Broken and Expelled Sand of a Delta of Lake Bonneville: A Record of Ancient Earthquakes?

Justin Oakeson

Document Type

Presentation

Journal/Book Title/Conference

USU Student Showcase

Publication Date

4-2014

Faculty Mentor

Susanne Janecke, Robert Oaks, Tammy Rittenour

Abstract

The research was conducted on an outcrop of deltaic sand deposited during the rise of Lake Bonneville, about 23,000 to 17,000 years ago. The outcrop, located near the mouth of Green Canyon, Cache Co., Utah, houses world-class examples of sedimentary deformation and slump structures; however the precise origin of these structures is uncertain. It is possible that these structures were earthquake-induced. The objective of the research was to ultimately broaden the understanding of the processes involved with the formation of the deformation and slump structures and thereby test if tectonic activity was indeed pertinent to the said structures. Data collected from on site analyses, combined with an analysis of aerial imagery and an analysis of part of the outcrop with photo mosaics revealed that there are 4 different ages of liquefied deposits. There are also three listric slumps, two of which dip west and one that dips east. The central slump was active twice. Some of the slumps produced scarps on the sea floor of Lake Bonneville; the scarps are overlapped by un-deformed sediment. All the sediment is lacustrine and dated from the transgression of Lake Bonneville to its high stand. Other features discovered include clay localized in the slip surfaces of the slumps and deformation structures that are brittle and some others that are ductile. It is interesting to note that an earthquake in Hansel Valley, in 1936, produced similar features. Data collected so far seem to indicate that the complex deformation is probably due to cluster of earthquakes on the East Cache fault during the highstand of Lake Bonneville.

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