Episodes 2019; 42(4): 321-332
Published online December 1, 2019
Copyright © International Union of Geological Sciences.
Lehrstuhl für Geodynamik und Geomaterialwissenschaft, Institut für Geographie und Geologie, Bayerische Julius-Maximilians-Universität, Würzburg, Germany; *Corresponding author, E-mail: email@example.com
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The International Subcommission on Cambrian Stratigraphy has introduced a number of internal subdivisions (i.e., series and stages), but most of the explanatory publications lack reliable data on the correlation between all Cambrian key continents. A comprehensive correlation chart is presented here to review and document correlatable biostratigraphic horizons within the system and correlation of biostratigraphic zones and regional series and stages, accompanied by explanatory remarks. The chart also presents important available non-biological correlation data, such as carbon isotope signatures and radiometric ages.
In 1999, the officers of
Geyer and Shergold (2000) reviewed and examined possibilities for Cambrian subdivisions on the basis of faunal horizons with potential for international correlation. The ISCS introduced a first global internal GSSP in 2003 for the base of the Furongian Series and Paibian Stage (Peng et al., 2004). It was followed by the GSSP for the base of the Drumian Stage (Babcock et al., 2007), the GSSP for the base of the Guzhangian Stage (Peng et al., 2006, 2009), the GSSP for the base of the Jiangshanian Stage (Peng et al., 2012), and the GSSP on the base of the Miaolingian Series and Wuliuan Stage (Zhao et al., 2018, 2019). The formal naming of the Terreneuvian Series and Fortunian Stage, defined by the GSSP for the Cambrian lower boundary, took place in 2007 (Landing et al., 2007).
The choice of GSSPs reflects the difficulties about the selection of globally recognizable biostratigraphic horizons, which in turn have to rely on the simplicity of interregional, intercontinental and global correlation. The long period between the introduction of the Jiangshanian in 2012 and the Miaolingian/Wuliuan in 2018 indicates the growing difficulties to arrive at a readily acceptable horizon. The reasons for these difficulties can be seen in real difficulties based on the presence/absence of biostratigraphically useful fossils; gaps/hiatuses in the successions; and simply a lack of data. In many cases, however, the difficulties result from differing taxonomic concepts; incomplete knowledge on the data of regions other than the specialties of the scientist’s particular working area; or even biased, nationalistic views that led to erroneous correlations.
In order to provide a sound base for future discussions on the stratigraphy of the Cambrian, a comprehensive correlation table is presented here for all key areas with Cambrian successions. The remarks on particular stratigraphic intervals and peculiarities on single Cambrian continents are kept here to a minimum if the key issues are already discussed in easily accessible publications.
The stratigraphical information in the columns include regional series (as far as available) and stages as well as the most reliable and usually latest established biostratigraphic subdivisions. Also included are radiometric age determinations and carbon isotope signatures that are regarded as significant. It should be noted that some of the radiometric ages refer to maximum ages (e.g., for the base of the Tommotian of the Siberian Platform) so that these apparently do not correlate precisely with ages from other regions in at the same levels.
The carbon isotope signatures are divided into significant positive (ochre stars) and negative (green stars) peaks. It is obvious that they do not plot to perfectly coeval events, which can be explained by different circumstances. Following the recognition of the SPICE (Steptoean Positive Carbon Isotope Excursion) event by Saltzman et al. (1998, 2000) and the HERB (HEllnmaria–Red Tops Boundary) event by Ripperdan (2002), a discrete scheme of carbon isotope signatures throughout has been suggested by Zhu et al. (2006), including the BACE (BAsal Cambrian carbon isotope Excursion), ZHUCE (ZHUjiaqing Carbon isotope Excursion), SHICE (SHIyantou Carbon isotope Excursion), CARE (Cambrian Arthropod Radiation isotope Excursion), MICE (MIngxinsi Carbon Isotope Excursion), AECE (Archaeocyathid Extinction Carbon isotope Excursion), ROECE (Redlichiid-Olenellid Extinction Carbon isotope Excursion), DICE (DrumIan Carbon isotope Excursion), and TOCE (Top of Cambrian Excursion). However, it appears to be the case that some of these peaks are not globally recognizable. Some, such as the HERB and TOCE signatures were subject to confusion. Both are now generally regarded as the representing same fluctuation in ocean chemistry (N3 peak of Li et al., 2017, for South China). In addition, additional excursions can be recognized. Here, it is suggested that the positive peak determinable in the
The Fortunian (Landing et al., 2007) is commonly regarded as a stage generally with a fossil content characterized largely by trace fossils. A common misunderstanding exists in the assumption that the complex trace
The choice of ichnofossils as indicators for the base of the Cambrian resulted from the insight that “Small Shelly Fossils (favoured as stratigraphical indicators in pre-trilobitic Cambrian strata until the late 1980s) were unsuitable for detailed biostratigraphic zonations and precise intercontinental correlation. They were assumed to be predated by ichnofossils as the relics of non-skeletonised earliest Cambrian bilaterian assemblages. Meanwhile it was shown that some of the earliest known skeletal elements at the dawn of bilaterians with mineralised sclerites occur in the established terminal Ediacaran–Fortunian boundary interval. Such taxa include
The development of ichnofossil assemblages as a reflection of evolutionary progress is subject of a number of articles. However, in most cases the age assignments are vague or based on co-occurring Small Shelly Fossils. Whether unmistakable arthropod traces of such ichnogenera as
Small Shelly Fossils or Early Skeletal Fossils from pre-trilobitic Cambrian strata have been extensively studied during the 1970s, 1980s and 1990s in numerous regions. However, little agreement has been reached during that period about the possibilities of intercontinental correlation by means of such bilaterian skeletal elements. During the last two decades, a mild revival in the study such faunas, particularly mollusks, tommotiids and brachiopods, has featured some biostratigraphic potential, although limitations by facies and taxonomic problems due to oversplitting obscure the true ranges of many of the potential biostratigraphic indicators.
Although most SSFs are of provincial distribution, some taxa, such as
The FADs of
Acritarchs have been regarded as biostratigraphically useful fossils in this stratigraphic as well, but the occurrences of the mostly cited
The onset of trilobites in earth history as the principle faunal elements and biostratigraphic indicators in the Cambrian is understood as an important step in biotic development. However, correlation of the oldest trilobite assemblages is proven to be extremely difficult because of (1) a distinct diachronism of the earliest appearance of trilobites in different regions, and (2) a yet unexplained pronounced provincialism that makes almost every earliest trilobite assemblage fairly unique. A few genera exist which have been suggested to have some intercontinental distribution, but they are so limited in their local stratigraphic ranges that their true biozones are poorly recognized (Palmer, 1998) or their generic assignment requires careful reexamination.
The oldest/lowest trilobites appear in many regions in strata that overlie unconformities. Most of these trilobite assemblages are found in facies that suggest shallow marine to nearshore deposition, and those biofacies are again characterized by endemic polymerid trilobites. Other fossils associated with these assemblages, such as archaeocyaths, molluscs, hyoliths, hyolithelminths, and other small shelly fossils, also have limited occurrences or show strong limitations to certain biofacies types, and thus have limited potential for intercontinental correlation.
These facts suggest that a series boundary at the first occurrence of trilobites will be inappropriate because it generally lacks the possibility of global biostratigraphic identification and correlation. Chemostratigraphic investigations revealed a carbon isotope excursion that occurred shortly after the FAD of trilobites (e.g., Brasier, 1993; Brasier et al., 1992, 1994), with a pronounced peak in the
Unfortunately, the FADs of trilobites in various regions are still erroneously interpreted in a number of cases. Prominent examples are the oldest trilobites in South China, which were once regarded as the oldest on earth (e.g., Luo, 1981; Zhang, 1987), but in fact are quite late arrivals. Yet, it appears that their true stratigraphic position is still not generally accepted. In addition, the correlation of the oldest/lowest
In general, correlation of Stage 3 from South China and Australia is often hampered by an incomplete understanding of the biostratigraphy of key areas such as West Gondwana and western Avalonia and disputable interpretations such as in Maloof et al. (2005, 2010) (e.g. Betts et al., 2018; Paterson et al., 2019).
The late early Cambrian (in the revised concept after the introduction of the Miaolingian Series and Wuliuan Stage) includes, or at least should include, strata that are traditionally assigned to the
This high position of the base of the Miaolingian and Wuliuan contributed to a skewed picture of Stage 4 when it comes to the situation in South China and Australia. A relatively high number of biozones have been recognized in the successions in South China (Fig. 1; see also Yuan et al., 2002), most of them correlating with strata that were traditionally regarded as Middle Cambrian in the European regions, and these zones obviously reflect a high frequency of modifications in the faunal assemblages. Nevertheless, it is almost certain that these zones cover only a relatively short period of time. Several of these zones correlate only with one or two zones recognized on the Siberian Platform, Morocco or southeastern Newfoundland. Nonetheless, recent developments show that levels within these “young zones were considered occasionally as suitable for designating a GSSP for the base of Stage 4 (e.g., Zhu et al., 2018). Particularly intriguing is that even the nomenclature of species characteristic of this interval is incompletely understood.
Correlation chart for the Cambrian biostratigraphic units of important regions/palaeocontinents with presently acknowledged regional series and stages as well as biostratigraphical units (slightly modified by the author in some cases). Colours indicate defined or suggested stages. Positions of correlation based on the FAD of accepted levels (discussed in the text) flagged at the right-hand margin; abbreviations: Wc, Watsonella crosbyi; FT, first occurrence of trilobites; HCST, Hebediscus attleborensis–Calodiscus lobatus–Serrodiscus–Triangulaspis band; Og, Ovatoryctocara granulata; Oi, Oryctocephalus indicus; Pg, Ptychagnostus gibbus; Pa, Ptychagnostus atavus; Pp, Ptychagnostus punctuosus; Ll, Lejopyge laevigata; Gs, Glyptagnostus stolidotus; Gr, Glyptagnostus reticulatus; IA, Irvingella in association with Agnostotes; En, Eoconodontus notchpeakensis; Cp, Cordylodus proavus. Significant positive carbon isotope peaks indicates by ochre stars, negative peaks by green stars. Radiometric age determinations from numerous authors (e.g., Bowring et al., 1993 (d); Landing et al., 1998 (a), 2015 (c), submitted (f); Zhu et al., 2009 (k); Wei et al., 2018 (m); Compston et al., 2008 (g); Harvey et al., 2011 (b); partly recalculated by Schmitz, 2012 (e); Nagovotsin et al., 2015 (h); Rogov et al., 2015 (i); Perkins and Walshe, 1993 (n); Karlstrom et al., under review (o); Isachsen et al., 1994 (p). Remarks on the columns: A number of stage names are used to date in a wrongly derived spelling. These orthographic mistakes are corrected (e.g., Botoman/Botomian; Delamarian/Delamaran; Dyerian/Dyeran; Marjumian/Marjuman; Topazian/Topazan). Baltica: The column for Baltica is dominated by the zones used in Sweden/Scandinavia, with an updated zonation for the Furongian as suggested by Terfelt et al. (2008). The early Cambrian stages are modified from Nielsen and Schovsbo (2011) using biostratigraphic results from Cederström et al. (accepted). Sibiria: “Sibiria is used as a name for the Palaeozoic continent, differing from “Siberia as the name for the modern-day geographic region. The chronostratigraphic units used in the column for the Siberian Platform is recombined from the established units (e.g., Lazarenko et al., 2011) and the revision suggested by Varlamov et al. (2013), which is not yet officially ratified. “Altay-Sayan” refers to the foldbelt region. The names for the subdivisions refer to the traditional “horizons” (горизон) which are not stages or any kind of chronostratigraphic units. The used units are from Korzhnev (2012) and Naimark and Pegel’ (2017). The transcription of the names is revised. North China: Abandoned traditional series and stages which were originally transferred from South China are shown in grey for better orientation. South China: Decisions on GSSPs prompted renaming and (partly) redefinitions on regional series and stages (Peng, 2009; National Commission Stratigraphy of China, 2014; Peng, 2018; Peng and Zhao, 2018), with revision of the established scheme. Due to better orientation and creation of homonyms the earlier scheme in shown in grey. Different biozones for the Fortunian through Drumian refer to differences between the platform and slope facies. The Parabadiella huoi Zone is spelled Abadiella huoi Zone in the modern schemes based on the erroneous assumption that Parabadiella is a junior synonym of Abadiella (see discussion in Geyer, in press). Laurentia: The column shows the traditional position of the lower boundary of the Ibexian Series and Skullrockian Stage. See also Babcock et al. (2011) for suggested internationalization of the Laurentian stratigraphy. Base of the Marjumian Stage indicated in the original definition (see Sundberg 2005), not as revised by Palmer (1998). Different biostratigraphic zonation used for the lower–middle Cambrian boundary interval reflect regional units.
The correlation of this upper part of Stage 4 has been subject of a thorough study by Sundberg et al. (2016). However, some of its data have been widely ignored to date and have not been taken into serious consideration for the Miaolingian/Wuliuan boundary proposals and decision (e.g., Zhao et al., 2018, 2019). A recent study on the upper part of the traditional lower Cambrian in Scandinavia and Baltica in general (Cederström et al., accepted) suggests a revision of the biostratigraphic concept as well as a revision of the correlation into other regions. The data of both articles are incorporated in the present correlation chart.
A boundary at the FAD level of
After two decades of discussions on the lower–middle Cambrian boundary, the ISCS introduced the Miaolingian Series and Wuliuan Stage (Zhao et al., 2018, 2019), defined by a GSSP in the Guizhou Province, South China, and based on the FAD of
A level that would have been much more appropriate for a global boundary has been discussed as an alternative GSSP candidate. It is characterized by the FAD of
The base of the
A second index fossil that allows a subglobal correlation within the Drumian is
The base of the
The index fossil of the base of the traditional Upper Cambrian is
The Paibian Stage and Furongian Series starts with the FAD of
A chemostratigraphic correlation is provided by the subglobally recognized SPICE positive δ13C excursion (e.g., Saltzman et al., 2000; Kouchinsky et al., 2008; Ahlberg et al., 2009; Ng et al., 2013; Schmid et al., 2018; Pruss et al., 2019).
The co-occurrence of the early species of the trilobites genus
Zemlya, Sweden, the UK, Canada, and the USA, Argentina, and possibly Antarctica. In Laurentia it ranges across the Steptoean–Sunwaptan Stage boundary; in Australia it defines the lower boundary of the Iverian Stage.
The Jiangshanian belongs to one of the most finely subdivided intervals in earth history. A large number of trilobite zones are established in regions such as Australia, South China, the Maly Karatau range in Kazakhstan or Scandinavia. However, most of them are regional schemes in which variations highly diverse assemblages contributes to an apparent rapid turnover that should not be confused with evolutionary changes.
Two alternative solutions have been suggested for the base of Cambrian Stage 10. A proposal for a GSSP of the base of the stage is based on the FAD of agnostoid
The FAD of
The suggested stage can also be bracketed by the HERB event, a high-amplitude negative carbon-isotope excursion that coincides with the
Global chronocorrelation within the Cambrian has made significant progress during the last three decades, leading to a mostly well accepted subdivision of the period into epochs and ages. Pending GSSPs for the remaining informal Series 2 and Stages 2, 3, 4, and 10 have a fair potential for global recognition. However, a major goal of the Cambrian community will be the recognition of regional markers that allow a fine-scale correlation between all major Cambrian continents. Fossil assemblages and physical markers that allow a reliable correlation need to be recognised in continents other than the wellstudied continents South China, Sibiria, Baltica, and Laurentia. It appears to be helpful if such correlation levels would be formally recognized and noted in correlation charts such as the one presented herein (Figure 1) and possible coded appropriately.
This article was made possible by research grant GE 547/22-1 of the Deutsche Forschungsgemeinschaft (DFG). An earlier version of the chart was circulated in 1999 among members of the