Concept information
Preferred term
Paleogene
Definition
- The Paleogene (also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use. During the Paleogene, mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. This period consists of the Paleocene, Eocene, and Oligocene epochs. The end of the Paleocene (56 Mya) was marked by the Paleocene–Eocene Thermal Maximum, one of the most significant periods of global change during the Cenozoic, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The global climate of the Palaeogene began with the brief but intense impact winter brought by the Chicxulub impact. This intense impact winter was terminated by an abrupt warming. After temperatures stabilised, the steady cooling and drying of the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI) that had spanned the last two stages of the Late Cretaceous continued. About 62.2 Ma, the Latest Danian Event, a hyperthermal event, took place. Around 59 Ma, the LKEPCI was brought to an end by the Thanetian Thermal Event, which ushered in a departure from the relative cool of the Early and Middle Palaeocene and the dawn of an intense supergreenhouse. From about 56 to 48 Ma, annual air temperatures over land and at mid-latitude averaged about 23–29 °C (± 4.7 °C), which is 5–10 °C higher than most previous estimates. For comparison, this was 10 to 15 °C higher than the current annual mean temperatures in these areas. At the Palaeocene-Eocene boundary occurred the Paleocene–Eocene Thermal Maximum (PETM), one of the hottest times of the Phanerozoic eon, during which global mean surface temperatures rose to 31.6. It was followed by the less severe Eocene Thermal Maximum 2 (ETM2) about 53.69 Ma. Eocene Thermal Maximum 3 (ETM3) occurred about 53 Ma. The Early Eocene Climatic Optimum was brought to an end by the Azolla event about 48.5 Ma, when large amounts of carbon dioxide were sequestered by Azolla. From this point until about 34 Ma, there was a slow cooling trend known as the Middle-Late Eocene Cooling (MLEC). Approximately 41.5 Ma, this cooling was interrupted temporarily by the Middle Eocene Climatic Optimum (MECO). Then, about 39.4 Ma, a temperature drop called the Late Eocene Cool Event (LECE) is detected in the oxygen isotope record. A breakneck drop in global temperatures and formation of continental glaciers on Antarctica marked the end of the Eocene. This sharp cooling was partly caused by the formation of the Antarctic Circumpolar Current, which significantly lowered oceanic water temperatures. In the earliest Oligocene occurred the Early Oligocene Glacial Maximum (Oi1), which lasted for about 200 kyr. After Oi1, global mean surface temperature continued to slowly decline over the Early Oligocene. Another major cooling event transpired at the end of the Rupelian; its most likely cause was extreme biological productivity in the Southern Ocean fostered by tectonic reorganisation of ocean currents and an influx of nutrients from Antarctica. In the Late Oligocene, global temperatures began to warm slightly, though they continued to be significantly lower than during the previous epochs of the Palaeogene and polar ice remained. (Adapted from: https://en.wikipedia.org/wiki/Paleogene)
Broader concept
Entry terms
- Early Tertiary
- Palaeogene
In other languages
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French
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Tertiaire inférieur
URI
http://data.loterre.fr/ark:/67375/QX8-7CT1V23G-H
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