Fossil Distribution across the Middle-Upper Devonian Boundary, Portage and Logan Canyons, North-Central Utah

Abstract

The discovery of Rensselandia cloudi Frost and Langenheim in the Samaria Limestone Member at the base of the Hyrum Formation in north-central Utah has revived the question of the age of the member and has led to a detailed study of ranges of the various elements of the fauna in the member. The study shows that the lower part of the member, through at least 56 ft at Portage Canyon and 45 ft at Logan Canyon, is of Middle Devonian age, whereas undoubted Upper Devonian fossils first appear at 100 ft up in the Portage Canyon section and at 86 ft up in the Logan Canyon section.