0000000000675646
AUTHOR
James F. Jenks
showing 17 related works from this author
A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, U…
2016
17 pages; International audience; n the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present p…
Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA).
2014
AbstractIn 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 lo…
Globacrochordiceras gen. nov. (Acrochordiceratidae, late Early Triassic) and its significance for stress-induced evolutionary jumps in ammonoid linea…
2013
<i>Globacrochordiceras transpacificum</i> 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 <i>Neopopanoceras haugi</i> Zone of late Spathian age (Early Triassic). The plicate r…
Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)
2015
40 pages; International audience; The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica-tion, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial …
Guodunites, a low-palaeolatitude and trans-panthalassic Smithian (Early Triassic) ammonoid genus
2009
11 pages; International audience; Based on new, bed-rock controlled material from Oman and Utah, USA, the Early Triassic genus Guodunites, which was recently erected on the basis of scarce specimens from northwestern Guangxi, South China, is now shown to be a representative of Proptychitidae. This solves the question of the previously unknown phylogenetic affinity of this genus. The genus is restricted to the late middle Smithian, and to date, its biogeographical distribution comprises Oman, South China and Utah, thus indicating an essentially low palaeolatitudinal distribution during the Early Triassic. Its palaeobiogeographical distribution further strengthens the existence of significant…
Transient metazoan reefs in the aftermath of the end-Permian mass extinction
2011
5 pages; International audience; 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 f…
Revision of the genus Anasibirites Mojsisovics (Ammonoidea): An iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction
2016
34 pages; International audience; The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end-Permian crisis, the nu…
Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): implications for the Smithian equatorial vertebrate eclipse
2017
AbstractThe Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygianBirgeria(Birgeriidae), attributed toB.americananew species andBirgeriasp.Birgeria americanan. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.7…
Biogeography of Triassic ammonoids
2015
After the end-Permian mass extinction, ammonoids experienced an explosive recovery followed by episodes of radiation and extinction. These events were associated with sudden biogeographic changes often closely related to major climatic and oceanographic changes. Previous biogeographic studies of Triassic ammonoids have rarely focused on a specific time-interval and were rarely based on quantitative methods. Thus, we will first review biogeographical methods and the biogeographical signals known from Triassic ammonoids. Secondly, we will focus on quantitative approaches that improve our knowledge of ammonoid biogeographical structuring and dynamics during the Triassic, and we will discuss co…
Biostratigraphy of Triassic Ammonoids
2015
The Triassic is a turning point in the evolutionary history of ammonoids, characterized by the flourishing Ceratitida and the appearance of the first heteromorphs. Following the end-Permian mass extinction, ammonoids were among the first groups to rediversify by producing many new taxa. Already in the late nineteenth century, the still currently recognized Triassic stages and substages were introduced. The historical development of Triassic ammonoid biostratigraphy is a good example of worldwide cooperation between many geographically-diverse research groups, which initially began in Germany and the European Alps. This cooperation was then extended to North America, Transcaucasia, North Ind…
Gastropod evidence against the Early Triassic Lilliput effect
2010
4 pages; International audience; 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-Trias…
Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery
2015
This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey (south-central Utah, USA). The studied Smithian deposits record a large-scale third-order sea-level cycle, which permits a detailed reconstruction of the evolution of depositional settings. During the middle Smithian, peritidal microbial limestones associated with a rather low-diversity benthic fauna were deposited seaward of the tidal flat siliciclastic red beds. Associated with siliceous sponges, microbial limestones formed small m-scale patch reefs. During the late middle to late Smithian interval, the sedimentary system is characterized by tidal flat dolostones of an interior platform, ooid-bioclast…
Late Griesbachian (early Triassic) ammonoids and nautiloids from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada.
2021
International audience; We document a relatively small but very important late Griesbachian ammonoid and nautiloid assemblage from the Dinwoody Formation at Crittenden Springs, Elko County, Nevada. This discovery represents the first significant report of late Griesbachian ammonoids in the low-paleolatitudes of eastern Panthalassa, and it also signifies the first report of Wordieoceras wordiei and two co-occurring taxa outside of the Boreal Realm. This similarity in ammonoid faunas, irrespective of paleolatitude, provides support for the concept of weak latitudinal diversity gradients following the end-Permian extinction. The finding is even more noteworthy given the Dinwoody Formation’s re…
Lithospheric strenght control over depositional environments and foreland accommodation in the Western USA Basin during the Early Triassic
2015
International audience
New Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: implications for taxonomy, biostratigraphy and biogeography.
2010
41 pages; International audience
Facies and depositional settings during the Smithin in the Torrey area (Early Triassic, Utah, USA)
2014
International audience; The Permian-Triassic transition records the most devastating biotic crisis of the Phanerozoic with 90% of the marine genera being eradicated. The aftermath of this extinction is usually portrayed by large environmental perturbations such as ocean acidification, anoxia, euxinia and fluctuating productivity. However, these fluctuating conditions and their impact on the nature and tempo of the biotic recovery are still under debate. Thus, it is important to decipher the nature of the depositional settings and their putative spatio-temporal variations in order to improve our knowledge of post-crisis environments. The present work focuses on well-exposed Lower Triassic se…
Data from: Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinc…
2016
The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end-Permian crisis, the number of valid species that should …