tidal modeling of an ancient tide dominated seaway part 1 model validation and application to global early cretaceous aptian tides abstract the utility of deep time global paleotidal modeling is evaluated with a series of modeling experiments focused on the early cretaceous aptian the results from a series of paleobathymetry sensitivity experiments indicate that despite paleogeographic and paleobathymetric uncertainty appropriate use of global paleotidal models complements and enhances stratigraphic and sedimentological methods before being applied to global paleotidal modeling the imperial college ocean model icom is validated for the computation of modern global tides the icom results only deviate slightly from a state of the art published model and were achieved with considerably less computational expense and without data assimilation the results from global paleotidal modeling of the early cretaceous aptian were assessed by comparison with the published geological record icom predicts high mesotidal to macrotidal ranges on the arabian platform around india especially to the north and west along the pacific coast between north and south america northeast of australia and around southeast asia the model predicts low microtidal ranges in the proto south atlantic ocean and weddell sea a further validation test assessed the ability of the model to predict the dominant tidal constituents diurnal or semidiurnal in the aptian lower greensand seaway of southeastern england and northern france during the aptian this region was connected to the boreal proto atlantic and neotethys oceans and now preserves superbly documented tidal deposits the model predicts low microtidal ranges in the proto central atlantic ocean and boreal ocean suggesting that they had little impact on tides in the lower greensand seaway higher tidal amplitudes especially of diurnal once daily tides are predicted in the northwestern neotethys ocean suggesting that this ocean was an important source of tidal energy to the lower greensand seaway sensitivity tests to paleogeographic and paleobathymetric uncertainty indicate that the model predictions are robust the prediction of predominantly diurnal tides is supported by published analyses of large dune scale deposits in the lower greensand of southeast england

holocene relative sea level change and rate of sea level rise from coastal deposits in the toyooka basin western japan this study presents relative sea level rsl change from 11 200 to 500 cal bp in the toyooka basin western japan diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment

oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

rock debris in an antarctic ice shelf we have discovered a band of stones and coarse sand in the ronne ice shelf antarctica some 60m above the ice shelf s base 40km from its seaward edge and 420km from the point where the ice originally went afloat a study of ice sounding radar data from across the ronne ice shelf has revealed other areas likely to contain debris in significant quantities it appears that basal debris at the margins of ice streams feeding the ice shelf can be buried in the ice shelf by sea water freezing on at the ice shelf base these findings are evidence for a mechanism active in a present day ice sheet shelf system which enables icebergs to transport large volumes of ice rafted debris and which also provides a potential mechanism for the formation of ice rises near ice fronts we anticipate that a seismics study of debris melted from the ice shelf and deposited beneath will provide a valuable control on the history of ice shelf ocean interactions

bedform topography and basal conditions beneath a fast flowing west antarctic ice stream a grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath similar to 140 km 2 of rutford ice stream west antarctica the subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water saturated sediments the two troughs are filled with deforming sediment whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream the deforming bed is very flat along flow but undulates across flow sliding areas show rougher bed topography cross stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction these bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation in places they form finger like mounds of material which extend into the sliding region further downstream mean bedform height is 22 m mean width is 267 m and many of them extend for at least 1 2 km along flow we interpret most of these bedforms as drumlins and one as a mega scale glacial lineation the juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas variable both spatially and temporally any theory of subglacial sediment rheology must also be able to account for our conclusion that at any given time pervasive deformation extends at least a few metres into the bed and can persist over a considerable area many km 2 bedform geometry and basal conditions concur with interpretations of former ice streams with evidence for increasing elongation ratio with distance downstream however those studies also identified bedrock cropping out at the ice bed interface for which there is no evidence on rutford ice stream c 2008 elsevier ltd all rights reserved

late cenozoic relief evolution under evolving climate a review abstract the present review paper is an attempt to summarize quantitative evidence of late cenozoic changes in topographic relief different meanings of the word relief as it is commonly used and detail the metrics used to quantify it we then specify methodological tools used to quantify relief change primarily low temperature thermochronometry and terrestrial cosmogenic nuclides and analyze published evidence for different regions our review first shows that relief changes and rates of changes are more important at mid than high or low latitudes and appear to be insensitive to mean precipitation rates it also show that relief change is positive relief increases in most of the reported cases 80 we subsequently define two functional relationships between relief and erosion depending on the chosen definition of relief and propose a conceptual model of landscape memory we conclude following others that erosion rates depend non linearly on relief evolution itself being a function of the spatial distribution and rates of erosion the relief increases documented in this review may be to erosion rate increases during the same timescales lastly we discuss the importance of glacial and periglacial processes on late cenozoic relief and erosion rate changes and stress the importance of frost shattering and glacial erosion at mid and high latitudes

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

inferring sites of subglacial erosion using the pb isotopic composition of ice rafted feldspar examples from the weddell sea antarctica the delivery of ice rafted debris ird from glaciated margins is a function of ice sheet dynamics shifts in supply and sourcing of ird can therefore identify episodes of ice sheet instability however records can be difficult to correctly interpret because the subglacial geology of the catchment areas which controls ird composition may be obscured importantly variations can also result from shifts in erosion sites due to changes in the basal ice sheet conditions this study evaluates where subglacial erosion has occurred in catchments that flow into the southern weddell sea antarctica by determining the pb isotopic compositions of individual ice rafted feldspars from late holocene marine sediments feldspar compositions match those of rock units inferred through extrapolation of outcrop magnetic and gravity data to compose areas where ice velocity bed roughness and shear stress are high significantly signals from areas where ice velocities are high but bed roughness and shear stresses are low were not recorded suggesting that there is reduced bedrock erosion in these regions major variations in ird composition in the weddell sea can result from changing the loci of subglacial erosion and do not necessarily correspond with major ice sheet instability

drowning unconformities palaeoenvironmental significance and involvement of global processes abstract drowning unconformities are stratigraphic key surfaces in the history of carbonate platforms they mostly consist in the deposition of deep marine facies on top of shallow marine limestones although large scale depositional geometries mimic lowstand systems track architecture these sedimentary turnovers are developed in relation with major sea level rise inducing an increase in the rate of creation of accommodation space that outpaces the capacity of carbonate to keep up this so called paradox of carbonate platform drowning implies that parameters other than purely eustatic fluctuations are involved in the demise of shallow marine ecosystems worldwide and at different times during earth history in depth studies of drowning unconformities revealed that changes in nutrient input clastic delivery temperature or a combination of them may be responsible for a decrease in light penetration in the water column and the progressive suffocation and poisoning of photosynthetic carbonate producers the examination of such case examples from various stratigraphic intervals and palaeogeographical settings thus helps in identifying and hierarchizing potential triggering mechanisms for drowning unconformities this is complemented by new data from early cretaceous successions from the helvetic alps during this time period the helvetic carbonate platform developed along the northern tethyan margin using both photozoan and heterozoan communities phases of healthy production were interrupted by several drowning episodes the latter are marked in the sedimentary record by condensation and associated phosphogenesis and glauconitisation from the earliest valanginian to the early to late barremian three drowning unconformities reflect the intermittent installation of a more humid climate and subsequent enhanced trophic conditions which first induced a switch from photozoan to heterozoan communities and then to long lasting drowning phases the latter encompass several sea level rise and fall cycles and may be linked to strengthened upwelling currents with the return to more oligotrophic conditions during the late barremian photozoan urgonian type communities took up again their development has been abruptly stopped at the end of the early aptian by a major emersion phase the subsequent drowning is documented in various peritethyan areas this initial crisis is followed by three other drowning phases that ultimately led to the replacement of shallow ecosystems by a deeper marine sedimentation in the cenomanian this long term trend in the evolution of the helvetic carbonate platform and of other peritethyan ecosystems may have been driven by more global phenomena in particular the progressive opening of the northern and equatorial atlantic may have impacted sea level by creating new oceanic basins the emplacement of submarine volcanic plateaus may have triggered sea level rise and fertilized deep oceanic waters through hydrothermal processes drowning unconformities thus record the interplay of local with long term processes and constitute regional sedimentary archives of global phenomena

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

evolution of cupido and coahuila carbonate platforms early cretaceous northeastern mexico the cupido and coahuila platforms of northeastern mexico are part of the extensive carbonate platform system that rimmed the ancestral gulf of mexico during barremian to albian time exposures of cupido and coahuila lithofacies in several mountain ranges spanning an 80 000 km 2 area reveal information about platform morphology and composition paleoenvironmental relations and the chronology of platform evolution new biostratigraphic data integrated with carbon and strontium isotope stratigraphy significantly improve chronostratigraphic relations across the region these data substantially change previous age assignments of several formations and force a revision of the longstanding stratigraphy in the region the revised stratigraphy and enhanced time control combined with regional facies associations allow the construction of cross sections isopach maps and timeslice paleogeographic maps that collectively document platform morphology and evolution the orientation of the cupido barremianaptian shelf margin was controlled by the emergent coahuila basement block to the northwest the south facing margin is a highenergy grainstone shoal whereas the margin facing the ancestral gulf of mexico to the east is a discontinuous rudist coral reef a broad shelf lagoon developed in the lee of the cupido margin where as much as 660 m of cyclic peritidal deposits accumulated during middle to late aptian time a major phase of flooding forced a retrograde backstep of the cupido platform shifting the locus of shallow marine sedimentation northwestward toward the coahuila block this diachronous flooding event records both the demise of the cupido shelf and the consequent initiation of the coahuila ramp the backstepped coahuila ramp aptianalbian consisted of a shallow shoal margin separating an interior evaporitic lagoon from a low energy muddy deep ramp more than 500 m of cyclic carbonates and evaporites accumulated in the evaporitic lagoon during early to middle albian time restriction of the platform interior dissipated by middle to late albian time with the deposition of peloidal miliolid rich packstones and grainstones of the aurora formation the coahuila platform was drowned during latest albian to early cenomanian time and the deep water laminites of the cuesta del cura formation were deposited this study fills in a substantial gap in the cretaceous paleogeography of the eastern gulf of mexico coast improving regional correlations with adjacent hydrocarbon rich platforms the enhanced temporal relations and chronology of events recorded in the cupido and coahuila platforms significantly improve global correlations with coeval economically important platforms worldwide perhaps con

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

geochemical and paleoenvironmental record of the early to early late aptian major episodes of accelerated change evidence from sierra del rosario northeast mexico abstract the lower to lower upper aptian succession of northern mexico documents the drowning of the shallow water cupido cupidito carbonate platform system followed by deposition of the deep water sediments of the la pena formation using 13 c stratigraphy geochemical and mineralogical information coupled with previous microfacies paleontological and total organic carbon toc data from a stratigraphic section which includes such lithological change this study identifies distinctive episodes of accelerated global environmental change and determines the paleoenvironmental conditions conducive to the deposition of toc rich intervals within the cupidito unit the oceanic anoxic event 1a oae 1a is recorded near the base of the section and the intra furcata negative excursion in the topmost beds of the unit the upper part of the section within the la pena formation is correlatable with the noire level organic carbon rich intervals occur in the lower and middle part of the oae 1a upper part of the cupidito unit base of the la pena formation and in the noire level equivalent reducing conditions within the sediment and oxic dysoxic at the seafloor locally controlled persisted both before and during oae 1a interval in the cupidito lagoon oxygen depleted conditions dysoxic anoxic were more permanent and stronger during the deposition of the base of the la pena formation and the noire equivalent level it is proposed here that deposition of the lower middle part of the oae 1a and the base of the la pena formation was influenced by climate controlled increases in detrital and accompanying nutrient influx that supplied especially biolimiting nutrients fe p fostering marine productivity and toc burial upwelling of nutrient rich deeper waters and minor arrival of nutrients from runoff both account for the domination of radiolaria and organic carbon burial during the noire level equivalent record of the oae 1a time equivalent facies in the cupidito lagoonal sediments confirms the diachronism of the cupidito la pena flooding heterozoan carbonate production in the cupidito ramp was uninterrupted during and after oae 1a periodic arrival of detrital components and nutrients during warmer humid periods accelerated platform drowning which peaked during the diachronic deposition of the la pena formation

tracking millennial scale holocene glacial advance and retreat using osmium isotopes insights from the greenland ice sheet high resolution os isotope stratigraphy can aid in reconstructing pleistocene ice sheet fluctuation and elucidating the role of local and regional weathering fluxes on the marine os residence time this paper presents new os isotope data from ocean cores adjacent to the west greenland ice sheet that have excellent chronological controls cores msm 520 and da00 06 represent distal to proximal sites adjacent to two west greenland ice streams core msm 520 has a steadily decreasing os signal over the last 10 kyr 187os 188os 1 35 0 81 in contrast os isotopes from core da00 06 proximal to the calving front of jakobshavn isbrae highlight four stages of ice stream retreat and advance over the past 10 kyr 187os 188os 2 31 1 68 2 09 1 47 our high resolution chemostratigraphic records provide vital benchmarks for ice sheet modelers as we attempt to better constrain the future response of major ice sheets to climate change variations in os isotope composition from sediment and macro algae seaweed sourced from regional and global settings serve to emphasize the overwhelming effect weathering sources have on seawater os isotope composition further these findings demonstrate that the residence time of os is shorter than previous estimates of 104 yr

quaternary geomorphic trends within southwest japan extensive wrench deformation related to transcurrent motions of the median tectonic line abstract large scale transcurrent faults contribute to anelastic deformations along convergent plate boundaries the inner zone of southwest japan has been subjected to shearing deformations during the quaternary associated with dextral motions of the median tectonic line which was activated as a right lateral fault by oblique subduction of the philippine sea plate considering the neotectonic framework the continental crust of the chugoku block in the western part of the inner zone is simplified as a granitic test piece under a simple shear geological and geographical data in the block are incorporated to produce a quantitative analysis of the deformation mode together with an empirical model of the rheology of an orogenic crust the present results indicate that the chugoku block behaves as a newtonian fluid and flows with a strain rate of about 10 14 s 1 under a tectonic stress of 10 mpa the mode of wrenching of the study area is compared with confined deformations of other plate margins in the same tectonic regime unique extensive wrench deformation as wide as 150 km along the median tectonic line is attributed to the absence of weak zones in the continental crust such as ductile melange belt or arc volcanism which is a common phenomenon in the area of active convergence the inner zone of southwest japan is immune from these major factors reducing the shearing strength of the crust because of the intensive intrusions of cretaceous granites and the regional quaternary thermal event

mis 21 and the mid pleistocene climate transition climate and sea level variation from a sediment core in osaka bay japan abstract we report climate and sea level variation for the marine oxygen isotope stage mis 21 encompassing the end of the mid pleistocene climate transition mpt based on pollen diatom and sulfur records from a 50 m thick sequence in a core from osaka bay an extremely warm climate coincided with the sea level highstand of substage 21 5 when the warm temperate element quercus cyclobalanopsis exceeds 40 of total arboreal pollen this was followed by a warm temperate to temperate and humid climate that continued until the end of mis 21 a linear age model shows that climate was dominated by precessional cyclicity with an inverse correlation between temperature and precipitation the postglacial sea level rise reached its highest peak in substage 21 5 when paleo osaka bay reached its maximum extent including kyoto and nara basins at this time pelagic diatoms were dominant in the central part of the bay sea level dropped below the osaka bay sill about 60 m at present during substage 21 4 followed by a rise above the sill in substage 21 3 and a drop at 21 2 sea level remained below the sill during substage 21 1 the thermal maximum and sea level peak occurred just after the rapid postglacial sea level rise after which there was a gradual decline in temperature and sea level accompanied by precession related oscillations these features are typical of the post mpt interglacials dominated by 100 ka cyclicity these features may be a sign of termination of the mpt

timing of the matuyama brunhes geomagnetic reversal decoupled thermal maximum and sea level highstand during marine isotope stage 19 recent high resolution magnetic and microfossil data from a long core penetrating the osaka group japan are astronomically tuned and reassessed to reveal detailed stratigraphic features across the matuyama brunhes mb polarity transition during marine isotope stage mis 19 the sediments have a uniform and high average accumulation rate of 63 cm ky astronomical tuning based on six calibration points including a clear mis 19 2 sea level lowstand dates the main mb boundary mbb to 777 6 ka the sea level peak of the mis 19 3 highstand to 780 7 ka and the climatic thermal maximum tm to 776 4 ka the mb transition began with a short lived normal polarity episode that occurred before the highstand at mis 19 3 and terminated with multiple rapid reversals that occurred between highstand mis 19 3 and lowstand 19 2 the tm just postdates the termination of the mb transition and occurs about 4000 years after the sea level peak the delayed tm is also observed at gesher benot ya aqov israel and on the mediterranean coast and possibly at lake baikal in high resolution records from chinese loess paleosols and deep sea sediments the rapid reversal zone of the mbb has a very similar climatostratigraphic character these magneto climatostratigraphic features in mis 19 are useful for correlating between terrestrial and marine sediments the delay in warming relative to the sea level highstand seems to have been due to a cloud albedo effect induced by an increase in galactic cosmic ray flux during an extremely low magnetic field intensity interval

identification and correlation of visible tephras in the lake suigetsu sg06 sedimentary archive japan chronostratigraphic markers for synchronising of east asian west pacific palaeoclimatic records across the last 150 ka abstract the lake suigetsu sg06 sedimentary archive from honshu island central japan provides a high resolution palaeoenvironmental record including a detailed record of explosive volcanism from japan and south korea thirty visible tephra are recorded within the 73 m long sg06 core which spans the last 150 ka here we describe and characterise these tephras based on major element glass composition which is useful for the identification and correlation of these tephras and the age models of the records in which they are found utilising the large number of radiocarbon measurements n 600 from terrestrial plant macrofossils in the lake suigetsu sg06 record we are able to provide precise and accurate ages for the tephras from eruptions within the last 50 ka glass compositional data of some of the largest eruptions from japan k ah at aso 4 aso a aso d and ata sampled at proximal outcrops are also presented these data show that the major element glass chemistry is distinctive for many of the visible sg06 tephra units and allows some of the layers to be correlated to known eruptions from volcanoes in japan and south korea namely k ah sg06 0967 u oki sg06 1288 at sg06 2650 aso 4 sg06 4963 sg06 4979 k tz sg06 5181 aso abcd sg06 5287 and ata sg06 5181 the following ages were obtained for the sg06 tephra units 3 966 4 064 cal ka bp 95 4 probability range for the sg06 0588 tephra 10 242 10 329 cal ka bp 95 4 probability range for sg06 1293 19 487 112 sg06 2012 ka bp 2 for sg06 1965 28 425 194 sg06 2012 ka bp 2 for sg06 2504 28 848 196 sg06 2012 ka bp 2 for sg06 2534 29 765 190 sg06 2012 ka bp 2 for sg06 2601 29 775 191 sg06 2012 ka bp 2 for sg06 2602 43 713 156 sg06 2012 ka bp 2 for sg06 3485 46 364 202 sg06 2012 ka bp 2 for sg06 3668 49 974 337 sg06 2012 ka bp 2 for sg06 3912 50 929 378 sg06 2012 ka bp 2 for sg06 3974 and improved ages for two of the most important tephra markers across japan the k ah 7 165 7 303 cal ka bp at 95 4 probability range sg06 0967 and at tephra 30 009 189 sg06 2012 ka bp at 2 sg06 2650

integrating satellite observations with modelling basal shear stress of the filcher ronne ice streams antarctica using inverse methods constrained by recent satellite observations we have produced a comprehensive estimate of the basal shear stress beneath the filchner ronne ice streams the inversions indicate that a weak bed approx 4 20 kpa underlies much of these ice streams compared to the ross ice streams the distribution of weak subglacial till is more heterogeneous with sticky spots providing much of the resistance to flow a weak bed beneath recovery ice stream extends several hundred kilometres inland with flow along this ice stream discrepancies between thickness measurements and flux estimates suggest the existence of a deep 1400 m trough not resolved by existing maps of subglacial topography we hypothesize that the presence of this and other deep troughs is a major influence on this sector of the ice sheet that is not fully incorporated in current models of ice sheet evolution

seismic evidence for a water filled canal in deforming till beneath rutford ice stream west antarctica 1 seismic data from rutford ice stream west antarctica show high amplitude reversed polarity reflections from parts of the bed only interfaces between ice and water or between water and sediment have the acoustic properties to produce such strong reflections ice sediment interfaces produce much weaker echoes the evidence suggests that an area of the ice stream measuring at least 1 km by 0 2 km is underlain by water with a depth of less than 1 m the data are consistent with the presence of a sub ice drainage system comprising shallow canals cut into the sedimentary substrate as predicted by theory

magnetostratigraphy of plio pleistocene sediments in a 1700 m core from osaka bay southwestern japan and short geomagnetic events in the middle matuyama and early brunhes chrons abstract a magnetic polarity stratigraphy spanning more than the past 3 2 myr was determined for a long 1545 m continuous sedimentary sequence of marine fluvial and lacustrine deposits from the osaka basin southwestern japan additionally two short geomagnetic reversal events were identified a short event at about 0 69 ma lasting for about 7 kyr in the early brunhes chron around the lower boundary of a marine clay deposited during a period of eustatic high sea level during the marine oxygen isotope stage 17 and another short matuyama event 1 60 1 58 ma correlated with stage 54 event and the early stage of the sangiran excursion accumulation rate was 0 3 0 4 mm yr from 3 to 2 ma and then increased by about 50 with a rate of 0 51 mm yr during the olduvai subchron high values of 0 59 mm yr were maintained from the upper olduvai boundary to the brunhes matuyama boundary from 1 77 to 0 78 ma with a peak at 0 74 mm yr during the jaramillo subchron these changes in accumulation rate probably reflect the history of tectonic subsidence of the drilling site the magnetic polarity stratigraphy provides a chronological framework for sedimentological paleoenvironmental tephrochronological and tectonic studies of the osaka basin

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

holocene crustal movement along the coast of western kobe and the 1995 kobe earthquake japan abstract the 1995 kobe hyogoken nanbu earthquake mj 7 2 in japan which has been attributed to the nojima fault of the rokko awaji fault system resulted in vertical uplifts of 0 19 m at tarumi and 0 07 m at akashi relative to takasago here we evaluate these uplifts in the context of holocene local tectonics derived from relative sea level rsl records for the purpose of this study we estimate the holocene relative uplift via a comparison study of observed and predicted sea level variations along the traverse from takasago to tarumi and akashi these estimates are then applied to evaluate the uplift associated with the fault system responsible for the 1995 earthquake as a rate of tectonic subsidence between 0 08 and 0 23 mm yr corresponds well with the rsl index points determined for takasago during the mid holocene uplift rates of 0 38 0 73 and 0 19 0 48 mm yr are derived for tarumi and akashi respectively relative to takasago this suggests that the cumulated vertical uplift due to the nojima fault activity with a recurrence interval of approximately 2000 yr may contribute at most 25 of the holocene uplift proposed for the tectonically active coast of western kobe

organized flow from the south pole to the filchner ronne ice shelf an assessment of balance velocities in interior east antarctica using radio echo sounding data 1 ice flow through central antarctica has the potential to transmit accumulation changes from deep interior east antarctica rapidly to the shelf but it is poorly constrained owing to a dearth of ice velocity observations we use parameters derived from airborne radio echo sounding res data to examine the onset areal extent and englacial conditions of an organized flow network tributaries feeding an ice stream draining from the south pole to the filchner ronne ice shelf we classified res flight tracks covering the region according to whether englacial stratigraphy was disrupted i e internal layers diverged significantly from the surface and bed echoes or undisrupted i e internal layers closely parallel surface and basal topography and we calculated subglacial roughness along basal reflectors where satellite measured surface ice flow speeds are available covering 39 of the study region regions of fast and tributary flow correspond with res flight tracks that exhibit more disrupted internal layers and smoother subglacial topography than their counterparts in regions of slow flow this suggests that disrupted internal layering and smooth subglacial topography identified from res profiles can be treated as indicators of past or present enhanced flow tributaries where neither satellite nor ground based ice flow measurements are available we therefore use these res derived parameters to assess the balance flux modeled steady state flow regime between the south pole and filchner ronne ice shelf the res analysis confirms that an organized flow network drains a wide region around the south pole into the filchner ronne ice shelf however the spatial extent of this network as delineated by the res data diverges from that predicted by currently available balance flux models

coats land crustal block east antarctica a tectonic tracer for laurentia undeformed rhyolite and granophyre in the coats land crustal block of east antarctica dated as 1112 4 ma are identical in age to both the umkondo large igneous province lip of the kalahari craton southern africa and the early keweenawan lip of laurentia north america although marine and satellite data demonstrate that coats land was close to kalahari within the gondwana supercontinent the coats land rocks yield pb isotope compositions strikingly distinct from those of the umkondo province yet indistinguishable from rocks of the keweenawan province the anorogenic red bluff granitic suite along the present day southern laurentian margin in the franklin mountains texas usa is of comparable age general rock type and pb isotope composition to rocks of coats land and may provide a piercing point for a coats land laurentia link paleomagnetic poles permit the coats land block to be close to this part of laurentia ca 1100 ma and allow juxtaposition of kalahari and southern laurentia ca 1000 ma the coats land crustal block may therefore be a critical tectonic tracer for placing laurentia within late mesoproterozoic and neoproterozoic paleogeographic reconstructions if this hypothesis is correct laurentia collided with the kalahari craton along antarctica s maud orogen which would represent a continuation of the ca 1000 ma grenville orogen of eastern and southern laurentia

quantifying subglacial bed roughness in antarctica implications for ice sheet dynamics and history abstract glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice sheet history superimposed over and in turn modifying preglacial topography lithology and geological structure insights into the formation of glaciated landscapes can in principle be obtained by analysing modern ice sheet beds but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the bed it is however possible to quantify roughness the vertical variation of the subglacial interface with horizontal distance along two dimensional images of the bed obtained from radio echo sounding res here we collate several case studies from antarctica where roughness calculations have been used as a glaciological tool to infer basal processes and ice sheet history over large 500 km 2 areas we present two examples from west antarctica which demonstrate the utility of bed roughness in determining the presence and extent of subglacial sediments glacial dynamics and former ice sheet size we also present two examples from east antarctica which illustrate how roughness provides knowledge of ice sheet dynamics in the interior and pre quaternary ice sheet histories in modern ice sheet settings characterising bed roughness along res tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field satellite and modelling investigations the technique also offers significant potential for the comparison of modern and former ice sheet terrains contributing to an improved understanding of the formation and evolution of glaciated landscapes

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

a glaciological map of filchner ronne ice shelf antarctica a set of landsat 5 multispectral scanner mss images of filchner ronne ice shelf was commissioned by the institut fur angewandte geodasie and recorded over a short period in early 1986 a mosaic of digitally enhanced images was constructed using all available ground control in due course it is planned to use the data for the production of a series of digital image maps at a scale of 1 1 000 000 meanwhile a line map has been prepared at a scale of 1 2 000 000 to show the principal glaciological features the new mosaic shows much more detail than earlier landsat images and extends coverage to higher latitudes more of the poorly known southern boundary of the ice shelf can be identified but floating ice still extends beyond the limit of coverage extensive ice rumples are revealed many of them undetected in earlier imagery flow bands can be tracked without a break from their ice stream source to the ice front over distances of up to 800 km even minor tributaries and sheet flow from the inland ice sheet between the ice streams yield narrow but identifiable flow bands ice thickness velocity and mass flux data are reviewed in order to underline their dependence on good mapping

evidence for iceberg armadas from east antarctica in the southern ocean during the late miocene and early pliocene abstract sediments from ocean drilling program site 1165 in the indian ocean sector of the southern ocean off prydz bay contain a series of layers that are rich in ice rafted debris ird here we present evidence that ird rich layers at site 1165 at 7 4 8 and 3 5 ma record short lived massive discharges of icebergs from wilkes land and adelie land more than 1500 kilometers to the east of the depositional site this distant source of icebergs is clearly defined by the presence of ird hornblende grains with 40ar 39ar ages of 1200 1100 ma and 1550 1500 ma ages that are not found on the east antarctic continent in locations closer to site 1165 this observation requires enormous amounts of detritus carrying drifting icebergs most likely in the form of large icebergs these events probably reflect destabilization surge and break up of ice streams on the wilkes land and adelie land margins of the east antarctic ice sheet in the vicinity of the low lying aurora and wilkes basins they occurred under warming conditions but each coast seems to have produced ice rafting events independently at different times the data presented here constitute the first evidence of far traveled icebergs from specific source areas around the east antarctic perimeter launch of these icebergs may have happened during quite dramatic events perhaps analogous to heinrich events in the north atlantic

stacking pattern of cyclic carbonate platform strata lower cretaceous of southern apennines italy detailed sedimentological analysis of aptian albian shallow water carbonate platform strata from monte faito southern italy reveal composite sea level change the organization of the lithofacies and their related diagenetic overprint have allowed the identification of 50 elementary cycles they often show exposure related diagenetic features superimposed on subtidal deposits suggesting drops of relative sea level elementary cycles are grouped into 16 bundles forming six superbundles the hierarchical organization of the cycles are interpreted to be related to composite eustatic sea level fluctuations driven by the earth s orbital perturbation in the milankovitch frequency band moreover the systematic variation of superbundle thickness and the general evolution of the lithofacies reflects variations of accommodation potential defining longer term environmental changes different lithofacies forming elementary cycles are frequently separated by bedding planes that when viewed in a sequence stratigraphic context are interpreted as transgressive surfaces maximum flooding surfaces or sequence boundaries this allows the recognition of lowstand transgressive and highstand deposits in the cyclic units considering both the bundle superbundle ratio and the sequence stratigraphic interpretation of the superbundles a chronostratigraphic diagram illustrating both gaps at bundle level and their expected location along the section was created it establishes that the section developed over about 2 4 ma

quaternary raised coral reef terraces on sumba island indonesia a spectacular sequence of coral reef terraces six steps broader than 500 meters and many minor substeps is developed near cape laundi sumba island between an ancient patch reef 475 meters high and sea level several raised reefs have been dated with the electron spin resonance and the uranium series dating methods the uplift trend deduced from these reefs is 0 5 millimeter per year most terraces although polycyclic in origin appear to correspond to specific interglacial stages with the oldest terrace formed 1 million years ago this puts them among the longest and most complete mid quaternary terrace sequences

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

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

east antarctic ice stream tributary underlain by major sedimentary basin marine and rift sediments exert a fundamental control on ice stream flow in the west antarctic ice sheet and hence on its mass balance and stability in contrast most ice streams in the much larger east antarctic ice sheet are thought to be relatively stable features resting on till perhaps underlain by crystalline rock any geological controls on east antarctic ice sheet enhanced flow remain largely unknown we present aerogeophysical evidence indicating that a region of enhanced ice flow in the interior of the east antarctic ice sheet is underlain by subglacial sediments 3 km thick and that these are influencing the flow regime of the overlying ice we show that subglacial sediments are important in modulating ice dynamics not just for the west antarctic ice sheet but also for its much larger neighbor and suggest that the sedimentary basin identified here may contain information on the neogene glacial history of this part of the east antarctic ice sheet

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

evaluation of holocene crustal movement in the ako plain western japan holocene sea level observations have been obtained from the ako plain in western japan in this coastal area the holocene crustal movements have been evaluated except the crustal response due to the last deglaciation by comparing observations and theoretical predictions of relative sea level rsl variations analyses of diatom assemblages and sedimentary sulphur in core sediments were used along with radiocarbon dates to derive the rsl variations a crustal movement rate between 0 2 mm and 0 2 mm per year corrected for the prediction fits well with the observed rsl index points owing to the constraint of the reconstructed palaeo mean sea level pmsl at 7300 cal bp the coast of the ako plain may have the best estimate of a tectonic subsidence rate of 0 0 2 mm yr the tectonic uplift rates along the tectonically active coast of western kobe were derived to be 0 3 0 7 mm yr and 0 11 0 45 mm yr for tarumi and tamatsu respectively relative to ako over the period concerned the relative uplift along the traverse from ako to western kobe is primarily the result of the crustal movement resulting from the active faulting of the rokko awaji fault system rfs

sequence stratigraphic architecture of the upper jurassic lower cretaceous deposits in the sayun masilah basin yemen a case study from masilah oilfields abstract twelve third order depositional sequences sq1 to sq12 are defined of the upper jurassic lower cretaceous succession in the masilah oilfields sayun masilah basin yemen based on analysis of well logs and integrated datasets biostratigraphic petrographic and seismic data these sequences which are bracketed by thirteen sequence boundaries sb1 to sb13 represent several stages of transgression and regression that caused changes in facies types the base of the sequences in this study unconformably overlies the basement complex at the start of the regional transgression represented by shuqra formation tst1 whereas the top is bounded by normal regression represented by qishn carbonate member hst12 the producing horizons in this succession are located in highstand and transgressive systems tracts of the lower and upper qishn clastic in the depositional sequences sq8 to sq11 the main producing sandstone reservoir of lower and upper qishn clastic that is recorded in four progradational highstand systems tracts hst8 hst11 is about 224 5 m it occurs as transgressive systems tract tst11 of the upper qishn clastic representing of about 67 m

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

global correlation of middle cretaceous sea level events seven albian sea level curves from localities around the globe have been correlated on the basis of the number and timing of transgressive regressive cycles shown the localities chosen were considered to have been tectonically stable there are 11 time lines placed in the different sections by use of graphic correlation they are based on the position of european ammonite zonal subzonal boundaries projected into sections in north america and the middle east the examined sea level sequences with durations of 0 3 2 7 m y appear to vary regionally and their global correlation cannot be demonstrated with the present stratigraphic resolution frequency trends show that albian sea level was statistically stable from the late early to the early late albian whereas it fluctuated rapidly in earliest and latest albian

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

sequence stratigraphy of lower cretaceous barremian albian carbonate platforms of northeastern mexico regional and global correlations abstract the lower cretaceous cupido and coahuila platforms of northeastern mexico form part of the extensive carbonate platform system that surrounded the ancestral gulf of mexico a sequence stratigraphic model for these barremian to albian platforms was constructed from regional correlations of vertical cycle stacking patterns constrained by newly acquired biostratigraphic data and c and sr isotope stratigraphy the cupido shelf lagoon barremian aptian is composed of up to 150 peritidal cycles which stack into high frequency sequences that are correlated across the shelf cupido high frequency sequences build into a lower partial composite sequence cu1 an overlying full composite sequence cu2 and the transgressive base of a third composite sequence cu co3 related to backstepping of the cupido platform the highstand part of cu co3 is recorded in evaporite and carbonate facies of the coahuila platform aptian albian more than 80 meter scale evaporite to carbonate cycles characterize the restricted interior of the coahuila platform and stack into two full composite sequences co4 co5 the coahuila platform was drowned in the latest albian or earliest cenomanian terminating shallow water carbonate sedimentation in the region regional correlations of the depositional sequences in northeast mexico with coeval platforms in texas and the northern gulf coast indicate that the lower two composite sequences of the cupido shelf correlate with the lower part of the sligo hosston platform in texas the transgressive systems tract of the third composite sequence of the cupido la pena is recorded in texas by the upper sligo and pearsall formations the highstand systems tract and the disconformable top of the third composite sequence coahuila platform is likely coeval with the upper glen rose platform in texas the fourth and fifth composite sequences are correlative with the fredericksburg platform and the washita devils river platforms of texas respectively we conservatively correlated our sequence stratigraphic framework with composite global sequences and eustatic curves derived from several other basins given the available time resolution results are variable but sequence boundaries at the top of cu co3 and co5 appear to have clear interbasinal equivalents

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

glaciology and geological signature of the last glacial maximum antarctic ice sheet dynamical changes in contemporary ice sheets account for significant proportions of their current rates of mass loss but assessing whether or not these processes are a natural part of ice sheet evolution requires inference from palaeo glaciological records however a robust mechanism for translating sparse geological data into meaningful interpretations of past glacier dynamics at the continental scale is lacking since geological archives can be ambiguous and often their chronology is only poorly constrained to address this we combine the interpretation of high resolution antarctic ice sheet model results with continent wide geological evidence pertinent to the dynamical configuration of the ice sheet during the last and possibly preceding glacial maxima we first focus on the thermal regime of the ice sheet its pattern and velocity of flow variability in likely subglacial erosion and sediment transport and how these characteristics evolve during glacial transitions we show that rapid basal sliding was restricted to discrete outlets that eroded and advected sediment toward and across the continental shelf primarily during the early stages of advance and retreat of the ice sheet highlighting the need to consider time transgressive behaviour in the interpretation of geological archives secondly we present new modelling that attempts to improve the fit of our numerical model to geologically based reconstructions in the ross sea by accounting for locally enhanced ablation in mcmurdo sound our new simulation achieves a much closer fit to empirically derived flow patterns than previously growth of the modelled last glacial maximum ice sheet takes place primarily by marine ice accretion in the major embayments as a consequence of cooler ocean temperatures and reduced sub ice shelf melting and at its maximal extent represents a grounded ice volume excess above present of approximately 8 3 m sea level equivalent this figure thus provides an upper bound on the possible antarctic contribution to deglacial meltwater pulses

holocene uplift derived from relative sea level records along the coast of western kobe japan abstract mid to late holocene sea level observations have been obtained from tamatsu and tarumi in western kobe japan in this tectonically active area we evaluate the local tectonic effect during the holocene by comparison between observations and predictions of sea level variations for the purpose of this study we analysed the diatom assemblages and carried out sulphur analysis of sediments these were used along with radiocarbon dates to derive relative sea level variations for the sites a rate of tectonic uplift of between 0 1 and 0 3 mm per year corrected for the prediction fits well with relative sea level rsl index points of tamatsu at 6415 5320 cal bp depending on the altitude of the rsl index point at about 5700 cal bp the best estimate of the rate of tectonic uplift for tamatsu is calculated as 0 11 0 25 mm yr over the period concerned a rate of tectonic uplift between 0 3 and 0 5 mm per year is derived for tarumi at about 7300 and 3835 3365 cal bp these values may explain the height distributions of the late pleistocene marine terraces along the coast of the western kobe providing a first approximation for rates of local crustal movements during the late quarternary

vertical to lateral transitions among cretaceous carbonate facies a means to 3 d framework construction via markov analysis the search for and extraction of hydrocarbons in carbonate rocks demands a thorough understanding of their depositional anatomy the complexity of carbonate systems however hinders detailed direct characterization of their volumetric heterogeneity information with which to construct a reservoir model must therefore be based on information gathered from wells or outcrops transecting the sequence of interest most particularly exploration wells are vertical presenting a problem for geostatistical modeling while understanding vertical stratal stacking is straightforward it is difficult to obtain lateral facies information though in some situations outcrop surfaces seismic data and horizontal wells may somewhat mitigate this bias the likelihood remains that the lateral dimension of a buried system will be vastly undersampled with respect to the vertical however through the principle of walther s law walther 1894 or due to the geometry of basinward inclined beds comparable facies frequencies and transition probabilities may link vertical and lateral stratal arrangements the implication being that a reservoir model competent at least in terms of transition statistics could be built against information harvested down core taking an interpreted outcrop panel from lewis canyon albian pecos river texas we use markov chains to first ascertain that vertical and lateral stratal ordering is nonrandom second we show lithofacies transition probabilities in the outcrop as being interchangeable between the vertical and lateral directions the work concludes by demonstrating the utility of an existing 3 d markov random field simulation to volumetrically model the lewis canyon outcrop on the basis of vertical facies transition tendencies statistical interrogation of the 3 d model output reveals the simulation to contain realistic facies associations compared to the outcrop this suggests that the reconstruction process based on markov chains produces a useful representation of 3 d heterogeneity in this lower cretaceous carbonate succession markov random field simulation might provide an important tool for prediction and simulation of subsurface carbonate reservoirs

climate and sea level during oxygen isotope stage 7b on land evidence from new zealand abstract strata at landguard bluff near wanganui new zealand preserve a clear record of relative sea level changes during oxygen isotope stage 7 two relative high sea level stands during stages 7a about 210 000 yr ago and 7c about 240 000 yr ago are separated by a relative low sea level stage 7b that was at least 32 m lower than present pollen analysis of sediment deposited during stage 7b indicates climate at the time was up to 3 c cooler than present the climate and sea level evidence from landguard bluff are consistent with oxygen isotopic evidence from deep sea cores indicating a marked cooling during stage 7 which is closely associated with a summer radiation minimum centered at about 230 000 yr ago in the northern hemisphere

antarctic sediment chronology by programmed temperature pyrolysis methodology and data treatment 1 we report a detailed programmed temperature pyrolysis combustion methodology for radiocarbon 14c dating of antarctic sub ice shelf sediments the method targets the autochthonous organic component in sediments that contain a distribution of acid insoluble organic components from several sources of different ages the approach has improved sediment chronology in organic rich sediments proximal to antarctic ice shelves by yielding maximum age constraints significantly younger than bulk radiocarbon dates from the same sediment horizons the method proves adequate in determining isotope ratios of the pre aged carbon end member however the isotopic compositions of the low temperature measurements indicate that no samples completely avoided mixing with some proportion of pre aged organic material dating the unresolved but desired young end member must rely on indirect methods but a simple mixing model cannot be developed without knowledge of the sedimentation rate or comparable constraints a mathematical approach allowing for multiple mixing components yields a maximum likelihood age a first order approximation of the relative proportion of the autochthonous component and the temperature at which allochthonous carbon begins to volatilize and mix with the autochthonous component it is likely that our estimation of the cutoff temperature will be improved with knowledge of the pyrolysis kinetics of the major components chronology is improved relative to bulk acid insoluble organic material ages from nine temperature interval dates down to two but incorporation of inherently more pre aged carbon in the first division becomes more apparent with fewer and larger temperature intervals

aptian albian sea level history from guyots in the western pacific relative sea level fluctuations are an important control on patterns of sedimentation on continental margins and provide a valuable tool for regional correlations one of the main objectives of combined ocean drilling program legs 143 and 144 was drilling the thick carbonate caps of a suite of seamounts called guyots scattered over the northwestern pacific the array of drowned cretaceous banks includes four carbonate banks of aptian albian age these particular carbonate banks display emergent surfaces if regional sea level falls faster than the rate of guyot subsidence or intervals of condensed parasequences and well cemented peritidal crypto algal flats if the rate of sea level fall is slightly less than guyot subsidence rapid rises of sea level following these sequence boundaries are recorded as drowning of the emergent horizons or as pronounced deepening of facies the cored lithologies and downhole geophysical and geochemical logs were used to identify depositional sequences and surfaces of exceptional shallowing or deepening a combination of biostratigraphic datums carbon and strontium isotope curves relative magnitude of surfaces of emergence relative thicknesses of depositional sequences sea level events and counts of upward shallowing cycles or parasequences were used to correlate sequences among the four sites after compensating for thermal subsidence rates at each guyot an identical pattern of major aptian albian eustatic sea level events is evident throughout this large portion of the pacific ocean there are approximately 12 aptian and 12 albian significant sequence boundaries of which a third were associated with major episodes of emergence when these events are compared with aptian albian relative sea level changes observed in european shelf successions the major sequence boundaries and transgressive surges can be easily correlated and it appears that both regions also display the same number of minor events therefore we can apply the relative timing of these events from the thermal subsidence rates and parasequence counts of the pacific banks to construct an improved scaling of the associated ammonite zones and biostratigraphic datums in the aptian albian interval an electronic supplement of this material may be obtained on adiskette or via anonymous ftp from kosmos agu org loginto agu s ftp account using anonymous as the username andguest as the password go to the right directory by typing apend diskette may be ordered from american geophysical union 2000florida ave n w washington d c 20009 15 00 payment mustaccompany order

triassic sand supply to the slyne basin offshore western ireland new insights from a multi proxy provenance approach to assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system a multi proxy approach helps ensure rigour in how provenance data are interpreted u pb geochronology of refractory zircon and relatively less stable apatite and pb isotopic analysis of labile k feldspar are employed in this study to reassess the provenance of triassic sandstones in the slyne basin offshore western ireland this approach aims at reducing the potential bias in each method producing a complementary dataset u pb zircon and apatite geochronology yields archean paleoproterozoic ages caledonian ages and previously unrecognized permo triassic ages pb isotopic analysis of k feldspar does not identify the permo triassic as a source the detection of permo triassic aged detritus may suggest that volcanism was more widespread than previously recognized these results support the hypothesis of a triassic drainage divide between the basins offshore western ireland and those onshore britain and in the irish sea sand supply was dominantly from the north with significant input from the flanks of the basin and previously unrecorded sources such as permian aged rocks playing an important role the provenance signal is consistent and homogenized throughout the sampled sequence indicating that the drainage system was long lived supplementary material details of laboratory and sample preparation data tables and summary pie charts for each sample are available at https doi org 10 6084 m9 figshare c 4571096

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

sea level variation during mis 11 constrained by stepwise osaka bay extensions and its relation with climatic evolution abstract marine oxygen isotope stage mis 11 has been described as a super interglacial because of its long duration more than 30 ka but this view is often refuted by the observation that the peak sea level and maximum temperature did not surpass other interglacials including the last interglacial we address this problem using data from coastal sediments we conducted diatom and sulfur analyses on two cores of high accumulation rate 0 52 m ka sediments from osaka bay japan a linear age model applied to the diatom data shows that sea level variations with precession cycles are correlated with oxygen isotopic events 11 3 11 24 11 23 11 22 and 11 1 diatom abundances reveal sea level increases and falls because of environmental changes caused by stepwise extension of the bay this extension can be verified and mapped using data from 15 other drill cores sea level was above the sill for osaka bay during the marine interval in osaka bay spanning 60 ka it was above the sill for kawachi bay during the marine interval in kawachi plain for a duration of 44 ka including events 11 3 and 11 23 the highest sea level was above the sill for kyoto bay during an interval of 16 ka centered at event 11 3 estimates of sill elevations together with geological data suggest that the sea level of mis 11 changed within a range from 60 m to 20 m palynological data from the same core show that the mis 11 climate around osaka bay was divided into early warm temperate and late cool temperate times with a boundary between events 11 3 and 11 24 during the marine interval in kyoto the climate was an extremely warm hypsithermal almost coincided with the warmest interval in antarctica where temperatures are 0 c

provenance and dispersal of glacial marine surface sediments in the weddell sea and adjoining areas antarctica ice rafting versus current transport abstract mineralogical and granulometric properties of glacial marine surface sediments of the weddell sea and adjoining areas were studied in order to decipher spatial variations of provenance and transport paths of terrigenous detritus from antarctic sources the silt fraction shows marked spatial differences in quartz contents in the sand fractions heavy mineral assemblages display low mineralogical maturity and are dominated by garnet green hornblende and various types of clinopyroxene cluster analysis yields distinct heavy mineral assemblages which can be attributed to specific source rocks of the antarctic hinterland the configuration of modern mineralogical provinces in the near shore regions reflects the geological variety of the adjacent hinterland in the distal parts of the study area sand sized heavy minerals are good tracers of ice rafting granulometric characteristics and the distribution of heavy mineral provinces reflect maxima of relative and absolute accumulation of ice rafted detritus in accordance with major iceberg drift tracks in the course of the weddell gyre fine grained and coarse grained sediment fractions may have different origins in the central weddell sea coarse ice rafted detritus basically derives from east antarctic sources while the fine fraction is discharged from weak permanent bottom currents and or episodic turbidity currents and shows affinities to southern weddell sea sources winnowing of quartz rich sediments through intense bottom water formation in the southern weddell sea provides muddy suspensions enriched in quartz the influence of quartz rich suspensions moving within the weddell gyre contour current can be traced as far as the continental slope in the northwestern weddell sea in general the focusing of mud by currents significantly exceeds the relative and absolute contribution of ice rafted detritus beyond the shelves of the study area

basal conditions beneath enhanced flow tributaries of slessor glacier east antarctica radio echo sounding data are used to investigate bed roughness beneath the three enhanced flow tributaries of slessor glacier east antarctica slow moving inter tributary areas are found to have rough beds while the bed of the northernmost tributary is relatively smooth a reconstruction of potential subglacial drainage routing indicates that water would be routed down this tributary and investigations of basal topography following isostatic recovery reveal that the bed would have been below sea level in preglacial times so marine sediments may have accumulated here together these factors are further support for the dominance of basal motion in this tributary reported elsewhere conversely although the other two slessor tributaries may have water routed beneath them they would not have been below sea level before the growth of the ice sheet so cannot be underlain by marine sediments they are also found to be rough and within the range of uncertainties it is likely that basal motion does not play a major role in the flow of these tributaries perhaps the most interesting area however is a deep trough where flow rates are currently low but the bed is as smooth as the northern slessor trough it is proposed that although ice deformation currently dominates in this trough basal motion may have occurred in the past when the ice was thicker

basal ice sequences in antarctic ice stream exposure of past hydrologic conditions and a principal mode of sediment transfer 1 the brightness distribution of sequentially extracted borehole camera imagery shows two distinct sequences of basal ice in kamb ice stream the upper sequence 7 3 m comprises clear ice and layers with dispersed and stratified debris the lower sequence 8 2 m consists of accretion ice with alternating layers of stratified and solid debris the two sequences have volumetric debris contents of about 5 and 20 respectively we infer that the upper sequence formed in a tributary where subglacial meltwater was abundant and that the lower sequence formed on the siple coast plain where basal freezing currently dominates the basal thermal regime the basal ice layer contains the equivalent of 2 1 0 4 m of frozen sediment the high volume of sediment is a result of debris rich layers interpreted to have formed by accretion in the stagnant phase of ice stream on off cycles fast ice streaming punctuated by entrainment of debris during stagnation episodes is consistent with inferred past flow of adjacent ice streams and geologic features in the ross sea our results show that sediment wedges near grounding lines may form by melt out of basal ice debris this is different from previous studies where it was assumed that sediment transfer occurs through sediment deformation within layers of subglacial till cumulative freezing in recurring ice stream cycles shows that entrainment of sediment by basal freeze on is an important erosion mechanism and that high sediment fluxes can occur when ice streams override coulomb plastic substrates

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

increased terrigenous influx but no drowning palaeoenvironmental evolution of the tunisian carbonate platform margin during the late aptian during the aptian some carbonate platforms of the sub tropical realm for example on the northern tethys margin or in the gulf of mexico were affected repeatedly by severe perturbations in the carbonate production factory and drowning preferentially during global warming events such as the early aptian oceanic anoxic event 1a and a prominent mid late aptian warming interval these platform growth crises have been explained mainly by strongly increased coastal runoff for example siliciclastics and nutrients in combination with pronounced eustatic sea level rises in the last few years increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events this raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas in this study upper aptian middle gargasian to uppermost clansayesian inner tropical carbonate ramp deposits of the serdj formation at djebel serdj north central tunisia are studied in detail with regard to microfacies lithology biostratigraphy and chemostratigraphy these data allow reconstruction of the palaeoenvironmental evolution of the tunisian carbonate platform margin and investigation of its response to the prominent mid late aptian warming interval the unusually expanded 600 m thick serdj formation consists of limestones marlstones and siltstones suggesting deposition within mid ramp to inner ramp palaeoenvironments deposits of the mid late aptian are represented by quartz rich platform carbonates and siltstones probably resulting from increased coastal runoff on the tunisian shelf as a response to global warming and accelerated water cycling the siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae carbonate platform drowning during the mid late aptian as reported from the sub tropical realm has not been identified a comparison with other tropical river influenced platforms suggests that none of them drowned during the mid late aptian one important reason might be widespread arid to semi arid climatic conditions within lower latitudes during that time promoting platform growth due to comparably low nutrient runoff

correlation of middle pleistocene crystal rich tephra layers from daisen volcano southwest japan based on the chemical composition and refractive index of mafic minerals abstract analyses of chemical compositions and refractive indices of mafic minerals have been effective correlation tools especially for crystal rich tephra layers containing isolated volcanic glass shards the analyses are applied to the correlation of the middle pleistocene tephra layers in the kinki and chubu districts central japan with those erupted from daisen volcano in the chugoku mountains west of the districts on the basis of chemical compositions of hornblende phenocrysts and refractive indices of hornblende orthopyroxene and cummingtonite phenocrysts four groups of tephra layers in the kinki and chubu districts are successfully correlated to bvs2 cpm gpm and hpm1 or dop tephra layers of the lowermost member of the daisen tephra formation the correlation reveals that two tephra layers bvs2 and cpm with estimated eruption ages of 410 ka and 370 400 ka respectively are present in the kinki district the hpm1 tephra about 210 ka is also widespread and recognized at the eastern foot of yatsugatake volcanoes about 400 km east of the source these tephra layers can contribute to establishing the regional correlation and chronology of the middle pleistocene sequences in central japan especially for the time from mis 7 to mis 11

a multiproxy provenance approach to uncovering the assembly of east gondwana in antarctica east gondwana is generally thought to have assembled through the amalgamation of indo antarctica and australo antarctica along the ediacaran cambrian kuunga orogen the location of a boundary between indo antarctica and australo antarctica within this key gondwana forming orogen remains controversial because extensive ice cover in east antarctica precludes traditional characterization of terranes here we integrated pb isotope analysis of detrital feldspar grains with u pb dating of detrital monazite and zircon grains from offshore sediments to infer the location of the onshore boundary between indo antarctica and australo antarctica new and compiled data from onshore basement exposures highlight the different age and pb isotope signatures of indo antarctica and australo antarctica holocene sediments offshore from mirny station queen mary land east antarctica have detrital feldspar pb isotope signatures and detrital monazite and zircon u pb ages that reflect contributions from both indo antarctica and australo antarctica the presence of both indo antarctic and australo antarctic crust beneath ice cover near mirny station implies proximity to a fundamental terrane boundary within the kuunga orogen which could coincide with a geophysical lineament at 94 e mirny fault the geophysical expression of this boundary extends into the subglacial interior of east antarctica where prior to more recent rifting it may have connected with one or more previously inferred gondwana forming sutures the revised geometry of the kuunga orogen suggests that the assembly of east gondwana involved dominantly strike slip motion in the mirny region coupled with high angle convergence between indo antarctica and australo antarctica to the west

controls on cyclostratigraphy of lower cretaceous carbonates and evaporites cupido and coahuila platforms northeastern mexico the lower cretaceous cupido barremian aptian and coahuila albian carbonate platforms of northeastern mexico exhibit thick successions of meter scale cycles deposited in three unique paleoenvironmental settings 1 the cupido shelf lagoon is composed of peritidal carbonate cycles deposited in the protected lee of a reef rimmed to barrier shoal margin 2 the restricted coahuila ramp interior consists of cyclic alternations of subtidal evaporites and peritidal carbonates 3 the deep water parts of both the cupido and coahuila platforms are composed of foraminiferal wackestones and lime mudstones interspersed with firmgrounds and hardgrounds in a cyclic arrangement vertical successions of meter scale evaporitic cycles and peritidal cycles exhibit systematic stacking patterns that build into intermediate scale high frequency sequences tens to hundreds of meters thick and large scale composite sequences hundreds of meters thick that can be correlated across the cupido and coahuila platforms these large scale stacking patterns are interpreted to reflect longterm accommodation events and when combined with the scale independent architecture of all genetic units permit the inference that all three meter scale cycle types on the cupido and coahuila platforms are also governed by relative sea level change the composition thickness and number of meter scale cycles within individual high frequency sequences can be highly variable across the cupido and coahuila platforms however even though the overall upward shallowing patterns are evident the lateral complexity of cycle architecture and distribution is interpreted to be a natural response to fluctuations in regional climate interacting with autogenic processes such as variations in carbonate production and dispersal intensity and frequency of tropical storms and monsoons thermohaline circulation patterns and ambient ocean chemistry and temperature these interacting processes created laterally variable physiographic and oceanographic conditions across the cupido and coahuila platforms complicating the sedimentary record generated by the composite sea level signal well documented evidence from barremian cenomanian pelagic cycles throughout the tethyan seaway strongly indicates that milankovitch driven climatic changes operated during the early cretaceous contemporaneous shallow marine cyclicity in several locations suggests that these climatic changes may have had globally widespread effects in an effort to link the shallow water and deep water realms we propose a model whereby milankovitch driven global climatic changes generated low amplitude high frequency eustatic fluctuations through some combination of thermal expansion and contraction of ocean water waxing and waning of small ice caps and alpine glaciers and changes in the storage capacity of aquifers and lakes to produce meter scale cycles across lower cretaceous shallow marine platforms

sea level variations during marine isotope stage 7 and coastal tectonics in the eastern seto inland sea area western japan relative sea level rsl observations for marine isotope stage mis 7 were obtained from three sites higashinada kakogawa and mitsu of the eastern seto inland sea area western japan we evaluated the magnitude of sea level highstands during mis 7 and the local tectonics based on rsl records of this coastal area for this purpose we analyzed diatom assemblages and sedimentary sulfur and carried out tephra analysis we also constructed a linear age model to determine the depositional ages of the sediments using altitudes of astronomical age control points obtained mainly from the present diatom data at the mitsu site rsls were estimated to be 22 87 0 50 m at the mis 7 5 highstand peak 234 6 ka below 20 17 m at 211 2 ka and below 20 00 m at 209 9 ka with a tectonic subsidence rate of 0 11 0 02 m ka since the last interglacial maximum at the mitsu site the elevation of the tectonically corrected mis 7 5 highstand peak may have been 2 94 5 19 m the tectonically corrected sea level elevations during mis 7 3 are inferred to have been below 3 06 4 72 m at 211 2 ka and below 3 09 4 70 m at 209 9 ka comparisons between the diatom inferred rsls and the isotopically derived sea level curve indicate that the mis 7 3 highstand peak was above 18 m and may have been lower than the mis 7 5 and 7 1 highstands based on the isotopically derived sea level curve and the rsl data from higashinada and kakogawa a tectonic subsidence rate of 0 26 0 32 m ka was derived for higashinada and a tectonic uplift rate of 0 17 m ka and 0 43 m ka and 0 26 m ka and 0 42 m ka these values indicate the intensity of crustal movements associated with active faulting of the rokko awaji fault system along this tectonically active coast

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

applications of detrital geochronology and thermochronology from glacial deposits to the paleozoic and mesozoic thermal history of the ross embayment antarctica

regional to global correlation of lower cretaceous hauterivian barremian shallow water carbonates of the southern apennines italy and dinarides montenegro southern tethyan margin abstract we propose a high resolution regional to global scale correlation of two hauterivian barremian shallow water carbonate platform sections belonging to different palaeogeographic domains of the southern margin of the tethys these successions are now located more than 500 km apart and are represented by 137 m of core drilled at monte raggeto southern apennines italy and by 80 m of well stratified rocks cropping out in the podgorica mountains dinarides montenegro they display three superimposed orders of stratigraphic cyclicity defined by elementary cycles grouped into bundles and superbundles and attributed to orbitally induced composite sea level fluctuations elementary cycles are interpreted as the precession and the obliquity periodicities 20 40 ky while bundles and superbundles correspond to the short 100 ky and long 400 ky eccentricity cycles respectively as both the ratios between the elementary cycles and the bundles and between the bundles and the superbundles do not always reflect the classical 5 1 and 4 1 relationship the sedimentary record of both the studied sections is likely to include omission of bundles or their portion the general evolution of depositional and diagenetic facies the vertical change in thickness of the cyclic units and the interpretation of superbundles as small scale depositional sequences suggest that elementary cycles and their groups are superimposed on lower frequency environmental oscillations these display an upward transgressive regressive trend t rt of the facies and testify to larger scale variations of accommodation potential on the shelf t rts sequence stratigraphic interpretation of the superbundles as well as the common occurrence of the biostratigraphic dated hauterivian barremian boundary in the studied sections support the long distance regional correlation between the successions to be carried out on the 100 ky scale moreover by assuming the maximum flooding intervals of time equivalent superbundles as virtually isochronous intervals we have detected stratigraphic gaps of 1200 and 600 ky in the monte raggeto and in the podgorica mountains sections respectively both sections are formed of 10 complete superbundles each of them testifying to the 400 ky long eccentricity hence the monte raggeto and podgorica mountains successions represent a duration of at least 4 0 my in terms of elapsed time regardless of gaps within the stratigraphic record finally a correlation between the orbitally induced compared sections and both the 3rd order tethyan stratigraphic cycles and the global cycle chart is suggested our study confirms that cyclically organized shallow marine carbonate platform deposits controlled by orbitally induced sea level fluctuations represent a powerful tool for high precision regional and global correlations this can be of fundamental importance for quantification of sedimentary diagenetic and evolutionary processes as well as for the understanding of autocyclic versus allocyclic control on sequence development

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

paleogeographic evolution of early deep water gulf of mexico and margins jurassic to middle cretaceous comanchean the paleobathymetric configuration of the early gulf of mexico is inferred from 1 cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data 2 distribution of jurassic and cretaceous platform and basinal facies and 3 hindcasting of subsidence history in the central basin substantial paleogeographic ambiguity results from uncertainty about 1 kinematics and timing of late triassic to jurassic extensional opening of the gulf basin which probably involved major strike slip faulting 2 the magnitude of subsequent compressive deformation on the western and southern basin margins and 3 possible accretion of allochthonous terranes the initial sub sea level topographic depression created by crustal extension is manifested by the distribution of callovian pre marine salt and oxfordian basinal marine facies late jurassic sea floor spreading split the main salt body and created a central deep water 1 km trough from the oxfordian to early neocomian ramp like platform margins generally underwent net retreat except in the northern gulf where major clastic progradation took place carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the cretaceous these cretaceous carbonate margins exhibit a variety of architectural styles including 1 in the northwestern gulf two cycles of progradation coahuilan and comanchean terminated by drowning events 2 in the southwestern gulf a single cycle of progradation 3 continuous aggradation along the florida and campeche escarpments paleobathymetric relief across cretaceous carbonate margins ranges from high and steep to low relief to ramplike the close of comanchean drowning event greatly and permanently reduced the extent of circum gulf carbonate platforms and especially rimmed margins locations of cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust by the distribution of salt and by clastic progradation eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the gulf but other paleoenvironmental variables such as nutrient abundance are probably important as well

crustal structure of the filchner ronne shelf and coats land antarctica from gravity and magnetic data implications for the breakup of gondwana understanding the tectonic evolution of the weddell sea embayment provides valuable insights on the breakup of gondwana existing geodynamic models for this region differ mainly in the nature of the crust beneath the filchner ronne shelf and the movement of the ellsworth whitmore mountains ewm crustal block new gravity data presented here constrain the area and timing of this ewm movement from its prebreakup position to its present day position the crustal thickness estimates of 29 5 km and 27 4 km derived from power spectral analysis as well as forward gravity modeling make the existence of oceanic crust beneath the filchner ronne shelf unlikely a new crustal unit consisting of precambrian crust has been identified with gravity and magnetic data and extends 175 km off the coast of coats land this crustal unit conflicts with the late mesozoic movement of the ewm in this area the effective elastic thickness of t e 35 5 km has been estimated from coherence spectra for the ronne shelf together with the crustal thickness of 27 km from refraction seismic studies and comparison with theoretical models the thermal age is estimated to be between 165 and 230 ma for the ronne shelf this age marks the last significant tectonic event in this area and is in good agreement with the breakup of gondwana it further makes later movements of microplates like the ewm in this region unlikely thus a filchner block consisting of continental crust should be considered in any geodynamic model of the early weddell sea evolution

controls on the evolution of carbonate mud mounds in the lower cretaceous cupido formation northeastern mexico abstract the lower cretaceous cupido formation in northeastern mexico represents part of an extensive post rift carbonate platform system that stretched across much of the gulf of mexico passive margin numerous sponge microbial mud mounds are found within the lower part of the cupido formation four mound types were identified at bustamante canyon and other localities in the state of nuevo leon mexico type 1 siliceous sponge microbial mounds contain boundstone core facies are the oldest mounds and are associated with adjacent deep ramp to basinal lime mudstone facies type 2 sponge microbial mounds also have boundstone core facies are associated with outer ramp wackestone packstone facies and overlie strata that contain type 1 mounds type 3 sponge microbial coral mounds contain only 40 50 boundstone core facies and overlie or are locally interstratified with type 2 mound bearing strata although type 3 mounds are associated with outer ramp packstone facies type 4 calcisponge microbial coral biodetrital dominantly skeletal packstone mounds are the youngest mounds and are associated with outer ramp packstone and ramp crest rudist packstone facies both the length and height i e synoptic relief of individual types 1 2 and 3 mounds range from a few meters to tens of meters only type 4 mounds reach several hundred meters in length and are up to 90 m thick although synoptic relief on type 4 mounds was minor systematic changes in the biota morphologies dimensions abundance stratigraphic distribution and facies associations of the lower cupido mounds were largely controlled by the initial ramp like depositional profile of the lower cupido platform and the long term second order accommodation trends that affected ramp evolution during early cretaceous time the ramp like profile was not conducive to transport of large volumes of allochthonous sediment from updip source areas to mound locations on the outer ramp this allowed slowly accumulating types 1 2 and 3 mounds to build synoptic relief because adjacent outer ramp facies accumulated at even slower rates in contrast type 4 mound cores contain abundant coarse grained skeletal sediment and also developed the least synoptic relief of all lower cupido mounds because of higher accumulation rates associated with adjacent grain rich ramp crest lithofacies we suggest that these systematic changes in mound attributes largely reflect long term second order accommodation loss and regional progradation of the lower cupido ramp during early cretaceous time accordingly the upward transition from type 1 to types 2 and 3 mounds and ultimately to type 4 buildups can be explained by the progressive shallowing of outer ramp environments as more updip facies tracts prograded eastward from late hauterivian to early aptian time there are few stratigraphic successions in the rock record that provide better evidence for the links between large scale stratigraphic relationships and mound evolution along low gradient carbonate ramps

global milankovitch cycles recorded in rock magnetism of the shallow marine lower cretaceous cupido formation northeastern mexico rock magnetic cyclostratigraphy was measured in the barremian aptian cupido cupidito formation northeastern mexico the goal was to develop an objective evaluation of palaeo environmental variability recorded in the formation that is independent of facies analysis and interpretation anhysteretic remanent magnetization arm was used to estimate magnetic mineral concentration variations for the upper 143 m of the formation which is characterized by metre scale carbonate cycles representative of innerand middle shelf marine environments isothermal remanent magnetization acquisition experiments and scanning electron microscope sem examination indicate that micron sized detrital magnetite from eolian dust carries the arm signal at the sampled sections from garcia and chico canyons 25 km apart arm records a synchronous 30 35 m oscillation with maxima coinciding with fourth order sequence boundaries superimposed with prominent high frequency variability calibrating the 30 35 m oscillation to a 405 kyr period long eccentricity cycle focuses the high frequencies into short eccentricity obliquity and precession index bands the precession band signal modulates with an eccentricity signature the arm signal is correlated between sections but decoupled from the interpreted fifthorder depositional cycles arm amplitudes diminish up section with facies suggesting deepening conditions that diluted magnetite concentration this probably signals a warming increasingly humid climate changing global circulation and or greater dispersal of magnetite grains earth s ancient shallow marine carbonate platforms are important archives of past global change their in situ biological genesis makes them sensitive indicators of physical conditions in shallow marine environments including temperature circulation and sea level wilson 1975 the accommodation space afforded by water depth is thought to govern the amount and type of sediment that accumulates at a given location water depth in turn is controlled by a combination of tectonic subsidence near shore deposition and global sea level which vary significantly through time schlager 2005 the commonly observed stacking of metrescale shallowing upward cycles in carbonate platform deposits has led to proposals of allocyclic v autocyclic forcing mechanisms the most widely cited allocyclic hypothesis is astronomically controlled eustasy fischer 1964 hardie et al 1986 autocyclic mechanisms involve infilling and oceanward progradation of sedimentation without eustatic change ginsburg 1971 to this day the allocycle v autocycle debate remains unresolved in understanding the origin of 10 10 year scale lithologic cyclicity in shallow marine carbonates schwarzacher 2000 burgess 2006 schlager 2010 full shallowing to sea level may not develop in response to every sea level oscillation subtidal missed beats resulting in amalgamated cycles conversely prolonged episodes of subaerial exposure may occur in inner platform settings that are only briefly or never flooded with every sea level oscillation leading to condensed or peritidal missed beats goldhammer et al 1990 ultimately facies analysis of shallow marine sections is limited in teasing apart the interplay of eustasy owing to climate change and subsidence arising from local tectonics this is in large part owing to the relatively subjective interpretation of lithofacies that is required from the stratigrapher therefore we need to develop facies independent from jovane l herrero bervera e hinnov l a housen b a eds 2013 magnetic methods and the timing of geological processes geological society london special publications 373 325 340 first published online april 25 2013 http dx doi org 10 1144 sp373 20 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics by guest on july 5 2013 http sp lyellcollection org downloaded from