The geological literature of the south Salento peninsula (around Capo S. M. di Leuca) shows a number of chrono- and lithostratigraphic setting reconstructions surprisingly high, regarding both the Cretaceous-Tertiary platform carbonates and the Quaternary marine-continental clastic deposits. As an example, the eastern well exposed coastal cliff has been considered belonging to: a Paleocene-Oligocene Calcari di Castro formation (SERVIZIO GEOLOGICO D'ITALIA, 1968); an undifferentiated succession of pre-Neogene formations (BOSSIO et alii, 1987); a Oligocene-Miocene clinostratified slope systems including reef tracts (BOSELLINI et alii, 1999, 2001). Moreover, the outcropping carbonate substratum of the west ionian coast up to the Pesculuse littoral has been referred entirely to the Cretaceous (SERVIZIO GEOLOGICO D'ITALIA, 1968) or locally made up by Miocene formations (BOSSIO et alii, 1987; CIARANFI et alii, 1988). Along this shore tract, the breccias and conglomerates overlying the above mentioned platform carbonates at Capo San Gregorio, have been referred to: weathering continental slope deposits (SERVIZIO GEOLOGICO D'ITALIA, 1968); shoreface deposits linked to a 3-4 m a.s.l. paleo-shoreline (COTECCHIA et alii, 1969); a marine conglomeratic lithostratigraphic unit named Leuca formation (BOSSIO et alii, 1987, 2001). Preliminary stratigraphic and sedimentological observations carried out at Capo San Gregorio allow us to distinguish the main features of breccias and conglomerates and to delineate their outcropping extensions, as briefly summarized. Some units have been observed: 1) weathering continental slope deposits characterized by a medium-coarse breccia (clasts of limestones, dolomitic limestones and calcarenites) within a well cemented reddish matrix spread all around the area. Frequently are present well cemented interlayered reddish hard crusts. The whole deposit is characterized by terrace shaped morphology; 2) debris-mud flow deposits showing embricated structures, wide sorted and rich in bauxite pisolites; they are usually associated to the aforementioned slope deposits; 3) well smoothed conglomerates (mainly limestones and calcarenites content) within a well cemented yellowish carbonate matrix, characterized by a wide sorting with clasts ranging from some centimetres up to some decimetres; 4) coarse conglomeratic level at the base of cross-bedding reddish calcarenites which shows a thickness of about of 0.5 m; more or less rounded pebbles are randomly present also within the overlying calcarenites 5) intraclastic breccia layers interbedded within carbonate platform succession; the best outcrop is located in point number 3 in the attached map, where the succession is thick about 15 meters. More considerations must be done regarding the evidences of the litological features above described. Here we preliminary approach some questions. The weathering continental slope deposits are widespread along the Salento southwest coast between Pesculuse and Leuca. Its well cemented reddish matrix could emphasize continental or transitional diagenetic processes during paleo-climatic favourable conditions, meanwhile their terraced morphologies seems to be undergone to erosion processes of shoreline retreat. Moreover, breccias in reddish matrix, containing terrestrial fossil bones, are described along the east Salento coast as the result of interglacial processes (DI STEFANO et alii, 1992). The well smoothed conglomerates (1 of fig.1) are evidently shoreface deposits. According to the literature, they can indicate a Tyrrhenian high stand (COTECCHIA et alii, 1969; DAI PRA & HEARTY, 1988). At Pesculuse area (about 5 km far from Capo San Gregorio towards North-West), D'ALESSANDRO & MASSARI (1997) have been recognized shoreface limestone conglomerates, whereas along the present shoreline, coarse clastic deposits in reddish matrix can be observed. Tacking into account that the platform carbonates of Capo San Gregorio are partially referred to the pre-evaporitic Messianian (BOSSIO et alii, 1987; CIARANFI et alii, 1988), a working hypothesis is to consider the strata containing the intraclastic breccia layers as part of the aforementioned deposits. Following this suggestion, the intraclastic breccias could be related to the analogous deposits contained within a reef complex of the south-east Salento coast, which is truncated by a erosion surfaces interpreted as indicator of relative fourth order sea-level fluctuation (BOSELLINI et alii, 2001). If the so called Leuca formation can be found at Capo San Gregorio, it hasn't the considerable extensions reported by BOSSIO et alii (1987) especially along the south-west side of Capo San Gregorio itself, where are mainly present both the weathering continental slope deposits and the intraclastic breccia layers (see 3 and B in fig. 1). We have also to mention that a detailed geological mapping of Est of Lecce zone (DELLE ROSE et alii, 2006), has carried out the presence of a decimetres breccias underling a centimetres phosphatized calcirudite in place of some tens of metres thick "Leuca formation" mapped by BOSSIO et alii (1999). As a consequence the aforementioned unit cannot be considered a formation according to the stratigraphic codes (NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE, 1983; COMMISSIONE ITALIANA DI STRATIGRAFIA DELLA S.G.I., 2003). In conclusion, as suggest by some characteristics of the Capo San Gregorio breccias and conglomerates, multidisciplinary analyses of these deposits can offer opportunities to understand paleo-environmental and climatic features of source areas as well as sedimentation ones. In order to optimize the management of all existing and collected geological data, a GIS data base will be implemented. The main aim is the availability of a mean able also to confront different geological interpretations and to discern among those sites that need further investigation. Not only maps can be introduced in the GIS data base but also stratigraphic sections, drill logs and all those not geological map data geographically linkable (DELLE ROSE et alii, 2006). REFERENCES BOSELLINI A., BOSELLINI F.R., COLALONGO M.L., PARENTE M., RUSSO A., VESCOGNI A. (1999) - Stratigraphic architecture of the Salento coast from Capo d'Otranto to S. Maria di Leuca (Apulia, southern Italy). Riv. It. Paleont. Strat., 105, 397-416. BOSELLINI F.R., RUSSO A., VESCOGNI A. (2001) - Messinian reef-building assemblages of the Salento Peninsula (southern Italy): palaeobathymetric and palaeoclimatic significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 175, 7-26. BOSSIO A., MAZZEI R., MONTEFORTI B., SALVATORINI G. (1987) - Evoluzione paleogeografica dell'area di Leuca nel contesto della dinamica Mediterranea. Quad. Ric. Cent. St. Geot. Ing., 11, 31-54. BOSSIO A., FORESI L.M., MARGIOTTA S., MAZZEI R., MONTEFORTI B., SALVATORINI G. (1999) - Carta geologica del settore nord orientale della provincia di Lecce, scala 1:25.000; settori 7, 8, 10 scala 1:10.000, Università di Siena. BOSSIO A., MAZZEI R., MONTEFORTI B., SALVATORINI G. (2001) - Note illustrative alla carta geologica della zona di S. Maria di Leuca. Soc. Tosc. Sc. Nat., 107, 97-163. CIARANFI N., PIERI P., RICCHETTI G. (1988) - Note alla carta geologica delle Murge e del Salento (Puglia centromeridionale), Mem. Soc. Geol. It., 41, 449-460. COTECCHIA V., DAI PRA G., MAGRI G. (1969) - Oscillazioni tirreniane e oloceniche del livello del mare nel Golfo di Taranto, corredate da datazioni col metodo del radiocarbonio. Geol. Appl. Idrogeol., 4, 93-147. COMMISSIONE ITALIANA DI STRATIGRAFIA DELLA S.G.I. (2003) - Giuda italiana alla classificazione e alla terminologia stratigrafica, APAT, quad. s. III, 9. DAI PRA G., HEARTY P.J. (1988) - I livelli marini pleistocenici del Golfo di Taranto. Sintesi geocronologica e tettonica. Mem. Soc. Geol. It., 41, 637-644. D'ALESSANDRO A., MASSARI F. (1997) - Pliocene and Pleistocene depositional environment in the Pesculuse area (Salento, Italy). Riv. It. Paleont. Strat., 103, 221-258. DELLE ROSE M., PAPPAFICO G., RESTA F. (2006) - Problematiche stratigrafiche e cartografiche del Pliocene ad est di Lecce. Atti 83a Riun. Est. Soc. Geol. It., Chieti, 12-16 settembre 2006. DI STEFANO G., PETRONIO C., SARDELLA R., SAVELLONI V., SQUAZZINI E. (1992) - Nuove segnalazioni di brecce ossifere nella costa fra Castro Marina e Otranto (Lecce). Il Quaternario, 5, 3-10. NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE (1983) - North American Commision on Stratigraphic nomenclature. The American Association of Petroleum Bulletin, 67, 841-875. SERVIZIO GEOLOGICO D'ITALIA (1968) - Carta geologica d'Italia a scala 1:100.000, Foglio 223 - Santa Maria di Leuca, II ed., Roma.
Stratigraphic and sedimentological insights about the Capo San Gregorio breccias and conglomerates (South Salento)
Delle Rose M;
2006
Abstract
The geological literature of the south Salento peninsula (around Capo S. M. di Leuca) shows a number of chrono- and lithostratigraphic setting reconstructions surprisingly high, regarding both the Cretaceous-Tertiary platform carbonates and the Quaternary marine-continental clastic deposits. As an example, the eastern well exposed coastal cliff has been considered belonging to: a Paleocene-Oligocene Calcari di Castro formation (SERVIZIO GEOLOGICO D'ITALIA, 1968); an undifferentiated succession of pre-Neogene formations (BOSSIO et alii, 1987); a Oligocene-Miocene clinostratified slope systems including reef tracts (BOSELLINI et alii, 1999, 2001). Moreover, the outcropping carbonate substratum of the west ionian coast up to the Pesculuse littoral has been referred entirely to the Cretaceous (SERVIZIO GEOLOGICO D'ITALIA, 1968) or locally made up by Miocene formations (BOSSIO et alii, 1987; CIARANFI et alii, 1988). Along this shore tract, the breccias and conglomerates overlying the above mentioned platform carbonates at Capo San Gregorio, have been referred to: weathering continental slope deposits (SERVIZIO GEOLOGICO D'ITALIA, 1968); shoreface deposits linked to a 3-4 m a.s.l. paleo-shoreline (COTECCHIA et alii, 1969); a marine conglomeratic lithostratigraphic unit named Leuca formation (BOSSIO et alii, 1987, 2001). Preliminary stratigraphic and sedimentological observations carried out at Capo San Gregorio allow us to distinguish the main features of breccias and conglomerates and to delineate their outcropping extensions, as briefly summarized. Some units have been observed: 1) weathering continental slope deposits characterized by a medium-coarse breccia (clasts of limestones, dolomitic limestones and calcarenites) within a well cemented reddish matrix spread all around the area. Frequently are present well cemented interlayered reddish hard crusts. The whole deposit is characterized by terrace shaped morphology; 2) debris-mud flow deposits showing embricated structures, wide sorted and rich in bauxite pisolites; they are usually associated to the aforementioned slope deposits; 3) well smoothed conglomerates (mainly limestones and calcarenites content) within a well cemented yellowish carbonate matrix, characterized by a wide sorting with clasts ranging from some centimetres up to some decimetres; 4) coarse conglomeratic level at the base of cross-bedding reddish calcarenites which shows a thickness of about of 0.5 m; more or less rounded pebbles are randomly present also within the overlying calcarenites 5) intraclastic breccia layers interbedded within carbonate platform succession; the best outcrop is located in point number 3 in the attached map, where the succession is thick about 15 meters. More considerations must be done regarding the evidences of the litological features above described. Here we preliminary approach some questions. The weathering continental slope deposits are widespread along the Salento southwest coast between Pesculuse and Leuca. Its well cemented reddish matrix could emphasize continental or transitional diagenetic processes during paleo-climatic favourable conditions, meanwhile their terraced morphologies seems to be undergone to erosion processes of shoreline retreat. Moreover, breccias in reddish matrix, containing terrestrial fossil bones, are described along the east Salento coast as the result of interglacial processes (DI STEFANO et alii, 1992). The well smoothed conglomerates (1 of fig.1) are evidently shoreface deposits. According to the literature, they can indicate a Tyrrhenian high stand (COTECCHIA et alii, 1969; DAI PRA & HEARTY, 1988). At Pesculuse area (about 5 km far from Capo San Gregorio towards North-West), D'ALESSANDRO & MASSARI (1997) have been recognized shoreface limestone conglomerates, whereas along the present shoreline, coarse clastic deposits in reddish matrix can be observed. Tacking into account that the platform carbonates of Capo San Gregorio are partially referred to the pre-evaporitic Messianian (BOSSIO et alii, 1987; CIARANFI et alii, 1988), a working hypothesis is to consider the strata containing the intraclastic breccia layers as part of the aforementioned deposits. Following this suggestion, the intraclastic breccias could be related to the analogous deposits contained within a reef complex of the south-east Salento coast, which is truncated by a erosion surfaces interpreted as indicator of relative fourth order sea-level fluctuation (BOSELLINI et alii, 2001). If the so called Leuca formation can be found at Capo San Gregorio, it hasn't the considerable extensions reported by BOSSIO et alii (1987) especially along the south-west side of Capo San Gregorio itself, where are mainly present both the weathering continental slope deposits and the intraclastic breccia layers (see 3 and B in fig. 1). We have also to mention that a detailed geological mapping of Est of Lecce zone (DELLE ROSE et alii, 2006), has carried out the presence of a decimetres breccias underling a centimetres phosphatized calcirudite in place of some tens of metres thick "Leuca formation" mapped by BOSSIO et alii (1999). As a consequence the aforementioned unit cannot be considered a formation according to the stratigraphic codes (NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE, 1983; COMMISSIONE ITALIANA DI STRATIGRAFIA DELLA S.G.I., 2003). In conclusion, as suggest by some characteristics of the Capo San Gregorio breccias and conglomerates, multidisciplinary analyses of these deposits can offer opportunities to understand paleo-environmental and climatic features of source areas as well as sedimentation ones. In order to optimize the management of all existing and collected geological data, a GIS data base will be implemented. The main aim is the availability of a mean able also to confront different geological interpretations and to discern among those sites that need further investigation. Not only maps can be introduced in the GIS data base but also stratigraphic sections, drill logs and all those not geological map data geographically linkable (DELLE ROSE et alii, 2006). REFERENCES BOSELLINI A., BOSELLINI F.R., COLALONGO M.L., PARENTE M., RUSSO A., VESCOGNI A. (1999) - Stratigraphic architecture of the Salento coast from Capo d'Otranto to S. Maria di Leuca (Apulia, southern Italy). Riv. It. Paleont. Strat., 105, 397-416. BOSELLINI F.R., RUSSO A., VESCOGNI A. (2001) - Messinian reef-building assemblages of the Salento Peninsula (southern Italy): palaeobathymetric and palaeoclimatic significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 175, 7-26. BOSSIO A., MAZZEI R., MONTEFORTI B., SALVATORINI G. (1987) - Evoluzione paleogeografica dell'area di Leuca nel contesto della dinamica Mediterranea. Quad. Ric. Cent. St. Geot. Ing., 11, 31-54. BOSSIO A., FORESI L.M., MARGIOTTA S., MAZZEI R., MONTEFORTI B., SALVATORINI G. (1999) - Carta geologica del settore nord orientale della provincia di Lecce, scala 1:25.000; settori 7, 8, 10 scala 1:10.000, Università di Siena. BOSSIO A., MAZZEI R., MONTEFORTI B., SALVATORINI G. (2001) - Note illustrative alla carta geologica della zona di S. Maria di Leuca. Soc. Tosc. Sc. Nat., 107, 97-163. CIARANFI N., PIERI P., RICCHETTI G. (1988) - Note alla carta geologica delle Murge e del Salento (Puglia centromeridionale), Mem. Soc. Geol. It., 41, 449-460. COTECCHIA V., DAI PRA G., MAGRI G. (1969) - Oscillazioni tirreniane e oloceniche del livello del mare nel Golfo di Taranto, corredate da datazioni col metodo del radiocarbonio. Geol. Appl. Idrogeol., 4, 93-147. COMMISSIONE ITALIANA DI STRATIGRAFIA DELLA S.G.I. (2003) - Giuda italiana alla classificazione e alla terminologia stratigrafica, APAT, quad. s. III, 9. DAI PRA G., HEARTY P.J. (1988) - I livelli marini pleistocenici del Golfo di Taranto. Sintesi geocronologica e tettonica. Mem. Soc. Geol. It., 41, 637-644. D'ALESSANDRO A., MASSARI F. (1997) - Pliocene and Pleistocene depositional environment in the Pesculuse area (Salento, Italy). Riv. It. Paleont. Strat., 103, 221-258. DELLE ROSE M., PAPPAFICO G., RESTA F. (2006) - Problematiche stratigrafiche e cartografiche del Pliocene ad est di Lecce. Atti 83a Riun. Est. Soc. Geol. It., Chieti, 12-16 settembre 2006. DI STEFANO G., PETRONIO C., SARDELLA R., SAVELLONI V., SQUAZZINI E. (1992) - Nuove segnalazioni di brecce ossifere nella costa fra Castro Marina e Otranto (Lecce). Il Quaternario, 5, 3-10. NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE (1983) - North American Commision on Stratigraphic nomenclature. The American Association of Petroleum Bulletin, 67, 841-875. SERVIZIO GEOLOGICO D'ITALIA (1968) - Carta geologica d'Italia a scala 1:100.000, Foglio 223 - Santa Maria di Leuca, II ed., Roma.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
