Cretaceous

Cretaceous Period
145–66 million years ago
O
S
D
C
P
T
J
N
Mean atmospheric O
2
content over period duration
c. 30 vol % [1] [2]
(150 % of modern level
Mean atmospheric CO
2
content over period duration
c. 1700 ppm [3]
(6 times pre-industrial level)
Mean surface temperature over period duration c. 18 °C [4]
(4 °C above modern level)
Key events in the Cretaceous
view •  discuss • 
-140 —
-130 —
-120 —
-110 —
-100 —
-90 —
-80 —
-70 —
An approximate timescale of key Cretaceous events.
Axis scale: millions of years ago.

The Cretaceous ( s/, kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago ( mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk).

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now- extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a large mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.

Geology

Research history

The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, [5] using strata in the Paris Basin [6] and named for the extensive beds of chalk ( calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous of Western Europe. [7] The name Cretaceous was derived from Latin creta, meaning chalk. [8]

Stratigraphic subdivisions

The Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use.

As with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico. This layer has been dated at 66.043 Ma. [9]

A 140 Ma age for the Jurassic-Cretaceous boundary instead of the usually accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. [10] Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. [11]

From youngest to oldest, the subdivisions of the Cretaceous period are:

Late Cretaceous

Maastrichtian – (66-72.1 MYA)

Campanian – (72.1-83.6 MYA)

Santonian – (83.6-86.3 MYA)

Coniacian – (86.3-89.8 MYA)

Turonian – (89.8-93.9 MYA)

Cenomanian – (93.9-100.5 MYA)

Early Cretaceous

Albian – (100.5-113.0 MYA)

Aptian – (113.0-125.0 MYA)

Barremian – (125.0-129.4 MYA)

Hauterivian – (129.4-132.9 MYA)

Valanginian – (132.9-139.8 MYA)

Berriasian – (139.8-145.0 MYA)

Rock formations

Drawing of fossil jaws of Mosasaurus hoffmanni, from the Maastrichtian of Dutch Limburg, by Dutch geologist Pieter Harting (1866).

The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type that is formed under warm, shallow marine circumstances. Due to the high sea level there was extensive space for such sedimentation. Because of the relatively young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide.

Chalk is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas.

In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast. The group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not easily consolidated and the Chalk Group still consists of loose sediments in many places. The group also has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as Mosasaurus.

In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls. Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean.

Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval. [12] These shales are an important source rock for oil and gas, for example in the subsurface of the North Sea.

Other Languages
Afrikaans: Kryt (geologie)
Alemannisch: Kreide (Geologie)
العربية: عصر طباشيري
asturianu: Cretaceu
azərbaycanca: Təbaşir dövrü
Bahasa Banjar: Kapur (pariuda)
Bân-lâm-gú: Creta-kí
башҡортса: Аҡбур осоро
беларуская: Мелавы перыяд
беларуская (тарашкевіца)‎: Крэйдавы пэрыяд
български: Креда
bosanski: Kreda (period)
brezhoneg: Kretase
català: Cretaci
Чӑвашла: Пурă тапхăрĕ
čeština: Křída
Cymraeg: Cretasaidd
español: Cretácico
Esperanto: Kretaceo
euskara: Kretazeoa
فارسی: کرتاسه
français: Crétacé
Gaeilge: Cailceach
galego: Cretáceo
한국어: 백악기
हिन्दी: चाकमय कल्प
Bahasa Indonesia: Kapur (periode)
italiano: Cretacico
עברית: קרטיקון
қазақша: Бор кезеңі
Latina: Cretaceum
latviešu: Krīts (periods)
Lëtzebuergesch: Kräid (Geologie)
مازِرونی: کرتاسه
Bahasa Melayu: Usia Kapur
Mìng-dĕ̤ng-ngṳ̄: Cretaceous
Nederlands: Krijt (periode)
日本語: 白亜紀
Nordfriisk: Kritj (geologii)
norsk nynorsk: Krittida
occitan: Cretacèu
oʻzbekcha/ўзбекча: Boʻr sistemasi (davr)
پنجابی: کریٹیشیس
Piemontèis: Cretass
Plattdüütsch: Kried (Geologie)
português: Cretáceo
română: Cretacic
Scots: Cretaceous
Simple English: Cretaceous
slovenščina: Kreda
српски / srpski: Креда (периода)
srpskohrvatski / српскохрватски: Kreda (period)
suomi: Liitukausi
Tagalog: Kretaseyoso
Türkçe: Kretase
українська: Крейдовий період
Tiếng Việt: Kỷ Creta
文言: 白堊紀
粵語: 白堊紀
中文: 白垩纪