The "Golden Shale": An indicator of coastal stability for Marble Point, McMurdo Sound, over the last four million years

A small sedimentary deposit near Gneiss Point on the western side of McMurdo Sound, previously identified as
shale, is described. The deposit is phillipsite, a zeolite that is believed to have formed from the deposition and alteration of
volcanic ash in a small ice-marginal saline lake. Other previously recorded occurrences of phillipsite in the dry valleys are
believed to be several million years old. A similar age for this deposit is suggested for the Gneiss Point deposit. This is
consistent with other weathering and landscape features found in the immediate area, including traces of halloysite in soils.
The deposit is very close to sea level but could not have formed if the site had been below sea level, indicating that there has
been very little uplift following that which caused the sea to retreat from the Wright Fiord.