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Re: Ice Sheets Caused Massive Sea Level Change During LateCretaceous

Dann Pigdon wrote:

>> However glacial dropstones in marine deposits requires that the glaciers
>> reach sea level, otherwise they couldn't calve into the sea. No glaciers do
>> this outside the subarctic (southern Alaska, Iceland) even today.

>I believe they do around the Strait of Magellan. Is that area sub-polar?

If You follow the usual definition that polar climate equals no month with an average temperature over 10 degrees centigrade it is. The warmest month in Ushuaia is 9.2 centigrade (about the same as Nome, Alaska). However the climate is extremely maritime so the winters are quite mild, about like Vancouver.

>The early adventures of the 'Beagle' (the ship that Darwin eventually
>sailed in) tell of the numerous dangers in the Strait, including large
>chunks of glacial ice.

>Besides, southern Australia WAS within the Antarctic circle during the
>Early Cretaceous.

Tierra del Fuego and adjacent parts of the southern Andes is quite likely the closest present-day analog to mesozoic antarctic/australian climate and vegetation. You can see Nothofagus forest (or at least scrub) growing right up to the glacier edge in some places.

However the scenario that started this thread with large icecaps growing and waning in the interior of Antarctica without reaching the ocean is unlikely. Glaciers typically develop on high wet mountains near the sea and only later expand inland later as the ice-cap grows.

Actually dropstones in the shallow seaway south of Australia seems quite plausible if there was Cretaceous glaciers in Antarctica. The uplifted southern rim of the rift between Australia and Antarctica seems a very likely place for glaciation to start.

Tommy Tyrberg