Symmetrical ripples are moderately common sedimentary structures.  In cross-section, when viewed perpendicular to the crests of the ripples, symmetrical ripple marks are more or less evenly shaped - they are symmetrical.  Their presence in sedimentary rocks is diagnostic of deposition in a shallow water environment with a two-directional, back-and-forth (oscillatory) current.  Symmetrical ripples marks are common in ancient shallow-water sandstone facies.



Symmetrical ripples (above & below) developed in biogenic, aragonitic (CaCO3), sand-size sediments on shallow subtidal seafloor just offshore from Sand Dollar Beach, northwestern San Salvador Island, eastern Bahamas.




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