Wave formed ripple marks created in shallow water conditions.
Photo by Asia Reid.
Display rock 18 is local Ordovician age sandstone with distinctive ripple marks.
How did this form?
Ripple marks can form on the sandy shoreface of a shallow sea when water motion is dominated by wave action. Waves cause an oscillatory motion in the water column. When the water is shallower than ½ the wavelength of the passing waves, the water motion will begin to sweep the sediment in a back-and-fourth motion, creating ripples. Wave ripples can be distinguished from current ripples by their symmetrical nature and their tendency to bifurcate, or divide into forks.
These wave-created ripple marks were formed locally when our part of the world was underwater during the lower-middle Ordovician Period, about 470 million years ago. The next time you’re at the beach, take a look for ripple marks beneath your feet.
Public domain image by Greg Benson via Wikimedia Commons.
Ripple patterns are created when the bottom sediment is swept back and forth by the action of passing waves.