ichnofabric characterization of a deep marine clastic system a subsurface study of the middle eocene ainsa system spanish pyrenees this paper documents a subsurface trace fossil and ichnofabric study of the proximal parts of a structurally confined and channelized sand rich lower slope and proximal basin floor deep marine system in the middle eocene ainsa basin spanish pyrenees five depositional environments are recognized based on sedimentary facies associations depositional architecture and stratigraphic context channel axis channel off axis channel margin levee overbank and interfan as well as a channel abandonment phase each environment is characterized by distinct and recurring ichnofabrics ichnological measurements and observations were recorded from six cores recovered from six wells drilled at a spacing of between 400 m and 500 m at outcrop and totalling 1213 m in length from channel axis to levee overbank environments there is a trend of increasing bioturbation intensity and ichnodiversity ichnofabrics in channel axis and channel off axis environments are characterized by low bioturbation intensity and low ichnodiversity thalassinoides dominated firmground ichnofabrics associated with erosive sediment gravity flows are common in these environments in contrast channel margin and levee overbank environments are characterized by ichnofabrics associated with high bioturbation intensity and ichnodiversity sediments of the interfan are characterized by the highest bioturbation intensity associated with burrow mottling and an absence of primary sedimentary structures this paper demonstrates that in core based studies ichnofabric analysis is an important and valuable tool in discriminating between different environments in channelized deep marine siliciclastic systems the results of this study should find wide applicability in reservoir characterization studies in the petroleum industry in field based analogue ichnofabric studies and other core based studies in deep water siliciclastic systems worldwide such as the integrated ocean drilling program

shock metamorphism of bosumtwi impact crater rocks shock attenuation and uplift formation shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures the distribution of shock metamorphism in drilled basement rocks from the 10 5 kilometer diameter bosumtwi crater and results of numerical modeling of inelastic rock deformation and modification processes during uplift constrained with petrographic data allowed reconstruction of the pre impact position of the drilled rocks and revealed a shock attenuation by 5 gigapascals in the uppermost 200 meters of the central uplift the proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure the results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure

chitinozoan biostratigraphy of the early caradocian lockne impact structure jamtland sweden the chitinozoan biostratigraphy in seven outcrops and four drilling cores in connection with the lockne impact structure has been investigated the impact event took place in early caradoc i e 460 4 ma ago and in beds corresponding to the lower part of the lagenochitina dalbyensis zone upper dalby limestone the contact between the impact related rocks and the secular postimpact sediments can be traced all over the impact structure and up to a distance of 50 km away from the presumed crater center the youngest postimpact sediments in the lockne impact structure correspond to the lower ora shale belonechitina hirsuta zone

a tem investigation of shock metamorphism in quartz from the vredefort dome south africa the origin of the vredefort structure in south africa is still debated several causes have been discussed namely asteroid impact internal gas explosion or tectonic processes evidence of dynamic rock deformation is pervasive in the form of planar features in quartz grains shatter cones veins of pseudotachylite and occurrence of coesite and stishovite high pressure quartz polymorphs a number of these characteristics is widely believed to support an impact origin however the planar features in quartz which are generally considered as one of the strongest indicators of impact are in the vredefort case considered as anomalous when compared with those from accepted impact structures we have investigated by optical and transmission electron microscopy tem the defect microstructures in quartz grains from different lithologies sampled at various places at the vredefort structure whatever the locality only thin mechanical brazil twin lamellae in the basal plane are observed by tem so far such defects have only been found in quartz from impact sites but always associated with sets of thin glass lamellae in rhombohedral planes 10 1n with n 1 2 3 and 4 at the scale of the optical microscope brazil twins in 0001 are easily detected in vredefort quartz grains because of the numerous tiny fluid inclusions which decorate them similar alignments of tiny fluid inclusions parallel to other planes are also detected optically but at the tem scale no specific shock defects are detected along their traces if these inclusion alignments initially were shock features they are now so severely weathered that they can no longer be recognized as unambiguous shock lamellae fine grained coesite was detected in the vicinity of narrow pseudotachylite veinlets in a quartzite specimen but stishovite was not found even in areas where its occurrence was previously reported finally definite evidence of high temperature annealing was observed in all the samples these observations lead us to the conclusion that our findings regarding microdeformation in quartz are consistent with an impact origin for the vredefort structure most of the original shock defects are now overprinted by an intense post shock annealing episode only the thin mechanical twin lamellae in the basal plane have survived

milankovitch forcing of bioturbation intensity in deep marine thin bedded siliciclastic turbidites abstract trace fossils have been used to infer a milankovitch type control on pelagic and hemipelagic sediments but there have been no comparable studies in deep marine siliciclastic turbidite successions here we present the results of a quantitative analysis of trace fossil abundance and intensity in an essentially continuous middle eocene 230 m long well a6 core comprising very thin and thin bedded siliciclastic turbidites in the deep marine ainsa basin spanish pyrenees after removing the sediment slides and debris flow deposits as these represent geologically instantaneous events approximately two orders of magnitude thicker than the typical laminated turbiditic sediments in the core spectral analysis was conducted on the bioturbation intensity data spectral analysis of bioturbation intensity in the a6 core suggests for the first time from a siliciclastic turbidite succession at a tectonically active plate margin thrust top basin in a foreland basin a cyclicity that is interpreted to reflect the 41 kyr and an 112 kyr possibly an average of the 95 and 125 kyr milankovitch frequencies we propose that this drove environmental changes in bottom water conditions in the ainsa basin most likely leading to critically varying levels of oxygenation stratification of bottom waters our age model for the ainsa basin 4 km of deep marine sediments in 10 myr yields an average sediment accumulation rate of 40 cm kyr 1 that is consistent with that inferred from the spectral analysis 30 cm kyr 1 for fine grained sedimentation an implication of these results is that global environmental change probably glacio eustasy acted as a driver on deep marine siliciclastic sedimentation patterns during the middle eocene

numerical modeling for target water depth estimation of marine target impact craters 1 marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor the geology of this marine target crater is influenced by the layer of water in the upper part of the target the influence increases with increased water depth the target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy the target water depth for a marine target crater is often estimated by facies analysis of sediments related to the impact crater unfortunately often with ambiguous results we propose to combine the conventional methods with numerical modeling of the target water depth based on the special target water related features of the crater we used geological data from the lockne crater as constraints in a simulation with the sova hydrocode the simulations were done for three different target water depths 200 m 500 m and 1000 m within the likely depth range for the middle ordovician sea in which the impact occurred in order to obtain the minimum estimated size of the lockne crater by an asteroid impact at 20 km s the water depth must have been slightly less than 1 km and the impactor radius must have been about 400 m it was not possible to generate a crater with the geological features of lockne for target water depths of less than about 500 m however the ratio may be further constrained by factors such as impactor density impact angle and impact velocity

shock barometry of the siljan impact structure sweden the siljan impact structure in sweden is the largest confirmed impact structure in western europe despite this the structure has been poorly studied in the past and detailed studies of shock metamorphic features in the target lithologies are missing here we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at siljan at 21 localities from an area approximately 20 km in diameter located centrally in the structure the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter the most strongly shocked samples recording pressures of up to 20 gpa occur at the very central part of the structure and locally in these samples higher pressures causing melting conditions in the affected rocks were reached pressures recorded in the studied samples decrease outwards from the center of the structure forming roughly circular envelopes around the proposed shock center based on the distribution pattern of shocked quartz at siljan the original transient cavity can be estimated at approximately 3238 km in diameter after correcting for erosion we conclude that the original rim to rim diameter of the siljan crater was somewhere in the size range 5090 km less

the ainsa fold and thrust oblique zone of the central pyrenees kinematics of a curved contractional system from paleomagnetic and structural data this work was funded by the project intectosal cgl2010 21968 c02 01 and by the grup de recerca de geodinamica i analisi de conques 2009sgr1198 secretaria d universitat i recerca del departament d economia i coneixement de la generalitat de catalunya josep poblet acknowledges financial support by research projects geociencias en iberia estudios integrados de topografia y evolucion 4d topo iberia csd2006 041 and desarrollo de fracturas y venas asociadas al plegamiento fraveple cgl2011 23628 funded by spanish ministries

early modification stage preresurge sediment mobilization in the lockne concentric marine target crater sweden lockne is a concentric impact structure due to a layered target where weak sediments and seawater covered a crystalline basement a matrix supported sedimentary breccia is interlayered between the crystalline breccia lens and the resurge deposits in the crater infill as the breccia is significantly different from the direct impact breccia and the resurge deposit we propose a separate unit name tramsta breccia based on the type locality i e the loc02 drilling at tramsta we use granulometry and a novel matrix line log method to characterize the sedimentology of the tramsta breccia the obliquity of impact combined with the layered target caused an asymmetric concentric transient crater which upon its collapse controlled the deposition of the breccia on the wide brimmed downrange side of the crater where the sedimentary target succession was removed during crater excavation wide overturned basement crater ejecta flaps prevented any slumping of exterior sediments instead the sediments most likely originated from the uprange side where the brim was narrow and the basement crater rim was poorly developed sediment rich and relatively unstable here the water cavity wall remained in closer proximity to the basement crater and aided by the pressure of the collapsing water wall unconsolidated black mud would flow back into the crater the absence of interlayered resurge deposits in the tramsta breccia and the evidence for reworking at the contact between the overlying resurge deposits and the tramsta breccia indicate that the slumping was a rapid process 75 s terminating well before the resurge entered the crater

sedimentological analysis of resurge deposits at the lockne and tvaren craters clues to flow dynamics the lockne and tvren craters formed about 455 million years ago in an epicontinental sea where seawater and mainly limestones covered a crystalline basement the target water depth for tvaren apparent basement crater diameter d 2 km was probably not over 150 m and for lockne d 7 5 km recent best fit numerical simulations suggest the target water depth of 500 700 m lockne has crystalline ejecta that partly cover an outer crater 14 km diameter apparent in the target sediments tvren is eroded with only the crater infill preserved we have line logged cores through the resurge deposits within the craters in order to analyze the resurge flow the focus was clast lithology frequencies and size sorting we divide the resurge into resurge proper with water and debris shooting into the crater and ultimately rising into a central water plume anti resurge with flow outward from the collapsing plume and oscillating resurge not covered by the line logging due to methodological reasons with decreasing flow in diverse directions at lockne the deposit of the resurge proper is coarse and moderately sorted whereas the anti resurge deposit is fining upwards and better sorted the tvren crater has a smoothly fining up section deposited by the resurge proper and may lack anti resurge deposits at lockne the content of crystalline relative to limestone clasts generally decreases upwards which is the opposite of tvren this may be a consequence of factors such as crater size i e complex versus simple and the relative target water depth the mean grain size i e the mean phi value per meter and standard deviation i e size sorting for both craters can be expressed by the equation 0 60 1 25

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

geophysical signature of malingen the minor crater of the lockne malingen doublet impact structure malingen is the 0 7km wide minor crater associated to the 10 times larger lockne crater in the unique lockne malingen doublet the craters formed at 458ma by the impact of a binary asteroid related

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

petrography and temporal changes in petrofacies of deep marine ainsa jaca basin sandstone systems early and middle eocene spanish pyrenees a petrographic study of 157 samples from the early to middle eocene deep marine sandy systems ainsa jaca basin spanish pyrenees shows that each system has a characteristic petrofacies three main petrofacies are recognized petrofacies 1 sandstones comprise mainly siliciclastic grains 80 subordinate terrigenous carbonate grains and negligible intrabasinal grains petrofacies 2 hybrid arenites are characterized by significant amounts 10 of intrabasinal carbonate grains petrofacies 3 calcilithites contain relatively abundant 10 extrabasinal carbonate grains on the basis of these petrofacies a revised correlation of the sandy systems is proposed between the more proximal ainsa basin and the more distal jaca basin sediments now separated by the boltana anticline across which it is impossible to actually trace out individual beds or sandstone packages between both basins the arenite composition in the ainsa and jaca basins is interpreted as being controlled mainly by synsedimentary tectonic processes that led to changes in sediment sources during basin evolution

the charo arro canyon mouth sheet system south central pyrenees spain a structurally influenced zone of sediment dispersal abstract detailed field and photogeological mapping of the charo canyon and arro sandbody which can be traced directly into the canyon shows the relationships between shelf slope canyon and base of slope deposition the charo canyon is incised into slope and shelf facies of the castisent group 50 5 49 5 ma and was a sediment conduit for turbidity currents and their deposits during the upper part of the castisent group and the santa liestra group 49 5 44 ma the arro sandbody downslope from the charo canyon belongs to the upper part of the castisent group unlike the overlying santa liestra channel complex the arro sandbody shows few features typical of a channel fill deposit but is characterized by a base of slope facies association in front of the canyon mouth the key factors influencing the internal architecture of the arro sandbody were variations in slope angle and an increase in sediment supply both factors being largely controlled by mid castisent thrust activity this paper describes the composite fill of the charo canyon and investigates its relationship to the depositional setting of the downcanyon deposits

a 130 year micro and macrofossil record from regeneration peat in former peasant peat pits in the peel the netherlands a palaeoecological study with agricultural and climatological implications abstract two pollen diagrams a macrofossil diagram and a microfossil diagram from regeneration peat in old peat pits in the peel a former raised bog area in the southern part of the netherlands are presented the pollen diagrams reveal the local and regional flora and vegetation history these diagrams are correlated in a detailed way with historical data concerning the economic history of the region in the past two centuries especially with respect to developments in agriculture and afforestation as shown in acreage curves of a number of cultivated plants the changes in local bog vegetation as shown in the micro and macrofossil diagrams are attributed to climatic changes and to the impact of human activities in the direct surroundings of the core peat accumulation appeared to be 240 490 g m 2 yr 1 in the period studied

high resolution correlation patterns in the turbidite systems of the hecho group south central pyrenees spain detailed bed by bed correlations in sheetlike lobes and basin plain elements of the hecho group were carried out through a hierarchical decomposition based on three orders of correlation this procedure provides the most detailed correlation framework with chronostratigraphic significance first order decomposition is based on physical correlation by mapping of major megaturbidites second order decomposition consists in matching a series of marker beds within first order units leading to the definition of units several metres thick finally third order decomposition relies on the matching of serial features within second order packages number vertical arrangement and facies features of beds and further testing the coherence of the downstream evolution of facies in single beds sheetlike lobes and basin plain are closely related and display a distinctive sheet like geometry basin plain beds are deposited by the same flows that build the sheetlike lobes with the existence of a transitional facies change from the lobe to the basin plain thickening of some beds towards the basin plain due to ponding of the fine grained silt and mud divisions a diagnostic feature of the basin plain controls the sheet like stacking pattern by balancing the wedging out of thinner lobe beds upcurrent from or within the basin plain as a consequence the whole area can be geomorphically classified as a basin plain which comprises both lobe and basin plain facies associations

detrital zircon u pb insights into the timing and provenance of the south pyrenean jaca basin we investigate how sedimentary systems respond to tectonic uplift during the last stages of infilling of a foreland basin massive conglomeratic deposits characterize the last stage of basin fill in the jaca basin the western portion of the south pyrenean foreland we conduct detrital zircon u pb geochronology in a 3000 m thick cenozoic section containing the transition from deltaic to alluvial environments with the aim of reconstructing changes of provenance in this key stage of evolution of the basin the last conglomeratic deposits of the basin belong to the san juan de la pena alluvial fan which has previously been assigned an early oligocene age our results show the presence of earliest miocene detrital zircons at the base of the fan zircon double dating reveals identical u pb and u th he ages which is indicative of a volcanic origin for these zircons we therefore conclude that this fan was deposited during early miocene times our data establish a new chronological framework for deformation and sedimentation in the south pyrenean foreland with strong implications for the dynamics and palaeogeography governing the last episodes of basin fill our results support synchronous sedimentation in the jaca piggy back basin and in the autochthonous ebro basin during the last stages of pyrenean compression in the miocene this work emphasizes the tectonic controls on the configuration of the drainage basin and gives insights into the evolution of the drainage network in internally drained basins supplementary material s1 extended zircon u pb la icp ms methodology s2 reduced detrital zircon u pb dataset for all analysis s3 all age spectra s4 zhe data s5 sample location for the analyzed samples are available at https doi org 10 6084 m9 figshare c 4507073

extraterrestrial chromite in the resurge deposits of the early late ordovician lockne crater central sweden the distribution of extraterrestrial chromite grains 63 mu m has been studied in the resurge deposit of the early late ordovician 458 ma lockne impact structure in central sweden a 1 kg sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite in total the sample contains 125 chromium spinel grains kg 1 most grains being chromite due to post depositional alterations the origin of several of the grains is dubious although it is clear that the major part of the chromites is of extraterrestrial origin 75 grains kg 1 most likely derived from the impactor the alterations are primarily due to the hydrothermal system induced by the impactor with zinc enrichment in the chromites as the most common characteristic the element chemistry of the least altered chromite grains indicates that the impactor was an ordinary l chondrite this concurs with a suggested increase in the flux of l chondritic asteroids to earth following the disruption of the l chondrite parent body at ca 470 ma more than 170 impact craters are known from around the earth but only few of the impactors have been identified mainly due to the low survival rate of projectile material further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the lockne structure c 2006 elsevier b v all rights reserved less

deconvolving tectono climatic signals in deep marine siliciclastics eocene ainsa basin spanish pyrenees seesaw tectonics versus eustasy the eocene deep marine siliciclastic fill of the ainsa basin spanish pyrenees gives unprecedented temporal resolution of the causes and timing of coarse clastic sediment supply to a deep marine basin early eocene tectonic subsidence linked to pyrenean orogenesis created the ainsa basin with water depths of similar to 400 800 m above a foundered shallow marine mixed carbonate and clastic shelf the similar to 25 sandbodies or channelized submarine fans in the basin were controlled by the similar to 400 k y milankovitch frequency with modes at similar to 100 k y and similar to 41 k y possibly stacked similar to 23k y influencing bottom water conditions in the basin causing periodic stratification in the water column across a submarine sill at the western basin margin early boltana anticline intrabasinal tectonics defined and controlled the position of eight sandy systems and their constituent fans in a process of seesaw tectonics by 1 westward lateral offset stacking of sandy fans due to growth of the eastern side of the basin represented today by the mediano anticline and 2 eastward orogenward back stepping of the depositional axis of each sandy system due to phases of relative uplift of the boltana anticline during basin infill uplift of the boltana anticline led to increasing basin narrowing and depositional confinement unlike the earlier depositional systems the youngest deep marine system was fed from a more southern sediment source between the growth anticlines as was the overlying deltaic system all the older deep marine sandy systems were fed from southeast point sources from canyons and erosional lower slope channels eroding the growing mediano anticline the depositional style outlined in this paper might be common to other active margins where siliciclastic basins evolve between active thrusts

the geology of the malingen structure a probable doublet to the lockne marine target impact crater central sweden the malingen structure is an approximately 700 m wide rimmed sediment filled circular depression in precambrian crystalline basement approximately 16 2 km from the concentric marine target lockne crater inner basement crater diameter approximately 7 5 km total diameter in sedimentary strata approximately 13 5 km we present here results from geologic mapping a 148 8 m deep core drilling from the center of the structure detailed biostratigraphic dating of the structure s formation and its age correlation with lockne chemostratigraphy of the sedimentary infill and indication for shock metamorphism in quartz from breccias below the crater infill the drill core reveals from bottom to the top approximately 33 m of basement rocks with increased fracturing upward approximately 10 m of polymict crystalline breccia with shock features approximately 97 m of slumped cambrian mudstone approximately 4 7 m of a normally graded polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone cf resurge deposits and approximately 1 6 m of secular sediments the combined data set shows that the malingen structure formed in conjunction with the lockne crater in the same marine setting the shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz slumped sediments and resurge deposits support an impact origin the stratigraphic and geographic relationship with lockne suggests the lockne and malingen craters to be the first described doublet impact structure by a binary asteroid into a marine target setting

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

architecture of the tectonically influenced sobrarbe deltaic complex in the ainsa basin northern spain abstract the syn tectonic sobrarbe deltaic complex eocene of the ainsa basin spanish pyrenees is confined by lateral thrust ramps and influenced by intra basinal growth anticlines six facies associations have been distinguished within the deltaic complex i slope marls and turbidite sandstones ii distal delta front silty and bioturbated sandstones iii proximal delta front and delta plain deposits tidal inlet tidal flat mouth bar bay distributary channel and floodplain environments iv biogenic deposits at flooding surfaces v collapse zone sediments and vi nummulite dominated shallow marine carbonates the deltaic complex comprises four composite sequences which each contain a number of minor sequences of the genetic maximum flooding surface bounded type regressive unconformities and their correlative surfaces separate the composite sequences cs and each cs can be divided into lowstand transgressive and highstand components at the base the comaron cs is a wnw prograding deltaic complex containing six minor sequences characterized by basinward stepping sandstone wedges separated by transgressive mudstones double regressive unconformities are often associated with these sandstone wedges proximally in the basin growth of the intra basinal arcusa anticline caused gentle folding of the comaron cs and syn growth strata at the base of the overlying las gorgas cs contain a prominent forced regressive sandstone wedge the las gorgas sandbody and display thinning of bedsets onto the crest of the anticline moreover it can be demonstrated that relative sea level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines the tectonic deformation caused a shift in the direction of deltaic progradation towards the north northwest as demonstrated by the well developed clinoforms in the highstand sequence set of the las gorgas cs a second phase of tectonic activity this time triggering large scale collapse of the delta front occurred at the transition between the las gorgas and barranco el solano cs tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum line of zero net vertical movement of the shoreline in the post tilt phase reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic to carbonate dominated sedimentation this phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic carbonate system dominated by large nummulite banks and bioturbated shoreface marls and sandstones finally a pronounced fall in relative sea level associated with the transition to the buil cs triggered slope instabilities and eventually established fluvial conditions all over the study area with the exception of the anticline crests the relatively high rate of tectonic subsidence in the study area suppressed relative sea level falls resulting in development of discontinuous lowstand strata and bounding surfaces the segmented nature of many regressive unconformities may be related to incremental growth of thrust related structures and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement precursors of progressive unconformities are seen in the upper proximal part of the comaron cs by downdip fanning and updip convergence of minor sequences these differentially tilted stratal units provide reliable indicators of syn sedimentary tectonism

detecting eustatic and tectonic signals with carbon isotopes in deep marine strata eocene ainsa basin spanish pyrenees we explore the potential of high resolution carbon isotope stratigraphy to provide an independent record of global sea level changes in a 1600 m thick succession representing 5 m y of slope sedimentation in the eocene ainsa basin of spain the restricted physiographic setting of the basin results in a bulk 13 c carb signal that accurately correlates with the coeval eustatic curve from the new jersey usa passive margin we show that much of the deep water sediment gravity flow sgf deposits are emplaced during eustatic lowstands and fine grained marly intervals between sgfs correlate with rising and highstand sea levels however we also detect a substantial interval of sgf deposition during a sea level highstand confirming the nonuniqueness of the controls on clastic deposition this approach provides a new way to assess the origin of depositional sequences and improve stratigraphic predictions in basins with limited chronostratigraphic control

synchronous extension and contraction in frontal thrust sheets of the spanish pyrenees the ainsa marine foreland basin of the southern pyrenees contains eocene deltaic and turbidite sequences that were deformed synchronously by both thrusting and extensional faulting during sedimentation two basin scale extensional truncation surfaces developed within a prograding imbricate thrust wedge in the footwall of the cotiella thrust sheet detailed mapping and analysis have shown that these features are major extensional detachment faults that produced complex sedimentological and stratal relations

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

filling the north european early middle eocene ypresian lutetian boundary gap insights from the pyrenean continental to deep marine record abstract the early middle eocene ypresian lutetian transition is represented by a hiatus in many north european sections including those in which the classic stratotypes were originally defined however the global stratotype section and point of the lutetian stage which is still pending definition should be placed at a globally correlatable event included within that unrepresented interval the pyrenean eocene outcrops display sedimentary successions that offer the rare opportunity to analyse the ypresian lutetian boundary interval in almost continuous sections and in very different settings seven reference stratigraphic sections were selected on the basis of their quality and correlated by means of biomagnetostratigraphic data this correlation framework casts light on the sequence of chronostratigraphic events that characterize the ypresian lutetian boundary interval which may prove useful in defining the main correlation criterion of the base of the lutetian all of the pyrenean sections show a similar sedimentary evolution despite being up to 350 km apart from each other containing deposits of different origins intrabasinal carbonate sediments siliciclastic sediments sourced from the iberian plate and terrigenous sediments sourced from the uplifting pyrenees and despite having been accumulated in different sedimentary environments from continental to deep marine and in different geodynamic settings piggy back basin foreland basin and cratonic margin this common evolution can be readily interpreted in terms of a sea level driven depositional sequence whose lowstand and transgressive systems tracts are included within the ypresian lutetian boundary interval the pyrenean ypresian lutetian depositional sequence can reasonably be correlated with depositional sequences from classic north european areas shedding light on the palaeoenvironmental history which in those areas has not been recorded furthermore these depositional sequences may possibly correlate with others from the antarctic ocean and from new jersey as well as with oceanic temperature variations suggesting that they might be the result of climatically driven glacioeustatic sea level changes should this hypothesis prove correct it would confirm previous suggestions that the onset of antarctic glaciations needs to be backshifted to the late ypresian at least

a new age model for the middle eocene deep marine ainsa basin spanish pyrenees abstract the middle eocene ainsa basin spanish pyrenees comprises 4 km of deep marine sedimentary rocks belonging to the hecho group despite extensive study of these exemplary deep marine clastic successions there has been no comprehensive chronostratigraphic framework that provides primary ages for the submarine fan and related deposits here we present a new composite basin stratigraphy based upon biostratigraphic analyses of the upper hecho group submarine fan and interfan deposits calcareous nannofossil data suggest that deposition of the gerbe through to guaso systems occurred during biozones np14 16 42 6 and 48 9 ma based on our age model additional biostratigraphic ages from the lower hecho group suggest that the entire hecho group no older than biozone np13 51 ma the improved chronostratigraphic control enables correlations between submarine canyons and submarine fans of the ainsa and jaca basins to be assessed our new age model provides a means of comparison of stratigraphic events with regional sections allowing a better understanding of the lateral and temporal evolution of these depositional systems from source to sink

milankovitch cyclicity within the middle eocene deep marine guaso system ainsa basin spanish pyrenees abstract the guaso system is the youngest deep marine stratigraphic component in the middle eocene deep marine ainsa basin in common with the older systems in the ainsa basin it was mainly fed from the east southeast by a range of sediment gravity flow processes including turbidity currents debris flows and suspended sediment river derived plumes e g hyperpycnal flows a study of the guaso system interfan sediments provides a 44 m long geochemical stratigraphic series constructed from spectral gamma ray k u and th content and bulk sediment geochemical data caco 3 toc 18 o and 13 c spectral and average spectral misfit analyses of these data identify obliquity and precession orbital modes as present with respective periods of approximately 10 and 6 m these cycles are interpreted as reflecting carbonate dilution cycles linked to variation in siliciclastic sediment input into the ainsa basin the presence of such orbitally induced carbonate dilution cycles is consistent with the identification of orbitally forced waxing and waning of coarse grained sediment supply within the coeval up system sediment supply system in the fluvio deltaic montanyana group of the tremp graus basin the presence of orbitally controlled sediment input to basin during interfan marlstone accumulation supplements to the growing body of evidence for the orbital control of sedimentation within the ainsa basin

shocked quartz grains from the malingen structure sweden evidence for a twin crater of the lockne impact structure the malingen structure in sweden has for a long time been suspected to be the result of an impact however no hard evidence i e shock metamorphic features or traces of the impactor has so far been presented here we show that quartz grains displaying planar deformation features pdfs oriented along crystallographic planes typical for shock metamorphism are present in drill core samples from the structure the shocked material was recovered from basement breccias below the sediment infill and the distribution of the orientation of the shock produced pdfs indicates that the studied material experienced low shock pressures based on our findings we can exclude that the material is transported from the nearby lockne impact structure which means that the malingen structure is a separate impact structure the seventh confirmed impact structure in sweden furthermore sedimentological and biostratigraphic aspects of the deposits that fill the depression at malingen are very similar to features at the lockne impact structure this implies a coeval formation age and thus also the confirmation of the first known marine target doublet impact craters on earth i e the lockne malingen pair

rotational velocity for oblique structures boltana anticline southern pyrenees abstract despite the large amount of paleomagnetic and structural studies on fold and thrust belts many key questions about rotational kinematics remain unsolved pace of rotation subsequent accommodation of the hanging wall etc excellent exposure conditions and syntectonic sedimentation related to the growth of oblique structures in the southern pyrenees allow an accurate investigation that sheds light on the rotational kinematics of thrust systems fifty nine paleomagnetic sites 819 specimens are homogeneously distributed in both limbs along the marine and continental sedimentary sequences contemporary with the uplift of the boltana anticline and its post folding evolution they indicate a clockwise rotation of about 52 during ypresian to priabonian times primary stable 350 580 c pre folding magnetization in the eocene rocks is attested by a positive fold test and the antipodality proof with magnetite and iron sulphide traces as magnetic carriers rotation velocity fits a logarithmic model and shows a low rate during the ilerdian middle lutetian interval ca 1 m y and much higher up to 10 m y in the late lutetian priabonian interval most of the clockwise rotation of the boltana anticline can therefore be constrained within the 42 35 m a interval partially post folding indicating a period of strong differential displacement in the southern pyrenean zone probably related to the emplacement of the underlying external sierras thrust sheets tozal alcanadre

shock metamorphism of quartz in nature and experiment ii significance in geoscience the occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies its utility is due to its almost ubiquitous occurrence in terrestrial rocks its overall stability and the fact that a variety of shock metamorphic effects occurring over a range of shock pressures have been well documented these shock effects have been generally duplicated in shock recovery experiments and thus serve as shock pressure barometers after reviewing the general character of shock effects in quartz the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored the short pulse lengths in experiments may account for the difficulty in synthesizing the high pressure polymorphs coesite and stishovite compared to natural occurrences in addition post shock thermal effects are possible in natural events which can affect shock altered physical properties such as refractive index and cause annealing of shock damage and recrystallization the orientations of planar microstructures however are unaffected by post impact thermal events except if quartz is recrystallized and provide the best natural shock barometer in terms of utility and occurrence the nature of planar microstructures particularly planar deformation features pdfs is discussed in some detail and a scheme of variations in orientations with shock pressure is provided the effect of post impact events on pdfs is generally limited to annealing of the original glass lamellae to produce decorated pdfs resulting from the exsolution of dissolved water during recrystallization basal 0001 pdfs differ from other pdf orientations in that they are multiple mechanical brazil twins which are difficult to detect if not partially annealed and decorated the occurrence and significance of shock metamorphosed quartz and its other phases namely coesite stishovite diaplectic glass and lechatelierite are discussed for terrestrial impact structures in both crystalline non porous and sedimentary porous targets the bulk of past studies have dealt with crystalline targets where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures in sedimentary targets the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets this is discussed along with examples of variations in the relative abundances of planar microstructures and their orientations which are attributed to textural variations in sedimentary target rocks examples of the shock metamorphism of quartz in distal ejecta such as at the k t boundary and from nuclear explosions are illustrated and are equivalent to that of known impact structures except with respect to characteristics that are due to long term post shock thermal effects finally the differences between the deformation and phase transformation of quartz by shock and by endogenic tectonic and volcanic processes are discussed we confirm previous conclusions that they are completely dissimilar in character due to the vastly different physical conditions and time scales typical for shock events compared to tectonic and volcanic events well characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

paleomagnetically derived folding rates southern pyrenees spain well dated syntectonic unconformities with the spanish pyrenees allow characterization of sedimentation and deformation within an orogenic foreland the spanish pyrenees are composed of a south vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the mediano anticline the largest of the transverse folds folding began in the early eocene and ended by 42 ma at which time an anticline 20 km long and 5 km in wavelength had been produced angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development fold growth resulted from west ward salt movement driven by prograding sediments and was characterized by 2 3 m y intervals of slow continuous limb tilting 2 2 4 2 m y preserved as progressive unconformities within syntectonic strata because the emplacement of the cotiella montsec thrust sheet was episodic intervals of slow fold growth were punctuated by intervals lasting

chronostratigraphy of the boltana anticline and the ainsa basin southern pyrenees the ainsa basin south central pyrenees is an exceptional example of a syntectonic foreland basin where structures oblique to the pyrenean trend are well preserved the absence of a complete chronostratigraphic frame motivated us to perform a detailed magnetostratigraphic study in the ainsa basin including the shallow marine continental transition three sections covering almost the entire eocene sedimentary fill were sampled ara coscollar and mondot covering 2450 m of the sedimentary pile with more than 1000 demagnetized specimens sample spacing of 2 7 m data from previous magnetostratigraphic studies eripol section allow us to complete the eocene record with an 840 m long profile within the bartonian priabonian interval overlying the sampled sequence characteristic remanent magnetization chrm directions were effectively isolated between 300 and 500 c magnetite is the main magnetic carrier with variable iron sulfide content and occasional hematite fold tests indicate a prefolding magnetization biostratigraphy based on shallow benthic foraminifera 15 localities and a locality with abundant charophyte gyrogonites help to constrain the local magnetostratigraphic record 20 reversals between the early ilerdian and the middle priabonian a global correlation based on a magnetostratigraphic composite section derived from this work allows us to propose a complete chronostratigraphic frame for the ainsa basin infill between 55 and 45 ma accumulation rates range from 2 to 53 cm k y responding to retrogradational to progradational features during the early lutetian and a progressive increase from the middle lutetian onward related to overall continentalization of the basin westward migration of subsidence is associated with progressively younger synsedimentary structures nucleating westward of the older ones in the south pyrenean basin

the south pyrenean eocene carbonate megabreccias revisited new interpretation based on evidence from the pamplona basin abstract the south pyrenean foreland basin contains numerous units of eocene carbonate megabreccias intercalated with siliciclastic turbidites and derived by resedimentation of shallow marine carbonate platforms previous studies were limited mainly to the foreland eastern part known as the jaca basin the present study from the pamplona basin a western part of the foreland trough sheds new light on the origin and regional significance of these south pyrenean eocene carbonate megabreccias specms the number of the specm units in the foreland basin is higher than previously recognized and their age is somewhat older than originally assumed the specm units appear to occur as time stratigraphic clusters which can be correlated with the relative sea level lowstands and linked with phases of tectonic activity the megabreccias were derived from a carbonate platform system hosted by the foreland basin s southern passive margin the episodic instability and mass wasting were triggered by phases of structural steepening forebulge uplift accompanied by high magnitude earthquakes with the former causing platform emergence increased load stresses and excess pore water pressure in the carbonate ramp the specm deposits were emplaced by cohesive debris flows evolving into high density turbidite currents an ideal specm unit consists of 1 an immature homogeneous debrite in the proximal part 2 a differentiated bipartite debrite and turbidite in the medial part and 3 an incomplete base missing debrite overlain by turbidite or a turbidite alone in the distal part the debrite component volumetrically predominates in the specm units and the original terms megaturbidite and seismoturbidite thus seem to be inappropriate for these deposits

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

in search of finiteness the limits of fine resolution palynology of sphagnum peat high resolution analysis of ombrogenous peats often reveals pollen frequencies that change markedly from one sample to the next indicating limited postdepositional mixing this raises the question whether with sufficiently thin samples seasonal differences in pollen deposition can be observed seasonal resolution in peat would provide a dating technique with an accuracy similar to that of other annually banded archives to study the limits of temporal resolution contiguous 0 5 mm thick slices of slightly humified sphagnum section cuspidata peat were palynologically analysed no seasonal patterns in the pollen stratigraphy could be observed this is ascribed to the mixing of pollen grains as a result of small scaled vertical water movements and to the horizontal mode of shoot layering in the sphagnum species the latter process may also be the cause of a smoothed annual signal because of the absence of seasonal differentiation the palynological distinction of annual peat layers is not feasible

shock metamorphism on the ocean floor numerical simulations abstract impact craters are unknown in deep ocean basins important reasons for this are that the ocean crust is younger than continents and the impacts are weakened by the water column laboratory experiments can show specific features of water impacts however impact velocities are too small

new 40ar 39ar dating of the clearwater lake impact structures quebec canada not the binary asteroid impact it seems abstract the two clearwater lake impact structures quebec canada are generally interpreted as a crater doublet formed by the impact of a binary asteroid here arguments are presented that raise important questions about the proposed double impact scenario new 40 ar 39 ar dating of two virtually fresh impact melt rock samples from the 36 km west clearwater lake impact structure yielded two statistically robust early permian plateau ages with a weighted mean of 286 2 2 2 2 6 ma 2 mswd 0 33 p 0 57 in contrast 40 ar 39 ar results for two chloritized melt rocks from the 26 km east clearwater lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component although individually weakly robust age spectra corrected for the trapped argon component and inverse isochron plots for the east clearwater melt rocks consistently yielded apparent ages around 460 470 ma no permian signal was found in either of these melt aliquots our new 40 ar 39 ar results reproduce earlier 40 ar 39 ar plateau ages 283 ma and 465 ma respectively for the two impact structures by bottomley et al 1990 and are in conflict with a previous statistically non robust rb sr age of 287 293 26 ma for east clearwater the combined cluster of apparent ages of 460 470 ma derived from four different samples across the impact melt sheet is very unlikely to represent a false age effect due to the incorporation of extraneous argon into the melt instead it strongly favors a middle ordovician age for the east clearwater impact and impact induced hydrothermal chloritization moreover the clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories an effect unexpected in the case of a permian double impact whereas the west clearwater impact affected ordovician carbonates incorporated into the impact breccia drill core reports from the 1960s concluded that clasts of ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the east clearwater lake impact structure which is overlain by 100 m of post impact sandstones shales and carbonates no resolvable impactor contamination has so far been detected in the west clearwater impact melt rocks whereas east clearwater carries a distinct ordinary possibly l chondritic impactor signature in its melt rocks east clearwater lake might thus represent one among a long list of ordovician impact structures in north america and northern europe that were presumably formed in response to the l chondrite asteroid breakup event 470 ma ago paleogeographic reconstructions show that the ordovician east clearwater impact probably occurred in a near coastal to shallow marine setting while the permian west clearwater impact hit continental pangaea along with the new 40 ar 39 ar data the paleomagnetic sedimentologic and geochemical findings suggest that the close spatial arrangement of the two clearwater lakes is most likely pure coincidence the two impact structures seem to represent a false doublet struck by impacts separated by 180 million years in time the new results for the clearwater lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on earth and on other planetary bodies in the inner solar system

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

constraints on the age of movement of the montsech and cotiella thrusts south central pyrenees spain palaeocene to oligocene thrusting in the pyrenees was synchronous with the development of the south pyrenean foreland basin collectively the tremp graus ainsa and jaca basins sedimentological and stratigraphical evidence from the foreland basin is used to constrain the age of movement of the montsech cotiella and external sierras thrusts movement on the emergent imbricate fan at the montsech front began in the early eocene illerdian during an early phase of thrusting that detached in the triassic evaporites in that region this phase of thrusting defined the tremp graus basin as a thrust sheet top basin following the early thrusting cuisian age tectonics in the tremp graus and ainsa basins was dominated by minor normal fault movements during flexural subsidence associated with thrust sheet loading growth of the boltana anticline to the west of the ainsa basin indicates that the ainsa basin had become detached as a thrust sheet top basin in the lutetian movement on the pena montanesa thrust and by inference on the cotiella thrust began in post lutetian times during the propagation of lower thrusts that involved pre triassic variscan basement thrusting in the external sierras caused folding and faulting of oligocene sediments indicating the continued southward propagation of basement involved thrusts in the upper eocene and oligocene many faults in the southern pyrenees have evidence of early normal and later reverse senses of movement indicating reactivation of normal faults during thrusting

shock metamorphic features and their zoning and orientation in the precambrian rocks of the manicouagan structure quebec canada abstract the manicouagan structure of impact origin is located in eastern quebec about 300 km north of the st lawrence river the complex is of triassic age the shock deformation of the more important rock forming minerals of the autochthonous or at least parautochthonous rocks within the structure is described four zones of shock metamorphism are delineated based on the deformation features of plagioclase 1 plagioclase without planar features 2 plagioclase with planar features 3 first occurrence of plagioclase with partial isotropization and 4 first occurrence of plagioclase with total isotropization these four zones are more or less concentric and indicate a general increase in the grade of shock metamorphism towards the centre of the structure however several small areas probably underlain by allochthonous rocks appear not to fit this general picture biotite and garnet show evidence of a shock orientation of their deformation features an impact origin for the structure is favoured the impact possibly triggering volcanism

orbital forcing as principal driver for fine grained deep marine siliciclastic sedimentation middle eocene ainsa basin spanish pyrenees abstract the relative importance of climate tectonics and or autocyclicity in driving deposition of laminated deep marine fine grained siliciclastic sediments in tectonically active basins remains controversial consequently the recognition of milankovitch periodicities in such successions remains poorly documented this study evaluates the cyclostratigraphy and its likely drivers in the middle eocene ainsa basin spanish pyrenees a basin that is known to have been associated with major syndepositional tectonics this basin was infilled by a thick succession of siliciclastic sediments characterised by an alternation of coarse grained sandbodies interpreted as submarine fans and finer grained packages of interfan fan lateral margin and channel levee overbank sediments this study presents time series analysis of outcrop spectral gamma ray and cumulative sandstone turbidite abundance data from eight fine grained essentially interfan sections located between coarse grained sandbodies submarine fans the 1 4 km of cumulative stratigraphy studied show that milankovitch cyclicity can be recognised throughout the entire stratigraphic evolution of the ainsa basin even though the basin was tectonically active and suggest that the accumulation of the interfan deposits was orbitally controlled orbital parameters most likely paced the cyclic delivery of the fine grained sediments mainly by river and delta supplied turbidity currents from the non marine and shallow marine tremp basin immediately to the east sediment accumulation rates determined from spectral analysis show a gradual decrease throughout the deep marine stratigraphy from 57 to 24 cm kyr this study shows that orbitally induced climate change acted as a principal driver on deep marine terrigenous sediment accumulation within a tectonically active basin high frequency climate variability therefore should be considered when studying controls on siliciclastic sedimentation in tectonically active regions

eocene biostratigraphy and magnetic stratigraphy from possagno italy the calcareous nannofossil response to climate variability a study of quantitative calcareous nannofossil biostratigraphy and magnetostratigraphy of a 68 m thick marine limestone section of late paleocene middle eocene age outcropping at possagno in northern italy shows that the section encompasses nannofossil zones np9 np15 equivalent to cp8 cp13b and chrons c24r c21n the paleocene eocene boundary was placed at the base a of d 13 c negative excursion from the literature that was found virtually coincident with the base of zone np9b the base of the middle eocene lutetian was placed at the base of chron c21r biostratigraphic events were generally found to be consistent with parallel events in recent time scales several potentially useful new events are also described in particular we detected the earliest specimens of dictyococcites at the base of chron c22r np12 np13 zonal transition which is several million years older than previous estimates correlation of possagno data to the oxygen isotope record from the literature allowed us to describe the temporal relationships between climate variability and calcareous nannofossil assemblages modifications in the nannofossil assemblage coeval to both the paleocene eocene thermal maximum petm and the early middle eocene long term climatic trend are recognized the short lived petm was coeval to provisional adaptations malformations and or ecophenotypes in the coccolithophores communities that were reabsorbed upon return to long term varying climatic conditions the early middle eocene long term climatic trend was instead coeval to true evolutionary trends with the appearance of the very successful noelaerhabdaceae clade whose offsprings include the most important bloom forming coccolithophorids in the modern ocean the early middle eocene can thus be considered the time in which nannoplankton communities set course toward modern structure triggering a reconfiguration of the global ocean life chain d 2005 elsevier b v all rights reserved

quantifying the kinematics of detachment folds using three dimensional geometry application to the mediano anticline pyrenees spain the kinematics of detachment folds have been described by three different models 1 hinge migration is responsible for fold amplification 2 fold amplification is due to limb rotation and 3 both hinge migration and limb rotation cause fold amplification a numerical method is proposed to determine which of these mechanisms is responsible for the formation of natural detachment folds this procedure consists of measuring and plotting geometric data collected from cross sections constructed across the termination of a fold where shortening dies out laterally or in an area with a lateral shortening gradient assuming that observed spatial variations in fold geometry reflect temporal geometric evolution the procedure allows determination of equations that govern the kinematics of the particular detachment fold analyzed to validate the results obtained from the application of this technique to natural examples they must be contrasted with other indicators of fold amplification mechanisms such as microstructures mesostructures and syntectonic sediment patterns this analysis is applied to an asymmetric growth fold the mediano anticline in the southern pyrenees of spain and shows that it grew due to limb rotation and minor hinge migration these data coupled with analysis of the growth stratal patterns using reverse and forward modeling techniques are used to derive deformation rates and to display the kinematics of this fold

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

thrust sequences in the eastern spanish pyrenees detailed mapping of the south pyrenean zone in the eastern spanish pyrenees shows that a great number of alpine thrusts affect the basement and the cover the geometry of the thrust structures and their propagation sequence can be interpreted from balanced sections the folding dies out downwards from the higher thrust sheets to the lower ones and demonstrates a piggy back thrusting sequence these thrusts form a duplex the sole thrust of this duplex is the vallfogona thrust the roof thrust is rooted somewhere within the axial zone the thrusts climb southwards from the axial zone basement up into tertiary cover sediments these thrusts have been folded so that they now dip to the south and form the southern side of the axial zone antiformal stack locally smaller antiformal stacks developed and produced strong folds in the higher thrust sheets the south pyrenean zone studied is equivalent to the gavarnie nappe and the connection between them below the detached south pyrenean central unit may be the nogueres zone

formation of pseudotachylitic breccias in the central uplifts of very large impact structures scaling the melt formation abstract the processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia ptb in impact structures have been strongly debated for decades variably an origin of these pseudotachylite friction melt like breccias by 1 shearing friction melting 2 so called shock compression melting with or without a shear component immediately after shock propagation through the target 3 decompression melting related to rapid uplift of crustal material due to central uplift formation 4 combinations of these processes or 5 intrusion of allochthonous impact melt from a coherent melt body has been advocated our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter to meter sized occurrences from the type location the vredefort dome this complex archean to early proterozoic terrane constitutes the central uplift of the originally 250 km diameter vredefort impact structure in south africa previously results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting likely during the early shock compression phase however for larger veins and networks it was so far not possible to isolate a specific melt forming mechanism macroscopic to microscopic evidence for friction melting is very limited and so far chemical results have not directly supported ptb generation by intrusion of impact melt on the other hand evidence for filling of dilational sites with melt is abundant herein we present a new approach to the mysterium of ptb formation based on volumetric melt breccia calculations the foundation for this is the detailed analysis of a 1 5 3 0 04 m polished granite slab from a dimension stone quarry in the core of the vredefort dome this slab contains a 37 5 dm3 breccia zone the pure melt volume in 0 1 m3 ptb bearing granitic target rock outside of the several decimeter wide breccia zone in the granite slab was estimated at 5 2 dm3 this amount can be divided into 4 6 dm3 melt 88 for which we have evidenced a limited material transport at maximum 20 cm and 0 6 dm3 melt 12 with at most grain scale material transport which we consider in situ formed shock melt the breccia zone itself contains about 10 dm3 of matrix melt assuming melt exchange over 20 cm at the slab surface between breccia zone and surrounding melt bearing host rock volume the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone meso and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences thus melt of the breccia zone could have provided the melt fill for all the small scale ptb veins in the surrounding target rock extrapolating this melt capacity calculation for 1 m3 ptb bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm3 melt scaling up 1000 fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m3 breccia zone could involve some 10 m3 melt these results demonstrate that large melt volumes i e large breccia zones can be derived in principle from local reservoirs however strong decompression would have to apply in order to exchange these considerable melt volumes which would only be realistic during the decompression phase of impact cratering upon central uplift formation or locally where compressive regimes acted during the subsequent down and outward collapse of the central uplift

high frequency detrital signals in eocene fan delta sandstones of mixed parentage south central pyrenees spain a reconstruction of chemical weathering in transit abstract high frequency sedimentation patterns in fan delta sediments of the eocene montanana group tremp ager basin south central pyrenees spain are represented by a series of couplets consisting of alternating sandy conglomerate and calcareous mudstone each couplet is several meters thick and was deposited within a time span of the order of 20 to 30 kyr previous studies indicated that the couplets cannot be attributed to one of the commonly recognized mechanisms for generating high frequency fluctuations i e sea level variations or autocyclic lateral switching of facies belts however the couplets can be explained as the result of intermittent variations of sediment supply results of detailed petrographic analysis and numerical statistical modeling of sandstone compositions confir this interpretation the bases of coarse grained units show a significantly higher quartz feldspar ratio than the tops which indicates that coarse grained sediments initially supplied to the basin after a period of mudstone accumulation were subjected to prolonged chemical weathering in the source area these systematic temporal shifts are superimposed upon compositional variations attributable to mixing of detritus from two different structural units in the lower reaches of the feeder system over longer time spans tectonics and climate were equally important in determining the sediment flux from hinterland to basin in the southern pyrenees which of these two factors exerted a dominant influence on the observed short term variations cannot be determined beyond reasonable doubt two cenarios of climatic physiographic variation are consistent with the observed sedimentation pattern and the information presently available 1 high frequency tectonic activity against a climatic background of seasonal subtropical conditions and 2 high frequency climate fluctuations against a tectonic background of high uplift rates and high altitude microclimate conditions in the source area the case history shows that provenance modeling techniques can be used to discriminate between intrabasinal and extrabasinal supply cycles moreover the identification of extrabasinal supply signals is a significant step towards the reconstruction of surface processes in source areas

pollen and macrofossils attributable to fagopyrum in western eurasia prior to the late medieval an intercontinental mystery abstract the widespread perception that buckwheat fagopyrum esculentum and f tataricum did not occur in western eurasia prior to the late medieval is challenged by numerous pollen finds we traced some 240 localities from the area with pollen or macrofossils attributed to fagopyrum in often much earlier time slices this paper evaluates various explanations for these finds within the context of palaecological methods vegetation history and cultural development the clear morphological characteristics make large scale misidentification of the pollen unlikely although some records are suspect contamination is improbable for the vast majority of the pollen diagrams also long distance transport of pollen of fagopyrum snowdenii or oxygonum from africa seems unlikely as the pollen rain of that continent hardly contains that pollen the option that fagopyrum was present in western eurasia already much earlier than the late medieval must therefore be seriously considered cultivated species may have reached the area by trade between the mediterranean and eastern chinese realms which was regular since 2000 bce as the low pollen values argue against large scale cultivation the taxon may merely have occurred as a weed or its pollen was transported with other products and subsequently re emitted the pervasive notion that buckwheat was cultivated on large scale by the scythians in the ukrainian realm since 800 bce is highly ambiguous and probably wrong there are some indications that wild fagopyrum or a related taxon may have occurred widespread in eurasia during the pleistocene glaciations and the early middle holocene i e predating 2000 bce

architecture of the castissent fluvial sheet sandstones eocene south pyrenees spain the castissent formation represents a phase of strong fluvial progradation within the fluvio deltaic montanyana group probably enhanced by the late ypresian sea level fall the structural setting is characterized by the emplacement of the south pyrenean nappes the major architectural feature of the formation is the superposition of three multilateral and multistorey sheet sandstone complexes a b and c interbedded in finer floodplain deposits and dark grey mudstones of brackish transitional origin the structure of the sheet sandstone complexes is exemplified by the detailed analysis of the lower sheet sandstone complex a 25 m thick 6 km wide and exposed over 25 km of its length three types of channel fill sandstones serve as components 1 lenticular bedded bodies interpreted as braided stream deposits 2 lateral accretion bedded bodies intepreted as meandering stream deposits and 3 ribbons originating from laterally stable and short lived offshoot or crevasse channels by coalescence and or stacking of these channel fill types higher order architectural units a1 a2 a3 have been formed that together build the sheet sandstone complex on the basis of downstream variation in proportion and geometrical relation between the channel fill components three depositional zones have been differentiated within the fluvial system each zone is characterized by specific architectural processes 1 alternation of minor aggradational degradational cycles in the proximal valley 2 generation of new alluvial belts in the intermediate nodal avulsion zone and 3 successive random avulsion processes with development of semipermanent crevasse channels or minor distributaries in the distal distributive zone the sedimentation of the castissent formation was structurally controlled by an interplay of vertical basement movement due to thrust stacking in the hinterland and surficial thrust displacement to the foreland resulting in alternating southward and northward shift of the fluvial system