GEOL 102 Historical Geology

Spring Semester 2018
The Cenozoic Era: The Paleogene

Detail of reconstruction of global paleogeography at 50 Ma (Eocene Epoch) by paleogeographer Ron Blakey

Phanerozoic Eon: 541.0 - 0 Ma

Although stratigraphers agree upon the names and dates of the Epochs of the Cenozoic, there has historically been considerable disagreement on the Periods of the Cenozoic:

This is the version shown in the graphic above. The "Quaternary" is formally reinstated as a "Period" that contained the Holocene and Pleistocene (and the latter has absorbed what was formerly the last stage of the Pliocene!) This follows an unsuccessful bid to create a "Quaternary Sub-Era". The "Tertiary" thus remains in limbo.

Paleogene Geology

Cenozoic is by FAR the best known Era, representing only 1.4 % of Earth History, yet the most commonly encountered rocks on the Earth's surface and on the sea floor.

Paleogeography and Geology of the Paleogene:
Paleocene-Eocene: continuation of Laramide Orogeny in Cordillera (began in Maastrichtian, Late Cretaceous). Uplifted blocks and down-dropped basins in central west (Utah, Colorado, etc.): very large lake deposits of oil shales. Beginning of Yellowstone volcanism (a mantle plume underneath the American West)

Last epicontinental sea of North America (Cannonball Sea) in Paleocene: interior of continent has been fully emergent since then.

Paleocene-Eocene climates very warm, comparable to Cretaceous.

The Paleocene-Eocene Thermal Maximum:

Dramatic temperature drop during late Eocene:

Late Eocene/Early Oligocene: rifting of Atlantic separates Laurentia from Europe and Greenland from North America (end of Laurentia proper). Asia and North America remain physically connected by Bering Land Bridge (periodically emergent or submergent)

During Late Eocene: Chesapeake Bay impact:

Starting in the Eocene, and continuing into the Miocene, the Alpine Orogeny:

Late Oligocene: as Laramide Orogeny ends, extensive erosion of upper surfaces of Cordilleran Mountains and infilling of intramontane basins.

Throughout late Paleogene: Andean Orogeny (actually begins in Late K and continues to today) and earliest stages of Himalayan Orogeny.

Marine Life of the Paleogene

Recovery from K/Pg extinction event. Coccolithophorids survive, but never recover old diversity. Foraminiferans, however, radiate greatly.

Nummulitids: giant disc-shaped forams common in the Eocene to Miocene of the Tethys.

Seagrass radiation in the Eocene: not true grass, but a marine (the ONLY major marine) group of angiosperms, with representatives possibly going back to the mid-Cretaceous (c. 100 Ma). In Eocene, however, spread across coastlines of world. They become a major habitat, and a major sediment-trapping source. Also, they represent the first case since the loss of the shallow algal films that photosynthesizers represent a large cover on the sea floor.

Scleractinian reefs begin again in latest Eocene, with switch to aragonite seas.

Sand dollars (VERY irregular echinoderms): evolved from sea biscuits (typical irregular burrowing echinoids). Evolution of sand dollars (Clypseasteroidea) was fairly rapid (during Early Eocene).

Giant predatory sharks (and shark radiation in general): some forms (up to 14 m long) replace the vanished marine reptiles as the top predators in the sea.

Continued diversification of teleosts. During Early Eocene, huge radiation of spiny-finned (acanthomorph) teleosts, including the perch family.

First penguins.

Origin of several lineages of marine mammals:

Terrestrial Life of the Paleogene

Radiation of freshwater teleosts during Eocene.

Appearance of freshwater diatoms.

Paleocene floras very similar to Cretaceous, but angiosperms become the dominant group. Widespread broadleaf forests around much of the world.

Mammals of the early Paleogene were considerably more primitive than their modern relatives. Tended to have:

During Eocene, establishment of the major radiations of mammals. Different continents dominated by different groups:

During Eocene and later, mammals tend to develop bigger brains, longer legs, and walk on toes.

Eocene sees first bats (flying mammals) and many marine mammal groups.

Also, major radiation of bird groups.

Major faunal turnover in late Eocene extinction: origination and diversification of many groups in North America; European fauna replaced by primarily Asian forms.

During the early part of the Oligocene: extinction of the multituberculates.

Some relevant videos:

To Lecture Notes.

Last modified: 27 April 2018

"Biota of the Paleocene-Eocene Thermal Maximum" (2011) by Aldo Chiappe (Paleocene on left, PETM in the middle, Eocene on right)