geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, Neocomian was a name given to the lowest stage of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

system. It is generally considered to encompass the interval now covered by the

Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 143.1 ±0.6 Ma and 137.05 ± 0.2 (million years ago) ...

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

and

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.6 ± 2 Ma and 125.77 (million years ago). The Hauterivian is preceded by the Valangi ...

, from approximately 145 to 130 Ma. It was introduced by

Jules Thurmann Jules Thurmann (5 November 1804, Neuf-Brisach in Haut-Rhin, France – 25 July 1855, Porrentruy) was an Alsatian French-Swiss geologist and botanist. He studied at the college in Porrentruy, then continued his education at the University of ...

in 1835 on account of the development of these rocks at

Neuchâtel Neuchâtel (, ; ; ) is a list of towns in Switzerland, town, a Municipalities of Switzerland, municipality, and the capital (political), capital of the cantons of Switzerland, Swiss canton of Neuchâtel (canton), Neuchâtel on Lake Neuchâtel ...

(Neocomum), Switzerland. It has been employed in more than one sense. In the type area the rocks have been divided into two sub-stages, a lower,

(from Valengin, Pierre Jean Édouard Desor, 1854) and an upper,

(from Hauterive, Eugène Renevier, 1874); there is also another local sub-stage, the infra-Valanginian or

(from Berrias, Henri Coquand, 1876). These three sub-stages constitute the Neocomian in its restricted sense. Adolf von Koenen and other German geologists extend the use of the term to include the whole of the Lower Cretaceous up to the top of the

Gault The Gault Formation is a geological formation of stiff blue clay deposited in a calm, fairly deep-water marine environment during the Lower Cretaceous Period (Upper and Middle Albian). It is well exposed in the coastal cliffs at Copt Point in Fo ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

. Eugène Renevier divided the Lower Cretaceous into the Neocomian division, embracing the three sub-stages mentioned above, and an Urgonian division, including the Barremian, Rhodanian and Aptian sub-stages. Sir A. Geikie (''Text Book of Geology'', 4th ed., 1903) regards Neocomian as synonymous with Lower Cretaceous, and he, like Renevier, closes this portion of the system at the top of the Lower Greensand (Aptian). Other British geologists ( A. J. Jukes-Browne, &c.) restrict the Neocomian to the marine beds of Speeton and Tealby, and their estuarine equivalents, the Weald Clay and Hastings Sands (Wealden). Much confusion would be avoided by dropping the term Neocomian entirely and employing instead, for the type area, the sub-divisions given above. This becomes the more obvious when it is pointed out that the Berriasian type is limited to Dauphine; the Valanginian has not a much wider range; and the Hauterivian does not extend north of the Paris basin. Characteristic fossils of the Berriasian are ''Hoplites euthymi'', ''H. occitanicus''; of the Valanginian, ''Natica leviathan'', ''Belémnites pistilliformis'' and ''B. dilatatus'', ''Oxynoticeras Gevrili''; of the Hauterivian, ''Hoplites radiatus'', ''Crioceras capricornu'', ''Exogyra Couloni'' and ''Toxaster complanatus''. The marine equivalents of these rocks in England are the lower Speeton Clays of Yorkshire and the Tealby beds of Lincolnshire. The Wealden beds of southern England represent approximately an estuarine phase of deposit of the same age. The Hils clay of Germany and Wealden of Hanover; the limestones and shales of Teschen; the Aptychus and ''Pygope diphyoides'' marls of Spain, and the Petchorian formation of Russia are equivalents of the Neocomian in its narrower sense.

References

* {{Refend Cretaceous geochronology Stratigraphy