Depositional and organic carbon-controlled regimes during the Coniacian-Santonian event: First results from the southern Tethys (Egypt)

Ahmed Mansour (Corresponding author), Michael Wagreich, Thomas Gentzis, Seare Ocubalidet, Sameh S. Tahoun, Ashraf M.T. Elewa

Publications: Contribution to journalArticlePeer Reviewed

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 environmental 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 occurrence 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 paleoceanographic 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.
Original languageEnglish
Article number104285
Number of pages18
JournalMarine and Petroleum Geology
Volume115
DOIs
Publication statusPublished - May 2020

Austrian Fields of Science 2012

  • 105105 Geochemistry
  • 105121 Sedimentology

Keywords

  • CORBs
  • Density stratified dinocysts
  • OAE 3
  • Paleoceanography
  • Redox conditions
  • Southern Tethys
  • SEDIMENTATION-RATE
  • DINOFLAGELLATE CYSTS
  • TROPICAL ATLANTIC
  • WESTERN INTERIOR
  • EARLY DIAGENESIS
  • PYRITE SULFUR
  • BLACK-SHALE DEPOSITION
  • RED BEDS
  • OCEANIC ANOXIC EVENT

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