Oligocene migration path for Apulia macromammals: the Central-Adriatic bridge

In the second half of the past century two important Tertiary landvertebrate fossil sites were discovered in Southern Italy, the first located in Western Gargano near Apricena and the second situated in Abruzzi in the outskirts of Scontrone. The vertebrate fossil assemblages of the two sites, which are characterized by the same remarkable endemic attributes, include small and large land mammals, a lutrine carnivore, testudines, crocodiles and birds of prey. The Scontrone bonebeds have a Tortonian age. The Gargano fossil vertebrates, which are contained in karstic fissure fillings, have been attributed to a time interval spanning from the Tortonian to the Messinian-early Pliocene, but their exact age remains still undefined. The characters of the faunal assemblage of both sites, showing no affinity with West-European or African Neogene faunas, suggest a possible provenance from the Balkan region. This paper is aimed at providing information on the migration path followed by the forerunners of the Gargano and Scontrone land mammals when they spread over Apulia. Our results are mostly based on the seismostratigraphic analysis of more than 6000 kilometers of reflection seismic profiles from the Adriatic offshore, tied to several tens of deep wells. The conclusion of this study is that, moving from the Balkan region, the terrestrial vertebrates crossed the present Central Adriatic Sea during the Oligocene (most likely around the early/late Oligocene boundary, i.e. around 29-30 Ma), when a severe sea-level fall exposed a landbridge connecting Dalmatia and Gargano via the Tremiti Islands. The seismostratigraphic investigation clearly indicates that the Dalmatia-Gargano landbridge was set up owing to three favourable circumstances: – the growth of prominent structural highs in the Central Adriatic area, mostly related to salt tectonics, which interrupted the continuity of the middle Liassic basinal domain. Vertical movements peaked between the late Liassic and the early Cretaceous, but the tectonics has continued, though less intense, until the Quaternary; – the occurrence of an important sea-level fall around the end of the early Paleocene, which caused in the whole Central Adriatic area a generalized absence of lower Paleocene deposits, as well as a widespread seaward progradation of upper Paleocene/Eocene shallowmarine carbonates over older deeper-marine deposits. Consequently, a wide shallow-water plateau spread between Gargano and the Dalmatian Islands, separating a Northern Adriatic Basin from a Southern Adriatic Basin; – the occurrence, finally, of a further particularly strong sealevel fall in Oligocene times (likely coincident with the well-known mid-Oligocene global sea-level fall), which caused a generalized exposure of the Central Adriatic area. The results of this study suggest a possible common origin of the giant insectivore Deinogalerix, recovered both at Scontrone and Gargano, and mainland counterparts distributed in the Balkan region during the second half of the Oligocene.