Abstract

Textural relationships observed in thin sections of chert-bearing carbonate rocks commonly indicate that chert, which originated by replacement of the carbonate host rock, has then been replaced by younger carbonate minerals. The principal evidences of such replacement reversals are: (1) localization of carbonate minerals along and adjacent to fractures in chert, (2) transection of authigenic siliceous textures by carbonate minerals, and (3) occurrence within carbonate minerals of inclusions that have been inherited from chert. In some chert-bearing carbonate rocks the textural relationships indicate that multiple replacement reversals have occurred between chert and carbonate minerals. The cause is not known, but data suggest that the reversals may occur in response to variations in pH where interstitial water is highly alkaline (above pH 9) or in response to variations in temperature where sediments have been deeply buried.

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