48 



are added to the ridge, ripple height continues to increase with velocity 

 until a point where height decreases and length increases. 



Bedding theory. Bedding is defined as the signature of migration of a 

 surficial bed form, or a morphologic feature having various systematic pat- 

 terns of relief which is created by the conditions of flow at the dynamic 

 interface between a body of cohesionless sediment particles and a fluid 

 (Davis 1983). Many authors have stated that bed form migration produces 

 internal stratigraphic records in subsurface sediments. These records pro- 

 vide clues to the processes, magnitudes, and directions of sediment trans- 

 port that formed them (Nittrouer and Sternberg 1981, Swift et al. 1983). 

 In other words, a specific process with a given magnitude and direction of 

 energy will produce a unique subsurface stratigraphic record. The reader 

 is referred to Reading (1978), Allen (1982), and Reineck and Singh (1986) 

 for comprehensive discussions of stratigraphic signatures of migrating 

 sedimentary features. 



Generally, there exist two classes of bedding; horizontal and cross- 

 bedding. Horizontal bedding is characterized by parallel beds graded at 

 any angle, usually resulting from flat bed sediment migration or the migra- 

 tion of sediment where no bed forms occur. 



Cross-bedding, which is the most common type of bedding encoun- 

 tered on the inner shelf, is defined as a single layer, or a single sedimenta- 

 tion unit, consisting of laminae that are inclined in a direction similar to 

 the principal surface of sedimentation. This sedimentation unit is sepa- 

 rated from adjacent layers by a surface of erosion, nondeposition, or 

 abrupt changes in character. 



Reineck and Singh (1986) indicate that different types of cross-bedding 

 result from the migration of different types and sizes of bed forms. Two 

 types of cross-bedding shown in Figure 13 include: 



a. Planar cross-bedding - cross-bedding in which bounding surfaces 

 form more or less planar surfaces. These units are tabular or 

 wedge-shaped. 



b. Trough cross-bedding - cross-bedding in which bounding surfaces 

 are curved surfaces and the unit is trough-shaped. 



Clifton (1976) classifies internal sedimentary structures on the inner 

 shelf into the following three classes: 



a. Planar parallel laminae (where lamina (singular) is a type of 

 bedding defined as the thinnest recognizable layer in a sediment 

 differing from other layers (commonly 0.05 to 0.10 mm thick)). 



b. Medium-scale ripple-foreset bedding (aforeset is a type of bedding 

 thicker than lamina produced by the deposition of sediment on the 

 downcurrent face of a bed form (Bates and Jackson 1984). 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



