Shihtiping: White tuff of the topmost Tuluanshan Formation

Shitiping (see Fig. 1 for stop location) is an uplifted marine terrace composed of pyroclastic flows, ignimbrite and volcanic breccias. It is capped with Holocene coral limestone. Ignimbrites are glassy pyroclastic rocks formed by pyroclastic flows during a single eruption and compose predominantly of vesiculated glasses. At this stop, the ignimbrite show both normal and reverse grading with occasionally large exotic blocks with impact structures. Rapid sedimentation is indicated by the fine-depleted ignimbrite whereas the angular blocks and contorted features (Fig. 2 and Fig. 3) suggest plastic deformation during sedimentation. The above features seem to suggest that the Shihtiping white tuff were the products of subaerial eruption and were accumulated in a subaerial setting during late Miocene (Song and Lo, 1988).

下述區域地質說明摘自何春蓀(1986)「台灣地質圖概論-台灣地質圖說明書」。經濟部中央地質調查所出版，台北，共164頁。：

都巒山層 都巒山層是覆蓋在奇美安山岩核心上的地層中的最下單位，為一個巨厚的火山岩層，直接掩覆在火成岩體之上或與火成岩體共存。都巒山層大部分由火山集塊岩、凝灰岩、或凝灰質沉積物組成，其成因顯然與下伏的奇美火成雜岩的火山活動有關，屬同一火山弧的產物，但是都巒山層也含少量玄武岩及石英安山岩。本層的厚度經估計為一千到一千五百公尺，岩性變化甚大。本地層由徐鐵良 (1956) 根據海岸山脈中的一個高峰都巒山所出露的厚層集塊岩命名。這個集塊岩層分布的面積略少於海岸山脈的一半，分布最廣的地方在山脈的中段，再向南北延伸。本層一部分是由在水中經過淘選以後的安山岩礫石所組成，代表火山碎屑岩經過再沉積以後的堆積，不是火山直接噴發的堆積物。

沿著海岸山脈的東斜面，在都巒山層火山集塊岩的上部或其附近有不連續的石灰岩凸鏡體出現。石灰岩的厚度由一公尺以下到超過十公尺，最厚處可達五十公尺，曾被命名為港口石灰岩。張麗旭 (1967) 發現在這些淺水石灰岩中有中新世早期到中期的浮游性有孔蟲，但是最近的化石研究 (鄭穎敏、魏國彥，1983) ，發現其中含有上新世的有孔蟲化石，而認定其時代為上新世 ;至於石灰岩中含有時代較老的化石，則被認為是移置化石。都巒山層本身缺少化石，其時代只能由其上覆岩層中的化石來推斷。最近根據超微化石的研究，指出都巒山層上部的時代在中新世中期到晚期之間，最新可以到達中新世與上新世的界線附近 (紀文榮等人，1981)。理查德等人 (Richard et al., 1986)最近的鉀氬放射性定年研究，指出都巒山層中岩石的年齡約在六．九 ~ 四．四百萬年之間。

	Figure 1. Geological map of the north-central Coastal Range (from Wang and Chen, 1993)
	Figure 2. White intermediate to acid tuff composed of welded volcanic glass shards and mafic minerals of pyroxene, hornblende, and opaque minerals at Shihtiping (photo by B.M. Jahn).
	Figure 3. White intermediate to acid tuff composed of welded volcanic glass shards and mafic minerals of pyroxene, hornblende, and opaque minerals at Shihtiping (photo by B.M. Jahn)
	Figure 4. 火山凝灰岩。
	Figure 5. 火山凝灰岩。
	Figure 6. 火山凝灰岩中的火山彈 。
	Figure 7. 野外一角。
	Figure 8. 野外一角。
	Figure 9. 火山凝灰岩中的沉積構造。
	Figure 10. 野外一角。