Please proceed to revised paper at http://www.scribd.com/tmcelvain_1
My present working hypothesis is that there was a mid-Tertiary impact of a comet or asteroid that was pulled apart by the earth’s gravity and resembled the Shoemaker-Levi comets impact of Jupiter. This enormous impact event materially affected the formation of the Southern Rocky Mountains and Colorado Plateau. This working hypothesis is a very broad brush history and obviously erroneous in the details.
The progress of my research and exploration for impact craters and shock metamorphism in the Southern Rocky Mountains, and Colorado Plateau has created a picture of the area that does not fit any of the present interpretations of the geologic history of this province. Over the past ten years as the enormity of the evidence began to accumulate I had to develop a working hypothesis to help me put everything into perspective. This hypothesis assumes a very large comet or asteroid (dirty snowball) impact created an impact crater consisting of millions of impacts by objects varying in size from large bolides to dust, all of which resulted in a giant crater some 1000 kilometers in width, and depending on how far the earths gravitational field extended the comet or asteroid the length could vary from 1000 kilometers to a chain impact two or more thousand kilometers in length. The proposed impact virtually blasted away or helped to remove huge volumes of the sediment from Mid-Tertiary down into the Precambrian, followed by isostatic readjustment that activated old faults and zones of weakness resulting in the present topography. Another interesting fact that I believe helps support my theory is that some of the structures on the western edge of the crater over print the Sevier Thrust Fault, which would date them post Laramide Orogeny, and not associated with the thrust faulting.
Figure B is an artist’s rendition of the Shoemaker-Levi comet impacting Jupiter. I believe this is a good algorithm to for me to use for my vision of the Mid-Tertiary, Southern Rocky Mountain – Colorado Plateau impact event.
Figure C below is a photo of some of the actual impacts of the bolides of the Shoemaker-Levi Comet on Jupiter. I do not believe the earths gravity is strong enough to pull the comet or asteroid this far apart. I believe the impacting objects would be much closer together and many would be right on top of each other.
On the digital elevation map D. below I have placed yellow circles where I have found evidence of shock metamorphism and other corroborating evidence of extra terrestrial impact. It is difficult to date some of these proposed impact structures, but many of them disturbed Eocene and earlier formations. The Sierra Madera structure has been dated as a Mid-Tertiary structure. There is a major Mid-Tertiary angular unconformity through out this area. The latest intense mountain building and rifting began about Mid-Tertiary, and a major period of volcanism also started about this time. The orange dots on the map are placed where I have collected samples of aeolian sand containing grains of quartz with possible PDF's at the base of the Ogallala Formation which I believe is distal ejecta and Mid-Tertiary in age.
Figure E below is an isopach map of the thickness of Early Tertiary sediment in the Rocky Mountains. The thickness data I used is the total thickness found in the Inter-Rocky Mountain Basin. Using these thickness figures and assuming the sediment was deposited in the Cretaceous Intercontinental Seaway trough instead of the various Inter Rocky Mountains. This is a slide showing the depth of Tertiary sediments deposited prior to the late Eocene unconformity in the various intermountain structural basins. I made an Isopach of the depths of this clastic wedge assuming that it was deposited in one continuous basin (The Cretaceous Intercontinental Seaway), and that Laramide deformation was pretty much confined to intensified thrusting along the Sevier Belts.
Copy of a cross section taken from The Evolution of North America,
1959, Philip B. King, Princeton University Press.
Figure G. below is a cartoon of a possible cross section of the active foreland basin before the impact event. With some magic from Photoshop I warped the previous slide to represent the subsidence caused by the vigorous renewed activity of the foreland and rapid deposition of clastic Tertiary sediments into the Intercontinental Seaway. The rapid deposition of clastic material would drive the seawater from the Intercontinental Seaway. The subsidence from this load of clastic material probably caused a lake to form east of the Sevier Belt where the fresh water Eocene shale was deposited.
Figure H below is a cartoon that illustrates how this proposed impact blasted away large amounts of sediment, effectively unroofing what will later become the southern Rocky Mountains and Colorado Plateau. The variation in the intensity of the bombardment would have removed much more sediment in one location than another. The intermountain basins then would represent areas of lesser bombardment and in the mountains where Precambrian rocks are exposed would represent areas of intense bombardment. In other words the older the rocks exposed at the surface the more that area has been bombarded. This would explain the structural nature of the intermountain basins and as an aside may help explain why the rather impermeable sandstones in these basins are fractured which greatly enhanced oil and gas production in these basins.
Figure I below is a carton of the result of isostatic readjustment after the impact. The differences in displacement in the mantle after the uneven removal of tremendous volumes of over burden would reactivate old Precambrian faults and form new ones in order to bring the mantle and continental rocks back into equilibrium.
Figure J. below is a photo of a digital elevation map of North America. If the comet was extended further by the earth’s gravity the impact tract could extend from Guadalajara Mexico into southwest Montana – notice the chain of circular structures. Besides the Colorado Plateau there is a very pronounced circular structure centered on Guadalajara Mexico and numerous smaller and less defined ones in-between. All these structures are on a plateau about the same elevation as the Colorado Plateau. This idea is purely speculative; I have not studied any rocks from Mexico.
The furthest south I have found quartz with planar microstructures is in Big Bend National Park in far west Texas. There also is a structure there called the Solitario the formation of which looks like an impact structure but researchers have not been able to convince the experts that the planar microstructures found there are definitive.
K. El Solitario
I believe more work should be done on this crater before it is completely condemned as an impact structure. The problem being that the only sedimentary rock with quartz is some one thousand meters below the present surface the Cretaceous and Tertiary sediments would have to be added, and the shock wave attenuated and lost enough energy traveling through the target rock to shock the quartz in this formation with enough energy to generate planar deformation structures.