Conodont palaeobiogeography and thermal maturation in the Caledonides

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Abstract
Conodont elements are important in biostratigraphy, in palaeoenvironmental and palaeobiogeographical analyses, and in assessing the thermal history of Lower Palaeozoic strata throughout the Caledonian belt. The differentiation of Ordovician conodont faunas into the North Atlantic and North American Midcontinent provinces is not closely comparable with the provincial patterns shown by other faunal groups and does not relate clearly to criteria for recognizing continental separation across the Iapetus Ocean. Some species associations adapted to cool, normal marine waters were able to cross the ocean at the time of its presumed maximum extent. The colours of conodont elements reflect the thermal history of strata and can be used in studies of low-grade metamorphism. In S. Wales, for example, metamorphic temperatures indicated by conodont colour are too high to he accounted for by simple burial beneath the known stratigraphical overburden under normal heat flow conditions. Elsewhere, conodont colour trends also serve to constrain and test models of metamorphism that involve sedimentary burial in subsiding basins, tectonic burial under nappes, or the thermal effects of intrusions.