mineral equilibria and the high radar reflectivity of venus mountaintops we studied the relationship between altitude and microwave emissivity the complement of power reflectivity in 10 highland regions of venus using the magellan data set above a critical altitude that ranges from 4 75 km on maxwell montes to 2 49 km on sapas mons emissivity undergoes an abrupt decrease to values so low 0 6 that the surface mineralogy on these mountaintops must differ from that at lower altitudes in such a way as to enhance the bulk dielectric constant of the highland surface material this emissivity effect probably is produced not by basalt minerals but by a secondary weathered mineral assemblage we developed the phase diagrams descriptive of equilibrium secondary mineral assemblages on venus as a function of altitude and atmospheric redox state the mineral responsible for low emissivity on mountaintops appears to be the electrical semiconductor pyrite fes2 variation from one highland area to another in the altitude at which pyrite becomes the stable fe mineral as opposed to magnetite at lower altitudes may be attributable to local modulation by topography of the atmospheric thermal profile the altitudes at which the magnetite pyrite phase boundary is encountered vary with the redox slate of the atmosphere and observed values of this altitude can be used to estimate an oxygen fugacity at plains level of 10 21 bars maat mons a volcanic peak almost as lofty as maxwell montes is the only high mountaintop on venus that has not weathered to a low emissivity mineral assemblage presumably this means flows at the highest altitudes are negligibly weathered and the volcano is relatively young

meltwater floods into the black and caspian seas during heinrich stadial 1 abstract deglaciation of the eurasian ice sheet dispensed vast amounts of meltwater laden with red brown clay into black and caspian sea s freshwater lakes between 16 350 and 15 400 calendar years bp the arriving sediment had a mineral composition and strontium neodymium isotope signatures 87sr 86sr and end consistent with the crystalline bedrock that lay beneath the ice sheet as opposed to sources from landscapes crossed by the rivers that carried meltwater to the lakes the magnitude and rapidity of the shifts of 87sr 86sr and 18o in shells of ostracods and mollusks an eight fold increase in sediment accumulation rate and a plunge of 1250 14c years in the radiocarbon reservoir age indicate a volume of meltwater sufficient to have replaced most or all of the pre existing lake water if the release of 25 000 km3 of water from the caspian into the black sea s new euxine lake was abrupt by judging the magnitude of erosion in the floor of the manych strait spillway this event qualifies as a megaflood deeply scoured furrows channel floor bars and swaths of mounds 5 20 km in length and 5 20 m in height are reminiscent of scabland landscapes the meltwater is coincident with heinrich stadial 1 when the alpine and eurasian ice sheets re advanced and temperatures of the black sea s lake surface remained cold sand grains within the red brown clay indicate they were transported by lake surface ice

late pleistocene holocene evolution of the northern shelf of the sea of marmara abstract chirp sub bottom profiling multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the sea of marmara som provide evidence of sea level excursions water exchanges between the adjacent mediterranean and black seas and oscillating salinity over the last 160 ka bp during the marine isotope stages mis 2 mis 3 mis 4 and mis 6 the som disconnected from the mediterranean sea and evolved into a lake during mis 1 mis 5 and mis 7 the som reconnected and became salty once again sapropels formed shortly after each invasion of mediterranean saltwater observed in our cores concurrent suboxic dysoxic conditions prevailed over quite shallow substrates on the shelf ancient shorelines are pervasive at 85 m on the northern shelf and in the region of prince islands coincident with the elevation of the modern bedrock sill in the canakkale dardanelles strait at times when global eustatic sea level dropped below this sill the surface of the som stabilized at its outlet and freshened thus this particular shoreline is interpreted as the edge of the most recent som lake that existed from about 75 ka bp to 12 ka bp the freshening is observed in very light 6 values of 18 o measured on freshwater molluscs and the complete absence of foraminifera two brief lacustrine episodes during mis 5 suggest that the level of the canakkale outlet might have been as shallow as 50 m in the past a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in unit l4 1 corresponding to mis 5b 18 o profiles and carbon 14 dating show that salinification of the som and the blossoming of bioherms evolved rapidly after the latest connection with the mediterranean at 12 ka bp however freshening proceeded more slowly once the connection was severed

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

recognition and significance of sharp based mouth bar deposits in the eocene green river formation uinta basin utah sandstone bodies in the sunnyside delta interval of the eocene green river formation uinta basin previously considered as point bars formed in meandering rivers and other types of fluvial bars are herein interpreted as delta mouth bar deposits the sandstone bodies have been examined in a 2300 m long cliff section along the argyle and nine mile canyons at the southern margin of the uinta lake basin the sandstone bodies occur in three stratigraphic intervals separated by lacustrine mudstone and limestone together these stratigraphic intervals form a regressive transgressive sequence individual sandstone bodies are texturally sharp based towards mudstone substratum in proximal parts the mouth bar deposits only contain sandstone whereas in frontal and lateral positions mudstone drapes separate mouth bar clinothems the clinothems pass gradually into greenish grey lacustrine mudstone at their toes horizontally bedded or laminated lacustrine mudstone onlaps the convex upward sandstone bars the mouth bar deposits are connected to terminal distributary channel deposits together these mouth bar channel sandstone bodies accumulated from unidirectional jet flow during three stages of delta advance separated by lacustrine flooding intervals key criteria to distinguish the mouth bar deposits from fluvial point bar deposits are i geometry ii bounding contacts iii internal structure iv palaeocurrent orientations and v the genetic association of the deposits with lacustrine mudstone and limestone

explosive volcanic eruptions from linear vents on earth venus and mars comparisons with circular vent eruptions 1 conditions required to support buoyant convective plumes are investigated for explosive volcanic eruptions from circular and linear vents on earth venus and mars vent geometry linear versus circular plays a significant role in the ability of an explosive eruption to sustain a buoyant plume on earth linear and circular vent eruptions are both capable of driving buoyant plumes to equivalent maximum rise heights however linear vent plumes are more sensitive to vent size for analogous mass eruption rates linear vent plumes surpass circular vent plumes in entrainment efficiency approximately when lo 3ro owing to the larger entrainment area relative to the control volume relative to circular vents linear vents on venus favor column collapse and the formation of pyroclastic flows because the range of conditions required to establish and sustain buoyancy is narrow when buoyancy can be sustained however maximum plume heights exceed those from circular vents for current atmospheric conditions on mars linear vent eruptions are capable of injecting volcanic material slightly higher than analogous circular vent eruptions however both geometries are more likely to produce pyroclastic fountains as opposed to convective plumes owing to the low density atmosphere because of the atmospheric density profile and water content on earth explosive eruptions enjoy favorable conditions for producing sustained buoyant columns while pyroclastic flows would be relatively more prevalent on venus and mars these results have implications for the injection and dispersal of particulates into the planetary atmosphere and the ability to interpret the geologic record of planetary volcanism

river inflow and salinity changes in the caspian sea during the last 5500 years abstract pollen spores and dinoflagellate cysts have been analysed on three sediment cores 1 8 1 4 m long taken from the south and middle basins of the caspian sea a chronology available for one of the cores is based on calibrated radiocarbon dates ca 5 5 0 8 cal ka bp the pollen and spores assemblages indicate fluctuations between steppe and desert in addition there are some outstanding zones with a bias introduced by strong river inflow the dinocyst assemblages change between slightly brackish abundance of pyxidinopsis psilata and spiniferites cruciformis and more brackish dominance of impagidinium caspienense conditions during the second part of the holocene important flow modifications of the uzboy river and the volga river as well as salinity changes of the caspian sea causing sea level fluctuations have been reconstructed a major change is suggested at ca 4 cal ka bp with the end of a high level phase in the south basin amongst other hypotheses this could be caused by the end of a late and abundant flow of the uzboy river now defunct carrying to the caspian sea either meltwater from higher latitudes or water from the amu daria a similar later clear phase of water inflow has also been observed from 2 1 to 1 7 cal ka bp in the south basin and probably also in the north of the middle basin

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

small scale stratigraphy in a large ramp delta recent and holocene sedimentation in the volga delta caspian sea the volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient f5 cm km and by being affected by the rapid sea level changes of the caspian sea at rates up to a hundred times the global sealevel rise this paper reports 1 the morphological and facies development of part of the lower delta during the last full sealevel cycle between 1929 and 1995 as monitored using remote sensing and field mapping and 2 the holocene development of the delta from outcrop data and augered transects during a sea level fall of 3 m between 1929 and 1977 rapid progradation of levees composed of fine sand took place along over 800 distributary channels along the delta front smaller distributaries became filled with clay and organics during the 3 m sea level rise from 1977 to 1995 aggradation occurred leading to deposition of silt and clay on the levees and minor filling of the flood basins sedimentation rates as established with 137 cs dating are up to 2 5 cm year total thickness of holocene deposits in the lower delta plain is 4 10 m

recent coastal evolution of the caspian sea as a natural model for coastal responses to the possible acceleration of global sea level rise abstract the caspian sea serves as an excellent natural laboratory for studies of coastal response patterns as it is highly variable in its water level over decadal and secular time scales coastal morphology presumably nearshore bottom slope and profiles of depositional coastal bodies or erosional scarps as well as rates and amplitudes of water level changes appear to be the most important factors of coastal response rates and patterns nearshore bottom slope determines not only shoreline retreat values according to the bruun rule but also the very patterns of coastal evolution for various morphological types of depositional coasts including deltaic coasts strict analytical prediction of coastal response to the accelerated sea level rise is yet to be solved analysis of every response pattern of depositional coasts to sea level changes requires a specific modification of the bruun rule however these equations should be regarded only as the means to estimate an order of magnitude of shoreline retreat or advance in many cases equations based on the bruun rule cannot be applied at all boundary conditions for each quantitative model should be thoroughly studied where possible longshore sediment drift sediment washover on to the landward slope of depositional coastal features and possible onshore or offshore aeolian sediment movement should be taken into account moreover applicability of the bruun rule based equilibrium approach will possibly diminish under the possible future acceleration of sea level rise

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

sefidrud delta and quaternary evolution of the southern caspian lowland iran abstract the southern caspian sea lowland in iran forms a thick sedimentary prism produced by interactions of marine deltaic and fluvial processes during the late neogene and quaternary deltaic and fluvial deposits have been developed mainly by the sefidrud which is the largest river of the country its drainage area ca 61 600 km 2 includes nearly the entire alborz mountain range and forms deep valleys gorges and a large delta at the southern coast of the caspian sea the sefidrud delta is so large that it covers one third of the large guilan mazanderan plain both from an aerial and volumetric point of view consequently the drainage network of the sefidrud represents the quaternary evolution of northern iran and can be used to test the hypothesized evolution of the region the sefidrud delta has been investigated using many short and long cores satellite images and lithofacies maps and the results show that this delta complex 1680 km 3 consists of a covered lower part and exposed upper deltaic sequences the lower and upper parts of the complex were formed during the early pleistocene and late pleistocene respectively the upper exposed alluvial and deltaic sediments represent a total progradation of approximately 50 km forming three separate delta subsequences d1 3 of which the last one d3 is the modern sefidrud delta the modern delta is a wave dominated blanket like sediment cover ca 30 m thick and 1550 km 2 produced during the last three millennia it was formed by 30 km progradation of six juxtaposed lobes each lobe corresponds to a long term sea level fluctuation of the caspian sea the active lobe ca 50 km 2 has been forming since 1550 ad late pleistocene deltaic sequences d1 3 particularly the modern one d3 were produced by relatively fast deposition due to high volume sediment load of the sefidrud it is suggested that they were produced after the opening of the rudbar gorge by river capture that in turn six times enlarged the drainage area previous deltaic progradation and marine transgressions were relatively slow and the development of the whole lowland at the southern caspian sea lasted ca 1 1 2 ma bp

theoretical modeling of eruption plumes on venus a theoretical model of eruption plume dynamics woods 1988 is used to investigate plinian eruption columns on venus results for a typical plume in terms of the temperature density velocity and radius as a function of height are given the effects of the atmospheric pressure the volatile content and species and the eruption temperature on the development of high convecting plumes are discussed demonstrating the combinations of initial conditions giving rise to either high convective plumes or low fountains feeding pyroclastic flows the results show that the development of high convecting plumes on venus requires an unlikely combination of high volatile contents high initial temperatures and high altitude eruptions leading to the conclusion that explosive eruptions on venus will generally lead to pyroclastic flows

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

development of the kura delta azerbaijan a record of holocene caspian sea level changes late holocene deposits of the kura delta indicate an alternating dominance of deltaic and shallow marine environments these major environment shifts are controlled by the high frequency sea level changes of the caspian sea the level of the caspian sea now at 27 m below global sea level gsl changes at rates of up to a hundred times as fast as global sea level allowing observation of sedimentary processes on a decadal scale that would take millennia in an oceanic environment the modern kura delta is a river dominated delta with some wave action along its north eastern flank and without tidal influence morphological and hydrological changes have been monitored for over 150 years continuing up to the present day using remote sensing imagery offshore sparker survey data onshore and offshore corings biostratigraphical analysis and radiometric dating enable a reconstruction of the holocene kura delta four phases of delta progradation alternating with erosional transgressive surfaces have been identified representing just as many cycles of sea level fall and rise the first cycle is represented by lowstand deposits truncated by a transgressive surface ts1 at ca 80 m below gsl ts1 is overlain by several metres of laminated clays and silts deposited during a late holocene forced regression h1 these deposits are truncated by the prominent reflector ts2 corresponding to the derbent lowstand around 1500 yr bp and subsequent transgression this transgressive surface is overlain by prograding shallowing upwards deposits h2 in turn truncated by a third transgressive surface ts3 correlated with a lowstand of ca 32 m below gsl the last phase h3 comprises an onshore progradational unit followed by an aggradational unit with an offshore veneer of clays and silts corresponding to the formation of the modern kura delta that started at the beginning of the 19th century

a full sea level cycle in 65 years barrier dynamics along caspian shores abstract the caspian sea being a closed basin shows much higher rates of sea level change up to 340 mm yr than the oceans it experienced a full sea level cycle with an amplitude of 3 m between 1929 and 1995 its coasts therefore present an attractive physical model to test predicted changes along oceanic coasts as a result of expected eustatic sea level rise and to validate sequence stratigraphical interpretations of ancient sediments along the wave dominated coasts with intermediate shore face slopes in dagestan low onshore bars were formed during the 1929 1977 sea level fall they represent minor short lived 1 2 years transgressive oscillations within the major regressional trend after the 1977 lowstand a prominent barrier lagoon system was formed which during the first phase of sea level rise 1977 1988 encroached landwards about 18 m each year by washover during storms continuous retreat between 1988 and 1995 however barrier size diminished lagoons widened and deepened apparently due to lack of coarse grained sediment supply discontinuous retreat the 1995 highstand prevented the barriers from being overstepped altogether sea level fall after 1995 again produced low bars without lagoons the caspian sea barrier coast demonstrates that for the formation of barrier lagoon complexes the combination of transgression and storms is essential barriers may show either continuous or discontinuous development at constant rate of sea level rise and constant offshore slope depending essentially on the availability of coarse grained sediments the rate of sea level rise as a factor in barrier behaviour cannot be viewed independently from barrier dimensions which in turn depend on wave base depth and maximum storm wave height relations between para sequence thickness and frequency and amplitude of sea level change in closed basins with an independent sea level regime may differ markedly from those in basins influenced by eustasy

amplitude frequency and drivers of caspian sea lake level variations during the early pleistocene and their impact on a protected wave dominated coastline the caspian sea the largest isolated lake in the world witnessed drastic lake level variations during the quaternary this restricted basin appears very sensitive to lake level variations due to important variations in regional evaporation precipitation and runoff the amplitude frequency and drivers of these lake level changes are still poorly documented and understood studying geological records of the caspian sea might be the key to better comprehend the complexity of these oscillations the hajigabul section documents sediment deposited on the northern margin of the kura basin a former embayment of the caspian sea the 2035 m thick well exposed section was previously dated by magneto biostratigraphic techniques and provides an excellent record of early pleistocene environmental lake level and climate changes within this succession the 1050 m thick apsheronian regional stage between ca 2 1 ma and 0 85 ma represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes sequences are regressing from offshore to coastal lagoonal or terrestrial settings and are bounded by abrupt flooding events sediment reveals a low energy wave dominated reflective beach system wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean water depth estimations of the wave baselines allow reconstruction of a lake level curve recording oscillations of ca 40 m amplitude cyclostratigraphic analyses display lake level frequency close to 41 kyr pointing to allogenic forcing dominated by obliquity cycles and suggesting a direct or indirect link with high latitude climates and environments this study provides a detailed lake level curve for the early pleistocene caspian sea and constitutes a first step towards a better comprehension of the magnitude occurrence and forcing mechanisms of caspian sea lake level changes facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake level fluctuations may form good analogues for other semi isolated basins worldwide

late quaternary caspian sea environment late khazarian and early khvalynian transgressions from the lower reaches of the volga river abstract this magnetic clay minerals and palynological study provides a record of two late pleistocene transgressions late khazarian and early khvalynian in the caspian sea through the analysis of present day lower volga terraces the results allow the clarification of some points about the caspian sea evolution during the considered periods early diagenetic iron sulphides greigite and pyrite are present in sediments of the lower part of the late khazarian and reflect restricted water circulation in the basin the change in iron sulphide mineralogy is most probably related to the change of the water level and its salinity low magnetic mineral contents with magnetite if any recorded in the upper part of the late khazarian atelian and early khvalynian reflect a well oxygenated basin and detrital material sources poor in magnetic minerals smectite is the dominant clay mineral in the late khazarian reflecting chemical weathering in its source area due to the wet and warm climate the upper part of this transgression is nevertheless marked by a stepwise relative decrease of smectite and an increase of illite attributed to a cooling climate during the atelian and early khvalynian periods phases of sandy deposits are characterised by equal proportions of illite and smectite similar to ukrainian loess chocolate clays are clearly dominated by illite both clay mineralogies are attributed to cool climate which favours physical weathering in the catchment area the conditions of chocolate clays deposition are unclear the recorded cooling during the last phase of the late khazarian and the 14c age on a well preserved bivalve shell suggest that it is probably much younger than the eemian interglacial and could correspond to the girkan transgression the 14c age for the early khvalynian sample suggests approximately a last glacial maximum age for this transgression

genesis of the baery knolls developed in the northern caspian plain there are many such forms on the north caspian lowland where the author and colleagues conducted detailed geologic and geomorphologic field surveys on the south the range of altitudes of baer knolls bk reaches 10 12 m and the hills have a general southwest orientation the described landforms are the same bk as those developed along the volga delta the sediments composing the bk consist of alternations of clay silt and sand they contain a rich complex of brackish water ostracods detritus and even whole shells which indicate their subaqueous genesis during the late khvalyn currents dominated in a large lagoon chocolate clay cc deposited in it these currents were not linked to the littoral zone with wave activity as granular composition of the deposits their sorting and type of lamination are not peculiar to sediments of a coastal marine zone they are characteristic of unidirectional currents with frequently changing velocities water from the lagoon flowed through the manych passage into the black sea in the late khvalyn hence last connection of the caspian black and black sea was at the end of the late khvalynian time early holocene at first the water overflowed through the manych passage minimal width of 2 km from the caspian to the black sea then it reversed and flowed from the black sea to the caspian sea at this time when the most recent alluvial dam had not yet formed yet in manych there was infiltration of cerastoderma glaucum to the caspian sea discusses the landforms similar to bk in particular the long ridges in the south of western siberia

the sedimentology and development of a modern sandspit miankaleh peninsula and a lacustrine lagoon gorgan bay caspian sea iran abstract gorgan bay is a 240 km 2 lacustrine lagoon on the southeastern margin of the caspian sea from which it is separated by the 48 km long barrier beach sandspit of the miankaleh peninsula to the north the northern windward side of the sandspit displays an eroded berm the bulk of the sandspit is characterized by the presence of beach ridges and transverse nebkha and parabolic dunes the southern leeward side of the sandspit faces the muddy low energy lagoon of gorgan bay the shore sediments are well sorted negatively skewed very fine to fine sands the sand dunes are composed of well sorted positively skewed fine sand grain types of the shore and dune sediments are very similar with quartz grains and small superficial ooids being the major constituents these similarities suggest the dune deposits represent windblown shore sediments in contrast the gorgan bay sediments are poorly sorted positively skewed very fine to coarse sands with abundant bivalves gastropods ostracods and charophyte oogonia clay minerals include chamosite illite and chlorite all of volcanic origin the presence of pyroxenes and amphiboles may suggest a provenance from the gorgan metamorphic complex the study shows that the growth of the miankaleh peninsula sandspit is a result of predominantly eastward longshore transport of littoral fine sands which has been thrown by storm waves above the mean spring tide waterline in the form of slightly curved beach ridges this has allowed the development of dry beach conditions backshore and the growth of vegetation the beach ridges have been successively accreted in an eastern direction younging to the east the formation of superficial ooids is mainly linked to low energy conditions however occasional high energy events existed and long hot summers may also have played also a role in ooid formation the sand was reworked by the prevailing northwesterly winds dune formation spit formation facilitated the infilling of the sheltered lagoon by the trapping of sediment derived from the gorgan metamorphic complex to the south

sedimentation in a discharge dominated fluvial lacustrine system the neogene productive series of the south caspian basin azerbaijan abstract the largely lower pliocene productive series and its regional equivalents contain the major hydrocarbon reservoirs of the south caspian basin examination of outcrops in the apsheron region azerbaijan has resulted in re interpretation of the depositional environments of the productive series the lower part of the productive series consists of sandstones and mudstones interpreted as channelised and sheetflood fluvial deposits intercalated with mudstones that represent short lived lacustrine transgressions of a regional caspian lake the upper productive series pereriva and younger suites comprises sandstone prone intervals interpreted as deposition during periods of increased fluvial discharge and sediment supply and mudstone prone intervals interpreted as deposition during periods of decreased discharge and therefore coarse grained sediment starvation sand prone reservoir intervals in the pereriva and overlying balakhany suites mainly comprise amalgamated low sinuosity braided fluvial sheet sandstones mudstone rich intervals form inter and intra suite seals comprising alluvial plain and lacustrine facies the succession displays an overall fining up trend which is controlled by long term climatic cooling decreased fluvial discharge and reduced coarse clastic input the modern volga caspian system is a partial analogue for the lower productive series in the apsheron region where fluvial and lacustrine conditions alternate on a low gradient ramp without evidence for a shelf break lake eyre australia may be a modern analogue for the upper productive series where there are fewer lacustrine influences discernible in the sedimentology and the overall setting resembles a dryland river terminal fan

orbital insolation ice volume and greenhouse gases abstract the specmap models of orbital scale climate change imbrie et al paleoceanography 7 1992 701 paleoceanography 8 1993 699 are the most comprehensive to date all major climatic observations were analyzed within the framework of the three orbital signals subsequently tuning of signals in vostok ice to insolation forcing has fixed the timing of greenhouse gas changes closely enough to permit an assessment of their orbital scale climatic role in addition evidence from several sources has suggested changes in the specmap 18 o time scale this new information indicates that the timing of co 2 changes at the periods of precession and obliquity does not fit the 1992 specmap model of a train of responses initiated in the north propagated to the south and later returning north to force the ice sheets in addition analysis of the effects of rectification on 100 000 year climatic signals reveals that all have a phase on or near that of eccentricity this close clustering of phases rules out the long time constants for 100 000 year ice sheets required by the 1993 specmap model a new hypotheses presented here revives elements of an earlier climap view hays et al science 194 1976a 1121 but adds a new assessment of the role of greenhouse gases as proposed by milankovitch summer mid july insolation forces northern hemisphere ice sheets at the obliquity and precession periods with an ice time constant derived here of 10 000 years changes in ice volume at 41 000 years drive ice proximal signals sst nadw dust that produce a strong positive co 2 feedback and further amplify ice volume changes at the precession period july insolation forces ice sheets but it also drives fast and early responses in ch 4 through changes in tropical monsoons and boreal wetlands and variations in co 2 through southern hemisphere processes these ch 4 and co 2 responses enhance insolation forcing of ice volume climatic responses at 100 000 years result from eccentricity pacing of forced processes embedded in obliquity and precession cycles increased modulation of precession by eccentricity every 100 000 years produces 23 000 year co 2 and ch 4 maxima that enhance ablation caused by summer insolation and drive climate deeper into an interglacial state when eccentricity modulation decreases at the 100 000 year cycle ice sheets grow larger in response to obliquity forcing and activate a 41 000 year co 2 feedback that drives climate deeper into a glacial state alternation of these forced processes because of eccentricity pacing produces the 100 000 year cycle the 100 000 year cycle began 0 9 myr ago because gradual global cooling allowed ice sheets to survive during weak precession insolation maxima and grow large enough during 41 000 year ice volume maxima to generate strong positive co 2 feedback the natural orbital scale timing of these processes indicates that ice sheets should have appeared 6000 3500 years ago and that co 2 and ch 4 concentrations should have fallen steadily from 11 000 years ago until now but new ice did not appear and co 2 and ch 4 began anomalous increases at 8000 and 5000 years ago respectively human generation of co 2 and ch 4 is implicated in these anomalous trends and in the failure of ice sheets to appear in canada

natural and anthropogenic influences on depositional architecture of the ural delta kazakhstan northern caspian sea during the past 70 years abstract this paper focuses on the ural delta in the northern zone of the caspian sea an area with particular characteristics where intense influence from anthropogenic and natural factors exists which acts on the fragile delta system we built a database to integrate the data from the published sources bathymetric survey and recent images in the geographical information system gis environment the results were linked to the caspian sea level csl curve which had many variations changing the ural delta system s dynamics and in its architecture in addition the anthropogenic changes contribute to shaping the actual ural delta architecture through the link between the results and csl we reconstructed an evolution model for the ural delta system for the last century and identified three different architectures for the ural delta determined by the energy that acted on the system in the last century and by the anthropogenic changes this work identifies six different delta phases which are shaped by csl changes during the last 70 years and by anthropogenic changes the delta phases recognized are i a lobate delta phase shaped during high csl before 1935 ii natural elongate delta 1935 1950 formed during rapid csl fall iii anthropogenic elongate delta 1950 1966 formed during rapid csl fall and after the ural caspian sea canal construction which modified the sedimentary deposition on the delta iv anthropogenic elongate delta 1966 1982 shaped during low csl phase v anthropogenic elongate delta 1982 1996 formed during a rapid csl rise phase and vi anthropogenic elongate delta 1996 2009 shaped during high csl that represent the last phase and actual ural delta architecture

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

relation of major volcanic center concentration on venus to global tectonic patterns global analysis of nasa magellan image data indicates that a major concentration of volcanic centers covering 40 percent of the surface of venus occurs between the beta atla and themis regiones associated with this enhanced concentration are geological characteristics commonly interpreted as rifting and mantle upwelling interconnected low plains in an annulus around this concentration are characterized by crustal shortening and infrequent volcanic centers that may represent sites of mantle return flow and net down welling together these observations suggest the existence of relatively simple largescale patterns of mantle circulation similar to those associated with concentrations of intraplate volcanism on earth

late cenozoic base level variations of the caspian sea a review of its history and proposed driving mechanisms abstract the caspian sea is characterized by significant variations in its base level during the late cenozoic and provides an important repository for long term records of both regional climate and tectonics due to its position within the interior of the eurasian continent and at the northern margin of the ongoing arabia eurasia collision zone the caspian also serves as an important moisture source for eastern eurasia including the northern tibetan plateau and thus the history of caspian base level variations represents an important and poorly understood constraint on paleoclimate reconstructions throughout eurasia prior work in the caspian region has largely focused on developing biostratigraphic age divisions and investigating the history of connection between the caspian black and mediterranean seas as well as the global ocean recent geochronologic work in the caspian and related basins has questioned previous correlations of hydrologic events in these different basins as a result prior estimates of the chronology and magnitude of caspian sea level variations may be incorrect here we synthesize previous work to develop a new caspian base level curve starting at the beginning of the meotian regional stage 7 ma we also present a new synthesis of potential driving mechanisms for the large variations in caspian base level and speculate on a possible cause for the enigmatic akchagyl transgression this synthesis highlights the dynamic range of caspian sea level which varied from 200 m above to in excess of 1000 m below its current level during the late cenozoic and provides a basis for future work investigating the tectonic and climatic drivers behind variations in caspian base level

late pleistocene dust dynamics and pedogenesis in southern eurasia detailed insights from the loess profile toshan ne iran abstract in southern eurasia recurrent phases of aridization dust source extension and enhanced aeolian sedimentation alternated with moister intervals promoting reduced deflation areas and dust accumulation in the context of late pleistocene climate changes weathering and soil forming intensity in this greater region are hence mainly governed by fluctuations in the balance between dust supply and moisture availability among the hitherto known sections the toshan loess soil sequence lps represents a key site due to the quality of the record and the multitude of available data giving detailed insights into the timing and magnitude of dust accumulation and soil formation of the region to elucidate these dynamics for much of the past 130 000 years bulk mineralogical and geochemical data are presented supplemented by a high resolution magnetic susceptibility record and by the results of a detailed micromorphological study of loess at toshan the last interglacial luvisol phaeozem like mis 5e and the early glacial interstadial steppic palaeosols mis 5 c and a are characterized by gradually increasing grain size and decreasing degrees in decomposition of micaceous and mafic minerals pronounced feldspar weathering is detected in the last interglacial and modern soils only which formed under reduced or absent dust deposition on penultimate and last glacial loess respectively postsedimentary the overall pedosedimentary conditions correspond to large scale trends of increasing drought dust accumulation and wind strength in southern eurasia in relation to decreasing moisture availability towards the early pleniglacial mis 4 causing soil formation under ongoing dust deposition synsedimentary similar intervals of synsedimentary soil formation are recorded during the interglacial interstadial stadial transitions of the early glacial and during pleniglacial mis 4 to 2 interstadials the latter are marked by gradual increases in magnetic susceptibility colour and decreasing texture conversely silicate weathering could not be detected suggesting that grain size fluctuations are a primary feature thus windy and arid pleniglacial conditions in southern eurasia were interrupted by intermittent phases of synsedimentary soil formation in response to short lived and relatively moist interstadials although the interrelation of these incipient soils throughout southern eurasia is afflicted with considerable restrictions the oscillatory pattern of the toshan lps bears great similarity with millennial scale oscillations recorded in limnic archives of western asia

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

geomorphology and volcanology of maat mons venus abstract full resolution fmidr magellan radar backscatter images have been used to characterize the geology and volcanology of the volcano maat mons on venus this volcano has often been identified by remote sensing techniques as one of the volcanoes on the planet that could have been recently active and is the highest volcano on venus with a relief of 9 km the summit of maat mons is characterized by a caldera complex 26 30 km in diameter with at least six remnant pit craters 10 km in diameter preserved in the walls of the caldera suggesting that multiple small volume 1 km in diameter on the flanks these pits appear to have formed by collapse with no effusive activity associated with their formation no evidence for explosive volcanism can be identified despite the relatively low atmospheric pressure 55 bar near the summit there is also a lack of evidence for lava channels deformation features within the caldera and thrust faults on the flanks indicating that the physical volcanology of maat mons is simpler than that of typical martian and terrestrial shield volcanoes preservation of fine scale 3 4 pixels structures within the pit craters and summit pits is consistent with geologically very recent activity but no evidence for current activity can be identified

on the rise of turbulent plumes quantitative effects of variable entrainment for submarine hydrothermal vents terrestrial and extra terrestrial explosive volcanism 1 the maximum height reached by a turbulent plume rising in a stratified environment is a key tool to estimate the flux released at its source particularly for large scale flows because flux can often be very hard to measure directly this height is known to be mainly controlled by the stratification of the ambient fluid source buoyancy flux and the efficiency of turbulent mixing between the plume and the external fluid the latter effect has been only superficially explored in spite of its fundamental control on the dynamics here we show that commonly used one dimensional models incorporating a constant entrainment coefficient do not provide satisfying predictions we propose a new model allowing for variable entrainment which gives excellent predictions of maximum heights reached by laboratory plumes in stratified environments we then apply our formalism to natural plumes produced by explosive volcanic eruptions under terrestrial paleo martian and venusian conditions and by submarine hydrothermal activity at mid ocean ridges source mass discharge rates deduced from maximum volcanic column heights for terrestrial eruptions are found to be greater than those estimated with the commonly used constant entrainment parameterization by a factor of 2 in the paleo martian atmosphere existing models overestimate plume heights by 14 27 in the current atmosphere of venus the maximum height reached by a volcanic plume is also found to be smaller than previously estimated for large eruption rates the source heat flux released by the tag field atlantic ocean deduced from several submarine hydrothermal plumes is found greater by a factor 3 with our model

evolutionary trend of the gorgan bay southeastern caspian sea during and post the last caspian sea level rise abstract the gorgan bay gb is a semi confined sedimentary environment at the southeastern corner of the caspian sea cs high sensitivity to eustatic sea level variations resulted in changes in the sedimentary facies and patterns of erosion sedimentation for the gb in the last caspian sea level cycle 1977 1995 therefore the evolutionary trend in coastal sedimentary environments was studied to determine the pattern of erosion and sedimentation related to sea level fluctuation cycles the sedimentology of the bay basin was studied in 500 km2 of the study area in 2001 in addition coastal changes over the two past and post periods of sea level rise were studied using satellite images landsat 7 with a resolution of 30 m and arcgis 10 1 software waves wave induced currents and sediment transport were simulated using the mike 21 software package mixed sediments particularly at the western and southern areas of the bay basin were detected through reworking of coarser barrier island sediments into deeper areas well sorted 0 35 0 5 sediments with 98 31 2 8 sand size particles were identified as the common texture along the wave dominated coasts sea progradation destruction of the beach profile and an increase in sea coverage of approximately 15 600 ha around the gb were other impacts of the cs level rise additional impacts included severe erosion and submergence of a 9000 ha area of the flat coastal plains slope 0 035 the results demonstrate that water level rise has strengthened the sediment accumulation in the bay inlet and basin at a mean rate of 0 430 mcm and 12 7 mcm respectively both field measurements and simulation results revealed the notable shoaling of the bay entrance at a mean rate of 0 2 m simulations concluded that annual longshore transport toward the bay inlet has occurred at a net rate of 80 000 m3 during the last cs level rise natural events after the eustatic cycle in the southeastern corner of the cs resulted in severe shoaling of the gb inlet and basin and restriction in the water exchange between the bay and open sea therefore comprehensive management practices to restore the gb capacity and its natural habitats are critically needed

the δ18o of atmospheric o2 from air inclusions in the vostok ice core timing of co2 and ice volume changes during the penultimate deglaciation one important question about the co2 climate connection is how increasing atmospheric pco2 levels affect climate and thereby the mass balance of continental ice sheets a record of atmospheric co2 variations over the last 160 000 years has recently been constructed by analyzing the trapped gas in the vostok ice core barnola et al 1987 the relationship between changes in atmospheric co2 and the size of the continental ice sheets has been difficult to ascertain because the co2 record is obtained from ice cores while the ice volume record has been constructed from the stable isotopic composition of biogenic caco3 in deep sea sediment cores in order to compare these two records in a more precise manner we present a record of the isotopic composition 18o of atmospheric o2 trapped in the vostok ice core and propose that it may be considered a proxy for the 18o of seawater and hence ice volume having a record of atmospheric co2 along with a continental ice volume proxy in trapped air in the same ice core allows us to compare the timing of changes in these two parameters with little uncertainty in the relative ages of important events our results suggest that during the penultimate glacial termination atmospheric co2 began to increase at least 3 kyr before the initial introduction of meltwater to the oceans possible errors in the relative age depth curve of the vostok ice core and uncertainties in the influence of biological and hydrologic processes on the 18o of atmospheric o2 introduce some uncertainty into our conclusions however our results are in general agreement with the observed phase relationship between atmospheric co2 and ice volume imbrie et al 1984 imbrie et al 1989 inferred from changes in the 13c difference between contemporaneous planktonic and benthic forams deposited in deep sea cores and the specmap ice volume record

from the allerod to the mid holocene palynological evidence from the south basin of the caspian sea pollen and dinoflagellate cysts have been analysed in a core from the south basin of the caspian sea providing a picture of respectively past vegetation and water salinity for the late pleistocene to middle holocene a relatively sharp lithological change at 0 86 m depth reflects a shift from detrital silts to carbonates rich fine silts from this depth upwards a holocene chronology is built based on ten radiocarbon dates on ostracod shells and bulk carbonates from the vegetation point of view the late pleistocene deserts and steppes were partially replaced in the most sheltered areas by an open woodland with pinus juniperus hippophae elaeagnus and even alnus quercus pterocarya and fraxinus related to the allerod palynozone this was interrupted by the younger dryas palynozone when artemisia reaches a maximum in a first instance followed by a very dry phase with only a slight return of pinus and quercus and the rare presence of ulmus zelkova from 11 5 to 8 4 cal ka bp an open landscape dominated by shrubs such as ephedra and progressively increasing quercus appeared the final spread of diverse evergreen and deciduous trees is delayed and occurs after 8 4 cal ka bp it is suggested that this delay is caused by an arid climate in the early holocene linked to high insolation and perhaps to a lake effect the dinocyst assemblages fluctuate between slightly brackish pyxidinopsis psilata and spiniferites cruciformis 7 psu and lower and more brackish impagidinium caspienense w13 psu in the lateglacial khvalynian highstand the assemblages remained dominated by relative low salinity taxa a late and brief increase of salinity occurred prior to 11 2 cal ka bp associated with the mangyshlak lowstand it is suggested that it was caused by a brief drop in meltwater flow from both the north and the southeast uzboy and a likely evaporation increase this lowstand occurs quasi at the same time as the end of a longer lowstand in the black sea the freshest waters are then inferred as having occurred between 8 4 and 4 4 cal ka bp linked to a connection with the amu darya and the melting glaciers on the pamir mountains

volcanic plume heights on mars limits of validity for convective models 1 previous studies have overestimated volcanic plume heights on mars in this work we demonstrate that volcanic plume rise models as currently formulated have only limited validity in any environment these limits are easily violated in the current mars environment and may also be violated for terrestrial and early mars conditions we indicate some of the shortcomings of the model with emphasis on the limited applicability to current mars conditions specifically basic model assumptions are violated when 1 vertical velocities exceed the speed of sound 2 radial expansion rates exceed the speed of sound 3 radial expansion rates approach or exceed the vertical velocity or 4 plume radius grossly exceeds plume height all of these criteria are violated for the typical mars example given here solutions imply that the convective rise model is only valid to a height of 10 km the reason for the model breakdown is that the current mars atmosphere is not of sufficient density to satisfy the conservation equations it is likely that diffusion and other effects governed by higher order differential equations are important within the first few kilometers of rise when the same criteria are applied to eruptions into a higher density early mars atmosphere we find that eruption rates higher than 1 4 109 kg s also violate model assumptions this implies a maximum extent of 65 km for convective plumes on early mars the estimated plume heights for both current and early mars are significantly lower than those previously predicted in the literature therefore global scale distribution of ash seems implausible

recent volcanic activity on venus evidence from radiothermal emissivity measurements abstract most highlands on venus have summit areas that display low radiothermal emissivity this is thought to result from weathering of primary rock which at high altitudes relatively low temperatures produces a distinctive pyrite bearing high dielectric constant mineral asemblage this paper treats exceptions to the rule high emissivity peaks at high altitudes and low emissivity domes at low altitudes which are related to volcanism on venus low emissivity plains domes tend to be spatially correlated with volcanoes having high emissivity summits both phenomena are interpreted to be manifestations of relatively recent volcanism the volcano summits display high emissivity because flows on them are too young to have had time to weather to the low emissivity mineral assemblage and nearby small volcanic domes on the plains are still seeping volcanic gases which permeating the pore space of the plains soil layer make the high dielectric constant pyritic mineral assemblage stable at the higher temperatures of plains altitudes of the volcanoes studied maat mons has undergone the most recent major episode of volcanic activity

volcanism and tectonics on venus we review recent developments in the study of volcanism and tectonics on venus venus s crust is basaltic dry and probably about 30 km thick the mantle convects giving rise to plumes and has a similar composition and mean temperature 1300 c but a higher viscosity 10 20 pa s than that of the earth inferred melt generation rates constrain the lithospheric thickness to between 80 and 200 km the elastic thickness of the lithosphere is about 30 km on average the present day lack of plate tectonics may be due to strong faults and the high viscosity of the mantle most of the differences between earth and venus processes can be explained by the absence of water venus underwent a global resurfacing event 300 600 ma ago the cause and nature of which remains uncertain the present day surface heat flux on venus is about half the likely radiogenic heat generation rate which suggests that venus has been heating up since the resurfacing event

low radar emissivity signatures on venus volcanoes and coronae new insights on relative composition and age abstract multiple studies reveal that most of venus highlands exhibit anomalously high radar reflectivity and low radar emissivity relative to the lowlands this phenomenon is thought to be the result of atmosphere surface interactions in the highlands due to lower temperatures these reactions are a function of rock composition atmospheric composition and degree of weathering we examine the magellan radar emissivity altimetry and sar data for all major volcanoes and coronae on venus we characterize and classify edifices according to the pattern of the variation of radar emissivity with altitude the volcanic highlands can be classified into 7 distinct patterns of emissivity that correspond to at least 3 discrete types of mineralogy based on the altitude temperature of the emissivity anomalies the majority of emissivity anomalies support the hypothesis of a weathering phenomenon at high altitude 6053 km but we also find strong emissivity anomalies at lower altitudes that correspond spatially to individual lava flows indicating variations in mineralogy within an evolving volcanic system the emissivity signature of tallest volcanoes on venus are consistent with the presence of ferroelectric minerals in their rocks while volcanic edifices in western ishtar terra and eastern aphrodite terra are consistent with the presence of semiconductor minerals sapas mons and pavlova corona are also consistent with ferroelectrics but at a different curie temperature than the other volcanoes in atla regio the spatial distribution of radar emissivity classes correlates to different geologic settings indicating that different mantle source regions deep shallow plumes and possible convergence zones may contribute to differences in mineralogy for the studied edifices finally we show that the emissivity signatures of idunn maat and other volcanic edifices are consistent with relatively fresh and unweathered rocks indicating recent or possibly current volcanism on venus

sea level related architectural trends in coarse grained delta complexes distinct stratigraphical styles of delta development can be related to basically different patterns of relative sea level base level change 1 an overall rise with periods of standstill and without significant fall rs 2 an overall rise with superimposed falls rf 3 an overall fall with superimposed rises fr and 4 an overall fall with periods of standstill and no significant rises fs the related stratigraphical models contain either preserved elements of prototype deltas or show characteristic trends in development from one prototype delta into another each stratigraphical model is characterized by lateral and vertical lithofacies features which can be reasonably well established from outcrop in coarse clastic basin margins where age control is poor sedimentological and stratigraphical delta models as presented here may help refining reconstructions of basin fill patterns and basin subsidence kinematics

glacial interglacial evolution of greenhouse gases as inferred from ice core analysis a review of recent results abstract ice core analysis provides the most direct evidence of changes in some major greenhouse gases co2 ch4 and n2o over the climatic cycle covering approximately the last 150 000 years a remarkable overall correlation is observed between the co2 or ch4 record and the climatic changes in the high latitudes of the southern hemisphere with lowest greenhouse gas concentrations found under full glacial conditions in terms of phase relationship co2 and ch4 are roughly in phase with the climatic signal during the deglaciation periods when entering the glaciation ch4 appears to decrease in phase with the antarctic cooling but co2 lags strikingly behind the ch4 record exhibits a marked signal which is most likely associated with the abrupt cooling of the younger dryas existing differences between co2 and ch4 records in comparison with climate reflect differences in sources which are mainly oceanic in the case of co2 and continetal in the case of ch4 for n2o only few data are available suggesting that the n2o concentrations may also have been lower during the last glacial maximum than during the holocene greenhouse gases are likely to have played an important climatic role in amplifying together with continental ice the initial orbital forcing of the glacial interglacial climatic changes

deltaic systems and their contribution to an understanding of basin fill successions s u m m a ry deltaic systems are prominent features of many clastic basin fill successions throughout the geological record and are also important as sites of fossil fuel reserves the process based classification of deltaic systems into fluvial wave and tide dominated types adopted in recent years remains valid but requires additional information on for example the sediment load of the system its position in the basin and the extent of synsedimentary deformation in order to be a meaningful characterization of a delta the range of delta types is further extended by research into ancient deltaic systems which can result in the definition of a non actualistic delta which differs from modern systems this is an important trend which should develop in the future as well constrained ancient systems are characterized to their full extent a further avenue of future research lies in examining the nature of links of deltaic systems to shelf slope and submarine fan systems with particular reference to depositional analysis of seismic stratigraphic information deltaic systems are important elements of many clastic basin fill successions they are important in their own right and have significant links with alluvial shelf slope and deep sea fan systems interpretations of sediment dispersal and deposition in clastic basins are often greatly enhanced if the position character and behaviour of basinmargin delta systems are constrained deltaic successions are also important economically organic rich shales and coals can be important as hydrocarbon source rocks sandstone bodies serve as reservoirs in numerous hydrocarbon provinces and significant coal reserves are hosted in deltaic successions modern and ancient deltaic systems have been extensively researched for many decades with many of the basic principles of sedimentation such as cyclicity facies and sequence analysis being developed and tested in these successions however despite the longevity and high quality of this research important problems still remain the aim of this paper is to review recent progress in deltaic studies and to identify outstanding problems which are currently attracting attention or might do so in the near future the paper commences by considering various aspects of deltas as discrete depositional systems and continues by discussing the links between deltas and other depositional systems in clastic basin fill successions

geomorphic response and 14c chronology of base level changes induced by late quaternary caspian sea mobility middle kura valley azerbaijan abstract recent geomorphological studies in azerbaijan reveal the importance of climato eustatic influences on landscape changes in the caspian sea basin during the last 40 ka radiocarbon dated fluvial landforms show that the paleohydrosystem of the middle kura valley and tributaries responded to regressive and transgressive phases of the caspian sea chrono sequences and landforms secured by 32 radiocarbon ages show strong correspondence between fluvial sediment accumulation and oscillations of base level in the caspian sea six phases of valley floor aggradation e g 27 000 13 000 11 000 3200 2900 2100 1600 1000 400 150 cal yr bp and seven phases of fluvial incision 37 000 37 000 27 000 13 000 11 000 3200 2900 2100 1600 1000 400 150 0 cal yr bp are recorded morphodynamics of the fluvial landscape show a strong correspondence with fluctuation in sea levels in the caspian sea the major upper pleistocene late glacial khvalynian c a 26 000 to 12 400 cal yr bp and various holocene transgressions as well as the mangyshlak c a 12 000 cal yr bp and derbent 6th 12th century ad regressions these data contribute to refining the caspian relative sea level curve for the last 30 ka using the chronology of changes in the aggradation or incision in the connected fluvial system

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

vostok ice core climatic response to co2 and orbital forcing changes over the last climatic cycle vostok climate and co2 records suggest that co2 changes have had an important climatic role during the late pleistocene in amplifying the relatively weak orbital forcing the existence of the 100 kyr cycle and the synchronism between northern and southern hemisphere climates may have their origin in the large glacial interglacial co2 changes

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

the wandering of the volga delta a response to rapid caspian sea level change due to its very low gradient and absence of tide and surf the volga delta is an even more extreme example of the fluvially dominated type than the mississippi delta however it differs from all other large delta systems in that it borders a closed basin the caspian sea now at 26 m below global sea level caspian sea level is much more dynamic than that of the world oceans and rises at present about 1 5 cm yr a hundred time the eustatic rate within the quatemary sea level oscillations of at least 5 orders of magnitudes have been distinguished which seem grossly out of phase with eustatic sea level between the weichselian early khvalyn highstand of 50 m and the early holocene mangyshlak lowstand at 80 m the apex of the volga delta has wandered over 700 km alongstream the present day volga delta is not a highstand deposit but probably represents a minor transgression in a major regressional stage the delta does not show a coarsening upwards sedimentary sequence but consists of a weichselian transgressional fining upwards sequence topped by eolian deposits in which the delta distributary channels have been incised present day sedimentation is limited to a narrow fringe along the delta front and to deeper waters over 200 km offshore sea level changes outpaced aggradation to such an extent that volga sediment is spread over the whole north caspian plain sequence stratigraphical principles are difficult to apply because sea level cycles of five orders of magnitude are superimposed and because there is not enough sediment loading or tectonic subsidence to create sufficient accommodation space

rapid holocene sea level changes along the iranian caspian coast abstract the caspian sea is well known for its rapid sea level change during 1929 1995 a full sea level cycle was observed first the sea level dropped 3 m with a lowstand in 1977 followed by a 3 m rise to 1995 after which the sea level has been relatively stable these oscillations are a specific feature of the caspian sea and its sedimentary record the main purpose of this study is to reconstruct the sea level curve in the holocene by using sedimentological and biostratigraphic analysis and radiocarbon dating along the iranian part of the caspian shore remote sensing images and historical maps show that two lagoons totally emerged and the gorgan delta prograded rapidly at a rate of around 160 m y 1 until the 1975 lowstand gorgan bay was reduced in size considerably and the connection to the sea was blocked due to growth of a spit and change in base level when sea level started to rise again the coastal morphology rapidly changed and the gorgan delta retrograded at the rate of around 140 m y 1 these sedimentary dynamics can be recognized in the preserved deposits in addition to the recent dynamics core data from the southeastern lowlands show four earlier highstands using characteristic barrier lagoon deposits early holocene sea level rose until a highstand was reached of ca 34 m this phase was followed by fluvial deposition in the gorgan delta associated with a base level fall there is also an evidence of sea level rise between 5000 and 2300 bp at ca 27 7 m on top of these deposits there is evidence of a highstand between 2700 and 2300 bp at ca 23 5 m the fourth highstand from the core data is dated to the little ice age at ca 24 m data from these last two highstands correspond well with other observations from the caspian region

effects of volcanic eruptions on the co2 content of the atmosphere and the oceans the 1996 eruption and flood within the vatnajokull glacier iceland abstract the october 1996 eruption within the vatnajokull glacier iceland provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic co2 volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption enabling measurement of 50 dissolved element fluxes the minimum concentration of exsolved co2 in the 1 1012 kg of erupted magma was 516 mg kg s was 98 mg kg cl was 14 mg kg and f was 2 mg kg the ph of the meltwater at the eruption site ranged from about 3 to 8 volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes equal to 0 1 of the mass of erupted magma the total dissolved solid concentration in the floodwater was close to 500 mg kg ph ranged from 6 88 to 7 95 and suspended solid concentration ranged from 1 to 10 according to h o c and s isotopes most of the water was meteoric whereas the c and s were of magmatic origin both c and s went through isotopic fractionation due to precipitation at the eruption site creating short cuts in their global cycles the dissolved fluxes of c ca na si s and mg were greatest ranging from 1 4 1010 to 1 4 109 mol the dissolved c flux equaled 0 6 million tonnes of co2 the heavy metals ni mn cu pb and zn were relatively mobile during condensation and water rock interactions at the eruption site about half of the measured total carbon flood flux from the 1996 vatnajokull eruption will be added to the long term co2 budget of the oceans and the atmosphere the other half will eventually precipitate with the ca and mg released thus for eruptions on the ocean floor one can expect a net long term c release to the ocean of less than half that of the exsolved gas this is a considerably higher net c release than suggested for the oceanic crust by staudigel et al geochim cosmochim acta 53 1989 3091 in fact they suggested a net loss of c therefore magma degassed at the ocean floor contributes more c to the oceans and the atmosphere than magma degassed deep in the oceanic crust the results of this study show that subglacial eruptions affecting the surface layer of the ocean where either mn fe si or cu are rate determining for the growth of oceanic biomass have a potential for a transient net co2 removal from the ocean and the atmosphere for eruptions at high latitudes timing is crucial for the effect of oceanic biota eruptions occurring in the wintertime when light is rate determining for the growth of biota have much less potential for bringing about a transient net negative co2 flux from the ocean atmosphere reservoir

large scale volcanic activity at maat mons can this explain fluctuations in atmospheric chemistry observed by pioneer venus magellan and pioneer venus orbiter pvo found high mountain terrains on venus 2 5 km above 6051 km planetary radius exhibit anomalously low radiothermal emissivity this is thought to result from weathering of primary venus rock which at high altitudes produces a distinctive high dielectric constant mineral assemblage deviations from the nominal altitude emissivity pattern have been used as a crude chronometric tool with which to date venusian landforms this technique indicates maat mons an unusually large shield volcano standing 9 17 km above 6051 km planetary radius at 2 1 n 194 3 e has undergone a recent episode of large scale volcanic activity a deduction also implied morphologically the present paper investigates whether a plinian eruption at maat mons could explain the enhanced concentrations of so2 gas in the upper atmosphere of venus that were detected by the pioneer venus uv spectrometer the results show for a minimum vent radius of 156 m a minimum eruption temperature of 1200 k and a magmatic volatile content of 5 wt a plinian eruption at the summit of maat mons can explain the anomalous concentration of so2 gas this would mean maat mons is an active volcano

surface processes in the venus highlands results from analysis of magellan and arecibo data the highlands of venus are characterized by an altitude dependent change in radar backscatter and microwave emissivity likely produced by surface atmosphere weathering reactions we analyzed magellan and arecibo data for these regions to study the roughness of the surface lower radar backscatter areas at the highest elevations and possible causes for areas of anomalous behavior in maxwell montes arecibo data show that circular and linear radar polarization ratios rise with decreasing emissivity and increasing fresnel reflectivity supporting the hypothesis that surface scattering dominates the return from the highlands the maximum values of these polarization ratios are consistent with a significant component of multiple bounce scattering we calibrated the arecibo backscatter values using areas of overlap with magellan coverage and found that the echo at high incidence angles up to 70 from the highlands is lower than expected for a predominantly diffuse scattering regime this behavior may be due to geometric effects in multiple scattering from surface rocks but further modeling is required areas of lower radar backscatter above an upper critical elevation are found to be generally consistent across the equatorial highlands with the shift in microwave properties occurring over as little as 500 m of elevation these surfaces are not simply characterized however by the absence of a highly reflective component surface morphology and radar scattering properties suggest that a mantling deposit forms at the highest elevations most likely by in situ erosion of the original rock in ovda regio this process mantles or has removed surface festoon structure at the 1 to 10 m scale implying a significant depth for the weathered layer similar radar dark areas occur in maxwell montes but are apparently unrelated to the current topography of the region possible reasons for these observations include mass wasting from areas of steep slopes compositional or age differences within the montes vertical tectonic shifts of relict contacts local topographic effects on surface temperature or errors in the magellan topography data in the rugged terrain while there is evidence for some of these effects in the existing data no single model at present appears to satisfy all occurrences of high altitude radar dark terrain new measurements of the surface and lower atmosphere chemistry of venus are needed to further refine these conclusions

fluvial response to an historic lowstand of the great salt lake utah understanding fluvial adjustments to base level changes benefits the fields of sequence stratigraphy geomorphology and petroleum geology this investigation is a modern case study of the channel dynamics of lee creek and the goggin drain two streams that are part of the jordan river drainage into the endorheic great salt lake of northern utah a lacustrine system that has experienced multiple decadal scale base level changes since 1965 the lake level has fluctuated in elevation more than 6 m transitioning from an historic lowstand 1284 m a s l and in 2009 2010 approaching an historic lowstand this study uses detailed aerial images fieldwork and lidar data to link the modern geomorphology and channel hydraulics to specific variations in sediment transport channel form and avulsion behavior although lee creek and the goggin drain are situated only a few kilometers apart and share similar shore zone gradients substrates and vegetation patterns and have been subjected to the same changes in lake level their channel forms have evolved very differently differences in discharge patterns are likely the most influential factor causing the meandering form of lee creek and the braiding channel of the goggin drain despite the differences in discharge total sediment eroded from the two streams is comparable and can be attributed to similar stream power unit stream width in the two streams although lee creek has not recently been avulsive three major avulsions of the goggin drain have taken place since 1965 two possible styles of avulsion are interpreted an allogenic response to changing base level and an autogenic response dictated by channel morphology and hydraulics despite a wealth of available information avulsions cannot be unequivocally attributed to one style or another caution should be used when attempting to link the complex process of avulsion to causal mechanisms copyright 2011 john wiley sons ltd

cyclic water level oscillations of the karabogazgol caspian sea system abstract the karabogazgol kbg water level oscillations were reconstructed in the last 200 years using the geochemical evolution of the uppermost meter of its sedimentary infill high resolution studies of the mineralogical composition of the kbg sediments show alternating periods of high concentration brines followed by periods of more dilute waters the relative water level reconstruction was based on statistical models factor analysis fa correspondence analyses ca and detrended correspondence analyses dca whilst the chronological framework was established using the 210 pb technique this reconstruction was compared with the instrumental water level record of the caspian sea showing a high degree of correlation r 2 0 83 the agreement between the reconstructed and the measured water level oscillations of the caspian sea indicates that environmental changes can be reconstructed from closed lakes provided that an accurate chronological control of sedimentary processes is available the water level reconstruction shows that the caspian sea water level fluctuations follow a cyclical pattern rather than an erratic one as has been suggested in the literature two main periodicities of 62 5 and 38 46 years have been found

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

transport of so2 by explosive volcanism on venus observations by the pioneer venus orbiter and many different types of analyses have suggested the possibility of contemporary explosive volcanism on venus the rise of volcanic eruption plumes on venus is reexamined using recent improvements in buoyant plume modeling the first order model applied to venus by previous authors features nonphysical discontinuous solutions for all of the model parameters and lacks internal consistency in the formulation of the governing equations this makes it difficult to assess the validity of the venus applications and conclusions derived from these models the model used here contains several improvements including two corrections to the formulation and a change in the criterion for the transition of the plume from the jet region to the buoyancy driven region the model used in earlier works assumed a discontinuous transition between these two regions resulting in an overestimate of the transition height as well as the maximum plume height the effect of the transition criterion is magnified on venus where the continuous solution appears to have very little dependence on initial vent size in contrast the discontinuous solution shows a very strong dependence on initial vent size the continuous solution used here indicates that plumes on venus become dominated by buoyancy effects almost immediately above the vent use of the discontinuous solution however suggests that jets up to 10 km above the vent are possible for the boundary conditions considered the combined effect of using the older model for conditions on venus is a 5 8 overestimate of the maximum plume height for vent radii ranging from 20 to 250 m the influence of latitude and elevation are also explored for large eruptions on venus plumes rising in the northern highlands would rise much higher than plumes with identical boundary conditions erupted in the equatorial lowlands this is due to the greater stability of the upper atmosphere at higher latitudes and the sharp decrease in atmospheric pressure as a function of altitude to examine the net effect of all the model assumptions and ambient influences eruptions are simulated for a range of conditions at maat mons and compared with results in the literature these simulations indicate that for small mass fluxes the new model predicts smaller plumes than the older model for larger mass fluxes however the new model predicts larger plumes than the older model because the maat mons summit elevation is already more than 9 km above the mean planetary radius the reduced atmospheric pressure results in a plume with enough buoyancy to more than compensate for all of the model effects these results continue to support the possibility that explosive eruptions on venus may be capable of producing plumes that rise buoyantly to heights detected by the pioneer venus orbiter

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

base level changes river avulsions and holocene human settlement dynamics in the caspian sea area middle kura valley south caucasus abstract geomorphological geochronological and geoarchaeological analysis focusing on six tributaries of the kura river provide valuable data concerning sedimentation rhythmicity and holocene human settlement distribution at a regional scale seven new radiocarbon dates from the upstream part of these hydrosystems complemented the existing radiocarbon dataset n 32 obtained downstream these data seem to indicate that upstream hydrosystems also reacted to marine regressions by powerful riverbed incisions and to transgression phases by thick valley infillings from at least as early as the upper pleistocene the retroactive morphogenic effects were also perceived in intra mountainous areas far from the caspian shoreline the land use patterns of the caucasian societies dwelling in the valley of the kura hydrosystem were affected by temporary river avulsions resulting in silty fans over the high terraces during the neolithic chalcolithic periods these river avulsions seem to be governed by local climate and base level changes linked to fluctuations of the caspian sea level over time this is spatially and diachronically evidenced in settlement distribution with almost exclusive localization on perched silty fans and river runoff from the key period of neolithic development in the region these new data must be considered in future geoarchaeological analyses concerning the caspian sea basin and will contribute to the enhancement of the relative caspian sea level curve for the past 40 ka

north atlantic control on precipitation pattern in the eastern mediterranean black sea region during the last glacial based on proxy records from western black sea cores we provide a comprehensive study of climate change during the last glacial maximum and late glacial period in the black sea region for the first time we present a record of relative changes in precipitation for nw anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration the good correspondence between reconstructed rainfall intensity in nw anatolia and past western mediterranean sea surface temperatures ssts implies that during the glacial period the precipitation variability was controlled like today by mediterranean cyclonic disturbances periods of reduced precipitation correlate well with low ssts in the mediterranean related to heinrich events h1 and h2 stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater sediment source concomitant to the meltwater inflow after 16 4 cal ka bp this change implies intensification of the northern sediment source and with other records from the mediterranean region consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the european continent the early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the mediterranean region leading simultaneously to more humid conditions in central and northern europe

venus volcanism initial analysis from magellan data magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of venus high resolution imaging data reveal evidence for intrusion dike formation and cryptodomes and extrusion a wide range of lava flows also observed are thousands of small shield volcanoes larger edifices up to several hundred kilometers in diameter massive outpourings of lavas and local pyroclastic deposits although most features are consistent with basaltic compositions a number of large pancake like domes are morphologically similar to rhyolite dacite domes on earth flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas perhaps komatiites may be present volcanism is evident in various tectonic settings coronae linear extensional and compressional zones mountain belts upland rises highland plateaus and tesserae volcanic resurfacing rates appear to be low less than 2 km 3 yr but the significance of dike formation and intrusions and the mode of crustal formation and loss remain to be established