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Re: Late Cretaceous Arctic Climates
It might be a little off topic, but I think this notion of an exact model
and can we or can't we get it right, with climate deterioration, is
something of a red herring. The most important lesson to learn from the
past is that Earth's climate is very sensitive, and dynamically unstable.
It's easy to mess it up. Doesn't matter exactly what you do to mess it up,
or how you contribute to pushing changes past the tipping point.
----- Original Message -----
Sent: Monday, July 27, 2009 9:02 PM
Subject: Re: Late Cretaceous Arctic Climates
Collin... exactly what I'm talkin' about. Eventually, the myth that "it
was too warm in the Mesozoic for ice" will melt away.
Interestingly enough, there's been quite a stir lately in the climatology
world about how climate models are really, really terrible at handling
CO2. If we can't get it right for today's and "recent" ice-age
And thanks for those references. I was missing one. ;-)
From: Colin McHenry <firstname.lastname@example.org>
Sent: Mon, Jul 27, 2009 4:15 pm
Subject: Re: Late Cretaceous Arctic Climates
There is indeed gathering evidence for glacial episodes in the Southern
Hemisphere during the Early Cretaceous;
Alley, N. F., and
Frakes. 2003. First known Cretaceous glaciation: Livingston Tillite
Cadna-owie Formation, South
Australian Journal of Earth Sciences 50(2):139-144.
A 2 m-thick diamictite occurs near the base of the Cretaceous Eromanga
Basin succession at Trinity Well, at the northern extremity of the
Flinders Ranges in South Australia. The diamictite consists of a matrix
of silt- and clay-size particles and a framework of sand and coarser
materials up to small boulder size. Scanning electron microscope study
reveals the presence of numerous quartz grains displaying extreme
nd surface textures attributed to glacial crushing. Sandy
sediments considered as fluvioglacial in origin and a locally developed
facies displaying flow structures attributed to solifluction processes
constitute the basal 3â5 m of the sequence. In places these directly
underlie the diamictite and rest with angularity on Neoproterozoic
Adelaidean strata. Conformably above the diamictite at the type
locality âRecorder Hillâ is a sequence approximately 15 m thick of fine
sand and silt units containing lonestones up to ~70 cm diameter and
hummocky cross-stratification. These sediments have been assigned to
the Cadna-owie Formation and are dated on palynology as Berriasian to
Valanginian. The occurrence of diamictite containing glacially affected
quartz grains contributes to our interpretation that the southern
margin of the Eromanga Basin, and at least the adjacent part of the
northern Flinders Ranges, were affected by glaciation in the Early
Cretaceous. The associated dropstone and solifluction facies and nearby
glendonite pseudomorphs after ikaite are further evidence of at least
intermittent cold climates at this time.
Which could at least go some way to helping explain the repeated
trangression/regression cycles in the Great Artesian Basin, as has been
suggested for other Cretaceous contexts;
Miller, K. G., P.
J. V. Browning, M. A. Kominz, J. C. HernÃndez, R. K. Olsson, J. D.
D. Feigenson, and W. Van Sickel.202003. Late Cretaceous chronology of
rapid sea-level changes: Glacioeustasy during the greenhouse world.
We provide a record of global sea-level (eustatic) variations of the
Late Cretaceous (99â65 Ma) greenhouse world. Ocean Drilling Program Leg
174AX provided a record of 11â14 Upper Cretaceous sequences in the New
Jersey Coastal Plain that were dated by integrating Sr isotopic
stratigraphy and biostratigraphy. Backstripping yielded a Late
Cretaceous eustatic estimate for these sequences, taking into account
sediment loading, compaction, paleowater depth, and basin subsidence.
We show that Late Cretaceous sea-level changes were large (.25 m) and
rapid (K1 m.y.), suggesting a glacioeustatic control. Three large d18O
increases are linked to sequence boundaries (others lack sufficient
d18O data), consistent with a glacioeustatic cause and with the
development of small (,106 km3) ephemeral ice sheets in Antarctica. Our
sequence boundaries correlate with sea-level falls recorded by Exxon
Production Research and sections from northwest Europe and Russia,
indicating a global cause, although the Exxon record differs from
backstripped estimates in amplitude and shape.
Stoll, H. M., and
Schrag. 1996. Evidence for Glacial Control of Rapid Sea Level Changes
Early Cretaceous. Science 272:1771-1774.
Lower Cretaceous bulk carbonate from deep sea sediments records sudden
inputs of strontium resulting from the exposure of=2
Strontium data from an
interval spanning 7 million years in the Berriasian-Valanginian imply
that global sea level fluctuated about 50 meters over time scales of
200,000 to 500,000 years, which is in agreement with the Exxon sea
level curve. Oxygen isotope measurements indicate that the growth of
continental ice sheets caused these rapid sea level changes. If
glaciation caused all the rapid sea level changes in the Cretaceous
that are indicated by the Exxon curve, then an Antarctic ice sheet may
have existed despite overall climatic warmth.
I've been talking about the extremely good possibility for
at least seasonal ice at the poles during the K for years. So, I for
one am glad to see yet another article that says this was probably the
case. And Guy, there's really every reason to believe that the South
Pole was the same... especially since, if memory serves, there were
already a good deal of elevated mountain ranges at the time, and land
completely cut off from the ocean. Isolate elevated land masses where
the sun doesn't shine for part of the year and ocean currents that are
obstructed due to those very same land masses, and you will get ice. I
don't think there is really any way to avoid it. Similar situation goes
for the North Pole as well (not so much the mountains, though there
were some such as the Brooks Range in AK=2
0for example, but definitely
the ocean current situation).
From: GUY LEAHY <email@example.com>
To: Dinosaur Mailing List <firstname.lastname@example.org>
Sent: Sun, Jul 19, 2009 11:16 pm
Subject: Late Cretaceous Arctic Climates
Interesting... wonder if the southern Polar oceans were similar?
Colin McHenry Ph.D.
Computational Biomechanics Research Group http://www.compbiomech.com/
School of Engineering (Mech Eng)
University of Newcastle
t: +61 2 4921 8879
m: 0412 659541