Correlating Measured Sections - White Bluffs, WA
I took a swing at correlating 26 of Kevin Lindsey's stratigraphic columns from White Bluffs (Lindsey, 1996, Appendix A). A couple day's work in Adobe Illustrator. My goal was to illustrate what he documented and to see if I could identify any trends relating to soil intervals (paleosols) and soft sediment deformation. Lindsey's detailed descriptions and sketches are broken up, paginated, and hidden in the back of an excellent report on the Ringold. His info deserves to be displayed properly...or at least in color.
A few observations...
a.) Deformed Sediments. Soft sediment deformation occurs in 6 zones (labeled A-F), mostly in lacustrine-sluggish fluvial-paleosol sediments of the Savage Island Member (a broad, low-relief floodplain). While reasonable to speculate about a potential earthquake origin (seismites), field inspection of the same strata at two dozen other nearby locations confirms the deformation is syn-sedimentary. The contorted beds do not appear to have been created by recurring earthquakes generated by Yakima Fold Belt faults. Green lines follow SSD horizons, lettered A through E in the figure above.
b.) Diatomite. Diatomite occurs at flooding surfaces (lake deepenings). Three lake fillings are floored by paleosol sequences and sometimes diatomite. Thin diatomite beds are basically shallow water indicators; shallow water paleosols. Diatomite is typically associated with warm, shallow, isolated Miocene lakes near George, WA. But diatomite lakes formed in the Pliocene, too. Off-channel lakes that seasonally dried to playas it would seem. They still actively mine diatomite near the summit of Frenchman Hills (IMERYS, Inc).
c.) Pleistocene Calcrete and Older Carbonate Cements. Calcrete is well developed in Early to Middle Pleistocene sediments and atop the post-Ringold unconformity. But carbonate cements also occur at deeper levels of the Ringold, in Pliocene strata. Cementation there is either a product of diagenesis (groundwater) or a signal a dryland climate (calcic soil formation in upland soils). The timing of first arrival of primary carbonate cementation is of interest to me. Did the global Pliocene climate make Eastern Washington dry or are dry conditions a local phenomenon (a Cascades rain shadow)? When did the Cascades grow tall enough to cast a rain shadow east? Was the Pliocene rise of the Cascades coincident with a global climate shift?
d.) Nodular Loess. Red, nodular, sandy loess was deposited in the Ringold basin between lake fillings. The loess sometimes grades laterally to fine grained sandstone - an upland to lowland transition?. Its distinctive nodular texture is the product of burrowing cicadas (dry upland hillslopes, above the water table). Gary Smith noted nodular loess in the Miocene-Pliocene Ellensburg Fm near Naches, WA. I recently found cicada-burrowed red silt mapped as "Ellensburg Fm" along Lander Road at Selah, WA and at Houghton Rd in the Rattlesnake Hills. So the Ringold contains Pliocene loess and Pliocene cicada (i.e., sagebrush steppe after ~5 Ma).
e.) Pliocene Loess. Lots of people have written about the Palouse Loess, which is Pleistocene in age and mostly studied near Pullman, WA. No one talks about loess in the Pliocene. But its a thing. Eastern Washington's dust-generating system was operating long before glacial times. Pliocene climate was about as close to today's climate as you get and there's no shortage of wind or dust today. During the last Ice Age, the supply of fine grained sediment got cranked up to eleven due to the megafloods, which deposited their sediment loads all over south-central Washington. Dump a bunch of silt and sand on the landscape and you'll soon find piles of thick loess downwind. But a sizeable dust source was present in the Pliocene, too. A fluctuating Ringold lake inundated and retreated from wide swaths of desiccated ground, leaving behind plenty of free silt. The challenge to geologists today involves preservation. Nearly all Pliocene strata in the region is bottomland and basin-fill deposits, which are too wet for loess. Upland paleosols - soil intervals between fillings of the Ringold lake (or preserved on ridges elevated above it) - are the exception. That's where the loess is. That's where geologists should be looking. Do Pliocene loess paleosols look any different than their Pleistocene counterparts? Whatever the answer, it won't be found in Pullman.
f.) Paleosols at Flooding Surfaces. Paleosols at the Lake #2/Lake #3 boundary are thick and continuous, indicating a long period of exposure following drainage of Ringold Lake #2. This is strongest paleosurface preserved in Lindsey's measured sections. By contast, paleosols at the Lake #1/Lake #2 boundary are weak to nonexistent. Instead, the boundary is highlighted by diatomite, shallow water deposits composed of diatom tests. Some suspect diatomite overprints volcanic ash. Apparently diatom colonies prefer to chew through ash. CaCO3 cements, some of which may be paleosols, occur at the flooding surface of Lake #1 and at deeper levels of the Taylor Flat Member (fluvial sands, gravels). Cements throughout the Taylor Flat Member may indicate a newtwork of shallow channels migrating across a broad, aggrading floodplain with large overbank areas where soils developed intermittantly and were subsequently buried. Alternatively, the deeper cements may represent post-depositional cementation by groundwater following certain bedding contacts. The Wooded Island Member shows few paleosols. Paleosols (capping calcretes) formed in youngest Ringold following drainage of the last lake (Lake #3), have been partially stripped away by Ice Age floods and wind. Nevertheless, this is the second strongest paleosurface in the sections.
Here's a PDF of the figure above. Please credit me if you redistribute it.
Your comments are always welcome: skyecooley@gmail.com
UW Professor Eric Cheney and I visited the White Bluffs in 2019. An enjoyable and inspiring outing. That visit prompted me to keep exploring strata on either side of the Pliocene-Pleistocene boundary. Way more interesting than basalt.
Soft sed def beneath fluvial ripple sands. Grainsize, water content, and a bit of disturbance by an overriding, more energetic flow appear to drive deformation. Geo-graffiti provided at no charge.
Deformation is consistently associated with paleosol intervals (former ground surfaces) in the Ringold. Orchard Scarp site located on the north side of Saddle Mountains near Taunton.
Soft sed def in lake beds with paleosol intervals. Watt Lane landslide located near Basin City, SE of Saddle Mountains.
Soft sed def in lakebeds with coarse calcrete gravel above. Ringold Road bluffs south of Saddle Mountains.
Soft sed def in lake beds at contact with disaggregated calcrete (rip-ups) and overlying paleosols. Coyan Road site is located east of Saddle Mountains at the nose of the anticline.
Soft sed def in lake beds at contact with overlying paleosols (left column). White Bluffs Overlook south of Saddle Mountains.
Green-gray wetland soils and reddish upland soils formed during low water periods in the Ringold lake basin. Shoaling of the lake exposed vast swaths of dry ground around the lake margin. Wind reworked some of the desiccated surface and redeposited it as loess. The red, silty-fine sand unit loess contains cicada burrows. Tough to say how far the shoreline retreated between lake fillings. Possibly a hundred meters, possibly just a few. White Bluffs Overlook.
How I correlated the sections. Scissors, colored pencils, some tape, and a wall in my office. Compilation and drafting in Illustrator.
Reference
Lindsey, K.A., 1996, The Miocene to Pliocene Ringold Formation and associated deposits of the ancestral Columbia River system, south-central Washington and north-central Oregon: Washington Division of Geology and Earth Resources Open-File Report 96-8, 176 pgs + Appendix.
