Submarine geology, sediment distribution and Quaternary history of Start Bay, Devon

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Abstract
An inter-disciplinary study has been undertaken in Start Bay, Devon. Geophysical data show that infilled channels dissect the bedrock surface of the Bay shoreward of a buried cliffline. Beyond this feature the surface resembles an abrasion platform. The three lithological units within superficial material are referred to as barrier, bay and bank deposits, Foraminiferal and sedimentological evidence, together with C-14 dates, indicate that a barrier-lagoon complex has migrated to its present position in response to oscillations of sea level during the latter stages of the Flandrian transgression. Analysis of vibrocore and other samples shows that wave and current processes are variously dominant in the upper 2 m of the superficial deposits. The relative stability of the Skerries Bank may be explained by the values of the residual currents which approach zero along its crest. Water particle velocities nearshore off Slapton Beach suggest that short period edge waves are responsible for shoreline cusps observed in the Bay. While experiments with tracer material indicate that longshore movement may variously depend on linear dimension, ratio or shape index, no clear relationship has been established with nearshore wave parameters. Evidence suggests that Start Bay is a closed system under present-day conditions, there being no nourishment of the foreshore from outside the area. The 1917 Hallsands disaster can be attributed to the legacy of dredging shingle from the intertidal zone between 1897 and 1902, combined with a critical combination of storm waves, gales and spring tides.

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