The last sea level changes in the Black Sea: evidence from the seismic data

High resolution shallow seismic data collected from the southwestern shelf of the Black Sea indicate five different seismic stratigraphical units. The lower three of them belong to the Upper Cretaceous-Eocene, Oligocene-Miocene and Early Quaternary (prior to Holocene) sediments, respectively. These units are considered as a basement for the recent sediments deposited related to the latest connection of the Black Sea and the Mediterranean. The surface of these units are truncated to form an etchplain developed before the Flandrian transgression. The fourth unit covers the older units by an onlap. Its contact with the older units seen at -105 m is the shoreline of the Black Sea prior to the last major sea-level change. The fifth unit has been deposited since drowning of the Black Sea shelf. The principal cause of drowning of the Black Sea shelf is not only the last sea level rise as it is at the shelves of the Sea of Marmara but also the opening of the Strait of Istanbul. It is also realised by the comparison of the shelf area and the Catalca-Kocaeli etchplain that, the present continental part of this etchplain has been considerably uplifted with respect to the shelf area along the present shoreline. This uplifting must have also reactivated the faults around the Strait of Istanbul foundering the strait valley and, thus, permitting the Mediterranean waters to pass into the Black Sea, and initiating the sudden drowning of the Black Sea shelf. (C) 1999 Elsevier Science B.V. All rights reserved

Late Quaternary sedimentation and tectonics in the submarine Sarkoy Canyon, western Marmara Sea (Turkey)

Influences of tectonics and late Quaternary sea-level changes on sedimentation in the submarine Sarkoy Canyon, western Marmara Sea (Turkey) were investigated using a total of 37 seismic reflection profiles and 12 gravity sediment cores (with 63-435 cm thicknesses). which C-14 were collected at water depths ranging from 62 to 245 m. C-14 ages of base sections in three cores (11.585, 11.845 and 24.915 ka BP) and upward fining of grain size in the cores suggest that these sediments must have been deposited since the sea-level lowstand at about 12 ka BP, when the conditions in the Marmara Sea began to change from lacustrine to the present marine phase. With some exceptions, siliciclastic mud (silt + clay > 90%) with low carbonate contents (< 15% CaCO3) is the dominant sediment type covering the floor of the canyon. The high organic carbon contents (1-2%) with slight downcore-increasing tendencies reflect higher primary organic productivities towards the early Holocene. Faults, sedimentation deformation structures, and submarine slides or stumps observed on seismic profiles, varying elevations of dated lowstand palaeoshores and low water contents (19-25%) of sediments at some sites together strongly indicate the important effect of neotectonics on sedimentation in this canyon. On the seismic profiles at least four stratigraphic units were recognized overlying the pre-Miocene basement. which indicate not only the effects of faulting and folding but also changing conditions and related depositional environments in and around the canyon. Geological evolution and thus the sea-floor morphology of the Sarkoy Canyon is controlled by both regional Plio-Quaternary tectonics and global Quaternary sea-level changes

The effects of the North Anatolian Fault zone on the latest connection between Black Sea and Sea of Marmara

The development of the Strait of Istanbul is also one of the principal results of the tectonics which led to the evolution of the North Anatolian Fault Zone (NAFZ) in the Marmara Region 3.7 Ma ago. High resolution seismic profiles from the Marmara entrance of the Strait of Istanbul show a folding which occurred after the deposition of the parallel reflected Tyrrhenian sediments. Over the Tyrrhenian strata, a fondoform zone of a deltaic sequence and marine sediments of the latest sea level rising are present. These sediments also display syn-depositional folding. This situation implies that a local compressional stress field was created over the area probably since the Wurm Glacial age. This recent variation of the tectonic regime in the northern shelf of the Sea of Marmara may indicate a significant change in the development of the NAFZ through the Sea of Marmara. This variation of evolution of the NAFZ affected the latest development of the Strait of Istanbul via clockwise rotation of the Istanbul and Kocaeli peninsulas by right-lateral shearing between two zone bounding faults. This rotation has led to the development of NNE-SSW left-lateral faults in the Strait of Istanbul and local compressional and tensional areas explaining the compressional structures seen in the southern entrance of the Strait of Istanbul. Therefore, the latest Mediterranean-Black Sea connection was established by means of the sufficient deepening of the Bosphorus channel by a variation in the evolution of NAFZ through the Sea of Marmara. (C) 2002 Elsevier Science B.V. All rights reserved

Late Quaternary sedimentation and tectonics in the submarine Sarkoy Canyon, western Marmara Sea (Turkey)

WOS: 000267235500011Influences of tectonics and late Quaternary sea-level changes on sedimentation in the submarine Sarkoy Canyon, western Marmara Sea (Turkey) were investigated using a total of 37 seismic reflection profiles and 12 gravity sediment cores (with 63-435 cm thicknesses). which C-14 were collected at water depths ranging from 62 to 245 m. C-14 ages of base sections in three cores (11.585, 11.845 and 24.915 ka BP) and upward fining of grain size in the cores suggest that these sediments must have been deposited since the sea-level lowstand at about 12 ka BP, when the conditions in the Marmara Sea began to change from lacustrine to the present marine phase. With some exceptions, siliciclastic mud (silt + clay > 90%) with low carbonate contents (< 15% CaCO3) is the dominant sediment type covering the floor of the canyon. The high organic carbon contents (1-2%) with slight downcore-increasing tendencies reflect higher primary organic productivities towards the early Holocene. Faults, sedimentation deformation structures, and submarine slides or stumps observed on seismic profiles, varying elevations of dated lowstand palaeoshores and low water contents (19-25%) of sediments at some sites together strongly indicate the important effect of neotectonics on sedimentation in this canyon. On the seismic profiles at least four stratigraphic units were recognized overlying the pre-Miocene basement. which indicate not only the effects of faulting and folding but also changing conditions and related depositional environments in and around the canyon. Geological evolution and thus the sea-floor morphology of the Sarkoy Canyon is controlled by both regional Plio-Quaternary tectonics and global Quaternary sea-level changes

On the origin of the Bosphorus

The Palaeozoic-Upper Cretaceous basement palaeomorphology of the Bosphorus (the Strait of Istanbul) bears the evidence of a valley of a palaeostream running to the Black Sea in the north, a palaeobasin deeper than -160 m opening to the Sea of Marmara in the south, and a barrier between these two features. This suggest that the northern part of the Bosphorus was formed mainly by fluvial activity, whereas the southern part developed as a basin by faulting. The recent sediment thickness exceeds 130 m in the basin, indicating that the southern part of the Bosphorus was once essentially depositional rather than an erosional

Stratigraphy of the sediment infill in Bosphorus Strait: water exchange between the Black and Mediterranean Seas during the last glacial Holocene

The sediment infill over the Paleozoic bedrock in the Bosphorus Strait consists of four sedimentary units which were deposited in the last 26,000 (14)C years B.P. The stratigraphy of these units suggests that this Dart of the Bosphorus was a freshwater lake between 26,000 and 5,300 (14)C years B.P., depositing sands with a freshwater mollusc fauna of Black Sea neo-euxinian affinity (Dreissena rostriformis, Dreissena polymorpha, and Monodaena pontica). The first appearance of euryhaline Mediterranean molluscs (e.g., Ostrea edulis, Mytilus edulis) was observed at 5,300 (14)C years B.P. in this part of the Bosphorus. Deposition of coarse Mytilus-bank and Ostrea-bank units suggests that the establishment of the present dual-flow regime in the Bosphorus took place at about 4,400 (14)C years B.P

Morpho-tectonic evolution of the Marmara Sea inferred from multi-beam bathymetric and seismic data

In an initial stage, the Sea of Marmara developed as a graben and, in due course, considerable volumes of sediments were deposited in this basin. Before 200 ka, a new fault (New Marmara Fault) cutting through the whole basin developed, which postdated large sub-marine land sliding in the western part of the basin. This mass movement created the Western Ridge. The initiation of this strike-slip fault indicates that the extensional stress regime was replaced by a new, shearing stress field. In the eastern part of the Marmara Basin, the New Marmara Fault consists of two branches. The northern one replaces the normal faulting at the bottom of the northeastern slope of the basin. As a result, this slope has been rejuvenated. The southern branch is located along the central axis of the basin, forming the major extension of the North Anatolian Fault Zone within the region. Two restraining bends were formed because of the counterclockwise rotation of that part of the Anatolian Block. This resulted the uplifting of the Eastern Ridge and the formation of the positive flower structure within the Tekirdag Basin. The establishment of the compressional regime around the Sea of Marmara also resulted in the northwest-southeast shortening of the initial Marmara Basin

Description of dynamics of the Tuzla Landslide and its implications for further landslides in the northern slope and shelf of the Cinarcik Basin (Marmara Sea, Turkey)

Seismic and multi-beam bathymetric data from the northern shelf and slope of the Cinarcik Basin, which is generated by the North Anatolian Fault Zone (NAFZ) located in the easternmost basin in the Marmara Sea, were re-interpreted to better understand the future sub-marine landslide susceptibility. Seismic data indicate that upper surface of the sub-marine extension of the Paleozoic rocks has an NNE-SSW oriented basin and a ridge type morphology controlled by the secondary faults of the NAFZ. Basins are fulfilled by Plio-Quaternary sediments, which are cut by strike-slip faults on the shelf and slope. The thickness of basin deposits reaches up to 130 m toward the linear northern slope of the Cinarcik Basin. A relatively recent sub-marine landslide, the Tuzla Landslide, cuts the slope of the Cinarcik Basin. The detailed morphological investigation indicates that the Tuzla Landslide is a deep-seated rotational landslide, which was likely triggered by activity of the NAFZ. Morphological analyses also indicate that the thick Plio-Quaternary deposits on the Paleozoic basement slid during the Tuzla Landslide event. This landslide is considered as a key event to understand the dynamics of the potential landslides on the northern shelf and slope of the Cinarcik Basin. Two areas locating on the eastern and the western sides of the Tuzla Landslide are considered as the potential areas for future sliding due to similarities of geological and geomorphological features with the Tuzla Landslide such as similar thick Plio-Quaternary deposits, similar slope morphology, and similar fault activity cutting the sediments. Considering this information. the purposes of the present study are to determine the dynamics of the possible landslide areas and to discuss their effects on the sub-marine morphology. In the light of the interpretations, the amounts of possible displaced material are obtained. Three different landslide scenarios due to possible slide surfaces for future landslides are developed and assessed. The first scenario is sliding of the sediments at the shelf break. The third scenario is a mass movement of almost whole basin deposits on the Paleozoic rocks. The latter one is evaluated as less important because of the volume of the displaced material, and the latter one is accepted as lowest possible event. Among the scenarios, the second scenario is accepted as the most critical and possible because of the amount of the slipped material and existence of faults rupture, which is considered as further sliding surfaces. These landslides will result in important changes in shelf. slope and basin floor in the study area. Crown Copyright (c) 2009 Published by Elsevier B.V. All rights reserved

Evidence and. implications of massive erosion along the Strait of Istanbul (Bosphorus)

The Strait of istanbul (Sol) (Bosphorus) is a narrow valley, which has evolved tectonically from a stream, and in which thick sediment deposits have accumulated in the course of its evolution. Detailed seismic and multi-beam bathymetric data have revealed that the upper parts of the deeper channel deposits consist of parallel strata, which have mostly been eroded subsequently to their deposition. The resulting erosion surface is represented by the present channel floor in the strait, the estimated volume of the eroded material being approximately 2 x 10(8) m(3). Erosion rate and seafloor morphology indicate that the flow direction was from the south to the north. This inner channel may have been formed by an abrupt flooding of the Black Sea by Mediterranean waters at the beginning of the latest connection between the Marmara and the Black seas Subsequently, the Mediterranean bottom current of the modern two-way flow system, which was established at about 5-4 ka b.p., has given the latest shape to the strait floor