phytodetritus entering the benthic boundary layer and aggregated on the sea floor in the abyssal ne pacific macro and microscopic composition abstract phytodetritus which can originate in surface waters following seasonal phytoplankton blooms is considered to be an important food resource for abyssal fauna we analyzed the composition of phytodetritus sampled discretely in situ at an abyssal station in the ne pacific the phytodetritus was collected during two time periods straddling a seasonal maximum in the flux of particulate matter into a sediment trap moored within the benthic boundary layer using the sediment trap record and concurrent time lapse photographs of the sea floor in addition to the results for the composition of sea floor phytodetritus we created a scenario for the origin accumulation and degradation of phytodetritus at the study site it appeared that the sediment trap record did not entirely account for the accumulation and composition of phytodetritus on the sea floor likely due to the undersampling of large sinking aggregates by the sediment trap within each sea floor sampling period two types of aggregated phytodetritus were identified based on macroscopic appearance loosely or strongly cohesive the loosely cohesive phyto detritus collected just before the maximum sinking flux was flocculent and contained large numbers of chain forming diatoms the bulk of the loosely cohesive phytodetritus collected one month later consisted of phaeodarians that appeared to have entrained both older and new diatom floc material the strongly cohesive discrete aggregates collected during both sampling periods appeared to be derived from zooplankton mucous webs although samples within each time period were heterogeneous microscopic composition of phytodetritus in terms of several phytoplankton and protozooplankton components differed significantly between sampling periods these results suggest that phytodetritus can change dramatically over a short time period this may have implications for the potential food resource and feeding behavior of abyssal fauna

correction to an extensive region of off ridge normal faulting earthquakes in the southern indian ocean by eric a bergman john l nabelek and sean c solomon

could the conventionally known abu roash g reservoir upper cenomanian be a promising active hydrocarbon source in the extreme northwestern part of egypt palynofacies palaeoenvironmental and organic geochemical answers abstract in different areas of the western desert of egypt the abu roash g member exhibits either a reservoir or source affinity thus thirteen cutting samples covering the abu roash g member were selected from the nest 1a well at matruh basin to investigate its hydrocarbon source potential palynological age dating of the section that is calibrated with foraminifera and ostracodes enabled a proper identification of the g member detailed analysis of the vertical distribution of particulate organic matter of this member shows two palynofacies types pf 1 reflects an outer middle shelf depositional environment of prevailed reducing suboxic anoxic conditions for the organic rich shales of the lower g member samples 1 8 while pf 2 reflects a minor regression that resulted in deposition of another organic rich shales of the upper g member samples 9 13 in an inner middle shelf setting under the same prevailing reducing suboxic anoxic conditions organic geochemical analysis reveals good to very good potential of the g member as a hydrocarbon source rock 1 8 2 41 avg 2 15 total organic content wt it also shows good to very good petroleum potential pp 4 8 11 avg 8 mg hc g rock pyrolsis and palynofacies analyses show kerogen type ii for the lower g member samples 1 8 which is characterized by high hydrogen index hi 396 and 329 mg hc g toc at depths 1500 and 1560 m and very high dominance of oil prone material amorphous organic matter aom marine palynomorphs and sporomorphs and very rare occurrence of gas prone material brown phytoclasts the upper g member samples 9 13 shows kerogen type ii iii which is characterized by a lower hi value of 213 mg hc g toc at depth 1340 m and it contains fewer amounts of gas prone material and relatively lower aom and marine palynomorphs in comparison to the upper g member maturation parameters t max 430 433 c production index pi 0 1 mg hc g rock and thermal alteration index tai 2 indicate the lower g member has already entered the early oil window kitchen and it is expected to produce oil the upper g member is expected to produce only oil with no gas shows because it is marginally mature t max 426 c pi 0 2 tai 2 the source potential index spi 5 3 t hc m 2 of the g member shows it as currently generating moderate quantities of oil in the area of nest 1a well consequently the organic rich shales of the g member are suggested here as a promising active oil source rock in that extreme northwestern part of the western desert of egypt however for commercial oil recovery from the abu roash g member it is highly recommended to explore the depocentre of matruh basin at about 150 km east the nest 1a well

ostracoda and palaeo oxygen levels with particular reference to the upper cretaceous of east anglia abstract it has been shown that the percentage of platycopina the sole remaining group of filter feeding ostracoda since the global extinction of the metacopina in the lower toarcian making up a fossil ostracod fauna can be used as a measure of dissolved oxygen in past oceans high levels of platycopids indicate low oxygen and vice versa a new scale is introduced here based mainly on the environmental oxygen levels of modern oceans and their equivalent percentages of living platycopids in order to evaluate the palaeo oxygen levels of the upper chalk in east anglia the effects of varying oxygen concentrations on the overall simple species diversity of the ostracoda is also shown to have important palaeoenvironmental implications the study is based on 79 samples from the santonian to lower maastrichtian of the trunch borehole and 126 samples from outcrops in suffolk and norfolk ranging from the coniacian to lower maastrichtian the coniacian is shown to have been a time of low to very low oxygen except for its upper part that was much better ventilated the santonian and lower campanian were low to very low in their dissolved oxygen while the upper campanian and particularly the lower maastrichtian had much higher oxygen levels notwithstanding these general trends oxygen levels appear to have fluctuated rapidly throughout the interval during times of both generally low and high oxygenation these variations in oxygenation are thought to have been associated with the oxygen minimum zone and its migrations onto the continental shelf and subsequent retreat to the continental slope this in turn is related to sea level fluctuations and this together with the potential for the application of this technique to sequence stratigraphy are discussed

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

reconstruction of outer shelf paleoenvironments in the turonian coniacian of southeast france micropaleontology sedimentology abstract micropaleontological analysis and sedimentological studies were undertaken on the turonian to the coniacian strata of the western part of the vocontian basin near nyons southeast france in order to understand the evolution of paleoenvironments microfacies examination shows an alternation of two types of deposits 1 sediments dominated by abundant sponge spicules echinoderm fragments and quartz packstones wackestones suggesting a shallow water environment and 2 sediments dominated by abundant calcispheres and planktic foraminifera providing evidence of a deeper water environment the biostratigraphy is based on a systematic analysis of planktic foraminifera about 50 taxa the first appearance of dicarinella primitiva associated with marginotruncana tarfayaensis and marginotruncana sinuosa indicates the beginning of the coniacian ostracoda corroborate the coniacian age given by planktic foraminifera amongst the benthic foraminifera nodosariidae verneuilinidae and eggerellidae are the most common families represented by the fauna the qualitative and quantitative changes of benthic and planktic foraminifera population parameters provide precise information about the paleoenvironmental conditions paleobathymetry sediment composition dissolved oxygen the biological system reflects high frequency sea level fluctuations a possible glacially and or tectonically induced mechanism is discussed in order to explain this kind of variations

late cretaceous cenozoic climatic variations of the northern antarctic peninsula new geochemical evidence and review aptian to pliocene time series of x ray fluorescence data from the antarctic peninsula are used to assess the degree of chemical weathering and maturity of sediments deposited prior and subsequent to the establishment of glaciation in west antarctica a continuous palaeoclimatic signal is inferred from comparing the results with previously published palaeotemperature and palaeobotanical data aptian cenomanian warm cool and santonian early paleocene warm cold cycles were followed by the global late paleocene early eocene climatic optimum subsequent steady decline in temperatures resulted in glacial conditions in the northern antarctic peninsula by early oligocene time under alternating cenozoic frigid cold climates and in sedimentary regimes dominated by physical weathering geochemical signatures were primarily indicative of provenance the development of cretaceous arboreal vegetation in the northern antarctic peninsula can be correlated with the major climatic cycles

ostracod response to habitat change in an early aptian shelf sea abstract changes in ostracod assemblage composition from the lower aptian of the lower saxony basin germany are investigated to estimate their potential as proxies for palaeoenvironmental habitat changes in an epicontinental setting the studied palaeoenvironmental factors include oxygen depletion increasing temperatures during oae 1a and an increasing water depth caused by the supra regionally recorded early aptian transgression in the late early aptian a distinct short term decrease of water depth is inferred five ostracod associations are recognized two are characterized by a unique composition of species and three are unique by dominance of certain species the stratigraphic record is unique for one association all other associations are exclusively occurring in short intervals of the section but are co occurring with the sub and superjacent ostracod association we observe a change from veeniacythereis acrocythere dolocythere dominated to cytherella dominated associations initiating well before oae 1a and ending slightly before the upper limit of oae 1a most likely triggered by increasing temperatures and affected by increasing water depth changing water depth proved to be the most important factor affecting the successive appearance of ostracod associations moreover ostracod associations change in dominance from cytherella to pontocyprella schuleridea and finally to neocythere dominated faunas parallel to an increasing water depth a re establishment of palaeoenvironmental conditions typical for the veeniacythereis dolocythere dominated association gave rise to a saxocythere batavocythere dominated replacement association although ostracods are very sensitive organisms with respect to oxygen deficiency the oxygen depletion during oae 1a was not a major factor for changing ostracod associations during black shale deposition ostracods vanished completely a recognized change in associations started before the anoxic period and ended afterwards high resolution ostracod studies appeared to be a very powerful proxy for changing water depth temperature and oxygenation in early cretaceous epicontinental settings like the lower saxony basin

testing the climatic significance of dropstones an example from southeast spain dropstones are clasts which pose a hydrodynamic paradox or which have an exotic lithology with uncertain provenance dropstones are usually associated with glacial processes and have recently been used to substantiate the presence of cool climatic phases in the geological record the aim of this paper is to demonstrate using an example from southeast spain that dropstones can be unreliable palaeoclimatic indicators and that greater care is required in their interpretation

integrated palynological organic geochemical and sequence stratigraphic analyses of the middle to upper cenomanian hydrocarbon reservoir source abu roash g member a depositional model in northwestern egypt abstract the current investigation provides further insight into the petroliferous characteristics of the abu roash g member which is regarded as an important rock unit for the egyptian oil industry forty seven samples covering the g member were selected from the bed 14 1 and bed 2 4 wells in the abu gharadig basin and from the abu tunis 1x well in the matruh basin both of which are located in the north western desert an independent dating of the g rocks of bed 2 4 by benthic foraminifera and ostracods in addition to palynological dating suggests a middle late cenomanian age and provides the biochronostratigraphic framework for the sequence stratigraphic analysis analysis of the vertical distribution of particulate organic matter defines three palynofacies types pf pf 1 represents the basal g where shales of the bed wells and calcareous shale of abu tunis 1x were deposited during a relative sea level rise in an outer middle shelf environment that experienced a notable high primary productivity prevailing reducing suboxic anoxic conditions supported preservation of very high amounts of amorphous organic matter aom in pf 1 pf 2 is equated to shales of the middle g of bed 14 1 and bed 2 4 and to calcareous shales and limestone of the upper g in abu tunis 1x pf 2 was deposited during a relative sea level fall in an inner middle shelf setting under better developed suboxic anoxic conditions pf 3 corresponds to the upper g of bed 14 1 and bed 2 4 and represents the shallowest setting where sandy and silty shales were deposited during a pronounced sea level fall in an inner shelf environment the same suboxic anoxic conditions were prevailing during deposition of pf 3 three bioevents were recorded which could be of palaeoecological and or biostratigraphic significance these are senegalinium aenigmaticum dinopterygium cladoides peak dinopterygium cladoides dinopterygium alatum peak and an acme of classopollis brasiliensis sequence stratigraphy of a transect of the four studied sections was carried out to understand the response of the particulate organic matter distribution and depositional system to the sea level changes three third order depositional genetic sequences were recognized and correlated with the global sea level curve kce 2 kce 3 and kce 4 the early highstand systems tract ehst of the genetically related kce 3 in all wells is characterized by relatively rich organic matter where combined remarkably low water circulation and insignificant dilution of organic matter with coarse terrigenous material probably supported good preservation of organic matter spatial distribution of the g rocks shows lateral facies changes this was inferred from sedimentation of an organic poor avg 0 8 toc wt coarse clastic sandy shales facies in the studied area in abu gharadig basin sedimentation changes laterally into a northeast and northwest organic rich finer clastic shale calcareous shales and argillaceous limestone facies in the western matruh basin the robust anoxic conditions and very low dilution of organic matter by terrigenous influx enhanced the organic richness avg 2 4 toc wt of these rocks which resulted in the formation of promising hydrocarbon source rocks thus for a successful hydrocarbon exploration in the north western desert the promising source section of the g member would be associated with shales calcareous shales and argillaceous limestone lithologies its depositional environment is mainly confined to outer middle and inner middle shelf settings that have widespread suboxic anoxic conditions and show ehst pattern in contrast the regressive intervals that are denoted by the lowstand systems tract lst and or the late hst lhst typify the relatively coarse clastics as good quality reservoir rocks that are characterized by poor organic richness due to dilution with terrigenous influx

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

ostracoda and dysaerobia in the lower jurassic of wales the reconstruction of past oxygen levels abstract the ostracoda are a subclass of small crustacea which inhabit most aquatic environments they have been recorded from the cambrian through to the recent the biology of one group of marine ostracoda the platycopina triassic recent enables them to better withstand decreased levels of dissolved oxygen in their immediate environment than other ostracods study of a number of geological sections has already shown that this suborder often dominates stratigraphical intervals which are considered to be representative of dysaerobic conditions in the light of this work the changing faunal composition of the lower jurassic of the mochras borehole wales is interpreted as a series of environmental changes which include fluctuating oxygen levels the degree of dysaerobia is assessed and its effect on the rate of faunal turnover is discussed

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

a late early albian marine transgressive pulse over northeastern australia precursor to epeiric basin anoxia foraminiferal evidence abstract a major transgressive pulse occurred during the late early albian in the western papuan basin and totally changed the character of foraminiferal faunas in the basin from impoverished agglutinated dominated assemblages to diverse calcareous assemblages a similar change is reflected in coeval deposits of other basins on the northeastern margin of the australian continent laura basin and northern carpentaria basin and to a lesser extent in the intracratonic eromanga and surat basins this pulse preceded the condensed section of the toolebuc formation in the eromanga basin of late middle albian to early late albian age and succeeded deposition of the first radiolarian rich units late aptian in all basins a rapid marine regression took place in the western papuan basin immediately after the latest albian 95 ma and reflected the final retreat of marine conditions in the intracratonic basins to the south foraminiferal biofacies indicate that the late early albian transgressive pulse resulted in peak sea levels in all basins between 200 m and 500 m deep along the northern edge of the cretaceous continent northern papuan basin decreasing to about 150 m in the northern carpentaria basin and the laura basin and to 50 100 m in the southeastern carpentaria basin northeastern eromanga basin and southwestern eromanga basin and to around 50 m in the surat basin the change in bathymetry during the transgressive pulse was greatest in the northern marginal basins possibly a deepening of over 100 m and decreased to the southeast about 10 20 m where increased sand deposition occurred although the transgressive pulse bought slightly more saline and more oxygenated bottom water far into the basin a barrier still existed in bottom waters across the central carpentaria basin between slightly brackish dysaerobic conditions to the south and normal marine conditions to the north after peak sea level was reached bottom water circulation within the southern carpentaria and eromanga sea decreased and this was accompanied by a decrease in sediment influx during the late middle albian through early late albian anoxic conditions existed in central parts of the epeiric basins and a condensed section of black shales represented by the toolebuc formation was deposited the late early albian sea level rise was partly controlled by eustatism but may also have been influenced in different areas by varying amounts of continental uplift and subsidence associated with tectonism in the volcanic arc along the eastern australian margin the transgressive pulse broadly coincides with albian transgressions reported widely from passive margins and epeiric basins elsewhere but precise correlation is difficult the consistently high sea level during the middle and early late albian and the regression at the end of the albian are out of phase with events on other continents and probably resulted from increasing tectonism along the eastern continental margin

high resolution variation in ostracod assemblages from microbialites near the permian triassic boundary at zuodeng guangxi region south china abstract after the end permian mass extinction epme the marine environment was considered extremely toxic mainly due to anoxic and high temperature conditions and ocean acidification consequently the ecosystem contained few organisms this paper describes a new ostracod fauna from the microbialite bearing permian triassic p tr strata at zuodeng guangxi region china one thousand and seventy ostracod specimens were extracted from forty eight samples fifty three species belonging to fourteen genera were identified ostracods primarily from the family bairdiidae were extremely abundant in the microbialites which suggests that ostracods were opportunists that could survive the epme within this special microbial ecosystem with sufficient food and scarce competitors and predators rather than undergoing a rapid and early recovery after the epme event ostracods having simultaneous paleozoic and meso cenozoic affinities coexisted in this fauna the similarities and differences among the ostracod faunas in the microbialite sections of the p tr boundary around the paleo tethys indicate that there was a long distance dispersal of ostracods but the faunas maintained endemism at the species level previous studies have regarded microbialites as whole units and it is difficult to detect environmental changes within a microbialite interval based on paleoecological groups of super families in this study high resolution sampling was applied to identify changes in the ostracod abundance diversity assemblages and proportion of five dominant species in the section which exhibited an evolutionary trend from the bairdia group to the liuzhinia antalyaensis bairdiacypris ottomanensis group furthermore the transition of the ostracod fauna could be divided into six stages according to changes in the dominant species groups suggesting that the microbialite environment was not entirely monotonous but fluctuated during the postextinction interval

late cretaceous terrestrial vegetation a near polar temperature curve quantitative estimates of terrestrial paleotemperatures near the north pole were derived from the physiognomy of the vegetation including leaf margin analysis from rocks of latest albian and late cretaceous age of the north slope of alaska during the latest albian and cenomanian mean annual temperature was approximately 10 3 c during the coniacian mean annual temperature may have been 2 3 c warmer than during the albian cenomanian but no higher than 13 c during the campanian and maastrichtian mean annual temperature would have been about 2 8 c although the ranges for the individual estimates overlap differences among the floras indicate that the relative changes in mean annual temperature did occur

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

an extensive anoxic event in the triassic of the south china block a pyrite framboid study from dajiang and its implications for the cause s of oxygen depletion water column oxygen deficiency has been considered as a potent driver of the extinction of marine benthos and is a main feature of marine environments in the aftermath of the end permian mass extinction the record of permian triassic anoxia is more complex than previously thought and is seen to vary between different palaeogeographic settings but a full understanding is hindered by a paucity of evidence during the permian triassic interval the south china block was located equatorially with palaeotethys to the north and western panthalassa to the south this specific configuration provides a unique opportunity to compare the extent and duration of oxygen deficiency in palaeotethys and panthalassa under broadly similar climatic conditions sedimentary facies and pyrite framboid size frequency distributions suggest that the oxygen poor conditions became widespread across the shallow marine carbonate platform of the south china block immediately above the permian triassic boundary and mass extinction level oxygen deficiency was most intense at the southern margin of the block where it met panthalassa proposed drivers of the expansion of oxygen minimum zones into platform settings include enhanced terrigenous input and or ocean stratification or alternatively the upwelling of nutrient rich deep ocean water the former mechanisms are theoretically more likely to have operated in the relatively restricted palaeotethys which was surrounded by ancient lands in contrast panthalassa would likely have experienced stronger oceanic circulation and therefore be more susceptible to the effects of upwelling although variations in the record of the south china block anoxic event might reflect local factors the greater intensity of oxygen deficiency and a concomitant larger negative shift in carbonate carbon isotopes on its panthalassan margin point to a key role for upwelling this mechanism was likely a major driver of the permian triassic global oceanic anoxic event which itself was at least partly responsible for the ongoing inhospitable conditions and delayed recovery following the end permian extinction

the cenomanian turonian boundary at eastbourne sussex uk a proposed european reference section the cenomanian turonian boundary ctb section at eastbourne sussex england is the thickest at outcrop in the anglo paris basin is rhythmic throughout rich in macro micro and nanno fossils and shows less diagenetic alteration than other sections in nw europe geochemical and biostratigraphic data are all related to detailed rhythmic lithostratigraphy allowing correlation with the global boundary stratotype section to within 20 000 years and accurate estimates of rates of changes very detailed stable isotope curves for oxygen and carbon are presented and show that the build up phase of the ctb carbon excursion had two portions separated by a trough patterns of occurrence of coarse fraction benthic foraminifera 250 mm show two peaks of extinction corresponding to the two build up phases of the carbon excursion benthic and planktic foraminifera ostracods and calcareous nannofossils all show declines in diversity and abundance across the ctb foraminifera also decline significantly in size key biomarker events for the ctb include first occurrences of the ammonites fagesia catinus and mammites nodosoides the bivalve mytiloides the planktic foraminifera helvetoglobotruncana praehelveticaand marginotruncana renzi and the calcareous nannofossils quadrum intermedium q gartneri and eprolithus octopetalus and last occurrences of the ammonite sciponoceras the planktic foraminifera rotalipora greenhornensis and r cushmani the calcareous nannofossils corolithion kennedyi axopodorhabdus albianus lithraphidites acutus rhagodiscus asperand microstaurus chiastius cyclostratigraphy allows very precise correlation of isotopic and bioevents with other sections in europe and north america eastbourne is recommended as a nw european standard section 1999 elsevier science b v all rights reserved

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

ostracod recovery after permian triassic boundary mass extinction the south tibet record lower to middle triassic ostracods from the tulong section south tibet are described here for the first time samples from the first two stages of the early triassic griesbachian and dienerian are barren of ostracods the following stage smithian revealed low diversity ostracod faunas a substantial diversification in taxa began at the base of the fourth stage spathian and developed into the first stage of the middle triassic anisian furthermore exploration of additional feeding modes is developed in the spathian and anisian with notable occurrence of filter feeding taxa high abundance of filter feeding ostracods in spathian and lower anisian units indicates that benthic habitats became oligotrophic these habitats typically harbored ostracod faunas of mesozoic affinities suggesting that the evolutionary turnover of ostracods was fostered by the declining input of nutrients from the spathian on marked faunal similarities with other tethyan areas mainly the northern part of tethys are observed during spathian and anisian times

cretaceous oceanic red beds as possible consequence of oceanic anoxic events article i nfo oceanic anoxic events oaes represent brief periods of burial of large amounts of organic carbon in the oceans during cretaceous time burial of organic carbon which preferentially sequestered isotopically lighter carbon during oaes resulted in positive 13 c excursions of 2 3 recognizable in global ocean these deposits are typically dark grey to black shales considered to be the result of interaction between extreme warm climate ocean circulation high bioproductivity and organic carbon preservation less interest has been given to periods between oaes when oxic deep sea deposits such as red marls and red shales were deposited during mid and late cretaceous the latter deposits are associated with very low content of organic carbon and oxic depositional environments which dominated western tethys in post turonian time up to the early eocene feedbacks among geochemical cycles in response to decreasing global temperatures increasing deep ocean circulation forced by high latitude deep water formation along the antarctic margin and widening and deepening of the interconnections between the oceanic basins may have been responsible for the major paleoceanographic change from deposition of organic carbon rich black shales during mid cretaceous to world wide deposition of cretaceous oceanic red beds corbs in the late cretaceous the presence of corbs sandwiched between mid cretaceous oaes may reflect major climate and paleoceanographic changes in a contrast to extremely warm climates during the oaes the corbs suggest cold periods and therefore oscillating climate shifts that have seldom been considered during modeling of cretaceous

new quantitative palaeocolimate data for the late cretaceous arctic evidence for a warm polar ocean abstract physiognomic analysis of four taphofloras one from the coniacian of n alaska one from the coniacian of kamchatka one from the turonian of kamchatka and one from the turonian of novaya sibir island using the clamp technique of wolfe 1993 yielded quantitative data on the mean annual warm month mean and cold month mean temperatures the length of the growing season mean annual precipitation mean growing season precipitation mean monthly growing season precipitation and the precipitation during the three consecutive driest months these new results represent the first application of multivariate statistical analysis of foliar physiognomy to determine palaeoclimatic parameters clamp to arctic cretaceous floras and demonstrate its robustness even in the context of vegetation which has no living analogues these new estimates were comparable to those from previous quantitative or qualitative sedimentological or palaeobotanical data where they were available but offer greater measurable precision the results also suggest that an arctic ocean with a winter surface temperature of approximately 6 c maintained n alaska coastal temperatures above freezing locally reversing the equator to pole temperature gradient a phenomenon not seen in the northern proto pacific this anomalously warm arctic ocean could have been produced by marine poleward heat transport precipitation in alaska kamchatka and novaya sibir island was predicted to have been high e g 1760 mm yr in the coniacian of n alaska reflecting a very weak polar high pressure cell and substantially different precipitation patterns to present

ostracod fauna from the permian triassic boundary interval of south china huaying mountains eastern sichuan province palaeoenvironmental significance thirteen species of ostracods in a sample of 400 specimens were extracted by hot acetolysis from three samples within the earliest triassic hindeodus parvus zone in the permian triassic boundary interval in the huaying mountains eastern sichuan province south china one new species langdaia laolongdongensis n sp was found ostracod preservation is good this study provides ostracod data that demonstrate a confirmation of palaeozoic holdovers in the earliest triassic in south china b consistency between the palaeoecological interpretation of ostracod faunas and previous environmental and oceanic interpretations that suggest poorly oxygenated waters invaded the shelf in the earliest triassic and demonstrate the value of ostracods in the analysis of these rocks and c evidence of palaeobiogeographical links are between south china and turkey and confirm that south china iran and turkey remain close from middle permian until at least the earliest triassic d 2004 elsevier b v all rights reserved

cool cretaceous climates new data from the albian of western australia although previous geological palaeobotanical and geochemical data from the albian of australia have suggested the possibility of cool palaeoclimates there are few well constrained stable isotope palaeotemperatures studies from this region in this paper we present the results of stable isotope analyses of dimitobelid belemnites from the albian gearle siltstone carnarvon basin western australia oxygen isotope values for diagenetically least altered samples give values ranging between 18 o 0 02 and 0 85 pdb which equate to a mean palaeotemperature of 10 08 c assuming w of 1 2 smow this value is broadly consistent with recently published isotope data from the albian antarctic and with estimates for mid cretaceous latitudinal temperature gradients implying that cool palaeoclimates occurred during a period of 9greenhouse9 earth

oxygen isotopic composition of carbonate concretions from the lower cretaceous of victoria australia implications for the evolution of meteoric waters on the australian continent in a paleopolar environment oxygen isotopic data from carbonate cements in concretions have been used to infer the isotopic composition of meteoric fluids present at the time of concretion growth in terrestrial sediments that were deposited within the early cretaceous south polar circle at 75 80 s carbon and oxygen isotope compositions have been determined on over 135 samples of carbonate from 45 concretions taken from 24 localities aptian albian in age in the terrestrial sedimentary basins associated with the otway and strzelecki groups southeastern australia the carbonate cements include calcite having 26 4 13c 19 6and3 6 18o 29 6 or siderite having17 6 18o 30 8 calcite cemented concretions are more abundant and are interpreted to represent early near surface cementation events on the basis of textural evidence such as high 30 porosities at the time of cementation and mineralogical evidence such as the preferential preservation within concretions of labile detrital grains including plagioclase pyroxene and amphibole the oxygen isotopic data indicate that meteoric fluids with very low 18o certainly less than 15 and probably on the order of 20 were involved in the precipitation of the early calcites the extremely low 18o values of the fluids involved in the early diagenesis of both the otway and strzelecki groups suggest that the catchment area of the river system that carried sediments to these basins had a cold high latitude climate with mean annual temperatures less than 5 c and quite possibly below freezing by analogy with the relationship between modern18o distribution of meteoric fluids and climate these new data suggest that the early cretaceous polar regions may not have been ice free

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

the use of ostracoda to reconstruct the oxygen levels of late palaeozoic oceans abstract it has been recently demonstrated that in post palaeozoic and modern oceans filter feeding ostracods totally dominate over deposit feeders during times of dysaerobia in modern oceans the filter feeding platycopida the sole extant group with this feeding strategy in terms of abundance completely dominate the oxygen minimum zone despite occurring there in low specific diversity the percentage of filter feeders has been used previously to locate kenoxic events and to determine palaeoxygen levels in liassic cenomanian and palaeogene oceans the term kenoxic is used to denote an event when oxygen levels were reduced most so called anoxic events which for the name implies total deprivation of oxygen were in fact kenoxic a kenoxic event produces dysaerobic rather than anaerobic conditions in the present paper upper palaeozoic ostracoda are analysed and it is concluded that the palaeocopida metacopina platycopina kloedenellacea and the paraparchitacea were filter feeders filter feeders were therefore much more diverse in the palaeozoic than subsequently in the palaeopsychrosphere all ostracods even podocopids acquired peculiar adaptations to allow them to live in the oxygen minimum zone using the percentage of filter feeding ostracod species of shelf seas as a guide relative oxygen levels for the seas which deposited the carbonate platforms of northwest europe during the emsian to visean interval are calculated changes in oceanic oxygen are related to global climatic changes especially in temperature and are therefore important in any considerations of palaeoclimatology our reconstructions for both dissolved oxygen and sea water temperatures from the late early devonian to the early carboniferous based upon the percentage of filter feeding species clearly depict the late devonian events as a time of low oxygen high temperatures and high filter feeders into the frasnian there was a subsequent cooling and improved oxygenation into the famennian and a glacial maximum marked by a low percentage of filter feeders in the lower tournaisian this was followed by a slight increase in the percentage of filter feeders into the visean a signal of lower levels of oxygen but continuing in a contrasted climate a model which yields reference points giving absolute values of oxygen is proposed for late palaeozoic benthic marine environments

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

the latest paleocene crisis in the deep sea ostracode succession at maud rise southern ocean during the late paleocene thermal maximum ca 55 50 ma mid bathyal ostracodes at maud rise in the southern ocean ocean drilling program site 689 underwent a sudden dramatic turnover synchronous with a global extinction in deep sea benthic foraminifers and with large scale short lived negative excursions in the stable isotope record of foraminiferal calcite a previously stable and long lived ostracode assemblage dominated by heavily calcified chiefly epifaunal taxa was replaced within 10 k y by a taxonomically novel association of small thin walled opportunistic and generalist forms that persisted for 25 40 k y thereafter ostracode faunas recovered and common bathyal formsreturned althoughspeciesweresmallerand orless heavilycalcifiedthanbeforethe turnover the complex fabric of change in ostracode shell morphology and assemblage composition and structure reflects both long term and sudden perturbations in seawater chemistry at this site ostracode data are in agreement with the hypothesis that the latest paleoceneextinctionsinthedeepseawerecausedbyachangeinthedominantsourcearea of intermediate water mass from high altitudes to the subtropics these data also suggest that warm saline waters persisted at maud rise for the next 100 k y

from naples 1963 to rome 2013 a brief review of how the international research group on ostracoda irgo developed as a social communication system abstract the 1st international symposium on ostracoda iso was held in naples 1963 the philosophy behind this symposium and the logical outcome of what is now known as the international research group on ostracoda irgo are here reviewed namely ostracodology over the last 50 years is sociologically analysed three different and important historic moments for the scientific achievements of this domain are recognised the first one between about 1963 and 1983 is related to applied research for the oil industry as well as to the great interest in the better description of the marine environment by both zoologists and palaeontologists another important aspect during this period was the work by researchers dealing with palaeozoic ostracods who had their own discussion group irgpo gradually the merger of this latter group with those dealing with post palaeozoic ostracods at various meetings improved the communication between the two groups of specialists a second period was approximately delineated between 1983 and 2003 during this time slice more emphasis was addressed to environmental research with topics such as the study of global events and long term climate change ostracodologists profited also from the research politics within national and international programmes large international research teams emerged using new research methods during the third period 2003 2013 communication and collaborative research reached a global dimension amongst the topics of research we cite the reconstruction of palaeoclimate using transfer functions the building of large datasets of ostracod distributions for regional and intercontinental studies and the implementation of actions that should lead to taxonomic harmonisation projects within which molecular biological techniques are routinely used combined with sophisticated morphological information expanded now in their importance the documentation of the ostracod description improved through new techniques to visualise morphological details which stimulated also communication between ostracodologists efforts of making available ostracod information through newsletters and electronic media are evoked

high paleolatitude late cretaceous paleotemperatures new data from james ross island antarctica oxygen isotope analysis of well preserved macrofossils from the santonian campanian of james ross island and the maastrichtian of vega island antarctica indicates that cool high paleolatitude temperatures prevailed during the late cretaceous and suggests that cooling occurred between the santonian campanian and the maastrichtian although more than 50 of the material showed diagenetic alteration 52 unaltered aragonite and calcite samples were analyzed mean delta sup 18 o and calculated paleotemperature values were minus 0 23 per thousand and 13 6 c respectively for the santonian campanian and 0 66 per thousand and 11 7 c respectively for the masstrichtian in conjunction with recent late cretaceous paleoclimatic data from high northern paleolatitudes these data indicate the presence of cool polar regions with broad climatic zonation during the late cretaceous this may have partly controlled faunal distributions

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

the platycopid signal deciphered responses of ostracod taxa to environmental change during the cenomanian turonian boundary event late cretaceous in se england abstract a multi proxy investigation of the cenomanian turonian boundary event ctbe near dover in southern england previously demonstrated that coincident with a major global positive carbon stable isotope excursion during oceanic anoxic event 2 oae 2 the diversity of nanoplankton dinoflagellates planktonic and benthonic foraminifera and ostracods was severely reduced this was attributed to decreasing levels of dissolved oxygen consequent on an intensification and expansion of the oceanic oxygen minimum zone omz into shelf seas in the case of the ostracods it was noted that as podocopid taxa became locally extinct platycopids became the dominant component of the fauna subsequently the platycopid signal hypothesis psh claimed that dominance of platycopids in ostracod assemblages could be regarded as a signal of dysaerobic conditions on the sea floor based on the premise that the filter feeding platycopids able to pass more water over their respiratory surface were better equipped than other benthonic ostracods to survive in water of reduced oxygen concentration the psh has been widely accepted and applied in palaeoenvironmental reconstructions of stratigraphic intervals ranging from the palaeozoic to the quaternary however the modern biological and ecological support claimed for the platycopid signal has been challenged platycopids are occasionally dominant in modern omzs but often they are not and in any case the same can be said about some podocopids apparently precise calibration scales published by some authors are not justified by available data furthermore platycopid signal indications of dysaerobic intervals in the english chalk succession often conflict with the evidence of macrofossils and trace fossils here we review old and new data from two ctbe sites in se england dover and eastbourne and advance an alternative interpretation of the platycopid signal based on the concept of the spread of oceanic oligotrophic conditions into the european chalk sea during oae2 we propose that ostracod assemblages overwhelmingly dominated by platycopids signify oligotrophy because living platycopids appear to be adapted to filter feed on nano and picoplankton which are predominant in oligotrophic conditions

late cretaceous and cainozoic bathyal ostracoda from the central pacific dsdp site 463 cainozoic deep sea ostracod assemblages from the summits of mid pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor however the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non guyot sites fifteen ostracod assemblages from dsdp site 463 late cretaceous pleistocene were studied to compare with those from nearby guyots three distinct faunal assemblages are recognised at site 463 assemblage a maastrichtian eocene assemblage b oligocene upper miocene and assemblage c upper miocene pleistocene although the palaeoenvironmental significance of these units is unclear sixty two ostracod species are identified the thirteen most abundant are discussed in the taxonomic section five of which are described as new between 30 and 100 of the species encountered in each sample are considered as endemic to site 463 while some of the remaining species were previously thought to be endemic to individual guyots similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations the presence of globally pandemic and geographically widespread taxa on sites such as the mid pacific mountains surrounded by abyssal depths which lie below the ccd indicates that some faunal exchange or migration of ostracods does take place this must be achieved within the intermediate waters and probably occurs passively

the geochemistry of the plenus marls at dover england evidence of fluctuating oceanographic conditions and of glacial control during the development of the cenomanian turonian δ13c anomaly

strontium isotope stratigraphy and oxygen and carbon isotope variation during the middle jurassic early cretaceous of the falkland plateau south atlantic abstract 87sr 86sr data of belemnites are presented from a middle jurassic early cretaceous succession from the falkland plateau deep sea drilling project sites 511 and 330 that was deposited in a periodically anoxic semi enclosed shallow water basin diagenetically screened strontium isotope values of 0 706789 rise to 0 707044 before increasing sharply to 0 707428 in the uppermost part of the sampled succession comparison with published strontium calibration curves suggests that the oldest samples were callovian to oxfordian in age whilst the remainder of the jurassic part of the succession consisted of kimmeridgian and early tithonian age sediments the nannofossil dinoflagellate and molluscan assemblages provide comparable age determinations the strontium isotope analysis of the youngest belemnites points to a hauterivian barremian age whilst age interpretations based upon the fauna provide a wide age range from the barremian to early albian strontium isotope stratigraphy of this succession hence offers increased age resolution providing data regarding the timing of episodes of bottom water anoxia which have been recorded throughout the south atlantic basin well preserved belemnite specimens display an oxygen isotope range between 0 08 and 2 22 pdb peedee belemnite international standard and a carbon isotope range from 2 35 to 1 33 pdb 13c values become increasingly negative through the late jurassic early cretaceous and in concert with the 87sr 86sr data reveal a trend that could be accounted for by increasing levels of weathering and erosion the oxygen isotope data if interpreted in terms of palaeotemperature are consistent with warm palaeotemperatures in the kimmeridgian and slightly cooler temperatures for the tithonian and early cretaceous parts of the succession the proposed relative kimmeridgian warmth based upon strontium isotope age assignments is thus in good agreement with other published palaeotemperature records

global cooling inferred from dropstones in the cretaceous fact or wishful thinking traditionally the cretaceous has been considered as a long period of global warmth a greenhouse world this view has been challenged in recent years by several lines of evidence palaeobotany stable isotopes and palaeoclimatic modelling in particular however although these data demonstrate that cooling is likely the only first hand evidence which demonstrates the presence of substantial ice build up in cretaceous high palaeolatititudes are dropstones these outsized or exotic clasts set in a fine grained sediment are often interpreted as a direct result of ice rafting the reliability of this dropstone evidence and particularly its validity is questioned in demonstrating ice age interludes within the cretaceous greenhouse

the platycopid signal of oxygen depletion in the ocean a critical evaluation of the evidence from modern ostracod biology ecology and depth distribution abstract the use of relative abundances of filter feeding platycopid ostracods in estimating past levels of dissolved oxygen in the ocean the platycopid signal hypothesis is examined paying particular attention to evidence from faunistic biological and ecological studies the degree of support for the hypothesis has been overstated available data on ostracod depth distribution show that previous claims for platycopid dominance in the oxygen minimum zone in different oceanic regions are misleading and based on only a few studies observations and experimental studies on living platycopids are limited in scope and should be treated with caution we conclude that previously published and widely applied calibrations of platycopid abundance against dissolved oxygen levels are inadequately justified by the available data any further application of the platycopid signal technique should necessarily address these criticisms

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

the early toarcian early jurassic ostracod extinction events in the iberian range the effect of temperature changes and prolonged exposure to low dissolved oxygen concentrations abstract the early toarcian extinction event once regarded as spanning in the late pliensbachian early toarcian boundary period actually occurred in two distinct phases in the early toarcian of the iberian range the first episode occurred in the mirabile subzone tenuicostatum zone and is characterised by the disappearance of about 12 of ostracod species and one suborder the metacopina superfamily healdioidea this study shows that this suborder disappears during stratigraphical intervals that are considered to be representative of low oxygen conditions in the iberian range the collapse of marine ecosystems affecting up to 40 of ostracod species in the elegantulum subzone serpentinum zone was most likely triggered by a sudden and widespread lethal increase in seawater temperature these combined processes of oxygenation and temperature change are considered to be responsible for the profound changes in marine environments that resulted in the early toarcian ostracod extinction in the iberian range

ecophenotypic variation of the devonian benthic ostracod species cavellina rhenana krommelbein 1954 a paleoenvironmental proxy for the ardenne france belgium and rheno hercynian realm abstract the morphological variation of the carapace of the ostracod species cavellina rhenana krommelbein 1954 is explored here quantitatively this species existed during the late givetian to the earliest frasnian and it is characteristic of the rheno hercynian area five morphological characters and several linear measurements of the carapace were analyzed on 260 complete carapaces coming from three different areas each of them representing a different paleoenvironment of the devonian ardennean platform the original species description and diagnosis are emended based on this newly observed variability in ornamentation sulcation curvature of the ventral margin marginal flattening and asymmetry of valves it is established herein that the morphological variation expressed in these five characters is independent of the ontogenetic growth morphological variation appears to be correlated with different types of facies reflecting a distinct depositional environment a high degree of morphological variation is found in facies of inner platform semi restricted environments while a low degree of variation is found in facies of outer platform open marine environments thus the degree of morphological variation of c rhenana is an indicator of the stability of the environment in the neritic realm while environmentally cued polymorphism is well documented in mesozoic to recent ostracods our study demonstrates the first devonian case of ecomorphism and suggests that intraspecific polymorphism of the ostracod carapace can be a useful tool for refining paleoenvironmental reconstructions