DEFINITION OF SINIAN

In Chinese literature, the Sinian Era refers to the latest

Precambrian falling approximately 850–615 million years

ago, and the corresponding system of rocks. The Sinian is the

approximate equivalent of the Russian Riphean and in more

recent international literature the Sinian would fall within the

Neoproterozoic. There is considerable variation in the definitions

and subdivisions of the Sinian in the scientific literature.

Some classifications have the Sinian Era starting at 800 million

years ago and ending at 570 million years ago, and divide

the era into the Sturtian Period (800–610 Ma), and Vendian

Period (610–570 Ma). In this scenario the Vendian is divided

into the Varanger Epoch (610–590 Ma) and the Ediacara

Epoch (590–570 Ma). Additional dating is clearly needed on

the ages of the boundaries of the Sinian since the basal Cambrian

rocks in China are suggested to be 615 Ma old, whereas

elsewhere the basal Cambrian is dated at 544 Ma.

Rocks of the Sinian System in China rest unconformably

on older deformed rocks of the Yangtze, North China, and

Tarim cratons but are best developed on the Yangtze craton.

Strata of the Sinian System are well exposed and have been

studied extensively near the Three Gorges of the Yangtze

River in Hubei Province. In these and other regions the lower

part of the sequence is comprised of clastic rocks including

many of glacial origin, and an upper calcareous and argillaceous

succession. Deeper water rocks of the Sinian System are

found around the margins of the Yangtze craton.

Sinian strata in China have abundant soft-bodied metazoan

fossils similar to the Vendian fauna, and these strata are

locally conformably overlain by rocks that bear shelly fauna

and thus are Cambrian. Remarkable faunal assemblages

including the earliest fossil records of multicellular life have

been found in 585–600-million-year-old Sinian strata in

southern China. These life-forms developed during global ice

age conditions associated with the formation of the supercontinent

of Gondwana and predate the more widespread and

diverse Ediacarian fauna.

See also CAMBRIAN; PRECAMBRIAN; PROTEROZOIC;

SUPERCONTINENT CYCLE; VENDIAN.

sinkhole See KARST.

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