ESTUARINE MIXING OF CLAY-MINERALS IN THE SOLENT REGION, SOUTHERN ENGLAND

The clay mineral composition of the fine fraction (<2 mu m) of surface sediments from the Solent Estuarine System was determined by X-ray diffraction, in order to understand the origin, distribution and transport pathways of fine-grained sediments within this environment. The spatial distribution of clay minerals in the region is shown to be due to estuarine mixing processes. Riverine input from the rivers Itchen, Test, and Hamble is characterized by high smectite content and a low kaolinite + chlorite to illite ratio. This input is believed to contain a substantial contribution of clay minerals derived from the Chalk. These fluvially derived clay minerals are mixed with a second clay mineral suite of marine origin, containing lower smectite and a higher kaolinite + chlorite to illite ratio. The clay minerals in the marine suite are believed to be derived mainly from Tertiary and/or Recent sediments by the reworking of bed material within the estuaries, or by tidal current and wave erosion of coastal outcrops. Mixing between these two sources occurs as a result of estuarine circulation dynamics.