Sand, gravel, cobbles, and boulders: Detrital thermochronology shows that one size does not tell all
Data files
Sep 11, 2023 version files 124.77 KB
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README.md
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Supplemental_data_tables_S1_and_S2_for_Dryad.xlsx
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Abstract
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.
README: Sand, gravel, cobbles, and boulders: Detrital thermochronology shows that one size does not tell all
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; >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://...
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.