Abstract:

In this paper we deal with a case scenario for the general geological setting and the morphotectonic evolution of the delta plain of Pineios River (Thessalia, Greece) and its margins. This work is based on the interpretation of geological and geomorphological data derived from (a) digitizing topographic map sheets of scale 1:5,000, (b) digital interpretation of recently acquired high spatial and spectral resolution satellite image, (c) tectonic geomorphology analysis, (d) field observations and (e) geophysical investigation. The fluvial deposits cover the largest part of the delta plain, whilst the coastal deposits crop out along the entire coastal zone. The remnants of a Pleistocene alluvial fan is observed in the western part of the delta plain and lies unconformably on Neogene formations comprised of sandstones, conglomerates and terra rossa. The alpine basement outcrops are found only at the southern and northern margins of the delta plain and include various lithologies such as crystalline limestones and metamorphic flysch (Ossa-Olympos unit), blue schists, gneisses and marbles (Ambelakia unit), metamorphic basic ophiolitic rocks and marbles (Pelagonian unit). The Neogene formations have undergone intense tectonic deformation resulting in several block rotations reaching the values of 10-30ο , towards south. The NW dipping normal fault zone located south of Omolio village strikes WSW-ENE and seems to play a significant role in the rotation of the Neogene formations. It is rather clear that the activity of this fault zone is highly related to the uplift of Ossa Mt along the southern margin of the delta plain and consequently to the development of extensional fractures (scarps) developed normally to the fault zone. These scarps are not tectonic faults and were created primarily by gravitational stresses. These structures have caused the segmentation of the uplifted block into smaller blocks, which were subsequently toppled. These large-scale toppling phenomena at the northwestern slopes of Ossa Mt have caused large gaps in the alpine basement rocks. These gaps have acted as selective surface water flow paths that have shaped impressive gorges. Pineios River found a new outlet to the Aegean Sea through the westernmost of the gorges, the Tempi gorge. It seems to have happened after the overall tectonic uplift of Olympos-Ossa-Pelion mountain range and the paleo-Pineios River flow blocking at the area south of Ossa Mt. Immediately after the aforementioned process, the area extending east of Tempi gorge began to evolve as the delta plain of Pineios River resulting in the progressive natural seaward shift of the shoreline due to the accumulation of Pineios fluvial deposits.

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