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A two metre core from this site contains a limnic mud overlying a silty clay containing mollusc shells. Above the limnic mud is about sixty-five centimetres of grey silty clay and then a surface organic unit of almost ninety centimetres of humified peat, of which the upper half is oxidized and crumbly, and unsuitable for palynology or radiocarbon dating. The tree and shrub pollen assemblage of the limnic mud comprises mainly birch with some willow and juniper, while the non-tree pollen is dominated by sedges with lesser grass percentages and some wetland herbs like Filipendula (meadowsweet). There are low percentages of micro-charcoal.
Birch percentages are much reduced in the overlying silty clay, with sedge frequencies abundant at over 60% of total pollen. Willow and grass pollen remain significant. Herbs tolerant of severe cold and disturbed soils increase in representation, such as Artemisia, Helianthemum, Thalictrum and Rumex. The more thermophilous Filipendula increases near the upper part of the clay. Open water conditions are shown by Pediastrum algae, with abundant pollen of aquatic taxa Typha angustifolia and T. latifolia near the end of the unit. Micro-charcoal frequencies are generally high.
Near the base of the surface peat unit there is a rise in birch pollen percentages to almost 50% of land pollen, replacing the high percentages of sedges and grasses. Aquatic pollen frequencies fall sharply. Hazel percentages start to rise slowly and pollen of deciduous trees like oak and elm become consistently recorded. The juniper pollen curve ends at about 65cm. At 50cm depth, before the peat becomes oxidized, hazel rises to high values of over 50%, with birch declining and sedges reduced almost to nothing. Herb pollen, including wetland types, fade from the record. There is little micro-charcoal.
The stratigraphy of a limnic unit separated from a surface peat sequence by a thick layer suggests deposition during the Late Glacial period, with Late Glacial Interstadial organic lake muds laid down under temperate climate and covered by inorganic inwash clays under severe cold conditions of the Late Glacial (Loch Lomond) Stadial, before deposition of peats under renewed temperate, Holocene climate. The pollen data support this, with open birch and willow woods established in the two organic units, but a sedge-tundra of open herbaceous vegetation dominant in the intervening cold phase. Climatic amelioration at the end of this phase allowed increased biological productivity in the wetland and terrestrial plant succession at the start of the Holocene and the transition to a wooded landscape. Juniper scrub was shaded out by birch woods, which were in turn replaced by hazel, creating a closed canopy ground cover, a succession typical of early Holocene woodland vegetation history in this region (Innes 2002, Innes and Blackford 2003). The record is truncated above this point. This Late Glacial and early Holocene record at the Flasks core 69 profile is comparable to others in the area from Dishforth Bog (Giles 1992), Bingley Bog (Keen et al 1988) and Tadcaster (Bartley 1962).
Five levels are proposed for radiocarbon dating. Date 1 at c. 55cm would provide an age for the rise of hazel pollen frequencies, a nationally significant biostratigraphic zone boundary. Further pollen levels will locate this event more closely. Date 2 at c. 65cm would date the final decline of juniper pollen. Date 3 at c. 83cm would date the early Holocene rise in birch pollen and the establishment of Holocene woodland. Date 4 at c. 154cm would date the end of temperate Interstadial conditions in the Late Glacial. Date 5 at c.184cm would date the onset of that Late Glacial temperate event. Further pollen counts are needed to locate these levels exactly.
Flasks core 69 provides a vegetation history through Late Glacial and early Holocene period up to the expansion of hazel woodland, broadly dated elsewhere to about 9000BP. Five dates on pollen zone boundaries and stratigraphic boundaries are proposed.