Clastic Dikes: Whence Upward Intrusion?

Upward tapering clastic dikes are very rare in the Touchet Beds and other Pleistocene-age deposits in the Channeled Scabland. Nearly all clastic dikes in the region are wedge-shaped and filled from above (Jenkins, 1925; Lupher, 1944; Black, 1979; Woodward-Clyde, 1981; Pogue, 1998; Cooley, 2020). One in one thousand is a reasonable estimate of the upward to downward ratio. Nevertheless, the literature - especially Hanford Site reports - contains a long history of misinterpretation of dike taper and propagation direction (Campbell, 1962; Bjornstad, 1990, Bjornstad and Teel, 1993; Bergeron et al., 1997; Bjornstad and Lanigan, 2007; Apted, 2017). The Hanford gray lit contains decades of erroneous reporting despite detailed sketches, clear photographs, and accurate descriptions published in the first two articles on the dikes, both peer-reviewed, by O.P. Jenkins (1925 in American Journal of Science) and R.L. Lupher (1944 in Geological Society of America Bulletin).

Jenkins, a journeyman field geologist who spent his early career mapping for state surveys, would later become the Director of the California Geological Survey. Lupher was a long time professor at Washington State College who late in his career would become the Supervisor of Field Geology for Shell Oil Company.

Geologist Olaf P. Jenkins examines a typical sheeted clastic dike in the Walla Walla Valley c. 1923. Jenkins published the first article (one of the best) on clastic dikes in Washington (Jenkins, 1925). Washington Geologic Survey photo archive.

I was able to trace the original "upward intrusion" error to a 1962 abstract authored by Robert C. Newcomb in Newsletter of the Geological Society of the Oregon Country (Newcomb, 1962). Newcomb, a USGS hydrogeologist, spent most of the 1950s and 1960s studying Tertiary and Quaternary sediments beneath the Hanford Nuclear Reservation.

Newcomb's abstract begins with perhaps the strangest description of a "typical" clastic dike I've ever heard,

The vertical section of a typical dike includes an irregular and involved "root" part at the bottom, a central "trunk" part, and an uppermost part where "branches" disperse and taper out.

He suggests the various parts indicate,

...the clastic dikes resulted from upward injections of ground water. Each hydraulic injection probably was caused by bank-storage effluent when a pressure difference was produced by a large lowering of Lake Lewis. Such a lowering occurred after a deterioration of the impounding dam and could have been a repetitious event. The first such lake lowering apparently produced a hydraulic lift and the injection of water into a equidimensional [sic] system of fractures. Later injections used mostly the established transverse dike planes and produced the many laminae of the dikes.

Newcomb's upward-pinching "branches" imply the dikes ascended from a remobilized (in situ, wet) layer at depth, though he presents no evidence supporting the assertion.

Newcomb overlooked a Hanford Operations Report published contemporaneously with his GSOC abstract by colleagues (Brown and Brown, 1962). He also seems to have failed to consult field crews who were actively mapping lands of the Columbia Basin Irrigation Project (Bingham, 1963) in which Newcomb's field area fell. Reports by the mapping teams adequately addressed clastic dikes.

Bingham (1963) identifies clear evidence of downward injection at White Bluffs,

The clastic dikes in the Touchet have long been known, but new exposures in the Pasco Basin show the dikes to have a polygonal pattern in plan view, which suggests shrinkage, possibly by drying. Also, several localities were found where clastic dikes of the Touchet-type materials have penetrated the underlying caliche and Ringold Formation as much as 150 feet.

Typical sheeted clastic dikes filled with Touchet Bed sediment intrude downward into oxidized sands of the Ellensburg Formation at Snipes Mountain, WA. Identical dikes intrude several other formations beneath Missoula Flood deposits at dozens of locations in Eastern Washington. My photo.

Why Newcomb's error lingered in the literature for so long is difficult to explain given the excellent work by Jenkins and Lupher. Both authors' findings plainly contradict Newcomb (1962) and he was certainly aware of the earlier articles.

Explanations involving professional arrogance or a lack of respect by the USGS geologist for the work of non-USGS geologists would be unfortunate. Contemporary accounts of similar treatment can be heard around geology campfires from time to time.

Perhaps there's an alternative explanation. Maybe Newcomb sought to curry favor with Richard Foster Flint, at that time an aging but still towering figure in post-WWII geoscience. In his earlier days, Flint had surveyed the Cheney-Palouse scabland tract (Flint, 1938), eventually working his way south into the Walla Walla Valley. There, Flint named the Touchet Beds at their type locality - the bluffs of the Walla Walla River south of Touchet, WA. Flint is first in the literature to mention the "sedimentary dikes" and postulate on their origin,

The Touchet beds commonly exhibit zones of warping and folding, and very commonly are cut by faults and sedimentary dikes. Intense folding, including miniature recumbent folds and overthrusts, is confined to thin zones, a few inches to a few feet in thickness, of fine-grained sediment. As these zones are underlain and overlain by non-deformed beds, they are the result of contemporaneous deformation, probably by slumping and sliding of water-saturated silty on gentle subaqueous slopes. Similar phenomena have been observed in glacial lake deposits in other regions. The Touchet silt and sand along lower course of the Snake River, near its mount, lie in broad gentle undulations affecting series of parallel beds up to 20 or 30 feet in thickness. The undulations are 20 to 100 feet long, and have amplitudes up to 10 feet. Their axes are generally transverse to the Snake River. These structures, too, may be the result of flow affecting the silts, possibly analogous to the 'mud lumps' [sand blows] off the mouth of the Mississippi River.

Flint's ideas were half-baked, clearly speculative, and based not on a thorough investigation at Touchet, but on his experience in other regions. He spent very little time in south-central Washington, much less examining clastic dikes in the area. Flint had bigger fish to fry.

Follow up work by Newcomb, focused specifically on the dikes and the sediments that host them, should have known to take the senior man's observations as preliminary at best. Was Newcomb a former student of Flint or connected in some other way?

To date, no peer reviewed publication provides evidence for Newcomb's "dewatering" origin, an idea echoed in later guidebooks (i.e., Reidel et al., 1992). With respect to clastic dikes at the Hanford Site, the only article that stands the test of time is Black (1979), a short report prepared by the Connecticut-based glacial geomorphologist for the U.S. Department of Energy following three days of legitimate field work.

Two legs of the same diabase dike pinch out in opposite directions. In this example, basaltic magma instead of wet sediment filled a fracture. From the limited vantage provided in the photo, the magma injection direction is unclear. We see only a portion of the middle of a dike, not its top or tail. Wider inspection of the exposure would resolve the question. A clear taper direction would soon emerge. Same with clastic dikes in the Columbia Basin: The middle only tells you so much. Locate their tops and terminations. Photo: The Grindstone peninsula at Winter Harbor, ME.

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