middle and late jurassic radiolarian palaeoecology versus carbon isotope stratigraphy abstract jurassic radiolarians are sensitive to palaeoclimatic palaeoceanographic changes recorded by the stable carbon isotope curve carbon isotopic variations have been linked to changes in ocean structure productivity and concentrations of greenhouse gases in the atmosphere in the middle upper jurassic terminilletto section of the umbria marche sabina apennines central italy well preserved radiolarians are present in a sequence of cherty limestones interbedded with platform derived carbonates the 13 c curve in the aalenian kimmeridgian interval indicates three main positive 13 c events in the lower bajocian late bathonian lower callovian and middle oxfordian the positive 13 c shifts are correlated to increases in visible chert in the outcrop and may represent periods of increased biological productivity of surface sea water spumellaria nassellaria ratios and the fluctuations of relative abundance of selected genera tend to correlate with 13 c and chert abundance values and seem to be related to episodes of high nutrient mobilisation from the base of the bajocian the radiolarian associations show a slight tendency towards diversification coincident with increasing 13 c values in the upper part of the middle bajocian last appearances prevail over first appearances associated with the peak of the 13 c event this may indicate maximum eutrophic conditions coincident with the late bathonian early callovian positive 13 c shift the radiolarian associations record a different trend with respect to the bajocian event when the 13 c values are increasing to a maximum radiolarian associations tend to be reduced in species diversity followed by a small diversification trend when the 13 c values are decreasing we speculate that during the callovian a more stressful palaeoenvironment due to high level of eutrophication is indicated by the combination of high productivity of biogenic silica and low carbonate input although varying preservational conditions may have influenced the observed trends in the radiolarian associations the good correlation between changes of sedimentation patterns radiolarian assemblages and 13 c positive anomalies open interesting avenues for further investigations concerning the palaeoecology of mesozoic radiolarians

gravity anomalies flexure and the elastic thickness structure of the india eurasia collisional system wehaveusedbouguergravityanomalyandtopographydatatodeterminetheequivalentelasticthicknessofthelithosphere te in the region of the india eurasia collisional system comparison of observed and modelled gravity anomalies along 1dimensional profiles suggest there are significant variations in te along strike of the himalaya foreland estimates decrease from a high of 70 km in the central region to 30 50 km in the east and west we have verified these inferences of spatial variations using a 2 dimensional non spectral interative flexure and gravity anomaly modelling technique the himalaya foreland forms a high te 40bteb100 km rigid block with a well defined edge as shown by the localisation of faulting and deformation along its northern margin other highteblocks occur to the north beneath the qaidam and sichuan basins the tibetan plateau forms a low te 0bteb20 km weak region that extends from the central part of the plateau into south western china tectonic styles in the india eurasia collisional system therefore involve both drigidt and dnon rigidt blocks where high te rigid blocks are present the stylesdominatedbyunderthrustingofthemorerigidblock wherethecollisionalzoneisnotconstrainedbyrigidblocks however the style appears to be dominated by lower crustal flow and a more continuous style of deformation d 2005 elsevier b v all rights reserved

acid processing of pre tertiary radiolarian cherts and its impact on faunal content and biozonal correlation the numbers of radiolarians visible in thin sections of chert rich rocks are commonly an order of magnitude greater than the numbers observed on the surfaces of fragments etched by hydrofluoric acid hf and typically orders of magnitude greater than the numbers of individuals found in hf processed residues destruction of radiolarians during both diagenesis and hf processing severely reduces faunal abundance and diversity and affects the taxonomic and biostratigraphic utility of chert residues the robust forms that survive the processing represent only a small fraction of the death assemblage and delicate skeletal structures used for species differentiation commonly preserved in limestone radiolarian faunas are either poorly preserved or dissolved in many coeval chert residues first and last occurrences of taxa in chert sequences are likely to be coarse approximations of their true stratigraphic ranges precise correlation is difficult between biozonations based solely on index species from cherts and those constructed from limestone faunas careful selection of samples in sequence use of weaker hf solutions and study of both chert and limestone faunas should yield better biostratigraphic information

patterns of biotic change in middle jurassic to early cretaceous tethyan radiolaria abstract the rate of taxic turnover of nearly 400 radiolarian species subspecies is analyzed in order to document long term biotic change of plankton during the middle jurassic to early cretaceous aalenian to aptian the pattern and dynamic of diversity change is described using four indices rate of species first and last occurrence rate of diversification and rate of turnover plots of cumulative sampling effort suggest that the analyzed data represent an adequate sample of total standing diversity for most examined stages rates of species first occurrence exceed rates of last occurrence for most of the middle jurassic except for the middle bajocian in contrast the late jurassic was a time of decreasing radiolarian diversity and the kimmeridgian records the lowest rate of diversification it is followed by a dramatic increase in first occurrences near the jurassic cretaceous boundary with as a result the highest rate of diversification recorded in the late tithonian regional radiolarian diversity was stable throughout most of the early cretaceous a stratigraphic permutation test was performed to assess the influence of uneven sampling on the observed pattern of taxic turnover and identified the intervals for which randomly obtained patterns are significantly different from the observed pattern the kimmeridgian and late tithonian events coincide with substantial climate derived perturbations in water cycling nutrient supply and oceanic productivity they point to a negative relationship between radiolarian macroevolution and changes in the state of nutrient availability although further work is needed to refine the temporal resolution of this relationship and to explore ecological aspects of its causal link with respect to radiolarian evolution

orogenic pulses in the alberta rocky mountains radiometric dating of major faults and comparison with the regional tectono stratigraphic record radiometric ages from regionally distributed thrust fault gouge show that the eastward propagation of the southern rocky mountain fold and thrust belt in canada occurred in four orogenic pulses that correlate with tectonic events of the cordilleran interior and with depositional patterns in the adjacent foreland in the main ranges the pyramid 163 0 ma simpson pass 161 7 ma and johnson creek 145 7 ma thrusts were related to the initiation of thin skinned deformation from jurassic terrane accretion and were partly contemporaneous with development of the first clastic wedge in the foreland basin in the front ranges the emplacement of the greenock thrust 103 1 ma and broadview snake indian thrust 99 2 ma was contemporaneous with development of cenomanian deltaic deposits in the immediate foreland three thrusts in the front ranges rocky pass 74 8 ma sulfur mountain 75 6 ma and clearwater 74 2 ma thrusts define a campanian phase of tectonic loading that led to the last major transgression in the southern portion of the alberta foreland along the eastern margin of the front ranges the mcconnell thrust 54 0 ma together with the muskeg 52 4 ma brule 53 9 ma and nikanassin 52 1 ma thrusts in the foothills recorded the last phase of regional contraction the late jurassic mid cretaceous late cretaceous and early eocene deformation pulses are separated by relatively long periods 40 m y 20 m y and 10 m y of tectonic quiescence these spatially and temporally restricted fault motion pulses contrast with gradual forward fault propagation while regional eastward progression of deformation is preserved

beginning of foreland subsidence in the columbian sevier belts southern canada and northwest montana subsidence analysis and geometry of jurassic cretaceous foreland strata in northwestern montana and southern alberta and british columbia suggest that loading by the fold thrust belt in canada began as much as 40 m y earlier than in montana in canada early foreland basin deposits are late jurassic age thicken rapidly westward and are restricted to a narrow belt within 30 km of the thrust belt in western montana contemporaneous deposits are widespread and do not increase markedly in thickness toward the thrust belt the unconformity overlying these deposits also changes from canada where it is angular to a disconformity in western montana near great falls between these two areas foreland geometry is transitional over a distance of 250 km beyond the transition zone early foreland basin geometries are broadly consistent showing late jurassic foreland subsidence in southern canada and early cretaceous initial subsidence in the united states

flexural rigidity of the basin and range colorado plateau rocky mountain transition from coherence analysis of gravity and topography stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography however the spatial resolution of coherence analysis has been limited by use of two dimensional periodogram spectra from very large 105 km 2 windows that generally include multiple tectonic features using a two dimensional spectral estimator based on the maximum entropy method the spatial resolution of flexural properties can be enhanced by a factor of 4 or more enabling more detailed analysis at the scale of individual tectonic features this new approach is used to map the spatial variation of flexural rigidity along the basin and range transition to the colorado plateau and middle rocky mountains physiographic provinces large variations in flexural isostatic re sponse are found with rigidities ranging from as low as 8 7x102o n m elastic thickness t 4 6 km in the basin and range to as high as 4 1x1024 n m t 77 km in the middle rocky mountains these results compare favorably with independent determinations of flexural rigidity in the region areas of low flexural rigidity correlate strongly with areas of high surface heat flow as is expected from the contingence of flexural rigidity on a temperature dependent flow law also late cenozoic normal faults with large displacements are found primarily in areas of low flexural rigidity while deformation fronts of mesozoic tertiary overthrusts occur 0 to 100 km east of the low rigidity region the highest flexural rigidity is found within the archean wyoming craton where evidence suggests that deeply rooted cratonic lithosphere may play a role in deter mining the distribution of tectonism at the surface

the geological significance of pb bi and pb sb sulphosalts in the damajianshan tungsten polymetallic deposit yunnan province china abstract the sanjiang tethyan domain in se asia is one of the most important mineral belts in china cu pb zn ag au and sn are the most important resources in this domain while the tungsten mineralization is poorly reported in this study we report on mineralogy in recent discovered damajianshan dmjs tungsten cu as mo bi polymetallic deposit in the southern part of sanjiang tethyan domain related to triassic quartz porphyry studies have shown that besides common ore minerals such as native bismuth bismuthinite ikunolite some specific minerals of pb bi and pb sb sulphosalts e g izoklakeite bournonite cosalite and boulangerite have also been found based on paragenetic mineral assemblages fluid inclusions and thermodynamic studies the physicochemical conditions were evaluated for the entire metallogenic process the sulfur fugacity logf s2 ranges from 9 7 to 37 with ore forming temperatures between 190 c and 330 c and the oxygen fugacity logf o2 ranges from 37 5 to 38 5 when the temperature is 250 c the sulfur fugacity and oxygen fugacity show strong fluctuations with broadly negative correlation indicating that these variations in physicochemical conditions should be responsible for mineral assemblages and are one of the most significant factors leading to the formation of the dmjs deposit our mineralogical studies provide new information for tungsten mineralization and further exploration of tungsten resources in the sanjiang tethyan mineralization domain

low latitudinal standard permian radiolarian biostratigraphy for multiple purposes with unitary association graphic correlation and bayesian inference methods abstract the ideal goal of biostratigraphic studies is to make stratigraphic ranges of all species clear and to fix globally synchronous biohorizons as age controls however it is difficult to achieve this goal in simple traditional ways and so a new solution is proposed for permian radiolarian biostratigraphy to achieve this goal including to establish a globally applicable biostratigraphy to estimate the numerical age of biohorizons and to determine stratigraphic ranges at species level all 400 known permian radiolarian species approximately 70 stratigraphic sections and 1560 samples from 350 previously published papers about the low latitude tethys and panthalassa oceans were analyzed issues of permian studies are summarized and a solution is proposed from the cenozoic point of view considering traditional methods as well as successful methods in cenozoic radiolarian studies here we implement newly proposed methods that have never been used for permian radiolarian studies unitary association method uam minimum disordered biohorizon algorithm mdba graphic correlation gc and reiteration estimation rounds rer of these our proposed rer is a new method to predict the probability of the estimated age for a sample by bayesian inference and joint probability both statistical methods as these four methods are applicable to any biostratigraphic study the principals and practical applications of these methods are carefully explained so non specialists can understand the logical procedure as a result 15 unitary association zones uazs are established for the entire permian biostratigraphic scheme by uam the numerical ages of 42 first occurrences fos are estimated from non parametric data from the middle guadalupian middle permian to the uppermost lopingian uppermost permian by mdba and gc and the statistical likelihood uaz ranges of 165 species in the entire permian were obtained using the rer procedure a usability test of our uazs shows that 97 96 of the 933 tested samples from previously published papers are well correlated and without contradiction within the statistical error of cenozoic synchronous biohorizons at 1 4 myr 23 of 42 fos are potentially regarded as synchronous events as the statistical likelihoods of uaz ranges are estimated by bayesian inference these ranges can be updated by anyone

evolution of mid cretaceous radiolarians in response to oceanic anoxic events in the eastern tethys southern tibet china abstract oceanic anoxic events oaes are well known from their widespread black shale and carbon isotopic excursions in the western and eastern tethys and atlantic ocean however the weakest link in the studies of the oaes is biological evolution sedimentological biostratigraphical and geochemical data from albian to coniacian strata in southern tibet recorded turnover events and fluctuations in diversity of the radiolarian fauna within the eastern tethys during oae 1d and oae 2 abundant radiolarian fossils were obtained from the gyabula formation with 93 species from 43 genera identified and assigned to the mid to upper cretaceous acaeniotyle umbilicata archaeospongoprunum tehamaensis crucella cachensis alievium superbum and dictyomitra formosa zones the association of carbon isotopic excursions black shale and radiolarian turnover indicates extensive changes in the ocean climate system nutrients are made increasing available to the marine plankton through submarine volcanic activity and rising sea level which were a likely cause of radiolarian turnover at or near the oaes active submarine tectonism volcanism leads to the expansion of the hypoxic zone and may cause many deeper dwelling forms to become extinct whereas most of the shallower dwelling radiolarians survive radiolarian evolution thus provides a useful record with which to seek understand relationships between climate paleoceanographic processes and plankton evolution

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

late cretaceous subsidence in wyoming quantifying the dynamic component the late cretaceous western interior basin of north america is generally considered to have been a retroarc foreland basin flexural backstripping of the stratigraphic record from 97 2 ma to 73 4 ma along a section perpendicular to the wyoming idaho salient of the sevier belt clearly demonstrates that there were components of subsidence in addition to those driven by the thrust and associated sediment loads the simulation demonstrates that the flexural foredeep is only 180 120 km wide and shows a forebulge located near the subsequent laramide rock springs uplift foredeep strata between the rock springs uplift on the east and the thrust front to the west were mostly involved in the eastward overlapping thrust belt or deeply truncated by inferred rebound after 78 5 ma the difference between the observed decompacted cumulative subsidence and the amount of subsidence that can be explained by simple flexural loading the residual subsidence increases from 800 m in eastern wyoming to 1 8 km near the thrust belt the westward thickening upper cretaceous sediment wedge filled the accommodation space generated by downward tilting to the west of the north american cratonic margin by underplating and mantle flow associated with the shallowly subducted farallon plate

development of palaeozoic mesozoic radiolaria in the northwestern pacific rim abstract investigations of radiolaria allow us to trace the evolutionary trends and rates of these siliceous microorganisms within the northwestern pacific there are several phases or megacycles in the development of radiolarian fauna in northeastern and eastern russia in ascending order these are ordovician silurian devonian carboniferous early permian late permian triassic middle jurassic middle callovian barremian aptian early campanian late campanian early paleocene and late paleocene to recent no evidence has been found for mass extinction at higher taxonomic levels or for instantaneous catastrophic extinction several of the cycles are characterised by increased diversity and morphological specialization immediately prior to extinction recognition of megacycles permits us to hypothesize a close relationship between radiolarian events and palaeoceanographic palaeoclimatic and tectonic changes which took place in the pacific probably a sharp change of palaeohydrography and the opening of the new submarine seaways led to the appearance and radiation of new higher taxa including the order nassellaria in the early mesozoic

flexural versus dynamic processes of subsidence in the north american cordillera foreland basin 1 dynamic subsidence related to subduction is an important process in retroarc foreland basin systems dynamic subsidence in the north american retroarc foreland has been proposed as dominant in the late cretaceous however questions remain about the nature of the subcrustal load and the basin response to such processes we present new isopach data using 130 data points covering a large portion of the u s and a revised flexural analysis of the sevier foreland higher rigidity associated with the wyoming craton can best model flexural subsidence directly prior to 81 ma we constrain the transition from flexural to nonflexural subsidence to 81 ma and correlate this with large late cretaceous progradation the locus of subsidence and the location of the subducted shatsky oceanic plateau suggest that dynamic loading from viscous flow above the subducting plate is the mechanism driving dynamic subsidence in the retroarc foreland basin of the north american cordillera

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

lithospheric 3 d flexure modelling of the oceanic plate seaward of the trench using variable elastic thickness summary whendescribingthemechanicalbehaviourofthelithospheremodelledasathinplate themost important parameter corresponds to itsflexural rigidity which is commonly expressed through the effective elastic thickness te this parameter is a measure of the stiffness of the plate and defines the maximum magnitude and wavelength of those surface loads that can be supported without suffering unelastic deformation realistic 3 d models of the flexural response of the lithosphere near the trench are scarce because of the mathematical and computational complexity we present a method for determining the flexure of the lithosphere caused by the combined effect of 3 d seamount loading and bending of the lithosphere near the trench our method consists on solving numerically the flexure equations of the reissner mindlin thin plate theory including variable thickness using the finite element method with mesh adaptation the method was applied to study the flexure of the oceanic nazca lithosphere beneath the o higgins seamount group which lies 70km seaward of the chile trench the results show that an elastic thickness te of 5km under the seamounts a te of 15km far from the trench and a te of 13km near the trench can explain both the down deflection of the oceanic moho and bending of the oceanic lithosphere observed in seismic and gravity profiles in order to study the impact of high trench curvature on the morphology of the outer rise we apply the same methodology to study and model the flexure of the lithosphere in the arica bend region 14 s 23 s results indicate that the te values are overestimated if the 3 d trench curvature is not included in the modelling

jurassic onset of foreland basin deposition in northwestern montana usa implications for along strike synchroneity of cordilleran orogenic activity stratigraphic provenance and subsidence analyses suggest that by the middle to late jurassic a foreland basin system was active in northwestern montana united states u pb ages of detrital zircons and detrital modes of sandstones indicate provenance from accreted terranes and deformed miogeoclinal rocks to the west subsidence commenced ca 170 ma and followed a sigmoidal pattern characteristic of foreland basin systems thin jurassic deposits of the ellis group and morrison formation accumulated in a backbulge depozone a regional unconformity and or paleosol zone separates the morrison from early cretaceous foredeep deposits of the kootenai formation the model presented here is consistent with regional deformation events registered in hinterland regions and challenges previous interpretations of a strongly diachronous onset of cordilleran foreland basin deposition from northwestern montana to southern canada

evolution of the northern cordilleran foreland basin during the middle cretaceous a detailed study of the middle late cenomanian belle fourche formation in southern alberta helps to elucidate the evolution of the cordilleran foreland basin during the middle cretaceous by combining isopach data from the study area with previously published research on middle cretaceous stratigraphy in adjacent areas of northern alberta and montana it is possible to defi ne the position of the proximal foredeep forebulge and backbulge depozones from late albian to cenomanian time the foredeep probably lay to the west of the present fold thrust belt in western montana from the late albian to middle cenomanian with the forebulge extending northwestward through the northwest corner of wyoming and curving northeastward through the present day location of calgary thick dunvegan deposits middle cenomanian of northwestern alberta are interpreted as foredeep deposits palinspastic reconstruction of the southern rocky mountains of alberta is consistent with a location of the foredeep within the area of the present fold thrust belt at the end of the middle cenomanian the forebulge retreated westward within alberta defi ning a nearly straight northwest southeast trend through the present position of the foothills and front ranges of alberta and northwestern montana the change in trend of the foreland basin at the end of the middle cenomanian may refl ect the change of convergence vectors along the western margin of north america during the middle cretaceous

early paleozoic radiolarian biozonation current knowledge of early paleozoic radiolarians permits the recognition of faunal assemblages and zones that constitute a biozonation this new zonation utilizes robust and relatively common easily recognized morphotypes it will facilitate rapid acquisition of previously unavailable age constraints for marine siliceous sedimentary successions in hitherto poorly understood early paleozoic orogenic collages

flexure of the lithosphere and the geodynamical evolution of non cylindrical rifted passive margins results from a numerical model incorporating variable elastic thickness surface processes and 3d thermal subsidence we present a new numerical model to calculate the surface deflection of a two dimensional yet variable thickness thin elastic plate the model is based on a multi grid finite difference solution of the fourth order differential equation that incorporates the terms arising from the non uniform thickness assumption the model has been developed to calculate the flexural response of the continental lithosphere subjected to an arbitrary instantaneous stretching the flexural model is coupled to a a finite element three dimensional thermal model incorporating the conduction advection and production terms that allows the computation of the thermal subsidence resulting from the stretching induced perturbation of the isotherms assuming that the effective elastic thickness is controlled by the depth to a given isotherm and b a finite difference surface process model that assumes that transport is linearly proportional to slope leading to a second order diffusion type partial differential equation the model also incorporates the effect of sediment compaction we present a series of simple benchmarks that demonstrate the accuracy of the model we also present results of simple 2d and 3d stretching experiments highlighting the importance of 3d flexural effects and the assumed variable elastic thickness on the development of a passive margin and its thermal evolution finally we perform a numerical experiment based on a stretching geometry derived from the present day geometry of the western africatransform margin to predict sediment accumulation patterns and a stratigraphic architecture which we can compare to observations

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

an iterative spectral solution method for thin elastic plate flexure with variable rigidity s u m m a r y thin plate flexure theory provides an accurate model for the response of the lithosphere to vertical loads on horizontal length scales ranging from tens to hundreds of kilometres examples include flexure at seamounts fracture zones sedimentary basins and subduction zones when applying this theory to real world situations most studies assume a locally uniform plate thickness to enable simple fourier transform solutions however in cases where the amplitude of the flexure is prominent such as subduction zones or there are rapid variations in seafloor age such as fracture zones these models are inadequate here we present a computationally efficient algorithm for solving the thin plate flexure equation for non uniform plate thickness and arbitrary vertical load the iterative scheme takes advantage of the 2 d fast fourier transform to perform calculations in both the spatial and spectral domains resulting in an accurate and computationally efficient solution we illustrate the accuracy of the method through comparisons with known analytic solutions finally we present results from three simple models demonstrating the differences in trench outer rise flexure when 2 d variations in plate rigidity and applied bending moment are taken into account although we focus our analysis on ocean trench flexure the method is applicable to other 2 d flexure problems having spatial rigidity variations such as seamount loading of a thermally eroded lithosphere or flexure across the continental oceanic crust boundary

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

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

influence of attenuated lithosphere and sediment loading on flexure of the deep water magallanes retroarc foreland basin southern andes flexural subsidence in foreland basins is controlled by applied loads such as topography water sediment and subcrustal forces and the mechanical properties of the lithosphere we investigate the controls on subsidence observed within the upper cretaceous magallanes retroarc foreland basin of southern south america to evaluate the impact of lateral variations in flexural rigidity due to late jurassic extension conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep water cenomanian turonian basin strata however models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns results satisfy paleobathymetric observations in the magallanes basin and suggest that lithospheric thinning is necessary to produce both long wavelength and deep subsidence during late cretaceous basin evolution results indicate that elastic thickness decreases westward from 45 25 km in the distal foreland to 37 15 km beneath the foredeep these findings are consistent with a westward reduction in crustal thickness associated with the jurassic extensional history of the patagonian lithosphere our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift we propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time these findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories

toarcian radiolaria from mt mangart slovenian italian border and their paleoecological implications abstract diverse and well preserved toarcian radiolarians have been recovered from a succession of organic rich shale with intercalations of siliceous limestone the succession is located at the slovenian italian border in the julian alps and was deposited on a subsided block pertaining to the south tethyan passive continental margin twenty spumellarian and 17 nassellarian genera were found in total thirty six taxa were identified to species level and one new species bistarkum mangartense n sp is described the assemblages show a high predominance of spumellarians over nassellarians spongy spumellarians especially orbiculiforma are markedly abundant pantanelliidae are generally rare but reach a pronounced peak of 13 in one stratigraphic level among nassellarians parahsuum is the most abundant but members belonging to syringocapsidae are scarce to absent in addition to paleolatitude and water column depth ecological conditions accompanying the early toarcian global anoxic event may have to a considerable extent determined the specific taxonomic composition of these radiolarian faunas

the cypress hills formation upper eocene to miocene a semi arid braidplain deposit resulting from intrusive uplift the upper eocene miocene cypress hills formation of the cypress hills plateau in southwestern saskatchewan and southeastern alberta is interpreted as a braidplain deposit the regional paleoslope dipped to the northeast and the east west distribution of outcrop exposes facies representing lateral variation across the slope of the braidplain overall the average clast size of the deposits decreases from west to east with western area sediments dominated by boulder sized gravels deposited on longitudinal bars the eastern outcrop area contains deposits of braided channels cut into and interbedded with finer interchannel material including lacustrine marlstones silcretes and debris flow deposits the latter commonly containing abundant fossils the gravels of the cypress hills formation are multicyclic they were originally derived from the western ranges of the rocky mountains during laramide orogenesis and later shed farther into the basin during rebound due to unloading of the laramide thrusts by

the modern foreland basin system adjacent to the central andes regional variations in sediment thickness internal structures average elevation and bouguer gravity define a four component foreland basin system adjacent to the central andes in the most proximal part of the foreland basin system the eastern subandean zone and westernmost chaco plain 1 3 km of cenozoic deposits overlies active folds and thrusts of the frontal andean orogenic wedge these wedge top deposits pass cratonward into a foredeep depozone containing a 3 4 km thick sedimentary prism that tapers toward and locally pinches out against a broad wavelength forebulge in the central eastern chaco plain the forebulge is underlain by precambrian mesozoic rocks and is largely covered by a thin veneer of quaternary alluvium east of the forebulge a thin 0 5 km saucer shaped accumulation of sediment beneath the pantanal wetland represents a back bulge depozone ancient counterparts of these four depozones can be identified in the central andes suggesting that modern basin architecture is the result of continuous eastward migration of the coupled orogenic wedge and foreland basin system since the late cretaceous paleocene