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Home , Calabrian (stage), Caulonia, Caulonia (ancient city), Fiumara, Monasterace, Stilo

N° 108 - 2007  Kaulonia, southern : Calabrian Arc tectonics inducing coastline shifts Kaulonia, Italie méridionale : mobilité tectonique de l’arc calabrien et variations des lignes de rivage à l’Holocène

Jean-Daniel STANLEY Geoarchaeology Program, MRC-121 Paleo, E-205 NMNH, Smithsonian Institution, Washington, D.C. 20013-7012, U.S.A. email: [email protected]

Abstract - Kaulonia, an settlement (~700 to 389 B.C.), in southern Italy. The approach used here, integrating geological and is positioned in a tectonically mobile setting on the Ionian coast of archaeological databases, serves to more precisely interpret settings where in southern peninsular Italy. Several extensive back-and-forth shoreline major nearshore changes have been driven largely by effects of structural migrations have occurred along this coast since the mid-Holocene. These mobility. large-scale shifts, from 100 m landward of the present shoreline to 300 m Résumé - La colonie grecque de Kaulonia (datée entre 700 et 389 avant offshore, are recorded by tracing the lateral distribution of archaeological J.-C.) est localisée dans une zone tectoniquement mobile. Notre étude géo- material and a distinct Holocene stratigraphic marker unit (beachrock-cobble archéologique a mis en évidence plusieurs déformations des rivages depuis sequence). Landward-directed (transgressive) shifts were induced during l’Holocène moyen. Les transgressions (jusqu’à 100 m à l’intérieur des côtes) tectonically calmer periods when phases of relative sea-level rise prevailed. sont mises en relation avec des périodes de calme tectonique. En revanche, In contrast, a major seaward (regressive) coastal migration resulted primarily des régressions (jusqu’à 300 m au large de la cote actuelle) sont attribuées from an important ‘see-saw’ phase, with uplift landward and at the coast and à des mouvements caractérisés par des soulèvements du substrat et des a downward seafloor tilt. This Calabrian Arc tectonic event, leading to this affaissements des fonds marins. Des mouvements similaires ont déjà été offshore displacement in the mid- to late Holocene, is also recorded elsewhere observés ailleurs en Italie du Sud.

1 - Introduction stretches identified on Mediterranean margins (Flemming 1969, 1998; Flemming & Webb 1986; Raban 1988; Morhange et al. 2005; The world’s coastlines have been subject to major lateral Marriner & Morhange 2007). Attention herein is paid to a rather displacement during the Holocene and, in the case of mid- and unusual coastline migration pattern in a long-inhabited sector lower latitude settings, these shifts were primarily directed at the archaeological site of Kaulonia located on the Ionian landward. Such transgressive shoreline migrations during Sea coast of Calabria in southern peninsular Italy (Fig. 1). this geologically recent period generally occurred as a result This sector is positioned within the Calabrian Arc, a tectonic of progressive effects of natural events, primarily relative sea- setting that during much of the denoted an active level rise as a function of climate change and subsidence of boundary between African and Eurasian plates (Figs. 1A, 2) seafloor surfaces. These effects, acting conjointly through time, and has been characterized by a record of considerable land have led to a shoreline advance landward and submergence of displacement (numerous studies, including Westaway 1993; previously subaerially exposed late to Holocene Bordoni & Valensise 1998; Parotto & Praturlon 2004; Moratti shelf platforms and coastal margins. During this period, & Chalouan 2006). powerful episodic natural phenomena have also induced Recently, it has been determined that the coastal stretch shoreline changes. These short-term events, numerous and examined here had been submerged in the early to mid- varied, include marked climactic fluctuations, hurricane and Holocene, and then subsequently became subaerially exposed strong storm surges, floods, tsunamis, earthquakes and fault seaward of Kaulonia (Stanley et al. 2007). This latter time- displacement, volcanic activity, substrate sediment compaction span included the 300- period when the settlement was and failure, and anthropogenic influences S ( hort 1999; occupied by the Greeks, starting about 2700 ago (Orsi Woodroffe 2002; and many others). 1916; Mertens 1976; Iannelli 1985, 2005; Iannelli & Rizzi 1985; However, while recognizing the overall importance of these Treziny, 1989; Barello 1995; Parra 2001). latter effects, the present study focuses especially on the role Coastal and nearshore stratigraphic, geophysical and of tectonic displacement that can locally disrupt the pattern archaeological databases have recently been collected to better of expected Holocene relative sea-level rise and landward interpret the causes of shoreline shifts in this sector (data in coastal advance. The aim of this investigation is to provide Stanley et al. 2007). These are integrated to determine why insight on the specifics of Holocene shoreline changes through and when the Kaulonia shoreline shifted back-and-forth over time in a highly mobile setting that has a long record of human a distance of at least 400 meters, during a period of less than occupation and settlement. There are many examples of such 5000 years in the mid- to late Holocene. 

Naples N A ITALY B ITALY Albanides Gulf of

Tyrrhenian Tyrrhenian Basin Sea K Straits of Squillace Gulf 39° MM Kaulonia Calabrian Hellenides Arc SICILY

0 200 km Ionian Sea Area of Greek 14° 18° 22° colonization

Fig. 1 - A, Location of Kaulonia (K), just north of Marina (MM) on the Ionian Coast of Calabria, southern Italy (modified after Crescentiet al. 2004); the archaeological site is positioned within the Ionian forearc basin of the Calabrian Arc (Fig. 2B). B, Kaulonia was in , a major sector of ancient Greek colonization. Fig. 1 - Localisation de Kaulonia

2 - Study area setting Monasterace Marina (MM in Fig. 1A). Kaulonia was conquered in 389 B.C. by Dionysius the 1st, of Syracuse, and its Kaulonia was a rather modest-size Magna Graecia colony, settlers deported to Locri, a colony positioned about 40 km to one of several on the Ionian coast of Calabria (Randall- the SSW. A settlement was then rebuilt at the original Kaulonia Maciver 1931; Schmiedt 1975). It was founded by the , site by the Brettii, a nomadic tribe in the 3rd century B.C., and a people from the Peloponnesus, and perhaps also by settlers was conquered once again, this time by the Romans in 205 B.C. from Kroton (Crotone), another Greek settlement located to the The gentle arcuate headland immediately to the north of the site northeast (Fig. 1B). Archaeological excavations at Kaulonia is known as Punta , or Cape of Columns (Fig. 3). It has had are positioned immediately north of the small coastal town of this name at least as far back as about 2000 years ago when the

Fig. 2 - A, Upper, Location of Kaulonia (K) shown on a simplified schematic tectonic map of the Calabria-Peloritani terrain (CPT), bounded by the Sanginetio (SL) and (TL) tectonic lines, and subduction types. K=Kaulonia. Lower, Structural section A-B across the Calabrian Arc depicts structural offset and nappes on land and at sea (modified after AROTTOP & PRATURLON 2004). Fig. 2 - Croquis structural simplifié du secteur étudié. 

10 m that subsided after time of Greek occupation (STANLEY modern modern et al. 2007). Diving observations and numerous closely-spaced Assi River Punta Squillace Gulf Stilo (<200 m apart) seismic profiles indicate that this headland was 5 m apparently without lagoon, or sufficiently deep waterway, or man-made port facilities to provide protected anchorage 1 Punta Stilo 2 shoreline (Fig. 3). Moreoever, recent analysis also shows that a sector of at 500 B.C. MON I the now-submerged surface, which currently lies at a depth of m 4 5 3 5 to 7 meters below mean sea level (msl), had been partially covered by stratified sandstone originally formed along the former beachline to foreshore zone during the latter half of the Holocene. Assi positions bollards

sandstone 10 m slabs MON II ancient wall archaeological material 10 m fault t shoreline depth 5 - 7 m terrace

presen KAULONIA N dune section former temple coastline 0 200 m

Fig. 3 - Paleogeographic scheme of the Kaulonia margin shows major Holocene coastal shifts: from former shoreline position (1), to seaward (2), and then return to the present coastline (3, 4). Dots represent mapped offshore archaeological material northeast of the Doric temple, Kaulonia’s major structure (after LENA & MEDAGLIA 2002). Cores MON I and II were recovered on and just landward of present coastal dunes. Interpretation of the offshore sector is based on dense coverage by geophysical lines (data in STANLEY et al. 2007). The time and spatial variations are discussed in text. Fig. 3 - Croquis géomorphologique présentant la mobilité des lignes de rivage à l’Holocène dans le secteur de Kaulonia. locality was cited by Pliny the Elder in his The Natural History. This suggests that columns may still have been visible to the Romans in this sector to about 2000 years ago, i.e. perhaps as long as 3 to 4 centuries after exile of the Greek settlers in 389 B.C.

It is thus of special interest in this respect that numerous large fluted column sections and other archaeological materials were discovered by divers in the mid- to late 1980’s at water depths to 7 m up to 300 m offshore Kaulonia. The description, depth and geographic coordinates of each of the more than 100 features were carefully recorded (Iannelli et al. 1993; Lena & Medaglia 2002; Medaglia 2002a, b). Archaeologists working at the site suggested that the numerous columns had been manufactured along the coast and/or unloaded from ships sailing to this once-active trading center in Greek time. Until recently, archaeologists postulated that the configuration of the coastal strip on which the columns were originally placed, prior to coastal submergence, was a small, distinctive, low- lying hook-shaped cape (Iannelli et al. 1993; Lena & Medaglia Fig. 4 - A, Construction block at a depth of about 6 m on seafloor off Kaulonia (after IANNELLI et al. 1993); boulders, of Assi River derivation, are to 60 cm 2002). in diameter. B, Stratified marker unit of beachrock-type sandstone (S) with large cobbles (C) in mid- and lower stratum; it is about 1 m thick (see scale) However, more recent geoarchaeological analysis using data and broken to form large rock slabs offshore (see Fig. 3). EC=erosional cut of unit by high-energy sand and water motion. C, Stratigraphically comparable from geophysical and coring surveys (the reader is directed welded sandstone (S)-cobble (C) unit exposed at the seaward-facing base of to high-resolution seismic profiles and lithological core logs coastal dune system north of the Doric temple (Stanley et al. 2007). See cm shown in Stanley and others 2007) indicates that the seafloor scale for thickness. Photos courtesy of S. Mariottini. Fig. 4 - A. Bloc de construction vers 6 m de profondeur. B. Vue sous-marine on which the columns were discovered was actually only a d’un affleurement de beach-rock. C. Vue à terre d’un affleurement de beach- small part of a broad arcuate (not small hook-shaped) headland rock comparable. 10

This surface seaward of Kaulonia, comprising sandstone slabs, 3 - Stratigraphic marker to define coastline cobbles and boulders and archaeological material (Fig. 4A,B), migrations appears to have been submerged completely beneath sea level during a time-span of approximately four to five hundred years. Based Recent geological evolution of the Kaulonia coastal margin on artifacts recovered on the seafloor, the period of lowering and its shoreline migrations are determined by using a distinct lasted from roughly 400 B.C. near the end of Greek occupation litho-stratigraphic marker (beachrock-and-cobble horizon) to the time of Roman rule in about the 1st century A.D. ranging from mid- to late Holocene age, depending on its location seaward (Fig. 4B) or landward (Fig. 4C) of the shoreline. Bathymetric measurements (Iannelli et al. 1993; Lena & This unit can be traced laterally for a distance of at least 400 m, Iannelli 1996) show that the present seafloor surface in the from two cores collected on land behind dunes, about 100 m study area extends fairly regularly seaward from the shoreline shoreward of the present coastline, to offshore sectors at least to a depth of ~6 meters. Here, it then levels or rises locally to 300 m seaward of the shoreline (Fig. 3). Throughout this broad ~3.5 meters below msl (in offshore bar-like fashion), before area, the marker unit presents a generally consistent thickness once again deepening progressively seaward to depths of (~1 m; Fig. 4B, C) and lithology. Beachrock sandstone is 20 meters and more on the Ionian shelf. It is on a segment of formed mostly of Assi River detrital mineral grains cemented this inclined offshore surface, in an area about 250 m by 500 m, by high Mg-calcite and dolomite, and pebbles and cobbles are that large column sections, column bases, construction blocks, of Assi headwater metamorphic and igneous composition. bollards and anchors were discovered (depicted as dots on Radiocarbon dating of the carbonate cement indicates that the Fig. 3), along with numerous potsherds and bronze, lead, and beachrock unit recovered in core MON I (position of maximum copper fragments (Lena & Medaglia 2002). The columns are ingression shown in Fig. 3), lying ~2 m beneath sediment with dated stylistically to about 480-470 B.C. Archaeologists have Greek artifacts, is of mid-Holocene (pre-4500 yrs B.P.) age determined that the large number of column sections (length (Stanley et al. 2007). Radiocarbon analysis of the moderately to 113 cm, diameter to 80 cm) and other materials on the to poorly consolidated stratified beachrock sandstone provides seafloor (Fig. 3) were not distributed haphazardly as a result of variable ages, including some to early Holocene. Samples shipwrecks (Lena & Medaglia 2002). Rather, these and other recording such older ages likely indicate dates of introduced archaeological features are positioned at, or proximal to, once- reworked (by groundwater, run off and other) and weathered exposed coastal nearshore surfaces upon which they were carbonate and dolomite that forms the cement rather than the worked and/or from which they were discharged from vessels. more recent time of beachrock formation. Larger column sections are usually positioned further seaward Archaeological examination of Greek materials discovered at greater depths than smaller sections. It has been suggested offshore indicates their ages as being approximately 2500 years that the construction materials were at Kaulonia for the building B.P. These construction features are commonly associated with of a temple or other major structure. However, excavations to the sandstone-conglomerate stratigraphic marker sequence date at the site have provided no evidence that such a project presently at depths of 5 to 7 meters below sea level (Figs. 3, was completed (Orsi, 1916; Treziny 1989; Iannelli 1992, 1997; 4B). Where found, it is of note that both archaeological material Parra 2001).

Offshore archaeological material rests on, and is associated with, large slabs of stratified Holocene sandstone strata interpreted as beachrock cemented in the mid- to late Holocene (Stanley et al. 2007). The sandstone, commonly with pebbles and cobbles (Fig. 4B, C), had once formed at, or possibly near, the spray zone (cf. Alexandersson 1972; Dalongeville 1984; Bernier & Dalongeville 1988; Fouache et al. 2005) and/or the shallow submerged sector of a former coastline (cf. Milliman 1974). These slabs are surrounded by rounded cobbles and large boulders (Fig. 4A) of igneous and metamorphic lithologies originally derived from headwaters of the Assi River in the Serre mountains (Ibbeken & Schleyer 1991). The now much smaller stream presently flows to the coast about 500 m north of the Kaulonia site. The most recent paleogeographic reconstruction (Fig. 3) has been compiled on the basis of geophysical survey profiles offshore and analyses of cores (length to 20 m) collected on land. It appears that ships arriving at the site were most commonly anchored close to shore and/or beached. Moreover, the Assi River at the time of Fig. 5 - Site locations (small numbers) of Tyrrhenian marine terraces on land Kaulonia’s existence flowed southeast of its present location and their elevation in meters above msl (bold larger numbers) in southern Italy. (Fig. 3), and vessels were thus probably also secured near, or K=Kaulonia. Map is modified from BORDONI & VALENSISE (1998), where these authors provide data (their Table 1) on terrace elevations and ages, and within, the channel mouth when the river was not in flood reference sources from where data are derived. (Stanley et al. 2007). Fig. 5 - Altitudes des terrasses tyrrhéniennes. 11 and marker unit offshore lie at least 2 to 3 m deeper than can probably from the coast seaward of the temple (see sandstone be readily accounted for by (1) recent strong coastal, shoreface slabs in Figs. 3, 4B; Stanley et al. 2007). Beachrock sandstone and seafloor erosion effects and (2) world sea-level stand and at Kaulonia is similar to that identified on many Mediterranean rise during the past 2500 years (cf. Fairbanks 1989; Lambeck & coasts (Alexandersson 1972; Dalongeville 1984). Of note are Purcell 2005). A third component affecting depth, (3) sea-floor those distributed along the Calabrian Ionian coastal margin subsidence of 2.5 ± 0.5 m or more during the past ~2500 years, and identified as late Holocene in age (Pirazzoli et al. 1997). appears to best explain the extra lowering of seafloor surface between the coast and inner shelf. This recent subsidence phenomenon alone would account for an averaged Holocene 4 - Causes of shoreline migrations long-term mean submergence rate of nearly 1 mm/year. To determine the causes of shoreline reversals at Kaulonia, it It is noted that this submergence rate value is quite similar is useful to assess several salient aspects of local to the rate of averaged long-term Quaternary uplift measured and tectonics. landward of the coast in this Calabrian sector, where a land • Chrono-stratigraphic interpretations that take into account surface rise of ~0.9 mm/year and greater has been recorded the spatial and temporal distribution of the inclined sandstone- (Westaway, 1993; Dumas and Raffy, 1994; Dumas et al. 1995; conglomerate marker unit serve to define coastal-inner shelf Bordoni & Valensise 1998; Ferranti et al. 2006). These paleogeographic changes through time and measure migrations different authors determine uplift landward of the Kaulonia of Kaulonia's coastline over a distance of 400 m since the mid- coast by measuring the present elevation of terraces of Holocene. The nearshore marker unit that defines coastal shifts Pleistocene and Holocene age that had once formed at or close from ~4500 to 2500 yrs B.P. is viewed as a time-transgressive to sea level. Particularly valuable in this respect are marine stratigraphic horizon. It indicates that the mid-Holocene terraces formed during the climatic optimum or maximum shoreline had shifted landward, submerging the coastal margin transgressive, known historically as the Tyrrhenian highstand, to ~100 m inland of the present shoreline at about 5000-4500 dated at about 125,000 years ago and most closely correlated yrs B.P. This was followed by a seaward-directed migration that with substage 5e of the oxygen isotope record. For example, then subaerially re-exposed the coastal margin at some time terrace levels in a proximal sector of southern Calabria (hills between ~4500 years B.P. and early occupation of the site by behind Marina and west of Soverato, denoted as sites the Greeks about 2700 years ago (coastal shift 1 to 2 in Fig. 3). 65 to 74 in Fig. 5) have been uplifted to elevations ranging from After that time, Kaulonia’s coastal margin, partially covered 90 to 113 m above msl (Cosentino & Gliozzi 1988; Bordoni & by the Greek column sections and other construction material, Valensise 1998). was subject to a second phase of Holocene submergence. This most recent event is dated after exile of the Greek population Seaward, the closely-spaced high-resolution geophysical in the 4th century B.C., and was probably underway by Roman profiles obtained in a 1 km2 area just off Kaulonia (Stanley et al. time in the 1st century A.D. (to 3 in Fig. 3). Transgression of 2007) record the presence of a distinct sub-bottom reflector the shoreline westward to its present position continued during that lies 1 to 4 m beneath the present sediment-water interface. most of the past 2000 years (to 4 in Fig. 3). This now-buried dense acoustic reflector is identified as the • A tectonic axis positioned close to the present coastal margin stratified sandstone-conglomerate marker unit (Fig. 4B) that (Fig. 2B) is suggested by the measured near-equivalent averaged forms the substrate upon which rest archaeological materials rates of land uplift (0.85 - 0.90 mm/year or more) and offshore (Iannelli et al. 1993), and which can be traced between the submergence (~1.0 mm/year). It appears that a geologically shallow nearshore and inner shelf. Unfortunately, after 1991, recent 'see-saw' motion (upward on land, downward offshore) both distinct horizon and associated archaeological features on took place in the proximity of the study area, with an axis the seafloor were almost entirely covered by storm-reworked positioned at or near the coast (Fig. 7B). None of the 48 high- sands (locally to 4 m thick) that had been driven shoreward (Dr. resolution, shallow penetration geophysical profiles (37 kms S. Mariottini, Associazione Culturale Kodros, 2006, personal of seismic line) that cross the entire seaward sloping surface communication based on dive records). A comparable unit, between the shoreline and 1000 m offshore Kaulonia record about 1.0 to 1.5 m thick and comprising sandstone welded upon major faults or other structural offset (Stanley et al. 2007, conglomerate, was observed as a 100 m-long subaerial exposure their figures 4-6). This suggests that late Holocene seafloor near the base of dunes north of Kaulonia’s temple (Fig. 4C) submergence occurred largely as the result of a downward- and also in sediment cores (elevations to near and above msl) directed tilt motion, with minimal offshore offset, at least recovered farther inland behind the dunes (MON I and II, in within the upper ~10 m of strata. Seismic activity then and Fig. 3). This would account for an incline of about 1:40, from subsequently may have caused some downslope and seaward +2 m above msl on land to -7 m offshore over a distance of less displacement of anthropogenic structures such as column than 400 m. sections. • The terrain on land, between the sector that extends from It has recently been observed that the base of the Doric just behind the dunes at the coast proper to hills that back temple at Kaulonia is formed of stratified carbonate-cemented Kaulonia, presents a markedly different configuration (Figs. sandstone similar lithologically to the one in the stratigraphic 5, 6). Sequences of and Quaternary deposits are marker unit discovered both on land and offshore. It appears characterized by numerous structural offsets and faults, and that this temple base material is formed of cut beachrock blocks also gravitative downslope slide and slump displacement (carta I believe were obtained locally by the Greek settlers, i.e. most geologica della calabria 1968; Patacca & Scandone 2004). 12

Fig. 6 - Structurally displaced terrain at the Kaulonia coast. A, B, Steep back-beach terrain in vicinity of the Doric temple (~10 m relief), formed of alluvial sediment partially fronted by dune sand. Arrows in A identify dipping (perhaps slide) bedding. C, View from offshore toward hill top (40 m elevation) on which lighthouse was built behind and north of the Doric temple; dissected and step-like topography, formed by marine and terrigenous Pleistocene and Quaternary deposits, record faulting and slump displacement. Also evident is tilted offset surface of the 10-m tectonic terrace that rises above the back-beach. D, View toward southeast, showing tectonically offset Pliocene and Quaternary terrain between base of lighthouse hill and the coastline (distance of ~260 m); arrow in distance points to base of Doric temple. Coast-parallel road SS-106 provides scale. Fig. 6 - Mobilité tectonique dans le secteur de Kaulonia.

Recent structural motion, for example, is recorded by Quaternary records a major shoreline regression to at least as far as ~300 m alluvial sediment strata that form the terrace-like (tectonic, non- seaward of the present coast by about 2500 years ago (Fig. 7B, 2). fluvial) platforms that abruptly rise above the beach and whose Finally, coastline migration reversal began once again in stratal surfaces are inclined (Fig. 6A, B). The top of the plateau- Roman time (Fig. 7C, toward 3), with the dominant landward like tectonic feature at the back-beach ranges from 8 m to 10 m shift (transgression) continuing during the past two millennia in elevation above msl (Fig. 6C), and its steep seaward face is until the shoreline reached its present position (Fig. 7C, 4). The partially fronted by dune sand. Exposures in back-beach dunes back-and-forth migration during the mid- to late Holocene is and terrains just behind the dunes, within 100 m of the present attributed primarily to uplift and a change in slope inclination of shoreline, reveal displaced and offset sediment sequences that the seaward-tilted surface off the present coast. During the early comprise both alluvial (some mud-rich) and nearshore (sand- to mid-Holocene, the gentle and relatively uniform offshore rich) strata (Fig. 6A, B). It appears that Kaulonia's coastal sloping surface induced the shoreline to migrate landward evolution during the Holocene has involved episodic uplift primarily as a result of relative sea-level rise (Fig. 7A). However, resulting in an irregular terrain morphology of sediment strata when the seafloor was subsequently uplifted near shore and landward of the coast (Fig. 6C, D). In marked contrast, the surface inclination increased, the shoreline began to reverse more continuous seafloor surface and subbottom Holocene direction seaward (Fig. 7B). strata offshore (seismic profiles in Stanley et al. 2007) appear modified more by a downward tilt motion seaward than by a As the coastline migrated back offshore, the previously series of major fault breaks as noted on land. submerged coast to inner shelf sector once again became subaerially exposed, and thus readily accessible to the Greeks Integration of the above observations is summarized here settling at Kaulonia. Exposed beachrock in the coastal area by a series of simplified diagrams (Fig. 7). The nearshore (Fig. 7B) was exploited by the settlers. For Kaulonia’s temple stratigraphic marker (sandstone-cobble unit) indicates that the base construction alone, it is calculated that the cut beachrock shoreline had transgressed to a position 100 m landward of the material would have covered a surface area of at least 1250 m2. present coast by 4500 years ago (Fig. 7A, 1). This key unit then This would be equivalent to a shore-parallel sandstone exposure 13

landward side of the coast in the study area and, concurrently, a substantial amount of offshore tilt. Since time of exile of the settlers from Kaulonia after ~2400 B.P., the local coastal margin has generally been affected by less powerful tectonic phases of landward rise and somewhat more gentle submergence of the offshore sector. These somewhat more stable conditions during the past 2000 years have resulted in an increased effect of relative sea-level rise rather than primarily of tectonics, thus causing the coastline’s landward shift to its present position.

5 - Conclusions

Holocene coastal evolution in the world’s low and mid-latitudes is most often characterized by marine transgression due largely to relative sea-level rise but, as reported in the present study, not all coastlines in these regions have migrated consistently or uniformly landward. This investigation demonstrates that marine regressions occurred on some coastal margins where effects of significant tectonic displacement exceeded those induced by more progressive eustatic or relative sea-level rise. The offshore coastline migration recorded at Kaulonia in the Calabrian Arc during the mid- to late Holocene was a response to increased structural mobility that affected this margin located within the mobile Ionian forearc basin. Geologically recent uplift pulses raising terrains landward of and at the shore most likely was the major cause of re-emergence of Kaulonia’s earlier submerged coastal margin. It is expected that this type of tectonically activated coastal regression also occurred at Fig. 7 - Simplified series of sketches to show use of archaeology, sedimentology and stratigraphy to explain major coastline shifts (1) to (4) various times during the Holocene in other structurally mobile at Kaulonia (see Fig. 3). Noted are lateral displacement of the beachrock- margins of the Mediterranean, such as in the Hellenic and cobble unit over a distance of 400 m in this mobile sector of the Ionian forearc arc settings. basin of the Calabrian Arc (Fig. 2B). A, Early to mid-Holocene transgression (black arrow) and westward coastline position (1), due primarily to effects of There is growing awareness of the need to improve protection relative sea-level rise. B, Reversed mid- to late Holocene seaward migration of coasts, especially in Mediterranean sectors where population of the shoreline (regression, black arrow) from (1) to (2) during mid- to late growth and a large number of municipal and industrial projects Holocene; this was primarily induced by a major tectonic uplift phase and ‘see-saw’ motion at or very near coastal axis. C, Post-Greek shoreline have considerably increased. Engineers and coastal managers migration once again shifted landward, largely the result of rise in relative tend to focus primarily on vulnerable, moderately stable, sea-level. No beachrock forms at present. Further explanation in text. low-lying margins, while some equally precarious nearshore Fig. 7 - Trois principales phases de mobilité des rivages à Kaulonia depuis l’Holocène moyen. sectors subject to major tectonic displacement have received substantially less attention. The major point herein is that 100 m long by 12.5 m wide and 40 cm or more thick (Stanley valuable insight on shoreline changes is to be gained where et al. 2007). Thus, once exposed and readily visible along information on geological structural mobility is integrated with the beach and foreshore, this deposit may well be one of the records of long-term human activity. This geoarchaeological major reasons the locality near the Assi River was originally approach also serves to better devise and implement more selected for colonization by the Greeks. effective long-term coastal protection measures. In a final phase, the shoreline once again migrated progressively landward. This has taken place during stabilization of the seafloor surface elevation and its inclination, and a relative sea 6 - Acknowledgements level rise that continued in Roman time (Fig. 7C, 3). The general quiescence phase appears to have persisted until the present My sincere thanks are expressed to Drs. M.P. Bernasconi, (Fig. 7C, 4). M.T. Iannelli, S. Mariottini, and T. Toth for their valuable Increase of seafloor elevation and inclination was likely advice and assistance with the initial Kaulonia field study, induced by one or several powerful, regionally important contributions to geophysical and core data collection, and tectonic pulses in the mid- to late Holocene. Geological studies providing essential photographic documentation. Any errors in this region (Gasparini et al. 1982; Dumas & Raffy 1994; Dumas introduced in this analysis that focuses on tectonic triggering et al. 1995; Pirazzoli et al. 1997), and in more distal parts of of shoreline migrations at Kaulonia are the responsibility southern Italy (Amato & Montone 1997; Cucci 2005), recorded of the author. Technical assistance with the present study evidence of increased regional arching and marked uplift that was provided by Ms. K. Carnes, Mr. T. F. Jorstad, and Ms. caused tectonic instability and deformation in the Calabrian M. Richardson, National Museum of Natural History (NMNH). Arc during this time-span. These caused increased uplift on the Constructive suggestions given by Dr. C. Vella and two 14

anonymous reviewers helped improve the manuscript. Funding kind auspices of the Soprintendenza, Beni Archeologici was obtained from the NMNH-Smithsonian Institution, della Calabria (Dr. M. T. Iannelli) and the University of Calabria and facilities in the field were made available through the (Dr. M.P. Bernasconi).

7 - References

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