three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

heavy mineral sands in the eucla basin southern australia deposition and province scale prospectivity the marine eucla basin in southern australia is emerging as a major new heavy minerals province in australia beach placers are associated with a series of partially buried cenozoic coastal barrier sands formed along an arcuate 2 000 km long basin margin the trace of which is up to 320 km inland of the present coastline the presence of high grade deposits with dominant zircon over ilmenite and lesser amounts of rutile and leucoxene was established with the discovery of the jacinth and ambrosia heavy mineral deposits in late 2004 an additional 10 heavy mineral prospects were subsequently identified and are at various stages of evaluation the eucla basin and its adjacent paleovalley system have a large areal extent that contains a complicated succession of marine and nonmarine strata spanning a wide range of depositional environments four distinct constructional phases for the development of shorelines can be recognized and correlated with major third order sea level events established by others from the marine depositional record as occurring during the middle eocene 42 5 ma late middle eocene 39 36 ma late eocene 36 34 ma and miocene pliocene 15 2 6 ma prevailing westerly winds built extensive dune systems by longshore drift sediment movement was from west to east detrital zircon rocks from the ooldea and barton barriers show a distribution of zircon age that is consistent with the proterozoic musgrave province to the north of the basin as the dominant primary source area of the heavy minerals with a contribution from the albany fraser orogen to the west the likelihood is that these heavy minerals have been recycled via sedimentary basins that flank the musgrave province and include the neoproterozoic to cambrian officer basin and permian to mesozoic deposits of the bight basin our current depositional model is summarized as follows 1 initial rapid transgression and deposition of a shallow marine sand sheet subsequently overlain by shallow marine limestone during middle eocene 2 a major eocene transgression and deposition of a shelf barrier and lagoonal shoreface marine complex during the late middle eocene 3 further transgression and highstand deposition during the late eocene 4 renewed transgression of barrier lagoonal and possibly flooding deltaic sand blanket in the southeastern coastal plain with neotectonic uplift tilting in the western eucla margin during mio pliocene time each stage of reworking increased the potential for heavy mineral concentration in placer deposits

paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

the discovery of emerged boring bivalves at cape omaezaki shizuoka japan evidence for the 1361 ce tokai earthquake along the nankai trough abstract this study found several in situ fossil shells of the boring bivalve penitella gabbii exposed in mudstone at an elevation of 1 05 1 35 m above mean sea level in a wave cut platform at cape omaezaki shizuoka central japan this region faces the nankai trough where great earthquakes m 8 occur with a recurrence interval of 90 200 years based on the upper limit of living p gabbii 0 8 m above mean sea level and geodetic data the total uplift of shells since the time of their active is estimated to be up to 2 5 m using 14c dates from the uplifted terrace deposits around the study area and shell fossils we propose that the emerged fossils provide new evidence for the pairing of the 1361 ce shohei koan tokai earthquake rupture of suruga trough and the eastern half of the nankai trough with the 1361 ce shohei koan nankai earthquake rupture of the western half of the nankai trough

the influence of tectonics on flank margin cave formation on a passive continental margin naracoorte southeastern australia abstract intensive cave development within the highly porous and permeable eocene middle miocene gambier limestone in southeastern south australia is restricted to a 1 11 km area at naracoorte the caves are overwhelmingly horizontal consisting of large solutional domes connected by smaller passages with bell holes small pendants and large non directional scallops on the walls and ceilings orientation is strongly controlled by nw se joints cave entrances have been opened by subsequent collapse and breakdown is common the caves are located on the kanawinka fault escarpment which was uplifted in the late miocene early pliocene and then overlain by a series of pleistocene carbonate strandline dunes deposited as the sea retreated following a late miocene transgression the coastline lay along the kanawinka escarpment at 0 9 1 1 ma when the caves formed just inland of the shoreline within the zone of enhanced dissolution at the seaward margin of the freshwater lens they have the typical flank margin cave morphology except that joint development adjacent to the fault caused the strong linear orientation parallel to the coastline the beach dune deposited to the west of the kanawinka escarpment shows that sea level had dropped sufficiently to completely drain the caves at 780 880 ka cave development was therefore confined to a period spanning 0 8 1 1 ma continuing gradual uplift through the pleistocene means that the caves are now 100 km inland obscuring the essentially coastal nature of the naracoorte karst speleogenesis at naracoorte reflects the interaction of neotectonics with coastal dissolution and emphasizes the role that tectonism can play in pleistocene karst development even on passive continental margins where glacio eustatic sea level fluctuations are generally ascribed as the dominant role

stratigraphic evidence of historical and prehistoric tsunamis on the pacific coast of central japan implications for the variable recurrence of tsunamis in the nankai trough abstract to complement historical written records of tsunamis in the nankai trough and reconstruct prehistoric tsunami records we conducted a coring survey at a coastal lowland in mie prefecture central japan we found 10 sand layers deposited from about 4500 to 500 years ago the layers are interpreted as tsunami deposits because of the presence of abundant bioclasts of marine organisms and sedimentary structures such as alternating sub layers of sand and silt rip up clasts and upward fining structures all of which are common in modern tsunami deposits at the study site no substantial seawater inundations and sand depositions have been recorded even for the largest typhoons to ever hit the region there are historical accounts of earthquake and tsunami damage along the nankai trough in 1498 1361 1096 887 and 684 ce estimated ages of the youngest three sand layers overlap well with tsunamis in 1498 1096 and 684 ce our results support the hypothesis suggested by archaeological studies that the 684 ce rupture extended farther eastward than the historical record indicates or that another tsunami occurred at some time close to 684 ce we did not find any sand layers that were definitely correlated with the tsunamis of 1361 and 887 ce which are thought to have occurred by multi segment ruptures of the nankai trough that includes the segment directly offshore from the study site if the sand layers found at the study site were deposited by the tsunamis of 1498 1096 and 684 ce and if the tsunamis of 1361 and 887 ce did not inundate the study site the tsunami recurrence interval during the relevant time period was about 400 years this finding does not support the widely believed hypothesis that earthquakes and tsunamis occur at regular intervals of approximately 100 years in this area in addition similar to the historical tsunamis intervals of geologically recorded prehistoric tsunamis at the study site vary from about 100 to 600 years the hypothesis of variable recurrence of earthquakes and tsunamis along the nankai trough should be tested by future geological and historical studies in unbiased way

geological evidence for past large earthquakes and tsunamis along the hikurangi subduction margin new zealand abstract the hikurangi subduction margin new zealand has not produced large subduction earthquakes within the short written historic period 180 years and the potential of the plate interface to host large m 7 to great m 8 earthquakes and tsunamis is poorly constrained the geological record of past subduction earthquakes offers a method for assessing the location frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments we review evidence of holocene coseismic coastal deformation and tsunamis at 22 locations along the margin a consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake to identify possible subduction earthquakes we use temporal correlation of earthquakes combined with the type of earthquake evidence likely primary fault source and the earthquake certainty ranking we identify 10 past possible subduction earthquakes over the past 7000 years along the hikurangi margin the last subduction earthquake occurred at 520 470 years bp in the southern hikurangi margin and the strongest evidence for a full margin rupture is at 870 815 years bp there are no apparent persistent rupture patches suggesting segmentation of the margin is not strong in the southern margin the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved the pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes demonstrating different modes of slip behaviour occur on the central hikurangi margin evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record large uncertainties remain in regard to evidence of past subduction earthquakes on the hikurangi margin with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes however areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future

holocene relative sea level change and rate of sea level rise from coastal deposits in the toyooka basin western japan this study presents relative sea level rsl change from 11 200 to 500 cal bp in the toyooka basin western japan diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment

topo oz insights into the various modes of intraplate deformation in the australian continent abstract as the fastest lowest flattest and amongst the most arid of continents australia preserves a unique geomorphic record of intraplate tectonic activity evidencing at least three distinct modes of surface deformation since its rapid northward drift commenced around 43 million years ago at long wavelengths several 1000s km systematic variations in the extent of neogene marine inundation imply the continent has tilted north down southwest up at intermediate wavelengths several 100s km several undulations of 100 200 m amplitude have developed on the 1 10 myr timescale at still shorter wavelengths several 10s km fault related motion has produced local relief at rates of up to 100 m myr over several million years the long wavelength north down tilting can be related to a dynamic topographic effect associated with australia s northward drift from the geoid low dynamic topography low now south of the continent to the geoid high dynamic topography low centred above the south east asian and melanesian subduction zones the short wavelength fault related deformation is attributed in time to plate wide increases in compressional stress levels as the result of distant plate boundary interactions and in space in part to variations in the thermal structure of the australian lithosphere at the intermediate wavelengths transient low amplitude undulations can be ascribed to either lithospheric buckling or the development of instabilities in the thermal boundary layer beneath the lithosphere in the latter case topographic asymmetries suggest the australian lithosphere is moving north with respect to the mantle beneath providing a unique attribution to the progressive alignment of seismic anisotropy and absolute plate motion observed near the base of the australian lithosphere

global cooling initiated stony deserts in central australia 2 4 ma dated by cosmogenic 21ne 10be stony deserts are durable indicators of aridity but until now have not been directly dated using 21ne and 10be produced in surface rocks by cosmic rays we show that australian stony deserts formed 2 4 ma at the time when global cooling initiated the quaternary ice ages and intensified aridity induced major landscape changes in central australia this is the first direct determination of stony desert ages using a new method for determining cosmogenic 21ne in the presence of various neon components from other sources

millennial scale crustal movements inferred from holocene sedimentary succession of the omoto plain northern sanriku coast northeast japan relevance for modeling megathrust earthquake cycles abstract crustal movements on a millennial timescale 103 104 years are important data for assessing the deformation of subduction zones during megathrust earthquake cycles such data did not exist until recently for the sanriku coast near the source region of the 2011 tohoku oki earthquake since the 2011 earthquake studies of holocene sedimentary successions have documented subsidence on the central to southern segment of the sanriku coast on a millennial timescale but comparable data are lacking for the northern sanriku coast this study derived millennial scale crustal movements from a well dated holocene sedimentary succession in the omoto plain on the northern sanriku coast sedimentary and fossil evidence record the following sequence of environmental changes influenced by sea level changes upward growth and landward progradation of a barrier and flood tidal delta from 10 000 9000 cal bp an estuarine environment from 9000 to 8000 cal bp after growth and progradation of the barrier and flood tidal delta ceased and a regressive delta and subsequent fluvial environment after 8000 cal bp thick deposit of delta to floodplain sediment since mid holocene is not apparent in the omoto plain whereas this feature typical of subsidence area is documented along the central sanriku coast although the absolute direction of the vertical deformation trend could not be well constrained in the study area because of compaction effects the evidence indicates that subsidence during the mid and late holocene was either absent or not noticeable on the omoto plain this difference in deformation histories corresponds to a contrast in coseismic subsidence during the 2011 earthquake between the northern sanriku coast small subsidence and the central to southern sanriku coast large subsidence the results of this study suggest that the northern and central to southern parts of the sanriku coast should be considered separately when assessing regional crustal deformation related to subduction

late holocene tectonics and paleoseismicity southern cascadia subduction zone holocene deformation indicative of large subduction zone earthquakes has occurred on two large thrust fault systems in the humboldt bay region of northern california displaced stratigraphic markers record three offsets of 5 to 7 meters each on the little salmon fault during the past 1700 years smaller and less frequent holocene displacements have occurred in the mad river fault zone elsewhere as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded carbon 14 dates suggest that the faulting subsidence and uplift events were synchronous relations between magnitude and various fault offset parameters indicate that earthquakes accompanying displacements on the little salmon fault had magnitudes of at least 7 6 to 7 8 more likely this faulting accompanied rupture of the boundary between the gorda and north american plates and magnitudes were about 8 4 or greater

late pleistocene and halocene sea level changes in japan implications for tectonic histories and mantle rheology abstract it is very important to separate the tectonic and glacial isostatic components in the observed holocene and late pleistocene sea level changes in tectonically active areas such as japan for studying tectonic processes and for constraining mantle rheology the separation can be achieved by considering the spatial dependence of the relative sea level on the geometry of the coastline around the site where sea level is evaluated in fact the relative sea level caused by the last deglaciation at sites in the embayment such as tokyo and osaka has a sea level curve with a high stand at mid holocene and that site situated on the tip of peninsula has a sea level curve culminating towards the present the geometric effect also causes the regional difference of the sea level variations in the late glacial phase in the japanese islands the regional difference of the predicted relative sea level is about 5 m at 6000 years ago 20 m at 10 000 years ago and 30 m at 18 000 years ago comparison between observations and predictions indicates that the observations at several sites in japan are consistent with the predicted sea level variations more systematic data is required for the period 18 000 years ago to the present in order to examine tectonic processes and mantle rheology

a new rhaetian δ13corg record carbon cycle disturbances volcanism end triassic mass extinction ete abstract the links between large scale volcanism carbon cycle perturbations and the biotic crises at the end triassic extinction event ete are not well understood the ete seems to be marked by three carbon isotope excursions cies likely triggered by different eruptive phases of the central atlantic magmatic province camp these three cies appear to occur during the late rhaetian close to the triassic jurassic boundary tjb but the relative timing connecting the volcanism carbon perturbations and extinctions is still subject to debate resulting from i the difficulties in long distance biostratigraphic correlations of rhaetian successions due to the step like extinction pattern characterizing the ete and to the lack of globally correlatable key fossil group s across the system boundary ii the limit of coverage of available 13c profiles to the system boundary interval rather than the entire rhaetian iii the inherent difficulties in correlating cies without clear biostratigraphic markers here we present a 13corg curve from the lombardy basin which covers for the first time the entire rhaetian using this chemostratigraphy we propose two possible correlations option 1 and option 2 with other late rhaetian to early hettangian successions worldwide these two possible correlations rely on a combination of paleontological ammonoids pollens conodonts lithostratigraphic and geochemical constraints option 2 in particular has important implications for the causality and geochronology of the ete events by suggesting that the sharp negative peak usually considered to be the initial cie in the lombardy might represent a carbon perturbation within the negative trend of the main cie this implies that a reconsideration of the succession of biotic events occurring during this time interval is required

deglacial changes in flow and frontal structure through the drake passage the oceanic gateways of the drake passage and the agulhas current are critical locations for the inflow of intermediate depth water masses to the atlantic which contribute to the shallow return flow that balances the export of deep water from the north atlantic the thermohaline properties of northward flowing intermediate water are ultimately determined by the inflow of water through oceanic gateways here we focus on the less well studied cold water route through the drake passage we present millennially resolved bottom current flow speed and sea surface temperature records downstream of the drake passage spanning the last 25 000 yr we find that prior to 15 ka bottom current flow speeds at sites in the drake passage region were dissimilar and there was a marked anti phasing between sea surface temperatures at sites upstream and downstream of the drake passage after 14 ka we observe a remarkable convergence of flow speeds coupled with a sea surface temperature phase change at sites upstream and downstream of drake passage we interpret this convergence as evidence for a significant southward shift of the sub antarctic front from a position north of drake passage this southward shift increased the through flow of water from the pacific likely reducing the density of atlantic intermediate water the timing of the southward shift in the sub antarctic front is synchronous with a major re invigoration of atlantic meridional overturning circulation with which we argue it may be linked

the tilting continent a new constraint on the dynamic topographic field from australia a pronounced latitudinal asymmetry in the present day morphology of the australian continental shelf is reflected in neogene stratigraphic relationships the northern australian margin has a broad shelf typically 200 500 km wide and a neogene record of stratal onlap relative to the continent sea levels are currently as high as at any stage during the neogene in contrast the southern shelf is typically less than 100 km wide and shows a record of progressive offlap with neogene palaeo shorelines commonly many hundreds of kilometres inland at elevations up to 250 m above present day sea level this continental scale reciprocal stratigraphy implies 250 300 m n down ssw up apparent vertical motion with respect to sea level since the mid miocene the apparent vertical motion can be attributed to variations in dynamic topography and the geoid along australia s nne plate circuit specifically the movement of the southern margin off the dynamic topography low geoid low presently centred on the australian antarctic discordance and the northern margin towards a dynamic topography low geoid high associated with the subduction realm to the north variations in the geoid appear to account for about 10 of the total apparent motion depending on assumptions about how the geoid field has evolved during australia s northward motion this inferred neogene continental scale dynamic n s tilting rate of 15 20 m myr provides a compelling new constraint on the nature of the earth s dynamic topographic field 2007 elsevier b v all rights reserved

an assessment of geochemical preparation methods prior to organic carbon concentration and carbon isotope ratio analyses of fine grained sedimentary rocks 1 this study summarizes organic carbon isotope 13c and total organic carbon toc data from a series of tests undertaken to provide an appropriate methodology for pre analysis treatment of mudstones from an upper carboniferous sedimentary succession in order to develop a consistent preparation procedure the main treatments involved removing both inorganic carbonate and hydrocarbons which might be extraneous before 13c and toc analysis the results show that decarbonating using hydrochloric acid causes significant reduction in 13c and total carbon tc of the bulk material due to the removal of inorganic carbonate these changes are most pronounced where soluble calcium carbonate rather than ca mg fe carbonate is present deoiled samples show only slightly higher mean 13c where visible bitumen was extracted from the bulk sample moreover the isotopic signatures of the extracts are closely correlated to those of their respective bulk samples suggesting that small yields of hydrocarbons were generated in situ with no isotopic fractionation in addition further 13c and tc analyses were performed on samples where mixing of oil based drilling mud with brecciated core material had been undertaken brecciated mudstone material did not display distinct isotopic signals compared to the surrounding fine grained material overall we show that the most accurate assessment of bulk organic carbon isotopes and concentration in these samples can be achieved through decarbonating the material prior to measurement via the rinse method however our results support recent findings that pre analysis acid treatments can cause variable and unpredictable errors in 13c and toc values we believe that despite these uncertainties the findings presented here can be applied to paleoenvironmental studies on organic matter contained within sedimentary rocks over a range of geological ages and compositions

landscape formation at the deuteronilus contact in southern isidis planitia mars implications for an isidis sea abstract two of the most widely studied landforms that are associated with a putative ocean that filled the northern hemisphere of mars are 1 the vastitas borealis formation vbf plain units that cover a larger portion of the northern lowlands of mars and 2 a candidate paleoshoreline e g the deuteronilus contact which represents the outer margin of the vbf the vbf and the deuteronilus contact are interpreted to result from a short lived late hesperian ocean that readily froze and sublimated similar landforms are also present in the impact basin of isidis planitia and suggest formation processes comparable to those that formed the vbf and the deuteronilus contact in the northern lowlands our study of the deuteronilus contact in isidis revealed geologic evidence that possibly supports the existence of a late hesperian early amazonian isidis sea for example numerous valleys that are incised into the plains of the southern isidis basin rim between 82 90 e and 3 6 n and trend a few tens of kilometers to the north following the general topographic gradient toward the center of isidis planitia a few of them reach the deuteronilus contact and continue as sinuous ridges in the isidis interior plains iip based on our findings we conclude that the geologic setting along the deuteronilus contact including the valleys and ridges is a result of 1 late hesperian short term fluvial activity 2 a late hesperian early amazonian short lived isidis sea that readily froze 3 subglacial drainage and esker formation and 4 subsequent sublimation of the proposed isidis ice sheet although the fluvio glacial model we introduce in our manuscript cannot fully explain the geologic setting possible alternative formation models including relief inversion and fluvio volcanic scenarios are even less capable in explaining the observed geologic setting along the deuteronilus contact

great cascadia earthquakes and tsunamis of the past 6700 years coquille river estuary southern coastal oregon cascadia subduction zone earthquakes dropped tidal marshes and low lying forests to tidal flat elevations 12 times in the last 6700 cal yr b p at the coquille river estuary in southwestern oregon the youngest buried soil preserved in tidal marsh deposits near the estuary mouth records the a d 1700 earthquake that ruptured the entire cascadia margin eleven other buried marsh and upland soils found in tributary valleys of the estuary provide repeated evidence for rapid lasting relative sea level rise interpreted as coseismic subsidence additional stratigraphic criteria supporting a coseismic origin for soil burial include lateral soil correlation over hundreds of meters fossil diatom assemblages that indicate a maximum of 1 2 3 0 m of submergence and sand deposits overlying buried soils consistent with earthquakeinduced tsunamis that traveled 10 km up the estuary twelve earthquakes occurred in the last 6500 6720 cal yr b p recurring on average every 570 590 yr intervals between earthquakes varied from a few hundred years to over 1000 comparisons of the coquille record to earthquake histories from adjacent sites in oregon southwestern washington and northwestern california suggest that at least two earthquakes in the last 4000 yr did not rupture the entire length of the subduction zone an earthquake 760 1140 cal yr b p in southwestern washington may have ruptured as far south as coos bay but probably stopped before it reached the coquille estuary because no buried soil records the event and tidal marsh conditions were set to record an earthquake an earthquake limited to a southern segment of the cascadia margin 1940 2130 cal yr b p probably did not rupture north of the coquille estuary an analysis of relative sea level histories from either side of the coquille fault failed to find conclusive evidence for late holocene vertical deformation however we cannot preclude recent upper plate faulting if the fault is active as geomorphic features suggest then constraints on the highest possible elevation of mean tide level allow a maximum vertical slip rate of 0 2 0 4 mm yr in the past 6200 6310 cal yr b p

proterozoic crustal evolution of the eucla basement australia implications for destruction of oceanic crust during emergence of nuna abstract the crystalline basement beneath the cretaceous to cenozoic bight and eucla basins in western australia has received comparatively little attention even though it lies on the eastern margin of one of the most mineral resource endowed regions on the planet this basement is characterized by a complex geological evolution spanning c 2 billion years but paucity of outcrop and younger basin cover present a daunting challenge to understand the basement geology in this work the composition of the unexposed proterozoic crystalline basement to the bight and eucla basins is investigated through zircon hf isotopes and whole rock geochemistry from new drillcore samples this region includes two geophysically defined basement entities the madura province containing 1 c 1478 ma sleeper camp formation which has variable isotopic signatures including evolved values interpreted to reflect reworking of rare slivers of hyperextended archean crust 2 1415 1389 ma haig cave supersuite with mantle like isotope values interpreted as melting of subduction modified n morb source and 3 1181 1125 ma moodini supersuite with juvenile isotopic signatures interpreted to reflect mixed mafic lower crustal and asthenospheric melts produced at the base of thinned crust the coompana province to the east of the madura province has three major magmatic components 1 c 1610 ma toolgana supersuite with chemical and isotopic characteristics of primitive arc rock 2 c 1490 ma undawidgi supersuite with juvenile isotope values consistent with extensional processes involving asthenospheric input and 3 1192 1140 ma moodini supersuite with strong isotopic similarity to moodini supersuite rocks in the madura province this new isotopic and geochemical data shows that the madura and coompana regions together represent a huge tract of predominantly juvenile material magma sources recognised include 1 depleted mantle producing morb like crust at c 1950 ma but also contributing to younger magmatism 2 recycled c 1950 ma crust reworked in primitive arcs and in intra plate settings and 3 minor evolved material representing fragments of hyperextended continent the observed isotopic evolution pattern is comparable to that of other central australian proterozoic provinces including the musgrave province the northern margin of the gawler craton and components within the rudall province linking these isotopic signatures defines the mirning ocean and its subducted and underplated equivalents in a global context we suggest c 1950 ma crust production reflects the onset of ordered oceanic spreading centres which swept juvenile crustal fragments into nuna

prolonged carbonate diagenesis under an evolving late cenozoic climate nullarbor plain southern australia abstract the nullarbor plain in southern australia the largest areal karst on the globe is a 240 000 km2 uplifted succession of cenozoic marine carbonates whose surface has been exposed for 14 to 15 m y the middle miocene nullarbor limestone forms the upper surface of the plain and hosts a complex and prolonged record of meteoric diagenesis such a complete record offers unique insights into the effects of climate tectonics sea level topography and hydrology on the style and placement of numerous diagenetic events in flat low lying carbonate plains alteration took place during three broad phases comprising eight stages that are interpreted to have formed against a background of dramatic climate change middle miocene phase one diagenesis took place under a humid climate and resulted in rapid mineral equilibration calcite cementation extensive karst development and finally widespread lacustrine and palustrine sedimentation resultant palustrine sediments especially terrestrial ooids are now preserved at the surface and in underlying karst cavities latest middle miocene to middle pliocene phase two diagenesis occurred during a prolonged period 8 m y of temperate climate and resulted in initial deep cave dissolution during low sea levels and later shallow cave development in the course of a high sea level onset of a somewhat more arid climate in the latest pliocene led to the development of the modern desolate landscape of the plain this final phase of diagenesis involved creation of solution pits filled with black limestone pebbles open and closed dolines with associated colluvium fill and pervasive pedogenic calcrete the nullarbor plain demonstrates that low lying carbonate plains can have low surficial erosion rates precisely record relative sea level positions be able to have extensive caves with extended periods of arrested calcite precipitation and finally host extensive terrestrial ooid deposits the importance of this comprehensive paragenetic record is its applicability to not only recognize unconformities in the rock record but to better appreciate the climate in which they formed

eocene spiculites and spongolites in southwestern australia not deep not polar but shallow and warm siliceous spongolite and spiculite are generally interpreted as deep and or cold water deposits largely because modern analogs are found mostly in cold and or deep water environments however extensive shallow water biosiliceous accumulations are present in late eocene age deposits of southern western australia the attributes and paleoenvironmental setting of these accumulations frame the specific climatic and or oceanographic constraints that allow such shallow neritic sediments to form the generally fine grained siliciclastic biosiliceous sediments accumulated in a nearshore shallow water setting around numerous islands and offshore from a warm temperate rainforest covered upland sponges compose a lithistid hexactinellid assemblage of mesozoic tethyan affinity confined to deep water in the modern ocean that migrated into neritic paleoenvironments during late eocene time lithistids dominated shoreface environments and were reworked into sponge conglomerate beaches while hexactinellids flourished offshore in muddy subshoreface environments these deposits also contain common soft demosponge spicules and a rare but otherwise normal marine calcareous biota the biosiliceous sediments grade offshore into bryozoan rich marls and limestones sponges outcompeted the calcareous benthos in these inner shelf environments because of elevated amounts of land derived nutrients that included high dissolved silica and a calm hydrodynamic setting these deposits suggest that neither temperature nor water depth are critical factors for prolific sponge colonization the rarity of such deposits in the rock record likely reflects the necessity for the coincidence of all of these factors or they are misinterpreted

investigating the record of permian climate change from argillaceous sedimentary rocks oman a standard method for the analysis of carbon isotope composition of bulk organic matter 13 c bulk in palaeoenvironmental and stratigraphic studies of sedimentary basins associated with hydrocarbons is suggested this method includes the removal of interstitial hydrocarbon within the sediments which is shown to have a negative effect on 13 c using the method a 13 c bulk trend c 21 to 24 was found within the lower permian al khlata and lower gharif formations of thuleilat 16 and 42 well sections south oman palaeontological and sedimentological evidence indicates considerable palaeoenvironmental change from a cold climate lowland fern flora and upland primitive conifer flora low in the sequence to a lowland cycad like and upland glossopterid or other gymnospermous flora higher in the sequence the lithologies range from glacial diamictite at the base to calcrete horizons and redbeds at the top it is therefore likely that the 13 c bulk trend is related to palaeoenvironmental change

crustal block kinematics and seismic potential of the northernmost philippine sea plate and izu microplate central japan inferred from gps and leveling data 1 we clarify the contemporary deformation observed by gps and leveling for the greater tokyo kanto eastern tokai and the izu islands region where the izu ogasawara bonin arc is subducting and colliding with the central part of the japan arc from these data we develop a kinematic model of fault sources with variable components of seismic and aseismic slip under the assumption that the contemporary deformation during 1995 2000 is representative of the long term interseismic strain field the geodetic data are inverted to estimate the rotation poles of the crustal blocks the degree of elastic strain accumulation on faults and the volumetric inflation sources beneath volcanoes the present crustal movements are explained by four crustal blocks the izu microplate the central japan block the pacific plate and the philippine sea plate along the suruga and sagami margins of the philippine sea plate lie strongly coupled faults which include sites of the 1854 m 8 4 tokai 1923 m 7 9 kanto and 1703 m 8 2 genroku kanto earthquakes in contrast the philippine sea plate boundary immediately north of the izu peninsula site of m 7 5 collisional earthquakes is only weakly coupled the boundary between the izu microplate and the philippine sea plate experiences left lateral motion with the rate of 30 mm yr most of this boundary is locked and thus has a large potential of future earthquakes the izu microplate is found to rotate rapidly clockwise at 10 myr with a rotation pole relative to the central japan block located just north of its northern boundary the pole and angular velocity of the izu microplate depends however on the assumed location of the boundary with the exception of the site of the 1938 m 7 earthquake swarm which we infer has the current potential to produce a m 8 1 earthquake the pacific megathrust has a very low seismic potential although the geodetic data have little resolving power for much of the pacific plate interface east of tokyo

paleoecological evidence for coastal subsidence during five great earthquakes in the past 1500 years along the northern onshore continuation of the nankai subduction zone abstract during the last 1500 years a marsh on the north coast of suruga bay central japan has experienced as many as five rapid submergence events this conclusion is supported by analyses of depositional facies and pollen and diatom assemblages in sediment cores from the ukishimagahara lowland on the footwall side of the fujikawa kako fault zone fkz the northern extension of the nankai and suruga troughs light colored silt or clay beds 30 50 cm thick deposited as the result of submergence events that drowned the marshland cover terrestrial peat or humic soils produced by the marshland vegetation radiocarbon ages and dated tephras suggest that in this lowland submergence events have occurred at aperiodic intervals of 100 400 years atmospheric phenomena can cause increased precipitation and flooding by rivers and typhoons but they cannot explain the cyclic submergence events at centennial timescales during the late holocene sea levels have been declining relative to land around the japanese islands so high sea levels cannot explain the periodic submergence of the lowland the most likely cause of these events therefore is coseismic subsidence of the lowland related to great earthquakes m8 0 occurring in the fkz or the suruga trough coseismic coastal deformation around the study area during the 1854 ansei tokai earthquake supports this hypothesis

sediment routing and basin evolution in proterozoic to mesozoic east gondwana a case study from southern australia abstract sedimentary rocks along the southern margin of australia host an important record of the break up history of east gondwana as well as fragments of a deeper geological history which collectively help inform the geological evolution of a vast and largely underexplored region new drilling through cenozoic cover has allowed examination of the cretaceous rift related madura shelf sequence bight basin and identification of two new stratigraphic units beneath the shelf the possibly proterozoic shanes dam conglomerate and the interpreted palaeozoic southern officer basin unit the decoration sandstone recognition of these new units indicates an earlier basinal history than previously known lithostratigraphy of the new drillcore has been integrated with that published from onshore and offshore cores to present isopach maps of sedimentary cover on the madura shelf new palynological data demonstrate progression from more localised freshwater brackish fluvio lacustrine clastics in the early cretaceous foraminisporis wonthaggiensis valanginian to barremian to widespread topography blanketing fully marine glauconitic mudrocks in the mid cretaceous endoceratium ludbrookiae albian geochronology and hf isotope geochemistry show detrital zircon populations from the madura shelf are comparable to those from the southern officer basin as well as cenozoic shoreline and palaeovalley sediments in the region the detrital zircon population from the shanes dam conglomerate is defined by a unimodal 1400 ma peak which correlates with directly underlying crystalline basement of the madura province peak ages of 1150 ma and 1650 ma dominate the age spectra of all other samples indicating a stable sediment reservoir through much of the phanerozoic with sediments largely sourced from the albany fraser orogen and musgrave province directly and via multiple recycling events the madura shelf detrital zircon population differs from published data for the upper cretaceous ceduna delta to the east indicating significant differences in sediment provenance and routing between the ceduna sub basin and central bight basin

evolution of porosity and pore geometry in the permian whitehill formation of south africa a fe sem image analysis study abstract since the advent of technologically efficient exploitation of economic hydrocarbon reservoirs in shales increasingly more research has been devoted to identifying and characterizing pore systems within shales however only a handful of these studies focused on the development of porosity in thermally mature unconventional reservoirs in this study the evolution of porosity and pore geometry in the permian whitehill formation is addressed with the aid of ultrathin sections 2 3 cm 10 20 m thick and field emission scanning electron microscopy fe sem on samples with mean random vitrinite reflectance values ranging from 1 03 to 4 07 ro we document a strong positive covariation of porosity and total organic carbon content toc in all localities however for samples with vitrinite reflectance values greater than 2 88 ro porosity per unit toc decreased by over 25 relative to samples with lower thermal maturities the positive covariation of thermal maturity and total porosity recorded here is unsurprising and have been documented previously in many gas shales however the dramatic decrease in porosity restricted to samples from localities that experienced advanced maturation ro 2 88 is viewed as an evidence that porosity decrease is directly related to late thermal decarboxylation of organic matter this is supported by the presence of pores and micro fractures infilled by fibrous grains including carbonates clays silicates and phosphates and residual fluid inclusions these grains were likely generated from re precipitation of framework grains previously dissolved by organic acids carboxylic phenolic that were generated during thermochemical decarboxylation of the om our findings do not only fill important gaps in the understanding of organic pore development including processes that create preserve and destroy porosity the porosities described here are also key to gas transfer from shale matrix to induced fractures during fracture stimulation programs

stratigraphic record of holocene coseismic subsidence padang west sumatra 1 stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of padang west sumatra along the mentawai segment 0 5 s 0 3 s of the sunda subduction zone each earthquake is marked by a sharp soil mud contact that represents a sudden change from mangrove to tidal flat the earthquakes occurred about 4000 and 3000 cal years b p based on radiocarbon ages of detrital plant fragments and seeds the absence of younger paleoseismic evidence suggests that late holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone our results point to a brief few thousand year window of preservation of subsidence events in tidal wetland stratigraphic sequences a result that is generally applicable to other emergent coastlines of west sumatra

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

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

ecogeomorphology in the australian drylands and the role of biota in mediating the effects of climate change on landscape processes and evolution

geological and exploration models of beach placer deposits integrated from case studies of southern australia abstract the processes leading to the formation of beach placer deposits generally begin inland and terminate at the coast including source rocks being weathered eroded and then transported by streams and rivers to the coast where the sediments are deposited in a variety of coastal environments the coastal sediments are reworked by the action of waves tides longshore currents and wind which are effective processes for sorting the mineral grains based on differences in their size and density resulting in laminated or lens shaped packages of sediments up to tens of meters thick that are rich in heavy minerals detailed studies of sedimentary basins as well as peripheral paleo valleys that drained sediment source areas are important tools in the exploration for heavy mineral resources knowledge of the paleo basin associated valley architecture and the source of heavy minerals concentrated in the shorelines and valleys are useful guides to the potential for and location of economic deposits evidence from sedimentology can be combined with that from other geological and geophysical characteristics to arrive at a general reconstruction of basin and paleovalley architecture and depositional environments complex paleogeography of the shorelines can influence or determine the sites of heavy mineral concentration heavy mineral sands tend to concentrate in certain shoreline settings during storm activity repeated storm erosion and reworking over centuries e g the southeastern coast of australia or millennia e g the eucla and murray basins of australia can progressively enrich heavy mineral sand deposits preservation of these deposits over a geological timeframe of millions of years can ensue through subsidence of coastal sediments and during sea level change that results in either shorelines migrating inland marine transgression or seaward marine regression potentially burying or stranding earlier deposits or reworking them to form younger deposits refinements in remote sensing and geophysical techniques data processing sedimentology and computer aided interpretations provide effective economic and efficient methods for modeling coastal reconstructions and for exploring provinces and terrains prospective for heavy mineral sand deposits landscape topography analysis combined with geophysical methods that can resolve physical property contrasts between the shoreline sediments and underlying sequences are increasingly used in mineral exploration to locate and to reconstruct paleoshorelines and paleovalleys australia has modern and ancient beach placer deposits both of which show many similar geologic features the formation of these heavy mineral deposits provides one of the best examples of applying knowledge of modern systems e g the west and east coasts of australia as an analogue to interpret and understand the geology and form of ancient deposits e g the eucla and murray basins of southern australia this study provides descriptive and exploration models of australia s heavy mineral sand deposits formed in coastal environments which can be applied to similar settings worldwide

etched linear dunefields of the nullarbor plain a record of pliocene pleistocene wind patterns across southern australia abstract the southern nullarbor plain is covered by low amplitude generally 1 2 m parallel ridges and swales with variable wavelength 300 900 m the ridges are stony the swales hold thin deposits of unconsolidated silt and clay the ridges and swales have previously been attributed to joint control but are not parallel to joints exposed in cave roofs instead they have a striking similarity to central australian linear sand dunes they are parallel regularly spaced and most importantly fork in a consistent direction they are here explained as the etched footprints of an extensive linear dune system that once covered much of the southern nullarbor rainwater collecting in the troughs between the sand dunes dissolved the underlying limestone to produce the swales recognition of this dune field fills a major gap in the distribution of linear dunes across australia the dunes have subsequently disappeared apart from red aeolian sand in dolines in the southeastern part of the nullarbor most of the sand was probably blown offshore the ridge and swales are oriented predominantly north south in the west and northeast southwest and northwest southeast in the centre and east due to deposition by northerly and westerly winds respectively as shown by directions of forking the north south nullarbor dunes are probably older and may have been deposited in the arid climate of the late neogene this would make them the oldest linear dunes in australia remnants of an early phase of linear dune activity that has been removed or overprinted elsewhere the change in wind direction shown by the dune orientation could represent northward migration of sub tropical high pressure systems during the late neogene

coseismic and pre seismic subsidence associated with great earthquakes in alaska abstract alternating beds of peat and mud in sediment sequences on the south central alaskan coast record coseismic and inter seismic relative land and sea level movements caused by repeated great earthquakes on the alaska aleutian subduction zone during the ad 1964 mw 9 2 earthquake tidal marshes and wetlands around upper cook inlet experienced up to 2 m of subsidence burying peat forming communities with intertidal mud here we use quantitative analyses of fossil diatoms within peat mud couplets to reconstruct land sea level changes for the 1964 and five earlier great earthquakes during the past 3300 years in contrast to geodetic observations that are limited to the present post seismic phase we quantify varying spatial patterns of uplift and subsidence through complete earthquake cycles relative land uplift characterises most of the inter seismic phase of each cycle at our sites whereas each great earthquake was preceded by a short period of pre seismic relative land subsidence

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

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

karst pocket valleys and their implications on pliocene quaternary hydrology and climate examples from the nullarbor plain southern australia abstract karst on the nullarbor plain has been studied and described in detail in the past but it lacked the determination of the karst discharge and palaeo watertable levels that would explain the palaeohydrological regime in this area this study explores the existence of previously unrecognised features in this area karst pocket valleys and gives a review on pocket valleys worldwide initial gis analyses were followed up by detailed field work sampling mapping and measuring of morphological geological and hydrological characteristics of representative valleys on the wylie and hampton scarps of the nullarbor plain rock and sand samples were examined for mineralogy texture and grain size and a u pb dating of a speleothem from a cave within a pocket valley enabled the establishment of a time frame of the pocket valleys formation and its palaeoenvironmental implications the pocket valleys document the hydrological evolution of the nullarbor karst system and the neogene pleistocene palaeoclimatic evolution of the southern hemisphere a review of pocket valleys in different climatic and geological settings suggests that their basic characteristics remain the same and their often overlooked utility as environmental indicators can be used for further palaeoenvironmental studies the main period of intensive karstification and widening of hydrologically active underground conduits is placed into the wetter climates of the pliocene epoch subsequent drier climates and lowering of the watertable that followed sea level retreat in the quaternary resulted in formation of the pocket valleys gravitational undermining slumping exudation and collapse which combined with periodic heavy rainfall events and discharge due to impeded drainage caused the retreat of the pocket valleys from the edge of escarpments

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

the nature of gold bearing palaeochannel sediments in the gidji area north of kalgoorlie western australia abstract remnants of an extensive palaeodrainage network are preserved in the kalgoorlie region of western australia as buried palaeochannels at gidji a major palaeochannel up to 60 m deep is infilled with sand and clay rich facies and overlain by younger alluvial colluvial sands and gravels aeolian sands and silts playa deposits red soils and lag materials the palaeochannel sediments consist predominantly of low crystallinity kaolinite quartz and minor smectite they contain very little muscovite illite or chlorite and can be readily distinguished from underlying in situ saprolite by their chemical characteristics particularly k al and mg al ratios low rare earth element contents and low k rb ratios these sediments were largely deposited during the mid late eocene as an homogenised mixture derived from a low relief and highly weathered pre eocene landsurface they have undergone post depositional weathering resulting in mobilisation and redeposition of iron as oxides oxyhydroxides the stratigraphy of the palaeochannel sediments indicates a change from dominantly fluvial to fluvio lacustrine conditions during deposition in areas of gold mineralisation the presence of palaeochannels complicates geochemical exploration areas of thick palaeochannel clays mask bedrock anomalies placer and supergene concentrations of gold associated with the palaeochannels can be confused with bedrock anomalies unless a multi element approach is taken the gidji palaeochannel environment contains a combination of bedrock and placer supergene gold anomalies primary bedrock anomalies generally have as sb and w as associated pathfinder elements some pathfinder elements e g as have been concentrated in ferruginous pisoliths and gravels or mechanically dispersed in near surface alluvial colluvial materials giving rise to false anomalies

differences in regolith weathering history at an acid and neutral saline lake on the archean yilgarn craton and implications for acid brine evolution abstract the yilgarn craton of western australia is composed of archean basement a variety of discontinuous cenozoic sedimentary rocks and thousands of ephemeral saline lakes many of these lakes have extreme chemistry with ph values down to 1 5 previous workers have suggested that the regionally acidic groundwater that feeds these lakes has reached its unusually low ph as the result of long term continental denudation and may be a characteristic of late stage continental weathering and may have been important in the geologic past however it is difficult to evaluate the relationship between weathering history and fluid chemistry here we use mineralogy major oxide geochemistry and trace element geochemistry to compare the weathering histories of rocks preserved in drill cores from below two saline lakes in this region one acid prado lake ph 3 and one neutral gastropod lake ph 7 the cores preserve a combination of relatively unweathered basement weathered saprolite detrital sediments and authigenic precipitates geochemical and mineralogical data show that while extreme chemical weathering has occurred at both sites there are significant differences between the two systems that may explain the difference in modern surface chemistry the regolith below the neutral gastropod lake is overall more highly weathered than at the acidic prado lake although the prado lake core material transitions through a greater gradient from less weathered to more highly weathered material up the core the prado lake core includes several meters of paleodrainage fill sediments on top of the weathered regolith which may have provided a rejuvenated source of reactive surfaces to locally generate acidity with further chemical weathering in a system already lacking buffering capacity in contrast there is only a thin veneer of detrital sediments which appear to have been sourced from proximal high weathered archean basement within the gastropod lake core the influence of the modern acid saline lake water and groundwater is reflected in the mineralogy and geochemistry of the regolith which no doubt complicates simple interpretations of geochemical records and weathering indices this study reveals new insight about the range of processes that have influenced the yilgarn craton one of the oldest intact pieces of archean crust in the world

five centuries of tsunamis and land level changes in the overlapping rupture area of the 1960 and 2010 chilean earthquakes a combination of geological and historical records from south central chile provides a means to address general questions about the stability of megathrust rupture patches and the range of variation expected among earthquakes and tsunamis along a particular stretch of a subduction zone the tirua river estuary 38 3 s records four large tsunamis and coseismic land level changes over the past 450 years within the overlapping rupture zones of the great subduction zone earthquakes of a d 1960 mw 9 5 and 2010 mw 8 8 sand layers 2 km up the tirua river represent the 2010 and 1960 tsunamis and two historical tsunamis most likely in a d 1751 and 1575 differing land level changes during these earthquakes likely denote differences in the spatial distribution of slip on the megathrust in both the strike and dip directions within the overlapping rupture zone with the uplift at tirua in 1751 and 2010 probably caused by slip extending farther landward and to greater depth than in 1575 and 1960 which showed subsidence or little change

facies and sequence stratigraphy of eocene palaeovalley fills in the eastern eucla basin south australia abstract the eocene succession filling palaeovalleys in the northeastern eucla basin south australia is interpreted using facies and sequence stratigraphic models based on relative sea level changes the dominantly fluvial sediments were deposited in incised valleys which graded basinwards to an estuarine coastal plain under warm and humid palaeoclimatic conditions sedimentological examination suggests a tidal influence in this fluvial succession fluvial estuarine shoreline facies associations can be recognised in these eocene sequences each of which comprises a diverse assemblage of lithofacies that can be grouped into lowstand and or transgressive and highstand system tracts since the palaeorivers had hydrological connection with the sea deposition was dominantly controlled by sea level changes results of the study indicate that two third order eocene eustatic cycles have largely controlled sedimentation the resulting key surfaces unconformity and transgressive tidal wave ravinement and maximum flooding surfaces bound depositional sequences which extend over significant areas and may be used in basin wide correlations of stratal packages

fragmentary evidence of great earthquake subsidence during holocene emergence valdivia estuary south central chile a reconnaissance of holocene stratigraphy beneath fringing marshes of the valdivia estuary where an m 9 5 earthquake caused 1 2 m of regional coseismic subsidence in 1960 shows only fragmentary evidence of prehistoric coseismic sub sidence in most of the 150 hand driven cores that were examined a distinct uncon formity separates 0 5 1 5 m of late holocene tidal and floodplain mud peat and sand from underlying middle holocene subtidal mud and sand at the las coloradas site where stratigraphy is best preserved two a horizons of marsh and meadow soils abruptly overlain by sand and mud probably record coseismic subsidence shortly fol lowed by tsunamis the amount of subsidence during the earthquakes proved difficult to reconstruct with a diatom transfer function because of differences between modern and fossil diatom assemblages maximum 14 c ages on macrofossils from the two a horizons at the las coloradas site of 1 7 1 3 ka and 2 7 1 7 ka allow correlation of the younger horizon with either of two of six 14 c dated a horizons buried by tsunami sand or post tsunami tidal sand 200 km to the south at maullin and with a lake wide mass wasting event in lago puyehue 100 km to the southeast tidal records of prehistoric coseismic subsidence at valdivia are scarce because of a sea level fall of 3 8 m over the past 6000 years erosion of marsh and meadow soils during subsidence induced flooding of the estuary and largely complete land level recovery during cycles of coseismic subsidence and postseismic uplift online material diatom species data from the las coloradas site valdivia estuary

episodic emergence in the past 3000 years at the akkeshi estuary hokkaido northern japan at the akkeshi estuary rapid emergence interrupted holocene submergence at least four times in the past 3000 years each emergence event produced an upward change from estuarine mud to freshwater peat while the estuarine mud abounds in brackish and marine diatoms freshwater taxa dominate the peat emergence events occurred from 1700 to 2300 1000 to 1300 and 500 to 700 cal yr b p an additional emergence event predated by several decades a volcanic ash that erupted in a d 1694 at least three of the events produced contacts abrupt enough to represent uplift during earthquakes such uplift may reconcile seemingly conflicting records of vertical crustal movement in eastern hokkaido this tectonically active area which is being subducted by the pacific plate at 8 cm yr contains marine terraces that imply 0 1 0 5 mm yr of net uplift in the late quaternary however these terraces adjoin tide gages that recorded 8 9 mm yr of steady submergence in the 20th century the terrace uplift need not conflict with the gaged submergence if the region is subject to occasional coseismic uplift as during the emergence events implied by holocene geology near akkeshi

sources of fine sized organic matter in north atlantic heinrich layers δ13c and δ15n tracers organic carbon oc and total nitrogen tn concentrations and stable isotope ratios d13c d15n of fine 50 m size fractions of deep sea sediments from the central north atlantic were employed to identify changes in sources of organic matter over the past 50 ka bp ambient glacial sediments are characterised by values that reflect mixtures of marine and terrestrial inputs averages 1s oc tn 7 6 0 8 d13c 22 8 1 0 d15n 5 5 0 6 d13c oc and tn concentrations shift to higher values during the holocene indicating a gradual decrease of fine terrigenous supply to the north atlantic the unchanged d15n record between last glacial and holocene stages indicates that the central north atlantic region remained oligotrophic at least during the past 50 ka bp but additional studies are required to support this result in terms of nitrogen oceanic budget during the phases of enhanced ice rafted detrital supply corresponding to prominent heinrich events hl1 hl2 hl4 and hl5 fine sized sedimentary organic matter has lower oc and tn concentrations contrasting sharply with those of ambient glacial sediments lower d13c down to 28 and d15n down to 1 6 values and high oc tn ratios up to 14 7 1 1 are found for hl1 hl2 and with lesser extent for hl4 these values reflect enhanced detrital supply originating from poorly differentiated soil horizons that characterise periglacial climate conditions and from organic matter bearing rock sources of the underlying geological basement during hl5 only the d13c offset records the input of fine size ice rafted organic matter gradually changing soil development conditions during the time interval covering hl5 to hl1 marine isotope stages 5 to 2 as well as varying erosion levels have been hypothesized on the basis of constant d13c increasing oc tn and decreasing d15n values

eocene stratigraphic succession in the eucla basin of south australia and correlation to major regional sea level events abstract using palynostratigraphy combined with analysis of lithostratigraphy and sedimentary facies of discontinuous outcrops and selected drillholes we have investigated whether the eocene sequences and their boundaries in the eucla basin of south australia were synchronous with major sea level events the correlation of eocene sequences and their boundaries in the eastern nearshore and onshore eucla basin indicates that these complex marine nonmarine strata fall into four sequences or allostratigraphic packages that can be seen from the offshore basin to nearshore and onshore basin including palaeovalleys key sedimentary surfaces disconformities a tidal wave ravinement surface transgressive surfaces maximum flooding surfaces bound the packages including three new revised units and are coincident with four third order sequence boundaries the eastern eucla basin stratigraphy accords with the general view of eocene sea level patterns and elucidates a stepwise evolution of marine and nonmarine environments

eocene cool water carbonate and biosiliceous sedimentation dynamics st vincent basin south australia middle and upper eocene biogenic sediments in the willunga embayment along the eastern margin of the st vincent basin are a series of warm temperate limestones marls and spiculites the middle eocene tortachilla limestone is a thin coarse grained quartzose biofragmental bryozoan mollusc calcarenite of stacked metre scale depositional cycles with hardground caps lithification aragonite dissolution and the filling of moulds by sediment and cement characterize early marine meteoric diagenesis further meteoric diagenesis at the end of tortachilla deposition resulted in dissolution fe oxide precipitation and calcite cementation the upper eocene blanche point formation is composed of coccolith and spiculite marl and spiculite all locally rich in glauconite turritellid gastropods and sponges decimetre scale units locally capped by firmgrounds have fossiliferous lower parts and relatively barren upper parts carbonate diagenesis is minor with much aragonite still present but early silicification is extensive except in the spiculite which is still opal a all depositional environments are interpreted as relatively shallow water high energy during the middle eocene and low energy during the upper eocene reflecting the variable importance of a basin entrance archipelago of carbonate highs marls and spiculites are interpreted to have formed under an overall estuarine circulation system in a humid climate basinal waters although well mixed were turbid and rich in land derived nutrients yet subphotic near the sea floor these low energy inner shelf biosiliceous sediments occur in coeval environments across other parts of australia and elsewhere in the rock record suggesting that they are a recurring element of the cool water carbonate shelf depositional system thus spiculites and spiculitic carbonates in the rock record need be neither deep basinal nor polar in origin the paradox of a shallow water carbonate spiculite association may be more common in geological history than generally realized and may reflect a characteristic mid latitude humid climate temperate water palaeoenvironmental association

identifying coseismic subsidence in tidal wetland stratigraphic sequences at the cascadia subduction zone of western north america tidal wetland stratigraphy reveals that great plate boundary earthquakes have caused hundreds of kilometers of coast to subside at the cascadia subduction zone however determining earthquake recurrence intervals and mapping the coastal extent of past great earthquake ruptures in this region are complicated by the effects of many sedimentologic hydrographic and oceanographic processes that occur on the coasts of tectonically passive as well as active continental margins tidal wetland stratigraphy at many cascadia estuaries differs little from that at similar sites on passive margin coasts where stratigraphic sequences form through nonseismic processes unrelated to coseismic land level changes methods developed through study of similar stratigraphic sequences in europe provide a framework for investigating the cascadia estuarine record five kinds of criteria must be evaluated when inferring regional coastal subsidence due to great plate boundary earthquakes the suddenness and amount of submergence the lateral extent of submerged tidal wetland soils the coincidence of submergence with tsunami deposits and the degree of synchroneity of submergence events at widely spaced sites evaluation of such criteria at the cascadia subduction zone indicates regional coastal subsidence during at least two great earthquakes evidence for a coseismic origin remains equivocal however for the many peat mud contacts in cascadia stratigraphic sequences that lack 1 contrasts in lithology or fossils indicative of more than half a meter of submergence 2 well studied tsunami deposits or 3 precise ages needed for regional correlation paleoecologic studies of fossil assemblages are particularly important in estimating the size of sudden sea level changes recorded by abrupt peat mud contacts and in helping to distinguish erosional and gradually formed contacts from coseismic contacts reconstruction of a history of great earthquakes for the cascadia subduction zone will require rigorous application of the above criteria and many detailed investigations

geochemistry and mineralogy of marine and non marine namurian black shales from the tansley borehole derbyshire the namurian black shales studied have a good palaeontological control pyrite illite and organic matter are higher in the marine shales and siderite and kaolinite are higher in the non marine shales the distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity the same control could account for the observed clay mineral distribution by differential flocculation the major element geochemistry closely reflects the above mineral variation mn and zr are higher in the non marine shales due to siderite and zircon respectively co cr rb y and ba are not significantly different and a detrital source mainly clay minerals is suggested in the marine shales the elements pb cu v ni sr and zn are significantly higher using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated the present element locations are thought from correlation analysis to be pyrite and organic matter by analogy with experimental work and modern environments the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors the element enrichment cannot be related directly to seawater concentrations unlike some black shales and the accumulation rates for pb and cu are thought to be unusually high

evaluation of eocene source rock for potential shale oil and gas generation in north cambay basin india abstract source rock potential of 108 representative samples from 3 m intervals over a 324 m thick shale section of middle eocene age from the north cambay basin india have been studied variation in total organic carbon toc and its relationship with loss on ignition loi have been used for initial screening screened samples were subjected to rock eval pyrolysis and organic petrography a toc log indicated wide variation with streaks of elevated toc a 30 m thick organic rich interval starting at 1954 m depth displayed properties consistent with a possible shale oil or gas reservoir toc wt values of the selected samples were found to vary from 0 68 to 3 62 with an average value of 2 2 the modified van krevelen diagram as well as hi vs t max plot indicate prevalence of type ii to type iii kerogen t max measurements ranged from 425 c to 439 c indicating immature to early mature stage which was confirmed by the mean vitrinite reflectance values r o of 0 63 0 65 and 0 67 at 1988 m 1954 m and 1963 m respectively quantification of hydrocarbon generation migration and retention characteristics of the 30 m source rock interval suggests 85 expulsion of hydrocarbon oil in place oip resource of the 30 m source rock was estimated to be 3 23 mmbbls per 640 acres the oil saturation index osi crossover log showed from a geochemical perspective moderate risk for producing the estimated reserve along with well location for tapping the identified resource

aperiodic recurrence of geologically recorded tsunamis during the past 5500 years in eastern hokkaido japan 1 along hokkaido s pacific coast near the town of kiritappu sandy deposits in a muddy lagoon and on a nearby beach ridge plain provide evidence for 15 tsunamis between 200 and 6000 years ago additional sand beds at the lagoon probably represent the historical tsunamis of a d 1843 and 1894 we observed the sequences of sandy deposits in continuous slices 2 to 4 m deep some of the deposits consist of just a single sand bed whereas others contain multiple units of sand muddy sand or sandy mud and mud caps including plant detritus we also found at the lagoon a 17th century tsunami deposit that thickens and thins regardless of elevation or distance inland we bracketed the ages of most of the inferred tsunamis by radiocarbon dating of detritus mainly seeds and leaves at the lagoon and charcoal at the beach ridge plain from pretsunami and posttsunami beds tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries within these uncertainties the inferred sequence of 15 prehistoric tsunamis at the lagoon beginning almost 6000 years ago can be matched tsunami by tsunami with the inferred history at the beach ridge plain 15 km away the sand sheet extents suggest that most of these tsunamis were larger than any generated at hokkaido in the last 200 years the intervals between these inferred outsized tsunamis average nearly 400 years but range widely from about 100 to about 800 years

a molecular and carbon isotope biogeochemical study of biomarkers and kerogen pyrolysates of the kimmeridge clay facies palaeoenvironmental implications abstract structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite a bituminous shale and an oil shale of the kimmeridge clay formation kcf in dorset were studied in order to gain insight into i the type and extent of water column anoxia and ii changes in the concentration and isotopic composition of dissolved inorganic carbon dic in the palaeowater column the samples studied fit into the curve of increasing 13 c of the kerogen 13 c toc with increasing toc reported by huc et al 1992 their hypothesis that the positive correlation between toc and 13 c toc is the result of differing degrees of organic matter om mineralisation in the water column was tested by measuring the 13 c values of primary production markers these 13 c values were found to differ on average by only 1 among the samples implying that differences in the extent of om mineralisation cannot fully account for the 3 difference in 13 c toc the extractable om in the oil shale differs from that in the other sediments due to both differences in maturity and differences in the planktonic community these differences however are not likely to have significantly influenced 13 c toc either all three sediments contain abundant derivatives of isorenieratene indicating that periodically euxinia was extending into the photic zone the sediments are rich in organic sulfur as revealed by the abundant sulfur compounds in the pyrolysates the prominence of c 1 c 3 alkylated thiophenes over n alkanes and n alkenes is most pronounced in the pyrolysate of the sediment richest in toc this suggests that sulfurisation of om may have played an important role in determining the toc 13 c toc relationship reported by huc et al 1992

stable carbon isotopes of amorphous kerogens from phanerozoic sedimentary rocks amorphous kerogens from phanerozoic sedimentary rocks may be divided into two groups on the basis of their 13c values h amorphous kerogens have isotopic values in the range of 24 to 20 per mil and l amorphous kerogens have isotopic values in the range of 35 to 26 per mil the occurrence of amorphous kerogens in the intermediate isotopic range from one rock unit in the data set suggests a weak continuum may exist between these two groups phytoplankton and to a lesser extent zooplankton and bacteria are considered to be the precursors for both kerogen types a plausible explanation for this dichotomy may be found in the source of co2 utilized by phytoplankton which is considered to be controlled by environmental factors h amorphous kerogens are expected to occur in silled basins that are overlain by expansive well circulated deep 500 m water where the prevailing source of carbon in the photic zone is atmospheric derived co2 conversely l amorphous kerogens are expected to occur in restricted basins that are overlain by stratified shallow 200 m water where the prevailing source of carbon in the photic zone may be organic derived co2

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

environmental control of carbon isotope variations in pennsylvania black shale sequences midcontinent u s a abstract a reversal of the conventional carbon isotope relationship terrestrial lighter than marine organic matter has been documented for two pennsylvanian desmoinesian cyclothemic sequence cores from the midcontinent craton of the central united states deep water organic rich phosphatic black shales contain a significant proportion of algal derived marine organic matter as indicated by organic petrography rock eval hydrogen index and c 27 c 29 sterane ratios and display the lightest 13c values max 27 80 for kerogen while shallower water more oxic facies e g fossiliferous shales and limestones contain dominantly terrestrial organic matter and have heavier 13ckerogen values to 22 87 for a stratigraphically adjacent coal 13c values for extract fractions were relatively homogeneous for the organic rich black shales with the lightest fraction often the aromatics being only 1 or less more negative than the kerogen differences between extract fractions and kerogens were much greater for oxic facies and coals e g saturates nearly 5 lighter than the kerogen a proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent extremely widespread pennsylvanian peat swamps which were rapidly submerged by transgression of the epicontinental seas in this setting marine organisms drew upon a co2 reservoir which was in a state of disequilibrium with the atmosphere being affected by isotopically light recycled co2 derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments

a systematic review of geological evidence for holocene earthquakes and tsunamis along the nankai suruga trough japan the nankai suruga trough the subduction zone that lies immediately south of japan s densely populated southern coastline generates devastating great earthquakes magnitude 8 characterised by intense shaking crustal deformation and tsunami generation forecasting the hazards associated with future earthquakes along this 700 km long fault requires a comprehensive understanding of past fault behaviour while the region benefits from a long and detailed historical record palaeoseismology has the potential to provide a longer term perspective and additional crucial insights in this paper we summarise the current state of knowledge regarding geological evidence for past earthquakes and tsunamis along the nankai suruga trough incorporating literature originally published in both japanese and english and enhancing available results with new age modelling approaches we summarise and critically evaluate evidence from a wide variety of sources palaeoseismic evidence includes uplifted marine terraces and biota marine and lacustrine turbidites liquefaction features subsided marshes and tsunami deposits in coastal lakes and lowlands while 75 publications describe proposed evidence from 70 sites only a limited number provide compelling well dated evidence the best available records enable us to map the most likely rupture zones of twelve earthquakes that occurred during the historical period this spatiotemporal compilation suggests that the 1707 ce earthquake ruptured almost the full length of the subduction zone and that earthquakes in 1361 ce and 684 ce may have been predecessors of similar magnitude intervening earthquakes were of lesser magnitude highlighting the variability in rupture mode that characterises the nankai suruga trough intervals between ruptures of the same seismic segment range from 450 years during the historical period over longer timescales palaeoseismic evidence suggests intervals between earthquakes ranging from 100 to 700 years however these figures reflect a range of thresholds controlling the creation and preservation of evidence at any given site as well as the genuine intervals between earthquakes at present there is no geological data that suggest the occurrence of a larger magnitude earthquake than that experienced in 1707 ce however few studies have sought to establish the relative magnitudes of different earthquake and tsunami events along the nankai suruga trough alongside the lack of research designed to quantify the maximum magnitude of past earthquakes we emphasise issues over alternative hypotheses for proposed palaeoseismic evidence the paucity of robust chronological frameworks and insufficient appreciation of changing thresholds of evidence creation and preservation over time as key issues that must be addressed by future research

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

topography boundary forces and the indo australian intraplate stress field the relative contribution of topographic e g ridge push continental margins and elevated continental crust and plate boundary e g subduction and collisional forces to the intraplate stress field in the indo australian plate iap is evaluated through a finite element analysis two important aspects of the iap intraplate stress field are highlighted in the present study 1 if substantial focusing of the ridge push torque occurs along the collisional boundaries i e himalaya new guinea and new zealand many of the first order features of the observed stress field can be explained without appealing to either subduction or basal drag forces and 2 it is possible to fit the observed shmax maximum horizontal stress orientation and stress regime information with a set of boundary conditions that results in low tectonic stress magnitudes e g tens of megapascals averaged over the thickness of the lithosphere throughout the plate this study therefore presents a plausible alternative to previous studies of the iap intraplate stress field which predicted very large tectonic stress magnitudes hundreds of megapascals in some parts of the plate in addition topographic forces due to continental margins and elevated continental material were found to play an important role in the predicted stress fields of continental india and australia and the inclusion of these forces in the modeling produced a significant improvement in the fit of the predicted intraplate stresses to the available observed stress information in these continental regions a central focus of this study is the relative importance of the boundary conditions used to represent forces acting along the northern plate margin we note that a wide range of boundary conditions can be configured to match the large portion of the observed intraplate stress field and this nonuniqueness continues to make modeling the iap stress field problematic while our study is an important step forward in understanding the sources of the iap intraplate stress field a more complete understanding awaits a better understanding of the relative magnitude of the boundary forces acting along the northern plate margin

shallow caves and blowholes on the nullarbor plain australia flank margin caves on a low gradient limestone platform abstract the nullarbor plain of southern australia is a very extensive limestone platform with relatively few large caves for its size but contains thousands of blowholes sub circular vertical shafts up to 1 2 m in diameter which often connect to similar sized sub horizontal passages recent detailed systematic surveys of large areas of the nullarbor plain have provided new distribution data showing that blowholes and associated shallow caves are concentrated in a 25 30 km wide band located 75 km inland the known density of these features up to 43 25 km2 underestimates the cave porosity because the strong draughts blowing from many of the blowholes indicate that they connect to extensive cave systems of small passages these shallow caves are relict phreatic features their entrances blowholes were opened as the land surface was lowered by denudation the band of blowholes and caves is located along the late miocene 6 ma shoreline across the nullarbor when there was a eustatic stillstand the caves formed in the zone of enhanced dissolution at the seaward margin of the freshwater lens along the carbonate coastline and can therefore be regarded as flank margin caves on a low gradient limestone platform a flank margin setting relatively unknown prior to this study the width of the band of flank margin caves which is substantially greater than previously documented for this cave type reflects the very low gradient of both the ground surface and water table together with the influence of tidal fluctuations and regression of the shoreline flank margin cave development stopped when the sea retreated rapidly in the late miocene early pliocene due to a period of tilting and uplift the band of flank margin caves has high permeability and substantial porosity and would therefore form an excellent largely overlooked type of palaeokarst petroleum reservoir

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

reconstructing the environmental conditions around the silurian ireviken event using the carbon isotope composition of bulk and palynomorph organic matter the carbon isotope composition 13c of bulk organic matter and two palynomorph groups scolecodonts and chitinozoans from the llandovery wenlock strata of gotland e sweden are compared to gain knowledge about carbon cycling in the silurian sub tropical shelf environment the 13c values of the palynomorphs are mostly lower than the 13c values of the bulk organic matter and the 13c values of the benthic scolecodonts are lower than those of the planktonic chitinozoans while the difference between bulk and palynomorph 13c may be in part a function of trophic state the lower values of the scolecodonts relative to those of chitinozoans which are assumed to live in the well mixed water column might imply an infaunal mode of life for the polychaetes that carried the scolecodonts lower 13c for the scolecodonts in the middle of the section may represent variations in primary marine productivity supported by acritarch abundance data oxidation of organic matter in the bottom waters or genera effects in general however trends between the three data sets are parallel indicating similarities in the low frequency environmentally forced controls the 13c data show a decreasing trend from the base of the section up to a horizon well below the base of the upper visby formation at this level and therefore probably several 10 kyr before the 13c increase in the carbonates the 13c organic values increase by 1 this perhaps is an expression of a changed composition of the bulk organic matter associated with the extinction events prior to the llandovery wenlock boundary

sea level changes and buried islands in a complex coastal palaeolandscape in the south of western australia implications for greenfield mineral exploration abstract weathering intensity changes due to climatic variability across tectonically stable portions of continental crust can generate a thick and extensive weathered cover resulting in regolith dominated terrains rdts mineral exploration in rdts is challenging because of the lack of bedrock outcrop and the difficulty of linking surface regolith geochemistry to the geology at depth complex weathering obscures the expression of the basement geochemistry in the regolith and therefore the footprints of mineral systems are difficult to detect the southeast of the yilgarn craton and the albany fraser orogen afo in the south of western australia is an rdt that extends along the coastline and the eucla basin this study proposes a landscape evolution model of the afo driven by transgression regression sea level changes that resulted in the formation of numerous islands and development of estuarine zones this model contrasts with the river system dominated landscape evolution present in the yilgarn craton this difference has significant implications for mineral exploration and geochemical interpretation of the regolith in this region weathering profiles developed on inland and on island are thicker and more mature than those developed in sea inundated areas even if in the yilgarn craton local areas display reworking of weathering profiles and other complexities from permian non marine tertiary sediments and quaternary fluvial and aeolian sediments at a regional scale if vertical geochemical mobility of elements has occurred on inland and on island are more reliable for understanding geochemical anomaly basement relationships whereas the marine inundated areas require a more detailed investigation because of the role of marine reworking of weathering profiles and possible mixture of sediments from different provenances landscape changes from the topographically high dissected yilgarn environment with thick saprolite development and uneven basement topography to the nearly flat regions dominated by sand dunes and thin saprolite development at the coastline these regions are the result of the erosional and depositional effects of successive sea level transgression regression cycles within this framework the following four different regolith settings have been identified in a progressive change from yilgarn craton environments to the modern coastline 1 albany 2 kalgoorlie norseman 3 esperance and 4 neale mapping the palaeocoastlines islands and estuarine zones as well as the region of influence of marine limestones and sediments can significantly improve the understanding of how surface geochemistry relates to the landscape and how it links with the geology at depth and therefore how it may reflect the presence of mineral systems understanding the difference in the landscape evolution between the afo and yilgarn craton is essential to properly calibrate mineral exploration protocols in both regions

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

palaeoecological and possible evolutionary effects of early namurian serpukhovian carboniferous glacioeustatic cyclicity early namurian serpukhovian carboniferous sedimentary cycles in the throckley and rowlands gill boreholes near newcastle upon tyne uk consist of fossiliferous limestones overlain by usually unfossiliferous black mudstone followed by sandstones and often by thin coal seams sedimentological and regional geological evidence suggests that the largest are high amplitude cycles probably of glacioeustatic origin 13 c bulk organic matter delineates marine and non marine conditions because of the large difference between terrestrial and marine 13 c and indicates that full marine salinity was only intermittent and resulted from glacioeustatic marine transgression superimposed on a background of inundation by freshwater from large rivers which killed off the marine biota palynology suggests that plant groups including ferns and putative pteridosperms were affected by changing sea level and that there is a theoretical possibility of connection between cyclicity and the first appearance of walchiacean conifer like monosaccate pollen such as potonieisporites long term terrestrial and marine increasing 13 c organic may reflect the onset of major glaciation in gondwana as there is evidence to suggest that the two are coeval but no specific mechanism can be suggested to link the trends

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

paleovalley related uranium deposits in australia and china a review of geological and exploration models and methods abstract the features and similarities in the geology of paleovalley related uranium mineralizing systems in australia and china can be used to refine strategies for exploration paleovalley related uranium resources include sandstone lignite and calcrete style deposits that are developed within the host sediments deposited in paleovalleys the paleovalleys incise either crystalline bedrock or older sedimentary rocks and uranium was deposited and concentrated by the influx of oxidized reduced groundwaters flowing in aquifers within the paleovalley fill the critical features of paleovalley related uranium deposits include sediment and uranium sources geological setting depositional environment age and relative timing of mineralization aquifer characteristics availability and distribution of reductants and preservation potential of the uranium mineral system this set of information provides a basis to establish the uranium mineralization model which can then be used to assist with generating targets for uranium exploration and prospectivity analysis of a region with respect to sino australian examples paleovalley related uranium deposits form mostly around the margins of sedimentary basins and the mineralization is commonly hosted within channel fills contained within paleovalleys developed upon or proximal to precambrian crystalline rocks that contain primary uranium sources the deposits that have been well studied show remarkably similar factors that controlled the formation of paleovalley related uranium deposits basement bedrocks with above background 2 8 ppm u levels of uranium 10 100 ppm that are linked to and or incised by paleovalleys are associated with these deposits and are the inferred source of the uranium in these regions extensive fluvial systems developed particularly during mesozoic and cenozoic times uranium from the bedrock was first dispersed into the sediments and then concentrated to form deposits through successive chemical remobilization precipitation and concentration the deposits formed in continental or marginal marine environments and commonly are associated with reduced lithologies containing pyrite and dispersed organic matter and or seams of lignite or show evidence of infiltrated hydrocarbons the mineralization is developed where oxidizing fluids carrying dissolved u reacted with reductants in the sediments geological geophysical and geochemical features of the paleovalleys and related uranium deposits are used to construct models to understand host sediment distribution fluid flow and ore genesis that can assist exploration for paleovalley hosted uranium deposits precise geometric definition of the basin margin and paleovalley architecture is important in identifying exploration targets and improving the effectiveness of drilling refinements in remote sensing geophysical and data processing techniques in combination with sedimentological and depositional interpretations provide an efficient approach for outlining the principal drainage patterns and channel dimensions to help reduce risk an exploration strategy should combine these technologies with a detailed understanding of the physicochemical parameters controlling uranium mobilization precipitation and preservation

the origins of the intraplate stress field in continental australia the ridge push force acting on the indo australian plate exerts a significant torque 8 5 1025n m about a pole at 30 3 n 34 5 e the angular difference between this torque pole and the observed pole of rotation for the plate 19 2 n 35 6 e is less than 12 and suggests that the ridge push force plays an important role in the dynamics of the indo australian plate we have used an elastic finite element analysis to study the predicted intraplate stress field in continental australia for four models which employ different boundary conditions to balance the ridge push torque acting on the plate the modeling indicates that a number of important features of the observed stress field within the australian continent can be explained in terms of balancing the ridge push torque with resistance imposed along the himalaya papua new guinea and new zealand collisional boundaries segments these features include n s to ne sw oriented compression in the northern australia and e w oriented compression in southern australia our analysis also shows that subduction processes along the northern and eastern boundaries provide only second order controls on the intraplate stress field in continental australia

buried inset valleys in the eastern yilgarn craton western australia geomorphology age and allogenic control abstract a contributory network of narrow fluvially incised valleys filled with a distinctive sequence of tertiary continental to shallow marine sediments is widespread throughout the eastern yilgarn craton in southwestern australia previously referred to as deep leads or paleochannels these are herein termed inset valleys to more accurately reflect their geomorphic expression and emphasize their subordinate and entrenched position with the bedrock surface of a much broader and older system of primary valleys owing to minimal denudation and tectonic deformation during the late cenozoic the inset valleys are excellently preserved and can be readily traced in boreholes and open cut mines throughout the eastern yilgarn craton and possibly also adjacent parts of southwestern australia with a combined catchment areal extent of at least documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmary

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

microfossil evidence for recurrent coseismic subsidence around lake hamana near the nankai suruga trough central japan abstract we reconstructed recurrent coseismic subsidence during the middle holocene from analyses of sedimentary facies and fossil diatom assemblages in a small drowned valley the shinjo lowland bordering lake hamana near the nankai suruga trough central japan the lake hamana region is known for coseismic subsidence during the 1707 hoei m8 6 and 1854 ansei tokai m8 4 earthquakes along the nankai suruga trough subduction zone a coring survey revealed three widely distributed peat layers in the lowland with a mud layer overlying each of the two lower peats with a sharp contact we traced the alternating peat mud beds for over 300 m along the long axis of a valley the fossil diatom assemblage analysis revealed that the peat layers were deposited in a freshwater pond marsh environment which changed abruptly to an estuarine to inner bay environment recorded by the mud layers from the sudden environmental change at the two peat mud contacts and our radiocarbon dating results we inferred that coseismic subsidence followed by an invasion of seawater into the lowland occurred at least twice during a great earthquake that occurred between 5645 and 6635 cal yr bp and during another great earthquake at ca 5700 cal yr bp within the mud layers the dominant diatom species changed gradually upward from nitzschia frustulum and cocconeis scutellum in the lower part to cyclotella striata and achnanthes submarina in the upper part these changes suggest that water depth and salinity gradually increased after the coseismic subsidence a possible cause of this gradual subsidence is postseismic subsidence following great nankai suruga trough earthquakes

late holocene great earthquakes in the eastern part of the aleutian megathrust abstract the great earthquake mw 9 2 of ad 1964 may not be typical of other megathrust earthquakes in the region during the last 4000 years we present new field data from three sites copper river delta the lower katalla river valley and puffy slough to enhance the temporal and spatial resolutions of the paleoseismic records of multiple great earthquakes differences in the spatial patterns of coseismic uplift and subsidence suggest different rupture combinations of the kodiak prince william sound and western yakutat segments of the plate boundary the longest and most comprehensive records all come from the prince william sound segment most sites here reveal net subsidence over multiple earthquake cycles except where probable upper plate faulting contributes locally to net uplift with measurable differences between sites only a few kilometres apart we identify the katalla area as a source of local seismic hazard similar to other locations in the western part of the yakutat microplate including the two mw8 ruptures in ad 1899 we use a bayesian radiocarbon modelling approach to estimate the age and recurrence intervals of multiple great earthquakes for the prince william sound segment of the megathrust the long interval 883 34 2 years between the penultimate earthquake and ad 1964 contrasts with the older earthquakes that have intervals ranging from 420 to 610 years with a mean of 535 years

rapid resetting of an estuarine recorder of the 1964 alaska earthquake tides and plants have already restored much of a landscape that the 1964 alaska earthquake destroyed at the head of a macrotidal estuary near anchorage in the vicinity of portage subsidence during the earthquake changed meadows thickets and spruce groves into barren tidal flats tidal flat silt and sand soon buried the pre earthquake landscape while filling intertidal space that the subsidence had made the flats supported new meadows and thickets by 1973 and new spruce by 1980 three new findings confirm that the flats aggraded rapidly and that their vegetation is maturing 1 most of the postearthquake deposits at portage date from the first decade after the 1964 earthquake their thickness of 23 sites in a 0 5 km 2 area was 1 4 0 2 m in 1973 1 6 0 2 m in 1991 and 1 6 0 3 m in 1998 2 many of the deposits probably date from the first months after the earthquake the deposits contain sedimentary couplets in which coarse silt or very fine sand is capped by fine or medium silt about 100 such couplets make up the lowest 0 5 m or more of the postearthquake deposits in two outcrops these couplets thicken and thin rhythmically both as groups of 5 20 couplets and as pairs of successive couplets probably the groups of thick couplets represent the highest tides the groups of thin couplets represent some of the lesser high tides and the pairs record inequality between twice daily high tides 3 in the 1980s and 1990s thickets expanded and spruce multiplied the vegetation now resembles the fossil assemblage rooted in the buried landscape from 1964 had the 1964 alaska earthquake been repeated a decade later the two earthquakes would now be recorded by two superposed buried landscapes near portage much more than a decade is probably needed to reset similar recorders at mesotidal estuaries of the cascadia subduction zone

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