Optical dating of aeolian sediments from the Sefton coast, northwest England

Abstract

Coastal dunes of Holocene age fringe the coast between Southport and Liverpool in northwest England, forming a natural barrier which prevents marine flooding of low-lying agricultural land in West Lancashire and north Merseyside. Although organic deposits associated with the back-barrier sediments have been dated by radiocarbon methods, the aeolian sands have not previously been dated directly. This paper presents the results of a pilot investigation carried out to assess the potential of optical dating of quartz in providing a chronostratigraphic framework for the coastal aeolian sand deposits. The initial results obtained from three sites are consistent with independent stratigraphie and radiocarbon dating evidence, and indicate that the method has potential, even where the sands have been affected by post-depositional weathering and leaching. Age estimates obtained using a total dose normalization method were found to give less scatter than estimates obtained using the natural normalization method. The optical dating results support radiocarbon evidence for a dune-forming episode at Formby Point around 3000 years ago, and are consistent with historical evidence that transgressive sand sheets invaded the western margin of Downholland Moss during the Middle Ages. Results from a third site, inland of Hightown, suggest that aeolian deposits previously mapped as part of the Shirdley Hill Sand were formed during the early to mid-Flandrian. These aeolian sediments, which were partially buried by estuarine silts during the later Flandrian transgression, may have been derived from marine or estuarine beach deposits associated with a lower sea-level.