Tectonic-Sedimentary Evolution of the North Tethyan Margin in the Central Pontides of Northern Turkey
Timur Ustaömer, Alastair Robertson, 1997. "Tectonic-Sedimentary Evolution of the North Tethyan Margin in the Central Pontides of Northern Turkey", Regional and Petroleum Geology of the Black Sea and Surrounding Region, A. G. Robinson
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The Central Pontides of northern Turkey is one of the best exposed seg-ments of the southern margin of Eurasia adjacent to the Tethys Ocean, at least from the Paleozoic onward, and its history can be taken as a guide to the tec-tonic evolution of the Pontides as a whole. A number of east-west-trending tectonic units record subduction-accretion and the growth of the south Eurasian margin. The Central Pontides also document Lower Cretaceous lithospheric extension related to opening of the Black Sea during the Late Mesozoic-Early Tertiary and a later active margin and collisional history.
Three time intervals exemplify the tectonic evolution of the Central Pontides. During the Late Paleozoic-Mid-Jurassic, Tethys was subducted northward, with development of an oceanic arc (the Çangaldağ Complex) and rifting of a continental fragment (istanbul and Devrekani units), related to transform and/or active margin processes, to form a back-arc basin system (the Küre Complex and equivalents) in latest Paleozoic-earliest Triassic times. This was followed in the Lower Triassic by collision of a seamount (the Kargi Complex) with the active Eurasian margin, leading to deep burial beneath accreted units, including ophiolitic rocks. This collision possibly triggered collapse of the Küre back-arc basin further north, also in the Lower Triassic. Southward closure of the Küre Basin by the Upper Jurassic finally led to accretion of the entire tectonic stratigraphy to the southern margin of Eurasia during the “Cimmerian orogeny.”
During the Late Jurassic–Early Cretaceous, the recently formed orogen sub-sided, possibly triggered by renewed northward subduction of Tethys, and carbonate platform sedimentation ensued during the Late Jurassic-Early Cretaceous. Crustal extension of the active margin then took place in the Early Cretaceous. The carbonate platform was dissected into half grabens, into which turbidites, debris flows, and olistoliths were shed. Early Cretaceous extension also activated exhumation of high-grade metamorphic rocks in the Central Pontides as a precursor to opening of the Western Black Sea marginal basin.
During the Late Cretaceous-Early Tertiary, the Western Black Sea Basin underwent sea-floor spreading, while the southern margin rapidly subsided, associated with northward emplacement of ophiolites and ophiolitic melange. During the Early Tertiary, the Pontides were sutured to the Anatolides to the south, resulting in south-vergent reimbrication of the Paleotethyan basement, especially in southerly areas, and north-vergent compression near the Black Sea coast.
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Regional and Petroleum Geology of the Black Sea and Surrounding Region
In 1967 and 1969, two oceanographic cruises were made in the Black Sea under the guidance of the Woods Hole Oceanographic Institute: The cruises included scientists from many countries and disciplines. Their aims were to determine the recent geological and geochemical evolution of the Black Sea, to map the shallow structure of the basin, and to study the interaction between the oxidized surface waters and the anoxic waters beneath them. The results were published 23 years ago, as AAPG Memoir 20 (Ross and Degens, 1974). During the 1969 cruise, the vessel Atlantis II collected 40 piston cores, which formed the basis of most of the subsequent geological studies that were restricted to very recent sedimentation. Speculations concerning the origin of the basin and the relationship of the geology offshore to that exposed around the margins of the Black Sea were rooted in pre-plate tectonic concepts of basin formation and were in any case hampered by a lack of relevant data (Brinkmann, 1974).
In 1976, the Glomar Challenger visited the Black Sea on Leg 42B of the Deep Sea Drilling Project and drilled and cored three deep-water sites (379, 380, and 381). Well 381 north of the Bosporus encountered sediments as old as Miocene, including some apparently deposited in shallow water (Ross, 1978).
The next major volume in Western literature to deal with the Black Sea was published a decade later, collecting papers presented two years earlier at a conference in Yalta. In this volume, a number of seismic reflection lines