I'm not sure at what horizon the evidence is in our locality but if you look at fig 4 in this paper at Sullem Voe the tsunami evidence is within the peat layer - a thick band of sand and peat lumps:
"
Storegga tsunami deposits in a peat outcrop in Sullom Voe, Shetland (Bondevik et al., 2003). Large rip-up clasts of peat and pieces of wood make up
a bed within the sand, with a distinct lower boundary. We interpret this as a result of at least two waves inundating the land. The first wave eroded the peat
surface and transported rip-up clasts of peat and sand..."
That paper is 10 years old.