18. the Sulphides of Certain Deep-sea Sediment Samples Collected on Dsdp

The manner of occurrence of sulphides (pyrite and pyrite melnikovite?) in a number of samples from the Philippine Sea is described and their genesis briefly discussed. Polished sections of consolidated material revealed both shards of volcanic glass and pyritized remains of microorganisms (Radiolaria?) in a pyrite matrix with a mosaic texture. The mosaic texture is thought to be due to early syneresis cracks and to late fracture during compaction. Some shards are partly or completely replaced by small units of commonly well-ordered, brownish pyrite. In addition, the shards often display essentially transverse, pyrite-filled fractures that are thought to have been due to tension that built up as the sulphide matrix changed from a gel state to a crystalline one. Sulphidization of the shards and microorganisms was followed by the development of the matrix pyrite and the pyrite occupying the fractures in the glass. Some sulphide spherulites, with a crude radial texture, and a few sulphide cylinders (portion of the spines of sea-urchins?) were mounted in cells on microscope slides and superficially examined. No pyrite framboids occur in the material examined. It is concluded that the sulphides were deposited at or near the water/sediment interface in an area of restricted circulation. It is considered that either the H2S and any elemental sulphur necessary for their syntheses was derived from seawater sulphate (SO4—) by biogenic processes. The source of the iron may have been hydrated iron oxide or the iron components may have originated at an unknown depth in the bedrock and subsequently migrated to the site of sulphide deposition.