planktonic foraminiferal biostratigraphy and assemblages in the bering sea during the pliocene and pleistocene iodp sites u1340 and u1343 abstract iodp site u1340 and site u1343 in the bering sea have been investigated with regard to planktonic foraminifers and fragmentation the base of site u1340 dates back to the early pliocene and the base of site u1343 to the early pleistocene site u1340 is situated at bowers ridge the southern bering sea site u1343 is situated near the gateway to the arctic ocean in the northern bering sea at both sites there are none or very few planktonic foraminifers during the pliocene and early pleistocene after 1 3 1 4 ma the planktonic foraminifers are continuously present for most of the samples examined three stratigraphic events have been identified in this study the first occurrence fo of neogloboquadrina inglei is observed at 1 4 1 5 ma although this event may be affected by poor preservation of foraminifers in older sediments the observed age of the change in the coiling ratio of neogloboquadrina pachyderma from right to left at 1 2 ma agrees with the dating of the same event at the californian margin the age of the last occurrence lo of n inglei also seems to match the same event from the californian margin at 0 7 ma this implies that these events are robust regional events for the entire northern pacific multivariate analyses of the quantitative planktonic foraminifer data show three main faunal assemblages the oldest assemblage from 1 3 1 4 ma to 1 2 ma is dominated by n pachyderma s l dex together with globigerina bulloides other species in this fauna are n inglei n pachyderma s l sin globigerina umbilicata and turborotalita quinqueloba after 1 2 ma the faunal assemblage is dominated by n pachyderma s l sin but the remaining species are the same as before at 0 7 ma n inglei disappears whilst the remaining fauna assemblage stays the same with n pachyderma s l sin still dominating reflecting subpolar polar conditions prior to 1 4 1 3 ma there are very few or no planktonic foraminifers low shell fragmentation and lower toc suggest that the lack of planktonic foraminifers in these sediments cannot be explained either by a shoaling of the carbonate compensation depth or by enhanced supralysoclinal dissolution instead we argue that the appearance of abundant foraminifers in the sediment reflects the same evolutionary adaption of n pachyderma sin to cold conditions to have occurred after 1 1 1 0 ma as in the north atlantic

relief and drainage evolution during the exhumation of the sierra nevada se spain is denudation keeping pace with uplift abstract we have performed a geomorphic analysis of the sierra nevada the highest range of the betic cordillera se spain with the aim to elucidate its late miocene to present day exhumation history the qualitative and quantitative analysis is based on filtered topography local relief swath profile analysis anomalies on stream orientation bulk erosion volume hypsometry and steepness index k sn all these parameters are intimately linked to river incision and development of drainage pattern having been calculated to assess the role of folding and faulting on the evolution of the sierra nevada moreover uplift rates in the core of the sierra nevada have been deduced from an extrapolation of the position of late tortonian to pliocene coastline deposits these data have been compared to apatite u th he fission track and 10 be cosmogenic data from se spain in order to evaluate the consistency among uplift thermal histories and denudation rates our preferred tectonic scenario is one that favors fast exhumation of the western sierra nevada in a nw se overall compressive setting produced by the convergence between the nubia and africa plates sub perpendicular to this compression a westward 4 mm year extensional hanging wall displacement promotes uplift and unroofing of the western part of sierra nevada

miocene stable isotopic stratigraphy and magnetostratigraphy of buff bay jamaica previously reported biostratigraphic relationships from middle upper miocene sections exposed near buff bay jamaica 18 n tropical bioprovince differ from the subtropical north atlantic sites 563 and 558 time scales for this interval rely on correlations established at these subtropical sites and the differences with the tropical section have implications to global correlations planktonic foraminiferal zones n13 and n15 are thick at buff bay but are virtually absent at sites 563 and 558 nannofossil zone nn9 is associated with zone n15 and uppermost zone n14 at buff bay but is associated with zone n16 at the other sites magnetostratigraphic data presented here further complicate the interpretation zone nn9 is associated with a thick normal magnetozone at sites 563 and 558 at buff bay it is associated with a thick reversed magnetozone although a secondary magnetization at buff bay makes it difficult to identify confidently miocene normal magnetozones the thick reversed magnetozone most likely represents the paleomagnetic field and correlates with chron c5r the magnetobiostratigraphic relationships require either diachrony of taxa or two mutually exclusive hiatuses in jamaica and the north atlantic we address this problem by analyzing benthic foraminiferal 18 o and 13 c from the buff bay section these isotopic data allow us to evaluate three hypotheses that reconcile the magneto bio and isotopic stratigraphic data and conclude that the first and last occurrences of five taxa were diachronous by 0 3 0 5 m y between tropical and subtropical locations this requires revised age estimates for late middle to early late miocene biostratigraphic datum levels we suggest that the ranges of several taxa are useful for endemic tropical or subtropical zonations but correlations between the low and midlatitudes were affected by an increase in latitudinal thermal gradients during the late middle miocene however we admit that further studies are needed before this issue is resolved

changing depth distribution of hiatuses during the cenozoic the differential effects of climate change sea level and water mass circulation on deposition erosion of marine sediments can be constrained from the distribution of unconformities in the world s oceans i identified temporal and depth patterns of hiatuses hiatus events from a large and chronologically well constrained stratigraphic database of deep sea sediments the paleogene is characterized by few several million year long hiatuses the most significant cenozoic hiatus event spans most of the paleocene the neogene is characterized by short frequent hiatus events nearly synchronous in shallow and deep water sediments epoch boundaries are characterized by peaks in deep water hiatuses possibly caused by an increased circulation of corrosive bottom water and sediment dissolution the plio pleistocene is characterized by a gradual decrease in the frequency of hiatuses future studies will focus on the regional significance of the hiatus events and their possible causes

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

biostratigraphy interpretations of oppel s zones abstract zones like those of oppel and hedberg s oppel zone are commonly interpreted as rock units delimited temporally a more restricted view is that they are rock units empirically defined by bioevents that occur in the same order in all sections methods used by oppel and definitions proposed by hedberg are reviewed to assess their adequacy for definition of biostratigraphic units and their ability to support temporal inferences although they are usually interpreted as chronostratigraphic units oppel defined his zones in stratigraphic space without temporal reference in contrast hedberg required that bioevents for his oppel zone should be approximately isochronous across their distribution but provided no operational way to identify such bioevents neither author clearly indicated how boundaries should be defined recourse to a principle of biosynchroneity to support inferences that stratigraphically ordered bioevents are temporal markers conflicts with knowledge of the biogeographies of modern taxa evolutionary theory explains why some bioevents occur in the same stratigraphic order but does not support the inference that they are isochronous events since its inception biostratigraphy has focused on ordered classifications like those of oppel stratigraphic codes should allow for a complementary category of biofacies zones that reflect depositional environments and are not constrained to occur in a particular order

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

the neogene genus streptochilus bronnimann and resig 1971 from the gulf of california abstract four species of the planktonic foraminiferal genus streptochilus from key neogene marine localities are documented in relation to the evolution of the gulf of california s globigerus s latus s macdougallae sp nov and s inglei sp nov planktonic foraminiferal bioevents and strontium isotopes in the bouse tirabuzon carmen and ojo de buey lithostratigraphic units constrain the local distribution range between 6 and 5 3 ma for the last three species whereas s globigerus appears locally at 5 5 ma and disappears between 3 79 and 3 46 ma in the imperial and trinidad formations the last occurrence of streptochilus latus and the first and last occurrences of s globigerus in the ancient gulf of california are correlated with bioevents calibrated in the equatorial pacific therefore they can be used as reliable local biostratigraphic markers the presence of streptochilus in the ancient gulf of california seems to correlate with upwelling in a pattern similar to that observed in the modern oceans

revision of the early middle pleistocene calcareous nannofossil biochronology 1 75 0 85 ma the extant nannofossil biostratigraphic and biochronologic framework for the early middle pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high quality low to mid latitude deep sea successions the quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals and the following biohorizons were defined first occurrence of medium sized gephyrocapsa spp last occurrence of calcidiscus macintyrei first occurrence of large gephyrocapsa spp last occurrence of large gephyrocapsa spp first occurrence of reticulofenestra asanoi re entrance of medium sized gephyrocapsa spp and last occurrence of reticulofenestra asanoi the detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales the degree of isochrony or diachrony of the biohorizons was evaluated biohorizons and are isochronous occurring close to marine isotope stages mis 55 and mis 22 respectively and and are slightly diachronous on the order of 30 40 kyr whereas biohorizons and are confirmed as diachronous on the order of 100 80 and 60 kyr respectively some of the events are clearly controlled by environmental conditions e g the last occurrence of r asanoi related to significant environmental changes associated with the first large amplitude glaciation of the late quaternary mis 22

from extension to transpression quaternary reorganization of an extensional related drainage network by the alhama de murcia strike slip fault eastern betics abstract the complex present day drainage network of the lorca totana area records the changing tectonic setting from extension to transpression in the eastern betics through a detailed morphometric analysis we evaluate the topographic response to this major change in the tectonic setting and the influence in the drainage of miocene extension and middle pleistocene to present day transpression the present day drainage network preserves geomorphic features inherited from late miocene extension that are being overprinted by a new transverse fluvial system this new system advanced towards the nw since the middle pleistocene in response to a localized base level drop related to the ne sw oriented alhama de murcia sinistral reverse fault geomorphic indexes calculated in this work suggest the present day activity of the alhama de murcia fault and the sierra de la tercia anticline the two major tectonic structures in the area the landscape rejuvenation associated with this process results in contrasting mountain front sinuosity values between old and new mountain fronts high slk index anomalies convex shaped and complex hypsometric curves knickpoints in river profiles contrasting slope area plots and high steepness index values this fluvial reorganization was driven progressively by successive fluvial captures preserved as wind gaps in the present day drainage network

how synchronous are neogene marine plankton events an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username andguest as the password go to the right directory by typing cdapend type ls to see what files are available type get and thename of the file to get it finally type exit to leave the system paper 94pa01456 how synchronous are neogene marine planktonevents by c spencer cervato h r thierstein d b lazarus andj p beckmann diskette may be ordered from american geophysicalunion 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order we analyzed the synchrony and diachrony of commonly used neogene biostratigraphic events from data published in the initial reports of the deep sea drilling project dsdp and in the proceedings of the ocean drilling program odp on the basis of the combined biostratigraphic and magnetostratigraphic evidence new neogene age models were constructed for 35 globally distributed dsdp and odp holes biostratigraphic events from the four major plankton groups calcareous nannofossils diatoms planktonic foraminifera and radiolarians were compiled from dsdp and odp reports after the elimination of possible sources of error such as stratigraphic hiatuses and reworking of specimens 124 biostratigraphic events that occurred in at least four holes were analyzed in detail for each event a biochronologic age estimate was derived by projection of the depth of the event onto the line of correlation of each hole and from these a global mean age for each event was calculated together with its standard deviation average standard deviations for event ages by fossil group are calcareous nannofossil first appearance datums fads 0 57 m y 21 events calcareous nannofossil last appearance datums lads 0 60 m y 25 events diatom fads 0 57 m y 7 events diatom lads 0 85 m y 14 events planktonic foraminifera fads 0 88 m y 22 events foraminifera lads 0 68 m y 16 events radiolarian fads 0 30 m y 9 events radiolarian lads 0 31 m y 10 events since the average sample spacing in the sites used for this analysis is only 0 185 m y we have examined the data for true patterns of diachrony and for other biases diachrony is more frequent among cosmopolitan than among endemic taxa thus there is a general trade off between the obtainable age precision and the geographic extent of a bioevent precision of age calibrations also decreases with increasing age although some of these features may be due to investigator bias they appear in part to be real phenomena and thus could also provide opportunities for further exploration of important paleobiological processes such as change in environmental gradients through time evolutionary adaptation of species populations and migration due to water mass changes

slab rupture and delamination under the betics and rif constrained from receiver functions abstract we map the lithospheric structure under the westernmost mediterranean convergent setting interpreting p receiver functions obtained from a dense seismic network no orogenic root occurs under the eastern and great part of the central betics however the subducted south iberian continental lithosphere is found beneath the western betics where the iberian moho reaches depths of approximately 65 km dipping gently towards the se meanwhile at the rif strong crustal and lithospheric thickness contrasts occur across the nekor nw se sinistral fault that overlies the region of present slab tearing east of the nekor fault there is no orogenic root and the crust has been thinned to approximately 22 km whilst to the west the crust reaches 55 km thickness and the maghrebian continental lithosphere is attached to the lithospheric slab imaged by tomography under the alboran basin these data suggest that subduction rollback under the alboran and algerian basins together with continental slab tearing or detachment producing edge delamination under the betics and rif have been the main tectonic mechanisms driving extension magmatism and regional uplift in the westernmost mediterranean since the late miocene until present the surface expression of edge delamination and slab tearing is marked by regional uplift denudation of hp rocks in elongated core complex type domes late miocene volcanism in the eastern betics and rif and by large ne sw strike slip transfer faults like the alpujarras crevillente torcal or nekor faults that accommodate strong gradients in crustal displacements the iberian slab is still attached to the oceanic slab imaged under the alboran basin at the western betics where intermediate depth seismicity recent dextral strike slip faulting and folding could reflect slab tearing meanwhile active faulting and differential gps measured displacements would mark slab tearing beneath the rif coinciding with the trace of the sinistral nekor fault

biochronology and evolutionary implications of late neogene california margin planktonic foraminiferal events the biochronology of eight events first or last occurrences among species of the planktonic foraminifer neogloboquadrina plexus have been examined in six pliocene to quaternary deep sea sequences drilled during odp leg 167 off the coast of california the sites form a meridional transect along the california margin from 318 nt o 418n covering an area under the direct influence of the california current and associated upwelling system using age models based on combination of calcareous nannofossil and radiolarian data and magnetostratigraphic chron boundaries ages were assigned to the events thus allowing investigations of their spatial and temporal distribution three of the events have been identified as clearly diachronous two of these seem to represent examples of latitudinal immigrations the evolutionary activity in the neogloboquadrinid clade on the california margin appears centered around 2 1 ma with most of the events occurring between 2 5 and 1 ma this interval was a time of major climate change no events have occurred after 0 7 ma supporting the notion that the extreme climate variations of the late pleistocene inhibited speciation assignment of ages to events defining boundaries of the california margin cm zones of kennett and others has enabled us to compare this zonation with the standard planktonic foraminiferal zonal schemes seven of the neogloboquadrinid events occurred during the last 2 5 myr suggesting that the time resolution of the cm zones including the coiling dominance zones of lagoe and thompson during this interval is at least twice that of the standard planktonic foraminiferal zonation the remaining pliocene is divided only into two cm zones compared to six standard planktonic foraminiferal zones one of the pleistocene neogloboquadrinids is formally described as a new species q 2000 elsevier science ltd all rights reserved

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

longitudinal to transverse drainage network evolution in the high atlas morocco the role of tectonics the high atlas of morocco is a still active linear intracontinental mountain chain in the nw african plate which results from weak crustal thickening associated with rift inversion during the cenozoic and from uplift related to mantle thermal doming a striking morphological feature of the high atlas is the occurrence of both transverse and longitudinal i e strike parallel drainage characterized by deep fluvial incision of more than 1000 m in low relief topography of the axial zone of the chain most of the transverse component of the drainage appears to postdate the longitudinal component as indicated by recent or incipient captures and wind gaps the longitudinal drainage is inherited from an early stage of fluvial organization controlled by the tectonic structures developed during upper crustal folding and thrusting in the post paleozoic cover amplification of n s regional slope in the western high atlas by continued crustal shortening and thickening triggered i higher erosion rates in transverse than in longitudinal catchments and ii captures of longitudinal streams by transverse ones creating a new organization of the drainage system toward the regional slope such evolution from a longitudinal to a transverse dominated drainage may represent a common mechanism of fluvial network development in mountain belts where the amplification of the regional slope results from long lived lithospheric convergence

new biostratigraphic magnetostratigraphic and isotopic insights into the middle eocene climatic optimum in low latitudes the middle eocene climatic optimum meco was a warming event that interrupted the long term eocene cooling trend while this event is well documented at high southern and mid latitudes it is poorly known from low latitudes and its timing and duration are not well constrained because of problems of hiati microfossil preservation and weak magnetic polarity in key sedimentary sections here we report the results of a study designed to improve the bio magneto and chemostratigraphy of the meco interval using high resolution records from two low latitude sections in the atlantic ocean ocean drilling program odp sites 1051 and 1260 we present the first detailed benthic foraminiferal stable isotope records of the meco from the low latitudes as well as the biostratigraphic counts of orbulinoides beckmanni and new magnetostratigraphic results our data demonstrate a 750 kyr long duration for the meco characterized by increasing 13c and decreasing 18o with minimum 18o values lasting 40 kyr at 40 1 ma coincident with a short lived negative 13c excursion thereafter 18o and 13c values recover rapidly the shift to minimum 18o values at 40 1 ma is coincident with a marked increase in the abundance of the planktonic foraminifera o beckmanni consistent with its inferred warm water preference o beckmanni is an important eocene biostratigraphic marker defining planktonic foraminiferal zone e12 with its lowest and highest occurrences lo and hos our new records reveal that the lo of o beckmanni is distinctly diachronous appearing 500 kyr earlier in the equatorial atlantic than in the subtropics 40 5 versus 41 0 ma we also show that at both sites the ho of o beckmanni at 39 5 ma is younger than the published calibrations increasing the duration of zone e12 by at least 400 kyr in accordance with the tropical origins of o beckmanni this range expansion to higher latitudes may have occurred in response to sea surface warming during the meco and subsequently disappeared with cooling of surface waters

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

40ar 39ar geochronology of biostratigraphically controlled miocene tuffs from central japan comparison with italy and age of the serravallian tortonian boundary abstract two volcanic tuffs of the tomioka area central japan were selected from a fossiliferous marine succession of late serravallian age miocene and dated using the incremental heating 40 ar 39 ar technique the kitamura tuff located 10 m below the regional first occurrence fo of the planktonic foraminifera globigerina nepenthes yielded a biotite age of 11 79 0 08 ma the baba tuff located 180 m above the previous one yielded ages of 11 26 0 09 ma biotite 11 29 0 12 ma sanidine and 11 3 ma plagioclase isochron ages are similar to the plateau ages the fo of g nepenthes is estimated to have an age of 11 76 0 10 ma in japan similarly precise results obtained from the central apennines biotite 11 48 0 13 ma lead to an age estimate of 11 53 ma for the same fo in an italian section the age difference between sections is of the same magnitude as the analytical errors however the potential diachronism of the biostratigraphic signal has been independently estimated at 0 25 ma the fo of g nepenthes and fo of neogloboquadrina acostaensis are commonly taken as index for the beginning of n14 and end of n15 foraminiferal biozones respectively in the italian section the time interval between the two signals i e the duration of the two biozones may be estimated at 0 3 ma the serravallian tortonian boundary located near the dated layers can be estimated to have an age of 11 25 0 20 ma

late miocene development of the western pacific warm pool planktonic foraminifer and oxygen isotopic evidence abstract the disappearance at 10 ma of the deep dwelling planktonic foraminifer globoquadrina dehiscens from the western pacific including the south china sea was about 3 myr earlier than its final extinction elsewhere accompanying this event at 10 ma was a series of faunal turnover characterized by increase in mixed layer warm water species and decrease to a minimum in deepwater species paleobiological and isotopic evidence indicates sea surface warming and a deepened local thermocline that we interpret as related to the development of an early western pacific warm pool the stepwise decline of g dehiscens and other deep dwelling species from the nw and sw pacific suggests more intensive warm water pileup than equatorial localities where surface bypass flow through the narrowing indonesia seaway appears to remain efficient during the late miocene planktonic 18o values from the south china sea consistently lighter than the tropical western pacific during the miocene also suggest similar to today more variable hydrologic conditions along the periphery than in the core of the warm pool stronger hydrologic variability affected mainly by monsoons and increased thermal gradient along the western margin of the late miocene warm pool may have contributed to the decline of deep dwelling planktonic species including the early extinction of g dehiscens from the south china sea region the late miocene warm pool became influential and paleobiologically detectable from 10 ma but the modern warm pool did not appear until about 4 ma in the middle pliocene

active fault segmentation in northern tunisia abstract active shortening structures in northern tunisia have developed by tectonic inversion since the pliocene after late miocene extensional collapse of the whole region restored plio quaternary deformation observed on reflection seismic lines indicates deformation rates around 0 6 0 8 mm yr in the studied segments and larger amounts of shortening to the west of northern tunisia 16 than to the east 7 which suggests tectonic inversion started earlier to the west and later propagated eastwards reaching northeastern tunisia in the late pliocene this shortening is registered on striated pebbles in quaternary alluvial terraces and fault slip data giving two populations of strain ellipsoids with n s and wnw ese maximum shortening morphometric analysis in combination with field fault segmentation mapping show that topographic uplift and drainage rejuvenation occurs in relation to 20 30 km long ene wsw reverse fault segments and related antiforms that are offset and linked by e w to wnw ese dextral and ne sw oriented sinistral faults the largest fully linked fault system is the alia thibar fault this 130 km long fault zone shows an helicoidal geometry with five different fault segments including reverse dextral sinistral and oblique faults due to the young age of tectonic inversion after late miocene extensional collapse of the region the present relief of northern tunisia is characteristic of a young thrust and fold belt with dominating axial valleys along synforms and an incipient transverse drainage development propagating from west to east

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

the deep sea microfossil record of macroevolutionary change in plankton and its study the deep sea planktonic microfossil record foraminifera coccolithophores diatoms radiolaria and dinoflagellates provides a unique resource for palaeobiology despite some geographical gaps due to poor regional preservation and intermittant time intervals lost to erosion most time periods for each cenozoic planktonic biogeographical province are preserved vast numbers of specimens and numerous deep sea cores provide abundant material and the opportunity to tightly integrate macroevolutionary and palaeoenvironmental data current documentation of this record is mixed catalogues for foraminifera and coccolithophores offer nearly complete species level clade histories but taxonomy for siliceous microfossils is incomplete published occurrence data is primarily stratigraphic and covers only a fraction of the total preserved diversity age models for some sections are excellent accuracy c 100 kya but for many other sections are still poor taxonomic errors age model errors and reworking displace fossil occurrences in time complicating palaeobiological analysis with additional taxonomic work careful collection of whole fauna floral assemblage occurrence data improved age models and the development of better data filtering and analysis tools to deal with data outliers the deep sea microfossil record can deliver its promise of providing the most complete detailed record of macroevolutionary change available to science

oligocene miocene biostratigraphy magnetostratigraphy and isotopic stratigraphy of the western north atlantic magnetostratigraphic records from western north atlantic deep sea drilling project dsdp sites 563 and 558 are correlated with the geomagnetic polarity time scale gpts berggren et ai 1984a 1984b using marine magnetic anomalies and selected biostratigraphic datum levels the magnetochronology established is used to make direct magnetobiostratigraphic correlations that agree with previous oligocene early miocene studies however we show that zones nn8 partim and nn9 and associated epoch 11 correlate with magnetic anomaly 5 chron csn this contrasts with previous indirect correlations of epoch 11 with anomaly sa and requires an upward adjustment of 1 5 2 0 m y for middle late miocene calcareous nannofossil zones we correlate the middle late miocene boundary with zone nn8 and earliest chron csn 10 4 ma

recent developments in quantitative stratigraphy abstract during the past 10 years about 150 scientists in 25 countries have collaborated under the auspices of the international geological correlation programme project no 148 evaluation and development of quantitative stratigraphical correlation techniques this paper reviews mathematical methods of stratigraphical correlation mainly in biostratigraphy but also in chronostratigraphy and lithostratigraphy sequencing methods treat the relative order of stratigraphic events such as the highest occurrences of fossil taxa as observed in many sections intervals between successive events in an ordered sequence can be estimated and the results expressed in linear time if a subgroup of the stratigraphical events can be dated recently such methods have been used to develop a new deep water benthic foraminiferal zonation for the cenozoic strata of the central and viking grabens north sea several regional hiatuses of 2 to 5 m y in duration can be recognized and matched to changes in sea level the same methods have been used for automated isochron contouring with error bars in depth or time units in cenozoic and cretaceous basins off eastern canada such information may be used for automated basin history analysis time successive assemblages of fossils can be established by using multivariate methods applied to co occurrences of events or by the method of unitary associations in conjunction with graph theory on the overlap of stratigraphical ranges other methods for stratigraphical correlation reviewed in this paper include the composite standard method and estimation of the age of chronostratigraphical boundaries using maximum likelihood and cubic spline interpolations attractions of quantitative stratigraphy are the use of rigorous methodology which highlights many properties of the data the ability to handle large and complex data bases in an objective manner and statistical evaluation of the uncertainty in the results generally little conceptual orientation is required in order to use these methods and thereby gain more information from a particular dataset

venus center of figure center of mass offset abstract magellan altimetry data reveal that the center of figure cf of venus is displaced approximately 280 m from its center of mass cm toward 4 4 s 135 8 e a location in aphrodite terra this offset is smaller than those of other terrestrial planets but larger than the estimated error which is no more than a few tens of meters we examine the possibility that the cf cm offset is related to specific geologic provinces on venus by deriving three simple models for the offset a thick crust model a hotspot model and a thick lithosphere model the offset caused by a region of thick crust depends upon the region s extent the crust mantle density contrast and the thickness of excess crust a hotspot related offset depends on the extent of the thermally anomalous region and the magnitude of the thermal anomaly offset due to a region of thick lithosphere depends upon the extent of the region the average temperature contrast across the lithosphere and the amount of excess lithosphere we apply the three models to venus plateau shaped highlands volcanic rises and lowlands respectively in an attempt to match the observed cf cm offset location and magnitude the influence of most volcanic rises and of ishtar terra on the cf cm offset must be quite small if we are to explain the direction of the observed offset the lack of influence of volcanic rises can be explained if the related thermal anomalies are limited to a few hundred degrees or less and are plume shaped i e characterized by a flattened sublithospheric head with a narrow cylindrical feeder tail the unimportance of ishtar terra is most easily explained if it lies atop a significant mantle downwelling

new calibration of neogene radiolarian events in the north pacific abstract new age models for twelve deep sea drilling project sites in the north pacific have been produced based on in order of importance in our dataset a recompilation of previously published diatom calcareous nannofossil and foraminifer first and last occurrences and magnetostratigraphy the projected ages of radiolarian first and last occurrences derived from the line of correlation of the age depth plots have been computed from these sites and 28 radiolarian events have thereby been newly cross calibrated to north pacific diatom and other stratigraphy several of the north pacific radiolarian events are older than in previously published equatorial pacific calibrations and some may be diachronous within the north pacific these patterns may be due to complex latitudinal patterns of clinal variation in morphotypes within lineages or to migration events from the north pacific towards the equator

detecting a sequence boundary across different tectonic domains an example from the middle miocene of the northern apennines italy sequence stratigraphic concepts can provide a powerful tool for understanding the tectono sedimentary evolution of areas extending across different tectonic domains an example is provided by the upper serravallian strata of the northern apennines where a sedimentological and biostratigraphic study allows a sequence boundary to be traced across the foredeep and piggy back basin successions turbidite sedimentation of predominantly alpine and subordinate apenninic provenance occurred in the apenninic foreland basin throughout the middle miocene deep water sedimentation in the foredeep was laterally associated with deposition in shelf to slope environments in the piggy back basins in the piggy back basin succession the upper serravallian sequence boundary is a laterally extensive unconformity within homogeneous marly deposits this unconfonnity is laterally correlative with the base of lenticular turbidite bodies a stratigraphic lacuna affecting zone n14 characterizes the marginal areas where glaucony rich deposits assigned to zone n15 unconformably overlie marls displaying association of zone n13 in the depocentres where no significant stratigraphic gap has been detected the sequence boundary is narrowly constrained to lowermost zone n14 the upper serravallian unconformity of the piggy back basins succession is correlative with time equivalent features in two distinct parts inner basin and outer basin of the foredeep in the inner basin the sequence boundary separates basin margin turbidites from overlying slope hemipelagites in a more external position outer basin the sequence boundary is the base of a characteristic mega turbidite of apenninic provenance turrito layer in other sectors of the outer basin where turbidite sedimentation was entirely of alpine provenance the sequence boundary has no clear physical expression the observed facies distribution in the study area suggests that an important thrusting event affected the northern apennines in the late serravallian resulting in submarine channel incision and nondeposition in the piggy back basins compressional activity in the foredeep was responsible for the closure of the inner basin and subsequent shifting of turbidite sedimentation in the outer basin slope instability led to widespread remobilization of previously deposited turbidites triggering turbidite events of huge volume the different characteristics of the sequence boundary in the various parts of the foredeep constitute an example of differential response of a multisourced supply system to tectonic deformation

biochronology of the mid pliocene sphaeroidinella event abstract morphological evolution in the late neogene planktonic foraminifer sphaeroidinella lineage involves a sudden increase of the percentage of specimens equipped with supplementary apertures from 70 in the mid pliocene about 3 5 ma this evolutionary transition marked by the first occurrence of specimens with large supplementary apertures in the lineage is denoted the sphaeroidinella event changes in the proportions of the supplementary apertures in the lineage were studied in 24 samples from odp hole 926a drilled in the equatorial atlantic ocean in addition detailed chronological models have been compiled for this section as well as for pliocene sections from dsdp holes 214 502a and 503b where evolution in the lineage have been analyzed previously stratigraphic correlation of the studied sequences suggests that the sphaeroidinella event took place at about 3 6 ma in the eastern equatorial pacific hole 503b and at 3 5 3 6 ma in the caribbean hole 502a while in the atlantic ocean hole 926a and in the indian ocean hole 214 the event occurred after 3 5 ma the inferred diachrony of the mid pliocene sphaeroidinella transition which is considered to represent a prime example of punctuated anagenesis suggests that this evolutionary modality may have an allopatric component its short duration on average less than 50 kyr and the detailed biochronology that could be established for this event qualifies it as a useful biostratigraphic tool in the low latitude pliocene oceans