OCR Text |
Show 21 Algal bioherms parallel the oolitic sands in deeper waters. They are mounds of calcium carbonate ( calcite and aragonite), which are three to thirty feet in diameter, 12 to 18 inches high, and range from a few inches to as much as 15 feet thick ( Cohenour, 1966). Troughs between mounds also contain oolitic sands ( Eardley, 1966). The deeper portions of the Lake are bottomed with gray clay. Except for brine shrimp fecal pellets, which occur throughout the Lake, the material is generally silt size ( 1/ 16 mm) or smaller. According to Eardley ( 1938, 1966), about 13 percent of this material was brought in by rivers and other surface inflow, 42 percent was blown in by winds, and 1.5 percent is organic. The balance consists of calcium and magnesium carbonates that were either organically or chemically precipitated within the Lake. According to Hedberg and Parry ( 1971), the clay fraction ( size less than 1/ 256 mm) consists predominantly of the clay minerals, illite and montmorillonite. There is a ridge in the Lake bottom which runs from Promontory Point southwest to Bird Island. This ridge represents a fault, as does the ridge in the sediments along the east shore of the South Arm of the Lake. ( Both faults are shown in Figure 2.) Displacement of these faults is small. About 90 percent of the surface inflow to Great Salt Lake is south of the Southern Pacific Railroad fill. The fill has restricted Lake circulation so that the North Arm of the Lake has acted as a large evaporation pond. The brines in the North Arm were saturated and, by 1970, precipitated about 1.2 billion tons of salt up to five feet thick on the bottom of the Lake in the North Arm. ( Goodwin, 1973.) This layer had |