Treptichnus Research Articles

Diachronous Increase in Early Cambrian Ichnofossil Size and Benthic Faunal Activity in Different Climatic Regions

In order to clarify the pattern of diversification and processes of biological activity during the Cambrian radiation, ichnofossils were comparatively studied in the early Cambrian sections of Newfoundland, South China and western Mongolia. Special attention was paid to size distributions of the most common ichnogenus, Planolites, and the densities of all the observed ichnofossils that preserve animal activity as expressed by bedding plane bioturbation indices (BPBI).From the Fortune Head section in Newfoundland, a clear size increase in the ichnogenus Planolites is confirmed from the Treptichnus pedum Zone to the overlying Rusophycus avalonensis Zone. The BPBI also shows much stronger biological activity in the R. avalonensis Zone than in the T. pedum Zone. In Meishucun, South China and Gobi-Altai, Mongolia, however, a variety of Planolites sizes had already appeared in the T. pedum Zone, and the BPBI's on some bedding surfaces of the T. pedum Zone are already comparable to those in the R. avalonensis Zone in Newfoundland. In the earliest Cambrian, diversification and increase in the biological activity of the benthic fauna were diachronous in the wide geographic scale, starting earlier at lower latitudes (South China and western Mongolia) than at higher latitudes (Newfoundland), reflecting differences in the onset of Cambrian benthic animal activity under different climatic conditions.

Widespread delayed mixing in early to middle Cambrian marine shelfal settings

The radiation of burrowing metazoans in the early Phanerozoic dramatically altered the properties of marine sediment, an event commonly referred to as the “Cambrian substrate revolution” or “agronomic revolution.” The advent of infaunalization, and especially biogenically-mediated sediment mixing, profoundly impacted the development of Phanerozoic biogeochemical cycling, including nutrient fluxes, organic carbon burial, seafloor oxygenation and sediment ecology. However, the timing of the development of mixed seafloor sediment has, historically, not been well constrained. Mixing has been assumed, in the absence of data, to occur at the Precambrian–Cambrian boundary with the appearance of the index fossil and three-dimensional burrow Treptichnus pedum. Herein we present new ichnological, stratigraphic and taphonomic data suggesting that, although significant developments in infaunalization—paleobiologically complex animal–substrate interactions, particularly burrow construction—occurred during the early and middle Cambrian, mixing remained suppressed throughout this interval. We demonstrate, using a novel multi-proxy approach, that shelfal sediment in the earliest Cambrian was essentially unmixed. Moreover, our findings indicate that even as late as the middle Cambrian—30millionyears after the Precambrian–Cambrian transition and well after the appearance of supposedly deposit-feeding trilobites—seafloor heterolithic shelfal sediment remained largely unmixed on a global scale. These findings challenge the current assumption that mixing occurred with the first appearance of three-dimensional burrows and hold important implications for the advent and development of modern-style biogeochemical cycling.

Is the fossil record of complex animal behaviour a stratigraphical analogue for the Anthropocene?

Abstract The base of the Cambrian System is recognized by a characteristic (marine) trace fossil suite assigned to the Treptichnus pedum Biozone, which signals increasing complexity of animal behaviour and demarcates the Cambrian from the (older) Ediacaran System (Proterozoic Eonathem). Ichnotaxa of the T. pedum Biozone are not the earliest trace fossils, and are preceded in the latest Proterozoic by a progressive increase in the diversity of trace-producing organisms and the communities they comprised, the structural and behavioural complexity of the trace fossils, and even the depth of burrowing in sediments. Parallels can be drawn with the increasing complexity of subsurface structures associated with human cities, which also reflect evolution of an increasingly complex community. Before the nineteenth century, these structures were limited and simple, but beginning with the development of London in the mid-nineteenth century as the world's first megacity, subsurface structures have become increasingly complex, reflecting the technology-driven behaviour of twentieth- and twenty-first-century humans.

Problematic Worms and Priapulid-like Fossils from the Nagaur Group, the Marwar Supergroup, Western Rajasthan, India

Worm-like problematic megafossils, comparable with priapulids, are reported from the Lower Cambrian Nagaur Formation of the Marwar Supergroup, Western Rajasthan, India. These fossils occur as positive epireliefs on the top surface of siliciclastic sandstone beds in the Dulmera area of Bikaner district, western Rajasthan. Occurrence of these structures is significant, as the fossil bearing strata also exhibit the preservation of trilobite traces and Treptichnus pedum (three-dimensional subhorizontal burrows). The latter is a Precambrian-Cambrian boundary marker fossil, which has a worldwide distribution. Recently, it has been experimentally demonstrated that priapulids (ecdysozoa) or similar organisms are responsible for the construction of treptichnid burrows. Co-occurrence of these body fossils and treptichnid burrows in the same stratigraphic horizon indicate their close relationship and supports the inferences that these organisms are responsible for the formation of T. pedum. It also projects strong evidence demarcating the Precambrian/Cambrian boundary in the Nagaur Group. These faunal remains are considered to be a significant tool in comparative studies of the evolution from invertebrate to vertebrate animals. Detailed study may certainly shed light on different aspects of macroevolution and radiation among animal clades, and the palaeoecology prevailing at the time of the Nagaur Sandstone deposition.

DEEP-WATER INCISED VALLEY DEPOSITS AT THE EDIACARAN-CAMBRIAN BOUNDARY IN SOUTHERN NAMIBIA CONTAIN ABUNDANT TREPTICHNUS PEDUM

Valley-filling deposits of the Nama Group, southern Namibia, record two episodes of erosional downcutting and backfill, developed close together in time near the Ediacaran-Cambrian boundary. Geochronological constraints indicate that the older valley fill began 539.4 ± 1 Ma or later; the younger of these deposits contains unusually well-preserved populations of the basal Cambrian trace fossil Treptichnus pedum. Facies analysis shows that T. pedum is closely linked to a nearshore sandstone deposit, indicating a close environmental or taphonomic connection to very shallow, mud-draped sandy seafloor swept by tidal currents. Facies restriction may limit the biostratigraphic potential of T. pedum in Namibia and elsewhere, but it also illuminates functional and ecological interpretation. The T. pedum tracemaker was a motile bilaterian animal that lived below the sediment-water interface—propelling itself forward in upward-curving projections that breached the sediment surface. The T. pedum animal, therefore, lived infaunally, perhaps to avoid predation, surfacing regularly to feed and take in oxygen. Alternatively, the T. pedum animal may have been a deposit feeder that surfaced largely for purposes of gas exchange, an interpretation that has some support in the observed association of T. pedum with mud drapes. Treptichnus pedum provides our oldest record of animals that combined anatomical and behavioral complexity. Insights from comparative biology suggest that basal Cambrian T. pedum animals already possessed the anatomical, neurological, and genetic complexity needed to enable the body plan and behavioral diversification recorded by younger Cambrian fossils.

Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary

The major evolutionary events that characterize the Precambrian–Cambrian transition are accompanied by profound ecological changes in the composition of benthic communities, the nature of the substrate, and the occupation of marine ecospace. The increased animal activity on and within the substrate is attested to by numerous trace fossils, such as the cosmopolitan Treptichnus pedum whose fi rst appearance is used as the global stratotype section and point (GSSP) to mark the base of the Cambrian. In spite of its major importance in biostratigraphy, the maker of Treptichnus trace fossils, and more generally of treptichnids, has long remained an enigma. Treptichnids were subhorizontal burrow systems produced in the subsurface and had a worldwide distribution throughout the Cambrian. Here we show, by using experimental ichnology, that the treptichnid burrow systems were most probably produced by priapulid worms or by worms that used the same locomotory mechanisms as the Recent priapulids (e.g., Priapulus). Their typical three-dimensional morphology with repeated arcuate probing branches suggests that their function was related to the feeding strategy of the worm such as predation or scavenging upon small epibenthic or endobenthic invertebrates. This interpretation is strongly supported by the preserved gut contents of Cambrian priapulids from the Burgess Shale Lagerstatte that contain effectively a variety of small epibenthic prey. The antiquity of treptichnids would designate priapulids as one of the earliest infaunal colonizers of the substrate that possibly interacted with epibenthic communities, thus playing a leading role (1) in the construction of the early marine food chain, and (2) as important subhorizontal bioturbators in the early stages of the “Cambrian Substrate Revolution.”

Facies development during late Early–Middle Cambrian (Tayan Member, Burj Formation) transgression in the Dead Sea Rift valley, Jordan

The transgressive Tayan Member of the upper Lower to Middle Cambrian Burj Formation (Jordan) has been investigated in several localities of the Dead Sea Rift valley, Jordan. The lower portion of this member consists of low-energy siliciclastics with indications of temporary, early pedogenetic processes, pointing to some stagnation during transgression. The upper portion of the member was deposited under higher energy conditions. Stromatolites, desiccation cracks, halite- pseudomorphs, laminated dolostones, and tepees, together with ripples, mud-clasts and scours point to a shallow intertidal to supratidal sabkha-related environment in a climate of tropical to subtropical aridity. The fossil content of the Tayan Member consists exclusively of trace fossils. Simple endobentic, worm- like r-strategists are common in some horizons. For the first time, Treptichnus pedum has been repor- ted from Jordan where it was found near the base of this member. The markedly reduced biodiversity together with sedimentological data led to the interpretation of a strongly stressed, paleoecologically unstable habitat. Regional comparisons with high-energy transgressive environments laid down at the same time show that the main factors controlling facies development and the migration of facies belts are (1) the topography of the flooded surface and of the hinterland (mainly with only a local effect), (2) the configuration of the coast (local effect), (3) the rate of subsidence and transgression (local to regional effects), and (4) climate (large regional effects). The combination and overlap of these factors controlled facies gradients and may explain special differences between the facies of the Jordanian and those of the near-by Israeli transgressive deposits on the one hand, but, also the obvious general similarity of Lower to Middle Cambrian transgressive successions in the Middle East and the Mediterranean part of Gondwana on the other hand.

EDIACARAN AND CAMBRIAN INDEX FOSSILS FROM SONORA, MEXICO

Abstract: The Cambrian index fossil Treptichnus pedum is reported from the Puerto Blanco Formation near Pitiquito, Sonora, Mexico, and new occurrences of the Neoproterozoic index fossil Cloudina are reported from the underlying La Ciénega Formation. Considered together, these fossils constrain the location of the Ediacaran/Cambrian boundary in Mexico. The suite of fossils in this sequence is important because it provides an independent biostratigraphic datum for constraining the position of Laurentia during the onset of metazoan diversification, for testing proposed lithostratigraphic correlations among western North American Neoproterozoic–Cambrian successions, and for testing regional tectonic paradigms such as the Mojave‐Sonora Megashear hypothesis.

The Precambrian-Cambrian Transition in the Southern Great Basin, USA

The Precambrian-Cambrian boundary presents an interesting stratigraphic conundrum: the trace fossil used to mark and correlate the base of the Cambrian, Treptichnus pedum, is restricted to siliciclastic facies, whereas biomineralized fossils and chemostratigraphic signals are most commonly obtained from carbonate-dominated sections. Thus, it is difficult to correlate directly between many of the Precambrian-Cambrian boundary sections, and to assess details of the timing of evolutionary events that transpired during this interval of time. Thick sections in the White-Inyo region of eastern California and western Nevada, USA, contain mixed siliciclastic-carbonate lithofacies, and therefore promote correlation between these classic, well-studied lithologic end-members. An integrated stratigraphic approach was applied to the White-Inyo succession, combining lithologic, paleontologic, and chemostratigraphic data, in order to address the temporal framework within the basin, and to facilitate worldwide correlation of the boundary. Results from the southern Great Basin demonstrate that the negative δ13C excursion that is ubiquitous in carbonate-dominated successions containing small shelly fossils occurs within stratigraphic uncertainty of the first occurrence of T. pedum. This global geochemical marker thus provides a link with the primary biostratigraphic indicator for the Precambrian-Cambrian boundary.

Lowermost Cambrian Ichnofabrics from the Chapel Island Formation, Newfoundland: Implications for Cambrian Substrates

Abstract Bioturbation long has been ‘blamed’ for eliminating late Proterozoic-style sedimentary structures and fabrics. While the presence of diverse and complex burrows in lowermost Cambrian strata is indisputable, analysis of Precambrian–Cambrian successions in southeast Newfoundland demonstrate that this burrowing style did not produce typical Phanerozoic-style ichnofabrics. Three hundred meters of the siltstone/sandstone facies of member 2 of the Chapel Island Formation were examined in the area of the Precambrian–Cambrian boundary stratotype. Gyrolithes, Planolites, and Skolithos occur as sand infills ubiquitously throughout siltstone beds, most commonly without direct contact with an overlying sandstone bed, as if “floating” in the siltstone. In contrast, Treptichnus pedum occurs as sand infills adhering onto the base of thin sandstone beds that have different grain size and texture than the burrow infills. Both of these burrow types represent a style of preservation in which the burrows are unattac...

Ediacaran fossils from the southwestern Great Basin, United States

Ediacaran fossils from the southwestern Great Basin may help constrain regional Vendian-Cambrian biostratigraphy and provide biogeographic links between facies in this region and elsewhere. Locally, trace fossils suggest the Vendian-Cambrian boundary occurs within or below the upper third of the lower member of the Wood Canyon Formation. Ediacaran soft-bodied and tubular fossils, including the frondlike fossil Swartpuntia and tubular, mineralized or agglutinated fossils similar to Archaeichnium Cloudina Corumbella, and Onuphionella occur in the lowermost Wood Canyon Formation. Discoidal forms referred to Nimbia occur in both the lowermost Wood Canyon Formation and the underlying strata of the Stirling Quartzite. These fossils occur directly below Lower Cambrian trace fossils, including Treptichnus pedum, and confirm the persistence of the Ediacaran biota to near the base of the Cambrian. These faunas may also help strengthen previously proposed correlation schemes between the two main facies belts of the southwestern Great Basin (the Death Valley and White-Inyo facies), because a nearly identical Vendian-lowest Cambrian succession of faunas occurs in both regions. Lastly, lack of cosmopolitan Ediacaran faunas in these strata suggests a paleobiogeographic link between the southwestern U.S. and southern Africa in Vendian time.

EDIACARAN FOSSILS FROM THE SOUTHWESTERN GREAT BASIN, UNITED STATES

Ediacaran fossils from the southwestern Great Basin may help constrain regional Vendian-Cambrian biostratigraphy and provide biogeographic links between facies in this region and elsewhere. Locally, trace fossils suggest the Vendian-Cambrian boundary occurs within or below the upper third of the lower member of the Wood Canyon Formation. Ediacaran soft-bodied and tubular fossils, including the frondlike fossil Swartpuntia and tubular, mineralized or agglutinated fossils similar to Archaeichnium Cloudina Corumbella, and Onuphionella occur in the lowermost Wood Canyon Formation. Discoidal forms referred to Nimbia occur in both the lowermost Wood Canyon Formation and the underlying strata of the Stirling Quartzite. These fossils occur directly below Lower Cambrian trace fossils, including Treptichnus pedum, and confirm the persistence of the Ediacaran biota to near the base of the Cambrian. These faunas may also help strengthen previously proposed correlation schemes between the two main facies belts of the southwestern Great Basin (the Death Valley and White-Inyo facies), because a nearly identical Vendian-lowest Cambrian succession of faunas occurs in both regions. Lastly, lack of cosmopolitan Ediacaran faunas in these strata suggests a paleobiogeographic link between the southwestern U.S. and southern Africa in Vendian time.

Precambrian-Cambrian transition: Death Valley, United States

The Death Valley region contains one of the best exposed and often visited Precambrian-Cambrian successions in the world, but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate. The recent discovery of Treptichnus (Phycodes) pedum within the uppermost parasequence of the lower member of the Wood Canyon Formation allows correlation of the Precambrian-Cambrian boundary to this region and provides a necessary global tie point for the Death Valley section. New carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary. For the first time, biostratigraphic, chemostratigraphic, and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the Cambrian explosion. Few Precambrian-Cambrian boundary sections contain both the facies-restricted boundary fossil T. pedum and carbon isotope data, as found in Death Valley. Thus, the Death Valley succession provides a critical link toward our understanding of the correlation between siliciclastic-dominated and carbonate-dominated Precambrian-Cambrian transition sections.

Complex trace fossils from the terminal Proterozoic of Namibia

We document for the first time the occurrence of the complex trace fossil Treptichnus from the terminal Proterozoic Nama Group, Namibia. These traces differ in detail from the Cambrian index fossil Treptichnus pedum , but document precursors with the same basic behavior. The producer of the trace is not known. In its complexity, however, this trace fossil provides strong evidence for advanced latest Proterozoic bilaterians.

Evolution and Ecology of Neoproterozoic-Lower Cambrian Trace Fossils, NW Canada

Neoproterozoic to subtrilobite Cambrian strata in the Mackenzie Mountains, Canada, provide a test case for the current paradigm of evolutionary stages in the development of the early infauna. Three predominantly siliciclastic formations (Ingta, Backbone Ranges, and Vampire formations) collectively exhibit 13 facies associations representing nonmarine to distal shelf environments, and can be subdivided into 18 simple sequences, each of 800,000-1,000,000 years duration. Trace fossil occurrences were digitized at the level of simple sequences and plotted on a matrix with facies associations (environment) on the x-axis and simple sequences (time) on the y-axis. This analysis shows that evolution was a first-order control on trace fossil distribution, and that environmental factors exerted an important second-order control. Trace fossils were most abundant in normal marine environments and less so in marginal-marine settings with fluctuating or brackish salinity. Eolian and fresh-water deposits were barren, presumably because animals able to tolerate these conditions had not evolved. Turbulence excluded organisms from shoreface environments. Several biostratigraphically important ichnotaxa (e.g., Treptichnus and Rusophycus), however, show broad environmental tolerance across the marine shelf Taphonomic factors led to fine preservation in interbedded sandstone-mudstone facies, but to diagenetic obliteration of trace fossils in most carbonate facies. Trace fossils provide a consistent indicator of the Neoproterozoic-Cambrian boundary. Four evolutionary zones can be recognized: (I) Simple burrows, (II) Treptichnus pedum Zone, (III) Rusophycus avalonensis Zone, and (IV) Cruziana tenella Zone. Global biostratigraphic and chemostratigraphic correlations imply that Zone I is terminal Neoproterozoic and the overlying three zones subtrilobite Cambrian in age. These zones are present in the Newfoundland Neoproterozoic-Cambrian boundary GSSP, the East European Platform, and elsewhere.

Terminal Proterozoic-Cambrian sequences in India: a review with special reference to Precambrian-Cambrian Boundary

The Terminal Proterozoic marine sequences, grading into Cambrian, are present in the Krol Basin (Lesser Himalaya), the Kashmir, Spiti-Zanskar and Kumaun Basins (Higher Himalaya) and in Marwar Basin (western India). These sequences postdate a major tectono-thermal event associated with Cadomian Orogeny and rest on eroded older successions which include well-dated Malani Igneous Suite (Malani Rhyolite 745 ±10 Ma; Siwana Granite 731± 14 Ma) in Western India and over the Salkhala Group with granites (745 ± 50 Ma) or the Simla Group in the Himalaya. This cycle of sedimentation terminated with Pan-African Orogeny in Late Cambrian. These sequences are dominantly siliciclastic in basins in Higher Himalaya while those in Krol Basin and Marwar Basin show development of thick carbonate-evaporite facies with or without phosphorite. From the Upper Vindhyan and Bhima Groups in central and south India, respectively a Chuaria-Tawuia Assemblage along with sphaeromorphida Acritarch of Early Neoproterozoic age has been recorded. The δ13C values range from +1.3 to +4.0 ‰ PDB and that of δ 18O from -5 to -9‰ PDB. These are, thus, not considered part of this sequence. In absence of age-determinating biota and radiometric dates from the basal part of the succession, the lower boundary of the Terminal Proterozoic cannot be delineated and dated. However, a significant depletion in values may be taken to mark the lower boundary.
 The upper boundary of the Terminal Proterozoic (Precambrian-Cambrian Boundary) cannot be demarcated in terms of GSSP due to the absence of trace fossils of Zone-1 (Harlaneilla podolika Zone) and Zone-II (Phycodes pedum Zone) in carbonate facies in Krol Basin and poor documentation of siliciclastic facies in Kashmir and Spiti-Zanskar Basins. The trace fossils correlative with ichnozone-III occur in all sections in the Himalayas and are useful for regional and global correlations. However, a significant depletion in δ13C values has been recorded in the carbonate facies of the Krol Basin between the horizons yielding Ediacaran and small shelly fossils of Meishucunian Zone-I. This has also been recorded in the Marwar Basin below the Phosphorite Bed. This depletion may be correlated with that recorded from the Precambrian-Cambrian transition in Siberian Platform, Anti Atlas Mountains, Morocco, China, etc. It may be taken into consideration to define and mark the boundary in the absence of trace fossils.

The Neoproterozoic of southwestern Africa, with emphasis on platform stratigraphy and paleontology

Neoproterozoic sediments in southwestern Africa occur in the Pan-African Kaoko, Khomas, Gariep, Vanrhynsdorp and Saldania Belts. They were deposited in response to rifting, break-up of a supercontinent (formed at ∼ 1000 Ma) and subduction and collisions of the Congo, Kalahari, Rio de la Plata and Malvinas plates. These collisions led to the formation of a Neoproterozoic/Cambrian supercontinent. This paper deals with the geology of the platform successions of the Kaoko, Khomas, Gariep and Vanrhynsdorp Belts. Deposition of the sediments occurring in these belts commenced ∼ 900 to 1000 Ma ago and probably ended between 500 and 520 Ma. The sediments record Wilson cycles that ended with the deposition of red beds. Palaeontological and carbon isotope studies on the Damara Sequence, Gariep Complex, Nama Group and Vanrhynsdorp Group make intra- and inter-basinal correlations possible. Prior to deposition of the Nama Group two, or perhaps three, glaciations took place over an extensive area in southwestern Africa, these being the Kaigas (Chuos) (∼ 725-700 Ma), Numees (∼ 650-600 Ma or ∼ 610-590 Ma) and possibly the Varianto (∼ 745-725 Ma) glaciations. The Numees tillite is overlain by a stratigraphic unit containing pinkish dolomite. During deposition of the Nama Group, the minor Vingerbreek (∼ 600-545 Ma) “glaciation” (or cold-water period) occurred. The major Kaigas (Chuos) and Numees and minor Vingerbreek glaciations correspond with low δ 13C isotope ratios and appear to have taken place at relatively low palaeolatitudes. The Riphean sediments were deposited predominantly during rifting and break-up of a supercontinent. During the late Vendian to early Cambrian, deposition of the Nama Group in southern Namibia and the penecontemporaneous Vanrhynsdorp Group in the Republic of South Africa took place in the Nama foreland basin. Detrital micas indicate that deposition of the Nama Group took place between 635 and 530 Ma. The Nama foreland basin, which was connected to a major ocean to the south, formed as a result of collisions between the Congo, Kalahari and Rio de la Plata plates. With the exception of the Nama Group, little is known about the palaeontology of the Neoproterozoic in southwestern Africa. The lower Nama Group is latest Proterozoic in age. It contains an Ediacaran fauna, a depauperate assemblage of organic-walled microfossils and a relatively well diversified ichnofauna with Brooksella, Diplocraterion and Nereites which are atypical of Vendian strata. Many trace fossils are exceptionally small. The occurrence of the shelly fossil Cloudina and probable calcified metaphytes in the lower Nama Group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the Proterozoic. The upper Nama Group is early Cambrian in age as indicated by the occurrence of the trace fossil Phycodes pedum. The upper Nama Group, dominated by red beds, contains a low-diversity ichnofauna with trace fossils of normal size. Bio- and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities, which occur in the Neoproterozoic of southwestern Africa, are related to the periods of formation of the Wonoka Canyons in south Australia.

Early Paleozoic chronology: a review in light of new U – Pb zircon ages from Newfoundland and Britain

The time scale for the Cambrian through Early Devonian periods is revised using new U–Pb ages from volcanic and pyroclastic rocks in sequences that are stratigraphically well defined. A rhyolite flow from the latest Precambrian, dated at 551.4 ± 5.8 Ma, gives a maximum age for the base of the Cambrian (Phycodes pedum Zone) at Fortune Bay, Newfoundland. The age ranges of several Ordovician and Silurian series are now established to within 2–3 Ma based on stratigraphically controlled samples from Britain. A basal Llandeilo ash has an age of 460.4 ± 2.2 Ma; a basal Caradoc lava has an age of 456.1 ± 1.8 ± Ma; and K-bentonites from the latest Llandovery and latest Ludlow have ages of 430.1 ± 2.4 and 420.2 ± 3.9 Ma, respectively. Using other data from the literature, we interpolate the base of the Cambrian to be near 545 Ma, the base of the Ordovician as ca. 495 Ma, and the base of the Silurian as ca. 443 Ma. While we have a good estimate for the base of the Middle Devonian (at ca. 391 Ma), the base of the Devonian is less precise, probably around 417 Ma.

Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time

Research Article| February 01, 1994 Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time Ed Landing Ed Landing 1New York State Geological Survey, The State Education Department, Albany, New York 12230 Search for other works by this author on: GSW Google Scholar Geology (1994) 22 (2): 179–182. https://doi.org/10.1130/0091-7613(1994)022<0179:PCBGSR>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ed Landing; Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time. Geology 1994;; 22 (2): 179–182. doi: https://doi.org/10.1130/0091-7613(1994)022<0179:PCBGSR>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Precambrian-Cambrian boundary global stratotype is the base of the Phycodes pedum Zone at Fortune Head, southeastern Newfoundland. The initial, two-stage radiation of the Phanerozoic fauna (the appearance of Phanerozoic-aspect trace producers and subsequent origin of diverse skeletalized metazoans) was earliest Cambrian. Fossil assemblages with deep, complex burrows or originally mineralized skeletal fossils (with exception of Cloudina) are Early Cambrian or younger. Correlation into Avalon indicates that strata once referred to the Proterozoic (e.g., Manykaian [or Nemakit-Daldynian] and Rovno stages) are lowest Cambrian and that the Siberian Tommotian Stage is middle Lower Cambrian. The thick sequence and complex epeirogenic history of the Placentian Series, as compared with the trilobite-bearing Branchian Series, suggest that most Early Cambrian time is represented by the subtrilobitic Lower Cambrian. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

ACRITARCHSA REVIEW

ACRITARCHSA REVIEW