Abstract

In most studies, tidal deposits are associated with shallow-water coastal areas. In contrast, this paper illustrates an ancient deep-water tidal environment located on the outer part of the Jura shelf. The Bajocian (mid-Jurassic) sediments are composed of fine-grained marly limestones that include several crinoidal limestone bars. These bioclastic bars are formed by stacked dunes and sand waves showing sedimentary structures typical of tidal environments. In order to interpret the sedimentology of the crinoidal limestones, the hydrodynamic behavior of crinoidal particles was investigated. Derived from a sedimentological, petrographical, and paleontological approach of the area, the results indicate that dunes and sand waves formed on the outer shelf at a depth of about 100-150 m under the occasional influence of tidal currents. Interpretation of seismic reflection data indicates a shelf-edge position located about 15 km to the SE.

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