Evidence for a Shallow Early or Middle Wisconsin-Age Lake in the Bonneville Basin, Utah

Abstract

Relatively complete stratigraphic records of the Bonneville cycle and of at least one and probably two earlier lacustrine are exposed along the Bear River below Cutler Dam in northern Utah between altitudes of 1290 and 1365 m. In most exposures the unconformity between the Bonneville Alloformation and the underlying unit, herein named the Cutler Dam Alloformation, is marked by slight erosional relief and by a weakly to moderately developed buried soil, herein named the Fielding Geosol. In truncated profiles, the Fielding Geosol reaches a maximum of stage II carbonate morphology. Wood from near the base of the Cutler Dam Alloformation yielded a 14C date of >36,000 yr B.P. (Beta-9845). Alloisoleucine/isoleucine (aIle/Ile) ratios of Sphaerium shells from the Cutler Dam beds average 0.15 ± 0.01 in the total hydrolysate, which is significantly greater than the average for Sphaerium shells of Bonneville age elsewhere in the basin. Therefore, the Cutler Dam Alloformation is older than 36,000 yr B.P., but much younger than deposits of the Little Valley lake cycle (140,000 yr B.P.?) which bear shells having significantly higher aIle/Ile ratios. The Cutler Dam Alloformation along the Bear River may be broadly correlative with marine oxygen-isotope stages 4 or 3. Fine-grained, fossiliferous, marginal-lacustrine facies of the Cutler Dam Alloformation are exposed at altitudes near 1340 m, and are probably the highest exposures of sediments deposited in the early or middle Wisconsin lake in the Bonneville basin.

Age of the Cutler Dam Alloformation (Late Pleistocene), Bonneville Basin, Utah

“…In the reference localities along the Bear River near Fielding (Fig. 1), the upper limit of the Cutler Dam AF is 1340 m above sea level, or about 210 m below the Bonneville shoreline (Oviatt et al, 1987). The surface area of the lake that formed during the Cutler Dam lake cycle was ∼22,000 km 2 , or nearly five times larger than the area of the modern Great Salt Lake (at an altitude of 1280 m asl).…”

“…The surface area of the lake that formed during the Cutler Dam lake cycle was ∼22,000 km 2 , or nearly five times larger than the area of the modern Great Salt Lake (at an altitude of 1280 m asl). Compared with the surface area of Lake Bonneville, the Cutler Dam lake was relatively small, however, amounting to 40% of the succeeding late Wisconsin lake that filled the basin to its threshold (Oviatt et al, 1987). Oviatt et al (1987) previously estimated an age range for the Cutler Dam AF from 80,000 to 40,000 yr B.P., broadly synchronous with MIS 4.…”

“…Compared with the surface area of Lake Bonneville, the Cutler Dam lake was relatively small, however, amounting to 40% of the succeeding late Wisconsin lake that filled the basin to its threshold (Oviatt et al, 1987). Oviatt et al (1987) previously estimated an age range for the Cutler Dam AF from 80,000 to 40,000 yr B.P., broadly synchronous with MIS 4. Their estimate was based on a nonfinite 14 C age of >36,000 yr B.P.…”

“…This study focuses on the Cutler Dam Alloformation (AF), which is interpreted to have been deposited in a lake that occupied the Bonneville basin during the early Wisconsin (Oviatt et al, 1987). We employ a relatively new Quaternary dating technique-optically stimulated luminescence (Aitken, 1998)to better constrain the age of the Cutler Dam AF.…”

Reinterpreted history of latest Pleistocene Lake Bonneville

“…Relations to the west with a gently south-sloping gravel bench (~4830 ft in south rising to ~4980 ft in north), between the highest Bonneville shoreline and the Provo shorelines, are unclear. However, the gravels below the paleosol may belong to the older Pokes Point or Little Valley lake cycle, and those above probably belong to the Bonneville or perhaps to the Little Valley lake cycle if it reached this height (Scott et al, 1983;McCoy, 1987;Oviatt et al, 1987;Oviatt et al, 1999). Dating by optical stimulated luminescence is in progress.…”