Η μέση και ύστερη ολοκαινική παλαιογεωγραφική εξέλιξη του Δέλτα της Ελίκης και οι εφαρμογές της στην αρχαιολογία

Abstract

The primary goal of this doctoral thesis is the understanding and interpretation ofnatural processes that contributed in the geomorphological development (evolution) andthey are conjoined with the history of human occupation in Helike area during theHolocene period. Adopting qualitative and quantitative methods, which are dictated by theneed of interdisciplinary approach of archaeological and environmental questions and bythe scientific reflection with regard to the environmental changes and their repercussions inthe activity of people that lived in Helike area, this research aims at:a) The study of factors that formed the landscape of Helike and in the pledge of theirrelation and interaction,b) The detection of spatial distribution of Holocene environments in the coastal plainof Helike delta,c) The description of natural activities that is related with the transport and thedeposition of sediments, interpreting the development of depositional environments duringHolocene period andd) Demonstration of the repercussions and effects on the diachronic development ofHolocene landscape of the study area in people and in the environment, representing theterrestrial and coastal paleogeographical character, creating paleogeographical scenario,that will portray the relationship between the environments in space and in time and willinterpret the relation of natural environment and human occupation.This thesis covers a wide range of field and laboratory methods. Sixteen sedimentcores were obtained from various locations in the delta plain using an Eijkelkamppercussion corer with barrel windows in common with sampling from six archaeologicaltest excavations. Sediment types, structure, color, organic constituents as well as contactdepths and bed characteristics were recorded from each core in the field. Laboratorystudies included determination of grain size, total organic matter, carbonate and carboncontent (Corg) and micro- and molluscan fossils of selected samples. The approximatepercentage of shells and terrigenous minerals in the sand fraction was estimated visually.Moreover, the laboratory analysis included the study of pollen spores. Results from these analyses were used along with stratigraphic data and eightradiocarbon dates to reconstruct the middle and late Holocene paleogeography of the studyarea. The systematic and in detail investigations of deltaic sediments of the Helike areagave the following results:1. The Helike fault, due to its listric geometry, has a rotated hanging wall blocktowards the south. This fact creates: a) elevation of the coast that creates a barrier,which prevents the draining of deltaic field of Selinous River to the sea during aflood event. The elevation rate of the coast is about 0.28 mm/year, b) it producesnegative relief between the hanging wall of the Helike fault and the main channelsof Selinous and Kerynites Rivers that flow along transform fault zones. Inconsequence, these rivers discharge into the open sea exclusively from the rivermouths, c) it causes a turn of the main fluvial channel of Selinous River. This leadsthe channel to a lateral movement from the place that it possessed in the beginningof late Holocene (mouth of Selinous River near the Aliki lagoon of modern Aigio)to its modern site (movement of the main channel from NNE to ESE).2. The establishment of a stagnant body of water in the delta of the Selinous Riverwas ascertained, in the end of the middle Holocene period. This existed almost inall the duration of the late Holocene. The presence of this body and its maintenanceare immediately related to a) the rotation of the hanging wall of the Eliki fault tothe south, which caused proportional subsidence of the deltaic area of the SelinousRiver behind the coast and b) the elevation of this coast and hence the weakness ofdraining of the deltaic field during a flood event.3. The hanging wall of the Eliki fault except its inclination to the south has rotatedsimultaneously from west to east. This caused differential subsidence in the deltaicplain with a maximum value at the end of Roman times and is characterized by theinitiation of increased sedimentation rate in the stagnant body of water and itsrestriction to the side of the Kerynites River.4. The restriction of stagnant body of water to the side of river Kerynites in thelocality of the B group of drillings is confirmed by the recovery of Roman building,which was excavated in Klonis field, likely age 500 A.D., in the place A group ofdrillings and archaeological sections. 5. The embayment that is occupied by the stagnant body of water and was created dueto Eliki hanging wall block rotation was mapped in the study area with precisionusing photogrammetric methods.6. The source area of the studied sediments is the Plio- Pleistocene sediments of thedrainage basin of Selinous River.7. The presence of a number of lithofacies in the sediments of Selinous delta wasrecognized and that combined with radiocarbon data allowed the description of thepaleogeographical history of delta. These facies are the following: a) lake, b)marsh, c) ephemeral lake, d) wetland, e) channel, f) proximal floodplain, g) distalfloodplain. Moreover, the changes of stagnant body of water are described using anumber of time stages during the late Holocene.8. The pollen analysis showed the presence of a lake that was evolving in successionthrough Holocene by saturated soil with the presence of shallow lake, turning toshallow lake and finally into a lake with extensive brackish or hyper salinemarshes. By the beginning or earlier than the late Holocene time the presence ofagricultural activity, as well as the reproduction and stock farming of cattles, wasestablished.9. The presence of a diachronically lacustrine body of water in the delta of SelinousRiver shows indirectly that the ancient city of Helike occurred over this lacustrinebody of water in an area between the old and new National road along the scarp ofthe Eliki fault.10. The destruction of the ancient city of Helike as well in buildings and activities nearthe stagnant body of water should be attributed to a strong earthquake from theAigion fault in combination with flash flood incident of the Selinous River. Thisflood covered probably all delta of Selinous River through the activation of inactivechannels and crevasses. The presence of these channels has been confirmed in thevarious time stages of development of the stagnant body of water. Neighboring ofsuch a channel was found in an industrial group of dye and weave with threereservoirs that belonged in the Early/ Middle Hellenistic Period showing thus theaction of channels in the locality of group A of drilling and archaeological sections.