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.


Microfacies analysis of upper devonian - lower carboniferous shallow water carbonates of the Yilanli formation in Zonguldak area, North Western, Turkey
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...
Stratigraphical, sedimentological, geochemical and cyclostratigraphical analyses of upper cretaceous (upper santonian- campanian) pelagic successions of Haymana and Mudurnu-Göynük basins of the Sakarya continent, Turkey
Afridi, Bakht Zamir; Yılmaz, İsmail Ömer; Department of Geological Engineering (2014)
The Upper Cretaceous (Upper Santonian-Campanian) successions were measured from two different basins of Turkey, Haymana basin and Mudurnu-Göynük basin. The measured Alagöz and Göynük sections are dominantly composed of red marly beds and fine grained siliciclastic green-gray beds with occasional interruption of fine grained turbiditic bedding. A variety of lithofacies are identified in the studied sections, including radiolarian packstone, silty marls, marls, mudstone, claystone, siltstone and fine grained ...
The Unaz Formation: A Key Unit in the Western Black Sea Region, N Turkey
Tuysuz, Okan; Yılmaz, İsmail Ömer; Svabenicka, Lilian; Kirici, Sabri (2012-01-01)
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...
Cenomanian - Turonian Oceanic Anoxic Event (OAE2) in the Sakarya Zone, northwestern Turkey: Sedimentological, cyclostratigraphic, and geochemical records
Yılmaz, İsmail Ömer; Altıner, Demir; Ocakoglu, Faruk; Acikalin, Sanem (2010-04-01)
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...
Tectonic evolution and paleogeography of the Kırşehir Block and the Central Anatolian Ophiolites, Turkey
van Hinsbergen, Douwe J. J.; Maffione, Marco; Plunder, Alexis; Kaymakcı, Nuretdin; Ganerød, Morgan; Hendriks, Bart W. H.; Corfu, Fernando; Gürer, Derya; de Gelder, Giovanni I. N. O.; Peters, Kalijn; McPhee, Peter J.; Brouwer, Fraukje M.; Advokaat, Eldert L.; Vissers, Reinoud L. M. (American Geophysical Union (AGU), 2016-4)
In Central and Western Anatolia two continent-derived massifs simultaneously underthrusted an oceanic lithosphere in the Cretaceous and ended up with very contrasting metamorphic grades: high pressure, low temperature in the Tavsanli zone and the low pressure, high temperature in the Kirsehir Block. To assess why, we reconstruct the Cretaceous paleogeography and plate configuration of Central Anatolia using structural, metamorphic, and geochronological constraints and Africa-Europe plate reconstructions. We...
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: