Morphology and internal structure of sand shoals and sandbanks off the Dorset coast, English Channel

Abstract

The morphology and internal structure of sand shoals and sandbanks around a coastal headland (Portland Bill, southern UK) are described on the basis of sidescan sonar and high‐resolution seismic data sets. Morphological and architectural evidence, combined with the spatial distribution and nature of the bedrock surface, indicates that the evolution of these deposits, especially the sandbanks, may not only be hydrodynamically controlled but also morphologically controlled. The internal structure of the sand shoals reveals a simple pattern of clinoforms dipping in the same direction as their steeper profile. In contrast, the internal structure of the sandbanks reveals that their lower seismic units consist of a sedimentary core interpreted as the remains of a lowstand deposit or an early stage of the bank development under different prevailing hydrodynamic conditions. The present morphology of the sandbanks is represented by upper seismic units characterized by large‐scale sandwave foresets dipping at 6–8°. The nature and morphology of the bedrock surface may also influence the development of sandbanks in some cases. For example, to the west of Portland Bill, the morphology of the bedrock surface (basal reflector) restricts the development of the Portland Bank. This information may explain the asymmetric evolution of sandbanks around Portland Bill.

Bedload sediment transport dynamics in a macrotidal embayment, and implications for export to the southern Great Barrier Reef shelf

“…Globally, numerous large meso-to macrotidal estuaries and deltas have been characterised, notably the Canadian Cobequid Bay-Salmon River (Bay of Fundy) system (Lambiase, 1980;Dalrymple, 1984;Dalrymple et al, 1990), the Bristol-Severn and Thames estuaries in the United Kingdom (Harris and Collins, 1985;Harris, 1988;Bastos et al, 2003), the Gironde in France (Allen and Posamentier, 1993;Berné et al, 1993), the Colorado Delta in northern Mexico (Carriquiry and Sánchez, 1999), the Yangtze system in China (Chen et al, 2000), and the Fly and Sepik Rivers of New Guinea (Baker et al, 1995;Kineke et al, 2000).…”

Large‐scale sediment bodies and superimposed bedforms on the continental shelf close to the Strait of Gibraltar: interplay of complex oceanographic conditions and physiographic constraints

“…Infl uence of pre-existing physiography on fl ow patterns Recent studies have highlighted the infl uence of bedrock topography on sand body development (Bastos et al, 2003). In the study area, a signifi cant number of major sediment bodies seem to be controlled by pre-existing physiographic features, such as sea-fl oor elevations with two main directions (NW-SE and ENE-WSW), and steep slopes ( Figure 5).…”

“…Their overall morphology and internal structures are indicative of long-term morphodynamic migration and sediment transport (Bassetti et al, 2006;Bastos et al, 2003;Berné et al, 1994). However, their plan view pattern does not seem to be as linear as typically in most tidal ridge environments (Liu et al, 2007), suggesting that hydrodynamic control is more complex in the study area.…”

“…However, recent studies report that in some shelf environments large-scale sandy bodies vary laterally signifi cantly, and those bodies may be categorized not only as sand ridges, but also as sand banks, shoals and sheets, developed under the infl uence of complex and variable hydrodynamic conditions and/or pre-existing bedrock morphology (Bastos et al, 2003;Liao et al, 2008;Liu et al, 1998).…”

Quaternary shelf structures SE of the South Island, imaged by high-resolution seismic profiling

“…As a result, boomer surveys have been widely and effectively used in shallow seas and lakes to make detailed maps of the upper 50Á200 m of geology (e.g. Dingle 1965;Bastos et al 2003;Grossman et al 2006;Upton & Osterberg 2007).…”