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qUAtERnARy MARInE tERRACES And fAULt ACtIvIty In thE noRthERn SECtoR of thE MESSInA StRAItS �SoUthERn ItALy�� C. Monaco, G. Barreca, A. Di Stefano, G. RistucciaDipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Scienze della Terra, Università di Catania, Italy

Introduction. Starting from Late Pliocene, and more markedly in the Quaternary, concurrently with back-arc extension in the Tyrrhenian Sea, the inner side of the Calabrian Arc, has experienced extensional deformation accommodated by normal faulting (Ghisetti, 1984, 1992; Tortorici et al., 1995; Monaco and Tortorici, 2000; Jacques et al., 2001). A prominent normal fault belt runs more or less continuously along the Tyrrhenian side of Calabrian, as far as the Messina Straits area. Extension along this fault system has a WNW-ESE azimuth, as documented by structural, seismological (CMT and RCMT catalogues) and GNSS velocity field (D’Agostino and Selvaggi, 2004; Goes et al., 2004; Mattia et al., 2009; D’Agostino et al., 2011; Palano et al., 2012) investigations.

Since the Middle Pleistocene, the Calabrian Arc has been also affected by strong uplift, which caused to the development of spectacular flights of marine terraces along the coast and, on land, a deep entrenchment of rivers with the consequent deposition of alluvial and/or transitional coarse grained sediments along the major depressions on top of pelagic sequences (DumasDumas et al., 1982; Ghisetti, 1992; Valensise and Pantosti, 1992; Westaway, 1993; Miyauchi et al., 1994).).

The Late Quaternary tectonics of the Calabrian Arc result from the interplay of distinct geodynamic processes (Westaway, 1993; Palano et al., 2012). This is reflected by the existence, within the deformation profile of the flights of coastal terraces, of both a long- and a short-wavelength signal, the former related to lower- or sub-crustal processes and the second arising from upper crustal displacements. According to Westaway (1993), 1.7 mm/yr of post-Middle Pleistocene uplift of southern Calabria is subdivided into 1 mm/yr regional (or deep) processes and the residual to distributed displacement on major faults, and mostly results in footwall uplift.

In order to determine the uplift rates and the late Quaternary contribution of the outcropping normal faults, a new mapping of the terraced deposits and surfaces, accompanied by measurement of inner-edge elevation, has been carried out on both sides of the northern sector of the Straits. The study is based principally on detailed field mapping on 1:10,000 scale digital topographic maps integrated with analysis of 1:33,000 and 1:10,000 scales aerial photographs and LANDSAT satellite images of the terrace surfaces. Their relative inner and outer edges have been mapped over the whole area with an error margin in the elevation of ±5 m. However, this margin basically depends on erosion and depositional processes following the emergence of the terraces and it is negligible in estimating the long-term Quaternary uplift rates involving time spans of tens to hundreds of thousands of years. This implies that the elevations above sea level (a.s.l.) of the paleo-shorelines reported in this work are to be considered as mean values.

The occurrence of a flight of marine terraces represents the result of the interaction between long-term tectonic uplift and Quaternary cyclic sea-level changes (Lajoie, 1986; Bosi et al., 1996) which are represented in the global eustatic curve derived from the Oxygen Isotope Time (OIT) scale. This curve (Waelbroeck et al., 2002 and references therein) shows a cyclic trend characterized by peaks corresponding to distinct marine interglacial high-stands, represented by the odd-numbered Marine Isotope Stages (MIS) and marine glacial low-stands, indicated by the even-numbered MIS. The uplift rates are estimated by subtracting the altimetry value of eachThe uplift rates are estimated by subtracting the altimetry value of each terrace from the sea level of the assigned Marine Isotopic Stage (MIS) and then dividing this value by the age assigned to the terrace through literature data (see below).

The Calabrian side. Along the Calabrian side, among Villa S. Giovanni and Piano di Matiniti, a complete sequence of ten Late-Quaternary fluvial-coastal terraces (Fig. 1) has been recognized at elevations ranging from 40 to 520 m a.s.l. (Fig. 2). The terraced deposits are

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formed by calcarenites, marine sands and conglomerates, more or less cemented, directly lying on the crystalline basement or on the early Pliocene (Trubi Fm.), infra-Pleistocene (Vinco calcarenites) or late-middle Pleistocene (Messina Gravels and Sands Fm.) sedimentary covers (Dumas et al., 1978; Ghisetti, 1981; Miyauchi et al., 1994). The marine deposits generally pass upwardS to continental reddish silt with

The terraced series is partly displaced by the Pezzo-Scilla and the Cappuccini faults that border the Campo Piale horst (Ghisetti, 1984, 1992) to the north and the south, respectively. The lowest (I order) terrace extends along to the coast, from Villa S. Giovanni to Porticello area, with inner edge around at 40 m a.s.l. Terraces II, III, IV, V and VI extend around the Campo Piale horst, extensively outcropping along the south-west side, between Villa S. Giovanni and Fiumara area, with inner edges at elevations of 60, 95, 120, 175 and 200 m a.s.l., respectively.

Fig. 1 – Morphotectonic map of the Messina Straits area showing the major Quaternary faults, the distribution of Quaternary terraces and the location of dated deposits.

Fig. 2 – Correlation between the altimetric position of the inner edges of marine terraces in the Calabrian side of the Straits and the high stands of the eustatic curve of Waelbroek et al. (2002), modified for uplift rate of 1.4 mm/yr.

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The complete terraced sequence of the remaining orders outcrops only along the Campo Piale horst, where the terraces VII, VIII and IX show inner edges at elevations of 285 m, 345 and 415 m a.s.l. Terrace X, the oldest and highest order of the whole flight of fluvial-coastal deposits, extending at elevations ranging from ~ 480 m to ~ 520 m upstream of Piano di Matiniti horst. These terraces are represented by wave-cut platforms directly resting on the crystalline substratum and covered by silts and reddish continental sands.

North of the Campo Piale horst, on the hangingwall of the Pezzo-Scilla Fault, the assignment of terraces to distinct orders is more complex. In this area only three terraced surfaces have been recognized: the terrace I shows a clear continuity parallel to the coastline; a second surface, with inner edges at elevations between 70 m and 90 m a.s.l., as been attributed to the terrace III outcropping on the Villa S. Giovanni area, suturing the western end of the Pezzo-Scilla Fault; a third surface, with inner edges at elevations among 100 m and 140 m a.s.l., has been attributed to the V order (MIS 5.5, 125 ka) by geomorphological correlations (see Miyauchi et al., 1994; Jacques et al., 2001).

As regards the age attribution, the finding of Strombus Bubonius in the Reggio Calabria area (Bonfiglio, 1972; Dumas et al., 1987) and the absolute dating obtained by thermoluminescence (TL) and optically stimulated luminescence (OSL) methods (Balescu et al., 1997), perfectly constraint the age of the terraced deposits between 60 and 330 ka. In particular, an age of around 60 ka has been attributed to the sandy deposits of the lowest terrace (I order), outcropping in the Acciarello place near Villa S. Giovanni (Balescu et al., 1997), while the morphological correlation of the terrace V with the Strombus Bubonius deposits (see also Miyauchi et al., 1994; Dumas and Raffy, 2004), has allowed to correlate this last to the MIS 5.5 (125 ka). This allowed us to correlate the other orders of terrace with the other positive peaks of eustatic curve occurred between the MIS 3.3 and the MIS 9.3. Terraces II and VI order cannot be correlated with positive peaks (see also Dumas and Raffy, 2004) and for this reason the terrace II has been attributed to the MIS 4 (74 ka), while the terrace VI has been attributed to the MIS 6.5 (167 ka).

The Sicilian side. Along to the Sicilian side of the Straits of Messina, among Capo Peloro, Ganzirri and Faro Superiore, on the structural high bounded by the Mortelle to the north and by the Ganzirri Faults to the south, six orders of terraces have been recognized (Fig. 1). TheirTheir inner edges range in elevation from 30 m to 170 m a.s.l. (Fig. 3). The terraced deposits are The terraced deposits are characterized by marls, sands and marine gravels thick up to 30 m lying unconformably on the Messina Gravels and Sands Fm. and covered by silts, sands and continental gravels, up to 20 m thick. The series is tilted of ~10-15° toward the south, due to the activity of the Mortelle fault. The series is tilted of ~10-15° toward the south, due to the activity of the Mortelle fault.

The lowest (I, II and III order) terraces only outcrop on the Capo Peloro area, west of the Pantano Piccolo area, with inner edges situated at elevations of 30 m, 45 m and 60 m a.s.l., respectively. On the terrace III the Granatari Cemetery is built. The terrace IV largely outcrops with inner edges southwards decreasing from 110 m to 75 m a.s.l. In this terraced deposits

Fig. 3 – Correlation between the altimetric position of the inner edges of marine terraces in the Sicilian side of the Straits and the high stands of the eustatic curve of Waelbroek et al. (2002), modified for uplift rate of 0.9 mm/yr.

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shells of Strombus Bubonius, have been found by Bonfiglio and Violanti (1983) at elevation of 85 m a.s.l. Toward the west, between Madonna dei Miracoli and Faro Superiore, terraces V and VI order with inner edges located at elevations from 140 m to 170 m a.s.l., respectively, discontinuously crop out. As regards the chronological attribution, the occurrence of Strombus Bubonius has allowed to correlate the terraces IV to the MIS 5.5 (125 ka) and to constrain the age of the terraces I, II, III, V and VI order, that can be correlated to the remaining marine high-stands occurred between the MIS 3.3 (60 ka) and the MIS 7.5 (240 ka). So, the I, II and III order terraces can be attributed to the MIS 3.3 (60 ka), to the MIS 5.1 (80 ka) and to the MIS 5.3 (100 ka), respectively, while the V and VI order terraces can be attributed to the MIS 7.1 (200 ka) and to the MIS 7.3-7.5 (215-240 ka).

Uplift rates and fault activity. In the Calabrian side, the Cappuccini fault was characterized by sin-sedimentary activity during the upper Pliocene-lower Pleistocene (Monaco et al., 1996), then it was sutured by the deposits of the VI terrace order, attributed to the 167 ka marine stand. The Pezzo-Scilla fault is considered still active in its north-eastern sector (Jacques et al., 2001; Ferranti et al., 2007; 2008), whereas on its western end it is sutured by the I order terrace, dated at 60 ka.

The uplift rates change in time and space and represent the sum of the regional signal, homogeneous in the last 700 ka (Westaway, 1993) and the co-seismic vertical deformation induced by the fault activity around the main Quaternary faults (King et al., 1988). These two components are added on footwall of the seismogenic faults, while on the hangingwall the co-seismic vertical movements are subtracted to the regional rate.

The estimated uplift rates range from 0.8 mm/yr for the period 330-60 ka, on the downthrown block of the Pezzo-Scilla fault, to 2.0 mm/yr (twice the regional component of 1.0 mm/yr estimated by Westaway, 1993) for the period 330-200 ka, on the Campo Piale high. The constant elevation of the I order terrace suggests an uniform uplift rate of 1.4 mm/yr along the entire coastal area, and, consequently, a deactivation of the western sector of the Pezzo-Scilla fault in the last 60 ka, even though the offshore activity of segments belonging to the same system is not excluded (see Selli et al., 1979; Ferranti et al., 2008). However, it is considered still active in the north-east segments, since it is considered responsible of one of the sequence earthquakes on February-March 1783 (Monaco and Tortorici, 2000; Jacques et al., 2001) and of the co-seismic uplifts of the coastal area between Scilla and Palmi area, situated on the footwall of the structure, in the last 5000 years (Ferranti et al., 2007, 2008).

As regards the Sicilian side, the terraced sequence is cut on structural high bounded by the Mortelle Fault to the north and by the Ganzirri Fault to the south. The tilting of ~10-15° toward south coud be related to the greater activity of the Mortelle Fault. The elevation of the inner edges of VI- II order terraces suggests an uplift rate slightly smaller than the regional component (Westaway, 1993) between 240 and 80 ka. This could be due to the late Quaternary activity of the Faro Superiore Fault (Fig. 1), being the terraced block located on its hanging wall. The uplift-rate has increased to 1.3 mm/yr in the last 60 ka, as indicated by the I order terrace elevation.

Uplift rates of 1.3-1.4 mm/yr for the last 60 ka have been estimated on both side of the Straits by long-term (see above) and short-term Holocene markers (see Antonioli et al., 2006; Scicchitano et al., 2011). They are probably related to the current activity of offshore structures (Selli et al., 1979; Guarnieri et al., 2004; Ferranti et al., 2008; Aloisi et al., 2012).

Acknowledgements. This work was partially funded by PRIN 2010–11 Project “Active and recent geodynamics of Calabrian Arc and accretionary complex in the IonianSea” (responsible C. Monaco).

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