bryozoans as carbonate sediment producers on the cool water lacepede shelf southern australia abstract modern sediments on the lacepede shelf and adjacent slope are typical mid latitude cool water palimpsest deposits dominated by bryozoan mollusc and quartz particles bryozoan bioclasts form autochthonous and to a lesser extent allochthonous accumulations across the grain size spectrum from mud to boulder size the bryozoan skeletons are grouped on the basis of architecture and style of disarticulation fragmentation into nine morphotypes erect rigid forms comprise 1 fenestrate 2 foliose 3 flat robust branching and 4 delicate branching morphotypes large adeona sp skeletons are recognised as a separate type of fenestrate form because of their distinctive shape mineralogy and restricted environment erect flexible forms are either 5 articulated branching or 6 articulated zooidal other important morphotypes are 7 encrusting 8 nodular arborescent and 9 vagrant differences in skeletal architecture result in distinct particle types encrusting morphotypes on soft organic substrates and the wide variety of erect rigid forms are broken into fragments erect flexible forms disintegrate upon death into definitive sand and silt size grains encrusting morphotypes on hard substrates nodular arborescent and vagrant forms remain whole and when large accumulate in place morphotypes are mineralogically distinct and so bryozoan sediment composition is environmentally controlled shallow water

genesis of palimpsest cool water carbonate sediment on the continental margin of southern australia abstract the continental margin of southern australia is a site of extensive quaternary cool water carbonate sedimentation seafloor sediments are a mixture of holocene biofragments and late pleistocene relict and stranded particles relict sediments produced during marine isotope stages 3 and 4 are generally preserved as iron stained intraclasts such grains in the great australian bight are photozoan in character they include symbiont bearing benthic foraminifers and coralline algal particles and indicate that the wide shelves were bathed in shallow relatively warm oligotrophic waters and floored by marine grasses similar to many modern shallow inboard embayments in the region today in contrast east of the great australian bight relict sediments are more heterozoan in character with coralline algal and molluscan facies on the inner shelf and bryozoan sediments on the outer shelf stranded sediments marooned during the sea level rise associated with marine isotope stage 2 are gray to buff in color and composed of both biofragments and intraclasts these particles are mainly heterozoan in character throughout the region with subtropical photozoan marine grassbank facies localized to portions of the inner great australian bight stranded sediments are interpreted to have accumulated in an areally restricted photic zone and upon an overall narrow shelf covered in cool nutrient rich waters swell driven seafloor sediment disturbance to depths of 100 m along the southern australian margin in conjunction with reduced rates of sedimentation that characterize the cool water carbonate realm have resulted in mixing of sediment currently being produced with exhumed relict and stranded sediments generated during previous sea level stands the composition of these deposits and the nature of their pre burial alteration are a function of sea level history late pleistocene relict sediments originally accumulated in low energy inboard environments but were modified in the surf zone during subsequent sea level fluctuations this resulted in the formation of intraclasts abraded infilled and cemented biofragments of local origin the widespread distribution of intraclasts and of composite grain assemblages derived from multiple sedimentary environments that display highly variable degrees of seafloor alteration may be signatures of modern cool water carbonate assemblages worldwide while such palimpsest sediments may complicate paleoenvironmental interpretation their differentiation in the rock record can be utilized to discern subtleties in paleoceanography and sea level history

middle miocene serravallian temperate carbonates in a seaway connecting the atlantic ocean and the mediterranean sea north betic strait s spain abstract miocene deposits in the contact area between the prebetic and subbetic domains betic cordillera s spain record the last stages of marine deposition on the southern iberian margin and the final closure of the north betic strait in the early tortonian late miocene serravallian middle miocene shallow water carbonates and mixed carbonate siliciclastics formed on a platform at the southern margin of the north betic strait these shallow water deposits informally termed the la escalera formation onlap an erosion surface carved into underlying miocene and older rocks carbonate components are mainly bryozoans coralline red algae molluscs and benthic and planktonic foraminifers typical of heterozoan lithofacies several facies types can be distinguished based on different grain sizes and sedimentary structures large scale geometries and stratigraphic facies relationships indicate that the la escalera formation was deposited on a homoclinal ramp attached to a deeply eroded emergent relief to the south a beach system developed at the southern margin with backshore lagoons and local incursions of coarse terrigenous sediments seawards of the beach system was a submarine dune belt that extended over several square kilometres at the northeastern end of the la escalera formation longshore currents shifted submarine dunes to the northeast maximum production of carbonate skeletons took place seawards of the dune field from this factory area skeletal debris was moved landwards and incorporated into the dunes and beaches whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross stratified sediments the finest grained particles accumulated below a storm wave base along with significant planktic debris carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans vertical variations of facies within the formation depict a major transgressive regressive cycle modulated by up to 10 higher frequency cycles despite its location in an atlantic linked basin the sedimentary model of the la escalera formation shows similarities to the models proposed for neogene mediterranean temperate carbonates which imply a relatively low energy regime on the ramp in comparison with the open ocean platforms this relatively low energy regime can be explained by the position of the north betic strait at the eastern end of the guadalquivir basin however hummocky and swaley cross stratified deposits are significantly more developed in la escalera deposits than in known examples of neogene mediterranean carbonates

the calcarenite di gravina formation in matera southern italy new insights for coarse grained large scale cross bedded bodies encased in offshore deposits excellent outcrops of the upper pliocene lower pleistocene calcarenite di gravina around matera southern italy provide continuous exposure of coarse grained clastic basin margin shoreline to offshore facies among these facies the most conspicuous and volumetrically important are the transition slope deposits that form large scale high angle cross bedded lithosomes these are laterally extensive parallel with the paleoshoreline and show seaward progradation we interpret them to represent avalanches of sediment swept out onto a depositional slope below wave base from the shoreface zone by storm waves and wind driven currents three types of building blocks are recognized based on bedding patterns and facies architecture embryonic parasequences mature parasequences and simple sequences parasequences formed during stillstands of sea level and simple sequences during high frequency cycles of relative change of sea level these building blocks are stacked in a backstepping configuration and onlap onto cretaceous limestone substrate backstepping is believed to be due to a tectonically forced transgression that is punctuated by high frequency cycles of sea level modern analogs for these building blocks are the holocene prograding prisms detected in high resolution seismic lines of the mediterranean shelves the reflection patterns of these seismic units resemble the bedding architecture of the matera simple sequences and parasequences and show similarities of shape size position and orientation of coastal setting and direction of progradation comparison of the holocene prisms and the pliocene pleistocene accretional units in matera indicates that they may represent the same begin page 662 genetic process progradation of clastic prisms below the wave base level the matera accretional units also show similarities with other examples of laterally extensive large scale cross bedded sand bodies encased in offshore deposits such as some sandbanks differentiating between these laterally extensive and seaward prograding cross bedded sand bodies and some coarse grained gilbert type deltas is difficult however if interpretations are based only on two dimensional 2 d outcrops in dip section without high resolution data it is also difficult to distinguish between transition slope and prograding shoreface lithosomes this difficulty may be acute where only seismic or well log data are available however certain other architectural characteristics such as stacking and preservation of facies belts and position of bounding surfaces as well as differences in associated sedimentary structures and fossil content may be used for interpretation the matera example provides a mechanism for emplacement in offshore settings of elongate and strandline parallel sand and gravel deposits that prograde seaward and that preserve a coarsening upward internal succession this article offers an interpretation for other ancient examples of large scale cross bedded lithosomes encased in offshore deposits

origin of late pleistocene bryozoan reef mounds great australian bight bryozoan rich biogenic mounds grew periodically on the prograding carbonate slope of the central great australian bight throughout pliocene pleistocene time cores from three odp leg 182 drill sites provide a record of mound growth during the last 300 000 years over a stratigraphic thickness of similar to 150 m these mounds the first such structures described from the modern ocean grew between paleodepths of 100 and 240 m we infer that the upper limit of growth was established by swell wave base and the lower boundary was fixed by an oligotrophic water mass detailed chronostratigraphy based on radiometric and u series dating benthic foraminifer stable isotope stratigraphy and planktonic foraminifer abundance ratios confirms that buildups flourished during glacial lowstands even numbered marine isotope stages but were largely moribund during interglacial highstands and are not extant today mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate flat robust branching encrusting nodular arborescent and delicate branching growth forms the packstone matrix comprises autochthonous and allochthonous sand size bryozoans benthic and planktonic foraminifers serpulids coralline algae sponge spicules peloids and variable glauconite and quartz grains together with mud size ostracods tunicate spicules bioeroded sponge chips and coccoliths intermound allochthonous packstone and local grainstone contain similar particles but they are conspicuously worn abraded blackened and bioeroded an integrated model of mound accretion during sea level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5 10 m culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils mound accumulation was relatively rapid 30 67 cm ky and locally punctuated by rudstones and firmgrounds intermound highstand deposition was comparatively slow 17 25 cm ky and typified by meter scale fining upward packages of packstone and grainstone or burrowed packstone with local firmgrounds overlain by characteristically abraded particles mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity such elevated trophic resources were both regional and local and thought to be focused in this area by cessation of leeuwin current flow together with northward movement of the subtropical convergence and related dynamic mixing

holocene carbonate sedimentation on the west eucla shelf great australian bight a shaved shelf the southern continental margin of australia is a cool water carbonate sedimentary province located in a high energy swell dominated oceanographic setting a vibrocore transect of 14c dated sediments across the centre of the eucla shelf is the first record of holocene shelf deposition in the great australian bight much of the seafloor shallower than 70 m water depth the base of wave abrasion is bare cenozoic limestone in some places encrusted by late pleistocene coral rich limestone that is cemented by high magnesium calcite 12 mole mgco3 the areally extensive 100 km wide hard bored substrate supports an epibiota of coralline algae minor bryozoans and soft algae or is covered by patches of holocene sediment up to 1 5 m thick generally a basal bivalve lag 3 ka overlain by quartzose bioclastic palimpsest sand this pattern of active carbonate production but little accretion on the wave swept mid to inner shelf is similar to that on other parts of the southern australian continental margin the term shaved shelf is proposed for this style of carbonate platform formed by alternating periods of sediment accretion cementation and erosion the palimpsest sand is typically rich in bivalves coralline algae and locally detrital dolomite outer shelf holocene sediment below the base of wave abrasion but inboard of the shelf edge is a metre thick unit of fine microbioclastic muddy sand with minor delicate bryozoans overlying a 9 13 ka rhodolith gravel some of this outer shelf sediment appears to have been resedimented the shelf edge is a sandy and rocky seafloor with active bryozoan growth and sediment production the holocene sediments are enriched in coralline algal particles and conspicuous large foraminifers cf marginopora and depleted in bryozoans as compared to coeval deposits on the lacepede and otway shelves off southeastern australia these differences are interpreted to reflect warmer waters of the leeuwin current and prevalent downwelling in this area as opposed to the general upwelling and colder waters in the east

foraminiferal biofacies on the mid latitude lincoln shelf south australia oceanographic and sedimentological implications foraminiferal assemblages on the southern mid latitude lincoln shelf comprise mixtures more strongly in shallow waters of holocene and relict pleistocene specimens over 200 benthic and 15 planktonic species were recorded and a higher diversity was found in the central and deeper parts of the shelf and slope cluster analysis identified five assemblages or biofacies nearshore assemblage a 50 m and inner mid shelf assemblage b 50 90 m are dominated by relict and recent shallow water species the outer mid shelf assemblage c 90 120 m contains more cibicidids and is transitional between the shallow and deep water assemblages outer shelf assemblage d 120 170 m is characterized by cibicidids and anomalinids and by a higher planktonic and benthic diversity and it can be subdivided into three sub assemblages d1 d3 unlike others assemblage d was not recognized from the most western transect samples the outer shelf to slope assemblage e 170 400 m is typically deep water having forms like hoeglundina elegans pullenia bulloides and melonis affinis the western great australian bight sector has the larger epifaunal benthic sorites marginopora group while the infauna is higher in the eastern neptune sector of the shelf we attribute these contrasts to the influence of the warm leeuwin current and to the mixing between gulf shelf and oceanic waters respectively a former lagoonal environment is largely responsible for the accumulation of relict tests during lower sea level periods of the late pleistocene when climate was more arid the lack of recent sediments preserved on the inner shelf is considered to be due to strong wave abrasion causing sediment starvation richer forarniniferal assemblages from the outer shelf to upper slope parallel an increasingly calcareous sediment faunal evidence indicates a warmer nearly oligotrophic condition on lincoln shelf compared to the mesotrophy on the adjacent lacepede shelf this difference may be due to the separation of these two shelves by kangaroo island acting as a local oceanographic environmental and biogeographic barrier

unravelling the origin of a paleogene unconformity in the latium abruzzi carbonate succession a shaved platform the latium abruzzi carbonate platform constitutes the sedimentary record from the triassic to the late miocene of the southern tethyan margin outcropping in the apennines this sedimentary succession is punctuated by an important hiatus between the end of the cretaceous and the early miocene this paleogene hiatus has long been interpreted as the result of prolonged subaerial exposure however no evidence of such exposure has ever been documented on the latium abruzzi platform this is contrary to the coeval and adjacent apulia and lessini carbonate platforms where a broadly developed paleokarst system formed between the eocene and the early miocene the assumption that the miocene marine transgression deeply eroded a karstified cretaceous substrate on the latium abruzzi platform is not supported because this surface appears in the field as a perfectly flat bioeroded paraconformable surface in this work a marine origin is proposed for this unconformity from late paleocene to early miocene the latium abruzzi carbonate platform was a shaved isolated platform exposed to wave action in the middle of the proto mediterranean area bioclastic sediment accumulated during transgressive and sea level highstand phases whereas in the following falling and lowstand stages sediment was eroded as the seafloor came into the zone of wave abrasion the sediment eroded from the platform was shed into the basin where it produced coarse bioclastic intercalations in the hemipelagites of the scaglia formation at the end of the oligocene when the adjacent basin was filled a small ramp was established in the transitional zone between the platform and the basin there cross bedded carbonates accumulated in middle to outer ramp environments the inner ramp remained within the zone of wave abrasion such that sediment generated there was washed out into the middle and outer ramp environments finally in the early burdigalian the mediterranean progressively evolved into closed sea during the initial stages of the closure of indo pacific connection the reduction of the wave base depth typical of an enclosed sea created increased accommodation space allowing sediments to accumulate and form the complete inner to outer ramp facies belts of the miocene latium abruzzi ramp

carbonate shelf edge off southern australia a prograding open platform margin the southern continental margin of australia is an extensive shelf that has been a site of cool water carbonate deposition since eocene time the platform has no rim and is swept by high energy waves and swells throughout the year the shelf is deep 40 to 100 m and typified by bryozoan rich sediments the shelf margin is a gentle incline that becomes progressively steeper seaward except where it laps down onto offshore terraces the edge of the eucla platform in the great australian bight is used to illustrate that the margin is a series of extensive prograding clinoforms progradation is interpreted to be the result of off shelf sediment transport and in place carbonate production by actively growing deep water bryozoa and sponges this area is a potential model for ancient high energy platform margins during geologic periods when large skeletal reef building metazoans were scarce

from source to sink a new perspective on the past dynamics of the murray canyon group from benthic foraminiferal communities abstract we present fossil benthic foraminiferal assemblage data from marine sediment core ss02 06 gc2 located in the abyssal plain of the murray canyon group offshore south australia the sedimentological characteristics indicate the presence of turbidite deposits showing classical bouma like sequences dated between 40 and 12 cal ka bp these results confirm the previous interpretation of the observed large deep water holes in the abyssal area where the core was sampled as being gouged by surges of high energy turbidity currents the presence of good indicator taxa and unique assemblages occupying specific bathymetric depths allows the determination of the source origin of the sediments making the turbidites three distinct faunal groups are found 1 mostly shelf species 2 mostly bathyal species and 3 mostly abyssal species in the sediment core these groups present a quasi systematic succession with nearly all bouma like sequences starting with the dominance of bathyal species in the coarse grained base followed by the dominance of shallow species in the silty part and finally with abyssal species in the clays to explain such phenomena turbidites triggered by mixed hyperpycnal hypopycnal flow processes and turbidity currents during periods of river floods are considered for the first time within the murray canyon group they are mostly related to periods of increased fluvial discharges during wet phases in the murray darling basin

subtidal carbonate cycles implications for allocyclic vs autocyclic controls thick successions of repetitive metre scale subtidal carbonate cycles require that short term sedimentation rates approximate long term accumulation rates in order to maintain submergence below peritidal depths intrinsic processes such as storm and wave reworking and redistribution may act to inhibit aggradation into the zone of optimal carbonate production the presence of subtidal vs peritidal carbonate cycles may be a function of energy regime that in turn may relate to platform morphology the ultimate control on stacked subtidal cycles appears to be eustasy acting in concert with intrinsic processes such as storm and wave reworking

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

nearshore temperate carbonate depositional systems lower tortonian agua amarga basin southern spain implications for carbonate sequence stratigraphy abstract the bryozoan rich lower tortonian carbonates of the agua amarga basin in southern spain province of almeria provide an example of sediments formed in a nearshore non tropical depositional setting based on data derived from logging of sections and from field mapping these lower tortonian carbonates form a depositional sequence which is subdivided into several depositional systems a lowstand systems tract which consists of volcaniclastic fan deltas and washover deposits formed on the leeward side of a basement shoal which delimited the basin towards the south a transgressive systems tract which is characterised by a landward encroachment of deposits is represented by submarine bars and dune deposits a highstand systems tract consists of progradational beach deposits owing to strong reworking and re distribution of the particles by currents and waves microfacies differentiation of the deposits in poor these tortonian non tropical carbonates display a style of deposition similar to siliciclastics suggesting that sequence stratigraphic concepts derived from tropical carbonates do not apply to non tropical carbonates

surficial cool water carbonate sediments on the otway continental margin southeastern australia abstract the otway continental margin of southern australia is a swell dominated open cool water carbonate platform it is partitioned into a series of depth related zones of biological sediment production and accumulation by three hydrodynamic interfaces 1 abrasion depth 70 m 2 swell wavebase 130 m and 3 storm wavebase 250 m the otway shelf profile drops steeply from the strandline the shallow shelf lies largely between 30 and 70 m and is a high energy zone of carbonate sediment production intensive destructive diagenesis and erosion the seafloor is characterized by widespread exhumed limestone substrates which host dense encrusting assemblages of molluscs sponges bryozoans and red algae loose sediment accumulation is patchy and consists of a thin quartz rich palimpsest gravel veneer the middle shelf 70 to 130 m is a zone of swell wave shoaling and production and accumulation of coarse mega rippled 2 d dunes bryozoan sands deep shelf areas 130 to 180 m accumulate finer bioclastic sands foraminiferal echinoid bryozoan that are intensely bioturbated and episodically reworked by storms grains are variably fragmented and marginally bored at the shelf edge and top of slope 180 to 350 m nutrient rich upwelling currents support laterally extensive aphotic biostromal hermal bryozoan sponge coral communities which generate and accumulate thick successions of muddy skeletal sand sediments of the upper slope 350 to 500 m are a bioturbated mixture of periplatform bioclastic debris and pelleted foraminiferal nannofossil mud turbidites and resedimentation features are common bioturbation and shelf derived skeletal content decrease progressively downslope and pelagic muds dominate below 500 m lower slope areas are cross cut by gullies and have low accumulation rates the base of slope is characterized by sediment apron deposits consisting of interbedded shelf derived coarse grained turbidites and pelagic ooze

early diagenesis of carbonates on a cool water carbonate shelf southern australia abstract the southern australian continental margin is an immense cool water carbonate factory the high energy open shelf is blanketed by heterozoan carbonates of both holocene and late pleistocene age three distinct grain types have been identified and radiocarbon dated these include 1 relict grains highly abraded iron stained intraclasts formed during the intermediate sea level stands of marine isotope stages 3 and 4 2 stranded grains gray and buff colored abraded biofragments and intraclasts marooned during the sea level rise associated with marine isotope stage 2 and 3 holocene grains unaltered biofragments formed during marine isotope stage 1 optical mineralogical and chemical characterization of grains of each age has revealed pathways of early diagenesis in this realm both calcitic and aragonite biogenic grains undergo dissolution while dissolution of calcitic components is minor and incomplete relict sediments are predominantly mg calcite aragonitic skeletons undergo significant dissolution within 30 000 years in contrast to early dissolution of aragonite micritic calcite cement with 12 mol mgco3 is a significant diagenetic phase in these sediments infilling many stranded and most relict skeletons similar cement precipitates between grains forming small numbers of cemented grain aggregates in most samples microprobe and icp ms analysis demonstrates fe oxides mn oxides and associated clay minerals discolor stranded and relict grains by coating grain surfaces and infesting micropores such coatings begin to form on holocene grains during or soon after formation the oxides scavenge trace elements including v ti cr and ree altering the elemental compositions of biogenic carbonate

evaluating the relationship between the carbon and sulfur cycles in the later cambrian ocean an example from the port au port group western newfoundland canada abstract we present a high resolution 34 s sulfate and pyrite and 13 c carbonate record from the middle upper cambrian port au port group a mixed carbonate siliciclastic succession exposed in western newfoundland canada the results illustrate systematic 34 s sulfate shifts of 15 over relatively short stratigraphic intervals 10 m likely 34 s sulfate pyrite ca 23 and a generally positive coupling between changes in 13 c carbonate and 34 s sulfate together these results indicate that middle to late cambrian sulfate concentrations were low and that the sulfate reservoir was more sensitive to change than it was in either terminal neoproterozoic or cenozoic oceans however a simple carbon c and sulfur s isotope box model of the late cambrian ocean illustrates that low sulfate concentrations alone fail to account for the 15 34 s sulfate shifts recognized in port au port strata such large shifts can be generated only if fluctuating oceanic redox is invoked marine anoxia forces reduced c s burial and elevated 34 s driving larger 34 s changes per mole of organic carbon buried the conclusion that later cambrian oceans featured both low sulfate levels and widespread subsurface anoxia supports hypotheses that link fluctuating marine redox conditions in the delayed recovery of skeletal animals and metazoan reefs from late early cambrian extinction

cooling dynamics of spatter fed phonolite obsidian flows on tenerife canary islands abstract relaxation geospeedometry has been applied to two series of clastogenic obsidian flows on tenerife to determine their thermal history across the glass transition the phonolite flows investigated were both generated by lava fountaining activity followed by rheomorphism of the deposits the detailed sampling resolution within the two series enabled an accurate quantification of their thermal history cooling rates within the investigated spatter fed flows vary over more than two orders of magnitude the highest cooling rates of 0 39 k min were modeled for the central vesiculated part of one flow the dense basal obsidian layers of both flows were cooled at substantially lower rates of 0 0042 and 0 0028 k min respectively there appears to be an influence of in situ vesiculation processes on the thermal budget of the investigated flows in addition the slow cooling rates for the basal portions of both flows seem to be associated with a stage of thermal buffering continual advective heat transport of hot material along a basal shear plane may sustain elevated temperatures associated with quasi isothermal annealing within this decollement numerical simulations based on conductive heat loss concepts fail to resolve the cooling history quantified through relaxation geospeedometry for the investigated flows the effects of vesiculation and thermal annealing on the cooling behavior of the clastogenic flows across the glass transition are discussed in the light of these new data in addition viscometric data on these phonolites are used to correlate the known cooling rates to viscosities at the glass transition

last interglacial and holocene trends in sea level maxima around australia implications for modern rates this paper defines the spatial trend in sea level around australia at 3 timescales namely at the time of the maximum of the last interglacial around 125 000 yr b p during the holocene maximum between 5000 and 6000 yr b p and over the last 20 years last interglacial elevations range from 2 m around the great barrier reef to 32 m in northeast tasmania trend surface analysis shows that over 77 of the noise in these sea level elevations can be accounted for by a pattern evidencing tectonic uplift towards the southern edge of the continent assuming a eustatic sea level at this time of 4 to 6 m most of the east coast of new south wales and the west coast of western australia can be considered tectonically stable while the southern edge of the continent has risen by at least 5 m and the north northeast corner has downwarped by at least 2 m the spatial pattern of the holocene maximum tentatively supports the continuation of this tectonic deformation sea level at this time reached 1 6 and 2 4 m above present high tide limits around the northern and southeastern coastlines of australia respectively this holocene pattern is weak because much of the data is dominated by local variations reflecting differential loading of the continental shelf by water during the holocene transgression the holocene trend surface does not support geophysical modelling implying a southern latitudinal downwarping of the crust produced by the melting of the antarctic ice sheet and the loading of the ocean crust with meltwater however the spatial pattern of modern trends appears to contain a remnant holocene signal fitting this isostatic model rather than the long term pattern of tectonic flexure since the last interglacial sea level is presently rising at a rate of 1 75 mm yr 1 in northern australia compared to only 0 75 mm yr 1 in tasmania these results imply that isostatic factors as well as previously identified climatic variables may be controlling present day variations in the rate of change of sea levels around the australian continent

an epeiric ramp low energy cool water carbonate facies in a tertiary inland sea murray basin south australia the murray supergroup records temperate water carbonate deposition within a shallow mesotrophic oligo miocene inland sea protected from high energy waves and swells of the open ocean by a granitic archipelago at its southern margin rocks are very well preserved and exposed in nearly continuous outcrop along the river murray in south australia most facies are rich in carbonate silt contain a background assemblage of gastropods especially turritellids and infaunal bivalves and are packaged on a decimetre scale defined by firmground and hardground omission surfaces bioturbation is pervasive and overprinted resulting in rare preservation of physical sedimentary structures facies are grouped into four associations large foraminiferan bryozoan echinoid bryozoan mollusc and clay facies interpreted to represent shallow water 50 m deposition under progressively higher trophic resource levels from low mesotrophy to eutrophy and restricted marine conditions from relatively offshore to nearshore regions a large scale shift from high to low mesotrophic conditions within lower miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow land locked sea overall low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity inshore heterozoan facies became progressively muddier and restricted towards the shoreline in contrast periods of wet climate led to rising trophic resource levels resulting in a shallowing of the euphotic zone a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids rates of carbonate production and accumulation were relatively low the murray basin is best described as an epeiric ramp wide facies belts developed in a shallow sea on a low angled slope reaching many hundreds of kilometres in length grainy shoal and back barrier facies were absent internally generated waves impinged the sea floor in offshore regions and because of friction along a wide and shallow sea floor created a low energy expanse of waters across the proximal ramp storms were the dominating depositional process capable of disrupting the entire sea floor

cool water carbonate sedimentology and eustasy pleistocene upper slope environments great australian bight site 1127 odp leg 182 the southern australian shelf is the largest area of the globe composed of cool water carbonates and provides the basis for the development of actualistic models of such sediments ocean drilling program leg 182 drilling of the sedimentary succession provides essential information to also decipher the dynamics of this depositional system sediment samples and geophysical logs from a core drilled on the eucla plateau off the coast of southern australia site 1127 have been used to study sedimentary cyclicity in an 800 m thick cool water carbonate pleistocene wedge this periplatform succession is dominated by bioclastic packstone and wackestone with minor intercalations of bioclastic grainstone fluctuations of stable oxygen isotope values in bulk carbonate samples parallel global climatic and related sea level fluctuations as predicted in the specmap curve the sea level controlled sedimentary cycles of the slope succession are several tens of meters thick lowstand deposits are relatively fine grained and include abundant sponge spicules whereas highstand deposits are coarser grained and contain abundant high mg calcite bioclasts aragonite content makes up to 36 of the cool water carbonates aragonite originates from tunicate spicules primary sea level controlled carbonate mineralogical and textural changes are likely to promote facies dependent differential diagenesis during later burial stages of such successions

submergent shorelines in the sw pacific evidence for an episodic post glacial transgression high resolution seismic profiles supported where possible by radiocarbon dates and regional stratigraphic data indicate that the last post glacial transgression in the sw pacific was episodic comprising major stillstands punctuated by rapid rises in sea level on the terrigenous continental shelf east of south island new zealand a succession of shorelines s8 s1 are recognized as follows s8 c 113 m 18 000 yr bp s7 c 88 m 17 000 yr bp s6 c 75 m 15 000 yr bp s5 c 56 m 12 000 yr bp s4 c 46 m 11 000 yr bp s3 c 28 m 9 500 yr bp s3a c 24 m 9 000yr bp s2 c 9 m 7 500yr s1 0 m 6 500yr bp with the exception of s8 and possibly s2 the shorelines are associated with wedges of sediment the size and presence of which imply that 1 sea level stabilized at some shorelines for a considerable period of time up to i 2 000 yr and 2 the intervening rises of sea level estimated to have been at least 10 12 m lo3 yr were too rapid to allow the reworking of the wedges into a transgressive sediment sheet as favoured in some current models on the great barrier reef shelf off queensland australia shorelines s8 sl have also been recognized with a further shoreline feature s4a occurring at c 39 m shorelines sla 0 m o yr bp slb 2 3 m 6 000 yr bp and slc 0 m 6 500 yr bp are recognized as discrete aspects of the post 6 500 yr bp sea level behaviour in north eastern australia the rapid rise in sea level at least between shorelines s5 12 000 yr bp and 53 9 500 yr bp is known to have outpaced reef growth causing in situ drowning of reefs located along the deeper shorelines all modern reefs so far drilled and dated began their development at or above s3 28 m 9 500 yr bp some of the shorelines particularly s5 appear to correlate between the northern and southern hemispheres on the basis of age succession and general depth of occurrence suggesting 1 that they may be global features controlled by the post glacial pattern of ice sheet decay and 2 that hydro isostatic adjustment may exert only a minor control on the depth of particular shorelines at least during the earlieg parts of the post glacial transgression

cyclicity in pleistocene upper slope cool water carbonates unravelling sedimentary dynamics in deep water sediments great australian bight odp leg 182 site 1131a abstract ocean drilling program site 1131 located in the central great australian bight recovered an expanded series of pleistocene cool water carbonates three distinct facies are arranged in repeating sedimentary cycles omission intervals form the base of the cycles and are overlain by laminated deposits the upper part of the cycles consists of bioturbated sediments facies cyclicity parallels glacial interglacial sea level changes firmground hardground surfaces formed during latest stages of sea level falls laminated sediments were deposited during later sea level fall and or early phases of the sea level lowstand and the bioturbated intervals are related to interglacial sea level highstands bottom current activity is interpreted to play an important control on facies and cycle development during the late stages of sea level fall upwelling currents winnowed the slope sediments leading to hardground formation during latest sea level falls and early sea level lowstands a relative increase in the ramp sediment supply to the slope leading to the formation of the laminated facies was also a response to the continued action of the near bottom upwelling currents that reworked previously deposited sediments along the slope during the early sea level rises laminated upwelling influenced facies were progressively covered by the bioturbated facies the adopted approach to decipher sedimentary cyclicity involving the integrated use of wireline logs geochemical data fms images and sedimentological analysis of the lithofacies has allowed to recognise subtle facies changes in upper slope settings of a distally steepened carbonate ramp and their relationship with the sea level as well as to unravel the importance of the oceanic current regime in the deposition style on the ramp that otherwise would remain unsolved this integrated method could be applied to study more precisely apparently homogeneous fine grained calcareous sediment successions of distal ramp outcrops

the miocene nullarbor limestone southern australia deposition on a vast subtropical epeiric platform abstract the early to middle miocene nullarbor limestone forms the vast karsted nullarbor plain in southern australia and may be the most extensive miocene carbonate deposit described to date these carbonates were deposited at southern paleolatitudes of 40 s and are interpreted to be subtropical to warm temperate in character because of the presence of certain genera of tropical coralline algae rhodoliths and articulated types large benthic foraminifera tropical molluscs zooxanthellate corals and micrite envelopes facies are dominated by skeletal grainstones and floatstones that accumulated in three interpreted paleoenvironments 1 seagrass banks upper photic zone 2 rhodolith pavements lower photic zone and 3 open seafloors lower photic to subphotic zone a decrease of tropical components from west to east across the platform implies that warm oceanic currents possibly related to a proto leeuwin current as well as a period of warm climate miocene climatic optimum resulted in subtropical deposition at southern latitudes the southern ocean extended inboard 450 km from the shelf edge during nullarbor limestone deposition but interpreted paleodepths did not extend much below the base of the photic zone a small slope angle 0 02 over a wide shelf 300 000 km2 implies deposition on an epeiric platform or epeiric ramp a miocene barrier reef was likely coeval with nullarbor limestone deposition therefore the inboard portion of the nullarbor limestone can be considered part of an extensive back reef lagoon system on a rimmed epeiric platform perhaps attaining a size similar to the modern great barrier reef system

seismic stratigraphy and geological evolution of the cenozoic cool water eucla platform great australian bight seismic images of the continental margin in the western great australian bight reveal the internal anatomy of a long lived cenozoic cool water carbonate shelf the cenozoic succession is divisible into seven seismic sequences that reflect four depositional phases phase a paleocene middle eocene is a progradational siliciclastic wedge deposited in a depositional sag and represents lowstand and transgressive sedimentation phase b middle eocene earliest middle miocene contains cool water ramp carbonates with biogenic mounds eocene oligocene overlain by a warm water flat topped platform rimmed by the early middle miocene little barrier reef coeval deep water carbonate deposition formed a multi lobed sediment apron this phase was terminated by gentle uplift and tilting throughout southern australia in the late middle miocene phase c late miocene early pliocene represents cool water lowstand wedge and ramp deposition and contains numerous biogenic mounds in the youngest sequence this phase is terminated by an unconformity attributed to marine erosion phase d pliocene quaternary is a thick succession of cool water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf and contains large deep water biogenic mounds this platform the first large cool water carbonate shelf imaged by high quality seismic reflection data demonstrates the interaction between regional tectonic and local and global paleo oceanographic processes as australia drifted northward during the cenozoic the great australian bight moved from high to middle latitudes and the regional oceanographic regime remained cool water largely because of coeval development of the antarctic circumpolar current in the evolving southern ocean short episodes of warm water deposition probably reflect incursions of a proto leeuwin current from the indian ocean whereas growth of the miocene coral algal little barrier reef resulted from a short term global increase in sea surface temperatures this platform dominated by stacked carbonate ramps is most similar to the west florida shelf but contains many more biogenic mounds the western great australian bight carbonate platform is an excellent modern analog for the mesoscale structure of cool water platforms in the older geologic record

modern carbonate and terrigenous clastic sediments on a cool water high energy mid latitude shelf lacepede southern australia the wide lacepede shelf and narrow bonney shelf are contiguous parts of the south eastern passive continental margin of australia the shelves are open generally deeper than 40 m covered by waters cooler than 18 c and swept by oceanic swells that move sediments to depths of 140 m the lacepede shelf is proximal to the delta of the river murray and the coorong lagoon shelf and upper slope sediments are a variable mixture of holocene and late pleistocene quartzose terrigenous clastic and bryozoa dominated carbonate particles bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m they can be grouped into four depth related assemblages coralline algae the only calcareous phototrophs are important sediment producers to depths of 70 m active benthic carbonate sediment production occurs to depths of 350 m but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions the shelf is separated into five zones the strandline is typified by accretionary sequences of steep shoreface beach and dune carbonate siliciclastic sediments similar shoreline facies of relict bivalve limestone cobble ridges are stranded on the open shelf the shallow shelf c 40 70 m deep is a wide extremely flat plain with only subtle local relief it is a mosaic of grainy quartzose palimpsest facies which reflect the complex interaction of modern bioclastic sediment production dominated by bryozoa and molluscs numerous highstands of sea level over the last 80 000 years modern mixing of sediments from relatively recent highstands and local introduction of quartz rich sediments during lowstands the middle shelf c 70 140 m deep is a gentle incline with subtle relief where holocene carbonates veneer seaward dipping bedrock clinoforms and local lowstand beach complexes carbonates are mostly modern uniform clean coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes the deep shelf edge c 140 250 m deep is a site of diverse and active bryozoa growth resulting accumulations are characteristically muddy and distinguished by large numbers of delicate branching bryozoa the upper slope between 250 and 350 m depth contains the deepest platform related sediments which are very muddy and contain a low diversity suite of delicate branching cyclostome bryozoa this study provides fundamental environmental information critical for the interpretation of cenozoic cool water carbonates and the region is a good model for older mixed carbonate terrigenous clastic successions which were deposited on unrimmed shelves

new zealand and australian cenozoic sedimentary cycles and global sea level changes a global sea level history determined by vail et al consists of 23 sea level cycles between the base of the cenozoic and the pliocene pleistocene boundary 65 to 1 8 ma we have examined the relation between this global sea level history and the new zealand and australian continental margin shallow marine sedimentary record sedimentary cycles in the australian cenozoic marginal marine sequences are bounded by unconformities of various durations the tectonic stability and aridity of the western and southwestern margin of australia during the cenozoic produced a sedimentary record dominated by hiatuses this contrasts with the relatively complete sequences of the tectonically more active southeastern marginal basins the four major sedimentary cycles in the australian cenozoic paleocene to early eocene middle to late eocene latest oligocene to late middle miocene and latest miocene to quaternary correlate with the supercycles ta tb tc td and te of vail et al in new zealand most of the cenozoic stages represent classic sedimentary cycles bounded by unconformities or correlative conformities formed as a result of large rapid eustatic sea level changes the marine tertiary sequence in new zealand consists of 23 stages of the 18 stage boundaries between the end of the paleocene 53 ma and the end of the miocene 5 ma 16 appear to correlate with the boundaries of eustatic sea level cycles eustatic sea level lowstands are well recorded as unconformities in new zealand as a result of its unique tectonic setting during the cenozoic for most of the early cenozoic until the middle oligocene 30 ma new zealand was generally subsiding after the middle oligocene this region began to be uplifted as the pacific australian plate boundary migrated onto new zealand climaxing in the latest cenozoic late pliocene quaternary thus exposing a nearly complete sequence of marine cenozoic strata well suited for the study of sedimentary cycles unconformities which form as a result of eustatic sea level changes represent a very useful correlation tool especially on continental margins with a sufficiently high terrigenous sediment supply and can be used to supplement paleontologic correlations their ultimate usefulness for correlation depends on the rapidity of the sea level changes or the speed at which sedimentary facies change in response to sea level changes if sea level changes rapidly 10 m 1 000 years stratigraphic resolution will be high 105 years but resolution decreases as the speed of sea level change decreases unconformities may well prove to be a vital tool linking the classic land based sections around the world with deep sea sections

holocene sediment dynamics on a cool water carbonate shelf otway southeastern australia the otway shelf is covered by cool ocean waters and veneered by bryozoan dominated carbonate sediments radiocarbon dating and stratigraphy of shelf vibracores and slope gravity cores document late pleistocene holocene deposition shelf sediments of the late pleistocene highstand 60 26 ky are rare either never having been deposited or having been removed during the following sea level fall 26 17 ky during the subsequent lowstand the shelf was exposed facies shifted basinward and beach dune complexes were constructed near the shelf edge the deep shelf was characterized by nondeposition and hardground formation and the shelf margin became locally erosional upper slope bryozoan sponge assemblages continued to grow actively and lower slope foraminifera and nannofossil ooze was increasingly enriched in hemipelagic terrigenous mud swept off the wide shelf coarse shelf debris and lowstand dune sands were erosively reworked and transported onto the upper slope and redistributed to deep slope aprons during early transgression 17 10 ky this event locally terminated shelf edge bryozoan and sponge growth continued erosive shoreface retreat formed a bored and cemented ravinement surface mantled by bivalves and lithoclasts across the open shelf base level rise reduced the amount of terrigenous material reaching the continental slope slower transgressive flooding from 10 to 6 5 ky allowed infilling of shallow embayments on the shelf and outer shelf sediment accumulation began by 7 ky sea level stabilized near its present level by 6 5 ky and the area is now partitioned into three zones by an energetic wave and swell regimen 1 inboard protected embayments and or beach dune complexes with high sediment accumulation rates about 100 cm ky 2 an open shelf where although sediment production is active accumulation is patchy 3 5 cm ky to nonexistent within the zone of wave abrasion and minimal about 23 cm ky between maximum abrasion depth and swell wave base and 3 a deep shelf edge and upper slope where sediment is accumulating at rates of 2 50 cm ky interpreted deep water 100 m bryozoan sponge mounds are growing at rates of 105 cm ky accumulation decreases progressively down slope with deep slope pelagic carbonate sedimentation at rates of 5 cm ky the late quaternary shelf record resembles that of flat topped warm water platforms with holocene sediment overlying pleistocene tertiary limestone but for different reasons much of this high energy shelf is still within lag depth more than 10 ky after flooding the steady state deep water shelf margin bryozoan factory has been largely unaffected by 50 100 m eustatic changes in sea level and has contributed to slow but continuous platform progradation the slow growth potential uniform profile of sediment production and distribution and inability of constituent organisms to construct rigid frameworks favor maintenance of a shallow ramp profile and makes the cool water carbonate system an excellent modern analog for interpretation of many ancient ramp successions

downslope migrating sandwaves and platform margin clinoforms in a current dominated distally steepened temperate carbonate ramp guadix basin southern spain during the late tortonian platform margin prograding clinoforms developed at the south western margin of the guadix basin large scale wedge shaped deposits here comprise 26 rhythms of mixed carbonate siliciclastic bedset packages and marl beds these sediments were deposited on a shallow water temperate carbonate distally steepened ramp a downslope migrating sandwave field developed in this ramp with sandwaves moving progressively down the ramp to the ramp slope where they destabilized folded and occasionally collapsed downslope sandwave migration was induced by currents flowing basinwards during the late tortonian the guadix basin was open north to the atlantic ocean via the dehesas de guadix strait and connected east to the mediterranean sea through the almanzora corridor according to the proposed current circulation model for the guadix basin for this time surface marine currents from the atlantic entered the basin from the northern seaway these currents moved counter clockwise and shifted the sediment on the ramp forming sandwaves that migrated downslope the development of platform margin prograding clinoforms by the basinward sediment transport mechanisms inferred here is known relatively poorly in the ancient sedimentary record moreover these wedge shaped geometries are similar to those found in some shelves in the western mediterranean sea and could represent an outcrop analogue to sub recent platform margin clinoforms revealed by high resolution seismic studies

high resolution sequence stratigraphy in tertiary carbonate rich sections by thin sectioned well cuttings thin sectioned well cuttings provide a low cost yet widely available and underused source of subsurface data that can be used to generate high resolution sequence stratigraphic frameworks in variably consolidated carbonate prone units in basins that lack cores or high quality suites of wire line logs because of the shallow 1 km depths of many cenozoic basins there is limited downhole mixing of cuttings although these carbonate prone basins are widespread globally they generally have not been subject to analyses of high resolution sequence stratigraphy because of the sparsity of outcrop and core data we used plastic impregnated thin sections of unwashed well cuttings from a paleogene carbonate prone succession from the coastal plain of north carolina to define the stacking patterns of the facies in the subsurface this data set along with biostratigraphic wire line log and seismic data was used to generate the framework of regional lithology based sequence stratigraphy systems tracts were determined by correlating vertical changes in the percentages of rock types in the well cuttings sequence boundaries were picked beneath units having the maximum abundance of quartz sandstone cuttings maximum flooding surfaces were picked beneath the units having the most abundant cuttings of deepest marine facies thus despite some downhole mixing thin sectioned well cuttings can be used to generate lithology based sequence stratigraphic frameworks for shallow carbonate prone sedimentary basins which previously were inaccessible except by expensive deep coring programs

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

surficial sediments on the continental shelf of tasmania australia abstract the continental shelf around the island of tasmania and in adjacent bass strait is veneered with quaternary palimpsest sediment composed of quartzose sand relict pleistocene carbonate particles and abundant holocene biogenic carbonate neritic deposits to water depths of 200 m are predominantly coarse grained ranging from gravels to sands to muddy sands the only true carbonate muds lie in the centre of bass strait this pattern reflects the overall high energy sea state and winnowing action of southward flowing currents along the outer shelf sediments can be resolved into three megafacies dominated either by quartzose sand inner shelf and around islands in bass strait relict carbonate particles mid shelf and near islands in bass strait or holocene biogenic carbonate inner to outer shelf facies can be distinguished depending upon whether bryozoans molluscs or other biofragments are dominant relict particles on the mid shelf are only present in large numbers on the western margin and around islands in bass strait they are a minor component of deposits on the eastern shelf this situation is interpreted to reflect higher overall carbonate production on the eastern shelf promoted by increased trophic resources via upwelling of subantarctic waters holocene molluscs especially infaunal bivalves are most prominent on the inner shelf holocene bryozoans are the most numerous particles overall and most abundant on the western shelf reflecting preferential conditions for growth probably promoted by episodic mid shelf upwelling bryozoan fragments can be separated into associations dominated by either 1 shallow water erect flexible articulated branching or articulated zooidal growth forms or 2 mid to outer shelf erect rigid fenestrate or flat robust branching types less abundant vagrant growth forms are limited to shallow waters whereas delicate branching forms are localized to deep waters nodular arborescent growth forms mainly celleporaria sp occur in both shallow and deep waters but are unusual on most of the shelf superimposed on this depth related distribution is a north to south cool to cold trend the whole spectrum of bryozoans is present on the shelf in the north whereas in the south bryozoan biofragments are mostly erect flexible with delicate branching forms restricted to the outer shelf and upper slope the change coincides with the furthest northward extent the subtropical convergence zone during winter surficial sediments in bass strait are most comparable to those on the extensive continental shelf to the west off southern continental australia where inboard sediment production takes place in environments populated by macroalgae but dominated by seagrasses where water depth is

facies analysis and sequence stratigraphy of a miocene warm temperate carbonate ramp montagna della maiella italy abstract the uppermost oligocene lower miocene to upper miocene ramp carbonates from montagna della maiella italy form a supersequence bounded by deeply incised truncation surfaces this supersequence is subdivided into four sequences each sequence is composed of skeletal limestones in its lower part and marly limestones in its upper part the lower parts of the sequences are foramol limestones which suggest deposition in the warm temperate climate zone changes in climate oceanography and relative sea level combined to control sedimentation in the four sequences in the lower parts of the two older sequences the skeletal sands built dunes suggesting high energy conditions the dominant skeletal grains in the oldest sequence are larger foraminifers and in the next sequence they are bryozoans this change reflects cooling around the time of the aquitanian burdigalian boundary in the lower parts of the two younger sequences of middle and late miocene age sediment sheets with red algal bryozoan oncoids suggest deposition under calmer conditions transgressive and highstand systems tracts are recognized in all sequences a shelf margin systems tract may be exposed in the second oldest sequence in contrast to the situation that exists when warm water carbonates are deposited sedimentation of the foramol limestones on this isolated ramp was unable to balance accommodation during sea level rise this led to hemipelagic sedimentation during sea level highstands conglomerates resulted from reworking along flooding surfaces

petrogenesis of cenozoic temperate water calcarenites south australia a model for meteoric shallow burial diagenesis of shallow water calcite sediments abstract the gambler limestone is one of several extensive shallow water shelf carbonates of eocene to miocene age exposed along the southern margin of australia it is a muddy to grainy bryozoan calcarenite with accessory benthonic foraminifers and echinoids the sediments originally composed almost entirely of calcite or mg calcite have been in vadose and phreatic environments for over 10 ma yet are virtually unlithified the only cements of any consequence are epitaxial on echinoids numerous karst features dolines caves speleothems and surface karren attest to prolonged residence in the meteoric zone the gambler limestone is presently one of the best fresh water aquuifers in australia most flow occurs through intergranular pores in sediments with over 30 porosity cementation is by minor intergranular pressure solution which has developed under overburden of less than 100 m the overlying naracoorte limestone miocene a calcarenite of warmer water aspect contains numerous aragonite molds and is well cemented we propose that such cool water limestones are a better model for the meteoric diagenesis of calcite sediments of all ages than are aragonite rich tropical sediments it is probable that many similar early and middle paleozoic calcite limestones may have been in the meteoric zone for prolonged periods yet contain little or no petrographic or geochemical record of such exposure

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

reef building and carbonate production modes in the west central tethys during the cenozoic abstract changing components rock textures lithofacies platform types and architecture throughout time are unique characteristics of carbonate rocks characterizing these attributes has been approached by 1 building reference models for specific phanerozoic intervals 2 recognizing the climatic impact in modulating carbonate production and 3 analyzing the influence of changing bio geochemical conditions the reference model approach is mostly based on biological evolution the climatic impact approach emphasizes temperature and the bio geochemical approach considers the changes in mg ca ratios and ca concentrations in the oceans to date however an analysis integrating all of these factors is still missing the analysis presented here includes all these factors but also co 2 which is fundamental for both photosynthesis and caco 3 precipitation here we analyze the waxing and waning of cenozoic reef limestones from the central tethys region through several steps 1 on the basis of rock volume rock textures associated sediments and light dependent skeletal components as records of light penetration and wave energy depth 2 on global environmental conditions 13 c 18 o p co 2 temperature and 3 on the basis of functionality nutritional requirements and available resources through the cenozoic water motion whether induced by surface or internal waves or by currents increased as the thermal gradients strengthened both with depth and with latitude active water motion is essential for plankton catchers such as corals but less so for many larger benthic foraminifers lbf pycnoclines in the meso oligophotic zone would then favor the benthic plankton catchers such as corals but would be detrimental for many lbf warm temperatures favored lbf the eocene lbf families predominated during lowering of atmospheric p co 2 by using respiratory co 2 to enhance the symbiont production of photosynthates under oligotrophic conditions and limited turbulence whereas the miocene families had to adapt to a progressive increase in turbulence the eurythermal coralline red algae however became preponderant producers in the mesophotic zone during times when the 13 c was relatively high this explains two apparent paradoxes 1 corals thrive best when the earth s high latitudes cool and 2 the dominance of corals and lbf is inversely correlated despite they both require tropical conditions and have similar trophic strategies mixotrophy

synsedimentary detrital dolomite in quaternary cool water carbonate sediments lacepede shelf south australia carbonate sediments on the lacepede shelf contain up to 25 colorless to orange to dark red dolomite particles as either single rhombs or rhomb clusters this dolomite is present in variable amounts across the shelf in quartzose bivalve bryozoan sediments which are a mixture of modern and relict late pleistocene particles rhombs range from sharply edged to abraded to completely rounded abraded aggregates are loosely cemented by high mg calcite and in places have pristine unabraded rhombs attached the dolomite is ca rich 44 mol mgco 3 fe poor and intricately zoned as seen under cathodoluminescence sr isotopes are compatible with precipitation from seawater of modern composition crystals from one locality have a 14 c age of 28 ka stable isotopes of carbon and oxygen are similar to those of dolomite precipitated from seawater the size composition and geochemistry of the crystals are incompatible with their originating in nearby holocene coorong and older tertiary dolomites the dolomite is interpreted as having formed initially during late pleistocene time a period of fluctuating sea level on the lacepede shelf in mildly reducing sediments just below the sediment water interface the crystals have since been reworked somewhat and dolomite may be forming on these nuclei today such scattered dolomite could be interpreted as postdepositional in ancient limestones when these sediments are buried the rhombs might act as nuclei for further precipitation of dolomite from subsurface fluids

subtropical to temperate facies from a transition zone mixed carbonate siliciclastic system palaeogene north carolina usa palaeogene passive margin sediments on the us mid atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate siliciclastic shelves this study utilizes well cuttings outcrop core and seismic data to document temporal and spatial variations in admixed bryozoan rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone this zone was situated between north flowing warm waters of the ancestral gulf stream carbonate dominated settings and south flowing cold waters of the ancestral labrador current siliciclastic dominated settings some degree of mixing of carbonates and siliciclastics occurs in all facies however siliciclastic prone sediments predominate in nearshore settings while carbonate prone sediments are more common in more open marine settings of the inner shelf break and deep shelf a distinctive dual break shelf depositional profile originated following a major late cretaceous to palaeocene transgression that drowned the earlier shallow platform this profile was characterized by prominent mid shelf break dividing the shallow shelf from the deep shelf and a major continental shelf slope break incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin storm wave base also contributed to the preservation of the dual break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid shelf break sediment fines in deep shelf facies were produced in place transported downdip from the shallow shelf by storm ebb currents and boundary currents and reworked from adjacent areas of the deep shelf by strike parallel boundary currents regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf with warmer waters and more humid climates favouring carbonate deposition and cooler more arid conditions favouring glaucony and siliciclastic dominated deposition continuous wave and current sweeping of the shallow shelf favoured deposition of mud lean facies across much of the shallow shelf skeletal components in much of the carbonate rich strata formed in warm nutrient rich subtropical waters as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages these indicators of warm water deposition within the bryozoan mollusk rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage such facies generally are associated with cooler water depositional settings

bryozoan distribution and growth form associations as a tool in environmental interpretation tasmania australia abstract the cool temperate carbonate sediments of eastern and western tasmania and bass strait composed of 29 50 of bryozoan skeletal grains two hundred and eighty three bryozoan bulk sediments around tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone bryozoans skeletons are grouped into 11 morphotypes according to architecture and style of disarticulation fragmentation encrusting forms erect flexible cellariiform and erect rigid robust branching adeoniform cheilostomes are consistently the most widespread with delicate branching cyclostomes the next most common growth form associations were grouped into four depth related settings strand line shallow shelf middle shelf and deep shelf this study demonstrates that bryozoan morphotype associations occupying different depth zones are valuable for providing fundamental paleo environmental information morphotype associations are related mainly to water depth water energy sedimentation rate and substrate in the strand line setting encrusting unilaminar and erect flexible articulated branching are abundant while in the shallow shelf erect flexible encrusting multilaminar erect rigid robust fenestrate and delicate branching are major growth forms the above associations indicate high to moderate energy levels moderate to high sedimentation rates and flexible to hard substrates in middle shelf areas erect rigid fenestrate robust and delicate branching cheilostomes and cyclostomes are the most common growth forms these associations indicate decreasing water energy lower sedimentation rate and presence of stable hard to soft substrates in the deep shelf setting the dominance of erect rigid robust fenestrate and foliose forms indicate deep quiet water low sedimentation rate and hard substrate

the holocene non tropical coastal and shelf carbonate province of southern australia abstract carbonate dominant sediments are currently forming and accumulating over the extensive marine shelf of the passive margin of southern australia a dearth of continental detritus results from both a very low relief and a predominantly arid climate the wide continental shelf is bathed by cold upwelling ocean waters that support luxuriant growths of bryozoans and coralline algae together with sponges molluscs asteroids benthic and some planktonic foraminifera the open ocean coast is battered by a persistent southwest swell resulting in erosion of calcrete encrusted pleistocene eolianites much sediment is reworked and overall shelf sedimentation rates are low high energy microtidal beach dune systems occur between headlands and along the very long ocean beach in the coorong region the northern more arid coastal areas also contain saline lakes that precipitate gypsum from infiltrated sea water and display marginal facies of aragonite boxwork to fenestral carbonate crusts with stromatolites and tepee structures in contrast the southern seasonally humid coorong region has a predominantly continental groundwater regime where sulphate is rare and the high summer evaporation precipitates dolomite magnesite and aragonite muds fenestral crusts breccias tepees and some stromatolites are also present st vincent and spencer gulfs both afford some protection from ocean swell but tidal amplitude and currents increase and a depth and inundation related zonation of plants and animals is established muddy carbonate sand accumulates on the sea floor below 30 m where filter feeding bryozoans bivalves and sponges dominate in shallower regions seagrass meadows contain a rich fauna that results in rapid accumulation of an unsorted muddy bioclastic sand mangrove woodlands backed by saline marsh with cyanobacterial mats are common and accumulate mud rich and gastropod bearing sediment as tidal amplitude and desiccation increase northward into both gulfs a supratidal zone bare of vegetation sabkha becomes the site for deposition of gypsum rich and fenestral calcitic mud

deepening upward subtidal cycles murray basin south australia abstract decimeter scale deepening upward cycles are the basic depositional motif of oligocene miocene murray supergroup limestones in the murray basin southeastern australia cycles formed in this large intracratonic basin on a centripetal temperate water epeiric ramp they reflect generation by trophic resource influenced carbonate production under mostly transgressive conditions listed from the base up each cycle is ideally composed of five parts part a biotically depauperate carbonates reflecting relatively shallow water restricted variably stressed highly mesotrophic environments part b increasingly biotically diverse limestones recording progressively more physical energy and less mesotrophic conditions upward om1 a conspicuous hardground to firmground surface formed during late transgression to stillstand during which wave sweeping and reworking contributed to omission and lithification part c relatively biotically diverse epifauna dominant sediments that were highly abraded during periods of condensed sedimentation under marginally oligotrophic conditions and om2 cycle boundary a rarely conspicuous surface representing arrested sedimentation and variable cementation as trophic resources increased and conditions for carbonate production deteriorated ten cycle types are grouped into four major styles clay cycles mollusc cycles echinoid cycles and bryozoan cycles these are interpreted to form a lithological continuum from inner restricted terrigenous locales to outer open marine bryozoan colonized environments deepening upward cycles were profoundly sensitive to autogenic factors such as nutrient influx terrigenous content and turbidity hydrodynamic energy water temperature salinity and water depth manifested in this intracratonic setting although these cycles share a similar sedimentological motif and hydrodynamic energy based cycle capping process with open shelf epicratonic shallowing upward subtidal cycles of tertiary age they formed in a very different way reflecting the distinctive intracratonic environment in which they formed murray basin cycles preserve a record of relative sea level rise whereas open shelf cycles accumulated mostly during relative sea level fall

cool water carbonates in an eocene palaeoestuary norseman formation western australia abstract numerous palaeovalleys formed extensive drowned estuaries during eocene transgressions along the southwestern part of the southern margin of australia the tertiary sediments of the cowan palaeovalley have been extensively drilled revealing deposition of the norseman formation during the middle eocene tortachilla transgression initial deposition occurred during transgression of the valley to form a drowned estuary sediments consisted of coarse grained muddy lithic iron and glauconite rich sands and gravels of mixed carbonate and quartz pure carbonates accumulated during the highstand produced by a typical shallow temperate water assemblage of bryozoans coralline algae echinoids and molluscs and were swept into shoals by strong tidal currents minor tropical components in the form of large benthic foraminifers and dasycladacean algae are present coarse bryozoan and trough cross bedded carbonate sands accumulated in the margins of the estuary and fine bryozoan sands in the deeper parts rhodoliths accumulated to form shoals in sheltered localities the spencer gulf and gulf st vincent of south australia provide close modern analogues to the cowan palaeovalley and the norseman formation modern carbonate sediments off esperance on the south coast of western australia contain tropical faunal elements within an otherwise temperate skeletal assemblage and also provide a modern analogue the norseman formation thus provides an excellent example of cool water carbonate deposition in near shore tide dominated environments this study complements and contrasts existing cool water shelf facies models based on tertiary carbonates deposited on deep shelves elsewhere in southern australia

the significance of marginopora vertebralis foraminifera in surficial sediments at esperance western australia and in last interglacial sediments in northern spencer gulf south australia abstract surficial sediments at esperance on the southern coast of western australia are predominantly bioclastic carbonates in which tests of foraminifera are a major constituent the megascopic species marginopora vertebralis is prolific occupying relatively protected areas of algal turf and seagrasses the abundance of this normally tropical foraminifer at southern latitudes can be attributed to the leeuwin current which brings warm waters from the tropics to southwestern australia and then eastwards past esperance into the great australian bight the leeuwin current is significantly warmer than the cool interfacing waters of the southern ocean that otherwise characterise the southern australian continental shelf last interglacial sediments of the glanville formation in northern spencer gulf of south australia host an assemblage of fossil foraminifera which is similar to that of the modern environment at esperance especially the presence of m vertebralis two bivalve molluscs anadara trapezia and pinctada carchariarium both characteristic of warm waters are also present in the glanville formation marginopora vertebralis and other faunal elements migrated to south australia by means of the last interglacial equivalent of the leeuwin current which apparently had greater definition at that time it may therefore be inferred that during other times of global warming and corresponding higher sea levels the palaeo leeuwin current had greater ecological influence across the continental shelf of southern australia thus warm water marine fossils in the glanville formation do not necessarily signify last interglacial water temperatures for the open southern ocean beyond the continental shelf similarly it cannot be assumed that these fossils necessarily indicate a last interglacial climate for terrestrial southern australian that was warmer than presently prevails

sediment waves with a biogenic twist in pleistocene cool water carbonates great australian bight abstract sediment waves composed of fine grained carbonate ooze with in place bryozoans are a characteristic element of the pleistocene of the great australian bight gab the low amplitude and strongly elongate sediment waves are up to 10 km long 1 km wide 40 m high and oriented sub parallel to contours immediately off the shelf slope break they are asymmetrical showing up slope migration and mainly occur in trains the sediment waves were drilled during odp leg 182 in 1998 and were interpreted as biogenic reef mounds new high quality seismic and multibeam bathymetry data were acquired on the galathea 3 expedition in 2006 allowing description of the morphology and internal architecture of the sediment waves in unprecedented detail leading to an alternative interpretation of their formation most sediment waves were initiated by preferential deposition on the landward side of irregular erosion surfaces sediment wave accretion took place under the influence of density driven currents which decelerated up the landward dipping flanks and accelerated down the seaward dipping flanks of the sediment waves the currents are interpreted as dense water cascades formed by summer evaporation and strong winter cooling by analogy with oceanographic processes in the present day gab the lithological composition varied with climate and sea level but sediment wave formation did not sediment waves formed and accreted during both glacials and interglacials in contrast to the previous interpretations which involved growth in glacial periods only bryozoans influenced the depositional environment by adding sediment trapping fine grained particles and stabilizing the muddy sea floor this caused the sediment waves to gain a more prominent sea floor relief than most muddy siliciclastic sediment waves formed by similar depositional processes the interpretation of the sediment waves as purely biogenic build ups is rejected and the sediment waves are most appropriately described as biogenically influenced sediment waves

soft sediment deformation induced by sinkhole activity in shallow marine environments a fossil example in the apulian foreland southern italy abstract soft sediment deformation structures are exposed in sea cliffs in the lower part of the calcarenite di gravina formation late pliocene early pleistocene in the cala corvino area n of monopoli adriatic sector of the apulian foreland southern italy deformation affects a thickness of about 5 m involving a lower calcareous terrigenous sand and gravel unit and an upper heavily bioturbated grainstone and packstone unit deformation is absent from the overlying part of the succession large scale soft sediment deformation structures are collapse features comprising irregularly elongated conical zones of sinking in vertical section narrow drop zones occur in the lower sandy gravelly facies and large gentle folds in the upper grainstone packstone beds the degree of deformation decreases upwards small scale soft sediment deformation structures adjacent to the large scale conical collapse structures are narrow vertically elongated load structures about 2 m high and 30 50 cm wide that involve only the basal terrigenous facies the distribution of small and large scale soft sediment deformation structures corresponds closely to zones of fracturing in the underlying cretaceous limestones and the elongation directions of soft sediment deformation structures correspond to the orientation of major fractures in the limestones the soft sediment deformation occurred due to collapse associated with karstic sinkhole formation along fractures in the bedrock geometrical relationships between deformed and undeformed sedimentary units show that deformation occurred in a shallow marine environment the structures at cala corvino provide a rare outcrop scale record of sinkhole induced soft sediment deformation occurring in a shallow marine environment