model for the combined flow origin of hummocky cross stratification many shallow marine sandstones are characterized by gently dipping trough cross stratification there appear to be significant similarities between this low angle cross stratification and typical hummocky cross stratification and it is proposed that much of what is currently recognized as hummocky cross stratification is related to low relief megaripple bed forms that are equilibrium structures for fine grained sand under combined wave surge and unidirectional currents the geometry that obtains when these bed forms migrate is low angle trough cross stratification high rates of sedimentation from incipient suspension and limited lateral migration of individual bed forms promote preservation of convex upward depositional surfaces hummocks between troughs highly unsteady flow leads to abundant internal scour and drape surfaces neither random scour and drape nor oscillatory currents seem sufficient to generate hummocky bed forms

near bottom particle concentration and flux temporal variations observed with sediment traps and nepholometer on the meriadzek terrace bay of biscay abstract the meriadzek terrace a 2100m deep plateau on the north east atlantic continental slope was chosen as the experimental site for a multidisciplinary programme to observe the parameters needed for a better understanding of biological processes in the benthic environment two approaches were used to study the input of particulate matter to the bathyal seabed sediment traps and indirect particle concentration measurements with nephelometry these two technologies do not measure particles of the same size range but as we are interested in the fluctuations of the particle supply their results are complementary vertical profiles of nephelometry show that over the meriadzek terrace there is 125m thick nepheloid layer immediately above the bottom the dynamics in the deep layer has been determined by measurements made with a module autonome pluridisciplinaire map an in situ monitoring device developed at ifremer which measures currents nephelometry temperature vertical profile near the bottom throughout six months of measurements in 1984 the currents at 0 5m and 120m above the bottom were subject to semi diurnal tidal oscillations the intensity of light scattering recorded with the nephelometer on the map was highly correlated with current velocities especially with semidiurnal tidal oscillations which seem to induce local resuspension there are also longer term fluctuations notably a very strong event which lasted several days during august this event lagged behind a period of high intensity of internal waves correlated with a reversal in current direction the sediment trap pieges a particules pap observations showed that the particle fluxes on the meriadzek terrace have a cycle of variation similar to primary production which is characterized by a maximum in may during the phytoplankton bloom and a minimum during january there was also interannual fluctuation these two kinds of results point out the different time scales from some hours to several months of the large temporal fluctuations which affect the near bottom particle behaviour

the objectives and reationale of hebble abstract hebble s precise aim is to develop and to test explicit predictions about the response of adhesive cohesive marine sediments to imposed and controlled stresses pursuit of this goal has necessitated a coordinated interdisciplinary effort to date including physical oceanographers sedimentologists radiochemists and biochemists and biological oceanographers

noble gases ar kr xe and halogens cl br i in fluid inclusions from the athabasca basin canada implications for unconformity related u deposits the formation of unconformity related uranium deposits in the proterozoic athabasca basin canada involved basin scale circulation of u bearing brines during high grade diagenesis 150 200 degrees c at similar to 1 6 1 5 ga the uo2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite sudoite dravite alteration quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable na ca and salinities of 25 35 wt salts and high u concentrations of up to 600 ppm u in order to further constrain the origin of these u rich brines we analysed the naturally occurring isotopes of ar kr and xe together with halogens cl br and i k ca and u in irradiated quartz and dolomite samples containing representative fluid inclusions this was achieved by the noble gas method for halogen measurement extended ar 40 ar 39 methodology using a combination of noble gas extraction techniques the fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar br cl ratios of 5 8 x 10 3 to 10 4 x 10 3 and molar i cl ratios of 1 8 x 10 6 to 8 2 x 10 6 these compositions lie over the top half of the modern day seawater evaporation trajectory consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater beyond the point of halite saturation the i cl ratios are much lower than is typical of fluids that have interacted with i rich organic matter present in many sedimentary basins or fluid inclusions found in mississippi valley type mvt pb zn ore deposits this is significant because provided the u rich fluid inclusions are representative of the ore stage fluids the low i cl ratios of the fluid inclusions do not favour fluid interaction with organic matter or hydrocarbons as a major process for localising u mineralisation the majority of samples contain fluid inclusions with age corrected ar 40 ar 36 of between the modern atmospheric value of similar to 300 and 450 these values are considered representative of the fluid s initial composition and are typical of upper crustal sedimentary formation waters the fluid inclusions nonradiogenic kr 84 ar 36 and xe 129 ar 36 ratios are slightly enriched in xe 129 relative to air and the fluid inclusions are estimated to contain 0 5 17 3 x 10 10 mol g 1 ar 36 which is up to twenty times the ar 36 concentration of air saturated seawater the data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic ar 40 within k rich basement rocks that would have been an important source of excess ar 40 was limited by temperatures of less than 200 degrees c taken together the halogen and noble gas composition of the u bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks showing that low temperature evaporitic brines dominated the mineralising system mineralisation is unlikely to have been triggered by fluid interaction with organic matter or mixing with voluminous basement derived fluids however the data do not completely preclude a role for volumetrically minor fluid or gas phases introduced by deep seated basement faults preferentially located at the sites of mineralisation

extreme light rare earth element mobilization by diagenetic fluids in the geological environment of the oklo natural reactor zones franceville basin gabon the anomalously high th la ratio 1 14 of the early proterozoic silicified sandstones of the franceville basin gabon compared to archean and proterozoic metasedimentary rocks th la 0 27 results from extreme light rare earth element ree migration during diagenesis monazite which represents the main light ree bearing phase in the sandstones was altered by diagenetic brines at 140 c and 1 kbar the alteration phase is a microcrystalline th silicate phase indicating low th solubility at these conditions light rees are simultaneously leached out together with p and u the increase in th la from detrital monazite to residual th silicate phase indicates that about 76 of the light rees were leached out corresponding to a global amount of 2 01 109 metric tons at the scale of the fa formation in the franceville basin uranium was also leached during monazite alteration and may have contributed significantly to the genesis of the high grade uranium deposits of the franceville basin that host the natural nuclear reaction zones

abraded sand volcanoes as a tool for recognizing paleo earthquakes with examples from the cisuralian talchir formation near angul orissa eastern india abstract one of the bedding planes of a sandstone unit belonging to the cisuralian talchir formation is well exposed along the nandir jhor river in eastern india it shows a few dozens of circular structures commonly with diameters of a few decimetres a concentration is found in an area of some 50 m 2 where 12 well developed specimens occur the structures are interpreted as abraded sand volcanoes which interpretation is supported by the occurrence on the same bedding plane of a sand volcano with a diameter of over a meter the concentrated structures thus represent a sand volcano field a phenomenon that has not been recognized earlier in the pre holocene geological record but that in recent times seems always to be related to an earthquake the structures described here might therefore help to recognize earthquakes that occurred in the geological past

hummocky cross stratification and post vortex ripples length scales and hydraulic analysis duke 1987 argues that the structure reported by greenwood sherman 1986 as hummocky cross stratification from a shallow lacustrine environment is instead bedding formed by simple post vortex oscillation ripples his primary concern is with the length scale of the structures identified in box cores however using measured flow data it is shown here that existing models of bedform generation based upon wave orbital velocity orbital diameter and grain diameter do not support a simple post vortex ripple interpretation in particular the relative steepness of the structure refutes such an origin the structural characteristics of the lacustrine cores most closely match those associated with classic hummocky cross stratification and were produced under a combined oscillatory quasi steady flow field

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

crandallite group minerals in the helikian athabasca group in alberta canada members of the crandallite group of aluminous hydroxy phosphates are present in trace amounts in every formation of the athabasca group in alberta the minerals of the group present in alberta form a solid solution series with end members goyazite sral3 po4 oh5 crandallite caal3 po4 oh5 and gorceixite baal3 po4 oh5 these minerals are present as cubes and subhedral grains 2 20 m across in isolation or in clusters interstitially in the athabasca group sandstones siltstones and tuffs petrographic study indicates an authigenic origin for the crandallite group minerals in the athabasca group their presence locally beneath quartz overgrowths and early diagenetic fluorapatite suggests formation very early in the post depositional history of the rock the presence of the crandallites within the regolith beneath the athabasca group and within a metamorphic rock fragment incorporated into the sandstone suggests more than one origin for the minerals and possibly a detrital component

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

clay mineralogy and isotope geochemistry of the alteration halo at the cigar lake uranium deposit the clay size fraction of the alteration halo associated with the cigar lake uranium deposit consists of illite with subordinate kaolinite sudoite al chlorite fe chlorite hematite and traces of an illite chlorite mixed layer mineral the kubler index of illite crystallinity ranges from 2 0 to 6 7 the most altered samples average 4 0 these data indicate that high grade diagenetic to anchizonal conditions have been reached within the alteration halo intensity ratios of the 002 and 001 illite reflections i 002 i 001 are generally greater than 0 4 the phengite muscovite boundary reflecting aluminum rich illites illite composition approaches hydromuscovite whereas 1m and 2m polytypes prevail regionally the presence of 3t and 2m polytypes in the alteration halo suggests that locally higher temperatures have been attained than the regional estimates of 180 220 c k ar dates for illite rich samples from 1255 to 1148 ma could reflect variable resetting of the k ar system during hydrothermal f

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

bedforms and bed material transport pathways in the changjiang yangtze estuary abstract bed features were mapped using a thermal depth recorder and a side scan sonar in the changjiang yangtze estuary and flows were observed and bed surface materials were sampled to investigate bed material transport pathways distinct scales and dimensions of dunes were observed in terms of the classification scheme of ashley ashley g m 1990 classification of large scale sub aqueous bedforms a new look at an old problem journal of sedimentary research 61 160 172 forming a dune set in the flood season large dunes occurred predominately in the surveyed area of the estuarine zone and two dimensional dunes predominated in the dry season while three dimensional dunes prevailed in the flood season sharp lee sides of dunes have low angles indicating a significant suspended load transport for the bedform migration and the majority of them face down estuary reflecting the controlling process by the ebb current the bed material migrations in terms of relative maximum gross transport show a satisfactory agreement with the sonar mapping in the dry season the relative maximum gross transport as an independent estimator of migration direction can be used to effectively determine the bed material transport directions in the changjiang estuary

a relative water depth model for the normandy chalk cenomanian middle coniacian paris basin france based on facies patterns of metre scale cycles abstract a relative water depth model for the chalk of the paris basin is proposed based on the lateral variations of the high frequency metre scale cycles which are characteristic features easily identified in the field the studied outcrops are the cenomanian middle coniacian cliffs of normandy the main result of this study is to highlight the importance of storm activity in the deposition of the chalk the relative water depth model is based on storm induced shell concentrations observed within the two components of the metre thick cycles the depositional interval itself and the top hiatal surface six types of shell concentrations are defined along with seven types of depositional facies making up the depositional units as well as eight types of hiatal surface three cycle associations differing in their thickness and the amount and type of non carbonate constituents can be identified in the lower to upper cenomanian the upper cenomanian to lower turonian and the middle turonian to middle coniacian a relative water depth profile model for all these cycles is based on the shell concentrations and a water depth equivalence is proposed between the three cycle associations lateral facies substitution diagram this model is tested using palaeocological data irregular echinoids and by correlating field sections in terms of stacking patterns most of the studied deposits accumulated above the storm wave base upper offshore zone or mid ramp

quantifying aluminium phosphate sulphate minerals as markers of acidic conditions during the permian triassic transition in the iberian ranges e spain abstract in this paper a method based on element mapping of randomly selected areas of thin sections on electron microprobe is proposed to quantify the relative contents of strontium rich hydrated aluminium phosphate sulphate aps minerals in siliciclastic continental sedimentary rocks the main problems for these minerals to be quantified are related to their small size low concentrations and optical properties by comparing the element maps obtained for the rocks in the study area of the iberian ranges e spain with the results of whole rock analysis and with factors indicating the presence of life bioturbation palaeosols and macro plant remains it has been possible to correlate relatively high levels of aps minerals in the first sedimentary record canizar formation after the permian triassic boundary with the lack of living organisms the aps are related to early diagenetic phases precipitated at low ph conditions and are therefore markers of formation in an acidic environment our findings suggest a long period of sustained acidic conditions followed by an environmental change linked with the recovery of life and with lower aps mineral contents this change is detected at the top of the canizar formation at the end of the spathian the method proposed could be used as a tool to address the environmental changes that took place during the permian triassic transition in continental environments

uranium deposits of franceville basin gabon role of organic matter and oil cracking on uranium mineralization abstract the lower proterozoic uranium deposits in the franceville basin gabon are mainly known to have hosted natural nuclear reactors however this basin also witnessed a former petroleum system which shows major occurrences of uranium ores associated with organic matter the uranium mineralization is the result of several episodes of oil generation and migration fluid mixing and hydrofracturing during burial at around 2 0 ga black shales were heated and expelled hydrocarbons which migrated in underlying sandstones the first episode of oil migration was synchronous with a silicification event produced by a hot low salinity fluid as shown by fluid inclusions trapped in quartz overgrowths the second episode was contemporaneous with quartz dissolution and is characterized by the mixing of hydrocarbons and oxidizing u bearing brine which resulted in the precipitation of uo2 inclusions in oil then oil to gas conversion generated overpressured gas trapped in pores with uraniferous bitumen nodules changes in the stress regime probably favored radial hydrofracturing around bitumen nodules and subsequently the development of a pervasive micro fracture network there uo2 precipitated together with cu fe sulfides through thermochemical sulfate reduction favored by the presence of hydrocarbons and methane

magmatic and metamorphic uraninite mineralization in the western margin of the trans hudson orogen saskatchewan canada a uranium source for unconformity related uranium deposits the genetic model for the giant unconformity related uranium deposits of the athabasca basin is still being debated with one of the main issues being the source of the uranium concentrated by mesoproterozoic era ca 1 60 1 00 ga diagenetic hydrothermal events at the interface between the athabasca basin and the underlying archean paleoproterozoic basement rocks currently accessory minerals like monazite zircon and or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high grade uranium deposits numerous occurrences of u mineralization of hudsonian age have been documented for decades all around the athabasca basin however so far these have not been regarded as viable u sources here a systematic and detailed study of two areas of basement rocks near the eastern part of the athabasca basin is presented i e the way lake property lying outside the current margin of the basin and the moore lakes property currently covered by the basin this study highlights the significant and widespread occurrence of hudsonian ca 1 81 1 76 ga uranium oxide uo2 mineralization in these zones two types of mineralization are identified and documented here magmatic uranium oxides related to granitic pegmatites and leucogranites which are more common and high temperature vein hosted uranium oxides which have the highest grades the two types were formed during the peak 1 82 1 81 ga and or postthermal peak 1 81 1 72 ga events related to the evolution of the trans hudson orogeny the magmatic uranium oxides formed by partial melting of wollaston group metasedimentary rocks the origin of the vein type occurrences is unclear but their high thorium and rare earth element ree contents suggest a high temperature process associated with ca and or na metasomatism the uranium oxides are associated with other u th and reebearing accessory minerals like u rich thorite thorite zircon and or monazite adding to the exceptional u contents 100 2 460 ppm of these uo2 bearing rocks up to 200 times more primarily enriched in u than other basement or basin rock types a 3 d model of a 1 300 630 200 m basement zone from the way lake property indicates that uraninite bearing granitic pegmatites and leucogranites represent 7 of the total volume of crystalline rock within this rock volume are approximately 8 121 assuming a mean u content of 250 ppm to 16 242 assuming a mean u content of 500 ppm tonnes u the u tonnage of this limited rock volume contained mainly by the hudsonian age uo2 corresponds to between 4 for mcarthur river and 103 for rabbit lake of the u tonnage of known unconformity related u deposits of the basin some of the studied rock samples even macroscopically fresh and located far away from any known unconformity related u deposit present clear evidence of alteration including clay minerals aluminophosphatesulfate aps minerals and uo2 dissolution indicating the percolation of the brines associated with the formation of unconformity related uranium deposits when the basin was far more geographically extensive due to geologic similarities between the studied zones and the basement domains from the eastern part of the athabasca basin i e the hearne province it is proposed that these domains hosted widespread hudsonianage uranium oxide protores these protores provided easily leachable uranium for the metal enrichment of basinal brines during their percolation within the basement and the formation of the unconformity related u deposits these observations bring new insight to the debate about the genetic model of unconformity related u deposits and reinforce the metal source potential of the basement compared to that of the sedimentary basin

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

spatial distribution and compositional variation of aps minerals related to uranium deposits in the kiggavik andrew lake structural trend nunavut canada the kiggavik andrew lake structural trend consists of four mineralized zones partially outcropping lying 2 km south of the erosional contact with the unmetamorphosed sandstone and basal conglomerates of the paleoproterozoic thelon formation the mineralization is controlled by a major e w fault system associated with illite and sudoite alteration halos developed in the archean metagraywackes of the woodburn lake group aluminum phosphate sulfate aps minerals from the alunite group crystallized in association with the clay minerals in the basement alteration halo as well as in the overlying sandstones which underwent mostly diagenesis aps minerals are sr and s rich svanbergite end member in the sedimentary cover overlying the unconformity whereas they are light rare earth elements lree rich florencite end member in the altered basement rocks below the unconformity the geochemical signature of each group of aps minerals together with the petrography indicates three distinct generations of aps minerals related to the following 1 paleoweathering of continental surfaces prior to the basin occurrence 2 diagenetic processes during the burial history of the lower unit of the thelon sandstones and 3 hydrothermal alteration processes which accompanied the uranium deposition in the basement rocks and partially overlap the sedimentary diagenetic mineral parageneses in addition the association of a first generation of aps minerals with both detrital cerium oxide and aluminum oxy hydroxide highlights the fact that a part of the detrital material of the basal thelon formation originated from eroded paleolaterite allochthonous regolith the primary rare earth element ree bearing minerals e g monazite ree carbonates and allanite of the host rocks were characterized to identify the potential sources of ree the ree chemical composition highlights a local re incorporation of the ree released from the alteration processes in the aps minerals of hydrothermal origin the distinctive geochemical signatures between diagenetic or sedimentary and hydrothermal aps minerals suggest a different source material in the thelon basin than in the athabasca basin

paleoproterozoic sediment recycling during multiphase orogenic evolution in fennoscandia the tampere and pirkanmaa belts finland abstract geochronology of detrital zircons and their overgrowths combined with whole rock geochemical and sm nd isotopic data can be used to distinguish different stages of sediment recycling and metamorphism during multiphase orogenic evolution this approach is applied to the paleoproterozoic sedimentary rocks of the tampere and pirkanmaa belts southern finland in the center of the composite svecofennian orogen the lower part of the tampere belt succession and bulk of the pirkanmaa belt are characterized by turbidites whereas the upper part of the tampere belt succession is dominated by 1 90 1 89 ga mature arc type volcanic rocks detrital zircon geochronology indicates that the tampere and pirkanmaa belts have a coeval 1 92 1 89 ga depositional and tectonic history ages of pre depositional zircon overgrowths vary from 1 91 ga to 2 0 ga with clusters at 1 92 ga and 1 98 ga within the pirkanmaa belt post depositional zircon overgrowths indicate metamorphic culmination at c 1885 ma in the vammala ni zone and at c 1875 ma in the northern part the lower conglomerates and graywackes in the tampere belt and their equivalents in the pirkanmaa belt are rich both in neoarchean and paleoproterozoic grains the latter ranging in age from 1 9 to 2 1 ga compared to these a sample from the vammala ni zone has an exotic provenance with at least c 1 90 ga 2 04 2 15 ga 2 38 2 48 ga and 2 57 2 63 ga components a sedimentary recycling and tectonic model for the central fennoscandia is proposed in which the paleoproterozoic keitele bergslagen continent was formed during an unnamed orogeny at 1 98 1 97 ga the archean norrbotten microcontinent was attached to the continent at 1 97 1 93 ga upper kaleva turbidites derived from the lapland kola orogen in the north were deposited before 1 92 ga on a passive margin of the archean karelia craton the karelia craton collided with the keitele bergslagen norrbotten continent at c 1 92 ga forming the lapland savo orogen subsequent evolution led to rifting and break up of the latter continent into two microcontinents in the hinterland at 1 92 1 91 ga the rift was developed into a subsiding passive margin of the keitele microcontinent with voluminous turbidite deposition now seen as graywackes in the tampere pirkanmaa and pohjanmaa western finland belts the turbidite material was derived from the rising lapland savo orogen and included recycled upper kaleva recycled sandstones and first cycle 2 03 1 97 ga detritus from keitele 1 93 1 92 ga savo arc material as well as detritus from the archean craton and its cover deposits the collision between karelia and keitele caused a subduction reversal and the onset of tampere arc volcanism at 1 90 ga arc derived materials started to deposit and were mixed with older sedimentary rocks and trench parallel distal turbidites from exotic source were being deposited in the accretionary wedge

facies flow and bedform patterns across a storm dominated inner continental shelf proterozoic kaimur formation rajasthan india abstract a comprehensive sedimentation model for an epeiric sea useful for further comparison and prediction is derived crom the proterozoic kaimur formation rajasthan india facies analysis of a steadily regressive shale quartz arenite sequence documents the patterns of flow sediment transport and deposition from beach to offshore across a storm dominated gently sloping

hummocky cross stratification is not produced purely under progressive gravity waves hummocky cross stratification is a type of bedding in sedimentary rocks caused by the draping of sand around low steepness three dimensional bedforms this distinctive form of stratification has been thought to be diagnostic of the former action of storm waves and hence its occurrence has been used to reconstruct ancient palaeogeographies and marine processes here i examine theoretical and empirical aspects of hummocky cross stratification pertaining to its origin and argue that the notion that it was produced purely under progressive storm waves is incompatible with observed hummock spacings and possible values of the ratio a under waves a is the amplitude of oscillation near the bed and is the bedform spacing my view is supported by recent observations on naturally occurring hummocky megaripples from the sea floor of the inner atlantic shelf of north america

stable isotope geochemistry of alteration associated with the key lake uranium deposit canada the key lake uranium deposit occurs within a shear zone that intersects the unconformity between early proterozoic basement gneiss and overlying middle proterozoic athabasca group sandstone uranium is concentrated near the unconformity and is associated with intense illite chlorite and kaolinite alteration the delta d and delta 18 o values of the clay minerals suggest that several different fluids have affected the ores and surrounding host rocks alteration of the basement gneisses associated with the uranium mineralization consists mainly of mg chlorite that equilibrated about 200 degrees c with a fluid having a delta d value near 20 per mil and a delta 18 o value near 5 per mil an illite rich sandstone alteration halo preserved only locally above the deposit equilibrated about 200 degrees c with a basinal brine having a delta d value near 65 per mil and a delta 18 o value near 5 per mil the uranium was concentrated near the unconformity by the mixing of these two distinct fluids the delta 18 o values of coexisting quartz and illite sampled from the shear zone hosting the uranium mineralization yield equilibration temperatures of 190 degrees to 230 degrees c which is postulated to be the temperature of the ore forming event fracturing in the sandstone above the deposit controlled late low temperature 50 degrees c kaolinitization of preexisting hydrothermal illite and chlorite by meteoric waters having delta d values of 50 or 30 per mil and delta 18 o values of 7 or 3 per mil the youngest event to affect the key lake deposit is related to the influx of modern meteoric waters that have lowered the delta d values but not greatly affected the delta 18 o values of some of the clay minerals associated with the shear and breccia zones this latest event has recrystallized much of the hydrothermal mg chlorite associated with the uranium to produce an fe mg chlorite with delta d values as low as 170 per mil

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

clay alteration associated with proterozoic unconformity type uranium deposits in the east alligator rivers uranium field northern territory australia clay minerals associated with the unconformity type uranium deposits of the east alligator rivers uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of uranium deposition within the altered basement underlying the kombolgie unconformity alteration develops a similar pattern at regional and smaller scales with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity e g faults fractures breccias these discontinuities were mechanically active during the hydrothermal activity the hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks the time space alteration sequence established in this study can be summarized as follows 1 early crystallization of illite illite smectite i s mixed layer minerals lree sr bearing aluminum phosphate sulfates aps in sandstones above the unconformity illite i s mixed layer minerals sudoite aps on both sides of the unconformity and in fault gouges and illite i s mixed layer minerals chlorite apatite deeper in the basement and 2 late precipitation of chlorite in the open fracture network mainly centered below the unconformity the main stage of uranium deposition was associated with chloritization in the basement rocks smaller particle size lath shaped or flaky morphology common interstratification with expandable layers lower crystallinity and mg rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and or chlorite hydrothermal illite can be distinguished from diagenetic and metamorphic illite phengite by its poor crystallinity along the c axis interstratification with minor amounts of smectite layers and a 1m polytype in which trans vacant octahedral sites predominate 1 mt chemically the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher mg content the hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size spherulitic habit poor crystallinity along the c axis and common association with corrensite and or chlorite corrensite mixed layers most of the hydrothermal chlorite is mg rich and has a structural formula close to that of clinochlore xfe 0 20 near the uranium deposits the spherules of hydrothermal chlorite are chemically zoned from xfe 0 10 to xfe 0 40 which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization the space time alteration sequence established for clay minerals and the observed transition of aps to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub basinal brines in turn these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron bearing phyllosilicates fe chlorite and biotite and iron sulfides of metamorphic origin the ore deposits are surrounded by zones in which the degree of fluid rock interaction was very high and chloritization is most abundant the octahedral mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of uranium orebodies in the basement rocks tens to hundreds of meters below the crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30 to 50 c lower than those expected at the peak diagenesis of the kombolgie sandstones near the unconformity

authigenic aluminium phosphate sulphates in sandstones of the mitterberg formation northern calcareous alps austria complex aluminium phosphate sulphate minerals of the hinsdalite group have been identified as early diagenetic precipitates in late permian sandstones of the northern calcareous alps western austria according to their chemical composition they can be regarded as solid solutions between woodhouseite svanbergite crandallite and goyazite the model proposed for their origin involves the dissolution of detrital apatite in a low ph environment and subsequent precipitation of aluminium phosphate sulphate minerals which clearly pre date syntaxial quartz cementation of the sediment their occurrence probably has been overlooked in other sandstones showing diagenetic apatite dissolution the recognition of such minerals could provide a significant insight into early phosphate diagenesis

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

uraniferous paleoplacers of the mesoarchean mahagiri quartzite singhbhum craton india depositional controls nature and source of 3 0 ga detrital uraninites abstract the quartz pebble conglomerate qpc hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2 2 ga atmosphere during pre great oxidation event pre goe such qpc paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content the mahagiri quartzite dated c 3 02 ga for their youngest detrital zircon population is developed unconformably over the mesoarchean singhbhum granite 3 44 ga to 3 1 ga the mahagiri quartzite includes a conglomerate pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts the alluvial fan braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds the uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin together with detrital pyrite and uraninite constitute the example of 3 0 ga paleoplacer closely comparable to the witwatersrand au u deposits epma and sem eds studies suggest that the uraninite grains are rich in th 4 wt s and ree y chemical formula calculations from epma analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from y ree and cation u4 u6 apfu ratios the u contents of the detrital uraninite grains from mahagiri are significantly lower than that of the ideal stoichiometric composition of uo2 this is mainly due to higher amount of heterovalent cationic substitution by th ree y pb and ca in mahagiri qpc uraninite structures and partial alteration and metamictization of uraninites alteration due to metamictization resulted in elevated concentration of si al p and ca in more altered and metamict uraninite grains the ree pattern is typically flat with comparable lree hree concentration the high th content flat ree pattern suggests that the uraninitere presents high temperature phases 350 c and are magmatic in origin the mahagiri detrital uraninite grains suggest existence of highly felsic and k rich richer than ttg granodiorite granite monzogranite suites ggm of rocks older than 3 1 ga in the singhbhum craton

geochemical modeling of the formation of an unconformity type uranium deposit petrologic studies of alteration associated with uranium mineralization in unconformity type uranium deposits have established a detailed paragenetic sequence of the preore and synore alteration in addition fluid inclusion studies have determined the presence of two distinct fluids and thermodynamic analysis of the alteration assemblages has defined their basic characteristics these fluids were probably basinal brines derived from the overlying sandstones and have been distinguished by their different salinities fluids responsible for alteration and ore formation were na ca cl brines speciation calculations suggest that the hydrothermal fluids responsible for the formation of unconformity type uranium deposits were distinguished by their high oxygen fugacity and relatively low ph uranium was transported mainly as uranyl chloride complexes reconstruction of the reactions associated with the formation of the deposits employing chemical mass transfer calculations helps unravel the geochemical processes operating during their genesis reaction path calculations indicate that fe present in aluminosilicates in the host rocks is the principal reductant of oxidized uranium present in the ore forming fluids the use of variable host rock lithologies results in the reproduction of mineralogical features unique to each deposit along with the characteristics common to all unconformity related uranium deposits the calculations show that the observed paragenesis is a function not only of the fluid chemistry but also of the host rock lithologies the modeling indicates that although an orebody can be produced with or without graphite as a reactant its presence leads to a better agreement with the observed alteration paragenesis

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

quaternary coastal plains as reservoir analogs wave dominated sand body heterogeneity from outcrop and ground penetrating radar central santos basin southeast brazil abstract sub seismic sand body characterization depends largely on understanding the heterogeneities observed in outcrops of equivalent depositional settings to subsurface reservoirs reservoir analogs outcrop information however rarely covers the whole depositional system ground penetrating radar gpr on the other hand is a powerful tool for the high resolution visualization of sand rich deposits in the shallow subsurface allowing for the description of their internal architecture relationships with depositional systems and its larger scale stratigraphic evolution the internal character of radar patterns can be interpreted with respect to facies seen in exposures leading to the prediction of heterogeneities below radar resolution in this paper we use gpr and outcrops to describe the heterogeneity of quaternary coastal plain deposits from central santos basin parana state southern brazil where pleistocene and holocene wave dominated regressive barriers and transgressive lagoons and estuaries were formed under the influence of quaternary sea level and climatic changes sedimentary facies reveal the predominance of sand deposited under the influence of tidal processes fair weather and storm wave processes radarfacies indicate a tendency of progradation of beach face reflectors over subtidal radarfacies within two regressive successions separated by a regional unconformity interpretation of gpr resulted in the definition of 13 radarfacies arranged in three associations reflecting major depositional systems 1 strandplains formed by prograding beach dune ridge sets over subtidal deposits 2 spit inlets with progradation of beach faces over subtidal deposits and longshore accretion of spits and 3 paleolagoons paleoestuaries sedimentary facies indicate that strandplains and spit inlets are predominantly sandy while a muddy composition is expected in paleolagoons paleoestuaries the distribution and evolution of these systems were controlled by base level oscillations and or sediment supply that resulted in the formation of two regressive barriers separated by a wave ravinement surface configuring two parasequences with a wide variety of inter and intra sand body heterogeneities this arrangement imprints a relatively high degree of compartmentalization within deposits that are traditionally considered continuous and homogeneous therefore the quaternary coastal plain of parana can be used as an analog for compartmentalized coastal reservoirs

shallowing upward cycles in pelagic troughs upper jurassic subbetic southern spain abstract abundant calcareous tempestites with chert and hummocky cross stratification hcs occur in upper jurassic successions milanos formation of the subbetic betic cordillera southern spain these calcareous tempestite beds are calcisiltites and very fine calcarenites with peloids and bioclasts and have thicknesses between 25 and 75 cm beds show symmetrical wave ripple lamination near the top and are usually capped with wave ripples according to palaeogeographic reconstructions these strata were deposited in a subsiding trough in the pelagic domain of the southern iberian continental margin which was the northwestern most border of the tethys calcisiltite and calcarenite beds deposited in this pelagic trough form small scale to large scale shallowing upward cycles shallowing upward cycles with calcareous tempestites in the lower part and oolitic limestone beds in the upper part have also been recognized in some sectors of the subbetic pelagic basin the large scale cycle occurs in the upper part of the jarropa radiolarite formation which directly underlies upper oxfordian kimmeridgian and tithonian strata of the milanos formation two types of large scale shallowing upward cycles have been recognized according to the presence or absence of thick units of oolitic limestone with large scale cross stratification the water depth during deposition ranged from below but near storm wave base at the base of the large scale cycles to very shallow carbonate platform at the top

unconformity related rare earth element deposits a regional scale hydrothermal mineralization type of northern australia rare earth element ree orebodies are typically associated with alkaline igneous rocks or develop as placer or laterite deposits here we describe an economically important heavy h ree mineralization type that is entirely hydrothermal in origin with no demonstrable links to magmatism the mineralization occurs as numerous xenotime rich vein and breccia orebodies across a large area of northern australia but particularly close to a regional unconformity between archean metasedimentary rocks of the browns range metamorphics and overlying proterozoic sandstones of the birrindudu group the deposits formed at 1 65 to 1 61 ga along steeply dipping faults there is no known local igneous activity at this time depletion of hrees in the browns range metamorphics together with the similar nonradiogenic nd isotope composition of the orebodies and the browns range metamorphics indicates that ore metals were leached directly from the browns range metasedimentary rocks we propose an ore genesis model that involves fluid leaching hrees from the browns range metamorphics and subsequently mixing with p bearing acidic fluid from the overlying sandstones in fault zones near the unconformity the union of p and hrees via fluid mixing in a low ca environment triggered extensive xenotime precipitation this mineralization is unlike that of any other class of ree ore deposit but has a similar setting to unconformity related u deposits of australia and canada so we assign it the label unconformity related ree further discoveries of this ree mineralization type are expected near regional unconformities within proterozoic intracontinental sedimentary basins across the globe

working with natural cohesive sediments summary of stabilizing and destabilizing biotic in uenceson natural cohesive sediment stabilizing destabilizingeps secretion extracellularpolymeric substances bybacteria and microphytobenthosenhances cohesion promotes occulation and hence deposition blistering trapping ofoxygen bubbles in bio lmsincreases buoyancy of thebio lm to such an extentthat it pulls away fromthe sediment sediment compaction burrowingmacrofauna increasesediment densityand hence stability pelletization theformationof faeces and psuedo faeces can enhanceerodibility increased drainage burrowand channel formationpromotes dewatering grazing organismsfeedingon intertidal ats causesphysical disturbance andresuspensionof the sediment andreduces the stabilizingin uence ofmicrophytobenthos network effects filamentous biotaramify through the sediment matrixbinding sediment particles together burrow cleaning somebenthic fauna cleantubes they inhabit inthe sediment giving riseto a localizedbenthic ux flow effects

mid depth calcareous contourites in the latest cretaceous of caravaca subbetic zone se spain origin and palaeohydrological significance abstract deep marine carbonates of late campanian to early maastrichtian age that crop out in the subbetic zone near caravaca se spain contain a thick succession of dm scale levels of calcareous contourites alternating with fine grained pelagites hemipelagites these contourites characterised by an abundance and variety of traction structures internal erosive surfaces and inverse and normal grading at various scales were interpreted as having been deposited under the influence of relatively deep ocean currents based on these contourites a new facies model is proposed the subsurface currents that generated the contourites of caravaca were probably related to the broad circumglobal equatorial current system the strongest oceanic feature of cretaceous times these deposits were formed in the mid depth 200 600 m hemipelagic environments at the ancient southern margin of iberia this palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage through which the broad equatorial current system flowed in the westernmost area of the tethys seaway regional uplift related to the onset of convergence between iberia and africa probably favoured the generation of the contourites during the late campanian to the early maastrichtian

hydrothermal clay mineral formation in the uraniferous paleoproterozoic fa formation francevillian basin gabon abstract the spatial distribution of neoformed clay minerals was investigated in the paleoproterozoic fa formation of the francevillian basin south east gabon which hosts high grade u ore deposits associated with the only known occurrence of natural nuclear reactors illite appears as the main clay phase in the lower fluvial unit in the mineralized upper fluvio deltaic tidal unit the clay assemblage is more diversified and commonly characterized by illite chamosite berthierine and chamosite berthierine mixed layers usually in association with alteration products of u bearing minerals the clay mineral assemblage thus potentially constitutes a mineralogical marker for the regional distribution of u ore deposits polytype species of the clay phases indicate mineral transformations in an environment characterized by a high fluid rock ratio according to crystalline structure mineral chemistry thermodynamic modeling and geochronology clay phases seem to be mainly hygrometer rather than exclusively a thermometer and their formation as well as associated dissolution precipitation of u bearing minerals took place between ca 2040 and 2010 ma ago at temperatures of about 240 30 c using previous burial estimates this suggests the operation of hydrothermal processes controlled by an external heat source likely associated with volcanism during deposition of the fd and fe formations hydrothermal activity involving oxidized fluids would have driven u remobilization and ultimately formation of high grade u ore deposits the thermal history proposed here allows for a better understanding of the conditions during burial of the sedimentary succession and the origin of its rich u endowment

a model dependent method for inverting vertical profiles of scattering to obtain particle size spectra in boundary layers abstract a method for obtaining particle size spectra from vertical profiles of scattering strength in planetary boundary layers is presented it is assumed that the boundary layer is horizontally homogeneous and that the vertical turbulent diffusion of particles can be modeled from a knowledge of the surface friction velocity equilibrium boundary layer profiles for each class of suspended particles are assumed to be established resulting from the balance between vertical turbulent diffusion and gravitational settling the forward problem thus models the depth dependent scattering as the sum across size classes weighted by number density and scattering cross section in accordance with established scattering theory constrained inverses produce the size spectra results of inversions from synthetic ocean data are presented for optical transmissometry and acoustic backscattering inversions of acoustic field data from the hebble experiment are also presented finally the applications of the work presented for the design of ocean boundary layer experiments its application in other fields and the directions for future research are discussed

hydrothermal alteration of monazite in the precambrian crystalline basement of the athabasca basin saskatchewan canada implications for the formation of unconformity related uranium deposits microanalytical studies of basement rocks below the athabasca sandstone basin indicate that monazite is the dominant uranium bearing mineral in the study area drill core samples of hydrothermally altered basement show that monazite is commonly altered to a th silicate phase and uranium has been significantly mobilized on average 75 of the uranium bound to monazite is leached out during monazite alteration in contrast no substantial mobilization of uranium from detrital minerals e g zircon has yet been observed in the athabasca sandstones it is suggested that hydrothermal alteration of granitic rocks especially potassic pegmatoids and potassic orthogneisses of the sub athabasca basement represents the most important uranium source for the unconformity type deposits

sediment concentration profiling in hebble using a 1 mhz acoustic backscatter system abstract as part of the high energy benthic boundary layer experiment hebble a 1 mhz acoustic backscatter system abss was deployed in 4800 m of water on the nova scotian continental rise the purpose of the instrument was to measure non intrusively a time series of the vertical concentration profile over the course of one year from september 1985 to september 1986 in this paper we discuss the details of the abss instrument the results of the time series data analysis and the implications of the results on sediment transport modeling in hebble the systematic variation in the abss and light transmissometry calibration with changes of particle size distribution caused by environmental variability is discussed a comparison of the abss estimates of particle concentration with those obtained from light transmissometers seems to indicate that the suspended particle size distribution changed surprisingly little throughout the experiment

early diagenetic origin of al phosphate sulfate minerals woodhouseite and crandallite series in terrestrial sandstones nova scotia canada hydrated alumino phosphate sulfate aps minerals of the woodhouseite and crandallite series are found as microcrystalline aggregates replacing volcanic glass and apatite and filling pores in sandstones of the fluvial lower cretaceous chaswood formation southeastern canada mineral grains from heavy mineral separates and rock samples were analyzed with an electron microprobe as the crandallite component of the grains increases ree and f content increases the aps minerals formed during early diagenesis as a result of the flux of meteoric water below the water table beneath regional intraformational unconformities at which oxisols had developed sulfate was derived from the oxidation of very early diagenetic pyrite and phosphate from dissolution of detrital apatite the aps minerals are commonly associated with detrital dolomite which may have played a role in increasing ph in the circulating meteoric water zoning of aps grains to lower s concentrations outward suggests that so2 4 concentration was a determining factor in aps mineralogy and mineral composition

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

time sequence observations of wave formed sand ripples on an ocean shoreface analysis of an 18 day time lapse film record of shoreface ripple development with concurrent measurements of near bottom flow and surface waves provides new insight on equilibrium bedform conditions adjustment of ripple planform to variable hydrodynamics and ripple migration behaviour the study was conducted in approximately 10 m water depth 1 km off martinique beach on the atlantic coast of nova scotia canada under low energy summer wave conditions significant wave height and peak period during the study averaged 0 7 m and 8 s respectively with extremes up to 1 7 m and 11 s during passage of three weak weather disturbances six mutually exclusive ripple types have been defined 1 short wavelength regular ripples 2 variable bifurcated ripples 3 variable terminated ripples 4 short crested ripples 5 long wavelength regular ripples and 6 chaotic ripples ripple wavelength ranged from 0 07 m to 0 24 m and displayed a strong reynolds number dependence together with other published field data the results suggest a lower limit of 0 06 m for the wavelength of wave ripples in ocean shoreface environments ripple orientation ranged through 38 and responded rapidly to changes in wave approach direction but did not conform to the orientation of the adjacent shoreline ripples were observed to migrate both on and off shore with and against the wave advance direction at rates up to 0 1 m h 1 associated with net flows other than wave induced onshore asymmetry and mass transport migration mainly of ripple types 1 and 2 occurred during the peak of storm events but showed no obvious correlation with measured near bottom flow magnitude or direction ripple behaviour demonstrates equilibrium with prevailing dynamic conditions when straight crested rippie types 1 and 5 are present disequilibrium in orientation or dimensions is expressed by increasing sinuosity bifurcation and crest termination in types 2 3 4 and 6

in situ measurements of particle settling velocity in the deep sea two instruments the remote optical settling tube and the benthic autonomous settling tube have been deployed on the nova scotian continental rise at a depth of 4820 m the few results obtained suggest that optical and gravimetric methods give comparable results assumptions about particle density little affect the settling velocity distribution but do scale the total magnitude by using a distribution of declining density with increasing size indicating increasing water content the total concentration inferred from the light attenuation by using mie theory is quite close to the total found from gravimetric data the coarser end of the size distribution changes more with overall change in concentration than the fine end the settling velocity distribution shows the presence of several modes the two principal ones can be matched with modal sizes of 3 3 m and 60 m in coulter counter data allowing inference of stokes density contrasts of 1 5 and 0 061 g cm 3 respectively at concentrations of about 200 mg m 3 more than 50 of the material has a settling velocity less than 2 10 4 cm s 1 probably 3 m in size but this percentage appears to decrease with an increase in total concentration

estimating nearshore bedform amplitudes with altimeters abstract estimates of the heights of large 0 1 0 4 m heights and 1 10 m horizontal lengths migrating bedforms on a sandy beach made with fixed single point altimeters are similar to heights estimated from profiles across the bedforms made with altimeters mounted on an amphibious vehicle that traversed the surf zone unlike many profiling systems the robust fixed altimeters can measure bedforms in bubbly sediment laden surf zone waters nearly continuously including during storms thus allowing investigation of the relationships between bedform heights and near bottom velocities to be extended to a wide range of wave conditions the fixed altimeter observations of migrating bedforms suggest a sandy surf zone seafloor is not always smooth during energetic conditions with strong mean currents and large wave orbital velocities

radiation induced defects in drusy quartz athabasca basin canada a new aid to exploration of uranium deposits room temperature powder electron paramagnetic resonance epr spectra of drusy quartz i e euhedral quartz crystals as coatings on or infillings in cavities and fractures from five uranium mineralized areas in the eastern athabasca basin saskatchewan canada reveal a suite of radiation induced defects these epr spectra also show that radiation induced defects in drusy quartz from different geologic occurrences are similar in nature but vary widely in abundance for example radiation induced defects in drusy quartz from altered basement rocks significantly below mineralization are close to or below detection limits providing the first line of direct evidence for previous suggestions that fluids from the underlying basement rocks were uranium deficient drusy quartz in ore samples and those from alteration haloes around uranium orebodies are characterized by elevated levels of radiation induced defects similarly drusy quartz from less altered sandstones near the present day surface hundreds of meters above mineralization where uranium rich minerals are generally absent contains abundant radiation induced defects comparison of epr spectra of drusy quartz from less altered sandstones before and after hf treatments reveals that radiation induced defects are uniformly distributed in individual crystals in contrast to the preferred concentration in the grain margins and along fractures in detrital quartz these results suggest that radiation induced defects in drusy quartz were most likely formed by bombardment of alpha particles emitted by uranium bearing fluids during crystal growth therefore detection of radiation induced defects in drusy quartz from less altered sandstones represents a new near surface technique for exploration of uranium mineralization in the athabasca basin

early diagenetic ree phosphate minerals florencite gorceixite crandallite and xenotime in marine sandstones a major sink for oceanic phosphorus

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

formation of u rich mineralizing fluids through basinal brine migration within basement hosted shear zones a large scale study of the fluid chemistry around the unconformity related cigar lake u deposit saskatchewan canada abstract the evolution of basinal brines through percolation into basement rocks is studied in the paleo to mesoproterozoic athabasca basin and its underlying basement this specific geological context includes the evolution of a nacl rich basinal brine to a u mineralizing cacl2 rich brine that is of particular importance for the understanding of the formation of giant u deposits the objective of this study is to determine the physico chemical parameters p t x of the basinal brines and their changes both within the athabasca group sandstones and the underlying basement lithologies on the scale of several km around the world class unconformity related cigar lake u deposit particularly this study focuses on the basement hosted fault systems that are considered to be the main fluid flow pathways a comprehensive study including microthermometry raman spectroscopy and la icp ms analyses was carried out on fluid inclusions as was a semi quantitative estimation of the microfracture paleoporosity based on the surface density of fluid inclusion planes initial nacl rich brines were trapped during early diagenesis c a 1 7 1 65 ga in dickite rich sandstones under a three to seven kilometers thick sedimentary cover at around 90 to 150 c under hydrostatic pressure or at 120 210 c assuming lithostatic conditions at the time of u deposits formation ca 1 46 1 29 ga these brines percolated through the entire basement but preferentially within the damage zones of some graphite rich faults formed during the ca 1 8 ga trans hudson orogeny and active during the subsequent retrograde metamorphism and exhumation ca 1 8 1 72 ga the circulation of the basinal brines into these structures was enhanced and structurally controlled by the microfracture network inherited from earlier brittle reactivation during basement uplift the resulting high microfracture paleoporosity in the vicinity of some but not all of these structures favored intense interaction between the brines and basement rocks that induced the formation of illite sudoite alteration haloes in the basement the percolating brines scavenged mn k ba sr and especially u and evolved from the original nacl dominant composition toward a higher salinity cacl2 rich composition the resulting u bearing brine mixed with the unmodified diagenetic nacl rich brine in above and all along the reactivated faults either during thermal convection in isobaric settings and higher temperatures 110 200 c or through episodic tectonic reactivation in isothermal settings through episodic pressure fluctuation in direct vicinity of the u deposits the interactions between the brines and the basement rocks were the strongest which is marked by the highest intensity of alteration of the host rocks thus the formation of ore forming fluids resulted from the interaction between nacl rich basinal brines and highly microfractured basement rocks this study reinforces the hypothesis that interaction with basement rocks enhanced by strong fluid flow in cataclastic zones can significantly modify the physico chemical characteristics of basin derived brines leading to the formation of mineralizing fluids and the genesis of giant ore deposits such as the unconformity related u deposits

rates of particle scavenging sediment reworking and longitudinal ripple formation at the hebble site based on measurements of 234th and 210pb between 1982 and 1986 seabed and water column samples were collected on five cruises to the hebble site two particle reactive radionuclides 234th and 210pb have been used to examine rates of particle scavenging in bottom waters sediment reworking in the surface seabed and formation of longitudinal ripples settling particles at the hebble site which have been resuspended by strong bottom currents and benthic storm activity scavenge approximately 60 of the 234th half life of 24 days produced in the bottom 100 m of the water column corresponding to removal of 15 dpm cm2 234th inventories from cores collected during a single cruise show substantial variability e g 1 18 dpm cm2 over the 8 km2 study area indicating that resuspended particles are not deposited uniformly across the seabed after storm events the activity of benthic fauna and non uniform deposition over a topographically variable seabed are important processes affecting boundary layer sedimentation and the development of radionuclide inventories in surface sediments the mean 234th seabed inventory from individual cruises to the hebble area varies to a greater extent 2 to 38 dpm cm2 than the mean 210pb inventory 47 to 82 dpm cm2 because 234th inventories are dominated by sedimentary processes associated with an individual storm event whereas 210pb inventories integrate these processes over several cycles of deposition and erosion sediments at the hebble site are biologically reworked very rapidly on a 100 day time scale with 234th mixing coefficients db 1 to 33 cm2 yr comparable to values observed in nearshore environments on time scales of months to years 210pb data indicate that strong currents and benthic storm activity have eroded and redeposited the upper 5 10 cm in 17 of the 20 cores examined reoccupying field sites during the 4 year field program provided the unique opportunity to evaluate steady state models commonly used to determine rates of sediment reworking 210pb profiles and inventories showed significant temporal variations at hebble sites occupied between 1982 and 1986 steady state models should not be used to evaluate profiles of 210pb or other tracers with comparable half life in a dynamic environment like the hebble area because steady state assumptions are not justified and rates of sediment reworking can be underestimated by nearly an order of magnitude 234th and 210pb analyses of core samples from two longitudinal ripples suggest that these sedimentary features form on a time scale of months and consist of a mixture of recently deposited material from the water column and older sediment from depth the absence of 234th activity in one of the ripples indicates that these bedforms may be stable for periods of months without significant growth

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

petrographie et mineralogie des halos d alteration autour du gisement de cigar lake et leurs relations avec les mineralisations around the cigar lake orebody the present zoneography of alteration halos reflects several alteration episodes some of which are anterior to and others coeval with the mineralizing events and have a regional extension the basement retromorphism is characterized by crystallization of muscovite with a low iron and magnesium content and of trioctahedral ferromagnesian chlorites the later regolith alteration more obvious at the top of the basement is marked by iron bearing 1t kaolinite by hematite and by local crandallite florencite and diaspore in the athabasca sandstones far from any mineralization the diagenetic quartzification was followed by crystallization of aluminous 2m hydromuscovite dickite and crandallite goyazite in the main pod the uraninite mineralization was dated 1341 12 ma in the sandstones it is surrounded by ferromagnesian chlorites with a variable sudoitic character this proximal alteration halo grades into a more distal envelope visible in the sandstone and in the basem

significance of aluminum phosphate sulfate minerals associated with u unconformity type deposits the athabasca basin canada aluminum phosphate sulfate aps minerals formed around the athabasca unconformity type deposits and those from their australian counterparts are chemically very similar showing the same continuum between the diagenetic sr rich aps minerals of the barren sandstones and the lree rich composition of the aps minerals in the hydrothermally altered sandstone the p and lree rich compositions were controlled by the transport and the redistribution of p and lree elements released from the dissolution of phosphate minerals principally monazite in the basement rocks and in the basin during the syn ore alteration processes the s sr ratio measured in the aps minerals from unaltered sandstone away from the unconformity and any mineralization is preserved during the syn ore alteration processes suggesting that the fluids involved in both the deep burial diagenetic processes and the syn ore alteration system were derived from a similar diagenetic reservoir in both the athabasca and kombolgie regions the trioctahedral chlorite host rock alteration around the australian basement hosted u deposits as compared to the illite and sudoite associated with the athabasca basement hosted along with the more lree rich aps compositions in the australian deposits suggests that the ph and oxygen fugacity f o 2 of the syn ore fluids differed in the alteration systems of the two regions at the time of the u deposition

sedimentary dynamics and evolutionary history of a late carboniferous gondwanic lake in north western argentina lacustrine deposits are well represented in the lower part of the late carboniferous agua colorada formation in the north west sierra de narvbez catamarca province argentina lake narvbez was one of the several water bodies formed in the region immediately after the gondwana glaciation shallow lake and deep lake delta progradation proceeded from the ese coarse grained delta plain and turbidite delta front deposits suggest that the delta was formed close to the headwaters short headed stream delta type during periods of high discharge river mouths acted as bypass zones and fine and very fine sands were transported further into the lake by underflow currents the clastic material supplied by the deltaic system was partially reworked by wave action sands accumulated in unstable conditions at the upper delta front as a consequence of delta progradation as a result of the addition of clastics in the steep delta front turbidity currents were formed spreading their load along the lower delta slope deep lacustrine deposits are typically stacked forming two different kinds of progradational turbidite lobe sequences type i lobes were formed in a basinal setting and were probably detached from their feeder systems as a result of sediment bypassing in a shallow lake during periods of low lake level these turbidite lobes are replaced upwards by type i1 lobes which were formed on the delta slope during periods of lake level rise that allowed the onset of delta progradation the presence of highly deformed sandstone bodies suggests rapid depositional rates in a high slope setting whereas the occurrence of hummocky cross stratified sandstones indicates wave reworking of the sands initially emplaced by turbidity currents therefore the inner part of type i1 lobes was formed above storm wave base the depositional history of lake narvaez can be traced through four evolutionary stages lake transgression formation of type i lobes formation of type i1 lobes and delta progradation tectonic activity was probably important at the early stage of lake evolution but the subsequent depositional history was mainly controlled by fluctuations of lake level the lacustrine transport system has been divided into three distinct zones delta

uranium bearing phases in a u mill disposal site in northern canada products of the interaction between leachate raffinate and tailings material abstract the above ground tailings management facility agtmf is a licensed tailings receiving facility at the key lake mine site northern saskatchewan canada tailings within the agtmf were deposited between 1983 and 1995 and are derived from mining and milling of the gaertner and deilmann ore bodies at key lake the tailings are primarily composed of quartz phyllosilicate and clay gangue minerals minor amounts of ni co s arsenides iron oxide minerals and gypsum they typically contain u concentrations on the order of between 50 and 300 ug g u a small area of the agtmf receives occasional mill process upset solutions with an initial ph range of 2 6 the solutions contain elevated activities of u bearing aqueous species and are rapidly buffered to neutral and sub alkaline ph values during interaction with surroundings tailings solids having a ph of approximately 10 this buffering and neutralization process results in the precipitation of gypsum and minor amounts of uranyl minerals phases of the autunite group chernikovite h3o uo2 po4 h2o 3 and troegerite h3o uo2 aso4 h2o 3 with minor nh 4 occur predominantly in the gypsum matrix but can also occur as crusts on silicates the occurrence of troegerite is due to elevated concentrations of as within the deposited tailings solids surface alteration on phyllosilicates within tailings affected by the mill process solutions results in elevated concentrations of k at the phyllosilicate water interface which are ideal nucleation sites for the formation of single crystals of zippeite k3 h2o 3 uo2 4 so4 2o3 oh use of nh4 sulfates and ammonia in the extraction and yellow cake precipitation cycles and subsequent entrainment of nh4 species in the tailings results in the occurrence of nh4 bearing phases of the zippeite and autunite group literature data on dissolution features dissolution kinetics and mineral solubilities suggests that the minerals of the autunite group control the mobility of u in the contact zone between the mill process solutions and the tailings