Neoproterozoic

Neoproterozoic
Name	Neoproterozoic
Color	Neoproterozoic
Top boundary def	Defined chronometrically
Top boundary GSSA	N/A
Top GSSA acceptance	N/A
Bottom boundary def	Defined chronometrically
Bottom boundary GSSA	N/A
Bottom GSSA acceptance	N/A
Caption map	Paleogeographic reconstruction of the supercontinent Rodinia.
Timeline	Neoproterozoic
Proxied oxygen	~12.5‰
Proxied co2	~130x PAL
Proxied temp	~15 °C

Neoproterozoic. The Neoproterozoic is the third and final era of the Proterozoic Eon, following the Mesoproterozoic and preceding the Paleozoic Era of the Phanerozoic Eon. It spans from approximately 1,000 to 538.8 million years ago, a time of profound geological and biological transformation on Earth. This era is renowned for extreme climatic events, the assembly and breakup of a supercontinent, and the emergence of complex multicellular life that set the stage for the Cambrian explosion.

Etymology and definition

The term derives from the Greek words *neos* (new), *proteros* (earlier), and *zōē* (life), effectively meaning "new earlier life." It was formally ratified as a geochronological unit by the International Commission on Stratigraphy. The base is defined chronometrically rather than by a specific Global Boundary Stratotype Section and Point, with its start marked by new isotopic dates from key formations like the Musgrave Province. The top is defined by the base of the Cambrian Period, which is marked by the first appearance of the trace fossil Treptichnus pedum at Fortune Head in Newfoundland and Labrador.

Subdivisions

The Neoproterozoic is subdivided into three geologic periods: the Tonian, Cryogenian, and Ediacaran. The Tonian (1,000–720 million years ago) witnessed the initial rifting of Rodinia and the rise of eukaryotic algae. The Cryogenian (720–635 million years ago) is defined by multiple severe global glaciations, often called "Snowball Earth" events. The Ediacaran (635–538.8 million years ago) is named for the Ediacara Hills of South Australia and is characterized by the first appearance of large, complex soft-bodied organisms known as the Ediacaran biota.

Geology and paleogeography

The era began with the supercontinent Rodinia largely intact, surrounded by the vast Mirovia ocean. Widespread continental rifting, evidenced by extensive diabase dike swarms like the Mackenzie dike swarm in Canada, initiated its breakup during the Tonian. This fragmentation led to the formation of new ocean basins, including the Iapetus Ocean, and increased tectonic activity along margins like the East African Orogeny. Sedimentary basins such as the Adelaide Geosyncline recorded these events. By the Ediacaran, continental fragments like Baltica and Amazonia were dispersing, setting the paleogeographic stage for the Phanerozoic.

Climate and glaciations

The climate was dominated by the extreme glacial events of the Cryogenian, particularly the Sturtian and Marinoan glaciations. Evidence from glacial deposits like the Rapitan Group in the Mackenzie Mountains and cap carbonates worldwide supports models of a fully frozen planet. These "Snowball Earth" episodes were likely triggered by a combination of low solar luminosity, continental configuration, and the drawdown of atmospheric carbon dioxide via silicate weathering. The subsequent rapid deglaciations and super-greenhouse conditions, recorded in formations like the Doushantuo Formation, had a profound impact on ocean chemistry and life.

Life and biosphere

Biological evolution accelerated dramatically. The Tonian saw the diversification of eukaryotic algae, as evidenced by microfossils like Bangiomorpha pubescens and acritarchs. The extreme glaciations acted as a evolutionary bottleneck and catalyst. In the Ediacaran, the first unambiguous large, complex multicellular organisms appeared, including iconic forms like Dickinsonia, Charnia, and Kimberella found in sites such as the White Sea coast and Mistaken Point. This period also records potential early animal embryos in the Doushantuo Formation and the first evidence of bilaterian animals from trace fossils.

Economic significance

Neoproterozoic rocks host numerous world-class mineral and hydrocarbon deposits. The era is particularly famous for major iron ore deposits, including the banded iron formations of the Urucum district in Brazil. It also contains significant stratiform copper deposits, such as those in the Central African Copperbelt spanning the Democratic Republic of the Congo and Zambia. The petroleum systems of the Siberian Platform, like those in the Vendian-age rocks, are economically crucial. Furthermore, glacial diamictites of this age are important sources for gold and diamonds in regions like West Africa.

Category:Proterozoic geochronology Category:Geological eras