Quaternary eustatic fluctuations, biochronology of continental deposits and neotectonic in North - Western Sicily (San Vito Lo Capo Peninsula - Trapani)

Abstract

: In the San Vito to Capo Peninsula (North - Western Sicily) Quaternary deposits un-conformably overlay a Mesozoic - Tertiary substrate. These deposits are marine and neritic, however, transitional and continental ones also occur. The marine terrain are mainly terrace deposits, while the continental ones, usually rich of fossil vertebrates, are predominantly preserved in morphological traps (wave cut notches, marine caves and karst cavities) and sometimes alternate with the terrace deposits. In the considered area we have identified seven order terraces related to the eustatic fluctuations and to the tectonic movements of the Late and Middle Pleistocene. The complete succession is exposed in the Piana di Cornino area and, partially, in the Piana di Castelluzzo, Piana di Sopra, Piana di San Vito Io Capo and in Zarbo di Mare areas. The various phases of marine high stand level are also recorded by wave cut notches and caves which are frequently filled by continental and/or marine deposits. The Piana di Sopra area has been studied more in the detail. In this area a wide top abrasion surface (I order terrace), dislocated by quaternary faults, ranges from 53 to 83 m a.s.l. Numerous marine cavities cut in the inactive cliffs of Piana di Sopra and the karst depressions located on the abrasion surface, contain deposits which yielded the most representative continental faunal assemblages of the Peninsula. These assemblages belong to the early Middle Pleistocene Elephas falconeri Sicilian Faunal Complex (Semaforo, Torre Isolidda 2 sites), to the Elephas mnaidriensis Complex (K22, Bivio, Caletta Cofano, Seno dell'Arena, Tonnara del Secco sites), late Middle Pleistocene - early Late Pleistocene in age and to the Lateglacial Casteflo Complex (K22 site). The geomorphological data, the relationships of Pleistocene marine and continental deposits with the terrace succession allowed us to propose a correlation of the ancient shore lines with the succession of marine high stand phases and consequently with the North Atlantic δ 18O isotope variation curve. This correlation has finally been constrained by the ages inferred by the mammal assemblages. Even though dating of the terraces and the related deposits retain some uncertainties, these data, integrated with mesostructural analyses, allowed to a draw palaeogeographic evolutionary model and to date the main Pleistocene tectonic events affecting the area. The VI order terrace has been dated to the Eutyirrhe-nian by the finds of a rich warm - temperate "Senegalense" fauna, including Strombus bubonius. Tectonic disturbance renders the dating of the older terraces and their correlation with mammal bearing deposits less direct. In the area, vertical movements produced 30 m maximum throws, while horizontal components seem to have played a remarkable role, locally causing tilting and folding also after the Tyrrhenian. In any case the terraces can be correlated with marine high stand levels as follows: The VII order terrace correlates with "neotyrrhenian" phase (isotopic sub - stage 5a or 5c); the VI order terrace with the Eutyrrhenian (isotopic sub - stage 5e); the V order one with the isotopic stage 7, the IV order terrace with stage 9; that of III order with the stage 11; and finally the II order one with the isotopic stages 13 - 15. The I order terrace has probably a polyphase origin during the late Early Pleistocene - early Middle Pleistocene. In the Piana di Castelluzzo area the different heights of the inner edge of Eutyrrhenian terrace are indicative of a greater tectonic uplift in the central part of this sector (18 m a.s.l.) respect to the marginal areas (on the average 10 m a.s.l.). The correlation of the mammal deposits with the terrace succession is consistent with the aminostratigraphic and radiometric dating known in literature for the Sicilian Faunal Complexes. The Elephas falconeri Complex is correlated to the interval between isotopic stages 17 and 9, while the Elephas mnaidriensis Complex between stages 8 and 4. Three main tectonic events occurred in the area: Just after the formation of the IS and IV order terraces (stage 12 ? and 8 ? respectively) and after the Tyrrhenian. A rather moderate average uplifting rate can be inferred from our data (about 0.11 - 0,14 m/kyr) during Middle to Late Pleistocene.