Chert and porcellanite from Deep Sea Drilling Project Site 436, northwest Pacific.

Abstract

Cretaceous chert and porcellanite recovered E of N. Honshu are texturally and mineralogically similar to siliceous rocks of comparable age at Sites 303, 304 and 307 in the NW Pacific. These rocks probably were formed by impregnation of the associated pelagic clay with locally derived silica from biogenic and perhaps some volcanic debris. Fine horizontal laminations are the only primary sedimentary structures, suggesting minimal reworking and transport. Collapse breccias and incipient chert nodules are diagenetic features related to silicification and compaction of the original sediment.-from Author