axial topographic relief associated with ridge transform intersections the axial depths of mid ocean ridges are consistently observed to increase along strike from the central part of a ridge segment to its intersection with a transform fault variations in the magnitude of this axial relief probably reflect variations in the magmatic and tectonic processes that characterize plate accretion and seafloor spreading at each individual segment constrained by observations from 41 ridge transform intersections we investigate the relative effect on axial depths of transform offset segment length regional depth and spreading rate we first solve for a model of ridge segment relief as a function of the age offset of the transform and the segment length both scaled by spreading rate through a series of regression analyses covering a range of spreading rate scalings we determine a model which predicts segment relief at both fast and slow spreading centers to within 240 m standard deviation we find that half segment scale deepening is more than a direct thermal effect of the juxtaposition of a cold lithospheric edge and the end of a ridge at a transform fault a second inversion problem is solved to determine the parameters that contribute to the absolute depth of the ridge axis we can show that the absolute depth of the shallowest section of a ridge segment is strongly dependent on regional depth and that this dependence is more complex at slow spreading ridges reflecting the common but not ubiquitous existence of a median valley there these results in combination with the segment relief analysis clearly indicate that the axial depth at a ridge transform intersection is a function of both long wavelength processes such as may control hot spot distribution and local tectonic factors including but not limited to transform offset

40ar 39ar dating and magnetostratigraphic correlation of the terrestrial cretaceous paleogene boundary and puercan mammal age hell creek tullock formations eastern montana the recovery and subsequent prolific radiation of mammals in the northern western interior of north america following the cretaceous paleogene k p boundary is well documented in rocks attributed to the puercan land mammal age the most complete puercan record is that of the tullock formation which crops out widely in garfield and mccone counties eastern montana the tullock formation overlies the dinosaur bearing hell creek formation and consists of a stratigraphic series of channel and overbank deposits from which well preserved puercan faunas have been collected these channel deposits are typically bracketed by widespread coal beds the irz and z coals mark the base of the puercan at the k p boundary as defined by the highest appearing local occurrences of in situ dinosaur fossils the highest stratigraphic occurrence of cretaceous pollen and an anomalously high concentration of the element iridium ir the irz coal is overlain sequentially by the z hfz y w and u coals fossil vertebrates

the cretaceous tertiary boundary stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

mass mortality and its environmental and evolutionary consequences the latest mesozoic and earliest tertiary sediments at deep sea drilling project site 524 provide an amplified record of environmental and biostratographic changes at the end of cretaceous closely spaced samples representing time intervals as short as 102 or 103 years were analyzed for their bulk carbonate and trace metal compositions and for oxygen and carbon isotopic compositions the data indicate that at the end of cretaceous when a high proportion of the ocean9s planktic organisms were eliminated an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere this resulted in a large increase of the atmospheric carbon dioxide during the next 50 000 years which is believed to have caused a temperature rise revealed by the oxygen isotope data the lowermost tertiary sediments at site 524 include fossils with cretaceous affinities which may include both reworked individuals and some forms that survived for a while after the catastrophe our data indicate that many of the cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans as suggested by an iridium anomaly at the cretaceous tertiary boundary

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

the cretaceous tertiary extinction modeling carbon flux and ecological response 1 it is widely recognized that a significant negative excursion in carbon isotopic 13c differences between planktic and benthic foraminiferal tests occurred at the cretaceous tertiary k t boundary we applied parametric and nonparametric breakpoint tests and statistical comparisons of different recovery models to assess the timing and pattern of recovery from this negative excursion at south atlantic deep sea drilling project dsdp site 528 and equatorial pacific dsdp site 577 our results indicate a two stage recovery with an initial recovery to an intermediate state of planktic to benthic 13c differences followed by a discontinuous shift to a final state with planktic to benthic 13c differences similar to preextinction values the final discontinuous shift in both the pacific and atlantic ocean sites occurred several million years after the k t collapse of planktic to benthic 13c differences both the first and second stages of recovery are best described by damped exponential relaxations the pattern and timing of this carbon cycle recovery may have been contingent on the occurrence of key biological events

the relationship between the iridium anomaly and palynological floral events at three cretaceous tertiary boundary localities in western canada profiles illustrating the abundance of iridium and the changes in the relative abundances of major groups within the palynoflora are given for three localities from western canada the peak abundance of iridium ranges from 1 35 to 5 60 ppb and corresponds to the base of a coal and to a floral extinction event at the three localities immediately above the iridium peak anomaly angiosperm pollen is conspicuous in the assemblage in contrast to the fern spore spike described for sections in the mid continental united states and at the morgan creek locality in south central saskatchewan

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

the cretaceous palaeogene boundary succession at stevns klint denmark foraminifers and stable isotope stratigraphy the cretaceous palaeogene boundary exposed at stevns klint denmark provides an important location for the investigation of the end cretaceous event in this work we have used a number of sections across the boundary including the little described expanded stratigraphic sequence at kulstirenden which is located 7 km north of hojerup where most published work is derived using stratigraphical micropalaeontological and stable isotope 18o and 13c data we have shown that there is clear evidence of shallowing in the latest maastrichtian prior to and across the cretaceous palaeogene boundary there are significant changes in sea water temperature including an important cooling event in the very latest maastrichtian the 13c record in the expanded boundary clay fish clay sequence at kulstirenden indicates a number of significant excursions of decreasing magnitude up section the evidence from the distribution of the foraminifers has been incorporated with previous work to develop a sequence stratigraphical interpretation for the succession that can be compared to other cretaceous palaeogene boundary successions in europe

axial morphology along the southern chile rise abstract morphology of four spreading segments on the southern chile rise is described based on multi beam bathymetric data collected along the axial zones the distribution of axial volcanoes the character of rift valley scarps and the average depths vary between segment 1 in the south terminating at the chile triple junction and segment 4 in the north which are separated by three intervening transform faults despite this general variability there is a consistent pattern of clockwise rotation of the southern most axial volcanic ridge within each of segments 2 3 and 4 relative to the overall trend of the rift valley a combination of local ridge transform intersection stresses and regional tectonics may influence spreading axis evolution in this sense

stratigraphic sequence and episodes of the ancient huanghe delta along the southwestern bohai bay since the lgm abstract the sedimentary evolution of the ancient huanghe yellow river delta in china is not well documented due to frequent river avulsions and limited deep cores in this paper 22 cores with lengths of 20 m at the coastal plain along the southwestern bohai bay were used the sedimentary facies were determined by grain size and microfossil analysis and carbon 14 dating the strata in the study area since the last glacial maximum lgm are divided into lowstand system tract lst transgressive system tract tst highstand system tract hst and retrograding system tract rst the lst which formed during the lgm to 10 8 ka bp consists of hard mud layer and overlying interfluvial lowland and flood plain deposits the tst that formed during 10 8 8 5 ka bp mainly include coastal marsh onshore sand bars and filled incised valleys the hst that formed during 8 5 2 6 ka bp mainly includes flood plain river channel delta front mouth bar and prodelta the rst that formed after 2 6 ka bp mainly includes crevasse splay interfluvial lowlands and distributary channel about eight episodes of the ancient huanghe delta are observed during the holocene and the names of the deltas are given by corresponding location names of cheniers 1 during 10 8 8 5 ka bp around ys3 and np1 cores without formation of cheniers during the transgression 2 during 8 5 7 4 ka bp around ys1 ys4 and np3 cores the dongsun shuiyicheng delta 3 during 7 4 6 1 ka bp around ck1 core the mashanzi delta 4 during 6 9 5 7 ka bp around gz3 core the miaozhuang zhaizhuang delta 5 during 4 6 3 5 ka bp around ys4 core the wuditai delta 6 during 3 0 2 6 ka bp around hh4 and hh1 cores the qikou delta 7 during 2 6 1 9 ka bp around ys7 and np1 cores the nanpaihe delta and 8 during 1034 bc 1099 bc around wangzidao and dakouhe the wangzidao delta

terrestrial carbon isotope records from coastal deposits algarve portugal a tool for chemostratigraphic correlation on an intrabasinal and global scale the carbon isotope signature of terrestrial organic matter om offers a valuable tool to develop stratigraphic correlations for near shore deposits a mid cretaceous coastal succession of the western algarve basin portugal displays a marked negative 13c excursion ranging from 21 2 to 27 8 in the early aptian followed by two shifts towards higher values up to 19 3 during the early and late aptian respectively the dominance of cuticle and leaf debris in the bulk om fraction is confirmed by optical studies rock eval pyrolysis and by comparison with the 13c signature of four different types of fossilized land plant particles correlation of two terrestrial 13cbulk om records from different study sites leads to a significant enhancement of the intrabasinal stratigraphic correlation within the algarve basin three prominent excursions in the portuguese records can be correlated with existing 13c curves from pelagic and terrestrial environments the general carbon isotope pattern is superimposed by small scale fluctuations which can be explained by compositional variations within the om

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

rapid 10 yr recovery of terrestrial productivity in a simulation study of the terminal cretaceous impact event abstract investigations of short term up to 103 yr environmental change across the cretaceous tertiary boundary provide evidence for reduced temperatures consistent with the injection of debris and sulphate aerosols into the upper atmosphere by a large impact event concomitant with this was a postulated massive addition of co2 to the atmospheric carbon reservoir by impact vaporisation of the chicxulub carbonate platform taken together a high co2 but low irradiance environment would have created unusual conditions for the operation of the terrestrial biosphere here we have evaluated this environmental influence on terrestrial ecosystems using a process based dynamic global vegetation model forced with post impact global climates derived by modification of the genesis atmospheric climate model simulation for the latest cretaceous our results suggest that terrestrial primary productivity initially collapsed and then recovered to pre impact levels within a decade global terrestrial carbon storage in vegetation biomass exhibited a similar collapse but complete recovery took place on a 60 80 yr timescale the recovery of both terrestrial net primary productivity and vegetation biomass was largely mediated by the high co2 concentration stimulating ecosystem photosynthetic productivity in the warm low latitudes an apparently rapid recovery of terrestrial ecosystem function stands in marked contrast to the situation for the marine realm where the organic carbon flux to the deep ocean was suppressed for up to 3 million years

the terminal cretaceous iridium anomaly in the red deer valley alberta canada neutron activation analysis following fire assay preconcentration in a nickel sulphide button allows processing of relatively large samples 25 g for precision analysis of platinum group elements using this method an iridium anomaly with maximum concentration of 3 36 0 04 ppb has been located at the cretaceous tertiary boundary at the base of the nevis coal seam in the red deer valley of alberta the iridium anomaly coincides with the disappearance of diagnostic late cretaceous palynomorphs including all but one species of aquilapollenites

effect of anisotropy on oceanic upper mantle temperatures structure and dynamics olivine and orthopyroxene crystals composing the oceanic upper mantle align under progressive simple shear strain because the thermal diffusivities r and viscosities of these min erals are anisotropic mineral alignment affects vertical heat flow and upper mantle dynamics the vertical thermal diffusivity of upper mantle peridotite decreases with progressive simple shear strain leading to higher temperatures in the shallow upper mantle than predicted by an isotropic half space cooling model this in turn causes higher surface heat flow shallower ocean basins weaker asthenosphere and slightly thinner lithosphere viscosity associated with an oriented sim ple shear strain r sh such as that caused by plate motion also evolves with progressive strain though r sh at high strains has not been characterized regardless of the evolution of r h with strain the effects of thermal diffusivity anisotropy on upper mantle temperatures surface heat flow lithosphere thickness asthenosphere viscosity and shear stress at the plate bottom remain evident shear heating elevates the geotherm by more than r anisotropy except in the youngest o ean and in cases with significant shear weakening or a slowly moving plate less than 3 cm yr the magnitude of shear heating effects depends on how r sh increases or decreases at high strains for models in whichsh increases as a function of strain shear heating elevates temperatures beyond reasonable upper mantle estimates i e above 1400oc suggesting that such strain induced viscosity increases are not likely we present a model for ocean upper mantle cooling and deformation that includes upper mantle thermal diffusivity anisotropy and shear heating this model predicts heat flow shear wave split times lithosphere thicknesses and basin depths which are consistent with observations but suggests that basal tractions on ocean plates are lower than previously thought

mechanisms for the origin of mid ocean ridge axial topography implications for the thermal and mechanical structure of accreting plate boundaries to better understand the implications of ridge axis morphology for the thermal and mechanical structure of accreting plate boundaries we examine mechanisms for the creation of stress supported axial topography and its dependence on parameters such as spreading rate asthenosphere viscosity and plate thickness near the ridge axis three basic mechanisms are considered 1 asthenospheric upwelling in a narrow steady state conduit beneath a ridge axis 2 mantle flow stresses due to plate spreading extending ridge axis lithosphere or melt segregation and associated mantle compaction and 3 topography supported by moments due to horizontal extensional stresses in a thickening lithosphere if mid ocean ridge topography is due to asthenosphere rising in a narrow conduit at the ridge axis then the conduit structure cannot be thermally controlled as the associated thermal structure has relatively broad flat isotherms instead of a conduitlike shape mantle flow associated with plate spreading alone induces no stress supported topography thus the intuitive notion that diverging flow at the ridge axis due solely to plate spreading produces the axial valley is incorrect vertical mantle flow at the base of a stretching accreting lithosphere and mantle flow associated with melt segregation can however lead to stress supported axial topography however for these mantle flow related processes to produce significant amounts of axial relief the mantle viscosity beneath the ridge axis must be on the order of 1020 pa s 1021 p poise significantly higher than generally accepted values of 1018 pa s 1019 p horizontal extensional stresses in a strong brittle lithosphere that thickens with distance from the ridge axis can produce axial topography of the form and amplitude observed on slow spreading ridges a continuum idealization of deformation due to faulting is used to examine this mechanism this model predicts the axial valley width is controlled by the plate thickness near the ridge axis an 8 km thick plate near the ridge axis would produce the 30 km wide axial valley observed at slow spreading ridges an increased lithosphere thickness of only several kilometers over the half width of the axial valley can produce kilometer scale relief to examine whether a plate 8 10 km thick at the ridge axis that thickens by several kilometers within 15 km of the axis is plausible at a slow spreading ridge thermal models that include both the heat of magmatic crustal accretion on the ridge axis and upwelling mantle flow beneath the axis are formulated hydrothermal cooling that increases the effective conductivity by about a factor of 10 is required for an 8 km thick plate to exist at a slow spreading ridge axis however even with this enhanced hydrothermal cooling the plate thickness at a fast spreading ridge axis and the resulting horizontal force in the plate are too small to result in appreciable topography while mid ocean ridge axial topography is strongly influenced by spreading rate other factors also shape axial structure for example the anomalously shallow slow spreading reykjanes ridge has an axial structure more like that of a fast spreading ridge and the anomalously deep intermediate spreading australian antarctic discordance has a median valley axial structure typical of a slower spreading ridge in addition within a given spreading segment there is often a systematic deepening of the ridge axis toward transform offsets these non spreading rate dependent axial topographic variations may be produced by variations in magmatic heat input associated with crustal emplacement which shapes the thermal structure and lithosphere thickness near the ridge axis

evidence for the recovery of terrestrial ecosystems ahead of marine primary production following a biotic crisis at the cretaceous tertiary boundary the fossil record demonstrates that mass extinction across the cretaceous tertiary k t boundary is more severe in the marine than the terrestrial realm we hypothesize that terrestrial ecosystems were able to recover faster than their marine counterparts to test this hypothesis we measured sedimentary 13 c as a tracer for global carbon cycle changes and compared it with palaeovegetational changes reconstructed from palynomorphs and cuticles across the k t boundary at sugarite new mexico usa different patterns of perturbation and timescales of recovery of isotopic and palaeobotanical records indicate that the 13 c excursion reflects the longer recovery time of marine versus terrestrial ecosystems

erratum microscopic planar features in quartz from scollard canyon alberta and the cretaceous tertiary boundary event quartz grains separated from the cretaceous tertiary k t boundary clay at scollard canyon alberta have prominent microscopic planar features these occur in 15 30 of the grains from the lower

sequential palynological changes across the composite cretaceous tertiary k t boundary claystone and contiguous strata western canada and montana u s a the boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution a basal brownish grey hackly claystone a middle brownish black sa

the paradox of the axial profile isostatic compensation along the axis of the mid atlantic ridge mantle bouguer gravity anomalies mba and bathymetry on three profiles covering more than 1000 km along the axis of the mid atlantic ridge mar are highly correlated suggesting that along axis topographic relief is locally compensated by variations in crustal thickness and or mantle density structure the quantitative relationship between topography and gravity on these profiles could be explained by the flexure of a thin narrow elastic strip representing the response to isostatic loads of an inner rift valley isolated from the rest of the plate by weak bounding normal faults the paradox is that across axis profiles show that the median valley is an uncompensated feature apparently created by a dynamic mechanism new extensive off axis coverage of the mar from 31 to 36 s shows that the high correlation does not persist outside the axial zone we suggest that the on axis correlation exists because the mechanism creating the median valley is controlled by the mantle thermal structure and along axis variations in crustal thickness both of which contribute to the mba if the mechanism is extension of a brittle ductile lithosphere the critical parameter controlling topographic relief is the thickness of the relatively stiff mantle layer immediately beneath the crust at the ridge axis a three dimensional 3 d thermal model incorporating passive mantle flow hydrothermal circulation the plate boundary geometry and variable magmatic heating associated with observed variations in crustal thickness predicts variations in the thickness of the stiff mantle layer that correlate with the observed axial topography we model the expected topography using cross axis sections of the 3 d thermal model and a 2 d finite element model of an extending lithosphere that incorporates temperature and strain dependent rheology as well as the flexural response of a thickening plate the predicted topographic signal produced by the combined dynamic and isostatic effects matches the amplitude of the observed axial bathymetry at the 18 mm yr 1 spreading half rate in our south atlantic survey the 2 d models also reproduce the observed rapid transition along the axis between rift valley no rift valley morphology we conclude that extensional forces acting on segmented oceanic lithosphere with varying rates of crustal production produce the highly variable morphology of the southern mar and the along axis correlation between mba and bathymetry

cretaceous tertiary palynofloral perturbations and extinctions within the aquilapollenites phytogeographic province a combination of detailed intermediate and large scale stratigraphic perspectives is necessary to understand the driving mechanisms for floral change across the cretaceous tertiary k t boundary because short term physical and biotic events occur within longer term trends most maastrichtian palynofloral extinctions have been identified within the northern circumpolar supra continental aquilapollenites province in mid continental north america the presence of a physically defined k t boundary provides opportunities to examine contemporaneous terrestrial palynofloras over a latitudinal also approximately paleolatitudinal distance of 3200 km seventy five percent of last appearances occur before the k t boundary at high latitudes and must have been caused by ongoing terrestrial processes palynofloral events directly associated with the k t boundary include both local last appearances and inferred extinctions and synchronous and diachronous changes in relative abundances two different styles of factors are reflected in these events the first possibly attributable to chemical or other profound atmospheric perturbations associated with the worldwide distribution of the fireball layer of the k t claystone resulted in extinctions of angiosperm with a zoophilous pollination strategy the second factor possibly reflecting energy released during the deposition of ballistically transported impact debris or hackly ejecta layer of the boundary claystone resulted in the selective northward attenuating removal of the canopy vegetation best documented for southwestern canada which was succeeded by a fern dominated vegetation in mid continental north america these consequences of the boundary event were mediated by independent preexisting circumstances climate regional and through time local depositional environment and ongoing background extinctions and origins

spike of pyrosynthetic polycyclic aromatic hydrocarbons associated with an abrupt decrease in δ13c of a terrestrial biomarker at the cretaceous tertiary boundary at caravaca spain the first vertical high resolution record of polycyclic aromatic hydrocarbons pahs of pyrosynthetic origin and the corresponding 13 c profile of a terrestrial biomarker across the cretaceous tertiary k t boundary at caravaca spain reveals the following in comparison with adjacent cretaceous marlstones the first thin horizon 0 to 0 5 cm 0 the k t boundary of the boundary clay layer is 1 enriched as much as 112 to 154 fold in typical pyrosynthetic pahs such as coronene benzo g h i perylene and benzo e pyrene and 2 shows an abrupt 13 c decrease of 1 4 1 8 in terrestrial higher plant derived n c 29 alkane the spike of pyrosynthetic pahs associated with an abrupt decrease in 13 c value of a terrestrial biomarker is interpreted to reflect the prevalence of extensive fires with subsequent 13 c decrease in atmospheric co 2 it is estimated that the geologically instantaneous combustion of 18 24 of the terrestrial above ground biomass would be necessary to account for the measured negative isotopic shift at the k t boundary on the basis of carbon mass balance between terrestrial above ground biomass and atmosphere

deformation of oceanic lithosphere near slow spreading ridge discontinuities abstract transform and non transform discontinuities that offset slow spreading mid ocean ridges involve complex thermal and mechanical interactions the truncation of the ridge axis influences the dynamics of spreading and accretion over a certain distance from the segment end likewise the spreading system is expected to influence the lithospheric plate adjacent to the ridge end opposite of the discontinuity tectonic effects of the truncated ridge are noticeable in for example the contrast between seafloor topography at inside corners and outside corners along axis variations in rift valley depth style of crustal accretion and ridge segment retreat and lengthening along such slow spreading discontinuities and their fossil traces oceanic core complexes or mega mullion structures are rather common extensional tectonic features in an attempt to understand deformation of oceanic lithosphere near ridge offsets the evolution of discontinuities and conditions that may favor oceanic core complex formation a three dimensional thermo mechanical model has been developed the numerical approach allows for a more complete assessment of lithosphere deformation and associated stress fields in inside corners than was possible in previous 3 d models the initial suite of results reported here focuses on deformation when axial properties do not vary along strike or with time showing the extent to which plate boundary geometry alone can influence deformation we find that non transform discontinuities are represented by a wide oblique deformation zone that tends to change orientation with time to become more parallel to the ridge segments this contrasts with predicted deformation near transform discontinuities where initial orientation is maintained in time the boundary between the plates is found to be vertical in the center of the offset and curved at depth in the inside corners near the ridge transform intersection ridge normal tensile stresses concentrate in line with the ridge tip extending onto the older plate across the discontinuity and high stress amplitudes are absent in the inside corners during the magmatic accretionary phase simulated by our models with the tested rheology and boundary conditions inside corner formation of oceanic core complexes is predicted to be unlikely during magmatic spreading phases additional modeling studies are needed for a full understanding of extensional stress release in relatively young oceanic lithosphere

magnetostratigraphic and biostratigraphic correlation of late campanian and maastrichtian marine and continental strata from the red deer valley to the cypress hills alberta canada two stratigraphic sequences red deer valley and cypress hills sections in alberta spanning the late campanian to paleocene are magnetostratigraphically and biostratigraphically characterized the red deer valley section had previously been studied but additional material has allowed the extension of the magnetozonation downwards into the bearpaw formation higher sample resolution has allowed the identification of a number of magnetosubzones in 32n 32r and 33n four reversed magnetosubzones have been identified in magnetozone 32n in addition to the one presently recognized in geomagnetic polarity time scales one normal subzone in 32r and one reversed subzone in 33n have also been recorded the 32r 33n boundary is shown to occur in the baculites cuneatus zone the campanian maastrichtian boundary is indicated to be at or near the baculites eliasi baculites baculus boundary at the top of 32n comparisons of the biostratigraphy between the two areas indicate that palynomorph ranges differ from data p

segmentation of the mid atlantic ridge between 24 n and 30 40 n the mid atlantic ridge mar extends for over 12 000 km from iceland to the bouvet triple junction in the south atlantic most of our knowledge of the geology of this slow spreading centre comes either from widely spaced low resolution echo sounding lines or from detailed studies of small areas using deep towed instruments or submarines high resolution multibeam bathy metry1 2 has been insufficient to define the variability of accretionary processes along this plate boundary here we present the results of a recent investigation of a 800 km long section of the mar carried out using the multibeam echo sounder seabeam3 analysis of these data reveals the scale and nature of the segmentation of the mar between the kane fracture zone 24 n and latitude 30 40 n

variation in lithospheric stress along ridge transform plate boundaries three dimensional numerical models of asthenospheric flow and deformation in the oceanic lithosphere predict variability in the stress field that reflects the geometry of the ridge transform boundary a series of 3 d boundary element calculations shows how spreading rate transform offset and segment length each influence the flow and stress fields that develop during plate driven asthenospheric flow beneath a ridge transform boundary the predicted patterns of stress supported seafloor relief generally follow those observed median valleys are predicted at slow spreading ridges vs no rift valley or in some cases a small axial high at fast spreading ridges nodal deeps occur at ridge transform intersections for offsets greater than 25 km longer segments have more along axis deepening than short segments which do not shoal much in their center the predicted amplitude of the stress supported topography is up to 20 across axis and 40 along axis of that observed for an assumed asthenospheric viscosity of 5 1019 pa s and a weak lithosphere local compensation

seismic anisotropy in the upper mantle 2 predictions for current plate boundary flow models 1 the anisotropic seismic structure due to flow induced mineral alignment is investigated for a series of models designed to simulate deformation in the upper mantle within a few hundred kilometers of a plate boundary the orientation distributions of olivine enstatite aggregates evolve along streamlines of each flow model based on each grains plastic response to the local stress strain field the effective elastic tensor for these textured aggregates provides predictions of p wave anisotropy and shear wave splitting throughout the model space p and s travel time delay patterns and fast shear wave polarization angles are found to vary significantly with incidence angle for a given model comparison of predicted fast p direction for our method versus a finite strain based estimate shows that agreement is acceptable for much of the model space but notable differences occur in regions up to several tens of kilometers in size two dimensional models of spreading center flow are presented for slow and fast rates and for several cases in which the ridge migrates over the deeper mantle the effect of flow in the third dimension is addressed in a few calculations for one comparison of flow in the mantle wedge at a subduction zone the introduction of trench parallel flow causes significant changes in the predicted patterns of p wave anisotropy magnitude more than orientation and sks splitting

high resolution organic carbon isotope record across the cretaceous tertiary boundary in south central alberta implications for the post impact recovery rate of terrestrial ecosystems and use of δ13c as a boundary marker a high resolution study identified a 13 c excursion of 1 8 to 2 3 in terrestrial organic matter across the cretaceous tertiary k t boundary at two localities in the scollard formation of south central alberta one of the northernmost occurrences of the k t boundary in terrestrial settings 13 c values are at their lowest within 6 cm above the k t boundary claystone and return to pre boundary levels within 10 cm above the boundary claystone statistical analyses reveal that the k t isotopic shift in alberta is related to the nature of floral changes that occurred across the k t boundary a radiometrically dated bentonite resting on the boundary hosting nevis coal at one of the localities permits us to estimate that the terrestrial carbon cycle recovered 100 000 years after the k t boundary event a value that supports an existing hypothesis that terrestrial ecosystems recovered more rapidly than marine ecosystems the organic carbon isotope record of the entire scollard formation demonstrates that the 13 c excursion across the k t boundary did not reach anomalously low values by late maastrichtian standards in alberta furthermore the occurrence of the k t carbon isotope shift within a restricted stratigraphic interval 10 cm greatly limits the probability of its preservation in the context of terrestrial sedimentary environments these observations suggest that on their own 13 c profiles may be unreliable for locating the k t boundary and possibly other geologically instantaneous events and that they should be used in combination with other approaches e g palynology to identify the k t boundary in sections lacking the boundary claystone and iridium anomaly resume une etude de haute resolution a identifie une excursion isotopique 13 c varient entre 1 8 et 2 3 dans

three dimensional mantle flow beneath mid ocean ridges we have studied the development of multiscalar mantle flow beneath mid ocean ridges using a three dimensional numerical technique modeling includes various modes of heating and the shear flow induced by plate motion away from a spreading center with and without transform offsets the computational box consists of two layers differing in their viscosities it is shown than when flow is generated by heat sources located for the most part in the lower layer convective cells have horizontal dimensions proportional to the entire thickness of the box it is only when flow is driven by buoyancy forces in the top layer or by transient cooling along the top interface that transverse rolls are found to be confined within the lop low viscosity layer these rolls remain generally located far from the ridge plane except in the case of a viscosity contrast of 3 orders of magnitude between the bottom and top layers we conclude that segmentation beneath mid ocean ridges requires both strong viscosity contrasts and the lack of deep convective flow marine geophysical observations suggest that mantle upwelling beneath mid ocean ridges is two dimensional sheetlike beneath intermediate fast and hotspot influenced spreading centers and three dimensional plumelike beneath slow spreading centers and ridges overlying cold regions of the mantle such as the australian antarctic discordance we propose that these observations can be explained by variations in the viscosity structure and temperature of the mantle along the mid ocean ridge system models including a transform offset show that the active portion of the transform is a region of mantle downwelling the toroidal flow induced by the offset shifts the plumes away from the ridge crests the effects of the toroidal field are strongly magnified when the return flow cannot penetrate in the lower layer due to a large viscosity contrast stresses generated by the flow partly explains the development of inside corner highs and the evolution of transform faults

maastrichtian paleocene foreland basin stratigraphies western canada a reciprocal sequence architecture palynological and magnetostratigraphic chronostratigraphic correlations of lower maastrichtian to paleocene strata along an east west western canada basin transect allow for the recognition of a reciprocal sequence architecture in nonmarine strata reference sections include three canadian continental drilling program cretaceous tertiary boundary project core holes and outcrops in alberta southern saskatchewan and north central montana the spatial and temporal position of the third order sequences provides evidence for the correlation of proximal sector regional disconformities and sedimentary wedges with distal sector sedimentary wedges and regional disconformities respectively the boundary between the two sectors is represented by a hingeline which separates the foreland basin syncline from the peripheral bulge the stratigraphies defined by reciprocal third order sequences are complicated by fourth order boundaries developed within proximal sedimentary wedges and with no correlative distal strata these results support tectonic control on foreland basin sedimentation a model for interpreting the various types of sequences in terms of foreland basin evolution vertical tectonics and orogenic cycles is provided it is argued that nonmarine sequence boundaries times of maximum uplift in the foreland region may be expressed as disconformities incised valleys top of mature paleosol levels or base of fluvial channels whereas nonmarine equivalents of marine maximum flooding surfaces times of maximum basinal subsidence may be indicated by extensive coal seams and or lacustrine sediments resume les correlations palynologiques magnetostratigraphiques et chronostratigraphiques des strates echelonnees du maastrichtien inferieur au paleocene le long du transect est ouest du bassin de la cordillere occidentale au canada permettent la reconnaissance d une ordonnance architecturale de sequences reciproques dans les strates continentales les coupes de reference incluent trois trous de forage carottes du canadian continental drilling program cretaceous tertiary boundary project et des affleurements localises en alberta dans le sud de la saskatchewan et dans le centre nord du montana la position spatiale et temporelle des sequences de troisieme ordre plaide pour la mise en correlation des discordances regionales et des depots sedimentaires en coin dans le secteur proximal avec les depots sedimentaires en coin et les discordances regionales dans le secteur distal respectivement une ligne de jonction represente la limite entre les deux secteurs qui separe le bassin d avant pays en forme de cuvette du bombement peripherique les stratigraphies definies par les sequences de troisieme ordre reciproques sont embrouillees par les limites de quatrieme ordre developpees au sein des depots sedimentaires en coin proximaux sans la presence de strates distales correlatives ces resultats appuient la these d un controle tectonique sur le bassin sedimentaire d avant pays on presente ici un modele interpretant les divers types de sequences en termes d evolution d un bassin d avant pays de tectonique verticale et de cycles orogeniques nous tentons de demontrer que les discordances les vallees entaillees les horizons sommitaux de paleosols matures ou la base des chenaux fluviaux peuvent aider a definir les limites des sequences continentales periodes de soulevement maximum dans la region de l avant pays tandis que les couches de charbon etendues et ou les sediments lacustres representent plutot les equivalents continentaux des aires d inondation maximale periodes de subsidence maximum du bassin traduit par la redaction catuneanu and sweet 703

rift valley no rift valley transition at mid ocean ridges a simple mechanical model for the axial topographic and gravity variations with spreading rate is developed the model emphasizes the rapid transition from one mechanism to another with changing spreading rate our model has a brittle layer over a ductile layer which are being pulled by forces away from the ridge axis there exists a potential failure zone of width lf where the stresses within the brittle plate exceeds its yield strength if the yield strength of the brittle plate is nearly constant this width is largely determined by the strain rate and the viscosity of the strong mantle the high ductility of oceanic crust at high temperatures relative to that of mantle at the same temperatures leads to the concept of a decoupling region a critical feature in this model the size of the decoupling region ld is determined by the thickness of the oceanic crust and temperatures within the crust if the decoupling region is small ld lf as shown to be the case for fast spreading ridges then each of the two layers responds separately to the horizontal stretching the brittle plate will be broken only at the axis and any buoyant force of the region would lift it up to form the rise crest high as a result of local isostasy the changing size of the decoupling region gives rise to the transition from atlantic type axial topography to pacific type as well as the transition from a high amplitude highly variable gravity signature to a low amplitude very uniform gravity signature parameters can be chosen so that such a transition occurs at a half rate of 35 mm yr which is the critical half rate suggested by both topographic and gravity data

new constraints on early tertiary palaeoproductivity from carbon isotopes in foraminifera one of the most pronounced features of marine sections at the cretaceous tertiary k t boundary is the negative excursion in biogenic carbonate 13c in the early tertiary carbon isotope record1 9 the coincidence of this excursion with the elimination of many marine plankton species supports predictions that large scale reduction of primary productivity in the oceans would disrupt the biological carbon pump resulting in a diminished surf ace to deep 13c gradient10 13c carbonate accumulation rates and other geochemical indices support the idea that the oceans were less productive in the early palaeocene9 here we present carbon isotope analyses of individual species of benthic and planktonic foraminifera spanning the k t boundary in oop hole 690c weddell sea antarctica which demonstrate that primary productivity following the k t extinctions may not have diminished to the extent or for the duration indicated by previous isotope studies the magnitude of the 13c gradient change is dependent on the species analysed reflecting differing depths of calcification seasonal contrasts and or disequilibrium effects the lack of any change in benthic 13c at the k t boundary indicates that the antarctic may not have been a significant source of deep water during the early palaeocene contrary to previous suggestion11 13

geophysical signatures of oceanic core complexes author posting the authors 2009 this article is posted here by permission of john wiley sons for personal use not for redistribution the definitive version was published in geophysical journal international 178 2009 593 613 doi 10 1111 j 1365 246x 2009 04184 x

elemental and stable isotope variations of organic matter from a terrestrial sequence containing the cretaceous tertiary boundary at york canyon new mexico abstract elemental and isotopic composition of organic matter from a terrestrial sequence including the palynological cretaceous tertiary k t boundary together with an ir anomaly at york canyon new mexico record information about paleoclimatological and environmental conditions six layers of coal carbonaceous shale and mudstone with high contents of organic material were selected for analysis a late cretaceous coal bed 10 m below the k t boundary and an early tertiary coal bed containing the k t iridium anomaly at its base were sampled intensively in the lower bed the isotopic ratios 13 c 12 c 15 n 14 n andd h and the elemental ratios c n andn h all varied sympathetically with one another over depth in contrast in the upper coal layer only the d h c n andn h ratios showed some coupling immediately above the k t boundary the 13 c values displayed a long term shift of 1 8 to more negative values while the hydrogen isotope ratios in these samples did not change significantly we interpret the covariations in both coal layers as sympathetic responses of the isotopic and elemental ratios to climatic and environmental changes as have been observed for younger sedimentary organic matter the long term 13 c shift during the early tertiary is similar to the trend observed for 13 c values of marine carbonates our data thus support the proposal that the carbon cycle was perturbed globally by the effects of a drastically decreased marine bioproductivity along the k t transition the uncoupling of variations in the climatically sensitive isotopic and elemental ratios seen in the early tertiary coal bed provides evidence for major geochemical and environmental changes in the york canyon area at the end of the mesozoic on the other hand the constancy of d values in the organic matter deposited at and above the k t boundary gives no indication of significant changes in the hydrologic climatic regimes as recorded in the d h ratios at the site for several thousand years following the event which produced the high ir concentrations our results provide constraints on models that have been advanced to explain that event and its consequences

late cretaceous to early tertiary magnetostratigraphy of a continental sequence red deer valley alberta canada the red deer valley exposes a conformable 350 m thick late campanian to early paleocene fluvial deltaic coal bearing sequence named the edmonton group systematic sampling and paleomagnetic analysis of the dominant lithologies mudstones sandstones and shales were carried out over five sections correlated by coal seams to provide some 500 sites stratigraphic levels primary detrital remanent magnetization directions after alternating field cleaning produce a polarity reversal pattern correlatable to sea floor magnetic anomalies 29 33 the campanian maastrichtian boundary based upon the first appearance of wodehouseia and the maastrichtian paleocene cretaceous tertiary boundary based upon an ir anomaly associated with dinosaur and cretaceous palynofloral extinctions correlate closely magnetostratigraphically with the marine foraminiferal section at gubbio italy radiometric dating of bentonites has indicated the ages of these boundaries to be approximately 71 and 64 ma respectively