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編號： 001

研究生：王為敏 Wang Wei-Min

論文名稱：臺灣澎湖群島近代土壤與古土壤之地球化學與風化化學之比較研究

The comparative study of the geochemistry and weathering chemistry of the modern soils and late Miocene paleosols in the Penghu Islands ( Pescadores ), Taiwan

指導教授：王明光 Wang Ming-Kuang, 葉學文 Yeh Hsueh-Wen

學位類別：博士

校院系所：國立臺灣大學農業化學研究所土壤環境與植物營養組

學年度： 85

出版年：民 86

論文頁數： 166

〔摘要〕

古土壤（ paleosols ）代表著過去地質年代中完整或部份的土壤剖面遺跡。由於全球對於古氣候變遷研究的重視，使得古土壤學家意識到經由古土壤反映古氣候的可行性。古土壤中的某些於成土過程中產生的理化性質，經過長時期保留下來，應可作為反映當時古氣候的指標。澎湖群島地勢不高，最高處海拔僅約 70 公尺（貓嶼），平頂方山為澎湖主要的地形，現今為高溫少雨乾燥的氣候。澎湖的地質主要由玄武岩層和沉積層交錯而形成，在玄武岩與沉積層交錯的假整合帶（ disconfor- mity ）上有古土壤的發育。本論文是以澎湖群島上的近代東衛紅土與玄武岩層間古紅土作比較。比較的重點，包括了土壤化育方面以及地球化學方面。企圖藉由土壤剖面中的理化性質，來推論近代氣候與古氣候的差異性。在土壤化育方面，解析的方法利用剖面形態化育特徵、土壤礦物組成、化學元素含量等。地球化學方面，則利用了剖面元素分佈圖、 Al2O3- （ CaO+Na2O ） -K2O 和 Al2O3- （ CaO+Na2O+K2O ） - （ FeOT+MgO ）三角圖，以及高嶺石類氧 -18 穩定同位素的分析。經過野外調查的結果，澎湖玄武岩層間的古土壤包括了，中新世中期（ middle Miocene, 16 ~ 14Ma ）、中新世晚期（ late Miocene, 12 ~ 10Ma ）古紅土。此兩時期的古紅土，連同晚中新世 / 上新世（ late Miocene / Pliocene, 8Ma 至今）玄武岩質東衛紅土，構成了澎湖地區土壤的時間序列（ soil time series ）系統。而東衛紅土層並未有玄武岩的覆蓋，且化育時間延續至近代。本論文先由東衛紅土層的土壤化育與風化化學方面作探討。東衛紅土顯現出良好的化育特徵，包括土壤的構造及土壤的化育層。元素含量則顯示出脫矽富鋁的化學型態。鹽基陽離子已大部份淋失。剖面發育的過程中則有受到海水的干擾。東衛剖面顯現出多層次化育（ polysequence ）的特徵。由化育初期，經第四紀時期氣候的作用下，澎湖東衛剖面的礦物轉變，早期由原生礦物形成高嶺石類，待氣候變得乾燥時另外生成蒙脫石類。東衛剖面最小的風化速率約為 6.3 × 10-5 cm year-1 。澎湖群島晚中新世時期的古土壤層，以土壤化育程度的角度來看，從無化育的沉積泥層到化育程度高的古紅土之間，還有過渡的弱度化育型古土壤。而化育程度高的古紅土（竹灣剖面）甚至可以達到氧化物土綱（ Oxisols ）的分類等級，因其僅含高嶺石類黏土礦物，包括禾樂石（ halloysite ）與高嶺石（ kaolinite ）。又剖面黏粒含量高（ > 60% ），富含赤鐵礦（ hematite ）礦物，反映出晚中新世時期的澎湖係屬於溫暖多雨、淋洗作用旺盛的氣候類型，與現在高溫少雨的氣候頗為不同。磚紅壤化作用（ laterization ）主導了澎湖古土壤的化育，化育的程度與全球海水準面（ eustatic curve ）的升降和當時的古地形有關，而化育的時間可能至少達到一百萬年之久。本論文另對於四個晚中新世古土壤剖面（竹灣兩個剖面、小門嶼剖面、講美剖面）進行仔細的分層，分析其主要元素含量以及土壤礦物組成。元素分析的結果顯示，紅壤化作用影響土壤的化育，表現在剖面鐵、鋁元素的富集，鉀、鈉、鈣、鎂元素的淋失。但因剖面某深度鈉、鎂、鈣元素含量的異常，顯示剖面曾受到海水的影響。澎湖古土壤並未因長期玄武岩層的覆蓋而有變質作用的發生。不過卻因鈉、鈣海水元素的加入，在 A-CN-K 圖中顯示出輕度的逆風化的方向。在本論文中亦針對澎湖竹灣、小門嶼古土壤中高嶺石類黏土礦物的 d18O 值進行測定。分析結果發現，隨剖面深度的增加 d18O 值有減小的趨勢。在剖面前 40 公分內的高嶺石類，其 d18O 值介於 +17 ~ +22o/oo 之間，顯示其為風化來源。但是剖面底層的高嶺石 d18O 值甚低，介於 +12 ~ +14o/oo ，暗示該高嶺石為水熱作用（ hydrothermal ）產物。並推測澎湖地區除了花嶼之外可能還另外的花崗岩體存在。綜上所述，澎湖古土壤露頭的調查並結合前人玄武岩定年研究，可建立出澎湖的土壤時間序列。而剖面形態、化學全分析、礦物組成、黏土礦物的氧 -18 穩定同位素含量的測定，反映出澎湖晚中新世古土壤的化育主要受到（ 1 ）古地形；（ 2 ）全球海水準面的升降；（ 3 ）高溫多雨的氣候類型三個主要因素的影響。而古地形與海水準面的升降決定了古土壤的母質因素。由東衛紅土層與晚中新世古紅土層的比較，澎湖地區自晚中新世時期至近代第四紀的氣候變化，是由高溫多雨轉變成高溫少雨的氣候類型。因此，本研究顯示出以古土壤反映古氣候的可行性。

Paleosols represent the whole or part of the soil profiles appeared in the geological history. The paleopedologists realized the potential and possibility of the reflection of paleoclimates by paleosols. Some reserved physico-chemical properties in paleosols could be the indicators of paleoclimates.The highest part in Penghu Islands is just 70 meters. The climate of the Penghu Islands now is high temperature and dry. Penghu Islands mainly consist with basalt lava interbeded with sediments. There are paleosols developed at the disconformity between the upper basalt lava and the lower sediments. The comparison of the modern soils (Tung-Wei red soils) and the basalt-interlayered red soils (late Miocene paleosols) is the main objective of this study, which included the aspects of the pedogenesis and geochemistry. Try to compare the difference between the modern climate and the paleoclimate by the physico-chemical properties reserved in soil and paleosol profiles. To decipher the paleoclimatic information, on the pedogenic aspect, use the field characteristics, soil mineral assemblage, and the contents of the chemical elements in the profiles. On the geochemical aspect, use the chemical element distribution in profiles, the Al2O3- (CaO+ Na2O) -K2O and Al2O3- (CaO+Na2O+K2O) - (MgO+FeOT) ternary diagrams, and the oxygen-18 stable isotope analysis.The field observations revealed that the paleosols interlayered in the basalt lava included the middle Miocene and the late Miocene paleosols. Combined with the modern Tung-Wei red soil profiles, they built up a soil time series of the Penghu Islands . The Tung-Wei red soils are not covered by the basalt lava and their pedogenic processes continued till now. Tung-Wei red soils have well pedogenic features, such as the soil structures and the soil horizonations. The contents of elements in this profile revealed the leaching of silica and the enrichment of alumina. Base elements were almostly leached out. The development of the profiles had been interfered by the ocean water and showed the polysequence features in profiles. In the early development, the mineral transformation in profiles was from the primary minerals to the kaolinite group minerals under wet and hot climate. After the change of the climate to be dryer in the late Quaternary, the mineral transformation was then from the primary minerals to the montmorillonite group minerals. From the calculation of the depth divided by the age of the profile, the minimum weathering rate of the Tung-Wei red soils is about 6.3×10-5 cm year-1.In view of the degree of pedogenesis, the late Miocene paleosols in Penghu Islands included non-developed sediments, weakly-developed paleosols, and highly-developed paleosols. Owing to the high content of kaolinite group minerals and free iron oxides (hematite), highly-developed paleosols could be classfied to Oxisols and reflect that the late Miocene climate of the Penghu Islands was high temperature and humid type, that was different to the modern dry and hot climate. Laterization is the dominant pedogenic process for the development of the paleosols in Penghu Islands . The degree of development of the paleosols depended upon the paleo-landscape and upon the eustatic curve. The developing time for late Miocene paleosols in Penghu Islands might be at least 1 million years.In this study, another four detailed sampling late-Miocene paleosols were analyzed by chemical element abundance and mineral compositions. The results showed that laterization process affected the pedogenesis of the paleosols, which were enriched with iron and aluminum and deficient with alkaline and alkaline earth elements. However, the abnormal enrichment of Ca and Mg occurred in some depths of the profiles represented that there happened the ocean lifting that could influence the pedogenesis of paleosols. The paleosols in Penghu Islands were not changed due to the long-term covered by the upper basalt lava. The metamorphism was not occurred. However, the addition of oceanic Ca, Mg, and Na resulted in a bit of reversal weathering trend in A-CN-K diagram. The oxygen-18 stable isotope contents of the kaolin minerals in Chu-Wan and Shiao-Men Yu paleosols were also measured. The results showed that as the increasing of the profile depth is, as the decreasing of the d18O value of kaolin minerals. In the top 40 cm of the profiles, the d18O values of kaolin minerals were +17 ~ +22 o/oo, and such kaolinite group minerals were weathering origins. However, the d18O values of the bottom kaolinite group minerals were +12 ~+14 o/oo, which were very much lower than the upper kaolinites. This implied that such kaolinites were hydrothermal origins. Maybe there existed another type of the granitic body except for Hwa Yu in the Penghu Islands.Combined the field survey of the paleosols and the dating of the basalts in Penghu Islands , the soil time series of paleosols could be built up. The fact revealed from the profile decriptions, the whole-soil elemental analysis, mineral compositions, and the measurement of the d18O value of kaolinite group minerals, reflected that the pedogenesis of the late Miocene paleosols was influenced by (1) the paleo-landscape, (2) the change of the Eustatic curve, and (3) the high temperature and rich rainfall of the climate type. By the comparison of the Thug-Wei red soils and the late Miocene red paleosols, it appeared that the climate from the late Miocene to the Quaternary in Penghu Islands was changed from high temperature and humid type to be dryer. This study revealed the possibility of the reflection of paleoclimates from the paleosols.

〔論文目次〕

誌謝

中文摘要

英文摘要

目錄

表目錄

圖目錄

第一章緒論

1 1 何謂古土壤？

1 2 古土壤於古環境和古氣候學研究的應用

第二章澎湖東衛地區玄武岩質紅土之土壤化育及風化作用之研究

2 1 前言

2 2 材料與方法

2 3 結果與討論

東衛剖面形態特徵

部份理化性質分析

剖面的礦物分析

全土元素分析與剖面元素之增加與損失

東衛紅土風化強度指標

2 4 結論

第三章澎湖群島晚中新世古土壤的研究 ( 一 ) －剖面形態特徵及土壤化育

3 1 前言

3 2 材料與方法

古土壤樣品之採集與製備

實驗室分析

3 3 結果與討論

澎湖晚中新世層間紅土之野外形態特徵

剖面形態之綜合討論

澎湖古土壤的基本性質

澎湖古土壤中高嶺石類黏土礦物的鑑定

其它礦物

由電子顯微鏡觀察礦物

澎湖晚中新世古土壤的分類及化育

3 4 結論

第四章澎湖群島晚中新世古土壤的研究 ( 二 ) －古土壤之地球化學及換質作用之研究

4 1 前言

4 2 材料與方法

4 3 結果與討論

竹灣剖面 ( 第一採樣點 ) － CWI

竹灣剖面 ( 第二採樣點 ) － CWI

小門嶼剖面－ SMY

講美剖面－ CM

以 A-CN-K 和 A-CNK-FM 三角圖解析古土壤的風化方向

4 4 結論

第五章澎湖古土壤中高嶺石類黏土礦物的 180 穩定同位素組成及高嶺石之來源

5 1 前言

5 2 材料與方法

5 3 結果與討論

δ 180 測定的結果

澎湖古土壤中高嶺石類δ 180 值的解釋

禾樂石的δ 180 值

澎湖晚中新世時期古氣候的推測

5 4 結論

第六章總論

第七章參考文獻

附錄