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Additionally, we used e Cognition software to automatically extract boulder outlines from aerial imagery to test for trends in boulder size and orientation. Minimum near-surface histories were calculated using the CRONUS Earth online calculator ( wrapper script 2.2, main calculator 2.1, constants 2.2.1 (see Balco et al. -------- GSA Data Repository Item 2017393, a detailed description of methodology, is online at ) based on the constant production rate model (Lal, 1991; Stone, 2000) using the regional northeastern U. Boulders at Hickory Run have experienced widely varying and substantial near-surface exposure.Clasts C1, C2, and C3 have more than triple the expected Be concentration than if they had been continuously irradiated underneath the boulder; all three have higher concentrations than the sample from the top of the boulder. 5), all but five samples fall below the upper constant exposure line, consistent either with exposure followed by erosion (between the upper and lower lines), with at least one episode of burial after initial exposure, or with exposure under cover followed by exhumation.
Hickory Run boulder field is ~2 km south of the Last Glacial Maximum (LGM) Laurentide Ice Sheet boundary (Pazzaglia et al., 2006; Sevon and Braun, 2000) in east-central Pennsylvania, USA (Fig.
1A), a temperate, forested, inland region of the Atlantic passive margin.
South of the boulder field, reversed magnetic polarity deposits indicate that the oldest, most extensive glaciation was in the early Pleistocene (likely Al concentrations they contain today?
” This question arises because there is no unique and agreed upon process model for boulder field development.
* Now at Pinnacle Potash International, Ltd., 111 Congress Ave, Suite 2020, Austin, Texas 78701, USA Manuscript received 31 Mar. Data show that boulders in the field have moved over time and can have cosmogenic nuclide concentrations equivalent to at least 600 k.y. We conclude that boulder fields survive multiple glacial-interglacial cycles, calling into question their utility as climatic indicators.