56 



Howard and Reineck (1972) defined a cross-shore sequence of internal 

 stratigraphic structures. In addition to a seaward-fining sediment grain 

 size trend, they found that physical sedimentary structures decrease and 

 biogenic structures increase in a seaward direction due to increasing depth 

 and position of the wave base. Howard and Reineck (1981) also examine 

 and describe the primary physical sedimentary structures and compare a 

 high-energy sequence at Port Hueneme, California, with a low energy, 

 tide-dominated sequence at Sapelo Island, Georgia. 



Howard and Reineck (1981) describe three facies associated with the 

 Port Hueneme, California, beach-to-offshore depositional stratigraphic se- 

 quence. This sequence includes nearshore, transition, and offshore facies. 

 The nearshore facies (+3.0-m to -9.0-m water depth)(inclusive of the fore- 

 shore facies from +3.0 m to 0.0 m, and the inner shelf {shoreface) facies 

 from 0.0 to -9.0 m) is composed primarily of parallel and cross-bedded ho- 

 mogeneous sand, and small-scale wave ripple laminae, while bioturbation 

 is only locally significant. Rounded rock-fragment pebbles are present 

 both individually and as layers in the foreshore and more commonly in the 

 swash zone. Alternating layers of coarse and fine sand are locally present. 

 Heavy minerals are abundant throughout and enhance the expression of 

 physical sedimentary structures. 



In sections of parallel laminated sand in the nearshore facies, the dip is 

 very low (3 deg) and therefore dip directions cannot be specified from 

 cores. Individual laminae pinch out at erosional contracts suggesting that 

 these are wedged-shaped laminae sets. Thickness of individual parallel 

 sets varies from 1 to 12 mm, with their average thickness being 1-2 mm. 

 Cross-bedded sand is characterized by sets 10 to 30 cm thick with individ- 

 ual laminae up to 2 cm thick. This sedimentary structure is found only in 

 the nearshore facies, and within this facies, increases with decreasing 

 water depth. Cross-bedding is most abundant in the vicinity of the mean 

 low water line and is commonly associated with coarse sand, and alternat- 

 ing sets of coarse and fine sand. Small-scale wave ripple laminae are re- 

 stricted mainly to the nearshore facies. Ripples are present on the bottom, 

 but were not preserved in cores. Bioturbation was practically nonexistent 

 out to a water depth of -6.3 m as wave activity dominated the sedimentary 

 sequence. Sand dollars were present in water depths from -6.5 to -8.7 m. 

 No shells or shell fragments were found in the nearshore facies (Howard 

 and Reineck 1981). 



The transition facies (-9.3-m to -18.7-m water depth) is a zone of fine 

 sand and silty sand characterized by an increase in biogenic over physical 

 structures that are commonly preserved as laminated-to-burrowed beds. 

 This laminated- to-burrowed bed sequence is also described by Howard 

 (1972), Howard and Reineck (1972), Golding and Bridges (1973), and 

 Bourgeois (1980). Howard and Reineck (1981) state that wave-ripple bed- 

 ding and parallel laminae are important structures in this facies. Hum- 

 mocky cross-stratification laminae are defined as laminae which are both 

 concave up (swales) and convex up (hummocks), possess many undulating 

 erosion surfaces, and dip into the swales at angles of approximately 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



