the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

modelling greenland ice sheet inception and sustainability during the late pliocene understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the greenland ice sheet in this regard one key event is the full glaciation of greenland that occurred at the end of the pliocene warm period which remains partially unexplained previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low co2 value or by imposing a partial ice sheet over the surface of greenland although they highlight some fundamental mechanisms none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the late pliocene through a series of simulations with the ipsl cm5a coupled climate model used to force the grisli ice sheet model we show that a drop in co2 levels does not lead to an abrupt inception of the greenland ice sheet high ablation rates in central and northern greenland combined with low accumulation prevent such an abrupt inception ice sheet inception occurs when low summer insolation and co2 levels below modern values are combined the greenland ice sheet being restricted to the southeast region where high topography favours this build up this ice sheet experiences only partial melting during summer insolation maxima combined with high co2 levels further growth of the ice sheet with recoupling experiments is important at 360 and 280 ppm during insolation minima thus the full glaciation at 2 6 ma could be the result of a cumulative build up of the greenland ice sheet over several orbital cycles leading to progressively more intense glaciations during low summer insolation periods although this result could be a shortcoming of the modelling framework itself the gradual glacial inception interpreted from the oxygen isotope record could support our scenario

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

the ca 1740 1710 ma leichhardt event inversion of a continental rift and revision of the tectonic evolution of the north australian craton abstract interpretation and modelling of high resolution regional geophysical data of the central leichhardt river fault trough in the mount isa inlier are used to determine the timing of a major basin inversion event following the development of the ca 1780 1740 ma leichhardt superbasin inversion of the leichhardt superbasin formed the regional north south trending leichhardt anticline during east west shortening the limbs of the anticline are overprinted by several east west trending wedge shaped non magnetic sub basins filled with ca 1710 ma calvert and isa superbasin successions these relationships suggest inversion of the leichhardt superbasin occurred between ca 1740 and 1710 ma the event is also known to have affected the northern and eastern north australian craton the scale of the inversion suggests it was a significant event that we have defined as the leichhardt event this event requires a major tectonic driver to the east of the north australian craton possibly the accretion of a micro continental ribbon to the east of the mount isa inlier the results of this study have implication for paleogeographic reconstruction of the australian continent during the formation of nuna because eastern north australian craton faced an ocean at ca 1740 1720 ma the results also challenge the significance and intensity of crustal shortening associated with the ca 1600 1500 ma isan orogeny throughout the western mount isa inlier

aeromagnetic patterns of half graben and basin inversion implications for sediment hosted massive sulfide pb zn ag exploration the inverted extensional basins of the palaeoproterozoic north australian craton are amongst the most metallogenically endowed on earth for sediment hosted massive sulphide shms pb zn ag deposits faults that evolved during the evolution of these basins are an important exploration vector as they have behaved as conduits for mineralizing fluids controlled facies architecture and impacted on hydrothermal convection cells we attempt to map out ancient normal faults using integrated structural and aeromagnetic analysis to identify faults that are either buried beneath younger cover or have been inverted during later orogenic events this technique can be used for targeting potential conduits for mineralising fluids during shms pb zn ag exploration as well as a tool to map the architecture of extensional basins we have constructed simplified cross sections of half graben and inverted half graben and have forward modelled their magnetic response the aeromagnetic signature of a pre inverted half graben shows that the tilt block is characterised by a shallow magnetic gradient related to the shallowing of the magnetic marker beneath the half graben normal offset of the marker unit across a normal fault is characterised by a steeper magnetic gradient as the depth to the marker horizon increases simplified cross sections of isolated growth anticlines and the hanging wall buttressing show that the general shape of the magnetic profiles are maintained until the half graben has been completely inverted and the magnetic marker horizon displays reverse offset along the reactivated normal fault

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

facies and sequence stratigraphic analysis in an intracratonic thermal relaxation basin the early proterozoic lower quilalar formation and ballara quartzite mount isa inlier australia the quilalar formation and correlative mary kathleen group in the mount isa inlier australia conformably overlie rift related volcanics and sediments and non conformably overlie basement rocks they represent a thermal relaxation phase of sedimentation between 1780 and 1740 ma facies analysis of the lower siliciclastic member of the quilalar formation and the coeval ballara quartzite permits discrimination of depositional systems that were restricted areally to either n s trending marginal platform or central trough palaeogeographic settings four depositional systems each consisting of several facies are represented in the lower quilalar formation ballara quartzite these are categorized broadly as storm dominated shelf sds continental c tide dominated shelf tds and wave dominated shoreline wds sds facies consist either of black pyritic mudstone intervals up to 10 m thick or mudstone and sandstone associated in 6 12 m thick coarsening upward parasequences black mudstones are interpreted as condensed sections that developed as a result of slow sedimentation in an outer shelf setting starved of siliciclastic influx vertical transition of facies in parasequences reflects flooding followed by shoaling of different shelf subenvironments the shoreface contains evidence of subaerial exposure continental facies consist of fining upward parasequences of fluvial origin and tabular 0 4 4 m thick aeolian parasequences tds facies are represented by stacked tabular parasequences between 0 5 and 5 m thick vertical arrangement of facies in parasequences reflects flooding and establishment of a tidal shelf followed by shoaling to intertidal conditions wds facies are preserved in 0 5 3 m thick stacked tabular parasequences vertical transition of facies reflects initial flooding with wave reworking of underlying arenites along a ravinement surface followed by shoaling from lower shoreface to foreshore conditions parasequences are stacked in retrogradational and progradational parasequence sets retrogradational sets consist of thin sds parasequences in the trough and c tds and probably wds parasequences on the platforms thick sds parasequences in the trough and tds subordinate c and probably wds parasequences on the platforms make up progradational parasequence sets depositional systems are associated in systems tracts that make up 40 140 m thick sequences bounded by type 2 sequence boundaries that are disconformities transgressive systems tracts consist of c tds and probably wds depositional systems on the platforms and the sds depositional system and suspension mudstone deposits in the trough the transgressive systems tract is characterized by retrogradational parasequence sets and developed in response to accelerating rates of sea level rise following lowstand condensed section deposits in the trough and the thickest tds parasequences on the platforms reflect maximum rates of sea level rise and define maximum flooding surfaces highstand systems tract deposits are progradational early highstand systems tracts are represented by tds and probably wds depositional systems on the platforms and suspension mudstone deposits in the trough and reflect decreasing rates of sea level rise later highstand systems tracts consist of the progradational sds depositional system in the trough and possibly thin continental facies on the platforms this stage of sequence development is related to slow rates of sea level rise stillstand and slow rates of fall lowstand deposits of shelf margin systems tracts are not recognized but may be represented by shoreface deposits at the top of progradational sds parasequence sets

local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern mount isa inlier australia review and analysis with autocorrelation and weights of evidence although major crustal lineaments may play an important role in mineralisation the relationship between lineaments and mineral deposits can be quite cryptic and structural controls may vary as a function of scale along lineaments major lineaments alone may be of limited use for detailed target generation the cloncurry lineament in the eastern part of the mount isa inlier is a crustal scale structure defined by potential field derived worms weights of evidence quantifies the association between mineral occurrences and this lineament autocorrelation is used to recognise structural controls on mineralisation at different scales by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot the weights of evidence analysis shows that au au cu cu au and cu deposits have a positive spatial correlation to the cloncurry lineament which suggests it that acted as a primary crustal scale control on the localisation of cu and au through focussing mineralisation systems on a broad scale however autocorrelation defines a variety of local structural controls which can be interpreted as shear zones variably oriented fault sets en echelon fault arrays and potentially the orientation of bedding and or iron formations which localise fluid flow and mineral deposition at finer scales the results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the mt isa inlier

the complete apennines orogenic cycle preserved in a transient single outcrop near san fele lucania southern italy orogenic cycles may be viewed as comprising two extensional stages that are separated by a stage of contraction this sequence has characterized the evolution of most mountain belts resulting from continental collision and the structural signature of individual stages is recognized on a wide variety of scales i e from microscopic to regional whereas the history of mountain belts is generally inferred from observations carried out at different sites the entire sequence of deformation is very rarely recorded in single exposures the double switch in tectonic regime that led to the development of the lucanian apennines in southern italy from pre orogenic drifting through synorogenic thrusting to post orogenic extension is preserved in a superb metre scale outcrop at serra manarella in the vicinity of san fele a late jurassic synsedimentary normal fault is sealed by strata affected by a mid pliocene thrust related fold this composite structure in turn is truncated by a mid pleistocene normal fault observation of these relationships represents a unique opportunity to unequivocally establish the relative chronology of deformations in the lucanian apennines and may provide useful constraints for regional cross section restoration

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

middle eocene to late oligocene antarctic glaciation deglaciation and southern ocean productivity during the eocene oligocene transition earth cooled significantly from a greenhouse to an icehouse climate nannofossil assemblages from southern ocean sites enable evaluation of paleoceanographic changes and hence of the oceanic response to antarctic ice sheet evolution during the eocene and oligocene a combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes a cooling trend started in the middle eocene was interrupted by warming during the middle eocene climatic optimum and by short cooling episodes the cooling episode at 39 6 ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from 39 1 to 36 2 ma we suggest that oligotrophic conditions were associated with increased water mass stratification low nutrient contents and high efficiency of the oceanic biological pump that in turn promoted sequestration of carbon from surface waters which favored cooling after 36 2 ma we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance this turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient antarctic ice sheet and or to iron delivery to the sea surface eutrophic conditions were maintained throughout the oligocene which was characterized by a nannofossil assemblage shift toward cool conditions at the eocene oligocene transition finally a warm nannofossil assemblage in the late oligocene indicates a warming phase

predictive modelling of prospectivity for pb zn deposits in the lawn hill region queensland australia a combination of geodynamic modelling mineral potential mapping and mineral deposit studies are commonly used to explore for mineral deposits this paper focuses on the mineral potential aspect exploring the interrelationship between a knowledge driven approach which uses subjective evidence based on expert knowledge and a data driven model based on bayesian probabilistic reasoning the limitations and strengths of these approaches provide an example of how blending human interpretation with computational models can be an effective way to aid exploration and ore genesis interpretation the study is focused on the lawn hill platform mount isa inlier situated in northwestern queensland australia the models are used to predict the mineral potential in the area focussing on sedex sedimentary exhalative deposits and vs vein style pb zn mineralisation the lawn hill region shows good mineral potential close to the termite range fault within areas marginal to known prospects and vein lode hosted deposits however there are lower favourability sites suggesting significant potential in the kamarga dome integration of the knowledge and data driven models is considered a potential way to more reliably assess the favourability of locating a century type system the use of this combined technique suggests that the highest favourability of locating a shale hosted mineralisation similar to century is close to this deposit along the termite range fault zone one particularly prospective site has been identified north of the edith cluster

new faults v fault reactivation implications for fault cohesion fluid flow and copper mineralization mount gordon fault zone mount isa district australia fluid flow leading to mineralization can occur both on newly formed faults and on faults that are reactivated subsequent to their initial formation conventional models of fault reactivation propose that under high pore fluid pressures misorientated faults may reactivate due to low fault cohesion timing and orientation data for a mineralized palaeo to mesoproterozoic terrain mount gordon fault zone mgfz indicate that multiple successive new orientations of predominantly strike slip faults developed between 1590 and c 1500 ma requiring that during the younger deformations some earlier formed faults were too cohesive and or had insufficient pore fluid pressures or other potential fault weakening effects to induce reshear low pore fluid pressures were probably not to blame for failed reactivation on all older faults because some young faults did form or reactivate due to high pore fluid pressures as evidenced by jigsaw fit dilatant breccias hypogene copper mineralization in veins and breccia infill and subvertical tensile quartz veins aligned subparallel to 1 the assumption that old faults consistently have little or no cohesion appears to be incorrect in this terrain many older faults display prominent quartz veins along their length which may explain this conclusion furthermore faults with high cohesion may have acted as barriers and compartments so that intersections between them and newly formed faults host mineralization not because of reactivation but because of interaction between new faults and cohesive materials defined either by fault precipitates or rock juxtaposition together these results and observations provide new simple tools to stimulate copper exploration within the region and in fault hosted terrains

three dimensional structure along the inverted palaeoproterozoic fiery creek fault system mount isa terrane australia abstract the nw dipping fiery creek fault system located in the northern mount isa terrane comprises numerous sub parallel faults that record multiple episodes of palaeo to mesoproterozoic movement hanging wall wedge shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension mount isa rift event ca 1710 1655 ma reactivation of the fault system during regional shortening and basin inversion associated with the mesoproterozoic isan orogeny ca 1590 1500 ma resulted in complex three dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system this has resulted in the development of discrete hanging wall deformation compartments that are characterised by different structural styles high strain compartments are characterised by relatively intense folding and the development of break back thrusts whereas low strain compartments are only weakly folded variations in hanging wall strain are attributed to selective reactivation of normal fault segments controlled by the pre inversion fault dip and lithological contrasts across the faults variation of the pre inversion fault dip is interpreted to have been caused by episodic tilt block rotation during crustal extension moderately dipping faults active early in the mount isa rift event show the greatest degree of reactivation whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall

the role of ductility contrast and basement architecture in the structural evolution of the crystal creek block mount isa inlier nw queensland australia abstract the leichhardt river fault trough of the mount isa inlier comprises fault blocks which exhibit different local deformational histories and structural orientations many structural patterns in the stratigraphically highest cover sequences do not occur in adjacent fault blocks that expose older and mechanically stronger rocks within the mount isa group sediments of the crystal creek block for example tight e trending upright folds appear to be at odds with the surrounding north south regional trends in this paper it is proposed that an inherited extensional fault geometry played a significant role in controlling the structural patterns developed during later shortening through the integration of detailed surface mapping and forward magnetic modelling an inverted half graben was identified beneath the crystal creek block exposing the underlying origin of local structural complexities structural inversion and buttressing against pre existing faults simultaneously removed extensional displacement across pre rift rocks and induced folds and faults in overlying sag phase sediments this led to the development of two structural levels characterized by different deformational styles and apparently distinct deformational histories

meridional contrasts in productivity changes driven by the opening of drake passage changes in atmospheric pco2 are widely suggested to have played a major role in both the long term deterioration of cenozoic climate and many superimposed rapid climate perturbations such as the pivotal eocene oligocene transition changes in marine productivity affecting the biological oceanic carbon pump represent one possible cause of past co2 variability here we explore the relationship between ocean gateway change and marine biogeochemistry specifically we use a fully coupled atmosphere ocean biogeochemical model ipsl cm5a to examine global ocean paleoproductivity changes in response to the opening of drake passage in our simulations we find that drake passage opening yields a spatially uniform decrease in primary productivity in the low latitude oceans while the high latitude response is more spatially heterogeneous mechanistically the low latitude productivity decrease is a consequence of a fundamental reorganization of ocean circulation when drake passage opens driven by the isolation of the southern ocean from low latitude water masses nutrient depletion in the low latitudes is driven by a marked decrease in the intensity of deep convection in the southern ocean which drives the accumulation of nutrients at depth and their depletion in the intermediate and upper ocean especially away from sites of subduction in the high latitudes the onset of the antarctic circumpolar current in the model exerts a strong control both on nutrient availability but also on regions of deep water formation the qualitative agreement between geographically diverse long term paleoproductivity records and the simulated variations suggests that drake passage opening may contribute to the long term paleoproductivity signal

compound tectonic fabrics in singly folded rocks from southwest virginia u s a abstract a compound tectonic fabric is associated with folded and faulted calcareous mudrock in the foreland fold and thrust belt of the appalachian orogen two approximately coplanar spaced cleavages evolved during one episode of folding an earlier close spaced 40 spacing domainal microfabric is overprinted by and transitional with a wider spaced 2 3 cm spacing spaced disjunctive cleavage development of the spaced cleavage from the domainal microfabric is considered due to a change in dominant deformation mode from controlled grain boundary sliding to pressure solution factors which determine whether single or compound cleavage fabrics develop in singly folded rocks may relate to the timing of cleavage forming deformation increments relative to metamorphic dehydration reactions at low metamorphic grade anchimetamorphism to low greenschist facies it is proposed that grain alignment cleavage will develop when reactions are concomitant with deformation whereas a spaced cleavage will develop when reactions are inhibited or have gone to completion compound tectonic fabrics result when reactions either undergo completion or are initiated during the period of cleavage formation there are three distinct geometrical associations of compound fabrics and folds these associations are determined by the relative timing of formation of the various cleavages with respect to the folding

a shortened intraplate rift system in the proterozoic mount isa terrane nw queensland australia the leichhardt river fault trough of the mount isa terrane developed a complex extensional architecture between approximately 1800 and 1600 ma forming the underlying template upon which compressional structures were superimposed during the 1590 to 1500 ma isan orogeny basin fill material accumulated during at least five multiphase periods of rifting and associated postrift subsidence forming a stacked succession of unconformity bounded sequences initial e w extension was associated with a massive magmatic event half graben greater than 50 km in width and of alternating asymmetry localized the extrusion of up to 4 km of continental tholeiites thereafter a period of n s extension resulted in southward tapering north tilted half graben in which synrift basaltic and siliciclastic strata accumulated n s extension was followed by regional postrift subsidence and the deposition of a laterally continuous quartzite carbonate package a multiphase period of e w to nw se extension ensued during which time two unconformity bounded sequences accumulated the stratal architectures of these sequences are strongly asymmetric in cross section exhibiting a pronounced rotational thickening toward the east consistent with their deposition in the hanging walls of east dipping tilt blocks between 15 and 40 km in width finally a period of n s extension resulted in the development of e w trending f1 drag synclines in the highest level cover rocks the association of angular unconformities and block bounding faults e w trending synclines and e w striking faults and the unique internal fold geometries of fault blocks suggest that many fault bounded blocks originated as coherent structural entities during rifting and continued to act as such during subsequent shortening

applicability of thin or thick skinned structural models in a region of multiple inversion episodes southern south africa abstract the deformation of the cape fold belt has been attributed to repeated structural reactivation of a mega detachment from the late proterozoic to the mesozoic 650 65 ma through the integration of onshore cross sections with observations from the offshore mesozoic extensional system this study evaluates the applicability of the mega detachment model regional scale cross sections through the permian triassic cape fold belt reveal that it comprises two main structural domains a northern domain dominated by northward verging and asymmetric folds and a southern domain comprising a series of approximately 8 km wavelength box folds the genesis of these box folds is attributed to motion on underlying high angle 45 reverse faults this variation between north and south in the fold belt is reflected by a similar variation in extensional geometry of the mesozoic normal faults as revealed by subsurface data the normal faults demonstrate a progressive increase in dip from 24 in the north to 60 in the south features commonly attributed to thin and thick skinned tectonic models are observed in both domains therefore it is not appropriate to describe the observed deformation as one of the two end members in addition the structures are inferred to have undergone at least two stages of inversion irrespective of dip this is not predicted by either end member model

the role of thrusting in the structural development of the mount isa mine and its relevance to exploration in the surrounding region resolution and prediction of the structure underground at mount isa from the surface geology is now possible using evidence for north to south movement on large scale thrusts during the first deformation at 1610 ma this evidence for the direction of movement during thrusting is preserved 1 macroscopically within three successive thrust imbricates as the north south alignment of respective truncations of older stratigraphic units by the angular unconformity at the base of the mount isa group 2 macroscopically and mesoscopically as a zone of vertical north south striking foliation with a horizontal stretching lineation that formed on a sinistral transform fault during dalong the wonga duchess belt 3 mesoscop ically as a regionally distributed north south oriented stretching lineation li that is locally well preserved on s0 surfaces in the hinges of folds with north south axial planes that formed during the second regional deformation and 4 microscopically as a horizontal north south aligned mineral elongation lineation defined by inclusion trails preserved in porphyroblasts that grew early during the second deformation adjacent to the wonga duchess belt the swing in strike of a large scale 70o west dipping lateral ramp on the western margin of the large scale kokkalukkanurker duplex from north south parallel to the direction of movement during thrusting to north northwest south southeast caused a portion of the meerenurker roof thrust lying on this lateral ramp to be overturned for at least 50 km near mount isa this overturning resulted from tilting the 70o west dipping lateral ramp through another 70 o as it rode obliquely north south over the north northwest south southeast striking portion of the same lateral ramp on the next imbricate to the south this generated the gross structural relationships seen in three dimensions at mount isa whereby the greenstone basement that truncates mount isa group rocks below the mine overlies them to the west the second deformation involved intense east west shortening and formed macroscopic folds that conveniently expose varying levels of the thrust pile generated during the first deformation in higher grade rocks west of mount isa and to either side of the wonga belt axial plane schistosity development and or reactivation of bedding during this deformation was quite intense and tended to obliterate and or rotate foliations and lineations formed during the first deformation only in the hinges of the folds formed during the second deformation where the deformation was less intense or silicification had occurred are earlier lineations preserved relatively unaffected by this event the geology of the mount isa valley and the rocks to the west of the mine is controlled by a series of north south striking high angle reverse faults that slice through the meerenurker thrust as it crosses the above mentioned lateral ramp on the western edge of the large scale duplex two of the faults mount gordon and mount isa dip steeply west with similar dis placements of 4 to 6 km west side up the other two faults holly and tastoka dip steeply east with the latter fault having a more significant displacement of 2 5 to 3 km east side up that greatly affects the geology on the eastern side of the mount isa valley the effects of these faults on the geometry produced by thrusting during the first deformation and folding during the second allow accurate prediction of the third dimension anywhere in the mount isa valley and the region immediately to the west consequently they can be used to predict the location of structurally controlled sites of potential copper mineralization similar to those found in the mount isa mine where mineralization formed during the third deformation

geochronology of early to middle proterozoic fold belts in northern australia a review abstract this geochronological review integrates geologically relevant isotopic data from the several early to middle proterozoic fold belts of northern australia a number of firm chronological benchmarks largely established by means of u pb zircon studies now provide a time framework within which to better quantify the tectonostratigraphic history of many of these terranes the apparent worldwide dearth of crustal events in the earliest proterozoic between 2500 and 2000 ma was broken in northern australia with the advent of a major crust forming episode between 1880 and 1850 ma ago these rocks may have evolved from an initial mantle or lower crustal melting and fractionation process about 400 300 ma earlier that is evidenced from sm nd model ages the extent involvement and or degree of assimilation of any pre existing archaean crust is small but whether or not it is negligible or zero is not satisfactorily known the 1880 1850 ma event the barramundi orogeny is well represented in northern australia both lithologically and analytically and the rocks that pre and post date it have a similar tectonic setting over very wide areas of the continent two consistent and widespread elements of this tectonism are regional metamorphism and deformation of the first cycle of supracrustals barramundi orogeny and crystallization of i type k rich felsic magmas closely following and in some cases overlapping with deformational processes in the halls creek inlier the ages of this rapid deep crustal to supracrustal tectonic transition cannot be distinguished within the range 1860 1850 ma this major yet short lived tectonism is mirrored in other fold belts such as pine creek tennant creek and mount isa in which u pb zircon ages give slightly older constraints of 1885 1870 ma 1920 1870 ma and 1885 10 ma respectively the ensuing felsic magmatism in these latter terranes continued for a few tens of millions of years with the crystallization and emplacement of comagmatic volcanic plutonic pairs throughout in the interval 1870 1860 ma in the georgetown and arunta inliers direct evidence of this otherwise ubiquitous event if present is masked by younger high grade metamorphism in the latter however metamorphic crustal components having approximate protolith ages of this order can be inferred from their evolved isotopic signatures the geochronological and geochemical coherency of the extensive early proterozoic 1870 ma magmatism contrasts with that of post 1800 ma magmatism which is less extensive generally anorogenic commonly bimodal in character and varies in age from one terrane to another several major sedimentary basins were being filled at this time major igneous events at 1790 1740 ma 1670 ma and 1500 ma are recognized elongate sublinear volcanic and plutonic belts 1790 1740 ma old are present at mount isa in high grade granitic gneisses of the arunta inlier a few u pb zircon ages and extrapolated rb sr protolith ages are coincident at about 1760 1750 ma indicating that this event may be important in the development of the division 2 sequences of that fold belt the platformal hart dolerite and oenpelli dolerite two of the largest mafic intrusions in the world were emplaced at 1762 25 ma and 1688 13 ma younger felsic plutonism and volcanism gave rise to rapakivi type granites in the mount isa tennant creek and the granites tanami inliers at 1670 ma a time close to that of the aileron deformational metamorphic event in central australia further at 1650 ma there is growing evidence of an unexpectedly coherent hydrothermal episode that reset or disturbed many rb sr ages gave rise to pegmatites and was possibly associated with mineralization in the davenport and eastern arunta inliers discrete middle proterozoic deformational events between 1610 and 1470 ma punctuate the tectonostratigraphic history in the arunta mount isa and georgetown fold belts where they are best documented

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

antarctic glaciation caused ocean circulation changes at the eocene oligocene transition a climate model is used to show that the growth of the antarctic ice sheet at about 34 myr ago drove changes in ocean circulation but the opening of ocean gateways had relatively little impact antarctica developed an ice sheet about 34 million years ago following a period of ice free conditions known as the super greenhouse climate previous research has suggested that ice sheet growth was driven by either the thermal isolation of antarctica arising from the opening of ocean gateways or by progressively lower atmospheric co2 content matt huber and colleagues now use a climate model to show that the growth of the ice sheet forced by changes in co2 drove the changes in ocean circulation in contrast the opening of the gateways had relatively little impact on ocean circulation two main hypotheses compete to explain global cooling and the abrupt growth of the antarctic ice sheet across the eocene oligocene transition about 34 million years ago thermal isolation of antarctica due to southern ocean gateway opening1 2 3 4 and declining atmospheric co2 refs 5 6 increases in ocean thermal stratification and circulation in proxies across the eocene oligocene transition have been interpreted as a unique signature of gateway opening2 4 but at present both mechanisms remain possible here using a coupled ocean atmosphere model we show that the rise of antarctic glaciation rather than altered palaeogeography is best able to explain the observed oceanographic changes we find that growth of the antarctic ice sheet caused enhanced northward transport of antarctic intermediate water and invigorated the formation of antarctic bottom water fundamentally reorganizing ocean circulation conversely gateway openings had much less impact on ocean thermal stratification and circulation our results support available evidence that co2 drawdown not gateway opening caused antarctic ice sheet growth and further show that these feedbacks in turn altered ocean circulation the precise timing and rate of glaciation and thus its impacts on ocean circulation reflect the balance between potentially positive feedbacks increases in sea ice extent and enhanced primary productivity and negative feedbacks stronger southward heat transport and localized high latitude warming the antarctic ice sheet had a complex dynamic role in ocean circulation and heat fluxes during its initiation and these processes are likely to operate in the future

provenance of the early mesoproterozoic radium creek group in the northern mount painter inlier correlating isotopic signatures to inform tectonic reconstructions abstract new in situ zircon la icpms geochronologic and hf isotope data from the radium creek group within the mount painter inlier provide important temporal constraints on the early mesoproterozoic palaeogeography of eastern proterozoic australia the entire radium creek group was deposited in a single basin forming phase and has a maximum depositional age of 1595 3 7 ma detrital zircon from these metasedimentary rocks have u pb age populations at ca 1595 ma 1660 1680 ma 1710 1780 ma ca 1850 ma and ca 2500 ma these grains are characterised by isotopically diverse and evolved sources and have crystallised within predominantly felsic igneous host rocks the relative age spectra and isotopic character has more similarity with the gawler craton than the arunta block curnamona province or the mount isa inlier these observations suggest that the mount painter province was adjacent to the gawler craton in the early mesoproterozoic our data supports a coherent south australian craton at ca 1595 ma and a contiguous continental mass that included the north and south australian cratons the mount painter inlier occupied a complex plate tectonic setting in the overriding plate of two convergent margins

geodynamic evolution of the proterozoic mount isa terrain the proterozoic mount isa terrain records the effects of four periods of intraplate tectonism the c 1870 ma barramundi orogeny was characterized by a massive felsic magmatic event and global correlations suggest a physical link between australia and laurentia at this time thereafter the terrain underwent an extensional history spanning 200 ma involving repeated episoded of rifting post rift subsidence and associated depositional and magmatic phases this protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25km above attenuated continental crust rifting was interrupted prior to the formation of ocean crust by the compressional isan orogeny 1590 1500 ma the isan orogeny was synchronous with low pressure high temperature metamorphism and widespread metasomatism in the waning stages of shortening the mount isa terrain evolved into a wrench system characterized by an extensive network of strike slip faults the current level of exposure in this terrain provides spectacular examples of superimposed rifts basin inversion and wrench geometries developed at middle to upper crustal levels

the respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the eocene oligocene transition the continental scale initiation of the antarctic ice sheet at the eocene oligocene boundary eocene oligocene transition eot 34 ma is associated with a global reorganization of the climate if data studies have assessed the precise timing and magnitudes of the ice steps modeling studies have been unable to reproduce a transient ice evolution during the eocene oligocene transition in agreement with the data here we simulate this transition using general circulation models coupled to an ice sheet model our simulations reveal a threshold for continental scale glaciation of 900 ppm 100 to 150 ppm higher than previous studies this result supports the existence of ephemeral ice sheets during the middle eocene as similar co 2 levels 900 1000 ppm have been reached episodically during this period transient runs show that the ice growth is accurately timed with eot 1 and oi 1 the two 18 o excursions occurring during the transition we show that co 2 and orbital variations are crucial in initiating these steps with eot 1 corresponding to the occurrence of low summer insolation whereas oi 1 is controlled by a major co 2 drop the two 18 o steps record both ice growth and temperature representing some 10 30 m eustatic sea level fall and 2 4 c cooling at eot 1 and 70 20 m and 0 2 c for oi 1 the simulated magnitude of the ice steps 10 m for eot 1 and 63 m for oi 1 and the overall cooling at various locations show a good agreement with the data which supports our results concerning this critical transition

a potential barrier to deep antarctic circumpolar flow until the late miocene the central scotia sea located between the south american and antarctic plates is an integral part of the marine conduit that permits eastward deep water flow from the pacific ocean to the atlantic ocean the geologic history of the central scotia sea is therefore critical for a full understanding of the initiation and subsequent evolution of the complete deep antarctic circumpolar current widely believed to have been a key factor in the history of antarctic glaciation here we present new evidence on the nature and age of the central scotia sea floor multibeam surveys and the first dredged samples indicate that a now submerged remnant volcanic arc may have formed a barrier to deep eastward oceanic circulation until after the mid miocene climatic optimum inception and development of a full deep antarctic circumpolar current may therefore have been important not in the drop in global temperatures at the eocene oligocene boundary as long surmised but in the subsequent late miocene global cooling and intensification of antarctic glaciation

constraints on long lived mesoproterozoic and palaeozoic deformational events and crustal architecture in the northern mount painter province australia abstract meta sedimentary and igneous rocks preserved in the hanging wall of the paralana fault northern mount painter province record a protracted ca 1600 myr multi staged metamorphic and poly deformational evolution related to mesoproterozoic and palaeozoic orogenic events the mount painter province was located near the margin of both the south australian craton and the north australian craton which allows comparisons of the tectonic evolution of these margins and provides context for the evolution of the eastern proterozoic australia for both the columbia and gondwana supercontinents within the mount painter province meta sedimentary rocks form part of a basin system developed adjacent to the margins of the gawler craton and curnamona province following the olarian wartakan orogenic system sedimentation was followed by ca 1590 1552 ma ductile deformation d 1 d 3 at mid to upper crustal levels preserving a rapid ca 6 myr burial and exhumation cycle initial deformation is characterised by the development of a layer parallel fabric s 1 s 1 is overprinted by recumbent north verging folds f 2 formed during mid to upper amphibolite facies peak metamorphism m 2 which are overprinted by tight upright shallow ne sw plunging folds f 3 d 3 folds developed contemporaneous with sinistral oblique shearing and the development of proto mylonitic to ultra mylonitic fabrics along the paralana fault zone the timing of d 3 deformation is constrained by the development of a penetrative steeply dipping foliation s 3 in the ca 1585 1569 ma shallowly emplaced mount neill granite and relatively undeformed granites dated at ca 1552 ma further constraint on the absolute timing of mesoproterozoic tectonism is provided through the dating of zircon growth from samples of the meta sedimentary radium creek metamorphics this dating reveals a 1555 16 ma metamorphic event interpreted to be the consequence of m 3 amphibolite facies regional metamorphism and accompanying metasomatism the transition between d 2 and d 3 is interpreted to reflect a shift from ca 1591 1585 ma n s shortening to ca 1585 1552 ma nw se shortening this episode of orogenesis is correlated with the ca 1585 1540 ma kararan orogeny in the northern gawler craton which distinctly postdates the ca 1600 1590 ma olarian orogeny as previously interpreted the mesoproterozoic structural architecture was reactivated during neoproterozoic extension d 4 and the ca 500 ma delamerian orogeny delamerian structures are formed in a predominantly brittle regime early thin skinned thrusting was followed by thick skinned deformation d 5 d 6 during which open f 5 folds developed above oblique lateral ramps and produced type 0 overprinting patterns with f 3 mesoproterozoic folds steeply plunging f 6 buckle folds with se trending axial traces are the last phase of deformation recorded both mesoproterozoic ductile deformation phases and the palaeozoic ductile brittle to brittle overprints were focussed along the paralana fault emphasising the repeated long lived evolution of this crustal scale fault system

normal faults in thrust sheets pre orogenic extension post orogenic extension or both abstract in fold and thrust belts that experienced both pre orogenic and post orogenic extension it may be difficult to establish whether observed normal faults pre dated post dated or were synchronous with thrusting geometrical structural patterns may be insufficient to constrain the relative chronology of extensional and contractional deformations the systematic use of kinematic criteria makes it possible to unequivocally define the timing relationships of reverse and normal fault development and hence to correctly unravel complex structural evolutions kinematic analysis in the southernmost umbria marche apennines of italy where both normal and thrust faults are present revealed a history of repeated tectonic inversion characterised by two distinct stages of extension separated by an episode of folding and thrusting structural overprinting relationships observed at thrust normal fault intersections were useful for i removing sequentially younger deformations and hence ii separating and quantifying the effects of orogenic contraction from those of both pre orogenic and post orogenic extension

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

the cloncurry lineament geophysical and geological evidence for a deep crustal structure in the eastern succession of the mount isa inlier the cloncurry lineament is a major feature evident from wavelet processed magnetic and gravity potential field data over the mount isa inlier eastern succession it is laterally continuous over 200 km of strike length and is inferred from the gravity data to extend to at least 30 km depth it delineates the contact between two major paleoproterozoic sedimentary sequences and is spatially associated with a number of mineral deposits including cannington ag pb zn ernest henry cu au and many smaller cu au deposits mapping and magnetic forward modelling along several profiles perpendicular to the cloncurry lineament suggests that it corresponds to the eastern margin of a 5 10 km wide deformation zone within the calc silicate dominated doherty formation the western boundary of this deformation zone is a distinct narrow fault zone the cloncurry fault the deformation zone consists of multiple generations of shearing and faulting accompanied by metasomatic alteration large variations in the magnetic response within the deformation zone can be modelled as sub vertical brecciation zones breccia types range from highly magnetic actinolite albite magnetite breccias through to late stage non magnetic quartz k feldspar hematite breccias the long lived history of multiple reactivation strike continuity width and vertical extent of the deformation zone suggest that it is a major crustal structure the structure may have originated during basin formation and later acted as a fluid pathway for alteration and base metal mineralization

refining our estimate of atmospheric co2 across the eocene oligocene climatic transition abstract the eocene oligocene transition eot followed by oligocene isotope event 1 oi 1 is a dramatic global switch in climate characterized by deep sea cooling and the first formation of permanent antarctic ice models and proxy evidence suggest that declining partial pressure of atmospheric carbon dioxide co 2 atm below a threshold may explain the onset of global cooling and associated ice formation at oi 1 however significant uncertainty remains in the estimated values and salient features of reconstructed co 2 atm across this interval in this study we present novel carbon isotope records from size separated diatom associated organic matter 13 c diatom preserved in silica frustules physical preservation of this material allows concurrent investigation of isotopic and cell size information providing two input parameters for biogeochemical models and the reconstruction of co 2 atm we estimate co 2 atm in two ways first we use size and reaction diffusion kinetics of a cell to calculate a co 2 atm threshold second we use the calibrated relationship between e p diatom and carbon dioxide from culture and field studies to create a record of co 2 atm prior to and across the transition our study from site 1090 in the atlantic sector of the southern ocean shows co 2 atm values fluctuating between 900 and 1700 100 p p m v across the eot followed by a drop to values in the order of 700 to 800 100 p p m v just prior to the onset of oi 1 our values and magnitude of co 2 atm change differ from previous estimates but confirm the overall trends inferred from boron isotopes and alkenones including a marked rebound following oi 1 due to the intricate nature of the climate system and complexities in constraining paleo proxies this work emphasizes the importance of a multi proxy approach to estimating of co 2 atm in order to elucidate its role in the emplacement of antarctic ice sheets at the eot

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

equatorial pacific productivity changes near the eocene oligocene boundary there is general agreement that productivity in high latitudes increased in the late eocene and remained high in the early oligocene evidence for both increased and decreased productivity across the eocene oligocene transition eot in the tropics has been presented usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the eot itself a complete record of the eocene oligocene transition was obtained at three drill sites in the eastern equatorial pacific ocean odp site 1218 and iodp sites u1333 and u1334 four paleoproductivity proxies that have been examined at these sites together with carbon and oxygen isotope measurements on early oligocene planktonic foraminifera give evidence of ecologic and oceanographic change across this climatically important boundary export productivity dropped sharply in the basal oligocene 33 7 ma and only recovered several hundred thousand years later however overall paleoproductivity in the early oligocene never reached the average levels found in the late eocene and in more modern times changes in the isotopic gradients between deep and shallow living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early oligocene that on average affected accumulation rates of barite benthic foraminifera and opal as well as diatom abundance near 33 5 ma an interval with abundant large diatoms beginning at 33 3 ma suggests an intermediate thermocline depth which was followed by further shoaling a dominance of smaller diatoms and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

asymmetric extension of the middle proterozoic lithosphere mount isa terrane queensland australia abstract the middle proterozoic mount isa basin of the mount isa terrane hosts several large pb zn ag deposits and is arguably one of the richest mineral provinces in the world the deformed remnants of this basin extend from the eastern margin of the leichhardt river fault trough through to the murphy tectonic ridge in the far north of the terrane the mount isa basin initially evolved in response to nw se directed extension during the mount isa rift event this event began before 1708 ma and had ceased by 1653 ma a sag basin continued to evolve thereafter until 1595 ma regional analysis of the highest level cover rocks of the mount isa basin reveals a notable difference in the locus of syn rift sedimentation syn rift magmatism and post rift subsidence although crustal extension was widespread across the mount isa basin tectonic subsidence was focussed along the n s oriented mount isa rift approximately 3 5 km of fluvial to shallow marine clastic sediments were deposited into isolated rift basins bimodal volcanism and emplacement of shallow level plutons occurred along the western and northwestern margins of the mount isa rift magmatic provinces mark the locus of significant subcrustal lithospheric thinning asthenospheric upwelling and mafic underplating within these magmatic provinces the syn rift sequences are fewer and thinner 750 2000 m and were dominantly deposited in subaerial environments suggesting a relatively stable uplift and subsidence history the position of maximum subcrustal lithospheric extension is determined by the position of greatest post rift subsidence this occurred beneath the northern mount isa terrane where the thickest post rift sequences are preserved and the depositional history is more protracted we propose that the evolution of the mount isa basin is a consequence of asymmetric extension of the middle proterozoic lithosphere

the role of ocean gateways in the dynamics and sensitivity to wind stress of the early antarctic circumpolar current the date of inception of the antarctic circumpolar current is debated due to uncertainty in the relative opening times of drake passage and the tasman seaway using an idealized eddy resolving numerical ocean model we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current we find that overlapping continental barriers do not impede a circumpolar transport in excess of 50sv as long as a circumpolar path can be traced around the barriers however the presence of overlapping barriers does lead to an increased sensitivity of the current s volume transport to changes in wind stress this change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress specifically when the pressure drop across continents is the main balancing sink of momentum the zonal volume transport is sensitive to changes in wind stress changes in zonal volume transport take place via altering the depth independent part of the circumpolar transport rather than that arising from thermal wind shear in such a scenario isopycnals continue to slope steeply across the model southern ocean implying a strong connection between the deep and surface oceans this may have consequences for the meridional overturning circulation and its sensitivity to wind stress

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

heterogeneous exhumation of the mount isa orogen in ne australia after 1 6 ga nuna assembly new high precision 40ar 39ar thermochronological constraints

multiply deformed terrains problems of correlation abstract the best tools available for carrying out a structural analysis in a complex area are overprinting style and patterns of orientation unfortunately all have limitations which are reviewed briefly and discussed in areas of continuous unfaulted outcrop the deformational history can be established purely on the basis of overprinting but even in such areas there can be problems since not all overprinting relationships are unambiguous most fold interference patterns are reliable overprinting relationships based on foliations however are commonly unreliable and various examples are cited and discussed even in areas where the sequence of deformational events can be established their temporal significance is unclear since the methods applied only determine local relative timing and absolute relationships must vary in space and time across an orogen

the influence of initial fold geometry on type 1 and type 2 interference patterns an experimental approach abstract experiments on superposed folding were performed in a plane strain pure shear rig using paraffin wax as an analogue for rocks a series of pre formed cylindrical folds were refolded with the compression direction acting parallel to the initial fold hinge direction the intermediate axis perpendicular to the first fold axial plane and the extension direction parallel to the first fold axial plane and perpendicular to its axis type 1 interference geometry roundness tightness and amplitude were varied to investigate the influence of first fold geometry on the interference patterns experimental folding of an initially planar layer oriented parallel to the first fold envelope provides a reference geometry for comparison the results suggest that hinge roundness has less influence on the interference pattern than other factors close initial folds refold into type 2 interference patterns which become even more pronounced as the tightness increases open folds produce type 1 interference patterns folds with the same interlimb angle and the same roundness produce different interference patterns depending on relative amplitude folds with relatively large amplitude are refolded into type 2 patterns whereas folds with small amplitude give clear dome and basin structures in a second set of experiments the compression direction also acted parallel to the first fold hinge but the orientations of the intermediate and extension axes were interchanged the interference patterns obtained are very similar to those in type 1 interference geometry suggesting that the major factor in determining whether type 1 or type 2 interference patterns develop is the initial fold geometry and not the kinematics of the second deformation

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

paleoproductivity nutrient burial climate change and the carbon cycle in the western equatorial atlantic across the eocene oligocene boundary paleoproductivity nutrient burial and carbon cycling were investigated across the eocene oligocene e o boundary begin to end 36 9 32 7 ma at 40 kyr resolution timescale of shackleton et al 1999 at ocean drilling program site 925 on the ceara rise in the western equatorial atlantic 3040 m present water depth 748 26 850 70 mbsf downcore bulk sediment records of biogenic barium total reactive phosphorus biogenic silica and calcium carbonate are interpreted to represent export production net nutrient burial biogenic opal production and inorganic carbon burial respectively the global positive excursion in 13c subsequent to the e o boundary is recorded at site 925 export production appears to have been externally forced by orbital parameters at eccentricity frequencies during the study interval based on spectral analysis of the biogenic barium and reactive phosphorus records biogenic silica production or preservation increased after the eocene oligocene boundary to a higher baseline although overall productivity and nutrient burial did not increase based on barium and reactive phosphorus records thus although absolute production did not increase at this site a shift in relative abundance of siliceous versus carbonate productivity may have resulted in a change in relative organic carbon burial this may have contributed to the positive excursion in global oceanic 13c subsequent to the eocene oligocene boundary although the silica maximum persists after the carbon isotope excursion ends

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

analysis and interpretation of composite foliations in areas of progressive deformation abstract in areas of progressive deformation where successive structures develop during a relatively continuous deformation within a geologically short time period traditional chronological notations of structural elements e g s 1 s 2 etc can give erroneous impressions of how large rock masses evolve in time and space we demonstrate from field examples that successive structures can develop which a are comparable in morphology and orientation but of different ages b are different in morphology but of comparable age and c show rapid morphological changes over short distances under such conditions correct identification of the relative age of structures is often difficult to impossible we consider the concepts of a composite foliation and of transposition cycles as vehicles to objectively evaluate the significance of different sets of structures in the evolution of larger rock masses we suggest that 1 structural elements be labeled using morphological notation adding numerical subscripts only when independent evidence is available 2 geologists more fully acknowledge and integrate the concept of deformation partitioning into their models and 3 when analyzing areas of multiple deformation more emphasis is placed on the relationship between domains of differing complexity integration of these three perspectives in the analysis will lead to a more realistic basis upon which to model the structural evolution of large rock masses

geochemistry of 1 8 1 67 ga mudstones and siltstones from the mount isa inlier queensland australia provenance and tectonic implications abstract sedimentary and volcanic rocks overlying basement in the mount isa inlier australia are subdivided into three cover sequences the upper two sequences range in age from 1800 to 1670 ma and each consist of rift and overlying sag phases of sedimentation fine grained siliciclastic sedimentary rocks in the upper two sequences define two distinct geochemical groups samples from groups i and ii are mainly from the lower and upper rift and upper thermal phases respectively one sample from the lower rift phase has affinities with group ii whereas samples from the lower thermal phase belong to both groups i and ii eu eu values are 0 70 to 0 85 for group iand 0 55 to 0 70 for group ii group i samples are characterized by lower la sc and th sc ratios and higher cr th ratios than group ii cr niand co concentrations are greater in group i than group ii groups i and ii also are distinguished on plots of eu eu vs lan smn and eu eu vs gdn ybn two samples from group i have elevated lree hree and lan ybn ratios that are attributed to intense weathering as revealed by their high chemical index of weathering values the geochemical data reflect a combination of local and more distant regional provenances and can be related to the tectonic evolution of the mount isa inlier group i samples are attributed to dilution of a mature post archean source by addition of recycled mafic volcanics group ii samples are typical post archean sediments derived from differentiated upper continental crust with no dilution by local sources the lower rift phase displays great geochemical variability samples from both groups that is typical of active tectonic settings such as rifts the great variability of samples from the lower sag phase both groups is surprising but probably reflects the diverse rock types beneath this basin stable tectonic conditions during this phase of sedimentation are indicated instead by major element geochemistry that records severe weathering similarity of the upper rift phase sample with some samples from the lower sag phase reflects recycling of the latter samples from the upper sag phase are remarkably uniform in composition group ii and reflect the stable tectonic conditions under which this basin developed

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

himalayan main central thrust and its implications for himalayan inverted metamorphism abstract within the scheme of south directed orogenic polarity in the himalayan region the main central thrust mct developed at an intermediate stage between the collisional tectonics at the indus tsangpo suture in the north and the latest underthrusting at the main boundary thrust mbt in the south the proposition that the mct marks the base of the high himalayan central crystalline zone against the inner sedimentary belt of the lower himalayas creates confusion in its definition and its location in kashmir and especially in the eastern himalayas the problem can be resolved by defining the mct as the basal thrust of the crystalline nappe sequences either rooted at or detached as klippe from the central crystalline zone characteristically the nappe sequences show inverted metamorphism which generally starts at the basal thrust the redefined mct from the chlorite biotite grades and reaches the kyanite sillimanite grades with migmatites and anatectic granites in the highest tectonic levels the metamorphic rank of both the substrate and the overthrust rock units in the vicinity of the mct is generally low the inverted metamorphism may be explained by intracontinental underthrusting and resultant downbowing of the isotherms the redefined mct does not appear to represent the thrust zone along which the continental underthrusting was initiated it developed to the south of this zone as a possible sole thrust of the nappe stack of the crystalline rocks that overrode the parautochthonous sedimentary sequences of the lower himalayas the sequence of events associated with the mct would probably be repeated in the mbt

the crustal scale architecture of the eastern succession mount isa the influence of inversion the three dimensional crustal architecture of the eastern part of the mount isa inlier is investigated from serial cross sections constructed using geological map data revised chronostratigraphy gravity magnetics worms multiscale wavelet edges of potential field data and seismic data the top part of the crust consists of rift and platform type metasediments that were deposited in three cover sequences from 1850 to 1610 ma these rocks constitute the mount isa eastern succession and they were intruded by mafic felsic plutons dykes and sills of various ages before and during the isan orogeny ca 1 6 1 5 ga the eastern succession overlies a felsic metamorphic basement which in turn sits on a tonalitic gabbroic lower crust the depositional basin architecture for the eastern succession was controlled by major n s trending structures that penetrated the lower crust and accommodated e w extension these structures also underlie major upper crustal structures such as the mitakoodi culmination and snake creek anticline that were formed by contraction in the isan orogeny positive inversion may therefore have been a key process in the evolution of the eastern part of the inlier and governs its architecture at the crustal scale inversion involved reactivation of basement penetrating structures which localised contractional structures in the cover sequences above as well as influencing pluton emplacement the felsic metamorphic basement may have been penetratively deformed during inversion the spatial association between the basin controlling and contractional structures suggests that either early extensional displacements were completely reversed by later contraction or that much of the eastern succession has remained essentially parauthochthonous relative to the basement

thrusting and duplex formation at mount isa queensland australia large scale repetition of mount isa and haslingden group rocks in the anticline north of mount isa is interpreted as the core of a thrust duplex which has been subsequently folded parallel to the direction of thrusting displacement of mount isa group rocks above the duplex is extremely significant to the regional geology and exploration for more mount isa style pb zn and cu orebodies interpretation of the geometry of the thrust belt indicates thrusting on different stratigraphical levels below and above the duplex during its formation horses formed from a heelwards protruding footwall ridge instead of a trough and the complex effects on stratigraphical cross sections through duplexes of sloping lateral footwall ramps on horses