Abstract Several canyons are observed along the Turkish margin of the western Black Sea that are associated with a prominent unconformity and interpreted to be the manifestations of the sea-level fall during the Messinian salinity crisis in the Mediterranean. In this study, their morphology, geometry and fill characteristics, as well as downslope evolution, are compared and contrasted using four 3D seismic surveys and some 2D regional seismic lines. Two types of canyon morphologies are observed in the study area: (1) shelf incising and (2) blind. Located in the western part of the study area and deeply incised into a wide shelf, the Karaburun Canyon extends roughly in a SW–NE direction. The fill of the canyon is almost absent on the shelf, where the canyon base is downlapped by a series of Pliocene clinoforms. A thin fill appears on the upper slope, which gets thicker towards the lower slope. The eastern part of the study area is dominated by a series of blind canyons (Boğaziçi canyons). They are typically confined to the continental rise, with their heads hardly reaching the lower slope. Their fill is entirely characterized by mass-transport complexes (MTCs). It is concluded that during the Messinian lowstand, the sediments within the Karaburun Canyon bypassed the wide shelf and were funnelled down to the continental rise and abyssal plain through the slope, which was followed by progradation of the basin margin during the relative sea-level rise in the Pliocene. A minimal imprint by tectonics in that particular area might have helped establish more stable conditions for the development of a relatively mature sediment dispersal system extending from the hinterland down to the basin centre. In this area, the shelf-slope morphology was dominantly shaped by the depositional geometries of the sedimentary packages. Being fully confined to the continental rise, the Boğaziçi canyons are situated in an area where shelf-slope morphology is governed by the Late Cretaceous volcanic arc. Parallel with the coastline, these volcanic edifices have created fairly steep dips; thus, leading to the development of an unstable basin margin and favouring MTC deposition at least since the Early–Middle Miocene. The width and relief of the canyons display a decreasing trend from west to east, which may be attributed to their relative distance from a possible drainage system in the vicinity of the Bosporus that might have acted as the major sediment supplier during this period.

Abstract Influences of tectonics and late Quaternary sea-level changes on sedimentation in the submarine Şarköy 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 were collected at water depths ranging from 62 to 245 m. 14 C 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% CaCO 3 ) 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 slumps 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 Şarköy Canyon is controlled by both regional Plio-Quaternary tectonics and global Quaternary sea-level changes.

Abstract The exploration for petroleum in the Black Sea is still in its infancy. Notwithstanding the technical challenges in drilling in its deep-water regions, several geological risks require better understanding. These challenges include reservoir presence and quality (partly related to sediment provenance), and the timing and migration of hydrocarbons from source rocks relative to trap formation. In turn, these risks can only be better understood by an appreciation of the geological history of the Black Sea basins and the surrounding orogens. This history is not without ongoing controversy. The timing of basin formation, uplift of the margins and facies distribution remain issues for robust debate. This Special Publication presents the results of 15 studies that relate to the tectonostratigraphy and petroleum geology of the Black Sea. The methodologies of these studies encompass crustal structure, geodynamic evolution, stratigraphy and its regional correlation, petroleum systems, source to sink, hydrocarbon habitat and play concepts, and reviews of past exploration. They provide insight into the many ongoing controversies regarding the geological history of the Black Sea region and provide a better understanding of the geological risks that must be considered for future hydrocarbon exploration. The Black Sea remains one of the largest underexplored rift basins in the world. Although significant biogenic gas discoveries have been made within the last decade, thermogenic petroleum systems must be proven through the systematic exploration of a wide variety of play concepts.

Abstract In western Turkey, the Alaşehir and Büyük Menderes grabens form east–west trending major tectonic structures. Their sedimentary fill is important for regional tectonic models for the late Cenozoic evolution of the Aegean region. These deposits are divided into four units dated between the early Miocene and Quaternary. We studied the magnetostratigraphy of two sections in the Alaşehir graben and one in the Büyük Menderes, partly covering the first and second sedimentary units. Detailed palaeomagnetic analysis allowed us to determine ChRM component for these rocks. The Zeytinçayı river and road sections (Alaşehir graben) record several polarity reversals, which are tentatively correlated to the interval C5Cn.3n–C5ADr (approximately between 14.6–16.6 Ma) of the ATNTS2004. This correlation is also supported by palaeontology and radiometric dating of syn-extensional intrusions. In the Eycelli section (Büyük Menderes graben) only three polarity zones are recorded, and their tentative correlation with the interval of C5Bn.1r–C5Br (14.88–15.97 Ma) is in overall in agreement with the record of Eskihisar sporomorph association in this formation. These results place the initiation of the Alaşehir and Büyük Menderes grabens in the early Miocene. The palaeomagnetic declinations from the Alaşehir graben indicate about 25° anticlockwise rotation, whereas that of the Büyük Menderes graben indicate a clockwise rotation of about 30–40°. These contradictory vertical-axis rotations might be explained by detachment faults in the region. In Tertiary formations of western Turkey, contradictory block rotations are common and likely reflect thin-skinned deformation in the area rather than rigid crustal movements. Therefore, average anticlockwise rotations in western Turkey cannot be used as evidence for the model of back-arc spreading in the Aegean region.

Abstract The evolution of Triassic reefs is characterized by a three-step development accentuated by three brief reef blooms, a long-lasting evolutionary renewal of reef biota, a strong diversification of "reef windows" including anactualistic siliciclastic settings, and a global latitudinal reef expansion from the northern to the southern hemisphere starting during the Carnian. Triassic reefs were formed in the Tethys and in western and eastern parts of the Paleo-Pacific Ocean of Panthalassa during a time range of > 50 Myr Tethyan reefs are concentrated in the Western Tethys, in a southern reef zone off the northern coasts of Gondwana, and on various plates drifting from Gondwana to the north. Most Panthalassan reefs are known from terranes originally situated in the ancient Pacific and now attached to Asia and western North America. Compositional reef types include microbial reefs, sponge reefs, coral reefs, dasycladacean algal reefs, pelecypod reefs, and serpulid reefs. The end-Permian extinction event resulted in the sudden disappearance of high-diversity Late Permian reefs in southern China and a global gap of inetazoan reefs in the Early Triassic and Early Anisian, lasting > 8 Myr. A few Permian-type Lazarus taxa reappeared in the Norian, indicating a prolonged existence in unknown refugia, possibly on the shelves of Panthalassan or Tethyan terranes. The Early Triassic is characterized by the exclusive dominance of microbial reefs. The recovery of metazoan-domina ted reefsduringthe Middleand Late Anisian lasted about2 Myrand took place in the Western Tethys and on the South China Plate, The Ladinian to the Norian-Rhaetian interval exhibits phases of differentiation, faunal turnovers, extinctions, and the continuous latitudinal expansion of reef domains from the Ladinian to the Norian-Rhaetian within a time range of > 40 Myr. Four evolutionary reef units are evident both for scleractinian corals and sphinctozoid sponges as well as for dasycladacean green algae with respect to the taxonomic composition and diversity of the reef faunas: Middle Anisian to Early Ladinian, Late Ladinian to Early Carnian (Cordevolian or Julian J, first reef optimum), Late Carnian to Early Norian (faunal turnover), and Norian-Rhaetian (second reef optimum). The Triassic reef ecosystem underwent a distinct three-step development starting with Scythian microbial reefs, followed by Anisian to Carnian and Norian-Rhaetian metazoan-dominated reefs. The second and the third intervals are distinguished by the biotic composition, dominating reef builders, size and abundance of reef structures, widths of reef windows, frequency of reef domains, depositional setting, and latitudinal distribution patterns. The change and turnover between the steps 2 and 3 took place during thelale Carnian-early Norianinterval within a time span of about 13 Myr. During this tune intervalmajorextinctions, climatic perturbations, and significant paleooceanographic changes occurred. High late Carnian-early Norian extinction rates of reef biota were compensated by synchronous high origination rates. The significant transition from middle Triassic and Carnian sponge-dominated reefs to late Triassic coral-dominated reefs indicates a change in principal environmental controls, possibly connected with rearrangements of oceanic surface circulation patterns and related nutrient input. Norian-Rhaetian microbial-serpulid reefs in the northwestern Tethys represent a peculiar reef type different from coeval sponge-coral reefs facing open-marine basins. All Triassic reefs were severely affected by a global crisis near the Triassic-]urassic boundary and disappeared totally in the Western Tethys and Southern Tethys as well as on the Pacific mieroplates. Lowermost Jurassic (Hettangian) reefs are extremely rare. Some late Triassic reef organisms (corals, encrusters) continued into the Middle Liassic The recovery of the metazoan reef system in the Liassic lasted at least 10 Myr. Quantitative survey: Reef abundance increased from the Middle Anisian to the Late Anisian and Early Ladinian, and then abruptly in the Ladinian, followed by a first reef optimum in the earliest Carnian (Cordevolian). A decrease from very abundant to common reef occurrence took place during the Late Carnian. The frequency and regional distribution of reefs were set back in the Early Norian, followed by a new gradual increase, resulting in a second reef optimum in the Late Norian. During this time platform margin reefs in the Tethys and reefal buildups in oceanic settings and in back-arc positions of the Pa nthalassan Paleo-Pacific were established The frequency of Rhaetian reefs was similar to that after the first reef optimum. The two reef optima, defined by great abundance and wide regional distribution of reefs, embrace remarkably short time intervals (Cordevolian about 1-2 Myr, Sevatianabout2 Myr). Similarly, the Illyrian reef bloom spanned only a relatively short time range. There are conspicuous differences in thepaleolatitudinal distributional patterns of reefs over time: The Late Absaroka I (including the earliest early Triassic to early Carnian interval) and Late Absaroka 11 (late Carnian to earliest Jurassic interval) supersequences differ in the increasing expansion of reefs from the northern to the southern hemisphere and in the extreme scarceness of reefs in the eastern Paleopacific off western North America during the Middle Triassic. Reef-free areas were common in the Northern Tethys during the Anisian and Ladinian. Extended reef-free areas south of the paleoequator occurred since the Late Carnian. The total latitudinal ranges of Tethyan reefs increased in time from approximately 2° S to about 25° N in the Anisian and Ladinian to 13° S to 25° N during the Carnian, followed by a maximum range of 35° S to 33“ N in the Norian and a similar range in the Rhaetian. Norian reef domains, partly associated with the development of attached or isolated carbonate platforms, covered areas of several hundreds to several thousands of square kilometers. The major compositional reef types exhibit differences with respect to their common latitudinal ranges: Microbial-sponge reefs of the Anisian occur between 5” N and 20° N, late Anisian-Ladinian-Carnian sponge-dominated reefs predominantly between 10" N and 30° N, and Norian-Rhaetian sponge-coral reefs and coral-dominated reefs between latitudes of about 30° N and 30° S. fluctuating patterns over time are recorded by reef abundance, changes in reef size, and the extension of reef occurrence from only within the northern hemisphere to both hemispheres. The increase in the number of isolated reef domains, distinct differences in the composition of reef biota in various parts of the Tethys and Panthalassa, and the regionally different associations of foraminifera, sponges, and corals in eastern and western Panthalassan reefs indicate an increasing control on reef distribution by fluctuating ocean current patterns, leading to pronounced differentiations of reef biota and reef types during the Norian.