Middle Jurassic Mali Formation of the Zayü area, Tibet—with a discussion of the age of the Chunjieqiao Formation

The Middle Jurassic Mali Formation in the Zayü area, Tibet, was originally assigned to the Lower Devonian Chunjieqiao Formation. Correlation of the lithostratigraphic sequences, rock associations, sedimentary geochemical characteristics and heavy minerals, studies of contact relationships with the underlying strata and discovery of the Bathonian bivalve assemblage indicate that this formation is equivalent to the Middle Jurassic Mali Formation in the Lhorong area in the same tectonic belt. Therefore the name of the Lower Devonian Chunjieqiao Formation should be discarded. The Mali Formation is a Middle Jurassic red molasse formation deposited in the Sanmiancun back arc extensional foreland basin or intermontane basin during the closing of the Nujiang oceanic basin in the Late Triassic Early Jurassic and strong collisional orogeny in the Lancangjiang arc and Sanmiancun arc.