late ordovician turinian chatfieldian carbon isotope excursions and their stratigraphic and paleoceanographic significance five positive carbon isotope excursions are reported from platteville decorah strata in the upper mississippi valley all occur in subtidal carbonate strata and are recognized in the mifflin grand detour quimbys mill spechts ferry and guttenberg intervals the positive carbon isotope excursions are developed in a platteville decorah succession in which background 13c values increase upward from about 2 at the base to about 0 vienna pee dee belemnite vpdb at the top a regional north south 13c gradient with lighter values to the north and heavier values to the south is also noted peak excursion 13c values of up to 2 75 are reported from the quimbys mill excursion and up to 2 6 from the guttenberg excursion although there are considerable local changes in the magnitudes of these events the quimbys mill spechts ferry and guttenberg carbon isotope excursions occur in units that are bounded by submarine disconformities and completely starve out in deeper more offshore areas closely spaced chemostratigraphic profiles of these sculpted pyrite impregnated hardground surfaces show that they are associated with very abrupt centimeter scale negative 13c shifts of up to several per mil possibly resulting from the local diagenetic effects of incursions of euxinic bottom waters during marine flooding events

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

a transferable method for the automated grain sizing of river gravels 1 the spatial and temporal resolution of surface grain size characterization is constrained by the limitations of traditional measurement techniques in this paper we present an extremely rapid image processing based procedure for the measurement of exposed fluvial gravels and other coarse grained sediments defining the steps required to minimize the errors in the derived grain size distribution this procedure differs significantly from those used previously it is based around a robust object detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions crucially without any user intervention or site specific parameterization the procedure is tested using a data set comprising 39 images from three rivers with contrasting grain lithology shape roundness and packing configuration and representing a very wide range of textures it is shown to perform more consistently than the best existing automated method achieving a precision equivalent to that obtainable by wolman sampling but taking between one sixth and one twentieth of the time the error in area by number grain size distribution percentiles is typically less than 0 05

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

sulphate reduction associated with hardgrounds lithification afterburn negative excursions in 13c profiles from platform carbonates that coincide with pyritised hardgrounds are commonly linked to subaerial exposure events but we show here that they can also result from subsurface bacterially mediated early cementation in addition to the precipitation of syndepositional marine cements a non soil derived origin for 13c depleted micrites offers an alternative origin and bathymetric interpretation for these surfaces the lower cretaceous lekhwair formation platform carbonate successions from offshore abu dhabi contain abundant hardgrounds that are important for both regional correlation and control of subsurface flow the micrite from these hardgrounds have average 13c values of 0 7 1 5 lower than non hardground micrites that are similar to contemporary open ocean values hardground 13c values are due to the addition of 13c depleted carbonate generated as a by product of sulphate reduction to the normal marine calcite that caused hardground lithification pyritisation of the hardgrounds occurred before during and after normal calcite precipitation the persistence of sulphate reduction after hardground lithification is shown by the presence of pyrite and low 13c micrite in sediment up to a few mm above the hardgrounds

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

stable carbon isotope record of shallow marine evaporative epicratonic basin carbonates ordovician williston basin north america secular variations in stable carbon isotope values of marine carbonates are used widely to correlate successions that lack high resolution index fossils various environmental processes however commonly may affect and alter the primary marine carbon isotope signal in shallow epicratonic basins this study focuses on the marine carbon isotope record from the carbonate evaporite succession of the upper katian upper ordovician red river formation of the shallow epicratonic williston basin usa it documents the carbon isotope signal between the two major ordovician positive shifts in 13c the early katian guttenberg and the hirnantian excursions eight 13c stages are identified based on positive excursions shifts from positive to negative values and relatively uniform 13ccarb values a correlation between carbon isotope trends and the relative sea level changes based on gross facies stacking patterns shows no clear relation based on the available biostratigraphy and 13c trends the studied williston basin curves are tied to the isotope curves from the north american midcontinent quebec anticosti island and estonia which confirm the late katian age aphelognathus divergens conodont zone of the upper red river formation the differences in the 13c overall trend and absolute values coupled with the petrographic and cathodoluminescence evidence suggest that the carbon isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated williston basin and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

estimating the settling velocity of bioclastic sediment using common grain size analysis techniques most techniques for estimating settling velocities of natural particles have been developed primarily for siliciclastic sediments therefore to understand how these techniques apply to bioclastic environments measured settling velocities ws of bioclastic sedimentary deposits sampled from a nearshore fringing reef in western australia were compared with settling velocities calculated using results from several common grain size analysis techniques sieve laser diffraction and image analysis and established models the effects of sediment density and shape were also examined by using a range of density values and three different models of ws sediment density was found to have a significant effect on calculated ws causing a range in normalized root mean square error of up to 28 depending upon settling velocity model and grain size method accounting for particle shape improved errors in predicted ws by 3 to 6 and removed any velocity dependent bias which is particularly important for the fastest settling fractions when shape was accounted for and measured density was used normalized root mean square errors were 4 10 and 18 for laser diffraction sieve and image analysis respectively the results of this study show that established models of ws that account for particle shape can be used to estimate settling velocity of irregularly shaped sand sized bioclastic sediments from sieve laser diffraction or image analysis derived measures of grain size with a limited amount of error collectively these findings will allow for grain size data measured with different methods to be accurately converted to settling velocity for comparison this will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments this article is protected by copyright all rights reserved

study of the recent sediment movement features in the vicinity of deepwater navigation channel yangtze estuary abstract intensive anthropogenic impacts have been implemented in the yangtze estuary during the last several decades which significantly modified the global and local hydro and morpho dynamics subsequently sediment movement characteristics in the vicinity of the deepwater navigation channel dnc change in accordance with such human interactions the present study is focusing on the recent sediment moving features around the dnc in between 2017 and 2019 after the elevation of the partition dike in 2016 five successive in situ regular campaigns for flood and dry seasons together with field surveys pre and post typhoon in 2018 were conducted to collect bottom surface sediment samples sand and silt samples with different physical properties were identified under the normal weather condition sand samples are generally found in the south channel sc and the middle reach of the north passage np whereas silt samples are prevailed elsewhere considering the different features in the grain size distribution curve of sand samples more attentions were paid to the spatiotemporal variations of sand samples grain size parameters of sand samples indicate that under the normal weather condition relatively pure sands with almost no silt constituent exist in the sc whereas relatively mixed sands with certain silt compositions are located in the middle reach of np nevertheless only relatively mixed sands could be found in the sc and there are no sand samples in the np after typhoon events subsequently the recent sediment movement characteristics in the vicinity of dnc were figured out under the normal weather condition relatively mild siltation owing to the back filings from the dike fields and seaward of dnc occurs in the middle and lower reaches of dnc which is consistent with the temporal variations of the magnetism analysis of sand samples in contrast intensive siltation occurs inside the dnc after the extreme weather events which comes from three possible provenances i e overtopping from the south dike back fillings from dike fields and seaward of dnc these findings provide some helpful information for the efficient management and reasonable regulation in the yangtze estuary

grain size variability on a rip channeled beach abstract grain size is an important variable when predicting beach morphodynamics beaches to the eye seem relatively uniform in grain size and morphodynamic modeling efforts usually assume a single mean grain size for an entire beach environment therefore estimating grain size is traditionally done by collecting only a few samples and averaging to characterize the mean grain size of the whole beach however some studies have shown that even small variations in grain size can have a significant effect on model results when predicting beach morphology changes here a mobile digital imaging system dis has been developed for surveying spatial and temporal variation in grain size across a beach following the ideas of rubin 2004 using an off the shelf camera and underwater housing macro photographs are taken of sand across a beach which produce estimates of mean grain size that are highly correlated with estimates from sieves r2 0 92 high resolution maps of mean surface grain size are produced using the dis with 1000 images over a 300 500 m area which suggest that large variations in grain size exist 0 2 0 7 mm over tens of meters with accuracies of 0 03 mm and that there is a correlation between spatial grain size variations and morphological variability

information on grain sizes in gravel bed rivers by automated image analysis abstract the time required in the field to characterize textural variation over gravel surfaces can be reduced by taking vertical photographs for subsequent image analysis we present modified edge detection algorithms which combine edge seeding with an image porosity concept and partial watershed segmentation the methods allow quick reliable and operator independent size analysis from a wide range of vertical bed surface images they are tested using 24 naturally lit images of an exposed river bed with mixed lithologies and partial burial of gravel by sand grain size percentiles derived by automated image analysis correlate closely with those from manual image analysis with only small and consistent degrees of bias they also correlate well with percentiles from field measurements with substantial bias which however is consistent so that it can be corrected for leaving a residual scatter of 0 25 where log2 mm over a wide range of bed conditions the bias depends somewhat on sand cover and the biggest residual discrepancies are for tail percentiles

sedinet a configurable deep learning model for mixed qualitative and quantitative optical granulometry i describe a configurable machine learning framework to estimate a suite of continuous and categorical sedimentological properties from photographic imagery of sediment and to exemplify how machine learning can be a powerful and flexible tool for automated quantitative and qualitative measurements from remotely sensed imagery the model is tested on a large dataset consisting of 400 images and associated detailed label data the data are from a much wider sedimentological spectrum than previous optical granulometry studies consisting of both well and poorly sorted sediment terrigenous carbonate and volcaniclastic sands and gravels and their mixtures and grain sizes spanning over two orders of magnitude i demonstrate the model framework by configuring it in several ways to estimate two categories describing grain shape and population respectively and nine numeric grain size percentiles in pixels from a single input image grain size is then recovered using the physical size of a pixel finally i demonstrate that the model can be configured and trained to estimate equivalent sieve diameters directly from image features without the need for area to mass conversion formulas and without even knowing the scale of one pixel thus it is the only optical granulometry method proposed to date that does not necessarily require image scaling the flexibility of the model framework should facilitate numerous application in the spatio temporal monitoring of the grain size distribution shape mineralogy and other quantities of interest of sedimentary deposits as they evolve as well as other texture based proxies extracted from remotely sensed imagery

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

catchment scale mapping of surface grain size in gravel bed rivers using airborne digital imagery 1 this study develops and assesses two methods for estimating median surface grain sizes using digital image processing from centimeter resolution airborne imagery digital images with ground resolutions of 3 cm and 10 cm were combined with field calibration measurements to establish predictive relationships for grain size as a function of both local image texture and local image semivariance independently acquired grain size data were then used to assess the algorithm performance results showed that for the 3 cm imagery both local image semivariance and texture are highly sensitive to median grain size with semivariance being a better predictor than image texture however in the case of 10 cm imagery sensitivity of image semivariance and texture to grain size was poor and this scale of imagery was found to be unsuitable for grain size estimation this study therefore demonstrates that local image properties in very high resolution digital imagery allow for automated grain size measurement using image processing and remote sensing methods

ca isotope study of ordovician dolomite limestone and anhydrite in the williston basin implications for subsurface dolomitization and local ca cycling abstract a difference of 0 61 is reported between dolomite 1 66 and its precursor limestone 1 05 in the yeoman formation red river equivalent of the williston basin southeastern saskatchewan the significance of the large difference found and the preference for light isotope enrichment in the dolomite is evaluated with assistance from 87 sr 86 sr ratios and dolomitization models previously proposed for the studied rocks in particular i explore the possibility that 44 ca values in dolomite reflect the 44 ca values of the dolomitizing fluids without any correction for mineral fluid fractionation this hypothesis is based on recent studies showing negligible isotopic fractionation between carbonates and ca 2 bearing waters at very low precipitation rates fantle and depaolo 2007 jacobson and holmden 2008 if correct calcium isotopes hold promise as a tool for discriminating among numerous hydrological models of dolomite formation as a case in point the 44 ca value of the yeoman dolomite 1 66 is too low to reflect ca derived from the following sources 1 the original limestone 1 05 2 overlying beds of anhydrite 1 28 or 3 evaporated seawater 0 25 paleozoic carbonates ranging as low as 1 7 appear to be the lightest source of ca in the basin succession suggesting that the mg containing dolomitizing fluid was a connate water with a previous history of water rock interactions with paleozoic carbonates possibly involving earlier episodes of dolomitization and light ca release into migrating basinal fluids the relatively high seawater 44 ca values inferred from measurements of yeoman limestone and lake alma anhydrite suggest that seawater in the williston basin 450 ma was 0 22 0 46 higher in 44 ca than the contemporaneous ocean based on globally distributed brachiopods farkas et al 2007 this finding suggests that 44 ca values preserved in the deposits of epeiric seas may bias the 44 ca reconstruction of the ocean secular record if local ca cycling effects are not taken into account equations describing the isotope balance of ca in an epeiric sea indicate that seawater 44 ca values may be higher lower or equal to the 44 ca value of the ocean depending on the sizes of local scale ca deposition and weathering fluxes in relation to seawater ca exchange fluxes

katian upper ordovician delta c 13 chemostratigraphy and sequence stratigraphy in the united states and baltoscandia a regional comparison delta c 13 values of numerous limestone samples from katian upper ordovician successions in oklahoma and the upper mississippi valley document the presence of at least three of the four positive excursions that have been recognized in the lower middle katian interval in the cincinnati region in ohio kentucky and indiana a comparison with estonia reveals that five out of the six positive excursions now recorded through the katian succession in the cincinnati region are present in the coeval stratigraphic intervals in estonia which suggests that these represent global perturbations in the carbon cycle a study of the relations between flooding events and delta c 13 excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level part of a previously published attempt to use upper ordovician sequence stratigraphy for trans atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy several of the sequences recognized in the cincinnati region do not appear to have counterparts in estonia which suggests that they do not reflect eustatic but local conditions c 2010 elsevier b v all rights reserved less

dolomitization of the capitan formation forereef facies permian west texas and new mexico seepage reflux revisited interpretation of seepage reflux dolomitization is commonly restricted to intervals containing evaporites even though several workers have modelled reflux of mesosaline brines this study looked at the partially dolomitized forereef facies of the capitan formation to test the extent of reflux dolomitization and evaluate the possible role of the near backreef mesosaline carbonate lagoon as an alternative source of dolomitizing fluids the capitan formation forereef facies ranges from 10 to 90 dolomite most of the dolomite is fabric preserving and formed during early burial after marine cementation before and or during evaporite cementation and before stylolitization within the forereef facies dolomite follows depositional units with debris flow and grain flow deposits the most dolomitized and turbidity current deposits the least the amount of dolomite increases with stratigraphic age and decreases downslope within the reef facies dolomite is restricted to haloes around fractures and primary cavities except where the reef facies lacks marine cements and in contrast is completely dolomitized this dolomite distribution supports dolomitization by sinking fluids oxygen isotopic values for fabric preserving dolomite 1 8 o 0 9 1 0 n 101 support dolomitization by sea water to isotopically enriched sea water these values are closer to the near backreef dolomite 1 8 o 2 1 0 7 n 48 than the hypersaline backreef dolomite 1 8 o 3 6 0 9 n 11 therefore the fabric preserving dolomite is consistent with dolomitization during seepage reflux of mainly mesosaline brines derived from the near backreef carbonate lagoon the occurrence of mesosaline brine reflux in the capitan formation has important implications for dolomitization in forereef facies and elsewhere first any area with a restricted carbonate lagoon may be dolomitized by refluxing brines even if there are no evaporite facies present secondly such brines may travel significant distances vertically provided permeable pathways such as fractures are present therefore the absence of immediately overlying evaporite or restricted facies is not sufficient cause to eliminate reflux dolomitization from consideration

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

late middle ordovician environmental change and extinction harbinger of the late ordovician or continuation of cambrian patterns positive excursions in carbon isotope compositions of carbonate 3 and organic carbon 4 6 from the late middle ordovician middle caradocian of the midcontinent and the eastern united states indicate widespread increases in productivity and rates of organic carbon burial that may have drawn down atmospheric p co 2 precipitating global cooling although not necessarily ice sheet formation these climatic changes were associated with regional orogenic uplift a relative rise in sea level changes in epeiric sea circulation patterns and carbonate platform destruction that led to regional extinction of marine benthos the combination of sea level rise changing ocean circulation and extinction in the middle caradocian is similar to the suite of environmental changes described for cambrian biomere boundaries suggesting shared causes for these events in contrast middle caradocian environmental changes are markedly different from the environmental patterns associated with the late ordovician mass extinction despite the evidence for long term cooling from the middle to the late ordovician

estimation of grain size distributions and associated parameters from digital images of sediment abstract a new technique to estimate the grain size distribution gsd from a digital image of sediment is proposed advancing the applicability of a suite of sedimentary look up catalogue approaches originated by rubin rubin d m 2004 a simple autocorrelation algorithm for determining grain size from digital images of sediment journal of sedimentary research 74 1 160 165 the outputs of an automated procedure to estimate the gsd from digital images of sediment are examined with reference to the distributions obtained from both manually sieving the corresponding sediment samples and axial measurements made on the grains in the images measures of grain size obtained from the imaging procedure correlate very well with grain size measures derived from both the number frequency and mass frequency curve as expected the gsd obtained from the new automated approach based on kernel density compared better with point counts because of a shared two rather than three dimensionality the gsd shape is not always mimicked exactly however the percentiles obtained from the cumulative gsd compare well with those from sieved distributions which allow for the first time computation of graphical sorting and skewness from digital images of sediment which are accurate reflections of those measures obtained for point count and sieved samples the new approach allows for realistic gsds from which the residual can be computed thus a numerical criterion upon which the grain size distribution from an image can be accepted or rejected finally a method is presented whereby two dimensional autocorrelogram fields are derived from image power spectra ellipsoids are fitted to isolines of autocorrelation coefficients and from this the dominant axial lengths and orientation of these isolines which could facilitate computation of major and minor axis lengths of grains in sample images as well as their dominant orientation in turn this could allow for parameterisation of axial ratios for parameterisation of 2d shape such analysis is completely automated rapid and non intrusive

cobble cam grain size measurements of sand to boulder from digital photographs and autocorrelation analyses a new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated photographs of sand to boulder sized sediment along the elwha river delta beach were taken from approximately 1 2 m above the ground surface and detailed grain size measurements were made from 32 of these sites for calibration and validation digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment r2 0 98 but poor estimates of the short axes r2 0 68 suggesting that these short axes were naturally oriented in the vertical dimension the autocorrelation method was successfully applied resulting in total irreducible error of 14 over a range of mean grain sizes of 1 to 200 mm compared with reported edge and object detection results it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set up of the camera 200 fold versus 6 fold the approach is considerably less sensitive to lighting conditions than object detection methods although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight the effects of wet and dry conditions are also evaluated and discussed the technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error which is correlated with the graphical standard deviation at an r2 of 0 69 the technique is transferable to other sites when calibrated with linear corrections based on photo based measurements as shown by excellent grain size analysis results r2 0 97 irreducible error 16 from samples from the mixed grain size beaches of kachemak bay alaska thus a method has been developed to measure mean grain size and sorting properties of coarse sediments copyright 2009 john wiley sons ltd

reefs during the multiple crises towards the ordovician silurian boundary anticosti island eastern canada and worldwide multiple latest ordovician rawtheyan hirnantian glaciations in central africa with concomitant global sea level lowstands and cooler restricted equatorial carbonate shelves and ramps interrupted by warmer interstadial highstands had a dramatic global impact on the tropical shallow water reef ecosystem and carbonate production with the ordovician silurian boundary strata on anticosti island as a global standard for a carbonate shelf ramp setting the latest ordovician and earliest silurian reveal three reef phases ended by three extinctions the first extinction towards the end of the rawtheyan affected the last richmondian type reefs vaureal formation mill bay member the second extinction was less pronounced ending with reefs at the base of the prinsta member ellis bay formation interpreted as the top of the normalograptus extraordinarius graptolite subzone the third and most severe extinction phase capped the laframboise patch reef complex ellis bay formation at the top of the no

a new and practical method to obtain grain size measurements in sandy shores based on digital image acquisition and processing abstract modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time consuming traditional sieving methodologies however the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface tripods to fix and maintain the camera angle orthogonal to the sand surface external illumination systems that guarantee the light level necessary for the image processing algorithms and special lenses and focusing systems for close proximity image capturing in some cases controlled image capturing conditions can make the fieldwork more laborious which incurs in significant costs for monitoring campaigns considering large areas to circumvent this problem it is proposed a new automated image processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it the accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples field tests where 64 samples spread over a beach stretch of 65 km and with grain size ranging from 0 5 mm to 1 9 mm were processed by both the proposed method and by sieving and finally by manual point count on all acquired images the calculated root mean square rms error between mean grain sizes obtained from the proposed image processing method and the sieve method for the 64 samples was 0 33 mm and for the image processing method versus manual point counts comparison with the same images was 0 12 mm the achieved correlation coefficients r were 0 91 and 0 96 respectively

the stable carbon isotopic composition of organic material in platform derived sediments implications for reconstructing the global carbon cycle in pelagic carbonate sediments the degree to which the 13c values of inorganic and organic fractions co vary has been used to interpret rates of production burial and decomposition of organic carbon this relationship is relatively consistent through time permitting estimates of organic carbon production and preservation however as the majority of pelagic sediments older than 200 myr have been subducted carbonate sediments deposited in epeiric seas and platforms are often substituted for pelagic carbonates in analyses of ancient global carbon cycling there are well known pitfalls to using shallow marine carbonate materials including diagenesis semi isolation of depositional environments and input of different types of sediments with varying inorganic 13c 13cinorganic values which can obscure any global signatures one method used to assess whether global changes in 13c are accurately represented by 13cinorganic records is to examine variations in the 13c of co occurring organic material 13corganic if a 13corganic record co varies with a co occurring 13cinorganic record it is argued that the signals must be related to variations in the global carbon cycle this assumption has been investigated by analysing the isotopic composition of the organic carbon preserved in the uppermost 150 m of periplatform sediments recovered during odp leg 166 from the western margin of great bahama bank the 13corganic values measured in this study were compared to previously published 13cinorganic records measured on identical samples thus allowing a study of the correlation between the two records through time these analyses showed that the correlation coefficient between 13cinorganic and 13corganic increased from the proximal location site 1005 r2 0 1 to the distal site site 1006 r2 0 63 the importance of platform derived carbonate and organic material at the proximal location site 1005 is reflected in the absence of a co variation between inorganic and organic 13c records which exhibit no correlation on the platform itself in contrast the co variance in 13c values at the basinal location site 1006 is explained by a two point mixing model which demonstrates the importance of both pelagic and platform derived carbonate and organic carbon in generating the positive correlation between the organic and inorganic 13c values this results in a correlation between 13cinorganic and 13corganic records at site 1006 that is unrelated to global carbon cycling such data question the applicability of using 13corganic values to support the ability of 13cinorganic values to record global carbon cycling in carbonates recovered from environments where multiple sources of carbonate and organic carbon contribute to the bulk 13c signal

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

digital grain size analysis based on autocorrelation algorithm abstract grain size is one of the most important parameters in geology and coastal engineering however all traditional methods are time consuming laborious and expensive in this study the autocorrelation technique which was first expounded by rubin 2004 was extended to estimate the size of well sorted sediments and the grain size distribution of mixed size sediments long and intermediate axes of well sorted sediments ranging from 1 to 20 mm obtained from applying the autocorrelation method are compared with the corresponding results measured using a vernier caliper using the autocorrelation technique the sediment mean size was calculated and was found to compare better with point counts than sieving regarding the mixed size sediment a nonlinear programming method which is different from the conventional least squares with non negativity method the kernel density method and the maximum entropy method was used to obtain the representative grain sizes and associated sediment inherent parameters such as mean diameter median diameter sorting skewness and kurtosis image pre processing was used in the present analysis to enhance the contrast of the recorded image and a conversion method applied to take into account the difference between the two dimensional digital image method and the three dimensional sieving method using the modified fitting points and the improved gaussian function fitting method the cumulative grain size distribution curve and the probability density curve of the mixed size sediments were obtained the enhanced autocorrelation technique that was developed from the traditional look up catalogue approach provided a more accurate estimation of the grain size distribution as well as the relevant physical parameters of the mixed size sediment

the control of deformation intensity around a fault natural and experimental examples abstract the deformation intensity around a wrench fault is studied through a comparison between a well known natural fault and experimental models each model consists of a horizontal paraffin wax layer containing a precut plane which was submitted to uniaxial compression the meyrueis fault in the jurassic formations of the causses massif southern french massif central gives the opportunity of estimating strain around a wrench fault the comparison of this fault with the experimental models shows a good similarity in relation to the following aspects variation of the principal strain axes around the fault rotation of the strain axes with time which confirms a non coaxial strain history heterogeneity of strain with some domains strongly deformed and others protected symmetry of these domains with respect to the fault and the strong influence of kinematic boundary conditions in the direction perpendicular to the compression these features provide new criteria for the interpretation of natural wrench faults

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

a simple autocorrelation algorithm for determining grain size from digital images of sediment abstract autocorrelation between pixels in digital images of sediment can be used to measure average grain size of sediment on the bed grain size distribution of bed sediment and vertical profiles in grain size in a cross sectional image through a bed the technique is less sensitive than traditional laboratory analyses to tails of a grain size distribution but it offers substantial other advantages it is 100 times as fast it is ideal for sampling surficial sediment the part that interacts with a flow it can determine vertical profiles in grain size on a scale finer than can be sampled physically and it can be used in the field to provide almost real time grain size analysis the technique can be applied to digital images obtained using any source with sufficient resolution including digital cameras digital video or underwater digital microscopes for real time grain size mapping of the bed

field test comparison of an autocorrelation technique for determining grain size using a digital beachball camera versus traditional methods abstract this extensive field test of an autocorrelation technique for determining grain size from digital images was conducted using a digital bed sediment camera or beachball camera using 205 sediment samples and 1200 images from a variety of beaches on the west coast of the us grain size ranging from sand to granules was measured from field samples using both the autocorrelation technique developed by rubin rubin d m 2004 a simple autocorrelation algorithm for determining grain size from digital images of sediment journal of sedimentary research 74 1 160 165 and traditional methods i e settling tube analysis sieving and point counts to test the accuracy of the digital image grain size algorithm we compared results with manual point counts of an extensive image data set in the santa barbara littoral cell grain sizes calculated using the autocorrelation algorithm were highly correlated with the point counts of the same images r 2 0 93 n 79 and had an error of only 1 comparisons of calculated grain sizes and grain sizes measured from grab samples demonstrated that the autocorrelation technique works well on high energy dissipative beaches with well sorted sediment such as in the pacific northwest r 2 0 92 n 115 on less dissipative more poorly sorted beaches such as ocean beach in san francisco results were not as good r 2 0 70 n 67 within 3 accuracy because the algorithm works well compared with point counts of the same image the poorer correlation with grab samples must be a result of actual spatial and vertical variability of sediment in the field closer agreement between grain size in the images and grain size of grab samples can be achieved by increasing the sampling volume of the images taking more images distributed over a volume comparable to that of a grab sample in all field tests the autocorrelation method was able to predict the mean and median grain size with 96 accuracy which is more than adequate for the majority of sedimentological applications especially considering that the autocorrelation technique is estimated to be at least 100 times faster than traditional methods

transferable wavelet method for grain size distribution from images of sediment surfaces and thin sections and other natural granular patterns in images of sedimentary or granular material or simulations of binary two phase granular media in which the individual grains are resolved the complete size distribution of apparent grain axes is well approximated by the global power spectral density function derived using a morlet wavelet this approach overcomes many limitations of previous automated methods for estimating the grain size distribution from images all of which rely on either identification and segmentation of individual grains calibration and or relatively large sample sizes the new method presented here is tested using i various types of simulations of two phase media with a size distribution with and without preferred orientation ii 300 sample images drawn from 46 populations of sands and gravels from around the world displaying a wide variability in origin biogenic and mineralogical size surface texture and shape iii petrographic thin section samples from nine populations of sedimentary rock iv high resolution scans of marine sediment cores and v non sedimentary natural granular patterns including sea ice and patterned ground the grain size distribution obtained is equivalent to the distribution of apparent intermediate grain diameters grid by number style for images containing sufficient well resolved grains root mean square errors are within tens of percent for percentiles across the entire grain size distribution as such this method is the first of its type which is completely transferable unmodified without calibration for both consolidated and unconsolidated sediment isotropic and anisotropic two phase media and even non sedimentary granular patterns the success of the wavelet approach is due in part to it quantifying both spectral and spatial information from the sediment image simultaneously something which no previously developed technique is able to do

middle and upper ordovician carbon isotope chemostratigraphy in baltoscandia a correlation standard and clues to environmental history abstract the baltoscandian epeiric sea was characterised by relatively slow but continuous carbonate deposition from the middle ordovician up to the silurian relatively good preservation of ordovician and silurian carbonate rocks in baltoscandia makes this region unique for chemostratigraphical and palaeoenvironmental studies previous palaeozoic carbon isotope studies have revealed isotopic events in different lithologies over the baltoscandian palaeobasin and some of them on different palaeocontinents we propose a composite carbon isotope curve for the baltoscandian region a new subdivision of the middle and upper ordovician succession into seventeen chemostratigraphic zones and an improved nomenclature of isotopic excursions based on analyses of 13 c carb data from 25 drillcore and outcrop sections of estonia latvia and sweden the composite carbon isotope curve is compared with biostratigraphical data on conodont and chitinozoan distribution the katian hirnantian interval with highly fluctuating isotopic values shows climatic cyclicity of about two million years in baltoscandia no abrupt changes occur in the dapingian sandbian part of the baltoscandian isotope curve but the mid darriwilian excursion nearly coincides with the onset of cooler temperatures similar to modern like equatorial sea surface temperatures and related global biodiversification increase suggesting a climatic background for this event

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

underwater microscope for measuring spatial and temporal changes in bed sediment grain size for more than a century studies of sedimentology and sediment transport have measured bed sediment grain size by collecting samples and transporting them back to the laboratory for grain size analysis this process is slow and expensive moreover most sampling systems are not selective enough to sample only the surficial grains that interact with the flow samples typically include sediment from at least a few centimeters beneath the bed surface new hardware and software are available for in situ measurement of grain size the new technology permits rapid measurement of surficial bed sediment here we describe several systems we have deployed by boat by hand and by tripod in rivers oceans and on beaches published by elsevier b v

comparison of earthquake strains over 102 and 104 year timescales insights into variability in the seismic cycle in the central apennines italy in order to study the existence of possible deficits or surpluses of geodetic and earthquake strain in the lazio abruzzo region of the central apennines compared to 15 3 kyrs multi seismic cycle strain rates horizontal strain rates are calculated in 5 km x 5 km and 20 km x 20 km grid squares using slip vectors from striated faults and offsets of late pleistocene holocene landforms and sediments strain rates calculated over 15 3 kyrs within 5 km x 5 km grid squares vary from zero up to 2 34 0 54 x 10 7 yr 1 and resolve variations in strain orientations and magnitudes along the strike of individual faults surface strain rates over a time period of 15 3 kyrs from 5 km x 5 km grid squares integrated over an area of 80 km x 160 km shows the horizontal strain rate of the central apennines is 1 18 0 04 0 12 x10 8 yr 1 and 1 83 4 43 3 80 x 10 10 yr 1 parallel and perpendicular to the regional principal strain direction 043 degrees 223 degrees 1 degrees associated with extension rates of ms 6 0 magnitude historical earthquakes have been reported to be as low as zero this demonstrates the importance of comparing the exact same areas and that strain rates vary spatially on the length scale of individual faults and on a timescale between 10 2 yr and 10 4 yr in the central apennines we use these results to produce a fault specific earthquake recurrence interval map and discuss the regional deformation related to plate boundary and sub crustal forces temporal earthquake clustering and the natural variability of the seismic cycle

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

late ordovician carbon isotope trend in estonia its significance in stratigraphy and environmental analysis abstract carbon isotope changes during most of late ordovician time from the mid caradoc kinnekulle k bentonite until the beginning of the silurian were investigated as the corresponding sequence of rocks is stratigraphically nearly complete in estonia an attempt was made to use it to elaborate the general pattern of carbon isotope changes in the late ordovician complications were caused by several local or regional hiatuses in the middle and late caradoc and hirnantian a total of 385 whole rock samples were studied from eight drill cores in northern and central estonia the following positive carbon isotope events were observed 1 the mid caradoc excursion peak 13c value 2 2 in the uppermost part of the keila stage also known in sweden 2 the first late caradoc excursion 1 9 in the lower part of the rakvere stage 3 the second late caradoc excursion 2 4 in the upper part of the nabala stage 4 the early ashgill excursion 2 5 in the lowermost part of the pirgu stage 5 the widely known large hirnantian excursion in estonia the peak value reaches 6 7 in the porkuni stage the study interval comprises a long 10 ma period characterized by low magnitude carbon isotope changes and a following brief 2 ma interval with large changes no obvious lithological preference for hosting the positive shifts was recorded in principle the 13c values exceeding the background values may occur in all types of rocks present in a sedimentary basin several 13c positive excursions values 1 5 to 3 in the mohawkian of north america are evidence that the minor caradoc and early ashgill 13c positive shifts in baltoscandia may have counterparts in laurentia if correctly correlated these shifts may have global significance the hirnantian excursion is usually linked to a major glacial event even if some carbon cycling mechanisms are not completely understood the environmental causes suggested for the earlier minor shifts range from global climatic and glacial events to very local changes in basin regime and sea level our study supports the primary role of climatic or climatically triggered oceanic processes

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

grain size information from the statistical properties of digital images of sediment abstract the autocorrelation technique for estimating grain size from digital images ofsand beds has been extended and validated for use on coarse sand 0ae7 mm and gravel up to 20 mm a number of aspects of the technique have beenexplored and some potential improvements suggested autocorrelation is justone suitable statistical method sensitive to the grain size of sediment in digitalimages four additional techniques are presented and their relative meritsdiscussed a collective suite of techniques applicable to the general problem ofgrain size estimation from digital images of sediment might broaden theapplicability to more sedimentary environments as well as improve itsaccuracy these techniques are compared using a large data set from a gravelbarrier beach in southern england based on over 180 samples mean grain sizeof sieved and imaged sediments correspond to within between 8 and 16 some theoretical aspects of the spatial arrangement of image intensity indigital images of natural sediments are addressed including the fractal natureof sediments in images which has potential implications for derivation ofgrain size distributions from images of sand sized material throughsegmentation and thresholding the methods outlined in this contributionmay also nd application in further uncovering the geometric structure ofsediment beds as well as in the simulation of sedimentation processes keywordsgrain size analysis digital images statistical models gravel beach introductiongrain size information from natural environ ments traditionally is obtained using methodssuch as sieving laser diffraction and settling which do not help measure equivalent propertiesof the sample in addition the slow and labour intensive nature of these methodologies has lim ited the spatial and temporal resolution at whichgrain size data are obtained where grain size isan important parameter such as in determiningsediment transport studies can be limited funda mentally by the dif culty in sampling for sedi ment at the required frequency a furtherdisadvantage is that sediment must be removedfrom the natural environment potentially alteringsubsequent system development in contrast photographic methods can be used to measuresediment size at a resolution comparable withmeasurements of hydraulic hydrodynamic andmorphological topographical conditions withoutdisrupting the sediment body by direct sampling the problem of deriving sediment size infor mation from digital images of sediment has beenapproached using two different families of tech niques the rst is based on edge detection andimage segmentation principles e g butler et al 2001 sime ferguson 2003 graham et al 2005 such techniques rely on marked image intensity contrasts between grains and gapsbetween grains interstices such that thresholdscan be speci ed to discriminate individual grainsfrom the background intensity levels e g sime ferguson 2003 thus far these methods aresedimentology 2009 56 421 438

multiple δ13c excursions spanning the cambrian explosion to the botomian crisis in siberia new high resolution 13 c data through the lower cambrian of siberia reveal multiple positive excursions coincident with phases in the explosion of invertebrate phyla nemakit daldynian to middle botomian stages comparison of the 18 o and trace element mg fe mu sr chemistry indicate that six new 13 c cycles are primary rather than diagenetic features with potential for global correlation positive 13 c excursions up to 3 indicate that fractional organic carbon burial rates were high but variable through the cambrian explosion values for 13 c dropped sharply from around 2 2 to 1 6 in botomian time coincident with mass extinction of the archaeocyathan reef biota the rapid fluctuation of the 13 c signal and the temporal coincidence of the pronounced negative shift with the extinction event hint that the 13 c record may record productivity variations during the early cambrian radiation

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

response of late ordovician paleoceanography to changes in sea level continental drift and atmospheric pco2 potential causes for long term cooling and glaciation abstract we performed sensitivity experiments using an ocean general circulation model at two stages of the late ordovician caradoc 454 ma ashgill 446 ma under a range of atmospheric pco2 values 8 18 pal pre industrial atmospheric level at high and low sea level the model results indicate that the long term cooling trend during the late ordovician can be explained by progressive cooling of the global ocean in response to falling levels of atmospheric pco2 sea level change and paleogeographic change these results also explain the occurrence of low latitude cool water carbonates in north america in all simulations a drop in sea level led to a reduction in poleward ocean heat transport this indicates a possible positive feedback that could have enhanced global cooling in response to sea level drop during the late ordovician alterations in poleward ocean heat transport linked to changes of atmospheric pco2 also indicate that there is a threshold of 10 pal above which ocean current change cannot be responsible for glaciation in the late ordovician continental drift could explain the observed global cooling trend in the late ordovician through a combined poleward ocean heat transport feedback and increased ice albedo effect if atmospheric pco2 was low during the entire late ordovician the model results further indicate that the response of meridional overturning to changes in paleogeography atmospheric pco2 and sea level is stronger than the response of surface circulation to these perturbations because the overturning circulation is so strong meridional overturning was the dominant mechanism for described changes in heat transport in the late ordovician

global carbon isotopic events associated with mass extinction and glaciation in the late ordovician mass extinctions and glacioeustatic sea level changes in the lower part of the hirnantian final stage of the ashgill are accompanied by shifts in marine stable isotope compositions previously published stable isotope changes have been used to identify the onset and demise of the gondwana glaciation and to suggest relationships between biotic changes and carbon cycling within the oceans however the existing isotopic data set had limitations because it was derived from ordovician low latitude settings and from carbonates or organic carbon in separate areas we report new data from ordovician high latitude carbonates and demonstrate parallel shifts in organic and carbonate 13c from baltica brachiopod shells from a high palaeolatitude periglacial setting in argentina have elevated 13c values similar to those described previously from low latitude sites the new data demonstrate that the positive hirnantian 13c excursion previously only recognised from low palaeolatitude areas was widespread and probably global in extent the poor preservation state of the brachiopods unfortunately prevented the determination of a reliable oxygen isotopic value from the same material preliminary carbon isotopic data from thermally immature organic matter from estonia provide the first indication of a synchronous shift in organic and inorganic 13c in sediments from the same basin this work provides new data of critical importance for constraining models of end ordovician palaeoceanography and climate change

photo sieving a method for grain size analysis of coarse grained unconsolidated bedding surfaces the photo sieving method enables the grain size analysis of particles 10 mm from unconsolidated openwork bedding surfaces the accuracy is equal to the machine sieving method the sediment surface is photographed in the field using a camera stand the enlarged print is digitized for computer processing by tracing the outlines of the pebbles from the size and shape of the projection area of the individual pebble images the computer determines the ellipsoids of revolution classifies these ellipsoids and establishes their grain size distribution in percentage by weight thus photo sieving differs distinctly from point counting techniques with the aid of photo sieving the surface grain size distributions of larger sedimentary systems may be regularly mapped alluvial fans braided rivers both onshore and offshore coasts or areas of relict sediments and manganese nodules are suitable for this method

ordovician oxygen isotopes and paleotemperatures abstract valid marine 18o proxies have been defined from three ordovician units and with previously estimated sea water 18o values we have calculated paleotemperatures for low latitude settings during a greenhouse climatic era valid marine proxies include marine equant bladed and translucent fibrous calcite these cements are interpreted to be valid marine proxies based on cathodoluminescence minor element content abundance of microdolomite and stable isotopic both altered marine and non marine calcite phases values valid marine proxies from the chickamauga alabama holston tennessee and kullsberg sweden formations have an overall range of 18o values in each unit that is confined to within 1 unlike altered marine cements which exhibit significantly wider ranges of 18o values we suggest a likely non glacial ordovician sea water value of 2 1 smow from which paleotemperatures can be calculated calculated paleotemperatures are broadly consistent with crowley and baum s 1995 late ordovician paleoclimatic model