东北平原西部沙地古土壤与全新世环境变迁

PALEOSOLS OF SANDY LANDS AND ENVIRONMENTAL CHANGES IN THE WESTERN PLAIN OF NORTHEAST CHINA DURING HOLOCENE

东北平原西部全新世以来广泛地发育了2—3层古土壤,主要有四次发育时期,即11000—7000、5500—4500、3500—2800和1400—1000aB.P.。古土壤与风成沙形成互层。它们的孢粉组合特征和物理化学性质的变化反映古环境的变迁。作者认为,该区全新世以来的环境变迁出现四个由干旱到半干旱、半湿润的旋回。半干旱、半湿润时期的自然景观为蒿类草原或稀树(榆树)蔼类草原,发育了沙质淡黑钙土。

2—3 paleosol layers were formed in the western plain of Northeast China during Holocene time. These paleosol layers interlayed with eolian fine sand layers. Their thicknesses are 0.3m, 1.0m and 2.0m respectively. The latter two layers with 1.0m and 2.0m thicknesses are distributed in the whole sandy land, from Qiqihar, Qiangguo to Chifeng, Zhangwu. Dated by ^(14)C, archeology and TL and analyzed by statistics, the formation periods of paleosols are divided from the results. The periods are 11 000—7 000, 5 500—4 500, 3 500—2 800 and 1 400—1 000 a B. P. According to the spore-pollen compositions in more than ten sand dune paleosol profiles, it is discovered that there are few spore-pollens in the sand layers and a few spore-pollens in the paleosol layers. The spore-pollen compositions in the paleosols are simple, mainly Artemisia (50—75%) and Chenopodiaceae. In the paleosols of 11 000—7 000 a B. P., the spore-pollen composition is Arternisia-Rubiaceae-Chenopodiaceae. The contents of Ephedra pollen in the lower and upper part of the layer are more than that in the middle part. But the contents of algae spore in the lower and upper part of the layer are less than that in the middle part. In the paleosols of 5 500—4 500 a B. P., the spore-pollen composition is Artemisia-Chenopodiaceae-Melilotus. There are some Salix sp. and Betula sp. pollens in the lower part of layer and some Ephedra pollens in the upper part. In the paleosols of 3 500—2 800 a B. P., the spore-pollen composition is Artemisia-Chenopodiaceae-Rubiaceae. There are some Kochia and Baryaceae. In the paleosols of 1 400—1 000 a B. P., the spore-pollen composition also is Arternisia-Chenopodiaceae-Rubiaceae. There are a few Pine pollens. The grain size of paleosol is relatively coarse, but still finer than that of eolian sand and becomes coarser from the bottom to the top of the profile. This fact reflects that the weathering environments during the paleosol formation periods were wetter than that during the eolian periods and became dryer from middle to late Holocene.