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Re: Bug Creek erosion (Re: extinction)



"James R. Cunningham" <jrccea@bellsouth.net> writes:
> Phil Bigelow wrote:
> > 

> > No channels of a similar massive scale existed during Hell Creek 
> time, and
> > nothing similar existed later in Tullock time.  These were 
> relatively
> > high-energy Missouri River-volume river(s) that were suddenly 
> created and
> > then existed for a geologically-short time period.

 
> What were their estimated drainage areas, as compared to the D.A. of 
> the
> Missouri?
> 

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I have measured the width of a single Bug Creek channel (unpublished, but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
coincidence??

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

<pb>
--










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