Loess soil questions
My newest planting site has loess soil. I've never gardened on loess before. (This is my 11th garden spot in this city.) I'm finding it quite easy to dig and interesting to observe. I am very surprised to find that in this older city neighborhood there seems to be virgin soil in the area where there was never a house standing. Three bands of soil are easily seen in digging deeply enough to plant small trees. All the layers are loess, but with slightly different color.
A thing that puzzles me is that I am finding some rocks in the loess. I've seen flint, what I think is red jasper, and something that I think is either a hard limestone or a dolomite. The flint and jasper (just one piece of the latter) are smaller than an English walnut. The limestone/dolomite has been perhaps the volume of a pint.
I don't understand how those rocks could be there without the soil having been disturbed previously. There aren't a lot of rocks, but I'm surprised to see them at all. How did they get into a very fine wind-deposited soil? Will loess "swallow up" rocks dropped on the surface in as little as 300 years? There was an Indian settlement here in the late 1600s. Unfortunately, I haven't noticed which layer of loess the rocks are emerging from. And the jasper I did not find until rain melted away the soil it was brought to the surface with.
Should I be doubting that this soil is even loess? (About a year ago I found it on a soils map defined as an 18c Urban Harvester Complex: "Fine-silty, mixed, non-acid, mesic typic udifluents." Of Harvester soil generally, I have in my notes, "generally consists of deep, moderately well drained soils on uplands, these soils formed in 12 to 40 inches of reworked loess fill material over truncated or buried loess soils. Moderately slow permeability. Harvester has less construction equipment disturbance than some other urban soil complexes."
" reworked loess fill material "-- what does that mean? Does that mean we are talking about soil that has been disturbed and has settled to a new baseline, a new norm, so to speak?
Ken
Fri, 03/11/2022 - 19:41
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Loess soils
I am not a soils expert, far from it, but what I know of geology in general and glacial periods in particular, loess is deposited by the wind that is omnipresent in the regions immediately ahead of glaciers. As to the erratics you mention, my first thought about flint and jasper was that both of them make pretty good stone tools. But why would anyone haul a piece of limestone/dolomite back to camp? Glaciers do very weird things with moving rocks around though, so it's quite possible that your stones were deposited by a glacial outflow during a retreat and subsequently sank into the loess through repeated freeze/thaw cycles. And/or later loess accumulation simply buried them. I do know that the Palouse region of eastern Washington has 100'+ deep loess soils and it is some of the finest pastureland and wheat growing country in the world. Interestingly, the Palouse also had a native "giant" earthworm that was said to smell of flowers when agitated! The famous Appaloosa horses of the Nez Perce were originally bred and raised on the Palouse.