oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index bfoi variations in oceanic primary productivity flux of organic carbon to the sediments and dissolved oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size wall thickness morphology and species composition of assemblages by many foraminiferal paleontologists aspects of these processes should be reflected by the benthic foraminiferal oxygen index bfoi based on these foraminiferal characteristics however analyses indicate that the bfoi correlates most strongly with dissolved oxygen levels in overlying water r2 0 81 weakly with oceanic primary productivity r2 0 55 and weakly with organic carbon flux to the sediments r2 0 51 although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages the bfoi is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in cretaceous and cenozoic oceans

ichnological characteristics of late cretaceous hemipelagic and pelagic sediments in a submarine high around the oae 2 event a case from the rybie section polish carpathians abstract the trace fossils alcyonidiopsis isp chondrites isp small and large palaeophycus isp planolites isp taenidium isp thalassinoides isp zoophycos isp and unnamed small spreite burrow structures have been found in the cenomanian turonian sediments in the rybie section they show significant stratigraphic variations in respect to the bonarelli level in the cenomanian from the base of the section up to just below the bonarelli level the fucoid marl in local lithostratigraphy a decrease in diversity and abundance of trace fossils and benthic foraminifers is present and related mainly to decreasing benthic food levels oxygenation changes have comparatively minor incidence but at least three thin anoxic layers occur about 2 m below the bonarelli level the bonarelli level shows the at least episodically anoxic sedimentation in the turonian part only small chondrites isp and planolites isp rarely occur the burial of organic matter and probably benthic food content was extremely low as revealed by red marls a gradual recovery of environmental conditions is marked by an increase in the diversity and abundance of trace fossils and benthic foraminifers by the turonian when grey marls egocina marl accumulated above the red marls the trends in ichnological record are confirmed by data on benthic foraminifers

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

landscape evolution and slide processes in a glacioisostatic rebound area a combined marine and terrestrial approach thick fine grained nonuniformly stratified deposits along a 20 km stretch coastline have been investigated using a combined marine and terrestrial approach the sediments were deposited rapidly in glaciomarine marine and submarine ice contact environments during the allerod and younger dryas periods rapid glacioisostatic rebound caused extensive modification of the landscape mainly by sliding slides in the area were affected by the bedrock morphology location and sedimentation rate of the glaciomarine sediments isostatic rebound presence of gas fluids in marine sediments and later river incision tides and groundwater flow spatial and temporal distribution of slide deposits in the marine stratigraphy and morphology of submarine and terrestrial features give detailed information of landscape evolution through time this is illustrated by conceptual profiles from three areas that explain the landscape evolution and changing processes during the rebound the most intensive slide activity both in frequencies and volumes and hence the most considerable landscape modification occurred early in the holocene period i e when the relative sea level fell most rapidly

foraminiferal response to sea level change organic flux and oxygen deficiency in the cenomanian of the tarfaya basin southern morocco the mohammed plage coastal section and well s13 in the tarfaya basin southern morocco are key sections to investigate the subsidence of the basin and the cenomanian eustatic sea level history results from a canonical correspondence analysis cca based on benthic foraminiferal assemblage counts and additional proxies percent planktic foraminifera planktic foraminifera morphogroups total organic carbon content toc show a general deepening trend for the investigated sections the most important factor identified in the ordination of species and samples is water depth the cca identifies bolivina anambra globulina lacrima lenticulina spissocostata and spiroplactammina sp as typical shallow water species praebulimina nannina gavelinella dakotensis gavelinella sp saccammina alexanderi and valvulineria lenticula as deep water species and gabonita levis gabonita obesa neobulimina albertensis lingulogavelinella asterigerinoides lenticulina gaultina haplophragmoides gigas haplophragmoides bauchensis and trochammina taylorana as unrestricted or intermediate species the temporal succession of benthic foraminiferal assemblages indicates repeated periods of shallowing within the general deepening trend in particular within the lower portion of the sections rotalipora brotzeni and r reicheli planktic foraminiferal zones restricted assemblages occurred when intensification of the oxygen minimum zone inhibited a diverse benthic community abundant high organic flux indicators at the base of the mohammed plage section indicate that an upwelling cell off northwest africa was already active during the early cenomanian c 2004 elsevier b v all rights reserved

cretaceous oceanic anoxic events and radially elongated chambered planktonic foraminifera paleoecological and paleoceanographic implications chamber elongation is a recurring morphological character in cretaceous and cenozoic planktonic foraminiferal evolution suggesting that the clavate body plan takes advantage through particular environmental conditions cretaceous planktonic foraminifera bearing radially elongated chambers become repeatedly a consistent component of assemblages in correspondence with the deposition of remarkable organic layers that record the effects of oceanic anoxic events oaes due to this apparent correspondence chamber elongation has been recently interpreted as an adaptation to low oxygen levels in the upper water column the paleoceanographic significance of planktonic foraminifera with radially elongated chambers remains however unclear we investigated in great detail the distribution and abundance of elongated chambered planktonic foraminifera in an interval of about 40 myr across the cretaceous oaes in different well dated sections the increased abundance of planktonic foraminifera with elongated chambers can be a markedly evident feature across the faraoni the selli and the bonarelli oaes however each event shows its own peculiarities remarkably the first radiation of the cretaceous elongated chambered morphotypes just predates the latest hauterivian faraoni event the selli event records the greatest diversification number of species of the group bearing elongated chambers however this was a period of great diversification in the planktonic foraminifera this evidence may suggest that radiation of these forms was driven by more than upper water column anoxia per se e g increased upper water column stratification greater productivity and or greater seasonality the albian oae1b oae1c and oae1d display the lowest abundance and diversity of this group conversely according to the available data the first appearances of the species muricohedbergella simplex and of the genus schackoina occur close to the oae1b and oae1d respectively in the italian record the relative abundance of radially elongated chambered forms appears to be larger before the onset of the bonarelli event with respect to the selli event the pattern involving this group across the bonarelli event appears more regular thus indicating that the onset and the end of the oae2 depend on very powerful global factors and are less influenced by local aspects we speculate that the relative abundance of planktonic foraminifera with radially elongated chambers may be proportional to the strength of the environmental perturbation related to the oaes thus reinforcing the idea that the ecological perturbation related to the oae2 was more severe for the former several lines of evidence suggest that water oxygenation could not have been the single controlling factor governing the development of elongate chambers the role of availability of food and the nature of food has been so far probably underestimated it is most likely that an interplay of several influential physical chemical and ecological factors i e dissolved oxygen concentration temperature salinity nutrients type of food trace elements was responsible for such a morphological adaptation we document linkages between the distribution abundance morphometric changes and evolution of the cretaceous radially elongated chambered planktonic foraminifera and the major igneous geological geochemical climate nutrification and biotic events and biocalcification trends

substrate influences on step pool sequences in the christopher creek drainage arizona abstract step pool sequences formed in alluvial and bedrock channel segments of the christopher creek drainage in central arizona suggest that bedform geometries may reflect subtle differences in relative substrate resistance and in the ratio of driving forces to resisting forces three alluvial channel segments and two bedrock channel segments along a 72 km2 drainage and a 4 km2 drainage facilitated comparison across different substrates and hydraulic environments as substrate resistance increased or the ratio of hydraulic driving forces and boundary resisting forces decreased channel gradient increased the ratio of step height to length normalized by gradient decreased and pool dimensions normalized by gradient decreased these changes in bedform geometry suggest that as the ratio of driving to resisting forces increases proportionally more flow energy is dissipated within the flow as turbulence and shearing as in the alluvial reaches rather than being applied to erosion of the channel boundaries

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

upper cretaceous palaeoenvironments and benthonic foraminiferal assemblages of potential source rocks from the western african margin central atlantic abstract upper cretaceous benthonic foraminiferal assemblages clay minerals kerogen types and carbonate microfacies are examined in organic rich sediments from western african coastal basins along a latitudinal transect extending from southern morocco to nigeria samples from onshore sections of the tarfaya basin southern morocco from dsdp site 369 from offshore commercial wells on the casamance shelf senegal from dsdp site 367 from odp site 959 and from onshore sections of the benue trough in nigeria are analysed organic rich sediments from these sites are characterized by smectiterich clay mineral assemblages high amounts of marine organic matter and a typical benthonic foraminiferal biofacies dominated by buliminids and bolivinids benthonic foraminifera provide robust proxy indicators of palaeoproductivity and organic matter flux to the seafloor the palaeobiogeographic distribution of benthonic foraminiferal biofacies can be used to identify areas and stratigraphic intervals of hydrocarbon accumulation lower turonian benthonic foraminiferal assemblages exhibit extremely low diversity and are strongly dominated by a gabonita biofacies in contrast to coniacian to maastrichtian assemblages which display higher diversity and contain numerous species of buliminella praebulimina afrobolivina bolivina and orthokarstenia the palaeobathymetric distribution of these high productivity benthonic foraminiferal biofacies reflects the establishment of a productivity driven oxygen minimum zone along the western african shelf associated with an upwelling system active off coastal africa during most of the late cretaceous the extent of the high productivity equatorial belt appears to have shifted latitudinally during the late cretaceous as sea level and circulation patterns changed the zone of highest productivity was broadest in the early turonian when it coincided with the maximum sea level rise and highest atmospheric temperature in the late cretaceous

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

occurrence and origin of submarine plunge pools at the base of the us continental slope high resolution bathymetric data from the new jersey and californian continental margins show a marked depression running along parts of the base of the continental slope detailed analysis reveals that the depressions are a series of discrete plunge pools with associated downslope topographic ramparts we have used new bathymetric data to create our own data base of over 150 examples and systematically analyse plunge pool morphology and location previous observations of plunge pools have been sparse plunge pools are up to 1100 m wide and 75 m deep with a mean diameter of 400 m and a mean depth of 21 m plunge pools only occur where there are sharp decreases in slope of more than 4 and are well developed where changes in slope exceed 15 we propose plunge pools can be created by two mechanisms firstly they may be due to reduced bed shear stress downstream of hydraulic jumps in submarine sediment laden density flows that causes the deposition of bedload and the creation of a sediment bar this bar then defines the downslope margin of a pool secondly the impact of high momentum sediment laden density flows can excavate a depression as has been observed for subaerial snow avalanches sediment deposited downslope of these impact pools is very poorly sorted and partly derived from erosion within the pool both mechanisms influence whether turbidity currents are generated from high density sediment laden density flows influence whether depositional flows are channelised and have implications for base of slope facies models

cyclic changes in turonian to coniacian planktic foraminiferal assemblages from the tropical atlantic ocean abstract abundance patterns of planktic and benthic foraminifera from a tropical atlantic drill site ocean drilling program site 1259 demerara rise suriname margin display a pronounced 400 kyr cyclicity uninterrupted throughout our 87 8 92 ma record between two clearly distinguishable assemblages 1 a pelagic foraminifer fauna which represents a deep oxygen minimum zone and 2 another assemblage representing a shallow oxygen minimum zone where the foraminifer fauna is dominated by a higher diversity population of mostly small clavate and biserial species common in epicontinental seas the cyclic changes in the long eccentricity band 400 kyr between these two assemblages are proposed to reflect changes in the mean latitudinal position of the intertropical convergence zone itcz associated fluctuations in precipitation and trade wind strength may have influenced the upwelling regime at demerara rise leading to the observed cyclicity of planktic foraminiferal assemblages the severe turonian to coniacian paleoclimatic and paleoceanographic changes in the atlantic ocean e g gateway opening cooling and glaciation however seem to have no influence on the composition of tropical planktic foraminiferal faunas there is no apparent relationship between foraminifer abundances and a major deflection in the stable isotope record interpreted elsewhere as a sign of the growth and decay of a large polar ice sheet

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

assessing pelagic palaeoenvironments using foraminiferal assemblages a case study from the late campanian radotruncana calcarata zone upper cretaceous austrian alps abstract two upper campanian sections in the austrian alps representing the north western tethyan biogeographic realm from either sides of the penninic ocean alpine tethys have been examined aiming at a high resolution assessment of foraminiferal assemblages the postalm section from the northern calcareous alps southern active margin and the oberhehenfeld section from the ultrahelvetics northern passive margin this study focuses on plankton biostratigraphy and foraminiferal palaeoecology of the radotruncana calcarata total range zone the postalm section displays cyclic red deposits with marls and marly limestones while we find uniform grey marls at oberhehenfeld the oberhehenfeld section from the ultrahelvetics can be correlated stratigraphically to the postalm section using foraminifera calcareous nannoplankton and stable isotope stratigraphy and provides a point of comparison from the northern margin of the penninic ocean the two sections show minimal difference in faunal composition and few distinct local stratigraphic signals palaeoenvironmental trends from the late campanian can be recognised relating the two sections from the austrian alps the depositional water depth can be reconstructed as some 500 800 m plankton assemblages show a remarkable stability despite the sudden appearance and disappearance of r calcarata hinting at the late campanian as a time interval of general foraminiferal stasis without significant evolutionary events we speculate that the origin and extinction of r calcarata are related to the prolonged evolution of ocean stratification during the campanian from the mid cretaceous sluggish hothouse during a time of general slow greenhouse climate decline

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

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

warm saline intermediate waters in the cretaceous tropical atlantic ocean during the cretaceous period warm deep and intermediate waters filled the oceans evidence from benthic foraminferal 18o and mg ca ratios suggests that the intermediate water masses in the proto atlantic ocean formed from high salinity waters sinking from shallow shelf seas

stable isotopes and geochemistry of a campanian maastrichtian pelagic succession mudurnu goynuk basin nw turkey implications for palaeoceanography palaeoclimate and sea level fluctuations this study focuses on the palaeoclimatic evolution and relative sea level fluctuations of the northern branch of neotethys during the late campanian early danian the studied succession ismailler section is located in the mudurnu goynuk basin nw turkey and dominated by apparently continuous pelagic muddy deposits stable isotopic and elemental compositions of the mudrocks are investigated in order to evaluate the palaeoceanographic conditions as well as broad tectonic reconstruction of the basin the mudrock geochemistry suggests a tectonic reorganization during late campanian as reflected by a distinct shift from felsic to mafic sediment provenance in the ismailler section five 13c events are identified four or which are well correlatable with major events in other records around the world such as the late campanian event lce campanian maastrictian boundary cmb and the late maastrichtian event lme the relative sea level variations in the basin typically match both short and long term global sea level fluctuations the remaining globally uncorrelatable 13c event does coincide with tectonic uplift and the abrupt negative 13c shift and is inferred to be the result of regional factors the dominance of worldwide events in the records of the relatively restricted ocean branch reflects the strength of global factors

foraminiferal and palynological biostratigraphy and biofacies from a santonian campanian submarine fan system in the voring basin offshore norway abstract foraminiferal assemblages from a santonian campanian submarine fan system in the northwestern voring basin offshore norway were investigated with the primary objectives to document the stratigraphic ranges of foraminiferal taxa calibrated with dinoflagellate cysts and to interpret foraminiferal biofacies of different fan sub environments previously proposed based on the analysis of ichnofossils the assemblages are composed of deep water agglutinated foraminifera dwaf without carbonate cemented taxa dwaf taxa of high biostratigraphic value are absent but the complete agglutinated nature of the assemblages and the presence of gerochammina stanislawi and rectogerochammina eugubina are similar to those of the lower campanian fenestrella bellii zone of the norwegian sea more reliable dating was provided by palynology and the age of the interval is estimated to be santonian to campanian the inner to middle fan assemblages contain small numbers of specimens and consequently the species diversity and relative abundance of morphogroups are inconsistent deep infaunal forms may be more common in this sub environment but because the abundance is low this observation should be treated carefully in contrast the abundance and diversity of the assemblages of the overbank fringe and basin plain sub environments are fairly high their morphogroup composition is also similar and comparable to each other when the assemblage size is large the assemblage from the interval with suggested hydrothermal activity is similar to those from outside the channel sub environment the presence of bottom water currents possibly in the form of a western boundary current in the basin is suggested based on the abundant occurrence of tubular forms in the overbank fringe and basin plain sub environments

the seismicity geomorphology and structural evolution of the corinth area of greece in the eastern gulf of corinth geological structure is closely reflected in the topography in the 1981 corinth earthquakes ground deformation accentuated existing geomorphological patterns we explore the relationship between seismicity and landforms in space and time the area examined extends beyond the epicentral region of the 1981 events and its evolution is traced over the last 40000 years to understand the relation between deep and superficial structures we discuss processes that occurred in the 1981 earthquakes and go on to propose that surface faulting appears only above linear faults at depth that move in earthquakes with magnitudes m s greater than six where faults at depth intersect or bend the faulting becomes distributed and prim ary faulting does not reach the surface here the surface manifestation of faulting at depth is surface folding and secondary faulting such regions are identified in maps of the eastern gulf of corinth evidence for the evolution of the fault systems is provided by eyewitness accounts of shoreline changes following the recent earthquakes historical and archaeological data pertaining to old sea levels and 14 c dates for molluscs collected from fossil shorelines the results of these studies broadly confirm an earlier view of j a jackson et al earth planet sci lett 57 377 397 1982 that motion has shifted from faulting south of the city of corinth to faulting in the perachora peninsula but the transfer is not complete areas lying between the two fault systems have moved up and down in historical and archaeological times indicating that both systems are still active the evidence for activity of the northern system points to a repeat time of 300 years for earthquakes com parable with those of 1981 the work discussed in this paper suggests that some of the features previously described as m arine terraces are fault controlled continental surfaces furtherm ore beach deposits at a num ber of different levels long regarded as successive shorelines are in fact contemporaneous the critical ages were obtained by radiocarbon dating of shell carbonate a technique which yields dependable results if applied to samples which have been carefully selected and pretreated palaeontological dating of the terraces in contrast is found to be misleading because the faunas are environm entally controlled and consequently diachronous

quaternary deformation of the isthmus and gulf of corinthos greece interdisciplinary data suggest that the quaternary late holocene and present day deformation patterns of the isthmus of corinthos greece are very similar and can be compared to a platelike body under torsion this hypothesis is consistent with the vertical differential motions observed in the adjacent corinthiakos gulf a possible explanation is that the back arc compressional zone is much wider than formerly believed and extends to an area of normal faulting parallel to the direction of the compression this stress field produces a central bulging in the southern coast and a depression in the northern coast of the corinthiakos gulf the easternmost ends of this depression and bulging are the southern and northern parts of the isthmus tilted to the east and to the west respectively

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 four sections documenting the impact of the late cenomanian oceanic anoxic event oae 2 were studied in basins with different paleoenvironmental regimes accumulation rates of phosphorus p bound to iron organic matter and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of oae 2 with an associated increase in 13 c values accumulation rates of p return to preexcursion values in the interval where the 13 c record reaches its fi rst maximum an offset in time between the maximum in p accumulation and peaks in organic carbon burial hydrogen indices and corg preact molar ratios is explained by the evolution of oae 2 in the following steps 1 an increase in productivity increased the fl ux of organic matter and p into the sediments the preservation of organic matter was low and its oxidation released p which was predominantly mineralized 2 enhanced productivity and oxidation of organic matter created dysoxic bottom waters the preservation potential for organic matter increased whereas the sediment retention potential for p decreased 3 the latter effect sustained high primary productivity which led to an increase in the abundance of free oxygen in the ocean and atmosphere system after the sequestration of co 2 in the form of black shales this oxygen helped push the ocean back into equilibrium terminating black shale deposition and removing bioavailable p from the water column

paleoceanographic changes at the northern tethyan margin during the cenomanian turonian oceanic anoxic event oae 2 abstract the late cenomanian early turonian oceanic anoxic event oae 2 represents major paleoceanographic and faunal perturbations samples from the northern tethyan margin rehkogelgraben eastern alps were investigated in order to trace the paleoceanographic processes paleoecologic conditions were reconstructed by combining the results of assemblage counts of indicative microfossil groups foraminifera and radiolaria assemblages size distributions and abundances show a tripartite subdivision for surface and bottom waters 1 oligotrophic surface conditions and oxic bottom waters with a reasonably high food supply for the late cenomanian interval 2 an oae period with black shales characterized by very low numbers but high diversities and a lack of high productivity indicators among planktic foraminifera low abundances of small sized benthic foraminifera indicate low oxic dysoxic conditions at the seafloor 3 post oae assemblages are characterized by mesotrophic planktic species and benthic foraminifera suggest oxic bottom waters it took about 300 ky to re establish a pelagic carbonate producing regime the semi enclosed basin situation of the penninic ocean is thought to be responsible for differences between the high productivity in the world ocean during the oae 2 and the overall absence of high productivity indicators and high foraminiferal diversities at rehkogelgraben the penninic ocean may have even served as a refuge during the environmental crisis

strength development with burial in fine grained sediments from the saguenay fjord quebec following a sedimentological and geotechnical investigation two main types of materials were identified in the saguenay fjord 1 organic rich sediments deposited by continuous sedimentation and 2 unbioturbated sediments deposited rapidly by episodic events the consolidation state of sediments with depth were analysed in all subsurface deposits sediments are overconsolidated irrespective of the depositional processes however in continuously deposited sediments strength develops more rapidly than in turbidites or mass flows in the surficial bioturbated layer strength and liquidity index gradients are at a maximum and the rate of strength variation can reach values as high as 9 kpa kpa results from one dimensional creep tests suggest that in the organic poor turbidites the strength development is controlled at least partly by thixotropic strengthening for bioturbated clays it appears that the viscosity and the aggregating potential of organic matter controls the evolution of the strength

development of the submarine channel in front of the nidelva river trondheimsfjorden norway abstract the nidelva submarine channel is a 4 km long and up to 100 m deep erosional feature seaward of a former outlet of the river nidelva in trondheimsfjorden norway mechanisms of channel evolution and sedimentary processes associated to its development are revealed by analyzing the sea bed morphology and the stratigraphy of the fjord sediments based on high resolution seismic data swath bathymetry imaging and gravity cores seismic data suggest that the submarine channel is eroded into late pleistocene clays filling a bedrock depression a thick holocene deltaic succession overlay the glacio marine clays seismic facies suggest that turbidity currents likely initiated downcutting of the channel in the early holocene these flows were guided by sea bed morphology and bedrock exposures favouring confluence and acceleration the area was subjected to glacio isostatic rebound and rapid fall of relative sea level in the holocene this resulted in a fast delta progradation likely with an enhanced activity of delta derived sediment gravity flows promoting incision in mid to late holocene such flows including hyperpycnal flows were responsible for deep incision of the channel laminated clay rich beds are interpreted as deposited by the overspill of turbiditic flows along the channel and likely originate from large terrestrial quick clay slides in the last 2000 years erosive flows initiated by mass wasting along the coast controlled the evolution of the channel after the mouth of the nidelva river moved to a more easterly position in the embayment present slope failure along the channel flanks seems to be controlled by the distribution of the laminated clay rich layers in the stratigraphy

disaster opportunists guembelitrinidae index for environmental catastrophes blooms of the disaster opportunist guembelitria species are proxies for environmental catastrophes whether impact or volcanism leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions during the late maastrichtian and early danian zones p0 and pla guembelitria blooms show global distributions but with the largest blooms 40 80 guembelitria in low and middle latitudes and only minor blooms 10 20 in high latitudes late maastrichtian guembelitria blooms are so far known from the indian ocean and eastern tethys the most intense guembelitria blooms 60 guembelitria occurred in shallow continental shelf areas slope shelf margins and volcanic provinces of the indian ocean what these environments have in common is high nutrient influx eutrophication either from continental runoff upwelling along continental margins or volcanic input at times of biotic crises guembelitria blooms may have spread rapidly to the exclusion of most or all other species much like today s red tides but with near global distributions a simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species within such highly stressed environments guembelitria is the only genus to thrive and without competition rapidly reproduce and exponentially increase their populations when nutrients are depleted populations rapidly decrease leading to ecologic niches for other generalists and ecosystem recovery small low o2 tolerant heterohelicid populations mark this second stage followed by small trochospiral and planispiral species with further environmental recovery increasing competition niche development and restoration of a well stratified water mass oligotrophic conditions are restored opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages this ecological succession is observed in association with mantle plume volcanism in the indian ocean and eastern tethys during the late maastrichtian and in association with the k t impact and volcanism during the early tertiary d 2004 elsevier b v all rights reserved

the terraces of corinth gerrce a detailed record of eustatic sea level variations during the last 500 000 years abstract between corinth and xylokastro 20 marine terraces reflect the interaction of the northern peloponnese uplift and the global eustatic sea level fluctuations during the last 500 000 years correlation of the terraces with oxygen isotope records in deep sea cores allowed accurate dating of these fossilized transgressive shorelines curves of altitude versus age have been plotted they show a regular decrease of the uplift rate and a frequent return of the sea level very close to the present day one not only during the interglacial periods 5 7 9 11 13 but also during glacial periods 3 1 3 3 6 8 the alternative would be to suppose very complicated and highly improbable vertical movements of the substratum to explain the regularity of the curves the rhythm of these high sea levels is around 20 30 ka since at least 330 000 years ago

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

the influence of the san gregorio fault on the morphology of monterey canyon abstract a side scan sonar survey was conducted of monterey canyon and the san gregorio fault zone off shore of monterey bay the acoustic character and morphology of the sonar images enhanced by seabeam bathymetry show the path of the san gregorio fault zone across the shelf upper slope and monterey canyon high backscatter linear features a few kilometers long and 100 to 200 m wide delineate the sea floor expression of the fault zone on the shelf previous studies have shown that brachiopod pavements and carbonate crusts are the source of the lineations backscatter in monterey canyon the fault zone occurs where the path of the canyon makes a sharp bend from wnw to ssw 1800 m here the fault is marked by nw se trending high reflectivity lineations that cross the canyon floor between 1850 m and 1900 m the lineations can be traced to ridges on the northwestern canyon wall where they have 15 m of relief above the low relief ridges bowl shaped features have been excavated on the canyon wall contributing to the widening of the canyon we suggest that shear along the san gregorio fault has led to the formation of the low relief ridges near the canyon wall and that carbonate crusts as along the shelf may be the source of the high backscatter features on the canyon floor the path of the fault zone across the upper slope is marked by elongated tributary canyons with high backscatter floors and u shaped cross sectional profiles linear features and stepped scarps suggestive of recent crustal movement and mass wasting occur on the walls and floors of these canyons three magnitude 4 earthquakes have occurred within the last 30 years in the vicinity of the canyons that may have contributed to the observed features as shown by others motion along the fault zone has juxtaposed diverse lithologies that outcrop on the canyon walls gully morphology and the canyon s drainage patterns have been influenced by the substrate into which the gullies have formed

bioevents and redox conditions around the cenomanian turonian anoxic event in central mexico abstract the xilitla section of central mexico western margin of the proto north atlantic is characterized by pelagic sediments enriched in marine organic matter using biostratigraphic and radiometric data it was dated at the latest cenomanian earliest turonian transition we identified an interval coeval with the faunal turnover associated with the oceanic anoxic event 2 oae 2 recording the heterohelix shift and the filament event for the first time in mexico an integral analysis of sedimentary facies pyrite and geochemical proxies reveals vertically variable redox conditions with prevailing anoxic to dysoxic bottom waters along with phosphorous and manganese depletion the highest content of total organic carbon and of certain redox sensitive trace elements rstes is found during part of the anoxic event confirming more uniform and constant oxygen depleted conditions this interval is also characterized by a significant enrichment in biogenic barium and elevated toc ntot ratios suggesting a link between productivity and anoxia sulfur isotope fractionation has a maximum value within the anoxic event favored by the increase in the flux of organic matter and intensified through sulfur recycling highly bioturbated beds representing short lived episodes of oxic conditions are intermittent within the oae 2 and become more frequent in the early turonian this study proposes a model similar to that of modern upwelling regions high marine productivity controlled organic matter burial and oxygenation at the seafloor varying between anoxic laminated facies with small pyrite framboids and dysoxic conditions bedding parallel bioturbated facies with inoceramid bivalves and large pyrite framboids interrupted by short term well oxygenated episodes thoroughly bioturbated facies with common benthic foraminifera general low oxygen conditions led to the formation of glauconite and pyrite bacterially mediated the enrichment of redox sensitive trace elements in sediments cd zn v and cr scavenged by organic matter and ni mo pb co and re by pyrite and resulted in mn and p depletion

orbital scale record of the late cenomanian turonian oceanic anoxic event oae 2 in the tarfaya basin morocco high sedimentation rates up to 12 cm kyear of laminated organic carbon rich biogenic limestones in the tarfaya basin provide an unusually high millennial resolution record of the late cenomanian oceanic anoxic event oae 2 the global positive carbon isotope excursion across the cenomanian turonian corresponds to 11 light dark sedimentary cycles we interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle on this time scale the main increase in delta 13 c values occurred over a short time interval of less than 20 kyear in the late cenomanian and reached a first maximum approximately 15 kyear prior to the bulk mainly coccoliths delta 18 o derived sea surface maximum temperature that occurs coeval to the extinction of rotalipora cushmani organic carbon accumulation rates follow obliquity cycles reaching a maximum approximately 10 kyear after the last occurrence of r cushmani then slowly decreasing during the early turonian thus the maximum temperature and the maximum organic carbon accumulation in the tarfaya basin lagged by at least 15 kyear behind the global carbon isotope shift and a proposed reduction of atmospheric co 2 content the climate change across the cenomanian turonian boundary probably occurred independent of co 2 levels and may have been controlled by different greenhouse gases water vapour and methane and changes in ocean circulation i e opening of the equatorial atlantic gateway

the biotic response to the late cenomanian oceanic anoxic event integrated evidence from dover se england the late cenomanian sea level rise was coupled with an expansion of the oxygen minimum zone the position of its upper surface may be discerned from the sequential effects on the benthonic and planktonic biota

palaeoecology of the biserial planktonic foraminifer heterohelix moremani cushman in the late albian to middle turonian circum north atlantic abstract the cretaceous heterohelix moremani cushman was the only biserial planktonic foraminiferal species from its first appearance in the late albian up to the cenomanian turonian boundary within that time it increased gradually in abundance relative to other planktonic foraminifera in five circum north atlantic sections it is generally rare in upper albian sediments common in most of the cenomanian and very abundant in sediments representing the latest cenomanian oceanic anoxic event short term variations on the overall abundance trend correlate with positive excursions in the bulk carbonate 13c record maximum rain rates of h moremani during oae2 show that this species was an opportunist that did well in extreme conditions but its overall distribution indicates that it is not necessarily a marker for very high palaeoproductivity environments stable oxygen and carbon isotope measurements on foraminiferal species indicate that h moremani was a surface water dweller at least in part of its geographic range but incorporated 13c out of equilibrium with ambient seawater it is depleted in 13c relative to other planktonic foraminifera which is attributed to vital effects related to its opportunistic character

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

the cenomanian turonian extinction and oceanic anoxic event evidence from southern tibet deep shelf locations on the perigondwanan margin of southern tibet record a major extinction of foraminifera and calcareous nannoplankton in the latest cenomanian top of the rotalipora cushmani zone this is followed by a low diversity survival interval that straddles the cenomanian turonian boundary whiteinella archaeocretacea zone during which only low diversity surface water dwelling foraminifera and nannoplankton and microfilaments are present rapid recovery in the early turonian saw the appearance of new species the reappearance of many lazarus species and the reestablishment of a diverse community of planktonic foraminifera that included a range of shallow to deep water column dwellers the extinction and survival intervals coincide with the development of dysaerobic facies characterised by small sized burrows and moderately large sized framboid pyrite populations at no time does the water column appear to have become sulfidic this study indicates that the end cenomanian oceanic anoxic and extinction events were also manifested in moderately high southerly palaeolatitudes on the southern margin of the tethyan ocean thereby increasing the known extent of this global event albeit with the proviso that the anoxic event was a dysoxic one

further evidence for the development of photic zone euxinic conditions during mesozoic oceanic anoxic events periods in earth history characterized by extensive organic carbon deposition so called oceanic anoxic events oaes are the subject of considerable scrutiny insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene a carotenoid found only in green sulphur bacteria and thus indicative of photic zone euxinia i e a water column containing free h 2 s in north atlantic deep sea sediments deposited during the cenomanian turonian boundary oae2 bonarelli event in this study we have used the distributions of chlorophyll and bacteriochlorophyll degradation products maleimides 1 h pyrrole 2 5 diones and high molecular weight porphyrins to examine further the cenomanian turonian boundary oae2 as well as other oaes of the early toarcian posidonienschiefer event and early aptian selli event in particular methyl isobutyl me i bu maleimide on structural grounds appears to be diagnostic of green sulphur bacteria this compound occurs in five of seven examined marls that record the early toarcian oae marche umbria italy further expanding the geographical range of toarcian sediments where evidence for photic zone euxinic conditions has been found me i bu maleimide occurs in three of six black shales spanning the livello selli marche umbria italy the type locality for the aptian oae1a providing the first evidence for photic zone euxinic conditions during this event with respect to the cenomanian turonian oae maleimide evidence for photic zone euxinic conditions was found in all the north atlantic sites investigated including those characterized by relatively organic lean sediments several tethyan sites and one site off western australia these data indicate that euxinic conditions were common in the water column during mesozoic oceanic anoxic events

ocean current intensification during the cretaceous oceanic anoxic event 2 evidence from the northern tethys mesozoic oceanic anoxic events oaes are expressions of major physical oceanographic changes at times of perturbation of the global carbon cycle a northern tethyan record of oae2 is preserved in expanded cenomanian turonian pelagic limestone sections seewen formation in eastern switzerland the new carbonate carbon isotope stratigraphy extracted from these limestones demonstrates that the oae2 is condensed in all the studied successions and only the onset of the 13c excursion 5 0 is present the condensed interval is characterized by dissolution features which are filled by a glauconite quartz sandstone this bed is overlain by a well sorted sandstone with intercalated limestone pebbles gotzis member which can be compared with palimpsest sands forming today along current swept shelves the wide distribution of this thin sandstone layer within oae2 indicates that an intense erosive east west trending shelf current was active during the highest sea level and most extreme carbon cycle perturbation of the oae2

low latitude sea surface temperatures for the mid cretaceous and the evolution of planktic foraminifera isotopic data from exceptionally well preserved foraminifera show that the subtropical north atlantic had sea surface temperatures ssts between 30 and 31 c during the late albian and early cenomanian these temperatures were warmer than average modern temperatures in the tropical western atlantic and support previous inferences based on diagenetically suspect material of albian tropical ssts of 30 c this finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle cretaceous greenhouse however our data do not support the concept of a super tethyan region of hypersaline waters in the western north atlantic during late albian and early cenomanian time because seawater salinities substantially higher than modern ones would require significantly higher ssts than those reported here isotopic analysis of mid cretaceous planktic foraminifera shows that planomalina ticinella and biticinella grew in surface waters and provide isotopic proxies for sst whereas deeper growing species include hedbergella rotalipora and praeglobotruncana none of these taxa display isotopic indications of photosymbiosis suggesting that this ecology did not evolve in planktic foraminifera before the late cretaceous contrary to previous hypotheses none of these species increased their depth habitat during their life cycles unlike many extant planktic foraminifera the rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles

the depth dependency of planktonic benthic foraminiferal ratios constraints and applications abstract study of the ratio between planktonic and benthic foraminifera in a great number of areas shows that variation of this ratio with depth can be described using organic matter flux equations essentially the share of benthic foraminifera in the total association is inversely proportional to depth as is the amount of organic matter resulting from primary productivity reaching the sea bottom variation in the p b ratio from area to area appears to be strongly dependent on the amount of inbenthic living foraminifera if the ratios are corrected for this the regressions between the proportion of planktonic foraminifera p and depth appear to be near identical in the gulf of mexico the gulf of california the west coast of the usa and the adriatic sea this regression can be described by depth e 3 58718 0 03534 p a study of the behaviour of this function in nine cores from the adriatic upper quaternary reveals that the palaeodepth reconstructions are not influenced by fluctuations in productivity and temperature but that they are significantly influenced by redeposition of fine grained deposits

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

water film in liquefied sand and its effect on lateral spread a one dimensional 1d saturated sand layer of 2 m in thickness in which a silt seam is sandwiched is liquefied by an instant shock it is found that a water film is easily formed beneath the silt seam with a thickness as thin as a few millimeters just after liquefaction in loose sand and that the film lasts longer than the postliquefaction settlement the effect of the water film on pore pressure distribution and sand settlement is intensively studied one gram shake table tests are then carried out for 2d models with or without seams of silt within a saturated sand layer in the former case water films formed beneath silt seams just after liquefaction enable the soil mass above them to glide because of an unbalanced force along the water films not only during but also after shaking in the latter case the soil deforms continuously mostly during shaking and stops afterward thus a significnat effect of water films formed beneath thin low permeability sublayers in a liquefied loose sand on the failure mode and timing in lateral spread is clearly demonstrated by these simple model tests

orbital time scale and new c isotope record for cenomanian turonian boundary stratotype previous time scales for the cenomanian turonian boundary ctb interval containing oceanic anoxic event ii oae ii vary by a factor of three in this paper we present a new orbital time scale for the ctb stratotype established independently of radiometric biostratigraphic or geochemical data sets update revisions of ctb biostratigraphic zonation and provide a new detailed carbon isotopic record for the ctb study interval the orbital time scale allows an independent assessment of basal biozone ages relative to the new ctb date of 93 55 ma gts04 the d 13 corg data document the abrupt onset of oae ii significant variability in d 13 corg values and values enriched to almost 222 these new data underscore the difficulty in defining oae ii termination using the new isotope curve and time scale estimates of oae ii duration can be determined and exported to other sites based on integration of well established chemostratigraphic and biostratigraphic datums the new data will allow more accurate calculations of biogeochemical and paleobiologic rates across the ctb