Upper Proterozoic and Lower Cambrian rocks of the Sheeprock Mountains, Utah: Regional correlation and significance

摘要

Apparently conformable upper Proterozoic and Lower Cambrian miogeoclinal rocks in the Sheeprock Mountains, Utah, attain a maximum thickness of at least 7,200 m. The sequence begins at the base with phyllite, quartzite, glaciomarine diamictite, and shale deposited near the northern edge of a subsiding basin. These rocks are assigned to the Sheeprock Group (2,700–4,300 m). Overlying quartzitic rocks (1,950–4,000 m) are correlated with specific formations of the Brigham Group (Huntsville sequence). Revision of earlier accounts of the stratigraphy in the Sheeprock Mountains is suggested by the recognition of low-angle faults that attenuate the stratigraphic section. Stratigraphic relations in the Sheeprock Mountains bear on regional correlation. The probable presence in the Deep Creek Range of two diamictite units separated by quartzite is reaffirmed. This sequence is grossly similar to that of the Sheeprock Mountains. It is suggested that the Caddy Canyon Quartzite (Brigham Group) inter-fingers to the south and west of the Sheeprock area with siltstone, shale, and some limestone. Possibly, no rocks exposed in the San Francisco Mountains and Canyon Range are older than the Caddy Canyon Quartzite. The McCoy Creek Group of western Utah and eastern Nevada is probably for the most part equivalent to the Caddy Canyon Quartzite. The Osceola Argillite (unit G, McCoy Creek Group) may be equivalent to the Inkom Formation, and it perhaps records a marine transgression that temporarily reduced the clastic supply. The correlation of the Mutual Formation of the platform sequence in the Wasatch Range to a lithologically similar unit in the miogeocline to the west remains the simplest interpretation, although the platform Mutual may be older than the unit of the same name in the miogeocline.