Structural Diagenesis of Siderite Layers in Black Shales (Albian Black Flysch, Northern Spain)

In this study, we describe the structural diagenesis of diluted turbidite and abyssal lutite deposits of the late Albian Black Flysch (western Pyrenees, northern Spain). We analyze and interpret an association of brittle and ductile soft-sediment deformation structures. To our knowledge, some of them are described for the first time, although they are known in other tectonic settings. We reconstruct a diagenetic history that commenced with a generalized siderite cement precipitation after siliciclastic turbidite deposition. Siderite replaced the finer-grained, diluted uppermost turbidite parts. Siderite precipitation was followed by calcite cementation in turbidites and by soft-sediment brittle (thrust planes, shear veins, and microveins) and ductile (fault-bend folds and culminations developed in relation to thrust-ramp strain) deformation structures. This occurred before hosting lutite lithification by dewatering and compaction.