Original articleProposed GSSP for the base of Cambrian Stage 10 at the lowest occurrence of Eoconodontus notchpeakensis in the House Range, Utah, USAProposition de la première apparition de Eoconodontus notchpeakensis dans le House Range, Utah, États-Unis, comme Point Stratotypique Mondial de la base de l’Étage 10 du Cambrien
Introduction
The various subcommissions of the International Commission on Stratigraphy have finished subdividing and defining boundaries between Eras and Systems of the Geological Time Scale. Recently, these subcommissions have shifted their work to dividing the various Systems into international series and stages. The International Subcommission on Cambrian Stratigraphy has divided the Cambrian System into four series and ten stages. The lower two series each have two stages, and the upper two series each have three stages. Stage 10 will be the highest stage of the highest Cambrian Furongian Series.
Two horizons have been proposed for the base of Stage 10. The lower horizon is at the First Appearance Datum (FAD) of the agnostoid arthropod Lotagnostus americanus (Billings, 1860). Peng et al. (2014) proposed placing the Global Boundary Stratigraphic Section and Point (GSSP) in the Wa’ergang section in Hunan, South China. Lazarenko et al. (2011) proposed a GSSP at the same level in the Khos-Nelege section in northern Siberia, Russia. Miller et al. (2011) and Landing et al. (2011) proposed placing the GSSP at a somewhat higher stratigraphic level, at the FAD of the euconodont Eoconodontus notchpeakensis (Miller, 1969) in the House Range in western Utah, USA.
The HERB Event is a distinctive negative carbon-isotope excursion that has been identified in several continents (Ripperdan et al., 1992, Ripperdan and Miller, 1995, Jing et al., 2008, Kouchinsky et al., 2008, Sial et al., 2008). The base of the HERB Event is less than half a metre above the proposed GSSP, and the peak of the excursion is within the relatively thin E. notchpeakensis Subzone. The base of the HERB Event and the negative excursion peak would be useful for identifying and correlating a GSSP based on the conodont horizon. Miller et al., 2011, Miller et al., 2014 identified three sections in western Utah that might serve as a GSSP and presented data on trilobites, brachiopods, carbon-isotopes, and sequence stratigraphy that would further characterize the proposed conodont horizon and increase the potential for its correlation. Each of these correlation tools will be discussed in separate sections of this paper.
Section snippets
E. notchpeakensis horizon in Utah
Miller et al. (2003) presented detailed range charts for conodonts, trilobites, and brachiopods and also defined sequence-stratigraphic units in several sections in western Utah. That paper also included detailed descriptions of 17 measured sections that are distributed across an area that is approximately 110 km from south to north, from Lawson Cove in the northern Wah Wah Mountains to the northern Drum Mountains in the north (Fig. 1B). Seven of these 17 sections include strata in which the FAD
Stratigraphy and lithology
Miller et al. (2012a) discussed and illustrated Cambrian and Ordovician strata in western Utah, which were deposited on a rapidly subsiding, tropical, passive-margin carbonate platform. Cambrian strata in the House Range are ∼ 3870 m thick, of which ∼ 850 m is assigned to the upper Cambrian Furongian Series. Relevant strata are assigned to the Notch Peak Formation and the House Limestone and include the Hellnmaria, Red Tops, Lava Dam, and Barn Canyon Members (Fig. 3). The proposed base of Cambrian
General aspects of conodont faunas
Conodonts are usually common to abundant in strata that would comprise Stage 10. Some of the oldest known species of euconodonts occur in the Hellnmaria Member of the Notch Peak Formation and are part of the Proconodontus Evolutionary Lineage (Miller, 1980), which includes Proconodontus tenuiserratus Miller, 1980, P. posterocostatus Miller, 1980, P. muelleri Miller, 1969, E. notchpeakensis (Miller, 1969), species of Cambrooistodus Miller, 1980, and species of Cordylodus Pander, 1856. These taxa
Conodont biostratigraphy
The proposed Stage 10 would include nine conodont subzones distributed among four zones (Fig. 3). The zones and subzones are interval zones, and the bases of zones are at the FAD of a specific species in the evolving Proconodontus Lineage. If the base of Stage 10 were placed at the base of the Eoconodontus Zone, then the upper part of the Jiangshanian Stage would include the P. tenuiserratus, P. posterocostatus, and P. muelleri Zones. Faunas diagnostic of those zones occur in the upper part of
Distribution and utility of conodont faunas
Conodont species used to construct this zonal framework have global distribution, and consequently the zones and subzones are recognized globally and are used for detailed correlation. In some countries the classification of zones and subzones differs from what is illustrated in Fig. 3, but correlation is still possible because the same species are so widely distributed. Miller et al. (2014, fig. 2) shows the global distribution of conodonts that are diagnostic of the Eoconodontus Zone; 55
Trilobite faunas and biostratigraphy
Miller et al. (2011) reported that the base of the Eoconodontus conodont Zone lies within a part of the Saukia trilobite Zone that is characterized by rapid turnover of species in numerous upper Cambrian trilobite families, among them the Dikelocephalidae, Entomaspidae, Eurekiidae, Illaenuridae, Plethopeltidae, and Ptychaspididae. Study of collections recovered from sections in Utah and central Texas over the past two years confirms that species from more than fifteen trilobite genera are
Brachiopod faunas and biostratigraphy
Although calcitic-shelled brachiopods are quite rare in the Hellnmaria and Red Tops Members, the zonation of Freeman and Stitt (1996) can be applied to these strata (Fig. 3). The proposed stage boundary is near the base of the Finkelnburgia Zone as defined in Oklahoma (Freeman and Stitt, 1996), and this genus has been reported previously from western Utah (Miller et al., 2003, Miller et al., 2011). The base of the Nanorthis brachiopod Zone (Freeman and Stitt, 1996) is based on the appearance of
Carbon-isotope stratigraphy
Carbon-isotope stratigraphy is a method of correlation that is independent of other methods, but when it is used with conodont, trilobite, and brachiopod biostratigraphy, the combination produces a very powerful framework for global correlation. Strata of the Notch Peak Formation contain a good record of variation in carbon-isotopes preserved in marine carbonates. The most easily recognized feature of the carbon-isotope record is the HEllnmaria–Red Tops Boundary (HERB) Event, a prominent δ13C
Sequence stratigraphy
Miller et al. (2003) divided the Notch Peak Formation and the House Limestone into thirteen sequences, many of which were subdivided into smaller sequence units that were identified as packages (Fig. 3). Several of these sequences comprise predominantly high-energy strata that are interpreted as sea level lowstand deposits, which are named and marked by shading on Fig. 3; unshaded intervals are highstand deposits. The rates of subsidence and sediment deposition in western Utah were so rapid
Summary
The relationships among trilobite, conodont, and brachiopod zonal units and sequence-stratigraphic units established in Texas, Oklahoma, and Utah are shown in Fig. 3. These different correlation tools form a tightly integrated framework that has been used for decades to produce very detailed correlations among upper Cambrian strata in other areas, such as in the other states identified in Fig. 1A, and elsewhere in Laurentia. These correlation tools are also integrated with carbon-isotope
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
Acknowledgements
We thank John Cutler for field assistance in Utah over many years. Ben Dattilo and Peg Rees helped collect some of the trilobites whose ranges are shown on Fig. 8. Michelle Miller and Mario Daoust provided French translations of parts of this manuscript. Dong Xi-ping and an anonymous reviewer contributed many helpful comments that improved the final text. Miller acknowledges financial support from National Science Foundation grants EAR 8108621, EAR 8407281, and EAR 8804352, as well as several
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2022, Journal of Asian Earth SciencesCitation Excerpt :Another distinct chemostratigraphic shift, named HERB event, has been globally recognized close to the first occurrence of the Eoconodontus notchpeakensis conodont Zone. The HERB event, a high-amplitude, negative carbon-isotope excursion so far identified in Laurentia, Australia, China and Argentina, starts less than half a metre above the base of the E. notchpeakensis Subzone, and the highest-amplitude peak of the HERB event is near the middle of that relatively thin subzone (Miller et al., 2015). However, a precise position of this isotope excursion cannot be recognized in the study area with any degree of certainty, because the stratigraphic interval of the two lowermost conodont-based zones at the Mila-Kuh stratotype is highly condensed and comprises mainly fine siliciclastic rocks with a few limestone layers and nodules.
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2022, Global and Planetary ChangeCitation Excerpt :However, no matching high-amplitude negative δ13C excursion has been observed in the lower Acerocarina Superzone of the studied sections (Fig. 4). It is of course theoretically possible that local environmental changes may have concealed a younger δ13Corg excursion in Scandinavia, but we tentatively assume that the discussed excursions are synonymous, following Zhu et al. (2019, 2020), Terfelt et al. (2014), Miller et al. (2015), Li et al. (2017) and Ahlberg et al. (2018), as well as the latest edition of the Geologic Time Scale volume (Peng et al., 2020). In the Grönhögen-2015 core, the onset of the excursion labelled as TOCE by Ahlberg et al. (2018) appears to start earlier than in the Håslöv-1 core described by Terfelt et al. (2014).
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