Early Cretaceous

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Early/Lower Cretaceous
~145.0 – 100.5 Ma
Chronology

The Early Cretaceous (

Ma
to 100.5 Ma.

Geology

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 in Svalbard the defining early Aptian Oceanic Anoxic Event 1a (OAE1a) was carbon isotope 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 Cretaceous large igneous provinces (LIP).[3]

The Ontong 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, the Kerguelen Plateau–Broken Ridge, together covering 2,300,000 km2.[5] Another LIP on the

superplume.[6]

During the opening of the South Atlantic the Paraná–Etendeka LIP produced 1.5 million km3 of basalts and rhyolites per year, beginning 133 Ma and lasting for a million years.[7]

The opening of the Central Atlantic continued as the

Newfoundland and to connect to the Canada Basin in the Arctic Ocean. With the opening of the Labrador Sea, Greenland became a separate tectonic plate and Laurentia became North America. The Proto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. The Falkland Plateau broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In the Panthalassic Ocean the Pacific Plate continued to grow; the Arctic 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]

Evolution

During this time many new types of

coelurosaurs, while survivors from the Late Jurassic
continued to persist.

Archaefructaceae, one of the oldest fossil families (124.6 Ma) was found in the Yixian Formation, China.[11]

This time also saw the evolution of the first members of the Neornithes (modern birds).[12]

boreosphenidan 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 was more closely related to metatherians (marsupials) than eutherians (placentals) and had feet adapted for climbing trees.[13]
Steropodon is the oldest monotreme (egg-lying mammal) discovered. It lived in Gondwana (now Australia) at 105 Ma.[14]

See also

  • Geological period

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References

Notes

  1. ^ International Commission on Stratigraphy. "ICS - Chart/Time Scale". www.stratigraphy.org.
  2. doi:10.18814/epiiugs/2004/v27i1/003
    . Retrieved 13 December 2020.
  3. ^ Midtkandal et al. 2016, Abstract
  4. ^ Taylor 2006, Abstract
  5. ^ Coffin & Gahagan 1995, The Plateaux, p. 1047
  6. ^ Wu et al. 2005, Abstract
  7. ^ Renne et al. 1992, Abstract
  8. ^ Seton et al. 2012, 140–120 Ma (Figs. 21 and 22)
  9. ^ Seton et al. 2012, 120–100 Ma (Figs. 22 and 23)
  10. S2CID 205458714
    .
  11. ^ Sun et al. 2002, Abstract
  12. ^ Lee et al. 2014
  13. ^ Luo et al. 2003, Abstract
  14. ^ Archer et al. 1985, Abstract

Sources

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