| Emu Bay shale Stratigraphic range: Upper Botomian Stage, Lower Cambrian. ca 517 mya |
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North Coast of Kangaroo Island, Emu Bay © David Simpson |
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| Type | Geological formation |
| Lithology | |
| Primary | Shale |
| Location | |
| Region | The north coast of Kangaroo Island, around Emu Bay and Cape D'Estaing |
| Country | South Australia, Australia. |
The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätten (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilobites. The Australian's Emu Bay Shale correlated with upper Botomian Stage of the Lower Cambrian.[1]
Its mode of preservation is the same as the Burgess shale, but the larger grain size of the Emu Bay rock means that the quality of preservation is lower.[2]
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The Emu Bay Shale of Kangaroo Island, South Australia, is Australia's only known Burgess-Shale-type Konservat-Lagerstätte, and includes faunal elements such as Anomalocaris, Tuzoia, Isoxys, Xandarella, and Primicaris, in common with other Burgess-Shale-type assemblages, particularly the Chengjiang Fauna in China, the closest palaeogeographically, although somewhat older. The site is also the source of magnificent specimens of trilobites such as Redlichia takooensis, Emuella polymera, Balcoracania dailyi, and Estaingia (=Hsuaspis) bilobata. Balcoracania and Emuella are genera of the distinctive Redlichiina superfamily Emuelloidea, known for numerous segments (over 60 in large Balcoracania specimens), and so far entirely restricted to Australia.
The depositional environment of the majority of Burgess-Shale-type assemblages is outer shelf, deeper water. The Emu Bay Shale in contrast, appears to represent relatively shallow water deposition, indicating that soft tissue preservation occurred in a range of environmental settings during the Cambrian. Some Emu Bay fossils display extensive mineralization of soft tissues, most often of blocky apatite or fibrous calcium carbonate, including the oldest phosphatized muscle tissue – the first thus far reported from the Cambrian. Mineralized soft tissues are apparently rare among Burgess-Shale-type biotas.
The type section of the Emu Bay Shale crops out on the east side of Emu Bay where it conformably overlies the White Point Conglomerate. Here it yields a rich assemblage of Hsuaspis, Redlichia, hyolithids, brachiopods, and the scleritome-bearing Chancelloria. At the Big Gully locality (8 km east of White Point), its presumed correlative is unconformable on the White Point Conglomerate and yields soft-bodied fossils in addition to the trilobites, including the giant predator Anomalocaris, Isoxys, Tuzoia, the presumed worm Palaeoscolex, the problematic Myoscolex, and a number of rarer elements. The Big Gully trilobites rarely preserve any trace of non-biomineralized tissue; a small number of specimens of Redlichia have been reported with antennae.
NOTE: Much of the text of this article was used with permission of Sam Gon III from his below referenced web site, in particular from the Emu Bay page
References about Australian Trilobites:
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