Archetypal Cruziana Ichnofacies Research Articles

Ichnology and Sedimentology of the Lower Cretaceous Wabiskaw Member (Clearwater Formation) Alberta, Canada

Identifying facies and paleoenvironmental interpretation of the rock record is complicated due to the interplay of independent variables (i.e. wave-, river- and tidal-input) in marginal- and shallow-marine environments. This study integrates sedimentology and ichnology to characterize the depositional environments of the Lower Cretaceous Wabiskaw Member. The deltaic and strand plain shoreface-offshore deposits of Wabiskaw Member of Clearwater Formation of northeast Alberta provide an excellent case study to evaluate the ichnological and sedimentological characteristics associated with laterally and vertically variable stresses in wave-influenced nearshore settings. The Wabiskaw Member is studied using four sedimentary facies associations (Ten sedimentary facies). Facies association 1(FA-1) consists of massive, sharp-based mudstones and lenticular sandstone with small-scale soft-sediment deformation features, syneresis cracks and small-scale oscillation ripples. The ichnological suite mainly includes small grazing and deposit-feeding traces, representing the Phycosiphon Ichnofacies. Facies association 1(FA-1) is interpreted to record deposition in a prodeltaic setting. Facies association 2 (FA-2) is fine-to-medium-grained sandstone and thin mudstone with current, oscillation and combined flow ripples. The low angle and trough cross-beds, soft-sediment deformation structure, mud chips and coal debris are common. The trace fossil suite includes sporadically distributed deposit-feeding traces belonging to the Rosselia Ichnofacies. This facies association is interpreted to be deposited in the delta front to a mouth bar setting. Facies association 3 (FA-3) is gray to bluish-gray mudstone with minor sandstone interbeds (massive, planar parallel to hummocky cross-stratified). FA-3 is moderate to highly bioturbated. The ichnodiversity and abundance is high with dominant horizontal and subordinate vertical traces, including the dominance of deposit and detritus feeding traces representing the archetypal Cruziana Ichnofacies ichnological suite. Facies association 3 (FA-3) is interpreted as being deposited in a storm-influenced offshore environment. Facies association 4 (FA-4) is upper fine to fine-grained glauconitic sandstone with minor mudstone interbeds at the base. Physical sedimentary structures including massive and planar (horizontal and low angle), hummocky, and swaley crossing-stratification. FA-4 is heavily burrowed with a diverse suite of horizontal and vertical traces of deposit and detritus-feeding structures, representing a proximal expression of Cruziana Ichnofacies. Facies association 4 (FA-4) represents distal lower to middle shoreface deposition. The Wabiskaw Member deltaic (prodelta-delta front) deposits, producing characteristic sedimentological-ichnological signatures, distinguishing these deposits from related strand plains. In addition to characteristic deltaic traits (e.g. soft-sediment deformation structures, fluid mud and syneresis cracks), these deposits commonly contain comparably stressed low-diversity and diminutive trace-fossil suites. On the other hand, fully marine strand plain shoreface-offshore complexes are characterized by comparably robust trace fossils with high ichno-diversity and bioturbation intensities.

A shallow-water depositional interpretation for the upper Miocene Chagres Formation (Caribbean coast of Panama)

The upper Miocene Chagres Formation, cropping out along the Caribbean coast of Panama, has been previously interpreted as the record of the last deep-water connection between the Caribbean and Pacific oceans based on bodyfossil paleodepth estimates. We test this interpretation by presenting an integrated ichnological and sedimentological analysis on eight coastal localities of the Chagres Formation (Toro Limestone and Chagres Sandstone members). The Toro Limestone Member accumulated under fully marine conditions in a mixed carbonate and siliciclastic marine shelf above storm wave base. Fluctuating high-moderate energy conditions modulated by a combination of tides and high energy currents likely led to the sparse bioturbation of Toro Limestone sediments, corresponding to an archetypal Cruziana ichnofacies assemblage. Bioturbation, dominated by Thalassinoides and Ophiomorpha isp., increases in the overlying Chagres Sandstone Member and corresponds to a proximal expression of the Cruziana ichnofacies. The Chagres Sandstone Member was deposited within the lower shoreface-upper offshore transition zone in a shelf with low sedimentation rates under combined storm, wave, and tidal influence, and includes fossils and sediments of continental origin suggesting proximity to a river mouth. Our results suggest that the Chagres Formation accumulated in shallow waters, contrasting with a previously proposed deep-water accumulation, and are consistent with deposition on a tectonically stable platform of the northern Canal Basin at the apex of the Panama orocline.

Integrating sedimentology and ichnology with rock typing and flow units: Implications for clastic reservoir characterization

Shallow marine clastic reservoir facies prediction, correlation, distribution, thickness, and quality remains a challenge. This study integrates sedimentology and ichnology with reservoir rock typing and flow units to characterize the Lower Cretaceous Wabiskaw Member reservoir. An integrated geologic depositional model is presented using sedimentological data (rock types, sedimentary structures, grain size), ichnological data (trace fossils intensity, size, diversity), reservoir characteristics (porosity, permeability), and well log data. The Wabiskaw Member strata are characterized using four facies associations (composed of nine sedimentary facies). Facies association 1 (FA-1) comprises dark grey to blue-grey mudstone with a distinctly lenticular appearance (Facies 1, 2). Ichnologically, a stressed archetypal Cruziana Ichnofacies represent FA-1. Facies association 2 (FA-2) is fine-lower medium-grained sandstone with thin mudstone interbeds (Facies 3, 4). A stressed ichnological suite of mixed Skolithos-Cruziana Ichnofacies is present in FA-2. Facies association 3 (FA-3) is dark grey to bluish-grey mudstone with minor sandstone interbeds (Facies 5, 6). Trace fossils of archetypal Cruziana Ichnofacies are present in FA-3. Facies association 4 (FA-4) comprises upper fine to lower fine glauconitic sandstone (Facies 7, 8, 9) with a high-density trace fossil assemblage. FA-1 and FA-2 represent deposition in a wave-influenced prodelta to delta front settings, whereas FA-3 and FA-4 represent deposition in the offshore-shoreface environment. The reservoir quality of various reservoir facies (F-3, F-4, F-7, F-8) is evaluated by comparing facies reservoir characteristics (porosity, permeability, pore throat radii, flow-storage capacity, oil saturation, and thickness). F-4 is the best and most productive reservoir (pore throat radius >20 μm, 18% flow, and 4% storage capacity) in the study area. F-7 is ranked second-best in reservoir quality based on petrophysical characteristics (pore throat radius between 10 and 20 μm, 36% storage 47% flow capacity). F-8 is ranked third in reservoir quality with pore-throat radii ranging from 4 to 10 μm (mesoporous), 23% storage, and ≤5% flow capacity. F-3 is ranked last amongst the Wabiskaw Member reservoir facies. It is micro-porous (pore-throat radii ranging from 2 to 4 μm) with 37% storage and ≤5% capacity flow.

The Upper Jurassic Faïdja Formation (Northwestern Algeria): Sedimentology, biostratigraphy and ichnology

The Faïdja Formation displays mixed siliciclastic-carbonate deposits distributed in three members, which are organised from bottom to top as follows: the Clayey Sandstone Faïdja Member; the Clayey Limestone Bel Aoura Member and the Sandy Claystone Douaouda Member. Sedimentological data indicate the evolution of a subsiding marine environment from the shelf edge to the lower shoreface, sporadically dominated by storms. New age based on recently collected ammonite fauna allowed us to update the age of the Faïdja Formation as Early-Late Kimmeridgian. Ichnological analysis reveals the occurrence of abundant and diverse invertebrate trace fossils, grouped in four ichnoassociations. Ichnoassociation -A- coincides with the lowermost part of the Clayey Sandstone Faïdja Member; it is distinguished by a combination of pre-graphoglyptids and post-depositional traces, ascribed to the distal Cruziana ichnofacies transitional to the Nereites ichnofacies, which indicates a lower offshore zone to shelf edge environment characterised by a low-oxygenated period (anoxic event), frequent storm events and nutrient frequency. Ichnoassociation -B- occupies the middle and upper parts of the Clayey Sandstone Faïdja Member, it is characterised by an abundance of post-depositional traces, corresponding to the archetypal Cruziana ichnofacies that indicates a lower to transitional offshore environment with short phases of low hydrodynamic energy. Ichnoassociation -C- corresponds to the Clayey Limestone Bel Aoura Member that coincides with a drastic facial change and depositional conditions; this association documents a proximal Cruziana ichnofacies, and indicates an upper to transitional offshore zone as a depositional environment. Finally, ichnoassociation -D- coincides with the Sandy Claystone Douaouda Member; it is ascribed to the proximal Cruziana ichnofacies, indicating a lower shoreface environment. The combined sedimentological and ichnological data indicates a relatively subsiding platform with shallowing upwards corresponding to distal, archetypal and proximal Cruziana ichnofacies, respectively.

Differentiation of delta and open marine deposits based on an integrated ichnological and sedimentological analysis of the Late Triassic Nayband Formation, Tabas Block, Central Iran

The palaeoenvironmental significance of trace fossil assemblages in the shallow marine deposits of the Late Triassic Nayband Formation of the Tabas Block, Central Iran has been assessed for the first time. The siliciclastic successions of the Nayband Formation, are highly bioturbated and allow relationships between changes in ichnoassemblages within a depositional system to be documented and placed in a palaeoenvironmental framework. The main purposes of this paper are: (1) to describe and illustrate the trace fossils assemblages of the Nayband Formation; (2) integration of ichnologic and sedimentologic data to evaluate different stress factors on the infaunal communities; and (3) to briefly discuss paleoenvironmental distribution of various trace fossil assemblages in order to differentiate between deltaic and non-deltaic shoreface successions. The Upper Triassic Nayband Formation has been studied and measured in one section, where the Nayband Formation is well accessible and continuously exposed. This section was logged and evaluated using physical sedimentology and ichnology in order to establish a basis for the interpretation of sedimentary processes (facies) and depositional systems. In this study, trace fossils (diversity, abundances, and ethologies) and the spatial arrangement of sedimentary structures are used to further refining the interpretation of environmental parameters such as hydrodynamic energy, water turbidity, substrate properties, food supply, temperature, oxygenation, salinity, and sedimentation rates. Based on facies characteristics and stratal geometries, the siliciclastic succession is divided into two facies associations, fluvial-dominated delta (FA), and open marine (FB). Twenty-eight ichnogenera have been identified in delta and open marine successions: The assemblage is dominated by Rhizocorallium, Thalassinoides, Ophiomorpha, Helminthopsis, Palaeophycus and Skolithos. Their distribution is clearly linked with lithofacies and depositional environments. High rates of fluvial discharge, high water turbidity, seasonally high rates of deposition and phytodetrital pulses in river-dominated deltas may cause marked variations in the temperature, oxygenation and salinity of the fluvial-dominated delta successions. All of these factors in combination lead to impoverishment in trace diversity and reduction in burrow size but to rapid colonization of the substrate by single-layer colonizers of opportunistic deposit feeders. Low ichnodiversity, low bioturbation intensities with highly bioturbated clusters shown by single colonization events by opportunistic, simple feeding strategies of trophic generalists and a paucity of suspension-feeding structures elements represent a “stressed”, non-archetypal Cruziana ichnofacies. The changes of behavioural complexity and the tiering profiles in the offshore-shoreface complex of the Nayband Formation when compared with the river-dominated delta successions represent the transition from epifaunal life habits with simple tiering structures to infaunal life habits with complex tiering pattern. The occurrence of diverse trace fossil suites attributable to the Zoophycos ichnofacies, the archetypal Cruziana ichnofacies and the Skolithos ichnofacies in wave-dominated shoreface-offshore complex point to stress-free environmental conditions in open waters due to persistent wave agitation, and hence, a wide colonization window.

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.

From freshwater to fully marine: Exploring animal-substrate interactions along a salinity gradient (Miocene Oficina Formation of Venezuela)

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.

Ichnological analysis of the Upper Miocene in the ANH-Tumaco-1-ST-P well: assessing paleoenvironmental conditions at the Tumaco Basin, in the Colombian Pacific

Tumaco is a frontier basin located on the SW Colombian Pacific coast. It is composed of a thick siliciclastic sequence up to reach 10,000 m-thick. In recent years, the National Hydrocarbon Agency-ANH has promoted new exploration wells in order to understand the sedimentary dynamic and its relationship with petroleum systems. One of them, the ANH-Tumaco-1-ST-P well has ∼3000 m (12,000 feet). We carried out sedimentological, geochemical, and micropaleontological detailed analyses with special attention to the ichnology on a 55 m-cored interval (from 1695.3 to 1640.4 m = 5563–5382 ft) in order to assess paleoenvironmental conditions. Beds are composed of green and gray mudrocks interbedded with lithic sandstones and fine-grained tuffs. Calcareous microfossil assemblages defined by the recovery of Uvigerina carapitana, Uvigerina laviculata, Uvigerina pigmaea, Globigerina woodi, Globigerionoides obliquus, Discoaster bellus gr., Catinaster coalitus, Reticulofenestra pseudoumbilicus and Sphenolithus abies indicated a Tortonian age, between CN6/CN7 biozones. Six sedimentary facies were identified: (1, 2) massive and laminated mudrocks, (3, 4) massive and normal-graded sandstones, (5) heterolithic beds, and in some cases (6) sandstones with soft-deformation structures. These rocks were accumulated in a shallowing platform-prodelta environment with continuous volcanic influence. Ichnotaxonomic analysis, conducted for the first time in the Colombian Pacific, allowed the identification of eighteen ichnogenera: Alcyonidiopsis, Asterosoma, Chondrites, Conichnus, Cylindrichnus, Diplocraterion, Ophiomorpha, Palaeophycus, Phycosiphon, Planolites, Rhyzocorallium, Schaubcylindrichnus, Scolicia, Siphonichnus, Taeinidum, Teichichnus, Thalassinoides, and Zoophycos. The ichnological association belongs to the archetypal Cruziana ichnofacies and its “distal” expression. By integrating lithofacies and ichnological results, two segments have been distinguished: 1) the lower one (1695.3–1677.1 m) dominated by massive and laminated mudrocks and 1 to 6 ichnofabric indexes and, 2) the upper segment (1677.1–1640.4 m) characterized by the increase of the sandstone facies, and ichnofabric indexes from 1 to 5. Along these segments, four ichnofabrics have been identified: 1) Phycosiphon-Planolites, 2) Planolites-Thalassinoides, 3) Zoophycos-Chondrites, and 4) Phycosiphon-Thalassinoides, reflecting stable sedimentary conditions with low-moderate energy, low-moderate sedimentation rates, and dominant aerobic facies. Minor variations in these parameters (sedimentation rate, energy conditions, substrate consistency, oxygenation and organic matter), however, induced changes in the macrobenthic tracemaker community, and consequently in the registered trace fossil assemblages.

Definition of sequences through ichnocoenoses and taphofacies: An example from the Sácaras Formation (early Cretaceous, eastern Spain)

Abstract An integrated taphonomical, ichnological and sedimentological analysis has been carried out on the Albian deposits of the Sierra Helada section (Province of Alicante, southeastern Spain). This allowed recognition and detailed characterization of the shallowing- and coarsening-upward sequences present in these deposits. Twenty sequences were detected throughout the section. They contain the following, from bottom to top: (1) the bottom of the sequence characterized by very fine-grained marls rich in echinoid tests and echinoid trace fossils with very little evidence of physical reworking—it records a distal platform, low-energy environment; (2) marls interbedded with fine-grained calcarenites, rich in large Thalassinoides and slightly reworked echinoid tests, with common bioclast-armored tubes ( Ereipichnus geladensis ), recording low-energy background conditions but increasing energy of the sedimentary events, (3) coarse-grained calcarenites rich in different types of small to large Thalassinoides and E. geladensis horizons, showing the intense and frequent action of storms and directed currents on the seafloor, and (4) coarse-grained, cross-bedded calcarenites, rich in Ophiomorpha nodosa , deposited under high-energy background conditions in the shallowest part of the sequence, recording the presence of shifting dunes in the inner platform. Occasionally, also the record of a rapid transgression has been pointed out through the presence of condensed tapho- and sedimentary facies and mixed ichnocoenoses at the top of the sequence just after an erosive surface. The defined ichnoceonoses and their distribution throughout the sequence reflect the shifting from a distal expression of the Cruziana Ichnofacies to the shallower archetypal Cruziana Ichnofacies and finally to the high-energy, shallow-water Skolithos Ichnofacies. The distribution of taphofacies and ichnocoenoses and development of the sequences all through the section show a general transgression followed by a regressive phase, which fit with the third-order curves described for the area on the basis of pure sedimentological analysis in previous studies ( Castro et al., 2008 ).

Integrated litho-ichnofacies and ichnofabric analysis of the lowermost part of the Kunzum La Formation along the Khemangar khad and the Parahio Valley sections, Spiti Region (Zanskar-Spiti-Kinnaur Basin), Northwest Himalaya, India)

The Cambrian sequence, designated as the Kunzam La Formation, is exposed along the cLassical Parahio Valley section and also on left bank of the Khemangar khad in the Parahio Valley (Spiti), the Latter constitutes the lowermost exposed part of the Kunzum La Formation. The lower part of the Parahio Valley section and outcrop near the left bank of the Khemangar khad were studied for integrated litho-ichnofacies and ichnofabric analysis. The study establishes a genetic reLationship of the strata of these two localities. Five lithofacies are recognised in both the examined sections. The lithofacies indicate a wave-dominated shallow marine environment of deposition for these Cambrian rocks. The overall calcuLated ichnofabric indices in 74 m exposed strata at the Khemangar khad locality range from ii1=80.% (represented by 25.8 m), ii2= 17% (represented by 5.4 m) and ii4=2.5 % (represented by 0.8 m). The 42 m rocks examined in the main Parahio Valley section indicate ichnofabric indices ranging from ii1=37% (represented by 17.8 m), ii2=21% (represented by 8.0 m), ii3=40% (represented by 15.2 m) and ii4=2.0% (represented by 1.0 m). The presence of archetypal Cruziana ichnofacies, parallel and wavy Laminations, hummocky cross stratification (HCS) and trough cross stratification (TCS) supports a wave-dominated shallow water environment from upper shoreface to middlelower shoreface setup for the deposition of the lowermost part of the Kunzum La Formation in the Parahio Valley.

Lower Ordovician (Arenig) shallow-marine trace fossils of the Pochico Formation, southern Spain: palaeoenvironmental and palaeogeographic implications at the Gondwanan and peri-Gondwanan realm

Nineteen ichnospecies belonging to thirteen ichnogenera (Archaeonassa, Catenichnus,Cochlichnus, Cruziana, Didymaulichnus, ?Diplichnites, Gordia, Lingulichnus, Lockeia, cf.Monocraterion, Planolites, Ptychoplasma, and Rusophycus) occur in the Pochico Formation(Arenig) in the Aldeaquemada section, Sierra Morena, southern Spain, just above the ArmoricanQuartzite. They belong to the archetypal Cruziana ichnofacies, indicating a lower shoreface-upperoffshore zone. The low degree of sediment reworking may be due to a high rate of sedimentation.The trace fossil assemblage, rich in large Cruziana, is typical of the Armorican Quartzite thatdeveloped on the margins of Gondwana and peri-Gondwanan microcontinents. The distribution ofichnofauna during the Early Ordovician was partly palaeogeographically controlled, althoughichnological data from the literature point to paths of migration between Gondwana, Baltica andLaurentia. Differences between the ichnofauna of Gondwana and Baltica could be conditioned byfacies (clastics in Gondwana and carbonates in Baltica) causing a taphonomic filter, becauseCruziana requires diversified clastic deposits for preservation. The ichnofauna would also beinfluenced by trophic group amensalism between filter feeding and deposit feeding fauna, theformer prevailing in Baltica and the latter in Gondwana.

Cambrian trace fossils of the Cruziana ichnofacies from the Bikaner-Nagaur Basin, north western Indian Craton

The Marwar Supergroup of the Bikaner-Nagaur Basin is composed of sediments deposited from the late Neoproterozoic (Ediacaran) to Upper Cambrian. The Nagaur Sandstone Formation of the Nagaur Group (uppermost division of the Marwar Supergroup) preserves trace fossils significant for establishing Early Cambrian biostratigraphic zones and depositional facies. Fifteen ichnospecies (and eight ichnogenera) identified in the Nagaur Sandstone Formation include “Treptichnus” pedum, Cruziana cf. tenella, Cruziana isp., Diplichnites ispp. A, B, and C, Gyrophyllites isp., Lockeia isp., Merostomichnites isp., Monomorphichnus gregarius isp. nov., Monomorphichnus isp., Planolites isp., Psammichnites isp., Rusophycus bikanerus isp. nov., Rusophycus cf. carbonarius, Rusophycus isp. and radial trace fossils.These trace fossils belong to ethological categories pascichnia, repichnia, cubichnia, and fodinichnia and represent arthropod and worm-like burrowing biota. The assemblage and a regional comparison with contemporaneous trace fossils in the eastern Gondwanan realm suggest that the sequence in the study area belongs to the Cruziana tenella Ichnozone and to Stage 2 (upper part of Terreneuvian), however the Middle Cambrian is not excluded. The trace fossil assemblage belongs to the archetypal Cruziana ichnofacies. Cross bedded sandstone, mud cracks and rainprints in the ichniferous strata of the Nagaur Sandstone Formation indicate deposition in an intertidal sand flat with channels that was exposed episodically.

Middle Turonian trace fossils from the Bystrzyca and Długopole sandstones

The Middle Turonian sediments of the Nysa Klodzka Graben (Bystrzyca Sandstone in the Stara Bystrzyca outcrop and the Dlugopole Sandstone in Dlugopole Gorne Quarry) contain trace fossils, which include Curvolithus simplex, ?Macaronichnus isp., Ophiomorpha nodosa, Ophiomorpha isp., Palaeophycus tubularis, Thalassinoides cf. paradoxicus, T. suevicus and Thalassinoides isp. The assemblage of trace fossils points to the proximal Cruziana ichnofacies, that characterizes the distal lower shoreface and the archetypal Cruziana ichnofacies, typical of upper offshore settings. The trace fossils evidence implies that sedimentation took place in a shallow basin with periods of a sudden sediment input, good oxygenation and normal salinity. The Bystrzyca and Dlugopole sandstones are deposits of the shallow epicontinental sea that were deposited between the fair-weather and storm-wave base, in the distal lower shoreface–upper offshore setting. The Bystrzyca Sandstone is recognized as storm-originated deposits, whereas the Dlugopole Sandstone is probably the part of prograding “accumulation terrace”. The source of material for the sandstone was the East Sudetic Island and probably also the Orlica–Bystrzyca Uplift. The studied sandstones are related to a regression that started in the early/middle Middle Turonian and caused a relative uplift of the surrounding land. The Middle Turonian sediments of the Nysa Klodzka Graben (Bystrzyca Sandstone in the Stara Bystrzyca outcrop and the Dlugopole Sandstone in Dlugopole Gorne quarry) contain trace fossils, which include Curvolithus simplex , ? Macaronichnus isp., Ophiomorpha nodosa , Ophiomorpha isp., Palaeophycus tubularis , Thalassinoides cf. paradoxicus , T . suevicus and Thalassinoides isp. The assemblage of trace fossils points to the proximal Cruziana ichnofacies, that characterizes distal lower shoreface and the archetypal Cruziana ichnofacies, typical of upper offshore settings. The trace fossils evidence implies that sedimentation took place in a shallow basin with periods of a sudden sediment input, good oxygenation and normal salinity. The Bystrzyca and Dlugopole sandstones are deposits of the shallow epicontinental sea that were deposited between fair-weather and storm-wave base, in the distal lower shoreface - upper offshore setting. The Bystrzyca Sandstone is recognized as storm-originated deposits, whereas the Dlugopole Sandstone is probably the part of prograding “accumulation terrace”. The source of material for the sandstone was the East Sudetic Island and probably also the Orlica-Bystrzyca Uplift. The studied sandstones are related to a regression that started in the early/middle Middle Turonian and caused a relative uplift of the surrounding land.

Onshore expansion of benthic communities after the Late Devonian mass extinction

A detailed ichnological analysis of the Upper Devonian–Lower Mississippian Bakken Formation of sub-surface Saskatchewan and the partially coeval Exshaw Formation of Alberta indicates the presence of an anomalous ichnofacies gradient. The distal Cruziana Ichnofacies, which in rocks of other ages is restricted to lower-offshore facies, here ranges from this setting to the lower shoreface. No archetypal Cruziana Ichnofacies is present in these deposits. This pattern is interpreted as resulting from the differential effects of the Late Devonian mass extinction in shallow-water ecosystems. The onshore expansion evidenced by ichnological data is consistent with the pattern displayed by the body-fossil record, which indicates a re-invasion of shallow-water environments by the Palaeozoic evolutionary fauna during the Late Devonian and into the Early Carboniferous. The ichnofauna studied is overwhelmingly dominated by deposit feeders, with suspension feeders being notably absent, further underscoring the importance of trophic type as a selectivity trait during mass extinctions.

Ichnology of the Late Carboniferous Hoyada Verde Formation of western Argentina: Exploring postglacial shallow-marine ecosystems of Gondwana

The postglacial interval of the Upper Carboniferous Hoyada Verde Formation of western Argentina contains an ichnofauna dominated by Psammichnites plummeri and Psammichnites implexus, with minor occurrences of Ptychoplasma vagans, Treptichnus bifurcus, Lingulichnus verticalis, Protovirgularia isp., Lockeia isp., Palaeophycus isp., scarce arthropod trackways and some bilobate structures. The particular features of this association indicate a depauperate expression of the Cruziana Ichnofacies, and suggest a context that differs from the expected in normal shallow-marine settings (i.e. archetypal Cruziana Ichnofacies). Integration of sedimentologic, ichnologic, sequence-stratigraphic and paleontologic data points to a prograding deltaic system influenced by wave action. Trace fossils have been extensively used to recognize stressed brackish-water environments in the late Paleozoic of Gondwana. However, the recognition of stressed settings needs to take into consideration the specific paleogeographic context of glacially influenced Gondwanan settings. A postglacial open sea adjacent to a paleotopographic high is considered as a possible scenario for the Hoyada Verde Formation. In this particular setting, coastal biotas could have been influenced to some degree by the salinity gradient triggered by freshwater release near to melting ice masses stored in highlands and also by freshwater plumes due to longshore currents. Regional factors (e.g. proximity to highlands and climate) may have played an important role in controlling the characteristics of Gondwanan ichnofaunas. This suggests that the distinction between normal-marine and brackish-water settings in glacially influenced environments using trace fossils may not be as straightforward as in non-glacial settings.

Sedimentological–ichnological model for tide‐dominated shelf sandbodies: Lower Cambrian Gog Group of western Canada

AbstractDunes and bars are common elements in tide‐dominated shelf settings. However, there is no consensus on a unifying terminology or a systematic classification for thick sets of cross‐stratified sandstones. In addition, their ichnological attributes have hardly been explored. To address these issues, the properties, architecture and ichnology of compound cross‐stratified sandstone bodies contained in the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains are described here. In these transgressive sandstones, five types of compound cross‐stratified sandstone are distinguished based on foreset geometry, sedimentary structures and internal heterogeneity. These represent four broad categories of subtidal sandbodies: (i) compound‐dune fields; (ii) sand sheets; (iii) sand ridges; and (iv) isolated dune patches; tidal bars comprise a fifth category but are not present in the Gog Group. Compound‐dune fields are characterized by sigmoidal and planar cross‐stratified sandstone in coarsening‐upward and thickening‐upward packages (Type 1); these are mostly unburrowed, or locally contain representatives of the Skolithos ichnofacies, but are intercalated with intensely bioturbated sandstone containing the archetypal Cruziana ichnofacies. Sand‐sheet complexes, also composed of compound dunes, cover more extensive subtidal areas, and comprise three adjacent subenvironments: core, front and margin. The core is characterized by thick‐bedded sets of cross‐stratified sandstone (Type 2). A decrease of bedform size at the front is recorded by wedges of thinner‐bedded, low‐angle and planar cross‐stratified sandstone (Type 3) exhibiting dense Skolithos pipe‐rock ichnofabric. The margin is characterized by interbedded sandstone and mudstone, and hummocky cross‐stratified sandstone. Sand‐sheet deposits exhibit clear trends in trace‐fossil distribution along the sediment transport path, from non‐bioturbated beds in the core to Skolithos ichnofacies at the front, and a depauperate Cruziana ichnofacies at the margin. Tidal sand ridges are large elongate sandbodies characterized by large sigmoid‐shaped reactivation surfaces (Type 4). Sand ridges display clear ichnological trends perpendicular to the axis of the ridge, with no bioturbation or a poorly developed Skolithos ichnofacies in the core, a depauperate Cruziana ichnofacies in lee‐side deposits, and Cruziana ichnofacies at the margin. While both tidal ridges and tidal bars migrate by means of lateral accretion, the latter occur in association with channels while the former do not. Because tidal bars tend to occur in brackish‐water marginal‐marine settings, their ichnofauna are typically of low diversity, representing a depauperate Cruziana ichnofacies. Isolated dune patches developed on sand‐starved areas of the shelf, and are represented by lenticular sandbodies with sigmoidal reactivation surfaces (Type 5); they typically lack trace fossils, but the interfingering muddy deposits are intensely bioturbated by a high‐diversity fauna recording the Cruziana ichnofacies. The variety of sandbody types in the Gog Group reflects varying sediment supply and location on the inner continental shelf. These, in turn, governed substrate mobility, grain size, turbidity, water‐column productivity and sediment organic matter which controlled trace fossil distribution.

Ichnological trends along an open-water transect across a large marginal-marine epicontinental basin, the modern Baltic Sea

Late Holocene sediments in the Baltic Sea provide an opportunity to study lateral changes in the assemblages of identifiable biogenic sedimentary structures (ichnofossils) in a large, high-latitude semi-enclosed sea with instrumentally determined gradients in biodiversity and environmental factors such as salinity and oxygen availability. Integrated sedimentological and ichnological analysis is carried out on 6 long cores collected along an open-sea, declining salinity transect across the basin. Muddy sediments in euhaline (Kattegat) and polyhaline (Mecklenburg Bight) sites are characterized by the archetypal Cruziana Ichnofacies, portrayed by subsurface deposit-feeding structures ( Scolicia and Planolites), surface deposit-feeding structures ( Skolithos), and structures that reflect both these feeding strategies ( Palaeophycus, Arenicolites/ Polykladichnus and unnamed biodeformational structures produced by bivalves). The ichnofossils are tiered to 3 levels. The Cruziana Ichnofacies is impoverished in the higher mesohaline Arkona Basin and even more so with declining salinity farther inland. The deepest, oxygen-restricted study sites (Gotland Deep and the western Gulf of Finland) below a permanent halocline are characterized by very small and shallow deposit-feeding structures ( Planolites and rare flat Arenicolites/ Polykladichnus), and poorly developed tiering. The nearly freshwater eastern Gulf of Finland is characterized by the Cenozoic archetypal Mermia Ichnofacies, dominated by narrow and shallow subsurface and surface deposit-feeding structures ( Planolites and flat Arenicolites/ Polykladichnus). Large Planolites (3–7 mm in diameter) at this site are untypical of Mermia Ichnofacies assemblages. These results confirm the earlier observations that marine forms dominate brackish-water ichnoassemblages, with the ichnofossil size and diversity decreasing with declining salinity. The results also confirm the predicted decreases in the ichnofossil size and vertical extent at low-oxygen levels. Poorly developed tiering is a particularly useful indicator of oxygen stress in the salinity-restricted system.

Evaluating delta asymmetry using three‐dimensional facies architecture and ichnological analysis, Ferron ‘Notom Delta’, Capital Reef, Utah, USA

AbstractDelta asymmetry occurs where there is strong wave influence and net longshore transport. Differences in the morphology and facies architecture between updrift and downdrift sides of asymmetric deltas are potentially significant for exploration and exploitation of resources in this class of reservoirs. Although delta asymmetry has been recognized widely from modern wave‐influenced deltaic shorelines, there are few documented examples in the ancient record. Based on an integrated sedimentological and ichnological study, the along‐strike variability and delta asymmetry within a single parasequence (Ps 6) is documented in continuously exposed outcrops of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation near Hanksville in southern Utah. Two intra‐parasequence discontinuity surfaces are recognized which allow subdivision of the parasequence into three bedsets, marked as Ps 6‐1 to Ps 6‐3. Four facies successions are recognized: (i) wave/storm‐dominated shoreface; (ii) river‐dominated delta front; (iii) wave/storm‐reworked delta front; and (iv) distributary channel and mouth bar. Dips of cross‐strata within distributary‐mouth bars and shorefaces show a strong downdrift (southward) component. Ps 6‐3 predominantly consists of river‐dominated delta‐front deposits, whereas Ps 6‐1 and Ps 6‐2 show an along‐strike facies change with shoreface deposits in the north, passing into heterolithic, river‐dominated delta‐front successions south to south‐eastward, and wave/storm‐reworked delta‐front deposits further to the south‐east. Trace fossil suites correspondingly show distinct along‐strike changes from robust and diverse expressions of the archetypal Cruziana Ichnofacies and Skolithos Ichnofacies, into suites characterized by horizontal, morphologically simple, facies‐crossing ichnogenera, reflecting a more stressed, river‐dominated environment. Further south‐eastward, trace fossil abundance and diversity increase, reflecting a return to archetypal ichnofacies. The overall facies integrated with palaeocurrent data indicate delta asymmetry. The asymmetric delta consists of sandier shoreface deposits on the updrift side and mixed riverine and wave/storm‐reworked deposits on the downdrift side, similar to that observed in the modern examples. However, in contrast to the recent delta asymmetry models, significant paralic, lagoonal and bay‐fill facies are not documented in the downdrift regions of the asymmetric delta. This observation is attributed to a negative palaeoshoreline trajectory during delta progradation and subsequent transgressive erosion. The asymmetric delta was induced by net longshore transport from north to south. The forced regressive nature of the delta precludes significant preservation of topset mud.