Llyn Gwernan
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Geology & landscape
Landscape processes: Glacial
Description
Description Llyn Gwernan is an important palynological site, notable for an unusual thickness of Devensian Late-glacial organic deposits. These deposits preserve a detailed pollen record which, together with radiocarbon dates, has allowed far greater resolution of Late-glacial environmental change in Wales than at other sites. Organic sedimentation began at about 13,200 BP, providing a minimum age for Late Devensian deglaciation of the area. Palynological evidence shows deterioration of climate from about 12,120 BP, eventually culminating in the Loch Lomond Stadial; there is no evidence for a Bolling oscillation recorded at some other sites. The onset of the Loch Lomond Stadial is defined by an abrupt lithological change from organic lake muds to clay-rich minerogenic sediment at about 11,160 BP and is accompanied by a change from tree, shrub and warmth-loving herb pollen to that of open habitat herbs. The transition between the Loch Lomond Stadial and the Flandrian occurred at about 10,040 BP which confirms dates from other sites.