The Kapanboğazı formation: A key unit for understanding Late Cretaceous evolution of the Pontides, N Turkey

Abstract

The Pontides forming the south-western continental margin of the Black Sea consist of two tectonic units, the Istanbul Zone in the west, and the Sakarya Zone in the central and eastern parts. The Sinop Basin in the Sakarya Zone is filled, from base to top, by Hauterivian to Albian turbidites, Cenomanian–Turonian red pelagic sediments, Turonian–Campanian magmatic-arc and related deposits, and by the uppermost Campanian to middle Eocene post-magmatic units developed on the southern passive margin of the Black Sea. Based on nannofossil, dinoflagellate, Foraminifera and Radiolaria data we describe the Kapanboğazı Formation, a Cenomanian–Turonian unit in the Sinop Basin, represented by red calcareous/siliceous pelagic shales, limestones and cherts passing gradually from the Albian black shales. These sediments possibly represent deepest depositional conditions of the basin during the Cenomanian–Turonian interval and also reflect the transition from an anoxic to an oxic palaeoenvironmental setting. The Istanbul Zone to the west was emerged during the deposition of the Kapanboğazı Formation in the Sakarya Zone.

In the Pontides, red pelagic sediments were deposited at different times during the Cenomanian–Maastrichtian interval. Because the Kapanboğazı Formation was deposited only in the Sakarya Zone and because it is present in limited outcrops due to structural reorganization and thick overlying volcanoclastic pile, most previous authors assumed Cenomanian–Turonian hiatus. Herein we describe detailed palaeontological data from this unit and discuss their importance to the interpretation of depositional history and tectonics of the Black Sea region, as well as climatic and eustatic implications.