coal depositional models for deltaic and alluvial plain sequences coal depositional models attempt to predict the distribution and geometry of coal beds within given sequences or provinces to date models proposed for coals of alluvial and deltaic origin have emphasized depositional environment as the controlling variable in this article i propose that subsidence regime and to a lesser extent sediment supply are the dominant controls upon coal distribution rather than environment of accumulation for this reason most existing coal depositional models are likely to have limited predictive capability

revision of the sauropod dinosaur diamantinasaurus matildae hocknull et al 2009 from the mid cretaceous of australia implications for gondwanan titanosauriform dispersal the osteology of diamantinasaurus matildae the most complete cretaceous sauropod described from australia to date is comprehensively reassessed the preparation of additional material from the type locality pertaining to the same individual as the holotype sheds light on the morphology of the axial skeleton and provides additional information on the appendicular skeleton the new material comprises two dorsal vertebrae an incomplete sacrum including four partial coalesced vertebrae the right coracoid the right radius an additional manual phalanx and a previously missing portion of the right fibula in this study we identify thirteen autapomorphic characters of diamantinasaurus and an additional five characters that are locally autapomorphic within titanosauriformes this work provided an opportunity to revisit the phylogenetic placement of diamantinasaurus in two independent data matrices diamantinasaurus was recovered within lithostrotia one analysis resolved diamantinasaurus as the sister taxon to the approximately coeval tapuiasaurus from brazil whereas the second analysis recovered diamantinasaurus as the sister taxon to opisthocoelicaudia from the latest cretaceous of mongolia the characters supporting the recovered relationships are analysed and the palaeobiogeographical implications of the lithostrotian status of diamantinasaurus are explored a brief review of the body fossil record of australian cretaceous terrestrial vertebrates suggests close ties to south america in particular and to gondwana more generally

a numerical model of deformation and fluid flow in an evolving thrust wedge abstract to investigate deformation and fluid flow in an actively deforming tectonic wedge we model the evolution of a large two dimensional 100 km long 5 km thick mechanically and hydrologically homogeneous and isotropic pile of sedimentary strata that is deformed to become a thrust wedge we compare both dry and wet cases in order to illustrate 1 the relative importance of fluids on wedge evolution and 2 the effect of brittle deformation on fluid flow we use an elastic plastic constitutive relation including a mohr coulomb failure criterion and a non associated flow rule and coupled fluid flow with bulk rock properties that approximate typical foreland sedimentary strata simulations are made both with and without dilation the model is fully dynamic but inertial forces remain small results show that deformation within the wedge is accommodated by reverse slip movement on shear bands which migrate in both directions through the wedge as both fore and back thrusts the model has features predicted by the critical taper theory 1 overall wedge geometry 2 crudely self similar growth during evolution 3 more intense deformation toward the rear of the wedge the models show strong overall in sequence faulting behavior with major thrusts isolating relatively undeformed packages which are moved in a piggyback manner upon the active thrusts intermittent out of sequence faulting does however occur in order to maintain the wedge taper fluid flow in the deforming wedge is dominated by topography but is also strongly affected by dilational plastic deformation in all simulations there is focused fluid flow within fault zones when mechanical time stepping is shut off uncoupled flow systems evolve to steady state where inflow equals outflow by subtracting the two states we isolate the mechanical fluid response from the total coupled system response the mechanical fluid response is manifest as contours of head and pressure difference and focusing of fluid flow in areas of active deformation in non dilational simulations these zones are quite localized and are a result of the contrasting stresses in and adjacent to a brittle shear zone in simulations with dilation the zones of head and pressure difference are broad and regional in extent they are ten times greater in magnitude than in non dilation simulations and they track a rock damage front that moves through the wedge

sandbox modelling of thrust wedges with fluid assisted detachments abstract we have used granular materials to model the development of thrust wedges where migrating pore fluids assisted in the formation of detachments the governing equations yield practical scales for linear dimensions stresses and time using compressed air as a pore fluid models a few centimetres thick were deformed in about half an hour model materials were sands of three different grain sizes and a loess they had suitable values of density permeability cohesion and internal friction fluid flow obeyed darcy s law at yield the materials satisfied a coulomb criterion for effective stresses models with various sequences of layers were submitted to horizontal shortening in a rectangular box compressed air entered through a sieve at the base the fluid pressure was uniform over the basal boundary in models made from a single material the style of deformation depended on the fluid pressure for no fluid flow the thrust wedge was short and high the surface slope attained large angles 30 and internal structures were mainly forethrusts for fluid pressures approaching lithostatic values thrust wedges were longer and lower and surface slopes attained smaller angles in models containing basal layers of small permeability detachments formed beneath them and the structural style was dominated by interacting forethrusts and backthrusts in multilayered models thin skinned detachments formed beneath less permeable layers in the sequence to understand how fluid flow controlled the first stages of detachment we calculated ideal vertical profiles of fluid pressure vertical normal stress effective stress and horizontal shear stress for multilayered models in the undeformed state the profiles are segmented because material properties vary from layer to layer sharp drops in shear strength occur at positions where detachments were observed in the sandbox models we infer that detachments resulted from large fluid pressures beneath relatively impermeable layers

the genesis and recognition of anastomosed fluvial deposits data from the st mary river formation southwestern alberta canada abstract data from modern fluvial systems show that the term anastomosed is best reserved for suspended load systems with multiple channels and very low slope that flow in regions where the hydrograph has a seasonal peak the interchannel areas are topographic lows relative to the channel hanks and are places where crevasse splay marsh and lacustrine sedimentation occurs channel geometry is intrinsically a function of the rate of sediment partitioning the coarsest sediment is deposited in the channels on the levees and in proximal splay complexes whereas the silts and clays are deposited on the rest of the floodplain extrinsic controls on the formation of these systems are geological and climatic they include a source of suspended sediment and a highly seasonal water budget preservat on of anastomosed fluvial deposits requires a mechanism for maintaining very low depositional slopes over geologic time scales data from the st mary river formation in southwestern alberta show that the stratigraphic equivalents of these rivers are ribbon sandstone bodies encased in thin sandstones shales and siltstones the total distribution of facies rather than proof of simultaneous flow in multiple channels can be used to interpret correctly a deposit as anastomosed fluvial although anastomosed fluvial deposits form in a variety of tectonic settings they are apparently most common in foreland basins because these basins provide suitable source rocks and thrusting as a mechanism that can maintain the low depositional slopes over millions of years the mutual interaction among source rock climate and subsidence all of which play critical roles in forming and preserving these distinctive fluvial deposits allows inferences to be drawn regarding paleoclimate and paleoslope that may help constrain models of basin evolution

a review of brittle compressional wedge models abstract fold and thrust belts and accretionary wedges form by compression of sedimentary sequences and basement rocks into forward and backward thrusts folds nappes and duplexes for over a century models have been used to investigate the essential characteristics of such brittle wedges here i review model studies of brittle thrust wedges in orthogonal compression focussing on critical taper theory analogue and numerical techniques for modelling brittle behaviour and the most commonly investigated variations in wedge model studies those in basal dip basal strength internal strength and surface processes many model results can be placed in the context of critical taper theory which provides analytical solutions for wedge taper angle and slip line orientations for a homogeneous material on the verge of failure throughout dynamic forward models have confirmed critical taper predictions of decreasing surface dip for increasing basal dip wider wedges with steeper forward thrusts and shallower backward thrusts for decreasing basal strength narrower wedges and enhanced exhumation for surface erosion and decreasing surface dip for increasing internal strength but analogue and numerical models have been able to take these results a step further by investigating the evolution of non critical thrust wedges and the effects of non homogeneous materials with decollement layers and strain weakening shear zones these results have highlighted the strong impact of heterogeneous materials on the internal structures of thrust wedges and raise the question whether the complexity of structures that are observed in many natural fold and thrust belts requires that lithological layering inherited faults or a wide range of rheologies need to be included in forward models of brittle thrust wedges

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

coal depositional models and the distinction between alluvial and delta plain environments abstract the distinction between coal bearing upper and lower delta plain deposits in the rock record may be based on the presence or absence of features indicative of basinal influence and on the geometry of coal seams discriminating between alluvial plain and upper delta plain sequences is more difficult but is considered possible on coal seam geometry and coal seam splitting patterns other features such as the cross sectional shape of channel deposits may also be useful

revised geology age and vertebrate diversity of the dinosaur bearing griman creek formation cenomanian lightning ridge new south wales australia abstract the mid cretaceous griman creek formation gcf which crops out near the town of lightning ridge in the surat basin of north central new south wales australia is noteworthy for its opalised vertebrate fauna the fossil assemblage comprises remains of aspidorhynchid teleosts lamniform chondrichthyans dipnoans chelid and possible meiolaniform turtles leptocleidid like and possible elasmosaurid plesiosaurians anhanguerian pterosaurs titanosauriform sauropods megaraptoran theropods ankylosaurians several forms of non iguanodontian and iguanodontian ornithopods crocodylomorphs enantiornithine birds and stem and true monotremes making it one of the most diverse mid cretaceous terrestrial vertebrate faunas in australia a detailed stratigraphic survey of twenty subterranean opal mines provides new information on the geology age and palaeoenvironment of the main fossil bearing beds vertebrate remains derive from the finch clay facies laterally extensive but discontinuous lenses of claystone that likely accumulated relatively rapidly in near coastal but freshwater embayments i e lagoonal conditions and probably represent a single roughly contemporaneous fauna u pb age dating of detrital zircons extracted from a distinct layer of volcanogenic claystone immediately overlying one of the opalised fossil bearing layers yields a maximum depositional age of 100 2 96 6 ma these new dates confirm an early to mid cenomanian age for the fauna rather than albian as has been reported previously the gcf at lightning ridge is therefore equivalent to the middle part of the winton formation queensland and several million years older than the sauropod dominated fauna at winton

experimental and field study of the effects of lithological contrasts on thrust related deformation 1 the influence of mechanical contrasts related to stratigraphy on thrust related deformation are investigated by sandbox modeling using combinations of granular materials possessing different mechanical properties and by structural analysis of a natural example from the spanish pyrenees the models used in this study consist of loose sand and glass microbeads in varied stratigraphic thicknesses and sequences and the natural example consists of a weakening upward sequence of sandstones and carbonates in both cases layers of different composition had a mechanical significance and accommodated shortening differently model sand and natural sandstone exhibited most shortening by thrust imbrication irrespective of stratigraphic position whereas glass microbeads and carbonates exhibited wider deformation zones and enhanced folding accompanied by displacement reduction along thrust surfaces cutting them transitions of structural style were guided by the stratigraphy rather than by a simple unidirectional propagation from a step up layer parallel shortening was accommodated by diverse mechanisms but did not vary significantly in layers which had different properties the magnitude with which mechanical contrasts were expressed in the models was influenced by the strength at the decollement zone the effect of mechanical contrast was more profound in models shortened above a low friction decollement

deformation patterns and structural vergence in brittle ductile thrust wedges an additional analogue modelling perspective abstract scaled physical models of brittle ductile thrust wedges investigated the causes leading to the development of the various structural styles observed in fold and thrust belts and accretionary prisms this study focused on some potential controlling factors such as 1 relative strength between the brittle overburden and the viscous decollement layer brittle ductile coupling 2 the effect of very low basal friction and 3 pre shortening rheological stratigraphy including decollement strength type 1 models had a single basal decollement whereas in type 2 models the decollement was embedded in brittle material simulating an upper roof sequence and a lower floor sequence other models investigated the effects produced by an horizon of mechanical weakness at the base of the viscous decollement type 1a and the role of decollement offset type 3 the experiments suggest the occurrence of a genetic relationship between the absolute values of shear stresses and the development of dominating hinterland or foreland verging thrust faults or dually verging thrusts by controlling the orientation of the 1 axis basal friction and decollement offset is found to effectively influence the deformation pattern and structural vergence and could explain the development of dominating backthrusts in cascadian type margins the decoupling of a frontal monocline via the upper decollement type 2 models produced passive roof duplex structures termed composite roof duplex when the frontal monocline coexists with outward fold propagation

frontal accretion an internal clock for bivergent wedge deformation and surface uplift 1 we propose a conceptual model of frontal accretion within bivergent wedges which is based on two dimensional sandbox simulations and the analysis of particle displacement fields each frontal accretion cycle consists of a thrust initiation an underthrusting phase and a reactivation phase the location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable therefore the frontal accretion cycle can be considered as an internal clock for wedge scaled deformation and surface uplift we further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle we estimate cycle duration to range between 104 and 105 years which is thus similar to the time frame of climatic cycles the proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic paleoseismologic and geologic estimates of fault slip

eocene hydromorphic paleosols significance for interpreting ancient floodplain processes abstract pervasive mottling iron oxide nodules and slickensides indicate that alluvial paleosols of the lower eocene willwood formation in the elk creek area of the bighorn basin wyoming were hydromorphic two basic groups of hydromorphic paleosols are present cumulative which show evidence for concurrent deposition and pedogenesis and simple noncumulative which show evidence for a single episode of deposition and pedogenesis lithologic packages consisting of vertically stacked simple paleosols and crevasse splay sandstones alternate with cumulative paleosols the simple paleosols are weakly developed indicating rapid deposition with relatively little time for pedogenesis cumulative paleosols show greater pedogenic development indicating significantly longer periods of pedogenic m dification and slower more episodic sediment accumulation differences between the simple and cumulative paleosols reflect differences in the deposition of their parent materials the packages of simple paleosols are similar to avulsion belt deposits described from the saskatchewan river and suggest that avulsion was significant in floodplain construction the upper parts of cumulative paleosols were formed on true overbank deposits which accumulated gradually after avulsion and establishment of a new channel the lower parts of many cumulative paleosols resulted from a prior episode of avulsion deposition and simple soil formation because hydromorphy is associated with texture these different depositional processes influenced lateral variations in hydromorphy of the cumulative paleosols paleosols in the elk creek area provide a simple means of identifying avulsions sediment accumulation rates suggest that avulsions occurred with a regular period of about 20 000 years and may have been induced by climatic cycles

thrust wedges and fluid overpressures sandbox models involving pore fluids the well known model for the critical taper of an accretionary wedge includes overpressure as a first order parameter fluid overpressures reduce frictional resistance at the base of a wedge but they also act as body forces on all material particles of the wedge in addition to that of gravity by means of sandbox modeling many workers have tried to verify the predictions of the critical taper model but few of them have so far incorporated true fluid pressures we have used scaled experiments in which compressed air flows through sand packs so as to model the deformation of overpressured wedges a new apparatus provides for a horizontally varying fluid pressure for example a linear variation as in the critical taper model we have done three series of experiments involving horizontal shortening of homogeneous or multilayered sand models for various gradients of fluid pressure as predicted by the critical taper model the apical angle of the resulting wedge depends on the overpressure gradient in homogeneous sand at a high overpressure gradient deformation becomes diffuse and looks ductile in multilayered models detachments form beneath layers of low permeability so that thrusts propagate rapidly toward the undeformed foreland the efficiency of a detachment and its ability to propagate depend not only on the fluid pressure but also on the permeability ratios between the various layers

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

refined age and geological context of two of australia s most important jurassic vertebrate taxa rhoetosaurus brownei and siderops kehli queensland abstract australia s jurassic vertebrate fossil record remains extremely sparse with only two dinosaur taxa and two temnospondyl amphibians identified to date of these the spectacular and extremely well preserved giant amphibian siderops kehli and the only known pre cretaceous sauropod in australia rhoetosaurus brownei are perhaps the most important the age of both specimens and the stratigraphic context of rhoetosaurus brownei are weakly constrained and imprecisely defined limiting our understanding of their evolutionary relationships within a broader gondwanan context to clarify and contextualise the evolutionary relationships and ages of these two iconic jurassic taxa we used u pb detrital zircon geochronology to date the sandstone matrix from around the bones of the historic museum specimens the robust maximum depositional age for siderops was calculated at 176 6 ma 2 ma indicating that it is no older than late toarcian which refines existing biostratigraphic estimates the rhoetosaurus maximum depositional age was determined to be 162 6 1 1 ma no older than early oxfordian demonstrating that the fossils are younger than expected and definitely recovered from the walloon coal measures

updated gondwana permian cretaceous earth history of australia abstract permo carboniferous glaciation confined to icecaps and mountain glaciers was followed by permian coal measures and early triassic barren measures and redbeds in the east terminally deformed in the mid triassic coal deposition resumed during the late triassic and tholeiite was erupted in the southeast after rifting the western margin was formed by the opening of the indian ocean at 156 and 132 ma at 140 ma a brief glaciation affected central australia by the 99 ma mid cretaceous the southern margin was finally shaped by the opening of the southeastern indian ocean the shoreline retreated to the present coast from the maximum aptian shoreline of an epeiric sea and the eastern highlands were uplifted to produce the present morphology of australia new data relate to the permo carboniferous and early cretaceous glaciations the kiaman reversed paleomagnetic interval events about the permian triassic boundary including possible impact craters advances in palynology invertebrate paleontology macrofloral paleontology and paleobiogeography the provenance of sediments by u pb ages and host rock affinity of zircons stable isotopes and biomarkers in petroleum systems coal environments calibrating the time scale with u pb ages of zircons fission track thermotectonic imaging geothermal energy and terranes split off the western margin

the australian central eromanga basin project an introduction abstract the australian bureau of mineral resources is carrying out a major multidisciplinary program of geological and geophysical studies in southwestern queensland in cooperation with the geological survey of queensland the project is aimed at providing information on the regional structure and depositional history of the central eromanga basin and the underlying adavale cooper and galilee basins the information being obtained is particularly relevant to a better understanding of the petroleum prospectivity of the area the program includes geophysical surveys involving 1400 km of new six fold cdp seismic reflection coverage on regional traverses up to 400 km long crossing the main structural elements of the area gravity measurements along all new seismic reflection traverses refraction surveys along two major east west and north south traverses and magnetotelluric soundings along the same major east west traverse landsat imagery studies are providing new perspective on many regional structures when used in conjunction with seismic and gravity information wireline logs and synthetic seismograms are being used with the new seismic data to re examine stratigraphic correlations palynologic and lithologic studies are underway to assist in determining depositional environments source rock maturation hydrological and geochemical studies are providing information on the generation and migration of hydrocarbons a significant feature of the program is the extension of the recording time of all new reflection data to 20 s to obtain good quality deep crustal reflection information comparable to that obtained on cocorp programs in the united states the reflection data is being interpreted with the refraction gravity and magnetotelluric data to investigate the relationship of deep crustal and upper mantle features to the sedimentary basins in the central eromanga basin area

structural complexity resulting from pervasive ductile deformation in the karakoram shear zone ladakh nw india 1 the nw se trending 800 km long dextral karakoram shear zone bounds southwest tibet we investigate an area immediately nw of the pangong lake where midcrustal rocks sections of the shear zone are exposed here the dominant shear zone is characterized by dextral mylonitic rocks sheared at amphibolite facies and partly retrogressed to greenschist facies these rocks define a kilometric se plunging inclined to recumbent fold in the footwall of a north directed oblique dextral thrust that exhumed anatectic rocks of the pangong range argon cooling ages reveal that the pangong range cooled from 700 c to 300 c between 18 15 and 10 ma contemporaneously with overthrusting toward the se closer to the pangong lake this kilometric fold is rotated from its nw se trend to an e w trend and the sense of shear changes to sinistral with a broadly north directed thrusting component the documented structures contradict predictions of normal movement in this area derived from considerations of rigid block behavior of the crust and support the interpretation that the system records dextral transpression thrusting and exhumation of the deeper and hot rocks exposed in the pangong range folding of the thrust footwall and the development of a sinistral e w trending shear zone are all compatible with transpression caused by a northward push by a rigid indenter such as the ladakh batholith

integration of channel and floodplain suites i developmental sequence and lateral relations of alluvial paleosols abstract the lower eocene willwood formation of the bighorn basin northwest wyoming consists of about 770 m of alluvial rocks that exhibit extensive mechanical and geochemical modifications resulting from eocene pedogenesis willwood paleosols vary considerably in their relative degrees of maturity maturity is defined as stage of development as a function of the amount of time required to form five arbitrary stages are proposed to distinguish these soils of different maturities in the willwood formation stage 1 soils the least mature are entisols stage 2 and stage 3 soils are intermediate in maturity and are probably alfisols and stage 4 and stage 5 soils the most mature are spodosols these stages are not only time progressive elements of an in situ maturation sequence for w llwood soil formation but in the lateral dimension they are also usually distributed sequentially study of willwood paleosols indicates that an inverse relationship exists between soil maturity and short term sediment accumulation rate the least mature willwood paleosols formed in areas of relatively high net rates of sediment accumulation on 1 channel levee and crevasse splay sediments of the proximal alluvial ridge and 2 deposits filling large and small paleovalleys formed by major episodes of gullying lowered baselevels in contrast the fine grained sediments of the distal floodplain where net sediment accumulation rates were relatively low experienced development of much more mature soils soils of intermediate maturities occur in the order of their stage on intervening proximal floodplain and distal alluvial ridge sediments adjacent bodies of sedimentary rock that differ in their ancient soil properties because of distance from areas of relatively high sediment accumulation are denoted by the new term pedofacies the remarkable sequence of paleosols in the willwood formation clearly illustrates several important principles of soil sediment interrelationships in aggrading alluvial systems that have broad application to other deposits this is especially true in view of the widespread distribution of paleosols in nearly all ancient fluvial rocks further study of willwood paleosols will not only enable precise lateral correlation of coeval alluvial sediments and thereby fluvial sedimentary events from the distal to the proximal realms of the floodplain but will also contribute to increasingly informative evaluations of the nature tempo and mode of alluvial succession

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

erosional control of the kinematics and geometry of fold and thrust belts imaged in a physical and numerical sandbox 1 we investigate the effect of systematically varying erosion intensity k on the geometry and kinematics of fold and thrust belts modeled using equivalent conditions in physical and numerical experiments similar material properties and boundary conditions were used to compare numerical experiments to those modeled in the sandbox using an erosion rule that removes mass from the scaled sand wedges according to rates expected from bedrock fluvial incision the geometry of both modeling approaches is quantitatively compared with that expected from analytical theory the fold and thrust belt growth rate is inversely proportional to k and is well predicted by theory except for the high erosion case in which both the numerical and the experimental sandbox grows supercritically a direct relationship exists between the erosion intensity and the number of fore shear bands and shear strain magnitude the number of fore shear bands decreases and their strain increases with erosion intensity the results indicate that realistic and mechanistic erosion rules can be applied to physical experiments to model mass removal and this approach opens up the possibility of calibrating strain history to erosion intensities for predictions in natural settings quantitative comparisons between the physical and numerical sandbox experiments indicate that deformation style and geometry of the thrust and fold belts are similar when identical rheologies and boundary conditions are used this benchmarking suggests that numerical experiments realistically model conditions observed in the simple cohesionless rheologies commonly employed in sandbox experiments this suggests that numerical simulation may reliably model experimental deformation in geological situations that are difficult to represent in scaled experiments because of the different scales and rheologies of natural orogenic wedges

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

extension during active collision in thin skinned wedges insights from laboratory experiments the occurrence of strike normal extension in mountain belts undergoing active contraction is not predicted by analytical solutions for the mechanics of purely frictional orogens to test the idea that ductile rocks at depth might allow extensional deformation to occur in otherwise frictional and contractional orogens we have conducted a series of analog experiments with purely frictional and layered frictional ductile rheologies by precisely measuring the horizontal deformation field we have quantitatively confirmed the qualitative observation that analog frictional wedges do not extend this is consistent with published numerical models and is in contrast to purely viscous models that commonly display coeval extension with contraction our modeling also demonstrates that layered frictional ductile models can during active convergence result in discrete extensional normal faulting even when only a relatively thin ductile layer is present the resulting extension though relatively small in magnitude compared to the active contraction can greatly modify the final profile of a convergent orogen and can lead to the formation of a broad plateau between the pro wedge and the retro wedge

new artificial granular materials for analogue laboratory experiments aluminium and siliceous microspheres abstract laboratory tests have been carried out to determine the physical properties of high sphericity and low density fine grained dry granular materials in particular we tested hollow aluminium microspheres and hollow siliceous microspheres shear tests have been carried out with a casagrande apparatus for different values of normal stress from 12 27 to 491 8 kpa in order to determine the frictional properties of the microspheres diagrams of the shear stress against displacement have been used to describe the strength of the investigated materials at different confining pressures the shear tests show that hollow aluminium and siliceous microspheres successfully replicate the mechanical behaviour of weaker layers within natural sedimentary successions undergoing deformation the use of these artificial granular materials in specifically designed experiments indicated that they can be successfully used for constructing more natural multilayers in the laboratory

effect of increased shear stress along a plate boundary fault on the formation of an out of sequence thrust and a break in surface slope within an accretionary wedge based on numerical simulations abstract we investigated the effect on accretionary wedge structure of increased shear stress which describes the frictional sliding resistance along a decollement arising from an increase in material friction or reduction in pore pressure to clarify the nature of the effect we performed numerical simulations using two models a stable friction model and an increased friction model the stable friction model produced a low angle smooth surface slope and an in sequence thrust whereas the increased friction model produced a break in surface slope scarp and an out of sequence thrust ost that cuts through the thrust sheet the ost formed via the connection of segments of two adjacent thrusts and its formation resulted in a change in the thickening mode of the wedge from thrust sheet rotation and back thrust activity to underplating this contrast in thickening mode between the landward high friction zone and seaward low friction zone resulted in the formation of a clear break in slope as the landward zone is steeper than the seaward zone consistent with critical taper theory the subduction of a basement slice or seamount can produce similar structures arising from an increase in resistance to basal shear sliding however the distinctive structures arising in an accretionary wedge as a result of increased shear sliding resistance include a flat basal plane and absence of slope failure sediments beneath the ost these structural features are observed in accretionary wedges of the nankai trough off muroto japan the sunda strait and the barbados ridge

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

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

role of preexisting topography and overburden on strain partitioning of oblique doubly vergent convergent wedges 1 scaled sandbox modeling was used to analyze the three dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event in the experiments the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden giving way to different effects on wedge response during the second phase of shortening during the second phase the models with an inherited heavy overburden show an anomalous orientation for riedel shears predating the development of a margin parallel strike slip fault these shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot suggesting a transient rotation of the stress applied by the obliquity of subduction in contrast experiments with a lighter overburden do not show this inconsistency in addition all the models displayed an unexpectedly high accretion rate during the second phase of shortening which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges

a large clawed theropod dinosauria tetanurae from the lower cretaceous of australia and the gondwanan origin of megaraptorid theropods abstract megaraptoridae comprises a clade of enigmatic gondwanan theropods with characteristic hypertrophied claws on the first and second manual digits the majority of megaraptorids are known from south america although a single genus australovenator plus additional indeterminate material is also known from australia this clade has a controversial placement among theropods and recently has been interpreted alternatively as a carcharodontosaurian or a tyrannosauroid lineage we describe new fragmentary but associated postcranial remains from the opal fields of lightning ridge middle albian griman creek formation in north central new south wales the new unnamed taxon exhibits a number of unusual features that suggest the presence of a hitherto unrecognised australian megaraptorid from an australian perspective the lightning ridge taxon predates australovenator by ca 10 ma and is minimally coeval with megaraptoran material reported from the eumeralla formation of victoria but potentially 6 1 9 5 ma younger it is also notable as the largest predatory dinosaur yet identified from australia and is only the second theropod known from more than a single element a bayesian phylogenetic approach integrating morphological stratigraphic and palaeogeographic information tested both the carcharodontosaurian and tyrannosauroid placements for megaraptora regardless of the preferred placement among tetanurae rigorous palaeobiogeographic analyses support an asian origin of megaraptora in the latest jurassic about 150 135 ma an early cretaceous about 130 121 ma divergence of the gondwanan lineage leading to megaraptoridae and an australian root for megaraptorid radiation these results indicate that australia s cretaceous dinosaur fauna did not comprise simply of immigrant taxa but was a source for complex two way interchange between australia antarctica south america leading to the evolution of at least one group of apex predatory dinosaurs in gondwana

change of tectono stratigraphic regime in the australian plate during the 99 ma mid cretaceous and 43 ma mid eocene swerves of the pacific the clockwise bend at 99 ma mid cretaceous in linear volcanic chains in the tropical pacific coincides with a change from pre 99 ma head on chilean type subduction of the pacific plate beneath eastern gondwana to 99 43 ma sinistral oblique mariana type subduction and strike slip breakup by simple sea floor spreading between australia and antarctica and by backarc spreading in the southwest pacific the 99 ma breakup of australia from antarctica is documented by a mid cretaceous unconformity this tectono stratigraphic change founded modern australia with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south the counterclockwise bend at 43 ma mid eocene the emperor hawaiian bend coincides with the onset of structure in the challenger rift of new zealand the eromanga cooper basin of central australia and the oil shale grabens of coastal queensland

analogue sandbox models of thrust wedges with variable basal frictions abstract scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges in isotropic cohesionless and anisotropic cohesionless materials variations in the basal coefficient of friction by using different materials as basal detachments combination of basal detachments and the anisotropy of the layered system have been investigated imbricate fans of dominantly foreland vergent thrust systems are developed in the way similar to those developed in accretionary prisms and in foreland fold and thrust belts critical taper wedges close to theoretically predicted geometries are developed for intermediate values of basal friction mb 0 47 whereas for the lower value of basal friction mb 0 37 low taper wedges are formed with slopes less than the theoretically predicted supra critical wedges are formed when the high basal friction mb 0 55 is either equal to or greater than the coefficient of friction of the deforming material in the wedges then the wedges have a high taper angle close to the angle of rest for the modelling material similar geometries developed when the experiments were carried out on combination of two materials with basal frictions as intermediate low low intermediate and low high the spacing of thrust faults increases with increased basal friction higher basal friction or anisotropy within the layered systems favours displacement along foreland vergent thrusts and eventually checks backward breaking thrusting

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

structural evolution of a three dimensional finite width crustal wedge abstract we present the results of three dimensional numerical experiments designed to study the response of a layer of crustal material subjected to convergence through an imposed basal velocity discontinuity and to surface processes erosion sedimentation we focus on the three dimensional response of the system arising from the finite width of the imposed velocity discontinuity in particular we describe the complex structures that develop around the wedge and their interactions with the loading unloading produced by the surface processes we show that the pro and retro shear zones that develop in a doubly vergent two dimensional wedge curve around the end of the velocity line discontinuity to merge into the strike slip structure that naturally develop i e as a consequence of the imposed boundary conditions along the edge of the wedge along the retro shear zone the stress orientation rotates along a vertical axis which implies that the retro shear zone is a pure thrust along all of its curved length whereas along the pro shear zone stresses rotate along a horizontal axis which in turn implies that the pro shear zone progressively evolves towards an oblique thrust in its curved section furthermore the outward motion i e perpendicular to the direction of imposed shortening along the curved section of the retro shear zone is accommodated by oblique extension along a secondary kinked structure antithetic to the retro shear zone we also show the complex evolution of the wedge when ductile flow and ductile strain softening is activated by increasing the imposed basal temperature in this situation the wedge is broader as structures develop at finite distances on either side of the line discontinuity and its dynamics resembles more that of a vise like orogen at the surface a flat plateau forms that accumulates sediment from the surrounding actively deforming mountain ranges until a channel breaks through one of the sides and flushes the inward draining basin of its sedimentary content the complex numerical models provide a detailed insight into the geometry and complex three dimensional structures within and at the margins of an orogen and how they can be affected by erosional processes at the surface

acceleration and deceleration of india asia convergence since the cretaceous roles of mantle plumes and continental collision 1 a strong 50 35 ma decrease in india asia convergence is generally ascribed to continent continent collision however a convergence rate increase of similar magnitude occurred between 65 50 ma an earlier increase occurred at 90 ma both episodes of accelerated convergence followed upon arrival of a mantle plume below and emplacement of a large igneous province lip on the indian plate we here first confirm these convergence rate trends reassessing the indo atlantic plate circuits then using two different numerical models we assess whether plume head arrival and its lateral asthenospheric flow may explain the plate velocity increases and whether decreased plume flux and increasing continent plume distance may explain deceleration even without continental collision the results show that plume head arrival can indeed lead to absolute indian plate motion accelerations on the order of several cm yr followed by decelerations on timescales similar to the reconstructed fluctuations the 90 ma increase could potentially be explained as response to the morondova mantle plume alone the 65 50 ma convergence rate increase however is larger than can be explained by plume head spreading alone we concur with previous hypotheses that plume induced weakening of the indian continental lithosphere asthenosphere coupling and an increased slab pull and ridge push efficiency are the most likely explanations for the large convergence rate increase the post 50 ma decrease is best explained by orogeny related increased trench resistivity decreased slab pull due to continental subduction and possibly restrengthening of lithosphere asthenosphere coupling upon plume demise

wood growth indices as climate indicators from the upper cretaceous cenomanian turonian portion of the winton formation australia abstract although the mid to late cretaceous is regarded as a global warm period increasingly a more complex picture of warming and cooling is emerging new techniques allow more precise dating of terrestrial localities opening opportunities for using climate proxy approaches on terrestrial fauna and flora to better capture the complexity of cretaceous climate here an attempt is made to understand the seasonality and inter annual variability of two newly dated localities from the upper preserved portion cenomanian turonian of the winton formation australia primarily quantitative approaches to palaeodendrology are used the results suggest both seasonality and high variability in climate conditions that affect growth between years including evidence for floods the longest series qm f44338 suggests oscillatory patterns of good and poor growth in a 15 year alternating cycle similar to the contemporary pacific decadal oscillation although other potential explanations should be considered and tested

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

steady state erosion of critical coulomb wedges with applications to taiwan and the himalaya 1 orogenic structure appears to be partially controlled by the addition to and removal of material from the mountain belt by tectonic accretion and geomorphic erosion respectively we developed a coupled erosion deformation model for orogenic wedges that are in erosional steady state and deform at their coulomb failure limit erosional steady state is reached when all material introduced into the wedge is removed by erosion that is limited by the rate at which rivers erode through bedrock we found that the ultimate form of a wedge is controlled by the wedge mechanical properties sole out depth of the basal decollement erosional exponents basin geometry and the ratio of the added material flux to the erosional constant as this latter ratio is increased wedge width and surface slopes increase we applied these models to the taiwan and himalayan orogenic wedges and found that despite a higher flux of material entering the former the inferred ratio was larger for the latter calculated values for the erodibility of each wedge showed at least an order of magnitude lower value for the himalaya relative to taiwan these values are consistent with the lower precipitation regime in the himalaya relative to taiwan and the exposure of crystalline rocks within the himalayan orogenic wedge independently determined rock erodibility estimates are consistent with the accretionary wedge sediments and metasediments and the crystalline and high grade metamorphic rocks exposed within taiwan and the himalaya respectively therefore differences in rock type and climate apparently lead to key differences in the erosion and hence orogenic structure of these two mountain belts

dynamics of sediment subduction accretion at convergent margins short term modes long term deformation and tectonic implications a conceptual model is proposed for the short term operation of subduction accretion systems at convergent margins the operation is described in terms of the mass fluxes among the four system components namely the accretionary or prowedge wedge p an uplifted plug u a retrowedge r and the subduction zone the latter consists of a conduit c of slowly moving and deforming material and an underlying subduction channel where material moves and deforms more rapidly a broad range of convergent margin types can be accommodated within the conceptual model framework with differing short term modes that depend on which of the p u r c components that are active finite element geodynamical model experiments are used to investigate whether these modes are dynamically feasible these experiments determine excitation of modes under controls that include model entry and exit mass fluxes flexural loading by accreted material and slab pull forces boundary velocities corresponding to subduction and subduction zone advance retreat distribution thickness and density of accreted sediment and internal frictional properties of the coulomb sediments that all modes with the exception of p in which only a prowedge is created are seen in the models provides support for the concepts and allows conditions that favor particular modes to be recognized in addition the finite deformation predicted by the models is used to infer the long term tectonic styles associated with both single mode evolutions and those that exhibit mode switching a steady state mass balance can occur for modes 0 pure subduction p c i e where components p and c are active or other modes when the surface mass denudation plus the subduction flux balances accretion plus tectonic underplating the p c mode is favored by subduction zone retreat and or an increasing subduction load and creates an apparent landward dipping backstop p u c is predicted to be the most common mode and it creates an apparent seaward dipping backstop p u r c is an inefficient mode but is favored by easily detached retrocrust or sediment and or a decreasing subduction load

depositional environment of the lower cretaceous upper albian winton formation at isisford central west queensland australia inferred from sandstone concretions abstract numerous vertebrate and plant fossils have been found in ex situ sandstone concretions near isisford in central west queensland since the mid 1990s these concretions are found in the lower cretaceous portion upper albian 100 5 102 2 ma of the winton formation the lower most winton formation is thought to have formed in a fluvial channel or flood basin setting proximal to the eromanga sea but due to the scarcity of good exposures the local depositional environment at isisford has not been ascertained minimal compression of vertebrate and plant fossils a lack of grain suturing predominantly cement supported fabric and fractures running through calcite cement as well as fossil bone and framework grains indicates that concretions formed during early diagenesis pre compactional or syndepositional calcite stable isotope 18ovpdb values range from 12 25 to 4 indicating mixed marine and meteoric pore waters and 13cvpdb values range from 5 3 to 4 1 indicative of both sulfate reduction and methanogenesis of organic material including decaying vertebrate soft tissues in the burial environment the mixed marine and freshwater signature suggests a marginal marine setting possibly deltaic or estuarine connected to the regressive epicontinental eromanga seaway at around 102 100 ma this is not inconsistent with the lithology from nearby cores coupled with isisford fossil vertebrate ecology personal observation our research demonstrates the utility of investigating ex situ concretions to refine paleoenvironments at localities where little or no outcrop is available and traditional facies analysis is impractical

subsidence in intracontinental basins due to dynamic topography the origin of anomalous tectonic subsidence ats of large intracontinental basins long after their most recent phase of extension and last thermal perturbation is the subject of a long standing debate we show that deep earth processes may contribute to the subsidence of these tectonically stable basins by analysing the tertiary mantle convection driven topography history of a global set of more than 220 intracontinental basins integrated into a plate kinematic framework most basins are affected by increasing negative dynamic topography over the last 70 myr due to the motion of many continents away from large mantle upwellings and towards downwellings previously located along the perimeter of the supercontinent pangaea during continental dispersal increasing negative dynamic topography causes dynamic subsidence of the basins creating additional accommodation space we utilise a parameter from a global crustal analysis of intraplate basins termed anomalous tectonic subsidence to quantify sediment accumulation not related to crustal stretching we propose that dynamic subsidence due to plate motions relative to the underlying mantle as well as variations in the large scale convection patterns can significantly contribute to the creation and destruction of accommodation space in intraplate basins