從地形與碳十四定年探討台灣西南部龜重溪流域的新期構造運動

Geomorphological and dating investigations through the active structures on the Kueichungchi River, southwestern Taiwan

張憲卿(Chang Hsien-Ching)

指導教授 ： 陳文山

國立臺灣大學/理學院/地質科學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.02287

摘要

台灣西南部龜重溪流域，河流由東往西向流，下游河段（六甲斷層下盤）貫
穿嘉南平原而至海岸，上游河段即為本研究區，係位於六甲斷層的上盤區域。依
地質構造分區，上游地區位於「西部麓山帶」，構造特徵為一系列覆瓦狀排列的
逆斷層與褶皺構造。由於台灣西南部普遍受到新期構造運動的影響，本研究區河
階地形非常發達；本研究乃利用定量地形學的方法，透過航照判釋、數值地形模
型及現地野外調查等工作，分析各種地形特性，並藉以探討與本研究區內活動構
造之關係。
本研究區內活動構造計有六甲斷層、北勢坑斷層、中坑斷層、崙後斷層、牛
山背斜及前大埔向斜等。其中六甲、中坑及崙後等斷層即前述之覆瓦狀排列的逆
斷層，而北勢坑斷層介於六甲與中坑斷層間之背衝逆斷層；牛山背斜及前大埔向
斜構造則為伴隨斷層而產生的褶皺構造。
本研究區域整體地形特徵受控於地質構造的分布。在六甲斷層以西區域，地
形整體顯現低緩之冲積平原特徵；六甲斷層以東地區，則進入緩起伏之丘陵區，
地形較高處多位於逆斷層前緣或背斜軸部，且每向東越過另一逆斷層系統，地形
高度逐步攀升。受地形高度控制之龜重溪上游河流系統，復受地質構造之影響，
故每在斷層位置或褶皺軸部即改變其河道流向。
本研究區普遍發育曲流河道，此種河流地形特徵可能受控於構造的活動性。
由河流曲度計測結果顯示：
1.新營斷層以西至雙春出海口區間為1.15。
2.新營斷層以東至六甲斷層區間為1.30。
3.六甲斷層至北勢坑斷層區間為1.60。
4.北勢坑斷層至中坑斷層區間為1.20。
六甲斷層上盤區，河階甚為發育，本研究尚利用五千分之一照像基本圖共計
測91 處河階地形之比高自4.5∼135 公尺；由DTM 階地、地形及定年資料等分
析結果，牛山背斜區依概略可區分為五至六階，前大埔向斜區亦可概略區分為三
階；分佈於牛山背斜軸部階數較多，且高位階地皆分佈於軸部附近。
本研究以定年標本資料，推算出三萬多年以來的下切速率如下：
1. 牛山背斜軸部下切速率2.8mm/yr。
2. 前大埔向斜軸部下切速率0.06mm/yr。
其中前大埔向斜軸部之河階年代（31880yr B.P.，比高9m）與牛山背斜軸部之高
位河階年代（35810yr B.P.，比高105m）相當，二者又都具有輕微紅土化現象，
故認為可以對比，且本研究區之下切速率也經研判出主應受構造抬升影響；故可
以推論牛山背斜區之抬升速率高於前大埔向斜區，可能為一新期構造甚為活躍地
區。

關鍵字

龜重溪

並列摘要

In this study, I will use terrace landform and geological dating information to
investigate the active structural characteristics of the Kueichungchi area, southwestern
Taiwan.
Within the studied area, the active geological structures are the Liucha fault, the
Peishikeng fault, the Chunkeng fault, the Lunhou fault, the Niushan anticline and the
Chientapu syncline.
For the nature of the geological structures, the Liucha fault, the Chunkeng fault
and the Lunhou fault are referred to as forward thrusting structures, the Peishikeng
fault as a back thrust structure and the Niushan anticline and the Chientapu syncline
as fault-related fold structures. Towards the east and west of the Luchia fault, low and
flat fluvial plain and undulated hilly land alternately display the geomorpholgical
characteristics of the region.
In general, higher topographic terrain could be correlated with the frontal portion of
the thrust structures and/or the axial portion of the anticline structures. Furthermore,
the general flowing direction and pattern of the river change depending on the active
geological structures encountered.
Large population of river terraces with various altitudes ranging from 4.5 to
135 meters could be identified along the Kueichungchi. Four to five levels of river
terraces could be grouped in the Niushan anticline region and 3 levels of river terraces
in the Chientapu syncline region, respectively.
Radioactive carbon age dating of the river terraces shows that the axial portion of
the Niushan anticline with the age 31880 B.P. could be correlated with the Chientapu
syncline with the age of 35810 B.P. of similar time span. These two river terraces are
not only correlatable for having the same age span of 31880 B.P. and
35810 B.P., respectively, but also for having similar degrees of slight red soil
development.
The river incision rate of the last 30 ky for the Niushan anticline and the
Chientapu syncline is 2.8 mm/yr and 0.06 mm/yr respectively.
Thus, the uplift rate for the Niushan anticline area is much larger than that for the
Chientapu syncline area.
Thus, the significance of active structures on the development of landform along
the Kuiechungchi drainage area in the southeastern Taiwan is well exhibited.
In the studied area, regional development of the geomorphological characteristics
is closely related to the active geological structures.

並列關鍵字

active structures

參考文獻

層復活、反轉與嘉南麓山帶褶鄒衝斷構造之發育。中國地質學會

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