Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees. (April 2021)

• Record Type: Journal Article
• Authors: Motte, Geoffrey; Hoareau, Guilhem; Callot, Jean-Paul; Révillon, Sidonie; Piccoli, Francesca; Calassou, Sylvain; Gaucher, Eric C.
• Is Part Of: Marine and petroleum geology. Volume 126(2021)
• Publication Date: 2021-04
• Subjects: Carbonate diagenesis -- Dolomite -- Breccias -- Hydrothermalism -- U–Pb dating -- Hyperextension -- Salt tectonics -- Jurassic; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2021.104932
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: The Meillon (Callovo-Oxfordian) and Mano (Tithonian) Formations are dolomitized carbonate reservoirs that actively produce oil and gas (Aquitaine Basin, France). In this study, the dolomitization conditions of their counterparts exhumed in the northwestern Pyrenees are detailed using a combination of field observations, petrography, fluid inclusion microthermometry, elemental and isotopic geochemistry, and carbonate U–Pb geochronology. Dolomitization occurred in several stages spanning from the Neocomian (pre-rift) to the Albian (syn-rift, associated with mantle exhumation and active salt tectonics). Both formations were first massively dolomitized in near-surface to shallow burial conditions during the Berriasian-Valanginian, likely triggered by the influx of marine-derived waters. Between the Barremian and the Albian, the Early Cretaceous rifting caused the upward influx of hot fluids associated with the partial to complete recrystallization of the initial dolomites. During the Albian, subsequent dolomites precipitated in both formations as high-temperature (T > 160 °C) vein- and pore-filling cement. Distinct fluid inclusion chlorinities and rare earth element patterns between the Meillon and Mano Formations point to fluid compartmentalization during this stage. Whereas dolomite cements indicate the involvement of evaporite-derived brines in the Meillon Formation, precipitation was likely related to clay-derived water in the Mano Formation. Lastly, a final episode of dolomite cementation occurred only in the vicinity of faults and volcanic intrusions during the Albian when the highest temperatures were recorded in both formations (T > 250 °C). These saddle dolomites precipitated from hydrothermal water with a mixture of mantle-, crustal-, and evaporite-derived waters channeled by faults and active diapirs. Subsequent quartz and calcite cement precipitation reveals a temperature decrease in a post-rift to inversion setting (post-Cenomanian) and indicates fluid compartmentalization between both formations. This study highlights the major control exerted by rifting, combined with the presence of diapiric salt, on dolomitization, making carbonate platforms of modern salt-rich passive margins potential targets for exploration. Highlights: The northwestern Pyrenean carbonates were affected by multi-phase dolomitization. U–Pb dating and SIMS with a conventional diagenetic approach highlight the control exerted by rifting and salt tectonics. Different fluids such as marine-, evaporite-, crustal-, mantle-, and clay-derived waters were involved in dolomitization. The distinct diagenetic evolution of the Meillon and Mano Formations reveals the presence of fluid compartmentalization.