euler deconvolution of the analytic signal and its application to magnetic interpretation euler deconvolution and the analytic signal are both used for semi automatic interpretation of magnetic data they are used mostly to delineate contacts and obtain rapid source depth estimates for euler deconvolution the quality of the depth estimation depends mainly on the choice of the proper structural index which is a function of the geometry of the causative bodies euler deconvolution applies only to functions that are homogeneous this is the case for the magnetic field due to contacts thin dikes and poles fortunately many complex geological structures can be approximated by these simple geometries in practice the euler equation is also solved for a background regional field for the analytic signal the model used is generally a contact although other models such as a thin dike can be considered it can be shown that if a function is homogeneous its analytic signal is also homogeneous deconvolution of the analytic signal is then equivalent to euler deconvolution of the magnetic field with a background field however computation of the analytic signal effectively removes the background field from the data consequently it is possible to solve for both the source location and structural index once these parameters are determined the local dip and the susceptibility contrast can be determined from relationships between the analytic signal and the orthogonal gradients of the magnetic field the major advantage of this technique is that it allows the automatic identification of the type of source implementation of this approach is demonstrated for recent high resolution survey data from an archean granite greenstone terrane in northern ontario canada

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

bolla bollana boulder beds a neoproterozoic trough mouth fan in south australia the bolla bollana formation is an exceptionally thick ca 1500 m rift related sedimentary succession cropping out in the northern flinders ranges south australia which was deposited during the sturtian mid cryogenian glaciation lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice sourced subaqueous fan system the diamictite facies association is dominant and comprises both massive and stratified varieties with a range of clast compositions and textures arranged into thick beds 1 to 20 m representing stacked ice proximal glaciogenic debris flow deposits a channel belt facies association most commonly consisting of normally graded conglomerates and sandstones displays scour and fill structure of ca 10 m width and 1 to 3 m depth these strata are interpreted as channelized turbidites rare mud filled channels in this facies association bear glacially striated lonestones finally a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear normally graded cycles from the lamina to bed scale these record a variety of non channelized turbidites probably occupying distal and or inter channel locations on the subaqueous fan coarsening and thickening up cycles capped by dolomicrites or mudstones are indicative of lobe build out and abandonment potentially as a result of ice lobe advance and stagnation dropstones recognized by downwarped and punctured laminae beneath pebbles to boulders in shale or in delicate climbing ripple cross laminated siltstones are clearly indicative of ice rafting the co occurrence of ice rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites comparison to pleistocene analogues enables an interpretation as a trough mouth fan most probably deposited leeward of a palaeo ice stream beyond emphasizing the highly dynamic nature of sturtian ice sheets these interpretations testify to the oldest trough mouth fan recorded to date

glaciomarine model for upper precambrian diamictites of the port askaig formation scotland descriptive techniques lithofacies codes and vertical profile analysis emphasizing lithofacies contacts and geometry allow objective characterization and comparison of diamict ite sequences irrespective of geologic age upper precambrian diamictites 650 600 m y of the middle dalradian port askaig formation in scotland are traditionally interpreted as products of repeated ice sheet advances over an emergent shallow marine shelf and deposition by in situ basal melt out the dalradian sequences are however fundamentally different from modern and pleistocene diamicts deposited by either lodgment or basal melt out and fail to show evidence of tractional processes associated with basal ice movement scottish diamictite sequences are similar to assemblages of massive and stratified diamict lithofacies of late pleistocene age deposited subaqueously below floating ice and recently described from the lake ontario basin of north america a glaciomarine depositional model may have implications for the origin and paleogeographical setting of other upper precambrian diamictites of similar age and stratigraphic context in east greenland spitsbergen and scandinavia

structural joint inversion coupled with euler deconvolution of isolated gravity and magnetic anomalies abstractwe generalized the euler deconvolution method to a joint scheme which consists of locating the horizontal and vertical positions of the top of potential field 3d sources these results were then used to constrain the depth to the top of the models obtained by cross gradient joint 3d inversions imposing fixed known values in the a priori models the coupling of both methods produced more realistic density and magnetization models for separate and joint inversions relative to those obtained by applying cross gradient joint inversion only this strategy was tested on a 3d synthetic experiment and on a real field data set from the northwest region of the baja california peninsula mexico after locating the vertical position of the source the algorithm uses this information to obtain density and magnetization models that enhanced their structural compatibility and reduces the ambiguity on the interpretation of their structural characteristics laterally and at surface

multiridge euler deconvolution potential field interpretation can be carried out using multiscale methods this class of methods analyses a multiscale data set which is built by upward continuation of the original data to a number of altitudes conveniently chosen euler deconvolution can be cast into this multiscale environment by analysing data along ridges of potential fields e g at those points along lines across scales where the field or its horizontal or vertical derivative respectively is zero previous work has shown that euler equations are notably simplified along any of these ridges since a given anomaly may generate one or more ridges we describe in this paper how euler deconvolution may be used to jointly invert data along all of them so performing a multiridge euler deconvolution the method enjoys the stable and high resolution properties of multiscale methods due to the composite upward continuation vertical differentiation filter used such a physically based field transformation can have a positive effect on reducing both high wavenumber noise and interference or regional field effects multiridge euler deconvolution can also be applied to the modulus of an analytic signal gravity magnetic gradient tensor components or hilbert transform components the advantages of using multiridge euler deconvolution compared to single ridge euler deconvolution include improved solution clustering increased number of solutions improvement of accuracy of the results obtainable from some types of ridges and greater ease in the selection of ridges to invert the multiscale approach is particularly well suited to deal with non ideal sources in these cases our strategy is to find the optimal combination of upward continuation altitude range and data differentiation order such that the field could be sensed as approximately homogeneous and then characterized by a structural index close to an integer value this allows us to estimate depths related to the top or the centre of the structure

precambrian permafrost horizons as indicators of palaeoclimate abstract periglacial phenomena such as polygonal wedge structures and microrelief features commonly preserved in fossil permafrost horizons can provide valuable information on palaeoclimate including indications of mean annual air temperature seasonal temperature range relative precipitation and evidence for long term 104 years oscillations of climate such features are known from early and late proterozoic rocks and indicate mean annual air temperatures as low as 12 to 20 c or lower and strongly seasonal periglacial climates these palaeoclimatic data together with information on palaeolatitude and proximity to palaeo sea level may impose strong constraints on palaeoclimate models for proterozoic glaciation

glacial sediments and erosional pavements near the cambrian precambrian boundary in western henan province china exceptionally well preserved glaciated pavements and a variety of glacigenic sediments comprising the luoquan formation in henan province central china are believed to have formed close to the cambrian precambrian boundary they may therefore be younger than the better known sinian tillites representing the changan and nantuo ice ages they perhaps belong to a distinct glacial epoch that is recorded elsewhere in china and in other continents but for which there is less evidence than for earlier late proterozoic glacial periods lithofacies represented in the luoquan formation are massive diamictite signifying deposition as lodgement or melt out till bedded diamictite waterlain till or glaciomarine glaciolacustrine sediments with dropstones rhythmites with dropstones glaciolacustrine or fjord deposits possibly varves tabular conglomerates and sandstones outwash deltaic or sub aqueous mass flow deposits lens shaped breccia deposits sub aqueous mass flow deposits and gravel sand wedges frost contraction crack infillings the glaciated pavements reveal well preserved striations grooves often intersecting 9plastically moulded9 forms crescentic gouges and steps on a regional scale the linear features are of variable orientation but they indicate a dominant ice flow direction towards the southeast all this evidence points to upland glaciation with erosion followed by deposition in a terrestrial glacial and glaciolacustrine environment

depositional environment and regional stratigraphic significance of the serle conglomerate a late proterozoic submarine fan complex south australia abstract the serle conglomerate is a lenticular unit 8 km 160 m at the top of the late proterozoic sturtian glacigenic yudnamutana subgroup in the northeastern part of the adelaide geosyncline in its type area at the west end of the fitton trough it can be subdivided into five stratigraphic units interpreted as the products of deposition in the mid to upper portions of a submarine fan complex progradation of submarine fans under conditions of eustatic sea level rise was probably due to concomitant fault activity and isostatic readjustments along the basin margins in an area about 10 km west of the type area similar conglomerates overlie glacigenic rocks of the yudnamutana subgroup with an erosional contact and therefore are younger than them there is no definitive evidence of glacial influence during deposition of the serle conglomerate so that previous correlations with glacigenic diamictites elsewhere in the adelaide geosyncline are unlikely there is no justification in this area for inferring two separate early sturtian glaciations

morphometric indices as indicators of tectonic fluvial and karst processes in calcareous drainage basins south menorca island spain this study proposes using morphometric indices to discriminate the processes that shape calcareous drainage basins to illustrate this a dem of the southern part of menorca island migjorn was created and basin slope drainage density hypsometric curve and integral and the area occupied by open and closed dolines were extracted from it these indices show an important dependence on tectonics which govern the morphology of these drainage basins and encourage the predominance of karst and or fluvial processes in the different sectors the morphometric indices are clearly influenced by the geological migjorn structure a carbonate upper miocene reef platform gently folded as an asymmetrical anticline the hypsometric integral and curve discriminate the influence of tectonics and structure whilst the drainage density and the proportion of open dolines are associated with basins with more pronounced fluvial processes a cluster analysis based on these indices discriminated three sectors where different forms and processes are found in the western and eastern sectors rounded basins without major fractures predominate the basins slope at less than 5 and karst processes outweigh fluvial processes the central sector however has steeper slopes a clearly defined drainage system and a predominance of fluvial over karst processes greater uplift in this sector has facilitated the formation of elongated basins that follow the main fracture lines copyright 2007 john wiley sons ltd

interpretation of regional aeromagnetic data by the scaling function method the case of southern apennines italy a complex aeromagnetic anomaly in southern apennines italy is analysed and interpreted by a multiscale method based on the scaling function we use multiscale methods allowing analysis of a potential field along ridges which are lines defined by the position of the extrema of the field at the considered scales the method developed and applied in this paper is based on the study of the scaling function of the total magnetic field it allows recovering of source parameters such as depth and structural index the studied area includes a pleistocene volcanic structure mt vulture whose intense dipolar anomaly is superimposed on a longer wavelength regional anomaly the interpretation of ridges of the modulus of the analytic signal at different altitude ranges allows recognition of at least three distinct sources between about 5 km and 20 km depth their interpretation is discussed in light of borehole data and other geophysical constraints a reasonable geological model for these sources indicates the presence of intrusions probably linked to the past activity of mt vulture

euler deconvolution in the presence of sheets with finite widths euler deconvolution of magnetic fields induced by sheets with nonnegligible widths provides source location estimates that are biased away from the true locations i have derived formulas for these biases and used the equations to model diffuse solution patterns that are owing to the interplay between integer structural indices and finite sources these patterns closely match solutions deconvolved from aeromagnetic data over northern canada motivated out of the necessity that complete harmonics be integral degreed i have investigated and discovered the ineffectiveness of noninteger structural indices in remediating the aforementioned biases in fact real numbers impart similar errors to multiple euler solutions causing ensembles of estimated origin loci to reside below the middle of the tops of wide sheets i have devised an approach requiring the inclusion of a term in the euler deconvolution kernel whose independent variable is the second horizontal derivative of the total field and whose partial slope to be solved is the sheet width this approach is appropriate only if the thickness does not exceed the depth however precision could be sacrificed in favor of accuracy because of the presence of the second derivative the application to aeromagnetic data over a diabase dike in northern canada yields a depth effectively coincident with a drilling depth

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

multiscale analysis of potential fields by a ridge consistency criterion the reconstruction of the bishop basement summary we use a multiscale approach as a semi automated interpreting tool of potential fields the depth to the source and the structural index are estimated in two steps first the depth to the source as the intersection of the field ridges lines built joining the extrema of the field at various altitudes and secondly the structural index by the scale function we introduce a new criterion called ridge consistency in this strategy the criterion is based on the principle that the structural index estimations on all the ridges converging towards the same source should be consistent if these estimates are significantly different field differentiation is used to lessen the interference effects from nearby sources or regional fields to obtain a consistent set of estimates in our multiscale framework vertical differentiation is naturally joint to the low pass filtering properties of the upward continuation so is a stable process before applying our criterion we studied carefully the errors on upward continuation caused by the finite size of the survey area to this end we analysed the complex magnetic synthetic case known as bishop model and evaluated the best extrapolation algorithm and the optimal width of the area extension needed to obtain accurate upward continuation afterwards we applied the method to the depth estimation of the whole bishop basement bathymetry the result is a good reconstruction of the complex basement and of the shape properties of the source at the estimated points

depth determinations of shallow hydrothermal systems by self potential and multi scale wavelet tomography in hydrothermal studies the depth of the hydrothermal system is always required but rarely known via traditional geophysical exploration techniques while previous studies have shown that continuous wavelet transform algorithms applied to self potential data can theoretically determine the depth of the hydrothermal fluids this study uses multi scale wavelet tomography with multiple wavelets field measurements and geophysical models to accurately determine this depth on stromboli waita and masaya volcanoes multi scale wavelet tomography of field measurements gives reproducible depth results supported by independent geophysical measurements and models and accurately locates the main water flow paths at shallow depths unlike other traditional geophysical methods multi scale wavelet tomography using self potential data is a low cost tool to rapidly determine depths of the shallowest hydrothermal structures this approach has the potential to significantly enhance our ability to locate geothermal systems and monitor active volcanoes

quantitative interpretation of magnetic anomalies from bodies approximated by thick bed models in complex environments magnetic prospecting is a rapid and inexpensive geophysical tool and one of the most widely used methods for geophysical prospection throughout the world however the noise factors such as inclined magnetization complex geological structure of investigated areas and uneven terrain relief strongly obscure the interpretation of observed magnetic anomalies the developed methodology of magnetic anomalies interpretation from models of thin beds and horizontal circular cylinders spheres in complex environments oblique magnetization rugged relief and unknown levels of the normal magnetic field using improved versions of characteristic points and tangents was presented in detail in the author s previous publications however many geological targets have a geometrical form of thick beds and thin horizontal plates and intermediate forms that crop up between these two models in this paper a methodology for interpreting magnetic anomalies produced by thick bed models in complex environments is explicitly described it shows that quantitative analysis of magnetic anomalies due to intermediate targets could be successfully carried out using the methodology developed for the thick bed model in the case of a thin horizontal plate with a large horizontal size two distinct anomalies from the left and right ends may be interpreted as anomalies from thin beds the interpretation methodology was successfully tested both on typical models and on real geological targets it was concluded that these methods could be effectively applied for quantitative analysis of magnetic surveys for geological geophysical mapping archeological target delineation ore body searching revealing oil and gas traps and solving other geological and environmental problems

deposition and palaeogeography of a glacigenic neoproterozoic succession in the east kimberley australia facies provenance and palaeocurrent analysis of the predominantly siliciclastic neoproterozoic succession of the east kimberley district of northwestern australia indicates southwesterly directed regional palaeoice flow directions associated with continental glaciation facies relationships at three key study sites in the east kimberley record glacial advance retreat and marine transgression and the likely effects of ice dynamics on local basin depositional history ice scour linked with provenance data indicate ice advance from the northeast additional ice flow data from the west kimberley and the daly river area of northern territory are consistent and record a regional palaeoice flow direction towards the southwest palaeocurrent data and facies relationships in the east kimberley however suggest that sediment transport directions within the east kimberley basin were influenced by a combination of ice induced lithospheric flexure pre existing topography and modification of basin topography and sediment dispersal paths by ice induced redistribution of debris a basin evolution model incorporating these concepts within the framework of ice advance retreat and marine inundation is proposed identification of regional ice flow trends of this scale should ultimately prove a useful tool in testing possible palaeogeographic reconstructions of continent configurations in a post rodinian world

euler deconvolution of gravity tensor gradient data tensor euler deconvolution has been developed to help interpret gravity tensor gradient data in terms of 3 d subsurface geological structure two forms of euler deconvolution have been used in this study conventional euler deconvolution using three gradients of the vertical component of the gravity vector and tensor euler deconvolution using all tensor gradients these methods have been tested on point prism and cylindrical mass models using line and gridded data forms the methods were then applied to measured gravity tensor gradient data for the eugene island area of the gulf of mexico using gridded and ungridded data forms the results from the model and measured data show significantly improved performance of the tensor euler deconvolution method which exploits all measured tensor gradients and hence provides additional constraints on the euler solutions

sequencing the sturtian icehouse dynamic ice behaviour in south australia the cryogenian record of south australia includes the type region of the sturtian glaciation the oldest of three pan global icehouse intervals during the neoproterozoic data are presented from previously little described sections at holowilena creek oladdie creek and hillpara creek in the central and southern flinders ranges where five facies associations are recognized these are 1 diamictite and conglomerate 2 interbedded heterolithic deposits 3 hummocky cross stratified sandstone 4 lonestone bearing siltstone and 5 ferruginous siltstone and sandstone the succession reveals significant lateral and vertical facies variation which is linked to a complex inherited palaeotopography and distance from the sediment source repeated stratigraphic occurrences of striated clasts and abundant ice rafted debris strongly support recurrent glacial influence on sedimentation the intercalation of gravitationally reworked diamictites dropstone bearing siltstone and dropstone free siltstone testifies to dynamic sedimentation within a periodically glacially influenced subaqueous environment sequence stratigraphic analysis identifies four glacial advance systems tracts separated by three glacial retreat systems tracts wherein hummocky cross stratified sandstones attest to open water conditions these findings support dynamic ice sheet behaviour in south australia and provide clear evidence for repeated intra sturtian ice sheet recession

problems in applying preservation facies and sequence models to sinian neoproterozoic glacial sequences in australia and asia abstract the sinian 800 530 ma is an extraordinary period of earth history characterized by the transition from simple to complex multicellular organisms and by extreme variations in climate eustasy and possibly tectonics understanding sinian stratigraphy may help interpret the co evolution of life and environment during the period though sinian successions are poorly dated and difficult to correlate preservation facies and sequence models based on mesozoic recent successions may be used to interpret them preservation models based on basin subsidence permit estimates of how thick and complete successions can be in different tectonic settings and how long it took for them to be deposited facies models for rift craton shelf slope and basin environments help in identification of these different tectonic settings sequence models facilitate interpretation of the interplay of tectonic subsidence eustasy rates of sedimentation and climate such models applied to the sinian successions of australia and asia indicate the following great shallowing upwards megacycles occur in sinian successions and each ends with regional glaciations deep rift basins formed around 850 800 ma preserve the oldest megacycles but these basins soon were filled with rapidly deposited glaciogenic sediments relatively complete sequences are found only in deep basins subject to repeated rifting cratons and shallow shelves preserve only the youngest megacycles older deposits have been removed by younger glacial advances deep shelves and slopes preserve one to three megacycles depending on the timing of the start of passive margin subsidence megasequences can be correlated based on limited radiometric dating and inferred regional distribution of unique rock types but these sequences are not developed to the same extent in all blocks problems in correlating the four great megacycles recognized elsewhere with those of asia will persist until the requisite facies analysis and u pb dating of interbedded volcanics are done

palaeoclimate implications from deep drilling of neoproterozoic strata in the officer basin and adelaide rift complex of australia a marine record of wet based glaciers abstract two prominent episodes of neoproterozoic glaciation in australia are recorded in the cryogenian sturtian

sm nd isotopic evidence for the provenance of sediments from the adelaide fold belt and southeastern australia with implications for episodic crustal addition abstract in south australia late proterozoic and cambrian sediments were deposited in basins formed within archaean to early mid proterozoic basement these sequences were subsequently deformed and uplifted by the cambro ordovician delamerian orogeny to form the adelaide fold belt in using the adelaide fold belt to address models for lithospheric evolution it is necessary to understand the mechanisms of basin formation and whether the sequences merely reflect reworking of existing cratonic material or if there were new crustal additions this study presents geochemical and isotopic data on the sediments and basement rocks to complement existing data on the delamerian igneous rocks as a means of investigating these questions the data reveal that the archaean mid proterozoic basement rocks of the gawler craton have nd depleted mantle model ages which average about 2 6 ga and nd values at 800 ma in the range 9 to 24 or at 500 ma from 11 to 28 the late proterozoic adelaidean sediments however have an average model age of 1 9 ga and initial nd values in the range 5 to 11 the sequence can be divided into lowermost rift phase sediments derived from erosion of local gawler craton material and a subsequent widely distributed thermal sag phase sedimentation whose isotopic signature is not compatible with the basement this implies that a more primitive or juvenile source was accessed via broadening of the provenance region the cambrian sediments have slightly older model ages 2 1 ga and lower nd 9 to 13 and can be interpreted as mixtures of basement and reworked adelaidean detritus the early palaeozoic sedimentary sequences of the lachlan fold belt to the east have isotopic compositions very like the south australian late proterozoic and cambrian sequences they have an average model age of 1 85 ma but much higher k 2 o na 2 o this indicates that the widespread flysch of eastern australia is the result of recycling of the late proterozoic and cambrian sediments by erosion of the adelaide fold belt with some modification by the mixture of the cambro ordovician mafic and felsic magmatic rocks in this orogen our data suggest regional intracontinental crustal evolution combined with recycling of older crustal material with new additions from the mantle during orogenesis and to a lesser extent episodes of extension and sedimentation

interpretation of magnetic data using an enhanced local wavenumber elw method this paper presents an enhancement of the local wavenumber method named elw for enhanced local wavenumber for interpretation of profile magnetic data this method uses the traditional and phase rotated local wavenumbers to produce a linear equation as a function of the model parameters the equation can be solved to determine the horizontal location and depth of a 2d magnetic body without specifying a priori information about the nature of the sources using the obtained source location parameters the nature of the source can then be inferred the method was tested using theoretical simulations with random noise over a dike body it was able to provide both the location and an index characterizing the nature of the source body the practical utility of the method is demonstrated using field examples over dikelike bodies from canada and egypt

the deep crust beneath the trans european suture zone from a multiscale magnetic model we present a 3 d interpretation of the deep magnetic sources beneath the main geological structure of central eastern europe the trans european suture zone tesz we used a multiscale analysis of aeromagnetic data based on a multiscale data set generated by upward continuation of the european and mediterranean magnetic project data set from 5 to 100 km altitude we also computed the multiscale total gradient t of the multiscale field both of the multiscale data sets allow us to discriminate the main crustal contributions to the field at various scales and we showed that at large altitudes the field is dominated by the sole effect of the tesz the multiridge geometric method was very useful in studying the complex features of the main crustal interfaces either shallow or deep the interpreted interfaces are largely agreement with geological models based on seismic surveys and in some cases complete the models out of the analyzed region in order to estimate the deepest source depths in the tesz region we applied the multiridge method to the large scales 50 100 km altitude obtaining a set of singular points at depths ranging between 35 and 40 km considering the heat flow trend and the geological models around the tesz area we found a meaningful correspondence among the location of the estimated singular points and the most abrupt variations and complex morphology features of the moho boundary the multiridge estimates are consistent with known structural information and can be used for a 3 d representation of the moho depth along the tesz

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

the association of sulphate evaporites stromatolitic carbonates and glacial sediments examples from the proterozoic of australia and the cainozoic of antarctica abstract carbonate sediments are often considered diagnostic of warm water environments and thus the occurrence of dolomite and limestone beds within and immediately overlying many late proterozoic glacial deposits tillites has long been a source of controversy stromatolites are also conventionally thought to be warm water indicators we describe two examples of stromatolitic dolomite occurring together with barite at the top of late proterozoic glacial sequences in the amadeus and ngalia basins of central australia problems of interpretation may be largely resolved after examination of published data on antarctic lakes antarctic lakes of high salinity occupy enclosed glacial basins in both the vestfold hills and the taylor and wright dry valleys lake bonney is the most comprehensively described example carbonate sediments sulphate evaporites and even stromatolites are common components of cold arid climate lakes the stromatolitic mats and their constructing cyanobacteria are similar to those described from warmer climates the tundra plains and lakes and coastal lagoons of northern canada and siberia are better geomorphic analogues for the proterozoic deposits and these too seem to contain analogous sediments but only brief descriptions are available we suggest that environments such as these provide modern analogues of the association of proterozoic glacial sediments with carbonates evaporites and stromatolites

the cryogenian record of glaciation and deglaciation in south australia abstract this paper reviews the state of our current knowledge of the cryogenian glacial and deglacial sedimentary records of south australia two distinct glacial intervals are recognised within rocks of cryogenian 850 630 ma age separated by an interglacial succession that by definition lacks glacial facies the glacial successions were laid down during the sturt and elatina glaciations each of these glaciations is arguably of global extent under the snowball earth hypothesis hoffman and schrag 2002 evidence for glaciation has been known for over one hundred years from the sturt tillite howchin 1900 when compared like for like in a systematic facies analysis both glacial successions show some similarities notably the occurrence of diamictites representing glacial deposition and slope reflux and dropstone bearing intervals but also show some dramatic differences notably deposition of the sturt succession was strongly influenced by extensional tectonics for which evidence is provided by dramatic thickness variations either side of major faults and palaeocurrent data sub basins formed during regional extension contain diamictites 4 6000 m thick e g the yudnamutana and baratta troughs in the northern and central flinders ranges respectively deposition of the younger elatina glacial deposits was locally influenced by diapirism in the central flinders ranges but otherwise these younger deposits seem to maintain a relatively constant thickness of

identification of sources of potential fields with the continuous wavelet transform complex wavelets and application to aeromagnetic profiles in french guiana a continuous wavelet technique has been recently introduced to analyze potential fields data first we summarize the theory which primarily consists of interpreting potential fields via the properties of the upward continued derivative field using complex wavelets to analyze magnetic data gives an inverse scheme to find the depth and homogeneity degree of local homogeneous sources and the inclination of their magnetization vector this is analytically applied on several local and extended synthetic magnetic sources the application to other potential fields is also discussed then profiles crossing dikes and faults are extracted from the recent high resolution aeromagnetic survey of french guiana and analyzed using complex one dimensional wavelets maps of estimated depth to sources and their magnetization inclination and homogeneity degree are proposed for a region between cayenne and kourou

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

stratigraphy and sedimentology of sturtian glacigenic deposits in the western part of the north flinders basin south australia abstract the late proterozoic sturtian succession in the northern part of the adelaide geosyncline is disposed in a southward closing arcuate outcrop belt that is largely fault bounded on its southern margin on the west side the glacigenic portion of the sturtian succession is between 100 and 800 m thick a thin discontinuous basal breccia is present on the older rocks of the burra group this is followed by a locally developed diamictite with associated lenticular sandstones interpreted as a tillite and glacial outwash deposits respectively the succeeding sturtian units are much more widespread unit 2 is a mudstone dominated heterogeneous succession of siliciclastic rocks formed by traction currents gravity flows and rain out from floating ice a second diamictite unit 3 is massive in the southeasterly part of the study area near the town of copley but is stratified and heterogeneous in an area to the northwest this diamictite is probably a marine deposit formed in the south by rapid rain out from floating ice and in the north by a variety of processes that largely reworked the glacigenic sediment the topmost unit 4 is also heterogeneous and resulted from the interplay of gravity flows traction currents and ice rain out palaeocurrents indicate a dominantly southeasterly transport but some herringbone cross bedding suggests tidal activity dolostones are present in unit 4 and stromatolitic bioherms were noted in the basal diamictite in this region the sturtian succession is considered to be the product of glaciation centred to the west and north feeding into an elongate basin here termed the north flinders basin palaeocurrent data and thickness changes suggest that the basin may have opened to the east in late proterozoic time this basin may have been separated from the main part of the adelaide geosyncline to the southeast by the shallow to emergent central flinders zone

late proterozoic glacial carbonates in northeast spitsbergen new insights into the carbonate tillite association carbonate rich glacial deposits from two discrete vendian glacial periods are described the older is represented by the 24 40 m thick petrovbreen member e2 of the elbobreen formation which contains abundant detrital dolomite clasts in e2 and their possible source rocks have positive 13 c and negative 18 o pdb values in contrast the carbonate mud fraction of e2 sediments has different cathodoluminescence characteristics from clasts slightly negative 13 c values and higher fe and mn concentrations than clasts oxygen isotopes vary from 2 5 to 4 5 pdb thought to be related to various seawater meltwater mixtures in the depositional environment preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy ostwald s ripening and coinciding with sulphate reduction the younger glaciation is represented by the wilsonbreen formation 170 m which has a distinctive glaciolacustrine middle carbonate member w2 w2 contains precipitated periglacial carbonates with high mn fe ratio both limestone rhythmitic and stromatolitic and dolostone rhythmites stromatolites and dolomite rich sandstones which are compared with carbonates in modern antarctic lakes evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values up to 10 5 pdb high na concentration and evidence for dissolved evaporites high mn concentration in detrital dolostones in w2 is suggestive of syn sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones the carbonate tillite association ultimately arises from the erosion of underlying carbonates which originated in this case under radically different climatic conditions glacial depositional waters then became carbonate saturated as a result of dissolution of detrital carbonate massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis in glacial lakes carbonate precipitated in response to evaporation or photosynthesis carbonate precipitation as the result of seawater freezing or in warm interglacial conditions is not yet established oxygen isotope value are inconsistent too heavy with the presence of high latitude meltwaters implying that glaciation extended to low latitudes as proposed by harland