The Stansbury shoreline, one of the conspicuous late Pleistocene shorelines of Lake Bonneville, consists of tufa-cemented gravel and barrier beaches within a vertical zone of about 45 m, the lower limit of which is 70 m above the modern average level of Great Salt Lake. Stratigraphic evidence at a number of localities, including new evidence from Crater Island on the west side of the Great Salt Lake Desert, shows that the Stansbury shoreline formed during the transgressive phase of late Pleistocene Lake bonneville (sometime between about 22,000 and 20,000 yr B.P.). Tufa-cemented gravel and barrier beaches were deposited in the Stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m. We refer to the fluctuations as the Stansbury oscillation. The Stansbury oscillation cannot have been caused by basin-hypsometric factors, such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin, or by changes in drainage basin size. Therefore, changes in climate must have caused the lake level to reverse its general rise, to drop about 45 m in altitude (reducing its surface area by about 18%, 5000 km2), and later to resume its rise. If the sizes of Great Basin lakes are controlled by the mean position of storm tracks and the jetstream, which as recently postulated may be controlled by the size of the continental ice sheets, the Stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the Laurentide ice sheet.
Bibliographical noteFunding Information:
This research was partially funded by the Utah Geological and Mineral Survey, the U.S. Geological Survey, and NASA Contract NASS-28753. Acknowledgment is also made to the Donors of The Petroleum Research Fund, administered by the American Chemical Society, for the partial support of this research. Ted Burr, Rose Ditley, Doug Ekart, Susan Green, and Bill Mulvey helped in the field. We are grateful to Platt Bradbury, who helped identify a sample of algae, to Rick Forester for ostracode identifications and helpful discussions, to Bob Thompson for sharing unpublished data, and to Bruce Bills and David McConnell for helpful comments on an earlier draft of the manuscript. We thank R. M. Forester, W. E. Scott, and G. I. Smith for critical and constructive reviews of the manuscript.
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