FIGURE 10 - uploaded by Kevin G Bylund
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Box plot comparison of H/D and U/D for Wordieoceras wordiei (Spath) vs. specimens from Arctic Canada, East Greenland and Siberia. Asterisks indicate values for holotypes of W. wordiei (blue) and W. decipiens (red).
Source publication
Abstract—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...
Citations
... The Otoceras concavum Zone and probably the lower part of the Otoceras boreale Zone were thus attributed to the Late Permian (Henderson and Baud, 1997). However, this age assignment is still debated (Shevyrev, 2006;Jenks et al., 2021). Baud and Beauchamp (2001) proposed a revised definition of the Griesbachian for Arctic Canada, which only includes the Ophiceras commune and Bukkenites strigatus Zones. ...
Ammonoids are key fossil indexes for Triassic biochronology, as all Triassic stages and substages were initially defined on ammonoid faunas. In recent decades, the temporal resolution of ammonoid biostratigraphical scales for the Early Triassic has been greatly improved. However, many uncertainties in zones correlation and superpositions remain, mainly due to sampling heterogeneities, preservation biases, and faunal endemicity. In this work, we present the first comprehensive Early Triassic ammonoid zonation from South Tibet, China, a previously poorly investigated region. Ammonoids were sampled from the Kangshare Formation at four sections (Selong, Paizi, Qubu and Xialong), representing a total of 140 species, ranging from the Griesbachian to the Smithian. These new robust data allow the construction of a high-resolution biostratigraphy using the Unitary Association (UA) method. A total of 22 Unitary Association zones (UAZs) were recognized, including two UAZs for the Griesbachian, nine for the Dienerian, and 11 for the Smithian. Then, we integrated data from neighboring basins, i.e., Spiti (India) and the Salt Range (Pakistan), and the new data from South Tibet to construct synthetic, laterally reproducible Dienerian-Smithian ammonoid UAZs, which include 12 UAZs for the Dienerian and 16 UAZs for the Smithian. Based on the newly obtained data and high-resolution biostratigraphic scales, we revised global correlations known for the ammonoid biostratigraphy in the Griesbachian, Dienerian and Smithian. Finally, the high-resolution ammonoid zones are generally in agreement with conodont zones in defining stage/substage boundaries. They also provide a robust and accurate time calibration for Early Triassic carbon isotope trends and temperature changes.
... These marine deposits generally correspond to the classical shale-limestone alternations of the Thaynes Group (sensu Lucas et al. 2007) representing relatively shallow water habitats. In northeastern Nevada, the Thaynes Group documents most of the Early Triassic, basal beds corresponding to the Griesbachian (lower Induan, Lower Triassic) and Dienerian (upper Induan, Lower Triassic) Dinwoody Formation (e.g., Jenks et al. 2021). The Montello Canyon locality is located ~10 km west to the small town of Montello. ...
Knowledge of the early evolution of post-Palaeozoic crinoids mainly relies on the well-preserved and abundant material
sampled in Triassic Konservat-Lagerstätten such as those from the Anisian Muschelkalk (Middle Triassic) of the
Germanic Basin. These crinoid-bearing Lagerstätten have been central to understanding the rapid evolution and diversification
of crinoids after the dramatic Permian/Triassic Boundary biological crisis that led the class to near-extinction.
The Encrinida are the emblematic crinoids of the Triassic. They are mainly known from rich fossil deposits where their
abundant ossicles are at the origin of the extensive crinoidal limestone beds of the German Upper Muschelkalk. So far,
they were first represented in the Middle Triassic by the family Dadocrinidae and genus Dadocrinus. In the present work,
a new species Dadocrinus montellonis sp. nov., is described based on a well-preserved, almost complete articulated specimen
from the Spathian (Lower Triassic) of Nevada (USA). The new species differs from other species of Dadocrinus by
its palaeobiogeographic position but also by its earlier stratigraphic occurrence and ancestral morphology. It represents
the first reported occurrence of Dadocrinus outside the Germanic Basin prior to the Middle Triassic and also the oldest
firm evidence of its presence in the Early Triassic (middle–late Spathian). This discovery sheds new light on the origin
of post-Palaeozoic crinoids. It suggests a much wider distribution than commonly assumed for the genus Dadocrinus
and implies that the first dadocrinids originated either in the Panthalassa or Tethys oceans, and then dispersed over long
distances in a relative short period of time.
... This means to come back to the Griesbachian Stage as primarily defined by Tozer (1965Tozer ( , 1967Tozer ( , 1994 in the Arctic Canada. The primarily defined Griesbachian is used as such by Dagys & Weitschat (1993), Dagys & Ermakova (1996), Zakharov et al. (2020), Bjerager et al. (2006) and Jenks et al. (2021) in the Induan chronostratigraphy from Verkhoyansk Basin (Siberia), East Greenland and western USA Basin. Another example of how the conodonts are preferentially used in redrawing the Triassic time scale, to the detriment of ammonoid biostratigraphy, particularly with regard to the Norian-Rhaetian stage boundary, is the case of the Sevatian Substage, traditionally the last substage of the Norian Stage (e.g., Zapfe, 1974;Krystyn, 1980Krystyn, , 1988Krystyn, , 1990Krystyn, , 1991Golebiowski, 1990). ...
The conodont Chiosella timorensis (Nogami, 1968) has for a long time been considered to be a suitable biotic proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. The recently acquired ammonoid record around that boundary clearly shows that the FAD of this conodont is located well below the boundary, i.e., in the late Spathian. In the present paper, it is underlined that the conodont Chiosella timorensis was promoted as a proxy for the nominated boundary in the early 1980s when the ammonoid record around the boundary was not yet well established. On the other side, until the mid 1990s the taxonomic definition and the lineage of the conodont Chiosella timorensis were not well stated, and even now there are still controversial interpretations of the taxonomic content of this conodont species. The new data achieved from the ammonoid/conodont record around the nominated boundary, especially in the western USA, and also in the Deşli Caira section in Romania, firmly demonstrate that the conodont Chiosella timorensis is a defunct proxy for the Olenekian-Anisian/Early-Middle Triassic boundary. As a consequence, the present data on the ammonoid-documented Olenekian-Anisian/Early-Middle Triassic boundary requires the recalibration of all physical events that have been tied to the FAD of the conodont Chiosella timorensis. The case of the Albanian Kçira-section, for which the chronostratigraphic interpretation of the ammonoid record is proved incorrect, definitely makes the conodont Chiosella timorensis a defunct proxy for the nominated boundary. Also, the case of the two Chinese sections recently proposed as being "exceptional" GSSP candidates for the Early-Middle Triassic boundary, which is based on an inconsistent ammonoid/conodont biochronology, fully strengthens this conclusion. The history of the controversial usage of the conodont species Chiosella timorensis in defining the Olenekian-Anisian boundary justifies a discussion about the usefulness of conodonts in the chronostratigraphic calibration of the standard Triassic timescale. One may conclude that the conodonts are not qualified, and have not a reasonable potential, to be used to define or to redefine the boundaries of chronostratigraphic units in the standard Triassic timescale, which have been basically defined on ammonoid biochronology.
