ABSTRACTSandyhaven Pill is a ‘drowned valley’ type of estuary. Thus the deposits differ from most other described estuarine deposits which are of ‘tidally influenced river’ type. The surface sediments may be divided broadly into wave‐dominated deposits (22% of area), tide‐dominated deposits (65%), deposits related to marginal cliff collapse (12%) and river‐dominated deposits (1%). Further subdivision shows that the subenvironments are nested in a progression up the estuary with trends to finer sediment size, reduced sorting and increased biogenic activity. The latter relates to a marine to estuarine faunal change and a strong relationship between the distributions of biota and depositional subenvironments. Over a 29 day period, reduction in wave height was reflected in wave‐dominated areas by shoreward movement of some subenvironment boundaries and by improved definition of symmetrical ripples. The tidal cycle had only a limited effect on the tide‐dominated sediments. The most reliable indicators of estuary trend are channels and asymmetrical ripples; but coring shows that ripples and other minor structures are rarely preserved. Heavy mineral analysis indicates that most of the estuarine sand came from offshore. Gradual sediment build‐up will result in a regressive sequence. If this were preserved under a later transgression, the resultant deposit would be an elongate sediment body bounded laterally by a coarse marginal facies. The sediment sequence would be inward and upward fining with diachronous facies boundaries sloping upwards towards the offshore end and towards t