Geochemical environment of the Coniacian-Santonian western tropical Atlantic at Demerara Rise

Christian März, Britta Beckmann, C. Franke, Christoph Vogt, Thomas Wagner, Sabine Kasten

Research output: Contribution to journalLiterature review

17 Citations (Scopus)

Abstract

Organic carbon-rich shales deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 were drilled during ODP Leg 207 at Demerara Rise. We present integrated high-resolution geochemical records of core intervals from ODP Sites 1259 and 1261 both from nannofossil biozone CC14. Our results reveal systematic variations in marine and detrital sediment contribution, depositional processes, and bottom water redox conditions during black shale formation at two locations on Demerara Rise in different paleo-water depths. A combination of redox proxies (Fe/S, P/Al, C/P, redox-sensitive/sulfide-forming trace metals Mn, Cd, Mo, Ni, V, Zn) and other analytical approaches (bulk sediment composition. P speciation, electron microscopy, X-ray diffraction) evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale. These extreme redox conditions persisted and were periodically punctuated by short-termed periods with less reducing bottom waters irrespective of paleo-water depth. Sediment supply at both sites was generally dominated by marine material (carbonate, organic matter, opal) although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites, winnowing bottom currents and/or variable detritus sources, along with less reducing bottom water at the proposed shallower location (ODP Site 1259). At Site 1261, located at greater paleo-depth, redox fluctuations were more regular, and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record. Strong similarities of the studied deposits exist with the stratigraphic older Cenomanian-Turonian OAE2 black shale sections at Demerara Rise, suggesting that the primary mechanisms controlling continental supply and ocean redox state were time-invariant and kept the western equatorial Atlantic margin widely anoxic over millions of years. (C) 2008 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)286-301
Number of pages16
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume273
Issue number3-4
DOIs
Publication statusPublished - 15 Mar 2009

Keywords

  • Oceanic anoxic event
  • Trace elements
  • Iron
  • Phosphorus
  • Sediment source
  • Redox changes
  • Enrichment factors
  • ODP LEG 207
  • EASTERN EQUATORIAL ATLANTIC
  • ANOXIC MARINE-SEDIMENTS
  • BLACK-SHALE DEPOSITION
  • WATER-COLUMN ANOXIA
  • OXYGEN MINIMUM ZONE
  • TRACE-METALS
  • ORGANIC-MATTER
  • CONTINENTAL-MARGIN
  • RICH SEDIMENTS

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