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

the belize margin revisited 1 holocene marine facies belize is best known for its 260 km long barrier reef and associated lagoon reef shoals but also exhibits a complete transition from near shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and in addition has three of the very few occurrences of caribbean atolls published holocene facies relationships on the belize shelf have been semi quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon this contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf supplemented by additional information to produce a modified factor analysis facies distribution for the entire shelf the resulting nine facies are extended seaward to include previously published analysis of sediment on the three belize off shelf atolls resulting in a total of 11 facies in addition the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that in places the distribution pattern clearly indicates a barrier platform source of lagoon deposited carbonate mud dunham s limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments

extreme waves in shallow and intermediate water depths this paper concerns the description of large transient waves in shallow and intermediate water depths it builds upon recent advances in the description of deep water waves and provides the first quantitative comparisons with a new kinematic model which has hitherto only been validated in deep water conditions a new series of experimental observations is presented in which the wave components within a random or irregular sea state are focused to produce a large transient wave group comparisons with both linear and second order solutions suggest that non linear wave wave interactions produce a steeper wave envelope in which the central wave crest is higher and narrower while the adjacent wave troughs are broader and less deep spectral analysis of the measured water surface elevation suggest that in addition to the development of significant long wave energy there is also a transfer of energy to the shorter high frequency harmonics this energy redistribution has a significant effect upon the underlying kinematics in particular the near bed velocities are shown to be in good agreement with the second order solution which includes the long wave or frequency difference terms first identified by longuet higgins and stewart furthermore the near surface kinematics are shown to be highly non linear indeed a linear wave theory based upon a correct representation of the freely propagating linear harmonics is generally found to under estimate the near surface horizontal velocity however if the linear calculations are based upon a measured wave spectrum the kinematic predictions suffer from high frequency contamination and require empirical correction in contrast the non linear numerical model presented by baldock and swan provides a good description of the measured kinematics over the entire water depth

contribution of calcareous nannoplankton to carbonate deposition a new approach applied to the lower jurassic of central italy abstract the upper pliensbachian lower toarcian somma section central italy which displays alternation of limestone marl lithotypes was investigated for its calcareous nannofossil and caco3 contents in order to evaluate the contribution of calcareous phytoplankton to the carbonate fraction of rocks a new method was applied combining a recently developed technique for nannofossil absolute quantification and measurements of nannofossil size our study suggests that nannofossils did not produce the bulk of carbonate mud in the studied section although they contribute to different extents to the pelagic carbonate fraction the contribution of both coccoliths and mainly the incertae sedis schizosphaerella to the carbonate fraction was important only in periods of reduced accumulation rates and or during clay deposition the highest estimated carbonate production by nannofossils in the studied section is around 83 of the total carbonate content but in a sample containing only 12 8 wt caco3 the observed limestone marl alternations therefore result from cyclical export of carbonate mud from the shallow latium abruzzi carbonate platform to the umbria marche basin and only subordinately from changes in nannoplankton productivity

geochemical and petrographical characterization of fine grained carbonate particles along proximal to distal transects the origin of carbonate ooze particles is often poorly understood this is due to their polygenic origin and potential post depositional alteration here the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown the focus is on grain size and morphology mineralogy and isotope signatures two contrasting proximal to distal transects were investigated 1 the miocene leeward margin of great bahama bank odp leg 166 and 2 the transition between the maiella platform and the umbria marche basin in central italy near the cenomanian turonian boundary in both case settings carbonate particles of biogenic origin include at least three groups of organisms i planktonic foraminifera ii calcareous nannofossils and iii fragments of unspecified neritic skeletal material two further particle types lack diagnostic structures and based on particle size and mineralogy are here referred to as iv macroparticles 5 20 m mainly xenomorphic and v microparticles 12 m mainly automorphic to sub automorphic macro and microparticles represent 50 to 80 of the carbonate phase in slope and toe of slope domains and share characteristic carbon and oxygen isotope signatures macro and microparticles are considered shallow water precipitation products subsequently exported into the slope and toe of slope domains macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and or bioinduced precipitation in the water column in some cases macro and microparticles may have an early diagenetic origin the identification of the origin of fine grained particles allows for a quantitative assessment of exported in situ and diagenetic carbonate materials in periplatform environments the data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite

carbonate periplatform sedimentation by density flows a mechanism for rapid off bank and vertical transport of shallow water fines existing theories of off bank sediment transport cannot account for rapid rates of sedimentation observed in bahama bank and florida shelf periplatform environments analysis of the physical processes operating during winter cold fronts suggests that accelerated off bank transport of shallow water mud may be achieved by sinking off bank flows of sediment charged hyperpycnal super dense platform waters

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

temporal and spatial distribution of whitings on great bahama bank and a new lime mud budget analysis of 69 shuttle and satellite images of the northern bahamas taken from 1965 to 1993 allowed us to calculate the regional and temporal distribution and longevity of 888 whitings on the great bahama bank at any time whitings cover between 35 and 200 km 2 in the area centered at lat 25 n and 78 50 w the highest occurrences of whitings are in april and october suggesting a seasonal component using a measured average of 10 6 mg l suspended sediment in typical whitings we calculated that 1 35 10 6 metric tons of lime mud are suspended every year if the suspended carbonate is precipitated in the water column these phenomena account for 280 of all of the holocene accumulated bank top mud and more than 40 of the total bank top mud and periplatform mud that have accumulated on the west side of great bahama bank

volcanic ash layers in the upper cretaceous of the central apennines and a numerical age for the early campanian at montagna della maiella and at gola del furlo central apennines two discrete layers of bentonic clay are intercalated within the pelagic furlo and turbiditic pelagic limestones maiella of the upper cretaceous basinal succession of the umbrian basin scaglia facies the bentonite layers are dated by planktonic foraminifera to the globotruncanita elevata zone early campanian and by calcareous nannofossils to the aspidolithus parcus zone cc 18 they fall into the reversed interval of chron 33 detailed correlation shows the layers to be of exactly the same age the upper layer is dated by u pb on magmatic zircons to 81 67 0 21 ma an age compatible with the cretaceous time scale of obradovich the mineralogy of the bentonitic clays is almost pure montmorillonite and contrasts sharply with the clay mineral assemblage of the enclosing pelagic and turbiditic limestones which is dominated by soil derived smectite and illite in different proportions the bentonite seams are interpreted as the submarine alteration products of wind borne volcanic ashes they can be followed with only minor changes in thickness over 200 km and must be derived from distant volcanic sources and related to extreme volcanic events a possible source area is present in the dinarides where upper cretaceous subduction related magmatic rocks are widespread

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

assessment of wave height distributions using an extensive field database abstract the present paper investigates the short term statistical distribution of wave heights specifically some of the most commonly applied wave height distributions are assessed using field measurements the latter comprise of wave radar observations from 10 different locations in the north sea and cover water depths between 7 7 m and 45 m in total the field database includes more than 200 million waves making it one of the largest of its kind in this water depth regime in using these data the accuracy of existing wave height distributions has been examined and guidance is provided concerning the best performing models and their domain of applicability additionally insights concerning the influence of key met ocean parameters are also provided taken together the results in this paper present an overview of the statistical behaviour of wave heights in finite water depths as observed in the field

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

field measurements of rogue water waves abstractthis paper concerns the collation quality control and analysis of single point field measurements from fixed sensors mounted on offshore platforms in total the quality controlled database contains 122 million individual waves of which 3649 are rogue waves geographically the majority of the field measurements were recorded in the north sea with supplementary data from the gulf of mexico the south china sea and the north west shelf of australia the significant wave height ranged from 0 12 to 15 4 m the peak period ranged from 1 to 24 7 s the maximum crest height was 18 5 m and the maximum recorded wave height was 25 5 m this paper will describe the offshore installations instrumentation and the strict quality control procedure employed to ensure a reliable dataset an examination of sea state parameters environmental conditions and local characteristics is performed to gain an insight into the behavior of rogue waves evidence is provided to demonstrate that rogue waves are not go

dynamics of tethyan carbonate platforms tethyan carbonate platforms are relatively short lived depositional systems which were born developed died and sometime resurrected in a tectonically active area in contrast with pericratonic platforms which are generally huge in size hundreds of kilometers across and show wide facies belts very gentle slopes ramps and transitional boundaries tethyan carbonate platforms are smaller tens of kilometers and have steep slopes generally faulted boundaries and abrupt facies changes it appears clear that the overall control on these two contrasting systems is the geodynamic milieu relatively stable in the first case where eustatic oscillations and long term subsidence are probably the main dictators quite dynamic and aggressive in the second one where carbonate platforms developed through the entire geodynamic spectrum rifting transtension transpression and collision of the wilson cycle primary controls on tethyan carbonate platforms appear to be tectonics most important and eustatic sea level oscillations which determine their emplacement growth and decay their overall shape and architecture are a function of these factors secondary factors affecting tethyan carbonate platform evolution are physiography oceanographic conditions and biology as a function of geologic time especially across the mesozoic tertiary boundary facies and facies distribution and to a lesser extent their shape are controlled by thesemore variables less

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

stable isotopic and carbonate cyclicity in lower cretaceous deep sea sediments dominance of diagenetic effects abstract oxygen and carbon isotopic variability of the dominant m carbonate fraction within bedded organic carbon rich lower cretaceous sediment intervals from various dsdp sites are closely correlated with preservational changes in the carbonates isotopic fluctuations are absent where carbonate contents vary little and where the carbonate fraction is dominated by biogenic phytoplankton remains within each of the studied intervals oxygen and carbon isotopic ratios become increasingly more negative in samples with carbonate contents higher than about 60 in which the proportion of diagenetic microcarbonate increases rapidly carbon isotopic ratios show a trend towards positive values in samples with carbonate contents of less than 40 and strong signs of dissolution the taxonomic composition of nannofossil assemblages varies little within single intervals despite significant differential diagenesis among individual beds this points towards ecological stability of oceanic surface waters during the deposition of alternating beds bedding is however closely related to changing bioturbation intensity indicating repeated fluctuations of the deep water renewal rates and oxygen supply various microbial decomposition processes of organic matter leading to bed specific differential carbonate diagenesis resulted in an amplification of primary bedding features and are considered responsible for most of the observed fluctuations in the stable isotopic ratios and carbonate contents

controls on grain size patterns in periplatform carbonates marginal setting versus glacio eustacy the importance of grain size as a fundamental property controlling other physically derived properties is well known recent grain size studies on periplatform sediments of the caribbean and western north atlantic have shown that grain size variability is coupled with changes in carbonate platform productivity and export in response to pleistocene holocene glacio eustacy these findings showed that periplatform sediments are dominated by fine grained material during sea level highstands and coarser material during sea level lowstands this paper addresses the question of grain size patterns in periplatform settings and their relationship to glacio eustacy furthermore it considers whether these patterns are applicable to different types of margin settings accretionary erosional here existing data pleistocene holocene from the accretionary western leeward margin of great bahama bank odp leg 166 and new data from the erosional eastern windward margin odp leg 101 are used the results show that the grain size patterns of both margins are controlled by late neogene sea level fluctuations the accretionary leeward margin sediments indicate the same grain size pattern as previously described in the literature however the erosional windward margin shows a reverse pattern with coarser sediments in interglacials and finer deposits in glacials this proposes that the leeward margin grain size pattern is controlled by the productivity export mode of the platform this is indicated by the platform top derived fine muds transported off bank to form a thick sediment wedge on the low angled slope during interglacials in contrast on the windward margin the sediment flux pattern is controlled by the impact of mass transport processes this is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep angled erosional slope is less apt for the deposition of excess fine material this material is eroded and or bypasses the slopes and is redeposited in the periplatform basin setting

quaternary surface water stable isotope signal from calcareous nannofossils at dsdp site 593 southern tasman sea oxygen isotope values from calcareous nannofossils in four cores spanning the quaternary from dsdp site 593 in tasman sea are compared with the 18o signal of planktonic and benthic foraminifers from the same samples the classic mid late quaternary isotope stages are exhibited with stage 12 particularly well developed when 18o values of nannofossils are adjusted for coccolithophore vital effects they indicate larger by 1 6 c surface to bottom paleotemperature gradients and greater by 1 3 c changes in mean sea surface temperature between full glacial and interglacial conditions than do 18o values from planktonic foraminifers along with the foraminifers the nannofossils record a bimodal distribution of 18o between the early and mid late quaternary indicating a significant change in global ice budget the 13c of nannofossils also shows a bimodal distribution but is opposite to that for the foraminifers nannofossil 18o values record a shift of 0 8 at isotope stage 8 corresponding to a major reduction in abundance of the previously dominant gephyrocapsids a shift in 13c of 1 5 also occurs at stage 8 and a shift in 13c of 1 2 at around stage 14 the 18o shift in nannofossils is at least a pacific wide phenomenon the 13c shifts are possibly global the 13c signal of nannofossils exhibits an antipathetic relationship to that of benthic foraminifers back to isotope stage 18 but no significant correlation beyond this level to the base of the quaternary this is interpreted as reflecting local productivity dominating global influences on 13c since stage 18 at dsdp site 593 the difference between nannofossil and benthic foraminifer 13c signals 13c tends to be maximum during glacial stages and minimum during interglacials throughout the section showing a strong correlation with the nannofossil 18o signal the increased partitioning of 13c between surface and bottom waters during the glacial periods may indicate heightened productivity in surface waters in the southern tasman sea at these times

an experimental study of large waves in intermediate and shallow water depths part i wave height and crest height statistics abstract this paper describes a series of laboratory observations undertaken in a purpose built wave flume the objective of the study was to simulate a range of realistic ocean spectra evolving over a number of mild bed slopes m the chosen sea states allowing a systematic investigation of the role of local water depth spectral peak period significant wave height spectral bandwidth and bed slope the focus of the present paper lies in the statistical distribution of both the wave height h and the wave crest elevation c the laboratory data being used to provide both an understanding of the importance of the various parameters and an assessment of the commonly adopted design distributions the results of the study have shown that both the wave height and the crest height distributions are primarily dependent upon the effective water depth k p d where k p is the wave number corresponding to the spectral peak and d the water depth and the sea state steepness 1 2 h s k p where h s is the significant wave height conversely the distributions are independent of the mild bed slope for m 1 100 and the spectral bandwidth the latter result being very different to that which arises in deep water following detailed comparisons across a wide parameter range the wave height distributions in the deeper water depths k p d 1 0 are shown to be in reasonable agreement with the forristall 1978 and glukhovskii 1966 distributions the latter becoming more important as the proportion of breaking waves increases as the water depth reduces the mendez et al 2004 distribution as well as the battjes groenendijk 2000 composite weibull distribution cwd become increasingly applicable however comparisons between sea states of varying steepness but with all other parameters held constant suggest that the empirical parameters on which the latter solution is based may not be universally applicable finally in the shallowest water depths k p d 0 5 none of the existing distributions provide a good description of the measured data all leading to an over estimate of the largest wave heights

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

seismic stratigraphy of the bahamas seismic reflection profiles from the straits of florida northwest providence channel tongue of the ocean and exuma sound reveal a seismic stratigraphy characterized by a series of prograding upper cretaceous and tertiary seismic sequences with seismic velocities generally less than 4 km sec overlying a lower cretaceous section of low amplitude reflections which are more nearly horizontal than the overlying prograding clinoforms and have seismic velocities greater than 5 km sec the prograding units are detrital shallow water carbonates shed from nearby carbonate banks into deep intrabank basins that were established in the late cretaceous the lower cretaceous units a e probably shallow water carbonate banks that were drowned in the middle cretaceous but which during he early cretaceous extended from florida throughout the bahamas region the seismic reflection profiles reveal a sharp angular unconformity at 5 sec two way traveltime in northwest tongue of the ocean suggesting a rift drift unconformity and deposition on thinned continental crust no such unconformity is seen in central and southeast tongue of the ocean or in exuma sound suggesting that these areas are built on oceanic crust

whiting related sediment export along the middle miocene carbonate ramp of great bahama bank modern aragonite needles are present all along the modern leeward margin of great bahama bank odp leg 166 while middle miocene sediments contain needles only in more distal areas sites 1006 and 1007 in contrast to the rimmed flat topped platform topography during the plio pleistocene the miocene great bahama bank morphology is a carbonate ramp profile this might imply a different location and precipitation type for miocene aragonite needles in this study aragonite needles in miocene sediments were isolated using a granulometric separation method furthermore the isolation of the various carbonate components enables the identification of primary versus diagenetic components the miocene aragonite needles are concentrated in the finest granulometric sediment fractions 12 m the fraction specific geochemical analyses 13c 18o and sr elemental abundance represent useful tools to assess the possible sources of the aragonite mud the geochemical variation of the fractions rich in pristine aragonite needles and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component both components indicate shallow water environments as the main sediment source area ramp top related fine grained particles now present at distal sites were likely exported as suspended material similar to present day transport mechanisms the scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded the granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine grained components

on the average shape of the largest waves in finite water depths abstractthis paper investigates the average shape of the largest waves arising in finite water depths specifically the largest waves recorded in time histories of the water surface elevation at a

palaeocene oceans and climate an isotopic perspective abstract the early cenozoic was a time of climatic and oceanographic transition from the cretaceous greenhouse world to the icehouse world of the neogene 18 o measurements shed light on ocean temperature and possible polar ice fluctuations during this interval while 13 c measurements monitor fluctuations in ocean productivity deep water circulation and atmospheric co 2 the major features from 18 o analysis of the early cenozoic are general cooling of surface waters with some evidence for transient cooling across the k t boundary surface water temperatures were at a cenozoic maximum in the early eocene whereas deep waters cooled then warmed during the palaeocene the 13 c of bulk carbonates is at a minimum at the start of the cenozoic due to the profound crisis in ocean surface water productivity associated with the extinctions of marine plankton at the cretaceous tertiary boundary thereafter 13 c values increase in bulk carbonates as well as planktonic and benthonic foraminifera to their cenozoic maximum in the late palaeocene c 60 ma after which time they again decrease over an interval of c 4 5 m y to a cenozoic low in the early eocene the increase in 13 c values characteristic of the palaeocene period is probably related to a combination of increasing surface water productivity and accelerated burial of organic carbon conversely the decline in 13 c into the early eocene is probably related to a decrease in ocean productivity and a deceleration in the rate of organic carbon burial benthic 13 c comparisons suggest that deep waters appear to have been predominantly formed in the high southern latitudes with the exception of a short lived interval near the palaeocene eocene boundary possibly associated with a transient climatic anomaly the late palaeocene thermal maximum the thermal change of palaeocene deep waters may be related to the changing productivity of surface waters by controlling atmospheric co 2 flux in a similar way to that proposed for the control of the pleistocene glacial cycles

conditional second order short crested water waves applied to extreme wave episodes a derivation of the mean second order short crested wave pattern and associated wave kinematics conditional on a given magnitude of the wave crest is presented the analysis is based on the second order sharma and dean finite water wave theory a comparison with a measured extreme wave profile the draupner new year wave shows a good agreement in the mean indicating that this second order wave can be a good identifier of the shape and occurrence of extreme wave events a discussion on its use as an initial condition for a fully nonlinear three dimensional surface wave analysis is given

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

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

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

the average shape of large waves in the coastal zone abstract the ability of the newwave focused wave group the scaled auto correlation function to represent the average shape in time of large waves in a random sea state makes it a useful tool for the design of offshore structures however the profile has only been validated against field data for waves on deep and intermediate water depths a similar validation is advisable when applying newwave to shallow water problems where waves are less dispersive and more nonlinear for this purpose data recorded by two channel coastal observatory cco wave buoys during two large storms in january 2014 are analysed to assess the ability of newwave to replicate the average shape of large waves in shallow water a linear newwave profile is shown to successfully capture the average shape of the largest waves from the perranporth and porthleven wave buoys during these large storm events the differences between the measurements obtained by a surface following buoy and a fixed sensor become important when considering the ability of a second order corrected newwave profile to capture weakly nonlinear features of the measured data a general expression for this effect is presented for weakly nonlinear waves on intermediate water depths leading to lagrangian second order sum corrections to the linear newwave profile a second order corrected newwave profile performs reasonably well in capturing the average features of large waves recorded during the january storms these findings demonstrate that the newwave profile is valid in relatively shallow water kpd values less than 0 5 and so may have potential for use as a design wave in coastal engineering applications

anisotropy of magnetic susceptibility in the scaglia rossa pelagic limestone abstract during folding of the scaglia rossa limestone in umbria italy deformation was mainly accommodated by pressure solution cleavage fossils between the cleavage planes appear visibly undeformed yet the limestone possesses a weak magnetic fabric the maximum and intermediate principal axes of the magnetic anisotropy ellipsoid define a distinct magnetic foliation plane within which a weak concentration of the maximum axes forms a magnetic lineation neither of these features is of sedimentary origin results from a slumped outcrop where bedding and a cleavage induced by overburden compaction have different attitudes show that the magnetic foliation is caused by the compaction comparisons with field derived structural data suggest that the magnetic lineation was produced tectonically during deformation of the apennine fold belt

orbitally induced limestone marlstone rhythms in the albian cenomanian cismon section venetian region northern italy sedimentology calcareous and siliceous plankton distribution elemental and isotope geochemistry abstract a multidisciplinary study of the upper albian cenomanian portion of the cismon section venetian region northern italy was undertaken in order to characterize the cyclic alternations of carbonate rich and carbonate poor layers and to investigate their possible origin and cyclic patterns limestone semicouplets are characterized by abundant radiolarians and micarbs micron sized calcitic fragments common planktonic foraminifera strong bioturbation good oxygenation as expressed by the mn and v v ni parameters high si al ratio low k al in the absence of pyrite and organic matter the marlstone semicouplets are on the contrary frequently laminated rich in pyrite and organic matter with common fish remains in the absence of radiolarians the mn and v v ni parameters indicate that the marlstone deposition occurred in dysoxic to anoxic conditions which allowed the preservation of organic matter the low si al ratio and high k al ratio the latter related to abundant feldspars indicate that marlstones received a substantial contribution from a terrigenous source the abundance of biogenic silica suggests that during limestone deposition surface waters were rather fertile due to an efficient recycling of nutrients from deeper waters the enhanced fertility was coupled with an efficient current system at the welloxygenated sea floor which prevented the organic matter from accumulating during marlstone deposition surface waters were less fertile than in the limestone semicouplets but still within the mesotrophic spectrum as indicated by the presence of fertility index species among calcareous nannofossils whereas the bottom waters were oxygen depleted to accommodate fertility at the surface with stagnation at the bottom the scenario implies an enhanced stratification caused by an increase in freshwater runoff monitored by 18o depleted values in the meantime the water discharge supplied the nutrients to the surface waters necessary for the calcareous nannofossils to proliferate the cyclic organization of limestone marlstone couplets as revealed by power spectral analysis seems to represent climatic cycles the alternating conditions are 1 efficient mixing highly fertile surface and near surface waters and a well oxygenated seafloor to 2 enhanced water runoff or decreased evaporation or both and oxygen depleted bottom waters we suggest that this deterministic sedimentary cyclicity could be explained by periodic orbital climatic cycles in tune with the milankovitch cycles within this scenario the latest cenomanian bonarelli level is an exceptional event marked by a large positive 13c spike it is characterized by high to very high fertility conditions in surface waters caused by increased upwelling that engendered high nutrient levels in near surface waters the enhanced production of organic matter was in excess for the oxygen available at the bottom floor thus allowing the organic matter to accumulate in the sediments

carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp miocene great bahama bank depositional geometries as imaged in seis mic lines logging data and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the miocene distally steepened carbonate ramp of great bahama bank the shedding pattern along the slope of this ramp is more complex than it is along the slope of the pliocene pleistocene flat topped carbonate platform compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically defined sequence boundaries two types of depositional sequences occur the first sequence is characterised by laterally traceable sequence internal reflections whereas the second type contains major intrasequen tial incisions erosional incisions and sedimentary infills of these canyons by turbidites formed during sea level lowstands as is indicated by the composition of the turbidites having a mixture of shallow water and pelagic particles highstand turbidites are charac terised by more extensive laterally traceable geome tries and by the occurrence of abundant shallow water particles in contrast to highstand turbidites shed from the pliocene pleistocene flat topped platform shal low water components in highstand turbidites of the miocene ramp are of skeletal origin the stacking pat tern of the periplatform deposits is controlled by sea level fluctuations four orders of sea level changes are distinguished third order cycles are delimited by sequence boundaries and fourth 100 000 a order cycles govern the bundling of turbidites into packages fifth 40 000 a and sixth 23 000 a order cycles are recorded in the background sediments and resolvable with spectral analysis

geophysical recognition and structure of carbonate platforms and platform edges on passive continental margins abstract recent multichannel seismic reflection profiles reveal the presence of possible carbonate platform edges of early cretaceous jurassic age now buried beneath the continental slope off the eastern united states seismic reflection characteristics include high amplitude hyperbolic reflections above a reflectorless mass seismic refraction studies measured relatively high velocities for the depth of burial below the high amplitude reflectors back platform stratified deposits form high amplitude continuous reverberatory reflectors which terminate seaward into the reflectorless mass of the platform edge landward dips of the back platform deposits occur by differential subsidence and back tilting of the more positively supported platform edge structure draping offbank deposits form onlapping reflectors inclined away from the platform edge to the adjacent basin such platform edge structures form buried escarpments of several kilometers relief as underpinnings of the younger continental slope these escarpments apparently exert control on the position of the subsequent shelf edge in some cases the carbonate platform edge has prograded well seaward of the deeper transition from continent to oceanic crust so the present shelf edge is above oceanic crust as off new jersey delaware dredging and deep sea drilling project studies have sampled the carbonate platform edge in a few places off the united states and these calibrated seismic characteristics are projected to interpret the as yet unsampled buried structures for thousands of km along strike

offbank transport of carbonate sands along open leeward bank margins northern bahamas abstract vigorous offbank transport of carbonate sands occurs along the west facing leeward open margins of little and great bahama bank large offbank oriented sand waves thick sand bodies covering reefs and shallow water sands mostly non skeletal obtained from adjacent deep flanks all demonstrate the existence of this shallow to deep pathway of sediment transport a variety of data suggests that transport occurs during storms and not during normal tidal current fluctuations an abundance of composite grains as well as vertical sequences of submarine cemented horizons seen via seismic profiling within the marginal sand bodies indicate cyclic periods of relative quiescence followed by moments of intense sediment movement current meter data obtained during six weeks of low wind activity show that critical threshold velocities for sand transport are only barely exceeded during portions of the tidal cycle these flows coupled with higher frequency bottom currents generated by surface gravity waves winnow the sands but do not provide significant net offbank transport offbank sand transport provides material to the shallow and deep bank margins enabling them to expand during sea level highstands each sea level fluctuation is likely to produce within the shallow margins a vertical sequence of basal reefs covered by a thick non skeletal calcarenite capped by a subaerially exposed diagenetically altered surface shallow water sands carried off the marginal escarpment help to construct deep flanks and large sediment drifts

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

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

timing and distribution of calciturbidites around a deeply submerged carbonate platform in a seismically active setting pedro bank northern nicaragua rise caribbean sea the sedimentological study of thirteen sediment cores from the periplatform setting surrounding pedro bank northern nicaragua rise caribbean sea shows that during the last 300 ka turbidite deposition is controlled by at least four factors 1 late quaternary sea level fluctuations 2 prolific fine grained sediment production and export resulting in oversteepening of the upper slope environment 3 the proximity to the bank margin and 4 local slope and seafloor morphology the most intriguing finding of this study is the paucity of turbidites with only 101 turbidites in 13 cores in this tectonically active setting near the caribbean plate boundary throughout the last 300 ka the frequency of turbidite input during interglacial stages is three times higher than during glacial stages also it is obvious that changes in sea level influence the timing of turbidite deposition this is especially evident during the transgressions resulting in rapid renewed bank top flooding subsequent neritic sediment overproduction and offbank export the flooding event during each transgression is usually recorded by the onset of turbidite deposition at various sites along several platform to basin transects in down and upcurrent slope settings overall however more turbidites are deposited during the regressive rather than the transgressive phases in sea level probably as a result of sediment reorganisation on the slope resulting in slope failure five cores show highstand bundling of calciturbidites i e higher number of turbidites during highstands than during lowstands in sea level

wave height distributions on shallow foreshores wave height distributions on shallow foreshores deviate from those in deep water due to the effects of the restricted depth to height ratio and of wave breaking laboratory data of wave heights on shallow foreshores of different slopes have been analysed to determine these effects and to derive generalised empirical parameterisations a model distribution is proposed consisting of a rayleigh distribution or a weibull distribution with exponent equal to 2 for the lower heights and a weibull with a higher exponent for the higher wave heights the parameters of this distribution have been estimated from the data and expressed in terms of local wave energy depth and bottom slope yielding a predictive model that is found to be significantly more accurate than existing expressions

the rate and consequences of sr diagenesis in deep sea carbonates we have used a diffusion advection reaction model for sr exchange during deep sea carbonate diagenesis to determine the rate and consequences of sr exchange between porewaters and bulk carbonate at six dsdp sites 590b 575 593 516 305 and 289 where the required sr concentration and isotopic composition data for the interstitial waters are available from the literature the model can reproduce both the sr2 and 87sr 86sr profiles in the porewaters at each of the sites by adjusting the rate of sr exchange due to solution reprecipitation as a function of sediment age we find that the rate of solution reprecipitation at all of the sites is highest for the youngest sediment 1 10 m y and decreases by about an order of magnitude over the first 10 m y of sediment age the effect of this exchange on the properties of the bulk carbonate is to reduce the sr content by 5 25 depending primarily on the sedimentation rate and shift the 87sr 86sr by as much as 0 00004 from the value the sediment had when first deposited isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate 87sr 86sr for stratigraphic correlation the average sr loss in the carbonate sections studied is about 15 from which we conclude that the sr flux from carbonate sediments to the overlying ocean is of the order of 15 of the riverine sr flux we also show that the isotopic composition of the diagenetic sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall sr budget that determines the sr isotopic composition of seawater the range of sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in sr content seen in pelagic carbonates as a function of age about 70 over the first 100 m y we conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself

linking the oxygen isotope record of late neogene eustasy to sequence stratigraphic patterns along the bahamas margin results from a paleoceanographic study of odp leg 166 site 1006 sediments abstract during odp leg 166 the recovery of cores from a transect of drill sites across the bahamas margin from marginal to deep basin environments was an essential requirement for the study of the response of the sedimentary systems to sea level changes a detailed biostratigraphy based on planktonic foraminifera was performed on odp hole 1006a for an accurate stratigraphic control the investigated late middle miocene early pliocene sequence spans the interval from about 12 5 ma biozone n12 to approximately 4 5 ma biozone n19 several bioevents calibrated with the time scale of berggren et al 1995a b were identified the odp site 1006 benthic oxygen isotope stratigraphy can be correlated to the corresponding deep water benthic oxygen isotope curve from odp site 846 in the eastern equatorial pacific shackleton et al 1995 proc odp sci res 138 337 356 which was orbitally tuned for the entire pliocene into the latest miocene at 6 0 ma the approximate stratigraphic match of the isotopic signals from both records between 4 5 and 6 0 ma implies that the paleoceanographic signal from the bahamas is not simply a record of regional variations but indeed represents glacio eustatic fluctuations the odp site 1006 oxygen and carbon isotope record based on benthic and planktonic foraminifera was used to define paleoceanographic changes on the margin which could be tied to lithostratigraphic events on the bahamas carbonate platform using seismic sequence stratigraphy the oxygen isotope values show a general cooling trend from the middle to late miocene which was interrupted by a significant trend towards warmer sea surface temperatures sst and associated sea level rise with decreased ice volume during the latest miocene this trend reached a maximum coincident with the miocene pliocene boundary an abrupt cooling in the early pliocene then followed the warming which continued into the earliest pliocene the late miocene paleoceanographic evolution along the bahamas margin can be observed in the odp site 1006 13c values which support other evidence for the beginning of the closure of the panama gateway at 8 ma followed by a reduced intermediate water supply of water from the pacific into the caribbean at about 5 ma a general correlation of lower sedimentation rates with the major seismic sequence boundaries ssbs was observed additionally the ssbs are associated with transitions towards more positive oxygen isotope excursions this observed correspondence implies that the presence of a ssb representing a density impedance contrast in the sedimentary sequence may reflect changes in the character of the deposited sediment during highstands versus those during lowstands however not all of the recorded oxygen isotope excursions correspond to ssbs the absence of a ssb in association with an oxygen isotope excursion indicates that not all oxygen isotope sea level events impact the carbonate margin to the same extent or maybe even represent equivalent sea level fluctuations thus it can be tentatively concluded that ssbs produced on carbonate margins do record sea level fluctuations but not every sea level fluctuation is represented by a ssb in the sequence stratigraphic record

the chronostratigraphic significance of seismic reflections along the bahamas transect abstract continuous cores drilled during the bahamas drilling project bdp and the ocean drilling program odp leg 166 along a transect from the top of great bahama bank to the basin in the straits of florida provide a unique data set to test the assumption in seismic stratigraphy that seismic reflections are time lines and thus have a chronostratigraphic significance seismic reflections that are identified as seismic sequence boundaries ssbs were dated by means of biostratigraphy in the five odp sites and by a combination of biostratigraphy magnetostratigraphy and sr isotope stratigraphy in the two bdp sites the seismic reflection horizons are carried across a variety of facies belts from shallow water carbonates over slope carbonates to drift deposits in the straits of florida within this system 17 ssbs were identified and dated despite the fact that the seismic reflections cross several facies belts their ages remain remarkably constant the average offset in all sites is 0 38 myr in no cases do the seismic reflections cut across time lines the age differences are the combined result of the biostratigraphic sampling frequency the spacing of marker species that required extrapolation of ages and the resolution of the seismic data in addition uncertainties of age determination in the proximal sites where age diagnostic fauna are rare add to the age differences between sites therefore it can be concluded that the seismic reflections which mark the ssbs along the bahamas transect are time lines and can be used as stratigraphic markers this finding implies that depositional surfaces are preferentially imaged by reflected seismic waves and that an impedance contrast exists across these surfaces facies successions across the sequence boundaries indicate that the sequence boundaries coincide with the change of deposition from times of high to low sea level in the carbonate setting of great bahama bank sea level changes produce changes in sediment composition sedimentation rate and diagenesis from the platform top to the basin the combination of these factors generates differences in sonic velocity and thus in impedance that cause the seismic reflection the impedance contrasts decrease from the proximal to the distal sites which is reflected in the seismic data by a decrease of the seismic amplitude in the basinal area

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

plagioclase dissolution related to oil residence time north coles levee field california diagenetic mineral zones characterize an originally homogeneous turbidite sandstone reservoir at north coles levee ncl the medium to coarse grained sands in the reservoir contain a 500 ft oil column with high water saturation extensive plagioclase porosity and associated diagenetic kaolinite occur in the lower third of the oil column plagioclase dissolution is greatest near the oil water contact kaolinite and plagioclase porosity are vary rare in the upper third of the oil column next to the gas cap previous work has sown that at ncl plagioclase dissolution occurred in the last several million years of the reservoir burial history nearly contemporaneous with oil emplacement clearly if plagioclase alteration was independent of the hydrocarbons a uniform alteration pattern would be expected the zonation pattern described here appears to be related to the presence of the oil thus diagenesis was most intense where the residence time of the hydrocarbon was greatest in the lower part whereas near the gas cap plagioclase diagenesis was minimal where the accumulation of gas effectively shut down feldspar dissolution these new results indicate that plagioclase porosity at ncl was an effect of oil emplacement perhaps due to acid components solubilized from the oil important implications of these findingsmore are 1 maximum porosity enhancement may be off structure away from the gas cap 2 tends to confirm the importance of acid components associated with hydrocarbons on feldspar dissolution and 3 diagenetic interpretations may differ if sample locations relative to gas oil water zones are not known less

density cascading off shelf sediment transport evidence and implications bahama banks abstract suspended sediment concentrations in shelf waters are often appreciable but sediments on their own rarely contribute enough density to cause suspension currents to transport them offshelf however sediment charged hyperpycnal high density waters are often generated over continental shelves because of the same set of air sea interactions intense heat and moisture flux responsible for thermohaline production and circulation of deep ocean water masses we propose the term density cascading to describe the processes by which hyperpycnal waters are released from shelf areas and together with entrained sediments sink to their compensation level in the adjacent ocean density cascading probably involves a range of physical processes from pelagic draping of slopes and basins with shelf muds to initiating turbidity currents capable of scouring canyons and plunge pools sediment bypassing of slopes and deposition of sands in deep basins thermodynamic air sea interactions can generate hyperpycnal water at all latitudes therefore density cascading has important implications not only to the sedimentology of modern carbonate platforms such as the florida shelf and bahama banks and stratigraphy in ancient limestones but also to offshelf sediment flux in siliciclastic environments

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

on estimating extremes in an evolving wave field abstract observations of waves as a time series from a fixed or moored sensor are shown to underestimate the extreme waves occurring in the vicinity the underestimate arises because of the difference in phase and envelope propagation of surface water waves so that the highest crest for example is recorded only when the crest coincides with the envelope maximum at the location of the wave recorder in addition the dispersive nature of water waves can lead to the coalescence of groups of waves as longer waves catch up to shorter slower waves so that the group shape changes markedly as the waves propagate moored accelerometer buoys introduce another error that exacerbates the underestimate of the highest crest the quasi lagrangian motion of the buoy leads to flattening of the crests and sharpening of the troughs so that apparent mean water level is raised and thus the height of crests above it is reduced an analysis approach to correct these underestimates is outlined and tested with observed data against the predictions of extreme values based on narrow banded random wave theory

changes in the pelagic fine fraction carbonate sedimentation during the cretaceous paleocene transition contribution of the separation technique to the study of bidart section abstract the bidart section southwestern france displays an almost complete late maastrichtian early danian transition as the cretaceous paleocene k p crisis mainly affects carbonate producers the aim of this study is to precisely evaluate the evolution of pelagic sediments composition across the boundary a new protocol for separation of fine carbonates into discrete size fractions was used 1 to precisely evaluate in weight of carbonate and not only number of particles per gram of rock the contribution of each carbonate component type foraminifera calcareous nannofossils and nonbiogenic carbonates calcite microparticles and calcareous macrocrystals and 2 to measure their isotopic signature and thus constrain the origin of these carbonate particles the maastrichtian pelagic carbonates are mostly biogenic 70 of the bulk carbonate but also contain nonbiogenic carbonates calcite microparticles 4 m due to their isotopic signature calcite microparticles cannot result from fragmentation and partial dissolution of biogenic remains and the most likely origin appears to be early diagenetic processes and or export from shallow water platforms the calcareous macrocrystals derive from an early diagenetic process the lowermost danian sediments are dominated by nonbiogenic carbonates between 50 and 80 of the bulk carbonate nevertheless two kinds of biogenic components are present thoracosphaera operculata and maastrichtian like calcareous nannofossils thoracosphaera operculata is an opportunistic calcareous dinoflagellate which frequently occurs at high abundances in basal danian sediments and is certainly in situ this is confirmed by it showing a danian isotopic signature the maastrichtian like calcareous nannofossils are nannofossils of taxa that indisputably occur in the maastrichtian but which do not occur consistently in later danian strata they show a maastrichtian type isotopic signature which strongly supports the inference that they are mainly reworked from the maastrichtian this study shows that nonbiogenic carbonates are important components of the pelagic carbonate even during periods of normal sedimentation in the crisis interval the biogenic carbonate production drops sharply while calcite microparticles and carbonate macrocrystals remain almost unaffected and represent the major part of the carbonate in the earliest danian sediments finally the sediments return to a composition similar to that of the maastrichtian in m pseudobulloides foraminifera zone

controls on modern carbonate preservation in the southern florida straits abstract the water masses in the florida straits and bahamas region are important sources for the northern atlantic surface ocean circulation in this study we analyse carbonate preservation in surface sediments located above the chemical lysocline in the florida straits and bahamas region and discuss possible reasons for supralysoclinal dissolution calcite dissolution proxies such as the variation of the foraminiferal assemblage fragmentation index benthic foraminifera index and resistance index displayed a good preservation in both areas the pteropod species limacina inflata showed very good preservation in sediments of inter platform channels from the great bahama bank providence channel exuma sound above the aragonite lysocline supralysoclinal aragonite dissolution however was observed at two water depth levels 800 1000 m and below 1500 m in the florida straits our observations suggest that the supralysoclinal dissolution in the florida straits is due to the degradation of organic material the presence of antarctic intermediate water aaiw may be a contributing factor for the significant aragonite dissolution in 800 1000 m the comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the l inflata dissolution index ldx might be an adequate proxy to reconstruct paleo water mass conditions in an area which is highly saturated with respect to calcium carbonate

sedimentation cycles and their diagenesis on the slope of a miocene carbonate ramp bahamas odp leg 166 numerous small scale depositional cycles are present in the miocene sediments of seismic sequence m along the margin of great bahama bank odp leg 166 these cycles consist of decimetre to metre scale alternations between light grey and dark grey black wackestones packstones the light grey layers are well cemented and nearly uncompacted they contain planktonic and benthic foraminifera and bioclasts bioturbation in these layers is moderate the dark grey wackestones packstones are uncemented strongly compacted and normally strongly bioturbated the main components are planktonic foraminifera and fine grained bioclasts the dark layers are rich in aragonite and organic carbon and contain around 80 carbonate the light layers show low aragonite and organic carbon contents combined with carbonate values of up to 97 5 light 13c and slightly negative 18o values were observed in the dark uncemented layers while the cemented intervals show heavy 13c values and slightly more positive 18o values the carbon isotope signal between the dark and the light layers shows variations of up to 1 45 both 13c and 18o co vary with carbonate content the formation microscanner images reflect the changes in carbonate mineralogy the natural gamma ray tool shows that variations in siliciclastic content of the examined succession displays a different frequency than the cyclic alternations in carbonate mineralogy the internal stacking pattern of the cycles is closely tied to sea level the dark layers are deposited during rising sea level while the light layers reflect sediment production and export during highstand and falling sea level these cycles thus represent a rather continuous sediment shedding pattern that is clearly related to the ramp morphology and differs from the highstand shedding pattern typical for rimmed flat topped platforms most measured parameters suggest that primary sediment composition played an important role in the cementation process the primary differences in composition were enhanced during shallow burial diagenesis the initially high content of metastable carbonate phases in the periplatform sediments triggered rapid cementation of the primary aragonite rich layers leading to the formation of the light beds dissolution of metastable high mg calcite and aragonite was followed by in situ precipitation of more stable dolomite and calcite diagenesis was enhanced by the coarse grain size of the primary aragonite rich layers in contrast the more pelagic dark calcite rich layers were only slightly affected by diagenesis and could preserve their aragonite content the uncemented layers subsequently were subject to strong mechanical compaction whereas the cemented beds stayed nearly uncompacted

observations of the shape and group dynamics of rogue waves surface elevation records from two locations in the northeast pacific are used to examine rogue waves and the relationship to wave groups three hundred individual rogue waves with heights greater than 2 2 times the significant wave height are found in analyzing 2 106 wave groups in contrast to recent nonlinear modeling results we do not find that rogue waves occur at the front of wave groups there is a tendency for steep waves to occur at the front of a group but these are not the largest waves of the group and do not meet the rogue wave criterion rogue waves are most commonly located in the center of the group but their height ratio to the neighboring crest is greater than in the average wave group assessing group dynamics in terms of spectral width suggests that random superposition of nonlinear waves is sufficient to explain the observations of individual rogue waves

the influence of carbonate platform morphology and sea level on fifth order petrophysical cyclicity in slope and basin sediments adjacent to the great bahama bank abstract despite several decades of study details of the relationship between sea level and other factors controlling carbonate sedimentation require clarification to address this issue odp leg 166 drilled a slope to basin transect adjacent to the great bahama bank to document neogene and quaternary sea level changes and to precisely date the major unconformities within the slope and basinal succession here we describe the complex connection between the cyclicities evident in a range of sediment physical property parameters at leg 166 sites and their relationship to sea level fluctuations diagenesis and the morphology of the adjacent carbonate bank margin the characteristics of fifth order petrophysical cycles in miocene slope sediments of the great bahama bank are fundamentally different from those in overlying late pliocene and pleistocene slope sediments these intervals are separated by an early pliocene sequence with characteristics that are transitional between the overlying and underlying sequences we interpret the more symmetric character of the miocene cycles as reflecting cyclic sedimentation controlled by the interaction between sea level fluctuations and the ramp morphology of the adjacent platform and the markedly asymmetric late pliocene and pleistocene cycles as representing the interaction between sea level and a rimmed platform morphology in the case of the miocene cycles diagenetic overprints cause values for petrophysical properties controlled by porosity to be inverted compared to cycles in essentially unaltered late pliocene and pleistocene sediments a detailed understanding of the relationship between petrophysical cycles diagenesis sea level fluctuations and platform margin morphology offers the potential to provide a proxy for inferring the controls on carbonate sedimentation in situations where the nature of the carbonate platform margin is unknown e g where regional seismic data is poor or absent and or where sea level effects cannot be reliably determined by other means these petrophysical proxies should be of greatest benefit where downhole logging data is used as the primary basis for sediment characterization

internal precipitation of microcrystalline carbonate a fundamental problem for sedimentologists abstract recent studies of submarine lithification have shown that microcrystalline carbonate or carbonate mud traditionally thought to represent ooze deposited in quiet water commonly forms as an internal precipitate below the sediment water interface this internally precipitated micrite alters the mud grain ratio of pre existing sedimentary deposits and invalidates classifications that relate the amount of micrite matrix in limestones to the degree of water energy associated with the environment of deposition

on the expected structure of extreme waves in a gaussian sea part ii swade scanning radar altimeter measurements abstract in a previous paper phillips et al an approximate theory was developed that predicted that the expected configuration of extreme waves in a random sea or the average configuration of an ensemble of extreme waves is proportional to the space time autocorrelation function of the surface displacement of the wave field as a whole this result is tested by examination of scanning radar altimeter measurements made during swade in four different sea states including a unimodal mature wave field a short fetch a wind generated sea crossing swell a very broad directional spectrum and a fetch limited wind sea with opposing swell in each of these the spatial autocorrelation function was found directly from the sra data the highest waves in each dataset were selected and their configurations averaged with respect to the crest these averaged configurations were in each case found to be consistent with the autocorrelation function

a stable isotope study of multiple species of planktonic foraminifera across sapropels of the tyrrhenian sea odp site 974 abstract the planktonic foraminifera globigerinoides ruber white variety globigerinoides elongatus orbulina universa globigerina bulloides globorotalia inflata and the fine fraction

origin and significance of isotope shifts in pennsylvanian carbonates asturias nw spain abstract the primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water an inadequate understanding of this variability as well as different diagenetic environments severely limit the interpretation of the stable isotope record of shoalwater carbonates in order to investigate this primary and diagenetic variability along a bashkirian moscovian platform to basin transect 13c and 18o analyses have been performed on more than 1000 matrix micrite carbonate cement and brachiopod shell samples in isotope analysis these different carbonate materials tend to complement each other inasmuch as they have different advantages and shortcomings the resulting data reveal spatial trends in 13c and 18o signatures from platform top lower values to basin higher values in the case of 13c from pristine brachiopods this trend can be explained by the long residence time aging of platform top water masses in the case of brachiopod 18o this variance is interpreted to reflect temperature differences between warm surface and colder bottom water separated by a permanent thermocline at about 150 to 200 m beneath the shelf break micrite and marine cement isotopic values from the platform interior were reset lowered during pervasive early meteoric diagenesis in contrast micrite and marine cement isotopic values from the outer platform slope and basin show higher values close to the assumed pennsylvanian seawater isotopic composition this implies that isotopic data from shoalwater carbonates including pristine brachiopod shells might not necessarily reflect paleoceanographic trends of the open ocean water masses because of changes in coastal water mass isotope signature and interaction with early meteoric fluids

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

geology of continental shelf onslow bay north carolina as revealed by submarine outcrops lithologic and stratigraphic data from rocks dredged from the continental shelf off onslow bay north carolina provide surface control for seismic studies of the southeastern united states continental margin and help to explain the distribution of potentially economic phosphate rich sediments on this shelf outcropping miocene rocks in this area indicate that the region has long been a positive geologic feature and has received relatively little pliocene and pleistocene sedimentation leached molluscan moldic calcareous quartz sandstones of late oligocene to early miocene age belgrade formation and middle to late miocene age pungo river formation crop out in southwestern and northeastern onslow bay respectively these two areas border a band of highly phosphatic su ficial sediments probably derived from unlithified phosphatic units of the pungo river formation lower pleistocene calcarenites that correlate with the waccamaw formation crop out on the sea floor near cape fear which bounds onslow bay on the south a core on frying pan shoals off cape fear after passing through pleistocene coquina calcareous quartz sandstone and oolitic sand penetrated upper pliocene calcarenites of the bear bluff formation and middle miocene phosphatic argillaceous sandstones of the pungo river formation samples from this core hole show that phosphate increases toward the top of the unindurated pungo river formation section indicating that this formation is probably the source of the high phosphate concentrations in the surficial sediments near cape fear wher the bear bluff calcarenites also crop out upper pleistocene units include oolitic limestones adjacent to the outer shelf calcareous quartz sandstones around cape fear and molluscan coquinas near cape lookout which bounds onslow bay on the north the outer shelf is blanketed by submarine lithified algal limestones and sandstones of holocene age

comparison of isotopic composition of planktonic foraminifera in plankton tows sediment traps and sediments planktonic foraminifera from plankton tows sediment traps and sediments in the central north atlantic were studied in order to understand what determines their oxygen and carbon isotope composition a clear separation of species and genera on a 18o vs 13c plot for all samples suggests that their isotopic composition is controlled to a certain degree by biological factors within a species population the globorotaliids show a positive linear correlation between 18o and 13c while the shallow dwelling spinose species mostly globigerinoides species do not show a definite trend the latter species when collected in plankton tows often show slight negative deviations from isotopic equilibrium with respect to oxygen all species deviate from carbon isotope equilibrium by 1 5 to 6 these deviations from equilibrium are probably caused by incorporation of isotopically light metabolic co2 into the skeleton which is enhanced by the activity of symbiotic algae during their ontogeny the average weight per individual of most species increases which indicates that calcification continues to a depth of about 100 m this additional skeleton roughly 50 by weight is isotopically heavier because temperatures are lower and photosynthesis of symbiotic algae stops below the photic zone therefore the skeleton of foraminifera collected in sediment traps below 400 m has an overall oxygen isotope composition that seems to be in equilibrium for caco3 deposited in the upper 100 m