Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai

Hai Xu,Bin Liu,Feng Wu

doi:10.1186/1467-4866-11-3

Abstract

The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO2, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO2, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment.

Highlights

Rb generally coexists with K in the K-rich minerals, such as K-feldspar, and biotite, etc.; while Sr tends to enrich in Ca-bearing minerals, e.g. the limestone and the Ca-bearing silicates such as hornblende, plagioclase and picrite [1]
In this study we studied the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements of the bulk surface sediments in Lake Qinghai in order to constrain the geochemistry of Rb/Sr ratios in sediments of Lake Qinghai
Spatial distribution of Rb/Sr ratio and major elements The Sr contents of the sediments of Lake Qinghai are much higher than those of the loess around. It is higher than Sr contents of loess in other regions in China [e.g. [10,11]], and higher than Sr contents of the upper continental crust (UCC) and that of the terrigenous shale [4]

Summary

Introduction

Rb generally coexists with K in the K-rich minerals, such as K-feldspar, and biotite, etc.; while Sr tends to enrich in Ca-bearing minerals, e.g. the limestone and the Ca-bearing silicates such as hornblende, plagioclase and picrite [1]. Factors that influence the material load to lakes are quite complex, such as the local climates, the chemical/physical property of the bedrock, vegetation cover, and human activities, etc. These variable factors may complicate the environmental significance of the Rb/Sr ratios of lake sediments to a high extent. Weathered catchment; while the physical weathering may play a dominating role in a highly weathered catchment For another scenario, if the physical loads in the catchment are very strong, even though the accompanied chemical weathering is expected to be enhanced, chemical composition of the lake sediments may be dominated by the terrigenous detritus but not the chemical/ biogenic depositions. In this study we studied the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements of the bulk surface sediments in Lake Qinghai in order to constrain the geochemistry of Rb/Sr ratios in sediments of Lake Qinghai

Background and method

Results

Dasch EJ