Ephemeral mud beaches, similar in genesis but smaller in scale to mud beaches and banks along the coast of Surinam and the Gulf Coast of Louisiana, form on the oolitic sand flats along the southeast margin of the Great Salt Lake. These mud beaches, 100 m or more long, approximately 5 m wide accumulate water-saturated mud lenses up to 40 cm thick on the oolitic sand surface. Some may be partly preserved as thin lenses of black mud within the top meter of light-gray oolitic sand.

The beaches appear to form as a result of attenuation and reduction of orbital wave motion by masses of dense, organic-rich, suspended fluid mud that rests on the oolitic sand surface lakeward of the shoreline. Orbital waves approaching the shore die out abruptly upon striking the edge of the fluid mud, allowing organic-rich mud to accumulate in a soupy, suspended form. Only compressional solitary waves propagate through the mud, jostling the mud curds and driving the mud shoreward.

Accumulation of mud beaches may be promoted by the absence of a deep-water mud sink in the Great Salt Lake. Suspended mud on the flat, less than 10 meter-deep lake floor may be periodically entrained and driven shoreward by waves. Once established on the lake margin, the fluid mud diminishes wave force and reinforces subsequent mud accumulation, forming the beaches. Partial preservation of the mud beaches probably reflects erosion, possibly during periods of wind setup on the oolitic sand flats.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah