impact of active faulting on the post lgm infill of le bourget lake western alps france we have used high resolution seismic imaging to detect and characterize the recent deformation recorded by the quaternary sediments of le bourget lake the last glacial episodes mis 6a and 2 i e riss and wurm scoured out an elongated over deepened basin to more than 300 m below the present lake level and the basin accumulated 150 m of post lgm to holocene sediments the well stratified character of the infill is locally disturbed by tectonic deformations and gravity reworking a northern fault zone in continuation with the left lateral strike slip culoz fault is imaged within the holocene and late glacial accumulations a southern fault zone is also detected which can be related to the sublacustrine continuation of a much smaller fault affecting the jura alpine foreland the col du chat left lateral strike slip fault different generations of fractures have been identified in the lake allowing correlation and mapping in pre quaternary substratum the culoz fault has a n 160 orientation within the post lgm sediments fractures related to the culoz fault have an orientation between n135 and 95 a cloos model 1932 is thus proposed to explain the observed pattern of lacustrine deformations the calculated horizontal slip rate for culoz fault during holocene is about 1 3 mm yr 1 and for the col du chat fault is around 0 6 mm yr 1

present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

constraints on the deep structure and dynamic processes beneath the alps and adjacent regions from an analysis of gravity anomalies summary gravity anomalies including terrain corrections over the western alps and the molasse basin are within 30 mgal of those calculated assuming local airy isostatic equilibrium but isostatic anomalies over regions nw and se of the alps exceed 50 mgal therefore mass excesses and deficits that must be supported by the strength of the lithosphere or by dynamically induced stress in the asthenosphere appear to be greater beneath the areas surrounding the alps than beneath the alpine chain itself attempts to account for the gravity gradient over the molasse basin and sub alpine chains and the small bouguer anomalies measured over the elevated areas of the vosges and black forest by the flexure of an elastic plate require an absurd set of parameters the high elevations of the vosges and the black forest are presumably due to high temperature in the underlying uppermost mantle but the deviations from isostatic equilibrium as well as the high temperature probably result from active upwelling in the asthenosphere beneath this area the absence of large isostatic anomalies over the alps and the failure of an elastic model to account for the gravity anomalies over the molasse basin suggest that the dynamic processes that flexed the european plate down to form the molasse basin and that built the alpine chain have waned the late cenozoic uplift of the molasse basin and the alps might be a consequence of a diminution or termination of downwelling of mantle material beneath the alps

flexural eustatic numerical model for drowning of the eocene perialpine carbonate ramp and implications for alpine geodynamics the paleocene2eocene nummulitic limestone formation of the alpine periphery occupies the lowermost part of a stratigraphic trinity above a major basal unconformity it is thought to have accumulated as a foraminiferal carbonate ramp at the distal featheredge of the underfilled north alpine and southwest alpine foreland basin we present the results of a numerical model that links carbonate sedimentation at the distal featheredge of a peripheral foreland basin to the flexural subsidence of an elastic plate subjected to a distributed load with a superimposed eustatic sea level history carbonate accumulation is treated as depth dependent model parameters are constrained by geological and geophysical observations of the alpine orogen and its peripheral foreland basin and from literature on the ecology of benthic foraminifers the generic alpine model shows that the carbonate ramp accumulates as a number of sedimentary cycles before rapid drowning giving rise to a retrogradational stratigraphic package terminated by a surface of accelerated transgression and backstepping running the model with sets of parameter values appropriate to the paleocene to middle eocene nummulitic limestone in central eastern switzerland and the late eocene nummulitic limestone

deformation in the jura mountains france first results from semi permanent gps measurements new gps estimates of relative motion across the jura mountain belt with respect to the eurasian plate indicate less than 1 mm yr of convergence considerably less than previous estimates velocity uncertainties have been evaluated by several methods and range from 0 2 to 0 5 mm yr for the semi permanent stations the major statistically significant strain feature inferred by the jura gps measurements is along arc extension compatible with tectonic studies that the detected deformation is small in magnitude highlights two important issues previous estimates are over stated and that the approach of using semi permanent gps installations is capable of detecting small tectonic signals using the upper bound as the rate of convergence we estimate that this would generate an earthquake of magnitude 5 5 5 every 15 to 75 yr

seismotectonics and 1 d velocity model of the greater geneva basin france switzerland the greater geneva basin located in south western switzerland and neighboring france is enclosed by the rotating north western edge of the alpine front and the jura mountains chain recently this basin has received increasing attention as a target for geothermal exploration historical and instrumental seismicity suggest that faults affecting the basin may still be active moderate magnitude earthquakes have been located along the vuache fault a major strike slip structure crossing the basin before geothermal exploration starts it is key to evaluate the seismic rate in the region and identify possible seismogenic areas in this context we deployed a temporary seismic network of 20 broadband stations from september 2016 to january 2018 to investigate the ongoing seismic activity its relationship with local tectonic structures and the large scale kinematics of the area our network lowered the magnitude of completeness of the permanent swiss and french networks from 2 0 to a theoretical value of 0 5 using a new coherence based detector lassie particularly effective to detect microseismicity in noisy environments we recorded scarce seismicity in the basin with local magnitudes ranging from 0 7 to 2 1ml no earthquakes were found in the canton of geneva where geothermal activities will take place we constructed a local minimum 1d p wave velocity model adapted to the greater geneva basin using earthquakes from surrounding regions we relocated the events of our catalogue obtaining deeper hypocenters compared to the locations obtained using the available regional velocity models we also retrieved 8 new focal mechanisms using a combination of polarities and waveform inversion techniques csps the stress inversion shows a pure strike slip stress regime which is in agreement with structural and geological data combining the background seismicity with our catalogue we identified seismogenic areas offsetting the basin

geochemistry of oolitic iron ores an electron microprobe study oolitic iron ores are made up of silicate oxide and carbonate minerals that are part of solid solution series the compositions of the minerals can depart from pure end members and show variation among deposits this variability can be quantified using electron microprobe techniques iron silicates are represented by chamositic clays both berthierine and chamosite glauconite was not seen in any of these samples berthierine predominates in younger deposits whereas the paleozoic ores studied contained only chamosite compositions of the chamositic clays however were independent of age iron oxides are mostly goethite in younger deposits or hematite in older deposits both minerals lack appreciable al in solid solution most analyses show small amounts of al but usually balanced by si in the same proportion as in chamosite indicating a slight admixture of clay iron carbonates are siderite with appreciable substitution of ca and mg but not of mn apatite is common but no iron phosphates were found the compositions of the silicates and carbonates are close to those reported for early diagenetic minerals from other types of sedimentary rocks indicating that ironstone formation does not require unusual chemical conditions other than a large supply of iron the analytical results can be used to argue against several hypotheses of ironstone genesis the lack of al in the goethitic and hematitic ooliths is inconsistent with an origin either by redeposition of soil ooliths or by oxidation and leaching of earlier chamositic ooliths the presence of high al contents in the chamositic ooliths shows that they cannot have formed from earlier aragonitic ooliths and the presence of small amounts of chamositic clay and apatite as discrete laminae in goethitic and hematitic ooliths suggests that this type of oolith could also not have formed by replacement of aragonite times of ironstone deposition show a correlation with climate and sea level stands that suggests a mechanism for generating locally high iron concentrations in seawater a combination of a warm humid climate and low average continental relief would intensify lateritic weathering and the formation of iron enriched detritus coincidence of this increased detrital iron supply with intensification and shallowing of the oxygen minimum layer in the ocean could lead to mobilization of iron from offshore shelf clastics to be redeposited near the shoreline in intertidal to shallow subtidal environments

nappe geometry in the western swiss alps abstract detailed geological mapping during the last 20 years in the western swiss alps has shown clearly that most of the lower basement nappes are fold nappes possessing normal and inverted limbs moreover their cores are made of strongly deformed gneisses indicating that important ductile strain took place during the formation of the fold nappes it is therefore probably wrong to imagine deep basement nappes as rigid slices as often actually claimed especially when interpreting seismic profiles true brittle type thrust nappes involving basement rocks only occur in the internal and upper parts of the belt cover nappes on the contrary are in most parts of the alpine belt thrust sheets following more or less the rules of thin skinned tectonics many basement fold nappes lost part of their sedimentary cover during or just before their formation by decollement along ductile horizons the result is that many cover thrust nappes in the external part of the alps are directly related to their original basement fold nappes

tephrochronology magnetostratigraphy and mammalian faunas of middle and early pleistocene sediments at two sites on the old crow river northern yukon territory canada abstract alluvial and lacustrine sediments exposed beneath late pleistocene glaciolacustrine silt and clay at two sites along the old crow river northern yukon territory are rich in fossils and contain tephra beds surprise creek tephra szt occurs in the lower part of the alluvial sequence at crh47 and little timber tephra ltt is present near the base of the exposure at crh94 surprise creek tephra has a glass fission track age of 0 17 0 07 ma and little timber tephra is 1 37 0 12 ma all sediments at crh47 have a normal remanent magnetic polarity and those near ltt at crh94 have a reversed polarity in agreement with the geomagnetic time scale small mammal remains from sediments near ltt support an early pleistocene age but the chronology is not so clear at crh47 because of the large error associated with the szt age determination tephrochronological and paleomagnetic considerations point to an mis 7 age for the interglacial beds just below szt at crh47 and at chester bluffs in east central alaska but mammalian fossils recovered from sediments close to szt suggest a late irvingtonian age therefore older than mis 7 further studies are needed to resolve this problem

palynostratigraphy of some pleistocene deposits in the western alps a review in the alps interglacial and interstadial deposits are rarely preserved due to the intense erosive effect of glaciers in the valleys fortunately some outcrops and cored sequences located in the field area ranging from lyon to evian provided sedimentary profiles datable by palynostratigraphy in a highly documented geomorphological context an overview of several palynological sequences studied in this large area is proposed and their position in a general chronostratigraphical pattern is discussed particular attention is paid to palynostratigraphical evidence whose relevance is tested with systematic comparisons with long reference european pollen sequences spanning several glacial cycles minimum ages are suggested for non glacial episodes corresponding to the deposits studied

facies analysis and palaeoclimatic significance of ironstones formed during the eocene greenhouse lower and middle eocene ironstone sequences of the naqb and qazzun formations from the north east bahariya depression western desert egypt represent a proxy for early palaeogene climate and sea level changes these sequences represent the only palaeogene economic ooidal ironstone record of the southern tethys these ironstone sequences rest unconformably on three structurally controlled cenomanian palaeohighs for example the gedida harra and ghorabi mines and formed on the inner ramp of a carbonate platform these palaeohighs were exposed and subjected to subaerial lateritic weathering from the cenomanian to early eocene the lower and middle eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies the distribution of low energy ironstone facies is controlled by depositional relief these deposits consist of lagoonal burrow mottled mud ironstone and laterally equivalent tidal flat stromatolitic ironstones the agitated water ironstone facies consist of shallow subtidal intertidal nummulitic ooidal oncoidal and back barrier storm generated fossiliferous ironstones the formation of these marginal marine sequences was associated with major marine transgressive regressive megacycles that separated by subaerial exposure and lateritic weathering the formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features such as colloform texture and alveolar voids implies periods of humid and warm climate followed major marine regressions the formation of the lower to middle eocene ironstone succession and the associated lateritic palaeosols can be linked to the early palaeogene global warming and eustatic sea level changes the reworking of the middle eocene palaeosol and the deposition of the upper eocene phosphate rich glauconitic sandstones of the overlying hamra formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions

crustal structure and dynamics in the rhine graben and the alpine foreland summary the rhine graben rift stretches for 300 km from basel to frankfurt the axis of maximum subsidence switches from west in the southern graben to east in the northern graben subsidence in the south began in the upper eocene and was interrupted in the mid miocene by a broad uplift of 1 1 5 km in the vosges schwarzwald black forest region whereas subsidence in the north proceeded continuously from the lower oligocene to the present a combined geophysical and geological interpretation of the rhine graben is presented in the form of a 3 d gravity model and 2 d flexural plate modelling from the alps across the alpine foreland to the rhenish massif modelling is based on crustal structure revealed by geologic gravity and seismic data including ecors dekorp and egt profiles the 3 d gravity modelling supports a modest density contrast of 0 3 g cm 3 at the crust mantle boundary since there is no evidence of a large scale upper mantle anomaly a dense lower crust 2 9 3 0 g cm 3 is proposed as the cause of this modest density contrast the presence of a dense mafic lower crust in south west germany is corroborated by lower crustal xenoliths elevated p wave velocities 6 7 7 2 km s 1 and high poisson s ratios 0 26 0 29 residual gravity and magnetic data reveal strong crustal heterogeneities particularly from the dense magnetic saxothuringian terrane to the light non magnetic moldanubian terrane the polarity of the asymmetric rhine graben reverses at this variscan tectonic boundary light graben fill can account for nearly the entire 20 40 mgal short wavelength gravity minimum but the presence of intrusive bodies ranging from granitic to mafic composition can also strongly influence the local gravity field 2 d modelling of the flexure of the european lithosphere along seven 1000 km long profiles indicates a flexural bulge of 1 1 5 km in the alpine foreland of southern germany which corresponds to an ene trending moho uplift of the same magnitude and to a band of free air gravity highs longer flexural wavelengths in the east indicate increasing lithospheric rigidity and increasing elastic thickness towards the bohemian massif the vosges schwarzwald dome is interpreted as the intersection of the oligocene rhine graben rift and associated rift flank uplift with the mid miocene flexural bulge

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

the jura mountains an active foreland fold and thrust belt abstract recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the swiss and french jura mountains combined with previously published stress data allow a detailed description of the contemporary state of stress in this fold and thrust belt and the adjacent foreland five stress provinces can be recognized with two different general orientations of maximum horizontal stress sh 1 the central and southwest provinces with a nnw sse to nne ssw orientation 2 the east northwest and southeast provinces with an e w to nw se orientation stress magnitudes are in general higher in the southern than in the northern jura mountains characteristic of the northern jura is an e w trending zone of low stress magnitudes which can be traced from the bresse depression south of besancon to the eastern end of the jura northwest of zurich boundaries of stress provinces show poor agreement with boundaries of tectonic units in the jura in addition stress provinces extend beyond the boundaries of the jura mountains into their foreland furthermore palaeo stress orientations show large discrepancies with respect to the contemporary stress orientation these findings are considered to indicate a termination of jura thin skinned foreland tectonics which probably took place some time between 9 and 4 ma according to palaeontological and tectonic evidence it is suggested that a new style of tectonics has commenced in the jura mountains deforming both the basement directly below the jura fold and thrust belt and the cover rocks in a similar mode

fission track ages of late cenozoic distal tephra beds in the yukon territory and alaska six distal tephra beds from the yukon territory and alaska have been dated by the fission track method zircon and glass ages were determined for the fort selkirk and lost chicken tephra beds but only glass ages for the others assuming that no track fading has occurred in the glass old crow and dawson tephra beds are younger than 120 000 and 52 000 years bp respectively mosquito gulch tephra is 1 22 ma old fort selkirk tephra is about 1 ma old the ester ash bed is 0 45 ma old and the best estimate of the age of lost chicken tephra is the range 1 7 2 6 ma it is evident from these results and from the known abundance of tephra beds within late cenozoic deposits of the yukon territory and alaska that application of the fission track method to distal tephra in conjunction with detailed characterization studies offers great potential for elucidation of the late cenozoic geologic history of alaska and the yukon territory

combining amphibious geomorphology with subsurface geophysical and geological data a neotectonic study at the front of the alps bernese alps switzerland abstract in the vicinity of lake thun at the front of the bernese alps switzerland we performed a multidisciplinary neotectonic study combining onshore and offshore geological data and geophysical measurements in order to identify potentially active fault structures paleoseismic reconstructions on the northern margin of the alps have documented several strong earthquakes with moment magnitudes 6 during the late quaternary which have long recurrence intervals of 1 000 to 2 000 years such earthquakes are expected to produce surface ruptures in this light we investigated the study area located near lake thun primarily for on fault evidence to date still a shortcoming in switzerland we detected several features indicating potential fault activity such as aligned subaquatic morphological depressions offset horizons observed in reflection seismic profiles of lake sediments and in ground penetrating radar images all delineating a fault trace observations of fluvial deposits in a nearby gravel pit in the prolongation of the inferred structure supports these findings a narrow zone with rotated long axes of pebbles inclining at 60 is clearly distinguishable and crosscuts the original bedding with predominantly horizontal orientation of pebble axes this zone further shows an apparent 1 1 m offset of oxidized horizons and is therefore considered as a potential fault plane in a normal faulting regime a dated radiocarbon age of 11 000 years bp of the gravel deposits hence suggests a younger fault activity during the holocene the einigen fault zone efz proposed on the basis of these observations is considered as a complex fault system with a combination of dextral strike slip and normal faulting as suggested by gpr images observations in the gravel pit and radar data independently show that it includes at least two fault strands however while five earthquakes with epicentral intensities i 0 vi and numerous smaller seismic events are known within less than 30 km epicentral distance to lake thun over the past 400 years none of these seem to coincide with the location of the efz

present day vertical displacements in the north western alps and southern jura mountains data from leveling comparisons two high precision leveling networks were successively surveyed in france the ngf measured during the 1886 1907 period and the ign69 measured from 1965 to 1979 the accuracy of these levelings standard deviation of 1 8mm km to 3 8mm km allows us to compute the vertical displacements of the benchmarks between two different eras the results indicate the occurrence of discrete zones of uplift and subsidence 1 a regional uplift up to 1 4 mm yr of the subalpine massifs 2 an important uplift of the internal jura up to 2 mm yr 3 a relative subsidence of the southern part of the jura 0 8 mm yr and 4 a relative subsidence of the bresse basin with respect to the external jura comparing the spatial distribution of zones of uplift and their respective vertical displacement rates with a regional structural cross section leads to the conclusion that present day uplift of the belledonne and bornes massifs and of the internal parts of the jura mountains can be explained by crustal shortening along a major basement involving thrust fault this fault ramps up under the bornes massif from a depth of 12 km to 7 km turns into a flat under the molasse basin ramps up to the top of the basement at the north eastern margin of the internal jura mountains and reaches the surface in the external jura the saleve ramp anticline is carried by a bifurcation of this thrust horizontal displacement rates of 6 mm yr at the bornes ramp 2 mm yr at the saleve ramp and 4 mm yr at the internal jura ramp have been determined by inversion of profiles of uplift rates whether this basement involving thrust fault was already active during the miocene main folding phase of the jura mountains or whether it was activated only during pliocene pleistocene times is subject to debate

a catalogue of late cenozoic tephra beds in the klondike goldfields and adjacent areas yukon territory preece s j westgate j a froese d g pearce n j g perkins w t 2011 a catlogue of late cenozioc tephra beds in the klondike goldfields and adjacent areas yukon canadian journal of earth sciences 48 10 1386 1418

the ml 5 3 epagny french alps earthquake of 1996 july 15 a long awaited event on the vuache fault the ml 5 3 epagny earthquake that occurred on 1996 july 15 in the vicinity of annecy french alps was the strongest event to shake southeastern france in the last 34 years moderate to serious damage in the annecy area is consistent with msk intensities of vii viii this earthquake occurred on the vuache fault a geologically well known morphologically clear nw se trending strike slip fault that links the southern jura mountains with the northern subalpine chains the hypocentre was located in mesozoic limestones at shallow depths 1 3 km the focal mechanism indicates left lateral strike slip motion on a n136 e striking plane dipping 70 to the ne abundant field evidence was gathered in the days following the main shock several hundred aftershocks were recorded thanks to the rapid installation of a 16 station seismic network all aftershocks occurred along the southernmost segment of the vuache fault defining a 5 km long 3 5 km deep n130 e striking rupture zone dipping 73 to the ne the fault plane solutions of 60 aftershocks were found to be consistent with left lateral slip on nw se striking planes at the se tip of the aftershock zone we found ground cracks parallel to the fault close to the annecy meythet airport runway at the nw tip near bromines we observed left lateral displacement of concrete walls in a building we also noticed flow changes in two springs close to that locality geodetic levelling across the fault revealed about 1 cm of uplift for the region north of the fault the recording of aftershocks with a six station accelerometric network showed that lacustrine deposits locally amplified the ground motion up to eight times which explains how this moderate magnitude shock could cause such heavy damage historical records draw attention to the central segment of the vuache fault which has been locked for at least 200 years situated nw of the 1996 aftershock zone between the mandallaz and vuache mountains this segment forms a 12 km long potential seismic gap where other m5 events or one single m6 event might occur

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

origin and palaeogeographical distribution of the viruan iron and phosphate ooids in estonia evidence from mineralogical and chemical compositions abstract the occurrence of iron ooid beds in the ordovician sequence of baltoscandia has been known for a long time in estonia the best developed ooid beds are known to occur at two levels in the lower oelandian to middle ordovician viruan boundary interval being restricted to the kunda and aseri lasnamagi stages respectively according to outcrop and subsurface data these ooid beds can be traced from hiiumaa island estonia to the st petersburg area russia in the east the geographic and stratigraphic distribution of the viruan oolite body indicates that the source material was derived from a land area located northwest to north northwest of tallinn the presence of well developed hardgrounds at the base of viruan oolite suggests that ooid formation took place during a deepening event two mineralogically different ooid groups have been identified in this study brown ooids composed of iron oxy hydroxides and apatite and light grey ooids composed primarily of carbonate fluorapatite the latter probably formed through early diagenetic alteration of the brown ooids brown ooids contain over 60 of iron oxy hydroxide and remnants of an unidentified silicate mineral the concentric lamination is composed of alternating laminae of phosphate francolite and iron oxy hydroxide the trace element abundances in the ooids are strongly influenced by the phosphate content as is the observed ree distribution pattern the chondrite normalized ree patterns are characterized by enrichment of the lighter ree and have a typical negative eu anomaly of about 0 7 shale normalized ree patterns have a hat shape similar to ree patterns found in conodonts and other biogenic apatite thin volcanic ash beds have been recorded at this level in sweden in estonia however there are no visible indications of volcanic material

constraints from 40ar 39ar geochronology on the timing of alpine shear zones in the mont blanc aiguilles rouges region of the european alps the mont blanc and aiguilles rouges massifs which form part of the external crystalline massifs of the western european alps record a young and fast exhumation history as established by an extensive low temperature thermochronology and geochronology data set various kinematic and dynamic models for oligocene to neogene deformation and exhumation of the aiguilles rouges mont blanc system have been proposed however the timing of deformation along major shear zones in and around the massifs which is crucial to these models is still controversial our new 40ar 39ar data from key deformation zones in the mont blanc area show that nw directed thrusting lasted from oligocene to mid miocene times in the mont blanc massif before a nw ward jump of the deformation front to below the aiguilles rouges massif which led to updoming of the aiguilles rouges and mont blanc massifs this deactivated the main nw verging shear zones and caused back folding and back thrusting east of the mont blanc as well as upward extrusion of the aiguilles rouges massif subsequently there was a switch to more coaxial shortening between the aiguilles rouges and mont blanc massifs associated with strain partitioning and related dextral strike slip deformation on the eastern side of the mont blanc massif

microporous and tight limestones in the urgonian formation late hauterivian to early aptian of the french jura mountains focus on the factors controlling the formation of microporous facies microporous and tight limestones with contrasting porosity and permeability values directly related to the microfabric of the micritic matrix outcrop in the urgonian formation of the french jura mountains this study investigates the factors controlling the differentiation between the microporous and tight facies and proposes a diagenetic model for the development and preservation of the microporosity in these limestones the petrophysical properties are not related to the depositional texture the petrographical content or the mineralogical composition however the tight layers contain indications of emersion e g bird eyes keystone vugs and desiccation cracks the sedimentation in very shallow conditions up to emersion is confirmed by the covariant more positive values of oxygen and carbon isotopes the microporous intervals systematically occur a few meters below the tight layers affected by emersion this position strongly suggests the importance of meteoric water input rapidly after sedimentation in the differentiation between tight and microporous limestones the diagenetic model proposed for the development and preservation of the microporous facies involves partial early cementation of the interstitial mud mainly composed of low mg calcite crystals sedimentation during a calcite sea period inside a meteoric phreatic lens by in situ dissolution reprecipitation processes hybrid ostwald ripening this early cementation partly preserves the original microfabric and intercrystalline microporosity and allows the carbonate sediment to resist compaction during burial the identification of the conditions favorable to the development of microporosity in these urgonian limestones may improve the knowledge and modeling of some microporous carbonate reservoir rocks

evidence for an early glacial maximum in the french vosges during the last glacial cycle the last glacial maximum is observed to have occurred between 18 000 and 20 000 years ago throughout northern europe here we present evidence for the surprising result that in the region of the french vosges the regional ice sheet advanced during the early part of the last glacial cycle and this expansion was considerably larger than that which occurred during the last glacial maximum from these results we conclude that the glacial maximum may not have occurred at the same time worldwide contrary to what has usually been assumed1

palaeogeographical relationships between alpine and jura glaciers during the two last pleistocene glaciations abstract two main moraine complexes are usually defined in the northwestern alpine piedmont the external moraine complex emc dated to the penultimate glaciation riss sensu lato and the internal moraine complex imc dated to the last glaciation wurm until recently the prevalent concept was that these two complexes had been built by glaciers originating in the central alpine zone this paper presents a new palaeogeographical diagram based on mapping and petrographical studies of these two moraine complexes and especially on the relationships between alpine and jura tills we reach the following conclusions 1 1 the jura glaciers were independent of the alpine glaciers during the two last pleistocene glaciations 2 2 the jura mountains formed a topographical barrier blocking and modifying the alpine glacier advance towards the northwest with the result that during the wurmian glaciation the maximum elevation 1200 m a s l of the alpine glaciers on the eastern margin of the jura was too low to allow alpine ice to enter the jura and during the rissian glaciation the greater thickness of the alpine glaciers resulted in their penetration only into the lower marginal zone of the jura 3 3 thus in the studied area the central alps were not the only centre of ice dispersal during the two last pleistocene glaciations on the northwestern jura slopes the corresponding moraine complexes were mainly built by glaciers emanating from the central jura

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

middle pleistocene mis 7 to holocene fossil insect assemblages from the old crow basin northern yukon canada abstract the old crow basin northern yukon provides a key record of environmental change in northwestern north america from the late middle pleistocene through the early holocene site chronologies are based on the presence of the old crow tephra oct 124 10 ka at three sites and provide a stratigraphic framework for observations ecological affinities of fossil insects indicate that pleistocene environments were dominated by dry tundra and steppe tundra forest insect species are relatively rare even during the last interglaciation mis 5e and it is only by considering the total insect assemblages that interglacial beds can be recognized last interglacial insects from these sites indicate a relatively wet and warm tundra environment with evidence for sparse forest vegetation rare taxa with strong affinities to warmer temperatures are present and could suggest a warmer than modern climate early holocene deposits yield a greater abundance of forest insects relative to mis 5 or 7 interglacial deposits fossil insect assemblages reflect the position of the sites above the arctic circle and in contrast to central yukon sites steppe insects are less common during cold stages and forest insects are less common during warm stages these data suggest overall that the contrast between cold and warm stages was less pronounced than in other regions of yukon and alaska and may indicate influence of persistent large regional lakes during the pleistocene

pre glacial and interglacial pollen records over the last 3 ma from northwest canada why do holocene forests differ from those of previous interglaciations we synthesize pollen spectra from eleven dated stratigraphic sections from central and northern yukon palaeomagnetic and tephra dating indicates the earliest assemblages representing closed canopy pinus and picea forest are middle late pliocene age more open forest conditions indicated by increased poaceae and with evidence of permafrost are dated at ca 3 ma while pinus pollen is abundant at 3 ma it is reduced in records after 2 6 ma and subsequent pleistocene interglacial forest records are repeatedly dominated by picea along with alnus and small but significant amounts of abies surface sample comparisons indicate that abies was more widespread and abundant in past interglaciations than at present and that middle pleistocene piceaeabies forest grew in the northern yukon porcupine basin 500 km beyond modern abies limits in contrast pinus which occurs today in southern and central yukon was not a significant component of these pleistocene interglacial forests late holocene pollen assemblages with rare abies and high pinus are the most distinct in the past 2 6 ma possible factors driving holocene difference are paleoclimate paludification changes in megafaunal herbivory and an unusual fire regime anthropogenic burning is a factor unique to the holocene and if it is shown to be important in this case it would challenge our notion of what constitutes boreal wilderness

age of some pleistocene interglacial beds and associated fossils in eastern beringia defined by fission tracks in glass shards of chester bluff tephra

interactions between tectonics erosion and sedimentation during the recent evolution of the alpine orogen analogue modeling insights 1 on the basis of a section across the northwestern alpine wedge and foreland basin analogue modeling is used to investigate the impact of surface processes on the orogenic evolution the basis model takes into account both structural and lithological heritages of the wedge during shortening erosion and sedimentation are performed to maintain a critical wedge frontal accretion leads to the development of a foreland thrust belt underplating leads to the formation of an antiformal nappe stack in the internal zones important volumes of analogue materials are eroded out of the geological record which in the case of the alps suggests that the original lengths and volumes may be underestimated the foreland basin evolves differently depending on the amounts of erosion sedimentation its evolution and internal structuring is governed by the wedge mechanics thought to be the main controlling mechanism in the development of the molasse basin in a feedback interaction with surface processes

on the eruption age and provenance of the old crow tephra abstract tephrochronology is used to correlate and reconstruct geographically disparate sedimentary records of changing environment climate and landscape throughout geologic time single tephra layers represent isochronous markers across broad regions thus accurate and precise radiometric constraints on the timing of eruption are critical to their utility the old crow tephra is found throughout eastern beringia and represents the largest preserved pleistocene ashfall event in the region despite its volume and significance as a stratigraphic marker the provenance of this tephra is debated and the interpreted eruption age of marine isotope stage mis 5 at 125 ka has vacillated to investigate provenance and eruption age we develop a geochemical fingerprint for the old crow tephra via titanomagnetite geochemistry and zircon crystallization cooling age via coupled u pb u th and u th he zircon geochronology our results indicate that old crow oxides are geochemically distinct from the commonly assumed source caldera system at the emmons lake volcanic center elvc zircon crystals from the old crow tephra range in age from proterozoic to pleistocene with concordant zircon u pb u th and u th he dates on the youngest population of grains suggesting crystallization in their parent magma and in turn eruption at 202 9 9 5 ka we discuss strengths and shortcomings of our radiogenic datasets in light of this result and review the far reaching implications of a change in old crow eruption age

reconstruction of late quaternary sea and lake level changes in a tectonically active marginal basin using seismic stratigraphy the gulf of cariaco ne venezuela abstract the gulf of cariaco is a marginal basin located between the cariaco basin and the paria gulf offshore ne venezuela along a system of active right lateral strike slip faults it is connected to the caribbean sea via a shallow 58 m deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands a dense grid of high resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill six unconformity bounded seismic stratigraphic units were identified in the upper 200 m of the sedimentary infill detailed seismic stratigraphic and seismic facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the gulf of cariaco i delta offlap breaks ii evaporites and iii erosional unconformities using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model a relative sea lake level history encompassing the last 130 kyr could be reconstructed in periods of connection with the open ocean reconstructed relative sea level correlates well with eustatic sea level in times of disconnection distinct lake level fluctuations occurred which sometimes resulted in total dessication of the gulf lake level fluctuations appear to correlate with major heinrich events stadials and interstadials mis 4 the lgm and the younger dryas were thus identified in the gulf of cariaco sedimentary record the last reconnection to the caribbean sea occurred during mwp1b around 11 5 kyr the very good fit of the cariaco sea lake level curve with the eustatic sea level curves both in terms of amplitude and of timing underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin despite its active tectonic setting

isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds abstract the age of silicic tephra beds that have experienced a simple thermal history can be accurately and precisely determined by application of the isothermal plateau fission track technique to hydrated glass shards age estimates obtained by this means compare very well with those based on co existing mineral phases using the k ar 40ar 39ar external detector fission track and thermoluminescence techniques this concordance contradicts the popular belief that hydrated glass shards give unreliable ages distal tephra beds many of which are difficult to date because of their fine grainsize low abundance of crystals and common presence of detrital grains are readily dated by the isothermal plateau glass fission track method this new advance should greatly facilitate the development of detailed chronologies of tephra bearing sedimentary sequences located far from volcanic centres

high resolution seismic reflection profiling of neotectonic faults in lake timiskaming timiskaming graben ontario quebec canada the timiskaming graben is a 400 km long 50 km wide north west trending morphotectonic depression within the canadian shield of eastern north america and experiences frequent intraplate earthquakes the graben extends along the border of ontario and quebec connecting southward with the nipissing and ottawa bonnechere grabens and the st lawrence rift system which includes a similar structure underlying the hudson valley of the eastern usa together they form a complex failed rift system related to regional extension of north american crust during the breakup of rodinia and later pangea the timiskaming graben lies within a belt of heightened seismic activity western quebec seismic zone with frequent moderate magnitude greater than magnitude 5 earthquakes including a magnitude 6 2 in 1935 these events threaten aging urban infrastructure built on soft glacial sediments post glacial landslides along the ottawa valley suggest earthquakes as large as magnitude 7 the inner part of the timiskaming graben is filled by lake timiskaming a large 110 km long post glacial successor to glacial lake barlow that was ponded by the laurentide ice sheet 9500 years ago the effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high resolution chirp seismic profiles late glacial lake barlow glaciolacustrine and overlying post glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor despite high sedimentation rates and indicate recent neotectonic deformation the lake timiskaming area provides evidence of post glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the north american plate

isostatic rebound active faulting and potential geomorphic effects in the lake lahontan basin nevada and california the high shoreline of the late pleistocene sehoo lake in the lahontan basin is used as a passive strain marker to delineate the magnitude and character of regional deformation since 13 ka the elevations of 170 high shoreline sites document that the once horizontal equipotential shoreline which traverses almost 4 of latitude and 3 of longitude is now deflected vertically about 22 m most of the deformation is attributed to isostatic rebound but a small down to the north regional tilting also appears to contribute to the overall deformation pattern active faults locally offset the high shoreline but cannot explain the regional upwarping attributed to isostatic rebound since 13 ka preliminary models of the rebound yield an upper mantle viscosity of 10 18 pa s that implies a maxwell relaxation time of about 300 yr the rapid earth response coupled with the rapid fall in lake level at the end of pleistocene time may have acted to divert some of the major rivers flowing into the basin from one terminal subbasin to another the regional deformation caused by the rebound may also have acted to control the present location of honey lake these shoreline data therefore support the potential for a link be

interaction of folding and thrusting during fold and thrust belt evolution insights from numerical simulations and application to the swiss jura and the canadian foothills abstract we use two dimensional numerical simulations to investigate the interaction of folding buckling and thrusting localized shearing during the structural evolution of fold and thrust belts ftb we model layer parallel shortening of mechanically strong layers resting above a weaker layer referred to as detachment we consider a viscoplastic rheology with linear viscosity and frictional plastic drucker prager yield criterion the detachment thickness is larger in one model half and only this geometrical thickness perturbation triggers folding and thrusting in the simulations we conduct a systematic analysis to quantify the impact of model parameters such as magnitude of the thickness perturbation or detachment rheology frictional or viscous on the ftb evolution the magnitude of the perturbation determines whether or not folding is favoured over thrusting and hence controls the progressive interaction of folding and thrusting during ftb evolution the asymmetry of modelled anticlines is proportional to the relative height of the initial perturbation we also adapt the model configuration to specific mechanical stratigraphies of two regions in natural ftb namely the haute chaine of the jura mountains switzerland and the foothills of alberta canada the modelled fold and thrust geometries agree with different types of observed anticlinal structures such as symmetric detachments folds and asymmetric thrust folds our results suggest that an initial stage of low amplitude buckling likely occurred prior to the main folding and thrusting phase we argue that folding and thrusting are equally important and interacting processes during the structural evolution of many natural ftb

late quaternary folding in the jura mountains evidence from syn erosional deformation of fluvial meanders the present tectonic activity of the jura fold and thrust belt is a matter of scientific debate at its north western front differentially uplifted palaeo meanders of the doubs river record late quaternary growth of the citadelle anticline associated with a minimum rock uplift of 13 m local rock uplift rates estimated from optical stimulated luminescence dating of oxbow lake deposits measure 0 17 0 05 mm per annum reconstruction of the deformation history reveals that buckling took place simultaneously with focused pleistocene river incision the structural geomorphic and temporal setting suggests that active deformation could possibly be sustained by incision related erosion these observations shed new light on the modes of recent deformation in the jura mountains and on the present day dynamics of the alpine orogenic front

40ar 39ar laser probe dating of the central european tektite producing impact event a new 40ar 39ar data set is presented for tektites from the central european strewn field moldavites this is the only strewn field that is entirely situated in a continental environment and still characterized by scattered ages 14 15 3 myr the main objectives of the study were to define more precisely the moldavite formation age and provide a good calibration for a glass standard proposed for fission track dating the laser total fusion ages obtained on chips from 7 individual specimens from the southern bohemian and moravian subfields are restricted to a narrow interval of time with an average of 14 34 0 08 myr relative to the 27 95 0 09 myr of the fish canyon tuff biotite this result gives a more precise age not only for the tektite field but also for its producing impact if the genetic link between the moldavites and the nordlinger ries impact crater is maintained then this new age has to be considered a reliable estimate for the ries crater also this new value places the formation of central european tektites within the lower serravallian period in the latest geologic timescales evidence of their impact products such as glass spherules or shocked minerals can therefore be sought in sedimentary marine formations in a more precisely defined age interval

foreland basin subsidence driven by topographic growth versus plate subduction the subsidence of foreland basins is classically thought to accelerate with time however a synthesis of data from numerous foreland basins recognizes a wide range of signals and rates our analysis investigates the influence of two broadly ubiquitous controlling factors 1 the upward and outward growth of mountain topography and 2 the subduction velocity of the underthrust lithosphere these two factors have contrasting subsidence signals the former tends to be slow and decelerates while the latter is more rapid and accelerates the geodynamic setting of a foreland basin determines the degrees to which these components dominate the final signal of tectonically induced subsidence in small collisional mountain ranges the common asymmetry of subduction defines a pro and a retro foreland basin based on model experiments and the synthesized data we demonstrate that pro foreland basins exhibit short lived usually 0 05 km m y 1 accelerating subsidence histories recording only a portion of the orogenic history of the mountain range type examples are the carpathian foredeep and the north alpine foreland basin in contrast retro foreland basins are characterized by relatively slow 0 05 km m y 1 protracted usually 40 m y subsidence that records the majority of the orogenic history a good example is the aquitaine foreland basin retro arc foreland basins such as the alberta basin appear comparable to collisional retro foreland basins examples where there is more protracted subsidence appear to record greater evidence of episodic loading and unloading as the topography of the range grows or shrinks in response to the balance between crustal thickening and erosion rates

late quaternary lacustrine paleo seismic archives in north western alps examples of earthquake origin assessment of sedimentary disturbances abstract the late quaternary sedimentary fills of several lakes of the north western alps are revealed to be possible paleo seismological archives in a moderately active seismo tectonic region the strongest historically reported events can be correlated with specific layers whose textures result from different processes i mass failures of sub aqueous slope deposits especially delta foresets evolving into hyperpycnal currents influenced by seiche effects and or multiple reflections on lake basin slopes ii in situ liquefaction and flowage and iii micro fracturing based on identification of the sedimentary signature of a well documented historical earthquake the paleoseismic interpretation can be extrapolated back to 16 000 yrs bp with a reconstruction of a time series and textural identification of slope failure related turbidites the most frequent earthquake signature the obtained time series are compatible with historical seismicity in terms of recurrence interval

estimating present day displacement fields and tectonic deformation in active mountain belts an example from the chartreuse massif and the southern jura mountains western alps abstract determination of relative movements between the alpine foreland and the external crystalline massif is a key point for the understanding of the present day tectonics of the western alps in this study we try to test the continuity of the present day tectonics with the mio pliocene deformation in particular we will test if the present day displacements are localized along the thrusts of the jura mountains or along a blind thrust in the bas dauphine molasse basin definition of relative movements is achieved by several methods including a comparison of two high precision leveling networks to estimate vertical displacements horizontal deformation measurements performed by triangulation triangulation and triangulation gps comparison in situ stress measurements performed in the different tectonic units and geomorphologic observations that constrain the location and the magnitude of the quaternary deformation comparison of leveling data demonstrates 1 an uplift of the southern bas dauphine molasse basin relative to its northern part 0 8 mm year also revealed by geomorphologic analysis 2 a significant uplift of the most external jurassian anticlines 0 8 to 2 mm year also recorded by the deformation of a paleo river bed and 3 an important uplift up to 2 mm year of the subalpine massifs the horizontal strain estimated from comparison of horizontal geodetic data triangulation gps shows 1 a nw se directed shortening between the eastern chartreuse massif and the bas dauphine molasses basin approximately 3 mm year 2 an e w directed shortening in the jura mountains approximately 4 3 mm year and 3 a dextral strike slip motion consistent with focal mechanisms along a nne ssw direction between the eastern chartreuse massif and the eastern belledonne massif these data reveal a present day strain partitioning between the belledonne external crystalline massif and the bas dauphine molasses basin the westward motion of the subalpine massifs is partitioned along two southern jurassian thrust folds and a dextral nne ssw strike slip shear zone between the chartreuse massif and the belledonne massif this strain partitioning is also accompanied by a stress partitioning between the alpine foreland and the external crystalline massifs

high resolution seismic stratigraphy of late quaternary fill of lake annecy northwestern alps evolution from glacial to interglacial sedimentary processes abstract lake annecy is a peri alpine lake of glacial origin remnant of the last glaciation the lake basin accumulated over 150 m of sediment since the last glacial maximum a dense grid of high resolution seismic data acquired during a 1993 sparker survey revealed the glacial and post glacial sedimentary infill the depth and morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface this paper focuses on the interpretation of the high resolution seismic facies of the infilling sediments of the lake basin in correlation with the results of the annecy core the quality and density of the seismic data allow in this case detailed analysis of the seismic facies in their three dimensional organisation and permit reliable interpretation in terms of depositional process and palaeo environmental setting the study reveals that the geometry and seismic facies of the infilling deposits are controlled essentially by the basin morphology and the characteristics of the sediment supply the sediment supply to the lake changes throughout the deglaciation from subglacial drainage to proglacial meltwater streams to alluvial streams and finally to the present day interglacial condition where authigenic sedimentation prevails the depositional patterns change accordingly from chaotic outwash deposits and glacio lacustrine muds at the base over axially aggrading lacustrine fans prograding alluvial fan deltas at the lake margins to finally a drape of lacustrine chalk and marl the interpreted sedimentary environment and deduced character of the sediment source are used to reconstruct the changing palaeo environment in the catchment area

an extensive middle to late pleistocene tephrochronologic record from east central alaska abstract chester bluff cb in yukon charley rivers national preserve ycnp alaska contains an extensive middle to late pleistocene tephra record within thick loess deposited on a terrace the regionally prominent old crow oc tephra 140 10 ka gi tephra 560 80 ka of fairbanks the preido hill prh tephra of the klondike and vt tephra 77 8 4 1 ka of both the klondike and fairbanks were found at cb the presence of these tephra beds will aid in correlating disparate paleoenvironmental records across eastern beringia there are 15 new tephra beds 11 from the wrangell volcanic field wvf and or hayes volcano one from the aleutian arc alaska peninsula aaap and three unclassified beds cb is normally magnetized indicating the entire sequence is of bruhnes age

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

petrography and chemistry of sandstones from the swiss molasse basin an archive of the oligocene to miocene evolution of the central alps oligocene to miocene fluvial sandstones from the swiss molasse basin were analysed for sandstone framework composition heavy minerals whole rock geochemistry and detrital chrome spinel chemistry samples were taken from the proximal part of the basin close to the alpine main thrust and are chronostratigraphically calibrated between 31 and 13 ma sandstone composition allows the identification of different source rocks and their variation in time and space place constraints on the oligocene to miocene evolution of the central alps in the eastern part of the basin sandstones document a normal unroofing sequence with the downcutting from austroalpine sedimentary cover into austroalpine crystalline rocks and slightly later at 21 ma into penninic ophiolites in the central part downcutting into crystalline basement rocks occurred at 25 ma and the removal of the sedimentary cover was much more advanced than in the east this may be interpreted as a first signal from the doming of the lepontine area at 20 ma extensional tectonics in the hinterland led to the first exposure of low grade metamorphic rocks from the footwall of the simplon fault in the central alps erosion of these rocks persisted up to the youngest sediments at 13 ma in the western part of the basin a contribution from granitoid and ultra mafic rocks is documented as early as 28 ma the source for the ultra mafic detritus is penninic ophiolites from the piemonte zone of the western alps which were already exposed at the surface at that time

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

deformation of brittle ductile thrust wedges in experiments and nature 1 even though the rheology of thrust wedges is mostly frictional a basal ductile decollement is often involved by comparison with purely frictional wedges such brittle ductile wedges generally display anomalous structures such as backward vergence widely spaced thrust units and nonfrontward sequences of thrust development laboratory experiments are used here to study the deformation of brittle ductile thrust wedges results are compared with natural systems in the jura mountains and the northern pakistan salt range and potwar plateau two series of three models are used to illustrate the effects of varying the basal wedge angle and shortening rate v these two parameters directly control variations in relative strength between brittle and ductile layers bd coupling wedges with strong bd coupling low and high v give almost regular frontward sequences with closely spaced thrust units and as such are not significantly different from purely frictional wedges weak bd coupling high and low v gives dominantly backward thrusting sequences intermediate bd coupling produces frontward backward oscillating sequences the spacing of thrust units increases as coupling decreases back thrusts develop in parts of a wedge where bd coupling is weak regardless of the thrust sequence wedges with weak bd coupling need large amounts of bulk shortening more than 30 to attain a state of equilibrium at which stable sliding along the base occurs on this basis we argue that a state of equilibrium has not yet been attained in at least some parts of the jura mountains and eastern salt range and potwar plateau thrust systems

3d cartographic modeling of the alpine arc we built a 3d cartography of the alpine arc a highly non cylindrical mountain belt using the 3d geomodeller of the brgm french geological survey the model allows to handle the large scale 3d structure of seventeen major crustal units of the belt from the lower crust to the sedimentary cover nappes and two main discontinuities the insubric line and the crustal penninic front it provides a unique document to better understand their structural relationships and to produce new sections the study area comprises the western alpine arc from the jura to the northwest up to the bergell granite intrusion and the lepontine dome to the east and is limited to the south by the ligurian basin the model is limited vertically 10 km above sea level at the top and the moho interface at the bottom we discarded the structural relationships between the alps sensus stricto and the surrounding geodynamic systems such as the rhine graben or the connection with the apennines the 3d model is based on the global integration of various data such as the dem of the alps the moho isobaths the simplified geological and tectonic maps of the belt the crustal cross sections ecors crop and nfp 20 and complementary cross sections specifically built to precise local complexities the database has first been integrated in a gis project to prepare their implementation in the geomodeller by homogenizing the different spatial referencing systems the global model is finally interpolated from all these data using the potential field method the final document is a new tri dimensional cartography that would be used as input for further alpine studies

present day geodynamics in the bend of the western and central alps as constrained by earthquake analysis summary the contrasted tectonics of the western central alps is examined using a synthesis of 389 reliable focal mechanisms the present day strain regime is mapped and interpolated for the entire alpine belt based on a newly developed method of regionalization the most striking feature is a continuous area of extension which closely follows the large scale topographic crest line of the alpine arc thrusting is observed locally limited to areas near the border of the alpine chain a majority of earthquakes within the alps and its forelands are in strike slip mode stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation the stress state is confirmed to be orogen perpendicular both for 3 in the inner extensional zones and 1 in the outer transcurrent transpressional zones extensional areas are well correlated with the part of the belt which presents the thickest crust as shown by the comparison with the bouguer anomaly and the average topography of the belt in the northwestern swiss alps extension is also correlated with currently uplifting zones these observations and our strain stress analyses support a geodynamic model for the western alps in which the current activity is mostly a result of gravitational body forces earthquakes do not provide any direct evidence for ongoing convergence in the alpine system but a relationship with ongoing activity of complex block rotations of the apulian microplate cannot be ruled out

phanerozoic oolitic ironstones geologic record and facies model oolitic ironstonesl composed predominantly of ooidsl of ferric oxide and chamosite accumulated throughout much of phanerozoic time figure 1 and some of them have been important ore deposits they are built of two very common products of weathering iron oxide and clay but they constitute a distinctive and subordinate sedimentary facies for which there is no simple modem analogue as a result considerable disagreement has attended more than 125 years of discussion about their origin early analyses of these rocks for example the minette are of france focused mainly on their chemical and mineral composition and on processes of diagenesis more recent work has described their sedimentary textures and structures as well as their general facies and depositional environments ad eleye 1973 brookfield 1973 corbin 1980 hallam 1975 karpov et a11967

oxygen isotope thermometry of quartz calcite veins unraveling the thermal tectonic history of the subgreenschist facies morcles nappe swiss alps combined structural analysis and oxygen isotope thermometry of syntectonic quartz calcite fibrous veins can be used to correlate the thermal history of deformed rocks with specific structural and tectonic events results are presented for the morcles nappe in the western helvetic alps switzerland where mineral parageneses illite crystallinity and fluid inclusion chemistry record an apparent peak metamorphic temperature gradient that increased across the morcles nappe from anchizonal conditions in the foreland to epizonal conditions in its hinterland root zone twenty seven quartz calcite veins were analyzed in this study in order to determine the temperatures of veining during formation and deformation of the nappe peak metamorphic temperatures ranged from 260 to 290 c in the shallower foreland localities and to 330 to 350 c in the deeper more hinterland localities at the end of s1 foliation formation related to large scale folding temperatures gradually decreased throughout the nappe during subsequent development of the s2 foliation and s3 crenulation cleavage uplift and erosion of the overlying nappe pile resulted in slow cooling of the morcles nappe during the waning stages of the alpine orogeny the dominant foliation forming deformation of the morcles nappe occurred at elevated temperatures over the course of 10 to 15 ma combined structure oxygen isotope analyses of quartz calcite veins yield better temperature and temporal constraints on the thermal histories of subgreenschist vein bearing tectonites than do other geothermometers

correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential pearce nicholas denton j s perkins w t westgate j a 2007 correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation icp ms analyses current status and future potential journal of quaternary science 22 7 pp 721 736 rae2008

the correlation between reduction in fission track diameter and areal track density in volcanic glass shards and its application in dating tephra beds abstract the relationship between the reduction in fission track diameter and the reduction in areal track density in hydrated glass shards has been investigated under varying annealing and etching conditions a near 1 1 relation is observed for adequately etched tracks following laboratory heating of induced tracks the partially reduced areal track density was renormalized with error

holocene event record of aysen fjord chilean patagonia an interplay of volcanic eruptions and crustal and megathrust earthquakes in the first months of 2007 the aysen region in southern chile was affected by a crustal seismic swarm its largest earthquake m w 6 2 occurred in april and had its epicenter in aysen fjord seismic intensities became so high that hundreds of onshore mass movements were triggered several of which entered into the fjord resulting in mass transport deposits mtds preserved at the fjord bottom here we present a holocene record of paleo earthquakes in the previously unstudied patagonian fjordland based on mtd stratigraphy high resolution seismic data retrieved using two different seismic systems sparker and topas reveal multiple older mtds on different stratigraphic levels correlation of the seismic stratigraphy with sedimentological data obtained from a long calypso core md07 3117 allows conclusion on the seismic origin of these deposits additionally radiocarbon dating permits constructing an age model validated by tephrochronology providing an age for the different mtd levels we thus present a highly detailed paleoseismological history of the aysen region including at least six major holocene earthquakes one of which is likely related to a known megathrust earthquake other earthquakes are related to activity of the liquine ofqui fault zone lofz forming the main source of seismic hazard in the area we can infer a general average recurrence time for lofz earthquakes of 2 100years in the vicinity of aysen fjord with clustered events during the early and late holocene finally we argue that cascading events causal link between volcanic and seismic events may be a frequent phenomenon along the lofz

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

late cenozoic metamorphism and mountain building in taiwan a review abstract the orogenic wedge of taiwan results from the late miocene collision of the chinese passive margin and the luzon volcanic arc because of the southward propagation of the collision over time and because of its extreme rates of deformation and erosion it has appeared as an ideal place to investigate mountain building processes here we review existing metamorphic and thermochronological data on late cenozoic burial and exhumation most of the island has been extensively investigated in particular in terms of zircon or apatite fission track and u th he thermochronology peak metamorphic temperatures have also been quantified from the raman spectroscopy of carbonaceous material along three transects in central taiwan the different datasets appear consistent and indicate that cooling rates and exhumation are more intense within the hsueshan range and within the tananao complex lateral variations from south to north are also observed and they can be interpreted in terms of different stages of exhumation and mountain building existing models provide a framework to analyze the data and discuss the limits of some previous interpretations in particular in terms of exhumational steady state or of recent acceleration of uplift and exhumation these models are also discussed in light of available data it appears that all of them fit thermochronological data within the tananao complex whatever the kinematics the depth of the wedge or the mechanism responsible for exhumation and that exhumation of the hsueshan range has been ignored in most models future models need therefore to consider the taiwan wedge as a whole additional constraints on peak metamorphic conditions on kinematics of shortening and exhumation or on the geometry of the wedge at depth need to be gathered to further unravel mountain building processes at the scale of the whole orogen

llanvirnian ord iron ooids in baltoscandia element mobility ree distribution patterns and origin of the ree abstract the chemical and mineralogical compositions of llanvimian ordovician iron and associated phosphate ooids from sweden estonia and russia have been examined the oolites are generally thin and lean mud supported and dominated by fe oxyhydroxide goethite limonite ooids one swedish oolite contains a mixture of chamosite goethite and hematite ooids and it is suggested that the two latter types were derived from chamosite ooids by early diagenetic alteration the ree distribution patterns were unaffected by these reactions all ooids in the area show a typical negative eu anomaly inherited from the source material major and minor element contents in limonite and chamosite ooids are similar whereas their ree patterns are different limonite ooids have a lree hree ratio from 1 to 2 4 and chamosite ooids from 3 to 5 the amounts of ree in the ooids are strongly dependent on the amount of phosphate

structural evolution of orogenic wedges interplay between erosion and weak decollements orogenic wedges commonly display an inner wedge where crystalline units have been exhumed and an outer wedge formed by imbricated sedimentary units detached from the basement analog experiments have shown that similar structures can emerge naturally in the presence of weak decollements due to the interplay between erosion and deformation in this study we further investigate this hypothesis using two dimensional visco elasto plastic numerical models our experiments assume a basal and an intermediate decollement within the wedge experiments with a frictional strength of the basal decollement lower or equal to that of the intermediate decollement show a structural evolution of fold and thrust belts dominated by out of sequence thrusting conversely when the intermediate decollement is weaker than the basal decollement distinct outer and inner wedges are formed this process leads to episodic migration of midcrustal ramps tectonic underplating and antiformal stacking facilitated by erosion comparison between our models and the himalayan wedge suggests a low effective friction 0 10 which is probably due to dynamic weakening during large m8 himalayan earthquakes the deeper decollement along which the lower plate thrusts beneath the high himalaya must be a thermally activated ductile shear zone with an apparent friction of 0 18 fold and thrust belts worldwide exhibit various architectures in which different decollement levels might be activated thus our study provides a framework to help assess under which conditions a variety of structures observed in orogenic systems can arise

deformation and displacement of the jura cover on its basement abstract the sedimentary cover of the internal jura displaced over its basement conforms well with the model of a thin skinned thrust sheet the wedge shaped sheet which includes a thick sequence of molasse deposited ahead of the alpine front slid over the basement cover interface the alpine crustal thrust sheets created a load at the south east end of the overthrust european plate molasse was deposited on the bent plate and the internal part of the basin was progressively affected by thrusting this process also induced deformation and displacements in the foreland gravity spreading in the internal molasse and a forward motion by rigid slipping movement led to a horizontal push causing deformation by indentation in the internal jura in the plateaux of the external jura there is very little extension in the cover and minimal shortening in the basement this shortening induced a decollement under the plateaux over the bresse graben gravity sliding occurred in the form of huge landslides these contrasts in the origin of the jura structures along a median cross section from thonon to arbois are shown by geophysical data construction of a balanced cross section and calculations of realistic mechanical models for the bending of the foreland plate and for the motion of the cover sheet

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

trace element microanalysis by la icp ms the quest for comprehensive chemical characterisation of single sub 10 μm volcanic glass shards funder nerc rono ne f021445 1 enhancing tephrochronology and its application intrepid project hiroshi machida commemorative volume

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

interactions between thin and thick skinned tectonics at the northwestern front of the jura fold and thrust belt eastern france 1 this study investigates spatial and temporal interactions of thin and thick skinned tectonics in a classical foreland setting located at the front of the jura fold and thrust belt in eastern france the working area coincides with the intracontinental rhine bresse transfer zone and represents the most external front of the deformed alpine foreland the investigation combines analyses of largely unpublished and newly available subsurface information with our own structural data including an exhaustive paleostress analysis and geomorphologic observations results are provided in the form of a new tectonic map and a series of regional cross sections through the study area the besancon zone forming the most external part of the thin skinned fold and thrust belt encroached onto the eo oligocene rhine bresse transfer fault system until early pliocene times thrust propagation was largely controlled by the late paleozoic to paleogene preexisting fault pattern that characterizes the rhine bresse transfer zone thick skinned deformation dominant throughout the avant monts zone located farther to the west was associated with compressional to transpressional reactivation of such faults overprinting and crosscutting criteria of fault slip data allow distinguishing between systematically fanning maximum horizontal stress axes that define the front of the thin skinned jura fold and thrust belt and consistently nw se directed maximum horizontal stress axes that characterize deformation of the autochthonous cover of the foreland which is affected by thick skinned tectonics tectonic and geomorphic analyses indicate that thick skinned tectonics started at a very late stage of foreland deformation post early pliocene geomorphic observations imply that deformation between mesozoic cover and basement is locally still decoupled however overprinting relationships and recent seismicity suggest that present day tectonic activity is thick skinned which probably reflects ongoing tectonic underplating in the alpine foreland

changes in dip and frictional properties of the basal detachment controlling orogenic wedge propagation and frontal collapse the external central betics case thin skinned fold and thrust belts ftbs have been extensively studied through both field examples and modelling the overall dynamics of ftbs are therefore well understood one less understood aspect is the combined influence of across strike changes in the detachment properties and the basement topography on the behaviour of an orogenic wedge in this paper we use field data together with reflection seismic interpretation from the external zones of the central betics ftb s spain to identify a significant increase in the wedge basal dip a basement threshold coinciding with the pinch out of a weak substrate this induced both changes to the wedge geometry and to the basal friction which in turn influenced the wedge dynamics the changing dynamics led to a transient stagnation of the ftb propagation topographic build up and subsequent collapse of the ftb front this in turn fed an important langhian depocenter made up of mass transport deposits coevally with the ftb propagation extension took place both parallel and perpendicular to the orogenic trend this case study illustrates how across strike changes in wedge basal properties can control the detailed behaviour of a developing ftb front but questions remain regarding the time space interaction and relative importance of the basal parameters

phanerozoic ironstones an introduction and review s u m m a r y ironstones particularly ooidal ironstones have long fascinated sedimentary geologists and have generated an enormous variety of interpretations but have remained poorly understood a recent upsurge in interest in this group of rocks has generated much new information derived from many different disciplines within the earth sciences the first part of this introduction examines recent advances and attempts to produce a synthesis of them with particular reference to the genesis of marine ooidal ironstones current models for the formation of marine oolitic ironstone formations are discussed and a working model based on various lines of recent research is proposed this model invokes the intrasedimentary formation of berthierine ooids in marine environments during postoxic diagenesis the ooids may be mechanically modified and mineralogically transformed by reworking as well as by later diagenesis goethite ooids may be oxidized berthierine ooids reworked lateritic ooids or primary grains the formation of oolitic ironstoneformations is favoured by a break in clastic sediment supply continued supply of iron and physical reworking many sedimentary environments may supply these parameters but changes in sea level leading to the flooding of land masses and the reworking of suitable terrestrial soils may be both an important source for the iron and provide a break in clastic sediment supply in the second part of this introduction the terminology and classification are discussed and conventions proposed the term berthieroid is introduced as a non specific term for material of undetermined berthierine or chamosite composition the term ironstone is proposed as a petrological term and as an informal lithostratigraphic term a deposit composed of ironstones may be termed an ironstone formation it is recommended that a dunham style of classification is employed petrographically with ironstone replacing the stone of the original carbonate classification the nomenclature of allochems in ironstones is also discussed a glossary of ironstone terminology is provided

formation and stratigraphic facies distribution of early jurassic iron oolite deposits from west central nevada usa abstract the stratigraphic context and geochemical proxy potential are described for a newly reported early jurassic marine iron ooid deposit in west central nevada u s a sedimentary analysis of the ferguson hill member in the sinemurian aged sunrise formation was conducted in the gabbs valley range of nevada u s a iron ooids were examined by transmitted light microscopy and electron scanning microscopy and found to consist of chamosite berthierine and amorphous silica in cortical layers of the sunrise formation sedimentological characteristics of the uppermost beds of the ferguson hill member show iron ooids are associated with transgressive deposits on the earliest known first post extinction metazoan carbonate factory identified in eastern panthalassa the ferguson hill member iron ooids are unique among most iron ooid deposits for being distributed grains within the carbonate the formation of such a deposit required concentrations of iron and silica and fluctuating oxidation reduction conditions sufficient to produce chamosite berthierine and silica while not completely shutting down the shallow marine carbonate factory for this reason iron ooids observed in shallow carbonate sections serve as a useful indicator of shallow water geochemical conditions in the sedimentary record

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

examples of biogenic support of mineralization in two oolitic iron ores lorraine france and gara djebilet algeria abstract after inspection it appears that oolites in the aelenian of lorraine and devonian of gara djebilet are very often nubecularidea the mineralization of these oolitic shaped elements results from a metasomatic process this observation supports the metasomatic theory and leads to the need for more attention being paid to the shaped elements of the microfacies

fluid escape features as a precursor of a large sublacustrine sediment slide in lake le bourget nw alps france the north western corner of lake le bourget is situated along an active fault zone and accommodated a large sediment supply from the rhone river until the end of the late glacial period on the delta slope the holocene sheet drape that covers the largest buried mass wasting deposit the hdu shows undulations small fractures and discontinuities that are attributed to downslope creep evidence for episodes of vigorous fluid expulsion is found in association with these discontinuities all these features are rooted at the top of the hdu and occur along two specific isobaths these observations indicate a close link between fractures and focused fluid flow we suggest that focused fluid flow triggered by earthquakes facilitates the formation of small scale faults that accommodate part of the downslope movement and eventually link up to form a headscarp of a large slide c 1 0 7 m 3

relating orogen width to shortening erosion and exhumation during alpine collision we investigate along strike width changes of the thickened accreted lower plate talp in the central and in the eastern alps we set the width of the talp in relation to the inferred amount of collisional shortening and exhumation along six orogen scale cross sections taking the present day along strike gradients in the amount of collisional shortening to represent the temporal evolution of the collisional wedge it may be concluded that the cross sectional area of the talp diminishes during ongoing shortening indicating that the erosional flux outpaced the accretionary flux higher amounts of collisional shortening systematically coincide with smaller widths of the talp and dramatic increases of the reconstructed eroded rock column higher amounts of shortening also coincide with larger amplitudes of orogen scale upright folds with higher exhumation and with higher exhumation rates hence erosion did play a major role in reducing by 30 km the vertical crustal thickness in order to accommodate and allow shortening by folding long term climate differences cannot explain alternating changes of width by a factor of almost 2 along straight segments of the orogen on length scales less than 200 km as observed from the western central alps to the easternmost eastern alps sedimentary or paleontological evidences supporting such paleo climatic differences are lacking suggesting that erosional processes did not directly control the width of the orogen

facies variations across the middle upper jurassic boundary in western europe and the relationship to sea level changes abstract a facies analysis of callovian oxfordian boundary beds has been carried out on numerous sections across western europe with the aim of constructing marine bathymetric curves for each geographic area onshore outcrops in northwest and northeast scotland and borehole cores from the beatrice field in the inner moray firth basin were studied virtually all the sediments are siliciclastic and often thick an early callovian transgression is recorded from skye and northeast scotland but the influence of local tectonics limits the lateral extent of distinctive lithological units within england the callovian succession differs considerably from that found elsewhere the most interesting unit is the upper callovian hackness rock a condensed bed with chamositic ooids which is thought to signify deposition at a time of rising relative sea level the basal oxfordian contains an organic rich clay that may reflect a period of maximum flooding associated with anoxic conditions and the clays above are likely to have been deposited during the ensuing regression in central and southern england the callovian oxfordian boundary occurs within the oxford clay the change from the lower to the middle oxford clay middle upper callovian boundary marks a regional shallowing of the sea signified by higher silt and kaolinite content while the topmost callovian the lamberti limestone is condensed and marks a time of relatively high sea level with a fall in the proportion of kaolinite four regions in france were studied normandy poitou burgundy and ardeche the normandy succession is very similar to that in dorset with the stage boundary occurring at the junction of two clay formations a period of maximum flooding occurred at this boundary before initial regression in the early oxfordian resulted in a renewed terrigenous input the other regions generally have a very condensed calcareous callovian often with a pelagic character the condensed iron ooidal limestones of the spanish iberian chain were deposited in a relatively deep water offshore setting the majority of sections record a phase of severe sediment starvation during the latest callovian and earliest oxfordian zones which are likely to reflect a period of maximum flooding in the swiss jura the most significant period of negligible sedimentation rates occurred in the two zones across the stage boundary clear deepening or shallowing trends cannot readily be recognised in the offshore succession of the swabian alb the comparison of a series of bathymetric curves has led to the recognition of regional sea level events in western europe during the callovian early oxfordian interval a regional sea level rise occurred during the middle and late callovian reaching its greatest extent in the latest callovian lamberti zone and highstand conditions and incipient sea level fall characterised the early oxfordian a literature review of boundary beds in seven further regions from five continents has shown that a middle callovian sea level rise and late callovian early oxfordian phase of high sea level can be recognised on a global scale the european regional sea level changes are therefore considered to be eustatic in origin and probably related to sea floor spreading in the atlantic a eustatic curve has been constructed and compared with two other such curves it differs from that of hallam also based on the facies analysis technique but is quite similar to that of exxon workers based on sequence stratigraphic concepts