Cretaceous Pelagic Red Beds and Black Shales (Aptian-Santonian), NW Turkey: Global Oceanic Anoxic and Oxic Events

The study areas located near the towns of Göynük, Mudurnu and Nall›han in the central northwesternpart of Turkey lie on the ‘Sakarya Continent’, which is one of the tectonic entities of the Cretaceous geology of Turkey. Measured stratigraphic sections comprise the Aptian pelagic carbonates and the overlying Albian–Coniacian turbiditic sequences, which are all capped by a Late Santonian red pelagic succession. Lower and Upper Aptian, Upper Albian and Cenomanian/Turonian marine black shales recognized in the sections are followed by Lower and Upper Aptian, Upper Albian and Turonian marine red beds. The black shales are generally silty, laminated, and include pyritized radiolarian and planktonic foraminifera. The red beds are composed of red-pink limestones, which are of packstone facies with abundant planktonic foraminifera, bivalve, echinoidea, iron infillings and coatings. They also include red silty marls with quartz, iron and glauconite minerals as well as bivalve fragments. Sedimentologic, sequence stratigraphic and cyclostratigraphic properties of black shales and red beds recorded along the measured stratigraphic sections have been determined and Fischer plot analysis has been applied for their correlation and coherency. Their sequence stratigraphic positions and cyclic nature indicate that black shales were generally deposited in the early transgressive system tracts. However, red beds represent the late transgressive/high-stand systems tracts. In some areas, the Upper Santonian red beds are observed in association with a drowning event and overlie a Type-3 sequence boundary. Their stratigraphic position and sedimentology are used to better understand the oceanic events and tectonic movements recorded in this basin. These black shales and red beds are recognized within coeval biostratigraphic intervals as in their global counterparts.