lateglacial

lateglacial vegetation

Peat bank at Tresta

You will need a spade to inspect this section at the base of the peat bank

 

Tresta

Significance: Tresta provides one of the few exposures of organic Late-glacial sediments on Shetland

The peat bank at Tresta was first described by Hoppe (1974). The section lies in the Burn of Tactigill (HU 371508). Here about three metres of peat rests on a 20 cm thick wedge of diamict, comprising matrix-supported pebbles in a loose, mica-rich sand. The sequence rests on 1.5 metres of very stony till with large tabular quartz sandstone blocks resting on almost vertically dipping green Devonian sandstone.

One peat lens, three metres below the base of the peat and 1 cm thick, gave a radiocarbon date of 11,135 years BP. A sample from the base the peat was dated to 5865 BP and a piece of wood from a depth of 2.64 gave a date of 5145 BP. Pollen analysis by Graeme Whittington of the basal organic sediments reveals low pollen concentrations and a sparse pollen flora. Spectra from the upper and lower organic muds show a vegetation dominated by grasses and sedges, with willow. In the organic sands, willow exceeds 30%, sedges are reduced and there is a wider range of taxa. The presence of Thalictrium, Rubiaceae, Caryophyllaceae and Huperzia selago all point to a very open landscape with a cold climate.

Roots and branches of silver birch exposed in the burn