glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

new age constraints for the salamanca formation and lower rio chico group in the western san jorge basin patagonia argentina implications for cretaceous paleogene extinction recovery and land mammal age correlations the salamanca formation of the san jorge basin patagonia argentina preserves critical records of southern hemisphere paleocene biotas but its age remains poorly resolved with estimates ranging from late cretaceous to middle paleocene we report a multi disciplinary geochronologic study of the salamanca formation and overlying rio chico group in the western part of the basin new constraints include 1 an 40ar 39ar age determination of 67 31 0 55 ma from a basalt flow underlying the salamanca formation 2 micropaleontological results indicating an early danian age for the base of the salamanca formation 3 laser ablation hr mc icp ms high resolution multi collector inductively coupled plasma mass spectrometry u pb ages and a high resolution tims thermal ionization mass spectrometry age of 61 984 0 041 0 074 0 100 ma for zircons from volcanic ash beds in the penas coloradas formation rio chico group and 4 paleomagnetic results indicating that the salamanca formation in this area is entirely of normal polarity with reversals occurring in the rio chico group placing these new age constraints in the context of a sequence stratigraphic model for the basin we correlate the salamanca formation in the study area to chrons c29n and c28n with the banco negro inferior bni a mature widespread fossiliferous paleosol unit at the top of the salamanca formation corresponding to the top of chron c28n the diverse paleobotanical assemblages from this area are here assigned to c28n 64 67 63 49 ma 2 3 million years older than previously thought adding to growing evidence for rapid southern hemisphere floral recovery after the cretaceous paleogene extinction important peligran and carodnia zone vertebrate fossil assemblages from coastal bni and penas coloradas exposures are likely older than previously thought and correlate to the early torrejonian and early tiffanian north american land mammal ages respectively

an inverted double seismic zone in chile evidence of phase transformation in the subducted slab data from two microseismic field experiments in northern chile revealed an elongated cluster of earthquakes in the subducted nazca plate at a depth of about 100 kilometers in which down dip tensional events were consistently shallower than a family of compressional earthquakes this double seismic zone shows a distribution of stresses of opposite polarity relative to that observed in other double seismic zones in the world the distribution of stresses in northern chile supports the notion that at depths of between 90 to 150 kilometers the basalt to eclogite transformation of the subducting oceanic crust induces tensional deformation in the upper part of the subducted slab and compressional deformation in the underlying mantle

cenozoic tectonic evolution in the central andes in northern chile and west central bolivia implications for paleogeographic magmatic and mountain building evolution a review of available stratigraphic structural and magmatic evolution in northernmost chile and adjacent peru and bolivia shows that in this region 1 compression on the paleogene intra arc during the middle eocene incaic phase formed the nne ssw oriented incaic range along the present day precordillera and western cordillera and 2 post incaic tectonic conditions remained compressive until present contrasting with other regions of the andes where extensional episodes occurred during part of this time lapse a late oligocene early miocene peak of deformation caused further uplift the incaic range formed a pop up structure bounded by two thrusts systems of diverging vergencies it represented a major paleogeographic feature that separated two domains with different tectonic and paleogeographic evolutions and probably formed the andean water divide this range has been affected by intense erosion and was symmetrically flanked by two major basins the pampa del tamarugal and the altiplano magmatic activity remained located along the previous late cretaceous early eocene arc with slight eastward shift further compression caused westvergent thrusting and uplift along the western eastern cordillera bounding the altiplano basin to the east by another pop up shaped ridge eastward progression of deformation caused eastvergent thrusting of the eastern cordillera and subandean zone

reassessment of the age and depositional environments of the eocene cayraz formation a reference unit for tethyan larger benthic foraminifera haymana basin central turkey abstract the cayraz formation a reference unit for tethyan ypresian middle late lutetian larger benthic foraminifera haymana basin central turkey is a thick 350 m shallow marine mixed carbonate siliciclastic sequence divided into lower middle and upper units the lower and upper units predominantly consist of rhythmic intercalations of limestone and marly silty beds with abundant larger benthic foraminifera lbf and the middle unit is composed of massive fine siliciclastic sediments mostly barren in lbf and macrofossils by studying three sections caya cayb and ye encompassing the lower unit we show that the cayraz formation ca 100 m thick displays notable vertical and lateral variability in benthic fauna and facies along an se nw transect at its type locality near cayraz village the distribution of lbf and facies patterns indicate a general shallowing upward trend with more open marine environments in the easterly section caya and restricted shallow marine to continental environments with low diversity fauna in the westerly section ye a depositional setting ranging from outer to inner ramp with continental influence only in the westerly section is proposed key orthophragminid and alveolinid taxa from the lower unit of the cayraz formation indicate shallow benthic zones sbz 9 10 for its lower part and sbz 12 for its upper part suggesting a late ypresian age the massive marly silty section of the middle unit of the cayraz formation overlies the alveolina bearing limestones in all sections and yielded abundant planktonic foraminifera suggestive of p9 zone this implies a sharp environmental transition from platform to basin across the ypresian lutetian boundary

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

lateritized tephric palaeosols from central patagonia argentina a southern high latitude archive of palaeogene global greenhouse conditions palaeosols of the koluel kaike formation a red colour banded pyroclastic succession from southern argentina constitute a proxy for eocene climate changes reticulated and vertically elongated ferric mottles along with iron and manganese nodules are the most significant climate indicators which originated by alternating cycles of waterlogging and drying conditions causing fe mn mobilization and fixation clay minerals vary from a kaolinite smectite suite in the lower and middle sections to a smectite kaolinite one in the upper part high concentrations of iron oxides hydroxides and kaolinite lack of exchangeable bases absence of carbonate cement presence of ironstone and redness of hue in most of the palaeosols suggest intense chemical weathering related to leaching and lateritization processes five pedotypes ordered in a stratigraphic sense were identified strongly developed red to orange chornk fragiaquult and kapenk plinthaquult pedotypes display argillic horizons abundant ferric nodules and slickensides they are dominant in the lower and middle sections and formed in seasonal humid and megathermic tropical conditions with a mean annual precipitation of 1200 to 1300 mm and a mean annual temperature of 15 c weakly developed less structured ornek vitrand and polnek placaquand pedotypes occur in the middle and upper sections and originated in sub humid and mesic megathermic conditions with a mean annual precipitation around 1000 mm and a mean annual temperature around 12 c the brownish soorsh argialboll pedotype exhibits a granular structure and is present at the uppermost part of the unit it developed in sub humid semi arid and mesic conditions with a mean annual precipitation of 600 to 700 mm and a mean annual temperature around 10 c this pedotype succession and clay mineral distribution indicates a decrease in chemical weathering and degree of soil development with time koluel kaike palaeosols from central patagonia are some of the first continental non palaeobiological data linked to the early palaeogene global warming in south america they show an especially close relationship with the early eocene climatic optimum and the following long term cooling and drying initiated by middle to late eocene time

new age constraints for early paleogene strata of central patagonia argentina implications for the timing of south american land mammal ages the rio chico group in the san jorge basin of central patagonia argentina preserves some of south america s most significant paleogene records of biotic and climatic change three of its constituent formations the penas coloradas las flores and koluel kaike host vertebrate faunas referred to the carodnia faunal zone the itaboraian south american land mammal age salma and the riochican salma however the precise absolute ages of these units and thus their associated faunas and paleoclimate records are poorly resolved herein we report new paleomagnetic and geochronologic results from these formations in south central chubut province argentina u pb dating of four volcanic ashes using both laser ablation multicollector inductively coupled plasma mass spectrometry and high resolution chemical abrasion isotope dilution thermal ionization mass spectrometry indicates ages of igneous crystallization of 51 403 0 037 0 045 0 071 ma for a level within the middle las flores formation and 46 714 0 012 0 026 0 057 ma 44 579 0 013 0 026 0 054 ma and 42 856 0 017 0 027 0 054 ma for levels in the lower middle and upper koluel kaike formation respectively combining these with previous isotopic ages in our new magnetostratigraphic framework we correlate the penas coloradas formation to chrons c27n 26r ca 62 5 to ca 61 6 ma late danian and the section from the middle las flores to the uppermost koluel kaike to chrons c23n to c19r ca 51 4 42 2 ma mid ypresian late lutetian we combine these data with other recently published chronostratigraphic results from paleogene units in patagonia to better constrain the ages of noteworthy paleogene plant and mammal fossil sites in patagonia and to develop a revised temporal calibration of the las flores vacan and sapoan faunas

integrated biomagnetostratigraphy of the alano section ne italy a proposal for defining the middle late eocene boundary the alano section has been presented at the international subcommission on paleogene stratigraphy isps as a potential candidate for defi ning the global boundary stratotype section and point gssp of the late eocene priabonian stage the section is located in the venetian southern alps of the veneto region ne italy which is the type area of the priabonian being exposed along the banks of the calcino torrent near the village of alano di piave it consists of 120 130 m of bathyal gray marls interrupted in the lower part by an 8 m thick package of laminated dark to black marlstones intercalated in the section there are eight prominent marker beds six of which are crystal tuff layers whereas the other two are bioclastic rudites these distinctive layers are useful for regional correlation and for an easy recognition of the various intervals of the section the section is easily accessible crops out continuously is unaffected by any structural deformation is rich in calcareous plankton and contains an expanded record of the critical interval for defi ning the gssp of the priabonian in order to further check the stratigraphic completeness of the section and constrain in time the critical interval for defi ning the priabonian stage we performed a high resolution study of integrated calcareous plankton biostratigraphy and a detailed magnetostratigraphic analysis here we present the results of these studies to open a discussion on the criteria for driving the golden spike that should define the middle eocene late eocene boundary

spatial and temporal uplift history of south america from calibrated drainage analysis a multi disciplinary approach is used to analyze the cenozoic uplift history of south america residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present day dynamic topography admittance analysis and crustal thickness measurements indicate that the elastic thickness of the borborema and altiplano regions is 10 km with evidence for sub plate support at longer wavelengths a drainage inventory of 1827 river profiles is assembled and used to investigate landscape development linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift erosional parameters are calibrated using observations from the borborema plateau and tested against continent wide stratigraphic and thermochronologic constraints our results predict that two phases of regional uplift of the altiplano plateau occurred in neogene times regional uplift of the southern patagonian andes also appears to have occurred in early miocene times the consistency between observed and predicted histories for the borborema altiplano and patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies finally the predicted pattern of incision across the amazon catchment constrains solid sedimentary flux at the foz do amazonas observed and calculated flux estimates match suggesting that erosion and deposition were triggered by regional andean uplift during miocene times

reservoir quality variation on an eocene carbonate ramp el garia formation offshore tunisia structural control of burial corrosion and dolomitisation abstract study of four closely spaced el garia formation reservoirs offshore tunisia has identified diagenetic controls on variation in reservoir quality the ashtart didon and zarat fields have been affected by significant dissolution porosity which occurred during burial diagenesis with vuggy pores preferentially forming in micritic sediment however inter crystalline porosity due to dolomitisation is the principal control on reservoir quality in the hasdrubal field this spatial variation in porosity type reflects to some extent the structural and sedimentological isolation of hasdrubal within the facies trend surrounded by deep water embayments and unlike the other studied fields not directly underlain by salt diapirs burial corrosion appears to have formed where mid to outer ramp mud rich el garia formation facies directly overlie salt domes a consequence of the circulation of aggressive fluids related to increased heat flow above the salt inorganic co2 focused into the reservoir prior to hydrocarbon emplacement by faults related to salt movement is the most likely candidate responsible for the burial dissolution porosity observed in the ashtart didon and zarat fields a salt diapir does underlie the most basinward north east margin of hasdrubal and minor dissolution porosity is present but we conclude that the absence of significant dissolution in hasdrubal is due to its offset position away from the highly faulted roof zone immediately above the salt although we favour this model we cannot rule out that the absence of dissolution porosity in hasdrubal may reflect the early emplacement of hydrocarbons from an older non bou dabbous formation source or differences in the timing of salt movement and consequent fault creation below hasdrubal compared to the other fields local temperature and or acid concentration effects or a different source of co2 differences in the distribution of dissolution porosity in the ashtart didon and zarat fields may be related to the presence of intra reservoir permeability barriers due to increased nummulithoclastic fragmented nummulites content this may also explain the strata bound nature of the dolomite in hasdrubal which like the dissolution porosity in ashtart is overlain by sediments with an increased nummulithoclastic content although dolomite is present in variable quantities in all of the studied fields the significant volume of dolomite in hasdrubal may reflect a local plumbing effect with dolomitising fluids entering the reservoir via a fault network that does not affect the other fields

climatic and ecologic changes during miocene surface uplift in the southern patagonian andes abstract the up to 4 km high southern patagonian andes form a pronounced topographic barrier to atmospheric circulation in the southern hemisphere westerlies and cause one of the most drastic orographic rain shadows on earth geologic data imply that this climatic pattern has been established or significantly enhanced during miocene surface uplift of this andean segment we report evidence for important climatic and ecologic changes in the eastern foreland of the patagonian andes that appear to be the result of this uplift to provide constraints on miocene plant ecosystems and precipitation in the eastern leeward foreland of the patagonian andes we determined carbon and oxygen isotope values of pedogenic carbonate nodules from a 500 m thick section of the continental santa cruz formation the age of these deposits was constrained by ar ar dating of intercalated tuffs which range from 22 to 14 ma at 16 5 ma the 13 c values increase by 3 the 18 o values decrease by 2 and the scatter in the oxygen isotope data increases significantly we interpret these changes as the consequence of 1 km surface uplift in this andean segment from the 18 o values and increased aridity to its east from the 13 c values and the increased scatter in the 18 o values sediments overlying the santa cruz formation are very limited in extent and volume and dominated by coarse conglomerates related to pleistocene and older glaciations it thus seems that by 14 ma deposition in the eastern foreland of the southern patagonian andes had essentially ceased as the result of rain shadow formation

the alpine evolution of the southern alps around the giudicarie faults a late cretaceous to early eocene transfer zone abstract data supporting relevant late cretaceous early eocene sinistral displacement along the giudicarie fault zone and a minor neogene dextral displacement along the periadriatic lineament are discussed the pre adamello structural belt is present only in the internal lombardy zone located w of the adamello massif this belt is unknown in the dolomites and surrounding areas located to the e of the giudicarie lineament upper cretaceous early eocene thick syntectonic flysch deposits of lombardy and giudicarie are well preserved along the southern and eastern border of the pre adamello belt s vergent alpine orogen towards the e in the dolomites and in the carnic alps and external dinarides only incomplete remnants of flysch deposits aptian albian and turonian maastrichtian in age are present they can be considered as equivalent to those of lombardy and giudicarie formerly in connection to each other along the n giudicarie corridor to the s the syntectonic flysch deposits are laterally replaced by the calcareous red pelagites of the scaglia rossa and by the carbonate shelf deposits of the friuli to the e and bagnolo to the s carbonate platforms the different location in the southern structural accretion of the eastern and western opposite blocks the dolomites versus the pre adamello belt can be related to the cretaceous eocene convergence in this frame the n giudicarie fault has been considered as part of a former transfer zone which produced the sinistral lateral displacement of the southern alps front for an amount of some 50 km during the late eocene to early oligocene the transfer zone was mostly sealed by the paleogene adamello batholith oligocene to neogene compressional evolution inverted the n giudicarie fault into a backthrust of the austroalpine units over the south alpine chain

middle eocene to early miocene sedimentary evolution of the western lombardian segment of the south alpine foredeep italy the main steps of the sedimentary evolution of the west lombardian south alpine foredeep between the eocene and the early miocene are described the oldest is a bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input possibly related to a rainfall increase in the alps between the middle eocene and the early chattian a volcanoclastic input is associated with an extensional tectonic regime coeval with magma emplacement in the southern central alps and with volcanogenic deposits of the european foredeep and apennines suggesting a regional extensional tectonic phase leading to the ascent of magma during late eocene to early oligocene two periods of coarse clastic sedimentation occurred probably controlled by eustasy the first during late eocene fed by a local south alpine source the second earliest oligocene in age supplied by the central alps in the chattian a strong increase in coarse supply records the massive erosion of central alps coupled with a structures growth phase in the subsurface it was followed by an aquitanian rearrangement of the alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems while subsurface sheet like geometry of aquitanian turbidites marks a strong decrease in tectonic activity

nummulitic banks in the upper lutetian buil level ainsa basin south central pyrenean zone the impact of internal waves nummulites a particularly abundant and diverse genus of larger benthonic foraminifera formed huge accumulations banks during the eocene which are often good hydrocarbon reservoirs especially in north africa despite their economical interest these accumulations are not well understood and their origin is still under discussion reasons for this debate are the absence of living nummulites accumulations and the high variability of facies including the size shape and extension of the banks which reflect the array of processes controlling sediment production and accumulation the nummulitic banks near santa maria de buil in the ainsa basin south pyrenean foreland basin are composed of recurrent facies associations within mappable bed units bounded by physical surfaces the depositional processes that produced the nummulites deshayesi accumulations are interpreted considering the shape of the banks the type of bounding surfaces the distribution of sedimentary textures nummulites test shapes and the associated skeletal components within the banks this integrative analysis indicates that nummulitic banks accumulated from mass flows with very poor sediment sorting textural and compositional differences among banks suggest that globose nummulites thrived in the shallower part of the mesophotic zone with abundant nummulithoclasts whereas flat nummulitic forms thrived in deeper mesophotic clay dominated settings interbedded with nummulitic banks coral biostromes and coral mounds bearing operculina discocyclina and asterocyclina represent in situ accumulation near the base of the photic zone internal waves waves that propagate along the pycnocline are thought to be the triggering mechanism for the density flows internal waves and induced bottom currents are sporadic but strong enough to bring sediments into suspension in contrast to surface waves both fair weather and storm whose impact is strongest near the sea surface and decreases with bathymetry the impact of internal waves is usually strongest in the mid shelf region and weaker in shallow water this explains the compositional character of the nummulitic banks

middle pleistocene age of the fossiliferous sedimentary sequence from tarija bolivia abstract the highly fossiliferous sediments of the tolomosa formation from tarija southern bolivia represent one of the most important localities in south america that documents the great american biotic interchange over the past several decades chronostratigraphic studies have indicated a middle pleistocene age for the tolomosa formation from 1 1 to 0 7 ma this interval correlates to the ensenadan south american land mammal age as it is characterized from classic localities in argentina recently however a new interpretation based on ams 14c ages indicates that the fossiliferous sediments from tarija are latest pleistocene i e

controls of subduction geometry location of magmatic arcs and tectonics of arc and back arc regions most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors combinations of 1 rapid absolute upper plate motion toward the trench and active overriding of the subducted plate 2 rapid relative plate convergence and 3 subduction of intraplate island seamount chains aseismic ridges and oceanic plateaus anomalously low density oceanic lithosphere cause low angle subduction under conditions of low angle subduction the upper surface of the subducted plate is in contact with the base of the overlying plate the wedge of low density asthenosphere is replaced by subducted lithosphere and the width of the arc trench gap either is significantly increased or a magmatic arc is not developed within the overlying plate the fourth factor is age of the subducting lithosphere subduction of young lithosphere produces two opposing tendencies 1 low angle subduction and increased arc trench distance owing to its low density and 2 decreased arc trench distance owing to its higher temperature two factors of secondary importance contribute to variation in subduction zone geometry and arc trench distance accretion of sediment in trenches depresses the upper portion of the subducting oceanic plate and causes the trench axis to migrate seaward prolonged subduction thickens the upper plate depresses the isotherms in the subducted plate and may create a broader arc both factors increase the arc trench gap the four primary factors also control development of other tectonic elements such as regional subsidence for example the amazon basin and a portion of the cretaceous interior seaway of western united states intra arc extension for example the basin and range province foreland fold and thrust belts and laramide style tectonics

depth transport functions and erosion deposition diagrams as indicators of slope inclination and time averaged traction forces applications in tropical reef environments abstract the trigonometric relationship between slope inclination the horizontallyacting time averaged traction force and the vertical depth of transport allowsthe estimation of one factor when both others are known depth transportfunctions can be deduced by comparing the depth distributions of livingorganisms and their skeletal remains and this paper simpli es this comparisonusing foraminifera in which a single test represents an individual differencesin distribution parameters between living individuals and empty tests allowdepth transport functions to be determined these functions differ betweenspecies at a single transect according to the varying buoyancies of the tests within a single species differences in depth transport functions betweenlocations are based on either slope inclination or traction intensities afterestablishing a mean depth transport function by averaging species characteristic functions the time averaged traction force acting on thestudied transect can be calculated transport intensities are also estimatedusing an erosion deposition diagram that combines the relative frequencydistributions of living individuals and empty tests the proportion of eroded parautochthonous and allochthonous tests mirrors the in uence of bothslope inclination and traction force for the deposition of empty tests to test themodel six species of symbiont bearing benthic foraminifers were investigatedat two transects in front of a nw paci c coral reef one transect is distinguishedby a strong slope attening below the steep reef slope 30 m whereas furthersteepening characterizes the equivalent part in the other transect thesedifferences are mirrored in the depth transport functions as well as in theerosion deposition diagrams of all species the time averaged traction forcesdiffer in intensities between transects because of the position of the reef frontwith respect to the predominant wind direction however the form of thefunctions is identical and distinguished by an increase from the surface to 35 mdepth followed by a decrease down to 105 m this can be explained bysuccessive onshore and offshore forces acting on the shallow slope such as thetropical cyclones that cross the region every summer keywords carbonate sands coral reef slopes foraminifera sediment trans port traction force tropical cyclones introductionsediment transport on the slopes and forereefareas greatly in uences the topography of coralreefs as carbonate produced by reef buildingorganisms is rapidly reduced to sediment especially at the reef front e g hubbard et al 1990 the overwhelming of reef growth bysedimentology 2001 48 1025 1046

automicrite in a nummulite bank from the monte saraceno southern italy evidence for synsedimentary cementation following introduction of the term nummulite bank there has been debate regarding interpretation of these types of deposits as autochthonous automicrite or allochthonous detrital micrite these banks are made up of large foraminifera and ill defined fine grained components the fine grained components consist mainly of micrites the recognition of automicrite has deep implications for the synsedimentary cementation and stabilization of the bank in order to distinguish between automicrite and detrital micrite the nanomorphology geochemistry and organic matter remains in the microfacies of a nummulite bank in the middle eocene of monte saraceno gargano southern italy were analysed optical and scanning electron microscope investigations showed that the micrites have been recrystallized to aggrading microsparite epifluorescence observations on selected micrite microsparite areas with peloidal texture revealed the presence of organic matter scanning electron microscope analyses on epifluorescent micrites showed that the microbial peloids have smaller crystal sizes than those in organic matter depleted areas the geochemical characterization of extracted organic matter performed through the functional group analyses by fourier transform infrared spectroscopy shows strong prevalence of the aromatic fraction over the aliphatic and carboxylic ones these characteristics of organic compounds indicate both their thermal maturation and their likely derivation from degradation of bacterial communities the local presence of peloidal anti gravity textures bright epifluorescence and organic molecules in clotted peloidal areas suggest that the metabolic activity of microbial communities could have induced precipitation of these micrites and consequently the syndepositional cementation of the nummulite bank this type of cementation can rapidly stabilize sediments and promote the depositional bank geometry

middle pleistocene climate change recorded in fossil mammal teeth from tarija bolivia and upper limit of the ensenadan land mammal age fossiliferous middle pleistocene sediments of the tarija basin of southern bolivia contain a classic ensenadan land mammal fauna new carbon isotopic data reported here for 50 specimens of the grazing mammals equus horse and cuvieronius mastodon documented from eight stratigraphic levels at tarija vary significantly in the 13c values of their teeth the pattern of variation appears to reflect the proportion of c3 and c4 grasses eaten during colder more c3 and warmer more c4 times within age limits set by associated magnetostratigraphy the cold periods can be correlated with particular even numbered stages in the marine oxygen isotope record and the warm periods can be correlated with odd numbered stages the oldest fossil teeth analyzed from the tarija section can thereby be assigned to stage 29 and the youngest to stages 17 or 15 that is the teeth range in age from about 1 1 myr to as young as 0 7 myr based on correlation of the upper part of the tarija beds to the isotopic stages the upper limit of the ensenadan land mammal age is between 0 7 and 0 6 myr which is younger than stated in most previous studies

a new chronology for middle eocene early miocene south american land mammal ages cenozoic south american land mam mal ages salmas have historically been correlated to the geologic time scale using 40 ar 39 ar dating and magnetostratigraphy at gran barranca 68 7 w 45 7 s one of south america s key areas for constraining salmas existing radioisotopic ages have uncertainties of up to 4 m y to better con strain the ages of mammalian assemblages we employed high precision 40 k y u pb dating using single zircon crystals we dated nine tuffs from the sarmiento formation containing middle eocene early miocene faunas barrancan mustersan tinguiriri can deseadan colhuehuapian and pin turan the new dates span from 39 861 0 037 ma to 19 041 0 027 ma the la can cha tuff occurring within the tinguirirican faunal level yielded an age of 33 581 0 015 ma confi rming that the vera member con tains the only fossiliferous geologic section encompassing the eocene oligocene transi tion in the southern hemisphere the pre deseadan fauna la cantera is 30 77 ma the age of the colhuehuapian is expanded to 21 1 20 1 ma and the pinturan may be as old as ca 19 ma the new u pb dates confi rm that at mospheric temperatures and vegetation remained constant across the eocene oligocene transition in patagonia and that hypsodonty occurred in south american un gulates much earlier than on any other conti nent additionally refi nement of the salma boundaries will eventually provide the con text necessary to compare faunal transitions across continents although currently too much data are missing to allow such compar isons finally the new ages provide a high resolution age model from which hypotheses about rates of environmental and evolution ary change at gran barranca can be tested

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

components facies and ramps redefining upper oligocene shallow water carbonates using coralline red algae and larger foraminifera venetian area northeast italy abstract chattian mixed carbonate siliciclastic deposits from two palaeogeographic units of southern alps the lessini shelf and venetian foreland basin of northeast italy are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components these ramp depositional systems are located in the western southern alps on the lessini shelf and in the eastern southern alps in the venetian foreland basin the successions show an extensive geographic distribution of at least 150 km 40 km at the southern margin of the southern alps palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators especially those of coralline red algae and larger foraminifera an inner to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth form proxy data the distribution along depositional strike shows variation from thinner carbonate dominated sequence in the west monti berici and monti lessini to a more variable mixed carbonate siliciclastic dominated environment to the east vittorio veneto alpago facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system the general facies succession shows a transgressive sequence from the proximal inner to proximal middle ramp a shoal belt of trough cross bedded sandstones occurs in a proximal inner ramp position in all of the studied areas in a gentle dipping homoclinal ramp most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting basinward environments proximal middle ramp constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements larger foraminifera represented by two larger foraminiferal assemblages are most diversified in the shallower settings near the fair weather wave base distal inner proximal middle ramp whereas coralline algae predominate in deeper areas proximal middle ramp constructing extensive rhodolith pavements rhodolith pavements are distinguished with respect to rhodolith shape size growth forms and coralline algal taxonomic composition larger foraminifera are interpreted with respect to shell structures shell architectures and comparable recent counterparts the analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical warm temperate transition the considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge this study will contribute to a better understanding of oligocene carbonates which have received less attention than their eocene or miocene counterparts

sequence stratigraphic significance of miocene to pliocene glauconite rich layers on and offshore of the us mid atlantic margin glauconite is generally agreed to be a reliable indicator of low sedimentation rate but little systematic work has been done to specify the role of glauconite in a sequence stratigraphic framework ocean drilling program leg 174a recovered a good record of late tertiary sediments along the shelf edge of the new jersey us atlantic margin and glauconite was present in many intervals of the cores sometimes in vertical proximity to sequence boundaries leg 174a glauconite was analyzed with binocular microscope xrd and sem to determine the percent of potassium and degree of maturity in order to relate occurrence to depositional environment seismic data were used to locate sequence boundaries and percent glauconite was visually estimated glauconite samples from site 1073 were found to have formed within a lowstand systems tract lst and as part of a distal condensed section cs within a transgressive systems tract tst these results are comparable to those from nearby site 903 of leg 150 which indicate a similar depositional setting for glauconite glauconites at shelf sites 1071 and 1072 likely formed in the tst as well onshore glauconite occurs mainly in transgressive systems tracts the miocene appears to be the upper limit of glauconite formation onshore as the magnitude of sea level change decreased present onshore locations became too nearshore to maintain sediment free environments and the zone of glauconite deposition moved seaward the same process did not occur offshore until the plio pleistocene low subsidence rate margins such as the us atlantic are subject more to the variations of sea level than to changes in sediment supply tectonics or other factors influencing their depositional patterns although glauconite occurrence is widespread in the stratigraphic record this study demonstrates that for low subsidence rate margins primary deposition of glauconite is largely restricted to the tst

carbonate sediment transport pathways based on foraminifera case study from frank sound grand cayman british west indies foraminifera can be used to determine the source s of carbonate sediment and the directions of sediment transport in shallow coastal lagoons such as frank sound on the south central coast of grand cayman these determinations based on the distribution of foraminiferal assemblages and tracer species numerically abundant species that live in known physiographic units and or ecological conditions show that the lagoonal sediments are a mixture of grains that originated in the lagoon and forereef the variable proportions of these foraminifera throughout the lagoon reflects the dynamic processes that control lagoonal sedimentation amphistegina gibbosa discorbis rosea and asterigerina carinata lived in the forereef environment the fact that these tracer species are found throughout frank sound and in the beach sands shows that they were transported across the reef crest and the lagoon abrasion resistant archaias angulatus a tracer species indicative of a lagoonal setting forms up to 50 of foraminiferal assemblages found in the lagoonal sediments preferential winnowing of small tests from these populations indicates sorting under high energy conditions the vertical distribution of the forereef and lagoonal foraminifera in the sediment blanket that covers the floor of frank sound indicates that these processes are temporally persistent transportation of forereef foraminifera into and around the lagoon and sorting of the lagoonal foraminifera cannot take place under normal conditions when the tranquil lagoon is characterized by weak currents storms and or hurricanes however generate short lived high energy events that can move and sort the sediment and foraminifera at the height of a storm water and sediment are moved over the reef and then piled and held onshore by the onshore winds and the constant flow of water over the reef and across the lagoon these currents can mix some of the lagoonal and forereef sediments as a storm wanes however the piled water flows offshore via strong rip currents that pass into the ocean through the channels which transect the reef these currents winnow and or strip sediment from the lagoon and may transport lagoonal sediments into the forereef area as a result residual lagoonal sediment is commonly characterized by larger and abrasion resistant foraminifera

sediment production and dispersal on foraminifera dominated early tertiary ramps the eocene el garia formation tunisia larger benthic foraminifera nummulites are common within eocene circumtethyan limestones despite their importance as sediment producers contradictions in the literature constrain current understanding about the location of the nummulites factory the el garia fm was deposited on a ramp with localized palaeohighs and whilst some authors suggested that the locus of nummulites production was in shallow water across the palaeohighs others concluded that production was significantly reduced over these palaeohighs and concentrated in the surrounding deeper 30 60 m water there are also marked dissimilarities between recent models in terms of the continuity correlation and resolution of depositional sequences to assess these models we integrate studies of the architecture and geometry of the el garia fm with detailed taphonomic biometric biofabric and palaeoecological characterization of nummulites tests we conclude that the highest rates of sediment production occurred in euphotic water over the palaeohighs and in nearshore environments nummulites on the palaeohighs were transported into the surrounding deeper water by oceanic and storm currents that swept the platform top producing a nummulitic sediment package that thickened and became increasingly fine grained and fragmented into outer ramp environments this transport exerted a major control on development of the ramp like geometries often seen at outcrop our findings question the validity of a recent sequence stratigraphic model that identifies decimetre scale milankovitch cycles even in largely allochthonous bio retextured mid outer ramp sediments our findings also suggest that the thin packages of el garia fm on the palaeohighs which have previously been interpreted as condensed sections that can be correlated with thicker more distal accumulations actually represent remnants of the sediment that was produced on the highs and exported into the basin

submarine lobes and feeder channels of redeposited temperate carbonate and mixed siliciclastic carbonate platform deposits vera basin almeria southern spain temperate carbonates and mixed siliciclastics carbonates of upper tortonian age were deposited on a narrow platform along the southeastern margin of the sierra de los filabres on the western side of the vera basin the temperate carbonates were unlithified or were only weakly lithified on the seafloor and so were easily prone to synsedimentary removal part of the shelf sediments were eroded reworked and redeposited in submarine lobes up to 40 m thick and 1 km wide the lobes consist of turbiditic carbonates calcarenites and calcirudites and mixed siliciclastics carbonates which contain up to 30 siliciclasts derived from the sierra de los filabres to the northwest and abundant bioclasts of coralline algae bivalves and bryozoans in the inner platform the feeder channels of the lobes cross cut beach and shoal deposits and are filled by strings of debris flow conglomerates up to 3 m thick and a few metres wide these channels presumably developed as the continuation of river courses entering the sea further towards the outer platform they pass into large channels up to several hundred metres wide and 20 m deep steeply cutting into the horizontally bedded strata of the platform significant quantities of platform sediment were removed by erosion during their excavation once abandoned they were filled by new platform sediments further towards the basin the channels associated with the lobes exhibit lateral accretion and internal cut and fill structures and are intercalated between hemipelagic deposits the channel filling sediments are in this latter case coarse grained carbonates and mixed siliciclastics carbonates lobe development concentrated first at cortijo grande on the western side of the

new 40ar 39ar dating results from the shanwang basin eastern china constraints on the age of the shanwang formation and associated biota abstract the fluvio lacustrine sequence of the shanwang basin eastern china preserves a rich and important terrestrial fossil fauna and flora the exceptional preservation of these fossils reveals the dynamics of ancient mammalian ecosystems and plant biology however the timing of this sedimentary sequence has been the subject of debate for decades here we contribute to this debate by presenting the detailed results of 40 ar 39 ar analysis of the basalts above below and within the shanwang formation these dates place stringent constraints on the age of shanwang formation and associated biota 40 ar 39 ar ages obtained from basalts of the niushan and yaoshan formations which underlie and overlie the shanwang formation are 21 0 2 5 ma 2 full external error and 17 3 1 5 ma 2 full external error respectively the 40 ar 39 ar age of the basalt in the shanwang formation is 17 18 ma given the age constraints of the basalts of the yaoshan and shanwang formations the age of the shanwang biota is estimated to be ca 17 ma late burdigalian of the early miocene indicating that the deposition of this fauna coincided with the onset of the mid miocene climatic optimum the results provide new age constraints on the shanwang mammal fauna and independently support interpretations that this fauna can be assigned to chronozone mn4 and correlated with middle orleanian of the european land mammal age and to late hemingfordian of the north american land mammal age biological diversity of the shanwang formation could reflect the global scale mid miocene climatic optimum

neogene history of sporolithon heydrich corallinales rhodophyta in the mediterranean region abstract most modern species of sporolithon live in tropical and subtropical areas and only one species of the genus s ptychoides occurs in the mediterranean sea the scarce present day populations of sporolithon in the mediterranean region are relics of a long history of the genus in this area since the early cretaceous analysis of data from the palaeontological literature combined with the study of both fossil samples and recent ones collected from italy and spain shows that during the miocene variations in the number of sporolithon species in the mediterranean region parallel changes in global temperature after a maximum species richness in the langhian early mid miocene coincident with the miocene climatic optimum the number of species decreased to just two before the messinian salinity crisis this marked decline follows the global cooling event that began at around 14 ma the closure of the connections of the mediterranean region with the indian ocean during the langhian left mediterranean sporolithon populations isolated from the main dispersal area of the genus after the messinian desiccation a single species s ptychoides re invaded the mediterranean basin during the early pliocene and continues to inhabit this temperate sea today the atlantic ocean is the most probable source of the re invading sporolithon plants

preliminar correlation of the pleistocene sequences of the tarija valley bolivia with the pampean chronological standard most of the mammal collections of the pleistocene from the tarija valley bolivia lack precise stratigraphic data some fossil collections were made under stratigraphic control but have not been described however mammals were used for correlation and comparison with the pattern established for the pampean region of argentina the bearing units have been referred either to the ensenadan and bonaerian stages the belgranan the ensenadan or the lujanian in a broad sense corresponding to the middle upper pleistocene or the upper pleistocene studies during the last twenty five years accomplished by american authors and based on magnetostratigraphy and absolute dating suggest that the tarija sequence corresponds to the ensenadan early middle pleistocene of the pampean standard recently italian scientists based on radiometric dating discarded this age and considered that the whole sequence belongs to the late pleistocene new biostratigraphic and systematic studies allowed the recognition of glyptodon munizi arctotherium angustidens and hippidion devillei exclusive taxa of the mesotherium cristatum biozone the biostratigraphic base for the ensenadan of the pampean region however collections include mostly putative endemic species or those characteristic of the equus amerhippus neogaeus biozone the biostratigraphic base for the lujanian of the pampean area in sum from a biostratigraphic point of view the tarija sequence has taxa from the lower to middle pleistocene ensenadan and the upper pleistocene lower holocene lujanian of the pampean area from a paleofaunistic standpoint the association recovered from the tarija valley shows significant differences with the typical pampean association the high frequency of remains of gomphotheriidae and equidae and in lower proportion of hydrochoeriidae and tapiridae are noteworthy members of these two latter families are restricted today to warm and wet climates most glyptodontidae records belong to glyptodon and in the pampean region this family is much more diversified

late miocene continental biota in northeastern patagonia peninsula valdes chubut argentina abstract a new vertebrate faunal assemblage was recently discovered from the uppermost part of the late miocene puerto madryn formation these deposits crop out along the southwestern coast of the peninsula valdes area near punta delgada chubut province argentina the exhumed vertebrate fauna includes a range of fish bird and mammal taxa of which the latter are most varied and abundant the new findings represent the first record of continental fossil vertebrates in the puerto madryn formation and this is the first assemblage of late miocene continental vertebrates recorded to the south of rio negro province it also includes the southernmost record of hydrochoeridae rodents dendrocygninae birds and loricariidae fishes the mammals suggest that the fossil bearing sediments are huayquerian in age the climate during the accumulation of late miocene deposits in this region is inferred to have been warmer and seasonally drier than that of today

a genetic classification of carbonate platforms based on their basinal and tectonic settings in the cenozoic abstract this paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps whilst the existing classifications have value in describing platform margin morphology at any one time the terms rimmed shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms research on cenozoic carbonate platforms from a range of different tectono stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first order genetic classification of carbonate platforms the basinal and tectonic setting of carbonate platforms is shown to control their occurrence the overall 3 d platform morphology the large scale stratigraphic features and depositional sequences climate ocean chemistry and biological evolution control grain types facies and some elements of platform margins but not the larger scale features considered in this new classification from a review of well exposed outcropping and seismically imaged cenozoic platforms it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting fault block salt diapir subsiding margin offshore bank volcanic pedestal thrust top delta top and foreland margin carbonate platforms these eight types are described using information from cenozoic platforms worldwide and the controls on their development are discussed many platform types e g subsiding margin offshore bank salt diapir thrust top and foreland margin are typical of particular classes of sedimentary basins others e g fault block volcanic pedestal and delta top are more widespread in their occurrence and occur in a range of basin types the value of this classification is that it is genetic rather than morphological the classification reflects the entire morphology and large scale stratigraphy of the platform and the controls on its development in addition the platform models can be used to understand the details of less well exposed or seismically imaged platforms so that they can be characterised and understood in terms of tectono sedimentary processes conversely the classification also provides valuable information on basin evolution as carbonate platforms house information on palaeoenvironments sea level change and are sensitive recorders of the tectonic environment

present day and fossil rhodolith pavements compared their potential for analysing shallow water carbonate deposits abstract coralline red algae represent the main biogenic components in most shallow water carbonate successions from the eocene to the recent they contribute significantly to sediment production on open platforms carbonate sediments formed by unattached coralline algae include rhodolith pavements rps which represent dense accumulations of rhodoliths as well as maerl which is composed of rhodoliths coralline algal branches and their detritus recent rps sampled off sesoko jima okinawa jima southern japan occur at depths of 50 70 m on a submarine terrace the taxonomic coralline composition is dominated by melobesioids associated with minor amounts of mastophoroids and sporolithaceans the rhodoliths are characterised by various nuclei an encrusting inner arrangement encrusting to warty outer growth forms and sub spheroidal shapes bioerosion encrustation and abrasion are the most prevalent taphonomic features possible fossil counterparts were identified in chattian and priabonian rps from middle ramp depositional systems from the venetian area north east italy a direct comparison between recent and fossil rps is possible by contrasting the constituent rhodolith characteristics including taxonomic composition nature of the nucleus inner arrangement outer growth forms size and shape as well as taphonomic signatures this allows factors controlling rhodolith formation and growth in rps to be compared especially with respect to hydrodynamic regimes and substrate type

new paleocene eocene paleomagnetic results from the foreland of the southern alps confirm decoupling of stable adria from the african plate abstract from the undeformed foreland of the southern alps paleocene through early miocene rocks mostly biostratigraphically well dated sediments with sub horizontal bed attitude were collected for a paleomagnetic study from 23 geographically distributed localities the samples were subjected to standard paleomagnetic measurements and evaluation while the miocene samples are unstable most of the older localities yielded statistically well defined paleomagnetic directions these are interpreted as primary for the compact marls supported by positive between locality tilt and reversal tests this large group of localities is characterized by ccw rotated declinations with respect to the present north combined with paleomagnetic directions of corresponding age from stable istria these allow definition of the apw for stable adria for the 61 6 33 9 ma interval which is significantly displaced from the coeval segment of the african apw due to the decoupling of the former to the latter by a moderate ccw rotation this post eocene final separation exact age is not constrained directly but estimated as end of miocene was preceded by a small cw rotation of adria with respect to africa suggested by unchanged orientation of the former across the cretaceous paleocene boundary while the latter continued its ccw rotation

problems in chronostratigraphy stages series unit and boundary stratotypes global stratotype section and point and tarnished golden spikes abstract stratigraphy is a magnificent subject magnificent in its breadth and scope magnificent in its importance to so many lines of human endeavor it is essentially that branch of geology which deals with the arrangement the distribution and the chronological succession of rock strata and other associated rock bodies with respect to any or all of the various characters properties and attributes which rocks may possess hedberg 1958 p 1881 chronostratigraphy the temporal ordering of geologic strata is at the heart of earth history in reviewing chronostratigraphic theory from d orbigny to hedberg we see that concepts and practices have evolved under pressure of constant improvements in time control and data quality such stimuli are naturally felt more strongly in the youngest part of the stratigraphic record where dating is most precise and the biostratigraphic data are most abundant and well preserved it is not surprising therefore to find that chronostratigraphy is conceptually more advanced in the cenozoic erathem than in the mesozoic and paleozoic erathems where biostratigraphy and chronostratigraphy are widely confused evidently out of necessity taking the five inter series boundaries in the cenozoic erathem as case histories we review their current status in relation to the lower boundary of the lowest standard stage above the boundary in light of the hierarchical principle recommended in the international stratigraphic guide hedberg 1976 salvador 1994 in each instance what should be a simple nested relationship turns out to be complex and difficult and in the cases of the proposed global stratotype section and point gssps for the eocene oligocene series boundary and the paleocene eocene series boundary there are discrepancies so large with regard to the base of the rupelian and ypresian standard stages respectively that some essential relaxation of the hierarchic rule seems to be required if the historic value of these long known stages is not to be violated since stage boundaries should not be defined a posteriori to fit series boundaries we propose here to reconsider the role of the standard stage as the obligate elemental subdivision in a rigidly hierarchical chronostratigraphic scale and suggest that series and subseries should be formalized and their boundaries defined by gssps we do not suggest that stages be abandoned on the contrary we propose to integrate them in a two step hierarchical chronostratigraphic framework so as to use them in complementary fashion with series and subseries however the boundary concept is more appropriate for stage than the gssp we recognize the need for precise and globally valid chronostratigraphic correlations based on gssps in attempts to understand the earth system while at the same time we emphasize the need for conceptual continuity with regard to the central place that the stage has played in chronostratigraphy over several decades

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

ternate formation a late eocene bioclastic submarine fan of the lombardian basin southern alps the ternate formation consists of some 150 m of redeposited bioclastic limestones channelized rubble beds and pebbly mudstones and subordinate hemipelagic marls with a late eocene fauna of planktonic foraminifera globorotalia cerroazulensis cerroazulensis zone parallel bedded massive or graded bioclastic limestones are overlain by channelized deposits large channels are up to 12 m deep some contain pebbly mudstones with large slabs and boulders of older marls and limestones in a matrix of middle eocene marls more typically the channels are filled by pebbly calcirudites grading into calcarenites and laterally wedging out over very short distances interchannel deposits are thin bedded graded calcarenites and thin green marls the bioclastic limestones contain mainly coralline algae larger foraminifera nummulitids discocyclina bryozoans echinoderms and other shallow water biota all lithic fragments are of local south alpine origin by far the most abundant are spiculitic limestones and marls of liassic age and upper cretaceous to middle eocene limestones and marls most of the redeposited calcareous sand and gravel was deposited in ephemeral channels which cut across each other in a very complex way and were briefly active this depositional system matches the suprafan environment of a prograding submarine fan of low transport efficiency the facies of the conglomerates themore local source of the lithic fragments and comparison with other lower tertiary bioclastic deep water deposits suggest short transport and deposition in one or a series of local bioclastic submarine fans the benthic foraminifera associated with the hemipelagic marls indicate deposition in the upper bathyal zone 600 1 000 m less

the role of stratotypes in stratigraphy part 3 the wood committee the berkeley school of north american mammalian stratigraphic paleontology and the status of provincial golden spikes abstract the north american land mammal ages defined in 1941 by the wood committee provide good examples of the use of strict nominal stratotypes in fixing the names and establishing the minimum durations of provincial biochronologic units the lithostratigraphic type sections of each age served a name bearing and exemplary function not a boundary defining function despite some inconsistencies in their work the common charge that the wood committee defined many of their ages as lithochrons is a myth nevertheless the potential or actual temporal overlap of some of the original nominal stratotypes of the ages is a significant problem and their redefinition is permissible in order to preserve the original intentions of the wood committee the berkeley school of north american mammalian stratigraphic paleontology has been the most influential force in theoretical discussions in this field since the 1960s d e savage retained most of the oppelian views of r m kleinpell while m o woodburne and d r prothero departed from that tradition and adopted some of the views of h d hedberg and w a berggren thus emphasizing single taxon definitions datum planes and boundary stratotype definitions for stages however recommendations by members of the berkeley school that we turn our land mammal ages into formal stages are ironic because their own writings show they still hold the anti hedbergian view that stages are flexible biostratigraphic biochronostratigraphic entities nevertheless in partial agreement with at least some members of the berkeley school the transformation of our provincial biochronologic units into golden spike defined ages stages would defeat their purpose which is to summarize our evolving knowledge of the true sequence of important paleobiological events in each major fossil group that occurred in a given province in principle and in practice hedberg s attempt to restrict the terms age stage to golden spike defined entities has failed however hedbergians and traditional stratigraphic paleontologists can find common ground if they will admit that aurichronologic and biochronologic units are both legitimate subcategories of geochronologic units if so hedberg s major program would be vindicated in that golden spikes would still be used to define the phanerozoic standard global geochronologic units while traditional stratigraphic paleontologists would retain the ability to modify the boundaries of their provincial ages stages as they saw fit provided that such modifications did not violate the strict nominal stratotypes of those ages stages

larger foraminiferal and coralline algal facies in an upper eocene storm influenced shallow water carbonate platform colli berici north eastern italy abstract facies analysis of priabonian shallow water carbonate successions in the outcrops near mossano eastern colli berici north eastern italy and the subsequent integration of palaeoecological data have been used to produce a detailed palaeoenvironmental model the facies distribution and the processes which controlled the larger benthic foraminiferal and coralline algal assemblages in the study priabonian storm influenced carbonate ramp are discussed in detail in the middle ramp trough cross bedded small nummulites and rhodolith packstones pass laterally into coralline algal crust wackestones these rhodoliths exhibit two well differentiated growth phases the first occurring during low water energy periods followed by a second developed during high energy events during which they were reworked and partially destroyed these facies pass laterally into orthophragminid rudstones and packstones characterised by orthophragminid tests and channel structures the latter were formed by storm induced return currents which swept the middle ramp creating distal middle ramp channel structures further toward the distal part of the middle ramp the return currents decreased in energy and discharged nutrients allowing the coralline crustose pavement to develop this is characterised by rhodoliths typically discoidal in shape up to 10 cm in diameter with a loose inner arrangement consisting of encrusting to foliose growth forms the occurrence of the channel structures in orthophragminid rudstones and in the coralline crustose pavement appears to be unique in upper eocene carbonate ramp depositional systems during the erosive events associated with the return currents these shallow water carbonates were unlithified or only weakly lithified and were therefore easily transported into deeper water ramp settings the model suggests that the significant changes of the middle ramp benthic communities with depth could have formed at least in part by offshore return currents which played an important role in both controlling substrates and in supplying nutrients

tertiary extension in the southern trento platform southern alps italy the southern trento platform southern alps ne italy was the locus of abundant mafic volcanism associated with paleogene extensional tectonics during the pal eocene and throughout the eocene a nnw sse trending graben the alpone agno graben aag developed in the eastern lessini mountains the graben was filled with basaltic volcaniclastics calcarenites and lava flows the aag is a half graben system probably bounded by rotational listric normal faults most faults in the graben dip towards the wsw paleostress analysis within the aag shows that during the eocene the direction of horizontal extension was ene wsw the volcanic activity continued into the oligocene however the relation between oligocene tectonics and volcanism remains unclear gravimetric and magnetic anomalies in conjunction with the crustal thickness variations suggest a locus of lithospheric thinning slightly off axis from the aag this can be explained by an overall asymmetric extensional geometry dominated by a wsw dipping detachment fault the paleogene geodynamic scenario of the trento platform suggests that the aag developed as a foreland extensional response to the active collisional convergence between the european and adriatic plates neogene compressional tectonics reactivated some of the paleogene normal faults as strike sup faults

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

biofabrics as dynamic indicators in nummulite accumulations biofabric interpretation of skeletal accumulations consisting of biologically standardized nummulite tests larger foraminifera is based upon 1 the ratio of small bodied a forms megalospheric and large bodied b forms microspheric and 2 on their packing and imbrication features in the eocene mokattam formation of egypt nummulites gizehensis occurs in limestones with four basic biofabrics in wackestones the nummulites float throughout the matrix and a forms strongly dominate over b forms approximating the ratio reported for undisturbed assemblages packstones however reflect various degrees of sedimentary reworking and winnowing of the original substratum by physical processes for packstones with edge wise imbrication and a forms strongly dominating over b forms in situ winnowing of fine grained matrix by waves can be inferred in contrast packstones composed of imbricated b forms suggest hydraulic sorting and selective removal of a forms by currents packstones composed almost entirely of a forms represent transport sorted allochthonous deposits biofabric analysis thus allows us to understand better the dynamics of skeletal accumulations such as nummulite banks whose commonly complex and extensive buildups can form hydrocarbon reservoirs

middle eocene nummulites and their offshore re deposition a case study from the middle eocene of the venetian area northeastern italy abstract the middle eocene calcari nummulitici formation from northeastern italy venetian area represents a shallow marine carbonate ramp developed on the northern tethyan margin in the monti berici area its main components are larger foraminifera and coralline red algal communities that constitute thick carbonate sedimentary successions middle ramp and proximal outer ramp environments are recognized using component relationships biofacies and sedimentary features the middle ramp is characterized by larger flattened lenticular nummulites on palaeohighs between which rhodoliths formed larger nummulites palaeohighs containing nummulites millecaput nummulites crassus nummulites discorbinus and nummulites cf gizehensis developed more basin wards the following relatively quiet environments of basin wards of the palaeohighs represent areas of maximum carbonate production the transition between the distal middle and the proximal outer ramp settings is marked in the study area by a large erosional surface which is interpreted to have been formed as a result of an erosive channel body filled in by deposits re sedimented from shallower depths these off shore re sedimented channelized deposits ascribed to the shallow benthic zone sbz 15 lying on hemipelagic marls planktonic foraminiferal zone e9 p11 allow for a biostratigraphic correlation to the late lutetian the studied deposits represented by packstone to rudstones were displaced whilst still unlithified the lutetian bartonian regression along with the local tectonic activity promoted the production of a high amount of biogenic shallow water carbonates mainly produced in the mossano middle ramp settings these prograded towards the basinal areas with high sedimentation rate of carbonate deposits characterized by the larger nummulites rudstones such high amounts of sediment led to sediment instability which potentially could be mobilized either by return currents due to occasional major storms or by earthquakes induced by tectonic activity these will have led to the offshore re deposition of the nummulites sediments into deeper water setting via the observed channels since potential migration pathways are short such distal re sedimented channel filled material surrounded by hemipelagic marls is optimally placed for the formation of potential subsurface oil reservoirs

stress distribution and geometry of the subducting nazca plate in northern chile using teleseismically recorded earthquakes summary the stress distribution along the subducting nazca plate in northern chile is analysed using focal mechanism solutions obtained from the inversion of long period p sv and sh waveforms of 15 earthquakes mb 5 5 and from 212 events with reported focal mechanisms which occurred between 1962 and 1993 a joint hypocentral determination was carried out to control the depth of 261 events mb 5 0 recorded at teleseismic distances a change from tensional to compressional stress field along the upper part of the subducting slab is associated with the maximum depth extent of the coupled zone this change occurs in northern chile at 200 250 km from the trench at depths of 60 10 km this depth is larger than the maximum depth observed for the thrusting interplate events 40 10 km probably meaning that at depths of between 40 and 60 km large low dip angle thrust events do not nucleate seismic slip however probably extends down to 40 km in depth the shallow dip angle up to 60 km in depth of the wadati benioff zone does not show variations along the strike of the trench however a gradual southward flattening of the slab is observed at distances greater than 200 250 km from the trench this change observed from about 21 s could be associated with a younger and probably more buoyant lithosphere than that observed to the north of this latitude there are two gaps located between the three main clusters of seismicity these gaps are clearly not related to detachments in the descending litosphere the first cluster is located in and beneath the seismogenic interplate contact and is characterized by reverse and thrust faulting events over a scarce tensional activity in the second cluster the compressional seismicity is scarce for teleseismic events and is located beneath the normal faulting events the third cluster corresponds to tensional events therefore these gaps in seismicity could be associated with alternating changes from compressional to tensional stress field in the subducting slab

calciclastic submarine fans an integrated overview abstract calciclastic submarine fans are rare in the stratigraphic record and no bona fide present day analogue has been described to date possibly because of that and although calciclastic submarine fans have long intrigued deep water carbonate sedimentologists they have largely been overlooked by the academic and industrial communities to fill this gap we have compiled and critically reviewed the existing sedimentological literature on calciclastic submarine fans thus offering an updated view of this type of carbonate slope sedimentary system calciclastic submarine fans range in length from just a few to more than 100 km three different types can be distinguished 1 coarse grained small sized most calciclastic submarine fans were formed on low angle slopes and were sourced from distally steepened carbonate ramps subjected to high energy currents under these conditions shallow water loose grainy sediments were transferred to the ramp slope and eventually funnelled into the submarine fan by sediment gravity flows these conditions seem to have been more easily met on leeward margins in which the formation of reefs was hampered by cool waters nutrient enrichment or oligophoty another circumstance that contributes to the transfer of shallow water sediments to the distal ramp slope is a low sea level forcing the carbonate factory closer to the slope break and destabilizing sediments by increased pore water pressure however the most important factor controlling the development of calciclastic submarine fans was the existence of an efficient funnelling mechanism forcing sediment gravity flows to merge downslope and build up a point sourced sedimentary accumulation in most cases this occurred through a major slope depression associated with tectonic structures an inherited topography or large scale mass failures

extension and basin formation in the southern andes caused by increased convergence rate a mid cenozoic trigger for the andes the southern andes between 33 and 45 s latitude are characterized by a series of complex basins that spanned the contemporaneous active continental margin which itself was characterized by volcanic activity the basins are filled with thick up to 3000 m accumulations of interbedded sedimentary and volcanic strata of late oligocene early miocene age we interpret that these basins developed during a phase of moderate extension within the plate margin system triggered by an increased rate of convergence of the farallon nazca and south american plates between 28 and 26 ma this history is inconsistent with models of convergence that link high rates of convergence of a continental margin and an oceanic plate to strong compressional coupling although extensional basins of this age are only well described in the southern andes the convergence history and volcanic chronology are similar farther north in the central andes 18 33 s leading to the speculation that extension may have characterized the late oligocene early miocene interval regionally we hypothesize that this extension was a necessary condition to subsequent building of the modern andes mountains

small mammal carbon isotope ecology across the miocene pliocene boundary northwestern argentina abstract the late miocene expansion of plants using the c 4 photosynthetic pathway in south america has been documented by tooth enamel carbon isotope ratios 13 c en however a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived this study develops a 13 c en record from a single 2500 m thick stratigraphic section in subtropical south america strata at puerta de corral quemado pcq northwestern argentina span 9 to 3 5 ma in age and existing paleosol carbonate data 13 c pc document c 4 expansion across the miocene pliocene boundary comparison of 13 c en data with 13 c pc data at high stratigraphic resolution refines understanding of this ecological event in south america small mammal 13 c en data in particular are complementary to that of large mammal and paleosol 13 c data small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of c 3 and c 4 plants explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents e en diet 11 as opposed to 14 for large mammals allows for unequivocal inference of c 4 vegetation 1 ma prior to that inferred from large mammal 13 c en data and 2 ma prior to 13 c pc data this multiproxy record demonstrates that c 4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion and that the expansion of c 4 plants was pulsed at pcq two periods of ecological change are demonstrated by 13 c and 18 o data at 7 ma and 5 3 ma coincident with the miocene pliocene boundary development of small mammal 13 c en records on other continents may provide similar insight into the early stages of the global c 4 event

tide influenced high energy environments and rhodolith associated carbonate deposition on the outer shelf and slope off the miyako islands southern ryukyu island arc japan sediments distributed off the miyako islands southern ryukyus japan include rhodoliths larger foraminifera cycloclypeus and or bryozoan dominated carbonates of low mud content on the outer insular shelf and planktonic foraminiferal mud free carbonate sand on the slopes sidescan sonograms show large scale 2 d subaqueous dunes in the deeper shelf sediments which suggest a nw se flow direction sea bottom photographs of the slope sediments to depths of 1000 m show small scale 2 d or 3 d ripples those sedimentologic features suggest the existence of relatively high speed currents on both the shelf and slope in the area current direction and velocity have been directly measured to clarify the origin and character of the current governing the area where the rhodoliths large foraminifera are distributed the results of measurements carried out at 14 stations at depth ranges of 14 to 799 m show that the direction and velocity of the currents on the shelf and slope change semi diurnally at most shelf stations the currents at high tide are to the north northwest i e from the pacific ocean to the east china sea conversely the currents at low tide are to the south southeast from the east china sea to the pacific ocean on the slope current movements are to the west at high tide and to the east at low tide it is concluded therefore that the currents on the shelf and slopes are tidally related current speed is small in protected areas and is high on the open shelf and shelf slopes the ryukyu island arc interrupts the tidal northwestern and southeastern flow this interaction probably develops substantial turbulence and topography induced upwelling and therefore forms a natural site for the formation of mud free and or coarse sediments with rhodoliths and large formainifera

carbonate production and offshore transport on a late jurassic carbonate ramp kimmeridgian iberian basin ne spain evidence from outcrops and computer modelling

spatial temporal changes in andean plateau climate and elevation from stable isotopes of mammal teeth abstract paleoelevation constraints from fossil leaf physiognomy and stable isotopes of sedimentary carbonate suggest that significant surface uplift of the northern andean plateau on the order of 2 5 1 km occurred between 10 3 and 6 4 ma independent spatial and temporal constraints on paleoelevation and paleoclimate of both the northern and southern plateau are important for understanding the distribution of rapid surface uplift and its relation to climate evolution across the plateau this study focuses on teeth from modern and extinct mammal taxa including notoungulates pyrotheres and litopterns spanning 29 ma to present collected from the altiplano and eastern cordillera of bolivia 16 2 s to 21 4 s and lowland brazil tooth enamel of large water dependent mammals preserves a record of surface water isotopes and the type of plants that animals ingested while their teeth were mineralizing previous studies have shown that the 18o of modern precipitation and surface waters decrease systematically with increasing elevations across the central andes our results from high elevation sites between 3600 and 4100 m show substantially more positive 18o values for late oligocene tooth samples compared to