Bilushan Fm
Type Locality and Naming
Central Taiwan. The naming section is located at Bilu Mountain on the border between Nantou County and Hualien County, Taiwan. Named the Bilushan bed by He Chunsun in 1986.
Lithology and Thickness
Predominantly dark gray slate and phyllite, with much thin- to thick-bedded, fine- to coarse-grained meta-sandstone and marble and many beds of conglomerate, as well as green to dark red metavolcanic rocks and local basal conglomerate. The thickness of the formation reaches a maximum of ~2200 m (“Heiyanshan bed”) in the central area and a minimum of only 500–750 m in the northern area.
Relationships and Distribution
Lower contact
Unconformable contact with the underlying Bihou Fm and Danan’ao Gr of Cretaceous.
Upper contact
Unconformable contact with the overlying Liguan Fm.
Regional extent
The formation represents all the Eocene strata east of the Lishan fault in the Central Range and is distributed in the mountains of Ilan, Kaohsiung, Pingtung, Hualien and Taitung. For lack of complete stratigraphic sections, there are some differences in lithology, thickness and metamorphic grade in different areas. From the above-mentioned counties and cities southward, different geologists have given it different names. These strata commonly contain calcareous rocks and gravels, but the north and south show some difference in lithology and metamorphic grade. The formation in the north is dominated by slate and phyllite, with significant amounts of metasandstone and marble; while the formation in the south consists dominantly of slate with small amounts of sandstone and limestone which have been metamorphosed only slightly. Metavolcanic rocks mostly appear in the northern and southern areas.
GeoJSON
Fossils
The Bilushan Formation contains large-sized foraminifera, mainly Nummulites sp., Discocyclina sp., Assilina formosensis and Spiroplectammina sp, and calcareous nannofossils, including about 42 genera and species such as Discoaster lodoensis, Coccolithus crassus and Sphenolithus obtusus. It belongs to zones NP12-NP16.
Age
Depositional setting
Additional Information