MÖssbauer Spectrometry to Study Diagenetical Processes of Red Beds and Sand Dikes in the Vallès-Penedès Half Graben

The Valles-Penedes neogene half-graben (NE of Spain) is filled with a thick succession of terrigenous rocks, the lowermost unit of the basin consists of red-coloured clays, sandstones and conglomerates (red beds) formed in an alluvial fan environment. In the upper part of this unit some vertical joints are filled with blue sand (sand dikes). Sand dikes are interpreted as having been formed in an early stage after sedimentation. Despite the colour difference, the common sediment source of both, red-coloured sediments and blue-coloured sand dikes is evidenced by almost identical results obtained by using different techniques: Petrographic microscope, Cameca electron microprobe, XRD and SEM. Mossbauer spectrometry has proven to be a useful technique providing significant data to explain the colour difference and helping to understand the diagenetical processes involved herein.