Geology Site Account

Summary

St. Osyth Marsh is an important site for documenting the changes in salt marsh growth, and is one of a few marsh areas in Britain to have been dated. It is part of Colne Estuary SSSI. The importance of the geomorphology of the marsh is included in the Site of Special Scientific Interest designation. The site extends from TM 090 144 to TM 130 126

-----------------------------------------------------------------

Site description

St. Osyth Marsh is an important site for documenting the changes in salt marsh growth, and is one of a few marsh areas in Britain to have been dated. The age of the marsh is about 4,300 years, the date provided by the analysis of a peat seam preserved in grey-black clay at the site. The characteristic assemblage of features - creeks, saltpans and salt marsh cliff - are all present here, and reflect the maturity of the marsh system. The saltpans have been intensively researched by geomorphologists, and provide much information relating to the formation and development of this unique coastal landform.

St. Osyth Marsh is also one of the few places in Britain where the development of wave-built protective beach ridges called cheniers has been described fully. Here the cheniers consist mostly of sand and gravel, unlike those further south on the Dengie peninsula which are made up almost entirely of shells. A rigorous study of the beach ridges at St. Osyth Marsh was carried out recently to determine their true form and origin using ground-penetrating radar and the results published in the journal Sedimentary Geology in 2003.