Boundaries and Subdivisions
The K–T boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna, with high iridium levels. There is also fossil evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but very short-lived climatic change may have happened in the very early decades of the Paleocene. There are several theories about the cause of the K-T extinction event, with most evidence supporting the impact of a 10 km diameter asteroid forming the buried Chicxulub crater on the coast of Yucatan, Mexico.
The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic. The Paleocene-Eocene Thermal Maximum upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and a major turnover in mammals on land.
The Paleocene is divided into three stages, from youngest to oldest:
| Thanetian | (58.7±0.2 – 55.8±0.2 Ma) |
| Selandian | (61.7±0.2 – 58.7±0.2 Ma) |
| Danian | (65.5±0.3 – 61.7±0.2 Ma) |
Additionally, the Paleocene is divided into six Mammal Paleogene zones.
Read more about this topic: Paleocene
Famous quotes containing the word boundaries:
“The boundaries which divide Life from Death are at best shadowy and vague. Who shall say where the one ends, and where the other begins?”
—Edgar Allan Poe (1809–1845)