Textures, Microstructures, and Lithologies of Japan Sea Sediments from the Lower Portion of Hole 799B, Leg 128

Abstract

Textures, microstructures, and major lithologies of samples from 750 to 1081 mbsf of Hole 799B, Leg 128, Japan Sea, were studied in 40 thin sections. The study provided evidence for the sequence of diagenetic mineralization for the lower portion where the sediments become well-lithified. The diagenetic sequence for the lower portion of Hole 799B revealed from crosscutting relationships in textures and structures is (1) hard, round, "D-phosphate" nodules and glauconite grains transported and deposited with the sediments; (2) "F-phosphate" streaks and pyrite framboids; (3) clay minerals; (4) rotation, flattening, and compaction; and (5) irregular glauconite grains. Fabric that has been defined by the subparallel to parallel optical orientation of clay minerals becomes more pronounced with increasing depth. Compaction enhances clay mineral fabric by flattening soft F-phosphate nodules, burrows, and microfossils (like the sponge Sagarites makiyama or Makiyama titanni).

Textural and Microstructural Evidence for Sediment Diagenesis in the Vicinity of the Chile Triple Junction

“…Phosphate concretions appear to be rare and poorly developed in samples from the Chile Triple Junction, in contrast to sediments from areas more strongly affected by coastal upwelling (Garrison and Kastner, 1990;Lindsley-Griffin et al, 1990;Griffin and Lindsley-Griffin, 1992). In these samples, phosphate occurs in the form of apatite or fluorapatite fish-bone fragments, hard crystalline nodules, soft friable concretions, phosphatic mud, and phosphatic fecal pellets.…”