為了解成岩珊瑚內化石鈾釷同位素行為，本研究收集台灣恆春半島墾丁珊瑚化石。並於每顆珊瑚樣品剖面鑽取三至五個分樣，進行測量分析分樣鈾同位素 (238U ， 234U) 和釷同位素 (230Th， 232Th) 的分布情形。結果顯示現今海平面鵝鑾鼻的未風化珊瑚238U活度值 2.28 ± 0.08 dpm/g，此結果和前人於其他墾丁區域報告的未風化珊瑚一致。龍磐 (海拔高度約80m) 和社頂公園 (海拔高度約150m) 的珊瑚238U活度值幾乎小於或等於1dpm/g，與現今墾丁珊瑚和不同的海洋點採取未成岩珊瑚較小。觀察風化珊瑚化石238U活度值顯示珊瑚成岩作用造成鈾同位素的嚴重流失於地下水。
某些珊瑚樣品 (230Th/238U) activity ≧ 1和成岩作用導致珊瑚鈾同位素流失的觀察結果一致，猜測成岩作用發生時間於35萬年內。值得注意的是同一顆珊瑚化石不同的部分 (234U/238U) activity = 0.98 ~ 1.08，此結果為珊瑚化石和地下水的鈾同位素交換作用，同一珊瑚不同部分的 (230Th/238U) activity活度也被發現有極大的變量，指出成岩作用在珊瑚化石不同部位造成不同程度的影響。總結這些發現，在封閉系統假設下這些珊瑚化石沒有可靠的鈾系列定年能。
為了評估對珊瑚中鈾系列定年的影響，假定珊瑚的鈾流失時序有三種可能性： (1) 成岩作用的鈾同位素流失發生在早期珊瑚形成的時期中， (2) 最近發生的鈾流失，或者 (3) 珊瑚形成後任何時間所發生的鈾流失。 第一種情形年代是可測得的,但需要所有分樣點中測量過的 (230Th/238U) activity 和 (234U/238U) activity 為一致，第二種情形只要當最近鈾流失能被校正時才可被測得，第三種情形則完全不能測得。

To understand the behavior of uranium-series isotopes in diagenetically-altered fossil corals, this study collected fossil corals from Kenting, Heng Chun Peninsula, Taiwan. After separating each coral sample into 3-5 sub-coral samples, we measured the distributions of uranium (238U, 234U) and thorium (230Th, 232Th) isotopes in each of these subsamples. Results show that the modern and unaltered corals collected from Eruanbi (鵝鑾鼻) at modern sea-level have 238U activities 2.28 ± 0.08 dpm/g in consistence with those of unaltered corals reported previously for other locations of Kenting. Corals from Lung-Pan (龍磐) at ~80 m a.s.l. (above sea-level) and She-Ding (社頂) at ~150 m a.s.l. have 238U activities mostly smaller or equal to 1 dpm/g, which are much smaller than those of modern corals at Kenting as well as the unaltered corals from various parts of world oceans. The observed decrease of 238U activities in altered corals suggests that the diagenesis of coral results in significant loss of uranium to groundwater.
Consistent with the observations on diagenesis-driven leads to loss of uranium from corals, 230Th/238U ratios are found in some corals to be significantly greater than 1, suggesting that significant diagenesis occurs during the last 350 kyrs. It is interesting that 234U/238U ratios from various parts of the same coral shows variable values of ~0.98 to 1.13, a result of exchange of uranium between coral and groundwater during the diagenesis. 230Th/238U ratios in various parts of the same coral were also found to vary significantly, suggesting various degree of diagenesis in various parts of the same corals. Based on these findings, we conclude that no reliable U-series dates can be obtained from those fossil corals by assuming a closed system for corals.
To evaluate the impact of diagenesis on U-series dating of corals, we proposed three possible about timing of uranium loss from the corals : (1) The uranium loss by diagenesis occurs in the early short period of coral formation, (2) the uranium loss occurs recently, or (3) U loss occurs at any time after coral formation. Case (1) is datable but requires that the measured 230Th/238U and 234U/238U ratios in all subsamples are the same with the uncertainty. Case (2) is datable only if the recent loss of U can be corrected. Case (3) is undatable.

參考文獻
中文參考文獻
1. 許中民 台灣南端恆春半島第四紀後期構造運動之研究，國立台灣大學地質研究所博士論文，P1-135，1986。
2. 石再添 墾丁國家公園地區的珊瑚礁定年及地形研究，墾丁國家公園管理處，P1-37，1989。
3. 林久芳 台灣恆春半島及東部海岸全新世隆起珊瑚之鈾系定年研究，國立台灣大學地質學研究所碩士論文，P1-119，1989。
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