Rhenium Isotopes Record Oxidative Weathering Intensity in Sedimentary Rocks

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Geochemistry Geophysics Geosystems Pub Date : 2024-10-28 DOI:10.1029/2024GC011795
A. J. Dickson, R. G. Hilton, J. Prytulak, D. Minisini, J. S. Eldrett, M. Dellinger, M. Stow, W. Wang
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Abstract

Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic-rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.

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铼同位素记录沉积岩的氧化风化强度
在地质时间尺度上,沉积岩中有机碳的氧化风化作用是大气中二氧化碳的主要来源,但由于缺乏可用的替代方法,地球过去这一排放途径的规模尚未直接量化。我们测量了从德克萨斯州南部未风化钻芯和风化露头取样的富含有机质岩石的铼同位素组成,这些岩石的地层演替可以紧密相关。在风化露头岩石中,超过 90% 的有机碳和 ∼85% 的铼被氧化风化,铼同位素组成也随之变低。从初始基岩中风化出的铼的同位素组成,在不同的铼损失率下,单个样本的计算值系统地变化了0.7‰。这种变化可以用同位素分馏系数 α = 1.0002-1.0008 来模拟。我们的研究结果表明,输送到海洋中的铼的同位素组成会因岩石有机物的风化强度而改变,海水中铼的同位素组成对过去的氧化风化和相关的二氧化碳排放很敏感。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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