middle late permian mass extinction on land the end permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years we propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land one terminating the middle permian guadalupian at 260 4 ma and a later one ending the permian period at 251 ma our evidence comes from new paleobotanical paleopedological and carbon isotopic studies of portal mountain antarctica and comparable studies in the karoo basin south africa extinctions have long been apparent among marine invertebrates at both the end of the guadalupian and end of the permian which were also times of warm wet greenhouse climatic transients marked soil erosion transition from high to low sinuosity and braided streams soil stagnation in wetlands and profound negative carbon isotope anomalies both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts such as the end guadalupian emeishan basalt and end permian siberian traps

holocene storage of siliciclastic sediment around islands on the middle shelf of the great barrier reef platform north east australia thick sequences of sediment surround the whitsunday islands on the middle shelf of the great barrier reef gbr platform much of this sediment is siliciclastic material deposited since the sea level highstand at around 6 5 ka this raises a mass balance dilemma because modern terrigenous discharge to the gbr platform is restricted to the inner shelf shallow seismic profiles and sediment samples were collected over 450 km2 around the whitsunday islands to quantify the mass of siliciclastic sediment for a dynamic model of the shelf the sea floor and pre holocene surfaces were mapped using 4584 stations along the seismic profiles and a graphical computer program the total volume of sediment between these two surfaces is 3 67 0 45 109 m3 this volume is composed of buried reefs 0 13 0 01 109 m3 medium 0 70 0 30 109 m3 and fine grained shoals 2 84 0 35 109 m3 the volume estimates combined with measurements of carbonate concentration density and porosity indicate that 1850 380 mt of holocene siliciclastic sediment surround the whitsunday islands in medium 510 225 mt and fine grained shoals 1340 155 mt the total mass of siliciclastic material is 1 7 2 6 times that stored in cleveland bay a similar sized repository on the inner shelf a simple numerical model has been constructed to explain this large quantity of holocene siliciclastic sediment the model results in the appropriate siliciclastic mass next to the whitsunday islands by integrating regional shelf processes over time unlike the present day rivers discharged sediment to the middle shelf during the early holocene this material was subsequently focused by northward transport into the vicinity of the islands a geomorphologically complex region that serves as a sediment trap although direct riverine inputs to the middle shelf have stopped during the present sea level highstand previously deposited siliciclastic sediment is continually being winnowed from the middle shelf and redeposited next to the whitsunday islands the transport and distribution of siliciclastic sediment on the gbr platform is thus influenced significantly by storage around islands on the middle shelf

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

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

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

palaeoecology of the conodonts hindeodus and clarkina during the permian triassic transitional period abstract detailed investigation of the distributions of the hindeodus and clarkina neogondolella conodont faunas has been undertaken on the p t boundary strata of the meishan section zhejiang province south china in association with detailed facies analysis this reveals that hindeodus increased and clarkina sharply declined in abundance during a phase of relative sea level rise which began at the end permian bed 25 and extended into early triassic this was associated with the development of anoxic conditions this distribution does not accord with previous suggestions that hindeodus was a nearshore shallow water taxon the decline of the supposed deeper water genus clarkina is also somewhat surprising but it may relate to the inhibition of a nektobenthic genus by dysoxic anoxic bottom waters the widespread facies and geographic distribution of hindeodus suggests it was a pelagic type unaffected by anoxic bottom waters hence the hindeodus lineage provides a reliable criterion for identification of the permian triassic boundary

proterozoic history and crustal evolution in southwestern colorado insight from u pb and sm nd data abstract new u pb age constraints and sm nd isotope data further establish the timing of magmatic and tectonic events from 1 8 to 1 4 ga in southwestern colorado and give insight into the interaction of crust and mantle systems during the assembly and evolution of orogenic belts along the southern margin of laurentia proterozoic orogenic events in the needle mountains led to crustal assembly thickening and tectonic reworking that was punctuated by periods of relative crustal stability pre 1 75 ga arc successions in southwestern colorado were produced and assembled into juvenile crust in an orogenic period that culminated in regional deformation and metamorphism that accompanied intrusion of synorogenic plutonic rocks from 1 73 to 1 71 ga emplacement of post orogenic plutonic rocks at 1 70 ga was followed by uplift and erosion and the deposition and deformation of siliciclastic sedimentary sequences paleoproterozoic crust underwent local melting and thermal metamorphism during invasion of felsic to mafic magmas at 1 43 ga that coincided with a pulse of intracratonic deformation invasion and melting of first cycle 1 8 1 7 ga crust at 1 71 and 1 43 ga involved heat and volatiles from mantle melts that were a catalyst for crustal melting and magmatic recycling sm nd isotopic signatures of 1 8 1 4 ga volcanic and plutonic rocks in southwestern colorado lend evidence to the emplacement of melts from depleted mantle and juvenile crust in the production continental crust with minor if any contamination by crust older than 1 8 ga the proterozoic magmatic record in southwestern colorado is consistent with continental growth by the addition of juvenile crust extracted from the mantle followed by periodic intracrustal growth during orogenic pulses in which mantle magmas underplate and melt the crust with consequent thickening

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

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

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

calibration of marine sediment core loggers for quantitative acoustic impedance studies abstract accurate density and p wave velocity measurements on marine sediment cores are needed for quantitative acoustic impedance studies an increasing number of international marine laboratories routinely measure p wave velocity and bulk density the product of which gives the acoustic impedance on marine sediment cores using automated core loggers mscls despite the progressive standardisation of mscls in recent years no standard calibration technique has been decided that will enable datasets from different marine laboratories to be validated and compared with confidence this problem is particularly acute for bulk density measurements because systematic mscl errors are typically much greater than 10 one solution is to use a calibration tube comprising a stepped aluminium insert inside a water filled core liner that mimics marine sediment porosities and velocities and that can be used during normal core logging the calibration tube enables a reliable gamma ray reference intensity to be measured and an apparent compton mass attenuation coefficient to be derived that is suitable for most marine sediments and that simplifies data processing the calibration tube results show that the mscl belonging to southampton oceanography centre soc used as part of the standard analysis procedure of the british ocean sediment core repository boscor gives measurement accuracies of better than 0 07 g cm 3 for bulk density and 0 3 for p wave velocity

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

north and south china collision along the eastern and southern north china margins abstract lithofacies distribution and petrography and intracontinental deformation in the north china block ncb and the south china block scb show an active continental margin flanked by the eastern ncb and a passive continental margin was present along the west side of the scb both margins initially trending n ne the tanlu fault possibly initiated as part of the subduction zone during paleozoic time along the eastern margin on the ncb the ncb and the scb were divided along the eastern southern north china margin by the qinling dabie tanlu sulu imjingang yanji zone from southwest to northeast these two continental blocks made contact first in the northeast during late early permian time finally in the southeast at late triassic time and the clockwise collision probably lasted to middle jurassic time the eastern suture the yanji imjingang sulu tanlu zone was dominated by contractional deformation the southern suture the qinling dabie zone was a transpression belt dominated by right lateral strike slip

facies analysis and sea level change at the guadalupian lopingian global stratotype laibin south china and its bearing on the end guadalupian mass extinction abstract the guadalupian lopingian boundary stratotype at penglaitan and the nearby tieqiao section near laibin south china record a series of major environmental changes within the jiangnan basin during a mid permian biotic crisis the sequence stratigraphic petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea level fall that led to the establishment of mid ramp conditions laibin limestone in settings that were previously dominated by radiolarian mudstones the regression also coincides with a low point of 87 sr 86 sr ratios the lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the emeishan flood basalt province 800 km to the west of laibin thus unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event subsequent environmental changes included transgression spread of dysoxic waters indicated by populations of small pyrite framboids and a major negative c isotope excursion all these phenomena have been previously related to the end guadalupian extinction but they in fact post date the crisis because a post extinction fauna of foraminifers is encountered at this time

positive relief over buried post glacial channels great barrier reef province australia abstract continuous seismic profiling on the continental shelf central great barrier reef province australia has delineated a major sub bottom reflector interpreted as the pre holocene surface channels eroded in this surface are infilled and overfilled by post glacial sediments filling is ascribed to estuarine backfilling during sea level rise followed by deposition of delta front deposits in many cases these fills create positive relief over buried channels hence modern shelf morphology may not be an accurate guide to the positions of pleistocene channels across the shelf

fringing reef growth on a terrigenous mud foundation fantome island central great barrier reef australia the leeward fringing reef at fantome island central great barrier reef province is a carbonate body which has developed under the influence of terrigenous sedimentation the reef flat is up to 1000 m wide and is surfaced by mobile sand and gravel with almost all live corals restricted to the seaward rim the reef slope has coral columns and heads on the upper part but below 5 m water depth it is a muddy substrate with scattered mounds of branching corals three high recovery cores show the reef is up to 10 m thick and developed over a gently sloping terrace of weathered pleistocene alluvium three post glacial stratigraphic units are recognised i carbonate reef top unit of coral rudstone and framestone including sinuluriu spiculite 2 lower slope unit of coral floatstone in a terrigenous muddy matrix and 3 transgressive basal unit of skeletal arkosic sand the acid insoluble content of matrix and of individual corals increases downwards coral growth rates decrease downwards reflecting slower growth in muddier environments radiocarbon dating shows that the reef prograded seaward at almost stable sea level an average vertical accumulation rate of 6 7 mm yr is indicated two age reversals are interpreted as material transported by storms or by erosion in response to a late holocene sea level fall the carbonate reef top unit has developed adjacent to and is environmentally compatible with a muddy terrigenous lower slope unit terrigenous influx has not changed during the holocene and terrigenous content of sediments is controlled by deposition on the reef slope of fine sediment winnowed from the reef flat and concentration of coarse sediment in the transgressive basal sheet

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

lithology mapping of a mixed siliciclastic carbonate evaporite system using 3d seismic and well data lower triassic jialingjiang formation sichuan basin southwestern china abstract high quality three dimensional 3d seismic data acquired in the central sichuan basin southwestern china offer an opportunity to map complex lithologies in a mixed siliciclastic carbonate evaporite system in the lower triassic jialingjiang t1j formation the formation consists of siliciclastics limestone dolostone anhydrite and salt the lithologies consist several source reservoir cap assemblages in the area lithologies in the t1j formation change rapidly in the vertical direction forming different interbed patterns in thin layers in the mean time the lateral extend of each lithology is complex this vertical and lateral distribution makes it difficult to predict lithology by single seismic attribute therefore principle component analysis pca was applied to tens of seismic attributes to extract useful information the first three components contain most 83 02 99 85 of the lithology information preserved in seismic attributes which were used to correlate with lithology content calculated by core calibrated wireline logs correlation coefficients of the three seismic components with lithologies are significantly higher 0 37 0 79 than those of individual seismic attributes near zero to 0 58 different assemblies of end member lithologies were selected from anhydrite siliciclastics tight dolostone limestone and salt to perform pca in different sequences lithologic content distribution of individual end members was shown by color blending method to map the lithology mixture sedimentary history in the t1j formation was reconstructed based on lithology mixture maps and regional geology background in the study area eight 4th order sequences were interpreted in the t1j formation only the second sequence was influenced by siliciclastic input forming a complete mixed siliciclastic carbonate evaporite system open platform and or restricted evaporative environment dominated the other seven sequences forming a mixed carbonate evaporite system

lead isotopic evidence for the origin of paleo and mesoproterozoic rocks of the colorado province u s a abstract lead isotopic ratios of k feldspars and whole rocks from 1 7 and 1 4 ga plutonic rocks of the colorado province are relatively non radiogenic for 207 pb 204 pb plotting below the average crust model curve of stacey and kramers 1975 indicating that the terrane was derived primarily from juvenile mantle material slightly more radiogenic ratios in the northern part of the terrane near the archean wyoming province suggest minor inclusion of an older component the data from 1 7 ga plutons plot in a broad field suggesting two episodes of re equilibration with whole rock pb probably related to heating events in the mesoproterozoic 1 4 ga and cretaceous 70 ma possible differences in calculated whole rock th u coupled with slight pb isotopic variations along the north south transect suggest either a terrane boundary through central colorado near salida and gunnison or fundamental differences in source rocks metasedimentary vs metavolcanic u pb analyses of multigrain splits of detrital zircons from quartzites throughout the colorado province have failed to identify archean detritus the oldest 207 pb 206 pb ages found in two samples of quartzite from northern colorado are about 2 0 ga perhaps derived from rocks of the trans hudson orogen in contrast to 2 75 ga detrital zircon in a paleoproterozoic quartzite from the southern part of the wyoming province while we are not yet able to discern if these ages are true provenance ages or mixtures of archean and paleoproterozoic components the absence of easily recognizable archean zircons supports other isotopic data and a conclusion that most of the paleoproterozoic crust of the colorado province was ultimately derived from a juvenile at 1 8 ga mantle reservoir

late quaternary sediment fluxes from tropical watersheds abstract inherited saprolite stores and continued weathering in quaternary time juxtapose abundant clay and fresh rock in tropical landscapes this influences sediment fluxes and affects the interpretation of sediment sequences derived from tropical watersheds detrital kaolinites derive from inherited saprolite sources as well as from soil clays and appear in delta and ocean sediments these sediments appear to correspond with sub milankovitch millennial scale cycles of climate change but may also record century scale episodes of rapid warming dansgaard oeschger events destabilisation of sediment sources and increased sediment fluxes in the late quaternary followed millennia of climatic deterioration cooling aridity and vegetation change and led to altered patterns of sedimentation during the last glacial maximum lgm sediment yield from slopes increased 10 around the lgm when rainfall was reduced by 30 60 and led to fan building and braided channels rainfall increased 40 80 from the lgm to the early holocene maximum and this led to channel cutting and major sediment fluxes to delta and ocean sinks vegetation recovery lagged the rapid warming by several millennia and was interrupted by younger dryas yd aridity influencing slope and stream behaviour holocene sedimentation has been by both vertical and lateral accretion increasing floodplain sediment stores

the carbon isotope excursion on gssp candidate section of lopingian guadalupian boundary an isotopic stratigraphically well documented outcrop in penglaitan guangxi province south china has been proposed as a candidate gssp for the lopingian guadalupian boundary correlatable outcrops from the west wing tieqiao section and east wing penglaitan section of the laibin syncline exhibit synchronous excursions in carbon isotopes the isotopic excursions 13c show the best placement of the boundary may lie at the base of bed 6k which coincides with the clarkina postbitteri conodont zone and with eustatic change 13c increases during the uppermost guadalupian jinogondolella granti conodont zone from the top of 3c to the base of 6i a 13c peak value of 5 is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression a gradual depletion of carbon isotopes occurs in the c postbitteri zone from bed 6e to 7b and this gradual 13c excursion also suggests the sequences around the guadalupian lopingian boundary at the candidate section are conformable during the middle later c postbitteri zone a 3 5 dramatic 13c depletion is recorded at the tieqiao section but only a 2 depletion at the deeper facies penglaitan section synchronous with conodont zones that mark eustatic changes

carbonate siliciclastic facies transition and reef growth on the northeast coast of barbados west indies abstract on most of the insular shelf around barbados carbonate sediments are now accumulating from the growth of reefs the contributions of the skeletons of carbonate secreting organisms and the erosion of the pleistocene coral cap that covers six sevenths of the island however after heavy rains water laden with siliciclastic sediment eroded from the scotland district where the coral cap is breached is discharged from four main rivers onto the northeast coast insular shelf the coarse grained material is transported as bedload onto an offshore sand ramp over the shelf break into deeper water or is incorporated into adjacent beaches the fine grained sediment is directed northward along the shore within a sediment plume by the equatorial current fine sediment settling out of the plu e is deposited on a spur and groove system and reefs growing on a deeper water platform north of the sand ramp nearshore the transition from the siliciclastic sediments to carbonate sediments is located on a submerged barrier reef at the seaward margin of a shallow water platform the facies transition on the deeper water platform is gradual near the southern edge of the deeper water reefs distribution of benthic biota and the growth of reefs are controlled by a combination of siliciclastic influx and shelf floor topography the deeper water reefs grow despite the periodic blanketing by fine siliciclastic sediment settling from the sediment plume that accumulates around them

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

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

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

late holocene sediment in nara inlet central great barrier reef platform australia sediment accumulation on the middle shelf of a tropical mixed clastic carbonate system nara inlet in the whitsunday islands is a natural depocenter for clastic and carbonate sediment on the middle shelf of the central great barrier reef gbr platform three sediment cores were collected from the inlet to understand sediment accumulation in this tropical mixed clastic carbonate system over time surface and subsurface sediment is comprised of two main components terrigenous clay and shallow marine carbonate similar to other regions on the middle shelf of the gbr platform the carbonate component 25 80 by weight and dominated by sr poor foraminifera tests and mollusc shells generally increases towards the surface radiocarbon ages derived from tests of benthic foraminifera indicate that the top 3 m of sediment accumulated within the last 3000 years but that the rate has slowed toward present day the change in clastic and carbonate abundance therefore indicates a system where both clastic and carbonate accumulation has decreased over time but where clastic accumulation has decreased faster reduced clastic accumulation may reflect progressive impedance of terrigenous input by a laterally growing fringing reef at the mouth of nara inlet likewise reduced carbonate accumulation may reflect preferential reef growth and carbonate deposition outside of the inlet even though clastic accumulation has decreased significantly over time the late holocene mass composition and distribution of clastic material in nara inlet implies a terrigenous source previously unrecognized in models for the evolution of the gbr platform large amounts of terrigenous sediment probably were stored around topographic highs on the middle shelf during lowstand and early transgression this clastic material was then removed over time mixed with autochthonous carbonate and deposited in embayments on the middle shelf the accumulation of sediment on the middle shelf of a tropical mixed clastic carbonate margin is not straightforward

the modern mixed carbonate siliciclastic abrolhos shelf implications for a mixed depositional model abstract high resolution seismic facies analysis and stratigraphy of a mixed carbonate siliciclastic shelf yields insights into sedimentation controlled by interactions among carbonate production siliciclastic sediment supply and changes in relative sea level high resolution seismic core and surface samples collected along the northern area of the abrolhos shelf brazil including the inner middle and outer shelf constrain the genesis of the shelf two sets of seismic sequences were identified a pleistocene sequence and pleistocene holocene sequence a subaerial unconformity from subaerial exposure during the last glacial maximum separates the two sequences the upper seismic sequence the focus of this study comprises retrograding aggrading transgressive and aggrading prograding regressive seismic geometries carbonate sedimentation predominated within the last postglacial transgressive phase the subsequent regressive phase was dominated by nearshore siliciclastic sedimentation at shallow depths up to 12 m below 12 m depth a transition occurs to mixed siliciclastic carbonate facies and ultimately carbonate sedimentation farther offshore seismic data indicate that holocene nearshore coral reef growth was influenced by the positive antecedent relief of a pleistocene reef platform and terrigenous sedimentation although siliciclastic carbonate mixed sedimentation has been reported in other successions during periods of regression siliciclastic sedimentation in northern abrolhos shelf is limited to nearshore settings rather than bypassing the shelf

permian palaeogeographic evolution of the jiangnan basin south china abstract the most striking geographic feature of the permian of south china is the jiangnan basin which intimately reflects the interplay between the yangtze and cathaysia blocks geographic and sedimentological evolution suggests that the jiangnan basin superposed on a precambrian collisonial megasuture and a folded early paleozoic deep basin was an extensional intracratonic basin it opened in the longlinian and became more passive and restricted in the latest maokouan the remarkably similar geographic patterns of the jiangnan basin in the early and late palaeozoic suggest that the yangtze and cathaysia blocks were coherent during the paleozoic

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

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

oceanography and patterns of shelf sediments mayaguez puerto rico abstract three rivers discharge onto the narrow insular shelf of mayaguez and anasco bays on the west coast of puerto rico the bays are bounded offshore by a discontinuous line of reefs the resulting pattern of carbonate and terrigenous sediments reflects both the source materials and the physical processes distributing sediments the carbonate sediments are found only near and on elevated reef structures terrigenous sediments are widely distributed and are encroaching over the coral reef areas a change in sediment distribution is occurring that will eventually result in loss of the reef environment except on the shelf edge this change is the result of increased sediment load in the rivers

the interactions of sea level change terrigenous sediment influx and carbonate productivity as controls on upper cambrian grand cycles of western newfoundland canada the upper cambrian stratal record in western newfoundland is complex and reflects the interplay and feedback between 1 changes in third order sea level 2 episodic incursion of terrigenous fines onto the paleoshelf and 3 productivity levels of the ancient carbonate factory mixed carbonate and terrigenous clastic rocks of western newfoundland are configured in large scale third order stratal patterns called grand cycles such cycles are tens to hundreds of meters in stratigraphic thickness and appear to span millions of years grand cycles are divided here into ribbon half cycles composed principally of ribbon rock and oolitic half cycles dominated by oolite stratigraphic distribution of shale in these rocks however is not everywhere coincident with large and small scale patterns in carbonate lithofacies and it suggests that the incursion of terrigenous clay and silt onto the ancient platform must be evaluated separately in part from the dynamics of carbonate accumulation areal and stratigraphic distribution of rock cycles record shifts in facies belts on the ancient platform presumably in response to third order changes in accommodation potential meter scale cycles in carbonate lithofacies are of two types peritidal cycles that fine upward and shelf cycles that coarsen upward thick successions of shelf cycles composed of ribbon rock are interpreted as highstand deposits and are separated by a sequence boundary marked by peritidal cycles from lowstand deposits comprising thick successions of ootite shelf cycles the former mid grand cycle transitions of previous workers are thereby reinterpreted in this study as sequence boundaries the long term position of sea level and thus the degree of platform inundation influenced the health of the platform carbonate factory during times of low sea level the platform was bathed in water more saline than open ocean sea water and it had a robust non skeletal carbonate factory that was resilient to poisoning by episodic influx of terrigenous fines onto the shelf in contrast the carbonate factory during highstands was less resilient to terrigenous poisoning and was susceptible to localized drowning by the reduction in the rate of carbonate sediment production the thick shale units are therefore interpreted to represent the coincidence of and interaction between 1 incursion of terrigenous fines onto the ancient platform and 2 a weakened highstand carbonate factory unable to recover from this terrigenous poisoning

carbon and conodont apatite oxygen isotope records of guadalupian lopingian boundary sections climatic or sea level signal abstract the guadalupian lopingian g l boundary 260 4 ma is one of the major extinction events in earth history that coincides with the emeishan large igneous province and palaeoclimatic changes carbon isotopes of whole rock samples were studied in order to document changes in the global carbon cycle in contrast to earlier studies we observe no major negative excursion in 13 c in the middle capitanian a positive 13 c excursion is observed in the latest capitanian with a 1 5 increase registered in the j xuanhanensis zone to c postbitteri hongshuiensis subzone followed by a decrease of 1 within the c postbitteri postbitteri subzone and a 2 decrease in the c dukouensis to c asymmetrica zone oxygen isotopes of conodonts from two g l boundary sections were measured in order to reconstruct conodont habitat and potential changes in water temperature oxygen isotope ratios of gondolellid conodonts are higher in comparison to oxygen isotope ratios measured on hindeodid conodonts suggesting that gondollelids lived in cooler and thus deeper waters compared with hindeodids the oxygen isotope record reconstructed from gondollelid conodonts suggests warming of water temperatures of about 4 c in the late capitanian j postserrata to j granti zone cooling of about 6 to 8 c across the g l boundary and in the earliest wuchiapingian and again significant warming in the wuchiapingian c dukouensis to c liangshanensis zone the temperature increase can be correlated with the main phase of emeishan volcanism suggesting that climatic warming may have resulted in an intensified hydrological cycle fertilisation of the oceans and enhanced primary productivity the latter documented in the positive late capitanian carbon isotope excursion however changes in sea level seem to parallel reconstructed water temperatures suggesting that changes in water depth in combination with superimposed climatic changes may be responsible for the observed temperature changes this study documents that oxygen isotope studies on permian conodonts should be performed on mono generic conodont samples and that oxygen isotopes not only provide valuable palaeoclimatic information but also may help to constrain the life habitat of conodonts

evolution of permian conodont provincialism and its significance in global correlation and paleoclimate implication the main components of asselian through artinskian conodont faunas found around the world are basically the same and the provincialism is indicated only by less common endemic elements such as gondolelloides and new genus a henderson in north pangea sweetognathus bucaramangus around the equator and vjalovognathus in eastern gondwana provincialism is marked by differences at the species level of mesogondolella neostreptognathodus and sweetognathus during the kungurian and becomes very distinct with differences at the genus level during the guadalupian and lopingian three provinces of permian conodonts referred to as the north cool water province ncwp the equatorial warm water province ewwp and the peri gondwana cool water province gcwp are recognized the ncwp is marked by gondolelloides in the early cisuralian dominance of neostreptognathodus and no or rare sweetognathus in the late cisuralian dominance of merrillina and mesogondolella and absence of sweetognathus in the guadalupian and dominance of merrillina and mesogondolella and absence of iranognathus in the lopingian the ewwp is characterized by the absence of gondolelloides and vjalovognathus in the cisuralian abundance of sweetognathus and pseudosweetognathus in the kungurian late cisuralian jinogondolella and sweetognathus in the guadalupian and clarkina and iranognathus in the lopingian the gcwp is marked by vjalovognathus merrillina in the cisuralian vjalovognathus merrillina and mesogondolella in the guadalupian and vjalovognathus and merrillina in the lopingian mixed faunas are recognized in regions bordering between the ewwp and gcwp including western timor during the artinskian pamirs during the kungurian and the salt range during the guadalupian and lopingian three different conodont zonations are proposed one for each of the three conodont provinces four potential horizons for inter provincial correlation of permian conodonts are recognized they are in ascending order 1 the first appearance of sweetognathus whitei which is closely related to the last occurrence of carboniferous type conodonts such as streptognathodus and adetognathus 2 the first appearance of neostreptognathodus pequopensis 3 the base of the jinogondolella nankingensis zone and 4 the base of the clarkina postbitteri iranognathus erwini zone the spatial and temporal distribution pattern of permian conodonts suggests that temperature is the primary controlling factor evolution of permian conodont provincialism reveals a glaciation during the asselian and sakmarian a global warming during the artinskian a climate cooling in north pangea during the kungurian a continuation of kungurian climate trends in the guadalupian a relatively minor warming during the wuchiapingian a returned cooling in the changhsingian and lower and middle griesbachian and a global warming in the late griesbachian which ended the permian conodont lineage

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

proterozoic contact relationships between gneissic basement and metasedimentary cover in the needle mountains colorado u s a abstract in the needle mountains of southwestern colorado proterozoic siliciclastic metasedimentary rocks of the uncompahgre group occupy a synclinorium bounded by 1690 ma gneissic and plutonic basement rocks stratigraphic facing of the uncompahgre group away from basement and local preservation of erosional features along the basement cover interface imply that the contact is an unconformity a 12 m thick zone of phyllite which commonly contains textural evidence of derivation from basement lithologies occurs everywhere along the contact tectonic fabrics within and near the contact zones locally record non coaxial deformation that resulted from upward movement of the cover relative to basement on each side of the synclinorium comparison of bulk chemistries of basement and contact zone samples indicates that hydration and the loss of cao mgo sio2 and na2o accompanied alteration of plagioclase quartz biotite bearing basement rocks to muscovite quartz fe ti oxide choritoid andalusite chlorite phyllites the micaceous zone along the contact is interpreted as a metamorphosed regolith that localized out of synform movement during folding of the basement and its parautochthonous cover localization of intense deformation within mechanically weak lithologic horizons such as regoliths along basement cover contacts can occur in situations where there is little relative displacement of the adjacent rocks and the stratigraphic significance of the boundary is preserved detailed petrographic and kinematic analysis may help distinguish such contacts from major fault boundaries

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

climate changes caused by degassing of sediments during the emplacement of large igneous provinces most mass extinctions during the last 500 m y coincide with eruptions of large igneous provinces lips the cretaceous tertiary extinction was synchronous with the deccan flood volcanism the permian triassic extinction with the eruption of the enormous siberian traps and the end guadalupian extinction with the emeishan volcanic province the causal link remains disputed however and many lips apparently had no significant impact on the biosphere here we show that a key control on the destructive consequences of lip emplacement is the type of sedimentary rock in basins beneath the flood basalts contact metamorphism around intrusions in dolomite evaporite coal or organic rich shale generates large quantities of greenhouse and toxic gases co 2 ch 4 so 2 which subsequently vent to the atmosphere and cause global warming and mass extinctions the release of sediment derived gases had a far greater impact on the environment than the emission of magmatic gases

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

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

the mid capitanian middle permian mass extinction and carbon isotope record of south china abstract conodont c isotope and fossil and facies data are presented for the capitanian middle permian mass extinction record seen in platform carbonates maokou and wuchiaping formations of south china where limestones interdigitate with the volcanic succession of the emeishan large igneous province the maokou formation provides an extinction record marked by the loss of keriothecal walled fusulinaceans and a turnover in calcareous algae in sections within the emeishan province this crisis occurs at the base of the oldest record of volcanism from the jinogondolella altudaensis conodont zone of mid capitanian age around the periphery of the emeishan province this extinction level lies within the upper part of the maokou formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events the assemblages of the uppermost maokou formation are characterised by typical late permian taxa although these levels still lie within the middle permian guadalupian series disaster taxa such as earlandia and diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction the crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts therefore a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate a composite 13ccarb curve calibrated against a high resolution conodont biostratigraphy reveals a major intra capitanian negative excursion of 5 superimposed on typically heavy 4 5 middle permian values this curve can also be recognised in panthalassan seamount carbonates of japan although this requires reassignment of apparently upper permian limestones to the middle permian in both china and japan the capitanian mass extinction occurs during the early stage of this major intra capitanian negative excursion assuming typical platform carbonate accumulation rates the records of the maokou formation suggest 13ccarb values fell at 0 01 kyr suggesting a catastrophic origin such as gas hydrate destabilisation is unlikely although a volcanic source is possible

phosphorus speciation in the sediment and mass balance for the central region of the great barrier reef continental shelf australia abstract solid phase p speciation has been determined in sediments from a transect across the central section of the continental shelf and slope of the great barrier reef gbr lagoon this region is characterized by a gradient of riverine aluminosilicate clay and silt nearshore seawards of which biogenic carbonate sediment predominates phosphorus speciation results show large variations along this transect organic p and authigenic apatite p are the major chemical forms of phosphorus in the central gbr continental shelf sediments post depositional reorganization of p was also observed converting organic p and iron bound p fe p to authigenic apatite p phosphorus burial rate was estimated from measurements of total p concentration and excess 210pb sediment mass accumulation rates burial efficiency varies significantly over the shelf inshore areas showed significant p remobilization from sediments to the water column up to 50 the mid and the outer shelf showed little evidence for remobilization except for coral reef platform sediments with more of the sediment p being in the less reactive authigenic apatite phases an appreciable fraction of this non labile authigenic apatite phase was identified as fish bone p sources and sinks over the central part of the gbr shelf were quantified using a mass balance approach this showed that coral sea shelf edge upwelling events are essential to satisfy the large p nutrient demand of the whole gbr lagoon p inputs due to upwelling events were greater than those contributed by local rivers over an average year

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

methane release from igneous intrusion of coal during late permian extinction events abstract unusually large and locally variable carbon isotope excursions coincident with mass extinctions at the end of the permian period 253 ma and guadalupian epoch 260 ma can be attributed to methane outbursts to the atmosphere methane has isotopic values 13c low enough to reduce to feasible amounts the carbon required for isotopic mass balance the duration of the carbon isotopic excursions and inferred methane releases are here constrained to 10 000 yr by counting annual varves in lake deposits and by estimating peat accumulation rates on paleogeographic maps the most marked carbon isotope excursions form linear arrays back to plausible methane sources end permian siberian traps and longwood bluff intrusions of new zealand and end guadalupian emeishan traps of china intrusion of coal seams by feeder dikes to flood basalts could create successive thermogenic methane outbursts of the observed timing and magnitude but these are unreasonably short times for replenishment of marine or permaf

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

basaltic volcanism and mass extinction at the permo triassic boundary environmental impact and modeling of the global carbon cycle the siberian traps represent one of the most voluminous continental flood basalt provinces on earth the mass extinction at the end of the permian was the most severe in the history of life in the present paper these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric co2 oceanic 13c and marine anoxia the latitudinal temperature gradient is reduced relative to today resulting in warmer temperatures at high latitudes the warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces resulting in an enhanced consumption of atmospheric co2 through weathering first the eruption of the siberian traps is accompanied by a massive volume of 13c depleted co2 degassed from the mantle and added to the ocean through silicate weathering thus lowering marine 13c second the rapid collapse in productivity induces a strong decrease in the global organic carbon burial this too tends to increase the proportion of light carbon in the ocean these two effects can explain the low 13c values across the pt boundary and methane release need not be invoked to explain the 13c fluctuations it is proposed that the phosphorus cycle which drives primary production in the model plays an important role on the recovery of productivity and the 13c variations

polyphase suprastructure deformation in metasedimentary rocks of the uncompahgre group remnant of an early proterozoic fold belt in southwest colorado isolated remnants of supracrustal rocks of the uncompahgre group in the needle mountains and uncompahgre gorge area have been subjected to polyphase deformation and greenschist facies metamorphism phase 1 structures recognized only in the west needle mountains include bedding parallel ductile shear zones f 1 mesoscopic folds and cleavage s 1 continued crustal shortening during phase 2 resulted in upright macroscopic folding f 2 and cleavage s 2 development in addition basement cover contacts were folded further shortening during phase 3 deformation resulted in conjugate shearing of cover rocks with the development of both a macroscopic f 3 fold and an s 3 crenulation cleavage in addition basement cover contact zones were activated as phyllonitic oblique slip reverse faults conjugate shearing resulted in lateral offset of stratigraphic units with loss of section conjugate reactivation of phase 1 ductile deformation zones was manifested by oblique dextral and sinistral slip the structural evolution of the uncompahgre group records the transition from a ductile north directed thin skinned fold thrust belt to the formation of a basement involved megamullion structure which was subjected to conjugate strike slip faulting to accommodate further shortening the results of this study indicate that the basal unit of the uncompahgre group was parautochthonous on basement a departure from some previous interpretations this implies that the metasedimentary cover rocks are younger than surrounding ca 1750 ma basement gneisses and ca 1690 ma granitoids the over all style of deformation may be analogous to the deep foreland suprastructure of an orogenic belt that developed between ca 1690 ma and 1600 ma in the southwestern united states

age provenance and tectonic setting of paleoproterozoic quartzite successions in the southwestern united states new field studies combined with u pb zircon geochronology constrain the ages of deposition and sedimentary provenance of paleoproterozoic quartzite successions exposed in the southwestern united states orthoquartzites were deposited in short lived basins at two times ca 1 70 and 1 65 ga during crustal assembly of southern laurentia the more voluminous ca 1 70 ga successions occur in southern colorado northern new mexico and central arizona and are interpreted here to be time correlative though not necessarily deposited in the same basins detrital zircon from quartzites and metaconglomerates exposed in southern colorado and northern new mexico is characterized by a single population with a relatively narrow range of ages 1 80 1 70 ga and minimal archean input 5 of grains analyzed peak detrital zircon ages 1 76 1 70 ga vary slightly from location to location and mimic the age of underlying basement unimodal detrital populations suggest local sources and a first cycle origin of the orthoquartzites within a short time interval 1 70 1 68 ga during unroofing of local underlying basement the maximum age of quartzite exposed at blue ridge colorado is constrained by the 1705 1698 ma coarse grained granitoid basement on which quartzite was deposited unconformably the minimum age of ortega formation quartzite new mexico is constrained by ca 1680 1670 ma metamorphic monazite overgrowths these dates agree with direct ages on the lower mazatzal group arizona and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca 1 70 ga yavapai orogeny regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca 1 66 1 60 ga mazatzal orogeny thus making them important time markers separating the yavapai and mazatzal orogenic events our model for syntectonic deposition involves extensional basin development followed by thrust closure possibly due to opening and closing of slab rollback basins related to outboard subduction the first cycle origin of orthoquartzites near the end of the arc collisions of the yavapai orogeny seems to contrast sharply with their extreme compositional maturity this can be explained in terms of protracted extreme diagenesis and or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the proterozoic similarities among quartzites exposed throughout the southwestern united states and along the laurentian margin suggest that they represent a widespread regional and perhaps global episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions a combination that might make these units a signature lithology for paleoproterozoic time

nucleation and growth of retrograde shear zones an example from the needle mountains colorado u s a abstract brittle and ductile deformation features are heterogeneously developed in late proterozoic retrograde normal slip shear zones that cross cut amphibolites and quartzo feldspathic gneisses in the needle mountains replacement of amphibolite grade minerals by greenschist facies assemblages is spatially related to transgranular fractures that cross cut the older gneissosity steeply dipping chlorite lined slip surfaces are associated with chlorite quartz muscovite filled dilational jogs and narrow breccia zones arrays of slip surfaces are transitional into similarly oriented phyllonite zones within which the foliation locally overprints early cataclastic zones the nucleation of these shear zones under greenschist facies conditions involved fluid infiltration along early transgranular fractures and hydration of fe mg bearing minerals initial displacement occurred by slip along these fractures and local cataclasite development fluids were episodically drawn into dilatant sites along these slip surfaces a transition to plastic deformation resulted directly from the metamorphic breakdown of feldspars and amphiboles to phyllosilicates which allowed strain localization into narrow phyllonite zones thus dilatancy produced by early brittle deformation appears to be the main process by which fluids infiltrate into developing greenschist grade retrograde shear zones reaction softening via hydration reactions causes a brittle to plastic transition and results in strain localization

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

coupled carbon isotopic and sedimentological records from the permian system of eastern australia reveal the response of atmospheric carbon dioxide to glacial growth and decay during the late palaeozoic ice age abstract proxy geochemical records from high latitude ice proximal deposits have the potential to provide key insights into past icehouse climates but such records are rare the permian system of eastern australia contains a rich record of environmental and climatic changes that occurred in areas proximal to glaciation during the acme and waning stages of the late palaeozoic ice age within this succession a wealth of fine grained organic matter rich facies provides an opportunity to construct a bulk 13corg record that records changes in atmospheric co2 through the permian fluctuations in 13corg track changes in climate determined independently on the basis of sedimentological criteria in the same strata these patterns are also broadly consistent with multiple proxy records derived from palaeoequatorial sites the results of this geochemical investigation 1 support recent studies using the high latitude ice proximal sedimentologic and stratigraphic record and palaeoequatorial geochemical proxies that document highly variable climatic conditions within the overall permian icehouse to greenhouse transition and 2 confirms that the sedimentary record of glaciation from eastern australia reflects global changes in atmospheric co2 on several m y order timescales

bypass margins basin restricted wedges and platform to basin correlation upper devonian canadian rocky mountains implications for sequence stratigraphy of carbonate platform systems abstract carbonate platforms can commonly keep up with relative sea level rise because of high rates of sediment accumulation and platform aggradation surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment if accumulation rates in basinal settings lag behind those of the platform a bypass or erosional margin can develop under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered we report here the results of high resolution stratigraphic analyses of two upper devonian isolated carbonate platforms in western alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences the slope and basin sequences surrounding the miette and ancient wall platforms consist of basin restricted onlapping wedges of fine grained background sediment deposited dominantly from suspension and coarse grained platform derived sediment redeposited by a variety of gravity flow mechanisms sequence boundaries are identified within the redeposited carbonate intervals identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry mineralogy and clast content of redeposited carbonate units highstand carbonates contain sheet like debris flows and turbidites with abundant slope derived clasts and background facies with high total carbonate content lowstand carbonates contain sheet like and channelized debris flows and turbidites with abundant platform derived clasts and background facies with low carbonate content and locally high amounts of organic carbon transgressive facies are dominated by initially carbonate poor and organic rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content these patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes lowstand redeposited carbonates indicate platform and platform margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions high siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine grained carbonate sediment successive stages of platform development at miette and ancient wall were controlled by accommodation changes driven by relative sea level fluctuations backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and patterns of slope development greater subsidence at ancient wall fostered the development of a steeper bypass margin and different slope evolution compared to miette slope oversteepening also initiated a process of slope readjustment that eventually reduced the platform to basin gradient and facilitated regressive platform progradation in conventional siliciclastic sequence stratigraphy basin restricted wedges are interpreted as lowstand deposits on the basis of their geometry and position relative to an updip margin wedge shaped basinal units along the miette and ancient wall bypass margins contain both highstand and lowstand facies that straddle sequence boundaries the results of this study provide objective criteria for differentiating systems tracts in carbonate slope and basin environments through mineralogic and compositional analyses providing more accurate correlation of detached platform and basin sequences interpretation of carbonate basin restricted wedges as purely highstand or lowstand deposits may lead to erroneous conclusions regarding sequence stratigraphy platform to basin correlation and the volumetric partitioning of sediments deposited in different systems tracts

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

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

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

emeishan basalts sw china and the end guadalupian crisis magnetobiostratigraphic constraints abstract a magnetostratigraphic investigation of the permian emeishan lip large igneous province was carried out on a composite section in ebian county close to the type area in sichuan sw china the main succession of twelve flows 175 m thick carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity the data enable a correlation to be proposed with an emeishan basalt sequence in western guizhou c 400 km to the se from our knowledge of the geomagnetic field9s reversal behaviour during the permian it suggests that the main lava pile along the eastern half of the emeishan basalt outcrop belt was erupted within a half to one million years using magnetobiostratigraphic data from the adjacent south china platform the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the maokou limestones constrained by conodont data the main emei basalts appear to be at least two biozones older 1 1 5 ma than the mid late permian boundary it is possible however that the emei basalt waning zone sequence which represents an explosive volcanic phase might be coeval with the end guadalupian biotic crisis thus arguments implicating emei basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative age constraints

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

pleistocene vegetation of the humid tropics of northeastern queensland australia abstract the humid tropics area of northeastern queensland has provided a substantial and detailed history of rainforest and rainforest savanna interactions from the pollen analysis of a number of sites on the volcanic atherton tableland through the latter part of the quaternary period a recent extension of the record to close to the base of the quaternary from examination of an offshore core provides a broad regional and temporal context for evaluation of the true significance of late quaternary changes it is apparent that the major sustained change in the vegetation of the region occurred relatively recently probably within the last 140 000 yr and that this change was time transgressive it involved the replacement of extensive moist rainforest by open eucalypt woodland and is considered to have been most likely caused by the burning activities of aboriginal people some aspects of the record from this region can contribute to the history of rainforest on a global scale but other features of it re inforce the unique nature of the development of australian vegetation patterns

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

progress problems and prospects an overview of the guadalupian series of south china and north america abstract the guadalupian epoch is marked by the formation of the pangean supercontinent global sea level change rifting and drifting of the cimmerian continents formation of large igneous provinces and dramatic biotic changes a high resolution biostratigraphic chemostratigraphic and high precision geochronologic framework of this critical transition is fundamental to understanding these events extensive studies of the latest cisuralian and guadalupian series in both south china and north america reveal the same conodont lineages but the conodont interval zones based on jinogondolella within the guadalupian series are slightly diachronous high precision u pb geochronological studies ca id tims method calibrate the base of the guadalupian series base roadian at 273 01 0 14 ma a previously reported age from an ash bed overlying the emeishan flood basalts 259 51 0 21 ma is adopted for the guadalupian lopingian boundary glb based on recently published geochronology and bayesian age modeling from the guadalupian series the base of the capitanian is constrained at 264 28 0 16 ma and the base of the wordian is interpolated to be 266 9 0 4 ma the illawarra reversal is of early middle wordian age both north america and south china possess a distinct negative 13ccarb excursion of 3 5 at the latest kungurian and early roadian lk er cie which coincides with the early stages of a significant 3rd order sea level rise the large end guadalupian 13ccarb negative excursion may have been affected by post depositional diagenesis or a warming event associated with the emeishan volcanism the 87sr 86sr ratios in both regions declined from the latest kungurian to the late capitanian but have different ratios and reveal several fluctuations in the middle guadalupian measured 18oapatite values suggest that the delaware basin was 3 4 c cooler than the eastern yangtze block analysis of a new high resolution database of marine taxa indicates only a minor pre lopingian diversity drop from 261 04 ma to 259 98 ma which coincides with the peak emeishan volcanism the widely perceived end guadalupian mass extinction in north america is evidently masked by and possibly an artefact of a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west texas basins

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

oxygen isotope evolution of biogenic calcite and apatite during the middle and late devonian oxygen isotope ratios of well preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the middle and late devonian by assuming an oxygen isotopic composition of 1 v smow for devonian seawater the oxygen isotope values of eifelian and early givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 c late givetian and frasnian palaeotemperatures calculated from 18o values of conodont apatite are close to 25 c in the early frasnian and increase to 32 c in the latest frasnian and early famennian oxygen isotope ratios of late givetian and frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite 18o values and give unrealistically warm temperatures ranging from 30 to 40 c diagenetic recrystallization of shell calcite different habitats of conodonts and brachiopods as well as non equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the 18o depletion of brachiopod calcite moreover the 18o depletion of brachiopod calcite with respect to equilibrium 18o values calculated from conodont apatite is too large to be explained by a change in seawater ph that might have influenced the oxygen isotopic composition of brachiopod calcite the realistic palaeotemperatures derived from 18o apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of palaeozoic oceans more faithfully than brachiopod calcite and do not support the hypothesis that the 18o 16o ratio of devonian seawater was significantly different from that of the modern ocean

evaluating the influence of tidal currents on the distribution of silt in nara inlet central great barrier reef australia a simple model is developed to infer flood tide dispersal of silt during fair weather conditions from spatial grain size variation of mixed carbonate siliciclastic silt on the bed of nara inlet a 3 km long shallow tropical embayment on the mid shelf of the central great barrier reef region australia the model uses settling velocities calculated for three dominant silt modes 23 28 and 41 m and measured tidal current data to predict the headward transport of silt by a large flood tide modelling was aided by the use of wind and currents 2000 wc2000 freeware a visualisation and analysis tool for vectorial data the model predicts the 23 28 and 41 m modes will be transported minimum headward distances of 1250 950 and 500 m respectively and compares well with the observed silt distribution on the bed the results indicate that under fair weather conditions flood tides control the distribution of silt consistent grain size trends of bulk and siliciclastic silt implies that siliciclastic and carbonate silt sized grains may exhibit similar hydraulic behaviour during transport by flood tides in nara inlet the model may be applied to embayments where fine sediment transport is dominated by flood tides it may also have application in identifying the controls on dispersal and accumulation of particle associated contaminants in embayments characterised by mixed carbonate and siliciclastic sediments

permo triassic boundary superanoxia and stratified superocean records from lost deep sea pelagic cherts of japan and british columbia canada recorded a long term and worldwide deep sea anoxic oxygen depleted event across the permo triassic or paleozoic and mesozoic boundary 251 2 million years ago the symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean panthalassa became totally stratified for nearly 20 million years across the boundary the timing of onset climax and termination of the oceanic stratification correspond to global biotic events including the end guadalupian decline the end permian extinction and mid triassic recovery

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

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope