terrigenous sedimentation and coral reef growth a conceptual framework abstract the role of terrigenous and non framework carbonate sedimentation has not been prominent in models of coral reef growth and evolution we derive and discuss a semi quantitative model which relates coral reef growth to sedimentation the model is independent of coral biology and is based upon the relative net rates of framework and non framework sediment accumulation and or removal the model might enable some forecasting of long term responses to changes in sedimentation regime and other environmental factors the occurrence of turbid zone reefs is successfully explained in regions of very high turbidity but with little or no net sediment accumulation potential future use of the model may include aiding prediction of the effects of other geological and oceanographic factors on the growth or demise of coralline communities

sequence architecture during the holocene transgression an example from the great barrier reef shelf australia abstract the application of sequence stratigraphic analysis to post glacial sediments requires the correct identification of sequence boundaries flooding surfaces and systems tracts the nature of coastal sediments deposited during sea level cycles is complex and misinterpretation is easy particularly in ancient sequences for which eustasy is inferred rather than demonstrated a large core seismic and radiocarbon database from cleveland bay in tropical queensland allows detailed analysis of the systems tracts and parasequences developed during the late holocene despite the large database a unique sequence stratigraphic interpretation is not possible because oscillations in the sea level curve apparently occurred at a frequency higher than the resolving power of radiocarbon dating our best estimate is that the final stages of the holocene sea level rise comprise four parasequences each deposited during episodic slowdowns in sea level rise and or a pulse of rapid sediment supply sea level pauses probably occurred at 12 10 m below modern levels at 8 5 ka bp followed by a fall to ca 17 m at 8 1 ka bp a very rapid transgression to ca 10 m at 7 9 ka bp a further transgression to ca 5 m at 6 8 ka bp and a final rise to the holocene highstand at 1 65 m at 5 5 ka bp the stratigraphic record of these sea level rises is complex occurs within the modern shore connected sedimentary wedge and comprises parasequences associated with shorelines at 11 m p11 17 m p17 10 m p10 5 m p5 and 1 65 m p 1 7 each parasequence comprises in ascending order onlapping estuarine shoreline sediment including mangrove mud and beach sand and progradational shallow bay muddy sand across the bay units up to and including the lower parts of the shallow bay mud correspond to the transgressive systems tract tst of the last 18 ka glacial interglacial cycle the particular parasequence represented being dependent upon location especially depth bay mud above this level corresponds to the post 5 5 ka bp highstand systems tract hst which comprises sand cheniers on the coastal plain and bioturbated muddy sand in the shallow bay the junction between the tst and the hst lies within the bay mud and corresponds approximately to the local flooding surface for the p 1 7 parasequence deposited at the 1 65 m shoreline offshore terrigenous tst strata do not occur over most of the middle and outer shelf which instead is veneered with a thin mid cycle shellbed the lower part of this shellbed is time equivalent to the later part of the tst and the upper part is time equivalent to the hst offshore the maximum flooding horizon mfh and peak eustatic sea level horizon pesh of the late pleistocene holocene sea level cycle lie at some level within the mid cycle shellbed nearshore the mfh and pesh lie within the shore connected sediment wedge at levels near the tst hst boundary however at no locality do either the mfh and pesh necessarily correspond to a physical boundary within the stratigraphy

growth and structure of fringing reefs in a muddy environment south thailand abstract most fringing reefs of the se coast of phuket thailand have wide up to 300 m intertidal reef flats and narrow 2 5 m reef fronts that abut the muddy forereef only a few meters deep these reefs prograde by splitting toppling and regeneration of reef front massive corals notably porites lutea splitting of massive corals is greatly aided by the boring action of upogebia sp shrimps and by planes of weakness developed within the colony skeleton by nestling bivalves the large size of toppled blocks ensures that some of the uppermost polyps are viable above the soupy forereef sediment surface cores indicate that the reefs are essentially tabular features consisting of mainly massive reef front corals grown on muddy foundations that have shallowing upwards sediment haracteristics 14c ages and leveling data of fossil former reef front corals exposed on the reef flat suggest that reef growth started in the mid holocene when sea level was at least 0 8 m higher than now since then the rate of lateral reef progradation has averaged 40 mm yr the preservation potential of these reefs is low because of the combination of a lack of organic or inorganic binding of the corals into a rigid frame and the unconsolidated nature of the underlying sediments

biofouling control for optical backscatter suspended sediment sensors abstract the use of optical backscatter instruments for measuring water turbidity for extended periods has been very limited due to the debilitating effect of biological fouling this is particularly the case in tropical coastal waters we describe a simple wiping mechanism attached to a logging nephelometer which can usually control fouling for up to a month even under conditions most favourable for fouling without a wiper deployment periods can be limited to only a few days scratching of the nephelometer by the wiper is not a major contributor to nephelometer error

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

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

a meta analysis of reef island response to environmental change on the great barrier reef reef islands on the great barrier reef are influenced by a range of environmental factors a meta analysis of 103 islands is presented to express variation in island size area and volume as a function of latitudinal and cross shelf gradients in regional oceanographic factors exposure to incident waves tidal range and tropical cyclone frequency and local physical factors position on the shelf area length and depth of supporting reef platform vegetative cover models performed well for unvegetated sandcays r2 0 89 vegetated sandcays r2 0 72 and low wooded islands r2 0 78 with a moderate level of variation explained when all islands were simultaneously regressed r2 0 58 future island dynamics were simulated for anticipated changes in cyclone regime wave activity and sea level for 38 islands mapped on the 1973 royal society and universities of queensland expedition to the northern great barrier reef change over the same 22 year period 1973 1995 was determined and the relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis 0 84 for unvegetated sandcays 0 81 for vegetated sandcays simulations of island area or volume change from 2000 to 2100 indicated that under a 30 decrease in tropical cyclone activity unvegetated sandcays continue to accrete at a lower rate whereas all island types erode under a 38 increase in tropical cyclone activity vegetated sandcays initially accrete at higher levels of cyclone activity entering an erosive state with a 60 increase in activity low wooded islands are unresponsive to environmental changes modelled a sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode greatest sedimentary losses occur within the central band of high cyclone activity between cooktown and mackay copyright 2015 john wiley sons ltd

development of an inshore fringing coral reef using textural compositional and stratigraphic data from magnetic island great barrier reef australia the stratigraphy of fringing coral reef environments and platforms provides unique insights into reef development and evolution this study used twelve sediment cores from three transects across a reef flat in nelly bay magnetic island ne australia to examine its development over the holocene the maximum thickness of the holocene reefal material based on seismic and bore log data was around 5 m and comparable to other fringing reefs in the great barrier reef gbr six different sedimentary facies were identified in the cores and two coincided with reef accretion the lower muddy sand with coral rubble and the upper siliciclastic sand with coral rubble radiocarbon and u series dates show that the nelly bay fringing reef initiated around 6300 yr bp on a gently sloping unconsolidated or weakly cemented pleistocene alluvial sedimentary facies the ages of four massive coral heads range between 5790 and 6290 calibrated c 14 yr bp were almost contemporaneous with reefal initiation indicating that conditions were favourable for reef growth around this time vertical accretion rates for the nelly bay fringing reef were on average about 0 5 mm yr over the last 6000 yr although rates were as high as 5 mm yr during initiation average lateral accretion rates varied from 98 to 120 mm yr which are comparable to rates of other fringing reefs in the region the age structure of the lower muddy sedimentary facies was consistent with the classic seaward prograding model of fringing reef development in contrast the upper siliciclastic sand with coral rubble facies was much younger in age 1100 yr bp than the models and appears to represent an erosional unconformity between the upper and lower reefal facies possibly linked to late holocene sea level fall this younger facies extends laterally across the reef flat and has no obvious prograding symmetry our integrated approach using multi proxy analyses of sediment cores from the nelly bay reef flat highlights the complex development of this reef which include changes in coral composition and rubble preservation reef evolution in response to sea level change and changes in reef accretion rates

stratigraphic control of the geochemistry of holocene inner shelf facies great barrier reef received 15 august 1994 revision accepted 28 june 1995 abstract cleveland bay and halifax bay are adjacent embayments situated on the inner shelf region o 20 m of the central great barrier reef shelf off townsville northeast australia these bays contain holocene sediments up to 5 m in thickness deposited during the last stages of the post glacial sea level rise x ray diffraction and x ray fluorescence techniques were used to examine the mineralogy and geochemistry of the main holocene facies sampled in 40 vibrocores the sediments of southern halifax bay and cleveland bay consist mainly of quartz ca 50 alkali feldspars ca 20 clay minerals ca 20 consisting of mixed layer clays smectite kaolinite and illite and carbonate ca 10 including aragonite and calcite the holocene facies sequence comprises in order of increasing age modern bay shoreline and mangrove sediments the oxides of the major components sioz a o fe203 mgo cao k o na o p o in halifax bay show the predicted linear correlations with geochemically related minor elements pb rb sr y zr ga zn ni co mn cr ti sc v ba and can be used to discriminate holocene facies however in cleveland bay these elements are poorly correlated within each facies and provide very poor facies discrimination these findings probably result from the presence of sandy shoreline sediments up to 2 m in thickness in the holocene sequence of cleveland bay with the consequent development of a weak oxic zone and migration of elements between adjacent facies a similar oxic zone is poorly developed in halifax bay because the shoreline facies there is either thin or absent that the chemical signatures of holocene inner shelf facies are spatially variable and are strongly influenced by the stratigraphy has wide implications for geochemical studies of marine sediments

development of equatorial delta front patch reefs during the neogene borneo abstract miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial mahakam delta in eastern borneo se asia patch reefs were initiated on unstable substrates on localized low relief bathymetric highs associated with delta front channels or distributary mouthbars in the process of abandonment patch reefs developed only in shallow waters formed low relief buildups lacked rigid frameworks and had gently sloping margins although the biodiversity of the patch reefs may be comparable with that of clear water systems all the organisms present were adapted to turbid water areas associated with siliciclastic and sometimes nutrient influx the patch reefs were transient features and their demise was influenced by increased siliciclastic and nutrient input perhaps at times associated with deepening carbonate production and bioherm or patch reef development can occur in turbid water delta front areas as localized or more regionally extensive units during any phases of eustatic sea level however development and preservation of turbid water carbonates is most likely during relative transgression or perhaps late lowstand periods this is in contrast with common highstand carbonates from clear water shelves where nearly pure carbonates interdigitate with siliciclastics it is the interplay between factors such as tectonics eustasy delta lobe switching shelf currents and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation

the relative importance of landward directed tidal sediment transport versus freshwater flood events in the normanby river estuary cape york peninsula australia variation in freshwater discharge into the tropical estuaries of northern australia is extreme between wet and dry seasons and the resultant effect upon sedimentary processes in relation to the geomorphological evolution of the coastal plain is largely undocumented observations of tidal height currents and suspended sediment concentrations were taken over a 3 week period in july 1994 dry season in the mesotidal normanby river estuary northeastern australia the estuary and adjacent inner shelf were surveyed using a 3 5 khz seismic system and an echo sounder and sampled with a total of 175 grab samples and 17 vibrocores sediment sampling occurred in july 1994 december 1994 and march 1996 the latter following the 1995 96 wet season flood tidal currents dominate the estuary at spring tides with peak velocities of 0 85 m s 1 recorded at the mouth measured tidally driven sediment transport is landward at the mid estuary site and extrapolation gives estimates of 15 000 30 000 tonnes of bedload and ca 50 000 tonnes of suspended load moved landward per year the surficial sediments in the main estuarine channel are inferred to be holocene and are 1 delta front sediments which extend to at least 6 km seawards of the mouth 2 lower estuarine silts located at 2 11 km landwards of the mouth and 3 channel dune sands 13 to 50 km i e nearly to the tidal limit all dunes surveyed on the river bed during the dry season showed a strong asymmetry with lee faces consistently facing landward whether surveyed at high or low water indicating landward bedload sediment transport in the dry season an underlying hard regional surface is exposed at 11 13 km landward of the estuary mouth in the absence of direct measurements we have estimated sediment transport during wet season freshwater flood events a major freshwater flood event may transport only 6000 32 000 tonnes of bedload seawards and modern wet season events appear incapable of supplying sand in significant quantities to the inner shelf we infer that for the late holocene the frequency magnitude and duration of wet season events has been insufficient to reverse the landward bedload transport driven by tidal currents in the dry season

marine biota response to clastic sediment influx a quantitative approach abstract there have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record this study presents the results of quantitative field petrographic and acid digestion analyses of samples from three cenozoic shallow water mixed carbonate volcani siliciclastic depositional environments the miocene wonosari formation of south java the miocene batu putih limestone of east borneo and the eocene collsuspina limestone of northeast spain carbonate production in these systems is dominated by larger benthic foraminifera coralline algae and corals analyses of the quantity grainsize and type of volcani siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow water carbonate producers larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx abundant up to 55 and 38 wt respectively at a range of grain sizes to coarse sand platy corals are also present within sediments containing a large proportion of insoluble material geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems however this study may aid our understanding of the likely effects of increased clastic influx today commonly anthropogenically related to marine carbonate environments over longer time periods

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

influence of paleo trade winds on facies patterns of the cambrian shanganning carbonate platform north china abstract the shanganning carbonate platform scp of the north china craton ncc was located in the trade winds belt during the cambrian which influenced its facies development in recent years numerous drillcores have been recovered from these units but the depositional environments and facies architecture of this large 2 0 105 km2 carbonate platform system have not yet been reported in detail in this study we integrate sedimentological and magnetic fabric data collected from outcrops and drillcores in order to document variation in microfacies and facies associations within the scp to infer paleowind directions and constrain the paleogeographic location of the scp and to evaluate eolian controls on platform development this analysis documented numerous carbonate microfacies belonging to six fabric types mudstone wackestone packstone grainstone framestone and dolostone along with rarer siliciclastic sediments these microfacies belong to facies associations representing tidal flat open platform platform margin slope and deep basinal depositional environments anisotropy of magnetic susceptibility ams measurements yielded mean paleocurrent directions for the early middle and late cambrian of 114 63 and 83 30 from paleo north respectively that were relatively consistent for 12 out of 13 platform margin sites all vectors being corrected for a post cambrian 150 clockwise rotation of the ncc these wind orientations are consistent with the scp shifting from south of the paleo equator in the early cambrian to north of it by the middle cambrian paleo trade winds influenced facies patterns across the platform producing a distinct windward leeward zonation the windward margin is characterized by well sorted oolitic grainstone as well as favositids coral and dasycladacean algal sponge framestone and the leeward margin by poorly sorted oolitic wackestone grainstone and fine bioclastic sediments the present study is innovative in 1 integrating microfacies and ams analyses in order to establish paleowind patterns and influences on an ancient carbonate platform 2 documenting windward leeward variation in quantifiable sediment properties across the scp and 3 constraining the paleo hemispheric location of the ncc during the cambrian

post glacial seismic stratigraphy central great barrier reef australia a regional programme of continuous seismic boomer profiling in the central great barrier reef province has identified a widespread shallow seismic discontinuity reflector a which is interpreted as the pre holocene surface nine seismic facies units are distinguished primarily on the basis of the seismic records but also with the aid of additional criteria such as location and surface sediment types two units underlie reflector a and are pre holocene these units are interpreted as a permo carboniferous bedrock and b pleistocene tertiary sediments consisting of both shelf wide terrigenous units and carbonate mounds and platforms under present reefs seven units are post glacial and overlie reflector a these units are interpreted as c fluvial estuarine channel fill d relict delta front deposits e relict transgressive veneer f coastal coarse and g fine deposits h modern reef and i reef talus in general post glacial sediment cover is very thin and in many places on the mid shelf the pre holocene units crop out substantial post glacial accumulations are limited to protected coastal embayments and to offshore reef masses

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

unmixing relationships as a method of deriving a semi quantitative terrigenous sediment budget central great barrier reef lagoon australia abstract semi quantitative estimates of unmixing and transport from a source sediment are derived using a new method based on particle size data the method utilises the entire size frequency distribution and avoids the application of distribution dependent statistics this method enables the modelling of polymodal sediments in this example we consider a single poorly sorted source and multiple depositional sinks each of the end point depositional environments is dominated by a single unmixing process we demonstrate that unmixing a poorly sorted sandy mud in the great barrier reef lagoon gives rise to a sediment budget that contains mangrove sheltered embayment mud near shore beach sand tidal flat muddy sand and chenier storm ridge sediments in proportions that are consistent with those observed in modern environments and stratigraphic records

new evidence for episodic post glacial sea level rise central great barrier reef australia abstract we present an extensive database of 364 radiocarbon dates from coastal and marine sediments of the central great barrier reef gbr shelf of which 110 are previously unpublished the elevation data have been reduced to a common datum australian height datum ahd and the various sources of error have been assessed using modern lithological and biological relationships with sea level the elements of the radiocarbon database have been converted into sea level indicators the upper bound of the assembled dataset corresponds to a best estimate sea level curve and the full dataset provides a narrow envelope for sea level rise on the gbr shelf for the last 11 12 kyr not including hydro isostatic crustal flexing the envelope is consistent with episodic rise in post glacial sea levels the rising post glacial sea level probably included stillstands or minor falls at ca 45 m ahd at ca 10 5 kyr b p 5 m 7 8 kyr b p 2 m ca 6 kyr b p and 1 7 m 5 5 kyr b p there is evidence for a significant fall in sea level between stillstands at 11 m 8 5 kyr b p and 17 m 8 2 kyr b p stillstand durations apparently ranged between the vertical spread in the derived sea level data is very wide the use of shell material for dating seems unreliable and prone to large and unpredictable errors data from bulk mangrove muds appear reliable for determination of ancient sea level but may at times result in sea level being placed up to 4 m below the true level in situ biogenic carbonates such as preserved oyster beds and coral micro atolls are the most reliable indicators of sea level position while deposits of mangrove mud give a useful first order approximation of ancient sea levels caution should be used in drawing sea level curves from few data points we conclude that the post 11 12 kyr b p relative rise in sea level was episodic on the central gbr continental margin more data are required to define clearly sea level change up to ca 20 m at 9 kyr b p

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

a synthesis of geochemistry and sm nd isotopes of archean granitoid gneisses in the jiaodong terrane constraints on petrogenesis and tectonic evolution of the eastern block north china craton abstract the jiaodong terrane is situated in the northeastern part of the shandong province in eastern china experiencing multi stage magmatism during the mesoarchean 2 9 ga and neoarchean 2 7 ga and 2 5 ga it consists dominantly of granitoid gneisses with minor amphibolite enclaves or lenses this study presents new whole rock geochemical and sm nd isotopic data for the archean granitoid gneisses from the jiaodong terrane in order to constrain their petrogenesis and tectonic setting geochemical studies and petrological features suggest that the protoliths of most granitoid gneisses are typical archean tonalitic trondhjemitic granodioritic ttg suites which are high in sio2 60 9 76 8 wt al2o3 12 6 16 8 wt na2o 3 3 5 3 wt sr 135 604 ppm and sr y ratios 13 9 84 but low in mgo 0 4 4 5 wt k2o 0 7 3 4 wt tio2 0 2 0 9 wt cr

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

modeled estimates of global reef habitat and carbonate production since the last glacial maximum estimated changes in reef area and caco3 production since the last glacial maximum lgm are presented for the first time based on a model reefhab which uses measured environmental data to predict global distribution of reef habitat suitable reef habitat is defined by temperature salinity nutrients and the depth attenuated level of photosynthetically available radiation par caco3 production is calculated as a function of par when minimum par levels were chosen to restrict reef growth to 30 m depth and less modern reef area totaled 584 746 10 km global carbonate production which takes into account topographic relief as a control on carbonate accumulation was 1 00 gt yr 1 these values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification to simulate reef habitat changes since the lgm the model was run at 1 kyr intervals using appropriate sea level and temperature values these runs show that at the lgm reef area was restricted to 20 of that today and carbonate production to 27 due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures nonetheless these values suggest that reef growth prior to shelf flooding was more extensive than previously thought a crude estimate of reef released co2 to the atmosphere since the lgm is of the same order of magnitude as the atmospheric co2 change recorded in the vostok ice core which emphasizes the role of neritic carbonates within the global carbon cycle this model currently addresses only the major physical and chemical controls on reef carbonate production but it provides a template for estimating shallow tropical carbonate production both in the present and in the past as such the model highlights several long standing issues regarding reef carbonates particularly in terms of better defining the roles of light temperature aragonite saturation state and topography on reef calcification

effects of coastal orography on landfalling cold fronts part i dry inviscid dynamics abstract in this study the interaction of cold fronts with idealized coastal terrain typical of the western united states and canada is considered two issues are examined first what are the factors that determine the strength of the coastal winds and second what are the orographic effects on the frontal evolution to address these issues the authors utilize a two dimensional boussinesq terrain following coordinate numerical model in which a uniform prescribed flow is forced to move over a plateau the resultant across mountain velocities are characterized by a zone of strongly decelerated flow upstream of the windward slope and a train of inertia gravity waves downstream a barrier jet oriented parallel to the mountain is produced by the coriolis force the variations of the magnitude of the upstream deceleration and the barrier jet over a wide range of froude numbers and rossby numbers are described steady linear theory applied to flow over a plateau shows that the upstream deceleration is dete

tidally induced clouds of suspended sediment connected to shallow water coral reefs abstract the bay of banten west java indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions the sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration ssc around the reefs arrays of in situ calibrated optical backscatter obs sensors were deployed across the reef slopes far field conditions were simultaneously monitored using an acoustic doppler current profiler adcp and a conductivity temperature and depth ctd probe equipped with an obs sensor in addition hydrographic surveys were conducted using the adcp attached to a small fishing boat navigating transects perpendicular to the reef islands the direct influence of river plumes was found to be insignificant waves act only in the uppermost few meters of the reef slopes where coral growth is most abundant and little sediment is available for resuspension tidal currents are the primary cause of high turbidity which was inferred from peaks in the diurnal and semidiurnal frequency bands of ssc spectra and the large depths where the turbidity variation sometimes initiates the entrained sediment disperses upward across the reef slopes which is likely due to a secondary current associated with bending of the flow along the curved hydraulically rough reef slopes in weakly stratified ambient waters changes in sediment availability variable critical shear stresses for erosion and deposition and the formation and evanescence of island wakes may explain the high variability of ssc at the reef slopes

shallow water marl limestone alternations in the late jurassic of western france cycles storm event deposits or both abstract the contribution of event deposits to various basin fills can be very significant higher than 90 in some cases events may lead to the formation of marl limestone alternations which can also result from cyclic changes in sea level or climate for example the marl limestone alternations of the late jurassic of western france contain abundant coarse grained accumulations that resemble storm deposits described in other western european successions the detailed analysis of facies evolution and hierarchical high frequency stacking pattern of depositional sequences of the phare de chassiron section ile d oleron western france allows the controls on marl limestone formation to be defined this section contains nearshore and shallow marine mud deposits that were exposed to high energy events elementary small and medium scale depositional sequences are defined the stacking pattern and the duration of these sequences suggest an orbital control on sedimentation precession 20 ka cycles notably controlled the formation of elementary sequences that correspond to marl limestone alternations the deposition of marly or carbonate mud occurred in this storm dominated system because of muddy sea beds the gentle slope of the shelf and the great amount of particles in suspension which reduced water energy resulting from storms sediment supply was also sufficient to limit bioturbation and favour the preservation of numerous storm deposits the production of carbonate mud was localised on positive structures and partly controlled by milankovitch scale sea level cycles transport by storms of carbonate mud to the adjacent marly depressions during high carbonate production periods led to the formation of calcareous beds marl limestone alternations in the late jurassic of western france therefore result from the combined effects of cyclic changes in carbonate production and high energy episodic events

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

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

new evidence for the holocene sea level high from the inner shelf central great barrier reef australia radiocarbon dates from fossil oyster beds of intertidal origin on magnetic island north queensland indicate that the local holocene maximum of relative sea level was attained no later than 5660 50 b p conventional uncorrected age and remained at 1 6 1 7 m above modern levels until 4040 50 b p given the tectonic stability of the area this implies that eustatic sea level remained at its holocene peak for at least ca 1600 yr the new high precision sea level data indicate sea levels 1 5 m higher than those of the same age inferred from buried mangrove deposits on the inner shelf in north queensland uncertainties in deriving relative sea level from such mangrove deposits may be a significant source of error in worldwide attempts to distinguish the eustatic and crustal warping components off relative sea level change especially in the tropics

the first microbialite coral mounds in the cenozoic uppermost paleocene from the northern tethys slovenia environmentally triggered phase shifts preceding the petm abstract upper thanetian microbialite coral mounds from the adriatic carbonate platform sw slovenia are described herein for the first time representing an important case study of extensively microbially cemented boundstones in the early paleogene the mounds are constructed primarily by microbialites associated to small sized coral colonies forming metric bioconstructions in a mid ramp setting detailed macroscopic and microscopic studies show that microbes are the major framework builders playing a prominent role in the stabilization and growth of the mounds with corals being the second most important component microbial carbonates represent up to 70 of the mounds forming centimetric thick crusts alternating with coral colonies the microbial nature of the crusts is demonstrated by their growth form and internal microfabrics showing accretionary binding and encrusting growth fabrics often with gravity defying geometries thin sections and polished slabs reveal a broad range of mesofabrics with dense structureless micrite leiolite laminated crusts stromatolites and clotted micritic masses thrombolites a first layer of micro encrusters including leiolites and thrombolites occurs in cryptic habitats whereas discontinuous stromatolites encrust the upper surface of corals a second encrustation the major mound construction phase follows and is dominated by thrombolites encrusting corals and other micro encrusters this sequence represents the basic constructional unit horizontally and vertically interlocked in an irregular pattern to form the mounds the processes which favored the deposition of these microbial carbonates were mainly related to in situ precipitation with minor evidences for grain agglutination and trapping processes scleractinian corals comprise moderately diversified community of small centimetric colonial massive platy encrusting and branching forms coral colonies are distributed uniformly throughout the mounds without developing any ecological zonation these features indicate that coral development remained at the pioneer stage throughout the mound growth the spatial relationships between corals and microbialites as well as the characteristics of microbial crusts and coral colonies indicate a strong ecological competition between corals and microbes a model for the evolution of the trophic structures during the mound growth is proposed with changes in the paleoecology of the main bioconstructors triggered by frequent environmental perturbations turbidity and nutrient pressure interpreted here as related to frequent recurrences of wet phases during the warm humid climate of the uppermost thanetian might have promoted temporary dominance of microbes over corals causing rapid environmentally driven phase shifts in the dominant biota