Hard Rock Taipei 硬石台北
Cited from web
沉積岩主要由小碎石堆積後，由海底或地表礦物、生物殘骸膠結化後形成岩石，沉積岩可以依照其組成成分區分成不同種類的沉積岩，如：碎屑沉積岩、生物沉積岩、化學沉積岩…等等。常見的沉積岩像是沙岩、石灰岩、或泥岩。沉積岩有獨特可鑑別的岩石特性 -- 波痕，波痕代表著在成岩過程中曾受到水流或是風的擾動。
cited from web
cited from web
火成岩座落在台北地層下方，分布在陽明山與台北北部海岸線，這樣分布的原因可能跟大屯火山群活動相關，大屯火山群最早在280萬至250萬年前開始活動噴發，這些火山活動的地質顯露在台北的北部區域。不過，台北的中心區域其實有更古遠的火成岩，像是公館凝灰岩，這些火成岩可能在8500萬年前的南澳造山運動時就已經成形。海底火山噴發後形成噴發岩與火山灰，隨著火山噴發後噴發岩顆粒與火山灰沉積在海底地表，這些火成岩可以在台北盆地下的地層之中找到。閱讀下方圖片的內容可以知道不同地層的時序關係，也可以知道台北的發展時間表 (Teng et al., 2001)。
cited and adapted from web
Hard Rock Taipei
What to do with this earth cache?
There are placed with different types of rocks in Gongguan. These rocks were collected from all regions from Taipei as evidence to see the plentiful rock composition in Taipei. Go to three points in Gongguan to recognize different rocks. Distinguish the Formation of geological properties from the information on the listing page and the virtual introduction board.
The questions are at the end of article.
Background Knowledge : Origin of Taiwan
The beginning formation of Taiwan Island was approximately at late Miocene (23.03 to 5.333 million years ago). The formation theories all agree that the uplift of Taiwan Island results from the collision of Philippine (PH) Sea Plate and Eurasian (EU) Plate. The EU Plate is sliding under the PH Sea Plate, resulting a convergent boundary lifting up Taiwan. Luzon Volcanic Arc belongs to PH Sea Plate becomes the Coastal Range or Haian Range. And the margin of EU Plate becomes the Central Mountain Range. Taitung Longitudinal Valley is the special contact between two Plates. The tectonic boundary was active while the collision occurred and it remains active nowadays.
Geology of Taipei
Taipei is a unique place because it was originally a hill at two millions years ago and became a basin due seismic activity on the Sanchiao fault between Linkou and Taipei at four hundred thousand years ago. At two hundred thousand years ago, volcanic lava cooled down and blocked Tamsui river’s gate to the sea. Taipei Basin became a dammed lake for a long while. Then, Tamsui River went through the rocks with water erosion at northern Taipei into the sea at approximately thirty thousand years ago. Taipei Basin is actually influenced by volcanic and river activities.
Moreover, Taipei is also affected by the tectonic activities with PH plate, EU Plate and Ryukyu Arc at southeast of Taipei city or New Taipei city. Southeast Taipei is affected by Xueshan Mountain Range with a suitable condition for the process of metamorphism.
Taipei basin is bounded by Yangmingshan to the north, Linkou mesa to the west, and Xueshan Mountain Range to the southeast. The main rivers in the basin include Dahan, Tamsui and Keelung. The geological environment makes plentiful rock composition in Taipei.
Classification of rocks
Explosive lava cooled down and through solidification into igneous rocks. The process of solidification into rock occurs below the surface as intrusive rocks. If the process occurs on the surface, lava becomes extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks. Or, it may be formed without crystallization into natural glasses. A common example of intrusive type is granite. Extrusive rocks, which result from magma on surface, turn into basalt or andesite.
cited from web
Sedimentary rocks are formed by the accumulation or deposition of small particles. Subsequent cementation of mineral or organic particles occurs on the ground of oceans or other bodies of water at the Earth's surface. Sedimentary rocks can be classified by composition, including Siliciclastic sedimentary rocks, Carbonate sedimentary rocks, Evaporite sedimentary rocks, Organic-rich sedimentary rocks, Siliceous sedimentary rocks, Iron-rich sedimentary rocks, or Phosphatic sedimentary rocks. Common sedimentary rocks includes sandstone, limestone, or mudstone.
Sedimentary rocks may have a unique feature. It might be distinguished with ripple marks. Ripple marks are sedimentary structures and indicate the activity of water or wind. Ripple marks make some sedimentary rocks with very unique texture.
cited from web
Metamorphic rocks are formed by subjecting rocks to different temperature and pressure conditions than those in which the original rock was formed. The metamorphism results in significant change in physical properties and chemistry of the stone. Metamorphic rocks can be totally changed into different color, texture, or appearance. Metamorphism has two main different types including Contact metamorphism and Regional metamorphism. Contact metamorphism is temperature-dominate metamorphism. It may be related to intrusive magma affecting surrounding rocks. The temperature is the main reason caused the minerals into the process of metamorphism. Regional metamorphism, also known as dynamic metamorphism, is majorly influenced by the pressure relating to tectonic activities. Regional metamorphism precisely is related to both temperature and pressure. The process often occurs at the mountain-building regions. Besides contact and regional metamorphism, there is another type of metamorphism. Pressure-dominate metamorphism, and temperature plays a small role, may produce unique rocks, such as jade. This mechanism termed burial metamorphism.
Foliation is a specific feature belongs to metamorphic rocks. The layering within metamorphic rocks is called foliation. The texture occurs when a rock is shortened during recrystallization. The structure of metamorphic rocks can be divided into two categories, foliated and non-foliated.
Rocks in Taipei
Rock composition in Taipei is influenced by the formation of Taipei basin and the tectonic activities in northern Taiwan.
Igneous Rock in Taipei
Igneous rocks are the main type under the surface in Taipei and located at Yangmingshan or northern coastline. The reason is related to the activity of Tatun Volcanic Group at northern Taiwan. Tatun volcanic group first explored at 2.8 Ma lasting to 2.5 Ma. Outcrops of this activity can be found at northern Taipei. However, there are some more ancient igneous rocks being found in the center of Taipei, such as Gongguan tuff. It may be formed after the Nanao Orogeny around 85 Ma. Volcano under surface explored into ancient sea forming extrusive rocks and volcanic ash. Following ejection and deposition, the ash and small particles are in the process of consolidation forming tuffs. It may be found in the era of Formation under the Taipei Basin. Read the picture from an article (Teng et al., 2001) to see each era of Formation and the timeline of Taipei. The most ancient Formation in Taipei is Wuchihshan Formation. Younger Formation is covered on the older Formation. Old Formation to young Formation under Taipei Basin is in sequence with Wuchihshan Formation, Mushan Formation, Taliao Foramtion, Shiti Formation, Nankang Formation, Nanchuang Formation, Kueichulin Formation, Banchiao Formation, Wugu Formation, Jingmei Formation, and Sungshan Formaiotn. From the indication of time line, Tatun volcanic activity is relatively young compared to other old Formations. The time of Gongguan tuffs should be much earlier than igneous rocks of Tatun.
Sedimentary rocks in Taipei
Due to the river activities and dammed lake ever, a layer of sedimentary deposit covered whole Taipei Basin. Sedimentary rocks are also the main type in Taipei, especially northwest and northern Taipei along the Tamsui River, like Beitou or Qilian. A special sedimentary rock, which is “Qilian Rock”, is discovered at Qilian in Taipei. The type of Qilian Rock is sandstone composed of much quartz. Qilian Rocks is hard enough and is a great material for buildings. Therefore, some historical sites still have this kind of rock material on the wall.
Metamorphic rocks in Taipei
Metamorphic rock is a type of rocks in Taipei. Metamorphic rocks is much fewer than the two other types of rocks. However, some metamorphic rocks can be found in southeast of Taipei. It might be due to the tectonic activities, resulting in the Xueshan Mountain Range, at southeast and east area of Taipei. The collision of PH Plate and EU Plate caused a huge mountain-building region in Taiwan. The region creates a condition for metamorphism of both temperature and pressure. Many different types of metamorphic rocks can be found in Taiwan. And the most prevalence type in Taipei might be slate. Though, some unique metamorphic rock can be found in southern Taipei, such as jade and marble.
Rock distribution in Taipei
The photo below shows the distribution of different rocks in Taiwan. As the indication, rocks in Taipei are plentiful with different types of rocks. The area in Taipei is covered with recent sedimentary layer, west sedimentary rocks, igneous, and slate in central mountain range.
(p.s. The light green region is “Slate in Central Mountain Range” as indicated. However, the region near southeast Taipei is actually belonging to the region of Xueshan Range.)
cited and adapted from web
1.1 請回答區塊A和B的岩石種類(A和B是相同的)。 1.2 請回答區塊C的岩石種類。
選擇題：A. 板岩 B. 泥岩 C. 砂岩 D. 花崗岩 E. 安山岩 F. 不是岩石
選擇題：A. 火成岩 B. 沉積岩 C. 變質岩
6. 自由選擇: 附上你在現場的照片、GPS位置圖、或是你的旅行蟲，感激不盡。
Go to spot in the picture below. (Photo discoloration) Building here is made with a type of rock discovered in Taipei.
1.1 What is the type of rocks in area A and B (A is equal to B)? 1.2 What is the type of rocks in area C?
Answer from the options : A. Slate B. Mudstone C. Sandstone D. Granite E. Andesite F. Not Rock
2. Do you find the ripple marks?
Find the group of rocks in the picture below. (Photo discoloration)
3.1 What are the types of these rocks?
Answer from the options : A. Igneous rock B. Sedimentary rock C. Metamorphic rock
3.2 What kind of features do you find?
4. Look deep. Rocks here are classified as the same category. How do their appearances looks so different? Try to explain it.
Find the introduction board
5. The rocks here is called Gongguan Tuff. They were formed at a specific era of Formation. Read the specific time on the board, and compare to the listing page to figure out which specific Formation under Taipei Basin.
6. Optional: a photo of you, your GPS or your TB at WP would be appreciated
Log this cache "Found it" and send me your suggested answers either via my profile, or via geocaching.com (Message Center) messaging, and I will contact you if there is a problem.
Sibuet & Hsu, 2004 How was Taiwan created?
Geology of Taiwan from wiki
Su et al., 2018 Tectonic controls on the stratigraphic development of the rifted Taipei Basin
Teng et al., 2001 Origin and Geological Evolution of the Taipei Basin