GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.2 663 Fig. 1 - Geological sketch map and key showing the range and distribution of different rock types in the Hampshire basin (estract from: British Geological Survey, 2017). resistivity value are observable in the T1 section above the cliff. T1 section shows between 5 m and -5 m of depth resistivity values ranging from 50-70 ohm·m associated with the sand of the Backlesham Group. The sand resistivity values are higher in the shallower unsaturated zone (above the water table) and lower in the deeper zone (fresh water saturated area). The highly conductive layer (less than 20. ohm·m) at the bottom of the profile is the response of a clayey horizon. Beyond the depth of -5 m the resistivity values remain around 20 ohm·m which are associated with the basal part of the Backlesham Group where is more present the fraction of clay. In sea zone the cross section P1 has the lowest values of resistivity of the section T1. In fact, resistivity values range from 0.1 to 20 ohm·m. A sand-filled paleo-channel, about 80-90.0 m wide, with resistivity values ranging from 5 to 15 ohm·m is clearly evident on the x-axis from 230 m to 320 m about in figure P1. This structure is also coherent with possible continuation of a on shore channel. The observation furthermore indicates the presence of a possible Late-Quaternary fault in transition zone which it could provide additional contribution on the origin of the Solent Channel. Sea-land survey has provided interesting results to detect the sedimentary structure near shore zone.