variations of biogenic particle flux in the southern atlantic section of the subantarctic zone during the late quaternary evidence from sedimentary and variations of intensity and composition of biogenic particle flux at the northern boundary of the present polarfrontal zone in the atlantic sector of the southern ocean are indicators of major changes of paleoenvironmentalconditions on glacial interglacial time scales during the late quaternary in order to estimate those pastchanges sediment accumulation patterns of two piston cores one from just north and one just south of thepresent day position of the subantarctic front were reconstructed using the 230thex method large contributionsof laterally supplied material were quantified and used to correct sediment accumulation rates during the lastglacial focussing of biogenic opal dominated material exceeded the original contribution from the surfacewater above by a maximum factor of 8 7 the initial activity ratio of 231paex 230thex was used as tracer forbiogenic particle flux and composition and indicates that during the glacial stages 2 and 4 the area of high opalproductivity was situated above the location of the southern core whereas the northern core has not beenreached by this northward shift during the last 130 kyr as shown by the pattern of focussing corrected bulkaccumulation rates if the position of the antarctic polar front has remained at the northern boundary of thehigh opal productivity area during the last 130 kyr the results suggest that was located exactly between thetwo core sites during glacial stages 2 and 4 a two box modeling approach involving particle flux and boundaryscavenging intensity of 231pa was applied to estimate the possible range of the 231paex 230thex ratio recordedin southern ocean sediments previous estimates on the export of 231pa from the atlantic into the southernocean are corroborated but the model suggests a low sensitivity of the 231paex 230thex ratio in southern oceansediments to variations of the residence time of north atlantic deep water in the atlantic ocean

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

231pa 230th fractionation by ocean transport biogenic particle flux and particle type 231pa and 230th are removed from the water column by a process of reversible scavenging which quickly removes 230th to the sediment 231pa is less efficiently scavenged onto particles than 230th and is therefore more effectively transported via advection and diffusion before it reaches the ocean sediment this study combines particle fields dust opal caco3 poc derived from observations with the bern3d intermediate complexity ocean model and an equilibrium scavenging model for isotopes the equilibrium partition coefficient for particulate versus dissolved isotope activity is varied with particle type the model can explain many of the features of the global 231pa and 230th distribution the success of such a simple model at representing the global pattern of 231pa 230th activity ratio supports the use of this proxy in paleoceanographic studies we use the model to address the controversy concerning which particle types are dominant in fractionating 231pa 230th in the ocean the lithogenic dust flux is found to be unimportant for 231pa 230th fractionation the ocean fractionation of 231pa 230th is dominated by the distribution of the caco3 and opal flux we also confirm that opal is a weak scavenger of 230th

hydrocarbon plays and global basin classification hydrocarbon plays and the global basin classification system have important connections after a basin has been classified its similarities or differences with other basins may be compared prolific hydrocarbon basins are categorized and the plays are compared to specific tectonic and depositional events some plays are controlled by basin initiating tectonic events such as interior fracture or interior sag and the type of sedimentation inherent in each basin type in more complex polyhistory basins oil and gas plays are commonly associated with combinations of various cycles or by basin modifying tectonics such as episodic wrenching subsidence foldbelts and basin tilt

boundary scavenging at the east atlantic margin does not negate use of 231pa 230th to trace atlantic overturning abstract the 231 pa 230 th method is a promising tool to reconstruct ocean circulation over the past glacial interglacial cycle however marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of atlantic meridional overturning circulation amoc by influencing the fractionation between the in situ produced 231 pa and 230 th in ocean water here we present 231 pa 230 th down core profiles from high particle flux areas off namibia and senegal covering the past 35 ka the 231 pa 230 th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses our results show that sedimentary 231 pa 230 th in the eastern atlantic margin is linked to particle flux but controlled primarily by the mode of the amoc our data suggest that during the past 30 ka the high productivity eastern margin was not capable of importing and storing significant amounts of 231 pa from the open ocean consequently the applicability of the 231 pa 230 th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231 pa sink

relevance of silicon isotopes to si nutrient utilization and si source assessment in antarctic waters 1 we analyzed 29si of dissolved silicate for eight water column profiles across the southern ocean south of australia in spring 2001 from the seasonal ice zone siz north to the subantarctic zone saz including the first isotopic compositions measured for si depleted seawaters all profiles display mixed layer enrichments in heavy si isotopes relative to deep water in accordance with preferential uptake of the light isotope by diatoms as silicate levels decrease from the siz northward across the polar front zone pfz to the saz surface and mesopelagic 29si signatures generally become progressively heavier but the most si depleted saz waters do not exhibit 29si values heavier than in the pfz this intricacy appears to derive from variations in the vertical and horizontal supply of silicate to surface waters and by applying a steady state open system model we estimate a fractionation factor 29 between diatoms and seawater of 0 45 0 17 independently of zones and phytoplankton community though encouraging these results are related to latitudinal changes in mesopelagic 29si values complexity in surface silicate 29si correlations and differences from previous studies which underline the need for caution in the use of silicon isotopes in paleoceanographic studies until systematic efforts have been undertaken to better understand modern variations

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

the water column distributions of thorium isotopes in the western north pacific abstract four vertical profiles of 230 th and 228 th were determined using large volume water samples in the western north pacific an almost linear increase of 230 th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain we developed a model which included a dissolved particulate transformation as well as parameters of the scavenging model application of the model to the vertical distributions of total and the geosecs particulate th isotopes 230 th and 234 th yielded the residence time of dissolved th with respect to adsorption to particles and the turnover time of particulate th to be 235 days and 57 days respectively the th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m day which continually release th into sea water as well as pick up th from the water along their journey to the bottom for 228 th a large excess over 232 th was observed throughout the water column with pronounced high concentrations in surface and bottom waters suggesting that the 228 th was derived from 228 ra diffused out of sediments the vertical distributions of 228 th seemed to be significantly influenced by lateral mixing along isopycnals

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

modeling the relationship between 231pa 230th distribution in north atlantic sediment and atlantic meridional overturning circulation down core variations in north atlantic 231paxs 230thxs have been interpreted as changes in the strength of the atlantic meridional overturning circulation amoc this modeling study confirms that hypothetical changes in the amoc would indeed be recorded as changes in the distribution of sedimentary 231paxs 230thxs at different sites in the north atlantic the changes in sedimentary 231pa 230th that we simulate are diverse and do not reflect a simple tendency for 231paxs 230thxs to increase toward the production ratio 0 093 when the amoc strength reduces but instead are moderated by the particle flux in its collapsed or reduced state the amoc does not remove 231pa from the north atlantic instead 231pa is scavenged to the north atlantic sediment in areas of high particle flux in this way the north atlantic 231paxs 230thxs during amoc shutdown follows the same pattern as 231paxs 230thxs in modern ocean basins with reduced rates of meridional overturning i e pacific or indian oceans we suggest that mapping the spatial distribution of 231paxs 230thxs across several key points in the north atlantic is an achievable and practical qualitative indicator of the amoc strength in the short term our results indicate that additional north atlantic sites where down core observations of 231paxs 230thxs would be useful coincide with locations which were maxima in the vertical particle flux during these periods reliable estimates of the north atlantic mean 231paxs 230thxs should remain a goal in the longer term our results hint at a possible seesaw like behavior in 231pa 230th in the south atlantic

fluxes of 230th and 231pa to the deep sea implications for the interpretation of excess 230th and 231pa 230th profiles in sediments abstract analysis of samples obtained with deep sea moored sediment traps deployed at 15 sites representing a wide range of oceanic conditions confirms that the flux of 230 th scavenged to the seafloor remains close to its production rate from the decay of 234 u in the overlying water column and generally validates the use of 230 th as a normalizing tool for paleoflux reconstruction after correction for trapping efficiency the flux of 230 th measured in the low flux regions amounts to 90 6 of the production rate with the notable exceptions of one site near the arabian sea upwelling and one site in the weddell sea a 230 th flux equivalent to 120 of the production rate was found in panama basin similar or more extensive scavenging of 230 th may be occurring at a pacific margin site off california and south of the polar front but these estimates are obscured by large errors on our trapping efficiency estimates in contrast the flux of 231 pa and the 231 pa 230 th ratio can vary strongly with particle flux following distinct trends in different oceanic basins in the atlantic ocean 231 pa fluxes and 231 pa 230 th are low and not sensitive to particle flux this is because of the short residence time of deep water in this basin resulting from thermohaline circulation which prevents the full development of lateral concentration gradients and full expression of boundary scavenging in the pacific ocean the sensitivity of 231 pa 230 th to particle flux is highest reflecting the longer residence time of deep water in the southern ocean 231 pa 230 th ratios are invariably high even when particle fluxes are low reflecting the predominance of opal which fractionates minimally between the two radionuclides interpretation of 231 pa 230 th recorded in sediments is thus complex in the atlantic this ratio is better suited for recording past changes in the strength of thermohaline circulation in the pacific it has the best potential for providing synoptic maps of past changes in particle flux in the southern ocean retrieval of information from 231 pa 230 th is more difficult and requires a more quantitative understanding of the influence of particle composition

seismic imaging of major tectonic features in the crust of phanerozoic eastern australia abstract crustal architecture can be recognised from seismic fabric characteristics and velocity information across phanerozoic eastern australia three major crustal sub divisions are identified from data in southern queensland they occur under west to east the nebine ridge taroom trough and new england fold belt with each crustal sub division having its own internal architecture but separated by major bounding structures geosutures these features are assessed against evolutionary models for the region the significant conclusions are as follows 1 1 the nebine ridge forms the southeastern part of the thomson fold belt but has a crustal architecture distinctly different from that under the central part of the fold belt tentatively supporting an evolutionary model involving fragmentation and eastward stretching and thinning of a precambrian australian craton the ridge crust has possibly been considerably altered by carboniferous plutonism and compressional events 2 2 between the nebine ridge and the crust under the taroom trough of the bowen basin there is a major low angle 5 10 geosuture the foyleview geosuture which extends from upper to lower crustal levels along a series of prominent horizons it was probably active during the major carboniferous tectonism which severely structured devonian basins west of the nebine ridge the geosuture forms the southeastern boundary of the thomson fold belt 3 3 the crustal architecture under the taroom trough has little obvious structure above an outstanding moho transition zone however the prominent meandarra gravity ridge striking along the trough axis highlights the possibility of high density mafic volcanics within the crust and the probability of a rift model being appropriate early in the trough s history the sedimentary basin architecture supports the concept of an early extensional history for the crust within a poorly defined n s trending strike slip regime 4 4 between the taroom trough and the new england fold belt we interpret a high angle geosuture extending through the crust the burunga mooki geosuture reactivation during late palaeozoic early mesozoic times produced a series of reverse faults along the uplifted eastern margin of the trough some of these structures are tentatively considered to be positive flower structures above deeper faults with strike slip movement the geosuture separates regions with distinctly different seismic fabrics and played an important role in the formation of the bowen gunne dah sydney basin system 5 5 within the new england fold belt crustal domains can be recognized associated with late palaeozoic oroclinal bending and early mesozoic trans tensional basins major oroclinal bending of the upper crust in the west of the fold belt is interpreted above a mid crustal detachment the texas detachment in the central part of the fold belt the seismic data support a trans tensional mechanism for the formation of triassic basins with steeply dipping bounding faults under the east of the fold belt an imbricate thrust stack accretionary wedge is clearly imaged above a mid crustal horizon the brisbane mid crustal detachment upper crustal deformation appears to have occurred above this detachment 6 6 from the nebine ridge to the coast the moho is clearly defined below a 3 km thick moho transition zone hast of the thomson fold belt the moho level is identified as a gently undulating feature at 36 38 km depth and probably re established after the major late palaeozoic tectonic events which formed the crust under the taroom trough and new england fold belt this contrasts with the middle palaeozoic lower crustal moho features which appear to be preserved under the thomson fold belt 7 7 the thickest crust under the nebine ridge about 44 km appears to be associated with lower crustal wedging from the east there is an apparent thinning of the non sedimentary crust under the deepest basin taroom trough of about 30 compared with the crust to the west and east no crustal thickening is evident in the region of oroclinal bending within the new england fold belt

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

nutrient cycling in the indian sector of the southern ocean over the last 50 000 years most high southern latitude records of carbon and nitrogen isotopic ratios and elemental ratios are from the antarctic and polar front zones thus hindering a comprehensive view of nutrient cycling in the southern ocean we present for the first time two records from the subantarctic zone and the southern subtropical zone of the indian ocean these records provide a latitudinal transect covering the main oceanographic systems of the southern ocean carbon and nitrogen content of the diatom bound organic matter increases during the last glacial in the antarctic and subantarctic zones but does not show a clear climate related signal in the subtropical zone comparison of these records with sea surface temperatures reconstructed at the core locations and record of dust deposition over antarctica suggests that eolian iron input possibly switched diatom physiology toward higher carbon to silica and nitrogen to silica uptake and storage south of the subantarctic front due to the dependency of photosynthesis on iron concentration levels conversely the northernmost core was too remote from any iron source over the last 50 000 years antarctic diatoms therefore have the sole potential to change the nutrient content of the waters escaping from the southern ocean hence providing partial support to the silicic leakage hypothesis as a potential cause of lower glacial atmospheric co 2

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

late quaternary sediment dating and quantification of lateral sediment redistribution applying230thex a study from the eastern atlantic sector of the southern ocean high resolution records of the natural radionuclide230th were measured in sediments from the eastern atlantic sector of the antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late quaternary high resolution dating rests on the assumption that the230thex flux to the sediments is constant short periods of drastically increased sediment accumulation rates up to a factor of 8 were determined in the sediments of the antarctic zone during the climate optima at the beginning of the holocene and the isotope stage 5e by comparing expected and measured accumulation rate of230thex lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated we show that lateral contributions locally were up to 6 5 times higher than the vertical particle rain rates at other locations only 15 of the expected vertical particle rain rate were deposited

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

a seismic refraction study of the quilpie trough and adjacent basement highs eromanga basin eastern australia abstract the jurassic cretaceous eromanga basin in eastern australia is a relatively undisturbed sedimentary sequence covering the devonian quilpie trough and the early palaeozoic canaway ridge and cheepie shelf seismic refraction recording across these three features with additional reflection gravity and well information has been used to determine the velocity structure to a depth of 10 km the thickness of the eromanga basin sequence along the traverse varies between 1 1 and 1 4 km with p wave velocities ranging from 2 0 to 3 8 km s the maximum thickness of the underlying quilpie trough is about 3 8 km but the base of the trough is hard to define the velocities in this devonian sequence range from 4 0 to 5 0 5 5 km s two small bodies with a velocity of 4 0 4 5 km s occur immediately below the eromanga basin sediments on the canaway ridge and the cheepie shelf they may be remnants of devonian sediments on an erosion surface the velocities within the ordovician basement are less below the canaway ridge than under the cheepie shelf and quilpie trough they reach 6 0 km s at 7 km depth below the ridge at 4 km depth under the shelf and at an intermediate depth under the trough from gravity modelling the density of the basement to the quilpie trough increases at a depth of about 7 km this may be related to volcanics found in the basement further north the canaway ridge has a lower density than the cheepie shelf or the basement of the quilpie trough relative vertical movement between these three features may in part be related to these density differences

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

p wave velocity features of the lithosphere under the eromanga basin eastern australia including a prominent mid crustal conrad discontinuity abstract the crustal structure of the central eromanga basin in the northern part of the australian tasman geosyncline revealed by coincident seismic reflection and refraction shooting contrasts with some neighbouring regions of the continent the depth to the crust mantle boundary moho of 36 41 km is much less than that under the north australian craton to the northwest 50 55 km and the lachlan fold belt to the southeast 43 51 km but is similar to that under the drummond and bowen basins to the east the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the north australian and lachlan provinces in particular there is a sharp velocity increase at mid crustal depths 21 24 km which has not been observed with such clarity elsewhere in australia the conrad discontinuity in the lower crust the many discontinuous sub horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust further emphasising the differences between the upper and lower crust the crust mantle boundary moho is characterised by an increase in velocity from 7 1 7 7 km s to a value of 8 15 0 04 km s the depth to the moho under the canaway ridge a prominent basement high is shallower by about 5 km than the regional moho depth there is also no mid crustal horizon under the canaway ridge but there is a very sharp velocity increase at the moho depth of 34 km the ridge could be interpreted as a horst structure extending to at least moho depths but it could also have a different intra crustal structure from the surrounding area the sub crustal lithosphere has features which have been interpreted from limited data as being caused by a velocity gradient at 56 57 km depth with a low velocity zone above it because of the contrasting crustal thicknesses and velocity gradients the lithosphere of the central eromanga basin cannot be considered as an extension of the exposed lachlan fold belt or the north australian craton the lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m consistent with an upper crustal basement of tightly folded meta sedimentary and meta volcanic rocks the crustal structure is consistent with a pericratonic or arc back arc basin being cratonised in an episode of convergent tectonics in the early palaeozoic the seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment

deep water provenance and dynamics of the de glacial atlantic meridional overturning circulation abstract reconstructing past modes of ocean circulation is an essential task in paleoclimatology and paleoceanography to this end we combine two sedimentary proxies nd isotopes e nd and the 231pa 230th ratio both of which are not directly involved in the global carbon cycle but allow the reconstruction of water mass provenance and provide information about the past strength of overturning circulation respectively in this study combined 231pa 230th and e nd down core profiles from six atlantic ocean sediment cores are presented the data set is complemented by the two available combined data sets from the literature from this we derive a comprehensive picture of spatial and temporal patterns and the dynamic changes of the atlantic meridional overturning circulation over the past 25 ka our results provide evidence for a consistent pattern of glacial stadial advances of southern sourced water along with a northward circulation mode for all cores in the deeper 3000 m atlantic results from shallower core sites support an active overturning cell of shoaled northern sourced water during the lgm and the subsequent deglaciation furthermore we report evidence for a short lived period of intensified amoc in the early holocene

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

beryllium 10 thorium 230 and protactinium 231 in galapagos microplate sediments implications of hydrothermal activity and paleoproductivity changes during the last 100 000 years biogenic particle fluxes from highly productive surface waters boundary scavenging and hydrothermal activity are the main factors influencing the deposition of radionuclides in the area of the galapagos microplate eastern equatorial pacific in order to evaluate the importance of these three processes throughout the last 100 kyr concentrations of the radionuclides 10be 230th and 231pa and of mn and fe were measured at high resolution in sediment samples from two gravity cores klh 068 and klh 093 high biological productivity in the surface waters overlying the investigated area has led to 10be and 231pa fluxes exceeding production during at least the last 30 kyr and probably the last 100 kyr however during periods of high productivity at the up welling centers off peru and extension of the equatorial high productivity zone a relative loss of 10be and 231pa may have occurred in these sediment cores because of boundary scavenging the effects of hydrothermal activity were investigated by comparing the 230thex concentrations to the mn fe ratios and by comparing the fluxes of 230th and 10be which exceed production the results suggest an enhanced hydrothermal influence during isotope stages 4 and 5 and to a lesser extent during isotope stage 1 in core klh 093 during isotope stages 2 and 3 the hydrothermal supply of mn was deposited elsewhere probably because of changes in current regime or deep water oxygenation a strong increase of the mn fe ratio at the beginning of climatic stage 1 which is not accompanied by an increase of the 230thex concentration is interpreted to be an effect of mn remobilization and reprecipitation in the sediment

10be and ba concentrations in west african sediments trace productivity in the past particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles in order to determine the influence of these processes on the depositional fluxes of10be and barium we have performed high resolution measurements on sediment core geob 1008 3 from the congo fan because the core is dominated by terrigenous matter supplied by the congo river it has a high average mass accumulation rate of 6 5 cm kyr biogenic10be and ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10be and ba which are assumed to be proportional to the flux of al2o3 the meanba al weight ratio of the terrigenous component was determined to be 0 0045 the unusualy high terrigenous10be concentrations of 9 1 109 atoms g al2o3 are either due to input of particles with high10be content by the congo river or due to scavenging of oceanic10be by riverine particles the maxima of biogenic10be and ba concentrations coincide with maxima of the paleoproductivity rates time series analysis of the10be and of ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr which also controls the rates of paleoproductivity in this core during the maxima of productivity the flux of biogenic ba is enhanced to a larger extent than that of biogenic10be applying a model for coastal scavenging we ascribe the observed higher sensitivity of ba to biogenic particle fluxes to the fact that the ocean residence time of ba is approximately 10 times longer than that of10be

two layer model of lithospheric compression and uplift exhumation in an intracratonic setting an example from the cooper eromanga basins australia seismic reflection profiles indicate the compressive nature of the structural style associated with the major uplift events in the cooper eromanga basins inversion geometries and reactivated features attest to a period of compression during late triassic early jurassic times in the eromanga basin compressional structural styles associated with late cretaceous tertiary are apparent many of the late cretaceous tertiary structures coincide with exhumation highs in late cretaceous tertiary times the two layer lithospheric compression model is considered as the most complete explanation of both the uplift of areas subject to compression and crustal thickening and of the regional uplift of areas not subject to any apparent late cretaceous tertiary compression in the model compression and thickening in the lower lithosphere is decoupled and laterally displaced from that in the upper crust thickening of the mantle lithosphere without thickening of the overlying crust can account for the initial subsidence then uplift of not inverted platform areas the opening of the tasman sea and the coral seas can lead to stress transmission in the interior of the continent these stresses are likely to generate uplift but cannot explain the distribution of uplift in areas not subject to compression

petroleum hydrogeology of the cooper and eromanga basins australia some insights from mathematical modeling and fluid inclusion data mathematical modeling and fluid inclusion data analysis are used to reconstruct the petroleum hydrogeology of the australian cooper and eromanga basins our analysis focuses on the development of topography and compaction driven groundwater flow systems and their role in heat redistribution petroleum generation and oil and brine migration during basin evolution finite element models of basin transport processes are constructed along northeast southwest aa and northwest southeast bb cross sections that generally follow the present day groundwater flow patterns through these basins numerical results are presented in the copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 19 1995 revised manuscript received july 3 1996 final acceptance november 11 1996 2independent consultant 12 rinzee road dracut massachusetts 01826 3csiro division of petroleum exploration 51 delhi road north ryde nsw 2113 australia 4department of geology and geophysics university of minnesota 310 pillsbury drive se minneapolis minnesota 55455 e mail mperson darcy geo umn edu 5gza geoenvironmental inc 380 harvey road manchester new hampshire 03103 6santos ltd 101 grenfell street adelaide sa 7000 australia this research is supported by a grant from the petroleum research fund administered by the american chemical society prf 24184 ac8 we would also like to acknowledge the orpha and george gibson hydrogeology endowment and the mcknight land grant professorship program at the university of minnesota we thank the csiro division of exploration geosciences for providing support for travel costs within australia data provided by santos ltd and the department of mines and energy south australia are also gratefully acknowledged computational work performed on this project was done at the gibson computational hydrogeology laboratory at the university of minnesota which is supported by the national science foundation under ear 94 05807 special thanks go to m a habermehl of the australian geological survey organization david gravestock of the south australia bureau of mines and mineral resources and mike congreves of santos ltd for their assistance on interpreting the petroleum geology and hydrogeology of the cooper and eromanga basins the review comments of joseph toth stefan bachu and michelle walvoord as well as discussions with ward sanford greatly improved the quality of this manuscript three dimensional model results presented in this paper are available in animated form on vhs videocassette and can be obtained by contacting mark person at the address listed for him as the corresponding author

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

ocean thermohaline circulation and sedimentary 231pa 230th ratio holocene sediments from the atlantic are characterized by 231pa 230th ratios below the production ratio of the two radionuclides in the water column 0 093 whereas holocene sediments from the southern ocean have 231pa 230th 0 093 this pattern of 231pa deficit and excess was ascribed to southward 231pa export from the atlantic by the atlantic thermohaline circulation thc as pa is scavenged less efficiently by marine particles and more effectively transported by the thc than th the same pattern is observed in deposits of the last glacial maximum lgm which led to a previous contention that the thc strength did not vary markedly through the last glacial termination here we embed a description of trace metal scavenging into a zonally averaged circulation biogeochemistry ocean model to explore the sensitivity of 231pa 230th in atlantic and southern ocean sediments to thc changes our results show that the production of biogenic opal which unlike other marine particles poorly fractionates th and pa in the southern ocean water column determines the spatial pattern of the sensitivity also 231pa 230th increases in the north atlantic but changes little in the south atlantic and decreases in the southern ocean as thc is reduced the mean 231pa 230th of the whole atlantic is therefore less sensitive to thc changes than the mean 231pa 230th of the north atlantic the current uncertainties in atlantic mean 231pa 230th are too large to rule out a twofold reduction of the thc at the lgm however the increase in north atlantic mean 231pa 230th simulated in response to a twofold thc reduction is larger than the observed change in the north atlantic mean 231pa 230th from the lgm to holocene comparing this change with the modeled sensitivity of north atlantic 231pa 230th to thc variations indicates that the thc at the lgm could not have been reduced by 30 of its present strength experiments of transient thc changes indicate that high resolution 231pa 230th records from north atlantic sediments could also document thermohaline oscillations on century to millennial timescales

velocity depth modelling using reflection and refraction data recorded in the central eromanga basin queensland australia abstract seismic refraction recordings along a line extending from mt howitt no 1 well to eromanga in southwest queensland over the eromanga and cooper basin sediments revealed two intra basement refractors not recorded by coincident reflection profiling these refractors were recorded at 3 5 km and 5 0 km depth between the basin basement unconformity at 2 4 km depth and a low velocity zone at about 8 0 km depth precise modelling of the refracted first arrival times showed that the basin structure and faults seen on the reflection profile extended into basement to at least 5 5 km depth with increasing displacement on the faults with depth causing lateral variation of structure and velocity a feature of the seismic refraction data in this region is a series of up to five multiples which can be observed from 10 km to at least 40 km distance travel time characteristics indicate that these multiples are waves refracted within basement and multiply reflected at the surface travel time modelling of the refracted first arrivals multiples and two way reflection times provides a tight constraint on velocity and structure to a depth of about 5 5 km

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

displacement transfer at thrust terminations in southern appalachians saltville thrust as example transition from faulting to noncylindrical folding involving rapid plunge change at the fold closure is the primary displacement transfer mechanism at the northern end of the south appalachian foreland fold and thrust belt regional thrust faults including the saltville narrows and st clair terminate in regional overturned asymmetric anticlines this mechanism of displacement transfer is distinct from thrust terminations where fold complexes of smaller noncylindrical folds converge toward the end of the fault trace the saltville thrust transition to the sinking creek anticline is representative of the southern appalachian structures deformation intensity patterns reflected by cleavage development mesoscopic folding and faulting suggest that the sinking cree anticline formed due to upwarping from shear thrusting at depth laboratory deformation analogs of folds formed above ramps support this contention experimentally produced folds are asymmetric overturned structures with high strains on overturned limbs and very low strains on upright limbs a deformation sequence involving shear thrusting with subsequent break thrusting may characterize fault propagation at thrust termini this will be important for layered sedimentary sequences where thick rigid members low in the sedimentary pile are overlain by thinner interbedded mechanically anisotropic strata

does sedimentary 231pa 230th from the bermuda rise monitor past atlantic meridional overturning circulation 1 ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes measurements of 231pa 230th ratios in a sediment core from the bermuda rise have been interpreted as evidence that the atlantic meridional overturning circulation amoc was weakened or completely eliminated during a period of catastrophic iceberg discharges heinrich event 1 h1 here we present new data from the bermuda rise that show further 231pa 230th peaks during heinrich 2 h2 and heinrich 3 h3 additionally a tight correlation between diatom abundances biogenic silica and 231pa 230th is discovered in this core our results redirect the interpretation of 231pa 230th from the bermuda rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties

early tectonic evolution of the thomson orogen in queensland inferred from constrained magnetic and gravity data abstract the crustal architecture as well as the kinematic evolution of the thomson orogen in queensland is poorly resolved because the region is concealed under thick phanerozoic sedimentary basins and the basement geology is known from limited drill holes combined potential field and seismic interpretation indicates that the thomson orogen is characterized by prominent regional ne and nw trending structural grain defined by long wavelength and low amplitude geophysical anomalies the smooth magnetic signature is interpreted to reflect deeply buried source bodies in the mid to lower crust short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions they appear to be focused along major fault zones that might have controlled the locus for magmatism the eastern thomson orogen is characterized by a prominent ne structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs the western thomson orogen consists of a series of nw trending structures interpreted to reflect reverse faults sedimentation and basin development are interpreted to have initiated in the neoproterozoic to early cambrian during e w to ene wsw extension possibly related to the rodinia break up this extensional event was followed by late cambrian shortening recorded in the maneroo platform and the diamantina river domain which possibly correlates with the delamerian orogeny renewed deposition and volcanism occurred during the ordovician and may have continued until late silurian resulting in thinned proterozoic basement crust and extensive basin systems that formed in a distal continental back arc environment our interpretation places the thomson orogen to the west of the neoproterozoic passive margin preserved in the anakie inlier the region is likely to represent the internal extensional architecture during the rodinia break up that has been subsequently extensively modified by multiple extensional basin forming events and transient episodes of crustal shortening and basin inversion

deep circulation changes in the central south atlantic during the past 145 kyrs reflected in a combined231pa 230th neodymium isotope and benthic δ13c record abstract previous work showed that south atlantic sediments have lower glacial than holocene 231pa 230th which was attributed to a switch in the flow direction of atlantic deep water debate exists however as to the degree to which two processes circulation and scavenging determine sedimentary 231pa 230th making this interpretation contentious here we address this issue using 145 kyr records of paleocirculation proxies benthic foraminiferal c 13 neodymium isotopes end and sedimentary 231pa 230th were all measured in a single sediment core from the south atlantic subtropical gyre this site largely excludes the influence of local productivity changes on 231pa 230th records measured 231pa 230th ranges between 0 041 during glacials and 0 055 during interglacial periods and is consistently lower than the production ratio indicating export of 231pa from the central south atlantic for the entire duration of the record the lower glacial 231pa 230th is regionally consistent suggesting that basin scale oceanographic processes cause the decrease in turn less radiogenic end and lower benthic c 13 confirm the classical picture of an increase in southern component water scw influence in the atlantic during glacial periods and point to a circulation control on the observed 231pa 230th decrease rather than a local productivity change we suggest that associated with this change in water mass distribution the dominant sink for 231pa shifted from the margins of the south atlantic and or the southern ocean during interglacials to the north atlantic during glacial periods indeed elevated 231pa 230th in the deep north atlantic during glacials supports this mechanism of northward transport of 231pa by scw

late quaternary changes in biogenic opal fluxes in the southern indian ocean abstract late quaternary sedimentary and paleoenvironmental conditions in the southern indian ocean have been reconstructed from radioisotope and proxy element profiles biogenic opal and organic carbon measured on five sediment cores taken along a transect across the indian sector of the antarctic circumpolar current dissolution corrected opal rain rates were used to reconstruct past changes of opal productivity for this region records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the antarctic polar front apf probably due to increased ice cover north of apf opal productivity was slightly greater during glacial periods than during the holocene probably in response to 1 the northward migration of the apf by approximately 5 latitude 2 a northward transport of si from the antarctic zone and 3 an increase of fe necessary for opal producing organisms via upwelling and the erosion of the kerguelen plateau we also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried si c ratio between glacial and interglacial sediment this decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing an increase in glacial export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern indian ocean are unlikely to have contributed to the glacial drawdown of atmospheric co 2 inferred from ice core data

late silurian early devonian adakitic granodiorite a type and i type granites in nw junggar nw china partial melting of mafic lower crust and implications for slab roll back abstract late silurian early devonian magmatism of the nw junggar region in the central asian orogenic belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes in this study we report results of zircon u pb ages and systematic geochemical data for late silurian early devonian largely granitic rocks in nw junggar aiming to constrain their emplacement ages origin and geodynamic significance the magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks e g adakitic granodiorite k feldspar granite syenitic granite gabbro and rhyrolite u pb zircon ages suggest that the granitoids and gabbros were emplaced in the late silurian early devonian 420 405 ma adakitic granodiorites are calc alkaline characterized by high sr 407 532 ppm low y 12 2 14 7 ppm yb 1 53 1 77 ppm cr mostly

intensification and variability of ocean thermohaline circulation through the last deglaciation neodymium isotope ratios in the authigenic ferromanganese oxide component in a southeastern atlantic core reveal a history of the global overturning circulation intensity through the last deglaciation from a minimum during the last glacial maximum lgm north atlantic deep water nadw began to strengthen between 18 and 17 kyr cal bp approximately 2000 3000 years before the bolling warming it exhibits a gradually increasing baseline intensity that plateaus in the early holocene tracks increasing northern hemisphere insolation and parallels atmospheric co2 concentration millennial scale fluctuations are superimposed on this baseline nadw increase corresponding to events in northern hemisphere climate records the millennial excursions show sharp increases associated with the pre bolling retreat of continental glaciers and the bolling warming itself a decrease with allerod cooling and a recovery through the younger dryas and early holocene the data confirm a close link between deep ocean circulation and north atlantic climate changes there is no clear linkage with meltwater pulses indicating that rapid meltwater additions did not trigger observable mode changes in nadw production however rapid changes in north atlantic sea ice cover show a strong relationship with the millennial perturbations of nadw flux to the deep southern ocean the data indicate that the baseline intensity of nadw reaching the cape basin is paced by northern hemisphere insolation and that north atlantic sea ice coverage acts as a major amplifying link between the oceans and the atmosphere d 2004 elsevier b v all rights reserved

sedimentary iron records from the cape basin abstract the iron hypothesis suggests that dust derived fe delivered to the southern ocean during glacial intervals fueled primary productivity and led to co 2 drawdown clear support for a dustier glacial atmosphere comes from ice core records of dust concentrations furthermore there is unequivocal proof from open ocean fe fertilization experiments that primary productivity in the modern day southern ocean is limited by fe however substantial hemipelagic detrital sources dilute and obscure the eolian signal here we present records of fe concentrations total and reducible and fe fluxes to highlight the importance of hemipelagic fe sources to the cape basin we illustrate that on average only 7 of the fe flux to site 1089 can be accounted for by particle settling indicating that redistribution by bottom currents accounts for an order of magnitude more fe than particulate scavenging processes distribution by surface currents or eolian deposition we also find that on average only 7 of the fe content is easily reducible furthermore we speculate that a significant source of dissolved fe to the bottom waters may come from re suspended bottom sediments

231pa and 230th in surface sediments of the arctic ocean implications for 231pa 230th fractionation boundary scavenging and advective export abstract activities of 231pa and 230th in surface sediments from the arctic ocean and greenland norwegian seas are used to examine the redistribution of these water column produced tracers between the low productivity interior basins and high particle flux marginal areas sediment 231paxs 230thxs ratios throughout the canadian and eurasian basins and the high particle flux chukchi slope region are essentially invariant average 0 063 0 014 n 39 and significantly below the water column production ratio 0 093 231paxs 230thxs ratios are also below the production ratio in the seasonally high productivity greenland norwegian sea basins average 0 082 0 024 n 13 though they are 30 higher than the interior arctic the low sediment 231paxs 230thxs ratios are attributed to the net export of 39 of dissolved 231pa produced in intermediate deep waters as opposed to 10 of 230th through fram strait the negligible 230th export combined with the reported low 230thxs inventory of basin sediments and high 230thxs inventory in chukchi slope sediments points to significant boundary scavenging of 230th in the arctic the invariant 231paxs 230thxs ratios further indicate that scavenging of 230th is comparable to 231pa i e fractionation to a similar degree between the two nuclides in both the interior basins and margins thus while significant boundary scavenging of both 231pa and 230th occurs in the arctic there is a distinct lack of basin margin fractionation and a sizable export of 231pa there is also likely to be export of other similarly particle reactive radionuclides e g 10be pu isotopes out of the arctic

imaging the basement architecture across the cork fault in queensland using magnetic and gravity data abstract the basement rocks in central queensland are largely obscured by the phanerozoic sedimentary succession and direct information comes only from sparse geological data 2 5d forward modelling of regional aeromagnetic and bouguer gravity data has been undertaken to unveil the crustal architecture at the junction of the proterozoic mount isa terrane and the phanerozoic thomson orogen in queensland the most prominent geophysical character is represented by the abrupt termination of positive nnw trending geophysical anomalies of the mount isa terrane against ne trending low amplitude gravity and magnetic anomalies of the diamantina river domain of the thomson orogen potential field forward modelling indicates that the lower basement crust of the thomson orogen is petrophysically indistinguishable from the crust of the proterozoic mount isa terrane we interpret that the prominent gradients associated with the cork fault represent the displacement and burial of the mount isa terrane crust under the thomson orogen in this context the cork fault is inferred to represent a fundamental crustal discontinuity but does not represent the eastern margin of rodinia because the thomson orogen is floored by precambrian continental crust initiation of the cork fault might have occurred as early as the mesoproterozoic at that time the cork fault was a major structure that developed during the separation of the mount isa terrane and the curnamona province it is inferred that this break up occurred during initial n s to nnw sse extension the cork fault formed part of a network of major north and south dipping normal faults active at that time the cork fault was repeatedly reactivated during the neoproterozoic rodinia break up and during the phanerozoic evolution of the tasmanides we suggest that the segment of the inferred tasman line along the southern termination of the mount isa terrane should be regarded as a set of structures offsetting the proterozoic crust rather than a simple lineament dividing the proterozoic and the phanerozoic australian continent

comparison of ice rafted debris and physical properties in odp site 1094 south atlantic with the vostok ice core over the last four climatic cycles abstract visual counts of ice rafted debris ird foraminifera and radiolaria were made for 1500 samples in site 1094 spanning the last four climatic cycles marine isotope stages 1 11 most but not all of the ird variability is captured by whole core physical properties including magnetic susceptibility and ray attenuation bulk density glacial periods are marked by high ird abundance and millennial scale variability which may reflect instability of ice shelves in the weddell sea region each interglacial period exhibits low ird and high foraminiferal abundance during the early part of the interglacial indicating relatively warm sea surface temperatures and reduced influence of sea ice ird increases and foraminiferal abundances decrease during the latter part of each interglacial indicating a return to more glacial like conditions glacial terminations i and v are each characterized by a step wise reduction in ice rafting punctuated by a brief pulse in ird delivery and reversal in 18o the coarse fraction of the sediment is dominated by ash and radiolaria and the relative abundance of these components is remarkably similar to the concentration of na in vostok each of these variables is believed to be controlled mainly by sea ice cover thereby providing a means for sediment ice core correlation

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

age of palaeozoic granites and metamorphism in the tuvino mongolian massif of the central asian mobile belt loss of a precambrian microcontinent abstract the tuvino mongolian massif tmm was previously interpreted as a precambrian block within the central asian mobile belt according to this idea it consists of tectonic slices composed of metamorphic rocks of pre mesoproterozoic basement that experienced two episodes of regional metamorphism and mesoproterozoic cover rocks that were reworked together with the basement during high grade metamorphism zircon u pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536 6 ma significantly later than the deposition of the cover rocks regional upper amphibolite facies metamorphism which affected all metasedimentary units of the tmm occurred in the short time interval of 497 4 to 489 3 ma we propose that there is no simple basement cover relationship in the tuvino mongolian massif instead the massif consists of tectonic domains composed of heterogeneous metasedimentary successions with distinct pre metamorphic and pre tectonic histories that were juxtaposed by thrusting prior to 497 ma and then metamorphosed under upper amphibolite facies conditions we suggest that this thrusting event was associated with early palaeozoic collisional processes related to amalgamation of the central asian mobile belt our new model for the evolution of the tmm implies derivation of neoproterozoic terrigeneous metasediments from 800 900 ma granitoids formed in an andean type active continental margin setting

faulting and graben formation in western and central europe rifts and rift related basins play a pre eminent role among the sedimentary basins of western and central europe through time grabens developed in a number of different megatectonic settings whereby the principal mechanisms governing their subsidence was crustal stretching and subcrustal erosion the level of volcanic activity associated with rifting is highly variable and can change significantly during the development history of a rift some rifts are totally non volcanic the development of rift domes is generally associated with volcanic activity uplifting of a rift dome can induce a reversal in the subsidence pattern of a rift intracontinental rifts with their thinned crust are prone to inversion when the respective craton is subjected to tangential stresses in the process of inversion the crust of rifts is mechanically thickened again

scavenging of 230th 231pa and 10be in the southern ocean sw pacific sector the importance of particle flux particle composition and advection abstract the scavenging of 230 th 231 pa and 10 be was studied in the pacific sector of the southern ocean along 170 w using measurements from surface sediments time series sediment traps and the water column all sediment traps collected an annual flux of 231 pa greater than the integrated rate of production by 235 u decay up to 5 5 times greater and a flux of 10 be greater than the global average deposition rate of 10 be up to 3 4 times greater fluxes of 230 th were on average close to the production rate in the overlying water column these large fluxes of 231 pa and 10 be and high unsupported 231 pa 231 th and 10 be 230 th ratios in the sediments are not associated with depletion of nuclides in the water column and therefore are not the result of the classical boundary scavenging mechanism we estimate that of the 231 pa and 230 th advected into the southern ocean as part of the large scale overturning circulation only those nuclides associated with the upper limb of this circulation i e those that pass through the surface as part of the wind driven ekman flow are scavenged efficiently the majority of the nuclides advected into the southern ocean and associated with the bottom water limb are not scavenged to the sediments of the southern ocean but are returned northward throughout the year the unsupported 231 pa 230 th and 10 be 230 th ratios of material reaching sediment traps at 1000 m at a given site increase with increasing particle flux this behavior is explained by a conceptual model in which th pa and be are scavenged reversibly by fine grained suspended particles at all depths while pa and be are in addition scavenged strongly by diatom rich aggregates in surface waters spatial variability in the annually averaged unsupported 231 pa 230 th and 10 be 230 th ratios of sinking particulate matter reflects primarily the variability in particle composition and in the ratio and quantity of nuclides upwelled to the mixed layer rather than variability in particle flux

beryllium 10 in deep sea sediments a tracer for the earth s magnetic field intensity during the last 200 000 years abstract we present a new approach for the reconstruction of the earth s magnetic field intensity during the last 200 000 years based on 10 be in deep sea sediments a simple box model that is able to describe boundary scavenging of 10 be in the ocean is used to study the sensitivity of 10 be to changes of water circulation and or varying particle rain rates the model is applied to separate transport and production signal in single 10 be records vertical sediment accumulation rates are used as input values for the model calculations the calculated scavenging factors are applied to correct the 10 be records for boundary scavenging the model corrected 10 be based paleointensity record correlates well with other records from very different archives

the mid crustal horizon under the eromanga basin eastern australia abstract long line explosion seismic recordings indicate that a major mid crustal p wave velocity increase exists under the eromanga basin which contrasts the crust of this region from its neighbouring tectonic provinces the velocity increase is shown to be a regional feature and to correspond to the upper boundary of a zone of discontinuous seismic reflections characteristic of the lower crust the velocity increase of 0 35 0 6 km s occurs over a small depth range at an average depth of 24 km this velocity gradient produces conspicuous wide angle reflections at distances greater than 60 km from the shot point the seismic data present the clearest evidence to date of the existence of a major mid crustal horizon in continental australia a feature not prominent in other cratonic provinces which have been investigated in detail the velocity in the lower crust below the horizon is 6 7 7 0 km s the horizon represents a boundary between the upper and lower crust which could imply a different tectonic history for these two zones

is there a 230th deficit in arctic sediments abstract in most of the global ocean the radionuclide thorium 230 is removed from the water column by adsorption onto particles and deposition in seafloor sediments at a rate approximately in balance with its local production by the decay of uranium dissolved in seawater allowing its use in assessing rates of marine processes however several previous studies have suggested that the flux of 230th to the sediments of the central arctic is far too small to balance its production in the overlying water column if this is so 230th produced in the low particle flux central arctic basins would be deposited elsewhere either by boundary scavenging at the margins or by export from the arctic to lower latitudes in order to evaluate this possibility we compare the expected 230th production and measured inventories for five sites in the western arctic combining previously published 230th data with reported ams radiocarbon dates and find no evidence for a substantial deficit of 230th in these sediments instead we find evidence for near balance in the 230th budget during both the holocene and late glacial periods these intervals are separated by a brief deglacial period of apparently higher sedimentation rates and 230th deposition during the holocene the average sedimentary inventory of 230th at these sites is largely within 30 of the water column production in good agreement with observations and model results from other ocean basins

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

fractionation of 230th 231pa and 10be induced by particle size and composition within an opal rich sediment of the atlantic southern ocean this study centers on the question how sensitive are 231pa 230th and 10be 230th to sediment composition and redistribution the natural radionuclides 231pa 230th and 10be recorded in deep sea sediments are tracers for water mass advection and particle fluxes we investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records we present new data on particle size specific 231pa and 10be concentrations an additional separation step based on settling velocities led to the isolation of a very opal rich phase we find that opal rich particles contain the highest 231pa and 10be concentrations and higher 231pa 230th and 10be 230th isotope ratios than opal poor particles the fractionation relative to 230th induced by the adsorption to opal rich particles is more pronounced for 231pa than for 10be we conclude that bulk 231pa 230th in southern ocean sediments is most suitable as a proxy for past opal fluxes the comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites however a simulation shows that particle sorting by selective removal of sediment winnowing could change the isotope ratios consequently 231pa 230th should not be used as paleocirculation proxy in cases where a strong loss of opal rich material due to bottom currents occurred

biogenic opal in southern ocean sediments over the last 450 000 years implications for surface water chemistry and circulation we present records of biogenic opal percentage and burial rate in 12 piston cores from the atlantic and indian sectors of the southern ocean these records provide a detailed quantitative description of changing patterns of opal deposition over the last 450 kyr the striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the southern ocean under different global climate conditions three broad depositional patterns can be distinguished northernmost records 39 42 s latitude are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity records from cores just north of the present antarctic polar front 46 49 s show even larger increases in opal burial rate during glacial intervals but have variance concentrated in the 100 and 23 kyr bands southernmost records 51 55 s are completely out of phase with those to the north with greatly reduced opal burial rates during glacial periods taken as a whole the opal records show no evidence for the increased total antarctic productivity predicted by recent geochemical models of atmospheric co2 variability the areal expansion of southern ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial interglacial opal patterns the excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region however local circulation changes may act to modify this basic signal possibly accounting for the observed differences in the opal variance spectra

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

distribution of organic walled dinoflagellate cysts in surface sediments of the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre abstract thirty two surface sediment samples from the southern ocean eastern atlantic sector between the subtropical front and the weddell gyre were investigated to provide information on the distribution of modern organic walled dinoflagellate cysts in relation to the oceanic fronts of the antarctic circumpolar current acc a clearly distinguishable distribution pattern was observed in relation to the water masses and fronts of the acc the dinoflagellate cysts of species characteristic of open oceanic environments such as impagidinium species are highly abundant around the subtropical front whereas south of this front cosmopolitan species such as nematosphaeropsis labyrinthus and the cysts of protoceratium reticulatum characterise the transition from subtropical to subantarctic surface waters the subantarctic surface waters are dominated by the cysts of heterotrophic dinoflagellates such as protoperidinium spp and selenopemphix antarctica the cysts of protoperidinium spp form the dominant part of the assemblages around the antarctic polar front whereas s antarctica concentrations increase further to the south the presence of s antarctica in sediments of the maud rise a region of seasonal sea ice cover reflects its tolerance for low temperatures and sea ice cover a previously undescribed species cryodinium meridianum gen nov sp nov has a restricted distribution pattern between the antarctic polar front and the acc weddell gyre boundary

geochronology and geochemistry of middle permian middle triassic intrusive rocks from central eastern jilin province ne china constraints on the tectonic evolution of the eastern segment of the paleo asian ocean abstract to constrain the permian early mesozoic tectonic evolution of the eastern segment of the paleo asian ocean we conducted zircon u pb dating and whole rock geochemical analyses on six middle permian middle triassic intrusive plutons in central eastern jilin province ne china zircons from the six plutons display distinct oscillatory zoning and striped absorption in cathodoluminescence cl images and th u ratios of 0 11 1 41 indicating a magmatic origin zircon u pb dating indicates that the intrusive rocks formed in the middle permian ca 260 ma to middle triassic ca 245 ma in central eastern jilin province the middle permian and middle triassic plutons are composed mainly of strongly deformed monzogranites with affinities to adakitic rocks which are formed from partial melting of thickened mafic lower crust in contrast the late permian the early triassic plutons in central eastern jilin province consist of a bimodal association including gabbros and granitoids and deformed monzonites which typically form in extensional settings these observations along with the results of previous studies on early middle permian granitoids in western jilin province indicate that the eastern segment of the paleo asian ocean underwent the initial closure in central western jilin province during the middle permian and the final closure in eastern jilin province in the middle triassic

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

biological fractionation of silicon isotopes in southern ocean surface waters 1 the fractionation of silicon isotopes by diatoms during silicification i e opaline cell wall formation provides a new tool for paleoceanographic studies of the silicon cycle here we examine the natural variations of the 30si 28si ratio in silicic acid si oh 4 and biogenic silica bsio2 in surface waters of the antarctic circumpolar current acc along 170 w the results provide direct evidence of biologically mediated fractionation of silicon isotopes with an enrichment factor of between 1 1 and 1 9 depending on the model employed comparison of the mass flux of bsio2 captured in sediment traps deployed in the study area with the silicon isotopic composition of that material establishes a direct linkage between diatom dynamics in surface waters and the isotopic signature of exported particles we calculated si oh 4 no3 utilization ratios from variations in silicon and nitrogen isotopic ratios in surface waters and sediment traps that agree well with direct observations of 4 1 in this region this work supports the use of variations in silicon isotopes in sedimentary opal as a proxy for relative si oh 4 utilization in surface waters

structural styles and basin evolution in eromanga region eastern australia the eromanga region of eastern australia has undergone at least four major tectonic cycles the results of which are recognized in the structures seen on seismic sections the late proterozoic early phanerozoic cycle ended with the formation of the thomson foldbelt which forms basement in the region the subsequent reactivations of the fault systems within this basement and deeper lithosphere have produced the structural styles now important as exploration targets most reactivations are interpreted as resulting from crustal shortening events affecting sedimentary strata deposited in an epicontinental shallow water environment with small strike slip adjustments affecting some structures the dominant style of deformation evident from the seismic sections is that seen across high angle thrust faults in other parts of the world with the amount of overthrusting being comparatively small generally the maximum throw on faults in the devonian strata can be measured in thousands of meters whereas those in the permian triassic and jurassic cretaceous strata are a few hundred meters at most the devonian sequences of the adavale basin and associated troughs were deformed during two carboniferous events the first with crustal shortening in a north south direction and the second in an east west direction associated small strike slip movements were accommodated along a number of faults including the warrego grenfield warbreccan and canaway faults southwest of our study area in the permian triassic cooper basin other workers have interpreted a northwest southeast crustal shortening event during the late permian and another wrench induced northeast southwest crustal shortening during the triassic during the middle tertiary a crustal shortening event regionally affected the jurassic cretaceous eromanga basin sequence and older sedimentary rocks this event is seen pro inently in a deformation zone between the canaway and cunnavalla faults with the direction of crustal shortening being northeast southwest small strike slip movements are interpreted as partially decoupling events from neighboring provinces the adavale basin and cheepie shelf to the east and southeast and the cooper basin and warbreccan dome to the southwest and northwest respectively in this partial decoupling the canaway cunnavalla warrego and warbreccan faults are interpreted as playing an important role the basin modifying tectonic episodes within the lithosphere control structural style these relatively small scale events have resulted in structures that provide attractive petroleum prospects

overlapping sr nd hf o isotopic compositions in permian mafic enclaves and host granitoids in alxa block nw china evidence for crust mantle interaction and implications for the generation of silicic igneous provinces abstract in general the mantle provides heat and or material for the generation of the silicic igneous provinces sips the rarity of mafic microgranular enclaves mmes however hampers understanding of the mantle s role in generating sips and the process of crust mantle interaction the widespread distributed mmes in the newly reported alxa sip provide an opportunity to study these processes this study integrates in situ zircon u pb age and hf o isotope analyses whole rock geochemistry and sr nd isotope results for the mmes and host granitoids in the alxa block sims zircon u pb dating reveals that there are two generations of mmes and host granitoids the mmes in the bayannuoergong batholith were formed at ca 278 ma similar to the age 280 ma of host granitoids and the mmes and host granitoids in the yamaitu pluton were formed at ca 272 270 ma all mmes have relatively low sio 2 50 7 61 4 wt and th 0 8 2 8 ppm but relatively high mgo 2 6 4 9 wt cr 23 146 ppm and ni 6 38 ppm contents compared to the host granitoids with sio 2 63 6 77 5 wt th 5 2 41 ppm mgo 0 23 2 1 wt cr 10 38 ppm and ni 5 14 ppm all mmes have whole rock sr nd and zircon hf o isotope compositions similar to their corresponding host granitoids the 280 ma mmes have lower whole rock e nd t 13 5 and higher initial 87 sr 86 sr values 0 7095 and zircon 18 o values 6 3 compared to the e nd t 11 5 initial 87 sr 86 sr values 0 7070 and zircon 18 o values 5 6 of the 270 ma mmes the occurrences of quartz xenocrysts k feldspar megacrysts corroded feldspars and acicular apatites indicate that the mmes are the products of the mixing between mantle and crust derived magmas the striking similarities in the zircon hf o isotopic compositions in both mme host granitoid pairs indicate that the granitoids and mmes have similar sources the granitoids are proposed to be mainly sourced from magmas generated by remelting of newly formed mafic rocks which were generated by earlier basaltic magmas underplating or injected into the mid to lower crust the continuing basaltic magma underplating and remelting of earlier formed mafic rocks in the mid to lower crust indicate that the mantle provided both heat and materials for the generation of the alxa sip the scenario also suggests that basaltic magma underplating may play a more important role in the crustal growth in the alxa sip than it is generally recognized in other sips

estimates of late quaternary mode and intermediate water silicic acid concentration in the pacific southern ocean the southern ocean plays a critical role in the exchange of carbon between the ocean and atmosphere over glacial interglacial timescales hypotheses used to explain late quaternary variations in atmospheric carbon dioxide co2 implicate changes in the nutrient dynamics and circulation of the southern ocean here we present silicon isotope delta si 30 records of late quaternary sponges and diatoms from the nz sector of the southern ocean analysis of our sponge delta si 30 records strongly suggests that the silicic acid concentration at mode and intermediate depths was higher during the lgm and the deglacial period compared to the present day our diatom delta si 30 record suggests biological productivity near of the polar front was greater during the deglacial period but not significantly different during the lgm compared to the present day taking our dataset in context with other regional paleoceanographic records we interpret the predicted elevation in lgm and deglacial silicic acid concentration to reflect a shoaling of water masses during the lgm and leakage of excess southern ocean dissolved silicon during the deglacial period c 2016 elsevier b v all rights reserved

crustal architecture across phanerozoic australia along the eromanga brisbane geoscience transect evolution and analogues abstract the crustal architecture across phanerozoic australia has been established from seismic data along an 1100 km long east west transect the eromanga brisbane geoscience transect this has enabled a better understanding of deep structures and processes that have controlled the development of major sedimentary basin systems it has shown that crustal dynamics throughout geological history have played an important role in the development of these sedimentary basins and that structures developed during the early palaeozoic have influenced and continue to influence basin systems the transect crosses three major basement provinces of the tasman orogenic system in eastern australia the thomson northern lachlan and new england orogens the basement geology in the transect region has until now been only poorly understood because it is largely obscured by the mesozoic cover rocks of the eromanga surat and clarence moreton basins the transect interpretation has firmly identified crustal scale ramp structures multiple intra crustal detachment surfaces strike slip fault architecture lower crustal magmatism underplating mono remobilisation and intra crustal terranes in the geological reconstructions of southern queensland the boundaries between the orogens the foyleview and burunga mooki geosutures have been identified as lithospheric scale structures that have influenced the evolution of the tasman orogenic system as a whole

north atlantic deep water export to the southern ocean over the past 14 myr evidence from nd and pb isotopes in ferromanganese crusts the intensity of north atlantic deep water nadw production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate here we present a new approach to reconstruct the overall strength of nadw export from the north atlantic to the southern ocean over the past 14 myr applying the deep water nd and pb isotope composition as recorded by ferromanganese crusts and nodules we present the first long term nd and pb isotope time series for deep southern ocean water masses which are compared with previously published time series for nadw from the nw atlantic ocean these data suggest a continuous and strong export of nadw or a precursor of it into the southern ocean between 14 and 3 ma an increasing difference in nd and pb isotope compositions between the nw atlantic and the southern ocean over the past 3 myr gives evidence for a progressive overall reduction of nadw export since the onset of northern hemisphere glaciation nhg the nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37 depending on location

orogen perpendicular structures in the central tasmanides and implications for the paleozoic tectonic evolution of eastern australia the curvilinear e w structures of the southern thomson orogen are approximately orthogonal to the general n s structural trend of the tasmanides of eastern australia the origin of these orogen perpendicular structures and their implications to tectonic reconstructions of eastern gondwana are not fully understood here we use geophysical data to unravel the geometry kinematics and possible timing of major structures along the boundary between the thomson orogen and the southern tasmanides delamerian and lachlan orogens aeromagnetic data from the southern thomson orogen show wnw e w and or ene trending structural grains corresponding to relatively long wavelength linear geophysical anomalies kinematic analyses indicate strike slip and transpressional deformation along these geophysically defined faults structural relationships indicate that faulting took place during the benambran late ordovician to middle silurian and tabberabberan late early to middle devonian orogenies however some of the described crustal scale structures may have developed in the cambrian during the delamerian orogeny interpretation of deep seismic data shows that the crust of the southern thomson orogen is substantially thicker than the lachlan orogen crust which is separated from the thomson orogen by the north dipping olepoloko fault a major lithospheric scale change across this boundary is also indicated by a contrast in seismic velocities together with evidence for the occurrence of delamerian deformation in both the koonenberry belt and northeastern thomson orogen and a significant contrast in the width of the northern tasmanides versus the southern tasmanides it appears that the southern thomson orogen may represent the locus of orogen perpendicular segmentation which may have occurred in response to along strike plate boundary variations

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

lower crustal involvement in upper crustal thrusting summary basement structures mapped in the devonian adavale basin eastern australia indicate two styles of lower crustal involvement in the formation of upper crustal structures the first style is typified by thrust features in the upper crustal sedimentary section and basement a response to lower crustal shortening over a wide area the second style includes lower crustal thrusting and thickening in a limited region with associated uplift of the upper crust these two styles suggest that the upper and lower crust were mechanically decoupled during palaeozoic compressive episodes 1 tectonic structures in the upper crust basement involved thrust faults have been mapped in the southern adavale basin australia using both bureau of mineral resources and industry seismic data finlayson et al in press these faults were grouped into two sets those striking predominantly north south gumbardo and corona and those striking predominantly east west como paradise and grenfield and form an orthogonal network of faults in this region fig 1 mechanical considerations dictate that these orthogonal thrust sets did not form synchronously relative thinning of stratigraphic units over basement faults has been used to date uplift movement on these faults retrodeformed sections produced by restoring the mid devonian cooladdi dolomite unit or its lateral equivalent were used to date initiation of thrusting the sections show that the east west striking thrusts developed first during the lower devonian in response to north south crustal shortening the thrust faults were separated by tear faults which transferred the relative strain between the fault blocks dalhstrom 1970 the second phase of tectonic activity commenced in the late devonian and continued into the carboniferous this phase is interpreted to be due to east west crustal shortening and reversed the roles of the thrust and tear faults developed during the previous episode leven et al in press the north south striking gumbardo and corona faults were reactivated as thrusts while previous thrusts acted as transfer faults for this deformation during the latter portion of this second tectonic episode sediments of the adavale basin were deformed into large scale predominantly north south trending folds the folding style of this later deformation contrasts with the faulting associated with the earlier episode carboniferous erosion which veevers et al 1984 suggest was caused by an extensive ice sheet effectively removed most of the sediment of the newly formed adavale basin leaving only the remnant synclinal cores these are represented in the southern adavale basin region by the cooladdi quilpie and blackwater troughs the wavelength of this basin wide folding is about 100 km and the amplitude in the case of the cooladdi trough exceeds 8 km but diminishes towards the west the warrabin trough to

phanerozoic granitoids in the central and eastern parts of central asia and their tectonic significance abstract the widespread occurrence of voluminous granitoids is a typical characteristic of the central asian orogenic belt caob in the central and eastern parts of central asia the granitoids occupy a total area more than 8 million km2 with three major area peaks at cambro ordovician carboniferous permian and jurassic six zircon age peaks at ca 500 430 370 330 300 290 260 210 170 and 145 110 ma the early paleozoic granitoids 540 440 ma with age peak at ca 500 ma mainly occur in the northwestern caob and are of calc alkaline i type they probably formed in a subduction setting 500 480 ma within the paleo asian ocean pao and subsequent microcontinental collision ca 460 ma the middle paleozoic granitoids 430 370 ma predominately occur in the nw and southern caob and are characterized by a high k calc alkaline affinity suggesting an accretionary and or a collisional setting the late paleozoic 350 260 ma granitoids are widespread in the caob and formed in variable tectonic settings within an intra continental regime or active continental margins in the pao and in the evolving mongol okhotsk ocean moo carboniferous granitoids 350 300 ma in the northern and northwestern caob exhibit a type alkaline features and formed in a post accretionary settings whereas granitoids in the southern caob show i type calc alkaline features and were generated in an arc setting permian granitoids 290 270 ma are predominantly of i a a type with alkaline signatures associated with coeval mafic magmatism and suggesting a post collisional or intraplate setting contemporaneous with a large igneous province lip in the tarim craton some 270 250 ma calc alkaline granitoids also occur in the southernmost caob combined with 250 245 ma high sr y granitoids these rocks reflect final closure of the pao during 270 250 ma early mesozoic mainly triassic granitoids occur mainly in the eastern caob or eastern central asia the early phase granitoids 250 230 ma are of i and s types whereas the mid and late phase granitoids ca 230 190 ma are of a type and transitional i a type or highly fractionated i type all these granitoids occur in variable settings intraplate post orogenic and continental arc related to three tectonics regimes namely the paleo asian ocean pao the mongol okhotsk ocean moo and the paleo pacific ocean ppo late mesozoic granitoids mainly occur in eastern central asia and were emplaced during 6 major magmatic events at 190 180 180 165 165 145 145 135 135 100 and 100 60 ma the 190 165 ma granitoids are of i type calc alkaline high k calc alkaline and evolved along active margins related to the mongol okhotsk and paleo pacific ocean domains the 145 120 ma granitoids are highly fractionated i transitional i a or a types with high k calc alkaline shoshonitic signatures the magmatic evolution from the late jurassic to early cretaceous coincided with a tectonic transition from contractional thickened crust to extensional thinning the 120 65 ma granitoid magmatism displays a southeastward younging trend suggesting a roll back of the paleo pacific oceanic plate the granitoids in the caob of eastern central asia show variable whole rock nd and hf in zircon isotopic compositions and most have juvenile signatures in some regions e g altai junggar and great xing an the volume of juvenile and slightly juvenile crust

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid cretaceous vertebrate fossil localities in the winton formation queensland australia the winton formation of central queensland is recognized as a quintessential source of mid cretaceous terrestrial faunas and floras in australia however sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited the intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved winton formation in the eromanga basin including isisford lark quarry and bladensburg national park twenty three facies and six repeated facies associations were documented indicating a mosaic of marginal marine to inland alluvial depositional environments these developed synchronously with the final regression of the eromanga seaway from central australia during the late albian early turonian investigations of regional and local scale structural features and outcrop core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin significant palaeoenvironmental differences exist between the lower and upper portions of the preserved winton formation warranting informal subdivisions a lower tidally influenced fluvial deltaic member and an upper inland alluvial member this work further demonstrates that the isisford fauna is part of the lower member of the preserved winton formation whereas fossil localities around winton including lark quarry and bladensburg national park are part of the upper member of the winton formation these results permit a more meaningful framework for both regional and global comparisons of the winton flora and fauna

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

a classification of thrust fronts variations in structural style at thrust fronts are examined to determine whether they represent different stages of typical thrust sheet development or unique events as orogenic stresses declined thrust fronts are classified as buried or emergent in which either the sole thrust died out in the subsurface or emerged to the synorogenic surface buried thrust fronts are subdivided into two types type 1 fronts end in broad zones of low strain type 2 fronts end in zones of high strain emergent thrust fronts may display significant horizontal displacement strongly emergent or limited displacements of about 1 km weakly emergent tip stick thrust fronts exhibit high strains and out of sequence thrusting different types of thrust fronts are linked by transitional tip li e anticlines and strike slip zones most thrust front types represent different stages of typical thrust sheet development but those in type 1 display atypical development unique to thrust fronts