Lower Jurassic benthic foraminiferal assemblages from shallow-marine platform carbonates of Mallorca (Spain): stratigraphic implications

Abstract

The stratigraphic distribution of larger benthic foraminifera and other microfossils, as analysed in thin-sections, has been investigated in three stratigraphic sections from the island of Mallorca (Son Maina, S’Heretat and Cuevas de Arta). These stratigraphic sections represent deposition in a Lower Jurassic shallow-water carbonate platform succession (Es Barraca Member, Soller Formation) of the Llevant Mountains. The microfossil assemblages contain abundant benthic foraminifera and calcareous algae, including the typical Liassic dasycladalean alga Palaeodasycladus mediterraneus (Pia) and the microproblematica Thaumatoporella parvovesiculifera (Raineri), which provide good age constraint of the succession. Three consecutive biozones have been recognized based on the stratigraphic distribution of foraminifera, including the evolutionary bioseries Mesoendothyra—Lituosepta—Orbitopsella spp., which are documented for the first time in the Balearic Basin: Biozone A (interval Zone) is characterized by the occurrence of small Siphovalvulina spp., Mesoendothyra sp. and rare Lituosepta ancestors. Biozone B (lineage Zone), whose lower boundary is defined by the first occurrence of Lituosepta recoarensis Cati and its top by the first appearance of Orbitopsella aff. primaeva (Henson). The uppermost part of biozone B shows an interval with transitional morphotypes between Lituosepta and Orbitopsella, indicating that the change between biozones B and C1 is gradual (B/C1 transition). This interval is characterized by the presence of very primitive forms of Orbitopsella. Finally, Biozone C1 (lineage Zone) is defined by the first occurrence of Orbitopsella aff. primaeva together with L. recoarensis. The upper boundary of the Biozone C1, which is defined by the first occurrence of O. praecursor s.l., is not recorded in the studied sections of the Es Barraca Member. This biostratigraphic zonation is consistent with a Sinemurian age for the Es Barraca Member with its top most likely not extending into the Pliensbachian. The proposed biostratigraphic scheme is comparable with those established for other western Tethyan margins such as the High Atlas of Morocco, the Southern Italian Alps or the Dinaric Alps of Slovenia and Croatia. The reconstruction of a depositional transect across the studied sections shows the progressive loss of the upper biozones towards the northeast, demonstrating the existence of significant hiatuses in some sections of the Llevant Mountains domain. These hiatuses point to an intra-lower Pliensbachian (Carixian) early stage of platform fragmentation, with areas affected by erosion or non-deposition, and areas with marine marly limestone sedimentation followed by deltaic siliciclastic progradation on the north-western part of Mallorca.