West Antarctic Ice Sheet Stability:
Glacial Record from the Ohio Range of
the Horlick Mountains in the Bottleneck
Hal Borns*, Aaron Putnam, UMaine
Robert Ackert, Sujoy Mukhopadhyay, Harvard.
December 15, 2004 to February 15, 2005
January 7, 2005

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Aaron standing near several perched granite erratics on the Discovery Ridge bench.

Tillite erratics on the Discovery Ridge upper sandstone/tillite terrace.

The Permo-Carboniferous stratigraphy exposed along the Discovery Ridge cliffs.  These are the upper sandstones, Glossopteris-containing shales, and coal units.

Sujoy’s snowy sled ride.





Evidence of a Permian Glaciation – Discovery Ridge Terraces

Another day in the Ohio Range, yet chock full of new ideas and experiences. The weather was rather calm, temperature about 0 degrees C, and the warm wind in the morning around 11 kts from the east. The visibility was still poor, with the ridges obscured in cloud, so we were again bound for Discovery Ridge. Instead of sampling ice-cored moraines, however, we climbed up to the granite/sandstone terrace in the Discovery gorge.

To access the terraced bench, we took the ski-doos as high as possible on the snowslope adjacent to the cliffs. With crampons on foot and axe in hand, we ascended the snowslope which brought us to the granite terrace. The bedrock granite looked significantly more weathered than the angular erratics seen in the moraines, and appeared to have been subject to wet-based glacial abrasion! The surface was very similar to what one might see on the stoss side of a roche moutonee in coastal Maine! Moreover, the ramp seemed to be on the lee side of the current ice flow, suggesting that the ice responsible for scraping and smoothing that granite was flowing the opposite direction, from west to east. A smattering of granite erratics lay perched on the bedrock surface, and the freshest looking rocks were sampled. It is my hunch that these erratics represented the oldest and most extensive ice-sheet elevation (perhaps from the Penultimate glaciation?)… Hopefully the samples will reveal this…

The view from the Discovery Ridge bench was spectacular! The vertical granite cliffs soar hundreds of meters into the air, and alpine glaciers flow into the ice sheet, with blue-ice zones revealing looping debris bands. Additionally, the ridge has a fascinating sequence of Permian sedimentary units comprising the Tillite sequence. Following the outcrop up the ridge, I noticed the glacially abraded granites topped by a cross-bedded sandstone unit. I believe the granite and the sandstone may be pre-Permian, as the sandstone was terraced and appeared abraded as well, followed by a sharp unconformity between it and overlying diamictite. The lithified diamict was likely a tillite because it was full of striated cobbles. The thin layer was then topped by a coarse-grained sandstone with pinched bedding suggesting lithified braided outwash (or deltaic sediments?). The sandstone then graded into a massive, shale outcrop with many inclusions of small pebbles and large cobbles. This, to me, appeared to be a massive marine mud full of dropstones. Sujoy agreed that it was a lithified aqueous deposit, but questioned whether or not it was marine or lacustrine (based on the assumption that Gondwanaland glaciations were primarily interior continental glaciers that didn’t necessarily see the ocean). Robert disagreed altogether, suggesting it was a lodgement till, based on the massive matrix.
Following the outcrop a little further up, another thin layer of braided outwash sands could be seen, followed again by the controversial massive diamict. In order to resolve this controversy, I followed the unit a far as I could before the others looked restless for dinner, and discovered that the unit graded into rhythmic laminae with layers deformed from the dropstones. So, I remain steadfast behind my hypothesis that it was an ice-proximal marine environment grading to distal (with the interruption of braded sands possibly indicating a small advance?). Margaret Bradshaw’s work also mentions permo-carboniferous fossiliferous marine sedimentary rocks topped by terrestrial shales and coal (which we will see at Mercer Ridge, I expect), indicating a very similar glacio-marine stratigraphy to sub-marine limit Maine (which, of course is only 12,000 years old, not lithified, with terrestrial living organics instead of coal)! I think the Permian ice denuded the granite and sandstone, deposited a thin layer of basal till, deposited coarse sands (possibly due to high discharge), and then as the ice edge retreated, a proximal high discharge deposited the massive marine muds. Calving icebergs contributed dropstones, and then an advance deposited another layer of the coarse sandy material from an increased discharge flow regime. With further retreat of the ice, sedimentation began to represent an increasingly more distal environment, with preservation of rhythmic laminae and marine fossils. With isostatic uplift, the shallow marine environment then became terrestrial, home to the Glossopteris flora.
Just a little story woven from a glimpse at the Discovery Ridge rocks. Perhaps this region was once the coast of Gondwanaland, maybe not too dissimilar from coastal Maine! It will be interesting to do a more thorough examination of the bedrock literature of Margaret Bradshaw, and see where my hypothesis stands.

After scrambling around on the ridge until 1900h, we became sucked into a snowy sphere of visibility (or rather, lack thereof). We slowly found our way back to camp, rattled by the jolts of sastrugi rendered invisible by the null depth perception in the ambient light. I must say, however, the pure white snow drifting across the glowing blue ice was quite spectacular.
So after a quick dinner, it is off to the sack. With hot water bottles keeping my feet warm, and a reorientation of my sleeping arrangement keeping my head above my feet in the constantly changing sub-tent snow/ice topography, I have to think that this is the epitome of life and comfort. Who would have thought such things could be so readily obtained in an environment known for its absolute harshness? I surely am not one to complain.

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