Publication: Caracterización y evolución de los fluidos diagenéticos que afectaron a los carbonatos del Aptiense superior del noroeste de la cuenca Vasco-Cantábrica
(Fm. Reocín)
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2016
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Sociedad Geológica de España.
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Abstract
El estudio combinado de microtermometría de inclusiones fluidas, geoquímica isotópica y petrología de las múltiples fases de dolomitización y cementación de calcita y dolomita que afectan a la Formación Reocín (Aptiense superior, noroeste de la cuenca Vasco-Cantábrica), ha permitido reconstruir la evolución de los fluidos durante la diagénesis de enterramiento y posterior exhumación orogénica de la cuenca. Durante la diagénesis temprana tuvo lugar la primera fase de dolomita (D1) y de cementos de calcita (C1, C2), a partir de fluidos meteóricos evolucionados o mezcla de fluidos. El segundo evento importante de flujo de fluidos durante el enterramiento dio lugar a la formación de dolomía de reemplazamiento (D2) y de recristalización (D3) y a cementos saddle de dolomita (D4, D5), que muestran un amplio rango de salinidades y temperaturas de nucleación relativamente bajas, lo que sugiere la interacción de fluidos que varían entre aguas marinas evolucionadas hasta salmueras altamente evaporadas. Este evento estuvo relacionado con la precipitación de sulfuros (mineralizaciones de Zn-Pb). El tercer evento de fluidos causó la precipitación de calcita (C3) que muestra muy bajas salinidades y las temperaturas de entrampamiento más altas, lo que sugiere precipitación a partir de la circulación de un fluido meteórico calentado en profundidad. La última fase diagenética está relacionada con un fluido frío, no-salino y oxidante, que causó la precipitación de calcita (C4), recristalización de la dolomita a calcita (dedolomita) y oxi-hidróxidos de Fe.
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) has allowed 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, nonsaline and oxidizing fluid. This fluid precipitated calcite (C4), recrystallized dolomite to calcite (dedolomite) and formed Fe-oxyhydroxides.
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) has allowed 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, nonsaline and oxidizing fluid. This fluid precipitated calcite (C4), recrystallized dolomite to calcite (dedolomite) and formed Fe-oxyhydroxides.