do seismic reflections necessarily have chronostratigraphic significance many seismic reflections from within sedimentary successions are thought to be generated along stratal surfaces because those surfaces are laterally continuous and have marked acoustic impedance contrasts as stratal surfaces are isochronous those reflections are then also taken as being chronostratigraphically significant in contrast seismic reflections are thought not to be generated along the boundaries of lithostratigraphic units because those boundaries are discontinuous and gradational nevertheless synthetic seismic analysis shows that seismic reflections should in many circumstances be expected to follow lithostratigraphic unit boundaries not stratal surfaces as these lithostratigraphic unit boundaries will generally be diachronous seismic reflections from within sedimentary successions should evidently not be treated as necessarily having chronostratigraphic significance

deuterium and oxygen 18 in precipitation and atmospheric moisture in the upper urumqi river basin eastern tianshan mountains the contribution of stable isotopes in meteorological climatological and hydrological research is well known this study analyzed the deuterium and oxygen 18 contents d and 18o of precipitation in event based samples at three stations glacier no 1 zongkong houxia along the upper urumqi river basin from may 2006 to august 2007 the 18o in precipitation revealed a wide range and a distinct seasonal variation at all three stations with enriched values occurring in summer and depleted values in winter a statistically significant positive correlation was observed between the 18o and d and local surface air temperature and better linear relationship existed between 18o and air temperature than that of d this suggests that paleoclimatic archives relating to precipitation 18o and d can be useful for qualitative temperature reconstruction the d excess in precipitation also exhibited a seasonal variability based on ncep ncar reanalysis data three dimensional isentropic back trajectories in hysplit model were employed to determine the moisture source for each precipitation event results indicate a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter and d excess can be used as a sensitive tracer of the moisture transport history

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

transport of atmospheric impurities over the qinghai xizang tibetan plateau as shown by snow chemistry abstract chemical records were recovered from samples collected from snow pits over two transects s n and se nw across the qinghai xizang tibetan plateau the records show that the flux of major ions in the regions to the north of mt tanggula is on the average 6 30 times higher than that of the regions to the south and 0 6 5 times higher than regions to the southeast it appears that mt tanggula provides a barrier to continental dust transported across the plateau from the north and to marine aerosols transported from the southeast the spatial patterns of snow chemistry as well as the total suspended particle tsp distribution along the northern qinghai xizang highway demonstrate that continental dust originates mainly from the deserts to the north while monsoon sources of moisture exert greater influence on snow chemistry on the southern part of the plateau seasonal variations of the major ions were also examined in a firn core drilled at a height of 7000 m on the dasuopu glacier and in a snow pit from the meikuang glacier eastern kunlun the choice of a high altitude site at dasuopu and the sampling season before snowmelt at meikuang avoided post depositional modification processes mainly the elution effect of meltwater thus guaranteeing the reliable recovery of the distribution of impurities in different seasons the peak of the impurities appear at dasuopu during the spring and at meikuang in the winter spring coinciding with the asian dust season however the amplitude of the seasonal variations at meikuang is much higher than at dasuopu ph values at the dongkemadi glacier are greater than 6 but at the dasuopu glacier himalayas they range between 4 and 7 5 the liquid conductivity lc from dongkemadi is positively correlated with the ph while at dasuopu lc is positively correlated with ph when ph is below 6 and negatively correlated with ph when it is greater than 6 this implies that during august to september the himalayan range is a transition zone between the transportation of continental dust and marine aerosols

an oxygen isotope paleothermometer from ice in siberian permafrost abstract there is a clear linear relationship between mean annual or seasonal air temperature at the earth s surface and the mean oxygen isotopic composition of precipitation in polar regions whereas this relationship is well preserved in polar ice caps it may not be in permafrost because freshly deposited snow in permafrost areas is subjected to great deflation and drifting by wind moreover melting and freezing within the snow cover and the active layer can lead to isotopic fractionation the 18 o of recent ground ice also depends on its geomorphic context and on the lithology content of organic matter of ice containing sediments nevertheless mean cold season air temperature near the ground surface and 18 o in recent ground ice are highly correlated therefore the 18 o of ground ice ice cement and segregated ice in permafrost areas can be used for paleoclimatic reconstructions

the origin and nature of seismic reflections of sharp based shoreface deposits upper jurassic siliciclastics northern france in order to advance understanding of the relationship between geological properties and their physical expression in reflection images this study has focused expertise in reflection geophysics petrophysics and sedimentology on the same geological object in this case a succession of upper jurassic sharp based shoreface deposits embedded in offshore marine shales in northern france this integrated approach to determine firstly the origin and nature of seismic reflections calibration and secondly to provide a means of extracting geological information from seismic imagery inverse calibration was built on the following analytical steps firstly detailed and extensive petrophysical analyses of outcrop plug samples continuous core and sonic well logs in combination with a quantification of mineralogical and textural properties allowed a direct conversion of acoustic properties impedance into sedimentological properties resulting in a quantitative physical sequence stratigraphic model secondly the integration of scale dependent acoustic measurements ranging from 0 01 m and 320 khz on cores up to the wavelength of field seismic data was established using an averaging algorithm an effective medium theory type as an upscaling approach this alternative to a vsp or check shot allows an optimized depth time conversion and hence determination of the origin of the seismic reflections with previously unattainable accuracy finally the shape and scale dependence of impedance contrasts were integrated into so called singularity parameters that directly link depositional changes with information from seismic reflections depositional changes in the shallow water domain are generally characterized by step functions whereas those in more distal depositional environments are represented by spiky functions this approach allows the recognition of the associated reflection events and vice versa it provides a unique opportunity to extract the character of impedance changes and thus changes in depositional environment from seismic reflection records in general

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

forward seismic modeling as a guide improving detailed seismic interpretation of deltaic systems example of the eocene sobrarbe delta outcrop south pyrenean foreland basin spain as a reference to the analogous subsurface albian cenomanian torok nanushuk delta of the colville basin npra usa abstract a forward seismic model of the middle eocene sobrarbe delta outcrop south pyrenees spain has been made to investigate its seismic signature the sobrarbe delta complex corresponds to a syntectonic sedimentary wedge locally thicker than 1000 m this 15 km long highly progradational and moderately aggradational sedimentary system presents sigmoid and oblique clinoforms characterized by slopes ranging from 0 2 to 5 7 along the clinoforms the classical deltaic depositional environments grade progressively from one to the other alluvial plain delta plain delta front and prodelta locally specific carbonate deposits occur corresponding to transgressive pulses the transition from delta front to prodelta is locally marked by large slide scars affecting clinoform morphology a detailed outcrop transect of the sobrarbe delta was converted to an acoustic impedance model by assigning petrophysical properties to each geological facies this model was then used to create synthetic seismic lines characterized by various input wavelets the resulting various peak frequency synthetic seismic lines have been interpreted and the seismic interpretation compared to the outcrop description to calibrate the seismic interpretation and assess the limits of that interpretation this work shows that the seismic stratigraphy methodology is consistent and allows the correct interpretation of most seismic sequences however composite reflections from rapid lateral facies transitions and higher frequency sequence boundaries can clearly lead to seismic interpretation mistakes the seismic facies of seven facies associations have been described providing guidelines to recognize them on actual seismic lines the synthetic seismic image of four selected systems tracts comprising good reservoir bodies has been analyzed to highlight recognition criteria which can be used to interpret analog deltaic systems in the subsurface and therefore enhance the prediction and characterization of the reservoir bodies that they hold these guidelines were systematically applied to a direct subsurface analog the torok nanushuk delta colville basin npra usa

isotope stratification in high mountain glaciers examples from the peruvian andes and himalaya fonte et sublimation des neiges et glaces analysees a partir d analyse d oxygene 18 et du deuterium

variations of chemical features in a monsoon glacier watershed southeastern tibet plateau the ph ec electric conductivity 18o and major ions in melt water precipitation runoff and groundwater samples which were collected in baishui basin were analyzed based on chemical analysis the characteristic variations are analyzed in this paper the melt water precipitation runoff and groundwater were ca2 mg2 hco3 type with similar ion compositions but showed different ion concentrations normally the content is high in groundwater and runoff water but low in melt water and precipitation from the upper basin glacier downward there was a general increasing trend for the total ion concentrations in basin hco3 and ca2 accounted for more than 80 of total ions in samples indicating that ions mainly came from limestone and water typical of carbonate solution water water rock interaction is the significant contributor to water geochemistry the concentration of inorganic ion in melt water had an obvious diurnal variation with temperature change the 18o values increases with the altitude decrease the similarity of 18o in runoff and groundwater samples was due to their frequent transformation in karst regions

seismic modeling of an early jurassic drowned carbonate platform djebel bou dahar high atlas morocco 1 along the southern margin of the high atlas of morocco early jurassic carbonate platforms developed in a transtensional rifted basin one of these platforms was the djebel bou dahar platform which grew to a vertical relief of 500 m drowned and was onlapped by deep marine sediments exceptional outcrops allowed detailed lithologic models of the platform to be made with a resolution of a few meters we constructed a geometric model from building blocks comprising particular rock types we estimated p wave velocities and bulk densities of these lithologies from hand specimens and we assumed these properties to be homogeneous and invariant throughout the building blocks we constructed time sections of reflectivity from vertical incidence and image ray migration techniques these time sections were convolved with 25 to 200 hz ricker wavelets to produce synthetic seismic sections large scale features such as the platform and the drowning unconformity were resolved regardless of the frequencies and modeling techniques used broad low frequency wavelets resulted in profiles with apparent truncation of bedding and basinward shifts in the point of onlap smaller scale features such as reef knolls and sand bodies at the platform margin were poorly resolved at frequencies up to 50 hz however we inferred the existence and location of these smaller features from the disturbance and distortion of other reflections this distortion is most obvious in image ray migration modeling because of the refraction of rays through the small scale features geometric effects caused lateral amplitude variations due to wavelet interference along the unconformity reflection where no petrophysical changes were modeled the seismic models of the djebel bou dahar in its present stage may be good analogs for seismic lines of deeply buried carbonate platforms to make a comparison with real seismic lines of less deeply buried platforms possible we reconstructed both the geometry and petrophysical properties and the subsequent seismic modeling of the djebel bou dahar carbonate platform as it was prior to the onset of deep burial at this stage impedance contrasts were at their maximum this study clearly demonstrates the significance of modeling the seismic response of a detailed outcrop based stratigraphic model and shows that seismic modeling of specific sequence stratigraphy can reveal what features are likely to be resolved under ideal conditions and what pitfalls may await the interpreter

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

tidal truncation and barotropic convergence in a channel network tidally driven from opposing entrances residual circulation patterns in a channel network that is tidally driven from entrances on opposite sides are controlled by the temporal phasing and spatial asymmetry of the two forcing tides the napa sonoma marsh complex in san francisco bay ca is such a system a sill on the west entrance to the system prevents a complete tidal range at spring tides that results in tidal truncation of water levels tidal truncation does not occur on the east side but asymmetries develop due to friction and off channel wetland storage the east and west asymmetric tides meet in the middle to produce a barotropic convergence zone that controls the transport of water and sediment during spring tides tidally averaged water surface elevations are higher on the truncated west side this creates tidally averaged fluxes of water and sediment to the east during neap tides the water levels are not truncated and the propagation speed of the tides controls residual circulation creating a tidally averaged flux in the opposite direction

seismic modelling of outcrop carbonate systems an application to the cretaceous platform to basin system of the maiella mountain central apennines italy

morphology hydrography and sediment dynamics in a mangrove estuary the konkoure estuary guinea the konkoure estuary in the republic of guinea is a poorly understood atypical mangrove system sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge morphology salinity erosion and deposition processes the settling of mud physico chemical processes and mangrove swamps here we present a consistent set of data aimed at characterising the estuary and thus increasing our understanding of tropical systems as well as studying the impact of human intervention in the region water elevations current measurements salinity suspended sediment concentrations bathymetry and sediment cover are presented following a 3 year survey of the konkoure estuary here we provide conclusive evidence that the lower konkoure is a shallow funnel shaped mesotidal mangrove fringed tide dominated estuary well mixed during low river discharge the estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides the konkoure estuary has been described as hypersynchronous and has three terminal outlets two of which are landward directed attesting to a tidal pumping effect while the third one is seaward directed and is controlled by the mangrove the suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the turbidity maximum zone tmz the location of the tmz is river controlled and is correlated with residual currents but not with salinity front a dam constructed 130 km upstream impacts on the hydrodynamics and reduces the salinity intrusion by about 25 it causes an increased low river discharge whereas its efficiency over high river flows is unclear

climatological significance of δ18 o in precipitation and ice cores a case study at the head of the urumqi river tien shan china stable oxygen isotope ratios 18 o of precipitation and ice core samples collected from the headwaters of the urumqi river tien shan china were used to test the relationship between 18 o and contemporaneous surface air temperature t a a strong temporal relationship is found between 18 o in precipitation and t a particularly for the monthly averages which remove synoptic scale influences such as changes in condensation level condensation temperature and moisture sources yao and others 1996 linear fits as high as 0 95 c for precipitation events and 1 23 c for monthly averages are found although the 18 o amplitude in ice cores drilled at the nearby urumqi glacier no 1 2 km from the precipitation sampling site decreased dramatically compared to the precipitation samples the ice core records of annually averaged 18 o are still positively correlated with contemporaneous air temperature especially summer air temperature at the nearby daxigou meteorological station nevertheless the relationship between the ice core 18 o records and contemporaneous air temperature is less significant than that for the precipitation samples due to depositional and post depositional modification processes which are highlighted by the successive snow pit 18 o profiles from the urumqi glacier no 1 our results might extend the application of high altitude and subtropical ice core 18 o t a records for palcoclimate reconstruction

the isotopic record at an alpine glacier and its implications for local climatic changes and isotopic homogenization processes stratigraphic variations of oxygen isotopes in the snow which accumulates during the winter at the norwegian glacier austre okstindbreen are not entirely eliminated after 1 2 months of ablation in the following summer the relationship between regional temperature changes and 18 o values in the snowpack is affected by many natural factors but 1989 90 winter air temperatures were reflected in the snow which remained on austre okstindbreen at 1350 m a s l in july 1990 there were many variations of 18 o values in the 4 1 m of snow above the 1989 summer surface but variations in the underlying firn were relatively small meltwater percolation modifies the initial variations of 18 o values in the snowpack at a site below the mean equilibrium line altitude on austre okstindbreen increased isotopic homogenization within a 10 day period in july accompanied an increase of the mean 18 o value although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers it can provide an estimate of the approximate trend of local temperature variations

three dimensional geological and synthetic seismic model of early permian redeposited basinal carbonate deposits victorio canyon west texas the lower permian outcrops of victorio canyon in the sierra diablo mountains in west texas show undisturbed stratigraphy of carbonate toe of slope and basinal deposits these rocks consist of a vertical stack of carbonate debris flow deposits and hyperconcentrated density flow deposits thick skeletal ooid grainstone deposited as basin floor fans various reworked muddy carbonate deposits and fine siliciclastic siltstones this succession was deposited within five sequences that include the upper hueco formation late wolfcampian through the bone spring formation middle leonardian using a ground based light detecting and ranging generated high resolution digital outcrop model dom aged as a template we mapped and digitized the stratigraphy of the toe of slope and basinal deposits on the 5 cm 2 in precision dom on the basis of the digitized stratigraphic contacts several regional surfaces were constructed and a 3 d geocellular model was built facies information within this model is extrapolated from measured section data using both a kriging algorithm and stochastic simulations using impedance values extracted from a subsurface analog a 3 d impedance model was created for both the kriged and the stochastic models both models incorporate fine scale stratigraphic architecture in addition the stochastic impedance model incorporates spatially correlated noise resulting in more realistic synthetic seismograms three dimensional synthetic seismograms were calculated at 20 40 and 80 hz the reservoir prone facies is skeletal ooid grainstone deposited as a 1 5 km 750 m 0 93 mi 2460 ft basin floor fan up to 15 m 49 ft thick this basin floor fan is subtly imaged in vertical seismic section at a frequency below 80 hz it is however better recognized on time slices with peak frequency as low as 20 hz and even better delineated on horizon slices that parallel the stratigraphy

seismic modeling of a strongly emergent thrust front west spitsbergen fold belt svalbard to improve our understanding of the seismic signature of contractional structures in foreland fold and thrust belts seismic modeling of a strongly emergent thrust front was carried out the modeled structures are a set of well exposed imbricated fault bend folds with steep forelimbs and moderately dipping backlimbs occurring in silicified upper permian carbonates and schists these structures present at the frontal part of the west spitsbergen fold and thrust belt are developed above a decollement layer in permian evaporites to simulate a synthetic migrated seismic section image ray modeling was carried out the acoustic impedances used in the modeling were obtained from laboratory measurements of rock samples a significant apparent structural high time high a well as non real folds and faults were created by the seismic reflection technique without the excellent field control these structures would have been interpreted as real indicating deformational features also structurally below the sole thrust in the area the time high would most certainly survive a traditional depth conversion procedure and could easily have been misinterpreted as a hydrocarbon trap high quality seismic reflection profiles in isfjorden paralleling the contraction direction and along strike from the modeled onshore section show many of the same structural features as in the synthetic model the seismic modeling demonstrates that care should be exercised when interpreting seismic sections in areas with contractional structures and suggests that modeling of xposed structural analog is a necessary supplement in detailed seismic studies of such complex contractional geometries

studies on holocene mangrove ecosystem dynamics of the braganca peninsula in north eastern para brazil abstract three sediment cores from the braganca peninsula located in the coastal region in the north eastern portion of para state have been studied by pollen analysis to reconstruct holocene environmental changes and dynamics of the mangrove ecosystem the cores were taken from an avicennia forest bosque de avicennia bda a salt marsh area campo salgado cs and a rhizophora dominated area furo do chato pollen traps were installed in five different areas of the peninsula to study modern pollen deposition nine accelerator mass spectrometry radiocarbon dates provide time control and show that sediment deposits accumulated relatively undisturbed mangrove vegetation started to develop at different times at the three sites at 5120 14c yr bp at the cs site at 2170 14c yr bp at the bda site and at 1440 14c yr bp at the fdc site since mid holocene times the mangroves covered even the most elevated area on the peninsula which is today a salt marsh suggesting somewhat higher relative sea levels the pollen concentration in relatively undisturbed deposits seems to be an indicator for the frequency of inundation the tidal inundation frequency decreased probably related to lower sea levels during the late holocene around 1770 14c yr bp at bda around 910 14c yr bp at fdc and around 750 14c yr bp at cs the change from a mangrove ecosystem to a salt marsh on the higher elevation around 420 14c yr bp is probably natural and not due to an anthropogenic impact modern pollen rain from different mangrove types show different ratios between rhizophora and avicennia pollen which can be used to reconstruct past composition of the mangrove in spite of bioturbation and especially tidal inundation which change the local pollen deposition within the mangrove zone past mangrove dynamics can be reconstructed the pollen record for bda indicates a mixed rhizophora avicennia mangrove vegetation between 2170 and 1770 14c yr bp later rhizophora trees became more frequent and since ca 200 14c yr bp avicennia dominated in the forest

sequence stratigraphy after the demise of a high relief carbonate platform carnian of the dolomites sea level and climate disentangled abstract sedimentary facies analysis aided by quantitative 3d georeferenced field data is applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the late triassic of the dolomites this multidisciplinary approach was the key to disentangle the timing of climatic change vs sea level fluctuation and their effects on shallow water carbonate depositional systems the carnian pluvial event a global episode of climate change worldwide documented at low latitudes involved increased rainfall and possibly global warming this climatic event begins before a drop of sea level and caused the demise of microbial dominated high relief carbonate platforms that dominated the dolomites region and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal oolitic grainstones a subsequent sea level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic bioclastic grainstones the crisis of early carnian shallow water carbonate systems of the dolomites generated a geological surface similar to a drowning unconformity although no transgression occurred as the high relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic skeletal siliciclastic ramps basins were rapidly filled the change of carbonate depositional systems was associated with an increase in siliciclastic input in turn triggered by the onset of a humid climatic event and only later to a sea level drop this evolution of carbonate systems cannot be interpreted in the light of sea level changes only climate change and consequent ecological changes in the main carbonate producing biotas induced significant modifications in depositional geometries this case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because despite a drop in shallow water carbonate production a combination of low subsidence and or sea level drop maintains the platform top at shallow depth

seasonal deuterium excess in a tien shan ice core influence of moisture transport and recycling in central asia 1 stable water isotope 18o d data from a high elevation 5100 masl ice core recovered from the tien shan mountains kyrgyzstan display a seasonal cycle in deuterium excess d d 8 18o related to changes in the regional hydrologic cycle during 1994 2000 while there is a strong correlation r2 0 98 between 18o and d in the ice core samples the regression slope 6 9 and mean d value 23 0 are significantly different than the global meteoric water line values the resulting time series ice core d profile contains distinct winter maxima and summer minima with a yearly d amplitude of 15 20 local scale processes that may affect d values preserved in the ice core are not consistent with the observed seasonal variability data from central asian monitoring sites in the global network of isotopes in precipitation gnip have similar seasonal d changes we suggest that regional scale hydrological conditions including seasonal changes in moisture source transport and recycling in the caspian aral sea region are responsible for the observed spatial and temporal d variability

parameters controlling sonic velocities in a mixed carbonate siliciclastics permian shelf margin upper san andres formation last chance canyon new mexico we have measured the acoustic properties and mineralogic composition of 48 rock specimens from mixed carbonate siliciclastic outcrops of the permian upper san andres formation in last chance canyon new mexico the goals were 1 identify and model the parameters controlling the sonic velocities 2 assess the influence of postburial diagenesis on the acoustic velocities the variation in sonic velocity in the 0 to 25 porosity range is primarily controlled by porosity and secondly by the ratio of carbonate siliciclastic material linear multivariate fitting resulted in a velocity porosity carbonate content transform that accurately predicts sonic velocity at different effective stresses the slope of the velocity porosity transform steepens with increasing carbonate content which may be explained by the higher velocity of carbonate minerals another reason may be the property of carbonate minerals to form more perfect intercrystalline boundaries that improve the transmission properties of acoustic waves and are less sensitive to changes in effective stress the velocity ratio vp vs is an excellent tool to discriminate between predominantly calcitic lithologies ratio between 1 8 and 1 95 and predominantly dolomitic and quartz rich lithologies ratio between 1 65 and 1 8 gardner s experimental curve overestimates and the velocity porosity transforms by wyllie and raymer underestimate the observed sonic velocities probably because they do not account for variations in texture carbonate mineralogy and pore geometry petrographic observations show that postburial diagenesis is minor and does not seem to significantly affect porosity therefore the outcrop data set can be regarded as a proxy for the subsurface analog these findings underline the significantly more complex acoustic behavior in mixed carbonate siliciclastic sedimentary rocks than in pure siliciclastics where mineralogic composition explains most of the observed relationships between porosity and sonic velocity

depositional cycles composite sea level changes cycle stacking patterns and the hierarchy of stratigraphic forcing examples from alpine triassic platform carbonates carbonate platform deposits record a complex interplay of numerous geodynamic variables of which eustasy subsidence and sediment accumulation are prime factors in determining both the kilometer scale depositional sequence scale and meter scale depositional cycle scale stratigraphic packaging in this study we looked particularly at composite eustasy that is superimposed sea level fluctuations with different frequencies defined as orders and different amplitudes and the role it plays in the linkage between meter scale cyclic stratigraphy and kilometer scale sequence stratigraphy specifically we have investigated the relationship between low frequency third order 1 10 m y period depositional cycles and their component high frequency fourth 0 1 1 m y and fifth 0 01 0 1 m y order cycles through detailed stratigraphic analyses of alpine triassic platforms complemented by computer modeling on the basis of our results we suggest that in general there exists a hierarchy of stratigraphic forcing driven by composite eustasy that results in organized stacking patterns thickness subfacies character early diagenetic attributes of high frequency typically fourth and fifth order shallow water carbonate cycles dictated by low frequency third order relative sea level effects we suggest that systematic vertical changes in stacking patterns of high frequency cycles across a larger depositional sequence are due to systematic and predictable differences in depositional space available during the rising and falling stages of a relative third order sea level change we also suggest that these systematic variations in cycle stacking patterns will exist regardless of the mechanism responsible for generating the high frequency cycles be it an autocyclic or allocyclic mechanism this approach has major implications for the use of high frequency fourth and fifth order cycle characteristics to identify third order cycles in outcrops and cores of shallow water carbonates where stratigraphic control may be less than desirable this would constitute a valuable bridge between cyclic stratigraphy at the meter scale and sequence stratigraphy at the seismic scale we present two examples from triassic buildups of the alps the ladinian latemar buildup and the norian dolomia principale where a systematic succession of high frequency cycle stacking patterns and early diagenetic features exists within an overriding third order cycle sequence reflecting the interplay of short term high frequency fourth fifth order eustasy and long term low frequency third order eustasy in accordance with the hierarchy of stratigraphic forcing central to the interpretation of these examples is the demonstration that true eustatic rhythms are recorded in the high frequency cyclicity as verified by time series analyses and the use of fischer plots these examples can be modeled by computer under conditions of lag depth constrained sedimentation uniform subsidence and composite eustasy we also present two examples one from the alpine triassic the norian lofer cyclothems and one from the pleistocene of south florida that lack both a systematic succession of high frequency cycle stacking patterns and identifiable composite rhythms in the stratigraphic record despite the existence of composite high frequency eustasy in these examples we call upon 1 local tectonic forcing in the form of short term deviations in subsidence via faulting lofer example and 2 large differences in the relative amplitudes of different orders of high frequency sea level oscillations pleistocene example to explain the lack of composite rhythms and we present computer simulations to illustrate the concepts an understanding of composite relative sea level changes and the potential for a hierarchy of stratigraphic forcing provides the link between cyclostratigraphy and sequence stratigraphy and also has important implications regarding the stratigraphy of early diagenesis

compositional variations during phases of progradation and retrogradation of a triassic carbonate platform picco di vallandro durrenstein dolomites italy in this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of triassic carbonate platforms in the dolomites italy for this purpose a succession was studied from the toe of slope of a triassic carnian carbonate platform picco di vallendro durrenstein dolomites italy the microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts the main input however was derived from the reefs on the platform retrogradation of the platform showed an increase of filaments and radiolarians open ocean biota as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins however the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt probably during relative sea level lowstands carbonate composition varies systematically with toe of slope progradation retrogradation and thus argues for carbonate production as the main driver of the geometries observed at the toe of slope

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

stable isotope ratios in precipitation and their relationship with meteorological conditions in the kumaon himalayas india summary for the first time environmental isotopic 2h 18o 3h data predominantly based on precipitation samples in the kumaon himalayas india have been used to understand the influence of various meteorological factors governing rainout processes in the region further the data are also used to understand the orographic effects in precipitation and to estimate the altitude effect in stable isotopic ratios in precipitation etc the interpretation of the isotopic data revealed that the source of moisture for winter october february and summer may precipitation in the kumaon himalayas is mainly from the western disturbances whereas for the remaining period the source is monsoonal southwest the 2 18o relationship in the local precipitation during the monsoon season shows a distinct seasonal effect with a slope of 7 6 the winter and summer precipitation samples measured higher environmental 3h compared to southwest monsoon samples thus indicating continental evaporated moisture there is wide range of altitude effects 18o variation per 100 m elevation 0 30 july august 0 57 september with the mean altitude effect being 2 61 and 0 36 per 100 m elevation for 2h and 18o respectively these values are different from that reported earlier for the region based on the isotopic compositions of springs rivers samples the altitude effect in successive precipitation is basically a temperature dependent phenomenon and is explained on the basis of adiabatic cooling related rainout process dry adiabatic lapse rate moist adiabatic lapse rate and saturated adiabatic lapse rate for moist air mass the altitude effect is found to be more reliable in case of 2 as deuterium is least affected by secondary evaporation the effect of secondary evaporation has been observed on the true altitude effect secondary evaporation of rainfall increases the oxygen isotopic ratios and the increase is directly proportional to the vertical distance travelled by the raindrops through air

tectonics of the dolomites southern alps northern italy abstract in post variscan times the dolomites underwent a number of tectonic events which may be summarized as follows permian and triassic rifting phases broke the area into n s trending basins with different degrees of subsidence a middle triassic transpressive event then deformed the region along a n70 e axis generating flower structures within the basement volcano tectonic domal uplift and subsequent caldera formation occurred at the same time as the late ladinian magmatism early jurassic rifting also controlled the subsidence which increased eastward this long period of deformation was followed by a pre neogene late cretaceous palaeogene e w ene wsw compression which generated a w vergent belt possibly equivalent to the folded foreland of the dinaric chain a 70 km e w section of the dolomites indicates shortening of at least 10 km during the neogene the dolomites as far north as the insubric lineament were the innermost part of a s vergent thrust belt the basement of the dolomites was thrust southwards along the valsugana line onto the sedimentary cover of the venetian prealps for at least 10 km this caused a regional uplift of 3 5 km the valsugana line and its backthrusts on the northern side of the central dolomites generated a 60 km wide pop up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural slip often forming triangle zones the shortening linked to this folding is about 5 km with neogene thrusts faulting and folding pre existing thrust planes on the north eastern side of the dolomites neogene deformation is apparently more strictly controlled by the transpressive effects of the insubric lineament and shortening of the sedimentary cover may be greater than in the central dolomites minor deformation linked to the giudicarie belt is present in the western dolomites the present structure of the dolomites is thus the result of a number of tectonic events of different significance and different strike only a 3 dimensional restoration can unravel the true structure of the dolomites

temporal changes of glacier hydrological systems indicated by isotopic and related observations at austre okstindbreen okstindan norway 1976 87

toe of slope of a cretaceous carbonate platform in outcrop seismic model and offshore seismic data apulia italy synthetic seismic models of outcrops in the early cretaceous slope of a carbonate platform on the gargano promontory southern italy were compared to an offshore seismic section south of the promontory outcrops of the same age on the promontory have the same sequence stratigraphic characteristics as their offshore equivalent and are the only areas where the transition from platform to basin of early cretaceous is exposed on land two adjacent outcrop areas were combined into one seismic scale lithologic model with the aid of photo mosaics measured sections and biostratigraphic data velocity density and porosity measurements on spot samples were used to construct the impedance model seismic models were generated by vertical incidence and finite difference programs the results indicate that the reflections in the seismic model are controlled by the impedance contrast between low porous intervals rich in debris from the platform and highly porous intervals of pelagic lime mudstone nearly devoid of debris finite difference seismic display showed best resemblance with the real seismic data especially by mapping a drowning unconformity

spatial and temporal variations of oxygen isotopes in snowpacks and glacial runoff in different types of glacial area in western china in order to improve understanding of spatial and temporal variations of stable isotopes in atmospheric precipitation snow cover and glacier meltwater in different regions of china samples were collected for isotopic analysis in four areas yulong mountain yunnan himalaya temperate glacier area samdain kangsang mountain nyainqentanglha shan subpolar glacier area the headwater area of the urumqi river tien shan subpolar glacier area and muztag mountain pamirs polar glacier area sampling was undertaken in both summer and winter between 2000 and 2003 the d 18 o values show a temperature altitude effect in new winter snow on yulong mountain reflecting the condensation and fractionation processes associated with the winter monsoon but a different more complex pattern in residual snow deposited during the summer monsoon this old snow is influenced by the precipitation amount effect solar radiation and evaporation and the water content of the snowpack the summer precipitation at samdain kangsang mountain is associated with the summer monsoon there is a marked precipitation amount effect during the long passage of the southwest india monsoon from the distant moisture source to samdain kangsang mountain and the summer precipitation is strongly depleted of the heavy isotope above 6000 m the high radiation flux causes much evaporation from the snow surface the associated 18 o enrichment of the snow is reflected in a reverse altitude effect the d 18 o values in the summer snowpack of the tien shan and muztag mountain decrease with increasing altitude and decreasing air temperature indicating a temperature altitude effect post depositional processes cause isotopic changes during the transformation of snow firn ice to meltwater the effects are much stronger at temperate than at polar glaciers moreover changes in the isotopic signal at both temperate and polar glaciers can result from evaporation sublimation ablation and drifting

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

decoupling of seismic reflectors and stratigraphic timelines a modeling study of tertiary strata from svalbard in sequence stratigraphic interpretations the key premise is that stratal surfaces effectively represent geologic timelines when applied to seismic sections the fundamental assumption is that primary reflections generally mimic stratigraphic timelines the main objective of this study was to test how well key reflectors in a seismic section couple to timelines to achieve the high level of ground control needed for such testing we combined photogrammetry and traditional sedimentologic fieldwork to optimize the geologic model we relied further on petrophysical analysis to derive a numerical model suitable for the simulation of seismic data in spite of laterally discontinuous vertical impedance contrasts vics false seismic continuity was created and we observed frequent decoupling of seismic reflectors and stratigraphic timelines these observations demonstrate how the low frequency seismic method fails to image normal complexity in a stratigraphic unit a seismic correlation test showed that the

stable isotope composition of precipitation across the southern patagonian andes 1 a surface water and precipitation transect across the southern patagonian andes at 47 48 s was conducted to assess how mountains affect the isotopic composition of precipitation this westerly wind region derives its moisture that falls as precipitation from the pacific orographic uplift of air over the andes causes pseudoadiabatic cooling and orographic precipitation on the western side and a strong rain shadow on the eastern side of the mountains these processes also produce a profound isotopic rain shadow with 18o values 4 lower in the east compared to the west on the windward western side of the andes the isotope values of precipitation and surface waters show weak although systematic trends with elevation but a pronounced correlation with distance from the main source of moisture pacific ocean a rayleigh simulation of precipitation 18o values as a function of condensation altitude matches our data well suggesting that other processes such as mixing of water sources and postcondensation evaporation are negligible and that topography is the dominant control on the isotope ratio of precipitation in contrast isotope ratios of waters on the leeward eastern side of the southern patagonian andes vary neither with elevation nor with distance from the mountains consistent with much of the precipitation on the leeward side being derived from precipitation carried over the andes by winds thus paleoprecipitation isotopic composition on the leeward side of orogens in similar climatic settings single moisture source and cool climate yield useful estimates of the elevation of these orogens but not local elevation

sedimentological petrophysical and seismic characterization of an upper jurassic shoreface dominated shelf margin the boulonnais northern france abstract the integration of high resolution 25 cm vertical spacing and continuous quantitative data on grain size carbonate content porosity density and p wave velocity from outcrop borehole and core over 1000 samples and a real seismic section allows a calibration of seismic sequence stratigraphic principles this approach has been tested in the boulonnais along the english channel coast in northern france on a succession of upper jurassic sharp based shoreface deposits embedded in offshore marine shales statistical analyses of grain size distributions allow a characterization of hydrodynamic conditions and depositional processes affecting low inclination shelf margins and create a framework for identifying locations of preferential and enhanced carbonate cementation which exerts primary control on reservoir and acoustic properties stratigraphic surfaces and systems tracts are quantified for physical properties and results in a quantitative mechanical sequence stratigraphic model the combination of this model with seismic wavelets and a contrast between this synthetic and a real seismic section shows that key bounding sequence stratigraphic surfaces are in fact discontinuous reflectors because stratal relationships of sharp based shoreface deposits are subtle physical contrasts are generally stratabound and the deposits are typically not very thick the geological recordings of sea level falls and potential reservoirs are easily overlooked or go unseen in seismic sequence stratigraphic analyses by defining key diagnostic seismic criteria for sharp based shoreface deposits this study contributes to the understanding of processes controlling sedimentary fills of epicontinental basins

altitudinal variation of the stable isotopes of snow in regions of high relief a major discontinuity in the variation of 18 o d with altitude in high mountains was first seen in data from mount logan yukon territory canada holdsworth and others 1991 the profile of vs altitude revealed three well defined regions 1 a lower monotonic fractionation sequence below 3 km 2 a middle layer typically 1 2 km thick within which values are nearly constant or stepped with altitude and 3 part of another fractionation sequence in the quasi geostrophic flow region above 5 3 km the middle region was inferred to be a mixed layer combining moisture from regions 1 and 3 this type of structure is now seen to occur on other high altitude mountains including cerro aconcagua argentina where observations reach almost 7 km the new observations confirm the general occurrence of a multi layered atmosphere during precipitation at high altitude glacier sites this structure is linked to synoptic scale polar cyclones where the middle layer is identified as being the signature of the warm front zone these results have implications for the common practice of using a specific spatially derived isotopic thermometer in the time domain for the paleoclimatic interpretation of high altitude ice core records

seismic expressions of a miocene prograding carbonate margin mut basin turkey the detailed stratigraphic architecture of a miocene intraplatform prograding carbonate margin outcropping in mut basin turkey was used to build two dimensional synthetic seismograms by normal ray tracing and finite difference exploding reflector methods the synthetic seismic models at various frequencies display the overall prograding architecture of the 1 5 km 0 95 mi 250 m 820 ft prograding margin even at 40 hz frequency however most of the complex stratigraphic architecture is below standard seismic resolution sigmoidal outcrop geometries create complex shingled seismic reflections that contain pseudodownlap pseudotoplap and various truncations at 40 hz frequency in addition reflections that do not correspond to any impedance contrast are generated by a tuning effect within the clinoform interference patterns created by the complex impedance distribution create reflections that change phase laterally and cross stratigraphic timelines several high impedance coral buildups at the slope break and on the platform top cause reflections to change phase and amplitude along the timeline in addition lateral impedance variations generate mounded reflections that in places cross timelines and resemble seismic images for buildups or anticlinal structures several of these resolution problems and interference patterns are reduced by an increase of the frequency for example at 80 hz peak frequency the sigmoidal geometries are better imaged improved resolution was also achieved on the synthetic seismic data simply by dividing trace spacing from 25 to 12 5 m 82 to 39 ft but keeping the modeling frequency constant indicating that for stratigraphic interpretation horizontal seismic resolution is at least as important as vertical seismic resolution this implies that adjusting the acquisition geometries would improve the seismic resolution without compromising depth by increased frequency for seismic interpretation this study shows how little of a complex stratigraphic architecture is truly imaged on seismic data and how complex impedance distribution can create false seismic reflection geometries that impede a correct seismic facies and sequence stratigraphic interpretation

constraining uncertainty in interpretation of seismically imaged clinoforms in deltaic reservoirs troll field norwegian north sea insights from forward seismic models of outcrop analogs forward seismic modeling of outcrop analogs has been used to characterize the seismic expression of clinoforms in different deltaic depositional environments and thus constrain uncertainty in interpretation of intra reservoir clinoforms imaged in seismic data from the troll field norwegian north sea three outcrop analogs from the cretaceous western interior seaway united states were studied to quantify the geometry distribution and lithologic character of clinoforms in fluvial dominated and mixed influence deltaic deposits outcrop derived geometric data were calibrated to sedimentological and petrophysical data from the krossfjord and fensfjord formations in the troll field and then used to create a suite of forward seismic models for comparison with real seismic reflection data from the troll field clinoforms were imaged in the forward seismic models in which they were 1 spaced wider than the tuning thickness 10 m 33 ft 2 marked by pronounced interfingering of facies associations with different acoustic properties and or 3 lined by relatively thick 50 cm 20 in carbonate cemented layers however where clinothems are thinner than the vertical resolution limit of seismic data destructive interference occurred creating misleading geometrical relationships furthermore our ability to image clinoforms is dependent on 1 the frequency of the seismic wavelet 2 the overburden velocity and or 3 the acoustic impedance contrast at the boundary between the overburden and the clinoform bearing target the established methodology has allowed characterization of deltaic clinoformal architectures in reservoir seismic data from the troll field and has facilitated a more robust interpretation by bridging the critical gap in resolution between well and seismic data

accommodation sedimentation development and massive early marine cementation latemar vs concarena middle upper triassic southern alps abstract massive early marine cementation mec is a major diagenetic feature of some carbonate platforms the comparison of two triassic buildups of similar size and preservation but contrasting degree of mec latemar dolomites and concarena lombardic alps allows for the investigation of differential cementation on carbonate platforms the assessment of the response of platform cementation to changes in accommodation sedimentation led to the identification of fundamental boundary conditions for mec 1 the time interval available i e a low rate of creation in accommodation space and 2 low carbonate production other important factors are 3 margin topography e g walled reefs and 4 effective fluid flow e g wave energy open and connected cavities provided by rigid frameworks the latemar mainly aggrading and locally retrograding lacks mec due to a high a s ratio i e creation destruction of accommodation in time a d a d t vs changes in sediment supply in time s d s d t and a low relief of the reefal margin in contrast the concarena in the beginning slowly and later rapidly prograding indicates mec owing to a low a s ratio and a distinct topography of the reef particular features of the concarena are cement arrangements of lenticular shape and considerable size in the back reef domain up to 3 m in diameter and 2 m in height these arrangements consist of botryoids and isopachous crusts of radiaxial fibrous calcite cements they represent one of the main components of the platform margin at concarena cathodoluminescence analyses of cements from both platforms quantifies the influence of shallow and deep burial diagenesis and shows that the majority 60 90 of all cements are of early marine origin

a groundwater conceptual model and karst related carbon sink for a glacierized alpine karst aquifer southwestern china summary in the jade dragon snow mountain jdsm region yunnan province sw china an extensive hydrochemical and stable isotopic study of a glacierized alpine karst aquifer was conducted during the period 2011 2014 the objectives of the study were first to establish a conceptual hydrogeological model of the karst groundwater system second to estimate the proportion of extra glacier melt water infiltrating the karst aquifer that is being induced by the regional climate warming third to calculate the karst related flux of carbon into the karst aquifer knowledge of the local hydrogeological background from previous work was the starting point of the hydrochemical and stable isotopic study some representative spring waters and recharge waters i e glacier melt water and rainwater were investigated both spatially and temporally by hydrochemical and isotopic techniques including analysis of major and some minor ions and o and h stable isotopes a conceptual hydrogeological model of a fracture diffuse flow karst groundwater aquifer was proposed the proportion of glacier melt water infiltrating into the karst aquifer was estimated by using the karst spring as a natural pluviometer and with stable isotope analysis results show that 1 the jdsm karst aquifer is a diffuse flow system 2 it has a number of discharge areas and the jinsha river is the karst drainage base level 3 the proportion of the glacier melt water penetrating the karst aquifer is 29 and 4 the karst related carbon sink is 26 67 3 44 t km 2 a 1 as co 2 which is lower than that in non glacierized karst aquifers but over ten times larger than the carbon sink flux from silicate weathering in non karst areas showing the control of both climate and lithology on the rock weathering related carbon sink and the significance of carbonate weathering in the global carbon cycle

discriminating between onlap and lithologic interfingering in seismic models of outcrops seismic models of outcrops have shown that near the limits of resolution the seismic reflection tool records rapid facies changes as false lap outs we examined one such outcrop the triassic platform flank of picco di vallandro durrenstein in northern italy to develop criteria for recognizing false lap out patterns using measured sections photo mosaics of the continuous outcrop and petrophysical measurements on samples two contrasting impedance models were constructed one model supported by field observation shows interfingering between basin marls and slope carbonates the second model shows onlap of basin marls against slope carbonates but with similar overall geometries to the first model vertical incidence seismic models were produced at frequencies between 50 and 150 hz and with displays of seismic amplitude as well as two seismic attributes instantaneous phase and reflection strength at 50 hz the two lithologic models are seismically indistinguishable both showing onlap of basin units onto the slope at 90 hz displays of instantaneous phase begin to reveal the stratigraphic interfingering whereas seismic amplitude displays require frequencies of 150 hz to do so reflection strength accurately portrays the distribution of the two major facies in the entire range of examined frequencies but does not show sufficient detail to reveal interfingering vs onlap the same trends were visible with finite difference modeling of the full waveform here the differences between interfingering and onlap become visible at 150 hz in the phase model where seismic amplitude displays at this frequency are still ambiguous the phase model however fails to differentiate between slope dip and the basin sediment wedge whereas this wedge is clearly mapped by the reflection strength a combination of instantaneous phase and reflection strength provides a decisive advantage over conventional amplitude displays in recognizing rapid facies changes in seismic reflection data

seismic response and construction of seaward dipping wedges of flood basalts voring volcanic margin geological and geophysical data from the 900 m of volcanic basement drilled at ocean drilling program site 642 provide the framework for studying seismic properties of huge extrusive constructions on volcanic margins the main part of the drilled section corresponding to a prominent seaward dipping reflector sequence consists of subaerially emplaced tholeiitic basalt flows and thin interbedded sediments the basalts exhibit a characteristic velocity and density lava flow distribution reflecting changing porosity pore aspect ratio distribution and alteration stacks of laterally continuous basalt flows appear to have thin layer transverse isotropic properties for typical wavelengths in multichannel seismic data vertical seismic profiling and average sonic log velocities are similar 3 77 km s and 3 88 km s respectively while comparable refraction velocities are 10 20 higher synthetic seismogram modeling based on downhole logs shows that basement reflectors originate from interference and tuning effects of numerous basalt flow and interbedded sediment interfaces though the most continuous reflectors are related to thick flows seismic models based on the characteristic velocity and density basalt flow distributions and site 642 stratigraphy show that reflector truncation and onlap may be caused by seismic interference phenomena in a sequence of landward thinning flows the base of the dipping reflector sequence reflector k correlates with flows in the lower part of upper series basalts while the transition from basaltic to underlying dacitic andesitic lavas correlates with a locally defined reflector a model for the breakup related volcanism includes 1 prebreakup dacitic andesitic volcanism 2 early breakup basaltic volcanism infilling the prebreakup relief 3 main breakup stage with intense focused volcanism large subsidence and lava pounding and 4 late breakup volcanism during a period of decreased subsidence and local off axis activity

low latitude ice cores record pacific sea surface temperatures matic records suggested that a more conventional temperature interpretation might be more appropriate with lower isotopic values during the presumed to be cooler little ice age and increasingly enriched precipitation during the 20th century warming phase thompson 2001 3 both of these conflicting interpretations suffer from inadequate calibration of the observed isotopic record in relation to climatic conditions during periods of snow accumulation on the ice caps here we use the results of on site meteorological measurements to determine the seasonality of the ice core record and then assess how the isotopic records relate to temperature precipitation and the larger scale circulation associated with snowfall at these high elevation sites we then extend the analysis to ice core records from the asian monsoon region this empirical approach to the interpretation of the isotopic record in low latitude ice cores complements theoretical studies by broecker 1997 and pierrehumbert 1999

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

stratal slice the next generation vail and his colleagues 1977a b laid a foundation for seismic chronostratigraphy by analyzing the relative rise of sea level indicated by coastal onlap these workers invented a novel way of converting a stratigraphic cross section in the depth or traveltime domain to a chronostratigraphic chart in the wheeler domain figure 1a and figure 1b with the widespread use of seismic data in the industry such conversion can now be achieved conveniently with the proper software at the basinal regional or prospect scale figure 1c and figure 1d

the m2 tide on the amazon shelf as part of a multidisciplinary amazon shelf sediment study amasseds moored and shipboard current measurements made over the amazon shelf during 1990 1991 have been analyzed to determine the dominant semidiurnal tidal constituent the m2 these results have been combined with coastal sea level data from within the amazon and para rivers the adjacent shelf and with satellite derived tidal elevation data from off the shelf to provide a more complete description of the m2 tide in this complex river shelf system near the amazon river mouth the m2 tide propagates across the shelf and through the mouth as a damped progressive wave with its amplitude decreasing and phase increasing upriver over the adjacent shelf north of cabo norte the m2 tide approaches a damped standing wave with large amplitudes greater than 1 5 m near the coast due to near resonance within the coastal embayment formed by the cabo norte shoal to the south and cabo cassipore to the north the observed m2 tidal currents are nearly rectilinear and oriented primarily across the local isobaths comparisons between tidal observations in both the north channel and the cabo norte cabo cassipore embayment and a simple variable width channel tidal model indicate that 1 most of the m2 tidal energy dissipation occurs over the mid and inner shelf in water depths less than 20 m and 2 fluid muds found there cause a significant reduction of order 50 in the effective bottom friction felt by the m2 tide the approximate resonant period of the cabo norte cabo cassipore embayment is 11 9 hours and at resonance the average energy dissipation per forcing period is roughly 2 2 times the average mechanical energy in the embayment this damping rate is large enough that the tidal amplification is rather insensitive to forcing frequency so that the response of the embayment to forcing over the semidiurnal band should be essentially the same the vertical structure of the m2 tidal current is examined at one outer shelf site located in 65 m water depth the observed semimajor axis increases logarithmically with height above bottom within the lowest 1 2 m and reaches a maximum in excess of 0 5 m s at approximately 11 m above bottom the mean ellipticity is small less than 0 1 and positive indicating clockwise rotation of a nearly rectilinear current and the semimajor axis is oriented within 10 of the local cross isobath direction the m2 phase increases with height above bottom with flood at the bottom leading flood at the surface by about 1 hour a simple local homogeneous tidal model with time and space dependent eddy viscosity simulates the observed near bottom velocity reasonably well however the model suggests that stratification above the lowest few meters may significantly affect the tidal boundary layer structure at this site the m2 energy flux onto the amazon shelf and into the amazon and para rivers has been estimated using current and surface elevation data and the best fit variable width channel model results the net m2 energy flux into the mouths of the amazon and para rivers is 0 47 1010w and 0 19 1010w respectively a net m2 energy flux of about 3 3 1010w occurs onto the shelf between the north channel of the amazon river and cabo cassipore this stretch of the amazon shelf accounts for about 1 3 of the global dissipation of the m2 tide

composition of seismic facies a case study in this case study we used simulated seismic data from outcrops on svalbard to analyze what seismic facies are composed of what the dominating factors in forming the facies are and which consequences this has for the interpretation results seismic facies analyses can be used to interpret environmental setting depositional processes and lithology here we found that noise is the most important factor in forming the seismic facies noise is defined as all reflections that cannot be ascribed directly to the reservoir model effects from overburden and processing dominated and the low frequency content of the seismic section complicated the seismic facies analyses the main reason for this is that the analysis relies heavily on identified internal patterns and low angle terminations such patterns and terminations are easily created by the seismic method itself by overburden effects and by artifacts generated when processing the data external form strong amplitudes and continuous reflections are robust seismic observations whereas the internal pattern and terminations are commonly deceptive identification of boundaries based on predefined patterns of terminations does not work here and uncritical use of seismic facies analysis in this interpretation case will create wrong reservoir models because of the size of the outcrops the results from this analysis are relevant for reservoir scale seismic interpretation and detailed interpretation for prospect evaluation in mature basins for seismic interpretation at a more regional scale it is probably less relevant

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

facies mapping from three dimensional seismic data potential and guidelines from a tertiary sandstone shale sequence model powderhorn field calhoun county texas we generated a set of three dimensional 3 d seismic models of a lower miocene progradational microtidal shore zone system at the powderhorn field calhoun county texas these models were based on detailed lithological mapping of 250 m of stratigraphic section over an area of 13 9 km the mapping was guided by detailed facies analysis based on wireline logs from 115 wells fourteen sandy depositional units averaging 3 30 m in thickness are encased in 15 shale units density neutron and spontaneous potential sp logs in five recently drilled wells were used to calculate effective porosity and shaliness which correlate well with p wave velocity and bulk density logs those properties were then extended to older wells lacking acoustic density and other porosity ogs through regression with sp and resistivity logs to build 3 d properties models including models of transit time and impedance the impedance model was mapped from x y z to x y t where t is two way vertical time the impedance model was converted to primary reflection coefficient series that were then convolved with zero phase wavelets of different frequencies to produce the seismic models the results show how the depositional facies at reservoir scale might be illustrated by 3 d seismic data and how the seismic resolution of depositional facies changes with seismic frequency stratigraphic position and facies patterns the powderhorn reservoir sequence is interpreted as a barrier bar lagoon depositional system associated with coastal stream plains bayhead deltas and small wave dominated deltas corresponding to frequent relative changes of sea level to detect these types of deposits the seismic frequency should be selected such that the seismic data are tuned to the maximum thickness to establish a linear relationship between seismic amplitude and facies and to achieve the best signal to noise ratio the facies associated with the environments where main sandstones are surrounded by muddy deposits such as coastal stream plain bayhead delta delta plain and backbarrier lagoon transition are well illustrated in our seismic model lack of muddy deposits for example in a wave dominated delta c uld result in obscure facies boundaries and therefore unclear lithofacies patterns in this study poorly compacted clean sandstone and pure shale have similar impedances and consequently produce similar seismic responses the resulting ambiguity may be reduced by careful analysis of facies relationships if some well data are available and probably by the amplitude vs offset avo method the stratal resolution of seismic imagery depends not only on wavelet frequency but also on the stratigraphic position of a given reservoir or the magnitude of geological interference

acoustic nonlinear full waveform inversion on an outcrop based detailed geological and petrophysical model book cliffs utah analog outcrops are commonly used to develop predictive reservoir models and provide quantitative parameters that describe the architecture and facies distribution of sedimentary deposits at a subseismic scale all of which aids exploration and production strategies the focus of this study is to create a detailed geological model that contains realistic reservoir parameters and to apply nonlinear acoustic full waveform prestack seismic inversion to this model to investigate whether this information can be recovered and to examine which geological features can be resolved by this process outcrop data from the fluviodeltaic sequence of the book cliffs utah are used for the geological and petrophysical two dimensional model eight depositional environments are populated with average petrophysical reservoir properties adopted from a north sea field these units are termed lithotypes here synthetic acoustic prestack seismic data are then generated with the help of an algorithm that includes all internal multiples and transmission effects a nonlinear acoustic full waveform inversion is then applied to the synthetic data and two media parameters compressibility inversely related to the square of the compressional wave velocity vp and bulk density are recovered at a resolution higher than the shortest wavelength in the data this is possible because the inversion exploits the nonlinear nature of the relationship between the recorded data and the medium contrast properties in conventional linear inversion these details remain masked by the noise caused by the nonlinear effects in the data random noise added to the data is rejected by the nonlinear inversion contributing to improved spatial resolution the results show that the eight lithotypes can be successfully recovered at a subseismic scale and with a low degree of processing artifacts this technique can provide a useful basis for more accurate reservoir modeling and field development planning allowing targeting of smaller reservoir units such as distributary channels and lower shoreface sands

carbonate platforms in the dolomites area of the southern alps historic perspectives on progress in sedimentology the area of the dolomites in the southern alps exhibits some of the best outcrops of carbonate platforms and platform to basin transitions in the world the region has attracted geologists since the early 19th century and has been a centre of stratigraphic and sedimentological research ever since the interpretation of the platforms in the dolomites as coral reefs dates back to the 1850s and was inspired by the work on modern reefs in the pacific and indian oceans at that time very soon however studies in the dolomites triggered developments of their own fieldwork on these triassic atolls led to a first understanding of the dramatic facies changes at the periphery of reefs and atolls including the recognition of slope facies and basinward transport of platform material by gravity in addition the platforms were used to prove long term syndepositional subsidence on the scale of kilometres as early as 1860 after world war ii the study of modern reefs and platforms led to process based facies models and this in turn guided the sedimentological analysis of the alpine mediterranean belt repeatedly however the roles became reversed and the alpine mediterranean platforms contributed to the fundamental underpinnings of sedimentology in the 1980s mountain size outcrops in the alps and the apennines were recognized as models for the interpretation of shoal water carbonates in seismic data seismic models of outcrops in the dolomites for instance gave rise to the concept of pseudo unconformities i e rapid lateral facies changes that appear as unconformities in seismic images in the 1990s the alpine mediterranean mesozoic along with the north american and european palaeozoic revealed the significance of microbially induced carbonate precipitation in constructing large limestone bodies studies of ancient rocks led this development because this particular carbonate factory is far less prominent now than it was at certain times in the past 2009 the authors journal compilation 2009 international association of sedimentologists

well log and seismic character of liuhua 11 1 field south china sea relationship between diagenesis and seismic reflections abstract an integrated analysis of log petrographic and seismic data shows that the seismic reflections of liuhua 11 1 field image variations in porosity crossplots of velocity versus porosity density versus porosity velocity versus density and velocity versus gamma ray demonstrate that the acoustic impedance contrasts and consequently seismic reflections represent the alternation of tight and porous zones a detailed examination of a continuous core suggests that the majority of porosity is related to a phase of leaching in the deep burial realm that postdates pressure solution this implies that seismic reflections do not necessarily image depositional surfaces on the other hand seismic interpretation of areally more extensive 2 d lines and lithofacies analysis indicate that these diagenetically induced porosity units correspond to depositional events we conclude that the late diagenetic overprint follows primary depositional bedding and therefore seismic reflections still image the depositional architecture of the carbonate platform

oxygen isotopes in glacier river water austre okstindbreen okstindan norway there is no discernible river discharge from austre okstindbreen norway in winter any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed in summer a baseflow component of discharge relatively depleted of 18 o is diluted by water more enriched in 18 o glacier ice meltwater with a high 18 o value passes rapidly through channelized systems and emerges in the glacier river within a few hours headward extension of the systems in late summer may tap water stored within the glacier since the previous summer s close down stored water also is released during early melt season events when the low capacity drainage systems cannot accommodate inputs the high 18 o value indicates that the probable source of the released water is glacier ice or low altitude snowfall stratigraphic variations of 18 o values resulting from changing weather conditions characterize the accumulating winter snowpack during the melt season the mean 18 o value of the residual pack rises the water leaving it depleted of 18 o passes slowly through the glacier smoothing out variations of supply 18 o values of rain vary between and within events and their effect on glacier river 18 o values is unpredictable

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

hydrochemical characteristics of typical rivers in a temperate glacier basin china this study focused on the chemical compositions of the rivers around yulong mountain one of the typical monsoonal temperate glacier regions in china water samples were collected from baishui sanshu and geji hydrological stations around mt yulong during rainy season the chemical analyses indicated that the river water around mt yulong was characterized by high ph values 8 0 and ec values varied from 36 4 to 71 7 s cm with an average of 52 6 s cm ca2 and mg2 were the dominant cations together accounting for about 90 of the total cations hco3 followed by so4 2 was the dominant anion obvious variations had been perceived during the rainy season river water chemistry in rainy season was mainly influenced by precipitation and rock weathering the proportions of na k ca2 mg2 and so4 2 from precipitation in river water were 23 44 9 66 3 10 17 81 and 10 48 respectively in addition the ion characteristics of river water were mainly influenced by carbonate weathering the human activities should not be ignored though its influence was little

seismic models of a carbonate foreslope to basin transition picco di vallandro dolomite alps northern italy detailed geologic cross sections augmented by laboratory calibration of lithology and acoustic impedance have been used to produce synthetic reflection seismic sections of a carbonate foreslope to basin transition two areas from the picco di vallandro region of the dolomite alps were modeled a progradational section and a retrogradational backstepping section the resulting models show how these complex areas of strata interfingering might be displayed on conventional reflection seismic lines in the area of progradation rapid stratigraphic thinning below seismic detectibility coupled with abrupt impedance changes produces a reflection discontinuity between steeply dipping reflections of the foreslope and gently dipping parallel reflections of the basin section this apparent downlap surface marks the toe of slope for successive clinoforms but does not correspond to a discrete stratigraphic surface in the backstepping example similar stratigraphic thinning and impedance changes create an apparent onlap surface wavelet interference causes complications in both examples these models indicate how stratigraphic complexity can be simplified by the seismic reflection process and suggest that caution should be exercised when using seismic data to construct general models in areas of complex depositional geometries and rapidly changing facies

seismic models of a mixed carbonate siliciclastic shelf margin permian upper san andres formation last chance canyon new mexico seismic models based on randomly distributed samples from the permian upper san andres formation last chance canyon new mexico verify that the most prominent seismic reflections are related to stratal geometry however at least some reflections arise from lateral facies transitions that are commonly associated with highly prograding mixed carbonate siliciclastic sediments understanding seismic reflections and reflection terminations in sedimentary rocks requires simulation of at least 2 d cross sections of the impedance distribution to investigate the cause of reflections in strongly prograding mixed carbonate siliciclastic shelf margins acoustic velocity and bulk density were measured on more than 60 plugs that spatially cover one higher order genetic sequence the resulting impedance values were gridded and contoured and the genetic sequence was repeated to create a cross section averaging impedance values for each lithofacies zone generated a second impedance cross section seismic models of both impedance cross sections revealed the following observations 1 reflections associated with the sequence boundaries are subject to amplitude and polarity phase changes and 2 at least one reflection within the high order sequences is related to subhorizontal facies changes and is associated with two pseudounconformities the contoured impedance model is suggested to closer resemble the true impedance function in outcrop and shows subtle vertical shifts and significantly higher impedance contrasts

characteristics of water stable isotopes and hydrograph separation in baishui catchment during the wet season in mt yulong region south western china glaciers are of crucial importance for the livelihood of the local populations which depend on their meltwater for water and energy supplies for this reason seasonal variations of oxygen 18 of glacial stream water and their sources within a small glacial catchment in south western china were investigated during the wet season the results showed significant difference of oxygen 18 existed among meltwater rainwater ground water and stream water and significantly seasonal variation of precipitation occurred during the observed period the streamflow of baishui catchment was separated into components of ice snowmelt and precipitation using oxygen 18 as shown by the result of the two component mixing model on average 53 4 of the runoff came from ice snowmelt during the wet season whereas the remaining 46 6 were contributed by precipitation in the catchment according to monthly hydrograph the contribution of snow and glacier meltwater varied from 40 7 to 62 2 and that of precipitation varied from 37 8 to 59 3 in wet season uncertainties for this separation were mainly caused by the variation of tracer concentrations the roles of glacier and snow meltwater should be noticed in water resource management in those glacial regions in south western china copyright c 2012 john wiley sons ltd

pseudo unconformities in seismic models of large outcrops traditionally seismic modeling has concentrated on one dimensional borehole modeling and two dimensional forward modeling of basic structural stratigraphic schemes which are directly compared with real seismic data two dimensional seismic models based on outcrop observations may aid in bridging the gap between the detail of the outcrop and the low resolution of seismic lines examples include the dolomites north italy the vercors se france and the high atlas morocco the seismic models are generally constructed using the following procedure a construction of a detailed lithologic model based on direct outcrop observations b division of the lithologic model into lithostratigraphic units c assignment of petrophysical properties to these lithostratigraphic units d ray tracing to compute time or depth sections of reflectivity e convolution of the reflectivity sections with source wavelets of different frequencies the lithologic detail modeled in the case studies led to some striking results particularly the discovery of pseudo unconformities pseudo unconformities are unconformities in seismics but correspond to rapid changes of dip and facies in outcrop none of the outcrop geometries studied were correctly portrayed seismically at 25 hz peak frequency however in some instances the true relationship would gradually emerge at peak frequencies of 50 100 hz the examples given in this study demonstrate that detailed outcrop derived seismic models can reveal what stratigraphic relationships and features are likely to be resolved under ideal or less ideal conditions and what pitfalls may befall the interpreter of real seismic data

effects of seasonal variability of accumulation on yearly mean δ18o values in antarctic snow the annual mean oxygen isotope content of antarctic snow is strongly influenced by the seasonal variability ofaccumulation since the annual mean 18 o value is frequently used to derive mean annual temperatures from ice cores changes in atmospheric circulation pattern can lead to large errors in the deduced temperature record at the german antarctic wintering base neumayer accumulation measurements have been carried out continuously over the last 16 years weekly readings of accumulation stakes combined with snow pits and shallow firn cores are used to investigate the influence of the seasonal variability of accumulation on the annual mean 18 o values and to estimate the possible error in the determination ofannual mean temperatures from ice cores by using the oxygen isotope record

connection between macrotidal estuaries along the southeastern amazon coast and its role in coastal progradation abstract sediment transport in the southeastern amazon coastal zone sacz is substantially affected by tidal asymmetry seasonal variation of the wind and wave regime and especially rainfall i e river discharge the regional climate and geological configuration have resulted in numerous estuaries and large mangrove covered coastal plains that partially divide the estuarine basins which are connected by tidal channels based on the investigation of the furo grande tidal channel we assess the relevance of connectivity on the sediment transport and evolution of the 8000 km2 sacz mangrove belt extensive sedimentologic and bathymetric surveys as well as hydrodynamic measurements including water level water and sediment flow and physical chemical characteristics of the water were undertaken at different seasonal periods water level variation along the channel shows that sediment transport convergence stc tends to be formed within the connecting channel as the tide propagates from both ends morphologic and sedimentologic results show the accumulation trend of fine sediments within the stc zone and this is relevant for mud retention and further delivery to the mangrove plains which may eventually lead to channel connection closure despite the stc results also show that there is an important net flux of suspended sediments between estuaries through the studied channel however the connected estuaries of taperacu and caete have substantial differences regarding riverine discharge and thus estuarine processes tidal propagation and sediment transport bottom sediments and morphology reflect long term trends and show stc migration towards the taperacu as a result of substantially smaller fluvial discharge in that estuary and therefore higher sediment accumulation rates compared to the caete estuary the migration of the stc prevents the closure of the connection and its maintenance preserves these channels as sediment flow conduits between estuaries the connectivity is a key process to redistribute mainly muddy sediments along this coastal sector which helps to explain the evolution and maintenance of the relatively homogeneous and widespread progradation of mangroves along the sacz with uneven mud supply

the aftermath of the carnian carbonate platform demise a basinal perspective dolomites southern alps in the dolomites of northernmost italy the carbonate platform growth came to a standstill late in the early carnian late triassic the response to this shutdown of shallow water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments giving rise to today s scenic landscape of the dolomites mapping in the central part of the dolomites and newly available core material has recently revealed a wellpreserved succession of basinal rocks within the heiligkreuz hospiz basin ital ospizio di santa croce basin in this paper the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin the uppermost st cassian formation the time equivalent basinal rocks to the prograding carbonate platforms is overlain by the heiligkreuz formation whose basal succession was deposited in a restricted and oxygen depleted environment immediately post dating the platform demise the succession consists mainly of mudrocks marlstones and peloidal packstones with abundant low diversity ostracod and pelecypod fauna and early diagenetic dolomite c and o isotope values of the basal heiligkreuz formation post dating platform demise average 2 ae4 and 2ae4 respectively and largely overlap the isotopic composition of st cassian carbonates a shift toward slightly lower d 13 c values in the heiligkreuz formation may reflect incorporation of isotopically depleted c released during bacterial sulphate reduction in the heiligkreuz sediments sedimentological palaeobiological and geochemical indices suggest that nearnormal marine conditions persisted long after the shutdown of shallow water carbonate platform growth although there are clear indications of severely reduced oxygen levels in the restricted heiligkreuz hospiz interplatform basin the early carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters it is inferred that anoxia extended at least temporarily to the top of the carbonate slope as indicated by the onlap of normal marine mounds by dark marlstones of the basal heiligkreuz formation

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid