Overview of the Bosphorus Depositional Fan from Data Sets Recovered on the Black Sea Shelf off the Strait of Istanbul

Since the preliminary mapping of the northern Bosphorus outlet of the Black Sea continental shelf by the 90’s NATO project, an important data set bringing morphological, seismic and sedimentological information is now available to describe there a shallow fan system consisting of a main channel and short distributary branches, levees, and sediment waves, correlative to a southern source flowing to the north. This paper brings complementary quantitative data from landscape at the eastern and western shelf area of the shallow fan system. It confirms that the Bosphorus outlet fan preserved on the shelf surface provides an important record of surface water flow. To deduce the history of the Marmara/Black Sea last connexion, it is fundamental to understand how surface water flow could have generated the observed morphology. To date, morphological studies propose only very short time estimates for the longevity of the necessary hydrological events responsible for this deposit. Here we propose a compilation of multibeam bathymetry data from previous studies completed with multibeam bathymetric data collected from new areas not previously studied, together with high resolution seismic data (Chirp) and gravity cores from the confluence of the Bosphorus and Black Sea. This compilation shows that this shallow fan delta is in all points comparable to a depositional fan with a branching pattern of channels mimicking a mostly exposed fan-shaped body prograding from the foot of a significant break in slope and extending from the outlet of the strait to the shelf edge. Although we do not entirely resolve the ongoing controversies, we provide extra data to obtain a wider view to this key area. Using analogue cases and flume studies, it is acceptable to propose that the distinct morphology of this form of fan delta could have been the result of a single event of basin-filling on a timescale of decades after a relatively strong Mediterranean-originated northerly flow into the partly sub aerially exposed shelf area earlier than 8.5ky BP reshaped by present day saline undercurrent processes.