CONODONT ALTERATION IN DEVONO-CARBONIFEROUS DOLOMITES FROM SOUTHERN BELGIUM

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 featur es. Most striking are the subhedral apatite crystals that surround the conodont denticles. Furthermore, fields of apatite crystals, irregula r apatite envelopes and apatite pseudomorphs after calcite occur on th e conodont surfaces. The higher CAIs as well as the textural alteratio n are probably related to dolomitization processes. Phosphates may hav e been supplied by decomposition of organic matter or by ascending sal ine fluids.