Diagenesis, carbonate cementation and resevoir quality evolution of Eocene deep-water marine turbidite sandstones of the Hecho Group, South-Central Pyrenees

Abstract

Sandstone turbidites from the Hecho Group in the South-Central Pyrenees are considered exceptional examples for reservoir modelling and outcrop analogous studies. The Hecho Group is divided into four major tectosedimentary units (TSU-2 to TSU-5) and the sandstone composition varies from quartzarenites to arkoses (TSU-2), lithoarenites to hybrid arenites (TSU-3 and TSU-4), and hybrid arenites (rich in carbonate bioclasts; TSU-5). In TSU-2, the lowermost and most deformed unit, calcite cement precipitation was related to tectonic deformation. In the other turbidite systems (TSU-3, 4 and 5) eodiagenesis is evidenced by precipitation of dolomite cement and pyrite, which are locally abundant in all sandstones. Overall, compaction was more important than cementation in destroying porosity. However, the precipitation of dolomite overgrowth and intragranular mesogenetic ferroan calcite occluded nearly completely the remaining porosity and halted further compaction. Dissolution of calcite and dolomite cements has resulted in creation of minor amounts of secondary porosity.