Sunday, January 11, 2009
2008 - A Banner Year in Grand Canyon Origin Research
Although financial analysts may cringe when you mention the year 2008, Grand Canyon geologists can smile wide - it was a banner year for geologic research regarding how and when the canyon may have formed. No less than ten new research papers were generated by a host of workers, who saw evidence ranging from a canyon that suddenly "appeared" on the landscape 5 to 6 million years ago, to that which advocates for a canyon that was cut in the same location (but into Mesozoic-age rocks now completely gone) over 50 million years earlier. You've got to love a landform as world famous as this, that can stump the experts and whose age cannot be resolved any clearer than by a factor of 10! The list of these papers was compiled by my colleague Carol Hill of Albuquerque who had a big hand in stimulating so much discussion of the topic.
A highlight during 2008 was a segment aired by Ira Flatow on "Science Friday" in March. He interviewed Victor Polyak about his controversial paper that suggested a portion of the Grand Canyon may have been in existence 17 Ma. And the first caller in to the segment was none other than the "dean" of Grand Canyon-origin geologists Ivo Lucchitta. You would have thought that Victor had suggested the canyon was only 17 weeks old from the response by some! In my opinion, the publicity about his paper was a good thing: having geology and the Grand Canyon in the national spotlight! But as so often happens, scientists shot themselves in the foot when the rash of negative publicity squashed any further exposure (NPR's "All Things Considered" was 'considering' (pardon the pun) running a longer piece about the canyon, but certain negative publicity generated by the "young canyon police" assured that it disappeared from the airwaves.
Here's the list of papers:
(1) December, 2007: Karl Karlstrom et al published in GSA Bulletin: 40Ar/39Ar and field studies of Quaternary basalts in Grand Canyon and model for carving Grand Canyon: Quantifying the interaction of river incision and normal faulting across the western edge of the Colorado Plateau. They argue for late Neogene uplift to drive the final 900 meter incision of the canyon.
(2) February, 2008: Steve Cather et al published in GSA Bulletin: The Chuska erg: Paleogeomorphic and paleoclimatic implications of an Oligocene sand sea on the Colorado Plateau. They suggest that deep incision of the landscape began after late-Oligocene/early-Miocene epeirogenic uplift of the Plateau.
(3) March, 2008: Polyak, Hill, and Asmerom published a very controversial paper in Science: Age and Evolution of the Grand
Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems. In this they argue that certain cave formations (speleothems) can document the progressive lowering of the water table which may document incision of the Grand Canyon. Some of the dates come out at around 17 million years ago. A battle of sorts ensues as "younger" canyon enthusiasts defend the sacrosact 6 million year date.
(4) March, 2008: Hill, Eberz, and Beucher publish in Geomorphology: A Karst Connection model for Grand Canyon, Arizona, USA. This paper explains how the integration of the modern Colorado River could have been accomplished by subsurface karst piping and eventual collapse in eastern Grand Canyon.
(5) March, 2008: Joel Pederson published in GSA Today: The mystery of the pre–Grand Canyon Colorado River—Results from the Muddy Creek Formation. Joel postulated how the paleo-upper Colorado River dissipated and infiltrated in the central-western Grand Canyon area, providing a potential source for Miocene spring and evaporite deposits in the Grand Wash trough, implying a groundwater-driven mechanism for capture of the upper drainage.
(6) April, 2008 Flowers et al published in GSA Bulletin: Unroofing, incision, and uplift history of the southwestern Colorado Plateau from apatite (U-Th)/He thermochronometry. An important new idea that suggests little post-Laramide uplift of the Plateau and that a "pre-Grand Canyon" was cut in Mesozoic-age rocks directly on top of todays canyon.
(7) May, 2008: Dick Young published a GSA Special Paper: Pre-Colorado River drainage in western Grand Canyon: Potential Influence on Miocene Stratigraphy in Grand Wash Trough. Showing his versatility in taking many sides of an argument, Young sees evidence for a "precursor western Grand Canyon that may have been filled with Hualapai Limestone.
(8) July, 2008: Hill and Ranney publish in Geomorphology: A proposed Laramide proto-Grand Canyon. Using data from the distribution of different gravel types both north and south of the modern canyon, they show that some kind of a barrier to gravel transport (a proto-canyon) may have been in existence during the Laramide.
(9) September, 2008: Two reviews of Polyak et al's March Science paper by Pederson et al, and by Pearthree et al: Comment on “Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems. Polyak et al gave a rebuttal to these two reviews: Response to Comments on the “Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems, defending their model and showing how most geologists don't really understand cave forming hydrology.
(10) November, 2008: Karlstrom et al paper in GSA Geology: Model for tectonically driven incision of the younger than 6 Ma Grand Canyon. Here they try to discount the Polyak et al idea.
(11) November, 2008: Ron Blakey and Wayne Ranney publish: Ancient Landscapes of the Colorado Plateau. Although not specifically related to the origin of the canyon, this book illuminates how the landscape of the entire Plateau came to be. It is a watershed work in that it can be used by professional geologists and it is useful to non-scientists as well.
This certainly was "The Grand Canyon Year". More papers are upcoming in 2009 so stay tuned to the topic and this blog! Right now I am off to Africa and South America on a lecturing trip. Watch for the updates and photos.
Posted by Wayne Ranney