Larger foraminifera: a key for the paleoenvironmental and paleogeographic interpretation of the Early Tertiary of Sardinia (Western Mediterranean)

The reconstruction of the geological history of Sardinia in Early Tertiary times is based on subsurface data from the lignite-bearing Sulcis basin, several scattered outcrops from Central-Southern Sardinia, and microfacies analysis of post-Eocene conglomerate clasts, which have been recently found and are as yet largely unpublished. These clasts testify to the extensive erosion of Paleocene-Eocene deposits, among which are also carbonate platform deposits, of which there is no remaining outcrop. In the lignitiferous Sulcis basin (Southeastern Sardinia), the late Thanetian transgression at the base of the lignite-bearing succession is characterized by orbitolitids and alveolinids. In Central-Eastern Sardinia, terrigenous and mixed deposits were formed during transgressive episodes in Early Eocene times, with Assilina-dominated facies in the early Ypresian of Southern Sardinia, and Nummulites-rich assemblages in central Eastern Sardinia near Orosei in the Late Ypresian. The conglomerate clasts, cropping out in several localities of SE Sardinia (Cuccuru’e Flores and the as yet unrecorded occurrences of Su Bandidu and Nurri), testify to the development of carbonate shallow-water environments rich in algae in the Early Paleocene, in the Thanetian and in the late Ypresian, and of larger foraminiferal deposits in the Ypresian. The inferred paleoenvironments and the transgressive-regressive successions are interpreted as a close analogue to the tectono-sedimentary history of the eastern Pyrenaic-Provençal region, thus confirming the position of Sardinia within this domain in the Early Tertiary. A comparison based on the shallow-marine larger foraminiferal record from this paleogeographic domain (which included Corsica, the Baleares and Calabria) allows a reconstruction of the paleobiogeographic and paleogeographic relationships of the northern part of the Western Mediterranean Neo-Tethys.