STRONTIUM ISOTOPE SYSTEMATICS OF CONODONTS - MIDDLE DEVONIAN, EIFEL MOUNTAINS, GERMANY

The Eifel Mountains lithological profile, the stratotype for the Middl e Devonian, was densely sampled for conodonts to delineate the Sr isot opic evolution of coeval sea water. The Sr-87/Sr-86 curve Obtained sho ws oscillations around a mean of about 0.7078 that have a frequency in the 10(5)-10(6) yr range and an amplitude in the 10(-5)-10(-4) range. These oscillations mimic those obtained on coeval brachiopods (Diener et al., 1996), but are shifted into more radiogenic domains by up to 10(-4). Model calculations suggest that the shift is clue to partial ( 30-40%) early diagenetic equilibration of conodonts with their enclosi ng bulk-rock matrix. The reality of partial recrystallisation is suppo rted by visible neoformed blocky apatite crystals on the surface of th e conodonts, despite their otherwise apparently excellent preservation , with CAI values of 1.5-2.5. We therefore suggest that studies antici pating use of conodonts as a recorder of paleoceanographic events shou ld be confined to specimens embedded in a relatively 'clean' matrix, s uch as pure limestone. Even these results should be cross-checked by c omparison with data on coeval low-Mg shells, such as brachiopods or be lemnites. (C) 1997 Elsevier Science B.V.