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Re: extinction



Response to Phil Bigelow's post of  Fri, 16 Jan 2004 12:07:46.

Hi Phil, for the record, here is my e-mail to you of last Wednesday:

"Just a private note to tell you how much I'm enjoying our exchanges on the dinosaur listserv. And, also to apologize for being slow with some of my responses. I've been intensely busy on some other things, and haven't had as much time as I hoped for the listserv. Maybe things will loosen up soon. For now, please bear with me, and I'll respond to your very good questions as soon as I can."

Phil, for your: "Your list is not sufficiently informative. What are the depositional environments at each of these sites? More importantly, what is the
*micro*-stratigraphy of these zones?," I simply do not have the time to abstract this information for you. I provided specific references for each site in my posts of Wed, 07 Jan 2004 13:19:20, and Wed, 07 Jan 2004 19:10:04 so that interested listmembers could examine the papers for themselves. Here are excerpts from my posts:


(i) Nanxiong Basin, South China: Zhao et al. titled "A possible causal relationship between extinction of dinosaurs and K/T iridium enrichment in the Nanxiong Basin, South China: evidence from dinosaur eggshells" (Palaeogeography, Palaeoclimatology, Palaeoecology, 2002, v. 178, pp. 1-17).

(1) Braggs, Alabama: Following are some quotations from the Donovan et al. paper "Sequence stratigraphy setting of the Cretaceous-Tertiary boundary in central Alabama" (SEPM Special Publication no. 42, 1988):

"Of the three iridium anomalies at Braggs, the lowest occurs in the late Maastrichtian, the middle near the K-T boundary, and the upper within faunal zone NP1 (Tertiary)....The presence of iridium at these flooding surfaces suggests that iridium was present in the open ocean from the latest Maastrichtian through earliest Danian....Thus, it appears that iridium was not introduced into the atmosphere during a unique event occurring at the K-T boundary, but was present in the atmosphere for a much longer period of time."

(2) Lattengebirge, Bavarian Alps: The Graup and Spettel paper "Mineralogy and phase-chemistry of an Ir-enriched pre-K/T layer from the Lattengebirge, Bavarian Alps, and significance for the KTB problem" (Earth and Planetary Science Letters, 95, 1989) notes that an almost complete K-T section at Lattengebirge, Bavarian Alps, has three iridium-bearing events over an extended period from latest Maastrichtian into early Danian. The oldest spike predates the K-T boundary by 14,000-9,000 years. Geochemically those spikes display the same signature as the K-T boundary layer, and should have the common source.

(3) Brazos River, Texas: The Ganapathy et al. paper "Iridium anomaly at the Cretaceous-Tertiary boundary in Texas" (Earth and Planetary Science Letters, 54, 1981) indicates two iridium spikes, one at the K-T boundary, and one below.

Certainly, you will want to study the data base, methodology, and conclusions drawn from each study. You can do that only by actually reading each individual paper.

Cordially,
Dewey McLean

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"Dewey M. McLean" <dmclean@vt.edu> writes:
 Response to Graydon Saunders' Wed, 14 Jan 2004 21:19:48 post.

 Graydon wrote:

 "How do you go from the million or so years of intermittent
 Deccan eruptions to the neat global iridium anomaly?"


 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)

Your list is not sufficiently informative. What are the depositional environments at each of these sites? More importantly, what is the *micro*-stratigraphy of these zones?