Stratigraphic transition and palaeoenvironmental changes from the Aptian oceanic anoxic event 1a (OAE1a) to the oceanic red bed 1 (ORB1) in the Yenicesihlar section, central Turkey

Hu, Xiumian
Zhao, Kuidong
Yılmaz, İsmail Ömer
Li, Yongxiang
We performed a detailed study of the stratigraphic transition from the early Aptian oceanic anoxic event 1a (OAE1a) to the oceanic red bed 1 (ORB1) along the pelagic Yenicesihlar section in the Mudurnu region of central Turkey. The Selli-equivalent level of the OAE1a (approximately 2.1 m thick) consists of black to dark-grey shales interbedded with grey marlstones with total organic carbon contents up to 2.05%. The carbon isotopic record shows a negative excursion (C3 stage, 0.58 m in thick) at the bottom of the Selli-equivalent black shales and a stepwise positive excursion (C4 to C6 stages, 1.52 m in thick) within the Selli-equivalent black shales. The OAE1a-ORB1 transitional interval (similar to 20.3 m in thick) displays an alternation of light-grey limestones with grey marls or shales that links the anoxic environment of the Selli-equivalent black shales at the bottom and the highly anoxic environment of the ORB1 at the top. The OAE1a-ORB1 transition corresponds to stable carbon isotopic C7 and C8 stages, and based on the cyclostratigraphy, the transition lasted for approximately 1.3 Myr, which is very close to the duration of the OAE1a (1.1-1.3 Myr). The delta O-18 values in the transitional interval are variable and generally show an increase towards the ORB1, when the climate became relatively cool.


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Ahmed, Nouman; Yılmaz, İsmail Ömer; Department of Geological Engineering (2016)
The Yılanlı Formation of Upper Devonian to Lower Carboniferous succession of the Zonguldak region were measured from Gökgöl section near Zonguldak city, NW Turkey. The studied section dominantly consists of limestone of grey – dark grey color with thin to thick beds of black shale and claystone. A variety of lithofacies identified in the studied section including limestone, dolomite, shale, claystone and mudstone. Nine microfacies are identified as grainstone, packstone, wackstone, mudstone, bindstone, ruds...
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The Pontide magmatic belt in the Western Pontides, which developed in response to the northward subduction of the northern branches of the Tethys Ocean, consists of two different volcanic successions separated by an Upper Santonian pelagic limestone unit, the Unaz Formation. The first period of volcanism and associated sedimentation started during the Middle Turonian and lasted until the Early Santonian under the control of an extensional tectonic regime, which created horst-graben topography along the sout...
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The Cenomanian/Turonian oceanic anoxic event as recorded in many parts of the world is characterized by presence of black shales and global carbon isotope peaks. Cyclic variations within the anoxic event and association with pelagic red beds are indicated by many studies. Global tectonic/volcanic controls on the origin and the chronostratigraphic position of the anoxic event within the global sea-level changes are important for understanding the paleoceanographic and paleoclimatic conditions during the depo...
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Özcan, Ercan; Less, Gyoergy; Okay, Aral; Baldi-Beke, Maria; Kollanyi, Katalin; Yılmaz, İsmail Ömer (2010-01-01)
The Eocene marine sequence in the southern part of the Thrace Basin (NW Turkey) involves a variety of platform and deep-marine olistostromal units, the stratigraphy of which have been vigorously debated in the past. A detailed analysis of larger foraminifera in these either foraminifera or foraminifera-coral-coralline algae-dominated platform and associated comparatively deeper-marine units permits us to establish a high-resolution biostratigraphy in the context of shallow benthic zonation (with SBZ zones) ...
Citation Formats
X. Hu, K. Zhao, İ. Ö. Yılmaz, and Y. Li, “Stratigraphic transition and palaeoenvironmental changes from the Aptian oceanic anoxic event 1a (OAE1a) to the oceanic red bed 1 (ORB1) in the Yenicesihlar section, central Turkey,” CRETACEOUS RESEARCH, pp. 40–51, 2012, Accessed: 00, 2020. [Online]. Available: