evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

new evidence for two highstands of the sea during the last interglacial oxygen isotope substage 5e sedimentologic stratigraphic and geochronologic analyses of a previously undescribed carbonate section on oahu hawaii provide new evidence for two distinct sea level highstands on oahu during the last interglacial period oxygen isotope substage 5e whereas electron spin resonance and uranium series ages 122 8 ka to 152 25 ka and 115 10 ka to 160 15 ka respectively of in situ corals place the age of the deposits within substage 5e it is the unique sequence of strata found in these exposures that reveals the two transgressions a highstand lagoonal deposit of coral algal bafflestone is overlain by large seaward dipping slabs of beach rock the beachrock deposited during a mid 5e regression is in turn overlain by a second highstand lagoonal deposit this sequence was deposited in a broad shallow back reef embayment that was very sensitive to fluctuations in sea level elsewhere along much of the shoreline of oahu an in situ coral algal framestone waimanalo formation representing the initial 5e highstand is erosionally truncated on its upper surface this erosional unconformity represents the mid 5e lowstand and separates the framestone from overlying seaward dipping planar bedded grainstone and rudstone leahi formation that accumulated during the second 5e highstand

chaotic deposition by a giant wave molokai hawaii a coral basalt breccia conglomerate is exposed 60 m above present sea level and nearly 2 km inland from the present shoreline on the southwest side of east molokai volcano molokai the conglomerate is preserved mantling interfluves between gullies and forms a blanket like deposit 0 5 to 3 m thick no evidence of a wavecut terrace either within the blanket or at its upper or lower limits of exposure can be found no coral was found in growth position unsorted basalt clasts as large as boulder size are subrounded to angular randomly oriented and vary from 2 3 to 50 volume of the deposit the size of the largest basalt and coral fragments shows almost no systematic variation with elevation distance inland or lateral position parallel to the shore two indistinct rock units are present in a few places a lower carbonate rich unit that we interpret as an onwash facies and an upper basalt rich unit an offwash facies the carbonate rich onwash facies is dominated by biogenic debris especially fragments of coral and beach rock and gastropod and bivalve shells the offwash facies contains 40 to 90 basalt cobbles and boulders in a matrix of finely broken biogenic fragments where the distinct facies are lacking the proportion of basalt clasts increases crudely from the lower to the upper part of the conglomerate at a single place and from lower to higher elevation out crops where the deposit overlies a cinder cone several carbonate bearing elastic dikes extend from the conglomerate as much as 10 m down into the basalt cinders this deposit was apparently laid down by a giant wave that broke over an outer reef similar to the present fringing reef and advanced as a turbulent bore over the back reef flat picking up a slurry of carbonate rich debris and depositing it on the slopes inland as the wave advanced the offwash picked up loose basalt debris on its return flow u series dating of coral fragments indicates that the age of this deposit is 240 200 ka indicating the wave is distinct from that which produced a similar deposit on lanai about 100 ka this giant wave was most likely caused by one of the many large submarine landslides that have been identified on the lower slopes of the major hawaiian islands

south carolina interglacial sites and stage 5 sea levels abstract amino acid and other studies have been made on the 30 km pleistocene sections of the intracoastal waterway between myrtle beach and little river south carolina our ratios differentiate the long established waccamaw oldest canepatch and socastee formations the ratios from the four laboratories that have worked in this area agree very well and apparent conflicts with u series dates may merely reflect an abundance of reworked corals our amino acid correlations with u series coral dates in south carolina bermuda and the mediterranean all argue that the classical canepatch and its horry clay date from isotope stage 5e and not as has been implied from stage 7 9 11 or 13 excavations and erosion have increased position fixing problems along the waterway and canepatch amino acid ratios and u series dates 460 000 100 000 yr b p at icw5 may be from an older unit the canepatch shows the double marine transgression visible in many stage 5e deposits pollen shows that the second transgression occurred late in the interglaciation and stratigraphic studies show that it reached 14 m it therefore fits very well antarctic ice surge models of stage 5 sea level and climate the socastee adds to the evidence for one or more sea levels above 0 m late in stage 5

records of cosmogenic radionuclides 10be 26al and 36cl in corals first studies on coral erosion rates and potential of dating very old corals we present results of measurements of cosmogenic 10 be 26 al and 36 cl and the indigenous intrinsic concentrations of the stable elements be al and cl in 120 200 kyr old corals from barbados and puerto rico the concentration levels of these radionuclides in the corals lie in the range 10 4 to 10 8 atoms g a comparison of the measured nuclide concentrations with those expected to be produced in the corals by nuclear interactions of energetic cosmic radiation shows that i the radionuclides 26 al and 36 cl are derived from in situ cosmic ray interactions in the corals after their formation but that ii the radionuclide 10 be owes its provenance in the coralline lattice primarily due to incorporation of dissolved beryllium in seawater in the lattice structure of the corals copyright 2005 elsevier ltd we discuss production rates and potential uses of cosmogenic radionuclides in corals and the implications of the measure ments reported here on the concentration of the cosmogenic radionuclides 10 be 26 al and 36 cl we show that the latter two radionuclides serve as gauges of coral terrace erosion rates whereas the cosmogenic 10 be is suitable for determining the ages of old corals of ages exceeding a few million years up to 10 myr the erosion rates of the corals range from 0 7 to 5 10 3 cm yr corresponding to an appreciable surface loss after aerial exposure 1 3 m since the last interglacial and 8m since the penultimate interglacial

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

tims u series dating and stable isotopes of the last interglacial event in papua new guinea the extensive flight of uplifted reef terraces which occurs along the vitiaz strait on the northern flank of the huon peninsula in png papua new guinea contains a particularly good record of sea level changes in the last 250 ky the huon terraces were the target of an international expedition which took place in july august 1988 in particular we searched for suitable samples for u series dating in a reef complex designated as vii which is correlated with the last interglacial episode and high sea level stand this complex is composed of a barrier reef viib a lagoon and a fringing reef viia twelve corals from these terraces and two corals from the older reef complex viii were selected for analysis the petrography oxygen and carbon isotope compositions and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium 230 th 234 u ages of the corals with 99 aragonite having primary textures and which show u sr ratios around 0 4 10 3 and initial 234 u values close to that of present seawater appear to be reliable the most reliable ages from complex vii corals fall in two tight groups centered at 118 ky and 134 ky corals with 234 u t values higher than 160 and u sr ratios substantially lower than seawater are assumed to have undergone diagenetic alteration which appears to be common in this area the simplest model for sea level height for terrace vii is a continuous rise between 134 and 118 ky alternatively there may have been two periods of rapid sea level rise in contrast in the bahamas there is evidence that sea level remained rather constant over the time interval 132 to 120 ky the absence of ages between 132 and 120 ky in png could be the result of changes in the local tectonic uplift rates during that time or erosion that disrupted the continuous record in any event we find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation or as a test of climatic models the older ages reported here precede the milankovitch solar insolation peak at 128 ky and the younger ages are 10 ky after this peak if the present high precision data are correct then it will be necessary to reassess the validity of the milankovitch theory of climatic changes the fundamental issue which must now be resolved is a means of identifying coral samples that have not been disturbed by diagenetic processes

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

234u 238u ratios and230th ages for hateruma atoll corals implications for coral diagenesis and seawater234u 238u ratios published results for corals that are more than ca 50 ka old from for example barbados and vanuata often yield initial 234u 238u activity ratios that are significantly greater than 1 144 0 004 the value for modern seawater this study reports results for corals from hateruma atoll japan and investigates the effects of diagenesis on the initial 234u 238u ratios of the corals hateruma consists of over 95 reef material of less than 500 ka in age because groundwaters associated with recent carbonates tend not to have elevated 234u 238u ratios the scope for increasing the 234u 238u ratios of hateruma corals through groundwater interaction should be minimal the corals examined range from those which show no petrographic or x ray evidence for diagenetic alteration and are pristine to those containing secondary cements of either aragonite or high or low mg calcite these various phases have been mechanically separated and analysed in agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples it is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial 234u 238u ratios of the six pristine corals three have anomalous 230th 238u ratios requiring u loss and or230th addition the remaining fifteen of the eighteen total analyses reported here yield ages from 1 6 ka to 260 ka no evidence for an increase in 234u 238u ratios in past seawater from this period has been found the best estimates for 234u 238u ratios are close to the current seawater value

strong sh to love wave scattering off the southern california continental borderland seismic scattering is commonly observed and results from wave propagation in heterogeneous medium yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging in this study we analyze broadband waveforms recorded by the southern california seismic network and observe strongly scattered love waves following the arrival of teleseismic sh wave these scattered love waves travel approximately in the same azimuthal direction as the incident sh wave at a dominant period of 10 s but at an apparent velocity of 3 6 km s as compared to the 11 km s for the sh wave back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the southern california continental borderland in particular the patton escarpment finite difference simulations using a simplified 2 d bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers the modeling suggests a relatively low shear wave velocity in the continental borderland

on the influence of stratification and continental shelf and slope topography on the dispersion of subinertial coastally trapped waves abstract the behavior of subinertial coastally trapped free waves in a continuously stratified ocean is examined using a two slope topography in which the continental shelf and slope are each represented by a single uniform slope surface intensified stratification is assumed in which the squared buoyancy frequency profile is of the form n2e z where n is the buoyancy frequency at the surface z 0 and the vertical decay scale normalized by the deep sea depth the continental slope is typically assumed to be steeper than the shelf two qualitatively different types of dispersive behavior are distinguished when n f a2 e h 2 where f is the coriolis parameter a2 the bottom slope of the continental slope and h the shelf break depth normalized by the deep sea depth then free waves may occur at any subinertial frequency and each dispersion curve rises to f at some finite alongshore wavenumber as in the case of baroclinic kelvin waves if n f a2 e h 2 then all of the free wave dispersion curves a

seismic scattering near the earth s surface the seismic coda is usually thought to be composed of waves scattered from the heterogeneities in the earth three classes of scattering mechanisms have been recognized repeated specular reflection of primary waves in a uniformly layered structure volume scattering of primary waves from localized volume heterogeneities and scattering of primary waves from irregularities in an otherwise generally layered structure the presence of the earth s surface complicates the description of all these scattering phenomena whenever the scattering obstacles are near or at the surface in this paper i review work which demonstrates the effects of scattering near the earth s surface emphasizing three general areas of investigation scattering of body waves from an irregular free surface scattering of body waves in irregular layers and propagation of surface waves across irregular topography or in irregular wave guides most of the effects of importance have been recognized in model studies of idealized geometries observational evidence in support of the model studies exists but is often inferred few controlled experiments to measure scattering have been performed

u series measurements in tyrrhenian deposits from mallorca further evidence for two last interglacial high sea levels in the balearic islands the campo de tiro type section for the tyrrhenian ecostratigraphic beds of the balearic islands shows four indurated littoral conglomerates and beach rocks unconformably superimposed the lower two units 1 and 2 are separated by a thin layer of reddish continental silts both contain a typical eutyrrhenian fauna whereas a neotyrrhenian fauna characterizes the overlying units 3 and 4 thu measurements by thermal ionisation mass spectrometry on mollusk shells from these deposits yielded ages of 135 ka unit 1 117 ka units 2 and 3 and a scatter of ages around 100 ka unit 4 the stratigraphic relationships and thu data indicate i that uranium was uptaken by mollusks shells but arca sp each time during a relatively short early diagenetic interval before cementation ensured a fair closure of the radioactive system ii two high sea stands characterized the last interglacial isotopic substage 5e of the balearic islands area iii the duration of this episode was 17 ka and iv the change in faunal assemblages and disconformity observed between units 2 and 3 are due to fluctuations in sea level and surface water conditions which occurred during the second high sea level episode of the last interglacial

high precision u series dating of corals from western australia and implications for the timing and duration of the last interglacial abstract u series ages using methods of thermal ionisation mass spectrometry tims are reported for last interglacial fossil reefs along the stable coastal margin of western australia thorium isotope ratios were measured with superior precision using methods of charge collection high levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors excluding the uncertainty in the decay constants by a factor of four over the precisions reported by many earlier tims workers uncertainties in 234u t determined from both 230th 238u and 234u 238u are also significantly smaller than previously reported allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified strict criteria were adopted to screen the new western australian data reliable ages range from 127 to 122 ka published tims observations from other localities have been assessed using the same strict criteria when these are combined with glacio hydro isostatic sea level models they indicate that the last interglacial period occurred from at least 130 to 117 ka however these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the last interglacial globally the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka in direct agreement with the narrow range in ages obtained from the western australian sites this may indicate that the last interglacial was of short duration extending from 127 to 122 ka only alternatively this interval may reflect a major reef building event in the middle of a longer duration 130 117 ka interglacial interval

scattering of teleseismic p waves by the japan trench a significant effect of reverberation in the seawater column abstract we detected a scattered wave train in data from the high sensitivity seismograph network in japan hi net following the arrival of the near vertically incident p wave generated by the 2009 earthquake mw 7 8 off the south island of new zealand the scattered wave train represented predominantly vertical ground motion at a period of 20 to 50 s and with an apparent velocity of 3 5 km s it propagated cylindrically westward through the kanto area of central japan array analysis showed that the scattered wave train developed beneath the pacific ocean near the boso triple junction southeast of the kanto area a 3d finite difference simulation of seismic wave propagation using a high resolution model incorporating subsurface structure topography and bathymetry revealed that the strong scattered waves that were generated along the japan trench and propagated normal to the trench axis represented multiple reverberations of seismic waves between the seafloor and the pacific plate boundary in addition strong reverberation of acoustic waves in the seawater column above the boso triple junction causes elongated scattered waves which reasonably explains our observations

continental shelf wave propagation in the mid atlantic bight a general dispersion relation abstractthe authors address the propagation of continental shelf waves in the mid atlantic bight an analytical model of the bathymetry in the region is constructed by representing the continental shelf as a gently sloping bottom which deepens linearly with offshore distance to the place where it meets the continental slope seaward of that point the bathymetry is modeled with an exponentially decaying function of distance the linearized barotropic equations of hydrostatic motion subject to the long wave approximation yield separate shelf and slope solutions which are matched at the shelf break to specify the eigenfunctions the associated eigenvalues define the dispersion relations for each of the modes wavenumber frequency pairs derived from noaa sea surface height stations along the coast are plotted on the first mode dispersion curve and the agreement is good the theory also shows good agreement with the wave data of d p wang

trapped continental shelf waves with a free surface a number of recent results have shown that within the shallow water rigid lid approximation alongshore variations in the bathymetry i e a submerged ridge can lead to continental shelf waves csws that are localised geographically at the ridge and then decay both along and away from the coast removing the rigid lid assumption introduces the superinertial poincare waves and a kelvin wave that is present at all frequencies this implies that the spectrum of the associated wave operator which is bounded for the rigid lid case is continuous and unbounded for the free surface case in the rigid lid case the localisation of modes are isolated eigenvalues lying above the continuous spectrum whereas any localised modes for the free surface problem must necessarily be embedded in the continuous spectrum the purpose of this work is to construct trapped csws analytically and numerically for a non rectilinear shelf a regular asymptotic method is employed by considering a slowly varying non rectilinear shelf with an approximate boundary condition at the shelf ocean boundary it is shown that even with the free surface present trapped csws do indeed exist for the submerged ridge topography comparison with highly accurate numerical results demonstrates the accuracy of the asymptotic method and also allows the consideration of shelves that abut an open ocean so avoiding the approximate boundary condition at the shelf ocean boundary

empirical method for measuring seasonality in deep sea cores we present an extended 100 000 yr oxygen isotope record from the mid atlantic ridge at lat 45 n obtained by using coincident isotope values from both warm and cold water planktonic foraminifera in the same subsamples throughout the core these isotope values reflect paleotemperatures independent of assemblage tolerances our record indicates much stronger seasonal fluctuations than previously reported and these isotope values can be used to identify glacial and deglacial events more precisely although the possibility of this type of record had been suggested by work on recent foraminifera this is the first extended record of this kind

upper mantle structures beneath usarray derived from waveform complexity tomographic imaging of the crust and upper mantle beneath the western united states has greatly improved with the addition of usarray data these models display many detailed images of both fast and slow blobs penetrating into the transition zone to study such features we apply a newly developed technique called multipath detector analysis to the sh waveform data the method simulates each observed body waveform by performing a decomposition by s t c s t 9lr 2 where s t is the synthetics for a reference model time separation 9lr and amplitude ratio c are needed to obtain a high cross correlation between a simulated waveform and data the travel time of the composite waveform relative to the reference model synthetics is defined as t a simulated annealing algorithm is used to determine the parameters lr and c we also record the amplitude ratio amp between the synthetics for the reference model relative to the data generally large lr values are associated with low amp s whereas the conventional tomography yields a travel time correction t our analysis yields an extra parameter lr which describes the waveform complexity with the array we can construct a mapping of the gradient of lr with complexity patterns a horizontal structure introduces waveform complexity along the distance profile in plane multipathing an azimuthally orientation lr pattern indicates a vertical structure with out of plane multipathing using such maps generated from artificial data we can easily recognize features produced by dipping fast structures and slow structures dss many of these features display organized waveform complexity that are distinctly directional indicative of dipping sharp edges here we process the array data for events arriving from various azimuths and construct maps of multipathing patterns the similarity between tomographic features and complexity maps is striking when features are dipping such as the slab structures beneath the cascade range and nevada strong complexity is observed from southeastern events arriving along these ray paths with split pulses separated up to 6 s for both this requires extended slab segments to at least 600 300 km with a 4 8 per cent velocity jump along the edges one of the most dramatic set of dss observations is associated with a slow northwest dipping conduit beneath yellowstone that extends into the transition zone a number of forward modelling experiments are included for the strongest patterns formed by sharpening present tomographic images

constraints on the age and duration of the last interglacial period and on sea level variations the relation between height and age of shorelines formed during the last interglacial period as revealed by coral reefs cannot be related directly to changes in ocean volume because of the effect of isostatic uplift in response to changes in ice sheet loading sea level changes at sites near the melting ice sheet such as bermuda and the caribbean islands differ from those along the australian margin modelling of these differences constrains the times of onset and termination of the last interglacial which are at variance with those deduced from oxygen isotope studies of deep sea cores

evolution of marine terraces and sea level in the last interglacial cave hill barbados the uplifted marine terrace of last interglacial stage 5e age at cave hill barbados has been investigated with views toward terrace architecture developmental processes and sea level history methods include stratigraphic analysis of new deep exposures precise 230th geochronology and geomorphic mapping cave hill was central to earlier studies that led to important ideas on reef and terrace evolution but with which we find significant disagreement we present a new model of terrace evolution that emphasizes the role of marine erosion deposition of carbonate cover during the full eustatic cycle rather than only at highstand and principal reef development during transgression rather than at highstand by keep up rather than catch up growth the new model and geochronology contribute to an improved understanding of surficial processes during emergence of uplifting coral coasts and of global sea level changes in the last interglacial transgression in stage 5e at cave hill was accompanied by progressive marine erosion of a terrace floor and receding seacliff and deposition of a seaward thickening reefal wedge on the floor and above limestones of stage 6 and 7 ages the wedge contains a diachronous basal acropora palmata fringe reef this is overlain by an in place a cervicornis reef that aggraded progressively during sea level rise the transgressive phase took place between 136 ka or earlier and ca 128 ka during highstand between ca 127 and 120 ka the floor and seacliff continued to recede landward re gression began at or after ca 120 ka and sea level fell 37 m below the highstand level by ca 115 ka in stage 5c the seaward front of the last interglacial terrace was eroded landward an uncertain distance the sea level record at cave hill has implications for timing and constituent events of the penultimate glacial the last interglacial highstand and the fall in sea level at the transition from stage 5e to stage 5d shoreline angles which are isochronous linear geomorphic features are the most accurate markers of sustained highstand levels highstand levels and uplift rates interpreted from a palmata in barbados are less accurate and lower because the coral grew mainly in transgression the coral derived data therefore include uncertainties of depths of growth and collapse

anomalous surface waves associated with deep earthquakes generated at an ocean ridge summary broad band seismograms observed at regional distances from deep earthquakes display large amplitude rayleigh and love waves with a predominant period of about 20 s although deep earthquakes in laterally homogeneous structures do not generate such surface waves since the propagation direction of the surface waves inferred from particle motion is approximately radial and the group velocity of the surface waves observed at each station is similar it can be assumed that the surface waves have travelled close to the great circle paths back projection allows us to determine the region in which these surface waves are generated manyof the zones from which the surface waves appear to originate are located close to the norfolk ridge where crustal structure has strong lateral heterogeneity this suggests that the surface waves are generated by the interaction of body waves from the deep earthquakes with this strongly heterogeneous crustal structure in order to investigate the eiect of such heterogeneity in crustal structure on seismic wave elds we have modelled the p sv wave eld using a pseudospectral method the results show that surface waves such as those observed can be generated by ridge structures and indicate that sedimentary layer thickness plays a very important role we suggest that such unexpected surface waves from deep earthquakes may prove useful for delineating heterogeneity in shallow structure

precise chronology of the last interglacial period 234u 230th data from fossil coral reefs in the bahamas a detailed study of 238 u 234 u 230 th ages was made for different coral species from two bahamian reefs to determine the time scale of the sea level high during the last interglacial period using recently developed mass spectrometric techniques for the measurement of u and th isotopes thirty seven coral samples were analyzed in replicate typical errors at 125 ky are 1 5 ky 2 and 3 ky time intervals appear to be well resolved this high precision permits detailed chronologic study with time resolution adequate to define stages of the reef s history these data demonstrate that the time between transgression and regression of the ocean in the last interglacial was about 12 ky after which sea level fell rapidly at more than 2 m ky the high sea level stand began possibly by 132 ky and certainly by 129 ky ago when sea level reached 6 m above present mean low sea level high sea level was sustained until 120 ky and then fell rapidly this time period covers the milankovitch insolation peak at 65 n but is not sharply defined and the sea level high lasted from about 4 ky before the insolation peak to 8 ky after it we find no evidence for a double peak of sea level rise in the last interglacial episode that is high stands at both 125 and 142 ky there appears to be some discrepancy between this precise chronology for a coral reef on a tectonically stable platform and the chronology assigned to deep sea sediments the present results show that the duration of the last interglacial led to a 12 ky period of high sea level stand which is much longer than the insolation peak the study area consists of two sizeable bank barrier coral reefs of sangamon age that crop out along the coast northwest of cockburn town on san salvador island and at devil s point on great inagua island the initial stage of reef development is not revealed at either site but the main parts of both reefs are well preserved at cockburn town the beginning of the reef was marked by colonization of acropora palmata on hardground areas and possibly other corals at 132 ky ago patch reefs at the southeastern flank of the developing reef were growing by 129 to 126 ky ago by 126 to 123 ky ago the crest of the reef was formed by the frame building coral a palmata and associated patch reefs flourished along its flanks a palmata coral heads grew upward to a mean low sea level 6 m above the present one the reef began to decline as sea level dropped at about 123 to 120 ky ago near two measured profiles at devil s point the top of a rubblestone dominated by a cervicornis and patch reef corals preserved in growth position have been beveled off and represent an ancient wave cut surface 230 th ages on corals below and above this surface indicate that it was cut at about 125 1 ky ago

deciphering the impact of sea level changes and tectonic movement on erosional sequence boundaries in carbonate successions a case study from tertiary strata on grand cayman and cayman brac british west indies abstract the stratigraphic architecture of carbonate successions that develop on geographically isolated islands reflects the balance between sea level highstands lowstands and tectonic activity this is readily apparent in the tertiary carbonate sequences on the cayman islands that are formed of the bluff group which includes the brac formation lower oligocene cayman formation middle miocene and pedro castle formation middle pliocene these strata are overlain by the pleistocene ironshore formation the unconformities that define the boundaries between these formations are variable because some developed during one cycle of past erosion others developed through two or more past erosional cycles and some are still developing today some unconformities like the one at the top of the cayman formation are geographically variable because they underwent different developmental histories in different areas the challenge with architectural complex successions like those on the cayman islands is that of deciphering the impact of sea level changes as opposed to tectonic influences during sea level lowstands the older carbonate successions were exposed on land and modified by surface and subsurface karst development at the same time marine erosional processes affected the coastal areas surface karst modification which commonly produced rugged topographies with erosional relief at least 62 m was controlled largely by rainfall runoff and stratal dip weathering on grand cayman at the end of the miocene for example produced a dish shaped topography with elevated peripheral rims in contrast uplift of the east end of cayman brac between the late pliocene 3 6 ma and 400 ka elevated the basal part of the cayman formation 33 m above sea level subsequent karst development which is still ongoing today removed most of the cayman formation on the eastern part of the island and produced peripheral rims that are higher than those on grand cayman during some lowstands like that between the late pliocene and 400 ka coeval coastal erosion led to the development of coastal benches that cut into the older carbonate strata the combination of karst development in the islands interiors and coastal erosion produced complex rugged topographies that strongly influenced patterns of deposition during the following highstand the complex stratigraphic architecture of the carbonate successions on the cayman islands reflects the variable impact of tectonics karst development and coastal erosion that was associated with each lowstand highstand cycle

scattering of teleseismic body waves by the lateral crustal heterogeneity at the pacific trench of mexico we examine the scattered field generated at the pacific trench of mexico upon the incidence of teleseismic body waves and the waveguide properties associated with the structure of the subduction zone in this study we analyze seismic records from a portable array perpendicular to the trench that show a distinctive phase with a phase velocity of graphic 1 following body wave phases this signal is better observed following phases with high incident angles such as ps sp and ss arriving from the ocean side of the trench and for events at teleseismic distances with magnitudes larger than m w 7 0 although weak scattered signals were detected for events down to m w 6 2 and for direct p and s phases we found that the lateral transition between the dipping slab and continental crust with an inclined boundary formed by the subducting slab at the trench generates a strong discontinuity that scatters seismic waves generating a secondary field with amplitude comparable to the incident wave this phase appears for incident body wave arrivals with characteristic wavelength comparable to the thickness of the continental crust analysis of the observed scattered field shows that the trapped waves are vertically polarized surface waves numerical modeling suggests that the impedance contrast at the trench and the geometry of the subducting slab form a waveguide like structure that efficiently generates and transmits trapped seismic waves along the continental margin 1 embed inline graphic 1 gif

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

the last interglacial ocean the final effort of the climap project was a study of the last interglaciation a time of minimum ice volume some 122 000 yr ago coincident with the substage 5e oxygen isotopic minimum based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean last interglacial sea surface temperatures sst were compared with those today there are small sst departures in the mid latitude north atlantic warmer and the gulf of mexico cooler the eastern boundary currents of the south atlantic and pacific oceans are marked by large sst anomalies in individual cores but their interpretations are precluded by no analog problems and by discordancies among estimates from different biotic groups in general the last interglacial ocean was not significantly different from the modern ocean the relative sequencing of ice decay versus oceanic warming on the stage 6 5 oxygen isotopic transition and of ice growth versus oceanic cooling on the stage 5e 5d transition was also studied in most of the southern hemisphere the oceanic response marked by the biotic census counts preceded led the global ice volume response marked by the oxygen isotope signal by several thousand years the reverse pattern is evident in the north atlantic ocean and the gulf of mexico where the oceanic response lagged that of global ice volume by several thousand years as a result the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years these regional lead lag relationships agree with those observed on other transitions and in long term phase relationships they cannot be explained simply as artifacts of bioturbational translations of the original signals

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

new data on the pleistocene of mallorca abstract stratigraphic geomorphologic and isoleucine epimerization studies at 15 sites in mallorca define four aminozones a c e and f g of increasing age that are related to transgressive regressive marine cycles from the holocene to the mid pleistocene calibration of aminozone e glycymeris aile ile mean from all sites 0 41 0 03 n 38 is provided by a 129 7 ka u series coral age on cladocora caespitosa from son grauet of the younger aminozones a relates to the holocene transgression and aminozone c to a mid to late isotopic stage 5 event 90 15 ka revealed only by supralittoral eolianites assigning an age to the older poorly resolved aminozones f and g called f g in this case is uncertain without supporting radiometric data but an age of 180 ka can be assigned to these aminozone s f g based on a kinetic model and other examples in the mediterranean several deposits previously dated u series molluscs between 75 and 300 ka appear to belong to the last interglacial complex stage 5 and aminozone e a proposed revision of the positive sea level history of mallorca shows multiple minor oscillations during the major last interglacial cycle stage 5 and two mid pleistocene sea levels one lower than present and the other at about 14 m a s l

bermuda sea level during the last interglacial bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of sea level fluctuation during the period 135 70 kyr has been reconstructed from 230th 234u dating of corals and speleothems amino acid racemization dating of molluscs and a reinterpretation of geological field relations during the past 5 yr bermuda has been the focus of an extensive geochronological programme which has included a detailed re examination of the geology to be reported elsewhere1 3 here we focus only on the latest interglacial sequence we use the stratigraphie nomenclature of land et al 4 but will present new age data and interpretations of geological relationships this information as it relates to the last interglacial period is given in tables 1 and 2 and summarized in fig 1 we show that during the last interglacial period sea level was only above its present level for a few thousand years at about 125 kyr when it stood at 4 to 6m at 105 and 85 kyr sea level rose to between 15 and 20 m as constrained by ages for submerged speleothems and eolianites at 95 kyr sea level in bermuda was at least 15 m below present level

coastal notches their morphology formation and function deep coastal notches develop through undercutting of steep coastal slopes consisting of rocks that are strong enough to support the weight of the overburden notches are found from the tropics to the poles and in a wide range of rock types virtually tideless to megatidal seas and high to low wave energy environments the emphasis in the literature has been on notches in calcareous rocks in warm microtidal seas and with the general assumption that they have been produced by bioerosion or chemical dissolution few scientifically rigorous attempts have been made to determine the processes responsible for notch formation in different environments and rock types however or to determine whether different processes produce distinct notch morphologies within the same tidal and wave environments the use of notches as palaeo sea level markers and to determine rates of tectonic uplift has been particularly important in the mediterranean notches are more difficult to employ for this purpose in the middle latitudes where higher waves and tides amplify the range of elevations over which the erosional mechanisms are effective as well as increasing the exposure and effect of rocks of variable resistance to erosion to maximize the utility of notches as sea level markers and to better understand and model their development in a wide range of environments we need to understand and be able to quantify the relationship between notch shape and size and the elevational efficacy of the various erosional processes

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

local amplification of rayleigh waves in the continental united states observed on the usarray abstract we develop a method based on ratios of amplitudes measured at adjacent stations to determine local amplification of surface waves across an array of seismic stations we isolate the effects of local structure from those of the earthquake and propagation by systematic averaging of ratios corresponding to many sources we apply the method to data recorded on the usarray for the years 2006 2011 and determine amplification factors at each station of the array for rayleigh waves at periods between 35 s and 125 s local amplification factors are spatially coherent and display variations of 10 at a period of 125 s and greater variations at shorter periods maps of local amplification exhibit spatial correlation with topography and geologic structures in the western and central united states at long periods the observed amplification factors correlate well with predictions from a regional crust and mantle model of north america at short periods correlations are weaker suggesting that the local amplification factors can be useful for constraining shallow structure better

localised continental shelf waves geometric effects and resonant forcing alongshore variations in coastline curvature or offshore depth profile can create localised regions of shelf wave propagation with modes decaying outside these regions these modes termed localised continental shelf waves csws here exist only at certain discrete frequencies lying below the local maximum frequency and above the far field maximum frequency for propagating shelf waves the purpose of this paper is to obtain these frequencies and construct both analytically and numerically and discuss csws for shelves with arbitrary alongshore variations in offshore depth profile and coastline curvature if the shelf curvature changes by a small fraction of its value over the shelf section of interest or an alongshore perturbation in offshore depth profile varies slowly over the same length scale then csws can be constructed using wkbj theory two subcases are described i if the propagating region is sufficiently long that the offshore structure of the csw varies appreciably alongshore then the frequency and alongshore structure are found from a sequence of local problems ii if the propagating region is sufficiently short that the alongshore change in offshore structure of the csw is small then the alongshore modal structure is given in an explicit uniformly valid form a separate asymptotic theory is required for curvature perturbations to shelves that are otherwise straight rather than curved comparison with highly accurately numerically determined csws shows that both theories are extremely accurate with the wkbj theory having a significantly wider range of applicability an idealised model for the generation of csws is also suggested a localised time periodic wind stress generates an evanescent continental shelf wave in the far field of a localised mode where the coast is almost straight and the response on the shelf is obtained numerically if the forcing frequency is close to that of an csw then the wind stress excites energetic motions in the region of maximum curvature creating a significant localised response possibly far from the forcing region

rapid fluctuations in sea level recorded at huon peninsula during the penultimate deglaciation about 140 000 years ago the breakup of large continental ice sheets initiated the last interglacial period sea level rose and peaked around 135 000 years ago about 14 meters below present levels a record of last interglacial sea levels between 116 000 years to 136 000 years ago is preserved at reef vii of the uplifted coral terraces of huon peninsula in papua new guinea however corals from a cave situated about 90 meters below the crest of reef vii are 130 000 2000 years old and appear to have grown in conditions that were 6 c cooler than those at present these observations imply a drop in sea level of 60 to 80 meters after 130 000 years sea level began rising again in response to the major insolation maximum at 126 000 to 128 000 years ago the early about 140 000 years ago start of the penultimate deglaciation well before the peak in insolation is consistent with the devils hole chronology

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

last interglacial sea stands on barbados and an early anomalous deglaciation timed by differential uplift three major sea level maxima between 137 and 120 kyr b p are documented by surveys of pairs of wave cut notches and other features associated with the broadly defined last interglacial coral terrace on barbados regression analysis of elevation differences between notch pair members as a function of their uplift rates at seven sites yields the age difference between first and third sea stands and their eustatic sea level difference these results when combined with stratigraphic data from the bahamas bermuda and western australia and a chronology based on age limits of corals from the bahamas and western australia yield an endpoint age and eustatic low tide elevation of 136 7 kyr b p and 7 4 m respectively for the first sea stand 126 kyr b p and 5 6 m for the second and 120 5 kyr b p and 3 0 m for the third the first sea stand is the result of an anomalous deglaciation that was completed during low northern summer milankovitch insolation this is contrary to the milankovitch hypothesis that orbitally controlled insolation largely determines the variations of glacial ice volume it implies that internal factors within the earth s climate system can be much stronger than the effects of insolation variations

rapid sea level changes at the close of the last interglacial substage 5e recorded in bahamian island geology rapid and abrupt relative sea level changes within the last interglacial substage 5e are recorded in the island geology of the tectonically stable bahamas from 132 to 118 ka reef growth reached a maximum elevation near 2 m as indicated by fossil reef elevation across the platform whereas bioeroded notches are incised in coastal cliffs as high as 6 m the end of the interval is characterized by voluminous eolianites exhibiting palm tree and frond impressions it is inferred that sea level for most of the interval remained near 2 m restraining reef growth and that the notch at 6 m represents a rapid and brief excursion just before the close of the substage the subsequent fall must have been rapid in order to leave the notch profile intact and mobilize windward lagoon ooids into dunes before cementation could anchor them in order to explain the rapid rise to 6 m glacial surging is invoked the subsequent fall also rapid may be a consequence of the surge flooding high latitudes and providing enough moisture to initiate reglaciation and drawdown

isobath variation and trapping of continental shelf waves since trosch proceedings of the 4th international conference on applied numerical modeling tainan taiwan 1984 ed h m hsia y l chou s y wang s j hsieh science and technology series vol 63 1986 pp 307 311 american astronautical society found trapped sub inertial oscillations in computations of low frequency variability in the lake of lugano models of trapping have generally considered evenly spaced isobaths parallel to shorelines with approximate boundary conditions at any shelf ocean boundary here an asymptotic analysis for slowly varying topography and accurate spectral computations demonstrate trapping on non rectilinear shelves it is shown that changes in any of three factors isobath curvature distance from the coast and the shelf break and the slope at the shelf break are sufficient on their own to give trapping continental shelves that abut smoothly onto the open ocean are considered thus avoiding the shelf ocean boundary condition approximation and allowing the accuracy of previous approximations to be assessed

arrival angle anomalies across the usarray transportable array abstract we construct composite maps of surface wave arrival angle anomalies using clustered earthquakes and an array method for measuring wave front geometry this results in observations of arrival angles covering the entire footprint of the usarray transportable array during 2006 2010 bands of arrival angle deviations in the propagation direction indicate the presence of heterogeneous velocity structure both inside and outside of the array we compare the observed patterns to arrival angles predicted using two global tomographic models the mantle model s362ani and the surface wave dispersion model gdm52 we use both ray theory based prediction methods and measurements on synthetic data calculated using a spectral element method both models and all prediction methods produce similar mean arrival angles and long wavelength patterns of anomalies which are similar to the observations predicted short wavelength features generally do not agree with the observations the spectral element method produces some complexity that is not obtained using the ray theory based methods this predicted complexity is similar in character to the observed patterns but does not match them

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

erosional modification of bahama escarpment the precipitous 28 to 40 bahama escarpment is characterized by abundant low energy restricted peritidal and lagoonal rocks and scarce high energy bank margin rocks of early and middle cretaceous age at depths of 2 000 m this indicates significant erosional modification of the slope all models of carbonate platforms have high energy facies at platform edges with low energy and restricted facies confined to platform interiors erosion has removed marginal deposits that constituted the original slope of the bahama platform and exposed peritidal and lagoonal facies rocks on the basis of widths of facies belts of middle cretaceous carbonate platforms in eastern mexico and of erosional benches apparent in seismic profiles across the bahama and blake escarpments an estimated 5 km of material has been eroded from the base of the escarpment greatest erosion occurred between the cenomanian and maastrichtian with additional erosion in the paleocene and oligocene as documented by tertiary and late cretaceous pelagic and forereef deposits that unconformably drape and fill fissures in the older shallow water rocks it is unclear whether erosion of the escarpment is occurring at present erosion of the slope deeper than 2 500 m is effected in part by spalling of joint blocks from shattered exposures jointing probably results from expansion of previously buried rocks exposed at the sea floor by erosion erosion of the bahama escarpment may have occurred by other processes acting in concert or individually at different times as well dissolution by corrosive water below the calcite compensation depth ccd and removal of sediments at the base of the slope by abyssal currents probably contributed most to erosional modification of the bahama escarpment bioerosion and jointing may aid dissolution by increasing surface area exposed to corrosive waters tectonic activity related to movements along fracture zone trends might have contributed locally to erosion of the bahama escarpment erosion of the bahama escarpment shallower than 2 500 m has been less extensive and apparently proceeds by slumping of large allochthonous blocks as indicated by the presence of an apparently intact eocene forereef deposit in the interval from 3 590 to 3 430 m off eleuthera island