臺灣中部海岸平原之生物地層及其古環境研究

Study on Nannobiostraigraphic and Paleoenvironmental of the Coastal Rlain, Mid-western Taiwan

謝英宗(Ying-Tzung Shieh)

《國立臺灣博物館學刊》 61卷3期 (2008/09) Pp. 1-18(i-i)

摘要

臺灣中部大肚一八卦山丘陵西側的海岸平原因缺乏露頭致使對該區地下地質的瞭解非常有限，本研究利用經濟部中央地質調查所為執行「臺灣地區地下水觀測」網水文地質調查研究，在臺灣中部海岸平原地區所鑽鑿的一系列深井岩心，分析其沉積物之超微化石和有孔蟲化石，探討臺灣中部海岸平原第四紀堆積層的生物地層及其古環境的變遷。由鑽井沉積物的有孔蟲化石種屬顯示本區的古環境是濱岸瀉湖。研究亦顯示灣臺中部海岸平原在最近100萬年來至少有四次海進和三次的海退。第一次到第三次海進紀錄的確實年代和機制尚不清楚，第四次海進應羊毛全新世全球海平面上升所造成。本區沉積速率變化極大，可能和陸相/海相環境的快速變化有關。由超微化石生物帶的研究顯示，臺灣中部海岸平原北側的堆積年代屬於NN19c超微化石生物帶，相當於頭嵙山層。其餘海岸平原區的堆積年代則晚於距今45萬年前的NN20超微化石生物帶，顯示臺灣中部海岸平原北側可能較早受到構造抬升的影響。

關鍵字

超微化石生物地層 ； 古環境 ； 海岸平原 ； 臺灣中部

並列摘要

For understanding subsurface paleoenvironmental changes and biostratigraphic correlation of hydrological investigation of the Underground Water Observation Network of Taiwan, there were six observation wells drilled on the mid-western coastal plain of Taiwan by the Central Geological Survey, MOEA. Based on nannofossil and foraminifera studying, there have been identified four transgression cycles since early Quaternary in study area; however, the age and cause of the first to third transgression events are not clearly understood yet. The fourth transgression period was recorded in the upper sediments in southern five observation wells, according to the nannofossil biostratigraphy and AMS C^14 dating results; the latest transgression period occurred during the Holocene Optimum Period. Huge and fast changes of sedimentation rate in core sediments may reflect different terrestrial and pelagic environments. Nannofossil biostratigraphic correlation showing Zone NNl9c (1.03 ~0 .45 Ma) of subsurface sediments in the northern part, the age of the other five observation wells in the southern part is younger than Zone NN20 (~0.45Ma). That indicate the northern side of mid-western coast plain of Taiwan was uplifted earlier than the southern side.

並列關鍵字

nannofossil biostratigraphy ； paleoenvironment ； coastal plain ； mid-western Taiwan