Revisión estratigráfica del Jurásico Superior de la Sierra Norte (Mallorca)

Abstract

Upper Jurassic deposits of the Sierra Norte of the Majorca lsland (Spain) have been revisited in sections selected from the areas of Alcudia, Cúber, Alfabia, Son Paxt, Aumedrá and Cala Fornells. The stratigraphic review has been based on biostratigraphic data previously obtained by the authors on 5,000 ammonites, favouring the zonal/subzonal recognition from the Middle Oxfordian to the Middle Berriasian, complemented by tintinnoids for the Upper Tithonian-Berriasian. The Alfabia Formation is recorded from the Middle Oxfordian (Antecedens Zone p.p.) to the Upper Kimmeridgian (Beckeri Zone p.p.); the Aumedrá Formation was deposited during a short interval within the Upper Kimmeridgian (Beckeri Zone p.p.) and the Lower Tithonian (Hybonotum Zone p.p.); the Son Torrelles Formation contains materials of the Lower Tithonian (Hybonotum Zone p.p.) to the Middle Berriasian (Occitanica Zone). The major stratigraphic discontinuity affects the basal part of the Alfabia Formation. Possible minar stratigraphic gaps in the intrazonal level have been detected in the Upper Oxfordian (Alfabia Formation) and could exist in the Aumedrá Formation, while gaps in the Son Torrelles Formation are more frequent; these latter are of local expression and are related to the bottom instability. The ammonitico rosso materials studied were deposited on an epioceanic plateau where the condensed sedimentation was almost exclusive during the Late Jurassic and the earliest part of the Cretaceous. The mudstones of the Aumedrá Formation represent a notable deviation in background depositional conditions, but of short duration; the return to ammonitico rosso depositional conditions, and their persistence (Son Torrelles Formation), occurred within the interval of greater instability in the basin during the Upper Jurassic