tertiary sedimentary history and structure of the valencia trough western mediterranean abstract we present here main results of the common depth point cdp data acquired during the valsis 2 cruise in 1988 in the valencia trough the profiles are tied in with industrial well data and this correlation allows the sedimentary and structural history of the region to be deduced the valsis cruise seismic profiles have been supplemented by a very dense grid of industrial seismic lines and these data permit us to establish an accurate depth to basement map the formation of the initial grabens coeval with those of the gulf of lions is related to the early miocene opening of the northwestern mediterranean basin and the barcelona graben is filled by the same sedimentary layers including evaporites as that of the provencal region nevertheless the valencia catalan grabens have been reactivated by young extensional tectonics which could be a consequence of the convergence of africa relative to europe the valencia trough is segmented by transfer faults which trend nw se these faults which have a more accentuated structural expression than the valencia and catalonia grabens may act as transform faults separating the individual balearic islands the transfer faults are in strike with volcanic ridges which have been sampled during the dsdp leg 13 the dense seismic grid allows us to delineate several widespread volcanic features in the valencia trough which have been active from the early miocene to the pleistocene however we note that the volcanic features are mainly miocene in age whereas the recent volcanism is restricted to a narrow zone columbretes islands the compressional tectonics which deformed the balearic islands does not appear to extend far towards the north we delineate the compressional front north of ibiza but we failed to determine any thrust or fold north of mallorca whereas an extensional tectonics is evident

bedload sediment transport dynamics in a macrotidal embayment and implications for export to the southern great barrier reef shelf abstract keppel bay is a macrotidal embayment on a tectonically stable tropical coast which links the fitzroy river with the great barrier reef continental shelf estuaries and deltas act as conduits between catchments and inner shelf environments therefore understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral reefs that are potentially vulnerable to enhanced river sediment loads furthermore the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries particularly in turbid episodic systems such as the fitzroy river and keppel bay our sedimentological analysis of seabed samples shear stress modelling and three dimensional acoustic imaging reveals that keppel bay is a mixed wave and tide dominated estuarine system areas of sediment starvation and shoreward transport characterise the offshore zone whereas a complex of both active and relict tidal sand ridges and associated subaqueous dunes dominate the relatively protected southern keppel bay transport within this region is highly dynamic and variable with ebb dominated sediment transport through tidal channels into the outer bay where there is a switch to wave dominated shoreward transport ultimately bedload sediments appear to be reworked back inshore and to the north and are gradually infilling the bedrock defined embayment our characterisation of the keppel bay system provides a detailed example of the physiography of the seaward portion of a tide dominated system and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography

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

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

sediment flux across the great barrier reef shelf to the queensland trough over the last 300 ky the continental margin off northeast australia comprising the great barrier reef gbr platform and queensland trough is the largest tropical mixed siliciclastic carbonate depositional system in existence we describe a suite of 35 piston cores and two ocean drilling program odp sites from a 130 240 km rectangular area of the queensland trough the slope and basin setting east of the central gbr platform oxygen isotope records physical property magnetic susceptibility and greyscale logs analyses of bulk carbonate content and radiocarbon ages at these locations are used to construct a high resolution stratigraphy this information is used to quantify mass accumulation rates mars for siliciclastic and carbonate sediments accumulating in the queensland trough over the last 31 000 years for the slope highest mars of siliciclastic sediment occur during transgression 1 0 million tonnes per year mt yr 21 and lowest mars of siliciclastic 0 1 mt yr 21 and carbonate 0 2 mt yr 21 sediment occur during sea level lowstand carbonate mars are similar to siliciclastic mars for transgression and highstand 1 1 1 4 mt yr 21 in contrast for the basin mars of siliciclastic 0 0 1 mt yr 21 and carbonate sediment 0 2 0 4 mt yr 21 are continuously low and within a factor of two for lowstand transgression and highstand generic models for carbonate margins predict that maximum and minimum carbonate mars on the slope will occur during highstand and lowstand respectively conversely most models for siliciclastic margins suggest maximum and minimum siliciclastic mars will occur during lowstand and transgression respectively although carbonate mars in the queensland trough are similar to those predicted for carbonate depositional systems siliciclastic mars are the opposite given uniform siliciclastic mars in the basin through time we conclude that terrigenous material is stored on the shelf during sea level lowstand and released to the slope during transgression as wave driven currents transport shelf sediment offshore q 2000 elsevier science b v all rights reserved

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

the relationship between water masses and benthic ostracod assemblages in the western coral sea southwest pacific abstract the bathymetric distribution of 67 ostracod genera identified in 42 sediment samples water depth range 370 3776 m from the western coral sea is documented statistical analyses of this dataset support preliminary observations that the vertical distribution of the ostracod fauna is largely controlled by the three water masses present in the studied area four ostracod assemblages are recognised assemblage i consisting mainly of ostracods present in the deep water assemblage ii consisting of ubiquitous ostracods and ostracods mostly confined to the antarctic intermediate water and assemblages iii and iv with ostracods characteristic of the western south pacific central water temperature food supply and dissolved oxygen level are believed to be the most important factors influencing the ostracods bathymetric zonation the present work establishes the potential of ostracods for use in palaeoceanographic reconstruction in the western pacific ocean

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

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

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

holocene and modern sediment storage in the subtropical macrotidal fitzroy river estuary southeast queensland australia the fitzroy river estuary is a macrotidal tide dominated estuary located in the dry tropics of central queensland and represents the major source of terrestrial sediment to the southern great barrier reef gbr lagoon the estuary currently receives most of its sediment during large episodic floods that are typically associated with cyclones mean annual sediment budgets for such systems are difficult to estimate due to the sporadic nature of flood discharge events which are highly seasonal and vary greatly in magnitude between years we have estimated the quantity and long term rate of accumulation of catchment derived sediment in the estuarine floodplain using the holocene stratigraphic sequence determined from a series of sediment cores dated with radiocarbon and optically stimulated luminescence osl methods approximately 13 760 million tonnes mt of fluvial sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 over the past 100 years sediment accumulation has been focused around mangrove and tidal creek environments which cover an area of 13 0 km 2 cores from the tidal creeks dated using cs c 137 pb 210 and osl provide sedimentation rates of approximately 15 mm yr 1 for the past 45 120 years or sediment mass accumulation of 1700 kt yr 1 which includes a component that is reworked into the estuary by tidal currents combined with the small amount of sediment that accumulates on the floodplain during floods similar to 1 mm yr 1 640 kt yr 1 we estimate that approximately 2350 kt yr 1 of sediment is trapped in the modem lower floodplain and estuary this estimate of sediment storage suggests that greater than 50 of the modem mean annual sediment discharge of the fitzroy river 4162 kt yr 1 may be retained in the lower floodplain and estuary these results provide useful insights into the spatial pattern of sedimentation long term rates of accumulation and estimates of sediment trapping in a tropical macrotidal sedimentary system crown copyright c 2007 published by elsevier b v all rights reserved

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

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

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

late quaternary siliciclastic carbonate sedimentation model for the capricorn channel southern great barrier reef province australia abstract a model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial interglacial cycle in the capricorn channel southern great barrier reef gbr stable isotope ratios grainsize carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level mbsl results show variations in the flux of terrigenous neritic and pelagic sediments to the continental slope over the last sea level cycle during the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl the percentages of quartz and feldspar in the cores decreased with water depth while the percentage of clay increased x ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the fitzroy river which debouched directly into the northwest sector of the capricorn channel at this time the cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite hmc during the glacial the influx of hmc and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial and also from hmc ooids precipitated at the head of the capricorn channel at this time mass accumulation rates mars are high 13 5 g cm 3 kyr 1 during the glacial and peak at 20 g cm 3 kyr 1 in the early transgression 16 14 ka bp mars then decline with further sea level rise as the fitzroy river mouth retreats from the edge of the continental shelf after 13 5 ka bp mars remain low 4 cm 3 kyr 1 throughout the holocene highstand data for the holocene highstand indicate there is a reduction in siliciclastic influx to the capricorn channel with little quartz and feldspar below 350 mbsl however fine grained fluvial sediments presumably from the fitzroy river were still accumulating on the mid slope down to 2000 mbsl the proportion of pelagic calcite in the core tops increases with water depth while hmc decreases and is present only in trace amounts in cores below 1500 mbsl the difference in the percentage of hmc in the deeper cores between the glacial and holocene may reflect differences in supply or deepening of the hmc lysocline during the glacial sediment accumulation rates also vary between cores in the capricorn channel and do not show the expected exponential decrease with depth this may be due to intermediate or deep water currents reworking the sediments it is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments comparison of the capricorn channel mars with those for other mixed carbonate siliciclastic provinces from the northeast margin of australia indicates that peak mars in the early transgression in the capricorn channel precede those from the central gbr and south of fraser island the difference in the timing of the carbonate and siliciclastic mar peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces the only common trend in the mars from the northeast margin of australia is the near synchronicity of the carbonate and siliciclastic mar peaks in individual sediment cores which supports a coeval sedimentation model

sources of periplatform carbonates northwest providence channel bahamas abstract sources and quantities of periplatform carbonate sediments have been determined in northwest providence channel bahamas by an end member method employing geochemical textural petrographic and sem data the holocene sediment over most of this open seaway 200 to 2 000 m deep between great bahama bank and little bahama bank is a drape of largely fine grained lime mud 50 cm thick shallow platform sources contribute 75 90 percent the remainder is planktonic foraminifera pteropods and coccoliths mud 62 m from each bank and the planktonic source are each geochemically distinct and can be quantified the two shallow platform sources dominate sedimentation in the deep basin trend surface maps of mud derived from each bank reveal no windward leeward asymmetry in cont ast to reported sand transport patterns this indicates that the fines are swept off both platforms by storm and tidal exchange concentric distribution of fines relative to source indicates no offset by currents suggesting that fecal pelleting must rapidly remove fine sediment from the water column canyon valleys and intercanyon highs have equal thicknesses of holocene sediment which indicates that pelagic processes of deposition presently dominate over gravity flow processes confirmation of this depositional process is that the deposition rate increased from 2 cm 1 000 years to 10 cm 1 000 years when postglacial sea level flooded the bank tops thus 80 percent of the present sedimentation rate results from bank top contribution furthermore the calculated mass of mud traceable to little bahama bank agrees excellently with the independent estimate of overproduction there in cores bank sediments resulting from the most recent sea level highstand sharply overlie planktonic sediments writing a sea level history in alternating stable and unstable mineral suites

eustatic and tectonic controls on deposition of hybrid siliciclastic carbonate basinal cycles discussion with examples changes in sea level represent one of the dominant controls on basinal sedimentation adjacent to mixed carbonate siliciclastic sediment source areas sedimentary responses to sea level change of the siliciclastic and carbonate components of these hybrid systems commonly result in deposition of alternating siliciclastic and shelf derived carbonate basinal deposits such deposition is particularly pronounced adjacent to carbonate platforms where alternate immersion exposure of the flat platform top results in carbonate highstand deposition and siliciclastic lowstand deposition in contrast small to moderate amplitude sea level drops in distally steepened ramp settings may expose only the inner part of the gently sloping shelf resulting in lowstand deposition of mixed sil ciclastic allodapic footnote 3 carbonate sediments along active margins tectonic uplift and subsidence of sediment source areas act as additional major controls on deposition of siliciclastic carbonate basinal cycles two of the most important tectonic effects are 1 uplift of siliciclastic sediment source areas resulting in increased erosion and swamping of carbonate shelf sources and 2 exposure or immersion of shelf carbonate sediment source areas due to vertical tectonic movements most published seismic stratigraphic studies of sea level control on deep sea sedimentation focus on lowstand deposition of siliciclastic sediment and commonly neglect the contribution of allodapic carbonate sediment deposited during sea level highstands however the examples discussed in this paper indicate that highstand carbonate deposits may make up a significant proportion of many hybrid carbonate siliciclastic basinal sequences

a new variant of saponite rich micrometeorites recovered from recent antarctic snowfall abstract eight saponite rich micrometeorites with very similar mineralogy were found from the recent surface snow in antarctica they might have come to earth as a larger meteoroid and broke up into pieces on earth because they were recovered from the same layer and the same location of the snow synchrotron x ray diffraction xrd analysis indicates that saponite mg fe carbonate and pyrrhotite are major phases and serpentine magnetite and pentlandite are minor phases anhydrous silicates are entirely absent from all micrometeorites suggesting that their parental object has undergone heavy aqueous alteration saponite serpentine ratios are higher than in the orgueil ci chondrite and are similar to the tagish lake carbonaceous chondrite transmission electron microscope tem observation indicates that serpentine occupies core regions of fine grained saponite pyrrhotite has a low ni concentration and mg fe carbonate shows unique concentric ring structures and has a mean molar mg mg fe ratio of 0 7 comparison of the mineralogy to hydrated chondrites and interplanetary dust particles idps suggests that the micrometeorites are most similar to the carbonate poor lithology of the tagish lake carbonaceous chondrite and some hydrous idps but they show a carbonate mineralogy dissimilar to any primitive chondritic materials therefore they are a new variant of saponite rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to antarctica

variability of surface ocean radiocarbon and stable isotopes in the southwestern pacific we present high precision radiocarbon 14c results and stable isotope 18o and 13c records for a coral from heron island 23 s 152 e and new stable isotope 18o and 13c records for annual coral bands from abraham reef 22 s 153 e in the southern great barrier reef studied earlier druffel and griffin 1993 these tracers provide unique information on the regional water mass history and together these data allow us to constrain the variability of circulation in the upper pacific over the past four centuries first we observe decreases in 18o of coral from abraham reef and heron island indicating an increase in sea surface temperature and or a decrease in surface salinity since 1850 second the small suess effect value 14c decrease from 1880 to 1955 due mostly to fossil fuel co2 observed previously at abraham reef druffel and griffin 1993 is confirmed in the measurements reported here from the heron island coral this value is low compared to those observed in other areas of the ocean druffel 1997 druffel and linick 1978 nozaki et al 1978 between 1880 and 1955 third we report alterations in the correlation between el nino events and the occurrence of low 14c which is indicative of long term change s in circulation in the sw pacific the 14c shifts reported here are not large but even small temporal changes in prebomb 14c suggest that important changes in the large scale state of the ocean have occurred such as a temporal change in circulation

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

tropical view of quaternary sequence stratigraphy siliciclastic accumulation on slopes east of the great barrier reef since the last glacial maximum generic models of continental margin evolution predict that siliciclastic fluxes to slopes should be maximal and minimal during major sea level lowstands and transgressions respectively here we document the opposite for the northeast australian margin the largest extant mixed siliciclastic carbonate depositional system cores from slopes of this margin consistently contain siliciclastic rich intervals 0 3 1 m thick in the upper few meters radiocarbon dates of planktonic foraminifera show that this interval was deposited between 12 and 7 ka and represents greatly increased siliciclastic fluxes during late transgression this massive terrigenous discharge to slopes occurred along at least 450 km of the margin irrespective of modern variations in bathymetry or climate although we cannot dismiss a significantly different early holocene climate with greatly enhanced sediment discharge available data instead suggest that rivers aggraded on the shelf during lowstand because of an extensive subaerially exposed reef system this phenomenon may occur on other margins rimmed by reefs requiring a major revision of concepts used to interpret mixed siliciclastic carbonate systems

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

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

massive siliciclastic discharge to slopes of the great barrier reef platform during sea level transgression constraints from sediment cores between 15 s and 16 s latitude and possible explanations abstract the northeast australian continental margin including the great barrier reef gbr platform provides an outstanding modern analogue for understanding sedimentation in tropical mixed siliciclastic carbonate depositional systems previous studies of cores from this margin have suggested that in contrast to widely accepted models maximum siliciclastic fluxes to slopes over the last 30 ky occurred when sea level transgressed the shelf ca 11 7 ka rather than when sea level was at a lowstand before 18 ka however climate and bathymetry can affect regional sediment deposition significantly and the cores examined to date have come from the southern queensland trough where the margin has a wet tropical climate and a broad shelf 50 km with gradual slopes in this study we examine the abundance and accumulation of siliciclastic material in four cores from lower slopes of the northern queensland trough where rivers drain a drier region and debouche onto a narrow shelf with steep incised slopes similar to previously examined cores all cores contain a dark greyish brown horizon within the upper few meters this horizon represents a low in carbonate content and corresponding high in siliciclastic material primarily clay and oxygen isotope stratigraphy shows that it was deposited during late transgression nominally between 11 and 7 ka moreover mass accumulation rate calculations demonstrate that this horizon reflects a significant rise in siliciclastic fluxes when combined with the previous work to the south it appears that slopes all along a large portion of the northeast australian continental margin received greatly enhanced inputs of siliciclastic material during late transgression independent of proximal climate and bathymetry two general explanations are offered for this observation 1 climate change induced highly variable riverine discharge over the past 30 ky with a prominent maximum coincident with late transgression or 2 the shelf stores large quantities of siliciclastic sediment during lowstand and releases this material to the slope during late transgression in either case siliciclastic accumulation on the northeast australia continental margin behaves completely opposite to predictions from conventional models

sediment fluxes to marion plateau southern great barrier reef province over the last 130 ky new constraints on transgressive shedding off northeastern australia generic models for sediment accumulation predict that fluxes of siliciclastic and neritic carbonate material to continental slopes of tropical mixed systems will be out of phase over cycles of sea level change siliciclastic and carbonate fluxes should be highest during lowstands and highstands respectively and condensed sections should form during transgressions recent studies have documented the opposite response for slopes along portions of the largest modern tropical mixed system the northeast australian margin siliciclastic and carbonate fluxes are in phase and highest during transgression an outstanding issue however is the extent of this response because studies to date have mostly focused on sedimentation over the last 40 ky off the central gbr province an area flanked by a narrow shelf and a wet tropical hinterland here we investigate mixed sediment deposition in a core from marion plateau offshore a wide shelf and a dry tropical hinterland in the southern gbr province bulk carbonate content and carbonate mineralogy were determined downcore while foraminiferal oxygen isotopes and radiocarbon ages were used to constrain ages and accumulation carbonate content and mineralogy vary predictably with changes in sea level over the last 130 ky carbonate and aragonite are more abundant during highstands and less abundant during lowstands however component mass accumulation rates reveal that highest fluxes of all material siliciclastic low mg calcite aragonite and high mg calcite occurred during transgressions sedimentation consistently diverges from conventional models in all cores examined to date from slopes of the northeast australian margin regardless of core location and modern differences in climate and physiography the unexpected sediment response could result from changes in climate particularly increased precipitation during deglaciations although this does not explain elevated fluxes of low mg calcite alternatively fluvial sediments and diagenetically altered carbonate aggraded on the shelf during lowstands and were eroded and transported to the slope during transgressions

bathymetric expression of the fitzroy river palaeochannel northeast australia response of a major river to sea level change on a semi rimmed mixed siliciclastic carbonate shelf abstract palaeo river channels record the response of alluvial and estuarine depositional environments to sea level change and are also important geological indicators of former subaerial unconformities earlier studies have characterised lowstand palaeochannels on the central great barrier reef gbr shelf of northeastern australia reporting channel entrenchment shelf aggradation and topographic control of rivers by the outer shelf reef barrier we report the bathymetric expression of a palaeochannel corresponding to the last glacial lowstand path of the fitzroy river a high sediment yield river in the southern gbr during regression and lowstand the fitzroy river palaeochannel entrenched into the low gradient middle shelf and may have begun to incise the steeper outer shelf between the exposed reef platforms the wide spacing of outer shelf reefs and the continuous seabed slope may have enabled the palaeo fitzroy to maintain connection with the lowstand shoreline without becoming trapped behind shelf edge reefs the palaeochannel now forms a prominent depression across the middle and outer shelf evidently the sloping inter reefal seabed of the southern gbr coupled with tidal processes and wave exposure has limited shelf aggradation since the transgression this finding provides evidence that modern bathymetry can reflect palaeochannel location on the gbr shelf our results offer new insights into the evolution of the southern gbr shelf and show that no single existing model is able to adequately explain the behaviour of lowstand palaeochannels on rimmed siliciclastic carbonate shelves

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

a complete pollen record of the last 230 ka from lynch s crater north eastern australia abstract recent drilling eventually reached to the base of the sediments of lynch s crater on the atherton tableland within the humid tropics of north eastern australia this paper incorporates results from the sequence extension into a complete record from the site much of which has only been presented previously in summary form a more certain chronology for the record is provided by recent radiocarbon dating on the topmost sediments and the application of time series analysis to the whole sequence this suggests that the vegetation and climate are forced essentially by northern hemisphere insolation and ice volume probably operating through sea level and sea surface temperature changes the extended record is considered to cover the last 230 000 years and the pattern of complex rainforest expansion during wetter interglacial periods and its replacement by drier rainforest and sclerophyll vegetation during drier glacials is maintained superimposed on this cyclicity are trends resulting from both the evolution of the lake basin as well as external influences that include climate and within the last 45 000 years people

glacial interglacial changes in the east australian current the east australian current eac is the western boundary current of the south pacific gyre transporting warm tropical waters to higher southern latitudes recent modelling shows that the partial separation of the eac 32 s and the coupled formation of the tasman front 34 s are caused by a steep gradient in the zonally integrated wind stress curl analysis of oxygen isotope ratios 18o in the planktonic foraminifer globigerinoides ruber from sediment cores from the coral sea and tasman sea indicates that the eac separation shifted northward to between 23 and 26 s during the last glacial we suggest these results indicate a significant change in the pacific wind stress curl during the glacial given recent evidence for el nino like conditions in the pacific during the last glacial with a reduction in the east west sea surface temperature sst gradient we suggest that weaker trade winds combined with more northerly stronger westerlies were associated with a change to the wind stress curl which repositioned the eac separation and tasman front in contrast by 11 ka bp the eac separation was forced south of 26 s this southward shift was synchronous with a rapid warming of tropical ssts and the onset of a la nina like sst configuration across the tropical pacific it appears that the south pacific trade winds strengthened accordingly causing the eac to readjust its flow this readjustment of the eac marks the onset of modern surface ocean circulation in the southwest pacific but the present eac transport was only achieved in the late holocene after 5 ka bp