Morphologic features of the Marmara Sea from multi-beam data
Introduction
The Marmara Sea is an inland sea, separating the peninsulas Thrace and Anatolia and connects the Black Sea–Mediterranean marine realms through the Turkish Strait System (Bosphorus and Dardanelles) (Fig. 1A–C). It consists of a very complex morphology including shelves, slopes, basins, sub-basins and ridges, with an area of about 11 110 km2. The origin and evolution of the Marmara Sea has been greatly affected and oriented by the North Anatolian Fault Zone (NAFZ) since Middle–Late Miocene (Ketin, 1968, Barka and Kadinsky-Cade, 1988, Şaroğlu and Yılmaz, 1991, Görür et al., 1997). Pınar (1942) indicated an E–W trending major fault system from Izmit Bay to Ganos Mountain System through the Marmara Sea. This first striking observation gave the opportunity to many investigators to develop various tectonic models which discuss and explain the mechanism of the NAFZ in the Marmara Sea. Şengör (1979) and Şengör et al. (1985) followed the suggestion of Pınar (1942) and showed an E–W-oriented fault zone along the Marmara Trough, whereas the same zone has been explained as an E–W-oriented graben by Ketin (1968) and developed by Crampin and Evans (1986) and Smith et al. (1995). In contrast to these single fault or graben models, a pull-apart model has been proposed by Barka and Kadinsky-Cade (1988). They have recognized the complex morphology of the ridges and basins along the Marmara Trough and explained the NAFZ as a NE–SW-oriented en-echelon fault system forming pull-apart depressions. This pull-apart model later developed by Wong et al. (1995) and Arminjo et al. (1999). Okay et al. (2000) showed that the NAFZ splits in two transtensional (oblique) faults following the northern and southern slopes in the Çınarcık Basin. The fault following the northern slope of Çınarcık Basin extends to the western Marmara Sea as major branch of the NAFZ cutting the basins and ridges. Siyako et al. (2000) suggested a similar model to that of Okay et al. (2000) by indicating the NAFZ with northern and southern boundary faults and a strike–slip fault along the central axis of the Marmara Trough. A buried E–W-oriented master fault consists of a complex numerous strike–slip and normal faults along the Marmara Trough has been offered by Aksu et al. (2000). The rising debate on the discrepancies and contrariness among these various models, explaining the tectonic evolution of the Marmara Sea, eventually has concluded with the necessity of a detailed bathymetric data giving the comprehensive morphological information about the Marmara Sea.
The earliest bathymetrical informations on the Marmara Sea were given for the southern entrance of Strait of Istanbul by Ploix and Manen (1854) and for the western Marmara Sea by Wharton (1887). Andrusov (1890) has prepared a bathymetric map of Marmara Sea, which has remarkable similarities to the contemporary maps, prior to the multi-beam bathymetric data. In 1901, Ottoman Emperor Government prepared an extensive bathymetric map of Marmara and Aegean seas. Ardel (1958), Ardel and Kurter (1971), and Ardel (1975) combined and interpreted the previous maps and explained the morphological features of the Marmara Sea. International Oceanic Commission (1981) collected bathymetric data from the Marmara Sea during the mapping study of the Mediterranean Sea. In the last decade of the twentieth century, some modern bathymetric maps were made using limited amount of seismic data (Smith et al., 1995, Wong et al., 1995). The latest development in mapping the sea floor of the Marmara Sea was achieved with the use of multi-beam by R/V Meteor of Federal Republic of Germany (Çağatay et al., 2000), TCG-Çubuklu of Turkish Navy, Department of Navigation, Hydrography and Oceanography (TN-DNHO), and R/V Le Suroit of IFREMER. In the most recent published study, İmren et al. (2001) used the multi-beam data collected by TN-DNHO together with multi-channel seismic profiles and showed a single strike–slip fault system connecting the northern branch of NAFZ in the east to Ganos Fault in the west.
In this study, we present a surface image of Marmara Region by gathering the same multi-beam bathymetric data (TN-DNHO) and unpublished bathymetric data collected by Turkish Navy with topographic data from the surrounding area of the Marmara Sea. The aim of this study is to determine the morphological features of the Marmara Sea as well as to contribute new information for the evaluation of the conflicting tectonic models. Detailed geological and structural analysis of these bathymetrical data together with seismic data will be presented elsewhere (Gökaşan et al., submitted).
Section snippets
Data collection and processing
The multi-beam bathymetric data were collected by the survey ship TCG-Çubuklu of TN-DNHO from the area I shown in Fig. 2 by SWATH system (Elac BCC Marko). It operates with 56 beams, at 50 kHz and has a range of 2500 m. This system employs a fan of echo sounders mounted in a covering approximately 120° below the survey vessel. Horizontal coverage of the beams is three times greater than depth of water column. Differential Global Positioning System was used for positioning the ship speed, holding
General morphology of the Marmara Sea
The morphologic features of the Marmara Sea are primarily composed of shelves, slope basins and ridges (Fig. 1C). Submarine canyons and submarine landslides constitute the secondary morphological characteristics and occur locally at the slopes. Shelf area has the largest proportion (55%) among the other morphological units (Table 1) and is delineated with a prominent shelf break at about 100 m water depth. Relatively steep slopes are mainly formed at shelf break–basin transition, whereas gentle
Geological implications of morphology
The previous proposed tectonic models will be compared with our detailed morphological data in this section. The earliest model suggested by Pınar (1942, Fig. 7A) and followed by Şengör (1979) and Şengör et al. (1985) indicates an E–W-oriented fault zone along the Marmara Trough. Although this model is conformable with the Marmara Trough, it cannot explain the complex deep morphology of the Marmara Trough. An E–W-oriented graben model proposed by Ketin (1968, Fig. 7B) and developed by Crampin
Conclusions
General morphological character of the Marmara Sea can be defined with two main features: one being widespread shelf areas which are flat and mainly wider in the southern part; and the other feature is the Marmara Trough including all the morphological units from shelf break to deep basins. Marmara Through consists of basins, ridges, and slopes that accommodate canyons and landslides. Contrary to the shelf area, complex and irregular morphology of the Marmara Trough clearly reflects that it has
Acknowledgements
We gratefully acknowledge the Captain and crew of the TCG-Çubuklu of TN-DNHO for their help during the bathymetric survey. Special thanks are due to Prof. S. Gözenç for providing the topographic maps. We are grateful to an anonymous referee and Dr. A. Hubert-Ferrari for their constructive reviews that improved the manuscript.
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