Pedogenesis of Fluvial Terrace Soils Related to Geomorphic Processes in Central Taiwan

Abstract

Pedogenetic features of the soils could be a proxy for revealing the landform surface processes. Our work first analyzed the particle size distributions and lithological discontinuities (LDs) of the soils in the midstream of the Zoushui River, central Taiwan. The results showed that the parental materials of the soils derive from mixed sediments of the Zoushui River and its tributaries, and the LDs of some soils suggested multi-depositional events with homogeneous lithology. Then, we proposed a soil chronosequence of Inceptisols, Ultisols, and Oxisols, over the Pleistocene timescale. There was a very well-defined semilogarithmic relationship between weighted profile development index (WPDI) values and soil age with correlation coefficients (r) greater than 0.9. The age of the soils did not certainly agree with the interglacials of the main marine isotope stage (MIS). However, the soils started to develop only after being aggraded by relatively warm and humid periods or by extreme rain events in cool and dry periods. Irrespective of whether the soils had started to develop, tectonic downcutting, providing clear altitudinal separation of the terrace treads, could inevitably happen later (or almost synchronologically) to ensure stabilities of the tread surfaces.