DOI: 10.6071/m3vh5w
title: Sand, gravel, cobbles, and boulders: Detrital thermochronology shows that one size does not tell all

description: Detrital thermochronology has been used to measure sediment source
 elevations, and thus to quantify spatial variations in sediment production
 and erosion in steep mountain catchments. Samples commonly include a small
 fraction of the sediment sizes present on mountain streambeds, which
 according to previous modeling, may not adequately represent sediment
 production where hillslope sediment sizes vary or where sediment breaks
 down during transport. Here we explore what can be learned from multiple
 sizes by quantifying source elevation distributions for 12 sediment size
 classes collected from Inyo Creek, eastern Sierra Nevada, California. To
 interpret these data, we use a new analytical framework that identifies
 both the elevations where sediment sources deviate from catchment
 hypsometry and the likelihood that observed cumulative deviations could
 occur by chance. We find that sediment in four gravel and cobble size
 classes originates preferentially from higher elevations, either because
 erosion rates are faster or because these sizes are disproportionately
 represented in the sediment from high elevations. Conversely, boulders in
 the stream originate mostly from low elevations near the sample point,
 possibly reflecting breakdown of boulders from high elevations during
 transport. While source elevations of finer sediment sizes are
 statistically indistinguishable from hypsometry, we show that these sizes
 are unlikely to be consistent with uniform sediment production because
 they cannot be considered in isolation from the coarser sizes. Our source
 elevation distributions from sand, gravel, cobbles, and boulders show that
 no one size can tell the rich story of sediment production and evolution,
 and highlight opportunities for future work.
description: # Sand, gravel, cobbles, and boulders: Detrital thermochronology shows
 that one size does not tell all [Access this dataset on
 Dryad](https://doi.org/10.6071/M3VH5W) This dataset includes apatite
 (U-Th)/He ages measured in 12 sediment sizes from Inyo Creek, California.
 One new bedrock age from the top of Lone Pine Peak is also reported, along
 with bedrock ages previously reported by Stock et al., 2006 and House et
 al., 1997. ## Description of the data and file structure (U-Th)/He ages
 are available as excel spreadsheets. The detrital dataset is reported in
 one spreadsheet, and is organized by sediment size class, from small
 (sand; 1-2 mm) to large (boulders; &gt;256 mm). Refer to the
 manuscript main text for sampling and processing protocols. The bedrock
 data are reported in a second tab of the excel file. The detritral dataset
 includes 713 individual crystal ages, for which we report the measured
 4He, 235U, 232Th, and 147Sm, along with analytical uncertainties (one
 standard deviation), alpha-ejection corrections, crystal mass, equivalent
 spherical radius, effective Uranium (eU) concentration, and the calculated
 age and uncertainty (one standard deviation). Of the 713 grains measured,
 14 of the detrital ages are considered outliers because they fall outside
 the 95% prediction interval of the bedrock age-elevation relationship, and
 therefore are excluded in the main analysis. A supplemental file that
 considers the possible effects of including outliers on our departure
 analysis is available through the publisher (see main text for details).
 ## Sharing/Access information The data published here are freely available
 to all users. Other data used in the manuscript was derived from the
 following sources: Hillslope observations of sediment size (Figure 7):
 Sklar, L.S., Riebe, C.S., Genetti, J., Leclere, S., and Lukens, C.E.,
 2020, Downvalley fining of hillslope sediment in an alpine catchment:
 implications for downstream fining of sediment flux in mountain rivers:
 Earth Surface Processes and Landforms, v. 45, p. 1828–1845. Bedrock ages
 (Figure 1): - Stock, G.M., Ehlers, T.A., and Farley, K.A., 2006, Where
 does sediment come from? Quantifying catchment erosion with detrital
 apatite (U-Th)/He thermochronometry: Geology, v. 34, p. 725–728,
 doi:10.1130/G22592.1. - House, M.A., Wernicke, B.P., Farley, K.A., and
 Dumitru, T.A., 1997, Cenozoic thermal evolution of the central Sierra
 Nevada, California, from (UTh)/He thermochronometry: Earth and Planetary
 Science Letters, v. 151, p. 167–179, doi:10.1016/S0012-821X(97)81846-8. ##
 Code/Software The Matlab code used to generate the departure plots (Figs.
 5 and 6) can be accessed here: -
 [http://...](http://..https://github.com/clairelukens/One-size-does-not-tell-all) This repository also includes the detrital (U-Th)/He ages for each sediment size class in a .csv file. The Matlab code includes three main files to 1) plot the kernal density estimators (KDEs) of the age distribution in each size class; 2) generate probability curves for the null hypothesis of uniform sediment production using a bootstrapping methods, and 3) calculate departures of our observed data from the simulations. The codes utilize several functions in the 'functions' folder, and a readme file that describes the workflow, which will generate the plots in Fig. 6 of the manuscript. The Matlab codes were generated using version 2021a.