identification of permian palaeowind direction from wave dominated lacustrine sediments lodeve basin france lacustrine environments are an excellent indicator of continental palaeoclimate in particular the sedimentary record of waves in lakes may be used to constrain atmospheric palaeocirculation wave ripples have been identified in a permian lacustrine basin the salagou formation 260 250 ma lodeve basin located in the southern french massif central part of the western european hercynian mountain chain wave ripple patterns are interpreted with regards to hydrodynamics and water palaeodepth it is shown that in the case of the salagou formation wave ripple orientations were controlled by the direction of the prevailing palaeowind the late permian wind blew from between north and 20 east of north possibly over several millions of years and certainly throughout the period of deposition of about 2000 m of strata in the lodeve basin permian lacustrine sedimentation is widespread and well preserved on the earth s surface and so wave ripple data may help constrain numerical modelling of the earth s past climates especially with regards to permian times outside of desert regions

sediment transport processes in an ancient mud dominated succession a comparison of processes operating in marine offshore settings and anoxic basinal environments abstract few studies describe and compare the transport mechanisms operating to disperse mud in different parts of basins instead the physical processes operating to disperse mud in offshore environments where storm and tidal processes are interpreted to dominate are generally considered in isolation from those occurring in basinal settings where changes in bottom water anoxia and suspension settling from buoyant plumes are mostly interpreted to dominate using microtextural mineralogical and geochemical data derived from the analyses of 151 thin sections obtained from the lower jurassic mudstone dominated succession exposed on the coast of ne england we investigate how varying sediment dispersal mechanisms bioturbation and early diagenesis operated to produce the lithofacies variability observed in particular we consider the processes of sediment delivery while bottom waters were interpreted to be euxinic analyses of these samples reveal that the succession is highly variable at millimetre to centimetre scales six main lithofacies were observed 1 sand and clay bearing silt rich mudstones 2 silt bearing clay rich mudstones 3 clay rich mudstones 4 clay calcareous nannoplankton and organic carbon bearing mudstones 5 fine grained muddy sandstones 6 cement rich mudstones these units are organized typically into stacked successions of sharp based normally graded thin

a sedimentary prelude to marinoan glaciation cryogenian middle neoproterozoic keele formation mackenzie mountains northwestern canada abstract continental margin deposition between the sturtian and marinoan aged global glacial periods is represented in nw canada by a siliciclastic to carbonate grand cycle the keele formation a 300 600 m thick carbonate and siliciclastic deposit comprises the upper part of this interglacial cycle sedimentary facies in the lower carbonate dominated member of the keele span a broad spectrum of depositional environments from below storm wave base to peritidal to continental and are disposed across a relatively narrow paleogeographic belt lateral arrangement of facies and the gradual stratigraphic transitions between them suggest deposition in a ramp setting local slump structures and occasional debrites in deep water facies imply that the ramp was distally steepened fluvial facies are concentrated at a single locality indicating that terrigenous clastic sediment was derived from a point source or sources most strata of the carbonates are bahamian in character and similar to phanerozoic warm water carbonates in that they contain abundant calcite ooids of interpreted original aragonitic mineralogy and have well developed muddy peritidal facies nevertheless close juxtaposition of deep and shallow water facies in keele rocks indicates high amplitude sea level change during deposition on the order of 100 m suggesting accumulation in a climatic icehouse period this interpretation implies that although the globe possessed polar and high altitude glaciers at this time sea surface temperature at least at tropical latitudes warmed dramatically between neoproterozoic glacial episodes the onset of marinoan glaciation here is heralded by an abrupt shift to nearshore marine siliciclastic sedimentary rocks these deposits form the upper member of the keele formation informally called the keele clastic wedge and directly underlie ice brook formation diamictites carbonates are rare and are restricted to mudstones and flat pebble conglomerates that lack any indication of tropical conditions

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

using relative sea level data to constrain the deglacial and holocene history of southern greenland this paper presents new holocene relative sea level rsl data collected from isolation basins close to the town of paamiut in south west greenland the data shows a rapid fall from a marine limit of c 52 m asl at c 10 9 cal ka bp to close to present by c 9 5 cal ka bp at rates of up to c 32 mm yr falling below present for the majority of the holocene before rising to present in the last 2000 years the elevation of the rsl lowstand is not well constrained but was at least below 3 m this pattern of rapid rsl fall during the early holocene matches the pattern seen at other southern greenland locations suggesting rapid largely simultaneous ice retreat from the area surrounding the qassimiut lobe at the start of the holocene occurring c 2000 years after the initial deglaciation of the extreme southern tip of greenland the rsl histories from this and other southern greenland locations are distinct to those recorded further north along the west coast and are in broad agreement with a pattern of vertical land motion and rsl predicted by the huy2 model simpson et al 2009 which predicts an 80 m drop in the contribution of vertical land motion to rsl at 10 cal ka bp between sisimiut and paamiut on the west coast despite this broad scale spatial agreement between the rsl data and the huy2 model it fails to satisfactorily predict the holocene rsl histories at paamiut and other southern greenland locations sensitivity tests indicate that the data model misfits are most likely due to an over estimate of the forcing during the holocene thermal maximum or the response to this forcing in southern greenland and error in the north american ice sheets component of the background deglaciation model our new data suggests that much of the southern part of the ice sheet acted differently to the area further north however rsl changes at paamiut are also largely impacted by regional and larger scale processes including a bulls eye of uplift centred on the west the impact of the holocene thermal maximum and the influence of the collapse of the north american ice sheets

ice water pits upon the yellow river delta plain abstract the erosion circular pit is a common sedimentary structure but its genesis is complex many erosion pits occur on the yellow river delta plain with some formed by ice water erosion the ice water pits are generally circular or semi circular in cross section and are typically 2 40 cm across and 2 20 cm in depth we identify four types of pits on the basis of their origin i pits that formed by liquefaction and tight arrangement ii pits that formed by spattering iii pits that formed by lateral leakage and iv pits that formed by bottom leakage the formation of the ice water pits is likely a function of many complex variables including frequent runoff channel structure ice run and fine sediment size the example of ice water pits from the yellow river delta plain offers a useful frame of reference for the interpretation of formation conditions and environment significances of some circular pits pot or pothole in ancient rocks

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

anatomy of a mixed marine non marine lowstand wedge in a ramp setting the record of a barremian aptian complex relative sea level fall in the central neuquen basin argentina

geostrophic versus friction dominated storm flow palaeocurrent evidence from the late permian brotherton formation england the late permian brotherton formation of northeastern england is a 0 75 m thick carbonate sequence which exhibits abundant erosively amalgamated hummocky cross stratification gutter casts and shallow scour fills suggesting deposition in a storm dominated platformal shelf setting the outcrop ca 15 m thick is divisible into three facies associations a basal transgressive interval 4 5 m thick facies association a which passes upwards into a thinly bedded argillaceous condensed section 1 m thick facies association b which in turn rapidly grades upwards into a 8 10 m thick regressive highstand succession of hummocky cross stratified amalgamated scour fills facies association c the dominance of hummocky cross stratification in all facies associations would suggest that post storm deposition and fairweather reworking was largely under oscillatory currents however the erosional palaeocurrent data indicate that facies associations a and b were deposited following combined oscillatory and geostrophically balanced shore parallel flows in contrast facies association c was deposited by infilling the scours of friction dominated offshore directed and downwelling jet like flows combined with oscillatory wave currents the dominance of geostrophic or friction dominated flows in the study area is interpreted to be controlled by relative sea level changes during transgressive conditions increasing accommodation permitted rotation of the downwelling pressure driven currents in the regressive phase particularly in the accommodation limited late highstand bottom friction was important in inhibiting flow rotation it is suggested that the paucity of evidence for geostrophic flows in the ancient record may in part be attributed to the palaeocurrent indicators in sand grade substrates being restricted to thin transgressive intervals or surfaces whilst in the volumetrically more important regressive deposits palaeocurrent data are largely contained within facies from the friction dominated zone

geometry distribution and fill of erosional scours in a heterolithic distal lower shoreface sandstone reservoir analogue grassy member blackhawk formation book cliffs utah usa

paleoenvironmental analysis of the ichnogenus zoophycos in the lower devonian tempestite sediments of the longmenshan area sichuan china abstract the trace fossil zoophycos is characteristic of the lower devonian in the longmenshan area of southeastern china three distinct storm generated or induced types of sedimentary sequences bearing zoophycos have been identified in shallow marine deposits of the bailiuping formation and the yangmaba formation the type a deposit is composed of siltstones with shell concentrations and wave ripples and small zoophycos at the top the type b deposit is characterized by fine graded sandstone with long wavelength hummocky cross stratification and black gray mudstone as well as the largest and densest zoophycos at the top the type c deposit has graded bioclastic limestone with short wavelength hummocky cross stratification muddy wackestone and large zoophycos at the top based on the features of the types of zoophycos the distribution zone of the zoophycos ichnogenus that preserved in tempestite sequence was built between the fair weather wave base and storm wave base in the lower devonian this research suggests that the distribution patterns of zoophycos formed in storm induced deposits may not provide significant clues for the estimation of relative water depths the hydrodynamic conditions and sedimentation rate are two important environmental factors of the development of the zoophycos in the lower devonian shallow marine deposits where it was mainly affected by storms between the fair weather and storm wave bases the abundance of zoophycos at the top of locally frequent storm deposits could indicate a fairly opportunistic behavior and they were formed in the early hst deposit which had a relatively stable environment with low energy and higher sedimentation rate

origin of shore normal channels from the shoreface of sable island canada a suite of modern shore normal channels was discovered on the southern shoreface of sable island canada repetitive multibeam and sidescan surveys of these features as well as box coring and sampling showed that the depressions were perennial features of the shoreface they occurred in fine and medium sand and were most abundant in depths less than 20 m they were up to 1 m deep and 50 m wide increased in size seawards and generally followed the seabed slope the channels dominated the inner shoreface becoming wider and deeper seawards to depths in excess of 40 m there is a continuum of scales in width and depth of these channels the smallest of which are equated with gutters preserved in the geological record the internal structure of the shoreface sediments where the gutters are found is characterised by normally graded tempestites composed of cut and fill structures overlying an erosion surface thus the environmental setting internal structure and scale are similar to ancient counterparts gutters have been interpreted to result from downwelling over palaeo shorefaces during ancient storms myrow 1992b the composition of gutter infill as well as the stability evolution associated bedforms and hydrodynamic conditions under which they formed were examined to verify genetic interpretations of the ancient counterparts the multi sensor benthic lander ralph was deployed within a field of shore normal channels for 17 days during late winter 1998 ralph burst sampled flow at hourly intervals whilst imaging the seabed resulting sequential imagery revealed the genesis of a group of five gutters during storm spin down that was coincident with the formation of large scale wave ripples this was followed by infilling of the gutters and wave ripple destruction within 20 hours by longshore sand transport the gutters were located within and parallel to a larger channel 50 m wide and 0 50 m deep they were formed by coastal set up and subsequent downwelling that was triggered by the rotation of storm winds from seawards onshore wind to landwards offshore wind the gutters formed within 2 to 3 hours during spin down of a winter storm under live bed conditions of sand transport wave height and mean tidal flows were well below those of the storm peak and so they were not directly responsible for creating the gutters the mechanism we propose for the evolution of gutters supports the geological interpretations that is a storm driven downwelling event as described by swift and niedoroda 1985 however the downwelling event appeared to take place suddenly rapid acceleration in flow briefly few hours duration and within narrow corridors guided by wider and deeper channels of the shoreface high turbidity during the time of gutter formation leads us to believe that the phenomenon of inner shelf turbidity currents as suggested by walker 1985 exists and may be instrumental in channel formation

mud rich density driven flows along an early ordovician storm dominated shoreline implications for shallow marine facies models abstract dynamic physical and biological seafloor processes shape the three dimensional stratal architecture of modern and ancient mud dominated continental shelves when evaluating a mudstone unit as a potential source reservoir or seal it is imperative to understand the physical biological and chemical seafloor processes that control mudstone depositional fabric and diagenesis this study presents sedimentological ichnological and geochemical data of exceptionally preserved mudstone originating from hyperpycnal and possible combined flow deposits in the lower ordovician tremadocian beach formation bell island group newfoundland seven mudstone facies are described based on textural compositional and ichnological characteristics mudstone deposits interpreted to originate from hyperpycnal flows are well cemented exhibit high chlorite illite ratios and contain sharp grain size changes commonly forming beds with tripartite subdivisions deposits of wave enhanced sediment gravity flows are in contrast poorly cemented illitic mudstone these mudstone facies exhibit decimeter thick wave or combined flow structures within siltstone and very fine sandstone beds as well as laterally discontinuous nonbioturbated mudstone layers beds of this facies have abundant mudstone on mudstone and mudstone on sandstone erosional contacts low organic carbon loading from the nonvegetated early paleozoic hinterland combined with a high reworking frequency on a shallow marine wave dominated shelf is inferred to have resulted in high remineralization efficiency and low preservation potential of reactive organic carbon burial efficiency and bioavailability of organic matter are considered to be the critical variables controlling infaunal colonization and bioturbation in mud dominated open coastline paleoenvironments this work demonstrates that ancient fine grained coastal systems are incompletely incorporated into sequence stratigraphic models owing to their atypical proximal to distal facies relationships it is proposed that the spatial organization of fine grained sediment and facies architecture in such systems are controlled by 1 frequency of sediment supply events 2 direction of mud transport 3 diagenetic reactivity of minerals and bioavailable organic carbon and 4 residence time of mineral grains and organic matter close to the sediment water interface

cambrian depositional history of the zanskar valley region of the indian himalaya tectonic implications a well preserved cambrian section in the zanskar valley of northern india has previously been interpreted to record the transition from a passive to an active tectonic margin related to cambrian ordovician orogenesis this interpretation has been used to support the tectonostratigraphic interpretation of other successions across the tethyan himalaya our detailed paleoenvironmental analysis significantly revises the tectonic and depositional history of these cambrian deposits no definitive record of impending cambrian ordovician orogenesis is recorded in these late middle cambrian rocks a critical transition from an 125 m thick stromatolite bearing carbonate deposit the karsha formation into shale and sandstone of the kurgiakh formation was interpreted to represent tectonically induced drowning of a carbonate platform siliciclastic strata of the kurgiakh formation were thought to record deep water flysch deposition in a tectonically active foreland basin next to an arc trench system this interpretation was based on sandstone beds with classic bouma sequences we show that these event beds in the kurgiakh instead contain hummocky cross stratification quasi planar lamination and combined flow ripple stratification all of which reflect deposition in shallow marine storm influenced environments thus although the karsha carbonate platform may have been drowned it did not culminate in deep sea flysch deposition and this in turn eliminates a major line of evidence linking kurgiakh deposition to the onset of cambrian ordovician orogenesis other aspects of cambrian ordovician deposits of northern india also shed doubt on the proposed link between kurgiakh sedimentation and the cambrian ordovician orogenic event first our improved biostratigraphic database suggests that the transition from the karsha carbonate to the kurgiakh formation may have predated the main phase of cambrian ordovician orogenesis as recorded by overlying ordovician molasse by as much as 20 30 my second published data from the ordovician molasse indicate northward paleocurrents which are parallel to those recorded by siliciclastic deposits of the parahio formation below the karsha and thus are at odds with standard models of foreland basin development for the cambrian ordovician event our sedimentological analysis of depositional cycles of the parahio formation indicates that these strata record storm influenced environments from offshore marine to shoreface to fluvial settings this is at odds with previous paleoenvironmental interpretations that ranged from deep sea flysch to intertidal deposits paleocurrent data for marine and fluvial facies of the parahio formation in both zanskar and the spiti valley to the south indicate northeast sediment transport this supports the view that the parahio and overlying carbonate of the karsha formation record the ancient northern passive margin of india during the cambrian and that these strata may be distal equivalents of the younger cambrian deposits of the lesser himalaya

stratigraphy of the late palaeoproterozoic 2 03 ga wooly dolomite ashburton province western australia a carbonate platform developed in a failed rift basin abstract this paper describes the sequence stratigraphy of the 2 03 ga wooly dolomite the uppermost stratigraphic unit of the horseshoe basin strata of which unconformably overlie the 2772 2410 ma hamersley province unconformably truncate folded 2210 ma dolerite sills and post date the 2195 2145 ma ophthalmia orogeny the horseshoe basin was an intracontinental rift that initiated at 2 05 ga with deposition of 360 m of fluvial and shallow marine siliciclastic sandstones beasley river quartzite followed by eruption of 2 7 km of flood basalt cheela springs basalt and culminated with deposition of 325 m of platformal carbonates and associated volcaniclastic and siliciclastic sediments wooly dolomite the three formations of the horseshoe basin stack conformably with tectonically driven unconformities developed only at a late stage within the wooly dolomite depositional systems of the wooly dolomite appear to have been compartmentalised but connected to an ocean five depositional sequences are identified depositional sequence 1 which developed conformably on the cheela springs basalt records the establishment of a carbonate platform coeval with volcaniclastic sedimentation but it was developed only in the southeastern most sector of the basin resedimented tuffs volcaniclastic siltstones are present in all of the depositional sequences but are most abundant in ds1 depositional sequence 2 cuts deeply into the cheela springs basalt and has a lower section of siliciclastic sedimentary rocks that is overlain by carbonate platform deposits the wyloo dome at an interpreted rift triple junction was an uplifted area until the late stage of ds2 implying that accommodation generation was also fault compartmentalised depositional sequences 3 4 and 5 have predominantly carbonate platform deposits and are also unconformity bound whereas ds4 and ds5 preserve a shelf slope transition subsidence in the horseshoe basin ended with basin inversion during the d1 panhandle deformation event which predated emplacement of an 2008 ma dolerite dyke swarm a subsequent rifting event recorded by the mcgrath basin led to a rift drift transition that finally initiated a west facing atlantic type continental margin

tempestite facies models for the epicontinental triassic carbonates of the betic cordillera southern spain this study focuses on storm deposits in the muschelkalk facies of the betic cordillera southern spain and interprets their deposition mechanisms three types of storm deposit are distinguished i pot gutter casts ii tempestite beds and iii storm winnowed deposits each deposit provides information about the carbonate platform environment in which it was deposited the tempestite models proposed are i the bypass zone tempestite model occurring in a muddy ramp at the epicontinental basin margin this model is characterized by potholes and gutters that form in a shoreline bypass zone during storms ii the gradient current tempestite model in which frequent tempestite beds are related to storm gradient currents thickness and grain size decrease towards the deep distal ramp and iii the winnowed deposit tempestite model whereby storm deposits are winnowed and deposited in the same environment with only short lateral transport having occurred this model evokes more restricted and shallower conditions lagoons or inland seas the distribution of all these deposits in the stratigraphic sections studied corroborate the eustatic third order cycle identified although the different features of the storm deposits and their positions in each section indicate a subsidence varying in time and space in the transgressive stage the margins of the epicontinental basin were a well developed ramp with potholes and gutters in contrast during the high sea level stage storm deposits generated tempestite beds or storm winnowed deposits in the different areas the epicontinental carbonate platform with ramp edges evolved into a complex depositional system of coastal and shallow marine environments with lagoons and restricted inland seas thus the epicontinental platform underwent substantial change from the late anisian to the late ladinian and this is reflected in its storm deposits

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

shelf storm flow dynamics insight from the mesoproterozoic rampur shale central india abstract the intracratonic rift related mesoproterozoic rampur shale in kudri india formed in the marine mid and outer shelf domain it bears a dominant imprint of shore parallel storm driven flow as predicted by oceanographers for modern shelves and thus differs from other ancient storm deposits in the geological record in the rampur shale gutters are shore parallel while tool marks of various kinds are both shore parallel and shore normal and show bipolarity in both directions hydrodynamic analysis and inter relationships between the flow features suggest that the storm driven flow was shore parallel dominantly unidirectional and steady initially and that it became increasingly unsteady thereafter while also becoming dominantly shore normal during peak oscillation as storm conditions waned the gutters were filled by sediments under dominant wave influence these rampur data are consistent with observations made in modern seas and suggest that storm driven flows in general have evolved in the same way over time although their geological records may vary in details because of local constraints

sole marks in storm event beds in the permo carboniferous talchir formation raniganj basin india abstract sole marks in storm event beds are described for the first time from talchir formation permo carboniferous of raniganj basin india gutters and grooves trending subparallel to wave ripple crests were formed by shore parallel geostrophic flow at the initial phase of storms during intensification of storms oscillation dominated shore normal current produced gutters grooves and bipolar bimodal prod marks and bounce marks at nearly perpendicular or highly oblique to the axis of major wave ripple crests superposition of shore normal oscillatory flow on shore parallel geostrophic current during peak storms is evident from curvilinear crosscutting and turnabout groove marks hydrodynamic interpretation of these sole marks interrelationship between palaeogeographic constraints governing the overall sediment dispersal pattern and the stratification architecture in storm event beds signify complex interplay of mutually perpendicular shore parallel and shore normal components of storm current in shallow marine setting

detailed 3 d depositional architecture of late jurassic carbonate anhydrite cycles brightling mine weald basin uk abstract quantifying the geometries of evaporite deposits at a 13 c and 18 o isotope analysis the stratigraphic interval contains five facies in stratigraphic order these include supratidal porphyritic nodular evaporite shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite subtidal shale and subtidal laminar marl capped by nodular anhydrite the interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal tidal flat facies and subtidal shallow marine facies laterally passed into the evaporative sabkha the cycles are interpreted as meter scale shoaling upward sequences likely controlled by localized high frequency changes in relative sea level and or sabkha hydrology spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam the variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution eolian processes and coastal erosion these observations indicate a similar mode of deposition to the modern day sabkha of the persian gulf we conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses but largely continuous lateral bedding at an interwell scale

a palaeoproterozoic dolomite vempalle formation cuddapah basin india showing phanerozoic type dolomitisation abstract the palaeoproterozoic vempalle formation of the cuddapah basin india significantly adds to our understanding of the evolution of precambrian marine carbonate systems and the redox state of the earth s early oceans a facies microfacies diagenetic geochemical examination of samples from a 1000 m long exposure in a freshly cut canal section shows that 10 15 of precursor limestone is still preserved in the vempalle formation in the form of remnant patches of calcimicrite and ooids with calcite spar cement the ooids preserving primary radial and concentric fabrics and radial fractures are considered to have been originally precipitated as calcite which may have been low mg in places the preserved calcite spar that is partially replaced by fabric destructive dolomite shows type i calcite twin lamellae petrographic observations demonstrate that vempalle formation dolomite formed through very early precipitation which in stromatolites preserved microbial filaments as well as through fabric destructive dolomitization during shallow to moderate burial vempalle formation dolomite is characterized by micritic dolomite crystals which suggest rapid early dolomitization of lime mud and micritic calcite from a supersaturated mg ca rich solution probably near surface or during shallow burial depletion of na and sr contents of vempalle formation dolomite along with negative 18o values indicate dolomite recrystallisation during burial and further replacement dolomite 13c values of 0 5 to 2 are likely inherited original marine values geochemical proxies trace elements and rare earths imply that cuddapah basin seawater and dolomitizing fluids were anoxic and ferruginous but not euxinic geochemical analyses also indicate that the burial diagenetic fluids evolved from eu enriched seawater that probably resulted from continental rifting around 1 9 2 0 ga this probable ocean chemistry is in contrast with the anoxic ferruginous and extremely high mg ca dolomite oceans that prevailed during proterozoic time the vempalle dolomite shows more similarities with dolomitised phanerozoic platform carbonates than typical precambrian dolomite with its well preserved textures and burial dolospar cements

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

the evolution of a thick shallow marine succession the south munster basin ireland the relatively fine grained late devonian to early carboniferous cork beds succession of the south munster basin includes continuous sections of paralic facies that are over 1000 m thick and individual sandstone units over 300 m thick however the succession does not reflect prolonged phases when facies belts were stationary but rather multiple stacking of small scale high frequency sequences each associated with pronounced migration of shorelines what seems to have been unusual about the south munster basin succession was that the geographical positioning of these high frequency sequences was fixed this resulted from an unusual combination of tectonics shelf hydrodynamics sedimentation rates and the textural maturity of the sediment within the basin of these tectonics was probably most critical particularly the juxtaposition of rapid subsidence in basinal areas and a basin margin zone to the north that was sufficiently up standing to pin the maximum extent of transgression during repeated highstands of sea level yet not so upstanding as to have diverted the major regional drainage system the embayed palaeogeography of the area may also have been influential

geodetic measurements of postglacial adjustments in greenland 1 we analyze data from seven continuous global positioning system gps receivers and one tide gauge all located along the edge of the greenland ice sheet to determine vertical uplift rates we compare our results with predictions based on the ice 5g deglaciation model of peltier 2004 results from the gps receiver at kellyville 1 2 1 1 mm a and from the tide gauge at nuuk 2 2 1 3 mm a indicate that ice 5g overestimates the subsidence rates at those locations by 2 1 and 1 1 mm a respectively kellyville and nuuk are located along the southwestern margin of the greenland ice sheet and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last 8 ka to its current position the ice 5g glaciation deglaciation history includes a readvance between the latitudes of 62 n and 72 n the gps measurements suggest the ice 5g readvance may be too large or mistimed our gps results at qaqortoq located at the southern tip of greenland suggest a secular subsidence rate of 0 3 1 1 mm a while ice 5g predicts an uplift rate of 1 0 mm a ice 5g assumes no ice sheet readvance in south greenland including no readvance of the qassimiut lobe the difference of 1 3 1 1 mm a can tentatively be explained as due to a 33 km readvance of the qassimiut lobe during the last 3 ka for the other gps sites the observed predicted uplift rates are 3 6 1 1 0 1 mm a at thule 0 0 1 1 2 0 mm a at scoresbysund and 0 4 1 1 1 7 mm a at kulusuk for thule kulusuk and scoresbysund the differences between the observed and predicted rates are on the order of 1 3 3 7 mm a though with opposite signs and indicate that ice 5g does not exactly reproduce the correct rebound signal at those locations

an epeiric ramp low energy cool water carbonate facies in a tertiary inland sea murray basin south australia the murray supergroup records temperate water carbonate deposition within a shallow mesotrophic oligo miocene inland sea protected from high energy waves and swells of the open ocean by a granitic archipelago at its southern margin rocks are very well preserved and exposed in nearly continuous outcrop along the river murray in south australia most facies are rich in carbonate silt contain a background assemblage of gastropods especially turritellids and infaunal bivalves and are packaged on a decimetre scale defined by firmground and hardground omission surfaces bioturbation is pervasive and overprinted resulting in rare preservation of physical sedimentary structures facies are grouped into four associations large foraminiferan bryozoan echinoid bryozoan mollusc and clay facies interpreted to represent shallow water 50 m deposition under progressively higher trophic resource levels from low mesotrophy to eutrophy and restricted marine conditions from relatively offshore to nearshore regions a large scale shift from high to low mesotrophic conditions within lower miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow land locked sea overall low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity inshore heterozoan facies became progressively muddier and restricted towards the shoreline in contrast periods of wet climate led to rising trophic resource levels resulting in a shallowing of the euphotic zone a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids rates of carbonate production and accumulation were relatively low the murray basin is best described as an epeiric ramp wide facies belts developed in a shallow sea on a low angled slope reaching many hundreds of kilometres in length grainy shoal and back barrier facies were absent internally generated waves impinged the sea floor in offshore regions and because of friction along a wide and shallow sea floor created a low energy expanse of waters across the proximal ramp storms were the dominating depositional process capable of disrupting the entire sea floor

the mackenzie delta sedimentary processes and facies of a high latitude fine grained delta the mackenzie delta is a large fine grained delta deposited in a cold arctic setting the delta has been constructed upon a flooding surface developed on a previous shelf phase delta there are three principal depositional zones the subaerial delta plain the distributary channel mouth region and the subaqeous delta the subaerial delta plain is characterized by an anastomosing system of high sinuosity channels and extensive thermokarst lake development this region is greatly influenced by the annual cycle of seasonal processes including winter freezing of sediments and channels ice jamming and flooding in the early spring and declining river stage during the summer and autumn deposition occurs on channel levees and in thermokarst lakes during flood events and is commonly rhythmic in nature with discrete annual beds being distinguishable in the channel mouth environment deposition is dominated by landward accretion and aggradation of mouth bars during river and storm surge induced flood events the subaqeous delta is characterized by a shallow water platform and a gentle offshore slope sediment bypassing of the shallow water platform is efficient as a result of the presence of incised submarine channels and the predominance of suspension transport of fine grained sediments facies of the shallow platform include silty sand with climbing ripple lamination offshore facies are dominated by seaward fining fine sand to silt tempestites sea ice scouring and sediment deformation are common beyond 10 m water depth where bioturbated muds are the predominant facies the low angle profile of the shallow water platform is interpreted to be the combined response of a fine grained delta to 1 storm sediment dispersal 2 autoretreat as a result of the increasing subaerial and subaqeous area of deposition as the delta progrades out of its glacial valley 3 limited water depth above the underlying flooding surface and 4 efficient nearshore bypassing of sediment through subice channels at the peak of spring discharge several indicators of the cold climate can be used as criteria for the interpretation of ancient successions including thermokarst lake development submarine channel scours freeze thaw deformation and ice scour deformation structures permafrost inhibits compaction subsidence and together with the shallow water setting also limits autocyclic lobe switching the cold climate can thus influence stratal architecture by favouring the development of regional scale clinoform sets rather than multiple smaller scale lobes separated by autocyclic flooding surfaces

late holocene relative sea level rise and the neoglacial history of the greenland ice sheet in west greenland early and mid holocene relative sea level rsl fall was replaced by late holocene rsl rise during the neoglacial after 4 3 cal ka bp thousand calibrated years before present here we present the results of an isolation basin rsl study completed near to the coastal town of sisimiut in central west greenland rsl fell from 14 m above sea level at 5 7 cal ka bp to reach a lowstand of 4 0 m at 2 3 1 2 cal ka bp before rising by an equivalent amount to present differences in the timing and magnitude of the rsl lowstand between this and other sites in west and south greenland record the varied interplay of local and non greenland rsl processes notably the reloading of the earth s crust caused by a neoglacial expansion of the greenland ice sheet gis and the subsidence associated with the collapse of the laurentide ice sheet forebulge this means that the timing of the sea level lowstand cannot be used to infer directly when the gis advanced during the neoglacial the rise in late holocene rsl is contrary to recently reported bedrock uplift in the sisimiut area based on repeat gps surveys this indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late holocene and that there has been a switch from subsidence to uplift at some point in the last thousand years or so

clinoforms paleobathymetry and mud dispersal across the western canada cretaceous foreland basin evidence from the cenomanian dunvegan formation and contiguous strata large scale muddy clinoform stratification is rare in cretaceous marine strata of the western canada foreland basin most offshore mudstone units show near parallel to gently diverging stratification that reflects differential basin subsidence the early to middle cenomanian dunvegan formation of broadly deltaic character is unusual in that it comprises a spectacular set of clinothems these clinothems have been mapped over a 950 km dip transect and downlap from nw to se onto a phosphatic condensed section termed the fsu marker our regional mapping shows that the fsu marker is of basin wide extent and marks the abrupt cessation of deposition for up to about 2 my in the south in the northwest the dunvegan formation forms a prominent wedge over 300 m thick interpreted to fill a high accommodation area muddy clinothems in this high accommodation area are relatively tall 80 m 115 m decompacted and extend about 80 km from the delta front to a zero edge at the downlap surface wave rippled and hummocky cross stratified fine sandstones of the upper delta front record the effects of storms and extend about 30 m 42 m decompacted below contemporaneous beach facies suggesting that effective wave base for sand transport was at about 40 m water depth mud was transported in deeper water presumably by storm driven flows towards the se the dunvegan formation gradually changes from a wedge to a tabular shape interpreted to indicate deposition in a low accommodation area in the transition from high to low accommodation areas clinothems become progressively less tall 50 to about 20 m 70 to about 29 m decompacted but longer 150 to 250 km the most down dip clinothems are essentially tabular and 400 km in extent in the high accommodation area offshore mud dispersal is inferred to have been limited by episodic geostrophic flows and possibly by permanent along shelf flows that swept mud probably suspended flocculated and pelleted into a shore parallel prism producing relatively short steep clinothems muddy clinothems downlap onto sandy condensed facies of the fsu marker the latter interpreted to have been deposited in shallow water prior to dunvegan deposition but which subsided below wave base in response to loading by the advancing deltaic clinothems in the southern low accommodation area tabular dunvegan mudstones suggest that the sea floor was able to aggrade to effective wave base i e about 40 m or less at which point wave resuspension of mud became frequent resulting in efficient off and along shore dispersal of mud by geostrophic currents the initiation of clinothem deposition is interpreted to coincide a with a phase of accelerated flexural subsidence in the northwest related to renewed tectonic loading and b possibly with the onset of large scale anticlockwise marine circulation at the inception of the greenhorn seaway in the early cenomanian together these tectonic and oceanographic events formed an effective sediment trap along the western margin of the seaway only after the western sediment trap had filled in late dunvegan time was mud again dispersed widely across the basin by storm processes in water less than about 40 m deep

record of continental to marine transition from the mesoproterozoic ampani basin central india an exercise of process based sedimentology in a structurally deformed basin abstract the mesoproterozoic ampani group of rocks a structurally deformed sedimentary package hosted within the bastar craton in central india was studied for process based facies and paleoenvironmental analyses outcrop mapping on 1 1500 scale deconvolution of deformation pattern and process based facies analyses have led to the identification of fifteen facies types clubbed under four facies associations a range of paleoenvironmental settings varying from continental fluvial to distal marine shelf is inferred deductive paleohydrology revealed poorly efficient dirty river character for the ampani river system with low water discharge however at times of catastrophic sheet floods release of sediments trapped at the river mouth in form of hyperpycnal underflows triggered formation of river mouth delta reworking of delta front sediment in wave dominated coastline resulted development of beach foreshore and shoreface proximal to distal variation in the relative proportion of bar and interbar products within the shoreface successions exposed at different studied sections is interpreted as signature of relative bathymetric variation the pro deltaic ampani shelf was storm infested tectonic perturbance in the basin hinterland in course of ampani sedimentation is inferred from occurrence of a disparately thick lobate high density flow deposit towards the top of shoreface succession and increase in feldspar content upward within the shoreface succession addition of detritus from a 1600 ma mesoproterozoic provenance in upper part of shoreface also strengthen the contention deconvolution of deformation pattern and delineation of environmental products ranging between continental and deep marine allowed us to infer the ampani sediment package as fining upward in character evolved in a transgressive mode

storm event beds in a paleoproterozoic rift basin aravalli supergroup rajasthan india abstract storm event beds in the paleoproterozoic riftogenic sedimentary succession of aravalli supergroup are described from a 12 8 m thick sandstone mudstone interbedded unit in zawar area rajasthan india the storm event beds include different primary structural assemblages indicating deposition from waning storm current sequential arrangement of beds with characteristic primary structural assemblages suggests deposition under a transgressive phase and overall retrogradational evolution of the storm succession provides evidence in favour of faster downsagging of the basin floor the pb zn sulphide ore bearing sedimentary succession of zawar records repeated downsagging and exhumation of the basin floor in the frame of continental rift tectonics

significance of pot and gutter casts in a middle triassic carbonate platform betic cordillera southern spain pot casts and gutter casts are described for the first time in the lower part of the majanillos formation a middle triassic carbonate unit located in the external zones of the betic cordillera southern spain their identification as well as their relation to tempestites enables the better interpretation of the depositional environments and the shoreline to offshore facies transition on the anisian muddy carbonate ramp of the southern iberian massif the majanillos formation contains three members which become progressively more marly towards the top well preserved pot and gutter casts and thin intercalations of calcarenite which are interpreted as tempestites are abundant in the lowest member above the pot and gutter casts thicker calcarenite beds which locally contain hummocky cross stratification predominate bioturbated nodular limestones are prevalent at the top of the member the remaining succession which records a long term triassic transgressive cycle consists mostly of fine grained limestones deposited in very shallow marine environments calcarenitic sediments only accumulated within potholes and gutters in the nearshore they developed during storms when strong currents transported sediment to the outer shelf where it was deposited as tempestite beds pot and gutter casts characterize sedimentation in the bypass zone it is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry it is proposed that gutter casts display a trend of increasing width thickness ratios towards the outer shelf the identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments

anomalously mild younger dryas summer conditions in southern greenland the first late glacial lake sediments found in greenland were analyzed with respect to a variety of environmental variables the analyzed sequence covers the time span between 14400 and 10500 calendar yr b p and the data imply that the conditions in southernmost greenland during the younger dryas stadial 12800 11550 calendar yr b p were characterized by an arid climate with cold winters and mild summers preceded by humid conditions with cooler summers climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and fohn effects it shows that regional and local variations of younger dryas summer conditions in the north atlantic region may have been larger than previously found from proxy data and modeling experiments

shallow marine event sedimentation in a volcanic arc related setting the ordovician suri formation famatina range northwest argentina abstract the loma del kilometro member of the lower ordovician suri formation records arc related shelf sedimentation in the famatina basin of northwest argentina nine facies grouped into three facies assemblages are recognized facies assemblage 1 massive and parallel laminated mudstones facies a locally punctuated by normally graded or parallel laminated silty sandstones facies b records deposition from suspension fall out and episodic storm induced turbidity currents in an outer shelf setting facies assemblage 2 massive and parallel laminated mudstones facies a interbedded with rippled top very fine grained sandstones facies d is interpreted as the product of background sedimentation alternating with distal storm events in a middle shelf environment facies assemblage 3 normally graded coarse to fine grained sandstones facies c parallel laminated to low angle cross stratified sandstones facies e hummocky cross stratified sandstones and siltstones facies f interstratified fine grained sandstones and mudstones facies g massive muddy siltstones and sandstones facies h tuffaceous sandstones facies 1 and interbedded thin units of massive and parallel laminated mudstones facies a is thought to represent volcaniclastic mass flow and storm deposition coupled with subordinated suspension fall out in an inner shelf to lower shoreface setting the loma del kilometro member records regress ive transgressive sedimentation in a storm and mass flow dominated high gradient shelf volcano tectonic activity was the important control on shelf morphology while relative sea level change influenced sedimentation the lower part of the succession is attributed to mud blanketing during high stand and volcanic quiescence progradation of the inner shelf to lower shoreface facies assemblage in the middle part represents an abrupt basinward shoreline migration an erosive based non volcaniclastic turbidite unit at the base of this package suggests a sea level fall pyroclastic detritus andesites and a non volcanic terrain were eroded and their detritus was transported basinward and redeposited by sediment gravity flows during the low stand the local coexistence of juvenile pyroclastic detritus and fossils suggests reworking of rare ash falls the upper part of the loma del kilometro member records a transgression with no evidence of contemporaneous volcanism biostratinomic paleoecologic and ichnologic analyses support this paleoenvironmental interpretations and provide independent evidence for the dominance of episodic sedimentation in an arc related shallow marine setting fossil concentrations were mainly formed by event processes such as storms and volcaniclastic mass flows high depositional rates inhibited formation of sediment starved biogenic concentrations collectively trace fossils belong to the cruziana ichnofacies low diversity scarcity and presence of relatively simple forms indicate benthic activity under stressful conditions most probably linked to high sedimentation rates contrasting sedimentary dynamics between normal shelves and their volcaniclastic counterparts produce distinct and particular signatures in the stratigraphic record arc related shelves are typified by event deposition with significant participation of sediment gravity flows relatively high sedimentation rates textural and mineralogical immaturity of sediments scarcity and low diversity of trace fossils and dominance of transported and reworked faunal assemblages genetically related to episodic processes

morphological adaptations of 3 22 ga old tufted microbial mats to archean coastal habitats moodies group barberton greenstone belt south africa microbial life was well established and widespread by the paleoarchean however the degree of evolutionary advancement such as microbial motility intra and inter species interactions phototropism or oxygenic photosynthesis by that time remains highly debated the 3 22 ga moodies group in the barberton greenstone belt bgb south africa are earth s oldest well preserved siliciclastic tidal deposits they exhibit a unique assemblage of microbial mats providing an excellent opportunity to decipher the morphological adaptations of microbial communities to different paleoenvironmental settings the fossil mats are preserved as kerogenous laminations 0 5 1 mm thick that can be traced laterally for 15 km in a 1000 m thick succession of fine to coarse grained tidal sandstones and conglomerates we here present a detailed stratigraphic and depositional facies analysis documenting the association of the three principal mat morphotypes with specific environmental settings 1 planar type in coastal floodplain 2 wavy type in intertidal and 3 tufted type in upper inter to supratidal facies all mat types indicate a flourishing phototrophic biota moreover the tufted morphology suggests an intricate level of coordinated growth commonly known from cyanobacterial mats in modern environments

flat pebble conglomerate its multiple origins and relationship to metre scale depositional cycles carbonate flat pebble conglomerate is an important component of precambrian to lower palaeozoic strata but its origins remain enigmatic the upper cambrian to lower ordovician strata of the snowy range formation in northern wyoming and southern montana contain abundant flat pebble conglomerate beds in shallow water cyclic and non cyclic strata several origins of flat pebble conglomerate are inferred for these strata in one case all stages of development of flat pebble conglomerate are captured within stormdominated shoreface deposits of hummocky cross stratified hcs fine carbonate grainstone a variety of synsedimentary deformation structures records the transition from mildly deformed in situ stratification to buckled beds of partially disarticulated bedding to fully developed flat pebble conglomerate these features resulted from failure of a shoreface and subsequent brittle and ductile deformation of compacted to early cemented deposits failure was induced by either storm or seismic waves and many beds failed along discrete slide scar surfaces centimetre scale laminae within thick amalgamated hcs beds were planes of weakness that led to the development of platy clasts within partly disarticulated and rotated bedding of the buckled beds in some cases buckled masses accelerated downslope until they exceeded their internal friction completely disarticulated into clasts and transformed into a mass flow of individual cm to dm scale clasts this transition was accompanied by the addition of sand sized echinoderm rich debris from local sources which slightly lowered friction by reducing clast clast interactions the resulting dominantly horizontal clast orientations suggest transport by dense viscous flow dominated by laminar shear these flows generally came to rest on the lower shoreface although in some cases they continued a limited distance beyond fairweather wave base and were interbedded with shale and grainstone beds the clasts in these beds show no evidence of extensive reworking i e not well rounded or condensation i e no rinds or coatings a second type of flat pebble conglomerate bed occurs at the top of upward coarsening metre scale cycles the flat pebble conglomerate beds cap these shoaling cycles and represent either lowstand deposits or in some cases may represent transgressive lags the clasts are well rounded display borings and have iron rich coatings the matrix to these beds locally includes glauconite these beds were considerably reworked and represent condensed deposits thrombolites occur above the flat pebble beds and record microbial growth before initial transgression at the cycle boundaries a third

upper lower cambrian depositional sequence in avalonian new brunswick the hanford brook formation emended is a thin up to 42 m upper lower cambrian depositional sequence that is unconformably bounded by the lower lower cambrian random formation and the middle middle cambrian fossil brook member of the chamberlain s brook formation these stratigraphic relationships of the trilobite bearing hanford brook formation indicate deposition on the avalonian marginal platform in the saint john new brunswick region and provide more evidence for a uniform latest precambrian cambrian epeirogenic history and cover sequence in avalon the hanford brook formation is a deepening shoaling sequence with i lower transgressive sandstone deposited in episodically high energy environments st martins member new ii highstand regressive dysaerobic mudstone fine grained sandstone with volcanic ashes somerset street member new and iii upper regressive planar and hummocky cross stratified sandstone long island member new trilobites are common in the distal somerse

depositional processes of the zhushadong and mantou formations early to middle cambrian shandong province china roles of archipelago and mixed carbonate siliciclastic sedimentation on cycle genesis during initial flooding of the north china platform to understand the depositional processes and environmental changes during the initial flooding of the north china platform this study focuses on the lower to middle cambrian zhushadong and mantou formations in shandong province china the succession in the jinan and laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone dolostone stromatolite thrombolite purple and grey mudstone and sandstone a detailed sedimentary facies analysis of seven well exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments including local alluvial fans shallowing upward carbonate siliciclastic peritidal cycles oolite dominant shoals shoreface and lagoonal environments these facies associations successively show a transition from an initially inundated tide dominated carbonate platform to a wave dominated shallow marine environment in particular the peritidal sediments were deposited during a large number of depositional cycles these sediments consist of lime mudstone dolomite stromatolite and purple and grey mudstones these shallowing upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea level the carbonate production was however interrupted by frequent siliciclastic input from the adjacent emergent archipelago the depositional cycles thus formed under the influence of both autogenetic changes including sediment supply from the archipelago and allogenic control of relative sea level rise in the carbonate factory a low relief archipelago with an active tidal regime allowed the development of tide dominated siliciclastic and carbonate environments on the vast platform siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea level this study provides insights on how a vast cambrian carbonate platform maintained synchronous sedimentation under a tidal regime forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea level during the early stage of basin development in the north china platform

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

stratigraphic evolution from shoreface to shelf indenting channel depositional systems during transgression insights from the lower pliocene sua member of the basal upper onzole formation borbon basin northwest ecuador abstract shelf indenting canyons and their tributary systems are fairly common constituents of quaternary shelves of active continental margins but they have been rarely reported from older successions recognition of these prominent geomorphologic features in the ancient record has important implications not only for a proper understanding of shoreface to shelf depositional systems but also from a petroleum exploration standpoint as they represent efficient conduits for moving coarse grained river and nearshore borne sediments to the adjacent slope even during periods of relative rise in sea level coastal exposures of the lower pliocene sua member in the surroundings of sua northwest ecuador preserve the unusual juxtaposition of incising submarine channels onto nearshore deposits this succession accumulated along a narrow active continental margin during tectonically induced transgression and affords a rare opportunity to evaluate the stratigraphic evolution of such systems from an outcrop perspective a comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order i a polygenetic regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary sb wrs ii a nearshore sand prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower shoreface bioturbated silty sandstones into inner shelf sandy mudstones iii two steep u shaped erosional features turbidite shelf entrenchment surfaces interpreted as shelf channels deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies iv a thick fining upward sedimentary succession laid down within the confines of the channels by high and low density turbidity currents and including both bed load traction and suspended load deposits the overall fining and thinning upward character exhibited by the infill of these channels is thought to reflect decreasing flow energies and is consistent with the gradual cut off of clastic influx to their upper reaches in response to progressive detachment from an adjacent coastal source during relative rise in sea level based on detailed analysis of facies and a sequence stratigraphic interpretation of outcrop data this study contributes to extend the existing sequence stratigraphic schemes further attesting that shelf sediment bypass and deep water sedimentation can take place at sea levels other than lowstand

rapid early holocene ice retreat in west greenland abstract the possible demise of the greenland ice sheet and its effect on global sea level rank among the most serious climate threats to society to improve our knowledge about the future behaviour of the ice margin we studied the ice sheet s response to early holocene warming in west greenland using 47 cosmogenic 10 be exposure ages 26 optically stimulated luminescence ages as well as 15 new and 28 previously published radiocarbon ages paired bedrock and boulder ages show that the entire area was covered by warm based ice during the last glacial maximum lgm although glacial erosion was insufficient to completely remove the upper rock surface containing 10 be inherited from a previous period of exposure in bedrock samples above an elevation of 800 m our compilation of 10 be and 14 c ages demonstrates that the ice sheet retreated from the outer coast to the present ice margin between c 11 4 and 10 4 cal ka bp in the godthabsfjord system and between 10 7 0 6 and 10 1 0 4 ka ago in buksefjord whereas the coast at sermilik became ice free at c 10 5 cal ka bp we find no significant changes in the retreat rates between the deep godthabsfjord system and the buksefjord sermilik region which is characterized by only a few narrow and shallow fjords however deglaciation was initiated c 700 900 years earlier in the godthabsfjord system indicating that the deep fjords probably triggered land based deglaciation by dynamic ice loss leading to an overall rapid early holocene ice retreat and drawdown of the ice sheet in west greenland these results demonstrate that even if there was a topographic control on the onset of deglaciation fast ice retreat is not restricted to deep fjord systems but may occur independently of the topographic setting

impact of dynamic sedimentation on facies heterogeneities in lower cretaceous peritidal deposits of central east oman this study based in the haushi huqf area of central east oman aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of lower cretaceous tidal flat facies within the tethyan epeiric platform field petrographic and geochemical data were acquired from the barremian aptian jurf and qishn formations that crop out in a 500 1000 m2 butte thus allowing for pseudo three dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies the interpretation presented here suggests that the main processes impacting sedimentation in the lower cretaceous peritidal environment of the haushi huqf were transport and erosion processes related to storm waves and currents the vertical evolution of the carbonate system is organized into six types of metre scale depositional sequences from subtidal dominated sequences to supratidal capped sequences which are bounded by regional discontinuity surfaces at subaerial exposure and submarine erosion surfaces associated with a base level shift sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events chemostratigraphy allows correlation between the haushi huqf and the age equivalent sections logged in the interior of the platform in oman the correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf this study is the first to discuss the controls on lower cretaceous peritidal carbonate cyclicity of the arabian epeiric platform the results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context

cambrian stratigraphy and depositional history of the northern indian himalaya spiti valley north central india recent work on himalayan tectonics indicates that prior to the cenozoic collision of india and asia an enigmatic cambrian ordovician event may have strongly infl uenced the regional geology of the himalaya stratigraphic and sedimentological analyses of well preserved cambrian deposits are critical for understanding the nature of this early tectonic event and its infl uence on the later tectonic evolution of the himalaya the parahio formation defi ned herein of the parahio valley spiti region in the tethyan himalaya of india is the best biostratigraphically resolved section of cambrian strata in the entire himalaya this formation consists of 1350 m of dominantly siliciclastic deltaic deposits the formation ranges from uppermost lower cambrian lungwangmiaoan stage to middle middle cambrian hsuchuangian stage representing a time span of 5 10 m y it contains numerous mediumscale shoaling cycles that range from storminfl uenced offshore deposits to thick trough cross bedded fl uvial facies many thin carbonate beds with abundant trilobite fossils directly overlie the fl uvial facies and represent transgressive systems tract deposits the cycles are interpreted to have resulted from delta lobe switching based on a lack of systematic stratigraphic changes in cycle or facies thicknesses this paleoenvironmental reconstruction contradicts previous interpretations of this unit that range from deep sea fl ysch to shallow marine tidalites in addition our paleoenvironmental analysis and paleocurrent data suggest that the uppermost lower to middle cambrian deposits of the lesser and tethyan himalaya are parts of the same ancient northward prograding fl uvial deltaic depositional system of the paleo tethys margin of india an angular unconformity with overlying ordovician conglomeratic rocks has considerable local relief with meter scale scours and a valley fi ll 100 m thick the scours have northeast southwest orientations which parallel both the paleocurrents in the underlying parahio formation as well as published paleocurrent readings from the coarse red beds of the overlying ordovician strata the cambrian ordovician unconformity is of regional extent and our recent biostratigraphic database indicates that the minimum hiatus associated with the unconformity in spiti is 15 m y our sedimentological analysis and associated paleocurrent data from the parahio formation along with additional data from units both above and below the unconformity indicate that published models portraying foreland basin development at this time with southward directed thrusting are problematic an alternate possibility that uplift took place south of the tethyan himalaya is also problematic because no published stratigraphic or structural evidence exists for such an uplift to the south for either the greater or the lesser himalaya lithotectonic zones

storm wave development of shore normal grooves gutters on a steep sandstone beach face abstract shore normal grooves gutters cut into the seabed have been reported widely from the marine geological record grooves commonly are spaced regularly across plane consolidated surfaces in the littoral and sub littoral zones and may be deeply incised despite their common occurrence in the rock record there are few detailed descriptions of examples from modern environments previously reported examples have been ascribed to erosion by wave induced currents especially storm driven near shore flows in particular examples from beach faces have been related to either wave swash or backwash however no conceptual model exists to explain the presence of grooves their morphology or their spacing alongshore herein quasi regularly spaced grooves on a soft sandstone beach face are described and interpreted to have formed due to wave breaking and swash zone processes consequent upon exceptional storms at sea the groove morphologies are quantified using terrestrial laser scanning numerical modelling of the translation from offshore waves to nearshore breaking waves provides estimates of the swash zone parameters a consideration of swash zone processes provides an explanation for formation of the grooves in particular the swash zone shear stress distribution and consequent bed erosion is a dome shaped function of distance across the beach face and this controls the cross shore variability in groove depths high speed sheet flows such as swash and backwash develop periodic shore normal high and low speed streaks alongshore consequent streaky erosion produces the quasi regular alongshore groove spacings however on any given beach face the specific spacing of grooves is likely a property not only of the local sheet flow attributes but also of larger scale morphological forcing this outcome suggests that spacing is an emergent property of the coupled sheet flow and larger scale forcing and thus specific spacings on any beach face remain unpredictable

terminal cambrian and lowest ordovician succession of mexican west gondwana biotas and sequence stratigraphy of the tinu formation the tinu formation of oaxaca state is the only fossiliferous lower palaeozoic unit between the laurentian platform in northwest mexico and gondwanan successions in andean south america the tinu traditionally has been referred to the lower ordovician tremadoc and regarded as having a provincially mixed fauna with laurentian avalonian and gondwanan elements bio and lithostratigraphic re evaluation demonstrates that the tinu is a gondwanan passive margin succession it includes a lower thin to 16 m condensed uppermost cambrian yudachica member new the yudachica nonconformably overlies middle proterozoic basement as a result of very high late late cambrian eustatic levels the yudachica changes from storm dominated but slightly dysoxic shelf facies fossil hash limestone and shale in the south to an upper slope facies with debris flows 50 km to the north three biostratigraphically distinct depositional sequences comprise the yudachica the yudachica has gondwanan aspect trilobites with low diversity conodonts characteristic of unrestricted marine temperate facies the upper tinu or rio salinas member new is a lower ordovician tremadoc depositional sequence that records strong early but not earliest tremadoc eustatic rise marked by graptolite and olenid bearing dysoxic mudstones higher strata shoal upward into shell hash limestones and proximal tempestite sandstones with upper lower tremadocian unrestricted marine temperate conodonts new taxa include orminskia rexroadae landing gen et sp nov from the cordylodus andresi zone this euconodont is related to hyaline coniform genera best known from ordovician tropical platform successions cornuodus clarkei landing sp nov resembles the coeval upper lower tremadoc tropical species scalpellodus longipinnatus ji barnes

eifelian givetian middle devonian high paleolatitude storm and wave dominated shallow marine depositional systems from the bidouw subgroup bokkeveld group of south africa abstract the sedimentology of the eifelian givetian middle devonian bidouw subgroup in the clanwilliam sub basin of south africa has been reassessed four distinct lithofacies associations are recognized a d and are representative of the deposits of offshore os offshore transition zone to distal lower shoreface otz dlsf proximal lower shoreface plsf and upper shoreface beach usf beach paleoenvironments these paleoenvironments are arranged as several t r controlled storm and wave dominated shallow marine depositional systems the presence of storm and wave dominated shallow marine depositional systems in the bidouw subgroup as well as the preceding emsian eifelian early middle devonian ceres subgroup provides an alternative explanation to storm and wave dominated delta and mixed wave and tide dominated delta models that have previously been proposed for the bokkeveld group sequence stratigraphic analysis of the bidouw subgroup suggests that although sedimentation occurred during two large scale second order transgressive events the succession was predominantly regressive third order and fourth order transgressive regressive t r sequences are more numerous with respect to the preceding ceres subgroup suggesting that the driver for t r cyclicity and relative sea level change was more active during the eifelian givetian than in the emsian eifelian of south africa these data are important since relative sea level change and its effects on paleoenvironmental change at high paleolatitudes during the devonian period are poorly known

seafloor erosion and sea level change early jurassic blue lias formation of central england abstract minor bedforms within the mudstone dominated early jurassic hettangian saltford shale member liasicus up to angulata chronozone of the blue lias formation in central england indicate weak seafloor erosion in a mid to outer ramp setting distal storm flows below maximum storm wave base are proposed as the most likely generative mechanism for silty scour and gutter casts that enclose concentrations of well preserved schlotheimiid ammonites and arthropod trace fossils within the upper part of the saltford shale probably angulata chronozone a discrete layer of reworked and bioencrusted limestone nodules signifies an episode of more persistent seafloor erosion the immediately overlying strata transitional to the hettangian sinemurian rugby limestone member are relatively bioturbated and feature fossils of macrobenthos as well as shell concentrations resembling relatively proximal storm beds this suggests that the reworked nodule horizon marks sea level fall rather than stratigraphic condensation associated with sediment starvation the biostratigraphic evidence raises the possibility that this erosional episode correlates with a mid angulata chronozone hiatus documented from the wessex basin southwest england equally however it could be linked to contemporaneous movement on one or more nearby faults affecting the southern part of the english east midlands shelf

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

pot and gutter casts from the chapel island formation southeast newfoundland abstract member 2 of the chapel island formation of southeast newfoundland contains a diverse suite of erosional structures known as pot and gutter casts these are particularly abundant in a lithofacies deposited in a nearshore zone characterized by erosion and sediment bypass during storm emplacement of sands the steep to overhanging walls of both pot and gutter casts imply rapid filling during the same storm events that created these depressions erosion is thought to have taken place under strong offshore directed unidirectional flow storm surge or other relaxation flow as with many sandstone tempestites the initial stages of the storm events were dominated by strong and in this case highly erosive unidirectional flow and the latter stages by oscillatory flow as evidenced by wave diagnostic lamination in the sandy infills pot casts have geometries and soles indicating vortex flow similar to that which forms potholes in bedrock in glaciated regions gutter casts that lead into potholes do so at their edge a requirement for generating rotary currents within the depression pot casts are commonly tilted relative to paleohorizontal and their direction of plunge is either upcurrent or downcurrent variation in geometry of the erosional structures from the chapel island formation and from erosional structures in general can be accounted for by the following substrate type diagenetic history of substrate and flow parameters such as pattern of water motion velocity and intermittency of flow

shallow water gravity flow deposits chapel island formation southeast newfoundland canada a remarkable suite of shallow water gravity flow deposits are found within very thinly bedded siltstones and storm generated sandstones of member 2 of the chapel island formation in southeast newfoundland medium to thick siltstone beds termed unifites range from non graded and structureless type 1 to slightly graded with poorly developed lamination type 2 to well graded with lamination similar to that described for fine grained turbidites type 3 unifite beds record deposition from a continuum of flow types from liquefied flows type 1 to turbidity currents type 3 calculations of time for pore fluid pressure dissipation support the feasibility of such transitions raft bearing beds consist of siltstone with large blocks or rafts of thinly bedded strata derived from the underlying and adjacent substrate characteristics suggest deposition from debris flows of variable strength estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters an assumed density of 2 0 g cm 1 and a compaction estimate of 50 gives a strength estimate of 79 7 dyn cm 2 and a depositional slope estimate of 0 77 the lithologies and sedimentary structures in member 2 indicate an overall grain size distribution susceptible to liquefaction inferred high sediment accumulation rates created underconsolidated sediments metastable packing types of sediment failure included in situ liquefaction disturbed bedding sliding and slumping raft bearing debrites resulted from sliding and incorporation of water locally hummocky cross stratified sandstone directly overlies slide deposits and raft bearing beds linking sediment failure to the cyclical wave loading associated with large storms the gravity flows of the chapel island formation closely resemble those described from the surfaces of modern mud rich marine deltas details of deltaic gravity flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side scan sonar

shallowing upward cycles in pelagic troughs upper jurassic subbetic southern spain abstract abundant calcareous tempestites with chert and hummocky cross stratification hcs occur in upper jurassic successions milanos formation of the subbetic betic cordillera southern spain these calcareous tempestite beds are calcisiltites and very fine calcarenites with peloids and bioclasts and have thicknesses between 25 and 75 cm beds show symmetrical wave ripple lamination near the top and are usually capped with wave ripples according to palaeogeographic reconstructions these strata were deposited in a subsiding trough in the pelagic domain of the southern iberian continental margin which was the northwestern most border of the tethys calcisiltite and calcarenite beds deposited in this pelagic trough form small scale to large scale shallowing upward cycles shallowing upward cycles with calcareous tempestites in the lower part and oolitic limestone beds in the upper part have also been recognized in some sectors of the subbetic pelagic basin the large scale cycle occurs in the upper part of the jarropa radiolarite formation which directly underlies upper oxfordian kimmeridgian and tithonian strata of the milanos formation two types of large scale shallowing upward cycles have been recognized according to the presence or absence of thick units of oolitic limestone with large scale cross stratification the water depth during deposition ranged from below but near storm wave base at the base of the large scale cycles to very shallow carbonate platform at the top

distinguishing eustatic and epeirogenic controls on lower middle cambrian boundary successions in west gondwana morocco and iberia major eustatic fall has been invoked to explain lower middle cambrian boundary sandstones and faunal replacements on a number of cambrian palaeocontinents this proposal has been tested on the moroccan and spanish margins of west gondwana and found to be inadequate to explain stratigraphical developments in these regions sandstone intervals long presumed to be regressive and late early cambrian in age are now shown to be early middle cambrian and composed of a lower regressive and an overlying transgressive sandstone separated by a regional unconformity only the lower tidalites i e tazlaft formation in morocco and lower daroca sandstones in spain record the hawke bay eustatic regression in west gondwana the tazlaft is overlain by a newly recognized unconformably overlying sandstone talelt formation that onlapped southern morocco with reactivation of a pull apart or transcurrent regime up to 150 m of erosion on uplifted blocks in the high atlas range and foundering of the souss basin to the south preceded onlap and deposition of the volcanic rich tatelt the correlative and depositional analogue of the upper daroca and lower valdemides formations in northern spain with folding and erosion a type 1 depositional sequence boundary also caps the tatelt at its contact with an overlying lower middle cambrian mudstone dominated succession this unconformity probably occurs in spain within the valdemiedes formation and corresponds to a faunal discontinuity called the valdemiedes geoevent the iberian daroca regression and moroccan asrir regression are misnomers as the sandstones on which they are based are composite units with a lower regressive interval that records eustatic fall and an upper transgressive unit that records epeirogenically driven onlap

morphology and facies architecture of a falling sea level strandplain umiujaq hudson bay canada coastal strandplain deposits near umiujaq eastern hudson bay canada were formed under falling relative sea level conditions resulting from postglacial isostatic uplift ground probing radar profiles across the strandplain reveal a lower progradational unit lpu discordantly overlain by an upper progradational unit upu which were correlated with stratigraphic sections exposed in incised valley walls the discordance is a wave erosion surface wes that separates fine shoreface sands of the lpu from coarse sand and gravel of the upu major basal downlap surfaces can be traced updip into marine terraces and define downstepping wedges the downstepping is interpreted as representing autocyclic morphological reconfiguration rather than a response to changes in the rate of sea level fall the internal architecture is strongly dependent on the accommodation and thus on antecedent topography a conceptual model for strandplain deposition under falling sea level incorporates a bipartite shallowing upward sandy succession when sufficient accommodation is available where accommodation space is limited a sharp based bar and beach sandbody directly overlies muddy deeper water deposits and the wes resembles a regressive surface of erosion

nehrp soil classifications for estimating site dependent seismic coefficients in the upper mississippi embayment abstract local soil conditions have a profound influence on the characteristics of ground shaking during an earthquake exceptionally deep soil deposits on the order of 100 1000 m deep are found in the upper mississippi embayment of the central united states shear waves sh from earthquakes in the new madrid seismic zone are expected to be strongly affected by the sharp impedance contrasts at the bedrock sediment interface attenuation of seismic waves in the soil column and the sh wave velocities of the more poorly consolidated near surface 50 m soils sh wave velocities of the near surface soils at nearly 400 sites in the upper mississippi embayment were determined using conventional seismic sh wave refraction and reflection techniques based on the average sh wave velocities of the upper 30 m of the soils sites in the mississippi river floodplain portion of the study area are predominantly classified as site class d 180 360 m s in accordance with the 1997 nehrp provisions sites away from the active floodplains in western kentucky and western tennessee the sh wave velocities of the upper 30 m of soils typically ranged from mid 200 to mid 300 m s several sites in western kentucky had averaged sh wave velocities greater than 360 m s thereby qualifying them as site class c 360 760 m s in accordance with the 1997 nehrp provisions one dimensional site effects including amplification and dynamic site period were calculated for a representative suite of sites across the upper mississippi embayment at latitude 38 5 although seismic attenuation is greater in the mississippi river floodplain i e thicker lower velocity material the site effects tend to be greater than in the uplands of western tennessee because of larger impedance contrasts within the near surface soils

deepening upward subtidal cycles murray basin south australia abstract decimeter scale deepening upward cycles are the basic depositional motif of oligocene miocene murray supergroup limestones in the murray basin southeastern australia cycles formed in this large intracratonic basin on a centripetal temperate water epeiric ramp they reflect generation by trophic resource influenced carbonate production under mostly transgressive conditions listed from the base up each cycle is ideally composed of five parts part a biotically depauperate carbonates reflecting relatively shallow water restricted variably stressed highly mesotrophic environments part b increasingly biotically diverse limestones recording progressively more physical energy and less mesotrophic conditions upward om1 a conspicuous hardground to firmground surface formed during late transgression to stillstand during which wave sweeping and reworking contributed to omission and lithification part c relatively biotically diverse epifauna dominant sediments that were highly abraded during periods of condensed sedimentation under marginally oligotrophic conditions and om2 cycle boundary a rarely conspicuous surface representing arrested sedimentation and variable cementation as trophic resources increased and conditions for carbonate production deteriorated ten cycle types are grouped into four major styles clay cycles mollusc cycles echinoid cycles and bryozoan cycles these are interpreted to form a lithological continuum from inner restricted terrigenous locales to outer open marine bryozoan colonized environments deepening upward cycles were profoundly sensitive to autogenic factors such as nutrient influx terrigenous content and turbidity hydrodynamic energy water temperature salinity and water depth manifested in this intracratonic setting although these cycles share a similar sedimentological motif and hydrodynamic energy based cycle capping process with open shelf epicratonic shallowing upward subtidal cycles of tertiary age they formed in a very different way reflecting the distinctive intracratonic environment in which they formed murray basin cycles preserve a record of relative sea level rise whereas open shelf cycles accumulated mostly during relative sea level fall

sedimentary structures sorby and the last decade henry clifton sorby pioneered in the last century the description and especially the hydrodynamic interpretation of sedimentary structures together with their use as palaeocurrent indicators research completed since the last syntheses were published a decade ago shows that work along these lines continues to be necessary and relevant particularly as regards the physical explanation of structures and to present significant challenges and opportunities perhaps the most pressing needs are for a better understanding of 1 bedforms in gravels silts and carbonate sediments 2 tidal and especially sand wave bedding 3 hummocky and swaley cross stratification and 4 soft sediment and dewatering structures in turbidites many sedimentary structures present a little exploited opportunity to quantify process rates and define short time periods from the rock record

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

the manciano sandstone a shoreface deposit of miocene basins of the northern apennines italy abstract well exposed diamond line cut quarry exposures of the manciano sandstone allow a detailed analysis of sandy fossiliferous nearshore deposits of the shelf of the northern apennines the manciano sandstone is characterized by medium to very coarse washed fairly well sorted lithic sandstone with thin interlayers of sandy conglomerates it displays two principal rhythmically alternating sandy facies a slightly burrowed mostly macaronichnus ophiomorpha skolithos units trough cross bedded locally showing possible tidal bundles with few whole scutella echinoid shells reworked on foresets or occasional large scale approximately 2 m planar cross bedded bar accretion units and b slightly finer darker coloured reddish brown sandstone units heavily bioturbated cruziana skolithos ichnofauna representing slightly more sheltered settings large oysters are present in near living position in a few thin layers and more commonly as reworked comminuted fragments in sandy layers many calcareous pebbles and oyster fragments are bored other fossils consist of echinoids scutella some balanids and reworked foraminifera and bryozoa the manciano sands were deposited primarily in a wave dominated shoreface containing migrating bars ridges and affected by wave induced possibly tidal enhanced currents this tidal influence confirms the opening of the miocene apenninic sea to oceans both the developing atlantic ocean to the west and through a long narrow seaway the asian portion of the tethys sea to the east

backset lamination produced by supercritical backwash flows at the beachface shoreface transition of a storm dominated gravelly beach middle pleistocene central italy abstract bedforms and resulting sedimentary structures of interpreted upper flow regime origin are fairly common in various ancient and modern depositional settings yet outcrop examples of shallow water strata dominated by sedimentary structures arising from such flow conditions are rarely documented this outcrop based study presents the first detailed analysis of mid pleistocene beachface shoreface strata containing sedimentary structures interpreted to have been formed by storm generated backwash flows during the transition in flow regime from supercritical to subcritical here we propose that moving down the steep beachface backwash flows rapidly accelerated and became thinner experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface and then waned to thicker and subcritical conditions just downflow of the hydraulic jump in this frame landward dipping backset laminae deposited on the downflow side of the trough evolved into thinner upper stage plane parallel laminae further downstream the transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals in concert with a progressive decrease in thickness and grain size of individual sets of plane parallel laminae and increase of gravel filled gutter casts

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

sequence stratigraphy and carbonate siliciclastic mixing in a terminal proterozoic foreland basin urusis formation nama group namibia abstract superb three dimensional exposures of mixed carbonate and siliciclastic strata of the terminal proterozoic urusis formation in namibia make it possible to reconstruct cross basin facies relations and high resolution sequence stratigraphic architecture in a tectonically active foreland basin six siliciclastic facies associations are represented coastal plain upper shoreface middle shoreface lower shoreface storm influenced shelf and pebble conglomerate siliciclastic shoreface facies pass seaward into and interfinger with facies of an open carbonate shelf four carbonate facies associations are present mid shelf shelf crest outer shelf and slope facies are arranged hierarchically into three scales of unconformity bounded sequences small scale sequences are one to tens of meters thick and span a few thousand years they consist of shelf carbonate with or without shoreface siliciclastic facies near the bottom medium scale sequences are tens of meters thick and span a few hundred thousand years they consist of shoreface siliciclastic facies in their lower parts which grade upward and pass seaward into shelf carbonate large scale sequences are tens to hundreds of meters thick and span 1 to 2 million years they are identified by widespread surfaces of exposure abrupt seaward shifts in shoreface sandstone patterns of facies progradation and retrogradation and shoreline onlap by medium scale sequences patterns of carbonate siliciclastic mixing distinguish tectonic from eustatic controls on the evolution of large scale sequences characteristics of eustatically controlled large scale sequences include 1 basal unconformities and shoreface sandstone that extend across the shelf to the seaward margin 2 retrograde carbonate and siliciclastic facies belts that onlap the shoreline together symmetrically during transgression and 3 upper shoreface sandstone that progrades seaward during highstand in contrast tectonically controlled sequences feature 1 basal erosion surfaces and upper shoreface sandstone that are restricted to near the landward margin and pass seaward into zones of maximum flooding and 2 asymmetric stratigraphic development characterized by landward progradation of carbonate from the seaward margin coincident with backstepping and onlap of the shoreline by siliciclastic facies a two phase tectonic model is proposed to account for the stratigraphic asymmetry of tectonically controlled sequences increased flexural bending during periods of active thrust loading caused submergence of the seaward margin and uplift of the landward margin rebound between thrusting episodes flattened the basin gradient and submerged the landward margin causing expansion of carbonate facies from the seaward margin and simultaneous transgression of the landward margin although the two phase model should apply to single lithology successions deposited in active foreland basins the mixing of carbonate and siliciclastic facies provides a particularly sensitive record of tectonic forcing the sensitivity may be sufficient for medium and small scale sequences to record higher frequency variations in flexural warping

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

air discharge pits on the yellow river delta plain abstract a large number of air discharge pits varying in size and shape are developed on the yellow river delta their planar cross sections are circular sub circular elongated and frequently irregular and their spatial configurations may be in form of a shallow dish to root like or other extremely irregular shapes they range in diameter from less than 1 cm to over 60 cm and their depth varies from less than 1 mm to more than 20 cm they most commonly occur individually or in groups on the point bar our investigation indicates that the occurrence of the air discharge pits is closely associated with the unique hydrological channel and hydrodynamic conditions caused by the intermittent flow interruptions of the yellow river and the fine sediments typical of the river course during a yellow river flow interruption an underground air saturation zone in the dry layer of the riverbed may be formed due to the lowering of the ground water level when flooding originates from the up stream section of the yellow river the water quickly inundates the channel and rapidly submerges the extremely dry river bed and point bar as a result due to the blocking effect caused by the silty sand and mud preferential percolation occurs along the outer edge of the point bar and levee trapping air in the process the resulting air pocket and pressure capsule are enclosed in the air saturation zone providing the source material required for the subsequent formation of air discharge pits the trapped air may also form a high pressure capsule caused by the slow downward percolation of the river water the differential relatively lower pressure on the point bar permits the trapped air to escape provided the air is discharged in a shallow body of water

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

facies and cycle architecture of a pleistocene marine terrace crotone southern italy a sedimentary response to late quaternary high frequency glacio eustatic changes abstract cyclic late pleistocene shallow marine deposits such as those forming the sedimentary cover of some marine terraces allow a detailed study of the architecture of nearshore to offshore cycles deposited under the influence of high amplitude glacio eustatic changes the capo colonna marine terrace located near crotone southern italy is composed of two cycles recording a low frequency retrogradational trend which is thought to be the result of a generalized base level rise during a late pleistocene interglacial stage superimposed on regional uplift cycles of the capo colonna marine terrace are composed of coarse grained lags siliciclastic shoreface deposits and mostly carbonate shelf deposits and their general stratigraphic architecture evidences relatively thin transgressive and thick regressive intervals the latter can be top truncated due to wave ravinement during a subsequent erosional transgression the architectural style of the capo colonna marine terrace cycles is thought to be linked to very rapid base level rises related to the late pleistocene high amplitude glacio eustatic changes climatic variations controlling the sediment supply rate are considered less effective in the present context present results allow a comparison with other cyclic successions developed under icehouse climatic regimes showing a discrete variability in their stratal architecture