environmental sciences research institute - University of Ulster

4.2 QUATERNARY SCIENCE
Stone run (block stream) formation in the Falkland Islands over several cold stages, deduced
from cosmogenic isotope (10Be and 26Al) surface exposure dating
Cosmogenic isotope (10Be and 26Al) surface exposure dating has been applied to valley-axis and hillslope stone runs
(relict periglacial block streams) and their source outcrops in the Falkland Islands, South Atlantic. The data indicate that
stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product
of the Last Glacial Maximum; the samples range in apparent 10Be age from 42 ka to 731 ka BP, but some of these are
minima. The results indicate that valley-axis stone runs may be up to 700-800 ka old, have simple exposure histories and
are composite landforms that developed over several cold stages. Analyses of some hillslope and outcrop samples also
demonstrate simple exposure histories with 10Be ages from 42 ka to 658 ka BP. In contrast, isotopic ratios from other
hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding;
the samples range in 10Be age from 59 ka to 569 ka BP and these are regarded as minimum age estimates. Larger stone
runs may be older than smaller runs and there is a possibility that stone runs older than 800 ka exist in other parts of
the Falklands. The assertion that glaciation in the Falklands was restricted to the highest uplands is supported by the
data. The potential for age determination of other boulder-strewn and bedrock landforms, using cosmogenic isotope
analysis, in order to extend the geochronology of Quaternary events and processes in this climatically sensitive area of
the South Atlantic Ocean is apparent.
Figure 1. View across the upper part of Prince’s Street stone run, East Falkland. Components of stone run
terrain (outcrops, hillslopes and valley-axis), sampled for cosmogenic dating are indicated and the arrow
points downvalley.
Peter Wilson, in collaboration with
Michael J. Bentley, Department of Geography, University of Durham
Christoph Schnabel, NERC Cosmogenic Isotope Facility
Richard Clark, Penrith, Cumbria
Sheng Xu, Scottish Universities Environmental Research Centre
11