Elsevier

Annales de Paléontologie

Volume 101, Issue 3, July–September 2015, Pages 199-211
Annales de Paléontologie

Original article
Proposed 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

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Abstract

The lowest occurrence of the conodont Eoconodontus notchpeakensis (Miller, 1969) has been proposed as the base of Cambrian Stage 10. The horizon is recognized in three sections in the House Range, western Utah, USA in the lower part of the Red Tops Member of the Notch Peak Formation. This horizon fits within a tightly integrated framework that includes conodont, trilobite, and brachiopod biozonations, as well as carbon-isotope stratigraphy and sequence stratigraphy. The proposed horizon is the base of the Eoconodontus conodont Zone. This horizon is in the lower part of the Saukiella junia Subzone of the Saukia trilobite Zone and is near the top of the Billingsella brachiopod Zone. The HERB Event is a high-amplitude, negative carbon-isotope excursion that has been identified in Laurentia, Australia, China, and Argentina. The start of the excursion is at a negative carbon-isotope peak that is 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. The HERB Event has been identified in strata with minimal faunal data, providing the possibility of identifying the base of Stage 10 in nearly unfossiliferous strata. The Notch Peak Formation has been divided into a detailed sequence-stratigraphic framework within a lithostratigraphic context, and some of the sequence boundaries have been identified in Australia and China. Conodonts diagnostic of the Eoconodontus Zone have been identified at 54 localities around the world, including in a succession of Cambrian deep-ocean radiolarian cherts. The Utah conodont zonation has been identified across Laurentia and in other parts of the world in facies ranging from continental slope to nearshore sandstone deposits. The variety of correlation tools and the integration of diverse data produce a superior framework for correlation of the proposed base of Stage 10 and for correlation of many horizons within Stage 10.

Résumé

La première apparition du conodonte Eoconodontus notchpeakensis (Miller, 1969) a été proposée comme base de l’Étage 10 du Cambrien. Cet horizon est reconnu dans trois sections du House Range, dans l’ouest de l’Utah, aux États-Unis, dans la partie inférieure du Membre Red Tops de la Formation du Notch Peak. Cet horizon est intégré avec précision dans un cadre qui comprend des biozonations à conodontes, trilobites, et brachiopodes, ainsi que de la stratigraphie isotopique du carbone. L’horizon proposé est la base de la sous-zone à Eoconodontus notchpeakensis de la zone à conodontes Eoconodontus. Cet horizon se trouve dans la partie inférieure de la sous-zone à Saukiella junia de la zone à trilobites Saukia, et se situe près de la limite supérieure de la zone à brachiopodes Billingsella. L’événement HERB est une excursion négative des isotopes du carbone de grande amplitude qui a été identifiée en Laurentia, en Australie, en Chine, et en Argentine. La base de l’excursion correspond à un pic négatif des isotopes du carbone qui se situe moins d’un demi-mètre au-dessus de la base de la sous-zone à E. notchpeakensis, et le pic d’amplitude maximale de l’événement HERB est enregistré au milieu de cette sous-zone relativement peu épaisse. L’événement HERB a été identifié dans des strates pauvres en faune, ce qui offre la possibilité d’identifier la base de l’Étage 10 dans des strates quasi non fossilifères. La Formation du Notch Peak a été divisée selon un cadre stratigraphique séquentiel détaillé dont certaines limites de séquence sont identifiées en Australie et en Chine. Des conodontes indicatifs de la Zone à Eoconodontus ont été identifiés dans 54 localités du monde entier, y compris dans une série de cherts à radiolarite cambriens déposés en domaine océanique profond. La zonation à conodontes de l’Utah a été identifiée à travers le Laurentia ainsi que dans d’autres parties du monde dans des faciès variés, allant des dépôts de talus continental à des grès de plateforme interne. La variété d’outils de corrélation et l’intégration de données diverses fournissent un cadre de corrélation remarquable de la base proposée de l’Étage 10 ainsi que de plusieurs horizons de l’Étage 10.

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, Pposterocostatus Miller, 1980, Pmuelleri Miller, 1969, Enotchpeakensis (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 Ptenuiserratus, Pposterocostatus, and Pmuelleri 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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