eustatic sea level record for the cenomanian late cretaceous extension to the western interior basin usa a combination of biostratigraphic markers ammonites inoceramid bivalves and carbon isotope excursions is employed to establish a high resolution correlation between the middle to late cenomanian successions of the western interior basin usa and the anglo paris basin southern uk sequences identified from sedimentologic criteria in the pueblo succession and elsewhere in the western interior basin are shown to coincide precisely with globally recognized sea level events and were therefore under eustatic control this evidence refutes arguments that cenomanian sequences in the western interior basin were formed by local tectonic events the interaction of longer term tectonic movements and more rapid eustatic change may have simply enhanced the amount of erosion associated with sequence boundaries a crossplot of radiometric ages derived from north american bentonites against an orbitally tuned time scale developed in the anglo paris basin provides support for the argument that the sequences were controlled by the 405 k y long eccentricity cycle

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

high sea surface temperatures during the early aptian oceanic anoxic event 1a in the boreal realm the early aptian was characterized by the widespread occurrence of anoxia in the oceans known as oceanic anoxic event oae 1a intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric co2 concentrations culminating in greenhouse conditions oae 1a can therefore be considered as a past natural experiment important to understand the future evolution of our climate paleotemperature estimates for oae 1a are however predominantly based on bulk oxygen isotopes which are susceptible to diagenetic overprinting while tex86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections here we reconstructed for the first time sea surface water temperatures ssts based on the tex86 paleothermometer from an oae 1a section from the middle northern latitudes 39 n paleolatitude we find a sst rise starting prior to oae 1a and reaching a maximum during the event with ssts of 31 34 c 4 9 c higher than those of older hauterivian lower aptian sediments from the same sedimentary basin the end of oae 1a is marked by relatively lower ssts of 30 c these observations are supported by belemnite based oxygen isotope d18obel data and calcareous nannofossils our integrated data set clearly indicates that super greenhouse conditions prevailed during oae 1a at northern latitudes ssts are similar to those estimated for coeval low latitudinal sites suggesting that an equable warm climate with reduced latitudinal gradients characterized the early aptian

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

carbon isotope signatures of pedogenic carbonates from se china rapid atmospheric pco2 changes during middle late early cretaceous time lower cretaceous pedogenic carbonates exposed in se china have been dated by u pb isotope measurements on single zircons taken from intercalated volcanic rocks and the ages integrated with existing stratigraphy 13 c values of calcretes range from 7 0 to 3 0 and can be grouped into five episodes of increasing decreasing values the carbon isotope proxy derived from these palaeosol carbonates suggests p co 2 mostly in the range 1000 2000 parts per million by volume ppmv at s z co 2 contributed by soil respiration 2500 ppmv and 25 c during the hauterivian albian interval c 30 ma duration such atmospheric co 2 levels are 4 8 times pre industrial values almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants rapid rises in p co 2 are identified for early hauterivian middle barremian late aptian early albian and middle albian time and rapid falls for intervening periods these episodic cyclic changes in p co 2 are not attributed to local tectonism and volcanism but rather to global changes the relationship between reconstructed p co 2 and the development of large igneous provinces lips remains unclear although large scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas suggested levels of relatively low p co 2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope 13 c excursions characteristic of the oceanic anoxic events oae1a selli event kilian and paquier events constituting part of the oae 1b cluster and oae1d short term episodes of high p co 2 coincide with negligible carbon isotope excursions associated with the faraoni event and the jacob event given that episodes of regional organic carbon burial would draw down co 2 and negative 13 c excursions indicate the addition of isotopically light carbon to the ocean atmosphere system controls on the carbon cycle in controlling p co 2 during early cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

climatic evolution across oceanic anoxic event 1a derived from terrestrial palynology and clay minerals maestrat basin spain studies dealing with the response of the continental biosphere to the environmental perturbations associated with cretaceous oceanic anoxic events oaes are comparatively rare here a quantitative spore pollen record combined with clay mineral data is presented which covers the entire early aptian oae 1a interval forcall formation maestrat basin east spain the well expressed oae 1a carbon isotope anomaly is paralleled by changes in the clay mineral assemblage and by a stepwise decline in the normalized frequency of classopollis pollen produced by xerophytic cheirolepidiaceae with lowest contents occurring during the positive 13 c shift in contrast araucariacites and inaperturopollenites pollen show a pronounced increase in relative abundance from low background values to become a significant component of the palynological assemblage during the classopollis minimum the observed changes in clay minerals and pollen distribution patterns are interpreted to reflect a major change in the composition of the hinterland vegetation of the maestrat basin most probably due to short lived but pronounced climatic cooling and changes in humidity temperature anomalies driven by organic carbon burial and associated co 2 decline have been postulated for all major mesozoic oaes the palynomorph record from the iberian maestrat basins indicates that the climax of this cooling episode was significantly delayed in comparison to the end of organic carbon rich deposition in the world oceans

carbon and oxygen isotope stratigraphy of the early cretaceous carbonate platform of pădurea craiului apuseni mountains romania a chemostratigraphic correlation and paleoenvironmental tool abstract stable c and o isotope records were obtained from carbonate rocks spanning the hauterivian to cenomanian interval collected in several sections from the carbonate platform of p durea craiului apuseni mountains romania in the absence of some key biostratigraphic marker species stable isotopes were applied as a tool for stratigraphic correlation and dating the composite 13c and 18o curves for the early cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes the hauterivian and the barremian limestones blid formation display lower 13c values 2 8 to 2 9 relative to the aptian albian deposits 2 6 to 5 4 ecleja valea m gurii and v rciorog formations the red detrital formation albian cenomanian is characterized by a highly variable distribution of the 13c values 3 5 to 3 9 based on the similarities between the c isotope curve established in p durea craiului and from other sections in the tethyan and the pacific regions two major oceanic anoxic events characterized by 13c positive excursions were clearly recognized the first is the oae1a event early aptian in the upper part of the ecleja formation and the valea m gurii formation the second is the oae1b event late aptian albian in the upper part of the v rciorog formation and in the subpiatr member the position of the aptian albian boundary is estimated to be at the upper part of the v rciorog formation immediately after the beginning of the 13c positive excursion the 13c data show major negative excursions during the barremian blid formation early aptian ecleja formation and late aptian v rciorog formation the o isotope variation pattern 10 2 to 2 1 is consistent with progressively warming temperatures during the early barremian followed by a cooling period a subsequent warming period culminated in the early aptian a significant cooling phase corresponds to the late aptian and early albian and the climate cooled again during the late albian and into the early cenomanian stage the data provide a better understanding of the early cretaceous sedimentation cycles in p durea craiului and create a more reliable framework for regional correlations

sequence development influenced by intermittent cooling events in the cretaceous aptian greenhouse adriatic platform croatia depositional sequences capped by peritidal carbonates and breccias on the aptian adriatic carbonate platform croatia were studied to evaluate evidence for glacioeustasy within an age framework constrained by carbon isotope chemostratigraphy sequence ad1 17 60 m 56 197 ft thick uppermost barremian lower aptian is dominated by shallow subtidal parasequences sequence ad2 7 13 m 23 43 ft thick lower aptian lowermost upper aptian contains oceanic anoxic event oae 1a associated with lagoonal laminated carbonates sequence ad3 3 8 m 10 26 ft thick probably is lower upper aptian and likely is separated by a major hiatus from sequence ad4 8 20 m 26 66 ft thick uppermost aptian which spans oae1b both ad2 and ad3 are dominated by peritidal parasequences updip in the lower transgressive systems tract and upper highstand systems tract and by subtidal parasequences elsewhere whereas sequence ad4 is dominated by shallow subtidal parasequences low accommodation rates 4 0 6 0 cm 1 6 2 4 in in the earliest aptian decreasing to approximately 1 0 cm k y 0 3 in k y later promoted widespread breccia development during relative sea level falls aided by tectonic warping the sequence capping breccias eccentricity dominated cyclicity restriction of peritidal facies to late highstands and coeval off shelf oxygen isotope records all suggest that sea level falls occurred during times of cooling and had a significant glacioeustatic component these intermittent cooler periods and continental ice buildup punctuated the aptian greenhouse climate

early aptian paleoenvironmental evolution of the bab basin at the southern neo tethys margin response to global carbon cycle perturbations across ocean anoxic event 1a 1 lower aptian carbonates in the bab basin at the southern neo tethys margin record significant environmental changes across oceanic anoxic event 1a oae1a a long lasting negative shift of carbon isotope ratios 13c associated with a distinct decrease in oxygen isotope ratios 18o in orbitolinid rich carbonates characterizes the onset of oae1a livello selli supporting a hypothesis that a long lasting volcanic co2 emission is the main cause of oae1a inducing global warming a bloom of microencrusters lithocodium and bacinella across the proto bab basin occurred synchronously at the beginning of the subsequent positive 13c excursion responding to the global carbon cycle perturbations the carbonates formed during the oae1a show higher strontium isotope ratios 87sr 86sr compared with those of global seawater this was likely caused by a local influx of isotopically heavier strontium along with nutrients into the proto bab basin these biotic proliferations were triggered by an increased nutrient supply induced by intensified continental weathering due to the global warming suggested by the increase in 18o values spatial variations in the 13c values among sites in the bab basin and its surrounding platform are related to local environmental factors such as the degree of mixing of basin water with ocean water and local removal of 12c by metabolic activity at the platform top the 13c profile of the studied core indicates global removal of organic carbon of oae1a began during the early stage of the second order transgression and lasted until the early stage of the highstand after the oae1a the livello selli corresponds to the early stage of this transgression

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

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

effects of clearcutting on rain on snow runoff in western oregon a new look at old studies results of updating and reanalyzing streamflow data from studies in two experimental watersheds in western oregon suggest that clearcut logging has altered snow accumulation and melt enough to have increased the size of peak flows caused by snowmelt during rainfall in a 96 ha clearcut watershed in the transient snow zone peak flows with return periods of roughly 3 8 years were higher than predicted by prelogging data in a similarly clearcut 10 ha watershed sizes of peak flows caused by melting of relatively deep snowpacks during rainfall were also higher after logging higher peak flows indicate a higher rate of water delivery to soils which in turn suggests increased potential for both hillslope and channel erosion

high frequency moderate to high amplitude sea level oscillations during the late early aptian insights into the mid aptian event galve sub basin spain abstract this paper presents a field based stratigraphic architecture research from the aptian of spain in which high frequency 7 cycles ma moderate to high amplitude 8 127 m sea level oscillations are evidenced by the repeated incision of palaeovalleys in a carbonate platform developed during the late early aptian in a rift setting global eustacy tectonic uplift and mantle dynamic topography are considered as potential mechanisms to explain the observed relative sea level record glacioeustacy is interpreted as the most reliable mechanism to drive the observed sea level oscillations however other mechanisms as oscillations of the groundwater capacity of sedimentary basins and sudden flooding of major a basin as the south atlantic rift are also considered a major cooling event is proposed to occur during the late early aptian as a response to a large scale episode of ignimbritic volcanism increased burial of organic carbon during the aptian oae 1a and a significant demise of carbonate platforms this cooling event is interpreted as the origin for glacioeustatic sea level oscillations during the mid aptian

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

a co2 decrease driven cooling and increased latitudinal temperature gradient during the mid cretaceous oceanic anoxic event 2 article i nfo the mid cretaceous is thought to be a greenhouse world with significantly higher atmospheric pco2 and sea surface temperatures as well as a much flatter latitudinal thermal gradient compared to the present this time interval was punctuated by the cenomanian turonian oceanic anoxic event oae 2 93 5 myr ago an episode of global massive organic carbon burial that likely resulted in a large and abrupt pco2 decline however the climatic consequences of this pco2 drop are yet poorly constrained we determined the first high resolution sea surface temperature sst record across oae 2 from a deep marine sedimentary sequence at ocean drilling program odp site 1276 in the mid latitudinal newfoundland basin nw atlantic by employing the organic palaeothermometer tex86 we found that ssts across the oae 2 interval were extremely high but were punctuated by a remarkably large cooling 5 11 c which is synchronous with the 2 5 5 5 c cooling in sst records from equatorial atlantic sites and the plenus cold event because this global cooling event is concurrent with increased organic carbon burial it likely acted in response to the associated pco2 drop our findings imply a substantial increase in the latitudinal sst gradient in the proto north atlantic during this period of global cooling and reduced atmospheric pco2 suggesting a strong coupling between pco2 and latitudinal thermal gradients under greenhouse climate conditions

theoretical effects of mechanical grain size reduction on gem domain states in pyrrhotite abstract recent laboratory experiments by halgedahl and ye 1999 show that domain widths in pyrrhotite change very little or not at all as a grain is mechanically thinned along one or two directions in their experiments particles were initially demagnetized in an alternating field until a global energy minimum gem domain state was attained surprisingly the overall positions of surviving walls and many small scale details in the shapes of curved walls were remarkably insensitive to thinning thus domain states that survived thinning were interpreted to be local energy minimum lem states as a first step toward providing a theoretical reference frame for the thinning results gem domain widths in pyrrhotite have been calculated here as grains are thinned to one fourth or less of their original size nine models assume one dimensional 1d thinning which greatly changes both particle size and shape two other models address the effects of three dimensional 3d thinning in which particles retain a cubic shape as their sizes are reduced if a particle can maintain a gem state while it is thinned seven of the nine 1d models and both 3d models predict that domain widths will adjust by amounts that are readily detected experimentally thus results of these calculations support the interpretation that lem states in pyrrhotite can be stable over a broad range of grain sizes and shapes the primary origin of this stability remains an unsolved problem however if this stability is intrinsic to the pure material then future micromagnetic models for pyrrhotite are required to investigate lem states and their stability as functions of grain size and grain shape on the other hand this stability could originate from the pinning of preexisting walls by defects halgedahl and ye 1999 whatever their origins the energy barriers that inhibit lem lem transitions could play a significant role in the acquisition of remanence and the temporal stability of the paleomagnetic signal in rocks

the barremian and aptian stepwise development of the oceanic anoxic event 1a oae 1a crisis integrated benthic and planktic high resolution palaeoecology along the gorgo a cerbara stratotype section umbria marche basin italy abstract the barremian and aptian were times of global plate reconfiguration and profound changes in the ocean climate system culminating in the worldwide deposition of lower aptian black shale layers oae 1a based on high resolution lithostratigraphic and micropaleontological analyses precursor conditions and timing of the anoxia are here reconstructed along a 33 06 m thick section in the proposed barremian aptian boundary gssp stratotype at gorgo a cerbara umbria marche basin italy a non uniform history of benthic foraminiferal diversification is interrupted by the selli level oae 1a and by three turnover points for both benthic and planktic organisms each highlighted by prominent breaks in lithology and outcrop morphology the first two points at 1 1 myr and 20 50 kyr prior to the onset of the oae 1a correspond respectively to the nannoconid bathypelagic calcareous nannofossils decline and crisis events and separate a pelagic limestone chert claystone lithological cycles of the uppermost maiolica formation showing frequencies reminiscent of orbital eccentricity and containing an oligotrophic barremian benthic and planktic assemblage dominated by k selected nannoconids and rhizammina b greenish grey cherty marls of the lowermost marne a fucoidi formation associated to declining sedimentation rates and eutrophic early aptian assemblages dominated by radiolarians and lituolid benthic foraminifera and c anoxic radiolarites and shales of the carbonate free selli level high magnitude and frequency assemblage fluctuations occur between the nannoconid crisis 25 cm below the lowermost oae 1a black shale layer and the selli level base with suggestions of bottom water acidification at 800 kyr after the oae 1a end a third turnover point in the basal reddish member of the marne a fucoidi highlights middle aptian assemblages characterized by a bloom of early macroperforate planktic foraminifera hedbergella spp and appearances of new benthic species marking a shift towards better oxygenation oae 1a oxygen and pelagic carbonate factory crises are here suggested to have been step wise and linked to global warming conditions

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

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

c isotope stratigraphy and paleoenvironmental changes across oae2 mid cretaceous from shallow water platform carbonates of southern mexico the stratigraphic and geochemical record of the mid cretaceous cenomanian turonian oceanic anoxic event 2 oae2 has been studied in numerous tethyan and proto atlantic hemi pelagic pelagic successions but little data comes from nearshore carbonate successions from the proto pacific region here we present the results of a combined stratigraphic and 13c study of c t platform carbonates from southern mexico which were deposited within the proto pacific two scales of sedimentary cyclicity are recognized high frequency peritidal and subtidal cycles 0 4 8 m display little evidence of cycle capping subaerial exposure and are not correlative between sections these relationships suggest that the amplitudes of high frequency sea level changes were minimal during the peak mid cretaceous greenhouse longer term transgressive regressive sequences 18 40 m are correlated between sections and using 13c trends can be correlated with sequences developed in northern europe and india the mexican successions were sampled at a high resolution 10 ky for stable isotopes inorganic organic carbon and oxygen total organic carbon insoluble residues and trace metals the 13ccarb curve matches global trends including 6 distinct isotopic stages permitting identification of oae2 despite the lack of characteristic anoxic facies using the 13ccarb trends we tie the previously identified ammonite planktonic foram and nannofossil biostratigraphy from england and the western interior seaway of colorado into the mexican sections the initiation of oae2 defined by an abrupt positive 3 4 13c shift coincides with a long term sea level rise though the sedimentary expression of the deepening is no greater than that observed for any of the other sea level events across the studied interval oae2 termination transition from gradually decreasing to background 13c values is not associated with a particular sea level trend stratigraphic changes in insoluble residues proxy for continental sediment discharge across oae2 are not correlative between sections and do not show consistent systematic relationships with 13c or sea level variations therefore do not support the hypothesis that oae2 was associated with increased continental derived nutrient influx two peaks in trace metal concentrations coincide with the abrupt increase in 13c ratios onset of oae2 and during the transition from elevated to decreasing 13c values near the c t stage boundary these trends are similar to those recorded in coeval deposits of the western interior seaway and are consistent with the hypothesis that oae2 development was related to the release of reduced metals during the short lived 1 my caribbean oceanic plateau basalt eruption in this scenario oxidation of the metals depleted the existing low dissolved o2 concentrations and thermally buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters stimulated primary productivity and further reduced o2 concentrations leading to widespread anoxia and a large positive 13c shift

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

global perturbation of the carbon cycle at the onset of the miocene climatic optimum the miocene climatic optimum mco ca 17 14 7 ma represents one of several major interruptions in the long term cooling trend of the past 50 m y to date the processes driving high amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic we present high resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional continuous carbonate rich sedimentary archive integrated ocean drilling program site u1337 eastern equatorial pacific ocean which offer a new view of climate evolution over the onset of the mco a sharp decline in delta o 18 and delta c 13 at ca 16 9 ma contemporaneous with a massive increase in carbonate dissolution demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle the rapid recovery in delta c 13 at ca 16 7 ma similar to 250 k y after the beginning of the mco marks the onset of the first carbon isotope maximum within the long lasting monterey excursion these results lend support to the notion that atmospheric pco 2 variations drove profound changes in the global carbon reservoir through the mco implying a delicate balance between changing co2 fluxes rates of silicate weathering and global carbon sequestration comparison with a high resolution delta c 13 record spanning the onset of the cretaceous oceanic anoxic event 1a similar to 120 m y ago reveals common forcing factors and climatic responses providing a long term perspective to understand climate carbon cycle feedbacks during warmer periods of earth s climate with markedly different atmospheric co2 concentrations

synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early aptian oceanic anoxic event 1a evidence for the release of 13c depleted carbon into the atmosphere 1 a common feature of records of the early aptian oceanic anoxic event oae 1a is the sharp negative 13c excursion displayed in both carbonate and organic matter at the onset of this event a synchronous negative 13c excursion has also been noted for terrestrial organic matter this negative excursion has been attributed to either an injection of 13c depleted light carbon into the atmosphere or in case of marine sediments recycling of 13c depleted co2 however most studies were done on separate cores and no information on the relative timing of the negative spikes in terrestrial versus marine records has been obtained here we examine early aptian core sections from two geographically distal sites italy and the mid pacific to elucidate the causes and relative timing of this negative spike at both sites increased organic carbon corg and decreased bulk carbonate contents characterize the interval recording oae 1a variously referred to as the selli event the organic material within the selli level is immature and of autochthonous origin measured 13c values of marine and terrestrial biomarkers largely covary with those of bulk organic carbon with lowest values recorded at the base of the organic rich section by contrast sediments enveloping the selli level exhibit very low corg contents and their extractable corg is predominantly of allochthonous origin hydrous pyrolysis techniques used to obtain an autochthonous pre selli 13c value for algal derived pristane from corresponding sample material yielded a negative 13c shift of up to 4 a negative 13c shift of similar magnitude was also measured for the terrigenous n alkanes the results are collectively best explained by means of a massive syndepositional rapid input of 13c depleted carbon into the atmosphere and surface oceans likely delivered either via methane produced from the dissociation of sedimentary clathrates or perhaps by widespread thermal metamorphism of corg rich sedimentary rocks

consequences of moderate 25 000 yr lasting emission of light co 2 into the mid cretaceous ocean future warming is predicted to shift the earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming this study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not vert similar 112 myr ago our study focuses on the cretaceous oceanic anoxic event oae 1b and explores how the earth system responded to a moderate not vert similar 25 000 yr lasting climate perturbation that is modelled to be less than 1 c in global average temperature using a new chronological model for oae 1b we present high resolution elemental and bulk carbon isotope records from dsdp site 545 from mazagan plateau off nw africa and combine this information with a coupled atmosphere land ocean model the simulations suggest that a perturbation at the onset of oae 1b caused almost instantaneous warming of the atmosphere on the order of 0 3 c followed by a longer not vert similar 45 000 yr period of not vert similar 0 8 c cooling the marine records from dsdp site 545 support that these moderate swings in global climate had immediate consequences for african continental supply of mineral matter and nutrients phosphorous subsequent oxygen availability and organic carbon burial in the eastern subtropical atlantic however without turning the ocean anoxic the match between modelling results and stratigraphic isotopic data support previous studies summarized in jenkyns h c 2003 evidence for rapid climate change in the mesozoic palaeogene greenhouse world the royal society 361 1885 1916 in that methane emission from marine hydrates albeit moderate in dimension may have been the trigger for oae 1b though we can not finally rule out alternative mechanisms following the hydrate mechanism a total of 1 15 1018 g methane carbon 13c 60 equivalent to about 10 to the total modern gas hydrate inventory generated the 13ccarb profile recorded in the section modelling suggests a combination of moderate scale methane pulses supplemented by continuous methane emission at elevated levels over not vert similar 25 000 yr the proposed mechanism though difficult to finally confirm in the geological past is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously this study shows that once set off this mechanism can maintain earth s climate in a perturbed mode over geological time leading to pronounced changes in regional climate

episodes of high productivity and cooling in the early aptian alpine tethys a palynological and organic geochemical study of the early aptian selli unit oceanic anoxic event 1a of the western tethys provides new information about paleoceanography and documents pronounced changes in the regional climate pattern it also emphasizes the role of oxic degradation of organic matter even at horizons with the highest rates of organic carbon corg accumulation the absence of anoxia indicates that enhanced primary production is the main reason for these organic carbon accumulations and variations in preservation are related to pulses in primary production and nutrient recycling despite the high productivity character of the selli unit black shales the 13ccarb values are not marked by a positive shift but by an interval of unchanged values warm climatic conditions for deposition of the selli unit are inferred from the presence of southern provenance pollen and low 18o values for the interval above the selli unit changes in the pollen spectrum and an increase in 18o values reflect a hitherto undocumented late early aptian cooler and more humid climate and or a reorganization of the tethyan oceanographic circulation pattern

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

impacts of orbital forcing and atmospheric carbon dioxide on miocene ice sheet expansion the processes causing the middle miocene global cooling which marked the earth s final transition into an icehouse climate about 13 9 million years ago myr ago 1 4 remain enigmatic tectonically driven circulation changes 5 6 and variations in atmospheric carbon dioxide levels 7 8 have been suggested as driving mechanisms but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult here we present high resolution climate proxy records covering the period from 14 7 to 12 7 million years ago from two complete sediment cores from the northwest and southeast subtropical pacific ocean using new chronologies through the correlation to the latest orbital model 9 we find relatively constant low summer insolation over antarctica coincident with declining atmospheric carbon dioxide levels at the time of antarctic ice sheet expansion and global cooling suggesting a causal link we surmise that the thermal isolation of antarctica played a role in providing sustained long term climatic boundary conditions propitious for ice sheet formation our data document that antarctic glaciation was rapid taking place within two obliquity cycles and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change