Neocomian
Encyclopedia
In geology
, Neocomian was a name given to the lowest stage of the Cretaceous
system. It was introduced by Jules Thurmann in 1835 on account of the development of these rocks at 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, Valanginian
(from Valengin, E. Desor, 1854) and an upper, Hauterivian
(from Elauterive, E. Renevier, 1874); there is also another local sub-stage, the infra-Valanginian or Berriasian
(from Berrias, H. Coquand, 1876). These three sub-stages constitute the Neocomian in its restricted sense. A. 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 or Albian
. 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, Nalica leviathan, Belémnites pistilliformis and B. dilatatus, Oxynoticeras Gevrili; of the Hauterivian, Hoplites radiatus, Cr-ioceras capricornu, Exogyra Couloni and Toxaster corn planatus. 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 1-hIs clay of Germany and Wealden of Hanover; the limestones and shales of Teschen; the Aptychus and Pygope diphyoides mans of Spain, and the Petchorian formation of Russia are equivalents of the Neocomian in its narrower sense.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, Neocomian was a name given to the lowest stage of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
system. It was introduced by Jules Thurmann in 1835 on account of the development of these rocks at 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, Valanginian
Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 140.2 ± 3.0 Ma and 136.4 ± 2.0 Ma...
(from Valengin, E. Desor, 1854) and an upper, Hauterivian
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 136.4 ± 2 Ma and 130 ± 1.5 Ma...
(from Elauterive, E. Renevier, 1874); there is also another local sub-stage, the infra-Valanginian or Berriasian
Berriasian
In the geological timescale, the Berriasian is an age or stage of the Early or Lower Creteceous. It is the oldest or lowest subdivision in the entire Cretaceous. It spanned between 145.5 ± 4.0 Ma and 140.2 ± 3.0 Ma...
(from Berrias, H. Coquand, 1876). These three sub-stages constitute the Neocomian in its restricted sense. A. 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 or Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
. Eugène Renevier
Eugène Renevier
Eugène Renevier Swiss geologist, was born at Lausanne, Switzerland, as a descendant of a noble family.In 1857 he became professor of geology and paleontology in the University of Lausanne...
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
Archibald Geikie
Sir Archibald Geikie, OM, KCB, PRS, FRSE , was a Scottish geologist and writer.-Early life:Geikie was born in Edinburgh in 1835, the eldest son of musician and music critic James Stuart 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, Nalica leviathan, Belémnites pistilliformis and B. dilatatus, Oxynoticeras Gevrili; of the Hauterivian, Hoplites radiatus, Cr-ioceras capricornu, Exogyra Couloni and Toxaster corn planatus. 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 1-hIs clay of Germany and Wealden of Hanover; the limestones and shales of Teschen; the Aptychus and Pygope diphyoides mans of Spain, and the Petchorian formation of Russia are equivalents of the Neocomian in its narrower sense.