re os isotopic composition of peridotitic sulphide inclusions in diamonds from ellendale australia age constraints on kimberley cratonic lithosphere abstract sulphide bearing diamonds recovered from the 20 ma ellendale 4 and 9 lamproite pipes in north western australia were investigated to determine the nitrogen aggregation state of the diamonds and re os isotope geochemistry of the sulphide inclusions the majority of diamond studies have been based on diamonds formed in the sub continental lithospheric mantle sclm below stable cratons whereas the ellendale lamproites intrude the king leopold orogen south of the kimberley craton the sulphide inclusions consist of pyrrhotite pentlandite chalcopyrite assemblages and can be divided into peridotitic and eclogitic parageneses on the basis of their ni and os contents a lherzolitic paragenesis for the high ni sulphide inclusions is suggested from their re and os concentrations regression analysis of the re os isotope data for the lherzolitic sulphides yields an age of 1426 130 ma with an initial 187os 188os ratio of 0 1042 0 0034 the upper limit of the uncertainty on the 187os 188os initial ratio gives a re depletion age of 2 96 ga indicating the presence of sclm beneath ellendale since at least the mesoarchaean with the lherzolitic diamond forming event much younger and unrelated to the craton keel stabilisation the nitrogen aggregation state of the diamonds and calculated mantle residence temperatures suggest an origin and storage of the ellendale diamonds in a stable cratonic sclm consistent with the king leopold orogen being cratonised by about 1 8 ga the diamonds do not show evidence for pervasive deformation or platelet degradation which suggests that the diamonds had a relatively undisturbed 1 4 billion year mantle storage history

a carbon isotope reference curve for ca 1700 1575 ma mcarthur and mount isa basins northern australia abstract shallow marine paleo and mesoproterozoic sedimentary successions are widely distributed in several major basins across northern australia the successions are only gently deformed and their stratigraphy is relatively continuous thus offering an ideal opportunity to document secular variations in carbon isotopes marine carbonate intervals from two of these major basins the mcarthur and mount isa basins have been sampled to document secular variation in 13ccarb from approximately 1700 to 1575 ma in all cases the samples have been tied to a well established sequence stratigraphy which along with u pb shrimp zircon dates provides a time resolution of the order of 1 m y the data presented here thus provide the most comprehensive and best dated 13ccarb stratigraphy yet obtained from such ancient rocks diagenesis occurred early in the carbonate rocks from both basins with the result that fluid movements were restricted and primary carbon isotopic signatures were retained the 13ccarb values from both basins vary within a very narrow range around a mean of 0 6 with extreme values seldom lying further than 1 from the mean that is the curves are essentially flat the results of this study combined with earlier studies on younger rocks imply that the global ocean reached a state of equilibrium in the mid paleoproterozoic and remained stable for much of the following billion years current models of the ocean suggest that to maintain the carbon mass balance relatively low levels of tectonic activity would be required which in turn suggests that the availability of nutrients such as phosphorus was stable and low prolonged nutrient stability may therefore have exerted a major influence upon the evolution of the biosphere over this time interval

lateral structural variations and drainage response along the misikantage anticline in the western kuqa fold and thrust belt southern tianshan nw china abstract the cenozoic kuqa fold and thrust belt kftb along the southern piedmont of the tianshan mountains nw china provides excellent chances for investigating active deformation and its controls on landscape topography in contrast to the well imaged eastern kftb the structural deformation in the western part complicated by the development of early stage salt structures still has not been well investigated on the basis of seismic reflection profiles well data and surface geology combined with previously determined paleomagnetic ages this study focuses on the deformation style onset and average shortening rate of the misikantage anticline in the western kftb together with the morphometric analysis of satellite images and digital elevation models dems we have demonstrated that 1 the misikantage anticline is an asymmetric detachment fold where the fold geometry amounts of shortening outcropping strata and channel network patterns vary along strike 2 syntectonic growth strata recognized from seismic profiles combined with paleomagnetic ages indicate that the folding started at 2 4 ma and resulted in 0 3 0 9 km of shortening yielding an average shortening rate of 0 12 0 38 mm yr 3 the landscape topography and drainage networks markedly change in response to lateral structural variations these findings would provide a basis for further comparisons of compressional structures between the eastern and western kftb which are also helpful in better understanding active folding in fold and thrust belts particularly where thick salt is involved in deformation

cenozoic deformation and crustal shortening in the foreland of southern tian shan nw china as a response to the india asia collision abstract investigations of geometry and kinematics of foreland fold and thrust belts provide key information for understanding how convergence is accommodated in deformed forelands of orogenic belts here we present the structural styles deformation ages and shortening rates of three en echelon anticlines located at the west end of the baicheng kuqa foreland fold and thrust belt the results indicate that the three anticlines developed above the eocene evaporites of the kumugeliemu group which constitute the decollement level in this typical thin skinned tectonics the initial growth of the east awate and north kalayuergun anticlines as indicated by the syn tectonic growth strata accumulations occurred at 5 3 ma with shortening rates of 0 70 0 77 mm yr and 0 40 0 43 mm yr respectively whereas the initial folding time of the middle kalayuergun anticline is 2 6 1 7 ma resulting in a shortening rate of 0 35 0 65 mm yr the shortening rates are lower when compared with foreland deformation in the middle and eastern parts of the baicheng kuqa fold and thrust belt such differences are mostly related to the strain partitioning caused by the nw se dextral strike slip kalayuergun fault as well as the influence of a dextral wrenching component in the west end of the baicheng kuqa fold and thrust belt our study suggests that episodic tectonic deformation in the southern foreland of tian shan has been a response to the ongoing india asia convergence since the latest miocene and the spatial variability of crustal shortening rates has depended on regional tectonic differences

discrimination of open water from sea ice in the labrador sea using quad polarized synthetic aperture radar abstract a method to differentiate open water from sea ice using quad polarization c band synthetic aperture radar sar imagery is presented based on the roughness properties of the sea surface scattering facets and the polarization ratio pr between vv and hh polarization backscatter from the sar images in quad polarization sar images the normalized radar cross section nrcs which is linked to sea surface roughness can be used to derive the orientation angle shift and its standard deviation as well as to compute the measured polarization ratio pr an x bragg backscatter model is explored to calculate a theoretical look up table for the polarization ratio as a function of incidence angle dielectric constant orientation angle shift and its standard deviation thus ocean surface backscatter can be identified as open water or sea ice by comparing the measured pr with a theoretical model for pr the proposed method is validated by comparison to collocated optical video images and manual visual interpretations estimates of the size shape and locations of open water from our method are shown to be in good agreement with observed data the overall accuracy of our algorithm is about 96 the classification accuracy for sea ice and open water is about 96 and 94 respectively

earth stress and reservoir quality evaluation in high and steep structure the lower cretaceous in the kuqa depression tarim basin china abstract knowledge of the state of the in situ stress field provides important insights into the petroleum engineering and geology the in situ stress orientation and magnitudes in the high and steep structure of lower cretaceous bashijiqike formation in kuqa depression were analyzed based on well log calculations and the impacts of in situ stress field on reservoir quality macroscopic reservoir properties and microscopic pore structure as well as fracture aperture were investigated the maximum horizontal stress shmax orientation was determined as nearly north south according to the image log derived drilling induced fractures and borehole breakouts the vertical stress sv shmax and minimum horizontal stress shmin magnitudes were calculated via well logs the result reveals a dominant strike slip stress regime shmax sv shmin in the bashijiqike formation in the kuqa depression the sv at the depth ranging from 5000 to 7100 m is 150 180 mpa and horizontal stresses shmax and shmin vary significantly from 130 to 210 mpa the horizontal stress difference is in the range from 40 to 70 mpa and fluid overpressures are commonly encountered the effective stress e has a positive relationship with the when the is less than 50 mpa intergranular pores can be preserved in layers with low values the microscopic pore structure will be complex and macroscopic reservoir quality will be poor with the increasing values in addition fractures are mainly corresponding with the layers where the value is low and the fracture aperture and porosity decreased significantly with the effective stress e by determining the magnitude and orientation of in situ stresses around the wellbore insights can be provided into the wellbore instability optimum drilling trajectories and reservoir quality evaluation

detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

the tectonics and petroleum system of the qiulitagh fold and thrust belt northern tarim basin nw china the timing of hydrocarbon charging relative to trap formation is a key factor for evaluating the exploration potential of the qiulitagh fold and thrust belt qftb on the north flank of the tarim basin data obtained by this study indicate that structural traps were filled by hydrocarbons in two episodes in this area at least four major deformation events have been identified for the period of late cretaceous to pliocene the first event occurred in late cretaceous and led to the formation of paleo uplift structures the second event was characterized by thrust features and occurred in latest oligocene the third and fourth events were represented by compressional structures that were developed in late miocene and late pliocene respectively based on oil and gas source rock correlations and 1 d basin modeling two episodes of hydrocarbon generation and migration are proposed to be responsible for oil and gas accumulations in the qftb the two episodes of hydrocarbon charging from a source kitchen north of the study area took place in early miocene and pliocene respectively since the qftb was uplifted in late oligocene and late miocene the hydrocarbon generated during all two periods could migrate toward this area to form oil and gas accumulations in suitable structures

effects of lateral friction on the structural evolution of fold and thrust belts insights from sandbox experiments with implications for the origin of landward vergent thrust wedges in cascadia various factors are inferred to influence the structural evolution of fold and thrust belts or thrust wedges but the effects of lateral friction such as that exerted by the opposite block of a strike slip fault in nature or by sidewalls in analogue models have rarely been given sufficient attention and hence are still far from being fully understood up to now seaward vergent and dually vergent thrust wedges have been satisfactorily explained by the classic coulomb wedge theory and can be well reproduced in analogue and numerical models in contrast landward vergent thrust wedges which are uncommon in nature e g those occurring in the cascadia subduction zone have not yet been adequately explained by the classic coulomb wedge theory and can only be reproduced in a few analogue models under particular conditions in order to look closer at the effects of lateral friction on the structural evolution of fold and thrust belts and to explore the origin of landward vergent thrust wedges we conducted a series of sandbox models under different conditions of lateral friction and various ratios of initial average lateral frictional stress to basal shear stress s d results of our models revealed that in the presence of a weak or ductile basal decollement the direction of lateral friction can dictate not only the deformation propagation direction and the surface slope direction but also the structural vergence of fold and thrust belts fold and thrust belts normally show a structural vergence in the same direction as the direction of lateral friction but a deformation propagation direction and surface slope direction opposite to the direction of lateral friction according to the results of models and the relationships between structural vergence and lateral friction direction occurring both in cascadia and the analogue models we propose that an extremely high s d ratio due to an extremely weak basal decollement and landward directed lateral friction exerted by the opposite blocks of basement involved strike slip faults are probably the two key factors responsible for the origin of landward vergent thrust wedges in cascadia this work illustrates that effects of lateral friction should be properly taken into account both in the kinematic analysis and designs of models to simulate fold and thrust belts in the presence of weak or ductile basal decollements

country wide high resolution vegetation height mapping with sentinel 2 abstract sentinel 2 multi spectral images collected over periods of several months were used to estimate vegetation height for gabon and switzerland a deep convolutional neural network cnn was trained to extract suitable spectral and textural features from reflectance images and to regress per pixel vegetation height in gabon reference heights for training and validation were derived from airborne lidar measurements in switzerland reference heights were taken from an existing canopy height model derived via photogrammetric surface reconstruction the resulting maps have a mean absolute error mae of 1 7 m in switzerland and 4 3 m in gabon a root mean square error rmse of 3 4 m and 5 6 m respectively and correctly estimate vegetation heights up to 50 m they also show good qualitative agreement with existing vegetation height maps our work demonstrates that given a moderate amount of reference data i e 2000 km2 in gabon and 5800 km2 in switzerland high resolution vegetation height maps with 10 m ground sampling distance gsd can be derived at country scale from sentinel 2 imagery

the fold test in palaeomagnetism summary the fold test suggested by mcelhinny is shown to be inappropriate more correctly one should determine whether the mean direction of a group of sites from one limb of a fold may be distinguished statistically from the mean direction of a group of sites from another limb details of the application of this test are given with examples it is shown that the test indicates significance under far less severe folding than does the test suggested by mcelhinny

palaeomagnetism of red beds from the kimberley group western australia implications for the palaeogeography of the 1 8 ga king leopold glaciation abstract the 1 8 ga king leopold glaciation in northwestern australia is recorded in the kimberley basin by subglacial erosional forms cut in an unconformity surface at the top of the speewah group and buried by glaciofluvial deposits at the base of the king leopold sandstone the lowest formation of the kimberley group the glaciofluvial deposits are conformably overlain by texturally mature locally glauconitic quartzarenite of shallow marine origin implying that glaciation occurred near sea level palaeomagnetic data for five sites 29 specimens in the hematite bearing elgee siltstone of the upper kimberley group in the northeastern kimberley basin gave a dip corrected mean direction of declination d 95 4 inclination i 13 8 95 9 7 indicating a palaeolatitude 7 0 5 3 5 0 results for red beds from five sites 28 specimens in the conformably overlying pentecost sandstone gave a dip corrected mean direction of d 94 1 i 13 0 95 11 7 6 6 6 4 5 9 combining our data for the elgee siltstone and pentecost sandstone with results for the elgee siltstone in the southeastern kimberley basin li z x 2000 palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia geophysical journal international 142 173 180 yielded a dip corrected mean direction for 17 sites of d 93 5 i 15 1 95 4 4 palaeolatitude 7 7 2 3 and an overall pole position at latitude p 5 4 s longitude p 211 8 e with confidence semi axes dp 2 3 and dm 4 5 a positive fold test at 99 confidence was obtained for the combined data for the 17 sites the basinwide concordance of results for the elgee siltstone and the positive fold test argue for an early magnetisation acquired prior to late palaeoproterozoic initial folding of the kimberley group and close to the time of deposition our results imply a low palaeolatitude for the kimberley group and the king leopold glaciation palaeomagnetic data for the 1 822 ga plum tree creek volcanics in the pine creek orogen to the east of the kimberley basin are consistent with northwestern australia being in low palaeolatitudes during the late palaeoproterozoic hence the enigma of glaciation near sea level in low palaeolatitudes which marks the neoproterozoic and early palaeoproterozoic applies also to the late palaeoproterozoic red beds from the lansdowne arkose of the speewah group also were studied but only directions ascribable to tertiary regolith weathering processes were found similar findings for the late palaeoproterozoic mcarthur basin in northern australia suggest some units in that basin also record tertiary regolith processes

detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

impact of backstop thickness lateral variations on the tectonic architecture of orogens insights from sandbox analogue modeling and application to the pyrenees 1 we performed sandbox analogue models to investigate the influence of along strike tapering of the backstop on the three dimensional architecture of natural doubly vergent thrust fold belts applying the results to a natural example as the pyrenees available geological and geophysical data indicate that the european crust which provided the backstop in the pyrenean orogen has a westward tapering on both the upper westward thickening of the mesozoic cover rocks and the lower westward rising of the moho envelope surfaces accordingly we performed laboratory models characterized by backstops with an along strike tapering of either the upper or the lower surface our results indicate a significant impact of backstop lateral tapering in thrust wedge architecture in terms of the outward propagation of the deformation fronts the width and elevation of the axial zone and the timing of thrust polarity reversal along strike when compared to the pyrenees our results support the inferred westward tapering of the european basement and its commonly accepted backstop role in the pyrenean orogen moreover comparison between the map pattern of the pyrenees and of laboratory experiments suggests that the along strike tapering of the bottom envelope surface of the backstop played a most important role on the three dimensional thrust wedge architecture than the tapering of the upper envelope surface

characteristics and deformation mechanism of salt related structures in the western kuqa depression tarim basin insights from scaled sandbox modeling abstract three scaled analog sandbox models are constructed to simulate the evolution of thick skinned shortening on broad and narrow salt basins these models simulate the evolution of the cenozoic salt salt related structures in the westernmost kuqa salt bearing depression quele area tarim basin the formation mechanism and the controlling factors of structural deformation in this area are investigated and discussed systematically model results show that the variable depositional width of the salt basin has a major controlling influence on the differential structural deformation in different longitudinal segmentations from east broad to west narrow in the western kuqa depression quele area model results also demonstrate that the early salt structure salt diapir has an important controlling role on the subsequent compressional structural deformation the pre existing thin overburden quele diapir which acts as a stress concentration zone during the subsequent shortening is deformed to the quele salt nappe on the basis of the model results it is suggested that the formation of the long distance quele allochthonous salt sheet is related with the pre existing quele diapir which displaces up paralleling the hanging wall and flows to the surface during the subsequent shortening

the mechanical relationship between strike slip faults and salt diapirs in the zagros fold thrust belt analogue models are used to study the mechanical relationship between basement strike slip faults and salt diapirs displacement along a strike slip fault in 1 g models resulted in extension along pre existing jogs and the formation of oblique extensional faults where reactive diapirs were triggered in some models in the centrifuge models prescribed cuts simulating pre existing structures were reactivated during simple shear deformation of the models resulting in formation of pull apart basins which were intruded by diapirs the models show that because of the low ratio of salt to overburden thickness in the zagros 0 15 0 35 it is unlikely that diapirs have formed solely if at all as a result of movement along basement strike slip faults two mechanisms are suggested first pre kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the zagros which were later downbuilt to their current geometry by additional sedimentation second movement along the strike slip faults e g the kazerun and mangarak faults induced oblique movement along nw se zagros structures folds or thrusts resulting in the formation of pull apart basins where diapirs were eventually intruded fault plane solution of shallow earthquakes supports the second scenario which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than zagros shortening and young southwestwards

the tectonostratigraphic history of the proterozoic northern lawn hill platform australia an integrated intracontinental basin analysis abstract the northern lawn hill platform nlhp comprises an area of approximately 16 000 km2 in north central australia thick packages of proterozoic strata outcrop in the region although large areas are also covered by younger strata the packages contain basin sediments and igneous rocks that span 400 m y we present a regional synthesis of approximately 150 m y of the tectonostratigraphic history of the area which hosts several world class base metals deposits the interpretation is based primarily on a sequence stratigraphic and structural interpretation of seismic data a common approach in the petroleum resource sector but rare in analyses of mineral resources models of subsurface geology and a basement template are provided using observed geopotential data that are iteratively calibrated with other data geochronological palaeomagnetic geochemical and sequence stratigraphic investigations on outcrop and drill core also are integrated into the history the seismic data allow separated outcrop belts to be confidently correlated for the first time geochronological data control the basin history delineated by this interpretation palaeomagnetic data allow the results presented here to be extrapolated regionally and globally although considered to be deposited on entirely intracontinental lithosphere the basin phases record significant fluctuations in the volume and geometry of accommodation space for sedimentation multiple pulses of deformation are recorded by changing depositional geometries we propose a history of re activation of a basement template and speculate on geodynamical mechanisms for accommodation space fluctuations and geometric variability the detailed understanding of the basin evolution of the nlhp gained by integrated basin analysis provides a powerful tool for predictive fluid flow models as an aid to resource exploration it should also provide a useful analogy in understanding tectonic processes and basin evolution of other similar aged intracontinental basins

the interaction of two indenters in analogue experiments and implications for curved fold and thrust belts abstract scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold and thrust belt the experimental set up has two adjacent indenters moving in parallel with a velocity difference the slow indenter moves with a relative velocity ranging from 40 to 80 of that of the fast one in a first experimental series quartz sand and low friction glass beads represent the sediment stack and its basal detachment respectively silicone oil simulates a viscous detachment in the second series of experiments the surface evolution and the spatio temporal strain distribution are derived from particle image velocimetry piv together with the 3d finite structure derived by cutting the models at the end of each experiment this allows the analysis of the structural evolution of the experimental wedges thrusting wedge development depends crucially on the relative velocity when the slow indenter moves with a velocity of more than 55 of the fast indenter a single curved thrust wedge develops the wedge becomes decoupled along strike slip zone at large velocity differences i e when the slow indenter moves slower than 55 of the faster indenter consequently the thrust front is strongly curved at high 55 60 and smoothly curved at low velocity differences 70 80 in all cases curvature increases during indentation along the most strongly curved portion of the thrust wedge the transfer zone rises particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front this implies distant effects of wedge growth active hundreds of kilometres along strike of orogens silicone oil as a detachment induces a low angle wedge which is less curved than in the glass beads experiments and shows variable thrust vergence with fore and back thrusts we compare our experimental results with the curved fold and thrust belts of the tajik basin in front of the hindu kush and pamir indenters our results are able to explain several first order features

the variety of subaerial active salt deformations in the kuqa fold thrust belt china constrained by insar abstract surface salt bodies in the western kuqa fold thrust belt of northwestern china allow study of subaerial salt kinematics and its possible correlations with weather variations ephemeral subaerial salt exposure during the evolution of a salt structure can greatly impact the subsequent development and deformation of its tectonic setting here we present a quantitative time lapse survey of surface salt deformation measured from interferometric synthetic aperture radar insar using envisat radar imagery acquired between 2003 and 2010 time series analysis and inspection of individual interferograms confirm that the majority of the salt bodies in western kuqa are active with significant insar observable displacements at 3 of 4 structures studied in the region subaerial salt motion toward and away from the satellite at rates up to 5 mm yr with respect to local references rainfall measurements from the tropical rainfall measuring mission trmm and temperature from a local weather station are used to test the relationship between seasonality and surface salt motion we observe decoupling between surface salt motion and seasonality and interpret these observations to indicate that regional and local structural regimes exert primary control on surface salt displacement rates

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

open shear fractures at depth in anticlines insights from the kuqa foreland thrust belt tarim basin shear fractures that close under compressive stress regime were described by previous workers here we show the existence of hinge parallel shear opening mode fractures at a certain depth within an anticline structure through core observations formation micro imager fmi log interpretations and production data studied reservoir is a tight sandstone body of cretaceous age which is emplaced in ks2 anticline with depth ranging between 6000 and 8100 m we explore the mechanism of hinge parallel shear fractures by stereographic technique and backtilting as well as show field evidences for opening displacements these shear fractures mainly consist of vertical tension set moderate dipping shear set steeply dipping shear set and sub horizontal shear set crosscutting relationships and surface textures suggest that although the moderate dipping shear set is older and maybe sealed by cements it may have been opened by local stress due to outer arc extension through folding calcite bridges with rhombohedral structures may support fracture walls helping them to remain open in case of compressive stress our work documents shear fracture openings in the anticline at depth and fluid flow in subsurface reservoirs

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

palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia summary a palaeomagnetic study of the elgee formation red siltstones and shales in the palaeoproterozoic kimberley basin of northwestern australia has been carried out all seven sampling sites revealed an extremely stable magnetic remanence carried by haematite the age of the formation is confined by precise shrimp u pb ages of early diagenetic xenotime from rocks both above and below it to be 1704 7 14 ma but this may represent a minimum age the youngest detrital zircon grains in the underlying formation provide a maximum age of 1786 14 ma for the formation the extreme stability of the remanence the dissimilarity of the remanent direction from expected younger palaeomagnetic directions and the lack of regional overprint in the 1790 4 ma hart dolerite just north of the study region support a primary origin for the remanence a marginally positive fold test also supports a primary origin the mean direction of d 92 2 i 14 9 a 95 6 4 gives a palaeopole at 4 4 s 210 0 e with dp 3 3 dm 6 5 this pole a previously reported palaeopole from the hart dolerite and ca 1700 ma overprint poles from the pilbara craton all agree with palaeopoles of similar ages from the mcarthur basin of northern australia palaeomagnetic results thus suggest that the north and west australian cratons were possibly joined together by approximately 1 7 ga

formation of orogen perpendicular thrusts due to mechanical contrasts in the basal decollement in the central external sierras southern pyrenees spain two series of analogue models are used to explore the effect of ductile frictional contrasts of the basal decollement on the development of oblique and transverse structures during thin skinned shortening these models simulate the evolution of the central external sierras ces southern pyrenees spain which constitute the frontal emerging part of the southernmost pyrenean thrust the ces are characterised by the presence of n s to nw se anticlines perpendicular to the pyrenean structural trend and developed in the hanging wall of the thrust system they detach on unevenly distributed triassic materials evaporitic dolomitic interfingering the models simulated the effect of adjacent ductile versus frictional decollements during shortening model series a tests the thickness ratio between overburden and the ductile layer whereas model series b tests the width perpendicular to the shortening direction of frictional decollement model results confirms that deformation reaches further in areas detached on a ductile layer whereas above frictional decollement areas shortening is accommodated by additional uplift and penetrative strain this replicates the structural style of the ces higher structural relief of n s anticlines with regard to orogen parallel structures absence of a representative ductile decollement in the core plunging towards the hinterland and foreland side closure not thrusted by the south pyrenean thrust

effects of mass waste events on thrust wedges analogue experiments and application to the makran accretionary wedge 1 olistostromes cover large portions of active thrust wedges like makran gulf of cadiz and offshore borneo olistostrome emplacement by submarine mass flow represents an instantaneous and massive mass redistribution that may influence thrust wedge mechanics different scenarios are experimentally tested they show that the postolistostrome wedge development depends on the thickness and extent of the added load these results are discussed after the example of the iranian makran wedge situated between the arabian and eurasian plates mass redistribution caused by a late miocene mass flow may explain a change in deformation style from intense folding and thrusting to gentle folding and eventually a jump of thrust imbrication toward the frontal offshore part of this active accretionary wedge

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

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

centrifuge modelling of thrust faulting structural variation along strike in fold thrust belts abstract the three dimensional geometry and the kinematic evolution of fold thrust structures are investigated by analog modelling using the centrifuge technique we focus on along strike structural variation and transfer of displacement between faults and folds the total horizontal shortening across the model fold thrust belts is constant yet there are systematic variations in shortening by the mechanisms of thrusting folding and layer parallel shortening these along strike changes in structural geometry and strain mechanism are manifestations of displacement transfer the model thrust faults have different amounts of thrust displacement at different points along strike the variation is accommodated by transfer of displacement to over or underlying faults or to en echelon faults by transfer of shortening into folding or by transfer of displacement into layer parallel shortening in the models it is clear that faults nucleate at points that are localized by earlier folding of competent units faults nucleated at different points along a single fold may propagate along the fold and link together to form major thrusts the thrust displacement in such cases varies from smaller values at linkage points to larger values at nucleation points the models have a stratigraphie succession like that of the central appalachian valley and ridge province after an equivalent amount of structural shortening the models exhibit structural features analogous to those of the valley and ridge the lowest competent unit equivalent to the cambro ordovician lithotectonic unit forms a large scale duplex like that of the waynesboro sheet the middle competent unit equivalent to the siluro devonian clastic units forms anticlinoria and synclinoria like those of the martinsburg sheet these structures are spatially associated with underlying culminations and depressions that reflect respectively large and small displacements on thrusts that ramp through the lowest competent unit however in the models it appears that the amplitude of buckling of the middle unit controls the amount of displacement on underlying thrusts whereas in the appalachians the structural culminations of the middle unit are interpreted to have been caused by large displacement on underlying faults

structural development at the leading edge of the salt bearing kuqa fold and thrust belt southern tian shan nw china abstract the tian shan is one of the largest and most active intracontinental orogenic belts in the world which has experienced complex deformation resulting in the formation of several fold and thrust belts ftbs in the piedmonts investigations on when and how the cenozoic compressional deformation has reached the leading edge of the ftbs will improve our understanding of the characteristics and mechanism of deformation propagation in contractional orogenic wedges in this study we focus on the kinematic evolution of the nanka south kalayuergun and yangtake anticlines at the southern limit of the western kuqa ftb where the paleocene eocene kumugeliemu formation e1 2km salt has been involved into deformation via the area depth strain ads analysis of petroleum seismic reflection profiles the results indicate that these two detachment folds have experienced two stage tectonic shortening almost synchronously since the late miocene which are in contrast to the previously inferred progressive eastward elongation the initial age of folding is temporally consistent with that of the yaken anticline in the eastern sector where the detachment is the miocene jidike formation n1j salt suggesting that salt probably has facilitated the basinward propagation of structural deformation to reach its external pinch out rapidly meanwhile the salt lubricated detachment has also promoted the lateral fold propagation and hence the present length was quickly reached at a very early stage the simultaneous episodic deformation at the leading edge demonstrated by our analysis is consistent with the results of analog and numerical modeling which would further our understanding of structural development and topographic expression in salt bearing ftbs

depositional ages of the stratiform base metal deposits at mount isa and mcarthur river australia based on u pb zircon dating of concordant tuff horizons potassium rich tuff beds occur interbedded with major stratiform pb zn mineralization in shales and dolomitic shales of the mount isa group northwest queensland and the mcarthur group northern territory these deposits are some 600 km apart yet they exhibit many similarities which together with regional correlations suggest that the deposits formed by similar processes and that the successions developed more or less contemporaneously zircon is sparsely distributed as tiny crystal fragments or phenocrysts in the tuffs and its morphology and u pb systematics affirm that it is primarily of igneous origin u pb zircon data from a tuff in the mineralized h y c pyritic shale member of the mcarthur group give an age of the tuff of 1 690 super 29 sub 25 m y and from a tuff in the mineralized urquhart shale of the mount isa group an age of 1 670 super 20 sub 17 m y these results are consistent with all other geologic controls and are regarded as the best estimates of the depositional ages of the groups the ages of the mount isa and mcarthur groups are thus the same to within the present experimental uncertainties essentially confirming geologic synchrony of these important sedimentary successions pooled whole rock data from several of the mount isa tuff marker beds give an updated rb sr age of about 1 480 m y interpreted as indicating that isotopic exchange and regional metamorphism had essentially ceased by this time

baltic sea ice concentration estimation based on c band dual polarized sar data high resolution ice concentration information is required for navigation purposes validating ice models and data assimilation the currently available operational ice concentration products are based on microwave radiometer data and their typical resolution is several kilometers we present an algorithm for the estimation of ice concentration based on dual polarized hh hv c band synthetic aperture radar sar data the algorithm is based on the multilayer perceptron mlp neural network ice concentration estimated based on the hh channel is used as one mlp input and the local incidence angle is used as another the additional inputs are based on the hv channel digitized finnish ice service ice charts which were also used as the training data the sar based hh channel ice concentration and the ice concentration based on a radiometer algorithm are used as reference data sets the results for the dual polarized algorithm show improvement compared to the algorithm based on hh polarized sar data only

not so simple simply folded zagros the role of pre collisional extensional faulting salt tectonics and multi stage thrusting in the sarvestan transfer zone fars iran abstract the sarvestan plain is bounded by highly elevated anticlines associated with thrusts or transpressional faults and hosts the nnw sse sarvestan transfer zone surface and subsurface geological data and 22 seismic lines allowed us to reconstruct the 3d geometry of the area mixed layer illite smectite and 1d burial and thermal modelling were used to constrain the complex geological evolution of the sarvestan plain where inherited structures strongly controlled the geometry of syn to post collisional contractional structures paleozoic mesozoic rifting related extension generated e w and nnw sse normal fault systems such faults were associated with changes in the thickness of the sedimentary cover lateral facies changes were later induced by the cretaceous obduction of ophiolites cropping out some tens of km north of the study area during the miocene the footwall and the hanging wall of the sarvestan fault had different thermal evolution this is tentatively explained by flow of cambrian salt from the plain area towards the hanging wall of the sarvestan fault associated with salt diapirism during lower middle miocene time salt tectonics is invoked also to explain at least in part the development of the overturned anticline in the hanging wall of the sarvestan fault an early phase of contractional deformation occurred in the middle miocene since 15 my i e after the deposition of the agha jari fm generating the e w oriented folds buried below the plain likely inverting inherited normal faults the erosion of these structures was followed by the deposition of the bakhtiari fm conglomerates in middle late miocene times a later phase of contractional tectonics generated the thrust faults and the anticlines bounding the sarvestan plain some 6 5 my ago the sarvestan dextral transpressional fault that likely acted as a strongly oblique ramp of the maharlu thrust mainly structured in this period although its activity may have continued until present

rbsb age determinations on precambrian carbonate rocks of the carpentarian mcarthur basin northern territories australia abstract the applicability and the uncertainty range of rb sr age determinations on carbonate rocks are discussed briefly a study of clay minerals isolated from carbonate rocks of the mcminn formation provides an isochron age of 1429 31 ma and thus the age for cessation of the proterozoic mcarthur basin sedimentation the eukaryots recently described in this area are therefore the oldest occurrences found in earth history a second sequence of measurements on a homogeneous dolomite siltstone ca 23 km southeast of the mcarthur river h y c pb zn deposits yields an rb sr age of 1537 52 ma for the upper barney creek formation in broad agreement with recent age determinations on feldspar beds of this horizon these data are compared with previous isotopic results from data presently available it can be concluded that the sediments in the mcarthur basin the type locality of the carpentarian were deposited between 1800 1400 ma

frequency of proterozoic geomagnetic superchrons abstract long term geodynamo evolution is expected to respond to inner core growth and changing patterns of mantle convection three geomagnetic superchrons during which earth s magnetic field maintained a near constant polarity state through tens of myr are known from the bio magnetostratigraphic record of phanerozoic time perhaps timed according to supercontinental episodicity some geodynamo simulations incorporating a much smaller inner core as would have characterized proterozoic time produce field reversals at a much lower rate here we compile polarity ratios of site means within a quality filtered global proterozoic paleomagnetic database according to recent plate kinematic models various smoothing parameters optimized to successfully identify the known phanerozoic superchrons indicate 3 10 possible proterozoic superchrons during the 1300 myr interval studied proterozoic geodynamo evolution thus appears to indicate a relatively narrow range of reversal behavior through the last two billion years implying either remarkable stability of core dynamics over this time or insensitivity of reversal rate to core evolution

geometric tests and their application to fault related folds in kuqa abstract for brittle rock deformation there are two main types of fault related folds found in foreland thrust belts i e fault bend folds and fault propagation folds the predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault bend folds and fault propagation folds have been tested in seismic profiles i e deep bashijiqike tugeerming kashangtokai east qiulitage deep east qiulitage and yakelike fault bend anticlines and bashijiqike yiqikelike and south yiqikelike fault propagation anticlines in the kuqa rejuvenated foreland thrust belt test results for the transformation from seismic time section into seismic depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable with geometric analysis and testing of the subsurface structures it is possible to predict the existence of the fault bend folds and fault propagation folds in the kuqa area this study provides convincing proof that the kuqa basin is a rejuvenated foreland basin

apparent polar wander and reversal stratigraphy of the palaeo mesoproterozoic southeastern mcarthur basin australia abstract approximately 1800 samples from volcanic clastic and carbonate sequences of the southeastern mcarthur basin in northern australia were analysed palaeomagnetically to define in detail the australian apparent polar wander path apwp for a period centred at 1670 ma and to develop a proterozoic reversal stratigraphy for correlation and dating twelve palaeomagnetic poles are interpreted as primary including two that are preliminary these increase the australian palaeomagnetic database for the proterozoic by 30 another ten poles record three or possibly four periods of overprinting the study also yields one of the oldest reversal records reported so far the ten better established primary poles were obtained from the lower three of the four main stratigraphic sub divisions of the basin the tawallah mcarthur and nathan groups these poles define an angular trajectory of about 120 for a time span of at least 75 m y and possibly exceeding 100 m y they confirm earlier preliminary results that suggested a major revision of the proterozoic apwp for australia the two preliminary poles were obtained from the youngest sub division of the basin the roper group and confirm a large age gap between the nathan and roper groups the poles for the oldest overprints were from igneous units in the tawallah group and appear to record metasomatism at the end of the last major period of volcanism in the basin the pole for the next overprint falls on the path near the apex of a hairpin bend it coincides with a likely period of rifting and high heat flow that accompanied the deposition of the upper mcarthur group the third overprint apparently acquired during the long time break separating the nathan and roper groups was found mostly in red dolomitic rocks the geomagnetic reversal record from this study represents an accumulated stratigraphic thickness of 2100 m excluding gaps where the polarity remained undetermined because of overprinting unstable remanences intervals not sampled or other causes reversal patterns from duplicate sections at different localities were compared for two formations and were found to be consistent several parts of the reversal column appear to be distinctive enough for use in stratigraphic correlation

intermediate decollement activation in response to the basal friction variation and its effect on folding style in the zagros fold thrust belt an analogue modeling approach although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains the interaction between basal and intermediate de

thrust and fold tectonics and the role of evaporites in deformation in the western kuqa foreland of tarim basin northwest china the kuqa foreland between the tarim basin and the tianshan mountains is rich in oil and gas based on field work and seismic profiles the structural styles and their formation mechanisms were determined and the role of evaporites in the deformation was demonstrated the main structural styles in the overburden are detachment folds large scale nappes triangle zones gentle and wide synclines fault propagation folds and pop ups the main structures in the substrate are small scale thrust faults duplexes pop ups and fault bend and fault propagation folds and formed mainly at the end of the pliocene under north south compression the evaporite layer in the lower section of the paleogene is the decollement zone for the disharmonic deformations in the overburden and in the substrate the detachment along the evaporite layer made it possible for compressive stresses to be transmitted farther in the overburden than in the substrate deformation in the overburden is more extensive than in the substrate at the leading edge of deformation at the trailing edge of deformation the structural highs in the overburden closely correspond to those in the substrate which is of significance for petroleum exploration in the western kuqa foreland

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

extensional salt tectonics in a contractional orogen a newly identified tectonic event in the spanish pyrenees a new coniacian early santonian extensional salt tectonics event has been identified in the cotiella thrust sheet of the central spanish pyrenees we present a new interpretation of the cotiella thrust system and describe exceptional outcrop examples of postrift gravity driven extensional growth faults the thrust sheet contains three kilometer scale extensional faults with as much as 5 5 km of coniacian lower santonian growth strata in their hanging walls these postrift listric growth faults detached on the prerift triassic evaporites on the uplifted and eroded southern flanks of early cretaceous rift basins early alpine late santonian maastrichtian contractional deformation reactivated and reversed the displacement on both the early cretaceous rift faults and some of the postrift salt detachment faults hanging walls of the listric growth faults deformed into major antiforms but the original extensional geometries are well preserved continued alpine shortening incorporated these reactivated extensional fault systems into the thin skinned thrust sheets of the southern pyrenees these postrift extensional structures account for significant thickness variations in the postrift succession and for along strike changes in the styles of the thrust structures the late cretaceous extensional salt tectonics is interpreted to result from gravity induced northward sliding on the early cretaceous rift margin toward the axis of the rift basin the listric growth faults are similar to those found on the gulf of mexico margin in the southern north sea and the south atlantic margins

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

petroleum geology and geochemistry of middle proterozoic mcarthur basin northern australia ii assessment of source rock potential five potential source rocks have been discovered in the middle proterozoic of the mcarthur basin the lacustrine barney creek formation mcarthur group and the marine velkerri formation roper group compare favorably in thickness and potential with demonstrated petroleum source rocks in the phanerozoic the former contains up to 7 total organic carbon toc and kerogen types i and ii toc values in the latter range up to 6 5 and the kerogen is type ii petrographic examination shows the organic matter is mostly lamalginite which on maturation yields nonfluorescent lamalginite and bitumen extractable hydrocarbon yields from mature samples indicate that good to excellent source rocks are present and there is ample evidence of migration having occurred tmax values derived from rock eval analysis may be used to define maturation levels in much the same way as in phanerozoic sediments at low maturation levels the reflectivities of lamalginite and bitumen are lower than vitrinite reflectance values calculated from methylphenanthrene indices but converge in the mature zone this convergence reflects both the inherent lower reflectivity of hydrogen rich macerals and the source control on methylphenanthrene indices at low maturity maturation levels in mcarthur group sediments vary from marginally mature to overmature with abrupt changes over short distances associated with faults hydrocarbon generation occurred prior to the deposition of the younger proterozoic sediments of the roper group in contrast the source rocks in the roper group re marginally mature to mature throughout the study area and are overmature only where they are affected by igneous intrusions considerations of burial history suggest that hydrocarbon generation may have occurred during deposition of the roper group although an early paleozoic timing cannot be excluded

spatial and temporal trends in precambrian nitrogen cycling a mesoproterozoic offshore nitrate minimum abstract fixed nitrogen is an essential nutrient for eukaryotes as n 2 fixation and assimilation of nitrate are catalyzed by metalloenzymes it has been hypothesized that in mesoproterozoic oceans nitrate was limited in offshore environments by low trace metal concentrations and high rates of denitrification in anoxic and episodically euxinic deep water masses restricting eukaryotes to near shore environments and limiting their evolutionary innovation to date this hypothesis has only been tested in the belt supergroup 1 4 ga with results that support an onshore offshore nitrate gradient as a potential control on eukaryote ecology here we present bulk nitrogen and organic carbon isotopic data from non isochronous cross basinal facies across the bangemall 1 5 ga and the roper 1 4 1 5 ga basins to better understand the extent and variability of onshore offshore nitrogen isotope gradients in the mesoproterozoic both basins show an average 1 2 enrichment in 15 n bulk from deep to shallow facies with a maximum range from 1 offshore to 7 5 onshore unlike the belt basin the bangemall and roper basins show some offshore 15 n bulk values that are enriched beyond the isotopic range associated with biological n 2 fixation alone this suggests a mixture of aerobic and anaerobic metabolisms offshore in shallow waters where 15 n bulk enrichment peaks an aerobic nitrogen cycle was evidently operating even though isotopic signatures of aerobic nitrogen cycling are seen in all parts of the bangemall and roper basins our data are consistent with a lateral gradient in nitrate availability within the photic zone with higher concentrations in near shore environments than offshore the variability in 15 n bulk values in each depositional environment and the consistently low 15 n bulk values from mesoproterozoic units compared to the paleoproterozoic and neoproterozoic suggest that nitrate concentrations in the global ocean were likely low this trend is now seen in all three mesoproterozoic basins so far examined and contrasts with the paleoproterozoic and neoproterozoic where nearly all 15 n bulk data plot above the n 2 fixation window thus we propose that the mesoproterozoic ocean was characterized by a nitrate minimum with the lowest concentrations in offshore environments this inference is consistent with a mesoproterozoic o 2 decline following a temporary paleoproterozoic o 2 peak and it further supports the idea that nitrate limitation offshore may have contributed to the restriction of photosynthetic eukaryotes to near shore environments delaying their rise to ecological dominance until the neoproterozoic era

assessment of categorical triple collocation for sea ice open water observations application to the gulf of saint lawrence monitoring the sea ice cover is important for both climate studies and ice operations such as shipping it is challenging to validate even basic essential variables such as the sea ice extent due to a lack of appropriate validation data instead of focusing on validation this paper looks at the use of categorical triple collocation ctc for the task of quantitatively comparing three colocated data sets ctc has been developed and used in earlier studies to rank binary data sets in this paper we extend earlier studies and bring in recent results from the binary classification community to estimate the class imbalance the relative proportion of each class ice or water we then use this class imbalance to obtain quantitative estimates of the proportion correct of ice sensitivity and the proportion correct of water specificity the methodology is first tested using toy data after which three data sets from the gulf of saint lawrence on the east coast of canada are used these data sets are from an ice ocean model a passive microwave sea ice concentration retrieval and a sea ice concentration retrieval from synthetic aperture radar sar by looking at both the sensitivity and the specificity it is found that the passive microwave data have difficulty in recognizing ice during freeze up but they perform well at obtaining the correct water observations this distinction cannot be made by ranking the data sets the ctc method is compared with and found to be complementary to a validation using ice water states from the interactive multisensor snow and ice mapping system

geological and palaeomagnetic significance of the kulgera dyke swarm musgrave block nt australia summary the kulgera dyke swarm consists of olivine tholeiites which have intruded late proterozoic transitional granulite gneisses and granites of the eastern musgrave block in central australia preliminary rb sr results suggest that the dolerites were emplaced at 1054 f 14ma in addition a rb sr age of 1060 f 10ma on a biotite from a pegmatite indicates thermal resetting of the country rock minerals during dyke emplacement palaeomagnetic investigations of the dykes yield a primary thermoremanent magnetization direction corresponding to a palaeomagnetic pole at 17 s 266 e ag5 12 in addition to this primary magnetization an overprint component was present in many of the samples providing a palaeomagnetic pole at 30 s 138 e ags 24 which is similar to previous results from other central australian rocks affected by the alice springs orogeny the results extend the area of influence of the carboniferous alice springs orogeny southward into the musgrave block further the results provide no evidence for an earlier late proterozoic petermann orogeny affecting the musgrave block in the kulgera region however the possibility that a petermann orogeny thermal overprint has been erased by the alice springs orogeny cannot be dismissed

late cenozoic transtensional fault belt discovered on the boundary of the awati sag in the northwestern tarim basin late cenozoic transtensional fault belt was discovered on shajingzi fault belt nw boundary of the awati sag in the northwestern tarim basin and numerous quaternary normal faults were discovered on aqia and tumuxiuke fault belts sw boundary of awati this discovery reveals quaternary normal fault activity in the tarim basin for the first time it is also a new discovery in the southern flank of tianshan mountains shajingzi transtensional fault belt is made up of numerous small normal faults horizontally the normal faults are arranged in right step en echelon patterns along the preexisting shajingzi basement fault forming a sinistral transtensional normal fault belt in profile they cut through the paleozoic to the mid quaternary and combine to form negative flower structures the late cenozoic normal faults on the sw boundary of awati sag were distributed mainly in the uplift side of the preexisting aqia and tumuxiuke basement involved faults and combined to form small horst and graben structures in profile based on the intensive seismic interpretation careful fault mapping and growth index analysis we conclude that the normal fault activity of shajingzi transtensional fault belt began from late pliocene and ceased in late pleistocene mid quaternary and the normal faulting on the sw boundary of awati sag began from the very beginning of quaternary and ceased in pleistocene the normal faulting on awati s sw boundary began a little later than those on the nw boundary the origin of shajingzi transtensional normal fault belt was due to the left lateral strike slip occurred in the southern flank of tianshan and then due to the eastward escape of the awati block a tensional stress developed the normal faults on its sw boundary

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

effect of basement structure and salt tectonics on deformation styles along strike an example from the kuqa fold thrust belt west china abstract the kuqa fold thrust belt kftb has a complex thrust system geometry and comprises basement involved thrusts decollement thrusts triangle zones strike slip faults transpressional faults and pop up structures these structures combined with the effects of paleogene salt tectonics and paleozoic basement uplift form a complex structural zone trending e w interpretation and comprehensive analysis of recent high quality seismic data field observations boreholes and gravity data covering the kftb has been performed to understand the characteristics and mechanisms of the deformation styles along strike regional sections fold thrust system maps of the surface and the sub salt layer salt and basement structure distribution maps have been created and a comprehensive analysis of thrust systems performed the results indicate that the thrust fold system in paleogene salt range can be divided into five segments from east to west the kela 3 keshen dabei bozi and awate segments in the easternmost and westernmost parts of the paleogene salt range strike slip faulting and basement involved thrusting are the dominant deformation styles as basement uplift and the limits of the cenozoic evaporite deposit are the main controls on deformation salt core detachment fold thrust systems coincide with areas of salt tectonics and pop up imbricate and duplex structures are associated with the main thrust faults in the sub salt layer distribution maps of thrust systems basement structures and salt tectonics show that paleozoic basement uplift controlled the paleozoic foreland basin morphology and the distribution of cenozoic salt in the kftb and thus had a strong influence on the segmented structural deformation and evolution of the fold thrust belt three types of transfer zone are identified based on the characteristics of the salt layer and basement uplift and the effects of these zones on the fault systems are evaluated basement uplift and the boundary of the salt deposit generated strike slip faults in the sub salt layer and supra salt layers at the basin boundary model a when changes in the basement occurred within the salt basin strike slip faults controlled the deformation styles in the sub salt layer and shear zone dominated in the supra salt layer model b a homogeneous basement and discontinues salt layer formed different accommodation zones in the sub and supra salt layers model c in the sub salt layer the thrusts form imbricate structures on the basal decollement whereas the supra salt layer shows overlapping discontinuous faults and folds with kinds of salt tectonics and has greater structural variation than the sub salt layer

the kuqa late cenozoic fold thrust belt on the southern flank of the tian shan mountains the kuqa fold thrust belt kftb a late cenozoic fold thrust belt on the southern flank of the tian shan mountains consists of several deformation zones trending nearly w e the main decollement fault of the kftb gradually rises southwards there are three regional main decollement faults in the triassic dark mudstone paleogene gypsum salt kumugeliemu formation and neogene gypsum salt jidike formation respectively and possibly a fourth in the jurassic coalbed laterally thin skinned structures are developed in the main segments of the kftb whereas thick skinned structures are in the root zone vertically the structural deformation above the cenozoic gypsum salt layers paleogene gypsum salt in the middle segment of the kftb and neogene gypsum salt in the eastern segment is characterized by decollement folding whereas that below is characterized by thrusting the kftb was resulted from the late cenozoic intra continental orogeny in the tian shan area under the far field effect of the india asia collision the deformation of kftb began folding and thrusting ca 23 ma when the far field effect of the india asia collision reached the tian shan area the deformation of kftb accelerated ca 10 5 2 and 1 0 ma in general the evolution of the kftb is forward propagating and the hinter parts of the kftb continue to deform while its front propagates southwards

geometry and evolution of fold thrust structures at the boundaries between frictional and ductile detachments abstract fold thrust belts formed above a ductile detachment typically contain detachment folds whereas those formed above frictional detachments contain fault related fold complexes such as imbricate thrust systems analog models using silica sand to represent sediments and silicone gel to represent salt were conducted to study the fold geometry fold fault relations and sequential development of structures formed in each setting and at the boundaries between the two settings the results showed a relatively thinner wedge above a ductile detachment so that the deformation front propagated farther forward than that above a frictional detachment the thrust front connects across the two settings with a significant change in position and a resulting change in orientation the geometry of the deformation front is strongly controlled by that of the detachment boundary so that an oblique detachment boundary results in an oblique thrust front in the transition zone modifications in the taper geometry also result from the presence of a frictional belt behind a ductile belt the width of the ductile detachment which limits the location of the deformation front and the lateral propagation of thrust faults between the two regimes the experimental models can be used to explain observed geometries in natural examples of fold thrust belts marked by transitions between frictional and ductile detachments

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

influence of syntectonic sedimentation and decollement rheology on the geometry and evolution of orogenic wedges analog modeling of the kuqa fold and thrust belt nw china

a revised magnetostratigraphy for the mid proterozoic gardar lava succession south greenland abstract new palaeomagnetic results from the ca 1300 ma gardar lava succession within the eriksfjord formation of south greenland are presented this study incorporates stepwise thermal demagnetisation of 256 samples from 66 lava flows from all three lava groups in this formation accompanied by principal component analysis the results identify two complete reversals n r n in the upper lava group and two r n and n r in the lower group with a possible palaeoexcursion in the lower group a minimum of two further reversals are predicted in the time interval represented by the sandstone units intercalated with the lava flows both complete reversals in the upper group exhibit inclination asymmetries of 30 this degree of asymmetry is satisfied by a geomagnetic field model equivalent to a dipole axially offset by 570 km however a more complex source is not precluded by the present evidence four new pole positions are calculated for the gardar lavas two for the upper lava group and one each for the middle and lower groups the middle lava group shows an anomalous mean direction and pole position which is unrepresentative of the remainder of the lava succession and is thought to record a virtual geomagnetic pole representative of a transitional field direction the presence of a non axial geocentric dipole field means that the use of the laurentian apparent polar wander path for dating the new poles is not valid

palaeomagnetism of mesoproterozoic limestone and shale successions of some purana basins in southern india the purana basins were long considered neoproterozoic basins until geochronology and palaeomagnestism showed parts of the chattisgarth and lower vindhyan basins to be a billion years older historically the successions in the chattisgarth basin are correlated with similar successions in the pranhita godavari and indravati basins in india differentiating between early late mesoproterozoic rocks and those spanning the mesoproterozoic neoproterozoic boundary is possible by comparing magnetic declination and inclination palaeomagnetism is therefore a very useful correlation tool here we report a new stenian aged palaeopole 50 1 n 67 4 e radius of cone of 95 confidence a 95 12 4 precision k 30 1 from carbonate and shale successions of the pranhita godavari and chattisgarth basins the c magnetization in addition an early diagenetic remagnetization component a was identified no primary or early diagenetic magnetizations were identified from the indravati basin here as well as in stratigraphically higher parts of the other two successions widespread younger magnetic overprints were identified b and b magnetic components our c palaeopole is constrained by palaeomagnetic stability field tests is different from known 1 4 ga and 1 0 ga indian palaeopoles but similar to a 1 19 ga palaeopole penganga group pranhita godavari basin deposition was probably initiated at around 1 2 ga a similar palaeomagnetic signature confirms its correlation with the raipur group chattisgarth basin of which the deposition spans most of the stenian period c 1 2 1 0 ga sedimentation in these groups began significantly later than c 1 4 and c 1 6 ga as suggested by ages reported from below the raipur and penganga groups respectively

salt structures and hydrocarbon accumulations in the tarim basin northwest china the tarim basin is one of the most important hydrocabon bearing evaporite basins in china four salt bearing sequences the middle and lower cambrian the mississippian the paleogene and the neogene have various thickness and areal distribution they are important detachment layers and intensely affect the structural deformation in the basin the kuqa depression is a subordinate structural unit with abundant salt structures in the tarim basin salt overthrusts salt pillows salt anticlines salt diapirs and salt withdrawal basins are predominant in the depression contraction that resulted from orogeny played a key function on the formation of salt structures growth strata reveal that intense salt structural deformation in the kuqa depression occurred during the himalayan movement from oligocene to holocene with early structural deformation in the north and late deformation in the south growth sequences also record at least two phases of salt tectonism in the yingmaili tahe and tazhong areas low amplitude salt pillows are the most common salt structures and these structures are commonly accompanied by thrust faults the faulting and uplifting of basement blocks controlled the location of salt structures the differences in the geometries of salt structures in different regions show that the thickness of the salt sequences has an important influence on the development of salt cored detachment folds and related thrust faults in the tarim basin salt sequences and salt structures in the tarim basin are closely linked to hydrocarbon accumulations oil and gas fields have been discovered in the subsalt intrasalt and suprasalt strata salt deformation has created numerous potential traps and salt sequences have provided a good seal for the preservation of hydrocarbon accumulations large and small scale faults related with salt structures have also given favorable migration pathways for oil and gas when interpreting seismic profiles special attention needs to be paid to the clastic and carbonate interbeds within the salt sequences because they may lead to incorrect structural interpretation in the tarim basin the subsalt anticlinal traps are good targets for hydrocarbon exploration

effects of topography on the curvature of fold and thrust belts during shortening of a 2 layer model of continental lithosphere abstract we have used analogue experiments to investigate the effects of surface topography on the curvature of fold and thrust belts under conditions of 1 initial relief but no erosion and 2 no initial relief but differential erosion sedimentation and transport in experiments where a 2 layer model lithosphere shortened and thickened in front of an advancing straight piston the geometry of the developing thrust wedge was very sensitive to variations in surface topography in models with an initially flat horizontal surface and in the absence of erosion and sedimentation thrusts were straight propagated forwards and nucleated at buckle folds far in front of an advancing piston around an initial topographic high plateau or cone thrusts tended to be arcuate forming salients towards the foreland initial plateaux and cones tended to behave rigidly while arcuate thrust slices formed around them to accommodate differential slip transfer zones developed on both sides of initial highs fault blocks rotated about vertical axes and thrusts moved in oblique slip within transfer zones in models with initially horizontal surfaces which were subject to differential erosion sedimentation and transport thrusts initially were straight but then progressively rotated around non eroded thickened and stronger areas these worked as indenters in front of which new thrusts nucleated at curved buckle folds these thrusts were also curved their apices being in front of the thickened non eroded areas in nature arcuate structural patterns are to be found around the altiplano of the central andes and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high elevations and that differential erosion at the scale of the entire andes may have contributed to oroclinal bending

object based landfast sea ice detection over west antarctica using time series alos palsar data abstract landfast sea ice fast ice is an important feature prevalent around the antarctic coast which is affected by climate change and energy exchanges with the atmosphere and ocean this study proposed a method for detection of the west antarctic fast ice using the advanced land observing satellite phased array l band sar alos palsar images the algorithm has combined image segmentation image correlation analysis and machine learning techniques i e random forest rf extremely randomized trees ert and logistic regression lr we used sar images with a baseline of 5 days that are not in the same orbit but overlap each other as overlaps between swaths in adjacent orbits are often available in the polar regions the underlying assumption for the proposed fast ice detection algorithm is that fast ice regions in sar images with a time interval of 5 days are highly correlated the object based approach proposed in this study was well suited to high resolution sar images in deriving spatially homogeneous fast ice regions the image segmentation results using the optimized parameters showed a distinct difference in the backscatter temporal evolution between fast ice and pack ice regions correlation and std of backscattering coefficients were found to be the most significant variables for the object based fast ice detection from two temporally separated images in overall the quantitative and qualitative evaluation demonstrated that the algorithm was an effective approach to detect fast ice with high accuracies the models well detected various fast ice regions in the west antarctica but misclassified some objects the misclassifications occurred toward the edge of fast ice regions with relatively rapid changes in backscattering between both data acquisitions on the other hand few fast ice objects were misclassified as uniform backscattering over time occurred by chance on very small objects far from the coast very old multi year fast ice regions with high backscattered signals were also a source for some misclassifications this may be due to the sensitivity of l band to snow structure to some extent and a thinner ice over the region with either ice growth no deformation or closing slight deformation between both images heavy snow load on the ice could be another error source for some misclassification as well the approach allowed for the reliable detection of fast ice regions by using l band sar images with a small local incidence angle difference

chronology of magmatism skarn formation and uranium mineralization mary kathleen queensland australia uranium mineralization is hosted in a metasedimentary sequence intruded by felsic and mafic bodies in which the zircon u pb systems are 1 730 to 1 740 m y old felsic dikes characterized by exceptionally high uranium contents crystallized at essentially the same time 1 737 or 15 m y primary rb sr systematics in these igneous rocks are profoundly disturbed u pb discordia establish age of uranium mineralization as 1 550 or 15 m y derivation of uranium protore in the host rocks prior to regional metamorphism and 1 550 m y uraninite formation was probably by ca 1 740 m y hydrothermal activity modified journal abstract

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

structural features of northern tarim basin implications for regional tectonics and petroleum traps the rhombus shaped tarim basin in northwestern china is controlled mainly by two left lateral strike slip systems the northeast trending altun fault zone along its southeastern side and the northeast trending aheqi fault zone along its northwestern side in this paper we discuss the northern tarim basin s structural features which include three main tectonic units the kalpin uplift the kuqa depression and the north tarim uplift along the northern margin of the tarim basin structural mapping in the kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike slip faulting the amount of strike slip displacement is estimated to be 148 km by restoration of strike slip structures in the uplift the kuqa depression is a mesozoic cenozoic foredeep depression with well developed flat ramp structures and fault related folds the baicheng basin a quaternary pull apart basin developed at the center of the kuqa depression subsurface structures in the north tarim uplift can be divided into the mesozoic cenozoic and the paleozoic lithotectonic sequences in seismic profiles the paleozoic litho tectonic sequence exhibits the interference of earlier left lateral and later right lateral strike slip structures many normal faults in the mesozoic cenozoic litho tectonic sequence form the negative flower structures in the north tarim uplift these structures commonly directly overlie the positive flower structures in the paleozoic litho tectonic sequence the interference regions of the northwest trending and northeast trending folds in the paleozoic tectonic sequence have been identified to have the best trap structures our structural analysis indicates that the tarim basin is a transpressional foreland basin rejuvenated during the cenozoic

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

fracture systems and petrophysical properties of tight sandstone undergoing regional folding a case study of the cretaceous reservoirs in the kuqa foreland thrust belt tarim basin abstract the kuqa foreland thrust belt of the tarim basin hosts a prolific hydrocarbon system the main reservoirs are characterized by tight sandstone with low porosity and ultra low permeability buried presently at more than 5000 m depth natural fracture systems have a significant impact on reservoir performance and it may form paths for fluid flow in tight sandstone reservoirs and therefore plays an essential role in controlling high production rates with the aim of analyzing the distribution of favorable reservoir we studied subsurface fracture patterns and petrophysical properties of the bashijiqike formation with data collected from dabei structure and keshen structure we document the presence of four fracture systems whose distribution is related to far field stress thrusting and folding in the keshen anticlines higher fracture intensities are observed in the limbs with principal east west hinge parallel fracture system direction the hinge parallel fracture system includes a moderate dipping fracture set and a vertical fracture set crosscutting relationships stress field inversion and fracture surface textures suggest that the moderate dipping fracture set consists of shear fractures and can be explained by intra layer shear caused by thrusting the vertical fracture set may be formed due to the local outer arc extension during folding the oblique fracture system shows scattering in strike and is supposed to be related to a shear event of locally left lateral strike slip whereas in the dabei anticlines the major system is hinge perpendicular fracture system nw se showing a trending of increasing fracture intensity from limbs to hinge the hinge perpendicular fractures system in the dabei anticlines consist of shear fractures and tension fractures stress inversion result shows it corresponds to northwest southeast orientation compression stage besides we analyzed petrophysical properties include porosity permeability young s module poisson ratio and compressive strength of the bashijiqike formation concerning their structural position within folds it indicates that the highest porosity and permeability are associated with dissolution and fracturing the compressive strength of different structural positions also restrict the variations of mechanical properties of rocks the best reservoir quality is suggested in the hinge zone and areas close to thrust the findings have given maybe helpful for providing favorable reservoir targets for prospecting in the compressional basin

along strike structural variation in a salt influenced fold and thrust belt analysis of the kuqa depression abstract the kuqa depression is associated with complex salt structures variation in fold geometries and subsalt fault activities were investigated using parallel cross sections to reveal detailed along strike variations within the keshen 5 segment and their controlling factors along strike variations were identified in both suprasalt and subsalt units linkages such as the location of a transfer zone were apparent while the distribution of variations above and below the salt layer were decoupled the results indicate that the pre existing salt wall is the key factor driving along strike variations because it acts as a weak zone that influences deformation propagation suprasalt structural variation results in different sediment depths which have a significant impact on subsalt fault activity in the eastern segment fault activity decreases from the hinterland to the basin in contrast owing to the pre existing salt wall and deep sedimentation near the hinterland in the western segment the fault beneath the salt wall is characterized by maximum displacement this study reveals the connection between suprasalt and subsalt deformation and the role of that a salt diapir plays in along strike structural evolution variations for the keshen 5 segment of the kuqa depression these findings are relevant for understanding along strike deformation propagation and structural variation in other fold and thrust systems

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

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

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

re os and mo isotope systematics of black shales from the middle proterozoic velkerri and wollogorang formations mcarthur basin northern australia joint application of the mo isotope paleoredox proxy and re os deposition age geochronometer to euxinic black shales has potential for tracing the evolution of ocean redox chemistry over geological time here we report new re os and mo isotope data for the mesoproterozoic velkerri formation roper group and paleoproterozoic wollogorang formation tawallah group mcarthur basin northern australia new re os ages of 1361 21 ma 2 n 14 mean square of weighted deviates mswd 1 3 model 1 and 1417 29 ma 2 n 12 mswd 1 3 model 1 constrain the depositional age of the velkerri formation and its contained biomarkers as well as acritarchs and microfossils from the roper group black shales from the upper velkerri formation have high mo abundances 105 119 ppm and degree of pyritization dop values 0 90 0 92 implying quantitative conversion of molybdate moo42 to thiomolybdate mos42 in overlying bottom waters the average 97 95mo 0 72 0 10 2 n 6 of these shales is consistent with previous data but represents a significantly more precise determination for global seawater 97 95mo at 1 4 ga this value is lighter than present day seawater by 0 85 and reflects expanded strongly euxinic deep ocean conditions h2s aq 11 m relative to oxic suboxic and weakly intermittently euxinic h2s aq 11 m marine deposition in the 1 4 ga oceans mass balance modelling suggests mo removal into strongly euxinic and oxic sediments may have comprised 30 70 and less than 15 respectively of the oceanic mo sink at 1 4 ga as opposed to 5 and 35 today respectively the re os radioisotope system in organic rich shales serves as a test for post depositional alteration that could affect the usefulness of paleoredox tracers such as mo stable isotopes re os isotope data for the wollogorang formation black shales are scattered and yield a highly imprecise date of 1359 150 ma 2 n 21 mswd 85 model 3 this age is younger than u pb zircon ages from interbedded tuffs that constrain the age of deposition at ca 1730 ma in conjunction with previous petrological geochemical and paleomagnetic data the re os isotope data suggest hydrothermal fluid flow through the wollogorang formation possibly associated with formation of the ca 1640 ma mcarthur river pb zn ag sedimentary exhalative deposit resulted in post depositional mobilization of re and os based on the degree of deviation of the re os data from a 1730 ma reference line open system behavior of re and os was greatest near the base of the black shale unit wollogorang formation black shales are enriched in mo 41 58 ppm but are characterized by variable 97 95mo 0 3 0 8 and dop 0 57 0 92 the lightest 97 95mo values occur near the base of the black shale unit based on the re os systematics hydrothermal fluids have probably overprinted the authigenic 97 95mo signature in those shales however the heaviest 97 95mo values in the wollogorang formation come from stratigraphically higher shales and are similar to those observed for the velkerri formation and thus may reflect seawater 97 95mo at 1 73 ga

climatology and variability of warm and cold fronts over north america from 1979 to 2018 abstractthis paper describes the development and analysis of an objective climatology of warm and cold fronts over north america from 1979 2018 fronts are detected by a convolutional neural networ

subdivision and correlation of late precambrian sequences in australia abstract the diversity of the australian precambrian record is used to empirically assess the application of all available techniques of correlation of late precambrian rocks lithofacies isotopic ages palaeontology and palaeomagnetism within the framework of latest lithostratigraphic geochronologic correlation charts lithostratigraphy is the main tool for intrabasinal correlation and mapping but isotopic ages will continue for some time yet to provide the main criteria for interregional correlation lithostratigraphic correlation is demonstrated over hundreds of kilometres but is generally constrained by tectonic controls to individual major crustal blocks climatic markers such as tillites may be correlated interregionally over thousands of kilometres the most exciting recent development in platform geochronology is the application of u pb zircon dating to fine grained tuffs illite may provide reliable minimum estimates but can be shown to be up to 150 ma too young glauconite and rb sr total rock shale ages have provided useful broad age estimates of sequences for which better methods are unavailable but only when based on cautious assessment and multiple sampling their ages may be either minimum or maximum stromatolites continue to demonstrate their potential for broad correlation when based on rigorous taxonomic study but the framework of time ranges of known taxa must be expanded for stromatolites to achieve their full potential especially for rocks older than 1000 ma acritarchs in black shales provide diverse and complex assemblages with excellent correlation potential but once again the australian taxonomic framework is still inadequate black cherts contain an evolutionarily conservative biota with only limited correlation potential recent palaeomagnetic studies based on both apwp and magnetostratigraphy demonstrate excellent potential for detailed correlations down to at least 1700 ma old however the present chronologically calibrated data base is sparse and must be supplemented by many more detailed studies through thick continuous rock sequences spanning substantial intervals of time the value of multidisciplinary correlation is elegantly demonstrated by very detailed and unambiguous correlation of combined palaeomagnetic isotopic age and stromatolite data across the 1700 ma mcarthur basin previous regional lithostratigraphic correlations have been conclusively and significantly revised with major implications to regional palaeogeography

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

salt rollers structure and kinematics from analogue modelling abstract salt rollers are low amplitude deflections of the upper surface of a salt layer which occur below zones of normal faulting in the overlying sediments they are widely recognised in association with tilted blocks or listric fault rollover systems laboratory experiments on brittle ductile models made of sand and silicone putty are used to study the modes of development the external shape and the internal structures of these salt rollers firstly flow and strain patterns within decollement zones are described finite strain combines layer perpendicular shortening and layer parallel shear additional flow cells within rollers perturb the laminar flow of the decollement inducing a passive folding of planar markers the same type of flow and strain patterns occur in all types of rollers ranging from those occurring below tilted blocks to those associated with growth faults finally an analysis of roller shapes through the measurement of aspect ratios and asymmetry ratios shows that the shapes of tilted blocks rollers and growth fault rollers which differ at initiation tend to converge with increasing deformation

subglacial meltwater channels and glaciofluvial deposits in the kimberley basin western australia 1 8 ga low latitude glaciation coeval with continental assembly a late palaeoproterozoic unconformity surface developed on low dipping sandstone in the kimberley region northwestern australia exhibits numerous linear parallel grooves 10 50 mm deep 40 80 mm wide and tens of metres long and other erosional forms including sichelwannen these features are interpreted as nye channels and sculpted forms eroded by subglacial meltwaters sandstone filled cracks exposed at the unconformity are viewed as periglacial frost fissures an overlying conglomerate facies 1 15 m thick at the base of the c 1800 ma king leopold sandstone kimberley basin succession contains poorly sorted pebble to boulder conglomerate and is interpreted as glaciofluvial in origin the orientation of the nye channels and sculpted forms and the palaeocurrent direction for the glaciofluvial deposits indicate westward ice flow the conformably following locally glauconitic quartzarenite of the king leopold sandstone probably accumulated in an epeiric sea implying that glaciation reached close to sea level transgression in northwestern and central australia at c 1800 ma may have been partly glacio eustatic glaciation was initiated to the east of the kimberley basin evidently in the halls creek orogen during a major phase of continental collision in australia and worldwide supercontinental assembly recognition of the king leopold glaciation which occurred in low palaeolatitudes c 2200 and 800 ma

sea ice concentration estimation during melt from dual pol sar scenes using deep convolutional neural networks a case study high resolution ice concentration maps are of great interest for ship navigation and ice hazard forecasting in this case study a convolutional neural network cnn has been used to estimate ice concentration using synthetic aperture radar sar scenes captured during the melt season these dual pol radarsat 2 satellite images are used as input and the ice concentration is the direct output from the cnn with no feature extraction or segmentation postprocessing the absolute mean errors of the generated ice concentration maps are less than 10 on average when compared with manual interpretation of the ice state by ice experts the cnn is demonstrated to produce ice concentration maps with more detail than produced operationally reasonable ice concentration estimations are made in melt regions and in regions of low ice concentration