Treptichnus Research Articles

Storm deposits and trace fossils of Xinji Formation (Cambrian Series 2) in the southern margin of North China Plate

The Xinji Formation (Cambrian Series 2) in the southern margin of the North China Plate developed typical siliciclastic storm deposits and abundant trace fossils. These deposits are characterized by essential indicators, such as erosional surfaces, lag deposits, blocky beddings, hummocky cross stratifications, horizontal or wavy beddings. Storm deposits in the study area are dominated by the development of hummocky cross stratifications, which is categorized into five storm deposit types based on the arrangement of different sedimentary units in the profile. These five types of storm deposits from I to V show the transition from proximal storm deposits to distal storm deposits, the gradual weakening of storm intensity, and the associated growth of quiescent intervals. The trace fossils are mainly developed in the sandstone-mudstone interbeds between storm events and include 14 ichnospecies in 11 ichnogenera: Didymaulichnus isp., Gordia marina, Helminthopsis tenuis, Oldhamia radiata, Palaeophycus striatus, Palaeophycus tubularis, Phycodes isp., Planolites beverleyensis, Planolites montanus, Planolites punctatus, Skolithos isp., Taenidium isp., Torrowangea rosei, Treptichnus pedum. By analyzing the ichnological index (burrow size, BPBI, ichnodiversity and ichnodisparity) from different storm deposits, it can be seen that from storm deposit type I to storm deposit type V, the ichnological index shows an increasing trend. Combined with the relationship between storm deposits and trace fossils, it is inferred that differences in storm intensity result in different colonization windows, and thus variations in ichnological index of preserved trace fossils. Based on the characteristics of storm deposits and distribution of trace fossils, the preservation forms of trace fossils under storm influence are explored.

Ordovician-Silurian trace fossils from the Takche Formation, Parahio Valley, Spiti Himalaya, India: biostratigraphic and paleoenvironmental significance

ABSTRACT The Ordovician-Silurian trace fossils from the Takche Formation exposed near the Gechang locality, Parahio Valley, Spiti region, Himalaya are described. Following trace fossils were found in the Takche Formation: Arenicolites isp. Aulichnites parkerensis, Archaeonassa fossulata, Catenichnus isp. Cochlichnus isp. Cruziana furcifera, Cruziana goldfussi, Cruziana semiplicata, Chondrites targoni, Chondrites isp. A, Chondrites isp B, Helminthodoichnites isp. Lockeia siliquaria, Laevicyclus mongraensis, Planolites isp. Phycodes circinatus, Phycodes rarus, Phycodes isp. Treptichnus pedum, Thalassinoides isp. and Zoophycos isp. The lowermost part of the Takche Formation yielded significant traces of Cruziana affinity i.e. Cruziana furcifera, Cruziana goldfussi, and Cruziana semiplicata suggesting Tremadocian-Darriwilian age (Lower to Middle Ordovician). The middle part of the Takche Formation is dominated by Zoophycos isp. Chondrites targoni, Chondrites isp. A, and Chondrites isp. B suggests a deeper water offshore setting. The uppermost part yielded Archaeonassa fossulata, Aulichnites parkerensis, Laevicyclus mongraensis, Planolites isp. Helminthoidichnites isp. Phycodes rarus, Phycodes isp. and scratch marks. Overall, the trace fossil assemblages indicate a shallow marine shoreface to offshore depositional setting.

The Lower Cambrian deposits of the Le Rozel Formation (Normandy, NW France): Insight into a newly described ichnofossil assemblage

The rise of morphological complexity and taxonomic diversity of trace fossils during the Cambrian Period has been a prominent focus to track the evolution and diversification of early animals. Here, we present a newly described trace fossil assemblage from the lower Cambrian Le Rozel Formation in Normandy (Northwestern France) composed of the following ichnogenera: Archaeonassa, Bergaueria, Helminthoidichnites, Helminthopsis, Nereites, Psammichnites, and Treptichnus. Trace fossils are exquisitely preserved on top of strata (i.e., epirelief), and are distributed through the entire thickness of the siliciclastic succession of about 200 m. This thick sedimentary succession shows sedimentary environments with ripples generated by unidirectional current processes or by oscillatory processes, such as hummocky cross-stratification (HCS) storm facies, tidal facies with flaser stratification, and unidirectional current ripples. In addition, syneresis cracks and microbially induced sedimentary structures (MISS) suggest that the Le Rozel Formation was deposited in a shallow marine shelf environment. New U-Pb dating of detrital zircon grains suggests a late Ediacaran maximum deposition age of 549 ± 3 Ma. This dating is supplemented by the substantial preservation of the three-dimensional burrow systems (Treptichnus pedum) and the large sediment bulldozers (Nereites, Psammichnites). Collectively, our findings suggest that the trace fossils assemblage was deposited during the Terreneuvian Epoch, beneath the first archaeocyaths and the first trilobite-bearing facies from both other lower Cambrian Carteret and Saint-Jean-de-la-Rivière Formation. The ichnofauna described from the Le Rozel Formation complements the worldwide trace fossil record around this critical time of life history.

The Ediacaran–Cambrian Chapel Island Formation of Newfoundland, Canada: evaluating the impact of outcrop quality on trace-fossil data sets at the Cambrian GSSP and less-explored sections

In 1992, the Chapel Island Formation at Fortune Head was selected as the Cambrian GSSP, which was placed at the first appearance of the ichnotaxon Treptichnus pedum. Although the transition from the Ediacaran to the Cambrian was well studied in Fortune Head and Grand Bank Head, it is also exposed at Lewin’s Cove and Point May. Here, we report new ichnologic and sedimentologic data sets from the four localities. Ichnologic data sets consist of bioturbation intensities, burrow width and depth, ichnotaxonomic composition, and stratigraphic appearances. Sedimentologic data sets include sediment grain size, bed thickness and architecture, sandstone/mudstone ratio, and physical sedimentary structures. In addition, the quality of each outcrop is evaluated (i.e., accessibility, lateral and vertical continuity, stratigraphic completeness, and type of exposure). At the four localities, the base of the Cambrian can be placed at the first appearance of Treptichnus pedum or of vertical trace fossils of the T. pedum Ichno-Assemblage Zone. In addition, Fortune Head, Grand Bank Head, and Lewin’s Cove display increases in ichnodiversity and bioturbation intensities that are concomitant with the first appearance of penetrative trace fossils. Point May stands out as a section with low ichnodiversity and an inconsistent data set on bioturbation intensities. Its limited data set is a consequence of poor bed surface exposures, which impact negatively on the preservation and visibility of horizontal trace fossils. This study demonstrates that evaluation of outcrop quality should be an essential procedure to any research addressing evolutionary trends that took place at this critical time of the history of life.

Pushing the boundary: A calibrated Ediacaran-Cambrian stratigraphic record from the Nama Group in northwestern Republic of South Africa

The Nama Group exposed on the Neint Nababeep Plateau along the Orange River in northwestern Republic of South Africa is now recognized as an expanded record of the Ediacaran-Cambrian transition that provides opportunity for an integrated stratigraphic approach in examining the geochemical and biologic evolution across this fundamental geologic boundary at unprecedented resolution. U-Pb zircon geochronology by the CA-ID-TIMS method on six intercalated volcanic ash beds in the Nama Group (from the Huns Member to the Nomtsas Formation) at this locality is used to construct a high-resolution, Bayesian, age-stratigraphic model, which allows a direct temporal calibration of the biostratigraphy and carbon isotope record from 539.63 ± 0.15 Ma to 537.95 ± 0.28 Ma (2σ internal errors). Across the border in the Witputs subbasin of southern Namibia, ash beds at the base of Nudaus Formation and within the Nasep Member yielded new U-Pb ages of 545.27 ± 0.11 Ma and 542.65 ± 0.15 Ma, respectively. Our combined geochronology reveals the detailed depositional history of the Nama Group at a regional scale, suggesting that a relatively low sediment accumulation rate in the Kuibis Subgroup and the lower Schwarzrand Subgroup was followed by accelerated sedimentation in the upper Schwarzrand Subgroup. This is consistent with a pattern of exponential increase in subsidence typical of foreland basins. Some of the observed chemostratigraphic trends throughout the Nama Group could relate to a shift from a seawater-buffered to a sediment-buffered regime of early marine diagenesis driven by this increase in sedimentation rate.Occurrences of soft-bodied erniettomorphs, calcified body fossils, and trace fossils within the Neint Nababeep Plateau are broadly consistent with known global biostratigraphic ranges. However, we document the youngest radioisotopically calibrated occurrences of Ediacaran-type fossils, which stratigraphically overlap with large and complex bilaterian ichnofossils, between 539.18+0.17/−0.26 Ma and 538.30+0.14/−0.14 Ma. Yet, the index fossil Treptichnus pedum remains undocumented from this section, and we suggest that its first regional occurrence may be younger than these strata. Despite relatively continuous and high rates of carbonate sedimentation across the Ediacaran-Cambrian boundary (as currently recognized), the upper Nama Group of the Neint Nababeep Plateau does not preserve the characteristic negative carbon isotope excursion observed within other basal Cambrian successions. One possible explanation for its absence is that this chemostratigraphic marker is not ubiquitous in all carbonate depositional environments. Alternatively, the basal Cambrian carbon isotope excursion, and perhaps the Ediacaran-Cambrian boundary as defined by the first appearance of Treptichnus pedum, might be >1 m.y. younger than currently recognized, postdating 538 Ma and, thus, suggesting a more condensed early Cambrian radiation. Difficulties in determining with confidence the first appearance datum of the index fossil Treptichnus pedum in the Nama Group highlight the challenge of a global biostratigraphic definition for the base of Cambrian and underscore the necessity of an integrated stratigraphic and radioisotope geochronologic approach to understand the tempo and patterns of environmental and biologic evolution across the Ediacaran-Cambrian boundary.

Ichnology and biostratigraphic significance of Cambrian trace fossils from the lowest stratigraphic level of Kunzam La Formation, Chandra Valley, Lahaul and Spiti, India

Trace fossils are abundant in the Cambrian Kunzam La Formation in the Lahaul and Spiti regions of the Himalaya. All previously known records belong stratigraphically to the upper part of the Cambrian Series 2/Stage 4 to the Miaolingian Series. In the present work, 15 ichnogenera comprising 26 recorded ichnospecies come from the lower part of the Kunzam La Formation exposed in the Chandra Valley, eastern Lahaul and Spiti, Himachal Pradesh. Three trace fossils associations, based on their sequence of appearance, are: (i) the Treptichnus pedum association (trace fossil association–I)-, a low diversity association, containing Planolites beverleyensis, Palaeophycus isp., and Treptichnus pedum, (ii) the Monomorphichnus association (trace fossil association–II) characterized by a sudden increase in trace fossil diversity and traces of arthropod/trilobite origin comprising Cruziana problematica, Cruziana isp., Catenichnus contentus,? Diplocraterion isp., Dimorphichnus obliquus, Dactylophycus isp., Lockeia siliquaria, Monomorphichnus multilineatus, M. lineatus, Planolites annularis, P. montanus, P. beverleyensis, Palaeophycus imbricatus, P. tubularis, Rusophycus didymus, R. leifeirikssoni, R. dispar, Rusophycus isp., Saerichnites abruptus, and serially repeated Rusophycus and Cruziana, Treptichnus pollardi and arthropod resting traces, and (iii) the Psammichnites association (trace fossil association–III) characterized by a dominant presence of large burrowing systems of Psammichnites gigas and traces of Diplichnites isp. and Ctenopholeus kutcheri. Considering the same rate of sedimentation for these deposits determined in the >50 km distant Parahio Valley and the stratigraphic position of the Psammichnites gigas assemblage zone in the Himalaya, these trace fossil associations probably fall within Cambrian Series 2, Stage 4, though the sudden increase in diversity and complexities of traces suggest an older age. Stratigraphically, the trace fossils presently described are the oldest yet recorded from the Cambrian of the Lahaul and Spiti regions.

Treptichnus pedum in the Três Marias Formation, south-central Brazil, and its implications for the Ediacaran-Cambrian transition in South America

The index ichnofossil Treptichnus pedum Seilacher 1955 and four types of Microbially Induced Sedimentary Structures (MISS) - variants of wrinkle and elephant skin structures – are the first fossils described from the Três Marias Formation, topmost unit of the Bambuí Group in south-central Brazil. Despite the stratigraphic importance and widespread occurrence of this unit in the São Francisco Craton and adjacent Brasília Fold Belt, its age is still poorly constrained between the Neoproterozoic and Early Paleozoic. This discovery is significant because the first appearance datum (FAD) of T. pedum has been used to define the Ediacaran-Cambrian boundary. Hence, the presence of T. pedum indicates an early Paleozoic age for the uppermost Bambuí Group and means that the Ediacaran-Cambrian limit must lie deeper in the Bambuí Group, somewhere between this level and that of the terminal Ediacaran index-fossil Cloudina sp. in the Sete Lagoas Formation, near the base of the group. Available age determinations on detrital zircon grains and chemostratigraphic correlations are consistent with an Ediacaran to Cambrian age for this group. Detailed paleontological prospection throughout the group may now proceed within a better constrained time frame and hopefully reveal additional fossil evidence of Cambrian as well as Ediacaran life in the Bambuí Group.

A link between rift-related volcanism and end-Ediacaran extinction? Integrated chemostratigraphy, biostratigraphy, and U-Pb geochronology from Sonora, Mexico

AbstractWe present chemostratigraphy, biostratigraphy, and geochronology from a succession that spans the Ediacaran-Cambrian boundary in Sonora, Mexico. A sandy hematite-rich dolostone bed, which occurs 20 m above carbonates that record the nadir of the basal Cambrian carbon isotope excursion within the La Ciénega Formation, yielded a maximum depositional age of 539.40 ± 0.23 Ma using U-Pb chemical abrasion–isotope dilution–thermal ionization mass spectrometry on a population of sharply faceted volcanic zircon crystals. This bed, interpreted to contain reworked tuffaceous material, is above the last occurrences of late Ediacaran body fossils and below the first occurrence of the Cambrian trace fossil Treptichnus pedum, and so the age calibrates key markers of the Ediacaran-Cambrian boundary. The temporal coincidence of rift-related flood basalt volcanism in southern Laurentia (>250,000 km3 of basalt), a negative carbon isotope excursion, and biological turnover is consistent with a mechanistic link between the eruption of a large igneous province and end-Ediacaran extinction.

A protracted Ediacaran–Cambrian transition: an ichnologic ecospace analysis of the Fortunian in Newfoundland, Canada

AbstractThe transition between the seemingly disparate Ediacaran and Cambrian faunas is both enigmatic and body-fossil poor. The Chapel Island Formation on the Burin Peninsula, Newfoundland, Canada, contains a rich diversity of ichnofossils, providing new insight into the nature of the Ediacaran–Cambrian transition and early Fortunian ecosystems. Five ichnoguilds are recognized within the Treptichnus pedum zone. Ichnologic data are analysed from an ecospace perspective, revealing a more protracted transition between Ediacaran and Cambrian ecosystems. Our analysis documents the appearance of limbs, vertical burrows and uncontroversial equilibrium structures, as well as the retention of ‘other’ feeding styles, such as microbial grazing and chemosynthesis.

Ichnological Significance of Upper Disang Formation and Lower Barail Formation (Late Eocene to Early Oligocene) of Nagaland, Northeast India, in the Indo-Myanmar Ranges

ABSTRACT The Upper Disang-Lower Barail Transition Sequences of Nagaland in northeast India, Indo-Myanmar Ranges (IMR) are found to preserve reasonably diverse biological sedimentary structures. Three ichnofacies were observed, Skolithos ichnofacies consisting of Bergaueria hemispherica, Gyrochorte comosa, Ophiomorpha nodosa, Skolithos linearis and Thalassinoides paradoxicus; Cruziana ichnofacies – Curvolithus simplex, Scolicia plana, Scolicia strozzii, Scolicia vertebralis, Treptichnus pedum, Taenidium diesingi and Palaeophycus tubularis; and Nereites ichnofacies – Chondrites targionii and Paleomeandron elegans. Presence of Skolithos and Cruziana ichnofacies suggest well oxidising, substrate rich depositional environment in the foreshoreface to offshore setting in general; and an overall possible fluctuation in the depositional bathymetry which is supported by the presence of Nereites ichnofacies in horizons alternating with Skolithos and Cruziana ichnofacies. The depositional system is proposed to be proximal to distal hyperpycnal-delta-fed turbidite system. Observation of sand spherules also suggests possibility of shoreline as one of the depositional environments.

Ichnology, palaeoenvironment, and ecosystem dynamics of the Early Cambrian (Stage 4, Series 2) Guanshan Biota, South China

The Guanshan Biota of the Wulongqing Formation (Cambrian Series 2, Stage 4) is a typical Burgess Shale‐type Lagerstätte, containing not only a diverse assemblage of exceptionally preserved body fossils but also abundant, sophisticated trace fossils. Detailed ichnological study of the lower part of the Wulongqing Formation from the Longbaoshan and Xinglongcun sections in the Kunming area, Yunnan, South China, reveals the presence of 17 ichnospecies, including Aggregatella isp., Cruziana isp., Didymaulichnus lyelli, Diplichnites isp., Guanshanichnus glockerichnoides, Monomorphichnus isp., Palaeophycus isp., Planolites beverleyensis, Planolites montanus, Planolites isp., Psammichnites isp., Phycodes isp., Skolithos verticalis, Thalassinoides isp., Treptichnus pedum, and two types of non‐specific coprolites. These trace fossils represent burrowing or locomotion behaviours of arthropods and vermes, and belong to the Cruziana and Skolithos ichnofacies. As the outcrop at the Xinglongcun section is not well exposed, a systematic sedimentary study was conducted at the Longbaoshan section. The Guanshan ichnofauna in the lower Wulongqing Formation at the Longbaoshan section occur in fine‐grained siliciclastic rocks with wavy bedding, lenticular bedding, and wrinkle structures, reflecting a tidal flat environment. The abundance of diverse trace fossils in the tidal flat facies indicate that many taxa, mostly arthropods, were able to colonize the very shallow marine environments, supporting the landward expansion of the Early Cambrian ecosystems.

Vendian Macrofossils of the Yudoma Group, Southeast of the Siberian Platform

An assemblage of Late Precambrian macrofossils consisting of five species (Aspidella terranovica, Beltanelliformis brunsae, Nenoxites curvus, Palaeopascichnus renarius, and Suvorovella aldanica), was discovered in the type sections of the Yudoma Group of the Siberian Platform. A unique feature of the assemblage is the presence of carbonate discoidal remains of Suvorovella, formed as a result of secondary incrustation of basal structures, similar to Aspidella. The accumulations of redeposited fragments of Suvorovella formed the rock resembling the Phanerozoic shell beds. Except for this taxon, all members of the Yudoma assemblage have a wide geographic distribution. Their stratigraphic distribution tends to occur in the youngest deposits of the Upper Vendian, directly underlying the beds with small shelly fauna (SSF) of the Nemakit-Daldynian Stage, Cloudina tubes, and traces of the Treptichnus pedum Zone.

Una biota transicional Ediacárica–Cámbrica en el anticlinal de Abenójar (Macizo Ibérico, España)

Se describe una secuencia conteniendo una biota transicional ediacárica–cámbrica, en el valle del arroyo de las Navezuelas, anticlinal de Abenójar (Grupo Ibor, Zona Centroibérica, España). La secuencia empieza con capas siliciclásticas de grano fino conteniendo Vendotaenia antiqua y moldes de Cloudina cf. hartmannae, uno de los primeros animales con esqueleto mineralizado. Continúa con carbonatos con Cloudina fosfatizadas, coincidiendo en muestra de mano con Vendotaenia antiqua y con protoconodontos semejantes a Protohertzina unguliformis, lo cual sugiere una edad ediacárica terminal o cámbrica basal. Las capas detríticas sobre este nivel contienen pistas fósiles simples de organismos sedimentívoros. Sobre un estrato superior de carbonatos con pequeños vendoténidos se ha hallado un conjunto de pistas fósiles de aspecto cámbrico, incluyendo Treptichnus pedum y madrigueras ornamentadas semejantes a la superficie ventral de Psammichnites. El hallazgo de protoconodontos es nuevo para la transición Ediacárico–Cámbrico en Europa, y esta es la tercera vez a escala mundial que este tipo de fósiles típicamente cámbricos son hallados junto con cloudínidos, típicamente ediacáricos, lo cual sugiere que la transición Ediacárico–Cámbrico fue biológicamente más gradual de lo que se pensaba anteriormente.

Organic‐walled microfossils from the Ediacaran–Cambrian boundary stratotype section, Chapel Island and Random formations, Burin Peninsula, Newfoundland, Canada: Global correlation and significance for the evolution of early complex ecosystems

Although a variety of trace and body fossils have been described from the Cambrian strata in the stratotype section (global stratotype section and point) of the Precambrian–Cambrian boundary in the Burin Peninsula, Newfoundland, a detailed analysis of its organic‐walled microfossils has been missing. The basal CambrianTreptichnus pedumIchnozone of the Chapel Island Formation is dominated by leiosphaerids and filamentous sheaths. The appearance ofGranomarginataapproximates the base of the overlyingRusophycus avalonensisIchnozone. Common process‐bearing acritarchs, represented by smallAsteridiumandComasphaeridium, first appear in the middle of the overlying Random Formation, and a more diverse acritarch assemblage at its top. The Random Formation also yields small carbonaceous metazoan fossils, the first report of this type of fossil in this formation. The initial low diversity of phytoplankton in the basal Cambrian strata, a holdover from Ediacaran extinctions, indicated that they have limited potential for precise global correlation of the global stratotype section and point. The pattern of increasing diversity of acritarchs through the lower Fortunian strata lagged behind and was potentially a response to the Cambrian radiation of metazoans, as most clearly represented by ichnofossils. The timing of phytoplankton radiation reflects a dynamic lag driven by metazoan‐induced changes in early Cambrian food webs.

Ichnostratigraphy of the Ediacaran-Cambrian boundary: new insights on lower Cambrian biozonations from the Soltanieh Formation of northern Iran

AbstractStrata in the Central Alborz Mountains, northern Iran, are interpreted to show continuous sedimentation from Ediacaran through Cambrian times. The Soltanieh Formation consists of five members: Lower Dolomite, Lower Shale, Middle Dolomite, Upper Shale and Upper Dolomite members. The clastic units (Lower and Upper Shale members) represent sedimentation in distal marine settings, ranging from the shelf to offshore, and contain abundant trace fossils of biostratigraphic utility. Four ichnozones have been recognized. Ichnozone 1, containingHelminthoidichnites tenuis,Helminthopsis tenuis, andCochlichnus anguineus, is early Fortunian based on small shelly fossils, and is interpreted as a distal expression of theTreptichnus pedumzone. Ichnozone 2, comprising the first occurrence ofT.pedum, is middle Fortunian, and is best regarded as the upper half of theTreptichnus pedumZone. Ichnozone 3 is late Fortunian–Cambrian Age 2, characterized by a sudden change in abundance and complexity of trace fossils. Main elements in this ichnozone includeCruziana problematica,Curvolithusisp., Phycodesisp.,Treptichnus pedum,Treptichnus pollardi, andTreptichnusisp. Ichnozone 4 is of Cambrian Age 2–Age 3 and marked by the first appearances ofPsammichnites gigas,Rusophycus avalonensis, andDidymaulichnus miettensis. Integration of trace fossils with small shelly fossils suggests that the Ediacaran–Cambrian boundary should be placed at the base of the Soltanieh Formation or within the Lower Dolomite Member. The delayed appearance ofT.pedumand the low ichnodiversity in the Lower Shale and lower interval of the Upper Shale reflect limited colonization of settings below storm wave base during the early Fortunian.

Treptichnus pedumand the Ediacaran–Cambrian boundary: significance and caveats

AbstractThe Ediacaran–Cambrian (E-C) boundary is based on the first appearance of the ichnofossilTreptichnus pedum. Investing an ichnotaxon with such biostratigraphic pre-eminence has been the focus of criticism. Points of contention have revolved around four main issues: (1) ichnotaxonomy, (2) behavioural significance, (3) facies controls and (4) stratigraphic occurrence. First, confusion results from the fact thatTreptichnus pedumwas originally referred to asPhycodes pedumand, more recently, some authors have placed it inTrichophycusorManykodes. However, the overall geometry of these burrows indicates they belong inTreptichnus.Second, regardless of its precise mode of feeding, the behaviour involved is iconic of the Cambrian explosion. Third, objections are based on the idea that trace fossils show a closer link to facies than body fossils. Notably, in contrast to common assumptions,T. pedumis not only present in the low-energy offshore of wave-dominated marine settings, but it occurs at considerably shallower water in intertidal and shallow-subtidal zones of tide-dominated systems, as well as in mouth bars of deltaic systems and lower shoreface to offshore transition zones of wave-dominated marine settings. Its broad environmental tolerance supports evolutionary innovations rather than facies controls as the main mechanism underlying the observed vertical pattern of distribution ofT. pedumin most E-C successions comprising shallow-marine deposits. Fourth, although treptichnids have been documented below the E-C boundary,T. pedumis not known from Ediacaran rocks. The delayed appearance ofT. pedumin E-C successions should be analysed on a case-by-case basis.

A new lower Cambrian shelly fossil biostratigraphy for South Australia: Reply

The diversification of animals during the Cambrian Period is one of the most significant evolutionary events in Earth’s history. However, the sequence of events leading to the origin of ‘modern’ ecosystems and the exact temporal relationship between Ediacaran and Cambrian faunas are uncertain, as identification of the Ediacaran–Cambrian boundary and global correlation through this interval remains problematic. Here we review the controversies surrounding global correlation of the base of the Cambrian and present new high-resolution biostratigraphic, lithostratigraphic and δ13C chemostratigraphic data for terminal Ediacaran to basal Cambrian strata in the Zavkhan Basin of Mongolia. This predominantly carbonate sequence, through the Zuun-Arts and Bayangol formations in southwestern Mongolia, captures a distinct, negative δ13C excursion close to the top of the Zuun-Arts Formation recognized as the BAsal Cambrian carbon isotope Excursion (BACE). In this location, the nadir of the BACE closely coincides with first occurrence of the characteristic early Cambrian protoconodont Protohertzina anabarica. Despite recent suggestions that there is an evolutionary continuum of biomineralizing animals across the Ediacaran–Cambrian transition, we suggest that this continuum is restricted to tubular forms, and that skeletal taxa such as Protohertzina depict ‘true’ Cambrian representatives that are restricted entirely to the Cambrian. Employing the first appearance of the trace fossil Treptichnus pedum to define the base of the Cambrian suffers significant drawbacks, particularly in carbonate settings where it is not commonly preserved. As T. pedum is the only proxy available to correlate the Cambrian Global boundary Stratotype Section and Point (GSSP) defined at Fortune Head, Newfoundland, we suggest that the GSSP be redefined elsewhere, in a new stratigraphic section that contains secondary markers that permit global correlation. We propose the nadir of the BACE as the favored candidate to define the base of the Cambrian. However, it is essential that the BACE be complemented with secondary markers. In many global sections the nadir of the BACE and the first occurrence of the genus Protohertzina are closely juxtaposed, as are the BACE and T. pedum. Hence these taxa provide essential biostratigraphic control on the BACE and increase potential for effective global correlation. We also recommend that an Auxiliary boundary Stratotype Section and Point (ASSP) be simultaneously established in order to incorporate additional markers that will aid global correlation of the Ediacaran–Cambrian boundary. The BAY4/5 section through the upper Zuun-Arts and Bayangol formations yields key shelly fossils and δ13C values and is therefore an ideal candidate for consideration as the GSSP for the Ediacaran–Cambrian boundary.

Ichnological evidence for the Cambrian explosion in the Ediacaran to Cambrian succession of Tanafjord, Finnmark, northern Norway

Abstract The Ediacaran to Cambrian transition of the Digermul Peninsula consists of an ichnologically rich, thick, conformable, shallow marine siliciclastic succession that crosses the Neoproterozoic–Cambrian boundary. The Tanafjord section has been independently dated by published palynological and new body fossil discoveries. As is also observed at the current Global Stratotype Section and Point (GSSP) for the Ediacaran–Cambrian boundary at Fortune Head in Newfoundland, Canada, there is a marked increase in burrow size and inferred behavioural diversity around the inferred boundary level at a surface without a significant hiatus. The diversity of this trace fossil assemblage presents an opportunity to compare the ichnological first appearance datums between the GSSP and another sedimentologically similar, but palaeogeographically remote, succession. We found that the first appearance datums of taxa in Finnmark broadly support the definition and stratigraphic extents of the Harlaniella podolica , Treptichnus pedum, Rusophycus avalonensis and Cruziana tenella zones. Our work shows that there is a marked increase in ichnodiversity in the lowermost Fortunian, mostly in the form of shallow tier traces. The main post-Fortunian ichnological innovation is the evolution of bulk sediment deposit feeding that is first evidenced by spreiten burrows at around the base of Cambrian Stage 2 in both the GSSP and in the Tanafjord section. Supplementary material: Additional images of trace fossils from the studied section are available at https://doi.org/10.6084/m9.figshare.c.3462561

Cambrian ichnofossils from the Zhoujieshan Formation (Quanji Group) overlying tillites in the northern margin of the Qaidam Basin, NW China

The Quanji Group is composed of siliciclastics and carbonates and was deposited on a relatively stable block, in the northern margin of the Qaidam Basin, NW China. It is one of the research hotspots in the Qilian-Qinling-Kunlun tectonic zones. However, it has long been argued whether the upper Quanji Group should be assigned to the Precambrian or the Cambrian for lack of convincing fossil evidence. The discovery of ichnofossils, including Rusophycus, Cruziana, Dimorphichnus, Treptichnus, Skolithos, Arenicolites, Palaeophycus, and Helminthopsis, indicates that the upper member of the Zhoujieshan Formation (top Quanji Group) is Cambrian in age, and at least above the Treptichnus (Phycodes) pedum Biozone, the lowermost biozone in the Cambrian. The lower member of the Zhoujieshan Formation should belong to the Cambrian. During the time when the upper member of the Zhoujieshan Formation was deposited, the northern margin of the Qaidam Basin was dominated by the Cruziana Ichnofacies, characterizing a lower-energy shelf (shallow) sea environment with moderate-rich oxygen contents. In addition, the conglomerates in the Hongtiegou Formation of the Quanji Group underlying the Zhoujieshan Formation were generally regarded as tillites. However, the dolostones of the lower member of the Zhoujieshan Formation are, in lithology and geochemistry, different from the typical cap-dolostones of the Doushantuo Formation in South China, so it is necessary to further study the origins of the lower member of the Zhoujieshan Formation and the conglomerates of the Hongtiegou Formation.

Proposed reassessment of the Cambrian GSSP

Since the time of its ratification in 1992, the Cambrian GSSP, 2.3m above the base of Member 2A (Quaco Road Member) of the Chapel Island Formation, Fortune Head section, Newfoundland, Canada, has been challenged as posing an ambiguous correlation level. Difficulties have been encountered in precisely correlating the horizon coinciding with the GSSP to strata on most paleocontinents, but especially to Siberia and South China (Gondwana). The GSSP point, which was intended to coincide with the base of the Treptichnus pedum (formerly Phycodes pedum or Trichophycus pedum) Ichnozone at the FAD of the trace fossil T. pedum, occurs above the first appearance of the trace in the stratotype section. Trace fossils of other forms in the stratotype provide a means of bracketing the position of the GSSP, but are imprecise guides for correlation globally. Other chronostratigraphic guides are unavailable at the stratotype because of a dominance of coarse siliciclastic lithologies and metamorphic overprint.To facilitate global correlation of the Cambrian base and ensure nomenclatural stability to the extent possible, discussion of the merits and perceived weaknesses of the Cambrian GSSP is sought. Possible solutions to the problems surrounding the current GSSP definition are addressed in hopes that the global scientific community will actively participate in developing a well-reasoned, practical solution that will stand the test of time.