Abstract

A geophysical survey has been made of the buried floor and infill of the Gilpin-Kent Valley, south Cumbria. The 18 km valley has been investigated using 50 seismic refraction spreads and 140 gravity stations. The survey has been integrated with data from boreholes and with the adjoining Morecambe Bay Barrage feasibility survey.

Five geophysical cross-sections of the valley are given, together with one from a former site investigation near Arnside. Maximum depth to bedrock on each profile lies between 40 and 90 m. The rock floor is dissected by faulting into segments of Silurian and Dinantian (Carboniferous) strata; the softer Silurian rocks have been preferentially eroded to form subglacial tunnel valleys with relief of up to 40 m. In the south the strike of the Carboniferous beds and the trend of some of the faults swing from north-south into a NE-SW direction, which governs the course of the River Kent to its mouth at Grange-over-Sands.

The valley fill consists mostly of silty clay, with some peat; beneath the clay is a horizon of gravel/cobbles that is up to 40 m thick in some of the tunnel valleys. Till has not been recognized in the survey; the gravel may be its reworked remains. The deep and irregular rock floor of the valley points to a glacial regime of vigorous erosion, both by ice and by melt water.

Geotechnical data from boreholes have been correlated, where possible, with seismic velocities and density.

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