palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

synsedimentary collapse of portions of the lower blomidon formation late triassic fundy rift basin nova scotia a chaotic mudstone unit within the lower blomidon formation late triassic has been traced for 35 km in the mesozoic fundy rift basin of nova scotia this unit is characterized by highly disrupted bedding that is commonly cut by small 0 5 m domino style synsedimentary normal faults downward movement of material geopetal structures variable thickness and an irregular partially faulted contact with the overlying unit the chaotic unit is locally overlain by a fluvial sandstone which is overlain conformably by mudstone although the thickness of the sandstone is highly variable the overlying mudstone unit exhibits only gentle regional dip the sandstone unit exhibits numerous soft sediment deformation features including dewatering structures convoluted bedding kink bands and convergent fault fans the frequency and intensity of these features increase dramatically above low points at the base of the sandstone unit these stratigraphic relations suggest buried interstratal karst the subsurface

sedimentary stratigraphy of eocene sheetflood deposits southern pyrenees spain the eocene monllobat formation of the southern pyrenees accumulated under continental non marine conditions the total thickness of 180 m consists of seven cycles defined by coarse member concentrations often sheets at the bases the lateral extent of the sheets defines the fixed positions of eight parallel trending alluvial systems separated by narrow zones of fine sediment sheetflooding dominated the sedimentation of these eight contemporaneous alluvial systems the sediment was supplied from the rising axial zone of the pyrenees the cycles were caused by variations in tectonic activity the positions and forms of coarse members were locally determined by contemporaneous faulting and folding of the alluvium

snow depth in eastern europe in relation to circulation patterns rotated principal components of the 500 hpa geopotential heights in the euro atlantic sector are used as indicators of circulation pattern intensity daily snow cover depth data for the years 1951 95 from 71 eastern european stations are examined maps of linear correlation coefficient between monthly change in snow depth and rotated principal components are presented the positive and negative extremes of each circulation pattern are analyzed and positive and negative snow depth signals indicated a daily analysis of relationships between snow depth and circulation pattern is performed for three locations the strongest impact of the atmospheric circulation on changes in snow depth is observed in the south and west of the study area where the eastern european ee and central european circulation patterns are found to have the greatest impact the north atlantic oscillation nao impact on the snow depth in eastern europe is limited to the beginning and the end of winter snow cover has low variability in northeastern europe where the scandinavian sc pattern is of greatest importance and low sensitivity to change in the atmospheric circulation the decrease in snow cover depth observed in spring is related to the nao sc and ee patterns the latter being important for snow cover depth fluctuations over northeastern europe in april

precambrian alluvial fan and braidplain sedimentation patterns example from the mesoproterozoic rjukan rift basin southern norway abstract an integrated approach of facies analysis geochemistry and paleohydrology provides new insight into the sedimentology and paleogeography of alluvial sediments in the precambrian here alluvial fan and braidplain sedimentation patterns are documented in a mesoproterozoic rift basin called known as the rjukan rift basin in southern norway the studied formation heddersvatnet formation consists of volcanoclastic breccias and conglomerates cross bedded sandstones with associated mudstones and subaerial basaltic lava beds deposited in a rift basin during the syn rifting phase based on genetically related major lithofacies associations and individual minor lithofacies the sedimentation is characterized by colluvial and screen apron deposits subaerial debris flows hyperconcentrated or sheet flood deposits in the proximal part representing waning flood cycles the distal part contains shallow water traction current deposits and associated subaerial continental flood basalts that flowed down the rift valleys the synsedimentary intra rift faulting formed seasonal or climatically controlled intrafan ponded lake with playa lake type cycles and shrinkage cracks the geochemical composition of the of the studied sandstones and mudstones suggests a passive rifted continental margin with minor to moderate chemical weathering possible in a semi arid arid paleoclimate clastic petrofacies of the sandstones indicate a locally uplifted and syn rift paleotectonic setting during the main sedimentation stage passing toward a post rifting stage of the depositional basin small scale structures within the sedimentary basin affected the depositional patterns of the heddersvatnet formation by creating local sites of uplift and erosion controlling the sediment transport and defining the accommodation space for deposition the sedimentation of the heddersvatnet formation reflects a tectonic base level fall which resulted in an accumulation of thick alluvial fan or braidplain sediments near uplifted flank s of the sedimentary basin this was combined with intensive erosion of the basement in the pre vegetation landscape which resulted in changes in the hydraulic geometry of flow and sediment discharge of stream channels the following criteria observed from the heddersvatnet formation are suggestive of an ancient alluvial fan and associated braidplain sedimentation 1 deposition close to the source area 2 slightly divergent paleoflows 3 high energy flows with waning flood cycles 4 abundance of poorly sorted and laterally extensive subaerial debris flows and related streamflows possible sheetfloods hyperconcentrated flows and their associations 5 great distribution of grain size and lithofacies changes in proximal vs distal parts 6 limited suite of sedimentary structures cross stratification ripple marks and desiccanation cracks 7 fault bounded basin graben with hanging wall close to uplifted flank s 8 paleoslope estimation indicating at least moderate paleotopographic highs 9 colluvial and scree apron breccias 10 lack of any typical braided stream channel fill conglomerates and floodplains and 11 channelized sediment bodies lacking extensive lateral continuity

large scale alluvial architecture and correlation in a triassic pebbly braided river system lower wolfville formation fundy basin nova scotia canada abstract determining what the controls are on the large scale 10 km horizontal architecture of coarse grained fluvial deposits is important for understanding subsurface fluid distribution and extraction from these important aquifers and hydrocarbon reservoirs this contribution describes the architecture of coarse grained fluvial sediments from an almost continuous lateral profile 27 km long by 115 m high in the upper triassic wolfville formation fundy basin nova scotia the lateral extent and quality of exposure allows development of a high resolution correlation scheme and definition of architectural elements the lower wolfville formation lithofacies composed of breccias conglomerates sandstones mudstones and paleosols comprises alluvial fan fluvial and ephemeral lake margin facies associations alluvial fan deposits form 15 of the studied section and are developed locally between the overlying fluvial facies and the unconformity with carboniferous strata where they infill remnant topography the succession is dominated 80 by pebbly sandstones deposited as part of a gravelly braided fluvial system and ends abruptly with a thin ephemeral lake margin facies association 5 the large scale architecture and sedimentology of the pebbly sandstone succession is documented with particular attention focussed on bounding surfaces and stacking patterns in the fluvial facies association two scales of development of erosion surface and cycles can be recognized the s surfaces can be correlated across the profile 27 km and show evidence of up to 10 m of erosion a significant facies or grain size change onlap and association with mature calcic paleosols the e surfaces can be correlated between 5 and 17 km display erosion of the regional extent of the e and s surfaces indicate that the gravelly fluvial system has a large scale sheet like geometry which comprises a series of stacked erosion dominated multi story bodies high resolution architectural elements are poorly defined in this coarse fluvial system and make it difficult to constrain the scale of the depositional system an individual high resolution cycle records braid plain development and is interpreted as a multi story channel belt the braid plain width is estimated at 19 km but the width of individual active channels is unknown the sediments were deposited in a proximal fluvial setting disconnected from marine influences we interpret the high resolution cycles and bounding e surfaces to record a progressive decrease in runoff and fluvial transport capacity indicative of a drying upward climatically driven signal the origin of the s surface bounded packages is more difficult to determine a variety of mechanisms are considered including changes in discharge driven by climatic fluctuations changes in stream power related to drainage capture within the source area and tectonic tilting an important aspect of the study is that the s surfaces can be identified and correlated for 27 km and provide an example of a robust high resolution correlation framework in coarse grained braided fluvial deposits that could be applied elsewhere in contrast the e surfaces do not display any significant changes in facies or grain size across them such that many of the smaller scale cycles could potentially be miscorrelated

palaeoenvironmental interpretation of fluvial red beds by statistical analysis of palaeocurrent data examples from the buntsandstein lower triassic of the eifel and bavaria in the german basin middle europe abstract palaeocurrent data from parts of the upper buntsandstein lower triassic of both the western eifel kyllburg schichten and eastern bavaria plattensandstein margin of the german triassic basin middle europe have been interpreted by circular directional statistics eigenvalue and eigenvector analysis autocorrelation analysis and vector trend analysis examination of current roses histograms of normalized vector magnitudes and plots of circular skewness of the distribution vs circular kurtosis together with the palaeocurrent plots indicate bimodal palaeocurrent distributions with bipolar orientations within long short and very short sedimentary sequences subset i of the directional data is interpreted to represent larger more continuous flows in a high energy regime of probably perennial type whereas subset ii may represent smaller partially episodic flows of probably ephemeral type with larger variability in direction and flow regime transport and sedimentation rates being significantly smaller than during deposition of subset i a part of the bimodal palaeocurrent distributions within short sedimentary sequences fits rather well into the general transport pattern other bipolarities are primarily interpreted as effects of superimposition of channels of different orientations as well as of main channels and crevasse splay channels and condensation of deposition from discontinuous or episodic flows the main mechanism creating the vertical succession of various directions is stacking of different substratum members to multistorey complexes by primary depositional restriction of formation and or secondary erosional removal of topstratum sediments the occasional occurrence of herring bone cross stratification representing bipolarities within very short depositional sequences testifies to probably episodic and random changes in water surface slopes allowing currents to reverse locally examination of long sedimentary sequences by autocorrelation analysis reveals changes of transport directions with time in a sinusoidal manner indicating a conformable environmental development of the alluvial watercourses which reflects a time cyclic trend of sedimentation by spatially continuous and time concordant shifting of the channel system the results of the statistical analysis enable an enhanced palaeoenvironmental reconstruction of the alluvial network which fits best to a transitional meandering thalweg braided channel pattern comparison of the statistical results especially in the light of vector trend surface analysis clearly reflects the different palaeogeographic positions of both investigated areas but rules out only minor influences of regionally different palaeoslopes on the alluvial depositional environment with the basic principles of fluvial style at the western margin eifel generally matching those at the eastern margin bavaria of the german basin

variations in fluvial style on the eocene oligocene alluvial fan of the scala dei group se ebro basin spain the scala dei group represents one of several coarse clastic wedges along the eastern margin of the tertiary ebro basin this group of eocene oligocene age is partly concealed by faulted and locally overthrust older sediments but a segment of oligocene age is spectacularly exposed for about 15 km along the newly constructed a2 motorway near the edge of the basin multistorey conglomerate channel bodies are composed of large scale foresets up to 3 m high representing side bars or possibly point bars smaller up to 40 cm normally graded beds with imbricated clasts represent diagonal or transverse bars and horizontally stratified sheets may be longitudinal bars flow was highly variable the multistorey conglomerate bodies are restricted to several crudely radiating axes representing major feeder systems and give rise to a goose foot depositional palaeomorphology towards the basin centre and in quiet zones between the main feeder axes single storey channel bodies of conglomerate and sandstone are common some plug like conglomerate and sandstone channel bodies are ribbons which are essentially straight in plan and other generally asymmetrical sandstone channel bodies preserve the point bars of channel bends where limited lateral migration took place many channel bodies possess extremely well developed wings representing levees and locally amalgamated crevasse splay sequences conspicuous crevasse channels cut through the levees the wings and crevasse channel bodies contain carbonate rich palaeosols this sequence is interpreted as an essentially distributive but ephemeral fluvial system

paleomagnetism of the triassic red beds of the lower fundy group and mesozoic tectonism of the nova scotia platform canada the lower fundy group red beds of the wolfville and lower blomidon formations in nova scotia and of wolfville equivalent units in new brunswick are exposed around the bay of fundy these red beds were sampled at twenty six shoreline sites for paleomagnetic analysis primarily by thermal step demagnetization methods samples from four sites proved too fragile to core however coating many of the rest of these poorly indurated samples and cores with waterglass enabled them to withstand the rigours of coring measurement and thermal cleaning a stable hematite remanence was found in all twenty one coherent sites with normal reversed and mixed polarities conglomerate and fold tests indicate the remanence is either primary or very early diagenetic its mean direction is d 196 5 i 3 8 95 7 2 which converts to a pole position of 45 3 n 97 1 e dp 3 6 dm 7 2 this pole indicates that the lower fundy group was likely deposited in the early triassic rather than in the middle and late triassic as currently thought it also indicates that the nova scotia platform was rotated about 8 clockwise after deposition of the lower fundy group and before extrusion of the north mountain basalts the consequences are briefly discussed for two alternative tectonic models of mesozoic motion on the minas geofracture that led to formation of the bay of fundy rift as the atlantic ocean basin started to open in early rather than middle triassic time the fundy group pole is similar to those from granitic plutons in maine thereby increasing the probability that there is a significant error in the mid triassic portion of the apparent polar wander path for north america finally magnetostratigraphic methods appear to be a promising way to subdivide and correlate between these red beds

facies sequences of a semi arid closed basin the lower jurassic east berlin formation of the hartford basin new england u s a the lower jurassic east berlin formation exposed in the centre of the hartford basin can be divided into six facies 1 laminated black mudstone is composed of very finely laminated organic bearing clay stone with common millimetre scale lenses of dolomitic siltstone 2 planar laminated mudstone is commonly mudcracked and composed of thickly laminated red green or grey mudstone with common centimetre scale lenses of sandstones 3 disrupted mudstone has a complex desiccation cracked fabric 4 planar and large scale trough cross stratified sandstones are composed of moderately well sorted medium to coarse grained arkoses 5 small scale cross stratified silty sandstones with common climbing ripple structure and 6 interbedded sandstones and mudstones which commonly carry desiccation cracks mudstone facies are organized into repetitive metre scale facies sequences which change gradationally upwards from laminated black mudstones to planar laminated mudstones to disrupted mudstones facies sequences have sharp tops and bottoms and record increasing desiccation upwards there are 15 such cycles in the upper 100 m of the formation in central connecticut they record long periods of dry playa mudflat aggradation punctuated by the rapid expansion and contraction of perennial lakes the sandy facies occur as single decimetre scale sedimentation units or as two or more stacked sedimentation units up to 1 m thick these record sheet floods across ephemeral floodplains

stochastic reservoir characterization using prestack seismic data reservoir characterization must be based on information from various sources well observations seismic reflection times and seismic amplitude versus offset avo attributes are integrated in this study to predict the distribution of the reservoir variables i e facies and fluid filling the prediction problem is cast in a bayesian setting the a priori model includes spatial coupling through markov random field assumptions and intervariable dependencies through nonlinear relations based on rock physics theory including gassmann s relation the likelihood model relating observations to reservoir variables including lithology facies and pore fluids is based on approximations to zoeppritz equations the model assumptions are summarized in a bayesian network illustrating the dependencies between the reservoir variables the posterior model for the reservoir variables conditioned on the available observations is defined by the a priori and likelihood models this posterior model is not analytically tra

cryptic eruption of mount ruapehu revealed by deposits of sediment laden streamflow in a steep mountain valley the 4 ka kiwikiwi formation whangaehu valley nz abstract a distinctive deposit of unaltered reworked volcaniclastic sediment here designated the kiwikiwi formation is described from the upper whangaehu valley at mount ruapehu new zealand the grain size distribution and sedimentary features of the unit suggest deposition from a sheetflow dominated alluvial system but simple sediment entrainment calculations show that the unit s granulometry is inconsistent with normal streamflow deposition at the observed steep depositional slope streams have produced deposits at mount st helens and mount pinatubo under similarly anomalous conditions following debris avalanche and or volcanic eruptions when highly charged with sediment and subject to common lahars debris flows and hyperconcentrated flows reported sediment transport rates from mount st helens toutle river and pinatubo s pasig potrero river show that a virtually unlimited supply of relatively fine grained sand range tephra renders some established sediment transport formulae inapplicable because the volume of available material effectively exceeds the transport capacity of the system we use simple equilibrium flow calculations to demonstrate that this sedimentary unit which has open porosity framework grain support and bedding characteristics compatible with alluvial sheet flows would not have been deposited under normal streamflow conditions this approach provides a means to confirm the role of capacity limitations on stream behaviour during the post eruptive sedimentary response phase in catchments overwhelmed by pyroclastic material and is particularly useful given the lack of clear depositional fingerprints for hyperconcentrated flow we further infer that because the material in the kiwikiwi formation is uniform unaltered and minimally abraded differs from older sediment in the valley overlies a 4 6 ka debris avalanche deposit and was emplaced from an over capacity stream by hyperconcentrated flows or extremely thinned ones and without evidence of interruption it represents the previously unidentified proximal products of an unstudied holocene eruption of ruapehu

controls on the architecture of a triassic sandy fluvial system wolfville formation fundy basin nova scotia canada implications for the interpretation and correlation of ancient fluvial successions abstract architectural element analysis was developed to describe and reconstruct fluvial system stacking patterns and understand the controls on fluvial architecture the architecture of braided fluvial systems at the scale of channel belts is still poorly understood and upscaling from outcrop observations to basin scale architecture remains partly speculative nonetheless predictive sedimentary models are necessary to understand the connectivity of sand bodies from small scale outcrop to basin scale this contribution presents a dataset from the late triassic sandy braided fluvial system of the fundy basin nova scotia canada we describe facies associations architectural elements and stacking patterns at different scales and discuss the controls on fluvial architecture and upscaling issues the studied section shows at the base multilateral stacked channel bodies with little preservation of fine grained floodplain facies it changes upwards into multistory stacked channel bodies that form channel belt complexes intercalated with thicker floodplain deposits based on grain size evolution large scale sequences encompass several channel belt complexes controls on channel and channel belt migration or avulsion are considered to be related to autocyclic processes in contrast large scale vertical evolution and grain size variations record allocyclic signals in particular gradual grain size variations suggest a climatic control which influences the bedload transport capacity of the depositing fluvial system architectural evolution including an upward increase in the preservation of floodplain units is considered to be due to an increase in generation of accommodation space we question the existing definition of the order of large scale sixth to seventh order bounding surfaces recognized previously and highlight difficulties associated with reconstructing development of a regional fluvial system using these bounding surfaces

unconfined flow deposits in distal sectors of fluvial distributary systems examples from the miocene luna and huesca systems northern spain abstract thin sheet sandstone beds in a continental succession may be the products of unconfined overbank flow or deposition in lacustrine environments in the distal parts of fluvial distributary systems these two settings may be intercalated recording fluctuations in lake level in response to climatic changes field studies of the luna and huesca fluvial distributary systems in the miocene of the ebro basin spain are here used to characterise sheet sandstone deposited in distal fluvial and lake margin environments in this study we document the facies and relationships between 322 individual sandbodies deposited in both alluvial settings as sheetfloods and in lacustrine settings as deltaic lobes the alluvial sandstone sheets were deposited from lateral and frontal sheetflood events when unconfined flow replaced channelised flow as the main transport mechanism the term sheetflood is used here to refer to sub aerial unconfined turbulent flow events that undergo expansion thinning and deceleration with increasing radial distance from source the depositional process is similar to modern floodouts and terminal splays of the channel country and lake eyre central australia such a process was thought to be the dominant depositional mechanism during lake lowstands the sheets formed in the lacustrine setting are interpreted as deltaic sediments deposited in a shallow gradient lake similar to the modern day volga delta caspian sea shallow water friction dominated deltaic processes are thought to have been the primary depositional mechanism in the distal sectors of the fluvial systems during lake highstands

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

emergence of subaqueous depositional environments in advance of a major ignimbrite eruption capel curig volcanic formation ordovician north wales an example of regional volcanotectonic uplift abstract the garth tuff of the ordovician capel curig volcanic formation comprises a laterally extensive sheet of largely welded rhyolitic ash flow tuff that can be traced from a proximal subaerial to a distal marine environment six facies associations are recognized within subjacent sedimentary successions facies are interpreted as deposits of stream dominated alluvial fans ephemeral streams braidplain lower delta plain delta front and shallow marine environments the development of a large scale coarsening and or shallowing upward sequence reflects the amount of differential tectonic uplift between fault bound highlands and depositional basin there is no evidence for volcanicity associated with sedimentation uplift resulted in aggradation and progradation of fan and braidplain deltas a basinward shift in the loci of dominant sedimentation and a 15 km advance in the position of the pre eruption coastline associated tilting of fault blocks influenced the position of fluvial systems on braidplain with channel belts localizing along one margin in the area of greatest subsidence the spatial correlation between pre emplacement geography and location of probable vent for garth tuff implicates upward and or lateral migration of the magma as the most likely mechanism driving these tectonic changes

the moenave formation sedimentologic and stratigraphic context of the triassic jurassic boundary in the four corners area southwestern u s a abstract the moenave formation was deposited during latest triassic to earliest jurassic time in a mosaic of fluvial lacustrine and eolian subenvironments ephemeral streams that flowed north northwest relative to modern geographic position deposited single and multi storeyed trough cross bedded sands on an open floodplain sheet flow deposited mainly silt across broad interchannel flats perennial lakes in which mud silt and carbonate were deposited formed on the terminal floodplain these deposits experienced episodic desiccation winds that blew dominantly east to south southeast formed migrating dunes and sand sheets that were covered by low amplitude ripples the facies distribution varies greatly across the outcrop belt the lacustrine facies of the terminal floodplain are limited to the northern part of the study area in a southward direction along the outcrop belt along the echo cliffs and ward terrace in arizona dominantly fluvial lacustrine and subordinate eolian facies grade mainly to eolian dune and interdune facies this transition records the encroachment of the wingate erg moenave outcrops expose a north south lithofacies gradient from distal erg margin to proximal erg interior the presence of ephemeral stream and lake deposits abundant burrowing and vegetative activity and the general lack of strongly developed aridisols or evaporites suggest a climate that was seasonally arid both before and during deposition of the moenave and the laterally equivalent wingate sandstone we interpret growth of the erg as a consequence of marine regression during the latest triassic through earliest jurassic that exposed sediments on the coast of the back arc sea to eolian reworking tectonic processes that created accommodation space enhanced preservation of the erg

avo classification of lithology and pore fluids constrained by rock physics depth trends elastic properties of rocks are strongly influenced by local geological trends and can change markedly even within a sedimentary basin critical geologic factors that control elastic properties are either related to depositional environment or burial history knowledge about the expected change in seismic response as a function of depositional or compactional trends will increase the ability to predict hydrocarbons especially in areas with little or no well log information in other words by understanding the geologic constraints in an area of exploration one can reduce the range of expected variability in rock properties and hence reduce the uncertainties in seismic reservoir prediction figure 1 depicts this problem where we assume there is well log control only in the shallow interval on the shelf edge before extending the exploration into more deeply buried zones or to more distal deepwater environments it is important to understand the rock physics trends in the area

anatomy and facies distribution of terminal lobes in ephemeral fluvial successions jurassic tordillo formation neuquen basin argentina in terminal fluvial fan systems characteristic proximal to distal variations in sedimentary architectures are recognized to arise from progressive downstream loss of water discharge related to both infiltration and evaporation this work aims to elucidate downstream trends in facies and architecture across the medial and distal zones of terminal fan systems which record transitions from deposits of channel elements to lobe like and sheet like elements this is achieved via a detailed characterization of ancient ephemeral fluvial deposits of the well exposed kimmeridgian tordillo formation neuquen basin argentina the fine sand prone and silt prone succession associated with the medial to distal sectors of the system has been studied to understand relationships between depositional processes and resulting architectures facies and architectural element analyses and quantification of resulting sedimentological data at multiple scales have been undertaken to characterize sedimentary facies facies transitions bed types architectural elements and larger scale architectural styles eight bed types with distinct internal facies transitions are defined and interpreted in terms of different types of flood events channelized and non channelized architectural elements are defined based on their constituent bed types and their external geometry the most common elements are terminal lobes which are composite bodies within which largely unconfined sandy deposits are stacked in a compensational manner a hierarchical arrangement of internal components is recognized proximal feeder channel avulsion events likely controlled the evolution of terminal lobe elements and their spatiotemporal shifts stratigraphic relations between architectural elements record system wide trends whereby a proximal sector dominated by channel elements passes downstream via a gradational transition to a medial sector dominated by sandy terminal lobe elements which in turn passes further downstream to a distal sector dominated by silty terminal lobe margin and fringing deposits this work enhances current understanding of the stratigraphic record of terminal fluvial systems at multiple scales and provides insight that can be applied to predict the facies and architectural complexity of terminal fluvial successions

depositional architecture of a maar pitted playa sedimentation in the hopi buttes volcanic field northeastern arizona u s a abstract primary and reworked tephra in the mio pliocene bidahochi formation of northeastern arizona was produced by and partly preserved in maar volcanoes and related hydrovolcanic structures the temporal and geometric relationships among lithofacies of the bidahochi formation illustrate the dynamic interplay between volcanism and sedimentation in an essentially closed sedimentary system maar volcanism in the low relief basinal environments of the bidahochi appears to have resulted in little net aggradation both because the total amount of magma erupted was relatively modest and because the large maar volcano craters produced areas of lowered base level within the basin that formed sediment sinks for much of the newly erupted tephra the volcanically eroded maar craters commonly contain deposits of lakes multiple stream channels and eolian dunes they formed an integral part of the basin s overall depositional environment and affected sedimentation in the playa lake stream systems beyond the vents both during and following the major eruptive period

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

petrochemical and stratigraphic aspects of north mountain basalt from the north shore of the bay of fundy nova scotia canada early jurassic quartz normative tholeiitic basalts occur in a series of fault blocks at four localities cap d or parrsboro five islands and bass river along the north shore of the bay of fundy major element and trace element data show that they represent outliers of the north mountain basalt nmb which from the south shore of the bay of fundy are well known diagnostic 87sr 86sr ratios 0 70609 indicate that a thick 90 m flow at five islands and cap d or represents the lower unit of nmb thus extending this single flow s lateral extent to 230 km thin flows overlying the thick flow at cap d or suggest that the middle unit of nmb also occurs on the north shore a thick flow at mckay head parrsboro area shows a variable sr isotopic composition that is probably a result of metasomatism with rb addition along the cobequid fault the average composition 0 70656 is similar to that of the upper unit of nmb if the flow does represent the upper unit then four thinner flows above it form an ov

late oligocene and miocene faulting and sedimentation and evolution of the southern rio grande rift new mexico usa abstract the distribution of nonmarine lithofacies paleocurrents and provenance data are used to define the evolution of late oligocene and miocene basins and complementary uplifts in the southern rio grande rift in the vicinity of hatch new mexico usa the late oligocene middle miocene hayner ranch formation which consists of a maximum of 1000 m of alluvial fan alluvial flat and lacustrine carbonate lithofacies was deposited in a narrow 12 km northwest trending northeast tilted half graben whose footwall was the caballo mountains block stratigraphic separation on the border faults of the caballo mountains block was approximately 1615 m an additional 854 m of stratigraphic separation along the caballo mountains border faults occurred during deposition of the middle late miocene rincon valley formation which is composed of up to 610 m of alluvial fan alluvial flat braided fluvial and gypsiferous playa lithofacies two new north trending fault blocks sierra de las uvas and dona ana mountains and complementary west northwest tilted half graben also developed during rincon valley time with approximately 549 m of stratigraphic separation along the border fault of the sierra de las uvas block in latest miocene and early pliocene time following deposition of the rincon valley formation movement continued along the border faults of the caballo mountains dona ana mountains and sierra de las uvas blocks and large parts of the hayner ranch and rincon valley basins were segmented into smaller fault blocks and basins by movement along new largely north trending faults analysis of the hayner ranch and rincon valley formations along with previous studies of the early oligocene bell top formation and late pliocene early pleistocene camp rice formation indicate that the traditional two stage model for development of the southern rio grande rift should be abandoned in favor of at least four episodes of block faulting beginning 35 ma ago with the exception of two northwest trending border faults of the caballo mountains block that may be reactivated along eocene compressional structures the majority of border faults and complementary basins throughout the history of the southern rio grande rift were north trending which challenges the conventional idea of a clockwise change in stress through time

climatology and variability of historical soviet snow depth data some new perspectives in snow indian monsoon teleconnections this study presents the monthly climatology and variability of the historical soviet snow depth data this data set was developed under the bilateral data exchange agreement between united states of america and the former union of soviet socialist republics the original data is for 284 stations for periods varying from 1881 upto 1985 the seasonal cycle of the mean snow depth has been presented both as spatial maps and as averages over key locations the deepest snow 80 cms day areas are found over siberia in particular over 80 100 e 55 70 n during march over the course of the annual cycle average snow depth over this region changes dramatically from about 10 cms in october to about 80 cms in march the variability is presented in the form of spatial maps of standard deviation to investigate the interaction of snow depth with indian monsoon rainfall imr lag and lead correlation coefficients are computed results reveal that the winter time snow depth over western eurasia surrounding moscow eastern eurasia in central siberia shows significant negative positive relationship with subsequent imr following the monsoon the signs of relationship reverse over both the regions this correlation structure is indicative of a midlatitude longwave pattern with an anomalous ridge trough over asia during the winter prior to a strong weak monsoon as the time progresses from winter to spring the coherent areas of significant relationship show southeastward propagation empirical orthogonal function analysis of the snow depth reveal that the first mode describes a dipole type structure with one centre around moscow and the other over central siberia depicting similar pattern as the spatial correlation structure the decadal scale imr variations seem to be more associated with the northern hemisphere midlatitude snow depth variations rather than with the tropical enso el nino southern oscillation variability

sedimentary evolution of the foreland basin in the ne tibetan plateau and the growth of the qilian shan since 7 ma we studied the magnetostratigraphy and sedimentary facies of a 550 m long drill core from the jiudong basin in the ne tibetan plateau our aims were to reconstruct the late cenozoic sedimentary evolution of this foreland basin and to determine the spatiotemporal pattern of growth of the qilian shan the magnetostratigraphy indicates that the sedimentary sequence was deposited during ca 7 0 ma from ca 6 7 3 0 ma the sediment accumulation rate increased gradually from similar to 30 mm k y to 120 mm k y which was associated with the gradual evolution of sedimentary facies from a shallow lake delta front to braided rivers the progradation of the depositional system from 7 ma to 3 ma probably reflects the growth of the relief of the qilian shan caused by tectonic uplift the occurrence of a continuous braided river environment from 3 ma to the present suggests that the high relief of the qilian shan developed before 3 ma an abrupt decrease of the sedimentation rate to similar to 46 mm k y during 3 0 1 8 ma and the deposition of coarse grained sediments indicates the uplift of the basin center we interpret this to reflect the propagation of the thrust system of the qilian shan into the basin along a southward dipping decollement from ca 3 ma climatic changes may have influenced the sedimentary sequence by introducing long distancetransported thin coarse sand gravel layers which are sandwiched within the sequence and likely were a response to cooling events or climatic transitions the widespread occurrence of deformation within the basin region in the ne tibetan plateau at ca 3 ma indicates that this date marks the basinward growth of the deformation system

sedimentary facies and environmental ichnology of a permian playa lake complex in western argentina abstract a moderately diverse arthropod ichnofauna occurs in permian ephemeral lacustrine deposits of the paganzo basin that crop out at bordo atravesado cuesta de miranda western argentina sedimentary successions are interpreted as having accumulated in a playa lake complex deposits include three sedimentary facies a laminated siltstone and mudstone b current rippled cross laminated very fine grained sandstone and c climbing and wave rippled cross laminated fine grained sandstone deposited by sheet floods under wave influence in the playa lake complex analysis of facies sequences suggests that repeated vertical facies associations result from transgressive regressive episodes of variable time spans the bordo atravesado ichnofauna includes cruziana problematica diplocraterion isp cf diplopodichnus biformis kouphichnium isp merostomichnites aicunai mirandaichnium famatinense monomorphichnus lineatus palaeophycus tubularis umfolozia sinuosa and umfolozia cf u longula the assemblage is largely dominated by arthropod trackways and represents an example of the scoyenia ichnofacies trace fossils are mostly preserved as hypichnial ridges on the soles of facies c beds being comparatively rare in facies a and b ichnofossil preservation was linked to rapid influx of sand via sheet floods entering into the lake four taphonomic variants types 1 4 are recognized each determined by substrate consistency and time averaging type 1 is recorded by the presence of low density assemblages consisting of poorly defined trackways which suggests that arthropods crawled in soft probably slightly subaqueous substrates type 2 is represented by low to moderate density suites that include sharply defined trackways commonly associated with mud cracks suggesting that the tracemakers inhabited a firm desiccated lacustrine substrate type 3 displays features of types 1 and 2 and represents palimpsestic bedding surfaces resulting from the overprint of terrestrial ichnocoenoses over previously formed softground suites type 4 differs from type 2 only in that assemblages display a high density of traces recorded by numerous superimposed trackways which suggests a major time gap of subaerial exposure before sheet flood entrance therefore type 4 surfaces are mostly interpreted as track imprinted omission surfaces

sedimentology and depositional setting of the dartmouth group bigbury bay south devon the lower devonian dartmouth group records some of the earliest stages in the evolution of the variscan basins of southwest england this thick mudstone dominated group has previously been interpreted as distal fluvial sediments deposited on a coastal mudplain the sequence at bigbury bay is made up of two large scale sedimentary cycles the base of each cycle consists of pebbly mudstones graded siltstones and sandstones massive mudstones and heterolithic sediments with sporadic phosphatic nodules these facies were deposited in substantial lakes they were modified by phases of syn sedimentary deformation which generated subaqueous debris flows and turbidites the overlying parts of the cycle making up the bulk of the succession consist of mudstone and thin sheet like sandstones these are fluvial and were probably deposited in mud dominated terminal fans each cycle represents a phase of rapid probably fault controlled subsidence followed by relative tectonic quiescence this behaviour may reflect pulses of rifting or extension in strike slip basins followed by thermal relaxation

fan delta sequence in the archean fig tree group barberton greenstone belt south africa abstract the fig tree group of the barberton greenstone belt in south africa records the onset of tectonism and significant terrigenous and volcaniclastic sedimentation following a period of predominantly effusive volcanism in the southern part of the greenstone belt the lower fig tree conformably overlies the onverwacht group and can be grouped into either 1 volcaniclastic deposits consisting of pyroclastic and reworked volcanic detritus or 2 non volcanogenic terrigenous deposits of sandstone and conglomerate these petrologic groups are further divided into six lithofacies the lithofacies within the lower fig tree formation can be grouped into two facies associations 1 a subaqueous delta front association made up of fine grained airfall pyroclastic and slightly reworked pyroclastic debris along with resedimented land derived sandstone and conglomerate and 2 a subaerial association that is interpreted as forming from deposition of sandstone and conglomerate by flashy ephemeral stream processes on an alluvial fan surface the stratigraphic sequence coarsens upward from predominantly siltstone and fine grained sandstone at the base to pebble and cobble conglomerate at the top this sequence is interpreted as forming from the progradation of a fan delta into a body of relatively shallow quiet water composition of clasts in the conglomerates indicates that immediately underlying greenstone belt rocks or coeval volcanic rocks were the source for these coarse sedimentary accumulations erosion of uplifted greenstone belt terrain was apparently only to shallow levels both tectonic and volcanic activity played a role in producing several cycles of fan delta progradation

isochronous fluvial systems in miocene deposits of northern pakistan a palacomagnetic isochron dated at about 8 1 myr bp and detailed lithostratigraph of a 40 m interval exposed along strike for 40 km establish the depositional patterns of two contemporaneous interfingering fluvial systems in the upper part of the meddle siwalik sequence the two systems referred to as the buff and blue grey differ in unit shape lithofacies bedding sequence palaeocurrent direction and sand composition interfingering occurs along the south west north east strike of the outcrops with the palaeodrainage directions of the two systems generally perpendicular to this line the axis of the blue grey system which deposited widespread sheet sands and silts lay toward the south west end of the study area the more complex axis of the buff system which deposited shoe string sand bodies and lage volumes of silt and clay lay toward the north east the source area for both systems was the rising himalyan belt to the north and noth east of the study area at maximum extent the blue grey system occupied a channel belt at least 25 km wide channel belt widths and depths for the buff system are 1 3 km and 3 7 m respectively current directions averge 94 for blue grey sands and 136 for buff sands blur grey sands contain 20 more rock fragments and are otherwise less mature than buff sands the buff system shows a verticla pattern of avulsion palaeosol formation and floodplain aggradation which we attribute to autocyclic processes of parallel rivers the blue grey system shows phases of erosion accompaniced laterally by plaeosol formation folowed by valley fill and overfowing of interfluve surfaces theis pattern may be caused by allocyclic presses affecting the source area we interpret the blue grey system as a major drainage from the interior himalayas perhaps the ancestral indus and the buff system as a complex of smaller drinages along the mountain front which were probably ributaries to the bluegrey syste vertebrate fossils including hominoid primates from the area are almost exclusively associated with lithofacies of the buff system and this probably refects both taphonomic and palaeoecological differences between the two systems

composition and architecture of braided and sheetflood dominated ephemeral fluvial strata in the cambrian ordovician potsdam group a case example of the morphodynamics of early phanerozoic fluvial systems and climate change abstract two fluvial facies associations braided and ephemeral fluvial are recognized in strata of the cambrian ordovician potsdam group in the ottawa embayment and quebec basin in northeastern north america braided fluvial sedimentation was dominated by the migration of coarse grained sandy dunes and rare unit bars and local gravels that built up low relief 0 4 5 m thick downstream accreting compound bars in very wide and shallow braided channels rare meter scale confluence scours incision and filling of decimeter thick bypass channels and thin 7 cm overbank deposition also occurred ephemeral fluvial sedimentation was dominated by the progradation of lobate terminal splays most of which were deflated and or reworked into thin 10 95 cm sheets by eolian processes during the long recurrence intervals between floods these strata were locally incised by rare 0 3 1 9 m thick scour filling high energy supercritical bedform strata and decimeter thick bypass channels both braided and ephemeral fluvial deposits consist of meter scale stacked high order stratal units separated by horizontal laterally extensive surfaces recording the recurring buildup avulsion and finally abandonment of channel belts in braided fluvial strata of the potsdam the dominance of thin 2 m elongated compound bars with low relief 5 bar margins and internal accretion surfaces 15 suggest that braided channels and in channel compound bars expanded laterally with negligible increase in flow depth during periods of increased discharge in the absence of bank stabilizing vegetation similar to other examples of the pre vegetated sheet braided style however in areas where bedrock topography inhibited the lateral expansion of channels thicker compound braid bars 1 2 3 5 m with higher relief accretion surfaces up to 35 like those observed in post silurian and modern systems preferentially formed in relatively deep channels ephemeral fluvial deposits here are similar to ephemeral examples throughout geologic history in that they mostly comprise poorly confined sheet like terminal splays that accumulated in topographic lows however compared to several post silurian examples strata in the potsdam exhibit considerably more eolian reworking of splays and preservation of supercritical bedform strata a manifestation of greater rates of surface water infiltration due to a lack of sheltering by rooted plants and propensity for unconfined flooding finally in the upper part of the potsdam two regional ephemeral fluvial units are interstratified with two braided fluvial units providing evidence for shifts in regional climate the sharp areally extensive surfaces that separate these fluvial systems are interpreted to approximate time lines and therein provide a means for relative and absolute chronostratigraphic correlation these changes are correlated with documented late cambrian to earliest ordovician global climate fluctuations with semiarid conditions and related ephemeral fluvial systems corresponding to global cooling events at ca 491 and 487 ma

the chinese pompeii death and destruction of dinosaurs in the early cretaceous of lujiatun ne china the lujiatun unit yixian formation yields some of the most spectacular vertebrate fossils of the jehol group lower cretaceous of ne china specimens are preserved both articulated and three dimensional unlike the majority of jehol fossils which are near two dimensional compression fossils the site has been referred to as the chinese pompeii because the dinosaurs and other animals were assumed to have been killed and buried by hot airborne volcanic debris and ash in a single event this has yet to be confirmed field and laboratory evidence for the sedimentological context of the fossils from the lujiatun unit is described in detail and used to assess whether the fossil remains correspond to a single depositional event and whether this event was the direct result of volcanic activity fossils of the lujiatun unit occur in several horizons of volcaniclastic sediments that represent multiple depositional events petrological analysis shows that the fossil bearing sediments were remobilised and deposited by water the lujiatun dinosaurs and other fossils were therefore not killed by a single airborne volcanic ash but in multiple flood events with a high load of volcaniclastic debris

succession of depositional environments in the neogene basin at aliveri evia greece abstract the neogene lignite bearing sequence in the southern part of the aliveri kymi basin was studied with regard to sedimentology palynology and coal petrology in order to establish the type and succession of environments involved and to compare them with modern analogues initial sediments of the prinias group were deposited in a wide shallow depression by means of a low competent drainage system which formed sandy alluvial fans interfan areas and ephemeral lakes as well as sand flats and vegetated mudflats in lateral sequences from the basin margins to a central perennial lake succeeding sediments of the prinias group were formed under the influence of the rising lake level in algal marsh various peat forming and open lake environments sediments of the koustoumalou group were deposited by a highly competent surficial drainage system in alluvial fan to braided and meandering fluvial environments this drainage system followed the south north trending axis of an asymmetrical graben while debris flows moved in from the steep flanks to the east

internal structure and environmental reconstruction of eocene transitional fan delta deposits monllobat castigaleu formations southern pyrenees spain abstract a detailed study has been made of a part 500 200 15 m of the eocene monllobat formation the conglomeratic bottomset foreset topset build up of a small fan delta passes into sand and mudstone layers ultimately the sandstone layers wedge into the mudstone due to concave upwards basal surfaces and convex top surfaces or due to thickening of intercalated mud layers sequences vary accordingly from coarsening upwards in the proximal parts to fining upwards distally both sequences are topped by a thin layer fining upwards the proximal fan deltaic part consists of interconnected lobes crescentic transverse bars deposited gravel on a slightly inclined top conglomerates of the moderately inclined foreset show some imbrication the bottomset consists of tabular cross bedded and cross laminated sandstone parallel laminated and tabular cross bedded sandstone layers drape rises of fine sediment in front of the fan delta face continued progradation brought about truncation of these backset sediments sandstone lobes of the distal part are not connected tabular croos bedding and parallel lamination are the main sedimentary structures climbing large scale bedforms are prominent on top surfaces most of the lobes are enveloped by blue grey mud layers covered by mottled mud terminate in foreset faces highly energetic inflow took place from a shallow braided stream with longitudinal bars the low sedimentary relief caused jetflow the high flow energy the large grain size range and the large quantities of sediment caused great differences from inflow models for the deltaic environment sedimentation was effected by flow deceleration expansion inertial forces friction or a combination of these phenomena were responsible for the deceleration expansion and inertial forces caused development of moderately inclined foreset faces due to expansion steeply inclined foresets were formed sand was deposited in shallow marine water and in scour pits in continental deposits during flow deceleration caused by frictional and inertial forces parallel laminated backsets connected with flat tabular sets developed due to flow deceleration by expansion and frictional forces the deposits were formed in the transition zone of a fan delta under a tropical climate with marked dry and wet periods wide braided streams entered a restricted shallow marine basin at right angles to the basin axis aggradation exceeded water depth progradation processes were influenced by large and small scale tectonic activity

sandstone body structures and ephemeral stream processes in the dinosaur canyon member moenave formation lower jurassic utah u s a abstract studies of fluvial sandstone body structures in the lower jurassic dinosaur canyon member suggest a threefold subdivision of the ephemeral stream deposits sandstone sheets with interbedded siltstones are less than 1 m thick and laterally extensive for hundreds of metres they are interpreted as sheetflood deposits simple channel sandstone bodies are a few metres thick and a few tens of metres wide they reflect solitary channel incision episodic migration and plugging multistorey channel sandstone bodies are a few metres thick and laterally extensive for hundreds of metres they are composed of several channel shaped storeys and exhibit only local incision the multistorey sandstone bodies are interpreted as braided ephemeral stream deposits two sandstone sheet subtypes with grooves and mounds respectively are interpreted as intermediate between the sheetflood deposits and solitary incised channel deposits on one hand and between sheetflood deposits and braided stream deposits on the other hand the solitary channels and braided streams are accordingly interpreted to be initiated from sheetfloods through differential erosion and differential deposition respectively this model of channel evolution from sheetfloods is probably applicable to other semiarid and arid fluvial environments dominated by surface runoff

filling the north european early middle eocene ypresian lutetian boundary gap insights from the pyrenean continental to deep marine record abstract the early middle eocene ypresian lutetian transition is represented by a hiatus in many north european sections including those in which the classic stratotypes were originally defined however the global stratotype section and point of the lutetian stage which is still pending definition should be placed at a globally correlatable event included within that unrepresented interval the pyrenean eocene outcrops display sedimentary successions that offer the rare opportunity to analyse the ypresian lutetian boundary interval in almost continuous sections and in very different settings seven reference stratigraphic sections were selected on the basis of their quality and correlated by means of biomagnetostratigraphic data this correlation framework casts light on the sequence of chronostratigraphic events that characterize the ypresian lutetian boundary interval which may prove useful in defining the main correlation criterion of the base of the lutetian all of the pyrenean sections show a similar sedimentary evolution despite being up to 350 km apart from each other containing deposits of different origins intrabasinal carbonate sediments siliciclastic sediments sourced from the iberian plate and terrigenous sediments sourced from the uplifting pyrenees and despite having been accumulated in different sedimentary environments from continental to deep marine and in different geodynamic settings piggy back basin foreland basin and cratonic margin this common evolution can be readily interpreted in terms of a sea level driven depositional sequence whose lowstand and transgressive systems tracts are included within the ypresian lutetian boundary interval the pyrenean ypresian lutetian depositional sequence can reasonably be correlated with depositional sequences from classic north european areas shedding light on the palaeoenvironmental history which in those areas has not been recorded furthermore these depositional sequences may possibly correlate with others from the antarctic ocean and from new jersey as well as with oceanic temperature variations suggesting that they might be the result of climatically driven glacioeustatic sea level changes should this hypothesis prove correct it would confirm previous suggestions that the onset of antarctic glaciations needs to be backshifted to the late ypresian at least

early ordovician alluvial fan deposits of the marmul oil field south oman fine grained shaly sands of the mahwis formation haima group form one of the reservoir intervals of the marmul field six lithofacies can be distinguished from cores shale clast conglomerates trough cross stratified sands horizontally stratified sands massive sands rippled sands and interbedded shales and sands horizontally stratified sands make up 45 of the cored reservoir two scales of fining upward sequence occur small sequences are 0 3 1 5 m thick and are interpreted as sheetflood deposits on the distal portions of semi arid alluvial fans the larger sequences are 25 50 m thick can be correlated on well logs fieldwide and probably represent periodic tectonic rejuvenation and erosional lowering of the sediment source area it is interpreted from regional correlation sediment provenance and a knowledge of possible source areas that the alluvial fans were predominantly sandy had radii of several tens of kilometres and formed an extensive apron bordering a highland area which lay to the southeast the thinly bedded and shaly character of these sheetflood sands causes problems of petrophysical log evaluation and hence oil in place estimation reservoir quality is related to lithofacies occurrence and variation in grain size the large scale fan sequences correspond to an upward decrease in porosity and permeability and form useful subdivisions for field scale correlation and reservoir prediction

sedimentary successions in ice marginal fans of the late saalian glaciation southwestern poland abstract the late saalian end moraines of southwestern poland contain several features that may be attributed to the formation that is predominantly controlled by the deposition of sorted waterlaid sediments these hills are essentially small alluvial fans with ice contact facies they have a semi conical form plano convex geometry their distal slopes are up to 5 and proximal slopes are between 5 and 20 the sedimentary sequences contain two units the lower unit comprises coarse grained material of gravel bed sheetflow facies and gravel bed channel facies with subordinate high energy channel flow facies and boulders up to 1 8 m in diameter the upper unit contains sand bed sheetflow facies and sand bed channel facies the sediment bedding is usually conformable with and parallel to the inclined fan surface these sequences represent typical proximal distal fan facies associations with a high energy and pulsatory water discharge in the proximal zone the fans in spite of their formation in the proglacial zone have geomorphological features and sedimentary sequences that are very similar to present day fans and are equivalent to sheetflow dominated or humid alluvial fans in non glacial environments

a middle proterozoic palaeokarst unconformity and associated sedimentary rocks elu basin northwest canada a major palaeokarst erosion surface is developed within the middle proterozoic elu basin northwestern canada this palaeokarst is named the sub kanuyak unconformity and truncates the parry bay formation a sequence of shallow marine dolostones that were deposited within a north facing carbonate platform under a semi arid climate the sub kanuyak unconformity exhibits up to 90 m of local relief and also formed under semi arid conditions when parry bay dolostones were subaerially exposed during a relative sea level drop of about 180 m caves and various karren developed within the meteoric vadose and phreatic zones their geometry size and orientation were largely controlled by northwest and northeast trending antecedent joints bedding and lithology near surface caves later collapsed forming valleys and intervening towers or walls and plains minor terra rossa formed on top of highs karstification was most pronounced in southern parts of bathurst inlet but decreased northward probably reflecting varying lengths of exposure time along a north dipping slope the kanuyak formation is up to 65 m thick and partially covers the underlying palaeokarst it consists of six lithofacies i breccia formed during collapse of caves as reworked collapse breccia and regolith ii conglomerate representing gravel dominated braided fluvial deposits iii sandstone deposited as braided fluvial and storm dominated lacustrine deposits iv interbedded sandstone siltstone and mudstone of sheet flood origin v dolostones formed from dolocretes and quiet water lacustrine deposits and vi red beds representing intertidal marine mudflat deposits rivers flowed toward the northwest and northeast within karst valleys and caves lakes were also situated within valleys marine mudflat sediments completely cover the palaeokarst to the north a regional correlation of the sub kanuyak unconformity with the intra greenhorn lakes disconformity within the coppermine homocline suggests that similar styles of karstification occurred over an extensive region the elu basin palaeokarst however was developed more landward and was exposed for a longer period of time than the coppermine homocline palaeokarst

quantitative relationships between numbers of fluvial cycles bulk lithological composition and net subsidence in a scottish namurian basin this detailed quantitative basin analysis of fluvial deposits in a subsiding namurian structural basin is aimed at discovering underlying statistical relationships between numbers of fluvial cycles bulk lithological composition and net subsidence which could be used as a background to future sophisticated computer simulation experiments and would also facilitate comparison with other ancient basins the succession studied lies between two widespread marine bands one of arnsbergian e2 and one of kinderscoutian r1 age and is dominated by upward fining cycles 94 of the semi cycles containing sand here termed grain size cycles are upward fining and the ratio of fine members mudstone siltstone to coarse members ranges from 0 23 to 5 0 trend surface analysis reveals basement structures which influenced sedimentation including a caledonoid graben correlation coefficient values and results of principal component analysis demonstrate that the numbers of rooty horizons and grain size cycles together with the total thicknesses of sandstone and of mudstone siltstone all tend significantly towards a linear relationship with the total thickness of strata and hence net subsidence the average thickness of grain size cycles tends towards an inverse linear relationship with net subsidence this probably reflects the presence of stacked relatively thin channel fills within persistent channel belts these belts tend to be localized in the areas of greatest subsidence within the basin and follow courses basically similar to channels already discovered in the underlying deltaic sediments the highest concentrations of mudstone siltstone tend to lie on the flanks of the basin but high local sand concentrations found at points on the margin where channels entered the basin from the nw and ne and left to the sw effectively disrupt any significant relationship between net subsidence and the proportion of sand coal has been selectively preserved on the flanks of the basin and the number of rooty horizons is greatest in an area of low subsidence which lay somewhat remote from the main channel belts

orbitally driven climate forcing in late pliocene lacustrine siderite rich clastic rhythms upper valdarno basin northern apennines italy abstract distinctive siderite rich lacustrine strata are exposed along the western margin of the upper valdarno basin northern apennines italy these late pliocene deposits belong to the castelnuovo synthem which is the oldest unconformity bounded stratigraphic unit of the basin fill facies analyses were performed on a paleomagnetically calibrated log depicting two palustrine to lacustrine systems separated by a short lived fluvial phase the lacustrine deposits are structured in rhythms and composed of lower clastic and upper siderite enriched beds the rhythmic stacking pattern has been analysed and subjected to a cyclostratigraphic analysis similar trends between a local facies derived base level curve and global isotopic stacks suggest climate forcing which is confirmed by the straightforward tuning of the lacustrine rhythms to precession related insolation phases clastic deposition has been linked to colder and drier phases involving vegetation retreat and enhanced sediment production and transport prevalent chemical deposition siderite instead occurs during hot and wet phases and is characterised by vegetation blooming and then a generalised reduction in clastic supply this mechanism is probably coupled with lake level fluctuations that are related to variations in the regional hydrological balance the orbital behaviour of the castelnuovo synthem is characterised by major sensitivity to precession but a weaker response to 100 ky eccentricity however eccentricity modulation is marked by a 400 ky minimum which recurs in correspondence with a sub aerial exposure between the two lacustrine bedsets no obliquity related rhythmicity has been recorded the succession investigated here is consistent with other pliocene palustrine to lacustrine circum mediterranean case studies the results have also been compared to a previous cyclostratigraphic framework elaborated from magnetic susceptivity allowing critical comparisons to be made between this latter proxy and the analysis of sedimentary facies cycles

autogenic dynamics of alluvial fans in endorheic basins outcrop examples and stratigraphic significance alluvial fans are relatively simple depositional systems due to the direct coupling of sediment sources and adjacent accumulation areas nonetheless general models of alluvial fan evolution and stratigraphy remain elusive due to the great sensitivity of such systems to allogenic controls and their strongly case specific responses autogenic processes intrinsic to alluvial fan dynamics can complicate stratigraphic architectures with effects not easily distinguishable from those of allogenic forcing a distinction is made here between lateral autogenic dynamics tied to spatial sediment distribution over fan surfaces and vertical autogenic dynamics related to independent incision aggradation cycles autogenic mechanisms have been highlighted recently by modelling studies but remain poorly constrained in field based studies examples are presented here from the margins of the cenozoic teruel and ebro basins spain where alluvial fans accumulated thick successions during phases of basin topographic closure and endorheic drainage which promoted forced aggradation fan successions consist of conformable architectures of stacked clastic sheets laterally continuous and with no evidence of internal unconformities inset architectures fan segmentation or preserved incised channels continuous aggradation in these closed basins strongly inhibited vertical autogenic dynamics in the form of fan head and through fan incision due to the forced rise in geomorphic base level and the creation of positive accommodation furthermore the lack of incised channels favoured widespread sediment transport and aggradation over broad fan sectors in relatively short time spans in contrast to the typical occurrence of active lobes and abandoned fan surfaces caused by lateral autogenic dynamics stratigraphic records of alluvial fans developed in endorheic basins are essentially complete and largely unaffected by autogenic processes the latter characteristic implies that they can be more unambiguously interpreted in terms of allogenic forcing because stratigraphic signatures are not complicated by the effects of complex fan autodynamics

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

dryland continental mudstones deciphering environmental changes in problematic mudstones from the upper triassic carnian to norian mercia mudstone group south west britain

a palaeomagnetic analysis of miocene fluvial sediments at pertusa near huesca ebro basin spain the magnetostratigraphy of two logged sections 1 km apart within this system consists of an upper zone of normal polarity and a lower zone of reversed polarity the lithostratigraphy and magnetostratigraphy are parallel the sands and silts are mainly pale yellow brown to dusky yellow and magnetic tests indicate that the magnetization is carried dominantly by ferric oxyhydroxides haematite and goethite the higher temperature natural remanent magnetization is probably due to detrital haematite which would have been partially aligned during fluvial deposition post depositional modification pdrm may have occurred during dewatering haematite pseudomorphing pyrite framboids indicates that early reducing conditions were succeeded by a more oxidizing regime which produced secondary magnetizations associated with fine grained haematite and goethite complete polarity zones are not delineated but the thicknesses present are not excessive compared with other continental miocene deposits the average palaeolatitude of 22 degrees is lower than would be expected for the miocene of northern spain probably due to incomplete averaging of secular variations and other sources of error including possible inclination error modified journal abstract

alluvial sedimentation patterns in the munster basin ireland post caledonian southern ireland witnessed the development of a ne sw orientated half graben known as the munster basin more than 7 km of non marine sediments accumulated in the basin during the late middle and late devonian marine conditions became established in the southern part of the basin at the end of the devonian in this paper a model for the evolving style of sedimentation in the basin and its periphery is constructed with the aim of identifying the major factors which controlled sedimentation patterns and the architecture of the basin fill the depositional history of the basin is considered in terms of four successive episodes during episode i gravelly alluvial fans flanked upland areas around the northeastern and northern basin perimeter these graded southwestwards to a floodplain dominated by sheet floods in the western part of the basin the first of three major fluvial influxes into the basin commenced during episode ii the first influx developed into a large sandy braided complex the sediment was derived from a distant source area located to the north and west of the basin and was transported diagonally across the basin towards the southeast episode iii witnessed a second influx which drained into the basin from the northeast and north river channels were of low sinuosity and graded distally to an ephemeral playa lake episode iv was marked by a third fluvial influx from the west and northwest this was confined to the southern half of the basin and drainage was directed towards the east the fluvial distributaries were flanked by permanently flooded overbank areas this influx coincided with the first marine transgression which advanced westwards the end of episode iv coincided with the beginning of the carboniferous and was marked by a major marine transgression sediment input to the basin was influenced by stable areas occupied by granitic plutons on either side of the basin and a southward downthrowing fault along its northern margin the drainage direction was principally controlled by e w trending within basin faults and an e w trending stable area located to the south the basin was fundamentally of the axial transport type the main drainage having been directed towards the east though there was also a strong lateral influx from the north northwest and northeast stable areas around the basin periphery resulted in either no sediment preservation or sequences of multistorey channel deposits while thick sequences dominated by fine grained floodplain or overbank deposits characterized areas of higher subsidence rate within the basin movement on the northern basin margin fault was probably the major cause of the first fluvial influx while regional subsidence of the basin and its northern periphery resulted in the second influx the third influx was a response to local subsidence in the southern part of the munster basin this also contributed to the simultaneous westward marine transgression in this area towards the end of the devonian source area denudation and retreat in association with a sea level rise were ultimately responsible for terminating the alluvial regime in the munster basin

models of miocene marginal lacustrine sedimentation in response to varied depositional regimes and source areas in the madrid basin central spain abstract a succession of lake complexes formed through miocene times in the madrid basin central spain the complex formed during the aragonian stage provides an outstanding opportunity to evaluate the role of source areas and depositional regimes in the construction of coeval marginal lacustrine deposits sedimentary facies of the aragonian lake indicate a shallow lake that was fringed to the nw and s by arkosic alluvium to the n by litharenitic alluvial fans and to the ne and e by alluvial fans distally dominated by large floodplains marginal lacustrine deposits in the arkosic realm mostly consist of mg smectites and dolomite sequences that laterally interfinger with sepiolite beds which were deposited in small discontinuous ponds in the distal alluvial fan areas occasionally micaceous rich sandy streams entered the lake forming sheets at their entry points in contrast the northern margin of the lake was formed by muddy flats which were influenced by fluctuation in the water table in this setting illitic mudstones are commonly interbedded with biotite rich flood sands showing a sheet like geometry meandering channels occasionally cut into the mud flats facies assemblages on this side of the lake were mainly derived from low grade metamorphic areas to the northeast the marginal lacustrine facies consist of silty clays carbonate paleosols and paludal to lacustrine limestones these facies reflect an interfingering between the lake and a wide stream floodplain system derived from a carbonate source area the mosaic of marginal lacustrine facies in the madrid basin during the aragonian is discussed in the light of lithological and geochemical factors related to variations in source areas

shale rock physics and implications for avo analysis a north sea demonstration shales normally constitute more than 80 of sediments and sedimentary rocks in siliciclastic environments shales are important both in controlling the overburden seismic wave propagation as well as the reflectivity contrast between cap rocks and reservoir rocks in prestack seismic data therefore during avo analysis it is crucial to understand the seismic properties of shales as a function of mineralogy and compaction in this study we derive the local shale trend for a north sea gas and oil field by integrating rock physics modeling with well log and seismic data analysis

fluvial sedimentology and revised stratigraphy of the triassic flagstone bench formation northern prince charles mountains east antarctica the flagstone bench formation ranges in age from earliest triassic to norian late triassic and is exposed in the beaver lake area of the northern prince charles mountains this sandstone dominated formation rests conformably on the bainmedart coal measures and represents the upper part of the permian triassic amery group it is divisible into three members the ritchie jetty and mckelvey members in ascending order nine sedimentary facies assignable to three facies associations major channel crevasse fan and flood basin deposits are recognized within the formation ritchie member sedimentation took place during a transition from consistently hygric to seasonally dry conditions and the unit comprises sandstone dominated sheet like channel deposits interspersed with few thin mottled haematite rich flood basin siltstones deposition took place under fluctuating discharge conditions chiefly within the channel tracts of axially northwesterly northeasterly flowing low sinuosity braided rivers the jetty member shows a gross upward fining profile dominated in the lower part by poorly sorted pebbly sandstones and in the upper part by ferruginous mudcracked siltstones mottled palaeosols calcrete and thin massive sandstone sheets this unit reflects deposition of easterly directed alluvial fans and extensive flood basin silt under a semi arid climatic regime the upper triassic sandstone dominated mckelvey member shows a return to axial drainage along the lambert graben with sedimentation occurring primarily within low sinuosity braided channel tracts under wetter climatic conditions

constraints on synrift intrabasinal horst development from alluvial fan and aeolian deposits triassic fundy basin nova scotia the authors would like to acknowledge shell e and p for funding this study rob raeside at the acadia university and liz kosters for their support during the field seasons we also would like to thank brian p j williams for enthusiastic discussions in the field

sediment dispersal and palaeohydraulics of oligocene rivers in the eastern ebro basin mapping of heavy mineral associations and diagnostic accessories in oligocene sediments of the eastern ebro basin has revealed two major provinces and several sub provinces the pyrenean province is characterized by an apatite tourmaline garnet association with diagnostic staurolite in the west western pyrenean sub province and micaceous composite grains plus chloritoid in the east eastern pyrenean sub province the catalanides province is characterized by an ultrastable angular brown tourmaline staurolite association with kyanite in the south west montsant sub province faceted garnets and rounded tourmalines in an intermediate position st miquel del montclar sub province and in the north east rounded and green tourmalines admixed with clinopyroxene apatite and micas derived from the pyrenees montserrat sub province palaeodischarges have been estimated from 30 channels distributed throughout both major provinces a gradual decrease in river discharge through oligocene times is indicated for the rivers of catalanides parentage although the discharges of high sinuosity streams alone remain uniform this decrease through time of catalanides drainage competitiveness is reflected in the greater areal extent of the pyrenean petrological province together with a progressive displacement south or south eastwards of basinal lacustrine facies the increasing dominance of pyrenean drainage during the oligocene may be due to more prolonged tectonic activity in the pyrenees compared to the more quiescent catalanides

structural stratigraphic and sedimentological characterisation of a wide rift system the triassic rift system of the central atlantic domain abstract the extension driven break up of the pangean supercontinent in the present day central and north atlantic domains commenced during permo triassic times permian rift processes in this region are generally attributed to crustal collapse during the latter part of the hercynian variscan orogeny but the triassic rifting style is more complex and the presence of a single over riding first order control is equivocal basement terrane structures and boundaries provide pre existing zones of weakness that had significant influences on the location timing orientation and extent of triassic rifting the 201 ma central atlantic magmatic province camp a large igneous province lip increased lithospheric heat flow at the end of rifting produced uplift and doming and also contributed to deformation and subsequent continental breakup analysis of the triassic basin structures in the central atlantic and north atlantic domains respectively georgia to nova scotia and conjugate margin and newfoundland iberia shows that four main basin types are geographically distributed 1 southern basins georgia to virginia small to medium size with limited growth structures 2 basins in the central east domain new jersey nova scotia wide basins with growth structures along long lived inherited bounding faults 3 basins in the central west domain offshore ns and morocco that comprise numerous half graben sub basins in a lower unit and an upper very wide tabular unit and 4 northern basins newfoundland portugal that are tabular and extremely wide basin architectures suggest that subsidence was regional in extent and not necessarily controlled by main faults variations in crustal characteristics are considered to have led to the development of the four main basin types stratigraphic data show that the onset of deposition in the central and southern north atlantic domain was restricted to a central segment between two main structural lineaments overall crustal rheology and inheritance exhibited first order controls on subsidence and basin development triassic basins in the central and north atlantic domain were all filled by continental deposits in various palaeo environments such as alluvial fan mega fluvial systems terminal fluvial systems fan delta fluvial systems permanent oxic and anoxic lakes playa lakes and saline lakes some of them interbedded with aeolian and volcanic deposits most basins were far from any marine domain but marine ingressions from the tethys domain are inferred from dolomite and marine fauna in portugal and from thick salt deposits in morocco and offshore canada during the late rhaetian a series of palaeogeographic maps are presented utilising plate reconstructions based on sahabi et al 2004 in order to summarize continental scale palaeo environment distribution our tectono stratigraphic model suggests that initial strain was accommodated in a central segment by inherited faults during the early and middle triassic during the carnian the rift domain was increasingly extended with the development of half graben basins in the central segment and some in the northern segment in both segments the initial strain re activated inherited faults and later the rift zones evolved towards significantly wider basins marked by the presence of a major erosional truncation surface across the basins and followed by lacustrine sedimentation that eventually overlapped paleo topographic highs subsidence of such regional extent is likely driven by thermal processes following a phase of extreme lithospheric thinning and lower crustal removal associated with mantle uplift the architecture of the triassic rifting has the characteristics of the wide rift mode very large basins with some active faults for which subsidence is driven by lower crustal flow within a high heat flow region nevertheless some faults were active during late triassic sedimentation but accounted for a relatively minor part of the overall subsidence pulses of active subsidence and topographic rejuvenation led to fluvial dominated deposition within basins non rejuvenation of hinterland led to more lacustrine dominated sedimentation and eventual connection of basins across topographic highs due to regional thermal subsidence during the latest rhaetian basins with the lowest elevations were possibly flooded by marine waters resulting in precipitation of thick salt deposits

toward a model for open and closed basin deposition in ancient lacustrine sequences the newark supergroup triassic jurassic eastern north america abstract climate and tectonics have a profound influence on the lacustrine sedimentary record because they affect hydrologic systems in depositional basins lakes in hydrologically closed basins tend to fluctuate in depth producing transgressive regressive sequences sometimes associated with evaporites lakes in hydrologically open basins tend to have stable shorelines producing thick sedimentary deposits that lack transgressive regressive sequences and evaporites in addition some lakes fluctuate between open and closed producing transgressive regressive sequences in which deep water sediments were deposited when the lake was overflowing and shallow water sediments capped by subaerial exposure surfaces were deposited when the basin was closed lacustrine deposits in the northern part of the newark supergroup consist of cyclic transgressive regressive sequences locally containing evaporites they are interpreted as deposits of hydrologically closed basins which occasionally became open at lake high stand in the southern part of the newark supergroup many of the lacustrine sequences are thicker lack evaporites and some contain coal and siderite these features suggest deposition in hydrologically open basins fluvial paleocurrents in at least one southern basin suggest through flow and open basin deposition thin lacustrine sequences interpreted as perennial floodplain lake deposits are associated with these fluvial systems and may also indicate open basin conditions

alluvial playa sedimentation in the lower keweenawan sibley group thunder bay district ontario the middle proterozoic sibley group is a mixed clastic carbonate red bed sequence located in the thunder bay nipigon area on the north shore of lake superior the lowest unit the pass lake forma

rock physics estimation of cement volume sorting and net to gross in north sea sandstones rock physics represents the link between geologic reservoir parameters e g porosity clay content sorting lithology saturation and seismic properties e g vp vs density elastic moduli rock physics models can either be used to interpret observed sonic and seismic velocities in terms of reservoir parameters or they can be used to extrapolate beyond observed range to predict certain what if scenarios in terms of fluid or lithology substitution rock physics models can also be used to estimate expected seismic properties from observed reservoir properties

alluvial fans and fluvial fans at the margins of continental sedimentary basins geomorphic and sedimentological distinction for geo energy exploration and development alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins their occurrence is determined by the area relief and hydrology of the catchment which ultimately control the relative ratios of sediment v flow discharge and runoff regimes fundamental morphological and process distinctions exist between these two kinds of deposystem which are seen as essentially different facies associations and internal architectures for the corresponding deposits alluvial fans commonly develop over short radial distances hundreds of metres to a few kilometres and are constructed by ephemeral flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits by contrast fluvial mega fans are fed by proper river systems which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies represented by hierarchically well organized fluvial deposits the general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction

chronology of neogene sedimentation stratigraphy and tectonism in the campo de talampaya region la rioja province argentina abstract chronostratigraphic paleoenvironmental and tectonic analysis of a 2320 m thick neogene continental section was conducted along the southern limit of the campo de talampaya magnetic polarity stratigraphy and fission track ages were used to develop a relatively precise geochronology the strata record a period of mixed evaporitic and terrigenous elastic sedimentation 20 6 1 ma that persisted in the distal bermejo basin during eastward migration of the precordillera fold thrust belt a critical transition of depositional environments and a change from western to eastern source areas occurred between 12 9 and 12 3 ma the saline mud flat environment of the rio manero formation derived from a western source and characterized by fine grained sandstones mudstones and evaporites yielded to a short period of playa lake deposition this was soon overwhelmed by deposition of the desencuentro formation composed of sandstones and mudstones with an eastern source area and deposited in a sand flat mud flat environment we propose that this stratigraphic transition resulted from initiation of uplift of the sierra de velasco a range of the sierras pampeanas located 65 km to the east northeast of the section basement clasts probably derived from the sierra de velasco are found in conglomeratic lenses beginning in the lower part of the desencuentro formation the modern campo de talampaya basin formed after deposition of the top of the alto de san nicolas paleomagnetic section 6 1 ma when west verging reverse faults uplifted the sierra morada and sierra de los tarjados all strata in the section were tilted eastward during these culminating uplift events

cycles of sand flat sandstone and playa lacustrine mudstone in thetriassic jurassic blomidon redbeds fundy rift basin nova scotia implications for tectonic and climatic controls the redbeds of the 220 m blomidon formation comprise more than 100 pairs of i sand flat sandstone distal alluvial fan and ii playa sandy mudstone and or lacustrine claystone these pairs are tectonic autocycles generated by rift basin subsidence and sagging along the glooscap fault zone that shifted loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated into topographically low areas intervals of intense and prolonged aridity are recorded in many of the sand flat sandstones and playa sandy mudstones by evaporite minerals principally gypsum precipitated by subsurface evolution of a caso4 nacl brine aridity is further demonstrated by intense disruption of sediment fabrics beneath evaporite crusts deep mudcracks eolian sandstone layers and patches and the presence of authigenic ca mg rich illite smectite and analcime during relatively wetter intervals claystone beds accumulated in shallow lakes that filled the playa depression lapping onto the sand flat

joint avo inversion wavelet estimation and noise level estimation using a spatially coupled hierarchical bayesian model the main objective of the avo inversion is to obtain posterior distributions for p wave velocity s wave velocity and density from specified prior distributions seismic data and well log data the inversion problem also involves estimation of a seismic wavelet and the seismic noise level the noise model is represented by a zero mean gaussian distribution specified by a covariance matrix a method for joint avo inversion wavelet estimation and estimation of the noise level is developed in a bayesian framework the stochastic model includes uncertainty of both the elastic parameters the wavelet and the seismic and well log data the posterior distribution is explored by markov chain monte carlo simulation using the gibbs sampler algorithm the inversion algorithm has been tested on a seismic line from the heidrun field with two wells located on the line the use of a coloured seismic noise model resulted in about 10 lower uncertainties for the p wave velocity s wave velocity and density compared with a white noise model the uncertainty of the estimated wavelet is low in the heidrun example the effect of including uncertainty of the wavelet and the noise level was marginal with respect to the avo inversion results

sudden changes in fluvial style across the permian triassic boundary in the eastern iberian ranges spain analysis of possible causes abstract the sedimentary record of the late permian and early triassic of the eastern iberian ranges shows four major sudden or very rapid vertical changes in fluvial style the late permian sedimentary cycle starts with the boniches formation of alluvial fan braided fluvial origin which grades vertically over within a few metres into the alcotas formation deposited by low to high sinuosity avulsion prone rivers with extensive floodplains the alcotas formation contains calcimorphic soils plant remains and pollen and spore assemblages however the upper third of the unit is devoid of all organic remains and soils and is characterized by a dominant red colour the sandstone levels were deposited by high sinuosity meandering rivers this major change took place during the late permian and is probably coeval with the emplacement of the emeishan basaltic large igneous province lip in se china rocks of the boniches and alcotas formations are separated by an angular unconformity from the overlying strata which consist of the late permian conglomeratic hoz del gallo formation of alluvial fan gravel braided fluvial origin and the sandy canizar formation of low sinuosity sandy river origin the permian triassic boundary lies probably between the upper part of the hoz del gallo formation and the first metres of the canizar formation late permian pollen and spore assemblages have been found in the hoz del gallo formation but the canizar formation is barren with the exception of an anisian middle triassic assemblage at the top tectonic extensional pulses in the iberian basin caused the changes observed between the lower and upper parts of the boniches formation at the base of the hoz del gallo formation and between the lower and upper part of this formation the changes observed in the uppermost part of the alcotas formation are not easily explained by tectonic causes nor those in the passage from the hoz del gallo formation to the canizar formation similar sedimentary characteristics of the sandy canizar formation such as amalgamated sandstone bodies erosion and reactivation surfaces dominant trough cross stratification tabular geometry absence of plant remains and pollen and spores and absence of silts and clays to those of coeval formations in places as far away as australia south africa and brazil suggest a global rather than local cause for these abrupt changes in fluvial style this global cause was probably die off of plant cover over extensive areas of the catchment related to the end of the permian mass extinction and possibly related to the emplacement of the west siberian basaltic large igneous province lip responsible for drastic atmospheric and marine changes

distal alluvial fan sediments from the upper jurassic of portugal controls on their cyclicity and channel formation the lusitanian basin of west central portugai is an iberian atlantic margin basin during a late jurassic rifting event a series of alluvial fans distributed coarse basement derived clastics southeastward from the western margin of the basin the distal part of this sequence which is about 140 m thick consists of heterolithic massive sandstone and massive mudrock facies arranged in crude fining upwards cycles 1 15 m thick these form discrete packets of sediment in a strongly aggrada tional sequence and are interpreted as the products of sheetflooding as the active area of sedimenta tion on the fan surface switched channelized flow was not necessarily an early feature of cycle development considerable fluctuations in discharge occurred and were probably related to climatic factors large quantities of tractional and suspended sediment were transported at high stages and were rapidly deposited as flows waned caliche soil profiles indicate a seasonal semi and climate however other features such as widespread soft sediment deformation the lack of desiccation structures and the absence of evaporites suggests that areas of active sedimentation often remained wet three fining upward megacycles are distinguished these indicate rapid advance of fan toes triggered by tectonic activity followed by gradual retreat

climatic and geomorphologic cycles in a semiarid distributive fluvial system upper cretaceous bauru group se brazil abstract studies of distributive fluvial systems and their preserved successions envisage the distribution and orientation of architectural elements to be primarily controlled by channels radiating outward from fan apices in many cases along an elongate basin margin conceptual models for such systems account for the downstream dynamics of the fluvial network but with limited consideration of temporal geomorphic variations resulting vertical organisation of architectural elements or of the interplay of factors controlling system dynamics to understand the external and internal architecture of distributive fluvial systems and the factors that influence their sequential facies organisation a sedimentary succession of the proximal portion of an upper cretaceous semiarid distributive fluvial system located at the north eastern margin of the bauru basin southeast brazil has been analysed in detail three fining and thinning upward fluvial sequences are identified forming an interval separated at the top and the bottom by two palaeosol profiles each sequence is formed of channel and floodplain deposits two types of channel deposits are identified one is composed of stacked sets of small scale dune deposits suggesting perennial and steady fluvial regime associated with more humid climate periods the other is composed of large scale sets indicative of flattened dunes associated with unsteady and fast changing fluvial flow formed in quasi supercritical flow regime conditions associated with drier climate periods the vertical alternation of these two types of channel deposits records the accumulation of a fluvial succession that responded to high frequency climate induced cyclic change in boundary conditions two palaeosol profiles at the top and at the bottom of the succession indicate temporary interruptions and cessation of the fluvial sedimentation likely related to avulsion of the fluvial belt thus the studied succession reveals high frequency climate induced allogenic sedimentary cycles that occur within a long period autogenic geomorphologic induced sedimentary cycle this work suggests that the internal architecture of the channel deposits can be used as a climate proxy and that climate and geomorphology act jointly as notable factors to control the vertical organisation of distributive fluvial systems

bayesian lithology fluid prediction constrained by spatial couplings and rock physics depth trends elastic properties of rocks are strongly influenced by geological trends and the uncertainties in the lithology fluids prediction can be reduced if these trends are included in the inversion model in this study lithology fluid classification constrained by depth trends avseth et al 2003 is considered in a spatial setting with a markov random field prior model for spatial coupling of the discrete lithology fluids classes

basement blocks and tecto sedimentary evolution in the pyrenees during mesozoic times the alpine tectonics in the pyrenean range is controlled by motions of basement blocks high primary range north pyrenean blocks these blocks belong to different tectonic units they are amygdaloid wedge shaped squeezed at their roots upthrust and displaced with their cover detached or not in a convergent shear zone between the european and iberian plates these basement blocks are distributed within isopic isofacial units with diachronous terrigenous prisms the stratigraphical analysis of their mesozo c cover reveals their relative position during the mid cretaceous continental break up which induced the separation of the two previously joined plates

the pleistocene end moraine fans controls on their sedimentation and location abstract this paper presents a model of end moraine sedimentation based on data from pleistocene ice sheet margins according to this model end moraines quite often constitute alluvial fans or coalesced fans formed at the ice margin by redeposition of supraglacial material three types of end moraine fan have been recognized those composed mainly of mass flow deposits type a equivalent to dry alluvial fan in nonglacial settings those containing both mass flow and waterlain sediments type b and those that contain mainly sorted waterlain material type c equivalent to wet alluvial fan in nonglacial settings for each type of fan several sedimentary subenvironments differentiated by distance from the ice front are identified the diagnostic processes on the end moraine fans are cohesive and cohesionless debris flows or grain flows types a and b or hyperconcentrated flows and sheetflows types b and c the type b fan seems to represent the most typical sequence in the end moraine zones but the type c fan is also quite common at the pleistocene ice sheet margins our studies also suggest that the terminal supraglacial drainage controls the type of end moraine fan sedimentary subenvironment moraine types a b c whereas subglacial hydrology and ice stream regime which determine the mobility of the ice front and larger scale conditions of sediment supply to the ice margin control the location and size of the end moraine fan

facies analysis of a back tilted lacustrine basin in a strike slip zone lower devonian scotland abstract lower devonian lower old red sandstone basins developed along active faults in northern scotland the dingwall strathpeffer basin is a half graben which thickens into the helmsdale polinturk fault a splay off the major strike slip great glen fault zone facies analysis allows the distinction of facies associations which represent alluvial fan perennial lake and playa mudflat ephemeral stream environments syn sedimentary faulting at the margin was the major control on alluvial fan sedimentation the lacustrine facies were fringed by alluvial facies but at times of high water level extended to the active basin margin sedimentary structures and pseudomorphs after gypsum suggest an arid to semiarid environment in which the alluvial fan stream and floodplain sedimentation was largely ephemeral during arid periods the basin centre lake environment was constricted and the surrounding mudflats experienced intense evaporation while after flooding episodes the lake increased in size the thickest lacustrine sequences occur close to the basin margin alluvial fans due to back tilting of the fault blocks fault motion and or climatic fluctuations caused significant interdigitation of the facies the mixture of alluvial fan and organic rich lacustrine facies close to the bounding fault offers some potential for trapping of hydrocarbons

sedimentology and architecture of the douglas creek terminal splay lake eyre central australia douglas creek terminal splay sited on the western shoreline of lake eyre north central australia covers a surface area of approximately 4 km2 with a down system length of 2 5 km from the distributary channels terminus to the splay fringe two distributary channels feed two sediment lobes which have amalgamated to form the terminal splay three primary facies associations have been identified sub dividing the creek terminus into distributary channel proximal and distal splay sections proximal splay sediments are characterized by erosionally based relatively thick 100 mm stacked sheets of coarse to medium sand which commonly display trough and planar cross bedding whereas the distal splay is characterized by thin generally 50 mm massive beds of very fine sand silt and clay the change in splay sedimentology is interpreted as reflecting the transition from bedload dominated deposition to suspended load dominated deposition from decelerating sheetfloods as they spread out from the channel onto the dry lake bed a proximal to distal splay transition zone is also noted where deposits of both facies associations interfinger laterally and vertically in scale geometry and facies associations the douglas creek terminal splay is very different to the often cited neales terminal splay complex located 70 km to the north it is suggested that these architectural differences reflect variations in discharge volume input sediment distribution and the degree of vegetation cover understanding the variation in terminal splay architecture has very significant implications for the modelling of analogous subsurface petroleum systems which at present relies on few modern day analogues

growth and fragmentation of the andean foreland basin during eastward advance of fold thrust deformation puna plateau and eastern cordillera northern argentina 1 the fault bounded cianzo basin represents a cenozoic depocenter between the puna plateau and eastern cordillera of northern argentina analysis of fold thrust relationships nonmarine sedimentation and detrital provenance at 23 24 s helps constrain the origin interconnectedness and subsequent uplift and exhumation of the cianzo basin a potential analog for intermontane hinterland basins in the andes structural mapping reveals a plunging syncline within the 6000 m thick upward coarsening cenozoic clastic succession in the shared footwall of the n striking e directed cianzo thrust fault and transverse ne striking hornocal fault growth strata within upper miocene levels indicate syncontractional accumulation adjacent to the hornocal fault measured stratigraphic sections show upsection changes from 1 paleosol rich distal fluvial sandstones 400 m paleocene eocene santa barbara subgroup to 2 braided fluvial sandstones and mudstones 1400 m upper eocene oligocene casa grande formation to 3 distributary fluvial megafan sandstones and conglomerates 3300 m upper oligocene miocene rio grande formation to 4 alluvial fan conglomerates 1600 m upper miocene pisungo formation the 40ar 39ar geochronological results for interbedded tuffs indicate continuous rio grande deposition from at least 16 34 0 71 to 9 69 0 05 ma sandstone petrographic results define distinct upsection trends in lithic and feldspar content potentially distinguishing the western cordillera magmatic arc from puna eastern cordillera thrust belt sources in addition to growth stratal relationships and 40ar 39ar ages conglomerate clast compositions reflect distinct lithologic differences constraining activation of the cianzo thrust and coeval reverse slip on the reactivated inverted hornocal fault finally detrital zircon u pb ages paleocurrents and facies patterns distinguish local from distal sources revealing a systematic forelandward eastward advance of eocene through upper miocene fold thrust deformation

sheet flow deposits of graded beds and mudstones on an alluvial sandflat playa system upper triassic blomidon redbeds st mary s bay nova scotia the 400 m of blomidon redbeds accumulated in a semi arid rift valley in the subtropics at st mary s bay these redbeds are 64 sandy mudstone playa mudflats 25 graded beds sandflats at the toes of alluvial fans 10 fissile claystone playa lakes and 1 channel sandstone stream channels flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north east as sheet flows on sandflats and playa mudflats deceleration of the sheet flows deposited graded beds 2 83 cm in thickness on the sandflats and thin layers of mud on the playas nine sequences consisting of arrangements of six lithologies compose 90 of the graded beds in order of decreasing abundance these are ripple cross laminated siltstone horizontally laminated mudstone fining upward ripple cross laminated siltstone ripple cross laminated sandstone horizontally laminated mudstone cross bedded sandstone horizontally laminated mudstone ripple cross laminated sandstone ripple cross laminated siltstone rippledrift cross laminated siltstone horizontally laminated mudstone fining upward ripple drift cross laminated siltstone cross bedded sandstone ripple cross laminated siltstone and cross bedded sandstone ripple cross laminated siltstone horizontally laminated mudstone the sheet flows perhaps up to 1 m in depth had a high concentration of suspended load deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration there are 32 thinning and fining up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone the cycles range in thickness from 1 3 to 13 3 m averaging 4 6 m each cycle is initiated by avulsion to a new active channel network on a fan gradual abandonment of the channel network produces the thinning and fining up cycle the cycles are grouped in three 60 70 m fining up megacycles upwards within each megacycle the packages of sandy mudstone compose a progressively larger proportion of the cycles each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor subsequent erosion gradually lowered the relief to yield a fining up megacycle