The development and fluctuation of Antarctica's Cainozoic glaciation - the terrestrial record

The Dry Valleys region, near McMurdo Sound in the southwest corner of the Ross Sea, displays a unique terrestrial record of multiple glaciations that involved complex interplay between outflow glaciers from the east Antarctic ice sheet, local mountain glaciers, and glacial marine incursions from the Ross Sea area. Although the geological record of glaciation is fragmentary, the fossil content of the glacial marine rocks, volcanic rocks intercalated with the glacial sequence, and freshwater lake sediments have permitted dating of glacial events back to Miocene times. Elsewhere in Antarctica, volcanic rocks that are thought to have been erupted either over early glaciated surfaces, or under glaciers, provide a means for estimating when Antarctic glaciation started. Dates range back to Oligocene limes in west Antarctica, and to early Miocene times in east Antarctica's Transantarctic Mountains although glaciological considerations appear to demand that glaciation started first in the latter area. These dates compare well with those derived by stratigraphical methods from sediment cores in the Ross Sea. Evidence for fluctuations in the Antarctic ice sheet is widespread with at least two glacial stands higher than the present one indicated at many places. The dating of volcanic rocks at Gaussberg in east Antarctica shows that at least one major fall in ice level has occurred in the past 5.5 x 104 years or so. The Dry Valleys glacial geology record also shows that at least 400 metres of uplift has occurred in the area since Miocene times. In addition some authors believe that the surrounding Transantarctic Mountains have risen up through the Cainozoic ice sheet. In the Prince Charles Mountains a preglacial erosion surface provides a datum against which glacial erosion, and the possible consequential isostatic uplift can be measured; a net uplift of 0.8 km is postulated. A similar glacial erosion related mechanism may explain uplift recorded in other parts of Antarctica. The Prince Charles Mountains also contain geomorphological features that might constitute evidence for surging in the Lambert Glacier system. Along most glaciers in the area the height of old moraines above the present ice level decreases with increasing ice surface elevation. The Fisher Glacier area is anomalous in that the old moraines are a constant height above the present ice surface; certain moraines in this area could also be explained in terms of surging.