🚀 go-pugleaf

Philip Deitiker <Donevenask@worlnet.att.net> wrote in message news:<zsTdc.4521$K_.136571@bgtnsc05-news.ops.worldnet.att.net>...
> icycalmca@yahoo.com (Daryl Krupa) says  in
> news:c70365ef.0404092336.33a0afb8@posting.google.com:
>
> >>   The dating in the 28 kya range seems to coincide with a
> >> period of warmer temperatures, but that ice-free corridor
> >> was still closed.
> > <snip>
> >
> >   Sorry, it had not yet been closed, at 28 kya.
> >   And there are many indications that it was not closed,
> >   ever,
> > before somewhere around 21-24 ka BP.
>
> It seemed odd it would be closed during a warm period but
> open in colder periods.

Philip:
  Yes, that would indeed seem odd, and I have not seen indications
that that was so.
  Perhaps you should show me where you get your information on
Quaternary paleoclimate, and then I might be able to resolve
the apparent discrepancy.

> What do you think the basis was of the 30 kya date on closing?

  It was reported as a date on organics below till, and below
a proglacial lake dammed by the last advance.
  The sedimentary environment was interpreted as being in contact
with glacial ice at the time of deposition of the organics, i.e.
just before the proglacial lake filled up and started overflowing
westward.
  That interpretation was disputed by Dyke, who did not see why
the organics could not have been deposited well before ice
advanced into the area, i.e. he thought that the organics gave
a maxiuum age for glacial advance, but not an exact age.
  Other dates in the region contradict the 30 ka age for ice advance,
as described by Dyke, et al. at the URL I cited earlier,
at the bottom of p. 13
(that's the page before the figure I suggested you look at):

http://tinyurl.com/2gys2

"The older age assignment is based on several radiocarbon dates
in the 30–40 14C ka BP range on plant material
below drift near the glacial limit and
below sediments of Glacial Lake Old Crow, which formed in
unglaciated Yukon Territory
[near Bluefish Caves, BTW]
when ice stood at the limit and blocked eastward drainage.
However, these dates do not necessarily closely limit
the age of the last ice advance.
In fact, the youngest dated material
below Glacial Lake Old Crow sediments is
a mammoth tusk with AMS dates of [25 14C ka BP and 24 14C ka BP].
Furthermore, a continuous series of AMS mammal bone collagen dates
between 24 and 40 14C ka BP from Old Crow Basin
precludes existence of the lake during that interval and the
abrupt termination of the series at ~24 14C ka BP likely signifies
flooding of the basin, as suggested by Thorson and Dixon (1983)."

  Now that you have read what Dyke wrote, has your question on
the 30 ka date been answered?

Daryl Krupa