Late tertiary glaciation and sea-level changes in Antarctica

Abstract

The age and history of the present Antarctic ice sheet have long been matters of speculation. Reports of Tertiary glaciation in Antarctica have been based on the presence of till-like deposits, only one of the several criteria proposed for the recognition of older glaciations. Nichols reviewed all reports suggesting a Tertiary beginning and concluded that the evidence was not compelling. Continued field and laboratory study of deposits, both marine and terrestrial, has provided an increasing amount of evidence to indicate a Tertiary beginning for Antarctic and possibly Arctic glaciations. In western Antarctica the Jones Mountains provide some detailed information that bears on the question. The Jones Mountains consist of a mainly granitic Mesozoic basement complex, truncated by a major erosional unconformity which is overlain by as much as 500 m of Late Tertiary volcanics. The erosion surface is essentially horizontal, and is marked by grooves, striations, chatter-marks, and other evidences of planation. Lenses of a till-like material occur at the base of the overlying volcanics. The areal extent, low relief, and freshness of the markings on the surface lead to the conclusion that Tertiary glaciation is involved. The physical and mineralogical characteristics of the till-like material indicate that glacier ice was probably present at the time of eruption of the volcanics. The evidence for sea-level changes in Antarctica since Tertiary time is difficult to interpret. Numerous strandlines have been called Recent. Most of the former shorelines are probably now buried under the ice cover although the Tertiary Pecten Conglomerate rests on a wave-cut platform 220–250 m high on Cockburn Island. The location, interpretation, and dating of former shorelines remain one of the little studied phases of Antarctic geomorphology.