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Coarse carbonate breccias as a result of water-wave cyclic loading (uppermost Jurassic – South-East Basin, France)

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Abstract

In the uppermost Jurassic of the central part of the South-East Basin of France, an association of lime mudstone beds, calcarenite beds and coarse carbonate breccia bodies form an informal stratigraphical unit called the ‘Barre Tithonique’. In the ‘Barre Tithonique’, gradual transitions from lime mudstone or calcarenite to breccia show different stages of deformation leading to progressive brecciation of the original lithologies. The study of the breccia facies, and the observed gradual transitions as a whole, document a new early diagenetic process in carbonate environments, resulting from water-wave and seabed interaction. Water-wave induced brecciation and its abundance in the ‘Barre Tithonique’ indicate that sea–seabed interaction was significant. Comparison with modern studies of the mechanics of wave–seabed interaction suggests that water depth was less than 200 m. It is demonstrated that sedimentary features such as channel-like structures, previously interpreted as being the result of erosion and deposition of mud-flows, were in fact produced by wave-induced, in situ reworking of lime mud, without any significant unidirectional flow or gravity induced displacement.

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