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.     

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).     

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.     

Vertical displacement and taphonomic filtering of nannofossils by bioturbation in the Cretaceous–Palaeogene boundary section at Caravaca,SE Spain

K?dzierski, M., Rodríguez‐Tovar, F.J. & Uchman, A. 2011: Vertical displacement and taphonomic filtering of nannofossils by bioturbation in the Cretaceous–Palaeogene boundary section at Caravaca, SE Spain. Lethaia, Vol. 44, pp. 321–328. At the Caravaca section, SE Spain, the position of the Cretaceous–Palaeogene (K–Pg) boundary is well‐defined, with multidisciplinary datasets from a thin rusty layer at the base of the 10 cm dark boundary layer. Nannoplankton assemblages containing the Danian taxon Neochiastozygus sp. and enriched in Thoracosphaera spp. are displaced below the K–Pg boundary into the trace fossils Zoophycos, Thalassinoides and Chondrites. These trace fossils are filled with dark‐coloured sediments of the dark boundary layer. The nannofossil assemblage from the 1‐cm thick interval below the boundary, enriched in Thoracosphaera spp. and Braarudosphaera spp., may have been displaced by Chondrites tracemakers, the traces of which are abundant in this interval. The downward transport of the Danian nannofossils into the Maastrichtian by the tracemakers seems to be one of the common mechanisms responsible for their apparent appearance below the K–Pg boundary. The dark boundary layer contains very rare Danian specimens and abundant Maastrichtian nannofossils. The Maastrichtian taxa were most likely conveyed up on to the seafloor by tracemakers during the Danian. The redistribution of nannoplankton down and up across the rusty layer (K–Pg), challenges the usefulness of nannofossils for high‐resolution stratigraphy of the K–Pg boundary. □Nannoplankton, Cretaceous–Palaeogene boundary event, biogenic mixing, trace fossils.     

Oxygen-related facies in Lake Pannon deposits (Upper Miocene) at Budapest-Köbánya

Oxygen availability is considered to have been a major factor in shaping the sedimentary facies and biofacies of a Late Miocene (8–8.5 Ma old) Lake Pannon sequence studied in the Kozma-street outcrop in Budapest-Köbánya. The sequence contains blue clays deposited in low-oxygen conditions between the storm and the fair-weather wave bases and thin intercalations of laminated fine sand interpreted as tempestites. The storms caused temporary oxygenation of the bottom and thus promoted bioturbation, as indicated by the presence of trace fossils belonging to the Arenicolites ichnofacies or a lacustrine equivalent of the marine Skolithos ichnofacies. Fully bioturbated sand layers with the infaunal Dreissenomya and other littoral molluscs indicate longer periods of bottom ventilation. The blue clays immediately above these sand layers also contain abundant and diverse mollusc fauna. Oxygen deficiency on the “shelf” of Lake Pannon was a local phenomenon probably caused by a high organic loading and/or a salinity-induced stratification.     

Environmental variability of Macaronichnus ichnofabrics in Eocene tidal‐embayment deposits of southern Patagonia,Argentina

The Middle Eocene Man Aike Formation of southern Patagonia, Argentina, offers the opportunity to study the palaeoecological and palaeoenvironmental significance of Macaronichnus ichnofabrics in a tide‐dominated, coastal embayment compound‐dune complex. Four recurrent Macaronichnus ichnofabrics are recognized: Macaronichnus IF‐1 characterized by Macaronichnus segregatis segregatis; Macaronichnus IF‐2 with M. segregatis segregatis, Ophiomorpha nodosa, Skolithos linearis and rare Palaeophycus tubularis; Macaronichnus IF‐3 typified by M. segregatis segregatis, O. nodosa, Asterosoma radiciforme and rare S. linearis; and Macaronichnus IF‐4 consisting of M. segregatis segregatis, Nereites missouriensis, A. radiciforme, O. nodosa, Rosselia socialis, S. linearis, P. tubularis, Planolites isp. and Chondrites isp. Variations in these ichnofabrics are linked to changes in local hydraulic conditions in the upper and lower trough areas of the compound dunes. In high‐energy, shallow and marginal marine environments, the Macaronichnus tracemaker is commonly the first to colonize the shifting, sandy substrates. Overprinting by other ichnoguilds occurs only after the physiochemical conditions became favourable and the colonization window length increases.     

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.     

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.     

Stable deep-sea macrobenthic trace maker associations in disturbed environments from the Eocene Lefkara Formation,Cyprus

Ichnological analysis of Eocene deep-pelagic whitish chalky calcilutites interstratified with high-energy calcarenite beds in the lower part of the Petra Tou Romiou section (southern Cyprus) was conducted to interpret the development and evolution of the trace maker associations during calcilutite deposition after high-energy episodes. The trace fossil assemblage from the chalky calcilutites consists of Chondrites isp. (Chondrites intricatus and Chondrites targionii), Planolites isp., Taenidium isp., Thalassinoides isp., and Zoophycos isp., typical of the Zoophycos ichnofacies. A composite chalky ichnofabric reveals a multi-tiered association of burrowing animals: the uppermost tier determines a mottled background, the upper tier shows the highest trace fossil abundance and diversity (Planolites, Taenidium and Thalassinoides), the middle tier features Zoophycos and large Chondrites, and the deepest tier consists mainly/exclusively of small Chondrites. This ichnofabric has an autocomposite character, associated with bioturbation by a single ichnocoenosis and gradual upward migration of the tiered macrobenthic community as the pelagic calcilutite sedimentation slowly progresses. There are no changes in the trace fossil assemblage between or within calcilutite intervals, regardless of the associated calcarenite beds. This supports a stable, mature, background calcilutite trace maker association, which recovers shortly after the deposition of high-energy calcarenites. In turn, there would have been a rapid re-establishment of paleoenvironmental conditions during pelagic calcilutite accumulation after episodic deposition of any calcarenitic material.     

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.     

Skolithos pipe rock and associated ichnofabrics from the southern Rocky Mountains,Canada: colonization trends and environmental controls in an early Cambrian sand‐sheet complex

Desjardins, P.R., Mángano, M.G., Buatois, L.A. & Pratt, B.R. 2010: Skolithos pipe rock and associated ichnofabrics from the southern Rocky Mountains, Canada: colonization trends and environmental controls in an early Cambrian sand‐sheet complex. Lethaia, 10.1111/j.1502‐3931.2009.00214.x The Lower Cambrian Gog Group of the southern Rocky Mountains of western Canada offers an opportunity to explore animal–sediment relationships in a high‐energy setting, during the early phase of Phanerozoic diversification. Its strata record a sand‐sheet complex on the broad pericontinental shelf of West Laurentia. Six ichnofabrics are recognized: Skolithos IF‐1 characterized by Skolithos linearis in planar cross‐stratified sandstone; Skolithos IF‐2 with Skolithos linearis and accessory Diplocraterion parallelum in ripple cross‐laminated, and planar and trough cross‐stratified sandstone; Skolithos IF‐3 with S. linearis and Planolites montanus in wavy‐ and flaser‐bedded sandstone, interfingering with bioturbated mudstone exhibiting P. montanus and Teichichnus rectus; Skolithos IF‐4, characterized by abundant Skolithos linearis in planar and trough cross‐stratified sandstone; Rosselia IF‐1 consisting of Rosselia isp. in planar cross‐stratified sandstone; and Rosselia IF‐2 consisting of scattered small Rosselia isp. in hummocky, cross‐stratified sandstone. The presence of contrasting ichnofabrics within a single early Cambrian sand‐sheet complex illuminates how the colonization trends of suspension and detritus feeders were controlled by factors specific to the various sub‐environments. □Gog Group, Ichnofabric, Lower Cambrian, Pipe Rock, Rosselia, Skolithos.     

川西南峨眉山地区上白垩统夹关组遗迹组构特征及其环境意义

川西南峨眉山地区上白垩统夹关组由一套厚层到块状中、细砂岩组成,夹有少量粉砂岩和泥岩,底部有砾岩。本组地层中发育有丰富的遗迹化石,共识别出9属11种。根据遗迹化石的分布情况,划分出了5种遗迹组构,即:Palaeophycus遗迹组构、Arenicolites遗迹组构、Skolithos遗迹组构、Planolites遗迹组构和Scoyenia遗迹组构;结合它们所分布岩层的沉积特征,认为前三者分别分布于河流环境中水动力强的边滩下部、水动力中等到较强的边滩中上部和边滩向堤岸过渡的环境,后两者分布于水动力较弱的天然堤环境。     

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.     

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.     

Stratigraphic application of Thalassinoides ichnofabric in delineating sequence stratigraphic surfaces (Mid-Cretaceous), Kopet-Dagh Basin,northeastern Iran

This study integrates ichnological and sedimentological data to refine depositional sequences and interpretations of sea-level dynamics for the shallow marine, Albian–Cenomanian Aitamir Formation in northeastern Iran. Three ichnofabrics are present in a succession of glauconitic mudstone and sandstone. This is a sequence that grades upward from a lower glauconitic sandstone unit with trough cross-stratification, hummocky and ripple cross-lamination into a fining-up unit of mudstone with intercalated sandstone beds. The lower unit contains an ichoassemblage of the Ophiomorpha–Palaeophycus ichnofabric (upper shoreface), whereas the upper unit bears ichnoassemblages of the Thalassinoides ichnofabric (in a distinctive level at the top cycle which demarcates the base of the next cycle) (middle shoreface) and the Chondrites–Planolites ichnofabric (lower shoreface). An upper shoreface–lower shoreface trend from the Ophiomorpha–Palaeophycus ichnofabric to the Chondrites–Planolites ichnofabric represents a deepening-upward sequence. An integrated sedimentological and ichnological approach has allowed the recognition of the internal organization of the sequence and the characterization of significant discontinuity surfaces at sequence scales. Thalassinoides ichnofabric reveals colonization of firmgrounds during prolonged times between erosion and deposition related to transgressive surfaces. Transgressive surfaces (sequence boundaries) are generally well-cemented and marked by increased glauconite content, and densely crowded, predominantly vertical or oblique, relatively large, very distinct, unlined, and uncompacted burrows (omission suite) and are associated with rare highly abraded and fragmented shell remains.     

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.     

塔里木盆地晚泥盆世东河塘组河口湾相遗迹化石

河口湾具有特定的环境条件和沉积组成,其遗迹化石具有半咸水沉积的遗迹群落特征。描述和分析塔里木盆地塔中4井区上泥盆统东河塘组河口湾沉积中的遗迹化石和生物扰动构造后,发现3类遗迹组构,其中Ophiomorpha遗迹组构发育在纯净砂岩中,与河口湾潮汐砂坝有关;Skolithos遗迹组构发育在薄层砂岩中,与河口湾砂坪有关;Palaeophycus遗迹组构发育在泥岩中,与河口湾泥坪、砂泥坪有关。     

Trace fossil analysis of lacustrine facies and basins

Two ichnofacies are typical of lacustrine depositional systems. The Scoyenia ichnofacies characterizes transitional terrestrial/nonmarine aquatic substrates, periodically inundated or desiccated, and therefore is commonly present in lake margin facies. The Mermia ichnofacies is associated with well oxygenated, permanent subaqueous, fine-grained substrates of hydrologically open, perennial lakes. Bathymetric zonations within the Mermia ichnofacies are complicated by the wide variability of lacustrine systems. Detected proximal–distal trends are useful within particular lake basins, but commonly difficult to extrapolate to other lakes. Other potential ichnofacies include the typically marine Skolithos ichnofacies for high-energy zones of lakes and substrate-controlled, still unnamed ichnofacies, associated to lake margin deposits. Trace fossils are useful for sedimentologic analysis of event beds. Lacustrine turbidites are characterized by low-diversity suites, reflecting colonization by opportunistic organisms after the turbidite event. Underflow current beds record animal activity contemporaneous with nearly continuous sedimentation. Ichnologic studies may also help to distinguish between marine and lacustrine turbidites. Deep-marine turbidites host the Nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids, recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea. Deep lacustrine environments contain the Mermia ichnofacies, which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems. The lower diversity of lacustrine ichnofaunas in comparison with deep-sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions. Increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies. Paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation. During the Mesozoic, bioturbation depth was higher in lake margin facies than in fully lacustrine deposits. While significant degrees of bioturbation were attained in lake margin facies during the Triassic, major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the Cretaceous.