the paleocene eocene transition at mead stream new zealand a southern pacific record of early cenozoic global change mead stream in marlborough new zealand exposes a spectacular 650 m thick stratigraphic section of well bedded micritic limestone chert and marl that was deposited on a south pacific upper continental slope from late cretaceous to middle eocene the 200 m upper paleocene lower eocene succession was examined for its lithology bulk carbonate carbon isotopes and assemblages of radiolarians calcareous nannoplankton and foraminifera so that it could be placed into a global context the interval displays several prominent carbon isotope anomalies and is correlated with south pacific radiolarian zones rp5 to rp9 and calcareous nannofossil zones np6 8 to np12 additionally planktic foraminiferal zones p4 to p6b are identified in uppermost paleocene and lower eocene strata mead stream has a near continuous paleocene lower eocene sediment record and three globally significant climate events the late paleocene carbon isotope maximum pcim the initial eocene thermal maximum ietm and the early eocene climatic optimum eeco have obvious expressions the pcim is a 50 m thick interval of biosiliceous micritic limestone in which 13c is 3 the lower part contains two organic rich biosiliceous mudstone units that may represent expansion of an oxygen minimum zone omz during a global increase in marine biological productivity the ietm is a 4 m thick interval in which 13c drops below 1 5 in a pattern seen at other locations the basal 2 4 m is a distinctive recessed marl rich unit that is defined herein as the dee marl the ietm is marked by a rapid decline in the nannoplankton genus fasciculithus short lived occurrences of discoaster cf araneus and morozovella aequa aequa and significant radiolarian faunal turnover owing to impoverished benthic faunas the benthic foraminiferal extinction event bfee is poorly defined the onset of the eeco is marked by a 1 negative 13c excursion a transition from limestone rich to marl rich facies and a marked decrease in radiolarian abundance compacted sedimentation rates vary between 1 4 2 7 cm kyr for upper paleocene lower eocene strata at mead stream although individual beds with average thickness of 10 cm were deposited too fast to directly represent cycles in orbital parameters time series analysis of bed thicknesses suggests that groups of beds may record milankovitch scale periodicity perhaps with a significant obliquity component thus the relative frequency and thickness of marl and limestone beds in this section is shown to be strongly influenced by climatic changes at a wide range of temporal scales from suborbital and orbital cycles to aberrant short term events and long term trends predominance of marl in ietm and eeco intervals indicates that episodes of extreme global warming resulted in reduced oceanic productivity and increased terrestrial discharge in the high latitude southwestern pacific

eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

orbitally forced climate signals in mid pliocene nannofossil assemblages downcore cyclic variation in high resolution nannofossil abundance records from mid pliocene equatorial atlantic odp sites 662 and 926 demonstrate the direct response by several pliocene taxa notably discoaster sphenolithus and florisphaera profunda to orbitally forced climatic variation in particular these records display strong obliquity and precessional signals reflecting primarily high latitude southern hemisphere changes influencing upwelling intensity and local low latitude insolation driven climatic changes via the productivity and or turbidity influence of amazon sourced terrigenous material at sites 622 and 926 respectively in seasonal studies of coccolithophorid assemblages only part of the variation observed can be explained by abiotic processes so it is perhaps not surprising that in this study few pliocene nannofossil taxa demonstrate significant correlations with each other or with physical environmental parameters only some variance in nannofossil abundances can be explained by the primary controls of temperature and productivity the rest is attributed to nonlinear responses to climatic changes biotic processes such as grazing predation viral infection and competition and or abiotic factors for which there is no readily available proxy e g salinity the lack of strong consistent intra and inter relationships of the nannoflora and the environment reflects an ecologically complex differentiated original community producing a complex integrated signal transmitted into the fossil record

changes in calcareous nannofossil assemblages during the middle eocene climatic optimum clues from the central western tethys alano section ne italy we present a study focused on changes in calcareous nannofossil assemblages of the alano section during the middle eocene climatic optimum meco this warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the chron c18r c18n transition ca 40 ma and lasting ca 500 600 kyr semi quantitative analyses on calcareous nannofossil assemblages have been carried out our results show that the meco interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa suggesting a relationship between biotic changes and stable isotope shifts paleoecological studies at species level and or based on morphometric criteria i e small placoliths sometimes show the opposite behaviour between changes observed at the genus level and those observed at lower taxonomic levels for instance a taxon thought to be better adapted to oligotrophic warm waters e g sphenolithus shows a prominent decrease if analyzed at genus level but an increase was instead recorded for s spiniger moreover taxa preferentially thriving in eutrophic cold waters as for instance small reticulofenestrids increase remarkably in abundance during this warming phase while medium large placoliths do not show any significant trend an increase in reworked mainly cretaceous specimens is also observed during the meco these lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make up of the calcareous nannofossil assemblages the increase in reworking may indicate an increase in terrigenous input due to increased chemical weathering likely produced by an enhanced hydrological cycle

ecological and evolutionary response of tethyan planktonic foraminifera to the middle eocene climatic optimum meco from the alano section ne italy abstract the enigmatic middle eocene climatic optimum meco is a transient 500 kyr warming event that significantly interrupted at 40 ma the long term cooling through the middle and late eocene eventually resulting in establishment of permanent antarctic ice sheet this event is still poorly known and data on the biotic response are so far scarce here we present a detailed planktonic foraminiferal analysis of the meco interval from a marginal basin of the central western tethys alano section northeastern italy the expanded and continuous alano section provides an excellent record of this event and offers an appealing opportunity to better understand the role of climate upon calcareous plankton evolution a sapropel like interval characterized by excursions in both the carbon and oxygen bulk carbonate isotope records represents the lithological expression of the post meco event in the study area and follows the 18 o negative shift interpreted as representing the meco warming high resolution quantitative analysis performed on both 38 m and 63 m fractions reveals pronounced and complex changes in planktonic foraminiferal assemblages indicating a strong environmental perturbation that parallels the variations of the stable isotope curves corresponding to the meco and post meco intervals these changes consist primarily in a marked increase in abundance of the relatively eutrophic subbotinids and of the small low oxygen tolerant streptochilus chiloguembelina and pseudohastigerina at the same time the arrival of the abundant opportunist eutrophic jenkinsina and pseudoglobigerinella bolivariana typical species of very high productivity areas also occurs the pronounced shift from oligotrophic to more eutrophic opportunist low oxygen tolerant planktonic foraminiferal assemblages suggests increased nutrient input and surface ocean productivity in response to the environmental perturbation associated with the meco particularly critical environmental conditions have been reached during the deposition of the sapropel like beds as testified by the presence of common giant and or odd morphotypes this is interpreted as evidence of transient alteration in the ocean chemistry the enhanced surface water productivity inferred by planktonic foraminiferal assemblages at the onset of the event should have resulted in heavier 13 c values the recorded lightening of the carbon stable isotope preceding the maximum warmth therefore represents a robust indication that it derives principally by a conspicuous increase of p co 2 the increased productivity of surface waters also supported by geochemical data may have acted as mechanism for p co 2 reduction and returned the climate system to the general eocene cooling trend the oxygen depleted deep waters and the organic carbon burial following the peak of the meco event represent the local response to the meco warming and suggest that high sequestration of organic matter if representing a widespread response to this event might have contributed to the decrease of p co 2 as well though the true mechanisms are still obscure several lines of evidence indicate a potential pressure on planktonic foraminiferal evolution during the meco event including permanent changes besides transient and ecologically controlled variations

constraints on glaciation in the middle eocene 46 37 ma from ocean drilling program odp site 1209 in the tropical pacific ocean the presence of glacial ice in the late middle eocene has been vigorously debated recently published sedimentary data from the high latitudes is suggestive of episodic cooling events and near freezing sea surface temperatures during parts of the late middle eocene constraints on ice volumes and the significance of excursions in open ocean foraminifera and seawater 18o reconstructions are less clear and there are few high resolution 18o records we present a new detailed record of benthic foraminiferal 18o from site 1209 that exhibits variations 18o benthic of 0 6 1 3 different approaches have previously been used to interpret 18o benthic including 1 an a priori assumption of a 50 contribution of temperature similar to what is reconstructed for the last glacial maximum recent change 2 applying oligocene calibrations between apparent sea level asl and 18o benthic or 3 assuming temperature and seawater 18o contributions can be partitioned through comparison with benthic mg ca using assumption 1 the record from site 1209 indicates changes in seawater 18o of 0 3 0 7 equivalent to 33 72 m m of asl assuming mean ice 18o of 45 using assumption 2 and two different end member calibrations the 18o benthic record implies changes in asl of 23 50 m or 50 108 m the third approach yields changes in seawater 18o of up to 0 6 to 1 4 we explore the compatibility of the results of each of these approaches with other studies that discuss evidence for ephemeral glaciations during the middle eocene with variable ice storage at one or both poles

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

biogeographic gradients of middle eocene oligocene calcareous nannoplankton in the south atlantic ocean middle eocene oligocene calcareous nannoplankton have been analyzed quantitatively for eight dsdp and odp sites ranging from the equatorial zone to 65 s latitude in the south atlantic ocean there is a general decrease in calcareous nannoplankton species diversity from the middle eocene through the oligocene and species diversity also decreases towards the higher latitudes similar to findings of other studies the drop of the species diversity of calcareous nannoplankton across the eocene oligocene boundary is not drastic delineation of latitudinal distribution patterns of individual species or groups and r mode cluser analysis permit the classification of warm water taxa coccolithus formosus discoasters helicosphaerids and sphenoliths temperate water taxa coccoliths pelagicus cyclicargoliths floridanus group reticulofenestra bisecta reticulofenestra samodurovii reticulofenestra umbilica and cool water taxa chiasmoliths isthmolithus recurvus and reticulofenestra daviesii the abundance of warm water taxa plummets whereas the abundance of cool water taxa sharply increases across the eocene oligocene boundary at the middle and high latitude sites reflecting a profound cooling event in these areas polar ordination and similarity analyses reveal that steep latitudinal biogeographic gradients had been established at least by the middle eocene the gradient greatly increases near the eocene oligocene boundary indicating more severe and permanent cooling at the high latitudes the biogeographic gradient data of this study conflict with the widely accepted inference from the oxygen isotopic data that the thermal gradients between mid latitudes and high latitudes are low or nearly flat for the paleogene oceans lower surface water salinities in the high latitudes may have lowered the 18o values of the planktonic microfossils but apparently did not have significant effect on latitudinal distribution patterns of calcareous nannoplankton which offers an independent means for estimating latitudinal thermal gradients

no extreme bipolar glaciation during the main eocene calcite compensation shift major ice sheets were permanently established on antarctica approximately 34 million years ago1 2 3 close to the eocene oligocene boundary at the same time as a permanent deepening of the calcite compensation depth in the world s oceans4 until recently it was thought that northern hemisphere glaciation began much later between 11 and 5 million years ago1 2 3 5 this view has been challenged however by records of ice rafting at high northern latitudes during the eocene epoch6 7 and by estimates of global ice volume that exceed the storage capacity of antarctica8 at the same time as a temporary deepening of the calcite compensation depth 41 6 million years ago9 here we test the hypothesis that large ice sheets were present in both hemispheres 41 6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial atlantic ocean these records allow at most an ice budget that can easily be accommodated on antarctica indicating that large ice sheets were not present in the northern hemisphere the records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled ocean temperatures increased and carbon isotope values decreased in the equatorial atlantic the nature of these changes around 41 6 million years ago implies common links in terms of carbon cycling with events at the eocene oligocene boundary4 and with the hyperthermals of the early eocene climate optimum3 10 11 our findings help to resolve the apparent discrepancy between the geological records of northern hemisphere glaciation6 7 8 and model results12 13 that indicate that the threshold for continental glaciation was crossed earlier in the southern hemisphere than in the northern hemisphere

organic carbon burial following the middle eocene climatic optimum in the central western tethys we present trace metal geochemistry and stable isotope records for the middle eocene alano di piave section ne italy deposited during magnetochron c18n in the marginal tethys ocean we identify a sim 500 kyr long carbon isotope perturbation event we infer to be the middle eocene climatic optimum meco confirming the northern hemisphere expression and global occurrence of meco interpreted peak climatic conditions are followed by the rapid deposition of two organic rich intervals le 3 toc and contemporaneous positive delta 13 c excursions these two intervals are associated with increases in the concentration of sulphur and redox sensitive trace metals and low concentrations of mn as well as coupled with the occurrence of pyrite together these changes imply low possibly dysoxic bottom water o 2 conditions promoting increased organic carbon burial we hypothesize that this rapid burial of organic carbon lowered global it p co 2 following the peak warming and returned the climate system to the general eocene cooling trend

late oligocene climatic changes evidence from calcareous nannofossils at kerguelen plateau site 748 southern ocean abstract palaeoecological changes in nannofossil assemblages in the southern ocean during oligocene times are examined through high resolution quantitative analyses of samples from ocean drilling program odp site 748 kerguelen plateau we quantitatively characterized the palaeoecological preference of groups of species and compared their general trends with those determined at maud rise odp sites 690 and 689 persico d villa g 2004 eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica palaeoecological and palaeoceanographic implications marine micropaleontology 52 153 179 we then attempt a correlation between the main assemblage variation and sea surface temperature sst changes in the southern ocean at this time relatively stable cool conditions are interpreted to have persisted from earliest to late oligocene times when an increase in abundance of temperate water taxa is recorded both at maud rise and kerguelen plateau before the mi 1 event this reveals a climatic event that probably involved both sites and which is comparable to that indicated by the global oxygen isotope curve miller k g wright j d fairbanks r g 1991 unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion journal of geophysical research 96 6829 6848 zachos j pagani m sloan l thomas e billups k 2001 trends rhythms and aberrations in global climate 65 ma to present science 292 686 693 in the uppermost oligocene at site 689 the temperate water taxa index temperate temperate cool 100 increases from 25 2 ma similarly at site 748 the temperate water taxa index indicates an increase in sst in the late oligocene from about 26 5 ma at the base of chron c8n 2n which is offset by about 1 m y between the two areas the reason for this time difference can probably be found in the location of site 748 with respect to site 689 and in the palaeoceanographic setting taking into account that site 748 lies north of a deep water passage that separates kerguelen plateau from antarctica and north of the present day front of the antarctic circumpolar current the presence of warm water taxa exclusively at site 748 corroborates this hypothesis

calcareous nannofossil fluxes and size fluctuations in the middle eocene 48 39 ma from ocean drilling program odp site 1209 in the tropical pacific ocean abstract pelagic carbonates constitute the majority of the ocean sediments particularly since the jurassic and record climatic and oceanic changes cenozoic sediments record glacial and interglacial periods as well as thermal maxima such as the petm paleocene eocene thermal maximum at ca 56 ma or the meco middle eocene climatic optimum that dates back to ca 40 ma the paleogene period shows variations in seawater temperature and atmospheric co2 as well as fluctuations of the carbonate compensation depth ccd in order to understand the actions and feedbacks between climate regulated amongst others by temperature partial pressure of co2 and atmospheric belts ccd fluctuations and pelagic carbonate producers the fluxes assemblages and sizes of calcareous nannofossils were studied from sediments dated between 48 and 39 ma including the meco interval calcareous nannofossils were analysed in from the odp ocean drilling project leg 198 site 1209a shatsky rise located in the tropical pacific the previously proposed age model for site 1209 has been slightly modified based on new calcareous nannofossil biostratigraphy recalibrated according to the gts 2012 in a long term perspective calcareous nannofossil assemblages and taxa size show significant changes during the middle eocene our data suggest that relatively oligotrophic conditions occurred between 48 and 45 ma interrupted by higher trophic conditions between 45 and 39 ma although oligotrophy occurred again during the meco discoaster spp show smaller sizes from 48 to 39 ma mirroring the global temperature decrease at 40 ma during the meco large sized reticulofenestrids with a peak of reticulofenestra umbilicus 14 m occurred whereas smaller but heavily calcified dictyococcites spp peak in the aftermath of the meco calcareous nannofossil fluxes show a significant increase with respect to background values during the caes carbonate accumulation event although they are low during the meco calcareous nannofossil fluxes seem to have had important impact on the oceanic carbon cycles by creating a carbonate flux to the ocean interior likely contributing to the ccd deepening

middle eocene to late oligocene antarctic glaciation deglaciation and southern ocean productivity during the eocene oligocene transition earth cooled significantly from a greenhouse to an icehouse climate nannofossil assemblages from southern ocean sites enable evaluation of paleoceanographic changes and hence of the oceanic response to antarctic ice sheet evolution during the eocene and oligocene a combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes a cooling trend started in the middle eocene was interrupted by warming during the middle eocene climatic optimum and by short cooling episodes the cooling episode at 39 6 ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from 39 1 to 36 2 ma we suggest that oligotrophic conditions were associated with increased water mass stratification low nutrient contents and high efficiency of the oceanic biological pump that in turn promoted sequestration of carbon from surface waters which favored cooling after 36 2 ma we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance this turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient antarctic ice sheet and or to iron delivery to the sea surface eutrophic conditions were maintained throughout the oligocene which was characterized by a nannofossil assemblage shift toward cool conditions at the eocene oligocene transition finally a warm nannofossil assemblage in the late oligocene indicates a warming phase

middle eocene regional climate instability evidence from the western north atlantic high resolution 3 k y d 18 o records from middle eocene mixed layer dwelling planktonic foraminifera from the western north atlantic show pronounced 1 variability the magnitude of change is greater than that seen in open ocean pleistocene records but could not have been caused by ice volume and or sea level fluctuations instead the oxygen isotope shifts resulted primarily from large oscillations in sea surface temperatures and indicate that the regional paleoceanography of the middle eocene western north atlantic was not consistently warm or stable the large shifts in sea surface temperatures could reflect variations in the position of the gulf stream relative to blake nose or variations in upwelling intensity

integrated biomagnetostratigraphy of the alano section ne italy a proposal for defining the middle late eocene boundary the alano section has been presented at the international subcommission on paleogene stratigraphy isps as a potential candidate for defi ning the global boundary stratotype section and point gssp of the late eocene priabonian stage the section is located in the venetian southern alps of the veneto region ne italy which is the type area of the priabonian being exposed along the banks of the calcino torrent near the village of alano di piave it consists of 120 130 m of bathyal gray marls interrupted in the lower part by an 8 m thick package of laminated dark to black marlstones intercalated in the section there are eight prominent marker beds six of which are crystal tuff layers whereas the other two are bioclastic rudites these distinctive layers are useful for regional correlation and for an easy recognition of the various intervals of the section the section is easily accessible crops out continuously is unaffected by any structural deformation is rich in calcareous plankton and contains an expanded record of the critical interval for defi ning the gssp of the priabonian in order to further check the stratigraphic completeness of the section and constrain in time the critical interval for defi ning the priabonian stage we performed a high resolution study of integrated calcareous plankton biostratigraphy and a detailed magnetostratigraphic analysis here we present the results of these studies to open a discussion on the criteria for driving the golden spike that should define the middle eocene late eocene boundary

middle eocene late oligocene climate variability calcareous nannofossil response at kerguelen plateau site 748 a major deterioration in global climate occurred through the eocene oligocene time interval characterized by long term cooling in both terrestrial and marine environments during this long term cooling trend however recent studies have documented several short lived warming and cooling phases in order to further investigate high latitude climate during these events we developed a high resolution calcareous nannofossil record from odp site 748 hole b for the interval spanning the late middle eocene to the late oligocene 42 to 26 ma the primary goals of this study were to construct a detailed biostratigraphic record and to use nannofossil assemblage variations to interpret short term changes in surface water temperature and nutrient conditions the principal nannofossil assemblage variations are identified using a temperate warm water taxa index twwt from which three warming and five cooling events are identified within the middle eocene to the earliest oligocene interval among these climatic trends the cooling event at 39 ma cooling event b is recorded here for the first time variations in fine fraction 18o values at site 748 are associated with changes in the twwt index supporting the idea that significant short term variability in surface water conditions occurred in the kerguelen plateau area during the middle and late eocene furthermore odp site 748 calcareous nannofossil paleoecology confirms the utility of these microfossils for biostratigraphic paleoclimatic and paleoceanographic reconstructions at southern ocean sites during the paleogene

responses of calcareous nannofossil assemblages mineralogy and geochemistry to the environmental perturbations across the paleocene eocene boundary in the venetian pre alps responses of calcareous nannofossil assemblages mineralogy and geochemistry to the environmental pertubartions across the paleocene eocene boundary in the venetian pre alps

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

climate and sea level perturbations during the incipient eocene thermal maximum evidence from siliciclastic units in the basque basin ermua zumaia and trabakua pass northern spain abstract based on carbon isotope stratigraphy and lithology a revised high resolution correlation is proposed between sections spanning the incipient eocene thermal maximum ietm in the basque region northern spain in three studied sections the ietm event is represented by a prominent non to low calcareous siliciclastic unit su 4 20 5 m thick during formation of the su sedimentation rates for siliciclastic material increased by a factor of two to five whereas detrital grain size decreased significantly kaolinite and chlorite became more abundant in the clay fraction and calcite dissolution in the water column intensified the su reflects a significant change in climate and hydrological regime towards a warmer and seasonally drier climate the drying caused perennial vegetation cover to collapse and led to increased continental erosion but also to reduced hydrodynamic energy of freshwater debouching into the oceans a coeval relative sea level fall probably related to tectonic uplift or doming affecting major parts of western europe increased the land sea slope and further enhanced erosion rates palynological studies support periodic vegetation during seasonal rain instead of permanent conifer forests prominent caliche soils in coeval continental deposits in northern spain also support warm semiarid conditions during the ietm event net evaporation increased under the subtropical high pressure cells including the basque region whereas more northerly latitudes became more wet the su has a similar origin as detrital units previously assigned to the early palaeogene so called siderolithic discharge in other parts of western europe

glacioeustasy during the middle eocene insights from the stratigraphy of the hampshire basin uk the sedimentary strata of the hampshire basin constitute some of the best preserved palaeogene sequences worldwide and include the traditional unit stratotype for the bartonian 36 9 41 4 ma the barton clay formation at alum bay on the isle of wight iow was studied to assess the evidence for middle eocene sea level variation in records of grain size sediment properties faunal assemblage foraminiferal diversity indices and foraminiferal stable isotopes sedimentary cycles of 1 10 myr third order and 0 2 0 5 myr fourth order duration are reported and interpreted to reflect 20 60 metre variations in water depth additionally an integrated magneto bio chemostratigraphical age model for the succession at alum bay is presented and new and published litho and bio stratigraphical markers are used to correlate additional successions based on this age model it appears that during the late lutetian and early bartonian 42 38 ma water depth variation identified within the basin was synchronous sedimentary and fossil evidence supports episodic uplift in the eastern part of the hampshire basin during the bartonian which at present precludes the calculation of eustatic sea level however the amplitude and frequency of water depth variations identified in the barton clay formation and correlations to published sea level curves are consistent with a component of these changes being glacioeustatic during the middle eocene there is also evidence for a large excursion delta 18o 1 per mille sign in the mono specific benthic foraminiferal oxygen isotope record alum bay 39 9 ma which is correlated to the isotope excursion at the middle eocene climatic optimum previously reported in the southern ocean and other localities a contemporaneous water depth increase of 40 m at alum bay may indicate that a component of this global oxygen isotope excursion results from a reduction in continental ice storage

reactive surface area of skeletal carbonates during dissolution effect of grain size abstract major advances have recently been made in quantifying the chemical parameters which control carbonate mineral reaction kinetics in natural waters one of the primary factors influencing rates of reaction is the amount of surface area per unit mass available for reaction for relatively smooth nonporous carbonates the relationship between reactive and total surface area measured by gas adsorption has proven simple however the dominant carbonates in the marine environment are biogenic and exhibit complex microstructures we have performed experiments to determine dinghy what proportion of the total surface area of these biogenic carbonates is actually available for reaction during dissolution three biogenic carbonates having widely differing microstructures halimeda coral and echinoid were chosen for study and comparison with rhombic calcite the influence of grain size on the relation between total surface area determined from gas adsorption and reactive surface area determined relative to rhombic calcite during dissolution in constant composition solutions was of primary concern unlike rhombic calcites total surface area for texturally complex biogenic grains varied slightly or not at all with increasing grain size however both rhombic calcite and biogenic carbonate dissolution rates were inversely related to grain radius this implies that much of the total surface area of biogenic carbonates is unavailable for reaction with the aqueous solution dissolution rates were a function of both grain size and microstructure we have defined an empirical roughness factor which quantifies the difference in reactive surface area between rhombic calcite and a given biogenic grain of equivalent size the roughness factor increased with grain microstructural complexity but was independent of grain size over the grain size range 51 513 microns studied the maximum roughness factor value observed was 7 for halimeda relative to a value of 1 for rhombic calcite our findings indicate that both microstructure and grain size can play important roles in controlling reactivity of biogenic carbonates during diagenesis the relative significance of grain size versus microstructure for carbonate dissolution rates in natural systems is discus ed

rapid fluctuations in mid latitude siliceous plankton production during the middle eocene climatic optimum odp site 1051 western north atlantic abstract the middle eocene climatic optimum meco 40 million years ago ma is one of the most prominent transient global warming events in the paleogene although the event is well documented in geochemical and isotopic proxy records at many locations the marine biotic response to the meco remains poorly constrained we present new high resolution quantitative records of siliceous microplankton assemblages from the meco interval of ocean drilling program odp site 1051 in the subtropical western north atlantic ocean which are interpreted in the context of published foraminiferal and bulk carbonate stable isotope 18o and 13c records high diatom radiolarian and silicoflagellate accumulation rates between 40 5 and 40 0 ma are interpreted to reflect an 500 thousand year kyr interval of increased nutrient supply and resultant surface water eutrophication that was associated with elevated sea surface temperatures during the prolonged onset of the meco relatively low pelagic siliceous phytoplankton sedimentation accompanied the peak meco warming interval and the termination of the meco during an 70 kyr interval centered at 40 0 ma following the termination of the meco an 200 kyr episode of increased siliceous plankton abundance indicates enhanced nutrient levels between 39 9 and 39 7 ma throughout the site 1051 record abundance and accumulation rate fluctuations in neritic diatom taxa are similar to the trends observed in pelagic taxa implying either similar controls on diatom production in the neritic and pelagic zones of the western north atlantic or fluctuations in sea level and or shelf accommodation on the north american continental margin to the west of site 1051 these results combined with published records based on multiple proxies indicate a geographically diverse pattern of surface ocean primary production changes across the meco notably however increased biosiliceous accumulation is recorded at both odp sites 1051 and 748 southern ocean in response to meco warming this may suggest that increased biosiliceous sediment accumulation if indeed a widespread phenomenon resulted from higher continental silicate weathering rates and an increase in silicic acid supply to the oceans over several 100 kyr during the meco

the apectodinium acme and terrestrial discharge during the paleocene eocene thermal maximum new palynological geochemical and calcareous nannoplankton observations at tawanui new zealand manifestations of profound perturbations in biogeochemical systems during the paleocene eocene thermal maximum petm include a prominent global negative 13c and a pronounced increase in the relative abundance of dinoflagellate cysts dinocysts assigned to the genus apectodinium while motile representatives of apectodinium were most likely thermophilic and heterotrophic the underlying causes of this dinoflagellate response are not well understood here we provide new insight by examining the palynology chemistry and calcareous nannoplankton across the petm in a continental slope section at tawanui new zealand across the petm marked changes in the relative abundance of apectodinium vary antithetically with significant changes in the 13c of carbonate and organic matter in general the high relative abundance of apectodinium relates to enhanced concentrations of dinocysts signifying a bloom of apectodinium in surface waters during the petm changes in apectodinium and 13c records correspond to variations in many other parameters including a smaller negative shift in bulk carbonate 13c than expected increased terrestrial palynomorphs elevated toc and c n ratios lower carbonate contents higher sio2 and al2o3 contents and lower si al ratios all of these variations can be explained by an increase in delivery of terrigenous material to the continental margin a peak in the relative abundance of glaphyrocysta dinocysts at the onset of the petm may indicate greater down slope transport of neritic material changes in calcareous nannoplankton abundances suggest increased nutrient availability in surface waters during the petm the combined results show that apectodinium dominated assemblages global perturbations in carbon isotopes and enhanced terrigenous delivery closely correspond in time at tawanui a sudden and massive carbon injection to the ocean atmosphere system may have enhanced weathering and increased terrigenous inputs to continental margins during the petm we further suggest that these inputs caused the apectodinium acme by elevating primary productivity in marginal seas

changes in southern ocean bottom water environments associated with the middle eocene climatic optimum meco abstract the middle eocene climatic optimum meco was a 650 kyr long interval of pronounced warmth superimposed on the long term eocene cooling trend we investigate benthic foraminiferal assemblage and fossil fish tooth cerium anomaly variability from ocean drilling program odp site 738 in the indian sector of the southern ocean southern kerguelen plateau to assess changes in bottom water chemistry and effects on benthic foraminiferal ecosystems the studied section spans 41 9 to 38 4 ma encompassing the meco as well as extensive pre meco and post meco intervals we report a marked faunal turnover at 40 4 ma 200 kyrs after the onset of the meco at 40 6 ma from an assemblage dominated by epifaunal benthic foraminifera to an infaunal dominated assemblage the infaunal domination persisted until the termination of the meco at 39 95 ma thereafter the pre meco assemblage returned this change is attributed to an increase in export productivity associated with the warming possibly caused by an increase in continental runoff or the influence of a more eutrophic surface water mass superimposed on the change in tropic state the ce ce record shows a positive excursion during the 100 kyrs long meco peak warming at around 40 05 ma indicative of a decrease in bottom water oxygen content synchronously infaunal benthic foraminifera drop briefly in abundance hence we suggest that the peak warming is associated with bottom water oxygen depletion potentially caused by elevated productivity and or a transient influence of an older oxygen depleted water mass

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

middle eocene climate cyclicity in the southern pacific implications for global ice volume we use a multiproxy approach to determine surface and bottom water temperatures off the coast of new zealand during the middle eocene and to constrain the 18o of seawater we use these data to place constraints on the size and variability of global ice sheets at that time the hampden section in south island is characterized by exceptionally well preserved micro fossils and clear sedimentary cyclicity providing a remarkable window into conditions at paleo latitude 55 s in the pacific ocean the cyclicity was studied in detail over a 4 m section corresponding to an interval of 70 k y ca 41 7 ma the sedimentary cycles are defined by fluctuations in the sand 63 m component occurring on a wavelength of 1 m corresponding to milankovitch scale frequency analyses of foraminifer oxygen isotopic 18 o and mg ca composition combined with tex86 analyses from organic carbon are used to generate records of seawater temperature and oxygen isotopic composition 18osw these indicate bottom water temperatures of 11 13 c and sea surface temperatures of 23 25 c with good agreement between the proxies temperature cyclicity with a magnitude of 1 5 c occurs in both surface and bottom waters approximately in phase with the sedimentary cycles estimates of 18osw have a mean value of 1 2 throughout the study section taken together the data suggest a largely ice free world with orbital scale cycles expressed as temperature and hydrological variation with little or no ice volume change

high resolution nannofossil biochronology of middle paleocene to early eocene at odp site 1262 implications for calcareous nannoplankton evolution abstract over the last several decades debates on the tempo and mode of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated i e with long periods of stasis alternating with short periods of rapid morphological change and generation of new species another major debate is focused on the question whether long term evolution is driven by or at least strongly influenced by changes in the environment or by interaction with other life forms microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions we present high resolution analyses of selected calcareous nannofossils from the deep sea section recovered at odp site 1262 leg 208 in the south eastern atlantic the studied section encompasses nannofossil zones np4 np12 equivalent to cp3 cp10 and chrons c27r c24n we document more than 70 biohorizons occurring over an about 10 myr time interval 62 5 ma to 52 5 ma and discuss their reliability and reproducibility with respect to previous data thus providing an improved biostratigraphic framework which we relate to magnetostratigraphic information and present for two possible options of a new paleocene stratigraphic framework based on cyclostratigraphy this new framework enabled us to tentatively reconstruct steps in the evolution of early paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and or species and of the phylogenetic relations between the genera fasciculithus heliolithus discoasteroides and discoaster as well as between rhomboaster and tribrachiatus the exceptional record provided by the continuous composite sequence recovered at walvis ridge allows us to describe the mode of evolution among calcareous nannoplankton new genera and or new species usually originated through branching of lineages via gradual but relatively rapid morphological transitions as documented by the presence of intermediate forms between the end member ancestral and descendant forms significant modifications in the calcareous nannofossil assemblages are often related to significant changes in environmental conditions but the appearance of structural innovations and radiations within a single genus also occurred during stable environmental conditions these lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control

post sampling dissolution and the consistency of nannofossil diversity measures a case study from freshly cored sediments of coastal tanzania abstract this study investigates the potentially deleterious effect of prolonged sample storage on the reliability of calcareous nannofossil species abundance and community diversity measures and their subsequent interpretation as paleoceanographic proxies nannofossil assemblages from two freshly cored successions of hemipelagic clay were documented over a one year period using a series of paired smear slides the first made from sediment samples within a day of coring and the second either 6 months or 1 year later diversity measured by shannon s h is consistent between the two sets for the majority of samples however significant changes both positive and negative were recorded in a number of cases and appear to be largely due to variations in smear slide thickness and not to post sampling dissolution there is no significant change in nannofossil fragmentation or abundance over time although the relative abundances of small dissolution susceptible placoliths of reticulofenestra minuta do appear to decrease with time in some samples counts of mineral grains show that there is a significant loss of fine 1 2 m cubic pyrite within months of drilling and this combined with the decline in abundance of r minuta suggests that limited pyrite oxidation coupled to carbonate dissolution is occurring geochemical analyses confirm that these sediments contain significant concentrations of sulphate one year after sample recovery which may be the result of gypsum formation associated with the oxidation of pyrite estimates of pyrite oxidation suggest that up to 3 of the original calcium carbonate has dissolved in the year after coring which could account for the observed loss of small placoliths effects of this kind are almost certainly confined to hemipelagic sequences rich in organic matter and or reduced iron but are frequently offset by the exceptional preservation of calcareous microfossils that can occur within such sediments

calcareous nannofossil changes in response to the spreading of the south china sea basin during eocene oligocene abstract numerous models have been proposed to constrain the process of the south china sea formation yet the paleogene paleoenvironmental researches are hindered by the paucity of long continuous well dated geological records in this work eocene to oligocene nannofossil biostratigraphy and assemblage changes in a sediment section from the northern south china sea were studied to shed light on these issues we established an age model to confine the studied section between 40 and 22 ma based on 17 calcareous nannofossil datum levels the age model enabled to date the most prominent seismic reflector t60 centered at 26 8 ma a regional tectonic event interpreted as corresponding to the ridge jump event in the early phase of south china sea spreading changes in nannofossil abundance and assemblage compositions imply continuous transgression and deepening of water depth from the late eocene to early miocene during the late eocene the studied area was a neritic sea with relatively eutrophic conditions supporting abundant r lockeri group and c pelagicus from 34 ma to 27 ma during the oligocene the earlier neritic environment was replaced by relative warm and oligotrophic conditions in a shallow sea as indicated by higher concentration of c floridanus sphenolithus spp and helicosphaera spp since 26 ma pelagic conditions prevailed small reticulofenestra

review of plausible chemical migration pathways in australian coal seam gas basins abstract coal seam gas csg or coal bed methane production has grown exponentially in australia over the last two decades with currently nearly 7000 productive wells and another 18 750 wells planned over the next five to ten years to address concerns over environmental contamination by hydraulic fracture fluids hff attributed to i incidents involving poor surface handling of hff and other fluids with potential migration pathways in soil and shallow groundwater and ii leakage pathways arising from hff injection into coal seams and unintended migration of these chemicals the national assessment of chemicals associated with coal seam gas extraction in australia the assessment was undertaken the assessment included a review of international studies on unconventional gas migration pathways to provide prior knowledge and comparison for use in the australian study the international literature highlighted that accidents with hff were mainly due to surface operations and included leaking equipment and spills contamination risks of groundwater from hydraulic fracturing itself were found to be very small based on analysis of micro seismic and groundwater hydrochemistry data geologic modelling of vertical fracture growth further reveals a low risk of leakage pathways developing in aquifers confined by deep shale formations this is due to limitations on the fracture growth vertically across aquitards often hundreds of meters thick retention within the shale of limited amounts of injected fluid and preferential fracture growth at shallow depths in the horizontal direction these arguments are broadly applicable to australian csg basins however important differences exist such as the reduced thickness in australia of the aquitards that separate the targeted gas resource from groundwater also hydraulic fracturing in australian coal seams is practised only when permeabilities are too low for gas extraction to be economical without stimulation from the nearly 10 000 csg wells drilled in the bowen and surat basins in queensland only 6 have received hydraulic fracturing to date the reduced risk of leakage pathways developing during csg production in australian basins is further corroborated by geologic criteria based on modelling and observations criteria include encountering certain favourable conditions during drilling injection i e i interfaces such as natural fractures faults and bedding planes which promote offsetting and branching or rock layers with higher fracture toughness causing the cessation or reduction in fracture growth ii narrow fractures due to a relatively higher elastic modulus leading to higher viscous flow loss iii high permeability layers and iv overlying layer s with a higher confining stress in addition to the leakage pathways considered in north american shale gas basins involving i pre existing fractures and faults or ii flow up the production well due to poor casing or cementing plausible chemical migration pathways in australian csg basins are due to iii connectivity via a fracture in or extended out of the coal seam formation between csg wells and water bores co located in the same formation and iv poor integrity water bores enhancing inter aquifer connectivity these plausible pathways are described and used in subsequent work as the basis of risk assessments for contamination at the local and regional scale

nannofossil assemblage fluctuations during the paleocene eocene thermal maximum at sites 213 indian ocean and 401 north atlantic ocean palaeoceanographic implications the paleocene eocene thermal maximum petm was an abrupt global warming event at f55 ma this event had profound effects on the biosphere quantitative investigations of calcareous nannofossil assemblages were performed across the petm at deep sea drilling project site 213 in the tropical indian ocean and site 401 in the bay of biscay north atlantic ocean at a temperate latitude calcareous nannofossil assemblages from both sites show major changes before during and after the petm fluctuations at site 213 are affected by selective dissolution of the least robust taxa by contrast assemblages in the lower part of the petm at site 401 show less diagenetic alteration and display high abundances of genera such as discoaster fasciculithus and ericsonia these taxa reflect relatively warm and probably oligotrophic surface waters abundances of the genus chiasmolithus an indicator of relatively cool and eutrophic waters decreased dramatically the upper portion of the petm is characterized by an increase in the abundance of toweius spp and zygrhablithus bijugatus interpreted as a return to cooler and more eutrophic conditions the elimination of fasciculithus was probably due to competition with the holococcolith species z bijugatus which occupied the same ecological niche the occurrences of long armed and asymmetrical discoaster species such as discoaster araneus discoaster anartios and discoaster okadai and rhomboaster species such as rhomboaster calcitrapa and rhomboaster cuspis are characteristic of the petm interval d 2004 elsevier b v all rights reserved

shelf and open ocean calcareous phytoplankton assemblages across the paleocene eocene thermal maximum implications for global productivity gradients abrupt global warming and profound perturbation of the carbon cycle during the paleocene eocene thermal maximum petm ca 55 ma have been linked to a massive release of carbon into the ocean atmosphere system increased phytoplankton productivity has been invoked to cause subsequent co2 drawdown cooling and environmental recovery however interpretations of geochemical and biotic data differ on when and where this increased productivity occurred here we present high resolution nannofossil assemblage data from a shelf section the u s geological survey usgs drill hole at wilson lake new jersey and an open ocean location ocean drilling program odp site 1209 paleoequatorial pacific these data combined with published biotic records indicate a transient steepening of shelf offshelf trophic gradients across the petm onset and peak with a decrease in open ocean productivity coeval with increased nutrient availability in shelf areas productivity levels recovered in the open ocean during the later stages of the event which coupled with intensified continental weathering rates may have played an important role in carbon sequestration and co2 drawdown

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

impact of groyne on channel morphology and sedimentology in an ephemeral alluvial river of bengal basin numerous groynes had been constructed on the dwarkeswar river to improve bank protection among them groynes adjacent to the village rautara of khandaghosh block west bengal have been studied which were constructed in the year of 2009 this study investigates the alteration of channel morphology sedimentology and flow characteristics influenced by emerged groynes through micro level field study an extensive field survey has been made with a dumpy level and fifty nine sediment samples were collected from the field different channel parameters such as degradation aggradation ratio braided index channel instability and bar occupied area indices have been used from 2003 to 2018 the simulation of channel flow has been done using hec ras it has been found that width depth w d ratio bankfull channel width channel area and sand bed length of the river decrease due to groyne construction on the other hand channel maximum bankfull channel depth depositional rate the difference between average depth maximum depth and braided index drastically increased increasing flow velocity flow deflection with coarse and poorly sorted multimodal sediments near the tip of the groynes as well as decreasing flow velocity curve flow path accelerated sedimentation with elevating river bed have been observed altogether result indicates that the emerged groynes are effective in protecting the river banks at the cost of channel degradation

an osmium isotope excursion associated with the late paleocene thermal maximum evidence of intensified chemical weathering in the latest paleocene an abrupt shift to more negative 13c values has been documented at numerous marine and terrestrial sites bralower et al 1997 cramer et al 1999 kaiho et al 1996 kennett and stott 1991 koch et al 1992 stott et al 1996 thomas and shackleton 1996 zachos et al 1993 this carbon isotope event cie is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4 6 c kennett and stott 1991 and more moderate warming in the subtropics thomas et al 1999 here we report 187os 188os isotope records from the north atlantic and indian oceans which demonstrate a 10 increase in the 187os 188os ratio of seawater coincident with the late paleocene cie this excursion to higher 187os 188os ratios is consistent with a global increase in weathering rates the inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate which acts to stabilize earth s climate walker et al 1981 estimates of the duration of late paleocene cie bains et al 1999 bralower et al 1997 norris and rohl 1999 rohl et al 2000 in conjunction with the os isotope data imply that intensified chemical weathering in response to warm humid climates can occur on timescales of 104 105 years this interpretation requires that the late paleocene thermal maximum os isotope excursion be produced mainly by increased os flux to the ocean rather than a transient excursion to higher 187os 188os ratios in river runoff although we argue that the former is more likely than the latter we cannot rule out significant changes in the 187os 188os ratio of rivers

calcareous nannofossils from the paleocene eocene thermal maximum of the equatorial atlantic odp site 1260b evidence for tropical warming abstract independent geological and micropaleontological lines of evidence suggest a 200 kyr period of intense warming covering the paleocene eocene boundary interval petm it has been suggested that this warming was initiated by a massive release of methane from the continental slopes among other groups of organisms calcareous nannofossils are characterized by a remarkable increase of warm water taxa during this interval here we report the tropical response of calcareous nannofossils to the paleocene eocene interval in odp site 1260b 283 15 276 35 mbsf the petm is about 1 38 m thick 279 88 278 5 mbsf as defined by the onset and termination of the 13c excursion and is marked by a 12 cm thick laminated clay layer at the start of the excursion a 30 cm thick interval 279 75 279 45 mbsf directly above the clay layer is characterized by common discoaster spp and coccolithus subpertusus syn ericsonia subpertusus and the first occurrences of discoaster araneus rhomboaster cuspis and tribrachiatus bramlettei all five taxa are interpreted as proxies for warm surface waters the increase of discoaster spp during the petm is solely caused by the onset of the new species d araneus which is here seen as a malformed discoaster related to specific petm conditions these possibly include an acidification of the surface waters and or higher salinity the rhomboaster tribrachiatus group which first occurs in the petm is also thought to be a proxy for increased salinity the abundance of the genus toweius indicative for mesotrophic conditions declines simultaneously discoaster abundance decreases in the later stages of the petm being substituted by chiasmolithus and campylosphaera indicating a change to more eutrophic conditions the genus fasciculithus very common in the tropical paleocene suffered a dramatic decline in the clay layer basal petm without recovering later in the eocene this decline and the subsequent extinction of fasciculithus a solid robust nannolith are here thought to be related to a calcification crises perhaps caused by a high co2 concentration and an acidification of the oceans the observed changes in the composition of the calcareous nannofossils were relatively short lived following the course of the petm which was characterized by warm surface waters with possibly low ph conditions

multiple early eocene hyperthermals their sedimentary expression on the new zealand continental margin and in the deep sea the paleocene eocene thermal maximum petm ca 55 5 ma was a geologically brief interval characterized by massive influx of isotopically light carbon extreme changes in global climate and profound variations in earth system processes an outstanding issue is whether it was an isolated event or the most prominent example of a recurring phenomenon recent studies of condensed deep sea sections support the latter but this finding remains uncertain here we present and discuss lithologic and carbon isotope records across two lower eocene outcrops on south island new zealand the petm manifests as a marl rich horizon with a significant negative carbon isotope excursion cie above in sediment deposited between 54 and 53 ma are four horizons with similar though less pronounced expressions marl beds of all five horizons represent increased terrigenous sedimentation presumably linked to an accelerated hydrological cycle five corresponding clay rich horizons and cies are found in deep sea records although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution the presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 c depleted carbon during the early eocene

the paleocene eocene thermal maximum as recorded by tethyan planktonic foraminifera in the forada section northern italy abstract the forada section in the venetian pre alps of northern italy represents an expanded record of the paleocene eocene thermal maximum petm at a depositional paleodepth of about 1 km 0 5 km high resolution planktonic foraminiferal analysis of this section in a time interval of approximately 1 3 myr across the paleocene eocene boundary reveals striking faunal changes that allow the identification of eight phases a h the late paleocene was represented by stable warm and oligotrophic surface water conditions phase a unstable environmental conditions start well before the onset of petm ca 150 kyr phase b and involved a change towards eutrophy as marked by the increase of subbotina and the concomitant decrease of morozovella this step is also characterized by enhanced fragmentation and dissolution the interval corresponding to the main body of the carbon isotope excursion cie is characterized by a marked increase of acarinina though with some differences in the species composition and relative abundance both in high and low latitudes particularly in the tethyan area forada is no exception to this pattern however at forada two prominent peaks in abundance of acarininids are recorded ca 30 kyr prior to the onset of the cie thus suggesting an increase in temperature heralding the onset of the petm phase c interestingly the lower peak in abundance of acarinina just precedes the 1 carbon isotope negative shift occurring below the onset of the main cie the basalmost eocene corresponding to the lower part of cie curve is represented by intense planktonic foraminiferal dissolution implying an extraordinary rise of the ccd this interval has an estimated duration of about 16 kyr phase d the dominance of acarininids in the lower part of the cie phase e f ca 14 and 22 5 kyr is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the forada depositional environment at that time these acarininids include at forada also the temporally constrained acarinina sibaiyaensis and a africana the morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the cretaceous anoxic events suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the petm the recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups e g biserials globanomalinids igorinids planorotalids and pseudohastigerinids occurring in the middle part of the cie ca 30 kyr after the onset of the petm indicates an initial environmental recovery phase g a new stable state is definitely reached in the upper part of the forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late paleocene conditions phase h however the perturbation during the petm produced significant changes in the ocean geochemistry that endured after the petm event as testified by the prominent high carbonate dissolution characterizing the marly levels and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages these striking oscillations were not present in the latest paleocene

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

eocene biostratigraphy and magnetic stratigraphy from possagno italy the calcareous nannofossil response to climate variability a study of quantitative calcareous nannofossil biostratigraphy and magnetostratigraphy of a 68 m thick marine limestone section of late paleocene middle eocene age outcropping at possagno in northern italy shows that the section encompasses nannofossil zones np9 np15 equivalent to cp8 cp13b and chrons c24r c21n the paleocene eocene boundary was placed at the base a of d 13 c negative excursion from the literature that was found virtually coincident with the base of zone np9b the base of the middle eocene lutetian was placed at the base of chron c21r biostratigraphic events were generally found to be consistent with parallel events in recent time scales several potentially useful new events are also described in particular we detected the earliest specimens of dictyococcites at the base of chron c22r np12 np13 zonal transition which is several million years older than previous estimates correlation of possagno data to the oxygen isotope record from the literature allowed us to describe the temporal relationships between climate variability and calcareous nannofossil assemblages modifications in the nannofossil assemblage coeval to both the paleocene eocene thermal maximum petm and the early middle eocene long term climatic trend are recognized the short lived petm was coeval to provisional adaptations malformations and or ecophenotypes in the coccolithophores communities that were reabsorbed upon return to long term varying climatic conditions the early middle eocene long term climatic trend was instead coeval to true evolutionary trends with the appearance of the very successful noelaerhabdaceae clade whose offsprings include the most important bloom forming coccolithophorids in the modern ocean the early middle eocene can thus be considered the time in which nannoplankton communities set course toward modern structure triggering a reconfiguration of the global ocean life chain d 2005 elsevier b v all rights reserved

eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica paleoecological and paleoceanographic implications abstract the evolution of the southern ocean climate during the late eocene late oligocene interval is examined through high resolution quantitative calcareous nannofossil analyses on samples from the southern ocean sections on maud rise and kerguelen plateau we determined the abundance patterns of the counted species to clarify the biostratigraphy which we correlated with high resolution magnetostratigraphy roberts a p bicknell s j byatt j bohaty s m florindo f harwood d m 2003a magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 in florindo f cooper a k o brien p a eds antarctic cenozoic palaeoenvironments geologic record and models palaeogeogr palaeoclimatol palaeoecol 198 145 168 florindo f roberts a p in press eocene oligocene magnetobiochronology of odp sites 689 and 690 maud rise weddell sea antarctica geol soc am bull and used this data to interpret paleoceanographic changes through the late eocene to late oligocene percentage plots of the individual species compared with r mode principal component and cluster analysis results allowed us to divide the assemblages into three groups temperate water taxa cool water taxa and no temperature affinity taxa we attempt correlations between these paleoecological groups and the major sea surface temperature sst variations with tectonic and paleoceanographic changes in the southern ocean during the late eocene the nannofossil assemblage data reveal that there were several minor sst decreases coolings from 36 to 34 ma before the eocene oligocene e o boundary a sharp cooling event dated at 33 54 ma earliest oligocene occurred about 160 kyr after the e o boundary which is dated at 33 7 ma relatively stable cool conditions are interpreted to persist until the latest oligocene when an increase in abundance of temperate water taxa which corresponds to an antithetical decrease in abundance of cool water indicators is recorded on the basis of our dating the opening of the drake passage allowing shallow water circulation began by 33 54 ma at the latest while the establishment of deep water connections through the tasmanian gateway occurred at 33 ma as suggested by exon et al proc odp init rep 189 2001 1

major shifts in calcareous phytoplankton assemblages through the eocene oligocene transition of tanzania and their implications for low latitude primary production a high resolution record of exceptionally well preserved calcareous nannofossil assemblages from tanzania is marked by two key transitions closely related to the climatic events of the eocene oligocene transition eot the first transition at similar to 34 0 ma precedes the first positive shift in delta o 18 and coincides with a distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures sst the second at similar to 33 63 ma is immediately above the eocene oligocene boundary eob and is associated with a significant drop in nannofossil diversity both transitions involve significant reductions in the abundance of holococcoliths and other oligotrophic taxa these changes in calcareous phytoplankton assemblages indicate 1 a widespread and significant perturbation to the low latitude surface ocean closely tied to the eob 2 a potential role for reduced carbonate primary production at the onset of global cooling and 3 a significant increase in nutrient availability in the low latitude surface ocean through the eot

early to middle eocene magneto biochronology of the southwest pacific ocean and climate influence on sedimentation insights from the mead stream section new zealand the mead stream section south island new zealand consists of a 650 m thick series of continuous well exposed strata deposited on a south pacific continental slope from the late cretaceous to the middle eocene we examined the uppermost paleocene middle eocene part of the section which consists of 360 m of limestone and marl for detailed magnetic polarity stratigraphy and calcareous nannofossil and foraminifera biostratigraphy magneto biostratigraphic data indicate that the section straddles magnetic polarity chrons from c24r to c18n calcareous nannofossil zones from np9a to np17 cnp11 cne15 following a recently revised paleogene zonation and from the waipawan to the bortonian new zealand stages i e from the base of the ypresian to the bartonian international stages the mead stream section thus encompasses 17 m y 56 39 ma of southwest pacific ocean history the ages of calcareous nannofossil biohorizons are consistent with low to midlatitude data from the literature indicating that during the early middle eocene the low to midlatitude calcareous nannofossil domain extended at least to 50 s 55 s in the south pacific correlation of the magnetic polarity stratigraphy from the mead stream section with the geomagnetic polarity time scale allows us to derive sediment accumulation rates sar which range between 8 and 44 m m y comparing the sar with paleotemperature proxy records we found that two intervals of increased sar occurred during the early eocene climatic optimum 52 50 ma and during the transient warming event peaking with the middle eocene climatic optimum 40 5 ma this correlation indicates that at mead stream the climate evolution of the early middle eocene is recorded in a sedimentation pattern whereby on a million year time scale warmer climate promoted continental weathering transportation and accumulation of terrigenous sediments

mode and tempo of the paleocene eocene thermal maximum in an expanded section from the venetian pre alps mode and tempo of an expanded paleocene eocene thermal maximum section in the venetian pre alps

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

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

episodes of intensified biological productivity in the subtropical atlantic ocean during the termination of the middle eocene climatic optimum meco the middle eocene climatic optimum meco is an 500 kyr interval of pronounced global warming from which the climate system recovered in 50 kyr the deep sea sedimentary record can provide valuable insight on the marine ecosystem response to this protracted global warming event and consequently on the ecological changes during this time here we present new benthic foraminiferal assemblage data from ocean drilling program site 1051 in the subtropical north atlantic spanning the meco and post meco interval 41 1 to 39 5 ma we find little change in the species composition of benthic foraminiferal assemblages during the studied interval suggesting that the rate of environmental change was gradual enough that these organisms were able to adapt however we identify two transient intervals associated with peak warming higher productivity interval hpi 1 40 07 39 96 ma and shortly after the meco hpi 2 39 68 39 55 ma where benthic foraminiferal accumulation rates increase by an order of magnitude these hpis at site 1051 appear to coincide with intervals of strengthened productivity in the tethys southern ocean and south atlantic and we suggest that an intensified hydrological cycle during the climatic warmth of the meco was responsible for eutrophication of marine shelf and slope environments

an early eocene carbon cycle perturbation at 52 5 ma in the southern alps chronology and biotic response an early eocene carbon cycle perturbation at 52 5 ma from the southern alps chronology and biotic response

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels