Abstract:

Earth forests are typical fluvial erosion landforms, which refer to a series of positive and negative relieves, such as column-shaped and wall-shaped forests, as well as gullies. The materials that composed the earth forests are previously deposited semi-loose to semi-consolidated fluvial and lacustrine strata. Therefore, the earth forests’ strata bear abundant information on regional environmental change. By applying grain size analysis to the sediments of earth forests’ strata, this study tentatively demonstrates the material composition and the regional sedimentary environment’s variation processes. A study on grain size characteristics of earth forest landform sediments in the Datong Basin can make clear its material composition and sedimentary environment and provide a scientific basis for the development and evolutionary history of earth forest landforms. Here, 23 sediment samples were collected from a stratum profile of earth forest, and their grain size grading, frequency distribution curves, and grain size parameters were analyzed. The results indicated that the earth forest in the Datong Basin was mainly composed of silt, with an average content of 50.6%, followed by clay, with an average content of 36.01%, and the contents of coarser grain size fractions were scarce. The frequency distribution curve showed uni-and bi-modal distribution patterns. The cumulative grain size frequency curves showed one-and two-segment distribution patterns, which indicated suspension and saltation loads, and each component’s content varied. With the increase in soil depth, the average particle size tends to fluctuate and become coarser. The sorting characteristics fluctuate from moderately poor to poor. The skewness changed from nearly symmetrical to negative and eventually positive. The kurtosis was mostly wide and medium. Sediments of the Datong earth forest were mainly formed in the aeolian, fluvial, and lacustrine sedimentary environments, and these strata were vertically interbedded. The formation of the earth forest is affected by internal and external forces, and its developmental and evolutionary process is closely related to the local climate change. The earth forests’ strata are usually deposited in the fluvial and lacustrine environments during relatively warmer conditions, while they are deposited by aeolian deposition during the arid climate.

Key words: earth forest, grain-size, sedimentary environment, Datong Basin