Stratigraphy, geochronology, and tectonics of the Salt Lake Formation (Tertiary) of Southern Cache Valley, Utah

摘要

This study synthesizes the deposition and tectonic evolution of the Tertiary deposits in southern Cache Valley, a narrow, north-trending valley in the northeastern Basin-and-Range Province. The surrounding mountains consist of Proterozoic and Paleozoic sedimentary rocks. Southern Cache Valley is an east-tilted half-graben. The oldest Tertiary sediments are on the west side of the basin, and the overall dip is to the east.;The Late Miocene to Early Pliocene Salt Lake Formation (Tsl) accumulated above the thin (to absent) Early to Middle Eocene Wasatch Formation (Tw) and the newly identified Fowkes and Norwood Tuff equivalents (Tfn; late Middle Eocene to Middle Oligocene).;The two post-Wasatch units consist of felsic tuff, tuffaceous sandstone, pebble to boulder conglomerate, limestone, and sandstone. Pebble counts, generalized measured sections, and detailed mapping permitted subdivision of the Tertiary deposits into mappable subunits. Numerous faults and N-trending folds are present in Tertiary deposits in the SW part of the area. The Cenozoic-Paleozoic contact is offset by normal faults. The faults with ENE trends offset both the Paleozoic and Tertiary rocks, and thus are younger than 5.1 Ma.;Thick gravels, rich in Paleozoic carbonates, dominate exposures in the east, near the East Cache fault zone. Few cobbles are present within the Tfn except near the base, whereas conglomerates rich in clasts of Paleozoic carbonates are intertongued with tuffaceous sediments throughout the Tsl, especially eastward. Up to 8,000 feet (3439 m) of the Tsl accumulated as the narrow Cache Valley basin formed during the Neogene by rapid eastward downfaulting.