interactions between sediment production and transport in the geometry of carbonate platforms insights from forward modeling of the great bank of guizhou early to middle triassic south china abstract carbonate platforms grow through the precipitation transport and final deposition of carbonate sediment out of seawater quantifying the relative contributions of initial production versus subsequent transport in determining the growth rates and geometries of platforms remains a significant challenge in this study stratigraphic forward modeling is used to quantify the roles of sediment production transport and deposition during each growth stage of a permian triassic carbonate platform with a complex growth history parameter optimization and sensitivity analysis show that within the range of reasonable values the morphology of the platform is most sensitive to sediment transport moderately sensitive to maximum carbonate production rate and least sensitive to the productivity depth curve the ramp to high relief steep sloped platform transition during early triassic time can be explained by any factor that limits sediment transport from shallow water areas of high production to the slope and basin reefs may play a role in limiting sediment transport on many platforms but other processes such as early marine cementation or carbonate production along the slope may be equally capable of yielding this shift in platform geometry in this particular case early lithification of ooid and skeletal shoals on the platform margin perhaps facilitated by unusually high carbonate saturation state of seawater may have inhibited sediment transport into the basin prior to the development of a reef on the platform margin later anisian progradation of the platform margin can be explained by the development of a slope factory rather than requiring increased sediment transport from the platform top the development of an escarpment margin in the ladinian is mainly influenced by accommodation in the slope profile created by antecedent anisian topography a general implication from the model results is that the growth of steep sloped carbonate platforms lacking slope factories may often be limited by transport of sediment from the platform top to accommodation on the slope rather than by the intrinsic production capacity of the platform top factory

the latemar a flat topped steep fronted platform dominated by microbialites and synsedimentary cements abstract facies analyses on the latemar isolated carbonate platform suggest a higher proportion of microbial carbonates compared to literature this is evident especially in the margin upper slope zone where microbial boundstone associated with tubiphytes calcareous sponges botryoidal aragonite and radiaxial fibrous cements extended down to 250 m water depth the latemar flat topped high relief platform has been subdivided into five different facies belts inner and outermost platform margin upper and lower slope each facies belt represents subtidal environments except for the inner platform which is characterized by a peritidal facies association point counting analysis was carried out on ca 90 thin sections to quantify the different platform components microbialite and cements are most abundant they represent respectively ca 40 and ca 34 of the whole platform volume these results suggest that carbonate production at latemar occurred in a m factory microbial carbonates as well as early marine cements are most abundant on the upper slope margin and outermost platform although microbialites are found in all facies belts the presence of supratidal sedimentary facies restricted only to the inner platform and of a completely subtidal outermost platform suggests a new depositional profile for the latemar the central portion is occupied by the flat platform interior cyclically subaerially exposed facies of the subtidal outermost platform surround the inner platform and display a progressive increase in depth toward the margin the margin is submerged and essentially constituted by microbial and cement boundstone the slope is characterized by steep clinoforms 35 dominated by in situ microbialites in the upper middle portion 0 250 m depth evidently precipitated by non light dependent microbially influenced processes the lower slope is mostly detrital poor in platform top derived sediments and dominated by margin and upper slope derived rudstone and grainstone all these observations are in agreement with the slope shedding model observed in the pennsylvanian microbial margin in asturias n spain and allow the interpretation of the latemar as a flat topped steep fronted platform dominated by microbialites and cement boundstones

a dynamical description of fall and winter mean current profiles over the northern california shelf abstract fall and winter mean current profiles from a midshelf water depth 90 m northern california site exhibit a similar vertical structure for several different years the alongshelf flow is poleward with a maximum velocity of 5 10 cm s 1 in the middle or upper water column there is an offshore flow of about 2 cm s 1 in the upper 20 30 m an onshore flow of about 2 cm s 1 in the interior depths 35 65 m and an offshore flow of about 1 cm s 1 within 20 m of the bottom profiles are similar for averages over timescales from weeks to months mean current profiles at other midshelf sites along northern california and two sites off peru also have a similar vertical structure the vertical shear in the mean alongshelf flow is geostrophic throughout the water column that is in thermal wind balance with the cross shelf density gradient for timescales of a week or longer the thermal wind balance extends to within 1 m of the bottom and reduces the mean near bottom alongshelf flow to 1 cm s 1 or less th

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

flow around a coastal bend a model of the santa barbara channel eddy a steady equatorward wind stress is applied over a two layer ocean infinitely deep lower layer west of an otherwise straight meridional coast with a right angle bend initial t 10 days response consists of an equatorward current kelvin wave that triggers a cyclone around the bend through viscous production and advection of vorticity a process akin to eddy shedding in flows without rotation the response at large times is governed by a kelvin wave forced by the equatorward weakening of the assumed positive wind stress curl which produces a poleward current near the coast application to the santa barbara channel cyclone is discussed and the cyclone formation process is further demonstrated with a three dimensional model with topography and stratification

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

the large scale coastal wind field along the west coast of north america 1981 1982 we study the statistical properties of the coastal wind field along the west coast of north america for two summers 1981 and 1982 coastal ocean dynamics experiments 1 and 2 respectively and the intervening winter using measured winds and geostrophic winds calculated from fleet numerical oceanography center atmospheric pressure analyses summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems the north pacific subtropical high and southwest u s thermal low and by their interactions with propagating atmospheric systems to the north in particular propagating cyclones and associated fronts are often followed by a northeastward intensification of the high producing strong upwelling events along the california coast this summer event sequence occurs more frequently and is displaced farther to the south on average during summer 1981 winter wind fluctuations are primarily driven by propagating cyclones and anticyclones and they tend to have larger variance and space scales than in summer a preference for poleward equatorward propagation exists in summer winter and the largest time scales are observed in summer 1982 coastal atmospheric boundary layer processes substantially modify winds within 100 200 km of the coast consequently measured wind fluctuations are strongly polarized in the alongshore direction and have means and rms amplitudes that can vary considerably between nearby stations along the coast calculated wind fluctuations are less polarized in the alongshore direction and have alongshore correlation scales about 60 larger than those for measured winds they represent fluctuations with alongshore wavelengths of 900 km rather well but represent poorly those with smaller wavelengths and those due to coastal atmospheric boundary layer effects

modeling studies of the coastal circulation off northern california statistics and patterns of wintertime flow we conduct modeling studies of the coastal circulation off northern california in the vicinity of the eel river 40 6 n the site of the 1995 2000 strata formation on margins strataform marine geology observational program using a series of nested hydrostatic primitive equation models to aid in the understanding of the shelf flow field that receives and transports sediments during the winter floods the basic objectives of our numerical studies are to model the continental shelf and slope flow and to understand the dominant dynamical processes we simulate the shelf and slope flow surrounding cape mendocino during 100 days in winter 1996 1997 using a 3 km resolution model embedded in a 9 km resolution regional model of the north pacific ocean the naval research laboratory s pacific west coast pwc model the validity of the model simulations is assessed by comparison with current measurements from a strataform shelf tripod outfitted with an acoustic doppler current profiler and with satellite altimetry good agreement is found between the amplitude and time variability of the 3 km resolution modeled and observed alongshore currents on the shelf the 3 km resolution model outperforms the 9 km resolution pwc model using statistical maps of flow variables strong alongshore variability in wintertime flow is documented the role of the forcing supplied by wind and river runoff in establishing this flow asymmetry between regions north and south of cape mendocino is examined using empirical orthogonal functions the evolution of a robust anticyclonic eddy over the shelf and slope adjacent to cape mendocino is described the eddy forms when strong poleward winds weaken and reverse direction during winter storms the important role of alongshore pressure gradients in the shelf circulation is documented

isolated stationary carbonate platforms the middle triassic ladinian of the marmolada area dolomites italy as a result of a phase of extensional tectonics in the western tethyan region a horst and graben topography formed during the middle triassic ladinian in northern italy horsts were sites of shallow water carbonate sedimentation while pelagic and volcaniclastic sediments were deposited in the grabens two carbonate platforms approximately 500 m thick can be distinguished in the marmolada area of the dolomites the marmolada platform proper which covered an area of 6 km2 and the costabella platform which extended for about 12 km in a nw se direction and was about 3 km across the facies of these isolated platforms reflect the influence of storms from the sw windward platform margins were characterized by a marine sand belt of skeletal and aggregate grainstones with a dominant platform directed cross stratification the central portions of the platforms were occupied by supratidal sand cays which are made up of storm washovers leeward parts of the platforms are composed of shallow subtidal sand flat deposits laterally discontinuous reefs chiefly composed of various calcareous algae are developed at the outer margins of the platforms along windward margins reefs may form a belt several hundred metres wide along leeward margins their width is commonly reduced to some tens of metres foreslope talus breccias surround the platforms clinoform bedding showing basinward dips of 30 40 is typical of this facies belt which is approximately 2 km wide basinal sediments only some tens of metres thick are radiolarian micrites abundant sediment gravity flow deposits expand the basinal sequence at the toes of windward margins and were probably triggered by storm return flows synsedimentary faults striking both nne ssw and nw se separate the bedded platform limestones from flank deposits and reefs they account for the stationary nature of the platforms neptunian dykes show preferred nne ssw and e w trends sinistral displacements are associated with nw se trending faults depressions in the basins filled with red turbiditic pelagic sediments show n s trends and are probably compressional in origin the structural pattern may have resulted from oblique nw se oriented extension of the e w trending middle triassic graben zone of the dolomites in the ladinian of the dolomites the stationary platform type can be distinguished from a retrograding type whereas continuously prograding platforms apparently did not develop

multiple negative carbon isotope excursions during the carnian pluvial episode late triassic abstract the carnian pluvial episode was a phase of global climatic change and biotic turnover that occurred during the early late triassic in marine sedimentary basins the arrival of huge amounts of siliciclastic sediments the establishment of anoxic conditions and a sudden change of the carbonate factory on platforms marked the carnian pluvial episode the sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as for example an extinction among ammonoids and conodonts in the ocean and a turnover of the vertebrate fauna and the flora on land multiple negative carbon isotope excursions were recorded during the carnian pluvial episode in both organic matter and marine carbonates suggesting repeated injection of 13c depleted co2 into the ocean atmosphere system but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood we here review the existing carbon isotope records and present new data on the carbon isotope composition of organic carbon in selected sections of the western tethys realm that record the entire carnian pluvial episode new ammonoid conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections the results provide biostratigraphically constrained composite organic carbon isotope curves for the carnian which sheds light on the temporal and causal links between the main carbon isotope perturbations and the distinct environmental and biotic changes that mark the carnian pluvial episode the carbon isotope records suggest that a series of carbon cycle perturbations possibly recording multiple phases of volcanic activity during the emplacement of the wrangellia large igneous province disrupted carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years

geometry and evolution of triassic high relief isolated microbial platforms in the dolomites italy the anisian latemar and carnian sella platforms compared abstract exceptional outcrop conditions in the dolomites of northern italy allow appreciation of facies variability depositional geometries and platform to basin relationships at seismic scale that developed during a complex sedimentary evolution this itinerary focuses on two triassic microbial carbonate platforms the latemar and sella providing examples of key concepts that are fundamental for the interpretation of subsurface geologic bodies by comparing these two microbial platforms a variability of facies architectures is highlighted the relatively easy access the exceptional exposure conditions and the variety of carbonate platform types that grew in the triassic of the dolomites make this region an ideal field geology laboratory for training geologists working in exploration and in addition provide potential outcrop analogs of subsurface carbonate reservoirs

edge modulated stagnant lid convection and volcanic passive margins the initial oceanic crust along volcanic passive margins is a factor of 3 greater than that of typical oceanic crust 20 versus 6 7 km convection driven by the edge of the continental lithosphere may cause mantle material to circulate through the shallow zone of significant melting beneath the nascent ocean basin and cause the volume of melted mantle to exceed that required to replace the diverging lithospheric plates this hypothesis is a well known alternative to mantle plumes i obtain dimensional scaling relations and develop numerical models which indicate that the melted volume is unlikely to be enhanced by a factor of 3 this conclusion agrees with the results of numerical calculations by nielsen and hopper 2002 2004 dimensional scaling provides the relationship which shows that the vigor of convection in terms of laterally averaged heat flow or flow velocity depends on the square of local thickness of the rheological boundary layer for linear viscosity the derivation does not involve undulations in lithospheric thickness and thus provides the inference that the vigor of stagnant lid convection depends only weakly on those features numerical models support this inference lithospheric edges do nucleate instabilities but these instabilities are similar in magnitude to those in models started with a tiny perturbation from laterally homogeneous temperature subsequent convection is also similar for models started with tiny perturbations and with large lateral variations in lithospheric thickness in terms of the scaling relationship the asthenosphere beneath the thin lithosphere within rifts is an unfavorable site for circulation and extensive melting the rheological boundary layer is in general thin below thin lithosphere which causes stagnant lid convection there to be weak care needs to be taken in numerical modeling of convection beneath passive margins starting conditions that drive large instabilities of features that could not have persisted in the earth need to be avoided models should start rifting only after mature stagnant lid convection is established

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

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

syndepositional fractures and architecture of the lastoni di formin carbonate platform insights from virtual outcrop models and field studies abstract the recent rapid improvement of unmanned aerial vehicles together with advances in photogrammetry and structure from motion techniques have enhanced the role of digital outcrop models in many field of geology due to the possibility to obtain quantitative information from large and inaccessible areas in this study we integrated digital outcrop modeling techniques and field survey to investigate the architecture of the middle triassic platform of lastoni di formin italian dolomites the research highlighted the presence of two superimposed carbonate bodies the lower unit cassian i is dominated by low angle clinoforms dipping north northeastward and prograding over the basinal san cassiano fm the upper unit cassian ii is characterized by a thick sequence of peritidal cycles connected northward to another generation of clinoforms the inner platform beds of the upper unit display a lateral thickening that is particularly evident near the shelf break and that has been interpreted as due to the increased subsidence and the consequent down to basin tilting of the outermost part of the platform moreover the structural analysis performed on the digital outcrop models and supported by field observations highlighted the presence of an early generation of faults and joints that indicate an early gravitational deformation of the buildup possibly caused by the platform progradation and compaction induced subsidence of the san cassiano basinal deposits these wnw ese synsedimentary structures are formed by normal faults and extensional joints that are oriented nearly perpendicular to the direction of progradation of the carbonate platform

results from a three dimensional nested biological physical model of the california current system and comparisons with statistics from satellite imagery 1 a three dimensional model of the california current system ccs from 35 n to 48 n extending offshore to 134 w is coupled with a four component trophic model the model reproduces many conspicuous characteristics in the ccs including complex filamentary mesoscale surface features seen in the pigment and temperature from satellite imagery wind driven coastal upwelling at appropriate spatial and temporal scales and the close correlation between prominent features seen in pigment and those in temperature observed by satellites abbott and zion 1985 statistical estimates of the characteristic spatial scales of variability as calculated from the coupled nested model agree with those previously estimated from satellite images for both surface temperature and pigment denman and abbott 1988 1994 model estimates of the characteristic temporal scales of variability from decorrelation times agree with those previously estimated from satellite images typical model decorrelation times lie between 2 and 4 days in agreement with calculations from earlier sequences of coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite images denman and abbott 1988 1994

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

flood dispersal and deposition by near bed gravitational sediment flows and oceanographic transport a numerical modeling study of the eel river shelf northern california 1 a large flood of the eel river northern california created a thick sediment deposit between water depths of 50 and 70 m in january 1997 the freshwater plume however confined sediment delivery to water depths shallower than 30 m mechanisms proposed to explain the apparent cross shelf transport include dispersal by oceanographic currents resuspension by energetic waves and gravitationally forced transport of a thin layer of fluidized mud field observations indicate that these processes were all active but cannot determine their relative significance or whether these mechanisms alone explain the location size and timing of deposition approximately 30 of the sediment delivered by the eel river is accounted for in the midshelf mud bed and inner shelf but the fate of the remaining 70 is uncertain a three dimensional hydrodynamic model was used to examine potential mechanisms of sediment transport on the eel river shelf the model includes suspended sediment transport and was modified to account for a thin near bed layer of fluidized mud it was used to simulate flood dispersal on the eel river shelf to compare the relative importance of transport within the near bed fluid mud layer to suspended sediment transport and to evaluate sediment budgets for floods settling properties of fine grained sediment both within the flood plume and the fluid mud layer critically impact depositional patterns to a lesser degree wind driven ocean currents influence the volume of sediment that escapes the shelf and wave magnitude affects the cross shelf location of flood deposits though dilute suspension accounts for a large fraction of total flux cross shelf transport by gravitational forcing appears necessary to produce a midshelf mud deposit similar in volume location and timing to those seen offshore of the eel river

global carbon cycle perturbations triggered by volatile volcanism and ecosystem responses during the carnian pluvial episode late triassic abstract the carnian pluvial episode cpe was a dramatic climatic event during the early late triassic the cpe has been recognized worldwide and is marked by the termination of carbonate platform successions and by pronounced negative 13c excursions denoted as the cpe excursion the onset of the cpe has been proposed to be linked with the volatile eruption of the wrangellia large igneous province w lip however this extreme climatic event remains disputed in terms of its precise global correlation timing of onset duration and global magnitude we compiled a database of 13 conodont biozone controlled stable isotope reference sections throughout the tethyan region after a reexamination of previously published conodont taxonomy from each section the statistics on the conodont assemblages zones yield a global set of 17 high resolution conodont unitary association zones uazs spanning the entire carnian successions a set of age tie points placed an age model on this global uaz scale we added paired 13ccarb and 13corg data from two sections in south china to other records in this global database and then normalized all carbon isotope datasets a pronounced negative 13ccarb excursion with a magnitude of 2 0 5 from an average of 3 to 1 is evident in these normalized trends and is recognized around the entire tethys realm the cpe excursion coincides with conodont uaz 4 234 ma through uaz 8 within the mazzaella carnica and paragondolella praelindae zones julian2 and has a duration of ca 1 5 myr we note that an apparent delayed onset of the cpe excursion in south china relative to elsewhere in the tethys as suggested by previous studies may have been an artifact caused by incomplete conodont stratigraphic records and or irregularities in taxonomic identification a carbon and phosphorus cycle model highlight the strong relationship between the eruption of the w lip and cpe excursion however the estimated amount of co2volatiles released by the w lip would directly account for only 25 of the total amount of light carbon required to explain the combined magnitude and duration of the global cpe excursion

severe downslope windstorm calculations in two and three spatial dimensions using anelastic interactive grid nesting a possible mechanism for gustiness abstract the clark nonhydrostatic anelastic code is extended to allow for interactive grid nesting in both two and three spatial dimensions tests are presented which investigate the accuracy of three different quadratic interpolation formulae which are used to derive boundary conditions for the fine mesh model application of the conservation condition of kurihara and others is shown to result in significant improvements in the treatment of interactive nesting a significant improvement in the solutions for interactive versus parasitic nesting is also shown in the context of forced gravity wave flow this result for the anelastic system is in agreement with the earlier results of phillips and shukla who considered the hydrostatic shallow water system of equations the interactive nesting model is applied to the simulation of the severe downslope windstorm of 11 january 1972 in boulder using both two and three spatial dimensions the three dimensional simulation results in a gustiness signature in the

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge

pulsating continents on venus an explanation for crustal plateaus and tessera terrains we propose that tessera terrains on venus represent continental crust that does not participate in the periodic recycling of the lithosphere through global subduction events we have studied the force balance on the boundary of a continental area that survives a global subduction event using an analytical model in the proposed model the ratio between the crustal and lithospheric mantle thicknesses controls the force balance if the crust thickness is less than 2 5 of the lithospheric mantle thickness the continental area will be compressed but if the crustal thickness is higher than 2 5 of the lithospheric mantle thickness the continental area will spread out and collapse consequently if the lithospheric mantle beneath a continental region is delaminated during a global subduction event the continent will collapse generating tessera inliers dominated by extensional tectonics but if a significant portion of lithospheric mantle remains then the continental area will be compressed generating a plateau by crustal shortening the observed plateau heights can be explained by this model a 2 km height plateau can be generated by a lithospheric mantle thickness of 40 km while a 4 km height plateau can be generated by a 90 km thick lithospheric mantle we have modelled this crustal thickening of a continental area by tectonic contraction using a thin viscous sheet approach with a newtonian viscosity for the crust the force from a hot mantle elevated during a global subduction event is enough to build up a plateau by compression in 50 ma using a viscosity for the continental crust of 1021 pa s and 200 ma for 5 1021 pa s during this compressional stage concentric fold and thrust belts are generated in the plateau continent erasing any impact craters that were present the subsequent stabilization of a new crust and lithosphere in the surrounding mantle changes the force balance allowing a moderate gravitational collapse of the plateau continent accommodated by radial grabens the pulsating continent model links for the first time the generation of crustal plateaus and the origin of the volcanic plains predicting the observed equivalent effective crater density for both terrains