Guankou Fm
Type Locality and Naming
Sichuan Basin - west. Zhao Jiaxiang and He Shaoxun erected the Guankou bed in 1945 at Guankou of the Dayi County, Sichuan. The reference section is at Guanyinya of Jiaguanchang of the Qionglai County, Sichuan.
Lithology and Thickness
The Guankou Formation is dominated by brown red and purple red mudstone and siltstone with dolomitic marl, gypsum and glauberite (a sodium-calcium sulfate mineral), with conglomerate at the base and with important gypsum salt bearing horizon in the middle part. It is 834.4 m thick.
Relationships and Distribution
Lower contact
The base of the formation marked by the occurrence of moderately thick-bedded granule-pebble conglomerate is distinguished from the underlying Jiaguan Fm consisting of thick-bedded clayey lithic quartz sandstone. The formation is in conformable contact with the underlying strata.
Upper contact
The formation is in conformable contact with the overlying strata (the Mingshan Fm of Paleocene).
Regional extent
The formation is extensively distributed in the northwestern part of the Sichuan basin and is well developed in Jiaguan of Qionglai and Baosheng of Lushan. It varies considerably both in lithology and thickness ranging from 400 to 1200 m from north to south. In Wangziyan of Guanxian and Baosheng of Lushan and Laochang of Tianquan, clear alluvial fans are observed, with the grain size varying from coarse in the west to fine in the east. To the east of the line linking Pengxian-Dayi-Lushan, the formation grades to brown red and purple red mostly rhythmic sandy conglomerate, lithic sandstone, siltstone and mudstone. Along the line linking Qionglai-Mingshan-Yaan, the formation is dominated by siltstone and mudstone with marl, gypsum and glauberite.
GeoJSON
Fossils
The formation contains abundant ostracods Talioypridea parva, T. gigantea, Limnocythere paomagangensis and a few foraminifera Nonion sichuanensis; Charophyte Grambastichchara longicanica and sporopollen grains Schizaeoisporites certus, etc. in its middle and upper parts.
Age
Depositional setting
It is made up of fluvial-brackish sediments deposited under the arid climate condition.
Additional Information