Middle Jurassic trace fossils from the Ridang Formation in Sajia County,South Tibet,and their palaeoenvironmental significance

An ichnofauna consisting of 18 ichnospecies (one of them new) in 14 ichnogenera are described for the first time from the Middle Jurassic Ridang Formation in Sajia County, South Tibet. The ichnofauna can be subdivided into two ichnoassemblages in ascending stratigraphic order: the Palaeophycus–Megagrapton ichnoassemblage in the lower and middle parts of the Ridang Formation, followed by the Cosmorhaphe–Nereites–Paleodictyon ichnoassemblage in the upper Ridang Formation. Overall, the trace fossils occur in a middle–distal turbidite fan sequence, as evidenced by both sedimentological analysis and the composition of the trace fossils. Several subenvironments of the middle–distal fan system have been recognized on the basis of the spatial distribution of the trace fossils. Typically, the channel-fill deposits in the middle part of the turbidite fan lack trace fossils, the interchannel and upper channel-fill (levee) subenvironments of the middle turbidite fan contain abundant facies-crossing trace fossils, in contrast to the distal part of the turbidite fan where deep-water trace fossils are dominant. The ichnofauna is similar to typical flysch ichnofaunas from Europe and North America in characteristics, and is interpreted to represent a typical deep-sea Nereites ichnofacies. The presence of these deep-sea trace fossils therefore would suggest that a continental slope environment existed in southern Tibet during the Middle Jurassic and the study area was located in a slope-abyssal plain setting.     

Deep-water trace fossils in the Ilfjellet rift basin (Middle Ordovician), central Norwegian Caledonides

The late Early to early Middle Ordovician Fjellvollen Formation, Central Norwegian Caledonides, is a part of the Ilfjellet Group volcano-sedimentary succession formed in a rift basin that opened along the Laurentian margin. Depositional facies and trace fossils indicate the Nereites ichnofacies, typically found in distal turbidites and deep marine deposits. The recovered trace fossils include ?Alcyonidiopsis, Chondrites, Dictyodora, Gordia, Helminthoidichnites, Macaronichnus, Monomorphichnus, Nereites, Oikobesalon, Palaeophycus, Protovirgularia and Treptichnus. No body-fossils have been reported from the Fjellvollen Formation, but the trace fossils indicate the presence of varied epi- and infaunas of arthropods, bivalves, gastropods and polychaets. The abundance of meandering and looping trace fossils is comparable to what is found in the inferrably time-equivalent Vuddudalen Group farther north, although lack of graphoglyptids like Megagrapton in the Fjellvollen Formation may indicate more proximal, unstable depositional conditions in fan-fringe and adjacent basin-plain settings.     

Ordovician Bathyal Trace Fossils From Metasiliciclastics in Central Norway and Their Sedimentological and Paleogeographical Implications

Numerous trace fossils are recognized in metasiliciclastic rocks of the Lower-Middle Ordovician Lower Hovin Group, Upper Ordovician Ekne Group and on roofing slates from an unknown locality (probably Ordovician) from the Trondheim region, central Norway. The trace fossil assemblages are dominated by meandering pascichnial forms, i.e., Helminthoidichnites in the Lower Hovin Group and Helminthoidichnites and Nereites in the slates. Protovirgularia, Dictyodora, ?Planolites and ?Palaeophycus are less common. Alcyonidiopsis, ?Trichophycus, Chondrites, cf. Chondrites, Gordia, ?Phycodes, ?Helminthopsis, cf. Naviculichnium, Treptichnus, Saerichnites, Megagrapton and ?Paleodictyon (Squamodictyon) are rare. The trace fossils were collected or observed at 17 different localities and represent assemblages belonging to the Nereites ichnofacies (deep-sea flysch deposits with thinly bedded turbidites). They reflect a distal Nereites subfacies (fan-fringe or basin-plain deposits) transitional to a Nereites/Paleodictyon subfacies (proximal fan facies). The trace fossil assemblages indicate an opportunistic style of colonization related to fluctuations in food supply introduced by turbidity currents.     

Trace fossils in the Ediacaran-Cambrian transition: Behavioral diversification, ecological turnover and environmental shift

After taxonomic revision, trace fossils show a similarly explosive diversification in the Ediacaran-Cambrian transition as metazoan body fossils. In shallow-marine deposits of Ediacaran age, trace fossils are horizontal, simple and rare, and display feeding strategies related to exploitation of microbial matgrounds. Equally notable is the absence of arthropod tracks and sinusoidal nematode trails. This situation changed in the Early Cambrian, when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground-based ecology (‘‘agronomic revolution’’). On deep sea bottoms, animals have been present already in the Ediacaran, but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners. As shown by the ichnogenus Oldhamia, this life style continued to be predominant into the Early, and to a lesser extent, Middle Cambrian. Nevertheless, there was an explosive radiation of behavioral programs during the Early Cambrian. When exactly the bioturbational revolution arrived in the deep sea is uncertain. In any case, the Nereites ichnofacies was firmly established in the Early Ordovician. The rich ichnofauna in the Early Cambrian Guachos Formation of northwest Argentina probably marks a first step in this ecological onshore-offshore shift.     

The changing face of the deep: Colonization of the Early Ordovician deep-sea floor, Puna, northwest Argentina

An Upper Tremadocian deep-sea ichnofauna from the Chiquero Formation of Puna, northwest Argentina, represents a link between Ediacaran and Cambrian microbial-mat dominated ecosystems and younger Ordovician deep-marine trace-fossil assemblages. This ichnofauna is preserved at the base of thin-bedded turbidites formed in the lobe fringe of a back-arc deep-sea fan. While Ediacaran–Cambrian deep-marine trace fossils are typically linked to matground grazing and feeding, microbial textures in the Chiquero Formation are rare and not associated with trace fossils. Morphologic patterns (e.g. radial trace fossils and networks) of the Chiquero ichnofauna indicate the onset of novel trophic types, recording trapping of microorganisms and bacterial farming. However, in comparison with younger Ordovician deep-sea ichnofaunas, graphoglyptids are relatively rare, poorly diverse, and geometrically simpler. This study indicates that the Early Ordovician was a pivotal point in the ecology of deep-sea infaunal communities. This Upper Tremadocian ichnofauna records the arrival of the Agronomic Revolution to the deep sea. Comparisons with slightly older and younger deep-sea ichnofaunas demonstrate that the colonization of the deep sea was a protracted process spanning the Early Paleozoic, lagging behind colonization of nearshore and offshore substrates.     

Spiral trace fossils from the Permian Ecca Group of Zululand

The presence of spiral trace fossils is reported for the first time from six localities in strata of the Vryheid Formation of the Ecca Group (Lower Permian) in South Africa. These localities are all in the northeast part of the main Karoo basin of sedimentation. The fossils arc assigned to the ichnospecies Spirodesmos archimedeus , representing the spiral trail or burrow of a deposit-feeding organism. In contrast to other reports of spiral trace fossils, the Spirodesmos traces described here were formed in a shallow-water environment. This is established on both sedimentary and ichnofacies evidence. Associated trace fossils include Skolithos, Corophioides and Siphonichnus , all of which arc members of the Skolithos ichnofacies of Scilacher. The occurrence of Spirodesmos in this ichnofacies suggests that these strata were deposited in a marine basin.     

Small Theropod Track Assemblages from Middle Jurassic Eolianites of Eastern Utah: Paleoecological Insights from Dune Ichnofacies in a Transgressive Sequence

New discoveries show that very small theropod tracks (cf. Wildeichnus) are abundant in the upper part of the Moab Member, recently assigned to the Curtis Formation (formerly considered part of the Entrada Formation) in the Mid-?Late Jurassic of eastern Utah. The tracks represent a distinct small-theropod ichnofacies associated with eolian dune deposits that is easily differentiated from the water-lain beds of the overlying Megalosauripus-Therangospodus ichnofacies, which comprises the single-surface Moab megatracksite. Pterosaur track assemblages, representing the Pteriachnus ichnofacies, are found a few meters above the megatracksite surface in the upper tongue of the Summerville Formation.

The small theropod ichnofacies is reminiscent of other early Mesozoic dune facies ichnofaunas from the Wingate and Navajo formations (Late Triassic and Early Jurassic) where small theropod tracks occur in association with other small tetrapod footprints. All such examples evidently represent a recurrent dune facies ecosystem dominated by diminutive vertebrates. Because the small theropod ichnofacies is one of three ichnofacies found in a thin stratigraphic sequence (<20 m) that contains no body fossils, it is clear that vertebrate tracks play an important role in providing insight into the paleoecology of units previously considered devoid of any useful fossil evidence. The three successive ichnofacies represent a transgressive transition from sand dunes, through sandy shoreline to shallow marine environments, each with its quite distinct vertebrate fauna.     

First Record of Graphoglyptids in Cyprus: Indicative Presence of Turbidite Deposits at the Pakhna Formation

Abstract

Ichnological analysis at the Pakhna Formation (Miocene, Cyprus) reveals, for the first time, the presence of graphoglyptid structures. The Pakhna Formation is dominated by pelagic/hemipelagic sediments, together with contourite, reworked turbidite and turbidite facies. Thus, a complex interaction between pelagic, bottom-current and gravitational sedimentation is envisaged. The discernment of facies is sometimes difficult, based principally on stratigraphic and microfacies features. The record of Helminthorhaphe as a component of the graphoglytid group supports the presence of turbidites, facilitating their differentiation from the other facies. Nereites ichnofacies, punctuating a dominant/background Zoophycos ichnofacies, would reflect changes in paleoenvironmental conditions. This record offers significant perspectives to advance in the study of bottom-current and gravitational processes through outcrop examples.     

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.     

Giant Bathysiphon (Foraminiferida) from Cretaceous turbidites, northern California

Straight-sided, tubular fossils occur together with a diverse assemblage of deep-water trace fossils in linegrained Franciscan turbidites at Point Saint George. Pacific Coast of California. Based on comparison with living abyssal organisms and on skeletal microstructure, these tubes are interpreted as recrystallized siliceous tests of the large abyssohenthic foraminiferid, Bathysiphon. Tubes found preserved in-place show that life orientation of the Franciscan species was vertical with the broader, mature end protruding several millimetres above the muddy seafloor. Positioned in this way the organisms probably were suspension feeders or carnivores. Bathysiphon and trace fossils taken together reflect a diverse deep-water benthic community that was disrupted (or locally eliminated) repeatedly by turbidity currents reaching the outer margins of a submarine fan. ▭ Bathysiphon, deep-water benthos, outer fan/basin floor, trace fossils, Franciscan Complex, flysch, Cretaceous.     

Tetrapod footprints of the lower permian choza formation at Castle Peak, Texas

The tetrapod track ichnofauna of the Lower Permian Choza Formation at Castle Peak, Texas, consists after augmentation of sample size and revision of three distinet ichnotaxa:Erpetopus willistoni Moodie, 1929,Varanopus curvidaetylus Moodie, 1929 andDromopus palmatus (Moodie, 1929). These are the tracks of protorothyridis, captorhinomorphs and araeoscelids, respectively. Castle Peak is the type locality of the ichnogeneraErpetopus andVaranopus. With the tetrapod ichnofauna of the Robledo Mountains Formation in New Mexico, the Castle Peak ichnofauna is the second Lower Permian track oecurrence that can be clearly correlated to the marine timescale. Both tetrapod ichnofaunas support assigning an age up to Artinskian to most Lower Permian red-bed tetrapod ichnofaunas of the North American Wolfcampian-Leonardian and the European Rotliegendes. The ichnogeneraBatrachichnus, Limnopus, Amphisauropus, Erpetopus, Varanopus, Dromopus andDimetropus characterize an Artinskian red-bed ichnofauna of Euramerican distribution.      

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.     

Silurian trace fossils in carbonate turbidites from the Alexander arc of southeastern Alaska

Early to Late Silurian (Llandovery‐Ludlow) body and trace fossils from the Heceta Formation of southeastern Alaska are preserved in the oldest widespread carbonates in the Alexander terrane. These fossils represent the earliest benthos to inhabit diverse shallow and deep subtidal environments in the region and are important indicators of early stages in benthic community development within the evolving Alexander arc. The ichnofossils are particularly significant because they add to a small but growing body of knowledge about trace fossils in deep‐water carbonates of Paleozoic age.

Carbonate turbidites that originated along a deep marine slope within the arc yield a low‐diversity suite of trace fossils consisting of five distinct biogenic forms. Simple burrows (Planolites, two forms), ramifying tunnels (Chondrites), and tiny cylindrical burrows (?Chondrites) represent the feeding activities (fodinichnia) of pre‐turbidite animals that burrowed in the lime mud before the influx of coarser sediment deposited by turbidity currents. These trace fossils are associated locally with cross‐cutting burrows created as domichnia (Palaeophycus). Rarer hypichnial burrows and endichnial traces were created by post‐turbidite animals that fed soon after the deposition of coarse detritus from turbidity flows.

Trace fossils in these deposits reflect much lower diversity levels than in Paleozoic siliciclastic turbidites. This difference may represent unfavorable environmental conditions for infaunas, differential preservation, or significant paleogeographic isolation of the Alexander terrane during the Silurian. Greater utilization of trace fossils in terrane analysis may help to resolve this issue and provide new data for reconstructing the paleogeography of circum‐Pacific terranes.     

Environmental distribution of trace fossils in the Jurassic of Kachchh (Western India)

Summary Trace fossils occur abundantly in Middle Jurassic rocks of the Kachchh Basin. They are found in environments ranging from beach sequences down to central parts of the basin. For stratinomic reasons, they are particularly well preserved in storm deposits. Their distribution pattern exhibits a clear relationship to the hydrodynamic conditions and, secondarily, to bathymetry, and follows the classic ichnofacies concept ofSeilacher (1967). High energy nearshore areas and submarine shoals are represented by members of the Skolithos ichnofacies such asOphiomorpha nodosa, Arenicolites, Diplocraterion parallelum, andRhizocorallium jenense. The storm-influenced ramp contains both members of the Cruziana ichnofacies (e.g.Rhizocorallium irregulare, Thalassinoides suevicus, Taenidium serpentinum, Chondrites) and the Skolithos ichnofacies (in particularOphiomorpha). The former were produced during interstorm phases, the latter are of post-storm origin. Carbonate ramp environments of low to intermediate energy also contain members of the Cruziana ichnofacies, whilst equivalent siliciclastic environments are characterized by a low-diversity Zoophycos ichnofacies. Low energy basinal environments of fine-grained substrates contain an impoverished Cruziana ichnofacies consisting ofChondrites, Trichichnus andThalassinoides suevicus. 32 ichnotaxa are briefly described, among themSphaerichnus lobatus ichnogen. et ichnosp. nov.     

Tetrapod and invertebrate trace fossils from aeolian deposits of the lower Permian of central-western Argentina

Abundant tetrapod footprints are described from the Early Permian Yacimiento Los Reyunos Formation including both collected and in situ specimens. The slabs come from several quarries at the Sierra Pintada and Sierra de las Peñas area, south-west of Mendoza, Argentina. The trace fossil assemblage, which constitutes one of the oldest known from Gondwana, comprises excellent-preserved tetrapod tracks (Chelichnusduncani, Chelichnusgigas and ‘pear-like’ footprints) and invertebrate simple sub-horizontal (Palaeophycustubularis) and vertical (Skolithos isp.) burrows formed in a aeolian dune field. The analysis of the tetrapod track producers indicates the presence of at least three different taxa of sprawling to semi-erect therapsids, thus suggesting the presence of members of this clade, or closest relatives, in the Early Permian of southern Gondwana. Moreover, a series of measurements and simple indexes were developed to estimate body proportions and locomotion styles of the putative trackmakers. The new assemblage, analysed in the context of other known Permian assemblages from Pangea, is one the few known in Gondwana to be present in an aeolian environment. The evaluation of the assemblage, in the light of aeolian ichnofacies (Chelichnus, Octopodichnus and Entradichnus), shows that it has common elements with the Chelichnus and Entradichnus ichnofacies.     

南极利文期顿岛晚三叠世复理石相遗迹化石

南极利文斯顿岛赫德半岛中的迈尔斯陡崖组主要是浅变质的石英长石杂砂岩、粉砂岩、泥岩和粉砂岩与泥岩互层等组成的复理石,厚度可能超过３０００m,形成于浊积扇的上扇和下扇部分,时代可能为晚三叠世。在复理石相岩石中发育一套深水的遗迹化石,共有１５个遗迹属、１６人遗变种,其中有１０个可以鉴定到遗迹种,两个比较种,４个只鉴定到遗迹属,未鉴定到遗迹种,１建立１个新遗迹属及新遗迹种,除新遗迹属种外,其余１４个遗迹属,１５个遗迹种都曾经在深海复理石相浊积岩内发现过,其中Ｂelorhaphe,Glockerichnus,Lophoctenium,Rhabdo-glyphus,Paleodictyon,Suborenzinia,Spirophycus,Strobilorhaphe,Tuberculicnus,Cochlichnus等,属于浊流前产生在复理石相泥岩内的高度分异的雕画迹（Ｇraphoglyptida),它们产于泥岩却保存为上覆砂岩底面的铸型凸起。别外,Ｆucusopsis和Neonereites却产生在砂岩内代表浊流后形成的沉积后遗迹组合,文内还描述３种浊流常见的无机构造,并上上述遗迹化石进行比较。     

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.     

北京昌平青白口系痕迹化石

北京昌平青白口系长龙山组和景儿峪组发育有丰富的痕迹化石,其中长龙山组产有Ｈｅｌｍｉｎｔｈｏｐｓｉｓ ｓｐ．,Ｃｏｃｈｌｉｃｈｎｕｓ ｓｐ．,代表潮下低能环境;景儿峪组产有Ｓｋｏｌｉｔｈｏｓ ｓｐ．和Ｍｏｎｏｃｒａｔｅｒｉｏｎ ｓｐ．,代表高能潮间环境。