Wiltshire Geology Group in the field

Bradford-on-Avon site maintenance 25/11/17 A fine, if cold, morning was spent removing leaves and clay, washed-down from the sides of the pit, to uncover a ‘hard-ground’ limestone seafloor in the Forest Marble Formation.  The latter is made up of alternating limestones and clays.  The surface is very uneven and, because it was solid, a diverse assemblage of bottom-dwelling sea creatures lived there until they were entombed by an influx of clay (The Bradford Clay).  An earthquake may have triggered slumping of a nearby clay deposit, resulting in a turbidity current which, as the mud settled, buried the fauna in situ 165 million years ago - see diagram below (d) & (e). Twelve people came along to help, from the Bath Geological Society and the WGG, which was great – any more and the pit would have been too crowded! Thanks to everyone and in particular to Sam Medworth, who sieved some of the clay at home and sent these brilliant photos of a selection of fossils: brachiopods, sponges, echinoid spines, fish vertebrae and a sea-lily stem ossicle he found!