stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

structure of the dingle peninsula sw ireland evidence for the nature and timing of caledonian acadian and variscan tectonics the palaeozoic rocks of the dingle peninsula provide a record of the evolution of the caledonides acadides and variscides the succession ranges from early ordovician deep water sediments through silurian shallow marine to non marine sediments and volcanic rocks to an old red sandstone ors succession topped by carboniferous marine shales comparison of structural styles in the unconformity bounded groups together with a detailed analysis of fault zones allows the tectonic history to be deduced the older rocks record caledonian processes on the margin of avalonia during early ordovician time and convergence then soft collision with laurentia during silurian time the dingle basin was developed during the late silurian early devonian transtension in the iapetus suture zone and was inverted in the latest emsian acadian orogenic episode post dingle group ors groups in the north of the peninsula were deposited in a syn rift footwall block to the main munster basin the acadian transpressional and munster basin extensional structures were reactivated or overprinted in the variscan deformation such that acadian folds are transected by variscan cleavage in both plan and vertical views after iapetus closure changes in the tectonic regime are believed to be a result of adjustments in the geometry of subduction of the rheic ocean

u pb zircon geochronology of silicic tuffs and chronostratigraphy of the earliest old red sandstone in the munster basin sw ireland

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

stratigraphical and structural relationships of the dingle group silurian county kerry ireland previous views on the relationship between the thick continental deposits of the dingle group and the older fossiliferous silurian rocks of the dunquin group are briefly reviewed detailed field evidence is presented showing that in the coastal sections of coosgorrib coosglass and coosshaun there is faulting between the two groups the same situation obtains at the northern end of the great blasket island fortunately inland exposures are sufficient to show that there is stratigraphical continuity from the lower ludfordian ludlow beds of the croaghmarhin formation at the top of the dunquin group into the purple siltstones of the dingle group the dingle group is followed uncomformably by upper old red sandstone essentially upper devonian

erg margin deposits in the lower jurassic moenave formation and wingate sandstone southern utah the moenave formation dinosaur canyon member and the closely associated wingate sandstone in southern utah represent the southwestern erg margin of the lower jurassic wingate erg the erg margin deposits which extend across a 50 to 100 km wide region are composed of dune eolian sand sheet mud flanked eolian sabkha ephemeral stream and lacustrine facies the succession is divided into a basal erg margin association 8 27 m dominated by eolian facies and an overlying erg margin association as much as 90 m thick composed mainly of fluvial and lacustrine facies the sediments of the basal association are composed of three drying upward or locally drying wetting upward sequences that can be traced from the erg margin 100 km slightly upwind that is toward the west northwest into the outer erg margin zone sequences of the inner erg margin zone contain dune facies in their upper parts sequences in the intermediate erg margin zone contain sand sheet facies and those in the outer erg margin zone contain sabkha facies the basal association thins markedly toward the west northwest sediments of the overlying association contain up to six drying upward or drying wetting upward sequences but are apparently only fully preserved in the outer erg margin zone individual sequences show much lateral variation but characteristically contain lower muddy ephemeral stream deposits and upper sandy ephemeral stream deposits sand sheet deposits or incipientdune deposits the general time trend is interpreted as a gradual change toward a more humid climate the stacked drying upward or drying wetting upward sequences suggest that this long term climatic change was characterized by a number of fluctuations between relatively arid and humid conditions these climatic fluctuations apparently controlled both sediment yield to the basin and the depositional conditions in the erg margin region during arid intervals ephemeral braided streams transported sandy bed load into the erg margin area where eolian reworking took place during humid intervals sheet floods and high sinuosity rivers transported a more mud rich sediment load into the basin where eolian activity was minimal

flexural cantilever models of extensional subsidence in the munster basin sw ireland and old red sandstone fluvial dispersal systems

formation of southern component water in the late cretaceous evidence from nd isotopes constraining deep ocean circulation during past greenhouse climatic periods such as the cretaceous is important for understanding meridional heat transfer processes controls on ocean anoxia and the relative roles of climate and tectonics in determining paleocirculation patterns ocean circulation models for the late cretaceous and early paleogene suggest that significant deep water production occurred in the southern ocean but cannot constrain when this process commenced or what the temporal relationship was between opening tectonic gateways and late cretaceous climatic cooling nd isotope data obtained from biogenic apatite fish teeth and bones are presented from lower bathyal and abyssal sites in the south atlantic and indian oceans during the mid cretaceous relatively radiogenic nd isotope values suggest that deep water circulation in these basins was sluggish with inputs likely dominated by seawater particle exchange processes and possibly easily weathered volcanic terranes in the campanian maastrichtian the nd isotopic composition of proto indian and south atlantic deep waters became less radiogenic suggesting the onset of deep water formation in the southern ocean southern component water scw consistent with paleogene reconstructions and ocean circulation models a combination of southern hemisphere cooling and the opening of tectonic gateways during the campanian likely drove the onset of scw

an eifelian u pb zircon date for the enagh tuff bed from the old red sandstone of the munster basin in nw iveragh sw ireland the first geochronological data from the minister basin sw ireland contradict the accepted biostratigraphical maximum age late givetian early frasnian of the oldest alluvium in the basin depocentre magmatic zircons from the enagh tuff bed a sub plinian air fall tuff within fluviatile old red sandstone of nw iveragh give a pb pb isotope age of 384 9 0 7 ma this confirms middle devonian probably eifelian sedimentation and allows possible early devonian basin initiation associated second cycle gravels suggest a pre 385 ma minimum age for the caherbla group of the dingle basin correlation with alluvium containing tetrapod trackways indicates a pre 385 ma age for the trace maker

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

structural and climatic controls on facies distribution in a mixed fluvial and aeolian reservoir the triassic sherwood sandstone in the irish sea

post acadian sediment recycling in the devonian old red sandstone of southern ireland abstract the upper devonian munster basin of southern ireland has traditionally been viewed as a post orogenic molasse deposit that was sourced from the caledonides of central ireland and subsequently deformed by the end carboniferous variscan orogenic event the basin fill is composed of super mature quartz arenite sandstone that clearly represents a second cycle of deposition the source of this detritus is now recognized as lower devonian dingle basin red bed sequences to the north this genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units micas plot in identical fields and define the same trends in addition the two sequences show increased textural and chemical maturity up sequence and define indistinguishable 40 ar 39 ar age ranges for the detrital mica grains partial resetting of the ar ages can be attributed to elevated heat flow in the region caused by munster basin extension and subsequent variscan deformation the combined evidence from southwest ireland therefore points to a caledonian or possibly taconian primary source area that initially shed detritus into the lower devonian dingle basin which was subsequently recycled into the upper devonian munster basin following mid devonian acadian basin inversion

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

the influence of domain size on the response characteristics of a hurricane storm surge model the influence of domain size on boundary condition specification and on computed storm surge response is investigated storm surge response along the florida shelf in the gulf of mexico due to hurricane kate is examined over three domains using two different open ocean boundary forcing functions a still water or zero elevation condition and an inverted barometer condition which accounts for the atmospheric pressure component of the meteorological forcing the first domain is relatively small and is situated primarily on the continental shelf in the region of intense storm surge generation a second domain includes the entire gulf of mexico basin the final domain covers the gulf of mexico contiguous basins and extends out into the deep atlantic ocean the computed storm surge response indicates that the small domain is inadequate since cross shelf boundaries are in regions of significant storm surge generation where surge and therefore boundary conditions are not known a priori also the behavior of resonant modes that are physically excited within the gulf of mexico due to the passage of the hurricane is unknown at the boundaries of this small domain the domain that includes the entire gulf of mexico captures the primary storm surge well but may not correctly model resonant modes in general these resonant modes are difficult to accurately set up by boundary condition specification since they may be dependent on interactions between the gulf and contiguous basins the primary storm surge response as well as resonant modes excited by the storm are best represented using a domain which encompasses the western north atlantic ocean the caribbean sea and the gulf of mexico this domain with deep atlantic ocean boundaries facilitates simple boundary condition specification and minimizes the influence of boundary conditions on storm surge generation in coastal regions basin resonant modes and basin to basin interactions are also captured

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

fluvial aeolian interactions part ii ancient systems an understanding of fluvial aeolian deposition derived from modern case examples in a previous study is applied to the permian cutler formation and cedar mesa sandstone on the colorado plateau these formations supply an excellent three dimensional exposure of intertonguing fluvial and aeolian strata four distinct facies associations form the bulk of the cutler formation and cedar mesa sandstone 1 aeolian dune deposits 2 wet interdune deposits 3 fluvial channel deposits and 4 overbank interdune deposits in addition two distinctive types of erosion surfaces are found within the cutler formation and cedar mesa sandstone pebble to granule rich erosion surfaces aeolian deflation surfaces and flood surfaces fluvial and aeolian intertonguing result in extensive tabular sheets of aeolian sandstone separated by flood surfaces and overbank interdune deposits fluvial channels are associated with the deposits overlying flood surfaces and are incised into the underlying aeolian sandstones overbank interdune deposits and wet interdune deposits cover flood surfaces and intertongue with overlying aeolian sandstones the primary characteristics of ancient fluvial aeolian deposition are overbank interdune deposits and pronounced extensive erosion surfaces flood surfaces which are parallel to underlying fluvial sandstones and thus trend parallel to the palaeoslope and palaeohydrological gradient

sedimentary record of erg migration the sedimentary record of erg eolian sand sea migration consists of an idealized threefold division of sand sea facies sequences the basal division here termed the fore erg is composed of a hierarchy of eolian sand bodies contained within sediments of the flanking depositional environment these sand bodies consist of eolian strata deposited by small dune complexes zibars and sand sheets the fore erg represents the downwind leading edge of the erg and records the onset of eolian sedimentation basin subsidence coupled with erg migration places the medial division termed the central erg over the fore erg strata the central erg represented by a thick accumulation of large scale cross stratified sandstone is the product of large draa complexes eolian influence on regional sedimentation patterns is greatest in the central erg and most of the sand transported and deposited in the erg is contained within this region reduction in sand supply and continued erg migration will cover the central erg deposits with a veneer of back erg deposits this upper division of the erg facies sequence resembles closely the fore erg region similar types of eolian strata are present and organized in sand bodies encased in sediments of the upwind flanking depositional environment s back erg deposits may be thin due to limited eolian influence on sedimentation or incomplete erg migration or they may be completely absent because of great susceptibility to postdepositional erosion tectonic climatic and eustatic influences on sand sea deposition will produce distinctive variations or modifications of the idealized erg facies sequence the resulting variants in the sedimentary record of erg migration are illustrated with ancient examples from western north america europe southern africa and south america

an emerging palaeoceanographic missing link multidisciplinary study of rarely recovered parts of deep sea santonian campanian transition from shatsky rise the cretaceous deep sea record of the santonian campanian transition is commonly interrupted by an extensive unconformity representing c 1 early campanian shift we propose the santonian campanian climatic transition was not gradual but was the first major cooling step after sustained mid cretaceous hothouse conditions supplementary material detailed analytical methods including biostratigraphic notes and sr isotopic chronology supplementary figures locality map additional geochemical isotopic and micropalaeontological results palaeomagnetic results global sr isotope compilation and age model benthic foraminiferal stable isotope compilation tables of microfossil occurrences and numerical data are available at http www geolsoc org uk sup18598

paleobiogeography of campanian maastrichtian foraminifera in the southern high latitudes abstract distributions of planktonic and benthic foraminifera have revealed antarctic land sea distributions oceanic surface gyre configurations and changes in the configurations of the tethyan transitional and austral realms during campanian maastrichtian time poleward changes in the diversity of total and keeled planktonic species of the southern hemisphere are compared for the early and late campanian and early and late maastrichtian latitudinal diversity gradients were weakest during the early campanian and more pronounced during the late campanian and maastrichtian shallow marine seaways within west antarctica are suggested by similarity of late cretaceous nearshore benthic and open ocean planktonic assemblages from southern high latitude land and drill sites and by the occurrence of recycle cretaceous marine microfossils from antarctic interior and continental margin localities development of a major water mass boundary between cool surface waters south of about 50 s paleolatitude and warmer surface waters to the north in the south atlantic and indian ocean may have caused biogeographic isolation of austral realm assemblages during late campanian and early maastrichtian time several planktonic foraminifera show significant diachroneity in their latitudinal distributions magnetobiostratigraphic data suggest that abathomphalus mayaroensis migrated from high to low latitudes whereas pseudotextularia elegans globigerinelloides subcarinatus globotruncanella citae globotruncanella petaloidea globotruncana bulloides and globotruncana subcircumnodifer made time transgressive poleward migrations the distribution of a mayaroensis is in agreement with isotopic evidence for late maastrichtian climatic cooling while that of p elegans correlates with a latest maastrichtian warming event about 66 8 66 6 ma delayed first occurrences of the other taxa cannot be explained by paleoclimatic factors alone variations in global eustatic sea level and orogeny between southern south america and west antarctica may have also influenced the taxonomic composition of southern high latitude foraminiferal assemblages

timing of deformation within old red sandstone lithologies from the dingle peninsula sw ireland finite strain analysis of deformed clastic sedimentary rocks below and above the acadian unconformity on the dingle peninsula sw ireland reveals that this boundary represents a significant bulk strain discontinuity the late emsian acadian event is primarily responsible for penetrative cleavage development and high strain in rocks below the unconformity and not as previously held the later variscan event which overprinted the peninsula with a weak and localized disjunctive cleavage the presence of apparent anticlockwise transecting cleavage and implied dextral closure of the dingle basin during the acadian event is compatible with northward convergence of armorica with respect to eastern avalonia

influence of trench width on subduction hinge retreat rates in 3 d models of slab rollback subduction of tectonic plates limited in lateral extent and with a free trailing tail i e free subduction is modeled in a three dimensional 3 d geometry the models use a nonlinear viscoplastic rheology for the subducting plate and exhibit a wide range of behaviors depending on such plate characteristics as strength width and thickness we investigate the time evolution of this progressive rollback subduction measure the accompanying return flow in the upper mantle and quantify the plate kinematics due to the 3 d geometry flow is allowed to accompany slab rollback around the lateral edges of the slab the toroidal component as opposed to 2 d geometry where material is forced to flow underneath the slab tip the poloidal component a simple force balance is provided which relates the speed of backward trench migration to the resistive forces of generating flow and weakening the plate our results indicate most of the gravitational energy of the system i e the negative buoyancy of the subducting slab is converted into a toroidal flow 69 a much smaller amount goes into weakening the plate 18 and the remaining amount goes into driving flow parallel to displacement of the slab 13 for the trench widths w we investigate 1500 km a maximum trench retreat rate occurs for trenches 600 km wide which is attributed to the interaction between a plate of finite width and the induced flow which has a lengthscale in the horizontal direction these numerical results quantitatively agree with comparable 3 d laboratory experiments using analogue models with a purely viscous plate material schellart 2004a 2004b including correlations between increasing retreat rate with increasing plate thickness trench width for maximum retreat rate 500 km and estimated amount of slab buoyancy used to drive rollback induced flow 70 several implications for plate tectonics on earth result from these models such as rollback subduction providing a physical mechanism for ephemeral slab graveyards situated above the more viscous lower mantle and endothermic phase transition prior to a flushing event into the lower mantle mantle avalanche

tectonic and hydrologic controls on cyclic alluvial fan fluvial and lacustrine rift basin sedimentation jurassic lowermost cretaceous todos santos formation chiapas mexico abstract the nonmarine upper jurassic lowermost cretaceous todos santos formation of central chiapas mexico was deposited in half graben basins formed during the early rifting stage of the southern gulf of mexico basin this formation consists of alluvial fan fluvial and lacustrine sequences that were deposited under arid climatic conditions alluvial fans were built outwardly from the elongate basin margins by runoff that flowed transverse to the basin axis whereas fluvial units were deposited by rivers that flowed parallel to the basin axis lacustrine deposition took place in a topographic depression adjacent to the basin margin the presence of alluvial fan and fluvial or lacustrine deposits in vertically stacked cyclic megasequences hundreds of meters thick indicates that the basin opography changed through time this cyclicity denotes that periodically fluvial or lacustrine environments occupied the basin margin position and at other times alluvial fan sedimentation occurred there cyclicity was caused by periodic changes from high to low rates of basin subsidene the response of these three depositional environments to basin subsidence differed due to the unique hydrologic controls on sediment transport and deposition in each environment lakes were maintained by springs that emanated from the fractured fault margin and by fluvial discharge fluvial discharge and deposition resulted from precipitation or annual snowmelt anywhere in the river s expansive drainage basin whereas alluvial fan sedimentation occurred only when there was infrequent significant precipi ation in the small drainage basin from which fan sediment was derived as a result of these hydrologic controls the lacustrine or fluvial environments responded more quickly to periods of active tectonic subsidence and migrated over the fans to occupy the basin margin depression aided by a decrease in basin subsidence alluvial fans eventually prograded and displaced the fluvial or lacustrine environments away from the basin margin

large terrestrial and marine carbon and hydrogen isotope excursions in a new paleocene eocene boundary section from tanzania recent onshore drilling expeditions in tanzania have yielded sediments spanning much of the late cretaceous and paleogene which show exceptionally good preservation of both calcareous microfossils and organic matter the interval of the paleocene eocene thermal maximum petm was recovered at tanzania drilling project tdp site 14 in 2004 the petm interval was identified using planktonic foraminifer and nannofossil biostratigraphy carbon isotopic measurements of planktonic foraminifera from the genus subbotina show a maximum measured negative shift in 13c values of approximately 4 5 which is significantly larger than has been observed for most deep sea foraminifer records higher plant derived n alkanes yield a ca 6 5 negative shift through the same interval as carbon isotope fractionation in higher plants varies amongst taxa and is influenced by humidity it is possible that this remarkably large shift in the n alkane 13c values records environmental and vegetation changes as well as changes in the 13c value of the ocean atmosphere reservoir however dramatic increases in humidity appear to be unlikely as higher plant biomarker d values shift to higher rather than lower values taken together the records suggest that the magnitude of the carbon isotope excursion cie in the ocean atmosphere reservoir may have been larger than has generally been accepted this has important implications for the source and quantity of 13c depleted carbon released at the petm

proximal braidplain deposits in the middle devonian malbaie formation of eastern gaspe quebec canada the middle devonian malbaie formation of eastern gaspe canada comprises sharply alternating conglomerate and sandstone units their petrography suggests derivation from the same source but palaeocurrents indicate different dispersal systems for the sand and gravel the principal conglomerate facies is horizontally stratified with well developed imbrication characteristic of deposition on a high energy proximal braidplain minor cross stratified conglomerate shows well defined size sorting attributed to avalanching down foresets and sorting within minor bedforms on bar tops the sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts alternating with lineated low angle to horizontally stratified sandstone or trough cross stratified sandstone the sandstone units were deposited on a proximal braidplain with highly variable discharge but the absence of calcrete indicates that dry periods were not prolonged the malbaie is the coarsest uppermost formation of a devonian clastic wedge formed during the acadian orogeny the uniformity of facies association and palaeocurrents particularly in conglomerate units indicates derivation from a broad upwarp to the south this implies that the acadian uplands resulted from straight compression in contrast to the localized uplifts formed by strike slip faulting during the carboniferous

late albian paleoceanography of the western subtropical north atlantic a late albian early cenomanian record 103 3 to 99 0 ma including organic rich deposits and a 13c increase associated with oceanic anoxic event 1d oae 1d is described from ocean drilling program sites 1050 and 1052 in the subtropical atlantic foraminifera are well preserved at these sites paleotemperatures estimated from benthic 18o values average 14 c for middle bathyal site 1050 and 17 c for upper bathyal site 1052 whereas surface temperatures are estimated to have ranged from 26 c to 31 c at both sites among planktonic foraminifera there is a steady balance of speciation and extinction with no discrete time of major faunal turnover oae 1d is recognized on the basis of a 1 2 13c increase 100 0 99 6 ma which is similar in age and magnitude to 13c excursions documented in the north atlantic and western tethys organic rich black shales are present throughout the studied interval at both sites however deposition of individual black shale beds was not synchronous between sites and most of the black shale was deposited before the oae 1d 13c increase a similar pattern is observed at the other sites where oae 1d has been recognized indicating that the site s of excess organic carbon burial that could have caused the 13c increase has have yet to be found our findings add weight to the view that oaes should be chemostratigraphically 13c rather than lithostratigraphically defined

maastrichtian north atlantic warming increasing stratification and foraminiferal paleobiology at three timescales 1 analysis of 944 single specimens of three species of late maastrichtian planktonic foraminifera racemiguembelina fructicosa contusotruncana contusa and rugoglobigerina rugosa from 38 samples spanning the last 3 myr of the cretaceous shows consistent isotopic trends through time consistent isotopic differences among taxa and high within sample isotopic variability throughout within sample variability does not change systematically through time for any taxon but average 18o values decrease by 1 5 and average 13c values diverge up section comparing taxa average 18o values are similar within most samples but average 13c values generally decrease from r fructicosa to r rugosa to c contusa in addition the within sample variability of individual 13c measurements is larger for r fructicosa than for either c contusa or r rugosa an observation which is consistent with a photosymbiotic habitat for r fructicosa in terms of maastrichtian paleoceanography the negative 18o trend of 1 5 corresponds to a temperature increase of 6 c and the divergence of 13c values up section suggests an increasingly stratified water column in the western atlantic through the late maastrichtian we suggest that these trends are best explained by increasing import of south atlantic waters into the north atlantic and an intensification of the northern hemisphere polar front

climatic cyclicity and accommodation space in arid to semi arid depositional systems an example from the rotliegend group of the uk southern north sea

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

distinctions and uses of stratification types in the interpretation of eolian sand abstract eolian and subaqueous cross strata cannot be distinguished reliably by many commonly cited criteria they can however generally be distinguished by the characteristics of their component types of stratification which represent processes of sorting and transport of the grain population on dunes eolian dune stratification types consist of grainflow cross strata grainfall laminae and wind ripple generated climbing translatent strata some of these types especially translatent strata have characteristics unique to the eolian realm these same stratification types are found to compose some ancient cross strata and their occurrence confirms the eolian interpretations of pans of the entrada jurassic navajo triassic jurassic and galesville cambrian formations a well as revealing emergent islands in the curtis formation jurassic previously considered to be totally marine in origin stratification types show a characteristic distribution on modern eolian dunes and differ in their relative abundances and structure on dunes of differing size and kind these same relations allow some estimates of the type shape and original height of ancient dune deposits as well as influencing the occurrences of surface features such as tracks and tipple forms the geological record of stratification types and other dune features is greatly affected however by the extent of the post depositional truncation of dunes

santonian campanian planktonic foraminifera from tanzania shatsky rise and exmouth plateau species depth ecology and paleoceanographic inferences abstract the santonian campanian interval is of particular interest as it encompasses a cooling trend after the late cretaceous greenhouse maximum warmth of the turonian as well as a possibly related major faunal turnover among planktonic foraminifera the recovery of pristinely preserved planktonic foraminifera from santonian campanian sequences in southeastern tanzania allows examination of faunal changes and documentation of species specific stable isotope 13 c and 18 o signatures these isotopic data are ideal for inferring species paleoecological preferences and for tracing major paleoceanographic changes this study reports the first 18 o and 13 c data generated on glassy specimens of marginotruncana coronata m undulata m marginata and m pseudolinneiana and sigalia carpatica additional results from shatsky rise ocean drilling program leg 198 hole 1210b and exmouth plateau odp leg 122 hole 762c provide geographic control on species habitat preferences and paleoceanographic context isotopic analyses suggest that double keeled species including globotruncana bulloides contusotruncana fornicata c plummerae and probably marginotruncanids inhabited the surface mixed layer whereas the biserial gublerina rajagopalani was a permanent thermocline dweller thus our study confirms recent suggestions that the depth distribution models based on shell morphology and analogies with modern taxa are not applicable at all the examined localities changes in planktonic foraminiferal assemblages are used to define several ecological intervals each one characterized by a distinctive taxonomic composition and or increasing decreasing species diversity combined geochemical and paleontological observations suggest that by the middle late campanian a stratified upper water column developed in tanzania while less stratified and or mesotrophic conditions prevailed at shatsky rise and exmouth plateau

a model for the development of the irish variscides a clear correlation exists in the southern irish variscides between extensional structures which controlled late palaeozoic sedimentation in the munster basin and contractional thrusts and folds of end carboniferous age this correlation is interpreted to indicate that the extensional structural framework of the basin including a basal low angle detachment and an array of superjacent normal faults was reused during transpressive inversion of the basin to produce the fold thrust belt the extensional framework which in turn was to some extent derived by reactivation of caledonian structures therefore exerted a fundamental control on the geometry and style of contractional deformation it is not evident that the detachment had a discrete link to the fold belt in south wales or the main variscan orogen in europe