Diyala Journal for Pure Science
Scientific Refereed Journal Published By College of Science - University of Diyala
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Diyala Journal for Pure Science DJPS
P- ISSN:2222-8373, E-ISSN:2518-9255
Volume 14, Issue 3 , July . 2018
Paleoceanographic Reconstruction of Upper Cretaceous, Black Shale Succession, Northeastern Iraq Using Geochemical Proxies to Indicate Paleoredox and Paleoenvironment Conditions
Khaldoun Ibrahim Ahmad, Salah Ali Hussain , Mutadhid Al-Obaidi
Year: 2018, Volume: 14, Issue: 3
Pages: 238 - 265, DOI: http://dx.doi.org/10.24237/djps.1403.444C
Thirteen outcrop samples of lithified black shale from the North of Iraq, Gulneri Formation, were analyzed for stable carbon and nitrogen isotopes of organic matter and for trace elements distribution to assess the source of organic matter and the redox state at the time of deposition, respectively. Paleoredox-sensitive (trace) elements including ratios of Ni, V, and Co indicate fluctuations between an oxic, dyoxic, and suboxic/anoxic conditions during the deposition of the formation. Specifically V/(V + Ni) suggests generally low oxygen during the deposition of the formation. Detrital iron oxides are present in some samples. Carbon isotopic values are depleted throughout the formation ranging between -26 to -24. The nitrogen isotopic values record negative values indicative of denitrification of amino acids or nitrogen fixation in the ocean. Mineralogical observations reveal the alteration of pyrite to iron oxides in the bottom of the formation. There are two potential indicators of the deposition setting: first, the lack of pyrite except at the bottom suggests a generally oxic setting. However, fluctuations in the V/Al ratio throughout the formation, low U and Mo and the presence of planktonic foraminifera suggests that the redox conditions fluctuated and were sometimes anoxic at least in the sediment.
Key words: Stable isotope, sensitive (trace) elements, Cretaceous, black shales, paleo-productivity, paleo-oxygenation.