Upper Miocene peri-Tyrrhenian Reefs in the Calabrian Arc : Sedimentological, tectonic and palaeogeographic implications

Abstract

A number of poorly known Late Toitonian-Eariy Messinian coral reefs occur in Late Miocene outliers in the vicinity of Santo Stefano and Milazzo, Sicily, and along the coastal margin of western Calabria in the vicinity of Palmi town and the Vaticano peninsula. Hie fully marine biota of the reefs invariably contains Porites sp. with subordinate numbers of other corals especially Tarbellastraea sp., Palaeoplesiastrea sp., and rare Favites sp. which form an open framework infilled by bioclastics and micrite. A significant aspect of the coral growth is the presence of both undulose and slender rod growth-forms of Porites within the same reef. Associated with these are coralline algae, both encrusting and ihodolitic. regular echinoids and molluscs such as pectinids, occasional Ostraea sp. and low spire and veimetid gatropods. Coral heads frequently are bored by Lithophaga sp., Gastrochaena sp. and clionid sponges. The reef substrates are typically coarse siliciclastic sands containing scattered Clypeaster altus echinoids and an admixture of lithic blocks, especially in close proximity to the underlying crystalline basement. The reef associations are developed with a sharp base directly above these siliciclastics in Calabrian outcrops whereas a progradational relationship is seen in the Sicilian sections. Most reefs have limited lateral extent and are restricted to a single exposure. Generally, they consist of brecciated reef debris with scattered in situ coral heads. The reefs of the Milazzo Peninsula are more extensive but appear mainly to be patch reefs situated on prograding banks of mixed siliciclastic and bioclastic sands. Only the reef around Palmi (Calabria) is at all laterally continuous, extending northwards for about 5 km. Contemporaneous strata in Calabria in the vicinity of Santa Domenica, Vaticano Peninsula, and at Santo Stefano di Camastra, (Sicily) shows that coralline algal biostromes were developed lateral to the reefs. Reefs facing directions in Calabria are generally towards the west or southwest whereas reefs in the N. Sicilian sections prograde and face northwards. The well exposed Milazzo Peninsula sections provide a depositional model for the local facing variations observed. Here, sediments prograde generally basinwards from crystalline ridges on the pre-Messinian marine planation surfaces. The reefs occupy the crest areas of such erosion al remnants. In the case of the Calabrian outcrops where pre-Messinian planation surfaces appear to have been much wider the discontinuous reef developments occupy sites close to the Tyrrhenian margin. The exposed reefs of this study are a small part of those presumed previously have existed around the western margin of the Peloritani-Calabrian Arc. Hie remaining reefs, today exposed at various elevations from sea level at Milazzo to several hundreds of metres altitude at the Capo Vaticano record the former position of a Late Miocene, Tynhenian-facing, low relief coastal zone, much of which has foundered during the later collapse of the Tyrrhenian Basin. These reefs, therefore, provide evidence to indicate that the southeastern Tyrrhenian Basin developed after the Early Messinian reef episode.