Annotated record of the detailed examination of Mn deposits of the Eniwetok Atoll

Some short cores from the shelf at about 800-1000 fathoms on the southwest flank of Eniwetok Atoll penetrated Pliocene deposits with little to no later sediment cover. The Quaternary deposits include much coarse reef debris, particularly the fragments of algae such as Halimeda and other shallow-water material up to several millimeters in grain size, mixed with varying amounts of pelagic Foraminifera. The Pliocene sediments (one may be upper Miocene) are pure pelagic deposits of much finer grain size, consisting of coccoliths and pelagic Foraminifera with no admixture of reef material. Bottom photographs show areas of well-developed ripple marks in coarse sediment (C. J. Shipek, manuscript) apparently formed only in the areas with the veneer of post-Tertiary coarse sediments. A brown impregnation at the top and extending down as mottling for a few centimeters is also usual in the Tertiary sediment of the cores. This seems to consist of iron and manganese oxides and adds somewhat to the induration.