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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 Central Range Backbone Ridges
General Geologic Features General Stratigraphy Stratigraphy of The Northern Part of The Hsuehshan Range Belt Stratigraphy of The Central and Southern Parts of The Hsuehshan Range Belt Stratigraphy of The Backbone Range Belt Geologic Structure and Metamorphism Geologic History
Stratigraphy of The Central and Southern Parts of The Hsuehshan Range Belt

SHIHPACHUNGCHI FORMATION

This is the oldest stratigraphic unit exposed in the Hsuehshan Range belt and was named by C. S. Lee (1979). It represents the lowest Eocene formation in the Yushan Block and forms a north-south elongate belt extending all the way from east of the Sun-Moon-Lake southward to south of the Tataka Pass in the Yushan Range. The type locality Shihpachungchi is a tributary of the Chenyulanchi stream north of Tungpu hot spring in Nantou- hsien. This formation consists mainly of black to dark gray slate with thin metamorphosed sandstone interbeds and intimate interlaminations of black slate and light gray sandstone. The latter lithology is one of the characteristic indicators to distinguish the Shihpachungchi Formation from other units. The sandstone intercalated in the slates is light gray, quartzitic, very compact, medium- to fine-grained, and partly calcareous. The basal part of this formation is dissected by a fault so that the total thickness of the unit is unknown. Greenish gray igneous rocks possibly in the form of dikes intruded into the Shihpachungchi Formation and could be mainly metadiabase in lithologic composition (P. T. Chang, 1984b). The largest intrusive body is exposed to the northwest of Tungpu hot spring. Another body is exposed along the ancient Patungkuan Path between Tungpu and Lolo. Due to precipitous topography, it is difficult to trace the extension of these igneous bodies. In addition, boulders of igneous rocks have been found in the stream beds in the Yushan area where the Shihpachungchi Formation is also exposed. Thus the igneous rocks may have a rather wide distribution in the Shihpachungchi Formation, although outcrops are mostly of small dimensions. Yen (1973) reported that Assilina has been found in the sandstone of the Shihpachungchi Formation exposed on the north side of Wanghsiangshan in the drainages of the Chunkengchi and the Shihpachungchi. In the same area, boulders containing Nummulites fossils have also been reported. On this paleontologic evidence, the age of the Shihpachungchi Formation is dated pre-late Eocene, and possibly early middle Eocene.

TACHIEN SANDSTONE

This unit was proposed by C. H. Chen (1977) and conformably overlies the Shihpachungchi Formation. The type locality Tachien is located on the central cross-island highway between Kukuan and Lishan. The type section, however, is exposed on the same highway between Kuangmingchiao and Tachien. This sandstone formation was originally mapped as the Paileng Formation but is now believed to be older than the Paileng and should be mapped as a separate unit. This formation is distributed mainly in the middle part of the Hsuehshan Range belt in the drainage areas of the Tachiachi, Hsilochi, Peikangchi, Chenyulanchi and the Yushan mountain block.
The Tachien Sandstone is composed mainly of white to light gray, fine- to coarse-grained quartzitic sandstone. The sandstone is thick-bedded to massive, with thin to thick interbeds of slate or metamorphosed shale. The shale is slightly carbonaceous. C. H. Chen (1979b) reported that the total thickness of the Tachien Sandstone is 2,700 meters. The lower part (650 m) consists of fine- to coarse-grained quartzite, green chloritic sandstone and siltstone, containing a little shale interbeds. The middle part (1,300 m) consists almost largely of coarse-grained to pebbly, massive, cross-bedded, quartzitic sandstone. The upper part (750 m) is composed of thick- bedded, medium- to coarse-grained sandstone interbedded with minor shale and coaly shale. The greenish sandstone in the lower part of the Tachien Sandstone contains an appreciable amount of volcanic detritus and serves as a diagnostic marker of this unit in the field. As the sandstone is compact and resistant, it forms a series of waterfalls in the Tungpu area such as the Yunlung, Tsaihung and I-Nu waterfalls, many of which are famous scenic resorts. In some places large quartz crystals are found in the sandstone; old quartz quarries can still be found, mostly abandoned for some time now.
Microfossils are scarce in the Tachien Sandstone, so the age of the formation cannot be determined with certainity. Tan (1944) found the fresh bivalve Corbicula baronensis in a number of localities in the Tachien Sandstone. Recently Wang and Chen (1978) discovered the gastropoda Turritella at Chienshan in the Yushan Range. Based on the opinion of Mollasca paleontologists, all these fossils could be Eocene in age.

CHIAYANG FORMATION

This formation was also proposed by C. H. Chen (1977) and the type locality Chiayang is located between the Tachien Dam and Lishan on the central cross-island highway in Taichung-hsien. The Chiayang Formation conformably overlies the Tachien Sandstone. This formation is composed chiefly of a thick series of slate with minor fine-grained sandstone and siltstone intercalations. Slaty cleavage is well-developed. Black chert nodules have been found in the slates. The sandstone interbeds increase from the east to the west whereas the thickness of the formation decreases from the east to the west. At the type locality, the total thickness of the Chiayang Formation probably exceeds 3,000 meters and the rock unit consists predominantly of slate with only minor interbeds of fine-grained sandstone. Westward along the central cross-island highway to the west of Chingshan, the total thickness of the Chiayang Formation is about 1,400 meters only where more medium- to coarse-grained, thick and well-bedded sandstone is intercalated in the slate. Fossils are generally lacking in the Chiayang Formation. L.S. Chang (1971) reported that Globigerinoides (?) was found in this formation. If this is ascertained, the age of the Chiayang Formation is not older than late Oligocene and possibly younger. As fossil evidence is scarce and not diagnostic, the age of the Chiayang Formation has to be verified by further study.
The lower part of the Chiayang Formation is usually characterized by a series of alternating black slate and light gray metamorphosed sandstone. The sandstone is fine- to medium-grained, in beds several centimeters to one and half meters thick. Due to the abundant sandstone, C. S. Lee (1979) ascribed the lower part of the Chiayang Formation to a separate rock unit, naming it the Yushanchushan Formation. This formation forms the main peak of the Yushan Mountain as well as the highest peaks of Tungshan and Nanshan in the Yushan Range, and some other high peaks in the Central Range. The Yushanchushan Formation is conformable with both the underlying Tachien Sandstone and the overlying Chiayang Formation. To avoid the use of too many stratigraphic units in the legend of a small-scale geologic map, the Yushanchushan Formation is included in the lower part of the Chiayang Formation on this map. Tomita and Tan (1937) found Assilina at Paiyunshanchuang, a small cottage at the foot of the Yushan Mountain and close to the type locality of the Yushanchushan Formation. Wang and Chen (1978) also found Assilina at Hsiananshan in the same formation. The age of the fossils is Eocene. Therefore, the age of the Chiayang Formation is tentatively dated as Oligo-Eocene.

MEICHI SANDSTONE

In central Taiwan the Meichi Sandstone conformably overlies the Chiayang Formation. The Meichi Sandstone was named also by C. H. Chen (1976) when he was mapping the geology in the Puli-Wushe area. This formation is proposed to replace the Szeleng Sandstone, the application of which is confined to northern Taiwan. Although these two sandstone units can be correlated in stratigraphic position, they are different in lithologic character. The type locality of the Meichi Sandstone is the stream Meichi which runs partly along the Puli-Wushe highway. The Meichi Sandstone forms a very narrow north-south belt on the eastern margin of the Hsuehshan Range belt for a length of more than 100 kilometers. This belt begins at Niutou and Tuchang in Ilan-hsien in the north. Further to the north and northwest, the equivalent unit is the Szeleng Sandstone as mentioned before. This belt of Meichi Sandstone extends southward along the stream Lanyanchi to Szuyuanyakou, the divide pass between the Lanyangchi on the north and the Tachiachi on the south. Southward it then enters the drainage area of the Tachiachi to Chiayang and Lishan on the central cross-island highway. It continues further south to Jenchihkuan near Wushe until it ends somewhere near the Sunhai logging road to the west of the mountain ridge Hsiukuluanshan.
The Meichi Sandstone is composed mainly of well-bedded, gray, fine- to coarse-grained compact sandstone and alternating interbeds of sandstone and dark argillite. Thin interbeds of carbonaceous shale are present in local sections. Near the top of the formation, one conglomeratic sandstone about 1 to 5 meters thick is commonly exposed, containing rice-sized quartz grains and shale granules. Some broken molluscan shells may be found in the sandstone which is often quite muddy. The quartz-grain conglomeratic sandstone may serve as a good marker to distinguish the Meichi Sandstone in the field (Wu, 1976). The thickness of the Meichi Sandstone is nearly 200 meters in the Lanyangchi drainage area but is 230 meters thick southward to Lishan in the Tachiachi drainage area. Further southward to Jenchihkuan, the thickness of the Meichi Sandstone increases to more than 600 meters.
The distribution of the Meichi Sandstone is limited to the eastern margin of the Hsuehshan Range belt on top of the Chiayang Formation. It is separated by the Lishan fault from the rocks in the Backbone Range belt on the east. Toward the western part of the Hsuehshan Range belt, the equivalent formation of the Meichi Sandstone is named the Paileng Formation which will be discussed in the next paragraph. No age-diagnostic fossil has yet been found in the Meichi Sandstone and the age of this unit is still not certain. As the Meichi Sandstone is stratigraphically correlated to the Szeleng Sandstone in northern Taiwan, it is ascribed tentatively to the Oligocene.

PAILENG FORMATION

The Paileng Formation is characterized by a thick series of white sandstone, and the name was proposed by Torii (1935) after the village Paileng on the northern bank of the stream Tachiachi to the west of the leading town Kukuan on the central cross-island highway. The Paileng Formation extends south from the Tachiachi valley across the Puli basin and the Jihyuehtan (Sun- Moon Lake) to the eastern tributaries of the Chenyulanchi in Nantou-hsien. It is distributed northward to the drainage areas of the Tachiachi and the Taanchi.
The Paileng Formation consists mainly of white to grayish white, fine- to coarse- grained quartzitic sandstone with interbeds of medium gray, compact sandstone and dark gray argillite or slate. Shaly interbeds are more abundant in the lower part. Sandstone beds are 20 centimeters to two meters thick and partly massive. The sandstone is cross-bedded, well-cemented, and conglomeratic to pebbly in places. Carbonaceous particles and coaly stringers are intercalated in the dark gray argillite at different horizons, mainly on the western margin of the outcrop belt. The coal is thin, irregular in thickness, and discontinuous; it is also graphitic, high in fixed carbon and low in volatile matter. Mining has been attempted in several places without success. The total thickness of the Paileng Formation is variable, ranging from 500 to 2,400 meters in different reported sections.
Recent stratigraphic studies indicate that the Paileng Sandstone can be correlated to the Szeleng Sandstone and the Meichi Sandstone in the northern part and the eastern part of the Hsuehshan Range belt respectively. Due to variations in lithofacies, the lithologic features of these three units are not identical, especially the discrepancy in formation thickness. The Paileng Formation is more that 2,000 meters in total thickness and may be up to 3,000 meters in maximum thickness, whereas the total thickness of both the Szeleng Sandstone and the Meichi Sandstone is only several hundred meters. On this ground C. H. Chen (1979b) is of the opinion that the Paileng Formation is most likely correlated to the combined Meichi Sandstone, Chiayang Formation and Tachien Sandstone, which are exposed in the eastern part of the Tachiachi drainage.
However, C. S. Lee (1976) believes that the Paileng Formation is correlated only to two units: the Meichi Sandstone (Szeleng Sandstone) and the Chiayang Formation. In an earlier Japanese paper, the Paileng Formation was subdivided into three members by Tan (1944). The upper member can be ascribed to the overlying Shuichangliu Formation. The middle member (Ha) is about 1,000 meters thick and is composed of coarse-grained white sandstone locally intercalated with carbonaceous slate or dark slate. The sandstone often weathers to a pinkish color which is quite characteristic. This sandstone member is considered by Lee to be the equivalent of the Szeleng Sandstone. The lower member (Hi) is formed of sandy slate alternating with sandstone. This part of the Paileng Sandstone may be correlated with the Chiayang Formation. Diagnostic fossils are insufficient for a definite age designation of the Paileng Formation, whose age is tentatively assigned to Oligocene or Oligo-Eocene on the basis of stratigraphic sequence.

SHUICHANGLIU FORMATION

In central Taiwan the Shuichangliu Formation conformably overlies the Paileng Formation or the Szeleng Sandstone. This is dominantly an argillaceous unit composed chiefly of black argillite or slightly metamorphosed shale. The overall metamorphic grade of the rocks is exceedingly low.
The Shuichangliu Formation was proposed by the faculty members of the Geology Department of the former Taipei (Taihoku) University during their field investigation of the earthquakes in the Taanchi drinage area in 1935. The type locality Shuichangliu is a small village northeast of Kuohsing in Nantou-hsien. Near the type locality this formation is composed of dark gray to black argillite which is glauconitic to pyritic in places. Locally glauconite may constitute up to 50 percent of the rock. Quartz and calcite veins cut the shaly sediments, which contain broken plant remains and dark red clay-ironstone concretions in some places. Gray, fine- grained, compact sandstone occurs at varying horizons in the argillite and slate, varying in bed thickness from 5 to 80 centimeters and up to more than one meter. The metamorphosed argillaceous sediments show splintery fractures and are elsewhere massive. Bedding is discernible only where sandstone interbeds are present. The Shuichangliu Formation is lithologically monotonous and without distinct marker beds. The normal sequence has been complicated by folding and repetition of beds and an accurate estimate of its total thickness is difficult. The estimated thickness is well over 1,500 meters.
The foraminifer faunas Globigerina ampliapertura (N1) and Gaudryina hayasakai were discovered by L. S. Chang (1963a) in the Shuichangliu Formation. The age of the faunas is late Oligocene so that the Shuichangliu Formation is correlated to the Tatungshan Formation and the Kankou Formation in northern Taiwan. The Shuichangliu Formation may be confused with the Chiayang Formation in field studies because both units are made up of similar dark gray argillaceous sediments. However, C. H. Chen (1979) has indicated that the Shuichangliu Formation can be differentiated from the Chiayang Formation on the basis of lower metamorphic grade, comparatively less sandstone interbeds, and the common occurrence of the fossil Gaudryina hayasakai.


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