Flute Casts
November 26, 2014
Photographer: Mike Zawaski; Mike's Web site
Summary Authors: Mike Zawaski; Jackie Phillips
Flute casts or sole marks are the preserved remnants of water flowing over and eroding sediments. To be preserved, softer sediment must wash over the surface and fill in the structures eroded by the water. The water scours a small depression that is steep on the upstream side and a lower angle on the downstream side. After the sediments have been buried deeply, lithified and uplifted, erosion removes the finer stone and leaves behind the more durable rock, exposing the casts of these scours. These structures appear in the Lykins Formation in the foothills above Boulder, Colorado. You can see the soft, easily erodible mudstone with more durable sandstone above preserving these erosional features. Note the mini-carabiner for scale. Photo taken on February 10, 2014.