stratigraphic sedimentological and palaeoenvironmental constraints on the rise of the urgonian platform in the western swiss jura urgonian type carbonates are a characteristic feature of many late early cretaceous shallow marine tropical and subtropical environments the presence of typical photozoan carbonate producing communities including corals and rudists indicates the prevalence of warm transparent and presumably oligotrophic conditions in a period otherwise characterized by the high density of globally occurring anoxic episodes of particular interest therefore is the exploration of relationships between urgonian platform growth and palaeoceanographic change in the french and swiss jura mountains the onset and evolution of the urgonian platform have been controversially dated and a correlation with other better dated successions is correspondingly difficult it is for this reason that the stratigraphy and sedimentology of a series of recently exposed sections eclepens vaumarcus and neuch tel and in addition the section of the gorges de l areuse were analysed calcareous nannofossil biostratigraphy the evolution of phosphorus contents of bulk rock a sequence stratigraphic interpretation and a correlation of drowning unconformities with better dated sections in the helvetic alps were used to constrain the age of the urgonian platform the sum of the data and field observations suggests the following evolution during the hauterivian important outward and upward growth of a bioclastic and oolitic carbonate platform is documented in two sequences separated by a phase of platform drowning during the late early hauterivian following these two phases of platform growth a second drowning phase occurred during the latest hauterivian and early barremian which was accompanied by significant platform erosion and sediment reworking the late barremian witnessed the renewed installation of a carbonate platform which initiated with a phase of oolite production and which progressively evolved into a typical urgonian carbonate platform colonized by corals and rudists this phase terminated at the latest in the middle early aptian due to a further drowning event the evolution of this particular platform segment is compatible with that of more distal and well dated segments of the same northern tethyan platform preserved in the helvetic zone of the alps and in the northern subalpine chains chartreuse and vercors

comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

magma reflection imaging in krafla iceland using microearthquake sources the details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry geophysics and volcanic hazard evaluation here we apply a relatively novel variation of seismic interferometry which we call virtual reflection seismic profiling vrsp to produce a high resolution image of a known crustal magma body the technique takes advantage of recent advances in both seismic instrumentation dense arrays and seismic analysis seismic interferometry we have applied this technique to data recently acquired at an iconic volcanic system krafla which lies on the mid atlantic ridge as exposed in northern iceland what make this particular site exceptional are encounters with rhyolitic magma in two drillholes k 39 and iceland deep drilling project 1 iddp 1 these known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth in this study we produced a stacked seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of p waves from microearthquakes generated by tectonic magmatic and or geothermal activity we observe a strong coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the iddp 1 wellbore we interpret this reflection to be from magma or magma related fluids additional coherent reflections may correspond to other components of the magma plumbing beneath krafla these results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters

proterozoic melting in the northern peridotite massif zabargad island os isotopic evidence the geodynamic history of the three zabargad peridotite bodies is the key to their significance as samples of the upper mantle currently there are two main hypotheses that differ greatly in their implications for the origin and age of the peridotite complex as a whole in the first the zabargad peridotite bodies all represent young asthenospheric mantle that was juxtaposed with ancient crustal gneisses during the opening of the red sea in the second the complex may represent a single package of residual mantle and lower crust of pan african age that was uplifted during the miocene in order to distinguish between these two models we have analysed five samples of zabargad peridotite and two pyroxenites for os isotopes the 187os 188os results range from 0 1198 to 0 1320 and correlate with al2o3 allowing an age inference for the northern body based on the os isotopic evolution curve for the bulk earth of 1 4 0 3 gyr this is at least as old as the previously inferred pan african age and may be older and agrees with previous suggestions that the northern and central peridotite bodies probably represent ancient continental lithospheric mantle while the southern body represents recent asthenospheric mantle our results from both central and southern bodies are consistent with either crustal age hypothesis

sequence stratigraphy and carbon isotope stratigraphy of an aptian mixed carbonate siliciclastic platform to basin transition galve sub basin ne spain

palaeoenvironmental and palaeoecological change on the northern tethyan carbonate platform during the late barremian to earliest aptian a major shift from urgonian oligotrophic carbonate accumulation to orbitolinid rich mixed siliciclastic carbonate deposition is observed near the barremian aptian boundary in many sections both within and outside the shallow marine tethyan realm this important facies change in the swiss helvetic alps is documented here and interpreted in the context of general palaeoenvironmental change to achieve this a detailed micropalaeontological sedimentological mineralogical and geochemical study has been carried out on six sections across the upper part of the lower schrattenkalk member late barremian the rawil member formerly lower orbitolina beds earliest aptian and the lowermost part of the upper schrattenkalk member early aptian the sediments of the rawil member exhibit inner platform facies with rudists miliolids orbitolinids and dasycladals to outer platform facies characterized by small benthic foraminifera orbitolinids crinoids and bryozoans stratigraphic trends in microfacies environments and the composition of microfossil assemblages indicate that the rawil member includes a transgressive systems tract and the base of a highstand systems tract which are composed of an increasing number of parasequences in distal directions five to nine in the sections studied here the sea level rise discerned in the rawil member is coeval with increased detrital input and phosphorus burial with maximum values up to 80 times and 21 times the background values in the subjacent part of the lower schrattenkalk member respectively furthermore the rawil member records the appearance of kaolinite indicating a change towards tropical and more humid climate conditions this change may have led to an increase in continental weathering rates and an associated increase in detrital and nutrient fluxes towards the ocean the phase of climate change observed near the barremian aptian boundary may have been triggered by a phase of intensified volcanic activity linked with the onset of the ontong java large igneous province and the rawil member may be the expression of a precursor episode to oceanic anoxic event 1a in the shallow marine environment

high resolution carbon isotope records of the aptian to lower albian from se france and the mazagan plateau dsdp site 545 a stratigraphic tool for paleoceanographic and paleobiologic reconstruction high resolution carbon isotope stratigraphy is established for the aptian to lower albian of the vocontian basin se france and correlated to the carbon isotope record of the mazagan plateau dsdp site 545 the carbon isotope stratigraphy of the vocontian basin is proposed as a standard reference curve for the aptian to lower albian due to the completeness and high temporal resolution of the stratigraphic succession the good biostratigraphical time control and the frequent occurrence of regional to global black shale horizons including oceanic anoxic events 1a oae 1a of the lower aptian and oae 1b of the lower albian the carbon isotope record appears better suited for long distance short term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types however the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography and to correlate regional to global black shale horizons in different marine environments this combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species based on the demonstrated diachroneity of important biostratigraphic markers of the aptian albian boundary the globally observed break point between the end of the uppermost aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13c values is an alternative criterion the distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the aptian to lower albian

drowning unconformities palaeoenvironmental significance and involvement of global processes abstract drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms they mostly consist in the deposition of deep marine facies on top of shallow marine limestones although large scale depositional geometries mimic lowstand systems track architecture these sedimentary turnovers are developed in relation with major sea level rise inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up this so called paradox of carbonate platform drowning implies that parameters other than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems worldwide and at different times during earth history in depth studies of drowning unconformities revealed that changes in nutrient input clastic delivery temperature or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers the examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities this is complemented by new data from early cretaceous successions from the helvetic alps during this time period the helvetic carbonate platform developed along the northern tethyan margin using both photozoan and heterozoan communities phases of healthy production were interrupted by several drowning episodes the latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation from the earliest valanginian to the early to late barremian three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions which first induced a switch from photozoan to heterozoan communities and then to long lasting drowning phases the latter encompass several sea level rise and fall cycles and may be linked to strengthened upwelling currents with the return to more oligotrophic conditions during the late barremian photozoan urgonian type communities took up again their development has been abruptly stopped at the end of the early aptian by a major emersion phase the subsequent drowning is documented in various peritethyan areas this initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the cenomanian this long term trend in the evolution of the helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena in particular the progressive opening of the northern and equatorial atlantic may have impacted sea level by creating new oceanic basins the emplacement of submarine volcanic plateaus may have triggered sea level rise and fertilized deep oceanic waters through hydrothermal processes drowning unconformities thus record the interplay of local with long term processes and constitute regional sedimentary archives of global phenomena

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

ecological succession palaeoenvironmental change and depositional sequences of barremian aptian shallow water carbonates in northern oman barremian and aptian shallow water carbonate facies uppermost lekhwair kharaib and shuaiba formations are described from outcrops in northern oman based on facies analysis and bedding pattern three orders of depositional sequences are defined third to fifth order and correlated between sections over the course of three third order sequences covering the barremian to lower aptian a third order depositional pattern is documented that consists of a succession of three distinct faunal assemblages discoidal orbitolinids and calcareous algae were deposited during early transgression microbialites and microencrusters dominate the late transgressive to early highstand facies and a rudist and miliolid dominated facies is typical of the highstand this ecological succession was controlled largely by palaeoenvironmental changes such as trophic level and clay influx rather than sedimentological factors controlled by variations in accommodation space orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow water carbonate response to global changes affecting late barremian to aptian palaeoclimate and palaeoceanography

surfaces with a long history the aptian top shu aiba formation unconformity sultanate of oman discontinuity surfaces in shallow marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric neritic seas understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo environmental analysis sequence stratigraphy reconstructions of sea level change and basin evolution in the present paper the aptian top lower shu aiba formation discontinuity in the sultanate of oman is taken as a prominent example of a regionally extensive 100 000 km2 surface with a long up to 10 myr and complex geological history the top shu aiba discontinuity formed on the topographically elevated domain of the oman platform and represents in essence the late aptian time interval coeval carbonates in the intrashelf bab basin and oceanic rim indicate forced regression and sequence wise gradual down stepping available regional sedimentological sequence stratigraphic petrographic palaeontological and geochemical evidence from outcrops and cored wells in oman is summarized in part complemented by new data and reviewed in a process oriented context in the field the discontinuity is expressed as a low relief stained surface with evidence for a marine hardground stage being dominant indistinct features that indicate a transient meteoric precursor stage isotope shifts meteoric cements circumgranular cracks etc are present but their interpretation requires careful and detailed work this feature is remarkable as a series of relative sea level falls with amplitudes of up to several tens of metres from the early to late aptian boundary to the end of the aptian are reported from the middle east and elsewhere despite the palaeogeographic position of the study area in the tropical climate zone evidence of deep cutting karst features characteristic for many long term exposure surfaces worldwide is scarce acknowledging the fact that the modern world offers no genuine analogues for the lower aptian carbonate system in oman morphological similarities between actualistic wave eroded coastal terraces and the top shu aiba discontinuity are discussed critically this discussion may imply that during an exposure time of several million years the top shu aiba discontinuity experienced repeated stages of shallow flooding and emergence with each transgression removing portions of the underlying rock record the data shown here exemplify the complexity of hiatal surfaces in epeiric neritic carbonates and may serve as a case example for other major discontinuities

palaeoclimate analysis using spectral gamma ray data from the aptian cretaceous of southern england and southern france abstract the abundance and half lives of potassium k uranium u and thorium th make these three elements the dominant sources of gamma rays detected in rocks both at outcrop and in the subsurface with the advent of the spectral gamma ray tool sgr the variation shown by these three elements in rocks has been considered to reflect sorting at flooding surfaces and changes in the weathering regime of sediment source lands k and u are considered to be more soluble than th thus elevated th to k or u ratios in soils and eroded clays can reflect hot humid climates and palaeoclimates this study makes an assessment of the usefulness of sgr data to palaeoclimate studies by comparing changing th k and th u ratios from a known period of palaeoclimate change to extensive published and new data from other analytical methods new sgr data from the cretaceous of southern england and southern france compare favourably to outcrop sedimentological facies interpretations and laboratory geochemical data palaeoclimate data from two other sections northern germany northern italy are compared as controls to the study together these analyses suggest that there was a gradual change from semi arid climate in the barremian and early aptian to a semi humid climate in the mid aptian superimposed on this long term rise in humidity were a number of short term ammonite zone length changes in th k and th u ratios and the abundance of climate sensitive materials this study shows that sgr data are more useful than originally thought when problems of overprinting from heavy minerals and diagenesis are overcome outcrop and borehole spectral gamma ray logs from mudstones or the clay rich beds of mixed successions may be used to interpret past patterns of hinterland weathering

condensation processes in shallow platforms abstract sequence stratigraphy allows elucidation of the time space relationships of deposits in sedimentary basins however the relative distribution of unconformities and condensed sections can neither be used as diagnostic criteria for particular palaeogeographic settings nor as indicators of maximum regional transgressions condensation processes also occur in the shallowest portions of platforms and during maximum regression episodes three separate processes of condensation are here distinguished stratigraphic sedimentary and taphonomic these three categories of condensation can be used to analyze patterns of sediment distribution and also to estimate lateral and vertical variations in sedimentation rates contrary to the usual interpretation the maximum values of rate of sedimentation and degree of accommodation of sediments as well as the highest relative sea level occur in the lowest levels of the shallowing upward sequences the distinction between these condensation processes allows one to predict that the degree of sedimentary and stratigraphic condensation will be higher towards the distal portions of the platforms whereas the stratigraphic condensation processes without sedimentary condensation will show the maximum intensity and frequency in the shallowest portions of the platforms

characterization and interpretation of discontinuity surfaces in a jurassic ramp setting high atlas morocco discontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings in sedimentary systems these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record from an applied perspective discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization here a total of 80 condensed surfaces s1 firmgrounds s2 and hardgrounds s3 from a jurassic middle and upper bajocian assoul formation ramp setting of the high atlas in morocco are carefully documented with respect to their morphology their secondary impregnation by fe and mn oxides and phosphates and their palaeoecological record a statistical frequency distribution of two surfaces of the s1 type 1 1 surfaces of the s2 type and 0 4 surfaces of the s3 type per 10 section metres is observed along a 220 m long carbonate succession based on two stratigraphically and spatially separated study windows and correlative sections the stratigraphic frequency distribution the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner specific features of the study site include the considerable stratigraphic thickness of the assoul formation and the conspicuous absence of subaerial exposure related features based on the data presented here firmground and hardground surfaces are best interpreted as maximum regression related features relative sea level lowstand results in a lowered wave base and wave orbitals and currents result in sea floor omission and lithification care must be taken to avoid overly simplistic interpretations as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal distal transects the data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models

carbonate platform sequence stratigraphy in a rapidly subsiding area the late barremian early aptian of the organya basin spanish pyrenees abstract a detailed sedimentological and stratigraphical study of the late barremian early aptian urgonian carbonate platform of the organya basin spanish pyrenees has identified four depositional sequences the first two sequences consist of transgressive and highstand systems tracts and the last two sequences of lowstand transgressive and highstand systems tracts sequence boundaries at the top of sequences or 1 and or 4 are type 1 boundaries with evidence of exposure and erosion sequence boundaries at the top of sequences or 2 and or 3 are type 2 with no evidence of exposure or erosion sand shoal high energy facies characterise the first sequence or 1 sequences or 2 and or 3 are dominated by lagoonal facies with an important accumulation of lacustrine facies at the base of or 3 a succession of lacustrine deep platform and sand shoal facies characterises sequence or 4 the last sequence also contains the record of an anoxic event oae 1a all these characteristics have been largely influenced by the high subsidence rate of the organya basin 1100 m of compacted limestone deposited in about 5 ma however the main global eustatic changes registered in other contemporaneous basins were also identified

spatial geochemistry of a carboniferous platform margin to basin transect balancing environmental and diagenetic factors abstract conventional one dimensional chemostratigraphy of marine carbonates assesses the chemical archive of individual stratigraphic sections and their correlation in space and time whereas this approach has shown to be of value when linking isobathymetric domains usually characterised by similar facies more caution is needed when correlations are extended across different physiographic settings and hence different facies belts here the spatial geochemical record of pennsylvanian platform margin to basin transects across a bathymetric range of about 800 m is documented and discussed in a process oriented context particularly the presence of layered palaeo water masses and their potential control on slope facies distribution and geochemical properties requires attention whereas carboniferous thermo and or chemo clines most likely affected depth related slope facies zonation it was facies change and hence variances in porosity permeability properties that controlled differential early burial diagenetic alteration specifically the lower slope related breccia facies is characterised by higher volumes of early burial carbonate cements this implies that these sediments entered the shallow burial domain with a considerable open pore space and gave way to an increased rock fluid ratio whereas the 13 c record is invariant with bathymetry the more diagenesis sensitive 18 o proxy records pronounced shifts observed across major facies boundaries from this it is concluded that although the primary controlling factor of slope facies distribution with depth is probably palaeoceanographic in nature it is differential rock fluid ratios that control the first order spatial shifts in 18 o composition these findings show that one dimensional chemostratigraphy will severely underestimate the complexity of three dimensional bathymetric data sets across platform margins this is of relevance for the interpretation of the geochemical archive of fossil carbonate platforms in general

diachronous evolution of late jurassic cretaceous continental rifting in the northeast atlantic west iberian margin 1 regional 2 d seismic reflection profiles outcrop and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest iberia alentejo basin the interpreted data indicate the bulk of late jurassic earliest cretaceous subsidence occurred in the present day continental slope area as shown by 1 significant thickening of synrift strata basinward from a slope bounding fault system sfs west of which the total thickness of sediment can reach more than 9 0 km and 2 relatively thin mesozoic strata east of the sfs where thickening of synrift units against principal faults is limited five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins which were located on the rift shoulder to subsiding tilt blocks west of the sfs these regressive events are correlated with major rift related events occurring on the deeper margin direct comparisons with the peniche basin of northwest iberia reveal that significant portions of the iberian lower plate margin were uplifted and eroded during the last stages of continental rifting this process was repeated at different times and in different areas as the locus of rifting and continental breakup migrated northward as a result two distinct rift axes are recognized in west iberia a first axis extending from the porto basin to the alentejo basin and a second axis located on the outer proximal margin north of 38 30n in addition the sfs delimited 1 prograding deposits of cretaceous paleogene age and 2 late cenozoic deposits draping the modern continental slope these latter facts demonstrate that on lower plate passive margins the relative position of the continental slope is established during the final rifting episode s preceding continental breakup

multichannel analysis and suppression of sea clutter for airborne microwave radar systems one efficient method to detect slow targets with low signal to clutter plus noise ratios is space time adaptive processing stap to apply stap to maritime radar systems the multichannel properties of sea clutter have to be known this paper investigates these characteristics for airborne microwave radar systems to detect vessels in the open sea it is shown that the motion of sea echoes and different sea scattering types cause different multichannel properties of sea clutter compared with land clutter this paper provides a mathematical basis to describe multichannel sea clutter and predict stap performance over water to confirm the derived properties several real multichannel sea data sets for different swell directions and sea states were acquired with the airborne radar system phased array multifunctional imaging radar pamir and simulations were conducted this paper demonstrates the reproducibility of real sea clutter multichannel characteristics for different sea conditions with the help of calculations and simulations which are proposed in this analysis

analytical model of surface uplift above axisymmetric flat lying magma intrusions implications for sill emplacement and geodesy abstract in this paper we develop a new axisymmetric analytic model of surface uplift upon sills and laccoliths based on the formulation of a thin bending plate lying on an elastic foundation in contrast to most former models also based on thin bending plate formulation our model accounts for i axi symmetrical uplift ii both upon and outside the intrusion the model accounts for shallow intrusions i e the ratio a h 5 where a and h are the radius and depth of the intrusion respectively the main parameter of the model is the elastic length l which is a function of the elastic properties of the bending plate and of the elastic foundation the model exhibits two regimes depending on the ratio a l when a l a l 5 the uplift is mostly restricted upon the intrusion when the elastic foundation is very stiff our model converges towards that of a clamped plate we provide as supplementary material a matlab function that calculates the surface uplift from the set of system and control parameters we discuss three possible applications of our model i the model can be used to describe sill propagation by introducing a propagation criterion for realistic values our model reproduces well the behavior of horizontal intrusions simulated in experiments ii the model can also be used to compute the critical size of saucer shaped sills it shows for instance that a soft elastic foundation favors the horizontal spreading of sills before they form inclined sheets iii we show that the classical mogi point source model cannot be used to constrain sill properties from the surface uplift we thus propose that our model can be used as a valuable alternative to both simple analytical models like mogi s and more complex numerical models used to analyze ground deformation resulting from sill intrusions in active volcanoes

rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms abstract it has sometimes been claimed that rudist bivalves competitively displaced corals from reef frameworks during the cretaceous this hypothesis combines two assertions 1 that the autecology of rudists was convergent with that of reef building corals and 2 that rudist formations commonly developed as reefs we dispute both assertions and thus reject the hypothesis of competitive displacement we argue instead that mobile sediments rather than frameworks dominated the margins and tops of most of the extensive carbonate platforms of the period and that it was on these non reefal biotopes that the rudists flourished definitions of reefs tend to combine two major elements 1 a robust biogenic framework with accompanying sedimentary and diagenetic components and 2 topographical relief such definitions are clearly rooted in recent coral reefs in which endosymbiotic zooxanthellae permit the extensive growth of colonial coral frameworks in shallow but relatively nutrient poor waters coralline algae and cementation may contribute significantly to the growth of rigid structures and topography is largely the legacy of pleistocene changes in sea level in rudist formations in contrast individual rudist congregations are volumetrically limited relative to sediment they are often loosely constructed and they evidently showed little if any original relief tabular and small lenticular units predominate these differences in structure and palaeoenvironmental situation between rudist and modern coralgal associations reflect the different autecologies of the constituent organisms the clonal growth of corals predisposes them to the development of frameworks projecting above the sediment surface herein termed superstratal growth by contrast the aclonal development of rudists was better suited to the opportunistic occupation of a variety of temporarily available substrata by large numbers of individuals in particular elevator rudists in which the entire commissure exhibited upward growth evidently grew with their shells largely embedded in and supported by the ambient sediment herein termed constratal growth moreover the tolerances and growth responses of rudists to such factors as water turbidity nutrients and current regime were quite different from those of the majority of reef building corals despite repeated assertions in the literature that rudists possessed zooxanthellae only a few species show any evidence for such a symbiosis and other evidence suggests that most lacked them in view of these differences in their preferred biotopes competition between rudists and corals is doubtful even though members of both groups co occur in many areas the relative decline of coral frameworks in the cretaceous was thus probably independently caused

magma bright spots mapped beneath krafla iceland using rvsp imaging of reflected waves from microearthquakes abstract the geometry and distribution of magma in the crust remain controversial topics with recent studies questioning the role of large magma chambers in this investigation high resolution 3d reflection images of crustal discontinuities beneath the krafla geothermal field in northern iceland were generated by applying vertical seismic profiling vsp techniques adapted from reflection seismology to microearthquake data exceptionally large amplitude reflections bright spots at a depth of 2 1 km correlate with rhyolitic magma encountered in the iddp 1 borehole although similarly bright reflectors at about 4 km correspond in depth to the top of an inferred magma chamber from previous seismic studies the scattered reflectivity that persists beneath this deeper reflector argues for a distributed magma system rather than a large feeder chamber

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

a volcanic co2 pulse triggered the cretaceous oceanic anoxic event 1a and a biocalcification crisis the aptian oceanic anoxic event 1a oae1a ca 120 ma ago is one of the most prominent of a series of geologically brief intervals in the cretaceous characterized by the deposition of organic carbon rich sediments oaes reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records however the triggering mechanisms for oaes remain controversial here we present a bulk rock and molecular marine and terrestrial bio markers c isotope record at unprecedented time resolution from the cismon section of northern italy that shows that oae1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle the documented sequence of events is most compatible with a trigger associated with increased co 2 emissions possibly leading to a doubling of p co 2 which in turn caused larger c isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the oae1a carbon cycle perturbation

progressive palaeoenvironmental change during the late barremian early aptian as prelude to oceanic anoxic event 1a evidence from the gorgo a cerbara section umbria marche basin central italy abstract during oceanic anoxic event 1a oae 1a 120 ma li et al 2008 organic carbon rich layers were deposited in marine environments under anoxic conditions on a global scale in this study palaeoenvironmental conditions leading to this event are characterised by studying the upper barremian to the lower aptian succession of the gorgo a cerbara section central italy for this an integrated multi proxy approach 13ccarb 13corg 18o phosphorus total organic carbon toc bulk rock mineralogy as well as redox sensitive trace elements rstes has been applied during the late barremian thin organic rich layers occur episodically and associated corg ptot ratios indicate the presence of intermittent dysoxic to anoxic conditions coarse correlations are observed between toc p and biogenic silica contents indicating links between p availability productivity and toc preservation however the corresponding 13ccarb and 18o records remain quite stable indicating that these brief periods of enhanced toc preservation did not have sufficient impact on the marine carbon reservoir to deviate 13c records around the barremian aptian boundary toc enriched layers become more frequent these layers correlate with negative excursions in the 13ccarb and 13corg records possibly due to a warming period as indicated by the 18o record during the earliest aptian this warming trend is reverted into a cooling trend which is then followed by an important warming step near the onset of oceanic anoxic event 1a oae 1a during this time period organic rich intervals occur which are characterised by the progressive increase in rste the warming step prior the onset of oae 1a is associated with the well known negative spike in 13ccarb and 13corg records an important peak in p accumulation rste enrichments and corg ptot ratios indicating the prevalence of anoxic conditions the selli level itself may document a cooling phase rste enrichments and corg ptot ratios confirm the importance of anoxic conditions during oae 1a at this site the gorgo a cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the ontong java plate basalt plateau which started already around the barremian aptian boundary and culminated into oae 1a

estimating ocean coherence time using dual baseline interferometric synthetic aperture radar a new technique for measuring the coherence time of the ocean surface at radar wavelengths has been developed and tested this technique requires an interferometric synthetic aperture radar system with at least two unique baselines along the direction of platform motion the coherence time of the surface may be presented as a high resolution coherence time map this technique was tested using the jpl airsar along track interferometer measurements of the ocean coherence at the l band were made at high spatial resolution under a variety of conditions a new operating technique that results in the required two baselines is described some parametric analysis is performed pertaining to the design of such a system a representative interferometric data set acquired at the strait of messina in 1991 is presented to illustrate the technique the interferometric phase data reveal and measure tidal currents flowing through the strait while the coherence time image shows considerable structure not visible in the backscatter or phase image coherence times in and around the strait were measured to be of the order of 0 1 s at the l band which is in agreement with previous estimates and measurements

the three dimensional seismic velocity structure of the east pacific rise near latitude 9 30 n three dimensional images of crustal seismic structure beneath the east pacific rise show pronounced axial heterogeneity over distances of a few kilometres a linear high velocity anomaly approximately 1 2 km in width and restricted to the uppermost 1 km of the crust is centred on the rise axis an axial low velocity anomaly at depths of 1 3 km varies in amplitude along the axis consistent with a zone of higher crustal temperatures midway between two discontinuities in the morphology of the rise axis this apparent thermal segmentation along axis is consistent with injection of mantle derived melt midway along a locally linear 12 km long segment of the rise

thin low velocity zone within the krafla caldera ne iceland attributed to a small magma chamber we examine seismograms from microearthquakes recorded at krafla central volcano in the northern volcanic zone of iceland during a short inflation period in 1988 we produce record sections for propagation both to the north and to the south of the center of the caldera by combining seismograms from many earthquakes the northern record section contains clear evidence of a low velocity zone lvz including a low amplitude diffraction of the p wave as it impinges on top of the lvz and high amplitude reflections from beneath the lvz the absence of clear shear waves indicates that the lvz is at least partially molten and should be interpretated as a magma chamber the magma chamber is less than 1 km thick with a top approximately 3 km beneath the surface we find no evidence for a lvz in the southern part of the caldera

the crustal magma chamber of the katla volcano in south iceland revealed by 2 d seismic undershooting summary results of a 2 d seismic undershooting experiment on the katla central volcano in south iceland are reported large localized traveltime anomalies 0 4 s are observed on an array within the katla caldera the traveltimes are forward modelled using a wavefront tracker developed in appendix a thus non linear effects encountered in traveltime tomography are avoided as well as common problems with ray tracing in the presence of strong lateral heterogeneity an extreme variation in compressional velocity is required to extend over a significant volume in order to model the data the resulting model is not unique but constraints on the allowable range of velocities 2 5 6 0 km s render the basic features well constrained a clear s wave shadow is closely associated with delays in traveltime due to a shallow slow anomaly low amplitude p waves go hand in hand with early arrivals due to thin structural features flanking the slow anomaly the model is interpreted in terms of a magma chamber containing extensively molten rock the magma chamber is shallow with a bottom at a depth of about 1 5 km below sea level 3 0 km below surface and measures about 5 km across the depth of the chamber is roughly at the level of buoyant equilibrium for basaltic melt in the crust owing to poor vertical resolution at shallow depths in the undershooting geometry the top of this shallow magma chamber is not well resolved on the other hand the bottom of the chamber is well resolved the chamber is underlain by rocks of average or high velocity for that depth the magma chamber is a persistent feature big enough 10 km3 to supply magma for large eruptions and to supply heat to permit remelting of hydrated basaltic crust to produce silicic magmas at shallow levels the chamber is fed by magma fracturing from below the model agrees with phenomenological models of magma chambers in iceland based on geological observations and provides a quantification of those models in terms of depth and size on the other hand it is fundamentally different from recent models of magma chambers at mid ocean ridges which may be more akin to the pervasive region of partial melt at depth beneath iceland this underlines the important effect of the icelandic hotspot on tectonics and volcanism in iceland and implies a substantially different crustal and thermal structure in iceland from that of normal mid ocean ridges

focal mechanisms and size distribution of earthquakes beneath the krafla central volcano ne iceland seismicity was monitored beneath the krafla central volcano ne iceland between 2009 and 2012 during a period of volcanic quiescence when most earthquakes occured within the shallow geothermal field the highest concentration of earthquakes is located close to the rock melt transition zone as the iddp 1 wellbore suggests and decays quickly at greater depths we recorded multiple swarms of microearthquakes which coincide often with periods of changes in geothermal field operations and found that about one third of the total number of earthquakes are repeating events the event size distribution evaluated within the central caldera indicates average crustal values with b 0 79 0 04 no significant spatial b value contrasts are resolved within the geothermal field nor in the vicinity of the drilled melt besides the seismicity analysis focal mechanisms are calculated for 342 events most of these short period events have source radiation patterns consistent with double couple dc mechanisms a few events are attributed to non shear faulting mechanisms with geothermal fluids likely playing an important role in their source processes diverse faulting styles are inferred from dc events but normal faulting prevails in the central caldera the best fitting compressional and tensional axes of dc mechanisms are interpreted in terms of the principal stress or deformation rate orientations across the plate boundary rift maximum compressive stress directions are near vertically aligned in different study volumes as expected in an extensional tectonic setting beneath the natural geothermal fields the least compressive stress axis is found to align with the regional spreading direction in the main geothermal field both horizontal stresses appear to have similar magnitudes causing a diversity of focal mechanisms

morphological patterns of aptian lithocodium bacinella geobodies relation to environment and scale lithocodium aggregatum and bacinella irregularis are now extinct shallow marine life forms of unknown taxonomic origin forming part of the tropical platform biota during much of the mesozoic these organisms experienced bloom periods and temporarily replaced rudist coral assemblages during parts of the early aptian within the limitations of time resolution this out of balance facies is coeval with the oceanic anoxic event 1a related black shale deposition in oceanic basins but the triggering factors remain poorly understood here a platform wide comparison of lithocodium bacinella geobodies and morphotypes from the sultanate of oman is presented and placed in its environmental bathymetric and physiographic context lithocodium bacinella geobodies reach from kilometre scale superstructures to delicate centimetre sized growth forms clearly scale matters and care must be taken when drawing conclusions based on spatially limited observational data whilst the factors that cause lithocodium bacinella expansion should probably be considered in a global context regional to local factors affected growth patterns in a more predictable manner here the unresolved taxonomic relationship remains the main obstacle in any attempt to unravel the response of lithocodium bacinella to specific or interlinked environmental parameters as different organisms respond differently to changing environment acknowledging these limitations the following tentative patterns are observed i lithocodium bacinella tolerated a wide range of hydrodynamic levels and responded to differences in energy level or physiographic settings margin intrashelf basin inner platform by obtaining characteristic growth forms ii lithocodium bacinella favoured low sediment input but had the ability to react to higher sedimentation rates by enhanced upward growth a feature perhaps pointing to a phototrophic metabolism circumstantial evidence for continuous growth within the upper sediment column is debated iii the availability of accommodation space had a direct influence on the maximum size of geobodies formed iv fluctuating nutrient levels and sea water alkalinity may have affected the growth potential of lithocodium bacinella understanding the relationship between lithocodium bacinella morphogenesis on a wide range of scales and local environmental parameters allows for better prediction of the spatial distribution of reservoir properties and also results in an improved interpretation of palaeoenvironments this study might represent a useful first step in this direction

the madotz urgonian platform aralar northern spain paleoecological changes in response to early aptian global environmental events abstract sudden addition of carbon dioxide to the atmosphere can reduce the caco3 saturation and weaken the biocalcification potential of marine organisms in shallow water and in open marine settings in this study the response of an aptian neritic carbonate environment to sudden addition of carbon dioxide at the beginning of oceanic anoxic event 1a is investigated the beginning of the oae1a was coupled with a major perturbation on the carbon cycle as indicated by a negative carbon isotope excursion in the sedimentary record this isotope anomaly is regarded as a proxy for massive addition of volcanic or methane derived co2 to the atmosphere within only a few 104 years the impact of a rapid change in atmospheric pco2 on biocalcifiers in low latitude shallow water settings can be studied in a well preserved aptian carbonate shelf succession cropping out today in the aralar mountains ne spain the madotz section n spain preserves a continuous shallow water record that was deposited on a mid latitude atlantic oriented mixed siliciclastic carbonate ramp lower aptian sediments consist of two neritic limestone successions separated by orbitolinid rich marlstone enriched in organic matter the lower neritic limestone succession ends with a submarine hardground and the transition from the lower neritic limestone to the orbitolinid marlstone coincides with a negative spike in the organic carbon isotope record this negative spike can be correlated with the negative carbon isotope anomaly marking the base of oae1a the paleoecological change coinciding with the base of oae1a occurred at a time of sea level rise and it coincided with a demise of heavily calcified nannoconids in the tethys and pacific oceans the paleoecological change observed in the madotz section corresponds to a comparable change seen in the more distal and more expanded carbonate ramp section igaratza at the aralar mountains ocean acidification caused by sudden increase in pco2 may explain reduced calcification potential of some shallow water calcifiers calcification crisis was amplified by rising sea level increasing temperatures and increased flux of detrital material and nutrients from continents into coastal seas

a volcanically induced climate warming and floral change preceded the onset of oae1a early cretaceous the aptian oceanic anoxic event 1a oae1a is preceded by a prominent negative c isotope excursion ncie attributed to major volcanism on the ontong java plateau that is supposed to lead to a pco2 increase and a climate change lower aptian sporomorph assemblages in two pelagic sections from the southern tethys margin n italy were analysed in order to test if the postulated climate changes affected the terrestrial vegetation at the base of the ncie the sporomorph assemblages comprise abundant bisaccate pollen reflecting a warm temperate climate several tens of kiloyears ka after the start of the ncie decreasing bisaccate pollen and increasing classopollis spp and araucariacites spp suggest the beginning of a long term temperature rise palynomorphs indicate that maximum temperatures were reached several tens of ka after the end of the ncie and the onset of oae1a the highest temperatures coincide with arid conditions which could reflect a northward shift of the hot arid northern gondwana floral province as a result of an increasing pco2 over 200 ka after the onset of oae1a reduced volcanic activity and or increased black shale deposition allowed for a drawdown of most of the excess co2 and a southward shift of floral belts

faroe iceland ridge experiment 2 crustal structure of the krafla central volcano the seismic velocity structure of the krafla central volcano is characterized by large variations in compressional velocity a 40 km wide high velocity dome extends from the lower crust 11 14 km depth beneath the volcano narrowing upward a magma chamber sits at its top near 3 km depth it is defined by both 0 2 0 3 s compressional wave delays and shear wave shadowing to be 2 3 km n s 8 10 km e w and 0 7 1 8 km thick the near surface structure uppermost 2 5 km of the krafla caldera is approximately flat lying with only minor lateral heterogeneities the crust beneath the magma chamber has low shear wave attenuation and anomalously high compressional and shear wave velocities shear waves reflected from a 19 km deep moho are clearly visible for some paths through the crustal volume below the magma chamber even though the more shallow diving s waves are severely attenuated the midcrust beneath the shallow magma chamber cannot contain partial melt or even be at near solidus temperatures the krafla central volcano plays a major role in crustal genesis along the plate boundary the high velocity dome in our view represents crust generated in and around the magma chamber which has subsequently been advected to greater depths

the early cretaceous drowning unconformities of the apulia carbonate platform gargano promontory southern italy local fingerprints of global palaeoceanographic events drowning successions which cap carbonate platforms and flanks bear palaeoenvironmental information which is useful for genetic stratigraphy they constitute predictive key markers in regional to global correlations an early cretaceous platform to basin transition has been investigated in apulia southern italy and two drowning unconformities dated as early valanginian and late early aptian have been documented they occur at the base of thick pelagic tongues wedging toward the platform and mark the base of two depositional sequences showing distinct transgressive regressive cycles timing of drowning processes based on biostratigraphy and dynamic stratigraphy allows the correlation of unconformities with global scale palae oceanographic events marked among others by positive spikes of well established 13c curves drowning signatures in the apulia carbonates fit the stratigraphic palaeoecological and possibly geochemical evidence found in global records at the same stratigraphic levels moreover it is proposed that the observed drowning events were caused by palaeoceanographic crises affecting factory productivity

early aptian algal bloom in a neritic proto north atlantic setting harbinger of global change related to oae 1a pervasive growth of microencrusters lithocodium bacinella characterizes short lived stratigraphic intervals in lower aptian shallow water carbonate platform settings of the central and southern tethys although a causal relationship between this peculiar shallow water facies and the early aptian oceanic anoxic event oae 1a seems likely the temporal and spatial distributions of lithocodium and bacinella mass occurrences in the rock record point to a rather complex pattern possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event oae 1a slightly pre or postdating the deposition of dark organic rich black shales in pelagic basins this study presents evidence for a punctuated and well expressed early aptian bloom of the ulvophycean green algae lithocodium aggregatum observed at the proto north atlantic margin lusitanian basin portugal similar to southern and central tethyan sections a lithocodium dominated interval temporally replaces the rudist dominated platform ecosystem this lithocodium rich horizon is composed of oncoidal floatstones and boundstones including a well exposed biohermal level and reaches a thickness of up to 6 m high resolution carbon isotope stratigraphy shown here clearly argues for lithocodium to represent a biotic harbinger of environmental change in the run up of oae 1a chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto north atlantic was coeval with an early aptian carbonate platform drowning episode observed in the northern tethys prior to oae 1a a regionally enhanced nutrient level and a relative sea level rise are suggested to have triggered the transient mass occurrence of lithocodium microencrusters which also may have been influenced by elevated atmospheric co2 concentrations related to the emplacement of the ontong java large igneous province upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients which tentatively diminished and finally interrupted the metazoan carbonate platform factory

on the estimation of wave slope and height varnance spectra from sar imagery a procedure is described for using synthetic aperture radar sar imagery to estimate two dimensional ocean wave slope and height variance spectra the logic underpinning the procedure is based both on the results of the numerical simulation of sar wave imagery and analytic descriptions of the sar imaging process the procedure when applied to sar imagery of waves acquired during the recent shuttle imaging radar mission sir b is shown to produce spectra that agree with independent measures of both the two dimensional slope and height variance spectra the implications of these results for future sar missions aimed at measuring ocean waves are considered

microbial foraminiferal episodes in the early aptian of the southern tethyan margin ecological significance and possible relation to oceanic anoxic event 1a two regionally significant microbial foraminiferal episodes 150 kyr each occur within the early aptian shallow marine platform in oman and throughout eastern arabia the stratigraphically lower of these two intervals is characterized by isolated or coalescent domes that share similarities with modern open marine stromatolites from the exuma cays bahamas the upper interval is predominantly built by a problematic lithocodium bacinella consortium in buildup and massive boundstone facies based on highresolution chemostratigraphy these shoalwater intervals are coeval with oceanic anoxic event 1a oae1a livello selli field evidence demonstrates that the buildup episodes alternate with stratigraphic intervals dominated by rudist bivalves this biotic pattern is also recognized in other coeval tethyan sections and is perhaps a characteristic shoalwater expression of the oae1a the short lived regional expansions of this microbial foraminiferal out ofbalance facies cannot be explained by local environmental factors salinity and oxygen level alone and the buildup consortia do not occupy stressed refugia in the absence of grazing metazoans judging from recent analogues the main fossil groups i e microbial assemblages macroalgae larger sessile foraminifera and rudist bivalves all favoured elevated trophic levels but with different tolerance limits the implication of this is that the influence of palaeofertility events possibly related to oae1a on carbonate platform community structures must be investigated the observations made in these coastal sections are a significant first step for the improved understanding of the early aptian period of biotic oceanic and climatic change

theory of synthetic aperture radar ocean imaging a marsen view this paper reviews basic synthetic aperture radar sar theory of ocean wave imaging mechanisms using both known work and recent experimental and theoretical results from the marine remote sensing marsen experiment several viewpoints that have contributed to the field are drawn together in a general analysis of the backscatter statistics of a moving sea surface a common focus for different scattering models is provided by the mean image impulse response function which is shown to be identical to the spatially varying frequency variance spectrum of the local complex reflectivity coefficient from the analysis has emerged a more complete view of the sar imaging phenomenon than has been previously available a new generalized imaging model is proposed

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

latitudinally different responses of tethyan shoal water carbonate systems to the early aptian oceanic anoxic event oae 1a ocean wide anoxic events represent intensively investigated anomalies in the global carbon cycle most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black shale deposition and carbon isotope excursions the study of ocean wide anoxic events and coeval shallow water settings is now increasingly seen as an interesting complementary approach but one that is not without problems whereas platform drowning characterizes the early aptian of the northern tethyan margin lithocodium bacinella rich facies and ongoing shoal water sedimentation at the southern tethyan margin oman bears important information on potential causes of carbon cycle perturbations the present paper seeks to test the supra regional relevance of the oman data by investigating coeval central tethyan limestones three lower aptian shoal water sections in istria croatia deposited on the isolated adriatic carbonate platform are investigated applying chemostratigraphy carbon and strontium and detailed sedimentological analysis the focus is on peritidal to lagoonal facies characterized by mass occurrences of lithocodium bacinella an enigmatic microencruster community lithocodium bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness with several layers merging to metre thick packages growth fabrics within the layers include oncoidal morphotypes lumps interconnected patches and columns layers and rare nodular to massive bindstone facies these growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart this widespread distribution suggests that specific lithocodium bacinella morphotypes might serve as regional stratigraphic markers the high resolution carbon isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium isotope data obtained from screened rudist low mg calcite the chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of early aptian oceanic anoxic event 1a moreover results indicate the near coeval nature of lithocodium bacinella bloom facies in istria and oman the outcomes of this study point to latitudinally different responses of tethyan shoal water carbonate systems platform drowning versus lithocodium bacinella blooms to the ocean wide anoxic event 1a

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

response of proto north atlantic carbonate platform ecosystems to oae1a related stressors abstract integrated biostratigraphic chemostratigraphic studies provide evidence that the proto north atlantic realm witnessed major changes in carbonate platform production in the run up of the early aptian oceanic anoxic event oae 1a whereas pervasive growth of lithocodium microencrusters represents an early harbinger of oae1a related environmental perturbation the subsequent replacement of oligotrophic rudist coral nerineid by mesotrophic orbitolinid oyster communities was clearly associated with the event itself in order to test the supra regional relevance of this major community replacement two shallow water sections in the southern lusitanian basin portugal are investigated by means of geochemistry carbon and oxygen isotopes cement petrography and detailed sedimentological analysis the focus is on a regional prominent discontinuity surface s4 at the transition between oligotrophic and mesotrophic carbonate platform production which might indicate that the major biotic change could have been associated with a phase of non sedimentation and possibly erosion the studied sections sao juliao crismina provide evidence that the major early aptian biotic turnover was preceded by numerous subordinate but significant changes in platform ecology which mirrored a series of progressive short term environmental changes in the course of oae1 several transient mass occurrences of orbitolinids indicate repeated phases of ecological stress arguably due to enhanced nutrient input and deepening small scale sea level changes at parasequence level below the major discontinuity surface are revealed by alternations of rudist assemblages dominated by clinger or recumbent forms as well as intercalated hardground and subaerial exposure stages expanded phases of subaerial exposure however can be largely ruled out following the geochemical and cement petrographic data presented here enhanced continent derived siliciclastic input characterising the lower orbitolinid oyster dominated limestones is in support of a shift to more humid conditions during the middle early aptian this is in line with palaeoclimatic data which propose a southward movement of the mid latitude arid climate belt during this time the documented rapid replacement of oligotrophic assemblages by various environmental stress adapted carbonate platform communities might be seen as explanation for ongoing early aptian proto north atlantic carbonate production during a time of widespread platform demise and drowning in the northern tethyan realm

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

relation between stratigraphic architecture and multi scale heterogeneities in carbonate platforms the barremian lower aptian of the monts de vaucluse se france abstract understanding the relationship between multi scale sedimentary heterogeneities and the stratigraphic architectures of carbonate platforms improves the interpretation of paleoenvironmental evolution in time and space such an approach improves the prediction of the spatial distribution of reservoir properties within carbonate stratigraphic units the reservoir scale stratigraphic anatomy and the growth history of a barremian aptian carbonate platform monts de vaucluse se france was based on 1 high resolution measured sections on outcrops 2 detailed microfacies analyses 3 paleoenvironmental interpretations 4 biostratigraphy using rudist bivalves foraminifera calcareous algae and locally echinoderm and ammonites and 5 sequence stratigraphic interpretations with a special focus on the identification of discontinuity surfaces with a significant stratigraphic correlation potential and critical environmental meaning the platform succession consists of subtidal mainly infralittoral with rare inter to supratidal deposits thirty types of elementary facies grouped in 12 facies associations have been defined the vertical and lateral changes in paleoenvironments together with the development of remarkable stratigraphic surfaces such as subaerial exposures marine erosional surfaces and drowning surfaces allow the definition of five stratigraphic sequences ranging from the late barremian to the earliest aptian these depositional sequences can be grouped into two distinct carbonate sedimentary systems characterized by specific sedimentary profiles and skeletal and non skeletal components 1 a carbonate platform with stronger hydrodynamic gradients rimmed by a narrow belt of high energy deposits with corals and rudistid rudstone facies and 2 a carbonate ramp dominated by orbitolinids fine grained facies including an elongated high energy oolitic shoal the two dimension architecture of the depositional sequences dimensioned geometries thickness and facies variations and the morphology of the shelf reflect a strong interaction between tectonic differential subsidence sediment production and global environmental conditions at the km scale the gorges de la nesque stratigraphic motif could represent a nested stratigraphic structure within the large scale model which could be implemented for up scaling petrophysical properties from the well to a full field model the association of coral facies to the rudist dominated system in the provence platform is a very clear proxy of the polarity of the carbonate platform and is critical for subsurface facies property modeling based on well data finally at the global scale the stratigraphic architecture and the step wise drowning events of the provence platform confirm and document the precursor events associated with environmental perturbations that affected the carbonate factory prior the oceanic anoxic event 1a oae1a

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

orbitolina episodes in carbonate platform evolution the early aptian model from se spain abstract among the orbitolininae palorbitolina lenticularis blumenbach is a common facies marker in upper barremian lower aptian shallow water mesogean deposits and was hitherto ascribed to specific but contrasting paleoenvironments within the carbonate platform facies suites the albacete prebetic area se spain illustrates a model in which the palorbitolina facies spread over the whole platform system the development of the palorbitolina sediments coincided with a transgressive trend at the end of an important terrigenous period this model could also be applied to similar middle crotaceous orbitolina facies

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

improved ocean surface velocity precision using multi channel sar this paper investigates new approaches to estimating the motion of the dynamic ocean surface using a multi channel synthetic aperture radar msar with m phase centers arranged in an along track configuration the objective of this paper is to determine the processing methods that produce the finest velocity resolution an issue that arises due to the finite coherence time of radar backscatter produced by the sea surface the investigation is carried out both theoretically using synthesized data produced from a modeled msar covariance matrix as well as experimentally using images collected with a 16 channel system three processing methods are considered linear regression along with a multi baseline phase progression estimation of the velocity centroid and coherent averaging of the shortest baseline interferograms both the theoretical and experimental results indicate that simple averaging of the shortest baseline interferograms often produces the best velocity precision

imaging the high temperature geothermal field at krafla using vertical seismic profiling abstract geophysical exploration and in particular active source seismic imaging of geothermal fields is important to assess and optimize the exploitation of natural heat sources for energy production and direct use the first multi offset moving source vertical seismic profiling vsp experiment over the high temperature geothermal field in krafla iceland was carried out in spring 2014 with the aim to test whether vsp is a suitable method to map volcanic stratigraphy fractures dykes steam zones and magmatic bodies at this site and for volcanic environments in general in this study we present a workflow for processing the sparse krafla vsp dataset recorded with receivers in either of two boreholes the analysis involved first arrival traveltime inversion and seismic reflection processing the seismic velocity model obtained by traveltime tomography reveals structural information between the two boreholes and can be linked to an existing geological model showing that the seismic velocities are mainly controlled by lithology the zero offset seismic reflection data were processed into two corridor stacks walk away vsp reflection data were migrated with a novel multicomponent kirchhoff migration algorithm that includes p and s wave isolation to obtain separate pp ps and ss migrated images the reflections imaged in the corridor stacks can be linked to the main lithological units known from borehole logging information migrated images from the walk away data reveal reflectors below and to the sides of the two boreholes considering a priori information such as hypocenter locations from earthquake seismology studies the reflectors can be related to changes in lithology fault zones dykes and possibly the top of the krafla magma chamber we found that vsp is potentially a useful method to image the key lithological boundaries and volcanic stratigraphy in the complex magmatic environment at krafla but a priori information proved to be essential to constrain the processing and interpretation of the sparse array dataset

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

interactions between environmental change and shallow water carbonate buildup along the northern tethyan margin and their impact on the early cretaceous carbon isotope record 1 the evolution of the early cretaceous northern tethyan carbonate platform was not only influenced by changes in sea level detrital influx and surface water temperature but also by changes in trophic levels we distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder water heterozoan communities superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy the initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general on the basis of a comparison between the temporal changes in an early cretaceous ammonite calibrated d 13 c record from southeastern france and coeval changes in the platform record we suggest that the history of carbon fractionation along the northern tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir but it was also influenced by the above mentioned changes in the ecology and geometry of the adjacent carbonate platform phases of photozoan carbonate production induced positive trends in the hemipelagic carbonate d 13 c record phases of heterozoan carbonate production pushed the d 13 c system toward more negative values platform drowning episodes implied an initial increase in d 13 c values followed by a longerterm decrease in d 13 c values

integration of micro gravity and geodetic data to constrain shallow system mass changes at krafla volcano n iceland new and previously published micro gravity data are combined with insar data precise levelling and gps measurements to produce a model for the processes operating at krafla volcano 20 years after its most recent eruption the data have been divided into two periods from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at krafla is decaying exponentially the net micro gravity change at the centre of the caldera is shown using the measured free air gradient to be 85 gal for the first and 100 gal for the second period after consideration of the effects of water extraction by the geothermal power station within the caldera the net gravity decreases are 73 17 gal for the first and 65 17 gal for the second period these decreases are interpreted in terms of magma drainage following a mogi point source model we calculate the mass decrease to be 2 1010 kg year reflecting a drainage rate of 0 23 m3 s similar to the 0 13 m3 s drainage rate previously found at askja volcano n iceland based on the evidence for deeper magma reservoirs and the similarity between the two volcanic systems we suggest a pressure link between askja and krafla at deeper levels at the lower crust or the crust mantle boundary after the krafla fires co rifting pressure decrease of a deep source at krafla stimulated the subsequent inflow of magma eventually affecting conditions along the plate boundary in n iceland as far away as askja we anticipate that the pressure of the deeper reservoir at krafla will reach a critical value and eventually magma will rise from there to the shallow magma chamber possibly initiating a new rifting episode we have demonstrated that by examining micro gravity and geodetic data our knowledge of active volcanic systems can be significantly improved

improved time control on cretaceous coastal deposits new results from sr isotope measurements using laser ablation sr isotope measurements of unaltered oyster shell calcite using laser ablation multi collector icpms techniques represent a powerful tool capable of establishing a chronostratigraphic framework for fossil near shore deposits this approach is tested on two shoal water successions from the portuguese algarve and lusitanian basins covering late barremian to albian strata 87 sr 86 sr values derived from low mg calcite of oyster shells fluctuate between 0 70717 0 00001 and 0 70746 0 00002 absolute values as well as stratigraphic trends match well with the global open marine seawater signal the new sr isotope results in combination with existing bio and chemostratigraphic records allow for identification of an early aptian biocalcification crisis at both studied localities and show that this event has severely affected coastal environments along the evolving atlantic siliciclastic intervals in the algarve section are interpreted as near shore equivalents of enhanced detrital shedding into shelf and deep sea environments as a consequence of increased chemical weathering rates during humid climate episodes

precise hypocentre relocation of microearthquakes in a high temperature geothermal field the torfajokull central volcano iceland the torfaj okull volcanic system is one of approximately 30 active volcanoes comprising the neovolcanic zones of iceland the central volcano of the system is the largest silicic centre in iceland with a caldera of approximately 12 km diameter its high temperature geothermal system is one of the most powerful in iceland torfaj okull is a source of persistent seismicity where both high and low frequency earthquakes occur to study this microseismicity in detail a temporary array of 20 broad band seismic stations was deployed between 2002 june and november these temporary stations were embedded in the permanent south iceland lowland sil network and data from nine adjacent sil stationswere included in this study aminimum one dimensional 1 d velocity model with station corrections was computed for earthquake relocation by inverting manually picked p and s wave arrival times from events occurring in the torfaj okull volcanic centre and its surroundings high frequency earthquakes from the torfaj okull volcanic centre were then relocated calculating a non linear probabilistic solution to the earthquake location problem subsequently we correlated the waveforms of these 121 events 2000 observations to define linked events calculated the relative traveltime difference between event pairs and solved for the hypocentral separation between these events the resulting high resolution pattern shows a tighter clustering in epicentre and focal depth when compared with original locations earthquakes are mainly located beneath the caldera with hypocentres between 1 and 6 km depth and lie almost exclusively within the geothermal system a sharp cut off in seismicity at 3 km suggests either that there is a marked temperature increase or that this is a structural boundary no seismic activity was observed in the fissure swarms to the northeast ne and southwest sw of the volcanic centre

drowning events development and demise of carbonate platforms and controlling factors the late barremian early aptian record of southeast france abstract in provence and languedoc se france four drowning events were identified in platform carbonates of late barremian bedoulian age their timing referred to ammonite zones or subzones is as follows 1 late barremian d1 at the gerhardtia sartousiana imerites giraudi boundary 2 middle bedoulian d2 at the deshayesites weissi deshayesites deshayesi boundary 3 mid late bedoulian d3 in correspondence with the roloboceras hambrovi subzone and 4 late bedoulian d4 at the deshayesites grandis dufrenoya furcata transition notwithstanding their relatively wide regional lateral continuity the depositional hiatus linkage with exposure paleobathymetric range and offset and geographical extent of drowning discontinuities are not uniform the late barremian drowning d1 is marked either by the development of a permanent intra shelf basin with ammonites associated with the re organization of platform basin relationships or by the wide extent of palorbitolina heteraster facies which develops to the detriment of the antecedent rudist facies the drowning event is followed by platform recovery during the early bedoulian but the corresponding development of shallow water carbonates is subsequently interrupted by the emergence of an uplifted bulge trending sub parallel to the provence languedoc margin the middle bedoulian drowning d2 is concurrent with the sealing of the antecedent paleotopography and the wide development of palorbitolina facies then bioclastic and coral facies tend to recover the mid late bedoulian drowning d3 is characterized by an overall deepening phase with ammonite bearing marly facies or cherty limestones shallow bioclastics being locally present the late bedoulian drowning d4 records the deposition of deep water marls evidence is lacking that global sea level changes or transgressive regressive cycles had a significant impact on drowning events and some evidence that changes in temperature and productivity of the ocean may have contributed to these phenomena in conjunction with other factors though distension fault activity is regarded as a major controlling factor for the origin of the late barremian deepening event its associated paleogeographic re organization ensuing emergence of the provence languedoc marginal bulge and its subsequent detumescence coeval with the middle bedoulian drowning associated changes in facies types from rudist to palorbitolina reflect sea water deepening coupled with trophic modifications as agents of differential subsidence tectonic phenomena are also testified by the contrasting regional patterns of paleobathymetric offsets combined with drowning events they are a clue for understanding thickness changes and coeval modifications in the overall orientation of the progradational polarity of the platform system towards the adjacent basinal areas environmental changes essentially the two main oae1a subevents are regarded as significant agents of the mid late and late bedoulian drownings whereas tectonic processes are also involved in the corresponding deepening however the effects of the oae events on the functioning of the shallow carbonate factory are poorly understood and still need to be investigated the rise in atmospheric carbon dioxide pressure and as a consequence the reduction of the calcification potential of benthic organisms both reported in the literature are not clearly reflected in the composition of the biota aragonite dominated organisms such as caprinid rudists thrive throughout the bedoulian the role of acidification in platform demise is therefore questionable

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

carbon isotope stratigraphy of early cretaceous urgonian shoal water deposits diachronous changes in carbonate platform production in the north western tethys abstract carbonate platforms are highly sensitive ecological systems that typically show rapid and characteristic response modes to environmental and climatic changes acting both on a regional scale and global scale a widely accepted hypothesis proposes that the late barremian stepwise establishment of the urgonian carbonate platform on the northern tethyan shelf was related to a gradual change from predominantly humid towards more arid greenhouse conditions this climate change resulted in the reorganisation of the carbonate platform ecosystem from heterozoan towards photozoan dominated assemblages and a decrease of organic matter burial in tethyan and boreal basins in order to decipher the palaeoenvironmental and climatic boundary conditions of these major changes in neritic and pelagic settings a precise chronostratigraphy of urgonian carbonate platform evolution is needed here we provide an integrated stratigraphic framework of lower barremian to lower aptian urgonian carbonate platform sections cluses forclaz located at the northern rim of the tethys subalpine chains ese france with special focus on sedimentological analyses and high resolution carbon isotope stratigraphy a characteristic barremian aptian carbon isotope pattern permits precise platform to basin correlation with cyclostratigraphic and ammonite dated pelagic and hemipelagic tethyan sections in the vocontian trough angles combe lambert glaise and umbria marche basin gorgo a cerbara similar to helvetic shoal water settings the carbonate platform in the subalpine chains experienced a gradual transition from heterozoan to photozoan dominated ecosystems this biogenic pattern points to a gradual change of the carbonate platform after the so called early barremian crisis towards an oligotrophic rimmed platform system urgonian limestone formation according to the chronostratigraphy of urgonian carbonate platform evolution in the subalpine chains established here the installation of a photozoan dominated rudist rich platform ecosystem referred to as urgonian limestones sensu stricto occurred at the early late barremian transition the onset of changes in the carbonate production mode heterozoan versus mixed heterozoan photozoan versus photozoan clearly predates the onset of similar lithological changes in the helvetic realm by about 1 0 to 1 2 myr the established chronostratigraphic framework points to a link between the change towards photozoan dominated limestones and fading palaeoenvironmental perturbations related to the mid barremian event which is associated with major faunal turnovers and the onset of cyclic black shale deposition in the central tethyan realm judging from palaeoenvironmental proxies including kaolinite phosphorus and black marl limestone ratios oscillating predominantly humid and relatively arid greenhouse conditions modulated the observed pattern in urgonian carbonate platform production mode and the varying frequencies of black shale deposits in the tethyan and boreal realms transient blooms of the orbitolinid foraminifera palorbitolina lenticularis at the onset of a marked upper barremian positive carbon isotope shift are interpreted to reflect increasing nutrient influx most probably related to accelerated hydrological cycling and or sea level rise these strata do not represent an over regional correlatable lithostratigraphic unit but likely an expression of progressive northern tethyan environmental and oceanographic change possibly related to ontong java large igneous province volcanism in the prelude of oceanic anoxic event 1a oae