Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo Research paper Depositional and organic carbon-controlled regimes during the Coniacian- Santonian event: First results from the southern Tethys (Egypt) Ahmed Mansour a,* , Michael Wagreich b , Thomas Gentzis c , Seare Ocubalidet c , Sameh S. Tahoun d , Ashraf M.T. Elewa a a Geology Department, Faculty of Science, Minia University, 61519, Minia, Egypt b Department of Geodynamics and Sedimentology, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna, Austria c Core Laboratories LP, 6316 Windfern Road, Houston, TX, 77040, USA d Geology Department, Faculty of Science, Cairo University, 12613, Giza, Egypt ARTICLE INFO Keywords: Southern Tethys Redox conditions Density stratified dinocysts OAE 3 CORBs Paleoceanography ABSTRACT Geochemical and palynological proxies were determined for 31 samples representing the upper Coniacian- lowermost Campanian Abu Roash A Member, collected from the BED2-3 well. This was done to assess the prevailing paleoredox conditions, productivity levels, and water-column settings to: (1) understand controls and mechanisms related to accumulation of organic carbon within the sedimentary record; (2) assess principal en- vironmental processes that triggered the preservation of organic matter-poor, calcareous shale and limestone facies of the Abo Roash A Member; and (3) to interpret the paleoceanographic settings and confirm the oc- currence of either Oceanic Anoxic Event 3 (OAE3) or Cretaceous Oceanic Red Beds (CORBs) within the Abu Gharadig Basin in the southern part of the Tethyan Ocean, Egypt. Sedimentation rates were reconstructed based on the biostratigraphic-age constraints of marine dinoflagellate cysts (dinocysts). Trace elements-based ratios and relationships were used in order to study the role of clastic terrestrial input. Three groups of dinocysts and freshwater Pediastrum algae were used to study the water-column conditions. Results showed that the Abu Roash A Member was deposited under oxic to intermittently dysoxic conditions in a distal inner to middle neritic environment, with varying sedimentation rates from 32 to 119 mm kyr-1. Productivity appeared to be a significant factor for determining magnitudes of the organic carbon accumulation; however, low productivity was prevalent during deposition. Carbonate content was high, which resulted in dilution of organic matter during varied rates of sediment input. Such results indicate that the paleoceano- graphic conditions in the southern Tethys witnessed the absence of prevalent oceanic anoxia (i.e., the Coniacian- Santonian OAE 3) and deposition of the CORBs as in several parts of the Tethys, the Pacific, and the Indian oceans. 1. Introduction In marine environments, the geochemical cycles of carbon and sulfur and the level of oxygen, are considered major factors that control the accumulation and deposition of organic matter (OM) (e.g., Berner, 1982). Accumulations of organic matter-rich black shale often reflect episodes of oxygen depletion in the water column (Schlanger and Jenkyns, 1976), mainly during episodes of anoxic and/or euxinic bottom-water conditions such as during OAEs (Jenkyns, 2010), com- pared to OM-poor facies deposited during enhanced ventilation (e.g., CORBs). CORBs are pelagic to hemi-pelagic sediments that were ex- tensively deposited during the Late Cretaceous with maximum dis- tribution from the middle Turonian to the Campanian (e.g., Neuhuber and Wagreich, 2009; Wagreich, 2009). They commonly form during intervals of relatively low siliciclastic input, low OM production and preservation, and low sedimentation rates versus active oxidation processes (Neuhuber and Wagreich, 2009). Thus, evaluating the mag- nitude and major drivers that control the accumulation of OM-poor sediments versus organic-rich facies has been the focus of numerous studies (e.g., Raiswell et al., 1988; Dean and Arthur, 1989; Babu et al., 2002; Rimmer et al., 2004; Tribovillard et al., 2006; Neuhuber and Wagreich, 2009; Wagreich, 2009, 2012; Jenkyns, 2010; Reolid et al., 2012; Alsenz et al., 2015; Neuhuber et al., 2016; Ocubalidet et al., 2018). Several geochemical studies agree that three major variables influence TOC content: preservation state, input, and dilution of OM (Schwartzkopf, 1993; Tyson, 1996, 2001; Bohacs et al., 2005; Hofmann https://doi.org/10.1016/j.marpetgeo.2020.104285 Received 15 September 2019; Received in revised form 5 February 2020; Accepted 6 February 2020 * Corresponding author. E-mail address: ahmedmans48@mu.edu.eg (A. Mansour). Marine and Petroleum Geology 115 (2020) 104285 Available online 11 February 2020 0264-8172/ © 2020 Elsevier Ltd. All rights reserved. T