Cenozoic History

Paleogene (66–23 Ma)

• Mammals and birds diversified following the end-Cretaceous extinction.

• The Laramide Orogeny continued into the early Cenozoic, producing major basement-involved uplifts across the Rocky Mountain region.

• India collided with Eurasia, beginning the development and uplift of the Himalayas.

• Africa and Arabia moved apart, initiating Red Sea rifting.

• Australia separated from Antarctica, and the North Atlantic continued opening.

• Global climates were initially warm, followed by long-term cooling and the development of Antarctic glaciation.

Neogene (23–2.58 Ma)

• Continued uplift and erosion shaped mountain ranges and sedimentary basins.

• The Isthmus of Panama developed, establishing a land connection between North and South America around 3 Ma, although the timing of the final marine separation remains debated.

• The connection changed ocean circulation and permitted major migrations of terrestrial animals between the continents.

• Grasslands expanded in many regions, and mammals adapted to changing habitats.

• The modern western North American tectonic system continued to develop, including San Andreas transform motion and Cascade volcanic activity.

Quaternary (2.58 Ma–present)

• Repeated glacial and interglacial cycles reshaped landscapes, especially at high latitudes and elevations.

• Glacial advances caused sea levels to fall; melting ice caused sea levels to rise.

• Glaciers carved valleys, deposited till, and transported sediment.

• Modern human evolution and expansion occurred during this period.

• The Holocene began about 11,700 years ago, following the last major glacial period.

Cenozoic western North America: important processes

• Laramide Orogeny: Basement-involved deformation and uplift created many Rocky Mountain ranges.

• Basin and Range extension: Crustal stretching produced alternating mountain ranges and basins farther west.

• San Andreas Fault: Transform motion accommodates movement between the Pacific and North American plates.

• Cascade volcanic arc: Subduction of the Juan de Fuca Plate beneath North America generates volcanism.

• Climate change: Long-term cooling, ice-sheet growth, and glacial cycles changed erosion, sea level, and sediment transport.