Diagenetic evolution of Tortonian temperate carbonates close to evaporites in the Granada Basin (SE Spain)
Résumé
The Granada Basin (SE Spain) is a small basin located in the central part of the Betic Cordillera, structured as such
in the late Tortonian and initially connected to the Atlantic Ocean and to the Mediterranean Sea. During the late
Tortonian, normalmarine conditions prevailed, leading to the deposition of skeletal carbonate sediments on platforms
around structural highs. The marine connections were later interrupted, first to the Atlantic Ocean and
then to theMediterranean Sea, and a thick evaporite sequence,marking the transition frommarine to continental
conditions,was deposited during the latest Tortonian. In thiswork, the diagenetic evolution of the Tortonian temperate
carbonates (TTC), underlying and close to the evaporite bodies, is revealed and discussed. The diagenetic
study includes petrographic analyses (conventional petrography, cathodoluminescence, and fluorescence), geochemical
analyses (major,minor and trace elements, and δ13C and δ18O stable isotopes), and microthermometry
of fluid inclusions. In the TTC, marine diagenetic processes such as micritization and fibrous calcite-cement precipitation
and mechanical compaction took place during or just after deposition (Eogenesis). An initial burial
event (Mesogenesis 1) is characterized by: 1) stabilization of the temperate-water carbonates by freshwater,
and 2) porosity occlusion via precipitation of low-Mg bladed and syntaxial/mosaic calcite cements. The TTC
were then subaerially exposed (or got close to the surface) during evaporite deposition and underwent pedogenesis,
Mg-smectite infiltration, and pyrite formation (Telogenesis 1). Subsequent brine-related diagenetic alterations,
such as dolomitization and silica, halite, and sylvite replacements of carbonate grains occurred during a
second burial episode (Mesogenesis 2) concomitant with theMessinian lacustrine deposition, this being followed
by chemical compaction (stylolite formation). Finally, the area was uplifted and the TTC exhumed.
Microstalactitic (dripstone) and fibre/whisker calcite cement precipitation and extensive dissolution relate to
this Pliocene–Quaternary late event (Telogenesis 2). In the study case diagenetic history is closely linked to
basin evolution, as diagenetic pathways of carbonate rocks were related to major geodynamic events, including
basin restriction leading to evaporite deposition, and several episodes of subsidence and uplift. Up to now, only
very fewdiagenetic studies have attempted to demonstrate this correlation between diagenetic history and basin
evolution.