Conodont alteration in Devono-Carbonif erous dolomites from southern Belgium

Abstract

Conodonts from selected Frasnian and Tournaisian dolomites in southern Belgium have Colour Alteration Index (CAI) values of 3.0-4.5 or 6.0-7.0. The textural alteration of these conodonts includes various features. Most striking are the subhedral apatite crystals that surround the conodont denticles. Furthermore, fields of apatite crystals, irregular apatite envelopes and apatite pseudomorphs after calcite occur on the conodont surfaces. The higher CAIs as well as the textural alteration are probably related to dolomitization processes. Phosphates may have been supplied by decomposition of organic matter or by ascending saline fluids.