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With the aim of improving the accuracy and applicability of OSL surface exposure dating, modified sampling and measuring procedures incorporating controlled exposure experiments (CEE) and OSL scanning methods were performed in a trial study on 11-year exposed quartzite rocks in Washington, USA, as well as millennial to decamillennial exposed quartzite surfaces a part of the Foothills Erratics Train in Alberta, Canada. CEE sampling approaches attempt to reliably determine exposure dating model parameters directly from the rock surface of interest using OSL saturated core samples subjected to controlled light exposures. OSL laser scanning measures are used in tandem to record sub-millimeter resolution OSL depth profiles from transverse slices of core surface samples. Scanning electron microscopy with energy dispersive spectroscopy analyses (SEM-EDS) is used additionally to identify and filter non-quartz OSL anomalies in scans to generate less scattered depth profile data which more closely follows depth profile forms of the first-order kinetic exposure dating model. The 11-year exposure study showcases that such measuring and sampling techniques can assist in acquiring precise depth profiles and accurate exposure ages, yet may face resolution issues in OSL data collection depending on rock sample composition. The trial exposure dating study on the Foothills Erratics Train, a site hosting millennial to decamillennial exposed quartzite erratic surfaces, aims to provide an enhanced timeline of glacial retreat for the Erratics Train, offering an interpretable timeline to when humans could have accessed an ice-free corridor to migrate into North America. [ABSTRACT FROM AUTHOR]

Optically stimulated luminescence (OSL) depth profiling utilizes an OSL-at-depth signal to extrapolate an exposure age from rock surfaces. Exposure ages are commonly obtained by fitting the forms of luminescence depth profiles, which depend on parameter estimates of light attenuation and defined rates of luminescence bleaching. Current procedures for obtaining these parameters for a rock surface require matching luminescence depth profiles from compositionally and morphologically matched rock surfaces with known exposure ages, which limits the accuracy and applicability of the technique. A modified procedure is presented to improve the accuracy and applicability of luminescence surface exposure dating, that aims to reliably determine light attenuation and luminescence bleaching parameters directly from the rock surface of interest using luminescence saturated samples subjected to controlled light exposures. Both this proposed 'controlled exposure experiment' technique and the proximal rock matching technique were tested on decade surface exposed quartzite quarry samples from eastern Washington, USA. Parameters derived from the controlled exposure technique, using natural sunlight equivalent to the sampling site, produced the most accurate ages. Data scatter in the luminescence depth profiles substantially limit age accuracies of all techniques. However, the trials of the controlled exposure experiment techniques show procedural insight and potential in offering comparable depth profiling applications to current extrapolative techniques at sites where either no proximal rock surfaces exist, or proximal samples are deemed problematic. A combination of incorporating equivalent solar paths and average solar radiations of the site may provide the most accurate parameter extrapolations for controlled exposure experiments, and the technique should be investigated with more refined datasets. • OSL depth profiles produced from two sample sources on the same quarry site are compared. • Controlled exposures using natural site-equivalent sunlight show promise for extrapolating parameters for exposure dating. • Insight into how simulated and natural sunlight exposures uniquely influence luminescence depth profiles. [ABSTRACT FROM AUTHOR]

• 3He concentrations in Miocene-age basalt decrease exponentially to a depth of ∼100 m. • Concentration-depth profile is diagnostic of 3He production by cosmic ray muons. • 3He production by muons must be considered when dating erosional events in old bedrock. Cosmic ray muons penetrate deeply into rock where they interact with atoms to produce cosmogenic nuclides. Incorporation of the muon contribution to the production rates of cosmogenic nuclides increases the accuracy of exposure dates, burial ages, and erosion rates inferred from measured nuclide concentrations. In the absence of empirical evidence, it is generally assumed that muons do not produce 3He, a cosmogenic nuclide commonly used for exposure dating. Here we assess whether muons produce 3He by measuring He isotope concentrations in pyroxene and ilmenite from a ∼300 m deep drill core and other subsurface samples of the mid-Miocene Columbia River Basalt in Washington, USA. 3He concentrations in our samples exhibit an exponential decline with depth with an e -folding length of 32.4 m, which corresponds to an attenuation length for 3He production of 8780 g cm−2. The deeply penetrating exponential is diagnostic of 3He production by cosmic ray muons. Assuming no erosion, we constrain the minimum surface muonogenic production rate to be 0.23 atom g−1 pyroxene yr−1, whereas when incorporating erosion the production rate is 0.45 atom g−1 pyroxene yr−1. 3He concentrations in samples deeper than ∼100 meters are consistent with model-based estimates of depth-independent nucleogenic production from the capture by 6Li of neutrons produced by alpha particle reactions on light elements. Measurements in other subsurface samples indicate that muon-produced 3He is prevalent across the Columbia Plateau. The penetration depth of muonogenic 3He production is substantially deeper, and the ratio of muon- to spallation-produced 3He is substantially lower, than found for other cosmogenic nuclides. Our results provide the first definitive empirical evidence for 3He production by muons, which has several implications for quantifying the timing and rates of Earth surface change and interpreting He isotope ratios. Importantly, despite the low production rates, landforms in the Channeled Scablands, which were formed by incision of the Columbia River Basalt by the late-Pleistocene Missoula floods, have high concentrations of 3He inherited from post-Miocene muon exposure. Hence 3He production by muons must be considered, particularly when dating rapid erosional events in old bedrock. Our findings indicate samples with less than several tens of meters of shielding by overlying rock will contain cosmogenic 3He that elevates 3He/4He ratios. Hence caution should be used when using 3He/4He ratios from samples at shallower depths to infer mantle sources of basalt. [ABSTRACT FROM AUTHOR]