distribution of calcareous dinoflagellates from the maastrichtian to early miocene of dsdp site 357 rio grande rise western south atlantic ocean the evolution of calcareous dinoflagellate communities has been investigated for the latest cretaceous to earliest neogene interval of the mid latitude south atlantic in doing so the response of calcareous dinoflagellates to cenozoic climatic change has been addressed for the first time trends in species composition and distribution patterns of wall types indicate significant changes which correlate with major palaeoenvironmental modifications a first major shift concerning the relative abundance of species and wall types occurred across the cretaceous tertiary boundary the associations remained stable during the entire paleocene and eocene only in the late eocene did a dramatic decrease in temperature cause a slight diversification a second major shift in the abundance patterns occurred across the eocene oligocene boundary the early miocene warming is possibly reflected in the distinct increase in relative abundance of one species the assemblages of calcareous dinoflagellates evidently react to major climatic changes during the cenozoic these poorly investigated organisms may thus provide an important contribution to the understanding of earth s palaeoclimatic evolution

suspended sediment transport in the surf zone response to cross shore infragravity motion a field experiment to investigate the magnitude and temporal and spatial scales of suspended sediment transport in the inner surf zone was conducted at san marine oregon on october 7 13 1984 instrumentation consisted of five electromagnetic current meters three strain gauge type pressure transducers and 25 optical backscatter sensors to measure the concentrations of suspended sediment the instruments were deployed approximately 70 m x seaward of the mean high water line mean depth h 1 1 1 3 m in a closely spaced cross shaped pattern data were collected for 68 min periods spanning high tide during the 7 day experiment during the experiment waves varied in angle of approach from shore normal to southwesterly offshore significant swell heights were 3 5 m with periods of 12 14 s local sea conditions with wind waves of approximately 8 s also occurred a visual estimation of the width of the surf zone indicated it to be approximately 500 m and the breaker pattern suggested that there were two longshore bars at approximately 200 and 500 m offshore the data resulting from the experiment encompass a broad range of wave and current conditions which included periods of extreme infragravity motion 30 t 300 s and weak longshore currents and periods of low infragravity motion and strong longshore currents periods of incident wave dominance also occurred the field study section of this paper qualitatively describes the sediment response to strong 240 cm s 1 low frequency 0 01 hz cross shore fluid motions which dominated the inner surf zone during two of the data runs the infragravity band accounted for 85 of the cross shore velocity variance the peak 0 01 hz of which was associated with shore normal standing waves concentration gradients of suspended sediment appear to be associated with diffusive processes and develop and decay on time scales of the infragravity motions rather than those of incident waves suspension events during times of infragravity dominance often persisted for periods of 30 45 s and reached peak concentrations of 20 40 g l 1 at elevations in excess of 26 cm mean suspended load was 3 4 times larger than that associated with incident wave motions the modeling section of the paper attempts to quantitatively describe the observed time dependent vertical suspended sediment distribution with a one dimensional turbulent diffusion model formulations of eddy diffusion and erosion rate coefficients associated with peak cross shore flows are found to agree with or fall within the range of values from previous laboratory and field studies and are used in the model the model is evaluated by its ability to reproduce the time dependent vertical distribution of suspended sediment and to estimate the observed mean suspended load and the correct direction and magnitude of the mean longshore and cross shore flux level above the bed z 31 cm of suspended sediment

global dinoflagellate event associated with the late paleocene thermal maximum the late paleocene thermal maximum or lptm ca 55 ma represents a geologically brief time interval 220 k y characterized by profound global warming and associated environmental change the lptm is marked by a prominent negative carbon isotope excursion cie interpreted to reflect a massive and abrupt input of 12 c enriched carbon to the ocean atmosphere reservoir possibly as a result of catastrophic gas hydrate release on time scales equivalent to present day rates of anthropogenic carbon input the lptm corresponds to important changes in the global distribution of biota including mass extinction of marine benthic organisms the dinoflagellate cyst record indicates that surface dwelling marine plankton in marginal seas also underwent significant perturbations during the lptm we report on the dramatic response of representatives of the genus apectodinium from two upper paleocene lower eocene sections in the southern new zealand and northern austria hemispheres where the dinoflagellate records are directly correlated with the cie benthic foraminifera extinction event and calcareous nannofossil zonation the results indicate that the inception of apectodinium dominated assemblages appears to be synchronous on a global scale and that the event is precisely coincident with the beginning of the lptm apectodinium markedly declined in abundance near the end of the lptm this apectodinium event may be associated with 1 exceptionally high global sea surface temperatures and or 2 a significant increase in marginal marine surface water productivity such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record

global cooling accelerated by early late eocene impacts at ocean drilling program site 689 maud rise southern ocean 18o records of fine fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late eocene extraterrestrial impact events a simultaneous surface water productivity increase as interpreted from 13c data is explained by enhanced water column mixing due to increased latitudinal temperature gradients these isotope data appear to be in concert with organic walled dinoflagellate cyst records across the same microkrystite bearing impact ejecta layer in the mid latitude massignano section central italy in particular the strong abundance increase of thalassiphora pelagica is interpreted to indicate cooling or increased productivity at massignano because impact induced cooling processes are active on time scales of a few years at most the estimated 100 k y duration of the cooling event appears to be too long to be explained by impact scenarios alone this implies that a feedback mechanism such as a global albedo increase due to extended snow and ice cover may have sustained impact induced cooling for a longer time after the impacts

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

maximum steepness of oceanic waves field and laboratory experiments 1 the breaking of waves is an important mechanism for a number of physical chemical and biological processes in the ocean intuitively waves break when they become too steep unfortunately a general consensus on the ultimate shape of waves has not been achieved yet due to the complexity of the breaking mechanism which still remains the least understood of all processes affecting waves to estimate the limiting shape of ocean waves here we present a statistical analysis of a large sample of individual wave steepness data were collected from measurements of the surface elevation in laboratory facilities and the open sea under a variety of sea state conditions observations reveal that waves are able to reach steeper profiles than the stokes limit for stationary waves due to the large number of records this finding is statistically robust

end cretaceous marine mass extinction not caused by productivity collapse an asteroid impact at the end of the cretaceous caused mass extinction but extinction mechanisms are not well understood the collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity strangelove ocean or export productivity living ocean which caused mass extinction higher in the marine food chain phytoplankton dependent benthic foraminifera on the deep sea floor however did not suffer significant extinction suggesting that export productivity persisted at a level sufficient to support their populations we compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the pacific southeast atlantic and southern oceans we conclude that end cretaceous decrease in export productivity was moderate regional and insufficient to explain marine mass extinction a transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites and recovery of productivity may have been as fast in the oceans as on land

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

spatial distribution of the calcareous dinoflagellate thoracosphaera heimii in the upper water column of the tropical and equatorial atlantic the horizontal and vertical distribution of the phototrophic calcareous dinoflagellate thoracosphaera heimii in the upper part of the water column 10 200 m of the equatorial and tropical atlantic ocean has been studied this first survey has been made to determine which part of the water column is inhabited by t heimii and is subsequently represented as a signal in the sediment record by this species the study concentrates on the fossilisable vegetative coccoid life stage of the species and differentiates between t heimii shells with cell content and empty ones the highest quantities of t heimii shells with cell content have been observed in water depths between 50 and 100 m and coincide with relatively lower temperatures and relatively higher salinities than respective surface conditions we propose that in the tropical equatorial atlantic the major part of the environmental signal given by t heimii can be assumed to represent the deeper levels of the upper water column

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

the effect of wave induced turbulence on the ocean mixed layer during tropical cyclones field observations on the australian north west shelf 1 field observations of water temperature on the australian north west shelf eastern indian ocean with the support of numerical simulations are used to demonstrate that the injection of turbulence generated by the wave orbital motion substantially contributes to the mixing of the upper ocean measurements also show that a considerable deepening of the mixed layer occurs during tropical cyclones when the production of wave induced turbulent kinetic energy overcomes the contribution of the current generated shear turbulence despite a significant contribution to the deepening of the mixed layer the effect of a background current and atmospheric forcing are not on their own capable of justifying the observed deepening of the mixed layer through most of the water column furthermore variations of a normally shallow mixed layer depth are observed within a relatively short timescale of approximately 10 hours after the intensification of wave activity and vanish soon after the decay of storm surface waves this rapid development tends also to exclude any significant contribution by wave breaking as small rates of vertical diffusivity for wave breaking induced turbulence would require longer timescales to influence the depth of the mixed layer

the cretaceous paleogene transition at galanderud northern alborz iran a multidisciplinary approach abstract we investigated the cretaceous paleogene k pg transition at the galanderud section northern alborz iran to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little studied area of the eastern tethys we applied a high resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages clay mineralogy rock magnetic properties stable isotopes and geochemistry in this section the k pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer a marked decrease in magnetic susceptibility a negative 2 2 13c excursion and a peak in iridium in the uppermost maastrichtian foraminifera are well preserved and diversified suggesting a stable mesotrophic environment by contrast the k pg boundary and basal danian is marked by high values of epifaunal benthic morphogroups low planktic diversity and high percentages of opportunistic species guembelitria cretacea and cervisiella operculata suggesting highly stressed and variable conditions partly due to the dramatic collapse of calcareous primary producers benthic foraminiferal assemblages indicate outer neritic uppermost bathyal depths with slight bathymetric variations the most peculiar and unique aspect of the galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the k pg boundary each marked by positive shifts in 13c and 18o values and consisting of 80 carbonate we propose that the chalk clay deposits in the basal danian reflect changes in seawater chemistry and dynamic changes in circulation upwelling alternating with episodes of enhanced weathering and runoff this section on the northern margin of eastern tethys provides new clues about the pattern of the k pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase

middle eocene to early oligocene paleoceanography of the antarctic ocean maud rise odp leg 113 site 689 change from a low to a high productivity ocean the sediment record from the middle eocene about 45 ma to the early oligocene about 33 ma on maud rise site 689 weddell sea paleodepth 1400 1650 m has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria diatoms benthonic and planktonic foraminifers sponge debris ostracods and echinoids accumulation rates of bolboforma spp vary parallel to these proxies productivity increased with time three episodes were found in which productivity increased sharply and productivity varied cyclically with a period of 430 ky the middle eocene ca 45 44 37 26 ma was a period of generally low productivity no opal was deposited and carbonate preservation was excellent during periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers ostracods and echinoids increased in spite of an increase in carbonate dissolution in the period ca 41 62 43 07 ma productivity rose in three distinct pulses clinoptilolite formed from biogenous opal is a common mineral in these sediments these three productivity maxima coincide with a mica rich unit mica probably originated from erosion on antarctica and was transported by an intermediate water depth current in the late eocene ca 36 9 34 95 ma productivity increased considerably and opal skeletons were deposited carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity because productivity increase exceeded or equalled rises in dissolution rates increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers sponge debris ostracods and echinoids in the late eocene early oligocene period 34 95 33 05 ma a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods the productivity increase is probably due to the increasing pole equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans in the uppermost late eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at site 689 a sediment interval with especially well preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity these intervals suggest a change in bottom water conditions from warm saline deep water wsdw which favors carbonate preservation to antarctic bottom water aabw which promotes carbonate dissolution cooling of surface waters over a period of 300 ky led to a thickening of the deep aabw layer and an upward shift of the overlying wsdw until the aabw finally reached the top of the maud rise in the area of site 689 this period of aabw influence on top of the maud rise lasted 200 ky

statistical analysis of bed thickness patterns in a turbidite section from the great valley sequence cache creek northern california abstract this paper explores the use of a monte carlo adaptation of runs analysis to analyze turbidite sequences for the presence of asymmetric bed thickness cycles waldron s test can be used to identify sequences that are dominated by either upward thickening or upward thinning cycles but not both our adaptation of runs analysis provides a robust technique that can indicate the presence of local thickness trends that are different from those expected in random sequences and can be used to evaluate the relative importance of upward thickening and upward thinning cycles as a case study 236 m of the upper cretaceous sites formation in the great valley group were measured and described in detail along cache creek in northern california this section had been previously interpreted as a s ccession of prograding submarine fan lobe deposits marked by asymmetric upward thickening cycles application of waldron s test indicates that the section is not dominated by upward thickening cycles as previously suggested monte carlo runs analysis demonstrates that small scale upward thinning cycles are as common as upward thickening cycles the simple progradation of submarine fan lobes does not adequately explain the thickness patterns seen in the section application of monte carlo runs analysis to other turbidite sections would be useful for quantitative identification and comparison of turbidite bed thickness cycles which should lead to development of better turbidite facies models

on the response of calcareous dinoflagellates to oligotrophy and stratification of the upper water column in the equatorial atlantic ocean abstract large numbers of calcareous dinoflagellate cysts and the vegetative calcareous coccoid species thoracosphaera heimii are generally found in sediments underlying oligotrophic and or stratified sub surface water environments it is difficult to distinguish between the relative importance of these two environmental parameters on calcareous cyst and t heimii distribution as they usually covary but this information is essential if we want to apply cysts properly in the reconstruction of palaeoenvironments and past surface water hydrography in the multi proxy core geob 1523 1 from the ceara rise region in the western equatorial atlantic ocean covering the past 155 ka periods of greatest oligotrophy are not synchronous with periods of greatest stratification ruhlemann et al mar geol 135 1996 127 152 mulitza et al geology 25 1997 335 338 mulitza et al earth planet sci lett 155 1998 237 249 giving us the unique opportunity to differentiate between the effects of both parameters on cyst accumulation the calcareous cyst record of the core reflects prominent increases in accumulation rate of nearly all observed species only during the nutrient enriched but more stratified isotopic sub stages 5 5 5 3 5 1 and 1 in this respect the distribution trends in the core are more similar to those of the eastern equatorial upwelling region geob 1105 4 than they are to those of the oligotrophic north eastern brazilian continental slope geob 2204 2 even though temporal changes in bioproductivity are principally in antiphase between the eastern and western equatorial regions we conclude that stratification of the upper water column and the presence of a well developed thermocline are probably the more important factors controlling cyst distribution in the equatorial atlantic whereas the state of oligotrophy secondarily influences cyst production within a well stratified environment

suitability of stable oxygen and carbon isotopes of calcareous dinoflagellate cysts for paleoclimatic studies evidence from the campanian maastrichtian cooling phase abstract in order to determine the possible usefulness of stable isotope measurements on calcareous dinoflagellate cysts for paleoceanographic and paleoclimatic studies we have produced oxygen and carbon isotope records of the species pirumella krasheninnikovii bolli h m 1974 jurassic and cretaceous calcisphaerulidae from dsdp leg 27 eastern indian ocean initial reports of the deep sea drilling project 27 843 907 for the latest campanian to earliest maastrichtian 73 68 ma of high latitude ocean drilling program hole 690c in the southern south atlantic eastern weddell sea foraminiferal stable isotope values characterize this time interval as a phase of continuous cooling superimposed by a short term strong cooling event between 71 and 70 ma that was detected at various sites in the mid to high latitudes this event is interpreted to reflect short term surface water cooling leading to changes in the mode and direction of deep water formation and possibly the growth of continental ice sheets our 18o values of calcareous cysts verify this event as well as the general cooling of surface waters during the latest campanian and early maastrichtian prior to this cooling event between 72 and 71 ma a negative excursion in accompanying 13c records of planktic and benthic foraminifera was observed this negative excursion and the subsequent positive one were proposed to reflect sea level fluctuations changes in productivity and or changes in the ratio of organic to inorganic carbon input to the ocean the 13c values of calcareous cysts show the positive excursion between 71 and 70 ma but don t show the expected negative excursion before in addition they yield extremely light carbon isotope values that probably resulted from photosynthetic processes as the stable oxygen isotope data of the calcareous dinoflagellate species p krasheninnikovii show isotopic shifts comparable to planktic foraminifera from the same locality and from various other sites in the pacific and south atlantic oceans we suggest that calcareous cyst oxygen isotopes can provide information for paleoceanographic reconstructions of sea surface water temperatures and paleoceanographic changes however the application of carbon isotope data from cysts of p krasheninnikovii appears to be questionable and investigations of different species are needed to further evaluate the reconstruction potential based on stable isotopes and to assess species specific vital effects

on the interaction between wind stress and waves wave growth and statistical properties of large waves abstractstatistical properties and development of wave fields with different wind forcings are investigated through parametric laboratory experiments thirty different random sea states simulated

palaeoenvironmental changes of the early pliocene zanclean in the eastern mediterranean pissouri basin cyprus evidenced from calcareous dinoflagellate cyst assemblages abstract the first 100 ka of the earliest pliocene zanclean sediments of the eastern mediterranean pissouri basin on cyprus have been investigated on calcareous dinoflagellate cyst assemblages these assemblages reflect the return in three phases to the open oceanic conditions following the messinian salinity crisis msc 5 33 ma ago the lowermost phase dominated by leonella granifera cysts indicates substantial land derived nutrient supply and low salinities this confirms earlier observations of enhanced continental water runoff during the earliest pliocene in the eastern mediterranean basin the second phase dominated by caracomia stella and calciodinellum albatrosianum cysts indicates a change to warmer meso to oligotrophic waters the third phase marks the first appearance and still continuing dominance of thoracosphaera heimii in the region in addition the endemic eastern mediterranean species lebessphaera urania peaks within this upper interval it probably survived the salinity crisis in the mediterranean the assemblage reflects the establishment of typical open marine well stratified and oligotrophic surface conditions similar but not yet identical to the situation in the mediterranean sea today this study points out a discrepancy between the fast refilling scenario 1 2 ka in the pissouri basin and a long time 100 ka environmental reorganisation in the surface waters as indicated by the calcareous dinoflagellate cysts the onset of the pliocene is also marked by the first appearance of calciodinellum elongatum and calciodinellum levantinum which must have migrated from the atlantic ocean

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

sharp crested breaking surface waves observed from a ship based stereo video system abstracta new ship based stereo video system is used to observe breaking ocean waves i e whitecaps as three dimensional surfaces evolving in time first the stereo video measurements of all waves breaking and nonbreaking are shown to compare well with statistical parameters from traditional buoy measurements next the breaking waves are detected based on the presence of whitecap foam and the geometry of these waves is investigated the stereo measurements show that the whitecaps are characterized by local extremes of surface slope though the larger scale crest to trough steepness of these waves is unremarkable examination of 103 breaking wave profiles further demonstrates the pronounced increase in the local wave steepness near the breaking crest as estimated using a hilbert transform these crests are found to closely resemble the sharp corner of the theoretical stokes limiting wave results suggest that nonlinear wave group dynamics are a key mechanism for breaking as the phase speed of th

clustering of earthquake events in the himalaya its relevance to regional tectonic set up abstract the earthquake events of himalaya of magnitude 5 0 from the time window 1905 2000 are statistically analysed the inter event time between earthquakes shows hurst phenomena of temporal clustering which are spatially located in five distinct domains along the himalayan fold thrust belt out of these two domains one around uttaranchal nepal border and the other around nepal sikkim border reveal maximum number of temporal clusters and thus considered as seismically most potential zones of the himalaya both these zones are located at the interface of the orthogonally disposed major tectonic discontinuities of the peninsular shield and himalayan fold thrust belt such zones are geologically most favourable locales for strain accumulation during later tectonic movement statistical analysis points towards a probability of recurrence of seismic events in near future in these two zones however validity of such statistical results can be ascertained by detailed geological and geophysical modelling of the terrain

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

a statistical test for significance of thinning and thickening upwards cycles in turbidites abstract in turbidite successions asymmetric cycles identified in vertical sections are often used as indicators of sedimentary processes in submarine fan models thickening and coarsening upwards cycles are thought to characterize depositional lobes whereas thinning and fining upwards cycles are believed to be produced by filling and abandonment of channels a non parametric statistical test based on the signs of differences between consecutive bed thickness values may be used to determine whether the cycles in a particular measured section are statistically significant the test can be modified to deal with bed thickness values that have been smoothed by moving averages and with multiple partial sections in an incompletely exposed unit

new chronology for the late paleocene thermal maximum and its environmental implications the late paleocene thermal maximum lptm is associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle we have developed a new orbital chronology for ocean drilling program odp site 690 weddell sea southern ocean by using spectral analysis of high resolution geochemical records the lptm interval spans 11 precessional cycles yielding a duration of 210 to 220 k y the 13 c anomaly associated with the lptm has a magnitude of about 2 5 to 3 we show that about 2 of the excursion occurs within two steps that each were less than 1000 yr in duration the remainder developed through a series of steps over 52 k y the timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial further we are able to correlate the records between odp sites 690 and 1051 western north atlantic on the scale of 21 k y cycles which demonstrates that the details of the 13 c excursion are recognizable between distant sites comparison of cycle records at sites 690 and 1051 suggests that sediment representing the interval 30 k y just prior to and at the onset of the lptm are missing in the latter location this unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k y of the start of the lptm

statistical analysis of facies clustering in submarine fan turbidite successions abstract the hurst statistic converted easily into a fractal dimension quantifies the degree of clustering of high and low values in spatial or temporal series of data in an effort to better understand the stratigraphic organization of submarine fan deposits the hurst statistic was calculated for nineteen turbidite sections that span a wide range of geological time tectonic settings facies characteristics and depositional environments three bed by bed variables were considered coarse division thickness i e net thickness in a single bed of conglomerate sandstone siltstone grain size and coarse division thickness percentage relative to thickness of overlying mudstone caps sixteen of the 19 turbidite sections analyzed 84 2 show the hurst phenomenon i e irregular long term clustering of high and low values of the three bed by bed variables this clustering is related to stratigraphic changes of sedimentary facies caused by lateral shifting of sub environments on a submarine fan surface there is no evidence that the clustering is controlled by sea level fluctuations the strength of the clustering inferred from hurst k values holds promise as an index to distinguish submarine fan sub environments preliminary results suggest that channel levee deposits tend to have strong clustering lobe interlobe deposits tend to display moderate clustering and basin floor sheet sand systems tend to have weak clustering combining facies characteristics with these statistical results provides more reliable criteria for the identification of submarine fan sub environments than are available from recently discredited models based on asymmetric cycles of bed thickness or grain size

re interpretation of the age and environment of deposition of paleogene turbidites in the andaman and nicobar islands western sunda arc abstract turbidites composed of sandstone shale alternations on the kalipur shibpur coast north andaman island classified under the palaeocene eocene mithakhari group in several recent papers are identified as and compared with the type section of the oligocene andaman flysch exposed at corbyn s cove south andaman island the kalipur turbidites were interpreted as the inner fan and the latter as the distal mid fan facies of a forearc submarine fan the turbidites of these two locations are separated by 250 km detailed studies concerning the identification and comparison have however revealed significant differences and the turbidite outcrops are not continuous between these two localities turbidites at kalipur shibpur and adjacent areas are part of a melange terrane normally gritty and coarse grained massive to locally graded bedded calcareous intercalated interstratified with conglomerates and reefoidal limestones and show a framework composition varying from volcanolithic to lithic poor arkosic sandstones deposited in several isolated basins fed by transverse supply of detritus from an accreted and uplifted ophiolite and arc massif the kalipur shibpur coast exposes marginally deformed sandstone dominated turbidites coherent units containing abundant ichnotraces late palaeocene foraminifera and rip up shale clasts indicating deposition in shallow water accretionary slope basins south of kalipur the ramnagar coast exposes mud rich turbidites showing accretion related deformation these deformed turbidites are interpreted as offscraped trench deposits further south on the rampur coast turbidites intercalated with reefoidal limestones containing late palaeocene foraminifera indicate deposition on the upper slope or on top of the accretionary slope basin in contrast classical bouma sequence bearing sandstone shale turbidites at corbyn s cove are part of a continuous outcrop belt of siliciclastic turbidites lack fossils carbonate facies and conglomerates and consist of compositionally uniform greywackes deposited in an open deep sea fan fed by axially transported detritus derived from the continental blocks of western burma these key differences together with previous mapping and stratigraphic studies confirm the incorrect identification of andaman flysch in north andaman island in recent papers the turbidites of these two locations were neither produced by the same sediment gravity flows nor deposited in the same forearc fan during the oligocene instead they were derived from different palaeographic domains deposited in different tectonic and sedimentary environments and also at different times this provides new insights into the paleogene turbidite deposition in this part of western sunda arc

a scale comparison of waves breaking on a beach abstract a measurement programme conducted in a small scale wave flume which comprised the breaking of periodic and random waves on a gently sloping beach was partly repeated in a large scale wave flume the results are used here to make a scale comparison the quantities considered in the comparison are wave heights set up and vertical profiles of maximum seaward maximum shoreward and time mean horizontal velocities it appears that both qualitatively and quantitatively scale effects in these quantities are virtually absent in the wave height range of 0 1 m to 1 5 m

anatomy of a forearc submarine fan upper eocene oligocene andaman flysch group andaman islands india abstract detailed facies analysis in the upper eocene oligocene andaman flysch group reveals fourteen different facies grouped into three different associations these facies associations represent two anatomical divisions of a submarine fan viz inner fan and depositional lobe in middle fan paleocurrent pattern high percentage of quartz in the sandstones and outer arc derived clasts in the inner fan channel conglomerates suggest dual sediment supply in this fan a longitudinal geometry of the basin has been inferred where juxtaposition of sediments of different proximality deterred development of any definite sequence pattern a tectonically induced active sediment supply in a rising sea level stand is thought to be responsible for development of the fan

a study of radiation stress and set up in the nearshore region abstract in this paper the variations of radiation stress and mean water level are studied for the two dimensional shoaling and breaking of progressive periodic waves on a plane gently sloping laboratory beach observations of radiation stress and mean water level were made for two initial conditions the observed variations are compared to the variations as calculated by a linear theory james nonlinear theory and a new nonlinear theory based on cokelet s work it is shown that the nonlinear theories are qualitatively and quantitatively superior to the linear theory thus indicating that the effects of finite amplitude are important for the present case

statistical appraisal of bed thickness patterns in turbidite successions andaman flysch group andaman islands india abstract the bed thickness distribution of two turbidite successions in the oligocene andaman flysch group india which differ in terms of their paleogeography and sediment supply has been assessed statistically the purpose was to evaluate depositional cyclicity using the non parametric waldron test and also to assess possible environmental control on the bed thickness magnitude distribution both sections reveal a positively skewed distribution in bed thickness patterns the z value obtained through waldron s test failed to reject the null hypothesis of randomness and thus discards a cyclic pattern juxtaposition of sediments of different proximalities in an elongated forearc fan complex is the possible cause for this absence of cyclicity the studied sections however differ in their bed thickness magnitude distribution slope turbidite successions with sediment supply solely from the outer arc reveals a scaling behavior while the outer fan succession with mixing of sediments from different sources show a negative exponential distribution this highlights the possible control of the depositional system and sediment supply on the bed thickness magnitude distribution of turbidite successions irrespective of the triggering mechanism unequivocal application of the power law distribution in turbidite successions demands reconsideration

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

eocene paleoceanographic evolution at 20 30 s in the atlantic ocean abstract oceanographic changes in eocene bottom water have been traced with oxygen and carbon isotope values and gradients and benthic foraminiferal assemblages the south atlantic sections chosen for this study are located on an east west traverse depositional depths range from middle bathyal through abyssal the dsdp sites are located on the walvis ridge site 363 in the angola basin sites 522 523 the brazil basin site 19 hole 20c and on the rio grande rise site 357 in abyssal sites of the south atlantic the eocene bottom water environment can be divided into two distinct regimes the early eocene and the late eocene the middle eocene is transitional faunal distribution pattern indicate that source areas where bottom water formed were probably different between the two regimes during the early eocene warm saline water formed possibly in the tethyan ocean east of gibraltar there is good evidence that the late eocene bottom water of the south atlantic recorded at lower bathyal down to middle abyssal environments was formed in southern high latitude regions first invasion of cooler bottom water is recorded at upper abyssal depths around 46 ma earliest zone p12 site 19 from 40 ma late zone p15 onwards this signal is recorded at all sites except middle bathyal depth site 357 selected faunal parameters allow reconstruction of bottom water oxygenation episodically increased abundance of epifaunal species indicate a renewal of the bottom water accompanying these faunal changes 13 c values of benthic foraminefera increase whereas vertical 13 c benthic planktonic foraminifera gradients decrease

statistical properties of mechanically generated surface gravity waves a laboratory experiment in a three dimensional wave basin a wave basin experiment has been performed in the marintek laboratories in one of the largest existing three dimensional wave tanks in the world the aim of the experiment is to investigate the effects of directional energy distribution on the statistical properties of surface gravity waves different degrees of directionality have been considered starting from long crested waves up to directional distributions with a spread of 30 at the spectral peak particular attention is given to the tails of the distribution function of the surface elevation wave heights and wave crests comparison with a simplified model based on second order theory is reported the results show that for long crested steep and narrow banded waves the second order theory underestimates the probability of occurrence of large waves as directional effects are included the departure from second order theory becomes less accentuated and the surface elevation is characterized by weak deviations from gaussian statistics

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

numerical study of three dimensional overturning waves in shallow water simulations in a three dimensional numerical wave tank are performed to investigate the shoaling and breaking of solitary waves over a sloping ridge the numerical model solves fully nonlinear potential flow equations with a high order boundary element method combined with an explicit time integration method expressed in a mixed eulerian lagrangian formulation analyses of shoaling and breaking wave profiles and kinematics both on the free surface and within the flow are carried out it is observed that the transverse modulation of the ridge topography induces threedimensional effects on the time evolution shape and kinematics of breaking waves comparisons of two and three dimensional results in the middle cross section of the ridge however show remarkable similarities especially for the shape and dynamics of the plunging jet

central arctic ocean paleoceanographic interpretations based on late cenozoic calcareous dinoflagellates abstract four calcareous dinoflagellate morphotypes interpreted to represent a single species thoracosphaera arctica n sp occur in upper miocene to holocene sediments of the central arctic ocean the calcareous fossils generally are rare except during one interval that of the latest pliocene to late pleistocene during this interval the fossil dinoflagellates were alternately abundant and rare in approximate coordination with greater and lesser times of foraminifera productivity dinoflagellates and foraminifera generally are rare during times of accumulation of abundant coarse textured ice rafted sediment during this interval the life cycle of the dinoflagellate that produces the arctic ocean calcareous fossil is unknown but the fossils probably are either resting cysts motile vegetative cells or hypnozygotes a vegetative cell origin better explains the co occurrence of foraminifera as well as the negative correlation with ice rafting this tentative interpretation leads to the conclusion that during the interval 2 0 to 0 7 m y b p the arctic ocean had relatively productive surface waters with very thin or even periodic absence of pack ice alternating with conditions more like that of the present during periods before 2 0 m y and since 0 7 m y the arctic ocean probably was ice covered with oceanographic conditions similar to that of the modern ocean these conclusions differ from previous interpretations that the arctic was continually ice covered had no surface productivity or was covered by a giant antarctic like ice cap

analysis of surf zone turbulence measurements of turbulent kinetic energy k under surf zone waves are analyzed to show how k varies over depth between breaker point and shoreline and how k depends on the beach slope it is found that the variation of k over depth is remarkably weak large values being measured a few percent of the depth above the bottom a simple model for the dissipation mechanism makes it possible to derive an empirical formula for the time averaged k that accurately describes all the data considered reliable

statistical analysis of turbidite bed thickness patterns from the alpine fold and thrust belt of western and southeastern greece abstract a statistical evaluation of turbidite bed thickness was performed for 11 turbidite successions which constitute part of foreland basins formed along the alpine fold and thrust belt of western and southeastern greece the purpose was to compare the results from this study with previously published investigations and discuss if and how statistical approaches could contribute to the environmental analysis of turbidite deposits in tectonically complex areas bed thickness datasets exhibit a clear non normal signal in their distribution behavior statistical analysis was focused on i fitting of widely used non normal theoretical distribution models using robust non parametric goodness of fit statistical tests and ii detecting the possible presence of asymmetric bed thickness cycles and or non random bed thickness clustering results indicate that the studied bed thickness datasets are well characterized by a bimodal lognormal distribution model probably reflecting deposition from both high and low density turbidity currents several datasets exhibit distributions characterized by power law tails exponential distribution types were not observed all datasets exhibit non random thinning upward bed thickness trends probably due to tectonically induced gravity flows proposed methods for identifying depositional sub environments using turbidite bed thickness statistics were found to have limited applicability observations of the present study may prove useful for the environmental analysis of turbidite deposits in fold and thrust belt areas characterized by limited outcrop exposures

statistical analysis of turbidite cycles in submarine fan successions tests for short term persistence abstract to statistically test and evaluate the significance of asymmetric upward thickening and thinning trends and other cyclic patterns in turbidite successions 28 bed by bed sections with a wide coverage in geological time tectonic settings facies characteristics and depositional environments were measured and described first 286 sandstone packets were selected from the 28 turbidite sections through statistically based segmentation then these packets were examined by three powerful correlation tests kendall s spearman s and pearson s correlation tests and four tests for randomness only 34 11 9 of the sandstone packets pass tests designed to identify asymmetry at the 10 significance level monte carlo simulation and calculation of cumulative binomial probabilities indicate that the number of asymmetric cycles identified in the original set of sandstone packets is indistinguishable from the number expected to result from random processes eighty six sandstone packets from five sections were tested for upward coarsening and fining trends forty two of these packets were from channel deposits and the rest from lobes and basin plain deposits only 25 29 of the 86 packets coarsen or fine upward however 33 50 of packets from coarse grained channel fills show asymmetric grain size trends mostly as upward fining cycles 15 of the 42 tested packets from channel deposits these upward fining trends in channel deposits are interpreted as the result of channel filling or the stacking of onlapping deposits at a channel mouth results from this study strongly suggest that asymmetric bed thickness cycles have essentially no statistical significance in turbidite successions and therefore cannot provide a key criterion for identification of sub environments in submarine fan systems it follows that models for submarine fans based on the widely publicized hypothesis of common asymmetric cycles should be reconsidered instead other criteria such as specific facies characteristics large scale geometry and degree of sand bed clustering may provide the best tools for discrimination of submarine fan sub environments in natural systems the disordered vertical arrangement of thicker and thinner beds likely results from irregular variations in flow volumes concentrations and precise pathways of turbidity currents over the short time scales represented by tens of meters of section most submarine fans are built by aggradation not progradation so that facies shifts are controlled mostly by channel switching and avulsion and not by progressive basinward or landward advance or retreat of one sub environment over another aggradation does not tend to generate asymmetric trends in bed thickness the same arguments are believed to hold for grain size trends in submarine fan packets except in the case of coarse grained channel deposits where upward fining is conspicuous

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

paleoceanographic and paleoclimatic evolution in the weddell sea antarctica during the middle eocene late oligocene from a coarse sediment fraction and clay mineral data odp site 689 abstract paleoceanographic and paleoclimatic variations from the middle eocene to the late oligocene in the antarctic area atlantic sector have been deduced from a coarse fraction and clay mineral analysis of odp site 689 leg 113 sediments in the middle eocene smectite rich sediments were a consequence of warm climate with alternating wet and dry seasons on the antarctic margins productivity in the maud rise area of the southern ocean was low no opal was deposited preservation of carbonate is very good carbonate preservation shows cyclic changes clinoptilolite is a common mineral at the middle late eocene boundary 40 8 ma productivity suddenly increased enough to allow preservation of opal skeletons clinoptilolite disappeared where opal appeared illite appearance points to cooling of antarctic climates the presence of detrital kaolinite indicates a change in oceanic circulation in the late eocene cyclic changes in productivity cycle length 0 42 ma were associated with clay mineral compositional variations sediments from colder highly productive periods generally contain more illite and less smectite than warmer ones the early oligocene was a period of very high productivity highest opal accumulation rates correspond to strongest carbonate dissolution cyclic changes in productivity with a mean cycle duration of 0 4 0 5 myr were associated with cyclic changes in clay mineral composition highest productivity intervals are generally those with highest smectite content because of strong erosion of sediments of the antarctic margins sediments from less productive warmer periods most of the time contain more illite in the late oligocene the intensity of physical weathering on antarctica was stronger as documented by increasing fluxes of illite muscovite amphiboles and talc ice expanded on the east antarctic continent lower productivity than in the early oligocene is indicated by lower accumulation rates of opal and weaker carbonate dissolution cyclic variations in productivity correlate to cyclic variations in illite and smectite contents as in the early oligocene

calcareous dinoflagellate associations and maastrichtian tertiary climatic change in a high latitude core odp hole 689b maud rise weddell sea abstract the distribution of calcareous dinoflagellates has been analysed for the maastrichtian miocene interval of ocean drilling project hole 689b maud rise weddell sea the investigation thus represents a primary evaluation of the long term evolution in high latitude calcareous dinoflagellate assemblages during the transition from a relatively warm late cretaceous to a cold neogene climate major assemblage changes during this interval occurred in characteristic steps 1 an increase in relative abundance of tangentially structured species particularly operculodinella operculata at the cretaceous tertiary boundary 2 a diversity decrease and several first and last appearances across the middle late eocene boundary possibly attributed to increased climate cooling 3 a diversity decrease associated with the dominance of calciodinellum levantinum in the late early oligocene 4 the reappearance and dominance of pirumella edgarii in the early miocene probably reflecting a warming trend 5 monogeneric assemblages dominated by caracomia spp denoting strong middle miocene cooling the results not only extend the biogeographic ranges of many taxa into the antarctic region but also indicate that the evolution of high latitude calcareous dinoflagellate assemblages parallels the changing environmental conditions in the course of the cenozoic climate transition therefore calcareous dinoflagellates contribute to our understanding of the biotic effects associated with palaeoenvironmental changes and might possess the potential for reconstructing past conditions the flora in the core includes one new taxon caracomia arctica forma spinosa hildebrand habel and streng forma nov additionally two new combinations are proposed fuettererella deflandrei kamptner 1956 hildebrand habel and streng comb nov and fuettererella flora futterer 1990 hildebrand habel and streng comb nov

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

carbon isotope evidence for unusual plankton blooms and fluctuations of surface water co2 in strangelove ocean after terminal cretaceous event abstract a decrease in 13c kerogen by 3 and increase in 13c carbonate kerogen by 1 2 has been observed in sediments at the k t boundary substantiating the occurrence of a strangelove ocean wherein dissolved co2 was enriched in 12c because of mass mortality or reduced plankton production a subsequent increase in 13c kerogen by 7 and decrease in 13c carbonate kerogen by 5 4 indicate a dramatic reduction in pco2 this decrease could be the consequence of depletion of co2 in surface waters because of unusual plankton blooms these environmental changes which characterize the strangelove ocean occurred after the terminal cretaceous event during this time rapid fluctuations in dissolved co2 of ocean surface waters may have caused significant perturbations in atmospheric pco2 levels and consequently major instability of the global climate

the cretaceous tertiary biotic transition mass extinctions are recognized through the study of fossil groups across event horizons and from analyses of long term trends in taxonomic richness and diversity both approaches have inherent flaws and data that once seemed reliable can be readily superseded by the discovery of new fossils and or the application of new analytical techniques herein the current state of the cretaceous tertiary k t biostratigraphical record is reviewed for most major fossil clades including calcareous nannoplankton dinoflagellates diatoms radiolaria foraminifera ostracodes scleractinian corals bryozoans brachio pods molluscs echinoderms fish amphibians reptiles and terrestrial plants macrofossils and palynomorphs these reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the k t biotic crisis available results suggest that many faunal and floral groups ostracodes bryozoa ammonite cephalopods bivalves archosaurs were in decline throughout the latest maastrichtian while others diatoms radiolaria benthic foraminifera brachiopods gastropods fish amphibians lepidosaurs terrestrial plants passed through the k t event horizon with only minor taxonomic richness and or diversity changes a few microfossil groups calcareous nannoplankton dinoflagellates planktonic foraminifera did experience a turnover of varying magnitudes in the latest maastrichtian earliest danian however many of these turnovers along with changes in ecological dominance patterns among benthic foraminifera began in the latest maastrichtian improved taxonomic estimates of the overall pattern and magnitude of the k t extinction event must await the development of more reliable systematic and phylogenetic data for all upper cretaceous clades

wave follower field measurements of the wind input spectral function part iii parameterization of the wind input enhancement due to wave breaking abstract this is the third in a series of papers describing wave follower observations of the aerodynamic coupling between wind and waves on a large shallow lake during the australian shallow water experiment auswex it focuses on the long standing problem of the aerodynamic consequences of wave breaking on the wind wave coupling direct field measurements are reported of the influence of wave breaking on the wave induced pressure in the airflow over water waves and hence the energy flux to the waves the level of forcing measured by the ratio of wind speed to the speed of the dominant spectral peak waves covered the range of 3 7 the propagation speeds of the dominant waves were limited by the water depth and the waves were correspondingly steep these measurements allowed an assessment of the magnitude of any breaking induced enhancement operative for these field conditions and provided a basis for parameterizing the effect overall appreciable levels of wave breaking occurred for the strong win

facies clustering in turbidite successions case study from andaman flysch group andaman islands india abstract bed thickness data of two turbidite sections viz corbyn s cove section south andaman and kalipur section north andaman those belong to oligocene andaman flysch group a forearc submarine fan system were assessed for facies clustering employing hurst statistics both the sections show hurst phenomenon and reveal clustering in terms of thick and thin beds forcing behind event bed depositions in either of the studied sections was assessed statistically and inferred to be non random and with cyclicities of irregular physical length the inferred paleogeography through hurst criteria though worked well for distal fan setting i e basin floor sheet sandstones of corbyn s cove section its unequivocal application in proximal fan deposits remains to be tested the mismatch in paleogeographic interpretation between hurst test result lobe interlobe and field observation channel levee for the inner fan deposit is explained through differential facies stacking between fans grow in sea level lowstand and highstand lower bed amalgamation poor sand to mud ratio and subordinately present thick event deposits may be the result of active growth of andaman flysch fan in sea level highstand and expressed in lower hurst k value for inner fan channel levee association kalipur section compared to many of the channel levee deposits of lowstand fan systems observed world over

palaeoenvironmental information gained from calcareous dinoflagellates the late quaternary eastern and western tropical atlantic ocean in comparison abstract the environmental preferences of calcareous dinoflagellates have been investigated over the last 140 ka by comparing material from two sediment cores one from the highly productive equatorial divergence of the eastern atlantic ocean and the other from the low productivity western tropical atlantic ocean pronounced differences in palaeoproductivity between the two sediment cores are indicated by high and variable organic carbon accumulation rates in the east in contrast to relatively constant and low values in the west calcareous dinoflagellates show just the opposite pattern high accumulation rates in the west and lower in the east at the equatorial divergence temporal variations of calcareous dinoflagellate and organic carbon accumulation rates show for the most part an inverse relationship high calcareous dinoflagellate content coincides with low organic carbon accumulation rates and vice versa in the investigated region and time interval enhanced production of calcareous dinoflagellates can be correlated to periods of reduced palaeoproductivity probably related to relatively stratified conditions of the upper water column

large eddy simulation of spilling and plunging breakers abstract a navier stokes solver with a free surface model is used for simulating wave breaking undertow and turbulence in breaking waves the free surface model is based on the volume of fluid concept turbulence scales larger than the grid scale are simulated directly while turbulence scales smaller than the grid scale are represented by a sub grid scale model two different approaches for the sub grid scale model have been applied which are the smagorinsky model and a model based on a k equation for the sub grid scale turbulence the waves approach the shore in shore normal direction and break on a plane constant sloping beach periodic spilling and plunging breakers are simulated for 20 and 16 wave periods respectively the set up undertow and turbulence levels are compared to experimental results despite the rather coarse resolution of the computational domain satisfactory results for the wave height decay and undertow have been obtained however the turbulence levels are over predicted when using the standard values of the model parameters and a complete answer to this problem has not been found furthermore the evolution of vorticity over the wave period has been studied it shows that at the initial breaking point vorticity is generated around the vertical as well as around the transverse axis later vorticity around the longitudinal axis offshore onshore direction is generated probably through deformation of vorticity around the other axis

the miocene palaeoenvironmental and palaeoceanographic evolution of the gippsland basin southeast australia a record of southern ocean change abstract the gippsland basin in southeastern australia preserves up to 2 5 km thick tertiary to recent marine carbonate sediments included in the seaspray group during the neogene the seaspray group carbonates of the mackerel and flounder petroleum fields lay at the shelfal to bathyal palaeoenvironmental transition an ideal palaeoceanographic setting to study the neogene history of events in the evolving southern ocean seismic foraminiferal and facies analyses of the miocene seaspray group sediments at the mackerel 1 and flounder 1 wells have revealed the following palaeoenvironmental history of the area relatively cool to temperate upwelling conditions prevailed in the area during the earliest miocene during this time low energy upper slope globigerina ooze calcareous mudstone was deposited in the oxygen minimum zone during the early to lower middle miocene upper slope marl was deposited in oligotrophic conditions the presence of neritic subtropical foraminifera and abundant shallow and deep dwelling warm to cool temperate plankton in the upper slope suggests that warm poorly stratified oceanic conditions prevailed in the region this upper early miocene warm phase and mid miocene climatic optimum in gippsland corresponds to a time when global ocean conditions were much warmer and less vertically and latitudinally stratified than at present these oceanic conditions were associated with a reduced east antarctic ice sheet a higher sea level a relatively weak antarctic circumpolar current and weak atmospheric and wind driven circulation during the upper middle miocene to late miocene cool phase after c 14 5 ma strong upwelling and cooler oceanic conditions prevailed in the outer shelf to upper slope canyon facies in gippsland the occurrence of common deep dwelling plankton taxa in this interval suggests that regional oceanic conditions became more vertically stratified during this time from 14 5 and 5 million years ago the middle to late miocene palaeoenvironmental change recorded in seaspray group sediments corresponds to global cooling and major antarctic ice sheet expansion when the world s oceans became more vertically and latitudinally stratified from around 14 5 million years the transition from a warm miocene optimum to cooler oceanic conditions was associated with a strengthened antarctic circumpolar current and more intense wind driven atmospheric circulation in the southern ocean

turbidite bed thickness statistics of architectural elements in a deep marine confined mini basin setting examples from the gres d annot formation se france abstract statistical analysis of bed thickness was performed for sampled turbidite successions from well documented architectural elements of the gres d annot formation to characterize confined deep water mini basins of the tertiary foreland basin of se france the purpose was to use advanced statistical processing techniques in order to evaluate whether a discrimination of different architectural elements is feasible through observed statistical signatures of bed thickness statistical methods were focused on i fitting of widely used non normal theoretical distribution models using robust non parametric goodness of fit statistical tests and ii detecting the possible presence of non random bed thickness clustering using existing and new clustering estimation methods results indicate that the bed thickness data are best characterized by a multi modal lognormal distribution model which probably reflects a background sedimentological process several datasets exhibit power law as well as exponential thick bedded tails the data also exhibit non random clustering of bed thickness discrimination of architectural elements in this confined turbidite succession seems to be feasible based on the characteristics of the observed composite lognormal distributions such as number and variability of the detected components the estimation of the degree of facies clustering has potential for the discrimination of architectural elements in confined basin settings if used in conjunction with alternative estimation methods such as periodogram estimation this methodology may now be applied to other confined turbidite successions be they outcrops with less certain architecture or subsurface datasets with borehole imaging

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

rapid diversification of planktonic foraminifera in the tropical pacific odp site 865 during the late paleocene thermal maximum the planktonic foraminiferal generamorozovellaandacarininarapidly in 10 k y diversified during the late paleocene thermal maximum lptm giving rise to such morphotypes asm allisonensis new species m africana anda sibaiyaensis single specimen isotopicanalysisconfirmsthatm allisonensisanda sibaiyaensisarerestrictedtothelptm carbon isotope excursion recorded at ocean drilling program site 865 equatorial pacific ocean the short lived 50 to several 100 k y excursion taxa attest to the ephemeral effectsofthelptmonthecalcareousplankton single specimenoxygenisotopedatashow that evolution of m allisonensis and a sibaiyaensis was accompanied by migration to deeper water depths ancestralm velascoensisanda soldadoensiswere extremely rare or absent during the early stages of the lptm but immigrated back into the study area to coexist with their descendants in later lptm horizons photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the lptm

geodynamic evolution of the outer arc forearc belt in the andaman islands the central part of the burma java subduction complex the andaman islands the central part of burma java subduction complex expose tectonostratigraphic units of an accretionary prism in an outer arc setting and turbidites of a forearc setting a number of n s trending dismembered ophiolite slices of cretaceous age occurring at different structural levels with eocene trench slope sediments were uplifted and emplaced by a series of e dipping thrusts subsequently n s normal and e w strike slip faults resulted in the development of a forearc basin with deposition of oligocene and mio pliocene sediments metapelites and metabasics of greenschist to amphibolite grade occur in a melange zone of ophiolites the eocene mithakhari group represents pelagic trench sediments and coarser clastics derived from ophiolites evidence of frequent facies changes predominance of mass flow deposits syn sedimentary basinal disturbance and wide palaeogeographic variation indicate deposition of eocene sediments in isolated basins of an immature trench slope setting deposition of the oligocene andaman flysch group in a forearc setting is indicated by the large scale persistence of beds lack of small scale lithological variation bimodal provenance less deformation a well defined submarine fan sequence and development predominantly on the eastern part of the outer arc the mio pliocene archipelago group includes alternations of siliciclastic turbidites and subaqueous pyroclastic flow deposits in the lower part and carbonate turbidites in the upper part suggesting its deposition in the shallower forearc compared to the siliciclastic oligocene sediments

calcareous nannofossil and dinoflagellate stratigraphy across the cretaceous tertiary boundary at hor hahar israel in israel the cretaceous tertiary k t boundary at hor hahar occurs within the interval from the top of the ghareb formation maastrichtian to just below the horizon of dark marl and clay within the overlying taqiye formation paleocene the studied interval contains all the calcareous nannofossil zones micula prinsii latest maastrichtian markalius inversus np1 earliest paleocene andcruciplacolithus tenuis np2 early paleocene they correlate in sequence with theabathomphalus mayaroensis p0 p1a p1b and p1c planktic foraminiferal zones the palynological assemblages consist mainly of dinocysts with only few pollen grains and spores these assemblages are used to interpret five stratigraphic phases of environmental change across the k t boundary in the hor hahar section in the latest maastrichtian there is an overwhelming dominance of the nannofossilmicula decussata which probably reflects environmental stress preceding the terminal cretaceous mass extinction a nearshore marine environment at the boundary is suggested by the increase in number of specimens of the dinocystcyclonephelium and by the predominance of terrigenous organic matter sediment there followed two episodes of transgression and regression the calcareous cyst producing dinoflagellatethoracosphaera futterer 1976 becomes dominant in two episodes at the boundary and approximately one meter above it it alternates in abundance with the organic walled dinoflagellates which suggests that different environmental parameters were operating for each group maastrichtian dinocysts decline in abundance toward the k t boundary they reach greatest abundance and species diversity at the same strata where foraminiferids recover after their mass extinction at the boundary calcareous nannofossils recover only later in the early paleocene changes in 13c and total organic carbon as as well as dinocyst and nannofossil composition indicate an episode of strong ecological stress about one meter above the boundary

regional conductance map of andaman and nicobar region abstract to image the electrical conductivity distribution fluxgate magnetometers are operated at five sites in andaman and nicobar region transfer functions are estimated for the period range 8 128 min from nighttime transient geomagnetic variations using robust regression analysis the observed induction arrows in andaman islands are found to point towards east despite deep sea located towards its west this indicates that fore arc basin andaman nicobar deep is more conducting than the region of outer non volcanic island arc thin sheet model requires the conductance of 10 000 35 000 s with increase conductivity towards the south for explaining the observed induction pattern the observed induction pattern at andaman nicobar stations can be explained in terms of high conducting cretaceous tertiary sediments filling the andaman nicobar deep high conductivity over invisible bank has been attributed to the partial melts volatile fluids derived from the subducting indian plate that are intruding into the eastern margin of fore arc basin through the west andaman fault waf the induction pattern at great nicobar station campbell bay may be related to the highly conducting sediments filling the mergui basin along with mafic intrusions also crustal transition occurs below the mergui terrace at the malayan coast contributing to the enhanced conductivity anomaly

a boussinesq model for waves breaking in shallow water abstract a simple description of wave breaking in shallow water is incorporated in the boussinesq equations by using the concept of surface rollers the roller is considered as a volume of water being carried by the wave with the wave celerity the effect of the roller is included in the vertical distribution of the horizontal velocity which leads to an additional convective momentum term the breaking criterion is related to the local slope of water surface and the thickness of the roller is determined from simple geometrical considerations although the model is simple it is capable of representing a variety of processes such as the initiation and cessation of wave breaking the evolution of wave profiles before during and after wave breaking the initial conversion of potential energy into forward momentum flux and the associated horizontal shift between the break point and the point where the setup in mean water level is initiated results are presented for regular and irregular wave trains and comparison with measurements shows good agreement