SILICA SEDIMENTATION IN THE ALTAI LATE ORDOVICIAN SHELF BASIN IN SOUTHWEST SIBERIA (RUSSIA)

摘要

Sources of silica both in the ancient and in the modern oceans include (1) products of volcanic and post-volcanic activity, such as (a) near underwater volcanoes and volcanic arcs in paragenesis with lavas of different composition and their tufts (terrigenous and carbonate) and (b) from the ocean floor in paragenesis with basalts and terrigenous rocks (cherts could be formed simultaneously both with basalt intrusion and as a result of post-effusive hydrothermal activation); (2) uprising of deep highly siliceous water along fault zones; and (3) river discharge. The process of SiO2 sedimentation in modern seas front undersaturated silica waters is conducted mainly by biogenic accumulation.