Lanashan Fm
Type Locality and Naming
The Third Area Survey Team of Sichuan Geological Bureau named it in 1974. The named section is located in Lana Mountain, Batang County, Sichuan Province. The original Lanashan Fm represented a formation above Tumugou Fm in Qamdo, Sichuan. Due to the difficulty in comparing the lithology and biota of the Lanashan Formation with that of the Lanashan Fm in the region, there are many disputes about its exact layer. The Third District Diversion Team of Sichuan Geological Bureau (1977) advocated the abolition of one member of the Lanshan Group (= Lanashan Fm?) and the replacement of the "Xiaoxueshan Group".
Synonym:
Lithology and Thickness
It is an assemblage of clastic rocks and carbonate rocks. The bottom is conglomerate, the upper and lower are metamorphic sandstone, slate and carbonaceous shale with coal line, and the middle is mainly composed of bioclastic limestone and dolomitic limestone with sand and shale. The thickness is 485 m.
Relationships and Distribution
Lower contact
In some areas, there is no peak, and it is conformably on the Tumugou Fm of the mid-Upper Triassic.
Upper contact
In some areas, it is conformably overlain by the Lamaya Fm of latest Triassic. In Daocheng area, the contact relationship between this group and the lower Fumiange Gr (is not clear.
Regional extent
It is mainly distributed in Xinlong, Dege, Litang, Yidun, Xiangcheng, Daocheng, Muli and other counties in Yidun, Sichuan Province. The lithology is different from that of the named section regionally, and can be divided into Lower and Upper sections according to the sedimentary cycle from coarse to fine. In the Lower part of the south, there are dark gray metamorphic sandstone and carbonaceous slate interbedded with limestone lens. In the Upper part, the carbonaceous slate is mainly interbedded with metamorphic sandstone strip and occasionally marl lens. The north is often dominated by schist sandwiched with quartzite, marble, and conglomerate at the bottom. In the area of Xiangcheng and Derong, occasionally intercalated basic to acid volcanic rocks. In the distribution range, the thickness is 2800 m in the north, gradually thickened to 3500 m in the south, and gradually thinned to the east.
GeoJSON
Fossils
There are abundant fossils, there are brachiopods, bivalves, gastropods, corals, ammonoids, sponges, algae and plants. Bivalves: Costatoria napengensis-Burmesia lirata assemblage; Unionites and small bivalves with brackish properties. Brachiopods: Rhaetina caucasica. Plants: Cladophlebis raciborskii, Todites shensiensis, Clathropteris meniscioides, Taeniopteris leclerei, Neocalamites carrerei, N. carcinoides, Nilssoniopteris jourdyi, Pterophyllum aequale.
Age
Depositional setting
The formation is a marine and continental interdeposit
Additional Information