Diatom records and sedimentary responses to sea-level change during the last 8000 years in Roudsea Wood, northwest England

Abstract

Diatom biostratigraphies are recorded in close stratigraphical intervals from two sites in Roudsea Wood, northwest England. These diatom sequences are used to reconstruct sediment surface elevation which is then compared with the mid- and late-Holocene sea-level history of the region. Four new sea-level index points are added to the sea-level data base for the region and the sea-level history is subjectively divided into three time periods for discussions. The established model of sediment surface elevation for Roudsea Wood suggests that the sedimentary responses to the changing sea level have varied through time and appeared as site-dependent. In Roudsea Wood Valley, a site sheltered from the estuary, the sedimentary equilibrium was not reached until the end of the first period around 6200 yr BP, coincided with the development of a sand barrier across the mouth of the valley. In Roudsea Marsh, a site opened to the estuary, the sedimentary equilibrium was reached as late as the end of the second period around 4200 yr BP. The rises in relative sea level during the final period only caused small landward shift in marsh zones and sandbank development. Together with the sea-level tendency and time-altitude models, the sediment surface model supported by high-resolution biostratigraphical data help enhance the understanding of the history of regional coastal evolution. This study concludes that the major input of sediments into the site occurred during the mid-Holocene.