Thursday, September 6, 2012

Multiple Events Caused K-Pg Mass Extinction?

Tobin have published work on a K-Pg section from Antarctica. From the latest issue of Palaeogeography, Palaeoclimatology, Palaeoecology:

Although abundant evidence now exists for a massive bolide impact coincident with the Cretaceous–Paleogene (K–Pg) mass extinction event (~ 65.5 Ma), the relative importance of this impact as an extinction mechanism is still the subject of debate. On Seymour Island, Antarctic Peninsula, the L√≥pez de Bertodano Formation yields one of the most expanded K–Pg boundary sections known. Using a new chronology from magnetostratigraphy, and isotopic data from carbonate-secreting macrofauna, we present a high-resolution, high-latitude paleotemperature record spanning this time interval. We find two prominent warming events synchronous with the three main phases of Deccan Traps flood volcanism, and the onset of the second is contemporaneous with a local extinction that pre-dates the bolide impact. What has been termed the K–Pg extinction is potentially the sum of multiple, independent events, at least at high latitudes.

I don't have access to the paper so just some general thoughts.

Gerta Keller and colleagues have also challenged the theory that a single meteorite impact caused the mass extinction 65 mya. Except, their theory is that the bolide impact everyone is familiar with, which is the Chicxulub impact event in Yucatan Mexico took place about 300,000 thousand years before the peak Deccan volcanism. They base this on observations made on K-Pg boundary sections in Mexico and Texas and some work in India published in Journal of the Geological Society of India and Earth and Planetary Science Letters which support a link between Deccan volcanism and regional extinctions.

So, was the Chicxulub meteorite impact before the peak Deccan volcanism as Keller and colleagues say or was it 200,000- 300,000 thousand years after Deccan volcanism as this new paper by Tobin et. al. suggests. The famous iridium anomaly observed in many K-Pg boundary sections has been dated to after the main phase of Deccan volcanism indicating that there was a meteorite impact some time after peak volcanism.

Or were there two impacts with the Deccan volcanism sandwiched in between? It does seem that the single bullet theory for the K-Pg mass extinction is under serious threat.

Science Daily summary of Tobin' s paper

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