Re: [asa] ICR for August - update

Back on Aug 9th, I wrote about some interesting YEC contradictions &
implications for flood geology in the Austin & Hoesch IMPACT article. In
that post, I said that I would consult one of their references about the
Late Jurassic age of the Independence dike swarm to confirm that
radiometric dating was used to determine the age of ~150 million years
(Ma). My update follows the relevant snippet from that previous post.
-----
<<4. Radiometric dating is an invalid way of determining ages (numerous
YEC sources including Morris and Austin.)>>

<<Austin & Hoesch don't claim to accept the validity of radiometric
dating. In fact, Austin has done several studies attempting to discredit
radiometric dating assumptions, techniques, or results. Thus my amazement
when I read the part in this IMPACT article where Austin & Hoesch suggest
that the source of the volcanic ash in the Late Jurassic Brushy Basin
Member of the Morrison Formation could be the Independence dike swarm in
the central Sierra Nevada Range with the statement: "The swarm of dikes
has long been interpreted as having opened as an event with an interpreted
age of ~150 Ma (Late Jurassic)". Now I didn't take the time to check out
their reference for this age for the dike swarm but I would be willing to
bet that it is based on radiometric dating. (I'll check it out from the
library when I return in a few days and will issue a retraction if I am
proved wrong.) If my assumption is correct, then Austin & Hoesch are
accepting radiometric ages when they are convenient but then turning
around and denying the validity of the technique and resulting numbers.>>
-----

The Austin & Hoesch reference for the age of the dike swarm was "Carl,
B.S., and Glazner, A.F., 2002, Extent and significance of the Independence
dike swarm, eastern California, in Glazner, A.F., Walker, J.D., & Bartley,
J.M., eds., Geologic Evolution of the Mojave Desert and Southwestern Basin
and Range: Boulder, Colo., Geological Society of America Memoir 195, pp.
117?130." As I suspected, this article contains a compiled table (p. 120)
of 61 published & unpublished radiometric dates (23 dikes, 8 volcanic
rocks, and 30 coeval plutons) done almost exclusively by uranium-lead
(U-Pb) dating of zircon crystals.

To get to the point of this update. Austin & Hoesch apparently accept
that the Brushy Basin Member of the Morrison Formation is Late Jurassic
but would deny that it is ~150 Ma. They summarize and conclude their
article with these statements: "The same watery catastrophe that buried
dinosaurs in Utah was accompanied by super-size volcanism from sources in
the west. The [geologic] record is best interpreted in durations of days
or weeks, not millions of years. The Genesis Flood provides the historical
framework used to understand supervolcanoes." Yet their logic escapes me.
 The Brushy Basin Member has been designated by geologists as Late
Jurassic based upon it's stratigraphic position and fossils (including
dinosaurs) - two assumptions commonly denied by YEC writers. The
approximate numeric age of the Brushy Basin Member has been determined by
radiometric dating of crosscutting dikes and from U-Pb dates of zircons in
contained ash fall layers - techniques commonly rejected by YEC writers.
So, unless they believe that the U-Pb dating methods give consistent
results, why search the scientific literature and cite possible volcanic
ash sources by correlating U-Pb dates? Remember, they believe that the
entire Brushy Basin Member was deposited in "days or weeks" and yet they
are trying to identify a volcanic event that may have happened during
those same hours of the one-year-long Genesis Flood. In their extremely
compressed time frame, there are hundreds of volcanic events in the
western U.S. that could have potentially supplied ash during those few
hours ... unless you are constrained by the data obtained from radiometric
dating.

Steve
[Disclaimer: The thoughts and opinions expressed herein are my own and
are not to be attributed to my employer.]
_____________
 Steven M. Smith, Geologist, U.S. Geological Survey
 Box 25046, M.S. 973, DFC, Denver, CO 80225
 Office: (303)236-1192, Fax: (303)236-3200
 Email: smsmith@usgs.gov
 -USGS Nat'l Geochem. Database NURE HSSR Web Site-
  http://pubs.usgs.gov/of/1997/ofr-97-0492/

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Received on Wed Aug 23 14:09:39 2006