abundant sr rich aragonite in eastern mediterranean sapropel s1 diagenetic vs detrital biogenic origin caco3 contents in eastern mediterranean sapropels are generally lower than in the enclosing marl sediments in sediments of a transect from 650 to 2100 m water depth at the sirte continental slope the opposite feature was observed although the increased sr ca ratios observed in these sediments agree with such feature observed in other eastern mediterranean s1 sediments their absolute magnitude is much higher the enhanced sr ca ratio in these sediments is associated with their aragonite content which for the sirte transect reaches levels of up to 40 wt the aragonite content and sr ca ratios in the s1 sediments of this transect decrease with increasing water depth and decrease with distance to the african coast for all eastern mediterranean cores in view of the lack of a coherent relationship with sedimentary reduced sulphur contents and porosity and considering the major amount of aragonite found specifically in the sediments of the sirte transect authigenic precipitation can contribute only a limited fraction at most sem observation and electron microprobe analyses showed that the needles and needle clusters are morphologically aragonite contain the highest sr ca ratio and are similar to skeleton fragments of the green alga halimeda consequently a detrital biogenic source is the likely mechanism for the major part of the aragonite enrichments found in s1 sediments possibly offshore directed surface water flows related to wind stress and or enhanced run off consistent with enhanced precipitation during sapropel s1 may have assisted in the transport of near coastal aragonitic organisms to more coast remote areas

simulating reef response to sea level rise at lizard island a geospatial approach abstract sea level rise will result in changes in water depth over coral reefs which will influence reef platform growth as a result of carbonate production and accretion this study simulates the pattern of reef response on the reefs around lizard island in the northern great barrier reef two sea level rise scenarios are considered to capture the range of likely projections 0 5 m and 1 2 m above 1990 levels by 2100 reef topography has been established through extensive bathymetric profiling together with available data including lidar single beam bathymetry multibeam swath bathymetry lads and digitised chart data the reef benthic cover around lizard island has been classified using a high resolution worldview 2 satellite image which is calibrated and validated against a ground referencing dataset of 364 underwater video records of the reef benthic character accretion rates are parameterised using published hydrochemical measurements taken in situ and rules are applied using boolean logic to incorporate geomorphological transitions associated with different depth ranges such as recolonisation of the reef flat when it becomes inundated as sea level rises simulations indicate a variable platform response to the different sea level rise scenarios for the 0 5 m rise the shallower reef flats are gradually colonised by corals enabling this active geomorphological zone to keep up with the lower rate of rise while the other sand dominated areas get progressively deeper in the 1 2 m scenario a similar pattern is evident for the first 30 years of rise beyond which the whole reef platform begins to slowly drown to provide insight on reef response to sea level rise in other areas simulation results of four different reef settings are discussed and compared at the southeast reef flat barrier reef coconut beach fringing reef watson s bay leeward bay with coral patches and mangrove beach sheltered lagoonal embayment the reef sites appear to accrete upwards at a rate commensurate with the rate of rise thereby maintaining their original profile and position relative to the sea surface and the leeward and lagoonal sites with a low accretion rate maintain a similar profile but slowly gain depth relative to sea level the result of this variable response is that elevated features of the reef platform such as reef patches and crests tend to become more pronounced

long shelf sediment transport and storm bed formation by cyclone winifred central great barrier reef australia three major sediment facies belts occur on the great barrier reef shelf an inner shelf prism of holocene terrigenous sand and mud a patchy middle shelf veneer of palimpsest muddy shelly calcsand 1 m thick above a weathered pleistocene erosion surface and an apron of modern carbonate mud and sand around reefs of the main reef tract these sediments were mobilized and strongly affected by the passage of severe tropical cyclone winifred central pressure 958 hpa which traversed the central great barrier reef shelf on february 1 1986 re surveys after the passage of cyclone winifred showed that i a storm induced shell lag and or a normally graded bed of terrigenous fine sand mud had been deposited at depths down to 20 m ii middle shelf longitudinal bedforms were widespread at depths of 28 35 m and comprised a furrowed substrate of palimpsest muddy shell gravel surmounted by 40 150 m wide ribbons of quartzose and bioclastic sand up to 15 cm thick iii fields of northward facing 1 2 m wavelength megaripples were present adjacent to zones of ribbons and in the alleys between ribbons iv five days after the cyclone mud was still settling from suspension and large parts of the inner shelf were bathed in muddy hypopycnal river plumes some of which reached 30 km seaward to the inner edge of the reef tract and v suspended mud derived in part by unmixing of the seabed was present throughout the shelf water column and a seaward thinning mud drape up to 40 cm thick had accumulated on and seawards of the inshore sediment prism tapering seawards to a few mm thick only over most of the middle shelf it is inferred that storm waves and currents associated with the passage of cyclone winifred caused widespread unmixing of bottom sediments offshore long shelf transport of bedload sand ribbons and megaripples was affected by powerful shelf parallel currents of velocity 1 3 m s as the storm passed the graded seaward thinning sand mud bed was deposited over the inner middle shelf on the middle shelf bioturbation and downward mixing of the mud drape started immediately after the passage of the cyclone and was well advanced after 3 months in this way the ephemeral seabed features produced by passage of a cyclone are gradually degraded and the storm layer stratigraphy becomes incorporated within a thin middle shelf veneer of muddy shelly calcsand

reef accretion and coral growth rates are decoupled in holocene reef frameworks abstract a central assumption of holocene reef models is that reef accretion rates are directly related to coral growth rates with reefs dominated by faster growing corals having higher accretion rates yet few studies have explicitly tested this assumption particularly in indo pacific region through high precision u th dating and palaeoecological reconstructions of coral community structure this study explores patterns of reef accretion mm yr 1 among late holocene reef frameworks from the inshore central great barrier reef modern assemblages were dominated by either slow growing goniopora 9 6 2 mm yr 1 or rapid growing branching acropora 89 6 mm yr 1 framework building corals despite a nearly 10 fold difference in coral growth rates rates of reef accretion were comparable between frameworks dominated by slow growing goniopora 8 6 1 3 mm yr 1 and rapid growing branching acropora 7 1 1 4 mm yr 1 u th chronologies indicate that accretion rates were continuous throughout the past 750 years r2 0 96 0 98 despite a temporal shift in framework building corals from acropora to goniopora that occurred 250 years ago that coral growth rates are decoupled from reef accretion at holocene scales indicates that previous models of accretion in pacific coral reefs may be based upon inaccurate assumptions the finding that ecological processes are decoupled from geological processes has implications for the management of modern coral reefs and suggests that maintenance of living corals regardless of taxonomic identify is important for accretion of reef frameworks

the importance of large benthic foraminifera to reef island sediment budget and dynamics at raine island northern great barrier reef low lying reef islands are among the most vulnerable environments on earth to anthropogenic induced climate change and sea level rise over the next century because they are low composed of unconsolidated sediment that is able to be mobilised by waves and currents and depend on sediments supplied by reef organisms that are particularly sensitive to environmental changes e g ocean temperatures and chemistry therefore the spatial and temporal links between active carbonate production and island formation and dynamics are fundamental to predicting future island resilience yet remain poorly quantified in this paper we present results of a detailed geomorphological and sedimentological study of a reef and sand cay on the northern great barrier reef we provide an empirical investigation of the temporal linkages between sediment production and reef island development using a large collection of single grain ams 14c dates large benthic foraminifera lbf are the single most important contributor to contemporary island sand mass 47 ranging from 36 to 63 at raine island reflecting rapid rates of sediment production and delivery standing stock data reveal extremely high production rates on the reef 1 8 kg m 2 yr 1 while ams 14c dates of single lbf tests indicate rapid rates of sediment transferral across the reef we also demonstrate that age is statistically related to preservation and taphonomic grade severely abraded tests moderately abraded tests pristine tests we construct a contemporary reef and island sediment budget model for raine island that shows that lbf baculogypsina marginopora and amphistegina contribute 55 of the sediment produced on the reef annually of which a large proportion 54 contribute to the net annual accretion of the island the tight temporal coupling between lbf growth and island sediment supply combined with the sensitivity of lbf to bleaching and ocean acidification suggests that islands dominated by lbf are likely to be very sensitive to short and long term climate change projections potential outcomes of this work relate to improving the understanding of the future change dynamics of reef islands in response to climate change

shallow water sclerosponges on jamaican reefs and a criterion for recognition of hurricane deposits we report here that excavation into the acropora palmata rubble on the reef crest at 4 m water depth on discovery bay reefs jamaica revealed the presence of numerous sclerosponges ceratoporella nicholsoni living attached directly to the coral branches 1 2 m below the rubble surface the coral branches excavated were deposited during a storm event in august 1980 and consequently lack the zoned crusts showing a succession from photophilic light loving to sciaphilic shade loving secondary frame builders which normally develop during slow steady incremental coral branch accumulation thus the nature and sequence of encrustations on coral rubble can indicate the speed of its accumulation

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

carbonate and terrigenous sediment budgets for two inshore turbid reefs on the central great barrier reef abstract inshore turbid zone reefs on the great barrier reef gbr occur within 20 km of the mainland coast under marine environmental conditions with respect to sedimentation rates turbidity and water quality that are generally considered marginal for reef growth despite this data from various benthic habitat assessments report high 30 coral cover in these environments and reef core records show them to be characterised by relatively rapid rates of vertical accretion 2 8 mm year a long term trend indicative of high net carbonate productivity and in situ carbonate framework accumulation however the lack of quantitative data on terrigenous sediment input and flux rates and on carbonate production rates has inhibited understanding of both ecological timescale rates of carbonate production and the aggregated long term net impacts of sediments on reef growth to address this knowledge gap a modern carbonate budget and terrigenous sediment model that quantified allochthonous sediment inputs onto within and off reef was developed at two inshore reefs middle reef and paluma shoals both are located within the central region of the gbr and are subjected to high terrigenous sediment load 11 000 tonnes year and fluctuating turbidity 5 to 100 mg l regimes based on sediment dynamic modelling over 81 of sediments delivered were transported off reef with net sediment accumulation limited to sheltered reef habitats net carbonate production was high 6 9 kg m2 year due to high coral cover 30 high coral calcification rates acropora average 6 3 g cm2 year and low bioerosion rates 0 3 to 5 kg m2 year but varied spatially with highest net carbonate production 10 kg m2 year within deep 2 m at lat windward reef zones high carbonate framework production has enabled middle reef and paluma shoals to vertically accrete rapidly middle reef establishing at depths of 4 m paluma shoals at 3 m depth and both reaching sea level in

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

quaternary atoll development new insights from the two dimensional stratigraphic forward modelling of mururoa island central pacific ocean knowledge about the quaternary evolution of mid ocean atolls comes mainly from drilling and field observations carried out on a number of pacific carbonate islands however little is known about the early to mid pleistocene atoll development history especially at margin and foreslope settings using previous field and subsurface data from mururoa atoll and a process based modelling software dionisos a two dimensional forward stratigraphic model of atoll development is proposed for the past 1 8 million years myr observational data from vertical to inclined coring seismic and bathymetric surveys indicate that from approximately 0 45 to 0 40 million years before present ma carbonate deposition at mururoa atoll resulted in a series of mostly prograding reef units the model is first constrained at the base by the shape and topography of the pre quaternary basement a number of sensitivity tests were performed to define the respective influence of variant parameters the best fit development scenario that accounts for the overall geometry and stratigraphic architecture of the quaternary sediment packages is obtained by using the sea level curve by miller et al 2005 uniform subsidence rate of 105 m myr 1 and carbonate production rates gradually increasing from 0 50 to 8 mm yr 1 between 1 80 ma and the present additional controlling parameters include subaerial erosion at a constant rate of 0 25 m kyr wave energy and sediment transport processes the stratigraphic forward model predicts a succession of three distinct types of carbonate systems that have developed since the earliest pleistocene toe of slope systems from 1 80 ma to about 0 80 ma open platform systems from 0 80 ma to 0 50 ma and framework reef systems from about 0 50 ma to the present the development of these different systems is most likely to be controlled by climate and changes in sea level cycles during the low amplitude 41 kyr cycle periods of the earliest pleistocene ambient conditions were not conducive to framework reef growth shallow water carbonate sedimentation was dominantly gravity driven operating along the platform foreslopes only during the mid pleistocene climate transition narrow open platform units have developed at the upper parts of the pre quaternary basement flanks with the onset of the high amplitude 100 kyr sea level modes and climate restoration reef frameworks started to be generated these models from mururoa agree with a number of previous studies suggesting that most of the true framework reefs were not initiated prior to 0 50 ma mururoa atoll is demonstrated to be a robust analogue for providing more realistic interpretations of the development history of pacific atolls further modelling with three dimensional dionisos could generate better predictions by taking into account hydrodynamic and transport parameters more accurately

impacts of cyclone yasi on nearshore terrigenous sediment dominated reefs of the central great barrier reef australia tropical cyclone tc yasi category 5 was a large 700 km across cyclone that crossed australia s queensland coast on the 3rd of february 2011 tc yasi was one of the region s most powerful recorded cyclones with winds gusting to 290 km h and wave heights exceeding 7 m here we describe the impacts of tc yasi on a number of nearshore turbid zone coral reefs that include several in the immediate vicinity of the cyclone s landfall path king reef lugger shoal and dunk island as well as a more distally located reef paluma shoals 150 km to the south in halifax bay these reefs were the focus of recent between 2006 and 2009 pre yasi studies into their geomorphology sedimentology and community structure and here we discuss data from a recent august 2011 post yasi re assessment this provided a unique opportunity to identify and describe the impacts of an intense tropical cyclone on nearshore reefs which are often assumed to be vulnerable to physical disturbance and reworking due to their poorly lithified framework observed impacts of tc yasi were site specific and spatially highly heterogeneous but appear to have been strongly influenced by the contemporary evolutionary stage and ecological make up of the individual reefs with site setting i e exposure to prevailing wave action apparently more important than proximity to the landfall path the most significant ecological impacts occurred at king reef probably a result of freshwater bleaching and at paluma shoals where widespread physical destruction of branched acropora occurred new coral recruits are however common at all sites and colony re growth clearly evident at king reef only localised geomorphic change was evident mainly in the form of coral fracturing rubble deposition and sediment movement but again these impacts were highly site specific the dominant impact at paluma shoals was localised storm ridge shingle sheet deposition at lugger shoal major offshore fine sediment flushing and at dunk island major onshore coarse sand deposition there was little geomorphic change evident at king reef thus whilst small scale and taxa specific impacts from cyclone yasi are clearly evident geomorphological changes appear minor and ecological impacts highly variable between sites and there is no observed evidence for major reef structural change the study suggests that the vulnerability of reefs to major physical disturbance events can be extremely site specific and determined by interacting factors of location relative to storm path and pre event geomorphology and ecology

the importance of quaternary records in reducing risk from tropical cyclones numerous late holocene records of tropical cyclones have been collected from north east queensland australia they are in the form of multiple sedimentary ridges paralleling the shore the ridges are composed of coral fragments or shell and sand or pure sand a method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events the results suggest that extrapolations of long term cyclone magnitude and frequencies from the 30 to 40 year long instrumental record which is the method commonly used to assess risk from this hazard substantially underestimate the risk from this hazard this is confirmed for the cairns region by an 800 year long high resolution isotope record of tropical cyclones preserved in a limestone stalagmite together the sedimentary and isotope records suggest that tropical cyclone activity in north east queensland has been in a phase of quiescence since before european settlement of the region in approximately ad 1870 it is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence

from platform top to adjacent deep sea new source to sink insights into carbonate sediment production and transfer in the sw indian ocean glorieuses archipelago abstract over the past ten years a huge amount of source to sink studies have aimed to unravel the tectonic climatic and other processes that shape the landscape from mountains to the deep ocean interestingly these studies have been mainly dedicated to siliciclastic or mixed systems for which the connection between drainage basins continental shelves slope and basin environments are often well constrained here we present a study focusing on a source to sink study dedicated to a pure carbonate system located in the sw indian ocean glorieuses archipelago extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition the lateral variability and volumes of neritic sands deposited on the platform top additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge corresponding to the export of carbonate sediments from the platform top toward the platform edge under the influence of dominant currents and wind driven processes high resolution seismic bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel levee complexes and turbiditic lobes which have accumulated on the seafloor on top of a 250 m thick sedimentary basin at 2000 3400 m water depth our study points out that carbonate sands and aragonitic mud produced on the platform top during the holocene have been shed to the adjacent basin we also demonstrate that this routing system was active at least throughout the last three glacial interglacial cycles this study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms 1 it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin 2 it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity 3 a first estimate of a carbonate source to sink system is proposed demonstrating that 0 57 km3 of sediments have been produced during the holocene 0 3 km3 being presently stored on the platform and the remaining having been exported to the deep basin

palaeo methane seepage history traced by biomarker patterns in a carbonate crust nile deep sea fan eastern mediterranean sea abstract we investigated lipid biomarkers in three depth intervals of a methane derived carbonate crust collected from a pockmark in the nile deep sea fan sampled during the nautinil cruise of the r v l atalante a diverse set of 13 c depleted archaeal and bacterial lipids were detected along this crust with 13 c values as low as 118 this provides evidence that anaerobic oxidation of methane was the main process that induced the formation of this carbonate crust archaeal lipid biomarker distributions revealed the presence of archaea belonging both to the anme 1 and anme 2 phylogenetic clusters with the former predominating the distribution and compound specific 13 c values of aom derived lipid biomarkers showed no significant variations with depth these results infer that the archaeal community structure and thus the local seepage environment remained relatively stable during the 5000 kyr period of the carbonate crust precipitation

a detrital sediment budget of a maldivian reef platform abstract sediment dynamics are an important control on the morphology and development of reef systems by actively removing and redistributing excess detrital sediment this study presents quantitative data from direct point measurements of sediment transport on the platform surface and fore reef slope of vabbinfaru reef north male atoll maldives a suite of sediment traps were used to construct actual rates of platform sediment fluxes and off reef export over different spatial and temporal seasonal scales to establish key sediment transport pathways findings showed that high sediment fluxes occur on vabbinfaru platform in the absence of major storm activity up to 1905 g m 1 d 1 with 95 of annual transport occurring during the southwest monsoon as a result of increased wave energy climate driven changes in the platform process regime caused a reversal of net sediment transport pathways between each monsoon season off reef export rates were high reaching a maximum of 12 58 kg m 1 y 1 for gravel and 407 g m 1 d 1 for sand sized sediment an estimated 127 120 kg is exported from the platform annually equating to a significant loss from the reef sediment budget and contributing to the long term geomorphic development of the fore reef slope and atoll basin detrital sediment reservoirs on vabbinfaru are not purely depositional carbonate sinks but rather temporary stores that are important in the transfer of sediment between reef zones

off reef transport of coral fragments at lizard island australia abstract the generation and movement of coral rubble is important to the sedimentary budget of a reef in sediment facies development and in the promotion of reef growth this study examined the rate of down slope transport of live and dead coral fragments from shallow reef fronts at lizard island on the great barrier reef australia ten large 1 m2 collecting trays were deployed and cleared annually for 4 years at each of two sites at the base 8 12 m depth of the steeply sloping fringing reef the rate of export of coral fragments down the reef slope was very high an average of 132 fragments weighing 1 87 kg was recorded each year per meter of reef front a mean of 2 25 of the fragments representing 43 species was alive in the trays at each annual census yielding an average rate of colonization onto the reef slope of 2 7 live fragments per meter of reef front per year reworking of hard calcareous substrates towards the slope promotes reef growth by two mechanisms 1 passive dispersal of live coral fragments to peripheral soft sediment habitats that are unsuitable for larval settlement and 2 subsequent colonization of rubble by coral larvae there were no major storms during the course of the study indicating that significant down slope transport of fragments can occur even in the absence of cyclones

conditions for a crustal block to be sheared off from the subducted continental lithosphere what is an essential factor to cause features associated with collision 1 crustal blocks are detached from the subducting lithosphere at various depths i call such phenomena shearing off and investigate the mechanical conditions for shearing off to occur in the continental lithosphere the buoyancy of the crustal block does not work selectively as a driving force until it has been sheared off and i suppose that shearing off occurs when the shear traction at the thrust whose maximum value is calculated from the strength along the thrust overcomes the strength of the boundary faults of the block and determine the depth of the leading edge of the subducted crustal block when shearing off occurs the temperatures of the slab and at its surface are calculated by the steady state formula of molnar and england 1990 as a function of the surface heat flow dip angle and convergence velocity of the subducted continental plate as the shear stress and temperature at the ductile part of the thrust zone are consistent with the flow law the shear stress at the brittle part is a strong function of the pore fluid pressure ratio i show that shearing off of an upper crustal block is possible only for a small value of such as 0 4 when the surface heat flow value is 70 mw m2 i suggest that the essential factor to cause shallow offscraping of crustal blocks in collision zones is not a buoyancy of the continental crust but a low value of which would result from a little amount of dehydration from the subducted continental plate

carbonate sediment production transport and supply to a coral cay at raine reef northern great barrier reef australia a facies approach abstract coral cays are low lying typically 2 mm grain size and the relative abundances of foraminifera and coral grains gravelly coral dominated sediment is concentrated at the reef margins whereas facies on and around the leeward cay are dominated by the sand size tests of benthic foraminifera mud is absent in reef sediments and reflects the prevailing high energy wave dominated setting as well as a paucity of mud producers benthic foraminifera tests are the major sediment component constituting an average proportion of 39 range 2 77 sediment derived from the skeletal remains of corals 24 1 65 mollusks 15 3 30 halimeda 14 4 36 and coralline algae 6 0 20 are present in lesser volumes foraminifera content is highest 40 on tidally emergent algal pavement where they live in greatest abundance and on the cay shorelines where their tests are deposited and comprise the bulk of beach sand 36 63 a comparison of the raine island data with other exposed modern reefs and platforms of the central and western pacific shows that occurrence and distribution of facies types is broadly consistent beyond these sedimentological data the taphonomy of foraminifera at raine island indicates that tests are vulnerable to destruction due to abrasion when transport and reworking is prolonged therefore the foraminifera rich facies adjacent to and on the cay disjunct from the source zones as well as taphonomic evidence imply that transport from the outer reef flat to the cay must be relatively quick these short temporal links between ecological source zones and depositional landforms are likely to have important ramifications for the contemporary management of reef associated landforms e g cays in the future

coral indicators of past sea level change a global repository of u series dated benchmarks fossil corals provide valuable data for reconstructing past sea levels as they are often well preserved in the fossil record and can be dated with u series methods here we present a global and internally consistent database of usingle bondth dated fossil coral sea level indicators including full consideration of all known associated uncertainties both vertical and chronological we include carefully determined taxon specific depth distributions rather than blanket depth uncertainty terms as used in most previous work this is based on a synthesis of extensive modern ecological information on depth ranges these ranges are found to be spatially variable between ocean basins between regions and on sub regional scales because depth itself is not limiting instead depth distributions arise from complex physical chemical and biological interactions with coral reef growth distribution and composition one of the main causes for recognition of the greater depth variability of coral taxa has been the routine inclusion of deep diving and rov surveys in coral ecological studies over the past few decades which has broken through the shallow water bias of early surveys by adding frequent observations on deeper occurrences although more are needed it is also clear from our assessment that coral habitat depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels and that application to sea level studies then requires these studies also to identify fossil corals to the species level samples identified only to the genus level give rise to wide uncertainties in habitat depth and hence sea level our database contains extensive metadata to assist evaluations of dating quality as well as geomorphic and stratigraphic metadata we demonstrate with examples how such metadata can help to evaluate sea level reconstructions for example by identifying outlier points one example discusses the last interglacial lig where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present which yields a mean age of 124 6 ka with 95 probability bounds at 118 5 and 129 5 ka we conclude with identification of key outstanding issues relating to i current incomplete understanding of tectonic setting including the current lack of independent verification of uplift subsidence rates and reliance of somewhat unsatisfactory and circular use of the elevation of last interglacial deposits ii the depth distributions of coral taxa and iii the complete documentation of stratigraphic geomorphological and other contextual information with suggestions for strategies to address these issues

late quaternary shedding of shallow marine carbonate along a tropical mixed siliciclastic carbonate shelf great barrier reef australia the north east australian margin is the largest modern example of a tropical mixed siliciclastic carbonate depositional system with an outer shelf hosting the great barrier reef gbr and an inner shelf dominated by fluvially sourced siliciclastic sediment wedges the long term interplay between these sediment components and sea level is recorded in the queensland trough a 1 2 km deep n s elongate basin situated between the gbr platform and the queensland plateau in this paper 154 samples from 45 surface grabs and six well dated piston cores were analysed for total carbonate content carbonate mineralogy and sr concentration to establish spatial and temporal patterns of carbonate accumulation in the queensland trough over the last 300 kyr surface carbonate contents are lowest on the inner shelf 5 and in the trough axis 60 because of siliciclastic dilution carbonate on the shelf is mostly sr rich aragonite and high mg calcite hmc whereas that in the basin is mostly low mg calcite once normalized to remove the effects of siliciclastic dilution surface sr rich aragonite and hmc abundances decrease linearly to background levels 100 km seaward of the shelf edge core samples show that over time normalized aragonite and sr abundances are greatest during periods of shelf flooding and lowest when sea level drops below the shelf edge this is consistent with changes in the production of coral and calcareous algae and the shedding of their debris from the shelf interestingly normalized hmc concentrations on the slope peak during periods of major transgression perhaps because of maximum off shelf transport from inter reef areas or intermediate water dissolution after accounting for siliciclastic dilution there are strong similarities in both spatial and temporal patterns of carbonate minerals between slopes and basins of the north east australian margin and those of pure carbonate margins such as the bahamas a limited set of basic processes including the formation and breakdown of carbonate on the shelf the transport of carbonate off the shelf and eustatic sea level probably controls carbonate accumulation in slope and basin settings of tropical environments irrespective of proximal siliciclastic sediment sources