the effect of base level changes and geological structures on the location of the groundwater divide as exhibited in the hydrological system between the dead sea and the mediterranean sea summary the effects of base sea or lake level changes on the location and elevation of the groundwater divide were examined in the hydrological system between the mediterranean sea and the dead sea steady state simulations were conducted with a 1 d analytical model and transient conditions were simulated using feflow groundwater modeling software two hydrological scenarios were simulated a a transition to a new steady state following the expected drop of 150 m of the dead sea level and b the time of the precursor of the dead sea lisan lake some 20 000 years ago when the lake level was about 250 m above the present day dead sea level and the mediterranean sea level was 120 m below its present one the results of the simulations show that the dead sea level drop has led to a progressive decline in the groundwater level up to several kilometers inland from the shoreline the hydraulic gradient increases and thus the discharge to the lake also increases at the expense of the storage and also due to a small enlargement of the recharge zone by a 600 m shift of the divide broadly the subsurface hydrological system is compartmentalized into several sections separated by low permeability fold structures bounding the mountainous uplands most of the groundwater recharge occurs in the uplands given this geometry and the available water level measurements analytical and numerical modeling results show that only changes in the dead sea level and recharge rate result in dramatic changes for the scenarios examined limited by the low permeability folds the effects of the dead sea level on the groundwater level are most pronounced in the vicinity of the judea desert lowland the folds also greatly limit migration of the groundwater divide associated with changes in the dead sea level transient simulations show a peak increase of 30 in the dead sea groundwater flux in 75 years resulting from drainage of lowland aquifers after more than 500 years the groundwater flux is expected to return to values no more than 4 higher than at the beginning of the simulation this small net increase is consistent with the small shift in the groundwater divide

a sedimentary prelude to marinoan glaciation cryogenian middle neoproterozoic keele formation mackenzie mountains northwestern canada abstract continental margin deposition between the sturtian and marinoan aged global glacial periods is represented in nw canada by a siliciclastic to carbonate grand cycle the keele formation a 300 600 m thick carbonate and siliciclastic deposit comprises the upper part of this interglacial cycle sedimentary facies in the lower carbonate dominated member of the keele span a broad spectrum of depositional environments from below storm wave base to peritidal to continental and are disposed across a relatively narrow paleogeographic belt lateral arrangement of facies and the gradual stratigraphic transitions between them suggest deposition in a ramp setting local slump structures and occasional debrites in deep water facies imply that the ramp was distally steepened fluvial facies are concentrated at a single locality indicating that terrigenous clastic sediment was derived from a point source or sources most strata of the carbonates are bahamian in character and similar to phanerozoic warm water carbonates in that they contain abundant calcite ooids of interpreted original aragonitic mineralogy and have well developed muddy peritidal facies nevertheless close juxtaposition of deep and shallow water facies in keele rocks indicates high amplitude sea level change during deposition on the order of 100 m suggesting accumulation in a climatic icehouse period this interpretation implies that although the globe possessed polar and high altitude glaciers at this time sea surface temperature at least at tropical latitudes warmed dramatically between neoproterozoic glacial episodes the onset of marinoan glaciation here is heralded by an abrupt shift to nearshore marine siliciclastic sedimentary rocks these deposits form the upper member of the keele formation informally called the keele clastic wedge and directly underlie ice brook formation diamictites carbonates are rare and are restricted to mudstones and flat pebble conglomerates that lack any indication of tropical conditions

anatomy of the buried burdekin river channel across the great barrier reef shelf how does a major river operate on a tropical mixed siliciclastic carbonate margin during sea level lowstand abstract a large palaeochannel on the northeastern australian continental shelf has been imaged by a series of shallow seismic reflection profiles the buried channel forms an important pleistocene route of the burdekin river and extends almost continuously for 160 km from the present coast to the outermost reef the channel floor profile steps across the shelf with alternating segments of gentle gradient flats and steeper gradient ramps channel sinuosity as interpreted from seismic records varies among segments between 1 and 1 72 with no consistent relationship between sinuosity and gradient the lower and upper parts of the channel fill have different geometry and reflection character suggesting channel excavation and initial filling occurred during a different regime than final filling in one section of the shelf about the 50 m isobath the channel is difficult to define and appears to have wandered significantly either because it has been modified by shoreface erosion ca 10 5 ka or because the river encountered a change in topography in front of karstified reefs as the channel passes between the numerous outer shelf reefs in water depths of 70 80 m it becomes progressively smaller conspicuously underfilled and absent entirely over the outermost 10 km of the shelf no discrete lowstand river mouth could be recognised on the present shelf edge the elevations of flat segments on the channel floor profile show considerable similarity to published elevations of stillstands or brief rises in sea level attained during the long term drawdown associated with the last glacial cycle 125 20 ka and are interpreted to have formed during this stepwise drop in sea level channels were cut and partially filled during the fall and lowstand and then backfilled during the holocene transgression the ancestral channel of the burdekin river therefore preserves a rare insight into the stratigraphic record of falling sea level during the last glacial

sea level control of stacked late quaternary coastal sequences central great barrier reef lithofacies analysis pollen assemblages and radiocarbon age dates of 20 stratigraphic drill holes are used to develop an evolutionary history for late quaternary sedimentation in two coastal embayments landward of the central great barrier reef different physiographic settings of the embayments result in two contrasting styles of sedimentary sequence a an exposed moderate energy beach barrier lagoon system wyvuri embayment and b a protected low energy muddy inlet fill sequence mutchero inlet despite sharp contrast in sequence style similar depositional cycles occur in both embayments in response to late quaternary sea level fluctuations including 1 a last interglacial highstand 2 m c 125 000 yr bp beach barrier wyvuri 2 an early to mid holocene 8000 6100 yr bp transgressive beach barrierlagoon wyvuri and estuarine infill mutchero and 3 mid holocene to present highstand beach barrier wyvuri and estuarine mutchero progradation preservation of such cycles in the stratigraphic record would produce a series of vertically stacked and offset linear barrier sands surrounded by lagoonal mud and fine grained shoreface sediment juxtaposed to muddy estuarine infills sea level elevations are well recorded by the upward transition from rhizaghoru dominated intertidal mangrove mud to freshwater swamp clearly identified by pollen analysis and by the basal contacts of beach barrier sediments which sharply overlie the upper shoreface transgressive sedimentation is interrupted in both embayments by a constructional beach barrier wyvuri and abbreviated progradation mutchero corresponding to a 5 m pause in relative sea level rise at c 6800 yr bp sea level control of fine scale coastal sedimentation patterns is beginning to be widely recognized and provides an accurate analogue for stacked ancient sequences

shelf wide erosion deposition and suspended sediment tranport during cyclone winifred central great barrier reef australia abstract observation of shelf sediments collected immediately before and after cyclone winifred crossed the central great barrier reef shelf 1 february 1986 confirmed that the storm produced a normally graded mixed terrigenous carbonate storm layer extending 30 km offshore in water up to 43 m deep distinct post winifred changes in the cross shelf distribution of organic carbon and carbonate in the mud fraction of the sediment suggest that suspended sediment transport was extensive and that the storm layer had multiple sediment sources on a shelf wide scale the storm layer is composed almost entirely of reworked shelf sediment erosion depths were greater on the mid shelf 20 40 m water depth than on the inner shelf 6 9 cm and 5 1 cm respectively particles finer than medium sand were eroded and transported out of the mid shelf the inner shelf portion of the storm layer formed by the combination of three sediment sources including 1 seaward transport of terrigenous sediment in buoyant freshwater flood plumes 2 resuspension and settling of inner shelf sediment and 3 resuspension and shoreward transport of mid shelf sediment mass balance calculations predict that at least 10 30 of the inner shelf storm layer is composed of mid shelf mud combined wave and wind forced currents probably resuspended mid shelf material and drove the suspended fraction alongshelf and shoreward a minimum distance of 15 km the results suggest that tropical cyclones are capable of sporadic but efficient cross shelf transport of suspended sediment on shallow cyclone prone shelves suspended sediment may easily be exchanged between adjacent sedimentary facies in ancient shelf sequences the transport history of the mud will be complex and stratigraphically equivalent facies may have similar mud types but completely different sands

high frequency of super cyclones along the great barrier reef over the past 5 000 years understanding long term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances1 2 3 4 5 for predicting present and future community vulnerability and economic loss6 and for assessing whether changes in the variability of such cyclones are induced by climate change7 our ability to accurately make these assessments has been limited by the short less than 100 years instrumented record of cyclone intensity here we determine the intensity of prehistoric tropical cyclones over the past 5 000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse grained alluvial fan deposits these features occur along 1 500 km of the great barrier reef and also the gulf of carpentaria australia we infer that the deposits were formed by storms with recurrence intervals of two to three centuries8 9 10 11 and we show that the cyclones responsible must have been of extreme intensity central pressures less than 920 hpa our estimate of the frequency of such super cyclones is an order of magnitude higher than that previously estimated which was once every several millennia12 13 14 and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events

holocene reef sequences and geochemistry britomart reef central great barrier reef australia holocene reef development was investigated by coring on britomart reef a mid shelf reef 23 km long and 8 km wide situated 120 km north of townsville in the central great barrier reef gbr two holes were drilled britomart 1 on a lagoon patch reef and britomart 2 on the windward reef crest the holocene reef 25 5 m is the thickest yet recorded in the gbr and overlies an uneven substrate of weathered pleistocene limestone mineralogical and geochemical analyses show that magnesian calcite and aragonite were converted to low mg calcite below the holocene pleistocene disconformity corals above the interface have 7500 8500 ppm sr but 1650 1500 ppm just below it decreasing to 400 800 ppm downwards the intermediate sr values could be due to partial replacement of aragonite by calcite or higher original sr content in the corals three units are recognized in the holocene 1 coral boundstone unit 2 coral framestone unit and 3 coral rudstone unit the coral boundstone unit forms the top 5 m of both cores and is algal bound coral rubble similar to the present reef top the coral framestone unit is composed of massive head corals diploastrea heliopora and porites sp and is currently forming in patch reefs situated in the lagoon and along the reef front the coral rudstone unit comprises coral rudstone and floatstone with unabraded and unbound coral clasts in muddy matrix this matrix may be up to 30 sponge chips radiocarbon dating indicates the reef grew more rapidly under the lagoon than under the reef front from 7000 to 5000 yr bp the rate of reef growth matched existing estimates of sea level rise but lagged approximately 1000 years 5 10 m behind it most of the reef mass accumulated between 8500 and 5000 yr bp as a mound of debris perhaps stabilized by seagrasses or algae accretion of the reef top in a windward direction between 5000 and 3000 yr bp created the present steep reef front profile

comparison of sonographs taken before and after hurricane diana onslow bay north carolina high resolution side scan sonar data collected from the middle continental shelf of onslow bay north carolina before and after an intense storm hurricane diana september 11 13 1984 were used to investigate the impact on this shelf surface wave hindcasting predicts that significant wave heights and periods were 6 m and 10 s during the storm9s passage and horizontal water velocity at the sea floor was 125 cm s comparison of prestorm and poststorm sonographs revealed no measurable sea floor changes distinct spatial patterns representing textural variations between miocene muddy sand and coarse holocene clean sand as well as extensive areas of loose rock debris appeared similar the storm dominated nature of this shelf surface results primarily from its sediment starved existence and the equilibrium that has been reached with the region9s ambient high energy setting

to the islands born the research potential of submerged landscapes and human habitation sites from the islands of nw australia this paper focuses on the continental shelf of nw australia and on models for change in littoral and offshore environments of relevance to human occupation over the last 50 kyr major island groups occur on the shelf including the montebello and barrow islands and those of the dampier archipelago at lowest sea level around 22 ka these would have been uplands that then became progressively isolated by subsequent sea level rise by integrating archaeological and zooarchaeological records from excavations on these islands with the geology and geomorphology we interpret palaeoeconomic resource potential in relation to changing sea level and coastline morphology the preservation potential for submerged archaeological sites and features is also assessed current archaeological evidence from these offshore islands indicates that the submerged coastal landscape is likely to have been a potentially rich environment for resources and human occupation even at times of lowest sea level and regional aridity should any exploration of submerged archaeology be carried out in this region it is likely to be rewarding offering unique insights into late pleistocene coastal occupation

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

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

holocene depositional history of the burdekin river delta of northeastern australia a model for a low accommodation highstand delta abstract the burdekin river of northeastern australia has constructed a substantial delta during the holocene delta plain area 1260 km2 the vertical succession through this delta comprises 1 a basal coarse grained transgressive lag overlying a continental omission surface overlain by 2 a mud interval deposited as the coastal region was inundated by the postglacially rising sea in turn overlain by 3 a generally sharp based sand unit deposited principally in channel and mouth bar environments with lesser volumes of floodplain and coastal facies the holocene burdekin delta was constructed as a series of at least thirteen discrete delta lobes formed as the river avulsed each lobe consists of a composite sand body typically 5 8 m thick the oldest lobes formed during the latter stages of the postglacial sea level rise 10 5 5 kyr bp are larger than those formed during the highstand 5 5 3 kyr bp which are in turn larger than those formed during the most recent slight sea level lowering and stillstand 3 0 kyr bp radiocarbon ages and other stratigraphic data indicate that inter avulsion period has decreased through time coincident with the decrease in delta lobe area the primary control on holocene delta architecture appears to have been a change from a pluvial climate known to characterize the region 12 4 kyr bp to the present drier enso dominated climate in addition to decreasing the sediment supply via lower rates of chemical weathering this change may have contributed to the shorter avulsion period by facilitating extreme variability of discharge more frequent avulsion may also have been facilitated by the lengthening of the delta plain channels as the system prograded seaward

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

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

siliciclastic sediment across the north queensland margin australia a holocene perspective on reciprocal versus coeval deposition in tropical mixed siliciclastic carbonate systems abstract according to conventional models of reciprocal sedimentation for tropical mixed siliciclastic carbonate systems shedding of carbonate material dominates slope and basin sedimentation during transgression and highstand while siliciclastic deposition dominates during lowstand this understanding permeates the stratigraphic literature and is the accepted depositional model on the great barrier reef gbr margin the results of this study however document coeval carbonate and siliciclastic highstand deposition on the gbr slope and basin seafloor sediment from queensland trough slopes and basin floor east of the gbr contains 20 to 50 terrigenous siliciclastic material one hundred and twenty six sediment samples were obtained from core tops and sediments grabs previously retrieved from shelf slope and basin environments of the north queensland margin these samples were analyzed for their carbonate content mineralogy and major element composition the amount of terrigenous siliciclastic material in sediment from the north queensland margin can be approximated by three independent methods 1 the noncarbonate residual 2 the sum of quartz clays and feldspars and 3 the sum of sio2 al2o3 fe2o3 and tio2 all three tracers show a distinct distribution of siliciclastic sediment across the margin shelf siliciclastic content is highest on the inner shelf decreasing eastward toward the gbr with the exception of relatively high siliciclastic content in several interreef passages queensland trough siliciclastic content is highest on the slope and basin between 15 and 17 s latitude decreasing to the south and east although the relative abundances of quartz and clay minerals vary across the margin the chemistry suggests a similar origin for the siliciclastic material moreover the zone of high siliciclastic abundance in queensland trough reflects enhanced siliciclastic accumulation siliciclastic material escapes the outer shelf to queensland trough through interreef passages between 15 and 17 s latitude it is then focused to the south by ocean currents siliciclastic sediment is likely sourced from a combination of rivers transporting holocene sediment to the gbr shelf and late pleistocene sediment eroded from the outer shelf and reworked to queensland trough siliciclastic material crosses the shelf although the mechanisms e g river plumes nepheloid layers tidal currents cyclones mushroom jets remain poorly constrained however shelf width is clearly an important factor in allowing cross shelf transport to occur mass balance calculations indicate that up to 13 of the late holocene annual riverine sediment output may be delivered to queensland trough modern and ancient mixed system depositional models must be reevaluated to allow for the possibility of coeval siliciclastic and carbonate deposition

neritic carbonate for six submerged coral reefs from northern australia implications for holocene global carbon dioxide abstract total contribution of six recently discovered submerged coral reefs in northern australia to holocene neritic caco3 and co2 is assessed to address a gap in global budgets caco3 production for the reef framework and inter reefal deposits is 0 26 0 28 mt holocene co2 production is 0 14 0 16 mt coral and coralline algae are the dominant sources of holocene caco3 although foraminifers and molluscs are the dominant constituents of inter reefal deposits the total amount of holocene neritic caco3 produced by the six submerged coral reefs is several orders of magnitude smaller than that calculated using accepted caco3 production values because of very low production a give up growth history and presumed significant dissolution and exports the contribution of submerged coral reefs to global holocene neritic caco3 is estimated to be 0 26 0 62 gt which yields 0 15 0 37 gt of co2 this amount of co2 is 0 02 0 05 of the 780 gt added to the atmosphere since 18 kyr bp contributions from australian submerged coral reefs are estimated to be 0 05 gt caco3 and 0 03 gt co2 for an emergent reef area of 47 9 103 km2 based on the growth history of the submerged coral reefs in the gulf of carpentaria maximum global holocene caco3 fluxes could have attained 0 3 gt yr 1 between 11 and 7 ka bp this additional caco3 would have culminated in a maximum caco3 production from all emergent and submerged coral reefs of 1 2 gt yr 1 and neritic caco3 production of 2 75 gt yr 1 the dilemma remains that the global area and caco3 mass of submerged coral reefs are currently unknown it is inevitable that many more submerged coral reefs will be found our findings imply that submerged coral reefs are a small but fundamental source of holocene neritic caco3 and co2

finite dispersal of a separative nepheloid plume by an internal hydraulic jump in a tropical mountainous river estuary this paper investigates the dynamics of an internal hydraulic jump in a river plume and associated suspended sediment dispersal field investigations were undertaken into the river plume generated by the herbert river australia following a moderate flood event induced by cyclone fritz in 2004 the forced plume experiences an abrupt transition from supercritical to subcritical via an internal hydraulic jump as defined by a mode 1 internal froude number computed using the phase speeds from the taylor goldstein equation the hydraulic theory of a two layer stratified flow was used to identify the plume shape and the mechanical energy loss within the jump the hydraulic jump energy loss is primarily transferred to the buoyancy driven potential energy uplifting the river plume intense stratification decreases the bottom stress damping the resuspension therefore a separative nepheloid dispersal system occurs at the jump section both the upper and lower nepheloid flows are confined to the inner shelf but have different dispersal behaviors and mechanisms the upper nepheloid flow which is primarily controlled by advection and settling satisfies an exponential decay law of the total suspended sediment concentrations versus the offshore distance the lower nepheloid flow dominated by deposition is detached seaward near the lift off point of the river plume a turbidity front associated with the jump may accumulate a large quantity of suspended sediments enhancing sediment release from the river plume these findings will promote in depth understanding of both the cross shelf sediment dispersal and muddy deposit on the shelf

contrasting facies patterns in subtropical and temperate continental slope sediments inferences from east australian late quaternary records abstract studies of latest quaternary continental slope sediments at two localities on the east australian margin have revealed markedly different responses to late quaternary sea level fluctuations offshore of noosa in the sub tropics the sediment is predominantly a mixture of fine metastable carbonate siliciclastic material and pelagic carbonate important features of the stratigraphy include a siliciclastic dominated facies deposited relatively slowly during the last glacial lowstand sedimentation rate 8 cm ka and a calcareous facies rich in metastable carbonate deposited more rapidly during the late post glacial transgression sedimentation rates 15 24 cm ka highstand and transgressive sedimentation rates are greater than lowstand rates by a factor of 2 5 6 due to increased shelf carbonate productivity after flooding of the mid shelf off sydney in temperate latitudes continental slope sediment is largely a mixture of fine siliciclastic material and pelagic carbonate mean sedimentation rates range from 2 to 5 cm ka over the last four oxygen isotope stages with mean glacial interstadial rates higher than holocene rates by a factor of 1 36 this largely reflects the transfer of siliciclastic mud from the shelf to the slope during sea level regression in both localities facies changes on the slope are not related to specific sea level states e g lowstand facies transgressive facies etc but reflect instead the interaction of changing sea level with shelf morphology

mesoscale circulation features of the great barrier reef region inferred from noaa satellite imagery abstract the commissioning of a noaa satellite receiving station at townsville in north queensland in 1988 greatly expanded the a vhrr coverage of the northeast australian region to include the entire great barrier reef system and marginal seas selected imagery from this and a southern station installed previously at aspendale victoria provide a valuable new perspective on oceanographic phenomena occurring in this ecologically significant region this perspective could not be attained using conventional ship board and in situ oceanographic sampling techniques a rich spectrum of mesoscale oceanographic features is revealed in the analyzed imagery and various features such as western boundary current meanders frontal shear waves eddies and jets are described the temporal and spatial variability of these features appears strongly linked to that of the larger scale coral sea current circulation several of the features identified are unique to the region others resemble features observed in other western boundary current systems but are significantly modified by the complex regional topography and by the presence of the great barrier reef gbr evidence has been found for a number of processes which have significant implications for the origin and maintenance of gbr ecosystems including shelf edge exchange processes stratified slope water intrusions onto the shelf and boundary layer mixing around reefs such processes provide a mechanism for injection of cool nutrient rich waters into the reef matrix the imagery provides a clear picture of a well organized but spatially complex frontal system existing in the southern coral sea which is associated with enhanced commercial and recreational fishing activity in the region the avhrr imagery has thus proven to be a valuable tool for spatial mapping of oceanographic features throughout the gbr region for hypothesis formation in dynamical and modeling studies and for ship board reconnaissance operations

cardium formation u cretaceous at seebe alberta storm transported sandstones and conglomerates in shallow marine depositional environments below fair weather wave base as a result of detailed mapping at seebe alberta we have defined five coarsening upward sequences in the turanian cardium formation the sequences begin with bioturbated mudstones and coarsen int

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

sediment provenance in a tropical fluvial and marine context by magnetic fingerprinting of transportable sand fractions the sources and fluxes of sediment to the great barrier reef lagoon from northeastern australian rivers have been the subject of much concern and study with the large catchments of the burdekin and fitzroy rivers thought to be the key sources at present here the utility of newly developed magnetic fingerprinting methods for identifying sediment provenance both onshore and offshore and in association with individual large flood events is investigated within the burdekin catchment sediments are mobilized from different subcatchments by runoff generated by intense localized rainfall events magnetic measurements were made on untreated and acid treated samples of river channel sediments within the burdekin river subcatchments and from the estuarine and inner shelf depocentres of burdekin river sediments the acid treatment removes all discrete magnetic particles and coatings and leaves magnetic inclusions protected within host silicate grains as the basis of the measured magnetic signature of a sample the magnetic properties of the acid treated samples display statistically distinct sediment provenance groupings sand samples from the upper burdekin river appear magnetically distinct from samples from tributaries of the burdekin e g hann creek fanning river and also from nearby coastal rivers including the haughton suspended sand samples from a burdekin flood event in 2000 appear to have a different source compared with those from floods in 1998 and 1999 comparisons of the terrestrial acid treated sand fractions with the same acid treated sand size fractions from transects taken offshore suggest that the surface sediments in upstart bay and bowling green bay have different sources some of these sources are as yet unidentified but may represent the unsampled lower discharge south western burdekin subcatchments and or along shore drift of sand from the south perhaps even from the fitzroy river over millennial timescales of cyclone pumping the magnetic inclusion method precludes any obfuscation or confounding of sediment source which might arise from hydraulic sorting and or post depositional magnetic diagenesis or authigenesis

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

hurricane induced sediment transport in open shelf tropical systems an example from st croix u s virgin islands hurricane hugo passed directly over st croix on 17 september 1989 sustained winds in excess of 110 knots gusts to 165 knots and waves 6 7 m in height accompanied the storm along the north coast wave height was lower ca 3 4 m due to the leeward position of the shelf in the deeper reefs at cane bay and salt river damage was confined primarily to the soft bodied benthic community e g sponges gorgonians coral damage was much less severe largely because of the buffering effects of the water column the greatest change observed after the storm was wholesale flushing of sand from shelf edge areas in salt river submarine canyon a minimum of 2 million kg of sediment were flushed into deeper water the transport rate associated with the storm was eleven orders of magnitude above that measured during fair weather and the volume of sediment that was removed from the canyon equalled roughly a century of normal sediment accumulation at cane bay 336 000 kg of sediment were flushed from a single channel with similar amounts removed from adjacent breaks in the shelf edge reef a current meter in salt river submarine canyon provided information on the timing and intensity of the oceanographic processes related to hurricane hugo as the storm approached waves piled water against the shoreface and in salt river bay as the storm passed over st croix the change in wind direction followed by a decrease in wave height triggered a release of water trapped in the bay and along the adjacent shoreline by waves earlier in the storm for a period of 4 6 hours net down canyon currents reaching 2 m s and oscillatory flows up to 4 m s occurred along the base of the western canyon wall removing up to 2 m of sand similar events were likely responsible for the wholesale removal of sand in eastern cane bay the paradoxical concurrence of wholesale sediment transport and low level reef damage is related to the protection from waves but not wind afforded by the north coast of st croix facing away from the direction of storm approach these observations and measurements provide our first opportunity to relate sediment export in such a high energy event to the physical processes that were responsible calculations based on post hugo measurements are in agreement with an earlier sediment budget for salt river canyon sediment export in cane bay exceeded the volume similarly predicted because such events are probably common on all exposed carbonate shelf margins storms like hurricane hugo are among the most important factors in the cycling of sediment through exposed open marine environments both now and in the geologic past the patterns of reef damage and sediment transport are much more complicated than previously envisioned and more thoughtful consideration of their variability and the processes responsible is essential to an understanding of the signature that will be left by major storms

cyclone pumping sediment partitioning and the development of the great barrier reef shelf system a review abstract the modern great barrier reef gbr is part of the world s largest and best known mixed terrigenous carbonate continental margin the gbr shelf contains three shore parallel sedimentary belts an inner shelf zone of terrigenous sedimentation at depths of 0 22 m a middle shelf zone of sediment starvation at depths of 22 40 m and an outer shelf reef tract with its inner edge at ca 40 m depth these zones are controlled by the dynamics of northward fair weather along shelf drift driven by southeasterly trade winds and by the regular passage of tropical cyclones cyclones cause wind driven north directed middle shelf flows in excess of 130 cm s which erode the seabed concentrate the sparse mobile sediment into sand ribbons and advect suspended load onto the outer part of the nearshore terrigenous sediment prism and into inter reef depocentres within the outer shelf reef tract cyclones largely control the input of new sediment into the gbr system via river flooding seabed erosion or reef breakage they also help to control the partitioning and dispersion of the three main shore parallel belts of sediment and hence stratigraphic accumulation acting as a sediment pump especially during interglacial highstands cyclones have exerted great control on the development of the modern gbr province and its sediments by maintaining a broad shelf parallel zone of episodically mobilised sediment and scoured seabed upon which coral reefs have been unable to form cyclones may also have partly controlled the timing of initiation of the first gbr at 0 6 mybp contrary to current models gbr storm beds are most likely to be preserved intact close to the shoreline and become coarser grained away from the shoreline for the central gbr highstand shedding only applies to carbonate sediment at the scale of local reefs system wide oceanographic controls cause high rates of carbonate sedimentation on the slope during both sea level rise and highstand concomitantly terrigenous sediment accumulates fastest on the slope during sea level rise and slowest during sea level lowstand and highstand

transport of mud on continental shelves evidence from the texas shelf abstract transmissivity and suspended sediment data from three cruises on the east texas continental shelf confirm that a bottom nepheloid layer bnl exists across the shelf this layer is most turbid in the nearshore and outer shelf regions in addition surface nepheloid layers exist close to shore due to river and bay outflows and on the outer shelf intermediate nepheloid layers are present as a result of quasi horizontal advection from the bnl the character of the bnl is not directly linked to local hydrography or substrate being instead a function of the shelf dynamics in the nearshore regime high energy coastal processes and high sediment input from bays and rivers maintain the bnl at the shelf edge the bnl is formed by near inertial internal waves and shelf waves which resuspend and transport fine sediment present day sediment deposition on the east texas shelf can be directly related to the above processes mud is accumulating in the nearshore environment due to river input and on the inner and midshelf regions as a result of deposition from bnls and snls on the outer shelf bnls and inls transport fine sediment further offshore so that in effect suspended sediment bypasses the outer shelf

marine geology of the sodwana bay shelf southeast africa abstract the geostrophic current controlled northern zululand shelf displays a unique assemblage of interesting physical sedimentological and biological phenomena the shelf in this area is extremely narrow 3 km and is characterised by submarine canyons coral reefs and steep gradients on the continental slope three submarine canyons occur in the study area and are classified as mature or youthful phase canyons depending on the degree to which they breach the shelf these canyons originated as mass wasting features which were exploited by palaeo drainage during sea level regressions shelf lithology is dominated by a series of coast parallel patch coral reefs which have colonised beachrock and aeolianite sequences that extend semi continuously from 5 to 95 m and delineate late pleistocene palaeocoastline events the unconsolidated sediment on the shelf is either shelf sand mainly terrigenous quartz grains or bioclastic sediment large scale subaqueous dunes commonly form in the unconsolidated sediment on the outer shelf due to the agulhas current flow these dunes occur as two distinct fields at depths of 35 to 70 m the major sediment transport direction is towards the south but occasional bedload parting zones exist where the bedform migration direction changes from south to north

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

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

geomorphology of submerged reefs on the shelf edge of the great barrier reef the influence of oscillating pleistocene sea levels the submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates eustatic sea level oscillations and oceanographic processes australia s north eastern submerged shelf edge reefs have previously been explored but all studies have been limited by either low resolution single beam profiles or by their limited spatial extent the aim of this study is to improve the understanding of the origin and development of submerged shelf edge reefs terraces and related features on the great barrier reef gbr and the influence of pleistocene sea level oscillations on their distribution and geomorphology we investigated the first large scale 1400 km2 3d bathymetry and acoustic backscatter dataset of four widely spaced sites located across ca 650 km along the shelf edge at ribbon reefs 1 5 noggin pass viper reef and hydrographers passage we provide a comprehensive description and systematic classification of the shelf edge features and constrain their spatial distribution and geomorphologic variability using a wide range of quantitative morphometrics fifteen features are defined four of which are the focus of this study including terraces pinnacles ridges and channels using modern reefs within the gbr for comparison we interpret these as fringing reefs patch and barrier reefs and tidal channels respectively the influence of gross shelf geomorphology and oceanographic factors driving the observed variability within and between sites is discussed in conjunction with mid late pleistocene sea level oscillations we observed two distinct types of reef growth characterised by the degree of development which we interpret as analogous to juvenile and mature modern reefs of the gbr juvenile reefs are very common and occur within each site at depths of less than 50 m to greater than 100 m they are defined as discontinuous peaked barrier reefs peaked patch reefs and fringing reefs mature reefs are less common and develop exclusively at a depth range of ca 50 70 m these reefs are defined as flat topped continuous barrier and double barrier reefs through a comparison with published mid late pleistocene sea level oscillations we note that the depth range of mature reefs is consistent with the depth of repeated low amplitude 20 m eustatic sea level oscillations and independent of the relative time spent at sea level we conclude that repeated low amplitude sea level rises provide the much needed accommodation space for vertical accretion that is not provided during stillstands without inducing reef drowning which can be caused by high amplitude sea level rise low amplitude sea level falls are also less detrimental than high amplitude falls in terms of habitat compression together the effects of enhanced reef accretion and limited habitat compression at depths of 50 70 m have lead to a concentrated net gain in vertical relief that is not observed elsewhere on the shelf edge

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

magnetostratigraphic dating of the proposed rhaetian gssp at steinbergkogel upper triassic austria implications for the late triassic time scale the global stratotype section and point gssp for the rhaetian stage has recently been proposed at steinbergkogel in austria we re sampled the steinbergkogel sections stk a and stk b c in high resolution to establish a robust magnetostratigraphy that allows global correlation the palaeomagnetic signal at steinbergkogel is composed of three components which can be separated by thermal demagnetization the highest temperature component revealed between 280 300 and maximum 600 c is of dual polarity and is interpreted as primary rock magnetic experiments showed that the signal is carried by magnetite our results allow correlation between the two individual steinbergkogel outcrops subsequently we correlate the two key biostratigraphic horizons for the base of the rhaetian the fo of m hernsteini and the fad of m post hernsteini to other sections of the tethys domain the correlation to the astronomically dated continental successions of the newark basin indicates that these positions for the base of the rhaetian are most likely determined in chrons e16n and e16r respectively this correlation is confirmed by cyclostratigraphic control on the marine pizzo mondello italy section where a combination of long period milankovitch cycles 175 myr and short eccentricity cycles 100 kyr provide additional correlation constraints respectively supporting a long duration of the rhaetian our study implies that the norian and rhaetian stages have durations of 17 and 9 myr

millennial scale changes in north atlantic deep water circulation during marine isotope stages 11 and 12 linkage to antarctic climate the time interval represented by marine isotope stages mis 11 and 12 ca 360 470 ka may contain the most extreme glacial and interglacial climate conditions of the late pleistocene sediments from the bermuda rise western north atlantic provide clues to the nature of climate variability during this period our geochemical records indicate that millennial scale climate instability and associated changes in north atlantic deep water nadw production occurred during both interglacial mis 11 and glacial mis 12 stage 12 is punctuated by a series of interstadial events that occurred at a 5 6 k y periodicity and the occurrence of ice rafted debris at various times during stage 12 indicates that icebergs were present at least as far south as 34 n during this glacial period within the limits of our correlation the atmospheric temperature changes recently reported for the vostok ice core for the stage 11 time period appear to be represented by coeval changes in nadw flow specifically warming in antarctica is associated with increased production of nadw

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

modern shoreface and inner shelf storm deposits off the east texas coast gulf of mexico abstract the modern shoreface and inner shelf sediments off the east texas coast on the gulf of mexico were examined using sediment cores and high resolution seismic data low sediment input and low effective accommodation space resulted in the overall thinness of the modern marine sediment cover in the region erosion on the inner shelf during historic 100 yr times produced patches of sand in a predominantly mud dominated environment storm beds are scarce on the inner shelf the shoreface succession off galveston island is characterized by offshore directed crosscutting storm channels of varying sizes the existence of these channels and the relatively high frequency of storms and hurricanes that have affected the region during historical imes are inconsistent with the paucity of storm deposits on the inner shelf the offshore directed channelized flows may have been prevented from going beyond the shoreface by strong along shelf storm currents that impinged on the shoreface in contrast to the storm record on the east texas shelf the central texas shelf shows a greater frequency of and more laterally persistent storm sand beds due to greater effective accommodation space and higher sediment supply there

the cyclone winifred storm bed central great barrier reef shelf australia abstract shelf sediments were collected immediately before 8 20 january 1986 immediatly after 9 10 february 1986 and one year after 27 february 1987 cyclone winifred crossed the central great barrier reef shelf on 1 february 1986 the storm produced a normally graded mixed terrigenous carbonate storm bed more than 11 cm thick covering an area at least 1 200 km2 and extending more than 30 km offshore to water depths greater than 40 m the storm layer encompasses two lithologically distinct shelf parallel facies belts the nearshore 0 25 m depth storm bed is 311 cm thick thins offshore and grades upward from medium sand to silty clay offshore 25 43 m depth the storm bed thickens to more than 11 cm and consists of normally graded well sorted relict quartz and skeletal gravelly sands capped by a thin mud veneer the cross shelf distributions of grain size mineralogy carbonate content and carbon isotope ratios were very similar before and after winifred suggesting the storm bed did not result from offshore directed storm currents but rather in situ resuspension and settling of the shelf sand with shoreward transport of mud in contrast to storm sedimentation models which predict thinning and fining offshore winifred created a layer that becomes thicker and coarser grained in deeper water in response to cross shelf substrate changes after one year the winifred storm layer was well preserved nearshore 30 m water depth below fairweather wave base preservation may not be a matter of insulating the layer from physical reworking below fairweather wave base but of burying it where rates of sediment accumulation outpace bioturbation the effects of storms similar in size to winifred may be well concealed in ancient shelf sequences subject to rapid biological remixing of storm layers

classification of sedimentary furrows and a model for furrow initiation and evolution sedimentary furrows are longitudinal bed forms which form in fine grained cohesive sediments of the deep sea floor as well as in similar sediments in estuaries and in large lakes deep sea furrows have been observed where bottom currents often flow in one direction at 5 to 20 cm sec currents are much stronger greater than 50 cm sec in furrowed estuarine environments but sediment accumulation rates are higher a review of furrows studied in a variety of locations and environments suggests that these bed forms fall into two broad morphological classes those developed in muddy cohesive sediments tend to have steep walls and flat floors while those developed in carbonate rich cohesive sediments are broad and have gently sloping walls at abyssal depths furrows can often be detected by their distinctive echo patterns on 3 5 khz echo sounders a series of similar evenly spaced hyperbolic echoes which often have their apices tangent to the sea floor however different furrow cross sections may generate distinctive hyperbolic echo patterns a model for furrow initiation and development in muddy cohesive sediments suggests that furrows develop in depositional environments swept by recurring directionally stable and episodically strong currents furrows are initiated when secondary circulations in the boundary layer align coarse generally light debris in sand ribbon like bed forms as the coarse light sediments move along the sea floor they abrade small longitudinal troughs into the muds the grooves may fill in during intervals between strong current events if sedimentation rates are too high once a furrow is established on the sea floor further development may be controlled by the balance between sediment deposition and erosion where deposition occurs continuously and erosion occurs only episodically during brief periods of increased current strength narrow furrows width 1 5 to 1 15 of spacing appear to develop where deposition exceeds erosion whereas wide furrows width 1 2 of spacing develop where erosion exceeds or equals deposition dissolution may play an important role in the formation and evolution of furrows in carbonate rich cohesive sediments secondary circulation patterns over established furrows may be strongly controlled by bed form topography

late quaternary sedimentation on the great barrier reef continental shelf and slope east of townsville australia cores collected in a shelf to basin transect from northeastern australia document the stratigraphic development of late quaternary deposits low sea level to 120 m slope sedimentation is dominated by prograding fluvial deposits with wave dominated deltas forming on the shelf edge and upper slope the onset of sea level transgression into the excavated shelf river channels on the outer shelf resulted in estuarine sedimentation along an indented coastline 15 000 11 000 yrs b p reducing terrigenous sediment supplies to the slope on the outer shelf halimeda muddy sandy gravels were deposited over a pleistocene limestone erosional surface from about 10 500 yrs b p transgression submerged the limestone outcrops and estuaries of the middle shelf where coral reef complexes formed the outer and middle parts of the shelf thus became dominated by carbonate sedimentation while the inner shelf received fluvial input mixed with locally derived carbonates the sequence is bounded by an unconformity clearly marked by erosional down cutting the results of the study are combined with those of previous workers to develop transgressive and continued high sea level system tract models the latter continued high sea level model is used to extrapolate present high sea level sedimentation patterns into the future providing a model for comparison with ancient sequences which may also have formed in such a depositional environment

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

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

the initiation of the southern central great barrier reef new multiproxy data from pleistocene distal sediments from the marion plateau ne australia abstract significant synchronous shifts in the chemistry mineralogy grain sizes and color of the sediments at 6 m below sea floor mbsf at odp site 1195 on the marion plateau ne australia are interpreted to reflect a major regional paleoceanographic change the initiation of the southern province of the great barrier reef gbr the onset of this massive carbonate production centre nearby resulted primarily in increased deposition of carbonate rich sediments of neritic origin both sedimentation rate and terrigenous input record a coincident decline attributed to inshore trapping of materials behind the reefs our best estimate places the development of reef framework in the southern part of the gbr between 560 and 670 kyr b p based on an age model combining magnetostratigraphic and biostratigraphic data the proposed estimation agrees with previous studies reporting an age between 500 and 930 kyr b p constraining more tightly their results however it does not support research placing the birth of the gbr in marine isotope stage mis 11 400 kyr nor the theory of a worldwide modern barrier reef development at that time

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

new constraints on the origin of the australian great barrier reef results from an international project of deep coring two new boreholes provide the first direct evidence of the age of the australian great barrier reef an inner shelf sequence total depth 86 m basal age 210 40 ka comprises a dominantly siliciclastic unit thickness 52 86 m overlain by four carbonate units total thickness 0 34 m a shelf edge and slope sequence total depth 210 m reveals three major sections 1 a lower section of resedimented flows deposited on a lower slope 2 a mid section including intervals of corals rhodoliths and calcarenites with low angle graded laminae and 3 an upper section of four shelf margin coral reef units separated by karst surfaces bearing paleosols sr isotope and magnetostratigraphic data indicate that the central great barrier reef is relatively young post bruhnes matuyama boundary time and our best estimate for the onset of reef growth on the outer barrier system is ca 600 280 ka this date suggests that reef initiation may have been related to the onset of full eccentricity dominated glacio eustatic sea level oscillation as inferred from large amplitude saw tooth 100 k y 18o cycles after marine isotope stage 17 rather than to some regional environmental parameter a major question raised by our study is whether reef margins globally display a similar growth history the possibility of a global reef initiation event has important implications for basin to shelf partitioning of caco3 atmospheric carbon dioxide levels and global temperature change during quaternary time

current subsurface seawater intrusion to base levels below sea level the imperial valley jordan dead sea rift and the afar and oattara depressions all regions below sea level and the only regions in the world so situated are characterized by saline and hypersaline groundwaters and lakes phenomena that to date have been solely attributed to ancient lagoons salt dissolution and evaporation current subsurface seawater intrusion is herewith suggested as an additional mechanism responsible for the salination of these regions this type of dynamic seawater flow is feasible where there is a a base level below sea level with a hydrological continuity between the two levels and b a low groundwater divide between the base levels with a shallow seawater freshwater interface situated above the base of the aquifer

cyclone frequency during the last 5000 years at curacoa island north queensland australia abstract a series of storm deposits at curacoa island a steep bedrock island in the palm group north queensland record the passage of cyclonic events storm ridge accretion occurs when cyclonic waves and surge combine to transport coarse sediment mostly broken coral onto the shore and deposit it above normal tidal levels narrow fringing reefs at curacoa act as a rapidly replenished sediment source augmented by lithic gravel transported longshore beachface stormberm ridge platform and washover deposits can accrete during a single event a series of storm ridges were examined via stratigraphic pits and trenches on two traverses deposits from 22 events were identified and their ages were determined using 68 radiocarbon dates from coral clasts most dates from each storm deposit formed statistically accordant groups only 15 of the dates were older than the group ages and were interpreted as reworked specimens accordant ages within each group were combined and converted to calibrated radiocarbon ages ridge ages decrease uniformly with distance from the oldest ridge indicating uniform depositional processes over the last 5000 years a time series of storm deposit ages indicates that cyclone frequency was statistically constant over the last 5000 years this suggests that cyclone frequency may not have been affected by sea surface temperatures in the region which appear to have been about 1 c warmer about 5000 years ago gagan m k ayliffe l hopley d cali j mortimer g chappell j mcculloch m head m j 1998 temperature and surface water balance of the mid holocene tropical western pacific science 279 1014 1018

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

four storm event beds and the tropical cyclones that produced them a numerical hindcast a three dimensional numerical prediction system for storm sedimentation has been constructed to compute a cyclonic wind field coastal circulation storm waves generated over the continental shelf the combined effects of steady currents and waves on the benthic boundary layer both suspended and bed load transport of sediment and conservation of the sea floor it has been used to hindcast the oceanographic and sedimentological responses of the western gulf of mexico to four historical tropical cyclones in order to investigate the effects of coastal configuration and storm variability on event bed genesis the simulations reveal several common responses to these storms 1 onshore flow to the fight of the storm track generally transports fine sediment landward 2 off shore flow to the left transports coarser sediment seaward and 3 for an observer facing the coast right to left along shelf flow transports finer sediment in deep water and coarser sediment in shallow water the main source of sandy sediment on the inner shelf is the shoreface which is eroded by currents driven by wind stress geostrophy and offshore flows associated with collapse of the coastal setup coastal geometry is the dominant factor in determining sedimentation patterns along the coast in front of each storm the volume of sediment transported obliquely onshore or offshore is a function of shelf gradient and coastal configuration steeper gradients constrain flow to a more longshore pattern concave coastlines promote greater shoreface erosion because of increased coastal setup none of the simulations reveals the vertical current structure predicted by the geostrophic model for continental shelf circulation because the calculated depth of the wind mixed layer exceeded local water depth everywhere over the shelf thus in these experiments most of the continental shelf fell within the friction dominated zone in which the upper and lower boundary layers overlap resulting in vertically uniform along shelf flow

paleoclimatic significance of phanerozoic reefs a database of pre quaternary phanerozoic reefs is used to test the significance of ancient reefs as paleoclimatic tracers the compilation of reef paleolatitudes through time and comparison with published paleoclimate curves shows that neither the width of the tropical reef zone nor the total latitudinal range of reefs is correlated with published estimates of paleotemperature however reefs trace paleoclimate indirectly algal reefs tend to prevail during icehouse climatic intervals and distinct high latitude reefs are only developed in cold intervals whereas during greenhouse episodes the reef zone usually ended abruptly at a particular latitudinal boundary in the subtropics additionally different biotic reef types tended to be concentrated in different latitudes the lowest latitudes have usually been occupied by coralline sponge or microbial reefs coral reefs tended to grow in intermediate latitudes and bryozoan reefs constantly occupied the highest latitudinal position

radiocarbon evidence for the timing and rate of island development beach rock formation and phosphatization at lady elliot island queensland australia abstract lady elliot island great barrier reef is a coral cay constructed from near concentric shingle ridges composed of coral tridacna shells and bioclastic sand bound by guano derived phosphatic cement radiocarbon dating of individual tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years a shallow platform reef existed at lady elliot since at least 6500 yrs b p shortly before 3200 yrs b p island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate 60 m ka 1 to leeward and 90 m ka 1 windward phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years the youngest cemented ridge top is less than 770 years whereas at the base of uncemented ridges phosphatization is a modern 1950 a d process similarly low level beach rock has continued to form within the last 25 years a significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of lady elliot island formed an eastern spit and stranded high level beach rock however the radiocarbon ages of tridacna samples from shingle ridges from lady elliot and curacoa islands are uniformly distributed kolmogorov smirnov test throughout the last 4000 years we interpret this to indicate no significant variation in ridge forming processes or fluctuation in average storminess during this interval

lowstand rivers need not incise the shelf an example from the great barrier reef australia with implications for sequence stratigraphic models a key tenet of many sequence stratigraphic models is that sea level lowering causes widespread fluvial incision of the subaerially exposed continental shelf and that river borne terrigenoclastic sediments bypass the lowstand shoreline via canyons to the continental slope and basin floor consequently the occurrence of incised channels is considered a fundamental criterion for the recognition of sequence boundaries in ancient shelf successions contrary to this we argue that rivers may not necessarily incise during glacio eustatic lowstands if they flow out onto a coastal plain flanked by a broad low angle shelf on the great barrier reef shelf fluvial incision did not occur during the last glacial maximum lgm but instead subaerial accommodation was created and infilled as contemporary rivers graded to the lgm bayline incision was restricted to the lowstand shelf break where canyons of limited extent formed by nickpoint retreat

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

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

holocene sediment lithofacies and dispersal systems on a storm dominated back arc shelf margin the east coromandel coast new zealand abstract holocene sediment lithofacies and dispersal systems on the east coromandel shelf new zealand are mainly characterised by an accommodation dominated regime in which autochthonous siliciclastic sediments were reworked through erosional shoreface retreat during the post glacial marine transgression 12 0 6 5 ka stabilisation of sea level at its present position ca 6 5 ka initiated onshore reworking of the autochthonous deposits into fine grained regressive barrier and shoreface sands while coarser sands remained offshore to form an erosional lag inner shelf deposit modern episodes of shoreface erosion rework fine and coarse autochthonous sands offshore and northwards into very large 0 5 2 5 m 250 1500 m submarine dunes the submarine dunes are similar in form to sand ridges on the north american atlantic shelf but with crests striking perpendicular to both the shoreline and generating flows allochthonous siliciclastic lithofacies are also important aspects of east coromandel shelf sedimentation and are transported offshore from infilled estuary systems to form very fine grained upper shoreface and muddy mid shelf sands the regional geology has a strong influence on shelf lithofacies and dispersal systems off the east coromandel coast southern shelf regions are associated with deep back arc basins which have formed major late cenozoic depocentres for sediments sourced from the taupo volcanic zone further north a shallow volcanic platform extends out across the shelf and forms a barrier to any large scale along shelf dispersal of sediments consequently lithofacies in northern shelf regions tend to be highly variable and reflect local catchment lithologies

the influence of carbonate platform morphology and sea level on fifth order petrophysical cyclicity in slope and basin sediments adjacent to the great bahama bank abstract despite several decades of study details of the relationship between sea level and other factors controlling carbonate sedimentation require clarification to address this issue odp leg 166 drilled a slope to basin transect adjacent to the great bahama bank to document neogene and quaternary sea level changes and to precisely date the major unconformities within the slope and basinal succession here we describe the complex connection between the cyclicities evident in a range of sediment physical property parameters at leg 166 sites and their relationship to sea level fluctuations diagenesis and the morphology of the adjacent carbonate bank margin the characteristics of fifth order petrophysical cycles in miocene slope sediments of the great bahama bank are fundamentally different from those in overlying late pliocene and pleistocene slope sediments these intervals are separated by an early pliocene sequence with characteristics that are transitional between the overlying and underlying sequences we interpret the more symmetric character of the miocene cycles as reflecting cyclic sedimentation controlled by the interaction between sea level fluctuations and the ramp morphology of the adjacent platform and the markedly asymmetric late pliocene and pleistocene cycles as representing the interaction between sea level and a rimmed platform morphology in the case of the miocene cycles diagenetic overprints cause values for petrophysical properties controlled by porosity to be inverted compared to cycles in essentially unaltered late pliocene and pleistocene sediments a detailed understanding of the relationship between petrophysical cycles diagenesis sea level fluctuations and platform margin morphology offers the potential to provide a proxy for inferring the controls on carbonate sedimentation in situations where the nature of the carbonate platform margin is unknown e g where regional seismic data is poor or absent and or where sea level effects cannot be reliably determined by other means these petrophysical proxies should be of greatest benefit where downhole logging data is used as the primary basis for sediment characterization

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

the role of topography and erosion in the development and architecture of shallow water coral bioherms tortonian messinian cabo de gata se spain abstract during the miocene mediterranean shallow water carbonates were rich in scleractinian corals which thrive in various depositional settings a tortonian messinian bioherm belt developing in a heterozoan dominated ramp was investigated along a 1 2 km continuous transect located in the cabo de gata region the interval studied displays four depositional environments from mid to inner ramp dominated by swell waves and storm energy deposited as a single large scale depositional sequence during a 3rd to 4th order transgressive regressive cycle the bioherms grew in three phases and were essentially composed of in place primary frameworks three coral genera were the main framebuilders porites tarbellastrea and rare siderastrea associated with melobesioid and mastophoroid red algae and bryozoans as secondary framebuilders the corals display five morphotypes from a fast growing branched type to slow growing domal to plate morphologies with an uncommon form of mesh porites as the dominant morphotype changes in coral morphotype and composition of micro encrusters communities reveal changes in hydrodynamics detrital influx and perhaps nutrient levels bioherms architecture was driven by sea level palaeotopography and erosion the coral framework was affected during its development by erosion surfaces metres to tens of metres deep and hundreds of metres wide unexpectedly these surfaces are better developed on the inner edges of the bioherms this could indicate the circulation of strong bottom currents between the volcanic palaeohighs and the synoptic relief created by the buildups finally a major sub aerial erosional episode associated with increasing detrital influxes ended bioherm development thus allowing the colonization of the dead coral substratum by red algae

storm impact and evolution of a mangrove fringed chenier plain shoal bay darwin australia abstract storms are considered to have significant impacts on the development of chenier plains particularly through the devastation of mangrove vegetation but also in terms of winnowing sand and shell from mudflats and forming chenier ridges shoal bay in the beagle gulf northern australia contains a small chenier plain which was struck by a severe tropical cyclone cyclone tracy on christmas day 1974 as it devastated the city of darwin the morphology vegetation and stratigraphy of the plain are described the plain is underlain by lower intertidal sand with shell hash a radiocarbon age of 6130 years bp indicates mangrove colonisation of this flat at the time that sea level stabilised around its present level after the postglacial transgression subsequently progradation of mudflats has occurred especially around 2300 years ago and shells of this age are found both in growth position from within the mudflats and incorporated into the shelly chenier ridges a further phase of build out and subsequent erosion is reflected by stumps and in situ bivalves being excavated presently on the foreshore radiocarbon dating about 900 1100 years bp within this context of evolution cyclone tracy can be seen to have had severe consequences upon the patterning of mangroves with extensive windthrow of ceriops and defoliation of rhizophora at the western end of the plain recovery of the mangrove vegetation has been gradual and is still incomplete however the storm had little influence on the pattern of landform development indeed the aerial photographic sequence indicates a trend by which sand shoals are gradually reworked landwards in places moving through mangrove vegetation the study suggests that rather than pronounced regional episodes of alternative mudflat buildout and erosion both processes occur simultaneously at different points along this foreshore

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

coral variation in two deep drill cores significance for the pleistocene development of the great barrier reef abstract variations in lithology and coral assemblages in drill cores from outer and inner shelf reefs are used to characterize the pleistocene development of the great barrier reef based on petrographic isotopic and seismic characteristics the outer shelf core from ribbon reef 5 is divided into three sections 1 a main reef section from 0 to 96 m is composed of six reef units 2 a rhodolith section from 96 to 158 m is interbedded with two thin reef units and 3 a basal section from 158 to 210 m is composed of non reefal skeletal grainstones and packstones two distinct coral assemblages identified in this core represent a shallow high energy community and lower energy community these two assemblages are repeated throughout the main reef section with some units recording transitions between assemblages and others composed of only a single assemblage these coral assemblage data also correlate with transitions recorded by coralline algae using similar criteria the inner shelf core from boulder reef is divided into two sections 1 an upper carbonate dominated section from 0 to 34 m is comprised of four reef units and 2 an underlying mud section from 34 to 86 m is composed of siliciclastics and two thin coral bearing units the four reef units in the upper section are dominated by a single coral assemblage representing a community typical of low energy turbid environments taken together these data indicate that 1 reef growth on the inner shelf initiated later than on the outer shelf 2 true reef turn on in outer shelf areas as represented by the main reef section in ribbon reef 5 was preceded by a transitional period of intermittent reef development and 3 the repeated occurrence of similar coral assemblages in both drill cores indicates that the great barrier reef has been able to re establish itself repeatedly producing reefs of similar composition over the last 500 ky despite major environmental fluctuations in sea level and perhaps temperature