Baishan Fm

Named by Sichuan First District Geological Survey Bureau, Team 2 in 1971. Type locality locates in Baishan, Shuanghe Township, Yanyuan County, Sichuan. The original Baishan Fm refers to a stratum located in eastern Sichuan between the Middle Triassic Yantang Fm and the Upper Triassic Lower Boda Fm (the Shemulong Fm in this book) composed of lower limestone and upper dolomite, and the period is set as Late Triassic. In 1978, Southwestern Regional Stratigraphic Table of Sichuan Province classified the named lower part of the Baishan Fm into the Yantang Fm, limiting the lithostratigraphic range of the Baishan Fm to a set of strata dominated by dolomite and evaporite, which is the upper section in the original meaning. We followed this usage in this book.

Mainly carbonate rocks. Lower and Middle sections are gray, dark gray, thin-thick layers of micrite or silty dolomite intercalated with silty crystalline limestone, partially composed of secondary salt breccias, small laminated bedding, bird 's eye structure and dry-crack structure are common. Upper section is gray and gray-black thick layers-massive sandy limestone, bioclastic micrite limestone, algae aggregates, spherulitic limestone, dolomitic limestone intercalated with lime dolomite and siliceous nodules limestone. Usually in 300-600 m thick.

Rare. Some long-lived ammonoids: Leiophyllites confucii, Beyrichites sp., Joannites sp., Proarcestes sp. and bivalves: Entolium discites are found only in the upper part.

The middle and lower sections of this Formation are typical coastal lagoon lacustrine deposits.