关键词: 黄土, 古土壤, 方解石, 夏季风降水

Abstract:

Carbonate content has been regarded as good proxy of aridification and monsoon change. However, the mechanism and relationship between them are still unknown. For this, a systematic sampling was carried out on modern soils, Holocene paleosol S0 and last glacial maximum loess L1 from the loess covered area to its source areas in northwest China. Samples were subsequently subjected to size fraction separation. Standard chemical analysis of calcite content from these different sized fractions demonstrates that the coarse and middle sized fractions contain very low content of calcite that changes in low magnitude and no any relationship with precipitation, while the fine fraction less than 2 μm presents a high content of calcite with a large magnitude change. Further, its content decreases with increase of precipitation from samples from modern soils and Holocene paleosol S0, and has no clear relationship with precipitation for samples from loess L1. This pattern of calcite change resembles variations of total calcite and carbonate content, indicating that the fine calcite is the major contributor for the variations of total calcite and carbonate content. This proves the fine calcite is indeed mostly originated from secondary calcite forming in pedogenesis, thus, its content reflects the degree of pedogenesis and summer monsoon change.

Key words: loess, paleosol, calcite, summer monsoon precipitation