The factors of psychometric lightness from loess-paleosol stratigraphy and their environmental significance

Abstract

The psychometric lightness of sediments in different environments 
such as lakes, loess-paleosols and topsoils is not only influenced by 
carbonate, organic matter, compounds of the different valence of 
iron, but also have obvious correlations with magnetization rate, 
pollen, sediment particles, heavy metal elements, weathering, and 
others. In this study, the analysis of carbonate, organic matter and 
major elements content of loess-paleosol strata in Caofeng from 
Pingliang and Nuanquanshan from Longxi in Gansu showed that 
the psychometric lightness value L* of loess-paleosol strata in 
Nuanquanshan has a good correlation with the organic matter 
content and the psychometric yellow-blue chromaticness value b*, 
while there is no obvious correlation with the carbonate content. On 
the other hand, it has moderate correlations with SiO2, Na2O and 
Na2O+K2O, and moderate-weak correlations with Al2O3, K2O, 
chemical index of alteration (CIA) and the paleoclimate index C. 
There are good correlations between L* and b* in the loess
paleosol section from Caofeng. Moderate-weak correlations are 
presented between total organic carbon (TOC) content in 
sediments, Al2O3 and paleoclimate index C, while weak 
correlations are recorded between L* values and SiO2, Na2O, K2O, 
Na2O+K2O and also in weathering index CIA. No correlations are 
detected between L* and carbonate content. The study indicates 
that different amount of precipitation leading to differences in the 
mineral weathering such as feldspar and mica, the sediment 
formation, the redox properties of the environment, and trace 
element components, which are intrinsic factors affecting L* during 
the formation of loess-paleosols. The formation of clay minerals 
and their content have significant impacts on L* during weathering. 
L* can possibly be increased in arid areas where the surface of 
sediment particles covers with carbonate minerals.