oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

world s highest tides hypertidal coastal systems in north america south america and europe abstract hypertidal systems can be defined as areas where spring tides have ranges greater than 6 m these very high tidal ranges results in unique patterns of sedimentation within hypertidal estuaries such systems are not common but they do occur on a number of continents this report will discuss six areas that have the highest tides in the world north america hypertidal systems occur within cook inlet in alaska usa leaf basin in ungava bay quebec province canada and the bay of fundy nova scotia and new brunswick canada in south america the straits of magellan and associated atlantic coastal settings exhibit hypertidal conditions european hypertidal systems include bristol channel and severn estuary in southwest england and the gulf of st malo in normandy france these six areas have the highest tides in the world and spring tidal ranges that regularly exceed 10 m all the six areas can be divided into intertidal sedimentological zones zone 1 is the outermost zone and contains longitudinal bars zone 2 exhibits laterally extensive sand flats zone 3 includes the innermost extent of tides and estuarine point bars annual and neap spring cycles have been documented in zone 3 and are probably the most indicative features of hypertidal systems the north american systems occur in high latitude cold climates where winter ice can have a minor or major impact on the development of sedimentary facies conversely the european and patagonia systems have climates minimal ice formation

ichnological characteristics of late cretaceous hemipelagic and pelagic sediments in a submarine high around the oae 2 event a case from the rybie section polish carpathians abstract the trace fossils alcyonidiopsis isp chondrites isp small and large palaeophycus isp planolites isp taenidium isp thalassinoides isp zoophycos isp and unnamed small spreite burrow structures have been found in the cenomanian turonian sediments in the rybie section they show significant stratigraphic variations in respect to the bonarelli level in the cenomanian from the base of the section up to just below the bonarelli level the fucoid marl in local lithostratigraphy a decrease in diversity and abundance of trace fossils and benthic foraminifers is present and related mainly to decreasing benthic food levels oxygenation changes have comparatively minor incidence but at least three thin anoxic layers occur about 2 m below the bonarelli level the bonarelli level shows the at least episodically anoxic sedimentation in the turonian part only small chondrites isp and planolites isp rarely occur the burial of organic matter and probably benthic food content was extremely low as revealed by red marls a gradual recovery of environmental conditions is marked by an increase in the diversity and abundance of trace fossils and benthic foraminifers by the turonian when grey marls egocina marl accumulated above the red marls the trends in ichnological record are confirmed by data on benthic foraminifers

nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

evidence for milankovitch periodicities in cenomanian turonian lithologic and geochemical cycles western interior u s a abstract the limestone marlstone bedding couplets of the bridge creek limestone member cenomanian turonian greenhorn formation were analyzed by applying spectral techniques to high resolution lithologic and geochemical data from a core the results suggest that the bridge creek contains a complex record of orbital cyclicity the dominant signal appears to be obliquity but signals corresponding to precession and eccentricity were also observed the development of the bedding couplets is interpreted to have resulted from a combination of factors including insolation controlled changes in higher latitude precipitation leading to dilution redox cycles and in lower latitude evaporation leading to changes in surface water conditions and productivity cycles in the calcareous plankton the data nterpreted to reflect redox cycles appear to be more strongly influenced by obliquity and show a weak precessional signal in contrast trends in the carbonate record show the opposite response the complex bedding pattern observed in the bridge creek limestone is interpreted to result from the competing influences of different orbital cycles expressed through different pathways of the depositional system and was also affected by changes in sedimentation rates related to relative sea level fluctuations aperiodic dilution by volcanic ash and changes in organic matter production and redox conditions related to a global oceanic anoxic event these factors complicate cycle analysis in the lower part of the member but leave a relatively undisturbed record in the upper bridge creek limes one

holocene history of the estuarine area surrounding portage alaska as recorded in a 93 m core a 93 m core obtained at portage alaska records four prograding cycles of estuarine deposition for the past 8230 100 years analyses of texture mineralogy paleontology and sedimentary structures enable definition of eight lithologic units mineralogic studies show that past and present sedimentation at portage has been largely mud and sand from the susitna river on the northwest side of cook inlet six radiocarbon dates from concentrated organic debris in the core and on the surface enable determination of sedimentation rates for four intervals and show rates to be higher and to vary more at depth than rates nearer the surface the glacier carved turnagain arm fiord has been receiving sediment for at least the past 14 000 years as estimated by extrapolation of calculated sedimentation rates to the thickness of unconsolidated sediment drilled at portage which totals approximately 300 m presently deposition is accomplished instantly as the result of tectonic subsidence and compaction of sediment

geochronology and calibration of global milankovitch cyclicity at the cenomanian turonian boundary new 40 ar 39 ar geochronology and global cyclostratigraphic calibration provide high resolution insights into the timing of geochemical fluctuations across oceanic anoxic event ii oae ii five new 40 ar 39 ar data from a single section in western canada suggest an age of 96 4 1 ma for the cenomanian turonian c t boundary this is 3 m y older than previously dated time series analysis e g wavelet transform reveals that oae ii was synchronously deposited worldwide over a period of 320 k y the preservation and stationarity of milankovitch cyclicity in sections across the atlantic indicates that no major fluctuations in sedimentation rate occur across the oae ii except for a minor short term decrease in the rate just before the c t boundary a 13 c org increase of 2 took place at the beginning of oae ii over a period of 110 k y and likely represents a period of worldwide excessive organic carbon burial during transgression leading to a 12 c depletion of seawater and sedimentation this interval was followed by a three step decrease to pre oae ii 13 c values

high resolution geochemical and biotic records of the tethyan bonarelli level oae2 latest cenomanian from the calabianca guidaloca composite section northwestern sicily italy abstract high resolution micropalaeontological and chemostratigraphic records for the upper cenomanian portion of the calabianca guidaloca composite section nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean the bonarelli level equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy and radiolarian assemblages as well as by the 13 c curve showing a marked positive excursion up to 4 7 the bonarelli level equivalent deposition is characterized by highly eutrophic conditions as testified by radiolarian proliferation black shale samples from the calabianca guidaloca composite section contain very high toc up to 26 and moderate to high amounts of caco 3 on average 20 among the planktonic foraminifera hedbergellids and globigerinelloids tolerated the environmental stress induced by the oceanic anoxic event 2 oae2 the occurrence of some benthic foraminifera testifies to dysoxic rather than completely anoxic conditions at the sea floor during the deposition of some portions of the bonarelli level equivalent based on micropalaeontological results and geochemical proxies 13 c d rb ti v ni ba si cr the bonarelli level equivalent is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle we propose that periodically increased riverine influxes triggered by enhanced humidity resulted in a sluggish circulation mode and consequent anoxic euxinic conditions favouring the preservation of organic matter at the sea floor spectral analyses performed on selected geochemical signals reveal within the main high productivity event a strong orbital climatic forcing represented by a long term eccentricity steered humidity cyclicity that amplifies a short term precession controlled productivity fluctuation

simulation of heterogeneity creep damage and lifetime for loaded brittle rocks abstract a grain based heterogeneous numerical model originated from the discrete element method is developed and applied for lac du bonnet granite basing on voronoi cells the modelled microstructure considers different mineral components and grain size the model takes into account elastic grain and elasto plastic contact deformation inter and intra granular fracturing and lifetime prediction on basis of subcritical crack growth the procedure is successfully applied to simulate uniaxial compression tests brazilian tests and uniaxial creep tests the damage processes are studied in detail and mode i and mode ii fracture toughness were determined the proposed modelling allows the simulation of time dependent behaviour in terms of the damage process during primary secondary and tertiary creeps until the final failure characterized by macroscopic fracturing shear band and or macroscopic tensile fracture all simulations have shown reasonable agreement with macroscopic results obtained from lab tests on granite but have in addition delivered deeper insight into the microscopic damage process the proposed modelling approach is recommended for brittle rocks

digital image based numerical modeling method for prediction of inhomogeneous rock failure abstract this paper presents a two dimensional digital image based numerical modeling method for prediction of inhomogeneous rock failure behavior under loadings actual inhomogeneities of granitic rocks are extracted from color images of the granite cross sections they are represented as the internal spatial distribution of three main granite minerals quartz feldspar and biotite the actual mineral spatial distribution on granite cross section is then incorporated into conventional numerical software packages to examine the rock failures under loading some digital image processing algorithms are presented to isolate and identify the main internal minerals and their distribution from color digital images a simple method is proposed to transform the actual image data into vector data for generation of finite meshes or grids the vector data are used directly as uniform square element meshes or grids that can be inputted into the existing software packages the finite difference software package flac is used as an example for the present investigation the conventional mohr coulomb and tensile stress failure criteria are used to examine the failure behavior of a circular granite cross section under the conventional brazilian indirect tensile test loading conditions the numerical results indicate that the vertical tensile crack initiates in a biotite located near the geometrical center of the granite cross section and the actual spatial distribution of the three minerals plays an important role in modifying the propagation pattern of the tensile crack from its theoretical position at the central vertical diameter of a homogeneous circular cross section the numerically predicted failure load and tensile strength values for inhomogeneous granite are much lower than the expected values

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

calcareous nannofossils of the cenomanian turonian boundary interval from the boreal realm wunstorf northwest germany abstract the cenomanian turonian boundary interval ctbi is marked by an intense climatic warming presumably caused by large magmatic eruptions this warming was characterised by one of the most prominent mesozoic perturbations of the carbon cycle the oceanic anoxic event 2 oae2 which is marked by a well pronounced positive carbon isotope excursion cie sediments of the oae2 interval often consist of organic rich black shales suggesting widespread bottom water anoxia during the ctbi this study focuses on calcareous nannofossils from the ctbi of a european section wunstorf core northwest germany a total of 105 samples were examined for calcareous nannofossils using the settling technique eight bioevents last occurrences corollithion kennedyi lithraphidites acutus first occurrences rotelapillus biarcus corollithion exiguum eprolithus octopetalus eprolithus eptapetalus quadrum gartneri eiffellithus eximius have been recognised throughout the middle cenomanian to middle turonian interval with the exception of eleven samples preservation is moderate to good calcareous nannofossils are abundant mean 2 0 billion specimens g sediment and highly diverse mean 58 species sample assemblages are dominated by watznaueria spp 32 3 prediscosphaera spp 13 4 zeugrhabdotus spp 11 2 and biscutum spp 10 5 pre oae2 and also post oae2 nannofossil assemblages show high abundances of biscutum spp 20 indicative for stable mesotrophic conditions the assemblages of the oae2 itself are marked by high values for watznaueria spp and low frequencies of biscutum spp making oligotrophic conditions during the oae2 likely high absolute abundances of organic walled dinoflagellates and the occurrence of frequent stress tolerant nannofossil genera like retecapsa spp in the organic rich intervals suggest however a deposition of black shales enhanced by high primary productivity thus dinoflagellates and calcareous nannofossils are interpreted to reflect different seasonal signals during the time of black shale deposition short term high fertile seasons allowed the blooming of the organic walled dinoflagellates whereas calcareous nannofossils dominated the longer oligotrophic seasons the black shale deposition was supported by the formation of large amounts of organic matter during fertile seasons as well as by surface water stagnation during oligotrophic seasons

late archaean tidalites from western margin of chitradurga greenstone belt southern india abstract tidalites are preserved within a metavolcano sedimentary succession of the late archaean bababudan group dharwar supergroup along the western boundary of the nnw sse trending chitradurga greenstone belt west dharwar craton southern india these may represent the oldest record of tidal processes in peninsular india millimetre thick sand mud alternations bidirectional cross strata mudstone draped sandy foresets reactivation surfaces indicating time velocity asymmetry sigmoidal cross strata and mudstone draped flaser lenticular bedding are displayed by the sandstone mudstone heterolithic facies in the upper part of the bababudan succession together implying a tidal depositional system thick thin pairs of rhythmic foreset bundles correspond to neap spring tidal cycles within a semidiurnal tidal system development of the studied coastal sediments suggests formation of stable platform along the western margin of the late archaean chitradurga greenstone belt

morphometric response of late aptian planktonic foraminiferal communities to environmental changes a case study of paraticinella rohri at poggio le guaine central italy abstract the aptian albian boundary interval represents a pivotal time of pronounced climate ocean changes associated with oceanic anoxic event 1b oae 1b that seriously influenced marine pelagic ecosystems the sedimentary successions record the first and most significant species turnover in the evolutionary history of planktonic foraminifera consisting of the selective extinction disappearance of large aptian species and resulting in inter specific size reduction the post extinction dwarfing as in the lilliput effect in the earliest albian assemblages in this study we investigate how the planktonic foraminifera respond to crucial environmental stress and if any intra specific decrease in test size predate the extinction pre extinction dwarfing paraticinella rohri was chosen as the most representative of the aptian planktonic foraminiferal taxa and its test size evolution was compared with the high resolution record of redox and productivity geochemical proxies through the uppermost aptian lowermost albian pelagic succession of poggio le guaine central italy our geochemical data document long term fluctuations characteristic of a system with transitions among different states oligotrophic mesotrophic eutrophic and oxic dysoxic anoxic the strong correlation of the large test size changes of pa rohri during its total range with higher productivity increased baexcess concentrations suggests that the trophic regime was the key factor controlling robust abundance and size variability in this taxon the progressive increase in surface water fertility during the late aptian offered optimum ecological conditions for planktonic foraminifera that increased in abundance size and specific diversity after the transient anoxic 113 jacob sub event smaller to dwarfed specimens of pa rohri and depauperate planktonic foraminifera assemblages faced high selective pressures due to more oligotrophic conditions transition to a more eutrophic ocean in the latest aptian irreversibly eroded their resilience and aptian dwarfed k strategist taxa became extinct the planktonic foraminifera turnover has been therefore the result of an irreversible and drastic regime shift toward a more eutrophic ecosystem that promoted the thriving of small sized opportunistic disaster planktonic foraminiferal species and the siliceous radiolaria

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

cenomanian turonian and δ13c and δ18o sea level and salinity variations at pueblo colorado stable isotopes of the surface dwelling planktic foraminifera hedbergella planispira its abundance variations and mineralogical analysis of the cenomanian turonian at pueblo co reveal cyclic variations in surface salinity due to changes in precipitation freshwater influx marine incursions and long term sea level fluctuations hedbergella planispira is a proxy for salinity variations as indicated by 2 4 more negative 18o values in intervals of peak abundances as compared to intervals with reduced populations negative 18o values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods accompanied by increased clastic transport more positive 18o values reflect more normal marine salinities as a result of arid periods and or marine incursions and correlate with intervals of increased biogenic carbonate deposition the magnitude of salinity variations during the low sea level of the hartland shale is twice that during the sea level transgression of the bridge creek limestone the rapid positive 13c shift that marks the onset of oceanic anoxic event 2 oae 2 at pueblo occurred over a period of about 100 ky 93 90 94 00 ma and coincided with the major sea level transgression that culminated in the deposition of the basal bridge creek limestone a positive 13c shift also occurred in the rotalipora cushmani zone prior to oae 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter the likely cause for oae 2 is depletion of 12c in the water column as a result of high primary productivity whereas an earlier r cushmani zone event was primarily caused by increased input of terrigenous organic matter both 13c events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters

cycle of earthquake induced aggradation and related tidal channel shifting upper turnagain arm alaska usa aggradation of intertidal sediment in upper turnagain arm a macrotidal estuary located in southern alaska near anchorage began because of subsidence caused by sediment consolidation and tectonic lowering of the land during the earthquake of march 27 1964 at the head of the arm decrease in percent sand of surface sediments with time and return of rodents pulmonate gastropods trees bushes and grasses to the intertidal region indicate that the rate of sediment deposition has slowed and the upper turnagain arm area has returned to a state of preearthquake equilibrium only 17 years after the event comparison of channel locations before and after the earthquake indicates the possibility of regional postseismic tilting of the estuary

new oxygen isotope evidence for long term cretaceous climatic change in the southern hemisphere a new composite 18 o record generated from calcareous fine fraction and bulk sediments from the exmouth plateau details long term cretaceous climatic change at mid latitudes in the southern hemisphere assessment of new and previously published 18 o data indicates that a mid cretaceous global climatic optimum was achieved sometime between the time of the cenomanian turonian boundary and the middle turonian when surface ocean paleotemperatures were the highest of the past 115 m y periods of cooling and warming that reversed the general patterns were superimposed on long term aptian turonian warming and turonian maastrichtian cooling trends respectively extrapolation of southern hemisphere paleotemperature trends to maastrichtian paleotemperature data from a low latitude pacific guyot implies that maximum mid cretaceous low latitude paleotemperatures could have been in excess of 33 c

nutrient spatial variation during intrabasinal upwelling at the cenomanian turonian oceanic anoxic event in the westernmost tethys an ichnological and facies approach abstract facies and ichnofabrics of two sections of the cenomanian turonian boundary interval are correlated and compared to evaluate changes in palaeoceanographic conditions controlled by palaeogeography in the distal zone of the westernmost tethys southern iberian continental palaeomargin the oceanic anoxic event oae 2 was interrupted by short aerobic or dysaerobic sub events with slight differences in facies and ichnofabrics these sub events display a tendency to expansion from the more distal section hedionda towards the proximal one el chorro the anoxia spread out from the open sea probably from slope upwellings higher diversity and abundance of trace fossils in comparatively distal position during the pre and post event intervals can be caused by a higher abundance of food available for tracemakers shape of the correlation bands of the oae 2 event suggests that the event started earlier by about a few tens of thousands years in the most distal areas than in proximal slightly higher bottom settings

novel grain based model for simulation of brittle failure of alxa porphyritic granite abstract a grain based model gbm is generally employed by many researchers to simulate the microcracking process of crystalline brittle rock by the distinct element method in this study a novel grain based model ngbm in two dimensional particle flow code 5 0 pfc2d 5 0 is proposed to emulate the brittle failure of crystalline rock first the ngbm scheme is introduced in which the flat joint model is employed to model the contacts in mineral grains and the smooth joint model is assigned to the grain interface contacts then compressive tests are performed using alxa porphyritic granite and the strength values are fitted with the hoek brown failure criterion third a ngbm was generated based on the petrographic texture of realistic rock such as mineral constituents grain size and distribution the input microscale parameters are carefully calibrated according the experimental results finally this model is applied to study the microcracking process of alxa porphyritic granite and the influence of spatial distribution of minerals it is found that a relatively high ratio of uniaxial compressive strength to tensile strength of each mineral or synthetic samples can be reproduced by the ngbm moreover the simulated results show this model can capture the nonlinear characteristic of the hoek brown failure criterion after modeling numerous mineral grains were cut across which is consistent with the actual experimental observation the tensile crack is over the shear crack in the models while the number of intra grain shear crack increases dramatically with increasing confining pressure in addition the numerical results indicate that the effect of spatial distribution of minerals has limited influence on the evolution of microcracks but has great impact on microcrack distribution in summary the proposed ngbm in pfc2d can well reproduce the realistic failure process of granitic rocks under different loading conditions

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

geochemical and palaeoecological record of the cenomanian turonian anoxic event in the carbonate platform of the preafrican trough morocco abstract geochemical analyses major and trace elements and palaeontological studies were carried out based on rock samples and thin sections collected from three outcrop sections goulmima ziz and tazzouguert in the upper cenomanian lower turonian in the carbonate platform of the preafrican trough south morocco in order to determine if oxygen depleted conditions affected the platform and to highlight the possible impact of oxygen variation on carbonate production particularly during the oceanic anoxic event 2 oae2 which took place in the late cenomanian during this interval the carbonate platform was composed of two contrasting environments a shallow water environment peritidal to mid ramp was developed in the east ziz and tazzouguert sections characterized by a high diversity and abundance of benthic organisms and in some cases by a high diversity of planktonic organisms associated with low concentrations of authigenic markers u mo v and cr redox proxies indicating oxic conditions in the west goulmima section the environment was deeper mid ramp outer ramp and redox proxies record a high enrichment an indicator of reducing conditions associated with a low diversity and abundance of organisms and the presence of buliminidae bottom waters were dysoxic and the palaeoproductivity was low at the sea surface thus during the late cenomanian oxygenation conditions were relatively good over the area of the preafrican trough even during the oae2 except in the deeper environments toward the west where bottom waters were depleted in oxygen during the cenomanian transgression and more precisely during the oae2 this dysoxia was linked to the influx of poorly oxygenated waters from the deeper anoxic basins of the atlantic and or tethys oceans geochemical palaeontological and sedimentological disturbances are recorded in the lower turonian everywhere in the outer ramp environments of the platform palaeontological proxies show a huge decrease in group diversity with the disappearance of benthic foraminifera except for the buliminidae which proliferated and only shallow water planktonic foraminifera survived geochemical proxies of redox conditions and palaeoproductivity show a marked enrichment in all three outcrop sections with higher values in the west this dysoxia occurred in response to a climatic change from warm with contrasting seasons to hot and wet which induced an increase of chemical weathering in the anti atlas to the southwest of the platform this substantial input of nutrients increased the palaeoproductivity which finally enhanced the consumption of o2 owing to the decay of organic matter moreover the late cenomanian transgression led to the supply of additional nutrients to the platform due to the leaching of soils

planktonic foraminifers across the bonarelli event oae2 latest cenomanian the italian record abstract a high resolution quantitative study of the planktonic foraminiferal assemblages across the bonarelli level oae2 latest cenomanian of italy from different areas and geological settings has allowed the recognition of several events and biotic changes including acmes and crises of different genera it provides evidence of a progressive and rapid change of palaeoenvironmental conditions reaching a climax coincident with the bonarelli event and of the subsequent gradual although not complete resumption of previous conditions the observed pattern is illustrated by marked changes in the assemblages that indicate five discrete phases of environmental perturbation within the marine ecosystem though there are several similarities our analyses highlight that each section has its own peculiarities clearly indicating more or less extreme environmental conditions

response of calcareous nannoplankton to the late cretaceous oceanic anoxic event 2 at oued bahloul central tunisia abstract oued bahloul is a reference section for the cenomanian turonian that was located on the north african palaeomargin where oceanic anoxic event 2 oae2 is represented by black limestones and grey marls biostratigraphic study allowed the identification of calcareous nannofossil uc3 to uc6 zones quantitative analyses of calcareous nannofossil assemblages indicate that high fertility surface water conditions predominated throughout most of the oae2 interval the most eutrophic conditions probably developed during deposition of the lowermost part of the whiteinella archaeocretacea zone uc3 to uc4 zones where nannofossil derived fertility indices reach high values and the small zeugrhabdotus gr predominates over biscutum spp the temperature index based on calcareous nannofossil assemblages indicates a warming at the beginning of the oae2 followed by progressive cooling the same trend indicated by 18 o bulk values the significant proportion of holococcoliths suggests high stress conditions in surface waters during most of the oae2 interval the enrichment in redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicates dysoxic conditions both in the deep water column and sea bottom at the beginning of the oae2 w archaeocretacea zone geochemical detrital proxies indicate an enhanced rate of terrigenous supply during the oae2 interval resulting from increased riverine influx related to a more humid climate enhanced fluvial run off increased nutrient input to marine surface waters contributing to eutrophication recorded by calcareous nannoplankton and planktic foraminifera plankton consumption of surface water nutrients increased organic matter production whose decay contributed to the decrease in dissolved oxygen generating increasingly dysoxic anoxic conditions and favoring preservation of organic matter although low latitude nannofossil assemblages such as those of oued bahloul reflect an increase in nutrient availability during the oae2 interval assemblages from mid latitude areas record a decreased nutrient content

late precambrian tidal rhythmites in south australia and the history of the earth s rotation sedimentary rhythmites of siltstone and fine sandstone from late precambrian c 650 800 ma glaciogenic formations in south australia are interpreted as distal ebb tidal deposits that record variability in the velocity and range of palaeo ebb tides variations in lamina thickness encode a full spectrum of palaeotidal cycles including semidiurnal diurnal fortnightly and monthly tidal cycles as well as the lunar apsides perigee and nodal cycles a half yearly oscillation is attributable largely to a beat between the fortnightly tidal cycles of luni solar conjunction and lunar declination the lunar nodal cycle is discernible as an amplitude modulation of this beat oscillation the data allow determination of the earth9s palaeorotation and the past dynamics of the earth moon system with an accuracy previously unattainable for the precambrian the late precambrian c 650 ma year contained 13 1 0 5 lunar months and c 400 20 days and the late precambrian lunar month c 30 5 1 5 days these values suggest an average equivalent phase lag near 3 since late precambrian time rather than the present value of 6 the period of 19 5 0 5 years determined for the lunar nodal cycle c 650 ma ago indicates a lunar distance 96 9 1 7 of the present distance the low rate of lunar recession since late precambrian time revealed by the rhythmite data militates against a close approach of the moon during the proterozoic precambrian sedimentary rhythmites may hold a key to the early history of the earth9s rotation

numerical simulation of lifetime and time dependent damage for granite by continuous and discontinuous approaches in this study the time dependent damage process of granite is investigated utilizing two numerical simulation schemes based on continuous method and discontinuous method numerical creep tests are carried out with both simulation schemes and mechanical responses and fracture patterns of rock specimens are analyzed the calibrated numerical models can successfully reflect the typical creep stages observed in the laboratory the predicted lifetime is in accordance with the laboratory test data comparisons are made between the two simulation schemes it is found that both schemes have unique features that can promote a genuine reflection of the time dependent damage process of the brittle rocks

record of tide wave influence on the coal bearing permian barakar formation raniganj basin india abstract the coal bearing barakar formation early permian of the raniganj gondwana basin was previously interpreted as continental fluvial sediments with little evidence for tide wave influences the present contribution details the sedimentary attributes of marginal marine tidal and wave activities preserved within an overall braided meandering fluvial depositional setting from the barakar formation tide dominated sedimentary features include i tidal bundle sequences showing sandstone foresets with mud drapes ii periodic variation in foreset thickness iii lateral and vertical accretion of cross strata bundles with a downcurrent change to sigmoidal cross strata iv mutually opposite cross strata sets separated by sub horizontal plane laminated sandstone mudstone and v alternate sand and mud dominated rhythmites draping of the tidal stratifications by wavy laminated muddy siltstone suggests immediate invasion by low energy silt mud depositing waves that helped preserve the tidal features during subsequent reworking open marine storm wave activities are evident from hummocky cross stratification and various types of wave ripples preserved separately within coarse to fine grained sandstone in the middle upper part of the succession recognition of tide storm influenced marine sedimentation significantly changes the existing paleogeographic model to a fluvial estuarine depositional environment

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

litho bio and chemostratigraphy across the cenomanian turonian boundary oae 2 in the vocontian basin of southeastern france the oceanic anoxic event 2 oae 2 was one of at least two large oceanic anoxic events during the cretaceous period and it is characterized in the stratigraphic record by double positive peaks in the 13c curves of carbonate and organic carbon since the positive 13c shift is believed to have resulted from massive burial of isotopically depleted organic carbon generated globally in anoxic oceanic environments the positive 13c shift tend to coincide with widespread deposition of organic rich sediments in the case of oae 2 however the organic rich horizons do not accord exactly with the two intervals with positive 13c shifts at many sites such as pueblo tarfaya eastbourne and gubbio e g tsikos h jenkyns h c walsworth bell b petrizzo m r forster a kolonic s erba e premoli silva i baas m wagner t sinninghe dameste j s 2004 carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities journal of the geological society london 161 711 719 the thomel level of the cenomanian turonian c t boundary in the vocontian basin southeastern france accumulated during the oae 2 and it is marked by frequent intercalations of black shale and organic rich marl detailed litho bio and chemostratigraphy analyses across the c t boundary in the vocontian basin indicate that the 13ccarbonate profile fluctuation across the thomel level corresponds well with changes in lithofacies total organic carbon toc and calcium carbonate caco3 abundance positive 13c excursions within the oae 2 correlate with basal and middle parts of the thomel level that are characterized by high toc low caco3 and predominantly contain organic rich sediments such as black shale and dark gray marl on the other hand negative 13c intervals within the oae 2 correspond with lower and upper parts of the thomel level that consist of marly limestone and limy marl with low toc and high caco3 values since the fluctuation of redox conditions during thomel level deposition in the vocontian basin coincides well with the global carbon burial rate indicated by its 13c profile the thomel level could be an ideal candidate for the reference section of the oae 2

the cenomanian turonian boundary event oae2 and palaeoenvironmental change in epicontinental seas new insights from the dinocyst and geochemical records abstract organic walled dinoflagellate cyst dinocyst and geochemical records across the cenomanian turonian boundary ctb are presented for the nw european reference section at eastbourne england dinocyst and nannofossil fertility indexes indicate that an upwelling driven productivity pulse accompanied a eustatic sea level fall that preceded by at least 40 kyr the global rise in 13 c values that marks the onset of oceanic anoxic event 2 oae2 and the deposition of black shales in the deep ocean a marine productivity collapse in the latest cenomanian is evidenced by the falling absolute and relative abundance of peridinioid dinocysts believed to be the product of heterotrophic dinoflagellates this biotic change accompanied transgression and sharply rising sea surface temperatures following an atlantic wide episode of short lived cooling geochemical tracers provide evidence of caribbean colombian plateau volcanism the increase in water depth caused by the latest cenomanian transgression resulted in less eutrophic waters in epicontinental seas where ctb biotic turnover was driven largely by water mass changes rather than oxygen depletion the species richness absolute abundance ratio of dinocysts is proposed as a water mass stability proxy

the lunar orbit in the late precambrian and the elatina sandstone laminae the discovery of layered sediments of the elatina formation of south australia has attracted intense speculation regarding their origin1 2 the formation 10 m layer of graded sandstone consists of a pattern of light bands of periodically varying thickness3 a sequence of dark bands separates on average 11 6 light bands the spacing of these dark bands exhibits a rich and complex spectrum previously the periodicity has been attributed to the sunspot cycle and unassigned but putative solar periods prompted by a letter from g e williams summarizing new field data from the adelaide region south australia which imply that the elatina varves may be tidal we re examined the dark band spectrum and propose a luni solar tidal interaction model as the source of the laminae

soft sediment deformation produced by tides in a meizoseismic area turnagain arm alaska turnagain arm is a semidiurnal hypertidal estuary in southeastern alaska with a recorded tidal range of 9 m contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the mw 9 2 great alaskan earthquake of 1964 horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas although many types of soft sediment deformation structures can be formed by earthquakes observations of sedimentation on tidal flats in the inner parts of turnagain arm in the summers of 2003 and 2004 show that a wide range of soft sediment deformation structures similar to those inferred to have been formed by earthquakes can form in macrotidal estuaries in the absence of seismic shock during sedimentation rate measurements in 2004 soft sediment deformation structures were recorded that formed during one day s tide either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1 8 m tidal bore structures consisted of flow rolls dish structures flames and small dewatering pipes in a bed 17 cm thick in the future if the flow rolls in turnagain arm were found in isolated outcrops across an area 11 km in length in an estuary known to have been influenced by large magnitude earthquakes would they be interpreted as seismites these examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms tidal flux tidal bores slumping flooding that can cause deformation in rapidly deposited unconsolidated silts and sands are orders of magnitude more common than great earthquakes

the cenomanian turonian boundary interval deep sea deposits in the zagros basin sw iran bioevents carbon isotope record and palaeoceanographic model abstract the cenomanian turonian c t boundary interval spanning the upper part of the sarvak formation in the zagros basin izeh zone has been studied to determine the timing and the possible cause of biotic turnovers coinciding with the intense environmental perturbations during the oceanic anoxic event 2 oae2 the upper cenomanian strata in the study section composed of light colour marlstone organic rich marlstone and shale bedding couplets record fluctuations in microfossil assemblages and organic carbon contents we suggest that the organic poor layers characterized by high abundance of radiolarians were deposited during cold periods under surface water eutrophication upwelling and ventilated seafloor in contrast water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic rich strata continued stratification and also increased runoff and primary productivity during warm intervals of oae2 led to expansion of oxygen minimum zone omz which may have caused extinctions of deep followed by intermediate water planktic foraminifera such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus planoheterohelix heterohelix shift event the 13c curve in the study interval reveals the diagnostic features of global c t boundary carbon isotope record including three positive peaks a b and c within the whiteinella archaeocretacea biozone these carbon isotope features and the most important bioevents in the study section are stratigraphically listed below 1 highest occurrences hos of th greenhornensis and th deeckei 2 ho of r cushmani and 13c peak a 3 ho of g bentonensis 4 onset of heterohelix shift event 5 13c peak b 6 13c peak c 7 filament event 8 lowest occurrence lo of h helvetica and 9 holywell event

cenomanian turonian carbonate and organic carbon isotope records biostratigraphy and provenance of a key section in ne sicily italy palaeoceanographic and palaeogeographic implications abstract in eastern sicily a series of highly organic rich black shales occur as exotic blocks 100 m across floating in tectonized sediments argille varicolori unit containing olistoliths of cretaceous palaeogene age a 19 metre section through one of these blocks near the town of novara di sicilia includes cyclically bedded black shales marlstones and claystones which have been dated using planktonic foraminiferal and nannofossil biostratigraphy on this basis the section is assigned to the latest cenomanian and clearly represents a manifestation of the oceanic anoxic event characteristic of that interval total organic carbon values range up to 23 and the relatively high hydrogen indices record the presence of marine organic matter of low thermal maturity high resolution carbonate and organic carbon isotope curves are comparable with those recorded elsewhere in indicating a significant positive excursion and confirm that in the novara di sicilia section the black shales are latest cenomanian in age by comparison with cenomanian turonian black shales exposed elsewhere in italy calabianca section western sicily livello bonarelli bottaccione gorge gubbio marche umbria the section of novara di sicilia is different in being more stratigraphically expanded however this section from eastern sicily does resemble extremely closely coeval sediments cropping out in tunisia and morocco this association is taken as evidence that the argille varicolori unit includes elements that were initially deposited on the north african shelf during cretaceous time

the cenomanian turonian boundary at eastbourne sussex uk a proposed european reference section the cenomanian turonian boundary ctb section at eastbourne sussex england is the thickest at outcrop in the anglo paris basin is rhythmic throughout rich in macro micro and nanno fossils and shows less diagenetic alteration than other sections in nw europe geochemical and biostratigraphic data are all related to detailed rhythmic lithostratigraphy allowing correlation with the global boundary stratotype section to within 20 000 years and accurate estimates of rates of changes very detailed stable isotope curves for oxygen and carbon are presented and show that the build up phase of the ctb carbon excursion had two portions separated by a trough patterns of occurrence of coarse fraction benthic foraminifera 250 mm show two peaks of extinction corresponding to the two build up phases of the carbon excursion benthic and planktic foraminifera ostracods and calcareous nannofossils all show declines in diversity and abundance across the ctb foraminifera also decline significantly in size key biomarker events for the ctb include first occurrences of the ammonites fagesia catinus and mammites nodosoides the bivalve mytiloides the planktic foraminifera helvetoglobotruncana praehelveticaand marginotruncana renzi and the calcareous nannofossils quadrum intermedium q gartneri and eprolithus octopetalus and last occurrences of the ammonite sciponoceras the planktic foraminifera rotalipora greenhornensis and r cushmani the calcareous nannofossils corolithion kennedyi axopodorhabdus albianus lithraphidites acutus rhagodiscus asperand microstaurus chiastius cyclostratigraphy allows very precise correlation of isotopic and bioevents with other sections in europe and north america eastbourne is recommended as a nw european standard section 1999 elsevier science b v all rights reserved

evidence for two great earthquakes at anchorage alaska and implications for multiple great earthquakes through the holocene abstract multiple peat silt couplets in tidal marsh sediment sequences at anchorage suggest up to five possible great earthquakes during the last 2500 years litho stratigraphic diatom and radiocarbon data of the youngest two couplets record the last two great earthquakes ad 1964 and 950 850 cal yr bp similar multiple peat silt couplets around cook inlet suggest recurring great earthquakes associated with marsh subsidence over large areas comparable in extent to that recorded in ad 1964 potential difficulties in interpreting evidence include lack of modern analogues for applying quantitative diatom transfer functions to parts of the fossil record and the observation that under certain sedimentary conditions co seismic subsidence in the case of ad 1964 of known magnitude is recorded by a transitional peat silt boundary this differs in diatom stratigraphy from a phase of pre seismic relative sea level rise recorded for other great earthquakes a field experiment to simulate co seismic subsidence identifies limited mixing at the top of submerged marsh sediment and indicates how mixing must be shown to differ from evidence for pre seismic relative sea level rise analysis of diatom assemblages from ice frozen intertidal sediment and melt out sediment demonstrates the importance of winter processes in transporting diatoms and their interpretation in fossil sequences winter processes may also be important in transporting organic material that leads to significant differences 120 2800 yr between radiocarbon ages from plant macrofossils and bulk peat samples this necessitates a new approach for establishing between site correlations recurrence intervals and spatial extent of great holocene earthquakes in southern alaska

short term euxinia coinciding with rotaliporid extinctions during the cenomanian turonian transition in the middle neritic eastern north atlantic inferred from organic compounds oceanic anoxic event 2 oae2 which occurred during the cenomanian turonian c t transition and lasted 1 m y is characterized by a positive global carbon isotopic excursion and stepwise extinctions in marine biota to examine temporal variations in the dissolved oxygen content of the water column shallow marine c t sediments from northern spain were analyzed for concentrations of dibenzothiophenes which are indicators of euxinic depositional environments and 2 3 6 trimethylarylisoprenoids which probably indicate photic zone euxinia the positive excursion in 13 c values of carbonates is accompanied by short term 10 3 10 4 yr and long term 10 5 yr increases in dibenzothiophene and 2 3 6 trimethylarylisoprenoid concentrations suggesting that the bottom water and photic zone of the eastern marginal sea of the north atlantic ocean were euxinic two of the short term increases in organic compound concentrations took place just after the last occurrence of the planktonic foraminifers rotalipora greenhornensis and r cushmani these transient maxima indicate that the extinction of both planktonic foraminifers was due to short term oaes lasting 10 3 10 4 yr

neap spring tidal cyclicity in laminated carbonate channel fill deposits and its implications salem limestone mississippian south central indiana u s a abstract limestone beds containing rhythmic parallel laminations occur within a channel fill sequence exposed locally in the salem limestone mississippian of indiana the laminations consist of carbonate grains and micrite in layers up to 2 mm thick capped by thin 0 1 0 3 mm drapes of organic matter each couplet was generated by mixed or semidiurnal tidal events during which carbonate sediment was mobilized and deposited by the dominant tide and organic material settled from suspension during slackwater conditions laminae thicken and thin systematically in a vertical sequence as a result of neap spring tidal current fluctuations that occur during a lunar month laminations are well preserved in certain beds ranging from 20 to 40 cm thick through much of the channel fill sequence other beds are extensively bioturbated and contain only a partial record of the laminations the sequence of bioturbated and unbioturbated units defines a rhythmic pattern suggesting periods of seasonal environmental restriction that precluded burrowing organisms estimation of sedimentation rates based on the neap spring tidal cycles indicates that deposition within the channel occurred very rapidly averaging 35 cm year a rate four orders of magnitude faster than calculated long term depositional rates

apogean perigean signals encoded in tidal flats at the fluvio estuarine transition of glacier creek turnagain arm alaska implications for ancient tidal rhythmites turnagain arm is a macrotidal fjord style estuary glacier creek is a small glacially fed stream which enters the estuary tangentially near girdwood alaska trenches and daily sedimentation measurements were made in a mudflat along the fluvio estuarine transition of glacier creek during several summers since 2003 each year the flats appear to erode during the winter and then accrete vertically in the spring and summer in each of the years studied tidal laminae in vertically thickening and thinning laminae bundles were deposited by twice daily tides in neap spring tidal cycles in 2004 bundles of thickening and thinning laminae couplets were noted in trenches cut into the flats five laminae bundles alternated between thicker and thinner bundles corresponding to the perigean high spring and apogean low spring tides well preserved apogean perigean cycles have rarely been documented in modern tidal flat sediments at this location vertical accretion of tidal rhythmites with well developed neap spring cyclicity is possible because of the near complete removal of the flat from the previous year which creates accommodation space for vertical accretion without significant reworking macrotidal conditions no reworking by infaunal invertebrates protection from the main tidal channel by a gravel bar and protection from storm waves and fluvial erosion by a recess in the sedge marsh that surrounds the flats all aid in preservation of rhythmites during aggradation the position of the flats relative to tidal range allows for accumulation of complete spring cycles and incomplete neap cycles in the summer of 2004 apogee and perigee were closely aligned with the new and full moons resulting in successive strong perigee and apogee tides which probably aided in the accumulation of successive thick thin spring cycles encoding the apogean and perigean tidal cycle the apogean perigean signal was not observed in subsequent years

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

the paleocene eocene thermal maximum as recorded by tethyan planktonic foraminifera in the forada section northern italy abstract the forada section in the venetian pre alps of northern italy represents an expanded record of the paleocene eocene thermal maximum petm at a depositional paleodepth of about 1 km 0 5 km high resolution planktonic foraminiferal analysis of this section in a time interval of approximately 1 3 myr across the paleocene eocene boundary reveals striking faunal changes that allow the identification of eight phases a h the late paleocene was represented by stable warm and oligotrophic surface water conditions phase a unstable environmental conditions start well before the onset of petm ca 150 kyr phase b and involved a change towards eutrophy as marked by the increase of subbotina and the concomitant decrease of morozovella this step is also characterized by enhanced fragmentation and dissolution the interval corresponding to the main body of the carbon isotope excursion cie is characterized by a marked increase of acarinina though with some differences in the species composition and relative abundance both in high and low latitudes particularly in the tethyan area forada is no exception to this pattern however at forada two prominent peaks in abundance of acarininids are recorded ca 30 kyr prior to the onset of the cie thus suggesting an increase in temperature heralding the onset of the petm phase c interestingly the lower peak in abundance of acarinina just precedes the 1 carbon isotope negative shift occurring below the onset of the main cie the basalmost eocene corresponding to the lower part of cie curve is represented by intense planktonic foraminiferal dissolution implying an extraordinary rise of the ccd this interval has an estimated duration of about 16 kyr phase d the dominance of acarininids in the lower part of the cie phase e f ca 14 and 22 5 kyr is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the forada depositional environment at that time these acarininids include at forada also the temporally constrained acarinina sibaiyaensis and a africana the morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the cretaceous anoxic events suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the petm the recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups e g biserials globanomalinids igorinids planorotalids and pseudohastigerinids occurring in the middle part of the cie ca 30 kyr after the onset of the petm indicates an initial environmental recovery phase g a new stable state is definitely reached in the upper part of the forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late paleocene conditions phase h however the perturbation during the petm produced significant changes in the ocean geochemistry that endured after the petm event as testified by the prominent high carbonate dissolution characterizing the marly levels and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages these striking oscillations were not present in the latest paleocene

lower cretaceous tides revealed by cross bedding with mud drapes the sand dominated folkestone beds widely exposed around the weald of south east england are of upper aptian to lower albian lower cretaceous age and range in thickness up to 84 m refs 1 3 their content of ammonites bivalves and sponges indicates a marine origin while their relative coarseness and the incorporation of drifted timber point to a shallow water deposition near land one striking sedimentary facies is formed by medium to coarse grained cross bedded sands in which several foreset and or bottomset surfaces support mud drapes although it was suggested4 that this facies may have been formed by the storm induced movement of sand waves i now consider that the facies is best explained by the migration of sand waves under the influence of strongly asymmetrical tides and that the mud drapes are formed at slack water a model of this process has been described elsewhere5 and i now describe measurements of a section which supports my earlier conjecture6that the separation of the mud drapes is systematically related to the phase of the spring neap tidal cycle at the time of deposition although criteria for recognizing tidal deposits have long been available it has not previously been possible to analyse a series of ancient sediments with a view to characterizing the tidal regime

potential links between ocean plateau volcanism and global ocean anoxia at the cenomanian turonian boundary the cenomanian turonian boundary is marked globally by the extinction of marine invertebrates and an increase in the accumulation and preservation of organic carbon rich sediments black shales the timing of this boundary also coincides with large scale volcanism from at least three large igneous provinces the caribbean and ontong java oceanic plateaus and the madagascar flood basalts in this paper we assess the possibility that hydrothermalism associated with large scale submarine magmatism was responsible for the reduction of dissolved o 2 in the oceans we investigate two potential mechanisms the oxidation of reduced material in hydrothermal effluents and the stimulation of primary productivity in the water column due to the injection of hydrothermal fe into surface waters with the first mechanism we find that a 10 000 km 3 submarine basalt eruption three orders of magnitude larger than recent midocean ridge eruptions could release enough reduced hydrothermal material to consume at least 6 percent of the dissolved o 2 in seawater in a well ventilated ocean such as the present ocean with the second mechanism we calculate that even a small percentage of the hydrothermal fe released from a single large flow could have led to a significant increase in primary productivity in areas where fe was the biolimiting nutrient such as open ocean areas in the pacific the potential impact of both of these o 2 reducing mechanisms at the cenomanian turonian boundary would have been significantly greater if cretaceous oceans were less well ventilated than the present oceans

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

study on nonlinear damage creep constitutive model for high stress soft rock rock engineering especially deep rock engineering undergoing long term effects of external loading and gravity all or most may gradually damage deformation or creep deformation accumulation leading rock structures to damage crack such as severe plastic deformation or even progressive failure in this paper based on the nonlinear damage creep characteristics of rock and damage variable a new nonlinear damage creep constitutive model of high stress soft rock is defined in series with the improved burgers model hooke model and st venant model this new nonlinear damage creep constitutive model can work out fairly reasonably explanations for the soft rock creep deformation a series of uniaxial compression creep tests were performed to study the creep damage characteristics of typical soft rock in jinchuan no 2 mine in the northwest of china using the increment step loading and single step loading the results of creep experiments and nonlinear damage creep constitutive model results are very consistent in this study the new model not only can reflect the whole course of creep deformation but also can reasonably describe the soft rock under different initial creep stage steady state creep stage and accelerated creep stage therefore the new nonlinear creep damage model is a reasonable reference model for the research of soft rock creep

the expression of the cenomanian turonian oceanic anoxic event in tibet the gongzha section of tibet china is located at the northern margin of the indian plate se tethys and is characterized by hemipelagic grey marls and marly limestones light grey limestones and silty limestones but no organic rich sediments high resolution biostratigraphy reveals an expanded cenomanian turonian ct boundary interval and the 13c record includes the main features of the classical positive carbon isotope excursion that characterizes the ct oceanic anoxic event the biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed except for a short interval marked by peak abundance of heterohelix that indicates a significantly dysoxic environment during the 13c b peak excursion the overall decreasing trend in redox sensitive trace elements rste during the maximum 13c excursion confirms the absence of significant longer lasting anoxia in the gongzha section enrichments in rste are linked to phases of increased detrital input chemical weathering indices suggest that the upper cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the ct boundary in the early turonian lower weathering indices suggest a warm drier climatic regime with reduced continental runoff phosphorus mass accumulation rates show a significant peak at the onset of the positive 13c excursion followed by a decrease up to the basal turonian this pattern is positively correlated with the long term decrease in detrital index as also observed in numerous other ct boundary sections e g eastbourne pueblo and whadi el ghaib sinai long term phosphorus accumulation in the gongzha section is therefore associated with changes in detrital input the overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of cenomanian coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

a 2d dem based approach for modeling water induced degradation of carbonate rock abstract the mechanical characteristics of sedimentary rocks such as carbonates are highly sensitive to the influence of water in carbonate rich regions rock failures induced by water corrosion have been widely reported such as the collapse of cliffs and rockslides in this study a 2d model was built to investigate the time dependent strength degradation of carbonate rocks under the influence of water first degradation laws for two types of bonds were derived based on the different behaviors of depositional and diagenetic cements in water then via developing customized code using the fish language the degradation laws were coupled with udec to build the numerical procedure finally the ability of the proposed model to reproduce the macroscopic short and long term behaviors of carbonate rocks under the influence of water was validated by comparing the numerical results with the lab observations and measurements the results show that the presented procedure is capable of simulating the strength properties of carbonate rocks submerged in water for different time periods uncoupled tests as well as the lifetime time to failure of rocks in a chemo mechanically coupled condition

neap spring cycles in a subrecent tidal channel fill 3665 bp at schoorldam nw netherlands abstract neap spring tidal sequences are described from an intertidal channel fill the channel fill consists of a larger scale thinning up and fining up sequence of parallel laminations on a smaller scale more or less regular thickening up to thinning up sequences are formed separated from each other by more or thicker clay laminae peat detritus or echinocardium spicules deeper lying sequences contain about 28 laminae higher up the sequences become more irregular and contain gradually a lesser number of laminae these thickening up to thinning up sequences are interpreted as neap spring tidal sequences formed by semi diurnal flood tidal currents hence ca 28 laminae per 14 days three types have been found a cm thick sand clay alternations b ripple like sand mud alternations and c mm thick sand clay alternations these types show transitions to each other type a was deposited at higher current velocities and type c at lowest current velocities type b features are not linsen and flaser bedding but ripple like features which during flood only moved one cross lamina followed by one slackwater lamina clay peat or spicules they are called rippled tidal couplets the pattern of neap spring sequences is compared with recent hw water levels in the north sea and related to mean high water levels mhw and mean sea level msl

analysis and modeling of the combined effects of hydrological factors on a reservoir bank slope in the three gorges reservoir area china abstract more than 5000 landslides have been identified in the three gorges reservoir tgr area since the impoundment in 2003 which posed great threats to the residential houses transportation on the yangtze and dam stability this paper focuses on the evaluation of the coupled influence of rainfall and reservoir water on deformation characteristics and failure evolution of the outang landslide in china based on field investigations a statistical pearson cross correlation coefficient analysis multi technique monitoring data and a numerical model this instability is a reactivated ancient landslide with a volume of approximately 90 mm3 located in the three gorges reservoir the slope behavior is featured with a short period of fast displacement and a relatively long period of semi constant displacement rates per hydrological year and displacements velocities quicken gradually upslope rainfall and reservoir water level are the main triggering factors of slope movement existing in the upper and the lower parts of the landslide respectively based on the numerical results the failure evolution of this landslide is a compounded push retrogression type failure process involving a a first rupture at the toe caused by the reservoir water level that will rapidly mobilize a second and subsequent collapses upwards retrogression type and b the rock mass at the upper part will be pushed out and failed downslope push type due to precipitation these results provide a comprehensive analysis of the outang landslide which is critical for its management as well as for disaster prevention and mitigation of analogous reservoir induced landslides

age and paleoenvironment of the cenomanian turonian global stratotype section and point at pueblo colorado biostratigraphy and stable isotopes indicate that the global stratotype section and point gssp at pueblo contains an essentially complete sedimentary record across the global ocean anoxic event oae 2 and the cenomanian turonian boundary the oae 2 d 13 c shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression which at its peak was marked by an incursion of oxygen rich waters creating a benthic oxic zone that lasted about 100 ky a mid cenomanian d 13 c shift sea level transgression and faunal turnover occurred about 2 my before oae 2 d 18 o values of the planktic foraminifer hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions whereas dominance by the low oxygen tolerant heterohelix species indicates a well developed oxygen minimum zone omz for most of the middle to late cenomanian and early turonian profound faunal changes accompanied these oceanographic events including the extinction of 30 of the species assemblage and an equal gain in evolutionary diversification though the overall combined relative abundances of outgoing and incoming species were less than 2 and 4 respectively of the total assemblages the faunal turnover began with the sea level transgression and rapid increase in d 13 c values and accelerated with the influx of oxygen rich deep water increased water mass stratification and competition during the benthic oxic zone the incursion of oxygen rich deep waters at this time was also observed in morocco and may represent a global event of a still unknown source d 2003 elsevier b v all rights reserved

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

reliability of lunar orbital periods extracted from ancient cyclic tidal rhythmites abstract ancient tidal periods extracted from the geologic record are useful to constrain and calibrate theoretical models of the evolution of the earth moon system analysis of rocks that contain such tidal periodicities termed cyclic rhythmites have tended to concentrate on long series and have focused on the more obvious periods for example neap spring periods have been the most widely discussed such information can be reliably extracted from bedform thickness series measured within laterally accreted tidal bundles and vertically accreted tidal laminae other lunar orbital data is also encoded in cyclic rhythmites however this additional information has been much less extensively applied to earth moon models herein short segments of well formed cyclic rhythmites are examined to determine how reliably the various tidal periods can be extracted via harmonic analysis rhythmite series analyzed here exhibit well formed neap spring tidal periods and also exhibit a prominent fortnightly inequality or a variation in the height of successive spring tides this inequality is related to the elliptical nature of the lunar orbit anomalistic month and it is demonstrated that this period can also be reliably extracted from cyclic rhythmites tropical periods which reflect the changing lunar declination that occurs during a tropical month have also been reported from cyclic rhythmites unlike synodic and anomalistic periods the apparent tropical periods extracted from some cyclic rhythmites do not always accurately correspond to the expected values in only a few cases can this period be reliably extracted from short segments of cyclic tidal rhythmite data this period is commonly only poorly encoded in rhythmites because 1 it tends to be masked by higher amplitude synodic periods and 2 it is not well expressed within predominantly semidiurnal tidal systems samples selected from the proterozoic and phanerozoic tend to be more common during specific intervals of geologic time these intervals were characterized by glacio eustatic flux and in some cases by unique continental configurations understanding these basic controls on rhythmite occurrences should aid in the discovery of additional examples

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

a record of the extraterrestrial 3he flux through the late cretaceous abstract late cretaceous 100 73 ma pelagic limestones were measured for helium concentration and isotopic composition to characterize the interplanetary dust flux using 3he as a tracer in the bottaccione section near gubbio italy three intervals of elevated 3he concentration were detected k1 in the campanian stage at 79 ma k2 in the santonian stage at 85 ma and k3 in the turonian stage at 91 ma all three of these episodes are associated with high 3he 4he and 3he non carbonate ratios consistent with their derivation from an enhanced extraterrestrial 3he flux rather than decreased carbonate sedimentation or dissolution while k2 is modest in magnitude and duration and thus is of limited significance k1 and k3 are each identified by a few myr interval with an 4 fold enhancement in mean 3he flux compared with pre event levels samples from odp hole 762c in the indian ocean spanning both k2 and k3 93 83 ma confirm the presence of a peak in the turonian stage suggesting that k3 is a global event the k1 and k3 3he events are similar in most respects to the two peaks previously detected in the cenozoic suggesting a similar origin these have been attributed to a major asteroid collision in the late miocene and to a shower of either comets or asteroids in the late eocene based on the age and temporal evolution of k1 we suggest that it most likely records the collision which produced the baptistina asteroid family independently dated at 80 ma the k3 event is less easily explained it is characterized by an unusually spiky and erratic temporal progression suggesting an unusual abundance of very 3he rich particles not previously seen in the sedimentary 3he record we suggest this episode arises either from a comet shower or from an asteroid shower possibly associated with dust producing lunar impacts

high stress late maastrichtian paleoenvironment inference from planktonic foraminifera in tunisia high resolution v5 10 kyr planktonic foraminiferal analysis at elles tunisia reveals major changes in the structure of the tethyan marine ecosystem during the upper maastrichtian during the first 1 5 myr of the late maastrichtian 68 3 66 8 ma relatively stable environmental conditions and cool temperatures are indicated by diverse planktonic foraminiferal populations with abundant intermediate and surface dwellers a progressive cooling trend between v66 8 65 45 ma resulted in the decline of globotruncanid species intermediate dwellers this group experienced a further decline at the climax of a rapid warm event about 300 kyr before the k t boundary at the same time relative abundances of long ranging dominant species fluctuated considerably reflecting the high stress environmental conditions times of critical high stress environments during the late maastrichtian and particularly at the k t boundary are indicated by low species diversity and blooms of the opportunistic genus guembelitria at warm cool transition intervals during the last 100 kyr of the maastrichtian rapid cooling is associated with accelerated species extinctions followed by the extinction of all tropical and subtropical species at the k t boundary fl 2002 elsevier science b v all rights reserved

late holocene relative sea level changes and the earthquake deformation cycle around upper cook inlet alaska abstract multiple peat silt couplets preserved in tidal marsh sediment sequences suggest that numerous great plate boundary earthquakes caused the coast around cook inlet alaska to subside over the past 3500 years field and laboratory analyses of the two youngest couplets record the well documented earthquake of ad 1964 and the penultimate one approximately 850 cal yr bp diatom assemblages from a range of modern day estuarine environments from tidal flat through salt marsh to acidic bog produce quantitative diatom transfer function models for elevation reconstructions based on fossil samples only nine out of 124 fossil assemblages analysed including previously published data for the ad 1964 earthquake have a poor modern analogue calibration of fossil samples indicate co seismic subsidence of 1 50 0 32 m for ad 1964 similar to measurements taken after the earthquake and 1 45 0 34 m for the 850 cal yr bp earthquake elevation standard errors for individual fossil samples range from 0 08 m in peat layers to 0 35 m in silt units lack of a chronology within fossil silt units prevents identification of changes in the rate of recovery and land uplift between the post seismic and inter seismic periods however preservation of multiple peat silt couplets indicates no net emergence over multiple earthquake cycles glacio isostatic movements from little ice age glacier advance and retreat explains a 0 15 m relative sea level oscillation recorded within the peat layer subsequently submerged as a result of the ad 1964 earthquake before both this and the 850 cal yr bp earthquake diatom assemblages suggest pre seismic relative sea level rise of 0 12 0 13 m representing possible precursors to great earthquakes

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes