Paleozoic Stratigraphy of Samaria Mountain, Idaho-Utah

Abstract

Strata of Ordovician through Early Permian age, at least 13,000 ft (3,960 m) thick, are exposed along a west-dipping homocline in the Samaria Mountain area about 12 mi south-southwest of Malad, Idaho. Beginning at the mountain front on the west side of Malad Valley, the following formations are exposed in sequence westward: Swan Peak Quartzite, 300+ ft (91 m); Fish Haven-Laketown Dolomite sequence, 1,540 ft (470 m); Water Canyon Formation, 455 ft (138 m); Jefferson Formation, 1,230 ft (375 m); Beirdneau Formation, 990 ft (300 m); Lodgepole Limestone, 330 ft (100 m); Humbug Formation 940 ft (286 m); Great Blue Limestone, 1,180 ft. (360 m); Manning Canyon Formation, 300 ft (91 m); and Oquirrh Formation, 5,000+ ft (1,520 m). The Phosphoria Formation is present in a single is lated outcrop. The Jefferson Formation is divided into two members: the Samaria Limestone Member (new name) and the Hyrum Member. A Devonian brachiopod fauna in the Samaria Limestone suggests a correlation with the fauna of the lower Devils Gate Limestone of Nevada and with the Allanaria allani fauna (Late Devonian) of the Waterways Formation in northeastern Alberta. The Lodgepole Limestone has four informal members; the lower three are characterized by Unispirifer centronatus and the upper crinoidal member contains Spirifer cf. S. rowleyi. Three members are recognized in the Oquirrh Formation: the West Canyon Limestone Member (Morrowan-Atokan), the middle member (Late Pennsylvanian), and the upper member (Early Permian). A major unconformity occurs between the West Canyon and upper members. The middle member is apparently an allochthonous complexly folded and thrust-faulted mass which overlies the upper member.