The Middle Jurassic flora of South Mongolia: Composition, age and phytogeographic position

The Nariin-Sukhait Flora from the terrigenous, coal-bearing deposits of the Orgilokhbulag Formation in the Nariin-Sukhait Coalfield, southernmost Mongolia, is documented for the first time. The Nariin-Sukhait Flora contains 57 fossil plant species belonging to liverworts, horsetails, ferns, cycadaleans, bennettitaleans, ginkgoaleans, leptostrobaleans, conifers and plants of an unknown affinity. Its floristic composition allows us to date the Orgilokhbulag Formation as Middle Jurassic. This flora is typical of the West Siberian Province of the Siberian Region. The boundary between this province and the North Chinese Province of the same region should be positioned further south than its previous placement, and the Nariin-Sukhait Flora existed close to this boundary. The parent plants grew in an alluvial plain characterised by rivers, oxbow lakes and swamps. The flora reflects a wet, most probably warm-temperate climate with some seasonality in temperature and/or precipitation. Two new fern species of the Nariin-Sukhait Flora are described: Coniopteris gurvantesensis Kostina et Herman and Sphenopteris gobiensis Kostina et Herman.

► Jurassic flora of southernmost Mongolia is described in details for the first time. ► Composition of the flora is discussed and fossil plants are illustrated. ► The flora belongs to the West Siberian Province of the Siberian Region. ► Two new fern species of the Nariin-Sukhait Flora are described.