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

style and timing of salt movement in the persian gulf basin offshore iran insights from halokinetic sequences adjacent to the tonb e bozorg salt diapir abstract the variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt diapirs and provides insights into the style of salt movement sedimentation interaction and the timing of halokinetic phases episodic movement of salt diapir is defined by wedge and tabular shaped salt related sedimentary strata halokinetic sequences adjacent to the diapir detailed mapping of depositional strata on 2d seismic sections adjacent to salt diapirs on the tonb e bozorg island persian gulf sw iran reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers the hormuz and fars salts respectively the hormuz salt deposited in the uppermost proterozoic mobilized in the lower paleozoic and then continued to move periodically to present and to create the deep salt structures in the tonb e bozorg region the fars salt deposited in the lower miocene and then started rising and created the central salt structure the tonb e bozorg island and several peripheral ring like salt structures around the island our results reveal that both the salt layers within the tonb e bozorg region grew by downbuilding and continued to move periodically by passive and active diapirism to the present salt movement sedimentation interaction during salt diapirism influences petroleum play and therefore is of interest in petroleum geoscience

oman exotic limestones in the uae oman border area with implications for middle upper permian neo tethyan rifting abstract the neo tethyan semail ophiolite in the uae oman region was obducted onto the arabian continental margin at the end of the cretaceous beneath the ophiolite are thrust stacked deep water mesozoic and older sediments and volcanics that include marine basalts and associated limestones of middle late permian and late triassic age these limestones are referred to as the oman exotic limestones the middle upper permian exotics are the rarer exotic type they were reef build ups on platforms that sank to ocean depths during rifting and were later engulfed by intrusive basalts an area to the east of al ain city uae exposes blocks of richly fossiliferous limestone exotic blocks within upper triassic marine basalts the studied exotics host foraminifera including dunbarula mathieui verbeekina sp tetrataxis sp geinitzina sp pachyphloia sp colaniella leei and calcareous algae mizzia velebitana rugose corals and abundant crinoids consistent with a murghabian dzulfian middle late permian age the exotics lack ooids show grainstone packstone lithofacies are only slightly affected by dolomitization these features are interpreted in a paleogeographic model involving an isolated carbonate platform comparable to the jabal qamar formation in the dibba zone that subsided during neo tethys rifting in the late permian lopingian dzulfian dorashamian

jurassic evolution of the arabian carbonate platform edge in the central oman mountains the jurassic sahtan group exposed in northern oman was deposited in shallow marine environments at the edge of the arabian platform facing the neo tethys hamrat duru basin the upper sahtan group is made up of a mixed siliciclastic carbonate unit overlain by pure carbonate deposits assigned to a bathonian and early callovian age on the basis of brachiopods and foraminifers these carbonate depositional systems were composed of outer oolitic shoals that underwent subaerial exposure and a deeper somewhat restricted gently dipping shelf interior oolitic material was shed off the platform edge into the deep sea depositional complex of the guweyza formation the sahtan group is affected by an important thickness reduction towards northeastern jabal akhdar the angular unconformity 0 2 at the top of the sahtan group is shown to result from tilting and top truncation of genetic sequences this unconformity is overlain by the rayda formation a veneer that shows an onlap pattern including a gradual deepening upwards facies evolution the minimal time span of the stratigraphic hiatus is mid callovian kimmeridgian oxfordian and kimmeridgian sequences were probably never deposited in this area because of lack of accommodation space and or because of subaerial exposure it is proposed herein that the unconformity was shaped by subaerial carbonate dissolution during a steady tectonically driven exhumation of the platform edge during the tithonian a major eustatic sea level rise caused transgression of the rayda formation upon the platform edge and normal shelf marine conditions resumed in the eastern arabian peninsula

whole flow field dynamics and velocity pulsing within natural sediment laden underflows sediment laden density underflows are important agents of erosion and deposition and are especially significant in the management of human made reservoirs pollutant dispersal and sediment deposition in the world9s oceans quantification of continuous sediment laden underflows in lillooet lake british columbia shows that the underflows descend along a distinct plunge line but although the input from the source is constant adopt a distinct pulsing in their velocity structure such velocity pulsing will produce temporally and spatially varying bed shear stresses sediment erosion and or deposition and fluid mixing and represents a central property of underflows that must be incorporated into models of density current behavior

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

the hawasina basin a fragment of a starved passive continental margin thrust over the arabian platform during obduction of the sumail nappe abstract a complete revision of the lithostratigraphy of the hawasina nappes in the eastern and central oman mountains as compared to that of the previous stratigraphy leads to a new palaeogeographical reconstruction of the basin five very distinct zones have been determined representing five principal structural units that succeed one another from the external to the internal zones as follows 1 1 the hamrat duru basin 2 2 the baid platform 3 3 the al avidh trough 4 4 the misfah platform and 5 5 the umar basin the history of the hawasina basin began in the late permian with the formation on the northeastern edge of gondwana of a vast intracontinental basin the hamrat duru basin however this basin became a passive continental margin only during the middle late triassic formation of the neo tethys by crustal spreading and accretion began at this time in the internal part of the basin and in continuity with the umar basin the misfah platform and the al aridh trough which formed at the same time within the hawasina basin from this period onwards the main geomorphological features of the basin and of the margin were fixed and persisted up to the late cretaceous the phase of extension by which the basin was subsequently affected during the late tithonian berriasian was mainly manifested by generalized subsidence these main stages in the formation and evolution of the hawasina basin are marked by extensive development of in general alkaline but in places transitional and locally tholeiitic morb magmatism the sediments of the hamrat duru basin are dominated by turbidites composed of material mainly derived from the arabian platform whereas the al aridh trough and umar basin are characterized by pelagic sediments however the al aridh and umar grabens also contain layers of breccia of variable extent containing clasts and blocks of late permian and late triassic shallow water carbonates derived from the adjacent baid and misfah platforms sedimentation in the hawasina basin thus began locally in the late permian and by the triassic it was taking place in the remaining parts of the basin continuing up to the late turonian early senonian when the basin closed and overthrusting during obduction of the sumail ophiolite occurred sedimentation ended the overthrusting took place in three stages 1 1 a southerly directed compressive pre early obduction phase during which the hawasina basin was detached from its substratum to form an obduction prism 2 2 an obduction phase sensu stricto which by gravitational mechanisms induced major displacement of the principal hawasina units and their piling up on the arabian platform with the outermost units at the base and the innermost at the top and 3 3 a late obduction phase which caused local north northeastward backfolding possibly associated with the development of a fracture cleavage which in the basal structural levels may pass into true schistosity

metamorphism and deformation along the emplacement thrust of the samail ophiolite oman abstract the base of the samail ophiolite is a metamorphic shear zone that provides key information about ophiolite emplacement the classic exposure of this metamorphic sole at wadi tayin consists of a few meters of garnet clinopyroxene mafic gneiss and 80 m of upper amphibolite facies mafic and quartzose tectonite overlying 150 m of lower amphibolite facies mafic and sedimentary schist the sole is bounded by faults but is internally coherent peak metamorphic temperatures decrease exponentially from 825 c at the top of the sole to 500 c at its base as documented by changes in grain size hornblende composition the disappearance of chlorite and epidote garnet clinopyroxene element partitioning and garnet hornblende partitioning the inverted peak temperature gradient decreases from 4000 c km in the upper 50 m to 100 c km in the lower 150 m contrary to earlier reports greenschist facies tectonites are not present at wadi tayin although the entire sole underwent greenschist facies retrogression driven by the influx of fluids from the overlying peridotite or underlying carbonate calculations based on an amphibolite constitutive relation reveal that although the section represents a lithologic continuum the lower 200 m of the sole is a relatively undeformed block whereas the uppermost 25 m represent material initially separated by tens to a couple of hundreds of kilometers and now integrated into a single column

rapid subsidence and preservation of fluvial signals in an otherwise wave reworked delta front succession early mid pliocene orinoco continental margin growth se trinidad abstract outcrops of the early mid pliocene orinoco delta succession on the atlantic facing trinidad continental margin demonstrate facies and stratigraphic architecture of a shelf margin developed in a setting of high sediment supply orinoco river and unusually rapid sediment accumulation subsidence averaging 1 km my the studied moruga clastic wedge of the orinoco margin consists of a series of topset to deepwater clinoforms with channelized sandstones river and mixed process delta front wave dominated delta front shoreface prodelta offshore transition shelf upper slope turbidite channels and mass transport deposits the succession is sand prone and generally consists of coarsening and thickening upward delta front lobes with hummocky swaley and wave ripple stratified sandstones indicating dominant storm wave reworking of the delta particularly when the delta lobes had reached outer shelf sites after long shelf transits the lower parts of distributary channels are well preserved and characterized by cross bedded to parallel laminated sandstones with mud clast lags the upper parts of channel fills were wave reworked during transgressions creating hummocky swaley cross stratified strata river dominated and mixed process wave and tide delta front deposits occur commonly within stacked coarsening upward units the river dominated delta front deposits exhibit parallel laminated to current ripple laminated intervals with normally graded thin beds changing upward to parallel and low angle cross lamination but mixed process delta front deposits also contain wave and bidirectional current ripples as well as discrete intervals of hummocky swaley cross stratification the preservation of the channel base as well as river and mixed process delta front deposits in the otherwise storm wave dominated atlantic facing setting suggests some sheltering of the coastal morphology and possibly low frequency of large storms but it is more likely that the unusually rapid subsidence at rates competing well with icehouse rates of eustatic sea level change and burial of deposits may have prevented the fluvial and tidal signals from being completely reworked by the storm waves in the studied outcrop area this study demonstrates an example of how the interactions of river tide and wave generated facies impacted stratigraphic architecture of a rapid subsiding shelf margin built by shelf edge deltas with high sediment supply

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

synchronous seafloor spreading and subduction at the paleo convergent margin of semail and arabia the semail ophiolite is the largest and best exposed ophiolite having preserved intact record of a precollision system related to neotethyan ocean closure breaking with the alternative models of ophiolite exhumation and emplacement this paper builds on integrating the joined contribution of tectonic evolution of the continental margin in the premise of the ophiolite obduction connecting the along strike segmentation of the ophiolite recorded in the lithospheric flow structure and recent high precision dating results in a 3 d model of evolution of the ophiolite and its continental margin during jurassic cretaceous time among the relevant characteristics newly accounted 1 the contamination of the ophiolite by fluids and magmas of continental origin 2 the discrimination of different types of metamorphics associated to the ophiolite and conventionally classified metamorphic soles 3 the instability of the arabian margin during the late jurassic cretaceous times 4 the new precise ages relating to overlapping of spreading and detachment and 5 the inferred vergence of neotethyan closure during late mesozoic are stressed the complex stem revealed may relate to processes associated with spreading center subduction at ridge trench transform rtt triple junction as documented along a convergent margin the semail ophiolite emplacement on the arabia continental margin would result from a temporary arabian platform directed subduction zone that consumed the southern tethyan plate during late jurassic cretaceous time

kinematic and paleomagnetic restoration of the semail ophiolite oman reveals subduction initiation along an ancient neotethyan fracture zone abstract the archetypal semail ophiolite of oman has inspired much thought on the dynamics of initiation of intra oceanic subduction zones current models invoke subduction initiation at a mid oceanic ridge located sufficiently close to the arabian passive margin to allow initiation of continental subduction below the ophiolite within 10 15 myr after the 96 95 ma age of formation of supra subduction zone crust here we perform an extensive paleomagnetic analysis of sheeted dyke sections across the semail ophiolite to restore the orientation of the supra subduction zone ridge during spreading our results consistently indicate that the ridge was oriented nne ssw and we infer that the associated trench close to the modern obduction front had the same orientation our data are consistent with a previously documented 150 clockwise rotation of the ophiolite and we reconstruct that the original subduction zone was wnw ward dipping and nne ssw striking initial subduction likely occurred in the ocean adjacent and parallel to a transform margin of the part of the arabian continent now underthrust below iran that originally underpinned the nappes of the zagros fold thrust belt subduction thus likely initiated along an ancient continental margin parallel fracture zone as also recently inferred from near coeval ophiolites from the eastern mediterranean and nw arabian regions subduction initiation was therefore likely induced by wn w es e contraction and this constraint may help the future identification of the dynamic triggers of neotethyan subduction initiation in the late cretaceous

application of sequence stratigraphic concepts to the upper cretaceous tununk shale member of the mancos shale formation south central utah parasequence styles in shelfal mudstone strata

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

bioturbation sedimentation rates and preservation of flood events in deltas abstract we examine the nature and number of event beds preserved in heterolithic prodelta and delta front strata in five proximal accumulation dominated pad north american delta systems including the quaternary gulf of mexico and the late cretaceous western interior seaway we also explore the continuum between pad more distal deposits of mud belts and thicker subaqueous delta clinoforms sdc sediment accumulation rates in modern pad and sdc systems are commonly on the order of several to severaltens of centimeters per year they also show that several event beds may be created annually with preservation depending on supply and reworking the pad heterolithics commonly comprise interbedded sand silt and clay these show normal and inverse grading and bouma sequences indicating deposition from turbidity currents and hyperpycnal flows that are interpreted as the products of river plumes generated during flood episodes re equilibrated rosselia socialis in stacked delta front turbidite bedsets in the cretaceous examples show that floods may occur as a cluster of events over several months shelf areas adjacent to river mouths may experience high rates of sediment delivery from rivers but oceanographic processes are instrumental in moving much of the silt and clay farther along the shelf direct hyperpycnal delivery from a river mouth on a low gradient shelf i e typically

origin and implications of a thrust bound gypsiferous unit along the western edge of jabal sumeini northern oman mountains abstract the oman mountains comprise a series of thrust sheets of neo tethyan oceanic rocks that were emplaced onto the arabian continental margin during obduction of the semail ophiolite during the late cretaceous three separate groups of anomalous gypsiferous bodies intrude the allochthonous units along faults over a distance of about 150 km in the hawasina window jabal qumayrah and jabal sumeini the bodies at jabal sumeini form a band about 4 km long and up to 100 m wide along a late stage thrust that restacks the allochthon over a post emplacement maastrichtian palaeogene sedimentary succession the gypsum shows evidence of flow folding and contains numerous clasts and rafts of a range of quartzose sandstones but with only a minor component from carbonates from the neo tethyan sumeini group in the hanging wall palaeogene limestones from the footwall succession are essentially absent strontium isotope ratios are high and intersect with the open ocean water reference curve for the late cambrian ordovician and late miocene pliocene they are also noticeably higher than the ratios from the two other gypsiferous outcrop areas in the oman mountains and from outcrops of ediacaran early cambrian salt domes in central oman however the regional stratigraphy points towards a source of the gypsum from either an ediacaran early cambrian ara group salt basin or from the lower fars formation early middle miocene and derivation of the sandstone clasts and rafts from thick lower palaeozoic clastic sequences the discrepancy with the ages inferred from the strontium isotope data can be attributed to deposition of the gypsum in restricted conditions not in equilibrium with the prevailing ocean water two models are presented for an ediacaran early cambrian and an early middle miocene source while the latter cannot be wholly discounted the stratigraphic and structural context point more strongly towards an ediacaran early cambrian ara group source of the gypsum this was extruded along deep rooted late cretaceous thrust faults that were reactivated during a period of cenozoic compression incorporating lower palaeozoic sandstone clasts from adjacent strata during extrusion or during an earlier phase of possible halokinesis this is consistent with existing models for the emplacement of the other two identified groups of gypsiferous bodies in the oman mountains and provides further evidence for the presence of smaller evaporite basins between the major hormuz and central southern oman salt basins

tectonic evolution of the northern oman mountains part of the strait of hormuz syntaxis new structural and paleothermal analyses and u pb dating of synkinematic calcite

permian age from radiolarites of the hawasina nappes oman mountains the hawasina napper of the oman mountains yielded permian radiolarians from cherts stratigraphically overlying a thick volcanic basement al jil formation at the base of the hamrat duru group this fauna represents the first permian radiolarians and radiolarites in the central and western tethyan realm a permain age for pelagic sequences within the hawasina complex of oman has major significance for regional paleogeographic reconstruction a clear differentiation between platform reefal sediments and basin radiolarites from the base of the late permian 255 ma is implied it suggests a flexure of the platform during permian time the present data implies that a zone of rifting was already developed adjacent to the northeast gondwana platform margin during the late permian the hamrat duru basin corresponds to an opening intracontinental rift area sphenochasm between arabia and northeast gondwana a reentrant of the paleo tethys

source to sink sediment budget analysis of the cretaceous ferron sandstone utah u s a using the fulcrum approach abstract this paper matches sediment fluxes estimated to have passed through an ancient river system with mapped downstream sediment volumes in a deltaic sink providing a test of the recently developed fulcrum approach to source to sink analysis this paper uses field measurements such as channel depth width and grain size to estimate paleodischarge in an ancient trunk channel of the cretaceous ferron sandstone in central utah the estimates of instantaneous discharge are then integrated over the geological duration of the river to estimate the total sediment volume delivered to downstream deltaic sinks in an attempt to balance the estimated sediment flux with the mapped deltaic deposits in the sink the bankfull channel depths calculated using the scaling relationship between the flow depth and the mean dune height vary from 3 3 to 5 5 m with an average depth of 4 4 m the corresponding bankfull channel width estimates vary from 50 to 80 m with an average value of 65 m calculated using scaling relationship between channel width and the width of accretion surfaces water discharge calculated for these bankfull dimensions vary from 2 7 10 2 m 3 s to 8 6 10 2 m 3 s also indicating that these rivers were routinely capable of generating hyperpycnal flows the instantaneous sediment discharge reaching the fulcrum was calculated using established sediment transport equations these instantaneous discharge values were first converted to mean annual sediment volume using the bankfull event durations recurrence intervals and a factor for the proportion of the total annual sediment load transported during the bankfull period based on empirical relationships from modern climate analogs and then projected over the average time duration of individual parasequences in the ferron notom clastic wedge which is approximately 14 kyr the mass balance across the fulcrum reveals that the average bedload sediment volume derived from the source about 3 km 3 matches with that deposited in the sink within a factor of two however underestimation of the bedload volume in the sink suggests sediment escape beyond the limits of currently mapped sink area previous models for the ferron indicate significant se deflection of sediment due to wave reworking which may account for the missing sandy sediment it is also possible that there is an overestimation of time duration for individual valleys resulting in higher sink volume estimation and larger source to sink mass imbalance monte carlo simulations based on probabilistic estimation were used to test the sensitivity of key parameters used in converting bankfull discharge to mean annual discharge the p10 p50 median and p90 values for the average annual bedload volume q mas are 9 1 10 4 m 3 1 7 10 5 m 3 and 3 7 10 5 m 3 respectively a q mas value between p50 and p90 yields a source to sink balance for bedload volume the current study establishes a mass balance across the fulcrum with a reduced range of uncertainty for the various parameters used uncertainty associated with bankfull channel dimensions has been reduced through inclusion of detailed outcrop data the uncertainty in estimating average annual sediment volume q mas from bankfull events is less than a factor of three this uncertainty can be further reduced by incorporating a more robust global discharge dataset from modern analog river systems despite many assumptions and uncertainties our study shows that the fulcrum method appears to be capable of balancing sediment budgets to within at least an order of magnitude in deep time sedimentary systems

quasi planar laminated sandstone beds of the lower cretaceous bootlegger member north central montana evidence of combined flow sedimentation abstract lower shoreface to shallow shelf strata of the bootlegger member of the lower cretaceous blackleaf formation are characterized by interbedded sandstone and mudstone sandstone beds are characterized by a peculiar planar lamination showing a subtle although perceptible undulation spacing to height ratios of the undulation are generally 100 or more typically the undulation shows no evidence of lateral accretion but only vertical aggradation and as a result most beds consist of a single laminaset aspects of quasi planar laminated beds indicate single event storm sedimentation and paleocurrent data indicate offshore sediment transport by its sedimentary characteristics and its similarity with a bed configuration generated in un experimental wave duct quasi planar lamination is produced by high energy combined flows this style of stratification should be common in the shallow marine stratigraphic record and its recognition should aid in interpreting high energy combined flow depositional events

cretaceous sedimentary rocks on the masirah ophiolite sultanate of oman evidence for an unusual bathymetric history autochthonous sedimentary rocks on the masirah ophiolite preserve a record of vertical movements of their oceanic basement the masirah ophiolite was formed in the uppermost jurassic and subsequently underwent thermal subsidence for about 20 ma as documented by pelagic sediments submarine alkali basaltic volcanism in the lower barremian marks the onset of rapid basement uplift to or above sea level carbonate platforms grew in barremian mid aptian time on highs of oceanic basement the uplift is interpreted as the result of transpressive tectonism along a large oceanic fracture zone the platforms submerged in the mid aptian and reached the ccd in the albian ribbon cherts were deposited during the albian to santonian time the first influx of siliciclastic detritus shed from the arabian craton is recorded in coniacian sandstones ophiolitic conglomerates interfinger in the campanian to mid maastrichtian with continent derived sandstones reflecting regional compressive tectonism crystalline exotics deposited in the late maastrichtian are derived most likely from the precambrian basement of arabia whilst the origin of the sedimentary exotics dated triassic to cretaceous remains unclear the masirah ophiolite was overthrust at the cretaceous tertiary boundary by an upper ophiolite nappe and emplaced onto the margin of southeast oman

permian climatic and paleogeographic changes in northern gondwana the khuff formation of interior oman abstract detailed stratigraphic paleontologic and petrographic data from the middle permian khuff formation exposed in the haushi huqf area of interior oman provide new insight into the permian climatic evolution of the northern gondwana margin and on the still debated timing of neotethys opening between gondwana and the cimmerian blocks the khuff formation is interpreted to record a major transgression of neotethyan waters in wordian times middle permian at a stage of full oceanization and tectonic quiescence when thermal subsidence caused final drowning of rift shoulders and deposition of marine carbonates onto vast portions of stable arabia the petrographic composition of middle permian sandstones indicates a post rift stage and documents a long term increase in mineralogic stability ascribed to a shift toward warm humid climatic conditions coupled with reduced relief and longer transit times of detritus from source to basin raising temperatures and northward latitudinal drift towards lower tropic latitudes throughout the permian are fully documented by rich transitional marine faunas and available paleomagnetic evidence

late jurassic to cretaceous evolution of the eastern tethyan hawasina basin oman mountains remnants of a mesozoic continental margin can be studied today in the nappe pile of the oman mountains successions of the arabian carbonate platform and the adjacent deep hawasina basin are preserved in the nappe pile and in the foothills of this mountain range the jurassic cretaceous sediment successions of the hawasina basin sumeini and hamrat duru group are focus of this study these basinal archives contain information on the response of an eastern tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the cretaceous turbiditic continental slope and basinal successions formed near the calcite compensation depth are difficult to date with biostratigraphy and sequence stratigraphy the available stratigraphic framework for the hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study therefore existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy the hawasina basin was affected by sea level variations by changes in oceanography and also by regional tectonics a first major modification of oceanography occurred at the end of the jurassic when pelagic maiolica type sediments were accumulated in the deep basin and on adjacent submarine highs lower member of huwar and sid r formations pelagic to hemipelagic conditions existed until the valanginian marked by a major carbon isotope excursion pelagic sediments were afterwards replaced by a succession of fine to coarse grained turbidites of hauterivian to aptian in age the transition into the mid cretaceous is marked by a sudden shift to fine grained siliceous or chert deposits at a time when sediments enriched in organic carbon were accumulated in the western tethys and atlantic oceans the continental slope as well as the hawasina basin seemed to have been well ventilated during early and mid cretaceous time siliceous limestones and chert are indicator of well mixed and nutrient rich surface water while absence of black shales suggests young and oxygenated deep water with a possible source on the vast arabian platform these peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the oceanic anoxic event 1a this article is protected by copyright all rights reserved

mud re distribution in epicontinental basins exploring likely processes abstract fine grained clastic sediments are very common in the interior deposits of ancient epicontinental seas not only do they make up the gross lithology in these basins but they can also be traced for more than 1000 km offshore from basin margins given that epicontinental seas were overall shallow and in many parts most likely less than 100 m deep basin floor slopes can safely be expected to be in the 0 01 to 0 001 range for much of depositional history known processes that bring muds to the basin margin and beyond are hypopycnal river plumes hyperpycnal fluvial discharge events storm setup relaxation flows and gravity driven fluidized muds with the exception of river plumes all of these processes require the presence of sufficient slope for sustained movement due to that constraint these processes combined might in the majority of situations have been able to move muddy sediments on the order of 100 km offshore whereas this is sufficient to distribute mud across marginal shelf seas it becomes problematic in the case of much larger epicontinental seas for example those of upper devonian or upper cretaceous times extended in places for thousands of kilometers and thus a process is needed that can move muddy sediments the rest of the way flume studies of the bedload transport of mud combined with observations from the rock record suggest that wind or tide induced bottom current circulation was most likely essential for moving muddy sediments from the periphery of epicontiental seas to their interiors remobilization of seafloor muds during frequently recurring lowering of sea level is likely to have aided in this process

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

detailed facies analysis of the upper cretaceous tununk shale member henry mountains region utah implications for mudstone depositional models in epicontinental seas abstract lower middle turonian strata of the tununk shale member of the greater mancos shale were deposited along the western margin of the cretaceous western interior seaway during the greenhorn second order sea level cycle in order to examine depositional controls on facies development in this mudstone rich succession this study delineates temporal and spatial relationships in a process sedimentologic based approach the 3 dimensional expression of mudstone facies associations and their stratal architecture is assessed through a fully integrative physical and biologic characterization as exposed in outcrops in south central utah sedimentologic characteristics from the millimeter to kilometer scale are documented in order to fully address the complex nature of sediment transport mechanisms observed in this shelf muddy environment the resulting facies model developed from this characterization consists of a stack of four lithofacies packages including 1 carbonate bearing silty and sandy mudstone cssm 2 silt bearing calcareous mudstone scm 3 carbonate bearing silty mudstone to muddy siltstone cms and 4 non calcareous silty and sandy mudstone ssm spatial and temporal variations in lithofacies type and sedimentary facies characteristics indicate that the depositional environments of the tununk shale shifted in response to the 2nd order greenhorn transgressive regressive sea level cycle during this eustatic event the tununk shows a characteristic vertical shift from distal middle shelf to outer shelf cssm to scm facies then from outer shelf to inner shelf environment scm to cms and to ssm facies shifting depositional environments as well as changes in dominant paleocurrent direction throughout this succession indicate multiple source areas and transport mechanisms i e longshore currents offshore directed underflows storm reworking this study provides a rare documentation of the greenhorn cycle as exposed across the entire shelf setting high resolution mapping of genetically related packages facilitate the development of process based depositional models that can be utilized for lateral correlations into the equivalent foredeep strata of the cretaceous interior

re evaluating the paleogeography of the river dominated and wave influenced ferron notom delta southern central utah an integration of detailed facies architecture and paleocurrent analysis abstract this study re evaluates the paleogeography of a river dominated and wave influenced deltaic system in a single parasequence 6a of the cretaceous ferron sandstone south central utah which was previously interpreted as a typical asymmetric delta the conceptual asymmetric delta model of bhattacharya and giosan 2003 has been widely applied to interpret ancient deltaic systems however reconstructed paleogeographies relying on this conceptual model are commonly not scaled to the architectural elements which could possibly lead to inaccurate interpretations especially when data are relatively sparse the extensively exposed ferron sandstone outcrops provide an opportunity to demonstrate how detailed facies architecture work can be integrated with regional facies relationships to elucidate a properly scaled paleogeography seven facies associations fa are identified in parasequence 6a and are arranged into two distinctively different successions the river dominated succession consists of prodelta distal delta front proximal delta front and terminal distributary channel fa while the wave and storm dominated succession comprises offshore shelf lower shoreface and upper shoreface fa the river dominated succession is muddier and less bioturbated than the wave and storm dominated succession facies architecture analysis shows that the river dominated proximal delta front facies consists of mouth bar and terminal distributary channel elements that are not seen in the wave and storm dominated facies the scales of mouth bars and terminal distributary channels suggest that they are rather small features compared with the river dominated delta lobe which is incompatible with the simple bar elongation asymmetric delta model presented by li et al 2011 instead parasequence 6a is interpreted to be a valley fed river dominated symmetric delta protected from waves by an updrift barrier system which is analogous to the modern mongky river delta on the west coast of madagascar the progressive change in orientation of west directed mouth bars to north directed and east directed lobes around the periphery of the river dominated delta indicates a highly radial lafourche type delta moving away from the protection of the barrier system there is a gradual change from highly river dominated facies to increasingly wave and storm influenced facies toward the southeast due to the entrenched nature of the feeder river associated with an incised valley system the parasequence 6a delta was bifurcation dominated rather than avulsion dominated this study shows that it is critical to integrate detailed facies architecture analysis in order to reconstruct properly scaled paleogeographies and hypothesizes that stable bifurcation dominated deltas should be more common than avulsion dominated deltas in a lowstand delta system due to the entrenched nature of the feeding trunk river which inhibits avulsion

thermo mechanical modeling of the obduction process based on the oman ophiolite case obduction emplaces regional scale fragments of oceanic lithosphere ophiolites over continental lithosphere margins of much lower density for this reason the mechanisms responsible for obduction remain enigmatic in the framework of plate tectonics we present two dimensional 2d thermo mechanical models of obduction and investigate possible dynamics and physical controls of this process model geometry and boundary conditions are based on available geological and geochronological data and numerical modeling results are validated against petrological and structural observations of the oman semail ophiolite our model reproduces the stages of oceanic subduction initiation away from the arabian margin the emplacement of the oman ophiolite on top of it and the domal exhumation of the metamorphosed margin through the ophiolitic nappe a systematic study indicates that 350 400 km of bulk shortening provides the best fit for both the maximum pressure temperature conditions of the metamorphosed margin 1 5 2 5 gpa 450 600 c and the dimension of the ophiolitic nappe 170 km width our results confirm that a thermal anomaly located close to the arabian margin 100 km is needed to initiate obduction we further suggest that a strong continental basement rheology is a prerequisite for ophiolite emplacement

factors controlling carbonate platform asymmetry preliminary results from the great bank of guizhou an isolated permian triassic platform in the nanpanjiang basin south china abstract a well exposed isolated carbonate platform the great bank of guizhou in the nanpanjiang basin of south china developed from the latest permian to the earliest late triassic platform strata are dissected by a faulted syncline exposing a complete cross section through the interior margins and flanks enabling a detailed assessment of depositional controls previous studies portrayed the platform as having a relatively symmetrical architecture even though much of the former work was focused on the platform interior and northern margin basin transition our research reveals five aspects of the southern margin facies and stratigraphy that are significantly different from those of the northern margin 1 subaerial exposure and unconformity developed on top of the upper permian sponge boundstone and in the overlying lower triassic strata 2 permian and triassic clasts chaotically admixed within early triassic breccias 3 lower triassic strata remarkably thinner on the southern margin 4 a much narrower tubiphytes reef facies preserved along the southern margin in the middle triassic and 5 large scallop shaped reentrants at the southern margin evident in satellite images three end member models may explain the asymmetry 1 antecedent topography of the underlying upper permian reef rimmed margin coupled with eustatic sea level fluctuation 2 differential tectonic uplift and 3 large scale submarine collapse of the platform margin subaerial exposure and admixing of permian and triassic clasts observed at yungan section is best explained by the tectonic uplift model however the submarine collapse model also explains several of the observations if it is associated with uplift s or sea level fall s submarine collapse is supported by large concave erosional reentrants scallops visible in satellite images taken together our observations suggest that a combination of tectonic uplift and margin collapse contributed to platform asymmetry further work promises to further constrain the details and timing of processes that contributed to the asymmetry

a depositional model for offshore deposits of the lower blue gate member mancos shale uinta basin utah usa depositional models that use heterogeneity in mud dominated successions to distinguish and diagnose environments within the offshore realm are still in their infancy despite significant recent advances in understanding the complex and dynamic processes of mud deposition six cored intervals of the main body of the mancos shale the lower blue gate member uinta basin were examined sedimentologically stratigraphically and geochemically in order to evaluate facies heterogeneity and depositional mechanisms unique sedimentological and geochemical features are used to identify three offshore environments of deposition the prodelta the mudbelt and the sediment starved shelf prodelta deposits consist of interlaminated siltstone and sandstone and exhibit variable and stressed trace fossil assemblages and indicators of high sedimentation rates the prodelta was dominated by river fed hyperpycnal flow mudbelt deposits consist of interlaminated siltstone and sandstone and are characterized by higher bioturbation indices and more diverse trace fossil assemblages ripples scours truncations and normally graded laminations are abundant in prodelta and mudbelt deposits indicating dynamic current conditions mudbelt sediment dispersal was achieved by both combined flow above storm wave base and current enhanced and wave enhanced sediment gravity flows below storm wave base sediment starved shelf deposits are dominantly siltstone to claystone with the highest calcite and organic content bioturbation is limited to absent sediment starved shelf deposits were the result of a combination of shelfal currents and hypopycnal settling of sediment despite representing the smallest volume sediment starved shelf deposits are the most prospective for shale hydrocarbon resource development due to elevated organic and carbonate content sediment starved shelf deposits are found in either retrogradational to aggradational parasequence sets or early distal aggradational to progradational parasequence sets bounding the maximum flooding surface an improved framework classification of offshore mudstone depositional processes based on diagnostic sedimentary criteria advances our predictive ability in complex and dynamic mud dominated environments and informs resource prospectivity

from marine bands to hybrid flows sedimentology of a mississippian black shale this study was funded by the natural environment research council nerc grant no ne l002493 1 within the central england training alliance centa consortium the study received case funding from the british geological survey nick riley carboniferous limited is thanked for sharing his expertise and assistance charlotte watts is thanked for providing field assistance nick marsh tom knott cheryl haidon and annika burns are thanked for offering expertise and laboratory assistance pete sadler university of california is thanked for compilation and provision of the background sediment accumulation rate dataset we thank all reviewers editor peir pufahl and elaine richardson editorial office for their valuable comments and advice which have significantly improved this manuscript

relative importance of processes that govern the generation of particulate hyperpycnal flows simple mathematical approaches are used to investigate the relative importance of salinity temperature dissolved load stratification of suspended load and estuarine mixing on the direct formation of particulate hyperpycnal currents from river outflow specifically the critical concentration of suspended sediment for hyperpycnal flow formation is related to a reference concentration that does not take any of these processes into account the results show that the most important process in reducing this critical concentration is estuarine mixing which can reduce it by several orders of magnitude the other processes are relatively secondary but can all reduce the critical concentration by about one order of magnitude examples from rivers where hyperpycnal flows are known to form illustrate the influence of the described processes

revisiting late paleocene lower wilcox deltas gulf of mexico river dominated or mixed process deltas abstract spatial and temporal changes in physical depositional processes of shallow marine deltas affect facies distributions which are critical for reconstructing paleogeography and predicting reservoir heterogeneities the updated interpretation of the classical ancient river dominated lower wilcox delta in the gulf of mexico suggests more significant process variations than previously suggested the dominance of the storm wave process is indicated by wave ripple laminae and combined flow ripple laminae in the fair weather intervals and hummocky swaley cross stratification and low angle laminae in the storm beds however the relatively simple alternation of fair weather beds and storm beds is complicated by the presence of 1 normal and inversely graded siltstone to very fine grained sandstone beds suggesting hyperpycnites generated during the river flooding season 2 mud dominated heterolithics with delicate mud rhythmites suggesting tidal modulation between the storm events the storm wave generated succession with preservation of both river flood and tidal signals during fair weather condition represents regressive shoreline to shelf outbuilding the wave dominated delta or shoreface deposits are commonly truncated by fluvial dominated tide influenced distributary channels then overlain by tidal heterolithics and gradually open shelf deposits suggesting the development of small estuaries during transgressive phases of the wilcox shoreline the interpreted mixed process delta is linked to the last growth stage of the lower wilcox group prior to inundation of the texas shelf by thick marine mudstones its depositional setting was characterized by the widest lower wilcox shelf 50 km and a weakening sediment supply resulting in a stronger wave and tide influence relative to a weak fluvial influence this work thus provides a well constrained example of the complex interplay of fluvial wave and tidal currents in a process stratigraphy where decreasing river flux and relative sea level rise allowed wave reworking to become the dominant theme even though the same system has been previously interpreted as a classic river dominated delta many existing interpretations of ancient deltas thought to have mainly been controlled by a single process may need to be revisited and revised to take into account the natural spatial and temporal variability inherent to the shallow marine realm

thin bedded reservoir analogs in an ancient delta using terrestrial laser scanner and high resolution ground based hyperspectral cameras abstract ground based terrestrial laser scanning and hyperspectral sensors were used to image fine scale heterogeneity in outcrops of prodeltaic heterolithic facies of parasequence 6 of the cretaceous ferron notom delta in southern utah previous work shows that parasequence 6 is an upward coarsening fluvial dominated wave influenced deltaic deposit containing heterolithic thin bedded facies representing distal delta front and proximal prodelta environments primarily the thin beds have been interpreted as turbidites storm beds tempestites and hyperpycnites these deposits represent analogs for thin bedded unconventional pay zones that lie at the margins of conventional deltaic sandstone reservoirs the terrestrial laser scanner was used to create a centimeter to decimeter scale digital representation of the outcrops in three dimensions hyperspectral sensors record electromagnetic radiation reflected off the outcrops in 840 contiguous bands which were then used to generate a spectral signature for each pixel sampled the spectral signatures are a function of mineralogy chemistry surface alteration grain size and cements and were used to distinguish thin mudstones from sandstones within an interbedded succession at the base of a deltaic parasequence comparison between the spectral signatures recorded from the outcrop and those of reference materials and with previous facies architecture studies enables lithofacies to be identified and subsequently accurately mapped hyperspectral data are then draped over the terrestrial laser scanner model to generate a spatially accurate detailed three dimensional 3d geologic map of the heterogeneity approximately 100 m of outcrop was imaged laterally with the hyperspectral camera and terrestrial laser scanner on the previously mapped distal delta front and prodeltaic facies of parasequence 6 bed thickness data based on measurements made along depositional dip versus strike show that bed geometries are anisotropic reconstruction of the plan view geometry shows that the thin beds are lobate to elongate in plan view profile and extend over distances of about 1 km indicative of the dispersive waning sediment transport processes found in storm influenced fluvial dominated deltas the lobate geometry suggests that beds are laterally discontinuous with a width to thickness ratio on the order of

hydromagmatic eruption during the buildup of a triassic carbonate platform oman exotics eruptive style and associated deformations abstract oman exotics represent remnants of a triassic carbonate platform also named misfah formation several basaltic intrusions or lava flows were coeval with the carbonate platform buildup we present field observations related to one of these volcanic events including associated deformation of the host rocks and interaction of volcanism with the sedimentation these observations allow us to reconstruct the structure of the volcanic conduit and vent and the successive stages of the evolution of the eruption the initial ascent of magma probably occurred along on a normal fault related to gravity driven sliding towards the platform edge magma was first emplaced in a saucer shaped sill a few tens of meters below the sea floor this intrusion provided a decollement layer that may have sped up the gravity driven sliding opening fractures that brought sea water into contact with the magma hence triggering a hydromagmatic eruption eruption was followed by the collapse of the host limestones that formed a megabreccia infilling the eruptive vent and prohibiting further contact between sea water and magma most of the magma was emplaced at depth in two superposed small magmatic bodies 300 100 m and 200 50 m in sections respectively that replaced the host sediments and uplifted the overlying vent despite the shallow submarine setting this eruption produced a vent quite similar to sub aerial maars developed in soft substrate this emphasizes that the rheology of the substrate may be more important than the amount of water to control magma water interaction in hydromagmatic eruptions in an active carbonate platform like misfah formation during triassic times the early diagenesis of lime mud determined the mechanical comportment of the sediment at the time of eruption and especially the way it could be mixed with the magma and or slide into the vent

seismic passive earth pressure coefficients for sands by taking the failure surface as a combination of the arc of a logarithmic spiral and a straight line passive earth pressure coefficients in the presence of horizontal pseudostatic earthquake body forces have been computed for an inclined wall placed against cohesionless backfill material the presence of seismic forces induces a considerable reduction in the passive earth resistance the reduction increases with an increase in the magnitude of the earthquake acceleration the effect becomes more predominant for loose sands the obtained results compared well with those reported in the literature using curved failure surfaces however the results available in the literature on the basis of a planar failure surface are found to predict comparatively higher passive resistance

facies architecture and stratigraphic evolution of a river dominated delta front turonian ferron sandstone utah u s a abstract facies architectural analysis of a river dominated deltaic parasequence in the turonian ferron sandstone member near factory butte utah was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta five architectural elements were identified using 21 measured sections paleocurrent measurements and bedding diagrams they are 1 prodelta pf 2 frontal splay fs 3 detached distal bars dbs 4 distributary mouth bars dmbs and 5 terminal distributary channels tdcs lower in the parasequence detached bars consist of proximally located cross bedded and quasi parallel laminated subaqueous bars that onlap the delta front slope and grade distally into finer grained distal delta front splays these bars translate downstream in a progradational aggradational degradational trajectory and are overlapped by adjacent bars forming a bar assemblage these bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet deposition of these bars occurs at the delta front to prodelta chokepoint presumably due to flow deceleration the distal bar assemblage is capped by an extensive but discontinuous shale drape suggesting local abandonment upper facies assemblages show a distinct switch to predominantly cross bedded distributary mouth bars corresponding to a decrease in water depth an increase in friction and a likely transition into planar versus axial jets this is indicated by aggrading cross bedded distributary mouth bars that overlie the distal bars laterally the mouth bar deposits are interstratified with terminal distributary channel deposits with prominent scour surfaces at the base separate distributary channels and their bars coalesce ultimately to build the entire delta lobe the detached distal bars prograde locally west to northwest and lack fair weather wave formed sedimentary structures suggesting a local embayment along the regionally northeast prograding shoreline low levels of ichnofaunal diversity indicate a stressed river dominated setting at the base of the section frontal splays and detached bars dominated by storm driven river flood deposits are deposited over muddy prodelta facies detached bars are likely initiated about 500 meters distal of the distributary channel in water depths of 10 30 meters based on the thickness of the parasequence once this subaqueous platform is constructed by the distal bar assemblage more proximal distributary mouth bars fill the remaining shallow water accommodation as the system continues to shallow distributary channels override and scour the bars reflecting reduced accommodation

evaluating along strike variation using thin bedded facies analysis upper cretaceous ferron notom delta utah thin bedded delta front and prodelta facies of the upper cretaceous ferron notom delta complex near hanksville in southern utah usa show significant along strike facies variability primary initiation processes that form these thin beds include surge type turbidity currents hyperpycnal flows and storm surges the relative proportion of sedimentary structures generated by each of these depositional processes events has been calculated from a series of measured sedimentological sections within a single parasequence ps6 1 which is exposed continuously along depositional strike for each measured section sedimentological data including grain size lithology bedding thickness sedimentary structures and ichnological suites have been documented parasequence 6 1 shows a strong along strike variation with a wave dominated environment in the north passing abruptly into a fluvial dominated area then to an environment with varying degrees of fluvial and wave influence southward and back to a wave dominated environment further to the south east the lateral facies variations integrated with palaeocurrent data indicate that parasequence 6 1 is deposited as a storm dominated symmetrical delta with a large river dominated bayhead system linked to an updip fluvial feeder valley this article indicates that it is practical to quantify the relative importance of depositional processes and determine the along strike variation within an ancient delta system using thin bedded facies analysis the wide range of vertical stratification and grading sequences present in these event beds also allows construction of conceptual models of deposition from turbidity currents i e surge type turbidity currents and hyperpycnal flows and storm surges and shows that there are significant interactions and linkages of these often paired processes

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

geomorphological and sequence stratigraphic variability in wave dominated shoreface shelf parasequences physical stratigraphy within shoreface shelf parasequences contains a detailed but virtually unstudied record of shallow marine processes over a range of historical and geological timescales using high quality outcrop data sets it is possible to reconstruct ancient shoreface shelf morphology from clinoform surfaces and to track the evolving morphology of the ancient shoreface shelf our results suggest that shoreface shelf morphology varied considerably in response to processes that operate over a range of timescales 1 individual clinoform surfaces form as a result of enhanced wave scour and or sediment starvation which may be driven by minor fluctuations in relative sea level sediment supply and or wave climate over short timescales 10 1 10 3 years these external controls cannot be distinguished in vertical facies successions but may potentially be differentiated by the resulting clinoform geometries 2 clinoform geometry and distribution changes systematically within a single parasequence reflecting the cycle in sea level and or sediment supply that produced the parasequence 10 2 10 5 years these changes record steepening of the shoreface shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation modern shorefaces are not representative of this stratigraphic variability 3 clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shore face progradation 10 5 10 8 years these controls determine the external dimensions of the parasequence

hamrat duru group revised stratigraphy of a mesozoic deep water passive margin in the oman mountains the stratigraphy of the hawasina complex is redefined and rationalized to conform with standard stratigraphical nomenclature previously proposed tectono stratigraphical units are abandoned in favour of a system that relies on the lateral correlation of lithofacies between structural units to this end the dibba dhera wahrah and al ayn formations are incorporated into an expanded hamrat duru group this group is divided into five formations the zulla guweyza sandstone guweyza limestone sid r and nayid and spans triassic to mid cretaceous cenomanian time it locally passes up into the syn orogenic sediments of the riyamah member of the muti formation the nomenclature of the deeper water chert dominated formations is left unaltered

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

estimating original thickness and extent of the semail ophiolite in the eastern oman mountains by paleothermal indicators abstract the oman mountains preserve permo mesozoic sedimentary rocks of the arabian passive margin that were overridden during late cretaceous time by deep water sediments of the hawasina units and by the semail ophiolite a portion of the neo tethyan oceanic crust and upper mantle passive margin sequences are exposed in the jabal akhdar culmination jac and in the jabal salakh range at the oman mountains thrust front samples of these sequences were investigated by x ray diffraction of the clay size fraction to evaluate the thermal evolution of the subophiolite rocks and estimate the thickness and extent of the obducted ophiolites the sedimentary succession from the northern flank of the jac shows a clay mineral assemblage characterized by long range ordered mixed layer i s with an illite content between 85 and 92 and the occurrence of pyrophyllite and or paragonite suggesting maximum paleotemperatures between 150 and 200 c in deep diagenetic conditions on the southern flank of the jac temperature dependent clay minerals indicate maximum paleotemperatures ranging between 120 and 150 c indicating a reduced ophiolite thickness towards the south ooid strain analyses of the subophiolite rocks from the northern flank of jac show a component of flattening and stretching in the z x plane as a result of plastic deformation and pressure solution on the southern flank such ductile deformation is absent suggesting a brittle rheology for the subophiolite carbonates and a reduced overburden 1d thermal modeling reveals that the sub ophiolite units of the jac were overthrust by 4 5 km thick semail ophiolite and hawasina units during the coniacian and exhumed since the campanian the subophiolite rocks of the jabal salakh range were buried under 1 35 km of synobduction clastics and overthrust by 2 km thick hawasina units suggesting a decrease of the thickness of allochthonous units from ne to sw consistent with strain analysis and their direction of emplacement

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

basic building blocks and process variability of a cretaceous delta internal facies architecture reveals a more dynamic interaction of river wave and tidal processes than is indicated by external shape abstract although delta building processes and the resultant facies and facies associations have been studied for over a century there remains a lack of well documented facies architectural studies of ancient deltas in this study architectural element analysis is applied to determine the basic building blocks of a cretaceous delta at the top of the upper turonian wall creek member exposed along the western flanks of the powder river basin wyoming we document the bed scale basic building blocks of this ancient delta and show them in the context of their facies and stratal variability and their hierarchical spatial arrangement within a single deltaic parasequence we also test the idea that external sand body shape may not reflect the internal facies complexity as has recently been suggested in studies of several modern deltas including the burdekin in australia the brazos in the gulf of mexico and the baram trusan in borneo five orders of bounding surfaces separate six facies architectural elements in the prodelta and delta front deposits these elements are prodelta fines pf frontal splay fs channel ch storm sheet ss tidally modulated deposit tm and bar accretion ba seasonal to decadal river floods are thought to represent the main building phases of the delta producing channels bars and frontal splay elements during intervening periods the delta was reworked by waves storms and tides producing tidally modulated and storm sheet elements due to the complex interactions of river effluents with waves storms and tides the delta is interpreted as mixed influenced regional sandstone isolith facies and paleocurrent maps help to reconstruct the paleogeography and show how the various architectural elements varied across the delta front the channels bars frontal splays and tidally modulated elements are found only near the distributary mouth whereas the storm sheets occur extensively away from the distributary mouth the plan view morphology of the studied delta shows a smooth fronted arcuate to cuspate shape which should indicate wave dominance in contrast our analysis of the internal facies architecture shows that the delta was constructed rapidly during major river floods with significant tidal reworking additional outcrop mapping shows that storm wave reworked sands are attached to the flanks of the system previously published delta models predict incorrectly that the tidal reworking of a river flood dominated system should result in a more bird foot shape versus the lobate geometry that is actually mapped our analysis of internal facies versus external shape matches similar observations on several modern deltas and suggests that external shape is a poor indicator of internal facies complexity

intra parasequence architecture of an interpreted asymmetrical wave dominated delta although modern wave dominated shorelines exhibit complex geomorphologies their ancient counterparts are typically described in terms of shoreface shelf parasequences with a simple internal architecture this discrepancy can lead to poor discrimination between and incorrect identification of different types of wave dominated shoreline in the stratigraphic record documented in this paper are the variability in facies characteristics high resolution stratigraphic architecture and interpreted palaeo geomorphology within a single parasequence that is interpreted to record the advance of an ancient asymmetrical wave dominated delta the standardville ab1 parasequence of the aberdeen member blackhawk formation is exposed in the book cliffs of central utah usa this parasequence and four others in the aberdeen member record the eastward progradation of north south trending wave dominated shorelines within the standardville ab1 parasequence distal wave dominated shoreface shelf deposits in the eastern part of the study area are overlain across a downlap surface by southward prograding fluvial dominated delta front deposits which have previously been assigned to a separate stranded lowstand parasequence formed by a significant allogenic change in relative sea level high resolution stratigraphic analysis of these deposits reveals that they are instead more likely to record a single episode of shoreline progradation characterized by alternating periods of normal regressive and forced regressive shoreline trajectory because of minor cyclical fluctuations in relative sea level interpreted normal regressive shoreline trajectories within the wave dominated shoreface shelf deposits are marked by aggradational stacking of bedsets bounded by non depositional discontinuity surfaces interpreted forced regressive shoreline trajectories in the same deposits are characterized by shallow incision of fluvial distributary channels and strongly progradational stacking of bedsets bounded by erosional discontinuity surfaces that record enhanced wave base scour fluvial dominated delta front deposits most probably record the regression of a lobate delta parallel to the regional shoreline into an embayment that was sheltered from wave influence wave dominated shoreface shelf and fluvial dominated delta front deposits occur within the same parasequence and their interpretation as the respective updrift and downdrift flanks of a single asymmetrical wave dominated delta that periodically shifted its position provides the most straightforward explanation of the distribution and relative orientation of these two deposit types

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

severe storms during earth history although severe storms are recognized as important agents in sediment transport many questions remain to demonstrate genetic links between specific sedimentary structures and textures and proposed generative agents a detailed physically based consideration of climatic and geographic controls on the generation and distribution of severe storms is presented on the basis of modern observations physical processes deduced from these observations and climate model experiments using past geographies the results suggest that simple latitudinal distinctions for storm type severe winter storm or hurricane or inference from estimates of global warmth are not adequate to consider genetic links for storm related deposits climate and geography produce substantial variability in storm generation rates and in storm distributions for example geography may inhibit poleward penetration of hurricanes or enhance a broad latitudinal distribution the record of tropical sea surface temperatures indicates that values may have been below hurricane generation thresholds during the eocene and glacial stages land sea distribution and associated thermal contrasts strongly influence the distribution and intensity of winter storms the results from models can be compared favorably with observations of probable storm sedimentation

fluid rock interactions associated with regional tectonics and basin evolution an integrated approach consisting of fracture analysis petrography carbon oxygen and strontium isotope analyses as well as fluid inclusion micro thermometry led to a better understanding of the evolution of fluid rock interactions and diagenesis of the upper permian to upper triassic carbonates of the united arab emirates the deposited carbonates were first marked by extensive early dolomitization during progressive burial the carbonates were affected by dolomite recrystallization as well as precipitation of vug and fracture filling dolomite quartz and calcite cements after considerable burial during the middle cretaceous sub vertical north south oriented fractures f1 were cemented by dolomite derived from mesosaline to hypersaline fluids upon the late cretaceous maximum burial and ophiolite obduction sub vertical east west fractures f2 were cemented by dolomite dc2 and saddle dolomite ds derived from hot highly saline fluids then minor quartz cement has precipitated in fractures from hydrothermal brines fluid inclusion analyses of the various diagenetic phases imply the involvement of increasingly hot 200 degrees c saline brines 20 to 23 nacl eq through one dimensional burial history numerical modelling the maximum temperatures reached by the studied rocks are estimated to be in the range of 160 to 200 degrees c tectonically driven flux of hot fluids and associated diagenetic products are interpreted to have initiated during the late cretaceous maximum burial and lasted until the oligocene miocene compressional tectonics and related uplift the circulation of such hydrothermal brines led to partial dissolution of dolomites dc2 and ds and to precipitation of hydrothermal calcite c1 in new mainly oriented north south f3 and pre existing reactivated fractures the integration of the obtained data confirms that the diagenetic evolution was controlled primarily by the interplay of the burial thermal evolution of the basin and the regional tectonic history hence this contribution highlights the impacts of regional tectonics and basin history on diagenetic processes which may subsequently affect reservoir properties

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

identification characterization and statistical analysis of mudstone aggregate clasts cretaceous carlile formation central alberta canada abstract while clastic mudstones and shale were traditionally interpreted to have been deposited in quiet water settings recent flume experiments and studies have shown that mud can be transported in and deposited by traction currents as migrating ripples of mud aggregates despite these recent advances mud aggregates have rarely been adequately described in the rock record these mud aggregates and the sedimentary structures they form in mudstone successions are difficult to observe in the rock record due to compaction which often obliterates the aggregates and flattens bedforms this paper documents unambiguously identifiable sand sized mudstone aggregates in thin sections and sem transported in traction and deposited in a series of prograding clinothems these aggregates were sufficiently indurated to locally preserve shelter porosity significantly improving the hydrocarbon reservoir properties grain size analysis of the aggregates was performed on thin sections as well as disaggregated samples measured by a laser diffraction grain size analyzer for comparison these analyses showed that sand sized aggregates often comprise more than half of the sediment volume while the clay rich composition of the carlile formation would suggest that it is a mudstone statistical analysis of these grain size measurements show that it could alternatively be described as a silty sandstone these findings potentially change how we think about mudstone classification fine grained sedimentation and mudstone dominated petroleum reservoirs

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

filter or conveyor establishing relationships between clinoform rollover trajectory sedimentary process regime and grain character within intrashelf clinothems offshore new jersey u s a abstract clinoform geometries and trajectories are widely used to predict the spatial and temporal evolution of sand distribution but most analytical approaches underplay the significance of topset and shelf process regime in determining how and when sediment is conveyed downdip or stored on the continental shelf we present an integrated study of clinoform rollover trajectory and detailed grain character analysis to assess the role of topset process regime in determining sand distribution and sediment character across clinothems this study targets the topset foreset and bottomset deposits of four successive miocene intrashelf clinothem sequences which represent deposition under either river dominated or wave dominated conditions seismic reflection data was combined with core analysis and grain character data derived from 664 samples collected from three cored research boreholes in river dominated clinothems the transfer of coarse grained sediment occurs under both rising and flat to falling clinoform rollover trajectories suggesting that process regime is more important in determining sediment delivery than clinoform trajectory river dominated systems are effective conveyors of sediment into deeper water wave dominated clinothems deposited exclusively under rising clinoform rollover trajectories largely retain sand within topset and foreset deposits wave dominated systems are effective sediment filters notably deposition under either river or wave dominated topset process regimes results in quantifiable differences in grain character attributes along clinoform profiles sediments in river dominated systems are coarser less well rounded and more poorly sorted and show greater intersequence and intrasequence variability than those in wave dominated systems prediction of sediment character is more challenging in river dominated systems this study highlights the need for caution when attempting to predict downdip sand distribution from clinoform trajectory alone and provides a novel perspective into downdip grain character profiles under end member topset process regime conditions the results of this study can be used to better constrain sediment grain size and grain shape distributions in process based forward models and have widespread applications in prediction of reservoir quality in both frontier and mature hydrocarbon basins

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

mesozoic early tertiary passive margin evolution of the pindos ocean nw peloponnese greece abstract sediment starved deep water slope basin facies of passive margins are of particular interest as they record an interplay of processes including plate tectonic evolution elastic sediment input pelagic deposition and relative sea level change in the past insights have come from deep sea drilling of non emplaced passive margins e g eastern u s a and from preserved sequences within sutured units e g the tethyan and iapetus orogenic belts deep water passive margin successions discussed here represent an excellent example of a relatively sediment starved slope basin setting related to the margin of a microcontinent within the neotethyan ocean in the eastern mediterranean region lithologies are preserved as a series of thrust sheets formed during suturing of the neotethys ocean thrusting resulted in regular in sequence thrusting such that the original slope margin setting can be restored with confidence compared to other tethyan passive continental margin abyssal successions e g oman these sedimentary rocks retain remarkable structural coherence allowing exceptionally detailed three dimensional reconstructions of facies patterns and palaeoceanographic conditions the sedimentary successions belong to the pindos zone of western greece pindos group and comprise deep water carbonate siliciclastic and siliceous rocks ranging in age from late triassic to eocene these rocks accumulated along the western margin of a small neotethyan oceanic basin i e pindos ocean separating the continental blocks of adria apulia and pelagonia the oldest sediments comprise disrupted siliciclastic turbidites largely derived from a metamorphic source to the west and deposited on young oceanic basement from the late triassic to latest maastrichtian variable thicknesses of hemipelagic carbonate and proximal carbonate debris flows accumulated in westerly areas while mainly hemipelagic carbonate and more distal calciturbidite were deposited further east this pattern was interrupted by an extended period of siliceous radiolarian dominated sedimentation during the aalenian to tithonian jurassic from latest maastrichtian onwards progressive closure of the pindos oceanic basin is recorded by a gradual change in sediment composition from dominantly carbonate deposition supplied from the gavrovo tripolitza carbonate platform to the west to siliciclastic sediment derived from the north and east during the eocene oligocene eastward subduction of the pindos ocean resulted in deep sea sedimentary lithologies being detached from their oceanic igneous basement as an accretionary prism and emplaced westwards onto the adjacent carbonate platform ending up as a series of thin skinned thrust sheets

sequence of thrusting and origin of culminations in the northern and central oman mountains abstract detailed mapping and structural analysis of three large scale culminations sumeini and asjudi half windows and haybi hawasina window in the oman mountains shows a considerably more complex history of deformation than a simple foreland or downward sequence of thrust development early thrusting processes tended to create a regular stacking order of imbricate slices and major thrust sheets complying with the rules of thrust propagation assembled progressively downwards and forwards in the direction of translation out of sequence thrusts can also be demonstrated in places by truncation of footwall structures folds imbricate slices etc gross strain differences between thrust sheets downward facing structures in footwall units and elimination of thrust sheets beneath late stage thrusts frequently cut up section through the previously assembled stack putting previously younger lower thrust sheets over previously older higher ones many of the culminations in the northern and central oman mountains were formed by ramping associated with this late stage leap frog rethrusting event

structure and evolution of the passive margin of the eastern tethys abstract an extensive passive margin was formed in the triassic along the periphery of arabia including the tauric carbonate platform this event is related to the opening of the mesozoic tethys when a number of microcontinents split off from gondwana triassic extension and continental rifting resulted in the formation of a structural pattern which is uniform from the dinarides to oman it includes the following elements 1 1 shelf 2 2 continental slope 3 3 deep basin probably with a floor of attenuated sialic crust 4 4 inner carbonate platform in the jurassic cretaceous stable conditions prevailed influenced only by eustatic oscillations of the sea level turbidites accumulated on the continental rise while cherts and radiolarites were deposited in the deep basins hawasina pichakun antalya pindus below the ccd level sedimentation on the shelf was controlled by north northeast transverse tectonic elements which also continued across the passive margin dividing it into a number of segments collision with an island arc led to obduction of the oceanic crust deformation of the passive margin and overthrusting of its sedimentary cover onto the arabian shelf obduction and deformation lasted for about 10 m y and created a new tectonic pattern with concentric structural zones surrounding the arabian promontory these zones include 1 1 the flysch basin a remnant of the closing tethys 2 2 an uplift a site of periodical emergence and erosion corresponding to the frontal part of the ophiolitic nappes 3 3 the border furrow a depocenter of low energy calcareous marls 4 4 the arabian shield constantly emerged during the tertiary tectonic deformation of these zones caused by the collision of arabia with eurasia began prior to the early miocene and it is still going on data on afghanistan demonstrate that its central part the gelmend argandab and kabul blocks belonged during the paleozoic and early mesozoic to the continental shelf of india

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions

perturbations in the carbon cycle during the carnian humid episode carbonate carbon isotope records from southwestern china and northern oman the carnian humid episode is an interval of prominent climatic changes in the late triassic we studied the carbon isotope 13c geochemistry of carbonates from sections in southwestern china and northern oman 13c records from the yongyue section western guizhou south china show a progressive positive shift from 1 4 to 2 8 in the early to middle julian 1 substage this positive trend is followed by a swift negative shift of c 4 2 from 2 8 to 1 4 in the julian 2 substage 13c from the wadi mayhah section northern oman shows a positive shift from 2 2 to 2 8 in the julian 1 substage followed by a negative shift of c 3 2 from 2 8 to 0 3 in the julian 2 substage the 13c records from the two study sections generally correlate well with each other as well as with published records pointing to a considerable input of isotopically light carbon starting in the late julian 1 substage such a large amount of light carbon probably derived from direct degassing and the sediment sill contact metamorphism of the panthalassan wrangellia large igneous province and contemporary tethyan volcanism the voluminous volcanogenic greenhouse gases probably contributed to the warming pulse in the middle carnian thus the dry wet climatic transition during the carnian humid episode is best interpreted as a warm climate driven intensification of the activities of the atmospheric circulation and hydrological cycle