S. Davis, me, et al 2014 AGU abstract proposed that a 400 km-long, 50 km-wide pre-30 Ma buried erosional and rift trough in Ross Sea could have last been eroded by ice, and this ice could have been from the earliest (33 Ma) East and/or West Antarctic Ice sheet. This was very controversial among our co-authors, and we allowed other possibilities, such as River erosion after rifting ceased, assuming restoring differential subsidence removes the huge reverse gradients of the major unconformity along the trough axes.
Related to this:
Question 1: Is large (Piedmont) glacial or ice stream erosion like River erosion, where the ice can cut down on the order of 1 km in 1 or 2 million years if out of equilibrium in one direction (while the bed would instead aggrade if out of equilibrium in the other direction. I know that cold-based ice streams/glaciers are frozen to their beds and do not erode.
Question 2: Do you know of examples of 50 km-wide and >500 m deep troughs known to be deeply eroded by ice in a couple of million years or less? I’m thinking Northern Hemisphere like Greenland, because ice had not been there for tens of millions of years. Laurentian Trough on the shelf of Atlantic Canada may be one example, but I have not been able to find papers or seismic reflection data that show the base of the sub-bottom trough (we have figures of the sea floor trough, which is 50 km-wide but only a couple of hundred meters deep.
I am being a bit lazy; I have an abstract deadline on this in a week and just have not had time to focus on looking into the literature because I have had to spend my time on the Ross Sea interpretation and other projects.
(Davis et al is a student abstract; is my project).
Thanks!
Chris
You should first look at the possibility of horsts and graben in the area. These are widespread along the shores of the Laptev Sea and between Greenland and Baffin Island,\and can produce similar features.
Thank you Stuart! Must be some kind of record for longest to go on ResearchGate without before getting an answer. I just presented this last week at ISAES meeting in India, and asked the same kinds of questions, and it does not seem like anyone is doing very much thinking about equilibrium in glacial erosion. But, Ross Powell did say that Oligocene Antarctic ice was quite warm and erosive. Various others think that there are other similar scale glacial troughs in Antarctica: some below the ice. The week and next I am working at OGS Italy with Chiara Sauli and Laura De Santis to restore my maps back to 30 or 33 Ma.
Yes, the trough occupies an extremely extended 80-55 Ma rift, and that is why it has differentially subsided so far. The deep closed basins are now 6 km, but will likely restore to 2 km depth, maybe less. But, they would likely have to have eroded to below paleo-sea level if 33 Ma glacial.
Chris
Thank you. this is useful. But, I suspect that most Norwegian fjords do not have the large scale of what I am studying: 50 km-wide eroded trough (hundreds of km-long). We are making progress on our paleotopography/bathymetry, but it is likely that the Ross Sea pre-30 Ma erosion had to cut to about 2 km below paleo-sea level (generally less, but in middle of the 2 closed basins, maybe 2 km).
If you have any references on such large troughs, please post them.
Chris
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