CLIMATIC CHANGES MODIFIED THE QUATERNARY COASTAL LINES IN THE MARMARA REGION, WESTERN PONTICS: WHAT ABOUT ACTIVE TECTONICS?

Geological and palaeooceanographic studies in the Marmara and Black Seas indicate modification of the Quaternary coastal lines by climatic changes that must in turn have influenced the prehistorical human life and settlements in the Pontics. The effect of active tectonics on the modification of coastal features is however relatively unknown. In an attempt to explore the modifying role of active tectonics on the coastal lines in the western Pontics, this presentation summarizes the field evidence and relevant literature for the Marmara region.

The Marmara region is a tectonically active belt in northwestern Turkey and has had an extensive paleogeographical evolution in relation to the development of the strike-slip North Anatolian Fault (NAF). There, in Pliocene the NW oriented intermountain basins bounded tectonically by former splays of NAF formed brackish and fresh lakes of the region. As post-Pliocene uplift and denudation caused termination of these lakes, a new generation of E-W and NE-SW oriented depressions formed concurrently along NAF, creating lakes, marshes and fluvial systems of Plio-Quaternary and Pleistocene. The post-Pleistocene and Holocene uplift and denudation accompanied by seismic activity of historical times caused the establishment of wide alluvial plains of the region suitable for human settlement that is consistent with the absence of archeological findings of pre-Bronze age (>5000BP) along the Bosphorous-Izmit Bay-Sapanca Lake-Sakarya river area. In accord with the presence of many elevated brackish-marine terraces and paleoshorelines in the region, the sedimentological, stratigraphical and geochronological features of the brackish or marine Pleistocene-Holocene sequence in the Izmit bay suggest tectonic activity intensified at different periods as may have been at about 35,000 yrs BP with more than 70 m of vertical displacement. Active tectonics continues to reshape the region as occurred in the 1999 earthquake sequence of Marmara.