八卦台地西南側地形面之分布及應用紅土化育程度於地形面對比之研究

透過野外調查，本研究於八卦台地西南側兩處三角切面頂部發現兩處殘餘地形面（PKW-N與PKW-S），並以化育層指數(HI)以及加權平均剖面化育指數(WPDI)量化其土壤化育程度，以之作為該地形面對比之依據。結果顯示，PKW-N與PKW-S之土壤化育程度均較PK-6（大莊面）高出許多，且二剖面B層之化育層指數最大佳均遠東側最高位階地PK-1（橫山面）之水準，是以將PKW-N、PKW-S與PK-1（橫山面）對比為同一階地形面，二者年代相當，如此意味著PKW-N與PKW-S均為八卦台地最高位地形面於西南側之殘餘。至於PKW-N與PKW-S上層土壤化育層指數較PK-1低了許多，推測原因可能為地形面之坡地地形造成表層土壤黏粒受流水搬運至坡腳而流失，加以剖面因土壤侵蝕而僅為靠近C層之剖面因而砂粒含量較高所致。

關鍵字

八卦台地；地形面；化育層指數；加權平均剖面化育指數

並列摘要

Based on field survey, remnants of geomorphic surfaces (PKW-N and PKW-S) were discovered on two triangular facet crowns in western limb of Paku tableland. This study describes soil morphology of PKW-N and PKW-S in an attempt to calculate horizon index (HI) and weighted mean profile-development index (WPDI) in order to compare the results to those of river terrace on southeastern to correlate their relationship. The degrees of pedogenesis on PKW-N and PKW-S are much higher than that of PK-6. The maximal horizon index of B horizons on these two geomorphic surfaces is similar to the degree of the highest terrace in southeastern Pakua tableland (PK-1). These results indicate that degrees of soil evolution in PKW-N and PKW-S are similar to PK-1, suggesting that they are of similar age, and probably the western remnants of the previous oldest geomorphic surface. As to the horizon indices of upper horizons in PK-N and PK-S are much lower than that of PK-1, this might be caused by downslope movement of clay, which results from downslope movement of overland flow in hillslope. It may also be that the profile of PKW-N and PKW-S is close to C horizon so that the sand content is relative higher.