| Description |
The tern Salt Lake group is here used to include all rocks that are post-Wasatch (Paleocene and Eocene) and pre-Pleistocene in age. On the basis of varied lithologies, soil profiles, erosional unconformities, and structural deformation, the Salt Lake group has been subdivided as follows; Traverse volcanics and Jordan Narrows units (oldest), Camp Williams unit5 Travertine unit, and the Harkers fanglomerate unit (youngest). The commonest rock types in the Traverse volcanics are reddish to purple andesites and sndesite breccias, augite and hi otite-hornblende latites and latite flows, and lesser amounts of rhyolite and basalt. A white marlstone is the dominant lithologic type of the Jordan Narrows unit. In addition it contains oolitic, argillaceous, and cherty limestones, sandstones, clays, and rhyolitic tuffs. These are all fresh water lacustrine deposits and were derived from and deposited almost contemporaneously with the Traverse volcanics. The Camp Williams unit is composed of red to tan colored mudstones and siltstones and a basal conglomerate of igneous detritus. All are poorly consolidated. The Travertine unit consists of a white dense, massive, travertine which contains some small lens-like accumulations of manganese dioxide. The Harkers fanglomerate unit is a light colored, poorly consolidated, torrential stream deposit and is composed of Paleozoic quartsites and limestones with smaller amounts of igneous fragments. Several mud rock flows occur in the Salt Lake group. Dips up to 30' are common and are most pronounced near demonstrable or inferred faults. Folding is possibly responsible for gentle regional dips. A fault mosaic has been mapped in the Jordan Narrows area. A pediment along the east flank of the Oquirrh Mountains is bounded on the west by a normal fault and on the east by the Bonneville shoreline. The pediment was eroded across rocks chiefly of the Salt Lake group. Later erosion has produced one and possibly two lower surfaces. The Tertiary geology of Tooele Valley and the Stansbury Mountains is slightly similar to that of lower Jordan Valley and the Oquirrh Mountains0 (1) Stratigraphically the resemblance is limited to the thick volcanic sequence and fanglomerate unit of the Stansbury Mountains both of which might be correlated with the Traverse volcanics and Harkers fanglomerate, respectively, in the Oquirrh Mountains. Ho sedimentary deposits have been found in Tooele Valley that would correspond to the Jordan Narrows, Camp IfLlliams, and Travertine units of Jordan Valley. (2) Remnants of an old pediment flank the Stansbury Mountains on the east, but this pediment is not as extensive or well-defined as the one comprising the Oquirrh Foothills. (3) Structurally Tooele Valley is depressed like the Jordan Valley block. Faulting has deformed the rocks of the Salt Lake group in the Stansbury Mountains and produced a regional dip eastward of 10 to 20. The sedimentary units of the Salt Lake group are nearly horizontal in the Oquirrh Mountains. The Rozel Hills are composed of interbedded basalt flows and lacustrine limestones of the Salt Lake group but differ from the Tertiary rocks of the Oquirrh and Stansbury Mountains in the following respects; the igneous rocks are limited to basalt flows; the limestones are the only sedimentary (Tertiary) rocks which crop out although marls, tuffs, and conglomerates occur in the subsurface; the rocks have a regional dip of 13 to the northeast. In conclusion the writer finds that variation in the sedimentary rocks from one locality to the next is the normal rather than the exceptional condition. This is probably true for the Basin and Range province as a whole due to numerous lakes, isolated block fault mountains intermittently rejuvenated, and widespread, spasmodic volcanic activity. Fossils are scarce and correlation difficult. An outline of the Tertiary geologic history of the Salt Lake group in Jordan Valley is proposed as follows: (1) Volcanism (early-0ligocene (?) to mid-Miocene (?) ) accompanied by lacustrine sedimentation. This was the time of deposition of the Traverse volcanics and Jordan Narrows units. (2) Disappearance of the lake, some deformation and erosion, and deposition of the fluvial Gamp Will jams unit in late Miocene (?) time. (3) Significant block faulting -along the east flank of the Oquirrh Mountains in early (?) Pliocene time and deposition of the Harkers fanglomerate. (4) Pedimentation of alluvial fans composed of Harkers fanglomerate culminating in late Pliocene. (5) Incision of the pediment during the Pleistocene. |
