(Table T1) Carbon composition and biogenic silica of ODP Hole 199-1221C sediments

The Paleocene/Eocene (P/E) boundary, at ~55 Ma, is characterized by a transient warm period lasting 10,000 yr. This interval is globally characterized by significant chemical and biological signals. Ocean Drilling Program Core 199-1221C-11X captured the P/E boundary section at a depth of 154 meters composite depth. Biogenic components of the sediment were measured across this interval in order to better define the events that occurred at the P/E boundary in the equatorial Pacific Ocean. A 26-cm interval low in CaCO3 was identified, whereas biogenic silica and organic carbon remained unchanged. Although CaCO3, biogenic silica, and organic carbon (C-org) production is controlled by different constraints, it is unlikely that an environmental factor would cease production by CaCO3-producing organisms without affecting biogenic silica or C-org production. The data indicate that the CaCO3 P/E boundary event was caused by a change in CaCO3 preservation rather than a change in CaCO3 production.

(Table 19, page 199) Minor constituents of one of the San Clemente iron concretions and its metallic core

The chemical and mineralogical composition of pelagic sediments from the East Pacific Ocean has been determined with the aim of defining the ultimate sources and the mechanisms of formation of the solid phases. The distribution of elements between sea-water, the pore solution and the various solid components of the sediments permits interpretations of the variations in time and space of the gross chemical composition of pelagic clays. For example, manganese, present in sea-water in a divalent form, is apparently oxidized at the sediment-water interface to tetravalent species which subsequently become a part of the group of ferromanganese oxide minerals which are found in the marine environment. It is suggested the rate of manganese accumulation in sediments is some function of the length of time the sediment surface is in contact with sea-water. The contribution of chemical species from the different geospheres is considered. The quantitative importance of pelagic clays in the major sedimentary cycle is studied on the basis of the distribution of the weathered igneous rock products between continental and pelagic deposits and sea-water. These analyses of a wide variety of pelagic clays allow a reformulation of the geochemical balance and it is concluded that pelagic clays account for approximately 13 per cent of the total mass of sediments produced over geologic time.