Saturday, May 26, 2007

Recent Movements of Ancient Rocks

Recent Earthquake and Earth Movements

There are manifestations of movement (thermal and mechanical) under the St. George, UT region, which is considered to be an active Geothermal Region (because of volcanic cones, with age less than 10k years and hot springs). Ι enclose photos of an isolated block of Navajo sandstone found in Snow Canyon State Park, which shows recent activity- that the Tablecloth has been yanked out from under the Silverware, so to speak- leaving the cutlery in place (a block of sandstone has remained in place while the underlying basement has rotated against the trend of the blackened fracture above). This is a clue to a recent earthquake (notice the sharp un-eroded edges of the overlying sandstone, which have been previously treated with Manganese and Iron-desert varnish). My interpretation is that this young movement, against the vertical force of gravity, has happened since the desert varnish left its footprint.
Geologists will generally categorize all indications of this sort as Laramide Thrusting (notice the thrust surface coated with Desert Varnish), and all would shake their heads in agreement.
This is a case of indoctrination, since the idea of Laramide thrusting occurring in rocks older than the Cretaceous is an easy assertion. Without case study, this is all it is- indoctrination.
These photos show that there was an isolated mesa, which had earlier been subject to the following events:
a. Since its emplacement in the Navajo sandstone, Jn, the sedimentary rock was sheared by a compressive force, causing it to fracture and fault along a 45 degree angle;
b. The cover of the rock was eroded away, leaving a mesa containing the hardened and fractured (or faulted) rock;
c. In the last few thousand years, desert varnish has formed on the walls of the sandstone left uneroded (varnish can accumulate within a few hundred or thousand years, but it forms only on rock surfaces open to air or moving water);
d. After blackening by varnish, the lower rock was moved diagonally or laterally (see the matching strata indications) - along the previous fracture surface. This is indicated by the youthfulness of the sharp edges protruding into the air.
Picture it this way: the earth moved laterally in the bed rock, as with an earthquake, underneath the mesa, rapidly- before the overlying sandstone was able to react. The mesa on top remained in place, while the underlying rock sheared beneath the blackened sandstone.
Study the photos to determine whether you have another analysis