The unaz formation: A key unit in the western black sea region, N Turkey

Abstract

The Pontide magmatic belt in the Western Pontides, which developed in response to the northward subduction of the northern branches of the Tethys Ocean, consists of two different volcanic successions separated by an Upper Santonian pelagic limestone unit, the Unaz Formation. The first period of volcanism and associated sedimentation started during the Middle Turonian and lasted until the Early Santonian under the control of an extensional tectonic regime, which created horst-graben topography along the southern Black Sea region. The lower volcanic succession, the Dereköy Formation, was deposited mainly within these grabens. This extensional period probably represents the rifting of magmatic arc, giving rise to the opening of the Western Black Sea back-intra-arc basin. The Unaz Formation commonly covers horsts and grabens developed before its deposition. This formation implies sudden subsidence of the region and termination of the volcanism during the Late Santonian. This period was interpreted as the time of the beginning of the oceanic spreading in the Western Black Sea Basin. The second period of magmatism developed on the Unaz Formation was more voluminous and was active during the Campanian. Stratigraphy, contact relationships and regional correlations indicate that the deposition of the Unaz Formation and similar deep marine red pelagic sediments in the Black Sea and Eastern Mediterranean region were probably controlled by local and regional tectonic events and sea level and/or climate changes.