Monday, October 29, 2007

Hiking in Arroyos East of Laverkin, UT quarry

Large Slumping Angles (faulting Dip- down to West)occur East of Quarry

Laverkin Quarry and slumping near Hf (S11, 13 T41S R13W)

A Google space photo is shown, to indicate the geographic and topographic changes near Hiway 9- ascending the cliffs, toward the town of Virgin, Utah. Orient your view by looking at the switchbacks to the east of the town and to the Black ridge to the north. Hf heads north between this mesa and the extension of it NE of Toquerville (the Pleistocene basalts have been sliced by Hf- which has several splays near Laverkin and Toquerville). Use the Freeway I-15 as a guide for focusing your gaze onto something familiar. Ash Creek is the N-S waterway to the west, and Laverkin Creek is east of that- flowing through the valley to the east of the Black Ridge. Hf has bifurcated, creating the weaknesses which allow the two creeks to parallel each other.
It is difficult to ascertain the quarry and faulting-slumping on this map, but it is just to the north of the obvious switchback on hiway 9. The quarry lies just east of the crossing of hiway 17 bridge over Laverkin Creek- being a light area, which is the result of digging and slumping. No hint is given of obvious fracturing, but Hf is easily followed by looking for the change of elevation along the scarp.
The N-S orientation of the fault can be readily seen, and it will be emphasized in photos, which show the fractures and their orthogonals (fractures which are at right angles to the dominant fractures seen in the outcropping rocks) along the path. The main interest is to answer the following questions:
1. Why does the fault create so many splays in the area of the quarry (helping to create the deposit, which has allowed more slumping as it is removed; the ancient river found these weaknesses and eroded more easily there, dumping its load of gravel in the ancient meanders or river bows)?
2. Is there movement laterally along the fault? Slickensides, near a graben on the rim above Laverkin, indicate that there is right lateral movement going toward Toquerville (a counterclockwise movement of the Colorado Plateau, CP).
3. Is there a continuity to the opening of a major fracture underlying Wet Sandy Creek NW of Toquerville- producing the large spring in Ash Creek there- proceeding along Hf to the south, and then to the quarry location and on up the Hf scarp towards the Virgin fissures to the SE? This would make a¯\ _ trace on a map, where the hyphens orient NW-SE and the diagonal underlies Hf.
4. In the field, we will look at the bedding angles displayed between the various faults or slumps, to see if there is rotation of the blocks as they slumped to the west and then rotated with a reverse movement later? This would happen if Hf has interfered, through time, with the slumping or faulting process.
5. Upon zooming in on the north side of the Virgin River (Search Google Earth), a faint NW-SE trace can be seen heading toward Laverkin quarry?, but the pixel density does not allow an inspection of this anomaly. This must be followed in the field.
6. There are various orientations of the major fractures shown on the map, both from the drastic turns of the river and with the mesas and scarps shown. Are these orientations consistent with a major fracture system?

Comments made after Re-Hiking the Laverkin quarry Arroyo:
a. A possible answer to 1, is that there is a transfer of movement (and of the stresses causing it) westward at Hf in this location. This has probably caused not only the multiple faulting splays, but has weakened the fractured zone to allow the ancient Laverkin Creek to enter the fractures.
b. There is movement laterally along Hf, but it has several possible reasons: CP may be rotating, the graben which abuts the slickensides has rotated downward (starting south just uphill from the slickensides), and there is slumping laterally- not only west from the slickensides, but also north. The entire lateral movement may just be a local feature, not part of the CP proper.
c. For 3, undoubtedly the large flowing spring at Toquerville indicates continuity for a fluid path, and the water flow is likely from the Pine Valley Mountains, but there are other large elevation gradients present, e.g. from the Zion NP region.
d. For 4, there is definitely a change of the bedding slope as seen in the Quarry Arroyo. The type of deposit is the only evidence showing reverse dip angle- large dip indicates there should be boulders in the deposit (there aren’t any in the lower strata), whereas slight dip angle in the overlying deposit indicate that there shouldn’t be boulders (they are present in the walls above the larger dip sediments).

e. The zoom-in of the area just north of the Virgin does show a color change on a line running NW-SE. This disappears before reaching the Hiway 9 switchback, but then this is the most distorted surface area (close to Hf, as it creates an up-to-the west bending of the crust);

f. The answer to 6 is not yet found.

Google Earth Map shows the gross landforms without regard to Geological Terms

Laverkin Quarry and slumping near Hf (S11, 13 T41S R13W)