4 Sedimentary Features/ 

 Stratigraphy of the Inner 

 Shelf 



40 



Introduction 



Mechanisms of cross-shore sediment transport on the inner shelf 

 greatly affect sedimentary features including morphological signatures 

 such as surficial bed forms, and stratigraphy (internal structure) of the in- 

 ner shelf. The first studies of inner shelf sedimentary features and strati- 

 graphy characteristics were those of Agassiz (1888), Grabau (1913), and 

 Johnson (1919). Johnson (1919), who developed the first model of conti- 

 nental shelf sedimentary characteristics, stated that: 



a. The shelf is a system in dynamic equilibrium both in terms of slope 

 and grain parameters. 



b. Given a nearshore sediment source, grain size decreases in an 

 offshore direction due to decreasing wave energy. 



Shepard (1932) stated that the shelf was composed of a mosaic of sedi- 

 ment sizes and types rather than a uniform seaward-fining trend in grain 

 size. He suggested that these sediments were deposited during periods of 

 lower sea level, particularly during the Pleistocene Epoch. Emery (1952, 

 1968) presented a classification of shelf sediments on a genetic basis con- 

 sidering the following types of materials: 



a. Authigenic, or formed or generated in place (e.g. glauconite or 

 phosphorite). 



b. Organic, or relating to a compound containing carbon as an essential 

 component (e.g. foraminifera, shells). 



c. Residual, or relating to an accumulation of rock debris formed by 

 weathering which remains in place (e.g. residual clay). 



Chapter 4 Sedimentary Features/ Stratigraphy of the Inner Shelf 



