Shallow Subtidal Environments Research Articles

Petrology of the Eureka Quartzite (Middle and Late Ordovician), Utah and Nevada, U.S.A.

The Eureka Quartzite is a sheet-like quartzarenite up to 200-m thick that was deposited on the eastern shelf of the Cordilleran miogeocline from Canada to California. It is the only sandstone lithosome from the Middle Cambrian through Devonian succession in the Great Basin and is remarkable in its purity of detrital and authigenic quartz, scarcity of bedding, and heterogeneity of both grain packing and quartz cement abundance. Sand sources ranged from the Peace River Arch in Canada to the Transcontinental Arch in mid-continental North America. The Eureka represents a third-order regressive–transgressive stratigraphic sequence, although whether the regression formed in response to eustasy or epirogenic uplift of western North America is unresolved. The near absence of detrital clay, body fossils, and subaerial features in addition to the presence of herringbone cross-beds indicate that the Eureka was deposited in intertidal and shallow subtidal environments except for minor eolian deposits. Bioturbation destroyed most primary stratification, although discrete burrows are rare. Textural features of quartz (superb roundness, bean grain shape, crescentic impact scars) indicate a prolonged episode of eolian abrasion prior to marine deposition. Regionally the detrital composition is 99.5 percent detrital monocrystalline quartz, 0.5 percent K-feldspar and carbonate allochems, and a trace of heavy minerals. From 2 percent to 4 percent feldspar and carbonate allochems that were initially present have been replaced by quartz during burial. The chief authigenic phases are quartz overgrowths with minor calcite (now dolomite) and illite. Spheroidal and amoeboid calcite-cemented concretions up to 3 cm in diameter formed at shallow burial depths, but all carbonate in the concretions has been leached in outcrop. The heterogeneity of grain compaction and amount of quartz cement resulted in beds that range from semifriable to sedimentary quartzites in the same outcrop. Compaction by the combination of grain rearrangement, pressure dissolution, and grain fracturing generated anomalously low intergranular volumes that average 14 percent in Nevada and 21 percent in Utah. The normal evolution of microquartz overgrowths ( 10 μm) during cementation was retarded; consequently, microquartz and mesoquartz cement (80 percent) dominate over macroquartz (20 percent), and they are the only cements in the least-cemented beds and laminations. Illite co-precipitated with microquartz and impeded quartz cementation by coating quartz crystal faces. Despite reaching temperatures >135° C for ∼100 million years, much of the Eureka, especially in Utah, remains incompletely cemented and retains porosity of ∼2 percent. The chief cause of cement heterogeneity appears to be authigenic illite abundance. Pressure dissolution of quartz at shale beds and clay drapes that formed stylolites was the most likely major source of silica for quartz cement. Invasion by hydrocarbons and hydrogen sulfide (H2S) resulted in the reduction of iron in hematite grain coats on quartz grains, a remnant of their eolian dune formation, the bleaching of beds, and the generation of pyrite (now hematite). The abundance of iron that now resides in pyrite/hematite suggests that red beds were once widespread. Outcrop and near-outcrop processes generated Liesegang bands of iron oxide, desert varnish, “pockmarks” where carbonate cement in centimeter-scale concretions dissolved, hematite pseudomorphs of pyrite, and minor opal cement.

Tectonic triggering of slump sheets in the Upper Cretaceous carbonate succession of the Porto Selvaggio area (Salento peninsula, southern Italy): Synsedimentary tectonics in the Apulian Carbonate Platform

Soft-sediment deformation structures crop out in the Upper Cretaceous carbonate succession in Porto Selvaggio cove in the western Salento peninsula, Apulian foreland, southern Italy. The deformed interval is about 13m thick and occurs between shallow-water limestones and dolostones formed in peritidal and shallow subtidal environments. It comprises well-bedded grey mudstones interlayered with dark grey laminated microbioclastic wackestones characterized by couplets of closely spaced dark and bright laminae marked by the parallel orientation of calcareous microbioclasts and thin-shelled bivalves. The low biological diversity, scarcity of burrowing biota, and presence of a well preserved fish fauna provide evidence of anoxic conditions occurring in morphological depressions within the platform, and a stagnant, stratified water body affected by weak bottom currents, indicating the sudden development of a localised and short-lived intraplatform basin. Two soft-sediment deformation horizons (slump sheets) separated by undeformed limestones with similar facies occur in this part of the succession. The lower, thicker slump sheet (1.0–1.3m thick) contains asymmetric and box folds. Well-developed décollement surfaces (locally containing thick brecciated zones) cut the folds, forming small-scale thrust-sheets and indicating mixed plastic to brittle behaviour. The upper, thinner slump sheet (0.25–0.35m thick) contains only asymmetric folds, indicating plastic behaviour only. The differences in deformation style are attributed to differences in facies. Measurements of fold-axis orientations in the slump sheets show that they moved in similar directions, recording the development of a local, gently dipping palaeoslope. Autogenic (internal) trigger mechanisms are ruled out by a detailed consideration of facies. The slump sheets were triggered by allogenic, tectonic effects, either the weakening of sediment by seismic activity or the tectonically induced steepening of slopes, or a combination of both. Tectonically induced steepening is consistent with localised and sudden vertical facies changes related to the creation of an intraplatform basin. The occurrence of slump sheets in carbonate platform successions is unusual since carbonate platforms are normally associated with shelves or low-angle ramps.

Thick brachiopod shell concentrations from prodelta and siliciclastic ramp in a Tortonian Atlantic–Mediterranean strait (Miocene, Guadix Basin, southern Spain)

Carbonate production by brachiopods in shallow-water habitats is generally expected to be not sufficiently high and temporally persistent to allow them to form very thick and densely packed shell concentrations. The formation of thick brachiopod concentrations requires long-term persistence of populations with high density of individuals, and such circumstances are assumed to be rare especially during the Cenozoic. However, here we show that the large-sized brachiopod Terebratula terebratula, the most common species in benthic assemblages with epifaunal bivalves and irregular echinoids, formed several decameter- to meter-thick, densely packed concentrations in shallow siliciclastic, high-energy environments, in a seaway connecting the Atlantic Ocean with the Mediterranean Sea during the Latest Tortonian (Late Miocene, Guadix Basin, southern Spain). This brachiopod formed (1) meter-scale, thick, parautochthonous concentrations in a prodelta setting and (2) thin, mainly allochthonous, tide- and storm-reworked concentrations in megaripples and dunes. The abundance of brachiopods at the spatial scale of the Guadix Basin seems to be mainly related to intermediate levels of sedimentation rate and current velocity because abundance and thickness of shell concentrations decline both (1) in onshore direction towards delta foresets with high sedimentation rate generated by debris flows and (2) in offshore direction with increasing levels of tide- and storm-induced substrate instability. Although brachiopods in dune and megaripple deposits are more fragmented, disarticulated, and sorted, and have a higher pedicle/brachial valve ratio than in prodelta deposits, taphonomic damage is still relatively high in prodelta deposits. Terebratula terebratula thus formed thick concentrations in spite of that disintegration processes were relatively intense along the whole depositional gradient. Therefore, population dynamic of this species was probably characterized by production maxima that were comparable to some Cenozoic molluscs in terms of their productivity potential to form thick shell concentrations in shallow subtidal environments. We suggest that temporal changes in brachiopod carbonate production have a significant spatial and phylogenetic component because multiple large-sized species of the family Terebratulidae, which underwent radiation during the Cenozoic, attained high abundances and formed shell concentrations in temperate regions.

Palaeoecology of the Spathian Virgin Formation (Utah, USA) and its implications for the Early Triassic recovery

The Spathian (late Early Triassic) Virgin Formation of south-western Utah (U.S.A.) yields a comparatively diverse benthic fauna that flourished ~2 Ma after the end-Permian mass extinction. In this study, we present quantitative palaeoecological data, which are analysed in the context of their depositional environments. This integrated approach helps to discriminate between effects of the end-Permian mass extinction event and local environmental factors on alpha diversity and ecological structure of the Virgin Fauna. Shallow subtidal environments yield the highest species richness and lowest dominance values as recorded in two benthic associations, the Eumorphotis sp. A Association and the Protogusarella smithi Association, both of which contain 20 benthic species (bivalves, gastropods, brachiopods, echinoderms, and porifers). Tidal inlet deposits yield a low diverse fauna (Piarorhynchella triassica Association) with a very high dominance of filter feeders adapted to high energy conditions. Another comparably low diverse fauna is recorded by the Bakevellia exporrecta Association, which is recorded in deposits of the offshore transition zone, most likely reflecting unconsolidated substrates. A single sample containing five bivalve species (Bakevellia costata Assemblage) is recorded from a marginal-marine setting. The Virgin fauna yields a bulk diversity of 30 benthic species (22 genera) of body fossils and 14 ichnogenera and, thus, represents the most diverse marine bottom fauna known so far from the Early Triassic. Our results suggest that oceanographic conditions during the early Spathian enabled ecosystems to rediversify without major abiotic limitations. However, taxonomical differentiation between habitats was still low, indicating a time lag between increasing within-habitat diversity (alpha diversity) and the onset of taxonomical differentiation between habitats (beta diversity). We suggest that taxonomical habitat differentiation after mass extinction events starts only when within-habitat competition exceeds a certain threshold, which was not yet reached in the Spathian of the investigated area. This interpretation is an alternative to previous suggestions that the prevalence of generalistic taxa in the aftermath of mass extinction events reflects protracted environmental stress. The onset of increasing beta diversity is a potential criterion for distinguishing two major recovery phases, the first ending with habitat saturation and the second ending with the completion of ecosystem differentiation.

Marine benthic invertebrates from the Upper Jurassic of northern Ethiopia and their biogeographic affinities

We present the first modern description of corals, brachiopods and bivalves from the Antalo Limestone in the Mekele Outlier of northern Ethiopia. This fauna is largely of Oxfordian age and lived in shallow subtidal environments and in small patch reefs. In combining our new data with fossil occurrence data from the Paleobiology Database, we conducted multidimensional scaling analyses to assess biogeographic patterns and the delineation of the Ethiopian Province for the Callovian to Kimmeridgian stages. Results suggest that an Ethiopian Province is indeed evident for our focal groups, but this is more confined than traditionally assumed. The so defined Ethiopian Province includes Tunisia, the Levant, Arabia and much of East Africa, but excludes Tanzania and India. The special status of India and Tanzania is perhaps due to latitudinal gradients in faunal composition.

Origin and paleoecology of Middle Jurassic hiatus concretions from Poland

Bored and encrusted carbonate concretions, termed hiatus concretions, coming from the Middle Jurassic (Upper Bajocian and Bathonian) siliciclastics of the Polish Jura, south-central Poland, have been subjected to detailed paleoecological investigation for the first time. The concretions possess variable morphology and bear distinct traces of bioerosion and encrustation as a result of exhumation on the sea floor during intervals of low sedimentation and/or erosion. The borings are dominated by Gastrochaenolites and Entobia. Epilithozoans, represented by at least 26 taxa, are dominated by sabellid/serpulid worm tubes and bryozoans, while sponges and corals are minor. No relationship between the concretion size and the number of encrusters has been found, suggesting that concretion size was not the primary factor controlling diversity. Stable isotope analyses and the presence of crustacean scratch marks and Rhizocorallium traces on many of the hiatus concretions indicate that they formed just below the sediment–water interface, within the sulfate reduction zone. Moreover, crustacean activities may have been a prelude to their origin, as shapes of many concretions closely resemble thalassinoidean burrow systems. It is also possible that crustacean activity around the concretions promoted their exhumation by loosening the surrounding soft sediment. The presence of borings and encrusters on different concretion surfaces, as well as truncated borings and a number of abraded epilithozoans, indicate that after the concretions were exhumed they were repeatedly overturned and moved on the sea floor, probably due to episodic storm-related bottom currents in shallow subtidal environment.

Colonial form, free-living corals, and macroborers from the Pleistocene of South Florida

Study of corallum shape in free-living colonies of Manicina, Siderastrea and Solenastraea collected from the Pleistocene Bermont formation in southern Florida indicates that they were mobile, either self-righting ( Manicina), or rotatory ( Siderastrea and Solenastraea), with colony forms that are the result of movement during growth. In rotatory corals, growth of a radial and centrifugal nature away from the corallum center indicates that rolling was frequent enough to maintain the health of individual corallites along the skeleton's entire spherical surface, as postulated previously by several authors. Post-mortem sponge boring and boring of sipunculid worms and the bivalves Lithophaga and Gastrochaena during the life of these colonies were common. Colonization by barnacles during the life of some colonies also occurred, but they were generally overgrown. Boring of rotatory coralla decreased the mass of the skeleton and probably increased the ease and frequency of rolling of round colonies. The presence of these rotatory coralla strongly suggests that the lower Bermont sediments accumulated on and around shallow banks populated by numerous free-living corals and some fixed corals such as branching Porites, along with a diverse molluscan assemblage indicative of a Thalassia (turtle grass) community. The Pleistocene Bermont formation also contains numerous well-preserved colonies of Manicina areolata, indicative of deposition in shallow subtidal environments with abundant sea grass. This species was well-suited to life in this environment, and to overturning by current action, as it has the capacity to right itself after overturning, either biologically or hydrodynamically or both. The Bermont specimens of Manicina all (100%) possess a flat or slightly concave base, typical of self-righting forms. Colonies collected in the Bermont formation show several types of macroborers, sponges, sipunculid worms, but above all, the bivalve genera Lithophaga and Gastrochaena as well as epibionts, bryozoans and serpulid worms. Manicina is associated stratigraphically with rotatory colonies of Siderastrea radians, but the two have not been found within the same lamina. However, the two, taken together, provide strong indications of depositional environments on banks populated by sea grasses and associated fauna.

Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section)

Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section) The Kudryntsi section in West Ukraine documents a major environmental change from hypersaline to marine conditions during the Middle Miocene. There are very few (or no) specimens of foraminifers in samples of the siliciclastic series (4 m thick, with limestone intercalations) which occurs above the gypsum (and below the transgressive deposits) in the southern part of quarry. The limestone intercalations are first sparitic and microsparitic, and then become pelletal. The pelletal depositional textures are interpreted as originated in restricted environments in contrast to mixed-fossil lithoclastic packstones/grainstones overlying the siliciclastic series. The diversity of fauna increases up section. Foraminifers, bivalves, ostracods and gastropods appear first and then, additionally, brachiopods, bryozoans, crinoids, and echinoids occur. Foraminiferal assemblages are dominated by elphidiids forming 70 to 90 % of the population. The most common species are Elphidium crispum (Linné) and E. macellum (Fichtel & Moll). The limestones show a wide range of δ13C values (from -1.6 ‰ to - 18.2 ‰) and δ18O values (from -0.2 ‰ to -9.4 ‰) indicating that the cementation and some recrystallization took place in meteoric-water-dominated fluid but the restriction-controlled trend can be recognized. The siliciclastic series was deposited in an evaporitic lagoon influenced by large inflows of continental waters carrying the siliciclastic and other detrital material from the older Badenian rocks as well as from their substrate. The Kudryntsi section documents a stepwise decrease in water salinity — from ca. 150-300 ‰ during the Badenian gypsum precipitation, through ca. 80-150 ‰ during deposition of the siliciclastic series to ca. 35 ‰ during sedimentation of the basal transgressive deposits. The basal deposits originated in shallow subtidal (0-20 m) environments of normal marine salinity (30-35 ‰) and temperate to warm waters (8-18 °C) as indicated by requirements of the E. crispum association in recent seas.

Anatomy of an anachronistic carbonate platform: Lower Triassic carbonates of the southwestern United States

Examination of Lower Triassic carbonate rocks from around the world has revealed the resurgence of atypical carbonates that were last common during the Proterozoic (‘anachronistic facies’). Anachronistic facies are attributed to a combination of post-extinction paleoecologic factors and widespread, harsh environmental conditions, particularly the presence of anoxic, alkaline waters in the global ocean. The marine rocks of the Moenkopi Formation (Virgin Limestone) of southern Nevada and laterally equivalent deep-water limestones of the Union Wash Formation of east-central California provide a means to reconstruct depositional environments across a Lower Triassic carbonate ramp and place the atypical facies and fabrics that occur within those rocks into a larger ‘Anachronistic Platform Model.’ Examination of shallow subtidal and intertidal facies reveal widespread ooid shoals in both the Union Wash Formation and Virgin Limestone, as well as the presence of small, fringing stromatolite bioherms in shallow subtidal environments of the Union Wash Formation. Inner to middle ramp environments of the Virgin Limestone contain aggregates of cabbage-head stromatolites that formed 1–2 m-high patch-reef bioherms, in addition to flat-pebble conglomerates, mud-chip facies and wrinkle structures. Deep-water facies from the Union Wash Formation contain synsedimentary calcium carbonate precipitates that form laterally extensive crusts in basinal environments, or interlocking mosaics of hemispheres and fans in outer ramp to slope environments. The results of this study reveal that carbonate sedimentation during the Early Triassic was controlled by a combination of biotic factors, environmental stresses, unusual oceanic chemistry and normal carbonate sedimentary processes that resulted in the development of carbonate platforms that had affinities to both Phanerozoic and Proterozoic depositional systems.

Recognising subtidal foraminiferal assemblages: implications for quantitative sea‐level reconstructions using a foraminifera‐based transfer function

AbstractMicrofossil‐based transfer function models are increasingly used to provide decimeter‐scale sea‐level change reconstructions. In this paper I demonstrate that in the tropical location of northern Australia problems arise in selecting the appropriate elevation range for the modern training set used to calibrate fossil calcareous foraminiferal assemblages. Most calcareous foraminiferal species found in cores occur in both modern intertidal and shallow subtidal environments. A lack of independent measures to indicate whether fossil assemblages come from intertidal environments forces use of a training set that includes intertidal and subtidal environments. This results in decreased precision compared to using a training set solely from intertidal environments. The widely used method of assessing model fit to fossil assemblages (modern analogue technique) often fails to discriminate between acceptable and unacceptable reconstructions. It is important to investigate a number of different measures including modern analogue technique, canonical correspondence analysis and changing bootstrapped sample specific transfer function errors to fully understand the level of similarity between modern and fossil foraminiferal samples, to judge the reliability of transfer function‐predicted sea‐level reconstructions. Copyright © 2008 John Wiley & Sons, Ltd.

Variations in Neoarchean microbialite morphologies: clues to controls on microbialite morphologies through time

AbstractThe Neoarchean Carawine Formation, Hamersley Group, Western Australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments. These distinctive structures are distributed in five shallow subtidal and two deeper‐water facies in the Oakover area of the Carawine Formation. The shallow subtidal facies are composed of biohermal and bedded stromatolites, centimetre‐scale ridge‐shaped microbialites and wavy‐laminated microbialites. The deeper‐water facies are composed of fenestrate microbialites, planar laminated dolostone and dolostone with rolled‐up microbial laminae. Microbialites in the Carawine Formation lie within a continuum of Archean to Proterozoic microbial facies. Some shallow‐water microbial facies in the Carawine Formation are similar to Proterozoic facies, such as large bioherms internally composed of a variety of stromatolite morphologies. In contrast, fenestrate microbialites grew in quiet subtidal environments and are common in Archean rocks but have not been documented in similar Proterozoic environments. The similarity of shallow‐water facies across the Archean–Proterozoic transition, before and after the oxidation of the atmosphere and surface oceans, indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes. Rather, stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment. In contrast, the absence of fenestrate microbialites from Proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans.

Crassostrea ariakensis in Chesapeake Bay: Growth, Disease and Mortality in Shallow Subtidal Environments

In April 2004, triploid native (Crassostrea virginica) and nonnative (Crassostrea ariakensis) oysters were deployed in cages at four sites along a salinity gradient in Chesapeake Bay. In Maryland, the lowest salinity site was located in the Severn River and two low to mid-salinity sites were located in the Choptank and Patuxent Rivers. The highest salinity site was located in the York River in Virginia. Growth, disease acquisition, and mortality were measured in the deployed oysters through August 2006. Although ANOVA revealed that the nonnative oysters were significantly larger at the end of the experiment than the native oysters at all sites, the differences were much greater at the Virginia site (59 mm) than in Maryland waters (9-23 mm). With the exception of C. ariakensis in the Severn River, Perkinsus marinus infected both species at all sites. Prevalences and weighted prevalences in both species remained relatively low throughout the experiment, but native oysters consistently acquired higher prevalences and weighted prevalences than C. ariakensis by August 2006. With the exception of several mortality-inducing events including winter freezing and hypoxic exposure, mortality was generally low in both species. No disease-related mortality was suspected in either species given the low weighted prevalences observed. In the York River, where a substantial natural spatfall occurred in 2004, more native spat were found on C. ariakensis than on C. virginica. To our knowledge, this is the first comparison of triploid C. ariakensis to triploid C. virginica conducted in the field. Because we did not observe substantial disease-related mortality, it is too soon to draw conclusions regarding the disease tolerance of C. ariakensis in the field or its viability as a replacement for the native species.

Upper Jurassic Platform succession with characteristics of a deeper water intraplatform trough (Mt. Svilaja, Croatia)

From the middle part of the Late Jurassic (Kimmeridgian), the hitherto uniform depositional environment of the Adriatic carbonate platform began to show differentiation. In the central part of the platform two intraplatform troughs were formed, one of which stretched from the Karlovac area southward and is known as the Lemeš Trough. The depositional processes that took place within this trough can be observed in the sedimentary succession of Mt. Svilaja. Based on investigated facies characteristics five lithofacies units were distinguished, representing three paleoenvironmental units: (1) shallow subtidal zone below the fair-weather wave-base; (2) intraplatform trough; (3) shallow subtidal zone above the fair-weather wave-base. The environmental changes are related to the tectonically-controlled retrogradation of the shallow subtidal platform, when the deeper-water intraplatform trough area, connected with the open Tethys realm, spread over the sunken part of the platform. Progressive infilling of the trough with bioclastic material led to the re-establishment of the shallow subtidal environment, and the area of the previously existing intraplatform trough was occupied by coral-hydrozoan reefal buildups.

Microfacies, microtaphonomic traits and foraminiferal assemblages from Upper Jurassic oolitic–coral limestones: stratigraphic fluctuations in a shallowing-upward sequence (French Jura, Middle Oxfordian)

The characterization and distribution of the microfacies and the microfossil assemblages of a Middle Oxfordian section from Jura Mountains composed by thick oolitic–coral limestones is analyzed. Six microfacies types (mainly grainstones) are differentiated mainly composed by ooids, intraclasts and bioclasts. Foraminiferal assemblages are dominated by agglutinated forms. Benthic microbial communities and sessile foraminifera are the main components of the encrustations. The whole set of microfossil assemblages is typical of shallow subtidal environments rich in “algae” (Cayeuxia, “Solenopora”, Thaumatoporella, Bacinella, Girvanella and Terquemella) and foraminifera such as Nautiloculina oolithica, Redmondoides lugeoni, Ammobaculites coprolitiformis, Troglotella incrustans and Rectocyclammina. The increasing upward record of debris of algae and Nautiloculina, and the decrease of serpulids, bryozoans, nodosariids and ophthalmidiids indicate a shallowing-upward trend. The stratigraphic distribution of microfacies and microfossil assemblages lead to differentiate two main successive phases. The first is a deeper subtidal environment in an open shelf, while the second is a shallow subtidal environment with evolution from winnowed to more restricted conditions. Microfabrics of radial to concentric ooids upwards in the section correspond to higher energy environments related to an oolitic shoal. This study shows how a very detailed analysis of microfacies, which integrates oolitic features, microfossil assemblages and microtaphonomy is potentially a useful tool for interpreting hydrodynamism and sequence evolution in marine carbonate shallow environments.

Bearriverops, a new Lower Ordovician trilobite genus from the Great Basin, western USA, and classification of the family Dimeropygidae

Bearriverops n. gen. is a distinctive clade of small, vaulted trilobites from the Lower Ordovician (Ibexian Series; Stairsian Stage) of Utah and Idaho. The genus includes at least seven new species known from silicified material of which five are well enough known to name: B. alsacharovi, B. borderinnensis, B. deltaensis, B. ibexensis, and B. loganensis (the type species). All are known from the lower Fillmore Formation in western Utah; B. alsacharovi and B. loganensis are also known from the Garden City Formation of southeastern Idaho. Both units record deposition in shallow subtidal environments above storm wave base. Bearriverops is characterized particularly by a suite of pygidial apomorphies apparently related to spiral enrollment. Its close relatives include a large group of mostly undescribed Skullrockian and Stairsian species with more conventional spinose pygidia. Together, the taxa are referred to Dimeropygidae, which is considered a senior synonym of Toernquistiidae. Cladistic parsimony analysis of Bearriverops indicates that B. alsacharovi and B. borderinnensis are sister taxa, and that B. loganensis, B. deltaensis, and the plesiomorphic B. ibexensis are successive sister taxa to this clade.

Vertebrate Remains on Ancient Rocky Shores: A Review with Report on Hadrosaur Bones from the Upper Cretaceous of Baja California (México)

The bones and teeth of vertebrates occur on shorelines in quantities sufficient to provide a guide to the range of animals that live both inland and offshore. Burial is necessary for any remains to enter the fossil record and coastal deposits representing intertidal and shallow subtidal environments are potential repositories of this record. A survey of 150 published reports on rocky shores from the Cambrian to the Pleistocene reveals approximately 5% in which vertebrate remains are listed and described. In all cases, the vertebrates involved are marine in habit, but there is no reason to suppose that the remains of land-dwelling vertebrates should be excluded from such deposits. The potential for dinosaur remains to be incorporated in marine coastal deposits is appraised with particular attention to the Upper Cretaceous of Baja California (México) and southern California (U.S.A.). Newly discovered hadrosaur (duckbill) dinosaur bones from the Eréndira area on the Pacific coast of Baja California (México) are described as related to a Late Cretaceous rocky shoreline.

Early Cretaceous benthic associations (foraminifera and calcareous algae) of a shallow tropical-water platform environment (Mljet Island, southern Croatia)

The Lower Cretaceous shallow-marine succession of Mljet Island in Croatia records the geological history of the southern part of the Adriatic Platform during its last tectonically quiet period, prior to the Late Cretaceous collision processes between the Adria Microplate and the Eurasian Plate. We studied the Early Cretaceous biostratigraphy of benthic foraminifera and calcareous algae in order to establish a precise, combined benthic biozonation for the Adriatic, which in turn facilitates a better understanding of the global distribution of these microorganisms during the Early Cretaceous. Thirty-four species from 26 genera of benthic foraminifera and 32 species of calcareous algae, distributed among 11 genera, were recovered from the Lower Cretaceous shallow-water carbonate rocks of Mljet Island in southern Croatia. Nine biostratigraphical units, eight of which are based upon the benthic foraminifera and calcareous algae, and one upon the microencruster Bacinella irregularis, have been distinguished within this interval: the Clypeina parasolkani-Humiella catenaeformis Interval Zone (Berriasian–earliest Valanginian), Epimastopora cekici-Pseudoclypeina? neocomiensis Interval Zone (Late Valanginian), Montsalevia salevensis Taxon-range Subzone (Late Valanginian), Clypeina? solkani Abundance Zone (late Early and Late Hauterivian), Salpingoporella melitae-Salpingoporella muehlbergii Interval Zone (Barremian), Bacinella irregularis Assemblage Zone (Early Aptian), Salpingoporella dinarica Abundance Zone (Late Aptian), Orbitolina ( Mesorbitolina) texana-“ Valdanchella” dercourti Interval Zone (Early Albian) and “ Valdanchella” dercourti Taxon-range Zone (Late Albian). The stratigraphical position of the main genera and species of benthic foraminifera and calcareous algae within the Berriasian–Albian interval is discussed, and the established biozones are correlated within the Adriatic Platform domain. The Early Cretaceous diversification of benthic foraminifera in the area investigated can be shown to follow the sea-level curves for that period, and the major foraminiferal turnovers coincide with global sea-level rise and fall. During relative sea-level rises, coupled with reduced oceanic circulation and expansion of nutrient-poor, shallow tropical waters, these organisms were able to diversify into various euphotic habitats, particularly within shallow subtidal environments of the platform interior. Regressive episodes resulted in the reduction of oligotrophic habitats and a decrease in species richness.

Surface traces and bioturbate textures from bubbler crabs: an indicator of subtropical to tropical tidal flat environments

The surface traces and bioturbate textures genereated by the bubbler crabsScopimera sp.,Dotilla blanfordi, Ilyoplax pusilla, etc., occurring in the tropical supra- to shallow-subtidal environments of the east coast of India have been studied. During foraging these organisms make various patterns on the substrate by their feeding pellets. These patterns are primarily dependant on grain-size characteristics, moisture conditions, and emergence level of the substrate. The crabs also produce typical ichnofabrics caused by back-filling of the burrows which do not exceed 10 cm in length. The internal fabric of the burrow-fills shows both concave-upward and concave-downward laminae resulting from upward or downward movement of the organism within the sediment. In sections perpendicular to burrow orientation the process of back-filling generates concentric laminae. Such a fabric occurs not only in coastal intertidal sediments, but also in sediments of estuarine point bars located 50 kilometres inland where these tiny crabs also occur. Such subsurface bioturbation features may represent a better tool for the identification of tidal environment than surface traces since the latter have a low preservation potential because of the erosional effects of wave and current action. The bioturbate texture, however, occurs over a wide range of the intertidal zone and, hence, in fossil record this bioturbate texture can be useful to identify tidal environments. These crabs can withstand a definite range of salinity and, therefore, this texture can also provide information about salinity conditions of palaeo-tidal environments.

Platform configuration, microfacies and cyclicities of the upper Albian to Turonian of west-central Jordan

We present a comprehensive facies scheme for west-central Jordan platform deposits of upper Albian to Turonian age, discuss Cenomanian and Turonian carbonate cycles, and reconstruct the paleogeographic evolution of the platform. Comparisons with adjacent shelf areas (Israel, Sinai) emphasize local characteristics as well as the regional platform development. Platform deposits are subdivided into fifteen microfacies types that define eight environments of deposition of three facies belts. Main facies differences between Cenomanian and Turonian platforms are: rudist-bearing packstones that characterise the higher-energy shallow subtidal (transition zone) during the Cenomanian, and fossiliferous (commonly with diverse foraminifer assemblages) wackestones and packstones of an open shallow subtidal environment. On Turonian platforms high-energy environments are predominantly characterised by oolithic or bioclastic grainstones and packstones, whereas peritidal facies are indicated by dolomitic wackestones with thin, wavy (cryptmicrobial) lamination. Rhythmic facies changes define peritidal or subtidal shallowing-up carbonate cycles in several Cenomanian and Turonian platform intervals. Cyclicities are also analysed on the base of accommodation plots (Fischer Plots). High-frequency accommodation changes within lower Cenomanian cyclic bedded limestones of the central and southern area exhibit two major ‘cyclic sets’ (set I and II) each containing regionally comparable peaks. Accommodation patterns within cyclic set II coincide with the sequence boundary zone of CeJo1. The lateral and vertical facies distributions on the inner shelf allow the reconstruction of paleogeographic conditions during five time intervals (Interval A to E). An increased subsidence is assumed for the central study area, locally (area of Wadi Al Karak) persisting from middle Cenomanian to middle Turonian times. In contrast, inversion and the development of a paleo-high have been postulated for an adjacent area (Wadi Mujib) during late Cenomanian to early Turonian times, while small-scale sub-basins with an occasionally dysoxic facies developed northwards and further south during this time interval. A connection between these structural elements in Jordan with basins and uplift areas in Egypt and Israel during equivalent time intervals is assumed. This emphasises the mostly concordant development of that Levant Platform segment.

The conodont fauna in the Middle Ordovician Eoplacognathus pseudoplanus Zone of Baltoscandia

Conodont faunas from the Eoplacognathus pseudoplanus Zone in five main areas of Middle Ordovician rocks in Sweden are described and discussed and compared with faunas of comparable age from neighbouring areas. The investigation is based on 118 samples which together yielded 175 114 conodont elements. The Swedish conodont faunas are intermediate between shallower-water faunas from the eastern part of Baltica and deeper-water faunas towards the west. Correlation with the Yangtze platform of south-central China is fairly easy, and the occurrence of key taxa, such as Histiodella, makes it also possible to correlate some levels with Laurentia. Although faunal lists for the Swedish localities are almost identical, the conodont taxa have their relative abundance maxima in separate areas: species of Protopanderodus and Periodon are most common in deeper-water settings, Eoplacognathus, Baltoniodus and Microzarkodina characterize intermediate areas, and Semiacontiodus is typical of shallow subtidal environments