ANALYSIS OF CLIMATE CHANGE IN OAE 2 IN THE CENOMANIAN/TURONIAN BOUNDARY: STABLE ISOTOPE, GEOCHEMICAL AND CYCLOSTRATIGRAPHIC APPROACH (WESTERN, NORTHERN AND SOUTHERN TURKEY)

The C/T boundary and associated black shales have been determined in different parts of Turkey. In the north of Turkey, on the western Sakarya Zone of Pontides (Goynuk and Mudurnu regions), in the Yenipazar Formation, the boundary displays cyclic alternation of bioturbated pelagic limestone/cherty limestone and black shale. A sudden change in the sedimentation is reflected by transition from the alternation of chert/cherty limestone and black shale below the boundary to the alternation of marl and limestone above the boundary (Yilmaz, 2008). In the central Sakarya zone of Pontides (Boyabat region), the boundary is recorded within deeper facies and characterized by alternation of reddish cherts/marls and black shales just below the boundary and red cherts and marls above the boundary (Yilmaz et al, 2010). In the south of Turkey, in pelagic successions of Taurides (Antalya region), the boundary is recorded within deeper facies and characterized by black shale and radiolarian chert alternations (Yurtsever et al., 2003). In shallow water carbonates of Taurides (Antalya region), the boundary was recorded within rudistic limestones and a positive excursion in C isotope was partially obtained (Sari, 2006).

Paleotemperature change at the C/T boundary has been recorded in the Ismailler stratigraphic section measured in the Yenipazar Formation in NW Turkey. Bulk d¹⁸O VPDB analysis of the samples collected around the boundary displayed a sudden shift in the values from -2,99 to -4,41 ‰. This displayed that a sudden change in the paleotemperature occurred at the boundary with relative fluctuation between 24-26 °C below and 30-32 °C above the boundary. Smaller perturbations in the temperature, 2-3 °C, have been recorded along the Milankovitch cycles composed of limestone and black shale alternations just below the boundary.

Superimposed small and large-scale climate changes displaying cyclic succession are associated with sea-level oscillations. A sudden climate change across the boundary with the association of volcanism is interpreted as possible cause of the warmest ocean water record. This event is remarkably developed in the Eastern Mediterranean Tethys Ocean recorded in the Göynuk area of the Sakarya Zone and proves the global equivalency of the Cretaceous Thermal Maximum.