Carbon and oxygen isotopic variations applied to the study of carbonate diagenesis in the Landraves Formations (Thanetian, Burgos, Northern Spain)

Résumé

We have studied the dolomitization and calcitization processes that have widely affected the Landraves Formation sediments (Thanetian) at Valdivielso Valley (Burgos). The unit was deposited in a shallow marine environment'with eventual tidal retouchings. The top of the unit coincides with an important sedimentary gap marked by the deposition of an Oligocene fluvial conglomerate. Whereas dolomitization could be early in origin and continuously and completely affected the sediments, the late calcitization processes originated from the mentioned rupture. In addition, some evaporitic nodules are indicative of subaerial exposure episodes towards the upper part of the unit. Dolomite isotopic values show slight variations (S1^ = +0.6 to +2.6%oPDB y §l80 = -7.7 to +2.2%oPDB), suggesting the temporal persistence of marine-evaporitic conditions; on the contrary, the calcite ones are lighter (5I3C = -5.9 to +2.2 %„ PDB y = -7.5 to +0.4 %o PDB) and denote a phreatic meteoric environment associated to a strong freshwater input