DOI: 10.1016/j.palaeo.2017.01.048
论文题名: Modeling the paleo-seawater radiogenic strontium isotope record: A case study of the Late Jurassic-Early Cretaceous
作者: Kristall B. ; Jacobson A.D. ; Hurtgen M.T.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2017
卷: 472 起始页码: 163
结束页码: 176
语种: 英语
英文关键词: Hydrothermal
; LIPs
; Sr concentration
; Weathering
英文摘要: While uniformitarianism underlies many aspects of the Earth sciences, modeling geochemical cycles throughout Earth history requires critically assessing the reliability and constancy of projecting modern fluxes and their isotope ratios into deep geologic time. In this study, we develop an iterative technique for modeling the radiogenic strontium isotope composition (R87 = 87Sr/86Sr) of seawater (sw) during the Phanerozoic utilizing as a constraint the composite record of McArthur et al. (2012) (McArthur, J. M., Howarth, R. J., & Shields, G. A. (2012). Strontium isotope stratigraphy. In F. M. Gradstein, J. G. Ogg, M. Schmitz, & G. Ogg (Eds.), The Geologic Time Scale 2012 (pp. 127–144): Elsevier). The model yields estimates for the Sr isotope composition of the riverine, submarine groundwater discharge, and diagenetic input fluxes. We use the Late Jurassic-Early Cretaceous segment of the marine Sr isotope record as a case study to demonstrate the efficacy of the new method. To begin, 87Sr/86Sr ratios are calculated for a combined riverine and submarine groundwater discharge flux (tw = total weathering) using a prescribed time-variable R87,sw determined from the LOWESS FIT 5 of McArthur et al. (2012). The calculated R87,tw values are checked against the range of R87,sw for the time interval of interest, as well as older carbonates available for weathering, to determine the reasonableness of the estimates. From these estimates, different prescribed R87,tw values are tested to identify the best match with target seawater 87Sr/86Sr ratios and the range of R87,sw. For model runs focusing on long time intervals (≳ 10 Myr), a single prescribed R87,tw value does not produce a reasonable match to the Sr isotope record. Testing the frequency of variation in R87,tw indicates that during the Early Cretaceous, R87,tw varied at least every 5 Myr, if not more frequently. The minimum frequency at which R87,tw changes likely varied throughout the Phanerozoic, as it depends on the variability of R87,sw and residence time of Sr. Model results also demonstrate the significance of estimating variation in the total hydrothermal (high and low temperature) input flux of Sr along with seawater Sr concentrations in the geologic past, which are key for properly estimating R87,tw. © 2017 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/67876
Appears in Collections: 过去全球变化的重建
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作者单位: Earth and Planetary Sciences, Northwestern University, 2145 Sheridan Road, Evanston, IL, United States
Recommended Citation:
Kristall B.,Jacobson A.D.,Hurtgen M.T.. Modeling the paleo-seawater radiogenic strontium isotope record: A case study of the Late Jurassic-Early Cretaceous[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2017-01-01,472