tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

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

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

global cooling accelerated by early late eocene impacts at ocean drilling program site 689 maud rise southern ocean 18o records of fine fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late eocene extraterrestrial impact events a simultaneous surface water productivity increase as interpreted from 13c data is explained by enhanced water column mixing due to increased latitudinal temperature gradients these isotope data appear to be in concert with organic walled dinoflagellate cyst records across the same microkrystite bearing impact ejecta layer in the mid latitude massignano section central italy in particular the strong abundance increase of thalassiphora pelagica is interpreted to indicate cooling or increased productivity at massignano because impact induced cooling processes are active on time scales of a few years at most the estimated 100 k y duration of the cooling event appears to be too long to be explained by impact scenarios alone this implies that a feedback mechanism such as a global albedo increase due to extended snow and ice cover may have sustained impact induced cooling for a longer time after the impacts

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

planktonic foraminiferal biostratigraphy and mechanisms in the extinction of morozovella in the late middle eocene the muricate planktonic foraminiferal genera morozovella and acarinina were abundant and diverse during the upper palaeocene to middle eocene and dominated the tropical and subtropical assemblages a significant biotic turnover in planktonic foraminifera occurred in the latest middle eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids these genera are extensively employed as palaeoclimatic and biostratigraphic markers and therefore this turnover episode is an important event in the record of the cenozoic planktonic foraminifera sediments from the western north atlantic ocean drilling program site 1052 were examined in order to investigate these extinction events in terms of both timing and mechanisms biostratigraphic events of the middle and late eocene have been examined with a sampling resolution of approximately 3 kyr these have been calibrated to the magneto and astrochronology to accurately define the timing of key biostratigraphic events particularly the extinction of morozovella spinulosa which is a distinct biomarker for late middle eocene sediments high resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form the large acarininids acarinina praetopilensis terminate 10 kyr prior to the extinction of m spinulosa and small acarininids acarinina medizzai and acarinina echinata continue into the upper eocene high resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western north atlantic to reconstruct sea surface temperatures ssts and deep water temperatures and the structure of the water column around this major biotic turnover whilst the extinctions of m spinulosa and a praetopilensis occur during a long term cooling trend the biotic turnover in the muricate group does not appear to be related to significant climatic change sea surface temperatures decrease slowly prior to the extinction events and there is no evidence for a large temperature shift associated with the faunal changes the turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae d 2003 elsevier b v all rights reserved

regional scale paleobathymetry controlled location but not magnitude of tidal dynamics in the late cretaceous western interior seaway usa despite extensive outcrop and previous sedimentologic study the role of tidal processes along sandy wave and river dominated shorelines of the north american cretaceous western interior seaway remains uncertain particularly for the extensive mid campanian c 75 77 5 ma tidal deposits of utah and colorado usa herein paleotidal modelling paleogeographic reconstructions and interpretation of depositional process regimes are combined to evaluate the regional scale 100 1000km basin physiographic controls on tidal range and currents along these regressive shorelines in the utah bight southwestern western interior seaway paleotidal modelling using a global and astronomically forced tidal model combined with paleobathymetric sensitivity tests indicates the location of stratigraphic units preserving pronounced tidal influence only when the seaway had a deep center 400 m and southern entrance 100 m maximum tidal velocity vectors under these conditions suggest a dominant south easterly ebb tide within the utah bight consistent with the location and orientation of paleocurrent measurements in regressive tide influenced deltaic units the modelled deep paleobathymetry increased tidal inflow into the basin and enhanced local scale 10 100 km resonance effects in the utah bight where an amphidromic cell was located however the preservation of bidirectional mudstone draped cross stratification in fine to medium grained sandstones requires tides in combination with fluvial currents and or local tidal amplification below the maximum resolution of model meshes c 10 km these findings suggest that whilst regional scale controls govern tidal potential within basins localized physiography exerts an important control on the preservation of tidal signatures in the geologic record

production of sulphate rich vapour during the chicxulub impact and implications for ocean acidification following the chicxulub impact many foraminifera in near surface waters perished but bottom dwelling species survived impact experiments suggest that sulphate in chicxulubs target rocks was released as predominantly sulphur trioxide which would have been converted to sulphuric acid in the atmosphere and swept down swiftly by larger particles acidifying the ocean surface

basaltic explosive volcanism but no comet impact at the paleocene eocene boundary high resolution chemical and isotopic records from egypt spain and denmark in the search for a triggering mechanism for the paleocene eocene p e boundary event 55 ma centimeter resolution chemical e g ir os pt and isotope e g os o 187 os 188 he 3 he 4 sr 87 sr 86 records across this boundary have been established for six uplifted marine sections in egypt spain and denmark the sections studied represent some of the stratigraphically most complete records across the onset of the carbon isotopic excursion cie and associated benthic foraminifera extinctions that mark the paleocene eocene boundary high sensitivity analyses failed to uncover evidence of extraterrestrial element or isotope enrichments in the six sections refuting the hypothesis of a major comet impact at the boundary preliminary searches for other impact indicative features such as spherules or shocked quartz also gave negative results in the danish section studied three basaltic ir rich ash layers occur at the paleocene eocene boundary but no similar ashes were found in egypt or spain the three ashes represent the earliest known manifestation of an unusual i to 2 million year long phase of explosive basaltic volcanism in the faero greenland region this volcanism is synchronous with major flood basalt effusions in east greenland and is associated with prominent paleogeographic changes in the high latitude north atlantic region discharge of mantle derived os to seawater during this volcanism may explain a small decrease in os o 187 os o 188 ratio at the paleocene eocene boundary in the zumaya section in spain the environmental perturbations at the paleocene eocene boundary appear to have been triggered by basaltic volcanism but any model for the detailed causal relation remains speculative c 2004 elsevier b v all rights reserved less

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

cretaceous tertiary boundary extinction pattern and faunal turnover at agost and caravaca s e spain abstract planktonic foraminiferal extinctions at caravaca and agost occurred over an extended time period similar to el kef and brazos river some species disappeared well below the boundary about 39 45 of the species but less than 15 of the individuals in the population became extinct at or near the k t boundary a second phase of extinction occurred at the top of the boundary clay po pla and the remaining cretaceous species except g cretacea disappeared in subzone pla species extinctions were selective eliminating geographically restricted large complex and deeper dwelling forms first and favoring survival of cosmopolitan small simple surface dwellers only surface dwellers survived the k t boundary event whereas all deeper dwelling species as well as some surface dwellers disappeared at the boundary we interprete the selective abundance decline during the latest cretaceous as a result of the seal level regression that reached a maximum just prior to the k t boundary the highly selective nature of the two phased species extinctions at and above the boundary we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the k t boundary a bolide impact however may have hastened the demise of an already declining cretaceous fauna

extinction and recovery of benthic foraminifera across the paleocene eocene thermal maximum at the alamedilla section southern spain abstract a complete succession of lower bathyal upper abyssal sediments was deposited across the paleocene eocene thermal maximum petm at alamedilla betic cordillera southern spain where the benthic foraminiferal turnover and extinction event associated with the negative carbon isotope excursion cie across the petm have been investigated detailed quantitative analyses of benthic foraminifera allowed us to distinguish assemblages with paleoecological and paleoenvironmental significance pre extinction fauna extinction fauna survival fauna including disaster and opportunistic fauna and recovery fauna these assemblages have been associated with significant parts of the 13 c curve for which a relative chronology has been established the correlation between the benthic turnover the 13 c curve the calcite and silicate mineral content and sedimentation rates allowed us to establish the sequence of events across the petm at alamedilla the benthic extinction event bee affected 37 of the species and it has been recorded over a 30 cm thick interval that was deposited in c a 10 ky suggesting a gradual but rapid pattern of extinction the beginning of the bee coincides with the onset of the cie 0 ky and with an interval with abundant calcite and it has been recorded under oxic conditions at the seafloor as inferred from the benthic foraminiferal assemblages and the reddish colour of the sediments we conclude that dissolution and dysoxia were not the cause of the extinctions which were probably related to intense warming that occurred before the onset of the cie the bee is immediately overlain by a survival interval dominated by agglutinated species the glomospira acme the low calcite content recorded within the survival interval may result from the interaction between dilution of the carbonate compounds by silicicate minerals as inferred from the increased sedimentation rates and the effects of carbonate dissolution triggered by the shoaling of the ccd we suggest that glomospira species disaster fauna may have bloomed opportunistically in areas with methane dissociation in and around the north atlantic the disaster fauna was rapidly replaced by opportunistic taxa which point to oxic and possibly oligotrophic conditions at the seafloor the ccd gradually dropped during this interval and calcite preservation improved towards the recovery interval during which the 13 c values and the calcite content recovered c a 71 25 to 94 23 ky and stabilized 94 23 ky coeval with a sharp decrease in sedimentation rates

spatial and temporal evolution of coastal depositional systems and regional depositional process regimes campanian western interior seaway u s a abstract this paper provides a critical review and regional synthesis of late cretaceous shallow marine deposits along part of the western margin of the western interior seaway of north america which contains the most extensively documented outcrop based studies of siliciclastic coastal depositional systems in the world the results of this synthesis are presented in the form of paleogeographic maps covering present day new mexico utah colorado and wyoming usa for five timeslices in the campanian these maps are used to evaluate the spatial and temporal evolution of regional depositional process regimes along a large 1000 m stretch of coastline the evolution of regional depositional process regimes is linked to tectonic and paleoceanographic controls on the western interior seaway which enables the results of this synthesis to be applied to prediction of depositional process regimes in other less intensively studied basins six gross depositional environments have been mapped for each timeslice 1 alluvial to coastal plain sandstones 2 coastal plain coals mudstones and sandstones 3 shoreline sandstones 4 marine mudstones 5 gravity flow siltstones and sandstones and 6 marine marls and chalk shoreline sandstones in each timeslice are interpreted in further detail using documented evidence for the three principal classes of depositional process wave tidal and fluvial and published reconstructions of coastal morphology which is widely considered to reflect depositional process regime based on these interpretations shoreline sandstones are assigned to five categories of depositional process regime 1 regressive wave dominated shorefaces and delta fronts 2 regressive river dominated delta fronts 3 regressive mixed tide and wave influenced delta fronts 4 regressive tide dominated delta fronts and 5 transgressive barrier islands back barrier lagoons and estuaries the accuracy of and uncertainty in classification of depositional process regime are critically evaluated additionally stratal thickness and sediment routing pathways have been interpreted in order to assess the impact of tectonic and paleoceanographic controls on spatial and temporal changes in all of the evaluated shallow marine successions thin tide influenced intervals were deposited in back barrier and lagoon systems associated with net transgressive shorefaces and estuaries however it is notable that all preserved tide dominated and tide influenced regressive deltaic systems are located along the northern margin of the utah bight a tectonically related embayment that had a pronounced expression during the middle campanian the southern margin of the embayment and coastlines to the north are conspicuously more wave dominated which supports their exposure to a larger wave fetch in contrast the northern margin of the embayment was relatively wave protected it is concluded that tidal range was amplified due to resonance of the principal semidiurnal tide in the strongly embayed geometry of the middle campanian utah bight

depositional remnants part 2 examples from the western interior cretaceous basin of north america the western interior cretaceous basin contains numerous examples of depositional remnants partially preserved portions of originally extensive depositional systems emphasis is placed on examples of accommodation remnants i e a type of depositional remnant whose overlying erosion surface displays little relief and is preserved in an area of locally increased accommodation variations in spatial accommodation have been attributed to synsedimentary tectonics erosional topography differential compaction and salt dissolution and are commonly associated with basement faults remnants range in size from small to very large basin scale and larger remnants commonly contain several smaller remnants remnants of shallow marine sandstone encased in shale are an important and common type of stratigraphic trap failure to recognize deposits as only remnants of depositional systems has led to misinterpretations of depositional environment and inaccurate paleogeographic reconstructions

catastrophic extinction of planktonic foraminifera at the cretaceous tertiary boundary evidenced by stable isotopes and foraminiferal abundance at caravaca spain we present data demonstrating constant 13c values in 12 common planktonic foraminiferal species which constitute 99 of the total specimens 63 mu m in assemblages collected across the cretaceous tertiary k t boundary at caravaca spain these latter values are in contrast to a rapid reduction in 13c in samples of the fine fraction of carbonate at the k t boundary and a subsequent negative shift of 13c of a benthic foraminiferal species these results indicate that the post k t occurrences of cretaceous planktonic species in lower danian sediments at caravaca are the result of reworking rapid decreases in the percentage abundance of well preserved specimens and in the number of specimens per gram of carbonate for the same 12 species at the k t boundary also suggest reworking and abrupt extinction at the k t boundary our data imply that sudden changes occurred within the pelagic ecosystem during the k t boundary event

bioturbation sedimentation rates and preservation of flood events in deltas abstract we examine the nature and number of event beds preserved in heterolithic prodelta and delta front strata in five proximal accumulation dominated pad north american delta systems including the quaternary gulf of mexico and the late cretaceous western interior seaway we also explore the continuum between pad more distal deposits of mud belts and thicker subaqueous delta clinoforms sdc sediment accumulation rates in modern pad and sdc systems are commonly on the order of several to severaltens of centimeters per year they also show that several event beds may be created annually with preservation depending on supply and reworking the pad heterolithics commonly comprise interbedded sand silt and clay these show normal and inverse grading and bouma sequences indicating deposition from turbidity currents and hyperpycnal flows that are interpreted as the products of river plumes generated during flood episodes re equilibrated rosselia socialis in stacked delta front turbidite bedsets in the cretaceous examples show that floods may occur as a cluster of events over several months shelf areas adjacent to river mouths may experience high rates of sediment delivery from rivers but oceanographic processes are instrumental in moving much of the silt and clay farther along the shelf direct hyperpycnal delivery from a river mouth on a low gradient shelf i e typically

iles clastic wedge development and sediment partitioning within a 300 km fluvial to marine campanian transect 3 m y western interior seaway southwestern wyoming and northern colorado a 300 km 186 mi transect was reconstructed across the 500 m 1640 ft thick 3 m y duration iles clastic wedge in southern wyoming and northern colorado using well logs and stratigraphic columns this wedge developed into the middlelate campanian aged western interior seaway by progradation from the active sevier fold and thrust belt and adjacent uplifted areas the wedge thickens basinward because late stage widespread uplift of the fold belt caused multiple unconformities across the proximal former foredeep reaches of the foreland basin transect analysis allows the wedge and its component sequences to be better understood and permits a two dimensional characterization of the sand and mud distribution the iles wedge exhibits 11 low gradient regressive transgressive high frequency sequences that were correlated across several hundred kilometers sediment partitioning analysis along the transect shows the following 1 within the regressive limb of the iles wedge the component higher order regressive compartments tend to thicken into the medial reaches of the wedge whereas transgressive compartments thicken landward this geometry is driven by preferential erosion in proximal areas during regression bypassing much sediment to the marine shorelines and transgressive backfilling into proximal areas previously eroded more deeply 2 the greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline deltaic facies of the regressive compartments 3 as the high frequency sequences develop the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge apparently reflecting stronger erosion and sediment bypass during these times

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

variability of lowstand wedges and their distinction from forced regressive wedges in the mesaverde group southeast wyoming the debate on the geometry and origin of shelf sandbodies has evolved from a discussion of how sands and gravels managed to move from shorelines far out onto muddy shelves to an acceptance that many of these sandbodies did not originate on the shelf but were simply resident there after a fall and subsequent rise of sea level in the efforts to reinterpret these sandstones there has been some tendency to underestimate how varied they can be data from eight such shelf sandstone tongues campanian in southeast wyoming are used to illustrate how variable lowstand prograding wedges can be and how these should in addition be distinguished from forced regressive wedges the depositional environments encountered in these two types of wedges are surprisingly different and the lowstand wedges which are frequently tidally influenced show a greater affinity with the overlying transgressive tract than with the preceding wave dominated forced regressive shoreface deposits

anomalous clastic wedge development during the sevier laramide transition north american cordilleran foreland basin usa new high resolution regional correlation and isopach maps provide evidence that 1 laramide style deformation began as early as ca 77 ma in central utah and 2 rapid 208 km m y 1 and extensive 400 km progradation of a clastic wedge was facilitated by reduced subsidence during the transition from sevier to laramide style deformation this study defi nes three campanian alluvialto marine clastic wedges that traversed 200 400 km eastward across the utah colorado segment of the cordilleran foreland basin wedges a and c are thicker successions with rising trajectory shoreline stacking patterns blackhawk formation and lower castlegate sandstone bluecastle tongue and rollins sandstone that refl ect relatively slow overall progradation 50 81 km m y 1 of narrow 10 20 km wide wave dominated shorelines in contrast wedge b consists of lower volume successions with a fl at to falling shoreline stacking pattern middle castlegate sandstone sego sandstone neslen formation corcoran and cozzette members of the iles formation that suggests rapid progradation 208 km m y 1 of embayed 60 80 km wide mixed energy wave and tide infl uenced shore lines wedges a and c prograded 200 250 km in more than 3 m y whereas wedge b prograded 340 400 km in 2 m y 170 km m y 1 the anomalously extensive wedge b is unique in the utah colorado segment because of its long extent rapid progradation rate dominance of tidally infl uenced facies long transit transgressions regressions and low accommodation nested sequence architecture stratigraphic relationships indicate development of wedge b coeval with both sevier and laramide style deformation in utah assuming a constant sediment supply the extensive 300 400 km sheet like amalgamated wedge wedge b may have been caused by 1 reduced subsidence driven by a fl exural interference pattern whereby two short wavelength 200 km fl exural profi les are superimposed during the uplift of both basement cored and thin skinned thrust belt 2 an increase in or eastward migration of dynamic subsidence during tectonic transitions associated with slab fl attening or rollback i e long wavelength fl exure or 3 reduced subsidence due to short wavelength fl exural interference augmented by the reduction or migration of long wavelength fl

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

chicxulub impact event is cretaceous paleogene boundary in age new micropaleontological evidence abstract high resolution and quantitative planktic foraminiferal biostratigraphy from two se mexico stratigraphic sections bochil guayal shows that the chicxulub related complex clastic unit ccu is synchronous with the ejecta rich airfall layer and the cretaceous paleogene k pg catastrophic mass extinction horizon in the el kef tunisia and caravaca spain sections the lowermost danian h holmdelensis subzone biozone p0 was identified in both sections in a thin dark clay bed just above the ccu proving that such bed is chronostratigraphically equivalent to the k pg boundary clay of the el kef stratotype these new micropaleontogical data confirm that the k pg impact event and the chicxulub impact event are the same one this contradicts the suggestion by others that the chicxulub impact predated the k pg boundary by about 300 ka

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

evidence and causes of the main extinction events in the paleogene based on extinction and survival patterns of foraminifera abstract we review the four main extinction events in the paleogene from the cretaceous paleogene boundary to the eocene oligocene boundary integrating the results obtained from a study of foraminiferal assemblages with other paleontological and geological data different survival strategies followed by the species are described and the duration of the phases of extinction survival and recovery is estimated the models and patterns of extinction of the foraminifera are highlighted we present a range of evidence and paleo environmental factors and analyze the possible causes of extinction a new terminology for mass extinction events is proposed sudden mass extinction would have happened virtually instantaneously and the process would have taken a few years or decades cretaceous paleogene boundary rapid mass extinction is defined as that which occurred in relatively short events around 100 kyr paleocene eocene and eocene oligocene boundaries slow mass extinctions are suggested to have lasted around 1 myr bartonian priabonian transition and may even have lasted for several million years

paleogene opening of drake passage the timing of events leading to the earliest connection between the pacific and atlantic oceans at drake passage is controversial but important because gateway opening probably had a profound effect on global circulation and climate a rigorous new analysis of marine geophysical data demonstrates a major change in the motion of the south american and antarctic plates at about 50 ma from n s to wnw ese accompanied by an eightfold increase in separation rate this would have led to crustal extension and thinning and perhaps the opening of small oceanic basins with the probable formation of a shallow b1000 m gateway during the middle eocene no change in south american antarctic motion is observed near the eocene oligocene boundary but a deep water connection developed between 34 and 30 ma when continued extension led to the initiation of seafloor spreading at the west scotia ridge these timings correlate with events seen in the oxygen isotope record from benthic foraminera and support the view that drake passage opening was the trigger for abrupt eocene oligocene climate deterioration and the growth of extensive antarctic ice sheets d 2005 elsevier b v all rights reserved

catastrophic mass extinction and assemblage evolution in planktic foraminifera across the cretaceous paleogene k pg boundary at bidart sw france abstract a high resolution biostratigraphic analysis of planktic foraminifers confirms that the bidart section at the eastern margin of the atlantic ocean exhibits a continuous and complete cretaceous paleogene k pg transition interval the biozones and subzones recorded in this section are less expanded than their equivalent in tunisian sections el kef global stratotype section and point gssp for the k pg boundary and elles auxiliary section but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the k pg transition throughout the uppermost 4 m maastrichtian the planktic foraminiferal assemblages are highly diversified containing up to 72 species these maastrichtian assemblages are rich in cosmopolitan taxa 70 dominated by small biserial morphotypes which belong mainly to the genus heterohelix which coexist with less abundant but highly diverse tropical and subtropical species the extinction pattern at the bidart section suggests a sudden catastrophic mass extinction at the k pg boundary which affected at least 53 out of 72 species the species becoming extinct include globotruncanids e g contusotruncana spp globotruncana spp globotruncanita spp and complex heterohelicids e g racemiguembelina spp pseudotextularia spp gublerina spp at the bidart section only archaeoglobigerina cretacea disappears 2 m below the k pg boundary event specimens of 18 small and even tiny maastrichtian species are found at the lowermost danian only a few of these species belonging to the genera of guembelitria hedbergella and heterohelix are considered to be real cretaceous survivor species whereas the specimens belonging to the rest are most probably reworked because they differ in their preservation throughout lowermost danian the planktic foraminiferal assemblages are dominated by opportunistic species of the genus guembelitria these opportunists are associated to small and poorly diversified pioneer globigerinids palaeoglobigerina spp and parvularugoglobigerina spp these assemblages became progressively more diversified across the early danian containing species with cancellate walls eoglobigerina spp parasubbotina spp subbotina triloculinoides and praemurica spp and new taxa of biserial heterohelicids woodringina spp and chiloguembelina spp suggesting a paleoenvironmental recovery

extraterrestrial ni rich spinel in upper eocene sediments from massignano italy evidence of a major cosmic event at the end of the eocene is given by the finding of at least one possibly two or more impact horizons containing microtektites microkrystites shocked quartz and unusually high iridium concentrations we report here the discovery in the global stratotype of the eocene oligocene boundary at massignano in italy of ni rich spinel a mineral that forms by the interaction of meteoritic bodies with the earth s atmosphere a maximum concentration of 800 crystals mg 1 corresponding to a flux of 2 107 crystals cm 2 is observed in a well dated layer 35 7 0 4 ma that also contains shocked quartz and iridium the crystals are found clustered in flattened spheroids the probable relic of their host bodies the chemical and physical characteristics of the spinel crystals indicate that the spheroids formed by interaction of dust particles in the upper part of the atmosphere rather than by ablation of large objects as proposed for the spinel bearing spheroids found at the cretaceous tertiary boundary the most likely explanation is that the dust particles were generated by a large cometary impact whether this impact is the one that produced microtektites and or microkrystites or another one that may have occurred shortly after or before is still questionable additional searching for ni rich spinel at other upper eocene sections may help to answer this question

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

foraminiferal turnover across the eocene oligocene transition at fuente caldera southern spain no cause effect relationship between meteorite impacts and extinctions we studied planktic and small benthic foraminifera from the fuente caldera section southern spain across the eocene oligocene transition benthic foraminifera indicate lower bathyal depths for the late eocene and earliest oligocene detailed highresolution sampling and biostratigraphical data allowed us to date precisely layers with evidence for meteorite impact ni rich spinel which occur in the lower part of the planktic foraminiferal globigerapsis index biozone and in the middle part of the small benthic foraminiferal cibicidoides truncanus bb4 biozone middle priabonian late eocene major turnovers of foraminifera occur at the eocene oligocene boundary only the impact did not occur at a time of planktic or benthic foraminiferal extinction events and the late eocene meteorite impacts did thus not cause extinction of foraminifera the most plausible cause of the eocene oligocene boundary extinctions is the significant cooling which generated glaciation in antarctica and eliminated most of the warm and surface dwelling foraminifera d 2005 elsevier b v all rights reserved

a case for a comet impact trigger for the paleocene eocene thermal maximum and carbon isotope excursion abstract we hypothesize that the rapid onset of the carbon isotope excursion cie at the paleocene eocene boundary 55 ma may have resulted from the accretion of a significant amount of 12c enriched carbon from the impact of a 10 km comet an event that would also trigger greenhouse warming leading to the paleocene eocene thermal maximum and possibly thermal dissociation of seafloor methane hydrate indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite rich shelf sediments that closely coincide with the onset and nadir of the cie at three drill sites on the atlantic coastal plain after considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron rich nanophase material at the cretaceous tertiary boundary we suggest that the cie occurrence was derived from an impact plume condensate the sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket published reports of a small but significant iridium anomaly at or close to the paleocene eocene boundary provide supportive evidence for an impact

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

impact origin of the chesapeake bay structure and the source of the north american tektites seismic profiles drill core samples and gravity data suggest that a complex impact crater 35 5 million years old and 90 kilometers in diameter is buried beneath the lower chesapeake bay the breccia that fills the structure contains evidence of shock metamorphism including impact melt breccias and multiple sets of planar deformation features shock lamellae in quartz and feldspar the age of the crater and the composition of some breccia clasts are consistent with the chesapeake bay impact structure being the source of the north american tektites

sharp based tide dominated deltas of the sego sandstone book cliffs utah usa the lower part of the cretaceous sego sandstone member of the mancos shale in east central utah contains three 10 to 20 m thick layers of tide deposited sandstone arranged in a forward and then backward stepping stacking pattern each layer of tidal sandstone formed during an episode of shoreline regression and transgression and offshore wave influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide influenced river deltas during a time of fluctuating relative sea level shale dominated offshore marine deposits gradually shoal and become more sandstone rich upward to the base of a tidal sandstone layer the tidal sandstones have sharp erosional bases that formed as falling relative sea level allowed tides to scour offshore marine deposits the tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts most delta top deposits were stripped during transgression where the distal edge of a deltaic sandstone is exposed a sharp based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand where more proximal parts of a deltaic sandstone are exposed a sharp based upward coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys or tide eroded estuaries formed during relative sea level lowstand or early stages of a subsequent transgression estuary fills are highly variable reflecting local depositional processes and variable rates of sediment supply along the coastline lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike estuarine fills cut into the forward stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward stepped deltaic sandstone tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines this contrasts with sandstones in similar basinal settings elsewhere which have been interpreted as tidally influenced only in transgressive parts of depositional successions

shocked quartz from the late eocene impact evidence from massignano italy this paper reports the discovery of shocked quartz grains within a well dated upper eocene marlstone at the massignano outcrop ancona italy the shocked quartz reaches a maximum concentration of 1 6 0 4 grains per cubic centimetre of bulk rock a modest ir anomaly is also coincident with the shocked quartz and together they strongly support an impact origin moreover this impact layer has a precise interpolated radiometric age of 35 7 0 4 ma although impact evidence found throughout the world indicates that at least two large impacts did occur during this time the actual number timing and environmental effects of these impact events remain unclear the late eocene was a critical time in earth history because of significant climatic biotic and environmental crises

radiolarian magnetobiochronology and faunal turnover across the middle late eocene boundary at ocean drilling program site 1052 in the western north atlantic ocean quantitative radiolarian assemblage analysis has been conducted on middle and upper eocene sediments zones rp16 to rp18 from ocean drilling program site 1052 in order to establish the radiolarian magnetobiochronology and determine the nature of the faunal turnover across the middle late eocene boundary in the western north atlantic ocean we recognize and calibrate forty five radiolarian bioevents to the magneto and cyclo stratigraphy from site 1052 to enhance the biochronologic resolution for the middle and late eocene our data is compared to sites in the equatorial pacific leg 199 to access the diachrony of biostratigraphic events eleven bioevents are good biostratigraphic markers for tropical subtropical locations south of 30 n the primary markers lowest occurrences of cryptocarpium azyx and calocyclas bandyca which are tropical zonal boundary markers for zones rp17 and rp18 provide robust biohorizons for correlation and age determination from the low to middle latitudes and between the atlantic and pacific oceans some other radiolarian bioevents are highly diachronous 1 million years between oceanic basins a significant faunal turnover of radiolarians is recognized within chron c17n 3n 37 7 ma where 13 radiolarian species disappear rapidly in less than 100 kyr and 4 new species originate the radiolarian faunal turnover coincides with a major extinction in planktonic foraminifera we name the turnover phase the middle late eocene turnover mlet assemblage analysis reveals the mlet to be associated with a decrease in low mid latitude taxa and increase in cosmopolitan taxa and radiolarian accumulation rates the mlet might be related to increased biological productivity rather than to surface water cooling

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

stratigraphy of late palaeocene events in the middle east implications for low to middle latitude successions and correlations we have investigated the upper palaeocene stratigraphical record in four sections in egypt and one in israel the sections are arranged on a depth transect across the southern tethyan margin in all sections a 13 c excursion and benthic foraminiferal extinctions coincide at a level within planktic foraminiferal zone p5 in three sections a bed sapropelic in two of the deeper profiles contains extraordinarily transient benthic and planktic foraminifera assemblages these planktic assemblages are dominated by acarinina and contain rare to common morozovella allisonensis and globanomalina luxorensis but unusually few other morozovella the extremely restricted stratigraphical range of m allisonensis to the lower part of the 13 c excursion enables 1 a three fold subdivision of zone p5 2 accurate correlation to the best sections spanning the 13 c excursion in the atlantic and pacific and 3 assessment of stratigraphical completeness over the 13 c excursion in other sub tropical successions discontinuities and especially dissolution intervals in many low to middle latitude marine successions elsewhere as in two middle east sections preclude an accurate correlation within the lower part of the 13 c excursion m allisonensis zone p5b three studied sections can provide the best coverage of the sequence of events over the onset and early part of the 13 c excursion in the middle east but as in most known sections probably none constitutes a complete upper palaeocene lower eocene record

the cretaceous palaeogene k p boundary at ain settara tunisia restructuring of benthic foraminiferal assemblages benthic foraminiferal assemblages in contrast to planktic foraminifera generally did not suffer mass extinctions at the cretaceous palaeogene k p boundary extinctions were fewer in deeper water however the outer shelf upper bathyal section at ain settara tunisia records a dramatic change in the structure of benthic foraminiferal assemblages across the k p boundary at the level of extinction of planktic assemblages and enrichment in ir and other geochemical anomalies highly diversified low dominance upper maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages strongly dominated by epifaunal morphogroups this extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply this in turn is the consequence of a sudden collapse in primary productivity probably resulting from the impact of the k p asteroid

palaeoenvironmental turnover across the palaeocene eocene boundary at the stratotype section in dababiya egypt based on benthic foraminifera the global stratotype section and point for the palaeocene eocene p e boundary was defined at dababiya quarry egypt at the base of the carbon isotope excursion cie we present the first detailed analysis of palaeocene eocene benthic foraminifera from dababiya in order to infer the palaeoenvironmental turnover across the p e boundary at dababiya the cie coincides with a major turnover in foraminiferal assemblages the last occurrence of angulogavelinella avnimelechi at the base of the cie may be correlated to the main phase of extinction of deep sea benthic foraminifera benthic foraminifera indicate that stressful conditions such as oxygen deficiency carbonate dissolution and changes in food supply persisted at the sea floor over most of the cie interval the main phase of recovery of benthic foraminifera is recorded c 250 cm above the p e boundary and it may be linked to increased productivity and oxygenation at the sea floor

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

what happens when the ocean is overheated the foraminiferal response across the paleocene eocene thermal maximum at the alamedilla section spain the global warming and major perturbation of the global carbon cycle that occurred during the paleocene eocene thermal maximum petm have been investigated in the lower bathyal upper abyssal alamedilla section spain geochemical anomalies and dramatic faunal changes including the globally recognized extinction event of deep sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils are associated with the petm at alamedilla biotic changes in the plankton and benthos indicate environmental instability 11 14 k y before the onset of carbon isotope excursion that marks the paleocene eocene boundary the reorganization of the planktic ecosystem points to warm and oligotrophic conditions in surface waters during the earliest eocene whereas faunal and geochemical data indicate that the extinctions of benthic foraminifera occurred over an interval with a high caco3 content and oxic conditions at the seafloor the proliferation of disaster taxa glomospira spp after the extinctions has been related to a potential source of isotopically light carbon in the western tethys and north atlantic significant changes in foraminiferal test size are documented across the petm we suggest that increased temperatures played an important role in benthic foraminiferal test size increasing their metabolic rates and consequently their food requirements decreased planktic foraminiferal test size may be related to decreased nutrient availability or surface water density however the differences in test size evolution among different species of both benthic and planktic foraminifera may be related to interspecific competition and ecological adaptations to direct or indirect consequences of the carbon addition during the petm

displacement along the red river fault constrained by extension estimates and plate reconstructions significant e w extension and or compression must have been generated by displacements along the red river fault rrf since its curvature does not match a small circle centered at the euler pole for the indochina south china plate pair the amount of extension perpendicular to the rrf offshore vietnam depends on the magnitude of left lateral displacement along the rrf in general the larger the left lateral displacement along the fault the smaller the amount of e w extension all purely strike slip models of the opening of the south china sea that assume large displacements 250 km along the rrf encounter major problems because they imply little extension or even considerable shortening offshore east vietnam this is inconsistent with the presence of large elongated basins offshore vietnam using a plate tectonic model we compare continental extension values implied by different magnitudes of displacement along the rrf with crustal stretching estimates derived from 2 d profiles modeled from gravity data we utilize 2 d gravity forward models to restore the extended continental margin crust to its original position prior to extension we find that substantial amounts of extension for offshore vietnam can only be modeled assuming moderate displacements along the rrf compatible with the presence of a southward subducting proto south china sea the total amount of ene wsw extension offshore northern vietnam constrained by our 2 d gravity profiles and gravity inversion increases southward from 36 to 89 km along the yinggehai basin these values of ene wsw extension are consistent with 250 km of left lateral displacement along the rrf

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago