Driving mechanisms of Holocene coastal evolution in the Bonifacio Strait (Western Mediterranean)
Introduction
The Bonifacio Strait is a narrow coastal stretch connecting the two main basins of the western Mediterranean Sea and dividing the islands of Corsica and Sardinia, the third and the second largest western Mediterranean Islands. At the end of the Last Glacial Maximum (LGM, ~20 ka), with sea level 120–140 m below present (e.g. Lambeck and Purcell, 2005), Corsica and Sardinia were connected, forming the largest Mediterranean island (with an area of about 47,000 km2) placed in the middle of the western part of the basin (Lambeck and Purcell, 2005). The progressive melting of the northern hemisphere ice sheets produced a very rapid sea-level rise until ~7.0 ka ago (e.g. Peltier, 2004; Lambeck et al., 2014) which resulted in the progressive development of the Bonifacio Strait and the separation of Corsica and Sardinia. Conflicting sea-level data are presently available in the literature (Vacchi et al., 2016, Vacchi et al., 2018) resulting in uncertainties regarding the timing and magnitude of this major palaeogeographic change. In particular, sea-level data from sediment cores performed in Sardinian coastal lagoons (Di Rita and Melis, 2013; Melis et al., 2017; 2018) show a significant departure from a sea-level stand derived from some Neolithic archaeological data (~7.3 ka BP) found in a submerged cave in north-eastern Sardinia (Palombo et al., 2011; Benjamin et al., 2017).
This paper aims to provide novel field data on the Relative Sea-Level (RSL) changes in this important Mediterranean sector, notably for the Holocene period (last ∼12.0 ka BP). We thus produced a new geological sea-level dataset that was coupled with geophysical models and GIS analysis to provide new insights into the coastal landscape modifications triggered by the postglacial sea-level rise on both sides of the Bonifacio Strait.
There is further archaeological interest in better constrain the palaeogeographic evolution of the Bonifacio Strait since it always represented the most rapid way to cross from Sardinia to Corsica. Archaeological evidence of human frequentation was recovered along both sides of the strait and dated from the Mesolithic to the Roman Times (e.g., Modi et al., 2017; Lugliè, 2018; Revelles et al., 2019). This narrow strait always represented a key crossroad not only for the crossing from Corsica to Sardinia but also for naval trading routes across the Western Mediterranean, notably linking the Spanish colonies to Rome (e.g., Medas, 2005; Opdebeeck, 2005; Reynolds, 2010). However, the extreme meteomarine conditions coupled with the complex geomorphology characterized by many emerging reefs have always made navigation in the strait very complex (e.g., Sorgente et al., 2012). This is not only testified by the number of historical shipwrecks found in the area (Opdebeeck, 2005; Boetto, 2012; Secci et al., 2013) but also by a large number of present-day maritime incidents, that make the passage of ships with dangerous goods presently strongly discouraged and subject to mandatory piloting (Sorgente et al., 2012).
Section snippets
Study area
Sardinia (~24,100 km2) and Corsica (~8640 km2) are the second and the third-largest islands of the western Mediterranean (the largest being Sicily). The Bonifacio Strait (hereafter BoS) separates the two islands with ~80,000 ha of sea, and hosts a large number of small islands, islets and sea shoals (De Muro et al., 2010; Buosi et al., 2012, Fig. 1A). The geology of both northern Sardinia and southern Corsica is dominated by the Hercynian batholiths of Upper Carboniferous-Permian age
Facies analysis and sea-level data from sediment cores
Sediment cores carried out in transitional environments represent one of the major sources of Holocene sea-level data along the global coastlines (e.g., Khan et al., 2019). In this paper, we used sea-level data derived from six cores that were recently drilled in Piantarella (southern Corsica) and Budelli (a small island placed in La Maddalena archipelago, ~8 km off the northern Sardinian coast) (Fig. 1C). Coring activity was carried out using a Cobra vibracorer with a hydraulic extraction
Depositional facies of Piantarella and Budelli cores
Piantarella cores reached the maximal depth of ~6.5 below the surface. They were performed on the border of the lagoon at elevations ranging from 0.24 to 0.07 m above the msl (Fig. 2A). In Piantarella 1, the core reached the granitic substrate. In Budelli, the cores did not exceed 1 m below the surface and all reached the granitic basement. They were performed in a brackish swamp developing in a backshore depression at elevations ranging from −0.25 to −0.5 m msl.
The multiproxy analysis of
Drivers of RSL changes in the Bonifacio Strait
The interplay between eustatic, GIA and tectonic components largely controlled the variability of postglacial RSL changes along the global coasts (e.g., Khan et al., 2015). In the Mediterranean Sea, crustal movements triggered by Holocene activity of major faults and/or volcanic activity often significantly influenced the RSL evolution (e.g., Pirazzoli, 2005; Morhange et al., 2006; Vacchi et al., 2019). This has often complicated the identification of the GIA component in the RSL record, which
Conclusions
The multiproxy investigation carried out on both sides of the Bonifacio Strait (southern Corsica-northern Sardinia) allows reconstructing ∼10 ka of RSL changes. The postglacial sea-level rise triggered the progressive development of this crucial sea stretch that presently connects the two major basins of the Western Mediterranean.
Our data are of particular interest because they are collected in one of the most tectonically stable areas of the Mediterranean and because minimally affected by
Declaration of Competing Interest
None.
Acknowledgments
We warmly thank Dr. Yuri Donno of the Parco Nazionale Arcipelago della Maddalena, Dr. Thomas Lorscheid and Dr. Alessandro Porqueddu for the support during the fieldwork in Budelli Island. Part of the fieldwork was carried out in the framework of the second MOPP-Medflood project (INQUA CMP 1603P) meeting in Palau (Sardinia, September 2017). MV is funded by the Rita Levi Montalcini programme of the Italian Ministry of University and Research (MIUR). This article contributes to the PCR “Approche
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