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Fundamental and Environmental Geology
Resource Geology
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Assigned Geological Investigation Project
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:::Fundamental and Environmental Geology
  The objective is to study the surface and subsurface geology of Taiwan and to present the results as geological maps to describe geological features such as structure, stratigraphy, minerals, and paleontology. The CGS also undertakes projects across many sectors, including Quaternary studies, engineering and subsurface testing of metropolitan areas of Taiwan, research on slopelands surrounding major metropolises, and marine geology mapping offshore Taiwan.
A. Geological Mapping
  In 2009, 3 quadrangles of 1/50,000 scale geological maps were reviewed and printed. In order to progressively complete the scale 1:50,000 geological quadrangle maps in the Central Range, the CGS began a 3-year geological mapping project of Guangfu Quadrangle in fiscal year 2009. The main achievements this year included scale 1:5,000/1:10,000 route geological maps and 1/25,000 geological drafts in the area of 9620-2-NW and 9620-2-NE Topographic Maps published by the Ministry of Interior. The main achievement of biostratigraphic study is that larger foraminifer-rich layers were found for the first time in the so-called "Meichi Sandstone"in the upstream valley of the Zhuoshui River, Wujie district, Nantou County, These fossil layers were intercalated in amalgamated hummocky-cross-stratification (HCS) sandstone. They are identified as Nummulites sp. of the early Eocene due to the involute chamber arrangement and falciform septal filaments in the external view. For an understanding of the lithology, sedimentary environment and depositional age of the Szeleng Sandstone, microfossils in a total of 168 samples collected from the northern Hsuehshan Range along the Northern-Cross Island Highway, Taipei-Ilan Highway, Lungtung Cap and a drill core in the Hsinhsein village are studied in 2009. Based on the results, it can be tentatively concluded that the Szeleng Sandstone was deposited in Late~Middle Eocene.
B. Quaternary Geological Investigation

In 2009, the Quaternary Geological Investigation performed a sequential stratigraphic analysis of Late Quaternary cores in the Changhua Coastal Plain. The Changhua Coastal Plain is situated in the frontal arc-continent collision belt of Taiwan and is an excellent region to study the interaction between tectonism and eustacy. Based on the results of sequential stratigraphic correlations of cores found that the terrestrial sediments at the top of sequence 3 that below the sequence boundary 2 (SB2) at the northern (SS-DU) area of well HT compared with southern (HB-HS) area are much thicker (about thicker 20-35 m) and the sediments thickness of sequence 2 (S2) at the northern area of well HT is thinner than southern area about 18-24 m. This indicated that basin subsidence rate is not consistent in the Changhua Coastal Plain. Before SB2, basin subsidence rate at the northern area of well HT was much faster, at about 40 ka ago, the southern area could be affected by neotectonic thrust activity and induced the relative subsidence rate became faster than northern area. After 20 ka, the basin subsidence rate slows down. The marine sediments covered area of sequence 1 (S1) that deposited during recent-16 ka and S2 that deposited in the period of 20-40 ka during maximum flooding are different and S2 is much smaller than S1. That should be controlled by the effect of eustatic sea-level change.

C. Shoreline Change Mapping and Analysis around the Taiwan Coast

The primary aim of this plan in this year focused on the coast area from the mouth of the Danshui River to Taidong. We use the FORMOSAT-2 images of 2006 and 2009 and the aerial photographs of 1978 to delimit the shoreline. We analyzed the trend of the shoreline change and, discussed the possible causes for major shoreline change, and estimated the long term shoreline change rate. According to the results, the eroded coast sections include: (1) the coast of Qianshui Bay in Sanzhi; (2) the coast of Jiqi in Hualian; (3) the coasts near Zhuangbin Road and the coasts of Lize in Yilan. The causes of the coastal erosion were wave erosion and influence of building projects. The north of Wushi Port, Fuxing Village, the north of Lanyang River, Lanyang River mouth, and the south of Xincheng River are depositional coasts in Yilan. The cause of the depositional coasts is those coasts close to the river mouth and the sand supplies are sufficient. The influences of typhoon events on shoreline changes are: (1) in the storm affected area, sand dune and beach were eroded by the storm surge and the sands were drifted by littoral current and deposit at the non-storm area; (2) the typhoon with heavy rain induced the river water rising suddenly, the sludge and drift woods were brought by flood to deposit in the river mouth and lowland.

D. Investigation and Research on Engineering and Subsurface Geology

From 2004, CGS had implemented a six-year project to investigate the engineering and subsurface geology of the metropolitan areas. In 2009, the study is aiming at the Hua-Lien and Tai-Dong areas. The study areas are mostly alluvial plains of the Pleistoncene age. The sedimentary environments, lithological strata distributions, and soil engineering properties all show great variability. Therefore, this study will utilize detailed borings and testing programs. The project is divided into four in-depth studies, which includes: (1) subsurface geology and lithology, (2) engineering geological properties of soils, (3) databank of borehole drillings, and (4) engineering environmental geological mapping and geological hazard susceptibility mapping. After completion of this project, geological grating profiles, liquefaction potential distributions, and geotechnical microzonation will be obtained for Hua-liena and Tai-Dong areas. These subsurface exploration data will be incorporated into the Geo2005 Database System to progressively establish the geological database for land planning and hazard mitigation. This database will be a valuable tool for better understanding of the geological environment and potential geotechnical problems in Taiwan.


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