long period perturbations in starlette orbit and tide solution continuous and dynamically consistent orbits have been computed using satellite laser ranging slr data to starlette for a one year period during 1976 and 1977 and the three year period from 1983 through 1985 a low degree and order ocean tide solution consisting of a total of 66 tidal parameters from 14 tidal constituents was obtained in a combined solution using both the one and three year starlette orbits an enhanced model of the schwiderski 1980 tide solution was used both as the a priori and the background tide model the model contains 368 tidal coefficients from 21 tidal constituents yearly values for the second degree annual tides sa which produce seasonal variations on the starlette node were obtained also these variations were found to have year to year fluctuations of more than 25 about the mean value and produced significant long period perturbations in the starlette orbit the starlette tide solution is in good agreement with the schwiderski tide solutions and with other satellite solutions including multi satellite tide solutions the average uncertainties are approximately 0 1 cm for the estimated semidiurnal and diurnal tides and 0 4 cm for the long period tides the discrepancies of effective k2 inferred from the starlette tide solution and other tide solutions are less than 0 01 the tide solutions were evaluated using orbit fits of a three year lageos and a one year starlette long arc the results indicate that the starlette tide solution produces significantly improved orbit fits for both lageos and starlette the uncertainties for the estimated tide model coefficients were used to predict tidal errors for the lageos orbit and were found to be consistent with the apparent tidal errors present in this orbit the computed secular change in the moon s mean motion due to tidal dissipation is 24 8 0 8 arc second century2 which is in good agreement with the results obtained from other investigations

solid pole tide in global gps and superconducting gravimeter observations signal retrieval and inference for mantle anelasticity abstract the mantle anelasticity plays an important role in earth s interior dynamics here we seek to determine the lower mantle anelasticity through the solution of the complex love numbers at the chandler wobble period the love numbers h 21 l 21 21 and k 21 are obtained in the frequency domain by dividing off the observed polar motion or more specifically the pole tide potential from the observed gps 3 d displacement field and sg gravity variation the latter signals are obtained through the array processing method of ose optimal sequence estimation that results in greatly enhanced signals to be extracted from global array data the resultant love number estimates h 21 0 6248 5 e 4 0 013 5 e 3 i l 21 0 0904 8 e 4 0 0008 2 e 3 i 21 1 156 2 e 3 0 003 1 e 3 i and k 21 0 3125 2 e 3 0 0069 3 e 3 i are thus well constrained in comparison to past estimates that vary considerably they further lead to estimates of the corresponding mantle anelastic parameters f r and f i which in turn determines under the single absorption band assumption the dispersion exponent of 0 21 0 02 with respect to the reference frequency of 5 mhz we believe our estimate is robust and hence can better constrain the mantle anelasticity and attenuation models of the earth interior

relations between relative changes in sea level and climate shifts pennsylvanian permian mixed carbonate siliciclastic strata western united states study of pennsylvanian virgilian permian wolfcampian strata of the western united states parts of idaho utah new mexico and kansas reveals complex relations between relative changes in sea level and shifts in climate relative falls in sea level are indicated by subaerial exposure of subtidal sediments and fluvial incision through subtidal sediments changes in the character of pedogenesis and sediment transport deposition and supply and the variable distribution of climatically sensitive lithofacies within cyclothems are interpreted to reflect shifts in climate during deposition of each cyclothem the majority of stratal relationships documented herein from a number of long term climatic sedimentologic and shelf settings are consistent with a hypothesis that relative highs in sea level are accompanied by more seasonal conditions whereas relative lows are characteristically more arid uncommon deviations are present however and may be due to 1 shoaling caused by sedimentation or tectonic uplift independent of a eustatic climatic signal 2 complex sedimentologic or geomorphic responses to climate change 3 leads lags or thresholds in either glacial advance and retreat or the climatic response to such changes this study shows that coupled climatic shifts and changes in sea level exert a pronounced but varied influence on stratigraphic architecture in depositional settings across late paleozoic ramps the proposed climatically enhanced cyclic and reciprocal sedimentation model predicts that during a single eustatic fall updip areas have features indicating a more seasonal or humid climate that are overlain or overprinted by characteristics suggesting more arid climate in downdip areas that were not subaerially exposed until the late stages of a eustatic fall only more arid climatic features are represented in the terrestrial or subaerial exposure features

revised predictions of long period ocean tidal effects on earth s rotation rate the rotational response of earth to long period tidal forces embodied in a zonal response function can be expected to vary with frequency because of variable contributions by the oceans mantle and core the zonal response function has been estimated from 9 years of international radio interferometric surveying iris universal time ut1 data and compared with theoretical predictions using a spherical harmonic tide model to compute the oceans dynamic response at semiannual monthly fortnightly and 9 day lunisolar tidal frequencies different amounts of mantle anelasticity have been considered for both the oceanic and solid earth responses predictions have been made assuming axial core mantle coupling which is either complete or absent additionally an extensive recalibration of the ocean model s frictional parameters was performed using constraints derived in part from space92 polar motion data zonal response function predictions have also been made employing this recalibrated ocean tide model our results indicate that any amount of core coupling can be ruled out at a fortnightly period and probably at a 9 day period but not at a monthly period our results also suggest that the mantle responds purely elastically at a 9 day period but may behave increasingly anelastically at longer periods a simple dispersive rule is postulated for periods ranging up to the 14 month chandler wobble period

the fortnightly and monthly tides resonant rossby waves or nearly equilibrium gravity waves abstract the fortnightly and monthly tides are discussed in the light of recent sea level observations and numerical modeling results within the tide gauge network of the low latitude pacific the fortnightly tide is shown to possess a large scale phase lag of roughly 10 40 degrees although the nonequilibrium part of the fortnightly tide is traditionally thought to be dominated by rossby wave dynamics it is shown via global shallow water modeling studies that this large scale phase lag is explicable in terms of remotely forced gravity waves whose origin is mainly in the arctic ocean although future observations outside the low latitude region of the pacific may eventually reveal rossby wave excitation the fortnightly tidal signal in the tide gauge network at hand appears to reveal at most only weak excitation of rossby waves compared to the phase lag due to remotely forced gravity waves the observed monthly tide appears to be only slightly closer to equilibrium than the fortnightly tide the reaso

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

an analysis of tidal variations in the length of day observations of the length of day lod corrected for the effects of variations in the angular momentum due to changes in wind velocity and atmospheric pressure ocean tide heights and currents and solid earth zonal tides were analyzed the apparent effect of atmospheric angular momentum aam on the astronomically determined lod is found to be much less at the highest frequencies than at lower frequencies for periods shorter than ten days there appears to be essentially no correlation between aam and lod the international earth rotation service iers standards 1992 model for the effects of zonal tides on the earth s rotation which includes ocean tidal effects adequately accounts for the observations of the variations in the length of day with periods between five and 180 days at the present level of accuracy a currently unexplained semi annual variation in the length of day remains but this may be due to the unmodeled effects of stratospheric winds the power spectrum of the remaining variations with periods less than twenty days is essentially that of a white noise process the amplitudes of the remaining unexplained variations in length of day are less than thirty microseconds this paper has been accepted by geophysical journal international for publication

role of temperature and nutrients in extinction of turritelline gastropods cenozoic of the northwestern atlantic and northeastern pacific abstract turritelline gastropods mesogastropoda turritelline are common to abundant components in many fossil cretaceous cenozoic and recent marine benthic communities but the environmental factors affecting their evolution and extinction are poorly understood this is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high nutrient conditions but thermal tolerances and preferences are unclear for extinct turritelline species turritellines were diverse and abundant throughout the new world for much of the cenozoic beginning in the early neogene through both extinction and range contraction however they started to disappear from higher latitudes on both atlantic and pacific coasts of north and central america the highest rate of extinction took place in the western atlantic in the plio pleistocene when almost all turritelline species in this area became extinct preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record this biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western atlantic at around the same time causes for turritelline extinction however appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western atlantic molluskan extinction event neogene turritellines in the western atlantic appear to have been adversely affected by collapse and or major reorganization of oceanic productivity associated with the formation of the isthmus of panama nutrients thus may have been more important than temperature change in controlling extinction probability in this group

phase relations for high frequency core mantle coupling and the earth s axial angular momentum budget abstract although it has long been thought that dynamical core mantle coupling is necessary for understanding decadal variations in the length of day lod the physics of the coupling mechanism are very poorly constrained there several hypotheses electromagnetic topographic gravitational viscous but it is notoriously difficult to distinguish between them on observational grounds there is both an expectation geophys j int 138 1999 679 and some evidence j geophys res 100 1995 8233 geophys res lett 24 1997a 1799 that there is significant core mantle coupling on much faster timescales down to subannual periods at such frequencies the core would no longer be the dominant driving force for lod but would instead interact with both the mantle and external reservoirs of angular momentum such as the atmosphere and ocean on these much faster timescales it is possible that some information that is obscured on decadal timescales becomes available in particular any characteristic timescales at very short periods may become observable here i examine the angular momentum budget of the earth on subannual to annual timescales for any additional implied constraints on the physics of angular momentum exchange between the core and the mantle i find that the discrepancy between atmospheric angular momentum and mantle angular momentum on timescales where the ocean is thought to be unimportant has a distinctive signature which is difficult to reproduce using simple models of core mantle coupling although an ad hoc frictional model does moderately well rather than indicating simplicity this may instead be symptomatic of great complexity in the physics of the core mantle boundary region

lateral continuity of facies and parasequences in middle cambrian platform carbonates carrara formation southeastern california u s a abstract lateral and vertical changes within a 40 m thick interval of peritidal carbonates middle cambrian jangle limestone member carrara formation se california produce a mosaic pattern of laterally continuous and discontinuous facies shallowing upward cycles 2 20 m thick parasequences and surfaces bounding parasequences this mosaic pattern was traced bed by bed across 1 8 km of continuously exposed outcrop and then correlated to sections in nearby ranges within parasequences contacts between successive subtidal facies tend to be sharp but may pass laterally into gradational contacts most subtidal facies extend laterally for less than 300 m passing gradationally over tens of centimeters to meters into other laterally adjacent subtidal facies lateral facies contacts between subtidal nodular ribbon rock and intertidal fenestral limestone are gradual over a few meters whereas contacts between vertically juxtaposed facies generally are sharp parasequence boundaries generally are sharp and locally show several tens of centimeters of erosional relief over lateral distances of several meters most parasequences and their bounding surfaces extend for the 1 8 km of outcrop studied and correlate to nearby ranges with varying degrees of confidence several parasequences however do not extend laterally for more than a few hundred meters and are not distinguishable in a vertical profile from those that extend laterally for tens of kilometers the stratigraphic relationships at eagle mountain southeastern california support a model in which the lateral continuity of parasequence surfaces is principally determined by accommodation variations and the lateral continuity of facies is most strongly influenced by the intrinsic dynamics of spatially and temporally heterogeneous sediment production the presence of parasequence boundaries of highly variable lateral extent suggests that the magnitude of accommodation variations was comparatively small consistent with the independent evidence for passive margin subsidence and transitional greenhouse conditions for the middle cambrian

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

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

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

an epeiric ramp low energy cool water carbonate facies in a tertiary inland sea murray basin south australia the murray supergroup records temperate water carbonate deposition within a shallow mesotrophic oligo miocene inland sea protected from high energy waves and swells of the open ocean by a granitic archipelago at its southern margin rocks are very well preserved and exposed in nearly continuous outcrop along the river murray in south australia most facies are rich in carbonate silt contain a background assemblage of gastropods especially turritellids and infaunal bivalves and are packaged on a decimetre scale defined by firmground and hardground omission surfaces bioturbation is pervasive and overprinted resulting in rare preservation of physical sedimentary structures facies are grouped into four associations large foraminiferan bryozoan echinoid bryozoan mollusc and clay facies interpreted to represent shallow water 50 m deposition under progressively higher trophic resource levels from low mesotrophy to eutrophy and restricted marine conditions from relatively offshore to nearshore regions a large scale shift from high to low mesotrophic conditions within lower miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow land locked sea overall low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity inshore heterozoan facies became progressively muddier and restricted towards the shoreline in contrast periods of wet climate led to rising trophic resource levels resulting in a shallowing of the euphotic zone a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids rates of carbonate production and accumulation were relatively low the murray basin is best described as an epeiric ramp wide facies belts developed in a shallow sea on a low angled slope reaching many hundreds of kilometres in length grainy shoal and back barrier facies were absent internally generated waves impinged the sea floor in offshore regions and because of friction along a wide and shallow sea floor created a low energy expanse of waters across the proximal ramp storms were the dominating depositional process capable of disrupting the entire sea floor

middle miocene deepwater paleoceanography in the southwest pacific relations with east antarctic ice sheet development a suite of middle miocene deep sea drilling project sites in the southwest pacific reveals large scale changes in deepwater circulation associated with east antarctic ice sheet eais variations from 16 5 to 13 8 ma oxygen and carbon isotopic records based on cibicidoides benthic foraminifera from a depth transect sites 590b 588a 591b and 206 from 1200 to 3150 m paleodepth at 35 s paleolatitude and from a meridional transect sites 588a 590b 593 and 594 from 30 to 48 s paleolatitude at intermediate water depth allow detailed examination of southwest pacific deepwater circulation from 17 5 to 12 ma significantly intervals of low 18o from 16 5 to 16 3 ma and perhaps at 15 7 ma were marked by similar 18o values at upper bathyal 1200 1500 m sites 588a and 590b and midbathyal 2100 m site 591b water depths small vertical 18o gradients during 18o minima may indicate warm saline deep water wsdw at midbathyal depths in the southwest pacific during intervals of inferred global warmth and low global ice volume increased vertical 18o gradients after 15 6 ma and especially after 13 8 ma indicate increased production of southern component water scw in association with eais growth these data are consistent with the hypothesis woodruff and savin 1989 that major eais growth was fostered by diminished meridional heat transport to the high southern latitudes related to the termination of tethyan indian saline water tisw and an increase in scw production during the early middle miocene after 15 6 ma further a maximum vertical carbon isotopic gradient of 0 8 at 13 6 ma suggests that southern component intermediate water sciw production and pacific deep water pdw strength were each at a maximum at this time and were critical to major eais growth the establishment of near modern 13c and 18o gradients following major eais growth from 14 0 to 13 8 ma marks a major step in the development of the neogene ocean cryosphere system

north sea pole tide dynamics s u m m a r y laplace tide equations ltes augmented to include linear bottom friction and chandler wobble forcing have been solved numerically for the pole tide in the north sea employing realistic bottom topography and geometrical boundaries the motivation for our study is the need to explain observations of enhanced pole tide amplitudes and eastward intensification along the southern boundary of the sea following wunsch 1974 the tidal dynamics are considered to depend on non equilibrium pole tide behaviour at the open northern boundary of the sea with reasonably small bottom friction and open boundary forcing the amplitude of the pole tide in the north sea is found to be close to equilibrium i e the coastal amplitudes do not match the observations however the phase lag obtained is close to those inferred from tide gauge analyses under these conditions the north sea has the potential to dissipate a considerable fraction 25 per cent of chandler wobble energy if much larger bottom friction is considered the resulting pole tide amplitudes are more highly variable within the sea and if the open boundary forcing is also much larger the tidal amplitudes match many of the observations in this case however the tidal currents dissipate an unacceptably huge amount of wobble energy an earlier version of this problem proposed by wunsch 1974 and reconsidered by dickman preisig 1986 in which time independent ltes are postulated in a north sea modelled with analytical bottom topography and a rectangular domainis also fully solved via the method of weighted residuals the solutions include one in which the non equilibrium portion of the tide height is nearly constant all over the domain the corresponding tidal currents are negligibly slow our work points to the importance of realistic bottom topography and coastline geometry in affecting the tidal dynamics such factors to date have not been considered in theoretical analyses of the north sea pole tide the realistic bathymetry and geometry produce a large variability in bottom friction which is inversely proportional to the water depth and thereby generate substantial dynamic behaviour despite the long period of the pole tide we find that these factors significantly enhance the tidal currents and promote an eastward intensification of the non equilibrium tide height near the southern coast

linked sequence development and global climate change the upper mississippian record in the appalachian basin the character and relative stratigraphic position of paleoclimatic indicators within upper mississippian strata of southern west virginia suggest a link between eustasy and patterns of continental to global scale atmospheric circulation at the cyclothem scale annual rhythms in marine facies and paleovertisols and lacustrine carbonates in terrestrial units indicate that seasonal semiarid climatic conditions prevailed during highstand progradation in contrast leached paleosols and coals that underlie sequence boundaries and occur within transgressive heterolithic facies are suggestive of humid climatic conditions during late highstand through early transgression milankovitch band glacial interglacial cyclicity may explain both sequence development and the evidence for late mississippian climate fluctuations in the appalachian basin shifts from seasonal to humid climatic conditions are attributed to systematic variation in monsoonal circulation whereby seasonal moisture became restricted to the equatorial belt during the lowstands of each 400 k y glacial interglacial cycle

accumulation rates of carbonate platforms the growth potential of carbonate platforms i e the maximum rate at which they can aggrade vertically is difficult to assess to estimate the growth potential from the conservative side and search for variations with time we have compiled published accumulation rates from the phanerozoic accumulation rates vary in a pattern with maximum rates up to 200 m ma or more not corrected for compaction in the late devonian permian late triassic late jurassic and mid cretaceous separated by intervals of reduced rates e g carboniferous early jurassic and late cretaceous the most dramatic drop occurs at the permo triassic boundary after which there is no documented platform growth this pattern resembles the evolutionary rhythm of bloom and demise of reefs and reef builders the observed maximum accumulation rate of 200 m ma over 10 6 10 7 yr is probably imposed by the maximum rate of long term relative sea level rise on passive margins the most favorable site for carbonate platform deve

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

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

experiments in tidal mass conservation summary a common feature of theoretical ocean tide models is their failure to conserve mass over the oceans this failure distorts the tidal solution and imparts ambiguity to the calculation of tidal effects on gravity crustal loading and earth rotation for example predicted effects of long period tides on rotation could be uncertain by up to 50 per cent in magnitude and 100 per cent in phase using the spherical harmonic tide theory developed by dickman 1989 the influence of various global conservation constraints on the tidal solution is explored an ocean wide mass conservation constraint implemented using lagrange multipliers produces a realistic and significantly more accurate and unambiguous tidal solution

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

constraints on q at long periods from earth s rotation in this work we assess constant q and frequency dependent q models of mantle anelasticity our assessment uses the degree 2 love numbers we had inferred previously from a comparison of observed and predicted changes in the length of day at monthly fortnightly and nine day lunar tidal periods the comparison accounted for variable contributions to the tidal signals by dynamic oceans and allowed for axial core mantle coupling that was either complete or absent the love number derived from an earlier analysis of the period of the chandler wobble is also employed we find that the similarity of the degree 2 love number inferred at a nine day period to that at seismic frequencies combined with the significant amount of relaxation at the chandler period together imply that q models operating within the seismic band cannot extend all the way to long tidal periods our analysis of q also allows us to refine estimates of the love number at fortnightly and monthly periods

wind driven export of weddell sea slope water the export of waters from the weddell gyre to lower latitudes is an integral component of the southern subpolar contribution to the three dimensional oceanic circulation here we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the antarctic peninsula and 5 years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold fresh westward flowing current this is often bottom intensified between 600 and 2000 dbar with velocities of over 20 cm s 1 transporting an average of 1 5 1 5 sv by comparison with hydrography on the continental slope within the weddell sea and modeled tracer release experiments we show that this slope current is an extension of the antarctic slope current that has crossed the south scotia ridge west of orkney plateau on monthly to interannual time scales the density of the slope current is negatively correlated r 0 6 with a significance of over 95 with eastward wind stress over the northern weddell sea but lagging it by 6 13 months this relationship holds in both the high temporal resolution bottom lander time series and the 20 year annual hydrographic occupations and agrees with weddell sea export variability observed further east we compare several alternative hypotheses for this wind stress export relationship and find that it is most consistent with wind driven acceleration of the gyre boundary current possibly modulated by eddy dynamics and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate level waters to lower latitudes

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

time partitioning in cratonic carbonate rocks dissimilarity in relations between thickness duration and accumulation rate in holocene sections metre scale phanerozoic cycles and epoch interval phanerozoic sequences reflects variation in the distribution of depositional and hiatal time at different scales of observation modern accumulation rates are strongly dependent on duration of deposition lower rates correspond to longer durations phanerozoic cycle thicknesses are similar to those of holocene sections suggesting that both formed while filling similar amounts of accommodation space however accumulation rates of phanerozoic cycles and sequences are about two orders of magnitude less than in modern settings and they show neither strong dependence on duration of accumulation nor significant variation over phanerozoic time hence net accumulation is primarily controlled by regional subsidence rate these relations also allow for determination of that fraction of cycle period recorded as rock and that corresponding to hiatal time at intercycle boundaries depending on subsidence rate and amount of compaction most cratonic carbonate units accumulated over 3 to 30 of the time represented by sequences in which they occur

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

fortnightly earth rotation ocean tides and mantle anelasticity summary this study of the fortnightly mf tide comprises three main topics 1 a new determination of the fortnightly component of polar motion and length of day lod from a multidecade time series of observed space geodetic data 2 the use of the polar motion determination as one constraint in the development of a hydrodynamic ocean model of the mf tide and 3 the use of these results to place new constraints on mantle anelasticity at the mf tidal period our model of the mf ocean tide assimilates more than 14 years of altimeter data from the topex poseidon and jason 1 satellites because the mf altimetric signal to noise ratio is very small it is critical that altimeter data not be overweighted the polar motion data plus tidegauge data and independent altimeter data give useful additional information with only the polar motion putting constraints on tidal current velocities the resulting ocean tide model plus the dominant elastic body tide leaves a small residual in observed lod caused by mantle anelasticity the inferred effective tidal q of the anelastic body tide is 90 and is in line with a frequency dependence with in the range 0 2 0 3

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

a complete spherical harmonic approach to luni solar tides summary in this work a spherical harmonic theory of ocean tides is presented the theory is based on laplace tide equations modified to include turbulence with constant eddy viscosity linearized bottom friction and oceanic loading and self gravitation variable bathymetry is also treated in harmonic terms and no flow boundary conditions are applied at continental coastlines the tide and boundary constraint equations are reduced to matrix form and solved by a weighted least squares procedure five zonal luni solar tides ranging in period from 14 days to 18 6 yr are investigated using the theory such tides have typically been difficult to compute using traditional numerical approaches the polar motion and changes in the length of day induced by these long period tides are calculated tidal solutions are compared extensively with results from other tidal theories and from recent satellite and sea level observations the greatest limitation to accurate prediction of zonal tides for any theory appears to be the marginal failure of all tide theories to conserve mass globally the use of additional mass constraints may be warranted

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

petrogenesis of cenozoic temperate water calcarenites south australia a model for meteoric shallow burial diagenesis of shallow water calcite sediments abstract the gambler limestone is one of several extensive shallow water shelf carbonates of eocene to miocene age exposed along the southern margin of australia it is a muddy to grainy bryozoan calcarenite with accessory benthonic foraminifers and echinoids the sediments originally composed almost entirely of calcite or mg calcite have been in vadose and phreatic environments for over 10 ma yet are virtually unlithified the only cements of any consequence are epitaxial on echinoids numerous karst features dolines caves speleothems and surface karren attest to prolonged residence in the meteoric zone the gambler limestone is presently one of the best fresh water aquuifers in australia most flow occurs through intergranular pores in sediments with over 30 porosity cementation is by minor intergranular pressure solution which has developed under overburden of less than 100 m the overlying naracoorte limestone miocene a calcarenite of warmer water aspect contains numerous aragonite molds and is well cemented we propose that such cool water limestones are a better model for the meteoric diagenesis of calcite sediments of all ages than are aragonite rich tropical sediments it is probable that many similar early and middle paleozoic calcite limestones may have been in the meteoric zone for prolonged periods yet contain little or no petrographic or geochemical record of such exposure

determination of oceanic dynamic barometer corrections to atmospheric excitation of earth rotation the excitation of earth s rotation by atmospheric pressure fluctuations on timescales from days to years is modified by the oceanic response to the pressure load that response has often been approximated as a static inverted barometer ib change in sea level but evidence from theory and both tide gauge and altimetric data suggests that the ib poorly models the sea level response at short periods static models also fail to account for the currents induced by the pressure loading the actual dynamic response of the oceans to barometric loads depends on frequency and on the spatial structure of the loading this work presents a green s function approach to determining the rotational effects of that oceanic response the green s functions characterize the rotational effects of the oceanic response to pressure loads described spatially by individual spherical harmonics for each harmonic of forcing they were computed at nine periods ranging from 4 days to 18 years and interpolated at intermediate periods computations were based on solutions to the author s dynamic spherical harmonic ocean tide model the effects on rotation of the dynamic barometer oceanic response are obtained by a convolution type combination of the green s functions with actual atmospheric pressure data results for data spanning the past decade will be illustrated using harmonically decomposed national center for environmental prediction ncep and european centre for medium range weather forecasts ecmwf pressure fields

the influence of a sudden climatic change on marine deposition in the kimmeridgian of northwest europe a sudden change from humid style to semi arid style deposition markedly affected the accumulation of the upper kimmeridge clay in southern england many of the changes appear to be related to a change in sedimentation rate at this time thus softground faunas are replaced by firmground faunas diagenetic dolostones formed in the methanogenic zone are replaced by sulphate reduction zone carbonate nodules and depositional gradients recorded by lateral biofacies changes becomes steeper the evidence available is in accord with a decline in offshore sedimentation rates during this interval other changes such as a decline in kaolinite abundance were more directly controlled by the drying out of the hinterland similar changes elsewhere in the marine geological record could be used as climatic indicators the climatic change is part of a wider northern hemisphere dry event which affect a broad area in the late jurassic the kimmeridge clay of southern england was one of the last depositional environments to be influenced by the climatic change at this latitude

transgressive surfaces of erosion as sequence boundary markers in cool water shelf carbonates abstract although sequence stratigraphy was first conceptualized in and applied to siliciclastic successions its methodology and concepts are applicable to the carbonate regimen provided that potential modifications to the existing models are appreciated that take into account the specificities of carbonate systems we demonstrate that some properties inherent to isolated i e continent detached shallow water temperate carbonate systems including their typical low diagenetic potential due to the prevalance of calcitic mineralogies the critical role exerted by storm waves and tidal currents on sediment dynamics e g shedding of sediments at wave abrasion depth during highstand and lowstand conditions and uneven sea bed topographies cause both the genesis and preservation of subaerial unconformities to be uncommon thereby rendering their use as sequence boundaries inappropriate instead transgressive surfaces of erosion tses that formed as wave base shifts upwards during early rise of relative sea level are readily identifiable in the field extensive and by their very nature are preserved in the rock record typically at the base of upward deepening stacked facies in pliocene cool water carbonate successions from new zealand the tses are characterized by starved sedimentation and burrowed network development and are overlain by coarse bioclastic shoreface sediments and shell beds in most cases the surfaces top truncate shoaling upward deposits but also deepening upward stacking facies in places emersive events rarely correspond to actual physical surfaces but diagenetic evidence preserved beneath tses indicates that occasionally subaerial surfaces had previously developed and were later modified into tses therefore we propose that tses are the most adequate unconformities to define high order depositional sequences 20 250 ka in the studied successions because by contrast with emersion surfaces their formation and preservation are not dependent upon cool water sedimentary facies and mineralogy and are favoured by the dynamics of the setting i e wave base shift and accommodation creation during relative sea level rise

a new look at sedimentation rates and the completeness of the stratigraphic record several recent papers have suggested that completeness of stratigraphic sections can be estimated by using the ratio of long term sedimentation rates to short term rates we show that the median short term sedimentation rates used in these papers are erroneous and are mostly an artifact arising from improper data manipulation to demonstrate the artificial character of short term median rates we have generated a series of plots assuming a constant sedimentation rate with fixed variance and defined limits of measurement precision these plots demonstrate that increasing variance in the time required to deposit sediments will result in spuriously high short term median sedimentation rates a new method for calculating median sedimentation rates which eliminates the problem of spurious median rates is then applied to make an improved estimate of expected completeness recalculated median values show that sedimentation rates for pelagic sediments are close to identical for both short term and long term tim

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

evidence for excitation of polar motion by fortnightly ocean tides the second degree zonal tide raising potential which is responsible for tidal changes in the earth s rotation rate and length of day is symmetric about the polar axis and hence can excite the earth s polar motion only through its action upon nonaxisymmetric features of the earth such as the oceans ocean tidal excitation of polar motion in the diurnal and semidiurnal tidal bands has been previously detected and examined here the detection of ocean tidal excitation of polar motion in the long period tidal band specifically at the mf 13 63 day and mf 13 66 day tidal frequencies is reported spectra of the space94 polar motion excitation series exhibit peaks at the prograde and retrograde fortnightly tidal periods after removing effects of atmospheric wind and pressure changes an empirical model for the effect of the fortnightly ocean tides upon polar motion excitation is obtained by least squares fitting periodic terms at the mf and mf tidal frequencies to the residual polar motion excitation series the resulting empirical model is then compared with the predictions of two hydrodynamic ocean tide models

the self consistent dynamic pole tide in non global oceans summary fluid dynamic theories of the pole tide are in conflict with pole tide observations the former predict that the oceanic response to the chandler wobble should be nearly static while the latter reveal the tide to possess significant non equilibrium characteristics resolution of the conflict would determine whether mantle anelasticity or non equilibrium oceans is responsible for a measurable contribution to the chandler period it is possible that resolution might be achieved through a more exact mathematical investigation of pole tide fluid dynamics than theories have carried out to date the theories have also neglected to consider a unique property of the pole tide its ability to lengthen the period of its own forcing function this property implies that the pole tide characteristics and effects on wobble cannot be correctly determined unless the tide and wobble equations are jointly solved this work constitutes a first attempt to determine accurately and self consistently the nature of the pole tide and its effects on the chandler wobble the laplace tidal equations modified by the addition of bottom friction but with no simplifying approximations are employed together with the liouville equations to elucidate pole tide characteristics this work is a first attempt because the earth model chosen is a crude one consisting of global oceans of uniform depth overlying a rigid mantle with a fluid core results for this model suggest that departures of the pole tide from equilibrium may indeed be minimal the relevance of these results to the actual pole tide however must await the application of our self consistent and more exact dynamical theory to the situation of realistic oceans

paleoclimatic and tectonic control on the accumulation of north american cratonic sediment variation in accumulation rate as a function of depositional latitude has been determined for north american limestone dolostone sand stone gray black shale red shale and evaporite rocks from tabulations by ronov and co workers from data in lexicons of united states and canadian stratigraphy and from isopach and lithofacies maps published in 1975 by cook and bally phanerozoic sediment is similar to that on other continents consisting of 63 terrigenous elastic facies 23 sandstone 40 shale 36 carbonate and 1 chert evaporite and other minor rock types latitudinal variation in accumulation rate is influenced primarily by past positions of foreland and intracratonic basins additional variation related to paleoclimate is recorded as strong dependence of limestone dolostone red shale and evaporite deposition on latitudes of accumulation a relation reflecting the importance of ambient temperature and meteoric precipitation on the formation of various authigenic phases poleward increase in dolostone total carbonate ratio in both hemispheres implicates the importance of syndepositional diagenesis in the formation of most dolostone sequences the ratio of sandstone total terrigenous clastic sediment exhibits little variation with latitude a constancy indicating that most sand and mud is derived from older sediment rather than from the weathering of crystalline rock as a result terrigenous lithofacies record little climatic influence in the proportional delivery of mechanically versus chemically derived weathering products to basins of accumulation

the expected duration of upward shallowing peritidal carbonate cycles and their terminal hiatuses meter scale accommodation cycles which dominate the stratigraphic record of peritidal carbonate accumulation might provide a time scale of unusually high resolution but the duration of the hiatuses that cap the resulting cyclothems is difficult to determine thousands of rates of peritidal accumulation from many different carbonate sections have been combined according to the length of the time span of measurement to describe a hypothetical average section because all sections are interrupted by hiatuses the average accumulation rate falls progressively with increasing time span and most steeply at the time spans that capture the highest proportion of hiatuses the process of combining rates from many sections cancels local differences in the distribution of hiatuses only hiatuses that have similar spacing and duration in a majority of sections will stand out after compilation the size and position of a pronounced inflection in the combined plot of accumulation rates against time span identifies a dominant cycle period of 100 000 yr of which the terminal hiatus accounts for 80 90 the expected cyclothem is 10 m thick because peritidal accommodation cycles begin and end with the sediment surface at sea level the expected cycle period can be estimated by finding the time span at which accommodation and accumulation rates balance the maximum duration of the hiatus is the time span at which rates of subsidence and sea level fall balance compilations of many empirical measurements were again employed to determine the relationship between time span and the rates of subsidence sea level change and net accommodation this second method confirms the results of the first and can be modified to predict the expected cyclothem in different climatic tectonic and depositional settings because quaternary data dominate short term rates the hypothetical average section best describes a passive margin in an icehouse climate with strong glacio eustatic fluctuations in sea level after modification for an extreme greenhouse climate devoid of ice caps the second method predicts that 20 000 yr accommodation cycles will be preferentially recorded the expected cyclothem is 2 m thick and accounts for about 50 of the cycle period increased subsidence rates whether on active margins in the initial phase of passive margin formation or at the seaward edge of a platform tend to extend the limit of cycle duration increase cyclothem thickness and partition less time to the bounding hiatus increased subsidence however raises the risk that the sediment surface will drown

spectral and geographical variability in the oceanic response to atmospheric pressure fluctuations as inferred from dynamic barometer green s functions 1 a decade ago a novel theoretical approach was developed dickman 1998 for determining the dynamic response of the oceans to atmospheric pressure variations a response nicknamed the dynamic barometer db and the effects of that response on earth s rotation this approach employed a generalized spherical harmonic ocean tide model to compute oceanic green s functions the oceans fluid dynamic response to unit amplitude pressure forcing on various spatial and temporal scales and then construct rotational green s functions representing the rotational effects of that response when combined with the observed atmospheric pressure field the rotational green s functions would yield the effects of the db on earth s rotation the green s functions reflect in some way the geographical and spectral sensitivity of the oceans to atmospheric pressure forcing we have formulated a measure of that sensitivity using a simple combination of rotational green s functions we find that the db response of the oceans to atmospheric pressure forcing depends significantly on geographic location and on frequency compared to the inverted barometer ib the traditional static model the db effects differ slightly at long periods but become very different at shorter periods among all the responses the prograde polar motion effects are the most dynamic with large portions of the north atlantic and some of the north pacific no larger than one third of ib but most of the southern hemisphere oceans at least 50 greater than ib

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

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

deepening upward subtidal cycles murray basin south australia abstract decimeter scale deepening upward cycles are the basic depositional motif of oligocene miocene murray supergroup limestones in the murray basin southeastern australia cycles formed in this large intracratonic basin on a centripetal temperate water epeiric ramp they reflect generation by trophic resource influenced carbonate production under mostly transgressive conditions listed from the base up each cycle is ideally composed of five parts part a biotically depauperate carbonates reflecting relatively shallow water restricted variably stressed highly mesotrophic environments part b increasingly biotically diverse limestones recording progressively more physical energy and less mesotrophic conditions upward om1 a conspicuous hardground to firmground surface formed during late transgression to stillstand during which wave sweeping and reworking contributed to omission and lithification part c relatively biotically diverse epifauna dominant sediments that were highly abraded during periods of condensed sedimentation under marginally oligotrophic conditions and om2 cycle boundary a rarely conspicuous surface representing arrested sedimentation and variable cementation as trophic resources increased and conditions for carbonate production deteriorated ten cycle types are grouped into four major styles clay cycles mollusc cycles echinoid cycles and bryozoan cycles these are interpreted to form a lithological continuum from inner restricted terrigenous locales to outer open marine bryozoan colonized environments deepening upward cycles were profoundly sensitive to autogenic factors such as nutrient influx terrigenous content and turbidity hydrodynamic energy water temperature salinity and water depth manifested in this intracratonic setting although these cycles share a similar sedimentological motif and hydrodynamic energy based cycle capping process with open shelf epicratonic shallowing upward subtidal cycles of tertiary age they formed in a very different way reflecting the distinctive intracratonic environment in which they formed murray basin cycles preserve a record of relative sea level rise whereas open shelf cycles accumulated mostly during relative sea level fall

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

the variation with frequency of the long period tides the oceanic response to long period tidal forcing in closed basins approaches equilibrium for periods much longer than a month for moderate values of dissipation at a given frequency the response is closest to equilibrium near the eastern wall of the basin global calculations of the mf and mm tides made using a 2 2 grid are presented changes in the length of day have also been computed for these tides

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics

ramp facies and sequence stratigraphic models in an epeiric sea the upper ordovician mixed carbonate siliciclastic glenwood and platteville formations wisconsin usa