International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

STABLE ISOTOPE EVIDENCE FOR METER-SCALE SEA LEVEL CHANGES IN LOWER CRETACEOUS INNER PLATFORM AND PELAGIC CARBONATE SUCCESSIONS OF TURKEY

Pages: 19 - 36

Authors: ISMAIL OMER YILMAZ, TORSTEN VENNEMANN, DEMIR ALTINER, MUHARREM SATIR

Abstract: In this study, stable C and O isotope compositions of bulk rock samples from Barremian-Aptian platform carbonates of the Taurides, the Pontides, and of their pelagic counterparts of the Sakarya continent in Turkey were measured for the first time. Platform carbonates and pelagic successions including a prominent black shale interval are composed of distinct sedimentary cycles in the form of meter-scale shallowing- upward sequences and limestone-marl/shale couplets, respectively. The biostratigraphy and the δ13C values allow this black shale interval to be correlated with the "Selli level". Variations in lithofacies and δ13C and δ18O values with the magnitudes of about 2 ‰ within the cycles indicate high frequency fluctuations in sea level, probably in response to alternate periods of cooling and warming occurring on Milankovitch-cycle scales even during the greenhouse-type Cretaceous. A good overall correlation between sedimentary cyclicity and variations in δ18O values suggests preservation of the primary isotopic signal.

Keywords: Barremian, Aptian, Taurides, Pontides, Sakarya, stable isotopes, cyclicity

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