A Marine Geoarchaeological Survey, Cape Sounion, Greece: Preliminary Results

Mediterranean Archaeology and Archaeometry, Vol. 14, No. 1, pp. 353-366 Copyright © 2014 MAA Printed in Greece. All rights reserved. A MARINE GEOARCHAEOLOGICAL SURVEY, CAPE SOUNION, GREECE: PRELIMINARY RESULTS George Papatheodorou 1, Maria Geraga 1 Dimitris Christodoulou1, Margarita Iatrou1, Elias Fakiris1, Stuart Heath1 and Kalliopi Baika2 1 Laboratory of Marine Geology and Physical Oceanography, Department of Geology, Univer- sity of Patras, Greece 2Ephorate of Underwater Antiquities, Greek Ministry of Culture Received: 06/05/2014 Accepted: 01/06/2014 Corresponding author: George Papatheodorou ([email protected]) ABSTRACT The present study presents the results of the preliminary marine geophysical survey conducted in 2006 at the gulf of Sounion, southern Attica, Greece. The site is of great archaeological importance since cape Sounion served as a navigational landmark and a naval fortress protecting the sea-lanes towards the metropolis of Athens and the silver mines of Lavreotiki during the Classical and Hellenistic periods. Parts of the coastal ancient installations are now submerged. The results of the collected geophysical data in- clude the examination of the seafloor texture and stratigraphy. Therefore a geomorpho- logical map of the gulf was constructed based on the configuration of the substrate and the seafloor stratigraphy. Archaeological remains lying on the seafloor have been detected on the sonographs and have been correlated with the results of previous studies. The development and the evolution of the gulf during the prehistoric period were evaluated via the sea floor stratigraphy and the prediction of sea level change in the area based on the eustatic and glacio-hydro-isostatic response. The sea level change during the historic period was examined and a relative sea level rise of at least 2,5-3,0 m was suggested for the last 2500 years based on the marine geophysical survey results. KEYWORDS: marine remote sensing techniques, relative sea level change, underwater archaeology, Sounion. 354 G.PAPATHEODOROU et al 1. INTRODUCTION smaller rock cut slipway (Kenny 1947), other constructions, such as submerged Cape Sounion is located at the southern ashlar walls of different dimensions were end of Attica peninsula (Fig. 1). During the detected and mapped for the first time on Classical and Hellenistic periods the Cape the north part of the Cape. These most and the ancient harbour city of Sounion probably belong to the coastal ancient city were of prime geostrategic importance lo- of Sounion that has not yet been systemati- cated on the main maritime route survey- cally surveyed or excavated underwater. ing all traffic and enemy fleets towards the A marine geophysical survey was under- metropolis of Athens and the silver mines taken as part of this multidisciplinary of Lavreotiki. On the Cape there are today study. The preliminary results of the un- visible important remains of the sanctuar- derwater remote sensing survey using a ies of Athena and Poseidon, the fortifica- subbottom profiler and a side scan sonar tion circuit and the settlement of the prom- system are presented in this paper. The ob- ontory, and of a naval base. The naval base, jective of the study was to shed light on the built originally by the Athenians in the 5th coastal palaeogeography of the Gulf of century BC lies at the northwestern side of Sounion by examining the subbottom stra- the cape and was incorporated in the for- tigraphy and the seafloor texture. Moreo- tress. It consisted of two rock-cut slipways ver, the marine geophysical survey was intended to house light patrol ships (Baika aimed at detecting targets of potential ar- 2012, 2013a, b with previous bibliography). chaeological and historical interest previ- ously unknown in the bay and wider area in order to estimate the extent of the submerged archaeological zone for all historical periods and proceed to the landscape reconstruction of the bay that served once as the ancient harbour of Sounion. The study of the palaeogeographical evolution of the coast has been proved very informative as the coastal zone has been an important focus of human activity since the Paleolithic period (Bailey and Flemming, Figure 1 Map showing the side scan sonar (black 2008). In the Mediterranean area multidis- colour) and the sub-bottom profiler (grey colour) ciplinary studies involving geoscientists tracklines conducted in the Gulf of Sounion. The and archaeologists examine the ancient index map shows the location of the study area. harbours as sites of rich-preserved geo- Today part of the ancient coastal zone archaeological records. These studies aim where the coastal settlement and the har- to the understanding of occupation histo- bour installations used to stand is sub- ries, human use and abuse of the Mediter- merged. Despite the great importance of ranean environment (i.e. Marriner and Cape Sounion in antiquity so far the un- Morhange 2007 (and references within) and derwater survey in the area is limited. In 2008, Marriner et al., 2008), the prediction 2004 and 2006, Baika lead a systematic mar- of relative sea level changes involving the itime archaeological survey using modern tectonic contribution (i.e. Flemming, 1996, mapping techniques. Wall and rock-cut Blackman, 2005), the response of the deltaic structures were located on the seabed in deposits to the coast (i.e. Vött 2007a) in as- the western and northern side of the cape sociation to the climatic changes (Marriner at a water depth of maximum 6m. Among et al., 2013) and the effects of natural haz- the already known archaeological remains ards to the coastal zone (i.e. Vött 2007b). of the double-shipshed complex, and a A MARINE GEOARCHAEOLOGICAL SURVEY, CAPE SOUNION, GREECE 355 Marine geophysical techniques have at submerged archaeological sites of south- been widely used in underwater archaeo- ern and western Black Sea (Coleman and logical studies regarding the detection and Ballard, 2007), at Dokos island where an investigation of archaeological sites such as ancient shipwreck dated at Early Helladic ancient shipwrecks (Quinn et al., 2002, II as discovered (Papatheodorou et al., Papatheodorou et al., 2005, Sakellariou et 2008), at Alexandria (Chalari et al., 2009), at al., 2007) due to the ability to investigate the site of the ancient and medieval har- and map the seabed and subsurface fea- bour of Kyllini/Glarentza (Pakkanen et al., tures at high speeds and independently of 2010) and in Zea and Mounychia ancient the water depth and the visibility harbours (Papatheodrou et al., 2012) . (Dellaporta et al., 2002). Furthermore, they In the present study two acoustic sys- have been widely used in studies focusing tems were used: (i) a side scan sonar sys- on the reconstruction of coastal palaeoge- tem consisting of a dual frequency (100 and ography at submerged sites of archaeologi- 500 kHz) towfish 272TD and a digital re- cal interest mainly by detecting and map- cording unit Edgetech 4100P topside and ping the preserved palaeo-shorelines and (ii) a 3,5 kHz subbottom profiling system by studying the local stratigraphy and Late consisting of a Model 5430A GeoPulse Quaternary geology (i.e. Van Andel and Transmitter, a Model 5210A GeoPulse Re- Lianos, 1984, Belknap and Mart, 1999, Laf- ceiver, a Model 1600 EPC “S” type Graphic ferty et al., 2006, Coleman and Ballard 2007, Recorder and an O.R.E. Model 132A/132B Papatheodorou et al., 2008, Chalari et al., over-the-side four transducers array. A 2009, Ferentinos et al., 2012). Hemisphere V100 GPS system with accura- cy of approximately 2,0 m was used for the 2. METHODOLOGY navigation and the positioning of the ves- Side scan sonar and high resolution sel. Side scan sonar lines having a length of subbottom profiling data were collected in 30,7 km and covering a total area of 1,44 2006. Side scan sonar produces acoustic km2, were surveyed in Sounion bay (Fig. 1). images called sonographs which portray The operational frequency was 100 kHz the seafloor texture and seafloor morphol- and in most tracklines, the slant range was ogy. The interpretation of the sonographs 50m. The lane spacing provided a 50% (Blondel, 2009) is based on the acoustic re- range overlap. The towfish height above flectivity (i.e. the coarser sediment material the seafloor ranged between 10% and 50% returns stronger acoustic signal) and on of the slant range. Sidescan-sonar data specific acoustic criteria (i.e. the presence of were processed using ISIS Sonar (Triton acoustic shadow, the parameters control- Elics) software and then were mosaicked ling the shape and the acoustic signature). with 0.5 meters resolution using DelphMap A subbottom profiling system provides an (Triton Elics) software. acoustic profile of a narrow section of the A total length of 19,7 km of 3,5 kHz subbottom beneath the path over which the subbottom profiles were acquired (Fig. 1) device is being towed. The signals are re- using a time base of 0,1 s and a 0,1 ms flected off the seafloor surface, the interfac- pulse length providing a vertical resolution es between strata and specific features that less than 0,5 m. Initially the acquired maybe buried in the sediments (Darmuth, acoustic profiles were processed using the 1975). The strength of this reflection is gov- software SBP-Am-An (Fakiris et al., 2007). erned by the reflection coefficient. In the SBP-Am-An software georeferenced the eastern Mediterranean Sea, side scan sonar profiles acquired and formatted them as together with 3,5kHz profiler have been SEG-Y files thus made them compatible for used to detect the shipwreck remains of further processing. The combined SEG-Y Navarino battle (1827) which took place at files were further processed using the SB- gulf of Pylos (Papatheodorou et al., 2005), Interpreter software. The results were im- 356 G.PAPATHEODOROU et al ported and georeferenced in GIS environ- and the small island located in the southern ment.

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