RE: Extinction

["Steve Brusatte" <dinoland@mailcity.com>]

On Fri, 24 Mar 2000 17:38:58   Phillip Bigelow wrote:
>
>Uhhh...  Not to throw a wrench into the smoothly running machinery of this
>discussion, but, question:  Was the trackway located below a known K-T
>boundary layer (~2 cm-thick layer containing iridium spike, shocked
>quartz, spherules, soot, etc.), OR was the trackway found in a zone that
>is *inferred* to be at K-T boundary because it appears to be at the same
>stratigraphic level as other known boundary layers in the formation?
>
>A BIG difference in terms of the recoverable science (and as you can tell
>from my question, I haven't read this particular Lockley book!)
>
>In the vast majority of the uppermost section of the Hell Creek Formation,
>the K-T boundary bed is missing, either because of Paleocene bioturbation,
>or because of localized intraformational unconformities (intervening
>erosion after the fallout layer was deposited).  Therefore, for the vast
>majority of the biostratigraphy of the Hell Creek Formation, the exact
>TIME boundary is unknown, and is instead extrapolated.  High-resolution
>biostratigraphers are old friends with this phenomenon, particularly those
>people who work on centimeter-scale stratigraphy. Few other
>biostratigraphers totally grasp the concept as readily, particularly those
>who work on paleo-megafauna in terrestrial settings. 

Well, good question.  I do not know the exact answer, but I believe that there 
was an iridium spike.  Lockley quotes, "To their surprise, as well as my own, 
it took less than a minute for me to find tracks only 15 inches below the 
iridium layer."  This is quoted from page 224 in The Eternal Trail.

Lockley also gives two other references:

Lockley, Martin.  "Tracking Dinosaurs."

Lockley, Martin and A. Hunt, "Dinosaur Tracks and other fossil footprints of 
the Western United States."

Steve




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