CENTRAL GEOLOGICAL SURVEY, MOEA

	Introduction
	Earlier Geologic Maps of Taiwan
	Geographic Setting
	General Geology And Geologic Provinces Of Taiwan
	Explanation Of Legend And Representation Of Geologic Data
	Eastern Central Range
	Western Central Range Backbone Ridges
	Western Foothills
	Eastern Coastal Range
	Geology Of The Hengchun Peninsula
	Major Geologic Features Of Taiwan
	Plate Tectonic Setting
	References

:::Western Foothills

General Stratigraphy	Oligocene Stratigraphic Units	Miocene Stratigraphic Units	Miocene Rocks on Tiaoyutai Island	Pliocene Stratigraphic Units
Quaternary Stratigraphic Units	Volcanism and Volcanic Rocks	Diastrophism and Orogenic Movements	General Structural Features	Geologic History

Miocene Rocks on Tiaoyutai Island

About 150 kilometers north-northeast off the main island of Taiwan lies the Tiaoyutai island of Ilan-hsien. This island is nearly four square kilometers in areal extent, 3.5 kilometers long and 1.5 kilometers wide. The southern side is marked by sharp cliffs, whereas a gentle dip slope descends to the north.

The northern coast is characterized by an arcuate shoreline. The highest peak on the island rises to 363 meters above sea level in the southwestern part. This island is composed of sandstone in beds several meters thick, interbedded with thin beds of claystone. The sandstone is white to grayish white and weathers to yellowish brown. Grain size is fine to coarse. Part of the sandstone is conglomeratic, with rounded to subrounded pebbles that reach a maximum diameter of 20 centimeters. The chief components in the sandstone are quartz, feldspar, rock fragments, and secondary clay minerals. Several coaly fine-grained sandstone beds about 10 to 20 centimeters thick are intercalated in the lower part and contain 3 to 4 layers of coaly shale. The coal is only several millimeters to 2 centimeters thick and discontinuous. The exposed thickness of the sandstone formation is about 150 meters. Beds strike east-west or east-northeast and dip to the north at 15o to 25o defining a broad arc convex slightly toward the north. No fossils have yet been found. On the basis of lithology and other characters, the sandstone formation on Tiaoyutai may be correlated with the Nankang Formation or the Shihti Formation of middle Miocene age on the main island of Taiwan. It is thus ascribed to the Juifang Group in this geologic map. However, the conglomeratic sandstone on Tiaoyutai has not been found in the Juifang Group on the main island of Taiwan.

:::© CENTRAL GEOLOGICAL SURVEY, MOEA

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