Symmetrical wave ripples, which tend to form in deeper water, do not mi- 

 grate and thus produce no stratigraphic record. Asymmetrical wave rip- 

 ples tend to form in shallow water. In addition, symmetrical wave ripples 

 have a poorer preservation potential than asymmetrical ripples, as asym- 

 metrical wave ripples migrate. Komar (1974) indicates that ripple spacing 

 of symmetrical wave ripples increases landward under short-period waves 

 but decreases landward under longer-period waves. 



Reineck and Singh (1986) discuss the formation of ripples as a function 

 of water depth and wave period. For wave periods of 2-4 sec, ripples 

 form out to a water depth of -25 m. Symmetrical suborbital ripples are 

 the dominant ripple type for these periods. No asymmetrical ripples form 

 and there exists a limited occurrence of flat beds. For wave periods of 

 5-8 sec, ripples form out to a water depth of -100 m and are dominated by 

 suborbital symmetrical ripples with some anorbital ripples forming at 

 higher velocities in fine- to medium-grained sand. Flat beds form under 

 large wave conditions except in coarse sand. For wave periods of 10 to 

 15 sec, ripples form to a water depth of -300 m. In deep water, symmetri- 

 cal suborbital ripples form in coarse sand while anorbital ripples form in 

 fine sand. It is possible that lunate ripples and flat beds form in medium 

 to coarse sand at higher velocities. Reineck and Singh (1986) also note 

 that maximum velocity, velocity asymmetry, and grain size increase in a 

 landward direction. 



Wave-formed sedimentary structures. Clifton (1976) presents a 

 model concerning the origin and interrelationship of wave-formed sedi- 

 mentary structures. Data collected from southern Oregon (high energy), 

 southeast Spain (relatively low energy) and Willapa Bay, Washington (low 

 energy), and previously collected data from Komar and Miller (1973, 

 1974), Komar (1974) and Dingier (1974) form the basis for this concep- 

 tual model. The processes responsible for these structures include: 



a. Wave parameters including height, period, maximum bottom orbital 

 velocity, and change in maximum bottom orbital velocity. 



b. Fluid factors (density, viscosity). 



c. Flow factors (existing mean currents). 



d. Bottom configuration factors (water depth over all and local slope). 



e. Sediment factors (grain size diameter, sorting, density, and shape). 

 /. Oscillatory currents just above the boundary layer. 



g. Length of oscillatory water movement. 



h. Velocity asymmetry of oscillatory currents. 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



53 



