Ichnology and sedimentology of a tide‐influenced delta in the Ordovician from the northeastern Alborz range of Iran (Kopet Dagh region)

The Middle–Late Ordovician Ghelli Formation in the Kopet Dagh region northeastern Alborz range of Iran is composed of siliciclastic rocks deposited in a variety of turbidite to marginal marine environments (deep marine clastic fan and related environments and prodelta, distal delta front, proximal delta front and distributary channels). The ichnology of the middle member of the Ghelli Formation is here reported. Combined sedimentological and ichnological analysis allows recognition of a tide‐influenced deltaic succession in the middle member of the Ghelli Formation consisting of three main facies associations: lower distributary channels, delta front and prodelta facies. Twenty‐two ichnogenera have been identified in this marginal marine succession: Arenicolites, Arthrophycus, Bergaueria, Chondrites, Conichnus, Cruziana, Cylindrichnus, Didymaulichnus, Diplichnites, Diplocraterion, Helminthopsis, Gyrochorte, Lockeia, Macaronichnus, Monomorphichnus, Palaeophycus, Planolites, Rosselia, Rusophcus, Skolithos, Teichichnus and ?Scolicia. Their distribution is clearly linked with lithofacies and depositional palaeoenvironments. The ichnological analysis reveals that the trace fossil suites developed in these environments indicate low diversity and low to moderate abundance of burrows, poor development of tiering and sporadic distribution. Low ichnodiversity and low bioturbation intensities with higher bioturbation clusters consist of facies‐crossing ichnogenera, and the impoverishment of suspension‐feeding trophic types indicates ‘stressed’, non‐archetypal expression of the Cruziana ichnofacies. The periodic higher intensities of bioturbation due to variations in hydrodynamic regimes of tidal currents reflect the archetypal of the Cruziana ichnofacies (and rare Skolithos ichnofacies).     

Controls on trace fossil diversity in an Early Cambrian epeiric sea: new perspectives from northwest Scotland

The Lower Cambrian Eriboll Formation of northwest Scotland is renowned for the high density, low diversity trace fossils (Skolithos ichnofacies) found in its upper Pipe Rock Member. Ichnofabric analysis of the member indicates that relatively small examples of Skolithos terminating at the same foreset boundary were formed during a brief colonization window after a single depositional event, that particularly long Skolithos specimens are equilibrichnia, and that palimpsests of Skolithos represent the marginal, slightly deeper water fringes of the Pipe Rock Member depositional environment. Nearest neighbour analysis, however, suggests that such palimpsests were uncommon. A much more diverse trace fossil assemblage is present in the overlying Fucoid Member (An t‐Sròn Formation), comprising Cruziana barbata, Dactylophycus, Didymaulichnus, Halopoa imbricata, ?Margaritichnus, Monocraterion, Monomorphichnus, Palaeophycus striatus, P. tubularis, ?Phycodes, Planolites montanus, ?Polarichnus, Rusophycus ramellensis, ?Psammichnites, Skolithos and various unidentified traces, and represents the Cruziana ichnofacies. Above the Fucoid Member, the Salterella Grit Member ichnofauna is more impoverished, yielding only Cruziana, Monocraterion, Rusophycus, Skolithos and ?Spirophyton. The ichnological variations between the Pipe Rock, Fucoid and Salterella Grit members are interpreted as being driven by changes in sea level. The low trace fossil diversity in the Pipe Rock Member indicates opportunistic colonization of laterally extensive, shoreface sediments deposited by regular influxes of terrigenous material, which were overlain by more distal, ichnologically diverse sediments (Fucoid Member) as sea level rose. A minor regression then caused an increase in terrigenous sediment input, producing an impoverished, proximal Cruziana ichnofacies (Salterella Grit Member).     

Ichnological analysis of Jurassic shallow to marginal marine deposits: example from Wagad Highland,Western India

Abstract

Jurassic deposits of shallow to marginal marine (delta) environments are widely reported from different continents of the world. This study shows inter-relationship of the animal-sediment behaviours in shallow and marginal marine conditions, suggesting an interpretation of the possible ichnodisparity. The Jurassic succession exposed at Washtawa Dome and Adhoi Anticline of Wagad highland, Kachchh comprises an approximately 341 m thick succession, divided into two formations – Lower Washtawa and Upper Wagad Sandstone. Eight sparsely to highly bioturbated sedimentary units show twenty-three identifiable ichnospecies from fifteen ichnogenera representing five ichnoassemblages broadly attributable to the Skolithos and the Cruziana ichnofacies, and developed in shallow-marine strandplain shoreface and delta depositional facies. The relative frequency statistical data reveals the dominant occurrence of feeding structures generated by polychaetes preferentially in quartz arenites. These structures represent sub-horizontal, sub-vertical and complex burrows, and show twelve and six categories of architectural designing Callovian-Oxfordian of shallow-marine shoreface and Oxfordian-Kimmeridgian shallow-water delta successions, respectively. The lower ichnodiversity and ichnodisparity associated with the Oxfordian-Kimmeridgian deltaic intervals represents a decrease in the exploitation of under-used ecospace, due to unfavourable environmental conditions rather than an expression of evolutionary radiation.     

Lithostratigraphy of the Lower Cambrian metaclastics and their age based on trace fossils in the Sand?kl? region, southwestern Turkey

In the Sand?kl? region of the Taurus Range of Turkey, greater than 3000 m in thickness metamorphosed siliciclastics and volcanics (Kocayayla Group) underlies the trilobite-and conodont-bearing Middle-Late Cambrian Hudai Quartzite and Çaltepe Formation.The Kocayayla Group, previously regarded as Infracambrian or Precambrian, is dated for the first time as Early Cambrian on the basis of trace fossils. Cruziana ?fasciculata, C. ?salomonis, ?Cruziana isp., ?Diplichnites isp., Monomorphichnus isp., Petalichnus isp., Rusophycus ?avalonensis, R. ?latus, Arenicolites isp., cf. Altichnus foeyni, Planolites isp., Skolithos isp., and ?Treptichnus isp. have been recognised. These trace fossils are considered Tommotian or younger in age but older than the overlying, trilobite and conodont bearing Middle Cambrian limestones of the Çaltepe Formation. The trace fossils were likely produced by trilobites, suspension feeding annelids and deposit feeding “worms”, probably polychaetes. Sections bearing abundant Skolithos represent the Skolithos ichnofacies, which is typical of high energy environments with loose sandy, well sorted to slightly muddy substrates in intertidal to shallow subtidal zones. The other trace fossils represent the Cruziana ichnofacies, which is typical of subtidal, poorly sorted and soft substrates, from moderate energy to low energy environments between the fairweather and storm wave base.The Kocayayla Group was deposited at an early stage in a shallow marine stable shelf condition. The shelf subsided in a later stage and was affected by normal faults along which mafic and felsic volcanic rocks erupted. The volcanic activity had ceased and a shallow marine clastic sedimentation took place in the final stage of the shelf development. The Kocayayla Group was deformed and metamorphosed before the deposition of the trilobite-bearing Middle-Upper Cambrian succession.     

The Trace Fossil Paleodictyon within The Cruziana Ichnofacies: First Record from The Devonian in Pennsylvania

Offshore marine deposits of hemipelagic dark-gray shales comprising the Middle Devonian Mahantango Formation have yielded the first evidence of the trace fossil Paleodictyon from Pennsylvania. Paleodictyon occurs in conjunction with a diversity of largely deposit-feeding trace fossils belonging to the Cruziana ichnofacies, and documents another example of a shallower-water occurrence of this ichnofossil in Paleozoic rocks.     

A diverse deep‐marine Ichnofauna from the Eocene Tarcau sandstone of the Eastern Carpathians,Romania

The Paleocene to Middle Eocene Tarcau Sandstone at Buzau Valley, eastern Carpathians, Romania, records sedimentation in a turbidite system. These strata contain a diverse and abundant pre‐ and postdepositional ichnofauna consisting of 35 ichnogenera and 54 ichnospecies. The predepositional assemblage is rich in graphoglyptids and ornate grazing trails; simple grazing trails, resting traces, and feeding structures also occur. The predepositional assemblage includes Acan‐thorhaphe, Belorhaphe, Cardioichnus, Circulichnus, Coch‐lichnus, Cosmorhaphe, Desmograpton, Fustiglyphus, Gordia, Helicolithus, Helminthopsis, Helminthorhaphe, Lorenzinia, Megagrapton, Paleodictyon, Paleomeandron, Protopaleodictyon, Scolicia (S. strozzii), Spirorhaphe, Spirophycus, Treptichnus, and Urohelminthoida. The ich‐nodiversity, composition, ethology, and morphologic complexity of the predepositional association are indicative of the Nereites ichnofacies. The postdepositional association essentially consists of dwelling, feeding, and grazing traces, and is represented by Chondrites, Glockerichnus, Halopoa, Nereites, Ophiomorpha, Phycodes, Planolites, Polykampton, Scolicia(S. prisca. S. striata), Taenidium, Thalassinoides, and Zoophycos. Palaeophycus occurs in both assemblages. Allochthonous Teredolites is present in wood fragments, The postdepositional association includes elements of the Skolithos ichnofacies and facies‐crossing forms that are commonly present in deep‐marine deposits, Elements of the Skolithos ichnofacies are present not only in the most proximal parts of the turbidite system, but also in distal parts. The number of predepositional forms greatly exceeds postdepositional ones, reflecting a dominance of K‐selected over r‐selected population strategies in a stable environment. High levels of ichnodiversity in the Tarcau Sandstone are comparable with deep‐sea ichnofaunas from the Polish Carpathians and with other flysch trace‐fossil assemblages of similar age. This abundant and diverse Eocene ichnofauna supports the idea of extremely rich deep‐sea ichnofaunas in the Cenozoic.     

Stellavelum arborensis igen., sp. nov., Stellavelum uncinum igen., isp. nov. and Termitichnus namibiensis isp. nov.; New Ichnofossils from Cenozoic deposits of Namaqualand,South Africa

Three new ichnotaxa are described from Cenozoic paralic to continental sediments on the west coast of South Africa. Stellavelum arborensis and Stellavelum uncinum are assigned to a mixed Skolithos and Cruziana ichnofacies and Termitichnus namibiensis is assigned to the Termitichnus ichnofacies. An interpretation of the sedimentary record shows that the Stellavelum trace makers were probably sediment ingesting annelids that lived in dense colonies in sheltered lagoonal environments during Neogene times. The Termitichnus namibiensis trace fossils are interpreted as actively backfilled termite nests which form an early to mid‐Pleistocene palimpsest, terrestrial ichnofabric which is superimposed on the older marine sediments.     

Trace fossil associations related to facies of an upper Ordovician low wave energy shoreface and shelf, Oslo-Asker district, Norway

Three trace fossil associations have been identified from facies interpreted as low wave energy upper, middle and lower shoreface deposits, transitional shoreface/shelf deposits and open epicontinental shelf deposits. These were developed in pre-regressive, regressive and transgressive phases associated with eustatic sea level changes caused by the upper Ordovician glaciation. The three associations are the Skolithos-Diplocraterion association, the Diplichnites-Phycodes association and the Thalassinoides association. The Skolithos-Diplocraterion association inhabited upper, middle and lower shoreface environments, the Diplichnites-Phycodes association a lowermost shoreface environment and the Thalassinoides association inhabited offshore epicontinental shelf environmcnts. The Skolithos-Diplocraferion and Diplichnites-Phycodes associations bear strong affinities with previously described Skolithos ichnofacies assemblages (indicating shoreline environments) and the Cruziana ichnofacies forms (indicating shallow water environments down to wave base) respectively. The Thalassinoides assemblage, however, closely compares with assemblages described from Mesozoic epicontinental shelf sequences. Trace fossil diversity achieves a maximum in the lowermost shoreface environment and reduces in deeper water and shallower water environments. This accords with diversity patterns identified in analogous Jurassic epicontinental palaeonvironments. The stratigraphic distribution of some trace fossil association boundaries accords with those of contemporary body fossil associations. However, several body fossil associations are included within the volume of distribution of a single trace fossil assemblage. □ Trace fossil association, shoreface and shelf, Oslo district, upper Ordovician.     

Trace fossils and their environmental significance in Dinantian carbonates of Belgium

Dinantian carbonates of the Tournai and Dinant regions, southern Belgium, contain several trace fossil assemblages. These assemblages consist of the following ichnogenera:Cruziana, Rhizocorallium,Scalarituba, Scolicia, Skolithos, Phycosiphon, Planolites andZoophycos. Scalarituba andPhycosiphon are reported for the first time from the Carboniferous of Western Europe. The ichnofossils occur in discrete ichnofacies.Skolithos andZoophycos ichnofacies occur within the Ivorian (Upper Tournaisian). TheCruziana andSkolithos ichnofacies are found in the Moliniacian (Lower Visean). In the Dinant region, ichnofossils record a change from infauna to epifauna at the Ivorian-Moliniacian transition. Woodgrained chert is recognized and corresponds stratigraphically and palaeogeographically with those from the Western Interior United States.     

Marine influence and incursion in the Gondwana basins of Orissa, India: A review

The Permian–Triassic succession of the Indian Gondwana Sequence was previously considered to have been deposited in a fluviatile-lacustrine environment. Similarly, earlier Lower Gondwanas of Orissa State (a major part of the Mahanadi Master basin) were considered entirely fresh water deposits. Faunal evidence is still scanty in this master basin. Ichnology and palynology along with a few sedimentary records are reviewed and analysed for inferring marine signature. The marine nature of the Talchir, Karharbari, Barakar, Barren Measures and Kamthi sediments of three major basins (Talcher, Ib River and Athgarh) in Orissa State was predicted on the basis of typical marine ichnofossils. Most of these sediments also contain acritarchs reflecting marine marginal environment throughout the Permian. Moreover, evidence of wave activity, salinity raise and discovery of phosphorite in Permian sediments also strengthen this view.Hence, the previous model of continental facies for the Lower Gondwanas is found to be incorrect. The ichnofossils (Skolithos and Cruziana ichno-facies), acritarchs (Foveofusa, Leiosphaeridia, Greinervillites, etc.) and other palynofossils of marine origin can be utilized as a tool for palaeoenvironmental reconstruction. In the Gondwana basins of Orissa (Mahanadi Master basin), consistent occurrence of marine acritarchs and trace fossils with some typical sedimentary structures such as wave ripples has been studied and reviewed from the Talchir (Early Permian) to Upper Kamthi (Triassic) formations at various time intervals. Here marine incursion could have occurred due to the well known global transgressions during Permian and Triassic.     

Plant Traces Resembling Skolithos

The ichnogenus Skolithos Haldeman 1840 is a simple tubular trace fossil that was initially described as a “fucoid” or seaweed impression, i.e., a fossilized marine plant. Today the tracemaker is commonly considered to have been a vermiform marine invertebrate, although this interpretation is not acceptable to all. It is the name giver to the archetypal, Seilacherian Skolithos ichnofacies, which is a widely acknowledged indicator of relatively high energy, shallow water, nearshore to marginal marine environments. Here we record and describe analogous cylindrical structures, unquestionably reflecting plant tracemakers. These have been recognized in Quaternary consolidated “coffee” sandrock and Recent coastal dune, marsh or swamp, and salt meadow settings from northern New Zealand and Sapelo Island, USA.

We conclude that Skolithos is not an unequivocal indicator of shallow marine settings. Our observations confirm the opinions of a number of previous workers who have expressed the need for caution when using this ichnotaxon as a shallow-water, higher energy palaeoenvironmental indicator, especially when supporting evidence is otherwise lacking. In particular we note that in high intertidal and non-aquatic settings, Skolithos may be a plant trace fossil rather than serve as evidence for invertebrate activities. At the present time there is pressing need for a thorough systematic revision of the Skolithos ichnotaxon.     

Trace fossils analysis of fluvial to open marine transitional sediments: Example from the Upper Devonian (Geirud Formation), Central Alborz,Iran

This study integrates ichnological and sedimentological data to interpret depositional environments of the mixed siliciclastic-carbonate fluvial to marine sediments of the Geirud Formation (Upper Devonian) in the central Alborz, northern Iran. Lithofacies analysis shows that these sediments are deposited in fluvial, tidal, shoreface, and shelf environments. Fluvial and tidal deposits are characterized by the presence of bi- to multi-directional cross beddings, reverse directional current ripples, low angle cross beddings, and herringbone cross beddings, with a few scattered Skolithos and Palaeophycus. Shoreface sediments, accumulated in a storm-influenced setting, are characterized by a preferentially interface and low diversity Cruziana ichnoassemblage (Rhizocorallium, Thalassinoides, Palaeophycus, Chondrites, and Ophiomorpha). In contrast to the fluvial-tidal assemblage, the storm-influenced shelf sediments display a highly diversified, mixture of dwelling and feeding forms (Arenicolites, Protovirgularia, Diplocraterion, Palaeophycus, Thalassinoides, Chondrites, and Helminthopsis), reflecting the presence of adequate food resources both in substrate and water column under normal salinity conditions. A fluvial-shelf replacement of the weakly to scarcely bioturbated sediments by the Rhizocorallium-Thalassinoides suite (Cruziana) – Chondrites-Helminthopsis (distal Cruziana) suite from the lower to upper parts of the succession clearly indicates an overall deepening upward in the Geirud Formation. In contrast to the lower part, generally of restricted environment, the upper part of the succession mainly shows open marine conditions. Ichnofabric development is controlled primarily by depositional conditions, e.g., bottom water oxygenation, sediment type, food abundance, and hydrodynamic level, which all exert control on substrate colonization style.     

Trace fossils from lower Cambrian Hongjingshao Formation,Yunnan, China: Taxonomy,palaeoecology, palaeoenvironment

The Hongjingshao Formation (Cambrian Series 2, Stage 3) yields abundant, complex trace fossils that have not been systematically investigated up till now. Our detailed ichnological study of the traces from this formation in Malong area, Yunnan, China, recognizes four groups: (1) simple horizontal or sub-horizontal burrows; (2) complex branched burrow systems; (3) arthropod trails and; (4) simple vertical burrows belonging to the Cruziana ichnofacies. A trophic web is reconstructed for the community in Hongjingshao Formation based on both trace and body fossils. The ichnological and sedimentological features of the formation indicate an intertidal setting. The trace fossil assemblage demonstrates that Early Cambrian organisms were able to colonize very shallow marine environments, which further supports the landward expansion of the Early Cambrian ecosystems.     

An integrative ichnological and taphonomic approach in a transgressive–regressive cycle: a case study from Devonian of Paraná Basin,Brazil

The palaeoenvironmental context of a section of the Devonian Ponta Grossa Formation (Paraná Basin) was examined using an integrated ichnological and taphonomic approach. Three taphofacies (T‐A, T‐B and T‐C) and six ichnofabrics are recognized. T‐A is mainly composed of disarticulated organisms and is associated with Chondrites, Planolites‐Palaeophycus, Asterosoma‐Zoophycos and Asterosoma‐Chondrites ichnofabrics, representing the Cruziana ichnofacies. The upward increase in diversity and abundance of body fossils for Taphofacies A can be explained by changes in sedimentation rates during aggradational to progradational phases. T‐B beds, represented by articulated brachiopods, occur in distal tempestites associated with the Skolithos ichnofabric (Skolithos ichnofacies) and represent higher hydrodynamic energy and oxygenation than in T‐A. Taphofacies C, characterized by a mix of articulated and disarticulated organisms, generally lacks bioturbation except for Chondrites ichnofabrics occurring only at the bed tops, suggesting low substrate oxygenation and low‐energy conditions. T‐C indicates the maximum transgression in the T‐R cycle, characterizing it as a good indicator of maximum flooding surfaces. The composite Asterosoma‐Teichichnus ichnofabric (bioturbation degree 5) occurs in layers without body fossils and represents suites of the Cruziana ichnofacies. This likely reflects intense intrastratal activity at all substrate levels, which facilitated the oxygenation of the substrate disallowing the preservation of organism remains. This observation indicates that the bioturbation is an important factor controlling the loss of taphonomic information within the TAZ, mainly when associated with detritus‐feeding trace fossils.     

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.     

Tetrapod Ichnofacies: A New Paradigm

We recognize three fundamental terms in ichnology: (1) ichnoassemblage, which is an assemblage of ichnofossils conceptually equivalent to an assemblage of body fossils; (2) ichnocoenosis, which is a trace fossil assemblage produced by a biological community that can be characterized by morphological criteria; and (3) ichnofacies, which refers to recurrent ichnocoenoses that represent a significant portion of Phanerozoic time. There are two different kinds of ichnofacies, ethoichnofacies (mostly invertebrate ichnofacies) and biotaxonichnofacies (mostly tetrapod ichnofacies). Nonmarine invertebrate ichnologists now recognize five archetypal ichnofacies (Mermia, Skolithos, Scoyenia, Coprinisphaera, Psilonichnus) to which we add the Octopodichnus ichnofacies. We propose a coherent and consistent classification and nomenclature for tetrapod ichnofacies. We name five archetypal vertebrate ichnofacies for nonmarine environments: Chelichnus, Grallator, Brontopodus, Batrachichnus and Characichnos ichnofacies.     

Trace fossils in fluvial deposits of the uppermost Stockton Formation (Late Triassic), Newark Basin,New Jersey

Abstract

Fluvial deposits of the uppermost Stockton Formation (Late Triassic), Newark Basin, west-central New Jersey have yielded an assemblage of trace fossils. Dominated by burrows, specimens include Cochlichnus anguineus, Helminthoidichnites tenuis, Planolites beverleyensis, Scoyenia gracilis, Spongeliomorpha carlsbergi, Treptichnus bifurcus, Treptichnus pollardi, plant remains, and an undetermined vertebrate trace fossil. The assemblage belongs to the Scoyenia ichnofacies. On the basis of stratification and primary sedimentary structures, the beds are interpreted as deposits in a meandering stream environment. Larval insects, wormlike forms, and arthropods are probably responsible for most of the animal traces in wet or moist channel, floodplain, and point bar sediments subject to subaerial exposure.     

Palaeoenvironmental implications of the ichnology and geochemistry of the Westbury Formation (Rhaetian), Westbury‐on‐Severn,south‐west England

Abstract: The Westbury Formation (Rhaetian) beds of Westbury Garden Cliff, Westbury‐on‐Severn, west of Gloucester, Britain, show an unusual combination of features. Both deep water and emergent characteristics are present within the sediments and the trace fossils. The ichnoassemblage consists of abundant Selenichnites, Planolites beverlyensis and Lockeia with rarer Oniscoidichnus, Chondrites, Rhizocorallium irregulare, Taenidium serpentium, an unusual form of Walcottia and Merostomichnites‐like traces. These trace fossils display an interesting relationship with the sediments: low‐energy Cruziana ichnofacies is found within high‐energy sandstones. The sandstones are interbedded with laminated mudstones, apparently deposited in deep water, but some aspects of the ichnoassemblage, preservation and sedimentation indicate shallower water. One new trace fossil, Radichnus allingtona igen. et isp. nov., closely resembles the traces of modern fiddler crabs and imply emergence, by analogy. This ichnofauna is similar to early stage disaster colonisation in recent experiments in Long Island Sound (south of Connecticut, USA) and with storm‐influenced deposits within the Cardium Formation (Seebe, Alberta, Canada). This indicates a lagoonal environment with influxes of sand and oxygen. Total organic carbon levels were found to fluctuate greatly between stratigraphic layers but remained relatively high. This implies low oxygen conditions. The abundance of sulphur (in pyrite) also supports an interpretation of anoxic conditions, and low sedimentation rates within the shale layers. A restricted shallow basin or lagoonal environment is proposed for the palaeoenvironment, with fluctuating oxygen influencing diversity.     

Cretaceous Nonmarine Trace Fossils from the Hasandong and Jinju Formations of the Namhae Area,Kyongsangnamdo, Southeast Korea

Nonmarine strata of the Cretaceous Hasandong and Jinju formations of the Sindong Group of the Namhae area, Kyongsangnamdo, southeast Korea, contain relatively diverse and abundant ichnofaunas including domichnia, fodinichnia, pascichnia, and repichnia. These ichnofaunas are systematically described herein and three ichnocoenoses, namely the Skolithos, Palaeophycus, and Chondrites ichnocoenoses, are defined based on their paleoenvironmental occurrence. The Skolithos ichnocoenose characterizes tabular laminated sandstone facies deposited on fluvial channel levées. It is dominated by infaunally produced ichnotaxa, particularly Skolithos magnus Howell, Planolites montanus Richter and Chondrites isp. type A, with reduced numbers of Skolithos verticalis (Hall) Taenidium barretti (Bradshaw) and rare examples of Circulichnus montanus (Vyalov), Cochlichnus anguineus Hitchcock, Helminthopsis abeli Ksi??kiewicz, Helimthopsis hieroglyphica Wetzel and Bromley, Laevicyclus isp., Planolites beverleyensis (Billings), Skolithos isp., Spirodesmos isp., Thalassinoides suevicus (Rieth), and rhizoliths. The Palaeophycus ichnocoenose characterizes floodplain environments and occurs in purple mudstones and associated massive sandstone facies of crevasse-splay deposits and dark gray to green shale facies of abandoned channels. Palaeophycus tubularis Hall and Planolites montanus Richter are the most characteristic ichnotaxa, while Beaconites coronus (Frey, Pemberton and Fagerstrom), Planolites annularius Walcott, Skolithos magnus Howell, Thalassinoides paradoxicus (Woodward), and sauropod and ornithopod tracks also occur but in reduced numbers. The Chondrites ichnocoenose occurs in dark gray to black mudstones deposited in marginal lacustrine environments. It is dominated by Chondrites isp. type B. with associated Beaconites antarcticus Vyalov, Helminthopsis hieroglyphica, Palaeophycus tubularis, Skolithos magnus, Taenidium barretti, and Torrowangea rosei Webby. The three ichnocoenoses recognized herein cannot be satisfactorily assigned to currently defined nonmarine ichnofacies, suggesting that existing models of such ichnofacies are in need of additional refinement.     

Heterogeneous distribution of trace fossils across initial transgressive deposits in rift basins: an example from the Springhill Formation,Argentina

In the Lago San Martín region (Santa Cruz Province, Argentina), the Springhill Formation (50–100 m thick) overlies the syn‐rift El Quemado Complex, showing outcrops with wedge geometry. Four sedimentological sections were measured in the field, and three depositional palaeoenvironments were interpreted. The Springhill Formation starts with fluvial deposits, characterized by channel‐fills and floodplains with palaeosol development, passing transitionally to a coastal plain and, finally, to marine sedimentation. The initial sandy transgressive deposits (Facies Association 9) are the main focus of this study, in which 10 ichnogenera (Arenicolites, Bergaueria, Cylindrichnus, Diplocraterion, Macaronichnus, Palaeophycus, Planolites, Ophiomorpha, Rosselia and Skolithos) are described. Two ichnoassociations (foreshore and shoreface) were defined, and their distribution was controlled by the local palaeoenvironmental conditions, mainly energy, bathymetry and grain size of sediments. A highly bioturbated surface (BI = 4) was recognized in Section 1 showing a limited occurrence and disappearing over short distances perpendicular to the palaeoshoreline. This surface shows a sharp sub‐horizontal gently undulating top contact with a bioturbation thickness between 15 and 25 cm. This type of surface has limited usefulness as a key correlative surface, because it is spatially restricted in rift basins due to the tectonic activity, which creates high accommodation space rates. A more accurate characterization of the initial transgressive deposits of the Springhill Formation – which is the most important reservoir in southern Patagonia – could provide new ideas to solve problems in sub‐surface studies.