deposits from wave influenced turbidity currents pennsylvanian minturn formation colorado u s a turbidity currents generated nearshore have been suggested to be the source of some sandy marine event beds but in most cases the evidence is circumstantial such flows must commonly travel through a field of oscillatory flow caused by wind generated waves little is known however about the interactions between waves and turbidity currents we explore these interactions through detailed process oriented sedimentological analysis of sandstone event beds from the pennsylvanian minturn formation in north central colorado u s a the minturn formation exhibits a complex stratigraphic architecture of fan delta deposits that developed in association with high topographic relief in a tectonically active setting an 20 35 m thick unconformity bounded unit of prodelta deposits consists of dark green shale and turbidite like sandstone beds with tool marks produced by abundant plant debris some of the sandstone event beds most abundant at distal localities contain reverse to normal grading and sequences of sedimentary structures that indicate deposition from waxing to waning flows in contrast proximal deposits in some cases less than a kilometer away contain abundant beds with evidence for deposition by wave dominated combined flows including large scale hummocky cross stratification we interpret the majority of these event beds as a record of deposition from hyperpycnal flows i e turbidity currents generated directly from highly concentrated river plumes which accelerated and decelerated in response to a rising and falling flood discharge additional support for this interpretation includes the following 1 a variety of sole marks including flute and gutter casts as well as tool marks made by relatively large up to tens of centimeters across woody debris i e groove prod and chevron marks 2 consistent unimodal orientation of sole marks and abundant ripple cross stratification which indicate strong downslope directed flow 3 a well documented sedimentological framework for the formation of fan delta deposits adjacent to nearby highlands and 4 plant fossils typical of middle to high elevation habitats that are abundant in the turbidite beds but absent in underlying and overlying shoreline and marginal marine deposits which have a separate floral assemblage differences in grain sizes vertical stratification sequences and bed thicknesses between outcrops are interpreted to result from the spatial distribution of wave effects the time history of hyperpycnal flows and the interaction of these processes the latter varied both spatially and temporally and produced a wide range of bed types which are incorporated into a new conceptual model for storm influenced hyperpycnal flows

stable isotopic and biomarker evidence of terrigenous organic matter export to the deep sea during tropical storms abstract the global export of organic carbon oc is intimately linked to the total flux of terrestrial sediment to the ocean with the continental margins receiving 90 of the sediment generated by erosion on land recent studies suggest that a substantial amount of particulate oc poc might escape from the shelf and be exported to the continental slope deep sea sector although the mechanisms and magnitude of such deep sea poc transfer remain unknown here we investigate hyperpycnal flow associated total suspended matter tsm collected from water depths of 3000 m near the bottom of sea floor in the gaoping submarine canyon gsc off southwestern taiwan elemental c n isotopic 13 c 15 n and biomarker compositions of tsm were investigated to understand its biogeochemical characteristics a two end member 13 c mixing model indicates that deep sea tsm contains 90 terrigenous oc while a similar mixing model using 15 n reveals a lower proportion 58 organic biomarkers of tsm suggest contributions from a mixture of resuspended continental margin derived marine organic matter om mar and terrigenous sources revealing that terrestrial oc likely mixes with nitrogen rich marine material during rapid transport this study documents that rapid transfer of terrigenous organic matter om terr into the deeper regions of gsc occurred within a week of typhoon morakot likely through hyperpycnal injection of sediment laden warm freshwater from southern taiwan evidence from this typhoon morakot induced hyperpycnal plume event in taiwan demonstrates that extreme storm events provide an efficient way to export terrigenous oc without oxidation to hitherto unknown water depths of deep sea in the oceania region

erosion by pyroclastic flows on lascar volcano chile pyroclastic flows generated in the 19 20 april 1993 eruption of lascar volcano chile produced spectacular erosion features scree and talus were stripped from the channels and steep slopes on the flanks of the volcano exposed bedrock and boulders suffered severe abrasion producing smoothed surfaces on coarse breccias and striations and percussion marks on bedrock and large boulders erosional furrows developed with wavelengths of 0 5 2 m and depths of 0 1 0 3 m furrows commonly nucleated downstream of large boulders or blocks which are striated on the upstream side and thereby produced crag and tail structures erosive features were produced where flows accelerated through topographic restrictions or where they moved over steep slopes the pyroclastic flows are inferred to have segregated during movement into lithic rich and pumice rich parts lithic rich deposits occur on slopes up to 14 whereas pumice rich deposits occur only on slopes less than 4 and mainly at the margins and distal parts of the 1993 fan the lithic rich deposits contain large up to 1 m lithic clasts eroded from the substrate and transported from the vent whereas pumice rich deposits contain only small typically 2 cm lithic clasts these observations suggest that lithic clasts segregated to the base of the flows and were responsible for much of the erosive phenomena the erosive features distribution of lithic clasts and deposit morphology indicate that the 1993 flows were highly concentrated avalanches dominated by particle interactions in some places the flows slid over the bedrock causing abrasion and long striations which imply that large blocks were locked in fixed positions for periods of about 1 s however shorter striae at different angles impact marks segregation of the deposits into pumice and lithic rich parts and mixing of bedrock derived lithic clasts throughout the deposits indicate that clasts often had some freedom of movement and that jostling of particles allowed internal mixing and density segregation to occur within the flows

time variations of δ15n of organic nitrogen in deep western subarctic pacific sediment over the last 145 ka we present 15n data of organic nitrogen 15non from a deep western subarctic pacific wsap sediment core over the last 145 ka to remove the effect of inorganic nitrogen in on bulk nitrogen bn we used the contents of in and bn and the isotopic ratios of in 15nin and bn 15nbn the contribution of in to bn was largest 59 and 15nin had lower values than 15nbn however the large contributions of in to bn and the distinct isotopic values did not largely change any variability associated with 15non in the 15nbn thus it is possible to use 15nbn in carrying out paleoceanographic research with 15n at least in the open wsap the 15non values have been affected by long term diagenesis making the values lower with depth in the sediment but the values during less productive colder periods were generally lower compared to those during neighboring productive warmer periods the results might indicate that 15non during the less productive colder periods i e glacial periods were lower than that during the productive warmer periods i e interglacial periods previous studies have reported that the biological production in wsap where it is limited by iron at present during glacial periods was at more reduced level than during interglacials despite there being more eolian dust supply during glacial periods this indicates that the increase of biological production with enhanced iron supply derived from eolian dust during the glacial periods did not occur if this is the case and alternatively the iron input from the subsurface layer to the surface mixed layer by ventilation process is more important as suggested by recent works the variations in 15non would be explained by the variations in the fe no3 ratio in the upwelled water although 15non has been affected by long term diagenesis in the sediment the usage of this isotopic ratio provides new implication regarding the past ocean circulation in the open wsap

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

insights into the emplacement dynamics of volcanic landslides from high resolution 3d seismic data acquired offshore montserrat lesser antilles we present results from the first three dimensional 3d marine seismic dataset ever collected over volcanic landslide deposits acquired offshore of the soufriere hills volcano on the island of montserrat in the lesser antilles the 3d data enable detailed analysis of various features in and around these mass wasting deposits such as surface deformation fabrics the distribution and size of transported blocks change of emplacement direction and erosion into seafloor strata deformational features preserved on the surface of the most recent debris avalanche deposit deposit 1 reveal evidence for spatially variant deceleration as the mass failure came to rest on the seafloor block distributions suggest that the failure spread out very rapidly with no tendency to develop longitudinal ridges an older volcanic flank collapse deposit deposit 2 appears to be intrinsically related to large scale secondary failure of seafloor sediments we observe pronounced erosion directly down slope of a prominent headwall where translational sliding of well stratified sediments was initiated deep reaching faults controlled the form and location of the headwall and stratigraphic relationships suggest that sliding was concurrent with volcanic flank collapse emplacement we also identified a very different mass wasting unit between deposit 1 and deposit 2 that was likely emplaced as a series of particle laden mass flows derived from pyroclastic flows much like the recent since 1995 phase of deposition offshore montserrat but at a much larger scale this study highlights the power of 3d seismic data in understanding landslide emplacement processes offshore of volcanic islands highlights 3d seismic data show new detail of volcanic landslide deposits offshore montserrat volcanic flank collapse material has been diverted around seafloor topographic highs this bending during emplacement has caused pronounced erosion into seafloor strata erosion can destabilize seafloor slopes which then fail as translational slides block distributions and surface deformation give insight into debris avalanche style

glaciohydraulic supercooling in iceland we present evidence of glaciohydraulic supercooling under jokulhlaup and ablation dominated conditions from two temperate icelandic glaciers observations show that freezing of sediment laden meltwater leads to intraglacial debris entrainment during normal and extreme hydrologic regimes intraglacial frazil ice propagation under normal ablation dominated conditions can trap copious volumes of sediment which forms anomalously thick sections of debris rich ice glaciohydraulic supercooling plays an important role in intraglacial debris entrainment and should be given more attention in models of basal ice development extreme jokulhlaup conditions can result in significant intraglacial sediment accretion by supercooling which may explain the concentration of englacial sediments deposited in heinrich layers in the north atlantic during the last glaciation

dispersal and transformation of organic carbon across an episodic high sediment discharge continental margin waipaoa sedimentary system new zealand abstract the rivers that drain active collisional margins of the southwest pacific deliver up to 35 of particulate organic carbon poc to the world ocean and are a key component of the global organic carbon flux however knowledge of the fate of terrestrial poc in the ocean is both limited and necessary for quantifying terrestrial and coastal ocean carbon budgets here the fate of terrestrial poc is determined off the high discharge waipaoa river sediment yield 15 mt y 1 based on a transect of seven cores from the river floodplain to the adjacent continental shelf and slope total organic carbon toc 13 c 14 c c n ratios and lipid biomarker compounds were used to determine biogeochemical characteristics of surface sediments from terrestrial source to marine sink and how these characteristics vary with river discharge complementary to surface sediments down core characteristics of three multi cores covering the shelf and slope regions were used to identify perturbations in sediment supply via major floods the presence of flood deposits allows us to compare their oc characteristics with non flood sediment thereby helping address the question of how flood events in the river catchment affect the transfer and fate of terrestrial oc through the marine environment results from this study show that as surface sediments are physically and biologically processed across the continental margin they gain a marine signature biomarker analyses of surface samples show decreases in terrigenous vascular plant sources with increasing distance offshore biomarkers also demonstrate that terrestrial oc is being transferred across the continental margin with plant sterols long chain alcohols and long chain fatty acids biomarkers indicative of vascular plants persisting as far offshore as the mid continental slope in contrast to ambient conditions represented by surface sediments rapid delivery by floods allows for more complete transfer of terrestrial carbon to the marine environment a 1 10 cm thick flood layer preserved from cyclone bola march 1988 contains a significant amount of terrestrially sourced oc which subsequently was rapidly buried by sediments delivered during less extreme conditions

tsunami generation by a rapid entrance of pyroclastic flow into the sea during the 1883 krakatau eruption indonesia 1 the 1883 eruption of krakatau volcano in indonesia was one of the most explosive volcanic events in history it was a marine caldera forming eruption that resulted in voluminous ignimbrite deposits and huge tsunamis we have used numerical simulations to investigate three major mechanisms for tsunami generation caldera collapse phreatomagmatic explosion and pyroclastic flow and have constrained the source parameters computed tsunami characteristics for each hypothesis are compared with observations at locations along the coasts of the sunda strait where tsunami data were obtained immediately after the eruption for the pyroclastic flow hypothesis two types of two layer shallow water models dense and light type models were used under different initial conditions pyroclastic flows are erupted from a circular source following a sine function that assumes waning and waxing phases caldera collapse was performed using a simple piston like plunger model in which collapse duration was assumed to be up to 1 h the phreatomagmatic explosion hypothesis was examined using simple empirical models for underwater explosions in shallow water with explosion energy between 1016 and 1017 j the results show that when a pyroclastic flow with a volume of 5 km3 and an average discharge rate of the order of 107 m3 s enters the sea the computed tsunami heights are broadly consistent with historical records in coastal areas including a tide gauge record at batavia now jakarta we conclude that a pyroclastic flow entering the sea is the most plausible mechanism of the 1883 krakatau tsunami

efficient transport of fossil organic carbon to the ocean by steep mountain rivers an orogenic carbon sequestration mechanism mountain building exposes fossil organic carbon oc fossil in exhumed sedimentary rocks oxidation of this material releases carbon dioxide from long term geological storage to the atmosphere oc fossil is mobilized on hillslopes by mass wasting and transferred to the particu late load of rivers in large fl uvial systems it is thought to be oxidised in transit but in short steep rivers that drain mountain islands oc fossil may escape oxidation and re enter geological storage due to rapid fl uvial transfer to the ocean in these settings the rates of oc fossil transfer and their controls remain poorly constrained here we quantify the erosion of oc fossil from the taiwan mountain belt combining discharge statistics with measurements of particulate organic carbon load and source in 11 rivers annual oc fossil yields in taiwan vary from 12 1 to 246 22 tc km 2 yr 1 controlled by the high physical erosion rates that accompany rapid crustal shortening and frequent typhoon impacts effi cient transfer of this material ensures that 1 3 0 1 10 6 tc yr 1 of oc fossil exhumed in taiwan is delivered to the ocean with 15 loss due to weathering in transit our fi ndings suggest that erosion of coastal mountain ranges can force effi cient transfer and long term re accumulation of oc fossil in marine sediments further enhancing the role of mountain building in the long term storage of carbon in the lithosphere

early diagenesis of recently deposited organic matter a 9 yr time series study of a flood deposit abstract in fall 2000 the po river italy experienced a 100 yr return period flood that resulted in a 1 25 cm thick deposit in the adjacent prodelta 10 25 m water depth in the following years numerous post depositional perturbations occurred including bioturbation reworking by waves with heights exceeding 5 m as well as periods of extremely high and low sediment supply cores collected in the central prodelta after the fall 2000 flood and over the following 9 yr allowed characterization of the event strata in their initial state and documentation of their subsequent evolution sedimentological characteristics were investigated using x radiographs and sediment texture analyses whereas the composition of sedimentary organic matter om was studied via bulk and biomarker analyses including organic carbon oc total nitrogen tn carbon stable isotope composition 13c lignin phenols cutin products p hydroxy benzenes benzoic acids dicarboxylic acids and fatty acids the 9 yr time series analysis indicated that roughly the lower half of the original event bed was preserved in the sediment record conversely the upper half of the deposit experienced significant alterations including bioturbation addition of new material as well as coarsening comparison of the recently deposited material with 9 yr old preserved strata represented a unique natural laboratory to investigate the diagenesis of sedimentary om in a non steady system bulk data indicated that oc and tn were degraded at similar rates loss 17 whereas biomarkers exhibited a broad spectrum of reactivities loss from 6 to 60 indicating selective preservation during early diagenesis given the relevance of episodic sedimentation in several margins this study has demonstrated the utility of event response and time series sampling of the seabed for understanding the early diagenesis in non steady conditions

contrasting styles of shelf sediment transport and deposition in a ramp margin setting related to relative sea level change and basin floor topography turonian cretaceous western interior of central utah usa abstract the turonian lower ferron sandstone and juana lopez members of the mancos shale in the western interior foreland basin form a series of regressive shoreface to shelf depositional complexes sourced from the sevier fold thrust belt to the west continuous dip parallel outcrop exposures around the northern and eastern edges of the tertiary san rafael anticline sra in central utah provide an insight into the origins of anomalous marine mudstone encased sandstones lower ferron strata consist of both coarsening and thickening upward and sharp based shoreface successions interpreted to have been deposited as sequential highstand and falling stage systems tracts overlying these shallow marine deposits is a surface that marks sediment bypass that is correlated down dip into coarse grained cross bedded sandstones interpreted as the deposits of channelised turbidity flows these turbidites are considered to be the products of sustained hyperpycnal flows exiting rejuvenated lowstand rivers based on sustained flow indicators such as dune scale cross bedding absence of genetically related slumps and delta front deposits in up dip areas surfaces of sediment bypass coarser grain sizes than the underlying shoreface deposits and regional palaeogeography the flows are interpreted to have been ignitive in proximal areas down a tectonically induced slope in the uplifted area of the farnham dome the change in depositional style from falling stage to lowstand systems tracts is attributed to increased rates of sediment supply to the shoreline promoting hyperpycnal flows a flooding surface caps the interval and separates the lower ferron sandstone from the overlying juana lopez member this interval in contrast consists only of heterolithic parallel and ripple laminated graded sandstone mudstone couplets interpreted to have been deposited by turbulent storm induced geostrophic flows the couplets are arranged into bundles and are interpreted as parasequences which in turn are arranged into a progradational parasequence set deposited during a period of sea level highstand divergent sole mark and bedform palaeocurrents from both members suggest slight eastward deflection of the turbulent flows off the proto sra further evidence for this topography is inferred from an absence of turbidites along the western side of the structure the inferred influence of local basin floor structures on sedimentation of these units has important implications for structural models for this basin for generalized sequence stratigraphic models applied to ramp type foreland basin sequences and for elucidating the origin of anomalous marine mudstone encased sandstone bodies

tropical cyclone driven erosion of the terrestrial biosphere from mountains the transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle measurements of particulate organic carbon load and composition in the liwu river taiwan during cyclone triggered floods suggest that tropical cyclones may facilitate the delivery of non fossil particulate organic carbon to the ocean and its subsequent burial the transfer of organic carbon from the terrestrial biosphere to the oceans via erosion and riverine transport constitutes an important component of the global carbon cycle1 2 3 4 more than one third of this organic carbon flux comes from sediment laden rivers that drain the mountains in the western pacific region3 5 this region is prone to tropical cyclones but their role in sourcing and transferring vegetation and soil is not well constrained here we measure particulate organic carbon load and composition in the liwu river taiwan during cyclone triggered floods we correct for fossil particulate organic carbon using radiocarbon and find that the concentration of particulate organic carbon from vegetation and soils is positively correlated with water discharge floods have been shown to carry large amounts of clastic sediment6 non fossil particulate organic carbon transported at the same time may be buried offshore under high rates of sediment accumulation7 8 9 we estimate that on decadal timescales 77 92 of non fossil particulate organic carbon eroded from the liwu catchment is transported during large cyclone induced floods we suggest that tropical cyclones which affect many forested mountains within the intertropical convergence zone10 may provide optimum conditions for the delivery and burial of non fossil particulate organic carbon in the ocean this carbon transfer is moderated by the frequency intensity and duration of tropical cyclones

submarine pyroclastic deposits formed at the soufriere hills volcano montserrat 1995 2003 what happens when pyroclastic flows enter the ocean the soufriere hills volcano montserrat west indies has undergone a series of dome growth and collapse events since the eruption began in 1995 over 90 of the pyroclastic material produced has been deposited into the ocean sampling of these submarine deposits reveals that the pyroclastic flows mix rapidly and violently with the water as they enter the sea the coarse components pebbles to boulders are deposited proximally from dense basal slurries to form steep sided near linear ridges that intercalate to form a submarine fan the finer ash grade components are mixed into the overlying water column to form turbidity currents that flow over distances 30 km from the source the total volume of pyroclastic material off the east coast of montserrat exceeds 280 106 m3 with 65 deposited in proximal lobes and 35 deposited as distal turbidites

theoretical analysis of tsunami generation by pyroclastic flows 1 pyroclastic flows are a common product of explosive volcanism and have the potential to initiate tsunamis whenever thick dense flows encounter bodies of water we evaluate the process of tsunami generation by pyroclastic flow by decomposing the pyroclastic flow into two components the dense underflow portion which we term the pyroclastic debris flow and the plume which includes the surge and coignimbrite ash cloud parts of the flow we consider five possible wave generation mechanisms these mechanisms consist of steam explosion pyroclastic debris flow plume pressure plume shear and pressure impulse wave generation our theoretical analysis of tsunami generation by these mechanisms provides an estimate of tsunami features such as a characteristic wave amplitude and wavelength we find that in most situations tsunami generation is dominated by the pyroclastic debris flow component of a pyroclastic flow this work presents information sufficient to construct tsunami sources for an arbitrary pyroclastic flow interacting with most bodies of water

a box model for non entraining suspension driven gravity surges on horizontal surfaces the propagation of and the deposition from a turbulent gravity current generated by the release of a finite volume of a dense particle suspension is described by a box model the approximate model consists of a set of simple equations a predetermined depth dependent leading boundary condition and one experimentally determined parameter describing the trailing boundary condition it yields predictions that agree well with existing laboratory observations and more complex theoretical models of non eroding non entraining suspension driven flows on horizontal surfaces the essential features of gravity surge behaviour have been observed and are captured accurately by the box model these include the increased rate of downstream loss of flow momentum with increased particle setting velocity the existence of maxima in the thickness of proximal deposits and the downstream thinning of distal deposits our approximation for the final run out distance xr of a surge in deep water is given by xr3 g oq3o w2s 1 5 where g o is the initial reduced gravity of the surge qo the initial two dimensional volume and ws the average settling velocity of the particles in the suspension a characteristic thickness of the resulting deposit is given by oqo xr where oo is the initial volumetric fraction of sediment suspended in the surge our analysis provides additional insight into other features of gravity surge dynamics and deposits including the potential for the thickening of currents with time the maintenance of inertial conditions and the potential for strong feedback in the sorting of particle sizes in the downstream direction at travel distances approaching xr box model approximations for the evolution of gravity surges thus provide a useful starting point for analyses of some naturally occurring turbidity surges and their deposits

resedimentation of cold pumiceous ignimbrite into water facies transformations simulated in flume experiments deposits and transport processes resulting from the resedimentation of cold unconsolidated ignimbrite into water were simulated by flume experiments the ignimbrite sample used was poorly sorted 2 4 3 fine ash rich 2000 kg m 3 and pumice 500 to ca 1300 kg m 3 as a result of the binding forces of the ash matrix the experiments involved resedimentation from a steep front onto the floor with or without an initial ramp of the water filled tank under both still and wave generated conditions larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action the mass of the collapse and proportion of pore space water strongly influenced the style of resedimentation and the deposits initial collapse events were from the top of the steep front and fell onto the floor the largest densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break in slope fine ash was transported in dilute turbidity currents and coarse unsaturated pumice clasts floated off moderate collapse events generated high density turbidity currents trapping pumice in the flow causing them to saturate these low density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit large collapse events slumped producing poorly sorted mounds similar in texture to the original starting material as the matrix of the ignimbrite sample became saturated with water moderate and large collapse events generated debrisflows and slurries that deposited massive poorly sorted deposits furthermore once more gentle slopes were established between the sample and deposit small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low relief ash channels the experiments show that excluding large collapse events and debrisflows resedimenting ignimbrite in water is effective at segregating low density pumice clasts from dense lithic clasts and fine ash experiments using fine ash poor ignimbrite and well sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches the grainflow deposits had textures similar to the fines poor starting material

composition and provenance of terrigenous organic matter transported along submarine canyons in the gulf of lion nw mediterranean sea abstract previous projects in the gulf of lion have investigated the path of terrigenous material in the rhone deltaic system the continental shelf and the nearby canyon heads this study focuses on the slope region of the gulf of lion to further describe particulate exchanges with ocean s interior through submarine canyons and atmospheric inputs nine sediment traps were deployed from the heads to the mouths of lacaze duthiers and cap de creus submarine canyons and on the southern open slope from october 2005 to october 2006 sediment trap samples were analyzed by cuo oxidation to investigate spatial and temporal variability in the yields and compositional characteristics of terrigenous biomarkers such as lignin derived phenols and cutin acids sediment trap data show that the dense shelf water cascading event that took place in the months of winter 2006 january february and march had a profound impact on particle fluxes in both canyons this event was responsible for the majority of lignin phenol 55 4 and cutin acid 42 8 inputs to submarine canyons with lignin compositions similar to those measured along the mid and outer continental shelf which is consistent with the resuspension and lateral transfer of unconsolidated shelf sediment to the canyons the highest lithogenic normalized lignin derived phenols contents in sediment trap samples were found during late spring and summer at all stations i e 193 46 g vp g 1 lithogenic at deep slope station when river flow wave energy and total particle fluxes were relatively low during this period lignin compositions were characterized by elevated cinnamyl to vanillyl phenol ratios 3 at almost all stations high p coumaric to ferulic acid ratios 3 and high yields of cutin acids relative to vanillyl phenols 1 all trends that are consistent with high pollen inputs our results suggest marked differences in the sources and transport processes responsible for terrigenous material export along submarine canyons mainly consisting of fluvial and shelf sediments during winter and atmospheric dust inputs during spring and summer

an 18 m thick volcaniclastic interval in pantelleria trough sicily channel deposited from a large gravitative flow during the green tuff eruption abstract a 30 m long piston core from the floor of pantelleria trough penetrated an 18 m thick volcaniclastic interval under and overlain by hemipelagic sediments the distribution and thickness of the interval is mapped in 3 5 khz profiles across the trough core sediments have been analysed for grain size carbonate content detrital petrology and physical properties such as bulk density and magnetic susceptibility chemical analyses of tephra and included minerals have been made by electron microprobe the volcaniclastic interval is correlated with the youngest large explosive eruption on pantelleria the 50 ka green tuff ignimbrite eruption on the basis of the sedimentation rate of overlying sediment calcareous nannofossil and foraminiferal biostratigraphy a calibrated radiocarbon age of 43 47 2 ka possibly infinite in the underlying marls and many similarities in tephra and mineral chemistry and abundance the lower 8 m of the volcaniclastic interval consists of poorly sorted massive units of lapilli tuff interpreted as resulting from the direct flow of a pyroclastic flow into the sea with the energetic hyperconcentrated flows crossing the length of pantelleria trough and eventually freezing on the low gradients the overlying 10 m thick turbidite probably developed from the dilute turbulent pyroclastic flow of the co ignimbrite cloud and the resulting turbulent subaqueous flow eroded bioclastic material from the shelf and deposited a well graded bed from sand through silt to mud the poorer sorting of the volcaniclastic interval compared with the green tuff ignimbrite on land supports the concept that ignimbrite deposits are sorted by aggrading bed processes

paleomagnetic evidence for high temperature emplacement of the 1883 subaqueous pyroclastic flows from krakatau volcano indonesia the paroxysmal 1883 eruption of krakatau volcano in indonesia discharged at least 6 5 km3 dense rock equivalent of pyroclastic material into the shallow waters of the sunda straits within a 15 km radius of the volcano progressive thermal demagnetization studies of individually oriented pumice clasts from a core sample of the submarine pyroclastic deposits show that 41 out of 47 clasts exhibit single component remanence with mean inclination of 2 4 the partial thermoremanent magnetization components of both pumice and lithic clasts are well grouped in orientation indicating that substantial cooling of clasts must have occurred following deposition estimated subaqueous emplacement temperature for such clasts is greater than 500 c rare two component lithic fragments exhibit inflection points on vector endpoint diagrams that mark the temperature below which the fragments acquired magnetization of similar orientation these inflection points range from 350 to 550 c indicating a minimum subaqueous emplacement temperature of 350 c paleomagnetic evidence for high emplacement temperature supports the hypothesis that proximal 1883 submarine pyroclastic deposits resulted from entrance of hot subaerially generated pyroclastic flows into the sea similar deposits have been interpreted from the geologic record but this is the first documented example of submarine pyroclastic flows from a historic eruption the krakatau deposits thus serve as an important modern analog for the study of pyroclastic flow seawater interactions

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

deep advective transport of lithogenic particles in panama basin sediment traps were deployed at several depths between 660 and 3800 meters in the panama basin the flux of lithogenic particles increased with increasing depth this increase was due primarily to particles of beidellite a smectite clay which was identical to the clay occurring in bottom sediment on the continental slope to the west of the sediment trap mooring the beidellite vertical flux at the panama basin station increased when an easterly current prevailed and decreased when the current reversed indicating that a major portion of smectite was transported horizontally at mid water depth to the mooring site from the nearby continental slope

sedimentary organic matter geochemistry of clayoquot sound vancouver island british columbia surface sediment samples from three interconnected fjords of clayoquot sound british columbia were density fractionated 1 6 g cm 3 to isolate discrete organic debris od from mineral associated organic matter mom total organic carbon oc values varied greatly ranging from 0 1 to 8 8 by weight with a general decreasing trend from fjord head to the continental shelf within the sediment terrestrial om was present either as vascular plant debris or soil mom down fjord the woody vascular plant material in the od fraction acquires nitrogen which is hypothesized to be due to the bacterial incorporation of nitrogen from the water terrestrial oc in the mom is incompletely replaced by marine oc within the fjords resulting in a 65 net loss of mom sediments deposited under oxic and intermittently anoxic water column conditions have organic carbon to surface area ratios oc sa ranging from 0 4 to 1 2 mg c m 2 similar to that of typical continental margin sediments given that temperate fjords contain an estimated 12 of the continental margin sediment deposited during the last 100 000 yr and that they bury at least a margin equivalent amount of oc either weight or surface area normalized we hypothesize that temperate fjords may contain 12 or more of the sedimentary oc buried during this time

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

stratified flow in pyroclastic surges stratified flow theory is applied to pyroclatic surges in an effort to gain insight into transport dynamics during explosive eruptions particle transport is assumed to be by turbulent suspension and calculations contained herein show that this is likely for many cases including the 18 may 1980 blast at mount st helens the discussion centers on the rouse number pn which represents a ratio of particle settling velocity to scale of turbulence the brunt vaisala frequency n which is the maximum possible frequency of internal waves the froude number fr representing the ratio of inertial forces to gravitational forces and the richardson number ri a ratio of buoyant restoring forces to turbulent mixing forces the velocity or flow power dependence of bed form wavelength in surge deposits is related to a velocity dependence of wavelength of internal waves in the turbulent surge this produces a decrease in dune wavelength with increasing distance from vent migration direction of bed forms is related tofr as it is defined for a continuously stratified flow proximal to distal facies variations in surge deposits reflect increasingpn andri as the flows move away from their sources this produces the progression from sandwave to massive to planar facies with increasing distance from vent where the long axis of topography is at low angles to the flow direction massive facies in topographic lows may from concurrently with sandwave facies on highs due to the higher particle concentration in the lows where long axis of topography is at high angles to flow direction denser lower parts of the surge may be dammed or blocked blocked material tends to form massive flows that may move down slope independent of the overriding surge a model incorporating turbulent transport stratified flow and time evolution of pyroclastic surges is proposed for deposits which have been attributed to both pyroclastic flow and pyroclastic surge transport by various workers during the initial high energy waxing phase of the eruptive event pn is sufficiently low that only coarse but poorly sorted material is deposited to form relatively coarse bottom layers as the event wanes remaining finer material is deposited through a thin bed load to produce overlying bedded and cross bedded veneer deposits throughout most of the event blocking occurs to produce relatively thick and massive deposits in valley bottoms

volcanogenic sedimentation in the iceland basin influence of subaerial and subglacial eruptions abstract cores recovered from the iceland basin show evidence of transport and deposition of volcaniclastic sediment from the eastern volcanic zone of iceland during the holocene and last glacial period three types of deposits have been identified tephra fall sediment gravity flows and bottom current controlled deposits tephra fall layers contain basaltic glass of composition that suggests katla volcano as the major source a chronology of the volcano activity is reconstructed back to isotopic stage 5d 120 000 yr glass chemistry of tephra in sediment gravity flows deposited south of myrdalsjokull canyon indicates a source in the grimsvotn lakagigar volcanic system these volcaniclastic gravity flows were most likely derived from jokulhlaups or large glacial floods at a time of a more extensive ice cover over the volcanic zone deposition of the sediment gravity flows has created a deep sea fan south of the canyon basalt glass composition age and depositional environment suggest that one early holocene turbidite sequence was derived from a large jokulhlaup of the grimsvotn area the volcanogenic sediment gravity flows were influenced by a strong contour current moving across the katla sediment ridges the contour current has winnowed the silt fraction and transported it downstream as suspended load the recovery of numerous silty volcaniclastic layers enriched in detrital crystals indicates that they contributed to the sedimentation of contourite drifts

how did thin submarine debris flows carry boulder sized intraclasts for remarkable distances across low gradients to the far reaches of the mississippi fan submarine density flows dominate sediment transport into many parts of the ocean and form submarine fans which are some of the largest sediment accumulations on earth previous studies often assumed that the distal fringes of submarine fans would be dominated by extensive sheet like deposits from dilute and expanded turbidity currents because only turbidity currents would transport large volumes of sediment for long distances across such low gradients deposits with a remarkable frondlike shape occur at the furthest fringe of the mississippi submarine fan understanding the emplacement process of these deposits is important because their frondlike shape suggests deposition from debris flows rather than turbidity currents previous analyses concluded that these deposits comprise a complex arrangement of thin interbedded turbidity current and debris flow deposits here we propose a different internal geometry for the frondlike deposits intervals previously described as in place turbidites are interpreted to be clasts within a single debrite interval that is 1 to 2 m thick this debrite interval is underlain by clean sand the debrite interval could have been emplaced by multiple debris flows or one event comprising multiple pulses clasts in the debrite interval are much bigger than previously thought including boulders with diameters that can exceed 50 cm we show that thin 2 m and extremely fluidal debris flows could have carried these boulders across gradients of only 0 06 to the fringes of one of the world s largest submarine fans without hydroplaning this long transport distance could occur if the density of the clasts was less than that of the surrounding debris flow emplacement of the basal clean sand layer appears closely linked to debris flow deposition because the clean sand layer pinches out in a location similar to that of the overlying debrite we therefore suggest that the basal clean sand most likely settled out from the overlying debris flows and that the clean sand is not a fore running turbidity current deposit shearing at the base of a mud rich debris flow would most likely produce a muddy basal sand interval rather than the clean sand that is observed this basal sand interval is therefore less likely to be a record of a lubricating layer with high pore fluid pressure on which the debris flows moved this study shows how thin and highly mobile debris flows can redistribute large volumes of sediment including bouldersized clasts long distances into the deep ocean across remarkably low gradients

sediment sorting in the deposits of turbidity currents created by experimental modeling of explosive subaqueous eruptions abstract deposits of turbidity currents induced by subaqueous volcanic eruptions are increasingly recognized in settings ranging from lakes to the deep sea these eruption fed density currents have high current temperatures and low density particles which affect current dynamics and deposit features field data indicate that deposit thickness and grain size decrease downflow at a changing rate this trend is similar for deposits of noneruptive turbidity currents but with volcanic activity the deposits often exhibit a break in slope of the profile of deposit thickness and grain size distribution here we present laboratory results on density currents that address the effects of variations in grain density and water temperature on flow properties and depositional processes parallel runs were performed under identical flow conditions using quartz sand and pyroclastic sediment each grain type was used in one series of runs in which a hot density current enters a cold environment and one series in which

cyclone induced hyperpycnal turbidity currents in a submarine canyon 1 density currents such as turbidity currents are major transport agents in various terrestrial lacustrine and marine environments worldwide however a gap exists between those who study the deposits by turbidity currents turbidite on a field scale and those who study turbidity currents using small scale laboratory experiments and theoretical numerical models we report two typhoon triggered hyperpycnal turbidity current events observed in a submarine canyon our findings verify turbidite sequences with the characteristics of suspended sediment carried by passing turbidity currents that displayed distinct waxing and waning phases our study also confirms the direct link between typhoon triggered hyperpycnal flows in a small mountainous river and turbidity currents in a nearby submarine canyon that transport sediment to the deep sea efficiently

terminal settling velocity of commonly occurring sand grains published measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form results are noticeably different from those for spheres of similar diameter and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape for quartz in water the three equations of different settling regimes correspond approximately to very fine sand fine to coarse sand and very coarse sand

a laboratory simulation of pyroclastic flows down slopes abstract laboratory experiments are described which explore the dynamical consequences of buoyant convective upflow observed above hot pyroclastic flows in nature the convection is produced by the hot ash particles exchanging heat with air mixed into the front and top of the pyroclastic flow this effect on the buoyancy due to the mixing of air and ash has been modelled in the laboratory using mixtures of methanol and ethylene glycol meg which have a nonlinear density behaviour when mixed with water intermediate mixtures of these fluids can be denser than either initial component and so the laboratory experiments were inverted models of the natural situation we studied meg flowing up under a sloping roof in a tank filled with water the experiments were performed both in a narrow channel and on a laterally unconfined slope the flow patterns were also compared with those of conventional gravity currents formed using fresh and salt water the presence of the region of reversed buoyancy outside the layer flowing along the slope had two significant effects first it periodically protected the flow from direct mixing with the environment resulting in pulses of relatively undiluted fluid moving out intermittently ahead of the main flow second it produced a lateral inflow towards the axis of the current which kept the current confined to a narrow tongue even on a wide slope in pyroclastic flows the basal avalanche portion has a much larger density contrast with its surroundings than the laboratory flows calculations show that mixing of air into the dense part of a pyroclastic flow cannot generate a mixture that is buoyant in the atmosphere however the overlying dilute ash cloud can behave as a gravity current comparable in density contrast to the laboratory flows and can become buoyant depending on the temperature and ash content in the august 7th pyroclastic flow of mount st helens hoblitt 1986 describes pulsations in the flow front which are reminiscent of those observed in the experiments as proposed by hoblitt the pulsations are caused by the ash cloud accelerating away from the front of the dense avalanche as a density current the ash cloud then mixes with more air becomes buoyant and lifts off the ground allowing the avalanche to catch up with and move ahead of the cloud the pulsing behaviour at the fronts of pyroclastic flows could account for the occurrence of cross bedded layer 1 deposits which occur beneath layer 2 deposits in many sequences

experimental turbidity currents entering density stratified water analogues for turbidites in mediterranean hypersaline basins experimental turbidity currents entering two layer density stratified water behave differently from similar currents flowing over the same topography into non stratified water experiments were designed as analogues for flows entering mediterranean hypersaline pools in both the hypersaline pools and the experiments the water density changes abruptly across a pycnocline turbidity currents generated on a platform at the level of the pycnocline behaved in one of three ways as they flowed from the platform into deeper stratified water 1 when the bulk density of the current was less than the dense water layer the current spread at the pycnocline the head of the current advanced rapidly when it lost contact with the bed grains settling out of the current fell through the dense water layer forming an extensive deposit in nature this behaviour will lead to turbidites with sharp but non erosive bases strongly developed grading and no traction features 2 when the bulk density of the current was greater than the dense water layer the current continued as an underflow plunging into the deeper water sedimentation lowered the bulk density of the current and the low density interstitial fluid caused the head to loft low density interstitial fluid convected from the body of the current lofting particles into the water column these particles were hydraulically sorted during upward transport and subsequent settling to the floor the resulting turbidites had a more limited extent than the deposits of either non lofting underflows or interflows by inference from the experiments natural deposits of this type may have local proximal erosion and traction features at the base and strongly graded tops 3 in some of the currents with high bulk density the rising turbid water reached the pycnocline and spread at that level as a secondary interflow the tail of the turbidity current which was less dense than the head and body of the current flowed above the pycnocline adding momentum to the secondary interflow the thin non erosive graded deposit from the secondary interflow may extend beyond the deposits of the primary underflow in all three cases but more pronounced in cases 2 and 3 the interaction of the current with the pycnocline displaced that surface and generated a wave that was reflected back and forth from each end of the pool the waves remobilized sediment on the ramp

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

organic carbon fluxes to the ocean from high standing islands the transfer of terrestrially derived yet poorly quantified organic carbon to the oceans is an important yet unagreed upon proportion of the world s carbon budget the few data that exist suggest that high standing oceanic islands in the southwest pacific may make important contributions to the overall terrestrial flux of particulate organic carbon poc to the oceans we have determined the poc flux from several streams in new zealand with those data and previous measurements from taiwan and papua new guinea we estimate the poc flux from high standing islands in the southwest pacific to be 48 1012 g c yr 1 a value slightly lower than previous estimates these islands which make up only 3 of earth s landmass contribute 17 35 of the estimated poc entering the world s oceans annually and thus may be important sources of terrestrial carbon to the ocean anthropogenic activities especially deforestation and forest harvesting have probably exacerbated the natural flux few to no data exist for many of these islands and thus a more detailed assessment awaits further measurements

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

tectonically controlled sedimentation impact on sediment supply and basin evolution of the kashafrud formation middle jurassic kopeh dagh basin northeast iran the kashafrud formation was deposited in the extensional kopeh dagh basin during the late bajocian to bathonian middle jurassic and is potentially the most important siliciclastic unit from ne iran for petroleum geology this extensional setting allowed the accumulation of about 1 700 m of siliciclastic sediments during a limited period of time upper bajocian bathonian here we present a detailed facies analysis combined with magnetic susceptibility ms results focusing on the exceptional record of the pol e gazi section in the southeastern part of the basin ms is classically interpreted as related to the amount of detrital input the amount of these detrital inputs and then the ms being classically influenced by sea level changes climate changes and tectonic activity facies analysis reveals that the studied rocks were deposited in shallow marine slope to pro delta settings a major transgressive regressive cycle is recorded in this formation including fluvial dominated delta to turbiditic pro delta settings transgressive phase followed by siliciclastic to mixed siliciclastic and carbonate shoreface rocks regressive phase during the transgressive phase hyperpycnal currents were feeding the basin these hyperpycnal currents are interpreted as related to important tectonic variations in relation to significant uplift of the hinterland during opening of the basin this tectonic activity was responsible for stronger erosion providing a higher amount of siliciclastic input into the basin leading to a high ms signal during the regressive phase the tectonic activity strongly decreased furthermore the depositional setting changed to a wave to tide dominated mixed carbonate siliciclastic setting because of the absence of strong tectonic variations bulk ms was controlled by other factors such as sea level and climatic changes fluctuations in carbonate production possibly related to sea level variations influenced the ms of the siliciclastic carbonate cycles carbonate intervals are characterized by a strong decrease of ms values indicates a gradual reduction of detrital influx therefore the intensity of tectonic movement is thought to be the dominant factor in controlling sediment supply changes in accommodation space and modes of deposition throughout the middle jurassic sedimentary succession in the pol e gazi section and possibly in the kopeh dagh basin in general

quantifying tidal signatures of the benthic nepheloid layer in gaoping submarine canyon in southern taiwan abstract the benthic nepheloid layer bnl has been observed in the head region of the gaoping kaoping submarine canyon kpsc throughout a year the top of the bnl could be as high as 100 m above the canyon floor in which the suspended sediment concentration ssc could be as high as 30 mg l in the bnl sand sized particles comprise the largest size class in the suspended sediment population based on three one month time series observations near the canyon floor of along canyon velocity water temperature and the volume concentration vc of clay very fine to medium silt coarse silt and sand size classes in 2000 2002 and 2004 the bnl is strongly modulated by the tides at semidiurnal diurnal quarter and sixth diurnal and spring neap frequencies in the course of a semidiurnal tidal cycle the flood up canyon current brings colder water from the seaward part of the canyon causing the ssc and the thickness of the bnl to increase the ssc immediately near the canyon floor also increases in response to the maximum flood and ebb currents of the m 2 tide the tidal to total energy ratio er of the along canyon flow is between 70 80 and between 50 80 among the suspended sediment of clay very fine to medium silt coarse silt and sand size classes the m 2 is the most important tidal constituent in the temporal variations of along canyon flow water temperature and the vc of the four size classes the local phase differences between the forcing velocity and the responses temperature and vc at the m 2 frequency show distinct phase lock that suggests patterns of standing and progressive internal tides suspended sediments in the bnl also respond to the m 2 forcing in a coherent fashion suspended sediment movements are strongly affected by nonlinear processes as indicated by the elevated values of the amplitude ratio of m 4 m 2 of the suspended sediment size classes comparing to that of the flow the cross canyon geometry and the slope of the submarine canyon floor affect the propagation of the barotropic and internal tides which in turn affect the nonlinearity generation in the bnl

pyroclastic flows and surges over water an example from the 1883 krakatau eruption pyroclastic deposits from the 1883 eruption of krakatau are described from areas northeast of the volcano on the islands of sebesi sebuku and lagoendi and the southeast coast of sumatra massive and poorly stratified units formed predominantly from pyroclastic flows and surges that traveled over the sea for distances up to 80 km granulometric and lithologic characteristics of the deposits indicate that they represent the complement of proximal subaerial and submarine pyroclastic flow deposits laid down on and close to the krakatau islands the distal deposits exhibit a decrease in sorting coefficient median grain size and thickness with increasing distance from krakatau crystal fractionation is consistent with the distal facies being derived from the upper part of gravitationally segregated pyroclastic flows in which the relative amount of crystal enrichment and abundance of dense lithic clasts diminished upwards the deposits are correlated to a major pyroclastic flow phase that occurred on the morning of 27 august at approximately 10 a m energetic flows spread out away from the volcano at speeds in excess of 100 km h and traveled up to 80 km from source the flows retained temperatures high enough to burn victims on the sw coast of sumatra historical accounts from ships in the sunda straits constrain the area affected by the flows to a minimum of 4x103 km2 at the distal edge of this area the flows were relatively dilute and turbulent yet carried enough material to deposit several tens of centimeters of tephra the great mobility of the krakatau flows from the 10 a m activity may be the result of enhanced runout over the sea it is proposed that the generation of steam at the flow seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective the buoyant distal edge of these ash and steam laden clouds lifted off into the atmosphere leading to cooling condensation and mud rain

particulate size spectra behavior and origin of nepheloid layers over the nova scotian continental rise 1 26 32 m measured by coulter counter on 10 cm 3 samples correlate linearly with light beam attenuation coefficient correlation between particle volume and weight concentration indicates lower apparent particle density for low concentration suspensions a feature that is attributed to aggregation during aging of the suspension particle size distributions show unimodal form with a peak at 4 m in high concentrations near the bed changing to a bimodal form with an additional mode at 16 m in low concentrations high above the bed 500 and 1000 m a b meters above bottom the presence of the coarse mode at 1000 m a b coupled with its increase in the lower 250 m of the water column suggests that it both settles from the surface and is resuspended from the bed ultrasonic disaggregation experiments show that much of the fine mode is of aggregates but the coarse mode is single solid particles distributions with a low volume concentration increase in volume when disaggregated and are interpreted as having a relatively large part of their total distribution in unmeasured sizes 32 m distributions with a high concentration decrease in counted volume on disaggregation inversions in the light attenuation profiles are taken to indicate the presence of former bottom mixed layers and their occurrence suggests thickening of the nepheloid layer by detachment and lateral injection of these turbid mixed layers they occur at levels sufficiently high as to provide a nepheloid layer over 1500 m thick over the adjacent sohm abyssal plain the coarse mode probably comprises solid particles with a calculated settling velocity of 12 m day its absolute concentration increases toward the bed but as a proportion of the distribution it increases upward it is thus thought to be particles of surface origin both settling to the bottom and in the lower 250 m of the water column resuspended from the bed the fine mode at 4 m has a spatially constant form thought to be controlled by physical coagulation mechanisms rates of coagulation estimated from shear mechanisms suggest that the postulated change of peaked into flat size distribution by particle aggregation and settling has a time scale of a few years rather than months which is probably long when compared with the lateral injection process lower in the nepheloid layer for that reason distribution with a fine mode peak are found well above the bottom mixed layer

sediment dynamics in a submarine canyon a case of river sea interaction this paper presents findings from a 1 month field experiment conducted during the flood season of 2000 on the southern coast of taiwan to examine the delivery of lithogenic siliciclastic sediment to kao ping submarine canyon from the nearby kao ping river and shelf sources and the transport of suspended lithogenic and nonlithogenic particles near the canyon floor collected time series data included simultaneous measurements of coastal winds salinity temperature flow field suspended sediment concentration ssc and size composition of suspended particles at the river mouth and inside the submarine canyon as well as results from seawater and sediment trap data other collected data included river discharge and sediment load and hydrographic measurements along and across the axis of the canyon during the experiment two significant episodic river sediment discharge events occurred relating to a typhoon and extreme precipitation conditions the findings show that theoretically the time difference between sand and clay siliciclastic grains to settle from the sea surface to the canyon floor is on the order of hours to months analogous to a sorting process river plume dynamics and the coastal wind field largely control the delivery of terrigenous fine grained sediment to the canyon inside the canyon the behavior of suspended lithogenic and nonlithogenic particles of different sizes can be differentiated into a coarse grained group sand which forms the drop in population and a fine grained group mud which forms the standing population each group has distinct spectral characteristics the coarse grained group is delivered directly to the canyon by the river effluent and by wave resuspension of the shelf substrate during the study period the net transport of suspended particles near the canyon floor was landward mostly by tidal currents whose direction was also modulated by spring neap tide both lithogenic and nonlithogenic particles contribute to high mass fluxes exceeding 700 g m 2 day 1 in the lower part of the canyon this river sea system represents a type of systems that consist of three geographically separated dynamic entities the river plume the shelf and the canyon under fair weather conditions the river plume and shelf processes are coupled through the tide and wind field the river and canyon form a direct source to sink link via coarse grained siliciclastic sediment during the flood season in both continuous and pulsed fashion in the typhoon season the shelf becomes a pulsed source region for coarse grained sediment

turbidite variability and architecture of sand prone deep water slopes eocene clinoforms in the central basin spitsbergen abstract the architecture and turbidite variability within six wedge shaped downslope thinning sand prone slope accumulations are documented from eocene shelf margins on spitsbergen the central basin formed as a small foreland or piggy back basin and the studied turbidites accumulated mainly on the slope portion of sand prone clinoforms that developed during depocenter migration and infilling of the basin the shelf margin clinoforms have amplitudes minimum water depths from 100 to 350 meters and their shelf slope and basin floor segments are well imaged and can be walked out along many of the mountainsides only a small percentage of the clinoforms are sand prone and these developed when sea level occasionally fell to or below the shelf edge of the sand prone clinoforms some had their sand budget partitioned mainly out onto the basin floor basin floor fans but most trapped the sand on the slope only the latter are now visible as downslope thinning wedges some 2 5 3 5 km in downdip extent the turbidites within this type of clinoform have been examined and classified the lower slope to base of slope segment of the studied clinoform complexes are dominated by lobes consisting of broad shallow channels and sheet like turbidites becoming heterolithic and muddy out on the basin floor beds on the lower slope vary from thick up to 4 5 meters ungraded or laminated sandstones to thinner ungraded sandstones with coarse cappings the middle slope segment of clinoform complexes is dominated by narrow channels chutes that feed downslope to progradational chute mouth lobes chutes contain ungraded and laminated sandstone beds up to 3 m thick whereas the chute mouth lobes show alternations of thinner ungraded to laminated or rippled sandstones these lobes become more heterolithic and muddy downslope the shelf edge to upper slope segment of clinoform complexes is dominated by upward coarsening and thickening sheetsands of steep fronted shelf edge deltas the sandsheets of the delta front can be traced updip into mouth bar and distributary channel sandstones it is argued that shelf margin accretion represented by the sand prone slope wedges was achieved mainly by sand laden currents that flooded from the shelf edge as hyperpycnal flows this hypothesis is supported by 1 the direct connection between channel and mouth bar systems at the shelf edge and the turbidites of the slope lobes 2 the systematic progradational character of the slope lobes 3 the absence of large scale slump scars gullies or canyons on the slope and 4 the dominance of a type of turbidite that implies deposition from sustained flow detailed examination of the architecture of one of the slope wedges shows that there are unconformities developed within the stratigraphy below the shelf edge and that these erosional terraces beheaded the deltas perched on the uppermost slope the erosion surfaces indicate fall of sea level to this position despite the magnitude of this fall up to 80 meters the lack of canyons on the slope prevented the construction of basin floor fans such falls of sea level on non canyoned slopes simply promote sand prone accretion of the shelf margin

sedimentary signatures of the entrance of coarse grained volcaniclastic flows into the sea the example of the breccia units of the las palmas detritic formation mio pliocene gran canaria eastern atlantic spain abstract the transformations of volcaniclastic gravity flows entering the sea remain poorly understood they are recorded by sedimentary signatures in the volcaniclastic sedimentation of the mio pliocene las palmas detritic formation lpdf of the volcanic island of gran canaria these gravity flows are contemporaneous with an erosive period on the island succeeding the emplacement of the fataga volcanic group and the beginning of the evolution of the roque nublo stratovolcano the sedimentary section that crops out at the mouth of a paleobarranco at las cuevas del guincho comprises subtidal calcareous and clastic sediments affected by wave and storm action units 1 and 3 beach gravels unit 4 volcaniclastic deposits represented by reworked phonolitic pyroclastic deposits unit 1 breccia deposits that contain juvenile and phonolitic gravels and blocks mainly incorporated at the shoreline unit 2 and a debris avalanche deposit at the top unit 5 the breccia deposits display a reversely graded base which disappears distally as a result of seawater incorporation and liquidization of the volcaniclastic mass and mixing with marine sediment this breccia unit is interpreted as having been emplaced by a granular mass flow after transformation of a block and ash flow deposit that entered the sea in the debris avalanche deposits thermal quenching of juvenile basaltic lava clasts and large inclined clastic intrusions of underlying marine sediments suggest that the debris avalanche entered the sea rapid subaqueous emplacement of the granular mass flow and of the debris avalanche deformed the sedimentary substratum water incorporation reduced the influence of the volcaniclastic flows on the substratum ams data confirm the effect of water ingestion and correlative loss of cohesion and allow also reconstruction of paleoflow directions that were normal to the paleoshoreline of the northern coast of gran canaria all these volcaniclastic gravity flow deposits and their textural characteristics are particularly useful in the reconstruction of processes that occur at the subaerial submarine transition and for the location of ancient shorelines

organic carbon and nitrogen contents and their isotopic compositions in surficial sediments from the east china sea shelf and the southern okinawa trough abstract the southern okinawa trough has been noted as an important depocenter for the particulate organic matter from the east china sea shelf in order to determine the major sources of sedimentary organic matter in the southern okinawa trough we analyzed surficial sediments from the east china sea shelf and the southern okinawa trough for organic carbon and nitrogen contents and their isotopic compositions in the decarbonated fraction distributions of total organic carbon content 13corg and nitrogen content all show a similar spatial pattern resembling the distribution of fine grained sediments the coastal belt of elevated organic carbon content extends southward from the changjiang mouth and veers offshore towards the southern okinawa trough just north of taiwan implying a pathway for channeling fine grained sediments from the inner shelf to the depocenter this distribution pattern is consistent with the shelf circulation the isotope compositions 13corg 15n of sediments from the southern okinawa trough fall between those of riverine particulate organic matter and the mid outer shelf sediments but overlap with those of the inner shelf sediments in addition the previously reported 13corg values of sinking particles collected by sediment traps in the southern okinawa trough are also close to those of the inner shelf sediments especially during high flux conditions therefore the isotopic evidence strongly supports the notion that a major fraction of the sedimentary organic matter in the southern okinawa trough may originate from the inner shelf

cyclone driven deep sea injection of freshwater and heat by hyperpycnal flow in the subtropics china 973 program 2009cb421200 program of introducing talents of discipline to universities b07034 academia sinica thematic program afobi taiwan nsc 98 2116 m 001 005

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

sources of sedimentary organic matter in the mississippi river and adjacent gulf of mexico as revealed by lipid biomarker and δ13ctoc analyses abstract changes in the organic matter om composition c n 13 c toc and lipid biomarker compounds of surface sediments 0 1 cm were examined along the dispersal pathway from mississippi river and marsh estuarine end members to the adjacent shelf and canyon regions of the gulf of mexico organic carbon content decreased fourfold from the marsh to the offshore sites with corresponding changes in organic matter sources biomarkers representing allochthonous higher plant and autochthonous algal plankton bacteria sources demonstrated regional differences in the sources of sediment organic matter som a two end member mixing model using 13 c toc indicated that c 3 vascular plant sources comprised 80 and 50 of the toc at the river and marsh sites respectively however sources of som differed in these regions with contributions of soil organic matter terrigenous plant sources dominant in the river 13 c toc 25 while marsh plants likely contributed to the enriched signatures found in the marsh sediments 13 c toc 18 allochthonous om contributions calculated from fatty acid and sterol biomarkers in the river and marsh regions 39 48 and 50 72 respectively differed from those determined using 13 c toc this was likely due to overlapping 13 c toc values for vascular plants and freshwater microalgae and the higher lipid content of the autochthonous sources although biomarkers representing terrigenous sources decreased with distance offshore they comprised approximately 17 34 of the fatty acid and sterols at even the most distal slope and canyon sites suggesting that these deeper regions could be an important sink for terrigenous carbon in contrast the shelf sites were enriched in algal material 60 78 autochthonous oc with biomarkers for diatoms dominating suggesting that terrigenous carbon is either diluted in or bypasses this region results from this study suggest that processes including hydrodynamic sorting diagenesis and variations in river flow should be considered in future studies investigating the fate of terrigenous om in coastal and shelf regions

the 1883 eruption of krakatau the 1883 eruption of krakatau was a modest ignimbrite forming event the deposits are primarily coarse grained dacitic non welded ignimbrite large explosions produced pyroclastic flows that entered the sea generating destructive tsunami grain size studies of the ignimbrite suggest that these explosions were not driven by magma seawater interaction the total bulk volume of pyroclastic deposits including co ignimbrite ash is estimated to be 18 21 km3

primary or secondary distal volcaniclastic turbidites how to make the distinction an example from the miocene of new zealand mahia peninsula north island abstract miocene marine volcaniclastic deposits occur in mahia peninsula north island new zealand and were sedimented in a forearc setting related to the hikurangi trench subduction system these deposits are interbedded with hemipelagic marls and correspond to simple or amalgamated centimetric to metric thick turbiditic sequences volcaniclastic material is mainly composed of vitric particles with crystals quartz plagioclase with minor biotite amphibole pyroxene and oxides which are well represented in the coarse grained fraction the glass shards are mainly rhyolitic in composition three types of volcaniclastic turbidites were distinguished with geochemical data because distinction is impossible on sedimentary characteristics 1 primary monomagmatic turbidites contain both magmatic bubble wall pumice and shards and phreatomagmatic blocky shards with few vesicles and hydroclastically fragmented pyroclasts vitric particles the chemical compositions of the vitric particles and the crystals are very homogeneous suggesting a cogenetic origin these turbidites directly result from unique eruptive events and are probably related to the entrance of hot subaerial pyroclastic flows into the sea which also led to their transformation into subaqueous gravity flows 2 secondary monomagmatic turbidites never contain phreatomagmatic pyroclasts and the glass compositions display a trend from andesites to rhyolites there is a strong linear correlation in the compositions that suggest that the glass particles are derived from the same magma crystals also show a compositional homogeneity these deposits reflect the succession of several eruptions related to a unique magmatic system and result of the reworking of volcaniclastic material after relatively short storage on the shelf 3 secondary multimagmatic turbidites do not display compositional homogeneity of their vitric and mineral components this implies that the volcaniclastic material has been stored during a relative long period on the shelf before remobilization and that this sedimentation records the volcanic activity of multiple magmatic sources consequently it has been possible to distinguish primary volcaniclastic turbidites that are directly related to the volcanic activity from secondary turbidites that result from reworking of previously deposited material on the shelf monomagmatic turbidites can be used as stratigraphic and magmatic markers whereas multimagmatic cannot multimagmatic turbidites however record the evolution of the volcanic arc during longer periods this leads to the conclusion that the mahia peninsula volcaniclastic turbidites distally record the evolution of the source volcanic arc

characteristics of submarine pumice rich density current deposits sourced from turbulent mixing of subaerial pyroclastic flows at the shoreline field and experimental assessment this study investigates the types of subaqueous deposits that occur when hot pyroclastic flows turbulently mix with water at the shoreline through field studies of the znp marine tephra in japan and flume experiments where hot tephra sample interacted with water the znp is a very thick pumice rich density current deposit that was sourced from subaerial pyroclastic flows entering the japan sea in the pliocene notable characteristics are well developed grain size and density grading lithic rich base pumice rich middle and ash rich top preponderance of sedimentary lithic clasts picked up from the seafloor during transport fine ash depletion in coarse facies and presence of curviplanar pumice clasts flume experiments provide a framework for interpreting the origin and proximity to source of the znp tephra on contact of hot tephra sample with water steam explosions produced a gas supported pyroclastic density current that advanced over the water while a water supported density current was produced on the tank floor from the base of a turbulent mixing zone experimental deposits comprise proximal lithic breccia medial pumice breccia and distal fine ash experiments undertaken with cold water saturated slurries of tephra sample and water did not produce proximal lithic breccias but a medial basal lithic breccia beneath an upper pumice breccia results suggest the characteristics and variations in znp facies were strongly controlled by turbulent mixing and quenching proximity to the shoreline and depositional setting within the basin presence of abundant curviplanar pumice clasts in submarine breccias reflects brittle fracture and dismembering that can occur during fragmentation at the vent or during quenching subsequent transport in water supported pumiceous density currents preserves the fragmental textures careful study is needed to distinguish the products of subaerial versus subaqueous eruptions

occurrence of hyperpycnal flows and hybrid event beds related to glacial outburst events in a late ordovician proglacial delta murzuq basin sw libya abstract a late ordovician glacially related delta is documented based on architecture and facies from outcrops in the western murzuq basin libya sandstone megabeds highlight clinoform geometries of a proglacial low angle shallow water delta the progradational wedge extends over 25 km from the sse to the nnw and is about 100 m thick two types of clinothems have been distinguished and eleven facies sequences are characterized in relation with their along slope positions sand prone facies sequences in type 1 clinothems relate to high magnitude low frequency glacial outburst floods generating a freshwater highly concentrated plunging hyperpycnal flow at the river mouth during the waxing stage the slope adjustment of an out of grade profile causes significant erosion the resulting additional sediment charge involves along foresets a downslope flow transformation into a co genetic sandy debris flow and high density turbidity flow hybrid event beds including linked debrites and turbidites are the resulting deposits in the lower slope decreasing sediment concentration of the high density turbidity flow leads to sediment lofting and to a second flow transformation resulting in a lower density turbidity flow and a concomitant rising sediment plume deposition results in crude ripple cross stratification debrite deposition is temporally restricted to an early segment of the rising limb of the flood hydrograph during the ensuing waxing stage uninterrupted sustained flow conditions maintain up to the peak flow permitting the aggradation of thick sandstone successions with crude ripple cross stratification during the waning stage backstepping of the whole depositional system leads to prevailing sedimentation in the delta plain setting mouth bar development and channel plugs are characterized by climbing dune cross stratification cdcs shale prone sedimentation in type 2 clinothems essentially corresponds to background ablation related sedimentation but also includes minor debrite bearing outburst related event beds this study documents the links between glacial outbursts hyperpycnal flows and hybrid beds in low angle delta settings and illustrates a type of proximal sand dominated hyperpycnite dam failure of subglacial lakes is inferred for the outburst generation comparison with modern and pleistocene examples may suggest that outburst events were days to several years in duration type 1 clinothem with a 1 40 ky recurrence period type 2 clinothem

linking river flood dynamics to hyperpycnal plume deposits experiments theory and geological implications turbid river plumes entering ocean or lake water of lesser density i e hyperpycnal plumes can plunge to form turbidity currents providing an important link between terrestrial sediment sources and marine depositional sinks a leading hypothesis suggests that hyperpycnal plume deposits accurately record the rising and falling discharge of a flooding river in terms of sediment size grading bedform sequence and deposit thickness which if correct has significant implications for unraveling river dynamics reservoir potential and earth history from marine event beds herein we present one of the first experimental flume studies aimed at testing this hypothesis results indicate that depth averaged hyperpycnal plume velocities can be uncorrelated or even anti correlated with river discharge at certain seabed locations because of translation of the plunge point resulting from temporal variations in discharge and sediment concentration through the duration of a river flood an advection length scale of settling sediment is found to be an important control on hyperpycnal plume deposits where coarse sediment sand is most likely to record multiple flow accelerations and decelerations related to plunge point translation even for a river flood with a single peaked hydrograph in contrast fine sediment mud is relatively insensitive to local plunge point dynamics and is most likely to preserve directly rising and falling river discharge finally it was found that the necessary fluvial sediment concentration to form a plunging plume can be much larger than the concentration typically used assuming density equivalence because of deposition upstream of the plunge point

effects of a major typhoon on sediment accumulation in fangliao submarine canyon sw taiwan abstract the fangliao submarine canyon cuts across the shelf and slope of southwest taiwan unlike other canyons along this margin there is no obvious connection to an individual fluvial sediment source on land two recent cruises to fangliao canyon provide insight into sedimentation associated with a major typhoon box and piston cores were retrieved from fangliao canyon in early january 2007 after a local earthquake and an extended period of low to moderate river flow in streams that are suspected of contributing sediment to the canyon similar cores were collected from the canyon in early october 2009 following one of the largest typhoons to hit taiwan in the past several decades typhoon morakot delivered several meters of rain to taiwan with the largest river floods occurring in the south and southwest regions in addition the coastal ocean environment was energized by significant wave heights 12 m comparisons of textural radioisotopic and geochemical data reveal likely sediment transport and depositional processes within and surrounding fangliao canyon typhoon morakot caused a layer 10 cm thick and greater throughout the canyon x radiographs of the 2007 cores show limited physical structure in most cases and the 2009 radiographs display obvious changes in sediment density relative to the underlying sediment as well as distinct physical lamination examining signals from different geochemical and radiochemical tracers for terrestrial sediment source indicates that the flood layer deposited by typhoon morakot came from several small mountainous rivers by comparing the results of the 2007 cruise with those from 2009 we gain significant insight to the close linkage between a line source of fluvial sediment and deposition in a submarine canyon as well as the role that tropical storm events can play in delivering sediment to these environments

subaqueous pyroclastic flows and ignimbrites an assessment an assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary hot gas rich pyroclastic flows mass flows which resulted from the transformation of gassupported flows into water supported ones and secondary mass flows carrying redeposited pyroclastic debris based on subaerial pyroclastic flows the term pyroclastic flow should be restricted to demonstrably hot gas rich mass flows of pyroclastic debris using this definition very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described in the majority of these cases the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate the only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the ordovician nearshore shallow marine ignimbrites of ireland and wales and miocene ignimbrites of southwest japan resulting from the passage of subaerially erupted pyroclastic flows into shallow water other possible examples are near vent dense clast deposits in the donzurobo formation of japan possible submarine intra caldera ponded ignimbrite successions in california and wales and near vent pumiceous deposits of ramsay island wales all other purported cases are either clearly the result of water supported mass flow transportation and deposition debris avalanches debris flows turbidity currents or lack adequate supporting evidence regarding the heat state or the palaeoenvironment only the shallow marine ignimbrites of ireland and wales show adequate evidence of welding but even these could have been nearly wholly exposed above sea level when welding occurred we conclude that when pyroclastic flows enter water they are generally disrupted explosively and or ingest water and transform into water supported mass flows and we suggest the various scenarios in which this occurs there is no evidence to suggest that welding in wholly subaqueous environments is common

reversing buoyancy in turbidity currents developing a hypothesis for flow transformation and for deposit facies and architecture a turbidity current that contains fresher or otherwise less dense water than its surroundings may initially be denser than the ambient and propagate as a bottom hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient seawater it is proposed that this reversal in buoyancy may be a significant mechanism controlling the structure and facies of turbiditic deposits buoyancy reversal followed by lofting may directly affect the relative distribution of fine and coarse material in the deposit while buoyancy reversal itself may mediate the transformation between dilute and highly concentrated suspension flows particularly in distal regions and thus lead to the formation of complex turbiditic beds in particular the generation of distal co genetic debrites may be expected similar transformations occur within dilute pyroclastic density currents where a mobile basal concentrated flow termed a surge derived pyroclastic flow develops through rapid sedimentation from the suspended load of the overlying surge the physical mechanisms involved in these processes are discussed leading to the proposal of some associated facies models these are compared with field data from the northern apennines with some striking similarities being noted as well as some differences on the basis of this discussion some directions are suggested for future experimental and modelling work on the topic

the isotopic composition of particulate organic carbon in mountain rivers of taiwan small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon poc to the oceans this input has implications for the geochemical stratigraphic record we have investigated the stable isotopic composition of poc 13corg in rivers draining the mountains of taiwan in 15 rivers the suspended load has a mean 13corg that ranges from 28 1 0 8 to 22 0 0 2 on average 37 samples per river over the interval of our study to investigate this variability we have supplemented suspended load data with measurements of poc in bedrock and river bed materials and constraints on the composition of the terrestrial biomass fossil poc in bedrock has a range in 13corg from 25 4 1 5 to 19 7 2 3 between the major geological formations using coupled 13corg and n c we have found evidence in the suspended load for mixing of fossil poc with non fossil poc from the biosphere in two rivers outside the taiwan central range anthropogenic land use appears to influence 13corg resulting in more variable and lower values than elsewhere in all other catchments we have found that 5 variability in 13corg is not controlled by the variable composition of the biomass but instead by heterogeneous fossil poc in order to quantify the fraction of suspended load poc derived from non fossil sources fnf as well as the isotopic composition of fossil poc 13cfossil carried by rivers we adapt an end member mixing model river suspended sediments and bed sediments indicate that mixing of fossil poc results in a negative trend between n c and 13corg that is distinct from the addition of non fossil poc collapsing multiple fossil poc end members onto a single mixing trend as an independent test of the model fnf reproduces the fraction modern fmod in our samples determined from 14c measurements to within 0 09 at the 95 confidence level over the sampling period the mean fnf of suspended load poc was low 0 29 0 02 n 459 in agreement with observations from other mountain rivers where physical erosion rates are high and fossil poc enters river channels the mean 13cfossil in suspended poc varied between 25 2 0 5 and 20 2 0 6 from catchment to catchment this variability is primarily controlled by the distribution of the major geological formations it also covers entirely the range of 13corg found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous poc if land sourced poc is preserved in marine sediments then changes in the bulk 13corg observed offshore taiwan could instead be explained by changes in the onshore provenance of sediment the range in 13corg of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans care should be taken in accounting for fossil poc in marine deposits supplied by active mountain belts

anatomy of a submarine pyroclastic flow and associated turbidity current july 2003 dome collapse soufriere hills volcano montserrat west indies the 12 to 13 july 2003 andesite lava dome collapse at the soufriere hills volcano montserrat provides the first opportunity to document comprehensively both the sub aerial and submarine sequence of events for an eruption numerous pyroclastic flows entered the ocean during the collapse depositing approximately 90 of the total material into the submarine environment during peak collapse conditions as the main flow penetrated the air ocean interface phreatic explosions were observed and a surge cloud decoupled from the main flow body to travel 2 to 3 km over the ocean surface before settling the bulk of the flow was submerged and rapidly mixed with sea water forming a water saturated mass flow efficient sorting and physical differentiation occurred within the flow before initial deposition at 500 m water depth the coarsest components 60 of the total volume were deposited proximally from a dense granular flow while the finer components 40 were efficiently elutriated into the overlying part of the flow which evolved into a far reaching turbidity current

numerical investigations of tsunamis generated by pyroclastic flows from the kikai caldera japan 1 tsunamis generated by a voluminous pyroclastic flow entering the sea during a caldera forming eruption at the kikai caldera japan were investigated by using a two layer shallow water model which is limited to the source conditions and their impact on coastal areas volume flux of the dense component of the pyroclastic flow was controlled by a sine function results showed that the maximum height of the tsunami was largest in models with the largest volume flux of the flows the approximate source conditions of the tsunami which can stir sediment particles on the sea floor were investigated using the non dimensional boundary shear stress results from our simulation showed that the shear stress to initiate movement of sediment particles was not easily achieved in areas where there was evidence of a tsunami a caldera collapse is thought more likely to have generated the huge tsunami rather than a pyroclastic flow

water and sediment discharge from small mountainous rivers taiwan the roles of lithology episodic events and human activities national science council of taiwan nsc96 2628 m 001 028 u s national science foundation and naval oceanographic office

behaviour of particle laden flows into the ocean experimental simulation and geological implications the behaviour of subaerial particle laden gravity currents e g pyroclastic flows lahars debris flows sediment bearing floods and jokulhlaups flowing into the sea has been simulated with analogue experiments flows of either saline solution simple suspensions of silicon carbide sic in water or complex suspensions of sic and plastic particles in methanol were released down a slope into a tank of water the excess momentum between subaerial and subaqueous flow is dissipated by a surface wave at relatively low density contrasts between the tank water and the saline or simple suspensions the flow mixture enters the water and forms a turbulent cloud involving extensive entrainment of water the cloud then collapses gravitationally to form an underwater gravity current which progresses along the tank floor at higher density contrasts the subaerial flow develops directly into a subaqueous flow the flow slows and thickens in response to the reduced density contrast which is driving motion and then continues in the typical gravity current manner complex suspensions become dense flows along the tank floor or buoyant flows along the water surface if the mixtures are sufficiently denser or lighter than water respectively flows of initially intermediate density are strongly influenced by the internal stratification of the subaerial flow material from the particulate depleted upper sections of the subaerial flow becomes a buoyant gravity current along the water surface whereas material from the particulate enriched lower sections forms a dense flow along the tank floor sedimentation from the dense flow results in a reduction in bulk density until the mixture attains buoyancy lifts off and becomes a secondary buoyant flow along the water surface jokulhlaups lahars and debris flows are typically much denser than seawater and thus will usually form dense flows along the seabed after sufficient sedimentation the freshwater particulate mixture can lift off to form a buoyant flow at the sea surface leading to a decoupling of the fine and coarse particles flood waters with low particulate concentrations 2 may form buoyant flows immediately upon entering the ocean subaerial pyroclastic flows develop a pronounced internal stratification during subaerial run out and thus a flow splitting behaviour is probable which agrees with evidence for sea surface and underwater flows from historic eruptions of krakatau and mont pelee a pyroclastic flow with a bulk density closer to that of sea water may form a turbulent cloud resulting in the deposition of much of the pyroclasts close to the shore dense subaqueous pyroclastic flows will eventually lift off and form secondary buoyant flows either before or after the transformation to a water supported nature

potential role of event driven sediment transport on sediment accumulation in the cariaco basin venezuela abstract a sediment density flow was observed in the eastern cariaco basin during september 2008 evidence suggests that this flow was likely triggered by a magnitude 5 2 earthquake that occurred on august 11 2008 with an epicenter located at 10 51 n 64 17 w off the city of cumana venezuela elevated suspended sediments near the bottom were observed at the mouth of the manzanares canyon 90 g m 2 over a depth of 165 m and decreased to 11 g m 2 over a depth of 40 m 42 km away from the canyon s mouth at the cariaco ocean time series site the sediment flux associated with this single event was 10 of the total annual sediment flux that typically reaches the cariaco basin deep seafloor carbon to nitrogen ratios and isotope composition confirm that most of the organic matter transferred by the sediment flow was of continental origin c n ratios of 17 67 13c of 27 04 and 15n of 6 83 our observations contribute to the growing body of evidence that suggests that submarine canyons are rapid efficient sediment conduits of particles from shallow to deep waters and that they should be included in efforts to constrain estimates of sediment and terrestrially derived carbon transport from the continental shelves to the deep ocean

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

subaqueous density flow processes and deposits of an island volcano landslide stromboli island italy stromboli is a 3000 m high island volcano rising to 900 m above sea level it is the most active volcano of the aeolian archipelago in the tyrrhenian sea italy major large volume 1 km 3 sector collapses four occurring in the last 13 kyr have played an important role in shaping the north western flank sciara del fuoco of the volcano potentially generating a high risk tsunami hazard for the aeolian islands and the italian coast however smaller volume partial collapses of the sciara del fuoco have been shown to be more frequent tsunami generating events one such event occurred on 30 december 2002 when a partial collapse of the north western flank of the island took place the resulting landslide generated 10 m high tsunami waves that impacted the island multibeam bathymetry side scan sonar imaging and visual observations reveal that the landslide deposited 25 to 30 10 6 m 3 of sediment on the submerged slope offshore from the sciara del fuoco two contiguous main deposit facies are recognized i a chaotic coarse grained metre sized to centimetre sized clasts deposit and ii a sand deposit containing a lower cross bedded sand layer and an upper structureless pebbly sand bed capped by sea floor ripple bedforms the sand facies develops adjacent to and partially overlying the coarse deposits characteristics of the deposits suggest that they were derived from cohesionless sandy matrix density flows flow rheology and dynamics led to the segregation of the density flow into sand rich and clast rich regions a range of density flow transitions both in space and in time caused principally by particle concentration and grain size partitioning within cohesionless parent flows was identified in the deposits of this relatively small scale submarine landslide event

late ordovician climbing dune cross stratification a signature of outburst floods in proglacial outwash environments climbing dune scale cross statification is described from late ordovician paraglacial successions of the murzuq basin sw libya this depositional facies is comprised of medium grained to coarse grained sandstones that typically involve 0 3 to 1 m high 3 to 5 m in wavelength asymmetrical laminations most often stoss depositional structures have been generated with preservation of the topographies of formative bedforms climbing dune cross stratification related to the migration of lower flow regime dune trains is thus identified related architecture and facies sequences are described from two case studies i erosion based sandstone sheets and ii a deeply incised channel the former characterized the distal outwash plain and the fluvial subaqueous transition of related deltaic wedges while the latter formed in an ice proximal segment of the outwash plain in erosion based sand sheets climbing dune cross stratification results from unconfined mouth bar deposition related to expanding sediment laden flows entering a water body within incised channels climbing dune cross stratification formed over eddy related side bars reflecting deposition under recirculating flow conditions generated at channel bends associated facies sequences record glacier outburst floods that occurred during early stages of deglaciation and were temporally and spatially linked with subglacial drainage events involving tunnel valleys the primary control on the formation of climbing dune cross stratification is a combination between high magnitude flows and sediment supply limitations which lead to the generation of sediment charged stream flows characterized by a significant relatively coarse grained sand sized suspension load concentration with a virtual absence of very coarse to gravelly bedload the high rate of coarse grained sand fallout in sediment laden flows following flow expansion throughout mouth bars or in eddy related side bars resulted in high rates of transfer of sands from suspension to the bed net deposition on bedform stoss sides and generation of widespread climbing dune cross stratification the later structure has no equivalent in the glacial record either in the ancient or in the quaternary literature but analogues are recognized in some flood dominated depositional systems of foreland basins

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

experiments on bidisperse constant volume gravity currents propagation and sediment deposition laboratory experiments show that the propagation and sedimentation patterns of particle laden gravity currents are strongly influenced by the size of suspended particles the main series of experiments consisted of fixed volume releases of dilute mixtures containing two sizes of silicon carbide particles 25 m and 69 m mean diameter within a 6 m flume polydisperse experiments involved mixtures of five different particle sizes and variation of the amounts of the finest and coarsest particles all variables apart from the initial relative proportions of particles were identical in the experiments the effects of mixing different proportions of fine and coarse particles is markedly non linear adding small amounts of fine sediment to a coarse grained gravity current has a much larger influence on flow velocity run out distance and sedimentation patterns than adding a small amount of coarse sediment to a fine grained gravity current the experiments show that adding small amounts of fine particles to a coarse grained current results in enhanced flow velocities because the fine sediment remains suspended and maintains an excess current density for a much longer time thus the distance to which coarse particles are transported increases substantially as the proportion of fines in the flow is increased our experiments suggest that sandy turbidity currents containing suspended fines will be much more extensive than turbidity currents composed of clean sand

sedimentology of the krakatau 1883 submarine pyroclastic deposits the majority of tephra generated during the paroxysmal 1883 eruption of krakatau volcano indonesia was deposited in the sea within a 15 km radius of the caldera two syneruptive pyroclastic facies have been recovered in scuba cores which sampled the 1883 subaqueous pyroclastic deposit the most commonly recovered facies is a massive textured poorly sorted mixture of pumice and lithic lapilli to block sized fragments set in a silty to sandy ash matrix this facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the krakatau islands on the basis of grain size and component abundances a less common facies consists of well sorted planarlaminated to low angle cross bedded vitric enriched silty ash entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated deflated components of pyroclastic flows as they traveled over water the basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction high temperature of emplacement and lack of traction structures and no significant hydraulic sorting of components the laminated facies was most likely deposited from low concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater the krakatau deposits are the first well documented example of true submarine pyroclastic flow deposition from a modern eruption and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences

sedimentation from gravity currents generated by turbulent plumes sedimentation from radially spreading gravity currents generated at the top of ascending sediment laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current for radial spreading this model predicts a gaussian distribution of sediment accumulation away from the source with an exponential constant b which depends on flow rate q and particle settling velocity v b nv q in the experiments described sedimentation occurs from gravity currents generated by ascent of buoyant particle laden plumes of fresh water in a tank of salty water the sediment accumulation shows close agreement with the theoretical model and the gaussian decay constant b can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line in s s0 br2 where r is the radial distance s is the sediment mass flux per unit area and s0 is the value of s at r 0 data from the dispersal of volcanic ejecta from a large c 24 km high plinian eruption column in the azores also show good agreement with the theory confirming that it is general and independent of scale and the nature of the fluid the experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity sedimentation of coarse grain sizes between the source and the corner occurs from the inclined plume margins and does not behave as predicted by the theoretical model

initiation of turbidity currents outcrop evidence for eocene hyperpycnal flow turbidites abstract the most widely used although not as widely documented explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites such instantaneous sediment failures generate short lived surge type flows that deposit turbidite beds described as bouma sequences in this communication we present data from the eocene central basin of spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds deposited by gradual aggradation from sustained flows sustained flows are long lived and more or less continuous they can be generated by a variety of mechanisms e g 1 instability during volcanic eruptions and the consequent remobilisation of unconsolidated material 2 seismically triggered subaerial sliding within the drainage 3 storm surges 4 retrogressive slope failure 5 breaching and 6 hyperpycnal flows our database shows that in the eocene central basin the sustained flows were generated by hyperpycnal flows i e by direct river effluent the hyperpycnal flow turbidites have been recognized on the basis of 1 physical connection between fluvial and turbidite channels at the shelf edge 2 abundance of thick turbidite sandstone beds 3 sand prone nature of the turbidite systems 4 downslope changes of individual thick sandy turbidite beds and their collapsed pinch out segments 5 great abundance of continental material leaves coal fragments in turbidite beds 6 low abundance of associated slumped or debris flow beds and 7 the occurrence of turbidites in systematically accreted shelf margins these features strongly suggest that hyperpycnal flow generated by direct river effluent deposited significant number of turbidite beds in the documented slope and basin floor turbidite successions we also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level the turbidite beds were studied in the context of seismic scale 1 15 km dip oriented outcrops by measuring detailed vertical sections following individual beds and packages of beds downslope for distances over 5 km lateral mapping and helicopter taken photomosaics

diagenetic and sedimentological controls on the composition of organic matter preserved in california borderland basin sediments compound specific radiocarbon 14c contents stable carbon isotopes and abundances of phytoplankton and vascular plant derived lipid biomarkers alkenones and fatty acids were obtained from santa barbara basin and santa monica basin sediments along with radiocarbon contents of planktic foraminifera and total organic carbon we investigated core top and prebomb sediment intervals at sites from the flanks and depocenters of the basins deposited under contrasting bottom water oxygen concentrations bulk organic matter generally has the lowest radiocarbon levels of all sediment constituents measured whereas planktic foraminifera tend to be the most radiocarbon enriched alkenones are systematically depleted in radiocarbon with respect to foraminifera short chain c14 c 16 c 18 fatty acids decrease rapidly in absolute abundance and relative to longer chain c24 homologues from core top to prebomb samples the loss of short chain fatty acids with depth is associated with 13c depletion of short chain fatty acids indicating preferential preservation of terrestrially derived fatty acids short chain fatty acids tend to be more 14c enriched relative to alkenones in core top sediments whereas longerchain homologues are generally the most radiocarbon depleted of the lipids studied here less refractory compounds e g short chain fatty acids are thus enriched in radiocarbon with respect to more recalcitrant biomarkers alkenones long chain fatty acids the lower 14c content of more refractory compounds reflects a larger proportion of laterally supplied preaged material greater preservation of labile organic compounds observed at the depocenters than in flank sediments results in the presence of younger biomarkers underlining the important influence of selective degradation of labile compounds on their radiocarbon ages

detrital fine grained sediment contribution from taiwan to the northern south china sea and its relation to regional ocean circulation article i nfo results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern taiwan and on the seafloor off taiwan in the northeastern south china sea scs combined with clay mineral records of the pearl river drainage basin rivers in luzon and the south china shelf and slope are used to semi quantitatively evaluate the detrital fine grained sediment contribution of taiwan to the northern scs the clay mineral assemblage of the taiwan sourced sediments consists dominantly of illite average 56 and chlorite 41 with very scarce kaolinite and smectite their respective distribution from the rivers and lakes to the seafloor off taiwan does not show obvious basin wide differences linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite present two end members of provenances the pearl river and taiwan for the south china shelf and slope assuming that kaolinite in the northern scs is provided completely from the pearl river the contribution of taiwan in clay minerals is evaluated as 29 to the south china shelf and 23 to the south china slope respectively accordingly the contribution of the pearl river to the south china shelf and slope is 52 and 31 respectively the luzon arc accounts for the rest of clay mineral components for the northern scs mainly by providing smectite the bashi strait crossed branches of the southward deep north pacific deep water and the northward surface kuroshio current in the western pacific may transport taiwan sourced suspended sediments westwards to the northern scs

channelled erosion through a marine dump site of dredge spoils at the mouth of the puyallup river washington state usa abstract channels are relatively common on river mouth deltas but the process by which they arise from river sediment discharge is unclear because they can potentially be explained either by negatively buoyant hyperpycnal flows produced directly from the river outflow or by flows generated by repeated failure and mobilisation of sediment rapidly deposited at the delta front channels eroded through a dump site of dredge spoils are described here from multibeam and older sonar data collected in commencement bay at the mouth of the puyallup river shallow channels on the seaward upper surface of the dump site away from any flows that could have been produced by delta front failures suggest that at least some hyperpycnal flows were produced directly from the positively buoyant river outflow up to 200 m from the edge of the river mouth platform the form of channel bed erosion is revealed by the longitudinal shape of the main eroded channel compared with the adjacent dump site profile it suggests that the channel evolved by its steep front retreating rather than by simple vertical entrenchment or diffusive like evolution of the profile a geometry interpreted as evidence that repeated failure of the bed occurred in response to shear stress imposed by bottom travelling flows model calculations based on shear strengths back calculated from the geometry of channel wall failures suggest that if the main channel were eroded solely by hyperpycnal flows their generation was remarkably efficient in order to create flows vigorous enough to cause channel bed failure besides the sediment concentration and discharge characteristics that have been considered to dictate the ability of rivers to produce hyperpycnal flows it is suggested that the timing of floods with respect to the tidal cycle should also be important because extreme low tides may be needed to ensure that coarse sediment is transferred vigorously to the edge of river mouth platforms

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

hollow carbonate pebbles a case study of selective secondary porosity generation neogene israel abstract neogene conglomerates are very common in israel in a few conglomerate localities in the hilly region of galilee northern israel a large number of the pebbles have internal cavities this puzzling phenomenon has not been documented previously in israel or elsewhere the studied conglomerates occur as lithified calcite cemented lenticular beds which alternate with reddish brown argillaceous mudstones the hollow pebbles constitute in fact only a special case of a wider range of related features the most relevant observations related to these occurrences are the following 1 the clasts are polymictic consisting of various limestones dolomites and minor cherts the hollow pebbles and related features however occur only in porous dolomites 2 calcitized dedolomitic hard rims characterize all the affected pebbles the thickness of these rims varies between a few mm and 1 2 cm 3 in part of the affected pebbles the dolomitic core inside the calcitic rims is preserved intact in others only the hard rim is preserved and the core is empty these are the hollow pebbles sensu stricto 4 late stage calcite spar occurs in some of the voids and in veins that cross the groundmass of the conglomerates the first step in the sequence of events leading to the production of the described occurrences is inferred to be the calcitization of porous dolomite pebbles resulting in the formation of dense rims around porous cores the next step involved the dissolution of the inner core of the pebble by acidic solutions leaving the calcitic rims almost intact the restriction of hollow pebbles and related features occurrences to conglomerate strata which are interbedded with argillaceous mudstones points to a causal relationship between the two accordingly the precipitation of calcite during the first step is attributed to the establishment of anoxic microenvironments within the porewater soon after the accumulation of the argillaceous material the reversal of conditions from carbonate precipitation to dissolution during the second step seems to be related to a change from reducing to oxidizing microenvironments following the emergence of the fluviatile sediments from the aquatic environments the critical requirements for obtaining the hollow pebbles seem therefore to be the presence of a suitable lithological type of pebble namely porous dolomite combined with a special sequence of depositional and diagenetic environments the apparent rarity of this combination seems to account for the lack of documentation on this phenomenon to this date

extreme storm events landscape denudation and carbon sequestration typhoon mindulle choshui river taiwan we have performed the first known semicontinuous monitoring of particulate organic carbon poc fluxes and dissolved si concentrations delivered to the ocean during a typhoon sampling of the choshui river in taiwan during typhoon mindulle in 2004 revealed a poc flux of 5 00 105 t associated with a sediment flux of 61 mt during a 96 h period the linkage of high amounts of poc with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of poc from the terrestrial system these fluxes when combined with storm derived co2 consumption of 1 65 108 mol from silicate weathering elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of co2

modeling of a dispersive tsunami caused by a submarine landslide based on detailed bathymetry of the continental slope in the nankai trough southwest japan abstract tsunamis caused by submarine landslides are not accompanied by seismic waves and thus may appear at the coast without warning in this study detailed bathymetric surveys with a multi narrow beam echo sounder were used to map submarine landslides on the continental shelf near cape muroto in the nankai trough off southwestern japan one of the surveyed submarine landslides was selected to supply dimensions for the simulation of a submarine mass movement by a two layer flow model in which the upper and lower layers correspond to seawater and turbidity currents respectively the time series of seafloor deformation during this simulated landslide was used as the boundary condition to drive a tsunami simulation the results showed strong directivity effects during tsunami generation in which pushing dominant positive tsunami waves propagated seaward in the direction of the submarine landslide and pulling dominant negative tsunami waves propagated landward both types of waves were strongly modified by frequency dispersion for pulling dominant waves a tsunami simulation that included dispersion boussinesq terms predicted greater maximum tsunami heights than a non dispersive tsunami simulation to avoid underestimation of tsunami heights we recommend including dispersion terms when modeling tsunamis caused by submarine landslides for disaster planning purposes