Some features of the Pliocene-lower Pleistocene sequence of the southern Salento

During Pliocene, the Mediterranean Sea was affected by large scale geodinamic events and a number of periods of sub-polar conditions presaging the entry of northern fauna. Pliocene is probably the most questionable series of the whole Salento geological record. Although the main lithological features have been recognized by DE GIORGI (1922), its sedimentological arrangement has not been well defined. Two lithostratigraphic units have recognized: Leuca Formation and Uggiano la Chiesa Formation. Nevertheless, their chronostratigraphic context as well as their relationships with younger Quaternary deposits, are object of several interpretations (BOSSIO et alii, 1987; BOSELLINI et alii, 1999; MASSARI & D'ALESSANDRO, 2000; D'ALESSANDRO et alii, 2004; DELLE ROSE, 2006). Geological surveys performed through the southwestern Salento peninsula allow us to recognize five lithological facies (unformal units or stratigraphic levels) linked to Mediterranean paleo-environmental and paleo-climatology events. Chaotic assemblage consists of blocks, breccias and pebbles within calcarenitic or calciruditic matrix and includes thin limestone lens. Marlstones are massive and contain coarse clasts, whereas glauconitic siltstones consist of bioturbated calcareous silty-sand beds. They are truncated by an erosive surface showing holes filled by phosphatized clasts. Phosphatized calcirudite contains a number of squashed marly inclusions and shows a three-folded partition (reverse grain-size grading basal portion; middle one contains a dense detritus component; normal grain-size grading upper portion) which suggest intra-platform grain flow re-sedimentation processes. Calcarenites and calcilutites consist of fossiliferous intensively bioturbated coarse to fine-grained beds bounded by diastems, containing Arctica islandica at the top. The sedimentological features of the chaotic assemblage indicate final Miocene exposed ridges dismantling and post-Messinian Salinity Crisis shallow marine deposition. The interbedded lens of limestones could represent deposits of a transitional continent-sea environment subject to intense evaporation under warm and dry climate (MASSARI & D'ALESSANDRO, 2000). The Early Pliocene Inundation (IACCARINO et alii, 1999) deepened the Salento shelf and leaded to the marlstones deposition probably at epibathyal paleo-depth. Glauconitic siltstones attest a relatively long phase of very low rate of sedimentation, in accordance with the general Mediterranean depositional setting during the lower-middle Pliocene (CITA et alii, 1999); the deposition of the aforementioned facies could be stopped not before than the upper Piacenzian. The encrustations of the clasts forming the skeleton of the phosphatized calcirudite probably developed below the euphotic zone and above the thermocline depths, i.e. between the deepest inner shelf and the shallowest middle shelf. The calcarenites and calcilutites were supplied from an expansive source area located to the north west of Salento as far as the Murge (DELLE ROSE, 2006). Sediments were piled toward Salento, reworked, sorted and transported by currents within the shelf. During the Gelasian, the flat land between Salento and Murge have been probably a inner shelf/ramp where erosion and off shore sediment transport was higher than carbonate production. Thin inner shelf/ramp successions draped local depressions, such as the Novoli graben (D'ALESSANDRO et alii, 2004). Calcarenites and calcilutites was deposited within a middle shelf/ramp, where the sediments derived from the inner zone and relict ones were bioturbated and reworked by waves. They can be related to the Calcarenite di Gravina Fm, widespread all over Murge and Bradanic Trough (TROPEANO & SABATO, 2000). The results carried out by southeastern