re evaluating evidence of australian eurypterids abstract eurypterids the so called sea scorpions are a group of extinct chelicerates with a diversity of over 250 species although the group has a distribution across most of the globe the majority of taxa are known from the northern hemisphere despite the general palaeontological interest in sea scorpions gondwanan specifically australian taxa have received little consideration to rectify this we collate data on australian sea scorpion material from the gogo melbourne and montys hut formations the humevale and muttama creek siltstones and the wilson creek shale the studied material spans the late silurian to the late devonian and highlights a rich pterygotidae fauna especially in the state of victoria we conclude that presently there is insufficient material to erect new taxa however further collecting of material especially the wilson creek shale and the montys hut formation will uncover more material to aid in understanding the most southern gondwanan eurypterids

ordovician faunas of burgess shale type the renowned soft bodied faunas of the cambrian period which include the burgess shale disappear from the fossil record in the late middle cambrian after which the palaeozoic fauna dominates the disappearance of faunas of burgess shale type curtails the stratigraphic record of a number of iconic cambrian taxa one possible explanation for this loss is a major extinction but more probably it reflects the absence of preservation of similar soft bodied faunas in later periods here we report the discovery of numerous diverse soft bodied assemblages in the lower and upper fezouata formations lower ordovician of morocco which include a range of remarkable stem group morphologies normally considered characteristic of the cambrian it is clear that biotas of burgess shale type persisted after the cambrian and are preserved where suitable facies occur the fezouata biota provides a link between the burgess shale communities and the early stages of the great ordovician biodiversification event

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

distribution and dispersal history of eurypterida chelicerata abstract the distribution and dispersal histories of eurypterida are examined in a phylogenetic and palaeogeographic context it is suggested that all the eurypterid clades originated and had most of their evolutionary history on the palaeocontinents of laurentia baltica avalonia the rheno hercynian terrane and some presence in siberia the siluro devonian stylonurina and the eurypterine superfamilies eurypteroidea and waeringopteroidea are confined in their entirety to these continents the late palaeozoic records of adelophthalmoidea and hibbertopteroidea in china south america and africa can be explained by rafting on the continental plates that amalgamated into the supercontinent pangaea however two clades have distributions that suggest abilities to cross open stretches of ocean the silurian and devonian pterygotoids and some devonian adelophthalmoids however one silurian mixopteroid and the basal swimming form onychopterella outside the core area suggest the dispersal patterns are more complicated the pterygotoids might be the only clade whose members frequently undertook oceanic excursions since almost all eurypterid evolution took place in laurentia baltica and avalonia and some in the early devonian of the rheno hercynian terrane prior to the carboniferous it is unlikely that many taxonomically rich pre carboniferous eurypterid faunas will be encountered outside of these palaeocontinents

ordovician and silurian global geography presidential address delivered 3 may 2000 the main palaeocontinents during the early ordovician were gondwana laurentia baltica and siberia and a brief survey is made of their limits in the ordovician and silurian in particular gondwana by far the largest continent is analysed as including a core of south america antarctica africa australia and peninsular india and also the marginal terranes all of which show faunal links with but which may not have been attached to the core of avalonia ibero armorica and other european fragments turkey arabia and terranes from the far east including south china sibumasu and parts of australasia changes within the benthic faunas reveal that baltica whilst isolated in the early ordovician became united with avalonia by the end ordovician and the two with laurentia by the mid silurian to form the new supercontinent of laurussia island arcs had distinctive faunas during the ordovician in particular those in the iapetus between laurentia baltica and gondwana and the huge kipchak arc which ran from baltica to siberia as the period progressed the iapetus arcs became subducted beneath or accreted to their neighbouring cratons and the kipchak arc gradually collapsed to form the core of the new kazakhstania terrane gondwana drifted over the south pole and this movement is reflected in the cratonic benthic faunas particularly brachiopods and trilobites which in the early ordovician had formed a cline between the high latitude faunas of north africa and the equatorial faunas of the far east and australia but by the devonian lived in much warmer seas in southern europe and cooler waters in antarctica the faunas also reflect the global palaeoclimates which were warm in the early to mid ordovician and mid to late silurian but which were much colder in the half million year period of the late ordovician and early silurian particularly in the latest ordovician hirnantian ice age with its attendant widespread hirnantia brachiopod fauna the relative closeness of the chief palaeocontinents by the early silurian enabled brachiopod and trilobite larvae to cross the narrower oceans enabling a relatively cosmopolitan benthic fauna to be established over much of the globe apart from the cooler water higher latitude clarkeia fauna to the south and the tuvaella fauna to the north

a new method for quantitative petrography based on image processing of chemical element maps part i mineral mapping applied to compacted bentonites most natural rocks or engineered materials display a multi scale heterogeneity ranging from the nanometer to the centimeter their spatial textural heterogeneity can be approached from chemical element maps acquired using various techniques sem epma sxam synchrotron xrf tem depending on the chosen magnification chemical map processing that yields quantitative petrographic information is improved here according to newly developed mineral thresholding methods that accommodate mixtures and solid solutions the complex case of an mx80 compacted bentonite is used as a test case the 14 major chemical elements of this sample were mapped using an electron probe microanalyzer and chemical map processing yielded a quantitative map of the 18 mineral species of bentonite with a spatial resolution of a few micrometers the textural heterogeneity of the solid part of the sample is thus visualized and quantified on an area ranging between 0 1 1 cm2 the method also provides a complete modal analysis of the sample the methodology is expected to have broad applications in earth and materials sciences

do red beds indicate paleoclimatic conditions a permian case study abstract terrestrial red beds have long been interpreted as desert deposits by comparison with modern red deserts more recently red beds have been interpreted as evidence of seasonally dry conditions and a permo triassic pangean monsoon red beds of cala viola sardinia are identified as paleosols and used to reconstruct late permian paleoclimatic conditions reconstruction of paleoenvironmental conditions based on the paleosols of the cala viola indicates warm humid conditions with no evidence of dry conditions as in a desert or of extreme seasonality as in a monsoon instead it is suggested that the red color of the paleosols is a result of former good drainage and that red color in general does not indicate specific paleoclimatic conditions

a new method for quantitative petrography based on image processing of chemical element maps part ii semi quantitative porosity maps superimposed on mineral maps visualizing and quantifying the spatial heterogeneity of rock textures i e mineral and porosity distributions is of great interest in petrology or for understanding petrophysical properties spatial heterogeneities are not accurately revealed by usual techniques based on microscopy or bulk physical measurements detailed mineral mapping is already available from processing of chemical element maps acquired using an electron probe microanalyzer part i the present paper is devoted to developing a new coupled method for obtaining porosity maps from the same initial data according to the difference between measured and theoretical sums of oxide weight percentages a mean porosity is semi quantitatively estimated for each pixel of the map i e not fully absolute or accurate all pores including nanometer size ones are taken into account whereas a sample area of several square millimeters is analyzed spatial resolution of a few micrometers the textural heterogeneities are thus visualized from the complementary maps of solids and voids by superimposing these two maps both the mean porosity and a porosity histogram associated with each rock forming mineral are obtained such porosity measurements integrate the pore amounts within mono crystals larger than the x ray emission volume or between nanometer size crystals of a matrix when porosity changes are associated with a given mineral various crystal arrangements dissolution etc pluri modal distributions appear on porosity histograms thresholding each histogram mode then allows these processes to be localized we used the mx80 bentonite to test this methodology which represents a useful tool to study the local deformations and alteration of each rock forming mineral as well as to model transport properties

a new ordovician eurypterid arthropoda chelicerata from southeast turkey evidence for a cryptic ordovician record of eurypterida a new species of eurypterid paraeurypterus anatoliensis gen et sp nov is described from the upper ordovician katian ort tepe formation of southeast turkey the single specimen preserving the carapace mesosoma and fragments of appendages appears morphologically intermediate between the eurypteroid families dolichopteridae and eurypteridae p anatoliensis retains the plesiomorphic conditions of crescentic eyes with enlarged palpebral lobes and a quadrate carapace with ornamentation consisting of small pustules but also displaying the derived characteristics of genal facets and a row of large acicular scales across the posterior of each tergite phylogenetic analysis incorporating each of the major eurypterine clades and all eurypterina having a three segmented genital operculum the triploperculate condition resolves eurypteroids to be an unnatural group with dolichopteridae and eurypteridae forming part of a grade leading to diploperculate eurypterina p anatoliensis is intermediate between the two eurypteroid families as is eurypterus minor from the pentland hills of scotland which is shown to be a distinct genus and assigned to pentlandopterus gen nov using the phylogenetic topology to infer ghost ranges for each of the major eurypterid clades reveals that the majority of eurypterid superfamilies must have originated by the katian indicating a largely unsampled record of ordovician eurypterids the occurrence of poor dispersers such as paraeurypterus in the ordovician of gondwana is puzzling and it has been suggested that they dispersed to the continent during periods of sea level lowstand in the sandbian and hirnantian however this does not explain the lack of ordovician species in north america and europe given the well sampled nature of these continents and an alternative is proposed whereby eurypterids originated in gondwana and radiated out to laurentia and baltica in the late ordovician and early silurian thus explaining their sudden appearance in the european and north american rock record

quantitative mineralogical characterization of sandstones by back scattered electron image analysis abstract methods are described for the quantitative analysis of both the composition of sandstones and the two dimensional morphology of their component mineral phases based on image analysis of back scattered electron bse images of flat sections mineral phases are distinguished largely by their gray levels intensities in the bse image where contrast derives almost entirely from the compositions of the phases although morphological criteria are applied where phases overlap in gray level the concentration of each phase in each image is then measured as proportional area and the average over many images gives an analysis of a significantly large area of the specimen morphological quantification is achieved in a totally objective way by operating a series of two dimensional opening t ansformations on segmented images of the component minerals and pores and the results are presented in the form of feature size histograms also summed over many image fields both the compositional and morphological analyses are capable of being fully automated

palaeoenvironments of early devonian fish and other aquatic fauna of the campbellton formation new brunswick canada abstract the palaeoecology and palaeoenvironments of the classic fish bearing strata of the campbellton formation are here described a well documented fossil assemblage includes acanthodian placoderm chondrichthyan and cephalaspid fishes tracheophyte remains eurypterids ostracods and molluscs as part of the old red sandstone continent the emsian campbellton formation occupied a small basin within the mountainous terrain of the acadian orogen and may have connected through a narrow seaway to a closing foreland basin the highest diversity of vertebrate fossils was found above a basal unconformity with val d amour formation volcanics marked by fissure fills and unstratified breccia representing a craggy irregular palaeosurface that provided shelter for some fauna and sediment for rapid burial of skeletal remains overlying prodeltaic calcareous siltstones are also highly fossiliferous and represent a low energy habitat occurrences of pterygotid eurypterids cephalaspids and chondrichthyans in deltaic sandstones place these taxa in a habitat that may have been variably fresh or brackish the surrounding landscape was vegetated with primitive tracheophytes and abundant plant debris is preserved throughout the basin the diverse assemblage of fish arthropods gastropods plants and microbial growths suggests that a trophically complex ecosystem was in existence

a new lagerstatte from the middle ordovician st peter formation in northeast iowa usa a new fossil fauna has been discovered from a recently recognized shale unit within the middle ordovician st peter formation in northeast iowa it contains a variety of invertebrates and vertebrates including soft body tissues impressions and 3 dimensionalpreservations the exceptional preservation reveals a new konservat lagerstatte the winneshiek lagerstatte and opens a unique window into the community that inhabited the margins of the laurentian cratonic seaway during middle ordovician transgression among the fossils several conodont assemblages including the apparatus of enigmatic coleodontids are preserved some conodont assemblages associated with soft body tissues are particularly noteworthy

stylonurine eurypterids from the strud locality upper devonian belgium new insights into the ecology of freshwater sea scorpions the upper famennian upper devonian strud locality has yielded very abundant and diversified flora as well as vertebrate and arthropod faunas the arthropod fauna mostly recovered from fine shales deposited in a calm confined floodplain habitat including temporary pools has delivered a putative insect and various crustaceans including eumalacostracans and notostracan spinicaudatan and anostracan branchiopods here we present the strud eurypterids consisting of semi articulated juvenile specimens assigned to hardieopteridae recovered from the pool and floodplain deposits as well as larger isolated fragments of potential adults recovered from stratigraphically lower coarser dark sandy layers indicative of a higher energy fluvial environment the strud fossils strongly suggest that as proposed for some carboniferous eurypterids juvenile freshwater eurypterids inhabited sheltered nursery pools and migrated to higher energy river systems as they matured

early devonian stylonurine eurypterids from arctic canada two new stylonurine eurypterids are described from the peel sound formation early devonian lochkovian of the northern coast of prince of wales island nunavut arctic canada associations including pteraspids and ostracodes indicate a fluvial depositional environment an almost complete stylonurid pagea plotnicki sp nov is recognized by its large size and lack of vaulting on the carapace and it provides evidence that stylonurus and pagea are sister taxa also a smaller incomplete rhenopterid assigned to leiopterella tetliei gen et sp nov is characterized by its broad turbinate carapace and lack of cuticular sculpture this assemblage provides the first canadian record of pagea and the youngest occurrence of a rhenopterid outside the rheno hercynian terrane indicating that these taxa were more geographically widespread than previously supposed

mineralogical mapping of scanning electron micrographs abstract a technique is described to map regions of back scattered scanning electron images according to the mineralogy of the specimen such a technique may be used to study in detail the micro mineralogy of geological materials in particular the size shape and distribution of the individual components may be studied such information could provide additional evidence on the origin and nature of such materials composite multi layered images are constructed from both back scattered images and x ray maps of the same area of relevant elements training areas representative of the different mineral classes present are defined and the statistics within these areas are used to classify the whole image changes in classification parameters appear to have little effect on the determined composition segmentation of an image by this means is superior to techniques using a single image following segmentation particle size parameters for the constituent mineral grains may be determined examples showing different size frequency distributions for the different minerals are included several practical points on the use of the method are also covered

gigantopteris schenk ex yabe in the capitanian wuchiapingian middle late permian flora of central shanxi in north china palaeobiogeographical and palaeoecological implications abstract the concept of the cathaysian flora was originally based on fossils from the permian of central shanxi province in north china but is now recognized to be valid for the flora of much of east asia during the carboniferous and permian periods although gigantopteris schenck ex yabe is characteristic and often distinctive of the cathaysian flora in general it has previously not been recorded in shanxi province within the central part of the north china recent investigations on the capitanian wuchiapingian middle late permian flora of the taiyuan east hill coalfield in shanxi have yielded well preserved specimens of gigantopteris dictyophylloides gu and zhi within the upper shihhotse formation contained within continental red beds interpreted as representing a floodplain environment discovery of g dictyophylloides extends the palaeogeographic distribution of the genus and shows that the permian flora of shanxi is more typical of the cathaysian flora than previously thought results also provide new information on the ecology of g dictyophylloides based on assessments of its occurrence within depositional sedimentary facies from which we conclude that this species thrived in alluvial fluvial sediments on the north china block we also conclude that the red beds of the upper shihhotse formation that yield gigantopterids most likely formed under a seasonally dry climate rather than a vague statement that these red beds were formed generally under arid conditions as previously thought

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

mineralogy of fine grained sediment by energy dispersive spectrometry eds image analysis a methodology the application of energy dispersive x ray eds spectrometry image analyses to geological geochemical and environmental studies is facilitated by recent increases in computer speed storage capacity and connectivity eds microbeam analyses provide digital element maps of mineral grains with brightness directly proportional to element abundance using computer based image analysis protocols combinations of eds element images can characterize grain mineralogy and quantify mineral abundance this approach is well suited to the analyses of fine sand and silt sized grains 0 425 0 010 mm a size fraction not amenable to quantification by other mineralogical analysis methods for this size range 50 to more than 300 grains can be readily mapped permitting mineral identification for concentrations 1 to be reliably distinguished

quantitative micro porosity and orientation analysis in soils and sediments a technique to quantify the fabric of soils and sediments involving image processing and analysis is described in this paper such techniques are becoming popular in the earth sciences but unlike most other studies which investigate the porosity of coarse grained sediments this method examines the fine porosity between clay size particles to be investigated the usual problems associated with thresholding a grey level image to provide the necessary binary image for analysis are partly overcome by the use of wiener filtering methods to remove much of the degradation inherent in all imaging systems a new algorithm based on the relative contrast histogram method is then used to determine the optimum value at which to set the threshold the micro porosity determined is in good agreement with gravimetric porosity measurements unlike normal methods once the procedure has been initiated no further action is required from the operator and the method can thus be used for batch processing of large numbers of images thereby enhancing the statistical reliability of the results extensions of the technique allow for the variation in micro porosity from one region of a specimen to another to be studied further by segmenting the original image into domains of sub parallel particles it is possible to examine the intra domain porosity contrary to expectations the porosity in horizontal domains is greater than that in the vertical domains

desiccation of late quaternary inner shelf sediments microfabric observations abstract palaeo desiccated crusts often form at the top of pre holocene shelf sediments during low sea level stands resulting in significant changes in the mechanical properties to assist in understanding these changes and the implications for quaternary geology the microfabric of sediment samples from the inner shelf off hong kong has been studied using scanning electron microscope techniques incorporating the latest methods of quantitative image analysis these studies have been supported by petrographic observations and chemical analyses of the pore fluids holocene marine sediments usually have a honeycomb fabric while pre holocene marine sediments are more compact in regions of high clay content the palaeo desiccated crust often possesses large planar voids filled with coarse silt sized particles this desiccated crust often contains relics of root traces filled with pyrite showing varying degrees of oxidation the release of amorphous iron acts as a cementation agent and binds large silt small sand grains giving a more compact fabric than that in neighbouring regions cementation in the pre holocene marine deposits creates strengthened open fabric arrangements which may initially withstand moderate loads further evidence of desiccation comes from the presence of halite crystals in the pore fluid which has salt concentrations below that of normal sea water

quantitative orientation and micro porosity analysis of recent marine sediment microfabric abstract impregnated samples taken from three different post depositional regimes within the mariana mounds hydrothermal area in the mariana trough were observed in the back scattered mode in the sem intensity gradient orientation analysis methods have been adapted to study the orientation patterns within the sediments representing one of the first applications of such quantitative microfabric methods to the study of natural materials orientation was specified by two separate parameters an index of anisotropy and a direction of orientation the index is generally low for any single image but by plotting the direction and anisotropy as a vector centred on the relevant specimen co ordinates consistent patterns of orientation were observed in the samples differences between the orientation patterns from the three environmental regimes were noted a new dispersion ratio parameter was used to assess within sample variations in a complementary study objective thresholding methods based on kohler s relative histogram method were used to segment the images assessments of porosity showed differences which were generally consistent with the trends noted from orientation analysis while this paper uses image analysis techniques to examine deep sea sediments the methods of analysis described are equally applicable to sediments on the continental shelf

permo carboniferous paleogeography and coal accumulation and their tectonic control in the north and south china continental plates abstract permo carboniferous strata in north china and south china were essentially controlled by paleogeography paleoclimate and plate tectonics during that time north china and south china were separate microcontinents located on opposite sides of the equator thus the characteristics of their coal deposits differ substantially in north china the coal seams were initially deposited on a north sloping epicontinental basin during the middle carboniferous by the middle of the late permian the locus of coal formation had shifted from the north to the south as a result of the uplift of the northern margin due to continental collision with the siberian plate as the paleoplate was situated in the low northern latitudes moist tropical climate and favorable geographic setting allowed the extensive development of late carboniferous and earliest permian peat swamps on the northern alluvial fluvial plain and central paralic regimes more significantly two thick coal sequences were formed in the transition belt between the alluvial apron and fluvial plain and the shoreline area where high groundwatertable fed by both rainwater and groundwater favored the formation of thick peat in swamps with northward drift the paleoplate entered the subtropic semiarid and arid climatic belt between the late early permian and early late permian coal formation was restricted to the paralic delta plain where locally oceanic wet climate and high groundwatertable prevailed following this the subduction of the paleo tethys beneath the southern margin of north china led to the upwarp of the southern margin and kept the delta system growing vertically for a considerable period so that it kept pace with shoreline fluctuations on the southern area the result was that multicycle deltaic coals were well developed at this stage in south china coal was formed in the coastal zone of an epeiric and shelf sea which connected the marinal basins the basins were frequently influenced by plate marginal tectonic movements and continental rifting related to back arc extension as a result coal formation was often interrupted by sea level fluctuations early carboniferous coal was deposited during the short regressions during the widespread transgression mainly on the restricted marine paralic plain where clastic deposition was active in the middle and late carboniferous no coal was formed because the paleoplate had drifted into a subtropic arid belt early permian coal accumulated at first in the northeast and later in the southwest due to tectonic influences in the late permian relatively thick and extensive coal was formed even though it was during a transgressive period in both the western and eastern margins under the equatorial hot humid conditions in general the seam geometry and quality particularly ash and sulfur of the coal was directly controlled by the geography and the changes in the depositional environments however the fluctuation in coal formation and the migration of thicker coal zones was indirectly controlled by paleoclimate and the sea level fluctuations in response to plate tectonic influences

buried or brined eurypterids and evaporites in the silurian appalachian basin abstract eurypterid bearing deposits from the late silurian appalachian basin are often interpreted as having been deposited under hypersaline conditions these interpretations are based on the close association of abundant eurypterid remains with evaporite deposits and structures such as salt hoppers in the salina and bertie groups to determine whether this association reflects life habitat or is the result of taphonomic or diagenetic processes the co occurrence of eurypterids and salt hoppers in the upper silurian appalachian basin was examined at several stratigraphic scales a survey of eurypterid remains from the prolific ellicott creek breccia member of the fiddler s green formation bertie group found that 2 of the 479 specimens surveyed are crosscut by salt hoppers or incipient halite structures in a regional survey displacive salt hoppers occurred in the same bed as eurypterid remains in 37 19 51 of all eurypterid bearing units in these units salt hoppers were typically the only structures found intimately associated with eurypterids sometimes crosscutting them the disruptive nature of the hoppers in the ellicott creek breccia for example suggests that they formed within the sediment rather than at the air water interface and that organic remains might have acted as nucleation points for developing halite crystals to explain these associations we present a depositional model in which displacive salt hoppers formed within nacl saturated groundwater as a result of surface evaporation in the vadose zone during regressive phases and only after eurypterid remains were buried in this scenario the intimate association of eurypterids and salt hoppers in these deposits reflects early stage diagenetic overprinting rather than conditions during life our model largely refutes the hypothesis that eurypterids were halotolerant organisms based on their co occurrence with salt hoppers we conclude that eurypterids preserved in upper silurian carbonate ramp deposits were primarily denizens of more normal marine or hyposaline subtidal settings

exceptionally preserved late ordovician biotas from manitoba canada there are few body fossil biotas known from early paleozoic accretionary shorelines and very few examples of ordovician soft bodied assemblages this study documents two recently discovered biotas from separate sedimentary basins in manitoba canada that provide unique information about tropical shoreline communities shortly before the late ordovician extinction event each site represents a distinct depositional environment but they share biotic elements including eurypterids xiphosurids and large problematic tubes the william lake biota representing more restricted conditions includes jellyfish that are among the best hydromedusan body fossils known rocks at the airport cove site deposited under more open circulation contain scolecodonts and noncalcified algae these biotas have some parallels with the recently described middle ordovician winneshiek lagerstatte but are also similar to some late silurian assemblages considered together early paleozoic marginal marine deposits are a rich but as yet poorly known source of paleobiodiversity data

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

yangquanoxylon miscellum gen nov et sp nov a gymnospermous wood from the upper pennsylvanian lower permian taiyuan formation of yangquan city shanxi province with reference to the palaeoclimate in north china a silicified gymnospermous wood yangquanoxylon miscellum gen nov et sp nov is described from the upper pennsylvanian lower permian taiyuan formation yangquan city shanxi province north china the pycnoxylic wood is composed of thick walled tracheids and thin walled rays it is characterized by mixed radial tracheid pits uniseriate and homogeneous rays occurrence of scalariform radial pitting and various types of cross field pitting there are four types of cross field pitting in y miscellum gen nov et sp nov including simple taxodioid phyllocladoid and araucarioid the absence of growth rings within fossil woods described here and reported previously from north china suggests a humid climate with minimal precipitation variations during the late pennsylvanian early permian

the winneshiek biota exceptionally well preserved fossils in a middle ordovician impact crater the winneshiek shale middle ordovician darriwilian was deposited in a meteorite crater the decorah impact structure in ne iowa this crater is 5 6 km in diameter and penetrates cambrian and ordovician cratonic strata it was probably situated close to land in an embayment connected to the epicontinental sea typical shelly marine taxa are absent the konservat lagerstatte within the winneshiek shale is important because it represents an interval when exceptional preservation is rare the biota includes the earliest eurypterid a giant form as well as a new basal chelicerate and the earliest ceratiocarid phyllocarid conodonts some of giant size occur as bedding plane assemblages bromalites and rarer elements including a linguloid brachiopod and a probable jawless fish are also present similar fossils occur in the coeval ames impact structure in oklahoma demonstrating that meteorite craters represent a novel and under recognized setting for konservat lagerstatten

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

revised stratigraphy and relationships of lower palaeozoic rocks eastern taurus mountains south central turkey lithostratigraphic terminology is revised for rocks of ordovician age in the eastern taurus the seydisehir formation of late middle cambrian to early ordovician age is shown to be applicable in the eastern and western taurus as well as in south eastern turkey near deg irmentas northeast of adana the seydisehir formation is overlain with inferred unconformity by clastic strata of ashgill age referred to the ort tepe formation first defined south of hakk ri in the border folds of southeastern turkey palaeontological evidence is cited for the early silurian llandovery age of the unconformably overlying halityayla formation farther south on the coast near ovacik where the ort tepe formation is as yet unrecorded a general model is proposed showing relationships of cambrian and ordovician rocks and faunas in southern and southeastern turkey