LOWER AND MIDDLE CAMBRIAN STRATIGRAPHY IN NORTHERN UTAH AND SOUTHEASTERN IDAHO

Abstract

The stratigraphic succession of Lower and Middle Cambrian sediments in northern Utah and southeastern Idaho as determined from 13 measured sections includes the basal medium- to coarse-grained Prospect Mountain Quartzite overlain by interbedded fine- and coarse-grained clastic rocks (Pioche Formation) that in turn are overlain by several hundred to a few thousand feet of carbonate rocks with a few thinly interbedded layers of fine clastics. The carbonate sequence includes the Langston Formation, Ute Limestone, Blacksmith Dolomite, and Bloomington Formation. Known occurrences of fossils are listed for the formations. Seventeen faunal groups are identified, and a sequence of faunizones is proposed. Cambrian deposits may be separated into (1) orthoquartzite; (2) greenish-brown, micaceous and arenaceous shale; (3) brown-weathering, calcareous sandstone; (4) rusty-brown-weathering dolomite; (5) green and buff fissile shale; (6) calcareous black shale; (7) mottled, silty, aphanitic, thinly bedded limestone; (8) Girvanella limestone; (9) intraformational conglomerate; (10) oolitic limestone; (11) “undifferentiated limestone”; and (12) “undifferentiated dolomite” facies. All these sediments probably were deposited in a shallow, chiefly transgressive, though oscillating, sea. This sea transgressed a low-lying but mature topography eastward to western Utah by earliest Cambrian (pre-Olenellus?) time and to eastern Utah by the end of Early Cambrian time. The area remained submerged during Medial Cambrian and much of Late Cambrian time.