shallow virtual source redatuming by multi dimensional deconvolution recently new on shore acquisition designs have been presented with multicomponent sensors deployed in the shallow sub surface 20 m 60 m virtual source redatuming has been proposed for these data to compensate for surface statics and to enhance survey repeatability in this paper we investigate the feasibility of replacing the correlation based formalism that undergirds virtual source redatuming with multi dimensional deconvolution offering various advantages such as the elimination of free surface multiples and the potential to improve virtual source repeatability to allow for data driven calibration of the sensors and to improve robustness in cases with poor sensor spacing in the shallow sub surface resulting in a relatively high wavenumber content we propose a new workflow for this configuration we assume a dense source sampling and target signals that arrive at near vertical propagation angles first the data are preconditioned by applying synthetic aperture source filters in the common receiver domain virtual source redatuming is carried out for the multi component recordings individually followed by an intermediate deconvolution step after this specific pre processing we show that the downgoing and upgoing constituents of the wavefields can be separated without knowledge of the medium parameters the source wavelet or sensor characteristics as a final step free surface multiples can be eliminated by multi dimensional deconvolution of the upgoing fields with the downgoing fields

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

extensional fault control on the sedimentation patterns in a continental rift basin el castellar formation galve sub basin spain in the galve sub basin the sedimentary record of the upper hauterivian lower barremian el castellar formation is divided into two stages by a marlstone interval with gypsum stage 1 shows a great variety of subenvironments and facies alluvial palustrine and lacustrine whereas in stage 2 an extensive shallow carbonate lake developed sedimentation was controlled by a system of south dipping ene wsw listric normal faults laterally bounded by nnw sse steeper transfer faults faults controlled sedimentation from a basin scale basin margins and main characteristics and evolution of sediments to a regional and a local scale thickness and facies distribution of the synrift series as well as the location and evolution of lakes and minor alluvial fans the changes between stages 1 and 2 are related to the passing from an independent movement of faults to the movement of all the extensional faults as a whole at a sole detachment level the interval with gypsum was caused by underground water flow changes associated with the interrelation and connection of the faults in the transition period these changes have been correlated with the transition from the rift initial stage to the rift climax stage which took place in the hauterivian barremian transition

linking lacustrine cycles with syn sedimentary tectonic episodes an example from the codo formation late aptian northeastern brazil the codo formation exposed in the eastern grajau basin northeastern brazil consists mostly of black shales limestones and evaporites arranged into several shallowing upward cycles formed by progradation of lake deposits three ranks of cycles are distinguished the lower rank cycles correspond to millimetric interbeddings of bituminous black shales with evaporites calcimud stones or peloidal wackestone packstone grey green shale with calcimudstone peloidal wackestone packstone or ostracodal wackestone grainstone and ostracodal wackestone grainstone and or calcimudstones with cryptomicrobial mats and ooidal pisoidal packstones the intermediate rank cycles average 1 7 m in thickness and are formed by complete and incomplete cycles complete cycles show a transition from central to intermediate and then to marginal facies associations and include two types c1 cycle with central lake deposits consisting of evaporites and black shales and c2 cycle with central lake deposits formed by grey green shale complete cycles were produced by the upward gradation from central to marginal environments of the lake or saline pan sabkha system incomplete cycles are those where at least one facies association is lacking having been formed by successions either with central and intermediate facies associations i1 or intermediate and marginal facies associations i2 the higher rank cycles are on average 5 2 m thick and consist of four depositional units that display shallowing upward successions formed by complete and incomplete intermediate rank cycles that vary their distribution upward in the section and are bounded by sharp surfaces while the lower rank cycles display characteristics that reveal their seasonal signature detailed sedimentological characterization and understanding of stratal stacking patterns related to the intermediate and higher rank cycles support a genesis linked to syn sedimentary tectonic activity this is particularly suggested by the high facies variability limited lateral extension and frequent and random thickness changes of the intermediate rank cycles additionally the four higher rank cycles recognized in the codo formation match with stratigraphic zones having different styles of soft sediment deformation structures attributed to seismic activities therefore the several episodes of lake shallowing recorded in the codo formation are linked to seismic pulses that alternated with sediment deposition this process would have created significant changes in the lake water level and resulted in sharply bounded successions with upward gradation from deeper to relatively shallower facies associations

source receiver interferometric redatuming using sparse buried receivers to address complex near surface environments a case study of seismic imaging quality and time lapse repeatability

controls on marine erg margin cycle variability aeolian marine interaction in the mid cretaceous iberian desert system spain the interaction between aeolian dunes of the iberian erg and tethys waters during the mid cretaceous led to a variety of sedimentary facies associations such as subtidal deposits aeolian dunes playa lakes coastal lakes with tidal creeks and marshes and lagoonal embayments with tide influenced delta deposits facies associations are organized in several stacked cycles every cycle is defined by a sand drift surface separating playa lake deposits below from aeolian dune deposits above followed by a transgressive surface separating aeolian deposits below from shallow marine deposits above the latter are covered by playa lake deposits and finally topped by the next sand drift surface similar marine erg margin cycles have been explained previously in terms of high order relative sea level variations normally controlled by glacioeustasy the studied erg margin developed during the mid cretaceous which is considered to be the archetypal example of a polar ice free greenhouse period this manuscript presents an alternative explanation for the cycles as caused by climate induced variations in the aeolian sediment supply in this scenario orbitally induced latitudinal shifts of the boundary between climate belts led to alternating periods of increased and decreased precipitation in the highland catchments of the back erg system variscan iberian massif when climate belts shifted to lower latitudes back erg highlands were under the influence of the northern warm humid belt while arid conditions prevailed in the lowland central erg increased precipitation in the highlands and the consequent recharge of ground water led to a rise of the phreatic level in the erg system that diminished wind erosion and windblown sediment input to the fore erg so that the desert margin contracted with ongoing basin subsidence this favoured the transgression the increased desert ground water flux favoured permanent coastal lakes in the fore erg margin and the local development of vegetation in places where such lakes lagoons were connected to the sea tidal channels were active as seen nowadays along the desert coast of qatar persian gulf when climate belts moved to higher latitudes the catchment areas in the back erg iberian massif were under the influence of the northern hot arid belt and a decrease of precipitation led to a drop of the phreatic level allowing deflation of dunes and exposed wadi channel floors and the formation of desert pavements and deflation lags in the back erg area this favoured the import of large volumes of windblown sand and dust forcing progradation of the erg and consequently a retreat of the coastline the sand fraction accumulated in climbing aeolian dunes and dust was trapped in extensive playa lake systems another long term allocyclic control is formed by active extensional tectonics that enhanced the creation of accommodation space especially in the first cycle a high ground water table sustained by subsurface water supply from the variscan iberian massif generated coastal fresh brackish lakes in which tide influenced meandering channels and salt marshes developed erg margin cycles thin upward in response to a decrease of the rate of basin subsidence suggesting that transgressions led to deep erosion of the underlying aeolian dune sands

improving imaging and repeatability on land using virtual source redatuming with shallow buried receivers abstracttime lapse surface seismic monitoring typically suffers from different sources of nonrepeatability related to acquisition imperfections as well as due to complexity of the subsurface placing sources and receivers below the surface can improve seismic data repeatability however it is not always possible to bury a large number of sources and therefore the next best option is monitoring with surface sources and buried sensors we have discovered that redatuming of surface sources to the shallow buried receivers produced a reliable image of target reflectors despite the fact that receivers were placed in the near field zone of the source we redatumed data with the virtual source method using crosscorrelation of the measured wavefields we found that redatuming also reduced nonrepeatability of seismic data associated with changes in acquisition geometry variable source coupling and daily seasonal variations in the near surface we developed these results with a synthetic case study using a reali

astronomical forcing of sedimentary cycles in the middle to late miocene continental calatayud basin ne spain abstract a high resolution cyclostratigraphic and magnetostratigraphic study was carried out on cyclically bedded successions of middle miocene lacustrine to distal alluvial fan floodplain deposits from the calatayud basin in northeast spain eight partially overlapping subsections near the village of orera are correlated in detail using distinct sedimentary cycle patterns or by following marker beds in the field together they form the orera composite section ocs sedimentary cycles are recognised on at least two different scales the basic small scale cycles in the ocs consist of an alternation of grey and occasionally red clays with white dolomite rich carbonate beds they are arranged in larger scaled so called large scale cycles based on repetitive changes in the overall carbonate clay lithology two other but less distinct types of intermediate scale cyclicity are also recognised in terms of depositional environment the cycle hierarchy is interpreted to represent periodic lake expansion over the palaeo alluvial fan floodplain area the palaeomagnetic results yield a reliable magnetostratigraphic record which confirms the cyclostratigraphic correlations between the subsections in detail rock magnetic experiments reveal that haematite is the main magnetic carrier of the primary component the magnetostratigraphy of the ocs is correlated straightforwardly with the geomagnetic polarity time scale this resulted in an age of 10 7 12 8 ma for the entire succession which is supported by fossil micromammal findings in addition it also reveals the presence of two possibly three short new polarity intervals based on the number of cycles in the ocs the average periodicity of the basic small scale cycles is approximately 23 000 yr while the large scale cycle indicates a periodicity of 400 000 yr this suggests that these sedimentary cycles are controlled by astronomically induced climate changes causing lake level fluctuations and thus resulting in the deposition of carbonate clay cycles the continental sequences of the ocs provide a unique opportunity to extend the astronomical polarity time scale into the middle miocene the overlap of such continental sequences in the mediterranean area with time equivalent astronomically induced marine sequences is fundamental for establishing marine continental bed to bed correlations and for understanding regional climate change

climatic vs tectonic signals in a continental extensional basin teruel ne spain from stable isotope δ18o and sequence stratigraphical evolution alluvial fans and shallow carbonate lakes interfered in the teruel half graben during the late miocene pliocene tectonic influence is recorded in alluvial and lacustrine palustrine successions with long term climate changes being recorded in detail in the isotopic signatures of carbonates episodes of tectonic activity induced alluvial fan progradation and lake retraction in the whole basin three lacustrine stages have been identified which support the idea that climate also exerted an important control on sedimentation the transition between stages 1 and 2 occurred during a tectonically calm episode due to an increase in aridity in the early turolian small fans with source areas next to the lake margin prograded inducing lake shore retraction the transition from stage 2 to 3 was caused by the superimposition of increasing tectonic activity and aridity effects our study demonstrates that discrimination of allogenic factors controlling sedimentation in continental closed basins is possible using sequence stratigraphy in combination with other techniques such as geochemistry of carbonates

cyclicity of triassic to lower jurassic continental red beds of the argana valley morocco implications for palaeoclimate and basin evolution abstract cyclical playa deposits form a prominent part of the continental clastic succession of the argana valley western high atlas of morocco the red beds formed in triassic to lower jurassic times during rifting of the north american and african plates detailed stratigraphic work revealed asymmetrical metre scale cycles in mudstone dominated successions that constitute the intermediate and upper portion of the basin fill sedimentary cycles commonly comprise ephemeral lake shales at the base playa mudflat mudstones in the intermediate part and both fluvial and aeolian sandstones at the top cycles of the aglegal member t4 are mainly characterized by analcime rich playa mudflat deposits displaying features indicative of palaeo vertisols cycles of the sidi mansour t7 and hasseine t8 members are represented by ephemeral lake or dry playa mudflat deposits grading into saline mudflat mudstones that are overlain by sheet flow and minor aeolian sandstones sedimentary cycles of the imerhrane member t9 comprise sheet delta sandstones at the base overlain by ephemeral lake and dry playa mudflat mudstones upper cycle portions consist of aeolian dune and sand sheet sandstones cyclicity is attributed to palaeoclimatic and associated palaeohydrological fluctuations probably within the milankovitch frequency band sedimentary facies of each cycle provide evidence for a gradual climatic drying with time the asymmetrical drying upward cycles possibly record the precession cycle since they are modulated by symmetrical i e oscillating drying wetting cycles of a lower frequency indicative of eccentricity a long term change in palaeoclimate ranging from semi arid conditions with seasonal precipitation t4 towards an arid non seasonal climate t8 is preserved within the cyclical units spanning a time interval of several million years individual cycles can be traced laterally for tens of kilometres correlative sections are almost identical in thickness suggesting a phase of tectonic quiescence during their deposition sediment accumulation was not restricted to small scale grabens but took place continuously throughout the exposed area of the argana valley implying that accommodation space has not been controlled by syndepositional tectonism

climate driven cyclicity in an early cretaceous synrift lacustrine series aguilon sub basin ne spain terra nova 24 407 416 2012 abstract lacustrine sedimentation is very sensitive to climate changes and its cyclicity analysis allows a better quantitation of the time of sedimentation than other methods climate and tectonic influence on sedimentation in a synrift basin is interpreted from the spectral analysis of a 49 m thick series which includes 88 deepening shallowing lacustrine cycles the interpreted position of the different facies with respect to the palaeolake shoreline and the depth of deposition are used as input for spectral analysis to recognise a clear climate signal it was necessary to eliminate the thicker cycles from the analysis results show power spectrum maxima confidence level 99 at 199 47 and 15 cm the first two are interpreted as representing short eccentricity and precession cycles respectively the 88 deepening shallowing cycles thus would reflect the influence of precession thicker cycles reflect short episodes with a significant increase of accommodation space due to synsedimentary tectonics

model based radiation pattern correction for interferometric redatuming in 4d seismic interferometric virtual source vs redatuming converts surface triggered source records into the equivalent records as if they originated from buried receiver locations by crosscorrelating downgoing waves with the corresponding upgoing waves theory suggests that when the receivers are surrounded by an enclosing boundary of sources then the vs has an isotropic radiation pattern and yield accurate response the resultant records should show improving the seismic repeatability and image quality comparing with non vs however in the presence of complex near surface intricate shallow structure and highly variable weathering layers can severely distort the ray path such that it produces the uneven angle coverage to the buried vs additionally near surface reverberations surface multiples and other mode converted waves may leak into the time gated early arrivals and further corrupt the direct wavefields abovementioned issues can result in distorted radiation patterns and contaminated responses of the v

astronomical climate control on paleosol stacking patterns in the upper paleocene lower eocene willwood formation bighorn basin wyoming the willwood formation of the bighorn basin wyoming usa is a thick succession of upper paleocene and lower eocene fluvial floodplain sandstones and mudstones reddish paleosols formed on the floodplain mudstones alternate rhythmically on various scales with heterolithic intervals of small channel sandstones and mudstones showing weak pedogenesis spectral analysis of redness in the willwood successions at polecat bench and red butte reveals significant spectral peaks corresponding to cycle thicknesses of 8 and 3 m the 8 m cycle reflects distinct clusters of 3 5 paleosols age constraints show that the period of this cycle closely matches the 21 k y climatic precession cycle the 3 m cycle corresponds to individual paleosols with a period of 7 8 k y this period is similar to millennial scale sub milankovitch cycles found in marine and lacustrine successions of pliocene pleistocene age precession and millennial scale climate variations probably affected paleosol development through cyclic changes from predominantly overbank to predominantly channel avulsion deposition with the latter periodically halting soil formation because of high sediment accumulation a new age model was developed for the paleocene eocene carbon isotope excursion cie at polecat bench based on the precessional origin of paleosol clusters the main body of the cie spans 5 5 precession cycles or 115 k y and the recovery tail of the cie spans 2 precession cycles or 42 k y this outcome is consistent with and independently confirms recent estimates of cie duration based on deep sea cores

refinement of the messinian apts from sedimentary cycle patterns in the lacustrine lava section servia basin nw greece a high resolution cyclostratigraphy and magnetostratigraphy is presented for the messinian lacustrine lava section from the servia basin in nw greece constraining more precisely the absolute ages of magnetic polarity subchrons c3an 1n and c3an 2n the section contains 15 distinct sedimentary cycles of alternating dark and light coloured marls while the gamma ray attenuation record reveals an additional five to six cycles the cycles in the lower half of the section are on average 5 3 m thick as opposed to the cycles in the upper part which have an average thickness of 3 1 m palynological results define the lithological alternations in both the lower and upper cycles in terms of periodic changes in humidity where the light marls represent the humid periods and the dark marls the relatively dry periods changes in cycle thickness and shifts in average gamma ray values suggest a rather abrupt decrease in sedimentation rate at v60 m in the section this is confirmed by the magnetostratigraphy which recorded four reversals which given the biostratigraphic constraints from the lava locality could be correlated unambiguously to subchrons c3an 1n and c3an 2n of the geomagnetic polarity time scale with this magnetostratigraphic time control the average duration of the cycles can be calculated to be constant in the entire section and similar to precession the astronomical origin of the cycles is confirmed by the results of spectral analyses of gamma ray and susceptibility time series the sedimentary cycles in the upper part of the lava section are unambiguously tuned to insolation using the typical clustering of the cycles that follows the eccentricity cycle the filtered gamma ray record centred at 41 kyr confirms the tuning in the upper part and allows tuning of the lower part the tuning results in accurate ages for the sedimentary cycles and polarity reversals that confirm the astronomical tuning of krijgsman et al nature 400 1999 652 655 but define more precisely the astronomical polarity time scale fl 2000 elsevier science b v all rights reserved

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

oligo miocene lacustrine microbial and metazoan buildups from the limagne basin french massif central the limagne basin french massif central is an extensive continental lacustrine system accommodating microbial and metazoan buildups from chattian to aquitanian age a description of these buildups and their associated biotic components in grand gandaillat and crechy quarries provides insights into their spatio temporal distribution patterns flats cauliflowers domes cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated columnar filamentous and caddisfly coated microfabrics two low gradient margin models emerged based on the changes in the distribution morphology and size of the microbial and metazoan rich deposits through time the first model applies to the chattian deposits in the grand gandaillat quarry and the second to the aquitanian deposits in the crechy quarry this study emphasizes the heterogeneity of marginal lacustrine carbonate siliciclastic cycles the lacustrine palustrine cycles of the limagne basin record i lacustrine deposits composed of microbial and metazoan buildups and organic matter rich marls indicating periods of high accommodation and ii palustrine deposits composed of mudstone and clayey paleosoils indicative of periods of low accommodation the cycles differ with thin and symmetrical deposits that dominate the chattian cycles whereas thicker and asymmetrical deposits mark the aquitanian cycles in addition the chattian buildups are exclusively microbial and only a few centimeters thick whereas the aquitanian ones are multiple meters in height and are composed of both microbes and metazoans climatic tectonism volcanic and local parameters are involved in the deposition of buildups and their organization in each different cycle climate may control the long term arid humid sedimentary succession tectonic may explain the difference in the deposit thickness between two cycles of different ages and localizations as well as the specific distribution of the buildups throughout the basin volcanism may control the chemical lacustrine conditions and local physiography may impact the soil removal ability of the lake margin

modelling hyperconcentrated flow in the yellow river a large amount of the total sediment load in the chinese yellow river is transported during hyperconcentrated floods these floods are characterized by very high suspended sediment concentrations and rapid morphological changes with alternating sedimentation and erosion in the main channel and persistent sedimentation on the floodplain however the physical mechanisms driving these hyperconcentrated floods are still poorly understood numerical modelling experiments of these floods reveal that sedimentation is largely caused by large vertical concentration gradients both in the channel during the rising stage of the flood as well as on the floodplains during a later stage of the flood these vertical concentration gradients are large because the turbulent mixing rates are reduced by the increased sediment induced density gradients resulting in a positive feedback mechanism that produces high deposition rates erosion prevails when the sediment is largely held in suspension due to hindered settling and is strengthened by the reduced wetted cross section caused by massive sedimentation on the floodplain observed patterns of erosion and sedimentation during these floods can be qualitatively reproduced with a numerical model in which sediment induced density effects and hindered settling are included copyright 2009 john wiley sons ltd

lacustrine system evolution during early rifting el castellar formation galve sub basin central iberian chain abstract a detailed sedimentological study of the first synrift deposits recorded in the galve sub basin of ne spain during the early cretaceous aided in the reconstruction of climatic and tectonic influences the el castellar formation is composed of siliciclastics and carbonates unit 1 claystones gypsum and carbonates unit 2 and marls and limestones unit 3 unit 1 facies formed in alluvial and palustrine plains a local alluvial fan and low energy shallow lake subenvironments low energy lacustrine facies characterised unit 2 in contrast palustrine low and high energy lake facies were identified for unit 3 the spatial and temporal distribution of lithofacies representing the several environments were used to propose a general lacustrine system evolution from isolated ponds and marshes to low energy shallow lakes and finally to an extensive high energy lake lake evolution is related to changes in the subsidence pattern from local to basin scale subsidence which was ultimately related to the transition from the initial rift to rift climax stage shallowing upwards lacustrine successions have been interpreted as climatically forced and linked to sediment and water supply both tectonics and climate determined the change from an overfilled to a balanced fill lake basin through time

magnetostratigraphy based astronomical tuning of the early pliocene lacustrine sediments of ptolemais nw greece and bed to bed correlation with the marine record continental deposits from the early pliocene lacustrine ptolemais basin in nw greece display rhythmical alternations of lignite and marl beds three parallel sections from this area are studied using magnetostratigraphy and cyclostratigraphy the presence of the greater part of the gilbert chron enables the recognition of astronomical periodicities in the succession especially the precessional influence is evident as it determines the lithological cycles the continental ptolemais composite section is correlated to the most recent astronomical time scale and thus to the marine reference section the rossello composite from sicily c g langereis f j hilgen the rossello composite a mediterranean and global reference section for the early to early late pliocene earth planet sci lett 104 1991 211 225 on a bed to bed scale it is concluded that lignite corresponds to an insolation minimum beige layer in the rossello composite and marl to an insolation maximum grey layer in the rossello composite this implies a precipitation increase during insolation maxima in early pliocene continental greece 1998 elsevier science b v all rights reserved

strengthening the virtual source method for time lapse monitoring time lapse monitoring is a powerful tool for tracking subsurface changes resulting from fluid migration conventional time lapse monitoring can be done by observing differences between two seismic surveys over the surveillance period along with the changes in the subsurface differences in the two seismic surveys are also caused by variations in the near surface overburden and acquisition discrepancies the virtual source method monitors below the time varying near surface by redatuming the data down to the subsurface receiver locations it crosscorrelates the signal that results from surface shooting recorded by subsurface receivers placed below the near surface for the mars field data redatuming the recorded response down to the permanently placed ocean bottom cable obc receivers using the virtual source method allows one to reconstruct a survey as if virtualsources were buried at the obc receiver locations and the medium above them were a homogeneous half space separating the recorded wavefields

seismic interferometry by tangent phase correction we present a modified interferometry method based on local tangent phase analysis which corrects the cross correlated data before summation the approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation for a given pair of receivers and a set of different source positions a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver the position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation signal tangent information the method uses mixed processing which is partially based on velocity model knowledge and on data based blind interferometry the approach can be used for selected events including reflections with different stationary conditions and projected points with respect to those of the direct arrivals to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary phase condition we discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse

the stratification and cyclicity of the dachstein limestone in lofer leogang and steinernes meer northern calcareous alps austria abstract the dachstein limestone of the northern calcareous alps contains massive limestone beds capped by dolomitic horizons groups of beds form bundles or stratification cycles and spectral analysis gives evidence of at least 3 orders of cycle frequencies the regularity in the repetition of the limestones and dolomites was first pointed out by sander 1936 sander b 1936 beitrage zur kenntniss der anlagerungsgefuege mineral petrogr mitt 48 27 139 and the repetition of definite groups by schwarzacher 1948 1954 schwarzacher w 1948 ueber die sedimentaere rhytmik des dachstein kalkes von lofer verh geol bundesanst 1947 heft 10 12 176 188 schwarzacher w 1954 ueber die grossrhytmik des dachstein kalkes von lofer tschermaks mineral petrogr mitt 4 44 54 the facies associated with the change from limestone to dolomite was interpreted by fischer 1964 fischer a g 1964 the lofer cyclothems of the alpine triassic in merriam d f ed symposium on cyclic sedimentation kansas geological survey bull 169 107 146 as an environmental change from lagoonal to peritidal and consequently as evidence of rising and falling sea level the present paper is based on the study of over 500 aerial photographs from the loferer and leoganger steinberge and also on a detailed section measured by paul enos and e samankassou in the steinernes meer it was found that the dachstein limestone from lofer and leogang comprised about 35 stratification cycles of approximately 20 m thickness this may correspond to a similar number of cycles in the steinernes meer where the spectral analysis gave a cycle thickness of 27 m and 13 6 m the interpretation of the bundle as being caused by the 100 ka eccentricity cycle is considered tenable

wavelet crosscorrelation based interferometric redatuming in 4d seismic interferometric virtual source redatuming crosscorrelates downgoing waves with the corresponding upgoing waves to convert records from surface source gathers to virtual gathers at the buried receiver locations the assumption is that the virtual source records show reduced effects of overburden complexity and therefore provide improved seismic repeatability and image quality in practice however the repeatability and quality of the redatumed data can be degraded by one sided illumination and inadequate preprocessing in the presence of complex near surface structure for land redatuming intricate shallow structure and highly variable weathering layers introduce surface multiples ground roll scattering noise interferences among different wave modes which additionally contaminate both down and upgoing wavefields to address these issues we propose a new interferometric redatuming method based on crosscorrelation in the wavelet domain specifically by transforming time offset data into local time sca

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

northern ice discharges and antarctic warming could ocean eddies provide the link a mechanism is advanced for explaining the antarctic warm events from 90 to 30ka bp which involves meltwater induced changes in the salinity gradient across the antarctic circumpolar current acc and consequent changes in the poleward heat transport by ocean eddies based on simple linear scale analysis the mechanism is shown to yield warming in the antarctic interior of roughly the magnitude seen in antarctic ice core records 2 c in response to ice discharges into the north atlantic consistent with observations the mechanism produces gradual antarctic warming and cooling as dictated by the time required for salinity anomalies to build up and dissipate across the acc the mechanism also allows the onset of warming or cooling to be tied to changes in atlantic overturning which is relevant here not for influencing ocean heat transport directly but for influencing the routing of meltwater from the north atlantic into the southern ocean the ideas presented here highlight the possibility that eddy processes in the ocean may play a first order role in aspects of climate variability on millennial time scales

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics