Tuesday, July 16, 2013

Sandpipes at Kodachrome Basin State Park, Utah

A couple months ago, we revisited the Kodochrome Basin State Park near Bryce Canyon National Park, Utah. I've been fascinated by the sandstone pipes that I saw here on our first visit about twelve years ago. My wife also found the pipes fascinating; she kept mentioning the erotic nature of the landscape.
There are over 50 sandstone pipes in the park; most are circular or oval in horizontal cross section. Some of these pipes are free-standing columns and others appear embedded in cliff-face outcrops. The largest of the pipes can reach 170 feet high and up to 50 feet in diameter. The pipes are well cemented and more resistant to erosion that often removed the softer surrounding sediments. Figures 1 through 3 show three of these pipes in the park.

Figure 1. Free standing sandstone pipe near campground at Kodachrome Basin State Park, Utah.
Figure 2. Sentinel Pipe southeast of campground.
Figure 3.  Sandstone pipe south of campground at sunset.
In Kodachrome Basin State Park and the surrounding area, the sandstone pipes are in the Jurassic Entrada and Carmel Formations (145-175 m.y.). The sedimentary environment in which the sandstones, shales, thin limestones and gypsum were deposited was shallow and near-shore marine and tidal flats that periodically dried out. During the Jurassic an inland sea extended from the north down into this part of south-central Utah.

The sandstone pipes at Kodachrome were probably formed during the deposition of the sediments and while the sediments were still saturated with sea water. This might be easiest visualized by imagining sands being deposited underwater near the coastline of the Jurassic sea. As sea level rose, the coast moved further to the east and finer grained clays were deposited on top of the saturated sand layers. As additional deposits of sands and clays occurred, the weight of the sediments and the overlying water cause the water in the underlying sands became over-pressured; the clays forming a cap that prevented the water from escaping the sand units. Perhaps a nearby earthquake provided the spark that disturbed the sediments enough that a small fault or other zone of weakness allowed the over-pressured water to escape upward toward the surface. As the water gushed upward, it included much of the sand from the saturated sand units as well as fragments from the upper clay and sand units that were ripped away by the ascending slurry. Some of the resulting pipes only extended through a few of the overlying sedimentary layers while others very likely broke the surface creating sand geysers. Perhaps, the sight of an erupting sand geyser may have caused some large Jurassic sauropod dinosaurs walking by to pause and look at what was happening.

The mechanism for this kind of soft-sediment deformation is called fluidization and is similar to what happens when you walk barefooted on wet sands near the water's edge. If the sand is saturated, it will squeeze up between your toes.

The outcrop at Shepard's Point, a few miles west of Kodachrome Basin State Park (Figures 4, 5, and 6), shows a large sandstone pipe in the cliff face that probably formed by the rapid eruption of saturated sands that probably broke the surface. After the eruption, the void left at depth caused the pipe and surrounding sediments to collapse. This can be seen by the sedimentary strata dipping down toward the pipe and the near vertical faults (down-arrows in Figure 6) on both sides of the pipe. This collapse feature formed much like calderas form following a volcanic eruption.
Figure 4.  Sandstone Pipe at Shepard's Point about 4 miles west of Kodochrome Basin State Park.
Figure 5.  Major Sandstone Pipe at Shepard's Point.
In Figure 6 I've outlined the sedimentary units in the outcrop at Shepard's Point and labeled the various sedimentary units alphabetically. I've also outlined the vertical pipes and numbered them to identify them. Besides the main pipe in the figure 6 (pipe #1) there is a second smaller pipe (#2). The uppermost unit in this outcrop is a Quaternary conglomerate layer that was deposited less than 2.5 m.y. ago, long after the major units exposed here were deposited, lithified, and heavily eroded. Although the source sedimentary unit for the main sandstone pipe (#1) is buried at some depth, the smaller pipe appears to have originated from sedimentary unit "D". Both pipes either broke the surface when then formed or intruded into overlying units that were eroded away prior to being capped by the uppermost conglomerate unit.

Figure 6.  Major Sandstone Pipe (Fig. 5) with Pipe and Strata Outlined.

Figures 7 and 8 show three smaller sandstone pipes in the same Shepard's Point outcrop a few hundred feet to the north. In this outcrop, the three pipes appear to originate from sedimentary unit "G". The diagonal line on the left side of Figure 8 shows a minor normal fault that may have occurred simultaneously with the three pipes. I would suspect the fault and all three pipes formed at the same time. All three pipes appear to have intruded only so far as sedimentary unit "B".
Figure 7. Smaller Sandstone Pipes at Shepard's Point.
Figure 8. Smaller Sandstone Pipes (Fig. 7) with Pipes and Strata Outlined.
I only spent about an hour at Shepard's point and the above description is rather sketchy. I would like to see more detailed work done on these pipes and the geology of the area. If you are a geology student looking for a thesis idea, feel free to contact me for additional information. Thirty-five years ago I did my MS thesis on similar soft sediment deformation. The small-scale folding I studied was the result of fluidization in Eocene (40 m.y.) oil shales of the Green River Basin of Wyoming; but, that's another story.

Next time you visit Bryce Canyon National Park or find yourself in this part of Utah, I recommend visiting Kodachrome Basin State Park. As my wife pointed out, the area is fascinating both for the geologist and non-geologist. The campground is one of the nicest and quietest park campgrounds in which we have stayed. If you happen to be there on a moonless night, you will likely see a spectacular display of stars.

1.  Baer, James L. and Steed, Robert H., 2010, Geology of Kodachrome Basin State Park, Utah in Sprinkel, Douglas A., et. al., Geology of Utah's Parks and Monuments, pp. 466-482.
2.  Hannum, Cheryl, 1980, Sandstone and conglomerate-breccia pipes and kikes of the Kodachrome Basin area, Kane County, Utah: Brigham Young University Geology Studies, v. 27, pp. 31-50.
3.  Hornbacher, Dwight, 1984, Geology and structure of Kodachrome Basin State Reserve and vicinity, Kane and Garfield Counties, Utah: Loma Linda, Loma Linda university, M.S. thesis, 179 p.


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