novel paleoecology of a postextinction reef famennian late devonian of the canning basin northwestern australia reefs are widely supposed to be particularly susceptible to mass extinction events and to survive only as low diversity remnant communities dominated by holdover or disaster taxa famennian late devonian reefs exposed in the windjana limestone of the canning basin northwestern australia demonstrate however that a novel reef ecology was established in the immediate aftermath of the frasnian famennian mass extinction here diverse calcimicrobes including rothpletzella spp shuguria spp ortonella and girvanella together with bryozoans brachiopods and stromatoporoid sphinctozoan and lithistid sponges grew as complex framework intergrowths in previously undocumented morphological forms forming spectacular elevated laminar to platy structures to 3 m in diameter and 0 35 m thick at least 15 morphospecies of lithistids are now identified where only two were previously documented these communities show no substantial reduction in biodiversity compared to frasnian counterparts nor any change in tiering or loss of complex ecological interactions these observations suggest that where stable carbonate platforms persisted after mass extinction events reef building could continue more important they demonstrate that no protracted interval of time was necessarily required either for recovery to ecological stability or for completely new reef ecologies to assemble such studies highlight the need to document ecosystem recovery after mass extinction events using detailed paleoecological analyses in addition to simple compilations of global biodiversity changes

stromatolitic framework of carbonate mud mounds abstract mud mounds are an important phanerozoic reef type generally formed in deeper water on carbonate shelf to basin slopes they commonly contain radiaxial calcite spar filled depositional cavities stromatactis but lack abundant metazoan framebuilders mud mounds are often flanked by steeply dipping bioclastic grainstones and sometimes attained widths and depositional reliefs of over a hundred meters they occasionally occur as basal cores on which developed shallow water metazoan constructed reefs stromatactoid mud mounds are composed of a framework of submarine cemented crudely reticulate masses or a succession of laminar crusts surrounded by cement filled cavities these cavities developed when unconsolidated sediment around the framework was removed by winnowing mud mound frameworks of all ages show strong geometric and petrographic similarities to shallow water cryptalgal structures especially thrombolites unlaminated stromatolites which occur in many phanerozoic shallow water reefs both thrombolites and mud mound frameworks are largely composed of lime mudstone cemented on the sea floor and contain fenestral fabric and diagnostic cryptalgal microstructure their depositional surfaces were irregular not bored or burrowed and rarely encrusted stromatolitic lamina ion although commonly not well developed in the subtidal zone anyway occasionally occurs in mud mounds it is proposed that mud mounds accumulated from organic probably blue green algal binding of locally derived lime mud and bioclasts deposited relatively slowly from suspension patchy distribution of algal mats resulted in areas of both bound and unbound sediment sporadic floodlike episodes of rapid sedimentation however temporarily smothered the living algal mat and also left layers of unbound sediment periods of winnowing washed out unconsolidated unbound sediment and promoted synsedimentary cementation of resulting stromatactoid cavities and algal bound framework

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

trapping and binding a review of the factors controlling the development of fossil agglutinated microbialites and their distribution in space and time trapping and binding of allochthonous grains by benthic microbial communities has been considered a fundamental process of microbialite accretion since its discovery in popular shallow marine modern examples bahamas and shark bay however agglutinated textures are rare in fossil microbialites and thus the role of trapping and binding has been debated in the last four decades recently renewed attention on this subject has produced new findings of fossil agglutinated microbialites those mainly formed by trapping and binding and analogous to modern examples but they are still few and geologically recent mainly post paleozoic when compared to the 3 5 gyr long record of microbialites in order to better understand this discrepancy between modern and fossil examples an extensive literature review is presented here providing the first thorough database of agglutinated microbialites which shows that all of them are formed in shallow marine environments and most under tidal influence in addition a lower cretaceous example is described including very diverse microbialites each of them formed in a particular paleoenvironment some of these microbialites developed in grainy settings but only those formed in marginal marine tide influenced environments accreted mainly by trapping and binding the surrounding grains being analogous of modern agglutinated microbialites and matching the environmental pattern observed in the literature database the combination of the literature review with the case study allows to discuss the factors that control and enhance trapping and binding a occurrence of grains in the microbialite environment b frequent currents that mobilize the grains and supply them onto the microbialite surface c high concentration and diversity of electrolytes in the water to increase the adhesiveness of the extracellular polymeric substances eps of the microbialite surface and d a caco3 saturation state not high enough to promote early and strong carbonate precipitation within eps which would eventually decrease its availability to adhere grains therefore this review shows that the keys to solve the trapping and binding debate may be environmental because the conjuction of these hydrodynamic and hydrochemical parameters is preferentially achieved in shallow marine settings and especially in those influenced by tides at least since mesozoic times this explains the limited environmental and stratigraphic distribution of microbialites mainly formed by trapping and binding and opens new ways to look geologically and microbiologically at this process so often cited and yet so rare

aquaplanet experiments using cam s variable resolution dynamical core abstracta variable resolution option has been added within the spectral element se dynamical core of the u s department of energy doe ncar community atmosphere model cam cam se allows for static refinement via conforming quadrilateral meshes on the cubed sphere this paper investigates the effect of mesh refinement in a climate model by running variable resolution var res simulations on an aquaplanet the variable resolution grid is a 2 222 km grid with a refined patch of 0 25 28 km resolution centered at the equator climatology statistics from these simulations are compared to globally uniform runs of 2 and 0 25 a significant resolution dependence exists when using the cam version 4 cam4 subgrid physical parameterization package across scales global cloud fraction decreases and equatorial precipitation increases with finer horizontal resolution resulting in drastically different climates between the uniform grid runs and a physics induced grid imprinting in the var res simulation

exploring a multiresolution approach using amip simulations abstractthis study presents a diagnosis of a multiresolution approach using the model for prediction across scales atmosphere mpas a for simulating regional climate four atmospheric model intercomparison project amip experiments were conducted for 1999 2009 in the first two experiments mpas a was configured using global quasi uniform grids at 120 and 30 km grid spacing in the other two experiments mpas a was configured using variable resolution vr mesh with local refinement at 30 km over north america and south america and embedded in a quasi uniform domain at 120 km elsewhere precipitation and related fields in the four simulations are examined to determine how well the vrs reproduce the features simulated by the globally high resolution model in the refined domain in previous analyses of idealized aquaplanet simulations characteristics of the global high resolution simulation in moist processes developed only near the boundary of the refined region in contrast amip simulations with vr g

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

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

the depositional record of the frasnian famennian boundary interval in a fore reef succession canning basin western australia abstract the effects of the global frasnian famennian f f biotic crisis on the shallow marine reef builders and associated biota in a laterally extensive late frasnian reef complex on the lennard shelf northern canning basin are recorded in the well exposed fore reef succession napier formation of the napier range the conodont defined f f boundary lies within a distinctive and mappable stratigraphic interval up to 15 m thick which separates highly fossiliferous frasnian from markedly less fossiliferous famennian carbonate and siliciclastic lithofacies marked lateral facies variation within the interval means that the actual boundary is not represented by a discrete bed or surface the interval is characterised by a range of lithofacies that record very low sedimentation rates on the slope and reworking and bioturbation of slope strata indicating a condensed interval with negligible sediment input from contemporaneous carbonate platform production siliciclastic lithofacies and abundant sponge debris are locally developed macrofossil content is generally very low but there is no evidence for anoxic or hypoxic conditions during deposition at a range of palaeowater depths allochthonous blocks of stromatoporoid bearing limestone are absent from the uppermost frasnian fore reef strata and stromatoporoid debris is significantly reduced prior to the end of the frasnian this suggests that extinction of the stromatoporoid reef margins occurred before the f f boundary with microbial communities dominating the platform margins prior to the famennian sedimentological and biostratigraphic evidence suggests that a series of sea level fluctuations in response to basin tectonism generated recurring or ongoing environmental stress in the stromatoporoid dominated reefal communities because of recurring reductions in living space influxes of siliciclastic sediment supply from the proximal highlands and quite possibly generation of toxic too saline or too nutrient rich lagoonal water these conditions were potentially superimposed on a global regime of incipient cooling climate leading to widespread glaciation in the late carboniferous

alluvial architecture paleohydrology and provenance tracking from the neoproterozoic banganapalle formation kurnool group india an example of continental sedimentation before land plants abstract an integrated study involving facies association analysis architectural element analysis paleohydrology and detrital zircon geochronology allowed detail insight of sedimentology and paleogeography of neoproterozoic banganapalle formation bf kurnool group detailed process based facies and paleoenvironmental analysis have led to the identification of fourteen facies types grouped under four different facies associations which record paleoenvironmental settings ranging between mid alluvial fan to distal fluvial plain whereas mass flows hyperconcentrated flows streamlets and sheet floods dominate the depositional process on the bf fan middle to distal surface streams of varied geometry viz braided and ephemeral meandering occupied the proximal and distal bf alluvial plain our study supports the emerging view that even without the buffering effect of land plants channels developed sinuous planform in pre vegetation time subject to low gradient and discharge of alluvial plain and adequate supply of fine detritus from occurrence of boulder gravelly mass flows boundary pebbly streamlet thalweg and pebbly granular sheet flood deposits in the alluvial fan thick silty muddy stable flood plain deposits in the distal alluvial plain and unequivocal southward paleocurrent irrespective of facies association it is inferred that the bf alluvial basin received mixed sediment from long term beveled source in the north and northwest from two u pb detrital zircon geochronology age clusters viz paleo to mesoarchean 3410 ma 3075 ma and neoarchean to late paleoproterozoic 2750 ma 2500 ma provenance for the bf is tracked in the north and northwest of the kurnool basin i e the ttg suite of the peninsular gneiss and volcanics hosted greenstone belts in the central and western dharwar craton a mixing of sediments from two different provenances is inferred a consistent low water discharge with marginal downstream increase is suggested for the bf alluvial system from paleohydraulic analysis except for some occasional spurts of high discharge in mid fan at times of intense rainfall in the hinterland

sedimentary facies analysis mineralogy and diagenesis of the mesozoic aquifers of the central perth basin western australia abstract assessment and successful exploration for and exploitation of aquifers in the perth basin require knowledge of their petrophysical and sedimentological characteristics and geometries this study provides a sedimentological and lithofacies analysis of core from the mesozoic yarragadee formation cadda formation cattamarra coal measures eneabba formation and lesueur sandstone of western australia recovered from pinjarra 1 cockburn 1 gingin 1 and gingin 2 wells provide insights into changes in depositional environment over time and space in the central perth basin in studied sections nine different fluvial dominated lithofacies have been identified in the yarragadee formation cadda formation and cattamarra coal measures that occur in similar proportions whereas the lesueur sandstone is dominated by coarse grained deposits of high energy fluvial systems vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells changes in the lithofacies linked to local depositional environments are probably associated with fluvial alluvial to fluvio deltaic systems that have complex 3d architecture including braided and to probably meandering systems and are affected by channel avulsion point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz with rare polycrystalline quartz a moderate amount of alkali feldspar and very minor amounts of garnet organic fragments muscovite and biotite these data show a lithofacies dependence of the proportion of minerals with little variation between equivalent lithofacies from different depths formations or wells grain size and sorting that have a first order control on porosity are strongly lithofacies dependent individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction quartz overgrowth cementation and authigenic clay mineral development lithofacies and depth are the main controls on permeability and so lithofacies distribution exerts a key control on hydraulic behaviour

lithification of peritidal carbonates by continental brines at fisherman bay south australia to form a megapolygon spelean limestone association abstract groundwater springs in the supratidal zone at fisherman bay south australia are the sites of aragonite precipitation and cementation of holocene marine carbonates lithification which commenced less than 3000 years bp and is still active has formed a cavernous limestone containing megapolygons tepees and speleothems including pisoliths floe aragonite and aragonitic pool deposits the emerging waters are from a continental source and have evolved from low alkalinity waters of pleistocene sand and clay coastal plain aquifers which have passed through an underlying tertiary marine carbonate aquifer the resulting waters have high pco2 total carbonate ca and sulphate concentrations they are close to saturation with respect to aragonite and their mmg2 mca2 ratios approach or exceed the critical aragonite precipitation value aragonite is precipitated from these waters when they approach the surface and evolve co2 features which taken together may diagnose ancient examples of this process include 1 primary aragonitic cements with high msr2 mca2 values 2 nonmarine 34s values in associated gypsum 3 two superimposed networks of surface polygons one delineated by extensional boundaries the other by tepees 4 high water vadose zone isopachous grain cements 5 interconnected speleothem lined cavities and 6 the presence of evaporites only in surface sediments possible ancient examples of peritidal carbonate lithification by saline spring waters rising from confined aquifers are recognized in descriptions of carbonates from west texas lombardy and the atlas mountains the areal extent of each of these deposits suggests that the process may be a geologically important feature and its products may be diagnostic of semi arid or arid zone paralic sedimentation

cross strata and bedforms of probable transitional dune to upper stage plane bed origin from a late precambrian fluvial sandstone northern norway a late precambrian fluvial sandstone sequence in northern norway is dominated by large scale cross sets that show either lenticular or tabular geometries in the streamwise sections the lenticular sets interdigitate and in places show nearly symmetrical formsets the tabular sets are in places solitary but are mainly grouped in cosets in both cross set types the cross strata range from concave up to sigmoidal in shape with the latter variety comprising subhorizontal to gently inclined topset strata with parting lineation that merge uninterruptedly downflow into the steeper 10 2 foresets within the cross sets the geometry and dip azimuths of the foresets are conspicuously consistent although the concave up and sigmoidal strata commonly alternate downcurrent the cross strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand both cross set types are interpreted as representing bedforms generated by flow in the dune to upper stage plane bed transition the lenticular cross sets probably represent periodic dunes but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes or rather as solitary to quasi periodic bars

fluvial origin of the lower proterozoic sioux quartzite southwestern minnesota the sioux quartzite of inferred early proterozoic age 1 760 1 630 m y occurs in southwestern minnesota eastern south dakota and adjoining parts of iowa and nebraska where it overlies a regolith developed on an older precambrian crystalline basement the rocks constitute a red bed sequence that was deposited by braided streams flowing over a deeply weathered land surface of moderate relief deposition was confined largely to fault bounded basins in a cratonic setting the basins subsided slowly and were rarely if ever areas of steep relief the sioux quartzite is a texturally and mineralogically mature quartz arenite sand grains are mainly monocrystalline quartz with rare grains of chert granular iron formation and quartzite scattered conglomeratic layers contain lithic clasts that include red quartzite chert iron formation vein quartz and rhyolite together with rare welded rhyolite tuff and granitoid gneiss stratigraphic intervals of conglomeratic orthoquartzite are interspersed throughout the basal two thirds of the formation whereas thin units of sericitic mudstone are most abundant in the upper third overall the upward fining of size grades in the sioux may indicate diminishing stream gradients and reduction of relief in source areas during deposition the diagenetic minerals diaspore kaolinite and quartz cement indicate an environment of intense leaching probably under warm humid climatic conditions during or closely following deposition detrital feldspar present in trace amounts in deeper parts of the stratigraphic section may have been more abundant originally but was destroyed by intrastratal reactions the sub sioux regolith is characterized by 1 fine grained kaolinite and sericite formed from intensively altered coarse grained metamorphic feldspar and 2 the presence of abundant secondary hematite and silica by virtue of its early proterozoic age its alluvial origin and its unconformable position above older proterozoic and archean rocks the sioux is inferred to have some potential for unconformity related athabasca type uranium deposits its provenance which includes older proterozoic iron formation and volcanic rocks greenstone enhances its potential for paleoplacer gold deposits

burial diagenesis in the upper devonian reef complexes of the geikie gorge region canning basin western australia the devonian carbonates of the geikie gorge region canning basin have undergone a long and complex diagenetic history that began in devonian seawater with extensive marine cementation of platform margin lithologies devonian lower carboniferous burial diagenesis was the most important porosity occluding episode because almost all primary porosity was destroyed by equant calcite cements nonluminescent to brightly luminescent to dully luminescent during this interval dolomitization and consequent secondary porosity development also occurred during early burial diagenesis the distribution and geochemistry of the major calcite cements and dolomite types are consistent with these phases having been precipitated from connate marine or basinal brines karstification and mi or calcite cementation took place during late carboniferous subaerial exposure minor calcite cementation occurred during permian cenozoic burial predominantly in secondary porosity within pervasively dolomitized lithologies karstification dedolomitization and calcite recrystallization took place in association with cenozoic meteoric diagenesis secondary moldic and intercrystalline porosity within the completely dolomitized lithologies were the longest lived porosity types in the carbonates some secondary porosity escaped both devonian carboniferous and permian cenozoic burial cementation probably due to a lack of nucleation sites for calcite cements within completely dolomitized lithologies

the cottons breccia ediacaran and its tectonostratigraphic context within the grassy group king island australia a rift related gravity slump deposit abstract the cottons breccia is part of the upper neoproterozoic ediacaran 586 572 ma grassy group exposed on king island tasmania this formation has been widely interpreted as an unambiguous tillite in support of tectono climatic models that invoke catastrophic latest neoproterozoic global glaciation however dissenting opinions interpret the cottons breccia as a tectonic breccia in this paper we review the tectonostratigraphy of the cottons breccia and the enclosing grassy group we find no unambiguous evidence for a direct glacial origin as postulated by some early workers an interpretation of the cottons breccia as a deposit within half graben in the shoulder regions of an actively developing latest neoproterozoic volcanic rifted margin is consistent with all the available sedimentological structural geochronological and tectonic evidence

the role of discharge variability in the formation and preservation of alluvial sediment bodies abstract extant planform based facies models for alluvial deposits are not fully fit for purpose because they over emphasise plan form whereas there is little in the alluvial rock record that is distinctive of any particular planform and because the planform of individual rivers vary in both time and space accordingly existing facies models have limited predictive capability in this paper we explore the role of inter annual peak discharge variability as a possible control on the character of the preserved alluvial record data from a suite of modern rivers for which long term gauging records are available and for which there are published descriptions of subsurface sedimentary architecture are analysed the selected rivers are categorized according to their variance in peak discharge or the coefficient of variation cvqp standard deviation of the annual peak flood discharge over the mean annual peak flood discharge this parameter ranges over the rivers studied between 0 18 and 1 22 allowing classification of rivers as having very low 0 90 annual peak discharge variance deposits of rivers with very low and low peak discharge variability are dominated by cross bedding on various scales and preserve macroform bedding structure allowing the interpretation of bar construction processes rivers with moderate values preserve mostly cross bedding but records of macroform processes are in places muted and considerably modified by reworking rivers with high and very high values of annual peak discharge variability show a wide range of bedding structures commonly including critical and supercritical flow structures abundant in situ trees and transported large woody debris and their deposits contain pedogenically modified mud partings and generally lack macroform structure such a facies assemblage is distinctively different from the conventional fluvial style recorded in published facies models but is widely developed both in modern and ancient alluvial deposits this high peak variance style is also distinctive of rivers that are undergoing contraction in discharge over time because of the gradual annexation of the channel belt by the establishment of woody vegetation we propose that discharge variability both inter annual peak variation and flashiness may be a more reliable basis for classifying the alluvial rock record than planform and we provide some examples of three classes of alluvial sediment bodies representing low intermediate and high very high discharge variability from the rock record that illustrate this point

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

sensitivity of a regional climate model to the resolution of the lateral boundary conditions the sensitivity of a one way nested regional climate model rcm to the spatial and temporal levels of information provided at its lateral boundaries is studied to unambiguously address these two issues a perfect prognosis approach called the big brother experiment bbe is employed it consists in first establishing a reference climate simulation called the big brother over a large domain and then using the simulated data for nesting another rcm called little brother integrated over a smaller domain the effect of degrading the resolution of lateral boundary conditions lbc spatially and temporally is investigated by comparing the big and little brother climate statistics for the total and fine scale components of the fields as well as for their stationary and transient components within the bbe framework using a 45 km grid point rcm it is found that the one way nesting approach gives satisfactory results for most fields studied when spatial resolutions degraded by up to a factor of 12 are imposed between the nesting data and the little brother for the lbc update interval 12 h appears to be the upper limit while little difference is found between update intervals of 3 and 6 h

paleovalley morphology and fluvial system evolution of eocene oligocene sediments auriferous gravels northern sierra nevada california implications for climate tectonics and topography in the northern sierra nevada california eocene oligocene fluvial sediments the auriferous gravels rest unconformably in well defined basement incised paleovalleys providing a record of paleolandscape geomorphology and drainage system evolution paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad terraced paleovalley segments which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition high gradient high energy deposits are present near the edges of these areas suggesting that tributaries and outlets resided in steeper narrow paleovalleys multiple strath terraces are common in broad paleovalleys indicating that incision events occurred both before deposition and during paleovalley widening followed by periods of aggradation broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system multiple upward fining cycles bounded by erosional surfaces are composed of alternating coarse grained channel belt and fine grained floodplain packages an overall upward fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys paleochannel slope estimates of 0 004 0 055 were obtained based on average grain sizes of coarse channel fills anomalously thick up to 11 m laterally continuous 1 3 km floodplain units containing kaolinite rich clay and oxisol intervals record high fine grained sediment supply driven by high rates of chemical weathering in the warm eocene climate based on sedimentary characteristics combined with floral and detrital zircon data braided stream deposition within the basin occurred from the late early eocene through late eocene and aggradation primarily occurred in broad lower gradient reaches behind a major bedrock knickpoint created in the late mesozoic early cenozoic possibly due to asymmetric batholith unroofing the diachronous localized nature of paleovalley incision and braided stream aggradation within the northern sierra nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients both internal and external drivers influenced the evolution of the fluvial system through 1 the pattern of basin filling as the locus of deposition migrated east to west 2 the warm eocene climate which increased chemical weathering and contributed a high sediment supply and 3 changes in base level due to eustasy and or laramide tectonism this record of laramide tectonics in the sierra nevada and basin and range is important for the timing of sierra nevada uplift for tectonic reconstructions of western north america and for studies of landscape evolution in tectonically active orogens

impact of lateral boundary errors on the simulation of clouds with a nonhydrostatic regional climate model abstracta nonhydrostatic regional climate limited area model lam was used to analyze lateral boundary condition lbc errors and their influence on the uncertainties of regional models simulations using the fully compressible nonhydrostatic lam d nicam were compared against the corresponding global quasi uniform grid nonhydrostatic icosahedral atmospheric model nicam and a stretched grid counterpart s nicam by this approach of sharing the same dynamical core and physical schemes possible causes of model bias and lbc errors are isolated the simulations were performed for a 395 day period from march 2011 through march 2012 with horizontal grid intervals of 14 28 and 56 km in the region of interest the resulting temporal mean statistics of the temperatures at 500 hpa were generally well correlated between the global and regional simulations indicating that lbc errors had a minor impact on the large scale flows however the time varying statistics of the surface precipitation showed that the

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

was phanerozoic reef history controlled by the distribution of non enzymatically secreted reef carbonates microbial carbonate and biologically induced cement throughout most of the phanerozoic reef rigidity resulted as much or more from early lithification by microbial carbonates and biologically induced cements non enzymatic carbonates than from biological encrustation of or by large enzymatically secreted metazoan skeletons reef framework is divided into four categories 1 skeletal metazoan 2 non skeletal microbialite stromatolite and thrombolite 3 calcimicrobe and 4 biocementstone in which small or delicate organisms serve as scaffolds for rigid cement crusts the last three categories are dominated by non enzymatic carbonates skeletal framework and non skeletal microbialite framework were the most abundant framework types through the phanerozoic the composition and abundance of skeletal framework was controlled largely by mass extinction events but most reefs consisted of both microbialite and skeletal organisms in a mutually beneficial relationship microbialite framework was abundant throughout the palaeozoic and early mesozoic but declined after the jurassic calcimicrobe framework was important during the cambrian early ordovician and devonian and biocementstone framework was important from the late mississippian to the late triassic the phanerozoic history of reefs does not correlate well with the stratigraphic distribution of large skeletal reef builders or with a variety of physicochemical parameters including sea level history wilson cycle or global climate cycles because non enzymatic carbonates result from induction by non obligate calcifiers and not enzymatic precipitation by obligate calcifiers the distribution of these carbonates was controlled to a larger extent by temporal changes in physicochemical parameters affecting the saturation state of sea water with respect to carbonate minerals changes in pco ca mg ratios cation concentrations and temperature may have affected the abundance of non enzymatic carbonates and hence reefs independently from the effects of these same parameters and mass extinction events on skeletal reef biota the decline in abundance of reefal microbialite and absence of calcimicrobe and biocementstone reef framework after the jurassic may be a result of relatively low saturation states of sea water owing to increased removal and sequestration of finite marine carbonate resources by calcareous plankton since the jurassic reef history is difficult to correlate with temporal changes in specific global parameters because these parameters affect skeletal biota and biologically induced carbonate precipitation independently hence reef history was regulated not just by skeletal reef biota but by parameters governing non enzymatic carbonates

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

pre vegetation fluvial floodplains and channel belts in the late neoproterozoic cambrian santa barbara group southern brazil abstract one key element to the understanding of the dynamics of pre vegetation fluvial systems is the reconstruction of processes operating on their floodplains given that in modern systems channel banks and floodplains are the environments most affected by plant colonization notwithstanding few pre vegetation floodplains have been described and major questions regarding their most basic characteristics are still unresolved in order to address these questions detailed analysis of coeval channel belt fluvial floodplain and alluvial fan deposits from the santa barbara group late neoproterozoic to early cambrian southern brazil was performed while floodplain facies resemble ephemeral stream deposits being coarser grained than modern floodplains and marked by the stacking of flood event cycles channel belt deposits show composite bars which do not present conclusive evidence for high water discharge variation the floodplain deposits show particular features common to other pre vegetation fluvial systems such as better preserved small scale structures lack of bioturbation and abundance of cross laminated sandstones while other features differ from previous depositional models namely abundant mudcracks and evidence of soil formation the lateral variation of depositional systems recorded in the santa barbara group shows contrasting signatures of water discharge variation in sand dominated coeval environments and offers an example of the relation between different alluvial environments before the evolution of land plants

architecture of pre vegetation sandy braided perennial and ephemeral river deposits in the paleoproterozoic athabasca group northern saskatchewan canada as indicators of precambrian fluvial style abstract the late paleoproterozoic athabasca basin contains more than 1 5 km of predominantly sandy strata most of which are of braided fluvial origin in the eastern part of the basin at mcclean lake sandstones and minor conglomerates of the read formation at the base of the succession are preserved within a steep walled valley system they consist predominantly of meter scale sheet elements characterized by massive and flat laminated fine to very coarse grained sandstone with minor discontinuous cobble and boulder conglomerate along lower set boundaries these are interpreted as sheet flood and stream flood deposits of a terminal dry land system deposited in an arid climatic setting analysis of closely spaced drill core indicates that late stage run off was confined to small shallow channels typically only a few tens of meters wide and a few meters deep overlying strata of the bird member of the manitou falls formation are predominantly coarse to very coarse grained sandstones with abundant small scale cross stratification and minor granule and small pebble conglomerate at mcclean lake these appear to have been deposited as sheet elements by semi ephemeral to perennial braided rivers under more humid conditions at key lake 160 km to the southwest architectural analysis of a 184 m wide section indicates that at least part of the bird member was deposited in deeper sandy braided rivers characterized by seasonally varied flow the closest modern analogue is the south saskatchewan river in which large simple flow transverse bedforms become exposed and dissected during falling stage and act as nuclei for sand flat development the presence of numerous low relief 4th order surfaces suggests continued reworking of bar tops during rising stage the incremental character of downstream accretionary elements suggests periodic migration of barforms during peak flood stages separated by periods of low flow this indicates similarities with modern perennial braided systems and is counter to the idea that all pre devonian fluvial systems should consist of stacked sheets formed by individual flood events thin gravel layers accumulated as lags on fourth order surfaces with discontinuous mud layers suggesting deposition within temporary ponds in channel thalwegs after major floods strata in overlying units indicate a return to semi perennial conditions

facies based rock properties characterization for co2 sequestration gswa harvey 1 well western australia abstract gswa harvey 1 was drilled as part of the south west co2 geosequestration hub carbon capture and storage project south west hub to evaluate storage volume injectivity potential and carbon dioxide retention capacity in the south western perth basin six cored intervals from the triassic lesueur sandstone contain nine lithofacies consistent with fluvial depositional environments the lower wonnerup member is dominated by fluvial lithofacies consisting of stacked beds of porous permeable sandstone deposited as high energy fill and barforms with rare finer grained swampy overbank deposits the overlying yalgorup member contains mainly floodplain palaeosols with low to moderate energy barforms the high to moderate energy fluvial facies typically have a low gamma response and contain clean medium to very coarse grained quartz dominated sandstones other clastic components include k feldspar 8 25 with trace muscovite garnet and zircon and interstitial diagenetic kaolinite up to 15 and fe rich chlorite up to 13 the low energy facies contain variably interbedded mudstone and thin moderate to well sorted fine grained sandstone typically with a high gamma response and are consistent with deposition under swampy overbank and palaeosol conditions these facies have significantly higher proportions of mica and diagenetic clays including smectite up to 8 and illite up to 10 and detrital plagioclase up to 21 and trace carbonate bioclasts high porosity and permeability in the cored intervals of the wonnerup member indicate good reservoir characteristics in terms of storage capacity and injectivity at depths relevant to co2 injection 1500 m high porosity and extremely variable permeability values in the yalgorup member were measured the variation is due to permeable vertical sandstone features in low permeability sandy mudstone and indicate limited sealing potential although the spatial connectivity of the vertical features cannot be resolved from the available core a preliminary assessment of the area as a ccs site seems favourable however the project is only in the early stages of its characterization and far more regional and site specific data are needed to evaluate how injected co2 may behave in the subsurface

tepee shaped agglutinated microbialites an example from a famennian carbonate platform on the lennard shelf northern canning basin western australia distinctive metre scale antiformal structures are well developed in a famennian carbonate platform in the chedda cliffs area of the lennard shelf reef complexes the structures are distinguished by chevron shaped crests and thickened cores and contain abundant non skeletal allochems ooids pisoids peloids and intraclasts of silt to pebble size and variably developed laminations and fenestrae the internal morphology and pervasive occurrence of fenestral clotted and wavy laminated fabrics suggest that these structures are microbial mounds composed of agglutinated stromatolites and thrombolites microbial fabrics most probably originated through sediment trapping and binding by microbial mats with early lithification involving microbial calcification and cementation of trapped sediment the facies and stratigraphic context of the mounds support a shallow subtidal transitional backreef to reef flat setting however alone these mounds do not provide unequivocal environmental information other large antiformal structures in famennian platforms on the lennard shelf previously described as tepee structures show morphological similarities to the chedda cliffs mounds which suggests that these other structures may also be microbial mounds the presence of microbial mounds in platform successions further highlights the importance of microbial communities in the lennard shelf reef complexes

evolving fluvial style in the kekiktuk formation mississippian endicott field area alaska base level response to contemporaneous tectonism the hydrocarbon reservoir at endicott field offshore from the sagavanirktok delta in northeastern alaska is found in the upper mississippian visean kekiktuk formation the trap is bounded by the northwest southeast trending tigvariak and mikkelson bay faults and the younger east west trending niakuk fault the kekiktuk comprises sandstones siltstones and mudstones with locally significant coals and conglomerates and is subdivided into three major reservoir zones based on the relative dominance of these lithologies zone 1 the lowest comprises mudstones siltstones and coals with subordinate isolated sandstones and represents deposition within a low lying swamp plain with very low net to gross ratio this zone is considered to be effectively nonreservoir major movement on the mikkelson bay and tigvariak faults created a half graben with uplift to the north and east and a very significant drop in base level this change resulted in fairly widespread deposition of zone 2 medium to coarse grained sandstones from sandy bed load braided streams however those sandstones thin significantly to the west away from the faults continuing tectonism at this time created local shifts in base level manifest as diversion of streams widespread abandonment and subsidence leading to the creation of a arge lake the lacustrine deposits are widespread and effectively divide zone 2 into two subzones those subzones are mappable sheet sandstones and constitute the best reservoir at endicott field in terms of net to gross ratio porosity permeability and sandstone connectivity base level shows evidence of rising dramatically at the end of zone 2 this rise is attributed to continuing tectonism within the basin and is particularly associated with the east west trending mid field fault system at endicott field as well as ongoing activity on the tigvariak mikkelson bay fault system thus at the base of zone 3 subzone 3a in the southern and eastern parts of the field the rocks are mudstones and widespread coals and contain at least one unequivocally marine mudstone these rocks are lower delta plain interdistributary bay fill deposits with rare distributary channel sandstones north and west of the mid field fault system the marine mudstone is absent and the facies changes significantly with the loss of dominant coal and a concomitant increase of dist ibutary channel sandstones reservoir properties of subzone 3a including connectivity are significantly different in this area subzone 3b is a thick accumulation of fine grained alluvial overbank deposits within which occur rare isolated anastomosed channel sandstones of limited connectivity this subzone makes minimal contribution to endicott field reserves subzone 3c is characterized particularly in its upper part by well developed fining upward cycles indicating mature meandering streams the relationships between these two highest subzones of the kekiktuk at endicott field indicate they represent an aggradational episode initiated by tectonically induced avulsion and set against a background of rising base level to the west at some distance from the tigvariak mikkelson bay f ult system zone 3 is much thinner than at endicott field and is dominated by mudstones and coals this evidence emphasizes the control that contemporaneous tectonism related to those faults had on sediment especially sandstone distribution within the kekiktuk formation base level changes can be identified within the end page 1723 kekiktuk formation in the north slope subsurface by careful lithofacies analysis and an awareness of key constraining indicators such as are revealed by palynology paleontology and structural geology by analogy with shallow marine rocks sequence stratigraphic concepts may be extended to continental successions however one must approach such problems with a full awareness of the impact of tectonism on base level and basin development

proterozoic platform sequences of peninsular india implications towards basin evolution and supercontinent assembly abstract a group of less disturbed and unmetamorphosed proterozoic platformal sediment package lying over deformed and metamorphosed archean to paleoproterozoic basement in several parts of peninsular india is informally termed as purana basins in indian stratigraphy the trend shift in the understanding of these basin fills in last two decades often supported by international collaborations has made significant advancements in respect to unconformity and sequence development relationship with accretion and break up of the supercontinents initiation and evolution of the basins in different tectonic set ups nature of sediment provenance paleoclimate and paleo weathering patterns and basin water chemistry geophysical backups encompassing the basins occasionally extending up to the craton and adjacent mobile belts helped in refining the understanding on the basement structure and tectonic forcings the present paper is an attempt towards the collation of the database generated in last two decades in order to present the status of current understanding on different purana basins with regard to interactions of physical chemical and biological parameters of the proterozoic earth

desert stream sequences in the sinai peninsula abstract desert sedimentary sequences of late quaternary age mainly subrecent were studied in several stream segments of wadi el arish northern sinai egypt morphologically these stream systems can be divided into three types confined open and terminal floodplains the confined and open floodplain sequences consist of repeated flood originated sedimentation units each around 50 cm thick an idealized sequence begins with mud clasts or either sand or pebble bearing plane beds reflecting the upper flow regime during peak flow stage of the flood these are overlain by cross bedded sands and climbing ripples lower intensities of the flow result in sequences beginning with cross stratified sands cracked mud layers represent the final desiccation stage of the flood in comparison with th confined floodplain units the open up to thousands of meters wide floodplain units are thinner 20 50 cm the horizontal strata are less developed and the mud layers are thicker the terminal floodplain which in the modern examples is a flat a few kilometers wide is the area where the remaining flood energy dissipates and therefore the resultant sedimentation units axe very thin usually less than 20 cm and consist of either finely laminated massive mud or cross laminated fine sand the wadi systems studied are in close geographic relationship with eolian dune fields nevertheless the wadi sequences consist of waterlaid units only

magnetic data interpretation for the source edge locations in parts of the tectonically active transition zone of the narmada son lineament in central india the study has been carried out in the transition zone of the narmada son lineament nsl which is seismically active with various geological complexities upwarp movement of the mantle material into the crust through fault fractures lamination and upwelling nsl is one of the most prominent lineaments in central india after the himalaya in the indian geology the area of investigation extends from longitude 80 25 e to 81 50 e and latitude 23 50 n to 24 37 n in the central part of the indian continent different types of subsurface geological formations viz alluvial gondwana deccan traps vindhyan mahakoshal granite and gneisses groups exist in this area with varying geological ages in this study area tectonic movement and crustal variation have been taken place during the past time and which might be reason for the variation of magnetic field magnetic anomaly suggests that the area has been highly disturbed which causes the narmada son lineament trending in the ene wsw direction magnetic anomaly variation has been taken place due to the lithological variations subject to the changes in the geological contacts like thrusts and faults in this area shallow and deeper sources have been distinguished using frequency domain analysis by applying different filters to enhance the magnetic data various types of derivatives to identify the source edge locations of the causative source bodies the present study carried out the interpretation using total horizontal derivative tilt angle derivative horizontal tilt angle derivative and cos derivative map to get source edge locations the results derived from various derivatives of magnetic data have been compared with the basement depth solutions calculated from 3d euler deconvolution it is suggested that total horizontal derivative tilt angle derivative and cos derivative are the most useful tools for identifying the multiple source edge locations of the causative bodies in this tectonically active and transition zone area as this area is highly prone to hydrocarbon bearing zone hence the integrated interpretation could reliably image various thrusts and faults boundaries and the source edge locations with dip and strike orientation along with the basement lineation in encouraging exploration for better understanding of the geo scientific data

depositional controls in a bedload dominated fluvial system internal architecture of the lee formation kentucky abstract sandstones of the early pennsylvanian lee formation central appalachian foreland basin were deposited in a low sinuosity bedload dominated fluvial system the internal architecture of the sandstones consists of a six fold hierarchy of bounding surfaces which are evaluated with respect to depositional controls minor first second and third order surfaces generally less than a few hundred meters in extent separate deposits of small to intermediate scale bedforms third order surfaces which dip gently in the downflow direction represent reactivation surfaces of downstream accreting macroforms major surfaces fourth fifth and sixth order are hundreds of meters to kilometers in extent fourth order surfaces separate deposits of individual macroforms fifth order bounding surfaces are erosional boundaries of major system scale channels individual sandstone members of the lee formation are bound by sixth order surfaces erosional at the base and gradational at the top deposits overlying major surfaces contain fining upward sequences the trends are more apparent with increased scale of the deposit these sequences represent responses of the fluvial system to various mechanisms that controlled sedimentation both fourth and fifth order surfaces are interpreted as results of autocyclic controls the nature of the lee formation fluvial system was such that a solitary major channel was relatively stable in one position within the alluvial plain for a significant period of time during this time the channel aggraded with the passage of one or more downstream accreting macroforms creating a fourth order erosional surface the channel eventually diverted its flow to another portion of the alluvial plain by avulsion creating a fifth order surface a gross fining upward trend and upward change in fluvial style for individual sandstone members both characteristic of paleovalley fills indicate that sixth order surfaces were controlled by allocyclic processes these characteristics and the stair step positioning of the sandstone members younger away from the alleghenian mountains to the east suggest that tectonic processes were the ultimate control on the system

braidplain sedimentation in a proterozoic rift basin the sao joao da chapada formation southeastern brazil abstract the sao joao da chapada formation 100 200 m thick is the basal unit of the middle proterozoic espinhaco supergroup this up to 3000 m thick and slightly metamorphosed sedimentary succession is exposed in the central part of the southern serra do espinhaco southeastern brazil detailed lithofacies studies were carried out to characterize the sedimentation and paleogeography of the sao joao da chapada formation six lithofacies are present horizontal to low angle cross stratified sandstones lithofacies sh sl trough cross stratified sandstones lithofacies st planar cross stratified sandstones lithofacies sp ripple cross laminated sandstones lithofacies sr massive to horizontally stratified conglomerates lithofacies gm and fine grained rocks lithofacies f these are usually arranged in fining and thinning upward successions characterizing waning flood cycles which are always bounded by erosional surfaces no complete cycles have been found however and the cycles are normally composed only of lithofacies sh sl and st the other lithofacies are rare the observed sedimentary structures and their arrangement the geometry of the bodies mainly sheet like to slightly lenticular the low relief morphology of the erosion surfaces bounding the waning flood cycles the coarse and poorly sorted texture of the sediments and the measured paleocurrent pattern unidirectional with little dispersion throughout the study area point to deposition on a wide ephemeral braidplain characterized throughout by relative uniformity of facies and paleocurrent directions water depths on this subsiding braidplain were maintained by high discharge streams debouching onto it from the upland catchment areas as these rivers spread onto the depositional plain the changes in gradient and substratum transformed them into channels of remarkable width and very large width depth ratios these rivers ran in braided tracts and floods were temporarily confined within banks in these tracts channel switching events associated with tilting and subsidence of the basin floor resulted in the accumulation of extensive sandstone sheets interfingering laterally with one another and succeeding one another vertically which built up a braidplain succession extending up to 35 km transverse to the paleoslope the sao joao da chapada braidplain flanked the west margin of a n s elongated rift basin

a review of the origin and setting of tepees and their associated fabrics carbonate hardgrounds often occur at the surface of shallow subtidal to supratidal lacustrine and subaerial carbonate shelf sediments these are commonly disrupted and brecciated when the surface area of these crusts increases in the subtidal environment megapolygons form when cementation of the matrix causes the surface area of the hardgrounds to expand similar megapolygons form in the supratidal lacustrine and subaerial settings when repeated incremental fracturing and fracture fill by sediment and or cement also causes the area of the hardgrounds to expand the arched up antiform margins of expansion megapolygons are known as tepees the types of tepees found in the geological record include 1 submarine tepees which form in shallow carbonate saturated waters where fractured and bedded marine grainstones are bound by isopachous marine phreatic acicular and micritic cements the surfaces of these brecciated crusts have undergone diagenesis and are bored unlike tepees listed below they contain no vadose pisolites or gravity cements 2 peritidal and lacustrine tepees are formed of crusts characterized by fenestral pisolitic and laminar algal fabrics this similarity in fabric makes these tepees of different origins difficult to separate peritidal tepees occur where the marine phreatic lens is close to the sediment surface and the climate is tropical they are associated with fractured and bedded tidal flat carbonates their fracture fills contain geopetal asymmetric travertines of marine vadose origin and or marine phreatic travertines and or terra rossa sediments the senile form of these peritidal tepees are cut by labyrinthic dissolution cavities filled by the same material lacustrine tepees form in the margins of shallow salinas where periodic groundwater resurgence is common they include groundwater tepees which form over evaporitic boxwork carbonates and extrusion tepees which also form where periodic groundwater resurgence occurs at the margins of shallow salinas but the dominant sediment type is carbonate mud these latter tepee crusts are coated and crosscut by laminated micrite the laminae extend from the fractures downward into the underlying dolomitic micrite below the crust both peritidal and lacustrine tepees form where crusts experience alternating phreatic and vadose conditions in time intervals of days to years cement morphologies reflect this and the crusts often contain gravitational meniscus vadose cements as well as phreatic isopachous cement rinds 3 caliche tepees which are developed within soil profiles in a continental setting they are formed by laminar crusts which contain pisolites and fractures filled by micritic laminae microspar spar and terra rossa most of the cements are gravitational and or meniscoid in ancient carbonates when their cementation and diagenetic fabric can be interpreted tepee structures can be used as environmental indicators they can also be used to trace the evolution of the depositional and hydrological setting

diversity and factors controlling widespread occurrence of syn rift ladinian microbialites in the western tethys triassic catalan basin ne spain abstract the fault block carbonate ramps of the ladinian middle triassic catalan basin hosted a wide variety of microbial deposits which formed during a syn rift stage stratigraphical and sedimentological analyses of these microbialites allow us to reconstruct two depositional models for such microbial deposits moreover new insights into the interplay between the intrinsic and extrinsic factors that controlled the widespread development of these microbialites are provided stromatolites ooidal muddy microbial laminites and thrombolites were analyzed on the basis of their geometry lamination and textural attributes these microbialites are distributed over two transgressive regressive sequences and coexisted during the fassanian early ladinian regressive stage later stromatolites and ooidal muddy microbial laminites developed during the longobardian late ladinian transgressive stage three types of lamina couplets reflect distinct accretion processes linked to water chemistry sediment supply and hydrodynamic conditions thrombolite textures were produced by accretionary binding and encrusting processes microbially mediated and pervasive cementation the widespread occurrence of microbial deposits is explained as a consequence of a biogeochemical cascade of events e g anoxic dysoxic seawater conditions volcanic activity upwelling of alkaline waters nutrient concentrations and microbial blooms which promoted favorable conditions for microbial growth in the tethys during the ladinian furthermore in the catalan basin syn rift fault induced subsidence and local water energy gradients exerted an essential role in the distribution of the three types of microbialites through space and time thrombolites were prone to grow in the hanging wall block of a half graben subtidal conditions whereas stromatolites and ooidal muddy microbial laminites flourished preferably in a foot wall block setting intertidal shallow subtidal conditions however the fact that thrombolites exhibit abundant botryoidal and isopachous fibrous marine cements corrosion and significant microbial evidence allow us to hypothesize about the relationship between thrombolite occurrence and hydrothermal fault controlled fluid circulation during the triassic rifting the two depositional models here proposed constitute a step forward the understanding of the platform to basin microbialite heterogeneity during the ladinian furthermore this work sheds new light on the mechanisms that likely promoted microbialite development during a period of major ecological restructuration and complex oceanographic conditions

sedimentation pattern in a trans himalayan quaternary lake at lamayuru ladakh india abstract located on the indo tsangpo suture zone lamayuru lake in western ladakh was created by neotectonic instability around 35 40 ka the valley fill sequence about 110 m thick reveals an interplay of lacustrine to fluvio deltaic to colluvial processes operating in response to changing climate and tectonic conditions based on integrated approach of sedimentology and palaeontological analysis we propose a sedimentation model for lamayuru lake with reference to changing climatic conditions and neotectonics the coarsening upward succession was divided into five lithofacies associations associations a e each association comprising one or more lithofacies represents a specific depositional environment and marks an independent episode of sedimentation a dominantly muddy sequence of facies association a a product of a lacustrine environment is followed by coarsening upward cycles association b composed of silt to sand that implies laterally shifting deltas thereafter thick sand and gravel deposits constituting fining upward fu unit cycles associations c and d represent deposition in a fluvial domain the upper part of association d composed of matrix supported gravel horizons was deposited as debris flows and marks the termination of sedimentation in the valley the clastic lithofacies facies associations a to d with plant fragments and charcoal presumably indicate warm humid climatic conditions in contrast association e comprising marl lithofacies occurring at four different levels is biogenic and indicates arid to semi arid climatic phases five main types of trace fossils including rhizoliths seem to be representatives of scoyenia ichnofacies and animal burrows indicating a thin population of soft bodied annelid and arthropod communities living under low energy condition nine fossiliferous horizons have yielded characteristic ostracods charophytes and gastropods indicating shallow low energy and cold water ecological conditions coarsening up lake succession extensive synsedimentary deformation tilting of lake beds and the entrenchment of the lamayuru drainage indicate basin evolution under an effective role of neotectonics in the area

upper devonian reefs and microbialite at maoying south china implications for paleoenvironmental changes abstract reefal carbonate deposits in south china preserve a record of community structure and environmental change across the frasnian famennian boundary and through the late devonian detailing a regional response to one of the largest mass extinction events in earth history the upper devonian frasnian to famennian limestone outcrops in the maoying area of northern ziyun county south china record a carbonate platform depositional setting with some patch reef development the upper devonian carbonate deposits in maoying area are distinctive from those in correlative sections in dushan county with rare argillaceous limestone and dolomitic limestone as well as less dolostone exposures to the south in the guilin area of northeastern guangxi province are similar to those seen in the study area upper devonian carbonates in the maoying area are divided into two lithologic groups reef limestones or dolostone beds composed of five lithologically distinctive intervals the upper devonian strata have a cumulative thickness of 530 m the upper devonian reefs in the maoying area were developed on a shell pavement of brachiopod and bivalve shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform patch reef development was limited to early frasnian time reef building organisms are dominated by massive and tabular stromatoporoids amphipora sp stachyodes sp and coral thamnopora sp while brachiopods and algae accumulated between stromatoporoid skeletal frameworks three evolutionary stages of the frasnian patch reefs including an initial development stage maturity stage and demise stage can be recognized according to sedimentary structures and fossil assemblage characteristics the frasnian strata overlying the patch reefs represent a well bedded back reef depositional setting and are mainly composed of amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons a prominent microbialite bed developed in the laminated limestone of the famennian carbonate platform consists of stromatolite and thrombolite framestone this bed can be correlated in horizon and age with microbial reefs and mounds in the famennian offshore carbonate platform in the huanan epeiric sea such as famennian microbial reefs and mounds in guilin this represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global frasnian famennian biotic extinction event which promoted the growth of microbialites during the latest devonian in south china

fluvial shallow marine glaciofluvial depositional environments of the ordovician system in jordan abstract the ordovician system cropping out in southern and west central jordan consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations the lower disi formation starts conformably above the late cambrian umm ishrin formation according to cruziana furcifera occurring in the upper third of the disi formation an early ordovician age is confirmed the disi formation consisting mainly of downstream accretion da fluvial architectural element was deposited in a proximal braidplain flowing n ne from the southerly located arabian nubian shield towards the tethys seaway the braidplain depositional environment evolved into a braidplain dominated delta through the middle and upper parts of the disi formation and the lower part of the overlying um saham formation the delta was replaced by siliciclastic tidal flats that in turn evolved into an upper to lower shoreface environment through the upper part of the um saham formation the depositional environment attained the maximum bathymetric depth during the deposition of the lower and central parts of the third unit the hiswa formation where offshore graptolite rich mudstone with intercalated hummocky cross stratified tempestites were deposited the tethys seaway regressed back through the upper part of the hiswa formation promoting a resumption of the lower upper shoreface sedimentation oscillation between the lower to upper shoreface depositional environment characterized the entire fourth unit the dubaydib formation as well as the tubeiylliat sandstone member of the fifth unit the mudawwara formation the depositional history of the ordovician sequence was terminated by a glaciofluvial regime that finally was gradually replaced by a shoreface depositional environment throughout the last unit the ammar formation

comparison of the bedform distribution and dynamics of modern and ancient sandy ephemeral flood deposits in the southwestern karoo region south africa abstract during january 1981 unusually high rainfall patterns in the semi arid southwestern karoo region of south africa gave rise to catastrophic floods in the area the most devastating of which was the ephemeral flash flood that partially destroyed the town of laingsburg flood waters at laingsburg spread from a dry river bed rising to a depth of 12 m within 7 h washing away houses and burying the town with up to 3 5 m of sand and silt facies sequences and bedforms in the laingsburg flood deposits are related to specific subenvironments and flow conditions during the flood event two large scale sedimentary units in erosive contact with each other were deposited by two major discharge pulses within the same flood event vertical and lateral variations in the bedform distributions reflect fluctuations in flow velocity and turbulence comparison is drawn between the laingsburg flood deposits and fluvial sandstones of the permian lower beaufort in the southwestern karoo the multistoried sandstone bodies composed mainly of a horizontally laminated lithofacies are interpreted as the products of a complex series of ephemeral flooding events individual storey units in the palaeochannel sequences are generally envisaged as the deposits of different floods however evidence from the modern flood shows that separate pulses of a single flooding episode can also produce a sequence of storey units bounded by erosive scours spectacular palaeosurfaces in the lower beaufort also have modern analogues in the laingsburg overbank deposits discussion on the preservation potential of delicate sedimentary structures and biogenic traces on these surfaces emphasizes the necessity for pulsatory deposition of bedload and suspended load material over short intervals of time by comparing facies profiles and surface bedforms the ephemeral fluvial facies model for the lower beaufort is critically appraised

braidplain evolution in the pennsylvanian south bar formation sydney basin nova scotia canada abstract the south bar formation is a 1 km thick alluvial succession in the pennsylvanian morien group of the sydney basin nova scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages the conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross stratified sandstone attributed to deposition in proximal braided rivers confined between bedrock ridges the sandstone assemblage shows uniformity of facies and paleocurrents across the basin and is interpreted as a distal braidplain deposit the pebbly sandstone assemblage is transitional between the other two both sandstone assemblages are dominated by trough cross stratified sandstone formed by dune migration in channel tracts about 4 m deep this succession differs markedly from platte river and icelandic sandy braidplain deposits which are mainly planar cross stratified sands formed by broad shallow flow the south bar sandstones are more like south saskatchewan river deposits but differ in 1 greater abundance of trough sets and 2 rarity of planar sets and other components of shallow water channel fill these features are ascribed to 1 inheritance of relatively deep channels from confined upstream reaches 2 maintenance of deep flow in active tracts by local confinement between temporary banks and 3 rapid avulsive abandonment of active tracts which inhibited development of channel fill sequences evidence for local temporary confinement is preserved as in situ and slumped channel margin mudrock units lateral and vertical transitions from the upper south bar formation to the mud rich waddens cove and sydney mines formations are ascribed to changes in channel pattern from braided to meandering the former is attributed to decreased slope the latter to eustatic rise in sea level

messinian stromatolite thrombolite associations santa pola se spain an analogue for the palaeozoic stromatolite thrombolite associations are the dominant facies forming large portions of the santa pola carbonate platform se spain during deposition of the terminal carbonate complex tcc the tcc the last period of marine sedimentation in the western mediterranean associated with the messinian salinity crisis comprises a ne sw trending thrombolite reef with occasionally interlayered stromatolite horizons and a predominantply stromatolite and oolite facies in the back reef area the stromatolites are mainly dome shaped but fine columnar or wavy undulose forms can occur the stromatolites form huge bioherms extending tens to hundreds of metres they are finely laminated with alternating layers of dolomicrite and dolomicrospar the dolomicrite layers appear to be a primary dolomite precipitate whereas the dolomite crystals in the dolomicrospar layers apparently formed around a meta stable nuclei which was subsequently dissolved or degraded the low content of sand sized particles in the stromatolitic layers indicates formation under low energy conditions possibly on a tidal flat as reported from other areas in the western mediterranean deposition of the tcc at santa pola was apparently cyclic whereby stromatolites generally terminate each depositional cycle subtidal conophyton stromatolites possibly the only known occurrence younger than palaeozoic are however found on the reef slope at the base of the first tcc depositional cycle the dolomitic nature of the unadulterated stromatolitic laminations and the association of stromatolites and thrombolites as platform builders were a common feature in the early palaeozoic but are unusual in post ordovician carbonate facies we propose that the conditions during tcc deposition were very restricted possibly reflecting an environment similar to that of the early palaeozoic

error and energy budget analysis of a nonhydrostatic stretched grid global atmospheric model abstracta nonhydrostatic stretched grid sg model is used to analyze the large scale errors generated by stretching horizontal grids and their influence on a region of interest simulations by a fully compressible nonhydrostatic global atmospheric model the nonhydrostatic icosahedral atmospheric model nicam and its sg regional model stretched nicam were performed for the months of march april and may of 2011 using various resolutions and stretching factors a comparison of week long accumulative precipitation amounts between the tropical rainfall measuring mission trmm satellite data and the quasi uniform and sg simulations showed that a stretched run better represents storms and associated precipitation because the errors generated in the outer regions with coarser grid spacing do not significantly affect the inner domain centered at the focal point for season long simulations in one particular set of stretched runs with the focal point located in the eastern united states the artificial s

salina margin tepees pisoliths and aragonite cements lake macleod western australia their significance in interpreting ancient analogs tepee structures banded aragonite cements and pisoliths are currently forming in lake macleod a carbonate evaporite salina in western australia although lake macleod is separated from the indian ocean by a barrier it lies 3 4 m below sea level which promotes the seepage of seawater through the barrier and its discharge from vents and seepage mounds around the margin of the salina discharging waters have precipitated and diagenetically altered carbonate sediments within these seepage mounds to form tepee structures of lithified protodolomite overlying cavities that are lined with banded aragonite cement and floored by both cement and pisoliths significant variations in 18o 5 1 pdb and 13c 5 5 pdb of the aragonite cements were documented and are thought to record shifts in the isotopic composition of the water brought about by the effects of evaporation influx of meteoric water and oxidation of organic water carbon 14 dating of cements indicates that cementation began about 3400 b p and has proceeded at a rate of about 0 2 to 0 4 mm 100 yr the highest rate occurring during evaporative episodes by analogy with lake macleod and other australian salinas peritidal tepee structures and associated diagenetic carbonates in the permian capitan reef complex may owe their origin to speleanlike diagenesis operative in a marine groundwater discharge zone

giant polygons in the realmonte mine agrigento sicily evidence for the desiccation of a messinian halite basin abstract the messinian realmonte salt deposit consists of a 400 600 m thick halite succession that can be divided into four main lith ologic units base to top a cumulates of plates settled out from a stratified water column b plate cumulates in a shallowing upward sequence containing six kainite layers near the top of the unit c cu mulates of skeletal hoppers with chevron overgrowths precipitated from a nonstratified water body and d skeletal halite and anhydrite spectacular vertical fissures cut through the upper part of unit b at its boundary with salt unit c these fissures are spaced at intervals of up to 5 m apart extend down to a depth of 6 m and are filled by red mud the salt beds affected by the fissures are commonly upturned buckled and are truncated and onlapped by the succeeding flat lying halite beds of unit c additionally the upturned layers are cut by vertical dissolution pipes that extend down to as much as a depth of 4 m below the fissured surface to explain the observed superimposed structures we propose two mechanisms both induced by the desiccation of the evaporite basin 1 when the salt surface was exposed the halite layers were buck led broke into polygonal crusts and formed tepee structures the buckling was caused by a net volume increase due to thermal expan sion and what is more important precipitation of new halite induced by evaporative pumping of brines moving up from the groundwater table the buckled salt layers were then affected by meteoric dissolu tion which created vertical pipes 2 the tepee structures and the associated zone of dissolution pipes are further crosscut by a new network of large polygons these new polygonal sets are outlined by deep fissures in which red silt collected blown by the wind or carried by episodes of surface flooding this type of deep contraction crack is known to be produced by volumetric changes induced by annual temperature fluctuations the documentation of contraction polygons and other exposure fea tures represents the first report of desiccation events during the de position of the sicilian salt no geological data are yet available to settle the questions if the salt of sicily is correlatable with the halite present beneath the floor of the mediterranean and if the desiccation of the realmonte salt basin could have been induced by a local tectonic causes uplift of the basin floor by thrust activity b simple evaporitic drawdown c basinwide drop of the mediterranean sea level or d complex interaction among these factors

evidence for climate shifts in the 2 0ga upper makgabeng formation erg south africa abstract eolian ergs and associated environs are sensitive to short and long term climatic changes in one of the oldest erg deposits the 2 0 ga makgabeng formation vertical changes in facies associations reflect one of the earliest records of short term climatic shifts in a continental setting the makgabeng formation is separated into lower and upper erg deposits by a playa or saline pan deposit the lower erg deposit consists of dune sets with thin lenses of dry and deflationary interdune strata that transition vertically to thicker damp to wet interdune strata a laterally persistent playa deposit in the middle of the section consists of mudstone with deep and shallow penetrating mud cracks and subordinate siltstone and sandstone interbeds above this lower mudstone interval the playa strata are sandy overlying the playa deposit the upper erg deposit consists of thick eolian sets with thin lenses of dry interdune deposits grain size change near the top of the upper erg deposit corresponds with the appearance of fluvial sheet flood eolian cross beds sculpted by mass flows and thin playa deposits vertical stacking of facies associations demonstrates temporal shifts in precipitation and fluctuating water tables fluvial and playa deposits record high water tables whereas low water tables are reflected in the core erg the transition from a lower to higher water table is recorded by wet interdune interspersed within the dune strata toward the top of this interval rapid climatic amelioration occurred near the termination of the makgabeng erg resulting in impingement of ephemeral river systems development of playas and generation of massive sand flows this 2 0 ga erg demonstrates the impact of climate change on erg development resulting from shifts in monsoonal impingement through time

tropical cyclone activity in nested regional and global grid refined simulations the capacity of two different grid refinement methods two way limited area nesting and variable mesh refinement to capture northwest pacific tropical cyclone tc activity is compared in a suite of single year continuous simulations simulations are conducted with and without regional grid refinement from approximately 100 20 km grid spacing over the northwest pacific the capacity to capture smooth transitions between the two resolutions varies by grid refinement method nesting shows adverse influence of the nest boundary with the boundary evident in seasonal average cloud patterns and precipitation and contortions of the seasonal mean mid latitude jet variable mesh on the other hand reduces many of these effects and produced smoother cloud patterns and mid latitude jet structure both refinement methods lead to increased tc frequency in the region of refinement compared to simulations without grid refinement although nesting adversely affects tc tracks through the contorted mid latitude jet the variable mesh approach leads to enhanced tc activity over the southern indian and southwest pacific basins compared to a uniform mesh simulation nesting on the other hand does not appear to influence basins outside the region of grid refinement this study provides evidence that variable mesh may bring benefits to seasonal tc simulation over traditional nesting and demonstrates capacity of variable mesh refinement for regional climate simulation

architectural elements and bounding surfaces in fluvial deposits anatomy of the kayenta formation lower jurassic southwest colorado abstract three well exposed outcrops in the kayenta formation lower jurassic near dove creek in southwestern colorado were studied using lateral profiles in order to test recent regarding architectural element analysis and the classification and interpretation of internal bounding surfaces examination of bounding surfaces within and between elements in the kayenta outcrops raises problems in applying the three fold classification of allen 1983 enlarging this classification to a six fold hierarchy permits the discrimination of surfaces intermediate between allen s second and third order types corresponding to the upper bounding surfaces of macroforms and internal erosional reactivation surfaces within the macroforms examples of the first five types of surface occur in the kayenta outcrops at dove creek the new classifications is offered as a general solution to the problem of description of complex three dimensional fluvial sandstone bodies the kayenta formation at dove creek consists of a multistorey sandstone body including the deposits of lateral and downstream accreted macroforms the storeys show no internal cyclicity neither within individual elements nor through the overall vertical thickness of the formation low paleocurrent variance indicates low sinuosity flow whereas macroform geometry and orientation suggest low to moderate sinuosity the many internal minor erosion surfaces draped with mud and followed by intraclast breccias imply frequent rapid stage fluctuation consistent with variable seasonal monsonal ephemmeral flow the results suggest a fluvial architecture similar to that of the south saskatchewan river through with a three dimensional geometry unlike that interpreted from surface studies of that river

platform margins reef facies and microbial carbonates a comparison of devonian reef complexes in the canning basin western australia and the guilin region south china devonian reef complexes were well developed in western australia and south china but no detailed direct comparison has been made between reef building in the two regions the regions differ in several respects including tectonic stratigraphic and palaeoceanographic palaeogeographic settings and the reef building styles reflect minor differences in reef builders and reef facies similarities and differences between the two reef complexes provide insights into the characteristics of platform margins reef facies and microbial carbonates of both regions here we present a comparison of platform margin types from different stratigraphic positions in the late devonian reef complex of the canning basin western australia and middle and late devonian margin to marginal slope successions in guilin south china comparisons are integrated into a review of the reefal stratigraphy of both regions reef facies reef complex architecture temporal reef builder associations 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally however carbonate deposition began earlier in south china carbonate complexes were also more widespread in south china and represent a thicker succession overall platforms in the canning basin grew directly on precambrian crystalline basement or early palaeozoic sedimentary rocks but in south china carbonate complexes developed conformably on older devonian siliciclastic strata pre frasnian reef facies in south china had more abundant skeletal frameworks than in canning basin reefs of equivalent age and famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in south china however late devonian platform margin types have been documented more completely in the canning basin deep intra platform troughs deep depressions containing non carbonate pelagic sediments nandan type successions that developed along syndepositional faults characterize devonian carbonate platforms in south china but have no equivalent on the lennard shelf canning basin where inter reef areas were more shallow the south china platform to depression pattern was generally continuous from the lower to upper devonian indicating that many pre devonian tectonic features continued to exercise considerable effect through deposition localized fault controlled subsidence was an important factor in both regions but similarities in 2nd order aggradation progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions

famennian mud mounds in the proximal fore reef slope canning basin western australia abstract famennian late devonian carbonate buildups and in particular mud mounds are poorly known in general and few have been documented in detail relatively small famennian mud mounds occur in proximal fore reef slope settings in the canning basin western australia the famennian platform margin facies passes from typical shoaling carbonate facies in the back reef through massive calcimicrobial cement rich reef margin facies to relatively steeply dipping 20 30 well bedded fore reef slope facies containing shelf derived winnowed grainy sediments and extremely coarse reef block debris isolated or coalescing mounds occur in the proximal slope immediately adjacent to and in some cases possibly grading into the margin facies mounds are elongate perpendicular to the margin and some had synoptic relief greater than 2 m mounds are lithologically variable and consist of varying proportions of micrite multiple generations of marine cement abundant rothpletzella renalcis poorly preserved sparry microbial crusts and sporadically distributed laminar stromatoporoids surrounding grainy slope facies abut and slope off of mound flanks mound facies are very similar to nearby reef margin facies with the exceptions that stromatoporoids have not been observed in margin facies and solenoporoid algae which occur in the margin have not been observed in the mounds stromatolites are conspicuously absent from both facies mound facies appear to be more closely related to frasnian and famennian calcimicrobe cement dominated reef margin facies than to famennian deep water stromatolite sponge mound facies such as those that occur elsewhere in the canning basin the observed canning famennian reef and mound frameworks were constructed by communities that appear to be very similar to earlier frasnian communities despite the frasnian famennian extinction event and provide good examples of microbial reef framework construction in a high energy setting

upland ecology of some late carboniferous cordaitalean trees from nova scotia and england abstract permineralised logs and charcoal fragments composed of dadoxylon type wood and derived from cordaitalean trees are described from the upper carboniferous westphalian of nova scotia and england they exclusively occur in sandstone bodies interpreted as the deposits of braided meandering and anastomosing river channels the architecture and ecology of this type of cordaitalean has not yet been satisfactorily described estimates of tree height using an allometric approach suggest that the largest trees attained an approximate height of ca 45 m the absence of true growth rings in the logs indicate that they grew under non seasonal humid tropical conditions however the presence of charred wood fragments implies that droughts of sufficient intensity to permit wildfire did occasionally occur the charcoal fragments are usually associated with incised poorly sorted chaotically bedded channel facies interpreted as flood deposits dramatic increases in runoff and sediment discharge are known to follow the destruction of vegetation in modern wildfire events and the high energy charcoal bearing channel facies described may represent a similar geomorphic response to cordaitalean vegetation fires geomorphic sensitivity to fire is greatest for steeply sloping terrains and it is therefore probable that the cordaitaleans described in this paper occupied upland settings this palaeoecological interpretation is supported by occurrence of the cordaitalean remains in river channel deposits immediately downstream of regions of palaeo upland and by the palynological record the presence of upland forests in late carboniferous times has important implications for numerical modelling of global geochemical cycles

a review of recent research in fluvial sedimentology this volume has been compiled to represent the current status of research into fluvial sedimentology as part of the proceedings for the 5th international conference on fluvial sedimentology 5icfs brisbane july 1993 the volume contains papers on a wide variety of topics representing the diversity of interests covered by the icfs this review serves to introduce these papers within the context of recent research post1988 in fluvial sedimentology icfs papers may be somewhat arbitrarily divided into those which report fundamental studies of sediment transport studies of modern alluvial and coastal systems studies of environmental management of fluvial systems facies analyses of ancient fluvial sequences studies of controls on alluvial stratigraphy and basin fill and applied sedimentological studies of fluvialhosted mineral resources it is interesting to compare the balance of papers in this volume with that of previous icfs volumes miall 1978 collinson and lewin 1983 ethridge et al 1987 marzo and puigdefabregas 1993 as a guide to changing emphasis in fluvial sedimentology figure 1 illustrates the distribution of papers over the five icfs meetings categorised as above among various trends two are worthy of comment the first being the marked peak in interest in controls on fluvial sequence and basin fill at the 4icfs and the second the influx of papers on environmental management in this volume although there has been a steady level of activity in fundamental aspects of sediment transport and bedform generation the rela

the hydrological significance of holocene tepees stromatolites and boxwork limestones in coastal salinas in south australia abstract holocene groundwater lakes salinas are common in the coastal zone of south australia they usually contain an evaporitic carbonate sequence that surrounds a central gypsum unit to form a bull s eye pattern of sediment distribution in the salina the evaporitic carbonates can be subdivided into three units a boxwork boundstone unit a veneer boundstone unit and an algal boundstone unit these units contain many interesting structures including tepees stromatolites and mound springs all of which show a megapolygonal outcrop pattern the salina carbonates have formed under a hydrological regime that has changed little since its inception some 6000 years ago consequently it has been possible to interpret the hydrological significance of the salina carbonates the salinas are fil ed by schizohaline surface waters whose water levels and salinities fluctuate seasonally all of the salina carbonates form where marine derived groundwater resurges from a surrounding dune aquifer into the margin of the salina tepee structures form in the veneer boundstone as a response to groundwater induced seasonal changes in the pore pressures of the underlying boxwork sediments the recognition of such groundwater tepees or other groundwater controlled structures in ancient carbonate sequences could aid paleohydrological interpretation of the ancient basin

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

proterozoic braided ephemeral fluvial deposits an example from the dhandraul sandstone formation of the kaimur group son valley central india abstract the dhandraul sandstone formation of the middle proterozoic kaimur group the vindhyan supergroup son valley india has been reinterpreted to represent a product of braided ephemeral fluvial environment the previous interpretation was shallow marine barrier bar evidences in favour of braided river deposition of the dhandraul sandstone are a cosets of low angle planar cross bed sets are closely associated with cosets of parallel laminated sets with particle streaming on bedding plane surfaces b vertical recurrence of planar laterally impersistent erosional surfaces that are invariably carpeted by red coloured intraformational shale pebble conglomerate c profuse development of ripple marks d sedimentary structures indicative of critical to supercritical flow conditions and e consistent palaeocurrent patterns

lithofacies and sequence development on an upper devonian mixed carbonate siliciclastic fore reef slope canning basin western australia detailed sedimentological and stratigraphical analysis coupled with conodont biostratigraphy of a fore reef slope succession in the napier range napier formation is used to develop a depositional model and relative sea level history for late frasnian to late famennian reef evolution in the canning basin of north western australia changes in sedimentary style on the slope reflecting differing rates of carbonate production on the platform are linked to third and higher order relative sea level fluctuations overlapping slope aprons accumulated along the base of a steep walled platform margin coarse carbonate debris was deposited adjacent to the margin as talus breccias via rockfall and debris flow breccias depositional slopes up to 45 and locally steeper are demonstrated using rotated geopetal cavity fills the predominance of channel filling lithofacies throughout the slope succession indicates the highly channelized nature of the aprons the middle slope is dominated by sandy oolitic peloidal turbiditic grainstones interpreted as sediment exported from an active platform the turbidites and associated debris flow breccias contrast with condensed carbonate intervals and deep water non fenestral stromatolites that record times of very low platform production lower slope turbidites and associated intraclastic breccias indicate widespread redeposition of sediment eroded from lithified and semi lithified limestones higher up the slope several third order sequences are recognized in the fore reef succession and these are composed primarily of transgressive and highstand deposits carbonate production was severely restricted in the early famennian coinciding with development of onlapping siliciclastic aprons during a relative sea level lowstand evidence for a subaerial exposure event is also preserved within the siliciclastic strata controls on sequence development are difficult to constrain although two sequence boundaries can be correlated with falls on the global sea level curve the reef complexes evolved in an active extensional regime and it is highly likely that tectonism in conjunction with eustasy controlled accommodation on the platform and therefore carbonate productivity

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