153 8. Hydro-stratigraphic study of the Hydrogeological Experimental Site of Poitiers, France the Bajocian, refer to Branger et al. (2026). The discontinuities (D) are numbered according to Gabilly et al (1985). The Aalenian stage is subdivided into three main terms with reference to ammonite zones (base to top): a) laminated marly limestones (Opalinum Biozone, 4–5 m), b) siliceous (cherty) formation (Murchisonae Biozone, 8–10 m), c) bioclastic and oolitic limestones (Bradfordensis and Concavum Biozones, 9–14 m), often partially dolomitized and locally displaying cavernous textures (c′ unit). A regional discontinuity (D5bis) separates the Opalinum and Murchisonae Biozones, while discontinuities D6 and D7 mark the base and top of the Concavum interval. The Bajocian comprises: d) decimetric limestone beds with Serpulid fossils (Ovalis Biozone, 1–2 m), e) bioclastic and pelletal limestones (Laeviuscula Biozone, 7–8 m), f) white oolitic limestones (top of Laeviuscula, 2–4 m), g) limestone beds of the Propinquans and Humphriesianum Biozones (9–10 m), topped by h) a crinoid-rich horizon, h) bioturbated limestones referred to as the burrowed limestones “Assise à terriers” (Garantiana Biozone, 5–6 m), and i) fine-grained gravelly limestones with flint nodules (Parkinsoni Biozone, 23–25 m). Discontinuities are identified at the top of the Laeviuscula zone (D7bis) and at the base and top of the Garantiana interval (D8 and D8bis, respectively). The Bathonian is more difficult to interpret due to gaps in biostratigraphic markers. Bathonian limestones lie above discontinuity D9. Gabilly (1978) subdivided this interval into: k) ctenostreon beds (possibly Zigzag Biozone?, 2–3 m), l) siliceous, bioclastic and pelletal limestones (15–16 m), m) bioturbated limestones (7 m). The overlying Callovian is easily recognizable due to its micropackstone texture and chalky appearance. Data available The borehole drilled during Mourier’s thesis (1983), near the HES, identified key marker horizons (notably the oolitic limestone of the Concavum Biozone and the crinoidal bed atop the Humphriesianum interval). Stratigraphic details for the supra-Toarcian aquifer were further refined using two cored boreholes (C1 and C2) described by the French Petroleum Institute (Gaumet et al., 2004). These cores made it possible to characterize the depositional facies (mudstone, packstone,
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