encrusting corals on a latest ordovician to earliest silurian rocky shore southwest hudson bay manitoba canada paleozoic tabulate corals are generally thought to have been free standing a flattened disc shaped to dome shaped morphology providing a degree of stability in shallow water high energy environments the ability to encrust has previously been suggested by patterns of competitive overgrowth in certain species definite proof of encrustation by favositid corals is exhibited in an extraordinary example of an ancient rocky shore exposed for 350 m on hudson bay near churchill manitoba carbonate strata attributed to the upper ordovician port nelson or lower silurian severn river formations locally transgress a massive precambrian quartzite an ancient shoreface is clearly marked by large smoothly eroded boulders of the dark quartzite commonly 2 10 m in diameter the boulders are buried in coarse carbonate debris but corals up to 20 cm in diameter are found cemented directly onto the surface of some boulders deep pitting of many boulders to a depth of 2 3 cm was contemporaneous and may have been promoted by unpreserved encrusters such as sponges or anemones

interferometer studies of equatorial f region irregularities and drifts a radar interferometer technique developed at jicamarca peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial f region our first results have shown that the most turbulent echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east west direction this slab may very well be the wall of a depleted region a plasma bubble sometimes the irregularities can be tracked as they move eastward or westward velocity profiles for the evening period obtained in this way show a strong shear with westward velocities at the lowest altitudes observed and eastward velocities above a plausible explanation for this shear is that the westward drifts are driven by electric fields produced by westward e region winds and mapped up along magnetic field lines while at higher heights where the electron density is greater the drifts are controlled by the f region dynamo driven by eastward winds

morphology faunas and genesis of ordovician hardgrounds from southern ontario canada abstract we have used associations of different microfacies to define facies or microfacies associations which form reasonably well defined sequences which we infer from analogies with recent and ancient carbonate environments to have been deposited in a shelf environment characterized by small scale topographic differentiation into shoal slope and basinal environments shoal environments are characterized by typically cross bedded well sorted bioclastic sands with intershoal areas consisting of interbedded bioclastic sands and heavily bioturbated finer grained carbonates slope and basinal environments are typically represented by proximal and distal cycles respectively these we compare with deposits of carbonate ramp bypass channels and with the more thoroughly studied deep water clastic submarine fans many of the strong variations in environmental energy in these proximal and distal cycles can be attributed to migration of channels on the fans and the effect of funnelling of storm surges down the channels although hardground morphology and faunas are mostly related to local effects such as intensity of scouring time of exposure topographic differentiation of the surface and other factors differing hardground types tend to be found in different environments smooth and rolling hardgrounds occur in the deeper distal environments where the beds were subject to only slight scour and often limited exposure before renewed sedimentation hummocky and undercut hardgrounds are characteristic of the middle parts of proximal cycles where they developed marginally to the main bypass channel and in intershoal areas both these areas are sites of intermittent sedimentation and moderate turbulence where cemented beds may be exposed for some time in environments optimal for attached benthos these hardgrounds usually contain the most diverse hardground biotas pebbly and reworked hardgrounds occur in coarse basal units of proximal cycles which are interpreted as the grain flow fillings of the central parts of bypass channels though isolated examples occur in intershoal areas and in the higher parts of proximal channels these hardgrounds contain low diversity faunas reflecting the stresses imposed by intermittent or constant abrasion though some contain more diverse faunal assemblages formed after redeposition

epibiotic relationships in mesoproterozoic fossil record gaoyuzhuang formation china epibiotic coccoid microfossils of probable cyanobacterial affinity were discovered in cherty stratiform stromatolites of the 1400 1500 ma gaoyuzhuang formation hebei province northern china sessile coccoids with polarized growth settled on cyanobacterial sheaths and developed dense populations these microfossils represent the earliest known occurrence of epibiosis in the fossil record with characteristics similar to those observed in modern aquatic environments the reported fossil epibionts are also the first known occurrence of proterozoic cyanobacteria of chamaesiphonalean affinity the presence of specialized epibiotic communities in gaoyuzhuang stromatolites demonstrates that epibiosis was well established and diversified by mesoproterozoic time reflecting early adaptation in response to competitive pressures for microbial attachment sites in ancient densely populated shallow water benthos or possibly the onset of specialized mutualistic relationships among cooccurring microorganisms

predatorial borings in late precambrian mineralized exoskeletons the late precambrian tube forming cloudina the earliest known animal to produce a mineralized exoskeleton shows evidence of having been attacked by shell boring organisms of more than 500 tubes from shaanxi province china 2 7 have rounded holes 40 to 400 micrometers in diameter the relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator selecting its prey for size if true this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the precambrian cambrian boundary

upper triassic norian cephalopod limestones of the hallstatt type oman norian crinoidal brachiopod limestones and cephalopod limestones of the hallstatt type occur as blocks in a hettangian calcareous breccia of the haliw formation in the oman mountains crinoidal and brachiopod packstones up to 12 m thick prevail in the lower part of the sequence and were deposited on a substrate of norian forereef breccia the overlying cephalopod wackestones up to 4 9 m thick have a basal white bed followed by red limestones with abundant planar and scalloped corroded surfaces and local stromatolites upward red nodular wackestones and finally slumped grey wackestones follow the analysis of geopetal fabrics in orientated samples shows that bedding of these facies is in fact inclined bedding inclinations varied between 15 and 29 in addition the restored dip directions demonstrate rotation indicating deposition on a gliding block the preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics such features generally interpreted as current induced are here interpreted as gravity induced the overall mud supported rock fabric thus indicates deposition under very low energy conditions the common mud supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags particularly in the crinoidal brachiopod facies and the lower stratigraphically condensed cephalopod limestones this indicates that deposition of lime mud alternated with periods of elevated current strength a comparison of the hallstatt type limestones and current influenced sediments on the northern slope of the little bahama bank suggests that condensed sequences of the hallstatt type are restricted to relatively shallow depths with strong fluctuation of contour following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean on steep slopes sediment bypassing may be an additional factor for stratigraphic condensation

paleokarst paleosol and rocky shore deposits at the mississippian pennsylvanian unconformity northwestern arkansas the mississippian pennsylvanian unconformity in northwestern arkansas contains pedogenically altered regolith preserved in low lying areas on paleokarst on the chesterian pitkin limestone the regolith is succeeded by transgressive rocky shore deposits of the cane hill member hale formation type morrowan pitkin cements reflect extensive meteoric phreatic diagenesis prior to karstiflcation and paleokarst features include large dissolution fragmented pitkin lithoclasts with numerous solution pipes on a low relief surface the overlying pedogenically altered regolith contains calcretized lithoclasts in clay matrix suggesting a shift from ever wet conditions to more seasonal rainfall prior to the pennsylvanian transgression that shift may represent local climatic change or short term fluctuations in mid carboniferous tropical climate the latter interpretation may support global climate models that predict warmer wetter tropics during periods of high latitude cooling basal cane hill strata consist of high energy shoreface boulder cobble conglomerate containing reworked pitkin clasts the conglomerate contains an unequivocal rockyshore community consisting of encrusting bryozoans and corals trypanites acrothoracican barnacle borings and possibly the earliest occurrence of gastrochaenolites preservation of poorly indurated paleosol beneath high energy transgressive deposits suggests very rapid transgression consistent with a glacio eustatic mechanism truncated pitkin strata were removed by karstification and subaerial erosion during the hiatus and not by erosion during transgression

late mississippian bryozoan microbial build ups on a drowned karst terrain port au port peninsula western newfoundland bryozoan and microbial carbonate build ups occur within the late mississippian mid visean codroy group on the port au port peninsula western newfoundland build ups formed only adjacent to a rocky cliffed shoreline filling narrow submerged palaeovalleys of a well developed late devonian early mississippian karst terrain the nearshore setting was a stressed environment as indicated by 1 the absence of normal marine biota such as corals echinoderms and calcareous algae 2 high numbers and low species diversity of dominant taxa bryozoans brachiopods and microbial communities and 3 abundant plant bearing siliciclastics deposited by the episodic influx of fresh water from adjacent uplands build up development was terminated by meramec time due to falling sea level and seaward progradation of terrestrial sediments preserved structural and constructional fabrics within the build ups include 1 thickets of bryozoans and microbial microthrombolites structurally enhanced by probable marine mg calcite and aragonite cements 2 multigeneration internal sediment and 3 small colonies of serpulid worms and terebratulid brachiopods submarine cementation within the build ups appears to have been abundant during arrested sedimentation whereas intermound sediments carbonates and siliciclastics were lithified only during burial diagenesis shallow burial fracturing stylolitization sulphide and sulphate mineralization and precipitation of phreatic iron poor calcite cement occurred during burial diagenesis codroy build ups are distinct from the more common mississippian mud mounds their internal characteristics and the geologic setting are more like other late palaeozoic and holocene bryozoan rich build ups

electrodynamics of the equatorial evening ionosphere 1 importance of winds in different regions the importance of winds at different altitudes and latitudes for the electrodynamics of the low latitude evening ionosphere is examined with a model of the global coupled ionosphere thermosphere system the model reproduces the main observed features of the evening equatorial plasma vortex and the prereversal enhancement pre of the vertical drift the electrodynamics is driven primarily by the zonal wind forced by the diurnally varying zonal pressure gradient force the zonal wind lags the zonal pressure gradient force owing to inertia when ion drag is important the time lag of the wind behind the pressure gradient force is shortened and the high altitude evening wind turns eastward earlier than the wind at lower altitudes where ion drag is less important therefore a vertical shear of the zonal wind tends to develop at altitudes around the transition between small and large ion drag at the bottom of the f region this wind shear is closely associated with the vertical shear in the zonal convection velocity that is part of the evening plasma vortex unlike previous studies we find that the winds driving the pre lie mainly on field lines with apexes above the peak of the equatorial f layer field lines that extend in magnetic latitude out to nearly 30 and encompass the entire evening equatorial ionization anomaly region contrary to previous suggestions the westward convection in the bottomside of the evening plasma vortex is found to weaken rather than strengthen the pre daytime winds have relatively little influence on the low latitude evening electrodynamics

on the generation and growth of equatorial backscatter plumes 2 structuring of the west walls of upwellings the west wall of large scale upwellings that develop in the bottomside of the nighttime equatorial f layer becomes structured by the wind driven gradient drift instability the same process that leads to the formation of striations in barium ion clouds upwellings are initiated by wavelike perturbations with long spatial wavelengths 400 km and are amplified by the collisional rayleigh taylor instability and sometimes assisted by the gradient drift instability in the case of an upward moving f layer the west wall structuring process is driven by an eastward neutral wind enhanced by reduced drag during the postsunset hours and a velocity shear in east west bulk plasma drift in the bottomside f layer west wall structures evolve in a manner analogous to primary plasma bubbles i e secondary plasma bubbles grow from the west wall their characteristics are compared with those of the primary bubbles and discussed in the light of existing theories

colonization of rugose corals by diverse epibionts dominance and syn vivo encrustation in a middle devonian givetian soft bottom habitat of the holy cross mountains poland abstract middle devonian givetian rugose corals from the holy cross mountains miloszow poland have been analysed with respect to epibiont colonization patterns solitary microconchid tubeworms and colonial bryozoans hederelloids and ascodictyids numerically dominate on the coral hosts moreover the same taxonomic groups of epibionts dominate both the larger heliophyllum acanthophyllum stringophyllum ceratophyllum cystiphylloides and smaller thamnophyllum corallites indicating the true pattern of epibiosis was achieved the presence of common bioclaustrated epibionts constricted and rejuvenated coral calyces as well as epibionts growing concordantly with the host s growth direction indicate that at least some corals were colonized during life the observed low number of overgrowth cases of various epibionts on coral hosts suggests that competition for hard substrate was negligible most probably due to abundant coral substrates on muddy sea bottom of the givetian sea at miloszow this epibiont community is similar to other known devonian encrusting communities which likely developed in a more nutrient rich palaeoenvironments and differs markedly from taxonomically poor assemblages developing in a more oligotrophic conditions the presence of rothpletzella encruster which is considered to be related to green algae indicates that the miloszow coral community dwelled within the limits of the photic zone

epibionts on shells in the sarka formation a sparsely occupied niche in the lower to middle darriwilian oretanian ordovician in the prague basin czech republic abstract epizoic invertebrates attached to shells are a rare component of the fauna of the sarka formation middle ordovician early to middle darriwilian of the prague basin barrandian area in the czech republic epibionts are known exclusively from siliceous nodules and consist of echinoderms edrioasteroids and possible crinoid holdfasts monoplacophorans and bryozoans all attached to a very small number of host taxa among them hyoliths are the strongly preferred substrate 60 of observed host shells with edrioasteroids possible crinoid holdfasts and the monoplacophoran pygmaeoconus attaching exclusively to these organisms epizoan holdfasts were also found on a unique ramose problematic fossil considered to be the first octocoral specimen from the sarka formation most of the host are interpreted have been colonized during life only a few shells were used for attachment post mortem all epibionts are attached to the outer surface of the shell with the exception of the monoplacophoran barrandicella which is attached to the internal surface of empty conulariid thecae some of the epibionts shed additional light on the mode of life of their hosts including the bivalve redonia which is shown to be semi infaunal rather than infaunal more generally epibionts in the sarka formation attest to a very low level of occupancy of this significant niche during the early stages of the great ordovician biodiversification event

disorientation of corals in late ordovician lime mudstone a case for ephemeral biodegradable substrate abstract massive coralla representing the tabulate coral agetolites occur on a lime mudstone bed in the upper ordovician xiazhen formation of southeastern china other fossils include solitary rugose corals bryozoans trilobites and mollusks in addition abundant spicules and spicule networks suggest that sponges were widespread the occurrence of intact unabraded fossils in micritic matrix and the absence of high energy sedimentary structures indicate deposition in low energy conditions thin section analysis of disoriented specimens demonstrates that geopetal indicators are consistent with stratigraphic up and differ from the growth axes of the corals implying that geopetal infillings formed after disorientation the growth axes of coralla were not redirected during life suggesting that the corals were either dead at the time of disorientation or died as a result of disorientation an examination of cyclomorphism indicates that the corals died at different times rather than during a single event a close association between sponges and corals is suggested by the presence of spicule networks in calices and intracorallum spaces of agetolites it is hypothesized that disorientation of corals was related to growth on biodegradable substrates we suggest that many coral larvae settled on sponges that formed sponge meadows disorientation of the resulting corals may have occurred when 1 a host sponge could no longer support the weight of a coral and collapsed 2 increasing weight or imbalance of a coral caused it to fall off the sponge or 3 a coral became detached when the sponge died and decomposed if the coral was alive sudden deposition in a disoriented position within muddy sediment resulted in its death disorientation of massive skeletons such as colonial coralla is most commonly attributed to water energy this study suggests that ephemeral substrates may have been involved in some cases

genesis and environmental significance of upper cretaceous shell concentrations from the cauvery basin southern india abstract upper cretaceous shallow marine calcarenites of the upper campanian maastrichtian kallankurichchi formation from the cauvery basin of southeastern india are rich in shell concentrations dominated by large bivalves with minor admixtures of brachiopods bryozoans and larger foraminifera rarely these concentrations occur as lenses or pavements but usually as beds 10 to 200 cm thick depending on the dominant skeletal elements five types of shell concentrations can be distinguished isognomon pycnodonte ceratostreon inoceramid platyceramus cataceramus and polyspecific concentrations these shell concentrations occur in various preservational states which reflect the gradual mixing and mechanical destruction of former communities analysis of the taphonomic signatures of their components and of the biofabric suggests that storm induced waves and currents reduced sediment input the settling behaviour of taxa and a high rate of production of biogenic hardparts were responsible in varying degrees for the formation of the various shell concentrations accordingly they can be classified as storm wave proximal tempestite and primary biogenic concentrations the shell concentrations formed below fair weather wave base in shallow subtropical low stress environments

a stepped karst unconformity as an early silurian rocky shoreline in guizhou province south china abstract where succeeded by marine strata karst unconformities signify a former rocky coastline such relationships may help sort out relative sea level changes and aspects of local geography controlling facies distribution an exceptional example of an early silurian karst shore is well exposed near the village of wudang in central guizhou province near the capital city of guiyang in south china here the lower silurian kaochaitien formation oversteps 63 m of paleotopographic relief in limestones belonging to the llanvirn guniutan formation and caradoc to early ashgill huanghuachong formation ordovician the corresponding rise in sea level took place coeval with tectonic uplift as confirmed by a regionally diachronous relationship in the ordovician silurian boundary across a 250 km track from central to northern guizhou province the change in sea level also fits with a global rise of sea level in late aeronian later llandovery early silurian time borings of the ichnofossil trypanites are reported from the karst surface of the huanghuachong formation and silurian strata fill sink holes in this unit over 5 m deep the silurian karst shoreline near wudang is integrated with other regional data to construct a paleogeographic map covering the northern half of guizhou province

late ordovician solitary rugose corals preserved in life position two late ordovician unattached solitary rugose corals from the beaverfoot formation in southeastern british columbia were almost certainly preserved in life position these unique specimens occur beneath large colonial corals and were thus shielded from high energy events that overturned and transported other individuals they confirm previous hypotheses that greatly curved solitary corals lay in the sediment with concave sides facing up and at least partly exposed whereas slightly curved forms were oriented in more upright positions

record of microendoliths in different facies of the upper ordovician in the cincinnati arch region usa the early history of light related microendolithic zonation abstract this study provides the first documentation of microendolithic borings made by cyanobacteria algae and fungi in invertebrate skeletons from the late ordovician of eastern north america samples from the upper mohawkian to cincinnatian series katian stage caradoc to lower ashgill of traditional usage limestones and calcareous shales of ohio indiana and kentucky were selected for study because of the excellent preservation of fossil shell material the substrates mostly are brachiopods and corals strata of the mohawkian lexington limestone and cincinnatian kope formation maysville and richmond groups have been recently studied in terms of facies sequence stratigraphy and paleoenvironments which facilitates a reliable comparison of the distribution of microborings and inferred environmental settings especially relative paleobathymetry this paper reports the first occurrence of 10 ichnospecies plus various conchocelis traces in late ordovician cincinnatian marine shells these traces have been previously observed in shells from younger geological periods their modern counterparts are produced by species of cyanobacteria green algae red algae and heterotrophic microendoliths considering the bathymetric index ichnocoenoses of microendoliths defined for the later phanerozoic it appears that only one or two light related bathymetric zones can be recognized in a few samples from the upper ordovician cincinnatian of ohio and kentucky but not in all deposits where they might have been expected the shallow euphotic zone iii and with less certainty the deep euphotic zone on the contrary our samples from the underlying lexington formation contain only borings of worms macrotubular form and some forms with unknown producers although they were collected in facies realms comparable to the younger samples given the present state of knowledge the best explanation for the appearance of these 10 ichnospecies and the first bathymetric index ichnocoenoses within the late ordovician is that they represent the early evolution of microendolithic ichnospecies and early emplacement of ichnocoenoses

orientation studies of waterlogged wood a paleocurrent indicator abstract fossil wood has been used extensively as a paleocurrent indicator and published evidence suggests that it may be aligned either parallel or perpendicular to a unidirectional current flume experiments on deposition of waterlogged wood show that most fragments are aligned parallel to the current for fragments with a high degree of symmetry however a perpendicular orientation is possible the dominant factors in controlling the orientation of wood fragments appear to be current velocity fragment shape and fragment size

taphonomy of holocene cryptic biotas from st croix virgin islands information loss and preservational biases surveys of submarine caves and overhanging ledges from st croix virgin islands provide new insights into the preservational processes active therein and into the taphonomy of ancient counterparts comparisons of preservable skeletonized versus nonpreservable unskeletonized components of these modern cryptic communities indicate that there is significant information loss in areals coverage taxonomic richness and diversity of fossilized examples quantitative estimates of such losses have been made in addition skeletal differences between early and late stage successional groups suggest biased representation of the former in the geologic record nonpreservable later colonizers may further erase the record of skeletonized forms through destructive life processes such forms of taphonomic information loss are probable in ancient counterparts and must be considered in accurate reconstruction of cryptic paleocommunities

paleoecology and sedimentary environment of the late devonian coral biostrome from the central devonian field russia the upper frasnian coral biostrome well exposed in the russkiy brod quarry central devonian field russia has been studied in detail with respect to paleoecology and sedimentary environment the biostrome formed by auloporid tabulates and solitary and colonial rugose corals originated in an offshore environment characterized by calmer periods with slow or halted sedimentation and more energetic periods when sedimentation rate increased the episodic higher sediment influx and stronger hydrodynamic regime are not only well expressed in the microfacies but also in the variability of colony integration of the rugose corals observed even within single coralla distinct development of constrictions rejuvenescences and deflection of growth directions in rugose corallites may also indicate unstable sedimentary conditions the latter features however may have in part also resulted from syn vivo biotic interaction with the associated auloporids both the facies and paleontological observations suggest that the biostrome originated by the colonization of deposited bioclasts by pioneering auloporids creating the framework for settlement of later generations of auloporids and rugose corals apart from abundant auloporids representing a single species and associated rugose corals the other encrusters are not numerous and poorly diversified represented by dominating foraminifers followed by single species of productid brachiopods stromatoporoids microconchids and cornulitids the coral associated macrobenthos has similarly a low diversity being represented by single species of spiriferid and rhynchonellid brachiopods and gastropods being developed in an offshore carbonate sedimentary system devoid of any organic rich deposits and characterized by extremely low abundance and diversity of suspension feeding organisms the biostrome is considered to have originated in a low productivity oligotrophic environment strictly dominated by heterozoan coral communities its development in a well oxygenated oligotrophic environment during the time when organic rich black kellwasser facies developed elsewhere additionally attests for multi causal scenarios for the frasnian famennian event during which other factors were responsible in different paleogeographic and facies settings

postsunset vortex in equatorial f region plasma drifts and implications for bottomside spread f recent high resolution incoherent scatter drift measurements conducted at jicamarca during solar minimum conditions indicate that a vortical plasma flow pattern accompanies the well known prereversal enhancement events observed in the equatorial f region the vortex is centered at 250 km altitude and about 2000 3000 km east of the evening terminator and is characterized by upward and downward flows to the west and to the east and eastward and westward flows on the top and the bottom respectively postsunset bottomside spread f events are observed to commence in the interior of the vortex in regions of westward plasma drifts the formation of the vortex implies localized charging of the postsunset bottomside f region in response to eastward neutral wind driven f region dynamo action

cryptic encrusting communities in a middle devonian mesophotic paleoenvironment of the holy cross mountains poland abstract the middle devonian givetian chaetetid sponges and alveolitid tabulate corals that inhabited mesophotic paleoenvironments of the southern shelf of laurussia holy cross mountains poland have been studied with respect to encrustation patterns these epibiotic communities are characterized by modest diversity and high dominance and show distinct polarization with respect to the exposed and cryptic sides of the host s skeletons the most abundant davidsoniid brachiopods and microconchids show strong preferences toward the lower cryptic sides while auloporid tabulate corals dominate on the exposed sides of the hosts the remaining and much rarer epibionts cornulitids and rugose corals show no clear preferences in some shallow water silurian paleoenvironments auloporids are known to dominate the cryptic sides of the hosts thus considering the auloporid tabulates as photosymbiotic corals their absence or rarity in the middle devonian cryptic habitats might have resulted from insufficient irradiance levels in otherwise depleted light conditions as a result the available space and lack or lower competition for the area with faster growing colonial auloporids enabled solitary encrusters to colonize the cryptic niches the scarce bioerosion traces and rather low diversity of epibionts in our case may indicate that these mesophotic reefs developed in a nutrient poor oligotrophic habitats the davidsoniid dominated cryptic encrusting communities were widespread in some paleoenvironments during the middle devonian being known from both laurussia and south china craton however such mesophotic cryptic communities characterized by distinct polarization in comparison to open surface environments contrast with other givetian deep water aphotic cryptic communities reported so far where such polarization is hardly visible

neoproterozoic reef microstructures from the little dal group northwestern canada basinal facies in the neoproterozoic little dal group contain large reefs up to 300 m in height and 8 km in diameter in contrast to the stromatolitic composition typical of earlier proterozoic buildups little dal reefs consist mainly of three different calcareous microfossils a tubule thread microfossil analogous to the calcimicrobe girvanella in paleozoic reefs formed laminar reticulate structures like those in ordovician bioherms a clotted to saccate microfossil comparable morphologically to paleozoic renalcis constructed botryoidal to encrusting masses an enigmatic component of multicellular appearance that has attributes of an early calcified metaphyte exhibits the encrusting sheetlike habit characteristic of middle to late paleozoic algae these reefs represent an intermediate stage between proterozoic stromatolitic buildups and paleozoic metazoan calcimicrobial reefs and biogenic mounds

stromatolites from the 3 300 3 500 myr swaziland supergroup barberton mountain land south africa a morphologically variable assemblage of stromatolites has been discovered in thin chert layers within the fig tree group of the swaziland supergroup south africa they are commonly low relief nearly stratiform laterally linked domes rarer forms include pseudocolumns and crinkly stratiform stromatolites the stromatolites grew on a substrate of altered komatiitic lava and sediments deposited on the lava surface and in most places are covered by later komatiitic flows abundant fine grained tourmaline included within the stromatolite laminae suggests that stromatolites formed in an environment dominated by boron rich hot spring emissions and evaporitic brines

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

patterns in bioclastic accumulation through the phanerozoic changes in input or in destruction evolutionary changes in the ecology and diversity of organisms that produce and destroy calcareous skeletons suggest that bioclastic concentrations themselves might have changed in nature through the phanerozoic empirical data from marine siliciclastic records of ordovician silurian jurassic and neogene ages indicate a significant increase in the thickness of densely packed bioclastic concentrations over geologic time from a primarily thin bedded brachiopod dominated record in the ordovician silurian to a mollusk dominated record with many more and thicker shell beds in the neogene jurassic shell beds vary in thickness with the paleozoic or modern affinities of the chief constituents suggesting along with other evidence that the phanerozoic increase was determined neither by diagenesis nor by a shift in taphonomic conditions on the sea floor but rather by the evolution of bioclast producers namely groups with 1 more durable low organic skeletons 2 greater ecological success in high energy habitats and 3 on the basis of indirect evidence higher rates of carbonate production these results suggest that 1 reproductive and metabolic output has increased in benthic communities over time and 2 the scale of time averaging in benthic assemblages has increased owing to greater hard part durability of modern groups

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

west wall structuring of equatorial plasma bubbles simulated by three dimensional hirb model west wall structuring of plasma bubble plasma density depletions in the equatorial ionosphere or so called equatorial plasma bubbles epbs are generated in the post sunset period and tend to have a very complex spatial structure especially the east west asymmetry of epbs has been reported by various observations using a high resolution bubble hirb model which is a newly developed three dimensional numerical model for the equatorial ionosphere small scale structuring at the west wall of large scale f layer upwelling is clearly reproduced for the first time it is not an eastward neutral wind but a vertical shear of zonal plasma drift velocity at the bottomside of the f region that plays an important role in accelerating the instability growth at the west wall and generating the east west asymmetry of epbs

phosphatic hardgrounds and stromatolites from the limestone shale boundary section at prossilion maastrichtian paleocene in the parnassus ghiona zone central greece abstract sedimentological analysis of the limestone shale boundary section upper maastrichtian upper paleocene at prossilion parnassus ghiona zone revealed that the upper maastrichtian sediments represent a shallowing pelagic sequence towards the top the sequence becomes highly condensed and owing to interruption of deposition at the cretaceous tertiary boundary culminates in a hardground through early lithification boring and mineralization of the substratum by phosphates and iron oxides several sedimentological features led us to assume that cementation lithification of the sediments took place in a shallow submergent to periodically emergent setting stratiform and columnar laminated phosphatic stromatolitic crusts have developed on the bored pavements during the late early paleocene trapping the pelagic sediments deposited phosphate is considered to be supplied to the sediment by a bacterially controlled precipitation from interstitially circulated solutions both the uppermost maastrichtian layers and stromatolitic crusts are cross cut by a system of thin slightly sinuous sheaths or tubular structures interpreted as calcified filaments or rhizolitic structures this fact suggests prolonged subaerial exposure as a result of which pedogenic alteration of the already lithified sediments began by progressive reorganization of the substrata by soil forming processes crusts of cryptocrystalline phosphate formed corresponding to phoscrete formations

pliocene pleistocene rocky shorelines trace coastal development of bahia concepcion gulf coast of baja california sur mexico abstract pliocene rocky shore deposits on the east coast of baja california sur mexico formed under the influence of tectonic events and changing relative sea level in the gulf of california depositional patterns are represented by two distinct styles of marine transgression level bedded deposits in semi enclosed basins form steep buttress unconformities similar in profile to basin fill detected through seismic stratigraphy such deposits are typical of sheltered rocky shores where erosion of terrestrial materials is limited by low wave energy and or slow rates of changing sea level ramp deposits form low angle 5 9 unconformities on exposed rocky shores where erosion is enhanced by high wave energy and or rapid rates of changing sea level these conform to the pattern of coastal or marine onlap in seismic stratigraphy with an area of 270 km2 bahia concepcion is one of the largest fault bound bays in the gulf of california it occupies a half graben structure that opens on the gulf to the north an additional 100 km of coastline was formed after pliocene flooding of the bahia concepcion graben sheltered rocky shores are represented by buttress unconformities between miocene volcanics comondu group and upper pliocene strata in small connected basins at the southeast end of the bay dating is based on clypeaster marquerensis sand dollar and associated mollusks in limestones from the bahia concepcion member of the infierno formation other unconformities with the comondu on the open gulf coast adjacent to bahia concepcion take the form of carbonate ramps at punta chivato 20 km north of the bay mouth the san marcos formation is traditionally considered early pliocene in age based on clylpeaster bowersi echinoid and solenastrea fairbanksi coral at san nicolas 15 km east from the southern terminus of the bay c bowersi likewise dates the basal pliocene parallel to the axis of the bay the bahia concepcion fault zone is no older than the miocene because it cuts through the comondu group the main expansion zone for the protogulf jumped over this zone to the east where lower pliocene conglomerates were deposited on a faulted coast between punta chivato and san nicolas along this front eroded andesite cobbles predominate as a component of the basal pliocene but rare granodiorite cobbles indicate a cretaceous source brought to the surface from considerable depth punta chivato bahia concepcion and the san nicolas areas retain widespread upper pleistocene rocky shore deposits unconformable with pliocene strata or the miocene comondu granodiorites eroded from punta san antonio also form the basis for an upper pleistocene rocky shore these deposits usually are near the 12 m elevation regionally associated with substage 5e terraces 120 135 ka their uniformity in elevation inside and outside bahia concepcion indicates that minor tectonic uplift was locked in step throughout the immediate region by that time

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

cryptic coral crinoid hanging gardens from the middle devonian of southern morocco an unusual and exceptionally well preserved cryptic community of cnidarians crinoids sponges and microbes developed in a submarine cavity of middle devonian age in the hamar laghdad area morocco the biota encrusted the cavity roof and grew predominantly in an upside down position forming spectacular hanging gardens the investigated assemblage differs strikingly from both its paleozoic and modern analogues it constitutes one of a very few known examples of fossil cryptic assemblages developed in relatively deep water settings and is the first report of a cryptic paleoecosystem dominated by rugose corals the results support the view that during the middle paleozoic there was no distinct polarization between open surface and cryptic faunas in deep water environments but keen competition for space already existed in devonian cryptic assemblages the regional species pool seems to have been the main determinant of the ecological succession and structure of this cryptic community

temporal change as an aspect of biogenic shell utilization and damage pleistocene of north carolina u s a abstract sediments and fossils of the smith gut and beard creek members middle pleistocene flanner beach formation record the development of an interglacial predominantly softbottom estuarine basin that consisted first of open bay then more restricted bay closed lagoonal and finally open lagoonal settings as barrier islands formed to the east and partitioned this segment of the north carolina coast within this series of beds were found the remains of a sequence of benthic paleocommunities that changed through time in step with gradually changing properties of the surrounding environments such as salinity levels seasonality water depth and substrate textures as such this faunal transition is an example of community replacement the gradual to abrupt substitution of one community for another owing to directional habitat alterations this long term subevolutionary pattern of faunal change also was resolvable in a study of macroscopic epi and endozoans and signs of predation in autochthonous fossil shells open bay fossil associations contained a rich variety of encrusters borers and evidences of predator prey interactions the suceeding restricted bay associations contained fewer types of epi and endozoans at slightly higher stratigraphy levels bay associations were replaced by comparatively species poor high dominance closed lagoonal associations containing still fewer encrusters and no boring organisms and in the highest fossiliferous levels of the flanner beach open lagoonal associations became enriched in epi and endozoans but never reattained the diversity of forms seen at lower levels in open bay associations predation signs vary throughout the sequence in frequency of occurrence not in kind the sequential change in shell utilization by encrusters and borers described here does not resemble succession like sequences observed over short time spans involving hard substrates faunas but rather is a conformational transition controlled by long term environmental changes

were limpets or mosasaurs responsible for the perforations in the ammonite placenticeras abstract we present evidence defending the hypothesis that specimens of the ammonite placenticeras from the upper cretaceous bearpaw formation of southern alberta were preyed upon by mosasaurs perforations linked to diagenetic modification of limpet home scars are anomalous features that are rare in comparison to true tooth marks point loading of the ammonite phragmocone wall by mosasaur teeth produced distinct perforations without the development of long angular fractures this was due to low pressure and rate of loading permitted by the unusually loose articulation of the lower jaw of mosasaurs combined with the nearly uniform internal support of the shell wall by complexly fluted septa and their sutures in contrast the body chamber which lacked septal support except at its posterior end tended to shatter remnants of the body chamber preserve distinctive notches that resemble tooth marks and sometimes show evidence of healing thorough reassessment of the perforations and associated features indicates that the large majority of perforations in shells of placenticeras at least those from southern alberta are best explained by predatory activities of mosasaurs the currently popular hypothesis that all perforations preserved in shells of cretaceous ammonites were produced by sediment loading and collapse of limpet home scars fails to explain many diagnostic features of the perforations these include the shape siting and arrangements of perforations as well as the equal puncturing of all size classes of alleged limpet home scars the limpet hypothesis also fails to consider structural differences between shells of ammonoids and nautilus and erroneously assumes point loading by sediment compaction furthermore the extreme rarity of limpets that had the potential of excavating home scars in placenticeras from the upper cretaceous bearpaw formation of alberta canada cannot be attributed to preservational bias and is at odds with the large number of perforated specimens known from this formation the mosasaur bite hypothesis on the other hand accommodates all of these features

age of settlement and accumulation rate of submarine coralligene 10 to 60 m of the northwestern mediterranean sea relation to holocene rise in sea level morphological and chronological studies have been carried out on coralline algal buildups coralligene situated between 10 and 60 m depth near marseilles and in corsica france despite the presence of occasionally sizeable quantities of iron hydroxide these constructions prove to be a reliable material for radiocarbon dating ages obtained using this method range from 640 120 yrs b p corsica scandola natural reserve 15 m to 7760 80 yrs b p marseilles grand congloue 52 m internal erosion surfaces within the buildups give evidence of discontinuous development the accumulation rate of the coralligene constructions is very low 0 006 0 83 mm yr 1 according to the depth and time period the higher values 0 53 0 83 mm yr 1 were recorded for the deeper constructions they correspond to a period between 8000 and 6000 yrs b p after 6000 yrs b p the only appreciable accumulation rates 0 11 0 42 mm yr 1 were recorded for constructions situated between 10 and 35 m depth whereas the accumulation rates of deep coralligene 50 m appear to be low or zero the age of the large constructions overhang 80 cm in width is positively correlated with depth r 0 95 p 0 005 their development occurred during the flandrian transgression the oldest structures today situated at 50 to 60 m depth started to develop when water depth was probably no greater than 10 to 15 m apart from in strongly shaded fissures on rocky coasts and areas subjected to heavy sedimentation the main framework building algal species was initially mesophyllum lichenoides ellis lemoine a high tolerant species to light hydrodynamic energy and temperature with the rise in sea level the coralligene structure gradually became available to other less tolerant algal species lithophyllum lithothamnion and the crustforming population diversified because of the good preservation of coralligene structures the reliability of radiocarbon dating and the correlation between the age and bathymetric position of the large coralligene structures except in areas of heavy sedimentation and fissures in shallow rocky coasts these buildups are considered to be of use as biological indicators of variations in sea level

taphofacies models for epeiric sea environments middle paleozoic examples abstract skeletonized organic remains display various modes of occurrence which may be used to better understand the sedimentary dynamics of strata within which they occur aspects of skeleton biostratinomy and early diagenesis are distributed nonrandomly within the stratigraphic record and therefore are useful in discriminating taphonomic facies for purposes of taphonomic comparisons skeletonized marine taxa are reduced to five generally defined types massive arborescent univalved bivalved and multielement different skeletal types display different attributes which reflect specific responses to physical chemical and or biological processes the taphonomic properties of disarticulation reorientation and sorting fragmentation corrosion and abrasion skeletal dissolution and early diagenesis display patterns which are predictable with respect to a variety of inter related physico chemical parameters these can be quantified through indices which evaluate relative frequencies of occurrence sedimentary events alter the temporal and spatial homogeneity of processes which generate background taphofacies and superimpose event related properties thereby generating composite taphofacies such events produce taphonomic signature which in themselves correspond to specific environmental conditions i e water depth and event intensity indeed background and event related processes interact to generate complex but nonetheless diagnostic facies attributes useful in reconstructing paleoenvironments the comparison of standard indices among beds should allow the recognition of stratigraphic patterns and facilitate the diagnosis of systematic gradients among taphonomic properties deductively derived taphofacies models corroborated by empirical data from paleozoic strata illustrate the distribution of taphonomic properties with respect to environmental energy turbulence background sedimentation rate and sediment oxygenation these parameters also indirectly influence other less obvious factors including bioturbation and sediment chemistry trends in the distribution of taphonomic properties taphonomic gradients permit us to map otherwise unrecognized trends in these environmental parameters across a hypothetical onshore offshore transect within a generalized epeiric sea setting taphofacies models provide the quantifiable basis by which evolution of taphofacies may be gauged and then related to biotic and abiotic phenomena moreover taphofacies models evaluate the preservability of skeletal remains in different environmental settings and therefore provide information important in paleoecological studies

brief sea level fall event and centennial to millennial sea level variations during marine isotope stage 19 in osaka bay japan detailed sea level variation was investigated for marine isotope stage mis 19 based on diatom and grain size analyses of a marine sequence in a core of the osaka group diatom sea level proxies represent precession related signals correlated with highstands mis 19 3 and 19 1 and lowstand mis 19 2 astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka 1 a rapid sea level fall event was found in the earliest mis 19 demonstrated by several independent sea level proxies of diatom and grain size this event began with a rapid sea level drop followed by a gradual recovery at about 783 782 ka a maximum abundance of pelagic diatom taxa at a core depth of 402 20 m evidently shows the highest sea level peak in mis 19 supported by many other proxies based on the diatom data sea level change across mis 19 1 is characterized by centennial to millennial fluctuations the sea level fall event began just after the onset of a cooling event previously reported from the same core observations of a comparable sea level fall signal in many deep sea core records suggest the event is global

distribution of living and dead diatoms in tidal wetlands of northern japan relations to taphonomy abstract this paper presents the results of a survey of the contemporary diatom distributions in four tidal marshes of eastern hokkaido northern japan distribution of living diatom cells as defined by cluster analysis have relations to vegetation and substratum and clearly to tide level comparison between living and dead diatoms in each cluster provides synecological information relating to diatom taphonomy in the tidal wetland environments four assemblages are recognized and they are summarized as follows 1 an upland assemblage consisting of autochthonous freshwater diatoms adapted to relatively dry conditions 2 a high marsh assemblage formed at or slightly above mean high tide level mhtl with only few allochthonous components 3 a low marsh assemblage formed below mhtl dead valves within this assemblage are repeated widely redistributed by tidal processes this assemblage is therefore a mixed assemblage comprising a combination of allochthonous and autochthonous diatoms 4 a tidal flat assemblage on death diatom valves in tidal flat are immediately redistributed by tidal currents and the dead diatom assemblage here has the characteristics of an autochthonous or residual assemblage autecological perspectives based on the distribution patterns can advance these interpretations dead valves of the epiphytic diatom cocconeis scutellum which possesses a raphid valve r valve and a rapheless valve p valve are common on two transects but only p valves are widely distributed beyond the seaweed zone which represents the actual habitat of this species such selective processes are related mainly to the life form characteristics of monoraphid species only r valves remain attached to their substratum on death the tychoplankton paralia sp is also a widely distributed species in the case of paralia their long chains float more readily than other specimens are transported easily by tidal currents and then trapped in entire tidal environments these observations suggest it is likely that concentrations of only p valves of c scutellum or paralia in the tidal marsh deposits should be treated as allochthonous components in the diatom assemblage

palaeoecological evidence for early aragonite dissolution in ancient calcite seas it has been proposed that shallow carbonate seas of upper ordovician and jurassic ages precipitated calcite as the primary calcium carbonate phase1 3 unlike such settings today it is expected that such seas were undersaturated with respect to the more soluble aragonite so that aragonitic invertebrate skeletons would have tended to dissolve here we describe examples in which this seems to have been the case our evidence consists of submarine cemented horizons in which aragonite fossils have been dissolved out to leave open moulds the walls of the moulds are encrusted by contemporaneous organisms confirming the early timing of the aragonite dissolution

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

directional orientations of solitary rugose corals unattached solitary rugose corals lying parallel to bedding are common in many ordovician and younger paleozoic units but their directional orientations have seldom been examined interpretations based on occurrences in north american upper ordovician and lower silurian strata provide a foundation for such studies distinct directional patterns resulted from preferred orientation with respect to water motion they indicate transportation rather than biologic orientation if it can be shown that the corals were not preserved in life position or were abraded to a significant degree before burial transported slightly curved specimens having trochoid to ceratoid form were aligned parallel to currents with the apex pointing upstream and or were rolled nearly perpendicular to currents or almost parallel to crests of advancing waves with the apex facing either way but directed slightly upstream therefore unimodal orientation patterns bimodal patterns with equal peaks that are opposite one another but

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

the cambrian substrate revolution and the early evolution of attachment in suspension feeding echinoderms abstract the cambrian characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time represents a pivotal point in the history of life this period also documents a major change in the nature of the sea floor neoproterozoic type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well developed mixed layer the effect of this transition on the ecology and evolution of benthic metazoans is termed the cambrian substrate revolution csr and this is thought to have impacted greatly on early suspension feeding echinoderms in particular according to this paradigm most echinoderms rested directly on non bioturbated soft substrates as sediment attachers and stickers during the cambrian epoch 2 as the substrates became increasingly disturbed by burrowing forming a progressively thickening mixed layer echinoderms developed new strategies for attaching to firm and hard substrates to test this model we evaluated the mode of attachment of 83 cambrian suspension feeding echinoderm species attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology these data were analyzed quantitatively to explore trends in attachment throughout the cambrian in contrast to previous studies the majority of cambrian clades eocrinoids helicoplacoids helicocystoids isorophid edrioasteroids and solutes are now interpreted as hard shelly substrate attachers only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures contrary to the predictions of the csr paradigm our study demonstrates that cambrian echinoderms were morphologically pre adapted to the substrate changes that occurred during the cambrian allowing them to fully exploit the appearance of hardgrounds in the furongian we find no support for the claim that the csr explains the peak in echinoderm diversity during cambrian epochs 2 3 or that it caused the extinction of helicoplacoids

paleoecology of gastropods preserved in turbiditic slope deposits from the upper pliocene of ecuador abstract upper pliocene gastropods preserved in turbiditic deposits from the upper onzole formation of northwestern ecuador provide an excellent window into the past for understanding paleoecological dynamics in deep water habitats such as shells used as substrata by epi and endobionts encrusters and bioeroders shell use by hermit crabs and predation shell repair and drilling just prior to the closing of the isthmus of panama previously paleoecological and taphonomic information was lacking for deep water mid to outer shelf and bathyal fossil gastropods in contrast to shallow water habitats that have been relatively well studied this study showed that while epibionts were relatively rare on the fossil shells because of curatorial bias endobionts bioeroders occurred on 51 of the 59 species examined of the bioeroders the trace fossil helicotaphrichnus commensalis was found on 27 of the species the presence of helicotaphrichnus indicates that hermit crabs were also a part of the deep water assemblage prior to burial by the turbidity flow although there are no body fossils of hermit crabs yet reported from this area using epi and endobiont criteria preserved on the shells the hermit crabs appeared to prefer shells that had large last whorl volumes recycling and retention of upper pliocene shells by recent hermit crabs biological remanie on the coast of ecuador also occurs which could lead to potential temporal anomalies in the fossil record in addition the trace fossil helicotaphrichnus is now reported for the first time from the upper pliocene of ecuador this trace fossil also occurred on bathyal shells suggesting that its bathymetric range may be much deeper than previously reported records of predation retained on the deep water fossils were common 66 of the species had shell repair 68 of the species had drilled shells and represented a variety of molluscivorous predators the durophagous predators e g crabs and drilling predators naticids octopods and muricids appeared to be selective in their choice of prey items high spired gastropods especially of the family turridae were statistically more likely to be affected by predators than all other prey species and groups examined shell architecture for other shell types examined however did not appear to affect the frequency of shell repair occurrence although predation is thought to be a generalist activity in deep water environments it may be that in certain areas specialist predators may be more common than previously considered thus fossil deep water communities may contain a rich legacy of paleoecological interactions that can then be used for evolutionary ecological questions pertaining to selective predation with depth variation in encrusters and bioeroders with depth and to compare differences in paleoecological structure of these molluscan communities before and after the closure of the isthmus of panama

ecological zonation during the carbonate transgression of a late ordovician rocky shore northeastern manitoba hudson bay canada late ordovician ashgillian carbonates belonging to the port nelson formation transgress a resistant rocky shore near churchill manitoba on the southwest flank of the hudson bay basin in canada examples of ancient rocky shores are very rare and this locality offers the first opportunity to document extensive offshore biological zonation with spatial reference to a well defined shoreline five biofacies zones are parallel to a 350 m long shoreface carved into the precambrian churchill quartzite eroded boulders of the dark quartzite blanket the shoreface and clast size is observed to decrease dramatically up section through 4 5 m of tan colored carbonates from an onshore to offshore position the ecological zones include 1 boulder encrusting favositid corals and a related high energy fauna 2 a shell pavement dominated by the inarticulate brahciopod monomerella 3 large free standing tabulate corals including palaeophyllum calapoecia and catenipora 4 tunneled trace fossils including chondritid thalassinoid and less common vertical volcano burrows and 5 surface cruziana burrows associated with rare large isotelid asaphacean trilobites siphuncular debris from aminocerid cephalopods abundantly scattered through zones 2 3 provides data on current orientation consistent with long shore drift a wide field of ripple marks preserved near the top of the stratigraphic sequence confirms that wave trains advanced shoreward at an indirect angle of about 45 although currents deflected by natural groin fields may have swept coarse clastics more seaward at some spots than others the biological zones are remarkably linear and persistent the churchill site is a comparatively simple case of landward migration by shore parallel biofacies primarily controlled by factors related to water depth and distance from shore this interpretation does not preclude the possibility that more random facies patterns may have existed in protected embayments or along more irregularly cliffed sectors of the ancient churchill coast

taphonomy of trace fossils at omission surfaces middle triassic east germany abstract in shallowing upward cycles of the east german thuringian muschelkalk middle triassic sedimentological probably storm events interrupted longer periods of low net sedimentation the ichnofauna changed with the diagenesis of the substrate it does not represent an ecological succession the presence of both firmground and hardground traces in the same samples indicates superimposed trypanites and glossifungites ichnofacies the ichnofabric of burrows was frozen by cementation during omission the amount of erosion controlling the preservation of the upper tiers borings in general both burrowing and boring has been intense but patchy and recruitment of tracemakers had been almost monospecific a hostile environment perhaps due to high salinity and or erosion may thus be assumed the type of preservation was governed by different reactions to sulphide production in different chemical microenvironments during early diagenesis in absence of significant amounts of iron h2s escaped into burrows or borings from the adjacent anaerobic sediment depending on local physicochemistry this resulted in calcite or pyrite precipitation well aerated parts of burrows facilitated the formation of celestite after reoxidation of sulphide on goethite encrusted hardgrounds pyrite rings were formed around numerous borings trapping the active h2s immediately after its formation these haloes were previously mistaken as excrements

fast thermospheric wind jet at the earth s dip equator 1 the thermospheric zonal wind forms a fast wind jet at the earth s dip equator instead of the geographic equator this remarkable feature is revealed in two sets of independent observations made two decades apart one is from the champ satellite during the year of 2002 and the other is from the de 2 satellite during aug 1981 feb 1983 both observations show that this wind jet is eastward at night with speed reaching 150 ms 1 and westward around noon with speed over 75 ms 1 these fast wind jets are observed during local times of fully developed equatorial ionization anomaly eia on the other hand a channel of slow wind is found on the dip equator during the period of 05 08 mlt which corresponds to local times before the eia develops these features strongly suggest the ion drag being the principle cause for shifting the wind jet from the geographic equator to the dip equator

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

teredolites wood substrates and sea level dynamics allochthonous logs and or teredolites clavate borings produced within xylic wood substrates occur in extraordinary abundance as sedimentary components in transgressive marine shelf deposits of the lower paleocene clayton formation in western alabama it is pro posed herein that the abundance and preservational state of these components were controlled by 1 an influx pulse of xylic substrates into marine and marginal marine environments 2 hydraulic concentration of substrates during ravinement and 3 condensation associated with sediment starvation all three of which are induced by sea level rise the proposed relations among fossil wood ichnofossils produced therein and sea level dynamics may be of use in the discrimination of sequence stratigraphic packages and their bounding surfaces these relations also have implications for paleobotanical prospecting and the biological evolution and stratigraphic distribution of marine organisms that inhabit xylic substrates

the development of a diatom based transfer function along the pacific coast of eastern hokkaido northern japan an aid in paleoseismic studies of the kuril subduction zone abstract this paper provides a dataset to develop a diatom based transfer function which is applicable to paleoseismic studies at southwestern kuril subduction zone northern japan modern diatom samples were collected from five transects from saltmarshes of lakes akkeshi and onnetoh along the pacific coast of eastern hokkaido the relationships between diatom species and environmental variables were elucidated by canonical correspondence analysis cca and partial ccas partial ccas associated with monte carlo permutation tests show that elevation accounts for a significant portion of the total variance in the diatom data therefore statistically significant transfer functions quantifying the relationship between modern diatom assemblages and elevation were developed using weighted averaging partial least squares and applied to fossil diatom assemblages from lake onnetoh the reconstructed curve of elevations contains five emergence and four submergence events and the transfer functions calculated the amplitude of four of the emergence events to be at least 1 m the results are consistent with paleoecological data produced by previous studies if these events represent uplift associated with interplate earthquake and subsidence during an interseismic period along the kuril subduction zone transfer functions of eastern hokkaido can contribute to reconstruction of the recurrence intervals and the amplitude of earthquakes