Abstract
The present study reports on the method for estimating the water depth from wave-formed ripple marks, using data obtained from field and laboratory. Ripples having crestlines approximately parallel to each other and to wave crestlines are classified into four types based on the relationship between ripple spasing and orbital diameter and on the ripple morphology-orbital vortex ripples (OVR), suborbital vortex ripple (SVR), anorbital vortex ripples, and anorbital planar ripples (APR). OVR form under short-period waves in the limited-fetch coast (lakes and bays) or in lagoon inside reef. The other three are observed in the exposed coast where long period waves prevail.
The water depth of formation of OVR can be calculated using the method for orbital ripples (e.g., Komar, 1974). As to SVR, the following relationship is established: λ/wT=8h/L, where λ is the ripple spacing, w is the sediment fall velocity, T is the wave period, L is the wave length. Based on this equation, the combinations of T and h for given λ and w (which is convertible into sediment grain size) can be obtained. Also the T-h relation can be obtained from AVR, because the following relation is found for AVR: λ/wT=6.6h/L. These results enable us to estimate the ancient water depth from ripple marks preserved in strata. Because APR may not be preserved in deposit, we are unable to use APR as an indicator showing the ancient water depth.
