(a) Detailed photograph of sample N showing well-preserved lucinid shells and pluri-mm nodules dispersed in an homogeneous micritic matrix. (b) and (c) Thin-section natural and polarized light illuminations showing clasts incorporated in a large mineralized vein. Five calcites C1 to C5 are very similar to the calcites identified in sample A1. Isotopic analyzes (C, O and Sr) were conducted on five samples (see text for details and Tab. 1 for values).