regional warming pliocene 3 ma paleoclimate of europe and the mediterranean the paleoclimate of the middle pliocene ca 3 ma was generally warmer than present particularly at middle to high latitudes it has been suggested that this period may represent an analogue for future climate change mechanisms that have been proposed to account for this warming are enhanced thermohaline circulation and or greater concentrations of co 2 in the atmosphere we present new climate model simulations supported by geological data that suggest that in the european and mediterranean region the climate was warmer by 5 c wetter by 400 1000 mm yr and less seasonal than present modeling results suggest that an intensification of the icelandic low pressure system and the azores high pressure system occurred during the middle pliocene as a direct result of higher annual sea surface temperatures and reduced ice cover in the northern hemisphere this change increased the surface pressure gradient over the region and strengthened annual westerly wind velocity by 4 m s 1 associated increases in wind stress by 20 n m 2 over the north atlantic ocean may have enhanced the flow of surface currents such as the gulf stream and north atlantic current which in turn would have sustained the higher sea surface temperatures these changes to the regional climate system would have driven greater atmospheric and oceanic transport of heat from equatorial regions to the north atlantic ocean particularly during winter such conditions are proposed as a likely cause of the warming indicated for europe and the mediterranean ca 3 ma

space time description of nonstationary trapped lee waves using st radars aircraft and constant volume balloons during the pyrex experiment abstract the third intensive observation period iop3 of pyrex was a case of strong lee waves generated by a southerly wind crossing the pyrenees chain upstream radiosounds and measurements obtained by aircraft along the chain transect and by constant volume balloons launched near the crest provided spatial characteristics of the lee wave at different times and heights values ranging from 7 to 14 km for the horizontal wavelength and from 3 to 5 m s 1 for the maximum amplitude of the air vertical velocity were observed the lee wave horizontal extent measured from the crest line reached 30 to 55 km in addition two very high frequency stratosphere troposphere vhf st radars one on the mountain mean axis and another downstream in the lee wave field observed the temporal variations of the vertical profiles of the vertical velocity the analysis of those observed variations and their vertical distribution allowed the stationarity of the wave to be studied the lee wave was found to be far from stat

stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

combining sequence stratigraphy geostatistical simulations and production data for modeling a fluvial reservoir in the chaunoy field triassic france reservoir modeling of the chaunoy field was performed by combining a sedimentological study a sequence stratigraphic analysis geostatistical simulations and the analysis of production data and fluid flow simulations the reservoir corresponds to the distal part of a middle triassic alluvial fan system in the paris basin france and is extremely heterogeneous and layered the reservoir mostly consists of small ribbon channel deposits interbedded with flood plain and lacustrine mudstones the channel amalgamation rate varied with cyclic lake level variations which directly controlled the reservoir geometry within a base level cycle during periods of low accommodation channels were amalgamated forming highly heterogeneous sand sheets as the accommodation increased channels became progressively isolated within flood plain mudstones finally a lacustrine transgression deposited lacustrine mudstones and induced thin but widespread vertical permeability barriers across the field as accommodation started to decrease considerable pedogenetic alteration occurred as shown by dolocretes and groundwater dolomites five cycles that constituted the reservoir layering framework were identified geostatistical simulations of lithotype distribution within these units were computed using the truncated random gaussian function method horizontal and vertical lithotype proportion curves and variograms were calculated from well data because of the wide well spacing it was not possible to determine the range of horizontal experimental variograms three lithotype realizations were simulated within a high resolution grid to compare short medium and long correlation lengths after assigning petrophysical properties to the lithotypes and upscaling fluid flow simulations were performed for the three realizations the three flow simulations were then compared to the 10 yr production history of the field the simulations showed quite a good match regardless of the variogram range except in the northern part of the field indicating a problem in the reservoir layering in this area this relative insensibility of the flow simulation to the correlation length probably is due to the high net pay within the amalgamated channel reservoir units and to the high number of conditioning wells however the flow simulation performed with the longest correlation length showed the best fit with the production history

scaling relationships of channel networks at large scales examples from two large magnitude watersheds in brittany france abstract we present a statistical analysis on two watersheds in french brittany whose drainage areas are about 10 000 and 2000 km 2 the channel system was analysed from the digitised blue lines of the 1 100 000 map and from a 250 m dem link lengths follow an exponential distribution consistent with the markovian model of channel branching proposed by smart 1968 the departure from the exponential distribution for small lengths that has been extensively discussed before results from a statistical effect due to the finite number of channels and junctions the strahler topology applied on channels defines a self similar organisation whose similarity dimension is about 1 7 that is clearly smaller than the value of 2 expected for a random organisation the similarity dimension is consistent with an independent measurement of the horton ratios of stream numbers and lengths the variables defined by an upstream integral drainage area mainstream length upstream length follow power law distributions limited at large scales by a finite size effect due to the finite area of the watersheds a special emphasis is given to the exponent of the drainage area a a that has been previously discussed in the context of different aggregation models relevant to channel network growth we show that a a is consistent with 4 3 a value that was obtained and analytically demonstrated from directed random walk aggregating models inspired by the model of scheidegger 1967 the drainage density and mainstream length present no simple scaling with area except at large areas where they tend to trivial values constant density and square root of drainage area respectively these asymptotic limits necessarily imply that the space dimension of channel networks is 2 equal to the embedding space the limits are reached for drainage areas larger than 100 km 2 for smaller areas the asymptotic limit represents either a lower bound drainage density or an upper bound mainstream length of the distributions because the fluctuations of the drainage density slowly converge to a finite limit the system could be adequately described as a fat fractal where the average drainage density is the sum of a constant plus a fluctuation decreasing as a power law with integrating area a fat fractal hypothesis could explain why the similarity dimension is not equal to the fractal capacity dimension as it is for thin fractals the physical consequences are not yet really understood but we draw an analogy with a directed aggregating system where the growth process involves both stochastic and deterministic growth these models are known to be fat fractals and the deterministic growth which constitutes a fundamental ingredient of these models could be attributed in river systems to the role of terrestrial gravity

dinoflagellate cysts and the paleoenvironment of late pliocene early pleistocene deposits of brittany northwest france abstract the marine pliocene facies of the redon clay is widely distributed in the western part of brittany the decrease in the abundance of tertiary pollen towards the top of the deposits coupled with the increase of pollen of boreal forest taxa and the development of ericaceae and poaceae indicates a late pliocene age the occurrence of the transgression maximum is recorded in calcareous beds which contain the highest concentration of microforaminiferal linings and dinoflagellate cysts hystrichokolpoma rigaudae and melitasphaeridium choanophorum along with achomosphaera andalousiensis and operculodinium israelianum make up these aseemblages the presence of dinoflagellate cyst assemblages with estuarine and neritic affinities but with an occasional oceanic form indicates sedimentation in coastal waters with a neritic influence the paleotopography exerts a control on the altitudinal distribution of the redon clays in the western part of brittany to the west of the rennes basin the pliocene pleistocene dinoflagelate cyst assemblages of southern england and northwestern france show a remarkable degree of homogeneity in their composition chiefly expressed in the apparent contradictory association of a andalousensis and o israelianum that suggest sedimentation in an unusual type of environment which arose in the context of climatic change and sea level variations at that time

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

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

the okavango fan and the classification of subaerial fan systems abstract controversy exists over the classification of fluvially formed subaerial fans authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers the okavango fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers the fan is a large 150 km radial axis shallowly sloping 0 00036 highly vegetated subaerial fan which can be subdivided into four subenvironments these are 1 the entry corridor or panhandle characterized by single and anastomosing meander belts 2 the upper fan characterized by meander belts diverging from the fan apex comprising peat confined meandering channels with interchannel swamps forming thick peats 3 the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with however little chance of peat preservation and 4 the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre existing aeolian and lacustrine deposits with the recognition of this new fan type the spectrum of subaerial fan types can be expressed in terms of 1 debris flow dominated fans of which the death valley fans are a member 2 braided river dominated fans of which the kosi fan is a member and 3 low sinuosity meandering losimean river dominated fans of which the okavango fan is a member this spectrum can be expressed in terms of variation in slope maximum size and percentage of surface vegetation but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface comparable ancient examples of the three fan types are recognizable many of which provide intermediates between the ideal end members debris flow dominated and braid dominated fan types are known from throughout earth history however the losimean fan type because of its reliance on confining vegetation may only have developed after the devonian period the spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows processes associated with braided rivers or processes associated with meandering and low sinuosity rivers

principles of regression and transgression the nature of the interplay between accommodation and sediment supply the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea level how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a 2 s and a super 1 5 s super 0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

genetic stratigraphic sequences in basin analysis ii application to northwest gulf of mexico cenozoic basin the northwest gulf of mexico cenozoic sedimentary wedge illustrates the application of genetic stratigraphic sequence analysis and documents several general conclusions 1 sequences defined by regional marine flooding are the principal genetic stratigraphic units of the basin fill continental margins are characterized by repetitive episodes of basin margin offlap punctuated by periods of transgression and marine flooding of the depositional platform 2 continental margin outbuilding is concentrated at one or more shelf edge deltaic depocenters separated by interdeltaic bights depocenters remain fixed during a depositional episode but commonly relocate during transgression and flooding 3 a distinct syndepositional structural style in prograding continental margins results in sporadic uplift of a basin fringing peripheral bulge and accentuates preservation of shelf margin facies along zones of extensional normal faulting and enhanced subsidence 4 genetic stratigraphic sequences commonly reflect an evolving interplay among two or even three variables for example early cenozoic gulf sequences are most closely related to tectonic events of the intraplate source terrane which in turn affect rate and location of sediment supply and basin margin response to loading late cenozoic sequences more closely reflect proposed eustatic cycles

a benthic foraminiferal record of middle to late pliocene 3 15 2 85 ma deep water change in the north atlantic abstract records of benthic foraminifera from north atlantic dsdp site 607 and hole 610a indicate changes in deep water conditions through the middle to late pliocene 3 15 to 2 85 ma quantitative analyses of modern associations in the north atlantic indicate that seven species fontbotia wuellerstorfi cibicidoides kullenbergi uvigerina peregrina nuttallides umboniferus melonis pompilioides globocassidulina subglobosa and epistominella exigua are useful for paleoenvironmental interpretation the western north atlantic basin site 607 was occupied by north atlantic deep water nadw until 2 88 ma at that time n umboniferus increased indicating an influx of southern ocean water sow the eastern north atlantic basin hole 610a was occupied by a relatively warm water mass possibly northeastern atlantic deep water neadw through 2 94 ma when sow more strongly influenced the site these interpretations are consistent with benthic 18o and 13c records from 607 and 610a raymo et al 1992 the results presented in this paper suggest that the north atlantic was strongly influenced by northern component deep water circulation until 2 90 2 95 ma after that there was a transition toward a glacially driven north atlantic circulation more strongly influenced by sow associated with the onset of northern hemisphere glaciation the circulation change follows the last significant sst and atmospheric warming prior to 2 6 ma

evolution of the western approaches trough abstract the western approaches trough corresponds to a major mesozoic rift which became partly inverted during the late oligocene and miocene sediments contained in this basin range in age from permian to neogene and are some 7000 m thick the rifting stage of the western approaches trough spans permian to aptian times there is only minor evidence for volcanic activity important wrench deformations preceded the accumulation of wealden clastics in the rapidly subsiding southwest channel basin and in the brittany trough early aptian wrench deformations coincided with crustal separation in the bay of biscay during the albian to early oligocene the western approaches trough was tectonically inactive and subsided regionally late oligocene to miocene compressional deformations induced the upwarping of a major anticlinorium having a structural relief of some 3000 m

changes in braided river morphology resulting from aggradation and degradation forty three experiments were completed in a large flume 1 8 x 18 3 m to examine the effects of sediment load sediment size and channel gradient on braided river morphology the laboratory results were supported by field research and analogs from the published literature subaerially exposed braid bars were formed by the dissection and further accretion of stalled linguoid dunes which are actively migrating bedforms bar forming processes and channel dynamics were the same in both sand and gravel bed channels however linguoid dunes stalled and were transformed into braid bars more frequently in gravel bed channels and therefore gravel bed channels were more intensely braided aggradation resulted in the development of more bars rather than in an increase in the size of preexisting braid bars the number of actively migrating linguoid dunes also increased with sediment load in the highly mobile sand bed channels conversely in degrading channels the number of braid bars decreased and average bar

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

high resolution sequence stratigraphy of an alluvial fan fan delta environment stratigraphic and geodynamic implications an example from the keuper chaunoy sandstones paris basin abstract facies analysis of the chaunoy formation conducted as the first stage of this study reveals that the corresponding fluvial system essentially involved bedload deposition 2 d and 3 d megaripple migration and debris flow deposition such processes are characteristic of alluvial fan depositional environments these alluvial fan deposits pass laterally eastward into a shallow lacustrine environment in stage 2 of the study electrofacies are defined by well log analysis and then matched with sedimentary facies defined by core analysis electrofacies associations and depositional environments are then inferred directly from well logs on this basis six electrofacies characterizing the main sedimentary facies associations and depositional environments within the chaunoy formation are defined channel lag deposits channel infilling lake or flood plain overflow deposits and paleosols stage 3 involves establishing correlations based on high resolution sequence stratigraphy within these continental deposits the procedure consists in analysing high frequency fluctuations in baselevel defined from sedimentological studies and calibrated on well log signatures the correlations show that the top of the chaunoy formation is diachronous the formation is subdivided here into three stratigraphic units from base to top chaunoy i ii and iii this study shows that the degree of preservation of continental deposits varies with stratigraphic cycle genetic sequences and genetic sequence sets are asymmetrical with the baselevel rise being better preserved than the baselevel fall while for minor cycle deposits may be similarly preserved during baselevel rise and fall the sequence stratigraphy pattern of the genetic sequences and the genetic sequence sets can result from climatic and or tectonic factors but their effects are difficult to distinguish at the scale of the minor chaunoy i cycle or the chaunoy ii cycle preservation is similar during the baselevel rise and fall that implies that the chaunoy minor cycles were influenced by load discharge resulting in greater accommodation space which could result from climatic or tectonic fluctuations the chaunoy formation was deposited as part of a major baselevel rise during the carnian liassic cycle during this cycle the paris basin was generally tilted to the northwest producing the intra marnes irisees superieures truncation which seems to have been induced by large scale wavelength tectonic deformation detailed isopach maps of minor baselevel cycles in chaunoy i with inferred depositional environments are used to define the extent of depositional environments and fault activity during baselevel rise and fall during emplacement of the braided alluvial fan and lacustrine deposits of the chaunoy formation fault activity which was confined to the western part of the basin controlled the preservation potential i e the thickness of the deposits and depositional environment profiles within the chaunoy i and ii cycles the increased thickness of the sandstone deposits to the northeast and the onlap at the top of chaunoy i can be explained by local fault activity and by the general tilting of the basin the chaunoy iii sandstones are confined to the western part of the basin and seem to have been controlled by local factors only

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

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

drainage network expansion of the salagou drainage basin s france an example of relief response to recent climate change continental erosion is known to be strongly controlled by climate but the way by which geomorphological systems respond to climate change still remains poorly understood recent numerical modelling suggests that drainage networks are subjected to strong spatial fluctuations but few studies of natural systems have addressed this phenomenon because of the difficulty of documenting the evolution of erosional landscapes a detailed field analysis has allowed reconstruction of the past topography of a drainage basin located in southern france where remnants of a past landscape are well preserved a change from a smooth to a present day dissected landscape is observed and related to a change in the dominant processes of erosion this evolution is interpreted in terms of fluctuations in drainage network extent in response to a holocene increase in precipitation

the deposits internal structure and geometry in six alluvial fan fan delta bodies devonian norway a study in the significance of bedding sequence in conglomerates discussion and reply

large scale relief development related to quaternary tectonic uplift of a proterozoic paleozoic basement the armorican massif nw france the topography of basements located in intraplate domains has often been interpreted in terms of planation theory by examining the remnants of paleosurfaces in this paper we address the significance of the present day drainage networks that erode such topographies by looking at the relief development on the armorican massif basement northwestern france using digital elevation model dem analysis the topography of this massif is characterized by large scale 250 km relief variations that define high elevation domains heds these domains control the pattern of drainage networks by setting the location of the main drainage divides and the polarity of the regional slopes large scale relief is strongly associated with the existence of scarps along inherited fault zones suggesting that relief development is mainly controlled by tectonics through fault reactivation a surface evolution study shows that drainage networks developed during the quaternary which corresponds to the timing of the tectonic activity which also led to relief development the study of quaternary fluvial erosion through a new method for measuring incision shows that the drainage basins of the heds record greater amounts of base level fall during quaternary times this implies that differential uplift is responsible for the large scale relief development of the armorican massif during the quaternary our study suggests that as seen in active settings the topography of basements corresponds to a dynamic signal between tectonics and erosional processes which can be used for example in the study of intraplate deformation

the accommodation concept in sequence stratigraphy some dimensional problems and possible redefinition abstract a debate is provoked here as to what is meant exactly by the term accommodation and how well this concept as it presently stands serves the conceptual and quantitative framework of sequence stratigraphy accommodation in terms of its original definition contains some conceptual flaws it represents a space that has three dimensional extent associated with a certain availability of sediment and thus is not really independent of sedimentation however this space is fairly unspecifiable because of the inherent difficulty of distinguishing real accommodation from the space which is very unlikely to be filled by sediment anti accommodation the accommodation concept cannot be extended to subaerial environments because the equilibrium profile of streams which is sometimes used for this purpose is difficult to recognize even if it existed a possible redefinition of accommodation is suggested as the thickness measured at a specified site and time of a space which becomes filled with sediments during a specified time interval this accommodation is not a space but the thickness of a space not something potential but an objective result not specifiable from the graded profile or geomorphic base level but from stratigraphic base level and not separated from sedimentation but partly dependent from it potential accommodation may be used to describe the maximum of possible accommodation at a specified site and time which can substantially coincide with the height of a water column at a given site and time

geomorphic and paleoclimatic implications of latest pleistocene radiocarbon dates from colluvium mantled hollows california radiocarbon analyses of charcoal from basal colluvium in 11 california hollows show a clustering of dates between 9000 and 15 000 b p an indication that changes in the storage and discharge of colluvium from hillslopes accompanied the pleistocene holocene transition hollows are sites of topographically induced convergence and deposition of colluvial debris and evacuation of this debris was apparently more thorough and possibly more frequent in the latest pleistocene perhaps due to a combination of changes in vegetation and rainfall characteristics one hypothesis is that greater storm intensities occurred in the latest pleistocene and induced a higher frequency of landslides in hollows and a regional extension of channel heads upslope relative to the holocene during the last pleistocene california hollows apparently contained smaller volumes of colluvium in storage the increased storage of debris during the holocene may have resulted in a diminished supply of sediment to stream channels

quantification of vertical movement of low elevation topography combining a new compilation of global sea level curves and scattered marine deposits armorican massif western france a wide range of methods are available to quantify earth s surface vertical movements but most of these methods cannot track low amplitude 5 ma e g cosmogenic isotope studies vertical movements characteristic of plate interiors the difference between the present day elevation of ancient sea level markers deduced from well dated marine deposits corrected from their bathymetry of deposition and a global sea level gsl curve are sometimes used to estimate these intraplate vertical movements here we formalized this method by re assessing the reliability of published gsl curves to build a composite curve that combines the most reliable ones at each stage based on the potential bias and uncertainties inherent to each curve we suggest i that curves which reflect ocean basin volume changes are suitable for the ca 100 to 35 ma greenhouse period ii whereas curves that reflects ocean water volume changes are better suited for the ca 35 to 0 ma icehouse interval and iii that for these respective periods the fit is best when using curves that accounts for both volume changes we used this composite gsl curve to investigate the poorly constrained paleogene to neogene vertical motions of the armorican massif western france it is characterized by a low elevation topography a variscan basement with numerous well dated cenozoic marine deposits scattered upon it using our method we identify low amplitude vertical movements ranging from 66 m of subsidence to 89 m of uplift over that time period their spatial distribution argues for a preferred scale of deformation at medium wavelengths i e order 100 km which we relate to the deformation history of northwestern european lithosphere in three distinct episodes i a phase of no deformation between 38 and 34 ma that has been previously recognized at the scale of northwestern europe ii a phase of low subsidence between 30 and 3 6 ma possibly related to buckling of the lithosphere and iii a phase of more pronounced uplift between 2 6 ma and present which we relate to the acceleration of the africa apulia convergence or to enhanced erosion in the rapidly cooling climate of the pleistocene

sediment routing system and sink preservation during the post orogenic evolution of a retro foreland basin the case example of the north pyrenean aquitaine bay of biscay basins abstract we investigated here the evolution of the sediment routing system i e the sediment transport and deposition evolution along successive depositional topographies and environments and the sink i e deposited sediments preservation in a foreland basin from the period of mountain belt shortening to its post orogenic stage the studied system is the north pyrenean retro foreland basin from 50 ma to today which is composed of a subsiding platform the aquitaine basin fed by the erosion of the pyrenees passing laterally to a slope and a deep sea plain the bay of biscay deep basin the ultimate area of deposition this study is based on a double seismic stratigraphic and structural analysis of an extensive seismic dataset and on an age model of the sediments combining biostratigraphy orbitostratigraphy and sequence stratigraphy with a time resolution of 0 1 ma four major periods of deformation corresponding to a single or a set of stratigraphic sequence boundaries were characterized the pyrenean shortening decrease may be recorded by a basin scale uplift at 49 8 ma late ypresian the paroxysm of the piggy back shortening and related uplift is dated at 35 8 ma priabonian the end of the pyrenees shortening transition to post orogenic conditions is well dated between 27 1 and 25 2 ma chattian a major west european scale deformation of possible mantle origin uplifted the basin from 16 4 to 10 6 ma late burdigalian to early tortonian these major periods of deformations controlled the sink preservation at the first order through the ratio between the accommodation space created by subsidence on the aquitaine platform asub and the siliciclastic sediment supply coming from the erosion of the pyrenees ssc a general model is proposed at the time of the foreland basin when asub ssc most of the sediments are preserved on the platform as a progradational aggradational wedge up to 25 2 ma here at the time of the post foreland evolution when asub the continental sediment routing system is mainly provided along nearly flat alluvial plains with extensive lakes and or humid zones i e the local base levels of the alluvial fans the aquitaine retro foreland was never overfilled

the neogene succession of the south western approaches great britain the outer continental shelf in the south western approaches is underlain by an oceanward dipping wedge of neogene strata up to 400 m thick that is divisible into three units a the early to mid miocene parallel bedded calcilutites of the jones formation which rest with a marked eastward overstep on palaeogene and cretaceous strata b the mid to late miocene cockburn formation which consists of calcarenites fashioned into a series of linear tidal ridges that are separated locally by an unconformity from the underlying unit c the plio pleistocene little sole formation which sits with a planar unconformity on the miocene strata and is divisible into a lower wedge like member restricted to near the shelf edge and an upper more widespread sheet like member palaeo bathymetric and seismo stratigraphic evidence indicates that the shelf and adjacent land areas have suffered epeirogenic movement since the early miocene

the oligocene and miocene outliers of west cornwall and their bearing on the geomorphological evolution of oldland britain the tertiary sediments preserved at st agnes crousa downs and polcrebo downs cornwall are described in detail the deposits at st agnes have yielded two contrasting floras one mid oligocene the other miocene in age the latter appears to be the first recorded proven miocene extant in the british landscape accordingly it has become necessary to distinguish two discrete outliers at st agnes that termed the st agnes formation sensu stricto miocene and the beacon cottage farm formation oligocene the local equivalent of the bovey formation a tripartite stratigraphy is proposed for the former the upper and lower members comprising wind blown sands and the middle member a colluvial slope wash deposit all were apparently formed under warm temperate conditions the sediments at crousa and polcrebo remain undated both preserve deep weathering profiles of tropical or subtropical type in the palaeozoic floor below and are themselves much affected by in situ deep weathering structurally all four outliers appear to be simple erosional relics of once more widespread and possibly thicker sheets no secondary structures have been identified all four apparently survived as a result of their locations on prominent watersheds originating in at least mid or even early tertiary times the geomorphological relations of the four outliers are considered in detail the sub st agnes surface is shown to be the homologue of a planation surface that is widely developed in west cornwall at an elevation of between ca 75 131 m above sea level asl the latter is redefined and termed the reskajeage surface its age is shown to be pre upper miocene rather than pleistocene as was previously widely held there is indirect evidence that it formed subaerially over a long period during mid tertiary times essentially it appears to be an etchplain of tropical and subtropical origins now largely stripped of its former saprolitic cover it is demonstrated that the grosser physiography of west cornwall was established by the end of the palaeogene at the latest and also that the area has probably never been inundated by tertiary seas except shallowly near to the end of that period i e by the st erth transgression the prolonged morphodynamic stability of the region as established in this paper has important consequences for the interpretation of landscape evolution elsewhere in areas of oldland i e post armorican western europe especially where datable tertiary deposits have yet to be recognized

regional vs contact metamorphism of garnet metapelites in the vicinity of late variscan granites central armorican domain brittany france late variscan granites intruded brioverian upper proterozoic and lower paleozoic pelitic sequences to the north of the south armorican shear zone in the vicinity of the granites brioverian garnet micaschists contain pre syn s2 assemblages with garnet staurolite and post s2 assemblages with staurolite andalusite andalusite appeared pre syn and post s2 in garnet free micaschists the garnets in the brioverian micaschists are zoned with increasing mg and decreasing mn and ca from core to inner rim only poor garnet zonations occur in paleozoic hornfelses of enclaves in the rostrenen granite the results of a microstructurally controlled application of garnet biotite geothermometers and garnet plagioclase geobarometers are similar to p t trends obtained by the gibbs method of garnet zonation modelling in the system ncfmnmash the p t paths of a pre syn s2 regional metamorphism are clockwise between 500 550 c 8 kbar and 700 c 5 kbar followed by cooling decompression they contrast with isobaric contact metamorphism between 500 and 700 c at 2 5 3 kbar in paleozoic hornfelses this points to a two stage variscan metamorphism with a pre granitic pressure dominated event in the brioverian micaschists followed by late variscan contact metamorphism and suggests the existence of a pre granitic tectonic boundary between the micaschists and overlying low grade sequences

alternate interpretation of the messinian salinity crisis controversy resolved a high resolution chronology of the mediterranean messinian salinity crisis is proposed two types of evaporite deposition may be distinguished those in marginal areas vs those in basinal ones their diachroneity is deduced from the stratigraphic relationships linking these evaporites to a major messinian erosional surface a two step model is proposed for the evolution of the salinity crisis through time during the first phase from 5 75 to 5 60 ma the deposition of marginal evaporites took place in response to a modest sea level fall in the second interval from 5 60 to 5 32 ma the mediterranean basin became isolated during this later period the deposition of basinal evaporites and the cutting of the mediterranean canyons took place

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

mio pliocene to pleistocene paleotopographic evolution of brittany france from a sequence stratigraphic analysis relative influence of tectonics and climate the mio pliocene in western europe is a period of major climatic and tectonic change with important topographic consequences the aim of this paper is to reconstruct these topographic changes based on sedimentological analysis and sequence stratigraphy for the armorican massif western france and to discuss their significance the mio pliocene sands of the armorican massif red sands are mainly preserved in paleovalleys and are characterized by extensive fluvial sheetflood deposits with low preservation and by pass facies this sedimentological study shows that the red sands correspond to three main sedimentary environments fluvial alluvial fan low sinuosity rivers and braided rivers estuarine and some rare open marine deposits marine bioclastic sands faluns of french authors two orders of sequences have been correlated across brittany with one or two minor a s cycles comprised within the retrogradational trend of a major cycle the unconformity at the base of the lower cycle is more marked than the unconformity observed at the top which corresponds to a re incision of the paleovalley network a comparison of the results of the sequence stratigraphy analysis with eustatic variations and tectonic events during the mio pliocene allows 1 to discuss their influence on the evolution of the armorican massif and 2 to compare the stratigraphic record with other west european basins the unconformity observed at the base of the first minor cycle may be attributed to serravallian tortonian tectonic activity and or eustatic fall and the unconformity of the second minor cycle may be attributed to late tortonian early messinian tectonic activity the earlier unconformity is coeval with the development of a smooth paleovalley network compared to the jagged present day relief a single episode of mio pliocene deformation recorded in brittany may be dated as zanclean thus explaining the lack of the maximum flooding surface except in isolated areas from this study five paleogeographic maps were drawn up also indicating paleocurrent directions three maps for the lower cycle tortonian retrogradational trend late tortonian to early messinian maximum flooding surface and messinian progradational trend and two for the upper cycle pliocene retrogradational trend and piacenzian maximum flooding surface these maps show 1 the variations of paleocurrent directions during the mio pliocene 2 the extent of estuarine environments during the maximum flooding intervals and 3 a paleodrainage watershed oriented nnw sse following the regional quessoy nort sur erdre fault during the retrogradational trend of the upper cycle and possibly during the progradational trend of the lower cycle the present day morphology of the armorican massif is characterized by 1 incised

landscape response to climate change insights from experimental modeling and implications for tectonic versus climatic uplift of topography we present the results of an experimental investigation of the concurrent action of tectonic uplift and climate variation on relief evolution we designed an experimental apparatus that allows the study of erosion of laboratory scale topographies that evolve under given uplift and rainfall rates for constant uplift and rainfall rates the experimental topography evolves toward a statistical steady state defined by a mean elevation constant with time starting from such a steady state and keeping the input uplift rate constant a subsequent change in the rainfall rate yields a change in the mean elevation of the landscape to a new equilibrium elevation an increase in precipitation yields a lower mean steady state elevation whereas for a decrease in precipitation the surface is uplifted we define this phenomenon as a climatically induced surface uplift as opposed to a tectonically induced surface uplift the climatically and tectonically induced surface uplifts correspond to different dynamics of denudation so that it is theoretically possible to differentiate between the climatic or tectonic causes of surface uplift from records of output sediment fluxes

origin of temporal compositional variations during the eruption of lake purrumbete maar newer volcanics province southeastern australia the pleistocene lake purrumbete maar eruption sequence of the newer volcanics province of southeastern australia records stratigraphic temporal and geochemical variations that cannot be explained by crustal processes such as fractional crystallisation and crustal contamination samples from the lake purrumbete maar have distinct trace element trends that correlate with stratigraphic height with decreasing incompatible element concentrations from the bottom of the sequence to the top indicating that the most enriched melts were ejected during the earliest eruption stages with the least enriched melts erupted in the final stages variations in rare earth element ratios indicate that these melts were formed by dynamic melting of garnet lherzolite mantle material consistent with other volcanic centres within the basaltic cones subprovince of the newer volcanics province the geochemistry of the erupted units at lake purrumbete also record minor differentiation of the melts by olivine fractionation although these processes alone cannot explain the observed geochemical variations in the eruption sequence further differentiation of the melts by different processes such as deep clinopyroxene fractionation or assimilation of metasomatised lithosphere may be responsible for the observed geochemical trends at lake purrumbete this shows the complexity of the plumbing system of monogenetic volcanoes but also shows the opportunities that these volcanoes provide to study these processes in detail as the geochemical variations that are preserved in this type of volcanism by fast magma ascent through the crust as evidenced by the presence of fresh mantle xenoliths predominantly reflect processes that occurred in the mantle rather than in the crust