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Recent work suggests that the C- and O-isotope composition of laminated soil carbonate rinds can provide high-resolution (100 s yr/sample) information about hydrologic processes and vegetation over tens of thousands of years. However, while this archive can potentially provide quantitative reconstructions, most interpretations have thus far been qualitative. In this study, we show how modern soil data and “clumped” isotope paleothermometry can be leveraged to constrain the conditions of rind formation for a sample from the western Colorado Plateau, Utah, USA. We can thus quantitatively interpret rind isotope values as vegetation composition (%C3–plants) and soil water oxygen isotope composition (δ18Osoil–water) over 35–5 ka. We validate the approach by demonstrating consistency between our record and other paleoarchives from the western USA. Laminated soil carbonate rinds therefore represent a new avenue for sub-millennial scale, quantitative investigations of paleoclimatology, paleoecology, archeology, and modeling questions down to the level of individual soils.

Deeper flows through bedrock in mountain watersheds could be important, but lack of data to characterize bedrock properties limits understanding. To address data scarcity, we combine a previously published integrated hydrologic model of a snow-dominated, headwater basin of the Colorado River with a new method for dating baseflow age using dissolved gas tracers SF6, CFC-113, N2, and Ar. The original flow model predicts the majority of groundwater flow through shallow alluvium (

New Paleomagnetic Secular Variation (PSV) data from Fish Lake, Utah, USA, along with previously published regional records, allow us to build an independently dated Western North America PSV stack (WNAM17) from about 35 to 15 ka that quantifies dating and paleomagnetic uncertainties. In February 2014, we recovered a composite 11-m-long sediment record from Fish Lake, Utah that retrieved glacially influenced and post-glacial sediments. Computed tomography (CT) scans and magnetic susceptibility were used to build a precise depth scale, while radiocarbon dating of terrestrial macrofossils and tephrostratigraphy provide tight age-control. Glacially influenced sediments have well-defined characteristic remanent magnetizations with all maximum angular deviation values

Surface exposure dating with terrestrial cosmogenic nuclides (TCNs) has become the primary method for determining numerical ages of Pleistocene mountain glacial deposits and landforms in the conterminous western United States (U.S.) and in numerous other glaciated settings worldwide. Recent updates to models of TCN production and scaling warrant a reconsideration of published exposure ages of moraines of the last two Pleistocene glaciations and associated paleoclimate inferences. Previously reported TCN exposure ages of moraines are recalculated here using newer production rates and scaling models for nuclides helium-3 (3He), beryllium-10 (10Be), aluminum-26 (26Al), and chlorine-36 (36Cl), in most cases yielding significant differences from originally reported ages. Recalculated TCN exposure ages of moraines of the penultimate glaciation display a high degree of variability for individual landforms, particularly toward the younger end of age distributions, suggesting that exposure history is affected by moraine denudation and that older age modes provide the best estimate of the depositional age of these moraines. Oldest exposure ages of penultimate glaciation moraines are well-aligned among mountain ranges across the western U.S. and yield a mean of 138 ± 13 ka, indicating that mountain glaciation occurred in step with global ice volume maxima during marine oxygen isotope stage 6. On average, terminal moraines of the last glaciation date to 19.5 ± 2.3 ka and correspond to the latter part of the global Last Glacial Maximum (LGM). Down-valley recessional moraines representing prolonged glacial stabilizations or readvances to ≥75% of maximum lengths have a mean exposure age of 17.0 ± 1.8 ka, suggesting that these moraine positions were last occupied during Heinrich Stadial 1. Evidence for multiple glacial culminations during the last glaciation is found in several mountain ranges and likely reflects at least two phases of Late Pleistocene climate: an earlier phase when glaciers attained their maximum length in response to cooling during the LGM, and a later phase when glaciers persisted at or readvanced to near-maximum lengths in response to sustained cold temperatures and/or increased precipitation.

Determining the ages of young volcanic rocks is important for understanding the tectono-magmatic development of geologic terranes. Usually, if rocks are old enough the 40Ar/39Ar or K–Ar techniques can provide reliable ages. However, when rocks are younger, they often lack enough daughter product to resolve an age. Cosmogenic 3He methods provide an alternative for determining the eruption age of relatively recent mafic/intermediate lava flows. We sampled morphologically young basaltic andesite flows south of Miller Knoll, near Panguitch Lake on the Markagunt Plateau in southern Utah. We took two samples in close proximity from two different areas on the flows and separated both olivine and pyroxene. The typical protocol is to crush mineral separates on-line to determine an inclusion-hosted magmatic 3He/4He component. Then the powders are heated in a furnace to release the total 3He and 4He component and the crushed component is subtracted to determine the cosmogenic 3He component. Unfortunately, in the case of the Miller Lake flows, 3He yield from on-line crushes was below detection. An alternative isochron approach, which obviates the need for crush data, was first described by Cerling and Craig (1994) and more fully by Blard and Pik (2008). In this approach the 3He/4He of the total gas released from furnace heating is plotted vs. 1/4He. If the samples plot on a line, then the resulting y-intercept is the magmatic 3He/4He and the slope of the line is the cosmogenic 3He component, which determines the exposure age. Our data create good isochrons (MSWD = 0.76 and 0.14) with magmatic 3He/4He of 4.7–4.9 Ra. Concentrations of cosmogenic 3He are 2.13 and 2.61 × 107 atoms g−1after correction for radiometric 4He using the R correction factor and measured and estimated U and Th concentrations in whole rock and minerals, respectively. Using the LSDn scaling routine and an online exposure age calculator, we determine zero erosion exposure ages of 32 ± 3 ka for the upper part of the flow and 34 ± 4 ka for the lower part of the flow.

The Payun Matru volcanic field encompasses more than 12,000 km 2 in the west-central Argentine province of Mendoza. The northwestern part of the field, called Los Volcanes, includes multiple basaltic lava flows and numerous cinder cones and scoria fields. We sampled primary lava flow features (tumuli, pahoehoe and aa flow surfaces) from two different basaltic lava flows and one fluvial strath for cosmogenic 3 He exposure age dating in the Los Volcanes area. Olivines from the sampled basalts have low concentrations of U and Th and a minimal radiogenic 4 He correction. We used the recently established R correction factor to correct our measured 3 He concentrations for magmatic 3 He and 4 He and radiogenic 4 He. Exposure ages for primary lava flow features covering a large area just east of where Route 40 crosses the Rio Grande range from 41 to 43 ka with external uncertainties on the order of 7%. A recently published K→Ar age of 26 ± 5 ka was sampled within a few hundred meters of three of our cosmogenic exposure age samples and appears to be from the same basalt flow. Given the large uncertainties associated with dating young lava flows, the K→Ar age and our cosmogenic ages are in reasonable agreement; however, they do not overlap within uncertainties and suggest possible systematic discrepancies between the two methods of up to 20% in this instance. A sample from a bedrock strath carved by the Rio Grande into basalt yielded a surface exposure age of 17 ± 1 ka. The toe of a much younger-looking aa flow about 5 km west of the Rt. 40 Rio Grande bridge yielded two ages of 0 and 2 ka, and is presumed to be historical.

Andesitic boulder deposits mantle straths cut in sedimentary bedrock high above the northern tributaries of the Escalante River in south-central Utah. The andesitic gravel deposits are derived from the southern escarpments of Boulder Mountain and Aquarius Plateau. The sedimentology and geomorphic expression of these deposits suggest they are from slurry-flow mass movements that have been reworked by fluvial processes. The andesitic boulders are significantly tougher than the local sedimentary bedrock and cause boulder armoring and topographic inversion. The andesitic boulders are also effective tools for fluvial incision when transported across weaker bedrock. Cosmogenic 3 He exposure-age dating of some of the largest boulders exposed on the treads of four different deposits range from 303 ± 48 to 1395 ± 241 ka. The tallest boulders exposed on the deposit surfaces tend to yield the oldest exposure ages, suggesting that boulder erosion and deposit erosion are controlling the exposure-age populations and indicating that even the oldest exposure ages from a given deposit are likely minimum age estimates. Using the oldest exposure age from each surface, we estimate maximum Escalante River northern tributary incision rates of 151–323 m Ma −1 for the period since 0.6–1.4 Ma.

Understanding the timing of mountain glacier and paleolake expansion and retraction in the Great Basin region of the western United States has important implications for regional-scale climate change during the last Pleistocene glaciation. The relative timing of mountain glacier maxima and the well-studied Lake Bonneville highstand has been unclear, however, owing to poor chronological limits on glacial deposits. Here, this problem is addressed by applying terrestrial cosmogenic 10Be exposure dating to a classic set of terminal moraines in Little Cottonwood and American Fork Canyons in the western Wasatch Mountains. The exposure ages indicate that the main phase of deglaciation began at 15.7 ± 1.3 ka in both canyons. This update to the glacial chronology of the western Wasatch Mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area, and indicates that the start of deglaciation occurred during or at the end of the Lake Bonneville hydrologic maximum. The glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western U.S. began retreating as many as 4 ka after the start of northern hemisphere deglaciation (at ca. 19 ka).

The High Plateaus of Utah include seven separate mountain ranges that supported glaciers during the Pleistocene. The Fish Lake Plateau, located on the eastern edge of the High Plateaus, preserves evidence of at least two glacial advances. Four cosmogenic 3He exposure ages of boulders in an older moraine range from 79 to 159 ka with a mean age of 129 ± 39 ka and oldest ages of 152 ± 3 and 159 ± 5 ka. These ages suggest deposition during the type Bull Lake glaciation and Marine Oxygen Isotope Stage (MIS) 6. Twenty boulder exposure ages from four different younger moraines indicate a local last glacial maximum (LGM) of ~ 21.1 ka, coincident with the type Pinedale glaciation and MIS 2. Reconstructed Pinedale-age glaciers from the Fish Lake Plateau have equilibrium-line altitudes ranging from 2950 to 3190 m. LGM summer temperature depressions for the Fish Lake Plateau range from −10.7 to −8.2°C, assuming no change in precipitation. Comparison of the Fish Lake summer temperature depressions to a regional dataset suggests that the Fish Lake Plateau may have had a slight increase (~ 1.5× modern) in precipitation during the LGM. A series of submerged ridges in Fish Lake were identified during a bathymetric survey and are likely Bull Lake age moraines.

Vertical geochemical sampling through the Diamante Tuff establishes patterns of zonation in the pre-eruption magma. Volcanic glass demonstrates a roofward increase in Fe and Cl, and a roofward decrease in Ca. Trace elements have no measurable zonation. Welded volcanic glass shows post-eruption loss of Fe, Mg and Cl as well as K gain. Our reported glass chemistry provides robust criteria for correlation to other localities. The Diamante Tuff is an important stratigraphic marker and recognition of this unit provides age control on Quaternary deposits, allowing determination of process rates and elucidating timing of tectonic and geomorphic activity.

Using air photos, satellite images, and field observations we mapped Quaternary glacial and mass movement deposits on the west side of Boulder Mountain in south-central Utah, USA. Prominent glacial moraines were deposited by outlet glaciers that emanated from an ice cap that existed atop Boulder Mountain. Cosmogenic 3 He exposure ages of these deposits range from 20.2 ± 1.5 to 22.5 ± 2.5 ka and indicate maximum ice advance during the global last glacial maximum (LGM). Three 3 He exposure ages of boulders from the Pine Creek slump deposit indicate that the slumping likely occurred at or before ∼ 125 ka. Eight 3 He exposure ages of boulders from the Miller Creek Potholes debris flow deposit range from 20.2 ± 2.0 to 50.4 ± 3.0 ka; five of those boulders yielded ages in the range of 26–33 ka and suggest emplacement of the debris flow deposit during that time. Both of these mass movement features cover prominent fault traces related to the Thousand Lakes fault but do not appear to be offset, suggesting that major faulting has not occurred since ∼ 125 kyr ago in this area.

Boulder Mountain, located in South Central Utah, is one of several mountain ranges on the Colorado Plateau that was glaciated during the late Pleistocene. Using 3He exposure-age dating (corrected for non-cosmogenic 3He with shielded samples), we determined 3He exposure-ages for boulders from the most well-preserved moraines in the Fish Creek drainage of Boulder Mountain. 3He exposure-ages indicate a last glacial maximum (LGM) advance ∼23,100 ± 1300 to 20,000 ± 1400 yr ago and a later and smaller advance ∼16,800 ± 500 to 15,200 ± 500 yr ago. This chronology is very similar to other cosmogenic glacial chronologies from the Western U.S. and suggests that the timing of glacial advance and retreat on the Colorado Plateau was generally in phase with the rest of the Western U.S. during the late Pleistocene.

The Quaternary history of the Capitol Reef area, Utah, is closely linked to the basaltic-andesite boulder deposits that cover much of the landscape. Understanding the age and mode of emplacement of these deposits is crucial to deciphering the Quaternary evolution of this part of the Colorado Plateau. Using cosmogenic 3 He exposure age dating, we obtained apparent exposure ages for several key deposits in the Capitol Reef area. Coarse boulder diamicts capping the Johnson Mesa and Carcass Creek Terraces are not associated with the Bull Lake glaciation as previously thought, but were deposited 180±15 to 205±17 ka (minimum age) and are the result of debris flow deposition. Desert pavements on the Johnson Mesa surface give exposure ranging from 97±8 to 159±14 ka and are 34–96 kyears younger than the boulder exposure ages. The offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial/interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition. Incision rates for the Capitol Reef reach of the Fremont River calculated from the boulder exposure ages range from 0.40 to 0.43 m kyear −1 (maximum rates) and are some of the highest on the Colorado Plateau.