Sea-Level Stands and Holocene Geomorphological Evolution of the Northern Deltaic Margin of Amvrakikos Gulf
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/259817890 Sea-level stands and Holocene geomorphological evolution of the northern deltaic margin of Amvrakikos Gulf... Article in Zeitschrift für Geomorphologie Supplementary Issues · March 2005 CITATIONS READS 13 153 6 authors, including: Serafeim Poulos Vasilios Kapsimalis National and Kapodistrian University of Athens Hellenic Centre for Marine Research 184 PUBLICATIONS 1,093 CITATIONS 71 PUBLICATIONS 693 CITATIONS SEE PROFILE SEE PROFILE Petros Pavlakis Hellenic Centre for Marine Research 32 PUBLICATIONS 768 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: PhD Thesis View project 14th International Congress of the Geological Society of Greece View project All content following this page was uploaded by Vasilios Kapsimalis on 22 January 2014. The user has requested enhancement of the downloaded file. Z. Geomorph. N.R Suppl.-Vol. 137 125-145 Berlin • Stuttgart March 2005 Sea-level stands and Holocene geomorphological evolution of the northern deltaic margin of Amvrakikos Gulf (western Greece) Serafim E. Poulos, Vasilios Kapsimalis, Christos Tziavos , Petros Pavlakis, George Leivaditis, Athens, and Michael Collins, Southampton with 10 figures and 4 tables Summary. The present contribution aims to identify the various sea-level stands in association with deltaic sedimentation processes, within Amvrakikos Gulf (western Greece); the latter is a semi- enclosed and relatively shallow (<65 m) embayment, separated from the open Ionian Sea by a rather narrow and shallow (< 10 m) passage. Furthermore, this investigation has been based, primarily, upon the identification of different sedimentary environments within sedimentary cores, radiocarbon dating of characteristic stratigraphic horizons; and, secondarily, upon subaerial and subaqueous geological and geomorphological characteristics as well as archeological evidence. On the basis of the above infor- mation, the Holocene evolution of the northern deltaic margin of the Amvrakikos Gulf is attributed to the active interaction between sea level rise, regional tectonism, riverine sediment supply and differen- tial rates of the sedimentation. The Holocene formation and evolution of the northern deltaic margin of the Amvrakikos Gulf is attributed primarily to the deltaic progradation of the River Arachthos, whilst the action of River Louros has been restricted only to its northwestern part. Although a regional curve of sea level rise for the Holocene period could not be constructed with accuracy, due to the above-mentioned complexity of the operating processes, it is most likely that in the beginning of the Holocene period (earlier than 10 000 years BP) sea water from the open Ionian Sea had already entered into the Gulf, occupying water depths 35-40 m below present mean sea level. Following, sea level was rising at a rate of 0.5+0.02 cm per year up to ca 2000 years BP. Within the last 2000 years, sea level has fluctuated within a range of 1-2 m. Zusammenfassung. Diese Arbeit hat zum Ziel, anhand der Ergebnisse der Deltasedimentation im Amvrakikos Golf (W. Griechenland) die verschiedenen Meeresspiegelniveaus zu identifizieren. Amvra- kikos Golf ist ein halbgeschlossenes Meer mit einerTiefe von weniger als 65 m. DieVerbindung zum offe- nen lonischen Meer kommt durch eine Enge mit einer Tiefe von ~ 10 m zustande. Im Rahmen dieses Studiums der Amvrakikos Gegend wurden Sedimentkerne untersucht, 14C Altersbestimmungen durch- geführt, geologische und geomorphologische Beobachtungen gemacht und archaologische Funde be- rücksichtigt. Die Ergebnisse aus diesen Versuchen führten zu einem synthetischen Bild der Evolution des Gebietes während des Holozäns. Diese Evolution hing mit den Meeresspiegelschwankungen, der lokalen Tektonik und der fluvialen Sedimentlieferung zusammen. Die Gegend wurde überwiegend vom Fluss Arachthos beeinflusst. Eine lokale Meeresspiegelstandskurve fur das Holozän konnte nicht mit Genauig- keit rekonstruiert werden. Auf jeden Fall beweisen die Daten aus dieser Arbeit, dass vor 10000 Jahren marines Milieu über dem Amvrakikos Golf herrschte. Der Meeresspiegelanstieg von diesem Zeitpunkt bis vor 2000 Jahren betrug 0,5+0,02 cm/Jahr. Während der letzten 2000 Jahre schwankte der Meeresspie- gel in einem Spektrum von 1-2 m. 0044-2798/05/0137-0125 $ 5.25 © 2005 Gebriider Borntraeger, D-14129 Berlin • D-70176 Stuttgart 126 Serafim E. Poulos et al. 1 Introduction Relative sea level history varies considerably around the world during the last glacial hemicycle (Newman et al. 1989 and Pirazzoli 1991) due to local, regional and global processes operating on different time and space scales. Hence, the determination of a single sea level curve of global applicability is impossible, according to Pirazzoli (1993). Furthermore, coastal landscapes repre- sent a sensitive interface for environmental changes, being the product of the interaction between terrestrial, marine and atmospheric processes. In active tectonic regions, e.g. Greece, coastal evo- lution within Holocene and, in particular, that of deltaic coasts and associated shorelines is gov- erned by eustatic sea level oscillations, tectonic displacements and sediment infill. Evidence for sea level changes is provided by a variety of archeological and geological indica- tors. The former refer to archeological structures and to their relative position with respect to shoreline, whilst the latter include a number of forms, such as submerged terrestrial and/or lagoo- nal vegetation and sedimentary phases, distinctive seismic reflectors in shallow offshore sedimen- tary stratigraphy and notches, provided by marine solution. Sea level studies based upon archeo- logical evidence have taken place for several locations along the Greek coastline, by Flemming (1978), Jacobsen & Farrand (1987), and van Andel (1987). Likewise, investigations based upon geo- logical evidence have been provided by Kraft et al (1977), Kraft & Rapp (1975), Kraft et al. (1980), Zangger (1991), Marzolff (1981), van Andel & Lianos (1983), Flemming (1978), Thommeret et al. (1981), Pirazzoli et al. (1994), Fouache (1999), and Dini et al. (2000). Moreover, in the case of the Aegean Sea, Lambeck (1996), on the basis of a mathematical model that describes the combined behaviour of eustatic change and crustal rebound, has described sea level change and shoreline migration for the past 20 000 years. Greece, as part of the eastern Mediterranean, is a region of active tectonism and one of the most rapidly deforming continental areas of the Earth (Jackson 1994). Recent coastal zone changes of the Aegean region have been attributed to paroxysmic phases of actual neotectonic evolution, related to differential (in space and time) movements of small tectonic blocks (Mourtzas 1990). Examples of relative sea level changes due to neotectonic activity have been identified in several locations within the southern (primarily) Aegean Sea (e.g. Peloponnese, Crete) by Mourtzas & Marinos (1994), Kelletat et al. (1976), van Andel (1987), Keraudren & Sorel (1987), and Collier et al. (1992). Sediment infill in coastal waters can cause vertical movements, due to changes in the surface loads; this is a process analogous to glacial unloading. Therefore, in Greece sediment accumula- tion in shallow bays and gulfs is comparatively limited to have an important loading effect over time-scales of 10,000 or so years (Lambeck 1996). However, increased sediment fluxes associated with deltaic evolution have been attributed locally to the build-up of new land surface and the migration of shorelines to seawards. A characteristic example for such a deltaic progradation in Greece relates to inner Thermaikos Gulf (NW Aegean Sea). Here, the deltaic plain of the Axios, Aliakmon and Gallikos rivers has prograded more than 20 km within historic times; caused the ancient city of Pella (the capital of ancient Macedonia) to change from a coastal city and harbour, to become a continental city (Stuck 1908). Similar examples of coastal progradation in historical times, related to riverine sediment influx for the Aegean region, have been reported by Zamani & Maroukian (1980), and Bruckner (1997). Sea-level stands and Holocene geomorphological evolution 127 The present contribution aims to identify the various sea-level stands within Holocene, in re- lation to deltaic morphological evolution of the northern margin of the Amvrakikos Gulf (wes- tern Greece). In addition, the curve of relative sea-level change of the Gulf (within the Holocene) is constructed; this has discussed in relation to neotectonic activity of the region and other pub- lished sea level curves. 2 The study area Amvrakikos Gulf is located in the northwestern part of Greece (eastern Mediterranean Sea) and is a shallow (water depths < 65 m) marine embayment, communicating with the open Ionian Sea through a narrow (about 600 m wide) and shallow (< 10 m, water depth) channel (Fig. l). The Gulf is a late Plio-Quaternary extensional basin, produced by backarc extensional faulting in western onshore Greece (Fig. 2). The entire northern terrestrial margin of the Gulf consists of the deltaic deposits of the rivers Arachthos and Louros, which cover an area of some 350 km2 (Fig. 3). The physical geographical characteristics of the drainage basins of the rivers Arachthos and Louros, together with those of the deltaic plain, are presented in Table 1. Between the two rivers the most important, in terms