Abstract

Hansel Valley, located at the north end of the Great Salt Lake in Box Elder County, Utah, is mantled by the lacustrine sediments of at least three Pleistocene lake cycles, These lake deposits overlie Paleozoic bedrock, Tertiary basalt, and Pre-Bonneville (Tertiary and Quaternary) alluvial fans. Shallow arroyo cuts, of which about 240 m were logged, expose the upper part of the lacustrine sequence. Sediments from at least three lake cycles occur: 1) compact bottom deposits from the Little Valley cycle; 2) bottom sediments from an intermediate cycle (informally termed the “Hansel Valley cycle”); and 3) beach gravel and bottom sediments from the Bonneville cycle. The previously undescribed “Hansel Valley cycle” lake may have only reached a maximum elevation of about 1342 m (4400 feet). Stratigraphic position, ostracode identification, and thermoluminescence (TL) dating suggest that the Hansel Valley cycle occurred roughly 75–80 ka (late Oxygen Isotope Stage 5). Sediments exposed and dated in Hansel Valley may be correlative with those described by other authors as the Cutler Dam cycle which are attributed to Oxygen Isotope Stage 4.

Hansel Valley is seismically very active and is the site of the largest and only historic earthquake to rupture the ground surface in Utah. Scarp heights up to as 50 cm were measured from the 1934 M6.6 event, which was contiguous with an older 6 km long scarp that crosses Lake Bonneville recessional shorelines. Two units of Bonneville bottom sediments exposed in arroyos show convolutions, roll structures, liquefaction features and slump blocks. Fault scarps, liquefaction features, and subsurface faults indicate one pre-Bonneville, possibly two Bonneville, and one post-Bonneville-age large earthquakes.