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Response to Graydon Saunders' Wed, 14 Jan 2004 21:19:48 post.
"How do you go from the million or so years of intermittent
Deccan eruptions to the neat global iridium anomaly?"
"A number of _diffuse_ iridium enrichment layers would make sense; I
can't see how a narrow, concentrated band of iridium can be explained by
long term flood basalt volcanism, nor how a fluoridated gas transport
mechanism could result in macroscopic particles of metallic iridium being
My posts of Wed, 07 Jan 2004 13:19:20 and Wed, 07 Jan 2004 19:10:04
note that several K-T sections from around the world display multiple
K-T transition iridium spikes:
1. Nanxiong Basin, South China (6 spikes)
2. Braggs, Alabama (3 spikes)
3. Lattengebirge, Bavarian Alps (3 spikes)
4. Brazos River, Texas (2 spikes)
Since those posts, I've recalled two more sites with multiple iridium spikes:
5. El Kef, Tunisia (2 spikes)
6. Beloc, Haiti (2 spikes)
The metallic iridium particles could have originated via an impact
event. But, who knows? The K-T boundary clay is seemingly a "lag"
deposit whose deposition may have spanned 40,000 to 50,000 years, or
possibly up to 100,000 years. Volcanic debris can float for long
distances via marine currents.