158 A new concept of karst development based on hydrogeology and geophysics Beneath the Oolitic Formation, the limestone is a bioclastic and peloidal facies characteristic of the Laeviuscula Biozone. A vuggy interval of black dolomite, likely related to pyrite oxidation contained in black clay, is clearly visible within the upper dolomitized section of the oolitic facies. Similar vuggy textures are observed at the Passelourdin cliff, located approximately 2 km south of the HES (Branger et al., 2026). At the base of this unit, two distinctive beds are consistently identified across all OPTV logs. The upper bed, approximately 0.60 m thick, is bounded by two pronounced joints and is rich in crinoids and bivalves. The lower bed, ranging (a) D7bis discontinuity (b) Lower sequence boundary (Oolitic unit/Formation) Figure 7 Sequence boundaries of the Oolite unit.
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