estimating internal wave spectra using constrained models of the dynamic ocean multi channel seismic method mcs with its ability to image events down to a lateral resolution of 10 m has been successfully applied to address questions in physical oceanography however to date these analyses have overlooked an important detail the imaged boundaries are dynamic and move on a timescale that can be resolved by the mcs method an important step in understanding the effect of the movement is calibration against constrained models we demonstrate in this paper that it is possible using careful interpolation to take high resolution models of dynamic water 160 m x 2 m spatial resolution and 15 min temporal resolution and generate models for synthetic seismic simulations 20 m x 4 m spatial resolution and 20 sec temporal resolution we show that moving water when ignored will distort analyses of wavenumber spectra estimated from seismic data since the relative movement of water masses and the seismic acquisition vessel will change the apparent slope of spectra citation vsemirnova e r hobbs n serra d klaeschen and e quentel 2009 estimating internal wave spectra using constrained models of the dynamic ocean geophys res lett 36 l00d07 doi 10 1029 2009gl039598

isotope geochemistry sr nd pb and petrogenesis of leucite bearing volcanic rocks from colli albani volcano roman magmatic province central italy inferences on volcano evolution and magma genesis the colli albani composite volcano is made up of strongly silica undersaturated leucite bearing rocks magmas were erupted during three main periods but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs the most alkali rich magmas restricted to the caldera forming period pre caldera are extremely enriched in incompatible trace elements and display more radiogenic sr 87sr 86sr 0 71057 0 71067 with slightly less radiogenic pb with respect to those of the post caldera period post caldera volcanic activity was concentrated in three different volcanic environments external to the caldera along the caldera edge and within the caldera the post caldera magmas produced melilite to leucitite bearing plagioclase free leucitites in contrast to the pre caldera lavas they are characterised by lower incompatible trace element abundances and less radiogenic sr 87sr 86sr 0 71006 0 71039 magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre caldera period the multiple caldera collapses dissected and partially obliterated the early magma chamber during the post caldera stage magmas were channelled through several pathways and multiple shallow level magma reservoirs were established a lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab derived component is suggested as the mantle source of colli albani parental magmas two different parental magmas are recognised for the pre and post caldera stages the differences may be related to the interplay between smaller degrees of melting for the pre caldera magmas and more carbonate rich recycled subducted lithologies in the post caldera magmas

rate of dune reddening in a humid tropical climate the formation of red beds has long interested geologists and pedologists1 3 it has been suggested that the nature and degree of reddening in dune sands can be a useful indicator of the relative age and environmental history of the sands several authors have concluded that dune sands undergo progressive reddening with time4 7 and james and stanley8 considered that coastal dunes might actually be mapped on the basis of colour however quantitative data regarding the rate of reddening in different environmental conditions are generally lacking i present here radiocarbon evidence from north east australia which suggests that red weathering profiles have developed in stabilized dunes of holocene age in humid tropical conditions within the past 7 500 yr

monsoonal variability in the northeastern arabian sea during the past 5000years geochemical evidence from laminated sediments abstract a high resolution laminated sediment record from the oxygen minimum zone in the northeastern arabian sea off pakistan was studied to reconstruct climatic variations to infer the monsoon driven moisture history in the northeastern arabian sea during the past 5000 years we have used three types of independant proxies 1 varve thickness 2 stable isotope ratios of planktic foraminifera and 3 inorganic geochemical composition on the basis of these proxies we have subdivided the sedimentary record into five intervals the first time interval from 5000 to 3900 yr bp period i is dominated by summer monsoon activity deduced from ti al zr al k al and sr ca ratios and oxygen isotope data of planktonic foraminifera slightly enhanced winter monsoon conditions can be inferred for the period from 3900 to about 3000 yr bp period ii maximum precipitation during enhanced winter monsoon activity at about 3100 yr bp was followed by an onset of aridification at 3000 yr bp which continued until about 2000 2200 yr bp period iii the textural mineralogical and geochemical data suggest that this aridification was a gradual century scale process rather than an abrupt event comparison to late holocene records in nw and sw india the near east and tropical africa supports our interpretation that period iii from 3000 to 2000 yr bp is characterized by a gradual change in the atmospherical moisture budget over much of this area reduced monsoonal rainfall may be linked to variations of eurasian snow cover as deduced from varve thickness and element to al ratios period iv from 2000 to about 1500 yr bp is characterized by a summer monsoon dominated sequence with higher precipitation than during period iii the 18o record shows an abrupt shift at 2000 yr bp coinciding with an increase of varve thickness which suggests a cooling of surface waters in the northern arabian sea present day conditions in the makran area were established at 1500 yr bp period v based on inorganic geochemical data and meteorological records at several stations in the makran we conclude that period v is dominated by precipitation during the winter season here declined rainfall associated with the summer monsoon may be related to a less northward position of the intertropical convergence zone itcz during summer and a stronger influence of winter monsoon linked phenomenona

major explosive activity in the monti sabatini volcanic district central italy over the 800 390 ka interval geochronological geochemical overview and tephrostratigraphic implications abstract a review of the existing chronological stratigraphic and chemo petrologic data of the major eruptive units from the early phase of activity 800 390 ka in the monti sabatini volcanic district msvd belonging to the ultra potassic magmatic region of central italy is presented along with new radioisotopic age determinations and geochemical analyses through the combined use of electron microprobe glass compositions selected trace element compositions and single crystal 40ar 39ar age determinations we provide a new chrono and chemo stratigraphic classification of the products emplaced in the 800 390 ka time interval besides giving insights on the petrologic evolution of the roman comagmatic region the large dataset provides fundamental information that is applicable to tephrostratigraphic studies in the wide region encompassing the tyrrhenian sea margin to the adriatic sea basin distal tephras from this volcanic activity also act as important geochronologic markers for the coastal sedimentary successions deposited in response to glacio eustatic fluctuations as well as for successions in the quaternary tectonic basins of the central and southern apennines an innovative approach based on the use of discrimination diagrams of zr y vs nb y ratios for fingerprinting altered volcanic rocks recently developed and successfully employed in archaeometric studies is here combined to the glass compositions for classifying the msvd deposits and tested on two distal tephra layers showing its potentiality for tephrostratigraphic correlation

great earthquake surface ruptures along backthrust of the janauri anticline nw himalaya abstract results of a paleoseismic trenching investigation on a backthrust in the northern margin of janauri hill at mehandpur 31 18 11 37 n 76 18 31 47 e sub himalayan range of the himachal himalaya are presented the active backthrust revealed the last event took place after 0 8 0 03 ka ago i e post ce 1200 the age of the last earthquake with a minimum fault slip 1 m along f1 fault and presence of single colluvium on the back thrust nearly matches with an earthquake event previously documented on the bhatpur forethrust of the himalayan frontal thrust system uplifted and truncated fluvial terraces due to displacement on the backthrust are preserved along several north flowing river valley sections in the northern limb of janauri anticline the long term vertical uplift rate calculated through dividing difference between current elevation and elevation of current river grade is 1 08 0 08 mm yr field evidence shows fore and backthrusts are active and they form simultaneously but displacements are episodic suggesting the backthrust develops either due to locking of forethrust or to accommodate a large amount of fault slip due to magnitude of earthquake event along the forethrust further the backthrust may be used as an indirect method of inferring the age of the last event that took place along the forethrust

quaternary fluvial volcanic stratigraphy and geochronology of the capitoline hill in rome in and around rome coastal and fluvial sediments influenced by quaternary sea level changes interfinger with accurately datable highly potassic pyroclastic volcanic units we describe the complex internal geology of the capitoline hill for centuries a place of leading importance in ancient rome and more recently a focus of archaeological research outcrops and many new drill cores reveal at least four cycles of valley cutting and filling probably recording the history of the tiber river in response to changes in sea level single crystal 40 ar 39 ar dates on sanidine give ages of 518 6 413 5 and 353 2 ka for three prominent volcanic units filling separate paleovalleys the roman region offers the potential for direct age calibration of the quaternary sea level record

luminescence chronology of aeolian deposition during the late quaternary on the southern margin of thar desert india abstract aeolian deposits constitute the uppermost lithostratigraphic unit in the southern margin of the thar desert they occur as poorly organized dunes resting on the upper part of a major fluvial sequence considerable evidence exists to show that the southern margin witnessed fluvial aggradation before the onset of dune accretion transition from a dominantly fluvial phase to aeolian deposition was gradational blue green light stimulated luminescence chronometry of six fossil dunes indicates that the dune building activity started around 26 ka and continued episodically until around 5 ka evidence of a phase of landscape stability is seen corresponding to the interval 11 9 ka this is also reflected by the presence of stone age artifacts microliths and fluvially reworked aeolian sand and corresponds to the strengthening of the southwest monsoon in the region a progressive northward shift through time in the parameters controlling dune building activity is seen aeolian accretion in the southern part mahi basin ended around 10 ka whereas in the northern sabarmati it continued until around 5 ka and in the case of core regions of thar it continued until 0 6 ka the southern margins of the thar desert thus have not experienced any major aeolian deposition since 5 ka

a 200 ka record of climatic change and dune activity in the thar desert india abstract an 18 4 m excavated dune section in the thar desert of india with a chronology based on 12 tl ages and a basal age of 190 ka has preserved 12 cycles of dune accretion soil formation calcrete development and subsequent erosion together with the presence of stone artefacts ranging in age from lower palaeolithic to mesolithic coeval with more humid climatic interludes phases of soil development and carbonate precipitation were relatively wet and phases of dune accretion relatively dry so that there were 12 significant moist intervals separated by 11 drier intervals during the past 190 ka the calculated time interval between successive phases of dune sand accumulation ranged from 22 2 ka to 15 8 ka with a mean of 19 0 ka these values are consistent with a precessional influence on dune activity and on the associated onset of early monsoonal activity in this region carbon isotopes measured on organic matter within the sand profiles show consistent values close to 21 6 1 pointing to deposition during a transitional climatic regime characterized by a change from open c3 grassland to c4 woodland or forest

markov chain monte carlo inversion of temperature and salinity structure of an internal solitary wave packet from marine seismic data marine seismic reflection technique is used to observe the strong ocean dynamic process of nonlinear internal solitary waves isws or solitons in the near surface water analysis of isws is problematical because of their transient nature and limitations of classical physical oceanography methods this work explores a markov chain monte carlo mcmc approach to recover the temperature and salinity of isw field using the seismic reflectivity data and in situ hydrographic data the mcmc approach is designed to directly sample the posterior probability distributions of temperature and salinity which are the solutions of the system under investigation the principle improvement is the capability of incorporating uncertainties in observations and prior models which then provide quantified uncertainties in the output model parameters we tested the mcmc approach on two acoustic reflectivity data sets one synthesized from a ctd cast and the other derived from multichannel seismic reflections this method finds the solutions faithfully within the significantly narrowed confidence intervals from the provided priors combined with a low frequency initial model interpreted from seismic horizons of isws the mcmc method is used to compute the finescale temperature salinity acoustic velocity and density of isw field the statistically derived results are equivalent to the conventional linearized inversion method however the former provides us the quantified uncertainties of the temperature and salinity along the whole section whilst the latter does not these results are the first time isws have been mapped with sufficient detail for further analysis of their dynamic properties

a pollen record of holocene climatic changes from the dunde ice cap qinghai tibetan plateau pollen preserved in ice cores from the dunde ice cap provides a sensitive record of holocene climatic changes and vegetational response in the northern qinghai tibetan plateau at time scales ranging from millennia to centuries and decades pollen analysis of the annually resolvable ice layers for a 30 yr period 1957 1986 suggests that total pollen concentration is correlated positively with summer precipitation and negatively with summer temperature thus it is a sensitive indicator of moisture availability and vegetation density in the steppe and desert regions around dunde high pollen concentrations between 10 000 and 4800 yr b p suggest that the summer monsoon probably extended beyond its present limit to reach dunde and westernmost tibet in response to orbital forcing the summer monsoon retreated time transgressively across the qinghai tibetan plateau during the middle holocene relatively humid periods occurred at 2700 2200 1500 800 and 600 80 yr b p probably as a result of neoglacial cooling prominent pollen changes during the medieval warm period 790 620 yr b p and the little ice age 330 80 yr b p suggest that the vegetation in the qinghai tibetan plateau region is sensitive to abrupt century scale climatic changes such as those anticipated in scenarios of greenhouse warming

the villa senni eruption alban hills central italy the role of h2o and co2 on the magma chamber evolution and on the eruptive scenario abstract the villa senni eruption unit vseu belongs to the tuscolano artemisio phase of volcanic activity in the alban hills volcanic district the closest to rome of the recent or active volcanoes of central italy the most important products of this eruption are represented by pyroclastic flow deposits named lower and upper flow unit lfu and ufu respectively three main rock types form vseu as follows 1 juvenile k foiditic scoria clasts of the lfu 2 juvenile phonotephritic scoria clasts of the ufu and 3 holocrystalline phonotephritic lithic inclusions italites in the ufu on the basis of the chemistry mineralogy and petrography of the three studied rock types their phase relations have been discussed other petrologic constraints from laboratory melting experiments are presented and used to investigate the role of volatiles on the evolution of the magma chamber system some broad implications on withdrawal pattern are also presented it has been verified the lfu rock type can be obtained from a parental melt of ufu composition by a co2 controlled crystal liquid fractionation of a solid assemblage close in composition to that of italites because it can be proved that the storage of magma occurred at shallow depth within the mesozoic carbonate country rocks it is proposed that co2 diffusion originating from thermal decomposition of wall rock carbonates controlled the evolution trend of the melt at the periphery of the magma chamber whereas the inner part of the magma body retained the volatile component essentially h2o of the original melt the corresponding eruption model is therefore comprehensive of an early eruptive phase lfu rock type involving the more differentiated central magma bulb whereas the late eruptive phase ufu rock type tapped the more mafic peripheral magma the italite xenoliths are believed to represent the chilled margins of the magma chamber

luminescence dating of fluvial and coastal red sediments in the se coast india and implications for paleoenvironmental changes and dune reddening abstract the holocene and late pleistocene environmental history of the teri sandy waste in local parlance red sands in the southeast coastal tamil nadu was examined using remote sensing stratigraphy and optically stimulated luminescence osl dating geomorphological surveys enabled the classification of the teri red sands as 1 inland fluvial teri 2 coastal teri and 3 near coastal teri dunes the inland teri sediments have higher clay and silty sand component than the coastal and near coastal teri suggesting that these sediments were deposited by the fluvial process during a stronger winter monsoon around 15 ka the coastal teri dunes were deposited prior to 11 4 0 9 ka and the near coastal dunes aggraded at around 5 6 0 4 ka we interpret that the coastal dunes were formed during a period of lower relative sea level and the near coastal dunes formed during a period of higher sea level dune reddening is post deposition occurred after 11 4 0 9 ka for the coastal teri dunes and after 5 6 0 4 ka for the near coastal teri dunes presence of microlithic sites associated with the coastal dunes suggest that the cultures existed in the region during 11 4 0 9 ka and 5 6 0 4 ka

post caldera activity in the alban hills volcanic district italy 40ar 39ar geochronology and insights into magma evolution we present 24 40ar 39ar ages for the youngest volcanic products from the alban hills volcanic district rome combined with petrological data on these products we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district the early mainly explosive activity of the alban hills spanned the interval from 561 1 to 351 3 ka after approximately 50 kyr of dormancy a mainly effusive phase of activity took place accompanied by the strombolian activity of a small central edifice monte delle faete this second phase of activity spanned the interval 308 2 to 250 1 ka after another dormancy period of approximately 50 kyr a new hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the monte delle faete edifice after an initial recurrence period of approximately 50 kyr which also characterized this new phase of activity the longest dormancy period approximately 80 kyr in the history of the volcanic district preceded the start of the activity of the albano and giuturna centers at 70 1 ka results of our study suggest a quasi continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka based on data presented in this paper we argue that the alban hills should not be considered an extinct volcanic district and a detailed re assessment of the volcanic hazard for the area of rome is in order

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

event stratigraphy paleoenvironment and chronology of se arabian deserts the geological record of the se arabian desert is exhibited in a variety of geomorphic features and their characteristic sediments ranging from alluvial fans to inland and coastal dunes and sabkhas together they suggest a large range of environmental and climatic variability between periods of relative aridity and humidity sedimentary events in the emirates appear to correlate broadly with high latitude glaciations which affected both the shamal winds and the extent of exposure of the arabian gulf in general the aeolian sands in the rub al khali responded to glacial events as a consequence of exposure of the floor of the arabian gulf during glacials when global sea level was low quartz sands from across the exposed floor of the arabian gulf were transported by the shamal winds south eastwards to the emirates and then south to the rub al khali the supply of shamal transported sand from the floor of the arabian gulf was cut off by high stands of sea level during interglacial periods the new coastal dunes miliolite rich in foraminifera and other cement assisting calcareous shell fragments were deflated down to the water table as their sand was transported further to the south leading to the creation of coastal sabkhas studies on aeolianites and the lacustrine deposits provide evidence of phases of enhanced humidity prior to the last glacial maximum and during the holocene in contrast the bedding attitudes of miliolites in se oman suggest that the wahiba sands were transported from south to north by a branch of the sw monsoon the depositional ages of these dunes indicate a close connection between the winds and coeval fluctuations of the sw monsoon the interdunal lakes and underlying dune sands reflect an active sw monsoon during the holocene this is also indicated by the aeolian and lacustrine records of the thar desert in india which likewise are controlled by the sw monsoon south and west of the oman mountains is a broad alluvial fan bajada that is mostly inactive today the oldest fluvial sediments are undated but preliminary age estimates suggest that some correlate with more humid earlier interglacials

the alban hills and monti sabatini volcanic products used in ancient roman masonry italy an integrated stratigraphic archaeological environmental and geochemical approach abstract the rocks of alban hills and monti sabatini volcanoes central italy and their associated epiclastic deposits have been extensively used as building material in ancient rome from about viiith century bce to ivth century ce however the identification of the source areas of these rocks is difficult due to the lack of an integrated stratigraphic and geochemical analysis of the relationships between the two volcanic districts and to the alteration affecting the primary products as consequence of weathering and pedogenetic processes here a comprehensive upgraded stratigraphic and geochronological review of the two volcanic districts corroborated by new geochronological data for several eruptive units and altered deposits is presented coupled to a complete geochemical background achieved by means of newly determined major and trace element analyses for all the main eruptive units a study of the alteration processes of the primary products is also presented and the age of the main weathering and pedogenetic phases associated to quaternary climatic changes are also investigated the results are integrated with those from literature in order to construct discriminant diagrams based on selected trace elements and allow us to characterize the primary and altered volcanic deposits in the rome area distinguish products of different volcanic districts discuss the effects of different weathering processes on the mobility of some elements and provide a reference frame for the provenance of the volcanic materials employed in ancient roman masonry the interdisciplinary data set and results presented here provide groundwork for volcanological climate pedological and archaeological provenance studies

direct temperature and salinity acoustic full waveform inversion 1 recent work has shown that full waveform inversion could be suitable to extract physical properties such as sound speed c density temperature t and salinity s from the weak impedance contrasts associated with the ocean s thermohaline fine structure the seismic inversion approaches proposed so far are based on the iterative inversion of c from multichannel seismic data while the rest of parameters t s and are determined in a second step using two equations of state and a local t s empirical relationship in this work we present an alternative to this approach using 1 d synthetic seismic data we demonstrate that the direct full waveform inversion of t and s using adjoint methods is feasible without the use of any local t s relationship and that the models of physical properties obtained with this approach are far more accurate than those inferred from c

eolian depositional episodes controlled by late quaternary relative sea level changes on the imbituba laguna coast southern brazil the late quaternary coastal eolian deposits of the imbituba laguna region santa catarina state southern brazil comprise two eolian depositional sequences separated by an unconformity the older eolian sequence a is correlated to the relative sea level rise of the last interglacial period the eolian sequence b was initiated during the relative sea level rise in the post glacial period and extends up to active dunefields the correspondence between the two eolian depositional episodes represented by these sequences and the relative sea level highstand phases is confirmed by thermoluminescence and optically stimulated luminescence dating this correspondence is explained by a conceptual model that links the availability of coastal sediments for eolian transport with relative sea level changes the link between relative sea level changes and coastal eolian sedimentation can be used to integrate coastal eolian systems to the sequence stratigraphy model

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

late glacial to post glacial sea levels in the western indian ocean late glacial to post glacial sea level changes provide direct evidence of the progress of melting of large ice sheets during the last deglaciation but although the correlation between ice and ocean volumes is incontrovertible the causal link is commonly obscured local effects including tectonics isostatic and hydroisostatic responses and equatorial ocean syphoning impose additional signals that hide the true picture a detailed regional study of the western indian ocean based on the analysis of drill cores carried out through modern reefs in combination with observations and sampling of reef foreslopes and investigations of outcrops provides a comprehensive data base sites from a range of tectonic settings include the microcontinental margins of madagascar the granitic seychelles and the isolated volcanic islands of reunion mauritius and the comoros in which the effects of subsidence can be shown to be small these cover a range of latitudes and comparisons with adjacent sites on continental margins allow the construction of sea level curves that closely reflect the eustatic response and disengage this from the effects of other mechanisms the mayotte foreslope in the comoro islands provides the first coral reef record of sea level change during the early deglaciation in the indian ocean 110 115 m below present sea level between 18 000 and 17 000 yr bp two distinctive reef terraces at 90 and 60 m water depth are dated at 13 600 yr bp and partly attributed to the younger dryas period 12 700 11 600 cal yr bp reef drowning at around 13 500 yr bp may correspond to meltwater pulse 1a and although there were surges in the rate of sea level rise most notably between 11 950 and 11 350 yr bp there is little evidence to support a well defined meltwater pulse 1b reconstructed holocene sea level curves are in good agreement and reflect a rapid sea level rise of about 6 mm yr 1 between 10 000 and 7500 yr bp followed by a clear inflection around 7500 yr bp when the rate fell to 1 1 mm yr 1 modern reefs started to grow 8000 9000 years ago in the post glacial period the rate of sea level rise was 1 1 5 mm yr 1 before stabilization at its present level 3000 2500 years ago curves for the 10 000 6000 yr 1 bp interval correspond closely with those predicted by theoretical models but lie below these in the subsequent period in particular and with the exception of the margins of the madagascar microcontinent influenced by hydroisostatic processes they do not reflect predicted higher sea level stands during the late holocene

spatial variation of diapycnal diffusivity estimated from seismic imaging of internal wave field gulf of mexico bright reflections are observed within the upper 1000 m of the water column along a seismic reflection profile that traverses the northern margin of the gulf of mexico independent hydrographic calibration demonstrates that these reflections are primarily caused by temperature changes associated with different water masses that are entrained into the gulf along the loop current the internal wave field is analyzed by automatically tracking 1171 reflections each of which is greater than 2 km in length power spectra of the horizontal gradient of isopycnal displacement ex are calculated from these tracked reflections at low horizontal wavenumbers kx 10 2 cpm ex kx 0 2 0 6 in agreement with hydrographic observations of the internal wave field the turbulent spectral subrange is rarely observed diapycnal diffusivity k is estimated from the observed internal wave spectral subrange of each tracked reflection using a fine scale parametrization of turbulent mixing calculated values of k vary between 10 8 and 10 4 m2 s 1 with a mean value of k 4 10 6 m2 s 1 the spatial distribution of turbulent mixing shows that k 10 7 m2 s 1 away from the shelf edge in the upper 300 m where stratification is strong mixing is enhanced by up to four orders of magnitude adjacent to the shoaling bathymetry of the continental slope this overall pattern matches that determined by analyzing nearby suites of ctd casts however the range of values recovered by spectral analysis of the seismic image is greater as a consequence of significantly better horizontal resolution

the volcanic aggregate of ancient roman mortars from the capitoline hill petrographic criteria for identification of rome s pozzolans and historical implications abstract we present a petrographic study of the pyroclastic flow deposits used to produce mortar aggregates pozzolane rosse pozzolane nere and pozzolanelle as well as dimension stones tufo del palatino and tufo lionato in ancient roman times in which we describe the characteristic textures and mineralogic assemblages of their juvenile fraction this petrographic dataset is employed to compare and classify through observation in thin section at the optical microscope and complementary trace element analyses as well as emp analyses on matrix glass on archaeological and bulk natural samples the composition of the volcanic aggregate of 11 samples of ancient roman mortars collected from several archaeological structures excavated on the capitoline hill by means of the combined petrographic and geochemical identification criteria illustrated in this work we recognize two main types of mortar aggregates characteristic of the republican and imperial ages respectively and a third type pertaining to the mediaeval epoch

thermoluminescence dating of quaternary red sand beds a case study of coastal dunes in sri lanka red sand beds that occupy extensive tracts of coastal humid tropics have conventionally been considered undatable results of a first successful attempt to provide an absolute chronology to these sediments based on thermoluminescence dosimetry are presented along with a discussion on the importance of an understanding of ambient geochemistry in the application of the thermoluminescence technique the results on the sri lankan coastal region indicate that the sea level in the region may have been affected by regional tectonics during the past 70 000 years based on in situ finds of geometric microliths in the red sands a date of ca 25 000 years is ascribed to them suggesting them to be substantially older than believed so far

the timing of linear dune activity in the strzelecki and tirari deserts australia abstract linear dunes occupy more than one third of the australian continent but the timing of their formation is poorly understood in this study we collected 82 samples from 26 sites across the strzelecki and tirari deserts in the driest part of central australia to provide an optically stimulated luminescence chronology for these dunefields the dunes preserve up to four stratigraphic horizons bounded by palaeosols which represent evidence for multiple periods of reactivation punctuated by episodes of increased environmental stability dune activity took place in episodes around 73 66 35 32 22 18 and 14 10 ka intermittent partial mobilisation persisted at other times throughout the last 75 ka and dune activity appears to have intensified during the late holocene dune construction occurred when sediment was available for aeolian transport in the strzelecki and tirari deserts this coincided with cold arid conditions during marine isotope stage mis 4 late mis 3 and mis 2 and the warm dry climates of the late pleistocene holocene transition period and late holocene localised influxes of sediment on active floodplains and lake floors during the relatively more humid periods of mis 5 also resulted in dune formation the timing of widespread dune reactivation coincided with glaciation in southeastern australia along with cooler temperatures in the adjacent oceans and antarctica

ocean internal wave spectra inferred from seismic reflection transects 1 internal waves affect many important dynamical processes in the ocean but in situ observations of internal waves are infrequent and spatially sparse here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean seismic images of the norwegian sea water column show reflections that capture snapshots of finestructure displacements due to internal waves horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the garrett munk tow spectrum of oceanic internal wave displacements spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave sloping boundary interactions

luminescence chronology of late holocene extreme hydrological events in the upper penner river basin south india field stratigraphy sedimentology and optically stimulated luminescence osl dating have been used to reconstruct the southwest monsoon variability in the semi arid region of southern india during the late holocene facies architecture and osl dating of the water lain sediment suggest prevalence of a weak hydrological regime around 3 ka following this a progressive strengthening of monsoon occurred till 2 ka after 2 ka and until 1 ka fluvial activity was nearly dormant indicating weakening of the monsoon presence of high magnitude flood deposits overbank sedimentation and pedogenesis during 1 0 6 ka indicate intensification of the southwest monsoon in the basin the onset of aridity was associated with episodic storm surge events that are manifested in the pond sedimentation and localised aeolian accretion this phase is bracketed between 0 5 ka and 0 2 ka a renewed phase of monsoonal activity was observed in the form of floodplain aggradation between 180 and 90 years ago in the past 70 years no significant change in the monsoon performance has been observed copyright 2007 john wiley sons ltd

isotopic sr nd and major element fingerprinting of distal tephras an application to the middle late pleistocene markers from the colli albani volcano central italy abstract we describe the diagnostic lithological and chemical features of distal tephras from major middle late pleistocene 560 36 ka explosive eruptions of the colli albani volcanic district central italy in particular we explore the time dependent variability of the sr and nd isotope compositions as a tool for recognising and pinpointing individual colli albani tephra in distal settings the distal tephras investigated are in lacustrine and fluvial sediments of central apennine intermountain basins located 70 km 100 km east of colli albani the recognition of the colli albani tephras is essentially based on the k foiditic composition of their glass which within the italian volcanological framework is a distinctive character of the colli albani pyroclasts in detail these tephras are attributed to the following eruptive units tufo pisolitico di trigoria 561 2 ka tufo del palatino tufo di bagni albule 530 2 527 2 ka tufo di bagni albule pozzolane rosse air fall sequence 517 1 to 500 3 ka pozzolane rosse 457 4 ka villa senni 365 4 ka and albano 5 7 41 7 to 36 1 ka these correlations are supported by 40 ar 39 ar dating of the distal tephras correlated to the pozzolane rosse 457 4 1 7 ka villa senni 365 2 ka and albano 5 7 41 9 ka and by 87 sr 86 sr measured on clinopyroxene crystals and fresh glassy scoria from distal colli albani tephras that range from 0 711 to 0 709 these ratios are similar to those that characterise the individual proximal correlative units and show the same decreasing trend over time in contrast the 143 nd 144 nd ratios for proximal and distal bulk samples and clinopyroxene increase from 0 51212 to 0 51215 from the oldest to the youngest tephra deposit in summary the study of sr and nd isotope compositions that is here applied on products from the colli albani volcanic district is a powerful complementary tool to the more traditional tephrostratigraphic methods e g componentry and electron microprobe analysis for fingerprinting of distal tephras over a large region of the central mediterranean and over a large time interval such as from 560 ka to 36 ka

multiphase late quaternary aeolian sediment accumulation in western south africa timing and relationship to palaeoclimatic changes inferred from the marine record abstract extensive aeolian deposits exist along the western margin of south africa from cape town through to the namib sand sea and represent a significant palaeoenvironmental archive recording millennial scale patterns of regional and hemispheric environmental change to establish the timing of dune development this study applies optically stimulated luminescence osl dating techniques to the aeolian features of the west coast in total 35 samples were obtained from six dune cores along a north south transect extending from elands bay 32 26 s 18 14 e to kleinsee 29 14 s 16 59 e ages from these dunes exhibit five distinct peaks suggesting phases of activity deposition at 4 5 16 24 30 33 43 49 and 63 73 ka the spatial and temporal extent of the data have allowed for correlations to be made with evidence from marine cores from the southeast atlantic and a more coherent regional environmental history to be developed results suggest that 1 environmental changes in this region are strongly linked to variations in wind strength and atmospheric circulation systems during the late quaternary and 2 luminescence ages from aeolian deposits cannot necessarily be equated with periods of increased aridity with other factors such as wind strength and sediment supply being of critical importance

elastic wave velocities in rocks from a lower crustal section in southern calabria italy compressional and shear wave velocities vp and vs have been measured on 14 rock samples recovered from a high grade metamorphic terrane in the southern part of the calabrian massif which is considered to represent a continuous section of a former deep continental crust the experiments have been carried out in a cubic anvil apparatus at constant confining pressures up to 600 mpa and temperatures ranging from 20 to 700 c using the ultrasonic transmission technique at 600 mpa the compressional and shear wave velocities range from 6 33 km s 1 to 7 74 km s 1 and from 3 54 km s 1 to 4 30 km s 1 respectively variations in velocity are strongly related to variations in mineralogy both vp and vs increase with increasing amphibole pyroxene garnet and sillimanite content the range of velocities measured in the granulite facies rocks under conditions of lower crustal depth is similar to the range of seismic velocities for the crust beneath calabria importantly the metapelite rocks with intermediate silica and high alumina contents have in situ compressional and shear wave velocities which are equivalent to the mafic rocks or even significantly higher the detected high velocity layer at a depth between 15 and 20 km can be explained by a sequence of garnet cordierite sillimanite gneisses for which actual velocities between 6 6 and 7 6 km s 1 have been determined experimentally

from pull apart basins to ultraslow spreading results from the western barents sea margin this paper describes results from a geophysical study in the area between the ultraslow knipovich ridge and bear island western barents sea the objective was to map the crustal structure along a profile crossing a pull apart rifted continental margin and oceanic crust generated by ultraslow spreading the results are based on modeling of wide angle seismic and gravity data together with interpretation of multichannel reflection data our results show a two layered oceanic crust in the western part of the profile the thickness of the oceanic crust is variable in the western 130 km ranging from 3 5 to 5 5 km east of km 130 the crustal thickness is relatively constant with values close to the global average for oceanic crust the oceanic crust is buried by a thick package of cenozoic sedimentary rocks the continent ocean transition cot is placed in the interval 207 255 km between unequivocal oceanic crust and the foot of the westernmost fault in the hornsund fault zone it is not possible to conclude whether this interval is oceanic crust or thinned and intruded continental crust but we favor the latter interpretation at least for the eastern part of the cot stretched continental crust is observed between hornsund fault zone and the knolegga fault here the sedimentary rocks have high velocities and are interpreted to be mainly of mesozoic and late paleozoic age in this interval moho depths increase abruptly from 15 km in the west to 27 km in the east crystalline basement velocities are observed close to the seafloor east of the knolegga fault we suggest that continental breakup north of greenland senja fracture zone occurred around 33 ma after a period of pull apart tectonics the spreading rate of the earliest seafloor spreading may have been higher than the present day spreading creating thicker oceanic crust close to the cot

observations and numerical modelling of the mediterranean outflow splitting and eddy generation during the canigo project the generation of dipolar eddies in the mediterranean water mw layers off south portugal was recorded by subsurface floats from february to november 1998 the role of the bottom topography on the spreading of the mw in the gulf of cadiz and on the generation of these mw eddies was studied in the framework of the medtop project some of the hydrological and velocity observations collected during medtop in 2001 and 2002 also revealed the association of anticyclones meddies and cyclones in the region just south of the portimao canyon the evolution of these structures is studied with subsurface floats deployed in the vortices the splitting of the mw plume in the gulf of cadiz and the generation mechanisms of the mw vortices in the region from portimao canyon to the estremadura promontory are investigated using a bottom following numerical primitive equations model in a regional ocean configuration incorporating the realistic topography of the iberian continental slope the model reproduces the mw division into different cores in the gulf of cadiz as well as the generation of baroclinic dipoles downstream of portimao canyon the role of the bottom topography in the eddy generation process is discussed

application of acoustic full waveform inversion to retrieve high resolution temperature and salinity profiles from synthetic seismic data 1 recent works show that multichannel seismic mcs systems are able to provide detailed information on the oceans fine structure the aim of this paper is to analyze whether 1 d full waveform inversion algorithms are suitable to recover the extremely weak acoustic impedance contrasts associated to the oceans fine structure as well as their potential to image meso scale objects such as meddies we limited our analysis to synthetic noise free data in order to identify some methodological issues related to this approach under idealistic conditions e g 1 d wave propagation noise free data known source wavelet we first discuss the influence of the starting model in the context of the multi scale strategy that we have implemented then we show that it is possible to retrieve not only sound speed but also salinity and temperature contrasts within reasonable bounds from the seismic data using neural network relationships trained with regional oceanographic data sets potentially the vertical resolution of the obtained models which depends on the maximum frequency inverted is of the order of 5 10 m whereas the root mean square error of the inverted properties is shown to be 0 5 m s for sound speed 0 1 c for temperature and 0 06 for salinity to conclude this study we have inverted synthetic data simulated along an oceanographic transect acquired during the eu funded geophysical oceanography go project the results demonstrate the applicability of the method for synthetic data as well as its potential to define oceanographic features along 2 d transects at full ocean depth with excellent lateral resolution

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

imaging meddy finestructure using multichannel seismic reflection data 1 this work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution 10 15 m we present seismic images of three meddies acquired in the gulf of cadiz sw iberian peninsula which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure the seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature t and salinity s data the core region characterized by smooth t and s variations is weakly reflective the double diffusive upper and lower boundaries and the lateral interleaving outer edges characterized by stronger t and s contrasts display strong reflectivity bands these new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans

dunefield activity response to climate variability in the southwest kalahari abstract aeolian activity on the crests of linear dunes in the arid southwest kalahari desert is primarily controlled by vegetation cover cover is temporally variable in response to rainfall with mobility index mi values and field based studies demonstrating the dynamic nature of aeolian processes in this dunefield landsat tm data for a drought 1984 and wetter 1993 year were analysed for two subscenes in the dune field one for a pastoral landscape and one for a conservation area to investigate the spatial dynamics of dune activity using the empirically determined 14 cover threshold as the limit to crestal aeolian activity tm band 3 data were found to best represent vegetation cover including senesced material at the end of the dry season the period when the potential for aeolian activity is normally high due to the wind strength at this time the extent of 0 14 cover areas ranged from 10 1984 to 3 1993 for the pastoral area and 16 1984 to 6 1993 for the conservation landscape the wetter 1993 image residuals have different spatial characteristics in the two subscenes with bare active dunes in the pastoral lands associated with locations of livestock pressure and those in the conservation area related to natural fire events the study demonstrates the spatial dynamics of temporally variable linear dune activity in the southwest kalahari and also shows that areas devegetated by drought can recover sufficient vegetation in wet years to limit the spatial extent of aeolian transport on dune crests

the onset of dune formation in the strzelecki desert south australia abstract this study is concerned with the late quaternary climatic chronology of the strzelecki desert dunefields in central australia the sand ridges comprise layers of quartz sand some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence osl deduced from the osl age of the oldest aeolian layer dated we conclude that the onset of aridity dates back to at least 65 ka older phases of aeolian activity though following a fluvial depositional phase 160 ka ago cannot be excluded although no aeolian layers giving evidence for this have been found in the two dunes dated here unconsolidated dune sands in the upper part of one section with late holocene 4 ka to modern depositional ages indicate a reactivation of the dunefield in recent times from the crosscheck of 14 c ages of the carbonated rootlets with osl results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development

acoustic waveform inversion for ocean turbulence abstractthe seismic oceanography method is based on extracting and stacking the low frequency acoustic energy scattered by the ocean heterogeneity however a good understanding on how this acoustic wavefield is affected by physical processes in the ocean is still lacking in this work an acoustic waveform modeling and inversion method is developed and applied to both synthetic and real data in the synthetic example the temperature field is simulated as a homogeneous gaussian isotropic random field with the kolmogorov obukhov spectrum superimposed on a background stratified ocean structure the presented full waveform inversion method is based on the ray born approximation the synthetic seismograms computed using the ray born scattering method closely match the seismograms produced with a more computationally expensive finite difference method the efficient solution to the inverse problem is provided by the multiscale nonlinear inversion approach that is specifically stable with respect to noise full

the age of the palaeodunefield of the northern murray basin in south australia preliminary results abstract a vast field of old desert dunes extends from northwestern eyre peninsula across yorke peninsula and the northern adelaide plains into the murray basin and northwestern victoria there are patches of parabolic forms but the sand ridges under review are of seif linear or longitudinal type they trend nw se in the west and west east in the east here we record luminescence dates for three dune sites in the waikerie district of the northwestern murray basin they range from respectively 151 25 3 ka 157 33 3 ka and a basal age of 59 6 ka with sand movement also indicated around 1906 and 1933 ce apart from the last named no unconformities are discernible in the sampled sections

late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania the western sahara desert in mauritania is dominated by extensive sand seas consisting largely of linear dunes analyses of landsat images geomorphic and stratigraphic studies and optically stimulated luminescence dating of dunes in the azefal agneitir and akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25 15 ka centered around the last glacial maximum 10 13 ka spanning the younger dryas event and after 5 ka the wind regimes that occurred during each of these periods were significantly different leading to the formation of dunes on three distinct superimposed trends northeast north northeast and north and the development of the sand seas as composite geomorphic features

co2 driven large mafic explosive eruptions the pozzolane rosse case study from the colli albani volcanic district italy generally the intensity and magnitude of explo sive volcanic activity increase in parallel with sio2 content pyroclastic flow forming eruptions in the colli albani ultrapotassic volcanic district italy represent the most striking exception on a global scale with volumes on the order of tens of cubic kilometres and k foiditic composi tions sio2 even 42 wt here we reconstruct the pre eruptive scenario and event dynamics of the 456 ka pozzolane rosse pr eruption the largest mafic explosive event of the colli albani district in particular we focus on the driving mechanisms for the unusually explosive eruption of a low viscosity mafic magma geologic petrographic and geochemical data with mass balance calculations supported by experimental data for colli albani magma compositions provide evidence for signif icant ingestion of carbonate wall rocks by the pozzolane rosse k foiditic magma moreover the scattered occurrence of cored bombs in pozzolane rosse pyroclastic flow deposits records carbonate entrainment even at the eruptive time scale as also tested quantitatively by thermal modelling of magma carbonate interaction and carbonate assimilation experiments we suggest that the addition of free co2 from decarbonation of country rocks was the major factor controlling magma explosivity high co2 activity in the volatile component coupled with magma depressurisation produced extensive leucite crystallisation at short time scales resulting in a dramatic increase in magma viscosity and volatile pressurisation which was manifested a change of eruptive dynamics from early effusion to the pozzolane rosse s highly explosive eruption climax

oxygen isotope evidence for a stronger winter monsoon current during the last glaciation a variety of palaeoclimate data from the northern indian ocean has shown that the asian summer monsoon was weaker during the last glacial maximum 18 000 years ago than it is today1 5 it has also been inferred from these data that the winter monsoon was stronger at that time5 here we present evidence that the transport of low salinity water from the bay of bengal to the arabian sea caused by the winter monsoon6 was higher during the last glacial maximum this inference is based on a negative excursion up to about 1 in magnitude in the oxygen isotope ratios of three planktonic foraminiferal species detected in a sediment core from the arabian sea by high resolution 1 2 cm sampling our results place an upper limit of about 4 000 years on the length of time during which the winter monsoon was stronger than today

a holocene late pleistocene aeolian record from lunette dunes of the western free state panfield south africa the greatest concentration of pans in southern africa occurs in the western free state province south africa a feature of many free state pans is their fringing lunettes located on the southern

physical chemical and sedimentological aspects of the mediterranean outflow off iberia a multidisciplinary study of the mediterranean outflow in the region west of the strait of gibraltar and off the southern and southwestern coasts of the iberian peninsula was developed in the frame of the canary islands azores gibraltar observations project two high resolution ctd surveys which included water sampling for chemical nutrients and dissolved oxygen and sedimentological analyses took place in september 1997 summer cruise and january 1998 winter cruise in the study region the correspondence between the high salinity mediterranean water mw layer and the low nutrient content and relatively high abundance of particles was a general result further details of the thermohaline analysis and of the geostrophic computations especially for the layer of mw are compared with the results obtained for the chemical properties and the sedimentological characteristics

marine seismic observation of internal solitary wave packets in the northeast south china sea recently the novel seismic oceanography method has been reported to be an effective way to study the energetic internal solitary waves isws in the northern south china sea an optimized seismic oceanographic cruise was carried out to observe such near surface isws on dongsha plateau in july 2014 several soliton trains rather than single solitons were captured using the seismic technique after seismic data processing one prototypical rank ordered isw packet on northeast side of dongsha island was clearly identified for further analysis this included waveforms propagation velocities and vertical velocities for individual solitons in this study an improved scheme was applied to derive the transient phase velocities from the seismic data which is verified from independent satellite and hydrographic data analytical predictions from korteweg de vries equation fit better than the extended korteweg de vries equation ignoring background currents our results show that the seismic method can be successfully used to image targets in shallow water below 40 m and that seismic oceanography is a promising technique for studying near surface phenomena with high spatial resolution

luminescence dating of late holocene dunes showing remnants of early settlement in cuddalore and evidence of monsoon activity in south east india abstract in this study dunes from south east india were dated using optically stimulated luminescence osl to reconstruct the depositional history a belt of dunes has developed parallel to the coast between pondicherry and karikal in tamil nadu south east india in the area between cuddalore and porto novo the dune belt is 5 km wide a transect from the coast to the most western dune inland was investigated changes in the environmental conditions are recorded in the dunes they show features including unconformities changes in the direction of bedding erosional features water escape structures and remnants of human settlements the osl results show that strong changes in the environmental conditions occurred about 100 and 300 years ago the latter event marks also the termination of settlement in this place the settlement period started about 1500 years previously the periods of sand mobility and stabilisation of the land surface by soil formation correlate with changes in the precipitation record of india the investigated dunes very likely reflect fluctuations in the monsoon activity during the last 3500 years in south east india

holocene sea level change on the southwest and south coasts of sri lanka abstract 14 c dates of coral and shell samples from sri lanka produce the following results nineteen samples from emerged coral reef patches on small headlands show two different age groups related to high sea levels 6170 70 5100 70 yr b p and 3210 70 2330 60 yr b p respectively buried coral deposits from the present backmarsh also indicate an age of 6110 80 5560 70 yr b p this substantiates the fact that these corals have thrived in bays or lagoons as a result of the marine transgression in the mid holocene comparing ages and heights of the samples with the mean low water spring level which is the highest level of present living corals it is concluded that the mean sea levels between 6170 70 5100 70 yr b p and 3210 70 2330 60 yr b p were at least 1 0 m higher than the present mean sea level

the flow of atlantic water through the strait of gibraltar abstract we describe and analyze observations of the water exchange through the strait of gibraltar the primary observations were taken in april 1986 and included data from moored recording instruments at four locations in the strait together with an intensive survey by ship these measurements included extensive ctd profiling acoustic doppler current profiling numerous profiles from expendable instruments and imaging using a high frequency echo sounder the analysis focuses on the internal hydraulics of the strait and in particular the presence of hydraulic controls and their influence on the exchange our observations during april 1986 show that the maximal exchange condition in which a subcritical flow is bounded by supercritical flow at both ends of the strait did occur although with various subtleties not explicitly incorporated in our previous theoretical developments the atlantic water moving east along the surface encounters a control at tarifa narrows in the eastern part of the strait the mediterranean water passes through controls both at camarinal sill and at spartel sill further west at our westernmost mooring at spartel the outflowing mediterranean water is continuously supercritical with little tidal variability the control at camarinal sill is periodically lost due to tidal action and reappears on a reverse flow during a falling spring tide tangier basin bounded by camarinal and spartel sills acts as an internal reservoir for the outflowing mediterranean water the interface rising and falling through each tidal cycle during spring tides the tangier basin interface rises high enough to flood the control at camarinl sill and produces a reverse flow of the lower layer when control is lost at camarinal sill a travelling bore is released this bore may modify the location of the control acting on the surface layer in tarifa narrows the atlantic water enters the alboran sea as a jet which may have a well defined northern boundary where it separates from the european coast this boundary may be identified by the presence of a slick although the internal jump west of camarinal sill is almost certainly an area of intense mixing frictional effects do not appear to be dominant in the subcritical portion of the flow

stochastic modeling of the reflective lower crust petrophysical and geological evidence from the ivera zone northern italy crustal scale seismic wave equation modeling demonstrates that wavelength scale velocity fluctuations can dominate the seismic response over a wide range of offsets and that a wide range of velocity distributions qualitatively can explain deep seismic data this range can be narrowed by studying the detailed petrophysical and structural properties of middle and lower crustal exposures the ivrea zone in the southern alps is a well studied sliver of extended lower continental crust brought into its present upright position as a result of late alpine lithospheric shortening the high degree of structural and petrophysical complexity and in particular the limited exposure of the ivrea zone favor a statistical rather than deterministic approach to develop a two dimensional crustal scale seismic model for this purpose we digitized two 1 25 000 geological maps from the central ivrea zone on a 60 m grid we find that the ivrea zone is characterized by a bimodal velocity distribution and a band limited self affine structure having a fractal dimension of 2 7 a characteristic horizontal scale of 500 to 1000 m and an aspect ratio around 4 0 assuming statistical stationarity a realization of this stochastic model was used to develop synthetic seismograms typical of ivrea type lower continental crust our results indicate that 1 ivrea type lower crust can explain qualitatively commonly observed lower crustal reflectivity 2 relatively minor changes in bulk composition and or metamorphic grade may lead to dramatic changes in reflectivity which cannot be explained by current generic models on the origin of lower crustal reflections and 3 travel time interpretation of the synthetic wide angle data may lead to erroneous large scale velocity structures

thermohaline fine structure in an oceanographic front from seismic reflection profiling we present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between the labrador current and the north atlantic current the images show that distinct water masses can be mapped and their internal structure imaged using low frequency acoustic reflections from sound speed contrasts at interfaces across which temperature changes the warm cold front is characterized by east dipping reflections generated by thermohaline intrusions in the uppermost 1000 meters of the ocean our results imply that marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena including thermohaline intrusions internal waves and eddies

mid depth internal wave energy off the iberian peninsula estimated from seismic reflection data energy levels of internal waves are estimated from seismic reflection data three legacy seismic sections from 1993 and 1997 obtained off the iberian peninsula have been analyzed for acoustic reflections within the water column the reflections are aligned continuously for up to several kilometers over large parts of the sections and in the depth interval from 200 to 2000 m depth variations of these reflections are thought to be caused by the background internal wave field from the variations we derive horizontal wave number spectra of normalized internal wave displacement the general slope of the power density spectra is remarkably consistent for all sections and agrees well with model spectra for internal waves significant differences within the sections can be found when sufficiently large subsections are averaged the spatial variation of the energy level indicates increasing internal wave activity with shallower water depths as well as near a subsurface eddy

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

basalts water or shear zones in the lower continental crust abstract bright sub horizontal laterally extensive multi cyclic layered reflections have now been recorded in the lower continental crust from many areas in contrast this reflection signature is rare in the continental upper crystalline crust and upper mantle and in the oceanic lithosphere with the present state of knowledge it is sensible to seek a single quantitative explanation for all such layering qualitative explanations for lower crustal layering abound and include igneous metamorphic structural and fluid related models measurements of reflection coefficients from the lower crust place strong quantitative constraints on possible models structurally induced anisotropy metamorphic layering or free fluids cannot realistically produce sufficiently bright reflections igneous layering or the juxtaposition of pre existing heterogeneities by shear zones can produce strong reflections results from crustal xenoliths helium isotope ratios palaeo geothermal gradients and chemistry of flood basalts together with numerical modelling of lithospheric extension and asthenospheric melting suggest that underplating and intrusion of the lower crust with mantle derived mafic igneous rocks is common the apparent spatial relationship between lower crustal layering and continental extension and the strength and continuity of the reflections suggest that underplating related to extension and or elevated mantle temperatures is a good explanation for lower crustal layering

estimating movement of reflectors in the water column using seismic oceanography the observation of spatial and temporal dynamics of the ocean is fundamental to understand global and regional aspects of water mixing physical oceanography has traditionally observed ocean structures with in situ measurements often limited in temporal and or spatial resolution in exploration seismology a set of techniques has been developed over the last decades to image and characterize the physical properties of sub seafloor structures by inversion methods at high horizontal resolution the two different fields have made contact in seismic oceanography where the well developed methods of marine reflection seismology have been applied to the dynamic ocean however one aspect so far ignored in seismic oceanography is the dynamical temporally varying nature of water structures here we show that it is possible to estimate temporal variations of reflectors in water structures as an inversion parameter the new dynamic property reflector movement velocity gives an additional parameter to characterize ocean water dynamics

reddening of dune sands evidence from southeast india thin section sem and tem analyses have indicated that the red teri sands of southeast india have formed from weathering in situ of coastal dune sands the data does not support a detrital origin for the red sands c14 dates indicate that dune deposition and weathering to a maximum depth of 10 m leading to the formation of a hematite koalinite and illite rich matrix has taken place rapidly over the past 25 000 years it is postulated that garnet was a major source of hematite ferric oxide

characterization of the sub mesoscale energy cascade in the alboran sea thermocline from spectral analysis of high resolution mcs data part of the kinetic energy that maintains ocean circulation cascades down to small scales until it is dissipated through mixing while most steps of this downward energy cascade are well understood an observational gap exists at horizontal scales of 103 101 m that prevents characterizing a key step in the chain the transition from anisotropic internal wave motions to isotropic turbulence here we show that this observational gap can be covered using high resolution multichannel seismic hr mcs data spectral analysis of acoustic reflectors imaged in the alboran sea thermocline shows that this transition is likely caused by shear instabilities in particular we show that the averaged horizontal wavenumber spectra of the reflectors vertical displacements display three subranges that reproduce theoretical spectral slopes of internal waves x 100 m kelvin helmholtz type shear instabilities 100 m x 33 m and turbulence x 33 m indicating that the whole chain of events is occurring continuously and simultaneously in the surveyed area

eruptive history and petrologic evolution of the albano multiple maar alban hills central italy a comprehensive volcanological study of the albano multiple maar alban hills italy using i 40ar 39ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and ii petrographic observations phase analyses of major and trace elements and sr and o isotopic analyses of the pyroclastic deposits shows that volcanic activity at albano was strongly discontinuous with a first eruptive cycle at 69 1 ka producing at least two eruptions and a second cycle with two peaks at 39 1 and 36 1 ka producing at least four eruptions contrary to previous studies we did not find evidence of magmatic or hydromagmatic eruptions younger than 36 1 ka the activity of albano was fed by a new batch of primary magma compositionally different from that of the older activity of the alban hills moreover the ree and 87sr 86sr data indicate that the albano magma originated from an enriched metasomatized mantle according to the modeled liquid line of descent this magma differentiated under the influence of magma limestone wall rock interaction our detailed eruptive and petrologic reconstruction of the albano maar evolution substantiates the dormant state of the alban hills volcanic district

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

relative contribution of temperature and salinity to ocean acoustic reflectivity 1 marine seismic data display laterally coherent reflectivity from the water column that is attributed to fine scale oceanic layering the amplitude of the different reflections is the expression of acoustic impedance contrasts between neighbouring water masses and therefore water reflectivity maps the ocean s vertical sound speed and density i e temperature and salinity variations here we determine the relative contribution of each parameter by computing the temperature and salinity partial derivatives of sound speed and density and using them to estimate reflection coefficients from a real oceanographic dataset the results show that the mean contribution of density variations is 5 10 while 90 95 is due to sound speed variations on average 80 of reflectivity comes from temperature contrasts salinity contribution averages 20 but it is highly variable and reaches up to 40 in regions prone to diffusive convection such as the top of the mediterranean undercurrent in the gulf of cadiz

resolution and illumination analyses in psdm a ray based approach prestack depth migration psdm should be the ultimate goal of seismic processing producing angle dependant depth images of the subsurface reflectivity but the expected quality of psdm images is constrained by many factors understanding all of these factors is necessary to improve depth imaging of geologic structures in all psdm approaches e g kirchhoff or wave equation migration always includes compensating for wave propagation in the overburden back propagation downward continuation etc before focusing back the reflected diffracted energy at each considered location in depth imaging ideally we would like to retrieve the reflectivity of the ground as detailed as possible to invert for the elastic parameters but the waves perceive the reflectivity through thick glasses seeing blurred structures and not necessarily all of them depending on the illumination only a filtered version of the true reflectivity is therefore retrieved being able to estimate these filters the so called re

full waveform inversion of reflection seismic data for ocean temperature profiles 1 we show that ocean temperature profiles can be accurately recovered using only acoustic methods employed at the sea surface using a towed air gun array and a hydrophone streamer thermohaline boundaries are ensonified at a suite of frequencies and angles yielding travel time trajectories and reflectivities these data are inverted via full waveform inversion to estimate sound speed and subsequently a temperature profile the high lateral data density of the seismic technique offers the potential of acoustically derived temperature profiles to be used to constrain models of ocean mixing and internal waves results on realistic synthetic data show that sound speed can be recovered with arbitrary accuracy when using broadband data with known source function and recording geometry application to field seismic data corroborated by expendable bathythermograph shows that even with a seismic acquisition system not specifically calibrated for seismic oceanography temperature contrasts within the ocean can be recovered to within one degree celsius

holocene and late pleistocene relative sea level fluctuations along the east coast of india abstract hermatypic coral colonies and intertidal fossil bearing grainstone packstone and sandstone beds of holocene and of a late pleistocene highstand are exposed above the present high tide level htl at a number of locations along the east coast of india from cape comorin to rameswaram being a passive margin boundary free from indications of late quaternary seismogenic movements this sector provides a benchmark for defining minor relative sea level perturbations during the late pleistocene and holocene highstands along a tropical coast lying between latitudes 5 n and 10 n a series of marine terraces carved on and locally blanketted by late pleistocene biotic and terrigenous accumulations occur at different elevations up to 4 4 m above ltl at manappad point possibly signifying discrete stillstand episodes followed by abrupt intervals of rising falling sea level sea level indicators of the holocene highstand occur in this sector as well as along the fringes of the godavari delta further north the holocene highstand reached nearly 3 m above ltl at 7 3 ka remained stable for approximately 1 7 kyr and was followed by a relative sea level fall between 5 2 and 4 2 ka there was a second pulse of relative sea level rise of a few metres leading to a fresh spurt in coral growth along the northern coast of mandapam and rameswaram this was nearly contemporaneous with fresh melting of ice sheets of antarctica the little ice age lia witnessed a minor 1 m relative sea level fall along this coast resulting in rapid diagenetic hardening and infiltration of goethite into the emerged foreshore sand at karikovil and its neighbourhood this was followed by a rise of the sea level during the last few centuries

holocene landscape dynamics in the ghaggar hakra palaeochannel region at the northern edge of the thar desert northwest india abstract precession forced change in insolation has driven de intensification of the asian monsoon systems during the holocene set against this backdrop of a weakening monsoon indus civilisation populations occupied a number of urban settlements on the ghaggar hakra plains during the mid holocene from 4 5 ka until they were abandoned by around 3 9 ka regional climatic variability has long been cited as a potential factor in the transformation of indus society however there remain substantial gaps in the chronological framework for regional climatic and environmental change at the northern margin of the thar desert this makes establishing a link between climate environment and society challenging this paper presents 24 optically stimulated luminescence ages from a mixture of 11 fluvial and aeolian sedimentological sites on the ghaggar hakra floodplain interfluve an area which was apparently densely populated during the indus urban phase and subsequently these ages identify fluvial deposition which mostly pre dates 5 ka although fluvial deposits are detected in the ghaggar palaeochannel at 3 8 ka and 3 0 ka post dating the decline of urbanism aeolian accumulation phases occur around 9 ka 6 5 ka 2 8 ka and 1 7 ka there is no clear link to a 4 2 ka abrupt climate event nor is there a simple switch between dominant fluvial deposition and aeolian accumulation and instead the osl ages reported present a view of a highly dynamic geomorphic system during the holocene the decline of indus urbanism was not spatially or temporally instantaneous and this paper suggests that the same can be said for the geomorphic response of the northern thar to regional climate change

optically stimulated luminescence dating of holocene relict foredunes guichen bay south australia abstract optically stimulated luminescence osl dating of quartz sand 106 150 or 150 200 m in bioclastic carbonate quartz sediments sampled from coastal relict foredunes beach ridges was undertaken to evaluate the utility of the osl method for studies of dune dynamics and to quantify rates of coastal progradation twelve sediment samples from a 4 km transect across a holocene embayment fill at guichen bay south australia were measured for their luminescence characteristics apart from one age inversion attributed to recent disturbance associated with mining the osl ages are in sequential order when considered in the context of their associated error terms the osl ages indicate an extremely rapid initial phase of sedimentation i e 1600 m within a few hundred years approximately 5 ka ago followed by a constant rate of progradation for the past 4 ka of 0 39 m a with a high level of association between distance across the embayment fill and luminescence age for this time interval an average rate of dune development of one dune every 80 yr from 3900 yr ago to the present day is apparent the osl ages for the late holocene indicate that the present beach state is largely in equilibrium with sediment supply

simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the kuroshio extension front 1 new simultaneous seismic reflection and physical oceanographic observations east of japan demonstrate the utility of the seismic reflection method in mapping oceanic fine structure synthetic seismograms calculated from temperature and salinity data confirm that seismic reflections correlate with physical oceanographic structures seismic reflections at the boundary between the warm kuroshio and the cold oyashio water masses correspond to well developed 10 m scale temperature fine structure vertical current profiles suggest that this fine structure is caused by interleaving of these two water masses we compare our seismic images with acoustic doppler current profiler adcp intensity maps and discuss similarities and the differences between seismic images and the adcp maps our study demonstrates that even relatively low energy seismic sources in this case a 3 4 l 210 in3 generator injector gi airgun can be used to image upper oceanic fine structure

early deglacial 19 17 ka strengthening of the northeast monsoon 1 earlier studies that mostly relied on bulk 14c dating indicated a weaker southwest monsoon swm and a stronger than present northeast monsoon nem during the last glacial maximum lgm 18000 14c years or 21000 calendar years ago we have analyzed a sediment core from the equatorial indian ocean where planktonic foraminifera were dated by accelerator mass spectrometry ams 14c 18o analysis of three species of foraminifera viz globigerinoides ruber globigerinoides sacculifer and globorotalia menardii reveals that the nem strengthened during the early deglacial period 15000 14c years ago or 18000 calendar years ago relative to the present and not during the lgm as surmised earlier

a stochastic view of lower crustal fabric based on evidence from the ivrea zone despite its complicated history the ivrea zone is considered to be a representative surface exposure of extended continental crust we have digitized two standard 1 25 000 geological maps from this area and evaluated their structural statistics because of the subvertical orientation of the ivrea zone these maps can be considered as small scale cross sections through the lower continental crust the autocorrelation functions of the digitized lithologies measured from these maps show a clear self similar or fractal rather than a gaussian or deterministic trend we found that an anisotropic von karman correlation function with an aspect ratio around 4 and a hurst number of 0 3 corresponding to a fractal dimension of 2 7 matches the observed data our results represent an explicit confirmation of previous indirect evidence for the fractal nature of lithospheric heterogeneities and provide the means to construct realistic crustal scale seismic models of ivrea type lower continental crust

3d ray born migration inversion part 2 application to the seg eage overthrust experiment the seg eage overthrust model is a synthetic onshore velocity model that was used to generate several large synthetic seismic data sets using acoustic finite difference modeling from this database several realistic subdata sets were extracted and made available for testing 3d processing methods for example classic onshore type data acquisition geometries are available such as a swath acquisition which is characterized by a nonuniform distribution of long offsets with azimuth and midpoints in this paper we present an application of 2 5d and 3d ray born migration inversion to several classical data sets from the seg eage overthrust experiment the method is formulated as a linearized inversion of the scattered wavefield the method allows quantitative estimates of short wavelength components of the velocity model first we apply a 3d migration inversion formula formerly developed for marine acquisitions to the swath data set the migrated sections exhibit significant amplitude artifacts and acquisition footprints also revealed by the shape of the local spatial resolution filters from the analysis of these spatial resolution filters we propose a new formula significantly improving the migrated dip section we also present 3d migrated results for the strike section and a small 3d target containing a channel finally the applications demonstrate that the ray born migration formula must be adapted to the acquisition geometry to obtain reliable estimates of the true amplitude of the model perturbations this adaptation is relatively straightforward in the frame of the ray born formalism and can be guided by the analysis of the resolution operator