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Sedimentological, cyclostratigraphical and sequence stratigraphical analysis of cretaceous Üzümlü formation (NW Turkey)

Keskinler, Salih Yiğit
High resolution sampling was performed along the Üzümlü Formation exposed near the Yeniceşıhlar village of Mudurnu (Bolu). Field and thin-section analyses showed that the Üzümlü Formation is composed of cm to m scale cycles of 4th and 5th order. The 4th order cycles are equivalencies of parasequences and have 0.4 Ma average duration. 5th order cycles are interpreted as episodic. Upper Albian (OAE1c or OAE1d) and Cenomanian/Turonian (OAE2) anoxic events are observed as black shale levels in the studied section. Position of black shale levels is interpreted using cyclostratigraphy and sequence stratigraphy. Four types of cycle are determined. A and B-type cycles are placed in transgressive and Highstand System Tract. C and D-type cycles are placed in Lowstand System Tract. Two type 3 and one type 1 sequence boundaries are recorded. The boundary between the Soğukçam Limestone and the Üzümlü Formation is interpreted as the first type 3 sequence boundary. The second one separates the Üzümlü Formation and the Yenipazar Formation and is observed at the top of the section. Type 1 boundary is represented by a conglomeratic level in the middle of the succession. Provenance analysis of sandstones indicates that during the Cenomanian the source area changed from magmatic arc setting to continental setting.