shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

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

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

evidence for a complex valanginian nannoconid decline in the vocontian basin south east france the early cretaceous is punctuated by widespread biocalcification crises these are characterized by decrease in the carbonate platform growth and in the pelagic realm by a decline in nannoconus relative abundance in the calcareous nannofossil assemblages the valanginian nannoconus decline started before the positive 13c excursion characterizing the weissert event the nannoconid decline is investigated in two sections of the vocontian basin la charce and vergol which are biostratigraphically well constrained and contain wellpreserved calcareous nannofossils absolute and relative abundances of nannoconus show a polyphased decline with a first decrease in the interval from the campylotoxus to the verrucosum ammonite subzones before the positive 13c shift and a second decrease from the end of the peregrinus to the base of the radiatus ammonite zones concomitant with the long term decrease in 13c these two declines are separated by an important increase in the nannoconus abundance from the verrucosum to the peregrinus ammonite subzones concomitant with a slight short term decrease of 13c biometric analysis shows size changes of n steinmannii and n kamptneri along the nannoconid decline the patterns of abundances and size changes seem to be related to paleoenvironmental changes mainly characterized by a temperature decrease and variable nutrient supply the described valanginian nannoconid recovery seems to occur during the most intense phase of the cooling event and is recorded in the vocontian basin as well as in the atlantic and tethys oceans these spatial correlations suggest a supra regional character for the valanginian nannoconid recovery event best recorded in the vocontian basin and at low latitudes

sea level reconstructions from the peri vocontian zone south east france point to valanginian glacio eustasy the valanginian is a period of global environmental change as illustrated by sedimentary palaeontological geochemical and climatic perturbations a production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions during the same time interval a major positive excursion in 13c the weissert event suggests perturbations of the carbon cycle from the latest early valanginian to the early hauterivian in order to better understand the link between these changes sea level fluctuations have been reconstructed in detail from the middle berriasian to the earliest hauterivian sections from the peri vocontian zone south east france have been investigated because of the good quality of outcrops on the carbonate platforms their margins and in the vocontian basin sections ranging from the most proximal zone swiss jura to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy and correlated at high resolutions using the identified small medium and large scale sequences as well as depositional geometries sea level fluctuations were reconstructed two main trends are evidenced during the studied interval i the peak amplitude magnitude of the sea level fluctuations increased gradually from the middle berriasian to the early valanginian and reached a maximum more than 50 m from the middle early valanginian to the valanginian hauterivian boundary and ii sea level variations were quite symmetrical during the late berriasian slightly asymmetrical during the early valanginian and strongly asymmetrical fast sea level rise slow fall from the latest early valanginian to the earliest hauterivian moreover three orders of sea level fluctuations were recognized in the sedimentary rocks of the peri vocontian zone platform basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea level variations mainly by the two eccentricity cycles of 100 and 400 kyr the increase in the amplitude of the sea level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the early valanginian fast transgressions followed by slower regressions would correspond to waxing and waning of high latitudinal ice during most of the valanginian especially from the latest early valanginian to the latest late valanginian glacio eustatic sea level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the valanginian

detrital zircon age constraints on the provenance of sandstones on hatton bank and edoras bank ne atlantic abstract u pb dating of detrital zircons shows that the provenance of cretaceous palaeogene sandstones on hatton and edoras banks sw rockall plateau comprises magmatic rocks dated at c 1800 ma and c 1750 ma respectively their depositional setting first cycle mineralogy and unimodal detrital zircon populations suggest that these sandstones are of local origin the zircon age data are therefore considered to provide constraints on these poorly understood areas of the rockall plateau the u pb dates are directly comparable with u pb zircon crystallization ages from granitoid rocks reported from the ketilidian belt of southern greenland and from the rhinns complex of western britain hf isotopic data from the edoras bank sample are consistent with derivation from a juvenile palaeoproterozoic block in conjunction with previously reported sm nd t dm model ages from the ketilidian belt rockall bank and the rhinns complex these data extend the known distribution of a large juvenile palaeoproterozoic terrane spanning the southern ne atlantic in contrast hf isotopic data from the hatton bank sample imply a large contribution from archaean crust the zircon population from edoras bank also contains sparse mesoproterozoic grains providing evidence for the presence of volumetrically minor grenville age intrusions in the southern part of the rockall plateau

from orogenic collapse to rifting a case study of the northern porcupine basin offshore ireland abstract offshore ireland the north atlantic opening is generally interpreted as successive 10 to 15 myr long rifting events during the mesozoic however their interaction is poorly documented in terms of structural inheritance and fault reactivation from extensive seismic and well data in the northern porcupine basin we show that extension actually evolved over an abnormal period of ca 220 myrs with overlapping tectonic stages that all together reflect the irish atlantic margin construction from the palaeozoic during the carboniferous extension initiated throughout the variscan and caledonian thickened crusts and controlled the deposition of generally slightly tilted continental clastics two subsequent rifting events during the triassic lower jurassic and upper jurassic lower cretaceous controlled shallow to deep marine sedimentation in separated sub basins that progressively widen and connect once extension localised along bounding faults we propose that extensional tectonics first controlled by a general orogenic collapse reflecting an early stage of stretching is then followed by several rifting periods that ultimately evolved toward the hyper thinning of the margin and shaped an aborted rift propagator this evolution is due to pre existing orogenic related structures and boundary conditions variations such a continuum of deformation although pulsed implies varying structural interactions of crustal scale that are often recorded in syn tectonic sediments

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

detrital zircon age constraints on basement history on the margins of the northern rockall basin detrital zircon dating has proven to be an effective way to constrain ages of submerged basement terranes on the margins of the northern rockall basin a region where direct evidence of crustal affinities is scarce or absent zircons have been dated from sandstones of palaeocene oligocene age known to have been derived from the east hebridean platform and west rockall and george bligh highs the results show that the hebridean platform is a westward extension of the lewisian complex with archaean and palaeoproterozoic ages that can be directly correlated with events identified in the outer hebrides and northwest scotland the detrital zircons derived from the hebridean platform also provide evidence for a mesoproterozoic thermal event and two phases of intrusions in the palaeozoic the rockall high consists of a palaeoproterozoic terrane dated as c 1760 1800 ma similar to ages previously determined from both basement samples and detrital sediment the data also provide evidence for the subsequent intrusion of alkaline igneous rocks in the palaeocene eocene the george bligh high represents an archaean terrane heavily affected by palaeoproterozoic tectonothermal events and was also the site of intrusion of alkaline igneous rocks in the palaeocene

age and crustal evolution of crystalline basement in western ireland and rockall 1department of geology university college dublin belfield dublin 4 ireland 2 royal ontario museum toronto canada 3 department of mineral resources engineering university of nottingham nottingham ng7 2rd uk 4 british geological survey keyworth nottingham ng12 5gg uk

geochemical and isotopic constraints on the nature and age of basement rocks from rockall bank ne atlantic an isotopic and geochemical reappraisal of samples from rockall bank ne atlantic indicates that the granulites and granites present on the bank have little anity with the lewisian of nw scotland with which they have been previously associated new pb rb sr and sm nd data together with existing k ar data indicate that the rocks formed at about 1625 ma although this is contemporaneous with late laxfordian events in nw scotland the high model p value of 8 03 indicates that the rocks were not derived by metamorphic reworking of ancient lewisian crust but largely represent pristine mantle contributions at this time in this sense the rockall terrane is comparable with the islay terrane which has a model p value of 7 9 but is apparently somewhat older c 1800ma the rockall basement rocks therefore represent a pre viously unrecognized crust formation event in the north atlantic region and reconstructions of proterozoic geology will need to take into account the presence of this crustal block of predominantly juvenile mantle derived material the rockall area may also be considered a likely source for the torridonian sediments of nw scotland our knowledge of the geology of the rockall plateau ne atlantic fig 1 has not advanced significantly since the review published by roberts 1975 subsequent work on the eastern ne atlantic area has largely concentrated on the development of the rockall trough which marks the eastern limit of the plateau as summarized by smythe 1989 and on the development of the volcanic passive margin that marks the

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

sequence development in an isolated carbonate platform lower jurassic djebel bou dahar high atlas morocco influence of tectonics eustacy and carbonate production six sequences each with a distinct shape stratal anatomy bounding surfaces lithofacies composition and stacking patterns were identified in the djebel bou dahar isolated carbonate platform which developed in a half graben in the high atlas marine rift basin during the early jurassic sequences are believed to have a complex multi process origin as the result of tectonic processes regional subsidence and fault block rotation overprinting the eustatic signal in addition changing carbonate producers with shifting centres of deposition and relative accumulation potential influenced the filling and anatomy of the accommodation space that had been created by the hybrid tectonic and eustatic processes sequences i and ii are tabular in shape and interpreted to primarily reflect the combined processes of uniform tectonic subsidence and eustacy which resulted in a ramp to shelf carbonate system with lagoon and tidal flat lithofacies onset of a rifting episode around the base of the lotharingian and fault block rotation were responsible for the development of the angular unconformity with the underlying sequence ii and the progressive development of a shallow water isolated platform and the wedge shaped depositional sequences iii to vi during the lotharingian and pliensbachian concurrent variations in palaeoceanographic conditions and in the carbonate factory caused a shift towards a flat topped platform geometry with high energy coated grains and sub photic sponge microbial deposition around the margin the aggradational to retrogradational character of sequences iii iv and vi is inferred to be a result of the combined effect of in situ carbonate production coupled with high rates of creation of accommodation space in the hanging wall environmental effects on carbonate production were the most probable cause for drowning of the djebel bou dahar platform during the toarcian but also influenced the filling and geometry of sequences iv to vi this study suggests that the commonly accepted model of pulse driven sequence development in half grabens may not be fully applicable for the djebel bou dahar where a more continuous rotation at sequence scale associated with subsidence pulses of the djebel bou dahar block seems to have interacted with eustacy and carbonate production to generate sequences continuous rotation is suggested by the presence of regular patterns of diverging strata and numerous minor exposure surfaces in lagoonal deposits of sequences v and vi in addition this study demonstrates that eustacy and variations in the carbonate factory might be as significant as tectonics in sequence development and platform drowning in carbonate platforms within rift basins this observation could imply that the effects of eustacy and the carbonate factory might not have been correctly recognized in other similar carbonate platforms due to a tectonic biased interpretation

provenance and paleodrainage patterns of upper jurassic and lower cretaceous synrift sandstones in the flemish pass basin offshore newfoundland east coast of canada upper jurassic to lower cretaceous synrift sandstones from two industry exploratory wells in the flemish pass basin were studied for provenance using heavy mineral proxies these sandstones were deposited during the north atlantic rifting stage at which time rifting intensified between iberia and the grand banks several heavy mineral methods were used including in situ u pb geochronology and morphological and chemical analysis of detrital zircons chemical discrimination of detrital tourmalines and heavy mineral ratios clastic bed load material entering the northern flemish pass basin during the tithonian to berriasian was connected to transport systems reaching west as far as 400 to 500 km 249 311 mi source areas to the west included igneous rocks and associated cover sequences of the avalon zone as well as the magmatic rocks metasedimentary rocks and associated cover sequences present in the central mobile belt the eastward directed input of bed load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin with deteriorating reservoir grade toward the east given the regional extent of drainage systems it is likely that similar constraints apply to equivalent sandstones in the adjacent east orphan basin by the valanginian barremian paleodrainage orientations had switched and bed load material began to enter the flemish pass basin from more proximal areas to the southeast with the avalon zone basement overall no evidence exists to support sediment sourcing from the iberian margin or the flemish cap galicia bank continental fragment to the east and material from these areas is instead interpreted to have been shed into the incipient atlantic ocean or bay of biscay also no evidence exists to support sourcing from grenville basement farther to the west implying that a drainage divide may have existed somewhere between central and western newfoundland west of which material was presumably being transported to the south or southwest

carbonate platform evidence of ocean acidification at the onset of the early toarcian oceanic anoxic event abstract the early toarcian oceanic anoxic event early jurassic 183 myr ago is associated with one of the largest negative carbon isotope excursion cie in the whole phanerozoic 3 7 estimates of the magnitude and rate of co 2 injection in the ocean atmosphere system are compatible with a scenario of ocean acidification many carbonate platforms drowned in the pliensbachian well before the early toarcian event in this paper we test the hypothesis of surface water ocean acidification by presenting data from a resilient carbonate platform the apennine carbonate platform of southern italy the studied sections document a dramatic shift of the carbonate factory from massive biocalcification to chemical precipitation lithiotis bivalves and calcareous algae palaeodasycladus mediterraneus which were the most prolific carbonate producers of pliensbachian carbonate platforms disappear during the first phase of the early toarcian cie before the most depleted values are reached we discuss the local versus supraregional significance of this shift and propose a scenario involving abrupt decline of carbonate saturation forced by co 2 release at the beginning of the early toarcian cie followed by a calcification overshoot driven by the recovery of ocean alkalinity attribution of the demise of carbonate platform hypercalcifiers to ocean acidification is supported by palaeophysiology and reinforced by experimental data on the detrimental effects of ocean acidification on recent shellfishes and calcareous algae

growth and demise of the jurassic carbonate platform in the intracratonic paris basin france interplay of climate change eustasy and tectonics it is usually very difficult to identify and quantify the relative influence of tectonics eustasy and climateon carbonate system evolution from sedimentary records in order to improve our understanding of these mechanisms we have traced for the first time the evolution of the eastern paris basin platform throughout the entire jurassic period this carbonate platform underwent eight successive growth and demise phases with different depositional profiles ranging from ramps to flat topped geometries the eight carbonate growth periods are compared with the standard sea level curves local tectonic regimes and recently published oxygen isotope and or clay mineralogy databases prograding heterozoan facies along ramp profiles mark periods dominated by second order eustatic sea level rise relatively cool sea surface temperatures and mesotrophic and humid conditions hettangian pliensbachian late oxfordian tithonian during these periods variable detrital contents in the sedimentary succession hampered the efficiency of shallow marine carbonate factories higher sea surface temperatures oligotrophic and humid conditions associated with either eustatic sea level rise or very high local subsidence occurred during the early bajocian and the mid oxfordian these seawater properties seem to have favoured the aggradation of scleractinian corals forming dome shaped bioherm buildups an oolitic and lime mud carbonate system deposited during the bathonian second order eustatic sea level fall is characterised by miliolid rich micritic facies on a rimmed ramp under stable cooler and drier conditions the secondorder maximum flooding associated with a sea surface temperature decline and or a seawater eutrophication caused at least five carbonate demise periods i e toarcian earliest late bajocian callovian oxfordian transition earliest late oxfordian and kimmeridgian

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

excess helium and argon of radiogenic origin in mediterranean brine basins extraordinary helium and argon signatures were observed in a recently discovered brine lake district in the eastern mediterranean sea at water depths of 3500 m in the urania basin 4he concentrations are enriched by a factor of up to 32000 compared to normal seawater low 3he 4he ratios of 1 10 7 and high 40ar 36ar ratios of up to 470 indicate a radiogenic source these data represent by far the highest radiogenic supersaturations ever observed in an oceanic environment we propose a new conceptional model assuming that the urania basin is fed by advective transport from a deep fluid reservoir below the messinian evaporite sequence the evaporite seal provides the unique condition for accumulating the extraordinary high amounts of radiogenic helium from deep sedimentary strata injection of radiogenic helium from brine pools like the urania basin may contribute significantly to the inventory of terrigenic helium in the deep waters of the eastern mediterranean

sedimentological and isotopic heterogeneities within a jurassic carbonate ramp uae and implications for reservoirs in the middle east abstract carbonate rocks are major hydrocarbon reservoirs in the middle east and across the world capturing the spatial distribution and dimensions of carbonate sedimentary facies is thus of interest for reservoir modelling and for the understanding of process sedimentology here we present data from a middle jurassic carbonate ramp outcropping on the musandam peninsula wadi naqab northern united arab emirate of ras al khaima which serves as an analogue for the hydrocarbon bearing units in the subsurface of the middle east with respect to stratigraphic age lithofacies types vertical stacking patterns and palaeogeographical setting seven closely spaced sections were logged across a 1900 1200 120 m fault bounded outcrop offering a pseudo 3d view of the stratigraphy sections were correlated bed by bed by walking key surfaces and or by using photopanels to produce a detailed lithofacies map stable isotopes carbon and oxygen were measured from micrite samples in order to provide chemostratigraphic constraints ten lithofacies types were identified in thin sections and hand specimens ranging from marls and mudstones to grainy oncolites and peloidal ooidal grainstones beds are organised in a layer cake architecture but individual bed thicknesses vary laterally lateral merging between different lithofacies types within beds is very common resulting in a complex facies mosaic at the scale of the outcrop lithofacies types have a maximum probability of 40 of being continuous between logged sections with the highest frequencies of lateral variations occurring in the open shallow part of the ramp where maximum wave and current energy are indicated by facies the vertical stratigraphic stacking pattern of the succession is characterised by metre scale shoaling upwards parasequences these are frequently capped by hardgrounds interpreted as composite surfaces with depleted carbon and oxygen isotope values being evidence for frequent exposure during relative sea level lowstand followed by flooding and formation of a condensed hardground the carbon isotope curves show a large amount of vertical isotope heterogeneity reflected by meteoric diagenesis around hardground surfaces and these are not always traceable laterally between the closely spaced neritic sections due to bias in sampling however if considering only the positive envelop of the carbon isotope curve and thus filtering out the meteoric diagenetic events carbon isotope chemostratigraphy becomes possible and confirms a bajocian age for the section the main conclusion of the study is that maximum heterogeneity of facies at the scale of 100 m or less is expected in an environment of deposition with high wave energy this has important implications for reservoir applications since rock facies often template flow units

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

alternation of microbial mounds and ooid shoals middle jurasssic morocco response to paleoenvironmental changes abstract the occurrence of neritic microbial carbonates is often related to ecological refuges where grazers and other competitors are reduced by environmental conditions or to post extinction events e g in the late devonian early triassic here we present evidence for middle jurassic bajocian microbial mounds formed in the normal marine shallow neritic setting of an inner ramp system from the high atlas of morocco the microbial mounds are embedded in cross bedded oolitic facies individual mounds show low relief domal geometries up to 3 m high and 4 5 m across but occasionally a second generation of mounds exhibits tabular geometries

gravity gradients and upper crustal tectonic fabrics ireland gravity gradients derived from an updated bouguer anomaly map of ireland reveal large scale lineaments many of which can be related to geological structures and tectonic development first horizontal derivatives of the anomaly calculated at various azimuths accentuate linear trends in different directions while the second derivative helps resolve near surface structure the dominant ne sw caledonian trending lineaments are interpreted as due to fault boundaries and folds in pre carboniferous basement and caledonian fault reactivation during the variscan orogeny subsidiary nne ssw trending lineaments are present as well as weaker nw se trending lineaments the largest negative anomalies are produced by late caledonian granites and widespread buried granitic rock in the middle to upper crust is proposed both exposed and inferred granites appear to be spatially related to intersections of ne sw with nne ssw and nw se trending lineaments the orientation of the dominant gravity trend changes from ne sw towards ene wsw going westwards across ireland and forms part of a more regional change in the caledonian gravity fabric recognised throughout the northeast atlantic region variscan e w gravity trends in the south of ireland overlay the caledonian trends relationships between gravity lineaments and anomalies support a thin skinned model for the variscan cover

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

carbon cycle perturbation in the middle jurassic and accompanying changes in the terrestrial paleoenvironment abstract carbon isotope analyses of fossil wood from the middle jurassic ravenscar group yorkshire ne england reveal a significant excursion toward light isotopic values 13c change of 3 to 4 at about the aalenian bajocian boundary 174 ma a positive carbon isotopic excursion is also shown for the middle bajocian 170 ma but is less clearly defined these isotopic patterns are very similar to the few published marine carbonate records available for this time in particular one based on belemnites from the hebrides basin nw scotland and others from pelagic limestones in italy the similarity of the terrestrial and marine isotope curves is an indication that the observed isotopic signal is a global phenomenon through parts of the ravenscar group the scarborough formation supplementary data from bulk organic carbon and palynofacies analysis confirm that isotopic curves based on bulk analyses may be strongly influenced by the balance of terrestrial versus marine organic matter present in th

the crustal structure of the rockall trough differential stretching without underplating the crustal structure along the axis of the rockall trough in the north atlantic has been studied along a 600 km refraction wide angle reflection transect containing three lines each 200 to 250 km long using explosives and ocean bottom seismometers one dimensional inversions of each section were made using the p method and forward modeling of the observed travel times in the next stage travel times and amplitudes were modeled using ray tracing techniques through two dimensional heterogeneous structures the results indicate that there are three sedimentary layers with velocities ranging from 2 km s to 4 5 km s the whole sedimentary section is up to 6 km thick and interpreted as late paleozoic to tertiary in age a two layer continental crust 5 to 7 km thick occurs along the length of the profile the upper crust 6 0 6 3 km s is circa 2 km thick and the lower crust 6 6 6 9 km s is circa 3 km thick a moho transition zone approximately 1 km thick lies at the base of the crust velocities in this transition zone increase from 6 9 km s up to 7 8 km s along the profile the underlying upper mantle has a laterally variable velocity between 7 6 and 7 8 km s unstretched crust onshore in ireland comprises a three layered crust with each layer approximately 10 km thick and a moho transition zone which is about 3 km thick the two upper layers in the onshore region are interpreted as corresponding to the upper crust in the rockall trough and indicate a stretching factor of 8 10 the velocity pattern in the lower crust in the rockall trough and under ireland are similar suggesting significantly less stretching 2 3 the differential stretching model is supported by the presence of the moho transition zone which is stretched by a similar factor to the lower crust the bulk stretching factor for the crust as a whole is in the range of 4 6 if this represents the lithospheric stretching factor significant underplating would be expected however if the stretching factor for the lower crust in the differential stretching model is more representative of overall lithospheric stretching little or no underplating is predicted the velocity patterns observed in the rockall trough indicate the absence of any significant underplating at the base of the crust such as that observed at the continental margin west of the hatton basin

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

neritic carbonate crisis during the early bajocian divergent responses to a global environmental perturbation abstract the early bajocian witnessed a global environmental perturbation characterized by faunal and floral turnovers and a positive carbon isotope excursion in italy this environmental perturbation coincided with an eutrophication event and a carbonate crisis but this has so far not been adequately reported from other settings leaving doubt about the extent and nature of these phenomena in this paper we are reporting on an extensive neritic carbonate factory demise that occurs in the upper lower bajocian of morocco more precisely in the upper propinquans lower humphriesianum zones this demise coincided with the acme of the global carbon isotope perturbation recorded by a 3 positive carbon isotope excursion in the bulk organic matter of morocco but not in the micritic phase due to the fact that the moroccan carbonate 13c record is more sensitive to local rather than global influences furthermore we observe that the lower bajocian of morocco is relatively enriched in arenitic siliciclastic deposits suggesting increased weathering and nutrient levels along the northwestern margin of africa during the early bajocian however comparison with neighboring european basins highlights the non uniqueness and different timing of the response of shallow water carbonates to the early bajocian environmental perturbations as some regions present no sign of carbonate factory crisis hence we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation we notably highlight the role of large early bajocian sea level fluctuation as a trigger for carbonate factory change and demise in morocco

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