Die Entwicklung des Acheloos-Deltas. Eine paläogeographisch-geoarchäologische Untersuchung zum holozänen Küstenwandel in Nordwest-Griechenland.

Im Gebiet des Acheloos-Deltas wurden 70 terrestrische Schlaghammerbohrungen abgeteuft. Zusätzlich konnte in Lagune von Etoliko aus dem Profundal ein Sedimentkern gewonnen werden. Aus den insgesamt 71 Bohrkernen wurden 80 Proben unterschiedlichen Materials mit Hilfe der Radiokohlenstoffmethode datier...

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Gespeichert in:
1. Verfasser: Schriever, Armin
Beteiligte: Brückner, Helmut (Prof. Dr.) (BetreuerIn (Doktorarbeit))
Format: Dissertation
Veröffentlicht: Philipps-Universität Marburg 2007
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  • Between July 2002 and September 2005 seventy terrestrial drillings were carried out in the Acheloos River delta plain. Additionally, a drilling was made from a raft in the profundal zone of the Lagoon of Etoliko. In total 80 samples from this 71 sediment cores were radiocarbon dated. Geoelectrical earth resistivity tomography (ERT) was used to get more information about the sedimentological structure in important regions of the Acheloos River delta plain. Also the focus was laid on accounts of ancient authors like Thukydides and Strabon and travellers from the nineteenth century, in case of (geo-)archaeological questions.The sedimentological history of the Acheloos River delta is very complex due to the fact that the Acheloos River neither disembogues into the open sea nor into a calm bay, but into the archipelago of the Echinad Islands. To reconstruct the Holocene sea level rise, 14 radiocarbon datings were used, 13 from peat samples and one from a piece of wood. In contrast to many other curves form the eastern Mediterranean, our sea level curve show no sea level maximum in the mid-Holocene close to or above the modern sea level. The presented curve show a continuous sea level rise up to the present day. After 2550 BC the curve shows a constant sea level rise with a low rate of 0.44 to 0.94 m/ka. Since the Middle Ages (13th cent. AD), the sea level rise has been strongly accelerating with a rate of 2.40 m/ka. The palaeogeographical evolution of the north-western part of the Acheloos delta plain is characterized by two special aspects which are presented for the first time in this PhD thesis. The first event is the very early progradation of a distributary from the north into the bay west of the Lesini mountain range from 6000 to 4500 BC. The distributary passed the Lesini mountain range in the north and entered the bay to produce a typical birds-foot delta. After this mid-Holocene progradation the delivered sediments sealed off the bay from the open sea and a large and long lasting lagoon was formed. Since that time the former island Trikardo could have been reached only via a lagoon and not from the open sea as some authors assumed. From a geoarchaeological point of view, the vicinity of the ancient harbour of Oiniadai was of major interest. Our results show that in the period the northern harbour and its shipsheds were used, it could only be reached via a lagoon and not directly from the open sea. A distributary was also freshwater supply for the northern harbour, presumably in order to improve the water conditions and to keep it open. From early Roman times on, the northern harbour lost its connection to the lagoon and silted up. The theorie of the existenz of a second harbour in the south, postulated by Murray (1982), must be rejected.We actually found a second harbour site at the south-eastern flank of the island. Ceramic fragments and other typical remains document that since late Helladic times, people have settled on this part of the island. This complements the rare records from Helladic times for southern Akarnania. For the eastern part of the delta plain the results of the raft-based drilling in the Lagoon of Etoliko show that the deep tectonic basin which was additional shaped by (gypsum-) karstic effects was filled with a freshwater lake since the late Pleistocene. The composition of microfossil assemblages together with other results from the surrounding terrestrial corings led to the conclusion that after around 4700 BC the freshwater lake was episodically affected by river water inflow from the Acheloos, especially in case of strong flood events during the winter season. Later, a permanent inflow of a river branch was established. Around 1200 BC, the sea level reached the sill between the Lagoon of Mesolongi in the south and the basin in the north and the saltwater inflow caused the development the Lagoon of Etoliko.The south-westernmost parts of the delta plain are the youngest ones. Only starting from ca. 200 BC, the river carried significant amounts of sediment into the region around the islands of Skoupas, Taxiarchis and Koutsilaris. Since around 500 AD the delta progradation has reached the western flank of Koutsilaris. South of the island of Skoupas the delivered sediments caused a beach ridge which cut off the bay from the open sea and turned it into a lagoon.The rate of horizontal delta progradation decelerated significantly when the river mouth reached the south-western region. This was caused by the steepness of the seafloor in this area. So much more sediment is needed for visible delta progradation. This is proven by the enormous sedimentation rates since the Middle Ages. North of the island of Skoupas the rate amounts to 6.00 m/ka and near the modern river mouth the rate rises up to 28.00 m/ka.