Diagenesis of Lower Cretaceous platform carbonates from the northwestem margin of the Basque Cantabrian basin (northem Spain).

Abstract : This work presents the results of a diagenetic study of Upper Aptian platform carbonates from the northwestern margin of the Basque Cantabrian basin (northern Spain). The study integrates petrographie, geochemical and microthermometric data, along with field observations aimed to define shape and distribution of the dolomite bodies. The Aptian-Albian platform deposits consist of limestones and minorsandstones, organic-rich maris and mudstones that were deposited in a shallow marine shelf environment within a rifting context. During the Late Aptian, two major faults controlled subsidence and sedimentation in the study area: the Cabuérniga and Bustriguado faults, which are oriented W-E and S-N respectively. Field observations reveal the presence of large elongated dolomite bodies that preferably replace the central part of the Upper Aptian carbonates. Although pervasive dolomitization destroyed most of the original textures, the dolomite front preferably followed a stratigraphie level of massive rudist boundstones and floatstone. Detailed petrographie, geochemical and isotopie studies (delta_Iso, delta- 13C, s7Sr/s6Sr) allowed to characterize multiple phases of dolomitization together with calcite and dolomite cement precipitation. The aim of the present contribution is to reconstruct the evolution of pore fluids during burial and subsequent tectonic uplift. The first dolomite phase (Dl, idiotopic and fluorescent micro crystals) and the first calcite cements (Cl and C2) are volumetrically minor and probably occurred during shallow burial. The C3 calcite cement and the D2 to D5 dolomite phases are characterized by progressively more negative delta-Iso values (from -5.45 to- 11.44%o PDB) and positive delta- 13C values (range 0.84 to 4.68%o PDB), and precipitated from a range of fluids, from meteoric to deep burial in origin. Finally, C4 calcite and dedolomite, with negative delta-Iso and delta- 13C values, precipitated from meteo rie fluids during basin tectonic inversion. The s7 Sr/s6Sr ratios of the different diagenetic phases range from 0.70754 to 0.70992. All these ratios are higher than the s7 Sr/s6Sr values inferred for carbonates precipitated from Aptian marine waters, suggesting prolonged interaction of the pore fluids during burial with more radiogenic Sr-bearing terrigenous minerais, sourced from meteoric water and/or basinal brines. Fluid inclusion microthermometry studies show an exclusive aqueous composition for the trapped fluids. Homogenisation temperatures for the D2 to D5 dolomite phases and for the C3 calcite are between 70 to 90°C. The final melting temperatures of ice for inclusions within these mineral phases reveal a wide range for the salinity (from 0.5 to 21.6eq.wt.%NaCl). These results suggest relatively low temperature fluids of high to low salinities, suggesting a variety of fluids from meteoric to basinal brines. This study allows recognition of different fluid flow events during the burial history of the platform carbonates, improving the knowledge of pore fluid evolution during burial in an extensional basin.
keyword : dolomite
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Contributeur : Françoise Bertrand <>
Soumis le : vendredi 7 mars 2014 - 16:51:35
Dernière modification le : mardi 15 mai 2018 - 14:50:02

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  • HAL Id : hal-00956995, version 1

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I. Lopez-Cilla, Idoia Rosales, Marta Gasparrini, J. Martin-Chivelet. Diagenesis of Lower Cretaceous platform carbonates from the northwestem margin of the Basque Cantabrian basin (northem Spain).. IAS Meeting of sedimentolgy, Sep 2013, Manchester, United Kingdom. 〈hal-00956995〉

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