The origin of clay minerals in soils of King George Island, South ShetlandIslands, West Antarctica, and its implications for the clay-mineral compositions of marine sediments

Clay minerals in the soils of King George Island, South Shetland Islands, W est Antarctica, were investigated to evaluate their influence upon the comp osition of marine sediments derived from them. Paleohydrothermal activity h as developed phyllic-argillic alteration zones in restricted areas of the v olcanic bedrock. Illite and kaolinite show a highly localized distribution in the soils of the phyllic-argillic zones, whereas chlorite dominates in t he soils of unaltered bedrock. The localized distribution indicates that il lite and kaolinite are residues from altered bedrock, whereas chlorite orig inates from unaltered bedrock. Smectite in the soils is rather uniformly di stributed with no relationship to the phyllic-argillic zones. It is mostly the alteration product of eolian pumice shards, which are found scattered t hroughout the soils on a microscopic scale. The eolian provenance of smecti te 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 no t indicate chemical weathering in the source area. Instead, their occurrenc e suggests that volcanism, igneous intrusion, and related hydrothermal alte rations were active in the South Shetland Islands during the Cenozoic.