tag:blogger.com,1999:blog-360614506818167717.post1154739635674125723..comments2024-01-27T16:00:39.065-08:00Comments on History of the Earth: Episode 377: The TepuisRichard Gibsonhttp://www.blogger.com/profile/03330538991049552829noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-360614506818167717.post-48017717359436504362017-12-10T11:47:46.146-08:002017-12-10T11:47:46.146-08:00Thanks for this!Thanks for this!Richard Gibsonhttps://www.blogger.com/profile/03330538991049552829noreply@blogger.comtag:blogger.com,1999:blog-360614506818167717.post-54874080565917270712017-12-08T20:33:25.251-08:002017-12-08T20:33:25.251-08:00There is the question of what uplifted the Roraima...There is the question of what uplifted the Roraima sandstones ... it's not known, to my knowledge. Could be either pre-Pangea/pre-Gondwana collisions, or more recent collisions involving the poorly understood Caribbean plate. Our own work suggests an age of several tens of millions of years.<br /><br />More recent theories, Richard, suggest that the Grand Canyon might be 70 million years old, not 6 or 7; it almost surely predates the uplift of the Colorado Plateau through which it slices.<br /><br />Remember that erosion is often FASTER in drier areas, because there is so little vegetation to soak up moisture or bind the soil. <br /><br />Remember also that the porous sandstone of the Roraima Formation would allow a lot of water to infiltrate rather than developing surface runoff in streams. Groundwater can dissolve rock, of course – but the silica in sandstones dissolves very slowly. Estimates of erosion rates (actually, rates of retreat of tepui edges) per million years aren't that high.<br /><br />Cheers, Tom Givnish (givnish@wisc.edu)Tom Givnishhttp://givnishlab.botany.wisc.edu/Welcome.htmlnoreply@blogger.com