入海河流沉积物反应态铍的控制因素及对风化程度的指示意义

Controlling factors of reactive beryllium in river sediments entering the oceans and implicationsfor weathering intensity

  • 摘要: 大陆风化过程是调控地质历史时期气候变化的重要机制。至今已提出多种基于硅酸盐沉积物元素地球化学组成的化学风化指标,并被广泛应用于表征各种地表环境下的风化程度。其中,随着大气10Be/9Be风化剥蚀指标的兴起,沉积物中反应态(铁锰氧化物为主)组分9Be占全样的比例(freac)被认为反映了原生矿物在化学风化作用中的溶解过程,有指示化学风化程度的潜力,且不受石英稀释作用的影响。然而,对于freac反映风化程度的可靠性,目前仍缺乏系统性研究。本研究搜集全球已发表的河流沉积物淋滤态Be数据,计算freac这一风化程度潜在指标,并评估freac的控制因素。结果表明,虽然freac会受到粒度和淋滤方式的影响,但是总体上freac与常用风化程度指标,如化学蚀变指数(CIA)存在显著正相关性。此外,freac与流域剥蚀速率之间存在显著的反相关性。因此,在统一分析粒度及淋滤方法的前提下,基于Be元素的指标freac在一定程度上可以反映中性或碱性水体流域中沉积物整体的风化程度,有望在今后被应用于陆相钻孔中示踪地表风化剥蚀过程的演变。

     

    Abstract: The continental weathering process is an important mechanism for regulating climate changes during the geological history. A variety of chemical weathering indices based on the elemental geochemical composition of silicate sediments have been proposed and widely used to characterize the degree of weathering in various environments. Among them, with the development of the meteoric 10Be/9Be denudation proxy, the proportion of reactive 9Be (mainly enriched in Mn-Fe oxides) relative to the bulk 9Be in sediments (freac) is considered to indicate the dissolution process of primary minerals during chemical weathering and has the potential to reflect the intensity of chemical weathering. However, the reliability of the freac proxy in indicating the weathering intensity still lacks a systematic assessment. We compiled the published data on the leachable Be in river sediments worldwide, calculated the freac index, and evaluated the controlling factors of freac. Results show that although freac could be affected, to some extent, by grain size and leaching methods, overall, there is a significant positive correlation between freac and commonly used weathering indicators such as the Chemical Index of Alteration (CIA), implying that the Be-based index freac can be used to indicate the overall weathering intensity of sediments in neutral or alkaline watersheds. In addition, there is a nonlinear negative correlation between freac and the denudation rate on catchment scale, suggesting that the higher the denudation rate, the lower the weathering intensity. In the future, the weathering proxy freac can potentially be applied in terrestrial sedimentary archives to reconstruct paleo-changes in Earth surface processes.

     

/

返回文章
返回