Emu Bay Shale

Emu Bay Shale
Stratigraphic range: Cambrian Series 2 (Cambrian Stage 4) ~514–512 Ma
North Coast of Kangaroo Island, Emu Bay
TypeGeological formation
Unit ofKangaroo Island Group
UnderliesBoxing Bay Formation
OverliesMarsden Sandstone (unconformity)
Thickness78 m (256 ft), of which the lowest 10 m are fossiliferous
Lithology
PrimaryShale
OtherSandstone
Location
Coordinates35°35′S 137°30′E / 35.583°S 137.500°E / -35.583; 137.500
RegionThe north coast of Kangaroo Island, around Emu Bay and Cape D'Estaing, South Australia
CountryAustralia
Type section
Named forEmu Bay
Emu Bay Shale is located in Australia
Emu Bay Shale
Emu Bay Shale (Australia)
Emu Bay Shale is located in South Australia
Emu Bay Shale
Emu Bay Shale (South Australia)

The Emu Bay Shale (EBS) is a geological formation in Emu Bay, South Australia, noted for its exceptional preservation of soft-bodied fossils, and is Australia's only known Cambrian Konservat-Lagerstätte. The Emu Bay Shale is dated to early Cambrian Stage 4, approximately ~514 to 512 Ma (Pararaia janeae zone) and correlated with the upper Botomian Stage of the Lower Cambrian. The EBS has a thickness of 78 metres (256 ft). The formation underlies the Boxing Bay Formation, and overlies the Marsden Sandstone.

More than 50 species of invertebrates including redlichiidans, non-biomineralized arthropods (including megacheirans, nektaspids, and hymenocarines), radiodonts, palaeoscolecids, a lobopodian, a polychaete, vetulicolians, nectocaridids, hyoliths, brachiopods, sponges, chancelloriids, several problematica and a chelicerate are known from the Emu Bay Shale.

Age & Geology

The lower Cambrian (Series 2) Emu Bay Shale is a formation of the Kangaroo Island Group, a stratigraphic group which is limited in range to the north coast of Kangaroo Island. When the sediments of the EBS and adjacent strata were laid, the landmass that is now South Australia was located on the palaeoequator in what has been referred to as the 'tropical carbonate development zone', and was a constituent piece along the margin of East Gondwana. The EBS has been biocorrelated to the lower Cambrian (Stage 4 of Series 2) Pararaia janeae trilobite Zone of the mainland, based on the occurrence of the trilobites Balcoracania dailyi, Estaingia bilobata and Redlichia takooensis. This is equivalent to both the middle–upper Botoman of Siberia, and to the Canglangpuan Stage of South China. According to the 2012 Geologic Time Scale, the age of the EBS is about 514 ± 1 million years ago, and is temporally contemporaneous with the Balang and Guanshan biotas of China, but younger than the Chengjiang and Sirius Passet Lagerstätten. A later 2023 study suggested that the Emu Bay Shale dated to around 512 million years ago instead, based on a correlation to a radiometric date of 511.87 ± 0.14 Ma in the contemporaneous Billy Creek Formation.

Palaeoenvironment

In a geological sense, Kangaroo Island is the southwesterly continuation of the Mt. Lofty Ranges. Along with the Flinders Ranges and Olary Arc, these are only a fraction of the Early Palaeozoic mountain folt belt known as the Delamerides.The mountain building associated with the Delamerides was resumed in the late Cenozoic, forming the current ranges of eastern South Australia. The Kangaroo Island Group, to which the EBS is a unit of, is only present in the northeastern coast of the island, and is thought to represent deposition near the modern northern boundary of an ancient rift basin, possessing in its margin alluvial fans. Rifting recorded in the strata is associated with the occurrence of deformation, which is linked to the Delamerian Orogeny, as well as wider deformation across most of the western margin of Antarctica and Australia. Thus, the deposits are considered to represent the prodelta of a fan delta located within a rift basin.

Although the EBS hosts a biota which is similar too those of other Cambrian Burgess Shale-type faunas, the aforementioned depositional setting and preservation style differs from the modern understanding of regular Burgess Shale-type and their typical taphonomy. This has even lead to Robert R. Gaines excluding the EBS from the global list of over 50 Burgess Shale-type deposits, awaiting further study.

Notable discoveries

In the EBS, phosphatized organic material of Isoxys and Myoscolex, and fossilized eyes have been documented, with a higher quality of preservation than other non-biomineralized eyes that are found in the Burgess Shale and Chengjiang strata. These eyes range from having more than 3,000 to at least 16,000 ommatidial lenses, the latter of which have been assigned to Anomalocaris.

In 2011, paired compound eyes 2–3 centimetres (0.79–1.18 in) long were described from the Emu Bay Shale and assigned to Anomalocaris. Some of these eyes preserve at least 16,000 hexagonally arranged lenses, comparable to the most acute compound eyes of living arthropods.

Paleobiota

The Emu Bay Shale yields a rich assemblage of fauna, including Estaingia, Redlichia, two species of the nektaspid arthropod family Emucarididae, Emucaris fava and Kangacaris zhangi, the scleritome-bearing Chancelloria, Anomalocaris, Echidnacaris, Isoxys, Tuzoia, Oestokerkus, a genus of leanchoiliid closely related to the well-known Leanchoilia, the early chelicerate Wisangocaris and the artiopodan arthropod Australimicola. An armoured lobopodian of the Family Luolishaniidae is known from a single specimen that closely resembles the species Collinsovermis monstruosus from the Burgess Shale. Also known are the palaeoscolecid worm Wronascolex, the problematic Myoscolex, "petalloids", Vetustovermis, and a number of rarer elements. The EBS trilobites rarely preserve any trace of non-biomineralized tissue; a small number of specimens of Redlichia have been reported with antennae.

Non-artiopod arthropods

Non-artiopod arthropods of the Emu Bay Shale
Genus Species Notes Images
Anomalocaris A. daleyae Radiodonta,

Anomalocarididae
Frontal appendage of A. daleyae.
Echidnacaris E. briggsi Radiodonta,

Tamisiocarididae
Echidnacris reconstruction.
Echidnacaris reconstruction.
Isoxys I. communis Isoxyida,

Isoxyidae
Life restoration of the related Isoxys curvirostratus.
I. glaessneri
Oestokerkus O. megacholix Leanchoilida,

Leanchoiliidae
O. megacholix reconstruction.
Parapaleomerus ?P. sp.
Tanglangia T. rangatanga Megacheira,

incertae sedis
A reconstruction of the closely related T. longicaudata.
Tuzoia T. australis Hymenocarina,

Tuzoiidae
Restoration of the related species T. burgessensis.
T. sp.
Wisangocaris W. barbarahardyae Habeliida,

Sanctacarididae
Wisangocaris life restoration.
Canadaspidida indet. sp. indet. Hymenocarina,

incertae sedis

Artiopods

Artiopods of the Emu Bay Shale
Genus Species Notes Images
Australimicola A. spriggi Protosutura incertae sedis
Reconstruction of Australimicola.
Balcoracania B. dailyi Redlichiida,

Emuellidae
B. dailyi fossil.
Emucaris E. fava Nektaspida,

Emucarididae
Emuella E. polymera Redlichiida,

Emuellidae
E. polymera fossil.
Eozetetes E. gemmelli Vicissicaudata incertae sedis
Estaingia E. bilobata Ptychopariida,

Estaingiidae
E. bilobata fossil.
Holyoakia H. simpsoni Corynexochida,

Dorypygidae
H. simpsoni fossil.
Kangacaris K. zhangi Nektaspida,

Emucarididae
Kangacaris (left) and Emucaris (right)
Megapharanaspis M. nedini Redlichiida,

Megapharanaspidae
Squamacula S. buckorum incertae sedis
A drawing of the closely related S. clypeata.
Redlichia R. takooensis Redlichiida,

Redlichiidae
R. takooensis fossil
R. rex
Xandarellida indet. sp. indet. Xandarellida,

incertae sedis

Non-arthropods

Non-arthropods of the Emu Bay Shale
Genus Species Notes Images
Chancelloria C. australilonga Chancelloriida,

Chancelloriidae
Myoscolex M. ateles Animalia,

incertae sedis
M. ateles fossil.
Nesonektris N. aldridgei Vetulicolida,

incertae sedis
N. aldridgei reconstruction.
Vetustovermis V. planus Chaetognatha,

Nectocarididae
Life restoration of Nectocaris, of which Vetustovermis has been suggested to be a synonym.
Wronascolex W. antiquus

(Formerly Palaeoscolex antiquus)

 Palaeoscolecidae,

incertae sedis
W. iacoborum
Brachiopoda indet. spp. indet. Brachiopoda,

incertae sedis
Choiidae indet. sp. indet. Protomonaxonida,

Choiidae
Demospongiae indet. spp. indet. Demospongiae,

incertae sedis
Hamptoniidae indet. sp.indet. Porifera,

Hamptoniidae
Hyolitha indet. spp. indet. Hyolitha,

incertae sedis
Leptomitidae indet. sp. indet. Porifera,

Leptomitidae
Luolishaniidae indet. sp. indet. Lobopodia,

Luolishaniidae
Life restoration of Collinsovermis, which closely resembles the Emu Bay Shale luolishaniid
"Petalloid" indet. sp. indet. incertae sedis
Polychaeta indet. sp. indet. Polychaeta,

?Burgessochaetidae
Priapulida indet. sp. indet. Priapulida,

incertae sedis
Rotadiscidae indet. sp. indet. Rotadiscidae

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Paterson, John R.; García-Bellido, Diego C.; Jago, James B.; Gehling, James G.; Lee, Michael S.Y.; Edgecombe, Gregory D. (January 2016). "The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana". Journal of the Geological Society. 173 (1): 1–11. Bibcode:2016JGSoc.173....1P. doi:10.1144/jgs2015-083. ISSN 0016-7649. S2CID 130614466.
  2. 1 2 Bicknell, Russell DC; Holmes, James D; García-Bellido, Diego C; Paterson, John R (2023-04). "Malformed individuals of the trilobite Estaingia bilobata from the Cambrian Emu Bay Shale and their palaeobiological implications". Geological Magazine. 160 (4): 803–812. doi:10.1017/S0016756822001261. ISSN 0016-7568. {{cite journal}}: Check date values in: |date= (help)
  3. ↑ J. B. Jago, Xiaowen Sun and Wen-long Zang (December 2002). "Correlation within early Palaeozoic basins of eastern South Australia" (PDF). pp. 1–22. Archived from the original (PDF) on 2009-10-13. Retrieved 2010-04-04.
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  26. 1 2 Pocock, K. J. (1970). "The Emuellidae, a new family of trilobites from the Lower Cambrian of South Australia". Palaeontology. 13: 522–562.
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  28. ↑ Edgecombe, Gregory D.; Paterson, John R.; GarcíA-Bellido, Diego C. (2017). "A new aglaspidid-like euarthropod from the lower Cambrian Emu Bay Shale of South Australia". Geological Magazine. 154 (1): 87–95. Bibcode:2017GeoM..154...87E. doi:10.1017/S0016756815001053. ISSN 0016-7568.
  29. ↑ Bicknell, Russell D C; Holmes, James D; García-Bellido, Diego C; Paterson, John R (2023). "Malformed individuals of the trilobite Estaingia bilobata from the Cambrian Emu Bay Shale and their palaeobiological implications". Geological Magazine. 160 (4): 803–812. Bibcode:2023GeoM..160..803B. doi:10.1017/S0016756822001261. ISSN 0016-7568.
  30. 1 2 Paterson, John R; Jago, James B (2006). "New trilobites from the Lower Cambrian Emu Bay Shale Lagerstätte at Big Gully, Kangaroo Island, South Australia". Memoirs of the Association of Australasian Palaeontologists. 32: 43–57. hdl:1959.14/10651. ISSN 2205-8877.
  31. ↑ Bicknell, Russell D.C.; Holmes, James D.; Pates, Stephen; García-Bellido, Diego C.; Paterson, John R. (2022). "Cambrian carnage: Trilobite predator-prey interactions in the Emu Bay Shale of South Australia". Palaeogeography, Palaeoclimatology, Palaeoecology. 591 110877. Bibcode:2022PPP...59110877B. doi:10.1016/j.palaeo.2022.110877. hdl:1959.11/52066. S2CID 246790425.
  32. ↑ García-Bellido, Diego C; Lee, Michael S Y; Edgecombe, Gregory D; Jago, James B; Gehling, James G; Paterson, John R (2014). "A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group". BMC Evolutionary Biology. 14 (1) 214. Bibcode:2014BMCEE..14..214G. doi:10.1186/s12862-014-0214-z. ISSN 1471-2148. PMC 4203957. PMID 25273382.
  33. ↑ Schroeder, Natalie I.; Paterson, John R.; Brock, Glenn A. (January 2018). "Eldonioids with associated trace fossils from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia". Journal of Paleontology. 92 (1): 80–86. Bibcode:2018JPal...92...80S. doi:10.1017/jpa.2018.6. ISSN 0022-3360. S2CID 197586878.

Further reading

References about Australian trilobites: