PALEOCLIMATIC INSIGHTS ON THE CENOMANIAN-TURONIAN OCEANIC ANOXIC EVENT (OAE2) FROM NORTHERN IRAQ BASED ON CALCAREOUS NANNOFOSSILS AND GEOCHEMICAL DATA

Safwan Al-Lhaebi

doi:10.46717/igj.53.2c.6rs-2020-09/06

Abstract

Calcareous nannofossils, mineralogical and geochemical investigations are carried out on the Cenomanian-Turonian boundary of the Gulneri Formation in the Azmir, Dokan and Degala sections, northern Iraq. Regarding the calcareous nannofossil data CC11 and CC12 biozones were identified. A detailed investigation was carried out to identify calcareous nannofossils species. On the basis of their stratigraphic distribution, two biozones were proposed in this study; Quadrum gartneri Interval Biozone (CC11) part and Lucianrhabdus maleformis Interval Biozone (CC12) part. Correlation with other calcareous nannofossils biozones from regional schemes led to conclude that the age of the Gulneri Formation in the studied sections is the early Turonian. Mineralogical (X-ray diffraction XRD) and trace elements geochemistry (X-ray fluorescence XRF) data along with the dominance of calcareous nannofossil Watznauria that indicates warm and arid climatic condition prevailing in the Cenomanian-Turonian transition.

Highlights

Oceanic anoxic events (OAEs) are distinct features of the Cretaceous ocean with widespread marine anoxia events accompanied with accumulation of large amounts of organic carbon on the ocean floor in an oxygen-depletion conditions (Schlanger and Jenkyns, 1976 and Schlanger et al, 1987)
Calcareous Nannofossil Biostratigraphy Regarding the calcareous nannofossil biostratigraphy, the age of the Gulneri Formation in Azmir and Degala sections must be considered late Cenomanian as Helenea chiastia which is a marker for the top of UC5 (UC5c) with the age of late Cenomanian is observed
Boundaries and discussion: The lower boundary of this biozone is not exposed in the studied area which is marked by first occurrence of Quadrum gartneri, the upper boundary is marked by the first occurrence of Lucianorhabdus maleformis, which did not record recently but the first occurrence of Eiffellithus eximius is recorded

Summary

Introduction

Oceanic anoxic events (OAEs) are distinct features of the Cretaceous ocean with widespread marine anoxia events accompanied with accumulation of large amounts of organic carbon on the ocean floor in an oxygen-depletion conditions (Schlanger and Jenkyns, 1976 and Schlanger et al, 1987). The Gulneri Formation that represent the Cenomanian-Turonian period in northern Iraq has been studied by many researchers that mentioned this formation may represent an oceanic anoxic event due to the presence of black layers rich in organic matter, dwarfing of some foraminiferal species, presence of low oxygen tolerant species and calcareous nannofossil distribution that may refer to anoxic conditions prevailing during deposition of these black layers (Buday, 1980; Abawi et al, 2006; Ameen and Gharib, 2014 and Al-Sagri, 2015). Other studies refer to a range of environmental conditions prevailing during deposition of the Gulneri rocks (dyoxic, suboxic, anoxic and euxinic) based on drowning due to differential subsidence (Haddad and Amin 2007) or common high organic matter content or oxygen deficient fossil species (Al-Dulaimy and Awadh, 2007). Mustafa and Tobia (2020) mentioned that the geochemical parameters have been used by to understand the paleo-oxygenation conditions of ancient sediments

Methods

Results

Discussion

Conclusion