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The Emu Bay Shale Konservat-Lagerstätte: a View of Cambrian Life from East Gondwanajohn R

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The Emu Bay Shale Konservat-Lagerstätte: a View of Cambrian Life from East Gondwanajohn R XXX10.1144/jgs2015-083J. R. Paterson et al.Emu Bay Shale Konservat-Lagerstätte 2016 Downloaded from http://jgs.lyellcollection.org/ by guest on September 24, 2021 2015-083review-articleReview focus10.1144/jgs2015-083The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East GondwanaJohn R. Paterson, Diego C. García-Bellido, James B. Jago, James G. Gehling, Michael S.Y. Lee &, Gregory D. Edgecombe Review focus Journal of the Geological Society Published online November 10, 2015 doi:10.1144/jgs2015-083 | Vol. 173 | 2016 | pp. 1–11 The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana John R. Paterson1*, Diego C. García-Bellido2, 3, James B. Jago4, James G. Gehling2, 3, Michael S.Y. Lee2, 3 & Gregory D. Edgecombe5 1 Palaeoscience Research Centre, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia 2 School of Biological Sciences & Environment Institute, University of Adelaide, Adelaide, SA 5005, Australia 3 Earth Sciences Section, South Australian Museum, North Terrace, Adelaide, SA 5000, Australia 4 School of Natural and Built Environments, University of South Australia, Mawson Lakes, SA 5095, Australia 5 Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK * Correspondence: [email protected] Abstract: Recent fossil discoveries from the lower Cambrian Emu Bay Shale (EBS) on Kangaroo Island, South Australia, have provided critical insights into the tempo of the Cambrian explosion of animals, such as the origin and seemingly rapid evolution of arthropod compound eyes, as well as extending the geographical ranges of several groups to the East Gondwa- nan margin, supporting close faunal affinities with South China. The EBS also holds great potential for broadening knowl- edge on taphonomic pathways involved in the exceptional preservation of fossils in Cambrian Konservat-Lagerstätten. EBS fossils display a range of taphonomic modes for a variety of soft tissues, especially phosphatization and pyritization, in some cases recording a level of anatomical detail that is absent from most Cambrian Konservat-Lagerstätten. Received 1 July 2015; revised 2 September 2015; accepted 16 September 2015 The lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) dailyi and Redlichia takooensis (Jell in Bengtson et al. 1990; Jago Konservat-Lagerstätte (Fig. 1) provides important information et al. 2006; Paterson & Brock 2007; Paterson et al. 2008). This regarding the composition of early animal communities and a win- equates to the Canglangpuan Stage (= upper Nangaoan–lower dow on the Cambrian radiation in Gondwana. One of the most Duyunian stages) of South China and the middle–upper Botoman intriguing aspects of the EBS is that although it yields a biota that of Siberia (Paterson & Brock 2007; Peng et al. 2012; Landing is taxonomically similar to Cambrian Burgess Shale-type biotas et al. 2013). Based on the calibrated 2012 Geologic Time Scale, (Paterson et al. 2008), its nearshore depositional setting (Gehling the numerical age of the EBS is 514 ± 1 Ma (see Peng et al. 2012, et al. 2011) and disparate preservation styles (e.g. Briggs & Nedin fig. 19.3). The EBS is approximately coeval with the Balang and 1997; Lee et al. 2011; Paterson et al. 2011) are at odds with our Guanshan biotas of China, but younger than the Chengjiang and current understanding of typical Burgess Shale-type deposits and Sirius Passet Lagerstätten (Peng et al. 2012). their associated taphonomic pathways and signatures (Gaines et al. The EBS is exposed in two areas of the northeastern coast of 2008, 2012b). This has led Gaines (2014) to explicitly exclude the Kangaroo Island: (1) the type section on the western side of Emu Bay EBS from the global list of more than 50 known Burgess Shale- (Daily et al. 1980); (2) Big Gully, to the east of Emu Bay (Fig. 1; type deposits, pending detailed comparative study. Gehling et al. 2011); it is only the latter site that hosts the Shelly fossils were first discovered in the EBS at Emu Bay Konservat-Lagerstätte. At Big Gully, the EBS unconformably in 1952 by Reginald Sprigg. In 1954, Brian Daily found large spec- overlies the Marsden Sandstone, a coarsening upward package of imens of the trilobite Redlichia in the EBS at Big Gully, east of Emu clastic sediments deposited in a shallow subtidal to shoreface set- Bay. However, the first description of soft-bodied EBS fossils was ting. The base of the EBS represents a sequence boundary and is not published until the late 1970s (Glaessner 1979). The history of marked by a conglomerate (up to 2 m thick) that contains various investigations on the EBS Konservat-Lagerstätte was documented clast types and sizes, including sandstone from the Marsden by Paterson et al. (2008) and Jago & Cooper (2011). Sandstone. Above the conglomerate, there is a sharp transition into mudstones that contain the Konservat-Lagerstätte, which is Age, geology and palaeoenvironmental setting restricted to the lower 10 m or so of the unit. Above this, sand- stones become increasingly prominent and, towards the top of the The Emu Bay Shale is a formation of the lower Cambrian (Series formation, contain large arthropod traces. The EBS is conformably 2) Kangaroo Island Group, a largely clastic shelf succession within overlain by the red–brown feldspathic sandstones of the subtidal the Stansbury Basin (Daily et al. 1980; Gehling et al. 2011; Jago Boxing Bay Formation, which also contain abundant arthropod et al. 2012). During deposition of the EBS and adjacent units, traces (Gehling et al. 2011). South Australia was located on the palaeoequator in the ‘tropical The interval of the EBS containing the Konservat-Lagerstätte carbonate development zone’ (Brock et al. 2000), and formed a consists of dark grey, typically laminated micaceous mudstone, part of the East Gondwana margin (Torsvik & Cocks 2013). The with common interbeds of siltstone (up to 5 cm thick) and fine sand- EBS correlates with the lower Cambrian (Series 2, Stage 4) stone (up to 20 cm thick) that probably resulted from intermittent Pararaia janeae trilobite Zone of mainland South Australia, based sediment gravity flows (Gehling et al. 2011). The mudstones show on the presence of the trilobites Estaingia bilobata, Balcoracania signs of small-scale fluidization, with the siltstones or sandstones © 2016 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://jgs.lyellcollection.org/ by guest on September 24, 2021 2 J. R. Paterson et al. (Gehling et al. 2011). This depositional setting is in stark contrast to the majority of other Cambrian Konservat-Lagerstätten, specifi- cally Burgess Shale-type deposits that formed in outer shelf envi- ronments, either near or immediately adjacent to the seaward margins of expansive carbonate platforms (e.g. Burgess Shale), or offshore of broad clastic shelves (e.g. Chengjiang) (Gaines 2014). The Emu Bay Shale biota: diversity and palaeobiogeographical affinities Of the 50+ species now known from the EBS, around 30% possess biomineralized structures, the remainder being entirely soft-bod- ied. However, in terms of the relative abundance of specimens, biomineralized taxa prevail because of the numerical dominance of the trilobite Estaingia bilobata (up to 80% of individuals on any given bedding surface). As in Cambrian Burgess Shale-type biotas (Caron & Jackson 2008; Caron et al. 2014; Zhao et al. 2014), species diversity and abundance in the EBS are dominated by panarthropods, which comprise 28 recorded species to date, with several yet to be described. The survey of the biota below is accordingly focused on arthropods, with taxonomic groups drawing on the classification of Legg et al. (2013). Other major groups represented include sponges, molluscs, brachiopods, cycloneuralian worms and a sin- Fig. 1. Geology of the area to the east of Emu Bay on the NE coast gle species of annelid. Some groups of debated affinity that are of Kangaroo Island, South Australia, showing the extent of the Emu known from other Cambrian Burgess Shale-type deposits are rep- Bay Shale at Big Gully, including the location of the main Konservat- resented by single species in the EBS, including chancelloriids, the Lagerstätte sites on the shoreline and at Buck Quarry (after Gehling probably deuterostome ‘cambroernids’ (incorporating the rotadis- et al. 2011). cids), and the vetulicolians (see Box 1; Fig. 2). occasionally loading into the underlying mudstones, resulting in Arthropods flame structures. The mudstones do not appear to be bioturbated Trilobites (especially where the soft-bodied fossils occur) and, in combination with the presence of sedimentary pyrite (McKirdy et al. 2011) and Five species have been identified in the EBS (Jell in Bengtson et al. 1990; Paterson & Jago 2006), two of which are abundant pyritized soft tissues (Paterson et al. 2011), indicate anoxia below (Estaingia bilobata and Redlichia takooensis: Fig. 3a) whereas the the sediment–water interface based on comparisons with Cambrian remaining three are very rare (Balcoracania dailyi, Holyoakia Burgess Shale-type deposits (Gabbott et al. 2004; Gaines & Droser simpsoni and Megapharanaspis nedini). The trilobites suggest 2005, 2010; Gaines et al. 2012a,b; Gaines 2014). Geochemical strong biogeographical connections with South China and studies also indicate anoxic conditions within the sediment
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