金門海岸地質地形調查(一)古寧頭海岸
一、研究緣起
金門海岸地景地形甚富變化，如加以調查和規劃將有利於保護並成為金門國家公園繼傳統聚落、閩南建築之外的一項重要特色及觀光資源。
本研究計畫今年以古寧頭海岸為範圍，預期達成以下目標：古寧頭海岸地質地形田野調查、古寧頭海岸各露頭岩石的標本採集及實驗室分析、探討古寧頭海岸地質地形成因，評估海岸地景保育課題，提升鄉土資源的研究及旅遊服務品質。
二、研究方法及過程
本研究對古寧頭一帶海岸地形的形態與分布進行野外調查，描述崖壁、海濱平台的分布，並特別注意海蝕作用目前是否正在進行中，以及「貓公石」在野外的分布與產狀。本研究調查海岸與潮間帶沈積物的分布，以詳細區分古寧頭一帶海岸的地形地景單元，並採集各不同岩石標本。
對古寧頭海岸與潮間帶沈積物，進行粒度分析，以了解此區域海岸侵蝕與沈積的強弱。對「貓公石」標本進行岩象學分析，以了解其岩象組織。對「貓公石」標本進行X光繞射儀分析，以了解其礦物成份。對紅土與「貓公石」標本進行鐵元素的感應耦合電漿吸收光譜儀（ICP-AES）元素分析。
三、重要發現
1、古寧頭的北山、南山、下埔下一帶海岸的地層大致相同，當地岩層主要分為三層。最上層為紅土層，厚度約為2公尺。中層為紅棕色至黃棕色高嶺土質砂岩的風化層，並具有鐵質網紋膠結（plinthite），厚度約為2-3公尺。最下層為紅棕色、黃棕色或灰白色不規則鐵質浸染的高嶺土質砂岩，厚度在5 公尺以上，未完全露出。本層為河相沈積。本層亦在南山海灘上出露，但因長期浸泡在海水中，較崖壁上同岩層鬆軟。
2、古寧頭海岸崖壁的分佈主要在南山及北山一帶海岸，其中北山斷崖的露頭良好，可以作為良好的地質教學剖面。由崖壁表面的風化，植被情形以及潮間帶的泥灘形成看來，目前的海岸侵蝕已經不活躍，古寧頭崖壁應為全新世中期的孓遺地形。目前的的崖壁崩塌係風化後受重力影響，與海蝕無關。
3、所謂貓公石主要是由石英砂粒、高嶺土及其他黏土礦物，以及氧化鐵所構成。岩壁上鐵網紋主要是由紅色的氧化鐵部份與灰白色的黏土礦物所構成，海邊的貓公石則單純由鐵質膠結石英顆粒所構成。推測貓公石成因主要是由上層紅土層中的鐵質向下淋溶至中層的風化長石砂岩，形成鐵網紋。崩落後再受到海水的侵蝕作用，移除黏土物質而形成。
4、目前北山附近的潮間帶間，分佈許多大小不一的貓公石，推斷係因古寧頭海岸在全新世中期高海平面時期受較高能量的波浪侵蝕，海岸向陸地後退時所留在原地。這些岩塊同時也成為良好的天然消波塊。
Abstract
keywords: Kinmen National Park, Guningtou, Coastal landform
1. Study purpose
The coastal landforms of Kinmen are very diverse. Investigation of those landforms should contribute toward better protection and can be used in land planning to make coastal landform a tourist’s attraction in addition to the famous Fukien architectures and traditional communities.
This project studies Guningtou coasts in this first year with the following objectives: field survey of coastal landform and coastal geology, sample collection and laboratory analysis, to discuss the origin coastal landform and coastal geology, and to evaluate the coastal conservation issues, in the hope to contribute in the local study and tourism.
2. Study methods
This study performed field investigation of types and distribution of coastal landforms with a focus on the distribution of so-called “mau-gong-shi”. Cliffs and shore platforms were described and sediments on beach and intertidal flat were investigated, in order to categorize all the elements of coastal landforms in the Guningtou area. Rock and sediment samples will also be collected. This study particularly paid attention to whether the coastal erosion is active or not.
Size analysis of the sediments on intertidal flat was performed. Samples of so-called “mau-gong-shi” were studied by standard petrography and mineral composition analyzed by X-Ray Diffractometry. Fe elemental analysis of samples of laterite, plinthite and so-called “mau-gong-shi” were conducted by ICP-AES.
3. Important results
(1). The stratigraphy in the Beishan, Nanshan and Xiapuxia of the Guningtou area are basically the same, and can be divided into three units. The uppermost unit is a laterite unit of 2 meters thick. In the middle is a red sandstone unit of 2 to 3 m thick, with kaolinite in matrix and well developed plinthite cementation. The lowermost unit is a reddish to brownish sandstone unit of fluvial facies, with kaolinite matrix and somewhat stained by iron oxide. This unit is not entirely exposed and the total thickness unknown but at least 5 m thick. In addition to cliff outcrop, this unit is also exposed on shoreface at Nanshan coast and appears much more soft than those on cliff.
(2). The cliff outcrops distribute along Nanshan and Beishan coasts, especially well developed at Beishan. The Beishan cliff can be a good site for public education purpose. On the basis of weathering on the cliff, plant coverage and the muddy flat in the intertidal zone, the coastal erosion is no longer active. The cliffs in the Guningtou area are believed to be relict landform developed in the middle Holocene. The current slumping is due to weathering and gravity, not caused by wave erosion.
(3). The so-called “mau-gong-shi” is composed of quartz sands, kaolinite and other clay mineral, and iron oxide. The plinthite on the cliff is made of red portion of iron enrichment and gray-white portion of kaolinte and other clays. Those washed by waves are composed of iron oxide and quartz only. It is interpreted that the origin of “mau-gong-shi” is that iron first leached from the laterite on top into the sandstone unit in the middle and form plinthite. The plinthite blocks were then fallen from the cliff, and with clays gradually being removed by waves, developed a very porous appearance.
(4). Many “mau-gong-shi” blocks are found on the intertidal flats at Beishan. It is interpreted that those blocks were left there when the cliff retreated in the middle Holocene when the sea-level was higher therefore wave energy stronger. Those blocks now serve as natural wave dissipation blocks.
金門海岸地景地形甚富變化，如加以調查和規劃將有利於保護並成為金門國家公園繼傳統聚落、閩南建築之外的一項重要特色及觀光資源。
本研究計畫今年以古寧頭海岸為範圍，預期達成以下目標：古寧頭海岸地質地形田野調查、古寧頭海岸各露頭岩石的標本採集及實驗室分析、探討古寧頭海岸地質地形成因，評估海岸地景保育課題，提升鄉土資源的研究及旅遊服務品質。
二、研究方法及過程
本研究對古寧頭一帶海岸地形的形態與分布進行野外調查，描述崖壁、海濱平台的分布，並特別注意海蝕作用目前是否正在進行中，以及「貓公石」在野外的分布與產狀。本研究調查海岸與潮間帶沈積物的分布，以詳細區分古寧頭一帶海岸的地形地景單元，並採集各不同岩石標本。
對古寧頭海岸與潮間帶沈積物，進行粒度分析，以了解此區域海岸侵蝕與沈積的強弱。對「貓公石」標本進行岩象學分析，以了解其岩象組織。對「貓公石」標本進行X光繞射儀分析，以了解其礦物成份。對紅土與「貓公石」標本進行鐵元素的感應耦合電漿吸收光譜儀（ICP-AES）元素分析。
三、重要發現
1、古寧頭的北山、南山、下埔下一帶海岸的地層大致相同，當地岩層主要分為三層。最上層為紅土層，厚度約為2公尺。中層為紅棕色至黃棕色高嶺土質砂岩的風化層，並具有鐵質網紋膠結（plinthite），厚度約為2-3公尺。最下層為紅棕色、黃棕色或灰白色不規則鐵質浸染的高嶺土質砂岩，厚度在5 公尺以上，未完全露出。本層為河相沈積。本層亦在南山海灘上出露，但因長期浸泡在海水中，較崖壁上同岩層鬆軟。
2、古寧頭海岸崖壁的分佈主要在南山及北山一帶海岸，其中北山斷崖的露頭良好，可以作為良好的地質教學剖面。由崖壁表面的風化，植被情形以及潮間帶的泥灘形成看來，目前的海岸侵蝕已經不活躍，古寧頭崖壁應為全新世中期的孓遺地形。目前的的崖壁崩塌係風化後受重力影響，與海蝕無關。
3、所謂貓公石主要是由石英砂粒、高嶺土及其他黏土礦物，以及氧化鐵所構成。岩壁上鐵網紋主要是由紅色的氧化鐵部份與灰白色的黏土礦物所構成，海邊的貓公石則單純由鐵質膠結石英顆粒所構成。推測貓公石成因主要是由上層紅土層中的鐵質向下淋溶至中層的風化長石砂岩，形成鐵網紋。崩落後再受到海水的侵蝕作用，移除黏土物質而形成。
4、目前北山附近的潮間帶間，分佈許多大小不一的貓公石，推斷係因古寧頭海岸在全新世中期高海平面時期受較高能量的波浪侵蝕，海岸向陸地後退時所留在原地。這些岩塊同時也成為良好的天然消波塊。
Abstract
keywords: Kinmen National Park, Guningtou, Coastal landform
1. Study purpose
The coastal landforms of Kinmen are very diverse. Investigation of those landforms should contribute toward better protection and can be used in land planning to make coastal landform a tourist’s attraction in addition to the famous Fukien architectures and traditional communities.
This project studies Guningtou coasts in this first year with the following objectives: field survey of coastal landform and coastal geology, sample collection and laboratory analysis, to discuss the origin coastal landform and coastal geology, and to evaluate the coastal conservation issues, in the hope to contribute in the local study and tourism.
2. Study methods
This study performed field investigation of types and distribution of coastal landforms with a focus on the distribution of so-called “mau-gong-shi”. Cliffs and shore platforms were described and sediments on beach and intertidal flat were investigated, in order to categorize all the elements of coastal landforms in the Guningtou area. Rock and sediment samples will also be collected. This study particularly paid attention to whether the coastal erosion is active or not.
Size analysis of the sediments on intertidal flat was performed. Samples of so-called “mau-gong-shi” were studied by standard petrography and mineral composition analyzed by X-Ray Diffractometry. Fe elemental analysis of samples of laterite, plinthite and so-called “mau-gong-shi” were conducted by ICP-AES.
3. Important results
(1). The stratigraphy in the Beishan, Nanshan and Xiapuxia of the Guningtou area are basically the same, and can be divided into three units. The uppermost unit is a laterite unit of 2 meters thick. In the middle is a red sandstone unit of 2 to 3 m thick, with kaolinite in matrix and well developed plinthite cementation. The lowermost unit is a reddish to brownish sandstone unit of fluvial facies, with kaolinite matrix and somewhat stained by iron oxide. This unit is not entirely exposed and the total thickness unknown but at least 5 m thick. In addition to cliff outcrop, this unit is also exposed on shoreface at Nanshan coast and appears much more soft than those on cliff.
(2). The cliff outcrops distribute along Nanshan and Beishan coasts, especially well developed at Beishan. The Beishan cliff can be a good site for public education purpose. On the basis of weathering on the cliff, plant coverage and the muddy flat in the intertidal zone, the coastal erosion is no longer active. The cliffs in the Guningtou area are believed to be relict landform developed in the middle Holocene. The current slumping is due to weathering and gravity, not caused by wave erosion.
(3). The so-called “mau-gong-shi” is composed of quartz sands, kaolinite and other clay mineral, and iron oxide. The plinthite on the cliff is made of red portion of iron enrichment and gray-white portion of kaolinte and other clays. Those washed by waves are composed of iron oxide and quartz only. It is interpreted that the origin of “mau-gong-shi” is that iron first leached from the laterite on top into the sandstone unit in the middle and form plinthite. The plinthite blocks were then fallen from the cliff, and with clays gradually being removed by waves, developed a very porous appearance.
(4). Many “mau-gong-shi” blocks are found on the intertidal flats at Beishan. It is interpreted that those blocks were left there when the cliff retreated in the middle Holocene when the sea-level was higher therefore wave energy stronger. Those blocks now serve as natural wave dissipation blocks.