from quantitative 3d seismic stratigraphy to sequence stratigraphy insights into the vertical and lateral variability of shelf margin depositional systems at different stratigraphic orders abstract a major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation identification is commonly dependent on the resolution of the data used i e seismic vs well data its dimension i e 1d vs 2d vs 3d or the criteria chosen to select sequence boundaries through shelf edge trajectory analysis the clinothem i e highest order seismic sequence identified on seismic data can constitute the elementary building block of an observation based and data driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy here we use high quality 3d seismic data to interpret a late tithonian early cretaceous shelf margin the lower barrow group lbg developed in the northern carnarvon basin on the north west shelf of australia based on full volume seismic interpretation techniques that integrate the 3d variability of the data when identifying seismic unconformities a high resolution seismic stratigraphic framework was built 73 interpreted clinothems with an average time duration of 63 000 yrs the computation of high frequency shelf edge trajectory angle tse curves on selected seismic cross sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data within the d lobispinosum interval 142 3 140 9 ma the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability which is here quantified of this shelf slope basin system the results show that the high frequency interplay between short term glacio eustasy i e milankovitch eccentricity cycles of 100 000 yrs and sediment supply locus of fluvial input along the margin impacted the three dimensional stratigraphic architecture of the lbg in contrast tectonic subsidence had a significant impact on the stratigraphic architecture of the lbg within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating decelerating the rates of accommodation creation however identification of long term glacio eustatic milankovitch cycles 400 000 yrs outside the main depocentre where the rates of accommodation creation due to rift related subsidence are moderate also suggests low frequency eustatic control therefore the vertical and lateral variability of the lbg results from variations in sediment supply and subsidence regime under local i e process regime currents regional i e tectonics and global i e eustasy climate forcing parameters interplaying across timescales in contrast to standard sequence stratigraphic workflows that are based on model dependent choices to select sequence boundaries quantitative 3d seismic stratigraphy constitutes an improved method to interpret 3d seismic data in shelf margin depositional systems within a sequence stratigraphic framework which provides an observation based and model independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers this work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4d variability of depositional systems and moves beyond the two dimensionality inherent to current sequence stratigraphic methods quantitative 3d seismic stratigraphy represents a first step towards the creation of 3d sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships source reservoir seal distribution across shelf margins

dropstones their origin and significance abstract dropstones are clasts which pose a hydrodynamic paradox or which have an exotic or extra basinal lithology with uncertain provenance recently dropstones have been consistently interpreted as the product of ice rafting and have been used to substantiate the presence of cool climatic phases in the geological record this review illustrates that not all dropstones are reliable as palaeoclimatic indicators dropstones are the product of two distinct entrainment and transport mechanisms by a rafting agent or as a projectile four main processes of transport and formation are identified biological rafting ice rafting floatation and projectiles biological rafting agents include vertebrate gastroliths and other stomach contents vegetational rafting and anthropomorphic activity ice rafting can be the product of ice bergs or seasonal sea river or lake ice floatation of clasts in calm waters has been recorded for stones up to 25 mm in length projectiles are most commonly of volcanic origin given the range of transport and depositional mechanisms reviewed we argue that great care is required in the interpretation of the origin of dropstones

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

concentrations of reduced sulphur in inclusion fluids associated with black shale hosted quartz vein gold deposits implications for mechanisms of transport and deposition of gold and a possible exploration tool abstract analyses of reduced s and other inclusion volatiles in vein quartz from the black shale hosted clogau st davids au deposit n wales show that a relation exists between elevated inclusion s content and au grade this relation is better at discriminating between high and low grade vein material than criteria based on the other inclusion volatiles analyses of material from a similar but subeconomic vein system yields a small number of samples with an auriferous signature on the basis of either s 2 content or co 2 ch 4 ratio but application of both criteria would reject all samples the concentration of reduced s species in metamorphic fluids thought to have transported au suggests that au hs 2 was the dominant au complex thermodynamic calculations indicate that up to 8 mg au kg h 2 o may have been transported in this manner gold precipitation in the ore body resulted from destabilisation of the au hs 2 complex probably either through reduction by the black shales or as a result of flashing of h 2 s into the ch 4 rich phase which was generated during the mineralising event

paleoenvironmental changes during the valanginian new insights from variations in phosphorus contents and bulk and clay mineralogies in the western tethys paleoenvironmental and paleoclimatic changes during the valanginian carbon isotopic excursion cie have been investigated in the western tethys for this purpose bulk rock and clay mineralogies as well as phosphorus p contents were evaluated in a selection of five sections located in the vocontian basin angles se france alvier e switzerland malleval e france and the lombardian basin capriolo n italy breggia s switzerland within the cie interval bulk rock and clay mineralogies are inferred to reflect mostly climate change the onset of the cie busnardoites campylotoxus ammonite zone is characterized by higher detrital index di sum of the detrital minerals divided by calcite contents values and the presence of kaolinite in their clay mineral assemblages in the late valanginian from the saynoceras verrucosum zone up to the end of the valanginian the samples show relatively variable di and lower values or the absence of kaolinite the variation in the mineralogical composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions associated with an increase in terrigenous input on the southern european margin during the cie towards an overall unstable climate associated with drier conditions in the late valanginian this is contrasted by a dissymmetry proximal vs distal along the studied transect the northern tethyan margin being more sensitive to changes in continental input compared to the distal environments p accumulation rates par present similar features in the vocontian basin p content variations are associated with changes in terrigenous influx whereas in the lombardian basin i e capriolo and breggia par values are less well correlated this is mainly because the deeper part of the tethys was less sensitive to changes in continental inputs the onset of the cie top of the b campylotoxus zone records a general increase in par suggesting an increase in marine nutrient levels this is linked to higher continental weathering rates and the enhanced influx of nutrients into the ocean in the period corresponding to the shift itself p contents show a dissymmetry between the vocontian and lombardian basins proximal vs distal for the sections of malleval alvier and angles a decrease in p concentrations associated to a decrease in detrital input is observed in capriolo and breggia par show maximum values during the plateau indicating a more complex interaction between different p sources the time interval including the top of s verrucosum zone up to the end of the valanginian is characterized by variable par values suggesting variable nutrient influxes these changes are in agreement with an evolution towards seasonally contrasted conditions in the late valanginian

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

quantification of hydrophone records of the 2004 sumatra tsunami the 2004 sumatra andaman tsunami was recorded by hydrophones of the international monitoring system at site h08 near diego garcia notably in frequency bands extending outside the range of the shallow water approximation despite the severe high pass filtering involved in this instrumentation we show that the spectral amplitudes recovered around t 87 s can be successfully explained by generation from the seismic source in the framework of the normal mode theory of tsunami excitation at the lower frequencies characteristic of more conventional tsunami waves 800 to 3200 s the signal is probably present in the hydrophone records but reliable deconvolution of its spectral amplitude is precluded by the fact that the instrumental filters lowered the tsunami signal to the level of resolution of the instrument digitizer in the context of distant tsunami warning hydrophone records could provide useful insight into high frequency tsunami components and even at lower more conventional frequencies provided that an unfiltered channel could be recorded routinely

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

late mesozoic north atlantic land bridges abstract current palaeogeographical reconstructions suggest that since the onset of the late jurassic and during the whole cretaceous period the landmasses of north america and west eurasia have been separated by seaway s exposed on the north atlantic rift system such a palaeogeographical setting should have limited the possibility of direct overland dispersals between the biotas of the two continents strong faunal affinities between the two sides of the north proto atlantic ocean presuppose faunal exchanges between the landmasses however suggesting the existence of ephemeral land bridges around the jurassic cretaceous boundary and the mid early cretaceous this study reviews the current faunal evidence and discusses palaeogeographical evidence that might better elucidate the existence of the postulated land bridges evaluation of the evidence leads to the conclusion that two land bridges were exposed 1 between east north america and iberia during the late kimmeridgian 154 ma and 2 between north america and fennoscandia via the barents shelf around the hauterivian barremian boundary 131 ma the former land bridge was terminated in the earliest tithonian 151 ma and the latter was terminated in the late early barremian 129 ma furthermore the latter land bridge was contemporaneous with regressive stages in both the mid polish trough and the sea strait crossing the russian platform allowing broad direct terrestrial communication among north america europe and asia in the earliest barremian

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

high sea surface temperatures during the early cretaceous epoch the early cretaceous epoch about 145 100 million years ago is generally thought of as a greenhouse period with high atmospheric co2 concentrations1 and high global mean temperatures2 but evidence for episodes of cooler conditions and even transient glaciations has been proposed3 4 5 6 7 8 9 here we present sea surface temperature records spanning the period from 142 to 128 million years ago berriasian barremian ages from low and mid latitudes reconstructed using the tex86 palaeotemperature proxy during this period we find sea surface temperatures exceeding 32 c at 15 20 n and averaging 26 c at 53 s these temperatures substantially exceed modern temperatures at equivalent latitudes and are incompatible with the notion of consistently cooler conditions in the earliest cretaceous moreover we find little variability in the sea surface temperature records even during the valanginian carbon isotope excursion 138 135 million years ago which was thought to be associated with marked temperature fluctuations5 we conclude that the earliest cretaceous was characterized by a warm stable climate with a lower meridional temperature gradient than today

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

an offset in tex86 values between interbedded lithologies implications for sea surface temperature reconstructions abstract the tex 86 tetraether index of tetraethers consisting of 86 carbon atoms sea surface temperature sst proxy is based on the distribution of isoprenoid glycerol dialkyl glycerol tetraether gdgt membrane lipids of pelagic thaumarchaeota that are preserved in marine sediments it is a valuable tool for reconstructing past ssts from sedimentary archives however there are still major uncertainties as to the effects of variables other than temperature on the proxy here we present the first study of gdgt variability across early cretaceous interbedded pelagic and shelf sourced turbiditic sediments from two deep sea drilling project dsdp sites in the western north atlantic the results indicate that a small but consistent offset in tex 86 ratios equivalent to 1 2 c of temperature difference occurs between interbedded lithologies of a similar age the offset can be attributed to spatial differences in sea surface temperatures or thaumarchaeotal populations between the shelf and the open ocean or to secondary diagenetic effects related to oxic degradation of the gdgts of these a difference in either thaumarchaeotal taxa or ecology between those living in the shelf and ocean areas seems most plausible regardless of the root cause of the offset these findings highlight the necessity of careful sample selection prior to tex 86 analysis to ensure robust interpretation of palaeotemperature trends

evidence for a regional warm bias in the early cretaceous tex86 record abstract the cretaceous period 145 66 ma provides an opportunity to obtain insights into the adaptation of the climate system to increased atmospheric greenhouse gas concentrations the organic paleothermometer tex86 is one of the few proxies available for reconstructing quantitative estimates of upper ocean temperatures of this time period here we show that the sedimentary tex86 signal in the early cretaceous north and south atlantic shows systematic differences to other cretaceous samples in particular the relative increase in the fractional abundances of the crenarchaeol isomer compared to crenarchaeol exhibits similarities with surface sediments from the modern mediterranean and red sea dedicated climate model simulations suggest that the formation of warm and saline deep waters in the restricted north and south atlantic may have influenced tex86 export dynamics leading to a warm bias in reconstructed upper ocean temperatures applying a regional calibration from the modern mediterranean and red sea to corresponding tex86 data significantly improves the model data fit for the aptian oceanic anoxic event 1a and the overall comparison with other temperature proxies for the early cretaceous our results demonstrate the need to consider regional and temporal changes of the tex86 temperature relation for the reconstruction of deep time ocean temperatures

cretaceous sea surface temperature evolution constraints from tex86 and planktonic foraminiferal oxygen isotopes it is well established that greenhouse conditions prevailed during the cretaceous period 145 66 ma determining the exact nature of the greenhouse gas forcing climatic warming and climate sensitivity remains however an active topic of research quantitative and qualitative geochemical and palaeontological proxies provide valuable observational constraints on cretaceous climate in particular reconstructions of cretaceous sea surface temperatures ssts have been revolutionised firstly by the recognition that clay rich sequences can host exceptionally preserved planktonic foraminifera allowing for reliable oxygen isotope analyses and secondly by the development of the organic palaeothermometer tex86 based on the distribution of marine archaeal membrane lipids here we provide a new compilation and synthesis of available planktonic foraminiferal 18o 18opl and tex86 sst proxy data for almost the entire cretaceous period the compilation uses ssts recalculated from published raw data allowing examination of the sensitivity of each proxy to the calculation method e g choice of calibration and places all data on a common timescale overall the compilation shows many similarities with trends present in individual records of cretaceous climate change for example both sst proxies and benthic foraminiferal 18o records indicate maximum warmth in the cenomanian turonian interval our reconstruction of the evolution of latitudinal temperature gradients low 48 palaeolatitudes reveals temporal changes in the valanginian aptian the low to higher mid latitudinal temperature gradient was weak decreasing from 10 17 c in the valanginian to 3 5 c in the aptian based on tex86 ssts in the cenomanian santonian reconstructed latitudinal temperature contrasts are also small relative to modern 14 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts compared with 20 c for the modern in the mid campanian to end maastrichtian latitudinal temperature gradients strengthened 19 21 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts with cooling occurring at low middle and higher palaeolatitude sites implying global surface ocean cooling and or changes in ocean heat transport in the late cretaceous these reconstructed long term trends are resilient regardless of the choice of proxy tex86 or 18opl or calibration this new cretaceous sst synthesis provides an up to date target for modelling studies investigating the mechanics of extreme climates

carbon cycle history through the jurassic cretaceous boundary a new global δ13c stack we present new carbon and oxygen isotope curves from sections in the bakony mts hungary constrained by biostratigraphy and magnetostratigraphy in order to evaluate whether carbon isotopes can provide a tool to help establish and correlate the last system boundary remaining undefined in the phanerozoic as well provide data to better understand the carbon cycle history and environmental drivers during the jurassic cretaceous interval we observe a gentle decrease in carbon isotope values through the late jurassic a pronounced shift to more positive carbon isotope values does not occur until the valanginian corresponding to the weissert event in order to place the newly obtained stable isotope data into a global context we compiled 31 published and stratigraphically constrained carbon isotope records from the pacific tethyan atlantic and boreal realms to produce a new global 13c stack for the late oxfordian through early hauterivian interval our new data from hungary is consistent with the global 13c stack the stack reveals a steady but slow decrease in carbon isotope values until the early valanginian in comparison the late jurassic early cretaceous 13c curve in gts 2012 shows no slope and little variation aside from the well defined valanginian positive excursion chemostratigraphic correlation durschning the jurassic cretaceous boundary interval is difficult due to relatively stable 13c values compounded by a slope which is too slight there is no clear isotopic marker event for the system boundary the long term gradual change towards more negative carbon isotope values through the jurassic cretaceous transition has previously been explained by increasingly oligotrophic condition and lessened primary production however this contradicts the reported increase in 87sr 86sr ratios suggesting intensification of weathering and a decreasing contribution of non radiogenic hydrothermal sr and presumably a concomitant rise in nutrient input into the oceans the concomitant rise of modern phytoplankton groups dinoflagellates and coccolithophores would have also led to increased primary productivity making the negative carbon isotope trend even more notable we suggest that gradual oceanographic changes more effective connections and mixing between the tethys atlantic and pacific oceans would have promoted a shift towards enhanced burial of isotopically heavy carbonate carbon and effective recycling of isotopically light organic matter these processes account for the observed long term trend interrupted only by the weissert event in the valanginian

a valanginian early cretaceous boreal nannoplankton excursion in sections from romania abstract in order to resolve both sea level and palaeoclimatic signals for the earliest cretaceous 161 calcareous nannofossil samples of berriasian to valanginian age have been studied from romania these samples are derived from three biostratigraphically well dated sections of tethyan litho and biofacies the nannofossil assemblages recorded are of high diversity reflecting stable warm water conditions typical for the earliest cretaceous of the tethys the floras are characterised by abundant watznaueria spp and nannoconus spp whereas other taxa are less common long term trends on the scale of 1 4 my are reflected by shifts from watznaueria spp dominated assemblages in the lower berriasian to nannoconus spp assemblages in the middle upper berriasian back to watznaueria spp in the upper berriasian lower valanginian and again to nannoconus spp in the upper valanginian these changes are thought to be caused by palaeoclimatic shifts periods with a dominance of cosmopolitan eurytopic watznaueria are thought to reflect cooler humid conditions and well mixed surface waters those with a dominance of nannoconus warmer conditions and a rather stabile surface water stratification crucibiscutum salebrosum very common at high latitudes is extremely rare in the romanian samples it occurs only at one specific interval of early late valanginian age saynoceras verrucosum ammonite zone associated with other rare boreal taxa also restricted to this particular level this boreal nannoplankton excursion is believed to be controlled by sea level rather than by climate since simultaneously tethyan ammonites found their way into the boreal realm

isotopic evidence for glaciation during the cretaceous supergreenhouse the turonian 93 5 to 89 3 million years ago was one of the warmest periods of the phanerozoic eon with tropical sea surface temperatures over 35 c high amplitude sea level changes and positive 18 o excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth new 18 o data from the tropical atlantic show synchronous shifts 91 2 million years ago for both the surface and deep ocean that are consistent with an approximately 200 000 year period of glaciation with ice sheets of about half the size of the modern antarctic ice cap even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets calling into question the common assumption that the poles were always ice free during past periods of intense global warming

lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins an example from the early cretaceous jiuquan basin northwestern china development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins however these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development this paper documents fan delta deposition alongside an intrabasinal structural high within the early cretaceous xiagou formation of the jiuquan basin china using subsurface geological and geophysical data deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts suggesting that deposition alongside the structural high is sensitive to lake level changes the temporal and spatial distribution of the fan deltas display retrogradational stacking patterns where fan deltas exhibit a decreasing lateral extent up sequence until fan delta deposition terminated and was replaced by deposition of fine grained lacustrine deposits the retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the xiagou formation subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation likely resulting from border fault movements these data suggest that non uniform stacking patterns in the lower parts of the xiagou formation reflect basin scale tectonic movements as the dominant control on synrift deposition patterns however later stages of xiagou formation deposition were characterized by uniform subsidence across the basin and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault these observations suggest that basin scale tectonic movements played a relatively limited role in controlling sediment deposition and imply a potential change to regional scale processes affecting fan delta deposition during later synrift stages climate change is favored here as the region scale control on the uniform retrogradational fan delta stacking patterns this assertion is supported by pollen assemblages isotope signatures and organic geochemical analyses which collectively suggest a change from a humid to semi arid environment during later synrift stages we suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin and regional scale processes that control rift basin deposition

latitudinal temperature trends in the northern hemisphere during the early cretaceous valanginian hauterivian abstract we present the first detailed stable isotope record 13c 18o for the valanginian lower cretaceous of the southern boreal realm the observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well dated sections in northwest germany a major positive carbon isotope excursion cie of 2 in the early late valanginian documents a perturbation of the carbon cycle this positive cie which is well known as the weissert event in the tethys is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes 35 39 65 north these findings suggest that the environmental changes indicated by the cie in the early late valanginian are synchronous thereby pointing to a global control the combined oxygen isotope data sets show long term fluctuations of up to 7 c with a cooling in the late valanginian for both the southern and the arctic part of the boreal realm whilst tethyan data document only a ca 1 c cooling based on a reliable bio and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the valanginian and supports the idea that a combination of regional and global factors caused such shifts

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

tropical sea temperatures in the high latitude south pacific during the eocene sea surface temperature sst estimates of 30 c from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the canterbury basin new zealand support paleontological evidence for a warm subtropical to tropical climate in the early eocene high latitude 55 s southwest pacific such warm ssts call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers even under hypergreenhouse conditions 2240 ppm co2 modeled summer ssts for the new zealand region do not exceed 20 c

early cretaceous palaeoceanography of the greenland norwegian seaway evidenced by calcareous nannofossils abstract reconstructions of the palaeoclimate of the early cretaceous are controversial varying from a warm temperate greenhouse world to icehouse conditions we studied calcareous nannofossil assemblages of sediments from north east greenland wollaston forland and kuhn o of late ryazanian barremian age in order to better understand the palaeoclimate and palaeoceanography of the high latitudes the calcareous nannofossil assemblages are characterized by abundant crucibiscutum spp and watznaueria spp biscutum constans and other boreal taxa they show also influxes of tethyan and low to mid latitudinal taxa like nannoconids e g nannoconus bermudezii nannoconus dolomiticus nannoconus steinmannii pentaliths micrantholithus hoschulzii micrantholithus obtusus conuspheres speetonia colligata and cruciellipsis cuvillieri in the upper ryazanian and lower hauterivian reconstructed surface water conditions indicated by fluctuations in the assemblage compositions suggest cool conditions for the late ryazanian a cold climate for the valanginian and warm climatic conditions for the hauterivian barremian high meridonial temperature gradients and cool cold climatic conditions in the high latitudes caused supposedly the formation of deep water in the south anyui gulf in the late ryazanian valanginian palaeoceanographic changes reflected in a counter balanced ocean current system in the greenland norwegian seaway allowed tethyan biota to spread as far north as north east greenland during the late ryazanian

the valanginian δ13c excursion may not be an expression of a global oceanic anoxic event abstract marine and terrestrial sediments of the valanginian age display a distinct positive 13 c excursion which has recently been interpreted as the expression of an oceanic anoxic episode oae of global importance here we evaluate the extent of anaerobic conditions in marine bottom waters and explore the mechanisms involved in changing carbon storage on a global scale during this time interval we asses redox sensitive trace element distributions rste uranium vanadium cobalt arsenic and molybdenum and the quality and quantity of preserved organic matter om in representative sections along a shelf basin transect in the western tethys in the polish basin and on shatsky rise om rich layers corresponding in time to the 13 c shift are generally rare in the tethyan sections and if present the layers are not thicker than several centimetres and total organic carbon toc contents do not surpass 1 68 wt palynological observations and geochemical properties of the preserved om suggest a mixed marine and terrestrial origin and deposition in an oxic environment in the polish basin om rich layers show evidence for an important continental component rste exhibit no major enrichments during the 13 c excursion in all studied tethyan sections rste enrichments are however observed in the pre 13 c excursion om rich barrande levels of the vocontian trough in addition all tethyan sections record higher mn contents during the 13 c shift indicating rather well oxygenated bottom waters in the western tethys and the presence of anoxic basins elsewhere such as the restricted basins of the north atlantic and weddell sea we propose that the valanginian 13 c shift is the consequence of a combination of increased om storage in marginal seas and on continents as a sink of 12 c enriched organic carbon coupled with the demise of shallow water carbonate platforms diminishing the storage capacity of 13 c enriched carbonate carbon as such the valanginian provides a more faithful natural analogue to present day environmental change than most other mesozoic oaes which are characterized by the development of ocean wide dysaerobic to anaerobic conditions

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

the greenland norwegian seaway a key area for understanding late jurassic to early cretaceous paleoenvironments the paleoclimatology and paleoceanology of the late jurassic and early cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks however because of the lack of outcrops most studies have concentrated on low latitudes in particular the tethys and the boreal realm where information has been based largely on material from northwest germany the north sea and england these areas were all south of 40 n latitude during the late jurassic and early cretaceous we have studied sediment samples of kimmeridgian 154 ma to barremian 121 ma age from cores taken at sites offshore mid norway and in the barents sea that lay in a narrow seaway connecting the tethys with the northern polar ocean during the late jurassic early cretaceous these sites had paleolatitudes of 42 67 n the late jurassic early cretaceous sequences at these sites reflect the global sea level rise during the volgian hauterivian and a climatic shift from warm humid conditions in volgian times to arid cold climates in the early hauterivian the sediments indicate orbital control of climate reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production trace element concentrations in the volgian berriasian sediments suggest that the central part of the greenland norwegian seaway might have had suboxic bottom water beneath an oxic water column both marine and terrigenous organic matter are present in the seaway sediments the volgian berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region the accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level it might be that the greenland norwegian segment was the deepest part of the transcontinental seaway bounded at both ends by relatively shallow swells the decline in organic matter content of the sediments in the valanginian hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose the same benthic foraminifera assemblages are encountered throughout the seaway endemic assemblages of arenaceous foraminifera in the volgian berriasian give way to more diverse and cosmopolitan valanginian hauterivian benthic communities that include calcareous species the foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier cretaceous changing to more fully oxygenated conditions later the calcareous nannoplankton particularly crucibiscutum salebrosum which is rare at low latitudes and abundant in high latitudes reflect the meridional thermal gradient they indicate that the greenland norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the tethyan and boreal realms this implies the existence of stable climatic belts during the early valanginian and hauterivian significant meridional temperature gradients and moderate ice house conditions

the effect of maturity and depositional redox conditions on archaeal tetraether lipid palaeothermometry recently we proposed a new organic sea surface temperature proxy tex86 based on the distribution of archaeal tetraether lipids here we have examined the effect of oxic degradation and maturity on this new temperature proxy our results show that oxic degradation does not appear to affect the tex86 values within the analytical error hydrous pyrolysis experiments suggest that thermal maturity does have an effect on tex86 sediments with relatively high amounts of 22s hopanes 22s 22s 22r ratios 0 1 or 17 21 h hopanes ratios 0 5 may have tex86 values which are biased towards lower values and thus lower sea surface temperatures

carbonate clumped isotope evidence for latitudinal seawater temperature gradients and the oxygen isotope composition of early cretaceous seas abstract in this study we investigated early cretaceous valanginian ca 135 million years ago climate from subtropical to boreal palaeolatitudes combined carbonate clumped isotope and oxygen isotope data derived from sub arctic boreal and sub tropical fossil belemnite rostra mollusca cephalopoda provide new palaeotemperature estimates as well as a constraint on the oxygen isotope composition of seawater our belemnite data reveal balmy high latitude marine temperatures ca 22 c and warm sub tropical temperatures ca 31 c supplementing our clumped isotope based temperature estimates with published tex86 data results in a conservative reconstruction of a latitudinal temperature gradient that is reduced compared to modern conditions we find that modelling efforts are close to reproducing tropical temperatures when high pco2 levels are considered warm polar temperatures imply however that data model discrepancies remain early cretaceous seawater oxygen isotope values show a modern profile and are much more positive up to 1 5 smow than typically assumed based on our findings if the positive cretaceous seawater 18o values are not considered carbonate 18o thermometry would underestimate temperatures most acute at middle and tropical latitudes

climate and paleoceanography controlled size variations of calcareous nannofossils during the valanginian weissert event early cretaceous abstract strata of valanginian age early cretaceous 139 8 132 9 ma record a 1 5 positive carbon isotope excursion cie the weissert event it coincides with volcanic activity of the parana etendeka large igneous province unlike the mesozoic oceanic anoxic events oaes no organic rich deposits documenting widespread perturbation of the marine carbon cycle are associated with the weissert event to study the impact of paleoceanographic changes in the valanginian on calcareous nannofossils this study analyzes coccolith size data of three species biscutum constans watznaueria barnesiae zeugrhabdotus erectus from northern germany and the western north atlantic further it presents a new valanginian carbon isotope record of organic material 13corg from northern germany the dataset records the weissert event cie in the late valanginian at both locations biometric analyses reveal size decreases of b constans coccoliths during the weissert event a size reduction of 1 m has been observed for northern germany 37 n and of 0 4 m for the north atlantic 23 n the different magnitudes of size decrease possibly reflect the different paleogeographic positions of the sites and the paleoceanographic response to the late valanginian climate variations proxy data support a link between a humid climate with increased weathering and the observed coccolith size variations this impacted nannoplankton communities either through the availability of light or by eutrophication and possibly nutrient limitation in addition to increased terrigenous input emissions of the parana etendeka volcanism possibly acted fertilizing furthermore widely dispersed volcanic emissions possibly caused increased concentrations of toxic trace metals in the surface ocean which affected marine primary producers

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

sedimentary dynamics and climatic implications of cretaceous loess like red beds in the lanzhou basin northwest china abstract the chinese loess has been widely studied in order to reconstruct cenozoic environmental change cretaceous loess like red beds with alternating red and gray layers in the lanzhou basin northwest china are well preserved and can be used for understanding the mesozoic environmental and climatic changes however the red beds and gray clays are less studied and their significance is not clear hence cretaceous red beds of the basin are studied the gray layers show horizontal lamination and are deposited in a lacustrine environment whereas the red layers show gradational change in texture and color and are analogous to paleosols the red and gray clays show similar immobile trace elemental compositions and identical grain size distributions suggesting that the sediments of the two deposits are derived from the same source and carried by identical transporting forces the dominant 2 10 m fine grain size component indicates that the deposits are sorted through long distance transportation in this context the magnetic properties of the red beds are mainly determined by post depositional environmental development hematite is the dominant magnetic mineral and some of the gray layers contains small quantities of magnetite therefore the red and gray layers develop on land and under water respectively the magnetic parameter irm 100mt eliminates the effects of ferromagnetic minerals and is sensitive to hard magnetic minerals thus it can be used as a proxy for paleoclimatic change its high values in the red layers correspond to a drier paleoclimatic environment

tex86 and stable δ18o paleothermometry of early cretaceous sediments implications for belemnite ecology and paleotemperature proxy application abstract recent studies have cast doubt on the unadjusted usage of jurassic and cretaceous 18 o paleotemperature data derived from belemnites since the latter data often reflect cooler paleotemperature estimates than would be expected in this study we address this problem by analysing rocks of barremian to early aptian age from two outcrops in northern germany using tex 86 paleothermometry along with 142 belemnite guards studied for their stable isotope 13 c 18 o and trace element composition magnesium strontium iron and manganese both tex 86 and 18 o bel indicate very warm water temperatures for a distinctive black shale sequence of late early barremian age hauptblatterton with temperatures of up to 29 c and 23 c respectively we observe a constant offset of tex 86 temperatures versus the 4 to 5 c cooler 18 o belemnite signal for this interval the late barremian sequence shows an increase of the 18 o bel values from 1 to 0 reflecting temperatures around 16 to 12 c while the contemporaneous tex 86 temperatures vary between 26 and 32 c the common occurrence of belemnites in the anoxic sediments of the early barremian implies however clearly a nektonic way of life similar to that of recent teuthids rather than a nektobenthic one like sepia this in turn suggests that the belemnites investigated here genera praeoxyteuthis aulacoteuthis oxyteuthis and neohibolites were active swimmers which inhabited a deeper habitat below the thermocline in an epicontinental sea of perhaps 100 to 250 m water depth the offset of the tex 86 and 18 o bel data is therefore interpreted to reflect temperature signals from two different depth habitats i e the tex 86 is selectively derived from warm sea surface waters and the belemnites likely occupied deeper and cooler waters with relative increasing salinities in the late barremian this study stresses the importance that the taxonomy paleobiology and ecology of the belemnite taxa genera species used for paleotemperature reconstructions must be considered before the 18 o bel signal can be further interpreted the variation of the 18 o signature gained from one belemnite population of 22 specimens by 1 1 suggests that the 18 o data of individual belemnites should be used with caution for reconstructing long termed paleotemperature trends

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

paleohydrogeological and thermal events recorded by fluid inclusions and stable isotopes of diagenetic minerals in lower cretaceous sandstones offshore nova scotia canada upper jurassic lower cretaceous sandstones of the scotian basin offshore eastern canada are important gas reservoirs previous studies of fluid inclusions in jurassic limestones and apatite thermochronology of cretaceous sandstones have suggested a late mesozoic thermal event fluid inclusions in different authigenic cements were analyzed to determine the temperature and composition of basinal fluid at the time of precipitation and the timing of hydrocarbon migration and entrapment fifty one sandstone samples were analyzed for stable isotope composition 18o and 13c of carbonate cements trapping temperatures for primary aqueous inclusions hosted in quartz overgrowths 89 175c and in late carbonate cements 138 173c are higher than predicted by two dimensional modeling from burial alone based on postrift geothermal gradients these inclusions contain high salinity fluids mostly 19 22 wt nacl equivalent second predominantly aqueous inclusions have much lower salinities 5 2 6 7 wt nacl equivalent and some contain liquid hydrocarbons late fe calcite cement in hauterivian sandstone shows negative values of 13 17 to 9 2 whereas cements in deeper and shallower sandstones have higher 13c values these data indicate that high temperature high salinity fluids preceded hydrocarbon migration the oldest and youngest rocks studied show less effect of high temperatures than do rocks that were buried to depths of at least 2 km 1 2 mi after 135 ma and before 100 ma both fluid inclusions and 13c of carbonate cement suggest that highest temperatures were achieved during burial at 115 to 105 ma this early cretaceous thermal event had a geothermal gradient of at least 55c km it is earlier than the previously reported event based on apatite fission tracks but is consistent with the fission track data the event is synchronous with regional evidence of volcanism and its peak coincides with rapid salt tectonic deformation in the deep basin hydrocarbon charge to the outer shelf wells occurred after this thermal event and thus not before the late cretaceous

isotopic evidence for temperature variation during the early cretaceous late ryazanian mid hauterivian oxygen and carbon isotopic compositions have been determined from the belemnite genera acroteuthis and hibolites sampled from the early cretaceous ryazanian hauterivian interval of the speeton clay formation filey bay england the speeton clay formation consists of a series of claystones and calcareous mudrocks deposited in an epicontinental sea 18 o values from belemnites which met petrographic and chemical criteria for well preserved skeletal carbonate indicate warm marine palaeotemperatures c 12 15 c for much of the early valanginian whilst cool temperatures

the valanginian carbon isotope event a first episode of greenhouse climate conditions during the cretaceous lower cretaceous pelagic carbonates outcropping along the southern alps of northern italy provide a record of tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle the carbonate c isotope stratigraphy established at five selected localities in the southern alps allows an accurate picture to be drawn of the duration and amplitude of the valanginian c isotope event 13c values near 1 25 1 50 determined in berriasian and lower valanginian sediments are replaced by more pdsitive 13c values near 3 in the late valanginian the carbonate c isotope excursion ends in the early hauterivian with values fluctuating between 1 5 and 2 the carbonate c isotope excursion is accompanied by a positive excursion in the total organic carbon c isotope curve the valanginian c isotope excursion identified in tethyan sediments correlates with a c isotope excursion recorded in the western north atlantic in the gulf of mexico and in the central pacific dsdp sites 534 391 535 and 167 by analogy with the aptian stage also marked by a significant positive c isotope excursion the time of positive 13c values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments a warm and humid climate possiblycoupled with a high atmospheric co2 content and a high global sea level may have triggered the acceleration of the global carbon cycling in this case the valanginian c isotope event would reflect a first episode of greenhouse earth conditions during the cretaceous

dinocyst stratigraphy of the valanginian aptian rurikfjellet and helvetiafjellet formations on spitsbergen arctic norway