further thoughts on popperian geophysics the example of deconvolution ziolkowski a 1982 further thoughts on popperian geophysics the example of deconvolution geophysical prospecting 30 155 165 popper s demarcation criterion should be applied to all our theories in geophysics to ensure that our science progresses we must expose our theories to tests in which they stand some risk of being refuted but if we have a theory which has no rivals it may be difficult in practice to devise a test in which the theory risks being refuted conclusively the example of the deconvolution problem for seismic data is considered for the case where the source wavelet is unknown it is shown that all our existing theories of deconvolutions are not scientific in popper s sense they are statistical models we cannot compare these models in a way that is independent of the geology for each model requires the geology to have a different set of statistical properties even in our chosen geology it may be extremely difficult to determine the most applicable model and hence determine the correct deconvolution theory it is more scientific to attempt to solve the deconvolution problem a by finding the source wavelet first deterministically or b by trying to force the wavelet to be a spike that is by devising a perfect seismic source a new method of seismic surveying which has been proposed to tackle the deconvolution problem by the first of these approaches is based on a theory which is open to refutation by a simple popperian test since the theory makes no assumptions about the geology the test has equal validity in any geology it pays to frame our theories in such a way that they may easily be put at risk only in this way will we establish whether we are on firm ground the alternative is simply to take things on trust

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

a basin system and fluid flow analysis of the zn pb ag mount isa type deposits of northern australia identifying metal source basinal brine reservoirs times of fluid expulsion and organic matter reactions paleoproterozoic rocks of northern australia host one of the world s largest base metal repositories and are the world s most important zinc repository the mcarthur mount isa cloncurry mineral belt contains several world class zn pb ag u cu and cu au deposits ewers and fergusson 1980 williams 1998 betts et al 2003 large et al 2005 fig 1 the province has the potential to host additional base metal and uranium reserves advances in exploration techniques in the 1980s led to the discovery of several major new zn and cu au deposits including cannington century ernest henry and osborne however recent exploration results have been disappointing and new exploration strategies are required if the region is to further its growth potential and if new resources are to be realized beneath shallow cover fig 1 map of northeastern australia showing the principal tectonostratigraphic subdivisions for the region the map highlights the areas of study covered by the thematic papers in this volume and the location of the principal zn pb ag cu and cu au deposits the locations of profiles p1 and p2 the comalco seismic grid and deep boreholes including desert creek 1 are shown in the inset map bottom left between 1975 to 1995 geoscientists from geoscience australia the geological survey of queensland and the northern territory geological survey mapped the paleoproterozoic outcrop belt of northern australia at a scale of 1 100 000 subsequently researchers at monash university undertook detailed studies of the deformation history of the mount isa block placing the ore deposits within a tectonic context e g o dea et al 1997 betts et al 1998 2003 betts and lister 2002 researchers at james cook university carried out structural metamorphic and mineralization studies across the mount isa block with their principal focus concentrating on the deposits and their immediate environs bell et al 1988

the uranium mineralization potential of the paleoproterozoic sioux basin and its relationship to other basins in the southern lake superior region abstract the paleoproterozoic sioux basin and the baraboo barron flambeau mccaslin and waterloo quartzites in northcentral usa are all supermature quartz arenites that are among the world s oldest redbeds these quartzites were deposited on a stable craton at ca 1750 ma following exhumation and uplift of penokean crust and major orogenic activity related to the amalgamation of archean microcontinents at ca 2 0 1 8 ga to form laurentia 40ar 39ar ages of 1615 1543 ma from diagenetic muscovite in the sioux basin provide the first geochronological evidence for mazatzal related deformation and low grade metamorphism of the quartzites during subsequent convergence on the southern margin of laurentia one muscovite sample from the sioux basin has a 40ar 39ar age of 1465 ma that likely corresponds with fluid and thermal resetting due to felsic magmatism in the region and is similar to 40ar 39ar ages for muscovite from the baraboo and waterloo quartzites thus the sioux basin and other quartzites in the region have experienced a similar tectonic and fluid history the sioux basin has similar sedimentologic characteristics as other paleoproterozoic basins in north america including the uranium rich athabasca basin canada that is host to some of the world s largest and highest grade unconformity type uranium deposits we compared key characteristics such as the stratigraphy character of diagenetic fluids paleoaquifer characteristics and composition of leachable pb in the sandstones from the sioux basin with the athabasca basin in order to evaluate the fluid history of the basin and the potential of the sioux basin to host unconformity type uranium mineralization based on the hydrogen and oxygen isotopic composition of muscovite m1 that formed during diagenesis at 150 200 c the pore fluids that were present during peak diagenesis in the sioux basin had 18o and d values of 0 5 to 5 2 and 32 to 46 respectively similar to those of the fluids associated with uranium mineralization and alteration in the athabasca basin however fluid flow in the sioux basin was likely restricted to relatively thin and discontinous proximal fluvial facies that could have been diagenetic paleoaquifers in contrast to the extensive paleoaquifers in the athabasca basin that promoted large scale diagenetic reactions and alteration that led to the formation of unconformity type uranium mineralization in addition the non radiogenic isotopic composition of leachable pb in the sioux basin sandstones indicates that the majority of the pb is from a normal crustal source inconsistent with mobilization of radiogenic pb from a uranium rich source such as a uranium deposit although the sioux basin shares similar general characteristics to the athabasca basin the results of this study suggest that it has a lower potential than the athabasca basin to host significant high grade unconformity type deposits

high resolution multi 2d seismic imaging of solfatara crater campi flegrei caldera southern italy from active seismic data abstract a multi 2d imaging of the solfatara crater inside the campi flegrei caldera was obtained by the joint interpretation of geophysical evidences and the new active seismic dataset acquired during the ricen experiment eu project medsuv in 2014 we used a total of 17 894 first p wave arrival times manually picked on pre processed waveforms recorded along two 1d profiles criss crossing the inner solfatara crater and performed a tomographic inversion based on a multi scale strategy and a bayesian estimation of velocity parameters the resulting tomographic images provide evidence for a low velocity 500 1500 m s water saturated deeper layer at west near the outcropping evidence of the fangaia contrasted by a high velocity 2000 3200 m s layer correlated with a consolidated tephra deposit the transition velocity range 1500 2000 m s layer suggests a possible presence of a gas rich accumulation volume thanks to the mutual p wave velocity model we infer a detailed image for the gas migration path to the earth surface the gasses coming from the deep hydrothermal plume accumulate in the central and most depressed area of the solfatara being trapped by the meteoric water saturated layer therefore the gasses are transmitted through the buried fault toward the east part of the crater where the ring faults facilitate the release as confirmed by the fumaroles starting from the eastern surface evidence of the gas releasing in the bocca grande and bocca nuova fumaroles and the presence of the central deeper plume we suggest a fault situated in the central part of the crater which seems to represent the main buried conduit among them plays a key role

sequence stratigraphy and evolution of the paleoproterozoic intracontinental baker lake and thelon basins western churchill province nunavut canada abstract the baker lake and thelon basins lie along the border between the rae and hearne domains of the western churchill province basin fill comprises the dubawnt supergroup a ca 1 85 1 70 ga succession of predominantly continental clastic and intercalated volcanic rocks that nonconformably and unconformably overlies granitic and supracrustal rocks most of late archean age the dubawnt supergroup comprises three second order sedimentary sequences that record deposition within a rift basin a modified rift basin and a thermal sag basin respectively the baker sequence is inferred to represent the principal phase in the development of baker lake basin a series of generally elongate northeast striking half graben and fault bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks faults parallel to the basin margin exhibit evidence for strike slip ca 1 83 1 81 ga the nature and timing of basin development and associated magmatism allows that it may be a transtensional basin that formed by lateral escape in response to crustal thickening during the trans hudson orogeny similar to the formation of mesozoic and cenozoic strike slip and associated rift basins on the margins of the tibetan plateau the overlying whart sequence was deposited in small basins formed by block faulting and tilting of the baker sequence basin fill comprises eolian and alluvial redbeds with intercalated rhyolite flows and epiclastic rocks distribution of facies and stratigraphy suggest that faulting occurred throughout deposition of the whart sequence but ceased before deposition of the overlying barrens sequence ca 1 72 ga deformation and basin formation can be linked to a regional episode of granite emplacement and associated thermal metamorphism ca 1 76 1 75 ga the barrens sequence represents deposition over a broader area primarily in thelon basin strata generally are thinner and flatter than underlying sequences and display lateral continuity indicating minimal influence from syndepositional faulting the depositional record reflects progressive upward fining and eventually the first record of marine transgression within the dubawnt supergroup these features suggest that the barrens sequence was deposited over a broad region of thermal subsidence likely related to cooling of previously attenuated continental lithosphere the barrens sequence may be a remnant of a huge cratonic sand sheet that included the thelon athabasca amundsen and elu basins a regional subsidence mechanism to account for these basins may be mantle downwelling linked to the late stage amalgamation of laurentia the tripartite sequence evolution of the baker lake and thelon basins represents a framework for future sequence correlation among late paleoproterozoic basins in laurentia and shares characteristics with the evolution of contemporaneous intracontinental basins from north central australia and southeastern brazil

klauder wavelet removal before vibroseis deconvolution the spiking deconvolution of a field seismic trace requires that the seismic wavelet on the trace be minimum phase on a dynamite trace the component wavelets due to the effects of recording instruments coupling attenuation ghosts reverberations and other types of multiple reflection are minimum phase the seismic wavelet is the convolution of the component wavelets as a result the seismic wavelet on a dynamite trace is minimum phase and thus can be removed by spiking deconvolution however on a correlated vibroseis trace the seismic wavelet is the convolution of the zero phase klauder wavelet with the component minimum phase wavelets thus the seismic wavelet occurring on a correlated vibroseis trace does not meet the minimum phase requirement necessary for spiking deconvolution and the final result of deconvolution is less than optimal over the years this problem has been investigated and various methods of correction have been introduced in essence the existing methods of vibroseis deconvolution make use of a correction that converts on the correlated trace the klauder wavelet into its minimum phase counterpart the seismic wavelet which is the convolution of the minimum phase counterpart with the component minimum phase wavelets is then removed by spiking deconvolution this means that spiking deconvolution removes both the constructed minimum phase klauder counterpart and the component minimum phase wavelets here a new method is proposed instead of being converted to minimum phase the klauder wavelet is removed directly the spiking deconvolution can then proceed unimpeded as in the case of a dynamite record these results also hold for gap predictive deconvolution because gap deconvolution is a special case of spiking deconvolution in which the deconvolved trace is smoothed by the front part of the minimum phase wavelet that was removed

enriched archean lithospheric mantle beneath western churchill province tapped during paleoproterozoic orogenesis ultrapotassic rocks of the christopher island formation baker lake basin were emplaced across an enormous area 240 000 km 2 minimum of the western churchill province ca 1 83 ga these rocks extend across the snowbird zone a geophysical feature postulated by others to represent a paleoproterozoic suture that welded the rae and hearne domains minette dikes and flows of the rae and hearne domains display identical nd 1830 values and incompatible element patterns and thus appear to have originated from a common lithospheric mantle source christopher island nd model ages cluster at 2 8 ga and nd data from one archean lamprophyre and three 2 45 to ca 2 2 ga mafic suites suggest that enriched lithospheric mantle sources beneath both the rae and hearne domains existed well before ca 1 83 ga inconsistent with paleoproterozoic suturing along the snowbird zone in contrast to commonly invoked models that envisage melting of local enriched domains christopher island ultrapotassic rocks appear to have originated from an extensive reservoir we suggest that such a reservoir was created during an archean metasomatic event perhaps owing to flat subduction and that it remained in nearly complete isolation until tapped during paleoproterozoic extension related to squeezing of western churchill crust between flanking wopmay and trans hudson orogens

vibroseis deconvolution a comparison of cross correlation and frequency domain sweep deconvolution ideally traditional vibroseis processing produces a band limited zero phase klauder wavelet through cross correlation of the sweep with the recorded signal an alternative wavelet processing method involves deconvolving the sweep from the recorded vibroseis trace this deconvolution can be achieved through frequency domain division we compare and contrast the advantages and disadvantages of sweep deconvolution versus cross correlation on synthetic and real data

architecture of pre vegetation sandy braided perennial and ephemeral river deposits in the paleoproterozoic athabasca group northern saskatchewan canada as indicators of precambrian fluvial style abstract the late paleoproterozoic athabasca basin contains more than 1 5 km of predominantly sandy strata most of which are of braided fluvial origin in the eastern part of the basin at mcclean lake sandstones and minor conglomerates of the read formation at the base of the succession are preserved within a steep walled valley system they consist predominantly of meter scale sheet elements characterized by massive and flat laminated fine to very coarse grained sandstone with minor discontinuous cobble and boulder conglomerate along lower set boundaries these are interpreted as sheet flood and stream flood deposits of a terminal dry land system deposited in an arid climatic setting analysis of closely spaced drill core indicates that late stage run off was confined to small shallow channels typically only a few tens of meters wide and a few meters deep overlying strata of the bird member of the manitou falls formation are predominantly coarse to very coarse grained sandstones with abundant small scale cross stratification and minor granule and small pebble conglomerate at mcclean lake these appear to have been deposited as sheet elements by semi ephemeral to perennial braided rivers under more humid conditions at key lake 160 km to the southwest architectural analysis of a 184 m wide section indicates that at least part of the bird member was deposited in deeper sandy braided rivers characterized by seasonally varied flow the closest modern analogue is the south saskatchewan river in which large simple flow transverse bedforms become exposed and dissected during falling stage and act as nuclei for sand flat development the presence of numerous low relief 4th order surfaces suggests continued reworking of bar tops during rising stage the incremental character of downstream accretionary elements suggests periodic migration of barforms during peak flood stages separated by periods of low flow this indicates similarities with modern perennial braided systems and is counter to the idea that all pre devonian fluvial systems should consist of stacked sheets formed by individual flood events thin gravel layers accumulated as lags on fourth order surfaces with discontinuous mud layers suggesting deposition within temporary ponds in channel thalwegs after major floods strata in overlying units indicate a return to semi perennial conditions

comparison of diagenetic fluids in the proterozoic thelon and athabasca basins canada implications for protracted fluid histories in stable intracratonic basins the paleoproterozoic thelon basin located on the border between nunavut and the northwest territories of canada is a contemporaneous analog of the uranium rich paleoproterozoic athabasca basin in canada early diagenesis resulted in precipitation of extensive hematite on the surfaces of detrital quartz grains throughout the thelon formation and minor hydroxy phosphate in veins locally continued diagenesis then resulted in syntaxial quartz cementation of detrital quartz at 130 c from fluids having ca 17 wt equivalent nacl similar to the athabasca basin cementation of this type is most pronounced in fine grained sequences in the thelon basin a period of extensive desilicification during continued burial was followed by formation at ca 200 c of peak diagenetic illite having ar ar ages of ca 1400 1690 ma in the thelon formation this illite was associated with fluids with 18 oa nd d values of ca 6 and 50 respectively similar to those during peak diagenesis of the athabasca basin although the timing salinity and isotopic composition of the peak diagenetic fluids in the thelon and athabasca basins are similar the peak diagenetic mineral assemblage in the athabasca formation is dickite and illite with minor dravite and goyasite rather than simply illite consequently the fluids at peak diagenesis which in the athabasca basin are synchronous with formation of world class unconformity type uranium deposits had different compositions in each basin post peak diagenesis in the thelon basin was quite distinct from that in the athabasca basin in that illite was replaced in the central portion of the basin by k feld spar and then sudoite which crystallized from saline brines at ca 1000 ma and 100 c evidence for later infiltration of these brines is absent in the athabasca basin although uranium mobilization at ca 900 ma from fluids having the same characteristics as those at peak diagenesis was pronounced in the athabasca basin recent incursion of meteoric waters along reactivated structures into the athabasca basin has variably affected hydrous and uraniferous minerals but evidence for this is lacking in the thelon basin the thelon basin reflects less intensive fluid rock interaction in its early history than that recorded in the basal units of the athabasca basin 132

sequential architecture in a fluvial succession sequence stratigraphy in the upper cretaceous mesaverde group prince canyon utah abstract five unconformity bounded sequences have been documented within a 1300 m thick succession of predominantly fluvial upper cretaceous and lower tertiary deposits in the price canyon area of the westernmost part of the book cliffs east central utah u s a this area experienced major tectonically induced changes in the paleogeography during deposition the earliest fluvial deposits in the study area were formed in a relatively simple foreland basin setting in front of the sevier orogenic belt and contain more marine influence than previously recorded following a gradual termination of thrusting sedimentation became increasingly controlled by uplift of the san rafael swell to the southeast our studies suggest that the fluvial systems in the upper part of the succession alternated bet een being confined within a valley open towards the north and being more directly eastward flowing on the basis of the observed sequences an idealized model of alluvial sequences whose internal architecture can be related to a fall rise fall cycle of the stratigraphic base level has been established upward or downward changes in the position of this base level dictate the creation and destruction of accommodation on the alluvial plain and therefore exert a direct control on the sequential architecture and sandstone body geometry of fluvial successions in our model the basal sequence boundary is overlain by an amalgamated fluvial sandstone sheet the sheet is succeeded by a fining upward more mudstone rich level with more isolated sandstone bodies and this level may culminate in a marine or lacustrine transgression the upper part of the sequence may show a coarsening upward trend heralding the next phase of base level fall and sequence boundary generation use of the suggested model has the potential to refine existing lithostratigraphic schemes and given the higher resolution and more detailed correlation may significantly improve paleogeographic reconstructions and aid in prediction of potentially hydrocarbon bearing reservoirs a revised and refined lithostratigraphy has been established on the basis of alluvial sequence analysis the lower half of the succession forms the youngest part of a major eastward prograding clastic tongue the mesaverde group and is campanian we divide this part into the blackhawk castlegate and price river formations the rest of the succession is maastrichtian to paleocene and is referred to the north horn formation this formation was deposited in an intermontane setting

quality control of surface consistent deconvolution on land dynamite data abstract seismic data with reliable amplitude and phase can significantly impact drilling programs by providing valuable descriptions of the reservoir and overburden especially for complicated or subtle plays processing steps such as velocity tomography and amplitude preserving migration are critical for producing high quality seismic images but equally important are surface related premigration processing steps that can significantly alter seismic amplitude and phase information such as deconvolution during land dynamite seismic acquisition source and receiver responses are affected by surface conditions and inhomogeneous weathering layers for example even with the exact charge size the response from each shot can vary greatly as the medium around the charge changes receiver recordings are affected similarly by near surface conditions an improper correction or a lack of correction for near surface anomalies during seismic preprocessing will reduce the subsurface resolution and negatively bias

hydrogeology sequence stratigraphy and diagenesis in the paleoproterozoic western thelon basin influences on unconformity related uranium mineralization abstract the paleoproterozoic statherian thelon formation consists of unmetamorphosed sandstone and conglomerate that was deposited in the thelon basin a continental basin in northern canada this study presents the first detailed sedimentological and sequence stratigraphic analysis of the expansive and under studied western thelon basin and its relation to uranium mineralizing processes in the vicinity of the boomerang lake unconformity related u prospect four lithofacies comprise the thelon formation in the western thelon basin consisting of breccia conglomerate sandstone and minor mudstone these are grouped into four facies associations that represent deposition in alluvial fans and braided fluvial streams three stratigraphic sequences were identified based on the recognition of widespread surfaces that mark significant periods of subaerial exposure or changes in depositional environment these unconformity bounded sequences are composite in nature and can be subdivided into six high frequency sequences hfs low accommodation and high accommodation systems tracts are delineated instead of the traditional systems tracts that are linked to changes in relative sea level as no marine deposits are recognized in the thelon formation two significant strataform paleohydrogeological units were distinguished in the thelon formation based on the relative timing of key diagenetic events such as compaction grain dissolution and cementation diagenetic aquicludes became isolated from basinal fluid flow due to stylolite catalyzed early diagenetic quartz cementation and occlusion of secondary intergranular macroporosity by kaolinite and muscovite and minor dickite during later peak diagenesis diagenetic aquifers conducted u bearing basinal fluids throughout diagenesis and are marked by an abundance of peak diagenetic dickite sequence stratigraphic correlation indicates that diagenetic aquicludes which were not effective at conducting u bearing basinal fluids overlie the unconformity at the boomerang lake prospect and extend along the entire strike length of a related exploration trend in contrast thick diagenetic aquifers lie approximately 10 km to the north of the boomerang lake prospect along a different exploration trend the western and eastern portions of the thelon basin experienced depositional environments and diagenetic conditions distinct from one another suggesting that they were separate sub basins the western thelon basin contains fewer of the well cemented facies that compartmentalized basinal fluid flow than the eastern thelon basin and contains a kaolin dominated diagenetic mineral assemblage rather than a muscovite dominated assemblage that is common in the eastern thelon basin in these regards the western thelon basin evolved more similarly to the eastern portion of the athabasca basin where thick regional kaolin rich diagenetic aquifers were fluid conduits for the movement of the u rich fluids that formed high grade unconformity related u deposits

development of coarse grained facies in lacustrine rift basins examples from east africa detailed studies of high resolution and multifold seismic reflection data from the two largest east african rift lakes malawi and tanganyika reveal a complex suite of coarse grained depositional facies these facies occur within specific regions of the controlling half grabens that compose the rift lakes sand prone environments include subaqueous channels and small drowned fluvial complexes channel systems range from large erosional canyons to deep water turbidite channel levee systems lowstand and highstand deltas of axial and shoaling side rivers are volumetrically important coarse grained facies fan deltas develop along the base of major border faults during lake lowstands subaqueous talus fan deposits occur along the base of the border faults during lake highstands lowstand deltas are the best preserved progradational facies in these rift lakes in addition to simple tectonic control drastic tectonically or climatically induced lake level change significantly regulates the production of coarse grained lacustrine synrift deposits

provenance of the proterozoic thelon basin nunavut canada from detrital zircon geochronology and detrital quartz oxygen isotopes abstract the paleoproterozoic thelon basin in nunavat canada is one of several large quartz dominated sedimentary basins developed on paleoproterozoic and archean rocks of the canadian shield coarse grained quartz to sub feldspathic sandstones and conglomerates of the thelon formation comprise the basin fill detrital zircons from the thelon formation have lam icp ms 207 pb 206 pb ages ranging from 3 94 to 1 78 ga but most are neoarchean 2 70 2 50 ga the 18 o values of quartz range from 7 7 to 13 9 and are typically 10 12 ages u zr ratios and oxygen isotopic compositions of detrital quartz are consistent with a predominantly neoarchean metasedimentary source such as surrounds the eastern thelon basin and comprises the bulk of basement rocks within the rae domain the three stratigraphic sequences of the thelon formation have 18 o ranges for detrital quartz and zircon ages that further constrain the source areas and support previous sequence stratigraphic interpretations the lower sequence contains reworked siltstone and sandstone clasts and 2 50 1 85 ga zircons indicating a contribution from paleoproterozoic terranes detrital quartz 18 o values range from 9 8 to 13 9 indicating a metamorphic source also which is consistent with a proximal source for the lower sequence the middle sequence contains zircons exhibiting the widest range of ages 3 94 1 78 ga a 3 4 ga paleoarchean zircon population cannot be correlated to the immediately surrounding basement and therefore indicates a distal source possibly in the order of 1000 2000 km away the upper sequence contains relatively few zircons due to extensive alteration but ages are predominantly early paleoproterozoic and neoarchean the upper sequence strata contain the lowest 18 o values of quartz indicating an influx of granitic material late in the depositional history of the basin the geochronology and geochemistry of detrital grains within the thelon formation indicate that the source areas evolved from predominantly proximal to distal and back to proximal as the basin filled

architecture and origin of an amalgamated fluvial sheet sand lower castlegate formation book cliffs utah abstract amalgamated fluvial sheet sandstones in the stratigraphic record are often interpreted as the deposits of braided rivers alluvial sequence stratigraphic models show these sheet sandstones overlying sequence boundaries and deposited during low rates of base level rise and fall since sequence stratigraphic models rely on the balance between creation destruction of accommodation and sediment supply is the sheet like nature of these units controlled by channel style by aggradation rates tied to base level changes or a combination of both the lower member of the castlegate formation in the book cliffs of eastern utah u s a was selected to answer these questions regarding the origin and architecture of amalgamated sheet sandstones the lower castlegate is 60 m thick and is underlain by a regional sequence boundary delineation of the alluvial architecture utilized a combination of outcrop photography measured sections and paleochannel dimension estimation at two outcrops in the type area architectural components within the outcrops were defined and include 1 basal thalweg fill units 2 inclined sandy or heterolithic barform deposits and 3 overbank siltstone and mudstone thalweg fill units represent deposition in the topographically lowest part of the channel and are preferentially preserved thalweg units exist as single units or as a composite of multiple thalweg units overlying thalweg units inclined barform deposits are in places preserved and genetically linked to an underlying thalweg fill unit bar accretion directions when combined with paleocurrent indicators show that lateral downstream and upstream accretion all occur in the lower castlegate overbank deposits are rarely preserved but where present they typically overlie bar deposits the architectural components stack to form a threefold cyclic hierarchy of 1 channel bar systems 2 12 m thick 2 channel belts 2 16 m thick and 3 stacked channel belt complexes 17 40 m thick complete channel bar systems are rarely preserved and occur locally as a succession of multiple stacked thalweg fill units the lack of barforms within a composite thalweg unit suggests that channel migration is the dominant process controlling preservation within channel bar systems possibly associated with a component of local avulsion channel belts are composed of stacked channel bar systems capped by a barform the barform is preserved due to a regional avulsion moving the active channel to another location within the floodplain isolating it from potential reworking stacked channel belt complexes are characterized by alternations of thalweg dominated and barform dominated channel belts the mechanism responsible for deposition at the stacked channel belt complex scale may be creation destruction of accommodation associated with base level changes paleochannel reconstructions show that channel flow depths using bar and underlying thalweg thickness were up to 7 6 m channel depth estimates utilizing a cross bed set thickness of 26 cm averaged 4 6 7 7 m these values were used to calculate channel widths which were estimated at 143 365 m up to a maximum of approximately 1 km regional paleoflow within the lower castlegate was dominantly southeast directed the architectural components paleochannel characteristics and paleocurrent data suggest the lower castlegate member was deposited in low to intermediate sinuosity rivers influenced by autocyclic processes at smaller scales and allocyclic processes at the larger outcrop scale

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

the proterozoic thelon paleosol northwest territories canada abstract beneath the 1 72 ga thelon formation in the northwestern part of the canadian shield an unmetamorphosed and undeformed paleosol is preserved on a variety of paleoproterozoic and archean protoliths this paper documents the paleosol referred to as the thelon paleosol in four localities where it developed on leucocratic schist gneiss and granite the thelon paleosol is characterized by these ascending changes from fresh protolith through paleosol to the unconformity a saprolitic disruption of the protolith resulting in ped and ferran formation b reddening of the paleosol as a consequence of hematitization c increase in dissolution of feldspar plagioclase alkali feldspar increase in the degree of iron oxidation in biotite chlorite and garnet and an increase in the abundance of neoform kaolinite illite and hematite cement d a loss of tio2 fe2o3 total feo mno mgo cao na2o k2o p2o5 u zr rb sr ba e a gain of fe2o3 and f an increase in cia values the fabric of the parent material appears to be the only soil forming factor that locally influenced paleosol development in comparison to thin profiles developed on massive relatively impervious protoliths thick profiles have developed on metamorphic protoliths in which the fabric has allowed deeper penetration of paleoweathering fluids the behaviour of iron in the profiles particularly profile 2 with a granite protolith and an increase in hematite towards the top of the profiles suggests that the thelon paleosol formed under an oxidizing atmosphere subsequent deposition of quartzose conglomerate and sandstone of the thelon formation has caused compaction of the thelon paleosol and this compaction probably was responsible for the formation of stylocumulates in the paleosol during diagenesis of the thelon formation the influx of diagenetic fluids into the paleosol produced veinlets of quartz and hematite a newly recognized microcrystalline hydrated alumino phosphate sulphate mineral and widespread pseudomorphs of illite after pedogenic vermiform kaolinite

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

proximal braidplain deposits in the middle devonian malbaie formation of eastern gaspe quebec canada the middle devonian malbaie formation of eastern gaspe canada comprises sharply alternating conglomerate and sandstone units their petrography suggests derivation from the same source but palaeocurrents indicate different dispersal systems for the sand and gravel the principal conglomerate facies is horizontally stratified with well developed imbrication characteristic of deposition on a high energy proximal braidplain minor cross stratified conglomerate shows well defined size sorting attributed to avalanching down foresets and sorting within minor bedforms on bar tops the sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts alternating with lineated low angle to horizontally stratified sandstone or trough cross stratified sandstone the sandstone units were deposited on a proximal braidplain with highly variable discharge but the absence of calcrete indicates that dry periods were not prolonged the malbaie is the coarsest uppermost formation of a devonian clastic wedge formed during the acadian orogeny the uniformity of facies association and palaeocurrents particularly in conglomerate units indicates derivation from a broad upwarp to the south this implies that the acadian uplands resulted from straight compression in contrast to the localized uplifts formed by strike slip faulting during the carboniferous

sedimentary structures exposed in bar tops in the brahmaputra river bangladesh the brahmaputra river is one of the world s largest sand bed braided rivers with a channel belt up to 15 km wide a mean channel depth of 5 m and maximum scour depths of up to 40 m the recorded discharge varies by around 60 000 cumecs every year following the annual monsoon producing dramatic stage fluctuations with the water level falling between 7 and 8 m from bankfull to low flow stage in the dry season large areas of bar top and channel bed are exposed and low flow channels cut natural sections through bar tops exposing the internal stratification elements of upstream downstream and lateral accretion are identified although the high width depth ratio of channels up to 500 1 results in extremely low depositional dips on bed bounding surfaces within the accretionary elements vertical and lateral changes in sedimentary structures are ubiquitous and varied but some patterns can be discerned channel deposits are dominated by sinuous crested dunes and trough cross stratification upper stage plane bed lamination often with a very low angle depositional dip has been observed in beds up to 4 m thick and is generally found at the base of the exposed bar top sections trough cross stratification in bar tops occurs in sets from 0 1 m to 3 m thick with rapid vertical and lateral changes in set thickness very large sets of trough cross stratification 3 m thick do not occur in the bar top sections current ripple lamination is most abundant on the tops of bars with very high rates of climb associated with high rates of sediment deposition from these observations a generalised vertical sequence of bar top origin might include trough cross stratification overlain by upper stage plane bed lamination isolated sets of trough cross stratification truncated and capped by current ripple lamination this sequence which is considered to represent the deposits of a single flood may occur within the upstream downstream or lateral accretion elements however it should be noted that vertical and lateral changes in facies are extremely abundant with many changes in sedimentary structures and reactivation surfaces within each depositional episode

the lower cretaceous way group of northern chile an alluvial fan fan delta complex abstract alluvial fan sediments of the lower cretaceous coloso basin in northern chile were deposited in a half graben and derived from andesitic volcanics of a former island arc transport directions were towards the east away from the present day peru chile trench grain flow density modified grain flow and sheetflow processes were responsible for most of the sediment deposition with cohesive debris flows playing only a minor part an early phase of conglomerate deposition coloso formation into a restricted basin records the transition from proximal fan facies with abundant grain flows and remobilized screes to mid fan facies dominated by sheetflows stratiform copper mineralization near the top of the lower conglomerates is related to the unroofing of the jurassic island arc this mineralization comprises copper sulphide cemented sands and gravels and formed by the reaction of mineralized detritus with diagenetic and hydrothermal solutions a later phase of deposition lombriz formation includes sandstones siltstones and conglomerates with a source area different from the coloso formation this change in source may be related to strike slip tectonics as the basin extended the lombriz conglomerates pass distally eastwards into red sandstones and purple siltstones with thin limestones deposited under marine conditions this sequence is interpreted as a major fan delta complex it passes conformably into marine carbonates of the tableado formation signifying the complete drowning of the basin in lower cretaceous times

contrasting patterns of alteration at the wheeler river area athabasca basin saskatchewan canada insights into the apparently uranium barren zone k alteration system previous studies on athabasca basin unconformity related uranium deposits have focused on major deposits and have not investigated sites with barren alteration systems that could clarify some of the critical factors controlling mineralization processes a paragenetic study of the wheeler river area reveals the presence of minerals that formed during the diagenetic the main hydrothermal which is subdivided into early mid and late hydrothermal substages and the late alteration stages the diagenetic stage consists of early quartz overgrowths siderite rutile hematite and abundant dickite in the pore spaces of the manitou falls formation the early hydrothermal alteration substage is characterized by pervasive 1mc muscovite alteration and minor goyazite clusters which formed from oxidizing basinal fluids at temperatures around 240 c prior to 1550 ma based on ar ar dates the mid hydrothermal alteration substage comprises dravite and sudoite in the basal 200 m of the manitou falls formation which are interpreted to have formed at temperatures around 175 c from fluids chemically distinct but isotopically similar to the basinal fluids involved during the early hydrothermal alteration substage the late hydrothermal substage was observed only at zone k of the wheeler river area and is characterized by the precipitation of clinochlore copper sulfides and florencite from reducing basement fluids emerging into the manitou falls formation at temperatures around 230 c creating a 250 m high by 250 m wide reducing halo oxidized uranium bearing basinal fluids interacted with the manitou falls formation during the early hydrothermal substage prior to the arrival of the reducing fluids during the mid and late hydrothermal substages and this precluded uranium precipitation the post hydrothermal alteration stage is characterized by formation of kaolinite after late hydrothermal clinochlore near fractures by meteoric waters a minimal amount of leachable radiogenic pb with a pb pb model age of 1907 ma that is older age than both the athabasca basin and the main mineralization event of 1590 ma was encountered at zone k indicating low probability of this area to host uranium mineralization however areas of possible unconformity related uranium deposits were identified outside zone k wherein significant amounts leachable radiogenic pb were observed

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

precambrian sequence stratigraphy abstract sequence stratigraphy studies the change in depositional trends in response to the interplay of accommodation and sediment supply from the scale of individual depositional systems to entire sedimentary basin fills as accommodation is controlled by allogenic mechanisms that operate at basinal to global scales the change in depositional trends is commonly synchronized among all environments established within a basin thus providing the basis for the definition of systems tracts and the development of models of facies predictability all classical sequence stratigraphic models assume the presence of an interior seaway within the basin under analysis and are centered around the direction and types of shoreline shifts which control the timing of all systems tracts and sequence stratigraphic surfaces in overfilled basins dominated by nonmarine sedimentation the definition of systems tracts is based on changes in fluvial accommodation as inferred from the shifting balance between the various fluvial architectural elements the method of sequence stratigraphy requires the application of the same set of core principles irrespective of the age of strata under analysis from precambrian to phanerozoic the study of precambrian basins is often hampered by poorer stratal preservation and by a general lack of time control however where sedimentary facies are well preserved the lack of time control may be partially compensated by a good knowledge of facies architecture and relationships as well as by paleocurrent data the latter are particularly important to understand the stratigraphic record of tectonically active basins where abrupt shifts in paleoflow directions allow one to infer tectonic events and map the corresponding sequence bounding unconformities arguably the most important contribution of precambrian research to sequence stratigraphy is the better understanding of the mechanisms controlling stratigraphic cyclicity in the rock record and hence of the criteria that should be employed in a system of sequence stratigraphic hierarchy there is increasing evidence that the tectonic regimes which controlled the formation and evolution of sedimentary basins in the more distant geological past were much more erratic in terms of origin and rates than formerly inferred solely from the study of the phanerozoic record in this context time is largely irrelevant as a parameter in the classification of stratigraphic sequences and it is rather the stratigraphic record of changes in the tectonic setting that provides the key criteria for the basic subdivision of the rock record into basin fill successions separated by first order sequence boundaries these first order basin fill successions are in turn subdivided into second and lower order sequences that result from shifts in the balance between accommodation and sedimentation at various scales of observation irrespective of the time span between two same order consecutive events sequences identified in any particular basin are not expected to correlate to other first and lower order sequences of other basins that may be similar in age but may have different timing and duration

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada