magnetostratigraphy of the willwood formation bighorn basin wyoming new constraints on the location of paleocene eocene boundary abstract the lower eocene willwood formation in the bighorn basin of wyoming preserves a rich and diverse mammalian and floral record the paleomagnetic behavior of the sequence of floodplain paleosols of varying degrees of maturation ranges from excellent to poor we present a magnetostratigraphic section for a composite section near worland wyoming by using a set of strict criteria for interpreting the step wise alternating field and thermal demagnetization data of 266 samples from 90 sites throughout the composite section correlation to the geomagnetic reversal time scale was achieved by combining magnetostratigraphic and biostratigraphic data from this section from a section in the clark s fork basin in northern wyoming and from dsdp site 550 with the isotopic data determined on a tuff near the top of our section our correlation suggests that the bighorn basin composite section in the worland area spans from within chron c24r to near the top of chron c24n or from approximately 55 to 52 ma this correlation places the paleocene eocene boundary within the vicinity of the base of the section cryptochron c24r 6 of cande and kent is tentatively identified some 100 m above the base of the section the temporal framework provided here enables correlation of the mammalian biostratigraphy of the bighorn basin to other continental sequences as well as to marine records it also provides independent chronological information for the calculation of sediment accumulation rates to constrain soil maturation rates we exclude an age as young as 53 ma for the paleocene eocene boundary and support older ages as recommended in recent time scales the location of a tuff dated at 52 8 0 3 ma at the older boundary c24n 1 is consistent with the age of 52 5 ma estimated by cande and kent and inconsistent with that of 53 7 ma from harland et al

geochemistry of late palaeocene and early eocene tephras from the north sea basin the late palaeocene to early eocene balder and sele formations of the north sea basin contain over 200 air fall water lain tephras these occur over the entire north sea area extending onshore into denmark nw germany the netherlands and se england they have also been recorded in the bay of biscay and goban spur areas of the ne atlantic and offshore mid norway results from cores drilled in two widely separated areas of the north sea have been integrated with earlier work on the northern north sea and danish sequences to demonstrate that the stratigraphic and geochemical development of the tephra sequence is regionally consistent this indicates that a single source or group of sources was responsible rather than a number of geographically separated intrabasinal volcanoes for which little geophysical evidence can be found the sequence comprises a lower group of sporadic thin tephras of variable composition including tholeiitic alkalic trachytic trachyandesitic and peralkaline varieties and an upper group of thicker more abundant tephras almost exclusively of fe ti tholeiitic composition general thickness trends and geochemical evidence indicates that the source volcanoes lay on the proto greenland scotland ridge with the tephras showing several features that ally them to the early palaeogene faeroe greenland igneous province the reasons behind the highly explosive nature of the basaltic magmatism remain enigmatic

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

recognition of chron c25n in the upper paleocene upnor formation of the london basin uk lithostratigraphic studies of four borehole cores drilled through the late paleocene lambeth group upnor woolwich and reading formations and basal london clay formation of central london have been supplemented with palaeomagnetic calcareous nannoplankton and palynological data the woolwich and reading formations and the lower london clay formation are reversely magnetized and were deposited during the early part of chron c24r the first record of both np9 and chron c25n hitherto missing from the paleogene record in southern england has been identified in the upnor formation formerly the woolwich bottom bed it provides a key reference marker for linking events associated with the paleocene eocene boundary positioned within chron c24r to the type area of the internationally recognized thanetian and ypresian stages work carried out to establish the chronostratigraphy of the paleogene in southern england fig 1 has been concerned principally with the late paleocene thanet sand formation and the early eocene london clay formation e g aubry et al 1986 ali et al 1993 knox et al 1994 the thanet sand formation lies within calcareous nannoplankton zones np6 np8 and magnetochrons c26r to c25r magnetochron nomenclature from cande kent 1992 the base of division b of the london clay formation sensu king 1981 coincides with the start of chron c24n 3n the intervening lambeth group upnor woolwich and reading formations harwich formation ellison et al 1994 and lower part of the london clay formation are allocated to chron c24r aubry et al 1986 indicated that an hiatus in excess of 0 6 million years marked by the absence of chron c25n separates the thanet sand formation from the lambeth group in recent years the drilling of fully cored boreholes fig 2 through the lambeth group in central london has provided a unique opportunity for multidisciplinary study one borehole in particular jubilee 404t bgs registration number tq 37 nw 2118 national grid reference tq 3363 7960 has become a key reference section for the lambeth group in central london ellison et al 1994 the main reasons for its importance are firstly the wide variety of lambeth group facies including marine sands brackish lagoonal muds and pedogenic horizons and secondly the presence 55

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

paleogene geochronology an integrated approach geochronology is the conceptual division of continuous time as measured geochronometry by the progression in an ordinal series of events this is best achieved by an approach which integrates four independent data sets magnetostratigraphy seafloor spreading magnetic lineation patterns biostratigraphy and isotopic ages this integrated approach results in an ordinal framework which can measure time with greater resolution though perhaps less accuracy than a radiometric approach alone a comparative analysis of two recently proposed paleogene geochronologic time scales is presented

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

oxygen and carbon isotope stratigraphy of the palaeogene and cretaceous limestones in the bottaccione gorge and the contessa highway sections umbria italy we have made oxygen and carbon isotope measurements on limestone samples of albian to eocene age recovered from the bottaccione gorge section in the umbrian apennines central italy additional measurements have been made on topmost maastrichtian and palaeocene sediments from the adjacent contessa highway section our data from the bottaccione gorge show 13c maxima at the cenomanian turonian boundary and during the palaeocene as well as a pronounced 13c minimum 7 metres above the clay layer at the k t boundary our data from the contessa highway show a 13c minimum 9 metres above the k t boundary clay these minima are probably diagenetic artifacts in the bottaccione gorge there is evidence for a hiatus in the early middle eocene the palaeocene of the bottaccione gorge appears to have been affected by slumping or faulting in addition to the diagenetic overprinting giving a spurious 13c recovery after the k t boundary the contessa highway section appears to be more complete the coniacian maastrictian is characterized by relatively stable 13c values our data indicate an increase in 18o and therefore possible cooling across the cretaceous tertiary boundary in both the bottaccione and contessa highway sections

chronology of the wasatchian land mammal age early eocene magnetostratigraphic results from the mccullough peaks section northern bighorn basin wyoming a reply the mccullough peaks section of the willwood formation in the northern bighorn basin wyoming has produced a rich fossil record of early eocene mammals spanning much of the wasatchian land mammal age the wasatchian is an especially significant period in mammalian evolution since it marks the first appearance of several modern orders of mammals including perissodactyla artiodactyla and true primates magnetostratigraphic analysis of paleosol horizons in the mccullough peaks region is used to correlate wasatchian land mammal zones to the geomagnetic polarity time scale a total of 135 paleomagnetic samples were analyzed from 37 levels in a 1480 m section that ranges from wasatchian zone wa 0 earliest sandcouleean subage to the base of zone wa 7 earliest lostcabinian subage progressive thermal demagnetization of samples from red b type and mottled red gray ab type soil horizons provides the most reliable results the characteristic magnetization is carried by hematite with unblocking temperature

the palaeogene time scale radiometric dating versus magnetostratigraphic approach numerical geological time scales rest firmly on the analysis of radiometric data since the discovery of oceanic magnetic stripes and their signification alternative time scales have been constructed whose numerical predictions are based on the hypothesis of a constant rate of sea floor spreading the most recent such scale uses only five tie points plus present day to subdivide a span of over 80 million years the present paper demonstrates that the rate of ocean floor spreading has varied markedly and without obvious pattern both in time and in space thus magnetostratigraphic scales based on large interpolations are fundamentally flawed an alternative scale based on a consideration of all radiometric data and using magnetostratigraphic data only for small interpolations is commended

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

non cryptic encrustation and pre burial fracturing in stromatoporoids from the upper visby beds of gotland sweden abstract examination of the upper surfaces of 27 high domical stromatoporoids from the silurian upper visby beds of gotland reveals that they were densely encrusted by a wide variety of epifaunal organisms these organisms showed clear preferences for either the apical or the basal portions of the coenosteum and though the diversity of the lower flank fauna was greater coverage by encrusters was twice as dense at the apex this is shown to have been due to the progressive burial of the substrates although most encrustation was opportunistic a few species are shown to have been pioneers while others were consistently late in developing spirorbid worms were gregarious in their late larval stages leading to clumped distributions the stromatoporoids themselves bear radial fractures which were clearly caused before burial and even prior to encrustation such cracks are easily distinguished from those due to compaction by overburden

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

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

nannoplankton zonation and the palaeocene eocene boundary beds of nw europe an indirect correlation by means of volcanic ash layers correlation of early palaeogene ash layers in dsdp hole 550 leg 80 goban spur with those of the north sea basin indicates that the base of nannoplankton zone np10 approximates the base of the sele formation of the north sea area the bases of the danish ash series the german ash bearing untereozan 1 and the paris basin sparnacian and the top of the woolwich reading bottom bed of the london basin if as is now common practice the palaeocene eocene boundary is placed at the np9 np10 boundary then the units listed above would constitute the basal units of the eocene in their respective countries the cessation of large scale pyroclastic activity took place at about the middle of the zone np10 interval

paleogene calcareous nannoplankton biostratigraphy of northwestern europe abstract the classic paleogene stages thanetian cuisian lutetian bartonian ludian and stampian defined in the epicontinental deposits of the anglo paris basin s are placed within a standard biostratigraphic framework based on an analysis of their calcareous nannoplankton floras relatively precise biostratigraphic correlations can be made with some chronostratigraphic units e g lutetian while biostratigraphic resolution of others e g ludian is limited important hiatuses are recognized between certain chronostratigraphic units only the base of the lutetian late np14 and bartonian mid np16 stages can be precisely determined in terms of calcareous nannoplankton zones with the recent study of the magnetic polarity history of the paleogene of southern england and recent advances in magnetobiostratigraphic correlations in deep sea cores it is possible to interpret the paleogene history of the anglo paris basin s in a synoptic global framework in which paleomagnetic stratigraphy provides the chronologic and eustatic variations the graphic units of northwestern europe within rather than at the boundaries of i e at dynamic element redefinition of the boundaries of the standard paleogene chronostratigraphic unconformities eustatically controlled depositional cycles would result in more precise correlations in terms of standard calcareous nannoplankton biostratigraphy

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

geochemistry of diabase dikes from the lewis hills massif bay of islands ophiolite evidence for partial melting of oceanic crust in transform faults the lewis hills massif of the bay of islands ophiolite is interpreted to have had a transform fault history in an oceanic fracture zone prior to its abduction diabase dikes from the lewis hills massif are divisible into two groups on the basis of their trace element compositions one group is similar to mid ocean ridge basalts and is termed the lh normal suite the other group termed the lh depleted suite is characterized by high cao ti zr and y zr with relatively low sio 2 zr and p 2 o 5 the low sio 2 abundances are suggestive of silica undersaturated rocks of the alkali basalt nephelinite series of magmas but the very low abundances of incompatible trace elements in these magmas contrast with their high abundances in most silica undersaturated rocks we interpret the geochemical characteristics of thesediabase dikes to indicate that the magmas from which they solidified were produced by partial melting of adcumulate gabbroic and troctolitic rocks at low pressures 2 3 kbar within the ophiolitic fracture zone the effects of partial melting of gabbroic and troctolitic rocks have not been documented in rocks described from present day oceanic fracture zones but samoles have not been obtained from those structural levels of fracture zones where such evidence mightbe found

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

northwestern european paleogene magnetostratigraphy biostratigraphy and paleogeography calcareous nannofossil evidence global calcareous nannofossil biostratigraphy is used to correlate the paleogene chronostratigraphic units of northwestern europe and standard nannofossil biozones such biostratigraphic correlations show that the lithostratigraphic sequence is discontinuous and allows interpretation of the paleogeography of northwestern europe during the paleogene and evaluation of the influence of global sea level eustatic changes on northwestern european stratigraphy a well documented unconformity occurs near the lower middle eocene boundary in the paris basin this unconformity which also can be traced in the london hampshire basin and in belgium correlates with a coastal offlap event presumed sea level of vail et al on the basis of magnetostratigraphic biostratigraphic correlations the duration of the hiatus associated with this unconformity can be estimated to be 0 6 to 1 5 m y in the hampshire basin and 2 to 4 m y in the paris basin

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