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A feasibility study for the investigation of submerged sites along the coast of Slovenia [2009]

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Maritime investigations along the Northern Adriatic coast have traditionally focused on the Roman and later archaeology. However, studies of post-glacial sea-level change and shoreline displacement suggest there is significant potential for the
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   The International Journal of Nautical Archaeology  (2009) 38  .1: 163–172doi: 10.1111/j.1095-9270.2008.00210.x  © 2009 The Authors. Journal Compilation © 2009 The Nautical Archaeology Society.Published by Blackwell Publishing Ltd. 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA.  BlackwellPublishingLtdJ.BENJAMIN&C.BONSALL:INVESTIGATIONOFSUBMERGEDSITESALONGTHECOASTOFSLOVENIA  A Feasibility Study for the Investigation of Submerged Sitesalong the Coast of Slovenia  Jonathan Benjamin and Clive Bonsall  School of History, Classics and Archaeology, University of Edinburgh, Old High School, Infirmary Street,Edinburgh, UK   Maritime investigations along the Northern Adriatic coast have traditionally focused on the Roman and later archaeology.However, studies of post-glacial sea-level change and shoreline displacement suggest there is significant potential for thediscovery of sites close inshore dating back to the early- to mid-Holocene, c  .9000 BC onwards. A feasibility study for theinvestigation of submerged sites along the coast of Slovenia was undertaken in 2005. Here we describe the project rationaleand research design, the survey and recording methods used, the logistical problems encountered, the results obtained (regardlessof age), and the prospects for future research in the region.© 2009 The Authors  Key words: Neolithic, underwater, Slovenia, Adriatic, Piran, survey.  S  ince the 1980s increasing attention hasbeen paid to the underwater archaeologicalrecord of Slovenia. This is due, in largepart, to the work of Dr Andrej Gaspari and theUnderwater Archaeology Group (  Skupina za podvodno arheologijo  ) in Slovenia (Gaspari, 1998;Gaspari et al.  , 2001; Gaspari 2003; Gaspari, 2006).Although an impressive range and quantity of archaeological materials have been recoveredfrom underwater sites in Slovenia, most of thisfieldwork has been conducted at inland riverinesites. Less emphasis has been placed on theSlovenian coastal zone at the head of the AdriaticSea (Fig. 1) where prehistoric activity is poorlydocumented and much of the underwater researchhas been concerned with Roman archaeology(Bonton-Tome, 1989; Knific, 1993; Gaspari, 2005).The impact of physical changes in the landscapeand coastline of the north-east Adriatic regionsince the Late Pleistocene has been significant,and it is widely accepted that sea-level rise duringthe earlier part of the Holocene would haveinundated many coastal sites dating to this period(Barfield, 1971; Marocco, 1991; Boschian, 1993;Budja, 1996; Biagi, 2003; Forenbaher and Miracle,2005). Furthermore the prehistoric record of coastalSlovenia, particularly that pre-dating the use of metals, is largely unknown (Mleku  z  , 2005a: figs26–9). The survey described in this paper representsan srcinal study of the potential for underwaterarchaeological discovery in the Slovenian Adriatic,particularly those areas that were submerged bythe post-glacial marine transgression (Fig. 2).On-site planning for the feasibility study of thenorth-east Adriatic Sea began in 2004. Designedas a non-disturbance survey, the approach wasbased on the predictive models developed byDanish archaeologists searching for submergedMesolithic and Neolithic sites in the Baltic Sea(Fischer, 1993; Fischer, 1995), as well as underwaterarchaeological methods established over the pasthalf-century (Bass, 1966; Wilkes, 1971; Muckelroy,1978; Dean et al.  , 1992). The diving was donemainly at depths of between 10 and 20 m, andwas designed not only to address archaeologicalquestions directly, but also to investigate thepotential effects of geological/sedimentological,topographic and biological conditions on theprospects for underwater archaeology in theSlovenian Adriatic. Assessing the physical andlogistical variables helped to predict zones of potential archaeological interest. The survey methodsand findings were systematically documented inline with standard archaeological practice; allcultural materials were recorded, regardless of age. The results of the initial (summer 2005) fieldseason and the methodologies employed arediscussed in this paper.   NAUTICAL ARCHAEOLOGY, 38  .1  164© 2009 The Authors. Journal Compilation © 2009 The Nautical Archaeology Society  The Slovenian Adriatic coast  Erosion patterns, sea-floor topography, and sea-levelchanges all influence the location of potentialsubmerged archaeological sites. The physicalenvironment and those variables that affectunderwater archaeological survey were principalconsiderations prior to the survey. The Gulf of Trieste is isolated from the rest of the AdriaticSea by a shoal between Grado, Italy, andSauvudria, the north-westernmost point of Istria,in Croatia. In between the Point of Sauvudriaand Punta Grossa (the modern Italian border),lie 46 km of coastline belonging to Slovenia. Thegulf itself is a relatively shallow basin with anaverage depth of 20–25 m (Ogorelec et al.  , 1991).The underlying geology of coastal Slovenia ispredominantly Eocene flysch except for a smalllimestone outcrop at Izola (Pav  s  i  c  and Peckmann,1996: fig. 1). Since the flysch comprises mainlylayers of clay marls and sandstone, withintermittent limestone units, erosion patternsdiffer greatly from those just a few kilometres tothe south-west in Croatian Istria, which consistsmainly of Cretaceous limestone. Coastal erosionof the flysch sediments has resulted in steep cliffsat the site of former ridges, while the interveningvalleys have evolved to become the predominantlymuddy Bays of Koper and Piran.The river systems along the coasts of Sloveniaand north-east Italy contribute to the underwaterenvironment by continuously depositing largequantities of sediment in the gulf (Ogorelec et al.  , Figure 1. Location map. (Clive Bonsall) Figure 2. Sea-level curve for the Northern Adriatic (basedon Lambeck et al. , 2004) superimposed on the long-termrecord from Barbados (Fairbanks, 1989). The dotted linesrepresent the upper and lower limits of predicted sea-levelsin the Northern Adriatic. The shaded zone represents theperiod during which farming is thought to have spreadthrough the region. (Clive Bonsall)   J. BENJAMIN & C. BONSALL: INVESTIGATION OF SUBMERGED SITES ALONG THE COAST OF SLOVENIA  © 2009 The Authors. Journal Compilation © 2009 The Nautical Archaeology Society165  1991; Vahtar, 2003). The main rivers of theSlovenian coast are the Ri  z  ana and Badasevicawhich terminate in Koper, and the Dragonja,which terminates at the salt-flats of the Bay of Piran and delineates the political border withCroatia. While the rivers deposit finer sedimentsin the bays, which create problems for underwaterarchaeologists, areas largely devoid of clay andsilt do occur sporadically along the coast. Sandybottom conditions are much more frequentfurther from the shore (Ogorelec et al.  , 1991).Present sedimentation rates in the inner baysof Koper and Piran are estimated to be in theorder of 5.3 mm per year (Ogrinc et al.  , 2005). Apeat layer at 26.5 m depth sampled by a sedimentcore (V6) taken from the inner salt marsh of Piran Bay gave a 14  C age of 9120 ± 120 BP (  c  .8110cal BC; Ogrinc et al.  , 2005), indicating an averageaccumulation rate for the overlying sedimentsof  c  .3 mm per year. This compares with anestimated sedimentation rate in the central Gulf of Trieste of just 1 mm per year, increasing to 2.5mm per year toward the Isonzo river mouth innorth-eastern Italy (Ogrinc et al.  , 2005). Furthersouth, in the Croatian waters of Istria, which areunderlain by limestone, offshore samples fromnear Pore  c  suggest a sedimentation rate of only0.03 mm per year (Ogorelec et al.  , 1991). Thesedata reflect the influence of local geology, soilsand erosion (essentially the difference betweenflysch and limestone) on the Holocene sedimentsof the sea-bed.Sedimentation is an important considerationin underwater archaeological fieldwork. Riversdraining the Eocene flysch deposit large amountsof sediment into the bays (Ogorelec et al.  , 1997),thus sedimentological factors must be acknowledgedas having a significant impact on the underwaterarchaeological potential of the Slovenian Adriatic.While this presents a considerable challenge, it doesnot mean that these areas lack archaeologicalpotential. Many variables impact site discovery(Flemming, 1983) and high sedimentation-ratesdo not always preclude the discovery of Stone Agematerial on the sea-bed (Fischer, 2007). Sedimentationcan also protect prehistoric archaeological sites(Geddes et al.  , 1983; Malm, 1995; Lübke, 2001;Momber, 2001). Therefore, the potential forunderwater archaeology in the Slovenian Adriaticshould not be assessed on the basis of sedimentationpatterns alone. Radiocarbon dates as old as9160 ± 50 BP (  c  .8230 cal BC), corresponding tothe Early Mesolithic, have been obtained fromcore samples taken from depths of just 0.5–2.0 mbelow the sea-floor at c  .22 m below sea-level(Ogorelec et al.  , 1997; Ogrinc et al.  , 2005: fig. 1),and this raises the possibility that archaeologicalmaterial from the late Stone Age may lie in situ  less than a metre below the sea-bed.The prevailing current of the Gulf of Triestehas a counter-clockwise motion, entering the gulf from the point of Savudria, Istria, and exiting atthe lagoons of north-eastern Italy (Ogorelec  et al.  , 1991; Vahtar, 2003). Salinity levels withinthe Gulf of Trieste range from 33 to 38.5% in thesurface layer, and a slightly saltier 36–38% closeto the bottom. Temperature varies substantiallyaccording to season, and surface temperaturescan be as cool as 8  °  C in the winter, reaching 24  °  Cin the summer. Bottom temperatures are lower,ranging between 8  °  C and 20  °  C (Ogorelec et al.  ,1991). Some tidal movement occurs in the NorthAdriatic, but the tidal range is generally small(<0.5 m) compared to the world’s major oceanbasins, though the amplitude rises gradually fromsouth to north in the Adriatic (Ogorelec et al.  ,1991; Vahtar, 2003).  Survey methodology  A preliminary assessment of potential surveylocations was undertaken in early 2004 using a1:75,000-scale chart of the Gulf of Trieste.Initially, modern political borders were ignored;emphasis was placed on depth and bathymetriccontours, and areas likely to represent submergedriver-mouths, inlets, bays, points, and headlands.The field survey began in June 2005 and allfindings of archaeological significance were reportedto the  Zavod za Varstvo Kulturne Dedi   ßç   ine  (Institutefor the Protection of Cultural Heritage). Teamsof two SCUBA divers surveyed under water on arotating basis. The two primary search-patternsemployed were the linear and circular surveymethods (Wilkes, 1971: fig. 2). In all cases, GPSlocations were taken from surface marker-buoys,using the GPS/Sonar unit on board the 21-ft diveboat.A linear, jackstay survey-pattern was adoptedusing two surface buoys, each attached to a 15 kgcement weight and connected by a 100-m negatively-buoyant rope. A pulley and counterweight systemattached to the underside of the surface marker-buoy ensured a taut line (Fig. 3). The marker-buoy would thus float vertically above the cementweight and the marker-buoy’s position wasrecorded by GPS. The pulley and counterweightsystem allowed for some movement of the line   NAUTICAL ARCHAEOLOGY, 38  .1  166© 2009 The Authors. Journal Compilation © 2009 The Nautical Archaeology Society  caused by wind and wave action. The 100-mhorizontal line on the sea-bed allowed the surveyorsto follow the desired survey path without having totake underwater compass readings, and enabledaccurate documentation of the area surveyed.At survey locations where a 100-m linearsurvey was not appropriate, for example where thesea-bed was cluttered with debris or the topographywas irregular, close-cover, circular survey wasemployed (Fig. 4, right). An area with a diameterof 20 m was covered by each circular survey.Each diver surveyed one half of the circle,starting at the deepest point and swimming in azigzag pattern. This survey technique, controlledlongitudinally by the length of the rope, allowedfor a more thorough close-cover survey of thearea by both divers, especially as overlap betweenthe areas covered by each diver often occurs.  Survey results  The first discovery of archaeological interestduring the survey was a circular stone feature(Fig. 5), recorded at approximately 7 m depth, tothe west of a well-defined headland, and less than100 m from the shore. It measures 3 m indiameter and consists of rounded stones rangingfrom 10 to 30 cm in length. In some places thestones are stacked on top of one another severalstones high. The feature is probably larger thanrecorded, since at the outer edge the stonesdisappear beneath the sand and grass on the sea-bed.There was no sign of other stones or archaeologicalmaterials in the immediate vicinity, and norecognizable artefacts associated with the feature.Although the lithology is sandstone, all thestones are heavily rounded; there were no angularfragments among them, which suggests they werenot derived from the flysch cliffs nearby. Fromthis evidence, reinforced by the opinions of regionalexperts (Smiljan Glu  sc  evi  ç  , Head of ZadarArchaeological Museum, Underwater Division,Croatia; Andrej Gaspari, Principal UnderwaterArchaeologist Zavod Slovenia; Dr CarloBeltrame, Underwater Archaeologist, Universityof Venice, Italy), the circular stone feature probably Figure 3. The pulley and counterweight system used to keep the survey line taut. (Jon Benjamin) Figure 4. Left: linear survey. Right: circular survey. (Jon Benjamin)   J. BENJAMIN & C. BONSALL: INVESTIGATION OF SUBMERGED SITES ALONG THE COAST OF SLOVENIA  © 2009 The Authors. Journal Compilation © 2009 The Nautical Archaeology Society167  represents ballast dumped from a ship, althoughit is conceivable that it is the remains of a shipwreck.  Punta Piran  A significant amount of time was spent surveyingthe near-shore waters around the Point of Piran.Piran, located on a peninsula and once part of the Republic of Venice, has been a documentedcentre of human activity for millennia (Ter  c  on,1993). Previous underwater archaeologicaldiscoveries near Piran include a Roman shipwrecksalvaged in the 1950s (Bonton-Tome, 1989;Knific, 1993); Roman and earlier, middle and lateLa Tène Iron Age materials have also been foundon land (Gu  s  tin, 1987). The sea-floor off thePoint of Piran shelves steeply, resulting in arelatively high depth:distance-to-shore ratio (Fig. 6).Bottom composition varies according to depthand location. To the west, just off the tip of thepeninsula, sandy or sandy-silt bottom conditionsprevail to depths of over 20 m. Along the southside of the peninsula, sediment cover increases inthickness and the silt content is higher, thoughthere are sandier areas on the south-west marginof the peninsula.  Portable artefacts identified  The results of the 2005 survey, and previousexpeditions (Knific, 1993), clearly demonstrate Figure 5. Stone feature protruding from the sandy sea-bed. (Jon Benjamin) Figure 6. Aerial photo of Punta Piran superimposed over a 3D rendering of the surrounding submerged landscape. The slopeangle is not as steep as it appears on the 3D rendering, as shown in the photo the right (knife = 10 cm long). (Jon Benjamin)
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