Molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the Early Jurassic
Abstract
Relatively brief periods of severe paleoenvironmental changeduring the Jurassic and Cretaceous were associated with thewidespread accumulation of organic-rich marine deposits, termedoceanic anoxic events (OAEs). These intervals involved abruptglobal warming of <IMG SRC="/math/sim.gif" ALT=" " BORDER="0">5-10 °C, higher rates of continentalweathering, elevated extinction rates, and large-scale perturbationsto the global carbon cycle. The major OAEs also overlapped temporallythe emplacement of large igneous provinces. However, despitebeing known as OAEs, the extent of seawater anoxia at thosetimes is undefined and the causative processes remain unclear.Here we show how changes in seawater molybdenum isotope ratios(a proxy for seawater anoxia) during the Toarcian (Early Jurassic)OAE define the onset and expansion of oxygen deficient conditions.Our data also place constraints on the areal extent of marineanoxia during the event and demonstrate that anoxia expandedand contracted periodically, broadly in line with precession-drivenchanges in <IMG SRC="/math/delta.gif" ALT="{delta}" BORDER="0">13 Corg. Despite their intermittent occurrence overgeological history, OAEs have an important contemporary relevancebecause the magnitude and high rates of environmental changethen were broadly similar to those occurring at the presentday.
- Publication:
-
Geology
- Pub Date:
- March 2008
- DOI:
- 10.1130/G24446A.1
- Bibcode:
- 2008Geo....36..231P