ABSTRACT

Boulder pavements are flat, tightly packed mosaics of ice-smoothed and striated boulders that occur in low gradient intertidal and lacustrine areas in polar regions. In the sub-Antarctic, intertidal boulder pavements are located in three morphogenetic environments spanning l0° of latitude. Some boulder pavements are composed of ice-pushed or ice-rafted boulders which have been forced into the substrate by the pressure of grounding ice blocks. Other pavements may result from wave-winnowing of glacial till at sea level which has been subsequently modified by grounding ice. Shallow depressions in the pavement surface may correspond to the loci of large grounded ice blocks, and this interpretation is supported by striation and boulder orientations on the ridges between the depressions

The occurrence of the pavement appears to depend on the following factors: a) a boulder supply; b) frequent onshore movement of floating ice; and c) a low-gradient intertidal zone. Given such conditions, the degree of development of the pavement seems to be controlled by the frequency of onshore ice movement because the best formed pavements occur in areas subject to the highest frequencies of freely moving floating ice.

The occurrence of raised pavements in the South Shetland Islands suggests that little morphogenetic change has occurred in the area since 9,000 years ago. Radiocarbon dating indicates that where the frequency of ice grounding is relatively low, periods in excess of 200 years are necessary for pavement development, whereas at locations where the ice-grounding frequency is high, pavements are well formed within 300 years.