CONODONT THERMAL ALTERATION PATTERNS IN PALEOZOIC ROCKS FROM BELGIUM,NORTHERN FRANCE AND WESTERN GERMANY

In this paper thermal patterns based on conodont Colour Alteration Ind ices (CAI) have been studied in the Devonian and Carboniferous rocks f rom Belgium, northern France and western Germany. Four maps (with the exception of the southeastern Rheinisches Schiefergebirge) have been c ompiled for the investigated area: one for the Eifelian and Givetian, a second for the Frasnian. another for the Famennian and one for the T ournaisian and Visean. Conodonts have not been found in Cambrian rocks from Belgium and northern France and as they are scarce in the Ordovi cian to Lower Devonian formations of this area, it was impossible to i ntegrate these CAI data into an isograd map. In Germany (in the easter n Rheinisches Schiefergebirge) only a few CAI values for the Lower Dev onian strata are available. In contrast to the Ardennes where in gener al conodonts show CAI values of 3.0-5.0, indices in areas adjacent to the Anglo-Brabant Massif, e.g. in the western Namur Synclinorium and i n the Eifel Hills, range between 1.5 and 2.0. Slightly higher values o ccur in the Campine Basin north of the Anglo-Brabant Massif. By compar ison with CAI data from Belgium, conodont colour alteration indices fr om the same stratigraphic horizons in some areas of the northern and e astern Rheinisches Schiefergebirge are up to one index higher. In most areas of the Rheinisches Schiefergebirge the level of metamorphism co rresponds to the anchizone. Regional variations in CAI data appear to be related to buried intrusions and associated hydrothermal activity. In the southeastern Rheinisches Schiefergebirge CAI data are not compl etely consistent but it is possible to discern an increase in coalific ation from the north to the south. High index values in the southern R heinisches Schiefergebirge are believed to result from regional metamo rphism and heating related to numerous intrusive bodies.