The high-rise Tibetan Plateau is much lower than it used to be, a new study of snail shells has revealed.
Scientists have revealed that at least one large area in southwest Tibet, the plateau's Zhada Basin, actually lost 3,000 to 5,000 feet of elevation sometime in the Pliocene epoch.
Researcher Katharine Huntington, a UW associate professor of Earth and space sciences, said that the basin is really high right now but they think it was a kilometer or more higher just 3 million to 4 million years ago.
The research team employed a cutting-edge geochemical tool, "clumped" isotope thermometry, using modern and fossil snail shells to investigate the uplift history of the Zhada basin in southwestern Tibet. Views range widely on the timing of surface uplift of the Tibetan Plateau to its current high (4.5km) over more than 2.5 square kilometers. Specifically, interpretations differ on whether the modern high elevations were recently developed or are largely a continuation of high elevations developed prior to India-Asian collision in the Eocene.
Clumped isotope temperatures of modern and fossil snail shells have recorded changing lake water temperatures over the last nine million years. This is a reflection of changes in surface temperature as a function of climate and elevation change. A key to their Zhada Basin paleo-elevation reconstruction is that Huntington and colleagues were able to contextualize them with sampling of modern and Holocene-age tufa and shells from a range of aquatic environments.
The scientists found markedly greater "clumping," as well as lower ratios of oxygen-18 to oxygen-16 in the ancient shells, indicating the shells formed at temperatures as much as 11 degrees Celsius (20 F) colder than average temperatures today, the equivalent of as much as 5,000 feet of elevation loss.
It was also found that the Zhada basin was significantly colder from three to nine million years ago, implying a loss of elevation of more than one kilometer since the Pliocene. While surprising given the extreme (4km) elevation of the basin today, the higher paleo-elevation helps explain paleontological evidence of cold-adapted mammals living in a high-elevation climate, and was probably the local expression of east-west extension across much of the southern Tibetan Plateau at this time.
The study is published in Geological Society of America Bulletin.