I could not read the article either, but one example is the Alabama Black Belt. Geologically that part of the deep South and its neighboring states is chalk, which over time has become covered in incredibly rich black soil. Perfect for growing things like cotton. Which, back in the not very recent past, was brutally made the responsibility of slaves. When the slaves were emancipated after the Civil War, many freedmen stayed on and ended up as sharecroppers, ultimately maintaining a deep well of Black American culture that persists to this day.

Edit: unpaywalled article on the human history[1], wikipedia[2], and geology[3]

[1] https://southernspaces.org/2004/black-belt/

[2] https://en.wikipedia.org/wiki/Black_Belt_in_the_American_Sou...

[3] https://encyclopediaofalabama.org/article/black-belt-region-...

I suspect he was referring to

https://en.wikipedia.org/wiki/Polder_model#Historical_backgr...