Johnson Lane, UT, United States
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Lucas S.G.,New Mexico Museum of Natural History and Science | Jenks J.F.,1134 Johnson Ridge Lane | Spielmann J.A.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010

The Triassic chronostratigraphic scale was built on two centuries of research on ammonoid biostratigraphy and biochronology. Two Triassic stage bases and all of the Triassic substages are currently defined by ammonoid bioevents. The study of Triassic ammonoids began during the late 1700s, and in 1895, Edmund von Mojsisovics, Wilhelm Waagen and Carl Diener published an essentially complete Triassic chronostratigraphic scale based on ammonoid biostratigraphy. This scale introduced many of the Triassic stage and substage names still used today, and all terminology of stages and substages subsequently introduced has been based on ammonoid biostratigraphy. Early Triassic ammonoids show a trend from cosmopolitanism (Induan) to latitudinal differentiation (Olenekian), and the four Lower Triassic substage (Griesbachian, Dinerian, Smithian and Spathian) boundaries are globally correlated by widespread ammonoid biotic events. Middle Triassic ammonoids have provinciality similar to that of the Olenekian and provide a basis for recognizing six Middle Triassic substages. Late Triassic ammonoids provide a basis for recognizing three stages divided into five substages. The main uncertainty for the future of Triassic ammonoid biostratigraphy is not the decline of the ammonoids as a tool for dating and correlation of Triassic strata but, rather, the dramatic decrease in the number of specialists, due to the lack of replacement of experienced palaeontologists who started their activity in the 1950s and 1960s. © The Geological Society of London 2010.


Olivier N.,CNRS Geological Laboratory of Lyon: earth, planets and environment | Brayard A.,French National Center for Scientific Research | Fara E.,French National Center for Scientific Research | Bylund K.G.,140 South 700 East | And 6 more authors.
Geological Magazine | Year: 2014

In Timpoweap Canyon near Hurricane (Utah, USA), spectacular outcrop conditions of Early Triassic rocks document the geometric relationships between a massive Smithian fenestral-microbial unit and underlying, lateral and overlying sedimentary units. This allows us to reconstruct the evolution of depositional environments and high-frequency relative sea-level fluctuations in the studied area. Depositional environments evolved from a coastal plain with continental deposits to peritidal settings with fenestral-microbial limestones, which are overlain by intertidal to shallow subtidal marine bioclastic limestones. This transgressive trend of a large-scale depositional sequence marks a long-term sea-level rise that is identified worldwide after the Permian-Triassic boundary. The fenestral-microbial sediments were deposited at the transition between continental settings (with terrigenous deposits) and shallow subtidal marine environments (with bioturbated and bioclastic limestones). Such a lateral zonation questions the interpretation of microbial deposits as anachronistic and disaster facies in the western USA basin. The depositional setting may have triggered the distribution of microbial deposits and contemporaneous marine biota. The fenestral-microbial unit is truncated by an erosional surface reflecting a drop in relative sea level at the scale of a medium depositional sequence. The local inherited topography allowed the recording of small-scale sequences characterized by clinoforms and short-distance lateral facies changes. Stratal stacking pattern and surface geometries allow the reconstruction of relative sea-level fluctuations and tracking of shoreline migrations. The stacking pattern of these small-scale sequences and the amplitude of corresponding high-frequency sea-level fluctuations are consistent with climatic control. Large- and medium-scale sequences suggest a regional tectonic control. Copyright © Cambridge University Press 2014.


Brayard A.,University of Burgundy | Nutzel A.,Ludwig Maximilians University of Munich | Stephen D.A.,Utah Valley University | Bylund K.G.,140 South 700 East | And 3 more authors.
Geology | Year: 2010

Size reduction in the aftermath of the Permian-Triassic mass extinction event has repeatedly been described for various marine organisms, including gastropods (the Lilliput effect). A Smithian gastropod assemblage from Utah, USA, reveals numerous large-sized specimens of different genera as high as 70 mm, the largest ever reported from the Early Triassic. Other gastropods reported from Serbia and Italy are also as large as 35 mm. Size frequency distributions of the studied assemblages indicate that they were not unusually small when compared with later Mesozoic and modern faunas. The occurrence of large-sized gastropods less than 2 Ma after the Permian-Triassic mass extinction refutes the Lilliput hypothesis in this clade, at least for the last ~75% of the Early Triassic. © 2010 Geological Society of America.


Brayard A.,French National Center for Scientific Research | Meier M.,University of Zürich | Escarguel G.,University Claude Bernard Lyon 1 | Fara E.,French National Center for Scientific Research | And 8 more authors.
Earth-Science Reviews | Year: 2015

A reduction in body size (Lilliput effect) has been repeatedly proposed for many marine organisms in the aftermath of the Permian-Triassic (PT) mass extinction. Specifically-reduced maximum sizes of benthic marine invertebrates have been proposed for the entire Early Triassic. This concept was originally based on observations on Early Triassic gastropods from the western USA basin and the Dolomites (N Italy) and it stimulated subsequent studies on other taxonomic groups. However, only a few studies have tested the validity of the Lilliput effect in gastropods to determine whether the paucity of large-sized gastropods is a genuine signal or the result of a poor fossil record and insufficient sampling. In combination with a review of the literature, we document numerous new, abundant, large-sized gastropods from the Griesbachian outcrops of Greenland and from the Smithian-early Spathian interval in the southwestern USA. We show that large-sized ("Gulliver") gastropods (i) were present soon after the PT mass extinction, (ii) occurred in various basins, sedimentary facies and environmental contexts (from shallow to deeper settings), and (iii) belong to diverse higher-rank taxa. Focusing on the western USA basin, we investigate areas from which microgastropod shell-beds were previously presented as being typical. However, we show that Gulliver gastropods do occur in the very same areas. Insufficient sampling effort is probably the main reason for the rarity of reports of large Early Triassic gastropods, which is supported by preliminary rarefaction-based simulations. Finally, it appears that the recently documented middle to late Smithian climate shifts and the severe end-Smithian extinction of nekto-pelagic faunas did not reduce maximum shell sizes of gastropods. © 2015 Elsevier B.V.


Brayard A.,University of Burgundy | Vennin E.,University of Burgundy | Olivier N.,CNRS Geological Laboratory of Lyon: earth, planets and environment | Bylund K.G.,140 South 700 East | And 6 more authors.
Nature Geoscience | Year: 2011

Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs from the western USA that comprise of various sponges and serpulids associated with microbialites and other eukaryotic benthic organisms. These metazoan-rich reefs were formed only 1.5 million years after the extinction, in contrast to previous suggestions of a much delayed recovery of complex benthic communities. We conclude that the predominance of microbial reefs following the mass extinction is restricted to short intervals of the earliest Triassic. We suggest that metazoan reef building continued throughout the Early Triassic wherever permitted by environmental conditions. © 2011 Macmillan Publishers Limited. All rights reserved.


Ware D.,University of Zürich | Jenks J.F.,1134 Johnson Ridge Lane | Hautmann M.,University of Zürich | Bucher H.,University of Zürich
Swiss Journal of Geosciences | Year: 2011

A well-preserved ammonoid fauna of Early Dienerian age has long been known from the lower portion of the Candelaria Formation in the old Candelaria silver mining district in Mineral and Esmeralda Counties, Nevada, but for a number of reasons, this fauna has never been studied in detail nor illustrated. Previous authors assigned this ammonoid fauna to the Early Dienerian Proptychites candidus Zone of Canada. In reality, it more closely resembles the Tethyan faunas than the higher palaeolatitude Canadian faunas, thus indicating the presence of some degree of equatorial faunal exchange between opposite sides of the Panthalassic Ocean during Early Dienerian time. It also indicates the onset of a provincialism, which contrasts with the cosmopolitan Griesbachian faunas. A rigorous taxonomic analysis of the Candelaria fauna allows us to differentiate the following ten species, which include two new species and one new genus (Mullericeras nov. gen.) belonging to the new family Mullericeratidae: Ambites lilangensis (Krafft, 1909), Ambites aff. radiatus (Brühwiler, Brayard, Bucherand Guodun, 2008), Ussuridiscus sp. indet., "Koninckites" aff. kraffti Spath, 1934, Mullericeras spitiense (Krafft, 1909), Mullericerasfergusoni nov. sp., Mullericeras sp. indet., Proptychites haydeni (Krafft, 1909), Proptychites pagei nov. sp., Vavilovites sp. indet. and Parahedenstroemia kiparisovae Shigetaand Zakharov, 2009. This Early Dienerian fauna correlates with the Ambites fauna known from the base of the Ceratite Marls in the Salt Range and from the base of the "Meekoceras" beds in Spiti (northern Gondwanian margin). The fauna also permits the precise dating of a shelfal anoxic episode on the equatorial North American margin. This anoxic event correlates in time with similar palaeoceanographic changes in the southern Tethys, which indicates that the Early Triassic biotic recovery was at least partly shaped by such discrete, short events rather than by pervasive and lingering adverse environmental conditions. © 2011 Swiss Geological Society.


Monnet C.,Lille University of Science and Technology | Bucher H.,University of Zürich | Brayard A.,French National Center for Scientific Research | Jenks J.F.,1134 Johnson Ridge Lane
Fossil Record | Year: 2013

Globacrochordiceras transpacificum gen. et sp. nov. is an ammonoid (Ammonoidea, Cephalopoda) with a shell characterized by plicate ribbing (rounded and undulating ribs strengthening on the venter without interruption), increasing involution through ontogeny, overhanging and deep umbilical wall, absence of tuberculation, subtriangular whorl section, globose adult shape with a closed umbilicus followed by an abrupt egressive coiling, and a subammonitic adult suture line. This new taxon occurs in Nevada (USA) and in Guangxi (South China). It has its typical occurrence within the Neopopanoceras haugi Zone of late Spathian age (Early Triassic). The plicate ribbing, suture line and general shell shape are diagnostic of the family Acrochordiceratidae. The large adult size, high degree of involution and subammonitic suture line of Globacrochordiceras markedly contrast with the next younger genus of the family (Paracrochordiceras of early Anisian age, Middle Triassic), which is evolute and displays a ceratitic suture shape. Shell coiling and suture line of Globacrochordiceras are closer to that of the youngest member of the family: Acrochordiceras carolinae (late middle Anisian). The latter is the end-member of a long-term morphological evolutionary trend of the family during the early and middle Anisian. This trend composed of classical increases in adult size (Cope's rule), shell involution and suture indentation, lasted ca. four Myr. The sudden morphological evolutionary jump between Globacrochordiceras and Paracrochordiceras at the Spathian/Anisian (Early/Middle Triassic) boundary may correspond to a generalized morphological reset of long-term trends, a process that differs from classic paedomorphic transformations. A dramatic global sea level change and carbon isotope positive excursion at the Early/Middle Triassic boundary both indicate stressful environmental changes that may have triggered this evolutionary jump. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Goudemand N.,University of Zürich | Orchard M.J.,Geological Survey of Canada | Bucher H.,University of Zürich | Jenks J.,1134 Johnson Ridge Lane
Geobios | Year: 2012

The First Appearance Datum (FAD) of the conodont Chiosella timorensis has been recently proposed as an index for the worldwide recognition of the Olenekian-Anisian Boundary (OAB, Early-Middle Triassic boundary). We here report the co-occurrence of C. timorensis with the ammonoids Neopopanoceras haugi (Hyatt and Smith), Keyserlingites pacificus (Hyatt and Smith), Subhungarites yatesi (Hyatt and Smith) and Pseudacrochordiceras inyoense (Smith), which are diagnostic of the late Spathian Haugi Zone. This shows that the previously published first occurrences of C. timorensis were still too poorly constrained, and it questions the adequacy of its FAD as a marker of the OAB. It challenges the significance of some observed lower stratigraphic occurrences of C. gondolelloides compared with C. timorensis. We revise the current criterion for the taxonomic separation of these two species and define a new Chiosella species (left in open nomenclature). The origin of Chiosella timorensis remains unknown but multi-element analyses suggest an affinity with the late Olenekian Neogondolella ex gr. regalis. Our reassessment of the material from the most important OAB sections (Desli Caira, Romania and Guandao, China) allows us to propose a new and more reliable biochronological scheme based on conodont maximal associations for the OAB. © 2011 Elsevier Masson SAS.


Hofmann R.,University of Zürich | Hautmann M.,University of Zürich | Brayard A.,French National Center for Scientific Research | Nutzel A.,GeoBio Center | And 5 more authors.
Palaeontology | Year: 2014

Based on the quantitative community analysis using species-level identifications, we track the restoration of benthic ecosystems after the end-Permian mass extinction throughout the Lower Triassic of the western USA. New data on the palaeoecology of the Thaynes Group and Sinbad Formation are provided, which fill a gap between the recently studied palaeoecology of the Griesbachian-Dienerian Dinwoody Formation and the Spathian Virgin Formation. In the Sinbad Formation and Thaynes Group, 17 species (12 genera) of bivalves, 7 species and genera of gastropods and 2 species and genera of brachiopods are recognized. The new bivalve genus Confusionella (Pteriidae) is described. A comprehensive review of the whole Lower Triassic succession of benthic ecosystems of the western USA indicates that mid- and inner shelf environments show incipient recovery signals around the Griesbachian-Dienerian transition, during the Smithian and, most profound, during the early Spathian. Ecological data from youngest strata of the Dinwoody Formation as well as stratigraphic ranges of species suggest that the late Dienerian was likely a time interval of environmental stress for benthic ecosystems. Despite some evidence for short-term environmental disturbances (e.g. shift of dominant taxa, transient drop in alpha-diversity) during the Smithian-Spathian transition, benthic ecosystems did not show any notable taxonomic turnover at that time, in contrast to the major crisis that affected ammonoids and conodonts. Whereas alpha-diversity of benthic communities generally increased throughout the Early Triassic, beta-diversity remained low, which reflects a persistently wide environmental range of benthic species. This observation is in accordance with a recently proposed model that predicts a time lag between increasing within-habitat diversity (alpha-diversity) and the onset of taxonomic differentiation between habitats (beta-diversity) during biotic recoveries from mass extinction events. The observation that beta-diversity had not significantly increased during the Early Triassic might also provide an explanation for the comparably sluggish increase in benthic diversity during that time, which has previously been attributed to persistent environmental stress. © The Palaeontological Association.


Romano C.,University of Zürich | Kogan I.,TU Bergakademie Freiberg | Jenks J.,1134 Johnson Ridge Lane | Jerjen I.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Brinkmann W.,University of Zürich
Bulletin of Geosciences | Year: 2012

A new marine fish assemblage from the late Smithian (Olenekian, Early Triassic) Anasibirites beds of the Thaynes Formation collected near Georgetown (Bear Lake County, south-east Idaho, USA) comprises actinopterygians (Saurichthys cf. elongatus, Actinopterygii indet.), sarcopterygians (Actinistia indet.), and possibly chondrichthyans. We review the global fossil record of the Triassic lower actinopterygian Saurichthys, which is used herein for a case study of trends in morphological adaptations as well as variations in palaeogeographic distribution and diversity dynamics of Early Mesozoic fishes. In the Early Triassic, Saurichthys already occupied a top position in marine food webs, with some species achieving body lengths of up to 1.5 m. Distribution of morphological characters in Saurichthys during the Triassic suggests trends towards a reduction in squamation, stiffening of the fins and axial skeleton, shortening of the postorbital portion of the cranium, and reduction in the number of dermal skull bones. The postcranial adaptations in particular helped to improve the fast-start ability of these ambush predatory fishes. The palaeogeographic range of Saurichthys changed from a virtually global distribution in the Early Triassic (indicating rapid dispersal within marine and freshwater ecosystems after the end-Permian mass extinction) to an occurrence mainly restricted to the north-western Tethys in the Late Triassic, and also towards increasing rarity within continental deposits. Modifications in the palaeogeographic distribution were accompanied by successive loss in global species richness and were possibly related to intra-Triassic extinction events, environmental alterations and/or competition.

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