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| [[Great Salt Lake]] | | [[Great Salt Lake]] |
| ==Environment and Geology==
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| The Great Salt Lake is a large Pleistocene lake that is a remnant of Lake Bonneville which was a fresh body of water (Spencer et al., 1984; Eardley, 1938; Post, 1977). The Great Basin, in which Lake Bonneville and other Pleistocene lakes formed, originated after the beginning of some extensive normal faulting (Eardley, 1938; Lindsay et al., 2016; Baskin, 2014; Gwynn, 1996). The Great Salt Lake is now a hypersaline body of water that is divided into a north-south end that is 300-miles long and an east-west end that is 180 miles long (Eardley, 1938). Due to evaporation, the north end is slightly more saline and with replacement of water only in the south (Post, 1977). The major source of freshwater inflow comes from three major rivers, the Bear, Weber, and Jordan rivers which enter the south arm (Lindsay et al., 2016; Baskin, 2014; Gwynn, 1996). Furthermore, due to the northward migration of water, the north arm is becoming increasingly enriched in minerals while the south-arm is slowly becoming depleted (Post, 1977, Lindsay et al., 2016). The geologic record indicates that the Great Salt Lake has gone through at least ten cycles in the last 100,000 years, and the present-day Great Salt Lake is at its lowest point in the most recent cycle (Post, 1977). Furthermore, the Great Salt Lake has no natural outlet to the sea and is thus a terminal lake (Post, 1977).
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| The land that surrounds the Great Salt Lake is primarily Mesozoic and Paleozoic sedimentary rock with the addition of some recent intrusive and extrusive rocks (Post, 1977). Within the lake, there are many small islands such as Gunnison, Dolphin, Black Rock, Antelope, and Fremont just to name a few (Earldey, 1938). The east of the lake is bounded by the Wasatch Mountain and the west is bounded by the Lakeside and Hogside Mountains (Eardley, 1938). The Wasatch Mountain and most of the east of the lake is primarily pre-Cambrian crystalline rock such as gneiss, schists, pegmatites, and granite (Eardley, 1938). The western side, however, is composed of Paleozoic and Algonkian limestone, shale, sandstone, and quartzite (Eardley, 1938).
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| The chemistry of both the north and south arm of the Great Salt Lake are markedly different. The south arm follows a composition that is more like the marine environment (thalassohaline) with the dominant ions being Na+ and Cl- (Post, 1977). The north arm, however, has an ionic composition that is dominated by Na+ and SO42- (Post, 1977). During the winter months in the north arm, when the temperature drops below 3°C NaSO4 will precipitate spontaneously out of solution to form an ~20 cm layer of hydrated NaSO4 at the bottom of the lake (Post, 1977). When the water temperature rises, the NaSO42- dissolves back into solution (Post, 1977).
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| Despite these harsh saline conditions, the Great Salt Lake has an extensive and diverse microbial community (Post, 1977; Lindsay et al., 2016; Weimer et al., 2009; Tazi et al., 2014). Due to the extensive microbial community and shallow conditions, microbialite structures are highly associated with the Great Salt Lake (Lindsay et al., 2016). Oolitic sands provide the base for much of the microbialite formation, and in addition microbialite structures will grow on lithified crusts of oolitic sands and lime muds resulting in reef like complexes (Lindsay et al., 2016; Riding, 2000).
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