Paleogeography

This is a paleogeographic animation I made using paleogeography reconstructed by Dr. Ron Blakey at Northern Arizona University. It covers 600 million years. I altered the Jurassic and Cretaceous to include polar ice. I feel that there is good enough evidence for the existence of polar ice to warrent including it. The Middle Jurassic to Early Cretaceous maps have ice that is supported by the evidence, while the ice I added for the Middle to Late Cretaceous is mostly my own speculation, but with good reason. It's been estimated that the ice, when present during the Mesozoic, was only a 3rd of the size of the polar ice caps today, were short-lived events, and possibly only of a seasonal nature. The waxing and waning of polar ice might have been partly responsible for the transgressions of the inland seas that inundated continents... the evidence for both often coincide with each other, and it makes perfect sense. For example, new isotopic data reported in the journal Science (11 Jan 2008) from the tropical Atlantic show synchronous shifts 91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap! Even the prevailing super greenhouse climate (35C ocean temps) was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming... which means that my speculation about ice during the Late Cretaceous was right. The positions/amounts of ice that I added are approximate and are based on both geologic and climate model evidence. As alluded too with the Science article, contrary to popular belief, the Mesozoic was not a tropical paradise. It was not a balmy equitable world in terms of climate. After all, look at the tropics today... they are far from being equitable. When land masses are at the poles, ice is a strong possibility (particularly in higher elevations, e.g., mountains, which is where I placed the majority of my ice unless geologic evidence warranted placing it all the way to the coasts) regardless of how balmy the rest of the planet is. I also tend to think that other time periods in this sequence could very well have had polar ice (land at the poles), but no or very little evidence has been reported.

For more paleogeographic images, including the ones I used to make this short animation, check out:
http://jan.ucc.nau.edu/~rcb7/RCB.html

Category:

Science & Technology

Tags:

• Paleogeography