马里萨赫勒地区风成沙特征、来源与发育时代

CHARACTERISTICS, ORIGIN AND DEVELOPMENT ERA OF EOLIAN SAND IN SAHELIAN REGION, MALI

马里萨赫勒地区是全球荒漠化强烈发展的区域之一，广泛分布于地表的各类风成沙是沙质荒漠化发生发展的物质基础。本区风成沙的粒度组成以细沙为主，极细沙次之，各类型沙丘沙的粒度特征有一定差异；重矿物组分以稳定矿物和极稳定矿物占绝对优势，并具有高稳定度和成熟度。风成沙主要来源于古沙丘活化供沙、现代流水作用供沙、干涸湖泊和河流故道供沙等。上新世以来，本区经历了上新世至第四纪初期、末次冰期。

The Sandy desertified land in Sahelian region of Northern Mali amounts to 254 880km 2, occupying 55.3% of the area, and the sandy desertification is still in the intensely developing stage. Various eolian sands spreading widely on the surface is the material base for the occurrence and development of sandy desertification. The grain size composition of eolian sand in the region is dominated by fine sand, followed by very fine sand. Bacause of the impacts of sand origin, accumulation condition and development course, there are some differences in the features of grain size of various dune sand. The eolian sand consists of 26 minerals, among which 21 are heavy minerals, Occuprging 0.1-2.0 percent. The stable and very stable minerals are dominating in these heavy minerals, and the heavy minerals have high stability and maturity. The eolian sand in this region mainly originates from reactivation of ancient sand dunes, modern fluvial action, dry lake deflation and older river courses. According to preliminary study, there are at least 4 major periods of eolian sand development in the region, i.e. Pliocene-early Quaternary, last glacial period, Holocene and modern times; among them the Holocene has 3 aeolian stages, namely early Holocene (10.3-9.2 ka B.P.), mid Holocene (6.8-5.8 ka B.P.) and late Holocene (3.5-1.8 ka B.P.). In the orderly fluctuated courses of alternately dry humid changes in the global climate the eolian sand underwent development, expansionfixation and soil formation in the region.