The late Ordovician Soom Shale Lagerstätte: an extraordinary post-glacial fossil and sedimentary record

Sarah E. Gabbott,Rowan J. Whittle,Johannes N. Theron,Claire Browning

doi:10.1144/jgs2016-076

Abstract

Fossils of the Late Ordovician Soom Shale Lagerstatte are characterized by exceptional preservation of their soft tissues in clay minerals. The low-diversity community lived in an unusual cold-water setting, dominated by anoxic bottom waters, in the immediate aftermath of the Hirnantian glaciation. Giant conodonts represented by complete tooth sets, and one with trunk musculature and liver preserved, unarmoured jawless fish, lobopods and enigmatic taxa are some of the more important fossils. Furthermore, this Lagerstatte also preserves biomineralized Ordovician taxa such as brachiopods, orthoconic nautiloids and trilobites. It is important in capturing the only known examples of many taxa, extending temporal ranges of others and providing a unique glimpse of a post-glacial refugium, at a time when other Lagerstatten are unknown.

Highlights

Fossils of the Late Ordovician Soom Shale Lagerstätte are characterized by exceptional preservation of their soft tissues in clay minerals
The late Ordovician Soom Shale Lagerstätte, Western Cape Province, South Africa has produced an array of marine fossils, many of which preserve spectacular details of their soft tissues
The Soom Shale Lagerstätte is distinctive in several ways: the host shale itself is conspicuous as the only fine-grained lithology in a 3000 m thick sequence of dominantly arenaceous rocks; the fossils record life in a cold-water, glacially influenced marine setting in the immediate aftermath of a mass extinction and major glaciation; the mode of preservation is the inverse of the ‘normal’ fossil record: in the Soom Shale the hard, biomineralized components of animals are demineralized, and are often comparatively poorly preserved, whereas nonbiomineralized decay-prone anatomy is frequently preserved in exquisite detail

Summary

Soom Shale Lagerstätte

Unusual composition of the fossils and that Soom taxa are often anatomically peculiar members of their kind. The only other possible vertebrates in the Soom Shale are the remains of naked and completely unbiomineralized agnatha, the largest of which is about 11 cm in length (Aldridge et al 2001) showing excellent preservation of the eyes, branchial structures and possibly the liver There are many other soft-bodied fossils with unknown affinities, which have yet to be identified, and others that are represented by a single occurrence where a tentative assignment awaits confirmation through discovery of other specimens (Aldridge et al 2001; Whittle 2007) One such occurrence is an unidentified arthropod with inwardly directed appendages of two distinct types: one is multiarticulate and biramous; the other is paddle-shaped with setiferous terminations (Fig. 4e)

Algae and plankton

Conclusions

Findings

Acknowledgements and Funding