Potassium isotope signatures in modern marine sediments: Insights into early diagenesis
Potassium isotope signatures in modern marine sediments: Insights into early diagenesis
复制标题
DOI：
10.1016/j.epsl.2022.117849
复制
发表时间：
2022-12
影响因子：
5.3
通讯作者：
Wenshuai Li;Xiao-ming Liu;Kun Wang;J. McManus;B. Haley;Yoshio Takahashi;Mohsen Shakouri;Yongfeng Hu
中科院分区：
文献类型：
--
作者：
Wenshuai Li;Xiao-ming Liu;Kun Wang;J. McManus;B. Haley;Yoshio Takahashi;Mohsen Shakouri;Yongfeng Hu
控制海洋钾(K)收支的沉积通量和K的同位素组成（δ 41k）可能提供有关全球钾循环的有价值的信息。然而，目前海洋中的沉积成岩作用是海水K收支中最不为人所知的组成部分之一。本研究提供了一个现代（< 50厘米）沉积物的数据集，这些沉积物来自一系列水文制度，包括大陆边缘环境（秘鲁边缘、加利福尼亚边境和墨西哥边缘）和深海环境（赤道太平洋）。我们测定了沉积物中K的同位素组成和来源，并与元素丰度和光谱分析结果进行了比较。沉积K/Al和Rb/K比值、K相分布和K同位素组成的广泛变化支持大陆风化作用（提供碎屑输入）和沉积成岩作用（构成海水K的重要汇）之间的相互作用。这些过程的最终结果可能改变各种海洋环境沉积物地层中的K元素和同位素收支。研究表明，钾主要由伊利石、海绿石和长石等矿体赋存，区域钾相分配调节了海相沉积钾收支。例如，主要来自陆相的伊利石（高达90%）中含有大量的钾，增加了Rb/K比值，在加利福尼亚边缘沉积（−0.57 ~−0.40‰）、墨西哥边缘的Pescadero斜坡（−0.42 ~−0.39‰）和赤道太平洋深海盆地（−0.56 ~−0.44‰）中产生低δ 41 K。相比之下，海绿石自生作用导致秘鲁边缘（- 0.35 ~ - 0.29‰）和墨西哥边缘（- 0.39 ~ - 0.27‰）的Rb/K比值降低，δ 41 K相对较高。尽管长石钾（< 20%）存在，但沉积物中的δ 41 K反映了碎屑伊利石（δ 41 K伊利石~ - 0.56‰）和自生海绿石（δ 41 K海绿石~ - 0.18‰）的主要贡献。结果表明，海绿石的形成在早期成岩作用中，特别是在大陆边缘，从海水中吸收了同位素轻K，是海水K（包括海水孔隙水中的K）（~ 1 ~ 16，平均~ 6 Tg K·yr−1）的重要汇。
The sedimentary fluxes controlling potassium (K) budget of the oceans and the isotope composition of K (δ 41 K) potentially yield valuable information about the global K cycling. However, at present sedimentary diagenesis in the oceans is one of the least well-known components of the seawater K budget. This study presents a dataset of the modern (< 50 cm) sediments from a range of hydrographic regimes including continental margin settings (the Peru Margin, California Borderland, and Mexican Margin) and deep-sea environments (the Equatorial Pacific). We determine the K isotope compositions and origins of K in the sediments and compare them with the results of elemental abundances and spectroscopic analyses. The wide variability in sedimentary K/Al and Rb/K ratios, K-phase distributions, and K isotope compositions support the interplay between continental weathering, which provides clastic inputs, and sedimentary diagenesis, which constitutes an important sink of seawater K. The net result of these processes potentially alters the K elemental and isotopic budgets in sediment strata of various marine environments. We demonstrate that K is dominantly hosted by illite, glauconite, and feldspars, and regional K-phase partitioning modulates marine sedimentary K budget. For example, considerable amounts of K hosted in illite (up to 90%) primarily of terrestrial origins increase Rb/K ratios, producing low δ 41 K in California Borderland sediments (− 0.57 to− 0.40‰), the Pescadero Slope from the Mexican Margin (− 0.42 to− 0.39‰), and Equatorial Pacific deep-sea basins (− 0.56 to− 0.44‰). In contrast, glauconite authigenesis causes decreases in the Rb/K ratio and relatively high δ 41 K at a site along the Peru Margin (− 0.35 to− 0.29‰), as well as at two other sites along the Mexican Margin (− 0.39 to− 0.27‰). Despite the presence of feldspar-K (< 20%), δ 41 K in the sediments reflects dominant contributions of detrital illite (δ 41 K illite∼− 0.56‰) and authigenic glauconite (δ 41 K glauconite∼− 0.18‰). We conclude that the formation of glauconite in the sediments takes up isotopically light K from seawater and serves as an important sink of seawater K (including K in seawater-derived porewater)(∼ 1 to 16, average∼ 6 Tg K⋅ yr− 1) during early diagenesis, especially on continental margins.