Late Quaternary depositional environments of Taipei Basin

• Main Authors: Peng, Chih-Hsiung, 彭志雄
• Other Authors: Louis S. Teng
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/57121605405597431971

碩士 === 國立臺灣大學 === 地質學系 === 86 === In order to better understand the sedimentary history of late Quaternary Taipei Basin, this study gathered deep boleholes data in the basin for faciesand depositional system analysis. The basin is filled with unconsolidated, interlayers of gravels, sands, muds and sand/mud interbeds, in which nine lithofacies were recognized according to the lithological characteristics. Most of the gravels are thicked-bedded, cobbly in size, poorly sorted and intercalated by brownish to reddish soil horizons. Thus, these gravels are believed to be deposited by debris flow in alluvial fans. Some of the gravels are pebbly in size, fairly sorted, clast supported and may be interbedded with sands, indicated these gravels were deposited by high energy river current in braided plain. Sands and muds are generally interlayered and they are often less than 20 meters in thickness. Sands may exhibit a sharp base paved with pebbles, in which usually fine upward into muds and contained abundant carbonaceous fragments an few vivianite. Thus, the fining-upward sequence isdeposited in channel or flood plain. Some muds, exceeded ten meters and nated, indicating these mud were deposited by suspension in a fresh-water lake. Neverthelesss, shells of lagoonal facies also appeared in few parts of sands and muds, indicating these sedimentswere deposited in a brackish-water lake. Using laminated muds in upper Panchiao Formation, gravel beds of alluvial fan in Chingmei Formation, and distribution of shell fossils in Sungshan Formation to be a bases of isochronous correlation, and then combined the results of pollen stratigraphy to set up time frame. Taipei Basin began to accumulated fluvio-lacustrine sediments in the middle Pleistocene. In the early stage, the basin was covered by alluvial fans, fluvial plains and a fresh- water lake. The Taipei Basin was once dammed by the pyroclastic flows derived from the north and became a big deep lake, in which laminated muds were widely accumulated. The depositional systems then returned to an alluvial fan - fluvial plain - fresh-water lake setting. Then the basin was filled up by a huge alluvial fan deposits in the late Pleistocene. In the early Holocene,marine incursion inundated the basin which became a brackish-water lake. The lake was then gradually filled up by the prograding river sediments from the basin margin.