apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

the role of autochthonous salt inflation and deflation in the northern gulf of mexico the deep water gulf of mexico can be divided into seven structural provinces on the basis of particular histories of mother autochthonous salt movement variations in sediment isopachs suggest that most of the deep water region was underlain by an inflated mother salt layer during the cretaceous to middle miocene the southern edge of this mega pillow was either the depositional edge of the salt or a basement structure partial deflation of this mega pillow during late miocene pleistocene sedimentation resulted in the formation of large structures overlying the mother salt this process of deep structuring was synchronous with progressive emplacement of shallow allochthonous salt to form the sigsbee canopy in the southern part of the present day deep water area recent seismic imaging of the large structures which are predominantly located below emplaced shallow salt allows interpretation of a range of structural geometrical styles including turtles folds thrusts and extensional faults salt feeder systems link the shallow salt via sub vertical or inclined stems numerous large structural traps are therefore developed between the shallow and mother salt levels sub salt traps due frequently to the geometrical interaction of the feeder systems and the deep geometries induced by mother salt flow deflation of emplaced salt produces welds which may be key to petroleum charge delivery to shallow traps common subsidence histories for individual basins within the seven proposed structural provinces suggest that basins largely developed as primary basins floored by flowing mother salt a positive implication of this model is that deep structures are likely to incorporate mesozoic source rocks

genesis of soils from holocene tidal deposits at the north sea coast abstract the southern north sea coast has served as an exemplification to analyse and discuss the genesis of soils from holocene tidal deposits the accumulation wedge of holocene tidal deposits at the north sea coast is artificially embanked for the most part in the enclosed area hinterland a variety of different soils developed disparate models attempting to explain the genesis of these soils deduce genesis of hinterland soils from recent foreland conditions disregarding that geogenic preconditions have fundamentally changed by consolidating and reviewing established literature we show that differences in geogenic preconditions are the initiating key for a feasible model describing geogenic preconditions to infer pedogenic processes we develop a model comprising four different development pathways high settling velocities and regular flooding as present in the foreland cause high inputs of mineral sediments and carbonate moderate sulfur dynamics and thus the development of calcareous soils synsedimentary decalcification prevails in irregularly flooded areas due to enduring low sedimentation rates low carbonate inputs and moderate sulfur dynamics under alternating redox states as mainly proposed for the unobstructed landscape high contents of soil organic matter som facilitate intensive sulfur dynamics creating potential acid sulfate soils pass which become extreme acid upon oxidation actual acid sulfate soils aass a great gradient in depositional conditions occurring at unobstructed plain coasts enables the deposition of deflocculated fine grained sediments which promotes the formation of very compact soils with low water conductivities although this proposed model is based mainly on conditions known from the german north sea coast it is shown that shaping geogenic and pedogenic processes are applicable to other humid coastal regions around the world

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

distinction between sortable silts and aggregated particles in muddy intertidal sediments of the east frisian wadden sea southern north sea abstract in muddy sediments the distinction between sortable silt and aggregated silty clay is important for the understanding of fine particle dynamics because both have different hydraulic properties the wadden sea of the southern north sea is severely depleted in fine grained sediments mainly due to high energy levels along the diked coastline as a result muddy sediments are restricted to a narrow belt along the diked mainland shore in the present study the mechanism by which this mud is deposited and how floc deposition and break up are reflected in the size distribution has been investigated for this purpose surficial sediments from four intertidal nearshore transects were monitored and repeatedly sampled in the course of two years high resolution grain size analyses were performed by an automated settling tube and a sedigraph particle analyser for the sand and mud fractions respectively the grain size frequency distributions of the fine fractions demonstrate that the wadden sea muds are composed of two subpopulations a well sorted coarse silt and an unsorted silty clay population a depletion of grain size around 8 m 7 phi demarcates the grain size boundary between the two populations suggesting that the finer mud population

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

mesozoic cenozoic unroofing of the southern appalachian basin apatite fission track evidence from middle pennsylvanian sandstones apatite fission track ages 137 pm 8 to 92 pm 7 ma and mean etchable track lengths 12 1 pm 1 8 to 12 9 pm 1 3 mu m are reported for 10 sandstones from the breathitt formation middle pennsylvanian at the northern end of the pine mountain overthrust in kentucky and virginia because all of the apatite fission track ages are 150 200 m y younger than the depositional age fission tracks that formed in the detrital apatite prior to deposition have been totally annealed thus maximum temperatures attained by these samples exceeded 110 pm 20 circ c the length distribution of etchable horizontally confined fission tracks precludes rapid 10 c m y cooling through the zone of partial annealing 60 125 c assuming a geothermal gradient of 25 pm 5 circ c km and a mean surface temperature of 15 c sandstones at the northern end of the pine mountain overthrust underwent slow erosional unroofing of 4 pm 1 km since the early cretaceous average rate of 28 pm 6 m m y the age t

high frequency 4th order sequence stratigraphy of early miocene deltaic shorelines offshore texas and louisiana abstract well logs and 3d seismic reflection data are integrated to image lower miocene depocenters of the upper texas and westernmost louisiana coastal and offshore areas although previously interpreted at a large scale 3rd order cycles the detailed stratigraphy and depositional history of the early miocene succession has not been fully developed the upper lower miocene interval from robulus l mfs10 to amphistegina b mfs9 has been further subdivided into five 4th order cycles each 200 300 m thick to provide finer scale stratigraphic detail and interpretation of depositional environments results of the finer scale correlations are presented in a series of sandstone percent maps overall the maps display a strike elongate sub parallel to the present day coastline orientation for the sandstone bodies which thin to the southeast basinward net sandstone thickness is relatively low in older cycles and increases in younger cycles suggesting an overall progradation of the deltaic system into the mapped area through time continued marine regression and southward movement of the shoreline are also confirmed by seismic amplitude maps after a major transgression associated with robulus l deltaic progradation occurred under rising sea level conditions deltaic sediments prograded southward and sandstone brought to the upper texas coast was distributed laterally by longshore currents to form strandplain coast lines maximum regression occurred during the interval mfs9 2 to mfs9 3 when a deltaic depocenter formed offshore texas in east high island area however sandstone thickness progressively decreased laterally to the east offshore louisiana where more shale was present and marine processes reworked deltaic derived sandstones into shore parallel bars there was a clear retreat of the shoreline during the youngest cycle marking the beginning of transgression associated with amphistegina b detailed stratigraphic interpretation at a 4th order scale shows more variability in the dominant shoreline processes during early miocene than previously thought recognition of sedimentary systems variability at a 4th order scale is critical for improved hydrocarbon exploration and in understanding potential future co2 storage in the area

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

reconstruction of a large deep crustal terrane implications for the snowbird tectonic zone and early growth of laurentia the 2800 km long snowbird tectonic zone is a well recognized but still enigmatic feature in the western canadian shield it has been interpreted as a paleoproterozoic continental suture or an archean strike slip fault system but here we suggest that the distinctive geometry of the central snowbird tectonic zone is primarily due to the interaction of crosscutting paleoproterozoic intracontinental thrust and strike slip shear zones having a length of hundreds of kilometers first a major zone of thrust sense shearing coeval with early continent continent collision between the superior and western churchill provinces accommodated uplift of a large exposure of granulite facies lower continental crust younger strike slip shear zones perhaps analogous to asian fault systems behind the himalayan orogen offset the thrust zone thus the current geometry and distribution of deep crustal rocks in this region represent a relatively late stage in the tectonic evolution of the western churchill province rather than an accretionary one earlier structures oriented at a high angle to the snowbird tectonic zone may record the fundamental accretionary history in this part of laurentia

multistage exhumation and juxtaposition of lower continental crust in the western canadian shield linking high resolution u pb and 40ar 39ar thermochronometry with pressure temperature deformation paths 1 new u pb titanite apatite rutile and 40ar 39ar hornblende muscovite biotite data are linked with existing pressure temperature deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive 20 000 km2 region of exhumed lower crust in the east lake athabasca region of the western canadian shield in the 200 m y between circa 1 9 ga high pressure granulite facies metamorphism and circa 1 7 ga unconformable deposition of athabasca basin sediments on the exhumed rocks our analysis reveals at least three distinct phases of unroofing at different rates specifically we distinguish 1 an early phase of extensional unroofing in the chipman domain at rates of 1 5 2 0 km m y from 1 0 gpa to 0 8 gpa associated with mafic magmatism and metamorphism 2 an episode of regional contractional uplift and associated unroofing along the legs lake shear zone at circa 1850 ma from 0 7 0 8 gpa to 0 4 0 5 gpa and 3 a final period of extensional unroofing at rates of 0 2 0 3 km m y from 0 4 to 0 5 gpa that culminated in transport of current exposures to near surface conditions the cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases the apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1 89 1 88 ga implies their juxtaposition at 0 7 0 8 gpa conditions regional east directed thrusting of the deep crustal domains as a coherent unit at 1 85 ga juxtaposed the granulites with middle crustal hearne domain rocks at 0 4 0 5 gpa conditions the detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of laurentia the temporal and spatial heterogeneity of exhumation patterns in the east lake athabasca region may be a common feature of the unroofing histories of lower crustal rocks

phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs a spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the earth s surface and hence the marine inundation of continents for past periods of high sea level the predicted geographical pattern of flooding correlates well with the geological record the high spatial correlation may result from increased plate velocities at these times leading to increased rates of subduction subsidence and inundation at convergent margins

how much systems tract scale three dimensional stratigraphic variability is present in sequence stratigraphy an answer from the middle miocene pearl river mouth basin prior sequence stratigraphic methods mainly employed two dimensional 2 d stacking patterns to reconstruct stratigraphic frameworks the future of sequence stratigraphy will pay more attention to systems tracts scale and three dimensional 3 d stratigraphic variability using 1 2 104 km2 4 63 103 mi2 3 d seismic data tied to regional 2 d seismic lines and 21 boreholes the present study examines systems tract scale and 3 d stratigraphic variability of the 14 8 13 8 ma pearl river shelf margin to deep water sedimentary prisms the studied prisms were divided into four main systems tracts namely highstand systems tract hst falling stage systems tract fsst lowstand systems tract lst and transgressive systems tract tst each systems tract is represented by a given clinoformal architecture and stacking pattern 1 clinothem sets with aggradation to progradation are hst 2 clinothem sets with progradation to degradation pd are fsst 3 clinothem sets with progradation to aggradation pa are lst and 4 clinothem sets with retrogradation are tst lst or hst in addition pearl river fsst and lst display downdip stratigraphic variabilities which are regionally manifested in at least three ways 1 shelf edge deltas linked downdip to basin floor fans 2 shelf edge deltas linked downdip without fans and 3 basin floor fans linked updip that lack deltas in along strike orientation the pearl river fsst could exhibit low angle progradation not just pd stacking the lst could present retrogradational stacking not just pa stacking therefore the physical position of a systems tract is reemphasized in terms of assigning a given systems tract the concepts of three systems tracts are then revised for chronostratigraphic significance the lst is the lowermost systems tract of a sequence presenting a normal regression of the shoreline as its diagnostic characteristic and including contemporaneous stratigraphic units laterally the hst is the upper systems tract of a sequence providing a normal regression of the shoreline as its diagnostic characteristic and including contemporaneous stratigraphic units laterally the tst is the middle systems tract of a sequence generating a backstep of the shoreline and excluding contemporaneous onlapping units of both the lst and hst laterally the fsst has not been revised because fsst may be a supply independent feature

coal quality coal rank variation and its relation to reconstructed overburden upper cretaceous and tertiary plains coals alberta canada near surface coals in the alberta plains occur in upper cretaceous and tertiary sediments the former represented by the belly river group horseshoe canyon formation and wapiti formation and the latter by the scollard member of the paskapoo formation statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations the coals discussed range in rank from subbituminous c to high volatile bituminous c these coals are variable in ash content and low in sulfur content the relationships among calorific value dry basis in kj kg and ash dry basis in and calorific value moist mineral matter free basis in kj kg and equilibrium moisture meq in were determined to be cvd 29 677 315 17 ashd and cvmmmf 31 816 442 05 meq respectively the maximum depth of coal seam burial dob in m was reconstructed on the basis of previously published graphs relating the equilibrium moisture loss to depth of coal seam burial using the relationship log10meq 1 865 0 000416 dob a least squares regression analysis of calorific value mmmf basis in k kg on the calculated depth of burial dob in m yielded the equation cvmmmf 14 748 6 25 dob indicating a coalification gradient determined on the reconstructed overburden of 6 25 kj kg m 0 82 btu lb ft of depth or overburden near surface coals in the alberta plains increase in rank toward the west southwest toward the foothills and mountains region because of progressively greater amounts of overburden that existed in that direction during the tertiary erosion has since removed between 900 and 1 900 m 3 000 and 6 200 ft of sediment with the greatest amount of removal occurring in a west southwest direction

o and pb isotopic analyses of uranium minerals by ion microprobe and u pb ages from the cigar lake deposit we apply a rapid and accurate in situ technique to make u pb isotopic measurements of complexly intergrown uranium minerals and oxygen isotopic analyes of uraninite from the unconformity type cigar lake uranium deposit secondary uranium minerals intergrown with uraninite such as coffinite usio4 nh2o and calciouranoite cau2o7 5h2o were identified by highresolution transmission electron microscopy hrtem in situ u pb results from three stages of uraninite and coffinite define well correlated arrays on concordia with upper intercepts of 1461f47 1176f9 and 876f14 ma f1r these ages are interpreted as the minimum ages of mineralization correlate with the timing of clay mineral alteration f1477 ma associated with these unconformity type uranium deposits the ages of magnetization events at 1600 1450 and 900 ma from the athabasca basin and the grenvillian orogeny at f1100 ma in situ u pb isotopic analyses of uraninite and coffinite can document the pb u heterogeneities that occur on the scale of 15 30 am thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits the high spatial resolution and precision of the ion microprobe allow us to measure d 18 o values of 20 100 am unaltered portions of uraninites from cigar lake the range of d 18 o values 33 9 to 20 4x are among the lowest reported for unconformity type deposits confirming that conventional fluorination analyses of material sampled at the mm scale are insufficient to avoid contamination from isotopically heavier coffinite and calciouranoite d 2002 elsevier science b v all rights reserved

depositional and structural evolution of the middle miocene depositional episode east central gulf of mexico a regional stratigraphic and structural framework has been established for the middle miocene sediment depositional episode from the shelf through the slope to the basin floor for the east central gulf of mexico two widespread transgressive deposits associated with the faunal tops amphistegina b 15 5 ma and textularia w 12 1 ma define the middle miocene depositional episode the middle miocene episode incorporates four genetic cycles each 1 2 m y bounded by regional maximum flooding surfaces and distal condensed sections two long lived extrabasinal fluvial deltaic axes the ancestral mississippi and the eastern tennessee systems provided the bulk of sediments that infilled the middle miocene depocenters salt related structural provinces controlled the location and configuration of the depocenters linked structural systems dominated by gravity spreading and an eastern minibasin province driven by differential subsidence were established during this period two depositional systems tracts characterize the constructional shelf margin of the middle miocene 1 a volumetrically dominant mixed load fluvial dominated platform delta shelf margin delta and delta fed apron systems tract and 2 a strand plain shelf and muddy slope systems tract however the offlapping shelf margin systems were punctuated by a large scale slope failure the harang collapse system associated with massive salt withdrawal and retreat of delta systems a large volume of sediment funneled by the harang collapse system bypassed the slope initiating a long lived submarine fan system the fan formed in a minibasin corridor and unconfined abyssal plain approximately 240 mi 384 km from the active shelf margins the fan system evolved from a structurally controlled elongate sand rich to mixed sand and mud fan to a large radial mixed sand and mud fan

late cenozoic flexural deformation of the middle u s atlantic passive margin despite the century long recognition of regional epeirogeny along the middle atlantic passive margin relatively few studies have focused on understanding postrift uplift mechanisms here we demonstrate that epeirogenic uplift of the central appalachian piedmont and subsidence of the salisbury embayment represent first order flexural isostatic processes driven by continental denudation and offshore deposition our results show that regional epeirogenic processes present on all atlantic type passive margins are best resolved by specific stratigraphic and geomorphic relationships rather than topography a simple one dimensional geodynamic model constrained by well dated baltimore canyon trough coastal plain and lower susquehanna river piedmont stratigraphy simulates flexural deformation of the u s atlantic margin the model represents the passive margin lithosphere as a uniformly thick elastic plate without horizontal compressive stresses that deforms flexurally under the stress of strike averaged vertically applied line loads model results illustrate a complex interaction among margin stratigraphy and geomorphology the isostatic response to denudational and depositional processes and the modulating influence of exogenic forces such as eustasy the current elevation with respect to modern sea level of fluvial terraces and correlative coastal plain deposits or unconformities is successfully predicted through the synthesis of paleotopography eustatic change and margin flexure results suggest that the middle u s atlantic margin landward of east coast magnetic anomaly is underlain by lithosphere with an average elastic thickness of 40 km flexural rigidity d 4 1023 n m the margin experiences an average long term denudation rate of approximately 10 m m y and the piedmont has been flexurally upwarped between 35 and 130 meters in the last 15 m y long term isostatic continental uplift resulting from denudation and basin subsidence resulting from sediment loading are accommodated primarily by a convex up flexural hinge physiographically represented by the fall zone our results elucidate an inherent danger in using topography alone to constrain late stage passive margin deformation mechanisms only through careful synthesis of field stratigraphic and geomorphic elements such as fluvial terraces coastal plain deposits and offshore stratigraphy can age control be extended from the offshore depositional setting to the erosionally dominated continent this study demonstrates that despite a relatively subdued topography the middle u s atlantic margin experiences progressive flexural isostatic deformation similar to that proposed for high relief margins characterized by great escarpments thus margin topographic diversity remains a function of other factors such as lithospheric composition and or structure supracrustal stratigraphy and structure degree of drainage integration drainage divide migration and climate

a world perspective on acid sulphate soils abstract generalizations about the morphology and genesis of acid sulphate soils at a regional scale are derived from a review of extensive though patchy soil survey data a general sequence of sedimentation accumulation of sulphides and burial of sulphitic material by peat or alluvium of low sulphide content and a parallel sequence of soil profile development are illustrated by examples of unripe sulphitic soils under a natural tidal regime artificially drained raw acid sulphate soils and ripe acid sulphate soils at various stages of development the world pattern has been driven mainly by postglacial sea level change but each regional pattern is determined by its unique sedimentary and geomorphological history distinctive patterns occur in deltas and estuaries and in humid and seasonally dry climates very extensive areas of ripe acid sulphate soils in areas that are not known to have experienced falls in relative sea level are ascribed to human activity forest clearance and soil erosion in catchments causing lower dry season river flows and piecemeal clearance of peat over the floodplains permitting the dry season water table to fall the implications for further agricultural development in other comparable areas include the absolute necessity to know the extent of potential acid sulphate soils and to maintain their water table above the sulphide datum most effective systems of management have been developed by farmers themselves but the sustainability of these systems is often doubtful due to their detrimental effects on the aquatic ecosystem

extending the time range of apatite u th he thermochronometry in slowly cooled terranes palaeozoic to cenozoic exhumation history of southeast sweden the use of u th he thermochronometry in old slowly cooled terranes has long been debated hence studies of natural setting are needed to verify the expected diffusivity behaviour of helium our results demonstrate that the u th he method can be applicable to samples older than 200 ma and that available helium diffusion models can reproduce the results obtained from the age vs depth trends in addition the results shed some light on the cross validation with the apatite fission track thermochronometer u th he thermochronometry on apatites has been applied to samples taken from drill cores in the precambrian basement in southeast sweden to unravel the time of exhumation of the uppermost 1 3 km of the crust much of the phanerozoic exhumation history in sweden is poorly constrained due to a large hiatus in the sediment record results from the drill cores yield he ages decreasing with increasing depth from similar to 270 ma at the surface down to similar to 120 ma at 1700 in depth the age vs depth trend shows an inflection point at similar to 1400 in depth which coincides with the upper boundary of the present helium partial retention zone a period of slow exhumation similar to 17 m my probably linked to the isostatic uplift of the caledonian foreland basin is revealed by the upper section of the trend in the data the results demonstrate that the area has not been reheated since the mid permian this argues against the existence of a thick mesozoic sedimentary cover in this region which if present at all cannot have exceeded 100 in in thickness furthermore the age vs depth trend below the inflection point allows dating the cessation of exhumation at approximately 100 ma the area has had no significant amount of sedimentation erosion or uplift since this time less

low long term erosion rates and extreme continental stability documented by ancient u th he dates zircon and apatite crystals from the western canadian shield yield u th he dates that are the oldest yet reported for terrestrial rocks zircon dates from 1 73 to 1 58 ga are consistent with independent geological and thermochronological constraints and indicate that the rocks were at temperatures 180 c and crustal depths 7 10 km since ca 1 7 ga apatite dates from 0 95 to 0 55 ga suggest residence of rocks at temperatures 40 50 c and crustal depths 1 5 2 km for 1 0 0 6 b y when interpreted using conventionally accepted apatite he diffusion kinetics and considering the proposed effect of radiation damage on apatite he retentivity our analysis implies long term integrated unroofing rates of 2 5 m yr since ca 1 7 ga these rates are significantly lower than the long term rates suggested by previous thermochronological data sets in continental interiors but are within the range of short term erosional estimates the results are consistent with the extreme stability of this region since the proterozoic

paleomagnetism and the evolution of fluids in the proterozoic athabasca basin northern saskatchewan canada in the athabasca basin diagenetic hematite of variable paragenesis occurs throughout the sandstones and underlying paleoregolith this hematite carries three distinct single component magnetizations a d 158 i 62 95 5 n 21 b d 11 i 36 95 7 n 6 and c d 18 i 79 95 3 n 27 in some areas of the sandstones such as near reactivated fault zones the diagenetic hematite has been altered to goethite which yields a very low intensity incoherent d magnetization ages for the a b and c magnetizations inferred from comparisons with paleomagnetic directions in precambrian rocks whose ages are known approximately are 1750 1600 1600 1450 and about 900 ma respectively the a magnetization is carried by the earliest formed hematite and its estimated age compares well with u pb ages of 1650 1700 ma for early diagenetic apatite u pb and rb sr ages of approximately 1500 and 900 ma for uraninite and illite coeval with hematite that carries the b and c magnetiza

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

apatite fission track and u th he data from fennoscandia an example of underestimation of fission track annealing in apatite abstract apatite fission track aft data from cratons have commonly been interpreted in terms of major episodes of sedimentary burial and subsequent denudation often in the absence of any remnant sedimentary rocks or other supporting geological evidence reconciling these interpretations with geologically documented denudation events or outcropping regional stratigraphy can be problematic also u th he ages from cratonic igneous rocks that are older than paired aft data are commonly discarded as too old even when the former are repeatable at the 2 confidence level for example aft data from central fennoscandia have been interpreted to reflect first burial by a caledonian foreland basin several kilometres in thickness and subsequently its denudation however throughout fennoscandia there is no direct evidence that such a deep extensive foreland basin ever existed and indeed some geological evidence points to the contrary additionally a significant number of u th he ages from fennoscandia are older than their aft pairs but have been interpreted by their authors as too old relative to the aft ages and not geologically meaningful despite repeatable results here we propose a new interpretation of aft data from fennoscandia that closely reflects the observed data yet is compatible with the generally accepted geological history discarding the hypothesis of a thick caledonian foreland basin we suggest that 1 aft ages in finland are too young rather than that the u th he ages are too old 2 repeatable sequences of u th he ages are more likely to record the true denudation history of cratons 3 the importance of radiation enhanced annealing at low temperatures has been overlooked and 4 fennoscandian aft data may be divided into an eastern domain strongly affected by radiation enhanced annealing where current aft annealing models are invalid and a western domain much less affected by radiation enhanced annealing where current modelling methods may appropriately be used to extract thermal histories in principle radiation enhanced annealing is also pertinent to the interpretation of young aft ages from apatites rich in emitter actinides the construction of a properly calibrated annealing model that fully incorporates the effects of radiation enhanced annealing is fundamentally important

regional structural setting and evolution of the mississippi canyon atwater valley western lloyd ridge and western desoto canyon protraction areas northern deep water gulf of mexico the structural framework and evolution from the middle jurassic to the present of the mississippi canyon atwater valley western desoto canyon and western lloyd ridge protraction areas consist of a complex history influenced by basement fabric multiple stages of salt movement and gravitational gliding a detailed tectono stratigraphic interpretation of the study area indicates that three main stages of salt movement controlled sediment dispersal patterns and the formation and evolution of intraslope minibasins these three stages of salt movement occurred during the cretaceous the paleogene and the neogene basement structures were the primary control on initial salt kinematics affecting gravity driven slope deformation and resulting in a wide variety of structural styles basement acoustic basement structures horsts grabens and half grabens formed prior to the deposition of the middle jurassic autochthonous louann salt these features are interpreted to have controlled the original thickness of the autochthonous salt layer and subsequent salt withdrawal patterns mesozoic structures such as extensional compressional gliding systems and expulsion rollovers formed above the autochthonous salt three levels of allochthonous salt systems are identified 1 approximate top barremian 2 top cretaceous and 3 intra neogene between 10 and 4 ma early emplacement of two allochthonous salt layers is present in the northeastern part of the study area whereas the neogene allochthonous salt system extends throughout the mississippi canyon western desoto canyon and northern atwater valley protraction areas salt from the autochthonous and two deep allochthonous salt layers was expelled vertically and basinward during theneogene feeding the younger allochthonous salt systems the autochthonous and deep allochthonous salt layers were detachments for many of the large neogene extensional growth faults and turtles and contractional anticlines and thrust faults structures whereas the neogene allochthonous salt system accommodated suprasalt minibasins associated with counterregional and roho salt systems these three allochthonous salt layers were successively loaded by gravity flow sediments resulting in deep above autochthonous or deep allochthonous salt layers and shallow supra neogene allochthonous salt minibasin formations and local development of extensive salt welds northwest southeast oriented strike slip structures active during the neogene are present in the salt province within the study area they are related to basinwide heterogeneities in the salt distribution and are controlled by differential basinward movement of adjacent suprasalt minibasins copyright 2017 the american association of petroleum geologists all rights reserved

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

inverse modeling of annealing of fission tracks in apatite 2 application to the thermal history of the peace river arch region western canada sedimentary basin

characteristics of a marshland soil built up from marine and peat material abstract the marine marshland area seawards of the sehestedter ausendeichsmoor is built up from marine and moor peat material the humic fluvisol investigated in this area is characterized 1 by sulfate depletion leading to intensive methanogenesis 2 by carbonate depleted soil sections and reduced ph values and 3 by high amounts of reduced sulfur compounds with respect to further development a quick acidification leading to soil properties which are characteristic of older but not currently seawater influenced humic fluvisols can be expected is seems likely that these older humic fluvisols initially developed under marine conditions

sulphur and iron geochemistry of holocene coastal peats nw germany a tool for palaeoenvironmental reconstruction abstract a drill core from the marshlands of nw germany covering the entire holocene was analysed at high resolution by geochemical xrf cirm ms and microfacies methods diatoms thin sections sem in order to provide information about the palaeoenvironmental development in addition microbial experiments were carried out with sulphate reducing bacteria srb and cellulose fermenting fungi in seawater using peat as substrate the core contains an intercalated reed peat layer 2 73 3 02 m and a basal peat 5 78 6 42 m the basal peat consists in the lowest part of fen woodland and raised bog peat while the upper part is formed by a reed peat bed the peat layers are characterised by a distinct enrichment of pyrite with negative bulk sediment 34 s values av 11 5 range 2 6 to 26 7 reflecting microbial sulphate reduction in some peat intervals under almost open system conditions with respect to the input of seawater sulphate pyrite occurs exclusively with framboidal texture in close vicinity to the organic matter which indicates localised pyrite formation at the decay site in microenvironments with high concentrations of dissolved fe microbial experiments reveal that peat does not represent an appropriate substrate for srb and that srb have to rely on the preceding decomposition of peat by other microorganisms in microenvironments the total sulphur content of the peat layers averages to 7 8 wt with a maximum value of 28 2 wt unusually found within the basal peat at the transition of fen woodland and raised bog peat the pyrite enrichments can be explained by two different scenarios which are related to the intensity of the sea level rise the first scenario applies to a moderate sea level rise and is decisive for the reed peats where pyrite formation coincides with peat growth a brackish zone is assumed for the peat forming environment which is influenced by iron rich freshwater and sulphate rich seawater as the freshwater forms the major fe source the amounts of pyrite increase to a certain degree with decreasing salinity in this environment the palaeosalinity is estimated by the investigation of littoral and pelagic diatoms the second scenario applies to the extensive pyrite formation within the basal peat at the transition of fen and bog peat this pyrite was likely formed after peat growth favoured by a steep sea level rise thin sections of this peat interval reveal clastic layers 1 3 mm with completely pyritised interfaces as these clastic layers contain marine pelagic diatoms e g paralia sulcata we propose that they are caused by tidal channel activities during a phase of a steep sea level rise the marine incursion led to a partial buoyancy of the basal peat at weak transition zones i e the transition from fen to bog peat as a result of the bouyancy marine suspended particulate matter can be introduced laterally in between the peat sections when the peat settles down a clastic layer remains whose interface with the peat may have favoured the inflow of waters of higher salinity therefore an enhanced formation of pyrite was possible due to the combination of sulphate rich ground water and iron rich peatland waters

denudational history along a transect across the drakensberg escarpment of southern africa derived from apatite fission track thermochronology 1 the denudational history of a 500 km long transect across the drakensberg escarpment on the high elevation passive margin of se africa is quantified on the basis of thermal history modeling of apatite fission track data for 15 deep borehole samples supplemented by an additional 10 outcrop samples a minimum of 4 5 km of denudation since formation of the margin 130 myr ago is estimated for the coastal zone with a marked early cretaceous episode of accelerated denudation broadly coincident with continental breakup samples from the swartberg borehole sw 1 67 located 30 km seaward of the present position of the drakensberg escarpment indicate a total depth of denudation of 3 1 1 2 km since 91 myr with a phase of accelerated denudation of 2 1 0 9 km at a mean rate of 95 43 m myr between 91 and 69 myr samples from the ladybrand borehole la 1 68 west of the lesotho highlands indicate 1 7 0 5 km of denudation since 78 myr with a phase of accelerated denudation at 82 43 m myr from 78 to 64 myr average denudation rates declined to about 10 m myr during much of the tertiary although the apatite fission track data do not provide any direct constraints on the denudational history of the lesotho highlands interpolation between the two boreholes constrained by geological evidence and extrapolated in situ produced cosmogenic 36cl derived denudation rate estimates suggests a pattern of denudation compatible with numerical modeling studies of escarpment evolution involving rapid river incision seaward of a preexisting inland drainage divide these patterns of denudation are incompatible with constant retreat of the drakensberg escarpment from an initial position near the present coast we suggest that the drakensberg escarpment formed by rapid post breakup river incision seaward of a preexisting drainage divide located just east of the present escarpment location and became pinned at this divide with subsequent retreat rates of only 100 200 m myr

exploiting radiation damage control on apatite u th he dates in cratonic regions abstract apatites from four pairs of samples of precambrian basement from the western canadian shield were analyzed by u th he thermochronometry to test for the influence of radiation damage on apatite u th he dates in this cratonic region recent studies have demonstrated that the accumulation of radiation damage increases the apatite he retentivity so that apatites with a span of effective u concentrations eu that experienced the same thermal history may be characterized by a range of closure temperatures in this investigation each sample pair consisted of a mafic dike cross cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eu the apatites yielded u th he dates from 846 to 123 ma and were positively correlated with eu within each sample pair these results can be explained using a model that tracks the evolution of he mobility in response to the accumulation of radiation damage when coupled with regional geological constraints the data appear to require partial to complete he loss due to burial and reheating in phanerozoic time new apatite fission track dates and length data were obtained for five of these samples the apatite fission track dates are proterozoic regardless of apatite eu thermal history simulations indicate that the apatite fission track data are compatible with the u th he results although the thermal histories are not identical in detail and the fission track results alone do not require phanerozoic heating together the data are consistent with burial of this region by 1 km of phanerozoic strata that were subsequently denuded thus pointing toward significant phanerozoic deposition in the north american cratonic interior hundreds of kilometers east of where previously documented the results suggest that exploiting radiation damage control on apatite u th he dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible

plate mantle coupling and continental flooding the flooding records of continents have been computed in dynamically self consistent models of plates and convection platforms flood following rapid translation of continental plates as may occur following supercontinent breakup in these models continental flooding is primarily controlled by deep mantle sources and continental hypsometry is strongly influenced by dynamic topography some models especially bottom heated ones predict more extensive flooding than has been observed during the phanerozoic however the computed flooding can be made consistent with the observations if the viscosity of the upper regions of the convecting system are significantly reduced compared to the deep regions the fluid is driven predominantly by internal heating or the convection is confined to a depth appreciably less than the width of the non subducting plate

tidal marsh sedimentation and resilience to environmental change exploratory modelling of tidal sea level and sediment supply forcing in predominantly allochthonous systems abstract the existence and function of tidally dominated and predominantly allochthonous marshes are ultimately contingent upon the operation of hydrodynamic and sedimentary processes within constraints imposed by the available accommodation space and sediment supply this paper re interprets published data relating to contemporary vertical marsh growth and sea level rise in the context of the conceptual model relating elevation sedimentation sea level rise sediment supply and tidal range this analysis is supported by numerical mass balance modelling of the equivalent parameter space and of the sensitivity of marsh hydroperiod and sedimentation to sea level and sediment supply forcing the effect of autocompaction on the translation of sedimentation into elevation change is also considered parameter space modelling provides a framework for the interpretation of field data and affords indicative insights into marsh resilience to change it is argued that the assessment of marsh response to external environmental forcing should be based not on empirical comparisons of sedimentation versus sea level rise but on the estimation of sediment supply and the efficiency with which this is depleted by deposition as metrics of marsh resilience this implies a shift towards more intensive process studies aimed at elucidating more fully the linkages between tidal marshes and adjacent estuarine and coastal systems model results also indicate significant variability in marsh sedimentation associated with 18 6 yr tidal modulation and meteorological processes at short term scales such variability further complicates the interpretation of sedimentation or elevation change data obtained from monitoring programmes of short duration longer term monitoring is of value however as a means of identifying important mechanisms of climate and sediment supply forcing that may contribute to the formation and maintenance of marsh sedimentary sequences

radiation damage control on apatite u th he dates from the grand canyon region colorado plateau individual detrital apatite grains from the esplanade coconino and moenkopi formations in the grand canyon region of the colorado plateau yield u th he dates from 104 to 5 ma the range of dates within each unit far exceeds analytical uncertainty but correlates with both he concentration he and effective u concentration eu these dates are all signifi cantly younger than the sandstone units indicating partial to complete he loss following deposition recently published laboratory diffusion data suggest that he retentivity in apatite increases with radiation damage forward models predict that the consequences of this effect will be manifested most clearly as a correlation between u th he dates and the he and eu in suites of apatites that 1 are characterized by a large span of eu and 2 had thermal histories in which suffi cient time elapsed for the apatite he diffusion kinetics to diverge prior to reheating and partial resetting apatites in the sedimentary units investigated fi t these cri teria using geologically reasonable deposition burial and unroofi ng histories simulations that include the effect of radiation damage on apatite he retentivity can reproduce the observed distributions of apatite dates and correlations with parent and daughter concentrations these results suggest that a span of u th he dates positively correlated with eu may provide important information regarding a sample s thermal history

mechanisms of land sea interactions the distribution of metals and sedimentary organic matter in sediments of a river dominated mediterranean karstic estuary this paper examines disposal of metals and the origin characteristics and distribution of sedimentary organic matter som in a mediterranean karstic estuary in the north eastern adriatic this environment offers a real time small model system for studies of geochemical processes in microtidal mediterranean estuaries that are infilling with sediments and classified as river dominated disequilibrium estuaries the results have shown that the longitudinal distribution of heavy metals in sediments follows the sedimentation dynamics and deposition pattern of river borne clay mineral particles the highest concentration of metals was found in the restricted upper part of the estuary characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter and decreases toward the open sea the vertical distribution of metals in sediment cores depends on the prevailing ph and eh conditions significant increases of the concentrations of metals in the uppermost strata are the result of recent anthropogenic inputs the share of the terrestrial component in

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

spatial patterns in accretion on barrier island salt marshes abstract on minerogenic barrier island salt marshes sedimentation is spatially heterogeneous although the main forcing factors for sedimentation are known much less is known about the characteristic sizes of this spatial patterning such patterning gives information on the spatial component of salt marsh formation and on the uncertainty in measured accretion rates we used variograms geostatistics to study the size of spatial patterns in the thickness of salt marsh deposits based on a database of over 10 000 soil cores these were taken at various spatial scales ranging from metres to kilometres along a chronosequence representing 10 150 years of salt marsh formation at three barrier islands in the wadden sea south eastern north sea the general complexity of salt marsh accretion was reflected in the observed patterns of the thickness of the marsh deposits the patterns were nested and ranged in horizontal size from 3 m on sites with micro topography to 900 m at the scale of the entire marsh their structure and size changed with salt marsh age and there was no characteristic pattern size although the pre marsh topography is an important large scale control during salt marsh development independent spatial patterns are superimposed when scaling up data on salt marsh sedimentation the presence of spatial patterning adds uncertainty to the prediction the consequence of the complexity of these patterns is that the spatial uncertainty is a not necessarily linear function of the area under consideration which can only be quantified if it is explicitly measured our findings therefore pose a cautionary note to studies of salt marsh resilience to sea level rise reliable estimates can only be derived if they are based on measurements that take into account the entire salt marsh

the carbonate evaporite lagoon of al dakhirah qatar an example of a modern depositional model controlled by longshore transport the southern coast of the arabian gulf is considered a good example of an arid carbonate depositional system the objective of this field investigation is to better elucidate the dynamic controls on the character and pattern of the depositional belts in a carbonate evaporite lagoonal setting the interpretation of this lagoon is based on combined field examination and laboratory analyses of surface samples and this has resulted in an updated depositional model for carbonate evaporite lagoonal settings this study highlights the effects of sediment transport by longshore currents with the formation of sand spits that gradually closed the lagoon during their southwards migration the associated narrow and elongated back barrier settings consist of tidal dominated muddy sediments affected by a network of tidal channels this wave dominated high energy system has generated several carbonate barrier and back barrier units that migrated southwards and seawards during the last few thousands of years this updated depositional model significantly differs from shoreline parallel facies tracts of the classical trucial coast model where the dominant wind is orientated perpendicular to the coastline conversely to the sediment belts of the trucial coast the al dakhirah lagoon displays a strongly asymmetrical pattern of the sediment belts marked by a southwards and seawards migration

sand in the salt marsh contribution of high energy conditions to salt marsh accretion abstract the environmental dynamics at barrier island salt marshes are reflected in lateral and vertical textural patterns of the marsh sediment during normal conditions fine grained sediment is deposited whereas during high energy conditions also sand accretion can occur this paper describes the occurrence and importance of sand deposits for the building of salt marshes the study was carried out in the wadden sea on the islands of schiermonnikoog nl terschelling nl and the peninsula of skallingen dk firstly we recorded the presence of sand in the sediment representing initial salt marsh formation the results indicate that part of the salt marsh developed under conditions that were dynamically enough for sand to be transported the spatial distribution of these conditions depends on soil elevation and location on the marsh modified by the presence of artificial sand dikes further we recorded the presence and thickness of sand layers within the salt marsh sediment sand layers are found on twenty percent of the marsh area and are partly associated with the local sources of the sand i e marsh creeks the salt marsh edge and washovers in total sand layers contribute less than ten percent to the volume of marsh deposits on schiermonnikoog we dated the layers using the thickness of the deposits and known marsh age the ages of the layers indicate that for the decadal occurrence of storms capable of depositing sand in the salt marsh the local hydrodynamics and availability of sand determine whether a site receives sand or not

ava simultaneous inversion of partially stacked seismic amplitude data for the spatial delineation of lithology and fluid units of deepwater hydrocarbon reservoirs in the central gulf of mexico this paper describes the successful application of amplitude versus angle ava inversion of prestack seismic amplitude data to detect and delineate deepwater hydrocarbon reservoirs in the central gulf of mexico detailedavafluid lithology sensitivity analysis was conducted to assess the nature ofavaeffects in the study area based on well log data standard techniques such as crossplot analysis biot gassmann fluid substitution ava reflectivity modeling and numerical simulation of synthetic gathers were part of theava sensitivityanalysis crossplot and biot gassmann analyses indicate significant sensitivity of acoustic properties to fluid substitution avareflectivity and angle gather modeling indicate that the shale sand interfaces represented by the top and base of the m 10 reservoir are associated with typical class iiiavaresponses caused by relatively low impedance gas bearing sands consequently prestack seismic inversion provided accurate and reliable quantitative information about the spatial distribution of lithology and fluid units within the turbidite reservoirs based on the interpretation of fluid lithologysensitive modulus attributes from the integration of inversion results with analogous depositional models the m series reservoirs were interpreted as stacked terminal turbidite lobes within an overall fan complex this interpretation is consistent with previous regional stratigraphic depositional studies

formation and evolution of the cigar lake uranium deposit based on u pb and k ar isotope systematics a systematic geochronological study was conducted on the cigar lake uranium deposit u pb and pb pb systematics were applied to different types of uranium ore and various associated sheet silicates were dated by the k ar method these two approaches define a widespread retrograde metamorphic event in the basement which occurred at about 1780 ma during the hudsonian orogeny and a four stage evolutionary model for the ore deposit this model is compatible with the history of other unconformity type uranium deposits in the athabasca basin the first stage in the evolution of the cigar lake uranium deposit is marked by uraninite crystallization at 1341 17 ma which in association with arsenides and sulpharsenides constitutes the mineralization of economic interest main orebody the second stage characterized by a fe kaolinite and fe illite paragenesis occurred locally at about 900 ma the third stage involved uranium mobilization at about 325 ma and is characterized by i preferential loss of radi