holocene reef growth in torres strait the platform and fringing reefs of torres strait are morphologically similar to reefs of the northern great barrier reef to the south except that several are elongated in the direction of the strong tidal currents between the coral sea and the gulf of carpentaria surface and subsurface investigations and radiocarbon dating on yam warraber and hammond islands reveal that the initiation and mode of holocene reef growth reflect antecedent topography and sea level history on the granitic yam island fringing reefs have established in some places over a pleistocene limestone at about 6 m depth around 7000 years bp emergent holocene microatolls of porites sp indicate that the reefs have prograded seawards while sea level has fallen gradually from at least 0 8 m above present about 5800 years bp on the warraber island reef platform drilling near the centre indicated a pleistocene limestone foundation at a depth of about 6 m over which reefs established around 6700 years bp reef growth lagged behind that on yam island microatolls on the mature reef flat indicate that the reef reached sea level around 5300 years bp when the sea was around 0 8 1 0 m above present on the reef flat on the western side of hammond island bedrock was encountered at 7 8 m depth overlain by terrigenous mud a progradational reef sequence of only 1 2 m thickness has built seaward over these muds as sea level has fallen over the past 5800 years reef flat progradation on these reefs is interpreted to have occurred by a series of stepwise buildouts marked by lines of microatolls parallel to the reef crest marking individual coalescing coral heads detrital infill has occurred between these this pattern of reef progradation is consistent with the radiocarbon dating results from these reefs and with seismic investigations on the torres reefs

drivers of holocene sea level change in the caribbean abstract we present a holocene relative sea level rsl database for the caribbean region 5 n to 25 n and 55 w to 90 w that consists of 499 sea level index points and 238 limiting dates the database was compiled from multiple sea level indicators mangrove peat microbial mats beach rock and acroporid and massive corals we subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on rsl we account for the local scale processes of sediment compaction and tidal range change using the stratigraphic position overburden thickness of index points and paleotidal modeling respectively we use a spatio temporal empirical hierarchical model to estimate rsl position and its rates of change in the caribbean over 1 ka time slices because of meltwater input the rates of rsl change were highest during the early holocene with a maximum of 10 9 0 6 m ka in suriname and guyana and minimum of 7 4 0 7 m ka in south florida from 12 to 8 ka following complete deglaciation of the laurentide ice sheet lis by 7 ka mid to late holocene rates slowed to

taphonomic differentiation of acropora palmata facies in cores from campeche bank reefs gulf of mexico a common assumption in the geological analysis of modern reefs is that coral community zonation seen on the surface should also be found in cores from the reef interior such assumptions not only underestimate the impact of tropical storms on reef facies development but have been difficult to test because of restrictions imposed by narrow diameter cores and poor recovery that assumption is tested here using large diameter cores recovered from a range of common zones across three campeche bank reefs it is found that cores from the reef front crest flat and rubble cay zones are similar in texture and coral composition making it impossible to recognize coral assemblages that reflect the surface zonation taphonomic signatures imparted by variations in encrustation bioerosion and cementation however produce distinct facies and delineate a clear depth zonation cores from the reef front zone 2 10 m depth are characterized by sections of acropora palmata cobble gravel interspersed with sections of in place but truncated a palmata stumps upper surfaces of truncated colonies are intensely bioeroded by traces of entobia isp and gastrochaenolites isp and encrusted by mm thick crustose corallines before colony regeneration and therefore indicate punctuated growth resulting from a hurricane induced cycle of destruction and regeneration cores from the reef crest flat 0 2 m depth are also characterized by sections of hurricane derived a palmata cobble gravels as well as in place a palmata colonies in contrast to the reef front however these cobble gravels are encrusted by cm thick crusts of intergrown coralline algae low relief homotrema and vermetids bored by traces of entobia isp and trypanites isp and coated by a dense peloidal micrite cement cores from the inter to supratidal rubble cay zone 0 5 m are only composed of a palmata cobble gravels and although clasts show evidence of subtidal encrustation and bioerosion these always represent processes that occurred before deposition on the cay instead these gravels are distinguished on the basis of their limited bioerosion and marine cements which exhibit fabrics formed in the intertidal zone these results confirm that hurricanes have a major influence on facies development in campeche bank reefs instead of reflecting the surface coral zonation each facies records a distinctive depth related set of taphonomic processes which reflect colonization alteration and stabilization following the production of new substrates by hurricanes

recent macroids on the kikai jima shelf central ryukyu islands japan sandy and gravelly carbonate sediments found off kikai jima southern japan a coral reef related island shelf represent the northernmost sub tropical carbonate deposits in the central ryukyu islands ryukyus on the kikai jima shelf at water depths of 61 to 105 m these sediments are characterized by macroid pavements since the abundance of very small and of exceptionally large macroids may indicate specific hydrodynamic controls regarding constraints on growth and taphonomy the detailed analysis of recent and fossil macroid pavements is meaningful ecologically and environmentally macroids ranging in size from ca 25 to 130 mm in diameter are spheroidal and sub spheroidal in shape and consist mainly of the encrusting foraminifer acervulina inhaerens and subordinate thin encrusting and lumpy coralline algae accessory components include bryozoans serpulids and to a lesser extent encrusting arborescent foraminifera homotrema and miniacina low sedimentation rates and occasional movement due to current action are indicated by sizes shapes and growth forms of the studied macroids the entobia gastrochaenolites trypanites maeandropolydora ichnocoenosis and the bioerosion index for coated grains introduced herein the deep water tidally induced current energy was sufficient to maintain multi directional growth spheroidal shapes of the larger macroids and to initiate macroid growth using the diverse biogenic remnants as nuclei the asymmetrical inner arrangement suggests possible periods of stability for the macroids the residence time of the coated grain in its original environment determines the size and morphology of the macroid and the selection of coating organisms the composition of the coating community is mainly a consequence of component growth rates in relation to turnover time and residence time long term studies are needed to assess the spatial and temporal resolution of present day encrusting communities across biogeographic provinces and shelf to slope regions

microbial deposits in the aftermath of the end permian mass extinction a diverging case from the mineral mountains utah usa the lower triassic mineral mountains area utah usa preserves diversified smithian and spathian reefs and bioaccumulations that contain fenestral microbialites and various benthic and pelagic organisms ecological and environmental changes during the early triassic are commonly assumed to be associated with numerous perturbations productivity changes acidifica tion redox changes hypercapnia eustatism and temperature changes post dating the permian triassic mass extinction new data acquired in the mineral mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures these data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the smithian early spathian the studied section records a large scale depositional sequence during the dienerian spathian interval during the transgression depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral microbial limestones shallow subtidal marine sponge microbial reefs to deep subtidal mud dominated limestones storm induced deposits microbialite sponge reefs and shallow subtidal deposits indicate the regression three microbialite associations occur in ascending order i a red beds microbialite association deposited in low energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure ii a smithian microbialite association formed in moderate to high energy tidal conditions where microbialites include stromatolites and associated carbonate grains oncoids ooids and peloids and iii a spathian microbialite association developed in low energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation hydrodynamics bathymetry and grain supply this study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions due to the presence of numerous metazoans associated with microbialites throughout the smithian increase in accommodation and spathian decrease in accommodation the commonly assumed anachronistic character of the early triassic microbialites and the traditional view of prolonged deleterious conditions during the early triassic time interval is questioned

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

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

early holocene sea level record from submerged fossil reefs on the southeast florida margin massive fossil outlier reefs are preserved seaward of the modern shelf and reef tract along the southeast florida margin thermal ionization mass spectrometric tims u th dating of 16 pristine acropora palmata and head corals cored from two transects document early holocene reef growth from 8 9 to 5 0 ka from approximately 13 5 to 7 m msl mean sea level these samples fill a gap in the florida keys sea level database and clarify the timing of a significant decrease in the rate of sea level rise a portion of this interval represented by a gap in the caribbean record of a palmata reefs has been interpreted as reef drowning during an inferred catastrophic sea level rise event of 45 mm yr or a 6 5 m rise between 7 6 and 7 2 ka attributed to west antarctic ice sheet instability and changes in marine ice extent between 8 and 7 ka continuous in situ shallow water reef growth in florida during this interval precludes the occurrence of exceedingly rapid rates of sea level rise and is consistent with the north atlantic record of deglaciation from 9 to 7 ka gaps in the early holocene sea level records for florida and the caribbean are thus more likely to be artifacts of limited sampling and or core coverage and not necessarily a result of drowning

impact of precipitation seasonality changes on isotopic signals in polar ice cores a multi model analysis abstract for central greenland water isotope analysis indicates a temperature difference of about 10 c since the last glacial maximum lgm however borehole thermometry and gas diffusion thermometry indicate that lgm surface temperatures were about 20 c colder than today two general circulation model studies have shown that changes in the seasonal precipitation timing in central greenland might have caused a warm bias in the lgm water isotope proxy temperatures and that this bias could explain the difference in the estimated paleotemperatures here we present an analysis of a number of atmospheric general circulation model simulations mostly done within the framework of the paleoclimate modeling intercomparison project the models suggest that the seasonal cycle of precipitation and surface mass balance over central greenland at the lgm might have been very different from today this supports the idea that the accuracy of the water isotope thermometry at the lgm in greenland might be compromised as a result of a modified surface mass balance seasonality however the models disagree on the amplitude and sign of the bias for central east antarctica a strong seasonality effect on the lgm isotopic signal is not simulated by any of the analyzed models for the mid holocene 6 kyr bp the models suggest relatively weak isotope paleothermometry biases linked to changes in the surface mass balance seasonality over both ice sheets

multi stage reef development on barbados during the last interglaciation by mapping the vertical and lateral distribution of reefal facies on the west and south coast of barbados we have produced a revised model of reef development for the last interglaciation we find that reef architecture around barbados has significant complexity including evidence for wave exposure related variations in reef geometry and at least 3 stages of reef development that were controlled by variations in sea level during the main stage of development an acropora palmata dominated reef crest aggraded 22 m in response to a minimum sea level rise of 20 m during stage 2 a sea cave was cut 3 4 m above the fossil reef crest possibly indicating that reef growth was terminated before sea level reached the highstand similar sequences elsewhere in the caribbean indicate that this early reef demise may not be a local phenomenon several reefs apparently stopped growing between 2 and 4 m and only in sheltered areas did they reach the highstand at 6 m as recorded by intertidal notches this pattern of reef demise has previously been related to rapid sea level rise at the end of the interglacial but stratigraphic data are equivocal the final stage of reef development on barbados occurred when sea level began to fall this fall was rapid leaving a thin but widespread veneer of reef crest deposits over the proximal reef front and discontinuous intertidal and shallow subtidal deposits capping the distal reef front although further dating is required to differentiate these three stages our only reliable u th tims date indicates that almost 50 of the exposed reef had accreted by 129 ka giving an estimate of 15 ka for the main aggradational stage furthermore reports of relict reef crests buried beneath these exposed deposits indicate that our revised model is incomplete and that earlier stages of reef growth occurred during the last interglaciation these earlier stages imply that sea level was at an interglacial level for as long as 20 ka supporting the devils hole record of interglacial duration unfortunately these estimates could not be verified directly because most of our u th data show major stratigraphic age reversals attributed to diagenesis this pattern is also evident in all other well dated reefal units in the caribbean and leads us to conclude that only diagenetically screened precise stratigraphically consistent coral dates can be used to directly estimate the duration of the last interglaciation

modern coral reefs of western atlantic new geological perspective contrary to popular belief of the late 1960s western atlantic holocene reefs have a long history and are not feeble novice nearshore veneers that barely survived postglacial temperatures rather the growth of these reefs kept pace with the rising seas of the holocene transgression and their development was for the most part controlled by offshore wave energy conditions and the relationship between changing sea levels and local shelf topography thus the outer shelves of the eastern caribbean in areas of high energy have relict reefs consisting predominantly of acropora palmata a robust shallow water coral the flooding of adjacent shelves during the postglacial transgression introduced stress conditions that terminated the growth of these reefs when about 7 000 r ago shelf water conditions improved scattered deeper water coral communities reestablished themselves on these stranded shelf edge reefs and fringing and bank barrier reefs began to flourish in shallow coastal areas at the same time the fragile and rapidly growing acropora cervicornis and other corals flourished at greater depths on the more protected shelves of the western caribbean and the gulf of mexico as a result late holocene buildups more than 30 m thick developed in those areas

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

mechanisms of spur and groove development and implications for reef platform evolution contemporary understanding of holocene coral reef development is based primarily on sub surface investigations of reef flat back reef and lagoon zones few studies of holocene fore reef development exist constituting a significant gap in our understanding of reef evolution the spur and groove sag zone is a distinct understudied feature of fore reefs worldwide we review sag development from previous studies and present 29 new sag short cores with 52 14c and u th ages from six fore reef regions of heron and one tree reefs the first such data from the great barrier reef remarkably we found that sags do not necessarily accrete in the same direction as their adjacent reef flat we identified three modes of reef flat and sag lateral accretion mode 1 lagoonward accretion of both the reef flat and sags mode 2 lagoonward accretion of the reef flat but seaward accretion of the sags mode 3 seaward accretion of both the reef flat and sags most sag zones five of the six studied accreted in a seaward direction modes 2 or 3 hydrodynamic conditions and local topography appear to be the dominant factors determining which mode occurs episodic high energy events are also likely to play an important role in sag formation our findings suggest that traditionally held models of reef evolution whereby lagoonal mature reefs fill developing into senile platform reefs may not hold rather reef flats may continue to expand seaward on their leeward and semi exposed fronts to increase in size while maintaining their lagoons

the performance of four spectral gcms in the southern hemisphere the january and july climatology and the semiannual wave abstract monthly mean sea level pressure slp data from four low resolution spectral gcms ecmwf t21 ccc ncar ccm and gfdl r15 are compared with observations for the southern hemisphere characteristics of the observed southern hemisphere january and july mean mass distribution are i high pressure areas in the subtropics ii a steep meridional gradient at midlatitudes iii a circumpolar trough in the antarctic iv a zonal asymmetry dominated by zonal wave 1 which has an almost complete phase reversal near 40 s v a double westerly wind maximum during the colder part of the year the ccc model reproduces some of these features the ecmwf model the ncar ccm and the gfdl models fail with respect to ii and iii all gcms underestimate the intensity of the stationary eddies none of the models considered reproduces the double westerly wind maximum another marked feature of the southern hemisphere circulation is the semiannual wave that dominates the annual curve of slp at mid and polar lat

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

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

evidence for smoothly falling sea level relative to north queensland australia during the past 6 000 yr post glacial sea level curves are expected to differ between different parts of the world as a result of global isostatic changes1 or perhaps other forms of geoidal changes2 i report here results from the inner part of the northern great barrier reef which seem to show a pattern of smoothly falling sea level during the past 6 000 yr the results are consistent with stratigraphical results from prograded mangrove coasts on the nearby north queensland mainland the region is remote from the tectonically active margin of the south west pacific ocean and the results contribute to the global data set relevant to isostatic changes being assembled by the international sea level project igcp project no 61 they also provide a baseline relevant to holocene coral reef growth in the inner great barrier reef

evidence for microbial life in synsedimentary cavities from 2 75 ga terrestrial environments fluviolacustrine sediments of the 2 75 ga hardey formation fortescue group australia preserve pendant columnar structures with stromatolitic lamination within synsedimentary cavities the millimeter sized finger like columns strongly resemble microbialites from modern basaltic caves and indicate the likely presence of microbial biofilms the ancient microbial columns are preserved by chert and locally occur as reworked clasts indicating a near depositional age for the structures sulfur isotopic analysis of pyrite in the columns and adjacent carbonaceous matrix yields 34scdt cdt canyon diablo troilite values between 8 5 and 19 showing significant fractionation characteristic of biological cycling of sulfur organic matter in cavity ceilings and shale matrix has 13cpdb pdb peedee belemnite values between 55 and 43 suggesting the presence of methanotrophs our results suggest that 2 75 ga terrestrial environments supported a microbial ecosystem including microbes that inhabited synsedimentary hollows extending the fossil record of coelobionts by 1 5 b y subsurface cavities represent a new habitable microenvironment for early life on earth and an analogue for ancient life on mars

holocene sea level changes and barrier reef formation on an oceanic island palau islands western pacific abstract internal facies and development of an oceanic island s barrier reef were revealed by the stratigraphical study of six drill cores in palau islands western pacific the holocene reef development is primarily constrained at its foundation by the antecedent topography of pleistocene substratum holocene barrier reef is an increment on the pleistocene barrier reef which had been subaerially exposed during glacial stages about 8300 cal year bp calibrated calendar years b p branching acropora facies initially formed a bank on the seaward side of a pleistocene limestone surface with a vertical accumulation rate as high as 30 m ka ka 1000 years after 7200 cal year bp when the sea level rise rate decreased reef crest facies caught up with the sea surface with an accumulation rate of less than 2 2 m ka corals found in the reef crest facies are similar to the present day reef crest corals dominated by acropora digitifera and a humilis after the reef crest was formed bioclastic sand and gravel facies prograded lagoonward of the reef crest and consisted mostly of reef derived materials the construction of patch reefs post dated the barrier reef formation the mature barrier reef provided calm conditions inside the lagoon which then led to the construction of patch reefs and fringing reefs sea level changes deduced from the accumulation curves show rapid rise before 7200 cal year bp followed by a slight rise of 4 m at its maximum this change in sea level rise rate inspired the change in reef facies from branching acropora to reef crest

coral reef records of quaternary changes in climate and sea level abstract although coral reefs have long been regarded as documenting climate change largely through its effects on sea level the temporal continuity and sensitivity to disturbance of their records appears to fall short of those provided by ice cores deep sea sediments and similar proxies the reasons for this anomaly relate principally to shifts in the loci of deposition the temporal windows in which accretion has been able to occur in a given place reflecting sea level at a particular height relative to the present datum are severely constrained where it has been possible coral growth and reef accretion have been and are sensitive to the signals provided by the environment in the form of changes in water depth temperature salinity nutrient supply turbidity and ph acidity concomitant with changes in sea level itself changes in these environmental parameters are directly or indirectly controlled by climate however because the responses of corals to stimuli are commonly site specific and the nature of the changes evoked so disparate it is likely that only major sea level cycles will provide evidence of a consistent global response in what has been a segmented record

relationship between species diversity and reef growth in the holocene at ishigaki island pacific ocean abstract coral reefs are influenced by global and local factors and living corals are currently faced with a potential loss of species diversity knowledge of the relationship between species diversity and reef growth during the holocene is important in terms of accurately reconstructing natural conditions prior to recent disturbances e g human impact pollution and over harvesting and in predicting future scenarios e g abrupt sea level rise coastal change and economic services this study seeks to characterize the holocene and present day reef at ishigaki island in the ryukyu islands focusing on spatial and temporal variations in the relationship between species diversity and reef growth the analysis is based on a drilling core obtained for the holocene reefs and quantitative species diversity data shannon and weaver s diversity index h obtained for the present day reef h was calculated for four coral communities surveyed at the ibaruma and fukido reefs the holocene sequence was dominated by the corymbose coral community e g acropora digitifera a hyacinthus goniastrea retiformis and platygyra ryukyuensis yielding an h value of 1 6 the encrusting coral community e g echinopora lamellose and pachyseris rugosa showed the highest diversity at the reef h 2 2 however this community was not one of the main reef builders during the holocene the massive coral community e g porites lutea and favites chinensis showed the lowest diversity h 0 6 it also made a minor contribution to reef building this community appeared in a shallow lagoon once sea level had stabilized the arborescent coral community e g a formosa and a nobilis was one of the main reef builders although yielding an h value of much less than 1 0 species diversity is not a prerequisite in terms of holocene reef growth thus a few species e g a digitifera a hyacinthus a formosa a nobilis g retiformis and p ryukyuensis from two main reef building communities are important for reef growth these corals that act as reefs are characterized by high growth rates having an upward reef growth rate of 2 12 m kyr 1 in the indo pacific during the holocene

bathymetric distribution of ichnocoenoses from recent subtropical algal nodules off fraser island eastern australia abstract coralline algal nodules living on the subtropical shelf off fraser island eastern australia from the inner to the uppermost outer shelf from 28 to 117 m water depth are pervasively bioeroded five ichnogenera have been identifed as nodule borers comprising one ichnotaxon attributed to bivalves gastrochaenolites one to sponges entobia and three to polychaetes and barnacles trypanites maeandropolydora rogerella microtraces comparable to those produced by fungi algae bacteria and or sponges are also present two ichnocoenoses have been recognised the shallow water ichnocoenosis egtm occurs at 60 m and shallower depths and includes all identified ichnogenera the deep water ichnocoenosis from 68 to 117 m is characterised by trypanites and the trypanites maeandropolydora network tm ichnocoenosis with a generally higher boring density than in shallower nodules decreasing size of algal nodules and reduced thickness of the coralline thalli probably explain the decrease in diversity of ichnogenera with depth as the larger bioeroders are excluded from the ichnoassemblages lower growth rates favour higher density of bioerosion in deeper algal nodules

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

facies pattern of western tethyan middle triassic black carbonates the example of gutenstein formation in silica nappe carpathians hungary and its correlation to formations of adjoining areas during the middle triassic a broad carbonate ramp developed at the western end of the tethys ocean in the early phase of the ramp evolution dark grey or black finely crystalline carbonates were deposited over a considerable part of the ramp in the aggtelek karst northeastern hungary carbonates of the aggtelek facies of the silica nappe are exposed in the latest early triassic bioturbated mudstones wackestones and occasionally packstones were formed in the outer ramp zone below the storm wave base during the early anisian oxygen depleted bottom conditions evolved gradual changes took place in the sedimentary features of mud dominated deposits that is attributed to increasing oxygen depletion as a result of density stratification of seawater in the deeper ramp areas remarkable ecological and sedimentary changes began with the colonisation by sponges and microbes in the aggtelek facies area that occurred coevally with a relative sea level fall the appearance of the foraminifer glomospira densa points to late early anisian age for these changes this unit is very variable in lithology and facies compared to the monotonous development of the lower units massive limestones and dolomites of microbial origin are ubiquitous additionally oolites with micro oncoids cross bedded and cross laminated bioclastic peloidal packstones grainstones thin bedded bioclastic wackestones mudstones laminated and brecciated dolomites with evaporite pseudomorphs and dolocretes are also present specific microfacies types i e automicrite varicoloured micrite microspar groundmass and cuneiform spongy microfabric preserved by cryptic microbial films are recognised and interpreted as sponge microbe mud mound deposits the microfacies of pilot samples from northern calcareous alps inner western carpathians and dinarides exhibit similar sedimentary features tectonic setting biota evolution after the end permian mass extinction relative sea level changes and hypersalinity may have been the most important controlling factors of the non skeletal carbonate factory which produced dark grey mud dominated deposits

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

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

high resolution regional climate model validation and permafrost simulation for the east european russian arctic a 15 year long 16 km horizontal resolution present day climate simulation has been conducted with the hirham4 regional climate model the model has been forced by the european centre for medium range weather forecasts reanalyses at the lateral boundary and over sea by sea surface temperature and sea ice concentrations from the same source the model domain is centered over the european part of arctic russia focusing on the usa river basin near the ural mountains it is demonstrated that with this fine mesh the model simulates the annual course and interannual variability in temperature and precipitation quite realistically furthermore the model captures the timing of permanent snow cover very accurately with less than 1 week discrepancy in both autumn and spring an interpretation of modeled subsurface layer temperatures in terms of mean annual temperature and a frost index reveals that the model captures present day regional permafrost patterns to a high degree of accuracy

biogeography of holocene coral species in the western indian ocean abstract understanding the relationship between coral biogeography and reef development is a key topic in sedimentology and paleoecology although the knowledge of coral reef growth and internal facies patterns during the holocene has increased since the 1970s the biogeography of holocene coral species in the indo pacific regions remains poorly constrained in this study we examined quantitative records of coral species based on data from five cores retrieved from two holocene reefs in the western indian ocean la pointe au sable reef on mauritius island and toliara reef on madagascar our results indicate that the dominant reef building corals on both reefs were isopora palifera acropora robusta abrotanoides complex some corals e g the a robusta abrotanoides complex and acropora digitifera from 6 ka were found in mauritius whereas these were not identified in the cores from madagascar before 1 5 1 ka this delay may have been controlled by ocean currents and or the competency period of the coral larvae a comparison of these coral assemblages with those in other regions seychelles mayotte ryukyu islands palau islands papua new guinea the great barrier reef new caledonia and vanuatu showed that i palifera was common in all of the studied regions whereas goniastrea retiformis probably migrated recently to mauritius and madagascar in response to prevailing surface ocean currents including the south equatorial current and the agulhas current one explanation for the late arrival of g retiformis to the study sites could be that the competency period of g retiformis larvae is shorter than that of i palifera moreover our quantitative analysis suggests that a given population size during the holocene may have contributed to the abundance of species in modern reefs this study emphasizes the need for further quantitative research on holocene coral species in other regions to better understand the temporal and spatial patterns of coral biogeography

styles of reef accretion along a steep shelf edge reef st croix u s virgin islands abstract seven horizontal cores were taken from the reef dominated margins of salt river submarine canyon st croix u s virgin islands at water depths of 14 30 m the pattern of east to west sediment transport in the area exerts a major control on present day reef morphology as well as accretionary styles recorded in the cores coral growth is inhibited by sedimentation on much of the eastern heavily stressed margin and slopes are gentle the regular pattern of alternating reef growth and sedimentary infill in the eastern cores reflects this highly variable environment on the west wall away from the source of incoming bedload sediment coral cover is much greater and a vertical reef wall forms the canyon margin slumping of the steep reef face has caused numerous repetitions of section and in some instances accretion rates higher than the growth rates of calcifying organisms occupying the present or past reef surface this slumping process along with the highly dissected character of the reef results in larger sections of reef framework separated by open or sediment filled vugs and caverns 14c dates indicate that this complex constructional history has resulted in at least 24 m of lateral accretion during holocene time average lateral accretion rates in the cores varied from 0 84 to 2 55 m 1 000 yr with the highest rate occurring in the core from deepest water intervals of rapid accretion within the cores were not generally related to patterns of in situ coral growth but rather with intervals of allochthonous material slumped from the shallower portions of the reef complex the character of the cores illustrates the potential importance of detrital material and late stage reworking in the accretion of shelf edge reefs the high rates of accretion at depth highlight potential problems with reef models based on net accretion paralleling the abilities of the present day surface organisms to produce calcium carbonate

thrombolitic clots dominated by filamentous cyanobacteria and crusts of radio fibrous calcite in the furongian changshan formation north china abstract as a variety of non laminated microbial carbonate or calcified microbialite thrombolites commonly comprise diffusely clotted micrites as their basic structural unit the current study is aimed at discussing the composition and forming mechanism of thrombolitic clots which most likely represent the product formed by calcification of extracellular polymeric substances it provides instances of sophisticated calcification of thrombolite forming microbial mat in the calcite sea that is expressed by the distinctive composition of thrombolites thrombolites in the top part of the furongian changshan formation are chiefly composed of chaotic large and small micritic clots as observed under low microscopic resolution however high density preservation of fossils of calcified sheaths of cyanobacteria is observed within most of the clots under higher resolution their distribution as groups or colonies suggests that they can be interpreted as subtifloria of girvanella group these microbial components together with the enigmatic epiphyton reflect fundamental features of microbial growth and suggest a microbial origin of these clots the general abundance of these calcified fossils within individual clots offers an instance for the formation of thrombolitic clots from sophisticated calcification of photosynthetic biofilms it refutes the traditional view that both the thrombolites and the oncoids develop by accretion of microbial mats dominated by coccoid cyanobacteria aggregation of several individual clots to form millimetric agglutinated clots shows that their formation is genetically related to sophisticated calcification of extracellular polymeric substances making up multiple biofilms within relatively thick microbial mats this inference is strengthened by their encrustation by radio fibrous calcite which leads to enlargement of the clots besides the clots benthic ooids pyrite and dolomite also developed in the current thrombolites which are largely attributed to microbially mediated organomineralization

fringing reef growth and morphology a review abstract fringing reefs are generally not simple veneers of coral growth along tropical shorelines extensive research over the past few decades based on radiocarbon dating of holocene reef deposits has indicated that they can develop in a complex variety of ways even though the surface morphology may appear relatively simple the principal factor that appears to determine the growth and morphology of fringing reefs is the available accommodation space sea level fluctuations are important primarily because the sea surface determines the absolute accommodation space for a given reef this means that a reef established during a period of sea level rise will be able to accrete vertically as space is created above it if however the reef establishes at or grows to the sea surface thereby occupying all the available accommodation space it can no longer accrete vertically and begins to build laterally the morphology and chronostratigraphy of a range of holocene fringing reefs are described on the basis of which six fringing reef growth models are identified in model a the fringing reef is established at depth and primarily accretes vertically towards the sea surface reef growth in model b initiates at sea level and due to the lack of vertical accommodation space grows laterally model c has a similar morphology to model b however the reef progrades over a non reefal sediment wedge episodic lateral and vertical growth occurs in model d with a stepwise progradation of the reef front the remaining models are characterised by seaward reef framework behind which unconsolidated sediments accumulate in model e reef crest growth forms a barrier leading to the development of a backreef lagoon model f has a similar morphology to model e except that the reef crest is formed by hurricane rubble accumulation rather than framework accretion and is periodically reworked

postglacial growth history of a french polynesian barrier reef tract tahiti central pacific bthe internal structure and growth pattern of tahiti reefs over the last 14 ka is reconstructed using sedimentological morphological and palaeobiological data coupled with radiometric dates in drill cores through the modern barrier reef flooding of the volcaniclastic deposits or the karst surface of a pleistocene reef started at 14 ka bp and coral growth began shortly after inundation the sequence in the tahiti barrier reef edge has formed predominantly through long term keep up growth controlled by stable environmental conditions while the adjacent backreef deposits did not start to accumulate before sea level stabilization around 6 ka the dominance of porites communities and the coeval occurrence of branching gracile lithophyllum in the lowermost part of the postglacial reef sequence 14 11 ka suggest the prevalence of uniformly moderate to low energy conditions and or growth in slightly deeper waters all over the drflled area during the early reef stages during the last 11 ka the reef frameworks developed in a high energy environment at maximum water depths of 5 6 m and were dominated by an acropora robusta danaihydrolithon onkodes association the local interlayering of other coralgal assemblages dominated by tabular acropora or domal porites reflects distinct diversification stages resulting either from the palaeotopographic control of the substrate or from slight and episodic environmental changes

early marine lithification and hardground development on a miocene ramp maiella italy key surfaces to track changes in trophic resources in nontropical carbonate settings abstract phosphatic and carbonate hardgrounds occur in a lower miocene nontropical carbonate succession in the maiella carbonate platform margin located in the central apennines multiple diagenetic events occurred at or near the sea floor before the deposition of the overlying sediment and included precipitation of inclusion rich calcite micrite iron oxides and phosphates later diagenetic features are limited to chemical compaction and precipitation of clear calcite cement we relate the development of these features to a two step model involving progressive intensification of upwelling on this carbonate margin which was triggered by regional changes in water circulation and modulated by sea level changes leading initially to precipitation of inclusion rich calcite with an increase in trophic resources related to the paleoceanographic conditions on the ramp increased flux of organic matter to the sea floor led to temporary formation of microbial biofilms these conditions were associated with extensive precipitation of micrite and phosphate microspherules in the uppermost sediment the lack of sedimentation provides the precondition to accumulate and preserve evidence for organic matter utilization in the uppermost sediment layer our study suggests that hardgrounds in nontropical carbonates might be used as indicators of circulation changes and can provide a useful link to major environmental changes in the ocean margin environment the occurrence of microbial micrite and phosphate microspherules precipitated in the absence of sedimentation near the sea floor as a response to higher nutrient supply provides a new and important criterion to differentiate nontropical carbonate facies deposited under the influence of higher nutrient supplies rather than temperature alone furthermore our study shows that local depletion in 13c at a key stratigraphic surface does not necessarily reflect meteoric exposure but may be related to microbial activity at the sea floor

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

inferred syngenetic textural evolution in holocene cryptic reefal microbialites heron reef great barrier reef australia cryptic microbialites in the heron reef framework occur as crusts of fingerlike microcolumns or branching dendrolites rarely more than 1 cm long microstructure of the most recently growing microbialite surfaces consists of coalesced 3 m scalenohedra that are indistinguishable from previously described mg calcite abiotic cement the transformation from submicrometer anhedral crystallites to 3 m scalenohedra is inferred to have occurred only during active microbialite accretion beneath a biofilm this syngenetic change from primary biologically induced microstructures to microstructures that are indistinguishable from abiotic cement has important implications for the recognition and interpretation of early marine microcrystalline carbonates and cements

origins and development of holocene coral reefs a revisited model based on reef boreholes in the seychelles indian ocean until recently concepts of coral reef growth and accumulation have been predominantly based on a darwinian model in this the upwards and outwards growth of a reef core a coral framework takes place over a foreslope consisting of reef talus with the simultaneous filling of the back reef lagoon by reef derived debris the principal adaptations of this pattern relate to the influence of relative changes in sea level and commonly ignore oceanographic factors such as storm frequency and severity boreholes through the outer edge of a fringing reef in the seychelles western indian ocean reveal a record of holocene sediment accumulation first established approximately 8 ka ago faunal and floral associations show that growth of this body began in relatively deep water but that this shallowed to 5 m within 1 ka subsequent accumulation was of keep up style but as the rate of sea level rise slowed shoaling became more frequent and aggradation was limited by reducing accommodation space constructional facies are characterised either by massive corals including leptastrea porites and faviids or by branching corals typically acropora of the danai robusta group coral surfaces may be encrusted by red algae foraminifera and vermetids and are commonly bored by filamentous algae clionids and molluscs however detrital facies are volumetrically dominant and the paucity of a constructional framework requires a re evaluation of models of reef accretion new models relate the geometry of accretion to the interplay between extreme storm events and fairweather hydrodynamic conditions these suggest that a contiguous framework forms in areas of moderate fairweather energy without extreme storm events severe storms destroy the continuity of reef structures and generate increasing volumes of coarse detritus low storm severity coupled with low fairweather hydrodynamic energy may promote the accumulation of fine grained reef derived sediments that inhibit framework growth while ecology reflects year by year sea conditions lithology and structure are controlled by exceptional storms with the effects of changing sea level superimposed

sequence stratigraphy of a late devonian ramp situated reef system in the western canada sedimentary basin dynamic responses to sea level change and regressive reef development the alexandra formation located in the northwest territories of canada is formed of a late devonian frasnian reef system that developed on a gently sloping epicontinental ramp in the western canada sedimentary basin high resolution sequence stratigraphic analysis of its deposits delineates two reef complexes that are separated by a type i sequence boundary the second reef complex developed on the outer ramp basinward of the first after sea level fell 17 m stratigraphic complexity of the second reef complex was a result of its initiation during forced regression and its development through an entire cycle of sea level rise followed by sea level fall its highstand systems tract was not characterized by high rates of carbonate production or sediment shedding rather these features took place as sea level fell after its highstand systems tract the sequence stratigraphic framework of this regressive reef system highlights a number of depositional parameters that differ from high relief shelf situated reef systems with steep narrow margins these have implications for understanding the controls on the development of ramp situated reef systems and the nature of reef systems with gently sloping profiles this study demonstrates that the development of stromatoporoid reef systems may be far more complex than generally realized and that high resolution sequence stratigraphy may provide the tools for better understanding of complex often enigmatic aspects of these systems

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

significance of shallow core transects for reef models and sea level curves heron reef great barrier reef a sequence of shallow reef cores from heron reef great barrier reef provides new insights into holocene reef growth models isochron analysis of a leeward core transect suggests that the north western end of heron reef reached current sea level by ca 6 5 kyr bp and then prograded leeward at a rate of ca 19 6 m kyr between 5 1 kyr and 4 1 kyr bp pre 1950 to the present reef margin a single short core on the opposing margin of the reef is consistent with greater and more recent progradation there further to the east one windward core reached modern sea level by ca 6 3 kyr bp suggesting near keep up behaviour at that location but the opposing leeward margin behind the lagoon reached sea level much more recently hence heron reef exhibited significantly different reef growth behaviour on different parts of the same margin mean reef accretion rates calculated from within 20 m of one another in the leeward core transect varied between ca 2 9 m and 4 7 m kyr depending on relative position in the prograding wedge these cores serve as a warning regarding the use of isolated cores to inform reef growth rates because apparent aggradation at any given location on a reef varies depending on its location relative to a prograding margin only transects of closely spaced cores can document reef behaviour adequately so as to inform reef growth models and sea level curves the cores also emphasize potential problems in u series dates for corals within a shallow ca 1 5 m zone beneath the reef flat apparent age inversions restricted to that active diagenetic zone may reflect remobilization and concentration of th in irregularly distributed microbialites or biofilms that were missed during sample vetting importantly the th containing contaminant causes ages to appear too old rather than too young as would be expected from younger cement

microbial domes and megaoncoids in miocene reefs in the mahakam delta in east kalimantan indonesia abstract coral patch reefs in the miocene mahakam delta in east kalimantan borneo indonesia developed in shallow marine turbid waters these reefs grew in delta front to prodelta environments under fluctuating siliciclastic input langhian patch reefs are well exposed in limestone quarries of the air putih area near the city of samarinda and include two different types of microbial carbonates in two sections 2 km apart in the northern section microbialites occur as low relief domes up to 2 m wide and 0 5 m high the domes show internal lamination and coralline algae and encrusting foraminifers interlayered with microbial micrite they developed around large coral fragments at the transition from reef deposits to fine grained siliciclastics microbialites in the southern section formed decimetre to metre scale nodules here termed megaoncoids around nuclei of large coral fragments microbial micrite with laminated to digitate fabrics intergrew with coralline algae and encrusting foraminifers to form the thick covers of megaoncoids small nodules were bound together in larger ones which are usually strongly asymmetric internally megaoncoids accumulated in a carbonate breccia laterally changing into coral boundstones in both sections microbialites grew on the flanks of shallow water low relief patch reefs in poorly illuminated low energy conditions flat domed microbialites formed on a nearly horizontal stable seafloor seawards of the patch reef the megaoncoids in the southern section formed as a result of downslope displacement of coral fragments coated by microbialite coralline algal encrusting foraminifer crusts the slope of the patch reef s flank favoured the falling and rolling of encrusted corals with the continued growth of microbial crusts on all sides of nodules in contrast to quaternary and recent occurrences of microbialites in indo pacific and caribbean reefs the samarinda microbialites are not components of the reef framework nor formed in deep water instead they developed in shallow turbid waters of the miocene mahakam delta in periods of arrested siliciclastic input

freshwater phytoherm reefs the role of biofilms and their bearing on marine reef cementation abstract bioconstructions in carbonate rich freshwater environments generally lead to the development of thick autochthonous tufa deposits in rivers systems these large plant dominated freshwater reef frameworks phytoherms are capable of damming the water courses to produce chains of lakes the resulting phytoherms profoundly modify both local environment and sedimentation patterns in their vicinity and provide a wide range of niches for biota subaqueous fringe cements coat all exposed surfaces they bind the ephemeral plant frameworks providing a cement framework and give rigidity to the bioconstructions peloids are intimately associated with the development of these cements and frequently infil intra reef and framework cavities evidence is presented to suggest that both micritic fringe cements and peloids are the product of biological mediation associated with a procaryote microphyte biofilm and the presence of organic detritus the bladed low magnesium calcite fringes which develop subsequently on the micrite fringes and peloids are possibly slower formed inorganic precipitates the close morphological similarities between phytoherm fringe cements and peloids and their marine reef counterparts are considered to be more than coincidental it is argued that procaryote microphyte biofilms are also responsible for micritic precipitates in the shallow photic marine realm with bacterial films possibly carrying the process deep into unlit reef cavities and conduits and deep water lithoherms

are catch up reefs an artefact of coring drill cores through modern coral reefs commonly show a time lag in reef initiation followed by a phase of rapid accretion to sea level from submerged foundations the so called catch up response but because of the difficulty of drilling in these environments core distribution is usually restricted to accessible areas that may not fully represent reef history especially if the reef initiated in patches or developed with a prograde or retrograde geometry as a consequence core data have the potential to give a misleading impression of reef development particularly with respect to the timing of initiation and response to sea level rise here we use computer models to simulate keep up reef development and from them quantify variations in the timing of reef initiation and accretion rate using mock cores taken through the completed simulations the results demonstrate that cores consistently underestimate the timing of reef initiation and overestimate the reef accretion rate so that statistically a core through a keep up reef will most likely produce a catch up pattern an initiation lag followed by a phase of rapid accretion to sea level this implies that catch up signatures may be an artefact of coring and that keep up reefs are significantly more common than previous core studies claim

alternation of microbial mounds and ooid shoals middle jurasssic morocco response to paleoenvironmental changes abstract the occurrence of neritic microbial carbonates is often related to ecological refuges where grazers and other competitors are reduced by environmental conditions or to post extinction events e g in the late devonian early triassic here we present evidence for middle jurassic bajocian microbial mounds formed in the normal marine shallow neritic setting of an inner ramp system from the high atlas of morocco the microbial mounds are embedded in cross bedded oolitic facies individual mounds show low relief domal geometries up to 3 m high and 4 5 m across but occasionally a second generation of mounds exhibits tabular geometries

diversity and factors controlling widespread occurrence of syn rift ladinian microbialites in the western tethys triassic catalan basin ne spain abstract the fault block carbonate ramps of the ladinian middle triassic catalan basin hosted a wide variety of microbial deposits which formed during a syn rift stage stratigraphical and sedimentological analyses of these microbialites allow us to reconstruct two depositional models for such microbial deposits moreover new insights into the interplay between the intrinsic and extrinsic factors that controlled the widespread development of these microbialites are provided stromatolites ooidal muddy microbial laminites and thrombolites were analyzed on the basis of their geometry lamination and textural attributes these microbialites are distributed over two transgressive regressive sequences and coexisted during the fassanian early ladinian regressive stage later stromatolites and ooidal muddy microbial laminites developed during the longobardian late ladinian transgressive stage three types of lamina couplets reflect distinct accretion processes linked to water chemistry sediment supply and hydrodynamic conditions thrombolite textures were produced by accretionary binding and encrusting processes microbially mediated and pervasive cementation the widespread occurrence of microbial deposits is explained as a consequence of a biogeochemical cascade of events e g anoxic dysoxic seawater conditions volcanic activity upwelling of alkaline waters nutrient concentrations and microbial blooms which promoted favorable conditions for microbial growth in the tethys during the ladinian furthermore in the catalan basin syn rift fault induced subsidence and local water energy gradients exerted an essential role in the distribution of the three types of microbialites through space and time thrombolites were prone to grow in the hanging wall block of a half graben subtidal conditions whereas stromatolites and ooidal muddy microbial laminites flourished preferably in a foot wall block setting intertidal shallow subtidal conditions however the fact that thrombolites exhibit abundant botryoidal and isopachous fibrous marine cements corrosion and significant microbial evidence allow us to hypothesize about the relationship between thrombolite occurrence and hydrothermal fault controlled fluid circulation during the triassic rifting the two depositional models here proposed constitute a step forward the understanding of the platform to basin microbialite heterogeneity during the ladinian furthermore this work sheds new light on the mechanisms that likely promoted microbialite development during a period of major ecological restructuration and complex oceanographic conditions

anatomy of a fringing reef around grand cayman storm rubble not coral framework abstract our fair weather perception of modern reefs has led to the implicit assumption that their development is controlled by processes that govern the siting of in place coral growth yet more ephemeral processes such as storms and hurricanes assume much greater importance over longer time scales because few reefs escape their influence to discover the importance of storms on reef development we analyze the zonation anatomy and architecture of a fringing reef complex around grand cayman we find that the surface zonation of in place corals is merely a facade and the reef core is in fact composed of meter thick layers of coral cobble rudstone capped by crusts of coralline algae the large size and abraded condition of the rudstone clasts shows that these layers are not the product of f ir weather processes but the result of destruction and deposition during hurricanes as hurricane waves cross coral mantled zones of the inner shelf they destroy live coral stands and deposit the clasts as a rubble layer covering the entire reef complex between storms this rubble foundation is stabilized by coralline algal crusts and recolonized by rapidly growing corals leading eventually to full reef regeneration before the next hurricane this cyclic pattern of destruction and regeneration consequently produces a fringing reef complex with a core composed of hurricane generated rubble not coral framework as previously assumed in addition to explaining reef anatomy hurricane control also explains the variation in reef architecture along shelf uniform reef location across shelf and reef absence along certain shelf sections as hurricane waves cross a mid shelf scarp they start to break and destroy coral growth over most of the inner shelf coral rubble generated by these waves is deposited 350 50 m from the mid shelf scarp on margins exposed to the largest waves but only 250 50 m on semi protected margins that experience smaller fetch limited waves in areas where the width of the inner shelf is 250 m hurricane waves throw rubble ashore and a fringing reef does not develop during sea level rise this influence of shelf width on rubble deposition controls the timing of reef nitiation and that in turn controls reef architecture reefs initiate first on low gradient coasts with wide shelves and gradually extend around higher gradient coasts as sea level rises and shelf width increases thus older reefs are located farther offshore front deeper lagoons and have thicker and narrower profiles than younger reefs

the co occurence of trypanites and glossifungites substrate controlled trace fossil assemblages in a triassic mixed siliciclastic carbonate depositional system baldonnel formation williston lake b c canada abstract detailed outcrop analysis of an upper triassic shallow marine mixed siliciclastic carbonate ramp succession in northwestern canada reveals numerous disconformities that are characterized by substrate controlled trace fossil assemblages although glossifungites assemblages and to a lesser extent trypanites assemblages are common in the upper carnian baldonnel formation in several horizons a pattern of paired trypanites glossifungites demarcated discontinuity surfaces occurs these paired surfaces occur in the same overall environmental setting and are interpreted to have the same general stratigraphic implications in each case the trypanites surfaces invariably occur lower in the section they penetrate into sandy bioclastic limestone and are infilled and overlain by a coarse grained detrital lag their development indicates early cementation in a coastal setting the trypanites surfaces form coplanar maximum regressive surfaces and transgressive surfaces of erosion and are correlatable on a regional scale the lags are overlain in turn by laminated calcareous siltstone denoting offshore deposition and bioclastic sandstone a return to shoreface depositional conditions the siltstone sandstone contacts are characterized by low diversity glossifungites assemblages which are interpreted as an amalgamated succession of storm induced wave ravinement surfaces emplaced in front of a rapidly prograding shoreface paired trypanites glossifungites surfaces in the baldonnel formation reflect fluctuations in relative sea level and sediment input in an overall low accommodation mixed siliciclastic carbonate ramp setting

lagoon shelf sediment exchange by storms evidence from foraminiferal assemblages east coast of grand cayman british west indies abstract the abundance and size distribution of ecologically diagnostic foraminiferal species are ideal tracers of sediment transportation and storm processes on the windward shelf of grand cayman during storm peak sediment in the lagoon and fore reef is suspended by large storm waves sediments of sand size and finer including forereef foraminifera species are moved shoreward by wind driven currents and deposited in a blanket behind the reef the fore reef foraminiferal assemblage is winnowed and the mean and median sizes of amphistegina gibbosa progressively decrease from the shelf edge into the inner lagoon as the storm wanes water piled in the lagoon drains via channels and sediment is transported offshore consequently lagoonal sediment that includes lagoonal foraminiferal t sts is carried out of the lagoon and deposited on the fore reef terrace and down the shelf escarpment this process produces winnowed lagoonal sediments because suspended fine sediments are preferentially transported during the long inter storm periods tranquil conditions are once again established and sediment exchange between the lagoon and on the fore reef terrace ceases during this time lagoonal organisms once again colonize the lagoon and bioturbation causes mixing of surface and subsurface sediments

carbonate and silicate biomineralization in a hypersaline microbial mat mesaieed sabkha qatar roles of bacteria extracellular polymeric substances and viruses in a modern peritidal microbial mat from qatar both biomediated carbonates and mg rich clay minerals palygorskite were identified the mat ca 5 cm thick shows a clear lamination reflecting different microbial communities the initial precipitates within the top millimetres of the mat are composed of ca mg si al s amorphous nanoparticles few tens of nanometres that replace the ultrastructure of extracellular polymeric substances the extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation successively crystallites of palygorskite fibres associated with carbonate nanocrystals develop commonly surrounding bacterial bodies micron sized crystals of low mg calcite are the most common precipitates together with subordinate aragonite very high mg calcite dolomite and ankerite pyrite nanocrystals and framboids are present in the deeper layers of the mat calcite crystallites form conical structures circular to triangular hexagonal in cross section evolving to crystals with rhombohedral terminations some crystallite bundles develop into dumb bell and stellate forms spheroidal organo mineral structures are also common within the mat nanospheres a few tens of nanometres in diameter occur attached to coccoid bacteria and within their cells these are interpreted as permineralized viruses and could be significant as nuclei for crystallite crystal precipitation microspheres 1 to 10 m in diameter result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves carbonates and clay minerals are commonly aggregated to form peloids tens of microns in size surrounded by residual organic matter magnesium silicate and carbonate precipitation are likely to have been driven by ph saturation index redox changes within the mat related to microenvironmental chemical changes induced by the microbes extracellular polymeric substances viruses and their degradation

anatomy of a modern coral reef flat a recorder of storms and uplift in the late holocene abstract cores from kabira reef ishigaki island southwest japan reveal the internal structure and temporal changes in sedimentary process of a complete coral reef flat the reef crest caught up with sea level at about 4000 yr bp since then it expanded oceanward and the reef pavement has grown landward the backreef structure is composed of bioclasts derived from the reef framework of all the bioclasts corals and coralline algae are most abundant coral fragments coarser than 3 0 o have dominated the backreef sediments since about 2000 yr bp benthic foraminiferal tests first occurred at about 4000 yr bp and their abundance increased significantly starting around 2000 yr bp shallowing of the reef crest is also indicated by the presence of the shallow water benthic foraminifera baculogypsina sphaerulata tests after 2000 yr bp the date 2000 yr bp is coincident with tectonic uplift at kabira reef kawana 1989 we consider this uplift to have caused a relative sea level fall that aided the deposition of coral fragments transported from the reef pavement by storms the relative sea level fall also caused subaerial exposure of the reef crest during low tides and the transition of reef building organisms from corals to shallow water species of benthic foraminifera resulting in a change noticeable in the constituents of backreef sediments the results of this study suggest that the coral reef flat and especially the backreef can be a faithful recorder of relative sea level changes

microscale observations of sulfate reduction correlation of microbial activity with lithified micritic laminae in modern marine stromatolites we report for the first time micrometer scale correlation of geologic and microbial processes in modern marine stromatolites precipitation of micritic laminae in these stromatolites was studied by comparing microstructure as observed in petrographic thin sections with microbial sulfatereduction activity two dimensional mapping of sulfate reduction rates was implemented by incubating a vertical section of a stromatolite face on silver foil coated with 35 so 4 2 our results show that sulfate reduction activity is high in zones of caco 3 precipitation and indicate that microbial activity produces lithified micritic laminae near the surface of the stromatolites similarities with micritic laminae in ancient stromatolites suggest that sulfate reduction may also have been an important mechanism of carbonate precipitation in these fossilized structures

developing carbonate platforms southern gulf of suez northern red sea abstract the ashrafi reef complex represents two small 8 10 2 km carbonate platforms and associated shoals located along the western side of the jubal strait at the gulf of suez s southern end these features are developing in an active marine environment that is operating within the geologic constraints of a tectonic trough characterized by mountainous fault controlled margins origin of the platforms is uncertain but the present morphology appears to be a product of the dynamic marine setting in which they are developing tidal flow between the red sea and the gulf results in strong rectilinear currents commonly 50 cm s 1 of the current velocities 5 10 cm s 1 can be attributed to surface currents driven by a regional unidirectional wind that blows from north to south down the axis of the gulf throughout the year side scan sonar data coupled with echo sounder profiles direct observations via scuba and bottom sampling indicate that the ashrafi platforms are actively building northward by windward reef accretion and extending to the south by sediment transport and accumulation the drumstick shape is a product of wave induced reef development along the northern margin and sediment distribution forced by strong tidal currents which coupled with unidirectional wind drift favors net transport to the south small reefs and hard grounds along the downdrift platform flanks assume a linearity consistent with the long axis of the platform the intensely mounded sediment of the platform flanks suggests that bioejection of particles in the mound building process together with a strong flow field is a downdrift sediment transport agent although the ambient salinity of surrounding gulf water is 41 platform top water masses were measured at 47 a lack of significant coral growth on the shallow platform top and the almost total exclusion of sediment producing calcareous green algae may be related to these hypersaline conditions sediments for the platform flanks are largely provided by the breakdown of platform margin reef communities and in situ organisms largely foraminifera

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

biofilm architecture of phanerozoic cryptic carbonate marine veneers thin 150 m micritic veneers lining crypts in paleozoic and mesozoic reef microbial and bioclastic carbonates have the dimensions and architecture of modern uncalcified bacterial biofilm morphologic attributes include rounded aggregate nanofabric internal channels external towers mushrooms and plumes all can be interpreted as characteristics of attached bacterial communities i e aggregates as microcolonies originally embedded in a matrix of extracellular polymeric substances channels as water conduits and or uncolonized nutrient poor spaces external protuberances as localized growths and plumes as surface streamers cryptic habitat favored pristine biofilm preservation by precluding disturbance and overgrowth and suggests aphotic and anoxic conditions these examples provide diagnostic morphologic criteria for wider recognition of biofilm in phanerozoic and older carbonates

episodic reef growth in the granitic seychelles during the last interglacial implications for polar ice sheet dynamics abstract we present a detailed taxonomic and lithologic analysis of fossil reefs in the granitic seychelles to improve constraints on global mean sea level behavior during the last interglacial sea level highstand 129 000 116 000 years ago in particular we have assessed the coralgal reef outcrops for any sedimentalogic evidence of sub orbital sea level oscillations that may have occurred during this warm interglacial period at the outcrop scale we observe at least three distinct episodes of reef growth punctuated by two discontinuities that typically manifest as coral rubble layers or extensive lateral encrustations of the hydrozoan coral millepora exaesa hiatuses in reef growth at other sites around the world have been interpreted as relative sea level falls and or environmental disturbances we have tested the hypothesis that these discontinuities that we refer to as disturbance horizons are related to ephemeral drops in sea level that have been inferred at last interglacial reef sites from other sites around the globe at two sites there is sedimentological evidence in the form of extensive dissolution and freshwater cements associated with the disturbance horizons that would require subaerial exposure followed by marine inundation at the remaining sites evidence is consistent with but not necessarily indicative of an ephemeral drop in sea level to establish if these disturbance horizons are coeval between the outcrops and if they are local or global features requires high precision dating of the disturbance horizons along with a critical analysis of sedimentary and chronological evidence from other sites around the globe if the disturbance horizons observed in the seychelles represent transient sea level falls or still stands during the last interglacial this would imply a dynamic behavior of the polar ice sheets during this past warm period

holocene reef development along the northeastern st croix shelf buck island u s virgin islands abstract eight cores were recovered from buck island underwater national monument u s virgin islands facies were defined based on recovered coral species fabrics observed in core slabs and thin sections and detailed notes on drilling character thirty six radiometric dates constrained the timing of reef accretion together these data provide a detailed history of reef development under varying regimes of sea level rise and physical oceanography holocene reefs around buck island initiated atop a broad antecedent bench at 13 16 meters below present sea level shelf flooding near buck island occurred as early as 9 500 years ago calbp but preserved reefs lagged by as much as 1 800 years earliest reef development was dominated by branching acropora palmata near the shelf edge and massive corals closer to buck island by 7 200 calbp a palmata apparently declined near the platform margin and was absent until ca 5 200 calbp throughout the study area over time the reefs closer to buck island built upward ca 16 m and seaward ca 50 m as the rate of sea level rise slowed and carbonate production increasingly exceeded the accommodation space that was being created reef topography and zonation became progressively more distinct with a palmata dominating the shallow reef crest branching coral apparently disappeared again between ca 3 030 and 2 005 calbp for reasons that are not clear this and the previous decline of a palmata mimic patterns seen around st croix and throughout the caribbean by 1 000 calbp the reefs close to buck island had largely assumed their present character and continued to track slowly rising sea level until the present around 1 200 calbp vertical accretion along buck island bar apparently ceased paradoxically the surface of this outer reef has historically been dominated by large stands of a palmata since the area was first described but rapid coral growth has not resulted in preservation of this species over the last millennium modern community structure mimics facies patterns seen in cores over the past 7 700 years the southern reef crest appears to have remained slightly shallower than its northern counterpart a condition that persists today observations after hurricane hugo in 1989 suggest that this difference in elevation is related to the piling up of debris on the broader southern reef crest by high waves from storms passing south of st croix also facies along the southern reef are more variable in species composition than their northern counterparts a condition that is exhibited by the modern reef community coral abundance and diversity in the cores total coral 20 30 dominated by a palmata are comparable to the community structure present in the late 1970s bythell et al 1993 hubbard et al 1993 in contrast fossil coral abundance and diversity are consistently higher than what was measured in the 1980s and early 1990s total coral 7 14 a palmata 2 after the onset of white band disease a putative pathogen which has recently decimated branching acroporids throughout the region the dominance of branching a palmata in the cores would seemingly reflect an absence of disease or other factors that would discourage its continued abundance in apparent contrast two lengthy gaps in the a palmata record reflect previous disappearances that roughly correspond to similar lapses elsewhere in the caribbean thus the spatial persistence of a species in the fossil record cannot necessarily be equated with its temporal continuity comparisons between changes in modern reefs on a time scale of decades and their fossil forebears must be made with great care understanding the role of short term changes and how they are reflected in the preserved record is thus critical to relating the late holocene a palmata gaps to the recent decline of the species this has important implications for our understanding of how preserved community structure relates to what actually existed in the past and could limit our ability to use the recent geologic record as a proxy to short term future changes in coral reefs

age accuracy and resolution of quaternary corals used as proxies for sea level the accuracy of global eustatic sea level curves measured from raised quaternary reefs using radiometric ages of corals at known heights may be limited by time averaging which affects the variation in coral age at a given height time averaging was assessed in uplifted holocene reef sequences from the huon peninsula papua new guinea using radiocarbon dating of coral skeletons in both horizontal transects and vertical sequences calibrated 2 sigma age ranges varied from 800 to 1060 years along horizontal transects but weighted mean ages calculated from 15 18 dates per horizon were accurate to a resolution within 154 214 yr approximately 40 of the variability in age estimate resulted from internal variability inherent to c 14 estimates and 60 was due to time averaging the accuracy of age estimates of sea level change in studies using single dated corals as proxies for sea level is probably within 1000 yr of actual age but can be resolved to 250 yr if supported by dates from analysis of a statistical population of corals at each stratigraphic interval the range of time averaging among reef corals was much less than that for shelly benthos ecological time averaging dominated over sedimentological time averaging for reef corals opposite to patterns reported from shelly benthos in siliciclastic environments c 2006 elsevier b v all rights reserved

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

evolution of the cloudy boundary layer during the autumnal freezing of the beaufort sea the beaufort and arctic seas experiment base occurred during september and october 1994 off the canadian beaufort coast in this paper we provide a description of the characteristics of the the cloudy boundary layer that were observed from a research aircraft during base and provide an interpretation for the coevolution of the atmospheric boundary layer and sea ice characteristics during the autumnal freezing of the beaufort sea observations from a total of 12 research flights are presented during the course of the experiment the underlying surface made a transition from late summer melt conditions to full fledged winter conditions all of the observed boundary layer cloud decks are associated with stable temperature profiles with temperature inversions occurring either above or within each of the cloud decks unlike observations of summertime boundary layer clouds no multiple layered clouds in the boundary layer were observed examination of the cloud phase indicates a transition from predominantly liquid phase clouds at the beginning of the experiment to predominantly crystalline clouds at the end of the experiment local interactions between the clouds and underlying surface were examined in several case studies including the effects of leads using a time series of soundings over a period of 5 days in conjunction with the the national center for environmental prediction analyses an air mass modification event was examined that began after the intrusion of warm air from the pacific ocean the evolution of the air mass is apparent in decreasing temperatures in the lower atmosphere and formation of a low level mixed phase cloud that evolves with time into a deeper cloud layer that is crystalline

discovery of a submerged relic reef and shoreline off grand cayman further support for an early holocene jump in sea level abstract drilling close to the base of a submerged sea cliff on the terraced eastern shelf of grand cayman has revealed a relic acropora palmata reef at a depth of 21 m below msl ten cores from its crest are principally composed of cobble sized clasts of a palmata set in a matrix of cemented skeletal grainstone the clasts have a distinctive succession of encrusters that indicate rapid burial a photophilic association of crustose coralline algae foraminifera and vermetid gastropods superimposed by a cryptic association of sclerosponges foraminifera and serpulids in addition to rapid burial u th thermal ionization mass spectrometer tims dating of coral clasts within 1 m of the relic reef surface indicates minor temporal mixing with ages between 8 9 and 8 1 ka such mixing and rapid burial is consistent with a hurricane deposit and is identical to deposits found on the crests of modern reefs in relation to its age the preservation of a 18 5 m intertidal notch cut into the submerged sea cliff on the western shelf of grand cayman implies that the crest of the relic reef has been lowered 1 5 2 m by marine abrasion bioerosion at a rate of 0 25 mm yr 1 reconstructing this eroded section using average holocene accretion rates indicates that the reef likely ceased accreting at 7 6 ka at a depth of 19 m comparing these data with other relic reefs in the caribbean indicates that the relic reef on grand cayman died within 160 years of relic reefs on barbados st croix st thomas and north florida this narrow interval of reef demise also coincides with the time when modern reefs were establishing themselves some 4 9 m higher upslope a fact that can only be resolved by invoking a rapid 6 m jump in sea level 7 5 ka ago such a jump would also account for two unexplained events around this time the restricted interval of global delta initiation and the catastrophic flooding of the glacially lowered black sea

internal precipitation of microcrystalline carbonate a fundamental problem for sedimentologists abstract recent studies of submarine lithification have shown that microcrystalline carbonate or carbonate mud traditionally thought to represent ooze deposited in quiet water commonly forms as an internal precipitate below the sediment water interface this internally precipitated micrite alters the mud grain ratio of pre existing sedimentary deposits and invalidates classifications that relate the amount of micrite matrix in limestones to the degree of water energy associated with the environment of deposition

reef coralgal assemblages as recorders of paleobathymetry and sea level changes in the indo pacific province the coralgal framework within the outer reef margin of many indo pacific reefs exhibits three main shallow water communities the environmental significance of which can be inferred by comparison with their modern counterparts a community dominated by tabular acropora gr hyacinthus cytherea with branching pocillopora damicornis p eydouxi montipora digitata occasional domal faviids and mm thick crusts of the coralline algae lithophyllum and mesophyllum mainly typical of the 6 15 m paleodepth range a community including robust branching acropora gr danai robusta a humilis a digitifera and subordinate favia stelligera echinopora gemmacea associated to vermetid gastropods and thick coralline crusts of hydrolithon cf onkodes and neogoniolithon cf fosliei flourishing in depths less than 6 m in medium to high water energy settings a community composed of domal porites cf lutea and p cf lobata with occasional acropora gr danai robusta and cm thick crusts of coralline algae in sheltered habitats in depths less than 10 m these biological assemblages allow us to determine relationships between reef growth and paleobathymetry and consequently to reconstruct regional relative sea level curves high water energy reefal assemblages provide stronger evidence for reconstructing sea level curves than low energy buildups because they have generally been controlled by a keep up growth mode subsiding reef sites seem to be more reliable indicators of sea level variations because they usually present expanded reef sequences

holocene cemented beach deposits in belize abstract two types of cemented beach deposits occur on reef islands off the coast of belize these are 1 intertidal beachrock that is dominantly cemented by marine aragonite and high magnesium calcite cements and 2 supratidal cayrock that is cemented mainly by vadose low magnesium calcite cements besides differences in position relative to present sea level and resulting early diagenesic features beachrock and cayrock can be distinguished on the basis of differences in composition texture geographical position and age whereas the composition of beachrock is similar to that of the adjacent marginal reef sediments cayrock is enriched in benthic foraminifera intertidal beachrock is moderately to well sorted and well cemented while supratidal cayrock is very well sorted poorly cemented and friable beachrock occurs preferentially on windward beaches of sand shingle gays on the middle and southern barrier reefs and on the isolated platforms glovers and lighthouse reefs cayrock only occurs on larger mangrove sand gays of the isolated platforms turneffe islands lighthouse reef and the northern barrier reef 14c dating of ten whole rock and mollusk shell samples produced calibrated dates between ad 345 and ad 1435 for beachrock and between bc 1085 and ad 1190 for cayrock the large scale distribution of beachrock in belize supports the contention that physical processes such as water agitation rather than biological processes control beachrock formation and distribution only on windward sides of cays that are close to the reef crest where large amounts of seawater flush the beaches considerable amounts of cements can be precipitated to produce beachrock cayrock forms due to cementation in the vadose zone and is only preserved on larger stable mangrove sand cays

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

selective blackening of bioclasts via mixing zone aragonite neomorphism in late triassic limestone zlatibor mountains serbia a peculiar facies of the norian rhaetian dachstein type platform carbonates which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments occurs in the zlatibor mountains serbia microfacies investigations revealed that the blackened bioclasts are predominantly solenoporaceae with a finely crystalline originally aragonite skeleton of fine cellular structure blackening of other bioclasts also occurs subordinately solenoporacean dominated reefs developed behind the platform margin patch reef tract were the main source of sand sized detritus the blackened and other non blackened bioclasts are incorporated in automicrite cement radiaxial fibrous calcite cements in the dissolutional cavities are also black dark grey or white reworked black pebbles were reported from many occurrences of peritidal deposits in those cases the blackening took place under pedogenic meteoric diagenetic conditions in contrast in the inner platform deposits of the ilidz ya limestone the blackening of bioclasts occurred in a marine meteoric mixing zone as indicated by petrographic features and geochemical data of the skeleton replacing calcite crystals attributes of mixingzone pore waters were controlled by mixing corrosion different solubility of carbonate minerals and microbial decomposition of organic matter in the moderate energy inner platform environment large amounts of microbial organic tissue were accumulated and subsequently decomposed triggering selective blackening in the course of early shallow burial diagenesis the d 18 o and d 13 c values of the mixing zone precipitates and replacive calcite do not produce a linear mixing trend variation mainly resulted from microbial decomposition of organic matter that occurred under mixing zone conditions the paragenetic sequence implies cyclic diagenetic conditions that were determined by marine meteoric and mixing zone pore fluids the diagenetic cycles were controlled by sea level fluctuations of moderate amplitude under a semi arid to semi humid climate

microatolls as sea level indicators on a mid ocean atoll microatolls are discoid corals with flat upper surfaces that develop when upward coral growth is constrained by exposure at low tide they have been widely viewed as important and relatively precise indicators of modern and paleo sea level positions because of their sensitivity to the water air interface though this has rarely been directly established by survey to a precise datum this study involved an accurate survey of 282 microatolls growing in a range of intertidal environments open reef flats interisland passages lagoons across the cocos keeling islands a mid ocean atoll in the indian ocean the upper surface elevation of modern microatolls was found to vary through more than 40 cm across the environments in which these corals occur on cocos representing more than 30 of the spring tide range much of the variation reflects subtle ponding at low water levels across extensive low gradient reef surfaces associated with interisland passages microatolls in open reef flat habitats are typically constrained within the narrowest and most consistent elevation range around the atoll the environment in which individual fossil microatolls occurred when they were alive is significant in reconstructing former sea levels

hurricane control on shelf edge reef architecture around grand cayman rimming the outer shelf of grand cayman is a submerged 87 km long shelf edge reef that rises to within 12 m of mean sea level it consists of an array of coral armoured buttresses aligned perpendicular to shore and separated by steep sided sediment floored canyons individual buttresses have a diverse coral dominated biota and consist of three architectural elements a shield like front wall colonized by platy corals a dome shaped crown colonized by head corals and a shoreward projecting spur covered by varying amounts of branching coral buttresses are commonly fronted by coral pinnacles that in some areas have amalgamated with buttress walls to produce pinnacle and arch structures as margin orientation changes shelf edge reef architecture shows systematic variations that are consistent with changes in fetch and height of hurricane waves along margins exposed to fully developed storm waves shelf edge reef buttresses are deep have large amplitudes and are dominated by robust head corals these characteristics are consistent with hurricane induced pruning of branching corals and the flushing of significant quantities of sand from buttress canyons by return flows along margins impacted by fetch limited storm waves reef buttresses are shallower have intermediate amplitudes and have a significantly higher proportion of branching corals these characteristics are consistent with less coral pruning and sand flushing by weaker hurricane waves along margins fully protected from storm waves the buttresses canyon architecture of the shelf edge reef breaks down producing a series of shallow undulating branching coral dominated ridges that merge laterally into an unbroken belt of coral these characteristics correspond with negligible amounts of pruning and flushing during hurricanes in addition to differences between margins local intra marginal changes in shelf edge reef architecture are consistent with changes in the angle of hurricane wave approach open sections of the shelf edge reef which face directly into storm waves are pruned of branching corals and the fragments swept back onto the shelf producing extensive spurs by contrast on more sheltered obliquely orientated sections storm waves sweep debris along and off shelf producing little or no spur development instead the debris shed seawards accumulates in front of the buttress walls and initiates the development of coral pinnacles over time repeated buttress pruning and canyon flushing during hurricanes not only controls reef architecture but may also influence accretion patterns vertical accretion is limited by the effective depth of storm wave fragmentation once this hurricane accretion threshold is reached the reef moves into a shedding phase and accretes laterally via pinnacle growth amalgamation and infilling consequently the reef steps out over its own debris in a kind of balancing act between lateral growth and slope failure a pattern widely recognized in ancient reefs

anaerobic diagenesis within recent pleistocene and eocene marine carbonate frameworks porewaters from a variety of recent pleistocene and eocene lithified marine carbonate frameworks displayed similar chemical characteristics highly depleted concentrations of dissolved oxygen 20 m elevated levels of dissolved methane 25 5000 nm and near seawater sulphate levels these porewaters also had low ph values 7 5 7 9 and contained elevated concentrations of sulphide 4 10 m dissolved inorganic carbon 2 05 2 46 mm and inorganic nutrients hydrocarbon composition data indicate that the methane is biogenic whereas the methane 13c values 47 4 2 7 0 suggest that it has been subject to oxidation the porewater dissolved inorganic carbon 13c values varied from 0 6 to 39 0 suggesting input of carbon dioxide from organic matter oxidation we conclude that anaerobic diagenesis involving bacterial degradation of organic matter is a common process in lithified marine carbonates and hypothesize that it may be an important factor controlling their carbonate geochemistry