Calcrete Growth in Alluvial Lowlands

A robust association between thick pedogenic calcretes (petrocalcic horizons) and lowland alluvial deposits is a key finding of my recent work in south-central Washington. This lowland association is hardly mentioned in previous articles. Calcretes that post-date the Ringold Formation formed in a lowland, basinal setting near a shallow water table or in gently-sloping alluvial fan-loess complexes on the flanks of Yakima Fold Belt ridges.


Neogene lowlands of the Columbia Basin. Visualize Late Tertiary Eastern Washington like this. The tan areas, identified as "overburden" for purposes of this map, provide an excellent picture of a formerly more-contiguous basin configuration. Today's basins are small fragments of a larger system separated by ridges of the Yakima Fold Belt. While we use the geographic terms "Pasco Basin", "Umatilla Basin", and "Kittitas Valley", its important to recognize that most were once and larger and previously connected to one or more of their neighbors. These post-basalt depocenters (~18 Ma to present) collected sediments shed from the surrounding highlands and from through-flowing rivers (basin-fill sediments). Some of the lowland deposits stabilized and became crusted with calcrete (a paleosol). And some of the words are theirs. May by USGS/Snyder and Haynes (2010, Plate 1). Quote from Normal MacClean.



Research Question: Did sedimentation diverge with rise of the Yakima Folds (lowland and upland)?


Five things that are field-testable:


1.) Is all of the Ringold atop Saddle Mts of alluvial origin (i.e., deposited in a lowland setting)?

- If yes, it was deposited prior to uplift.

- If no, then the "ridge Ringold" seds should reflect deposition in a windy, dry, elevated landscape (i.e., loess-fanglomerate-colluvium-paleosol complex). And it would not really be Ringold.

2.) Are both upland and lowland facies associations present in the YFB region?

- Lowland/Valley seds = Alluvium-flood gravel-paleosols (Othello flats) - Upland/Ridge seds = Loess-fanglomerate-colluvium-paleosols (Saddle Mts ridge)

3.) Are the oldest calcretes - those resting atop uppermost Ringold - older than 3 Ma?

- If yes, then long-standing Ringold dates from tephras, fish fossils, land mammals, paleomag, and plant fossils must be thrown out and replaced by older ages. Not likely.

4.) Do the same calcretes at Othello (lowland) occur atop Saddle Mountains (upland)?

- I say yes.


5.) Are ancient megaflood gravels, that we saw at Othello, also atop Saddle Mts? - Not sure. Unlikely.


Capping calcretes. View looking east along the crest of the Saddle Mountains anticline. The ridge today stands some 600m above Crab Creek Valley. The overhanging white layer continues down the ridge. The unit is several meters thick and consists of calcrete paleosols developed in various sedimentary parent materials. The calcretes didn't form on top of the ridge. They formed in a low-elevation, low-relief alluvial plain prior to ridge uplift. Tectonism brought them here - at least some of them.


CaCO3 beards. Cobble-sized clasts with very thick lower-half rinds of CaCO3 in an alluvial fan deposit. Saddle Mountains.



Frosting. Calcrete beard on a cobble, inverted. Carbonate frosting? So postmodern.


Tubes. Silty-sandy beds between thick calcrete ledges and/or carbonate-encrusted fanglomerates contain abundant root casts and filaments (trace fossils) consistent with a lowland, alluvial setting. Saddle Mountains.


Crusts. Carbonate-silica cements fill cracks in certain basalt bedrock surfaces. Most occurrences seem to have had some thickness of overlying sediment removed by erosion and/or were exposed for a long period (i.e., bare crests of anticlines). Saddle Mountains.


Extra crusty. White carbonate crust atop basalt bedrock at the Corfu Landslide Overlook thins to nothing just uphill of here.


Alluvium up high. Though she may not be able to say exactly what to call it, the penitent geologist knows in her gut the brownish-red sediment capped by a two-meter thick calcrete is an alluvial deposit. Saddle Mountains.


Ash? A light gray bed of crossbedded sandstone at Smyrna Bench is anomalous. It may be volcanic ash reworked by water or wind. Certainly, its an alluvial lowland deposit.


Water-lain ash. Volcanic ash that looks like this didn't get deposited on the top of a high ridge. Or even a low ridge. In fact, there is no ridge. This ash fell in a pond or a shallow, quiet lake. Saddle Mountains.


Nick always finds it. The rhyolitic Cougar Point ash, the type section of which is in the Owyhee-Jarbidge region of southern Idaho, is an airfall ash that has been reworked by water in central Washington (see the crossbeds?) Here, the ash is several meters thick and overlain by the Elephant Mountain flow, which bakes its top red. The depositional setting was a stream valley, fan surface, or lowland plain. Screenshot from Nick Zentner's YouTube video "Saddle Mountains - Volcanic Ash from Yellowstone Explosion".


Deeper cements. I've become convinced that the calcrete-bearing interval in south-central Washington (1-20m thick), the so-called "Plio-Pleistocene unit", is nearly identical to Micoene sedimentary interbeds in the Columbia River Basalt Group, like the one shown here. Its about the same thickness and has a similar geographic extent as many of the named interbeds. That's a new take. CRB volcanism simply shut off before it could be enclosed by basalt. Saddle Mountains.


Cemented bedrock on the cheap. Cements form crusts directly on bedrock in places. Big fan of cheap sunglasses. Saddle Mountains.


Red gravel. The red gravelly deposit with a fine grained matrix is a debris flow shed from high on the north flank of the Saddle Mountains ridge. Here, it overrides and truncates a green-gray wetland mudstone ribboned by vertical and horizontal stringers of calcrete (a mature soil profile or 'paleosol'). The debris flow deposit formed in the blink of an eye. The cemented soil surface took tens of thousands of years to develop.


Real geologists. Geologist Israel C. Russell, 2nd from right (?), leading his U.S. Geological Survey party across the moraines of the Malaspina Glacier, Yakutat District, Alaska. They were tougher than you. USGS photo.



It is remarkable what you will find if you just go out there and look for yourself. Too many Geologists spend their careers tromping about in the footsteps of others, regurgitating old ideas, and fearing its all they've got. The literature on the geology of Eastern Washington documents this well. Except for the writings on basalts and floods, the literature is weak.


How are we training young Geologists today? Are you minting the alumni that will support your program in the future? All the great geology departments have generous, connected alums. Are your graduates leaders or followers?


Leaps not steps. It's no longer OK to hike in 5 miles with your grad student, whack off a chunk of rock, hike out, and spend the next 2 years staring down a microscope at it. Time to change that tune, Professor. Yes, yes, of course lab work and incremental advances matter, but field work matters more, especially in today's world. Field work is discovery. With discovery we leap. The office and its microscope can wait. Go outside, take your students with you, discover something.





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