Links between physical and chemical weathering inferred from a 65-m-deep borehole through Earth's critical zone.

Published

Journal Article

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.

Full Text

Duke Authors

Cited Authors

  • Holbrook, WS; Marcon, V; Bacon, AR; Brantley, SL; Carr, BJ; Flinchum, BA; Richter, DD; Riebe, CS

Published Date

  • March 14, 2019

Published In

Volume / Issue

  • 9 / 1

Start / End Page

  • 4495 -

PubMed ID

  • 30872686

Pubmed Central ID

  • 30872686

Electronic International Standard Serial Number (EISSN)

  • 2045-2322

International Standard Serial Number (ISSN)

  • 2045-2322

Digital Object Identifier (DOI)

  • 10.1038/s41598-019-40819-9

Language

  • eng