Monday, 17 November 2014

Back To Basics: Stratigraphy 101

This is a pop quiz. Most of you will breeze through it. But if just one of you is surprised by the answer, and thereafter remembers the lesson learned, archaeology's status as a scientific discipline will be safe for another day.

You've just dug a test pit.
The purpose of the test pit was to see what's under the surface.
What you see looks like this.

Credit and thanks to: Jim Turenne, the photographer. Westport Vineyards, Massachusetts. 
The upper sediments are unbedded fines. They overlie sediments transported by a different depositional process. 

When you dig the next hole do you treat the dark brown sediments near the surface as a "natural" level and dig arbitrary levels/spits within it? What about the pale-coloured material beneath it? What about the rust-coloured dirt underneath that? 

Did you answer "Yes" to any of the preceding questions? Bzzzzzzt. No points. No! Changed my mind. You lose points!

It's completely astonishing to me that there are people out there who call themselves archaeologists who wouldn't know a soil profile if it . . .  well, if it walked up and slapped them in the face in a field situation. A! Ston! Ish! Ing! 

And, if you think there aren't archaeologists out there who'd have made such a colossal blunder, think again.

There are just two stratigraphic 'layers' in this view: the upper fines and the lower gravelly stuff. The horizontal colour changes are soil horizons, the result of pedogenesis—differential weathering, in situ, of the sediments themselves. They are not 'stratified' in any geological or archaeological sense of the word. To treat them as such is to waste your time and the time of anyone coming after you trying to interpret your field observations.

I'm done. 


  1. Concur. It seems there is no rigor in archaeology to consistently differentiate between soils and sediments. They are not interchangeable. Knut would be going crazy.

    1. Spot on! It was such a privilege to have been his student.

    2. While it's correct that the upper portion of the profile contains a soil (which appears to extend into the underlying gravels), it may be incorrect to say there is no stratification in the upper portion, absent a mechanical or microscopic analysis. As Frank Leonhardy would say, there's always stratigraphy, you just can't see it. He would also tell you to describe the profile before making any claims: you need to offer proof those are unbedded or massive fines. A cleaner profile might help. I do very much agree about soil formation - it is very disheartening to see a structural B horizon described as a stratum. My picky comments aside, your larger point is well taken and I heartily agree,

    3. Thanks for dropping by, Ken. All good points. Although I have to say, without wishing to put too fine a point on it, with respect to the late Frank Leonhardy's assertion that there's always stratification, I've worked in California's Coast Ranges, where the ground squirrel and the pocket gopher roam [sung to the tune of "Home on the Range"]. Seldom, much to the discouragement of archaeologists, do you find unconsolidated sediments that aren't completely mixmastered by those pesky burrowers—or could have been in the past—which obviates any effort to use depth as a relative dating technique. Although I haven't made a study of it, others have, and it's well-enough documented. As for the profile I've used here, it's meant to be more a schematic representation than an object of study in and of itself. My ire—the reason I've presumed to lecture to the readers about it—arises out of just such sedimentary circumstances as the schematic is meant to illustrate. Unconsolidated, unbedded, fine sediments that had been laid down in immediate post-glacial times, and which had been for the most part stabilized by the evolving floral communities, which naturally contributed mass and elevation to the upper part of the sedimentary column through time, but which, themselves, were effectively unbedded. An interpretive nightmare ensued because people in the field WERE 'following' soil horizons as if they were meaningful stratigraphic entities. Just. Crazy. Anyway, thanks again for your points—all well taken.


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