Abstract

Dissolution of 61 samples from a 183-meter section of the Upper Ordovician/Silurian Fish Haven and lowermost Laketown Dolomites at Tony Grove Lake yielded more than 6,400 conodont elements assignable to more than 40 species. Graphic correlation with the Red River Province composite section, using the ranges of 27 species, indicates that the base of the Fish Haven is latest Edenian and that the rate of rock accumulation was greater than in sections of the Red River Province. Lithologic evidence and the occurrence of a mixed Ordovician/Silurian species association in samples from the upper 4 meters of the Fish Haven and lowermost 1.5 meters of the Laketown indicate the presence of a disconformity at the base of the mixed association. Graphic correlation and age-diagnostic latest Ordovician conodonts show that the disconformity correlates with the base of the Aphelognathus shatzeri conodont chronozone. The Silurian association includes species common to both the Oulodus? nathani and the Distomodus kentuckyensis zones and indicates that those strata are no younger than early Fronian in age (C_1-2).