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Re: Bug Creek erosion (Re: extinction)

At 5:45 AM -0800 1/10/04, Phil Bigelow wrote:

Because the outcrops are so limited in areal extent, there is no published data on the source areas of the Bug Creek channels. Below the K-T boundary, the Hell Creek Fm. was a basin for the Absoroka highlands, the highlands around Butte, MT, and parts of Sask. and Manitoba. Mainly, the volcanic highlands around Butte. Some published sources even claim an emerging Black Hills source. So it was a relatively large drainage area.

I have measured the width of a single Bug Creek channel (unpublished, but
carefully following the channel's margin) at  roughly 30 meters.  This
would qualify it as a Missouri River-size channel.

Unfortunately, there just aren't enough preserved B.C. channels to work
out the dep. environments.   If the B.C. beds are braided stream
deposits, then there could have been more than one Missouri River-scale
river channel existing at one point in time.  That's a LOT of drainage in
a small area.  But it's pure speculation.  More than likely, the B.C.
system was of the more common single-channel meandering river type.

Strangely, a lot of sedimentological changes occured, not *at* the K-T
boundary (which is within the Hell Creek Fm.), but rather further
up-section.  The overlying Paleocene Tullock Formation doesn't look at
all like the Hell Creek Formation (the H. C. was well-drained, the
Tullock was swampy).  And the formation boundary is typically 1-3 meters
above the K-T boundary.  Delayed environmental effects or just

Go figure.  It's puzzling enough to give a dinosaurophile a headache.

Two thoughts about this --

Could the Bug Creek streams you're finding be the result of a single massive catastrophe, like the bursting of a dam of accumulated volcanic deposits by a large lake built up behind it? The small area makes me wonder.

There might be interesting analogies with the Karoo deposits from the Permo-Triassic boundary, where stream flow changed dramatically, as Peter Ward and others have reported. -- Jeff Hecht