Geophysical imaging of regolith in landscapes along a climate and vegetation gradient in the Chilean coastal cordillera

Abstract Erosion at Earth’s surface exposes underlying bedrock to climate-driven chemical and physical weathering, transforming it into a porous, ecosystem-sustaining substrate consisting of weathered bedrock, saprolite, and soil. Weathering in saprolite is typically quantified from bulk geochemistry assuming physical strain is negligible. However, modeling and measurements suggest that strain in saprolite may be common, and therefore anisovolumetric weathering may be widespread. To explore this possibility, we quantified the fraction of porosity produced by physical weathering, FPP, at three sites with differing climates in granitic bedrock of the Sierra Nevada, California, USA. We found that strain produces more porosity than chemical mass loss at each site, indicative of strongly anisovolumetric weathering. To expand the scope of our study, we quantified FPP using available volumetric strain and mass loss data from granitic sites spanning a broader range of climates and erosion rates. FPP in each case is ≥0.12, indicative of widespread anisovolumetric weathering. Multiple regression shows that differences in precipitation and erosion rate explain 94% of the variance in FPP and that >98% of Earth’s land surface has conditions that promote anisovolumetric weathering in granitic saprolite. Our work indicates that anisovolumetric weathering is the norm, rather than the exception, and highlights the importance of climate and erosion as drivers of subsurface physical weathering.

Saprolite

Soil production function

Bedrock

Regolith

10.1130/g48191.1

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Citations (21)

Surficial weathering of kaolin regolith in a subtropical climate: Implications for supergene pedogenesis and bedrock argillization

Geoderma (2018)

Qian Fang Hanlie Hong Harald Furnes Jon Chorover Qing Luo

Regolith

Bedrock

Supergene (geology)

Laterite

Parent material

Parent rock

10.1016/j.geoderma.2018.09.020

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Citations (11)

Pedogenic clay formation from allochthonous parent materials in a periglacial alpine critical zone

CATENA (2021)

Jeffrey S. Munroe Peter C. Ryan Atticus Proctor

Bedrock

Regolith

Illite

Saprolite

Parent material

10.1016/j.catena.2021.105324

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Citations (7)

Soil, regolith, and weathered rock: Theoretical concepts and evolution in old-growth temperate forests, Central Europe

Geoderma (2020)

Pavel Šamonil Jonathan D. Phillips Pavel Daněk Vojtěch Beneš Łukasz Pawlik

Regolith

Saprolite

Bedrock

Soil production function

Soil horizon

Parent material

Biogeochemical Cycle

10.1016/j.geoderma.2020.114261

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Citations (22)

Quantification of Long-term Rates of Bedrock Weathering and Soil Production Using Terrestrial Cosmogenic Nuclides: Principles, Methodology, Current Research Status, and Perspectives

Journal of Geography (Chigaku Zasshi) (2017)

Yuki Matsushi

This paper reviews the methodology and applications of terrestrial cosmogenic nuclides as a tool for quantifying rates of geomorphic processes. The review starts from systematics in the production of cosmogenic 10Be and 26Al in quartz, and 36Cl in calcite, and then describes the basic modeling of the accumulation of those nuclides under varying denudation rates. Procedures for sample preparation and nuclide measurement using accelerator mass spectrometry are also summarized. Recent research reveals denudation rates of bare rock surfaces for both silicates and carbonates, as well as soil production rates from saprolite beneath the soil layer on hillslopes. The empirical formulation of soil production rates as a function of soil thickness enables us to test hypothetical transport laws of soil particles through a combined analysis with topographic parameters of hillslopes. Chemical processes contributing to soil production and denudation have been quantified with a coupled approach using cosmogenic nuclide analysis and geochemical mass balance method. However, linkages across climate conditions, element leaching, and denudation rates are still debated because of timescale discrepancies between soil and saprolite formation. Climate seems to affect soil production indirectly by reducing the mechanical strength of saprolite resulting from chemical weathering of bedrock. A theoretical framework is presented for modeling saprolite weakening and denudation, which connects bedrock weathering, erodibility of uppermost saprolite, soil production and transport with steady-state topography of hill-noses.

Saprolite

Cosmogenic nuclide

Denudation

Bedrock

Soil production function

Nuclide

Regolith

10.5026/jgeography.126.487

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Citations (7)

Geomorphic inferences from regolith thickness, chemical denudation and CRN erosion rates near the glacial limit, Boulder Creek catchment and vicinity, Colorado

Geomorphology (2005)