44 



a. Broad, flat plateaus. 



b. Fluvial valleys and related deltas excavated during the Quaternary 

 Period (from approximately 2 million ybp to the Recent (present) 

 Period inclusive of the Pleistocene and Holocene Epochs)(Evemden 

 et al. 1964, Pratt and Schlee 1969). 



c. Shoal and retreat massifs (landward migration of deltas during 

 transgression [or rising sea level]). 



d. Terraces and scarps. 



e. Cuestas. 



/. Sand ridges. 



Duane et al. (1972) summarized these studies and discussed both inner 

 shelf-detached and shelf- attached shoals. Linear northeast-trending inner 

 shelf-detached shoals trend from the shoreline at an angle between 5 deg 

 and 25 deg, are located in water depths of up to -30 m, measure approxi- 

 mately 25 to 500 m in length, have reliefs of up to 10 m, have side slopes 

 of a few degrees, and extend for tens of kilometers. These sand bodies are 

 composed of well-sorted medium- to coarse-grained sands and are similar 

 in lithology to adjacent beaches. In some instances, clusters of shoals 

 merge with the shoreline in depths as low as 3 m. 



Inner shelf-attached shoals are shoals that are landward of the wave 

 base (about -8 m)(Duane et al. 1972)(although these features are located 

 in the nearshore zone, they are not similar in nature to surf zone/nearshore 

 bars). These shoals appear to form in response to the interaction of south- 

 trending, shore-parallel, wind-generated currents with wave and storm- 

 generated bottom currents during winter storms. Aggradation of crests 

 occurs during storm waves, while degradation occurs during fair-weather 

 waves. These shoals are believed to have formed during lower sea levels 

 associated with the Wisconsin stage of glaciation (the most recent and far- 

 thest south continental glaciation advancement approximately 21,500 ybp 

 to 10,000 ybp during the Pleistocene Epoch) (Evemden et al. 1964, Pratt 

 and Schlee 1969). The shoals are modified by present-day coastal proc- 

 esses, as they are in equilibrium with shelf processes. If these shoals were 

 not in equilibrium with present-day processes, they would erode and 

 disappear. 



Field and Roy (1984) also document elongate, shore-parallel shoals on 

 the lower inner shelf in southeast Australia. These bodies are 10-30 m 

 thick and parallel the coast for 40 km. The upper parts of these sand bod- 

 ies are composed of sand transported downslope from the upper inner 

 shelf and surf zone. Surface sediments of ridges are well-sorted and 

 coarser than surrounding sediments. No seaward fining trend exists. In- 

 ternally, beds are parallel to the slope of the inner shelf and there is no evi- 

 dence of cross- bedding, thus making it difficult to determine the exact 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



