extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

mom analysis of dipole antennas in crosshole borehole radar and field experiments in this paper we propose a method of moments mom analysis that includes the borehole effects on crosshole borehole radar and we verify that the mom represents the crosshole borehole radar data correctly we derive the far field approximation of an electric field radiated by an electric point source in this derivation we assume that the point source is in a cylindrically layered medium while the observed electric field is in another cylindrically layered medium the equations that are derived are used as a transfer function to connect the two impedance matrices one for the transmitting antenna and the other one for the receiving one in these matrices the influence of the scattered field by the borehole is included completely we conducted field experiments in granite with a controlled borehole medium in order to investigate the influence of the borehole in this paper we estimated the relative amplitude and the group delay of the received signals between the water filled borehole case and the air filled borehole case this paper showed that the estimated amplitude and delay depend on the frequency and that the proposed mom could predict these frequency dependencies

the early toarcian anoxia a synchronous event in the western tethys an approach by quantitative biochronology unitary associations applied on calcareous nannofossils during the early toarcian major paleoenvironnemental and paleoceanographical changes occurred leading to an oceanic anoxic event oae and to a perturbation of the carbon isotope cycle although the standard biochronology of the lower jurassic is essentially based upon ammonites in recent years biostratigraphy based on calcareous nannofossils and dinoflagellate cysts is increasingly used to date jurassic rocks however the precise dating and correlation of the early toarcian oae and of the associated 13c anomaly in different settings of the western tethys are still partly problematic and it is still unclear whether these events are synchronous or not in order to allow more accurate correlations of the organic rich levels recorded in the lower toarcian oae this account proposes a new biozonation based on a quantitative biochronology approach the unitary associations ua applied to calcareous nannofossils this study represents the first attempt to apply theuamethod to jurassic nannofossils the study incorporates eighteen sections distributed across western tethys and ranging from the pliensbachian to aalenian comprising 1220 samples and 72 calcareous nannofossil taxa the biograph savary j guex j 1999 discrete biochronological scales and unitary associations description of the biograph computer program memoires de geologie de lausanne 34 282pp and ua graph copyright hammer o guex and savary 2002 softwares provide a discrete biochronological framework based upon multi taxa concurrent range zones in the different sections the optimized dataset generates nine uas using the co occurrences of 56 taxa these uas are grouped into six unitary association zones ua z which constitute a robust biostratigraphic synthesis of all the observed or deduced biostratigraphic relationships between the analysed taxa the ua zonation proposed here is compared to classic calcareous nannofossil biozonations which are commonly used for the southern and the northern sides of tethys the biostratigraphic resolution of the ua zones varies from one nannofossil subzone or part of it to several subzones and can be related to the pattern of calcareous nannoplankton originations and extinctions during the studied time interval the late pliensbachian early toarcian interval corresponding to the ua z ii represents a major step in the jurassic nannoplankton radiation the recognized ua zones are also compared to the carbon isotopic negative excursion and tocmaximum in five sections of central italy germany and england with the aim of providing a more reliable correlation tool for the early toarcian oae and of the associated isotopic anomaly between the southern and northern part of western tethys the results of this work show that the toc maximum and 13c negative excursion correspond to the upper part of the ua z ii i e ua 3 in the sections analysed this suggests that the early toarcian oae was a synchronous event within the western tethys

wind tunnel evaluation of a wedge shaped aeolian sediment trap abstract a detailed set of tests in a wind tunnel investigated the characteristics of flow and sampling efficiency of a low cost sediment trap that can be used in wind tunnels and field applications the trap is constructed of thin sheet aluminum and has a wedge shape 32 internal inlet angle with a 20 500 mm rectangular inlet orifice that extends 40 mm beyond the wedge form relatively unimpeded airflow through the trap is achieved by the large exit area 130 500 mm which is covered with fine stainless steel mesh 62 5 m openings 60 porosity and collected all but the finer silt sediment sizes despite its angular shape the trap has good characteristics of flow and a very high sampling efficiency 90 over a wide range of wind velocities because of its near isokinetic characteristics of flow results also indicate that this trap and others that have wide side profiles are very sensitive to incident wind angle incident angles 5 significantly reduce the sampling efficiency and promote scour around the trap inlet

ammonite faunal turnover tracing sea level changes during the jurassic betic cordillera southern spain ammonite faunal turnover has been used to trace changes in sea level during the jurassic in the betic cordillera southern spain i e westernmost tethys major turnovers recorded in the jurassic succession are interpreted as extinction phenomena and as appearance diversification and radiation bioevents of the various ammonite associations they are explained as being due to falls and rises in sea level respectively the ten most abrupt diversification and radiation bioevents have been detected in the ammonite associations associated with pelagic jurassic sedimentary rocks all of these bioevents can be linked with sea level rises most coinciding with the eustatic increases of the same age expressed in the eustatic curves of hallam and haq et al the relative sea level falls including eustatic ones coinciding with extinctions are recorded as stratigraphic breaks and stratigraphic condensation phenomena in the betic jurassic succession the seven most significant extinction events recognized in the betic jurassic are also largely attributable to eustatic falls we conclude that the proposed faunal turnover curve is predominantly the expression of global changes in sea level and it can be considered as a basis for plotting a jurassic eustatic curve

paleomagnetism of jurassic radiolarian chert above the coast range ophiolite at stanley mountain california and implications for its paleogeographic origins upper jurassic red tuffaceous chert above the coast range ophiolite at stanley mountain california lat 35 n long 240 e contains three components of remanent magnetization the first component a removed by 100 200 c has a direction near the present day field for southern california and is probably a recently acquired thermoviscous magnetization a second component b removed between 100 and 600 c is identical to that observed by previous workers in samples of underlying pillow basalt and overlying terrigenous sedimentary rocks this component has constant normal polarity and direction throughout the entire section although these rocks were deposited during a mixed polarity interval of the geomagnetic field the b magnetization therefore is inferred to be a secondary magnetization acquired during accretion uplift or miocene volcanism prior to regional clockwise rotation the highest temperature component c removed between 480 and 680 c is of dual polarity and is tentatively interpreted as a primary magnetization although it fails a reversal test possibly due to contamination by b separation of the b and c components is best shown by samples with negative inclination c directions and a corrected mean direction using only these samples indicates an initial paleolatitude of 32 n 8 paleobiogeographic models relating radiolarian faunal distribution patterns to paleolatitude have apparently been incorrectly calibrated using the overprint b component few other paleomagnetic data have been incorporated in these models and faunal distribution patterns are poorly known and mostly unquantified the available data therefore do not support formation of the coast range ophiolite at stanley mountain near the paleoequator or accretion at 10 n paleolatitude as has been previously suggested based on paleomagnetic data but indicate deposition near expected paleolatitudes for north america 35 n 4 during late jurassic time

foraminifera and ostracodes across the pliensbachian toarcian boundary in the arctice realm stratigraphy palaeobiogeography and biofacies

modeling 3d porosity and permeability from gpr data in the ellenburger dolomite central texas three dimensional porosity and permeability were modeled in an ellenburger carbonate reservoir analog from 2d crosshole and 3d surface survey ground penetrating radar gpr data two dimensional gpr crosshole velocity tomography 3d migration of the gpr surface data and porosity and permeability calibration to gpr attributes results in 3d porosity and permeability predictions that provide a consistent model of the paleocave structures and facies distributions picking the maximum instantaneous amplitude of the direct arrival wavelet for velocity tomography reduces uncertainties caused by a low signal to noise ratio uncorrelated noise and the interference between reflections and critical refractions at the earth air interface the gpr velocity is anisotropic with an average vertical to horizontal velocity ratio of 0 93 which is attributed to the dominance of the relatively horizontal orientation of the maximum porosity and permeability porosity and permeability trends are influenced by regional northe

carbon isotope records of the early jurassic toarcian oceanic anoxic event from the valdorbia umbria marche apennines and monte mangart julian alps sections palaeoceanographic and stratigraphic implications the toarcian oceanic anoxic event ca 183 ma coincides with a global perturbation marked by enhanced organic carbon burial and a general decrease in calcium carbonate production probably triggered by changes in the composition of marine plankton and elevated carbon dioxide levels in the atmosphere this study is based on high resolution sampling of two stratigraphic successions located in valdorbia umbria marche apennines and monte mangart julian alps italy which represent expressions of the toarcian oceanic anoxic event in deep water pelagic sediments these successions are characterized by the occurrence of black shales showing relatively low total organic carbon concentrations compared with coeval strata in northern europe generally 2 and low hydrogen indices on this basis they are similar to other toarcian black shales described from the tethyan region the positive and negative carbon isotope records from the two localities permit a high resolution correlation such that ammonite biostratigraphy information from valdorbia can be transferred to those parts of the monte mangart section that lack these fossils spectral analyses ofd 13 corg values and of caco3 percentages from the sedimentary records of both the valdorbia and monte mangart sections reveal a strong cyclic pattern best interpreted as an eccentricity signal which hence implies a duration of ca 500 kyr for the negative carbon isotope excursion based on the carbon isotope curves obtained the high resolution correlation between the italian successions and a section in yorkshire northern europe confirms the supposition that the apparent mismatch between the dating of the toarcian oceanic anoxic event in the boreal and tethyan realms is an artefact of biostratigraphy

inversion of tracer test data using tomographic constraints 1 we have developed a methodology for inverting tracer test data using zonation information obtained from two dimensional radar tomograms to improve the typically overly smooth hydraulic conductivity fields obtained from conventional inversion of tracer test data the method simultaneously yields two dimensional estimates of hydraulic conductivity as well as petrophysical relationships that relate hydraulic conductivity to radar velocity these relationships can be assumed to be stationary throughout the area of investigation or to vary as a function of zonation using a synthetic three dimensional hydraulic conductivity field we apply the developed inversion methodology and explore the impact of the strength and stationarity of the petrophysical relationship as well as the impact of errors that are often associated with radar data acquisition such as unknown borehole deviation we find that adding radar tomographic data to tracer test data improves hydrogeological site characterization even in the presence of minor radar data errors the results are contingent on the assumption that a relationship between radar velocity and hydraulic conductivity exists therefore the applicability of the proposed method may be limited to field sites where this condition is partially or fully satisfied

aeolian creeping mass of different grain sizes over sand beds of varying length creep is an important mode of aeolian sand transport but it has received little attention in previous studies due to experimental difficulties and insufficient theory in this study we conducted 116 groups of experiments with three repeats for each group in a wind tunnel to measure the creeping mass of four different mean grain sizes 152 257 321 and 382 m over six bed lengths 2 0 3 5 5 0 6 5 8 0 and 10 0 m at six different friction velocities 0 23 0 35 0 41 0 47 0 55 and 0 61 m s we attempted to develop a comprehensive model of the aeolian creeping mass by analyzing the effect of wind velocity the particle size and the sand bed length based on the experimental data the primary conclusions are as follows 1 the complex relationship among the wind velocity the grain size the length of the bed and the surface shape determines sand creep there was no unified formula to express the effect of particle sizes and the sand bed length on aeolian creeping masses and their effects appeared to depend on each other and wind velocity whereas the creeping mass increases with increasing wind velocity for any particle size with any length of sand bed 2 this paper presented a predicting model to determine the aeolian creeping mass whose calculating results can match to experimental data with correlation coefficients r2 of 0 94 or higher 3 the effect of grain size on creeping mass can be classified into three categories the creeping mass increases with increasing grain size the creeping mass initially decreases and subsequently increases with increasing grain size and the creeping mass fluctuates with the grain size 4 the effect of increasing bed length appears to depend on the grain size for mean grain sizes of 152 257 and 321 m creep initially increases with increasing bed length before decreasing above a certain value while for a mean grain size of 382 m the creeping mass gradually increased with increasing bed length the results help to elucidate aeolian creep and provide an intense foundation for advanced study

traveltime tomography of crosshole ground penetrating radar based on an arctangent functional with compactness constraints abstractregularization has been an effective technique to provide unique and stable solutions for crosshole ground penetrating radar gpr traveltime tomography the traditional form of this method in which a low order differential operator was used commonly yields a smooth solution that may not be appropriate when anomalies occur in block patterns such as voids or irregular objects the minimum support ms functional can be used to improve the resolution of blocky structures however in crosshole gpr traveltime tomography the ms functional is unable to resolve residual artifacts whose departure from an a priori model are smaller than the focusing parameter selected from a trade off curve in addition it would result in severe instability and yield a trade off curve with poorly defined corners when the focusing parameter nears the precision of the apparatus we have developed a new stabilizing functional based on the arctangent at function that effectively removes the artificially small values i

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

paleoceanographic changes of the late pliensbachian early toarcian interval a possible link to the genesis of an oceanic anoxic event abstract secular records of the elemental and isotopic composition of belemnite calcite were studied in pliensbachian and toarcian sections from the yorkshire coast uk and southern germany to investigate oceanographic change during an interval prior to and including the toarcian oceanic anoxic event oae records from southern germany are correlated to the uk stratigraphy using strontium isotope stratigraphy the geochemical trends measured from belemnite calcite are consistent between the two sections and are interpreted in terms of temperature and salinity of the northwest european epi continental sea the data suggest that a dramatic environmental change coincided with the toarcian oae belemnite mg ca sr ca and na ca ratios increase by a factor of between 1 7 and 2 coincident with a 3 negative shift in 18o from the mid tenuicostatum zone until the lower falciferum zone of the uk ammonite biostratigraphy a period of 0 6 0 7 myr taken at face value the mg ca and 18o data argue for an abrupt warming of 6 7 c and substantial freshening during this interval global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes prior to these events data from lower in the yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper pliensbachian margaritatus zone to the toarcian lower tenuicostatum zone this earlier event may also have been important in causing density stratification in the northwest european epi continental sea

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

the blown sand flux over a sandy surface a wind tunnel investigation on the fetch effect abstract detailed wind tunnel tests were conducted to examine the fetch effect of a sandy surface on a sand cloud blowing over it the results suggest that the fetch length of a sandy surface has a significant effect on both the vertical flux profile and total horizontal flux the sand flux over a sandy surface increases with height in the very near surface layer but then decays exponentially in agreement with the widely accepted conclusion the decay function can be expressed by q aexp h b where q is the sand flux at height h coefficient a that tends to increase with wind speed implies the influence of wind while coefficient b that defines the relative decay rate shows the influence of both the fetch and wind the relative decay rate increases with fetch when the fetch length is short then becomes constant when the fetch reaches a certain length the threshold fetch length over which the relative decay rate keeps constant increases with wind speed the average saltation height generally increases with fetch both the relative decay rate and average saltation height show that the fetch effect on the flux profile becomes more significant when the wind speed increases the total sand transport equation for the total fetch can be expressed by q c 1 ut u 2u3 g where q is the total sand transport rate u and ut are the wind velocity and threshold wind velocity at the centerline height of the wind tunnel respectively g is gravitational acceleration is the density of air and c is a proportionality coefficient that increases with the fetch length implying that the total sand flux increases with the fetch length

effects of the magnus and saffman forces on the saltation trajectories of sand grain abstract saltating sand grains are the primary component of airborne sand and account for 75 of all sand transport flux the saltation height and horizontal distance traveled by sand grains are key factors in sand control engineering in addition to gravity and aerodynamic drag the magnus and saffman forces also play important roles in saltation to quantify the magnitudes of these forces in saltation we used high speed multi flash photography to observe the movement of saltating sand grains in a wind tunnel this proved to be an efficient technique for determining the movement and rotational velocities of grains of natural sand with grain sizes ranging from 0 2 to 0 3 mm and shear velocities u of 0 67 0 83 and 0 87 m s 1 the rotational speed of saltating sand grains varied between 200 and 800 rev s 1 mean clockwise and anticlockwise rotational speeds were nearly identical and both increased with increasing saltation height with saltation heights divided into 1 cm intervals the rotational speeds followed a lorentzian distribution calculations based on a saltation model showed that the maximum increases in saltation height and in horizontal distance due to the magnus force were 10 2 and 24 9 respectively the rate of increase of both parameters increased with increasing lift off angle the maximum increases in saltation height and horizontal distance of sand grains caused by the saffman force were only 4 6 and 3 7 respectively

predicting aeolian sand transport revisiting the white model the derivation and history of the frequently cited aeolian transport model of white are considered in light of the continued replication of an error in the original expression the error may have escaped notice because the expression is still dimensionally correct and it yields predictions that appear reasonable in comparison with both the predictions of other models with field data the incorrect expression has come to be identified as a distinct model however the correct formulation of the white model is in fact a rearrangement of the kawamura model with a slightly smaller c 6 empirical coefficient 1997 john wiley sons ltd

geochemical arguments for identifying second order sea level changes in hemipelagic carbonate ramp deposits second order transgressive regressive t r cycles previously recognized using sedimentological criteria in lower jurassic hemipelagic deposits from northern spain are distinguishable based upon bulk rock organic geochemistry total organic carbon toc and hydrogen index hi and the stable carbon isotope compositions from belemnite rostra there is a coincidence between regressions and decreasing 13cbel toc and hi values and between transgressions and increasing 13cbel toc and hi values the 18o and mg ca records from the belemnite rostra are not always in phase with the t r cycles the 18obel record reveals however a prominent excursion towards higher values within the spinatum zone that correlates according to our results with a regression and with negative shifts in mg ca 13cbel and toc on the other hand an excursion in the 18obel towards lower values in the serpentinus zone also correlates with a peak transgression and with positive shifts in mg ca 13cbel and toc these two excursions have been identified in other european regions as geochemical perturbations of the same characteristics this suggests a link between second order relative sea level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea water temperature salinity and water circulation during the early jurassic terra nova 18 233 240 2006

the impact of the central atlantic magmatic province on climate and on the sr and os isotope evolution of seawater abstract there is a wide range of geochemical sedimentological and palaeontological evidence suggesting that the interval at the end of the triassic and the beginning of the jurassic some 200 ma ago was a time of major environmental change the supercontinent pangaea began to rift eustatic sea level rose and there was a mass extinction in marine and terrestrial biota the eruption of at least 3 10 6 km 3 of basaltic lavas that comprise the central atlantic magmatic province camp also took place at that time and was intimately associated with the onset of rifting of pangaea emplacement of this large igneous province occurred within a relatively very short period of perhaps no more than 1 ma although relatively little of camp now remains the original province was extremely large extending from present day nova scotia to bolivia and from central southern usa to morocco of major relevance to the environmental impact of the camp was its relatively rapid emplacement and its original location across the equator recent advances in our understanding of the weathering of silicate rocks and in particular of fresh basaltic rocks have highlighted the importance of the weathering process in influencing environmental change in this contribution we examine the details of the seawater sr and os isotope records that span the triassic jurassic boundary in order to understand the nature and course of environmental change at that time correlation of sr isotope data from mainland europe and the uk shows that the rapid rate of decrease in the 87 sr 86 sr ratio of seawater which had started in the early rhaetian late triassic came to an end in the late rhaetian close to the triassic jurassic boundary at that time the 187 os 188 os ratio of seawater had also decreased to particularly low values in the late rhaetian the seawater 87 sr 86 sr ratio rapidly increased from 0 70765 to 0 70775 and then it and the seawater 187 os 188 os ratio both remained approximately constant for the duration of the hettangian the first 3 ma of the jurassic apart from a transient excursion to radiogenic os isotope values i e high 187 os 188 os ratios near the triassic jurassic boundary the unradiogenic 187 os 188 os ratio of seawater during the hettangian is interpreted as reflecting a major perturbation to global weathering patterns that was caused by the rapid weathering and erosion of the camp immediately after its emplacement we suggest that the rapid increase of seawater 87 sr 86 sr ratios in the late rhaetian and the approximately constant 87 sr 86 sr ratios throughout the hettangian were caused by the input of a large amount of additional radiogenic sr to the oceans which was likely to have been derived from a readily weathered lithology such as carbonate or evaporite at the start of the sinemurian the 87 sr 86 sr ratio of seawater began to decrease while at the same time the 187 os 188 os ratio of seawater increased to more radiogenic values we interpret the trends in the seawater sr and os isotope compositions at the start of the sinemurian as evidence that much of the camp had been removed by chemical weathering by which time the camp had ceased to have a major influence on earth s environment the patterns of change in the seawater sr and os isotope records that occurred in the latest triassic and earliest jurassic show many similarities with those that took place in the pliensbachian toarcian 183 ma ago overlapping the eruption of the karoo ferrar igneous province in both cases the seawater sr and os isotope records indicate that there was a relatively very brief interval during which rates of continental weathering increased greatly the similarities in the responses of the seawater sr and os isotope records at those times strongly suggest that the eruption and subsequent erosion of basaltic large igneous provinces have played a major role in defining the course of environmental change in the past

the response of marine phytoplankton and sedimentary organic matter to the early toarcian lower jurassic oceanic anoxic event in northern england abstract early toarcian organic rich sediments reflecting the lower jurassic oceanic anoxic event were investigated in the brown moor borehole north yorkshire northern england integrated micropalaeontological calcareous nannofossils and dinoflagellate cysts and geochemical rock eval pyrolysis analyses reveal a sequence of changes mainly driven by palaeoecological shifts these changes mainly involve the composition source and preservation rate of sedimentary organic matter as well as algal population dynamics a sequence of successive disappearances of individual species during the early toarcian dactylioceras semicelatum and harpoceras exaratum ammonite subzones affect the composition of the phytoplankton assemblages which become gradually dominated by opportunistic taxa this range top sequence is followed by the temporary disappearance of both calcareous nannofossils and dinoflagellate cysts the disappearance event which are replaced by tasmanites an increase in type ii kerogen marks this interval these modifications were related to a gradual water stratification and to the development of a stable pycnocline these factors controlled the development of an oxygen minimum zone within the water column and the distribution of nutrients in the surface waters the disappearance event is coincident with the maximum extent of the oxygen minimum zone a repopulation event and an increase in type iii kerogen mark the end of the phytoplankton crisis in the upper part of the h exaratum ammonite subzone preadapted survivors e g biscutum dubium biscutum finchii and crepidolithus crassus mainly characterise the repopulated calcareous nannofossil assemblages whereas a significant turnover affected the dinoflagellate cyst community the re established phytoplankton populations are a response to the gradual restoration of mixed marine waters characterised by meso eutrophic conditions at the surface and by sustained nutrient regeneration the integrated calcareous nannofossil and dinoflagellate cyst biostratigraphy provided a reliable biochronological framework for the brown moor borehole succession allowing correlation with lower toarcian anoxic strata in central italy the integrated micropalaeontological approach indicates some diachroneity of lower jurassic ammonite zones in the boreal and tethyan realms

early jurassic mass extinction a global long term event the end pliensbachian extinction event 187 ma has been interpreted either as one of 10 global periodically recurring mass extinctions of the past 250 m y or as a minor localized european event elevated levels of family extinction spanned five ammonite zones during the late pliensbachian and the early toarcian an interval of 7 5 m y and were distributed unequally in the boreal tethyan and austral realms detailed sampling of invertebrate macrofaunas through complete expanded sequences in northwest europe shows that most species extinctions occurred in the early toarcian following a regional anoxic event the early jurassic mass extinction event took place over a long time scale and it was global in extent

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

selective extinction among early jurassic bivalves a consequence of anoxia analyses of taxonomically standardized data sets demonstrate several statistically robust extinction patterns in early jurassic bivalve species from northwest europe and the andean basins of south america in both regions extinction intensities were significantly enhanced in late pliensbachian and early toarcian time as compared to all other time intervals the same intervals except for the early toarcian of south america also represent times of unusual extinction selectivity with infaunal taxa suffering distinctly more than epifaunal forms as infaunal suspension feeders are extremely rare components of early jurassic oxygen controlled macrofaunas these results are entirely compatible with sedimentological and geochemical data suggesting that widespread anoxia was a principal cause of the diversity crisis although many biotic traits that enhance survivorship during background times seem to be irrelevant during major mass extinctions patterns of survivorship selectivity may provide more distinct clues to the causes of less severe mass extinctions

waveform inversion of crosshole georadar data influence of source wavelet variability and the suitability of a single wavelet assumption waveform based tomographic imaging of crosshole georadar data is a powerful method to investigate the shallow subsurface because of its ability to provide images of electrical properties in near surface environments with unprecedented spatial resolution a critical issue with waveform inversion is the a priori unknown source signal indeed the estimation of the source pulse is notoriously difficult but essential for the effective application of this method here we explore the viability and robustness of a recently proposed deconvolution based procedure to estimate the source pulse during waveform inversion of crosshole georadar data where changes in wavelet shape with location as a result of varying near field conditions and differences in antenna coupling may be significant specifically we examine whether a single average estimated source current function can adequately represent the pulses radiated at all transmitter locations during a crosshole georadar survey or whether a separate source wavelet estimation should be performed for each transmitter gather tests with synthetic and field data indicate that remarkably good tomographic reconstructions can be obtained using a single estimated source pulse when moderate to strong variability exists in the true source signal with antenna location only in the case of very strong variability in the true source pulse are tomographic reconstructions clearly improved by estimating a different source wavelet for each transmitter location

mass extinction and recovery of the early toarcian early jurassic brachiopods linked to climate change in northern and central spain abstract the early toarcian mass extinction event represented the most important mesozoic and cenozoic turnover of the population of brachiopods and severely affected other benthic fauna two main hypotheses have been proposed to explain the synchronous and global mass extinction an oceanic anoxic event or a warming episode to test both hypotheses the dynamics of the brachiopod assemblages below and above the extinction boundary are analyzed and compared with the seawater paleotemperature variations calculated from the 18 o data recorded in belemnite rostra five sections from northern and central spain well dated with ammonites have been selected for this study the sections show no indication of sedimentary breaks and contain abundant brachiopods which have been grouped into four assemblages the changes observed in the brachiopod assemblages show a close correlation with the changes in the seawater paleotemperatures the oldest assemblage assemblage 1 coincides with a cooling interval recorded to have taken place in the latest pliensbachian paleobiogeographical reconstruction shows that this assemblage was distributed at paleolatitudes between 30 and 45 n with a preference for relatively cool waters with the rise of temperatures that took place during the earliest toarcian tenuicostatum zone assemblage 1 was substituted by assemblage 2 which composed of different species of the same genera but considerably restricted to the warmer waters of lower paleolatitudes between 28 and 35 n coinciding with the rapid and pronounced increase in seawater temperature recorded at the tenuicostatum serpentinum zonal boundary all of these brachiopod species disappeared in the studied localities marking clearly the extinction boundary predominant southward currents through the laurasian seaway precluded the possible migration of the brachiopods to cooler northern waters the brachiopods disappearance is independent from the oxygenation degree of the sea bottom and therefore the rapid warming seems to be the most plausible cause of the mass extinction after the extinction event the recovery of the brachiopods was uneven subsequent to a brief pause recovery was rapid in central spain and in other southern areas of western tethys whereas in northern spain and in the whole of europe north of the french central massif brachiopods did not recover until the mid to late toarcian times

diversity dynamics and mass extinctions of the early middle jurassic foraminifers a record from the northwestern caucasus abstract the early middle jurassic foraminiferal assemblages of the northwestern caucasus including a total of 315 species and 68 genera were analysed to establish the principal diversity patterns at substage level of resolution an overall conclusion is that the number of species varied significantly in contrast to the number of genera the most diversified were late sinemurian pliensbachian late toarcian early aalenian and late bajocian assemblages significant diversity drops have been documented in the early toarcian and in the middle aalenian the first of them corresponds to the well known mass extinction which regionally was initiated in the pliensbachian and terminated when rapid late toarcian diversification began the second event could be considered as a regional evidence of a new mass extinction that appeared in the middle aalenian and was most likely associated with the aalenian bajocian regional anoxic event also recorded in the carpathian part of the western tethys the most intense foraminiferal turnovers took place in the toarcian and in the middle aalenian early bajocian the lazarus effect in spite of its high value has not much influenced the estimation of principal diversity trends

early hettangian ammonites and radiolarians from the queen charlotte islands british columbia and their bearing on the definition of the triassic jurassic boundary abstract the triassic jurassic boundary t j boundary interval is one of the most important but poorly understood intervals in the phanerozoic here we fully document the ammonite and radiolarian successions at several sites in the queen charlotte islands qci british columbia eleven ammonite taxa are described and eighteen radiolarian taxa are discussed with the radiolarian genus tipperella described as new type species t kennecottensis n sp there are two continuous t j boundary sections in the qci one is located at kennecott point on graham island section i the other on the southeastern shore of kunga island section iii a second section at kennecott point contains fossils of early hettangian age only section ii radiolarian faunas include taxa from the upper rhaetian globolaxtorum tozeri zone in the two continuous sections and the lower hettangian canoptum merum zone in all three sections in each section the lowest hettangian fossils are radiolarians and a few collections contain rare rhaetian holdovers these mixed faunas may equate with the lowest hettangian ammonite zone the spelae zone of the north american succession the upper portion of section i contains a sparse ammonite fauna which indicates an early hettangian age this section has also provided carbon isotope data with a negative excursion spanning the t j boundary section ii contains a more diverse early hettangian ammonite assemblage that permits correlation of the upper portion of this section with the lower hettangian minutus zone section iii has been previously proposed as a potential basal hettangian global stratotype section and point gssp in addition to an outstanding radiolarian fauna the section contains moderately diverse early hettangian ammonites that permit correlation of the lower portion of the section with the minutus and pacificum zones and the upper portion with the lower hettangian polymorphum zone this section has previously provided a u pb date of 199 6 0 3 ma from 3 6 m below the t j boundary currently there are four candidates and no ideal gssp for the basal hettangian a section in new york canyon nevada has also been proposed as a potential gssp this section is easily accessible and provides a virtually complete ammonoid succession but lacks geochronology and microfossils the section on kunga island in the qci provides geochronologic data and excellent radiolarian constraints in essence the sections at kunga island in the qci and new york canyon in nevada are complementary close correlations between the two sections are possible using ammonite faunas we suggest the section from nevada be designated as holostratotype for the basal hettangian and the qci section be designated as a parastratotype to improve recognition of this interval

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

effect of antennas on velocity estimates obtained from crosshole gpr data to obtain tomographic images with the highest possible resolution from crosshole ground penetrating radar gpr data raypaths covering a wide range of angles between the boreholes are required in practice however the inclusion of high angle ray data in crosshole gpr inversions often leads to tomograms so dominated by inversion artifacts that they contain little reliable subsurface information here we investigate the problems that arise from the standard assumption that all first arriving energy travels directly between the centers of the antennas through numerical modeling we show that this assumption is often incorrect at high transmitter receiver angles and can lead to significant errors in tomographic velocity estimates when the antenna length is a significant fraction of the borehole spacing

borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1 this paper discusses the borehole radar system ramac developed within the framework of the international stripa project which can be used in three different measuring modes single hole reflection cross hole reflection and cross hole tomography the reflection modes basically provide geometrical data on features located at some distance from the borehole in addition the strength of the reflections indicate the contrast in electrical properties single hole reflection data are cylindrically symmetrical with respect to the borehole which means that a unique fracture orientation cannot be obtained a method has been devised where absolute orientation of fracture zones is obtained by combining single hole reflection data from adjacent holes similar methods for the analysis of cross hole reflection data have also been developed and found to be efficient the radar operates in the frequency range 20 60 mhz which gives a resolution of 1 3 m in crystalline rock the investigation range obtained in the stripa granite is approximately 100 m in the single hole mode and 200 300 m in the cross hole model variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross hole tomographic imaging to yield maps of radar velocity and attenuation the cross hole measurement configuration coupled withmore tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties the analysis of the radar data has provided a consistent description of the fracture zones at the stripa cross hole site in agreement with both geological and geophysical observations less

evolutionary patterns and palaeobiogeography of pliensbachian and toarcian early jurassic radiolaria recent studies on the global distribution of pliensbachian and toarcian polycystine radiolarians allowed us to examine faunal turnovers and the biogeography through this critical time interval around a major ecologic and biotic crisis the analysis is based on the distribution of 167 species belonging to 69 genera significant variations in the ratio between the number of originating and extinct species have been recognized during the early early pliensbachian fads greatly exceeded lads and the maximum diversity was reached in the late early pliensbachian the trend then reversed with the number of lads exceeding fads throughout the late pliensbachian and early toarcian extinction interval recovery started in the middle and late toarcian when the number of fads again surpassed the number of lads three differing evolutionary patterns are observed amongst radiolarian genera through the studied time interval the largest group diversified rapidly in the early pliensbachian and experienced higher extinction rates in the late pliensbachian and early toarcian a second group exhibited no major changes and a third group of mainly spongy spumellarians was successful during the extinction interval the overall trend of radiolarian diversity is in a fairly good agreement with that of other marine faunas ammonites and also benthos but shows an inverse correlation with diversity trends of phytoplankton correlation with concomitant environmental changes indicates that radiolarian radiation extinction rates were not consistently linked with temperature fluctuations or sea level changes it is also evident that the diversity decrease started well before the early toarcian negative 13c peak and the oceanic anoxic event oae the extinction interval corresponds well to the duration of a short term anomaly in the strontium isotope record including the rapid decrease of 87sr 86sr values in the late pliensbachian as well as the rapid increase in the early toarcian this coincidence supports the hypothesis that the predominance of extinctions over originations was caused by a series of climate and environmental changes related to intensified magmatic activity some distinct biogeographic differences have been observed generic differences are most strongly displayed by the presence or absence of a particular genus or by changes in abundance while species differences range from greater variability to having completely different species in separate palaeolatitudinal realms two groups of genera are distinguished those that are common to abundant in the tethys low latitudes and rare to absent in mid to high latitudes and those common to abundant in mid to high latitudes and rare to absent in the tethys

numerical modeling of borehole georadar data high frequency electromagnetic em wave propagation phenomena associated with borehole georadar experiments are complex to improve our understanding of the governing physical processes we present a finite difference solution of maxwell s equations in cylindrical coordinates this approach allows us to model the full em wavefield associated with borehole georadar experiments and to assess the adequacy of ray based methods currently used to interpret the observed amplitudes our results indicate that because shallow boreholes are often water filled the finite length of the boreholes as well as changes in material properties along a borehole wall can have major effects on the amplitude behavior of borehole georadar data as a result of waveguide phenomena the radiation pattern of a vertical electric dipole source located in a water filled borehole may be distorted significantly with respect to the corresponding reference radiation pattern in a homogeneous medium even greater distortions of the radiation pattern result when the electric dipole source is located near material boundaries or near the upper or lower end of a borehole this study indicates that some of the basic assumptions of conventional ray based amplitude tomography often are not fulfilled for borehole georadar data and that the derived constraints on the attenuation and conductivity structure should be regarded as qualitative in nature the algorithm and the results presented in this study do however offer the perspective to alleviate some of these inherent problems and thus help to make ray based georadar attenuation tomography a more reliable and effective tool for probing the shallow subsurface

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

new range data for marine invertebrate species across the early toarcian early jurassic mass extinction abstract we have reinvestigated the marine mass extinction interval that occurred during the early toarcian which was a time of widespread marine anoxia the ranges of marine benthic invertebrates are significantly altered using new observations from the cleveland basin uk goniomya rhombifera is reported for the first time from the whitby mudstone formation and together with an increased epifaunal bivalve diversity indicates a brief relatively oxygenated period towards the end of the event the new data together with published results suggest three apparent extinction horizons on a global scale the first is just above the pliensbachian toarcian boundary and the following two are in the semicelatum ammonite subzone as a result of the signor lipps effect there may be only one or possibly two true extinctions the youngest extinction horizon coincides with the first of the abrupt carbon isotope shifts that characterize this interval and with increases in sea surface temperature continental weathering rates and seawater anoxia pseudomytiloides dubius is the only abundant benthic macroinvertebrate during the most hostile environmental conditions but it and all other benthic species are almost entirely absent for many thousands of years immediately after each abrupt negative carbon isotope shift supplementary material a compilation of the late pliensbachian and early toarcian marine biotic changes and a discussion of the systematics of the key faunal elements are available at http www geolsoc org uk sup18353

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the toarcian early jurassic in central and northern spain comparison with other european sections the early toarcian mass extinction marks one of the critical events in the history of the earth many of these events have been linked to important climate changes two sections of the toarcian showing high resolution ammonite based biostratigraphy are studied in central and northern spain stable isotope datasets based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates allowed the construction of 13c curves and a 18o based palaeotemperature comparison of the extinction pattern with other sections in europe and northern africa shows that the early toarcian mass extinction boundary occurred at the tenuicostatum serpentinum transition and that the organic rich facies linked to the oceanic anoxic event and the associated negative 13c excursion are diachronous from a latest pliensbachian cooling interval a first increment of seawater temperature averaging about 4 5 c started around the pliensbachian toarcian boundary and developed during the earliest toarcian tenuicostatum biochron marking the beginning of the main extinction interval from the tenuicostatum serpentinum transition up to the bifrons biochron a rise in seawater temperature averaging 5 7 c to 7 8 c was recorded this warming interval which started rapidly and which seems to be synchronous at least in western europe is considered one of the main factors responsible for mass extinction for some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere but it does not seem to be recorded in belemnite calcite and the origin of these possible gases is largely debated in the literature additional isotope excursions were found in the studied sections in spain during the middle and late toarcian a negative 13cbel excursion has been recorded at the latest bifrons biochron above this shift the illustris vitiosa subzones thermal peak which represents a 2 3 c t could be linked to one of the tectonomagmatic activity peaks recorded in the karoo basin a renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in nw europe and western tethys an interesting thermal peak has also been detected in belemnites of the insigne subzone t is in the order of 3 c and in both sections the thermal peak is included into a 13cbel negative excursion of about 1 5 relative synchrony with the new age for the karoo main magmatic activity 178 180 ma indicates that the 13c negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases at this short interval noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of nw europe and tethys are observed the uppermost levesquei subzone thermal peak has only been recognized in the deposits of the section located in central spain and coincides with a positive 13c excursion

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

on the rate of aeolian sand transport a simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning the curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well established peak in fact the theory developed in the paper can explain the peaked shape of this curve three empirically determined coefficients in the formula can be given a physical interpretation the formula is shown to fit transport rates measured in wind tunnel experiments well except for very coarse sand formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

multivariate analysis of cross hole georadar velocity and attenuation tomograms for aquifer zonation 1 we have investigated the potential of combining cross hole georadar velocity and attenuation tomography as a method for characterizing heterogeneous alluvial aquifers a multivariate statistical technique known as k means cluster analysis is used to correlate and integrate information contained in velocity and attenuation tomograms cluster analysis allows us to identify objectively the major common trends in the tomographic data and thus to reduce the information to a limited number of characteristic parameter combinations the application of this procedure to two synthetic data sets indicates that it is a powerful tool for converting the complex relationships between the tomographically derived velocity and attenuation structures into a lithologically and hydrologically meaningful zonation of the probed region in addition these synthetic examples allow us to evaluate the reliability of further petrophysical parameter estimates we find that although absolute values of the tomographically inferred petrophysical parameters often differ significantly from the actual parameters the clustering approach enables us to reliably identify the major trends in the petrophysical properties finally we have applied the approach to a cross hole georadar data set collected in a well studied alluvial aquifer a comparison of the clustered tomographic section with well log data demonstrates that our approach delineates the hydrostratigraphic zonation

field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach the vertical and horizontal distributions of aeolian mass flux were measured at oceano dunes california and these data were used to evaluate a numerical model of saltation grain size analyses showed that the distributions of the modal sediment size class corresponded closely to those of the total sediment population and modelling thus focused on replicating the distributions of the mean grain size although much previous work has assumed that the mean launch speed of saltating particles varies in proportion to shear velocity simulations using a constant mean launch speed were found to yield the closest approximations to the mass flux distributions observed in the field both exponential and gamma distributions of launch velocity produced realistic simulations although the latter approach required the inclusion of an additional reptation component to achieve good results a range of mean launch angles and an equivalent sphere correction were also found to generate comparable results providing the other input parameters could be varied freely all the modelling approaches overestimated the proportion of mass flux occurring at the bottom of the vertical distributions and underestimated the proportion occurring at the upwind end of the horizontal distributions no theoretical shortcoming that would account for these small but systematic discrepancies could be identified and experimental error thus represents a more plausible explanation the conclusion that mean grain launch speeds are essentially constant and independent of shear velocity suggests that the additional kinetic energy extracted by grains under more energetic wind conditions is largely transferred to the bed and that increases in the transport rate are therefore driven primarily by the ejection of additional grains it is suggested that the kinetic energy of rebounding grains is constrained by the ability of the bed to resist deformation equivalent to a plastic limit hence grains of larger mass diameter rebound from the bed at lower speeds and follow shorter lower trajectories as has been widely observed previously

a process based model for aeolian sediment transport and spatiotemporal varying sediment availability aeolian sediment transport is influenced by a variety of bed surface properties like moisture shells vegetation and nonerodible elements the bed surface properties influence aeolian sediment transport by changing the sediment transport capacity and or the sediment availability the effect of bed surface properties on the transport capacity and sediment availability is typically incorporated through the velocity threshold this approach appears to be a critical limitation in existing aeolian sediment transport models for simulation of real world cases with spatiotemporal variations in bed surface properties this paper presents a new model approach for multifraction aeolian sediment transport in which sediment availability is simulated rather than parameterized through the velocity threshold the model can cope with arbitrary spatiotemporal configurations of bed surface properties that either limit or enhance the sediment availability or sediment transport capacity the performance of the model is illustrated using four prototype cases the simulation of two wind tunnel experiments from literature and a sensitivity analysis of newly introduced parameters

improving crosshole radar velocity tomograms a new approach to incorporating high angle traveltime data to obtain the highest resolution ray based tomographic images from crosshole ground penetrating radar gpr data wide angular ray coverage of the region between the two boreholes is required unfortunately at borehole spacings on the order of a few meters high angle traveltime data i e traveltime data corresponding to transmitter receiver angles greater than approximately 50 from the horizontal are notoriously difficult to incorporate into crosshole gpr inversions this is because 1 low signal to noise ratios make the accurate picking of first arrival times at high angles extremely difficult and 2 significant tomographic artifacts commonly appear when high and low angle ray data are inverted together we address and overcome thesetwo issues for a crosshole gpr data example collected at the boise hydrogeophysical research site bhrs to estimate first arrival times on noisy high angle gathers we develop a robust and automatic picking strategy based on crosscorrelations where reference wav

paleoenvironmental and paleoecological implications of permian guadalupian radiolarian and geochemical variations in the lamar limestone delaware basin west texas usa abstract geochemical proxies integrated with well preserved radiolarian data from the lamar limestone and lower part of the reef trail member of the bell canyon formation provide insights into paleoceanographically and climatically driven controls on radiolarian distribution in the northern part of the delaware basin of west texas during late guadalupian time data from a section of the lamar limestone 8 9 m 500 kyr interval indicate that major variations between sphaerellarian dominated and follicucullus dominated faunas appear to be controlled by fluctuations in nutrient supply and salinity geochemical parameters of bulk carbonate carbon and oxygen isotopes 13 c carb and 18 o carb organic carbon isotope 13 c org and total organic carbon toc were analyzed and show variations on two scales on a fine scale sphaerellarian dominated beds are associated with a relatively siltier lithology higher toc and higher radiolarian richness but lower diversity and are interpreted as the result of a rise in productivity stimulated from increased terrestrial input the radiolarian variations and geochemical evidence imply that the permian spongiose spumellarians are more opportunistic than follicucullus albaillellids in response to eutrophication on a broad scale 18 o carb variations in limestone samples are interpreted mainly as a proxy for paleosalinity in response to changes in basin circulation mg ca ratios from the carbonate fraction co vary with 18 o carb and are used as an additional paleosalinity proxy in this basin the limestone beds in the middle part of the section have lighter 18 o carb values compared to limestone beds above and below and likely represent the interval when the delaware basin was less restricted and had relatively normal marine salinity impacts of diagenesis are mild but are likely the cause for systematically light 18 o carb values in silty limestone beds in the middle interval the mg ca ratios and 18 o carb values in the limestone samples both increase from the middle to the top of the section implying a gradually enhanced evaporitic environment coupled with increased salinity towards the top section collectively these data paint a picture of intermittent restriction in the delaware basin prior to the change to a dominantly evaporative regime in the late permian and on a finer scale show pronounced and frequent ecological fluctuations that appear to be driven by fluxes in terrestrial input and to some extent paleoproductivity

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

orbitally forced ice sheet fluctuations during the marinoan snowball earth glaciation the presence of dynamic ice sheets during snowball earth glaciations is controversial geological evidence and ice sheet modelling suggest that ice sheets may have responded to orbital forcing when pco2 reached a certain threshold

characteristics of particle size for creeping and saltating sand grains in aeolian transport creep and saltation are the primary modes of surface transport involved in the fluid like movement of aeolian sands although numerous studies have focused on saltation few studies have focused on creep primarily because of the experimental difficulty and the limited amount of theoretical information available on this process grain size and its distribution characteristics are key controls on the modes of sand movement and their transport masses based on a series of wind tunnel experiments this paper presents new data regarding the saltation flux obtained using a flat sampler and on the creeping mass obtained using a specifically designed bed trap associated with four friction velocities 0 41 0 47 0 55 and 0 61 m sec 1 these data yielded information regarding creeping and saltating sand grains and their particle size characteristics at various heights which led to the following conclusions i the creeping masses increased as a power function q 1 02 14 19u 3 of friction wind velocities with a correlation r2 of 0 95 ii the flux of aeolian sand flow decreases exponentially with increasing height q a exp z b and increases as a power function q 26 30 428 40 u 3 of the friction wind velocity iii the particle size of creeping sand grains is ca 1 15 times of the mean diameter of salting sand grains at a height of 0 to 2 cm which is 1 14 times of the mean diameter of sand grains in a bed and iv the mean diameter of saltating sand grains decreases rapidly with increasing height whereas while at a given height the mean diameter of saltating sand grains is positively correlated with the friction wind velocity although these results require additional experimental validation they provide new information for modelling of aeolian sand transport processes

measurement of sand creep on a flat sand bed using a high speed digital camera in this study a novel method for measuring sand creep along a flat bed was developed specifically a high speed digital camera was employed to record the sand creep movement with an unsigned image subtraction a new image queue could be formed from the original experimental images the particle tracking was then calculated after which the velocity and trajectory of the creep of sand grains was obtained in addition the creep fluxes of the different sand samples could also be calculated based on the velocities of the creep grains

analysis of eccentered dipole antenna for borehole radar a dipole antenna in a borehole may be placed away from the center of the borehole and this eccentricity produces additional complicated electromagnetic fields which may influence borehole radar signals in this paper we analyze an eccentric dipole antenna in a borehole for borehole radars our approach is an extended version of the pseudoanalytical formulation that was previously applied for analyzing an induction logging tool and a dielectric logging tool the proposed equations are suitable for modeling the finite dipole antenna utilizing a method of moments the eccentricity of the radar sonde has two consequences first it modifies the antenna characteristics such as its impedance and second it changes the electromagnetic field inside the borehole owing to the change of the structure of the cylindrical layers these two changes are evaluated by the proposed algorithm and two types of experiments the first one is a measurement of the input impedance of a monopole antenna which is in cylindrical layers on a ground plane in air the second one is about the transmission between two antennas one of which is eccentered in cylindrical layers this experiment was done in granite at a field test site and on a ground plane in air in the field experiments we controlled the position of the radar sonde in a borehole and made the antenna eccentered artificially we found that a 4 cm displacement resulted in changes of 4 db in amplitude and 4 ns in time delay comparing the experimental and calculated data obtained by the present method shows the validity of the proposed analytical formulation

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

application of a new 2d time domain full waveform inversion scheme to crosshole radar data crosshole radar tomography is a useful tool in diverse investigations in geology hydrogeology and engineering conventional tomograms provided by standard ray based techniques have limited resolution primarily because only a fraction of the information contained in the radar data i e thefirst arrivaltimesandmaximumfirst cycleamplitudesis included in the inversion to increase the resolution of radar tomograms wehavedevelopedaversatilefull waveforminversion scheme that is based on a finite difference time domain solution of maxwell s equations this scheme largely accountsforthe3dnatureofradar wavepropagationandincludes an efficient method for extracting the source wavelet from the radar data after demonstrating the potential of the newschemeontworealisticsyntheticdatasets weapplyitto two crosshole field data sets acquired in very different geologic hydrogeologic environments these are the first applications of full waveform tomography to observed crosshole radar data the resolution of all full waveform tomograms is showntobemarkedlysuperiortothatoftheassociatedraytomograms small subsurface features a fraction of the dominant radar wavelength and boundaries between distinct geological hydrological units are sharply imaged in the fullwaveformtomograms

geostatistical inference using crosshole ground penetrating radar high resolution tomographic images obtained from crosshole geophysical measurements have the potential to provide valu able information about the geostatistical properties of unsaturat ed zonehydrologic statevariablessuchasmoisturecontent un der drained or quasi steady state conditions the moisture con tentwillreflectthevariationofthephysicalpropertiesofthesub surface which determine the flow patterns in the unsaturated zone deterministicleast squaresinversionofcrossholeground penetrating radargprtraveltimesresultinsmooth minimum variance estimates of the subsurface radar wave velocity struc ture whichmaydiminishtheutilityoftheseimagesforgeostatis tical inference we have used a linearized stochastic inversion technique to infer the geostatistical properties of the subsurface radar wave velocity distribution using crosshole gpr travel times directly expanding on a previous study we have deter minedthatitispossibletoobtainestimatesofglobalvarianceand mean velocity values of the subsurface as well as the correlation lengths describing the subsurface velocity structures accurate estimation of the global variance is crucial if stochastic realiza tions of the subsurface are used to evaluate the uncertainty of the inversion estimate we have explored the full potential of the geostatisticalinferencemethodusingseveralsyntheticmodelsof varying correlation structures and have tested the influence of different assumptions concerning the choice of covariance func tionanddatanoiselevel inaddition wehavetestedthemethod ology on traveltime data collected at a field site in denmark there inferred correlation structures indicate that structural dif ferences exist between two areas located approximately 10 m apart anobservationconfirmedbyagprreflectionprofile fur thermore the inferred values of the subsurface global variance and the mean velocity have been corroborated with moisture content measurements obtained gravimetrically from samples collectedatthefieldsite

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

radio tomography and borehole radar delineation of the mcconnell nickel sulfide deposit sudbury ontario canada in an effort to reduce costs and increase revenues at mines there is a strong incentive to develop high resolution techniques both for near mine exploration and for delineation of known orebodies to investigate the potential of high frequency em techniques for exploration and delineation of massive sulfide orebodies radio frequency electromagnetic rfem and ground penetrating radar gpr surveys were conducted in boreholes through the mcconnell massive nickel copper sulfide body near sudbury ontario from 1993 1996 crosshole rfem data were acquired with a jw 4 electric dipole system between two boreholes on section 2720w ten frequencies between 0 5 and 5 0 mhz were recorded radio signals propagated through the sudbury breccia over ranges of at least 150 m at all frequencies the resulting radio absorption tomogram clearly imaged the mcconnell deposit over 110 m downdip signal was extinguished when either antenna entered the sulfide body however the expected radio shadow did not eventuate when transmitter and receiver were on opposite sides of the deposit two dimensional modeling suggested that diffraction around the edges of the sulfide body could not account for the observed held amplitudes it was concluded at the time that the sulfide body is discontinuous according to modeling a gap as small as 5 m could have explained the observations subsequent investigations by inco established that pick up in the metal cored downhole cables was actually responsible for the elevated signal levels both single hole reflection profiles and crosshole measurements were acquired using ramac borehole radar systems operating at 60 mhz detection of radar reflections from the sulfide contact was problematic one coherent reflection was observed from the hanging wall contact in single hole reflection mode this reflection could be traced about 25 m uphole from the contact in addition to unfavorable survey geometry factors which may have suppressed reflections included host rock heterogeneity disseminated sulfides and contact irregularity velocity and absorption tomograms were generated in the sudbury breccia host rock from the crosshole radar radar velocity was variable averaging 125 m mus while absorption was typically 0 8 db m at 60 mhz kirchhoff style 2 d migration of later arrivals in the crosshole radargrams defined reflective zones that roughly parallel the inferred edge of the sulfide body the mcconnell high frequency em surveys established that radio tomography and simple radio shadowing are potentially valuable for near and in mine exploration and orebody delineation in the sudbury breccia the effectiveness of borehole radar in this particular environment is less certain

the significance of an early jurassic toarcian carbon isotope excursion in haida gwaii queen charlotte islands british columbia canada abstract during the early toarcian there was a significant disruption in the short term active carbon reservoir as revealed by carbon isotope records which show a broad positive shift that is interrupted by a large 5 7 negative excursion 13 c org carbon isotope excursion co occurs with the deposition of organic rich shales in many areas this perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia the two leading hypotheses as to the cause of this event invoke either global or regional controls here we present carbon isotope data from haida gwaii british columbia canada showing a significant perturbation within a temporally constrained early toarcian succession that was deposited in the northeastern paleo pacific ocean these data reinforce the concept that the short term active carbon reservoir was affected globally and assist with the correlation of ammonite zonal schemes between western north america and europe the 13 c org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7 8 5 in 13 c wood in the early toarcian kanense zone this negative excursion also coincides with increasing total organic carbon toc from 0 4 to 1 2 these data suggest that the early toarcian carbon isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle deep marine shallow marine atmospheric

mapping sand layers in clayey till using crosshole ground penetrating radar fluid transport through clayey tills governs the quantity and quality of groundwater resources in the northern hemisphere this transport is often controlled by a three dimensional network of macropores biopores fractures and sand lenses within the clayey till at present a non destructive technique that can map and characterize the sand lens network does not exist and full excavation or extensive drilling is therefore the only solution acquisition and modeling of crosshole ground penetrating radar gpr may provide the answer to this problem we collected one and two dimensional crosshole gpr data at a field site in denmark between four 8 m deep boreholes with horizontal distances varying between 2 64 5 05 m we show that the depth thickness and tilt of a coherent sand layer within the clayey till approximately 0 4 0 6 m thick as well as the underlying sand formation can be mapped accurately using the gpr data we efficiently identify the sand as a highly resistive section with high electrom

stepwise atmospheric carbon isotope excursion during the toarcian oceanic anoxic event early jurassic polish basin abstract during the mesozoic 250 64 ma intervals of about 0 5 myr were subject to severe environmental changes including high sea surface temperature and very low oxygen content of marine water these oceanic anoxic events or oaes occurred simultaneously with profound disturbance to the carbon cycle the carbon isotope anomaly in the early jurassic that marks the toarcian oceanic anoxic event t oae at 182 ma is characterized in marine sections by a series of dramatic steps towards lighter values herein we present new carbon isotope data from terrestrial organic matter phytoclast separates collected through a late pliensbachian middle toarcian coastal and marginal marine succession in the polish basin a setting where hinterland climate and sea level change are well recorded the results show that the shift to light carbon isotope values in the woody organic matter and therefore also in atmospheric carbon dioxide similarly occurred in major steps the steps are here correlated with those identified from marine organic matter where they have previously been attributed to 100 kyr eccentricity forcing of climate the results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean atmosphere system in a series of rapid bursts additionally a link between the carbon isotope steps and shoreline movements can be demonstrated individual peaks of the negative excursion are mostly associated with facies indicative of sea level rise flooding surfaces however at the same time inferred higher atmospheric carbon dioxide content may be expected to have resulted in increased rainfall and temperature leading to accelerated weathering and erosion and consequently increased sediment supply progradation and regression causing some mismatches between isotope shifts and inferred sea level changes enhanced abundance of megaspores derived from hydrophilic plant groups and marked increase in kaolinite are coincident with the overall development of the negative isotope excursion the combined data suggest that each 100 kyr cycle in carbon isotope values was characterized by increasingly severe palaeoclimatic change culminating in extremely hot and humid conditions co incident with the peak of the final most negative carbon isotope excursion the chemostratigraphic correlation allows very precise dating of the late pliensbachian middle toarcian coastal and marginal marine sedimentary succession in the polish basin

transport mass of creeping sand grains and their movement velocities 1 aeolian sand transport is an important component of material circulation above terrestrial surfaces and can include processes of creep saltation and suspension the complex movement of material and energy during aeolian transport has meant that these processes have previously been examined in isolation although a significant amount of research has been conducted on aeolian sand transport this focused primarily on saltation as a result there are few data available on sand grain creep primarily due to a lack of theoretical models and the difficulty of direct measurements in this study we present novel methods and instrumentations to accurately measure the transport mass and the velocity of creeping sand grains using data collected with above instrumentations and a ladder sampler at four friction velocities u 0 26 0 35 0 47 and 0 56 m s 1 in a wind tunnel we studied the transport mass of creeping sand grains and their movement velocities as well as other key parameters of aeolian sand transport four major conclusions can be drawn from this study 1 the transport mass q0 of creeping sand grains increases with increasing frictional wind velocity u the relationship between these variables is represented by the power function q0 0 053 9 195u 2 800 2 the contribution of creep to total aeolian sand transport decreases with increasing frictional wind velocity creep contributed 57 of total aeolian transport at the lowest frictional wind velocity but only 19 at the highest velocity 3 the threshold frictional wind velocity for entrainment was 0 158 m s 1 4 the movement velocity of creeping sand grains ranged from 0 to 0 14 m s 1 but more than 70 of recorded velocities were less than 0 02 m s 1 although the results of this study require further validation they provide a strong basis for future research and help deepen our understanding of aeolian sand transport

rapid warming and ostracods mass extinction at the lower toarcian jurassic of central spain abstract here we present the results of the study of two lower toarcian carbonate sections located in the iberian range of central spain analyses of stable isotope on belemnite calcite allowed calculation of seawater palaeotemperature variations which were compared with the stratigraphical distribution of ostracods these organisms are particularly sensitive to ratios of temperature and salinity variations and hence are good indicators of climate changes from a cooling interval with seawater temperatures of 13 2 c recorded at the pliensbachian toarcian transition seawater temperature began to rise in the lowermost toarcian tenuicostatum zone reaching average temperatures between 14 6 c and 16 3 c during the time of deposition of this zone coinciding with this seawater warming up to 85 of the ostracods species progressively disappeared during a period of approximately 300 kyr marking the extinction interval the extinction boundary located around the tenuicostatum serpentinum zonal boundary coincides with a marked increase in temperature in the serpentinum zone on which average seawater temperatures of 22 c have been calculated warming continued through part of the middle toarcian bifrons zone reaching average temperatures of 24 7 c readjustment of the ostracod population allowed recovery of these faunas in the upper serpentinum zone although the extinction of a major ostracod group the healdioids was also recorded the correlation between mass extinction and warming infers a causal relationship comparison of the results with the records of stable isotopes in belemnites and in bulk carbonates as well as toc and facies analysis suggests that the anoxia linked to the early toarcian oceanic anoxic event was not the main responsible for the ostracod mass extinction

recalibrating aeolian sand transport models a quality controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models those of bagnold kawamura zingg owen hsu and lettau and lettau and to recalibrate the empirical constants in those models shear velocity estimates were obtained using the von karman constant and an apparent von karman parameter models were recalibrated using non linear regression and non linear regression with least squares lines forced through axes origins recalibration using the apparent von karman parameter and forced regression reduced the empirical constants for all models the disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude the recalibrated lettau and lettau model provided the greatest statistical agreement between observed and predicted transport rates with a coefficient of determination of 0 77 evaluation of the results suggests that our estimations of threshold shear velocity may be too slow causing errors in predicted transport rates copyright 2012 john wiley sons ltd

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

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

paleotemperature variations of early jurassic seawater recorded in geochemical trends of belemnites from the basque cantabrian basin northern spain abstract here we present new o isotope mg ca and sr ca data of early jurassic belemnites from the basque cantabrian basin of northern spain a succession deposited in a periodically anoxic restricted hemipelagic basin nearly 200 pliensbachian lower toarcian belemnites were collected and examined using optical cathodoluminescence and chemical techniques to constrain the effects of potential diagenetic alteration after a precise diagenetic screening of samples 176 belemnites were selected to provide records of changes in seawater geochemistry and temperature the records show a fairly good correlation of 18o with mg ca ratios r 0 65 and a weak correlation of 18o with sr ca ratios r 0 34 the oxygen isotope data if interpreted in terms of paleotemperature have revealed a period of relatively uniform and warm seawater temperatures during the early pliensbachian followed by a sharp temperature drop during the late pliensbachian earliest toarcian the onset of this cooler period occurred within the protogrammoceras celebratum subzone and the coolest seawater temperatures were reached at the end pliensbachian pleuroceras spinatum zone this was followed by a rapid seawater warming during the harpoceras serpentinus zone of the early toarcian in addition the data set provides new information regarding paleoceanographic conditions for anoxic events in a critical region of connection between the boreal and tethys realms it is the background to relatively high 18o values that prevailed during the anoxic episodes concerning the impact of the early toarcian anoxic event in northern spain the detected 18o and mg ca excursions reached their minimum and maximum respectively during the lower h serpentinus zone while the anoxic black shale interval developed earlier during the upper dactylioceras tenuicostatum lowermost h serpentinus zones

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments