台中地區第四紀沉積環境研究與大地構造意義

Quaternary Depositional Environment and Tectonic Significances of the Taichung Area, Central Taiwan

黃進達(Chin-Da Huang)

指導教授 ： 李通藝

國立臺灣師範大學/理學院/地球科學系/碩士(2007年)

摘要

本研究主要探討台中地區(包含濱海平原與台中盆地)，於第四紀之沉積環境變遷與其在大地構造上之意義。本研究之研究材料主要為經濟部中央地質調查所於本區域鑽探的岩心，包括濱海平原區的華龍、三光、高美、清水、梧棲、忠和、大肚、伸東及全興井；加上位於台中盆地內的烏日及大里，共11口井。本研究藉由記錄岩心組成顆粒與沉積構造，利用沉積學原理與相模式，分析岩心之岩相組合，解釋沉積環境；再藉由層序地層學原理，進行各井對比並劃分層序，建構台中地區的地下地層與沉積環境變遷模式。對比濱海平原跟台中盆地兩區之古沉積環境，可發現濱海平原區的沉積主要受沉積物供應、全球海水面升降與構造運動(台地隆起時造成之沖積扇)控制；而台中盆地中只有辮狀河平原的沉積環境。
從現代大肚溪河系分布可發現，台中盆地內所有大肚溪支流都至烏日匯聚成大肚溪主流才出盆地，而烏日岩心從底至頂也一直出現辮狀河沉積環境，與現代情形相符。由於大肚井岩心中，山前沖積扇和辮狀河環境交替出現，代表在大肚台地隆起時，大肚溪即在此發育，因此應為先成河，再加上後成影響(在台地抬升同時加速下切)，持續由大肚台地與八卦山台地交接處流出盆地。另外，比較大肚、烏日、大理岩心的沉積環境相變情形，推斷大肚溪三角洲可能由於水流量較小且台中盆地仍未被沉積物填滿，使大肚溪沉積物大部分沉積於台中盆地，造成大肚溪在濱海平原區的三角洲較不易發育。
劃分高美、清水、梧棲、忠和、大肚、全興與伸東7口井的層序並對比後，建構出濱海地區晚第四紀以來沉積環境變遷模式如下：
1. 海進面時期(8234至32710年前之間) –此時為海進面，海岸線較現今更向西，區域內沉積環境大部分為辮狀河平原。
2. 海進體系域時期 –此時期相對海水面持續上升，海岸線向東遷移，沉積環境從河口灣轉變為濱面與潮坪，為海進體系域。
3. 最大海漫面時期(2866至6397年前之間) –此時為最大海漫面(MFS)，海岸線到達此次沉積層序中最東側，沉積環境除了最東側為潮坪環境以外，大部分為遠濱過渡帶。
4. 高水位體系域時期 –相對海水面開始下降，海岸線逐漸向西遷移，全區沉積環境由遠濱過渡帶轉變為濱面以及潮坪，形成高水位體系域(HST)。

關鍵字

第四紀 ； 大肚溪 ； 沉積環境 ； 豬背盆地 ； 車籠埔斷層 ； 層序地層

並列摘要

The research used core data to study the Quaternary depositional environment and their tectonic significance of the Taichung aera (including the coastal plain and the Taichung basin), in central Taiwan. The research materials used 11 cores drilled by Central Geological Survey, MOEA, including Hualong, Sanguang, Gaomei, Cingshuei, Wuqi, Zhonghe, Dadu, Shendong, Quanxing cores in the coastal plain, and Wurih, Dali in the Taichung basin. The sedimentary composition and structure of all the cores were logged, and used the sedimentary theorem and facies model to explain the depositional environment. After that, the sequence stratigraphy there is applied to divide and correlate the sequences, and to build the depositional history of the Taichung area. By contrast, the depositional environment in the coastal plain is controlled primarily by sediment supply of the braid rivers, global sea level, and tectonics (deposition of alluvial fan resulted from the uplift of the tableland). But the depositional environment in the Taichung basin is only braidplain.
According to distribution of the Dadu river drainage pattern, all tributaries in Taichung basin converge in Wurih, and the records of the braided river deposition accumulated continuously in the Wurih core. The Dadu river processes are thought to be a combination of superposition followed by antecedence. Because the alluvial fan and braidplain facies appeared alternately in the Dadu core, it indicates that the Dadu river was antecedence here when the Dadu tableland rose, and mixed process of superposition (speed up to erosion with the Dadu tableland rising). In addition, after comparing with the flow data of Dadu river and Jhuoshuei river, we can infer that the reason why the Dadu river delta developed slowly due to the fact that the river flow is smaller and the sediment is used to fill the Taichung basin first.
Using sequence stratigraphy theory to separate the sequence and correlate the 7 cores (Gaomei, Cingshuei, Wuqi, Zhonghe, Dadu, Quanxing, and Shendong), the model of depositional environment change in the coastal plain can be built up:
1. Transgressive surface – at this time, the sea level began to rise. The depositional environment is all braidplain.
2. Transgressive systems tract –at this time, the sea level continued to rise, so the coast line migrated to the east, the depositional environment changed from the estuary to shoreface and tidal flat. They were in the transgressive systems track.
3. Maximum flooding surface –at this time, the sea level rose to the highest, the coastal line migrated to the tableland. The depositional environment was mostly tidal flat, except for the east (tableland) was the offshore.
4. Highstand systems tract –the sea level began to drop down, and the coastal line migrated westward, all the depositional environment changed from offshore to the tidal flat. The highstand systems track (HST) started.

並列關鍵字

Quaternary ； Dadu River ； Depositional environment ； Piggyback basin ； Chelongpu fault ； Sequence stratigraphy

參考文獻

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