The Yanan Formation, alternatively spelled the Yan'an Formation (), is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

, it is also alternatively considered a group. The age of the formation is uncertain, with estimates ranging from

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

to Bajocian. It is divided up into 5 members, with the designation of Y1 through Y5. Y2, Y3 and Y4 are predominantly dark shales, while Y1 and Y5 are composed of sandstones, coal beds and interbedded mudstones. The depositional environment at the time was when the Ordos Basin formed a large inland lake, surrounded by floodplains. The dark shales have been explored for the potential of producing shale gas. The coal has also been explored for the production of

coalbed methane Coalbed methane (CBM or coal-bed methane), coalbed gas, coal seam gas (CSG), or coal-mine methane (CMM) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, Au ...

. The formation is also notable for its fossil content, with dinosaur footprints having been found in the formation. The dinosaur ''

Lingwulong ''Lingwulong'' is a genus of dicraeosaurid sauropod dinosaur from the Middle Jurassic of what is now Lingwu, Yinchuan, Ningxia, China. The type and only species is ''L. shenqi'', known from several partial skeletons. It is the earliest-aged neo ...

'' was formerly thought to have been found in this formation, but the strata was later attributed to the overlying Zhiluo Formation.

References

{{reflist Geologic formations of China Jurassic System of Asia Lower Jurassic Series Middle Jurassic Series Jurassic China Shale formations Sandstone formations Mudstone formations Coal formations Coal in China Fluvial deposits Lacustrine deposits Ningxia Paleontology in Inner Mongolia Paleontology in Shaanxi