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Clastic Dikes: Whence Upward Intrusion?

Upward tapering clastic dikes are very rare in the Touchet Beds. Nearly all clastic dikes in the Channeled Scabland 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 - seems to have latched onto the idea early and has yet to let go. Hanford reports going back decades routinely misinterpret dike taper and propagation direction (Newcomb, 1958; Campbell, 1962; Bjornstad, 1990, Bjornstad and Teel, 1993; Bergeron et al., 1997; Bjornstad and Lanigan, 2007; Apted, 2017). Errors have somehow persisted 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 the American Journal of Science and R.L. Lupher (1944) in the Geological Society of America Bulletin.

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

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

I was able to trace the original "upward intrusion" error to a 1962 abstract authored by Robert C. Newcomb in a Newsletter of the Geological Society of the Oregon Country. Newcomb, a USGS hydrogeologist, spent most of the 1950s and 1960s studying Tertiary and Quaternary sediments beneath the Hanford Nuclear Reservation. He spent several years at Hanford, but inexplicably missed things. Big things. Obvious things.

Newcomb's GSOC 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 layer at depth (in situ, wet), though he presents no evidence supporting the assertion. No one ever has.

Newcomb overlooked a Hanford Operations Report published contemporaneously with his GSOC abstract authored by colleagues (Brown and Brown, 1962). The USGS man failed to consult field crews mapping the geology of the soon-to-be-built Columbia Basin Irrigation Project (Bingham, 1963) inside which Newcomb's study area fell. Reports by the mapping teams adequately addressed clastic dikes; he could have just quoted them.

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

The clastic dikes in the Touchet [Beds] 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 [Plio-Pleistocene] caliche and [Pliocene] 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 that underlie Missoula Flood deposits at dozens of locations in Eastern Washington. My photo.

Why Newcomb's errors have lingered in minds of Hanford staffers for so long is difficult to explain given the excellent work by Jenkins. Lupher, BIngham, and the Browns. Their findings plainly contradict Newcomb's, yet he was certainly aware of their articles if not the their phone numbers. Was he an complete introvert, a hermit, a lone wolf?

A USGS geologists snubbing the good work of non-USGS geologists would be unfortunate. However, accounts of such treatment can still be heard around campfires from time to time. An odd incentive structure that.

Perhaps there's an alternative explanation for Newcomb's folly. Its a stretch, but maybe Robert sought to curry favor with Richard. Richard Foster Flint was in Newcomb's orbit and was still a towering figure in the Geosciences. Flint had surveyed the Cheney-Palouse scabland tract in the 1930s and even ducked into the Walla Walla Valley briefly. There, Flint named the Touchet Beds at their type locality - the bluffs of the Walla Walla River south of Touchet, WA, and mentions the "sedimentary dikes",

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 probably based on his experience in some other region. He spent very little time in south-central Washington, much less examining clastic dikes in the area. Flint had bigger fish to fry.

Newcomb's follow up work, which focused specifically on the dikes and the sediments that host them, plainly missed the mark. Newcomb should have recognized Flint's observations as preliminary. Was Newcomb a total brown noser? Did he lose a bet with Flint? Seeking a promotion? Why select Flint's throw-away opinion over the good work of four other geologists? Who teaches that?

To date, no peer reviewed publication supports Newcomb's "dewatering" origin for the dikes, though the idea persisted into the 1990s (i.e., Reidel et al., 1992) and in some minds may still. 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 a Connecticut glacial geomorphologist for the U.S. Department of Energy following three days of field work.

Two legs of the same diabase dike pinch out in opposite directions. In this example basaltic magma instead of wet sediment fills 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 propagation direction question. Its the same with clastic dikes in the Columbia Basin: The middle tells you nothing. Locate dike tops and terminations, then speculate on origin. Or swallow your pride and quote Jenkins and Lupher. Photo: The Grindstone peninsula at Winter Harbor, ME.



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