigated the hydrodynamic controls over residual fluxes of terrigenous sediment in the bay observations of wind waves currents and suspended sediment concentrations in 1998 and 1999 revealed contrasting dynamic turbidity conditions influenced by tides monsoon driven flows and locally generated waves the most sediment rich suspensions originate from the shallow coastal margin of an inactive delta where waves resuspend sediment and small creeks discharge freshwater and sediment because of coupling between monsoonal wind throughflow in the bay and wave height when wave induced resuspension peaks seasonally during the northwest monsoon an eastward throughflow prevents the nearshore reefs in the bay from being directly exposed to turbid water masses generated in the eroding delta in inshore waters tidal asymmetry and the spatial variation of current amplitudes cause residual sediment transport largely depending on the availability of erodible sediment in the center of the bay where there is a patch reef complex the tidal and subtidal currents are weak and therefore here there is a zone where sediment accumulates

coral reefs of the turbid inner shelf of the great barrier reef australia an environmental and geomorphic perspective on their occurrence composition and growth investigations of the geomorphic and sedimentary context in which turbid zone reefs exist both in the modern and fossil reef record can inform key ecological debates regarding species tolerances and adaptability to elevated turbidity and sedimentation furthermore these investigations can address critical geological and palaeoecological questions surrounding longer term coral sediment interactions and reef growth histories here we review current knowledge about turbid zone reefs from the inner shelf regions of the great barrier reef gbr in australia to consider these issues and to evaluate reef growth in the period prior to and post european settlement we also consider the future prospects of these reefs under reported changing water quality regimes turbid zone reefs on the gbr are relatively well known compared to those in other reef regions they occur within 20 km of the mainland coast where reef development may be influenced by continual or episodic terrigenous sediment inputs fluctuating salinities 24 36 ppt and reduced water quality through increased nutrient and pollutant delivery from urban and agricultural runoff individually and in synergy these environmental conditions are widely viewed as unfavourable for sustained and vigorous coral reef growth and thus these reefs are widely perceived as marginal compared to clear water reef systems however recent research has revealed that this view is misleading and that in fact many turbid zone reefs in this region are resilient exhibit relatively high live coral cover 30 and have distinctive community assemblages dominated by fast growing acropora montipora and or sediment tolerant species turbinaria goniopora galaxea porites palaeoecological reconstructions based on the analysis of reef cores show that community assemblages are relatively stable at millennial timescales and that many reefs are actively accreting average 2 7 mm year where accommodation space is available despite recent anthropogenic pressures these turbid zone reefs challenge traditional views on the environmental conditions required for active reef growth but given their proximity to land and associated stresses current knowledge on these less well understood reefs should be synthesised to aid coastal management directives terrigenous sediments are a dominant influence on turbid zone reef occurrence composition and growth and therefore the assessment of their future prospects will require a detailed understanding of the sedimentary regimes under which they occur and of their differential response modes

early history of scleractinian corals and its geological consequences conventional views have implied that scleractinian corals were hermatypic and thus were potentially reef building from the onset of their appearance in early mesozoic time in shallow shelf carbonate environments however for almost 25 m y they held rather subordinate positions and generally did not participate in extensive ecologic reef framework evidence from both north america and europe demonstrates that triassic corals had ecologic preferences quite different from those in the cenozoic a key step in the evolutionary success of these corals may have been the advent of a symbiotic association with algae this association believed to have developed at the end of the triassic could have been responsible for thrusting scleractinians into prominent positions as reef builders and may account for their dramatic radiation in mesozoic time

syn depositional alteration of coral reef framework through bioerosion encrustation and cementation taphonomic signatures of reef accretion and reef depositional events the development of coral reef framework and the preservational character of both in situ and rubble coral is strongly influenced by a range of physical chemical and biologically mediated taphonomic processes these operate at or just below the reef framework water interface and can be defined as having either a constructive or destructive effect upon primary reef framework i e coral constituents constructional activities add additional calcium carbonate to the primary framework structure via secondary framework growth and early cementation destructive processes which remove or degrade primary and secondary framework carbonate are associated with the effects of either physical mainly storm disturbance or biological erosion termed bioerosion key bioeroding groups include the grazing fish and echinoid groups as well as the activities of an array of infaunal borers these include specific groups of sponges bivalves and worms termed macroborers as well as cyanobacteria chlorophytes rhodophytes and fungi termed microborers the relative importance of each process and the rates at which they operate vary spatially across individual reef systems in addition many of these processes leave distinctive signatures on or in the coral framework in some cases e g calcareous encrusters these are the skeletons of the organisms themselves whilst in other cases the organism may leave behind a trace of their activity e g macro and microborers these represent useful palaeoenvironmental tools firstly because they often have good preservation potential and secondly because the range and extent of many of the individual species groups and processes involved exhibit reasonably well constrained environment and or depth related distributions as a result these taphonomically important organisms or processes can be used to delineate between reef environments in core or outcrop and to aid the interpretation of reef depositional processes and events this review summarises current understanding regarding the distribution of these species processes within contemporary reef settings and considers the suites of taphonomic signatures that may aid in the recognition and interpretation of depositional environments and events

hyperconcentrated flows on a forested alluvial fan of eastern canada geomorphic characteristics return period and triggering scenarios the assessment of the dominant flow type on alluvial fans usually refers to two categories debris flow fans i e sediment gravity flows and fluvial fans i e fluid gravity flows here we report the results of combined morphometric stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods mud floods or transitional debris flows are the dominant fan building process in eastern canada these flows produce transitional facies between those of debris flows which consist of a cohesive matrix supported diamicton and those of river flows which display more distinct stratification the size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows the fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit however these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology tree ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterized by a return period of 9 25 years for the period 1934 2008 although most of the analyzed events occurred after 1970 historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales this evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan according to these scenarios two distinct hydrologic regimes emerge the torrential rainfall regime and the nival regime related to snowmelt processes hydrogeomorphic processes occurring in a cold temperate climate and particularly on small forested alluvial fans of north eastern north america should receive more attention from land managers given the hazard they represent as well as because of their sensitivity to various meteorological parameters copyright 2014 john wiley sons ltd

taphonomic signatures of turbid zone reef development examples from paluma shoals and lugger shoal inshore central great barrier reef australia numerous coral reefs and coral communities occur along the nearshore regions of the central great barrier reef australia coastline these develop under conditions of episodically high wave induced sediment resuspension and turbidity and terrigenoclastic sediment accumulation cores recovered from two such reefs at paluma shoals and lugger bay are used to assess the taphonomic features and processes associated with framework development in such settings reef framework development is dominated by the accumulation of mainly rubble coral and isolated in situ coral colonies the reef fabric varies from clast to matrix supported in character and the matrix comprises poorly sorted mixed terrigenoclastic carbonate sediments taphonomic signatures from the different reef sites and facies show little variability and thus a distinct suite of taphonomic criteria indicative of nearshore turbid zone reef development are delineated the degree of both calcareous encrustation and internal bioerosion exhibits a high degree of between clast variability and many clasts are preserved in near pristine condition where present calcareous encrustation is restricted to thin isolated crusts comprising mainly of the coralline algae lithoporella or lithothamnion and isolated serpulid worms and cemented bivalves no biological binding of framework constituents occurs bioerosion is dominated by traces of entobia sp sponge borings and locally gastrochaenolites sp bivalve traces although only a limited suite of bioerosion trace morphologies is present there is little or no cementation of the reef framework and only isolated acicular aragonite or peloidal micrite cements occur within intra skeletal cavities significant occlusion of primary and secondary skeletal porosity by uncemented fine grained mainly terrigenous sediment is however common throughout the reef sequence the taphonomic criteria identified all have good preservation potential and should be readily identifiable within core sections such criteria thus have potential for aiding the recognition of reefs that either developed under similar environmental conditions of high turbidity and terrigenous sediment accumulation or which were subject to similar conditions during more short lived phases of reef accretion

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

bioerosion in an equatorial middle jurassic coral sponge reef community callovian matmor formation southern israel abstract the matmor formation middle jurassic callovian 165 161 mya in southern israel contains abundant coral sponge patch reefs and large crinoids which have been extensively bioeroded by bivalves worms barnacles phoronids and others producing eight ichnospecies it is significant for the evolutionary history of bioerosion because this is the first equatorial middle jurassic boring ichnofauna to be documented when compared to contemporaneous ichnofaunas this assemblage is of average diversity and abundance but has only rare sponge borings and contains abundant specimens of oichnus paraboloides as shallow pits on crinoid stems the matmor formation surprisingly lacks carbonate hardgrounds which are otherwise abundant in subtropical and temperate equivalents

channel avulsion on alluvial fans in southern arizona historical aerial photographs and field observations on five fluvially dominated alluvial fans in southern arizona demonstrate that channel avulsion invariably occurs where bank heights are low and often at channel bends channel abandonment occurs through stream capture when overland flow from the main channel accelerates and directs headward erosion of smaller channels heading on the fan surface five distinct channel morphologies observed on the fans are related to different stages of the avulsion process and can be used to identify areas on a fan surface that are prone to avulsion a descriptive model of channel avulsion illustrates how the morphology of a single channel reach will evolve through time as it captures the main flow path and is itself eventually abandoned immediately following avulsions small preexisting channels that capture flow from the main channel will typically experience three fold or greater increases in channel width subsequent large floods can be stably conveyed through these high capacity reaches an uninterrupted sequence of sediment charged small flows however will eventually begin to back fill the wide channels as vegetation growth stabilizes the banks the stabilized and back filled channels are now prone to abandonment during large floods because the decrease in the channel s capacity leads to the generation of overland flow beyond the margins of the shallowed channels the action of the small aggrading floods is critical in the avulsion process since the greatest amount of overland flow is generated where bank heights are lowest as a result both small and large floods are effective agents of landscape change on the fans channel avulsions on the five fans are not completely random events in space and time because their occurrence is controlled by the relative positioning of low banks along the main channel and smaller channels draining the fan surface consequently the location and timing of future channel avulsions can potentially be anticipated in an effort to improve flood hazard assessment on fluvial fans in the rapidly urbanizing southwestern united states

fringing reef growth on a terrigenous mud foundation fantome island central great barrier reef australia the leeward fringing reef at fantome island central great barrier reef province is a carbonate body which has developed under the influence of terrigenous sedimentation the reef flat is up to 1000 m wide and is surfaced by mobile sand and gravel with almost all live corals restricted to the seaward rim the reef slope has coral columns and heads on the upper part but below 5 m water depth it is a muddy substrate with scattered mounds of branching corals three high recovery cores show the reef is up to 10 m thick and developed over a gently sloping terrace of weathered pleistocene alluvium three post glacial stratigraphic units are recognised i carbonate reef top unit of coral rudstone and framestone including sinuluriu spiculite 2 lower slope unit of coral floatstone in a terrigenous muddy matrix and 3 transgressive basal unit of skeletal arkosic sand the acid insoluble content of matrix and of individual corals increases downwards coral growth rates decrease downwards reflecting slower growth in muddier environments radiocarbon dating shows that the reef prograded seaward at almost stable sea level an average vertical accumulation rate of 6 7 mm yr is indicated two age reversals are interpreted as material transported by storms or by erosion in response to a late holocene sea level fall the carbonate reef top unit has developed adjacent to and is environmentally compatible with a muddy terrigenous lower slope unit terrigenous influx has not changed during the holocene and terrigenous content of sediments is controlled by deposition on the reef slope of fine sediment winnowed from the reef flat and concentration of coarse sediment in the transgressive basal sheet

platy coral patch reefs from eastern panthalassa nevada usa unique reef construction in the late triassic abstract upper triassic lower norian reefal buildups near mina nevada represent some of the earliest scleractinian coral reefs from eastern panthalassa the small patch reefs 20 40 m high and 50 150 m wide obvious metre scale elevation above the surrounding sediments are from the luning allochthon and grew on an inner to middle ramp or in a deep lagoon the mina patch reefs were constructed by several different coral ecomorphotypes platy tabular domal massive and branching corals interpreted to have had zooxanthellate symbionts and record subtle coral zonation within the reefs based on modern coral ecomorphotypes platy to tabular corals at mina grew in the lower euphotic zone stressed by low light conditions and the massive or domal corals inhabited shallower water possibly above fair weather wave base and were stressed by wave energy unlike most other late triassic reef ecosystems where phaceloid branching corals or calcareous sponges constitute the principal bioconstructors the platy to tabular corals were the primary builders in the mina patch reefs the mina reefs are also unique because cryptic and cavernous internal environments epibionts cryptobionts and thick microbial crusts are rare or absent the combination of platy coral dominance with the lack of epibionts cryptobionts microbial crusts suggests that the norian reefs from mina nevada represent a unique form of scleractinian reef construction from the late triassic

the influence of sponge borings on aragonite to calcite inversion in late pleistocene strombus gigas from grand cayman british west indies abstract large robust strombus gigas lived in a variety of habitats in the ironshore lagoon that existed on grand cayman during the late sangamon highstand approximately 125 000 years ago some well preserved shells are still entirely aragonitic whereas others have been transformed completely to calcite permeability of the host rock and sponge boring intensity were the most important controls on the extent of aragonite to calcite inversion sponge borings played a critical role in the inversion process because they provided conduits through which the reactive diagenetic fluids could penetrate the dense gastropod skeleton each boring acted as a nucleus from which inversion fronts could spread into the shell as a result the radial fabric of the neomorphic calcite crystals around th sponge borings contrasts sharply with the mosaic of equant calcite that formed in areas devoid of sponge borings it seems that bioerosion is at least on a local scale as important as other factors in controlling the meteoric alteration of carbonate sediment the 18o values of neomorphic calcite 7 1 to 4 9 approximately 3 more depleted in 18o than the original aragonite confirm the role of meteoric water in the aragonite to calcite transformation 13c values of the diagenetic calcite 0 2 to 4 5 are similar to those in the original aragonite suggesting that the former was inherited from the latter

upper jurassic reefs of smackover formation united states gulf coast the occurrence of reefs in the smackover formation an upper jurassic oxfordian sequence that has been recognized in the subsurface of the united states gulf coast requires a revision of existing depositional models that have been based exclusively on subsurface data gathered from nonskeletal carbonate reservoirs these reefal buildups are 10 to 130 ft 3 to 40 m thick commonly elongate and several square kilometers in plan they developed seaward of oolite shoals on paleostructures of three types that created subtle topographic highs on an otherwise ramplike sea floor 1 basement ridges 2 faulted basement highs and 3 upthrown salt cored fault blocks reef rubble zones have reservoir quality porosity throughout the smackover trend but reef framework is a ta get only where diagenesis has been favorable although only a few reefs have produced commercial hydrocarbons attractive porosities and permeabilities mean phgr of 15 mean k of 20 md result from freshwater leaching dolomitization or fracturing the biota forming smackover reefs is similar to that described for sponge and algal buildups and patch reefs from the late jurassic of europe reef framework is constructed by digitate and branching stromatolitic blue green algae tubiphytes sp and marine cements the biota varies through the smackover trend reefs in southern arkansas and northern louisiana are more diverse in these reefs encrusters and binders produce constructional microframework cavities on and between corals primarily actinastrea skeletal algae parachaetetes sp and cayeuxia sp lithistid and hexactinellid sponges bryozoans and hydrozoans the cavities are commonly filled with marine cements and geopetal sediments a vertical biotic zonation in cores of the reef interval suggests that the reef commu ity of organisms evolved through time the reefs are commonly underlain and overlain by subtidal peloidal lime packstones containing oncolites and scattered fossils and they can develop in close proximity to subtidal quartz sands

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

oxfordian upper jurassic coral reefs in western europe reef types and conceptual depositional model comparative sedimentology and palaeoecology of oxfordian upper jurassic coral dominated reefs of england france italy and switzerland has been used to 1 identify and characterize different types of late jurassic coral reefs with regard to their litho and biofacies and 2 develop a depositional model for these reefs relating different reef types to each other within a palaeoenvironmental framework eight generic reef types and one associated reef facies are recognized these are i biostromal units dominated by platy microsolenids developed within clean limestone facies ii biostromal units dominated by platy microsolenids developed within marly facies iii reefal thickets dominated by tall dense phaceloid colonies developed within pure carbonate muds iv microbial coral reefs dominated by massive branching ramose and phaceloid colonies v large high diversity reefal units associated with large volumes of bioclastic material vi small species poor reefs developed within mixed carbonate siliciclastic facies vii microbial coral reefs dominated by massive colonies viii reefal thickets dominated by branching ramose colonies with widely spaced branches developed amongst sand shoals and coral debris channels and ix conglomerates rich in rounded coral fragments the reef associated facies the development of these different constructional and compositional reef types is interpreted as being primarily a function of light intensity hydrodynamic energy levels and sediment balance a conceptual depositional model based on these parameters can be used to predict the spatial and temporal distribution of different reefal carbonates and highlight sedimentological and palaeoecological trends in reef development

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

palaeoenvironmental significance of carbon and oxygen isotope stratigraphy of marine triassic jurassic boundary sections in sw britain abstract carbon isotope stratigraphy is a useful tool for stratigraphic correlation especially for strata deposited during major perturbations of the carbon cycle that affected the marine terrestrial and atmospheric reservoirs for the triassic jurassic boundary effectively defined by a first order mass extinction major fluctuations in carbon isotope values have been well documented but these datasets have generally been derived from bulk rock samples hence the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained here carbon and oxygen isotope data are presented from well preserved oyster shells liostrea comprising low magnesium calcite a mineral species relatively resistant to diagenetic alteration samples were obtained from lavernock point glamorgan wales a coastal section close to a candidate stratotype for the base of the jurassic at st audrie9s bay somerset england the carbon isotope signature from st audrie9s bay previously defined on the basis of analysis of bulk organic matter is confirmed by our new data major features are 1 the upper part of an initial9 negative isotope excursion in the lowest part of the section followed by 2 a pronounced positive excursion and 3 an extended main9 negative isotope excursion in the highest part of the section the data confirm that the carbon isotope stratigraphy previously documented from bulk organic matter in sw england records the chemical composition of the contemporaneous seawater bulk carbonates sampled over the same interval near lyme regis england show similar trends to those from oyster calcite in the lower part of the study section but there are more 13 c depleted values up section these lower values probably result from an admixture of primary and diagenetic carbonate palaeotemperatures calculated from oxygen isotope values from lavernock point oyster shells are relatively cool at the beginning of the positive carbon isotope excursion and increased by up to 10 c during the main negative carbon isotope excursion the new results are compatible with the view that positive carbon isotope excursions correspond to times of low atmospheric carbon dioxide content whereas negative carbon isotope excursions correspond to times of high atmospheric carbon dioxide content as is also found to be the case during the early jurassic toarcian oceanic anoxic event the mg ca and sr ca ratios and 18 o of investigated liostrea hisingeri show no correlation supporting data from modern bivalves that indicate that incorporation of mg and sr is controlled mainly by factors other than temperature

investigating complex isochron data using mixture models the isochron technique for dating geological events is widely used in many fields of isotope geochemistry however data sets can be complex and many samples may not behave as closed systems resulting in excess scatter around a regression line in certain data sets however excess scatter may result when geological samples are partially reset or when samples are comprised of multiple components recording different geological processes separated in time and or initial isotope composition here we introduce a new approach for investigating evidence of such multicomponent mixtures within isochron space we provide a mathematical framework to resolve the number of mixture components without requiring any prior knowledge of this number crucially the model reports the proportion of each individual sample that belongs to each mixture component allowing the user to return to the samples and independently test model outputs with other techniques it is important to distinguish accurate and meaningful ages and initial daughter isotope compositions from the meaningless values that are caused by mismatch between geological processes and the models that we use to describe them first we demonstrate our new model on a synthetic data set to show that it can successfully separate distinct isochrons in a complex mixture we further validate our approach with a previously published data set using the 187re 187os system in bitumen and 147sm 144nd system in magmatic rocks we identify discrete components in these data sets and using complementary geological observations discuss the implications of treating these scattered data as recording multiple geological processes

carbonate hosted zinc lead deposits in the lower cambrian of hunan south china a radiogenic pb sr isotope study zinc lead deposits hosted by lower cambrian carbonate rocks near huayuan in the hunan guizhou orogenic belt southern china have been studied by means of pb and sr isotopes the deposits are characterized by two mineralization stages 1 a main economic stage comprising cockade style sphalerite galena pyrite marcasite fluorite barite and calcite and 2 a subsequent noneconomic stage with nodular rosette sphalerite saddle dolomite and bitumen both ore stages are postdated by a generation of late calcite main stage sulfides 206pb 204pb 18 162 18 225 display a steep linear trend on conventional pb pb diagrams which indicates binary mixing of lead components bearing the imprint of ancient 207pb dominated crustal rocks and reservoirs with elevated th u ratios possibly located in the lower crust nodular rosette sphalerites fall outside this line but reflect a second mixing trend between mineralizing fluids characterized by 206pb 204pb 18 3 and lead isotopically similar to specific main stage cockade sphalerites suggesting either remobilization of pb from main stage ores or contemporaneous mixing of three distinct lead components in the course of an evolving hydrothermal event the 87sr 86sr ratios of diagenetic and hydrothermal carbonate cements and barites range from 0 70905 to 0 71006 and increase systematically with the paragenetic sequence indicating progressive mixing of marine sr derived from the lower cambrian carbonate host rocks with radiogenic sr supplied by external mineralizing fluids in order to identify possible local metal sources u pb and rb sr analyses were performed on six whole rock samples from the lower cambrian sequence and their time integrated pb and sr isotope evolution was compared to the isotopic signature of the mineralization whereas shales and black shales of the cambrian balang and niutitang formations underlying the ore bearing qingxudong carbonate unit appear to be possible external sources for the radiogenic sr found in hydrothermal carbonates the u pb data do not permit these shales to be considered as primary source rocks for the ore lead both the pb and the sr isotopes indicate mineralizing fluids that had interacted with various external metal sources some of them most probably being located in sedimentary or crystalline basement rocks this refutes prevailing genetic models favoring the hydrocarbon and metal rich lower cambrian niutitang black shales as the most likely source reservoir for the zn and pb in the deposits of the huayuan district the pb and sr isotope mixing trends observed for the ore and gangue preciptates reflect small scale heterogeneous fluid systems that were not capable of producing large deposits this may indicate that the huayuan district is not a favorable target for future exploration of economic ore deposits it also limits the prospects of successful radiometric dating of the mineralization since conventional geochronologic models require initial isotopic homogeneity

carbonate production by rudist bivalves the record of late barremian requieniid communities from provence se france abstract rudist bearing sediments from platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france were investigated on a 46 km wide transect after seven stratigraphic sections to quantify the role of rudists in the corresponding stratigraphic system by using various proxies the regional stratigraphic contribution of total thickness of rudist beds is relatively high 43 1 each rudist community type possesses a specific skeletal contribution of skeletal content in the range of 19 2 to 31 5 at a stratigraphic scale including rudist rich and rudist free beds the skeletal contribution drops to 13 8 this value is derived from the standard skeletal contribution obtained for each community type combined with the stratigraphic contribution of rudist beds in vertical successions and horizontal stratigraphic units a closely related value 12 8 is obtained from calculations using specific lateral dimensions of rudist bodies and their spacing i e modules depending on community types each community has a particular potential quantitative contribution to the overall regional stratigraphic system rudist production is deduced from the cyclostratigraphic approach of accumulation rates for each community type estimates of caco 3 net production are in the range of 19 to 50 kg m 2 ka 1 these values are very low when compared with those obtained at a biological scale for modern bivalves late cretaceous rudists and recent coral reefs the geological scale used for our estimates may partly account for this difference whereas low accommodation rates linked to cretaceous greenhouse conditions appear a potential important factor in this respect the low net production of requieniid dominated communities sediment dwellers not framework builders also reflects their limited sedimentogenetic power

a method to assess fluvial fan channel networks with a preliminary application to fans in coastal british columbia abstract the channel network on a fluvial fan distributes sediment across the fan surface and determines fan development we present a method to characterize fan channel networks fcns so that the effect of controls e g sediment supply on the fcn can be evaluated we then do a preliminary test of the method using three fans in coastal british columbia the method uses a set of three measures 1 the spatial extent of hydrogeomorphic activity measured as the percentage of the contemporary fan surface area occupied by active channels 2 the topologic structure using node counts to measure channel network complexity and 3 a sediment budget to indicate the proportion of sediment that is stored on the fan loosely characterized by comparing the second largest clast size of sediment at the fan apex or intersection point with the second largest clast at the toe of the fan these measures were applied to two fan deltas and one partial fan delta in northern vancouver island british columbia using channel surveys conducted in 2006 and 2007 all three fans are located within 30 km of each other have similar climatic physiographic and vegetation settings and have natural channel networks each fan has perennial channel flow at the fan apex watershed areas range from 19 5 to 35 6 km2 and contemporary fan areas range from 0 2 to 0 7 km2 the melton relative relief ratio ranges from 0 24 to 0 30 and none of the fans show evidence of debris floods or debris flows in addition to testing the efficacy of the fcn measures we use these fans to explore the question of whether fans in similar geomorphic settings and with similar controls develop similar fcns results show the fans have between 4 7 8 5 of the contemporary fan surface occupied by the active channel network topologic node counts indicate that the two fan deltas have a similar level of channel complexity with 42 54 nodes in total the partial fan delta channel network is approximately half as complex with 23 nodes in total all three fans have boulder sized sediment 30 50 cm at the fan apex on the two fan deltas the largest sediment at the toe of the fan is 10 12 cm indicating that much of the sediment delivered to the fan apex is stored on the fan in contrast the partial fan delta has 18 20 cm sized sediment transported into the axial valley river at the toe of the fan and a wider and steeper outlet channel indicating that a greater proportion of sediment is exported from the fan although the axial river does not visibly incise into the fan deposits the lower channel complexity and coarser sediment output indicates that the axial river truncates the toe of the partial fan delta the two fan deltas have similar fcns supporting the idea that fans in similar geomorphic settings develop similar fcns the partial fan delta is in a different geomorphic setting that was not identified prior to analysis of the fcns and has a different fcn this study also examines the effects of a large regional storm event that occurred between the 2006 and 2007 surveys one fan had increased active area two fans had increased total node counts and two fans increased output clast size after the flood event indicating the measures are sensitive and respond to disturbance further investigations of fcns may have utility in hazard assessments addressing how fans respond to changes in sediment supply or discharge regime how vegetation type affects fcns or the effect of other watershed processes or fan attributes

floral changes across the triassic jurassic boundary linked to flood basalt volcanism one of the five largest mass extinctions of the past 600 million years occurred at the boundary of the triassic and jurassic periods 201 6 million years ago the loss of marine biodiversity at the time has been linked to extreme greenhouse warming triggered by the release of carbon dioxide from flood basalt volcanism in the central atlantic ocean in contrast the biotic turnover in terrestrial ecosystems is not well understood and cannot be readily reconciled with the effects of massive volcanism here we present pollen spore and geochemical analyses across the triassic jurassic boundary from three drill cores from germany and sweden we show that gymnosperm forests in northwest europe were transiently replaced by fern and fern associated vegetation a pioneer assemblage commonly found in disturbed ecosystems the triassic jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons which in the absence of charcoal peaks we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava we conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone instead we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction

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

evidence for the episodic turn on and turn off of turbid zone coral reefs during the late holocene sea level highstand terrigenous sediment accumulation within nearshore marine environments is regarded as a major factor inhibiting carbonate production and coral reef accretion while recent ecological and geological research into reef development under long term terrigenous sediment influence questions the overly simplistic nature of such views understanding of the time scales of reef initiation and growth and the morphodynamics of reef accretion in these settings remains limited here we present evidence to support recent suggestions that once established rapid reef accretion and progradation is possible but that the restricted accommodation windows in which such reefs develop often result in short lived ephemeral phases of reef building specifically we describe two discrete periods of reef growth within one small 600 m wide coastal embayment around a high island on the terrigenous sediment dominated inner shelf of the central great barrier reef australia these reef building phases occurred at either end of the holocene sea level highstand the first during the late postglacial marine transgression and early highstand 6900 4500 calibrated cal yr b p the second following the late holocene regression and stillstand 1600 cal yr b p to present an 3000 yr hiatus occurred between these events probably as a function of subtle changes in sea level and associated shoreline morphodynamics

reef expansion during the triassic spread of photosymbiosis balancing climatic cooling the paleoreefs database indicates that reef abundance increased profoundly during the triassic period from a pronounced low in the early triassic to a major peak in the norian this expansion is also evident when standardizing for sampling corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders whereas the contribution of hypercalcifying sponges and microbes decreased during the triassic the numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis such that the norian reef boom might be explained by the spread of photosymbiosis in corals the geographical expansion of reefs was far less pronounced especially concerning palaeolatitude late triassic reef growth was limited to more or less the same latitudinal range as modern reefs as oxygen isotope data and new modeling results indicate declining temperatures and co2 concentrations during the late triassic the lack of latitudinal expansion might be attributed to global cooling reef development during the triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling

platy corals from the middle triassic of upper silesia poland implications for photosymbiosis in the first scleractinians abstract coral patch reefs from middle triassic upper pelsonian lower illyrian strata in the upper silesia region of southern poland germanic domain of the peri tethys are rare examples of the first scleractinian buildups the shallowing upward succession in the tarnow opolski quarry records a transition from sponge to coral patch reefs interbedded with bioclastic limestones coral pillarstones built by thin branching volzeia szulci are succeeded by platy pamiroseris silesiaca constructing two platestone layers each up to 50 cm thick serial sections through platestones revealed flat to undulose growth form of p silesiaca the maximum observable dimension of the coral plates is 24 cm wide typically up to 12 cm while thickness of most plates is 1 1 5 cm coral plates are interlayered with crinoidal wacke to packstone and microbialites which are locally important component of the platestone platy corals grew in a shallow turbid water environment with changing but dominantly moderate hydrodynamics net sedimentation was low as indicated by the epibionts encrusted to the undersides of the coral plates and locally common microbial fabrics growth interruptions of p silesiaca record events of storm induced sediment input and resuspension of carbonate mud based on the euphotic floor model the flattened morphology of p silesiaca is interpreted as an optimal growth form in a turbid low light environment platy scleractinian assemblages from silesia are the oldest occurrences of this ecological coral group mostly representing deeper mesophotic habitats and support the hypothesis that some of the earliest scleractinians had photosymbionts like modern zooxanthellae

late jurassic coral microbial reefs from the northern paris basin facies palaeoecology and palaeobiogeography abstract during the late middle oxfordian patch reefs grew on the northern margin of the paris basin according to the facies analysis of the reef and inter reef sediments the environment was a warm clear and agitated sea with highly episodic sedimentation the bioherms were a short lived phenomenon during the third phase of regional reefal development sequence stratigraphically they are associated with a highstand system tract volumetrically and trophically dominant organisms were microbes now represented by massive clotted leiolite stalactitic hemispheroids with purely thrombolitic texture are restricted to open caves corals were of structural reef building importance due to their rapid upward growth the patch reefs are characterised by thickets of ramose corals which developed a very open framework in the vicinity of these patch reefs though in hydrodynamically higher energy environments grew thickets of more stoutly branched corals however they are rarely preserved in situ and are generally represented as abundant coral rubble the reef taxa are characterised by the notable absence of several groups e g oysters serpulids bryozoans pectinids occurring at other localities where reefs of similar age developed in similar environmental conditions the reefs also have strikingly modern aspects to them in particular the presence of cryptic elements within caves and a sponge dominated borer association dwellers belong to various life form types although encrusting taxa are exceedingly rare this may be explained by the presence of soft microbial films on most surfaces the palaeoecological analysis suggests that the major controls on faunal composition and high diversity were elevated nutrient levels highly episodic sedimentation and probably seasonal environmental disturbances structural and functional aspects of the reef community grazers trigger framebuilders borers trigger binders binders hamper borers allow ecological comparisons to be made with contemporaneous as well as recent reefs the unique combination of ecological factors resulted in a specialised previously undescribed community which differs from both tethyan and northern localities in various aspects these include cavities with cryptofauna prominence of grazing gastropods and high faunal diversity in a microbially dominated build up

reefs are not so different they follow the evolutionary pattern of level bottom communities there is a pervasive attitude that reels were isolated from the mainstream of evolution and that their history had quite a different pattern from the level bottom marine biota however three striking similarities exist between the evolution of reefs and other marine communities 1 reef composition and ecologic structure were governed by the composition of the three phanerozoic evolutionary faunas 2 reefs were decimated by the major extinction events of the geologic record 3 reefs conform to the pattern of level bottom community evolution intervals when reefs were absent were due either to the absence of appropriate frame building organisms in the biota for example in the middle and late cambrian or to the absence of reefs following extinction events before frame building organisms re evolved a reef building mode of life

disentangling the hettangian carbon isotope record implications for the aftermath of the end triassic mass extinction 1 this study provides an organic carbon stable isotope 13corg record calibrated with detailed ammonite biostratigraphy following the end triassic biological crisis precise correlation between this crucial fossil group and the 13corg record is key to understanding feedbacks between biological and environmental events following mass extinction the latest triassic and hettangian 13corg record shows several negative and positive excursions the end triassic negative shift coinciding with the mass extinction interval is followed by a positive excursion in the earliest hettangian psiloceras spelae beds which marks the onset of recovery in the marine ecosystem this positive trend is interrupted by a second negative 13corg excursion in the p pacificum beds related to a minor ammonite extinction event this pattern of the 13corg curve culminates in the uppermost hettangian angulata zone major positive excursion this indicates that both the ecosystem and the carbon cycle remained in a state of perturbation for at least 2 ma although the recovery of some pelagic taxa already began at the base of jurassic the early and late hettangian positive 13corg excursions have been confused in several recent papers here we show that during the hettangian there are indeed two distinct positive 13corg excursions phases of anoxia and further pulses of central atlantic magmatic province volcanism during the hettangian might have inhibited the full recovery for that interval of time the main liasicus angulata organic positive cie carbon isotope excursion during the late hettangian might be related to gradual decreasing of pco2 due to protracted high organic burial and coincides with a second phase of recovery as indicated by a pulse of ammonoid diversification

mid holocene coral community data as baselines for understanding contemporary reef ecological states land use changes and associated deteriorations in water quality are cited as major drivers of marine ecosystem change and can modify community abundance and diversity on coral reefs this study uses palaeoecological data derived from a mid holocene age coral reef in the wet tropics region of australia s great barrier reef to develop a record of coral community composition and diversity from a period that significantly pre dates european settlement in the region major changes in catchment sediment and nutrient yields since european settlement have been documented and thus the data presented provides a baseline against which to compare contemporary ecological datasets natural variations in coral assemblage composition as preserved in core records clearly occurred in this mid holocene reef and were associated with the reef shallowing to sea level as it accreted vertically comparisons between modern and mid holocene coral community data from equivalent water depths did not reveal marked shifts in coral community composition and diversity suggesting the long term persistence of a resilient coral assemblage over these time periods

extinction trajectories of benthic organisms across the triassic jurassic boundary abstract we analysed diversity and abundance patterns of benthic organisms across the triassic jurassic t j boundary based on the paleobiology database pbdb which compiles palaeontological collection data on a global scale while sepkoski s sepkoski j j jr 2002 a compendium of fossil marine animal genera bulletins of american paleontology 363 1 563 compendium on the stratigraphic ranges of marine animal genera suggests that the dominant macrobenthic groups of the late triassic experienced significant extinctions prior to the t j boundary a significant end triassic extinction peak is evident from pbdb s data this rhaetian extinction peak is found in both an analysis of the raw data of stratigraphic ranges and a sample standardized analysis of occurrence data 41 of all mesobenthic and macrobenthic genera crossing the norian rhaetian boundary became extinct within the rhaetian although this rate suffices to characterize the end triassic extinction as a true mass extinction against a middle triassic to middle jurassic background significantly reduced rhaetian origination rates add to the strong diversity depletion in the earliest jurassic as for other mass extinctions evidence for selective extinction is meagre when the analysis is limited to the boundary interval alone and when focused on taxonomic and ecological characteristics of individual genera when taxa are separated by environmental preferences however several determinants of extinction risk become evident suggesting that reef dwellers had a significantly higher extinction risk than level bottom dwellers taxa with an inshore preference were more strongly affected than offshore taxa taxa preferring carbonate substrates were more strongly hit than taxa preferring siliciclastic substrates and taxa preferentially inhabiting low latitudes had higher extinction rates than taxa more common at intermediate and high latitudes much of this selectivity is not independent and also seen in the intervals of background extinctions suggesting that the end triassic mass extinction represents an intensification of background extinctions but not a qualitatively different macroevolutionary regime one possible exception is related to preferences for depositional environments suggesting a selective rhaetian extinction in reefs and inshore settings

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

the mississippi valley type fluorite ore at jebel stah zaghouan district north eastern tunisia contribution of ree and sr isotope geochemistries to the genetic model abstract the fluorite district of zaghouan north eastern tunisia is characterized by f ba pb zn ore deposits mineralization occurs within stratabound to stratiform bodies either within jurassic back reef limestone uplifted blocks or along unconformity surfaces that separate them from the overlying sequence fluorite mineralization also occurs within fractures crosscutting the uplifted limestone blocks and their overburden despite the similarity of the liassic series throughout the major part of the district stratabound fluorite deposits formed subsequent to a strong epigenetic dolomitization souissi et al 1998 and occurring along the lower middle liassic unconformity are known only at jebel stah and at the adjacent jebel kohol four petrographic types of fluorite are recognized the finely laminated karst deposits fl1a the macrogranular fluorite fl1b resulting from the recrystallization of fl1a and the megacrystalline fluorite fl2 associated to calcite in lodes and fluorite in geodes fl3 this study gives new arguments in terms of the genetic model of the fluorite ore of jebel stah and by using trace metal elements mte rare earth elements ree and sr isotope geochemistry the mte geochemistry shows that the epigenetic dolomites and the fluorite fl1a bear higher concentrations in mn and zn with respect to the fluorites fl1b fl2 and fl3 while the latter are depleted in all mte but enriched in co the similarity of their ree patterns indicates that the latter are coeval and that fl1a fluorite may be considered as the early ore generation the same argument confirms that this geochemical imprint has been inherited from a hydrothermal fluid that had remained in equilibrium with shales at depth fluorite deposition appears related to an oxidized fluid derived from a sedimentary basin fluid circulation may have been triggered in response to hydraulic fracturing within a high geothermal gradient setting especially along the major structural trends fl1b fl2 and fl3 fluorites have been generated from the residual fraction of the ore fluid at later stages of mineralization and in a closed system both mineralization and the epigenetic dolomites are characterized by sr isotope ratios that are higher than the barren lower middle liassic rocks indicating that the sr cannot be derived from the wallrocks however these ratios are higher than the triassic seawater yet consistent with those of the paleozoic period thus the fluorite ore of jebel stah is believed to be remobilized from primary ore deposits which are suspected to be hosted in the late series within this period

a coral reef in the telkwa range british columbia the earliest jurassic example an end triassic mass extinction profoundly affected reef ecosystems that flourished in the late triassic tethys seaway the collapse of late triassic coral sponge reefs was followed by an early jurassic hettangian sinemurian perturbation interval with a near global absence of reefs and sharp reductions in diversity a jurassic sinemurian reef in the hazelton group of central british columbia appears to fill the gap its paleoecology and composition show it to be the first large framework example in north america and perhaps the world it demonstrates that the reef building triassic coral phacelostylophyllum survived the extinction event and was constructing reefs in early jurassic time during a global reef eclipse the reef is a 48 m thick bioherm that grew within the island arc complex of stikinia following a decrease in volcanism reef building began with bivalves growing upon water lain tuffs the reef was dominated by large dendroid phaceloid corals primarily phacelostylophyllum rugosum a spe

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

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

evaluation of bitumen as a 187re 187os geochronometer for hydrocarbon maturation and migration a test case from the polaris mvt deposit canada abstract re os analyses of bitumen from the polaris mississippi valley type zn pb deposit demonstrate the potential utility of the re os system for establishing the absolute timing of hydrocarbon migration and generation the polaris deposit is hosted by carbonate rocks of the upper ordovician thumb mountain formation and sulphide mineralization during late devonian time is constrained by a rb sr sphalerite date of 366 15 ma and a paleomagnetic date bitumen occurs in open space fillings and coatings and is interpreted to have formed during the main and late stages of sulphide mineralization samples of bitumen were taken from a variety of locations from the main deposit at polaris re and os contents are 3 78 ppb and 55 1155 ppt respectively the 187re 188os ratios are very high ranging from 300 to 1800 and the os isotopic composition is moderately to highly radiogenic with 187os 188os ratios ranging from 3 3 to 13 7 calculated 187os 188os ratios at 366 ma are variable but an obvious grouping is defined by 11 of 16 analyses on a re os isochron diagram and these data yield a re os date of 374 9 ma mswd 12 model 3 in agreement with rb sr sphalerite and paleomagnetic dates for mineralization at polaris the combined dates suggest that the migration of fluids responsible for both pb zn mineralization and bitumen formation at polaris was broadly contemporaneous and was coeval with the late devonian ellesmerian orogeny though considerable further research is required to understand the re os isotopic systematics of migrated hydrocarbon systems bitumen re os geochronology may provide the possibility of establishing a more comprehensive understanding of mvt deposits sedimentary basin and petroleum systems

the end permian mass extinction and its aftermath on an equatorial carbonate platform insights from ichnology terra nova 22 195 202 2010 abstract a semi quantitative analysis of the endobenthic activity across the permo triassic boundary ptb was carried out on a 445 m thick well core interval from the persian gulf by logging the degree of bioturbation trace fossil distribution and ichnodiversity id this analysis enables for the first time the evaluation of recovery of endobenthic organisms after the end permian mass extinction by direct comparison of post extinction lower triassic with pre extinction upper permian units the results indicate that the studied shallow marine carbonate platform within an equatorial setting acted as oxygenated refugee for the biotic recovery traces of suspension and deposit feeders reappear simultaneously shortly after the extinction event but are reduced in size macroborings so far unknown from the lower triassic occur where suitable firm or hard substrate was available recovery took place in two phases early induan 50 pre extinction id and 20 30 bioturbation and late induan 75 id and almost 90 bioturbation re established

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

fluid inclusion and carbon oxygen and strontium isotope study of the polaris mississippi valley type zn pb deposit canadian arctic archipelago implications for ore genesis the polaris deposit is one of the largest mississippi valley type deposits in the world with 22 million tonnes of ore at 14 zn and 4 pb contained in a single compact orebody surrounded by dolomitized host rocks using detailed sampling of carbonates in the orebody and the dolostone halo this paper aims to characterize the temporal and spatial evolution of the mineralizing system and to understand the mechanisms that controlled the accumulation of this large compact zn pb deposit five types of dolomite have been distinguished including three replacement rd and two pore filling dolomites pd the paragenetic order is rd1 rd2 rd3 pd1 and pd2 pore filling calcite pc postdates all other minerals in most cases sulfides and dolomite did not co precipitate but sphalerite and galena largely overlap with rd3 and pd1 various dolomites are dissolved or replaced by sulfide precipitating fluids sulfides in turn can be overgrown by dolomites colloform texture in sphalerite is widespread fluid inclusions were studied in rd3 pd1 pd2 sphalerite and pc the overall ranges of homogenization temperatures t h and last ice melting temperatures t m ice for fluid inclusions in dolomites and sphalerite are from 67 to 141 c and from 46 7 to 27 0 c respectively consistent with warm basinal brines with high salinities and ca na ratios gas chromatographic analysis of these fluid inclusions indicates low concentrations of hydrocarbons 0 06 mol c o and sr isotopes were analyzed for all dolomites and pc as well as for the fine grained host limestone and early diagenetic calcite sc rc the isotopic values of rd2 rd3 pd1 and pd2 cluster tightly and form largely overlapping domains with respect to the host limestone they are depleted in 18o similar in 13c and slightly enriched in 87sr there are no regular spatial variations for fluid inclusion and isotope data indicating an overall geochemical homogeneity in the hydrothermal system however certain samples close to the fracture zones in the orebody with slightly elevated t h and 87sr 86sr values and depleted 18o values suggest that the fracture zone was the conduit for the hot brines based on the geological and geochemical characteristics of the deposit we propose that sulfide precipitation at polaris was caused by mixing of a reduced metal rich sulfur poor fluid with a reduced metal poor sulfur rich fluid at the site of mineralization the metal carrying fluid ascended along fractures from below the deposit and was hotter than the host rocks whereas the reduced sulfur carrying fluid was delivered to the site of mineralization laterally and was in thermal equilibrium with the host rocks this model can readily explain the dissolution of dolomite during sulfide precipitation and the abundance of colloform sphalerite as well as the low concentrations of hydrocarbons in fluid inclusions

importance of wave induced bed liquefaction in the fine sediment budget of cleveland bay great barrier reef data from a three year long field study of fine sediment dynamics in cleveland bay show that wave induced liquefaction of the fine sediment bed on the seafloor in shallow water was the main process causing bed erosion under small waves during tradewinds and that shear induced erosion prevailed during cyclonic conditions these data were used to verify a model of fine sediment dynamics that calculates sediment resuspension by both excess shear stress and wave induced liquefaction of the bed for present land use conditions the amount of riverine sediments settling on the bay may exceed by 50 75 the amount of sediment exported from the bay sediment is thus accumulating in the bay on an annual basis which in turn may degrade the fringing coral reefs for those years when a tropical cyclone impacted the bay there may be a net sediment outflow from the bay during the dry tradewind season fine sediment was progressively winnowed out of the shallow reefal waters

the hydrodynamic and sedimentary setting of nearshore coral reefs central great barrier reef shelf australia paluma shoals a case study the great barrier reef gbr shelf contains a range of coral reefs on the highly turbid shallow inner shelf where interaction occurs with terrigenous sediments the modern hydrodynamic and sedimentation regimes at paluma shoals a shore attached turbid zone coral reef and at phillips reef a fringing reef located 20 km offshore have been studied to document the mechanisms controlling turbidity at each reef waves currents and near bed turbidity were measured for a period of 1 month bed sediments were sampled at 135 sites on the inner shelf muddy sands are widespread with admixed terrigenous and carbonate gravel components close to the reefs and islands except on their relatively sheltered sw side where sandy silty clays occur at paluma shoals the coral assemblage is characteristic of inner shelf or sheltered habitats on the gbr shelf dominated by galaxea fascicularis up to 50 coral cover and is broadly similar to that at phillips reef further offshore and in deeper water the sediments of the paluma shoals reef flats consist of mixed terrigenous and calcareous gravels and sands with intermixed silts and clays whereas the reef slope is dominated by gravelly quartz sands the main turbidity generating process is wave driven resuspension and turbidity ranges up to 175 nephelometric turbidity units ntu in contrast at phillips reef turbidity is 40 ntu probably occurs for a total of 40 days each year and relatively little time is spent at intermediate turbidities 15 50 ntu the extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning autotrophy and heterotrophy in response to different levels of turbidity sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux btf of sediment to the sea floor i e 10 000 btf over three orders of magnitude greater than the holocene average for halifax bay of 3 btf as elsewhere along the nearshore zone of the central gbr dry season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments the location of modern nearshore coral reefs is controlled by the presence of suitable substrates which in halifax bay are pleistocene and early holocene coarse grained and relatively stable alluvial deposits

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

structure and development of detrital reef deposits in turbid nearshore environments inhaca island mozambique coral communities are intermittently developed along the seaward margins of wide up to 500 m intertidal flats that fringe the western margins of inhaca island southern mozambique the coral communities occur in an environment that can be considered as marginal for coral growth in the sense that they are subject to high turbidity levels which results in rapid light attenuation and to the effects of periodic smothering and burial associated with a mobile siliciclastic dominated sediment substrate these constraints limit coral community development both spatially and bathymetrically in addition historical evidence suggests that the main sites of coral growth shift over decadal timescales due to periodic sediment remobilisation such rapid rates of turnover restrict the development of rigid framework deposits and in contrast the main depositional product of coral growth is an abundance of branched mainly acropora sp coral rubble rubble production is aided both by intense internal bioerosion sponge bivalve and worm traces and by periodic storm damage much of this rubble accumulates along the channel margins and provides a substrate for subsequent coral recruitment the deposits can be distinguished from those associated with clear water reef environments by 1 the lack of a rigid reef framework either comprising of in situ coral or encrusted coral rubble 2 the distinct lack of rubble encrustation syn depositional cementation and 3 the predominance of a siliciclastic rich sediment matrix the deposits indicate however a long term history of coral community occurrence in sites dominated by siliciclastic sedimentation cores recovered from a transect across the tidal flats identify a coral rubble floatstone facies extensively developed along the western margins of the island it comprises mainly branched coral rubble often heavily bioeroded but sparsely encrusted along with spheroidal rhodoliths and molluscan fragments set within a poorly sorted mixed siliciclastic carbonate sediment matrix 14c dating indicates that most of the rubble deposits date from the period 6500 4700 years bp which corresponds to a period of regional sea level highstand a detailed growth chronology cannot be established due to the lack of in situ coral but rapid rubble deposition and reef flat progradation around 350 m can be inferred for this period equivalent to an average progradation rate of around 0 2 m year 1 over the subsequent 4700 years progradation of only around 25 m has occurred this may be attributed to reworking and erosion of the seaward margin of the deposits during periods of fluctuating sea level between 4700 and 900 years bp or to a lack of seaward accommodation space

bioerosion traces in the great barrier reef over the past 10 to 30 kyr abstract bioerosion traces preserved in coral reef framework provide insight into past environmental conditions and reef health however few studies have explored the relationship between bioerosion reef growth history and environmental changes the international ocean drilling program iodp expedition 325 sampled late glacial to deglacial reef sequences that developed from 30 to 10 ka on the shelf edge adjacent to the modern great barrier reef gbr this study quantifies spatiotemporal patterns of macrobioerosion intensity macrobioerosion intensity referred to as bi of trace ichnogenera entobia sponges gastrochaenolites bivalves and maeandropolydora trypanites worms based on detailed observations of 13 drill holes from two cross shelf transects in two regions hydrographers passage in the southern central gbr and noggin pass in the north our high resolution stratigraphic and temporal records of bioerosion activity are defined and compared to published multi proxy paleoenvironmental interpretations from the exp 325 cores coralgal assemblages geochronology and lithology are used to understand the controls on the multi scale spatiotemporal patterns of bioerosion across and along the gbr shelf and within individual holes noggin pass is characterized by significantly higher bioerosion activity than hydrographers at each transect changes in bioerosion intensity are observed to be coeval with some major reef sequence boundaries however due to the unconsolidated nature and limited recovery many boundaries have inconclusive trends statistical analysis is used to interpret the relationship of bioerosion intensity to various factors including paleo water depth lithology coral and algal assemblages transect location geomorphic feature vertical accretion and reef sequences terrigenous sediment flushing depositional regime and a pronounced latitudinal gradient in sea surface temperature are likely to have contributed to the significant regional differences in bioerosion intensity between northern and southern transects and also during reef demise bioerosion at both transects is highest in the proto barrier reef 4 sites when compared to all fringing terrace reefs reef 3a 3b and 4 higher bioerosion tends to occur when vertical accretion is at its extremes its lowest and highest limits the enhanced bioerosion alongside lowest reef accretion in a sea level rise scenario reef 3a 3b and 4 might have contributed to reef degradation prior to its demise

siliciclastic and volcaniclastic influences on equatorial carbonates insights from the neogene of indonesia in active tectonic areas of humid equatorial regions nearshore shallow water environments are commonly sites of near continuous siliciclastic influx and or punctuated volcaniclastic input despite significant clastic influence neogene carbonates developed in se asia adjacent to major deltas or volcanic arcs and are comparable with modern mixed carbonate clastic deposits in the region research into delta front patch reefs from borneo and fore arc carbonate platform development from java is described and used to evaluate the effects of siliciclastic and volcaniclastic influx on regional carbonate sedimentation local changes in carbonate producing biota and sequence development regional carbonate development in areas of high siliciclastic or volcaniclastic input was influenced by the presence of antecedent highs changes in the amounts or rates of clastic input delta lobe switching or variations in volcanic activity energy regimes and relative sea level change a variety of carbonate producing organisms including larger benthic foraminifera some corals coralline algae echinoderms and molluscs could tolerate near continuous siliciclastic or volcaniclastic influx approximately equal to their own production rates these organisms adopted various strategies for coping with clastic input including a degree of mobility morphologies adapted to unstable substrate inhabitation or shedding sediment and shapes adapted to low light levels local carbonate production was also affected by energy regime clastic grain sizes and associated nutrient input clastic input influenced the inhabitable depth range for photoautotrophs the zonation of light dependent assemblages and the morphology and sequence development of mixed carbonate clastic successions this study provides data on the dynamic interactions between carbonate and non carbonate clastic sediments and when combined with information from comparable modern environments allows a better understanding of the effects of siliciclastic and volcaniclastic influx on carbonate production

geological setting and fluid inclusion characteristics of a lead copper barium occurrence hosted in a neoproterozoic mafic sill at kiatak northumberland island northwestern greenland abstract we describe a pb cu ba occurrence in northumberland island northwestern greenland mineralization occupies the brecciated upper contact domain of a neoproterozoic diabase sill belonging to the franklin thule dike swarm 720 716 ma with pyrite bearing black shales of the dundas group upper thule supergroup the host tholeiitic diabase sill is of different composition low tio 2 and p 2 o 5 than the locally crosscutting dikes high tio 2 and p 2 o 5 chloritization carbonatization and silicification are intense in proximity to sulfides coarse grained open space filling galena and minor chalcopyrite are accompanied by 2 generations of calcite and 2 of barite galena contains significant amounts of ag av 400 ppm sb av 700 ppm se av 20 ppm traces of bi cd and sn fluid inclusions in the gangue of the kiatak occurrence indicate two fluid types prior to galena precipitation a cacl 2 nacl rich aqueous brine 20 wt eq nacl cooled from temperatures 300 c and was trapped first in early calcite and with further cooling in barite together with solid bitumen inclusions following galena crystallization secondary inclusions containing a similar brine but of lower salinity higher ca na ratio and lower temperature were trapped in calcite corrosion of galena was followed by precipitation of lower temperature 100 c barite from a second fluid comprising immiscible water and ch 4 despite its location in the contact between shale and large mafic sill the low temperature mineralization postdates the cooling of the sill and may be related to basinal fluid circulation controlled by regional extensional faults parallel to diabase dikes although uneconomic the kiatak occurrence may be witness to a larger metallogenic process that could have formed significant sedex type metal concentrations in strata within the thule supergroup

the middle triassic magnetostratigraphy from the peri tethys basin in poland abstract the paper presents the first complete magnetic polarity scale obtained for the middle triassic of the northern peri tethys area the roetian and muschelkalk deposits of southern poland upper silesia the holy cross mountains were studied paleomagnetically the obtained paleopole a 52 n 143 e fits well to the middle triassic ca 240 ma segment of the stable european apwp a set of various quality characteristic directions isolated in 106 samples was used for construction of the composite polarity scale this peritethyan scale has been tied with conodont zonation and referred to the scale erected earlier in the tethyan realm comparison of both scales indicates that the whole roetian succession in the southern polish basin should be correlated with the latest olenekian the normal marine sedimentation ceased in the polish basin as early as in the late fassanian time the obtained magnetostratigraphic scale combined with the sequence stratigraphic framework enables a reliable chronological correlation of the late olenekian ladinian succession over the entire peri tethys basin

environmental reconstruction of a late burdigalian miocene patch reef in deltaic deposits east kalimantan indonesia abstract most studies of cenozoic shallow water mixed carbonate siliciclastic depositional systems have focused on their sedimentology to date however comprehensive analyses of biotas and biofacies of indo west pacific reefs that developed in mixed carbonate siliciclastic systems are lacking this study describes the palaeoenvironment and biodiversity of a late burdigalian patch reef that developed in a mixed carbonate siliciclastic depositional system the studied exposure is located at the northeast margin of the kutai basin near bontang indonesia and is approximately 80 m wide and 25 m thick multi taxon analysis of the most abundant fossil groups including larger benthic foraminifera corals coralline algae and bryozoans aims to provide a model for environmental interpretation that will allow comparison with similar deposits of indo west pacific region based on fossil content and lithology five different facies types have been distinguished foraminiferal packstone fp bioclastic packstone with foralgal communities bp thin platy coral sheetstone cs platy tabular coral platestone cp and shales s among larger benthic foraminifera smaller and more robust forms dominate in the fp and bp facies while larger and flatter forms are the most abundant in the cs and cp facies thin platy corals are dominant in the cs facies and gradually change into thicker platy tabular forms in the cp facies assemblages and growth forms of coralline algae show no major differences between the facies types and are dominated by melobesioids and sporolithon the majority of bryozoan species are encrusting and were found only in the cs facies light dependent organisms occurring in the reef indicate low light conditions typical for mesophotic reefs the relatively small size of this reef complex and quite distinct vertical changes in the facies types combined with the high siliciclastic content in most of the units points to strong terrigenous input affecting water transparency as the main factor controlling the reef growth

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

upper jurassic microsolenid biostromes of northern and central europe facies and depositional environment abstract microsolenid biostromes are a common and important reef type in many upper jurassic reefal sections comparative study of these biostromes in western europe allows the characterisation of this distinct biostrome type in terms of its taxonomic composition palaeoecology and sedimentary regime the biostromes are characterised by a coral community of relatively low generic diversity being dominated by the microsolenidae family of corals the coral skeletal biovolume is generally high and is overwhelmingly dominated by platy ecomorphotypes sedimentologically these biostromes developed in low energy marl and limestone regimes which were subject to low sedimentation rates and varying degrees of siliciclastic influx in contrast to the coral fauna the associated fauna shows a high generic diversity in particular a rich assemblage of echinoids and bivalves in addition the coral plates provide an ideal habitat for a well developed and strongly polarised encrusting and boring fauna top surfaces show limited post mortem encrustation by serpulids and cementing bivalves and are also bored by lithophagan bivalves the undersides of the plates show a highly developed and diverse cryptic fauna of serpulids thecidean brachiopods bryozoans calcareous sponges and sclerosponges it is concluded that the main control on the development of these biostromes was low light intensities though low energy level and low background sedimentation rates were also important it is suggested that relatively high nutrient levels may have also played a significant role the conditions for microsolenid biostrome development prevail in relatively deep water environments and hence these are the first coral dominated reefal structures to have developed in deeper water shallowing upward sequences the corals in these biostromes have adapted to these conditions by developing a strongly platy growth form but also reducing their growth rates substantially the microsolenids are particularly adapted to these environments in two ways 1 they secreted an extremely porous calcium carbonate skeleton which in environments where calcification rates are slow such as deep water environments is a distinct advantage 2 in response to the limited potential of phototrophy in these environments the microsolenids have developed a pennular septal structure which is suggested to be a means of improving heterotrophic feeding trophic analysis of the reef fauna reveals that the nutrient limitation model developed for present day coral reefs cannot be applied to these biostromes it is demonstrated that the microsolena and the present day agariciid leptoseris show a number of significant morphological and ecological similarities

effects of vegetation on braided stream pattern and dynamics 1 investigations using a 16 m by 2 m recirculating experimental flume model of an ephemeral braided river indicate that the presence of large and erosion resistant plants within the channel e g trees or shrubs can have a significant impact on channel pattern and planform dynamics simulations show that these plants have two effects first they act as obstructions in some cases forcing the flow to divide this flow separation can allow the deposition of a small island immediately in the lee of the plant splitting the channel the net result is a substantial increase in the number of channels and correspondingly the braid index this is in direct contrast to previous studies where increased levels of vegetation in perennial streams have decreased the braid index second the plants stabilize braid bars and can form relatively stable islands in their lee significantly reducing the longitudinal migration of islands typically associated with braided rivers

modelling of suspended sediment transport in coastal areas under waves and currents abstract a coupled hydrodynamic suspended sediment transport model including waves and currents was developed four models a nested grid circulation model 2 d and 3 d a refraction diffraction dissipation wave propagation model a wave current bottom boundary layer model and a quasi 3 d suspended sediment concentration ssc model are integrated the model system has been applied to cleveland bay australia to study ssc in january and march 1993 when two high ssc events 100 mg l 1 were observed during an intensive field monitoring programme the swell has been found to be the dominant suspension mechanism and thus an important factor of high ssc in the bay the model was able to predict the high ssc events in january and march 1993 a net deposition rate in cleveland bay was estimated to be about 0 1 mm year 1 a figure consistent with geological evidence

the hettangian corals of the isle of skye scotland an opportunity to better understand the palaeoenvironmental conditions during the aftermath of the triassic jurassic boundary crisis at ob lusa isle of skye scotland six distinct coral beds were observed in a modern outcrop where a hettangian succession is exposed the coral associations are monogenic belonging to lepidophyllia a massive cerioid genus the lowest bed has relatively well developed colonies that form small bioconstructions whereas the other beds have small and dispersed colonies that are completely drowned in the matrix their morphology and size can vary but the general growth fabric is dominated by platy colonies this type of growth fabric is defined as a platestone the most surprising characteristic of these specimens especially for the platy corals is their growth pattern many samples do not exhibit the classical growth polarity because they are bifacial geochemical analyses 180 13c were conducted on oyster shells that were associated with the corals the results indicate that the mean palaeotemperature was approximately 22 c sedimentological analysis revealed shallow settings where the hydrodynamic energy and siliciclastic inputs fluctuated the general faunal assemblage of the outcrop had low diversity and was mainly composed of allochthonous bioclasts the corals at ob lusa clearly did not live under ideal environmental conditions for the development of corals

sea level controls on the post glacial development of the great barrier reef queensland abstract the central great barrier reef is situated on a 125 km wide continental shelf with a shallow shelf break at ca 70 m in consequence the earlier post glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf the reef province only started to assume its modern dimensions after ca 10 ky b p when sea level stabilised at depths around 28 m reef growth since 18 ky b p has been controlled by the episodic nature of the post glacial transgression being related to shorelines s8 to s1 developed at estimated eustatic depths and ages of 114 m 18 ky b p 88 m 17 ky b p 75 m 15 ky b p 56 m 12 ky b p 45 m 11 ky b p 39 m 10 ky b p 28 m 9 5 ky b p 23 m 9 ky b p 9 m 7 5 ky b p and 0 m 6 5 ky b p rates of sea level rise as high as 12 m ky 1 occurred between stillstands outpacing coral growth response and resulting in many mid outer shelf reefs being drowned in situ

high resolution ammonite and carbon isotope stratigraphy across the triassic jurassic boundary at new york canyon nevada the triassic jurassic boundary is generally considered as one of the major extinctions in the history of phanerozoic the high resolution ammonite correlations and carbon isotope marine record in the new york canyon area allow to distinguish two negative carbon excursions across this boundary with different paleoenvironmental meanings the late rhaetian negative excursion is related to the extinction and regressive phase the early hettangian 13corg negative excursion is associated with a major floristic turnover and major ammonite and radiolarian radiation the end triassic extinction early jurassic recovery is fully compatible with a volcanism triggered crisis probably related to the central atlantic magmatic province the main environmental stress might have been generated by repeated release of so2 gas heavy metals emissions darkening and subsequent cooling this phase was followed by a major long term co2 accumulation during the early hettangian with development of nutrient rich marine waters favouring the recovery of productivity and deposition of black shales

cenozoic carbonates in southeast asia implications for equatorial carbonate development cenozoic equatorial carbonate production was at its most extensive and diverse in the seas of southeast asia yet the carbonates of this region remain poorly documented this paper presents the first published review of carbonate deposition during the cenozoic collating sedimentological data for carbonate successions throughout the region current models of warm water carbonate platform evolution sedimentation and facies distribution inspired by studies of the classic sub tropical areas provide inadequate analogues for the evaluation of modern or cenozoic equatorial carbonates in southeast asia the equatorial carbonates differ in being dominated by bioclasts coated grains and associations with evaporites or dolomites are rare the carbonate systems occur in a range of depositional settings which were often affected by coeval tectonism siliciclastic input or volcanism an understanding of the carbonate depositional environments spatial facies distributions and controls on deposition and diagenesis is essential in order to characterize equatorial carbonate development and to evaluate their considerable economic potential

experimental steep braided flow application to flooding risk on fans flooding processes occurring on alluvial fans are considerably different from those occurring along single thread rivers with well defined floodplains active erosion rapid sedimentation and the uncertainty in flow path make the prediction of flood evolution and extent difficult based on a large scale experiment this study investigates the long term evolution of the flow on a steep noncohesive sediment surface resembling a complex of merged alluvial fans the results are pertinent to the assessment of flooding hazard on alluvial fans at any given time the average flow occupancy was 21 of the surface however the flow was characterized by active channel switching and overflow processes the percentage of the surface remaining dry was found to decay harmonically with time a reworking time was defined as the time at which half of the surface that was initially dry remained dry whereas the other half was inundated at least once an empirical expression was developed in which reworking time is proportional to the average cross sectional area of flow and inversely proportional to the sediment supply

scleractinian assemblages under sediment input their characteristics and relation to the nutrient input concept abstract in the geological record scleractinian dominated turbid water bioconstructions that accumulated under substantial terrigenous input along with shallow neritic marls rich in well preserved corals are common these occurrences indicate that beyond some threshold the ecologic and taphonomic effects of sedimentation prevail over the effects of nutrification field data and experiments on recent corals show that some taxa cope well with terrigenous turbidity and sedimentation and acclimate to increased heterotrophy colonial corals resilient to sediment input commonly are massive to platy forms of high skeletal plasticity and with large polypars to effectively reject sediment or are branched species providing a very small sedimentation area cleaned by feeble currents or small polyped massive taxa that tolerate intermittent veneering by sediment these corals may comprise siltation assemblages of recent turbid water reefs and level bottoms in siliciclastic environments conversely excess input of even low amounts of dissolved inorganic nutrients into clear waters adversely affects many coral species fossil turbid water bioconstructions twb were situated in inner shelf to shore zone settings or near storm wave base on shelves or ramps did not stack into reef complexes mostly show a cluster to segment fabric are scarce in or devoid of frame pores with marine cement and lacked a high carbonate slope relative to fossil clear water buildups preserved in pure limestone successions fossil twb contain moderately diverse coral assemblages with an increased proportion of sediment resistant forms aside from coral behaviour that is elusive in fossils the sediment resistance of corals was mainly determined by colony shape and polypar size but small polyped sediment tolerant corals became common since the early cretaceous late jurassic to cretaceous turbid water coral assemblages are dominated by plocoid or thamnasterioid forms corresponding cainozoic assemblages consist mainly of cerioid and plocoid taxa in fossil twb bioerosion and encrustation are similar or higher than in contemporaneous clear water buildups under higher sediment input accumulation of discrete twb was quenched and level bottoms of both corals and soft substrate biota formed in the resulting coral marls depending on turbidity sedimentation and substrate stability the coral fauna consists largely of both solitary corals and mainly sediment resistant pseudocolonial colonial forms or is dominated by solitary corals many corals show growth anomalies resulting from partial mortality due to episodic rapid sedimentation and unstable substrate in coral marl environments because of terrigenous input nutrient levels probably were elevated yet macroboring and encrustation are very scarce beyond some threshold of terrigenous sediment input and accumulation the ecologic and taphonomic effects of sedimentation and unstable substrate prevail over the effects of nutrient enrichment during the meso cainozoic evolution of scleractinians increasing photoautotrophy and progressive invasion of oligotrophic environments is in contrast to a late cretaceous to cainozoic increase in the relative number of reefs in marginal marine siliciclastic settings this trend may be explained by second order sea level fall and shrinking of epicontinental carbonate seas and isolated platforms driving corals to more narrow attached shelves and by a wider total trophic range in which distinct coral assemblages can thrive as a result of coral evolution and diversification

carbon cycle perturbation and stabilization in the wake of the triassic jurassic boundary mass extinction event 1 the triassic jurassic boundary mass extinction event t j 199 6 ma is associated with major perturbations in the carbon cycle recorded in stable carbon isotopes two rapid negative isotope excursions in bulk organic carbon 13corg occur within the immediate boundary interval at multiple locations and have been linked to the outgassing of 12c enriched co2 from the central atlantic magmatic province in british columbia a positive 13corg excursion of 5 vienna peedee belemnite v pdb spans part or all of the subsequent hettangian stage here we examine the significance of these carbon isotope excursions as records of global carbon cycle dynamics across the t j boundary and test the link between carbon cycle perturbation stabilization and biotic extinction recovery patterns a combination of 13corg and palynological analyses from the late triassic to early jurassic in the mingolsheim core germany suggests that organic carbon isotope variations are best explained as the result of both compositional changes in terrestrial versus marine input and disturbance and recovery patterns of major terrestrial plant groups across the t j boundary a new high resolution 13ccarb record from the val adrara section in the southern alps italy spanning from the uppermost rhaetian through lower sinemurian does not exhibit a negative excursion at the t j boundary but does record a large positive 13ccarb excursion of 4 v pdb in bulk carbonate that begins at the t j boundary and reaches a local maximum at the early late hettangian boundary values then gradually decrease reaching 0 5 at the hettangian sinemurian boundary and remain relatively constant into the early sinemurian complementary 13ccarb data from 4 more sections that span the hettangian sinemurian boundary support carbon cycle stabilization within the upper hettangian our analyses suggest that isotope changes in organic carbon reservoirs do not necessarily require a shift in the global exogenic carbon reservoir and that the positive excursion in the carbonate carbon isotope record is best explained as the combined result of an increase in atmospheric pco2 leading to accelerated carbon cycling decreased skeletal carbonate production and increased organic carbon burial lasting several hundred thousand years the termination of the positive inorganic carbon isotope excursion coincides with the recovery of marine skeletal carbonate producers and coeval changes in terrestrial vegetation and reflects the gradual reduction in pco2 and the stabilization of the global carbon cycle during the sinemurian

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

the depth of pelagic deposits in the tethyan jurassic and the use of corals an example from the apennines abstract assessing the palaeobathymery of pelagic deposits is rather speculative as proof through lithology or fossils significant for depth estimates is sparse this is unfortunate as the bathymetric history of pelagic successions allows to conceive the evolution of continental margins and oceanic basins discoveries in coral biology bring an unexpected impact on basin analysis evidence strongly suggests that pennular corals fossil and modern constitute a zooxanthellate group with an outstanding specialization in colonizing deeper parts of the marine photic zone this adaptation includes light amplification by autofluorescent pigmented cells and particular feeding witnessed by peculiar gastric ducts and skeletal features such corals occur in the umbria marche and sabina apennines on top of late jurassic submarine highs and at basin margins values of palaeodepth relative to pelagic deposits are provided by corals and other environmental data because depth reconstruction involves classical tethyan facies such as ammonitico rosso aptychus limestone and radiolarian cherts we must note that these results do not meet with actualistic models relying on carbonate dissolution for estimating depth deposits viewed as bathyal to abyssal could also have accumulated within or just below the photic zone thus a new insight opens on mesozoic bathymetries regarding vast areas middle east to caribbean and on subjects ranging from platform drowning to regional extension styles

relationship between sediment supply and avulsion frequency in braided rivers the interplay between sediment supply s s sedimentation rate s r and the frequency of channel avulsion a f exerts a primary control on alluvial architecture in order to investigate the effect of sediment supply on avulsion frequency four froude scale model experiments of an aggrading braided river were undertaken in which the magnitude of s s was progressively increased over an eightfold range the value of a f increases at a rate slower than the increase in s s contrary to the trend previously reported by bryant falk and paola in their experimental study on alluvial fan dynamics these results suggest that the relationship between a f and s s is dependent upon bed slope and that the response of a f to an increase in s s in unconfined braided rivers may be different than that on steep alluvial fans

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

volcanic degassing necessary to produce a caco3 undersaturated ocean at the triassic jurassic boundary abstract carbon cycle model calculations have been conducted to test the idea that the entire ocean became undersaturated or nearly undersaturated with respect to calcium carbonate at the triassic jurassic t j boundary a low degree of saturation at this time has been cited to explain the relative lack of carbonate sediments especially those that originally contained the more soluble minerals aragonite and highly magnesian calcite sensitivity analysis indicates that only extreme conditions of massive and short lived degassing of co2 and so2 from camp volcanism could have led to an undersaturated ocean with total degassing of 21 000 gtc as co2 and 57 000 gts as so2 an undersaturated ocean with respect to all calcium carbonate minerals could have persisted for 20 40 ka but only if the volcanic degassing lasted for no longer than 50 100 ka with half this amount of total degassing over 100 ka a very low degree of supersaturation possibly stabilizing only low magnesian calcite could have been maintained for 20 ka