Fabrics of silica diagenesis in Portlandian and Corallian beds are described and five major types are distinguished--mosaic quartz, chalcedonic overlays, spherulitic chalcedony, lutecite, and microcrystalline granular quartz. The fabrics are dated by relation to carbonate diagenetic fabrics and two major epochs of silicification are demonstrated, separated by a period of calcite cementation. The Corallian beds show a lack of silicification probably caused by reduction of porosity by calcite cements early in the diagenetic history.

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