Boulders and landscapes preserved beneath cold-based, nonerosive
glacial ice violate assumptions associated with simple cosmogenic
exposure dating. In such a setting, simple single isotope exposure ages
over estimate the latest period of surface exposure; hence, alternate
approaches are required to constrain the multi-stage exposure/burial
histories of such samples. Here, we report 28 paired analyses of 10Be and
26Al in boulder samples from Thule, northwest Greenland. We use numerical
models of exposure and burial as well as Monte Carlo simulations to
constrain glacial chronology and infer process in this Arctic region
dominated by cold-based ice. We investigate three specific cases that can
arise with paired nuclide data: (1) exposure ages that are coeval with
deglaciation and 26Al/10Be ratios consistent with constant exposure; (2)
exposure ages that pre-date deglaciation and 26Al/10Be ratios consistent
with burial following initial exposure; and (3) exposure ages that predate
deglaciation and 26Al/10Be ratios consistent with constant exposure.
Most glacially-transported boulders in Thule have complex histories; some
were exposed for tens of thousands of years and buried for at least
hundreds of thousands of years, while others underwent only limited
burial. These boulders were recycled through different generations of
till over multiple glacial/interglacial cycles, likely experiencing
partial or complete shielding during interglacial periods due to rotation
or shallow burial by sediments. Our work demonstrates that the landscape
in Thule, like many high-latitude landscapes, was shaped over long time
durations and multiple glacial and interglacial periods throughout the
Quaternary.