Caracterización y evolución de los fluidos diagenéticos que afectaron a los carbonatos del Aptiense superior del noroeste de la cuenca Vasco-Cantábrica (Fm. Reocín)

Abstract

Combined microthermometry of fluid inclusions, isotope geochemistry (18O, 13C, 87Sr/86Sr) and petrography of multiple phases of replacive dolomite and calcite and dolomite cements from the Upper Aptian Reocín Formation (northwestern Basque-Cantabrian basin) hasallowed to reconstruct the fluid evolution during burial diagenesis and subsequent orogenic uplift of the basin. The oldest replacive dolomite (D1) and calcite cements (C1, C2) occurred during early stages of diagenesis under evolved meteoric or mixed fluids. The second important fluid event occurred during intermediate-late burial. It was accompanied by pervasive dolomitization (D2), dolomite recrystallization (D3) and saddle dolomite cements (D4, D5), which exhibit a wide range of salinities and relatively low trapping temperatures, suggesting the interaction of fluids ranging from evolved sea-water to evaporated brines. This event was accompanied by sulfide precipitation (Zn-Pb deposits). The third fluid event was accompanied by precipitation of calcite (C3) that displays very low salinities and the highest trapping temperatures, suggesting precipitation from a hot, deep-circulating meteoric fluid. Finally, the last diagenetic stage was caused by a cool, non-saline and oxidizing fluid. This fluid precipitated calcite (C4), recrystallized dolomite to calcite (dedolomite) and formed Fe-oxyhydroxides.