Schwartz, Hobson, and Musialowski (1981) distinguished between fair- 

 weather and storm bedding features. They found that storm sequences are 

 marked by: 



a. Beds with sharp lower contacts. 



b. Normal textural grading (fining of sediment grain size in an upward 

 direction). 



c. Laminae bedding throughout or upward transition from laminated 

 bedding at the base to bioturbation in the upper part of the sequence. 



Studies by Curray (1960), Hayes (1967c), and Morton (1981) as re- 

 viewed by Nummedal and Snedden (1987) show that fine sand moves off- 

 shore from the inner shelf during storms and hurricanes. Nummedal and 

 Snedden (1987) summarize that once transported to the continental shelf, 

 little sediment is returned by post-storm flow. The primary sediment 

 source is the portion of the inner shelf between mlw and the break in slope 

 onto the more gently dipping continental shelf. These sediments are rede- 

 posited as thin-graded, centimeter-thick, fining-upward, sand bed se- 

 quences with sharp erosional bases on an otherwise muddy shelf. 

 Hummocky cross-stratification is present. Hayes (1967c), who studied in- 

 ner shelf sedimentation caused by Hurricane Carla (September 1961) docu- 

 mented that these beds have a sharp upper contact, suggesting that some 

 erosion occurred after the Hurricane Carla deposition. The beds have a 

 scoured sole-marked base and are floored by a coarse lag of pebbles or 

 shell fragments. Hummocky cross-stratification is common. This sug- 

 gests that little sand is returned onto the inner shelf and beach from the in- 

 ner shelf after a hurricane. 



In measuring bed level changes during a storm. Green et al. (1988) 

 noted that bed changes at the -8-m depth included 6 cm of accretion over 

 4.5 days of low-energy flow associated with currents as measured with a 

 digital sonar altimeter prior to the onset of the storm. During the initial 

 phase of the storm, 5 cm of scour was followed by 15 cm of rapid accre- 

 tion. This accretion was coincident with the organization of surface 

 waves into long-period swell, and maximum accretion was coincident 

 with the most highly skewed waves. Onshore sediment transport corre- 

 lated strongly with erosion of the bed, and offshore transport with accre- 

 tion of the bed. 



Gagan, Chivas, and Herczog (1990) showed that Cyclone Winifred 

 (1 February 1986) produced a normally graded, mixed terrigenous- 

 carbonate bed sequence 1 1 cm thick in water depths up to -43 m extending 

 30 km offshore. Cross-shelf distribution of organic carbon in the sedi- 

 ment indicated that suspended sediment transport was extensive and that 

 the storm layer was the result of the following three sources: 



a. Landward transport of reworked, resuspended mid-shelf sediment. 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



61 



