Links between physical and chemical weathering inferred from a 65-m-deep borehole through Earth's critical zone.
Abstract
As bedrock weathers to regolith - defined here as weathered rock, saprolite, and soil
- porosity grows, guides fluid flow, and liberates nutrients from minerals. Though
vital to terrestrial life, the processes that transform bedrock into soil are poorly
understood, especially in deep regolith, where direct observations are difficult.
A 65-m-deep borehole in the Calhoun Critical Zone Observatory, South Carolina, provides
unusual access to a complete weathering profile in an Appalachian granitoid. Co-located
geophysical and geochemical datasets in the borehole show a remarkably consistent
picture of linked chemical and physical weathering processes, acting over a 38-m-thick
regolith divided into three layers: soil; porous, highly weathered saprolite; and
weathered, fractured bedrock. The data document that major minerals (plagioclase and
biotite) commence to weather at 38 m depth, 20 m below the base of saprolite, in deep,
weathered rock where physical, chemical and optical properties abruptly change. The
transition from saprolite to weathered bedrock is more gradational, over a depth range
of 11-18 m. Chemical weathering increases steadily upward in the weathered bedrock,
with intervals of more intense weathering along fractures, documenting the combined
influence of time, reactive fluid transport, and the opening of fractures as rock
is exhumed and transformed near Earth's surface.
Type
Journal articleSubject
Science & TechnologyMultidisciplinary Sciences
Science & Technology - Other Topics
BEDROCK
MODEL
DISSOLUTION
UNDERSTAND
OXIDATION
REGOLITH
POROSITY
RATES
TIME
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https://hdl.handle.net/10161/21225Published Version (Please cite this version)
10.1038/s41598-019-40819-9Publication Info
Holbrook, W Steven; Marcon, Virginia; Bacon, Allan R; Brantley, Susan L; Carr, Bradley
J; Flinchum, Brady A; ... Riebe, Clifford S (2019). Links between physical and chemical weathering inferred from a 65-m-deep borehole
through Earth's critical zone. Scientific reports, 9(1). pp. 4495. 10.1038/s41598-019-40819-9. Retrieved from https://hdl.handle.net/10161/21225.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Daniel D. Richter
Professor in the Division of Earth and Climate Science
Richter’s research and teaching links soils with ecosystems and the wider environment,
most recently Earth scientists’ Critical Zone. He focuses on how humanity is transforming
Earth’s soils from natural to human-natural systems, specifically how land-uses alter
soil processes and properties on time scales of decades, centuries, and millennia.
Richter's book, Understanding Soil Change (Cambridge University Press), co-authored
with his former PhD

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