Abstract

Many detrital and diagenetic minerals show a large variety of cathodoluminescence colours (CL) due to their chemical composition and/or defects in the crystallographic structure. Digitized colour images of the emitted CL allow to distinguish and quantify detrital and authigenic phases with high accuracy. Quantification leads to a better knowledge of the detrital minerals and the paragenesis of diagenetic phases. As an example, Triassic siliciclastics, carbonates and sulfates cored in two deep wells in the Ardeche region were studied. These sediments contain both detrital and authigenic minerals which often show luminescence. More than 1300 CL images and plane-polarised light microphotographs were taken from samples of the GPF Ardeche Ba1 and MM1 wells using a Technosyn MKII cold cathodoluminescence device. The images were digitized at high resolution and stored on CD-ROM. The different mineral phases have been segmented and their area proportion were calculated using modern image analysis software packages. Quantification of the detrital components (e.g. quartz, feldspar) their degree of alteration and the amount of diagenetic phases (e.g. dolomite, magnesite, celestite and phosphate) can be used to determine the chemical composition of the rock.

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