Stratigraphic Revision of Brindisi-Taranto Plain
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Mem. Descr. Carta Geol. d’It. XC (2010), pp. 165-180, figg. 15 Stratigraphic revision of Brindisi-Taranto plain: hydrogeological implications Revisione stratigrafica della piana Brindisi-Taranto e sue implicazioni sull’assetto idrogeologico MARGIOTTA S. (*), MAZZONE F. (*), NEGRI S. (*) ABSTRACT - The studied area is located at the eastern and RIASSUNTO - In questo articolo si propone una revisione stra- western coastal border of the Brindisi-Taranto plain (Apulia, tigrafica delle unità della piana Brindisi – Taranto e se ne evi- Italy). In these pages, new detailed cross-sections are pre- denziano le implicazioni sull’assetto idrogeologico. Rilievi sented, based on surface surveys and subsurface analyses by geologici di superficie e del sottosuolo, sia attraverso l’osser- borehole and well data supplied by local agencies or obtained vazione diretta di carote di perforazioni sia mediante inda- by private research and scientific literature, integrated with gini ERT, hanno permesso di delineare gli assetti geologici e new ERT surveys. The lithostratigraphic units identified in di reinterpretare i numerosi dati di sondaggi a disposizione. the geological model have been ascribed to the respective hy- Definito il modello geologico sono state individuate le unità drogeologic units allowing for the identification of the main idrogeologiche che costituiscono i due acquiferi principali. aquifer systems: Il primo, profondo, soggiace tutta l’area di studio ed è costi- a deep aquifer that lies in the Mesozoic limestones, made tuito dai Calcari di Altamura mesozoici, permeabili per of fractured and karstic carbonates, and in the overlying fessurazione e carsismo, e dalle Calcareniti di Gravina pleisto- Lower Pleistocene calcarenite; ceniche, permeabili per porosità. Il secondo superficiale, è a shallow aquifer that is formed by the middle-upper Plei- costituito dai depositi pleistocenici calcarenitici e sabbiosi stocene marine calcarenitic and sandy deposits overlying the permeabili per porosità, ed è sorretto dalle argille anch’esse lower Pleistocene clays, holding a phreatic ground water pleistoceniche. L’identificazione all’interno di questo secondo body. acquifero, della unità delle Sabbie di Brindisi, che ne costi- The Brindisi sands are part of the shallow aquifer, con- tuisce la parte inferiore, consente di modificare i precedenti stituting its lower hydrogeologic unit. The identification of modelli geologici ed idrogeologici. Le ricerche effettuate met- this body permits the modification of previous models. The tono comunque in evidenza la necessità di maggiori studi di results of this research indicate the importance of the de- dettaglio con particolare riferimento ai depositi pleistocenici. tailed geological mapping of the Brindisi – Taranto area par- A questo scopo, a causa dell’estensione nel sottosuolo di que- ticularly in order to clarify the stratigraphy and ste unità, quasi ovunque mascherate dalle coperture conti- hydrostratigraphy of the Pleistocene successions. ERT data nentali recenti, indispensabile sarà l’uso e lo sviluppo delle proved itself to be indispensable in the definition of the dif- metodologie ERT che si sono dimostrate altamente affida- ferent hydrogeological units. bili e risolutive. KEY WORDS: Brindisi – Taranto plain, Electrical Resistivity PAROLE CHIAVE: Acquifero superficiale, piana Brindisi – Ta- Tomography (ERT), Hydrogeologic units, Shallow aquifer, ranto, Stratigrafia, Tomografia Geoelettrica (ERT), Unità Stratigraphy. idrogeologiche. (*) Dipartimento di Scienza dei Materiali, Università del Salento, via per Monteroni, 73100 Lecce 166 MARGIOTTA S. - MAZZONE F. - NEGRI S. 1. - INTRODUCTION AND PREVIOUS stratigraphic logs is homogeneous in the Brindisi – WORKS Taranto plain (fig. 1) but, in the Brindisi area nu- merous borehole and piezometer logs have been The studied area is located at the eastern and carried out to assess the contamination from some western coastal border of the Brindisi - Taranto industrial sites (fig. 2). In the third phase these data plain (fig. 1), that is part of the Apulian foreland. have been processed taking into account the This is the emerged area of the Apulian Plate, con- geological model. The collated data have been sisting of a thick basement made of Mesozoic inserted in input to a Geographical Information limestones (SELLI, 1962; D’ARGENIO et alii, 1973; System (GIS). In this phase, also the hydrological D’ARGENIO, 1974; RICCHETTI, 1980; CIARANFI et and geotechnical data (piezometric levels, flow, alii, 1983). They are covered by Plio-Pleistocene de- permeability of the various formations, physical and posits, resulting from the sedimentary cycle of the granulometric characteristics) available from private Bradanic foredeep (RICCHETTI et alii, 1988; research and scientific publications (CHERUBINI et RICCHETTI, 1967, 1980; DOGLIONI et alii, 1999). alii, 1987) have been processed. In the fourth phase, Gravina Calcarenite (yellowish calcarenites of ERT surveys were carried out in particular selected Early Pleistocene) and subapennine Clays (grey- areas in order to clarify the features of the shallow blue silty clays of Early Pleistocene) represent the aquifer. The Electrical Resistivity Tomography (ERT) litho-stratigraphic units of this cycle in the studied is widely used in the detection and investigation of area (CIARANFI et alii, 1992). These deposits are shallow-depth targets. ERT has been applied with covered by marine terraced bioclastic deposits great success in solving geological (LEUCCI et alii, (Middle-Late Pleistocene) (BENTIVENGA et alii, 2004, CARDARELLI, 2006) and hydrogeological 2004) and by Holocene to recent continental de- (FURMAN et alii, 2004, MARGIOTTA & NEGRI, 2005) posits. In accordance with this geological model a problems. In the fifth phase, the hydrogeologic deep regional karsic aquifer in mesozoic carbonate units and the main aquifer systems have been rocks and a shallow aquifer in Terraced Deposits defined and parametrized. have been identified (COTECCHIA, 1977; CHERUBINI et alii, 1987; RICCHETTI & POLEMIO, 1996). Detailed biostratigraphical (COPPA et alii, 2002) 2. - MORPHOLOGICAL SETTING studies have assigned to Early and Middle Plei- stocene a sequence of yellowish muddy sands The morphology of the area is characterized, cropping up along the Brindisi sea–cliff about one both on the Adriatic and the Ionian coast, by a kilometre south of our study site. The Authors do broad plain, slightly sloping towards the sea, in many not identify contact with the overlying and under- places marked by a drainage network made of small lying units and indicate the uncertain and discor- natural and/or man-made channels. The altitude is dant ascriptions of this sequence in literature (DI between 30 and 40m asl, decreasing towards the GERONIMO, 1969; GENTILE et alii, 1996) to formal coastal zone. The Adriatic coastline in the sur- lithostratigraphic units. rounding area of “Cerano” power station is com- In the Taranto area, also BELLUOMINI et alii posed of a vertical cliff that reaches a maximum (2002) describe a transgressive clayey – sandy unit height of 15m. Cliff height decreases northward (about 4m thick) overlying the subapennine Clay until it gives place to a number of coastal depres- Formation that is attributable to the Middle Plei- sions whose bottom is bsl (e.g. the “Salina Vecchia”). stocene age; lack of borehole log data do not per- The drainage system in the area is well deve- mit the assessment of the extension and thickness loped. It is characterized by numerous shallow of this unit in the subsurface. channels that in many cases run directly into the Our purpose is to clarify the geological and geo- sea (e.g. “Fiume Grande”, “Foggia Rau”, “Fiume physical features of the subsoil for hydrogeologic Piccolo”, “Canale Palmarini – Patri”, “Canale Cil- purpose. This work has been carried out in five di- larese”). Some of them are cut by the present cliff stinct phases. The first is the geological study that whereas the lower course of main streams has was organized in surveys of the surface and of the been submerged due to Holocene sea level rise, subsoil via direct observation of borehole cores forming narrow inlets like the “Canale Pigonati”, (figg. 1, 2, 3); the second is characterized by the “Seno di Levante” and “Seno di Ponente”, which identification of existing wells in the area, collec- form the natural port of Brindisi. tion of stratigraphical data (about 1000, figure 1 Watersheds are hard to identify. Numerous and 3) drawn from borehole cores and supplied by smaller channels flow into broad depressions local agencies, from private research and from sci- which are very prone to flooding. There is a broad entific literature (RADINA, 1968; TEDESCHI, 1969). marshy area near the mouth of the “Canale di The distribution of the data deriving from the well Scarico”. STRATIGRAPHIC REVISION OF BRINDISI-TARANTO PLAIN: HYDROGEOLOGICAL IMPLICATIONS 167 Fig. 1 – Collected well data in the studied area. – Area di studio con ubicazione dei dati a disposizione provenienti da carote di perforazione. On the Ionian coast, the area is marked by wet corresponding to the Murge hills, immediately zones, dune belts, lagoon areas and coastal springs to the west of the Brindisi area, and to the east of (fig. 4). The drainage system, in this area, is well- the Taranto one; the succession is made of alter- developed but, in many places, it has a temporary nating limestones and dolomitic limestones, both character; as usual in karst areas, it is of secondary