| Early/Lower Cretaceous | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 143.1 ± 0.6 – 100.5 ± 0.1Ma | |||||||||
.png) A map of Earth as it appeared 120 million years ago during the Early Cretaceous Epoch, Aptian Age | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Chronostratigraphic name | Lower Cretaceous | ||||||||
| Geochronological name | Early Cretaceous | ||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Epoch | ||||||||
| Stratigraphic unit | Series | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | Not formally defined | ||||||||
| Lower boundary definition candidates |
| ||||||||
| Lower boundary GSSP candidate section(s) | None | ||||||||
| Upper boundary definition | FAD of thePlanktonic ForaminiferRotalipora globotruncanoides | ||||||||
| Upper boundary GSSP | Mont Risoux,Hautes-Alpes,France 44°23′33″N5°30′43″E / 44.3925°N 5.5119°E /44.3925; 5.5119 | ||||||||
| Upper GSSP ratified | 2002[2] | ||||||||
TheEarly Cretaceous (geochronological name) or theLower Cretaceous (chronostratigraphic name) is the earlier or lower of the two major divisions of theCretaceous. It is usually considered to stretch from 143.1 Ma to 100.5 Ma.
Proposals for the exact age of the Barremian–Aptian boundary ranged from 126 to 117 Ma until recently (as of 2019), but based on drillholes inSvalbard the definingearly Aptian Oceanic Anoxic Event 1a (OAE1a) was dated to 123.1±0.3 Ma, limiting the possible range for the boundary to c. 122–121 Ma. There is a possible link between this anoxic event and a series of Early Cretaceouslarge igneous provinces (LIP).[3]
TheOntong Java–Manihiki–Hikurangi large igneous province, emplaced in the South Pacific at c. 120 Ma, is by far the largest LIP in Earth's history.[4] The Ontong Java Plateau today covers an area of 1,860,000 km2. In the Indian Ocean another LIP began to form at c. 120 Ma, theKerguelen Plateau–Broken Ridge, together covering 2,300,000 km2.[5]Another LIP on theLiaodong Peninsula, China,c. 131–117 Ma, lasted for 10 million years. It was the result of the subduction of theKula andPacific plates, which was probably caused by asuperplume.[6]
During the opening of the South Atlantic theParaná–Etendeka LIP produced 1.5 million km3 ofbasalts andrhyolites, beginning 133 Ma and lasting for a million years.[7]
The opening of the Central Atlantic continued as theMid-Atlantic Ridge spread north to separate theIberian Peninsula from the banks ofNewfoundland and to connect to theCanada Basin in the Arctic Ocean. With the opening of theLabrador Sea, Greenland became a separate tectonic plate andLaurentia becameNorth America. TheProto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. TheFalkland Plateau broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In thePanthalassic Ocean the Pacific Plate continued to grow; theArctic Alaska-Chukotka terrane formed the Bering Strait. Continued rifting opened new basins in the Indian Ocean, separating India, Antarctica, and Australia.[8]
By 110 Ma the Mid-Atlantic Ridge reached south into the Proto-Caribbean and South Atlantic, effectively separating South America from Africa, and continued rifting in the northern end completed the longitudinal extent of the Atlantic. In Panthalassa the Ontong-Java Mega-LIP resulted in the formation of new tectonic plates and in the Indian Ocean the Kerguelen LIP began to push India northward.[9]
During this time many new types ofdinosaur appeared or came into prominence, includingceratopsians,spinosaurids,carcharodontosaurids andcoelurosaurs, while survivors from theLate Jurassic continued to persist.[citation needed]
Angiosperms (flowering plants) appeared for the first time during the Early Cretaceous;[10]Archaefructaceae, one of the oldest fossil families (124.6 Ma) was found in theYixian Formation, China.[11]
This time also saw the evolution of the first members of theNeornithes (modern birds).[12]
Sinodelphys, a 125 Ma-oldboreosphenidan mammal found in the Yixian Formation, China, is one of the oldest mammal fossils found. The fossil location indicates early mammals began to diversify from Asia during the Early Cretaceous.Sinodelphys were more closely related tometatherians (marsupials) thaneutherians (placentals) and had feet adapted for climbing trees.[13]Steropodon is the oldestmonotreme (egg-lying mammal) discovered. It lived inGondwana (now Australia) at 105 Ma.[14]
Oil in thePrudhoe Bay Oil Field has been interpreted as being sourced from theTriassicShublik Formation shale and carbonate, Lower Cretaceous highly radioactive zone shale, andLower JurassicKingak Shale.[15]
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