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.