OCR Text |
Show GEOLOGY AND GEOCHEMISTRY Concerns of the geology and geochemistry of the Great Salt Lake include rock, mineral and soil formation and the nature of the soils around and beneath the Lake. Tables 1 and 2 give chemical and geological information for reference and Figure 2 shows a generalized geological map. GEOLOGICAL FORMATION The Great Salt Lake lies in a complex series of down- faulted blocks called grabens, which are surrounded by up- faulted blocks called horsts. The horsts are represented by the islands and mountains around the Lake-- Promontory Range, Fremont Island, Antelope Island, Stansbury Island, and Carrington Island. Smaller islands include Gunnison, Cub, Dolphin, Bird and Egg Islands. Antelope and Fremont Islands consist of Precambrian rocks ( more than 600 million years old). The rock types are principally schists, gneisses, pegmatites, and granites. The other islands and ranges are composed chiefly of Paleozoic rocks ( from 600 million to 225 million years old), much of which is limestone, shale, sandstone and quartzite. The Paleozoic and Precambrian rocks are well- consolidated. The grabens contain Tertiary rocks ( 70 to 2 million years old) and sediments of Pleistocene ( less than 2 million years old) and Recent ( less than 10,000 years old) ages. Cook and others ( 1966) estimate that the maximum thickness of these sediments is more than 8,000 feet and less than 12,000 feet. Underlying the Tertiary rocks are Paleozoic and Precambrian rocks. Detailed lithology of the Tertiary rocks is not known, but they |