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Re: extinction



> There was no vast, general, catastrophic extinction
> of life at the K-T boundary.

Dalila Zaghbib-Turki, Narjess Karoui-Yaakoub, Rakia Said-Benzarti, Robert
Rocchia & Éric Robin: Révision de la limite Crétacé-Tertiaire de la coupe
d'Ellès (Tunisie): Proposition d'un nouveau parastratotype, Géobios 34 (1),
25 -- 37 (30 June 2001)

Oh yes there was. The planktonic forams look as if they had met a
Terminator. The mentioned paper has _impressive_ figures; the site it
describes has better resolution than El Kef and may well become the next
stratotype for the K-T boundary. For the sake of name-dropping, even Gerta
Keller has used figures from this paper, which show the catastrophic
extinction of planktonic forams _precisely_ at the boundary, in one of her
own articles.

> My last two posts cited Peter Vail, the father of sequence
> stratigraphy, whose works have allowed us to better understand the
> history of the K-T transition. Geologists who ignore Peter Vail are
> like physicists who ignore Albert Einstein, or biologists who would
> dismiss Charles Darwin, or geneticists who would flip off Watson and
> Crick.

To be fair, I ignore Einstein's dislike of Heisenberg's Uncertainty
Relation, and I dismiss Charles Darwin's theory of inheritance, which has
become useless because of e. g. the work of Watson & Crick.

> "Eustatic falls and rises produce major changes in basin
> configuration, stratal patterns, and sedimentation rates, as well in
> oceanic geochemistry. The major eustatic fall in the latest
> Maastrichtian, marked by the withdrawal of epicontinental seas
> throughout the globe [refs], and the subsequent eustatic rise had a
> tremendous effect on global depositional patterns, as well as on the
> biotic and geochemical conditions in the world's oceans. Globally,
> the K-T boundary is marked by a period of marine terrigenous-sediment
> starvation."

Just a few days ago I found again the paper which suggests that the pattern
of sea-level change was more complex, especially that it wasn't synchronous
around the globe, but that transgressions in two half-hemispheres correlated
to regressions in the other two.

> "The faunal K-T boundary occurs with this transgressive systems
> tract, which is dated from the latest Maastrichtian through the
> earliest Danian."

Yes, it took four million years -- much, much longer than the mass
extinction, which occured quite precisely in its middle.

> "Of the three distinct iridium anomalies at Bragg (Fig. 8), the
> lowest occurs in the late Maastrichtian, the middle near the K-T
> boundary, and the upper within faunal zone NP1. These anomalies
> coincide with marine-flooding surfaces interpreted as parasequence
> boundaries."

Hasn't meanwhile the K-T boundary been defined via the Ir anomaly? (Like the
Pal-Eocene boundary has recently been defined via an excursion of the
12C-13C ratio.)

> "The presence of iridium at these flooding surfaces suggests that
> iridium was present in the open ocean from the latest Maastrichtian
> through earliest Danian and was concentrated on the Alabama
> paleoshelf during periods of terrigenous-sediment starvation caused
> by rapid sea-level rises."

This interprets what happened in the whole world by examining just one site.
It does not mention any of the terrestrial Ir anomalies, which obviously
can't have been created by this concentration process.