deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

accumulation patterns of tertiary calcareous nannofossils around extinctions quantitative analysis of accumulation of tertiary calcareous nannofossil species allows a precise evaluation of their extinction patterns and thus of their biostratigraphic value accumulation of species commonly shows marked variability indicating that short sample intervals are necessary for estimating the true ranges the stratigraphic resolution which can be achieved is primarily determined by the sediment accumulation rate and the depth of homogeneous sediment mixing caused by bioturbation at about the time of extinction the accumulation usually shows a final sharp decline which often is followed by a tail of strongly reduced accumulation having a duration in the range of 2 3 103 to 4 5 105 years it is shown that this tail represents accumulation caused either by true production or postdepositional sediment mixing because of the difficulties involved in distinguishing these two casual mechanisms from each other biostratigraphic indications defined by the final sharp decline are generally superior in terms of synchroniety and ease of identification to those defined by the absolutely last occurrence

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

a new basis for recognizing the paleocene eocene boundary in western interior north america fossil pollen grains from paleocene eocene rocks of the bighorn basin of wyoming allow important sequences of terrestrial vertebrate fossils to be correlated with standard marine microfossil zonations the paleocene eocene boundary as based on pollen evidence falls within the wasatchian land mammal age much higher than the boundary used by some fossil mammal workers this discrepancy partly results from multiple definitions of the paleocene eocene boundary but may also indicate faulty mammal based correlations to the type sparnacian of france

late paleocene to middle eocene calcareous nannofossil biochronology from the shatsky rise walvis ridge and italy abstract the precision of late paleocene to middle eocene nannofossil datums is investigated by means of quantitative methods and correlated to the magnetic polarity stratigraphy using sequences from the northwest pacific southeast atlantic and italy it is the rule rather than the exception to find tails of very reduced abundances prior to or after a range of consistent and higher abundances the absolutely first or final occurrence of a species therefore seldom provides a synchronous datum when material from different geographic areas are compared on the other hand synchroneity is often confirmed when the initial sharp rise or the final sharp decline in abundance is used as datum level the use of datums not employed in the two principal existing nannofossil zonal schemes can substantially improve the biostratigraphic resolution two established zonal markers show abundance patterns making them unsuitable as datums the first occurrences of ellipsolithus macellus base np4 diachronous and tribrachiatus nunnii base np10 and paleocene eocene boundary too rare and too short range in open ocean sections the first occurrence of either fasciculithus spp or sphenolithus spp is a better marker near the base of np4 the first occurrence of discoaster diastypus at 56 6 ma represents a suitable replacement for recognition of the paleocene eocene boundary

eocene bathyal and abyssal benthic foraminifera from a south atlantic transect at 20 30 s abstract eocene age zone p6b p17 benthic foraminiferal faunas from 207 samples of atlantic ocean dsdp sites 19 20 357 363 522 and 523 were analyzed along a transect located at approximately 30 s and spanning the depth range from upper lower bathyal to lower abyssal there is a distinct abyssal bathyal faunal boundary in the eocene which was located above lower bathyal site 363 in zone p6b dropping below that depth for the remaining early and middle eocene it rose again to lower bathyal depths estimated between 1500 1800 m at the beginning of the late eocene abyssal faunas are highly dominated by spiral forms an abyssal faunal association 1 with codominant nuttalides truempyi and quadrimorphina together with abyssamina and clinapertina prevailed at lower abyssal depths hole 20c in the early eocene at upper abyssal depths site 19 and 523 it persisted in the middle eocene a n truempyi dominant 25 of the total fauna association 2 appeared at lower abyssal depths in early middle eocene at upper abyssal depths it first occurred in zone p12 interchanging with association 1 in the late middle eocene in early zone p15 an association with increased abundance of nuttallides umbonifer and high abundance of globocassidulina subglobosa replaced the n truempyi dominant association this replacement is observed at lower bathyal and abyssal sites all sites except site 357 and is the most pronounced faunal change observed in the eocene bathyal faunas contain uvigerinids bolivinids lenticulina high percentages of buliminids and are characterized by the absence of highly dominant species

an analysis of recent deep sea benthic foraminiferal morphotypes from the norwegian and greenland seas abstract benthic foraminifera from 36 core tops from the norwegian and greenland seas have been placed into morphotype categories based on test shape nature of coiling and the presence or absence of wall pores these morphotypes have distinctive patterns with water depth and are related to species specific microhabitat preferences the morphotype data are used to reconstruct the water depth distribution of foraminiferal microhabitats in the region infaunal morphotypes exist predominantly in shallow water sediments 1500 m the morphological patterns documented in this study are similar to those observed on the southwestern continental margin of norway demonstrating that these patterns exist over a large part of the greenland and norwegian seas

paleocene eocene boundary changes in atmospheric and oceanic circulation a southern hemisphere record deep sea drilling project dsdp site 215 provides an expanded section across the paleocene eocene boundary the most complete mid latitude sequence from a southern hemisphere location in the indo pacific area the events of this transition occurred during a span of about 1 2 m y oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1 0 per thousand a decrease most likely related to warming of deep ocean waters turnovers of benthic foraminifera accompany delta sup 18 o changes and culminate in the predominant extinction event at the end of the paleocene epoch carbon isotope ratios also shift dramatically toward lighter values near the end of the paleocene beginning about 0 45 m y after oxygen isotope values start to change the intensity of southern hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0 45 m y later a significant reduction of zonal wind strength at the paleocene eocene boundary until now observed only at northern hemisphere locations appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean

magnetic polarity stratigraphy and biostratigraphy of paleocene and lower eocene continental deposits clark s fork basin wyoming paleomagnetic samples were collected at 273 sites within a 2012 m continental sedimentary sequence in the clark s fork basin near powell wyoming the lower 1158 m is in the polecat bench fm while the upper 854 m is within the willwood fm although significant secondary components of magnetization were present alternating field demagnetization to 300 oe peak field revealed the polarity of the primary component of the natural remanent magnetism a well defined polarity zonation is observed the polecat bench fm is dominantly of reversed polarity but does contain two normal polarity zones the willwood fm in this section is entirely of reversed polarity abundant tiffanian clarkforkian and wasatchian faunas indicate that the age range of the sediments is from late paleocene through early eocene these age constraints along with the characteristic polarity sequence allow the magnetic polarity sequence to be correlated with the magnetic polarity time scale the section correlates with the magnetic polari

faunal turnover of intermediate water benthic foraminifera during the paleogene in new zealand abstract analysis of benthic foraminifera in upper cretaceous through oligocene bathyal sediments from east coast north island new zealand demonstrates that the catastrophic extinction event of intermediate water 100 1000 m taxa occurred approximately 58 57 ma during the latest paleocene early eocene global warming the following middle eocene cooling produced stepwise origination events signifying the greatest turnover of the fauna most of the extinct species are aerobic forms whereas the surviving taxa are dysaerobic forms this interpretation suggests that a change of environment to low oxygen conditions was the main cause of the extinction following the extinction event a dysaerobic fauna occupied the intermediate water for about one million years the stepwise appearance of new aerobic species in the middle eocene indicates a gradual increase of dissolved oxygen in the intermediate water

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

oceanographic and climatic implications of the palaeocene carbon isotope maximum we have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the palaeocene and early eocene successions at dsdp site 577 shatsky rise north pacific a composite section derived from dsdp leg 74 sites walvis ridge south atlantic and a composite section from odp leg 113 sites maud rise weddell sea the 13c records of palaeocene and early eocene foraminifera at site 577 and the leg 74 sites show that an increase in 13c values in surface waters at 64 ma end of zone p1 resulted in increased vertical carbon isotope gradients 13c between surface and deeper dwelling planktonic foraminifera and between surface dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle late palaeocene zone p4 this steepening also occurs in the latest palaeocene of the composite leg 113 section and can be explained by an increase in surface ocean productivity this increase in productivity probably resulted in an expansion of the oxygen minimum zone omz benthonic 13c values increased during the late palaeocene in site 577 and the composite leg 74 section suggesting that the palaeocene carbon isotope maximum was composed of both within ocean reservoir increased surface water productivity and between reservoir organic carbon burial ftactionation effects the benthonic 13c increase lags the surface ocean 13c increase in the early palaeocene 63 64 ma suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation moreover inter site 13c comparisons suggest that the locus of deep to intermediate water formation for the majority of the palaeocene and the earliest eocene was more likely to have been in the high southern latitudes than in the lower latitudes oxygen isotope data show a decline in deeper water temperatures in the early and early late palaeocene followed by a temperature increase in the late palaeocene and across the palaeoceneeocene boundary we speculate that these changes in deeper water temperatures were related to the flux of co2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes

atlantic eocene planktonic foraminiferal historical biogeography and paleohydrographic indices abstract analysis of a quantitative and synoptic data base of eocene atlantic planktonic foraminifera has illuminated many facets of foraminiferal faunal structure and composition reflective of bioprovince and useful for empirical establishment of ecologic and paleohydrographic indices tropical indigenes such as the morozovellids turborotaliids subquadrate acarininids and some globigerinathekids dissolve most rapidly along with juveniles of most species tropical faunas are high in diversity and dominance include oxygen minimum indices such as the biserial heterohelicids only in high productivity times such as the middle eocene are dominated by genera with high numbers of species and species consistently typical of warm water regions until the late eocene when faunas include a higher number of middle than lower latitude types truly tropical genera are replaced by subtropical eutrophic indicators such as the globigerinathekids and contract to the florida current region prior to their extinctions at the end of the middle eocene atlantic late paleogene tropical forms first appear in the gulf of mexico at the end of the middle eocene middle latitude faunas include high numbers of chiloguembelinids pseudohastigerinids small and biconvex morozovellids round and globigerinid form acarininids low spired subbotinids in the late middle eocene high spired subbotinids large and typical globigerinids in the late eocene these forms have intermediate dissolution susceptibilities middle latitude faunas are often high in diversity in midddle latitude frontal regions dominance is low even in warm intervals when tropical indigenes increase in number in middle latitude faunas especially in boundary currents low latitude species penetrate temperate areas also during cool eutrophic periods of vigorous circulation such as the late middle eocene typical of temperate slope faunas are high abundances of high spired subbotinids and small sized catapsydracids high latitude faunas are usually low in diversity except in the middle to late eocene when frontal regions were located in the southern labrador sea and over rockall bank typical forms are the low spired subbotinids until the late middle eocene globorotaloids catapsydracids tenuitellids and in the late eocene the biserial heterohelicids indigenous species are the most solution resistant and many are mesopelagic during warmings rare low latitude indices penetrate high latitudes subpolar faunas have greatest affinities with middle latitude faunas at these times

paleocene pleistocene benthic foraminiferal evidence of major paleoceanographic events in the eastern south atlantic dsdp site 525 walvis ridge abstract benthic foraminifers in the size fraction greater than 0 073 mm were studied in 88 paleocene to pleistocene samples from deep sea drilling project site 525 hole 525a walvis ridge eastern south atlantic clustering of the samples on the basis of the 86 most abundant foraminifers in total 331 taxa were identified allowed separating two major assemblage zones the paleocene to eocene interval and the oligocene to pleistocene interval each of these in turn were subdivided into three minor subzones as follows lower upper paleocene approx 62 4 to 57 8 ma upper upper paleocene 56 6 to 56 2 ma lower and middle eocene 55 3 to 46 8 ma upper oligocene to middle miocene 25 3 to 16 ma middle miocene to pliocene 15 7 to 4 2 ma and lower pleistocene 0 4 to 0 02 ma with only minor differences with the previous zone some very abundant taxa span most of the column studies bolivina huneri cassidulina subglobosa eponides bradyi e weddellensis gavelinella micra oridorsalis umbonatus etc several of the faunal breaks recorded coincide with conspicuous minima in the specific diversity curve thus suggesting that the corresponding turnovers signal the final stages of periods of faunal impoverishment at least one major bottom water temperature drop as derived from 18o data is synchronous with a decrease in the foraminiferal specific diversity on the other hand a specific diversity maximum in the middle miocene might be associated with a 13c increase at approx 16 to 12 ma highest foraminiferal abundances up to 600 800 individuals per gram of dry sediment occurred in the late paleocene and in the early pleistocene in coincidence with the lowest diversity figures calculated the magnitude of the most important faunal turnover recorded between the middle eocene and the late oligocene is magnified in our data set by the large hiatus which separates the middle eocene from the upper oligocene sediments considerably smaller overturns occurred within the late paleocene in coincidence with changes in the specific diversity absolute abundance of foraminiferal tests and 13c and in the middle miocene in coincidence with a specific diversity maximum and a 13c excursion new information on the morphology and the stratigraphic ranges of several species is furnished for all the taxa recorded the number of occurrences total number of individuals identified and first and last appearances are listed

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

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

equability continentality and tertiary climate the crocodilian perspective the distributions of fossil crocodilians are used to examine north american continental paleoclimates for four time periods in the cenozoic control groups provide a qualitative means of examining the completeness of the record and thus the validity of crocodilian patterns by analogy with the range of the extant american alligator alligator mississippiensis the patterns imply that mid to high latitude continental interiors during the eocene and miocene did not undergo seasonal temperature extremes as great as those observed in such areas today this is compatible with the paleobotanical data during both the late oligocene and the pleistocene times of major glaciation crocodilians were restricted to more maritime localities

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

latest paleocene lithologic and biotic events in neritic deposits of southwestern new jersey in the southwestern new jersey coastal plain four drill holes contain continuous neritic sedimentation across the paleocene eocene boundary calcareous nannofossil zone np 9 np 10 boundary significant lithologic and biotic changes occur in these strata near the top of the paleocene global warming increased precipitation and other oceanographic and climatic events that have been recognized in high latitude deep oceanic deposits of the latest paleocene also influenced mid latitude shallow marine and terrestrial environments of the western north atlantic the diverse well preserved calcareous nannofossil flora that is present throughout the entire new jersey boundary section accurately places these events within the uppermost part of the upper paleocene zone np 9 several rapid but gradational changes occur within a 1 1 m interval near the top of zone np 9 the changes include 1 a change in lithology from glauconitic quartz sand to clay 2 a change in clay mineral suites from illite smectite dominated to kaolinite dominated 3 a change in benthic foraminiferal assemblages to a lower diversity fauna suggestive of low oxygen environments 4 a significant increase in planktonic foraminiferal abundance and 5 an increased species turnover rate in marine calcareous nannofossils pollen was sparse in the new jersey drill holes but terrestrial sporomorph species in virginia exhibit increased turnover rates at a correlative level foraminiferal assemblages and lithology indicate that relative sea level rose in new jersey at the same time as these late paleocene events occurred in late biochron np 9 the higher sea levels influenced sediment type and absolute abundance of planktonic foraminifers in the deposits above the initial increase of kaolinite in the upper part of zone np 9 the kaolinite percentage continues to increase and the maximum kaolinite value occurs in the uppermost part of zone np 9 there are few changes in either the sediments or the biota precisely at the zone np 9 np 10 boundary in new jersey the clay rich deposits with a high kaolinite clay mineral suite the lowered diversity benthic foraminiferal assemblages the abundant planktonic foraminiferal specimens and the calcareous nannofossil assemblages continued essentially unchanged into the earliest eocene zone np 10 within the lower part of zone np 10 the kaolinite percentage decreased to very low values

planktic foraminiferal diversity as indicator of ocean environments abstract the combination of the number of species simple diversity an information function shannon diversity and a measure of equitability is used to characterize modern ocean environments based on planktic foraminiferal faunas regional environmental conditions can be recognized as deviations from the global latitudinal trend simple diversity number of species offers relatively little resolution itself because it is sensitive to the addition of rare species variable conditions such as the highly productive spring bloom and upwelling are characterized by relatively low diversity and equitability values relatively high diversity and a lesser increase in equitability are found in mixing zones of adjacent water masses in extreme conditions diversity is low whereas equitability is intermediate to high modern patterns can be applied to fossil sections to reconstruct regional paleoceanographic conditions thus relatively low shannon diversity with low equitability in maastrichtian heterohelicid faunas from el kef tunisia is interpreted as indicating variable conditions an increase in simple diversity mostly traces evolution of the heterohelicids as a group which diversified during the maastrichtian the number of species through time is a function of available niches and as such related to oceanic circulation on a global scale therefore when applying modern patterns to fossil sections a distinction has to be made between global diversity trends and regional environmental change the correlation between cenozoic stable isotope record and number of planktic foraminiferal species suggest indeed that simple diversity registers changes in global circulation maximum number of species occurred in the maastrichtian the middle eocene and the early middle miocene in these three instances the maxima are found after the start of a cooling trend and are interpreted as transition periods between two modes of ocean circulation causing the temporary coexistence of old and new species

scale dependence of apparent stress for earthquakes along the subducting pacific plate in northeastern honshu japan apparent stress which quantifies the ratio of high frequency spectral amplitude to the direct current level of source displacement spectra is known to reflect the source rupture process whether this parameter depends on the seismic moment has not yet been well established because of the difficulties in the reliable estimation of high frequency source spectra to overcome this problem we estimate s wave source spectra by using site amplification factors and attenuation factor graphic 1 which are systematically measured by the coda normalization method analyzing horizontal components of velocity seismograms recorded at 70 borehole seismic stations of hi net national research institute for earth science and disaster prevention in northeastern honshu japan we estimate site factors and graphic 2 in the 0 5 32 hz frequency band by using these factors we evaluate the source spectra of 225 small to moderate earthquakes that occurred in and around the subducting pacific plate site amplification factors we obtained strongly depend on frequency and the frequency dependence clearly changes with the lithology and geologic age of rock obtained graphic 3 values decrease with frequency in proportion to the reciprocal of frequency the apparent stresses estimated from s wave spectra clearly increase from 104 to 107 pa with the seismic moment increasing which cannot be attributed to the limited frequency band and other artificial causes the power of scale dependence is estimated as 0 39 0 44 for the seismic moment range from 1011 to 1017 n m some of the scale dependence of apparent stress is attributed to the scale dependence of brune s stress drop 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

eocene paleoceanographic evolution at 20 30 s in the atlantic ocean abstract oceanographic changes in eocene bottom water have been traced with oxygen and carbon isotope values and gradients and benthic foraminiferal assemblages the south atlantic sections chosen for this study are located on an east west traverse depositional depths range from middle bathyal through abyssal the dsdp sites are located on the walvis ridge site 363 in the angola basin sites 522 523 the brazil basin site 19 hole 20c and on the rio grande rise site 357 in abyssal sites of the south atlantic the eocene bottom water environment can be divided into two distinct regimes the early eocene and the late eocene the middle eocene is transitional faunal distribution pattern indicate that source areas where bottom water formed were probably different between the two regimes during the early eocene warm saline water formed possibly in the tethyan ocean east of gibraltar there is good evidence that the late eocene bottom water of the south atlantic recorded at lower bathyal down to middle abyssal environments was formed in southern high latitude regions first invasion of cooler bottom water is recorded at upper abyssal depths around 46 ma earliest zone p12 site 19 from 40 ma late zone p15 onwards this signal is recorded at all sites except middle bathyal depth site 357 selected faunal parameters allow reconstruction of bottom water oxygenation episodically increased abundance of epifaunal species indicate a renewal of the bottom water accompanying these faunal changes 13 c values of benthic foraminefera increase whereas vertical 13 c benthic planktonic foraminifera gradients decrease

magnetic polarity stratigraphy and biostratigraphy of middle late paleocene continental deposits of south central montana exposures of the fort union formation on the divide between hunt creek and cub creek in the northern clark s fork basin carbon county montana were selected for magnetostratigraphic study of the transition between the torrejonian and tiffanian land mammal ages paleomagnetic samples were collected from 25 sites within a 160 m thick section of the fort union formation at that location rock magnetic analyses indicate that alternating field demagnetization to peak fields in the 10 to 40 mt interval successfully removed secondary components of natural remanent magnetism nrm characteristic nrm directions define three polarity zones a 50 m thick normal polarity zone bracketed by two reversed polarity zones the cub creek local faunule cc 2 to 3 or ti 1 occurs within the upper portion of the normal polarity zone cub creek local faunules cc 1 cc 3 and eagle quarry all ti 1 occur in the upper reversed polarity zone these data along with faunal and magnetostratigraphic data from the san

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

atlantic eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography reconstruction of atlantic ocean vertical and meridional water characteristics is based on combined synoptic fossil census data stable isotope records and measurements of individual planktonic foraminiferal species correlations between planktonic foraminiferal indices and specific water types and or chemical conditions are used to trace seven stages in the history of atlantic circulation during eocene climatic changes 1 warm equable probably saline productive ocean of the early eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water 2 early middle eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters 3 maximal partitioning of water types faunas and bioprovinces in middle eocene zone p11 accompanying maximum planktonic foraminiferal diversity accelerated near surface and deepwater cooling and intensified upwelling 4 latest middle eocene zone p14 maximal planktonic foraminiferal evolutionary overturn during accelerated cooling deep and surface water ventilation and transformation of tropical surface water habitat with the expansion of temperate water types and faunas this accompanied the reduction of meridional heat transport in boundary currents 5 late eocene bottom water and middle latitude cooling broadening of meridional temperature gradients and expanded oxygen minimum but faunal homogenization following the decreased import of mediterranean water ourflow 6 weakening and or shoaling of the nutricline an oxygen minimum and the thermocline preceding a diminution of primary productivity at the eocene oligocene boundary and 7 earliest oligocene low productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small sized individuals the increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic forcing mechanism in the latest middle and late eocene

post 125 ma carbon storage associated with continent continent collision tectonic fragments subjected to high pressure metamorphism in the alps contain up to 1 vol each of dolomite and graphite indicating that significant amounts of carbon bearing sediment were transported to depths greater than 50 km during the alpine orogeny the absence of a cretaceous tertiary volcanic arc on the overriding plate suggests that much of the subducted carbon remains at depth today averaged over the length of the alpine chain and the estimated amount of subduction that occurred in the past 125 m y 10 16 kg of carbon was buried because of collision in the alpine region additional consideration of the himalayan chain suggests that more than 10 17 kg of carbon has been buried since 125 ma by continent continent collision transfer of this amount of carbon from atmospheric and sedimentary reservoirs into a deep seated metamorphic reservoir may help explain the significant decrease in global surface temperature that occurred from 125 ma to the present

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

oceanic crust production and climate during the last 100 myr in order to evaluate the possible influence of oceanic crust production on climatic changes during the past 100myr variations in total oceanic crust for this period including production at mid ocean ridges oceanic plateaus and back arc basins were calculated using the most recent and accurate time scales the rates presented here differ from those of larson 1991a b on cenozoic fluctuations and show that 1 maximum production values occurred during the cenomanian palaeocene and late oligocene early miocene and 2 minimum values occurred in campanian maastrichtian late eocene and middle miocene significantly variations of oceanic crust production correspond with variations in the 18o of deep water benthic foraminifera maximum values of oceanic crust production correspond with minimum values of 18o and minimum production values with maximum values of 18o this latter synchronism suggests that changes in land sea relationships and atmospheric co2 related to major fluctuations in oceanic crust production were the main cause of mid cretaceous warming and late cretaceous cooling and of climatic quasi cycles having a periodicity of 33 38 million years over the last 100 myr this is the first report showing variations of ocean crust production synchronized with the cenozoic climate changes

ocean nutrient distribution and oxygenation limits on the formation of warm saline bottom water over the past 91 m y it has been proposed that deep water formation in the oceans would be quite different during geologic intervals with reduced equator to pole temperature gradients salinity rather than temperature differences might drive the deep ocean circulation saline water would tend to form at subtropical latitudes where evaporation exceeds precipitation we point out a likely consequence of warm saline bottom water formation on ocean chemistry the tendency to drive the ocean toward anoxia this effect is not due to the previously noted lower oxygen solubility with increasing ocean temperature but rather to the increased efficiency with which plankton will extract nutrients from convecting waters at low latitudes the present ocean nutrient content is sufficient to induce deep water anoxia if circulation were to change yet anoxia is rare in the paleoceanographic record a simple ocean chemical model makes explicit the tradeoffs between mean ocean nutrient content and circulation parameters that will satisfy the geologic observations of an oxygenated ocean since the mid cretaceous barring decreases of ocean phosphate on the order of 30 50 deep water formation at high latitudes was a major source of ocean ventilation in the warmer past

early eocene biotic and climatic change in interior western north america imprecise correlation of the marine and terrestrial fossil records has been a major obstacle to understanding migration and extinction of continental biotas and early cenozoic climate change new sup 40 ar sup 39 ar data from the willwood formation in the bighorn basin of wyoming establish an age of 52 8 plus minus 0 3 ma for earliest lostcabinian late wasatchian faunas and coeval early eocene floras strata just beneath earliest wasatchian faunas can be correlated with the np9 np10 boundary in marine sedimentary units which has an interpolated age of approximately 55 7 ma this new information allows the authors to estimate the durations of the wasatchian approximately 5 m y and the lostcabinian approximately 2 m y and shows that the continental biotas are coeval with the acme of cenozoic warmth inferred from delta sup 18 o measurements of foraminifera from 58 to 50 ma paleoclimate in the continental interior at about 45 degree n was warm and equable but patterns of temperature change inferred from continental floras do not track precisely the marine delta sup 18 o record

organic carbon exhumation and global warming during the early himalayan collision organic carbon eroded and oxidized from marine sediments on the passive and active neo tethyan margins during the early indian asian collision may have been sufficient to shift the carbon isotopic ratios of late paleocene early eocene marine carbonates toward lighter values and may have contributed to coeval global warming via the greenhouse effect new limits on the timing of collision and the organic carbon content of himalayan sedimentary sources and sinks allow us to estimate the net paleogene flux our calculations suggest that continental collisions play a fundamental role in the global carbon cycle and climate through the exhumation as well as burial of organic carbon

distribution of paleogene planktonic foraminifera analogies with the recent abstract distribution patterns and morphologies of modern and paleogene planktonic foraminifera in the atlantic ocean were compared although many paleogene and modern planktonic foraminifera are homeomorphs they are not ecomorphs morozovellid homeomorphs of the modern higher spired globorotaliids inhabited warmest layers of the mixed layer the planorotalitids homeomorphic with modern low trochospiral globorotaliids have different geographic ranges they predominated at temperature and higher latitudes where they grew to largest sizes the cool water low spired subbotinids little resemble the non spinose modern neogloboquadrinids which dominate polar faunas today spinosity of paleogene polar forms indicates that they could have been carnivorous or omnivorous rather than herbivorous like the modern neogloboquadrinids early paleogene polar seas may have been relatively oligotrophic for at least part of the year some paleogene genera may have been ecomorphic with their modern analogues the dentoglobigerinids and globoquadrinids occupied equatorial and offshore upwellings much as neogloboquadrina dutertrei does today because the globorotaloids and catapsydracids deposited calcitic crusts and register most enriched oxygen isotope values they may have lived within and below the thermocline like some modern globorotaliids globorotaloids and catapsydracids may have been strictly herbivorous as are most modern non spinose species their predominance in later paleogene lower latitude upwellings but their near exclusion from polar regions indicates that subeuphotic equatorial waters may have been more eutrophic paleogene type warming in zones p1d p3a p5 p6 7 late p12 late p16 late p19 and early p22 involves proliferation evolutionary diversification and poleward migration of thermophilic forms but decreased species abundance at low latitudes and diminished numbers of fertility indices the guembelitrids biserial heterohelicids globigerinathekids globoquadrinids or dentoglobigerinids neogene type warmings in zones p4 and probably p alpha and p21a involved diversification of cooler water taxa retreat of thermophilic forms from higher latitudes and their concentration in lower latitudes and proliferation of fertility indices under these conditions oxygen isotope records include lower latitude warming but cooling of temperature and higher latitudes and tropospheric waters planktonic foraminiferal diversity and population structure reflect changes in oceanic fertility and the depth of the thermocline cooling and eutrophication resulting in a contraction of the trc trophic resource continuum in atlantic surface waters from late middle eocene through mid oligocene time explain the low diversities extinctions of morphologically complex thermophilic species increased dominance of opportunistic subeuphotic and temperature species proliferation of euphotic and subeuphotic fertility indices and geographic expansion of siliceous primary producers

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

the cenozoic ocean circulation based on ocean general circulation model results abstract a series of ocean general circulation model gcm experiments for paleocene eocene miocene and present day continental geography with atmospheric forcing prescribed from atmospheric gcm experiments is utilized to investigate the changes in surface and deep water ocean circulation through the cenozoic the experiments illustrate a number of similarities with previous observation based reconstructions although the timing of the development of particular gyre systems and the nature of the high southern latitude circulation are generally different than previous interpretations in addition the model results suggest substantial changes in the sites of deep water formation including a middle eocene subtropical source because of a number of experimental limitations the experiments should be considered largely as a sensitivity analysis of the role of changing geography in modifying the ocean circulation

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

an observational study of hurricane boundary layer small scale coherent structures abstract data with high temporal and spatial resolution from hurricanes isabel 2003 and frances 2004 were analyzed to provide a detailed study of near surface linear structures with subkilometer wavelengths of the hurricane boundary layer hbl the analysis showed that the features were omnipresent throughout the data collection displayed a horizontal and vertical coherency and maintained an average orientation of 7 left of the low level wind a unique objective wavelength analysis was conducted where wavelength was defined as the distance between two wind maxima or minima perpendicular to the features long axis and revealed that although wavelengths as large as 1400 m were observed the majority of the features had wavelengths between 200 and 650 m the assessed wavelengths differ from those documented in a recent observational study to evaluate the correlation between the features and the underlying near surface wind field time and spectral analyses were completed and ground relative freque

paleocene and eocene kaolinite distribution in the south atlantic and southern ocean antarctic climatic and paleoceanographic implications abstract clay mineral associations of paleocene and eocene age have been examined in six drilled sequences from the southern south atlantic and southern ocean these sites are located to provide three depth transects across intermediate water masses widespread abundance of pedogenic smectite at all locations suggests globally warm climates and alternating wet and dry seasons on the adjacent continental margins including antarctica as was the case during the late cretaceous remarkably kaolinite is observed only in paleocene eocene sediments at the highest latitudes of these sites and must have originated from antarctica the restriction of kaolinite to the antarctic region is inferred to have resulted from especially higher rainfall there during the paleocene eocene relative to the lower latitude areas examined this inferred high rainfall is considered to have resulted from globally warm temperatures that increased poleward latent heat transport compensating for a strong heat deficit in the antarctic region relative to the tropics kaolinite was not observed in the latest cretaceous maastrichtian sediments of maud rise antarctica kaolinite first appears in the clay mineralogical assemblages in the earliest paleocene 64 to 64 5 ma at a time of relatively cool intermediate waters and before a warming trend of surface waters currents at intermediate water depths transported fine terrigenous sediments from the antarctica during the latest paleocene and early eocene 59 to 52 ma at a time when the oxygen isotopic strongly in east antarctica during the latest paleocene and early eocene 59 to 59 ma at a time when the oxygen isotopic data indicate maximum warmth of surface and intermediate waters of the southern ocean these are interpreted to reflect a paleocene maximum of antarctic rainfall this development peaked at 57 3 m close to the paleocene eocene boundary a time of maximum warmth based on oxygen isotopic data increased illite content and associated chlorite and random mixed layer clays at the end of the middle eocene 41 ma suggest local development of poorly weathered soils on antarctica favored by a cooling of the southern ocean coeval extension of kaolinite into shallower water depths and similar clay mineral associations in shallower and deeper sites indicate the development of cooler conditions led to an increasing influence of antarctic environments upon intermediate water masses at high latitudes

an oceanwide view of palaeogene plate tectonic events abstract the tectonic events taking place during the palaeogene are discussed ocean by ocean three predominant periods of tectonic changes are determined separating periods of continuous stable seafloor spreading these periods of change occur at the palaeocene eocene boundary 56 53 m y at the eocene oligocene boundary 42 35 m y and during the early middle eocene 35 30 m y during the course of writing this review it became very evident how much marine surveying and data analysis took place during the early 1970s this decade showed great leaps forward in our understanding of seafloor anatomy and tectonics

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate

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

timing and duration of himalayan metamorphism within the indian plate northwest himalaya pakistan in indian plate rocks defining the footwall of the indo asian suture in the upper kaghan valley ukv of northern pakistan we resolve four phases in a continuum of himalayan metamorphism and deformation with peak metamorphic pressures of 7 2 0 7 kbar and a minimum estimate for peak temperature of approximately 540 c to attach an absolute age to himalayan metamorphism we used the shrimp ion microprobe to obtain u pb ages on the rims of zircons from granites metamorphosed during the earliest phase of himalayan orogeny four granite samples give a mean u pb age of 47 3 ma zircons from the malakand granite of the swat region 200 km west of the ukv have rims that also give a mean u pb age of 47 3 ma cores of these zircons yield u pb ages of 254 291 ma which approach the previously published rb sr isochron age of 297 4 ma for the peshawar plain igneous province suggesting an expanded areal extent of this carboniferous igneous suite the metamorphic ages of 47 3 ma document that the thermal cu

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

magnetic and calcareous nannofossil stratigraphy of the lower palaeogene formations of the hampshire and london basins a magnetostratigraphic study of the lower palaeogene formations exposed in the hampshire and london basins southern uk has led to the identification of eight stratigraphically distinct normal polarity magnetozones within an otherwise reverse polarity sedimentary sequence which spans the late palaeocene to middle eocene a complementary study of the calcareous nannofossil biostratigraphy of these sections and related sections elsewhere in nw europe allows a correlation of this succession of normal polarity magnetozones with the biostratigraphically calibrated geomagnetic polarity timescale based on marine magnetic anomalies it is concluded that the normal polarity chrons corresponding to anomalies 20 21 and 23 are recorded within the huntingbridge earnley and wittering divisions of the bracklesham group respectively that anomalies 24a and 24b are represented within divisions d to b2 of the london clay and anomaly 26 is represented in the lower part of the thanet beds an additional normal polarity magnetozone within the oldhaven beds is believed to represent a short normal polarity event between anomalies 24b and 25 anomalies 22 and 25 appear not to be represented in the uk lower palaeogene succession because of major unconformities at the early middle eocene boundary within the wittering division of the bracklesham group and within the late palaeocene respectively the former appears to correlate with a widespread erosional event in the oceans identified from seismic records vail et al 1979 and interpreted as reflecting a major eustatic sea level fall

eocene equator to pole surface ocean temperatures a significant climate problem eocene surface ocean paleotemperature data which illustrate a reduced equator to pole temperature gradient cooler tropical sea surface temperatures and a relatively small global temperature warming 2 c present a significant climatic enigma if the reconstructions are correct such a temperature distribution can be achieved through greater poleward heat transport by the ocean however the mechanism for a greater oceanic role is uncertain in addition the results from climate models for conditions of a substantially greater poleward heat transport by the oceans indicate a weak atmospheric circulation and highly seasonal continental interior climates the weak atmospheric circulation is consistent with the record of continent derived eolian sediment recovered in deep sea cores however the eocene paleobotanical evidence from continental interiors indicates a very mild seasonality the lack of consistency between model results oceanic data and terrestrial data defines the nature of the problem of eocene climates the solution must involve reinterpretation of at least one major source of information