Mesozoic Española

Geologists today read the earth’s biography as a finite set of patterns grounded in the laws of thermodynamics that recurred in different environments. After Mazatzal, more volcanic fields formed and joined the continental mass, cementing us in. We moved with the Laurentian mass, sometimes joined with other continental masses, sometimes alone. At times we were in temperate latitudes, and at others on the north pole.

In the Triassic phase of the Mesozoic era we were part on the supercontinent Pangea sitting on the equator. The sun beat down most days of the year. Much of the land was arid, too far from the surrounding ocean to get any rain. The mass was so large, heat rising from the center was trapped by a crust that never cooled.

Accumulated heat began melting the underside of the crust. It forged an opening that divided Pangea into Laurasia on the north and Gondwana on the south. Water flowed through. The first rocks found in this country that mark this movement are the Stockton Formation from 237 to 207 million years ago. They’re part of a larger group of basins found from Nova Scotia to Georgia.

Dinosaurs roamed the Abiquiu area some 205 million years ago.

Rifting tends to be followed by volcanic activity along the rupture. Around 185 million years ago, still in the Jurassic age, a line of volcanos formed under the Atlantic ocean. When they erupted, sea levels rose, and Laurasia was pushed away.

About 125 million years ago, the outer edge of Laurasia was located somewhere in Utah when it began slipping over the heavier Falleron plate. Ocean crust is made of basalt, continental of granite. The contact began forcing up deeply buried rocks.

Meantime, sea waters had risen enough to flow down from what is now Hudson’s Bay. They flooded the area between the Laramide mountains on the west and the Appalachians on the east. Sarah Machin and her colleagues have found zircons in the Albuquerque area that indicate the waters were there by 99.4 million years ago.

All that preceded it was washed away by the great Western Inland Sea of the Cretaceous period. However, dinosaurs left their tracks along the western shore near modern Clayton.

The eastern edge of the Farallon plate reached western New Mexico about 80 million years ago,
when the central Rockies began rising. It was about the time North America finally broke away from Europe.

Farallon continued creeping under the continental crest until it began pushing up the western Santa Fé range of the southern Sangre de Cristo about 74 million years ago.

Sometime around 66 million years ago, the planet collided with a massive comet or asteroid that left a layer of iridium in the clay. The dust blocked the sun, killing off species of plants that depended on photosynthesis. Some 57% of those in North America disappeared.

The loss of forage, in turn, decimated animal populations, including the dinosaurs. The mammals that survived lived on insects and worms. Water plants and animals, along with fungus, were less affected.

Exactly where, why, and how the mass extinction occurred is still being debated by scientists, but the fact it happened is accepted. It’s recorded in clay and fossils.

Notes:
Landman, Rachel L. and Shari A. Kelley. "Low-temperature Thermochronologic Constraints on the Tertiary Cooling and Unroofing History of the Southern Sangre De Cristo Range, New Mexico," Geological Society of American, annual meeting, 2013.

Machin, Sarah, Jeffrey Amato and Spencer Lucas. "The Age of the Encinal Canyon Member of the Dakota Formation: New Insights into the Early-late Cretaceous Transgression of the Western Interior Seaway into North-central New Mexico," New Mexico Geological Society, annual meeting, 2013.

Graphics:
1. Pangaea as visualized by Kieff, uploaded to Wikimedia Commons, 20 October 2009.

2-3. Breakup of Pangaea as visualized by US Geological Survey; "Historical Perspective," last updated 7 August 2012 by J. M. Watson.

4. Diagram showing the dark blue oceanic crust of the Farallon plate sliding under the tan continental crust of the North American plate to force up the Rocky Mountains; uploaded to Wikimedia Commons by Melanie Moreno, May 2006.