Pedogenic properties of surface deposits used as evidence for the type of landform formation of the Tadu tableland in central Taiwan

The Tadu tableland is located at the deformation front of the Western Foothills in central Taiwan. The surface of the tableland is covered by reddish soils and gravels, and is folded symmetrically with gently dipping strata running toward both wings. Previous geomorphic studies suggested a fluvial terrace landform developed on the surfaces of the tableland. However, other suggestions have been proposed in recent years. This study attempts to solve the argument by examining the pedogenesis of surface deposits.Five soil pedons were sampled to the depths of C horizons in the surface deposits of the tableland. Strong migration of illuvial clay was indicated by the accumulation of significant clay coatings in the sub-surface soils. These soils were classified as Paleudult and Kandiudult of Ultisols according to Soil Taxonomy. In addition, their morphological characteristics were further quantified in terms of soil development by the horizon index and weighted profile development index (WPDI). The WPDI values of 0.64–0.73 for the soils of the Tadu tableland agree with those of Ultisols developed on the Pakua tableland. Both qualification and quantification assessments indicate all soils of the Tadu tableland are equivalent in terms of degree of pedogenesis. As a result, all the geomorphic surfaces on the tableland probably developed at the same time, which rules out the interpretation of fluvial terraces developing on the tableland. The pedogenic evidence conditionally supports the recently proposed kinematic model for the development of the Tadu tableland.