Mineralogy and Diagenesis: Their Effect on Acoustic and Electrical Properties of Pelagic Clays, Deep Sea Drilling Project Leg 86

Abstract

Analysis of pelagic clay samples from Sites 576, 578, and 581 shows that physical, acoustic, and electrical trends with increasing burial depth are related to mineralogical and diagenetic changes. The properties of interest are bulk density (p), porosity (Φ), compressional-wave velocity (1^) and velocity anisotropy (A p), and electrical resistivity (R o) and resistivity anisotropy (A r). In general, as demonstrated in particular for the brown pelagic clay, the increase in p, V p , R o , and to a lesser extent A p and A T , with increasing depth is primarily caused by decreasing Φ (and water content) as a result of compaction. The mineralogy and chemistry of the pelagic clays vary as a function of burial depth at all three sites. These variations are interpreted to reflect changes in the relative importance of detrital and diagenetic components. Mineralogical and chemical variations, however, play minor roles in determining variations in acoustic and electrical properties of the clays with increasing burial depth.

Sediments of the Hawaiian Arch: X-Ray Mineralogy and Microfabric

“…This composition is similar to that of pelagic clays sampled elsewhere in the North Pacific (Schoonmaker et al, 1985). The impact of eolian deposition is evident in the increased amounts of illite and quartz both for the last 2.5 m.y.…”

“…The relative proportions of detrital components at Site 842 are similar to those in North Pacific pelagic clay sampled at Sites 576, 578, and 581 of DSDP Leg 86 . Twenty-nine samples of pelagic clay from the Leg 86 sites have the following mean composition: 78% total clay minerals, 15% quartz, and 7% Plagioclase (Schoonmaker et al, 1985). In comparison, Site 842 sediments contain an average of 78% total clay minerals, 4% quartz, and 10% Plagioclase (Table 1).…”

Eolian Deposition on the Ontong Java Plateau since the Oligocene: Unmixing a Record of Multiple Dust Sources

“…This assemblage closely resembles the bulk composition of modern aerosols derived from Asia and collected in the northwest Pacific (Blank et al, 1985), and of Recent, Quaternary, and Cenozoic dust derived from Asia and transported to the northwest Pacific by the prevailing westerlies (Blank et al, 1985;Leinen, 1989;Schramm, 1989;Schoonmaker et al, 1985;LeNotre et al, 1985). On the basis of this compositional similarity, we infer that dust derived from Asia has been supplied to OJP since the Oligocene (recorded as Fl of PCA1, Table 3), with greatest relative importance in the middle Miocene (Fl of PC A3) and the Pliocene through Quaternary (Fl of PCA2).…”

“…Older sediments recovered at sites further to the north record activity of the easterlies before the Miocene and indicate that the easterlies consistently supplied less dust than the westerlies (Janecek and Rea, 1983;. On the basis of limited data, Schoonmaker et al (1985) conclude that dust supplied by the easterlies to sediments at DSDP Site 576 before approximately 20 Ma was relatively quartz-poor and smectite-rich.…”

“…Several good long-term records of atmospheric circulation are available from the North Pacific, including those from LL44-GPC3 (JanecekandRea, 1983;Schramm, 1989) and DSDP Sites 576 and 578 Schoonmaker et al, 1985;LeNotre et al, 1985;Rea et al, 1985;Schramm, 1989); these findings have been summarized by Rea (1989). Leinen (1989) has also presented useful information about the composition of dust supplied to the North Pacific from three different source areas during the late Quaternary.…”