On the Development of Autochthonous Blockfields in the Grey Basalts of Sub-Antarctic Marion Island

Sub-Antarctic Marion Island has experienced a periglacial climate since the Last Glacial Maximum. Post-glacial allochthonous openwork accumulations appear to be well developed below 750 m a.s.l., although basalt surfaces exhibit only poorly developed autochthonous blockfields. Bedrock disintegration appears to be confined to a single layer of detritus, probably formed by pressure release on deglaciation. Holocene environmental conditions have not produced chemical weathering products and have preserved the layer of mechanically derived residuals. At altitudes above 750 m a.s.l., blockfield formation appears to be limited by former permanent snow cover. Given the ideal conditions for frost action throughout the Holocene, the absence of well-developed mechanically derived detritus supports the argument for longer time intervals of formation and the non-periglacial origins of autochthonous blockfields.