the paleogeography of paleozoic and mesozoic storm depositional systems a reply we welcome discussion of our paper on the paleogeography of storm systems but can demonstrate that the major points raised in duke s discussion were considered and discussed already in our original text let s take his points in turn 1 alternative mechanisms for formation of hummocky stratification duke objects to some of the alternative modes of origin which we suggested as possibilities only one of these dealt with stratification within dome dunes readers familiar with mckee s 1979 p 98 102 his figs 57 and 58 work should not experience any difficulty observing similarities between bedding in the upper part of dome dunes and hummocky stratification we did not state that the large angle stratification at the core of the dome dune was hummocky stratification and duke s remarks

the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

energy balance constraints on 18o based paleo sea surface temperature estimates oxygen isotope based paleo sea surface temperature estimates from the tropics consistently indicate values well below that of the present 27 c with some estimates from the middle tertiary reaching as low as 15 c using an energy balance model allows a test of several scenarios for producing and maintaining such cool tropical temperatures of particular interest are 1 increased cloud cover 2 increased zonal wind speed and 3 increased poleward energy transport the latter is the most likely process since enhanced poleward energy transport would lead to warmer poles a point which agrees well with high latitude geological and paleontological evidence however none of the scenarios tested could provide the degree of equatorial cooling needed to be in agreement with paleotemperature estimates in summary published estimates of cool equatorial surface temperatures must be questioned since they cannot be supported by energy balance arguments or geological evidence

the fujita ziegler model a new semi quantitative technique for estimating paleoclimate from paleogeographic maps abstract the fujita ziegler model combines approaches developed by t t fujita and a m ziegler of the university of chicago to produce semi quantitative retrodictions of paleoclimates based on paleogeographic maps that include the sizes and positions of land and sea areas and the positions and extents of upland areas based on such paleogeographic maps the fujita model extrapolates past values of surface air pressure from present day relationships among air pressure land area latitude and season zonal mean air pressure for each latitude and season is hypothesized to depend on the amount of land area at that latitude and deviations from this mean over major bodies of land or water are hypothesized to depend on the area of the relevant body at that latitude fujita diagrams both illustrate these hypottheses and permit application of the model to paleogeographic maps surface air pressure maps based on these diagrams can be used to qualitatively retrodict seasonal windflow patterns and ocean currents tests of the fujita model on the recent geography suggest that most major air pressure cells are positioned accurately and that the values at the centers of cells are within 2 3 mb of measured values at low and middle latitudes and within 5 mb at the poles because the fujita model extrapolates from a partly glaciated world its retrodictions for ice free times are suspect particularly near the poles the ziegler model infers the areal and seasonal distribution of precipitation from reconstructed patterns of winds and ocean currents on paleogeographic maps retrodictions are based on 1 mechanisms that lift air including global patterns of atmospheric circulation intertropical convergence zone regional storm systems extratropical cyclones and relatively local lifting mechanisms orographic effects land sea breezes and summer convective thunderstorms 2 sources of moist air i e bodies of warm water upwind and 3 mechanisms that interfere with convection e g upwelling zones and trade wind inversions tests of the ziegler model on the recent geography accurately retrodicted seasonal precipitation at low and middle latitudes but did less well near the poles comparison with maps of the seasonality of precipitation in the recent shows that the model accurately retrodicted most ever dry and ever dry regions results emphasize the importance of accurately retrodicting the effects of orography moisture source and upwelling zones on precipitation

a facies model for internalites internal wave deposits on a gently sloping carbonate ramp upper jurassic ricla ne spain abstract internal waves are waves that propagate along the pycnocline the interface between two density stratified fluids even though internal waves are ubiquitous in oceans and lakes their impact in the sedimentary record has remained largely unrecognized internal waves can remobilize the sediment from the depth at which the internal waves break onto the sea floor in shelf or ramp settings internal wave deposits internalites have to be distinguished from tempestites while in slope and deeper settings internalites require distinction from turbidites the upper kimmeridgian carbonate ramp succession cropping out near ricla ne spain provides some key evidence to differentiate the depositional processes induced by breaking internal waves from those related to surface storm waves sandy oolitic grainstone eventites previously interpreted as tempestites contain evidence of reworking by turbulent events related to breaking internal waves underlying rationale are 1 they occur in distal mid ramp position detached from the coeval shallow water successions 2 they do not have the characteristic coarsening and thickening upward trend of storm deposits 3 they gradually thin out to disappear both up dip and down dip interbedded with mid ramp lime mudstones and 4 they show little or no erosion towards the shallower areas a facies model for internalites produced by two sediment populations sand and mud on a gently sloping carbonate ramp is proposed the individual internalites occurring at ricla include several architectural elements sequentially organized in dip direction which can be related to the flows associated with breaking internal waves erosion in the breaker zone swash run up and tractive backwash flow individual internalites stack with down and up slope shingling configuration in dm thick packages thought to reflect the up slope and down slope migration of the breaker zone in turn related to depth variations of the palaeo pycnocline packages occur in dm to m thick clusters suggested to reflect changes in sediment supply and or variations in water stratification affecting the energy of internal waves

shallow water and sub storm base deposition of lewis shale in cretaceous western interior seaway south central wyoming shallow and deep water below storm base clastics of the lewis shale were deposited in south central wyoming during a part of the late cretaceous maestrichtian core log and outcrop data indicate that the lewis shale consists of a thin transgressive marine shale overlain by a thicker coarser progradational interval the initial transgression of the lewis sea occurred during the maestrichtian baculites eliasi range and the maximum westward and northward extent of submergence was in areas of the rock springs and wind river uplifts the sea in which the lewis shale was deposited opened eastward into the north american western interior seaway shale in the lowermost lewis is black carbonaceous bioturbated and commonly contains shell debris and was deposited in hallow water the central basin floor changed from shallow to sub storm wave and sub storm current depths seemingly in response to eustatic sea level rise and coeval tectonic subsidence deepening of the basin began at the time of dominance of baculites eliasi to b grandis maestrichtian sandstone and shale of the upper lewis shale are mostly related to distributary systems that entered the basin first from the northeast during b grandis to b clinolobatus range and later possibly from the south during b clinolobatus southwest progradation from a northeastern delta suggests significant uplift in the wind river upthrust area concurrent with lewis sedimentation many hydrocarbon producing sandstones in the lewis shale are thickly bedded and massive and some show fluid escape structures thin sandstones are typically characterized by grading bouma sequences and sole markings turbidity currents are believed to be responsible for deposition of all these sandstones unburrowed shale and shale containing burrows made by a restricted infauna are interbedded with reservoir sandstones at wamsutter field the shale is interpreted to indicate anaerobic to dysaerobic conditions and water depths of 500 650 ft 150 200 m or more

stratal architecture and platform evolution of an early frasnian syn tectonic carbonate platform canning basin australia facies architecture and platform evolution of an early frasnian reef complex in the northern canning basin of north western australia were strongly controlled by syn depositional faulting during a phase of basin extension the margin attached hull platform developed on a fault block of precambrian basement with accommodation largely generated by movement along the mount elma fault zone recognition of major subaerial exposure and flooding surfaces in the hull platform from outcrop and drillcore has enabled comparison of facies associations within a temporal framework and led to identification of three stages of platform evolution stage 1 records initial ramp development on the hangingwall dip slope with predominantly deep subtidal conditions that prevented any cyclic facies arrangements this stage is characterised by basal siliciclastic deposits and a major deepening upward facies pattern that is capped by a sequence boundary towards the footwall north west and a major flooding surface towards the hangingwall stage 2 reflects the bulk of platform aggradation significant platform growth towards the hangingwall and the development of reef margins and cyclic facies arrangements thickening of this stage towards the hangingwall indicates that accommodation was generated by rotation of the fault block and overlying platform stage 3 records a major flooding and backstep of the platform margin the hull platform illustrates important elements of margin attached carbonate platforms in a half graben setting including i prominent but limited coarse siliciclastic input that does not have a major detrimental effect on carbonate production near the rift margin in arid to semi arid settings ii wedge shaped accommodation created by syn depositional rotation of fault blocks and tilting of the hangingwall dip slope resulting in shallow water facies and subaerial exposure up dip of the rotational axis and deeper water facies down dip and iii evolution of a ramp to rimmed shelf coincident with a sequence boundary flooding surface that is accelerated by tilting of the hangingwall dip slope during fault block rotation

spatial heterogeneities in a bioclastic shoal outcrop reservoir analogue architectural cyclical and diagenetic controls on lateral pore distribution abstract the distribution of pores in carbonate rocks is controlled by the synergy of different factors such as the initial sediment environment processes and diagenesis prediction of the texture related pore distribution to evaluate reservoir quality is still a challenging task in geothermal and hydrocarbon exploration in order to degrease these uncertainties 3d facies models are produced on the basis of facies types and their relationship to petrophysical properties however several studies have shown that these relationships are often rather controlled by diagenesis that is often described as a sequence for an entire reservoir two outcrops as part of the same bioclastic shoal reservoir analogue present two different architectural styles i layer cake architecture and ii high angle foreset architecture in order to identify petrophysical trends and related controlling factors both outcrops were mapped and studied in detail based on the investigation of 41 thin sections microfacies types were defined and diagenesis was analysed in addition permeability porosity was measured and pores were digitally characterized although both outcrop successions studied are associated with the same reservoir interval varied architecture leads to fundamental differences in the porosity permeability distribution petrophysical trends in the layer cake architecture are mainly controlled by cyclicity and channel features compared to layer cake architecture trends in the high angle foreset architecture are dominantly controlled by the depositional environment both outcrops show differences in their diagenesis while layer cake architecture suffered the entire sequence large parts of the high angle foreset architecture were not influenced by late burial and telogenetic processes as a consequence primary porosity is persevered within the high angle foreset architecture in addition results of this investigation indicate that primary porosity has a bigger influence on good permeability values compared to telogenetic associated vug enhancement this investigation therefore demonstrates that individual carbonate reservoirs can suffer different diagenetic pathways moreover the study highlights the potential of outcrop studies to improve the principal understanding of fundamental trends within potential subsurface reservoirs

a comparison of gcm simulated cretaceous greenhouse and icehouse climates implications for the sedimentary record abstract two general circulation model simulations of mid cretaceous climate are presented one representing a greenhouse and the other representing an icehouse world through a comparison of greenhouse and icehouse palaeoclimates differences in processes which are intrinsically linked with climate such as continental weathering and snow and ice accumulation may be observed a number of conspicuous and discrete climatic differences can be seen between the two simulations which may be translated into a number of identifiable signatures in the sedimentary record the climate at mid high latitudes in the icehouse simulation was more arid than the greenhouse simulation and could result in deposition of smectite dominated clay suites in contrast the climate of low latitudes of the icehouse simulation resulted in a moister climate than the greenhouse simulation which could affect the weathering regimes and result in deposition of kaolin dominated clay suites thus cool climate episodes do not necessarily result in a global increase in aridity the icehouse simulation predicts a small permanent icecap at high latitudes which could account for the origin of dropstones in marine sediments furthermore a sea level fall as a consequence of an accumulation of ice at high latitudes may also increase continentality and surface albedo which may also contribute to the causes of the drier climate at high latitudes hurricanes are likely to be more frequent in greenhouse than icehouse climates mid latitude depressions also important for generating storms are likely to be both intense and frequent during icehouse and greenhouse periods of the middle cretaceous

a palaeoclimate model for the kimmeridgian abstract most attempts at using numerical general circulation model gcm to simulate mesozoic climates have studied the late cretaceous and have focused on the enigmaof apparently equable global climates however this climate regime lasted throughout the mesozoic and it is of interest to examine other periods we present the results of an integration for the late jurassic using a relatively detailed and high resolution model there is generally good agreement between the model climate and the existing geological data in particular the simulation predicts no permanent ice cover near either pole arid conditions over the southwestern usa seasonally arid climate over southern europe and winter storminess over europe and australia however the surface temperatures over siberia and southeastern gondwanaland drop below zero for a significant part of the winter

oligocene storm induced lacustrine deposits in the yaxi area of the jiuxi basin northeastern margin of the tibetan plateau abstract storm induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow thin bedded sandstone siltstone and interlayered mudstone deposits of the oligocene jianquanzi member in the yaxi area of the jiuxi basin along the northeastern margin of the tibetan plateau were formed by shallow lacustrine storm generated flows petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub mature to immature based on investigation of drill cores six storm deposit lithofacies are identified including massive or graded sandstone parallel and trough cross bedded sandstones hummocky cross stratified sandstone wave rippled sandstone and siltstone massive or horizontal bedded mudstone and structurally deformed sandstone and mudstone in a vertical succession these lithofacies occur as three fining upward lithofacies associations each of which represents different architectural elements and depositional processes of proximal to distal storm deposits the relatively coarse proximal architectural element is formed by strong density flows and unidirectional dominated combined flows the transitional architectural element is dominated by unidirectional and oscillatory dominated combined flows to pure oscillatory flows resembling tb e divisions of the classic bouma sequence the relatively fine distal architectural element is dominated by unidirectional dominated combined flows with a very weak oscillatory flow component the origin of storms responsible for these deposits is attributed to asian winter monsoons associated with the paleoclimatic and paleogeographic setting

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

magnesian andesites from the island of skyros greece geochemistry and regional significance high magnesian andesites outcrop in a subvolcanic complex in the island of skyros in the central aegean sea mineralogical indicators of this high mg content include bronzite and clinopyroxene phenocrysts the former with high cr 2 o 3 and some phlogopite plagioclase oligoclase andesine and fe ti oxides were late phases to appear at the liquidus whole rock geochemistry shows trace element features similar to those of subduction related rocks radiometric dating indicates an early serravallian middle miocene age approximately synchronous with the onset of post orogenic rifting and extension of the aegean sea this tectonic setting is consistent with an origin by adiabatic decompression of mantle peridotite previously modified by subduction related fluids

comparative sedimentology of shelf carbonates of the middle ordovician st paul group central appalachians abstract observations of present day environments are commonly used to aid in the interpretation of ancient sedimentary sequences this approach is used to determine the paleoclimate and depositional processes operating during formation of the limestones and dolostones of the lower middle ordovician st paul group row park and new market formations of maryland and southern pennsylvania a 200 m thick carbonate platform deposit within the group six facies defined by suites of sedimentary structures faunal assemblages and early diagenetic features are arranged in a large scale regressive transgressive sequence these consist of facies i lower burrowed peloidal facies facies ii burrowed skeletal facies facies iii lower laminated peloidal facies facies iv stromatolitic peloidal facies facies v upper laminated peloidal facies and facies vi upper burrowed peloidal facies a comparison of the st paul group deposits with those of the modern peritidal carbonate environments of shark bay western australia the abu dhabi and trucial coast areas of the persian gulf and andros island and the great bahama bank reveals 1 an overall similarity in features between the st paul group and the sediments of andros island and the great bahama bank and 2 a dissimilarity between those two deposits and the sediments of shark bay western australia and shoreline areas of the persian gulf for example the supratidal zones of the latter two typically contain evaporite minerals e g gypsum and anhydrite whereas the supratidal deposits of andros island and the st paul group are freshwater algal marsh and lake sediments the subtidal deposits of shark bay and the persian gulf generally are mechanically layered skeletal sand the subtidal deposits of the great bahama bank and the st paul group are bioturbated peloidal micrites the st paul group and the great bahama bank deposits are similar on a facies scale down to fine details observed microscopically bahamian modern analogs of the facies of the st paul group are for facies i shallow restricted bank and subtidal pond environments for facies ii a normal marine subtidal environment similar to the shoals which rim parts of the great bahama bank for facies iii and v tidal channel levee pond and marsh subenvironments of the channeled belt environment hardie and garrett 1977 for facies iv levee marsh and freshwater lake subenvironments of the interior of andros island and for the facies vi a semirestricted subtidal bank environment based on the features of the st paul group and by analogy with modern deposits the st paul group was deposited in a low energy rainy environment where deposition was controlled by storm processes many facies display penecontemporaneous marine cements and dissolution features

storm deposits and storm generated coarse carbonate breccias on a pelagic outer shelf south east basin france uppermost jurassic limestones of the south east basin france are organized into four facies associations that were deposited in four distinct zones 1 peritidal lagoonal limestones 2 bioclastic and reefal limestones 3 pelagic lime mudstones 4 lime mudstones calcarenites coarse breccias calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave induced combined flow in subzone 4a both vertical and lateral transitions from lime mudstone calcarenite to breccia indicate in situ brecciation under wave cyclic loading breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor deposits in subzone 4a record relatively long periods 400 kyr of sedimentation below wave base alternating with periods of deposition under wave induced currents and periods of in situ deformation in this zone storm waves were attenuated by wave sediment interaction and wave energy was absorbed by the deformation of soft sediment with reference to present day wave attenuation water depths in this zone ranged between 50 and 80 m landwards of the attenuation zone in zone 3 storm waves were reduced to fair weather wave heights storm wave base was not horizontal and became shallower landwards as a consequence water depth and wave energy were not linearly related on a small area of the seaward edge of subzone 4a cobbles were removed by traction currents and redeposited in subzone 4b there they formed a 100 m thick wedge which prograded over 3 km and was built up by the stacking of 5 to 20 m thick cross stratified sets of coarse breccia this wedge records the transport and redeposition of cobbles by a high velocity unidirectional component of a combined flow the increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel like structure of the downwelling in the gulf formed by the basin in more distal subzone 4c the hydrodynamic effect of wave induced currents was quasi permanent and brecciation by wave sediment interaction occurred only episodically this indicates that seawards of the attenuation zone hydrodynamic storm wave base was deeper than mechanical storm wave base uppermost jurassic carbonates were deposited and soft sediment deformed on a hurricane dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration located seawards of a zone of sedimentation below wave base

paleogeographic orientation of the sino korean plate based on evidence for a prevailing silurian wind field abstract the regional geology of southern inner mongolia records relationships between an upper silurian coastline and a small island on what was formerly the continental shelf of the sino korean plate north china block in both cases rocky shorelines are defined by unconformities between strata of ludlow age in the xibiehe formation and underlying igneous rocks of ordovician age the paleoisland occurs near bater obo about 50 km south of the chinese mongolian border the diorite core of this geological inlier is oriented on an axis n 55 e a simple dichotomy of exposed windward versus sheltered leeward environments accounts for contrasting carbonate facies on the flanks of the paleoisland wider corroboration of a prevailing silurian wind field is supported by evidence from other unconformities about 30 km to the southwest where a linear paleoshore extends for 15 km on an average bearing of n 60 e siliciclastic sandstone derived from a granodiorite source in the gushan area now sits in close proxi

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

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

tidal littoral offshore shelf deposits lower cambrian gog group southern rocky mountains canada abstract nearly 600 m of shallow marine fine to coarse grained quartzites interbedded with shales of the lower cambrian gog group are exposed at the spiral tunnels section kicking horse pass yoho national park facies are defined and interpreted on the basis of sedimentary structures as follows 1 interbedded shale and sandstone pelagic sediments with interbedded coarse grained bottom current deposits 2 massive to laminated shale pelagic sediments 3 conglomerate storm deposits 4 linsen bedded sandstone in shale bedload deposits with pelagic or suspended sediments 5 planar tabular cross bedded sandstone small scale bedload deposits from two dimensional megaripples large scale sand wave or sand ridge deposits 6 trough cross bedded sandstone three dimensional ripple and megaripple deposits 7 low angle to horizontally stratified standstone shoaling wave deposits and 8 massive sandstone well sorted deposits large scale 1 5 m thick lateral accretion epsilon deposits also occur facies trends are interpreted as reflecting the migration and aggradation of offshore sand ridges larger sand ridge complexes are comprised of amalgamated individual sand ridge accumulations progradation of sand ridge complexes yield coarsening upward sequences whereas retreat of sand ridge complexes yield fining upward trends overall the sequences are poorly defined mainly a consequence of the interaction of sand ridge and inter ridge swales theoretical considerations of the early cambrian configuration of continents earth moon separation and paleoceanographic conditions suggest that storms were not that important in the emplacement of the sand ridge complexes major offshore current systems are interpreted as being tidally driven with perhaps a secondary littoral or geostrophic current influence the thick sequence of the section 500 m along with a consistent trace fossil signature suggests that the gog group was deposited under shallow marine offshore shelf settings of a rapidly subsiding passive continental margin this is consistent with the geophysical model for the proto pacific margin which during the early cambrian was characterized by very rapid thermal subsidence

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

bathymetry and paleoecology of silurian bethic assemblages late llandoverian new york state late llandoverian marine shales in new york state are highly fossiliferous and provide and opportunity to examine gradients of biofacies the williamson and willowvale formations llandoverian c6 were deposited during a major transgressive episodes in and adjacent to the axis of a narrow ne sw trending central appalachian foreland basin the williamson shale is a black to dark green graptolite bearing unit of the upper clinton group of western new york state it grades eastward into gray fossiliferous shales and coquinoidlimestones of the willowvale formation orientation analysis of graptolites monograptus clintonensis indicates paleoccurents dominantly from the northeast to east the presence of rippled cross laminated sandstone beds tempestites within dark gray graptolitic facies of the lower williamson indicates that the darl shale facies was deposited in dysaerobic to marginally aerobic water slightly below storm wave base poorly fossiliferous green shales higher in the willimason appear to slow deposition in dysaerobic water and suggest a gradual deepening graded brachipod coquinoid limestones interpreted as storm layers occur near the middle and top of the williamson and in the willovale shale and indicate deposition of these sediments above maximum storm wave base the faunas of the williamson and willowvale shales are subdivisible into five vertically and laterally adjacent associations as follows a ichnofossil chondrites b monograptid chonetes cornutus c eopletodonta atrypta d palaeocyclus bryozoan and e eocoelia chonetes cornutus associations this spectrum of fossil associations appears to parallel the increasing frequency of bottom disturbance by waves and currents from deeper basinal areas to higher energy outer and low energy inner shallow shelf settings the fossil associations of the williamson a c probably belong to the deeper benthic assemblages 4 5 but developed in environments within to slightly below storm wave base about 50 80 m deep the willowvale fauna c d representing benthic assemblages 3 4 inhabited somewhat shallower better oxygenated environments of the photic zone probably at depths of approximately 20 50 m the easternmost to slightly southeastward equivalent of williamson willowvale fauna e evidently represents shallow water benthic assemblage 2 these conclusions indicate the need for a critical reevaluation of the bathymetric relations of benthic assemblages 3 5 a new interpretations of approximate depths for this range is presented herein

the paleogeography of paleozoic and mesozoic storm depositional systems a discussion in their study of ancient storm deposits marsaglia and klein 1983 devoted considerable attention to hummocky cross stratification hcs and swaley cross stratification scs this discussion is concerned primarily with their remarks about these inferred storm generated structures and will be limited to 1 alternative mechanisms for generation of hcs and scs 2 vertical sequences involving hcs and scs 3 data used to establish generalizations about hcs and scs and 4 criteria used to characterize storm influences in ancient geographic settings

palaeoenvironmental significance of toarcian black shales and event deposits from southern beaujolais france new sedimentological biostratigraphical and geochemical data recording the toarcian oceanicanoxicevent t oae arereportedfromamarginalmarinesuccessioninsouthernbeaujolais france the serpentinum and bifrons ammonite zones record black shales with high 1 10 wt total organic carbon contents toc and dysoxia tolerant benthic fauna typical of the schistes carton facies well documented in contemporaneous nearby basins the base of the serpentinum ammonite zone however differs from coeval strata of most adjacent basinal series in that it presents several massive storm beds particularly enriched in juvenile ammonites and the dysoxia tolerant miniaturized gastropod coelodiscus this storm dominated interval records a marked negative 5 carbonate and organic carbon isotope excursion being time equivalent with that recording storm and mass flow deposits in sections of the lusitanian basin portugal pointing to the existence of a major tempestite turbidite event over tropical areas during the t oae although several explanations remain possible at present we favour climatically induced changes in platform morphology and storm activity as the main drivers of these sedimentological features in addition we show that recent weathering most probably due to infiltration of o2 rich meteoric water resulted in the preferential removal of 12 c enriched organic carbon dramatic toc loss and total destruction of the lamination of the black shale sequence over most of the studied exposure these latter observations imply that extreme caution should be applied when interpreting the palaeoenvironmental significance of sediments lacking toc enrichment and lamination from outcrops with limited surface exposures

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

lower triassic storm dominated ramp sequence in northern hungary an example of evolution from homoclinal through distally steepened ramp to middle triassic flat topped platform

grain size distribution and cementation of the cretaceous mzamba formation of eastern cape south africa a case study of a storm influenced offshore sequence abstract the late cretaceous mzamba formation of the eastern cape south africa is a storm influenced succession deposited in an offshore marine environment the succession is composed of two fundamental lithofacies very fine sandstone and packstone shell bed lithofacies the former represents background sedimentation in a relatively deep water low energy offshore environment whereas the latter represents storm deposits occurring with variable periodicity within the quiet offshore environment the storm generated packstone lithofacies shows a bimodal grain size distribution with two saltation fractions on the cumulative frequency diagrams together with negative skewness parameters and a relatively wide kurtosis of grain size distribution these characteristics are indicative of offshore storm generated sediments initial cementation of the storm influenced sediments occurred in a marine phreatic environment when isopachous rims of phosphate isopachous fibrous rims of smectite and micrite calcite cements were formed these cementation textures also support the offshore tempestite origin of the mzamba sediments the original marine phreatic diagenetic environment of the mzamba sediments changed to a meteoric phreatic environment probably at the end of mesozoic following deposition of the overlying cainozoic sediments the mzamba formation entered a burial diagenetic environment where the sediments were affected by elevated temperature and pressure finally the sediments were entered into a meteoric vadose zone due to tectonic uplift or sea level fall new dissolution pores and pendant calcite cement were created

proximal distal facies relationships and sedimentary processes in a storm dominated carbonate ramp kimmeridgian northwest of the iberian ranges spain abstract facies analysis of the upper kimmeridgian rocks in the outcrops located near ricla zaragoza province northeast spain and the integration of the resultant data in a broader context the northern part of the iberian basin has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the kimmeridgian carbonate ramp using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail model 1 corresponds to the development of a mixed carbonate siliciclastic ramp during a slow rise and stillstand of sea level sequence 1 hst whereas model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level sequence 2 tst carbonate production was higher in the shallow ramp domains coral reefs and oolitic shoals in model 1 and reefs in model 2 than in deeper domains where there is no indication of significant pelagic or benthic production the activity of unidirectional return flows induced by winter storms and hurricanes played an important role in the redistribution of the sediment across the ramp generating different coarse grained deposits in the inner and mid ramp settings dunes lower scale bedforms and tempestites occur in model 1 and storm lobes bars and tempestites in model 2 moreover a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents stillstand of sea level in model 1 involved a rapid progradation of the inner and proximal mid ramp carbonate and siliciclastic facies the rapid relative sea level rise of model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep ramp domains the presence of relatively thick sections in the outer ramp settings instead of condensed sections as observed in model 1 during times of sea level rise model 2 can mainly be explained by the increase of the shallow production in the reef dominated areas

internal architecture of mixed tide and storm influenced deposits an example from the alcântara formation northern brazil abstract the uppermost portion of the itapecuru group is exposed in the eastern margin of the sao luis basin northern brazil where it consists of two units the alcantara formation cenomanian and the cujupe formation late cretaceous early tertiary rossetti d f truckenbrodt w 1997 revisao estratigrdfica para os depositos do albiano terciario inferior na bacia de sao luis ma norte do brasil bol mus paraense emilio goeldi ser cienc terra in press the alc ntara formation which contains the large scale structures discussed in this paper consists of deposits attributed to mid to upper shoreface foreshore tidal channel and lagoon washover environments attributed to a regressive barred shoreline several types of large scale cross bedding i e simple foreset compound mixed undulatory and intricately bounded were recognized in the shoreface facies association these structures are interpreted to record the interaction of storm and tidal processes the storm influence is suggested by a combination of factors mostly including a the genetic association with other storm generated sedimentary structures i e swaley cross stratification and undulating parallel lamination with internal truncations b the deposition on prominent surfaces formed by storm erosion which are defined by large scale either symmetrical or asymmetrical scours arranged in a regular repeating pattern c the sedimentary features formed under combined unidirectional and oscillatory flow processes e g compound mixed bedding with superimposed either swaley cross sets or complexly truncating cross sets with highly undulating boundaries large scale undulatory and intricately bounded cross beddings and d the lateral change in structural styles within short distances which records frequent modification from asymmetrical to symmetrical nearly symmetrical bedform profiles more likely to occur under storm generated combined flows the tidal signature is locally recognized by regularly spaced thick thin sandstone bundles defined by reactivation surfaces and or mud drapes which are attributed to tidal ebb flood cycles the analysis of paleocurrent distribution suggests that vigorous southwestward oriented storm flows interacted with local tidal currents on the shoreface to promote the landward transport of significant volumes of sand which resulted in the large scale cross stratification described in this paper in addition a secondary southeastward directed oblique to shore parallel combined flow would have periodically interacted with the main flow the origin of this oblique to shore parallel flow is attributed to either the refraction of the main storm waves as they approached the paleocoastline or the interference of a separate storm episode which competed with the major landward moving one this complex storm flow pattern can be related to past penecontemporaneous seismic activity i e tsunamis as suggested by the paleogeography of the study area during the cenomanian combined with the structural history of the sao luis basin and the sedimentary features recognized in the alcantara formation

controls of mud mound formation the early devonian kess kess carbonates of the hamar laghdad antiatlas morocco the origin and development of early devonian late pragian to late zlichovian predominantly uppermost zlichovian as indicated by conodont faunas mud mounds of the hamar laghdad area in the eastern antiatlas morocco are controlled by extrinsic and intrinsic factors extrinsic factors include the existence of a paleohigh lochkovian volcaniclastics unidirectional currents and repeated storm events as well as sea level fluctuations intrinsic biologically induced factors are the preferred growth of organisms on the top and the flanks of the mounds because of more favourable ecological conditions and a rapid synsedimentary lithification of the steep mound flanks by interskeletal cementation of auloporid tabulate corals the mounds developed in an epicontinental basin below the wave base but within the range of storms the formation of the mounds started within the uppermost part of the bedded crinoid facies of the kess kess formation with the hydrological accumulation of a bioclastic pile this elevation became settled by crinoids and high diverse tabulate corals producing bioclastic sediment binding activities of the organisms were missing calcareous algae and stromatoporoids are completely absent baffling by thamnoporid tabulate corals might have occurred locally but was not important for the development of the mounds steep slopes to the north and less steep slopes to the south may be the result of north northwest to south southeast trending currents derived from orientation patterns of orthocone nautiloids in the uppermost beds of the kess kess formation a synsedimentary cementation of the flanks possibly triggered by submarine interskeletal cementation of patchily distributed auloporid colonies protected the bioclastic sediment against redistribution by frequent storms indicated by densely spaced eventstone intervals and partly also by the common stromatactis like structures within the mound facies accumulation of more parautochthonous bioclastic sediment within the mounds as compared to the intermound area therefore is caused by a self sustaining system of hydrologic piling of sediment triggered by storms preferred settlement of organisms upon these piles producing bioclastic sediment and coeval biocementation of the growing mound flanks this model differs from existing mud mound models in the lack or only minor significance of binding and baffling in the lack of mound facies sequences and in the greater importance of extrinsic control factors

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

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

hummocky cross stratification is not produced purely under progressive gravity waves hummocky cross stratification is a type of bedding in sedimentary rocks caused by the draping of sand around low steepness three dimensional bedforms this distinctive form of stratification has been thought to be diagnostic of the former action of storm waves and hence its occurrence has been used to reconstruct ancient palaeogeographies and marine processes here i examine theoretical and empirical aspects of hummocky cross stratification pertaining to its origin and argue that the notion that it was produced purely under progressive storm waves is incompatible with observed hummock spacings and possible values of the ratio a under waves a is the amplitude of oscillation near the bed and is the bedform spacing my view is supported by recent observations on naturally occurring hummocky megaripples from the sea floor of the inner atlantic shelf of north america

biotic changes and their control on oligocene miocene reefs a case study from the apulia platform margin southern italy abstract the oligocene miocene represents for the cenozoic a period of extensive reef development and is characterized by a number of important changes influencing both carbonate producing biota and architecture of reefs and carbonate platforms the mediterranean region in particular was characterized during this time by a complex palaeogeographic and climatic history with stepwise transition towards cooler conditions biotic turnovers and the complete disappearance of zooxanthellate corals and reefs at the very end of the miocene a comparative study of two reef complexes that in different times chattian and messinian grew in the same physiographic and depositional setting i e the stable undeformed eastern margin of the apulia platform eastern coast of the salento peninsula southern italy highlights evolutionary ecological and climatic changes that differentiate oligocene and late miocene reef biota of the region in particular the study illustrates how different reef biotic assemblages can produce different reef types frameworks and growth fabrics along reef tracts and reef slopes the chattian reef is characterized by a homogeneous reef building biota being largely dominated by a high diversity and abundant coral fauna associated with a moderate presence of coralline algae and thus forming a single reef type in contrast the messinian reef shows a very low coral diversity but several other reef building components with abundant and varied secondary reef builders coralline algae halimeda encrusting foraminifera bryozoans serpulids and microbial associations the reef therefore is characterized by a heterogeneous reef building biota that forms different frameworks and growth fabrics the feedback to the environment of this different biotic composition is very evident in the two reefs and especially in the slope during the chattian a slope mainly consisting of gravity displaced debris resulted from the abundant production of reef rubble associated with a relatively poor framebuilding capacity conversely during the messinian a biologically stabilized slope resulted from proliferation of a variety of binding organisms that strongly colonized the substrate the climatic cooling which occurred during the miocene may be considered the main controlling factor of the diversity turnovers and changes that affected the coral fauna but other environmental factors such as changes in nutrient regimes and in hydrodynamic conditions of the sea associated with the emerging apennine chain may have played a role in determining differences in the reef biota and in the reef facies

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

feature and duration of metre scale sequences in a storm dominated carbonate ramp setting kimmeridgian northeastern spain abstract metre scale sequences may result from the combined effects of allocyclic and autocyclic processes which are closely inter related the carbonate ramp that developed northwest of the iberian basin during the late kimmeridgian was affected by northwestward migrating cyclones marl limestone alternations that settled in mid ramp environments contain abundant mm to cm thick coarse grained accumulations that have been related to these events the aim of this paper is to determine the impact of storm induced processes on the metre scale sequence features four sections r3 r4 r6 and r7 which are 5 to 7 m in thickness were studied bed by bed along a 4 km long outcrop which shows the transition between the shallow and the relatively deep realms of the middle ramp metre scale sequences were defined and correlated along this outcrop according to the detailed microfacies analysis of host fine grained deposits palynofacies and sequence stratigraphic analyses and carbon and oxygen isotope measurements the evolution through time of sedimentary features such as the size of quartz grains and the relative abundance of grains other than quartz i e muscovite bivalve ooid and intraclast does not correlate from one section to the other suggesting that the finest as well as the coarsest sediment was reworked in these storm dominated environments small and medium scale sequences are defined according to changes in alternation marly interbed and limestone bed thickness and correlated from one section to the other because of the effects of storms on sediment distribution and preservation sequence boundaries coincide with thin alternations and marly interbeds in the most proximal sections i e r3 r4 while they correspond to thin alternations and limestone beds in the most distal sections i e r6 r7 field observations and palynofacies analyses confirm this sequence stratigraphic analysis the excursions in carbon and oxygen isotope values are consistent with the lithological correlations but in themselves are not conclusive marl limestone alternations and small and medium scale sequences are hierarchically stacked suggesting an orbital control on sedimentation with alternations lasting 20 kyr small scale sequences 100 kyr and medium scale sequences 400 kyr as biostratigraphic analyses and spectral analysis are not the most appropriate tools to validate this time calibration in such a short interval and highly dynamic system an alternative approach is developed which is based on the quantification of the rates of sediment accumulation preservation and sea level rise

turbidite to storm transition in a migrating foreland basin the kendal group upper silurian northwest england the uppermost windermere supergroup kendal group of northwest england records the passage from wenlock and lower ludlow deep water flysch deposits to upper ludlow and p idoli shallower water molasse deposits within an evolving foreland basin an upwards progression is preserved from oxygen poor basin slope turbidite deposits through more oxygenated bioturbated dilute density flow deposits to storm and wave influenced sediments the storm influenced sediments display hummocky cross stratification a skolithos ichnofacies shelly lags and symmetrical wave ripple cross lamination convolute lamination increases in magnitude and frequency in the upper part of the sequence apparently nucleated above ripple crests tropical hurricanes probably controlled storm deposition as suggested by late silurian palaeogeographic reconstructions structures in the heterolithic muddy siltstones suggest deposition in a lower energy wave influenced setting mud drapes short wavelength symmetrical ripples and multi directional ripple cross lamination are common the kendal group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry bounded to the northwest and northeast by topographic slopes as well as a temporal trend facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through ludlow and p idoli time probably ahead of a rising mountain front to the north the increase in pre lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

the control of depositional depth tectonic uplift and volcanism on sedimentation processes in the back arc basins of the western pacific ocean nine sediment types are recognized in cores recovered by the deep sea drilling project from back arc basins in the western pacific these include submarine fan turbidites debris flows silty basinal turbidites biogenic pelagic carbonate sediments resedimented carbonates biogenic pelagic silica sediments pyro clastics hemipelagic clays and pelagic clays most of these sediments were deposited independent of basinal rifting spreading processes the transition from biogenic pelagic carbonate sediments into overlying pelagic clays is the only sedimentary sequence dependent on basinal tectonic processes through post rifting subsidence associated with heat loss hemipelagic clays and silty turbidites are controlled by sediment yield from continental sources and by climatic change whereas deposition of biogenic pelagic sediments depend on ocean circulation and on latitudinally defined productivity zones coarse pyroclastics are the product of local volcanic periodicity whereas ash deposition is contr

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

an unusual muddy epeiric carbonate reservoir the lower muschelkalk middle triassic of the netherlands the mud dominated lower muschelkalk carbonates middle triassic are a unique reservoir currently producing gas in the dutch de wijk field numerous gas shows scattered over the netherlands onshore and offshore suggest further currently unrecognized potential this study complements an extensive subsurface data set with selected outcrop information to localize missed opportunities and evaluates the factors controlling the development of this unusual reservoir type the muddy carbonates are deposits of a storm dominated epeiric carbonate ramp with negligible depositional gradient different marlstone dolomudstone and lime mudstone facies types reflect the low energy coastal plain to inner ramp and higher energy midramp to proximal outer ramp depositional environments the best reservoir facies is recognized in distal inner ramp algal dolomudstones porosity up to 24 and permeability up to 32 md because of the variable intensity of early facies related diagenesis the reservoir quality of dolomudstones decreases markedly in landward and seaward direction from the distal inner ramp the stacking of decimeter to meter thick reservoirs is reflected by a fourfold hierarchy of depositional cycles that can largely be recognized with conventional wire line logs high resolution outcrop and subsurface correlations reveal that stacks of thin bedded reservoir units most probably pinch out within a few kilometers and that their lateral continuity should not be overestimated despite the epeiric layer cake setting local reservoir occurrences are commonly situated above paleohighs of tectonic or halokinetic origin not only the reduced thickness of the lower muschelkalk above these paleohighs but also the presence and lateral extent of local reservoirs might be detected with seismic data the general facies and reservoir patterns exemplified by the lower muschelkalk may also be of use for reservoir prediction in similar epeiric settings elsewhere for instance in the middle east

internal wave deposits in jurassic kermanshah pelagic carbonates and radiolarites kermanshah area west iran abstract we report eventites generated by turbulence events triggered by breaking internal waves in jurassic pelagic muds deposited in a graben area located between the arabian and bisotoun carbonate platforms at the kermanshah basin west iran the 43 m thick studied pliensbachian aalenian succession at kermanshah includes sponge spicule radiolarian limestones and cherts with cm to dm thick intercalations of pyroclastic beds and coarse grained deposits formed by neritic derived grains and reworked pelagic material breaking of internal waves in localized areas reworked the available sediment on sea floor including the erosion of cohesive pelagic muds and the resuspension of neritic derived grains which were resedimented from the bisotoun platform most probably by storms or turbidity currents the generated internal wave deposits include flat and round pebble limestone conglomerates formed by deposition of pelagic clasts and neritic derived grains near the breaker zone laminated packstone grainstones deposited by high energy upslope swash and downslope backswash flows cm thick packstone grainstones with asymmetrical starved ripples and hummocy crossstratification generated downdip by waning of backwash flows and internal wave oscillatory flows these internal wave deposits predominate in the pliensbachian early toarcian and were related to internal waves developed along a thermocline linked to climate warming and excited by submarine volcanic eruptions storms or tectonic shaking

sedimentary evolution and drowning of a passive margin shelf giumal group zanskar tethys himalaya india palaeoenvironmental changes during final break up of gondwanaland

stable isotopic composition of meteoric calcites evidence for early mississippian climate change in the mission canyon formation montana abstract the lower mississippian mission canyon formation of central to southwestern montana was deposited under dominantly semiarid to arid climatic conditions during osagean to early meramecian times following deposition a pronounced climatic shift to more humid conditions occurred during middle meramecian times this climatic change is indicated by extensive post depositional karst fabrics and in the stable isotopic composition of early meteoric calcite cements and diagenetically altered sediments early meteoric calcite cement in mission canyon limestones is generally nonluminescent and fills intergranular and fenestral porosity petrographic data indicate that this cement formed during intermittent subaerial exposure of the mission canyon platform during osagean times this initial generation of meteoric calcite cement has 18o values from 8 1 to 2 6 pdb these data and the oxygen isotopic values from nonluminescent skeletal grains and micrite in host limestone indicate that osagean meteoric water may have had 18o values as low as 6 0 smow a second generation of petrographicalty similar but isotopically distinct calcite cement fills biomolds and porosity within solution collapse breccias in the mission canyon formation this cement generation postdates earlier nonluminescent osagean calcite cement and is volumetrically most abundant near the top of the mission canyon formation 18o values from these cements and from nonluminescent lime mudstone clasts and matrix in solution collapse breccias range from 13 8 to 8 2 pdb these data indicate that meramecian meteoric water may have had 18o values as low as 12 0 however a higher temperature burial overprint on the 18o values of the calcite cement cannot he ruled out the more positive 18o values of the osagean calcite components probably indicate warm and arid conditions during short term 104 yr subaerial exposure along intraformational sequence and parasequence boundaries the more negative 18o values from meramecian calcite components and the extensive karst associated with the post mission canyon unconformity may have developed because of cooler and more humid climatic conditions and possible rain out effects during middle meramecian times a dramatic shift towards cooler and more humid climatic conditions may be coincident with the onset of major continental glaciation in the early carboniferous the post mission canyon unconformity has been attributed to a major fall in sea level that may have glacio eustatic origins growth of continental glaciers during a time of global cooling would have caused migration of polar fronts further toward the paleoequator these polar fronts in turn would have pushed moist mid latitude weather systems toward the paleoequator resulting in cooler more humid conditions in low latitude settings during icehouse times

late jurassic paleogeography and paleoclimate in the northern iberian basin of spain constraints from diagenetic records in reefal and continental carbonates abstract sedimentation in the northern part of the iberian basin during the early kimmeridgian was characterized by the development of coral reef complexes of the torrecilla en cameros formation which were situated along a seaway that connected the boreal and tethys domains along the northern portion of that seaway close to the boreal sea early diagenesis of the torrecilla fringing reef complex was controlled by rising sea level and by local tectonism leading to alternations of submergence and reefal exposure while exposed reef corals were neomorphosed and dissolved when the corals were submerged secondary porosity was filled by calcite cements precipitated from marine derived waters during the latest stages of reef development rate of sea level rise could no longer keep pace with tectonic uplift and while younger accretionary units continued to be deposited older units were exposed subaerially leading to the precipitation of meteoric calcite cement and to the development of a paleosol this stage of diagenesis also affected the reef complex during late kimmeridgian times as the boreal and tethys coastlines progressively retreated to the north and southeast respectively progressive retreat of the boreal sea and subsequent late jurassic to early cretaceous rifting that formed the cameros basin resulted in the deposition of tithonian continental carbonates directly on these reefal units oxygen isotope compositions of these continental carbonates are 3 more negative than kimmeridgian meteoric cement suggesting an evolution in the isotopic composition of meteoric water in response to an increasing continental effect on meteoric precipitation in contrast early kimmeridgian reef complexes of the torrecilla en cameros formation in the southern sectors of the seaway closer to the tethys sea were exposed during the late kimmeridgian as the tethys coastline retreated leading to dissolution of corals and subsequent precipitation of meteoric calcite cement oxygen isotope compositions of these meteoric cements are 2 more negative than time equivalent meteoric calcites precipitated in the northern torrecilla reef complex given the regional paleogeography this difference suggests that sources of meteoric water must have been different for the northern and southern sectors and probably reflects southward transport of air masses and water vapor from the boreal sea to the northern torrecilla sector and northwest transport of water vapor from the tethys sea to the southern sectors tithonian berriasian continental carbonates which unconformably overlie reef complexes in the southern and northern sectors exhibit an opposite trend with the 18o of continental carbonates in southern sectors being 1 6 more positive than time equivalent carbonates that overlie the torrecilla reef complex to the north this shift in the trend of the isotopes between northern and southern sectors is coeval with paleogeographic changes that occurred in response to late jurassic early cretaceous rifting of the iberian plate and the progressive retreat of boreal and tethys coastlines during this time continental carbonates in both the southern and northern sectors of the seaway precipitated from meteoric waters that were sourced from the tethys sea to the southeast more negative 18o values in the northern torrecilla sector reflect enhanced continental fractionation effects as the influence of the boreal sea derived meteoric waters diminished

sequence stratigraphy and platform evolution of lower middle devonian carbonates eastern great basin lower middle devonian carbonates 270 400 m thick of the eastern great basin were deposited along a low energy westward thickening carbonate platform six regional facies representing peritidal shallow subtidal stromatoporoid biostrome deep subtidal slope and basin environments are recognized four third order 1 5 2 5 m y durations transgressive regressive sequences are identified across the platform to basin transition based on deepening and shallowing patterns in regional facies intensity and stratigraphic distribution of subaerial exposure features and stacking patterns of fourth to fifth order upward shallowing peritidal and subtidal cycles transgressive systems tracts along the basin slope are characterized by upward deepening successions of proximal through distal turbidites overlain by fine grained hemipelagic deposits shallow platform transgressive systems tracts are composed of stacks of thicker than average peritidal cycles overlain by subtidal cycles or noncyclic deep subtidal facies maximum flooding zones along the shallow platform are composed of stacked peritidal cycles dominated by subtidal facies noncyclic deep subtidal facies or distinct deeper subtidal units within successions of restricted shallow subtidal or peritidal facies highstand systems tracts along the basin slope are composed of hemipelagic deposits overlain by distal through proximal turbidites highstand systems tracts along the shallow platform are characterized by upward shallowing succession of cyclic peritidal through shallow subtidal facies sequence boundary zones 2 16 m thick along the shallow platform are composed of exposure capped peritidal and subtidal cycles that exhibit upsection increases in the proportion of tidal flat subfacies and increases in the intensity of cycle capping subaerial exposure features sequence boundary zones along the basin slope 6 20 m thick are composed of upward shallowing successions of proximal turbidites or by platform margin peloid shoal deposits the absence of exposure features and meter scale cycles within basin slope sequence boundary zones indicates that the combined rates of third through fifth order sea level fall rates were less than tectonic subsidence rates sequence stratigraphic correlations between contrasting facies belts of the basin slope section na and the edge of the shallow platform section tm were independently verified with high resolution conodont and brachiopod biostratigraphy correlation of sequences 1 4 with transgressive regressive sequences of similar age in the western midwestern and eastern united states western canada and europe indicates they are eustatic in origin systems tract scale correlations across the study area indicate that the platform evolved from a homoclinal ramp to a distally steepened ramp then into a flat topped platform sequences 1 2 an incipiently drowned intraplatform basin developed during sequence 3 as the result of third order sea level rise and differential sediment accumulation rates between the platform margin and intraplatform basin during deposition of highstand systems tract 3 progradation infilled the intraplatform basin resulting in a flat topped platform a distally steepened ramp developed during transgressive systems tract maximum flooding zone 4 and evolved into a flat topped platform during highstand systems tract 4 deposition the four sequences stack in an aggradational to slightly progradational pattern keep up style sedimentation and are bound by sequence boundary zones rather than unconformities suggesting that greenhouse climate modes and second order accommodation gains related to the lower portion of the second order kaskaskia sequence controlled sequence scale stacking patterns

sedimentary evolution of a shallow carbonate ramp kimmeridgian ne spain unravelling controlling factors for facies heterogeneities at reservoir scale abstract the facies evolution of a late jurassic latest kimmeridgian shallow carbonate ramp was reconstructed after the analysis and correlation of 21 logs in a 20 30 km outcrop area located south of zaragoza northeast spain the studied succession belongs to the higueruelas formation which is of potential use as an analogue for understanding facies heterogeneities in certain hydrocarbon carbonate reservoirs e g the arab formation persian gulf the studied succession is arranged in nine sedimentary units bounded by discontinuity surfaces that can be traced over kilometres facies analysis permitted the reconstruction of two sedimentary models showing the transition from inner ramp subenvironments i e intertidal lagoon backshoal washover shoal sand blanket to the mid ramp foreshoal and offshore domains an oncolitic peloidal oolitic and an oolitic peloidal dominated ramp the oncolitic peloidal oolitic dominated ramp is characterized by peloidal oolitic and oncolitic dominated shoal sand blankets that developed in higher energy inner areas protecting peloidal oolitic backshoal and oncolitic lagoon domains including a mosaic of stromatoporoid carpets peloidal facies with fenestral porosity accumulated in an intertidal belt or as patches on top of the shoal sand blankets and washover deposits offshore from the shoal sand blankets chaetetid stromatoporoid coral rich buildups grew on the more proximal mid ramp surrounded by peloidal and peloidal bioclastic grain to mud supported facies an oolitic peloidal dominated ramp developed in a second stage of the evolution of the platform characterized by the presence of a wide restricted peloidal bioclastic oolitic lagoon on the inner ramp grading into a backshoal area dominated by storm related intraclastic peloidal deposits stromatoporoid carpets disappeared and oncolitic dominated deposits were constrained to the foreshoal and backshoal domains and locally to local ponds that developed in the intertidal belt or the restricted lagoon internal and external factors controlling facies heterogeneity and the sedimentary evolution of the carbonate ramp include resedimentation topographic relief and long to short term sea level fluctuations

the occurrence of isorenieratane and 24 n propylcholestanes in paleogene lacustrine source rocks from the dongying depression bohai bay basin implications for bacterial sulfate reduction photic zone euxinia and seawater incursions abstract lacustrine organic rich source rocks shales and mudstones were examined to assess the depositional environment and organic input sources of the third and fourth members of the eocene shahejie formation bohai bay basin china major organic contributions to the shahejie formation from dinoflagellates diatoms botryococcus and marine pelagophyte chrysophyte algae were determined using n alkane distributions gammacerane index and diagnostic steranes traces of higher plant biomarkers suggest that terrigenous organic inputs were limited the pervasive presence of carotane aryl isoprenoids paleorenieratane renieratane isorenieratane 2 methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria purple sulfur bacteria chromatiaceae green sulfur bacteria chlorobiaceae and sulfate reducing bacteria the extent of h2s content bacterial sulfate reduction and photic zone euxinia pze were evaluated by determining the aryl isoprenoids ratio air 0 7 9 0 the presence of isorenieratene derivatives and the fate of sulfur in the water column there was a decrease of pze extent and duration from the northeast to the southwest of the palaeo lake and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the shahejie formation abrupt environmental perturbations in the third member of the shahejie formation are indicated not only by significant changes in parameters such as the pristane phytane and carotane n c20 alkane ratios the gammacerane index the isorenieratane c18 aryl isoprenoid and the air but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple green sulfur bacteria as well as seawater incursions the unexpected occurrence of intact c30 4 desmethylsteranes 24 n propylcholestanes in the shahejie formation is first reported here after very careful checking and provides unambiguous biological evidence for at least two marine transgression events reaching the eocene dongying palaeo lake the organic enrichment of the petroleum source rocks in the shahejie formation is a consequence of combined indigenous lacustrine algal production the constrained and favourable preservation conditions and significant bacterial contributions and marine organic matter inputs to the lake

a stochastic parametrization for deep convection using cellular automata a cellular automaton ca is introduced to the deep convection parametrization of the high resolution limited area model aire limitee adaptation application de la recherche a l operationnel alaro the self organizational characteristics of the ca allow for lateral communication between adjacent numerical weather prediction nwp model grid boxes and add additional memory to the deep convection scheme the ca acts in two horizontal dimensions with finer grid spacing than the nwp model it is randomly seeded in regions where convective available potential energy cape exceeds a threshold value both deterministic and probabilistic rules coupled to the large scale wind are explored to evolve the ca in time case studies indicate that the scheme has the potential to organize cells along convective squall lines and enhance advective effects an ensemble of forecasts using the present ca scheme demonstrated an ensemble spread in the resolved wind field in regions where deep convection is large such a spread represents the uncertainty due to subgrid variability of deep convection and could be an interesting addition to an ensemble prediction system

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

outer ramp cycles in the upper muschelkalk of the catalan basin northeast spain the upper muschelkalk triassic of the catalan basin eastern spain was deposited upon a carbonate ramp of homoclinal type located in an intracratonic setting the rasquera unit in the upper muschelkalk mostly consists of outer ramp carbonates arranged in upward shallowing cycles five cycles from 1 5 to 12 m thick are recognised each cycle shows an upward coarsening of grain size an upward increase in bed thickness and an upward change in fossil content reflecting an upward shallowing of the environment in the complete cycle marlstone and shale pass up into marlstone with thin bedded line mudstones containing pelagic bivalves the succeeding thin bedded and nodular limestones with shaley partings contain a more varied fauna and are bioturbated they pass up into thick bedded skeletal wackestones packstone coquinas locally cap the cycles and have a diverse benthic fauna as well as the alga tubiphytes occurring as bioclasts encrustations around skeletal grains and forming microbuildups although some of the thin beds were deposited during weak storms there is little evidence of intense storm activity petrological sedimentological and palaeontological criteria and the geological setting allow the recognition of distal intermediate and proximal facies on a relatively deepwater carbonate ramp

hummocky cross stratification like structures in deep sea turbidites upper cretaceous basque basins western pyrenees france hummocky cross stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf sedimentary structures named hummocky cross stratification like structures similar to true hummocky cross stratification have been observed in the turonian senonian basque flysch basin south west france the bathymetry 1000 to 1500 m suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf the morphology of these three dimensional structures shares similarities with the morphology of hummocky cross stratification despite a smaller size the lateral extent of these structures ranges from a few decimetres to many decimetres they consist of convex up domes hummock and concave up swales with a non erosive base four types of hummocky cross stratification like geometries are described they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations in the basque flysch hummocky cross stratification like structures are only found in the tc interval of the bouma sequence hummocky cross stratification like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages this observation suggests that hummocky cross stratification like structures are linked genetically to the turbidity current but form under a very restricted range of parameters these structures sometimes show an up current upslope migration trend antidunes in the described examples they could result from standing waves forming at the upper flow interface because of kelvin helmholtz instability

ice age hurricanes and tropical storms we compare pleistocene tropical cyclones with present day storms in this study through the use of a three dimensional numerical model simulating hurricane development and processes1 the characteristics of atlantic ice age tropical storms are derived from reconstructions of the 18 000 bp climate the last glacial maximum or lgm and the giss goddard institute of space studies general circulation model s lgm simulation2 3 the simulation results indicate that although the structure of the ice age atmosphere was colder and more stable it had the potential to support development of tropical cyclones such storms however would be substantially weaker than contemporary storms this investigation demonstrates the value of integrating numerical models of varying spatial scales in climatic research

tectonic and eustatic control on a mixed siliciclastic carbonate platform during the late oxfordian kimmeridgian la rochelle platform western france boreal and tethyan realms of western europe present significant sedimentological paleontological and stratigraphic differences the purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences detailed sedimentological palynofacies and calcareous nannofossil analyses were performed on two sections from the la rochelle platform western france the pas section includes part of the late oxfordian and early kimmeridgian and the rocher d yves section is assigned to the late kimmeridgian they correspond to monotonous marl argillaceous limestone alternations limestones are essentially mudstones with echinoderms bivalves and foraminifera that suggest low energy open marine conditions highly bioclastic and or peloidal deposits occur commonly and show wackestones to wacke pack grainstones textures these deposits indicate frequent high energy events and are interpreted as storm deposits marls dominate in the most proximal depositional environments while calcareous deposits are more important in more distal environments the rocher d yves section is globally more marly than the pas section suggesting a more proximal setting palynofacies are dominated by woody particles suggesting shallow water proximal depositional environments calcareous nannofossils are ascidian spicules coccoliths and schizospheres watznaueria britannica dominate calcareous nannofossil assemblages in the pas section the rocher d yves assemblages are quasi exclusively composed of cyclagelosphaera margerelii and indicate more proximal paleoenvironments than those of the pas section different orders of depositional sequences are defined with sequence boundaries corresponding to the most rapid relative sea level falls they are hierarchically stacked and correlate on the basis of ammonite zones with the sequences of contemporaneous sections from tethyan and boreal realms the stacking pattern of these sequences suggests an orbital control on sedimentation small medium and large scale sequences correspond to precession 20 ky cycles and to 100 ky and 400 ky eccentricity cycles respectively the elementary sequences have durations shorter than 20 ky the kimmeridgian was a period of global sea level rise that ended in the late kimmeridgian more proximal depositional environments in the rocher d yves section late kimmeridgian than in the pas section early kimmeridgian imply a progradation of the la rochelle platform during the kimmeridgian this progradation resulted from a slowdown of the subsidence in the aquitaine basin during the kimmeridgian corresponding to the first steps of atlantic ocean opening high frequency cycles on the la rochelle platform formed in sync with milankovitch orbital cycles while tectonics controlled the formation of the low frequency cycles