A River Terrace Soil Chronosequence of the Pakua Tableland in Central Taiwan

Abstract

Soils science and fluvial geomorphology meet on the subject about flights of river terraces whose treads rise like stairs above active channels. The Pakua tableland in central Taiwan consists of widely unpaired terraces, including six levels in altitude formed by successive river incision. The terraces serve as geomorphic markers to gauge the differential or absolute deformation of the land surface but such application is hampered by the absence of well-documented ages. Six representative soil pedons were selected from the six levels of terraces in the tableland (from the highest pedon PK-1 to lowest pedon PK-6) to characterize the soil properties in a chronosequence and to relate the pedogenic processes in the major terraces to the formation and evolution of the landscape in the study area. The soil morphological, physical, and chemical properties as well as the clay mineral variation showed that pedogenic intensity is strongly dependent on the terrace levels with varying formation age. The soils can be divided into three domains as Hapludox for pedon PK-1, Paleudult (or Hapludult) for pedons PK-2, PK-3, PK-4, and PK-5, and Dystrudept for pedon PK-6, based on Soil Taxonomy. The degree of soil development increases with altitude in a sequence from PK-1 to PK-6 forming a postincisive type of soil chronosequence in accord with the evolution of the geomorphic surface by successive river incision in the study area. Based on the crystallinity ratios of free iron, the soils give an estimated age of 40-400 ka for the river terraces of the tableland.

Geomorphological and paleoclimatic implications of soil development from siliceous materials on the coral-reef terraces of Liuchiu Island in southern Taiwan

“…Sesquioxidic soils in Taiwan were generally found on the terrace landscapes derived from Quaternary alluvium deposits, such as on the coral-reef terraces (Liao et al 2006). The degrees of time-dependent change in soil properties, including pH, particle sizes and Fe and Al oxyhydroxides, on different terraces reflect soil development and landscape evolution (Markewich and Pavich 1991;Merritts et al 1991;Tsai et al 2006).…”

Pedogenic correlation of lateritic river terraces in central Taiwan

“…2). However, the lowering of the river by erosion is insufficient to keep pace with the rapid uplift of the anticline, preventing the development of river terraces located lower than PK-6 (Yang, 1986;Tsai et al, 2006). The defeated river diverted around the nose of the anticline at the southern end of the tableland.…”

“…Most of the river terraces mentioned above are covered by red soils and gravels, and hence are designated as Ota et al (2002), and the age of PK-1 in the range from Liew (1988), Mouthereau et al (1999) and Tsai et al (2006). The age with superscript "a" based on pedologic correlation, and superscript "b" interpolated from Fig.…”

“…No satisfactory regional correlation of terraces can be achieved based on the geomorphic parameters mentioned above. Tsai et al (2006) reported a soil chronosequence of the Pakua terraces, and estimated the ages by the ratio of (Fe d − Fe o )/Fe t . In this study, the weighted mean of the PDIs (hereafter termed WPDI) and the pedogenic iron are calculated and compared as a basis for regional terrace correlation.…”

Evolution and significance of soil magnetism of basalt-derived chronosequence soils in tropical southern China

“…Fe d /Fe t usually can be used to validate the chronosequence reliability because it is a good indicator of the wearthering degree of soils [10,[21][22][23][24][25], The increase of Fe d /Fe t in B horizons with soil age proved the reliability of the studied chronosequence soils (Figure 1). …”