TY - JOUR
T1 - How Particle Size Influences Oxidation of Ancient Organic Matter during Weathering of Black Shale
AU - Gu, Xin
AU - Brantley, Susan L.
N1 - Funding Information:
Much of the work here would not have been possible without the many contributions of Michael Hochella over the years. Hochella was one of the first geoscientists to relate observations across scales from angstroms to meters, and the authors follow in his large footsteps. The authors thank Bob Hilton and three anonymous reviewers for their constructive comments, which greatly improved the quality and clarity of this paper. The geochemical, mineralogical, and microscopic analyses in this study were completed at the Laboratory for Isotopes and Metals in the Environment (LIME) and Materials Characterization Laboratory (MCL) in The Pennsylvania State University. Paul Grieve and the Appalachian Basin Black Shales Group at The Pennsylvania State University are acknowledged for sampling at the quarry and access to the bedrock core, respectively. Funding was derived from grants to Susan L. Brantley from the U.S. Department of Energy (DOE) Office of Basic Energy Sciences (OBES) (DE-FG02-05ER15675) and Xin Gu from the United States Geological Survey (USGS) (104b Award G21AP10576 through the Pennsylvania Water Resource Research Center). Access to the small-angle neutron scattering instruments was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology (NIST) and the National Science Foundation (NSF) under Agreement DMR-1508249. This work was partially supported by the U.S. DOE Office of Biological and Environmental Research through the Critical Interfaces Scientific Focus Area at the Oak Ridge National Laboratory (ORNL), which is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. DOE. The U.S. DOE will provide public access to these results of federally sponsored research in accordance with the U.S. DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). Work at Shale Hills was supported from the Susquehanna Shale Hills Critical Zone Observatory [NSF Division of Earth Sciences (EAR) Grants 12-39285 and 13-31726], part of Penn State’s Stone Valley Forest, which is funded by the Penn State College of Agriculture Sciences, Department of Ecosystem Science and Management and managed by the staff of the Forestlands Management Office.
Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.
PY - 2022/6/16
Y1 - 2022/6/16
N2 - Weathering continuously converts rock to regolith at Earth's surface while regulating the atmospheric concentrations of CO2and O2. Shale weathering is of particular interest because shale, the most abundant rock type exposed on continents, stores much of the ancient organic carbon (OCpetro) buried in rocks. Using geochemical and mineralogical analysis combined with neutron scattering and imaging, we investigated the weathering profile of OCpetroin saprock in a black shale (Marcellus Formation) in the Ridge and Valley Appalachians in Pennsylvania, U.S.A. Consistent with the low erosion rate of the landscape, we discovered that Marcellus is completely depleted in carbonate, plagioclase, and pyrite in saprock below the soil layer. On the contrary, only â 60% of OCpetrowas depleted in saprock. By comparing the pore structure of saprock to bedrock and samples combusted to remove organic matter (OM), we confirmed that the large particles of OM are preferentially depleted, leaving elongated pores of tens to hundreds of micrometers in length, while the smaller particulates of OM (ranging from â 5 to â 200 nm) are largely preserved during weathering. The retarded weathering of small OM particles is attributed to their close association with mineral surfaces in the shale matrix. The texture of OM in shale is underappreciated as an important factor that controls porosity generation and the weathering rate of OCpetro.
AB - Weathering continuously converts rock to regolith at Earth's surface while regulating the atmospheric concentrations of CO2and O2. Shale weathering is of particular interest because shale, the most abundant rock type exposed on continents, stores much of the ancient organic carbon (OCpetro) buried in rocks. Using geochemical and mineralogical analysis combined with neutron scattering and imaging, we investigated the weathering profile of OCpetroin saprock in a black shale (Marcellus Formation) in the Ridge and Valley Appalachians in Pennsylvania, U.S.A. Consistent with the low erosion rate of the landscape, we discovered that Marcellus is completely depleted in carbonate, plagioclase, and pyrite in saprock below the soil layer. On the contrary, only â 60% of OCpetrowas depleted in saprock. By comparing the pore structure of saprock to bedrock and samples combusted to remove organic matter (OM), we confirmed that the large particles of OM are preferentially depleted, leaving elongated pores of tens to hundreds of micrometers in length, while the smaller particulates of OM (ranging from â 5 to â 200 nm) are largely preserved during weathering. The retarded weathering of small OM particles is attributed to their close association with mineral surfaces in the shale matrix. The texture of OM in shale is underappreciated as an important factor that controls porosity generation and the weathering rate of OCpetro.
UR - http://www.scopus.com/inward/record.url?scp=85131137354&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85131137354&partnerID=8YFLogxK
U2 - 10.1021/acsearthspacechem.1c00442
DO - 10.1021/acsearthspacechem.1c00442
M3 - Article
AN - SCOPUS:85131137354
SN - 2472-3452
VL - 6
SP - 1443
EP - 1459
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 6
ER -