did the last sea level lowstand always lead to cross shelf valley formation and source to sink sediment flux 1 it is commonly believed that the efficiency of sediment flux from continents to oceans is maximized during relative sea level rsl lowstands by means of cross shelf valleys that are directly connected to the continental slope and deep marine environment while such conditions have been documented for the last rsl lowstand along several continental margins there is increasing evidence that radically different conditions persisted during the last glacial maximum lgm elsewhere with lowstand shorelines that remained on the continental shelf here we analyze the relationship between the lgm 21 ka shoreline and the shelf edge for the gulf of mexico off the united states and the bay of biscay off france a geophysical model is used to compute shoreline positions corrected for isostatic movements and the shelf edge position is quantified by means of curvature the conditions in the two study areas differed markedly throughout the gulf of mexico study area lgm sea level dropped to a point commonly 40 m below the shelf edge consistent with conventional sequence stratigraphic models while in the bay of biscay the modeled lgm shoreline remained well landward of the shelf edge in places separated by hundreds of kilometers these observations hint at potentially significant implications for 1 the source to sink sediment flux from continents to oceans and its variation in time and space 2 sequence stratigraphic models that predict deep marine sedimentation as being particularly prominent during rsl lowstands and 3 the occurrence of paleovalleys and related features on the continental shelf in addition our findings raise fundamental questions about the mechanics of shelf edge formation

sea level change along the french atlantic and channel coasts since the time of the last glacial maximum abstract holocene sea level change along the french atlantic and english channel coast is not uniform because of the response of the crust to the changing ice and water loads in late pleistocene and holocene time the pattern of the spatial variability is a north south trend of decreasing sea levels levels at any time this results primarily from the isostatic response to the melting of the fennoscandian ice sheet superimposed upon this is a mainly east west trend resulting from the isostatic response of the crust to the addition of the meltwater into the atlantic ocean the combined effect is that at any time sea levels vary spatially along this coastline by amounts that are predicted to reach 20 m from the time of the last glacial maximum to about 10 000 radiocarbon yr ago about 15 m at 8000 yr ago and about 10 m at 6000 yr ago thus observations of past sea levels should not be combined into a single sea level curve unless first corrected for the glacio hydro isostatic factors alternatively the data should only be used to construct regional curves for relatively short sections of the coastline such as pas de calais and picardie normandie cotes du nord finistere or the vendee and charente maritime region even within such constrained regions the spatial variability may still be of the order of a few meters analysis of the observational data by region indicates that major oscillations in sea level are unlikely to have occurred that levels at no location exceeded the present mean sea level and that there may have been a small 3 m increase in eustatic sea level over the past 6000 yr palaeoshorelines and palaeo water depths for the english channel and the atlantic coast shelf have been predicted using the isostatic and eustatic models and the results indicate that in situ marine deposits older than 6000 7000 yr are unlikely to be found along many sections of the present coastline

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

late pleistocene and holocene palaeogeography of the lower tagus valley portugal effects of relative sea level valley morphology and sediment supply abstract because of the deep glacial incision the lower tagus valley hosts a sedimentary record since 20 000 cal bp making this a unique site along the european atlantic margin with respect to palaeogeographic and sea level changes based on nine cross sections and 55 radiocarbon dates together with a newly created relative sea level curve we constructed five palaeogeographic maps of the infill of the lower tagus valley since 20 000 cal bp we illustrate that relative sea level rise and fluvial sediment supply were the prime forcing factors determining the depositional history and palaeogeographic changes around 20 000 cal bp a deeply incised braided river existed which was directly connected to the ocean across the narrow continental shelf after that 12 000 cal bp the gradually moister and warmer climate caused a change to a single channel river during the following period 12 000 7000 cal bp relative sea level rise resulted in a transgression in the lower tagus valley and the establishment of extensive tidal environments after relative sea level rise had ended 7000 cal bp the valley was progressively filled by a fluvial wedge and tidally influenced bayhead delta since 1000 cal bp the valley fill history was dominated by increased sediment input due to human induced degradation of catchment slopes generally climate was of subordinate importance during the entire studied period merely causing a single channel river resulting from the change from the cold heinrich event 1 to the temperate bolling allerod interstadial despite the tectonic activity in the region neotectonic uplift or subsidence was limited as supported by the horizontal relative sea level curve since 7000 cal bp neotectonics played a minor role due to the large distance from the fennoscandian ice sheet and the narrow continental shelf which prohibited strong glacio and hydro isostatic movements

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

seaward pinching out and internal stratigraphy of the gironde incised valley on the shelf bay of biscay abstract an incised paleovalley offshore the estuary mouth of the gironde river southwest france was evidenced recently comptes rendus de l academie des sciences de paris 326 1998 701 nevertheless its seaward extension to the shelf break was still unknown new high resolution geophysical data were acquired on the continental shelf in order to follow the incision until the shelf break after processing the seismic lines the shape of the valley was identified and the valley fill in terms of sequence stratigraphy was interpreted the valley fill contains a single sequence corresponding to a fifth order cycle 20 kyr the three systems tracks described onshore by allen and posamentier journal of sedimentary petrology 63 1993 378 sepm society for sedimentary geology special publication tulsa 1994 225 are present offshore the lowstand is poorly developed and is only present in the proximal part of the incised valley the transgressive systems tract tst constitutes the bulk of the valley fill it is composed of landward prograding estuarine clinoforms in the distal part of the valley early tst phase 1 and of landward migrating tidal inlet fill deposits in the proximal part of the valley late tst phase 2 the thin early highstand systems tracts hst strata downlap seaward onto the maximum flooding surface and caps the tst as expected in this wave and tide dominated environment the tidal and wave ravinement surfaces which bound the tst are particularly well developed the valley incision tapers 50 km offshore of the estuary mouth the depth of the basal sequence boundary gradually decreases seaward and is locally truncated by the wave ravinement surface around 70 m below the mean sea level these observations indicate that during the lowstand times rivers do not always generate continuous cross shelf incised valleys they may adjust to a rapid drop in base level by modifying their channel morphology i e deep large channels located upstream change downstream to shallow anastomosed channels with a weaker erosional ability therefore the lowstand fluvial channels will be poorly developed and will eventually died out in the proximal part of the shelf because they are unable to keep pace with a phase of rapid sea level drop similar observations have already been reported for the english channel paleoriver geological society special publication london 1996 203 these de geologie marine universite de bordeaux 1 1997 265

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

time integrated 3d approach of late quaternary sediment depocenter migration in the tagus depositional system from river valley to abyssal plain quantification of sediment volumes in continental to deep ocean basins is key to understanding processes of sediment distribution in source to sink depositional systems using our own and published data we present the first quantification of sediment volume changes in basins along the course of a major southwest european river during the deglaciation the salient points of this quantitative record in the tagus and equivalent north atlantic basins show crucial roles for sea level climate and land use in the distribution of sediments the bypass of sediments starved the tagus basins and subsequently sedimentation mainly occurred on the tagus abyssal plain during the sea level lowstand of the last glacial maximum the main sediment depocenter rapidly shifted via the continental shelf to the lower tagus valley during sea level rise in the deglaciation period finally the main sediment depocenter shifted further landward into the lower tagus valley during sea level high stand in the holocene during the high stand phase last 7 ky sediment flux increased up to 2 5 times due to climate and land use changes the average catchment denudation rate during the last 12 ky 0 04 0 1 mm y is in agreement with those of other european catchments our study clearly demonstrates the added value of detailed knowledge of 3d depocenter distribution size and chronology this allowed us to identify an increased sediment flux during the last 7 ky which was not identified using local observations from boreholes alone the uniqueness of the tagus depositional system lies in the combination of a large accommodation space in the bedrock confined lower tagus valley the steep lowstand surface gradient and the narrow continental shelf with canyons indenting the shelf break

delta growth and river valleys the influence of climate and sea level changes on the south adriatic shelf mediterranean sea abstract incised valleys across continental margins represent the response of fluvial systems to changes in their equilibrium dynamics mainly driven by base level fall forced by glacial eustatic cycles the manfredonia incised valley formed during the last glacial sea level lowstand when most of the southern adriatic shelf was sub aerially exposed but the outer shelf remained under water the pronounced upstream deepening of the valley is ascribed to river incision of the mis5e highstand coastal prism and related subaqueous clinoform under the influence of mis5 4 sea level fluctuations while the downstream shallowing and narrowing mainly reflects the impact of increased rates of sea level fall at the mis3 2 transition on a flatter mid outer shelf until 15 ka bp the valley fed an asymmetric delta confined to the mid outer shelf testifying that continental and deep marine systems remained disconnected during the lowstand sea level rise reached the inner shelf during the early holocene drowning the valley and leading to the formation of a sheltered embayment confined toward the land at this time part of the incision remained underfilled with a marked bathymetric expression this mini basin was rapidly filled by sandy bayhead deltas prograding from both the northern and southern sides of the valley in this environment protected by marine reworking and where sediment dispersal was less effective the accommodation space was reduced and autogenic processes forced the formation of multiple and coalescing delta lobes bayhead delta progradations occurred in few centuries between 8 and 7 2 ka cal bp confirming the recent hypothesis that in this area the valley was filled during the formation of sapropel s1 this proximal valley fill representing the very shallow water equivalent of the cm thick sapropel layers accumulated offshore in the deeper southern adriatic basin is of key importance in following the signature of the sapropel in a facies tract ideally from the shoreline to the abyss

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

reconstructing the interacting effects of base level climate and tectonic uplift in the lower mino river terrace record a gradient modelling evaluation the origin of the lower mino river terraces in the nw iberian peninsula has been a topic of debate since the 1940s various hypotheses about their main controlling factors have been put forward but general consensus is still lacking field studies of terrace distribution and the weathering of quartzite pebbles in the terrace deposits demonstrated that terrace longitudinal correlation is not parallel to the current river bed in addition the longitudinal profile model fluver2 was used to simulate the profile evolution of the mino river over the past 450 ka a reconstructed longitudinal profile and an offshore climate record were used as inputs several scenarios with variable uplift rates were investigated and evaluated against properties of four selected reaches along the river for a match with the number of terraces their relative altitude timing and sediment thickness an uplift scenario with a net constant vertical uplift rate of 0 08 m ka 1 yielded the best results the best fit scenarios indicate that base level changes from glacioeustatic changes in combination with tectonic uplift are the main driving forces of the observed terrace formation and valley incision contrary to most nw european fluvial systems the timing of upstream controlled sediment supply has a less dominant effect on terrace formation this can be explained by the close proximity to the narrow passive atlantic margin

southern menderes massif an incipient metamorphic core complex in western anatolia turkey in the southern sector of the menderes massif north of selimiye milas augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed palaeozoic envelope the granitic rocks exhibit a moderately dipping mylonitic foliation and nne ssw trending mineral elongation lineation the progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked from bottom to top by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite the kinematic indicators exhibit a top to the south down dip sense of shear these structures are attributed to exhumation of the granitic rocks of the massif along a major south dipping normal sense shear zone that accommodated crustal extension during late oligocene collapse of the orogen in western turkey thus the southern menderes massif may be interpreted as the exhumed footwall of a major extensional shear zone and possibly as an incipient core complex

geomorphology and sequence stratigraphy due to slow and rapid base level changes in an experimental subsiding basin xes 96 1 subsidence is a major factor in the accumulation and architecture of natural basin fills a recently built experimental facility experimental earthscape facility xes at st anthony falls laboratory of the university of minnesota incorporates for the first time a flexible subsiding floor in its design thus the experimental basin can model erosion and deposition associated with independent variations in sediment supply absolute base level change and rates and geometries of subsidence the results of the first experiment in a prototype basin 1 1 6 0 8 m are described here wherein the stratigraphic development associated with first slow and then rapid base level cycles in a basin that has a sag geometry has been analyzed a videotape of the experiment and subsequent serial slicing of the dried strata in the basin allow interpretation of the sequence development under conditions of precisely known changes of absolute base level subsidence and sedimentation relative base level changes which strongly varied in the basin owing to the sag geometry of subsidence seem to exert primary control on sedimentary patterns although autocyclic changes were also important style of sequence boundaries differed between slow and fast base level falls during the slow base level fall an incised valley developed once the shoreline prograded out of the zone of maximum subsidence suggesting that incision at the shoreline may be very sensitive to changes in relative base level once started however the valley quickly widened by knickpoint retreat into a broad low relief erosion surface that stretched across the entire basin as erosion took place at the knickpoint deposition occurred immediately downflow so both the knickpoint and the upstream limit of deposition migrated landward together producing a strong time transgressive erosion and onlap sequence the stratigraphic begin page 818 record of this sequence boundary is a single yet very subtle widespread unconformity that becomes conformable downstream which is difficult to trace in stratigraphic cross section in contrast the incised valley that formed during the rapid base level fall was relatively narrow deep and lengthened over time as deposits at the mouth of the valley were gradually exposed and incised through wholesale backfilling of the incised valley did not begin until the rapid base level rise started as a result the rapid base level change produced a more easily recognized incised valley in the stratigraphic record than did the slow base level change potential reservoir development within the strata is evaluated by means of a gray scale proxy for porosity four distinctive zones of enhanced reservoir quality occurred in the basin the most proximal part of the basin the upper part of growth fault bounded sedimentary wedges deep water forced regressive systems tract composed of grainflow deposits and transgressive systems tract formed during the rapid base level rise this distribution of relatively porous units suggests that for a variety of reasons rapid sea level cycles may produce the best reservoir units

the discovery and significance of a sedimentary hiatus within the carboniferous taiyuan formation northeastern ordos basin china reply the paper by jiang et al 2012 documented a hiatus and overlying incised valley fill between the lower pennsylvanian taiyuan formation ct1 and the upper pennsylvanian taiyuan formation ct2 herein we provide credible evidence suggesting that the incised valley fill mentioned by jiang et al 2012 is a barrier island our work also indicates that the contact between ct1 and ct2 is continuous and without hiatus the paleozoic ordos basin has two stages of sedimentary environments the early paleozoic marine carbonate deposition and the late paleozoic carboniferous to permian transformation from paralic to terrestrial most scholars believe that the carboniferous taiyuan formation is a barrier lagoon tidal flat system zhao and liu 1990 hao et al 2007 luo et al 2011 that formed during the relatively large scale transgression at the north china block the predominant sedimentary environment of the taiyuan formation is the barrier shoreline and has been documented as a barrier island lagoon and swamp chen et al 2001 yang et al 2005 hao et al 2007 luo et al 2011 in particular jiang et al 2012 confirmed the facies of ct1 as a barrier tidal system and interpreted the interval of ct2 as a northeast southwest trending incised valley fill and further claimed a hiatus between the ct1 and ct2 units well d23 locates in the incised valley fill as mentioned in figure 14 of jiang et al 2012 its core of the lower ct2 above the bottom coal of d23 figure 1 suggests that it is tidal in origin based on the following sedimentary structures lens starved ripples ripples and flaser beddings herringbone bedding and tidal bundles couplet figure 1 the fining upward succession with erosive based structures of tidal origin is a tidal inlet figure 1c h the coarsening upward succession with parallel

rates of delta progradation during highstands consequences for timing of deposition in deep marine systems estimated times required for 24 modern river systems to form a shelf edge delta range from 8 5 ka to 116 5 ka depending on fluvial sediment supply delta width shelf volume and shelf transport rates these values indicate that transport of sand into deep marine systems is likely to be significant during third order highstands of relative sea level factors such as shelf transport dynamics may slow delta progradation while submarine canyons cutting the shelf may reduce the time before deep marine deposition occurs interpreting ancient sand rich deep marine strata as lowstand deposits without sufficient palaeogeographic information may not therefore always be appropriate

estimating past continental ice volume from sea level data we predict sea level change since the last glacial maximum lgm at four far field sites barbados bonaparte gulf huon peninsula and tahiti using a revised theoretical formalism this formalism includes a time varying shoreline geometry an accurate treatment of sea level variations near regions of ice retreat and the influence of glacial cycle perturbations in earth rotation we elucidate the physics of far field sea level change by de constructing the predicted signal into spatially uniform versus spatially varying components as well as isolating contributions due to the ice load the ocean load and the rotational potential we demonstrate that the sum of these three contributions plus the spatially uniform sea level fall associated the with retreat of grounded marine ice sheets can produce a significant difference between predictions of sea level change at far field sites and the eustatic or meltwater curve associated with the adopted ice model this difference is site and time dependent for example the total sea level rise since the lgm predicted using our ice earth model can be either smaller e g barbados or larger e g tahiti than the eustatic sea level change finally we review procedures that have been applied to estimate continental ice volume from far field sea level observations and apply these procedures to data from barbados and bonaparte gulf applying an ice earth model that is tuned to fit the barbados data we estimate a change in grounded ice volume from the lgm to the present of 43 5 51 106 km3 based on barbados data and an lgm ice volume estimate of 51 106 km3 based on bonaparte gulf data our results for the bonaparte gulf data are consistent with the recent study by yokoyama et al nature 406 2000 713 these lgm ice volume estimates map into a eustatic or meltwater sea level rise of 115 135 m taking into account plausible variations in the adopted radial earth model introduces uncertainties in the range of 1 5 106 km3 for ice volume estimates based on the barbados data

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

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

external controls on turbidite sedimentation on the glacially influenced armorican margin bay of biscay western european margin abstract sequence stratigraphic models predict increased sediment delivery to deep water areas during sea level lowstand the armorican margin bay of biscay western european margin is an interesting area to test this hypothesis because the margin has a wide continental shelf still partly flooded during sea level lowstand and the armorican turbidite system has experienced fluctuating sediment fluxes since the last glacial period the stratigraphic response of the armorican turbidite system to sea level oscillations and climate changes was assessed for the last 35 000 years through the study of the guilcher crozon and audierne levees millennial timescale resolution chronostratigraphy allowed us to reconstruct the sediment accumulation and turbidite frequency thickness and grain size over this period of time we found that the armorican turbidite system was sediment starved during highstand conditions ca 8 0 ka and that glacial conditions favoured sediment delivery to the deep bay of biscay however contrary to what would be expected from sequence stratigraphic models the turbidite flux did not reach a maximum during the lgm lowstand ca 26 20 ka but at the onset of termination i between ca 20 and 17 ka this makes the armorican turbidite system a transgression dominated one this sediment pulse can be interpreted as a huge increase in the meltwater discharge of the fleuve manche palaeoriver in response to the decay of the british and fennoscandian ice sheets at that time despite the rising sea level a large deltaic system had to have developed on the outer shelf leading to the delivery of the fleuve manche sediment load into the canyon heads on the other hand our dataset suggest that the delivery of sediment into canyons was mainly forced by the winnowing and reworking of the sediment stored on the wide drowned shelf during the last glacial period between ca 35 and 20 ka and between 17 and 8 ka these findings illustrate the competing influences of accommodation and sediment supply on the armorican margin over the last 35 000 years with a shelf acting as a buffer for the sediment supply signal for most of the period except during the last deglaciation at that time the western european sediment routing system was reactive the climatic signal rapidly propagated from the southern limb of the european ice sheet to the armorican turbidite system finally our study demonstrates that precise reconstruction of turbidite flux in deep water areas added to knowledge about the morphology of the margin and the palaeoenvironmental changes fluvial system shoreline position etc are crucial for determining the response of turbidite systems to external forcing

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

sites of river derived sedimentation in the ocean most of the world9s rivers have discharged sediment on wide continental shelves and in estuaries since the last rise in sea level in most cases sediments are thus trapped on these areas and are not deposited on the now relict submarine fans oceanward of these rivers the conclusions are based on remote sensing on data in the literature on present sedimentation rates on the shelves and the submarine fans and on river sediment discharges for the 22 rivers studied these submarine fans will remain cut off from their fluvial sources until the shelves and estuaries are filled and sediments can bypass these areas the time required to fill these shelves and estuaries ranges from 2 600 to 3 400 yr for the ganges brahmaputra to 1 to 1 2 m y for the yenisei ob for most river systems sea level will change before shelves and estuaries are filled with sediments

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

categorizing the morphologic variability of siliciclastic passive continental margins the basic morphology of the continental shelf slope and rise on passive continental margins has many variations in the modern ocean environment through using a satellite derived bathymetric data set of the global ocean we have developed a classification for the shape of modern siliciclastic dominated passive margins the classification subdivides 50 margins into five distinct shape categories based on each margin s pattern of sea floor slopes as a function of depth by comparing these shape categories with the underlying stratal architecture sediment input and present degree of canyon incision of the margins we find apparent correlations between these factors and basic margin shape in general gently sloped margins tend to occur in regions with high sediment input few modern canyons and unstable substrates higher gradient margins tend to have lower sediment input more modern canyons and a variety of subsurface architectures these results suggest two important conclusions 1 morphology differences among modern siliciclastic passive margins can be objectively and systematically categorized and 2 these shape differences seem to be related to aspects of the modern sedimentary environment despite the fact that the margins have evolved over geologic time

identification of possible quaternary deformation in the northeastern mississippi embayment using quantitative geomorphic analysis of drainage basin asymmetry to investigate neotectonism in the mississippi embayment east of the new madrid seismic zone we identified geomorphic domains that show evidence of ground tilting during quaternary time transverse basin profiles were converted to two dimensional vectors that denote channel position with respect to basin divides these basin asymmetry vectors record the net direction and degree of lateral migration of trunk streams more than 2500 vectors were measured and spatially averaged within 400 km 2 bins this field of 300 mean vectors delineates several domains that show preferred directions of stream migrations possibly driven by ground tilting the timing of stream migration was interpreted using across valley distributions of quaternary alluvial terraces comparison of our mean vector field with subsurface structures suggests that some domain boundaries may be related to reactivated faults late quaternary activity is suggested for two northeast striking faults of the southeastern reelfoot rift margin we acquired two seismic profiles showing near surface faulting beneath scarps that follow the domain boundary associated with one of these northeast striking faults big creek fault zone reelfoot thrust seismicity ends on the south against this fault suggesting that the rift margin has dextral slip accommodating northeastward movement of the thrust hanging wall our vector field also suggests late quaternary movement on the reelfoot thrust and on two other northwest striking faults here termed the hatchie river fault and the wolf river fault several other weak domains may imply minor elements of neotectonism our results demonstrate that morphometric analysis of drainage basin asymmetry can be an effective reconnaissance tool within neotectonic settings

transgressive systems tract of a ria type estuary the late holocene vilaine river drowned valley france the understanding of control parameters of estuarine infilling at different scales in time and space is important for near future projections and better management of these areas facing sea level change during the last 20 years the stratigraphy of late quaternary estuaries has been extensively investigated leading to the development of depositional models which describe the sedimentary facies distribution according to changes in sea level tidal range and wave activity but few of them describe in detail the influence of the estuarine geomorphology on the atlantic coast recent studies provide a detailed understanding of the sedimentary infill succession of incised valleys during the late holocene transgression with recent emphasis on the macrotidal bay of the vilaine river in south brittany the latter has shown the importance of the inherited morphology in controlling the preservation of the sedimentary deposits however until now there has been little information available on the geometry of the underlying bedrock of the estuary and its immediate approaches including the holocene history of the most proximal part of the vilaine river estuary the recent acquisition of very high resolution seismic reflection chirp and sediment core data in the vilaine estuary provides the opportunity to address several of these issues leading to the identification of the controlling factors that played a role in the sedimentary filling of the estuary the estuary of the vilaine river is one of the most sheltered estuaries of the atlantic coast and thus shows an excellent record of the successive transgressive phases since the last glacial period the valley of this ria type estuary is incised in the hercynian magmatic and metamorphic rocks of the armorican massif along the striking branches of the south armorican shear zone and filled with well stratified sediments the study of the morphology of the substratum in the estuary reveals narrow paleovalleys 1 km wide with a maximum depth of 20 m the shapes and dimensions of these paleovalleys are comparable with those observed upstream in the present day vilaine river valley facies analysis of seismic and sedimentary data complemented by 21 ams radiocarbon age dating enables the reconstruction of the infilling of the estuarine valley the valley is filled by pleistocene to early holocene alluvial coarse grained pebbly sands overlain by mid to late holocene marine sands silts and muds from 10 000 to 5000 cal bp the marine transgression shows a rapid initial phase of transgression followed by a progressive slowing down which can be recognised over more than 90 km in an upstream direction the rapid transgression developed homogeneously over the entire length of the estuary with a widespread expression of tidal currents tide dominated estuary the slow phase of the transgression gives rise to a differentiated expression of the hydrodynamic factors according to the geomorphological setting the sedimentary deposits of the innermost and narrow part of the estuary reflect a strong control of tidal and river currents when the influence of tidal currents increases at the expense of fluvial control in a downstream direction the sedimentary filling of the outer reaches of estuary shows a strong influence of tidal currents modulated by changes in sea level where from 5700 to 3000 cal bp the progressive decrease in accommodation space promotes the expression of wave action wave dominated estuary finally from 5000 years bp to present day the stabilisation of sea level gives birth to scour and lag sedimentary morphologies scour and lag estuary the sedimentary record appears thus strongly marked by the holocene transgression and the geomorphological setting where hydrodynamic parameters superimposed on the geomorphological and eustatic contexts expressed in different ways in time and space govern the evolution of the estuarine system

a diatreme hosted gold deposit at montana tunnels montana a bulk minable gold silver deposit at montana tunnels southwestern montana is located in the central part of a diatreme this diatreme was emplaced along the faulted contact between andesitic volcaniclastic rocks assigned to the late cretaceous elkhorn mountains volcanics and a sequence of quartz latitic ignimbrites which are part of the lowland creek volcanics of middle eocene age a north northeast striking swarm of quartz latite porphyry dikes was emplaced during the waning stages of lowland creek volcanism the two largest dikes dated at 45 to 50 m y middle eocene were intruded into the diatreme prior to the cessation of brecciation and mineralization the diatreme underlies a 1 km 2 area and is known from drilling to extend steeply downward for at least 310 m the principal rock type in the diatreme is a matrix rich breccia it is characterized by a sand size tuffaceous matrix of quartz latitic composition containing fragments of contiguous volcanic wall rocks and intrusive rocks derived from the late cretaceous boulder batholith the batholith is inferred to underlie the montana tunnels area foundered blocks of volcanic wall rocks lie at various attitudes against the walls of the diatreme and within it those composed of elkhorn mountains volcanics underwent hydraulic brecciation after they sank into the diatreme blocks interpreted to be composed of pyroclastic base surge deposits from a subaerial tuff ring and a piece of carbonized wood subsided into the diatreme from the palcosurface the diatreme is separated into two unequal parts by a west northwest striking oblique slip fault sulfide minerals in the diatreme occur as disseminations in the breccia matrix and in sub ordinate amounts as widely spaced multidirectional veinlets and as the matrix to brecciated blocks of elkhorn mountains volcanics all forms of mineralization consist of pyrite sphalerite galena minor chalcopyrite and rare electrum accompanied by a gangue of manganocalcite siderite and minor quartz clastic grains and fragments of the sulfides and gangue minerals are common and attest to multiple alternating episodes of brecciation and mineralization in the ore zone the introduction of abundant manganocalcite and siderite was accompanied by pervasive sericitic alteration but only weak kaolinization and silicification sericitization grades outward beyond the ore zone to chlorite montmorillonite carbonate alteration an assemblage that also characterizes the interiors of the late mineral dikes in the diatreme gold occurs in electrum with a fineness of about 550 as inclusions of less than 200 mu m in pyrite and sphalerite inclusions of electrum and galena were precipitated together silver is present mainly in solid solution in galena the montana tunnels gold silver deposit is characterized geochemically by anomalously high concentrations of zinc lead and manganese and in comparison to many volcanic hosted precious metal deposits is low in arsenic antimony and mercury this metal association and the low fineness of the gold are features shared by the wau gold deposit in papua new guinea it is suggested that the mineralized diatreme observable at montana tunnels was emplaced several hundred meters beneath the palcosurface upon which a gold bearing maar volcano like that partly preserved at wau was constructed

glacial isostatic adjustment and the radial viscosity profile from inverse modeling 1 a formal inverse procedure is used to infer radial mantle viscosity profiles from several observations related to the glacial isostatic adjustment process the data sets consist of late pleistocene and holocene sea level data from scandinavia the barents sea central europe canada and the far field as well as observations of changes in the earth s rotation and gravitational field and present day uplift and gravity changes in scandinavia inferences of mantle viscosity are robust against assumptions such as the a priori viscosity model and model discretization however the quality of ice sheet reconstruction remains crucial for the inverse inference the importance to discuss regional mantle viscosity models in view of the lateral variability in mantle properties has been evident our inference suggests a two order of magnitude increase of mantle viscosity with depth and volume averaged upper and lower mantle viscosities around 7 1020 and 2 1022 pa s respectively mantle viscosity does not need to increase sharply across the 660 km seismic discontinuity the viscosity profiles suggested are also able to reconcile the large scale geoid anomaly related to mantle convection

fluviodeltaic response to sea level perturbations amplitude and timing of shoreline translation and coastal onlap 1 alluvial river systems respond to changing sea level by adjusting channel length through shoreline translation and coastal onlap offlap at the alluvial basement transition the magnitude and timing of shoreline translation and coastal onlap offlap relative to the driving sea level signal depend on the dynamics of the fluvial system and have important implications for interpreting ancient fluviodeltaic deposits i obtain analytical solutions to a diffusive geometric model of fluviodeltaic response to sea level perturbations that treats the shoreline and alluvial basement transition as moving boundaries fluviodeltaic behavior is most sensitive to the ratio of the period of eustatic cycling to the fluvial response time which varies with the length and water discharge of the fluvial system the square root of this ratio provides a first order estimate of the fraction of the fluvial long profile affected by eustatic forcing the fluviodeltaic system behaves as a low pass filter with respect to eustatic cycling the amplitude of both shoreline translation and coastal onlap offlap increase with increasing cycle period within a relatively narrow bandwidth in which the fluvial response time is comparable to the cycle period only small time lags develop between shoreline response and eustatic forcing the time lag between maximum coastal onlap and maximum sea level increases without bound as the forcing period decreases relative to the fluvial response time model predictions agree with experimental data and differ considerably from the model predictions of pitman 1978 and angevine 1989 which suggest that fluviodeltaic systems are strong high pass filters to sea level cycling

sea level fall below the shelf edge without basin floor fans a fall of sea level to below the shelf edge formation of type 1 sequence boundary increases greatly the likelihood of sand delivery into deep water basin floor areas although an unusually high sediment supply can bring significant volumes of sediment to the shelf edge at any time an eocene ypresian data set from seismic scale mountainside outcrops of shelf slope clinoforms illustrates that a fall of sea level below the shelf edge produces significant sand accretion on the shelf margin but brings no sand out onto the basin floor fall and subsequent rise of relative sea level are documented by the style and topographic position of successive shelf edge to slope clinoforms each representing a shelf edge delta with its greatly extended slope apron of turbidite lobes sheets and chutes a downslope shift of clinothems at the shelf edge and a headward cannibalization of the oldest perched slope deltas are the criteria for recognition of 1 the time interval of sea level fall and 2 the position of sea level below the shelf edge the lowest sea level is recorded by the most basinward clinothem set with a high density of erosive turbidite chutes at its upper surface the sequence boundary wave eroded terraces at its updip near shelf edge end identify the shoreline position at lowest sea level aggradation and landward stepping of clinothems reflect subsequent rise of relative sea level the fall to rise configuration and especially the occurrence of peak erosion at the time of lowest sea level are compelling evidence for placing the type 1 sequence boundary at the fall to rise turnaround and not along the surface onto which the clinothems downlap the excellent exposure downdip as well as along strike of the clinoform complex demonstrates the absence of sand accumulation beyond the base of slope the slope turbidites were produced from dilute nonignitive flows and caused significant shelf margin accretion the data show that such slopes can be extremely sand prone and that sea level fall below the shelf edge does not necessarily result in basin floor sand deposits beyond the base of slope particularly where canyons have not been eroded into the slope

global to local scale parameters determining relative sea level changes and the post glacial isostatic adjustment of great britain abstract observations of relative sea level rsl change in great britain since 16 kyr bp and models of post glacial isostatic adjustment provide constraints on reconstructions of the british and antarctic ice sheets from the last glacial maximum to the present we use the global model from an earlier investigation modified ice 4g vm2 with lithospheric thickness 90 km which gives good rsl fits globally as well as for much of the british data a revised ice model for great britain that fits with recently published observations on ice limits and heights fails to explain all the misfits between rsl observations and predictions much more significant improvements result from models that incorporate a different chronology for the partial deglaciation of antarctica while keeping the total ice melt 17 m the same as in ice 4g vm2 the results suggest antarctic melting of 3 m ice equivalent sea level by 15 kyr bp only 1 m contribution to the 24 m rise of mwp1a with the major melting 12 5 kyr bp and a small amount of melting 1 0 0 3 m between then and 3 or 2 kyr bp these modifications produce rsl predictions for barbados that show the major changes in rate of sea level rise but with an offset up to 1 kyr compared to the observations possible explanations that remain to be investigated further are a delay in the melting of ice from some other region a reduction in the total melt derived from antarctica and a refinement of the 1 kyr temporal resolution assumed in the construction of the theoretical solution

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

relation of sequence stratigraphy to modern sedimentary environments one method of testing the concept of sequence stratigraphy is to compare it to quaternary sediments in which chronology stratigraphic relations and facies geometry are more clearly understood than in older rocks rapid deposition rates during quaternary glacial eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record in the northern gulf of mexico the late wisconsinan holocene mississippi river has deposited a type 1 sequence that includes lowstand transgressive and high stand systems tracts characteristics of modern mississippi river sedimentary environments support the methodology used in sequence analysis but the short time taken for sequence generation here raises important questions about sequence time scales correlation and driving mechanisms

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

timing of the last sequence boundary in a fluvial setting near the highstand shoreline insights from optical dating we investigated by means of optical dating the chronostratigraphic nature of the sequence boundary associated with the last glacial in a sandy to gravelly compound paleovalley fill just landward of the highstand shoreline in the rhine meuse delta netherlands laterally extensive fluvial strata deposited during oxygen isotope stage 4 coeval with a major sea level fall unconformably overlie estuarine deposits from stage 5 or fluvial deposits from the penultimate glacial stage 6 these chronostratigraphic relationships differ substantially from widely used models and indicate 1 that sequence boundary formation in this setting was associated with the onset of pronounced sea level fall shortly after 80 ka 2 that the time gap represented by the sequence boundary may be extremely small 10 k y 3 that the age of the sequence boundary may decrease both updip and downdip of the highstand shoreline and 4 that our study does not provide viable diagnostic criteria for a sea level controlled sequence boundary above the falling stage systems tract despite the high frequency high amplitude glacio eustatic regime that might be considered ideal for the formation of an unambiguous unconformity the last sequence boundary in this setting is commonly cryptic

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

ice sheet and solid earth influences on far field sea level histories previous predictions of sea level change subsequent to the last glacial maximum show significant systematic discrepancies between observations at tahiti huon peninsula and sunda shelf during lateglacial time 14 000 to 9000 calibrated years before the present we demonstrate that a model of glacial isostatic adjustment characterized by both a high viscosity lower mantle 4 1022 pa s and a large contribution from the antarctic ice sheet to meltwater pulse ia 15 meters eustatic equivalent resolves these discrepancies this result supports arguments that an early and rapid antarctic deglaciation contributed to a sequence of climatic events that ended the most recent glacial period of the current ice age

controls on late quaternary incised valley dimension along passive margins evaluated using empirical data incised valleys are canyon like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium gradient profiles in response to sea level fall most of these valleys flood during sea level rise to form estuaries incised valley morphology strongly controls the rate of creation of sediment accommodation valley fill facies architecture and the preservation potential of coastal lithosomes on continental shelves and affects coastal physical processes nonetheless little is known about what dictates incised valley size and shape and whether these metrics can be used to explain principal formation processes the main control on alluvial channel morphology over human time scales is discharge this is based on numerous empirical studies and is well constrained because all variables are easily measured at this short time scale knowledge of long term river evolution over a complete glacio eustatic cycle on the contrary remains largely conceptual experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified in spite of this difficulty existing models of incised valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms highlighting sea level and shelf gradient morphology as the dominant controls on valley incision although valleys are cut by rivers whose channels are a direct reflection of discharge little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls the late quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables including sea level tectonics substrate lithology and drainage network characteristics are accurately constrained here 38 late quaternary valleys along the coast of two different passive continental margins are compared which suggests that valley shape and size are governed primarily by upstream intrinsic controls such as discharge valley width depth and cross sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea level

the discovery of santorini minoan tephra in western turkey dispersal of volcanic ash from the violent bronze age minoan eruption of the santorini volcano in the southern aegean has been the subject of much research1 6 a sediment core taken from a small mountain lake in western turkey contains a layer of tephra from the minoan eruption the santorini origin is established by refractive index major glass chemistry and stratigraphic position the lake is located north of the recognized dispersal area for the tephra this deposit provides evidence for dispersal of the minoan tephra well to the northeast of santorini and implies that the west coast of asia minor must have experienced heavy tephra fallout from the bronze age eruption the minoan tephra has not previously been identified from sites in turkey

climatic and morphologic relationships of rivers implications of sea level fluctuations on river loads the characteristics of 279 rivers that discharge into the world oceans are analyzed in terms of their basin hydrology river discharge morphometry basin slope and area river length extension of the continental shelf seaward of the river mouth and climate precipitation statistically reliable relationships are found between discharge and basin area and between sediment load and a combined function of basin area and slope these functions are used to demonstrate how river hydrologic features would be strongly influenced by sea level fluctuations particularly under the influence of continental shelf emergence a fall in sea level toward a glacioeustatic lowstand would induce the merging of rivers on the subaerial continental shelf thereby allowing giant rivers to form for example rivers of western europe would reorganize themselves into two or three very large rivers sediment concentration carried by these mega rivers would decrease and thus the number of hyperpycnal plumes generated at river

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

rapid and widespread response of the lower mississippi river to eustatic forcing during the last glacial interglacial cycle the lower mississippi valley provides an exceptional fi eld example for studying the response of a continental scale alluvial system to upstream and downstream forcing associated with the large orbitally controlled glacialinter glacial cycles of the late quaternary however the lack of a numerical chronology for the widespread pleistocene strata assemblage known as the prairie complex which borders the holocene fl oodplain of the lower mississippi river has so far precluded such an analysis here we apply optically stimulated luminescence osl dating mainly on silt sized quartz from prairie complex strata in total 27 osl ages indicate that the prairie complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7 5e and 5a thus the aggradation of the prairie complex is strongly correlated with the sea level highstands of the last two glacialinterglacial cycles fluvial incision during the sea level fall associated with the mis 5a mis 4 transition extended as far inland as 600 km from the present day shoreline testifying to the dominant downstream control of fl stratigraphic architecture in the lower mississippi valley in addition the short reaction time of the lower mississippi river suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed

backwater and river plume controls on scour upstream of river mouths implications for fluvio deltaic morphodynamics sediment flux from rivers to oceans is the fundamental driver of fluvio deltaic morphodynamics and continental margin sedimentation yet sediment transport across the river to marine boundary is poorly understood coastal rivers typically are affected by backwater a zone of spatially decelerating flow that is transitional between normal flow upstream and the offshore river plume flow deceleration in the backwater zone as well as spreading of the offshore plume should render rivers highly depositional near their mouths leading to sedimentation and eventual elimination of the backwater zone at steady state this reasoning is counter to observations of riverbed scour erosional bed forms and long lived backwater zones near the mouths of some coastal rivers e g mississippi river united states to explain these observations we present a quasi 2 d model of a coupled fluvial backwater and offshore river plume system and apply it to the mississippi river results show that during high discharge events the normal flow depth can become larger than the water depth at the river mouth resulting in drawdown of the water surface spatial acceleration of flow and erosion of the riverbed as proposed by lane 1957 the transition to drawdown and erosion is ultimately forced by spreading of the offshore river plume this points to the need to model coupled river and river plume systems with a dynamic backwater zone under a suite of discharges to accurately capture fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine depositional sinks

near field hydro isostasy the implementation of a revised sea level equation summary we describe how the existing sea level equation incorrectly predicts the change in sea level and thus the ocean load in ice covered subgeoidal geographic regions during periods of deglaciation we go on to present a new sea level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self consistent manner by employing a well known spectral technique application of the new theory to predict relative sea level rsl histories and present day 3 d solid surface deformation rates in northeastern canada based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 1020 and 5 1021 pa s respectively demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load predictions of rsl curves show a discrepancy of 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice sheet histories this error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory in addition predictions of 3 d deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea level theory in contrast estimates of inverse decay times from the predicted rsl curves are insensitive to within the observational error to the improvement in the surface load introduced by the new theory thus viscosity structure inferences based on this parametrization and the original sea level equation are unaffected by the error in the ocean load finally the new theory predicts a eustatic i e globally uniform rise in sea level over the postglacial period that is 11 m lower than that determined via the original theory therefore estimates of the global ice budget at the last glacial maximum based on far field rsl data and the original sea level theory will be too small by 10 per cent

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

geometry lateral variation and preservation of downlapping regressive shelf deposits eastern tyrrhenian sea margin italy abstract the shelf of the eastern tyrrhenian sea margin changes substantially in width shelf break depth and sea floor steepness over relatively short distances largely owing to pronounced lateral changes in subsurface geologic structure remnants of late pleistocene prograded coastal deposits are locally preserved on the middle and outer parts of the shelf we recognize two major controls on the distribution lateral extent thickness and preservation potential of these prograded deposits first prograded downlapping deposits formed only where the physiographic shelf break was deeper than the lowstand shoreline thus providing accommodation space for the lowstand deposits second the proximity and relative size of sediment sources and the local coastal dispersal system apparently infl enced the geometry of the deposit midshelf and shelf margin bodies composed of seaward steepening downlapping reflectors were deposited as thin to thick continuous prograding sheets over an irregular eroded shelf surface and onto the shelf edge during the latest fall and lowstand of sea level decreased sedimentation at the end of this lowstand resulted in net erosion during sea level rise shoreface erosion created a major marine erosional ravinement surface landward of the 120 m isobath and much of the downlapping deposits were removed preservation of these downlapping deposits is largely a function of their thickness thick continuous deposits are common on the shelf edge whereas on the midshelf only thin remnants are preserved locally where depressions or morphologic steps were present in the shelf surface

the fleuve manche the submarine sedimentary features from the outer shelf to the deep sea fans bathymetric seismic and coring surveys have been carried out since the beginning of the 1990s on the outer shelf the slope and the continental rise of the western approaches margin most of the sedimentary features studied belong to a sedimentary system built up since the oligocene and fed by a palaeoriver the fleuve manche that flowed in the english channel during eustatic lowstands a geomorphological map details the spatial distributions of the palaeovalleys on the outer shelf the drainage basin like organised canyons on the slope and the channel levee and lobe complexes on the rise the obvious channel canyon connections and the assessed palaeovalley canyon links demonstrate that the fleuve manche was the single source for terrigeneous fluxes of the armorican deep sea fan when it was one of two sources of the celtic deep sea fan amongst parameters controlling the sedimentation two factors play a major role i subsidence controlled the possibly messinian riverine incision the turbidite activities during lowstands as well as marine infilling of the seawards part of the fleuve manche ii quaternary sedimentary supplies were influenced by the melting ice sheets and the connections with the onshore catchment basins copyright 2003 john wiley sons ltd

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

high altitude plio quaternary fluvial deposits and their implication on the tilt of a horst western anatolia turkey abstract this study investigates the origin and regional tectonic implications of high altitude plio quaternary fluvial deposits developed over the bozdag horst which is an important structural element within the horst graben system of western anatolia turkey a total of 23 deposits occur near the modern drainage divide comprising fluvial to occasionally lacustrine deposits the deposits are all elongated in n s direction with a width length ratio of 1 10 the largest of them is of 13 km in length with a maximum observable thickness of about 100 110 m morphological lithological deformational characteristics of these deposits and the drainage system of the area all suggest that the deposits were formed due to uplift and southward tilting of the bozdag horst this tilting which is estimated as 1 2 to 2 2 caused accumulation of the stream load along channels flowing from south to north all the deposits were later dissected by the same streams with the exception of one deposit which still preserves its original lake form these deposits are of quaternary age which corresponds to the latest n s directed extensional tectonic phase in the region

an experimental study of the effects of base level change on fluvial coastal plain and shelf systems abstract several of the concepts of sequence stratigraphic models were tested by experiments in a large flume using different gradients for successive runs a physical model of a fluvial drainage basin coastal plain continental shelf and continental slope was constructed in all experiments initial gradients of the coastal plain and shelf were identical systematic raising and lowering of the water surface simulated the changes in relative sea level i e base level that are similar to most sequence stratigraphic models base level changes significantly affected the shelf area but they had little effect on the fluvial drainage basin during base level falls fluvio deltaic progradation occurred fluvial aggradation occurred only during periods of base level stillstand or rise because of the slow rate of head ward erosion of incised valleys a significant time gap existed from the time base level first fell below the shelfbreak and the development of a cross shelf bypass valley during this lag time deposition occurred on the exposed shelf to form a fluvial braid plain concurrently channels developed at the shelfbreak and grew by headward erosion at various rates continuous incision and widening of these channels formed valleys these valleys were not linked directly to the main drainage basin unt l ultimately one captured the flow from that drainage at that point other valleys were abandoned and ceased to grow during the subsequent base level rise the single large cross shelf valley filled with coarser sediments while the other valleys partially filled with finer suspended load sediments the main cross shelf valley also supplied coarser sediments to the slope