identification of tsunami deposits considering the tsunami waveform an example of subaqueous tsunami deposits in holocene shallow bay on southern boso peninsula central japan abstract this study proposes a tsunami depositional model based on observations of emerged holocene tsunami deposits in outcrops located in eastern japan the model is also applicable to the identification of other deposits such as those laid down by storms the tsunami deposits described were formed in a small bay of 10 20 m water depth and are mainly composed of sand and gravel they show various sedimentary structures including hummocky cross stratification hcs and inverse and normal grading although individually the sedimentary structures are similar to those commonly found in storm deposits the combination of vertical stacking in the tsunami deposits makes a unique pattern this vertical stacking of internal structures is due to the waveform of the source tsunamis reflecting 1 extremely long wavelengths and wave period and 2 temporal changes of wave sizes from the beginning to end of the tsunamis the tsunami deposits display many sub layers with scoured and graded structures each sub layer especially in sandy facies is characterized by hcs and inverse and normal grading that are the result of deposition from prolonged high energy sediment flows the vertical stack of sub layers shows incremental deposition from the repeated sediment flows mud drapes cover the sub layers and indicate the existence of flow velocity stagnant stages between each sediment flow current reversals within the sub layers indicate the repeated occurrence of the up and return flows the tsunami deposits are vertically divided into four depositional units tna to tnd in ascending order reflecting the temporal change of wave sizes in the tsunami wave trains unit tna is relatively fine grained and indicative of small tsunami waves during the early stage of the tsunami unit tnb is a protruding coarse grained and thickest stratified division and is the result of a relatively large wave group during the middle stage of the tsunami unit tnc is a fine alternation of thin sand sheets and mud drapes deposited from waning waves during the later stage of the tsunami unit tnd is deposited during the final stage of the tsunami and is composed mainly of suspension fallout cyclic build up of these sub layers and depositional units cannot be explained by storm waves with short wave periods of several to ten seconds common in small bays

a shallow marine emergent sequence from the northwestern sector of the last british ice sheet portballintrae northern ireland abstract at portballintrae northern ireland a well preserved emergent facies sequence formed around 17 kyr b p as the late devensian ice sheet withdrew from the continental shelf three main lithofacies assemblages are recognised 1 at the base of the sequence a massive muddy diamict was formed by resedimentation of an unstable sedimentary apron deposited in a tidewater setting 2 rhythmically bedded sand and mud units contain a wide range of wave diagnostic features and are separated from the underlying diamict by both transitional and wave eroded planar contacts palaeowave calculations suggest deposition in a coastal tract open to atlantic waves the preservation and range of boreo arctic foraminifera present are also typical of a lower shoreface storm influenced setting 3 interbedded gravel and sand facies are separated from the underlying rhythmically bedded facies by a planar wave cut surface this facies occurs as crudely organised beds within cross cutting shallow scours which are associated with off shore directed storm induced sediment pulses overall the coarsening upwards sequence is explained by tidewater sedimentation during ice wastage rapid isostatic rebound and isostatic deceleration in the late glacial an isostatic tectonic model comprising a forebulge on the outer continental shelf and a peripheral trough on the inner shelf is presented to resolve the apparent discrepancies between onshore and offshore sea level data

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

palaeoenvironments palaeogeography and physiography of a large shallow muddy ramp late cenomanian turonian kaskapau formation western canada foreland basin the kaskapau formation spans late cenomanian to middle turonian time and was deposited on a low gradient shallow storm dominated muddy ramp dense well log control coupled with exposure on both proximal and distal margins of the basin allows mapping of sedimentary facies over about 35 000 km2 the studied portion of the kaskapau formation is a mudstone dominated wedge that thins from 700 m in the proximal foredeep to 50 m near the forebulge about 300 km distant regional flooding surfaces permit mapping of 28 allomembers each of which represent an average of ca 125 kyr more than 200 km from shore calcareous silty claystone predominates whereas 100 to 200 km offshore mudstone and siltstone predominate from about 30 to 100 km offshore centimetre bedded very fine sandstone and mudstone record along shelf sse directed storm generated geostrophic flows five to thirty kilometres from shore decimetre bedded hummocky cross stratified fine sandstone and mudstone record strongly oscillatory wave dominated flows whereas some gutter casts indicate shore oblique apparently mostly unidirectional geostrophic flows nearshore facies are dominated by swaley cross stratified or intensely bioturbated clean fine sandstone interpreted as recording respectively areas strongly and weakly affected by discharge from distributary mouths shoreface sandstones grade locally into river mouth conglomerates and sandstones including conglomerate channel fills up to 15 m thick locally brackish lagoonal shelly mudstones are present on the extreme western margin of the basin there is no evidence for clinoform stratification which indicates that the kaskapau sea floor had extremely low relief lacked a shelf slope break and was probably nowhere more than a few tens of metres deep the absence of clinoforms probably indicates a long term balance between rates of accommodation and sediment supply mud is interpreted to have been transported 250 km offshore in a sea bed nepheloid layer repeatedly re suspended by storms fine grained sediment accumulated up to a mud accommodation envelope perhaps only 20 to 40 m deep continuous re working of the sea floor by storms ensured that excess sediment was redistributed away from areas that had filled to the accommodation envelope being deposited in areas of higher accommodation further down the transport path the facies distributions and stratal geometry of the kaskapau shelf strongly suggest that sedimentary facies especially grain size were related to distance from shore not to water depth as a result the 100 to 300 m depth interpreted from calcareous claystone facies for the more central parts of the interior seaway might be a significant overestimate

depositional and stratigraphic architecture of the santonian emery sandstone of the mancos shale implications for late cretaceous evolution of the western interior foreland basin of central utah u s a abstract the santonian emery sandstone member of the mancos shale is a continental to shallow marine succession that prograded into the cretaceous western interior seaway of western north america sediment sourced from the uplifted sevier orogen to the west fed a shoreline in the adjacent subsiding north south trending foredeep these sandstones are now superbly exposed along a 120 km long strike parallel continuous outcrop in the cliffs of the wasatch plateau of central utah shoreface parasequences are composed of coarsening upward successions of hummocky cross stratified and intensely bioturbated sandstones indicating deposition at a storm dominated shoreline two distinct depositional complexes record eastward and northeastward shoreline progradation at the northern and southernmost extremities of the plateau respectively in the subsurface emery strata comprise a thick succession of coal bearing coastal plain deposits the emery sandstone records a period of long term paralic progradation to aggradation containing at least 17 parasequences arranged into three 600 kyr regressive transgressive cycles that are recognizable in both complexes each cycle comprises only highstand and transgressive systems tracts and erosional sequence boundaries are absent absence of erosional sequence boundaries is attributed to high rates of subsidence in the foreland basin at this time santonian glacio eustatic sea level fluctuations are proposed to account for the high frequency cyclicity whilst longer term aggradation may be a function of organic controls on shoreface stacking patterns by immobile raised coal mires lying landward of the shorefaces when placed in a temporal and spatial context the emery sandstone provides a missing link in the understanding of long term controls on late cretaceous depositional systems in the central utah segment of the foreland basin and allows inferences to be made regarding foreland basin dynamics in particular thrust tectonics is postulated to have played a major role in governing the architecture of late cretaceous strata in central utah marked along strike thickening of the emery sandstone in particular is attributed to long lived elevated rates of subsidence in northern utah and southern wyoming during the late cretaceous that is adjacent to concentrated zones of thrust nappes a north dipping depositional slope is inferred from this subsidence distribution aligned approximately parallel to the structural grain of the hinterland load northeastward progradational directions of successive turonian santonian and early campanian regressive wedges in this part of the western interior basin are attributed to the presence of this tectonically induced regional slope gradient sediment sourced to these late cretaceous shorefaces is likely to have been sourced through structural recesses within the thrust front resulting in a spatial alignment of several successive regressive wedges and implicates an important long lived kinematic control on sediment supply of late cretaceous regressive wedges only the emery sandstone does not temporally coincide with reported periods of active thrusting suggesting that the regression was a consequence of factors other than uplift related elevated rates of sediment supply

the western grand banks of newfoundland transgressive holocene sedimentation under the combined influence of waves and currents abstract the surficial sediments on the western grand banks of newfoundland have been reworked from older deposits primarily late wisconsinan glacial and glaciomarine sediments during the post glacial sea level fall and holocene rise winnowed medium to coarse sands and lag gravels that are generally less than 0 5 m thick chracterize the areas above the lowstand elevation at 110 to 120 m the holocene sediments which have accumulated in the deeper interbank channels isolated basins and on the upper continental slope are thicker and consists of the fine sands and muds that were removed from the banks the deposits below the lowstand elevation coarsen upward because little deposition occured during the sea level rise in general the holocene succession becomes thicker and finer grained to the south active sediment movement occurs at all depths less than about 110 m wave ripples composed of sandy gravel form to depths in excess of 100 m in response to long period 15 s surface waves but the predominant bedforms consist of current generated sand ribbons megaripples and sandwaves which exhibit unidirectional migration azimuths toward the southwest even though the storm current directions are highly variable and the maximum sediment transport rates are directed toward the east or southeast the bedform orientation and resultant transport are instead parallel to the southerly and southwesterly storm currents which occur during the prolonged post storm spin down period and to the weak 1 labrador current and the orbital motion associated with the largestwaaves thus the interaction of the oceanic current and wave orbital motion with the directionally variable strom currents is responsible for the consistent orientation of the current generated bedforms and for the distribution of holocene deposits

sedimentary and volcanic facies recording the neoarchaean continent breakup and decline of the positive δc excursion abstract the palaeoproterozoic kalix greenstone belt at the northern end of the bothnian bay in sweden comprises three groups the lower group a ca 3000 m thick unit of subaerially erupted tholeiitic intraplate basalts interbedded with fluviatile conglomerates represents the volcano sedimentary succession deposited in a rift setting these units are truncated by a break up unconformity above which is the middle group an 800 m thick succession of dolograinstones stromatolitic dolostones arenites volcanoclastic and mafic volcanic rocks stromatolite morphologies and the occurrence of distinctive sedimentary structures including planar and herringbone cross bedding hummocky cross stratification symmetrical and asymmetrical ripples desiccation cracks and tepees indicate markedly variable depositional environments associated with transition from a marine influenced rifted margin to a rimmed carbonate shelf sedimentation was accompanied by subaerial mafic volcanism and syndepositional tectonics the upper group a more than 2000 m thick unit of deep water shales was deposited on the drowned carbonate platform of the middle group in response to tectonically enhanced subsidence this study provides a detailed palaeoproterozoic depositional history of the fennoscandian shield from rifting to passive margin development associated with both dispersal of the neoarchaean supercontinent and decline of the proterozoic positive isotopic excursion of 13 c 12 c in sedimentary carbonates in contrast to many previously reported 13 c rich palaeoproterozoic carbonates which were deposited in non marine to restricted or partly restricted settings the carbonate facies reported herein were well connected to the oceanic realm and thereby represent a good opportunity to test restricted marine versus open marine models for how the carbon cycle functioned in deep time

pyrite and marcasite coated grains in the ordovician winnipeg formation canada an intertwined record of surface conditions stratigraphic condensation geochemical reworking and microbial activity sulfide coated grains are enigmatic sedimentary particles that occur in sediments ranging in age from archean to jurassic although their oolitic and pisoidal texture suggests energetic and agitated conditions their mineralogy seems to require a reducing and stagnant environment because of this conflict they have long been considered diagenetic replacements of precursor iron oxide chamosite or carbonate ooids coated iron sulfide cis grains from the ordovician winnipeg formation of saskatchewan canada formed as primary diagenetic precipitates under shallow burial conditions involving intermittent episodes of tractional reworking grain abrasion reburial and precipitation of further concentric laminae these iron sulfide grains are found in shallow marine sandstones with indications of episodic wave reworking and indicate sufficient organic matter burial to promote reducing pore waters and iron sulfide formation horizons with strong enrichment of iron sulfide grains up to 40 indicate negative net sedimentation to facilitate geochemical reworking of iron cis grains formed during intervals of maximum sediment starvation when organic matter was enriched in surface sediments and rare storm waves intermittently reworked the surface sediment alternating laminae of pyrite and marcasite within these grains point to substantial fluctuations in pore water ph driven by intermittent oxidation of previously formed iron sulfides filamentous and coccoid structures within cortical laminae suggest microbial involvement in lamina formation through providing a growth medium for sulfate reducing bacteria and potentially a template for mineral growth coated iron sulfide grains of the winnipeg formation preserve a combined record of condensation seafloor reworking fluctuating chemical conditions in the surface sediment and high surface productivity this information rich record is made even more valuable by the fact that the host sediment consists largely of heavily bioturbated monotonous sandstones that could not provide these insights on their own merit

faunal transport within event horizons in the british upper silurian many marine fossil concentrations are considered the result of episodic sedimentological events and in particular those due to storms most storm or tempestite concentrations are identified as autochthonous or parautochthonous assemblages created by a variety of winnowing processes within shallow water environments in contrast samples described here from both a shelf and a basinal setting within the ludlow upper silurian succession of the welsh basin reveal the presence of a biota transported by tempestite activity into a setting dominated by a more offshore biota tempestite horizons from within an outer shelf mud dominated setting include shelly lenses with a transported fauna abounding in gastropods tentaculitids and atrypid brachiopods the background sediment being rich in graptolites cephalopods and small strophomenid brachiopods within the basinal area distal tempestites range from minor siltstone layers to thicker bioclastic limestone lenses the siltstones are largely graptolitic dominated by bohemograptus with some small brachiopods whilst saetograptus colonus is the only common graptolite in the limestones which also contain a fauna of broken brachiopods and bryozoa the transport of assemblages distally into a variety of settings represents a potential source of error in palaeoecological analysis transported assemblages may however provide evidence of the composition of both benthic and pelagic shallower water faunas no longer known in situ

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

record of tide wave influence on the coal bearing permian barakar formation raniganj basin india abstract the coal bearing barakar formation early permian of the raniganj gondwana basin was previously interpreted as continental fluvial sediments with little evidence for tide wave influences the present contribution details the sedimentary attributes of marginal marine tidal and wave activities preserved within an overall braided meandering fluvial depositional setting from the barakar formation tide dominated sedimentary features include i tidal bundle sequences showing sandstone foresets with mud drapes ii periodic variation in foreset thickness iii lateral and vertical accretion of cross strata bundles with a downcurrent change to sigmoidal cross strata iv mutually opposite cross strata sets separated by sub horizontal plane laminated sandstone mudstone and v alternate sand and mud dominated rhythmites draping of the tidal stratifications by wavy laminated muddy siltstone suggests immediate invasion by low energy silt mud depositing waves that helped preserve the tidal features during subsequent reworking open marine storm wave activities are evident from hummocky cross stratification and various types of wave ripples preserved separately within coarse to fine grained sandstone in the middle upper part of the succession recognition of tide storm influenced marine sedimentation significantly changes the existing paleogeographic model to a fluvial estuarine depositional environment

hummocky cross stratification like structures and combined flow ripples in the punta negra formation lower middle devonian argentine precordillera a turbiditic deep water or storm dominated prodelta inner shelf system abstract turbidity current and storm induced deposits may exhibit similarities in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow on the basis of detailed analysis of sedimentary facies strata geometry and palaeocurrent data the present study reinterprets the punta negra formation pnf lower middle devonian argentine precordillera previously considered as a depositional system of deep water as a storm dominated prodeltaic shelf depositional system in the sandstone beds of the pnf planar low angle and undulating laminations with weakly asymmetric hummocky and swaley bedforms combined flow ripples accretionary hummocky cross stratification like hcs like and anisotropic hcs like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits different hypotheses on the origin of the oscillatory currents have been examined the most convincing interpretation is that the oscillatory component of the velocity is attributed to storm induced waves the palaeocurrent data indicate offshore current directions suggesting that the unidirectional flow was a gravity induced bottom current inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing waning behaviour of the depositional flows interbedding of sedimentary structures undulating laminations low angle and parallel laminations and combined flow ripples in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity this organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents the terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains the mineralogical and textural immaturity of the sandstone composition and the relative scarcity of bioturbation which was likely controlled by fresh water input and a high rate of sedimentation storm influenced hyperpycnal flows generated subaqueous channelised forms at the mouth of the river deltas which later filled with sand at the distal end of the channelised forms lobe shaped sandstone beds were deposited evolving distally into thin sandstone beds alternating with sandy mudstone

a depositional model for storm and tide influenced prograding siliciclastic shorelines from the middle devonian of the central appalachian foreland basin usa a stratigraphic motif observed in many foreland basins is the development of basinward tapering siliciclastic wedges characterized by various scales of depositional cycles the middle devonian givetian mahantango formation in the central appalachian foreland basin is such an example it consists of both small and large scale thickening and coarsening upward cycles the small scale cycles are typically less than 10 m thick whereas larger scale cycles are generally a few tens of metres thick and commonly contain several of the smaller scale cycles outcrop based facies analyses indicate that the depositional cyclicity resulted from episodic progradation of a regionally straight tide dominated shoreline onto a storm dominated shallow marine shelf the depositional model for this ancient shallow marine system consists of a vertical facies succession in which storm dominated offshore marine mudstone and fine sandstone pass gradationally upward into storm dominated nearshore marine shelf and shoreface sandstone overlain by in proximal sections tide dominated shoreline sandstone pebbly sandstone and mudstone transgressively reworked lag deposits cap most of the thickening and coarsening upward packets in this model coarse grained rocks rather than implying basinward shifts of facies are a consanguineous part of the stacked shoaling cycles lateral facies relationships show that the dominance of storm vs tide generated sedimentary features is simply a function of palaeogeographical position within the basin proximal sections contain tidally influenced sedimentary features whereas more distal sections only display evidence for storm influenced deposition these results suggest caution when inferring palaeoceanographic conditions from sedimentological datasets that do not contain preserved examples of palaeoshorelines

style contrast between forced regressive and lowstand transgressive wedges in the campanian of south central wyoming hatfield member of the haystack mountains formation

combined flow origin of edgewise intraclast conglomerates sellick hill formation lower cambrian south australia unusually thick coarse grained edgewise intraclast conglomerates occur at eight or more horizons within subtidal nodular and ribbon bedded wackestones and packstones of the lower cambrian sellick hill formation south australia the intraclast beds are flat based and laterally discontinuous forming bar like structures that must have exhibited bathymetric relief of as much as 1 m the internal fabrics of these beds are variable thinner beds are dominated by flat lying intraclasts thicker beds contain both chaotic randomly oriented steeply inclined intraclasts and clusters of fan shaped vertically stacked edgewise intraclasts the sellick hill formation intraclast conglomerates are inferred to have been formed by intense storm generated combined flows on a broad subtidal carbonate ramp superimposition of wave induced oscillatory motions on geostrophic bottom flows during large storms generates short lived but exceptionally high instantaneous shear stresses in the bottom boundary layer entrainment of the relatively large intraclasts occurs through sliding rather than pivoting edgewise fabrics are a product of asymmetric acceleration and deceleration of intraclasts during passage of waves and the chaotic nature of collisions between intraclasts moving within the boundary layer collisions between intraclasts impart a rotating moment causing intraclasts to tip up during maximum fluid shear stress lodgement or packing of clasts in vertical or steeply inclined positions occurs within scours where intraclasts can wedge between other vertically inclined clasts or where intraclasts are pinned in steep orientations by collisions with shallowly inclined intraclasts differential erosional resistance of the intraclast deposits probably led to the development of sharp lateral changes in thickness the sellick hill formation intraclast conglomerates record erosion and reworking of subtidal subfairweather wave base environments by exceptionally intense and presumably rare storm flows the intraclast horizons represent a substantial loss in stratigraphic resolution due to widespread erosion of the ramp

late archaean clastic sedimentary rocks shamvaian group of the zimbabwe craton first observations from the bindura shamva greenstone belt the 2 65 ga old shamvaian group sedimentary rocks occur as a folded succession in the central part of the bindura shamva greenstone belt of zimbabwe the strata comprise distinct shear zone bounded tectonostratigraphic units which may be stratigraphically arranged as follows the lower part of the succession is represented by a transgressive fining upward sequence of alluvial fan conglomerate overlain by fluvial braid plain pebbly sandstone and marine shoreface sandstone detritus was derived from a mid archaean granitoid gneiss terrain situated to the east sediment supply and subsidence rate must have been high shallow shelf sedimentation was followed by deep water sub wave base deposition by turbidity currents giving rise to a thick succession of fine to coarse clastic material the turbidite deposits were locally overlain by shallow marine sandstone and fluvial to alluvial fan conglomerate an upward increase in the abundance of intermediate and felsic volcanic clasts suggests an increase in the proximity of a volcanic terrain such as a volcanic arc deposition was followed by layer parallel shearing during thrust belt style tectonism major shear zones developed preferentially along the contact between shallow and deep marine facies associations basin initiation may have been related to extensional tectonics possibly on rifted continental crust whereas later stages of basin history were characterized by compression suggesting a foreland or fore arc basin setting sedimentary facies stratigraphy and facies distribution are remarkably similar to some late archaean sedimentary sequences of the superior province in canada

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

3 d process modelling of ancient storm dominated deposits by an event based approach application to pleistocene to modern gulf of lions deposits abstract a new numerical model was developed for 3 d characterization of deposits generated by storms along clastic coasts away from major rivers it is based on the assumption that the preserved sedimentary heterogeneities result mainly from a succession of deposits generated during both fair weather periods and major events storms in our case hydro sedimentary processes are first modelled during these major storms i transport parallel and transverse to the coast of suspended sediment by the strongest unidirectional currents littoral drift and downwelling currents ii sea bed erosion due to shear stress generated by unidirectional and wave induced oscillatory currents iii deposition of sediment fair weather deposits are modelled by an average deposition process the results of the numerical model i e the description of the sedimentary deposits are multi lithologic in three dimensions and with a flexible vertical resolution the latter is one of the main strengths of the model because the vertical description of the deposits can be adapted to the duration and extent of the simulation in order to save computation time very precise results definition of less than 1 mm can be obtained at a small time scale for storms lasting several hours to several days and reservoir scale results at a longer time scale the numerical model was applied to the gulf of lions which is located off the southern french coast in the north western mediterranean first present day storm deposits are simulated in order to validate the storm process modelling then sedimentary deposits formed over several thousands of years during the pleistocene are simulated in order to validate the sediment deposit modelling the model results fit well with observations and validate the approach of simulating the shelf deposits and their associated sedimentary heterogeneities at reservoir scale with an event and process based method this innovative approach seems promising for providing future geological models with realistic petrophysical properties

depositional processes on oceanic island shelves evidence from storm generated neogene deposits from the mid north atlantic oceanic islands such as the azores in the mid north atlantic are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines and into deeper environments such disruptive events create deposits denominated tempestites whose characteristics reflect the highly dynamic environment in which they were formed tempestites from oceanic islands however are seldom described in the literature and little is known about storm related sediment dynamics affecting oceanic island shelves therefore the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization transport and deposition taking place on insular shelves during and after major storms in santa maria island azores a sequence of neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity thus preserved and later exposed through uplift and erosion because it was overlain by a contemporary coastal lava delta the water depth at the time of deposition could be inferred constituting an excellent case study to gain insight on the still enigmatic processes of insular shelf deposition sedimentological palaeontological petrographic and palaeo water depth information allowed the reconstruction of the depositional environment of these sediments the sequence typifies the characteristics of a tempestite or successive tempestites formed at ca 50 m depth in a steep energetic open insular shelf and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf the authors claim that cross shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high energetic environments such as the insular shelves of open sea volcanic islands

the upper mississippian bluefield formation in the central appalachian basin a hierarchical sequence stratigraphic record of a greenhouse to icehouse transition abstract the upper mississippian chesterian bluefield formation is the basal unit of the predominantly siliciclastic mauch chunk group in the appalachian basin this formation developed in a northeast southwest oriented foreland trough fronting the alleghanian highlands to the southeast regional cross sections and isopach maps of the bluefield formation in southeastern west virginia southwestern virginia and southeastern kentucky define a depocenter in the southeastern part of the study area and a paleovalley system along the basin margin to the northwest at most localities facies that make up the bluefield formation are stacked into 1 15 m thick upward shallowing parasequences each of which is capped by a flooding surface these parasequences are stacked into four regionally correlatable depositional sequences on the margins of the depocenter incised valleys and fewer meter scale parasequences characterize the depositional sequences stacking of parasequences into sequences reflects a hierarchy of greenhouse type fifth order and icehouse type fourth order sea level cycles superimposed on a differential subsidence history related to early alleghanian thrust loading the bluefield depocenter experienced greater total accommodation which prevented incision during lowstands instead lowstands are typified by preservation of fifth order coal bearing parasequences in the depocenter basin margin areas experienced less total accommodation which resulted in development of fourth order lowstand valleys and erosion of parasequences this study demonstrates that both tectonic and eustatic forcing mechanisms controlled stratigraphic evolution of the bluefield formation

a numerical study of sediment transport and event bed genesis during tropical storm delia some event beds tempestites are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short lived storms to test this hypothesis a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field three dimensional coastal circulation wind waves generated over the continental shelf the combined effect of steady and oscillatory currents within the benthic boundary layer suspended and bed load transport of sediment and conservation of the seafloor this model system is used to hindcast winds currents waves and resulting sedimentation during tropical storm delia which passed over the texas louisiana shelf on september 3 4 1973 sensitivity to the initial substrate is investigated in four experiments using uniform silt uniform sand a mud line at the 20 m isobath and a simplified modern sediment distribution modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid latitude geostrophic storm circulation model because the predicted depth of the wind mixed layer is greater than the water depth over the shelf shelf currents in excess of 2 m s flow predominantly along the coast to the southwest during most of the storm driven by the wind stress and the trapped coastal wave which peaks at 180 cm near galveston significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf these waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm s the region of highest stresses always lies to the right of the storm track viewed down the path and moves across the shelf with the eye of the storm three general sediment transport paths are evident 1 onshore transport of finer sediment over the outer shelf to the right of the storm track 2 westward directed along shelf transport of predominantly fine sediment between approximately 40 m and 20 m water depths and 3 minor offshore transport of sand from the shoreface to depths less than 30m the resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1 and covers an area of approximately 3 104 km2 to the right of the storm track aside from local transport associated with finer sediments these results are relatively insensitive to initial sediment type comparison of model results to observed data from buccaneer platform shows that the different models performed adequately during the peak of the storm except for a significant underprediction of the significant wave height by the wind sea model the estimated uncertainty in the calculated combined shear stresses u based on errors produced by the individual model components is most dependent on the wave bottom orbital amplitude the total uncertainty in u is estimated to be approximately 7

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

isotopic events in the grip ice core a stratotype for the late pleistocene an event stratigraphy for the last termination based on the stratotype of the grip ice core record has been outlined for the north atlantic region it is suggested that such an approach to stratigraphic subdivision may o er a more satisfactory alternative to conventional stratigraphical procedures for those parts of the recent quaternary record that are characterised by rapid and or short term climatic uctuations 1999 elsevier science ltd all rights reserved

the world s lead zinc mineral resources scarcity data issues and opportunities abstract lead and zinc keep humanity powered and sheltered yet a comprehensive understanding of pb zn resources in known mineral deposits has been lacking leading to uncertainty over when we might expect the supply of these metals to face potential constraints addressing this we compile an extensive database of the world s known pb zn mineral deposits and provide in depth analyses of their contained resources ore grades economic value by products and geological settings our data indicate that at least 226 1 mt pb and 610 3 mt zn are present within 851 individual mineral deposits and mine waste projects from 67 countries and one in international waters at an average grade of 0 44 pb and 1 20 zn the identified resources are dominantly present within sediment hosted pb zn deposits 490 6 mt pb zn cu which contain the equivalent of vms skarn porphyry epithermal and mixed sediment hosted deposits combined and 49 of these resources are reported in australia russia peru and canada alone the reported pb zn resources appear to be sufficient to meet global demand for both pb and zn until 2050 although this estimate is most certainly a minimum as our case studies indicate a prevailing trend of deposits cumulatively producing well beyond their reported resources over time indeed despite increasing historical production of pb and zn estimated reserves and resources have also increased and this is expected to continue we also present an analysis and review of additional aspects affecting the future sustainability of pb zn resources including an account of the history of pb zn mining case studies and trends in reporting classifications of the dominant pb zn mineral deposit types analysis of reported by product companion metals review of tailings resource potential and case studies on the numerous challenges in environmental management historically faced for pb zn mining these analyses alongside our comprehensive resource data indicate that the future supply of pb and zn is likely to be governed by prevailing economic social and environmental factors much more so than sheer resource constraints

sediment transport in the shelf canyon swatch of no ground bay of bengal the swatch of no ground is a shelf canyon that deeply incises the bengal shelf near the ganges brahmaputra river mouth cuts the foreset beds of the subaqueous river delta and acts as temporary depocenter between river mouth and bengal fan sedimentation rates in the swatch of no ground are highest near the canyon head at 50 cm a 1 decreasing to 15 cm a 1 in 600 m water depth the canyon deposits consist of intercalated fine silt clay and coarse silt sand grained deposits in seismic profiles small scale sedimentary structures and parallel bedded layers reveal that sediment in the canyon is mainly deposited from suspension during fair weather conditions tidal currents are the dominant mechanism that transports plumes of suspended river load towards the canyon forming fine grained silt clay layers during storm conditions sediment is resuspended on the inner shelf and subaqueous delta east of the canyon storm generated bottom currents transport the resuspended sediment alongshelf to the canyon where the particles are trapped and form graded coarse silt sand layers channels and gullies in the swatch of no ground indicate active gravity driven currents with an erosional character in the upper canyon and non depositional character below 450 m suggesting that persistent or ephemeral currents presently export sediment to the bengal fan numerous slumps and slides observed in the canyon show small scale acoustically transparent layers that indicate sediment liquefaction presumably initiated along the steep canyon margin these mudflows move downslope and halt where the canyon gradient decreases one widespread acoustically transparent layer with an age of approximately 140 160 years bp can be traced throughout much of the canyon and is probably the result of large scale sediment remobilization triggered by a catastrophic event like an earthquake this may represent decennial to centennial scale events that remove large quantities of sediment and prevent the canyon from rapid infilling

coherence of surf zone and shelf current flow on the texas u s a coastal margin implications for interpretation of paleo current measurements in ancient coastal sequences abstract measurements from the texas coastal margin a microtidal fetch limited wind dominated shallow sea reveal a strong correlation in timing and direction of surf zone and shelf flow during both fairweather and storm events coherence of current motion is statistically significant at many frequencies cycle lengths and is highest during storm events the lack of a significant lag between surf zone and shelf flow indicates that both respond rapidly to changes in the magnitude and direction of the wind field the alongshelf component of the wind stress is a major force in generating currents both on the shelf and in the surf zone as exhibited by comparison of numerical predictions and observed velocities during the 140 day study period current flow was mainly directed alongshelf to the northeast and southwest driven by southerly fairweather and northerly storm winds respectively however the threshold for generation and migration of megaripple bedforms in upper shoreface bar troughs was exceeded only during storm events when surf zone flow was oriented to the southwest along the coast this observation coupled with the knowledge that storm generated bedforms have the highest preservation potential imply that multi event traction bedding in upper shoreface bar troughs of analogous ancient environments will be dominated by unimodal alongshore current orientations large scale bedforms which respond to this time averaged flow on the shelf are expected to display a similar unimodal alongshelf orientation with a low angle deviation toward the offshore direction careful study of paleo current measurements in a well documented ancient shelf to shoreline sequence in the cretaceous of new mexico reflects this similarity in transport kinematics

microfabric and taphonomic analysis in determining sedimentary processes in marine mudstones example from silurian of new york abstract microfabric evidence from mudstones combined with taphonomic information provides important clues to sedimentary processes the microfabric of the lewiston member rochester shale silurian wenlockian of new york has yielded evidence of episodic sedimentation from storm generated sediment plumes or tempestites a cardhouse arrangement of clay flakes in the mudstones indicates rapid deposition of flocculated clay in addition taphonomic observations such as the presence of articulated crinoids buried in life position also indicate rapid burial by the flocculated clay sediment four intervals of lewiston mudstones show evidence of periods of background sedimentation during which skeletal debris slowly accumulated these conditions were punctuated by brief events of deposition from storm generated silty clay sediment plume that rapidly hours to days covered the depositional site this study provides an example of the utility of an integrated microfabric and taphonomic analysis in determining the nature of mudstone depositional processes

from extension to tectonic inversion mid cretaceous onset of andean type orogeny in the lhasa block and early topographic growth of tibet

the role of wave reworking on the architecture of storm sandstone facies bell island group lower ordovician eastern newfoundland stacked shallow marine cycles in the lower ordovician bell island group of bell island newfoundland show upward thickening and upward coarsening sequences which were deposited on a storm affected shelf in the beach formation each cycle has a facies sequence comprised from base to top of dark grey mudstones light grey mudstones tabular sandstones and mudstones lenticular sandstones and mudstones and thick bedded lenticular sandstones reflecting a progressive increase of wave orbital velocities at the sediment surface the mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents the lenticular sandstones in the succeeding facies are wave reworked sands commonly lying in erosional hollows and having erosional tops and internal hummocky cross stratification planar lamination is relatively uncommon and sole marks are mainly absent in this facies oscillatory currents were dominant and accumulated sand in patches generally 10 30 m in diameter the facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms mud partings and second order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds this interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events the thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings in the overlying redmans formation the process of amalgamation progressed even further so that nearly all the mud partings were removed resulting in the formation of thick bedded tabular sandstones sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled the rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb there is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb the thick bedded facies of the beach formation and the thick bedded tabular facies of the redmans formation represent periods of maximum sea level fall the stacked cycles in the beach formation are interpreted as an aggradational high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the redmans formation the recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies

wave modified turbidites combined flow shoreline and shelf deposits cambrian antarctica sandstone tempestite beds in the starshot formation cen tral transantarctic mountains were deposited in a range of shoreline to shelf environments detailed sedimentological analysis indicates that these beds were largely deposited by wave modified turbidity currents these currents are types of combined flows in which storm generated waves overprint flows driven by excess weight forces the interpreta tion of the tempestites of the starshot formation as wave dominated turbidites rests on multiple criteria first the beds are generally well graded and contain bouma like sequences like many turbidites the soles display abundant well developed flutes they also contain thick divisions of climbing ripple lamination the lamination however is dominated by convex up and sigmoidal foresets which are geometries identical to those produced experimentally in current dominated com bined flows in clear water finally paleocurrent data support a tur bidity current component of flow asymmetric folds in abundant con volute bedding reflect liquefaction and gravity driven movement and hence their orientations indicate the downslope direction at the time of deposition the vergence direction of these folds parallels paleocur rent readings of flute marks combined flow ripples and a number of other current generated features in the starshot event beds indicating that the flows were driven down slope by gravity the wave component of flow in these beds is indicated by the presence of small to large scale hummocky cross stratification and rare small two dimensional ripples wave modified turbidity currents differ from deep sea turbidity cur rents in that they may not be autosuspending and some proportion of the turbulence that maintains these flows comes from storm waves such currents are formed in modern shoreline environments by a com bination of storm waves and downwelling sediment laden currents they may also be formed as a result of oceanic floods events in which intense sediment laden fluvial discharge creates a hyperpycnal flow event beds in the starshot formation may have formed from such a mechanism oceanic floods are formed in rivers of small to medium size in areas of high relief commonly on active margins the starshot formation and the coeval douglas conglomerate are clastic units that formed in response to uplift associated with active tectonism sedi mentological and stratigraphic data suggest that coarse alluvial fans formed directly adjacent to a marine basin the geomorphic conditions were therefore likely conducive to rapid fluvial discharge events asso ciated with storms the abundance of current dominated combined flow ripples at the tops of many starshot beds indicates that excess weight forces were dominant throughout deposition of many of these beds

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

geostrophic circulation or shallow marine turbidity currents the dilemma of paleoflow patterns in strom influenced prograding shoreline systems in ancient storm influenced prograding shoreline sequences sole marks mainly tool marks from hummocky crossstratified storm deposits are commonly oriented normal to paleoshoreline and the trend of paleobathymetric contours in the basin asymmetrical tool marks typically indicate flows directed offshore several workers have attributed their formation to storm generated shallow marine turbidity currents this interpretation conflicts with observations from modern shelves where storm driven circulation generally is geostrophically balanced and time averaged bottom currents approximately parallel bathymetric contours and the local shoreline the resolution of these apparently conflicting observations may lie in the realization that tool marks and many other small paleoflow indicators form almost instantly as the result of instantaneous flow conditions very near the bed beneath storm generated flows in the shallow ocean instantaneous and time averaged characteristics of the bottom boundary layer generally exhibit little similarity storm generated tool marks are formed by the movement of large tools within the thin less than 1 m inner boundary layer resulting from the superimposition of waves and currents the orientation of the peak instantaneous shear stress moving large tools under such combined flows mainly reflects wave orbital motions which typically are normal to shore the magnitude of stress is greatly increased in the offshore direction and decreased in the onshore direction by superimposition of a steady current with an offshore component of flow but the direction of stress is only slightly affected in ancient storm influenced sequences therefore shore normal tool marks generally were not formed by turbidity currents rather their orientation is best attributed to shoaling waves approaching the coast at a very high angle asymmetrical tool marks are directed offshore due to enhanced shear stress on the offshore stroke of waves superimposed on a geostrophic current with an offshore flow component tool marks do not reflect the time averaged bottom flow direction in fact they provide almost no information concerning steady bottom currents in contrast high angle cross beds formed in coarser sediment by the migration of dunes and sandwaves although relatively rare in offshore storm deposits generally reveal approximately shore parallel flows in ancient systems cross beds closely reflect the time averaged flow direction in the outer boundary layer of a geostrophic current for three reasons 1 the net transport direction for sand moving as bed load beneath a combined flow lies between the directions of peak instantaneous shear stress and time averaged shear stress 2 large ripples disrupt the thin inner boundary layer and 3 long time intervals relative to wave induced velocity oscillations are required to form large ripples