Abstract

During the last years, lagoonal-continental and marine Oligo-Miocene deposits have been recognized in some areas of Salento (Southern Italy). Del Prete & Santagatt (1972) described lagoonal-continental sediment underlying the well-known Miocenic formation of Pietra leccese cropping out near the "Vito Fazzi" hospital of Lecce. They referred this lagoonal deposit to Tortoniano (Miocene). Later, other important outcrops of these deposits were recognized near S. Maria al Bagno (Nardo, Lecce) by Bossio et alii (1992) and near Galatone (Lecce) by Esu et alii (1994) and Colella (1994), respectively along the roadside of the Gallipoli-Lecce highway and along a cut of South East railway. Moreover Barbera et alii (1993) referred to late Oligocene a shallow marine calcarenite, rich in Scutelle, cropping out in a quarry near Galatone. Recently Bossio et alii (1999) recognized, near Lecce, two different informal units referred to the Oligo-Miocene transition, the Galatone Formation (lagoonal-continental deposits) and Lecce Formation (shallow marine deposits). Bossio et alii (1999) proposed to formalize the Galatone Formation. Notwithstanding these researches, at present, the stratigraphic relationships between Galatone Formation and Lecce Formation in consequence of extended soil cover have not been defined. Electromagnetic geophysical investigation using Ground Probing Radar (GPR) has been carried out to define the geometric relationship between these two units. The GPR data have been collected with a SIR SYSTEM 2 of Geophysical Survey Systems, Inc (GSSI). The GPR survey interested two areas near Lecce. Firstly, ground penetrating radar test measurements have been carried out along two artificial cuts to assess the reliability of this methods for imaging and characterising different lithological facies of this method and to choose the best performing antenna and set up. Tests indicate a 200MHZ antenna to be a good compromise between resolution and depth penetration. Data have been acquired with continuous profile. For each lithostratigraphic unit, in each of the two investigated areas, velocity analyses using Common Depth Point (CDP) and Wide Angle Reflection and Refraction (WARR) techniques have been performed. Standard procedures for data processing have been applied using Radan 3 and Seismic Unix software tools. Radar profiles indicate a clear lithological stratification making it possible to individuate subhorizontal Lecce Formation layers overlying, with angular unconformity, slightly folded Galatone Formation layers.

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