Genlong Fm
Type Locality and Naming
Named by Hou Liwei et al. in 1991. The named section is located in Changtai Genlong Gully, Baiyu County, Sichuan.
Synonym:
Lithology and Thickness
The volcanic rocks are mainly volcanic and are divided into two lithologic sections. Lower section is mainly composed of several eruptive rhyolites consisting of gray-green to dark green amygdaloidal and plagioclase porphyritic basaltic andesite, andesitic basalt, basalt, massive andesite, and ingenious crystalline tuff with incomplete exposure at the bottom. Upper section consists of volcanic breccia, andesite, basaltic andesite, ingenious andesite, rhyolite interbedded with ingenious tuff and a small amount of basalt. The upper section consists of multiple eruptive rhythms of lenticular biotite and sedimentary volcanic clastic rocks. The total thickness is greater than 1500 m.
Relationships and Distribution
Lower contact
The contact relationship with the underlying stratigraphy is unknown. Next older regional unit is the Lieyi Fm of Middle Triassic.
Upper contact
[not given; and schematic stratigraphic column had shown a "Miange Fm" which is not in present lexicon, so was merged into age-span of this Genlong Fm. Next younger unit is the Lanashan Fm of Norian.
Regional extent
The group is distributed in Baiyu Gengke, Changtai and Nalenghai, Xiangcheng Dongjun and Muyu in Sichuan. In Nalenghai, the group consists of two eruptive-sedimentary subcycles with generally metamorphosed rocks and an outcrop thickness of 1029 m. In Xiangcheng Dongjun, the lower part of the group consists of eruptive-sedimentary subcycles of basalt, andesitic basalt with sandstone, slate, tuff and conglomeratic tuff. The upper part is gray and gray-black fine sandstone interbedded with slate, interspersed with a small amount of lenticular muddy tuff. The total thickness is 985 m.
GeoJSON
Fossils
The lower part contains the bivalves Chlamys sp., Entolium aff. decoratiformis, Gervillia sp., G. cf. praecursor, Plicatula sp., Plagiostoma sp., Palaeocardita sp., Halobia sp. and Gastropoda fossils.
Age
Depositional setting
It is a submarine volcanic eruption deposit.
Additional Information