Clay minerals in the soils of King George Island, South Shetland Islands, West Antarctica, were investigated to evaluate their influence upon the composition of marine sediments derived from them. Paleohydrothermal activity has developed phyllic-argillic alteration zones in restricted areas of the volcanic bedrock. Illite and kaolinite show a highly localized distribution in the soils of the phyllic-argillic zones, whereas chlorite dominates in the soils of unaltered bedrock. The localized distribution indicates that illite and kaolinite are residues from altered bedrock, whereas chlorite originates from unaltered bedrock. Smectite in the soils is rather uniformly distributed with no relationship to the phyllic-argillic zones. It is mostly the alteration product of eolian pumice shards, which are found scattered throughout the soils on a microscopic scale. The eolian provenance of smectite associated with pumice shards is supported by a uniform distribution of smectite, coexistence of fresh and altered pumice shards, and rather short exposure after deglaciation. Smectites likely have been formed in a remote source around volcanic craters and reworked by repeated eruptions.

Formation of clay minerals by chemical weathering as suggested in previous studies appears to be insignificant on King George Island, even though the climate is warmer and more humid than in other Antarctic regions. Smectite and kaolinite in seafloor sediments around the South Shetland Islands do not indicate chemical weathering in the source area. Instead, their occurrence suggests that volcanism, igneous intrusion, and related hydrothermal alterations were active in the South Shetland Islands during the Cenozoic.

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