poly: Varangian deep freeze

--- Forwarded mail from devans@gps.caltech.edu (David Evans)

Subject: Varangian deep freeze

Hi Damien,

Joe K. forwarded your message to me, with the question
from David Brin. In 1994 a paper came out saying that
we need not fuss over the Neoproterozoic glaciations
because none of the data suggested latitudes less than
25 degrees, a number arrived at by taking something like
today's climate and reducing solar luminosity by 6%,
or the expected value for about 700 million years ago.

That paper ignored the most reliable data, simply discounted
the results, from southern Australia which imply a paleo-
latitude of 2.7 +/- 3.7 degrees (i.e., right on the equator)
for glacial deposits that can be mapped laterally onto the
cratonic shelf with terrestrial periglacial frost features
preserved. What we had was very cold glacial conditions,
at sea level, on the equator. This is all in the comment by
Williams and Schmidt, EPSL 1995, on the original paper
by Meert and Van der Voo, EPSL 1994 v.123.

I am compiling an exhaustive list of all the Neoproterozoic
glacial deposits (or allegedly so) in the world--about 80
of them (Meert and Van der Voo considered about 15 in
their compilation). I find it strange that not a single polar
latitude has yet to be found for these glacial deposits, yet
some of them seem to lie directly on the Equator. Much
more work needs to be done to round out the dataset, however,
because only a handful have reliable paleolatitude determinations.
So the story might change in the next decade or two. My
paper will come out sometime this year, I hope, in a SEPM
special volume on Neoproterozoic Earth history.

Please forward this to David Brin. Thanks,
Dave

--- End of forwarded message from devans@gps.caltech.edu (David Evans)

--- Forwarded mail from devans@gps.caltech.edu (David Evans)

Subject: Varangian deep freeze

Hi Damien,

Joe K. forwarded your message to me, with the question
from David Brin. In 1994 a paper came out saying that
we need not fuss over the Neoproterozoic glaciations
because none of the data suggested latitudes less than
25 degrees, a number arrived at by taking something like
today's climate and reducing solar luminosity by 6%,
or the expected value for about 700 million years ago.

That paper ignored the most reliable data, simply discounted
the results, from southern Australia which imply a paleo-
latitude of 2.7 +/- 3.7 degrees (i.e., right on the equator)
for glacial deposits that can be mapped laterally onto the
cratonic shelf with terrestrial periglacial frost features
preserved. What we had was very cold glacial conditions,
at sea level, on the equator. This is all in the comment by
Williams and Schmidt, EPSL 1995, on the original paper
by Meert and Van der Voo, EPSL 1994 v.123.

I am compiling an exhaustive list of all the Neoproterozoic
glacial deposits (or allegedly so) in the world--about 80
of them (Meert and Van der Voo considered about 15 in
their compilation). I find it strange that not a single polar
latitude has yet to be found for these glacial deposits, yet
some of them seem to lie directly on the Equator. Much
more work needs to be done to round out the dataset, however,
because only a handful have reliable paleolatitude determinations.
So the story might change in the next decade or two. My
paper will come out sometime this year, I hope, in a SEPM
special volume on Neoproterozoic Earth history.

Please forward this to David Brin. Thanks,
Dave

--- End of forwarded message from devans@gps.caltech.edu (David Evans)
Received on Fri Jan 23 19:45:28 1998