(Table 1) Geochemistry of ODP Hole 128-798B

Because of heterogeneity, average values of sediment composition can be difficult to establish accurately in fine-grained rocks. As a result, derived values (such as biogenic silica accumulation rates) can be unreliable, and stratigraphic or spatial trends in composition indeterminate. Samples that reflect interval averages, such as well cuttings, have proven to be more valuable than conventional samples for determining compositional averages and trends reliably (Isaacs, 1987; Isaacs et al., 1990). If properly calibrated, geochemical and gamma-ray logs can also be useful.
As part of calibrating the gamma-ray and geochemical logs taken during Leg 128 (Ingle, Suyehiro, von Breymann, et al., 1990), a sampling method similar to that employed by LeClaire and Kelts (1982) was used. Channel or strip samples representing interval averages were obtained from Cores 128-798B-13H through -15H, and analyzed for major oxides (Bristow and deMenocal, 1992).
Splits of these samples were also analyzed for U and Th to compare with data from the natural gamma-ray spectroscopy tool (GST, trademark of Schlumberger Inc.). At the same time, the splits were analyzed for a variety of other major and minor elements.