Silicification of deep-sea sediments and the oxygen isotope composition of diagenetic siliceous rocks from the western Pacific, Pigafetta and east Mariana Basins, Leg 129

Abstract

Ocean Drilling Program Leg 129 recovered chert, porcellanite, and radiolarite from Middle Jurassic to lower Miocene strata from the western Pacific that formed by different processes and within distinct host rocks. These cherts and porcellanites formed by 1) replacement of chalk or limestone, 2) silicification and in-situ silica phase-transformation of bedded clay-bearing biosiliceous deposites, 3) high-temperature silicification adjacent to volcanic flows or sills, and 4) silica phase-transformation of mixed biosiliceous-volcaniclastic sediments. Petrologic and O-isotopic studies highlight the key importance of permeability and time in controlling the formation of dense cherts and porcellanites. The formation of dense, vitreous cherts apparently requires the local addition and concentration of silica. The influence of permeability is shown by two examples. -from Authors