A high-resolution seismic study in Sakarya Delta and Submarine Canyon, southern Black Sea shelf
Introduction
The Sakarya submarine delta and canyon are distinctive morphological features of the narrow southern continental shelf-slope transition of the Black Sea (Fig. 1). The Black Sea has been subjected to dramatic geological and oceanographical changes during the late Quaternary in relation with its connection with the Mediterranean Sea through the Aegean and Marmara Seas via the Straits of Çanakkale (Dardanelles) and İstanbul (Bosphorus). It was isolated from the Mediterranean Sea and became a freshwater lake (Neoeuxinian phase, 22–9 kyr BP, Federov, 1971; Ross and Degens, 1974; Nevesskaya, 1974), during the last glacial when the global sea level fell below the level of the sill located at the northern approaches of Bosphorus. During this period, the shelf areas of the Black Sea were exposed to subaerial erosion and excavated by rivers, until at about 10–9 kyr BP, when glacial meltwater filled the Black Sea Lake and drowned the shelf areas (Degens and Ross, 1974; Stanley and Blanpied, 1980; Aksu et al., 1999). Ryan et al. (1997) suggested that this invasion occurred as an abrupt drowning and submerged the exposed continental shelf area to a depth of more than 100 m lower than the present level of the Black Sea at 7150 yr BP. The evidences of such a rapid transgression, has also been found from the high-resolution seismic profiles from the Strait of Istanbul and its exit to the Black Sea shelf at a water depth of about −105 m. (Demirbağ et al., 1999). Winguth et al. (2000) pointed out that the lowstand level during the last glaciation was at −151 m, by examining the seismic data collected from the northwestern Black Sea. Ballard et al. (2000) found a paleo-shoreline at a depth of 155 m in the southern shelf of the Black Sea, indicating that the flood had occurred between 7460 and 6820 yr BP.
Evidence of sea level changes is observed in the continental shelf of the Black Sea. The Sakarya delta presents a good feature to determine the sea level changes in the Black Sea. The sedimentary evolution of the northern shelf and the prevailing coastal processes (Ryan et al., 1997; Joashvili, 1995; Joashvili and Papashvili, 1994; Repina, 1996) and riverine influxes into the Black Sea (Shimkus and Trimonis, 1974; Hay, 1994; Algan et al., 1999) were investigated by various authors. However, there are few studies concerning the sedimentary evolution in relation to sea level changes in the southern Black Sea shelf area (Okyar et al., 1994; Okyar and Ediger, 1999; Demirbağ et al., 1999).
A submarine canyon including two canyon heads is found in front of the Sakarya Delta, which extends to 1500–2000 m depth, and is an important morphological feature in terms of sources of eroded sediment and/or pathways of sediment mass transport into the Black Sea deep basin. Compared to other submarine canyons along the north Anatolian coast, these canyons are cut deeply into the shelf and have steep walls as noted by Erinç (1958). However, no previous investigation has been carried out on this canyon system.
In this paper, we present the result of the examination of high-resolution seismic reflection profiles from the Sakarya submarine delta and the canyon on the southern shelf of the Black Sea, with the aim of determining the sedimentary evolution of the Sakarya Delta and the Sakarya submarine canyon as well as to contribute new data on the late Pleistocene–Holocene sea level changes in the Black Sea.
Section snippets
Bathymetry
The study area consists of a narrow shelf and a submarine delta dissected deeply by a submarine canyon (Fig. 2) to a water depth of about 50 m. The shelf is limited by the shelf break at −100 m isobath and is generally less than 10 km wide. The delta lobe is dissected by the canyon at a short distance (1.5 km) from the river mouth and can be followed up to 5 km on both sides of the river mouth. The submarine canyon includes two discrete heads that cut through submarine delta and shelf. The canyon
Methodology
A total of about 160 line-km of single-channel digital seismic reflection profiles (23 profiles) were acquired on board of R/V Arar of the University of Istanbul in May 1999 (Fig. 1). The sparker records were collected using 1.25 kJ multi-electrode sparkarray and an 11-element, 10-m-long surface-towed hydrophone streamer. The seismic source is less than 1 m in length with 30 discharging electrodes (6 kV and 30 mF), spaced about 5 cm apart. Sampling interval was , record length was 250 ms two-way
Seismic stratigraphy
Three distinctive seismic units were defined on the basis of their seismic reflection configurations and continuity observed on the seismic profiles, using the technique described in Mitchum et al. (1977). The present-day compound deltaic complex of the Sakarya River is termed Unit 1; a lowstand deposit located at the edge of shelf break is termed Unit 2; and the oldest unit bounded by an angular unconformity beneath the shelf is termed Unit 3.
Unit 1 is a progradational seismic unit composed of
Discussion
The characteristic seismic profiles across the Sakarya Delta reveal the existence of a major unconformity, which has truncated the deposits beneath the delta (Unit 1). This unconformity is ubiquitous in the study area and indicates the low stand of the Black Sea, during the latest glaciation. The sedimentary wedge of Unit 2 defines the position of low sea-level stand at that time, which was about 105 m below the present level. Their toplap termination on the upper surface resulted from a
Conclusion
Analysis of high-resolution seismic profiles from the Sakarya Delta and Submarine Canyon System has revealed oblique prograding Sakarya prodelta deposits (Unit 1) which mainly developed during the Holocene highstand over a widespread erosional surface cut in Unit 3. The latter, represents the older folded and faulted stratified basement below the prodelta deposits. The marked truncation at the top of Unit 3 indicates the subaerial exposure of the shelf area during the latest lowstand of the
Acknowledgements
We gratefully acknowledge the Captain, officers and crews of the R/V Arar (University of Istanbul, Institute of Marine Sciences and Management) for their help in data acquisition during the cruise. We thank Dr. C. Eastoe (Isotope Geochemistry Laboratory of the University of Arizona) for age determination of the samples. Special thanks to Prof. Dr. A. Kurter and Dr. A. Ertek for their helpful discussion during the preparation of this paper. This study presents part of the results of a research
References (38)
- et al.
Oscillating quaternary water levels of the Marmara Sea and vigorous outflow into the Aegean Sea from the Marmara Sea–Black Sea drainage corridor
Marine Geology
(1999) - et al.
Further evidence of abrupt Holocene drowning of the Black Sea shelf
Marine Geology
(2000) - et al.
Late Glacial–Holocene palaeoceanography of the Sea of Marmaratiming of connections with Mediterranean and Black Sea
Marine Geology
(2000) - et al.
The last sea level changes in the Black Seaevidence from the Seismic data
Marine Geology
(1999) - et al.
Morphological and seismic characteristics of the Kaoping Submarine Canyon
Marine Geology
(1993) - et al.
The influence of the San Gregorio fault on the morphology of Monterey Canyon
Marine Geology
(1998) - et al.
Ascension submarine canyon, California—evolution of a multi-head canyon system along a strike slip continental margin
Marine Geology
(1986) - et al.
Seismic evidence of shallow gas in the sediment on the shelf off Trabzon, southeastern Black Sea
Continental Shelf Research
(1999) - et al.
Seismic stratigraphy of the southeastern Black Sea shelf from high-resolution seismic records
Marine Geology
(1994) - et al.
An abrupt drowning of the Black Sea shelf
Marine Geology
(1997)
Upper Quaternary water level history and sedimentation in the northwestern Black Sea
Marine Geology
Sediment and water influxes into the Black Sea by Anatolian rivers
Zeitschrift für Geomorphologie
Geologic relations between Black Sea and Anatolia
Karadenizin Denizaltı Morfolojisi (in Turkish)
İstanbul Üniversitesi, Coğrafya Enstitü Dergisi V
Postglacial transgression of the Black Sea
International Geology Reviews
Anadolu’nun Karadeniz kıyılarının neotektoniğine bir yaklaşım (in Turkish)
Yerbilimleri Geosound
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2018, GeomorphologyCitation Excerpt :The discrepancy between the depths of the paleoshorelines in the study area (−100 to −120 m) and in the whole Black Sea (−155 m mapped by Ballard et al., 2000) can be accounted for differential isostatic and/or tectonic adjustment. The existence of several active faults marked on the seismic section (Fig. 4) support this idea, as also mentioned in previous seismic studies (Gökaşan, 1996; Demirbağ et al., 1999; Algan et al., 2002). In the inner shelf, a smooth seafloor was observed on the bathymetry except some linear features traced over short distances, local elongated highs and one eroded anticline (Fig. 5).
Late Quaternary deep-sea sedimentation in the western Black Sea: New insights from recent coring and seismic data in the deep basin
2013, Global and Planetary ChangeCitation Excerpt :Hyperpycnal flows are supposed to be responsible for the deposition of a large volume of sediments on the slope and the deep basin (Popescu et al., 2001). Only a few studies have focused on small parts of the central Turkish shelf (Duman et al., 2006), the Sakarya delta and submarine canyon (Algan et al., 2002), and off the Bosporus strait (Aksu et al., 2002b). In addition, Tekiroglu et al. (2001) and Dondurur and Cifci (2009) have provided a description of the eastern Turkish margin morphology.
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2012, Quaternary InternationalCitation Excerpt :One theory assumed that a sudden transgression, which allowed the reconnection of the Black Sea with the Mediterranean Sea, throughout the Bosphorus Sill and the Marmara Sea, took place (i.e., Ryan et al., 1997, 2003; Ballard et al., 2000, scientists who related this important rise of the sea level with the prehistoric flood myths). Some authors, such as Ballard et al. (2000), Lericolais et al. (2007, 2009) and Algan et al. (2002) reported a submerged coastline with wave cut-terraces, coastal dunes and beaches, enriched in Dreissena at various depth extending from the Romanian shelf up to the Turkish one, near the Sinop Peninsula, therefore supporting the flood hypothesis. The other theory indicates that the invasion of the saltier Mediterranean waters into the Black Sea was a gradual event (Fedorov, 1971; Görür et al., 2001; Kaminski et al., 2002; Yanko-Hombach, 2007; Yanko-Hombach et al., 2007b, among many others).