CC-BY-NC.Īreas outside the maximum extent of Pleistocene glaciation contain landforms thought to have been produced during cold climate periods (Clark and Ciolkosz, 1988) by frost action and mass wasting (periglaciation). © The Geological Society of America, 2017.
* Now at Pinnacle Potash International, Ltd., 111 Congress Ave, Suite 2020, Austin, Texas 78701, USA Long and complex boulder histories suggest that climatic interpretations based on the presence of these rocky landforms are likely oversimplifications. Cosmogenic nuclide data demonstrate that Hickory Run, and likely other boulder fields, are dynamic features that persist through multiple glacial-interglacial cycles because of boulder resistance to weathering and erosion. Measurements of samples from the top and bottom of one boulder and three underlying clasts as well as 26Al/ 10Be ratios ( n = 25) suggest that at least some boulders have complex exposure histories caused by flipping and/or cover by other rocks, soil, or ice. Here, we use in situ cosmogenic 10Be and 26Al to quantify the near-surface history of 52 samples in and around the largest boulder field in North America, Hickory Run, in central Pennsylvania, USA.īoulder surface 10Be concentrations ( n = 43) increase downslope, indicate minimum near-surface histories of 70–600 k.y., and are not correlated with lithology or boulder size. In high and mid-latitudes, boulder fields are thought to form and be active during glacial periods however, few quantitative data support this assertion. Boulder fields are found throughout the world yet, the history of these features, as well as the processes that form them, remain poorly understood.