Maastrichtian Anoxia and Its Influence on Organic Matter and Trace Metal Patterns in the Southern Tethys Realm of Egypt during Greenhouse Variability

Douaa Fathy; Michael Wagreich; Esraa Fathi; Mohamed S Ahmed; Mahmoud Leila; Mabrouk Sami

doi:10.1021/acsomega.3c01096

Maastrichtian Anoxia and Its Influence on Organic Matter and Trace Metal Patterns in the Southern Tethys Realm of Egypt during Greenhouse Variability

ACS Omega. 2023 May 22;8(22):19603-19612. doi: 10.1021/acsomega.3c01096. eCollection 2023 Jun 6.

Authors

Douaa Fathy¹, Michael Wagreich², Esraa Fathi³, Mohamed S Ahmed⁴, Mahmoud Leila⁵, Mabrouk Sami¹

Affiliations

¹ Geology Department, Faculty of Science, Minia University, El-Minia 61519, Egypt.
² Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, Vienna 1090, Austria.
³ Department of Agricultural Microbiology, Faculty of Agriculture, Minia University, El-Minia 61519, Egypt.
⁴ Geology and Geophysics Department, College of Science, King Saud University 2455, Riyadh 11451, Saudi Arabia.
⁵ Geology Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt.

Abstract

Maastrichtian organic-rich sediments of Egypt were deposited under a warm greenhouse climate along the stable African shelf. This study presents an integrated analysis of the geochemical, mineralogical, and palynological data from Maastrichtian organic-rich sediments in the northwest Red Sea region of Egypt. The aim of the study is to assess the impact of anoxia on the enrichment of organic matter and trace metals and to reconstruct a model for the formation of these sediments. The sediments are hosted within the Duwi and Dakhla formations, covering an interval of ∼1.14-2.39 million years. Our data indicate variable bottom-water oxygen-level conditions for early and late Maastrichtian sediments. The C-S-Fe systematics and redox geochemical proxies (e.g., V/(V + Ni), Ni/Co, and U_authigenic) suggest dysoxic to anoxic depositional conditions for the late and early Maastrichtian organic-rich sediments, respectively. The early Maastrichtian sediments contain abundant small-sized framboids (average = 4.2-5.5 μm), suggesting anoxic conditions, while the late Maastrichtian sediments have larger framboids (average = 4-7.1 μm), indicating dysoxic conditions. The palynofacies analyses reveal the high abundance of amorphous organic matter and confirm the predominance of anoxic conditions during deposition of these organic-rich sediments. The early Maastrichtian organic-rich sediments have a significant Climate concentration of Mo, V, and U, indicating high biogenic production rates and distinct preservation conditions. Additionally, the data imply that oxygen deficiency conditions and low sedimentation rates were the main factors controlling the preservation of organic matter in the studied sediments. Overall, our study provides insights into the environmental conditions and processes that led to the formation of the Maastrichtian organic-rich sediments in Egypt.