Fossil reef

What’s more surprising than a short walk on a coral reef near… Marseilles! This incredible situation is indeed possible because of the main feature of hard corals: a carbonate skeleton that fossilizes easily.

Some of us probably know the little port of Carry-le-Rouet, located about thirty kilometers from Marseilles (France).

A continuous succession of continental and marine sediments of late Oligocene (28 MY) to early Miocene (20 MY) age is exposed along the coast of this very typical Mediterranean village. The Carry-le-Rouet sedimentary succession is an excellent climatic archive. Just after the port, when you start to walk along the rocky shores, it is easy to remark the very usual aspect of a ‘reef’ which extends along the shore over more than 1 kilometer.

One can quickly realize that all the rocks are full of fossils and it is easy to recognize some ‘best-sellers’ such as Acropora or Caulastrea species! The most diversified coral community occurred during the warmest period of the Aquitanian (23My). The diversity consists of in-life-position, coalescent or scattered, massive colonies of poritids and faviids, bundles of mussids, dendrophyllids and of fragments of branching acroporids (Galloni, 2003).

Porites

Turbinaria

Tarbellastrea

Mussismili

Caulastrea

Acropora

The alternation of branching acroporitids fragments and muddy sediment suggests episodic storm-deposition in a relatively deep lagoon, as observed nowadays in the Caribbean (Demory et al. 2011). 

Associated organisms are molluscs (gastropods and lamellibranches), echinoids (scutellids), red coralline-algae. 

Mollusc assemblage

Lamellibranch deposit

Gasteropod shells

Coralline red algae

It is well known by palaeontologists that the Mediterranean shores exhibit a large number of fossil corals including different reef types. During the Oligocene and Miocene age, shallow-water of the Mediterranean region were rich in scleractinian corals, their diversity is considered to be strongly controlled by changes in sea-surface water temperature. Indeed, coral reefs occurrences match the glacial to interglacial transition and the most diversified coral environment matches the warmest period. Thus within an increasing need of data for better understanding the response of reef corals to climate change, the Mediterranean fossil reefs represents a unique paleontological database for investigating spatio-temporal changes in reef ecosystems.

References

GALLONI F (2003) Organisation sédimentaire et anatomies récifales des systèmes carbonatés à silicoclastiques oligo-miocènes inférieurs de Provence et du bloc corso-sarde. – PhD Thesis, Université of Provence, Marseille, 300 p.

FRANÇOIS DEMORY, GILLES CONESA, JULIEN OUDET, HABIB MANSOURI, PHILIPPE MÜNCH, JEAN BORGOMANO, NICOLAS THOUVENY, JULIETTE LAMARCHE, FRANCK GISQUET and LIONEL MARIÉ (2011) Magnetostratigraphy and paleoenvironments in shallow-water carbonates: the Oligocene-Miocene sediments of the northern margin of the Liguro-Provençal basin (West Marseille, southeastern France). Bull. Soc. géol. Fr., t. 182, no 1, pp. 37-55