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Myrow, Louis Derry ’81: Himalaya Uplift Changed Composition of Oceans

Colorado College Geology Professor Paul Myrow has authored a paper with a CC alumnus in the highly regarded journal Earth and Planetary Science Letters. The article by Myrow and Louis Derry '81, a professor in the Department of Earth and Atmospheric Sciences at Cornell University, titled "Neogene Marine Isotopic Evolution and the Erosion of Lesser Himalayan Strata: Implications for Cenozoic Tectonic History," attempts to explain in part changes in the world's oceans over the last 16 million years.

Myrow, Derry, and their co-authors from eight other institutions discuss results of stratigraphic studies undertaken from across the Himalaya to Rajasthan, India, which shares a border with Pakistan. They show that in the latest Cambrian Period, about 500 million years ago, the present-day northern part of India was the edge of a continent with a sea to the north and rivers draining off the continent into an ancient marine basin.

The geologists found that some of these Cambrian (and slightly older) deposits contain an abundance of the element Os, which in this case has high ratios of two Os isotopes (187Os/188Os). The ratio starts to change in the oceans about 16 million years ago and continues to rise until the present. There has been no satisfactory explanation for this rise, although some scientists thought that uplift in the Himalayas might play a role. Additionally, at about 16 million years ago, there was a change from rapidly increasing to less rapidly increasing linear trends in two isotopes of Strontium (Sr) in the oceans.

"We contend that the shifts in Strontium and Osmium isotopes in the ocean are dynamically linked to changes to uplift along major faults in the Himalayas, and thus the types of rocks being eroded," Myrow said. "Specifically, we postulate that a change in the movements of faults in the Himalaya 16 million years ago led to uplift of Cambrian rocks that increased the Os ratios, and reduced the erosion of rocks that were increasing the Sr ratios. These simultaneous changes altered the isotopic composition of the world's oceans.

"Our model explains how changes in the isotopic composition of the ocean over the last 16 million years resulted from changes in tectonic forces, shifts in fault activity, and erosion of different rocks, all of which was initiated simultaneously approximately 16 million years ago," Myrow said.

Myrow first met Derry at a CC reunion in the early 1990s and they kept in touch. Derry has returned to CC to give lectures, and he and Myrow started working on this research about eight years ago.

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