ABSTRACT

Rhomboid ripples, previously unreported in carbonate rocks, are present in intertidal carbonates deposited on a Silurian coastal sabkha (Tymochtee Dolomite, Celotex quarry, north-central Ohio). Unlike modern rhomboid ripples, which form in siliciclastic sand, these probably formed from silt-size grains of carbonate. Formation of the rhomboid ripples required bed-load transport of sediment by water that was very shallow (a few centimeters) and fast moving (Froude number > 1), and contained oblique shock waves created by the ripples themselves. Such flow conditions developed locally as water ran off intertidal flats after high tide. Mudstone drapes on the rhomboid ripples were formed from suspension fallout of carbonate mud, clay, and organic matter following storms, and are not gene ically related to the ripples. The rhomboid ripples, along with abundant low-angle (< 10°) cross-bedding and erosion surfaces, document that much of the original carbonate sediment in the sabkha was subjected to reworking and traction transport resulting from storms and tidal currents.