Mid- and late-Holocene sea-level changes in Roudsea Marsh,northwest England: a diatom biostratigraphical investigation

Abstract

Diatoms, vascular vegetation, sediment data and water salinity from contemporary intertidal environ ments in Roudsea Marsh, northwest England, are used to define altitudinal relationships between diatom assem blages and reference water levels. Comparison of these data with the high-resolution diatom biostratigraphy of a fossil marsh sequence allows identification of fluctuations of relative sea level in the mid- and late Holo cene. Two oscillations in relative sea level are recorded. A rise in sea level (> 0.6 m) led to the inundation of the site after 6000 BP and was followed by a fall in sea level (c. 1 m) around 4700 BP. A second rise in sea level (> 0.5 m) occurred before 2420 BP and was followed by a relatively stable or smaller rise of sea level during the last millennium. The use of diatom groups based on marsh altitude was successful.