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  • 學位論文

嘉義海岸平原區末次冰期以來古沉積環境之研究

Sedimentary Environment of the Chiayi Coastal Plain Since the Last Glacial Epoch

指導教授 : 陳文山

摘要


本研究區域北以朴子溪為界,南至曾文溪流域北段,東緣與西部麓山帶前緣為鄰,西緣連接台灣海峽,主要在嘉義縣、市以及台南縣的範圍之內。利用民國87 年至92 年,中央地質調查所於嘉義地區的18 口鑽探岩心為研究主體。先就各種岩性以及特徵,將其分類為14 個岩相-1 個礫岩相、7 個砂岩相、1 個砂泥岩互層相以及5 個泥岩相。並藉由砂質沉積物組成分析建立三種分類:Type 1、Type 2 以及Type 3,用以辨識沉積物來源,並輔助岩相組合來解釋沉積物是否受沿岸流作用的影響。 本研究利用岩相特徵並參考現生環境建立沉積模型,認為此區域在末次冰期以來具有二種沉積體系:曲流河作用與潮汐(或包括沿岸流作用)作用。各沉積體系可細分以下9 種次環境:曲流河相、河口砂洲相、沼澤相、潮坪相、潮汐水道、潟湖相、沿岸砂洲相、潮下帶相以及遠濱過度帶相。藉由層序分析,推論出末次冰期時,研究區域出露地表,接受風化與侵蝕作用形成土壤層,同時造成古八掌溪的遷移與下切,形成二個下切河谷。藉由剖面對比,建立本研究區域的沉積史。 約18000年前,全區域出露地表,形 成土壤層與下切河谷。約14000年前,海水面逐漸上升,在二個下切河谷形成江灣。 約12000-11000年前由於受到新仙女木亞冰期影響,環境略微淺化,海岸線向海側 遷移。約8000年前,海水已經覆蓋全區域,並入侵至西部麓山帶前緣。約5000年前, 沉積環境逐漸變淺。海岸線向海側遷移。5000年前至今,沉積物持續大量朝海側堆 積,海岸線位置持續向海側遷移。約400年前古籍記錄當時平原區呈現數個內海,之 後因人為開發造成內海快速淤積,海岸後退至今日的位置。

並列摘要


The study used 18 cored boreholes in Chiayi coastal plain which were provided by the Central Geological Survey. Based on the grain size, sedimentary textures and bioturbation, it can be divided into fifteen lithofacies. The sediment composition was classified into three types of Type 1, Type 2, and Type 3, and explaining that the sediments were formed by the longshore current and fluvial processes. Based on the modern environment of the coast, it can be subdivided nine environments of meander river, river mouth bar, marsh, tidal flat, tidal channel, lagoon, longshore bar, subtidal and offshore transition zones. Based on the depositional environment analysis and radiocarbon dating data, wedescript five stages of depositional environment during the late Pleistocene - Holocene. (1) Before 18000 yr BP (the last glacial epoch) : This area formed a subaerial environment and developed two incised valleys. (2) During 14000 yr BP: Due to the sea-level rising, the shoreline was migrated to the eastward, and the incised valley was formed a drowned valley. (3) During 12000-11000 yr BP (the Younger Dryas event): The sea-level rising rate is slightly slow. The shoreline was migrated eastward to the frontal foothills. (4) During 8000 yr BP: The maximum marine flooding stage was formed at 8000 – 8500 yr BP. The shoreline was still at frontal foothills. (5) During 5000 yr BP: The sediments continuously progradated to the seaward, hence, the shoreline was retreated and migrated to the westward.

參考文獻


Thomas, R.G., Smith, D.G., Wood, J.M., Visser, J., Calverley-Range, E.A., and Koster,
Dalrymple, R.W., 1992, Tidal depositional systems, in Walker, R.G. and James, N.P.,
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被引用紀錄


楊詠然(2016)。末次最大冰期以來台灣西部平原的環境變遷〔碩士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU201602157
黃進達(2007)。台中地區第四紀沉積環境研究與大地構造意義〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-2910200810572206

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