SP-04 The Middle and Upper Ordovician Conodont Faunas of Minnesota

Abstract

About thirty-five thousand identifiable conodonts were recovered from samples of Middle and Upper Ordovician sedimentary rocks of Minnesota. One section was sampled in detail for each formation except the Glenwood, which was sampled at three localities in east-central and southeastern Minnesota. Thirty-three form species or groups of form species <Ire described as biological or natural species. Form species comprising a natural species are associated by similarities in stratigraphic range, abundance ratios, size, and secondary characteristics. Problems stemming from the presently used invalid dual nomenclature can be solved by applying the name of the earliest described form species to the natural species according to the rules of zoological nomenclature. The Middle and Upper Ordovician strata of Minnesota can be subdivided into ten biostratigraphic zones on the basis of the stratigraphic distribution of conodonts. An increase in European elements at the expense of American mid-continent elements in the Galena and Dubuque Formations represents a major shift in conodonts with respect to pre-Galena faunas.