Paleoceanographic changes of the Late Pliensbachian-Early Toarcian interval: A possible link to the genesis of an Oceanic Anoxic Event

T. R. Bailey, Yair Rosenthal, J. M. McArthur, B. van de Schootbrugge, M. F. Thirlwall

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241 Scopus citations

Abstract

Secular records of the elemental and isotopic composition of belemnite calcite were studied in Pliensbachian and Toarcian sections from the Yorkshire coast, UK, and Southern Germany, to investigate oceanographic change during an interval prior to and including the Toarcian Oceanic Anoxic Event (OAE). Records from Southern Germany are correlated to the UK stratigraphy using strontium isotope stratigraphy. The geochemical trends measured from belemnite calcite are consistent between the two sections, and are interpreted in terms of temperature and salinity of the northwest European epi-continental sea. The data suggest that a dramatic environmental change coincided with the Toarcian OAE. Belemnite Mg/Ca, Sr/Ca, and Na/Ca ratios increase by a factor of between 1.7 and 2 coincident with a 3‰ negative shift in δ18O from the mid- tenuicostatum zone until the lower falciferum zone of the UK ammonite biostratigraphy (a period of ∼0.6-0.7 Myr). Taken at face value, the Mg/Ca and δ18O data argue for an abrupt warming of 6-7°C and substantial freshening during this interval. Global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes. Prior to these events, data from lower in the Yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper Pliensbachian margaritatus zone to the Toarcian lower tenuicostatum zone. This earlier event may also have been important in causing density stratification in the northwest European epi-continental sea.

Original languageEnglish (US)
Pages (from-to)307-320
Number of pages14
JournalEarth and Planetary Science Letters
Volume212
Issue number3-4
DOIs
StatePublished - Jul 25 2003

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Keywords

  • Belemnites
  • Black shale
  • Mg/Ca
  • Oxygen isotopes
  • Paleotemperature
  • Strontium isotope stratigraphy

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