台灣西南部珊瑚礁母質紅土假說可能性之初探

在台灣西南部，散佈著隆起珊瑚礁石灰岩丘陵或台地，如高雄地區的大、小崗山、半屏山、壽山、鳳山台地，以及恆春半島的恆春西台地、墾丁高位珊瑚礁、鵝鑾鼻台地等，多數覆蓋有厚層的紅土，其母質來源至今仍尚爭議。本研究透過土壤剖面形態描述、土壤層與下覆地層關係之觀察，指出珊瑚礁石灰岩上覆之紅土特性，並非完全與石灰岩有直接的關係。部分土壤直接覆蓋在石灰岩上，且土體下方混有石灰岩塊或碎屑，而整個土壤質地又相當均勻，此意味這些土壤的母質來源，可能與石灰岩中的不溶性矽酸鹽類物質有關。然而，隆起珊瑚礁石灰岩中不可溶物質多在10%以下，僅壽山的KHR-2、墾丁地區的KTR-3和KTR-5含量在10%以上。在不考慮堆積和侵蝕等作用影響下，形成1 m厚之土壤所需石灰岩厚度多在3-8 m以上。惟各隆起珊瑚礁石灰岩的厚度，除壽山石灰岩外最厚處可達500 m外，其餘地區多在100 m以下，若考量到其上所覆蓋的土壤厚度，則生成該厚層土壤所需的石灰岩，應相當接近現有的石灰岩厚度，或佔現有石灰岩厚度的極大比例，因此若這些土壤均從石灰岩母質所風化而來，則與現實情況不吻合。唯壽山一地之土壤較無法排除完全由石灰岩母質所化育而來的可能性。

關鍵字

脫鈣紅土；紅土；珊瑚礁石灰岩；母質來源

並列摘要

Several coral-reef terraces or tablelands covered by thick terra-rossa like soils widely distributed in South-west Taiwan. Traditionally, it has been believed that the soils originate in the residue of dissolution coral reef limestone. However, the origins of the soils were regarded as the fluvial deposits by some geologists. In this study, evidences based on the thick profile descriptions of the soils on coral reef limestone suggest that instead of overlaying on the coral reef, some soils cover directly on the fluvial pebbles. It means that these soils might not be derived from the limestone. Besides, the contents of siliceous residue of most dissolution limestone were less (＜20 %). It indicates that unreasonable thickness (20-50 m) of reef limestone in south-west Taiwan were required for dissolving to produce 3-6 m thick soils. Therefore, the hypothesis, which the parent materials of terra-rossa like soils in south-west Taiwan were the residue of dissolution coral reef limestone, is highly impractical. Nonetheless, due to thick limestone (＞500 m) as well as high contents of residue of dissolution limestone, the opinion, which the soil on Sou-san reef hills possibly origins from the residue of dissolution limestone, is possibly supported. Further analysis, such as mineralogy, is necessary.

並列關鍵字

Terra Rossa ； red soils ； reef limestone ； soil origins

國際替代計量

台灣西南部珊瑚礁母質紅土假說可能性之初探

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