how to interpret understand and predict stratal geometries using stratal control spaces and stratal control space trajectories interpreting and predicting basin margin stratal geometries requires understanding of controls such as variations in supply and accommodation ideally based on independent quantitative evidence stratal control spaces are a new tool to analyze controls on strata a stratal control space is an area volume or perhaps a higher dimensional space defined by a range of values of the controlling processes subsidence sediment supply and eustasy a three dimensional stratal control volume with axes of subsidence sediment supply and eustatic rates of change can be populated with probabilities derived from analysis of time series of subsidence supply and eustasy these empirical or theoretical probabilities indicate the likelihood of occurrence of any particular combination of control rates defined by any point in the volume the stratal control volume can then be analyzed to determine which parts of the volume represent relative sea level fall and rise where in the volume particular stacking patterns will occur and how probable those stacking patterns are for outcrop and subsurface analysis using a stratal control area with eustasy and subsidence combined on a relative sea level axis allows similar analysis and may be preferable a stratal control trajectory is a history of supply and accommodation rates interpreted from outcrop or subsurface data or observed in analogue and numerical experiments and plotted as a series of linked points forming a trajectory through a stratal control space two theoretical and one actual outcrop example are presented to demonstrate how stratal control trajectories can be analyzed to determine which controls are dominant the accommodation supply trajectory range ratio astrr is a useful metric to characterize trajectory geometry trajectories with astrr 1 can be considered accommodation dominated and astrr 1 indicates a supply dominated trajectory calculating the range of stratal control probabilities along the trajectory indicates the probability of the rates of change of subsidence supply and eustasy required to form the interpreted stratal geometry both types of stratal control trajectory analyses can provide important additional understanding and prediction of how why and where stratal geometries form

chemical evolution of magmas in the proterozoic terrane of the st francois mountains southeastern missouri 1 field petrographic and major element data major element chemical data for plutonic and volcanic rocks of the eastern st francois mountains indicates that ring plutons of the butler hill caldera are low silica granites and chemically distinct from the high silica butler hill granite and grassy mountain ignimbrite additionally the ring plutons silvermine stono knoblick and slabtown granites are characterized by abundant mafic inclusions whereas these are almost completely absent in butler hill granite silvermine granite is mostly of a medium grained variety but cliffs along the st francis river expose gradations upward to a high silica fine grained cap rock least squares mixing calculations indicate that the cap rock could have formed by the fractional crystallization of plagioclase hornblende biotite magnetite and sphene all of which are liquidus phases in the medium grained silvermine granite the chemical similarity of the fine grained cap rock to butler hill granite and grassy mountain ignimbrite suggested that silvermine granite might be a sample of the parental magma from which the high silica rocks were derived least squares mixing calculations indicate that butler hill granite magma could have been derived from the composition of the average medium grained silvermine by fractional crystallization of the same liquidus phases indicated above the major element composition of grassy mountain ignimbrite can be derived from the average butler hill granite magma by fractional crystallization of plagioclase alkalic feldspar quartz biotite and magnetite all of which are liquidus phases in butler hill granite textural and chemical variations in butler hill granite from northeast to southwest suggest that the body was internally differentiated and that the present distribution of rock types is due to tilting and erosion the internal zonation of butler hill granite can be accounted for by fractional crystallization of plagioclase alkalic feldspar quartz biotite sphene and magnetite the chemical data and calculations indicate that the primary magma emplaced at the beginning of igneous activity was of silvermine type the magma crystallized fractionally so that the magma chamber became compositionally zoned with high silica magma in the upper part the top most part of this material was erupted to form grassy mountain ignimbrite during formation of the butler hill caldera subsequently more of the high silica magma was emplaced into the volcanic material in the caldera during resurgent doming after formation and resurgent doming of the butler hill caldera some of the parental magma from deeper in the chamber leaked upward into the ring fracture or into arcuate faults within the caldera forming the ring plutons the abundant mafic inclusions in the ring plutons may be earlier crystallized magma carried upward during intrusion one of the ring plutons silvermine granite apparently formed a sill like intrusion and underwent in situ differentiation a body of foliated granodiorite exposed as a giant inclusion in granite at hawn state park east of the principal exposures of the st francois mountains has the mineralogy major element chemistry and trace element chemistry to be a sample of the cumulate resulting from the processes in the magma chamber

mio pliocene to pleistocene paleotopographic evolution of brittany france from a sequence stratigraphic analysis relative influence of tectonics and climate the mio pliocene in western europe is a period of major climatic and tectonic change with important topographic consequences the aim of this paper is to reconstruct these topographic changes based on sedimentological analysis and sequence stratigraphy for the armorican massif western france and to discuss their significance the mio pliocene sands of the armorican massif red sands are mainly preserved in paleovalleys and are characterized by extensive fluvial sheetflood deposits with low preservation and by pass facies this sedimentological study shows that the red sands correspond to three main sedimentary environments fluvial alluvial fan low sinuosity rivers and braided rivers estuarine and some rare open marine deposits marine bioclastic sands faluns of french authors two orders of sequences have been correlated across brittany with one or two minor a s cycles comprised within the retrogradational trend of a major cycle the unconformity at the base of the lower cycle is more marked than the unconformity observed at the top which corresponds to a re incision of the paleovalley network a comparison of the results of the sequence stratigraphy analysis with eustatic variations and tectonic events during the mio pliocene allows 1 to discuss their influence on the evolution of the armorican massif and 2 to compare the stratigraphic record with other west european basins the unconformity observed at the base of the first minor cycle may be attributed to serravallian tortonian tectonic activity and or eustatic fall and the unconformity of the second minor cycle may be attributed to late tortonian early messinian tectonic activity the earlier unconformity is coeval with the development of a smooth paleovalley network compared to the jagged present day relief a single episode of mio pliocene deformation recorded in brittany may be dated as zanclean thus explaining the lack of the maximum flooding surface except in isolated areas from this study five paleogeographic maps were drawn up also indicating paleocurrent directions three maps for the lower cycle tortonian retrogradational trend late tortonian to early messinian maximum flooding surface and messinian progradational trend and two for the upper cycle pliocene retrogradational trend and piacenzian maximum flooding surface these maps show 1 the variations of paleocurrent directions during the mio pliocene 2 the extent of estuarine environments during the maximum flooding intervals and 3 a paleodrainage watershed oriented nnw sse following the regional quessoy nort sur erdre fault during the retrogradational trend of the upper cycle and possibly during the progradational trend of the lower cycle the present day morphology of the armorican massif is characterized by 1 incised

novel 3d sequence stratigraphic numerical model for syn rift basins analysing architectural responses to eustasy sedimentation and tectonics syn rift clastic sedimentary systems preserve a complicated stratigraphic architecture that records the interplay of tectonics eustatic sea level and storage and routing of sediments previous conceptual models describe and explain changes in depositional stacking patterns along a fault segment however stacking patterns and the nature of key stratigraphic surfaces is challenging to predict accurately with conventional sequence stratigraphic models that do not consider the three dimensional interplay of subsidence sedimentation and eustasy we present a novel geometric 3d sequence stratigraphic model syn strat which applies temporally and spatially variable fault scale tectonic constraints to stratigraphic forward modelling as well as allowing flexibility in the other controls in time and space syn strat generates a 3d graphical surface that represents accommodation although the model has the capacity to model footwall variation here we present model results from the hangingwall of a normal fault with temporal and spatial dip and strike predictions made of stacking patterns and systems tracts for a given set of controls sensitivity tests are tied to the depositional architecture of field based examples from the loreto basin gulf of california and alkyonides basin gulf of corinth here the relative influence of major sedimentary controls different subsidence histories varying sedimentation distribution including along strike variation in stacking patterns are assessed and demonstrate the potential of syn strat for reducing subsurface uncertainties by resolving multiple scenarios in addition the model demonstrates the nature of diachroneity of key stratigraphic surfaces that can arise in syn rift settings which could be represented by a bypass surface sequence boundary or reservoir seal maximum flooding surface in the rock record enabling a quantitative assessment of these surfaces is critical for prospect analysis in hangingwall half graben fills where these surfaces are heavily relied upon for well correlations that are used for hydrocarbon volume and production rate predictions

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

experimental measurement of the relative importance of controls on shoreline migration abstract shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors the most important of these are thought to be the stratigraphic trinity eustatic sea level subsidence and sediment supply in ancient rock sequences it is generally difficult to disentangle the effects of these variables here we analyze the relative influence of sea level subsidence sediment supply and other controlling variables on shoreline migration in an experimental basin equipped with a subsiding floor the experiment used a linear hinge type subsidence profile for which the rate was kept constant in time constant overall sediment supply and base level variation on two time scales that were first applied separately and then superimposed although base level was the only controlling variable that was externally varied in time the base level changes induced changes in other variables indirectly e g by changing the partitioning of sediment between the fluvial and offshore segments of the system we examine the relative importance of measured direct and indirect changes in all the governing variables through the use of a moving boundary equation for shoreline migration when measured values are used for all the variables in the equation shoreline migration rate throughout the run can be predicted with a maximum r2 of 0 92 starting with this optimal prediction of the observed shoreline behavior we successively replace variables in the equation with their run averaged values degrading the prediction the relative loss of prediction accuracy as each variable is replaced is a measure of the importance of that variable in accounting for the observed shoreline migration by this measure base level is the most important variable followed in turn by sediment supply to the foreset geometry of the foreset and the average subsidence rate over the foreset from the shoreline migration equation we also derive a quantitative version of the a s ratio often applied in sequence stratigraphy the new formulation reduces to a form comparable to the traditional descriptive a s ratio if changes in foreset slope gain or loss of sediment to the fluvial system and spatial variation in subsidence rate are all negligible

shoreline autoretreat substantiated in flume experiments abstract under conditions of constant sediment supply s to the basin and a steady rate of rise a in relative sea level the autoretreat theory predicts that shorelines can retreat landwards at a relatively early stage of delta growth and attain an autobreak state after which the existing subaqueous slope begins to be starved of sediment and thereby lose its clear delta front configuration a numerical model based on this theory further suggests that shoreline migration depends on the inclination of basin s basement slope and subaqueous depositional slope and to a lesser degree on the inclination of subaerial depositional slope two dimensional flume experiments in which a miniature delta is subject to steady forcing a const 0 s const 0 were conducted to test the expectations of the autoretreat theory the experiments consisted of two different series of runs one was of modulation associated with a narrow range of the ratio of water discharge to sediment discharge q s the other was of q s modulation with kept nearly constant the q s ratio was mostly responsible for changes in but also affected to some extent all experimental runs substantiated the landward turnaround feature of shoreline accretion i e autoretreat and the geometrical break of the delta front shape during its retreat phase i e autobreak the obtained shoreline trajectories hold their geometrical patterns even after they were nondimensionalized in terms of the s a ratio a key hypothesis confirmed in the experiments is that a and s can never balance each other both of the experimental series brought some systematic change of shoreline trajectories but the variations of shoreline trajectory due to modulation were much more striking than those related to q s even these contrasting results are consistent with the numerical predictions the present experimental results support the applicability of the autoretreat concept to natural environments and help clarify the processes governing the regression and transgression of a shoreline on a constructional margin

large scale architecture in non marine basins the response to the interplay between accommodation space and sediment supply sedimentary successions of non marine basins can be considered in terms of accommodation space and sedimentary supply changes changes in accommodation space controlling the large scale architecture of non marine basins are different in areas with high and low sedimentary supplies uplift of intrabasinal monoclines and anticlines reduced the available accommodation space resulting in changes in both the geometry of the depositional sequences and the large scale architecture of fluvial mudflat and shallow carbonate lacustrine deposits main drainage fluvial systems record areas with a high sedimentary supply while mudflats and shallow fluctuating lakes represent areas that received less sediment two end members in the large scale architecture of main drainage fluvial system in the almazan basin spain are i ribbon shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits mainly in the a2 depositional sequence and ii sheet like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats in the upper part of a3 ribbon shaped channel fills formed in areas of high accommodation space and sheet like channel fills formed in areas of reduced accommodation space

upper plate magma poor rifted margins stratigraphic architecture and structural evolution abstract although it is generally accepted that many distal magma poor rifted margins are asymmetric and can be divided into lower and upper plate margins little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished this is due to the fact that most papers focused on the so called lower plate margins while the upper plate margins remained less well understood mainly due to the lack of public accessible drill hole data the aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate magma poor rifted margin in order to provide such a template we focused on 2 seismic sections the ion 1000 line east indian margin and the screech 2 line newfoundland margin and describe key km scale outcrops from the fossil european margin exposed in the western central alps all of which document classical upper plate margins based on these data we show that upper plate magma poor rifted margins can be characterized by a staircase type architecture with terraces t 1 t 2 t 3 and ramps r 1 r 2 that result as a consequence of an evolution through a coupling exhumation and breakup stage we also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin from these observations we develop a conceptual model for the evolution of upper plate margins and discuss the applicability of this model for different strain rates rates of subsidence and sedimentation rates

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

a meta study of relationships between fluvial channel body stacking pattern and aggradation rate implications for sequence stratigraphy a quantitative comparison of 20 literature case studies of fluvial sedimentary successions tests common assumptions made in published models of alluvial architecture concerning 1 inverse proportionality between channel deposit density and floodplain aggradation rates and 2 resulting characteristics of channel body geometries and connectedness our results do not support the relationships predicted by established stratigraphy models the data suggest that channel body density geometry and stacking pattern are not reliable diagnostic indicators of rates of accommodation creation hence these architectural characteristics alone do not permit the definition of accommodation based systems tracts and settings and this calls into question current sequence stratigraphic practice in application to fluvial successions

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

neodymium isotopic constraints for the origin of mesoproterozoic felsic magmatism gawler craton south australia mesoproterozoic felsic magmatism of the gawler range volcanics and hiltaba suite granites occurred at 1585 1595 ma across much of the gawler craton south australia nd isotopic analysis of this felsic magmatism combined with petrological and geochemical arguments suggest derivation by partial melting of both paleoproterozoic and archean crust the majority of samples analyzed have nd isotopic and geochemical characteristics compatible with the involvement of paleoproterozoic crust stabilized during the 1 85 1 71 ga kimban orogeny as sources for the mesoproterozoic magmatism others require derivation from sources dominated by archean rocks this cycle of paleoproterozoic crustal stabilization followed by involvement of this crust mesoproterozoic felsic magmatism is one previously documented from many parts of mesoproterozoic laurentia on the basis of models proposing east australia antarctica to be the conjugate landmass at the rifted margin of western north america it appears that the voluminous mag

autogenic attainment of large scale alluvial grade with steady sea level fall an analog tank flume experiment a graded river conveys its sediment load without net deposition or erosion the graded state is thought to represent the long term response of alluvial rivers to steady external forcing we show here that alluvial rivers building deltas can be in grade as an autogenic response to steady sea level fall consider an antecedent graded river profile the upstream end of which consists of an alluvial bedrock transition and the downstream end of which is a fixed overfall where constant sea level is maintained the antecedent graded profile is then drowned by a jump in sea level after which sea level drops the result is a new river profile ending in a prograding delta that deposits on top of the antecedent profile if the rate of sea level fall is constant and the length of the antecedent reach is sufficient the new profile eventually becomes parallel or quasi parallel to the antecedent profile maintaining grade as it progrades in the experiments reported here series of graded river profiles with prograding deltas are created by stacking fluviodeltaic systems each graded profile and its associated delta is stacked on its immediate predecessor for each fluviodeltaic system a graded alluvial profile is attained with any constant rate of sea level fall provided that the antecedent profile is of sufficient length experiments suggest that this autogenic approach to grade is more rapid for higher rates of sea level fall lower rates of sediment supply and higher water discharges

evolution and architecture of a large felsic igneous province in western laurentia the 1 6 ga gawler range volcanics south australia the gawler range volcanics grv of south australia are an intracontinental subaerial large igneous province lip formed during supercontinent assembly in the mesoproterozoic like many lips the grv are intraplate were erupted over a geologically short time 2 million years and are dominated by voluminous lavas however the grv are overwhelmingly dominated by felsic units the grv are essentially undeformed and have not been deeply buried so that their original textures are exceptionally well preserved furthermore they are well exposed in very gently northward and eastward dipping sections up to 4 km thick allowing assessment of the facies architecture and evolution of this felsic volcanic lip the evolution of the grv can be clearly separated into two main stages initial eruptions at numerous volcanic centres produced small to moderate volume geochemically distinct felsic lavas and lava domes together with ignimbrites and minor mafic and intermediate lavas forming a sequence 0 5 to 3 km thick volcanic activity in this lower sequence varied from effusive to explosive and was not much different in style or products from phanerozoic felsic volcanic provinces however the second stage produced at least three voluminous felsic units each of which represents about 1000 3000 km3 of magma moreover the dominance of evenly porphyritic textures and lack of pyroclastic textures pumice shards broken crystal lithic clasts in these units suggests that they were erupted effusively and flowed as lavas each of these felsic lavas are generally dominated by a single uniform composition and commonly mingled with a subordinate and compositionally distinct lava

source to sink analysis of continental rift sedimentation triassic cuyo basin precordillera argentina abstract the northernmost outcrops of the triassic extensional cuyo basin in western argentina reveal a basal coarse conglomerate overlain by a thinning fining upward siliciclastic red bedded section with subordinated tuffs and microbial rich carbonates cerro puntudo formation unconformably covered by a second coarse conglomerate el relincho formation which were previously interpreted as two rifting events an integrated analysis of facies associations stacking patterns paleocurrent and provenance was carried out in order to reveal the rift sedimentation using a source to sink approach besides the traditional controls in continental basins e g sedimentation tectonics and climate this study considers possible drainage pattern evolution in order to differentiate isolated versus integrated depocenter stages u pb zircon data corroborate our analysis and reveal a volcanic basement source of 256 8 3 5 ma permian lopingian and a sedimentation age of 249 8 2 5 ma early triassic for a tuff interbedded within the cerro puntudo formation complementing previous age of 243 8 1 9 ma middle triassic at the top of this unit stratigraphic stacking allows the interpretation of three evolutionary stages a first stage represented by thick massive boulder volcanic rich conglomerates characterizing alluvial fan deposition indicates strong tectonic activity of border faults first rifting event these features suggest high surface gradient and high available space controlling accommodation and dispersal of gravity and debris flow deposits paleocurrents to the east reveal largely north south normal faults located to the west and sediment supply from a proximal volcanic source area a second stage represented by a notable fining thinning upward facies including fluvial and palustrine stromatolites with pedogenetic features deposits indicates a transition to tectonic quiescence these facies associations developed in a context of low sedimentation rate limited tectonic relief and low accommodation space a third stage is represented by greenish well rounded coarse grained polymictic conglomerates of el relincho formation that unconformably truncate the cerro puntudo formation these conglomerates are interpreted as perennial braided fluvial systems with paleocurrents to the northwest indicating drainage reorganization primarily influenced by climate change and combined tectonic reactivation previously considered the second rifting event climate change affected sediment delivery and allowed regionally connectivity and overfilling of the depocenters in this last stage northwest axial transport from variable sources within the precordillera to the southeast is inferred from provenance analysis indicating open linked depocenters this study suggests a new stratigraphic correlation for the northern part of the cuyo basin implying that during the first rifting event a semi arid climate prevailed with development of isolated and independent depocenters first and second stages whereas above the unconformity initiating the second rifting event third stage depocenters were interconnected in the light of our source to sink analysis such paleogeographic change allowed overfilling and laterally linkage of separate half grabens along the cuyo basin whereas tectonic reactivation may better explain renewed conglomerate deposition climate change toward more humid conditions allowed previously separated depocenters to be connected through axial drainages

zircon u pb dating in the vicinity of the olympic dam cu u au deposit roxby downs south australia isotopic data are presented for granitoids and felsic volcanics from the stuart shelf of south australia some of which are spatially associated with the olympic dam cu u au deposit relatively unaltered quartz monzodiorite more extensively altered quartz syenite and felsic volcanics yield zircon u pb ages of 1 590 super 5 sub 4 1 613 super 20 sub 19 and 1 576 super 22 sub 19 m y respectively the zircons from this group of rocks the olympic dam suite have similar morphologies and similar 206 pb 208 pb ratios suggesting an intimate genetic relationship their ages are comparable to the gawler range volcanics cropping out approximately 130 km to the southwest in the gawler orogenic domain close to the olympic dam deposit the zircon u pb system of olympic dam suite quartz syenite was contaminated by barite precipitated from hydrothermal fluids associated with the mineralization the barite is readily removed by air abrasion which restores the reversely discordant and spuriously young zircons to more normally discordant positions on the concordia diagram the abraded zircons then have u pb ages similar to uncontaminated olympic dam suite zircons the barite lead must be enriched in 206 pb which is concluded to be derived from radium extracted from u bearing rocks and admitted to the ba crystal lattice site deformed and altered basement granitoids on the stuart shelf have complex zircons with discrete cores and overgrowths which yield complicated u pb isotope systematics the cores are estimated to be about 1 800 m y old and the overgrowths probably less than 1 730 m y old these granitoids are temporally correlated with basement rocks of the gawler orogenic domain comparable apatite u pb and biotite rb sr isotope dates from all the granitoids and from thin veins in the acropolis prospect suggest regional cooling through the respective blocking temperatures about 350 degrees 400 degrees and 300 degrees c between 1 602 or 7 and about 1 542 m y the acropolis apatite date suggests at least some stuart shelf mineralization was emplaced at or before about 1 602 m y a maximum age for the olympic dam mineralization is set by the olympic dam suite quartz syenite zircon age 1 613 super 20 sub 19 m y our data do not place minimum age limits on the mineralization

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

yardea dacite large volume high temperature felsic volcanism from the middle proterozoic of south australia the yardea dacite is a large volume felsic volcanic unit from the middle proterozoic gawler range volcanics of south australia it has been previously described as an ignimbrite however some samples contain no petrographic evidence for a pyroclastic origin but have characteristics compatible with final crystallization from a nonfragmented magma these samples may have erupted as lavas but others are likely to be extremely densely welded ignimbrites suggesting a compound nature for the unit geothermometry and phase equilibria indicate that the yardea dacite originated from a high temperature 1000 c felsic magma with a low water content 2 the yardea dacite is not associated with a known caldera of the valles type and shares many characteristics of recently described cenozoic felsic volcanic rocks from the western united states interpreted as rheoignimbrites or as unusually extensive lavas

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

principles of regression and transgression the nature of the interplay between accommodation and sediment supply the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea level how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a 2 s and a super 1 5 s super 0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

detrital zircon ages improving interpretation via nd and hf isotopic data abstract the bulk of sedimentary provenance studies use similarities in the detrital zircon age patterns or barcodes in sedimentary systems and potential source regions to make interpretations about palaeogeographic settings while this age only approach is generally considered to be effective it is limiting because the timing of zircon growth events may not be unique to specific terrains and important rock forming events may be associated with little zircon growth to a significant extent these limitations can be overcome by employing additional isotopic data sets such as sm nd and lu hf that provide information on the crustal evolution of the source region and allow comparisons with sedimentary packages as an example the age spectra of detrital zircons in palaeoproterozoic metasedimentary rocks in the eastern gawler craton in southern australia are virtually identical to the dominant zircon growth timelines in adjacent older domains of the gawler craton presenting a prima facie case that it was the source region however whole rock nd isotopic data indicate that the pre existing proto gawler craton was isotopically too crustally evolved e nd 1850 ma 10 to have supplied the bulk of the sediment to the relatively more juvenile metasedimentary units e nd 1850 ma 1 to 5 in addition zircon hf isotopic compositions from ca 2000 ma detrital zircons in the metasedimentary rocks e hf 2000 ma 2 to 5 are significantly more juvenile than 2000 ma rocks in the adjacent gawler craton e hf 2000 ma 2 to 5 the combination of bulk rock nd and hf zircon data suggest that the gawler craton is not a viable source region for the metasedimentary packages despite the striking similarity between detrital zircon ages and zircon crystallisation events within the craton

volcanism of the palaeoproterozoic bushveld large igneous province the rooiberg group kaapvaal craton south africa abstract the volcanic rocks of the rooiberg group represent the uppermost unit in the palaeoproterozoic transvaal supergroup and form one of the largest provinces of silicic volcanic rocks in the world although stratigraphically associated with the transvaal basin fill the rooiberg group is petrogenetically linked with the larger bushveld magmatic event for which emplacement was preceded by the extrusion of the vast rooiberg lava flows in the northern part of the kaapvaal craton like many silicic dominated large igneous provinces lips which are increasingly recognised in the rock record the rooiberg group volcanics are intracontinental subaerial and are dominated by voluminous lava flows originally the rooiberg group is inferred to have covered an area of more than 200 000 km2 of which after erosion an area of 50 000 67 000 km2 remains the lava flows form a stratigraphic succession up to 6 km thick and are divided into four formations in ascending order dullstroom damwal kwaggasnek and schrikkloof due to a scarcity of reliable geochronological data the temporal span of the rooiberg group is poorly understood the rooiberg group consists of basaltic to rhyolitic lava erupted from fissural volcanism with estimated eruption temperatures of the rhyolitic lavas exceeding 1000 c minor explosive eruptions are represented by pyroclastic rocks and subordinate sedimentary interbeds originated from sandy fluvial and lacustrine processes the rocks are essentially undeformed and have not been buried so that their original textures are well preserved the bushveld complex and the associated rooiberg group lava flows are proposed to have formed as a result of partial melting of subcontinental lithosphere and lower crust by a mantle plume this thorough review of the geochronology physical volcanology and geochemistry of the rooiberg group enables construction of a geodynamic model

nd isotope and petrogenetic constraints for the origin of the mount angelay igneous complex implications for the origin of intrusions in the cloncurry district ne australia abstract the mesoproterozoic mount angelay igneous complex contained intrusions that were emplaced into amphibolite facies metasedimentary rocks during two periods of 1550 and post 1540 ma magmatism sm nd isotopic analysis together with mineralogical and chemical considerations suggest that the intrusions were produced from a paleoproterozoic crustal source with a t 2 model age 2200 ma on geochemical and petrological grounds the 1550 ma trondhjemitic intrusions are interpreted to have been produced by melting of amphibolite under garnet stable conditions 8 10 kbar the late syn to post peak metamorphic timing of these intrusions suggested that they were associated with the tectono thermal event that produced regional peak metamorphic mineral assemblages the post 1540 ma intrusions are k rich and consist of two groups of synchronously emplaced intrusions 1 a high k monzodiorite and monzogranite suite that range between 51 and 77 wt sio 2 and 2 a high k na enriched hornblende monzonite the chemistry and mineralogy of these intrusions suggested that they were derived via plagioclase stable and garnet unstable melting 2 o p 2 o 5 cr v and zn compared with slightly younger high k monzonite which is interpreted to have formed via one of two mechanisms 1 melting of a low k amphibole and plagioclase rich source or 2 melting of residual material that produces a potassic and incompatible element rich melt these magmas likely contained mantle derived material particularly the k rich intrusions of mafic composition the heat required for the production of post 1540 ma intrusions appears to have been generated by the intrusion of high t mantle derived mafic material into the crust 25 30 km 8 10 kbar this model is consistent with the synchronous emplacement of mafic and felsic magma and the lack of a consanguineous regional metamorphic association and suggests high t high degree partial melting in localised pockets within fertile source regions in the crust an increase in sm nd model source age and decrease in end with increasing sio 2 in the k rich intrusions suggests the incorporation of juvenile material in the more mafic rocks the origin of this component is unknown but it may represent either the incorporation of mantle derived material during melting or the partial melting of crust with a younger mafic component on a district scale the 30 million year period over which the k rich post 1540 ma intrusions were emplaced suggested that mantle derived material continued to be injected into the crust a mantle component to these rocks and the global distribution of proterozoic intrusions with similar geochemical affinities strongly suggests a world wide period of mantle induced crustal melting at that time the dominant paleoproterozoic isotopic composition of most of these intrusions suggests melting of similarly composed and matured source rocks

contributions to sequence stratigraphy from analogue and numerical experiments the sequence stratigraphic model although no longer focused on eustasy and accommodation has been until recently based largely on observation and interpretation of outcrop and subsurface data this approach may be restrictive if the current model places limits on what is observed and how observations are interpreted to make progress in our understanding of strata the sequence stratigraphic model and method should be tested against and fully incorporate theoretical and experimental results that provide new knowledge of 1 autogenesis 2 intrinsic stratigraphic responses 3 alluvial grade and 4 scales appropriate to single depositional systems evolving with relative sea level changes more extensive inclusion of analogue and numerical experimental results could lead to significant modification and refinement of existing sequence stratigraphic models

evolution of the rhone delta plain in the holocene abstract the delta plain of the rhone shows many sandy beach ridges cropping out at the surface we propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form morphologies of the lobes depend on four principal factors 1 the variation of the relative sea level which constitutes the morphogenic base level 2 the fluvial input volume of water discharge and sedimentary input number and position of the mouths 3 marine dynamics volume and direction of the longshore drift dominant wave direction 4 the accommodation space created by the rise of relative sea level along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea our conclusions are the main holocene paleo delta lobes of ulmet and saint ferreol were contemporaneous being deposited from 4000 to 2000 yr bp however the fluvial style of their downstream channel meandering for ulmet channel and linear for saint ferreol and the lobe morphologies of both channels are contrasted rounded in the case of ulmet and elongated for saint ferreol the role of the accommodation space is confirmed by two recent drillholes traversing the entire holocene succession which reveal a prior stage of sedimentary filling in the case of the saint ferreol lobe thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe the decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of rhone however the high rate of progradation of saint ferreol lobe after 2900 bp is probably a consequence of the increase of human activity after this date the variation of relative sea level remains an important factor controlling the evolution of the rhone delta after 6000 bp the local stabilization of the relative sea level between 4585 bp and 3520 bp played an important role in the triggering of coastal progradation saint ferreol lobe eastern margin rhone delta

mass balance effects in depositional systems abstract net deposition is necessarily accompanied by overall loss of sediment mass from the transport system on long time scales the deposition compensates for subsidence and creates the stratigraphic record although its spatial pattern changes and it can be locally stopped or reversed depositional mass loss is a fundamental driving influence on the morphology and behavior of depositional systems mass extraction to deposition leads directly to facies changes as sediment flux declines indirectly it usually leads to down channel sediment fining as deposition preferentially removes coarser particles laboratory experiments illustrate the effects of systematic mass extraction on fluvial channel stacking and deposit grain size and show how a mass balance framework allows consistent comparison of facies despite major shifts in depocenter location mass balance analysis of experimental fluvial and turbidite systems and a turbidite mini basin from the gulf of mexico show a change from channel dominated to lobe dominated deposits at about 80 total mass extraction experimental and field studies also show a close connection between rate of mass loss and rate of downstream grain size fining as predicted by a mechanistic theory based on mass balance these are first steps towards a framework for quantitative basin analysis based on mass extraction a mass balance framework allows for consistent quantitative comparison across basins of varying scale and shape mass balance frameworks can account for overall and or generic mass balance effects and help separate them from local effects one way to use such generalized models effectively is to view the results as reference cases of down transport change resulting from the basic interplay of spatial mass extraction pattern and sediment supply where such reference cases do not provide detailed predictions of specific field cases they can still provide a baseline to separate local case specific features from generic system behavior the approach is analogous to the way the geoid serves as a reference case against which to measure gravity anomalies

the upper jurassic lower cretaceous alluvial fan deposits of the kalaza formation central asia tectonic pulse or increased aridity the topographical evolution of tectonic systems as well as the sedimentation pattern and depositional environments in the associated basins are controlled by both tectonics and climate in the region of the tien shan central asia the jurassic lower cretaceous period was marked by complex low intensity tectonic deformation and major climate changes from humid to arid conditions jurassic to semi arid conditions cretaceous using the sediment record in the junggar tarim and fergana basins to describe the tectonic evolution of the tien shan area during the mesozoic thus requires differentiation between the tectonic and climatic influences on sedimentation the conglomerates of the upper jurassic lower cretaceous kalaza formation were commonly associated with renewed tectonic activity resulting from the docking of the lhasa block along the southern margin of asia from sedimentology and sequence stratigraphy analyses of several sections in the junggar tarim and fergana basins we reassess the main factors controlling the deposition of this formation we show that while some tectonic activity persisted throughout the jurassic cretaceous transition the switch from the sandy deposits of the upper jurassic qigu formation to the coarse deposits of the kalaza formation is largely linked to the development of an arid climate

braided rivers within an arid alluvial plain example from the lower triassic western german basin recognition criteria and expression of stratigraphic cycles based on a detailed sedimentological analysis of lower triassic continental deposits in the western germanic sag basin i e the eastern part of the present day paris basin the conglomerat basal gres vosgien and conglomerat principal formations three main depositional environments were identified i braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits ii marginal erg i e braided rivers aeolian dunes and aeolian sand sheets and iii playa lake an ephemeral lake environment with fluvial and aeolian sediments most of the time aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity such as wind worn pebbles ventifacts sand drift surfaces and aeolian sand sheets in such arid continental environments stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension elementary stratigraphic cycles i e the genetic units have been identified for the three main continental environments the fluvial type fluvial aeolian type and fluvial playa lake type at the time scale of tens to hundreds of thousands of years these high frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland lower triassic deposits from the germanic basin are preserved mostly in endoreic basins the central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the hercynian variscan appalachian mountains consequently a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments

modeling the growth limit of the changjiang delta river deltas grow in response to sediment discharge from the land it is not clear however whether or not there is a limit for such growth conceptual geometric models are used in this paper in association with the principle of mass conservation in an attempt to answer this question preliminary analyses of the changjiang delta indicate that delta growth is constrained by a number of factors the original topography bathymetry sediment supply sediment retention in the estuary sea level rise ground subsidence the quantity of sediment supply per unit area and the sediment retention index for the subaqueous delta decrease as the delta progrades towards deeper water resulting in a decreasing rate of growth the limit of growth is reached when the index approaches zero i e the shoreline reaches the shelf edge if the combined effect of sea level rise and ground subsidence is considered together with decrease in the sediment discharge from land the limit is reached at an earlier stage for the changjiang delta the model output using hypothesized sediment retention index estimates implies that the delta growth will reach its limit in the near future this will occur sooner if the sediment output of the river is reduced to 60 of its original level in response to the upstream basin changes further knowledge however is required of the retention index together with the information on future changes in river input and the character of the sediments in order to improve the accuracy of the simulations

hematite breccia hosted iron oxide copper gold deposits require magmatic fluid components exposed to atmospheric oxidation evidence from prominent hill gawler craton south australia

late paleo mesoproterozoic plate margin deformation in the southern gawler craton insights from structural and aeromagnetic analysis abstract the integration of structural analysis of outcrop and aeromagnetic interpretation has revealed a complex tectonic evolution for the southern gawler craton that reflects the regional tectonic signal during the late paleo to early mesoproterozoic results suggest that exposures at yarlbrinda hill comprise the margin of a highly deformed st peter suite pluton emplaced within the southwestern gawler craton at ca 1611 ma d 1 at outcrop records east to northeast directed ductile thrusting regionally this deformation overprints north south trending dextral yarlbrinda shear zone fabrics within ca 1622 ma st peter suite granite and ca 1690 1670 ma tunkillia suite granite progressive east to northeast directed thrust movements led to exhumation of the deformed ca 1611 ma granite d 2 deformation is recorded by the brittle reactivation of first generation mylonitic fabrics accompanied by cataclasis alteration and pseudotachylite development d 3 records a switch to northwest southeast shortening which led to the folding and tear faulting of the d 1 2 shear zone a switch to extension and subsequent rotations of the principle stress axes led to hiltaba suite granite emplacement and contemporaneous faulting under east west extension during d 4 and west northwest east southeast extension during d 5 deformation of ca 1622 ma st peter suite granite is consistent with movement on the yarlbrinda shear zone and requires the st peter suite to have been emplaced into or adjacent to the ca 1690 1670 ma tunkillia suite prior to shear zone activity and on the overriding plate during subduction d 1 d 3 deformation is constrained by the emplacement of ca 1580 ma hiltaba suite granite and correlates with the wartakan orogeny in the southeastern gawler craton and the olarian orogeny in the curnamona province a 52 disparity between the shortening directions in these respective areas suggests different degrees of mesoproterozoic rotation which likely aided the formation of an intervening basin province the remnants of which are presently preserved in the mount painter inlier the record of convergent deformation is geochronologically constrained to a 30 myr period and places this region of the central gawler craton near a late paleoproterozoic convergent plate margin prior to a period of transient extension beginning at ca 1580 ma the continental scale signal of tectonic events can be recognized at the outcrop scale highlighting the importance of detailed outcrop studies in sparsely exposed areas

petrogenesis of the proterozoic gawler range volcanics south australia the post orogenic bimodal gawler range volcano plutonic province developed in south australia between 1600 and 1500 ma ago vast felsic ash flow tuff units and intercalated volumetrically minor basalt flows comprise a thick comparatively undeformed volcanic pile that is intruded in many places by the extensive comagmatic hiltaba granite the geochemical and petrographic features of the felsic volcanic rocks point to an origin in high temperature dry partial melting of a comparatively refractory mafic intermediate granulitic sialic crustal source heat was probably supplied during a period of crustal rifting and underplating associated with an episode of mantle diapirism which also generated the primary basic magmas for the basaltic rock suite the primary felsic magmas differentiated along broadly calc alkaline trends to yield a variety of products many of which do not conform to a single line of liquid descent owing to appreciable incorporation of an accumulative crystal component in differentiated high k2o residual liquids the gawler range volcanics have comparable geochemical petrographic characteristics and field settings to several other proterozoic volcanic suites in australia thus implying a similar origin this analogy extends to the familiar proterozoic rapakivi granite suite of the northern hemisphere suggesting development in response to a unique globe encircling tectonic regime that was fundamentally different to that which has spawned modern calc alkaline volcanic arcs

age of the barramundi orogeny in northern australia by means of ion microprobe and conventional u pb zircon studies abstract u pb zircon geochronological studies are used to quantify the tectonostratigraphic history of a major crust forming event in early proterozoic terranes of northern australia magmatism and tectonic processes associated with this event the barramundi orogeny appear similar over very wide areas about one third of the australian continent the barramundi event marks the deformation metamorphism and cratonization of the earliest proterozoic 2 0 1 9 ga basinal successions and it was followed by and closely linked to extensive orogenic felsic magmatism the yaringa metamorphics are an inlier of paragneiss and schist that pre dates 1865 3 ma leichhardt felsic magmatism and younger basin formation in the mount isa inlier from an ion microprobe u pb zircon study of massive and migmatitic gneiss the time of yaringa metamorphism is established at 1890 8 ma recognized younger proterozoic deformations in the interval 1610 1550 ma are generally not evident in zircon u pb systems but have totally reset local rb sr whole rock values conventional u pb work on multi grain zircon samples of yaringa gneiss gives a geologically meaningless age 2090 40 ma that is an artifact of complex zircon growth part of which was initially inherited from a 2 55 to 2 2 ga provenance and the other major part of which was formed in situ during the 1890 ma high grade metamorphism predictably for simple zircon systems in low grade metavolcanic terranes conventional and ion microprobe zircon ages are in close agreement dating of volcaniclastic sequences above and below the barramundi tectonic break in the pine creek inlier brackets the orogeny in this terrane to a similar time frame 1885 1870 ma some zircons which crystallized at this time form selvedges around older cores whose age of 2100 2000 ma may be relics of an earlier deep crustal underplating the uniform chemistry of post barramundi felsic magmatism and the similar tectonic setting of the areally extensive barramundi event are mirrored by their temporal coherency cycles of geosynclinal deposition burial metamorphism and uplift took place during intervals of several million years or less implying comparable rates for early proterozoic orogenesis to those established for tertiary and quaternary settings

the functioning of sediment routing systems using a mass balance approach example from the eocene of the southern pyrenees abstractsediment routing systems link source regions undergoing erosion with depositional sinks and involve a volumetric or mass budget understanding how these source to sink systems function is key to stratigraphic prediction but estimation of their surface sediment discharges and depositional fluxes on geological time scales is a challenging problem we recognize a paleosediment routing system from the geological record in the mid late eocene escanilla formation and time equivalents of the tectonically active wedge top region of the southern pyrenees by mapping the 200 km long fairway of the escanilla sediment routing system we obtain the sediment budget and grain size fractionation of three time intervals each of 2 5 2 6 m yr duration over the time period 41 6 33 9 ma four thousand cubic kilometers of sediment sourced principally from two feeder systems in the high pyrenees was deposited in a period of 7 7 m yr the positions of moving boundaries characterized by rapid reduction in the perc

metamorphism in the olary block south australia compression with cooling in a proterozoic fold belt the sedimentary and igneous rocks comprising the lower proterozoic olary block south australia were deformed and meta morphosed during the mid proterozoic olar ian orogeny the area is divided into three zones on the basis of assemblages in metapelitic rocks higher grade conditions occurring in the south east mineral assemblages developed during peak metamorphism which accom panied recumbent folding include andalusite in zones i and i1 and sillimanite in zone 111 upright folding and overprinting of mineral assemblages occurred during further com pression the new mineral assemblages includ ing kyanite in zone i1 and kyanite and sillimanite in zone 111 the timing relationships of the aluminosilicate polymorphs together with the peak metamorphic and overprinting parageneses imply an anticlockwise p t path for the olarian orogeny pressure increasing with cooling from the metamorphic peak

shoal water deltas in high accommodation settings insights from the lacustrine valimi formation gulf of corinth greece the stratigraphic architecture of shoal water deltaic systems developed in low accommodation settings is relatively well known in contrast the features of shoal water deltas developed in high accommodation settings remain relatively poorly documented especially when compared with the available data sets for gilbert type deltaic systems developed in the same settings the lacustrine valimi formation gulf of corinth greece provides an opportunity to investigate the facies assemblage and architectural style of shoal water deltaic systems developed in high accommodation settings the studied interval accumulated during the pliocene and pleistocene and represents part of the early syn rift gulf of corinth succession six facies associations each described in terms of depositional processes and geometries have been identified and interpreted to represent a range of proximal to distal deltaic sub environments delta plain distributary channel mouth bar delta front prodelta and open lake the facies associations and their architectural elements reveal characteristics which are not common in traditionally described shoal water deltas of note different facies arrangements are observed in the distributary channels in different sectors of the delta passing from thick single storey channel fills embedded within delta plain fines in landward positions to thin amalgamated and multi storey channels closer to the river mouth this study proposes a new depositional model for shoal water deltas in high accommodation settings documenting for the first time that shoal water delta deposits can form a substantial part of stratigraphic successions that accumulate in these settings the proposed depositional model provides new criteria for the recognition and interpretation of these deposits the results of this study have applied significance for reservoir characterization

proterozoic anorogenic magmatism and its orogenic connections there is a major belt of proterozoic so called anorogenic igneous rocks that extends from the baltic shield through southern greenland and eastern canada to southern usa all rocks are situated within a zone of 1 9 1 6 ga arc accretionary orogens that consist of juvenile mantle derived material especially accretionary prism sediments that provided the fertile source for abundant granitic crustal melts there were two main periods of formation of the anorogenic rocks 1 76 1 55 ga rocks are mainly rapakivi granites and rhyolites that formed about 60 200 ma after the last compressional events in the svecofennian ketilidian and penokean orogens the time lag being caused by the slow thermal relaxation of thickened lower crust that had commonly been depleted by the extraction of earlier granitic crustal melts 1 45 1 4 ga anorogenic rocks are mainly rhyolites and peraluminous granites in central southern usa and anorthosites in eastern canada that formed in the continental margin of the grenvillian ocean the subduction of which led to the grenville orogen these anorogenic igneous rocks formed in extensional regimes during the formation and breakup of a 1 5 ga supercontinent

postglacial sea level rise and sedimentary response in the guadiana estuary portugal spain border abstract the study of sedimentological features foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted after 14 c dating the first assessment of the post glacial transgression in guadiana river estuary the holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year bp the holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr bp an accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer trochammina began ca 9800 year bp when sea level was about 39 m below present between 7500 and 7000 year bp the central part of the estuary started to accommodate coarser sediments partially introduced from the continental shelf the first phase of holocene sea level rise at a rate of 0 85 m century terminated ca 6500 year bp since then lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary after a second phase of slower rise at the rate of 0 3 m century which lasted until ca 5000 year bp the sea approached the present level

three dimensional accommodation analysis of the keuper of the paris basin discrimination between tectonics eustasy and sediment supply in the stratigraphic record abstract during the keuper the paris basin was an intracratonic sedimentary basin filled by continental deposits using paleo environmental isopach and paleo altitude maps we estimate the variations of accommodation rate at the scale of stratigraphic minor hemi cycle 1 3 ma an analysis of the short and long wavelength accommodation variations allows us to assess the relative influence of tectonics eustasy and sediment supply on the stratigraphic record our data suggest a pattern of subsidence along three trends e w in the carnian e w to nne ssw in the norian and ne sw in the norian rhaetian during the keuper the paris basin accurately records the different phases of the opening of the tethys ocean associated with a rotation of the extension direction the norian cycle could thus reflect the intraplate stresses in a transitional period between the triassic and the liassic

timing of iron oxide cu au u hydrothermal activity and nd isotope constraints on metal sources in the gawler craton south australia the eastern gawler craton hosts australia s premier uranium bearing iron oxide copper gold iocg belt the 500 km long olympic cu au u province in addition to the olympic dam cu u au and prominent hill cu au deposits numerous barren and weakly mineralized iocg prospects are present in the province new geochronological data for hydrothermal minerals combined with constraints from host rock ages demonstrate that alteration and associated iocg mineralization formed between 1570 and 1600 ma in three districts of the province this iocg hydrothermal activity temporally overlaps with magmatism of the hiltaba suite and gawler range volcanics titanites in paragenetically early magnetite bearing alteration in the olympic dam and prominent hill districts yield u pb ion probe ages of 1576 5 and 1567 10 ma respectively molybdenite in veins crosscutting magnetite biotite and albitic alteration in the moonta wallaroo district have re os ages of 1574 6 and 1599 6 ma respectively these represent minimum ages of the iocg alteration assemblages in this district a muscovite 40ar 39ar age of 1575 11 ma provides a minimum age of paragenetically later hematitic alteration in the olympic dam district neodymium isotope compositions were determined for 44 whole rock samples from barren and weakly mineralized cu au prospects and host rocks in the olympic dam and prominent hill districts the new geochronological framework enables comparison of the nd isotope data across two iocg districts at the time of formation of the olympic dam deposit ca 1590 ma magnetite rich weakly cu mineralized alteration from five prospects yields a relatively narrow range end 1590 values of 5 8 to 4 1 both hematite and magnetite rich alteration yield generally similar end 1590 values that match values from fresh and weakly altered paleoproterozoic metasedimentary and metagranitic rocks 6 6 to 3 5 as well as from most felsic hiltaba suite intrusions and gawler range volcanics in the eastern gawler craton ca 6 to 4 these data are consistent with crustal sources for ree and by implication for associated copper in the barren and weakly mineralized prospects mineralization and alteration in these minor iocg systems can be geochemically discriminated from the giant olympic dam deposit where greater inputs of mantle derived ree and other ore components are evident 2007 society of economic geologists inc

origin of rare earth element enriched hematite breccias at the olympic dam cu u au ag deposit roxby downs south australia hematite breccias the host rocks to cu u au ag ore at the olympic dam deposit occur as steeply dipping northwest striking dikelike bodies within fractured granite the breccia complex has a strike length of over 5 km and extends to depths greater than 1 km both the deposit as a whole and the individual breccia bodies are zoned from weakly brecciated sericitized and hematized granite on the margins through heterolithic breccias to hematite quartz microbreccia at the center hematite occurs as euhedral laths and fine grained aggregates in the matrices of all breccia types in veins and fragments as pseudomorphs after feldspar and rarely as pseudomorphs after siderite and magnetite relict magnetite is rare and most iron oxide was deposited as hematite heterolithic breccias include fragments of earlier breccia and veins minor sedimentary rocks including bedded hematite and laminated barite also are present as clast components in the upper portion of the deposit volcaniclastic conglomerate and siltstone occur in a fault bounded block approximately 500 x 500 m in plan view copper iron sulfides occur as interstitial grains most common microveinlets and rare clasts they are most abundant in heterolithic breccias and are zoned laterally from chalcocitebornitc to chalcopyrite pyrite zonal boundaries are subparallel to steep breccia contacts copper iron sulfides commonly are intergrown with fluorite and locally rim corroded quartz grains the breccias are highly enriched in light lree and heavy rare earth elements hree avg approximately 5 000 ppm ree in hematite rich rocks total lree content and la lu ratios are correlated with hematite abundance maximum la values 10 000 x chondrite occur in hematite quartz microbreccias from the geographic center of the deposit five hydrothermal ree phases have been identified bastnaesite florencite monazite xenotime and britholite they occur in all breccia types and in a variety of habits disseminated in quartz sericite matrices of granite breccia in quartz sericite veins interstitial to hematite laths intergrown with barite in laminated sedimentary rocks and as inclusions in hematite and in sulfide grains the hematite breccias formed by progressive hydrothermal brecciation and iron metasomatism of the granite host minor sedimentary components preserved as blocks and fragments within the upper portion of the deposit point to a near surface environment for the breccia complex textural relations indicate that most of the copper was introduced late relative to hematization and brecciation based on spatial relations between barren zones oxidized sulfide grains and high grade chalcocite ore some supergene redistribution of copper probably occurred the abundance of ree in hydrothermal phases ree enrichment of altered relative to unaltered wall rock concentration of ree in the center of the system and variable slopes of chondrite normalized patterns combined with the lack of evidence of intrusion of unusual magmas at the present level of exposure attest to extensive transport and deposition of ree by hydrothermal fluids responsible for hematization and breccia formation this study demonstrates hydrothermal ree mobility on a scale previously undocumented and suggests that ree may be particularly mobile in f rich hydrothermal systems

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

felsic metavolcanic rocks related to the broken hill pb zn ag orebody australia geology depositional age and timing of high grade metamorphism two key issues related to the origin of the massive broken hill pb zn ag orebody are the genesis of its host rocks and their depositional age these granulite facies layered gneisses have been ascribed alternately to volcanic and nonvolcanic regimes determination of the depositional age of the sequence has never been seriously addressed north of broken hill amphibolite facies precursors to the granulite facies gneisses show compelling evidence of a volcanic origin in their texture chemistry and zircon morphology these felsic metavolcanic rocks are in the upper part of the broken hill group stratigraphically equivalent to the broken hill orebody the present work traces textural zircon morphological and isotopic changes across the amphibolite to granulite facies transition in order to determine the primary depositional age of this supracrustal sequence and the timing of highgrade regional metamorphism ion microprobe shrimp u pb data on zircons from the lower grade amphibolite facies felsic metavolcanic rocks define a major magmatic population at 1690 or 5 ma this is considered to be the age of zircon crystallization and eruption of felsic volcanics in this part of the broken hill group these shrimp data clarify inheritance and discordance problems that had plagued conventional multigrain u pb analyses zircon results from granulite facies stratigraphic equivalents of these rocks near southern cross and at broken hill have patterns similar to those of the amphibolite facies rocks including igneous relics that provide the same primary age additionally zircon in the highest grade granulite facies rocks approximately 800 degrees c forms metamorphic overgrowths surrounding the magmatic relics these younger zircon selvedges have a pooled age of 1600 or 8 ma which determines the timing of this granulite facies event consistent u pb monazite results yield this same age 1599 or 9 ma suggesting that the monazite blocking temperature is close to that of zircon or that cooling to 725 degrees c was achieved relatively rapidly this is some 60 m y younger than the previously accepted age for high grade metamorphism at broken hill irrespective of metamorphic grade in the gneisses all biotite rb sr ages have been reset to approximately 480 ma a reflection of early paleozoic delamerian orogenesis inherited zircon grains interpreted as xenocrysts and in some cases mantied by 1690 ma igneous rims have older proterozoic to late archcan ages 1780 2700 ma the presence of xenocrystic zircon components points to an ensialic tectonic setting for the broken hill block and reflects accidental incorporation in the felsic volcanic protoliths of lithic fragments and or complex igneous sources such as found in crust exposed in the gawler craton to the west the 1690 or 5 ma depositional age determined here provides a firm chronologic tie between the early proterozoic sequences enclosing major stratiform pb zn ag orebodies at broken hill mount isa 1670 or 19 ma and mcarthur river 1690 or 27 ma in northern australia in light of the uncertainties over timing and mode of origin of these deposits the similar ages of their host sequences have important implications for early proterozoic tectonics and metallogeny

the accommodation concept in sequence stratigraphy some dimensional problems and possible redefinition abstract a debate is provoked here as to what is meant exactly by the term accommodation and how well this concept as it presently stands serves the conceptual and quantitative framework of sequence stratigraphy accommodation in terms of its original definition contains some conceptual flaws it represents a space that has three dimensional extent associated with a certain availability of sediment and thus is not really independent of sedimentation however this space is fairly unspecifiable because of the inherent difficulty of distinguishing real accommodation from the space which is very unlikely to be filled by sediment anti accommodation the accommodation concept cannot be extended to subaerial environments because the equilibrium profile of streams which is sometimes used for this purpose is difficult to recognize even if it existed a possible redefinition of accommodation is suggested as the thickness measured at a specified site and time of a space which becomes filled with sediments during a specified time interval this accommodation is not a space but the thickness of a space not something potential but an objective result not specifiable from the graded profile or geomorphic base level but from stratigraphic base level and not separated from sedimentation but partly dependent from it potential accommodation may be used to describe the maximum of possible accommodation at a specified site and time which can substantially coincide with the height of a water column at a given site and time

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

accessory minerals and the geochemical evolution of crustal magmatic systems a summary and prospectus of experimental approaches it has recently been recognized that accessory minerals in continental rocks may contain a substantial fraction of the whole rock complement of trace elements and geochemically important isotopes this observation is in itself interesting but its importance is magnified many fold when one considers the possible consequences to the geochemical rearrangement that accompanies crustal melting if for example an accessory phase is insoluble in early formed partial melts it may effectively retain in the residue many incompatible elements e g ree and daughter isotopes e g radiogenic pb that would otherwise be partitioned into the melt in addition should an unmelted accessory mineral e g zircon be entrained in a departing melt fraction it may carry with it radiogenic components pb nd143 hf176 characteristic of the source region the effectiveness of phases such as zircon apatite sphene allanite epidote and monazite in the roles noted above can only be gauged from knowledge of the three fundamental accessory phase parameters i e 1 the solubilities of the accessory minerals in crustal melts 2 the equilibrium mineral liquid partition coefficients for the trace element and isotopes of interest and 3 the diffusivities that govern the rates at which equilibrium will be approached in general these parameters can only be measured in laboratory experiments and relatively few data have been accumulated to date it does seem clear however that apatite generally is residual insoluble during crustal melting and zircon can be depending on melting conditions and abundance of zircon in the source petrographic and geochemical studies indicate that monazite allanite and epidote may also be highly insoluble in some cases but the specific circumstances that promote insolubility remain unknown the few experimentally determined partition coefficients now available for apatite and zircon agree qualitatively with natural rock data on mineral separates however preliminary diffusion measurements and inferences from natural systems suggest that trace element and isotopic equilibrium between undissolved accessories and crustal melts is in fact rarely approached ironically it is this very disequilibrium in the form of preserved diffusion profiles that may afford the most information on time temperature histories of melting events continued experimental interest in the fundamental accessory phase parameters will eventually provide the tools that will enable rigorous assessment not only of the timing and duration of crustal melting episodes but also of the extent of melting and re distribution of trace elements and radiogenic isotopes

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

large scale fluvial grade as a nonequilibrium state in linked depositional systems theory and experiment 1 a graded river conveys its sediment load without net aggradation or degradation grade is thought to represent the equilibrium state of a river system subject to steady allogenic forcing we address the concept of grade in linked depositional systems through a combination of mathematical modeling and flume experiments we develop a moving boundary morphodynamic model of fluviodeltaic sedimentation and use it to quantify the conditions necessary for a state of sustained grade in an alluvial deltaic system developing on a uniformly sloping shelf to test our theory we conducted a series of flume experiments in which we constructed laboratory scale fluviodeltaic systems under specific relative sea level histories on large spatiotemporal scales our theoretical and experimental results suggest an alternative view of grade as an intrinsically nonequilibrium state that requires a fall in relative sea level under conditions of stillstand or rise in relative sea level the equilibrium graded profile does not exist and the alluvial river will always aggrade with a steady sediment supply alluvial grade can be sustained if relative sea level falls with a specific square root of time dependence common sequence stratigraphic conceptualizations of alluvial river response to sea level change suggest that rivers aggrade and degrade in response to relative sea level rise and fall respectively we show that rivers can remain aggradational if the rate of sea level fall is sufficiently small the boundary between aggradational and degradational states is the graded state described here that associated with a relative sea level fall that varies with the square root of time

mass balance constraints on stratigraphic interpretation of linked alluvial coastal shelfal deposits from source to sink example from cretaceous western interior basin utah and colorado u s a abstract experimental work suggests that the rate of upstream to downstream loss of sediment from an active depositional system to permanent storage exerts a fundamental control on stratigraphic architecture this rate of sediment mass loss is determined by the spatial distribution of tectonic subsidence and rate of sediment supply the character of input sediment grain size distribution and composition is the third parameter that affects stratigraphic architecture we apply this concept in a mass balance framework to linked alluvial coastal shelfal deposits of the upper cretaceous castlegate sandstone blackhawk formation star point sandstone and mancos shale western interior basin utah and colorado usa facies partitioning and sediment budgets are estimated for eight stratigraphic intervals in order to compare temporal dynamics of the sediment routing system from erosional source to depositional sink mapping of each stratigraphic interval and its constituent segments from upsystem to downsystem was achieved along a representative dip oriented 2d cross section over a distance of c 350 km using extensive outcrop exposure and densely spaced subsurface wells the cross section provides time averaged estimates of the spatial distribution of deposition grain size data show that there is limited downsystem fining of any particular facies within the castlegate sandstone but that the proportion of facies changes systematically downsystem to accommodate an overall fining trend therefore it is reasonable as a first approximation to use facies proportions as a textural replacement for grain size sediment supply characteristics for each of the eight stratigraphic intervals are constrained by total facies proportions in each interval for each stratigraphic interval we assess the level of interaction between alluvial and coastal to shelfal segments of the routing system comparison of the downsystem mass balance characteristics of the eight stratigraphic intervals suggests that there were depositional gains and losses of shallow marine shale in the five youngest intervals which can be attributed to along strike sediment transport this result is consistent with increased interaction through time with vigorous wave and tide driven circulation in the seaway as the sediment routing system advanced out of a sheltered embayment in response to decreasing tectonic subsidence in the youngest stratigraphic interval the upstream unconformable base of the castlegate sandstone is marked by a pronounced increase in the sand to gravel grade mass fraction of the fluvially supplied depositional volume this marked increase can be attributed to hinterland unroofing and or cannibalization of wedge top basins leading to import of coarse grained sediment into the castlegate fluvial system our results demonstrate the value of analyzing downsystem sediment loss i e downsystem mass extraction within a mass balance framework as a simple and practical tool to quantify the relationship between accommodation and sediment supply and thus to decode past external forcing mechanisms from stratigraphic architecture

lower triassic sequence stratigraphy of the western part of the germanic basin west of black forest fluvial system evolution through time and space abstract the aim of this paper is to analyse the fluvial evolution of the lower triassic in the western part of the germanic basin through time and space as well as the impact of the geodynamic and climatic setting on the preservation of fluvial deposits the lower triassic crops out only in the vosges massif and the black forest so well log studies are required to realise sequence stratigraphy correlations and establish comparisons with others parts of the germanic basin in a first step we use well log data analyses to characterise the electrofacies associations in the triassic and then define the well log signatures of each formation in a second step the characterisation and recognition of genetic sequences and their stacking pattern allow us to define seven minor cycles integrated into two major cycles finally the quantification of the lithologies at different stages of basin evolution leads to the reconstruction of paleoenvironmental maps to illustrate facies evolution through space and time a comparison with cycles defined in the germanic basin allows us to propose correlations of the lower triassic on either side of the rhine graben and leads to a discussion of the evolution of fluvial systems through time and space during the scythian the fluvial style is characterised by braided fluvial systems evolving laterally into lake deposits towards the central part of the germanic basin during this stage the basin was a huge depression with very few marine connections in its extreme eastern part the stratigraphic cycles represent rhythmic fluctuations in relative lake level that could be attributed to sediment supply and or lake level variations in an arid setting four minor stratigraphic cycles are observed that are integrated within a single major stratigraphic cycle during the period of the stratigraphic base level rise of the major cycle a maximum of 233 m of sediment would represent a duration of sedimentation in the paris basin of at least 1 8 m y during the period of the stratigraphic base level fall of the major cycle a maximum of 65 m of sediment would have accumulated over 2 5 m y on the western edge of the germanic basin the top of the scythian is marked by a major sedimentary break characterised by a planation surface with preservation of the first paleosols followed by the hardegsen unconformity this unconformity is tectonically deformed leading to the development of a new sedimentation area in the west of the basin the fluvial sedimentation above this discontinuity shows a trend towards enhanced development of floodplain or lacustrine type environments at its western margin with the formation of paleosols the fluvial systems are linked with sabkhas and then with a shallow sea connected to the tethys ocean in this context the stratigraphic cycles are caused by variations in relative sea level and or sediment supply the fluvial deposits are preserved in an exoreic basin

refined proterozoic evolution of the gawler craton south australia through u pb zircon geochronology abstract through the application of both conventional u pb zircon analyses and small sample u pb isotopic analyses the nature and timing of tectonic events leading to the formation of the gawler craton have been defined more precisely constraints on deposition of early proterozoic iron formation bearing sediments have been narrowed down to the period 1960 1847 ma deformed acid volcanics including the economically important moonta porphyry have zircon ages of 1790 and 1740 ma the voluminous acid gawler range volcanics and correlatives to the east were erupted over a short interval at 1592 2 ma and were intruded by anorogenic granites at 1575 ma small sample zircon analyses proved to be an extremely valuable adjunct to conventional analyses generally yielding more concordant data which forced a curved discordia through an upper intercept slightly younger than from a conventional straight line discordia

u pb geochronology of middle proterozoic felsic magmatism surrounding the olympic dam cu u au ag and moonta cu au ag deposits south australia

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

lithology and hydrothermal alteration control the distribution of copper grade in the prominent hill iron oxide copper gold deposit gawler craton south australia the prominent hill iron oxide copper gold iocg deposit located in the gawler craton of south australia contains ca 278 million metric tons mt of ore at 0 98 cu 0 75 g t au and 2 5 g t ag in contrast to the predominantly granite hosted olympic dam iocg deposit prominent hill is mainly within unmetamorphosed sedimentary rocks comprising coarse clastic to laminated argillaceous lithologies with some volcaniclastic components and variable carbonate including local massive dolomite essentially unmetamorphosed sedimentary rocks and structurally underlying mafic to intermediate composition lavas inferred to be members of the lower gawler range volcanics host the economically mineralized hematite breccias the volcanic sedimentary package was downfaulted and tilted along a major east west fault north of which similar but regionally low grade metamorphosed rocks were affected by subeconomic skarn mineralization and on a more regional scale of the mount woods domain intruded by granitic and gabbroic bodies hydrothermal alteration and mineralization at prominent hill involved pervasive and texturally destructive replacement of formerly calcareous dolomitic and siliciclastic breccia components hydrothermal alteration minerals comprise hematite magnetite siderite ankerite quartz sericite chlorite kaolinite fluorapatite fluorite barite ree u minerals including monazite uraninite and coffinite together with cu sulfides including chalcopyrite bornite and chalcocite in the highest grade ore brecciation and replacement caused mechanical mixing as well as chemical alteration of primary lithologies such that sedimentary contacts became obscured mass balance calculations identify al ti si and zr as least mobile components during hematite chlorite sericite to weak hematite quartz alteration because zr was not regularly assayed in drill cores we use concentration ratios of ti al and si from the deposit scale assay database to delineate the distribution of lithochemical units prior to hydrothermal alteration and cu mineralization the resulting lithochemical model based on one horizontal and five vertical cross sections is used as a basis for mapping alteration patterns calculated from molar fe si fe si al k na and k al ratios these chemical patterns in conjunction with mineral stoichiometry indicate that the spatial distribution of hematite chlorite variably phengitic sericite and or illite kaolinite quartz bearing alteration is superimposed on the pattern of interpreted lithologic contacts the alteration patterns confirm visual logging results showing that hematite enrichment correlates only partially with the distribution of cu grades of 0 25 wt a subvertical body of complete replacement by hematite and quartz with consistent but subeconomic gold enrichment forms a cu barren core in the central and eastern parts of the deposit zones of increasing k al and k na ratios extend upward and westward from this cu barren core transgressively overprinting lithologic contacts the degree of hematite quartz replacement can be measured by a hematite quartz alteration index here termed the hmsi value fe si fe si al which inversely correlates with the normal probability for cu grade areas of highest cu grade 1 wt spatially correlate with irregular zones having intermediate molar alteration indices 0 34 k al 0 40 20 k na 36 and hmsi 0 98 hematite breccias and cu ore deposition developed after tilting of the host sequence into its present steep orientation as indicated by geopetal structures within the breccia matrix thus the economic mineralization occurred late in the deformational history of the region and after extrusion of the lower gawler range volcanics the formation of the prominent hill orebodies occurred during or after upthrusting of deeper seated rocks containing subeconomic cu in skarns north of the fault faulting as well as ore formation may be related to orogenic processes in the central and northern part of the mount woods domain iron oxide introduction was decoupled from and at least partly preceded hydrothermal deposition of high grade cu geochemical and petrographic data indicate that economic cu mineralization occurred together with mildly acidic hematite chlorite sericite siderite alteration of originally carbonate illite and feldspar bearing sedimentary rocks the presence of copper enrichment with an intermediate degree of cation leaching from the host rocks indicates that ph neutralization of initially highly acidic metal transporting fluids was an essential factor causing cu sulfide deposition distinct ranges in na k al ratios and low hmsi values offer potential as exploration indicators pointing toward higher ore grades these results from prominent hill are consistent with recently published mineralogical studies at the giant olympic dam deposit indicating similar ore depositional controls despite lithologically different host rocks

early deep magnetite fluorapatite mineralization at the olympic dam cu u au ag deposit south australia the olympic dam iron oxide copper gold iocg uranium silver deposit south australia is hosted in the large olympic dam breccia complex within the 1 59 ga roxby downs granite this breccia complex formed through multiple stages of hydrothermal activity and texturally destructive brecciation that affected the granite the deepest diamond drill hole to date rd2773 end at 2 329 m intersected weakly altered in situbrecciated granite 370 2 329 m and a quartz phyric felsic unit 2 010 2 265 m these two rock units host coarse grained hydrothermal minerals from 2 150 m to the end of the drill hole the main minerals in this assemblage are magnetite hematite pyrite fluorapatite and quartz with minor disseminated chalcopyrite sericite chlorite rare earth element ree fluorcarbonates monazite uraninite thorite galena sphalerite anhydrite schorl rutile and pyrrhotite the assemblage is cut by abundant multiphase veinlets and calcite fluorite barite veins a zircon u pb age for the felsic unit 1591 11 ma implies that this unit is broadly coeval with the granite whereas u pb ages for hydrothermal uraninite 1593 5 5 1 ma fluorapatite 1583 3 6 5 ma and hematite 1592 15 ma indicate that deposition of the u ree rich hydrothermal magnetite fluorapatite pyrite quartz assemblage and replacement of magnetite by hematite occurred soon after emplacement of the granitic host rocks sm nd dating of ubiquitous calcite veins suggests formation at 1 54 ga the deep 1 59 ga magnetite fluorapatite pyrite quartz assemblage at olympic dam resembles those characteristic of iron oxide apatite deposits and many other sensu stricto iocg deposits this study confirms that the 1 59 ga event involved significant and widespread iocg mineralization in the olympic cu au province

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

the olympic dam copper uranium gold deposit roxby downs south australia a new type of stratabound sediment hosted ore deposit the deposit is estimated to contain in excess of 2 000 million metric tons of mineralized material with an average grade of 1 6 percent copper 0 06 percent uranium oxide and 0 6 g metric ton gold proterozoic graben fill sediments were deposited in an arid subaerial environment during rifting or strike slip faulting the stratabound sulfide mineralization is syngenetic or syndiagenetic and is probably related to local volcanism uranium and rare earths were deposited during and after the sulfide mineralizing phase unusual features are the association of copper uranium rare earths and gold the association of reduced sulfur species such as chalcocite and bornite with high hematite concentrations and the occurrence of stratabound copper and uranium minerals in sedimentary rocks deposited in a very high energy environment modified journal abstract

petrology geochemistry and origin of a major australian 1880 1840 ma felsic volcano plutonic suite a model for intracontinental felsic magma generation in australia a major period of felsic volcanism and granite emplacement occurred between 1880 and 1840 ma towards the end of the early proterozoic these volcanics and granites covering at least 37 000 km2 are compositionally uniform over large areas the felsic magmas are predominantly i type being derived from infracrustal sources which have never been exposed to surficial weathering processes when compared with early archaean and phanerozoic i type granites the 1880 1840 ma suite has distinctively high levels of k2o rb zr la ce th u and low mgo and cao contents even at relatively low sio2 levels of 60 65 the 1880 1840 ma rocks are characterized by low initial 87sr 86sr ratios and negative nd values chemical and isotopic modelling on these volcanics and granites suggest that they formed from mantle derived sources that are around 2300 2000 ma old there is no evidence of a major archaean component in these granites the sources are interpreted to have formed as a result of polygonal small scale mantle convection which led to extensive underplating of archaean crust during this underplating event large volumes of incompatible element enriched mantle derived material accreted to the base of the lower crust and fractionated significantly the more fractionated part of this source was remelted between 1880 1840 ma to produce the voluminous felsic volcanics and comagmatic granites present in nearly every proterozoic domain of australia the actual underplating event between 2300 2000 ma is believed to have triggered the formation of early proterozoic sedimentary basins which occur in a polygonal pattern and appear to wrap around archaean nuclei the composition of these felsic melts and the tectonic setting operating during their emplacement precludes genesis by contemporaneous subduction of oceanic crust all are generated by processes of vertical accretion in an intracontinental environment

insights into magma histories through silicate oxide crystal clusters linking the hiltaba suite intrusive rocks to the gawler range volcanics gawler craton south australia the roxby downs granite rdg host to the supergiant olympic dam deposit and the gawler range volcanics grv in south australia both contain clusters of touching silicate and oxide minerals here we report on the geochemistry and petrography of these rocks and their contained mineral clusters before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the rdg and other members of the hiltaba suite and the grv crystal clusters in the rdg comprise magnetite apatite titanite biotite zircon which are typically enveloped in a plagioclase crystal matrix in the grv crystal clusters comprise pyroxene titanomagnetite plagioclase apatite zircon display variably glomeroporphyritic equigranular poikilitic and loosely packed habits and are enclosed by texturally varied groundmass of the grv lavas studied pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts this suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir there are no compositional contrasts between phenocrysts and crystals in grv clusters and mg of pyroxenes are consistent with those predicted from whole rock compositions implying that all analysed crystals including those in clusters were formed within or were at least equilibrated to the host lavas precursors rather than entire histories as isolated crystal clusters entrained by melt flow intergrowth textures and mafic magmatic enclaves suggest that the majority of grv crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption consistent fe ti oxide apatite zircon plagioclase assemblages and textures in both the grv and rdg suggest a shared genetic scenario although an extended model is needed to account for the transformation of grv type to hs type crystal clusters for hot and dry magmas such as those that formed the grv and rdg cooling causes pyroxene fe ti oxide plagioclase in grv type crystal clusters to react with each other and the melt forming hs type magnetite titanite biotite feldspar crystal clusters rejuvenation events implicated in the liberation of grv type crystal clusters may be important drivers of magmatic hydrothermal iron oxide deposit formation

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

petrogenesis of a mesoproterozoic quartz latite granitoid suite from the roxby downs area south australia abstract mesoproterozoic granitoids from the roxby downs area south australia show a range in composition from mafic quartz monzodiorites 56 sio 2 to felsic granites 71 sio 2 and are interpreted as consanguineous on the basis of similar age isotopic composition and mineralogical and geochemical characteristics these granitoids have geochemical similarities with other mesoproterozoic granitoids the world over including enrichments in k 2 o rb ba th u rare earth elements ree nb y zr and depletions in mgo cao sr cr ni v sc relative to typical phanerozoic calc alkaline granitoids the mafic granitoids have mineralogical textural and geochemical features consistent with an origin as cumulates from a more felsic primary magma and the felsic granites likely represent the fractionated residual melt to this accumulation process none of the granitoids from the batholith preserve the primary magma composition which is deduced to be similar to abundant quartz latite volcanic rocks of the region it is estimated by geochemical modeling that about 27 fractionation of observed phenocrysts from a primary quartz latite is required to produce a typical felsic granite 71 sio 2 production of the primary quartz latite magma was likely the result of partial melting of existing paleoproterozoic crust in response to intrusion into the crust of mantle derived magmas the combination of widespread crustal melting contemporaneous granulite facies metamorphism and mantle derived magmatism suggests involvement of large scale tectonothermal processes in the origin of these granitoids the petrogenesis of these rocks and similar occurrences in laurentia and baltica indicates that processes involving reworking of existing paleoproterozoic crust were similar throughout many continental areas during the mesoproterozoic

estimation of the paleoflux of terrestrial derived solids across ancient basin margins using the stratigraphic record a simple inversion scheme for estimating sediment flux from ancient shelf margin successions is presented here by treating shelf margin clinothems as the product of deposition associated with migration of a shelf edge clinoform with constant shape at a rate equal to the shelf margin progradation rate assuming sediment conservation deposition can be broken into components of 1 response to subsidence and sea level changes and 2 basinward migration of the clinoform profile sediment flux can therefore be estimated with knowledge of progradation rate subsidence sea level change rate and clinoform dimensions an advantage of this methodology is that it requires only two dimensional data i e dip oriented cross sections rather than three dimensional volumes making it ideal for use with sparse data sets as well as with outcrops this methodology is also useful for analyzing areally limited data sets because it can predict the flux of sediment transported beyond the area of data coverage the approach is able to accurately reproduce the sediment flux estimates of previous workers from several margins the fox hills lewis zambezi new jersey and north slope margins using both volumetric and forward modeling methods not only are the predicted distributions for sediment flux across ancient shelf margins similar to distributions predicted by more data intensive theoretical models the estimated magnitudes for paleofluxes favorably compare with measured loads from modern rivers growth of continents is achieved in part by accretion of sediment on shelf margins the rates and patterns of continental expansion are therefore partially dependent on the magnitude and distribution of mass transfer from eroding hinterlands to continental margins fluxes which also play a critical role in global biogeochemical cycles flux estimates cast into a mass balance framework suggest that approximately two thirds of continental margin sediments are exported past the shelf edge into deeper water at long term geologic time scales this finding implies that two thirds of the terrestrial derived particulate organic carbon poc delivered from rivers to the ocean can be stored in deep water over geologic time scales the observations presented here indicate that repetitive delivery of sediment to margins by shelf edge deltas is fundamental to the long term process of margin accretion

nd isotopic evidence from wopmay orogen for 2 0 2 4 ga crust in western north america abstract nd isotopic data from the 1 9 ga wopmay orogen n w t canada strongly suggest the involvement of crust in the range of 2 0 2 4 ga remnants of three compositionally diverse magmatic arcs 1940 1902 ma 1890 1880 ma and 1875 1840 ma are preserved in wopmay orogen each of the three arcs originated west of the limit of exposed archean crust nineteen samples of plutonic and volcanic rocks from the three arcs yield a narrow range of initial e nd from 1 8 to 0 3 there is no apparent correlation between e nd and geographic distribution nor with whole rock chemistry sio 2 54 75 two basalt samples from west of the archean have initial e nd s between 2 and 3 two 1 87 ga granites which intrude through archean crust have much lower initial e nd s of 5 9 and 8 6 the data from the three magmatic arcs are best interpreted in terms of a source region which had a very limited range of e nd at 1 9 ga which we interpret as 2 0 2 4 ga crust presumably hottah terrane basement wopmay fault zone is therefore the surface manifestation of a suture between 2 0 2 4 ga hottah terrane and the archean slave craton there is a growing body of data which suggests that much of western north america may be underlain by 2 0 2 4 ga crust geochronologic and isotopic data from other precambrian cratons also suggest that 2 0 2 4 ga crust may be much more widespread than previously thought models of crustal growth which interpret 1 9 1 7 ga crust as mixtures of archean crust and proterozoic depleted mantle may be overestimating the amount of juvenile material added to the crust in this time period

allogenic controls on the fluvial architecture and fossil preservation of the upper triassic ischigualasto formation nw argentina abstract the upper triassic ischigualasto formation in nw argentina was deposited in a fluvial system during the synrift filling of the extensional ischigualasto villa union basin the expansive exposures of the fluvial architecture and paleosols provide a framework to reconstruct the paleoenvironmental evolution of this basin during the upper triassic using continental sequence stratigraphy the ischigualasto formation deposition can be divided into seven sequential sedimentary stages the 1 bypass stage 2 confined low accommodation stage 3 confined high accommodation stage 4 unstable accommodation stage 5 unconfined high accommodation stage 6 unconfined low accommodation stage and finally 7 unconfined high accommodation stage the sedimentary evolution of the ischigualasto formation was driven by different allogenic controls such as rises and falls in lake levels local tectonism subsidence volcanism and climate which also produced modifications of the equilibrium profile of the fluvial systems all of these factors result in different accommodations in central and flank areas of the basin which led to different architectural configurations of channels and floodplains allogenic processes affected not only the sequence stratigraphy of the basin but also the vertebrate and plant taphocenosis therefore the sequence stratigraphy can be used not only as a predictive tool related to fossil occurrence but also to understand the taphonomic history of the basin at each temporal interval

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

vibracoring a new method for coring deep lakes abstract a major limitation facing lacustrine researchers is an inability to take long 6 to 18 m continuous sediment cores in water depths greater than several metres at a low cost these problems have limited the advancement of palaeolimnology and quaternary stratigraphy working from a frozen lake surface new developments make it possible to take 18 m long vibracores in water depths of at least 55 m high frequency low amplitude vibrations are transferred down a series of 6 m long 7 6 cm diameter core tubes 3 inch aluminum irrigation pipe rigidly coupled end to end vibrations liquify sediment adjacent to the core tube walls thus allowing penetration of the sediment a core catcher prevents sediment from extruding out of the tube end during extraction this cost effective and labour efficient two persons coring system has been achieved by developing rigid core tube couplers a hand powered drum cable hoist and a set of operation procedures the hoist cable end is attached to a clamp 1 m above the core catcher and at each coupler along the pipe string at 6 m intervals lifting or lowering using a drum cable hoist allows for quick coupling and decoupling of core tubes although vibracoring is an improvement over other systems it still has portability limitations because of the bulk and weight of the equipment and large amount of pipe required for deep coring three sleds are required to transport equipment from the nearest vehicle access to the coring sites

preserved initial in apatite from altered felsic igneous rocks a case study from the middle proterozoic of south australia abstract strontium isotope data from a suite of hydrothermally altered middle proterozoic granitoids and a related felsic volcanic rock show that the total rock systems have been disturbed as a result of hydrothermal alteration as such unambiguous determination of initial 87 sr 86 sr is not possible using total rock data with consequent loss of valuable petrogenetic information in contrast initial 87 sr 86 sr values derived from apatite are uniform when compared with the discordant total rock analyses evaluation of strontium diffusion kinetics in apatite together with geological and isotopic evidence presented here suggest that initial 87 sr 86 sr derived from apatite preserves the igneous initial 87 sr 86 sr and that 87 sr 86 sr in apatite is unlikely to have been modified as a result of igneous cooling or hydrothermal alteration this study shows that under some conditions apatite is resistant to 87 sr 86 sr modification and can yield petrogenetic information not attainable from total rock analyses data presented here together with data obtained in other studies indicate that the strontium isotope system in apatite is more resistant to modification than feldspar and biotite this approach may be of widespread application in determining initial 87 sr 86 sr of similarly altered ancient igneous rocks

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

the geochemical evolution of proterozoic granitoids near port lincoln in the gawler orogenic domain of south australia abstract proterozoic granitoids in the port lincoln area of the gawler orogenic domain of south australia changed in mineralogy and composition through time two older suites the 1843 ma massena bay orthogneisses and the 1843 ma donington pyroxene granitoids have curvilinear trends on a modified acf diagram and relatively unfractionated hree consistent with compositional evolution through pyroxene and plagioclase dominated crystal fractionation on the other hand the 1757 ma colbert and 1709 ma moody suites have modal hornblende more strongly fractionated hree and rectilinear trends on the acf diagram they probably require hornblende and plagioclase dominated fractionates and or amphibole garnet as a residual phase during partial melting superimposed on this two fold subdivision of older and younger granitoid suites according to degree of hree fractionation and acf trends there are also progressive compositional changes from the oldest to the youngest granitoids for example at comparable sio2 levels the granitoid suites become progressively richer in k lree zr nb ti and p but mg ca sc v ni and cr progressively decrease these secular compositional patterns are similar to those described for the mt isa region of northern australia including the ewen kalkadoon magmatic association to which the donington suite bears many compositional similarities normalised incompatible element plots for the port lincoln area granitoid suites have similar shapes to penecontemporaneous mafic dykes major and trace element modelling allows derivation of the granitoids by partial melting in the lower crust of mafic granulites compositionally analogous to the mafic dykes proterozoic crustal growth in the port lincoln area probably took place by vertical accretion through underplating of new mafic material to the lower crust and subsequent remelting of this to yield magmas of granitoid composition

sediment transport model for the eocene escanilla sediment routing system implications for the uniqueness of sequence stratigraphic architectures abstract stratigraphic architectures are fundamentally controlled by the interplay at different temporal and spatial scales of accommodation and sediment supply modulated by autogenic responses of the sediment routing system and its constituent segments the flux and caliber of sediment supply is a function of climate catchment area and tectonics in the source regions and unraveling these forcing mechanisms from the observed stratigraphic architecture remains a key research challenge the mid to late eocene escanilla sediment routing system had its source regions in the south central pyrenean orogen northern spain and transported sediment from wedge top basins along tectonic strike to marine depocenters by constructing a volumetric budget of the sedimentary system it has been demonstrated that there were marked changes in the grain size distribution released from the sediment sources and also in the position of the gravel front across three 2 6 myr time intervals from 41 6 to 33 9 ma classical sequence stratigraphic interpretations would relate the movement of depositional boundaries such as the gravel front to changes of base level either in isolation or in combination with sediment supply herein we explore the possibility that the position of the gravel front was primarily driven by variability of grain size distributions released from the source regions as a result of changes in catchment uplift rate and or surface run off using a simple model of sediment transport that captures first order processes we simulate the lateral movement of gravel deposition in the proximal part of the escanilla sediment routing system movement of the gravel front is a function of both accommodation generation and the transport capacity of the sediment routing system we assume that the transport capacity is a linear function of the local slope and the water flux by assuming that the observed thickness of deposits is equivalent to the accommodation available during deposition we then use the stratigraphic architecture to constrain the change in catchment size and water flux over the three time intervals of the escanilla paleo sediment routing system multiple scenarios are investigated in order to find the most plausible tectonic and climatic history model results indicate that during the mid eocene there was an increase in catchment length and sediment flux most likely driven by tectonic uplift in the pyrenean orogen subsequent marked progradation of the gravel front during the late eocene was the consequence of reduced transport capacity due to a reduction in surface run off the latter model result is in agreement with records of pollen taxa that indicate increased climatic aridity in the late eocene the combination of a sediment transport model with a full sediment budget makes it possible to test the non uniqueness of these results

evolution and emplacement of high fluorine rhyolites in the mesoproterozoic gawler silicic large igneous province south australia the gawler range volcanics grv and the hiltaba suite hs of south australia form a silicic dominated large igneous province the gawler slip emplaced in an intracontinental setting during the mesoproterozoic emplacement of the grv lasted for a short period of time 2 ma and can be separated into two main phases the first phase lower grv is composed of thick 3 km sequences erupted from distinct centres and includes small to moderate volume up to 150 km3 felsic lavas ignimbrites and minor mafic and intermediate lavas the upper grv include extensive felsic lavas that are up to 1000 of km3 in volume and 200 km across using well preserved quartz hosted melt inclusions we investigated the composition of the lower grv including major trace and volatile elements the results indicate high concentrations of k2o 7 8 wt rare earth and high field strength elements and low concentrations of ca mg ni cr sr and ba in comparison with felsic continental crust overall melt inclusion compositions match whole rock geochemical characteristics we demonstrate that the grv magma was f rich 1 3 wt and had high temperature for a silicic magma high f concentrations and high temperature would have resulted in lower than usual polymerisation of the melt and relatively low viscosity these characteristics help explain how very voluminous felsic magma was erupted effusively and emplaced as lavas other intracontinental slip contain extensive felsic lavas and ignimbrites which appear to share similar geochemical characteristics we also show that selective alteration caused depletion of whole rock compositions in some trace elements namely pb u and sn