Dredged Basalt from Giacomini Seamount

Abstract

DURING the cruise in July 1965 of the RV Acona of the University of Alaska Institute of Marine Science, two angular blocks of basalt (15×12×5 cm³ and 20×15×9 cm³) were dredged from the summit area of Giacomini Seamount (56° 24′ N, 146° 34′ W), at a depth of 790 m (Fig. 1). Several hundred igneous, metamorphic and sedimentary pebbles, cobbles and boulders were also recovered in the dredge haul; they showed a wide range of rounding and a very thin coating of manganese oxide, and were very similar to those recovered from the summit areas of Gilbert, Miller, Pratt and Ga-3 Seamounts in the Gulf of Alaska Seamount Province, as previously reported by Menard¹ and others. Menard concluded that these gravels were ice-rafted glacial drift, an interpretation which is strongly supported by the presence of faceted and striated rocks among the Giacomini erratics.