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Bedrock (234U/238U) disequilibrium and its impact on inferring sediment comminution age in Taiwan Island.
- Source :
-
Applied Geochemistry . Feb2023, Vol. 149, pN.PAG-N.PAG. 1p. - Publication Year :
- 2023
-
Abstract
- Among many 234U–238U disequilibrium applications, the " comminution age " approach enabled quantitative constraints of sediment transport timescale since the genesis of detrital sediment. This method requires a critical assumption regarding the initial bedrock (234U/238U) activity ratios (A 0), typically assumed to be in secular equilibrium (=1). However, this supposition needs further validation as more authors proposed preferential leaching as a vital mechanism that produces U-series disequilibrium among bedrocks. To address this uncertainty and to examine the extent of impacts responsible for the bedrock (234U/238U) disequilibrium, we compiled the published A 0 covering a wide range of lithologies. In this study, the global A 0 values ranged from 0.700 to 1.280, with an average of only 0.981 ± 0.070 (2σ; n = 160). This widely observed 234U deficiency among global bedrocks cannot be resulted from the direct α-recoil of 234U alone but is attributed to the preferential release of 234U from the microfissures created in rock diagenetic history. To further evaluate the impact of A 0 on comminution age calculation, the Zhuoshui River (Taiwan Island) sediment comminution age was re-calculated using the newly measured A 0 from the Zhuoshui River basin, which is 0.978 on average. The newly derived comminution age was nearly three-fifths shorter than the values estimated using A 0 = 1 in the previous study. Our case study demonstrated that assuming bedrock secular equilibrium could lead to overestimated comminution age, inferring a significantly lengthier sediment transport timescale across the river basin; therefore should be carefully constrained to provide a holistic perspective of catchment-scale earth-surface processes. • Bedrocks are not always in a "closed system" due to the micro-fissures formation. • An "open system" through preferential leaching led to bedrock U-disequilibrium. • Zhuoshui River bedrock (234U/238U) is much more depleted than expected. • Comminution recalculation inferred nearly 3/5 shorter ages than assuming unity. [ABSTRACT FROM AUTHOR]
- Subjects :
- *BEDROCK
*SIZE reduction of materials
*SEDIMENT transport
*WATERSHEDS
*SEDIMENTS
Subjects
Details
- Language :
- English
- ISSN :
- 08832927
- Volume :
- 149
- Database :
- Academic Search Index
- Journal :
- Applied Geochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 161442281
- Full Text :
- https://doi.org/10.1016/j.apgeochem.2022.105550