giant middle eocene bryozoan reef mounds in the great australian bight this paper reports the discovery of extensive middle eocene bryozoan reef complexes along the paleoshelf edge of the great australian bight gab the complexes form the earliest carbonate deposit in the gab which is the largest cenozoic cool water carbonate province on earth the bryozoan reef mounds previously misidentifi ed as volcanic bodies were deposited parallel to the shelf margin for more than 500 km along strike individual reef mound complexes are 60 150 km long as wide as 15 km and as thick as 200 m and dwarf all previously described examples superimposed on the distal margin of an underlying paleocene to mid eocene siliciclastic delta complex the reef mounds provide a critical insight into changing paleoenvironments of the australo antarctic gulf ca 43 ma coinciding with global and continent wide climatic and tectonic events the rapid growth and demise of reef mound building bryozoans raises new questions regarding the interplay of southern ocean opening ocean currents and biosphere interactions

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

syenite associated disseminated gold deposits in the abitibi greenstone belt canada a distinct group of gold deposits in the abitibi greenstone belt is spatially associated with quartz monzonite to syenite stocks and dikes the deposits occur mainly along major fault zones in association with preserved slivers of alluvial fluvial timiskaming type sedimentary rocks the deposits consist of disseminated sulfide replacement zones with variably developed stockworks of quartz carbonate k feldspar veinlets within zones of carbonate albite k feldspar and sericite alteration the syenitic intrusions are broadly contemporaneous with deposition of timiskaming sedimentary rocks and together with disseminated gold mineralization they have been overprinted by subsequent regional folding and related penetrative cleavage disseminated gold orebodies occur within composite syenitic stocks or along their margins along satellite dikes and sills and along faults and lithologic contacts away from intrusions orebodies in these different positions are interpreted to represent proximal to distal components of large magmatic hydrothermal systems centered on and possibly genetically related to composite syenitic stocks

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

a review of te and se systematics in hydrothermal pyrite from precious metal deposits insights into ore forming processes abstract pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including au and co and the semi metals as se sb te and bi as such in many hydrothermal ore deposits where pyrite is the dominant sulphide phase it can represent a major repository for these elements furthermore the concentrations and ratios of au as and co in pyrite have been used to infer key ore forming processes however the mechanisms controlling the distribution of te and se in pyrite are less well understood here we compare the te and se contents of pyrite from a global dataset of carlin type orogenic au and porphyry epithermal deposits to investigate 1 the potential of pyrite to be a major repository for these elements and 2 whether te and se provide insights into key ore forming processes pyrite from carlin type low sulphidation and alkaline igneous rock hosted epithermal systems is enriched in te and se compared to pyrite from high sulphidation epithermal and porphyry cu deposits orogenic au pyrite is characterised by intermediate te and se contents there is an upper solubility limit for te as a function of as in pyrite similar to that established for au by reich et al 2005 and this can be used to identify te present as telluride inclusions which are common in some epithermal porphyry and orogenic au deposits physicochemical fluid parameters such as ph redox and temperature as well as crystal chemistry control the incorporation and concentration of se and te in pyrite neutral to alkaline fluids have the ability to effectively mobilise and transport te fluid boiling in porphyry epithermal systems as well as wall rock sulphidation and oxidation in carlin type and orogenic au deposits can effectively precipitate te in association with pyrite and au in contrast se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature irrespective of ph and f o 2 hence we propose that the se contents of pyrite may be used as a new geo thermometer for hydrothermal ore deposits furthermore the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for te and se in carlin type and some epithermal systems and thus pyrite can be considered to be of economic interest as a potential source for these elements

evolution of a deep water carbonate platform upper cretaceous to pleistocene sedimentary environments on the west florida margin abstract deep water carbonates have been accumulating on the west florida margin since the early late cretaceous although the depositional style and sediment types have changed through time seven coreholes drilled by exxon record the establishment of two gently dipping aggradational ramps the first in the late cretaceous to oligocene and the second in the middle to late miocene to the present these dominantly pelagic depositional environments followed episodes of downslope transport of shallow water grains diluting background pelagic sedimentation and producing progradational ramps that built seaward this study traces the evolution of the deep water west florida sedimentary systems and contrasts the older aggradational ramp characterized by both foraminiferal and radiolarian oozes as well as volcanic ash with the late neogene ramp whose biogenic components are mainly foraminifera and coccoliths the cycles of progradation separated by periods of ramp aggradation developed as eustasy interacted with prolonged subsidence of the margin early late cretaceous as well as oceanographic changes caused by closure of the suwannee strait late oligocene to early miocene and of the isthmus of panama middle to late miocene the major transitions in environments recorded in the west florida ramp platform thus resulted from the superposition of climatic tectonic and oceanographic events on global sea level changes

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

genetic sequence stratigraphy of cool water slope carbonates pleistocene eucla shelf southern australia the south australian eucla shelf belongs to the world s largest cool water carbonate sedimentary system during the pleistocene it exported large amounts of sediment to the shelf edge and upper slope resulting in an expanded sedimentary wedge wedge internal clinoforming seismic reflectors suggest a stacking of the deposits into genetic sequences high resolution stable oxygen and carbon isotope point counting grain size and carbonate mineralogical xrd analyses were carried out to characterize these genetic sequences along a dip parallel transect of three odp leg 182 drill holes located between the shelf edge and upper slope oxygen and carbon isotope fluctuations show that the genetic sequences formed as a response to sea level fluctuations within the genetic sequences facies differentiation and sediment volume partitioning occur along the transect lowstand deposits are fine grained and contain more sponge spicules and micrite highstand deposits are coarse grained with tunicate spicules brown bioclasts as well as bryozoan and corallinacean debris boundaries separating highstand and lowstand deposits are triggered by sea level fall and are expressed as abrupt grain size changes or as turning points in grain size trends analyzed components vary in abundance along the transect genetic sequences show dip parallel variations in thickness combined with changing relative proportions of lowstand versus highstand deposits

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

variability of repeating earthquake behavior along the longitudinal valley fault zone of eastern taiwan 1 two major clusters of repeating earthquake sequences res are found on two fault patches near the longitudinal valley fault lvf in eastern taiwan the chihshang segment to the south and the hualien segment to the north the 25 m 2 3 4 6 res on the hualien segment are widely distributed in a nne direction over a distance of 45 km whereas on the chihshang segment the 30 m 2 2 3 4 res have a shorter along strike extent of about 15 km the longer spatial extent of res on the hualien segment may indicate a wider distributed creeping zone at depth m 3 8 res are observed on the hualien segment and are characterized by quasiperiodic recurrence statistical analysis of the size and number of earthquakes adjacent to the res indicates that the smaller number of large earthquakes in the vicinity may explain the quasiperiodic recurrence of res we argue that on the hualien segment m 4 or larger earthquakes are isolated enough in space to facilitate the occurrence of repeated ruptures

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

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

the west central florida inner shelf and coastal system a geologic conceptual overview and introduction to the special issue abstract this paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west central florida this is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large scale control on coastal geomorphology the availability of sediments and the level of wave energy in order to understand the holocene geologic history of this depositional system a regional study defined by natural boundaries north end of a barrier island to the apex of a headland was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques it is the purpose of this introductory paper to define the character of this coastal inner shelf system provide a historical geologic perspective and background of environmental information define the overall database present the collective objectives of this regional study and very briefly present the main aspects of each contribution specific conclusions are presented at the end of each paper composing this volume

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

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

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

cenozoic biogenic mounds and buried miocene barrier reef on a predominantly cool water carbonate continental margin eucla basin western great australian bight the southern continental margin of australia is the largest area of cool water carbonate shelf deposition on the globe interpretation of 5495 km of airgun seismic reflection data in the western part of the great australian bight indicates that the 700 m thick cenozoic section of the offshore eucla basin was deposited largely as a prograding cool water middle to high latitude carbonate ramp characterized by widespread development of broad low relief biogenic bryozoan sponge shelf and upper slope mounds the succession also contains a spectacular and extensive 475 km long buried middle miocene barrier reef the miocene little barrier reef parallel to the modern shelf edge this rimmed carbonate platform margin represents an episode of warm water sedimentation during a global climatic optimum probably coupled with strong eastward flow of a proto leeuwin current the late miocene eustatic sea level fall produced an areally restricted debris apron sequence at the foot of the reef escarpment the carbonate platform is capped by a neogene cool water carbonate ramp succession typified by aggradational to sigmoidal sequences punctuated by periods of cold water sea floor erosion interpretation of this succession in the light of global and local tectonic and oceanographic events illustrates the dominant influence of water temperature on carbonate platform and reef growth throughout the cenozoic

gold deposits of the northern margin of the north china craton multiple late paleozoic mesozoic mineralizing events the northern margin of the north china craton is well endowed with lode gold deposits hosting a resource of approximately 900 tonnes t of gold the 1 500 km long region is characterized by east trending blocks of metamorphosed archean and proterozoic strata that were episodically uplifted during variscan indosinian and yanshanian deformational and magmatic events at least 12 gold deposits from the daqinshan yan liao includes the zhangjiakou yanshan and chifeng gold districts and changbaishan gold provinces contain resources of 20 100 t au each most deposits are hosted in uplifted blocks of precambrian metamorphic rocks although felsic paleozoic and mesozoic plutons are typically proximal and host 30 of the deposits the lodes are characterized by sulfide poor quartz veins in brittle structures with low base metal values and high au ag ratios although phyllic alteration is most common intensive alkali feldspar metasomatism characterizes the wulashan dongping and zhongshangou deposits but is apparently coeval with variscan alkalic magmatism only at wulashan stepwise 40ar 39ar geochronology on 16 samples from gangue and alteration phases combined with unpublished shrimp u pb dates on associated granitoids suggest that gold mineralizing events occurred during variscan indosinian and yanshanian orogenies at circa 350 250 200 180 150 and 129 ma however widespread permo triassic 250 ma and early jurassic 180 ma thermal events caused variable resetting of most of the white mica and k feldspar argon spectra as well as previously reported k ar determinations compiled and new stable isotope and fluid inclusion data show that most 18o values for ore stage veins range from 8 to 14 indicating a fluid in equilibrium with the precambrian metamorphic basement rocks d values from fluid inclusions range widely from 64 to 154 which is indicative of a local meteoric component in some veins and highly variable 34s data 7 to 17 even within individual deposits indicate various local country rock sources for sulfur fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 c and are consistently characterized by low salinity h2o co2 ch4 n2 solutions although the data are largely consistent with that from orogenic gold veins intrusion related veins and epithermal veins are also recognized the multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the north china craton electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0239 2

supply of allochthonous sediment and its effects on development of carbonate mud mounds mississippian lake valley formation sacramento mountains south central new mexico u s a abstract carbonate mud mounds in the mississippian lake valley formation new mexico can be classified according to their external morphology internal growth phases and paleogeographic location along the lake valley ramp most of the lake valley mounds grew during a complete third order accommodation cycle alamogordo nunn tierra blanca interval 3 6 myr duration which directly influenced mound biota facies types and the physical interactions between the mounds and sediment gravity flows that transported skeletal sediment around and over the mounds during the regressive phase of the cycle lenticular mounds are found in updip parts of the preserved lake valley ramp which largely consists of outer ramp facies most lenticular mounds grew exclusively during deposition of the transgressive alamogordo member when outer parts of the ramp were somewhat sediment starved coarse grained carbonate gravity flow deposits nunn and tierra blanca members typically onlap lenticular mounds and only locally interfinger with mound core facies these relationships indicate lenticular mounds were buried by carbonate gravity flow deposits which accumulated much faster than mound cores could aggrade the sediment gravity flows constructed shingled lobes sand sheets and oblique clinoforms and were erosive at times which also probably helped to shape lenticular mounds transitional mounds are typically located downdip from the lenticular mounds and had an initial lenticular growth phase which was followed by aggradational growth of mound cores aggradational mound cores were locally modified by submarine erosion or failure which created sharp stratal truncation surfaces that were later onlapped by gravity flow deposits after the aggradational phase and stratal onlap mounds with remnant seafloor relief served as substrates for continued growth during deposition of the tierra blanca member this final growth phase in transitional mounds records minor aggradation and significant typically asymmetric lateral accretion which suggests that 1 the mounds had grown to some accommodation limit possibly storm wave base and 2 the complex dispersal and accumulation patterns for the gravity flows also influenced how mound cores accreted laterally for example the upcurrent sides of some transitional mounds were buried preferentially by onlapping tierra blanca gravity flow deposits whereas their downcurrent sides locally accreted for significantly greater distances and with very different stratal geometries hemispherical mounds are located farthest downdip on the lake valley ramp they are the largest mounds and contain all three lenticular aggradational and accretionary growth phases later growth phases of hemispherical mounds have steeply dipping mound core to flank relationships with abrupt facies transitions because of their distal position along the lake valley ramp and greater distance from the progradational sand bodies the hemispherical mounds were the dominant sources for coarse grained carbonate sediment to adjacent non mound environments during nunn and tierra blanca time thus the distance of lateral accretion and overall morphology of hemispherical mounds were not affected greatly by allochthonous sediment from updip parts of the ramp

detecting magmatic derived fluids using pyrite chemistry example of the chibougamau area abitibi subprovince quebec abstract magmatic fluids are an important carrier of precious and base metals in many mineralized systems porphyry deposits intrusion related gold systems irgs volcanogenic massive sulfides vms recognizing magmatic inputs is essential for understanding metallogenic processes and for developing accurate exploration models and the importance of fluids exsolved from magmas remains a source of much debate for some contexts such as irgs and orogenic gold deposits this study aims to identify magmatic fluids in the chibougamau area northeastern corner of the neoarchean abitibi subprovince canada using pyrite chemistry this is achieved by comparing the chemistry of pyrites recovered from the cu au magmatic hydrothermal porphyry systems of the chibougamau area to background compositions i e the chemistry of pyrites from weakly mineralized rocks from the same area analyses of quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms are processed in three distinct manners to better evaluate the trace elements controlled by silicates oxides sulfides and sulfosalt inclusions and the trace elements that are structurally bound to pyrite detailed investigation of the trace element content of pyrite indicates that most elements are controlled by silicate inclusions some reflect the composition of the host rock others correlate with the mineralizing style and only te and bi are discriminant of the porphyry systems of the chibougamau area tellurium is structurally bound to pyrite or forms telluride nanoparticles in the study area while the distribution of bi is controlled by galena and chalcopyrite inclusions and pyrite chemistry is interpreted using absolute te values and bi ratios bi pb and bi cu this study provides insight into the cu au magmatic hydrothermal systems of the chibougamau area it also has implications for the way pyrite chemistry can be used to probe for magmatic fluids in other mineralized contexts

cenozoic eucla basin and associated palaeovalleys southern australia climatic and tectonic influences on landscape evolution sedimentation and heavy mineral accumulation abstract the eucla basin including the vast nullarbor plain lies on the margins of the yilgarn musgrave and gawler cratons in southern australia and owes its distinctive landscape to a unique set of interactions between eustatic climatic and tectonic processes over the last 50 ma understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits and the sediments derived from them contain remobilised gold uranium and heavy minerals in particular a remarkably preserved palaeoshoreline sequence along the north eastern margin of the eucla basin is highly prospective for heavy mineral placer deposits the record of marine marginal marine estuarine fluvial and lacustrine environments as constrained mainly by an extensive borehole dataset reflects major depositional events during the palaeocene early eocene middle late eocene oligocene early miocene middle miocene early pliocene and pliocene quaternary these events reflect the key role of eustatic sea level variation which during highstands inundated the craton margins flooding palaeovalleys to up to 400 km inboard of the present coastline however a systematic eastward migration of the depocentre across the eucla basin during the neogene together with apparent flow reversals in a number of palaeovalley systems draining the gawler craton suggest that the eucla basin has also been subject to differential vertical movements expressed as a west side up east side down tilting of 100 200 m this differential movement forms part of a broader north down southwest up dynamic topographic tilting of the australian continent associated with relatively fast 6 7 cm yr northward plate motion since fast spreading commenced in the southern ocean at 43 ma we suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits largely through multistage eastward reworking of near shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems

genesis of oxidized and reduced type granites the genesis of oxidized type magnetite series and reduced type ilmenite series granites is discussed on the basis of thermodynamic considerations we show that so 2 in the magma can oxidize augite to form magnetite with decreasing temperature because the so 2 h 2 s buffer line intersects with the augite magnetite quartz buffer line on a 1 t f sub o 2 diagram when the magma contains so 2 above 250 ppm and the f sub o 2 is constrained by the so 2 h 2 s buffer the magma forms oxidized type granites 0 2 modal magnetite on the other hand when the so 2 content is less than 250 ppm the magma solidifies as a reduced type granite 0 2 modal magnetite if the f sub o 2 of the magmas is buffered by h 2 o h 2 co 2 co or ch 4 co 2 no magnetite will crystallize and reduced type granites will be formed as a result the genesis of oxidized type and reduced type granites can be attributed to the difference in volatile components in magmas

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

behavior of major and trace elements including ree during paleoproterozoic pedogenesis and diagenetic alteration of an archean granite near ville marie quebec canada abstract this paper presents a complete set of chemical data from a pre 2 0 ga weathering profile that formed on the archean granite near ville marie quebec examination of data from two sections of the paleosol indicates that na ca p and sr were lost from the paleosol whereas ti nb th zr hf and ta remained immobile during chemical weathering and all subsequent alteration rare earth mobility during genesis of the ville marie paleosol closely follows the pattern of early stages of chemical weathering in modern profiles average concentration of ree in both profiles is 20 40 lower than what is found in the fresh granite suggesting mobilization during pedogenesis hrees seem to be less mobilized than the lrees la sm n ratios gradually decrease toward the top of the paleosol but the values remain very close to that of the protolith gd yb n values remain unchanged in the weathering profile la yb n values in the weathering profile are quite variable and generally lower than that of the protolith eu eu and ce ce values are essentially the same as those of the protolith but two samples from the uppermost part of the profile have developed positive cerium anomaly of 0 3 relative to the protolith

formation mechanism of deep cambrian dolomite reservoirs in the tarim basin northwestern china abstract well ts1 which is located in the north uplift of the tarim basin northwestern china has a total depth of 8408 m and is the deepest petroleum well in the world the well penetrates a high quality upper cambrian dolomite reservoir from 6884 m to 8408 m the porosity of this dolomite increases with increasing depth reaching 9 1 at a depth of 8407 56 m a large number of dissolution pores are present in the core retrieved from well ts1 some of the pores are partially filled with coarse dolomite crystals which display saddle shapes and undulose extinction the pore filling dolomites have high concentrations of fe and mn averaging 3158 1 and 172 5 ppm respectively the concentration of ba is up to 4000 3 ppm the oxygen isotope composition of the pore filling dolomites is relatively light and the 18 o values range from 10 9 to 5 1 the 87 sr 86 sr values are relatively high ranging from 0 709361 to 0 709975 the mineralogical and geochemical features demonstrate that the pore filling dolomites were precipitated from hydrothermal fluids that significantly altered the deep cambrian dolomite reservoirs during upward migration along faults and fractures in the permian according to petrologic geochemical and seismic features the dolomite reservoirs were first dissolved by meteoric water during or shortly after deposition and were then significantly altered by hydrothermal fluids during burial a porosity variation model was proposed for the deep dolomite reservoirs that were influenced by hydrothermal fluids the model of increasing porosity with increasing depth in well ts1 indicates that there may be high quality dolomite reservoirs in the deep strata of basins where hydrothermal fluids are active the small amount of liquid hydrocarbon obtained from cores at a depth of more than 8400 m demonstrates that the deep dolomite reservoir is still suitable for hydrocarbon accumulation due to an unusually low geothermal gradient of approximately 20 c km the deep strata in basins with similar geological parameters may therefore be potential exploration targets elsewhere in the world

geochemistry and stratigraphic correlation of basalt lavas beneath the idaho chemical processing plant idaho national engineering laboratory thirty nine samples of basaltic core were collected from wells 121 and 123 located approximately 1 8 km apart north and south of the idaho chemical processing plant at the idaho national engineering laboratory samples were collected from depths ranging from 15 to 221 m below land surface for the purpose of establishing stratigraphic correlations between these two wells elemental analyses indicate that the basalts consist of three principal chemical types two of these types are each represented by a single basalt flow in each well the third chemical type is represented by many basalt flows and includes a broad range of chemical compositions that is distinguished from the other two types basalt flows within the third type were identified by hierarchical k cluster analysis of 14 representative elements fe ca k na sc co la ce sm eu yb hf ta and th cluster analyses indicate correlations of basalt flows between wells 121 and 123 at depths of approximately 38 40 m 125 128 m 131 137 m 149 158 m and 183 198 m probable correlations also are indicated for at least seven other depth intervals basalt flows in several depth intervals do not correlate on the basis of chemical compositions thus reflecting possible flow margins in the sequence between the wells multi element chemical data provide a useful method for determining stratigraphic correlations of basalt in the upper 1 2 km of the eastern snake river plain

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

a 300 m long depth profile of metabolic activity of sulfate reducing bacteria in the continental margin sediments of south australia odp site 1130 derived from inverse reaction transport modeling reaction transport modeling of dissolved species in interstitial water allows for the inversion of transport processes and thus facilitates the detailed investigation of signals which are usually blurred by diffusion and advection here i present a case study from the south australian continental margin odp leg 182 site 1130 where i use reaction transport modeling to derive a depth transect of volumetric sulfate reduction rates site 1130 located on the shelf slope in 500 m deep water is of special interest as an upwelling sulfate rich brine allows for an extended sulfate reduction zone which reaches to a depth of at least 300 mbsf the obtained reduction rates vary from 600 pmol cm 3 yr 1 at 30 mbsf to 63 pmol cm 3 yr 1 at 300 mbsf the depth integrated sulfate consumption equals 65 10 6 mol yr cm 2 which is similar to other shelf slope settings without advecting sulfate this suggests that the primary control on sulfate reduction rates is organic matter reactivity rather than sulfate availability however similar to other odp leg 182 sites the interstitial water chemistry in the upper 30 mbsf is inconsistent with a diffusive advective transport system while the actual process causing this remains elusive pyrite burial rates from this zone suggest that sulfate reduction rates in this zone are at least 60 times higher than those derived from reaction transport modeling assuming diffusion and advection alone

tertiary coastal dunes of the eucla basin australia abstract on the northeast margin of the nullarbor plain in western south australia there is preserved an assemblage of coastal aeolian landforms that includes coastal dune dune ridge and possible beach ridge one of these landforms is the ooldea range a 650 km long coastal dune that lies 25 300 km from the present coast these landforms are believed to have formed at the end of the eocene after maximum marine transgression in the eucla basin the ooldea barton and paling ranges formed in a tectonically stable region of topographically subdued terrain their orientation and position may be related in part to crustal fractures that were active during initial break up of australia and antarctica the large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks growth may have begun as chains of barrier islands which amalgamated to form large coast parallel dunes during progradation these coastal dunes provide evidence about climate at and after the time of their formation their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component this occurred at a time when the climate is likely to have been temperate if the interpretation of the dunes age is correct they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the eocene their excellent preservation in the landscape today some 34 37 million years after formation is remarkable implied is a degree of aridity for much of the remainder of the cainozoic this appears to have been more significant in the nullarbor plain region than in the southeastern part of australia other factors responsible for their preservation are likely to include vegetation cover the permeability of their quartz sands subsequent history of sea level and hydrodynamics of the basin

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

methanogenesis and sulfate reduction in marine sediments a new model a number of studies have shown that methanogens are active in the presence of sulfate under some conditions this phenomenon is especially exemplified in carbonate sediments of the southern australian continental margin three sites cored during ocean drilling program odp leg 182 in the great australian bight have high concentrations of microbially generated methane and hydrogen sulfide throughout almost 500 m of sediments in these cores the sulfate reducing and methanogenic zones overlap completely that is the usual sulfate methane transition zone is absent amino acid racemization data show that the gassy sediments consist of younger carbonates than the low gas sites high concentrations of the reduced gases also occur in two odp sites on the margin of the bahamas platform both of which have similar sedimentary conditions to those of the high gas sites of leg 182 co generation of these reduced gases results from an unusual combination of conditions including 1 a thick quaternary sequence of iron poor carbonate sediments 2 a sub seafloor brine and 3 moderate amounts of organic carbon the probable explanation for the co generation of hydrogen sulfide and methane in all these sites as well as in other reported environments is that methanogens are utilizing non competitive substrates to produce methane within the sulfate reducing zone taken together these results form the basis of a new model for sulfate reduction and methanogenesis in marine sediments the biogeochemical end members of the model are 1 minimal sulfate reduction 2 complete sulfate reduction followed by methanogenesis and 3 overlapping sulfate reduction and methanogenesis with no transition zone

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

seismic geomorphology and growth architecture of a miocene barrier reef browse basin nw australia abstract the cenozoic succession of browse basin is characterized by a carbonate system that developed from a non tropical ramp in eocene lower miocene times to a tropical rimmed platform in the middle miocene the evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle miocene tropical reef system the first reef structures developed during the early middle miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction subsequently they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km the barrier reef itself comprises three distinct ridges separated by progradational steps the second and third step are separated by a karstified horizon which is interpreted to represent the global sea level fall shortly before the serravallian tortonian boundary the following third ridge formed in a slightly downstepped position during the sea level lowstand and initial transgressive phase further sea level rise during the early tortonian first drowned the barrier reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior the similar evolution of the browse basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea level changes relatively large subsidence rates in the study area possibly augmented the eustatic sea level rise in the tortonian and hence contributed to the drowning of the reef system however the initiation and final demise of the reef system was also governed by global and regional climate variations the first seismically defined reefs developed simultaneous to a maximum in the transport capacity of the indonesian throughflow which brings warm low salinity waters to the north west shelf reef drowning followed the restriction of this seaway close to the middle to early miocene boundary this near closure of the indonesian seaway possibly led to a regional amplification of the global middle to late miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea level

oligocene and miocene carbonate platform development in the browse basin australian northwest shelf abstract extensive 2d and 3d seismic reflection data calibrated by wells provide new insights into the lateral extent morphology internal architecture and age of carbonate platforms in the subsurface of the browse basin australian northwest shelf nws the oldest carbonate build ups are interpreted as a giant bryozoan build up complex of oligocene age 34 03 27 8 ma in the late burdigalian tropical reef growth began and numerous reef rimmed carbonate platforms progressively coalesced into an extensive barrier reef from the mid langhian to the early tortonian the browse basin contained an elongate along margin barrier reef system over 500 km long this barrier reef possibly extended in the southwest into the northern carnarvon basin after the early tortonian reefs on top or landward of this major barrier reef system were smaller and less connected this significant reduction in area covered by reef rimmed platforms likely resulted from cooling following the mid miocene climate optimum and relatively high subsidence rates the reef rimmed carbonate platforms that formed between the late burdigalian and the early tortonian are very similar throughout the browse basin platform development after the early tortonian was regionally diverse high subsidence rates in the northern browse basin are interpreted to have promoted the development of thick aggrading platforms lower subsidence in the south led to thinner more widespread platforms recurrently shifting location in response to eustatic change the final phase of reef decline around 6 ma coincides with an increase in current driven drift sedimentation current related winnowing of sediments from the lagoons and slopes of the remaining carbonate platforms likely contributed to their final drowning

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

genesis of blackened limestone clasts at late cenozoic subaerial exposure surfaces southern australia abstract black limestone clasts are present across the globe at modern and ancient subaerial exposure surfaces and in intertidal and supratidal environments these problematic clasts are particularly abundant at multiple subaerial exposure surfaces across southern australia the genesis of such exceptionally preserved clasts can be interpreted through universal fabrics across wide geographic regions and geologic ages regardless of location or age all south australian blackened clasts studied have a similar microstructure that is dominated by porous micritic laminae and chambered tubules such laminae are interpreted to represent calcified root cells and occur in two different varieties 1 micrite walled tubules with hollow centers that are thought to represent calcification in the rhizosphere or outer surfaces of the root and 2 tubules consistent with calcification of both the medulla and cortex which preserved medulla cortex and parenchymatic cells along with xylem vessels preserved root fabrics are present only in the blackest clasts and are consequently thought to be the main mechanism driving limestone blackening the dark coloration in southern australian clasts is derived from the impregnation of partially decayed terrestrial organic substances these organic substances were trapped in the cellular structures of roots as they calcified and were subsequently prevented from further decay and oxidation a threshold of approximately 7 weight organic carbon is needed in the insoluble residue to produce the distinct black coloration in limestone this process occurs at the base of slightly organic rich humic soil profiles where they interact with underlying carbonate bedrock b c soil horizon roots both physically and chemically through acid secretion corrode the underlying limestone and provide the calcium bicarbonate needed in the root calcification process specific semiarid flora have the ability to calcify their cellular structures which could explain why blackened clasts occur at only some unconformities this result means that the formation of blackened clasts via root calcification and entrapment of organics relies upon specific conditions of semiarid plants and climate along with organic soils such conditions would be restricted to a specific climate regime and when combined with the new proposed blackening mechanism herein could help explain their limited distribution and occurrences worldwide

petrology and geochemistry of the shuiquangou syenitic complex northern margin of the north china craton the palaeozoic shuiquangou complex is a major syenitic intrusion along the northern margin of the north china craton that hosts a number of gold deposits despite the heterogeneity of the complex in terms of texture and modal mineralogy mineral compositions whole rock chemistry as well as radiogenic isotope compositions show a well constrained magmatic evolutionary trend the whole rock major element and ree trends are broadly consistent with fractional crystallization dominated by clinopyroxene amphibole and accessory minerals initial nd sr isotopic compositions suggest that the parent magmas to the complex were ultimately derived from an enriched mantle with relatively high initial 87 sr 86 sr ratios and negative nd values the enrichment of the mantle source was probably inherited from an older lithospheric mantle beneath the north china craton sr isotopic data indicate that the rb sr system was disturbed by later alteration processes whereas nd isotopes are essentially unaffected and exhibit a broad trend consistent with simultaneous fractional crystallization and country rock assimilation afc quantitative modelling indicates that a very high bulk distribution coefficient for nd and low ratios of assimilation to crystallization are needed to produce the observed nd isotope evolutionary trend

palaeogeographical influence on late eocene biosiliceous sponge rich sedimentation southern western australia late eocene nearshore shallow marine environments within the bremer and western eucla basins of southern western australia were characterized by the thick deposition of spongolite and spiculite deposits epibenthic sponge communities dominated estuaries and topographically complex basin margin embayments archipelagos while cool water carbonates with up to 10 sponges accumulated in open shelf environments the transition from a biosiliceous to calcareous epibenthos was related to the degree of palaeogeographical protection within basement protected embayments there was an offshore gradation from shoreface spongolite and pure spiculite to a muddy spiculite facies towards central embayment areas calcareous fossils are rare throughout embayment facies but rapidly increase in more open outer archipelago areas this depositional relationship occurred along 2000 km of the late eocene southern australian coastline palaeogeographical protection from strong currents acted in concert with 1 a planar low gradient inland topography with sluggish run off supplying fine grained sediment nutrients and abundant dissolved silica and 2 a microtidal setting weak to moderate swells and opposing wind and coriolis surface current forcing which inhibited water exchange between embayments estuaries and the open shelf this situation led to an embayment water chemistry that encouraged prolific sponge growth calcareous spiculites record the mixing front between these embayment waters and normal open shelf waters supporting cool water carbonates

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

surficial sediments of the great australian bight facies dynamics and oceanography on a vast cool water carbonate shelf abstract the great australian bight gab the largest sector of the southern australia continental margin is a site of cool water carbonate sedimentation throughout ranging from locally warm temperate inboard to cool temperate outboard surficial sediments are a mixture of calcareous pleistocene skeletal and lithic intraclasts relict grains and holocene biofragments with minor amounts of quartz inboard the inner shelf is an area of abundant macrophytes and seagrasses active carbonate sediment production and accumulation and little relict sediment the huge middle portion is a shaved shelf with active sediment winnowing and mostly relict sediment the outer shelf and upper slope is a variably productive sediment factory characterized by prolific calcareous epibenthic growth on hard substrate subaqueous islands shedding particles into surrounding sands and muds patterns of holocene sedimentation are linked to modern oceanographic parameters in this high energy setting characterized by overall downwelling prolific rhodoliths occur on the nw inner shelf where shallow summer waters are the warmest in the gab these warm saline nutrient depleted waters then drift eastward across the shelf suppressing heterozoan carbonate production on the central and eastern mid shelf this arrested production in the eastern gab is countered locally by summer coastal upwelling along western eyre peninsula with bryozoan rich sediment extending well inboard onto the mid shelf the outer shelf and upper slope is an area of prolific bryozoan growth likely linked to upwelling except in the central gab a region of year round downwelling where the area is one of off shelf fine sediment transport and carbonate mud deposition these patterns in the central gab at least are present in the underlying holocene and pleistocene suggesting that the general modern oceanographic dynamics and resultant carbonate sedimentation have persisted throughout the quaternary

catastrophic collapse of the west florida carbonate platform margin a large truncation surface has been discovered on seismic reflection profiles along the distally steepened ramp of the west florida carbonate platform margin this structure interpreted as a submarine slide scar is at least 120 km across and up to 30 km wide the slide has removed as much as 300 350 m of late paleogene and early neogene strata collapse occurred in the middle miocene within an episode of seaward progradation during a relative sea level highstand postcollapse depositional sequences thicken abruptly across the structure this suggests catastrophic slope failure gravitational instability created by high rates of sediment accumulation is believed to have been the triggering mechanism such large scale platform margin collapse is likely to generate megabreccia debris flows as well as aid in the landward retreat of precipitous high relief carbonate escarpments

hypersulfidic deep biosphere indicates extreme sulfur isotope fractionation during single step microbial sulfate reduction coexisting dissolved sulfide and sulfate from hypersulfidic interstitial waters of a 380 m long sediment core show a large isotopic difference of up to 72 caused by in situ microbial sulfate reduction this is considerably larger than the assumed biological maximum of 46 derived from laboratory studies with pure cultures of sulfate reducing bacteria similar high fractionations inferred from sedimentary metal sulfides have been previously explained by a multistage process involving sulfide reoxidation and disproportionation of sulfur intermediates our data show that extreme isotopic differences between sulfate and the reduced sulfur species can also be generated during microbial single step fractionation this result indicates that the sulfate reducing communities and or their cellular metabolic activities in the deep biosphere may differ from those observed in near surface sediments or the water column

hydrothermal alteration and ore forming fluids associated with gold tellurium mineralization in the dongping gold deposit china abstract the dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in china and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit the alteration minerals include orthoclase microcline perthite quartz sericite epidote calcite hematite and pyrite with the quartz pyrite and hematite assemblages closely associated with gold mineralization the phases of hydrothermal alteration include i potassic alteration ii potassic alteration silicification iii silicification epidotization hematitization iv silicification sericitization pyritization and v carbonation mass balance calculations in potassic altered and silicified rocks reveal the gain of k2o na2o sio2 hfses and transition elements tes and the loss of rees most major elements were affected by intense mineral reactions and the ree patterns of the ore are consistent with those of the syenites gold silver and tellurium show positive correlation and close association with silicification fluid inclusion homogenization temperatures in quartz veins range from 154 c to 382 c peak at 275 c 325 c with salinities of 4 9 wt nacl equiv at temperatures of 325 c the fluid is estimated to have ph 3 70 5 86 log fo2 32 4 to 28 1 with au and te transported as au hs 2 and te22 complexes the ore forming fluids evolved from high ph and fo2 at moderate temperatures into moderate low ph low fo2 and low temperature conditions the fineness of the precipitated native gold and the contents of the oxide minerals e g magnetite and hematite decreased followed by precipitation of au and ag bearing tellurides the hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock hosted hydrothermal gold deposit

spatial and temporal patterns of cenozoic dynamic topography around australia 1 despite its importance the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known we present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding australia our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf these anomalies were determined from a combined dataset of 200 seismic reflection and wide angle images of well sedimented oceanic crust they have amplitudes of between 1 km and 0 5 km and their spatial variation is broadly consistent with long wavelength free air gravity and shallow seismic tomographic anomalies along the northwest shelf a regional depth anomaly of 300 to 700 m intersects the adjacent continental shelf the temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform which fringes the shelf and records a dramatic switch from progradation to aggradation during neogene times three dimensional seismic mapping calibrated by boreholes was used to calculate water loaded subsidence histories at rollover points of clinoforms along the shelf at 9 3 ma the rate of subsidence increases from 5 to up 75 m myr 1 generating a subsidence anomaly of 300 to 700 m the amplitude of this anomaly varies along the shelf and cannot be generated by glacio eustatic sea level variation instead we propose that a regional subsidence episode which affects both the proximal shelf and the distal oceanic basin was generated by convective drawdown by combining our results with other published estimates of uplift and subsidence a map of australia which shows the spatial and temporal pattern of dynamic topography is presented most but not all of australia s epeirogeny can be attributed to rapid northward motion of the australian plate over a pre existing pattern of convective circulation

late pleistocene bryozoan reef mounds of the great australian bight isotope stratigraphy and benthic foraminiferal record 1 cores from sites 1129 1131 and 1132 ocean drilling program odp leg 182 on the uppermost slope at the edge of the continental shelf in the great australian bight reveal the existence of upper pleistocene bryozoan reef mounds previously only detected on seismic lines benthic foraminiferal oxygen isotope data for the last 450 000 years indicate that bryozoan reef mounds predominantly accumulated during periods of lower sea level and colder climate since stage 8 at sites 1129 and 1132 and since stage 4 at the deeper site 1131 during glacials and interstadials stages 2 8 the combination of lowered sea level increased upwelling and absence of the leeuwin current probably led to an enhanced carbon flux at the seafloor that favored prolific bryozoan growth and mound formation at site 1132 at site 1129 higher temperatures and downwelling appear to have inhibited the full development of bryozoan mounds during stages 2 4 during that time favorable hydrographic conditions for the growth of bryozoan mounds shifted downslope from site 1129 to site 1131 superimposed on these glacial interglacial fluctuations is a distinct long term paleoceanographic change prior to stage 8 benthic foraminiferal assemblages indicate low carbon flux to the seafloor and bryozoan mounds although present closer inshore did not accumulate significantly at sites 1129 and 1132 even during glacials our results show that the interplay of sea level change eustatic and local linked to platform progradation glacial interglacial carbon flux fluctuations linked to local hydrographic variations and possibly long term climatic change strongly influenced the evolution of the great australian bight carbonate margin during the late pleistocene

classification of submarine canyons of the australian continental margin abstract submarine canyons influence oceanographic processes sediment transport productivity and benthic biodiversity from the continental shelf to the slope and beyond however not all canyons perform the same function the relative influence of an individual canyon on these processes will in part be determined by its form shape and position on the continental margin here we present an analysis of canyon geomorphic metrics using an updated national dataset of 713 submarine canyons surrounding mainland australia these metrics attributes for each canyon are used to classify them into canyon types across a hierarchy of physical characteristics separately for shelf incising n 95 and slope confined blind n 618 canyons we find that the canyon metrics describe a wide variety of canyon form and complexity that is consistent with a population of canyons that has evolved at different rates around the australian margin since the break up of gondwana the large number of slope confined canyons is interpreted to reflect dominance of slope mass wasting processes over erosive turbidity flows from fluvial and shelf sources on an arid continent the distribution of submarine canyons around the australian margin is not regular with clusters occurring in the east southeast west and southwest where the margin is steepest the classification result provides a quantitative framework for describing canyon heterogeneity for application in studies of geological controls on individual canyons canyon oceanography and canyon biodiversity

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

quaternary bryozoan reef mounds in cool water upper slope environments great australian bight bryozoan reef mounds are common features in the geological record occurring within mid ramp slope paleoenvironments especially in paleozoic carbonate successions but until now have not been recorded from the modern ocean recent scientific drilling in the great australian bight ocean drilling program leg 182 has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200 350 m these structures have as much as 65 m of synoptic relief and occur both as single mounds and as mound complexes they are unlithified have a floatstone texture and are rich in delicate branching encrusting and or nodular arborescent flat robust branching fenestrate and articulated zooidal bryozoan growth forms the muddy matrix is composed of foraminifers serpulids fecal pellets irregular bioclasts sponge spicules and calcareous nannofossils the 14c accelerator mass spectrometry dates of 26 6 35 1 ka indicate that the most recent mounds the tops of which are 7 10 m below the modern seafloor flourished during the last glacial lowstand but perished during transgressive sea level rise this history reflects changing oceanographic current patterns strong upwelling during lowstands and reduced upwelling and lowered trophic resources during highstands large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions the mounds are similar in geometry scale general composition and paleoenvironments to older structures but lack obvious microbial influence and extensive synsedimentary cementation such differences reflect either short term local conditions or long term temporal changes in ocean chemistry and biology

large scale reorganization of ocean currents offshore western australia during the late quaternary abstract the history of coastal surface currents in the eastern indian ocean over the last 130 kyr has been studied through the application of the fi 2 transfer function to planktic foraminifera in deep sea cores in a n s transect offshore western australia the concept of sea surface temperature sst gradient residuals is the amount by which the sea surface temperature gradient of a given time differs from that in the modern sea the sst gradient residuals for several episodes of climate extremes in the late quaternary the last glacial maximum 20 kyr b p the last interglacial maximum 122 120 kyr b p and at the end of the penultimate glaciation 130 kyr b p indicate that areas north of 18 s off western australia have changed very little during the extremes in climate over the last 130 kyr while south of 18 s there have been significant changes in surface water temperatures large areas of anomalously cool surface water were established off north west cape 22 s 24 s during both glacial and interglacial extremes these reflect the increased influence of the west australian current on the surface water circulation during the last glacial maximum and at the end of the penultimate glaciation cold sea surface temperature anomalies were established near to the coast indicating that the leeuwin current did not warm the coastal zone as it does today during the last interglacial maximum the leeuwin current flowed as an intensified current in a narrow zone close to the coast but did not significantly warm surface waters offshore as far as 20 25 s where a zone of cold water was maintained