Paleogene

Paleogene
Name	Paleogene
Period	Paleogene
Time start	66
Time end	23.03
Unit	Period/epoch
Named by	John Phillips
Type	Geologic period

Paleogene The Paleogene marks the early part of the Cenozoic Era following the end of the Mesozoic, spanning from about 66 to 23 million years ago. It contains pivotal intervals in which global climate, biogeography, and mammalian, avian, and floral lineages diversified after the end-Cretaceous crisis, shaping subsequent Neogene and Quaternary histories.

Overview

The Paleogene succeeded the Cretaceous and preceded the Neogene within the Cenozoic and is subdivided into epochs that record major shifts recognized at sites such as Hell Creek Formation, Messel Pit, and Fayum Depression. During this interval, faunal radiations and floral turnovers are documented in stratigraphic sequences studied by researchers associated with institutions like the Smithsonian Institution, Natural History Museum, London, and University of California. Key fossil localities include the Green River Formation, Brule Formation, Willwood Formation, Bighorn Basin and marine sections correlated with the Chicxulub crater impact evidence and global isotope records used by groups such as the International Commission on Stratigraphy.

Stratigraphy and Subdivisions

Stratigraphically the Paleogene comprises the Paleocene, Eocene, and Oligocene epochs, each subdivided into stages calibrated by magnetostratigraphy, biostratigraphy, and chemostratigraphy developed by projects like the International Chronostratigraphic Chart and datasets from the Integrated Ocean Drilling Program. Regional stage names—such as the Thanetian, Ypresian, Lutetian, Bartonian, and Priabonian—are tied to type sections and stage stratotypes described in publications by paleontologists linked to the University of Cambridge, American Museum of Natural History, and Bureau of Economic Geology. Correlation across continents uses index fossils like foraminifera tied to work from the Scripps Institution of Oceanography and nannoplankton zonations developed by researchers at the National Oceanography Centre. Chronostratigraphic markers include the K–Pg boundary identified in sections sampled during expeditions by institutions such as the Geological Society of America.

Paleoclimate and Environmental Changes

Paleogene climate underwent dramatic swings: early Paleocene warmth transitioned to the Paleocene–Eocene Thermal Maximum (PETM) and later cooling culminating in Oligocene Antarctic glaciation. The PETM is characterized by rapid carbon isotope excursions recorded in cores from the Walvis Ridge, Equatorial Pacific, and sites investigated by the Deep Sea Drilling Project and Ocean Drilling Program. Drivers have been debated among researchers from the Max Planck Institute for Chemistry, Lamont–Doherty Earth Observatory, and ETH Zurich, invoking massive carbon release, volcanism associated with the North Atlantic Igneous Province, and greenhouse feedbacks influenced by CO2 proxies derived by teams at the British Antarctic Survey. The establishment of the Antarctic Circumpolar Current and opening of gateways such as the Tasmanian Gateway and Drake Passage contributed to oceanographic reorganization documented in paleoceanographic reconstructions by the National Oceanic and Atmospheric Administration and paleoclimatologists at the University of Oxford.

Flora and Fauna Evolution

Terrestrial ecosystems saw rapid radiations: mammals such as early Perissodactyla, Artiodactyla, Primates, and Carnivora diversified alongside marsupials in Gondwanan remnants studied by teams at the University of Melbourne and Museo Argentino de Ciencias Naturales. Avian groups including early Passeriformes and neoavian lineages appear in deposits like the Green River Formation and Messel Pit investigated by paleornithologists at the Natural History Museum, Tring. Plant assemblages shifted from angiosperm recovery and expansion of Fagales and Laurales to the spread of grass precursors preceding extensive Poaceae proliferation; palynological records were produced by laboratories at the US Geological Survey and University of Copenhagen. Marine realms hosted foraminifera, nannoplankton, and early cetaceans such as archaeocetes documented by researchers at the International Centre for Cetacean Research and museums including the Royal Belgian Institute of Natural Sciences.

Tectonics and Paleogeography

Continental configurations and plate motions during the Paleogene were shaped by ongoing fragmentation of Pangaea remnants, continued separation of Africa and South America, northward drift of India culminating in collision with Eurasia, and active rifting in the North Atlantic influenced by the Iceland plume and North Atlantic Igneous Province. Mountain building events include the initial phases of Himalayan uplift and reactivation of the Alps and Rocky Mountains, studied by tectonicians at the California Institute of Technology and ETH Zurich. Sea-level changes recorded in sequences from the Paris Basin, North Sea, and Mediterranean reflect interactions among eustasy, sediment supply, and basin subsidence investigated by the International Association of Sedimentologists.

Major Extinction and Biotic Events

Biotic turnovers bracket the Paleogene: the K–Pg extinction event at the boundary with the preceding Cretaceous eliminated non-avian dinosaurs and reshaped ecosystems, with impact evidence tied to the Chicxulub crater and iridium anomalies first noted in sections studied by teams including researchers from the University of Arizona and Geological Survey of Canada. Within the Paleogene, the PETM produced significant extinctions and migrations among benthic foraminifera, mammalian dispersals across land bridges such as the Bering Land Bridge and North Atlantic Land Bridge, and regional extirpations linked to climate forcing documented by paleobiologists at the Smithsonian Tropical Research Institute and Paleobiology Database. Subsequent Oligocene cooling coincided with faunal turnovers leading into the Neogene faunal assemblages cataloged by curators at the American Museum of Natural History.

Category:Geological periods