The sequence stratigraphic framework of carbonate diagenesis within transgressive fan-delta deposits: Sant Llorenç del Munt fan-delta complex, SE Ebro Basin, NE Spain

Abstract

Abstract The Eocene (Bartonian–Priabonian) Sant Llorenc del Munt fan-delta complex formed at the front of the Catalan Coastal Range as a result of Alpine deformation. Alluvial fan and fan-delta progradation into the Ebro Basin was arrested by repeated transgressive episodes, thus producing a hierarchy of transgressive–regressive sequences. This study focuses on the two transgressive–regressive fundamental sequences that comprise the El Marcet Unit, a succession of predominantly clastic deposits of shallow-marine and coastal plain origin. Sandstones and conglomerates within the El Marcet Unit are cemented by calcite. Under cathodoluminescence these cements display varying degrees of luminosity. On the basis of differences in luminosity and stable isotopic composition, temporal relationships between the various cements have been established. Cementation commenced in the soil zone with the local formation of calcretes. Early burial cements precipitated in the vadose zone from waters of meteoric origin, and later cements in the shallow phreatic zone. Stable isotopic evidence suggests that all cements probably precipitated from pore waters of essentially the same origin, but at varying burial depths and with varying contents of organically derived carbon. Calcite cements formed by the remobilisation of biogenic and clastic carbonate, and from pedogenic CO 2 . The formation of early cements was facies-dependent and principally controlled by the distribution of shell material. Variations in cement distribution related to the observed cyclicity of the unit are also apparent. The abundance of early cements increases towards the top of progradational sequences, and early cements dominate the upper sequence, while late cements dominate the lower sequence.