Evaluating the geological, geomorphic and geophysical evidence for the re-location of Odysseus’ homeland, “Ancient Ithaca”
Hunter, Kirsten Lisa
The application of geological and geophysical methods on the Ionian Island of Kefalonia has provided a new-found basis by which to test the hypothesis that Ancient Ithaca, the home of Odysseus as described in Homer’s epic the Odyssey, a subject which has perplexed academics for centuries. Although popular belief places Odysseus’ homeland on Ithaki, a small mountainous island lying to the east of Kefalonia, its location does not fit Homer’s descriptions of Ancient Ithaca since it is described as a “low-lying” island lying “furthest to the west” (facing dusk not dawn). Being land-locked and connected to the rest of Kefalonia by a narrow (6 km x 2 km) isthmus called the Thinia valley, the Paliki Peninsula of Western Kefalonia provides a better geographical fit. However, it has generally been dismissed as a candidate for Ancient Ithaca since it is not an island today and the topography of the connecting isthmus rises to a height of c. 200 m along the centre of the Thinia valley. Despite these obstacles and based on a quote by the ancient geographer Strabo made around 1 BC, Bittlestone et al. (2005) proposed that during the Mycenaean Era an ancient seaway (“Strabo’s Channel”) could have existed where Thinia stands today and the valley’s present topography is due to landslide deposition which eventually closed the seaway. This thesis presents the results of a 3-year geological, geomorphological and geophysical investigation of “Strabo’s Channel”. The investigation was carried out using a survey programme of complimentary non-invasive geophysical techniques calibrated by 17 shallow sedimentary cores and combined with surface geological mapping and geomorphological observations. In addition to a helicopter-mounted electromagnetic (HEM) survey acquired for Northern Paliki, gravity measurements were taken across the Thinia isthmus, and resistivity and seismic refraction surveys were carried out at strategic sites. Marine shallow seismic reflection surveys were also undertaken in the coastal areas adjacent to the isthmus to chart postglacial transgression into these shallow coastal areas and to reconstruct the paleo-geography of Northern Paliki since the Last Glacial Maximum (LGM) (c. 21 500 BP). The survey area is sited in the Pre-Apulian isopic zone of the Hellenide thrust belt which represents a structurally-inverted passive continental margin subsequently affected by foreland contraction and overprinted by neotectonic (outer-arc) deformation resulting from African-Eurasian plate collision. The results showed that the geology and geomorphology of Thinia was far more complicated than originally believed. The bedrock geology records the Cretaceous-Quaternary evolution of an extensional-compressional regime brought about through the foreland-migration of the Hellenide fold-and-thrust deformation in the Early Miocene which reactivated earlier south-easterly-dipping extensional faults. The peninsula was affected by further Late Quaternary, Holocene and recent neotectonic deformation caused by the formation of the dextral Kefalonia Transform Fault (KTF) and slope failure resulting from the generation of steep slopes. The shallow marine seismic reflection survey showed clear differentiation between the tectonised “pre-Holocene” and onlapping postglacial sediments separated by a prominent erosional surface associated with the LGM sea level lowstand of -120 m. The survey detected a buried drainage valley deeply-incised into the pre-Holocene of the Gulf of Argostoli indicating that a major glacial river drained from Thinia during this lowstand. During postglacial sea level rise this valley was infiltrated by marine waters to form a ria, flooding two large glacial lakes which acted as depocentres for postglacial sediments. While the prevalence of slope collapse of the steep valley sides in Thinia favoured the idea that “Strabo’s Channel” was infilled through repeated deposition of landslide debris, the presence of bedrock at the surface of Thinia ruled out the possibility that the present valley topography was built-up through Late Holocene deposition of landslide material between Kefalonia and Paliki. The onshore tests confirmed the presence of a thick deposit of steeply-dipping and tectonised marine sediments within the valley. Biostratigraphic analysis of core samples dated these as Early Miocene to Early Pleistocene (Gelasian) indicating marine waters existed along the valley until at least 1.80 million years ago, an order of magnitude younger than previously reported in the area. However, no new independent sediment younger than Early Pleistocene was retrieved in the cores obtained for this study despite the findings of an earlier borehole which appeared to contain Late Quaternary and Holocene marine fauna (Ehux). The geophysical surveys and cores failed to detect the sides or bottom of a channel or evidence of substantial clastic debris within the proposed channel route thus ruling out the possibility that a buried marine-level channel which extended from “sea-to-sea” had existed during the Late Bronze Age. One strategic area of investigation was the upland site of a suspected paleo-lake (Lake Katachori) which overlapped the proposed route of Strabo’s Channel at ~170 m elevation. Although the presence of freshwater algae within the upper few metres confirmed a lacustrine environment, the geophysical and core evidence showed it was shallow (6 m thick) and was sited on steeply easterly-dipping Plio-Pleistocene sediments uplifted to ~170 m above sea level. The occurrence of freshwater algae admixed with uppermost Plio-Pleistocene sediments probably represents a basal reworked basal lag deposit thus, implying departure from marine depositional setting occurred in Thinia sometime after the Gelasian (1.80 Ma). Coring at Livadi Marsh suggested that while the marsh was flooded during the Bronze Age to a depth of c. 1.2 m, making it a candidate for Ancient Ithaca’s harbour, no significant coseismic uplift appears to have occurred since the Late Bronze Age. Current coastal position was due to progradation and aggradation of marsh sediments with no more than 1.2m of coseismic uplift. The lack of Holocene-Late Quaternary sediment relating to an uplifted marine channel and the presence of Lake Katachori may tentatively be explained through the uplift and westwards translation of the sediments of central Thinia through establishment of a contractional-extensional linked gravity driven rotational slip linking the listric “Agia Ioanni Fault” with the Atheras Thrust. The boreholes detected shear-thrusting and steep dips within the Miocene and Plio-Pleistocene marl sediments demonstrating that the area experienced strong tectonic dislocation which is in favour of this model however further tests are required to investigate this and whether it could feasibly have occured in the required timescale.