Sunlight Bleaching Effects of Optically Stimulated Luminescence on Modern Debris Sediments： Chenyulan River and Ninety-Nine Peak
Date Issued
2007
Date
2007
Author(s)
Wu, Tzu-Shuan
DOI
en-US
Abstract
Continuous technological development in luminescence dating techniques has facilitated extensive application to a variety of geologic samples, such as completely bleached sediments from aeolian and shoreface environments or even partially bleached sediments from fluvial environments. Using the luminescence method, the burial ages of sediments last exposed to daylight can be determined, and applied to research areas in paleoclimatology, paleoseismology and archaeology.
In Taiwan, earthquakes trigger numerous and serious landslides, the source of disastrous debris flow while heavy rainfalls and typhoons generate unconsolidated landslide material. The rapidly deposited sediments are often found within fluvial terraces, composed of boulders, cobbles and pebbles embedded with sandy matrix. To study the neotectonic activity, knowledge of the burial ages of fluvial terraces is essential. Due to the short transported distance, probable exposure to daylight bleaching is the major concern in the reliability of the luminescence dating of such a deposit.
Two individual sites of modern debris deposits in central Taiwan are selected for the luminescence analysis: (1) 4 samples (one from matrix, one from sandy layer, one from outwash sand and one from channel deposits) were collected in the middle reach of one of the tributaries of Chenyulan River. (2) 3 samples (one each from matrix, fluvial sandy bar and outwash channel deposits) were collected near the Ninety-Nine Peak.
Regeneration Protocol was adopted as the routine procedure. In finding the most efficient way, both single aliquot and single grain methods were applied to extract the well bleaching portion from debris deposits. Sediments from different debris facies are separately determined. Our results reveal that the single grain approach provides best way to deal with those debris materials. In addition, the residual signals were smaller in the outwash samples than the matrix of the debris flow itself. It can be concluded that even a short distance could still give enough light to bleach certain parts of debris sediments. The longer transportation distance of the fluvial deposits facilitates the bleaching and increases the reliability of the luminescence dating method, especially for the young material.
Subjects
現生
土石流沉積物
光螢光
部分曬退
單顆粒法
modern
debris sediments
OSL
partial bleaching
single grain
Type
thesis
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