Syn- and Post-Tectonic Gypsum Cements in Fractured Gypsum Rocks (Vilobí Gypsum Unit, Miocene, Ne Spain)

Abstract

PROCEEDINGS, GEOFLUIDS VII ¿ International Conference IFP Energies nouvelles, Rueil-Malmaison (France), June 6-8, 2012 ; The Vilobí Gypsum Unit (upper Burdigalian) is located in the Penedès Half-graben (northeast of the Iberian Peninsula). This unit consists of a succession of secondary (predominant, coming from hydration of anhydrite) and primary (limited to the top interval) laminated-to-banded gypsum and laminated lutites-carbonates. This succession is affected by 5 fractures sets due to the fragile deformation related to the Neogene extensional stages recorded in the region. These fragile structures are partly or totally cemented by four gypsum cements types (fibrous, millimetrical crystals, aligned and macrocrystalline gypsum), resulting from fluid circulation along the fractures. A successive isotopic enrichment (¿34SVCDT, ¿18OVSMOW) from the host-gypsum rocks and the different fracture infillings is evidenced, thus suggesting chemical recycling processes. The strontium ratios of gypsum cements suggest higher fluid interaction during the macrocrystalline cements precipitation, with respect to the fibrous infillings. ; Financial support by the I+D+I Spanish Government research projects CGL2010-18260, CGL2009-11096 and Grup Consolidat de Recerca "Geologia Sedimentària" (2009 SGR-1458).