(Table 1) Coarse-fraction (0.1 to 0.05 mm) mineralogy at DSDP Leg 55 Holes

This chapter was previously intended to trace volcanic episodes through the Neogene and Pleistocene geological history recorded in the sedimentary sections drilled on the Emperor seamounts. Drilling disturbance, poor core recovery, and incomplete stratigraphic sections recovered from the seamounts have frustrated that plan, however. Moreover, the Leg 55 sedimentologists found in their smear-slide studies that transported island-arc tephra is scarce in the sediments, if present at all. So we have restricted our objective to description of the volcaniclastic admixture in sediments, as determined by mineralogical and geochemical data. We studied geochemistry of bulk samples (see Murdmaa et al., 1980), coarse-fraction mineralogy, and additional smear slides. The results obtained, however, do not tell much more about the volcaniclastic matter than did shipboard core descriptions.

(Table 1) Chemistry of two samples of the red weathered layer at DSDP Hole 55-432A

One argument for the subaerial formation of Nintoku Seamount in the Emperor chain is the occurrence of a red claystone interlayered between two basalt flows in Hole 432A. Detailed study of this material, presented here, defines its nature and composition and strongly indicates its subaerial formation.