White Pocket Confounds

The Wave....on crack....a.k.a. White Pocket.

The wonders of White Pocket on the Paria Plateau just south of the Utah border remain somewhat of a mystery. This colorful slickrock fantasyland--formerly known only by local ranchers and later by a handful of adventurous photographers--has officially come out of obscurity. National Geographic recently published an article on the Vermilion Cliffs National Monument which included some excellent photos of White Pocket. I've heard there's already been a serge of visitation since the magazine's release. Surprisingly, there is very little published by the scientific community that tries to explain the odd geology found there.

I remember when the much more famous and oft-visited Wave, just 6 miles to the west, made a big splash several years ago. The striped and smooth, water-worn surfaces of The Wave make for incredible photography, but a geologist could rather mundanely explain the phenomenon in terms of groundwater geochemistry, permeability, and oxidation states of iron.

White Pocket, on the other hand, is not nearly as easily explained. Yes, white Pocket shares many of the same components that makes the Wave so special: both areas are carved from Jurassic-age Navajo Sandstone and both exhibit drastic color changes due to differing oxidation states of iron. But at White Pocket, you need to take the geology displayed at the Wave and literally shake it all up. The striped Navajo Sandstone is there, but it is contorted to impossible angles (way beyond the angle of repose), swirled, and even folded over on itself. Much of this contorted rock is covered by a thick mass of featureless bleached-white sandstone that weathers into rounded polygons or "cauliflower". Locally, slices of the laminated sandstone are intermixed with the bleached sandstone. It is a sort of beautiful chaos.

A geologist will quickly proclaim soft sediment deformation, meaning the contortions and jumbling at White Pocket occurred back in Jurassic time while the sand was saturated and before the sand was completely lithified (turned into rock). Soft-sediment deformation is not that uncommon in the Navajo. Although the Navajo erg (sand sea) stretched from present-day southern California to Wyoming, and is often compared to the modern Sahara Desert, we now know that while arid, the Navajo desert had a relatively high water table and that sizable oases and small lakes occupied low areas between the massive dunes. Therefore, small sand slumps (saturated sand slumping into the steep lake margins) and even fresh-water limestone beds are not that uncommon. But I've never seen anything in the Navajo Sandstone on the Colorado Plateau at the grand scale of the soft-sediment features at White Pocket.

Retired petroleum geologist Marc Deshowitz has poked around White Pocket as much as anyone I know. He envisions a huge sand-slide mass, triggered by an earthquake, detaching from a tall dune and traveling rapidly downslope. As the mass slid and tumbled downslope, it ripped up chunks of laminated sand beneath that intermixed with the basal part of the slide. The sand mass eventually filled a large pond or oasis. This large sand mass is the featureless bleached-white sandstone or "cauliflower rock" seen today. The instantaneous loading from the sand mass caused pressure adjustments within the underlying saturated sand resulting in contortions and fluid escape structures such as sand volcanoes. Marc has identified at least 25 of these features.

Questions remain. The fine laminae and cross-beds beneath the slide mass are remarkably well-preserved. This may indicate all of the sand involved was buried under a fairly thick column of additional sediment. In other words, the slide plane may have been several 100 feet below the surface. This overburden pressure would have allowed the plastic-like contortions but still keep things somewhat in order.

Also, we may never know what exactly triggered the deformation. I like the earthquake idea, but other possibilities include a bolide (meteorite) impact, a prolonged precipitation event, or unusually rapid burial.

There's much to contemplate out at White Pocket, and I'm sure I'll be back.  Hopefully its remoteness and difficulty in getting there will keep visitation numbers reasonable, so we can avoid the whole permit nightmare that now plagues The Wave.

Featureless white sandstone or "cauliflower rock" lies over red, contorted, and laminated sandstone at White Pocket.

Zoe, Ava, Kandi, and Susie Knudsen follow contorted laminated sandstone beds. Note chunks of laminated sandstone intermixed with the white sandstone in the upper left part of photo.

Overturned laminated sandstone beneath bleached sandstone.

The basal portion of the white sandstone intermixed with underlying laminated sandstone.

Investigating near-vertical beds of the laminated facies. Hector Knudsen photo.

The white sandstone or "cauliflour rock" exhibits an interesting polygonal pattern.

 

Convoluted beds of Navajo Sandstone at White Pocket.

Iron concretions or "Moqui marbles" litter laminated sandstone at White Pocket.

Hector Knudsen photo.

Frozen in geologic time. Zoe and Ava get a closer look at where the white sand mass had plowed up the underlying laminated sands.

Large-amplitude folds within the laminated sandstone.

A rollover structure formed when the white sand mass was transported over the laminated sand.

Looking closer at the rollover structure beneath the white sandstone. Amazing.