stratigraphy correlation and sedimentary history of adelaidean late proterozoic basins in australia abstract adelaidean late proterozoic time is represented by the precambrian portion of the thick sequence in the adelaide geosyncline its stratotype basin in south australia comparable adelaidean sedimentation including the deposition of glaciogenic sediments is recorded in other intracratonic and epicratonic basins extending northwards across australia in the adelaide geosyncline which lies to the east of the gawler craton and its cratonic platform cover the stuart shelf up to 15 km of mainly shallow water sediments accumulated partly in intracratonic troughs and perhaps partly on a miogeoclinal continental shelf the earliest sedimentation is associated with rifting and basic volcanism with an estimated age of ca 1100 ma it commenced with basal blanket sands shelf carbonates and basaltic volcanics followed by mixed carbonate clastic and evaporitic beds callanna beds the overlying burra group consists of a number of west derived possibly deltaic cycles and magnesite bearing platform carbonates the unconformably overlying late adelaidean umberatana group contains the lower glacial beds including the sturt tillite interglacial siltstone dated at about 750 ma and carbonate and the upper glacial beds the post glacial wilpena group commences with a distinctive cap dolomite above the upper glacials and contains mainly fine to medium clastics and the ediacara metazoan assemblage late adelaidean sedimentation patterns are sufficiently similar in the officer amadeus ngalia and georgina basins of central australia and in the kimberley region western australia to suggest interconnection with the adelaide geosyncline to the south in the amadeus basin the early adelaidean sequence is younger than about 1050 ma but cannot be directly correlated with the early adelaidean formations of the adelaide geosyncline however the late adelaidean glacial and younger sequences are readily correlated they include the lower glacial areyonga formation and the arumbera sandstone i containing elements of the ediacara assemblage in the georgina and ngalia basins mainly late adelaidean sequences including thick glacials can mostly be correlated with the amadeus basin in the kimberley region earliest adelaidean clastics may be represented but only the late adelaidean glaciogenic and associated sediments can be correlated with confidence the tillites commonly overlie glaciated pavements the lower glacials are represented only in a graben while the upper glacials and succeeding sequence are more widespread post glacial shales have been dated at ca 670 640 ma the dominantly carbonate and clastic sequences of the bangemall basin western australia cannot be directly correlated with any type adelaidean but geochronology suggests an earliest adelaidean age ca 1050 ma

structure and evolution of the intracratonic basins of central australia summary the central australian geology is dominated by a series of parallel sedimentary intracratonic basins whose history spans time from the late proterozoic to the carboniferous the basins are separated by regions of exposed proterozoic crust that have a history of significant uplift the formation of the basins cannot be explained by conventional thermal or stretching mechanisms nor does the foreland basin model provide an adequate explanation for their occurrence the geophysical observations particularly gravity point to a structure whereby the crust is considerably thicker under the basins than it is under the regions where basement rock is exposed this suggests that the crust as a whole is involved in the process that led to the basin formation a mechanical model is developed which is based on the supposition that the lithosphere has been in a state of horizontal compression for long time intervals the lithosphere is considered as a viscoelastic plate that has been subjected to a small normal load distributed in an irregular manner under compression initial deflections due to this load are magnified according to the plate s physical properties the magnitude of the compressive force and the wavelength spectrum of the initial perturbations because of the viscosity the deflections grow with time at a rate that is determined by the balance of forces acting on the plate and by the lithosphere s rheology both the elastic and viscous deformations are much enhanced if erosion of the uplifted areas occurs with the sediments deposited into the downwarps these deformations take place at stresses that are much less than the buckling stresses as bending stresses increase with time failure by thrust faulting is predicted to occur within the basins with the exposed basement being thrust over the basins the model has been applied to the central australian region starting at about 900myr ago the first basins to develop are the officer and amadeus basins with uplift occurring in the intervening musgrave block initial rates of uplift and basin subsidence are small but they can increase rapidly with time if the compressive force is main

timing the breakup of a proterozoic supercontinent evidence from australian intracratonic basins in the late proterozoic several broad shallow intracratonic depressions appeared across a vast area of central australia the basins which all contain shallow marine to fluvial successions appear to have been tenuously interconnected through much of their history analysis of their fill by means of tectonic subsidence curves suggests that they are the product of two separate and distinct periods of crustal extension one at about 900 ma and a second at about 600 ma these extensional episodes were probably the result of failed rifting events that almost fragmented the australian continent during the late proterozoic the second period of extension almost certainly relates to the breakup of a proterozoic supercontinent the results suggest that sediments preserved in the relatively protected environment of interior basins may provide a more subtle record of major tectonic events than continental margin sequences that were exposed to major continental interactions

neodymium strontium isotopic evidence for extreme contamination in a layered basic intrusion abstract neodymium and strontium isotopic analyses from the kalka layered basic intrusion central australia are arrayed parallel to the sr axis of a nd sr isotopic correlation diagram and are removed from the normal basaltic field initial 143 nd 144 nd ratios are almost constant and typical of continental basalts whereas initial 87 sr 86 sr ratios vary greatly and range to high values 0 7049 0 7088 acidic granulites from the country rock lie upon the continuation of the kalka trend at higher 87 sr 86 sr ratios outlining a mixing system between granulite and normal basaltic magma if average granulite acted as a contaminant isotope dilution calculations show that amounts assimilated reached as high as 25 bulk contamination is confirmed petrologically by the abundance of orthopyroxene particularly as basal orthopyroxenites and the restriction of olivine to less contaminated levels analogies between kalka and several other major layered intrusions such as the bushveld complex suggest that large scale contamination was a significant aspect of their genesis

climate and vegetation history of the midcontinent from 75 to 25 ka a speleothem record from crevice cave missouri usa four missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago ka the thorium 230 dated records reveal that between 75 and 55 ka the midcontinental climate oscillated on millennial time scales between cold and warm and vegetation alternated among forest savanna and prairie temperatures were highest and prairie vegetation peaked between 59 and 55 ka climate cooled and forest replaced grassland at 55 ka when global ice sheets began to build during the early part of marine oxygen isotope stage 3

sequence stratigraphy and depositional controls in late proterozoic early cambrian sediments of amadeus basin central australia the amadeus basin is an isolated intracratonic basin at the center of the australian continent which because of its location and geometry provides an ideal opportunity to investigate depositional controls to this end more than 6 000 km of seismic data in conjunction with a field and well log program have been used in a study of the late proterozoic early cambrian arumbera sandstone the arumbera sandstone was deposited as two major depositional sequences in a shallow marine and deltaic or coastal plain setting similar to that of the devonian catskill delta of north america sediment was supplied from the southwest by heavily laden braided streams during the deposition of the first sequence when sea level was at its maximum sedimentation appears to have been largely aggradational as sediment supply balanced or exceeded basin subsidence the sediments were probably deposited in a coastal or delta plain setting where small scale deltas prograded across the carbonate platform sediments of the julie formation during the accumulation of the second sequence sea level fell rapidly exposing large areas of sediment deposited during the first cycle and restricting edimentation to two steep sided rapidly subsiding subbasins deposition was largely progradational as major deltaic complexes developed on the southern and southwestern margins of the subbasins between the major delta complexes a depositional environment similar to that of the first sequence predominated in the deep subbasins the arumbera sandstone forms a continuous depositional unit across the proterozoic cambrian boundary the unconformable nature of that boundary over much of the earth possibly could be the result of a major eustatic sea level drop the final geometry of the arumbera sandstone and the nature of its sediments were determined largely by local subsidence rates subsidence briefly outstripped sediment supply during a stage of crustal extension as the basin evolved during deposition of sequence 1 depositional space and facies distribution were however fine tuned by salt tectonics and major sea level cycles as at passive margins sequence boundaries appear to be controlled by sea level cycles other variables such as climate the lack of vascular plants and the uplift of the source area were also factors in controlling deposition

teleseismic travel time anomalies and deep crustral structure in central australia summary teleseismic travel times have been recorded along two lines of instruments traversing the amadeus basin and southern arunta block of central australia for the purpose of examining the deep crustal and upper mantle structure underlying these features pronounced differential travel times approaching 1 5 s and with major azimuthal variation have been recorded most of the useful observations originated from events to the north japan marianas and to the east fiji tonga at epicentral distances of 40 65d a few observations of southerly azimuth events macquarie ridge and south sandwich islands were also recorded the inferred structure beneath the basin and block exhibits major lateral variations the essential aspects of which are 1 a zone of relatively high velocity material dipping steeply northwards such that the continuation of its southern edge to the surface coincides approximately with a mylonitic shear zone known as the redbank deformed zone 2 a steeply dipping zone of relatively low velocity material immediately to the south of this shear zone and partly underlying the high velocity zone if the travel times are interpreted in terms of an undulating moho variations in moho depth of 20 km occur over horizontal distances of less than 50 km with relatively shallow moho depths occurring immediately to the north of the redbank deformed zone such an interpretation is consistent with the gravity anomalies observed across the geological structures the inferred structure is out of hydrostatic equilibrium and departures from local isostasy approach 150 mpa these stress differences must have persisted during the 300 ma following the alice springs orogeny that led to the present crustal structure evidence in the form of the surface topography and seismicity suggests that some stress relaxation has occurred and still is occurring but not at the shear zone itself at the time of the orogeny the structure may have been close to isostatic equilibrium but as erosion took place complete local rebound did not occur either because horizontal compressive forces still operated or because the strength of the lithosphere increased with time

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

current aspects of basin analysis abstract current research in basin analysis focuses on interdisciplinary integration of geodynamics mathematical and physical modelling and sedimentary geology these efforts are organized into a research framework emphasizing basin formation nature of the basin fill maturation diagenesis of the basin fill and timing of events research in geodynamics permits development of a proposed classification of sedimentary basins in which basin types are discriminated according to nature of the plate margin basin position on or within a tectonic plate nature of the crust and geodynamic models or known process of formation a summary of current research developments on sedimentary basin fills focuses on the interdisciplinary solutions developed to understanding carbonate distribution through time origin of black shales sea level history and global sedimentary cycles maturation of basin fills requires an understanding of both thermodynamic aspects of mineral phase changes and changing character of the chemistry of flow of water through porous sediments during basin evolution summary case histories from the illinois basin and the appalachian basin illustrate these approaches

the evolution of the mobile zones of gondwana and laurasia in the late precambrian abstract the tectonic evolutions of gondwana and laurasia in the late precambrian show some differences which become more striking after the late riphean 1000 700 m y when gondwana separated from pangea these differences include distributions of aulocogens and intrageosynclines as well as zones of non geosyncline tectono thermal reworking of basement geodynamics of interiors in gondwana and laurasia were quite different during the vendian early cambrian the fragmentation of laurasia and the opening of the iapetus and the paleo asian ocean coincide in time with the pan african orogeny and equivalent orogenies in gondwana

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

proterozoic plate tectonics in canada with emphasis on evidence for a late proterozoic rifting event abstract several early proterozoic fold belts in the canadian shield have been interpreted in terms of plate tectonic processes the most impressive evidence comes from those preserved on the margins of archaean cratons such as the wopmay orogen and the penokean fold belt there are striking similarities in the stratigraphic successions of many widely separated early proterozoic fold belts within the canadian shield most of these are currently best interpreted in terms of some modified version of plate tectonics post grenville rocks contain several independent lines of evidence that support a major episode of continental fragmentation stratigraphic and sedimentological evidence from the cordilleran region records a dramatic change from widespread development of essentially platformal marine sediments l mackenzie mountains supergroup through rift related evaporites and clastics u mackenzie mountains supergroup to a largely resedimented sequence ekwi or windermere supergroup that has been interpreted as a continental margin facies a closely comparable succession of facies can be documented in other parts of the world but perhaps the closest analogue is found in s e australia it has been suggested that these two regions may formerly have been juxtaposed and represent the sundered fragments of a late proterozoic supercontinent relevant to these interpretations are geochemical data such as 34s values from late proterozoic evaporites and 87sr 86sr measurements from carbonates and processes involved in precipitation of glacially related iron formations such as those of the rapitan group in the n cordillera preservation of late proterozoic ophiolites in north africa provides additional evidence of plate tectonic processes at that time these several lines of evidence all suggest a significant period of late proterozoic continental breakup which produced many of the continental margins that were and are the loci of subsequent phanerozoic orogenic activity

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

upper proterozoic evaporites in the amadeus basin central australia and their role in basin tectonics the amadeus basin an isolated intracratonic basin in the center of the australian continent contains an upper proterozoic to mid paleozoic stratigraphic succession of shallow marine sediments that in places exceeds 14 km in thickness the gillen member of the bitter springs formation which occur toward the base of the upper proterozoic succession includes evaporites which are among the world9s earliest 0 8 to 0 7 ga because of their age the evaporites have been cited in discussions of sea water chemistry and have been the focus of scrutiny for early life forms in spite of their importance the evaporites are poorly known particularly from the viewpoint of their depositional and tectonic setting in an attempt to rectify this deficiency more than 6 000 km of seismic data were analyzed in conjunction with a field and well log study of the unit the late proterozoic amadeus basin appears to have consisted of two major poorly circulated anoxic sub basins which perhaps opened to the ocean to the southeast through the adelaide geosyncline data relating to facies are limited but suggest that deposition of the evaporites was cyclic and followed the patterns identified in other major evaporite basins the carbonates and sulfates being closer to the basin margins and later stage halite and possibly potassium salts being toward the basin center the evaporites were deposited in a shallow marine setting at the time of a relative sea level high stand the apparent sea level high may relate to basin dynamics whereas the cyclicity of the evaporites may be due to eustatic sea level controls acting on the barrier to allow intermittent inflow of sea water salt tectonism began shortly after the evaporites were deposited and continued throughout basin development consequently most of the major anticlinal structures have salt cores the geometry of the salt structures suggests that during their growth the mean strain rate was 10 16 s 1 a rate typical of large salt structures growth on these salt structures has played an important role in controlling later sedimentation particularly during the cambrian

development of the late proterozoic to mid paleozoic intracratonic amadeus basin in central australia a key to understanding tectonic forces in plate interiors the intracratonic amadeus basin in central australia is a complex composite basin covering 17 000 km with at least nine distinct episodes of evolution between 900 and 300 ma these have been identified in neighboring central australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early australian plate in the absence of direct geological evidence for thermal events in the amadeus basin after the initial period of subsidence ended possibly at about 800 ma the correlations found between events in the amadeus basin those in the neighboring interconnected basins and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms this suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide throughout the history of the amadeus basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified there were also transitional periods when neither compression nor extension dominated so that other processes masked the effects of weak horizontal stresses the most recent compressional thrust belt concentrated at the northern margin between 300 and 400 ma and has partly obscured the record of earlier basin shape and size

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

tectonic development and metallogeny of the kanmantoo trough in south australia abstract the kanmantoo trough is the sedimentary and tectonic link between the adelaide geosyncline composed of late proterozoic sediments and volcano sedimentary sequences of the tasman fold belt system in eastern australia cambrian flyschoid sediments of the kanmantoo trough were likely deposited on a marginal shelf reflecting tectonic activity to the west and a continental margin to the east the sediments may extend eastwards under the murray basin but the tectonic significance of the padthaway ridge and of mafic volcanics northeast of that region are poorly understood copper mineralisation is scattered throughout the kanmantoo trough and is commonly associated with the intersection of northwest trending fracture zones and pyritic sedimentary horizons

effects of finite rifting times on the development of sedimentary basins abstract most thermo mechanical models for the development of sedimentary basins have assumed that the rifting responsible for the formation of the basin occurred instantaneously and have examined the post rift development of the basin this assumption greatly simplifies the mathematical treatment but is not in accord with what is found in nature where 10 to 50 m y rifting events commonly accompany the formation of sedimentary basins and continental margins the effects of a finite rifting time on the development of sedimentary basins are examined using an analytic technique which allows an arbitrary rifting history in both time and space and which considers the effects of both vertical and horizontal heat transfer this technique allows the thermal structure of the lithosphere to be calculated throughout the rifting event and thus permits the subsidence history and surface heat flow of the developing basin to be traced the effect of a finite duration extension event is that heat is lost during rifting increasing the syn rift subsidence at the expense of the post rift lateral heat flow which was not included in previous studies of the effect of finite rifting times has a significant effect on the subsidence history distribution of sediments and thermal history in particular the post rift subsidence is decreased by more than 25 for a 20 m y rifting event and by more than 10 15 for a rifting event as short as 10 m y this will significantly decrease the subsidence rates in the post rift stage and implies that inferences concerning the structure development and thermal history of the basin derived from using curves to interpret backstripped subsidence can be greatly in error variations in syn rift sediment accumulation and lithospheric thermal structure at the end of rifting resulting from different rifting histories can interact with other factors such as the flexural response of the lithosphere to sediment loading to affect the final width of the basin the total amount of sediments that accumulate and the basin stratigraphy

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

the chronometric age of the sinian cambrian boundary in the yangtze platform china the cambrian and precambrian sedimentary strata in the center and west part of the yangtze platform are in continuous successions in which the tiantzushan member and the meisuchun formation are exceedingly rich in shelly fossils in co operation with the stratigraphic study in depth and in order to determine the isotopic age for the precambrian cambrian boundary in the yangtze platform a number of isotopic age determinations have been made mainly on the sequences in the yangtze gorges area together with those from some other areas in the yangtze platform in this paper the authors summarize all of these results and infer 610 or 10 ma as an age for the sinian cambrian boundary in the yangtze platform if the golden spike is considered to be placed at the bottom of the meishucun state modified journal abstract

origin and epeirogenic history of the williston basin evidence from fission track analysis of apatite we have tested the hypothesis that the lithosphere beneath the williston basin was heated uplifted and eroded prior to basin subsidence this was accomplished by fission track dating of apatite from samples of basement rock beneath and adjacent to the basin apatite fission track ages of basement rocks beneath the basin range from about 4 ma near the center to 554 ma near the eastern edge combined with stratigraphic evidence the ages suggest that at least 3 km of basement were eroded prior to subsidence of the williston basin rates of apparent uplift and erosion were on the order of 0 10 to 0 15 km m y apatite fission track ages of basement outcrop samples on the eastern flank of the basin range from about 572 ma to 441 ma these ages suggest that erosion of the flank occurred from the early cambrian to the late ordovician we conclude that timing of uplift of the basement prior to subsidence of the williston basin is consistent with the thermal origin hypothesis of basin formation

terminal fold belt deformation relationship of mid carboniferous megakinks in the tasman fold belt to coeval thrusts in cratonic australia megakinks in the meridional tectonic grain of the tasman fold belt were formed by north south compression in the mid carboniferous and appear to be related to the same stress system that formed intracratonic thrusts in central australia during the alice springs orogeny

upb and rbsr geochronology and geological evolution of the harts range ruby mine area of the arunta inlier central australia abstract supracrustal and meta igneous rock units from the ruby mine area of the harts range eastern arunta inlier central australia have been dated by the zircon u pb and rb sr total rock tr and mica methods a well defined zircon discordia for a weakly deformed specimen of the bruna granite gneiss yields an age of emplacement of 1748 4 5 ma thereby constraining the minimum age of the irindina supracrustal assemblage metapelitic gneiss within the supracrustals and a meta igneous ultramafic boudin from the associated harts range meta igneous complex yield highly discordant zircon data revealing a strong early palaeozoic overprint rb sr tr data from anorthositic gneisses associated with the ultramafic boudin are highly disturbed also apparently during the lower palaeozoic however rb sr model age calculations and the zircon u pb data suggest a maximum age of about 2000 ma for the supracrustal and meta igneous rocks and argue for new proterozoic crust formation zircon u pb data from a deformed pegmatite emplaced in the meta igneous complex yield an emplacement age of 520 4 5 ma further pointing to lower palaeozoic magmatism and deformation correlations of u content and calculated 206 pb 238 u age for the ultramafic boudin zircons suggest that new growth of low u zircons occurred during retrogression associated with this event the sr isotope systematics of the anorthositic gneisses can also be interpreted in terms of introduction of palaeozoic sr our data suggest lower palaeozoic possibly delamerian tectonothermal activity to be more important in the evolution of the harts range area than previously recognised on the other hand rb sr mica ages for deformed and undeformed pegmatites and tr isochrons for the latter show that pervasive tectonothernal activity had ceased by about 315 ma and that regional cooling occurred between about 345 and 325 ma local shear zone biotite resetting may have persisted to about 300 ma consistent with the previously recognised alice springs orogeny possible dilational pb loss in the bruna zircons occurred at about 103 ma

csem technology as a value driver for hydrocarbon exploration abstract the use of the controlled source electromagnetic csem method as a risk reduction tool in marine hydrocarbon exploration is gaining increased acceptance in the oil industry this is related to the ability to map resistivity contrasts in the sub surface and thus aid the detection of hydrocarbons which are typically more resistive than surrounding rocks whereas acoustic seismic energy allows for mapping sub surface structures that may contain hydrocarbons electromagnetic em energy can often say something about the fluids contained within the structures numerous successful csem case stories have been published over the past several years however there are also quite a few stories about failure cases although not well documented in the literature such failure cases may reflect the lack of understanding of the csem technology and how csem data can act as a value driver in order to understand this it is necessary to handle uncertainties and decisions associated with the technology these include geological uncertainties noise models survey designs forward modelling parameters inversion migration parameters and pre processing of real data a proper handling of these uncertainties and decisions will aid in defining and constraining the chance of geologic success and geologic success case net present value for prospects prior to drilling wells as such the csem technology has a significant potential to increase exploration efficiency if applied correctly

an interpretation of the tectonostratigraphic framework of the murray basin region of southeastern australia based on an examination of airborne magnetic patterns abstract new pixel map representations of regional total magnetic intensity data reveal previously unknown characteristics of the basement concealed beneath thin cainozoic sediments of the murray basin in southeastern australia interpretations of magnetic patterns in terms of structural features allow a revised interpretation of the nature of the tectonostratigraphic framework underlying and flanking the basin the magnetic data indicate that arcuate or curvilinear structural trends under the murray basin do not conform with those of the exposed lachlan fold belt to the east and suggest that the basement concealed beneath the basin together with that exposed in the victorian highlands to the south forms a distinct composite tectonostratigraphic terrane beneath the southwestern murray basin proterozoic lower cambrian metasediments of the padthaway ridge of the kanmantoo fold belt display a northwesterly trending structural grain and a previously unsuspected continuity of structural trend with adelaidean cambrian rocks of the mount lofty ranges to the west in the south cambrian volcanics of the black range and stavely greenstone belts have similar magnetic response and appear to be components of a single elongate and strongly magnetic domain which extends to the northwest for at least 400 km stavely belt to the north a similar but entirely concealed northeasterly trending magnetic domain can also be interpreted as volcanics lake wintlow belt together these two magnetic domains appear to form an arcuate zone of volcanics with a concave to the east configuration located at a possible suture between the lachlan and kanmantoo fold belts beneath the western murray basin in the south the magnetic imagery indicates that metasediments of the cambro ordovician stawell belt produce magnetic patterns distinct from those produced by the metasediments of the adjacent ordovician bendigo belt which can itself be subdivided into a number of areas of distinct magnetic pattern magnetic domains can be interpreted in terms of concealed proterozoic and palaeozoic structural belts and tectonostratigraphic terranes reconstructions suggest that much of the murray basin may be underlain by a former microcontinental block or rifted marginal plateau of precambrian crust now welded to the precambrian craton to the west deformation of the kanmantoo and adelaide fold belts adjacent to and beneath the western and southwestern margins of the basin can be attributed to late cambrian early ordovician convergence between the microcontinental block and the craton volcanics of the arcuate stavely and lake wintlow belts are interpreted to be located at the suture between the microcontinental block and the craton in addition the presence of concave to the east curvilinear magnetic trends in the cambro ordovician metasedimentary belts beneath the murray basin suggests that these successions as well as the volcanics of the heathcote and mount wellington belts may form allochthonous sheets these were possibly emplaced from the east during late ordovician devonian deformation possibly related to convergence of a further microcontinental block underlying the adjacent lachlan fold belt to the east of the murray basin

metallogeny and tectonic development of the tasman fold belt system in new south wales abstract the northwestern corner of new south wales consists of the paratectonic late proterozoic to early cambrian adelaide fold belt and older rocks which represent basement inliers in this fold belt the rest of the state is built by the composite late proterozoic to triassic tasman fold belt system or tasmanides in new south wales the tasman fold belt system includes three fold belts 1 the late proterozoic to early palaeozoic kanmantoo fold belt 2 the early to middle palaeozoic lachlan fold belt and 3 the early palaeozoic to triassic new england fold belt the late palaeozoic to triassic sydney bowen basin represents the foredeep of the new england fold belt the tasmanides developed in an active plate margin setting through the interaction of east gondwanaland with the ur precambrian and palaeo pacific plates the tasmanides are characterized by a polyphase terrane accretion history during the late proterozoic to triassic the tasmanides experienced three major episodes of terrane dispersal late proterozoic cambrian silurian devonian and late carboniferous permian and six terrane accretionary events cambrian ordovician late ordovician early silurian middle devonian carboniferous middle late permian and triassic the individual fold belts resulted from one or more accretionary events the kanmantoo fold belt has a very restricted range of mineralization and is characterized by stratabound copper deposits whereas the lachlan and new england fold belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes the earliest deposits in the lachlan fold belt are stratabound cu and mn deposits of cambro ordovician age in the ordovician cu deposits were formed in a volcanic are in the silurian porphyry cu au deposits were formed during the late stages of development of the same volcanic are post accretionary porphyry cu au deposits were emplaced in the early devonian on the sites of the accreted volcanic arc in the middle to late silurian and early devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism in the silurian and early devonian numerous sn w mo and base metal au granitoid related deposits were formed a younger group of mo w and sn deposits resulted from early middle carboniferous granitic plutonism in the eastern part of the lachlan fold belt in the middle devonian epithermal au was associated with rifting and bimodal volcanism in the extreme eastern part of the lachlan fold belt in the new england fold belt pre accretionary deposits comprise stratabound cu and mn deposits pre early devonian stratabound cu and mn and exhalite au deposits late devonian to early carboniferous and stratabound cu exhalite au and quartz magnetite late carboniferous s type magmatism in the late carboniferous early permian was responsible for vein sn and possibly au as ag sb deposits volcanogenic base metals when compared with the lachlan fold belt are only poorly represented and were formed in the early permian the metallogenesis of the new england fold belt is dominated by granitoid related mineralization of middle permian to triassic age including sn w mo w and au ag as sb deposits also in the middle permian epithermal au ag mineralization was developed during the above period of post orogenic magmatism sizeable metahydrothermal sb au w and au deposits were emplaced in major fracture and shear zones in central and eastern new england the occurrence of antimony provides an additional distinguishing factor between the new england and lachlan fold belts in the new england fold belt antimony deposits are abundant whereas they are rare in the lachlan fold belt this may suggest fundamental crustal differences

metallogeny and tectonic development of the tasman fold belt system in victoria current evidence suggests that most of victoria is underlain by a relatively thick 20 km basement of sialic composition of assumed proterozoic age this basement is nowhere exposed and its structural relationship with exposed palaeozoic rocks is conjectural this uncertainty has resulted in both ensimatic and ensialic tectonic models being proposed for victoria during the cambrian mineralization associated with cambrian igneous activity shows a variety of styles from minor orthomagmatic chromite deposits through au and cu deposits of syngenetic or epigenetic origin to fe mn ba occurrences of exhalative volcanogenic affiliation cambrian volcanism and associated sedimentation was followed by the deposition of dominantly quartz rich turbidites with interbedded shale and siliceous units subsequent to the epi ordovician benambran orogeny late silurian crustal extension caused several rifts to open along roughly orthogonal nw and ne aligned fractures within these fault bounded depressions thick acid volcanic sequences were deposited in close association with shallow marine sediments mineralization in these upper silurian rocks comprises polymetallic base metal sulphide lenses and minor disseminations at least some of which are of exhalative volcanogenic affiliation the silurian rifts were obliterated and their rocks strongly deformed during the bindian bowning deformation during late silurian to early devonian time this in turn was followed by another episode of crustal extension and rifting during which the formation of a broad meridional trough marks the buchan rift a very thick sequence of largely subaerial bimodal volcanics is overlain by shelf limestone and mudstone a variety of minor base metal barite manganese and iron mineralization is hosted by these volcanics and shelf sediments the mid devonian tabberabberan orogeny was followed in the late devonian by bimodal volcanism and granite intrusion and red bed type non marine sedimentation in central victoria thick bimodal volcanics were erupted into a series of cauldron subsidences and intruded by comagmatic granites bimodal volcanism also occurred in the mount howitt province farther east but was followed by deposition of extensive fluviatile and lacustrine sediments mainly mudstone sandstone and minor conglomerate in the mansfield basin these contain minor sedimentary copper occurrences there are four distinct episodes of granite emplacement in victoria namely late cambrian early ordovician delamerian in the glenelg zone early silurian benambran in the highlands zone early devonian bindian in the grampians ararat bendigo highlands and mallacoota zones and middle devonian carboniferous post tabberabberan in the ararat bendigo melbourne howqua and highlands zones data for the delamerian granitoids are sketchy but in the remaining groups s type granitoids predominate with the exception of eastern victoria east of the yalmy fault i s line where only i and a type granitoids occur a variety of sn mo w deposits and prospects are associated with the benambran and younger intrusive phases victoria is a major gold province which has produced nearly 2 5 106 kg gold primary gold occurs in a number of geological settings including veins and disseminations spatially associated with mafic cambrian volcanism vein deposits in turbiditic sequences of central and eastern victoria veins associated with mafic and intermediate intrusives of mid to late devonian age and minor amounts associated with a variety of granitoids and porphyry dykes

relationships between deformation and basin evolution in the intracratonic amadeus basin central australia abstract tectonic subsidence curves based on the sedimentary record are used here to study basin evolution and to indicate deformational periods in the history of the intracratonic amadeus basin in central australia the basin developed during an initial period of extension at about 900 ma in the late proterozoic stage 1 was subjected to another period of extension at about proterozoic cambrian boundary time when there was also a shortening event on the southwest margin stage 2 and was shortened during the late devonian early carboniferous stage 3 stage 1 extension in the southwest and northwest corners of the basin was associated with rift basin sediments and volcanics previously regarded as basement to the amadeus succession in the metamorphic arunta complex on the northern margin of the basin a dolerite dyke swarm is considered to have been emplaced during this event extension in a n s direction associated with stage 2 occurred only in the northern part of the basin at the same time a major compressional event the petermann ranges orogeny was occurring along the southern margin in the north the sediment fill at this time firstly thickens rapidly towards the northern margin and then thins dramatically at the margin implying a half graben structure and the presence of a major bounding fault in the southwest the petermann ranges orogeny caused detachment of the sediments above the salt horizon in the bitter springs formation northward transport folding of the sediment pile and formation of major basement cored nappes during stage 3 a foreland basin associated with southward directed overthrust sheets of the alice springs orogeny formed in the northern part of the basin horizontal shortening was of the order of 50 100 km and hence the present basin margins are structural rather than depositional the structures that developed during this stage dominate the structural pattern of the basin

thermal and isostatic consequences of simple shear extension of the continental lithosphere abstract quantitative results are presented for a model involving large scale simple shear of continental lithosphere the locally compensated finite element model includes the effects of sedimentation radiogenic heat production in the crust and sediments and finite rates of extension flexural effects during firting are examined using a simple shear model with a uniform initial elastic thickness the locally compensated model predicts that a breakup unconformity develops on the upper plate when extension occurs at typical plate tectonic velocities subsidence occurs as the upper and lower lithospheric plates separate extension creates the potential for large accumulations of sediment 20 km most of which is syn rift if sedimentation keeps pace with subsidence the effect of flexure is to modify the shape of the detachment surface and the uplift patterns on the flanks of the upper and lower plate sedimentary basins a model which incorporates flexure predicts significant uplift of the lower plate as it is unloaded by the upper plate during extension the wernicke simple shear model can be distinguished from its opposite end member the mckenzie pure shear model by the predicted asymmetry in thermal evolution higher predicted heat flux within the upper plate uplift subsidence histories and stratigraphic development of the upper and lower plates

overthrust terranes in the lachlan fold belt southeastern australia the paleozoic history of the lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments four major terranes developed adjacent to the gondwana continental margin and were overthrust in the middle devonian to form a partly composite crust for southeastern australia