Mantle Degassing Induced Dead Ocean in the Cretaceous-Tertiary Transition

  1. E.T. Sundquist and
  2. W.S. Broecker
  1. Dewey M. Mclean

Published Online: 18 MAR 2013

DOI: 10.1029/GM032p0493

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present

How to Cite

Mclean, D. M. (1985) Mantle Degassing Induced Dead Ocean in the Cretaceous-Tertiary Transition, in The Carbon Cycle and Atmospheric CO: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0493

Author Information

  1. Department of Geology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900605

Online ISBN: 9781118664322

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Keywords:

  • Carbon cycle (Biogeochemistry)—Congresses;
  • Atmospheric carbon dioxide—Congresses;
  • Geological time—Congresses;
  • Paleothermometry—Congresses;
  • Geology, Stratigraphic—Congresses

Summary

Prior to the terminal Cretaceous marine extinctions about 65 m.y. ago (polarity chron R29), ecological stability prevailed suggesting steady state between rate of mantle CO2 degassing and uptake by surficial sinks. The extinctions were characterized by ecological instability that persisted into the Early Tertiary; instability was coeval with the Deccan Traps flood basalt volcanism in India that flooded earth's surface with 2.6×106 km3 of lavas; radiometric ages concentrate around 66–60 m.y., with the main volcanic activity around 65 m.y. during a reversed-to-normal polarity sequence; most Deccan Traps basalts were erupted during the Deccan Reversed Magnetic Polarity Epoch, with some activity into the overlying Nipani normal. Using the geomagnetic time scale of Harland et al. the Deccan Reversed Interval is R29, and the Nipani N29. Ages of lower and upper boundaries of R29 are 65.39 and 64.86 m.y. (5.3×105 years); based on this duration for the bulk of Deccan Traps volcanism, the rate of basalt production was 4.91 km3/yr versus modern mid-ocean ridge basalt production of 1.2 km3/yr. Deccan Traps total mantle CO2 release was about 5×1017 moles CO2, released at a rate of 9.6×1011 moles/yr, versus the modern release rate of about 4.1×1012 moles/yr. Nearly 25% of total annual CO2 release from all other sources, Deccan Traps CO2 addition would have upset steady state, with release exceeding uptake, leading to CO2 buildup in the atmosphere and marine mixed layer, triggering ecological instability. Reduced mixed layer photosynthesis and CaCO3 production indicated in the record evidence of failure of the Williams-Riley pump (productivity plus gravity pump of CO2 from shallow into deep oceans), producing dead ocean conditions which would have triggered additional CO2 release and global ecological instability. The dinosaurs seem to have become extinct during magnetic polarity chron R28.