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Re: Late Cretaceous Arctic Climates - RESEND
There is indeed gathering evidence for glacial episodes in the Southern
Hemisphere during the Early Cretaceous;
Alley, N. F., and L. A. Frakes. 2003. First known Cretaceous glaciation:
Livingston Tillite Member of Cadna-owie Formation, South Australia.
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
angularity and 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 3–5 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
‘Recorder Hill’ 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. Sugarman, J. V. Browning, M. A. Kominz, J. C.
Hernández, R. K. Olsson, J. D. Wright, M. D. Feigenson, and W. Van
Sickel. 2003. Late Cretaceous chronology of large, rapid sea-level
changes: Glacioeustasy during the greenhouse world. Geology 31(7):585-588.
We provide a record of global sea-level (eustatic) variations of the
Late Cretaceous (99–65 Ma) greenhouse world. Ocean Drilling Program Leg
174AX provided a record of 11–14 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 D. P. Schrag. 1996. Evidence for Glacial Control of
Rapid Sea Level Changes in the Early Cretaceous. Science 272:1771-1774.
Lower Cretaceous bulk carbonate from deep sea sediments records sudden
inputs of strontium resulting from the exposure of continental shelves.
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 for example, but
definitely the ocean current situation).
From: GUY LEAHY <firstname.lastname@example.org>
To: Dinosaur Mailing List <email@example.com>
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