The Lantian formation is a 150 m-thick sequence of rocks deposited in southern China over around 90 million years in the Ediacaran

Ediacaran

The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...

 period. Its algal macrofossil

Macrofossil

Macrofossils are preserved organic remains large enough to be visible without a microscope. Most fossils discussed in the article Fossil are macrofossils.-Macrofossil contrasted with Microfossil:...

s are the oldest large and complex fossils known.

Sedimentology

The rocks were deposited in shallow seas, in the photic zone

Photic zone

The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...

 yet below storm wave base, yet were deposited in predominantly anoxic conditions

Dead zone (ecology)

Dead zones are hypoxic areas in the world's oceans, the observed incidences of which have been increasing since oceanographers began noting them in the 1970s. These occur near inhabited coastlines, where aquatic life is most concentrated...

. The fossils are located on the bedding planes, and are randomly oriented.

The lowest part of the formation consists of a cap dolostone

Dolostone

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...

, marking the end of the Marinoan glaciation

Marinoan glaciation

The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 635 Ma during the Cryogenian period. The glaciation may have covered the entire planet, in an event called the Snowball Earth...

 and start of the Ediacaran. Above this is black shale containing the Lantian biota fossils. Above this are layers of dolomite, and shale followed by limestone. The highest part of the formation is black shale again. Above the formation is the Piyuancun formation consisting of silicious rock. The Lantian formation overlies diamictite

Diamictite

Diamictite : through and µεικτός : mixed) is a poorly or non-sorted conglomerate or breccia with a wide range of clasts, up to 25% of them gravel sized...

 from the Cryogenian

Cryogenian

The Cryogenian is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran...

.

Taphonomy

The fossils are preserved as carbonaceous films in a Burgess Shale type preservation

Burgess shale type preservation

The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 40 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion...

al fashion.

Age

Originally presumed to be Cambrian in age, the formation is now correlated with the Doushantuo formation

Doushantuo Formation

The Doushantuo Formation is a Lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils...

, with an overlying formation also falling in the Ediacaran period.