biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

palaeoceanography of lower cretaceous alpine platform carbonates shallow water carbonate platforms evolve in an interplay of local regional and global dynamics thereby generating a detailed record of environmental conditions platform sediments constitute important archives of past environmental change and as such they are increasingly analysed for the information they contain on wider scale patterns the integration of this information with palaeoceanographic data obtained from deeper water sediments provides a powerful tool to develop a more diverse and complete image of past environmental change in this contribution the remains of the northern tethyan carbonate platform of early cretaceous age cropping out in the western swiss jura and the helvetic alps are used to illustrate the advantage of a palaeoceanographic approach in their interpretation the tools applied are biostratigraphy and chemostratigraphy carbon and strontium isotopes in order to obtain a precise age model for correlation with hemi pelagic sediments in adjacent basins sequence stratigraphy as a means to reconstruct the impact of sea level change phosphorus stratigraphy as a proxy for trophic levels facies and microfacies analyses as a gateway to gain better insight into the carbonate factory and the detailed analysis of platform drowning unconformities as an indicator of wider scale palaeoenvironmental change it is shown that changes from periods of predominantly photozoan to predominantly heterozoan carbonate production near the berriasian valanginian boundary and middle early aptian coincided with substantial increases in phosphorus burial rates and major carbon isotope excursions furthermore the majority of the platform drowning episodes occurred just prior to and during episodes of major palaeoenvironmental change and last but not least the platform itself may have influenced the chemistry of adjacent basins and the carbon isotope composition of associated carbonates by the export of periplatform ooze

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

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

instability in tropical pacific sea surface temperatures during the early aptian the cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric co2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events oaes yet the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained here we present a ighresolution record of sea surface temperatures ssts reconstructed using the tex86 paleothermometer for a sequence of early aptian organic rich sediments deposited during the first cretaceous oae oae1a at shatsky rise in the tropical pacific ssts range from 30 to 36 0c and include two prominent cooling episodes of 4 0c the cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter sst instability recorded during the early aptian in the pacific is comparable to that reported for the late albian early cenomanian in the atlantic suggesting that such climate perturbations may have recurred during the cretaceous with concomitant consequences for biota and the marine environment

carbon isotope stratigraphy in shallow water carbonates implications for cretaceous black shale deposition a barremian to albian succession on mount kanala part of a tethyan isolated carbonate platform was investigated for its 13c variations the limestone sequence is composed of a series of peritidal shallowing upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure despite significant impact of diagenesis the observed changes in 13c can be very well correlated with deep water sections from different ocean basins and shallow water carbonate platforms in the middle east this lends further support to the applicability of 13c variations for stratigraphic purposes in shallow water limestones using the 13c signal time resolution in lower cretaceous platform carbonates can be significantly increased independent of bio zonations often hampered by ecological variability cyclostratigraphic analysis of the aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing upward cycles coincide with global positive 13c excursions this and the fact that positive shifts in the 13c record are preserved within shallow water limestones provide evidence that black shale accumulation in the ocean basins occurred during sea level rise and flooding of platform tops integration of carbon isotope cyclo and sequence stratigraphic results from different carbonate platforms indicate that strong positive global 13c shifts and concurrent organic carbon burial during black shale deposition are ultimately caused by rapid rises of eustatic sea level hence the rate of change of eustatic sea level is considered to play a crucial role in black shale accumulation in the global ocean basins during the cretaceous

palaeobathymetric reconstruction of peritidal carbonates late barremian urgonian sequences of provence se france abstract peritidal platform carbonates of late barremian age early cretaceous cropping out in the marseille region provence se france tend to be arranged stratigraphically in deepening up or shallowing up sequences seven facies types lithofacies were defined in the studied stratigraphic interval ranging from supratidal to shallow subtidal settings there is a good correspondence between the inferred relative water depth of facies and their average bed thickness cumulative thickness of facies types expresses quantitatively their palaeobathymetric range and provides an estimate of their average water depth calculations show that the palaeobathymetry of supratidal intertidal facies types is from 0 to 40 cm i e a pertaining to a palaeotidal microtidal range the average palaeobathymetry of rudist facies ascribed to subtidal settings fluctuates between 40 cm and nearly 160 cm measuring a large number of beds belonging to both shallowing up and deepening up sequences and averaging the results appear relevant to minimise the effect of compaction pressure solution and synsedimentary progressive or abrupt changes in accommodation which are expected to modify bed thickness and its original palaeobathymetric significance the method proposed here has a good potential for palaeobathymetric reconstruction of ancient peritidal carbonates

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

the geochemistry of co and cu in the kafue river as it drains the copperbelt mining area zambia abstract samples of the dissolved 0 45 m phases have been collected in the kafue river during a 1 year cycle within the mining area the concentrations of co cu and s in the river occasionally increase more than 100 times compared to concentrations upstream from the mining area the highest concentrations of dissolved cu 3 4 m and fe 4 2 m are found during high water discharge probably indicating a washout of leached weathering products from spoil heaps high levels of co appear to originate from one point source the location where the co ore is treated in the kafue river secondary mn and fe rich particles are formed on which co and cu respectively are enriched the elements associated to secondary fe and mn particles are enriched at the sediment surface in the river due to redox processes hence secondary particles and sorbed trace elements may be resuspended and transported further downstream in the river system however very high concentrations of cu 1 and co 0 1 in the sediment are caused by primary sulphides

shelf geometry response to changes in relative sea level on a mixed carbonate siliciclastic shelf in the guyana basin abstract differences in the shelf margin geometry for various depositional regimes show how siliciclastic and carbonate margins respond differently to changes in accommodation space during the cenozoic sequences of carbonate and siliciclastic sediment were deposited in the guyana basin on the passive continental margin of ne south america study of the sequence geometries reveal significantly different geometric responses to changes in relative sea level of intervals dominated by carbonates to intervals dominated by siliciclastics using the geometrical shelf break as a reference point aggradation and progradation rates for the carbonate and siliciclastic depositional systems were measured in siliciclastics the lateral position of the margin remains roughly stationary with relative sea level rises in the order of 30 m my at higher rates the margin retreats at lower rates it progrades carbonate margins remain stationary or slightly progradational even with relative sea level rises of up to 100 m my the fastest rates observed in this study this illustrates the strong tendency of carbonate platforms to stack their margins and keep up with relative rises in sea level rather than gradually retreat landward as do siliciclastics this observation may explain why carbonate platforms preferentially try to defend a margin prior to ultimate backstepping the high aggradation potential of carbonate margins also gives onlap and downlap termination patterns on seismic profiles where carbonate platforms develop on sloping siliciclastic shelves the resulting unconformities are a result of differences in sediment dispersal between the two systems and not necessarily from changes of relative sea level

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

chemostratigraphic correlation of barremian and lower aptian ammonite zones and magnetic reversals based on carbon isotope stratigraphy we correlate the ammonite dated barremian reference section near angles se france with the magneto and biostratigraphically dated succession at cismon northern italy the results confirm the previous correlation of the lower barremian ammonite and magnetostratigraphy by channell et al 1995 and show that the base of cm0 selected as the stage boundary between the aptian and the barremian coincides with the stage boundary defined by ammonite stratigraphy the upper barremian carbon isotope record of the cismon section displays two positive 13c excursions whereas the data from angles show only one shift towards more enriched values the absence of the second upper barremian 13c excursion at angles indicates that up to 50 of the barremian stage is missing in the selected reference section the gap occurs most probably within the giraudi ammonite zone and is related to the 12d maximum flooding surface of jacquin et al 1998

a platform to basin transition for lower aptian carbonates shuaiba formation of the northeastern jebel akhdar sultanate of oman abstract the platform to basin transition of the lower aptian shuaiba carbonate platform throughout a large part of the arabian peninsula has hitherto mainly been documented from subsurface data and has widely been regarded as having been progradational in northeastern jebel akhdar however the shuaiba platform did not prograde and was scarp bounded early lithification accounts for the rigid nature of the scarp a biological framework being nearly absent early exposure surfaces neptunian dykes sills internal breccias and other sediment features as well as the geographic coincidence of the platform scarp with older and younger scarps suggest a tectonic control of margin morphology and dynamics a contemporaneous peak of allodapic sediments and reactivation of older basement structures in adjacent basins also tends to indicate the importance of structural influence on platform margin organization

scaling of sedimentation rates and drowning of reefs and carbonate platforms the rule that sedimentation rates decrease as the time interval increases has been examined by a procedure that avoids the mathematical problem of plotting a variable time against its inverse the test confirms that the scaling trend has real physical meaning in the time range of 10 1 108 yr sedimentation rates change roughly proportionally to the inverse of the square root of time this report proposes and evaluates the hypothesis that the growth potential of reefs and carbonate platforms follows the same scaling trend the trend implies that a growth of 104 m yr sustained over 103 yr an upper limit of reef growth in the holocene translates into 102 m yr sustained over 107 yr decrease of the growth potential with increasing time solves the paradox of drowned platforms if the decrease results largely from environmental factors and not simply from increase of the time fraction of subaerial exposure

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

major palaeoenvironmental perturbation in an early aptian carbonate platform prelude of the oceanic anoxic event 1a the early aptian oceanic anoxic event oae 1a was characterized by intensified greenhouse climate conditions widespread accumulation of organic deposits in open marine settings major perturbations in the c cycle and a generalized increase in terrestrial runoff sedimentological diagenetic and chemostratigraphic analyses of lower aptian platform carbonates from the north cantabrian basin n spain illustrate the regional impact and effects of those global conditions on shallow marine environments the studied interval outlines four stages of platform evolution stage 1 earliest bedoulian is defined by an initial rapid marine transgression that led to deposition of shallow water oligotrophic photozoan skeletal assemblages and by a later interval of subaerial exposure stage 2 early bedoulian starts with a rapid transgression followed by deposition of grainstones that yield heterozoan assemblages more typical of mesotrophic conditions along with ferruginized oolites stage 3 early bedoulian is defined by the drowning of the carbonate platform and subsequent deposition of open marine marls which are thought to represent the local expression of the oae 1a finally stage 4 shows the return of shallow water photozoan carbonate sedimentation the carbonate o and c stable isotope records have revealed prominent negative excursions during deposition of the marly interval of the stage 3 which may be associated with the important global changes that occurred at the onset of the oae 1a the change in skeletal assemblages that preceded the isotopic excursions and the platform drowning documents conditions of environmental stress caused by a combination of local and global factors the global change coupled with increased basin subsidence triggered the drowning of the platform by progressive reduction of the growth potential of the carbonate factory

seismic reflection study of upheaval dome canyonlands national park utah the origin of upheaval dome in canyonlands national park of southeastern utah has been a topic of controversy among geologists and planetary scientists the structure has long been thought to have been created by salt diapirism from the underlying paradox formation recent studies have suggested that impact could have formed the dome to test the various hypotheses we acquired processed and interpreted seismic reflection data within and adjacent to the structure both conventionally stacked and prestack migrated images show 100 m relief in the paradox formation contrary to salt diapirism hypotheses further we have identified features within the images typical of impact structures such as listric normal faults having displacements toward the center of the dome deformation occurs in two depth ranges with the faulting that created the central uplift appearing only above the hermosa formation in the upper 800 m of the structure the images also suggest limited fracturing of the hermosa and salt flow in the paradox formation perhaps due to gravitational relaxation of the crater form our image of a nearly flat top of the paradox salt strongly favors an impact origin for upheaval dome

the barremian aptian turnover of biota in northwestern europe evidence from belemnites abstract neocomian valanginian barremian and gault aptian albian are lithostratigraphic terms used in the last century to divide the sub chalk cretaceous of northern europe the division is based on significant palaeoceanographic and palaeogeographic changes in the early aptian these changes are linked to a major turnover of marine floras and faunas which occurred simultaneously in the boreal realm the tethys and the indo pacific ocean various floral and faunal elements became extinct in the aptian both in the tethys and in the boreal realm while on the other hand new genera and species evolved marked changes in the diversification rate were observed for organisms with a different mode of life plankton nekton benthos apart from calcareous nannofossils foraminifera and ammonites this turnover also occurs in belemnites and the suborder belemnitina was completely replaced by the suborder belemnopseina the northwestern european barremian is characterised by the very successful belemnite family oxyteuthididae belemnitina which was completely replaced by the genus neohibolites belemnopseina in early aptian times this aptian turnover which is expressed by a homogenisation of marine floras and faunas is best explained by significant palaeoceanographic changes occurring in the early aptian the sea floor spreading rate which increased at the barremian aptian boundary significantly peaked in the late early aptian a mantle plume in the pacific possibly caused an additional production of oceanic crust both processes caused a major sea level rise this in turn resulted in a major change of the palaeoceanographic setting and restricted marginal seas like the northwestern european basins in barremian times became drowned the more open oceanic setting of the aptian enabled cosmopolitan floras and faunas to spread worldwide the aptian saw the radiation of planktonic foraminifera which played only a minor role in pre aptian times these palaeoceanographic changes from restricted marginal seas to a more homogeneous pelagic setting are considered to be the main cause for the significant changes in the composition of belemnite faunas

evolution of the northern nicaragua rise during the oligocene miocene drowning by environmental factors abstract possible causes to explain platform drowning have been hotly debated by carbonate sedimentologists for more than a decade now in this paper we present multiple evidence to explain the drowning of a carbonate megabank that covered most of the modern northern nicaragua rise nnr during an interval spanning from late oligocene to early miocene by the interaction of several environmental factors the recovery during odp leg 165 of late oligocene to middle miocene sedimentary sequences in the sub seafloor of the modern channels and basin pedro channel and walton basin respectively that dissect the nnr site 1000 and south of the rise in the colombian basin site 999 combined with information from dredged rock samples allows us to explore in more detail the timing and possible mechanisms responsible for the drowning of the megabank and its relationship to miocene climate change the modern system of isolated banks and shelves dissected by a series of intervening seaways and basins on the nnr has evolved from a continuous shallow water carbonate megabank that extended from the honduras nicaraguan mainland to the modern island of jamaica available information suggests that this megabank broke apart and partially drowned in the late part of the late oligocene at around 27 ma and finally foundered during the late early miocene around 20 ma resulting in limited neritic coral growth in the areas where the modern isolated carbonate banks and shelves are occurring today available information also suggests that the southern and central parts of pedro channel were already a deep water area before the major episode of platform drowning and its formation predates the initiation of the caribbean current however after the partial drowning of the megabank the channel has become a major pathway for the caribbean current stratigraphic units identified in deep water carbonates sampled at odp sites 999 and 1000 help to constrain the environmental setting leading to the drowning of the banks changes in lithology and mass accumulation rates of both the carbonate and non carbonate fraction parallel stable isotope shifts and likely indicate regional changes in climate and circulation during the late oligocene middle miocene interval carbonate mass accumulation rates mars at site 999 suggest increased regional productivity during the early miocene terrigenous mars at both sites 999 and 1000 show a general increase from the burdigalian through the serravallian the temporal association among episodes of neritic platform deposition followed by increased productivity as identified by higher carbonate mars and positive excursion in carbon isotopes suggests that oceanographic changes such as local upwelling and nutrification have led to the partial drowning of the nnr megabank

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

the lower cretaceous mesogean benthic ecosystems palaeoecologic aspects and palaeobiogeographic implications abstract douville s mesogee was based on an organismic assemblage and therefore defined mainly as a palaeobiogeographic entity the palaeoecologic analysis of douville s lower cretaceous reference taxa as well as that of a lot of other taxonomic groups and the discussion on their palaeobiogeographic meaning according to the concepts of modern marine biogeography especially the bathymetric thermic relationships result in the definition of three main organismic assemblages whose mesogean significance is discussed the key reference taxa and associated biota indicate that the definition of the lower cretaceous mesogee implies characteristic palaeoenvironmental conditions this definition substantial for the whole cretaceous means that mesogee is not simply a palaeobiogeographic entity but also an ecosystem corresponding to the area of distribution of warm shallow water carbonate platforms

bioevents and palaeoenvironmental changes in carbonate platforms the record of barremian urgonian limestones of se france abstract biostratigraphic studies of barremian platform carbonates from se france and nearby regions indicate the last occurrence lo horizons of some common shallow water taxa firstly two dasycladale algae piriferella paucicalcarea and salpingoporella genevensis which have their first occurrence in the upper hauterivian disappear in the lower barremian at the nicklesia pulchella kotetishvilia compressissima transition secondly a rudist bivalve the genus agriopleura which has its first occurrence in the upper hauterivian has its lo in the lower upper barremian within the gerardhtia sartousiana zone the specific stratigraphic levels of the above bioevents recorded in platform carbonates may be used for dating corresponding ammonite free successions stratigraphic implications are constrained by the biogeographical extent of the key species which is essentially the western and central european margin of the mediterranean tethys the joint lo of p paucicalcarea and s genevensis are inferred to have been linked with oceanographic and climatic changes i e a cooling event platform carbonates were interrupted by a drowning event represented by a maximum flooding surface or transgressive surface shallow water orbitolinidae record significant extinctions and deep water ammonites show a significant turnover similarly modifications in ammonite faunas bottom currents temperature changes i e cooling and a major extinction among the family orbitolinidae coincided with the lo of agriopleura platform perturbations including exposure possibly a sequence boundary and basin margin instability both with a tectonic background were associated with this event the foregoing events and the linkage of palaeobiogeographic changes that is the migration of the key taxa towards southern latitudes in correspondence with the lo bioevents indicate that thermal changes including seasonality appear to have been the prominent controlling factor

carbonate platform drowning and oceanic anoxic events on a mid cretaceous carbonate platform south central pyrenees spain abstract the cenomanian turonian carbonate platform of the south central pyrenees northern spain records an abrupt transition from benthic carbonate deposits to pelagic deposits near the cenomanian turonian c t boundary this shift coincides with a globally recognized oceanic anoxic event oae characterized by the widespread deposition of organic rich sediments in deep marine environments a positive d13c excursion of up 3 is recorded in carbonate and organic carbon deposited near the c t boundary and provides evidence of a direct link between the c t boundary oae and the demise of shallow benthic carbonate production on the pyrenean platform furthermore carbon isotope tratigraphy provides a means for dating the platform drowning event on the shelf where biostratigraphic control is poorly constrained an analysis of the shape of the carbon excursion suggests a depositional hiatus or a period of condensed sedimentation at the drowning surface on the shelf sedimentological paleontological and geochemical evidence suggests that the platform was drowned near the c t boundary as a result of changing environmental conditions pelagic rich strata overlying the drowning surface are highly bioturbated and concentrations of redox sensitive elements mn fe cr cu and zn indicate deposition under well oxygenated conditions the pelagic sediment contains abundant calcispheres which are interpreted to be opportunistic organisms that inhabit eutrophic but unstable environments elevated concentrations of ba p and si in the form of chert nodules observed in the pelagic facies are typical of modern and ancient upwelling systems petrographic evidence for oxygen deficiency is limited to the lower slope region the warm mid cretaceous clim te and a global rise in sea level resulted in changes in oceanic circulation patterns increased organic productivity and a shift in the trophic structure to one that favored planktonic productivity over benthic productivity pelagic deposition persisted for approximately 1 to 1 5 m y longer than the oae the time difference between the end of the oae and the reestablishment of a shallow benthic platform is attributed to increased accommodation caused by the turonian sea level rise and tectonic subsidence

plate tectonic control on the evolution of cretaceous platform carbonate production carbonate producing biota on cretaceous carbonate platforms changed from early cretaceous aragonitic coral algal and coral rudist associations to turonian maastrichtian calcite dominated rudist associations abundance patterns of rudist bivalves examined from a large database show a shift from barremian cenomanian aragonite dominated to post cenomanian calcite dominated shells these skeletal mineral changes agree with a decrease in the mg ca ratio of seawater owing to high rates of production of oceanic crust during the barremian early turonian and its effect on seawater saturation with respect to aragonite and calcite increasing sr concentrations in biotic calcite from the barremian to the maastrichtian reflect the shift from aragonite dominated to calcite dominated platform sedimentation because aragonite precipitation is a major sink for seawater sr it is speculated that a particularly low mg ca ratio and the corresponding low supersaturation of seawater with respect to aragonite during the middle cretaceous was a major cue for the radiation of calcite dominated rudist bivalves which became important carbonate producers on turonian maastrichtian carbonate platforms changing mg ca ratios of seawater are not considered to have caused middle cretaceous crises in the evolution of carbonate platforms but seawater composition could have selected for calcite dominated biota when carbonate production resumed

deciphering the message of early cretaceous drowning surfaces from the helvetic alps what can be learnt from platform to basin correlations drowning unconformities are a frequent feature of carbonate platforms and generally express the incapacity of shallow marine ecosystems to adapt to abrupt sea level rise and or palaeoenvironmental change during the late hauterivian and early barremian the helvetic carbonate platform experienced a major drowning phase documented by the phosphate and glauconite rich altmann member it has been shown that a drowning unconformity in the form of a hardground at the base of the altmann member on the pilatus summit central switzerland results from a complex polyphased diagenetic history that includes two main phases of phosphogenesis using carbon isotope stratigraphy biostratigraphy and sequence stratigraphy the correlation of this drowning unconformity from the helvetic domain with more distal and more complete sedimentary archives allows reconstruction of the sequence stratigraphic context of the drowning surface and also an estimation of the amount of time represented by the episodes of condensation unconformities associated with the altmann member drowning phase developed during transgressive episodes when strong currents arrived onto the previously subaerially exposed platform and periods of phosphogenesis may have lasted up to 2 8 myr variations in trophic levels and hitherto less well known intervening emersion phases played an essential triggering role for the altmann drowning phase high resolution studies of drowning unconformities unravel the diversity of palaeoenvironmental parameters involved in the unfolding of such crises during the evolution of carbonate platforms

temperature controlled deposition of early cretaceous barremian early aptian black shales in an epicontinental sea abstract a continuous 103m thick mudstone sequence of barremian early aptian age recently exposed in northern germany has been logged and analyzed with respect to its macrofaunal content and its geochemistry 13c 18o based on common belemnite and rarer ammonite findings a detailed biozonation has been established covering the complete barremian early aptian interval including the mid early aptian fischschiefer the deposition of which occurred during oceanic anoxic event 1a quite common throughout the sequence are finely laminated black shales blatterton with high toc contents of up to 7 these laminated black shales with caco3 contents of up to 60 are interbedded with dark and carbonate poor clays on the scale of decimeters to several meters oxygen depletion of bottom waters is indicated for the laminated intervals since these are barren of any benthic fossils a salinity driven stratification of the water column during more humid periods was caused by a more intense run off from the nearby hinterland this and increased surface water productivity are seen as a possible cause for the lamination with observations being mainly based on micropalaeontological evidence dinoflagellates calcispheres calcareous nannofossils stable isotope studies 13c 18o performed on belemnite guards show 13c values of 0 to 2 for the barremian a distinctive positive excursion of 4 directly above the early aptian fischschiefer correlates well with the global positive 13c excursion of mid early aptian age following the oceanic anoxic event 1a this first record of the 13c positive excursion from the boreal realm therefore confirms the global nature of the signal a shift in 18o values of about 2 in the late barremian early aptian is interpreted as a temperature decrease by 8 c this cooling goes along with a shift from the thick up to 6 5m early barremian hauptblatterton to thin 10cm to 20cm laminites blatterton in the late barremian during the deposition of the hauptblatterton very warm conditions caused a long lasting 500kyrs stable water stratification the cooler temperatures of the late barremian reduced the stability of the water stratification resulting in rather short termed alternations of thin laminites and dark clays these observations suggest a temperature controlled peak of anoxic conditions in the early barremian hauptblatterton and subsequently short termed changes from anoxic to suboxic conditions in the late barremian and early aptian

impact of early aptian carbon cycle perturbations on evolution of a marine shelf system in the basque cantabrian basin aralar n spain abstract 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 reflecting a major perturbation in the global carbon cycle this carbon cycle perturbation is recorded in the c isotope stratigraphy in this study we present a new carbonate and organic carbon isotope record across oae1a from expanded shallow marine sections igaratza and iribas in the basque cantabrian basin n spain the sediments studied were accumulated on a mixed carbonate siliciclastic and carbonate shelf the 13 c carb and 13 c org curves obtained show a pronounced negative spike in the deshayesites weissi zone and a subsequent positive excursion within the newly described d deshayesi d furcata transition zone approximately equivalent to the upper d deshayesi zone of other sections specific changes in facies patterns and a reduction in neritic carbonate production predate the negative c isotope perturbation these changes coincide with global carbonate crises in neritic and pelagic environments corresponding with the beginning of oae1a selli level a condensed interval rich in ammonites is observed this horizon is linked to a major transgression with high biodiversity the ammonite bloom suggests enhanced primary productivity in the surface waters of the basque cantabrian basin at improving environmental conditions for selected biocalcifiers the ultimate recovery of shelf carbonate deposition occurred after oae1a and it coincided in time with the most positive values of the carbon isotope excursion based on carbon isotope stratigraphy it has been deduced that black shales corresponding to selli level are missing in aralar so that anoxia is not recorded in the studied sections of the marine shelf environment an organic rich interval aparein level postdates the early aptian major positive excursion the aparein event should be considered in the future research of oaes

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

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

carbon isotope composition of lower cretaceous fossil wood ocean atmosphere chemistry and relation to sea level change the carbon isotope composition of fossil wood fragments collected through a biostratigraphically well constructed aptian lower cretaceous shallow marine siliciclastic succession on the isle of wight southern britain shows distinct variations with time the results indicate that the stratigraphic signature of delta sup 13 c sub wood through the aptian was influenced primarily by fluctuations in the isotopic composition of co sub 2 in the global ocean atmosphere system as registered in marine carbonates elsewhere and was not governed by local paleoenvironmental and or paleoecological factors negative and positive excursions in delta sup 13 c sub wood through the lower aptian occur in phase with inferred transgressions and regressions respectively a pattern that contrasts with that observed in many previous studies for different time intervals the relationship between delta sup 13 c variations and relative sea level change is tentatively interpreted as a response to various climatic and eustatic factors relating to rapid sea floor spreading thermal uplift of ocean floor emplacement of plateaus volcanic co sub 2 emissions weathering and sedimentary rate

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

time contrasting palaeobiogeographies among hauterivian lower aptian rudist bivalves from the mediterranean tethys their climatic control and palaeoecological implications abstract from the mediterranean tethys the hauterivian barremian rudist genera lovetchenia agriopleura pachytraga and offneria simplex show contrasting palaeobiogeographies through time lovetchenia is a western european form in the hauterivian whereas it is an eastern european and apulian form in the late barremian and early aptian agriopleura is also a western european form in the late hauterivian and barremian p p whereas in the early aptian this genus is only found on the southern tethyan margin pachytraga documented from the hauterivian of both the european and southern tethyan margins disappeared during the barremian and re occupied western europe and some parts of africa during the early aptian offneria simplex a barremian form from the caribbean province is recorded in the uppermost lower barremian of se france the regional disappearance of these taxa is not linked to platform or rudist community demise whereas community changes reflect the resulting modifications in biodiversity there is a good correspondence between the regional disappearance of western european taxa cooling events documented by oxygen isotope studies and biological interchanges between the boreal and tethys realms the regional disappearance of lovetchenia and possibly pachytraga are coeval with the pseudothurmannia ohmi cooling episode whereas that of agriopleura is coeval with the ancyloceras vandenheckii cool episode by contrast the intrusion of offneria simplex in western europe coincides with the coronites darsi warm peak thermal shifts between cool and warm episodes fluctuate from 3 to 5 c and the thermal threshold assumed to control the demise of western european taxa is in the range of 18 to 20 c a value similar to those controlling the geographic distribution of modern coral reefs or the boundary between tropical and subtropical seas the southward displacement of the rudist biomes also accounts for the migration of climatic belts and a decreasing of 3 to 5 c in palaeotemperatures spatial contractions of lovetchenia and agriopleura biomes and the o simplex intrusion suggest that these rudists were more sensitive than others to the thermal regime this observation shows that rather than considering rudists in general as tropical some of them may have been both tropical and subtropical and others tropical for pachytraga other factors than temperature possibly oceanographic changes may have been responsible for the overall mediterranean disappearance of this genus in the barremian

drowning of the upper marble falls carbonate platform pennsylvanian central texas a case of conflicting signals abstract marble falls and smithwick formation carbonates and shales were deposited on the western margin of the slowly subsiding fort worth basin of central texas during early pennsylvanian time the upper marble falls member carbonate platform back stepped towards the west southwest as smithwick outer shelf slope black shales drowned platform margin areas to the east the shelf to basin profile observed from subsurface data from the fort worth basin and outcrops from the llano uplift area records platform drowning however the platform began to shoal upwards as it back stepped towards the west southwest due to the presence of the llano uplift paleobathymetric high the geometry of these facies tracts was controlled primarily by a combination of subsidence and second order sea level change while the development of sequences and unconformities was controlled by third order sea level changes and environmental factors and not subsidence the termination of platform deposition in the fort worth basin was caused by the interplay of third order sea level changes environmental deterioration in advance of siliciclastic burial and a lack of accommodation space the depositional history of the upper marble falls carbonate platform does not fit classic examples of drowned platforms described from other areas but may be typical of platforms in slowly subsiding basins

phanerozoic trends in skeletal mineralogy driven by mass extinctions changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal mineralogy of marine calcifyers an investigation of the original skeletal mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the mg ca ratio of the oceans marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite long term changes in the estimated mg ca ratios of sea water tend to correspond to changes in the prevailing mineralogy of these creatures1 2 high mg ca ratios are expected to favour the spread of aragonitic organisms whereas calcitic taxa are thought to benefit from low mg ca ratios3 4 5 6 here we test these patterns throughout the phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms we find that mass extinctions are more important in regulating long term patterns of skeletal mineralogy than the mg ca ratios of the global oceans furthermore selective recovery from mass extinctions is usually more important than selective extinction in driving the phanerozoic pattern of skeletal mineralogy but even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the mg ca ratio of the oceans thus providing further evidence for the complexity of biotic recoveries7

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

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton