Distribution Of Trace Fossils Research Articles

Using Ichnofossils to Correlate Oil-Bearing Deposits in the Devonian Clastic Succession (Pashyian and Timanian Horizons) of the South Tatar Arch

This article outlines the results of the first-ever ichnological study of the Middle Devonian clastic succession in the South Tatar Arch. The analysis of the stratigraphic distribution of trace fossils in the boreholes revealed several levels with biogenic structures such as ichnofossils and bioturbation, which proved useful for the correlation of the boreholes. The boundary interval of the Pashyian and Timanian Horizons is made up by a succession of three layers: bioturbated siltstones with Spirophyton burrows, limestones, and mudstones with Lingulichnus burrows. The interval can be traced over the entire area of the South Tatar Arch and may serve as an additional marker for the boundary between the horizons.

Environmental controls on trace-fossil distribution in the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation (Argentina): Implications for the analysis of fine-grained depositional systems

Over the past years, the interest in organic-rich, fine-grained depositional systems has been growing due to the increasing relevance of unconventional shale reservoirs and several breakthroughs in the study of mud. However, the paleoenvironmental application of ichnologic analyses of these systems is still hindered by the scarcity of discrete trace fossils, small burrow size, and difficulty in obtaining fresh rock samples. The Upper Jurassic-Lower Cretaceous, Vaca Muerta Formation is the most important fine-grained unconventional reservoir in South America, and hence, contains a large density of cores that provide fresh cross-section views with detailed information on mudstone. An ichnologic analysis was carried out on cores and outcrop to develop an integrated ichnologic-sedimentologic model and to understand environmental controls on trace-fossil distribution. The Vaca Muerta Formation shows indistinct bioturbation represented by biodeformational structures generating irregular-laminated and massive mudstone fabrics, and discrete bioturbation and biodeposition structures mostly associated with tuff and heterolithic successions. Trace fossils were grouped into nine ichnocoenoses that illustrate organism responses to environmental controls. Abundant biodeformational structures in mudstone are associated with soupy substrates, whereas a change to softgrounds or loosegrounds occurs during coarser-grained sedimentation (associated with contourite drift, fluid mud flow, slope hemipelagic, and volcanic ash sedimentation), enhancing preservation of discrete traces. Locally, higher-energy events associated with exhumation of consolidated sediment generated firmgrounds colonized by the producers of the Thalassinoides isp. ichnocoenosis. In terms of oxygen, increased bioturbation index, penetration depth, burrow size, and ichnodiversity record an increase in bottom and interstitial water oxygenation. Moreover, an overall food-rich environment precluded specialized feeding and the development of tiered communities. The present study provides a clear picture of the relationship between substrate and oxygen controls in trace-fossil composition and distribution, contributing to the understanding of taphonomic controls and paleoecologic dynamics in fine-grained depositional systems, and providing an additional tool to refine sedimentologic and sequence stratigraphic analyses in similar mudstone successions elsewhere.

Evolutionary and ecologic controls on benthos distribution from an upper Cambrian incised estuarine valley: Implications for the early colonization of marginal-marine settings

Estuarine deposits of the Furongian Pico de Halcón Member of Argentina contain trace and body fossils that allow assessing the role of evolutionary and environmental factors on early colonization of marginal-marine environments. The outer region of the estuary was characterized by a subtidal sandbody flanked by tidal flats. Vertical burrows of suspension feeders and probably passive predators are abundant in the high-energy areas of the outer estuary. Horizontal trilobite and vermiform trace fossils record the activities of mobile deposit, detritus, and suspension feeders in more protected settings. Arthropod trackways, vertical burrows, and horizontal vermiform burrows have been recorded in middle estuarine deposits. The occurrence of trackways attests the ability of some late Cambrian marine arthropods to periodically migrate inland following tidal channels or via salt-water wedges. No trace and body fossils have been found in inner valley areas. Outer and middle estuarine deposits contain the trilobite Neoparabolina frequens argentina. Its record in brackish-water settings is envisaged as a result of its generalist nature and ability (physiologic or behavioral) to cope with a wide array of conditions, flexible resource requirements, and successful spreading.Although trace-fossil distribution along the salinity gradient reflects the basics of the “brackish-water model”, the remarkably low ichnodiversity in the middle estuary and the lack of trace fossils in the inner estuary are interpreted as reflecting evolutionary controls. Teichichnus assemblages, forming monospecific occurrences or with Planolites, in fine-grained, heterolithic facies seem to be remarkably persistent through geologic time. The studied trace fossils yield insights on attempts of some clades to expand into stressful brackish-water settings early in their evolutionary histories. In addition, comparison of the environmental tolerance of the Furongian benthos with other occurrences in younger early Paleozoic estuarine settings allows to track early steps of the colonization of brackish-water environments as it developed during the Ordovician Radiation.

UNLOCKING THE ARCHITECTURE OF THE COLONIZATION WINDOW: ICHNOFABRICS FROM UPPER CRETACEOUS TIDE-INFLUENCED MEANDER-LOOP DEPOSITS

ABSTRACT Studies dealing with the colonization window typically emphasize two major features: duration (short term vs. long term) and frequency of colonization (episodic vs. continuous). However, our understanding of tide-influenced meander loops requires consideration of an additional feature, the architecture of the colonization window, which comprises not only the spatial dimension and geometry of the colonization surface, but also its evolution through time. Tide-influenced meander-loop systems show a heterogeneous trace-fossil distribution that reflects the variety of processes operating along the point-bar and overbank colonization surfaces. Ichnofabric analysis of tide-influenced meander-loop deposits from the Upper Cretaceous Tremp Formation (Pyrenees, Spain) provides valuable insights into the sedimentary and ichnological dynamics of these marginal-marine systems and allows the importance of stratal geometry controlling the colonization window to be evaluated. Six ichnofabrics are identified in point bars and associated overbank deposits. These ichnofabrics differ in bioturbation index (e.g., higher in the upper part than the lower-middle parts of point bars), preservation of primary sedimentary fabric (typically preserved in the lower-middle parts of point bars), inferred behavior and trophic types (e.g., dominance of dwelling or feeding structures in the lower-middle and upper parts of point bars, respectively), and other features such as depth of penetration, ichnotaxonomic composition, presence or absence of root trace fossils and/or mottling, or number of superimposed suites. The key environmental factor controlling the nature and distribution of ichnofabrics is the morphology of the point-bar lateral-accretion surfaces and their evolution through time. The architecture of the colonization window is here linked to the helicoidal flow and discharge changes in meandering channels, and the successive development of lateral accretion units with time.

The influence of hybrid sediment gravity flows on distribution and composition of trace‐fossil assemblages: Ordovician succession of the north‐eastern Alborz Range of Iran

ABSTRACTThe distribution of conventional subichnofacies in deep‐water fan systems (i.e. Ophiomorpha rudis–Paleodictyon–Nereites‐subichnofacies) depends on the presence of fully turbulent non‐cohesive flows such as low‐density turbidites and high‐density turbidites. However, changes in flow state between laminar and turbulent conditions can affect the distribution style of conventional subichnofacies. This study deals with the effects of environmental or ecological stressors as a result of hybrid sediment gravity flows (hybrid event beds) on distribution and composition of trace fossils in the deep‐marine depositional system of the Ordovician Ghelli Formation in the north‐eastern Alborz Range. The spatial distribution and sedimentological character of hybrid sediment gravity flows, in particular their abundance in the down‐dip parts of lobe‐related facies associations, are interpreted as products of longitudinal and lateral transformation from turbidity currents to debris flows promoted by incorporation of significant claystone and mudstone clasts into the flow by seafloor erosion and flow bulking. Seven trace‐fossil assemblages were recognized in the channel and lobe‐related facies associations. The observed spatial distribution of trace‐fossil assemblages in the interpreted frontal and lateral lobe fringes, somewhat contrasts with conventional subichnofacies distribution models. The development of cohesive flows and rapid emplacement of turbidite, banded and debrite beds could be accompanied by fluctuations in physico‐chemical conditions and, hence, the time available for colonization and the lifestyle of producers. This study suggests that, compared to the archetypal models of the subichnofacies in down‐dip parts of lobe‐related facies associations, ichnodiversity and density of bioturbation are drastically reduced, and trace fossils are limited to simple, shallow‐tier feeding strategies. Commonly, the presence of cohesive flows may have forced the producers in the Paleodictyon and Nereites‐subichnofacies to migrate into lateral lobe fringe with more participation of low‐density turbidites. This study shows that, in addition to sedimentological and architectural criteria, ichnological criteria can also be used to distinguish between frontal and lateral lobe‐fringe deposits in unconfined systems.

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

The intensity, extent, and ecosystem-level impact of bioturbation (i.e. Agronomic Revolution) at the dawn of the Phanerozoic is a hotly debated issue. Middle Cambrian fan-delta deposits in southwestern Saskatchewan provide insights into the paleoenvironmental extent of the Agronomic Revolution into marginal-marine environments. The studied deposits reveal that several environmental stressors had direct impact on trace-fossil distribution and bioturbation intensities in Cambrian fan deltas. Basal and proximal subaerial deposits are characterized by very coarse grain size and absence of bioturbation. Mid-fan and fan-toe deposits were formed under subaqueous conditions and are characterized by rapid bioturbation events in between sedimentation episodes when environmental stressors were ameliorated, providing evidence of a significant landward expansion of the Agronomic Revolution. Transgressive marine deposits accumulated after the abandonment of the fan-delta system display high levels of bioturbation intensity, reflecting stable environmental conditions that favored endobenthic colonization. The presence of intense bioturbation in both subaqueous fan delta and transgressive deposits provides further support to the view that Cambrian levels of biogenic mixing were high, provided that stable environmental conditions were reached. Our study underscores the importance of evaluating sedimentary facies changes to assess the impact of environmental factors prior to making evolutionary inferences.

Thomas Webster's Tulip Alcyonium (Lamellaecylindrica, trace fossil) in the Upper Greensand Formation (Albian) of the Isle of Wight

Large, ramified burrow systems with a thick lamination and bulbous enlargements are common in the Upper Greensand Formation (Albian) of Ventnor, Isle of Wight. From there, these trace fossils were first described by Thomas Webster more than two centuries ago. Although also characteristic outside their area of original description, these structures and Webster's fabulous documentation have fallen into oblivion and only recently were assigned to the ichnogenus Lamellaecylindrica. The two included ichnospecies, L. paradoxica and L. ludwigae reflect different behaviours of their trace maker (possibly a holothurian) in adaption to variations in the sedimentary conditions and current energy. A comparison of the associated ichnofauna with that of the Upper Greensand Formation at Lyme Regis, about 100 km to the west, reveals subtle but significant differences in the trace-fossil distribution, ichnodiversity and ichnoabundance, indicating a proximal (lower shoreface to offshore transition) to distal (inner shelf) depositional trend from west to east. Given the total bioturbation of the greater part of this shelf succession, these subtle variations in the ichnofauna provide valuable information for interpretation of the depositional environment and differences in the energy level where primary sedimentary structures are absent.

Reassessing Early Triassic wrinkle structures from moderate-high latitudes: An updated interpretation of metazoan colonization in matground ecosystems after the Permian-Triassic mass extinction

Wrinkle structures have occurred on our planet for 3.2 billion years. They, therefore, if proved to be biogenic origin, could represent one of oldest life forms on Earth. Such distinct microbial mats were commonly present in the Precambrian, and were also widespread in shallow marine siliciclastic settings in the Cambrian and aftermath of major Phanerozoic mass extinctions, but their interactions with metazoans remain varied. Here, I reassess abundant wrinkle structures which were documented previously from the Lower Triassic successions of two moderate-high latitudinal localities, the southern Qilian basin of west China, and the northern Perth Basin of Western Australia in both northern and southern hemispheres. Wrinkle structures commonly occurred at the interface between a fine sandstone bed and an overlying siltstone or mudstone bed. Both burrowing and shelly benthos were sporadically distributed in wrinkle structures, contrasting with the biomass in non-wrinkled layers. Although wrinkle structures may be preserved in well‑oxygenated habitable habitats together with diverse benthos, they proliferated during anoxic transient periods or when storm-influenced sediments were deposited. The co-occurrence of wrinkle structures with trace fossils and benthos such as bivalves reflects an animal-sediment interaction, instead of an animal-mat interaction, and caution therefore should be made when documenting the interactions between microbes and metazoans in fossil records. Grazing activities by both infaunal deposit-feeders and bivalves were absent on the wrinkled surfaces, while horizontal burrows and infaunal bivalves cross-cut and disrupted the wrinkled surfaces, implying that trace fossils post-dated the formation of the wrinkle structures, and the organisms mainly exploited in buried microbial mats. The distribution of trace fossils and benthos on wrinkled surfaces from these two studied localities do not support the concept of microbial refugia or the preferential preservational window hypotheses. MISS including wrinkle structures and microbialites have been documented from both low- and high-latitude regions, and their relatively sparse occurrences in moderate- to high-paleolatitudes regions may be due to sampling bias. The proliferation of microbes such as cyanobacteria in the aftermath of the mass extinction was not related to selectivity of climate zones and seawater temperature in shallow marine settings.

Siliciclastic and bioclastic contouritic sands: Textural and geochemical characterisation

The purpose of this study is to differentiate and characterise contouritic sands in two different locations with variable sediment compositions (siliciclastic and bioclastic) based on a multiproxy approach that includes the analysis of sedimentary texture, semi-quantitative geochemistry, microfacies and ichnological information, as well as a Principal Component Analysis (PCA) applied to geochemical and sedimentary data on sediment cores. The integration of sedimentological analyses and the PCA permits also to the differentiation between fine-grained deep-water deposits such as hemipelagites, muddy contourites and hyperpycnites. A depositional model is proposed here, based on geochemical and sedimentological characteristics of the Holocene-highstand Mozambique Channel upper slope sands, and glacial-lowstand Corsica Contourite Depositional System middle slope sands. The upper continental slope of the Mozambican margin is characterised by siliciclastic sandy contourites, muddy contourites and muddy hyperpycnites. Mozambique siliciclastic sandy contourites constitute large accumulations of well-sorted very fine to coarse sand with evidences of strong winnowing and reworking under high-energy conditions. The sedimentary facies represents highstand contourite sands and shows a reversely-graded trend. The contourite drift on the Pianosa ridge (eastern flank of the Corsica Trough) consists of bioclastic sandy and muddy contourites and hemipelagites. Bioclastic sandy contourites are made up of shallow-marine winnowed bioclasts with a reversely- and normally-graded trend and represent lowstand contourite sands. The PCA in the two environments —showing a distinctive geochemical signal— allows for differentiation of the contourite deposits. In siliciclastic sands, reworking is marked by an accumulation of Si, Zr, and Sr in fine- to medium-grained sands. In bioclastic sands, reworking is less evident but it is characterised by accumulations of Ca and Sr. The reworking and winnowing bottom current effects are also observed at the microfacies scale. Both types of contourite deposits show evidences of intermittent depositional conditions depending on the ichnodiversity, distribution and abundance of trace fossils. This work is useful to discriminate similar fine-grained deposits in different continental margins which would contribute to a better understanding of sedimentary deposits and processes in deep-marine environments.

Zoophycos and related trace fossils from the Chefar El Ahmar Formation, Upper Emsian-Frasnian Ia-Ib (Ougarta, SW Algeria)

The Upper Emsian to Frasnian Ia-Ib strata of the Marhouma area (or “km 30” outcrop), exposed in the Ougarta Range (SW Algeria) belong to the Chefar El Ahmar Formation. On the basis of distinct lithological and palaeontological features, this formation is subdivided into three members (Lower Marly Limestones Member, Middle Marly Limestones Member, and Upper Marly Limestones Member). The studied beds show low to moderate diversity of trace fossil assemblage which contains thirteen ichnotaxa: Chondrites intricatus, Chondrites isp., Chondrites cf. targionii, Circulichnis cf. montanus, Cochlichnus isp., Neonereites biserialis, Neonereites multiserialis, Nereites isp., Palaeophycus isp., Planolites isp., Thalassinoides isp., Zoophycos aff. cauda-galli, and Zoophycos isp. A. The two latter ichnotaxa are the most common trace fossils in the assemblage and occur at three different levels showing different bioturbation intensities. The first Zoophycos-bearing level (Zl 1) is characterised by an overall high bioturbation intensity reflecting a very high oxygenation rate and nutrient supply, allowing the development of large and dense Zoophycos specimens. The second Zoophycos-bearing level (Zl 2) has a considerable reduction of bioturbation intensity as compared to the previous level, with an abundance of Chondrites, which is probably due to radical palaeoecological changes that suggests dysoxic and stressful conditions. The third Zoophycos-bearing level (Zl 3) is characterised by an overall moderate bioturbation intensity. The distribution of trace fossils was influenced by lithology, sedimentation rate, energy level (storm events), bottom oxygenation, and nutrient supply. The lithofacies and trace fossils of the Chefar El Ahmar Formation both indicate a depositional environment fluctuating from the lower shoreface to lower offshore zone.

Detrital zircon age and biostratigraphic and chemostratigraphic constraints on the Ediacaran–Cambrian transitional interval in the Irkutsk Cis–Sayans Uplift, southwestern Siberian Platform

AbstractA number of ecological and geochemical transformations occurred during late Ediacaran and early Cambrian time, the effects of which are difficult to overestimate. However, the strong linkage of biostratigraphic and chemostratigraphic methods with lithofacies makes the localization of the Precambrian–Cambrian boundary and its correlation with lithologically contrasting sections highly debatable. We analyse the taxonomy and stratigraphic distribution of small skeletal fossils and trace fossils, the carbonate carbon and oxygen isotope composition, and U–Pb detrital zircon age in the Ediacaran–Cambrian transitional interval of the Irkutsk Cis–Sayans Uplift (southwestern Siberian Platform). This interval (Moty Group) comprises a transgressive succession with red-coloured alluvial to deltaic siliciclastic deposits (Shaman Formation) and overlying shallow-marine carbonates (Irkut Formation). The lower Irkut Formation hosts sporadic and poorly preserved tubularCambrotubulusfossils, which are known from both the terminal Ediacaran Period (c. 550–541 Ma) and the Terreneuvian Epoch (541–521 Ma), and typical Fortunian trace fossils, including an index ichnotaxon of the Cambrian boundaryTreptichnus pedum. The biostratigraphic and carbonate carbon isotope data and U–Pb concordia ages of 531.1 ± 5.2 Ma (mean weighted, 530.6 ± 5.3 Ma) of the five youngest zircon grains from the lower Irkut Formation indicate that at least the shallow-marine carbonates of the upper Moty Group correspond to the Cambrian Stage 2 (c. 529–521 Ma). In the Irkutsk Cis–Sayans Uplift, the Cambrian Period tentatively began before or during the accumulation of the alluvial to deltaic siliciclastic Khuzhir and Shaman formations, and this crucial divide remained unmarked in the palaeontological and isotopic records.

Cold-seep fossil macrofaunal assemblages from Vestnesa Ridge, eastern Fram Strait, during the past 45 000 years

Four cores from Vestnesa Ridge on the western Svalbard margin from water depth of 1200 m have been studied. The Vestnesa Ridge is known for the presence of numerous pockmarks and active methane gas seepage is often observed in the form of acoustic gas flares. Three of the cores were collected from a pockmark with active seepage of methane and one core was taken just outside the seepage area for comparison. The cores show a range of influence from methane from no seepage (control core), moderate seepage, strong seepage to very strong seepage. All cores have been analyzed for the distribution of macrofossils, trace fossils, planktic foraminifera, stable isotopes, geochemistry and sedimentology. The main purpose of the study is to improve knowledge about the fossil macrofauna and past methane emissions in the area. The results show a major difference between the fauna recovered from cores taken inside a pockmark with chemosymbiotic bivalves and in some cases with a rich macrofauna  and from the core recovered outside the pockmark that contained no macrofauna. The faunal relationships with the sedimentary environments confirm a close connection between the macrofauna and the presence/absence of cold-seepage, particularly seen in the occurrence of chemosymbiotic bivalves Archivesica arctica, Isorropodon nyeggaensis, potentially chemosymbiotic Rhacothyas kolgae and polychaetes. A barren zone in the core that was taken from the deepest part of the pockmark may indicate that a blow-out took place in the late glacial and the deglaciation into the early Holocene at c. 21,000–9000 years.

Tracking Silurian-Devonian events and paleobathymetric curves by ichnologic and taphonomic analyzes in the southwestern Gondwana

Abstract Trace fossils have been used worldwide to access paleoecologic data in sedimentary sections. In Parana Basin (southern Brazil), trace fossils are stratigraphically well distributed; however, they are understudied if compared to body macrofossils or microfossils. Only few studies applied ichnology to the Silurian-Devonian strata, and mostly focused in an ichnotaxon. This comprehensive study aims to analyze the ecospace colonization represented by trace fossils in a Silurian-Devonian section from Parana Basin, and to associate the paleoenvironmental data provided by trace fossils with the decline of the Malvinokaffric Realm. In this sense, trace fossils were analyzed in six sedimentary sections to encompass the whole outcropping supersequence. The vertical distribution of trace fossils (Glossifungites, Skolithos and Cruziana ichnofacies) was compared with the distribution of the Malvinokaffric macrofossils. Paleoecologic and ichnodisparity analyzes allowed to infer dominance of stable conditions throughout the Silurian-Devonian section; however, some levels express dysoxic to anoxic conditions, and in others the high energetic conditions biased the ichnologic record. The stratigraphic distribution of Zoophycos suggests a change in the basin configuration during Eifelian, which might be related to the decline in the diversity of the Malvinokaffric fauna.

ICHNOFABRICS FROM A CRETACEOUS EOLIAN SYSTEM OF WESTERN ARGENTINA: EXPANDING THE APPLICATION OF CORE ICHNOLOGY TO DESERT ENVIRONMENTS

The Lower Cretaceous (Valanginian) Mulichinco Formation of the Neuquen Basin in western Argentina is host to important hydrocarbon reservoirs, encompassing a wide variety of sedimentary facies, including thick eolian deposits in its lower interval in proximal positions. Ten ichnofabrics are characterized based on the analysis of cores from the El Mangrullo oil field. These ichnofabrics have been grouped in four associations, representing eolian dunes, eolian sand sheets, interdunes, and fluvial sheet floods. In terms of the ichnofacies model, both the Scoyenia and Octopodichnus-Entradichnus ichnofacies are identified. Ichnologic information has been integrated with sedimentologic and sequence-stratigraphic information. The studied succession comprises a 3rd-order depositional sequence that is subdivided into three 4th-order sequences stacked in a backstepping pattern as a result of a rise in the water table. The base of the 3rd-order sequence is represented by the intra-Valanginian unconformity that in this area separates marine deposits below from continental deposits above. Overall the 3rd-order sequence reflects the vertical transition from a dominance of eolian dune deposits to eolian sand sheet and fluvial sheet flood deposits, the latter intercalating with marginal-marine intervals. Application of available conceptual frameworks to understand trace-fossil distribution in desert environments suggests that the eolian Mulichinco ichnofauna indicates a temporal evolution from hyper-arid to arid and semi-arid conditions. The results of the present analysis argue against the common assumption of deserts as barren of life and provide further support to the notion of an archetypal eolian ichnofacies. This study expands the realm of application of ichnology in subsurface to eolian environments by providing a characterization of an ichnofauna from a desert setting based on core analysis.

Corrigendum: Salt tectonism and distribution of brackish-water trace fossils in the Cretaceous McMurray Formation, Athabasca Oil Sands, Alberta Foreland Basin

A proposed salt tectonism-saline seep model provides a novel alternative to the two widely accepted but irreconcilable depositional models for middle McMurray Formation strata of the Lower Cretaceo...

An Updated Review of the Avian Footprint Record from the Yacoraite Formation (Maastrichtian-Danian), Northwestern Argentina

The Yacoraite Formation (Maastrichtian–Danian; Balbuena Subgroup; Salta Group), from Northwestern Argentina, represents a shallow epeiric unit which is the result of transgressions in the Andean basin of South America. Herein, we study the avian footprints from the Maimará locality, Jujuy province, and Quebrada del Tapón ichnosite, Salta province. The avian footprints from the Maimará locality is less diverse, made up: cf. Alaripeda isp., Avipeda isp., cf. Gruipeda filiportatis, and cf. Gruipeda isp. The avian track record from the Quebrada del Tapón ichnosite is composed of: cf. Alaripeda isp., Ardeipeda cf. egretta., Gruipeda filiportatis (=Yacoraitichnus avis) and others Gruipeda or compared to this ichnogenus, cf. Uhangrichnus isp., and several indetermined avian footprints. Both ichnological assemblages have tracks assigned to shorebirds or Charadriiformes. The facies distribution of trace fossils reinforces the overall model of a shorebird tracks dominance in moderate to low energy settings. This distribution can be divided into three sub-environments: (1) a moderate to high energy shoreline under wave action, (2) a supratidal body of ephemeral ponds, far away from direct wave influence and (3) a landward position, beyond the ephemeral ponds system. We have included all the ichnoassemblages within the shorebird ichnosubfacies as a subset of the Scoyenia Ichnofacies.

Salt tectonism and distribution of brackish-water trace fossils in the Cretaceous McMurray Formation, Athabasca Oil Sands, Alberta Foreland Basin

A proposed salt tectonism-saline seep model provides a novel alternative to the two widely accepted but irreconcilable depositional models for middle McMurray Formation strata of the Lower Cretaceous Athabasca Oil Sands deposit. Established interpretations of a fluvial axial channel belt along the eastern Alberta Foreland Basin contrast with a hundreds-of-kilometres long estuarine marine–fluvial transition zone setting that was characterized by brackish-water trace fossil laden beds. The architecture of a highly sinuous fluvial meander channel belt with bank-full depths of 30–40 m furthermore is not compatible with an estuary having a tens-of-metres thick salt wedge extending hundreds-of-kilometres upstream. This new model proposes that the removal of the underlying 100 m thick Middle Devonian salt section occurred across thousands of square kilometres and resulted in voluminous saline seeps up-section into river channel fills of the middle McMurray Formation. Southward transgression by a Boreal Sea tongue terminated fluvial lower McMurray Formation deposition, and transported brackish-water larvae inland along the tide-impacted backwater length. This zoology was sustained along the fluvial channel belt by the saline seeps that elevated salinity levels in channel muds as the fluvial system dominance reasserted. Brackish-water macroinvertebrates rapidly adapted to new terrestrial food sources in these fluvial channels, precluding the necessity for a salt wedge to have extended inland for hundreds of kilometres. This research presents the first quantitative analysis of the McMurray Formation trace fossil distribution patterns. Quaternary saline surface seep trends are proposed to represent intermittent seepage up-section since the Early Cretaceous.

Big bedding planes: Outcrop size and spatial heterogeneity influence trace fossil analyses

Roadcuts, core, cliffs and even mountainside exposures often limit the lateral extent to which we can assess bioturbation on bedding planes, simply because exposures of such surfaces are generally rare or small. Such constraints may hamper paleoenvironmental and paleoecological interpretations drawn from facies where most bioturbation is bed-parallel or patchily distributed. To explore how acute such constraints are, we conducted a pilot study of bioturbation in three exceptionally large (>5 m2), well-exposed, paleoenvironmentally similar bedding planes from the Cambrian of Wisconsin. The goal was to test the hypothesis that trace fossils and biogenic sediment disruption can be distributed heterogeneously at the scale of meters to decameters. Mapping the size variation and distribution of trace fossils across these bedding planes reveals variable patchiness. Individual bioturbated patches tend to be large (m-scale), but the density of biogenic sediment disruption within these patches is quite heterogeneous. In addition, bioturbated areas are separated by zones of undisturbed sediment that vary in size from <0.5 m2 to >3 m2. These observations suggest that ancient bedding planes, like modern substrate surfaces, can exhibit considerable lateral bioturbation heterogeneity at a range of spatial scales. Caution is thus urged when extrapolating the distribution and diversity of trace fossils and other biogenic sedimentary structures across broad sedimentary horizons based on small (≤1 m2) bedding plane exposures.

Ordovician and Silurian ichnofossils from carbonate facies in Estonia: A collection-based review

Trace fossils are common in the Ordovician and Silurian shallow marine carbonate succession of Estonia, with 45 ichnofossil genera and five bioclaustration structures identified, representing 31 categories of architectural designs and nine categories of ethological classification. Diverse soft sediment traces, bioerosional traces and bioclaustrations occur both in the Ordovician and Silurian. Diversity of trace fossils is similarly high in the Late Ordovician and Silurian, but markedly lower in the Middle Ordovician. This could be explained by the fact that during the Late Ordovician, Baltica drifted to the subtropical climatic zone where ichnofauna is usually more diverse than in temperate climatic settings. In addition, the Great Ordovician Biodiversification reached its peak in the Late Ordovician for many groups of organisms, which further contributed to the increase in ichnodiversity. Distribution of trace fossils is also controlled by the type of sedimentation, so that the mixed carbonate-siliciclastic systems prevailing in the Late Ordovician and Silurian have higher ichnodiversity than the pure carbonate settings of Middle Ordovician age. Feeding and locomotion traces are relatively rare in the Ordovician and Silurian of Estonia with the exception of the feeding structure Arachnostega, which is formed inside of protective shells and therefore has abundant occurrences. Bioerosional trace fossils may be extremely common in places, with a large number of different genera in the Upper Ordovician, supporting the idea of the Ordovician Bioerosion Revolution.

Prevention of infectious complications in predicted severe acute pancreatitis (SAP) – a single center randomized controlled trial

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.