Year: 2007
Type: article
Abstract: Paleosols, or fossil soils, document past atmospheric composition, climate, and terrestrial landscapes and are key to understanding the composition and evolution of the Earth's atmosphere and the environments in which life developed and evolved. Micromorphological, geochemical and isotopic studies of two Precambrian weathering profiles (Steep Rock, Canada and Hokkalampi, Finland) place constraints on the age of soil formation, document pedogenic processes and post-pedogenic alteration and metamorphism, and yield information about the terrestrial environment at a critical time in Earth history. The textures and geochemistry of the Early Proterozoic Hokkalampi paleosol and the Archean Steep Rock paleosol are consistent with in situ, subaerial weathering under varying soil redox conditions. The upper portion of both profiles have lost greater than 40% of their iron relative to the parent material, similar to Phanerozoic vertisols, while retaining Fe3+/Fe2+ ratios greater than 1. Redistribution of phosphorus in the Steep Rock profile and thorium in some Hokkalampi profiles suggests that organic ligands could have enhanced the mobility of redox-sensitive elements. In addition, copper mobility in the Steep Rock profile could indicate the presence of oxygen in the soil. Loss of base cations in both paleosols is similar to modern ultisols or oxisols, which form in warm, moist environments. Whole rock Rb-Sr isochrons indicate that post-pedogenic potassium metasomatism affected both weathering profiles, and the apparent ages are consistent with the timing of regional greenschist metamorphic events. Whole rock Sm-Nd isotope data demonstrate that rare earth element (REE) systematics were largely unaffected by metamorphism, and that the observed mobility and fractionation of REE could represent a record of Precambrian weathering processes. In the Hokkalampi profiles, Sm-Nd isotope data suggest that pedogenesis took place 2.35±0.19 Ga; this also places a minimum age for Huronian glaciation in the area. The Sm-Nd age of 3.02±0.09 Ga for the Steep Rock paleosol suggests that pedogenesis occurred very soon (less than 60 Ma) after emplacement and erosional uplift of the parent granitoid. This study demonstrates that Rb-Sr and Sm-Nd analysis combined with geochemical, field, and microscopic examination of Precambrian paleosols can help constrain the nature and timing of ancient Earth-surface processes.
Author: Sherry Stafford
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDG: Life on land
Open Access status: green
Funders: National Science Foundation, National Aeronautics and Space Administration, Pennsylvania Space Grant Consortium, University of Pennsylvania, University of Pittsburgh, Pennsylvania State University, NASA Astrobiology Institute, National Institute on Aging, National Cancer Institute, National Institute of General Medical Sciences, National Institute of Neurological Disorders and Stroke
Awards: Systems Approaches to Novel Molecular Mechanism in Alzheimer's Disease, RNA splicing dysfunction in Alzheimer's disease, Multi-level Integrative Proteomics to Alzheimer's Disease Pathways, Synergistic Interaction of amyloid-beta and alpha-synuclein in Lewy body Dementia, Technician Support: Geochemistry Laboratories at the University of Pittsburgh, Phase I, Proteomics Approaches to Protein Turnover, Cancer Center Support Grant (CCSG)
OpenAlex ID: W32894271